CA1250531A - Pressure swing adsorption with intermediate product recovery - Google Patents
Pressure swing adsorption with intermediate product recoveryInfo
- Publication number
- CA1250531A CA1250531A CA000475574A CA475574A CA1250531A CA 1250531 A CA1250531 A CA 1250531A CA 000475574 A CA000475574 A CA 000475574A CA 475574 A CA475574 A CA 475574A CA 1250531 A CA1250531 A CA 1250531A
- Authority
- CA
- Canada
- Prior art keywords
- bed
- gas
- readily adsorbable
- component
- adsorbable component
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 238000001179 sorption measurement Methods 0.000 title claims abstract description 76
- 239000013067 intermediate product Substances 0.000 title abstract description 27
- 238000011027 product recovery Methods 0.000 title abstract description 18
- 238000000034 method Methods 0.000 claims abstract description 65
- 238000006073 displacement reaction Methods 0.000 claims abstract description 40
- 239000007789 gas Substances 0.000 claims description 166
- 239000000203 mixture Substances 0.000 claims description 46
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 44
- 238000010926 purge Methods 0.000 claims description 43
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims description 36
- 239000001257 hydrogen Substances 0.000 claims description 33
- 229910052739 hydrogen Inorganic materials 0.000 claims description 33
- 239000003463 adsorbent Substances 0.000 claims description 30
- 238000012545 processing Methods 0.000 claims description 26
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 claims description 24
- 229910002092 carbon dioxide Inorganic materials 0.000 claims description 19
- 229910052757 nitrogen Inorganic materials 0.000 claims description 19
- 229910052786 argon Inorganic materials 0.000 claims description 18
- 238000003795 desorption Methods 0.000 claims description 15
- 238000003860 storage Methods 0.000 claims description 15
- 238000000926 separation method Methods 0.000 claims description 12
- 239000001569 carbon dioxide Substances 0.000 claims description 10
- 125000004122 cyclic group Chemical group 0.000 claims description 10
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims description 9
- 238000011084 recovery Methods 0.000 claims description 7
- 230000003247 decreasing effect Effects 0.000 claims description 2
- 230000000977 initiatory effect Effects 0.000 claims description 2
- 239000002699 waste material Substances 0.000 claims description 2
- 125000004435 hydrogen atom Chemical class [H]* 0.000 claims 7
- 238000010521 absorption reaction Methods 0.000 claims 1
- 238000004064 recycling Methods 0.000 claims 1
- 239000000047 product Substances 0.000 description 42
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 18
- 229910002091 carbon monoxide Inorganic materials 0.000 description 11
- 239000011800 void material Substances 0.000 description 10
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 9
- 150000002431 hydrogen Chemical class 0.000 description 8
- 150000002500 ions Chemical class 0.000 description 8
- 239000012535 impurity Substances 0.000 description 5
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 4
- 238000011161 development Methods 0.000 description 4
- 238000004519 manufacturing process Methods 0.000 description 3
- MWUXSHHQAYIFBG-UHFFFAOYSA-N nitrogen oxide Inorganic materials O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 3
- 238000013459 approach Methods 0.000 description 2
- 239000000470 constituent Substances 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 239000002808 molecular sieve Substances 0.000 description 2
- 229940099990 ogen Drugs 0.000 description 2
- 230000003647 oxidation Effects 0.000 description 2
- 238000007254 oxidation reaction Methods 0.000 description 2
- 238000000746 purification Methods 0.000 description 2
- 230000000717 retained effect Effects 0.000 description 2
- URGAHOPLAPQHLN-UHFFFAOYSA-N sodium aluminosilicate Chemical compound [Na+].[Al+3].[O-][Si]([O-])=O.[O-][Si]([O-])=O URGAHOPLAPQHLN-UHFFFAOYSA-N 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 101100384339 Arabidopsis thaliana CBL4 gene Proteins 0.000 description 1
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 1
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000002708 enhancing effect Effects 0.000 description 1
- 239000002737 fuel gas Substances 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000000741 silica gel Substances 0.000 description 1
- 229910002027 silica gel Inorganic materials 0.000 description 1
Landscapes
- Separation Of Gases By Adsorption (AREA)
Abstract
PRESSURE SWING ADSORPTION
WITH INTERMEDIATE PRODUCT RECOVERY
Abstract of the Disclosure A pressure swing adsorption process is used to achieve intermediate product recovery by the introduction of a gas displacement step before, simultaneous with or subsequent to pressure equalization between beds of a multi-bed adsorption system. A cocurrent depressurization step is then employed to achieve intermediate product recovery.
A portion of said intermediate product or of the more readily adsorbable component recovered from a bed advantageously being employed to provide displacement gas for another bed in the adsorption system.
WITH INTERMEDIATE PRODUCT RECOVERY
Abstract of the Disclosure A pressure swing adsorption process is used to achieve intermediate product recovery by the introduction of a gas displacement step before, simultaneous with or subsequent to pressure equalization between beds of a multi-bed adsorption system. A cocurrent depressurization step is then employed to achieve intermediate product recovery.
A portion of said intermediate product or of the more readily adsorbable component recovered from a bed advantageously being employed to provide displacement gas for another bed in the adsorption system.
Description
PRESSURE SWING ADSORPTION
WITH INTERMEDIATE PRODUCT RECOVERY
Back~round of ~he Invention Field of the Invention The invention rslates to the purification of gaseæ. More particularly, it relates to a process for enhancing the- recovery of the intermediate component of adsorbable feed ~as mixtures.
DescriPtion of the Prior Art The pressure swing adsorption (PSA) process provides a highly desirable means for separating and purifying gases, such as hydrogen, contained in a feed gas mix~ure thereof with impurities ~hat are selectively adsorbed by one or more adsorbent beds in a PSA system. Adsorption occurs in such beds at a higher adsorption pressure, with the selectively adsorbable impurities thereafter being desorbed by pressure reduc~ion to a lower desorption pressure.
The beds may be purged at said lower pressure for fureher desorption and removal of impurities, îf desired, before repressurization to the higher adsorption pressure for adsorption of impuriti2s ~rom additional quantities of the feed gas mixture as the processing sequence is carried out, on a cyclic basis, in each bed in the adsorption system.
The PSA process is commonly employed in multi-bed systems. The ~agner pa~ent U.S.
3,430,418, discloses a PSA process and system employing a~ least four adso~bent beds arranged for carrying out a particular PSA processing sequence on D-13,543 , ,Olæs~s3~ '
WITH INTERMEDIATE PRODUCT RECOVERY
Back~round of ~he Invention Field of the Invention The invention rslates to the purification of gaseæ. More particularly, it relates to a process for enhancing the- recovery of the intermediate component of adsorbable feed ~as mixtures.
DescriPtion of the Prior Art The pressure swing adsorption (PSA) process provides a highly desirable means for separating and purifying gases, such as hydrogen, contained in a feed gas mix~ure thereof with impurities ~hat are selectively adsorbed by one or more adsorbent beds in a PSA system. Adsorption occurs in such beds at a higher adsorption pressure, with the selectively adsorbable impurities thereafter being desorbed by pressure reduc~ion to a lower desorption pressure.
The beds may be purged at said lower pressure for fureher desorption and removal of impurities, îf desired, before repressurization to the higher adsorption pressure for adsorption of impuriti2s ~rom additional quantities of the feed gas mixture as the processing sequence is carried out, on a cyclic basis, in each bed in the adsorption system.
The PSA process is commonly employed in multi-bed systems. The ~agner pa~ent U.S.
3,430,418, discloses a PSA process and system employing a~ least four adso~bent beds arranged for carrying out a particular PSA processing sequence on D-13,543 , ,Olæs~s3~ '
- 2 - ~
a cyclic basis. This sequence includes higher pressure adsorption, cocurrent depressurization to intermediate pressure with release of void space gas from the discharge or product end of the bed, countercurrent depressurization to a lower desorption pressure, and repressurization to a higher adsorption pressure. Wagner discloses the passing o~ released void space gas from one bed directly to another bed initially at its lower desorption pressure. The pressure in the two beds is thereby equalized at an intermediate pressure.
Additional void space gas can be released from the product end of the bed being cocurrently depressurized, with such void space gas being used to provide purge gas to another bed in the PSA
system before such other bed is repressurized from its lower desorption pressure. After each bed has been repressurized to an intermediate pressure level by such pressure equalization, it is ~urther repressurized from the intermediate level in part by the countercurrent addition of product effluent to the product end of the bed being repressurized.
In a further development in the art, the Fuderer et al patent U.S. 3,986,849, disclose~ the use of at least seven adsorbent beds, with the feed gas mixture being in~roduced to the ~eed end of at least two adsorbent beds, in overlapping identical processing cycles, at all stages of the PSA
processing sequence. Each bed, in turn, undergoes three pressure equalization steps prior to repressurization to the higher adsorption pressure, with said steps being carried out in a particular manner achieving higher product purity.
D-13,543 SOS3~ `
, .
The PSA process, as represented by the disclosures of such patents, is a highly desirable and practical commercial pLocess for the purification of gases such as hydrogen. It has the advantage of being capable of producing very high purity product, e.g. in excess of 99.9 percent pure hydrogen product. The PSA process can be used to treat a wide range of available feedstocks, and is not limited to use with a particular hydrogen-con-taining or other feed gas stream. Mo pretreatment or post treatment steps are required as part of the process, other than such conventional impurity removal as may be desirable or required ~o avoid undue degradation of the adsorbent. In addition, there is very little pressure drop between the feed gas stream and the product gas so tha~ the product gas is available at the adsoLption pressure level for further use downstream of the PSA system and for repressurization of each bed to said adsorption pre6sure from a lower de~orption level or from the intermediate pressure level achieved during one or more pressure equalization steps carried out as indicated above.
It is al80 known in the art that selective adsorption process, such as the PSA process referred to above, can be employed to recover the more strongly adsorbable component Erom a gas mixture as the desired product. For example, the PSA process can be employed to recover 99% carbon dioxide from a gas mixture containing said carbon dioxide as a more readily adsorbable component, ~ogether with other, less readily adsorbable components, such as methane, D-13,543 _ 4 _ ~Z~s3~
hydrogen, nit~ogen and the like. The processing cycles employed for such puspo~es are essentially the same as those employed when the PSA process is utilized for the production of the less readily adsorbable component.
When 6uch well-known PSA cycles are employed for the separation of gas mixtures containing a number of components, the less readily adsorbable component and~or the more readily ad~orbable component, as recovered during the adsorption and/or desorption 6teps, respec~ively, may contain component~ having intermediate adsorbable chsracteristics, vis-a-vis the more readily and the less readily ad60rbable components of the mixture~ themselves, depending upon the proces~ing condition~ under which the PSA proce~6 is carried out. Thus, in the separation of a gas mixture containing hydrogen, argon, nitrogen and carbon monoxide, with hydrogen being the les~
readily ad~orbable component and carbon dioxide being the more readily adsorbable component, high purity hydrogen can be recovered with the more readily ad~orbable component ~eparated therefrom comprising a mixture of argon, nit~ogen and carbon monoxide. Similarly, high purity C0 can be recovered as a more readily adsorbable component wi~h the les6 readily adsorbable component comprising a mixture o~ hydrogen, argon and nitrogen. It i6 also possible to employ known PSA
cycle~ ~o a~ to obtain a lighter, less readily adsorbable component comprising hydroyen and argon, and a heavier, more readily adsorbable component compri6ing ni~rogen and carbon monoxide.
D-l3~s43 _ 5 _ ~2~3~
There ara practical applications in the art, however, where it would be desirable to recover the intermediately adsorbable component as a separat0 product of desired purity rather than to ha~e said component recovered (l) with the less readily adsorbable component, (2) with the more readily adsorbable component, or (3~ as part of a waste stream also containing said less and more readily adsorbable components. As used herein, the teLms "intermediately adsorbable component"
"intermediate component" and "intermediate product"
are used to denote a single gas constituent or more than one such constituent of a gas mixture alsa having a less readily adsorbable component and a more readily adsorbable component. In the illustrative gas mixture referred to above, it may thus be desired to recover argon as an intermediate component, while recovering hydrogen as a less readily adsorbable component and a mixture of CO and nitrogen as a more readily ad~orbable component. In other circum tances, it may be desirable to recover nitrogen as an intermediate component, with a mixture of hydrogen and argon comprising a less readily adsorbable component and a mixture of CO and additional nitrogen comprising the more readily adsorbable component. In another variation, i~ may be desirable to separate and recover a mixture of argon and nitrogen as an intermediate component, apart from hydrogen as the light, less readily adsorbable component and CO as the heavy, more readily adsorbable component. It has not hertofore been feasible to make such separa~ions and D-13,543
a cyclic basis. This sequence includes higher pressure adsorption, cocurrent depressurization to intermediate pressure with release of void space gas from the discharge or product end of the bed, countercurrent depressurization to a lower desorption pressure, and repressurization to a higher adsorption pressure. Wagner discloses the passing o~ released void space gas from one bed directly to another bed initially at its lower desorption pressure. The pressure in the two beds is thereby equalized at an intermediate pressure.
Additional void space gas can be released from the product end of the bed being cocurrently depressurized, with such void space gas being used to provide purge gas to another bed in the PSA
system before such other bed is repressurized from its lower desorption pressure. After each bed has been repressurized to an intermediate pressure level by such pressure equalization, it is ~urther repressurized from the intermediate level in part by the countercurrent addition of product effluent to the product end of the bed being repressurized.
In a further development in the art, the Fuderer et al patent U.S. 3,986,849, disclose~ the use of at least seven adsorbent beds, with the feed gas mixture being in~roduced to the ~eed end of at least two adsorbent beds, in overlapping identical processing cycles, at all stages of the PSA
processing sequence. Each bed, in turn, undergoes three pressure equalization steps prior to repressurization to the higher adsorption pressure, with said steps being carried out in a particular manner achieving higher product purity.
D-13,543 SOS3~ `
, .
The PSA process, as represented by the disclosures of such patents, is a highly desirable and practical commercial pLocess for the purification of gases such as hydrogen. It has the advantage of being capable of producing very high purity product, e.g. in excess of 99.9 percent pure hydrogen product. The PSA process can be used to treat a wide range of available feedstocks, and is not limited to use with a particular hydrogen-con-taining or other feed gas stream. Mo pretreatment or post treatment steps are required as part of the process, other than such conventional impurity removal as may be desirable or required ~o avoid undue degradation of the adsorbent. In addition, there is very little pressure drop between the feed gas stream and the product gas so tha~ the product gas is available at the adsoLption pressure level for further use downstream of the PSA system and for repressurization of each bed to said adsorption pre6sure from a lower de~orption level or from the intermediate pressure level achieved during one or more pressure equalization steps carried out as indicated above.
It is al80 known in the art that selective adsorption process, such as the PSA process referred to above, can be employed to recover the more strongly adsorbable component Erom a gas mixture as the desired product. For example, the PSA process can be employed to recover 99% carbon dioxide from a gas mixture containing said carbon dioxide as a more readily adsorbable component, ~ogether with other, less readily adsorbable components, such as methane, D-13,543 _ 4 _ ~Z~s3~
hydrogen, nit~ogen and the like. The processing cycles employed for such puspo~es are essentially the same as those employed when the PSA process is utilized for the production of the less readily adsorbable component.
When 6uch well-known PSA cycles are employed for the separation of gas mixtures containing a number of components, the less readily adsorbable component and~or the more readily ad~orbable component, as recovered during the adsorption and/or desorption 6teps, respec~ively, may contain component~ having intermediate adsorbable chsracteristics, vis-a-vis the more readily and the less readily ad60rbable components of the mixture~ themselves, depending upon the proces~ing condition~ under which the PSA proce~6 is carried out. Thus, in the separation of a gas mixture containing hydrogen, argon, nitrogen and carbon monoxide, with hydrogen being the les~
readily ad~orbable component and carbon dioxide being the more readily adsorbable component, high purity hydrogen can be recovered with the more readily ad~orbable component ~eparated therefrom comprising a mixture of argon, nit~ogen and carbon monoxide. Similarly, high purity C0 can be recovered as a more readily adsorbable component wi~h the les6 readily adsorbable component comprising a mixture o~ hydrogen, argon and nitrogen. It i6 also possible to employ known PSA
cycle~ ~o a~ to obtain a lighter, less readily adsorbable component comprising hydroyen and argon, and a heavier, more readily adsorbable component compri6ing ni~rogen and carbon monoxide.
D-l3~s43 _ 5 _ ~2~3~
There ara practical applications in the art, however, where it would be desirable to recover the intermediately adsorbable component as a separat0 product of desired purity rather than to ha~e said component recovered (l) with the less readily adsorbable component, (2) with the more readily adsorbable component, or (3~ as part of a waste stream also containing said less and more readily adsorbable components. As used herein, the teLms "intermediately adsorbable component"
"intermediate component" and "intermediate product"
are used to denote a single gas constituent or more than one such constituent of a gas mixture alsa having a less readily adsorbable component and a more readily adsorbable component. In the illustrative gas mixture referred to above, it may thus be desired to recover argon as an intermediate component, while recovering hydrogen as a less readily adsorbable component and a mixture of CO and nitrogen as a more readily ad~orbable component. In other circum tances, it may be desirable to recover nitrogen as an intermediate component, with a mixture of hydrogen and argon comprising a less readily adsorbable component and a mixture of CO and additional nitrogen comprising the more readily adsorbable component. In another variation, i~ may be desirable to separate and recover a mixture of argon and nitrogen as an intermediate component, apart from hydrogen as the light, less readily adsorbable component and CO as the heavy, more readily adsorbable component. It has not hertofore been feasible to make such separa~ions and D-13,543
3~
recoveries of inte~mediate components of gas mixtures in a manner com~at~ble with conventional, convenient PSA proces~ing. Upon the development of such convenient processing capability for intermediate product recovery, those skilled in the art will appreciate that a variety of practical commercial PSA operations could be advantageou ly carried out 60 aB to achieve desirable intermediate product recovery.
one approach heretofore suggested for such development of intermediate product reco~ery capabili~y is set forth in European Patent Specification 0 008 88Z, published December 30, 19~1, in the name of Shivaji Sircar. Disclosed ~5 therein is the separation of multicomponent feed gas mix~ure having a primary key component, a secondary key component and a tertia~y component. For this purpose, an adsorption system comprising a plurality of bed pairs, i.e., two beds in series, is provided, with each bed pair functioning in the manner of a single bed in accordance with the conventional PSA
processing techniques referred to above. The feed gas mixture pa~ses through a first bed of the pair and then through the other, with a tertiary component adsorption front established in the first bed and a secondary key component ad60rption ront being establi6hed in the second bed of the pair.
The flow of the feed gas mixture is then interrupted, and gas flow between the beds are discontinued. The beds are then separa~ely subjected to rin6ing, product reduction, purge and partial repressurization steps prior to the re-e~tablishing D-l3~s43 ~ZS~)S3~
of flow therebetween to achieve final repres~uriæation, initiation of the flow of the feed gafi mixture thereto and repetition of the processing cycle. While the disclosed process can be employed for intermed;ate product recovery, the complex processing steps necessarily associated with the use of pairs of adsorbent beds in multi-feed systems, together with the associated complexity of lines, valves, controls and the like, serve to limit the practical applicability of th~ process. There remains in the art, thereafter, the need for an improved PSA process capable of facilitating intermediate product recovery in a prac~ical, convenient manner.
It is an object of the invention, therefore, to provide an improved PSA process capable of enabling intermediate product recovery to be achieved.
It is another object of the invention to provide a process facilitating said intermediate product recove~y in a manner compatible with conventional multi-bed PSA ~ystems.
It is a further object of the invention to pcovide a PS~ process having advantageous flexibility in recovering desired intermediat~
product from multicomponent feed gas mixtures.
With these and other objects in mind, the invention i~ hereinafter set forth in detail, the novel featu~es thereof being particularly pointed out in the appended claims.
D-13,543 ~LZ50~3~
Summary of_the Invention The intermediate component of a feed gas mixture is recovered as a separate product in PSA
processing by first assuring that the less readily adsorbable component of a ~ulticomponent feed gas mixture is essentially completely removed from an adsorbent bed and by then employing a cocurrent depressurization step to remove said intermedia~e component from the product end of the bed. In various adsorption systems having four or more beds, particularly desirable processing cycles are employed, with a portion of the more readily adsorbable component recovered during countercurren~
depressurization or a portion of the intermediate component product being conveniently employed as said dis~lacement gas introduced, on a cyclic basis, to each bed in the adsorption system.
Detailed_Dascrip~ion of the Invention The PSA process of the invention relates to conventional PSA proce6sin~ in which each bed of an adsorption system undergoes, on a cyclic basis, higher pres6ure ad~orption, cocurrent depressurization to intermediate pressure level(s) with release of void space gas from the product end of the bed, countercurrent depressurization ~o lower de60rption pressure with the release of desorbed gas f Lom the feed end of the bed, with or without purge of the bed, and repre~surization to higher adsorption pressure. The ob~ects of the invention are accomplished, in the separation of a feed gas mixture containing a less readily adsorbable component, an intermediate component and a more D-13,543 ~;~SOS31 g Leadily adsorbable component, by employing a cocurrent displacement step in which the less readily adsorbable component is essentially completely removed from the adsorption bed. The bed is then cocurrently depee6suri~ed with the intermediate component being discharged from the product end thereof as a product of desired pueity.
In the multi-bed ad~orption systems to which the invention is directed, the displacemen~ gas used for each bed is advantageou~ly obtained by diverting a portion of the gas releaæed from that or another bed in the system during the cocurrent depressurization or ~he countercurrent depressurization steps, although other ~uitable ~isplacement gas may also be employed if available with respect ~o the overall processing operation in which PSA with intermediate product recovery is being employed.
Those skilled in the art will appreciate that the high pressure adsorption step of the PSA
procesz comprises introduciny the feed ga~ mixture to the ~eed end of the ad~orbent bed at a higher ad~orption pressure. The less readily adsorbable component passe6 through the bed and is discharged from the product end thereof. An adsorption front or fronts are established in the bed with said fron~s likewise moving through the bed from ths feed end towaed the product end thereof. When the feed gas contains a less readily adsorbabla component. an inteemediate component and a more readily adsorbable component, a leading adsorption front of said intermediate component will be established and move through the bed in the direction of the product or D-13,543 di6charge end thereof ahead of a trailing adsorption front of the more readily adsorbable component. By the use of a cocurrent displacement gas essentially free of the less readily adsorbable componant, thus having a molar concentration of intermedia~e and/or more readily adsorbable components, the less readily adsorbable component that remains in the void spaces of the adsorbent bed ahead of the leading adsorption front can be essentially completely displaced from the bed. This enables the intermediate component to be thereafter discharged from the product end of the bed as a product of desired eurity by cocurrently depressurizing ~he bed. As will be indicated below, the cocurrent depressurization step for intermediate product recovery is desirably carried out in addition to the cocurrent depressurization step or steps conventionally employed wherein the void space gas thus released being u~ed for pressure equalization with other beds or to provide purge gas to such beds. Countercurrent depressuriæation of the bed i8 carried out subsequent to the intermediate product recovery 6tep, as in conventional PSA processing. When the gas remo~ed from the bed during either the conventional cocurrent depressurization step or the countercurrent depressurization step, or a portion thereof, is diverted to the feed end of another bed for use as the displacement gas, it will be appreciated that said gas is repres~urized sufficiently to enable displacement of less readily adsorbable component from the void spaces of the bed to be accomplished. In effect, an impurity front D-13,543 11- ~L251~531 existing in one bed is moved in the direction of either the feed or the product end of one bed and released gas i6 introduced to another bed so as to facilitate the displacement of less readily adsorbable component from that bed.
The invention can advantageously be practiced in multi-bed PSA 6ystem~ having at lea6t four adsorbent beds therein. Preferably the invention can be utilized to advantage in sy6tems having four to ~ix adsorbent beds, although it will also be appreciated that the invention can also be employed in larger ~y6tem6 having 6even or more beds. It will also be appreciated that, as in conventional practice, the feed ga6 can be passed to either one bed at any given time or may be passed to at least two beds at any given time depending upon the particular proce66ing cycle de6ired for any given application of the invention. Also a6 in conventional practice, the invention may employ one, two, three or more cocurrent depre6surization step6, if desired, with the gas relea6ed from the product end of the bed during said step6 being u6ed by pre66ure equalization and provide purge purpo6es as indicated above. The invention thus has a de6irable flexibility in recovering intermediate product during PSA proces6ing operations that are es6entially compatible with the established and advantageous commercial practice as set forth in the patents referred to above and a6 otherwise known in the art.
It i8 within the scope of the invention to ~eparate any feed gas mixture containing a less D-13,54~
~;~S~53~
- lZ - -readily adsorbed component, an intermediate component and a more readily adsorbable component, with said component being understood to comprisQ one ga~ or more than one gas having relatively similar ad~orption characteristics with respect to the adsorbent e~ployed and the separation and intermediate product recovery desired. U~ing 5A
molecular sieve or other such conventional adsorbent with respect to a gas mixture containing hydrogen, argon, nitrogen and carbon monoxide, hydrogen will be the least adsorbed, argon will adsorb more strongly than hydrogen, nitrogen will be adsorbed more ~trongly than argon, and carbon monoxide will be the most readily or strongly ad~orbed of all the components. In the practice of the invention, it i6 readily feasible to recover either argon, nitrogen, or bo~h, as the intermediate componen~ at a desired purity level. For such purpose, the feed gas mixture is introduced to the feed end of a~
adsorption bed at a higher adsorption pres~ure, with the les6 readily adsorbable component, i.e., hydrogen or hydrogen together with argon, being removed from the product end of the bed. A
displacement gas essQntially free of hydrogen and having a molar concentration of said nitrogen and/or carbon monoxide greater than in the feed gas mixture is introduced to the feed end of the bed so as to displace residual amounts of hydrogen component from the void spaces of the bed and from the bed itself.
The bed is also cocurrently de2ressurized so as to release additional void space ga~ from the product end of the bed. This may be carried out either D-13,543 - 13 _ lZS~S3~
before said cocurrent displacement step, during or after said step. Those skilled in the art will appreciate that the cocurrent depressurization step and said cocurrent displacement step will be carried out so as to essentially completely displace hydrogen from the bed, with said essentially complete displacement being consistent with the intermediate product purity specification established for any particular application. The bed is then further cocurrently depressurized to discharge ~he intermediate component, i.e. argon, from the product end of the bed as a product at the desired purity. The bed may then be countercurrently depressurized to a lower desorption pressure. The gas removed from the feed end of the bed during this step comprises said more readily adsorbable component, a portion of which may be used to provide the co-purge or displacement gas recycled and added to the feed end of the bed or to another bed in the system. The bed is then repressurized to ~aid higher adsorption pressure. The gas released from the product end of the bed during the cocurren-t depressurization of the bed, comprising hydrogen, may be used to purge the bed at its lower desorption, pressure prior to repressurization thereof. Optionally, the bed may be so purged without a preceding, separate countercurrent depressurization step. As carried out in the manner of this embodiment of the invention, an intermediate component, such as argon, or nitrogen or a mix~ure thereof, may be recovered at a desired purity level from the original feed gas mixture.
D-13,543 ~LZS~31 .
In another illustrative example, it is desired to employ the PSA proce6s of the invention to obtain a moderate purity, e.g. minimum 75%, carbon monoxide s~ream having a maximum of 7~
5 hydrogen from a partial oxidation gas available at 12-13 bar and having the following composition in mol. %: hydrogen, 62%: C0, 31%: CH4, 1.5%; C02, 3.5% and other (including nitrogen, and argon~, 2.0%. The C0-containing product gas is to be employed in the production of a chemical intermediate by a process ~hat consumes C0 and produces C02. A C0 and C02-rich gas is purged from the reaction by which the chemical intermediate is produced, with t~is purged gas containing about 55% C0 and about 20-25% C0z. This gas, essentially free of hydrogen and having a molar concentration of both intermediate and more readily ad60rbable components greater than in the feed gas mixture to the PSA system, can thus be used as the displaceme~t gas used to displace hydrogen in the less readily adsorbable component from the beds of the adsorption 6y~tem. For this separation, a four bed adsorption sy6tem may be conveniently employed, with the 6~ hydrogen-containing feed gas being introduced to the feed end of each adsorbent bed, in ~equence, at 12-13 bar. In this embodiment of the invention, the cocurrent displacement step is carried out after the initial feed-adsorption step, with cocurrent depressurization for pressure equalization and provide purge purposes being carried out after ~aid displacemen~ step. The pressure is reduced to about 4.5 bar during such D-13,543 _ 15 -cocurrent depre~suriz~tion steps. The bed i~ then further cocurrently de~re~surized from 4.5 to 1.5.
bar, with ~he desired C0-rich intermediate product being recovered fro~ ~he produc~ end of the bed during thi~ ~tep. Countercurrent depres~urization to 1 bar and purging of the bed are then carried out prior to repres~uriza~ion of the bed to higher adsorption pre6sure for use in the treatment of additio~al quantities of the feed gas ~ixture a~
cyclic operatio~6 are continuously carried out in ~aid bed. The practice of ~he invention can be illu~trated by Table I below with respect to the indicated four hed embodiment of the invention.
TABLE_I
B~D N0 CYCLE
_ ~ , ~ ~ ! ~
I ~ ~/C ~ ~o o Y
I _ l __ 3 B~ D ~ / ~ ~/C / ~ ~3D
_ __ l _ ___ . ~ / /~ I BO O ,D ~ _ L a/C i In thi8 Table, A represents an ad60rption step at higher ~dsorption pressure, with the feed gas mixture bei~g introduced to the feed end of the bed and the les~ readily adsorbable component being discharged from the produc~ end thereof: c represant6 ~ocurrent di~placement by the in~roduction of ga6 e6~entially ~ree of the les~
D-13~543 i3~L
readily adsorbable component to the feed end of the bed so as to essentially completely displace said less readily adsorbable component from the be~ 1 represents a cocurrent depre6surization-pressure equalization step between a bed that has completed its cocurrent displacement 6tep and a bed that has been purged at lower desorption pressure E
represent6 a cocurrent depres6urization step with release of additional quantities of les6 readily adsorbable component and passage of said gas to an external storage vessel for use in providing purge gas to a bed in said system BD represents a cocurrent depres6urization step with discharge of said intermediate component rom the product end thereof as C0-enriched product of desired purity enhancement; D represents a countercurrent depressurization step; P repre~ents a purge step using gas withdrawn from said external storage vessel and R represent6 repres6urization to higher adsorption pressure. In the process of the illustrated example, it will be seen that only one bed of the system undergoes the adsorption -cocurrent displacement processing sequence at any given time in the overall cycle. The moderate purity hydrogen product obtained in this example, i.e. at a 90-94% purity, can be recycled -to the main gas stream to the partial oxidation unit. The more readily adsorbable component, which is C02, is removed from the bed during steps D and P, along with part o the methane and the C0 not recovered as intermediate product during step BD.
It will be seen from the Table that the PSA
cycle of this embodiment of the invention is similar D~13,543 - 17 - ~2~S3~
to the conventional PSA cycle, with the incorpora~ion of said C and 8D æteps being entirely compatible with such conventional prQcessing. The proce6~ described is very ad~antag~ous in the production of intermediate component C0 having practical produc~ specifications 8UC~ as indieated above from a multicomponent feed gaB mixture .
A~ an illustrative exa~ple of the flexibility available in the practice of the invention, the gas separation and intermediate product recovery of the example above can also be con~eniently carried out in a five bed adsorption system in which only one bed is on adsorption ae any given time and a portion of the intermediate component i8 employed for r~cycle to the feed end of a bed as displacement ga~. The processing cycle employed in thi~ embodiment i6 illustIated in Table II below:
TABLE II
ED N0. CYCLE
~1 C ~1~
~1 ~ ~4 c /~
l , _ _~ ._ _~
3 f5'0 1 fl J~? ~ C ~ ~7 ~ _~ . _ . ~ ~
~ D ~ ~ ~ C
~ ~ = ~ A
D-13,543 5~i3~L
, - 18 -In this Table II, A, C, 1, E~ BD, P and R
all have the same meanings as in the Table I example above. It will be seen that each bed, in turn, undergoes adsorption: cocurrent displacemen~;
cocurrent depressurization - pressure equalization with the third higher number bed, with the latter bed beiny repressurized from its lower desorption pressure: further cocurrent depressurization with release of additional quantities of less readily adsorbable ~omponent and passage of said gas to an external storage vessel for use in providing purge gas to a bed in the system; cocurrent depressurization with discharge of the intermediate component from the product end of the bed; providing purge gas to the product end of said bed from the external storage vessel, with the bed decreasing to its lower desorption pres~ure during said purge step, without the inclusion of a separate countercurrent depressurization s~ep prior to purging of the bed; pressure equalization with passage of gas to said bed from another bed in the system initially at higher pressure: and rQpressurization of the bed to higher adsorption pressure. As the displacement gas used in step C, it is convenien~ to divert or recycle a por~ion of the intermediate componen~. discharged from the product bed of the bed during step BD for repressurization and introduction to the bed as displacement gas during step C.
As another illustrative example of ~he practice of the invention, an off-gas from a s~eel converter, having a composition consisting D-13,543 ~25~)S3~
essen~ially of nitrogen, carbon monoxide and carbon dioxide, may be treated to recover carbon monoxide as a desired intermediate product. Such an off-gas, containing 15% nitrogen, 69% C0 and 16% C02 on a mol basis, is introduced to an adsorption system containing 8iX beds, with each bed containing 45 vol.% activated carbon adsorbent and 55 vol.% 13X
type molecular sieve adsorbent. At this higher adsorption pressure, a leading C0 adsorption front is established and moves in the direction of the produc~ end of each bed ahead of a trailing C02 ~ront, while the less readily adsorbable component, i.e. nitrogen that may contain some C0, is discharged from the product end of the bed. This gas, or a portion thereof, may be used for the repressurization of another bed. The bed is then cocurrently depressurized with release of less readily adsorbable component, i.e. nitrogen, a~d passage of said gas to another bed in the system, initially at lower pressure and undergoing repres~urization, for pressure equalization between the beds. The bed is then further cocurrently depressurized with release of additional quantities of les~ readily adsorbable component and passage of gaid gas to an external storage vessel for use in providing purge gas to a bed in the system.
Simultaneously with ~aid cocurrent depressurization step6 indicated above, a cocurrent displacement ~tep is carried ou~ by introduction of gas essentially free of the le68 readily adsorbable component to the feed end of the bed. Further cocurrent depressurization is then carried ou~ with discharge D-13,543 ~Z~31 ! - 20 ~
of the desired C0 intermediate component from the product end of the bed. The bed is then countercurrently depressurized to remove the ~08t readily adsorbable ~omponen~, i.e. C02~ fro~ the ~eed end of the bed. In this ambodiment, which i8 illu6trated in Table III below, a por~ion of this countercurrent depressurization ga~ i8 diverted for pressurization and use as the di~placement gas for anot~er bed in the system. The bed i~ then purged with the purge ga6 bei~g ~rovided from 6aid external ~torage ve6sel, ~f er which the bed i6 repreSBUri2ed to higher ad60rption pre~sure.
TABLE_III
~ED N0. CYCLE
~ A ~ c ~ ~ Y
;Z _ ~ 1/ C ~- , ~,_ ' /~
3 ~ ~ /~ /~ / G / ~ 7 67 '1/ 6' / iz --/~ I / ' c ~' "~
~ ~ ~ ~ 7~zr~
In thi Table, A, 1, C, E, BD, D, P and R
have the same meaning~ as in Table I above. In this illustrative exa~ple of the invention, the feed gas mixture i~ introduced into the bed at a pressure of 25 9 bar, with the processing cycle being 6een to D-13,543 ~LZ~iiO53~
include only one bed on said adsorption step at any given time. The bed pressure is reduced to 4 bar during the cocurrent displacement, cocurrent depressurization - pressure equalization and provide purge steps, i.e. during steps 1, C and E. During cocurrent depressurization ste~ BD during which intermediate component CO is recovered, further depressuri2ation to 1-2 bar occurfi, and 99% CO is extracted from the product end of the bed.
Countercurrent depressurization step D is carried out ~o 0.4 bar, with the gas thereby released from the feed end of the bed containing about 42% CO2 and 52~ CO. This gas is conveniently repressurized and introduced to another bed in the æystem as the di~placement gas used during step C. Ga~ obtained during step D in the illustrated Table can thus advantageously be used as displacement gas for the second higher numbered bed in the system, for example, such gas from step D of bed 5 can be used for introduction to bed 1 during step C therein, and gas from step D of bed 1 can be used as displacement gas for bed 3. In the passing of cocurrent depressurization gas to an external storage vessel, those skilled in the art will appreciate that it is desirable that said gas, which i~ added to 6aid ves6el in an indirect pressure equalization as opposed to direct pressure equalization in which the gas pa~ses directly from one bed to another, be added to the external vessel with plug flow so as to maintain the component composition profile of the gas a6 it is removed from ~he bed. By such means, the highest purity purge gas will be added and D-13,543 - 22 - 12S~S3~
retained in the external vessel first with less pure gas being ~o added and retained separately. Upon subsequent release of gas from said vessel through the same end at which gas was added thereto, relatively more impure and then relatively more pure gas will be discharged from the vessel, enabling, for examele, purge to be carried out using the most pure gas for the final portions of said purge stap.
The purge gas effluent, having a composition of 36~6 mol % nitrogen, 24.4 mol % CO and 39.0 mol % CO2, may desirably be used as a fuel gas to enhance the overall gas separation operation.
It will be understood that various changes and modifications can be made in the details of the PSA process with intermediate product recovery as herein described and illustrated above without departing from the scope of the invention as set forth in the appended claims. Thus, the number of beds employed, the number of cocurrent depressurization-pre~sure equalization steps employed, whether or not 6uch pressure equalizations are direct or indirect through an external storage vessel, whether the displacement gas employed is available from an external source or is supplied by diverting a portion of the intermediate product or the countercurrent depressurization gas~ as in the various examples above, may all be varied depending upon the circumstances and results desired in any given application. Likewise, the multicomponent gas separation desired, the in~ermediate component to be recovered and the desired purity level thereof, the use of countercurrent depressurization, with or D-13,s43 - 23 - ~ S3~
without purge, or the use of a purge step, with or without countercurrent purge, the use of an external vessel for providing purge gas or the alternate use, also in accordance with conventional practice, of cocurrent depressurization - direct provide purge to another bed, may be subject to wide variation within the scope of the invention. It will be appreciated that PSA system~ necessarily incorporate various conduits, valves, and other control features to accomplish the necessary switching of adsorbent beds from one step to the next, in appropriate sequence as, in conventional PSA operations. It will also be appreciated that the invention can be carried out using any suitable adsorbent material having a selectivity for various components of a feed gas mixture over other such components, thereby providing a less readily adsorbable component, an intermediate componen~ and a more readily adsorbable component. Suitable adsorbents known in the art and commercially available include zeolitic molecular sieve6, activated carbon, silica gel, activated alumina and the like. The Kiyonaga patent, U.S.
3,176,444, and the patents referred to above contain further information concerning the various known adsorbents used for PSA operations and suitable for use in the prac~ice of the invention.
From the description and examples above, it will be seen that the invention provides a hi~hly practical means for separating and recovering an intermediate component from a feed gas mixture. The process of the invention enables such desirable intermediate product recovery to be achieved in an D-13,543 - 24 ~ 3~
advantagaous manner compatible with conventional ~ulti-bed PSA processing. Thus, the processing and mechanical complexity of employing pairs of said beds to achieve the desirad recovery of the intermediate component is obviated, and the invention is carried out with only relatively minor modification of existing PSA processing techniques.
In highly desirable embodiments, the countercurrent depressuriza~ion gas or a portion of the intermediate component product is readily recycled for use as the displacement gas in the cocurrent depressurization - less readily adsorbable component displacemant step that enables desired intermediate product recovery to be accomplished upon further cocurrent depressurization of the bed. A variety of desirable gas separations, such as the recovery of CO from basic oxygen furnace gas, are thus made possible for use in practical commercial operations. Such applications enhance and extend the development of the PSA technology in providing practical, commercially feasible approaches for meeting the growing gas separation and recovery requirements of industrial societies.
D-13,543
recoveries of inte~mediate components of gas mixtures in a manner com~at~ble with conventional, convenient PSA proces~ing. Upon the development of such convenient processing capability for intermediate product recovery, those skilled in the art will appreciate that a variety of practical commercial PSA operations could be advantageou ly carried out 60 aB to achieve desirable intermediate product recovery.
one approach heretofore suggested for such development of intermediate product reco~ery capabili~y is set forth in European Patent Specification 0 008 88Z, published December 30, 19~1, in the name of Shivaji Sircar. Disclosed ~5 therein is the separation of multicomponent feed gas mix~ure having a primary key component, a secondary key component and a tertia~y component. For this purpose, an adsorption system comprising a plurality of bed pairs, i.e., two beds in series, is provided, with each bed pair functioning in the manner of a single bed in accordance with the conventional PSA
processing techniques referred to above. The feed gas mixture pa~ses through a first bed of the pair and then through the other, with a tertiary component adsorption front established in the first bed and a secondary key component ad60rption ront being establi6hed in the second bed of the pair.
The flow of the feed gas mixture is then interrupted, and gas flow between the beds are discontinued. The beds are then separa~ely subjected to rin6ing, product reduction, purge and partial repressurization steps prior to the re-e~tablishing D-l3~s43 ~ZS~)S3~
of flow therebetween to achieve final repres~uriæation, initiation of the flow of the feed gafi mixture thereto and repetition of the processing cycle. While the disclosed process can be employed for intermed;ate product recovery, the complex processing steps necessarily associated with the use of pairs of adsorbent beds in multi-feed systems, together with the associated complexity of lines, valves, controls and the like, serve to limit the practical applicability of th~ process. There remains in the art, thereafter, the need for an improved PSA process capable of facilitating intermediate product recovery in a prac~ical, convenient manner.
It is an object of the invention, therefore, to provide an improved PSA process capable of enabling intermediate product recovery to be achieved.
It is another object of the invention to provide a process facilitating said intermediate product recove~y in a manner compatible with conventional multi-bed PSA ~ystems.
It is a further object of the invention to pcovide a PS~ process having advantageous flexibility in recovering desired intermediat~
product from multicomponent feed gas mixtures.
With these and other objects in mind, the invention i~ hereinafter set forth in detail, the novel featu~es thereof being particularly pointed out in the appended claims.
D-13,543 ~LZ50~3~
Summary of_the Invention The intermediate component of a feed gas mixture is recovered as a separate product in PSA
processing by first assuring that the less readily adsorbable component of a ~ulticomponent feed gas mixture is essentially completely removed from an adsorbent bed and by then employing a cocurrent depressurization step to remove said intermedia~e component from the product end of the bed. In various adsorption systems having four or more beds, particularly desirable processing cycles are employed, with a portion of the more readily adsorbable component recovered during countercurren~
depressurization or a portion of the intermediate component product being conveniently employed as said dis~lacement gas introduced, on a cyclic basis, to each bed in the adsorption system.
Detailed_Dascrip~ion of the Invention The PSA process of the invention relates to conventional PSA proce6sin~ in which each bed of an adsorption system undergoes, on a cyclic basis, higher pres6ure ad~orption, cocurrent depressurization to intermediate pressure level(s) with release of void space gas from the product end of the bed, countercurrent depressurization ~o lower de60rption pressure with the release of desorbed gas f Lom the feed end of the bed, with or without purge of the bed, and repre~surization to higher adsorption pressure. The ob~ects of the invention are accomplished, in the separation of a feed gas mixture containing a less readily adsorbable component, an intermediate component and a more D-13,543 ~;~SOS31 g Leadily adsorbable component, by employing a cocurrent displacement step in which the less readily adsorbable component is essentially completely removed from the adsorption bed. The bed is then cocurrently depee6suri~ed with the intermediate component being discharged from the product end thereof as a product of desired pueity.
In the multi-bed ad~orption systems to which the invention is directed, the displacemen~ gas used for each bed is advantageou~ly obtained by diverting a portion of the gas releaæed from that or another bed in the system during the cocurrent depressurization or ~he countercurrent depressurization steps, although other ~uitable ~isplacement gas may also be employed if available with respect ~o the overall processing operation in which PSA with intermediate product recovery is being employed.
Those skilled in the art will appreciate that the high pressure adsorption step of the PSA
procesz comprises introduciny the feed ga~ mixture to the ~eed end of the ad~orbent bed at a higher ad~orption pressure. The less readily adsorbable component passe6 through the bed and is discharged from the product end thereof. An adsorption front or fronts are established in the bed with said fron~s likewise moving through the bed from ths feed end towaed the product end thereof. When the feed gas contains a less readily adsorbabla component. an inteemediate component and a more readily adsorbable component, a leading adsorption front of said intermediate component will be established and move through the bed in the direction of the product or D-13,543 di6charge end thereof ahead of a trailing adsorption front of the more readily adsorbable component. By the use of a cocurrent displacement gas essentially free of the less readily adsorbable componant, thus having a molar concentration of intermedia~e and/or more readily adsorbable components, the less readily adsorbable component that remains in the void spaces of the adsorbent bed ahead of the leading adsorption front can be essentially completely displaced from the bed. This enables the intermediate component to be thereafter discharged from the product end of the bed as a product of desired eurity by cocurrently depressurizing ~he bed. As will be indicated below, the cocurrent depressurization step for intermediate product recovery is desirably carried out in addition to the cocurrent depressurization step or steps conventionally employed wherein the void space gas thus released being u~ed for pressure equalization with other beds or to provide purge gas to such beds. Countercurrent depressuriæation of the bed i8 carried out subsequent to the intermediate product recovery 6tep, as in conventional PSA processing. When the gas remo~ed from the bed during either the conventional cocurrent depressurization step or the countercurrent depressurization step, or a portion thereof, is diverted to the feed end of another bed for use as the displacement gas, it will be appreciated that said gas is repres~urized sufficiently to enable displacement of less readily adsorbable component from the void spaces of the bed to be accomplished. In effect, an impurity front D-13,543 11- ~L251~531 existing in one bed is moved in the direction of either the feed or the product end of one bed and released gas i6 introduced to another bed so as to facilitate the displacement of less readily adsorbable component from that bed.
The invention can advantageously be practiced in multi-bed PSA 6ystem~ having at lea6t four adsorbent beds therein. Preferably the invention can be utilized to advantage in sy6tems having four to ~ix adsorbent beds, although it will also be appreciated that the invention can also be employed in larger ~y6tem6 having 6even or more beds. It will also be appreciated that, as in conventional practice, the feed ga6 can be passed to either one bed at any given time or may be passed to at least two beds at any given time depending upon the particular proce66ing cycle de6ired for any given application of the invention. Also a6 in conventional practice, the invention may employ one, two, three or more cocurrent depre6surization step6, if desired, with the gas relea6ed from the product end of the bed during said step6 being u6ed by pre66ure equalization and provide purge purpo6es as indicated above. The invention thus has a de6irable flexibility in recovering intermediate product during PSA proces6ing operations that are es6entially compatible with the established and advantageous commercial practice as set forth in the patents referred to above and a6 otherwise known in the art.
It i8 within the scope of the invention to ~eparate any feed gas mixture containing a less D-13,54~
~;~S~53~
- lZ - -readily adsorbed component, an intermediate component and a more readily adsorbable component, with said component being understood to comprisQ one ga~ or more than one gas having relatively similar ad~orption characteristics with respect to the adsorbent e~ployed and the separation and intermediate product recovery desired. U~ing 5A
molecular sieve or other such conventional adsorbent with respect to a gas mixture containing hydrogen, argon, nitrogen and carbon monoxide, hydrogen will be the least adsorbed, argon will adsorb more strongly than hydrogen, nitrogen will be adsorbed more ~trongly than argon, and carbon monoxide will be the most readily or strongly ad~orbed of all the components. In the practice of the invention, it i6 readily feasible to recover either argon, nitrogen, or bo~h, as the intermediate componen~ at a desired purity level. For such purpose, the feed gas mixture is introduced to the feed end of a~
adsorption bed at a higher adsorption pres~ure, with the les6 readily adsorbable component, i.e., hydrogen or hydrogen together with argon, being removed from the product end of the bed. A
displacement gas essQntially free of hydrogen and having a molar concentration of said nitrogen and/or carbon monoxide greater than in the feed gas mixture is introduced to the feed end of the bed so as to displace residual amounts of hydrogen component from the void spaces of the bed and from the bed itself.
The bed is also cocurrently de2ressurized so as to release additional void space ga~ from the product end of the bed. This may be carried out either D-13,543 - 13 _ lZS~S3~
before said cocurrent displacement step, during or after said step. Those skilled in the art will appreciate that the cocurrent depressurization step and said cocurrent displacement step will be carried out so as to essentially completely displace hydrogen from the bed, with said essentially complete displacement being consistent with the intermediate product purity specification established for any particular application. The bed is then further cocurrently depressurized to discharge ~he intermediate component, i.e. argon, from the product end of the bed as a product at the desired purity. The bed may then be countercurrently depressurized to a lower desorption pressure. The gas removed from the feed end of the bed during this step comprises said more readily adsorbable component, a portion of which may be used to provide the co-purge or displacement gas recycled and added to the feed end of the bed or to another bed in the system. The bed is then repressurized to ~aid higher adsorption pressure. The gas released from the product end of the bed during the cocurren-t depressurization of the bed, comprising hydrogen, may be used to purge the bed at its lower desorption, pressure prior to repressurization thereof. Optionally, the bed may be so purged without a preceding, separate countercurrent depressurization step. As carried out in the manner of this embodiment of the invention, an intermediate component, such as argon, or nitrogen or a mix~ure thereof, may be recovered at a desired purity level from the original feed gas mixture.
D-13,543 ~LZS~31 .
In another illustrative example, it is desired to employ the PSA proce6s of the invention to obtain a moderate purity, e.g. minimum 75%, carbon monoxide s~ream having a maximum of 7~
5 hydrogen from a partial oxidation gas available at 12-13 bar and having the following composition in mol. %: hydrogen, 62%: C0, 31%: CH4, 1.5%; C02, 3.5% and other (including nitrogen, and argon~, 2.0%. The C0-containing product gas is to be employed in the production of a chemical intermediate by a process ~hat consumes C0 and produces C02. A C0 and C02-rich gas is purged from the reaction by which the chemical intermediate is produced, with t~is purged gas containing about 55% C0 and about 20-25% C0z. This gas, essentially free of hydrogen and having a molar concentration of both intermediate and more readily ad60rbable components greater than in the feed gas mixture to the PSA system, can thus be used as the displaceme~t gas used to displace hydrogen in the less readily adsorbable component from the beds of the adsorption 6y~tem. For this separation, a four bed adsorption sy6tem may be conveniently employed, with the 6~ hydrogen-containing feed gas being introduced to the feed end of each adsorbent bed, in ~equence, at 12-13 bar. In this embodiment of the invention, the cocurrent displacement step is carried out after the initial feed-adsorption step, with cocurrent depressurization for pressure equalization and provide purge purposes being carried out after ~aid displacemen~ step. The pressure is reduced to about 4.5 bar during such D-13,543 _ 15 -cocurrent depre~suriz~tion steps. The bed i~ then further cocurrently de~re~surized from 4.5 to 1.5.
bar, with ~he desired C0-rich intermediate product being recovered fro~ ~he produc~ end of the bed during thi~ ~tep. Countercurrent depres~urization to 1 bar and purging of the bed are then carried out prior to repres~uriza~ion of the bed to higher adsorption pre6sure for use in the treatment of additio~al quantities of the feed gas ~ixture a~
cyclic operatio~6 are continuously carried out in ~aid bed. The practice of ~he invention can be illu~trated by Table I below with respect to the indicated four hed embodiment of the invention.
TABLE_I
B~D N0 CYCLE
_ ~ , ~ ~ ! ~
I ~ ~/C ~ ~o o Y
I _ l __ 3 B~ D ~ / ~ ~/C / ~ ~3D
_ __ l _ ___ . ~ / /~ I BO O ,D ~ _ L a/C i In thi8 Table, A represents an ad60rption step at higher ~dsorption pressure, with the feed gas mixture bei~g introduced to the feed end of the bed and the les~ readily adsorbable component being discharged from the produc~ end thereof: c represant6 ~ocurrent di~placement by the in~roduction of ga6 e6~entially ~ree of the les~
D-13~543 i3~L
readily adsorbable component to the feed end of the bed so as to essentially completely displace said less readily adsorbable component from the be~ 1 represents a cocurrent depre6surization-pressure equalization step between a bed that has completed its cocurrent displacement 6tep and a bed that has been purged at lower desorption pressure E
represent6 a cocurrent depres6urization step with release of additional quantities of les6 readily adsorbable component and passage of said gas to an external storage vessel for use in providing purge gas to a bed in said system BD represents a cocurrent depres6urization step with discharge of said intermediate component rom the product end thereof as C0-enriched product of desired purity enhancement; D represents a countercurrent depressurization step; P repre~ents a purge step using gas withdrawn from said external storage vessel and R represent6 repres6urization to higher adsorption pressure. In the process of the illustrated example, it will be seen that only one bed of the system undergoes the adsorption -cocurrent displacement processing sequence at any given time in the overall cycle. The moderate purity hydrogen product obtained in this example, i.e. at a 90-94% purity, can be recycled -to the main gas stream to the partial oxidation unit. The more readily adsorbable component, which is C02, is removed from the bed during steps D and P, along with part o the methane and the C0 not recovered as intermediate product during step BD.
It will be seen from the Table that the PSA
cycle of this embodiment of the invention is similar D~13,543 - 17 - ~2~S3~
to the conventional PSA cycle, with the incorpora~ion of said C and 8D æteps being entirely compatible with such conventional prQcessing. The proce6~ described is very ad~antag~ous in the production of intermediate component C0 having practical produc~ specifications 8UC~ as indieated above from a multicomponent feed gaB mixture .
A~ an illustrative exa~ple of the flexibility available in the practice of the invention, the gas separation and intermediate product recovery of the example above can also be con~eniently carried out in a five bed adsorption system in which only one bed is on adsorption ae any given time and a portion of the intermediate component i8 employed for r~cycle to the feed end of a bed as displacement ga~. The processing cycle employed in thi~ embodiment i6 illustIated in Table II below:
TABLE II
ED N0. CYCLE
~1 C ~1~
~1 ~ ~4 c /~
l , _ _~ ._ _~
3 f5'0 1 fl J~? ~ C ~ ~7 ~ _~ . _ . ~ ~
~ D ~ ~ ~ C
~ ~ = ~ A
D-13,543 5~i3~L
, - 18 -In this Table II, A, C, 1, E~ BD, P and R
all have the same meanings as in the Table I example above. It will be seen that each bed, in turn, undergoes adsorption: cocurrent displacemen~;
cocurrent depressurization - pressure equalization with the third higher number bed, with the latter bed beiny repressurized from its lower desorption pressure: further cocurrent depressurization with release of additional quantities of less readily adsorbable ~omponent and passage of said gas to an external storage vessel for use in providing purge gas to a bed in the system; cocurrent depressurization with discharge of the intermediate component from the product end of the bed; providing purge gas to the product end of said bed from the external storage vessel, with the bed decreasing to its lower desorption pres~ure during said purge step, without the inclusion of a separate countercurrent depressurization s~ep prior to purging of the bed; pressure equalization with passage of gas to said bed from another bed in the system initially at higher pressure: and rQpressurization of the bed to higher adsorption pressure. As the displacement gas used in step C, it is convenien~ to divert or recycle a por~ion of the intermediate componen~. discharged from the product bed of the bed during step BD for repressurization and introduction to the bed as displacement gas during step C.
As another illustrative example of ~he practice of the invention, an off-gas from a s~eel converter, having a composition consisting D-13,543 ~25~)S3~
essen~ially of nitrogen, carbon monoxide and carbon dioxide, may be treated to recover carbon monoxide as a desired intermediate product. Such an off-gas, containing 15% nitrogen, 69% C0 and 16% C02 on a mol basis, is introduced to an adsorption system containing 8iX beds, with each bed containing 45 vol.% activated carbon adsorbent and 55 vol.% 13X
type molecular sieve adsorbent. At this higher adsorption pressure, a leading C0 adsorption front is established and moves in the direction of the produc~ end of each bed ahead of a trailing C02 ~ront, while the less readily adsorbable component, i.e. nitrogen that may contain some C0, is discharged from the product end of the bed. This gas, or a portion thereof, may be used for the repressurization of another bed. The bed is then cocurrently depressurized with release of less readily adsorbable component, i.e. nitrogen, a~d passage of said gas to another bed in the system, initially at lower pressure and undergoing repres~urization, for pressure equalization between the beds. The bed is then further cocurrently depressurized with release of additional quantities of les~ readily adsorbable component and passage of gaid gas to an external storage vessel for use in providing purge gas to a bed in the system.
Simultaneously with ~aid cocurrent depressurization step6 indicated above, a cocurrent displacement ~tep is carried ou~ by introduction of gas essentially free of the le68 readily adsorbable component to the feed end of the bed. Further cocurrent depressurization is then carried ou~ with discharge D-13,543 ~Z~31 ! - 20 ~
of the desired C0 intermediate component from the product end of the bed. The bed is then countercurrently depressurized to remove the ~08t readily adsorbable ~omponen~, i.e. C02~ fro~ the ~eed end of the bed. In this ambodiment, which i8 illu6trated in Table III below, a por~ion of this countercurrent depressurization ga~ i8 diverted for pressurization and use as the di~placement gas for anot~er bed in the system. The bed i~ then purged with the purge ga6 bei~g ~rovided from 6aid external ~torage ve6sel, ~f er which the bed i6 repreSBUri2ed to higher ad60rption pre~sure.
TABLE_III
~ED N0. CYCLE
~ A ~ c ~ ~ Y
;Z _ ~ 1/ C ~- , ~,_ ' /~
3 ~ ~ /~ /~ / G / ~ 7 67 '1/ 6' / iz --/~ I / ' c ~' "~
~ ~ ~ ~ 7~zr~
In thi Table, A, 1, C, E, BD, D, P and R
have the same meaning~ as in Table I above. In this illustrative exa~ple of the invention, the feed gas mixture i~ introduced into the bed at a pressure of 25 9 bar, with the processing cycle being 6een to D-13,543 ~LZ~iiO53~
include only one bed on said adsorption step at any given time. The bed pressure is reduced to 4 bar during the cocurrent displacement, cocurrent depressurization - pressure equalization and provide purge steps, i.e. during steps 1, C and E. During cocurrent depressurization ste~ BD during which intermediate component CO is recovered, further depressuri2ation to 1-2 bar occurfi, and 99% CO is extracted from the product end of the bed.
Countercurrent depressurization step D is carried out ~o 0.4 bar, with the gas thereby released from the feed end of the bed containing about 42% CO2 and 52~ CO. This gas is conveniently repressurized and introduced to another bed in the æystem as the di~placement gas used during step C. Ga~ obtained during step D in the illustrated Table can thus advantageously be used as displacement gas for the second higher numbered bed in the system, for example, such gas from step D of bed 5 can be used for introduction to bed 1 during step C therein, and gas from step D of bed 1 can be used as displacement gas for bed 3. In the passing of cocurrent depressurization gas to an external storage vessel, those skilled in the art will appreciate that it is desirable that said gas, which i~ added to 6aid ves6el in an indirect pressure equalization as opposed to direct pressure equalization in which the gas pa~ses directly from one bed to another, be added to the external vessel with plug flow so as to maintain the component composition profile of the gas a6 it is removed from ~he bed. By such means, the highest purity purge gas will be added and D-13,543 - 22 - 12S~S3~
retained in the external vessel first with less pure gas being ~o added and retained separately. Upon subsequent release of gas from said vessel through the same end at which gas was added thereto, relatively more impure and then relatively more pure gas will be discharged from the vessel, enabling, for examele, purge to be carried out using the most pure gas for the final portions of said purge stap.
The purge gas effluent, having a composition of 36~6 mol % nitrogen, 24.4 mol % CO and 39.0 mol % CO2, may desirably be used as a fuel gas to enhance the overall gas separation operation.
It will be understood that various changes and modifications can be made in the details of the PSA process with intermediate product recovery as herein described and illustrated above without departing from the scope of the invention as set forth in the appended claims. Thus, the number of beds employed, the number of cocurrent depressurization-pre~sure equalization steps employed, whether or not 6uch pressure equalizations are direct or indirect through an external storage vessel, whether the displacement gas employed is available from an external source or is supplied by diverting a portion of the intermediate product or the countercurrent depressurization gas~ as in the various examples above, may all be varied depending upon the circumstances and results desired in any given application. Likewise, the multicomponent gas separation desired, the in~ermediate component to be recovered and the desired purity level thereof, the use of countercurrent depressurization, with or D-13,s43 - 23 - ~ S3~
without purge, or the use of a purge step, with or without countercurrent purge, the use of an external vessel for providing purge gas or the alternate use, also in accordance with conventional practice, of cocurrent depressurization - direct provide purge to another bed, may be subject to wide variation within the scope of the invention. It will be appreciated that PSA system~ necessarily incorporate various conduits, valves, and other control features to accomplish the necessary switching of adsorbent beds from one step to the next, in appropriate sequence as, in conventional PSA operations. It will also be appreciated that the invention can be carried out using any suitable adsorbent material having a selectivity for various components of a feed gas mixture over other such components, thereby providing a less readily adsorbable component, an intermediate componen~ and a more readily adsorbable component. Suitable adsorbents known in the art and commercially available include zeolitic molecular sieve6, activated carbon, silica gel, activated alumina and the like. The Kiyonaga patent, U.S.
3,176,444, and the patents referred to above contain further information concerning the various known adsorbents used for PSA operations and suitable for use in the prac~ice of the invention.
From the description and examples above, it will be seen that the invention provides a hi~hly practical means for separating and recovering an intermediate component from a feed gas mixture. The process of the invention enables such desirable intermediate product recovery to be achieved in an D-13,543 - 24 ~ 3~
advantagaous manner compatible with conventional ~ulti-bed PSA processing. Thus, the processing and mechanical complexity of employing pairs of said beds to achieve the desirad recovery of the intermediate component is obviated, and the invention is carried out with only relatively minor modification of existing PSA processing techniques.
In highly desirable embodiments, the countercurrent depressuriza~ion gas or a portion of the intermediate component product is readily recycled for use as the displacement gas in the cocurrent depressurization - less readily adsorbable component displacemant step that enables desired intermediate product recovery to be accomplished upon further cocurrent depressurization of the bed. A variety of desirable gas separations, such as the recovery of CO from basic oxygen furnace gas, are thus made possible for use in practical commercial operations. Such applications enhance and extend the development of the PSA technology in providing practical, commercially feasible approaches for meeting the growing gas separation and recovery requirements of industrial societies.
D-13,543
Claims (40)
1. A pressure swing adsorption process for the separation of a feed gas mixture containing a less readily adsorbent component, an intermediately adsorbent component and a more readily adsorbent component, with recovery of said intermediate component as a desired product, in an adsorption system having at least four adsorbent beds, in each of which, on a cyclic basis, undergoes a processing sequence comprising:
(a) introducing the feed gas mixture to the feed end of the adsorbent bed at a higher adsorption pressure, with the less readily adsorbent component being discharged from the product end of the bed, and with a leading adsorption front of said intermediate component being established in the bed ahead of a trailing adsorption front of said more readily adsorbable component;
(b) introducing to the feed end of the bed a displacement gas essentially free of the less readily adsorbent component, the molar concentration of said intermediate and/or more readily adsorbable components being greater in said gas than in the feed gas mixture, said gas being introduced such that the less readily adsorbable component is essentially completely displaced from the bed prior to initiation of intermediate component recovery:
(c) cocurrently depressurizing said bed with discharge of said intermediate component from the product end thereof as a product of desired purity:
(d) countercurrently depressurizing and/or purging the bed to remove said more readily adsorbent component therefrom; and (e) repressurizing said bed to the higher adsorption pressure, whereby the intermediately adsorbable component can be recovered as a separate product of desired purity rather than being recovered with the least readily adsorbable component, or with the more readily adsorbable component or as a waste stream with said less and more readily adsorbable components.
(a) introducing the feed gas mixture to the feed end of the adsorbent bed at a higher adsorption pressure, with the less readily adsorbent component being discharged from the product end of the bed, and with a leading adsorption front of said intermediate component being established in the bed ahead of a trailing adsorption front of said more readily adsorbable component;
(b) introducing to the feed end of the bed a displacement gas essentially free of the less readily adsorbent component, the molar concentration of said intermediate and/or more readily adsorbable components being greater in said gas than in the feed gas mixture, said gas being introduced such that the less readily adsorbable component is essentially completely displaced from the bed prior to initiation of intermediate component recovery:
(c) cocurrently depressurizing said bed with discharge of said intermediate component from the product end thereof as a product of desired purity:
(d) countercurrently depressurizing and/or purging the bed to remove said more readily adsorbent component therefrom; and (e) repressurizing said bed to the higher adsorption pressure, whereby the intermediately adsorbable component can be recovered as a separate product of desired purity rather than being recovered with the least readily adsorbable component, or with the more readily adsorbable component or as a waste stream with said less and more readily adsorbable components.
2. The process of Claim 1 and including cocurrently depressurizing said bed to remove least readily adsorbable component gas from the product end thereof prior to the introduction of cocurrent displacement gas to the feed end of said bed.
3. The process of Claim 1 and including cocurrently depressurizing said bed to remove less readily adsorbable component gas from the product end thereof at the same time cocurrent displacement gas is introduced to the feed end thereof.
4. The process of Claim 1 and including cocurrently depressurizing said bed to remove residual less readily adsorbable component gas from the product end thereof subsequent to the time that cocurrent displacement gas is added to the feed end thereof.
5. The process of Claim 1 in which the bed is countercurrently depressurized to lower desorption pressure to remove said more readily adsorbable component therefrom.
6. The process of Claim 1 in which said bed is purged to remove said more readily adsorbable component therefrom.
7. The process of Claim 1 in which said bed is countercurrently depressurized to lower desorption pressure and is purged at said lower pressure to remove said more readily adsorbable component therefrom.
8. The process of Claim 1 and including diverting a portion of the intermediate component gas discharged from the product end of one bed for use as displacement gas for another bed included in said adsorption system.
9. The process of Claim 1 and including recycling more readily adsorbable component gas removed from the feed end of one bed, or a portion thereof, as displacement gag to the feed end of another bed in the absorption system.
10. The process of Claim 9 in which a portion of said more readily adsorbable component removed from the feed end of said bed is removed from the system.
11. The process of Claim 1 in which less readily adsorbable component gas released from the product end of the bed during cocurrent depressurization step (b) is introduced into another bed for pressure equalization purposes.
12. The process of Claim 2 in which less readily adsorbable component gas released from the product end of the bed during cocurrent depressurization thereof is passed to an external storage vessel to be used to provide purge gas to a bed in said system.
13. The process of Claim 1 in which the adsorption system comprises four adsorbent beds with each bed undergoing the following processing sequence, in turn, on a cyclic basis:
(a) adsorption at higher pressure;
(b) cocurrent displacement with said gas essentially free of the least readily adsorbable component with only one bed undergoing the adsorption - cocurrent displacement sequence at given time;
(c) cocurrent depressurization with release of less readily adsorbable component and passage of said gas to another bed undergoing repressurization for pressure equalization purposes:
(d) cocurrent depressurization with release of less readily adsorbable component and passage of said gas to an external storage vessel for use in providing purge to a bed in said system;
(e) cocurrent depressurization with discharge of said intermediate component from the product end of the bed;
(f) countercurrent depressurization to remove said most readily adsorbent component from the bed;
(g) providing purge gas to said bed;
(h) pressure equalization with another bed normally at higher pressure: and (i) repressurization to higher adsorption pressure.
(a) adsorption at higher pressure;
(b) cocurrent displacement with said gas essentially free of the least readily adsorbable component with only one bed undergoing the adsorption - cocurrent displacement sequence at given time;
(c) cocurrent depressurization with release of less readily adsorbable component and passage of said gas to another bed undergoing repressurization for pressure equalization purposes:
(d) cocurrent depressurization with release of less readily adsorbable component and passage of said gas to an external storage vessel for use in providing purge to a bed in said system;
(e) cocurrent depressurization with discharge of said intermediate component from the product end of the bed;
(f) countercurrent depressurization to remove said most readily adsorbent component from the bed;
(g) providing purge gas to said bed;
(h) pressure equalization with another bed normally at higher pressure: and (i) repressurization to higher adsorption pressure.
14. The process of Claim 1 in which the adsorption system comprises five adsorbent beds, with one bed on adsorption and another bed on said cocurrent displacement step at all stages of the overall processing sequence, with each bed undergoing the following processing sequence:
(a) adsorption at higher pressure;
(b) cocurrent displacement;
(c) cocurrent depressurization with release of the less readily adsorbable component for passage to another bed undergoing repressurization for pressure equalization therewith.
(d) cocurrent depressurization with discharge of said intermediate component from the product end of the bed;
(e) purge or vacuum desorption to remove said more readily adsorbable component from the bed;
(f) pressure equalization by the passage thereto of gas from another bed being cocurrently depressurized; and (g) repressurization to adsorption pressure.
(a) adsorption at higher pressure;
(b) cocurrent displacement;
(c) cocurrent depressurization with release of the less readily adsorbable component for passage to another bed undergoing repressurization for pressure equalization therewith.
(d) cocurrent depressurization with discharge of said intermediate component from the product end of the bed;
(e) purge or vacuum desorption to remove said more readily adsorbable component from the bed;
(f) pressure equalization by the passage thereto of gas from another bed being cocurrently depressurized; and (g) repressurization to adsorption pressure.
15. The process of Claim 1 in which each bed undergoes the following processing sequence, in turn, on a cyclic basis:
(a) adsorption at a higher adsorption pressure;
(b) cocurrent displacement by the introduction of gas essentially free of the less readily adsorbable component to the feed end of the bed;
(c) cocurrent depressurization with release of less readily adsorbable component and passage of said gas to another bed in the system undergoing repressurization for pressure equalization between said beds;
(d) cocurrent depressurization with discharge of intermediate component from the product end of the bed;
(e) countercurrent depressurization to remove said more readily adsorbable component from the feed end of the bed;
(f) pressure equalization with passage of gas to said bed from another bed in the system initially at higher pressure; and (g) repressurization of said bed to higher adsorption pressure.
(a) adsorption at a higher adsorption pressure;
(b) cocurrent displacement by the introduction of gas essentially free of the less readily adsorbable component to the feed end of the bed;
(c) cocurrent depressurization with release of less readily adsorbable component and passage of said gas to another bed in the system undergoing repressurization for pressure equalization between said beds;
(d) cocurrent depressurization with discharge of intermediate component from the product end of the bed;
(e) countercurrent depressurization to remove said more readily adsorbable component from the feed end of the bed;
(f) pressure equalization with passage of gas to said bed from another bed in the system initially at higher pressure; and (g) repressurization of said bed to higher adsorption pressure.
16. The process of Claim 15 and including, after step (c), further cocurrent depressurization of the bed with release of additional quantities of less readily adsorbable component and passage of said gas to an external storage vessel for use in providing purge gas to a bed in said system, and further including providing purge gas from said external vessel to the bed following countercurrent depressurization thereof.
17. The process of Claim 15 in which said less readily adsorbable component comprises hydrogen, said intermediate component comprises CO, and said more readily adsorbable component comprises a carbon dioxide-rich stream.
18. The process of Claim 15 in which said less readily adsorbable component comprises nitrogen, said intermediate component comprises CO, and said more readily adsorbable component comprises carbon dioxide.
19. The process of Claim 15 in which said less readily adsorbable component comprises hydrogen, said intermediate component comprises argon, and said more readily adsorbable component comprises CO.
20. The process of Claim 19 in which said intermediate component also comprises nitrogen.
21. The process of Claim 16 in which said adsorption system consists of at least four beds.
22. The process of Claim 15 in which said cocurrent displacement step (b) and said cocurrent depressurization step (c) occur at the same time.
23. The process of Claim 22 and including, after said simultaneous steps (b) and (c), further cocurrent depressurization of the bed with release of additional quantities of gas from the product end of said bed and passage of said gas to an external storage tank for use in providing purge to a bed in said system, and further including providing purge gas from said external vessel to the bed following countercurrent depressurization thereof.
24. The process of Claim 23 in which said less readily adsorbable component comprises hydrogen, said intermediate component comprises CO
and said more readily adsorbable component comprises carbon dioxide and methane.
and said more readily adsorbable component comprises carbon dioxide and methane.
25. The process of Claim 15 in which each bed undergoes the following processing sequence, in turn, on a cyclic basis:
(a) adsorption at a higher adsorption pressure, with only one bed in the system being on its adsorption step at any given time;
(b) cocurrent displacement by the introduction of gas essentially free of the least readily adsorbable component to the feed end of the bed;
(c) cocurrent depressurization with release of less readily adsorbable component and passage of said gas to another bed in the system for pressure equalization between said beds;
(d) further cocurrent depressurization of the bed with release of additional quantities of less readily adsorbable component and passage of said gas to an external storage vessel for use in providing purge gas to a bed in said system;
(e) cocurrent depressurization with discharge of intermediate component from the product end of the bed;
(f) providing purge gas to said bed from said external storage vessel, the bed decreasing in pressure to a lower desorption pressure during said purge thereof;
(g) pressure equalization with passage of gas to said bed from another bed in the system initially at higher pressure; and (h) repressurization of said bed to higher adsorption pressure.
(a) adsorption at a higher adsorption pressure, with only one bed in the system being on its adsorption step at any given time;
(b) cocurrent displacement by the introduction of gas essentially free of the least readily adsorbable component to the feed end of the bed;
(c) cocurrent depressurization with release of less readily adsorbable component and passage of said gas to another bed in the system for pressure equalization between said beds;
(d) further cocurrent depressurization of the bed with release of additional quantities of less readily adsorbable component and passage of said gas to an external storage vessel for use in providing purge gas to a bed in said system;
(e) cocurrent depressurization with discharge of intermediate component from the product end of the bed;
(f) providing purge gas to said bed from said external storage vessel, the bed decreasing in pressure to a lower desorption pressure during said purge thereof;
(g) pressure equalization with passage of gas to said bed from another bed in the system initially at higher pressure; and (h) repressurization of said bed to higher adsorption pressure.
26. The process of Claim 25 in which said adsorption system comprises at least five beds.
27. The process of Claim 25 and including diverting a portion of said intermediate component gas discharged during cocurrent depressurization step (e) as said cocurrent displacement gas of step (b).
28. The process of Claim 27 in which said adsorption system comprises at least five beds.
29. The process of Claim 27 in which said less readily adsorbable component comprises hydrogen, said intermediate component comprises CO, and said more readily adsorbable component comprises carbon dioxide and methane.
30. The process of Claim 27 in which said less readily adsorbable component comprises hydrogen, said intermediate component comprises argon, and said more readily adsorbable component comprises CO.
31. The process of Claim 30 in which said intermediate component also comprises nitrogen.
32. The process of Claim 1 in which each bed undergoes the following processing sequence, in turn, on a cyclic basis:
(a) adsorption at a higher adsorption pressure;
(b) cocurrent depressurization with release of less readily adsorbable component and passage of said gas to another bed in the system initially at lower pressure and undergoing repressurization for pressure equalization between said beds;
(c) cocurrent displacement by the introduction of gas essentially free of the less readily adsorbable component to the feed end of the bed;
(d) cocurrent depressurization with discharge of intermediate component from the product end of the bed:
(e) countercurrent depressurization to remove the most readily adsorbable component from the feed end of the bed;
(f) pressure equalization with passage of gas to said bed from another bed in the system initially at higher pressure; and (g) repressurization of said bed to higher adsorption pressure.
(a) adsorption at a higher adsorption pressure;
(b) cocurrent depressurization with release of less readily adsorbable component and passage of said gas to another bed in the system initially at lower pressure and undergoing repressurization for pressure equalization between said beds;
(c) cocurrent displacement by the introduction of gas essentially free of the less readily adsorbable component to the feed end of the bed;
(d) cocurrent depressurization with discharge of intermediate component from the product end of the bed:
(e) countercurrent depressurization to remove the most readily adsorbable component from the feed end of the bed;
(f) pressure equalization with passage of gas to said bed from another bed in the system initially at higher pressure; and (g) repressurization of said bed to higher adsorption pressure.
33. The process of Claim 32 and including, after step (c), further cocurrent depressurization of the bed with release of additional quantities of less readily adsorbable component and passage of said gas to an external storage vessel for use in providing purge gas to a bed in said system, and further including providing purge gas from said external vessel to the bed following countercurrent depressurization thereof.
34. The process of Claim 32 in which a portion of the countercurrent depressurization gas recovered during step (e) is diverted for use as the displacement gas for another bed in the system.
35. The process of Claim 32 and including, after step (c), further cocurrent depressurization of the bed with release of additional quantities of less readily adsorbable component and passage of said gas to an external storage vessel for use in providing purge gas to a bed in the system, and further including, upon completion of cocurrent depressurization step (d), providing purge gas from said external vessel to the product end of the bed during countercurrent depressurization step (e).
36. The process of Claim 33 in which said adsorption system comprises six beds.
37. The process of Claim 32 in which said less readily adsorbable component comprises hydrogen, said intermediate countercurrent comprises CO, and said more readily adsorbable component comprises carbon dioxide.
38. The process of Claim 32 in which said less readily adsorbable component comprises nitrogen, said intermediate component comprises CO, and said more readily adsorbent component comprises carbon dioxide.
39. The process of Claim 32 in which said less readily adsorbable component comprises hydrogen, said intermediate component comprises argon, and said more readily adsorbable component comprises CO.
40. The process of Claim 39 in which said intermediate component also comprises nitrogen.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000475574A CA1250531A (en) | 1985-03-01 | 1985-03-01 | Pressure swing adsorption with intermediate product recovery |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000475574A CA1250531A (en) | 1985-03-01 | 1985-03-01 | Pressure swing adsorption with intermediate product recovery |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1250531A true CA1250531A (en) | 1989-02-28 |
Family
ID=4129936
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000475574A Expired CA1250531A (en) | 1985-03-01 | 1985-03-01 | Pressure swing adsorption with intermediate product recovery |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1250531A (en) |
-
1985
- 1985-03-01 CA CA000475574A patent/CA1250531A/en not_active Expired
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