GB2467921A

GB2467921A - Carbon dioxide absorption and desorption

Info

Publication number: GB2467921A
Application number: GB0902800A
Authority: GB
Inventors: Ian Kirk Houston
Original assignee: ORIGO IND Ltd
Current assignee: ORIGO IND Ltd
Priority date: 2009-02-19
Filing date: 2009-02-19
Publication date: 2010-08-25
Also published as: GB0902800D0; WO2010094923A3; WO2010094923A2

Abstract

A method of absorbing CO2from a gas that includes a volume, V1, of CO2 comprising: providing a CO2-absorption substrate, and contacting the gas with the substrate, whereby a volume, V2, of CO2is absorbed from the gas by the substrate, wherein the substrate comprises a porous material, the composition of which comprises at least one chemical element having an atomic number of 13 or greater, onto which any one or more of the following CO2-absorbers is adsorbed: a primary, secondary or tertiary amine, or a quaternary ammonium compound. Also a method of desorbing CO2from a CO2-rich absorption substrate, the substrate having any one or more of the following CO2-absorbers adsorbed onto it: a primary, secondary or tertiary amine, or a quaternary ammonium compound and a pre-absorbed volume, V3, of CO2, the method comprising: treating the substrate with an acid, thereby releasing a volume, V4, of the absorbed CO2.

Description

DESCRI PTION

Methods of Absorption and Desorption of Carbon Dioxide, and Apparatus for Each The present invention relates in a first aspect to a method of absorbing carbon dioxide (C02) from a gas, and in a second aspect to a method of desorbing pre-absorbed carbon dioxide from a substrate in preparation for its use elsewhere. The invention furthermore relates to CO2 absorption/desorption apparatus.

Pollution management, especially air pollution management with an emphasis on CO2 emissions into the atmosphere, is currently high on the global political, economic and environmental agendas. This is because of an increasing amount of scientific evidence indicating that CO2 emissions are having an increasingly detrimental effect on both human health and the health of our ecosystems.

A number of solutions have been proposed to address the problem of increasing CO2 emission including: -reduction in the levels of CO2 emissions themselves, for example by the use of cleaner hydrocarbon-based fuels and by the use of alternative fuels; -capturing CO2 emissions from the atmosphere and treating for subsequent storage in another medium, e.g. by reaction with calcium oxide (quicklime) to form calcium carbonate (chalk).

In the latter group of solutions, it is furthermore known to use amine-based sorbents to extract CO2 from gas streams, especially exhaust/flue gas streams from industrial processes, such as power stations and chemical manufacturing operations. The sorbents can be provided in solution, e.g. an aqueous solution, or in solid form, e.g. impregnated onto a porous substrate. However CO2 absorption into an amine-based sorbent is a temperature-dependent process; above a certain threshold temperature, desorption of CO2 occurs, often undesirably.

It is therefore an aim of the invention to provide a method for improved CO2 absorption, especially improved absorption efficiency. It is a further aim of the invention to provide a method for controllable CO2 desorption, from which desorbed CO2 may then be taken for further processing, such as use in bio-fuel manufacture.

It is moreover an aim of the invention to provide a suitable CO2 absorption/desorption apparatus.

Accordingly in a first aspect the present invention provides a method of absorbing CO2 from a gas that includes a volume, V1, of CO2 (a C02-containing gas) the method comprising: providing a C02-absorption substrate, and contacting the gas with the substrate, whereby a volume, V2, of CO2 is absorbed from the gas by the substrate leaving a C02-deficient gas, wherein the substrate comprises a porous material, the composition of which comprises at least one chemical element having an atomic number of 13 or greater, onto which any one or more of the following C02-absorbers is adsorbed: a primary amine, a secondary amine, a tertiary amine, a quaternary amrnonium compound.

The substrate may be organic or inorganic; if organic it will therefore comprise at least one chemical element other than hydrogen (atomic number of 1), carbon (atomic number of 6) and oxygen (atomic number of 8).

The C02-absorbers may be adsorbed onto the surface of the porous substrate, including adsorption into the pores by treating the substrate with a solution of one or

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more C02-absorbers in a suitable solvent to distribute them, and subsequently evaporating off the solvent. For the avoidance of doubt, the term "pore" and its derivates include both a depression in a surface and also a bottomless aperture in the surface. Once adsorbed, the C02-absorbers are ready to absorb CO2 molecules that come into contact with them.

In one embodiment of the invention, the substrate is preferably a polymeric material having porosity suitable for adsorption of C02-absorbers. Further preferably the polymeric material is a polysulfone.

In an alternative embodiment of the invention, the substrate is preferably in the form of a metallic network, further preferably a nickel foam. Such a network material inherently has porosity suitable for adsorption of C02-absorbers.

Advantageously, the volume of CO2 absorbed from the gas by the substrate, V2, may be more or less equal to the volume of CO2 contained in the gas prior to its treatment, V1, that is to say V1 = V2. The closer V2 is to V1, the more efficient the absorption method is.

The C02-absorbers described above may be of the form R1R2R3N (and the quaternary ammonium compound similarly of the form R1R2R3R4N) wherein each of R1, R2 and R3 (and R4 as appropriate) is independently selected from the group consisting of hydrogen, a linear alkyl, a branched alkyl, a cyclic alkyl, a substituted linear alkyl, a substituted branched alkyl, a substituted cyclic alkyl, an aryl, a substituted aryl, an arylated alkyl (aralkyl), a substituted aralkyl, a heterocyclic, a substituted heterocyclic, a hetero-aryl and a substituted hetero-aryl.

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However preferably any two of R1, R2 and R3 (and R4 as appropriate) may be independently selected from the group consisting of hydrogen and the non-sterically bulky substituents having between 1 and 6 carbon atoms inclusively, and the remaining R is (are) a sterically bulky substituent(s) having at least 6 carbon atoms.

Indeed the C02-absorber may be selected from any one or more of the following amines: dehydroabietylamine, butylamine, octylamine, benzylamine, x-methylbenzylamine, 2-amino-2-ethyl-1, 3-propanediol, diphenylamine, ethanolamine, diethanolamine, triethanolamine, piperazine, 2-methylpiperazine, N- methylpiperazine, homopiperazine, piperidine, morpholine, pyrrolidine, c-aminopyridine, 3-aminopyridine, y-aminopyridine and spermine.

The step of contacting the gas with the substrate preferably occurs in the presence of water (H20), which is present in an amount such that the ratio of C02: H20 is at least 1:1. An equilibrium exists between CO2 plus H20 and carbonic acid (H2C03), the bicarbonate ion (HCO3) and the carbonate ion (C032), which is beneficial to the method of the invention.

Advantageously water vapour may be comprised in the C02-containing gas, especially where the gas is a product of hydrocarbons combustion, occurring in e.g. an internal combustion engine of a vehicle, a gas turbine, a refinery fluestack, a power station or in another industrial plant.

Typically the gas may comprise at least 5 % by volume of CO2 prior to contacting the substrate. However this may be at least 10 % or even 20 % depending upon the conditions of CO2 emission.

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The step of contacting the gas with the substrate may occur at a temperature of between 5 °C and 100 °C, preferably between 10 °C and 85 °C, and further preferably between 15 °C and 70 °C. Such a temperature is believed to be optimal for enabling absorption of CO2 from the gas.

In addition to the foregoing, the method of the invention may further comprise the step of pre-treating the absorption substrate with an alkali metal compound, MX, such that the C02-absorbers form an R1R2NM intermediate prior to contacting the gas with the substrate. This intermediate is a powerful base and may be used to drive the CO2 and H20 equilibrium described above in the direction of the carbonate ion. Advantageously the metal, M, is lithium.

Absorption of CO2 by the substrate thus preferably forms of any one or more of the following absorption compounds: an amine carbonate, an amine hydrogen carbonate, a quaternary ammonium carbonate, a quaternary ammonium hydrogen carbonate.

Although the method of the invention may be performed in any environment in which the level of CO2 in the atmosphere is desired to be reduced, including both open and closed systems, the substrate is preferably provided in a re-sealable chamber which has a gas inlet, for introduction of the C02-containing gas, and a gas outlet, for exhaustion of the C02-deficient gas.

Beneficially gas introduction to, and exhaustion from, the chamber may be performed continuously such that there is a negligible residence time of the gas in the chamber (subject to the gaseous flow rate through the chamber), and this maximum gaseous throughput to achieve increased absorption efficiency.

Turning now to the second aspect of the invention, there is provided a method of desorbing CO2 from a C02-rich absorption substrate, the substrate having any one or more of the following C02-absorbers adsorbed onto it: a primary amine, a secondary amine, a tertiary amine, a quaternary ammonium compound and a pre-absorbed volume, V3, of C02, the method comprising: treating the substrate with an acid, thereby releasing a volume, V4, of the absorbed Co2.

For the avoidance of doubt, a C02-rich absorption substrate is one having a volume, V3, of CO2 pre-absorbed onto it. The substrate itself may be organic or inorganic, and is preferably porous. The C02-absorbers may be adsorbed onto the surface of the substrate, including adsorption into its pores, where such exist.

Preferably the acid used is an organic acid, which may be selected from the group consisting of: acetic acid, lactic acid, citric acid, malic acid and tartaric acid. Such weak acids may the by-product of another industrial process or they may be formed by oxidation from a corresponding alcohol. In any case, the acid preferably has a low carbon footprint".

Alternatively, the acid may be an inorganic acid, in which case it may be selected from the group consisting of: sulphuric acid and phosphoric acid.

The acid used may furthermore be a mixture of different acids.

Advantageously the volume of CO2 desorbed/released, V4 may be more or less equal to the volume of pre-absorbed C02, V3, that is to say V3 = V4. The ratio of V3 to V4 is dependent on the amount and/or concentration of acid used, and as such, CO2 desorption is controllable.

In addition to the foregoing steps for desorbing C02, the invention preferably further comprises the step of preheating the substrate so that the C02-absorption compound forms a carbonate prior to treating it with the acid.

Typically the substrate may be preheated to a temperature of at least 40 °C, and preferably up to around 120 °C. This temperature range appears to be optimal in terms of carbonate formation, whilst maintaining the integrity of the substrate and preventing its degradation.

Furthermore following the step of treating the substrate with the acid, the method may also comprise the step of treating the acidified substrate with an alkali to regenerate the C02-absorption property of the substrate. The alkali is preferably an excess of aqueous ammonia.

Although the method of the invention may be performed in any environment in which it is desired to desorb a volume of absorbed CO2 from a substrate, including both open and closed systems, the substrate is preferably provided in a re-sealable chamber which has an inlet, for introduction of the acid, and an outlet, for exhaustion of desorbed CO2.

Advantageously, in the method of desorbing CO2 described above according to the second aspect of the invention, the CO2 may be pre-absorbed by the substrate according to the first aspect of the invention. Thus the two methods may be considered as complementary and may be co-operable with one another.

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Turning now to the third aspect of the invention, there is provided a CO2 absorption/desorption apparatus comprising a re-sealable chamber having an inlet, for introduction of a C02-containing gas and/or an acid, and an outlet, for exhaustion of a C02-deficient gas and/or desorbed CO2. One piece of apparatus may thus be suitable for sequentially performing each of the two methods of the invention without modification.

Preferably the apparatus comprises at least two such chambers adapted so as to be cyclically operable, such that when CO2 absorption occurs in one chamber, previously absorbed CO2 desorption occurs in the other chamber, in a complementary manner.

For a better understanding the present invention will now be more particularly described by way of non-limiting example.

Example I -COAbsorption A C02-absorber solution was made by dissolving 20.Og (0.12 moles) of benzyltrimethylammonium hydroxide (a quaternary ammonium compound) in lOOmI of water under ambient conditions. The solution was mixed with methylated spirits and applied to a polysulfone substrate (the composition of which includes sulphur atoms, having an atomic number of 16). The substrate was allowed to dry at room temperature, during which time the methylated spirits evaporated. A suitable polysulfone substrate is available under the trade name UDELTM Polysulfone P-1700 from Solvay Advanced Polymers, Georgia, USA. Alternatively, the substrate could be a nickel foam (the composition of which includes nickel atoms, having an atomic number of 28). Such a metallic foam is available under the trade name lncoFoamTM from Inco Special Products (www.incosp.com).

The resultant C02-absorption substrate was placed into a re-sealable stainless steel chamber, having a gas inlet and a gas outlet, which was then sealed to the atmosphere. Pure gaseous CO2 was pumped into the sealed chamber through the gas inlet at a rate of 0.5 litres/minute for 2 minutes. A gas analyzer (GreenLine 8000 Flue Gas Analyzer available from E Instruments Group of Pennsylvania, USA) was arranged to contemporaneously analyze the gas exiting the chamber via the gas outlet. The results showed 91 % absorption of CO2.

This result was confirmed with a laboratory experiment, in which pure gaseous CO2 was bubbled through the C02-absorber solution at a rate of 0.5 litres/minute for 2 minutes. The resulting solution was heated under reflux for 45 minutes whilst being sparged with nitrogen. The exiting gas was passed through a fine glass sintered bubbler into aqueous sodium hydroxide. Back-titration of the aqueous sodium hydroxide yielded the result that 2.Og of CO2 had been absorbed (76 % absorption), with the concomitant formation of benzyltrimethylammonium carbonate.

The resulting solution of benzyltrimethylammonium carbonate was then made up to a total volume of lOOrnI by addition of distilled water and cooled to a temperature of less than 20 °C. Pure gaseous CO2 was bubbled through the solution at a rate of 0.5 litres/minute for 2 minutes to form a solution of benzyltrimethylammonium hydrogen carbonate.

The resulting solution was heated under reflux for 45 minutes whilst being sparged with nitrogen. The exiting gas was again passed through a fine glass sintered

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bubbler into aqueous sodium hydroxide. Back-titration of the aqueous sodium hydroxide yielded the result that 2.4g of CO2 had been absorbed (91 % absorption), with the concomitant formation of benzyltrimethylammonium carbonate.

Example 2 -CO2 Desorption Subsequent to analysis of the exiting gas from the sealed chamber in Example 1, the substrate inside the chamber was treated with a slight excess of citric acid (a weak organic acid) until effervescence ceased. The gas analyzer yielded the result that all of the absorbed CO2 had been desorbed, i.e. the full 91 % was desorbed and detected.

Again this result was confirmed with a laboratory experiment. The benzyltrimethylammonium carbonate finally formed in the laboratory experiment described in Example 1 above was intermittently treated with a slight excess of citric acid and sparged with nitrogen until the observed effervescence ceased. The exiting gas was passed through a fine glass sintered bubbler into aqueous sodium hydroxide. Back-titration of the aqueous sodium hydroxide yielded the result that 2.8g of CO2 had been absorbed, representing a 91 % recovery of CO2 over the three stages (two in Example 1 and this in Example 2).

Example 3 -CO2 Desorption A further laboratory experiment was performed to assess CO2 desorption. 104g (0.30 moles) of diethanolamine hydrogen carbonate (a C02-absorption compound) was suspended in 500m1 of isopropyl alcohol and heated to reflux whilst being sparged with nitrogen. The exiting gas was bubbled into a stirred solution of 200g (0.62 moles) if diethanolamine in 2000m1 of methylated spirits (95 %) at 0 °C whereupon a precipitate was formed.

The precipitate was filtered and titrated with more methylated spirits (95 %) and subsequently filtered and dried under ambient conditions to yield 84g of diethanolamine hydrogen carbonate, representing an 81 % recovery of CO2 over the two stages.

In summary, a porous substrate such as a potysulfone or a metallic foam can be impregnated with an amine C02-absorber, contacted with a gas containing CO2 and have CO2 (up to 100 %) absorbed from the gas by the substrate. Furthermore CO2 can be desorbed from a C02-rich absorption substrate, which may or may not be formed by the absorption method of the invention, using an acid, such as a weak organic acid, with subsequent regeneration of the absorption substrate.

Claims

SCLAIMS: 1. A method of absorbing carbon dioxide (Ca2) from a gas that includes a volume, V1, of CO2 (a C02-containing gas) the method comprising: providing a C02-absorption substrate, and contacting the gas with the substrate, whereby a volume, V2, of CO2 is absorbed from the gas by the substrate leaving a C02-deficient gas, wherein the substrate comprises a porous material, the composition of which comprises at least one chemical element having an atomic number of 13 or greater, onto which any one or more of the following C02-absorbers is adsorbed: a primary amine, a secondary amine, a tertiary amine, a quaternary ammonium compound.
2. A method according to claim 1 wherein the substrate is a polymeric material.
3. A method according to claim 2 wherein the polymeric material is a polysulfone.
4. A method according to claim 1 wherein the substrate is a metallic network.
5. A method according to claim 4 wherein the metallic network is a nickel foam.
6. A method according to any preceding claim wherein V1 = V2.
7. A method according to any one of the preceding claims wherein the C02-absorbers are of the form R1R2R3N (and the quaternary ammonium compound is similarly of the form R1R2R3R4N) wherein each of R1, R2 and R3S(and R4 as appropriate) is independently selected from the group consisting of hydrogen, a linear alkyl, a branched alkyl, a cyclic alkyl, a substituted linear alkyl, a substituted branched alkyl, a substituted cyclic alkyl, an aryl, a substituted aryl, an arylated alkyl (aralkyl), a substituted aralkyl, a heterocyclic, a substituted heterocyclic, a hetero-aryl and a substituted hetero-aryl.
8. A method according to claim 7 wherein any two of R1 R2 and R3 (and R4 as appropriate) is independently selected from the group consisting of hydrogen and the non-sterically bulky substituents having between 1 and 6 carbon atoms inclusively, and the remaining R is (are) a sterically bulky substituent(s) having at least 6 carbon atoms.
9. A method according to claim 7 or claim 8 wherein the C02-absorber is selected from any one or more of the following amines: dehydroabietylamine, butylamine, octylamine, benzylam me, cL-methylbenzylamine, 2-amino-2-ethyl- 1,3-propanediol, diphenylamine, ethanolaniine, diethanolamine, triethanolamine, piperazine, 2-methylpiperazine, N-methylpiperazine, homopiperazine, piperidine, morpholine, pyrrolidine, a-aminopyridine, 3-aminopyridine, y-aminopyridine and spermine.
10. A method according to any preceding claim wherein contacting of the gas with the substrate occurs in the presence of water (H20), which is present in an amount such that the ratio of C02: H20 is at least 1:1.
11. A method according to claim 10 wherein water vapour is comprised in gas.S
12. A method according to claim 11 wherein the gas is a product of hydrocarbons combustion.
13. A method according to any preceding claim wherein the gas comprises at least 5 % by volume of CO2 prior to contacting the substrate.
14. A method according to any preceding claim wherein contacting the gas with the substrate occurs at a temperature of between 5 °C and 100 °C.
15. A method according to any of claims 7 to 14 further comprising the step of pre-treating the absorption substrate with an alkali metal compound, MX, such that the C02-absorbers form an R1R2NM intermediate prior to contacting the gas with the substrate.
16. A method according to claim 15 wherein the metal, M, is lithium.
17. A method according to any preceding claim wherein absorption of CO2 by the substrate forms of any one or more of the following absorption compounds: an amine carbonate, an amine hydrogen carbonate, a quaternary ammonium carbonate, a quaternary amrrionium hydrogen carbonate.
18. A method according to any preceding claim further comprising providing the substrate in a re-sealable chamber which has a gas inlet, for introduction of the CO2-containing gas, and a gas outlet, for exhaustion of the C02-deficient gas.
19. A method according to claim 18 wherein gas introduction and exhaustion is performed continuously.
20. A method of desorbing CO2 from a C02-rich absorption substrate, the substrate having any one or more of the following C02-absorbers adsorbed onto it: a primary amine, a secondary amine, a tertiary amine, a quaternary ammonium compound and a pre-absorbed volume, V3, of CO, the method comprising: treating the substrate with an acid, thereby releasing a volume, V4, of the absorbed CO2.
21. A method according to claim 20 wherein the acid is an organic acid.
22. A method according to claim 21 wherein the organic acid is selected from the group consisting of: acetic acid, lactic acid, citric acid, malic acid and tartaric acid.
23. A method according to claim 20 wherein the acid is an inorganic acid.
24. A method according to claim 23 wherein the inorganic acid is selected from the group consisting of: sulphuric acid and phosphoric acid.
25. A method according to any of claims 20 to 24 wherein V3 = V4.
26. A method according to any of claims 20 to 25 further comprising preheating the substrate so that the C02-absorption compound forms a carbonate prior to treating it with the acid.
27. A method according to claim 26 wherein the substrate is preheated to a temperature of at least 40 °C.
28. A method according to any of claims 20 to 27 further comprising treating the acidified substrate with an alkali to regenerate the C02-absorption property of the substrate.
29. A method according to claim 28 wherein the alkali is an excess of aqueous ammonia.
30. A method according to any of claims 20 to 29 further comprising providing the substrate in a re-sealable chamber which has an inlet, for introduction of the acid, and an outlet, for exhaustion of desorbed CO2.
31 A method according to any of claims 20 to 30 wherein CO2 is pre-absorbed by the substrate according to the method of any of claims 1 to 19.
32. CO2 absorption/desorption apparatus comprising a re-sealable chamber having an inlet, for introduction of a C02-containing gas and/or an acid, and an outlet, for exhaustion of a C02-deficient gas and/or desorbed CO2.
33. CO2 absorption/desorption apparatus as claimed in claim 32 comprising at least two such chambers adapted so as to be cyclically operable, such that when CO2 absorption occurs in one chamber, previously absorbed CO2 desorption occurs in the other chamber.
34. A method of absorbing CO2 from a C02-containing gas substantially as hereinbefore described.
35. A method of desorbing CO2 from a C02-rich absorption substrate substantially as hereinbefore described.
36. CO2 absorption/desorption apparatus substantially as hereinbefore described.