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WO1987002031A1 - Traitement selectif de gaz contenant des olefines au moyen du procede mehra - Google Patents

Traitement selectif de gaz contenant des olefines au moyen du procede mehra Download PDF

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Publication number
WO1987002031A1
WO1987002031A1 PCT/US1986/001674 US8601674W WO8702031A1 WO 1987002031 A1 WO1987002031 A1 WO 1987002031A1 US 8601674 W US8601674 W US 8601674W WO 8702031 A1 WO8702031 A1 WO 8702031A1
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WIPO (PCT)
Prior art keywords
stream
solvent
column
ethylene
gas
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.)
Ceased
Application number
PCT/US1986/001674
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English (en)
Inventor
Yuv R. Mehra
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
El Paso Hydrocarbons Co
Advanced Extraction Technologies Inc
Original Assignee
El Paso Hydrocarbons Co
Advanced Extraction Technologies Inc
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Priority claimed from US06/784,566 external-priority patent/US4617038A/en
Priority claimed from US06/808,463 external-priority patent/US4692179A/en
Priority claimed from US06/828,988 external-priority patent/US4680042A/en
Priority claimed from US06/828,996 external-priority patent/US4696688A/en
Priority claimed from US06/854,383 external-priority patent/US4743282A/en
Priority to GB08712199A priority Critical patent/GB2189805A/en
Priority to BR8606899A priority patent/BR8606899A/pt
Application filed by El Paso Hydrocarbons Co, Advanced Extraction Technologies Inc filed Critical El Paso Hydrocarbons Co
Publication of WO1987002031A1 publication Critical patent/WO1987002031A1/fr
Priority to NO872183A priority patent/NO872183L/no
Priority to KR870700472A priority patent/KR870700587A/ko
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G OR C10K; LIQUIFIED PETROLEUM GAS; USE OF ADDITIVES TO FUELS OR FIRES; FIRE-LIGHTERS
    • C10L3/00—Gaseous fuels; Natural gas; Synthetic natural gas obtained by processes not covered by subclass C10G, C10K; Liquefied petroleum gas
    • C10L3/06—Natural gas; Synthetic natural gas obtained by processes not covered by C10G, C10K3/02 or C10K3/04
    • C10L3/10—Working-up natural gas or synthetic natural gas
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C7/00—Purification; Separation; Use of additives
    • C07C7/11—Purification; Separation; Use of additives by absorption, i.e. purification or separation of gaseous hydrocarbons with the aid of liquids
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
    • C10G5/00—Recovery of liquid hydrocarbon mixtures from gases, e.g. natural gas
    • C10G5/04—Recovery of liquid hydrocarbon mixtures from gases, e.g. natural gas with liquid absorbents
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
    • C10G2300/00—Aspects relating to hydrocarbon processing covered by groups C10G1/00 - C10G99/00
    • C10G2300/10—Feedstock materials
    • C10G2300/1025—Natural gas

Definitions

  • This invention relates to recovery of olefins from pyrolyzed hydrocarbon gases and especially relates to recovery of olefins from cracked hydrocarbon gases by absorption with a preferential physical solvent.
  • Olefins have a wide variety of petrochemical uses. Ethylene is a principal building block of the petrochemical industry. Its largest single use is the conversion to low-and high-density polyethylenes, which are used in packaging, communications, construction, automotive, manufacturing of home appliances, and many other industries. Other major uses include oxidation to ethylene oxide and chlorination to ethylene dichloride.
  • Olefins are generally produced by thermally or catalytically cracking gaseous or liquid hydrocarbons to make cracked gases.
  • Three general methods of separating or concentrating the components of cracked gases for the recovery of ethylene of moderate and high purity have been available for many years.
  • the other two utilize fractional distillation in two variations, the first being a straight low-temperature fractionation process and the second involving absorption into liquid having low vapor pressure, thereby avoiding very low temperatures in the fractionation system.
  • Low-temperature fractionation a refinement of the stepwise liquefaction method, was used as of about the mid-1960' s in the majority of ethylene plants in operation, as described in "Low Temperature Fractionation of Light Hydrocarbons", by A.W. Pratt and N.L. Foskett, Transactions of the American Institute of Chemical Engineers, Vol. 42, 1946, page 149.
  • the predominant feedstock is composed of ethane, propane, butanes, naphtha, gas oil, condensate, and other hydrocarbons derived from petroleum cracking.
  • These feedstocks are pretreated and cracked by conventional steam crackers.
  • the cracked gases leave the cracking furnaces at 815 to 1,200°C. These gases are quenched and cooled down to about 27 to 49°C at pressures less than 210 Kpa.
  • the above feedstocks may also be catalytically cracked under appropriate operating conditions.
  • the cracked gases comprise hydrogen, methane, carbon monoxide, carbon dioxide, acetylene, ethylene, ethane, methyl acetylene, propadiene, propylene, propane, butadienes, butenes, butanes, C 5 's, C 6 -C 8 non-aromatics, benzene, toluene, xylene, ethyl benzene, styrene, C 9 to 200°C gasoline, 200+°C fuel oil and water.
  • These gases are compressed in multi-stage compression units to pressures in the order of 2,800 to 4,200 Kpa.
  • Some heavier hydrocarbons and water are separated.
  • the separated hydrocarbons are stabilized and may be utilized as part of the feed to the fractionation train.
  • the uncondensed gases after compression are further dried by molecular sieves or activated alumina to a water dew point of less than -100°C.
  • the cracked gases may be dried at an intermediate pressure level consistent with the interstage pressure of the multi-stage cracked gas compressor.
  • the dry gases are then chilled in a series of steps to cryogenic temperatures of -129°C through a complicated set of equipment utilizing extensive heat exchange and ethylene and propylene refrigeration systems.
  • the purpose of chill-down is to separate ethylene and heavier hydrocarbons from the methane and hydrogen present in the cracked gases.
  • the remaining stream of methane and hydrogen is further separated into hydrogen-rich and methane-rich streams within the cryogenic chill-down train.
  • a part of the separated hydrogen stream is preferably further purified by using conventional pressure swing adsorption techniques before utilizing it for hydrogenating acetylenes to desirable products while the methane-rich stream is used as fuel gas for the steam cracking furnaces.
  • the separated liquid streams, containing ethylene and heavier hydrocarbons, are further fractionated in a low-to-high-pressure demethanizer (1,100 to 3,200 Kpa).
  • the low-pressure demethanizer utilizes ethylene refrigerant for the overhead condenser while the high-pressure demethanizer uses low-level propylene refrigerant, sometimes in conjunction with an expander unit, for such condensation.
  • the specification of methane in the bottom of the demethanizer is quite stringent since methane represents an impurity when present with the ethylene product.
  • the olefin plants are known to be energy intensive.
  • the charge gas compressor requirements can vary between 37,000 aad budget4D,000 horsepower (PS) while the corresponding requirements for the propylene refrigeration system can vary from 18,000 to 22,000 PS and those for the ethylene refrigeration system can vary from 4,000 to 8,000 PS.
  • the total compression energy can vary between 60,000 and 70,000 PS, thereby requiring large capital investment and representing a significant cost of operation related to energy consumption.
  • the specific energy consumption of an olefins plant can vary between 3,100 and 7,500 Kcal/kg of ethylene product. This represents about 25.4% to 62.4% of the gross heating value of ethylene of 12,017 Kcal/kg. It is important to note that the cracking system for olefin production appears to have been improved and refined to an operating state of high efficiency. Even though the steam crackers require significant amounts of fuel, since the cracking process occurs at extremely high temperatures, most of the energy expended in the cracking furnaces is recovered through extensive use of waste heat recovery equipment.
  • Another cost-reducing step is to revise existing facilities in order to optimize feed and energy requirements, possibly including co-generation systems with various units.
  • a third step is to make full use of computer control in order to maximize plant operating efficiency.
  • a fourth step is to replace obsolete plants within a facility with more efficient plants using improved technology.
  • the next stage for improving efficiency of olefin production is believed to be replacement of low temperature plants for recovery and separation of olefins from cracked gases.
  • the plants were mainly of the thermal decomposition type, operating primarily on ethane and propane, in which the cracked gases were fed to an absorber-stripper column producing fuel gas as overhead and a rich solvent which was fed to a de-ethanizer column as the first component of a fractionation train, as shown in Figure 1 of U.S. Patent 2,573,341 which is Figure 2 of the drawings of this invention, as representative absorption prior art.
  • the absorption method is discussed for an absorption-type recovery plant in an article in
  • This ethylene plant of Monsanto Chemical Co. at Texas City, Texas was mainly used for producing ethylene and operated primarily on ethane and propane. Typical ultimate ethylene yields were 75 wt.% from ethane, 48 wt.% from propane, or 25-32 wt.% from gas oil. At a conversion per pass of about 45% when cracking propane, yields were about 16.7 wt.% of ethylene and 15.8 wt.% of propylene, once through.
  • the ethylene was separated along with the ethane and heavier components by means of low-temperature absorption with an aromatic distillate produced in the process and containing more than 50% benzene and toluene by weight and appreciable quantities of naphthenes, among which cyclopentane and cyclohexane had been identified.
  • Typical analyses of three ethylene-bear ing streams were given in this article: (a) a typical coke-oven gas, (b) a refinery off-gas, and (c) the effluent from a pyrolysis unit charging propane and operated to yield a maximum amount of ethylene.
  • ethylene concentration was 4-27 mol % and diluents lighter than ethylene were 94-17 mol %, thereby bracketing most commercial gases from which ethylene or ethylene + propylene might be economically recovered.
  • a gas exchanger and inlet gas chiller removed about 1/2 of the heat of absorption outside of the absorber but they consequently lowered mean effective absorber temperature, and the oil content of the residue gas leaving the top of the column was in equilibrium with the oil at the minimum temperature of -7°C, thereby minimizing oil loss.
  • the overhead is fuel gas, and the bottoms are fed to a de-ethanizer column, having a reboiler at its bottom and a condenser for its overhead from which a portion of the condensate is returned to the de-ethanizer column as reflux.
  • the lean oil rate is not over 4.2 kg per kg of feed, an amount which assures the retention of 99 mol% of the ethylene entering the rectifier absorption tower.
  • Absorption exemplified by the process in Figure 1 of U.S. Patent No. 2,573,341, was stated on page 651 of the Nelson book to be the process mainly used for ethylene recovery as of about 1948. In the mid-1950's, a number of absorption plants were in operation which utilized refrigerated lean oils such as propane, butane, or light aromatic fractions.
  • the specification also indicates that the process was limited to ethylene as its product and was not flexible enough to provide additional desirable byproducts such as propylene, which was sent to the heaters for cracking, and acetylene, which was totally ignored in the process and also recycled. Further, other unreacted paraffins and olefin fractions heavier than ethylene were recycled to the cracking furnaces in order to make the aromatic distillate to be used as the absorber oil, even though a market existed for the propylene and undoubtedly for the butadiene at that time, thereby creating another economically wasteful aspect of the process. As the seventh reason, the degrees of freedom for operating the Kniel process were restricted by using only temperatures and lean oil flow rates. Pressure, however, was also available as a control factor. Neglecting to use it may have led to some of the problems of the process.
  • Kniel absorption process consequently seems to have suffered from the following problems: A. wasteful burning of hydrogen, propylene, and acetylene;
  • the extractive flashing embodiment of the Mehra Process comprises extracting the natural gas streams with a preferential physical solvent, flashing the rich solvent, and compressing, cooling, and condensing the desired C 2 + hydrocarbons, as disclosed in U.S. Patents 4,421,535, 4,511,381, 4,526,594, and 4,578,094 and in United States Serial Nos. 758,351 and 759,327.
  • the condensed hydrocarbons are then selectively demethanized to retain selected C 2 +, C 3 +, or C 4 + hydrocarbons, and the removed C 1 , C 1 +C 2 , or C 1 +C 2 +C 3 hydrocarbons are recycled to the extraction step.
  • the extractive flashing embodiment is described on pages 7 and 8 of the October 14, 1985 issue of the Gas Processors
  • the extractive stripping embodiment of the Mehra Process comprises contacting a raw gas stream with a preferential physical solvent in an extractive stripping column comprising an upper extraction section and a lower stripping section.
  • the gas enters the column below the extraction section and flows upwardly where it contacts lean preferential physical solvent which, after entering the extraction section at the top of the column, flows downwardly and counter currently to the upwardly moving gas stream.
  • the contact takes place over mass transfer surfaces, such as packing or distillation trays.
  • the solvent leaving the bottom of the extraction section is rich in C 1 and heavier hydrocarbons.
  • This C 1 +-rich solvent enters the stripping section of the column and flows downwardly, where it comes in contact with the upward-flowing stripped vapors from the reboiler at the bottom of the column.
  • the stripped vapors consist primarily of undesired components, such as methane if the desired objective is recovery of ethane and heavier hydrocarbons, or methane and ethane if the desired objective is the recovery of propane and heavier hydrocarbons, and so forth, depending upon the desired recovery objectives.
  • a system that can effect such separation via a less energy-intensive route can be useful in many existing olefin plants. More specifically, the demethanizer column is an especially high-intensive energy user in a low-temperature fractionation plant because it requires extremely cold temperatures. An improved process that can eliminate the demethanizer column is accordingly needed.
  • a third area inviting improvement is the production of high-purity ethylene, at ethylene recovery levels better than 98% and at ethylene purities beyond 99.9%, in a more economical fashion by reducing energy consumption at a reasonable cost.
  • At least one extraction column is an extractive stripping column.
  • Each extractive-stripping column contains a stripping section, having a heat input means, and an extraction section thereabove. Either or both of the extractive-stripping columns can additionally be provided with a rectification section which is disposed above the extraction section and comprises a partial condenser which receives the overhead stream from the top of the column, an accumulator, and a reflux line to the top of the column.
  • Each extractive stripping column is a part of a solvent loop. The same solvent can be employed in both loops.
  • the second extraction column produces the hydrogen-rich gas product stream as its overhead and a rich solvent bottoms stream which is fed to the second distillation column, identified as the methane product column (MPC). It produces the methane-rich gas product stream as its overhead and regenerated solvent for the second solvent loop as its bottoms stream.
  • the ethylene extraction column extracts most of the methane as well as the ethylene and other C 2 + hydrocarbons (both saturated and unsaturated) in its rich solvent stream, producing the hydrogen-rich gas product stream as its overhead.
  • the rich solvent stream is fed to the first distillation column (SRC) which regenerates lean solvent for the first solvent loop and produces C 1 + hydrocarbons as its overhead stream for feeding to the mid-section of the second extraction column, which is the methane product column (MPC).
  • SRC first distillation column
  • MPC methane product column
  • the lean solvent stream is fed to the top of the second extraction column (MEC), which generally has no stripping section but may employ one if methane and hydrogen specifications dictate the need therefor, while the overhead EEC stream is fed to its bottom.
  • the second extraction column (MEC) may operate at a higher pressure than the EEC, but the operating pressure of the MEC must be less than the critical pressure for the gas-liquid mixture in the MEC.
  • the MEC overhead stream is hydrogen-rich gas product. Its bottoms stream of rich solvent is flashed to produce a methane-rich gas product stream and lean solvent which is fed to the top of the ethylene extraction column.
  • the EEC/MEC embodiment produces one product from its extraction columns and two products from its distillation columns.
  • the EEC/MPC embodiment produces two products from its extraction columns and one product from its distillation columns.
  • the EEC/MEC/FV embodiment produces one product from its extraction columns, one product from its flash vessel, and the third product from its single distillation column.
  • the cracked gases need not be compressed to a typical pressure of 3,600 Kpa but instead need compressing only up to 2,200-3,200 Kpa in order to extract ethylene and heavier hydrocarbons from the typical cracked or refinery gases.
  • the process of this invention utilizes the Mehra Process technology concept for separating the components of a compressed, sweetened, and dehydrated cracked gas stream of an olefin facility by effectively using a preferential physical solvent for scrubbing the gas stream and preferentially removing selected hydrocarbons therefrom. Additional solvent information is given in United States Serial No. 808,463.
  • the process begins at the low pressure inlet to the cracked gas compressor which represents the first tie-in point, since the manufacture of ethylene, i.e., the cracking process, is outside the scope of this invention.
  • Other products of this invention process are a hydrogen-rich gas stream and a methane-rich gas stream. These three products, namely ethylene-plus, methane-rich and hydrogen-rich, are thereafter to be treated in the same manner as currently in the prior art.
  • the process of this invention relates to the separation of ethylene and heavier hydrocarbons from methane and hydrogen gases present in the cracked gases of an olefins plant, refinery off-gas streams, coke-oven gas streams, or synthesis gas streams. Since the Mehra Process concept is applicable to any gas stream containing olefins derived from any feedstock and since it addresses the separation processes which are currently energy intensive, the Mehra Process is potentially suitable for retrofitting any of the worldwide ethylene facilities, currently having 49 million metric tons per year of equivalent installed ethylene capacity.
  • the three steps common and identical to a typical olefins facility and the process of this invention are cracking, waste heat recovery, and de-ethanizing, plus any succeeding steps in downstream equipment, such as ethylene/ethane fractionators, depropanizers, propylene/propane fractionators, debutanizers, etc..
  • the extraction unit is further capable of separating hydrogen from methane, thereby producing two separate gas streams as products.
  • the cracked gases leaving the waste heat recovery unit are compressed in a multi-stage compressor to a desired pressure in the range of 1,100 to 3,200 Kpa.
  • the compressed gases may be optionally cooled down to a temperature of no less than -29 °C prior to extraction.
  • the cracked gases enter an Ethylene Extraction Column (EEC), which may consist only of an extraction section and a stripping section with side and bottom reboilers.
  • EEC Ethylene Extraction Column
  • This column may additionally utilize an overhead partial condenser for generating reflux for a rectification section in order to achieve extremely high recoveries, in the order of 98 to 99%, of ethylene present in the cracked gases when feedstocks and severity of cracking result in excessive amounts of methane in the cracked gases, thus minimizing the loss of valuable ethylene with the overhead stream.
  • an overhead partial condenser for generating reflux for a rectification section in order to achieve extremely high recoveries, in the order of 98 to 99%, of ethylene present in the cracked gases when feedstocks and severity of cracking result in excessive amounts of methane in the cracked gases, thus minimizing the loss of valuable ethylene with the overhead stream.
  • an EEC may consist of a. rectification section with an overhead condenser at the very top, a middle section for extraction of ethylene and heavier hydrocarbons with a preferential physical solvent, and a bottom stripping section with side and bottom reboilers.
  • a simple reboiled extraction column consisting of an extraction section at the top and a stripping section with appropriate side and bottom reboilers, may well be equally suited for desired recoveries, of course depending upon the economic optimization of parameters of capital and energy consumption.
  • the purpose of the extraction section is to recover ethylene and heavier hydrocarbons from the cracked gas stream entering at the bottom of the extraction section and flowing upwardly through mass transfer medium, such as packing or fractionation trays or alternatively utilizing HIGEE TM trays, while contacting the downwardly flowing preferential physical solvent which is fed to the EEC at a solvent flow rate which is selectively adjusted within the range of 0.1 to 70 cubic meters of solvent per thousand normal cubic meters of the gas stream and in response to the composition and flow rate of the gas stream.
  • mass transfer medium such as packing or fractionation trays or alternatively utilizing HIGEE TM trays
  • the solvent stream leaving the bottom of the extraction section of the EEC is stripped of undesirable methane by effectively utilizing additional mass transfer medium in the stripping section of the column.
  • the stripping vapors are preferably generated by heating the rich solvent stream in side and/or bottom reboilers, but they can be from an outside source of compatible gas stream.
  • the source of heat energy can be external or waste heat as recovered through the lean solvent loop.
  • the solvent containing ethylene and heavier hydrocarbons leaving the bottom of the stripping section of EEC does not contain more than permitted amounts of undesirable components, such as methane, in accordance with the specifications of ethylene product.
  • the vapors leaving the top of the extraction section carry with them some of the desirable components such as ethylene, the recovery of which is desired to be in the order of 98 to 99%.
  • a rectification section may suitably be provided to effectively carry out the desired rectification, resulting in improved recoveries of the ethylene component of the cracked gas stream.
  • the overhead vapors are partially condensed to generate adequate amounts of reflux for the rectification section.
  • the rectification section also recovers any physical solvent that may be carried away with the methane and hydrogen streams.
  • the solvent containing only the desired components of ethylene and heavier hydrocarbons may be further heated if economically desirable before processing in the Raw Product Column (RPC).
  • RPC Raw Product Column
  • the extracted hydrocarbons from the cracked gas stream are separated from the physical solvent.
  • the rectification section is operated so as to minimize the solvent losses with the hydrocarbon product from the overhead of the column.
  • the operating conditions at the top of the column are preferably such that the overhead can be condensed by available condensing media, such as air or cooling water.
  • the temperature of the bottoms is generally less than the equivalent boiling temperature for pure component solvent.
  • a small amount of heavier hydrocarbons may remain with the lean solvent in order to keep the size of RPC within economic criteria.
  • the overhead product from RPC is further processed in the de-ethanizer and downstream equipment as conventional steps.
  • the stripped solvent from the bottom of RPC. is recycled to the top of the extraction section of EEC after cooling the lean solvent to the desired temperature via a heat recovery loop and lean solvent cooler, similar to but not restrictive to the arrangement in Figure 4.
  • any liquids formed and separated at the interstage pressure levels of the cracked gas compressor may be stabilized for further processing in the fractionation train of a typical olefins plant.
  • This stream therefore, enters EEC at an appropriate location in the stripping section, preferably in between the stripping and extraction sections. Since a Mehra Process plant does not require high pressures for extraction of ethylene plus components, it may be economically advantageous to provide a secondary but parallel extraction column operating on a common solvent loop with the first column and operating at an intermediate pressure level consistent with the desired interstage pressure of the cracked gas compressor.
  • the obvious advantage of doing this would be to selectively extract C 3 + or C 4 + hydrocarbons from the cracked gas in order to further reduce the compression requirements of the cracked gas compressor. It would be preferred, but not necessary, to utilize an operating pressure level of the secondary parallel extraction column that is slightly higher than the operating pressure of the Raw Product Column (RPC).
  • RPC Raw Product Column
  • the rich solvent stream from the bottom of the parallel extraction column is such that it meets the same requirements of undesirable components, such as methane, as applicable to EEC, so that it can be combined together with the rich solvent stream from EEC before processing in RPC.
  • EEC primarily comprise hydrogen and methane.
  • this stream is then fed to the Methane Extraction Column (MEC) where methane is selectively extracted from the hydrogen-methane stream with a preferential physical solvent in solvent loop No. 2.
  • MEC Methane Extraction Column
  • the column is operated under stringent specifications of hydrogen content in the methane stream which is leaving through the bottom of MEC while most of the contained methane in the feed to MEC is recovered with the bottoms.
  • the operational objective of MEC is to maintain a low methane content in the hydrogen stream leaving the top of the column.
  • a rectification section may advantageously be employed on top of MEC.
  • the hydrogen product leaving MEC may be further processed before use thereof within the olefins plant, such as for hydrogenating acetylene to ethylene.
  • the rich solvent containing methane and remaining amounts of unrecovered ethylene is separated from the solvent in loop No. 2 by fractionating the methane in the Methane Product Column (MPC).
  • MPC Methane Product Column
  • the solvent thus stripped is recycled to the top of MEC for further extraction of methane.
  • the solvent in loop No. 2 is treated in a similar fashion as the solvent in loop No. 1 by heat recovery and cooling to desired temperature for extraction in MEC.
  • Another advantage of this invention process is that the olefins plant becomes more flexible towards the choice of processing various feedstocks. In most of the designs, there has always been a grave concern over how much flexibility ought to be built in so as to keep the plant most economical at all times. A significant amount of restriction is caused by the limitations of the refrigeration systems and the cryogenic chill-down trains. With the use of the
  • the preferential physical solvents are defined for the purposes of this invention as having a minimum relative volatility of methane over ethylene of at least 5.5 (thereby defining its improved selectivity toward ethylene over methane) and in addition a solubility of at least 7.0 normal cubic meters of gaseous hydrocarbons per cubic meter of the solvent (thereby defining its hydrocarbon loading capacity), or, alternatively, a preferential factor of at least 38.
  • the preferential factor for physical solvent selection for using the Mehra Process concept in this invention is defined as a product of relative volatility of methane over ethylene multiplied by the solubility of ethylene in physical solvents, specified as normal cubic meters of ethylene per cubic meter of solvent (Nm 3 /m 3 ).
  • the ideal preferential physical solvent would have a selectivity toward ethylene over methane of at least 10.0 and would simultaneously possess a hydrocarbon loading capacity of at least 21.2 Nm 3/m3.
  • a preferential factor of at least 49 is highly preferred.
  • a preferential factor of 70 is highly preferred.
  • the preferential physical solvent is selected from the group consisting of dialkyl ethers of polyalkylene glycol, N-methyl pyrrollidone, dimethylformamide, propylene carbonate, sulfolane, glycol triacetate, and C 8 to C 10 aromatic compounds having methyl, ethyl, or propyl aliphatic groups specifically constituting a sub-group of mesitylene, n-propyl benzene, n-butyl benzene, o-xylene, m-xylene, p-xylene, and mixtures thereof and aromatic streams rich in mixed xylenes and other C8- C 10 aromatics.
  • the process of this invention is also able to utilize two different solvents. Equipping the first extraction column with a rectification section is particularly desirable if the solvents are different.
  • the process of this invention produces a high-purity ethylene product at high recovery levels and also produces usefully pure product streams of hydrogen and methane.
  • the process is additionally believed to be characterized by extremely low solvent losses, reduced maintenance requirements, simplified apparatus requirements and lower capital costs, elimination of freeze-ups, increased onstream time, enhanced flexibility, and capability of using a wide variety of feedstocks.
  • this process is equally capable of manufacturing propylene, with the same characteristics and advantages.
  • Figure 1 is a schematic drawing for a typical olefin facility in which cracked gases are recovered and partially separated by the low-temperature fractionation process.
  • Figure 2 is a schematic drawing of an older olefin facility showing the Kniel process of U.S. Patent No. 2,573,341 for recovery and separation of cracked gases by solvent absorption.
  • Figure 3 is a simplified schematic drawing showing the process of Figure 1 with the Mehra process, for recovering and separating cracked and/or refinery gases by solvent extraction, substituted for the cryogenic chilling train and demethanizer of Figure 1.
  • EEC ethylene extraction column
  • MPC methane product column
  • RPC raw product column
  • FIG. 6 is a schematic flowsheet showing a third embodiment of the Mehra process in which ethylene extraction (EEC) column separates the hydrogen and methane from its rich solvent containing the ethylene and heavier hydrocarbons.
  • EEC ethylene extraction
  • the H 2 /CH 4 overhead stream is again extracted with lean solvent to recover an H 2 -rich gas stream and produce a methane-rich bottom stream which is flashed to recover a CH 4 -rich gas stream.
  • the process shown schematically in the flow sheet of Figure 4 comprises a rectifying-extractive-stripper column referred to as the ethylene extraction column (EEC) 20 and a raw product column (RPC) 30 in the first solvent loop and a methane extraction column (MEC) 60 and a methane product column (MPC) 70 in the second solvent loop.
  • EEC ethylene extraction column
  • RPC raw product column
  • MEC methane extraction column
  • MPC methane product column
  • MPC methane product column
  • the compressed, cooled, sweetened, and dehydrated gas passes through line 13, selectively including optional gas cooler 15, to the midsection of SEC 20.
  • the gas thereafter flows upwardly through extraction section 23, while flowing past the downwardly moving lean solvent from line 49, and then enters rectification section 25, while flowing past the downwardly moving reflux from line 35, and finally leaves the column through line 24 as the overhead stream.
  • the combined reflux and solvent pass through extraction section 23 into stripping section 21 while meeting upwardly moving vapors produced from bottoms liquid, after it has been heated by recycling through line 26 and reboiler 27, and from intermediate liquid, after it has been heated by recycling through line 28 and side reboiler 29.
  • a portion of the upwardly moving vapors is extracted by the combined reflux/solvent liquid.
  • the remaining vapors rise to the extraction section and mix with the incoming gas stream from line 13.
  • the hot bottoms liquid from the column is discharged through line 22a, passes through lean/rich solvent cross exchanger 33, and is then fed through line 22b to the midsection of RPC 30.
  • Column 30 comprises a stripping section 31 and a rectification section 35.
  • the upwardly moving gases pass through rectification section 35, while encountering downwardly moving lean solvent from reflux line 54, and leave the system as the overhead stream through line 34, to be condensed in overhead condenser 51, pass through line 52, and enter accumulator 53 from which a portion is recycled to the top of RPC 30 by reflux pump 55 through line 54, while another portion is pumped by product pump 57 through line 56 to produce ethylene and heavier hydrocarbons to be fed to the de-ethanizer and other downstream equipment.
  • Another portion of uncondenaed gases may be selectively recycled, if economical to do so, through line 59 to cracked gas compressor 12.
  • Overhead stream 24 passes through overhead condenser 31 and line 32 to enter accumulator 34 from which liquid is recycled through line 35 by reflux pump 36 to the top of rectification section 25 in EEC 20.
  • the first solvent loop and its columns and auxiliary equipment are thus completely described.
  • Uncondensed gases in accumulator 34 are passed through feed line 33 to the midsection of methane extraction column (MEC) 60, between stripping section 61 and extraction section 65.
  • the gases from line 33 pass upwardly through extraction section 65, while meeting lean solvent from line 89, and leave the column as a hydrogen-rich gas product stream 64.
  • the downwardly descending lean solvent from line 89 passes through extraction section 65, while effectively picking up materials from the gas stream entering through line 33, and enters stripping section 61, while meeting ascending vapors and picking up methane therefrom and while losing hydrogen to the vapors.
  • the liquid bottoms material in the column is heated by recycling through line 66 and reboiler 67.
  • the bottoms material in the column is discharged through lines 62a and 62b, and lean/rich solvent cross exchanger 73 to be fed to the midsection of MPC 70.
  • Column 70 comprises a stripping section 71 and a rectification section 75.
  • the gases, which have been heated in exchanger 73, pass upwardly through rectification section 75 while meeting downwardly descending reflux material from line 94.
  • the overhead stream from the column leaves through line 74, overhead condenser 91, and line 92, to enter accumulator 93. From this accumulator, liquid material is recycled through lines 94 and reflux pump 95 to the top of rectification section 75 of MPC 70. Vapor from accumulator 93 is discharged as a methane-rich gas stream through line 99.
  • the heated bottoms material, now lean solvent is discharged through line 72 to pass through lean/rich solvent cross exchanger 73, line 81, reboiler 67, lean solvent cooler 83, line 85, lean solvent pump 87, and feed line 89 to the top of extraction section 65 of MEC 60.
  • the second solvent loop and its columns and associated equipment are thus completely described.
  • EEC 20 the purpose of EEC 20 is to selectively extract all hydrocarbon components of inlet gas stream 13 by effectively utilizing the selectivity of the preferential physical solvent in stream 49.
  • MEC 60 The purpose of MEC 60 is to isolate most of the hydrogen as its overhead stream in line 64 and to isolate most of the methane as a part of the rich solvent stream in line 62a.
  • MPC 70 The purpose of MPC 70 is to isolate substantially all of the remaining methane in methane-rich gas stream 99, which includes small quantities of C 2 and C 3 hydrocarbons, and to regenerate the lean solvent in stream 72.
  • Figure 4 shows a system in which two entirely different preferential physical solvents may be used, if so desired, in two solvent loops.
  • the second or secondary loop is directed to recovery of a hydrogen-rich gas stream and then to recovery of a methane-rich gas stream while regenerating the solvent.
  • the two loops are connected by the overhead stream from the first loop being the feed gas stream for the second loop.
  • the solvent utilized in loop No. 2 of Fig. 4 will be relatively more selective towards methane over hydrogen when compared to similar characteristics of the solvent used in solvent loop No. 1.
  • a first solvent is preferably an aromatic distillate, such as mesitylene or a C 8 -C 10 monocyclic aromatic haying at least one alkyl side chain and having a lower boiling point and a higher preferential factor than the solvent in the second loop which may be dimethyl ether of polyethylene glycol (DMPEG), for example.
  • DMPEG polyethylene glycol
  • Each loop passes through two columns, one column being an extractive stripping column and the other column being a distillation column.
  • Each extractive stripping column has at least a stripping section and/or a rectification section and/or an extraction section.
  • Each of the four columns is also equipped with a reboiler for heating its bottoms material.
  • the first column of each loop is an extractive stripping column, and control of its performance is partially effected by control of the temperatures and flow rates of the lean solvent streams being fed to the upper portions of the columns.
  • the first column of the first section is additionally provided with reflux which is fed to the column at a feed point spaced above the feed point for the lean solvent stream, thus defining a rectification section therebetween.
  • the second extractive stripping column is preferably not provided with reflux, but may have it if fairly pure hydrogen is desired.
  • FIG. 5 illustrates a two-column extractive-stripping process for a gas stream containing olefins, for example, in which there is initial separation of the hydrogen from all of the hydrocarbon components within the first column.
  • This process utilizes ethylene extraction column (EEC) 120, solvent regenerator column (SRC) 130, methane product column (MPC) 140, and raw product column (RPC) 150.
  • EEC ethylene extraction column
  • SRC solvent regenerator column
  • MPC methane product column
  • RPC raw product column
  • the heated rich solvent in exchanger 127 passes through line 131 to enter column 130, slightly below its middle. Liquid in the bottom of column 130 circulates through line 135 and reboiler 136 to be heated. Bottoms from column 130 leave through line 133 and pump 137 to enter heat exchanger 127 and pass through line 128, reboiler 126, and solvent cooler 129 to enter the top of column 120 as lean solvent.
  • An overhead stream leaves column 130 through line 134, is cooled in reflux condenser 134a, enters accumulator 138, and separates into uncondensed and condensed hydrocarbons.
  • the latter leave through line 139a, are pumped by reflux pump 139 to the pressure of column 130, and enter the top of column 130 as reflux.
  • the uncondensed hydrocarbons leave accumulator 138 through line 141 to enter column 140, slightly below its middle.
  • Liquid in the bottom of column 140 circulates through line 145 and reboiler 146 to he bjeated. Bottoms leave column 140 through line 143 to enter rich/lean solvent exchanger 147 for heating therein.
  • An overhead stream of C 1 gas product leaves the top of column 140 through line 144.
  • An overhead stream leaves the top of column 150 through line 154 and is partially condensed in condenser 161 before entering reflux accumulator 162. Condensed liquid in accumulator 162 leaves through line 163 and is pumped by reflux pump 167 to the top of column 150.
  • Figure 6 illustrates a separation and recovery process for a gas containing olefins which has been compressed, cooled, sweetened, and dried.
  • the process utilizes two extraction columns which may be disposed as separate columns or superimposed as a single tall column. These are a first or bottom ethylene extraction column (EEC) 170 and a second or top column (MEC) 190.
  • EEC ethylene extraction column
  • MEC second or top column
  • the process also utilizes a flash vessel (FV) 200 and a raw product column (RPC) 210.
  • FV flash vessel
  • RPC raw product column
  • the inlet gas stream in line 171 enters EEC 170, slightly below its middle, and passes upwardly to meet downwardly descending lean solvent from line 178.
  • Liquid in the bottom of column 170 circulates through line 175, and reboiler 176, and line 177 to be heated and returned to column 170.
  • Bottoms in column 170 leave through line 173 to enter and be heated in rich/lean solvent exchanger 181.
  • An overhead stream in line 179 leaves the top of column 170, passes through optional compressor 185 and line 191, and enters MEC 190 near its bottom.
  • a reboiler may initially be employed in order to obtain an additional stripping section below the feed location which is slightly below the middle of the column.
  • Bottoms leave column 190 through line 193 to enter flash vessel 200, wherein the bottoms are separated into a methane-rich gas product stream, which leaves vessel 200 through overhead line 209, and a bottoms stream which leaves vessel 200 through line 203 and solvent pump 205 before entering the top of column 170 through line 178.
  • An overhead stream leaves the top of column 190 through line 199 and passes through optional power recovery turbine 187 to leave as a hydrogen-rich gas product stream in line 197.
  • the liquid portion leaves through line 225 and is pumped by reflux pump 226 through line 218 to enter the top of column 210.
  • the solvent requirements for EEC 170 may be significantly lower than those for MEC 190. Therefore, it may be economically desirable to bypass a substantial portion of solvent in line 178 via line 206 to lean solvent line 183. By doing so the equipment sizes for EEC 170 and a portion of the solvent loop, including units 176, 181, 210, 216, 221, 223, and 226 and their associated piping can be significantly reduced.
  • EXAMPLE An existing olefins facility, as shown in Figure 1, is investigated for upgrading by replacing the chilling train and the demethanizer column with a Mehra process extraction system, as illustrated in Figure 3. Portions of the propylene refrigeration system are to be retained for use with the Mehra Process extraction units. The ethylene refrigeration system can be shut down, thereby further reducing the load on the propylene refrigeration system. Replacement of the molecular sieve or dehydration unit of Figure 1 with the glycol dehydration unit of Figure 3 is to be considered on a basis of cost effectiveness, but for purposes of this example, it is assumed that the molecular sieve units stay in service.
  • the Mehra process extraction system, using o-xylene as one of the preferential physical solvents, is as shown in Figure 6.
  • the composition of the hydrogen-rich gas product in line 199 should be noted because its hydrogen content is 93.4% on a kg-mol basis. Furthermore, its solvent content is merely 0.0017% on a kg-mol basis and its ethylene content is essentially zero.
  • the composition of the methane-rich gas product in line 209 is also noteworthy because its methane content is 89.5% on a kg-mol basis.
  • its solvent content is 0.04% on a kg-mol basis and its ethylene content is 0.043% on a kg-mol basis.
  • composition of the stream of ethylene and heavier hydrocarbons in line 224 is 56.3% ethylene, 22.3% ethane, and 0.030% methane on a kg-mol basis. Its o-xylene content is 0.0032% on a kg-mol basis. Recycle Ratio
  • the raw hydrocarbon product is further fractionated downstream into ethylene and ethane. Doing so while obtaining sufficiently high purity in the overhead ethylene stream requires a high performance level in the ethylene fractionator column.
  • ethylene fractionator column As is clear from Table II, at about 72 mol % ethylene in a feedstream to an ethylene fractionator column containing only ethylene and ethane, as in stream 224, an ethylene product, with purity of 99.95 mol % and at a recovery level of 99.94%, could be produced. This performance the Kniel process could not achieve even while utilizing a demethanizer column, yet such a column is plainly not required by the Mehra Process.

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  • Chemical & Material Sciences (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Organic Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Water Supply & Treatment (AREA)
  • Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
  • Production Of Liquid Hydrocarbon Mixture For Refining Petroleum (AREA)

Abstract

Procédé de stripage extractif gaz-liquide utilisant au moins un solvant physique préférentiel dans au moins une boucle de solvant, chaque boucle passant à travers au moins deux processus individuels: le stripage extractif et la distillation. Au moins le premier processus de stripage extractif peut comporter en plus un bloc de rectification disposé sur un bloc d'extraction. Trois produits sont réalisés à partir des flux de gaz du craquage thermique ou de gaz de raffinerie: un flux de gaz riche en hydrogène, un flux de gaz riche en méthane, et un flux de C2=+ hydrocarbures qui constitue le flux d'alimentation pour un train de fractionnement traditionnel d'une installation de fabrication d'oléfines. On peut produire de l'éthylène de façon économique à partir du flux de produit C2=+ hydrocarbures à un taux de récupération d'au moins 99,5% et avec une pureté d'au moins 99,9%.
PCT/US1986/001674 1985-10-04 1986-08-15 Traitement selectif de gaz contenant des olefines au moyen du procede mehra Ceased WO1987002031A1 (fr)

Priority Applications (4)

Application Number Priority Date Filing Date Title
BR8606899A BR8606899A (pt) 1985-10-04 1986-08-15 Processo para a producao de um fluxo de produto rico em hidrogenio,de um fluxo de produto rico em metano e de um fluxo de produto de etileno e hidrocarbonetos mais pesados(c2=+)
GB08712199A GB2189805A (en) 1985-10-04 1986-08-15 Selective processing of gases containing olefins by the mehra process
NO872183A NO872183L (no) 1985-10-04 1987-05-25 Selektiv bearbeidelse av gasser inneholdende olefiner ved mehra-prosessen.
KR870700472A KR870700587A (ko) 1985-10-04 1987-06-03 메라(Mehra)법에 의한 올레핀 함유 가스의 선택적 처리방법

Applications Claiming Priority (10)

Application Number Priority Date Filing Date Title
US784,566 1985-10-04
US06/784,566 US4617038A (en) 1985-07-26 1985-10-04 Process for using preferential physical solvents for selective processing of hydrocarbon gas streams
US06/808,463 US4692179A (en) 1982-05-03 1985-12-13 Process for using alkyl substituted C8-C10 aromatic hydrocarbons as preferential physical solvents for selective processing of hydrocarbon gas streams
US808,463 1985-12-13
US828,988 1986-02-13
US06/828,996 US4696688A (en) 1985-12-13 1986-02-13 Conversion of lean oil absorption process to extraction process for conditioning natural gas
US828,996 1986-02-13
US06/828,988 US4680042A (en) 1985-12-13 1986-02-13 Extractive stripping of inert-rich hydrocarbon gases with a preferential physical solvent
US06/854,383 US4743282A (en) 1982-05-03 1986-04-21 Selective processing of gases containing olefins by the mehra process
US854,383 1986-04-21

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WO1987002031A1 true WO1987002031A1 (fr) 1987-04-09

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EP (1) EP0241485A1 (fr)
AU (1) AU6284086A (fr)
BR (1) BR8606899A (fr)
ES (1) ES2001293A6 (fr)
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WO (1) WO1987002031A1 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN110963881A (zh) * 2019-12-18 2020-04-07 宁波同润和海科技有限公司 一种回收炼厂催化装置干气中各种有效组分的方法
CN110981684A (zh) * 2019-12-18 2020-04-10 宁波同润和海科技有限公司 一种回收炼厂加氢装置尾气中各种有效组分的方法

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2780580A (en) * 1953-03-04 1957-02-05 Lummus Co Production of ethylene
US2804488A (en) * 1954-12-27 1957-08-27 Phillips Petroleum Co Separation and recovery of ethylene
GB2142041A (en) * 1983-06-24 1985-01-09 El Paso Hydrocarbons Extracting natural gas streams with physical solvents

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2780580A (en) * 1953-03-04 1957-02-05 Lummus Co Production of ethylene
US2804488A (en) * 1954-12-27 1957-08-27 Phillips Petroleum Co Separation and recovery of ethylene
GB2142041A (en) * 1983-06-24 1985-01-09 El Paso Hydrocarbons Extracting natural gas streams with physical solvents

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN110963881A (zh) * 2019-12-18 2020-04-07 宁波同润和海科技有限公司 一种回收炼厂催化装置干气中各种有效组分的方法
CN110981684A (zh) * 2019-12-18 2020-04-10 宁波同润和海科技有限公司 一种回收炼厂加氢装置尾气中各种有效组分的方法
CN110963881B (zh) * 2019-12-18 2022-08-23 宁波同润和海科技有限公司 一种回收炼厂催化装置干气中各种有效组分的方法
CN110981684B (zh) * 2019-12-18 2022-09-13 宁波同润和海科技有限公司 一种回收炼厂加氢装置尾气中各种有效组分的方法

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GB2189805A (en) 1987-11-04
AU6284086A (en) 1987-04-24
GB8712199D0 (en) 1987-06-24
EP0241485A1 (fr) 1987-10-21
BR8606899A (pt) 1987-11-03
ES2001293A6 (es) 1988-05-01

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