WO1998009712A1

WO1998009712A1 - Method of selective chemisorption of reactive-active gases

Info

Publication number: WO1998009712A1
Application number: PCT/IB1996/000904
Authority: WO
Inventors: Zinaida T. Dimitrieva
Original assignee: DESTINY OIL ANSTALT
Current assignee: DESTINY OIL ANSTALT
Priority date: 1996-09-09
Filing date: 1996-09-09
Publication date: 1998-03-12
Anticipated expiration: 1999-03-09
Also published as: AU6751896A

Abstract

Environmental protection. Technology for refining inert gases, perfect gases. Micro-electronics manufacture, cryogenic and laser technology. The method involves the chemisorption of O2, CO2, H2S, BF3, BCl3, SF6, SCl6, CH3, C2H6, C3H8, C2H4 and C3H6 by multi-functional adsorbents. Lithium compounds from the following classes are used as selective chemisorbents: lithium halogenides and/or lithium alkyl(aryl) oxides, and/or lithium arilides, and/or lithium alkylborates (arylborates), and/or lithium alkyl borons (aryl borons), and/or lithium tetrafluorborons (tetrachlorborons), in individual form and/or in the form of mixtures, with any combination of these compounds and with any mass ratio between the constituents. Chemisorption is carried out under static and/or dynamic conditions at increased and/or normal pressure.

Description

METHOD OF SELECTIVE CHEMISORPTION OF REACTIVE-ACTIVE GASES

TECHNICAL FIELD

The invention relates to technology for the chemisoφtion of active gases: oxygen, carbon dioxide, hydrocarbons, ammonia, hydrogen sulphide and halogenides. The invention can therefore be used most successfully in the field of the thorough refining of inert and perfect gases (nitrogen, argon, helium, neon, xenon and krypton). In this connection, the obvious areas of application for the invention are in contemporary micro-electronics, the more advanced type of cryogenics and laser technology, particularly eximer lasers.

Other applications for the invention can be found in the technology of oxygen transport (transmission), for example oxidation reactions, or in the maintenance of vital processes.

BACKGROUND ART

In known methods, the problem of removing (extracting) oxygen from gas mixtures is solved with the help of zeolites, which absorb oxygen in accordance with the molecular screen principle (US-PS 2810454: cL C01B23/00: US 3155468, cL C01B21/04: DE 2400492, 2457842 C2, 2521264 Al, 26 15951 C2, cL B01D53/04). According to these methods, the process of refining the oxygen out of the inert or perfect gas consists of cooling the contaminated gas to 140K, to 87K, or to the boiling temperature of the gas, and then sending it through an A-type or 13X type synthetic zeolite, with molecular cell (pore) dimensions of between 2.8 and 4.2» , and with a spherical granule diameter of 2.5mm. The temperature of the column filled with zeolite is lowered by stages, at a rate of 5 - 10° a minute, with periods of constant temperature lasting not less than 40 minutes. The oxygen is absorbed on the zeolites at a pressure of between 1.47 and 29.41 bar. The desorption (evacuation) of the oxygen from the zeolites is carried out using a carrier gas, with adjustable pulse heating of the column up to the ambient temperature. The basic drawbacks of methods of extracting oxygen from gas mixtures by means of molecular screens (zeolites) stem from the complexity of synthesising highly selective, high-capacity zeolites, in relation to oxygen or to any other gas, and also to the absence of any possibility of adjusting (controlling) the efficiency of the process by which the oxygen is absorbed onto the zeolites. Moreover, the technology for -using zeolites in the refining of perfect gases is burdened with (complicated by) the extremely unfavourable gas temperature regime and gas pressure. The degree of refining of perfect gases achieved with the help of zeolites is unsatisfactory for contemporary laser technology.

Even more complicated is the technology for refining perfect gases which is based on the method of catalytic conversion of molecular oxygen (O^on the activated surface of metals of varying valency (Fe, Cu, Ni, Co, Si, Ti, Cr, Mn, Mo, Zn, Sn, Pb, Mg, Ge, W (GB 13 92823, cL H 01S-3/1-34; DE 2422574 Al, DE 3632995 C2, cL B 01 D 53/00; DE 2553554, cL B 01 D 53/14, DD 224229 Al, cL B 01 D.5.3/02; DE 3926015 C2, cL B01D53/00) and on an activated surface of copper oxide (DE-OS 1 544007, cL B01D5.3/02), nickel oxide (DE-OS 1217348 and 1217.346, cL B 01 D.5.3/00), or manganese oxide (DE-OS 1667129, cL B OlD.5.3/04; DD 205338, cL B01D53/02). Depending on the nature of the catalyst and the process conditions, 1 mol of activated metal (M) acquires from 1/2 to 1 mol of O₂ , and, under the best conditions, 1 mol of activated metal oxide acquires a maximum of 1/2 mol of O₂. The catalytic conversion of O₂ on the surface of the metals and their oxides corresponds to the following reactions: M + V2O₂ -→ MO, MO + ^x £>z —> MO₂, M + O₂— > MO₂. The catalyst, containing the metal and/or metal oxide, is prepared in the following manner. An alkaline solution of a bivalent metal sa , MCO₃ or M(NO₃), or M(OH)₂ (M = Cu, Ni, Mn, Fe, etc.) is applied to a surface SiO₂ or AI2O₃, is dried out from the water and is set out to MO₂ at 700 - 800°. The decomposition reaction reducing the metal salts to MO₂ at 700 - 800° gives a 50 - 80% yield in the best case. The metal dioxide is then reduced to the metal (M) or to MO, in a hydrogen atmosphere, at 100 - 200°, under high pressure.

The activated metal can also be obtained by reducing the salts of metals in a hydrogen atmosphere at high pressure and at high temperature. The catalysts are recuperated after the addition of O₂ in a hydrogen atmosphere.

The method of refining nitrogen out of a perfect gas consists of bringing a gas mixture into contact with titanium or barium heated to 400 - 800° (DE 2553554, cL B 01 D 53/14).

A method is known for the application of activated coal as an adsorbent of methane, in the process of extracting it from helium (DE 3716899, cL B 01 D 53/04).

The method of extracting CO2 from a combustion exhaust gas, which comprises the step of bringing, consists of sending this gas through an aqueous solution of a mixture of organic amines, with the formulae R(CH₂NH2) and NHm [(CH-dn

at atmospheric pressure, where R is a metylene chain with a number of carbon atoms ranging from 1 to 5, m = 1 or 0, n = 2 or 3 (EP 0647462 Al, cL B 01 D 53/14). However, this method is not suitable for refining carbon dioxide out of perfect gases.

DISCLOSURE OF INVENTION

The aim of the invention is to create a method for the selective and universal chemisorption of such reactive-active gases as oxygen, carbon dioxide, ammonia, hydrogen sulphide, boron and sulphur halogenides, ethylene, propylene, methane, ethane and propane, which are typical pollutants of perfect and inert gases. None of these active gases is a pollutant of atmospheric air.

The technical solution in this method lies in the fact that the selective chemisorbents used, according to invention, are lithium compounds from the following classes: lithium halogenides (LiF, LiCl) and/or lithium alkyl(aιyl) oxides (CH₃OIi, t-QH OLi, HsOLi, HsCHzOLi) and/or lithium arylides (lithium naphtalinide, lithium triphenylmethylide), and/or lithium alkyl(aryl)borates ([B(OCH₃)₄]Li, [B(O-t-C4H₉)4]Li, [BtO Hs^Li, [t-C^BfOC-sHsWU

[B(OCH₂C₆H₅)₄]Li,

and/or lithium alkylborons (arylborons) [B(CH₃)₄]Ii, [Bft-C JLi, [B( H₅)₄]U[B(CH2C₆H₅]₄Li, and/or BRJi, BCUl

Lithium chemisorbents are used both individually and in the form of a mixture of compounds, with any composition and with any mass ratio between the constituents.

In order to avoid (exclude) the destruction of the chemisorbents during their thermoregeneration, they take the form of lithium alcoxides, lithium alkylborates, and lithium alkylboron compounds, with exclusively isomeric structures. By reason of the multi-functionality and the high electron acceptance capacity of lithium, the lithium chemisorbents, according to invention, can simultaneously adsorb all the reactive-active gases listed above. Contrary to the physical adsorption, the chemisorptbn method makes it possible to extract (remove) pollutants from gas mixtures in very small quantities.

To increase the efficiency of the chemisorptkm method and increase the amount of chemisorbent available, it is preferable to use compounds with low molecular mass and mixtures. The quantities of chemisorbents available can be equal to 10 - 15 cycles of chemisoφtion - thermodesoφtion The waste chemisorbents of active gases, according to invention, are regenerated by thermodesoφtion at 220 - 250° in a vaccuum, or in a current of dried nitrogen or argon.

The method of chemisoφtion for O₂, CO₂, NH₃, H₂S , BF₃, BC1₃ SF₆, SCI*. CH₃, CzH,, C Hs, C2H1, C₃H6 and their mixtures causes the gases and the adsorbents to come into contact in dynamic and/or static conditions at higher and/or normal pressure.

In using the method of chemisoφtion of gases in dynamic conditions with the aim of excluding or reducing the pressure gradient in the filter and increasing the efficiency of chemisorbents, according to invention, they are applied to the surface of fibres of carbon and/or basalt and/or glass and/or asbestos and/or the chemisorbent is diluted by a dispersed neutral material. Quartz glass and/or silica gel and/or sand and/or marble and/or granite and/or kaolin is / are used as (a) thinner(s).

Such parameters of the chemisoφtion method as the bulk speed of filtration of gas mixtures, the pressure (resistance) in the filter, and the efficiency of adsoφtion of the gases are controlled with the assistance of a selection of fibre thicknesses, density of fibrous material, particle dimensions, poly-dispersability of the thinner material and number of filter sections (beds). The degree of extraction of the pollutants from the gas mixture (or the degree of refining of the gases) is monitored with the help of mass spectrometry, gas chromatography and gas analysers, with the use of high-sensitivity laser sensors.

MODES FOR CARRYING OUT THE INVENTION

Example 1 A sample of absolutely dry LiF weighing 0.13 g (0.005 mol) is preliminarily vacuum-treated (0.01

Pa) and then exposed to an atmosphere of trifluoric boron (BF₃) at 1.8 atmospheres and at 20°, for a period of 1.5 - 2.0 hours. Following the adsoφtion of the BF₃ and the formation of a complex, the sample is vacuum-treated again at 20° for 50 - 60 minutes to remove the suφlus of (free) trifluoric boron and weighed.f The mass of the sample has increased by 0.34 g. (0.005 mol BF₃).

After vacuum treatment, this sample, with a total weight of 0.47 g (0.005 mol LiBF₄), is exposed in an oxygen atmosphere at normal pressure and at 20° for 45 minutes. Following chemisoφtion of molecular oxygen, the adsorbent sample is again vacuum-treated to remove the gas phase and the physically adsorbed O₂. The chemisorbed oxygen is desorbed by gradually heating of the sample (at a linear heating rate of 10 - 15 r.p.m.) up to 235°. The quantity of thermo-desorbed oxygen, determined by gravimetric analysis and gas chromatography, is 0.321 g (0.01 mol O₂).

Example 2

A sample of regenerated LiBF₄ complex, weighing 0.47 g (0.005 mol) after chemisoφtion of oxygen (example 1) is vacuum-treated (0.01 Pa) and exposed in a CO₂ atmosphere at 1.5 atmospheres and at 20° for a period of 50 - 60 minutes. Following the chemisoφtion of the carbon dioxide, the adsorbent sample is vacuum-treated to remove the gas phase and the physically adsorbed CO2, after which the mass of the adsorbent is determined. The chemisorbed CO₂ is desorbed by gradual heating of the sample up to 245°. The quantity of adsorbed and desorbed CO₂

Example 3

A sample of absolutely dry IiCl weighing 0.85 g (0.02 mol) is preliminarily vacuum-treated (0.03 Pa) and then exposed in an oxygen atmosphere at 1.2 atmospheres and at 18° for 15 - 20 minutes. Following the chemisoφtion of molecular oxygen, the sorbent sample is vacuum-treated again to remove the gas phase and the physically absorbed CO2. After the determinat n of the molecular mass of the sorbent, the chemisorbed oxygen is desorbed by gradual heating of the sample to 240°. The quantity of adsorbed and thermodesorbed CO₂ is 3.6 g (0.045 mol). Following thermo- regeneration, the LiCl is again tested by chemisoφtion of oxygen under the same conditions. The quantity of thermodesorbed oxygen after the second cycle is 3.4 g (0.043 mol). In analogous conditions (1.0 - 1.5 atmospheres, 15 - 20°), the sorbents LiF, CH₃OL, t-QHgOLi,

CβHsOLi and QHsC^OLi adsorb all active gases. If the calculation is made on the basis of 1 mol of adsorbent, they adsorb (mol): O₂: 2 - 2.5; CO₂: 1.8 - 2.0; NH₃: 1.7 - 2.0; H₂S: 2.0; BF₃ (BCI₃):

0.8 - 1.0; SF₆ (SCIβ): 1.0 - 1.5

The chemosorbents listed simultaneously adsorb BF3 (BCI3) and any other gas (whatever) from the above list.

Example 4

A sample of a complex [t-C H₉B(CH2C₆H₅)₃]Li, amounting to 0.696 g (0.002 mol) is preliminarily vacuum-treated (0.01 Pa), and then exposed in an oxygen atmosphere at 1.5 atmospheres and at 17° for a period of 50 - 60 minutes. After chemisoφtion of the molecular oxygen, the adsorbent sample is again vacuum-treated to remove the gas phase and the physically adsorbed O₂. Once the molecular mass of the sample of oxidised adsorbent has been determined, it is exposed in a propane atmosphere at 1.5 atmospheres and at 17° for a period of 50 - 60 minutes. The adsorbed oxygen and propane are desorbed by gradual heating of the sample (heating rate 12 - 13° / minute) to 250° in a vacuum (0.01 Pa) over 2.0 hours. The thermodesoφtion products are quantitatively analysed using gravimetry and gas chrornatography. The quantity of thermodesorbed oxygen amounts to: 0.16 g (0.005 mol O₂). For propane, the figure is 0.528 g (0.012 mol C^h).

Example 5

A sample of a complex [BfCHzCβHs rtLi, amounting to 0.764 g (0.02 mol) is preliminarily vacuum-treated (0.01 Pa), and then exposed in an atmosphere which is a mixture of ammonium and ethane gases at 1.5 atmospheres and at 17° for a period of 70 - 80 minutes. Following the chemisoφtion of the gases, the complex sample is again vacuumed to remove the gas phase and the physically adsorbed NH₃ and C2H5. The mass of the complex sample comprising the chemosorbed gases is determined by means of gravimetry. The absorbed ammonia and ethane on the complex are thermodesorbed by gradually heating of the sample up to 240 - 250° in a vacuum (0.01 Pa) over

2.0 hours. The quantities for the thermodesorbed gases, determined by gravimetry and gas chromatography, amount to: 0.068 g (0.004 mol NH₃) and 0.24 g (0.008 mol C₂H_δ). The thermo- regenerated complex sample is again exposed, under the same conditions as described above, in an atmosphere of ammonia and ethane. The suφlus gases and the physically adsorbed gases are extracted by vacuum-treating the complex sample. Following the thermodesoφtion of the adsorbent, under the same conditions as described above, the quantities for the chemosorbed gases amount to: 0.065 g (0.0038 mol NH₃) and 0.27 g (0.009 mol C₂H6).

After the sample has been tested 5 times, using the procedure for chemisoφtion-thermodesoφtion of ammonia and ethane in accordance with the methodology set out above, the chemisoφtion capability of the complex for these gases remains at the same level as after the second test of this adsorbent complex

Example 6

A complex sample

amounting to 0.422 g (0.001 mol) and a sample of ( Hs^CIi, amounting to 0.25 g (0.001 mol) are mixed, vacuum-treated (0.01 Pa) and exposed in an atmosphere of oxygen and propane at normal pressure and at a temperature of 18° for a period of 45 - 50 minutes. Then the samples are vacuum-treated again to extract the swplus and physically adsorbed gases. Following the determination of the sample mass, the chemosorbed gases are thermodesorbed at 235 - 240° by gradually increasing the temperature in a vacuum (0.01 Pa) over 1.5 hours. The quantities for the chemosorbed and thermodesorbed gases amount to: 0.192 g (0.006 mol O₂) and 0.44 (0.01 mol C^). If the lithium triphenyl-methalenide, ( H^CIi in the mixture of adsorbents is replaced by lithium naphthalenide, CιoH₇Ii, in a quantity amounting to 0.001 mol (0.134 g), under the same conditions, the quantities for the chemosorbed and thermodesorbed gases amount to 0.224 g (0.007 mol O₂) and 0.704 g (0.016 mol C h).

Example 7

A complex sample [B(C6H₅)]4Li, amounting to 0.652 g (0.002 mol) and a complex sample [t-C4H₉OB(OCH₂C6H₅)₃] i, amounting to 0.412 g (0.001 mol) are mixed, vacuum-treated (0.01 Pa) and exposed in a CO₂ atmosphere at 1.2 atmospheres and at 18° for a period of 60 minutes. The mixture of the samples is again vacuum-treated to extract the suφlus gases and the physically adsorbed gases. Following the determination of the mass of the samples, the chemosorbed gases are thermodesorbed at 230° by gradually increasing the temperature in a vacuum (0.01 Pa) over 1.5 - 2.0 hours. The quantities for the chemosorbed and thermodesorbed gases amount to 0.264 g (0.006 mol CO₂) and 0.224 g (0.008 mol C₂H,).

Example 8

In order to test the method of selective chemisoφtion in the refining of reactive-active gases from perfect and inert gases, a multi-section or multi-bed filter is prepared. The first bed of the filter contains IiF or LiCI, mixed with any compound from the lithium alcoholate class (CH₃OLi, t-

and/or mixed with any compound from the Rli class (lithium naphthalenide, ( Hs CLi) and a fibrous material. In the first bed, the mixture of these adsorbents is applied to the surface of a fibre made of carbon and/or basalt, and/or glass, and/or asbestos. The second section (bed) of the filter contains the same fibre as the first bed, to the surface of which is applied any compound from the lithium alkylborate (arylborate) class: ([B(OCH₃)₄]Li, [B(O-t- CH^U [B(O H₅)₄] [t-CΛOB OCfiHs i, [B(OCH₂ H₅)4]U [t-

C₄H₉OB(OCH₂C₆H₅)₃]Li, and/or any compound from the lithium alkylboron (arylboron) class: ([B(CH₃) ] [Btt-G-Hs^l [B(C6H₅)₄] [B CHzQ-Hsjr-tLi), and/or BE4U (BCUi). The third section (bed) of the filter consists of a mixture of compounds from all the classes listed, diluted (mixed) with a hard dispersed material, for example quartz sand or silica gel, or marble or granite or kaolin If necessary, the number of such sections (beds) in the filter can be doubled or tripled. Refined argon is passed through a filter prepared in such a manner and preliminarily vacuum- treated, to displace the residue (traces) of air. Following this procedure, 5 m³ of the argon are filtered, containing the following pollutants per m³: 0.5 -10g^'2 O₂, 1.8 ^• lOg^"3 C₃H₈. 2.5 ^• lOg^"2 CO₂, 0.1 • lOg^"3 BF₃. The argon is filtered at a bulk rate of 500 L/hour at 17°. The degree of refining of the argon is checked using mass spectrometry and laser spectroscopy. For one cycle of gas mixture filtration, the pollutant content per m³ of argon amounts to: 0.7 ^• lOg^"4 O₂, 1.5 ^• 10g^'5 C3H8, 2 ^• lOg^"

⁴ CO₂, 0.3 ^• lOg^"6 BF₃. Following the second cycle of gas mixture filtration, at a bulk rate of 250

L/hour, the pollutant content per m³ of argon amounts to: 0.15 -lOg^*7 O₂, 0.32 ^• lOg^"7 CO₂. After the second filtration cycle, no propane and trifluoric boron could be detected in the argon

Claims

1. Method of selective chemisoφtion of reactive-active gases, including the physical adsorbtion of oxygen onto the surfaces of metals and zeolites, distinguished by the fact that it includes the chemisoφtion of gases by multi-functional electron-acceptor adsorbents.

2. Method as paragraph 1, distinguished by the fact that lithium compounds from the following classes are used as selective multi-functional chemisorbents: lithium halogenides (LiF, IiCI) and/or lithium alkyl(aryl) oxides (CH₃OU, t-C₄H₉OU HsOLi, H₅CH2OL0, and/or lithium arylides (lithium naphthalenide, ( -Hs^CLi), and/or lithium alkylborates (arylborates) ([B(OCH₃)₄]Li, [B(O-t-C4H₉)₄]Li, [B O H-JjLi, [t- CHsOB O Hs^Li, [B(OCH₂C6H₅)₄] [t-C₄H₉OB(OCH₂C6H₅)₃] and/or lithium alkylborons (arylborons); [B(CH₃)₄]Li, [B(t-C₄H₉)₄]Li, [B(C₆H₅)₄U), and/or BRdi, BCLU, in individual form and/or in the form of a mixture with any composition and with any mass ratio between the constituents.

3. Method as paragraph 1, distinguished by the fact that the chemosorbents of the reactive- active gases, which may be diluted with dispersed (powdered) neutral materials, are applied to the surface of fibres.

4. Method as paragraph 3, distinguished by the fact that carbon fibre and/or basalt fibre, and/or fibreglass, and or asbestos fibre, and/or quartz glass, and/or silica gel, and/or sand, and/or marble, and/or granite, and/or kaolin, is / are used as (a) carrier(s) and (a) thinner(s) of chemisorbents.

5. Method as paragraph 1, distinguished by the fact that the chemisoφtion of oxygen, carbon dioxide, hydrocarbons, ammonium, hydrogen sulphide, trifluoric boron (boron trichloride), hexafluoric sulphur (hexachloric sulphur), water vapours and their mixtures is carried out by bringing the gases into contact with adsorbents under dynamic and/or static conditions at temperatures of 20° and below, at increased and or normal pressure.

6. Method as paragraph 1, distinguished by the fact that the chemisorbents of the gases are regenerated (recuperated) by thermodesoφtion at 220 - 250° in a vacuum or in a current of dried inert gas.