Enhancing separation of acid gases from a process stream or a flue gas

Abstract

The present description relates to processes for the desorption of an acid gas, such as carbon dioxide, from an acid gas loaded carbonate solution generated by absorption of the acid gas from an acid gas containing stream into an absorption solution based on carbonates such as potassium carbonate. The process can include: contacting the acid gas loaded carbonate solution with desorption enhancement structures that comprise acid surfaces at desorption conditions such that the acid surfaces cause a shift in equilibrium to promote release of the acid gas from the gas loaded carbonate solution; and producing an acid gas depleted solution and an acid gas stream. The acid surfaces can provide enhancements that can facilitate reduced energy requirements for desorption in carbonate based systems. Systems and uses where acid surfaces are implemented to enhance desorption in carbonate based solutions are also described herein.

Description

[0001] ENHANCING SEPARATION OF ACID GASES FROM A PROCESS STREAM OR A FLUE GAS

[0002] TECHNICAL FIELD

[0003] The technical field generally relates to acid gas capture and more specifically to enhanced desorption of acid gases, such as CO2, from a loaded carbonate solution using acid surfaces.

[0004] BACKGROUND

[0005] Removing acid gas from a gas fluid can include an absorption stage where the acid gas is absorbed into a liquid, followed by a desorption stage where the liquid loaded in acid gas is treated to promote release of the acid gas. In certain systems, such as those that employ carbonate solutions as the absorption liquid, the energy required in the desorption stage to heat the liquid to promote acid gas release is significant to the point that such systems may not be feasible or practical in many contexts. There is a need for a technology that overcomes at least some of the challenges in this field.

[0006] SUMMARY

[0007] In some implementations, there is provided a process for desorption of an acid gas from an acid gas loaded carbonate solution generated by absorption of the acid gas from an acid gas containing stream into an absorption solution based on carbonates formed with an element of the first and second groups of the periodic table of elements, the process comprising: contacting the acid gas loaded carbonate solution with desorption enhancement structures that comprise a non-soluble supports and acid surfaces supported by the non-soluble supports at desorption conditions such that the acid surfaces cause a shift in equilibrium to promote release of the acid gas from the gas loaded carbonate solution; and producing an acid gas depleted solution and an acid gas stream.

[0008] In some implementations, the acid gas comprises CO2. In some implementations, the carbonates comprise potassium carbonate. In some implementations, the acid gas containing stream comprises flue gas. In some implementations, the acid gas containing stream comprises an industrial gas stream. In some implementations, the absorption solution has a concentration below a precipitation concentration in the overall capture system. In some implementations, the acid surfaces comprise a proton-donating surface. In some implementations, the acid surfaces comprise one or more of the following: FeC., SbFs and AICIs Supported on graphite, AhO, SiO, Zeolites, & clays (e.g. AICI / AI2O, ZnCh / Acid treated clays, FeCI / graphite, SbFs / graphite, AlCI / graphite, Vanadium phosphates and aluminophosphates, CaO ZrCh; SimO ZrO, YbO ZrO, aluminum chlorofluoride, ACF. (AICIF, Xs().O5 0.25), aluminum bromofluoride, ABF. (AIBrF, X-0.05 0.25)); heteropoly acids (HPAs) such as HPWO and HPMo.O.; silica-supported Nation (SAC-13); alumina, amorphous silica-alumina, amorphous silica-alumina molecular sieves such as microporous aluminosilicates or Zeolites (e.g. HZSM-5, H. Y. H X) and mesoporous aluminosilicates such as M41S (e.g. MCM-41 . SBA-15, MCF); silica- magnesia, Silica-Zirconia, alumina-boria, titania-boria, tungstate-alumina, and tungstate Zirconia; AlCI / mesoporous silica, CrO / ZrO., Sulfated Zirconia, pillared clays (PILC) and acidic porous clay heterostructures (PCH). Any suitable Bronsted acid surface may be used herein. For example, amorphous silica-alumina molecular sieves such as microporous aluminosilicates or Zeolites (e.g. HZSM-5, H. Y. H X) and mesoporous aluminosilicates such as M41S (e.g. MCM-41 , SBA-15, MCF); heteropoly acids (HPAs) such as HPWO and HPMo.O.; silica supported Nation (SAC-13), and combinations thereof. In some implementations, the acid surfaces comprise an electron-acceptor surface. In some implementations, the electron-acceptor surface comprises one or more of the following: FeCI., SbF and AICIs Supported on graphite, AI2O, SiO, Zeolites, & clays (e.g. AICI / AI2O, ZnCI2 / Acid treated clays, FeCI / graphite, SbF5 / graphite, AlCI / graphite, Vanadium phosphates and aluminophosphates, CaO ZrO. SmO-ZrO: YbO, ZrO, aluminum chlorofluoride, ACF. (AICIF, Xs(0.05-0.25), aluminum bromofluoride, ABF (AIBr, F. X-0.05-0.25), and combinations thereof. In some implementations, the acid surfaces comprise a combination of electron-acceptor surface and proton-donor surface. In some implementations, the acid surfaces comprise alumina, amorphous silica-alumina, amorphous silica-alumina molecular sieves, silica-magnesia, silica-Zirconia, alumina- boria, titania-boria, tungstate-alumina, and tungstate Zirconia; AlCI / mesoporous silica, CrO / ZrO., sulfated zirconia, pillared clays (PILC) and acidic porous clay heterostructures (PCH). In some implementations, the non-soluble supports comprise graphite, polymer material, metal material, ceramic material, or a combination thereof. In some implementations, the contacting of the acid gas loaded carbonate solution with the acids surfaces is performed at a temperature between 20°C and 120°C. In some implementations, the contacting of the acid gas loaded carbonate solution with the acids surfaces is performed at a pressure between 20 000 Pa and 100 000 Pa. In some implementations, the concentration of the carbonates in the absorption solution is 0.5 to 2.5 mol / liter. In some implementations, the contacting of the acid gas loaded carbonate solution with the acids surfaces is performed in a stripping unit that receives the acid gas loaded carbonate solution directly from an absorption unit. In some implementations, the contacting of the acid gas loaded carbonate solution with the acids surfaces is performed in a pretreatment desorption unit that receives the acid gas loaded carbonate solution directly from an absorption unit and produces a pretreated solution that is supplied to a stripping unit for further removal of the acid gas. In some implementations, the acid gas loaded carbonate solution is supplied to a stripping unit to produce a partially stripped solution that is then supplied to a desorption unit for further removal of the acid gas to produce the acid gas depleted solution. In some implementations, the non-soluble support and the acid surfaces are composed of the same material. In some implementations, the desorption enhancement structures are provided in powder form. In some implementations, the desorption enhancement structures are provided in particle form free in solution, optionally sized and having physical properties for separation from the solution optionally using one or more separation mechanisms including gravity, density, size, and magnetic properties. In some implementations, the desorption enhancement structures form a packing material over which the acid gas loaded carbonate solution flows. In some implementations, the desorption enhancement structures are free in solution within the acid gas loaded carbonate solution. In some implementations, the desorption enhancement structures are provided to reduce heat requirements of the desorption by at least 20%, 30%, 40%, 50%, 60%, 70% or 75% versus a base case without acid surfaces. In some implementations, the contacting of the acid gas loaded carbonate solution with the acid surfaces is performed in a pretreatment desorption unit and the acid gas depleted solution is withdrawn and supplied to a stripper unit to produce a regenerated solution for recycling back as at least part of the absorption solution for further absorption of the acid gas. In some implementations, the contacting of the acid gas loaded carbonate solution with the acid surfaces is performed in a polishing desorption unit that is downstream of a primary stripper unit, and the acid gas depleted solution from the polishing desorption unit is recycled back as at least part of the absorption solution for further absorption of the acid gas. In some implementations, the contacting of the acid gas loaded carbonate solution with the acid surfaces is performed in a packed column. In some implementations, there is provided a system for desorption of an acid gas from an acid gas loaded carbonate solution generated by absorption of the acid gas from an acid gas containing stream into an absorption solution based on carbonates formed with an element of the first and second groups of the periodic table of elements, the system comprising: a desorption vessel comprising a liquid inlet configured to receive the acid gas loaded carbonate solution; a desorption chamber in fluid communication with the liquid inlet and configured to receive the acid gas loaded carbonate solution therefrom; a liquid outlet in fluid communication with the desorption chamber and configured to withdraw an acid gas depleted solution; and a gas outlet in fluid communication with the desorption chamber and configured to withdraw an acid gas stream. The system also includes desorption enhancement structures provided in the desorption chamber, the desorption enhancement structures comprising a non-soluble supports and acid surfaces supported by the non-soluble supports at desorption conditions such that the acid surfaces cause a shift in equilibrium to promote release of the acid gas from the gas loaded carbonate solution. The system can be implemented as a pretreatment unit or a polishing unit, for example, that is part of a desorption stage that also includes a stripper unit. The system can also have one or more features mentioned above for the process and / or as described or illustrated herein.

[0009] In some implementations, there is provided the use of acid surfaces for accelerating desorption of an acid gas from an acid gas loaded carbonate solution generated by absorption of the acid gas from an acid gas containing stream into an absorption solution based on carbonates formed with an element of the first and second groups of the periodic table of elements.

[0010] BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Fig 1 is a process diagram of an example acid gas capture arrangement.

[0012] Fig 2 is a process diagram of another example acid gas capture arrangement.

[0013] Fig 3 is a process diagram of another example acid gas capture arrangement.

[0014] Fig 4 is a process diagram of yet another example acid gas capture arrangement.

[0015] Fig 5 is a graph of carbonate-bicarbonate-carbonic acid system showing relative amounts versus pH. Fig 6 is a graph of desorption amount versus time for experimental data.

[0016] DETAILED DESCRIPTION

[0017] The present description relates to acid gas capture, such as CO2 capture, in which a desorption stage includes the use of acid surfaces to promote CO2 gas release and a reduction in energy requirements. For example, the technology can include a capture process that includes an absorption stage in which generates an acid gas loaded solution which is supplied to a desorption stage which generates an acid gas depleted solution aided by the presence of acid surfaces that are contacted by the solution and promote desorption from the solution.

[0018] Turning to Fig 1 , a capture system 10 includes an absorber 12 that receives an acid gas containing stream 14 and an absorption solution 16 and enables the production of an acid gas depleted stream 18 and an acid gas loaded solution 20. The absorption solution is a carbonate based solution, that is, carbonates formed with elements of the first and second groups of the periodic table of elements, such as potassium carbonate. The acid gas loaded solution 20 is supplied to a desorber 22 and optionally passes through a heat exchanger 24 for heating and producing a heated acid gas loaded solution 26. The heated acid gas loaded solution 26 flows through the desorber 22 and comes into contact with acid surfaces 28 that are present in the desorber 22. The acid surfaces 28 can be provided on supports, such as packing material or internal structures of the desorber that are fixed or free in the desorber chamber. The acid surfaces 28 aid in promoting release of the acid gas from the loaded solution and producing an acid gas stream 30 and an acid gas depleted solution 32. The acid gas depleted solution 32 can then be recycled back as at least part of the absorption solution 16, optionally passing through the heat exchanger 24 to indirectly heat the loaded solution.

[0019] In some implementations, the acid gas includes CO2 and the acid gas containing stream 14 includes a CO2 containing gas resulting from the combustion of fossil fuels and / or from chemical reactions present in some industrial processes. It is noted that various sources of CO2 containing gas can be used as a feed to the absorption stage. The CO2 containing gas can have various concentrations and compositions and the absorption stage can be adapted accordingly. The absorption solution 16, which can also be referred to as a carbonate absorption solution herein, is carbonate based but could also include one or more other chemical, biological, or complex additives. The carbonate absorption solution can be potassium carbonate as a preferred embodiment. It is also noted that the carbonate absorption solution can be based on magnesium carbonate or another element of the first and / or second groups of the periodic table of elements. In some implementations, the carbonate absorption solution used for CO2 capture from a flue gas can have a concentration of the carbonate ranging from 0.01 mol / liter to the maximum concentration avoiding the formation of bicarbonate precipitation, the bicarbonate ion generally being the least soluble of the carbonate-bicarbonate couples used for preparing acid gas absorption solutions. More specifically, in the case of CO2 capture from a post-combustion gas mixture, the maximum concentration of a potassium carbonate solution may be between 1.5 to 2.5 mol / liter, the maximum concentration being determined by the absorption temperature used in the absorption stage, and the temperature determining the maximum solubility that can be achieved at that temperature. It is also noted that the carbonate concentration can be above 0.05 mol / liter, 0. 1 mol / liter, 0.2 mol / liter, 0.5 mol / liter, 0.8 mol / liter, or 1.0 mol / liter, and can be below 3.0 mol / liter, 2.5 mol / liter, 2.3 mol / liter, 2.0 mol / liter, or 1.8 mol / liter for acid gas capture applications. Regarding process temperature, it is noted that carbonate solution solubility increases with temperature and thus design could, in some implementations, aim to reach the highest concentration that is reasonably below the crystallization concentration at the coldest location in the process, which may be the bottom of the absorber. For example, the maximum solubility of K2CO3 at 20°C is about 8 mol / L and at 100°C 11 mol / L; these concentrations correspond to 16 and 22 mol / L respectively of equivalent KHCO3. The solubility of KHCO3 is only 2.2 mol / L at 20°C which means that the process is ideally controlled with respect to how much of the carbonate is converted during capture to avoid reaching that concentration. A similar approach could be taken when evaluating operating conditions for other carbonate solutions.

[0020] The acid surfaces can have various physical and chemical properties, and can be implemented in various ways, some of which will be described herein. In some implementations, the acid surfaces are attached to non-soluble supports that are present in the desorption stage. The acid surfaces can be present in one or more units that are used for desorption, including a main stripper or secondary desorption units before or after a main stripper, for example. The acid surfaces can include acidic species that are covalently bonded, entrapped, immobilized, or otherwise connected to or supported by the non-soluble supports. The non-soluble supports can thus have various properties and designs depending on the nature of the acid surfaces as well as the operating conditions of desorption. The acidic surfaces can be provided in soft, rough, porous or any intermediate form and where the contact between the loaded absorption solution and the acid surface is at favourable conditions for mimicking the acidic conditions in the loaded absorption solution and to facilitate the CO2 release in its gaseous form. The supports can be composed of various materials and can have various properties, such that the supports enable securing the acid surfaces (e.g., metal, graphite, ceramic, polymeric, and so on). In some implementations, the acid surfaces are provided within a desorption chamber that is operated under desorption conditions including temperature and pressure without additional intervention. It is noted that the non-soluble supports can have low or zero solubility in the carbonate solution of the process implementation, where the non-solubility enables the acid surfaces to be supported for the desorption process while not necessarily being permanently fully insoluble.

[0021] In another implementation, the acidic surfaces can be enhanced by means of electrochemical reactions, where electricity can be supplied to the desorption equipment (e.g., certain equipment internals, the acid surfaces themselves or any combination thereof) such that the performance of the acidic surfaces is improved, maintained, or regenerated using electrically supported reactions or surfaces. One example approach to using electricity for generating protons could be to use a water electrolyser, such as the ones used for producing hydrogen. The electrolyser can be of various types found on the market such as, for example, an alkaline electrolyser, a solid-oxide electrolyser, or a proton-exchange electrolyser (PEM). The electrolyser could also be provided with adapted configurations for this particular process in order to improve the performance or the Faradic efficiency of such implementations. A salt splitter unit could also be used. The electricity-enabled unit (salt splitter or electrolyser) could be used as the desorption unit, e.g., as unit 22, 102 or 200 in Figs 2, 3 and 4 respectively.

[0022] It is noted that the acid surfaces can have various chemical and structural properties and can be implemented using various materials. A notable property of the acid surfaces is that it offers an acidic surface to the solution put in contact with it. In such a configuration, the ions present in the solution can access the acidic conditions of the acid surfaces and either diffuse to / from it or be entrained by the bulk liquid. The ions can also temporarily bond with the acid surfaces. The acid surfaces are provided and act as an acid in the carbonate solution at the process conditions of the desorption stage.

[0023] In some implementations, the acid surfaces can include proton donor (Bronsted acid) surfaces, electron acceptor (Lewis acid) surfaces, and any combination thereof. Any suitable acid surface (of the Bronsted or Lewis type) may be used herein. For example, the acid surface may be a proton-donating surface, or an electron- acceptor surface. Preferred surfaces are proton-donators as they offer the immediate protons donors desired to acidify the surrounding solution. Examples of acid surfaces include, but are not limited to, FeC., SbFs and AICIs supported on graphite or another support material, ALO, SiO, zeolites in general and clays (e.g., AICI / AI2O, ZnCh / acid treated clays, FeCI / graphite, SbFs / graphite, AlCI / graphite, vanadium phosphates and aluminophosphates, CaO, ZrC>2; SimO ZrO, YbO ZrO, aluminum chlorofluoride, ACF. (AICIF, Xs().O5 0.25), aluminum bromofluoride, ABF. (AIBrF, X-0.05 0.25)); heteropoly acids (HPAs) such as HPWO and HPMo.O.; silica-supported Nation (SAC-13); alumina, amorphous silica-alumina, amorphous silica-alumina molecular sieves such as microporous aluminosilicates or Zeolites (e.g. HZSM-5, H. Y. H X) and mesoporous aluminosilicates such as M41S (e.g. MCM-41. SBA-15, MCF); silica-magnesia, Silica-Zirconia, alumina-boria, titania-boria, tungstate-alumina, and tungstate Zirconia; AlCI / mesoporous silica, CrO / ZrO., Sulfated Zirconia, pillared clays (PILC) and acidic porous clay heterostructures (PCH). Any suitable Bronsted acid surface may be used herein. For example, amorphous silica-alumina molecular sieves such as microporous aluminosilicates or Zeolites (e.g. HZSM-5, H. Y. H X) and mesoporous aluminosilicates such as M41S (e.g. MCM-41 , SBA-15, MCF); heteropoly acids (HPAs) such as HPWO and HPMo.O.; silica supported Nation (SAC-13), and combinations thereof.

[0024] Any suitable mix of Bronsted acid surface and Lewis acid surface may be used herein. For example, alumina, amorphous silica-alumina, amorphous silica-alumina molecular sieves, silica-magnesia, silica-Zirconia, alumina-boria, titania-boria, tungstate-alumina, and tungstate Zirconia; AlCI / mesoporous silica, CrO / ZrO., sulfated zirconia, pillared clays (PILC) and acidic porous clay heterostructures (PCH).

[0025] The acid surfaces are chemically active by mimicking the acidic conditions where the speciation in the carbonate absorption solution favours the acid gas in its gaseous form and not in its ionic (and soluble) form, the latter being typically the bicarbonate form that is the most soluble in the carbonate-bicarbonate system. More specifically, for CO2 as the acid gas, the active surface is an acid surface having a pH lower than 6 (pH < 6) that tends to facilitate and promote the formation of gaseous CO2 (CO2 (g>) as opposed to the bicarbonate (HCCh') form or the soluble form of CO2 (COs2-)- Fig 5 presents the three states CO2 can take in a carbonate solution as a function of pH of the solution. More specifically, Fig 5 shows the chemical speciation found in a carbonate solution generated after CO2 addition and where CO2 is mostly under its gaseous form for pH below 6 while the bicarbonate (HCO3-) and the soluble CO2 (COs2-) are found in very low concentrations in that pH range.

[0026] The acid surfaces are provided on supports that have non-soluble properties in the carbonate absorption solution. In particular, in some implementations the supports can be substantially or completely non-soluble, but alternatively the supports could be partially soluble as long as enhanced activity is enabled. The supports can be sized and configured for deployment in the desorption equipment that is used for the process. For example, the supports can be packing material used in a packed column or the supports can be formed as a coating around a core that can itself be a packing material.

[0027] Various equipment and system arrangements can be used in the context of the present technology. The equipment and system arrangement can depend on process design and other factors. In some implementations, the desorption is performed in a stripping vessel which may be a packed column and the acid surfaces are deployed in the packed column and / or in a desorption unit located upstream or downstream of the packed column. The desorption can be performed using a rotating packed bed (RPB) or other enhanced equipment. The equipment type used for contacting the carbonate absorption solution with the acidic surface can be that generally found in the gas contacting industry at large and not limited to the acid gas treating industry. For example, the stripper can be a packed tower with internals promoting mass transfer between the gas and the liquid. The packing of the tower can be structured or random and the packing may support the acid surface in various ways. The acid surface may also be put in contact with the carbonate absorption solution by other means and / or equipment, inside or not of the stripper vessel. The stripper can also involve moving internals as sometimes encountered with rotating beds. The fixed or moving internals of the stripper do not negatively influence the performance of the acid surface. Operating conditions can vary depending on process design, although one advantage of the present technology is that lower energy input can be provided in the desorption stage compared to conventional carbonate based capture operations. For example, the temperature range used for optimal contacting of the acid surface and the carbonate absorption solution can be that normally found in acid gas capture processes involving absorption and stripping, i.e., between 20°C and 120°C. It is noted that desorption temperatures can be provided in part based on the operating pressures as well. The desorption temperature can be between 30°C and 80°C or between 40°C. In some implementations, the temperature could be around 70°C (plus or minus 1 , 2, 3, 4 or 5°C, for example) for potassium carbonate based solutions, as the bicarbonate decomposes into CO2 and K2CO3 around that temperature, although the temperature could be lower given the impact of the acid surfaces on the process. The acid surfaces themselves can also be heated and maintained at a different temperature than that of the carbonate absorption solution fed to the stripper. For example, the acid surfaces can be maintained at any temperature between 20°C and 120°C, the surface temperature being different or equal to the carbonate absorption solution temperature fed to the equipment containing the acid surface. The means for maintaining such a temperature difference between the acid surfaces and the rich carbonate absorption solution can be one or more of those found in the gas capture or processing industry, e.g., heat transfer fluids, electrical heating, internal and external heat transfer devices, etc. For example, the supports could be hollow defining channels through which a heat transfer fluid is flowed to provide higher temperature to the acid surfaces compared to the solution fed into the desorption unit. For example, the temperature difference could be at least 3°C, 5°C, 7°C or 10°C to provide a desired heat flux, and it is noted that notably higher AT could be provided.

[0028] The energy supplied to the stripper and / or the vessel with the acidic surfaces can be supplied under many forms. The supplied heat is shown on Figs 2, 3, and 4 and is indicated by an input marked “Q”. There are various methods and equipment that can be used to provide the heat depending on the system and process design. For example, a reboiler could be used in conjunction with the stripper. In some implementations, a stream of regenerated solution is circulated through a heat exchanger in which the second side is circulating a heat transfer fluid at a temperature above the temperature of the capture solution. Heat is hence transferred to the capture solution and brought back in the stripper and / or the vessel containing the acidic surface. Other configurations can achieve the same goal. For example, the heat savings that can be achieved in example processes described herein can be at least 20%, 30%, 40%, 50%, 60%, 70% or 75% versus base cases without acid surfaces.

[0029] In the case of CCh-rich carbonate solution formed from an element of the first group in the periodic table of elements, the contact time between the rich capture solution and the acid surfaces can be varied to maximize or optimize the acid gas release and can range from one second to many minutes, preferably from 5 seconds to one minute, and even more favourably from 10 to 30 seconds. The carbonate solutions formed from other elements than that of the first group can be processed or treated with similar conditions.

[0030] The absolute pressure of the contacting conditions between the rich capture solution and the acid surface can range from 0.1 atm (approximately 10 000 Pa) to 2 atm (approximately 200 000 Pa). These pressure conditions would generally be found in the stripper of the process implemented to capture the acid gas. More specifically, in the case of post-combustion CO2 capture involving a potassium carbonate solution as the capture solution, the pressure during the acid surface and the rich capture solution could range between 0.2 to 1 atm (20 000 Pa to 100 000 Pa).

[0031] It is noted that the overall capture system can be implemented with a temperature swing between absorption and desorption, where the desorption stage is operated at a higher temperature to encourage CO2 release which is further aided by the acid surfaces. The temperature swing could be from 10 to 100°C, 20 to 80°C, or 30 to 70°C, for example.

[0032] There are various potential advantages facilitated by the acid surfaces in a carbonate solution, such as reduced equipment size, reduced heat input requirements in desorption, and obtaining a leaner regenerated solution which can enhance absorption.

[0033] In the technology described herein, the gas capture process configuration can be as simple as including only an absorber and a stripper in fluid communication, the stripper containing the acid surfaces providing accelerated stripping of the acid gas (e.g., CO2) from the rich capture solution. This example configuration is illustrated in Fig 2. The overall process could be made more efficient by separating the primary stripper from the desorption vessel containing the acid surfaces and such a configuration is illustrated in Figs 3 and 4. In the first case (Fig 3), a stripper 100 is used first and the acid surfaces are contacted with the stripped capture solution 101 only after primary stripping, either partial or complete, of the capture solution and in the conditions already described above. In this configuration, the desorption vessel with acid surfaces 102 can be viewed as a polishing unit that removes residual acid gas present in the stripper output liquid stream 101. The stripper produces a stripper gas 104 and the acid surfaces enhanced desorption vessel 102 produces a regenerated solution 106 recycled back into the absorber 12. In addition, a recycle stream 108 from the desorption vessel 102 can be recycled back into the stripper 100, while another stream 110 can be output as well. The recycle stream 108 can be recycled gas or recycled liquid (e.g., regenerated solution). In this configuration of Fig 3, the main stripper 100 is provided as a first desorption unit and the acid surfaces enhanced desorption vessel 102 is provided as a second desorption unit to make up the overall desorption stage of the gas capture system. It is noted that other configurations are possible with more than two desorption units arranged in series where at least one has acid surfaces.

[0034] In a second case illustrated in Fig 4, the loaded capture solution 20 is first contacted with the acid surfaces under the conditions already described above and only after is the capture solution sent to the stripper for partial or complete stripping. In this scenario, the loaded solution 20 is first supplied to an acid surfaces enabled desorption vessel 200 which produces a gas stream 202 and a partially depleted solution 204. The partially depleted solution 204 is then supplied to a secondary stripper 206 that can be a standard stripper unit that is not enhanced by acid surfaces. The secondary stripper 206 produces a regenerated solution 208 for recycling back to the absorber 12 and a stripper gas stream 210. The secondary stripper 206 can also produce a recycle stream 212 that is sent back into the acid surfaces enabled desorption vessel 200. The recycle stream 212 can be recycled gas or recycled liquid (e.g., regenerated solution). In this configuration, the desorption vessel with acid surfaces can be viewed as a pretreatment unit that removes acid gas prior to the main stripper.

[0035] These two example process configurations, shown in Figs 3 and 4, are for illustrative purposes only and do not limit the applicability of the technology to other configurations. For instance, it should be noted that one or more pretreatment desorption units equipped with acid surfaces and / or one or more post-stripper desorption units equipped with acid surfaces can be implemented and also the main stripper can also have acid surfaces therein or not. EXAMPLES & EXPERIMENTATION

[0036] Tests were performed to assess certain performance characteristics of acid surfaces in CO2 desorption in carbonate solutions and results are summarized in Fig 5. In the tests presented herein, comparative experiments were performed to assess desorption using acid surface additives compared to no additive. In particular, the tests were conducted in batch mode and the operating conditions included 63°C, unless otherwise indicated in Fig 5 where the impact of 20°C and 40°C is shown, a potassium bicarbonate solution concentration at 1 ,5 M which corresponds to 100% loading of a potassium carbonate solution at 0.75. In the tests, a 20 ml quantity of loaded solution was contacted with 2 g of particles or acidic powder having acid surfaces for 0, 15, 30, 45, 60 and 120 minutes, under agitation, and then the quantity of released CO2 was measured by titration of the CO2 depleted solution with HCI. The acid surface particles that were assessed here were ZSM5-pellets, Amberlyst 15, and ZSM5-powder. The graph of Fig 5 shown that for equivalent desorption times, the acid surfaces facilitate approximately twice the CO2 release. ZSM5 is an aluminosilicate zeolite belonging to the pentasil family of zeolites with a general formula of NanAlnSi96-nOi92- 16H2O (0<n<27). Amberlyst 15 is an acidic sulfonic acid macropolymeric resin. It is notably shown that the acid surfaces promote rapid and high desorption of CO2 at lower temperatures and thus lower energy input requirements for carbonate based CO2 loaded system.

Claims

CLAIMS1 . A process for desorption of an acid gas from an acid gas loaded carbonate solution generated by absorption of the acid gas from an acid gas containing stream into an absorption solution based on carbonates formed with an element of the first and second groups of the periodic table of elements, the process comprising: contacting the acid gas loaded carbonate solution with desorption enhancement structures that comprise a non-soluble supports and acid surfaces supported by the non-soluble supports at desorption conditions such that the acid surfaces cause a shift in equilibrium to promote release of the acid gas from the gas loaded carbonate solution; and producing an acid gas depleted solution and an acid gas stream.

2. The process of claim 1 , wherein the acid gas comprises CO2.

3. The process of claim 1 or 2, wherein the carbonates comprise potassium carbonate.

4. The process of any one of claims 1 to 3, wherein the acid gas containing stream comprises flue gas.

5. The process of any one of claims 1 to 3, wherein the acid gas containing stream comprises an industrial gas stream.

6. The process of any one of claims 1 to 5, wherein the absorption solution has a concentration between7. The process of any one of claims 1 to 6, wherein the acid surfaces comprises a protondonating surface.

8. The process of claim 7, wherein the acid surfaces comprise one or more of the following: FeC., SbFs and AICIs Supported on graphite, AI2O, SiO, Zeolites, & clays (e.g. AICI / AI2O, ZnCh / Acid treated clays, FeCI / graphite, SbFs / graphite, AlCI / graphite, Vanadium phosphates and aluminophosphates, CaO ZrC>2; SimO ZrO, YbO ZrO, aluminum chlorofluoride, ACF. (AICIF, Xs().O5 0.25), aluminum bromofluoride, ABF. (AIBrF, X-0.05 0.25)); heteropoly acids (HPAs) such as HPWO and HPMo.O.; silica- supported Nation (SAC-13); alumina, amorphous silica-alumina, amorphous silica- alumina molecular sieves such as microporous aluminosilicates or Zeolites (e.g. HZSM-5, H. Y. H X) and mesoporous aluminosilicates such as M41S (e.g. MCM-41.SBA-15, MCF); silica-magnesia, Silica-Zirconia, alumina-boria, titania-boria, tungstate-alumina, and tungstate Zirconia; AlCI / mesoporous silica, CrO / ZrO., Sulfated Zirconia, pillared clays (PILC) and acidic porous clay heterostructures (PCH). Any suitable Bronsted acid surface may be used herein. For example, amorphous silica- alumina molecular sieves such as microporous aluminosilicates or Zeolites (e.g. HZSM-5, H. Y. H X) and mesoporous aluminosilicates such as M41S (e.g. MCM-41 , SBA-15, MCF); heteropoly acids (HPAs) such as HPWO and HPMo.O.; silica supported Nation (SAC-13), and combinations thereof.

9. The process of any one of claims 1 to 8, wherein the acid surfaces comprise an electron-acceptor surface.

10. The process of claim 9, wherein the electron-acceptor surface comprises one or more of the following: FeCI., SbF and AICIs Supported on graphite, AI2O, SiO, Zeolites, & clays (e.g. AICI / AI2O, ZnCI2 / Acid treated clays, FeCI / graphite, SbF5 / graphite, AlCI / graphite, Vanadium phosphates and aluminophosphates, CaO ZrO. SmO-ZrO: YbO, ZrO, aluminum chlorofluoride, ACF. (AICIF, Xs(0.05-0.25), aluminum bromofluoride, ABF (AIBr, F. X-0.05-0.25), and combinations thereof.

11. The process of any one of claims 1 to 8, wherein the acid surfaces comprise a combination of electron-acceptor surface and proton-donor surface.

12. The process of claim 11 , wherein the acid surfaces comprise alumina, amorphous silica-alumina, amorphous silica-alumina molecular sieves, silica-magnesia, silica- Zirconia, alumina-boria, titania-boria, tungstate-alumina, and tungstate Zirconia; AlCI / mesoporous silica, CrO / ZrO., sulfated zirconia, pillared clays (PILC) and acidic porous clay heterostructures (PCH).

13. The process of any one of claims 1 to 12, wherein the non-soluble supports comprise graphite, polymer material, metal material, ceramic material, or a combination thereof.

14. The process of any one of claims 1 to 13, wherein the contacting of the acid gas loaded carbonate solution with the acids surfaces is performed at a temperature between 20°C and 120°C.

15. The process of any one of claims 1 to 14, wherein the contacting of the acid gas loaded carbonate solution with the acids surfaces is performed at a pressure between 20 000 Pa and 100 000 Pa.

16. The process of any one of claims 1 to 15, wherein the concentration of the carbonates in the absorption solution is 0.5 to 2.5 mol / liter.

17. The process of any one of claims 1 to 16, wherein the contacting of the acid gas loaded carbonate solution with the acids surfaces is performed in a stripping unit that receives the acid gas loaded carbonate solution directly from an absorption unit.

18. The process of any one of claims 1 to 16, wherein the contacting of the acid gas loaded carbonate solution with the acids surfaces is performed in a pretreatment desorption unit that receives the acid gas loaded carbonate solution directly from an absorption unit and produces a pretreated solution that is supplied to a stripping unit for further removal of the acid gas.

19. The process of any one of claims 1 to 16, wherein the acid gas loaded carbonate solution is supplied to a stripping unit to produce a partially stripped solution that is then supplied to a desorption unit for further removal of the acid gas to produce the acid gas depleted solution.

20. The process of any one of claims 1 to 19, wherein the non-soluble support and the acid surfaces are composed of the same material.

21. The process of any one of claims 1 to 19, wherein the desorption enhancement structures are provided in powder form.

22. The process of any one of claims 1 to 19, wherein the desorption enhancement structures are provided in particle form free in solution, optionally sized and having physical properties for separation from the solution optionally using one or more separation mechanisms including gravity, density, size, and magnetic properties.

23. The process of any one of claims 1 to 22, wherein the desorption enhancement structures form a packing material over which the acid gas loaded carbonate solution flows.

24. The process of any one of claims 1 to 22, wherein the desorption enhancement structures are free in solution within the acid gas loaded carbonate solution.

25. The process of any one of claims 1 to 24, wherein the desorption enhancement structures are provided to reduce heat requirements of the desorption by at least 20%, 30%, 40%, 50%, 60%, 70% or 75% versus a base case without acid surfaces.

26. The process of any one of claims 1 to 25, wherein the contacting of the acid gas loaded carbonate solution with the acid surfaces is performed in a pretreatment desorption unit and the acid gas depleted solution is withdrawn and supplied to a stripper unit to produce a regenerated solution for recycling back as at least part of the absorption solution for further absorption of the acid gas.

27. The process of any one of claims 1 to 25, wherein the contacting of the acid gas loaded carbonate solution with the acid surfaces is performed in a polishing desorption unit that is downstream of a primary stripper unit, and the acid gas depleted solution from the polishing desorption unit is recycled back as at least part of the absorption solution for further absorption of the acid gas.

28. The process of any one of claims 1 to 27, wherein the contacting of the acid gas loaded carbonate solution with the acid surfaces is performed in a packed column.

29. A system for desorption of an acid gas from an acid gas loaded carbonate solution generated by absorption of the acid gas from an acid gas containing stream into an absorption solution based on carbonates formed with an element of the first and second groups of the periodic table of elements, the system comprising: a desorption vessel comprising: a liquid inlet configured to receive the acid gas loaded carbonate solution; a desorption chamber in fluid communication with the liquid inlet and configured to receive the acid gas loaded carbonate solution therefrom; a liquid outlet in fluid communication with the desorption chamber and configured to withdraw an acid gas depleted solution; anda gas outlet in fluid communication with the desorption chamber and configured to withdraw an acid gas stream; and desorption enhancement structures provided in the desorption chamber, the desorption enhancement structures comprising a non-soluble supports and acid surfaces supported by the non-soluble supports at desorption conditions such that the acid surfaces cause a shift in equilibrium to promote release of the acid gas from the gas loaded carbonate solution.

30. The system of claim 29, comprising one or more features as recited in any one of claims 1 to 28.

31. Use of acid surfaces for accelerating desorption of an acid gas from an acid gas loaded carbonate solution generated by absorption of the acid gas from an acid gas containing stream into an absorption solution based on carbonates formed with an element of the first and second groups of the periodic table of elements.

32. The use of claim 31 , comprising one or more features as recited in any one of claims 1 to 30.

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