Method and apparatus for low-temperature regeneration of acid gas absorbing composition using catalyst

Abstract

A method for regenerating carbon dioxide and hydrogen sulfide from acid gases using a catalyst containing a Group 2 element is provided. This method reduces the energy required for the regeneration process, enabling an efficient and cost-effective method for regenerating acid gases.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Patent Application No. 17 / 933,727, filed September 20, 2022, the entire contents of which are incorporated herein by reference.

[0002] This document relates to a method for catalytically recovering carbon dioxide (CO2) and hydrogen sulfide (H2S) from acid gases. This document also relates to an efficient and cost-effective method for recovering CO2 and H2S from aqueous absorption solutions. [Background technology]

[0003] The capture of carbon dioxide (CO2) and hydrogen sulfide (H2S) from acid gases has become a key focus in the oil and gas industry due to climate change concerns and policies. CO2 and H2S capture from natural gas typically involves the use of amine processes or potassium carbonate, which are energy-intensive. This is primarily due to high regeneration temperatures, the temperature threshold at which acid gases are released from the acid-gas-rich aqueous absorbent solution, and steam stripping. While amine-based methods with lower regeneration temperatures of approximately 120°C (393 K) have been developed, these methods still require large amounts of energy.

[0004] Therefore, there is a need for a method that allows for the efficient and cost-effective recovery of CO2 and H2S from acid gases, as well as a method that reduces the energy required for the acid gas absorbent regeneration process. Summary of the Invention

[0005] Provided in the present disclosure is a method for removing carbon dioxide (CO) from an air or gas stream, the method comprising contacting the air or gas stream containing CO with an aqueous composition containing an aqueous carbonate (or amine) solution and a regenerated catalyst under conditions to form an aqueous bicarbonate composition; separating the CO-containing gas stream from the aqueous bicarbonate composition; heating the aqueous bicarbonate composition to from about 45° C. to less than about 100° C. to obtain the aqueous carbonate composition; and recovering the CO-containing gas stream, wherein the regenerated catalyst contains an element from Group 2 of the periodic table.

[0006] In some embodiments of the method, the regenerated catalyst contains magnesium or calcium. In some embodiments, the regenerated catalyst is magnesium carbonate. In some embodiments, the concentration of the regenerated catalyst in the aqueous composition is from about 0.01 mg / L to about 400 mg / L.

[0007] In some embodiments of the method, the heat source is a recovered or renewable heat source, hi some embodiments, the heat source is selected from low pressure steam recovered from other processes, hot water recovered from other processes, or the sun.

[0008] In some embodiments, the method further comprises recycling the aqueous carbonate composition after separating the CO2-containing gas stream from the aqueous bicarbonate composition.

[0009] In some embodiments, the method further comprises cooling the aqueous carbonate composition prior to recycling the aqueous carbonate composition and after separating the CO2-containing gas stream from the aqueous bicarbonate composition. In some embodiments, the cooling source is ambient air or the sea or ocean.

[0010] In some embodiments of the method, the air or gas stream is an acid gas.

[0011] Also provided in the present disclosure is a method for removing hydrogen sulfide (HS) from a gas stream, the method comprising: contacting the gas stream containing HS with an aqueous composition containing an aqueous carbonate (or amine) solution and a regenerated catalyst under conditions to form an aqueous hydrosulfide composition; separating the gas stream containing HS from the aqueous hydrosulfide composition; heating the aqueous hydrosulfide composition to about 60°C to less than about 100°C to obtain an aqueous hydroxide composition; and recovering the gas stream containing HS, wherein the regenerated catalyst contains an element from Group 2 of the periodic table.

[0012] In some embodiments of the method, the regenerated catalyst contains magnesium or calcium. In some embodiments, the regenerated catalyst is magnesium hydroxide. In some embodiments, the concentration of the regenerated catalyst in the aqueous composition is from about 0.01 mg / L to about 400 mg / L.

[0013] In some embodiments of the method, the heat source is a recovered or renewable heat source, hi some embodiments, the heat source is selected from low pressure steam recovered from other processes, hot water recovered from other processes, or the sun.

[0014] In some embodiments, the method further comprises recycling the aqueous hydroxide composition after separating the H2S-containing gas stream from the aqueous hydrosulfide composition.

[0015] In some embodiments, the method further comprises cooling the aqueous hydroxide composition prior to recycling the aqueous hydroxide composition and after separating the H2S-containing gas stream from the aqueous hydrosulfide composition. In some embodiments, the cooling source is ambient air or the sea or ocean.

[0016] In some embodiments of the method, the air or gas stream is an acid gas, hi some embodiments, the air or gas stream is a sour gas.

[0017] Also provided in this disclosure is a method for treating acid gases, the method comprising contacting an acid gas stream with an aqueous composition containing an aqueous carbonate (or amine) solution and a regenerated catalyst to form a combined gas-liquid composition; heating the gas-liquid composition to from about 60° C. to less than about 100° C. to separate a gas stream containing CO, HS, or both from the gas-liquid composition; and recovering the gas stream containing CO, HS, or both, wherein the regenerated catalyst contains a Group 2 element of the periodic table.

[0018] In some embodiments of the method, the regenerated catalyst contains magnesium. In some embodiments, the regenerated catalyst is magnesium carbonate or magnesium hydroxide. In some embodiments, the concentration of the regenerated catalyst in the aqueous composition is from about 0.01 mg / L to about 400 mg / L. [Brief explanation of the drawings]

[0019] [Figure 1A] FIG. 1A shows the reactions involved in the acid gas regeneration process, illustrating the catalytic decarbonation step. [Figure 1B] FIG. 1B shows the reactions involved in the acid gas regeneration process, showing the catalytic dehydrosulfidation step. [Figure 2] FIG. 2 illustrates an exemplary energy-efficient carbon dioxide capture process. [Figure 3] FIG. 3 illustrates an exemplary energy-efficient acid gas treatment process. [Figure 4] FIG. 4 illustrates an exemplary energy-efficient direct carbon dioxide capture process. [Figure 5] FIG. 5 is a graph showing exemplary catalytic and uncatalyzed decarboxylation at 55° C. DETAILED DESCRIPTION OF THE INVENTION

[0020] The present disclosure provides a method for regenerating CO2 and / or HS from acid gas using a catalyst containing a Group 2 element (alkaline earth metal) of the periodic table. Also provided is a method for regenerating an acid gas absorbent using a catalyst containing a Group 2 element (alkaline earth metal) of the periodic table. The disclosed method is efficient and cost-effective. In some embodiments, the method reduces the energy required for the acid gas absorbent regeneration process compared to known methods that do not use such a catalyst. In some embodiments, the method reduces the energy required for the acid gas (CO2 and / or HS) regeneration process compared to known methods that do not use such a catalyst. In the disclosed method, the use of a catalyst allows acid gas to be separated and regenerated at a lower temperature than the same process without a catalyst. Thus, the present disclosure provides a method for regenerating acid gas at a low temperature, for example, below about 120°C. In some embodiments, the acid gas is regenerated at a temperature of about 45°C to less than about 100°C, for example, about 45°C to about 65°C, for example, about 50°C to about 55°C, or about 60°C to about 65°C. In some embodiments, the reclaimed acid gas is free of residual amines. In some embodiments, the reclaimed acid gas is used for enhanced oil recovery (EOR) or to enrich the atmosphere of agricultural and / or aquaculture plants or greenhouses. In some embodiments, the reclaimed acid gas is CO. In some embodiments, the reclaimed acid gas is H. The disclosed methods also provide a simple and selective method for direct air carbon capture (DACC) that does not involve the use of hazardous materials or chemicals, such as amines.

[0021] The disclosed method provides a simple, efficient, and cost-effective method for regenerating acid gases, carbon dioxide (CO2), and hydrogen sulfide (HS), from metal carbonates and / or amine solutions from an amine process or a carbonate process. In some embodiments, the method is used in conjunction with an amine process. In some embodiments, the method is used in conjunction with a carbonate process. In some embodiments, the carbonate process is an "accelerated" carbonate process, in which an accelerator is used to increase the dynamics of the carbonate process. In some embodiments, the accelerator accelerates carboxylation. The accelerator may be an organic compound, an inorganic compound, or an enzymatic compound that accelerates carboxylation. Suitable accelerators include, but are not limited to, organic compounds such as amines and amino acids, inorganic compounds such as vanadates, borates, and arsenates, or enzymatic compounds such as carbonic anhydrase and mimicking metalloenzyme compounds. In some embodiments, the metal carbonate and / or amine solution is a potassium carbonate solution. In some embodiments, the metal carbonate and / or amine solution is a methyldiethanolamine (MDEA) solution. The disclosed acid gas regeneration method uses a catalyst containing a Group 2 element of the periodic table. In some embodiments, the catalyst contains magnesium or calcium. In some embodiments, the catalyst contains magnesium. In some embodiments, the catalyst is magnesium carbonate. In the disclosed method, a carbonate catalyst, such as magnesium carbonate, is carboxylated to form a bicarbonate, such as magnesium bicarbonate. Magnesium bicarbonate (Mg(HCO3)2) decarboxylates at relatively low temperatures (about 45°C to about 55°C, i.e., about 318K to about 328K) to produce magnesium carbonate and CO2, while other bicarbonates, such as sodium bicarbonate and potassium bicarbonate, decarboxylate at much higher temperatures (above 120°C or above 393K). In some embodiments, the catalyst is magnesium hydroxide. In the disclosed method, a hydroxide catalyst, such as magnesium hydroxide, is hydrosulfidated to form a hydrosulfide, such as magnesium hydrosulfide.Magnesium hydrosulfide (Mg(SH)2) dehydrosulfidates with water to produce magnesium hydroxide and H2S at relatively low temperatures (about 60°C to about 65°C, or about 333K to about 338K). This low regeneration temperature means that renewable or recovered heat can be used to separate H2S and CO2 gas from the aqueous solution, requiring less energy than the same process without such a catalyst.

[0022] Conventional CO2 capture methods (such as the amine process or the use of potassium carbonate) require high regeneration temperatures. The disclosed method utilizes a regenerated catalyst containing a Group 2 element of the periodic table to separate acid gases at temperatures lower than those required by such conventional methods. In some embodiments, temperatures as low as about 45°C to about 65°C are used.

[0023] The disclosed method is an improved process for regenerating and recovering carbon dioxide and hydrogen sulfide from natural gas, e.g., natural acid gas. In some embodiments, the disclosed method improves upon the amine process by using less energy. The disclosed method employs a bicarbonate / carbonate cycle to overcome the high energy penalty of the regeneration step and prevent scaling due to hardness. The catalytic reaction for the regeneration step is shown in Figures 1A-1B.

[0024] 1A illustrates the catalytic decarboxylation step of the disclosed method. In some embodiments, the method comprises adding two equivalents of absorbent M M HCO3 with the catalyst M D CO3 and M M 2CO3, CO2, and H2O. FIG. 1B illustrates the catalytic dehydrosulfurization step of the disclosed method. In some embodiments, the method comprises: M The catalyst of the present disclosure, M D CO3 or M D (OH)2, and 1 equivalent of M M This involves obtaining OH and H2S.

[0025] In some embodiments, M M is an alkali metal from Group 1 of the periodic table (alkali metals). In some embodiments, M M is selected from potassium and sodium. In some embodiments, M M is potassium. In some embodiments, M M is sodium. In some embodiments, M M is in the ammonium salt form (RNH + In some embodiments, M M is an amine that reacts with carbon dioxide to produce primarily ammonium bicarbonate salts. In some embodiments, the amine is a nitrogen-containing heteroaromatic amine. Examples of suitable nitrogen-containing heteroaromatic amines include those disclosed in U.S. Pat. No. 11,123,684. In some embodiments, the amine is a hindered amine. Examples of suitable hindered amines include those disclosed in U.S. Pat. No. 9,707,512. The bicarbonate salts of such absorbents decarbonate at high temperatures (e.g., above about 100° C. (373 K)), but have high loading capacities due to the high solubility of the bicarbonate species.

[0026] In some embodiments, M D is an alkaline earth metal of Group 2 (alkaline earth metals) of the periodic table. In some embodiments, M D is selected from magnesium and calcium. In some embodiments, M D is magnesium. In some embodiments, M D The bicarbonates of these metals decarbonate at low temperatures (e.g., about 45°C to about 55°C, or about 313K to about 328K), but the carbonates and bicarbonates of these cations have relatively low solubility, which can lead to the formation of carbonate scale on piping. However, the inventors of the present disclosure have surprisingly found that the bicarbonates of metal M D We found that these drawbacks could be overcome by introducing a cation exchange reaction using M as a regenerating catalyst. DCations, such as Mg and Ca cations, cannot be used as absorbents because they readily form scale. However, without wishing to be bound by any particular theory, it is believed that these cations can be used as decarboxylation catalysts because cation exchange reactions are possible. Furthermore, the cations can be used at mass concentrations much lower than their solubility values ​​(catalyst amounts of about 10 ppm or less).

[0027] In the method of the present disclosure, the regenerated catalyst is present in an absorbent solution containing a carbonate or an amine. In some embodiments, the absorbent solution is an aqueous solution. In some embodiments, the concentration of the regenerated catalyst in the absorbent solution is from about 0.01 mg / L to about 400 mg / L, e.g., from about 0.01 mg / L to about 350 mg / L, from about 0.01 mg / L to about 300 mg / L, from about 0.01 mg / L to about 250 mg / L, from about 0.01 mg / L to about 200 mg / L, from about 0.01 mg / L to about 150 mg / L, from about 0.01 mg / L to about 100 mg / L, from about 0.01 mg / L to about 50 mg / L, from about 0.01 mg / L to about 25 mg / L, from about 0.01 mg / L to about 10 mg / L, or from about 0.01 mg / L to about 5 mg / L. / L, about 0.01 mg / L to about 1 mg / L, about 1 mg / L to about 400 mg / L, about 1 mg / L to about 350 mg / L, about 1 mg / L to about 300 mg / L, about 1 mg / L to about 250 mg / L, about 1 mg / L to about 200 mg / L, about 1 mg / L to about 150 mg / L, about 1mg / L to about 100mg / L, about 1mg / L to about 50mg / L, about 1mg / L to about 25mg / L, about 1mg / L to about 10mg / L, about 1mg / L to about 5mg / L, about 5mg / L to about 400mg / L, about 5mg / L to about 350mg / L, about 5mg / L to about 300 mg / L, about 5 mg / L to about 250 mg / L, about 5 mg / L to about 200 mg / L, about 5 mg / L to about 150 mg / L, about 5 mg / L to about 100 mg / L, about 5 mg / L to about 50 mg / L, about 5 mg / L to about 25 mg / L, about 5 mg / L to about 10 mg / L, about 10 mg / L ~ approx. 400 mg / L, approx. 10 mg / L ~ approx. 350 mg / L, approx. 10 mg / L ~ approx. 300 mg / L, approx. 10 mg / L ~ approx. 250 mg / L, approx. 10mg / L~about 50mg / L, about 10mg / L~about 25mg / L, about 25mg / L~about 400mg / L, about 25mg / L~about 350mg / L, about 25mg / L~about 300mg / L, about 25mg / L~about 250mg / L, about 25mg / L~about 200mg / L, about 25mg / L to about 150mg / L, about 25mg / L to about 100mg / L, about 25mg / L to about 50mg / L, about 50mg / L to about 400mg / L, about 50mg / L to about 350mg / L, about 50mg / L to about 300mg / L, about 50mg / L to about 250mg / L,About 50 mg / L to about 200 mg / L, about 50 mg / L to about 150 mg / L, about 50 mg / L to about 100 mg / L, about 100 mg / L to about 400 mg / L, about 100 mg / L to about 350 mg / L, about 100 mg / L to about 300 mg / L, about 100 mg / L to about 250 mg / L, about 100 mg / L to about 200 mg / L, about 100 mg / L to about 150 mg / L, about 150 mg / L to about 400 mg / L, about 150 mg / L to about 350 mg / L, about 150 mg / L to about 300 mg / L, about 150 mg / L to about 250 mg / L, about 150 mg / L to about 200 mg / L, about 200 mg / L to about 400 mg / L, about 200 mg / L to about 350 mg / L, about 200 mg / L to about 300 mg / L, about 200 mg / L to about 250 mg / L, about 250 mg / L to about 400 mg / L, about 250 mg / L to about 350 mg / L, about 250 mg / L to about 300 mg / L, about 300 mg / L to about 400 mg / L, about 300 mg / L to about 350 mg / L, about 350 mg / L to about 400 mg / L, or about 0.01 mg / L, about 0.05 mg / L, about 0.1 mg / L, about 0.5 mg / L, about 1 mg / L, about 5 mg / L, about 10 mg / L, about 25 mg / L, about 50 mg / L, about 100 mg / L, about 150 mg / L, about 200 mg / L, about 250 mg / L, about 300 mg / L, about 350 mg / L, or about 400 mg / L.

[0028] The reactions depicted in Figures 1A and 1B can be used in a method for CO2 capture and acid gas treatment. This method involves the use of a catalyst containing a Group 2 element of the periodic table. Accordingly, provided in the present disclosure is a method for capturing carbon dioxide (CO2). A description of the process (100) is shown in Figure 2. An air (or gas) stream (109) is passed through a filter (101) to remove solid particles (e.g., dust) suspended in the air (or gas) stream. This stream (109) is then injected into the bottom of a contactor (or absorber) (103). An aqueous carbonate (or amine) stream (117) containing a regenerated catalyst is passed countercurrently to the gas stream (109) through the contactor (103). The carbon dioxide-depleted air (or gas) stream exits the top of the contactor (103). Aqueous bicarbonate stream (110) exits the bottom of the contactor (103) and enters the economizer (104), which recovers some heat from the liquid stream (115). Hot bicarbonate and / or hydrosulfide stream (112) enters the bottom of the flash column (105). The aqueous solution at the bottom of the column is heated using a heat exchanger (106). The hot aqueous solution separates CO2 stream (113), which is recovered at the top of the flash column (105). Aqueous solution stream (114) is sent to the pump (107). Aqueous solution stream (115) exits the pump (107) and is sent to the economizer (104) and then to the cooler (108) via (116). Liquid stream (117) exiting the cooler is sent to the top of the contactor (103).

[0029] The air (or gas) stream (109) can be an air or gas stream containing carbon dioxide, hydrogen sulfide, or both. In some embodiments, the air or gas stream contains carbon dioxide. In some embodiments, the air or gas stream contains hydrogen sulfide. In some embodiments, the air or gas stream contains carbon dioxide and hydrogen sulfide. In some embodiments, the air or gas stream is natural gas. In some embodiments, the air or gas stream is an acid gas.

[0030] An aqueous carbonate (or amine) stream (117) containing regenerated catalyst is passed countercurrently to the gas stream (109) through the contactor (103). In some embodiments, the regenerated catalyst is a catalyst of the present disclosure. In some embodiments, the regenerated catalyst comprises a Group 2 element of the periodic table. In some embodiments, the regenerated catalyst comprises magnesium or calcium. In some embodiments, the regenerated catalyst is magnesium carbonate. In some embodiments, the concentration of the regenerated catalyst in the aqueous carbonate (or amine) stream is from about 0.01 mg / L to about 400 mg / L.

[0031] The aqueous solution entering the bottom of the flash column (105) is a bicarbonate and / or hydrosulfide stream (112). In some embodiments, the flash column is selected from a demister, a packed column, and a stirred vessel. The aqueous solution is heated using a heat exchanger (106). In some embodiments, the solution is heated to about 45°C to about 80°C, e.g., about 45°C, about 50°C, about 55°C, about 60°C, about 65°C, about 70°C, about 75°C, or about 80°C. In some embodiments, the aqueous stream (112) contains bicarbonate and the solution is heated to about 45°C or above. In some embodiments, the aqueous stream (112) contains hydrosulfide and the solution is heated to about 60°C or above. In some embodiments, the aqueous stream (112) contains bicarbonate and hydrosulfide and the solution is heated to about 60°C or above. In some embodiments, the heat source is low-temperature heat recovered from another process, such as low-pressure steam or hot water. In some embodiments, the low heat is renewable heat, such as heat from the sun. In some embodiments, the low heat is renewable heat, such as from the sun, such as in tropical climates.

[0032] The aqueous solution stream (115) exits the pump (107) and is sent to an economizer (104) and then to a chiller (108). In some embodiments, the chiller's cold source is ambient air. In some embodiments, the cold source is ambient air in a continental climate. In some embodiments, the cold source is a sea or ocean. In some embodiments, the cold source is a sea or ocean in a tropical climate.

[0033] The liquid stream (117) exiting the cooler is sent to the top of the contactor (103). In some embodiments, the contactor is a falling film column, a packed column, a bubble column, a spray tower, or a gas-liquid agitated vessel.

[0034] Also provided in this disclosure is a method for treating acid gases. The method involves the use of a catalyst containing a Group 2 element of the periodic table. A description of the process (200) is shown in Figure 3. An acid gas stream (208) is injected into the lower part of a contactor (or absorber) (201). An aqueous absorption liquid stream, free of a regenerated catalyst (219), is passed countercurrently to the gas stream (208) through the contactor (201). At the upper part of the contactor, a sweet gas stream (210) exits the contactor (201). An aqueous bicarbonate and hydrosulfide solution stream (209) exits the lower part of the contactor (201) and enters an economizer (202) to recover some heat from the liquid stream (216). The hot bicarbonate and hydrosulfide stream (211) mixes with a smaller, cooled stream (212) loaded with regenerated catalyst before entering the bottom of the flash column (203) via (213). The aqueous solution at the bottom of the column is heated using a heat exchanger (204). The hot aqueous solution separates into an acid gas stream (214), which is recovered at the top of the flash column (203). The aqueous solution stream (215) is sent to a pump (205). The aqueous solution stream (216) exiting the pump (205) is sent to an economizer (202) and then to a cooler (206) via (217). The liquid stream (218) leaving the cooler is sent to a membrane filtration system (207). The permeate (219), containing amines in water, is sent to a contactor (201). The catalyst-containing retentate (212) is mixed with the acid gas-rich absorbent stream (211). The mixture (213) is sent to the flash column (203). Depending on the hydrosulfide ion concentration, the retentate can be sent directly to the flash column (203) to avoid potential scaling of magnesium hydrosulfide (Mg(SH)2) or magnesium sulfide (MgS) in the piping.

[0035] The acid gas stream (208) can be any gas stream containing carbon dioxide, hydrogen sulfide, or both. In some embodiments, the acid gas stream contains carbon dioxide. In some embodiments, the acid gas stream contains hydrogen sulfide. In some embodiments, the acid gas stream contains carbon dioxide and hydrogen sulfide. In some embodiments, the acid gas stream is natural gas. In some embodiments, the acid gas stream has a temperature of about 25°C to about 60°C.

[0036] The cooled stream (212) entering the bottom of the flash column (203) contains a regenerated catalyst. In some embodiments, the flash column is selected from a demister, a packed column, and a stirred vessel. In some embodiments, the regenerated catalyst contains a Group 2 element of the periodic table (an alkaline earth metal). In some embodiments, the Group 2 element of the periodic table is selected from beryllium, magnesium, calcium, strontium, barium, and radium. In some embodiments, the Group 2 element of the periodic table is magnesium. In some embodiments, the Group 2 element of the periodic table is calcium. In some embodiments, the regenerated catalyst is a carbonate. In some embodiments, the regenerated catalyst is magnesium carbonate. In some embodiments, the regenerated catalyst is a hydroxide. In some embodiments, the regenerated catalyst is magnesium hydroxide. In some embodiments, the acid gas stream contains hydrogen sulfide and the regenerated catalyst is a hydroxide. In some embodiments, the acid gas stream contains hydrogen sulfide and the regenerated catalyst is magnesium hydroxide. In some embodiments, the acid gas stream contains carbon dioxide and the regenerated catalyst is a carbonate. In some embodiments, the acid gas stream contains carbon dioxide and the regenerated catalyst is magnesium carbonate. In some embodiments, the acid gas stream contains carbon dioxide and hydrogen sulfide and the regeneration catalyst is a hydroxide. In some embodiments, the acid gas stream contains carbon dioxide and hydrogen sulfide and the regeneration catalyst is magnesium hydroxide. In some embodiments, the acid gas stream contains carbon dioxide and hydrogen sulfide and the regeneration catalyst is a carbonate. In some embodiments, the acid gas stream contains carbon dioxide and hydrogen sulfide and the regeneration catalyst is magnesium carbonate. In some embodiments, the regenerated catalyst of the present disclosure allows for the separation of carbon dioxide, hydrogen sulfide, or both at a lower temperature than the temperature of the same process without the regenerated catalyst.

[0037] The aqueous solution entering the bottom of the flash column (203) is heated using a heat exchanger (204). In some embodiments, the solution is heated to about 60°C to less than about 100°C, e.g., about 60°C, about 65°C, about 70°C, about 75°C, about 80°C, about 85°C, about 90°C, about 95°C, about 96°C, about 97°C, about 98°C, or about 99°C. In some embodiments, the heat source is low-temperature heat recovered from another process, such as low-pressure steam or hot water. In some embodiments, the low-temperature heat is renewable heat, such as heat from the sun. In some embodiments, the low-temperature heat is renewable heat from the sun, such as in tropical climates.

[0038] The aqueous solution stream (216) exits the pump (205) and is sent to an economizer (202) and then to a chiller (206). In some embodiments, the chiller's cold source is ambient air. In some embodiments, the cold source is ambient air in a continental climate. In some embodiments, the cold source is a sea or ocean. In some embodiments, the cold source is a sea or ocean in a tropical climate.

[0039] The liquid stream (218) exiting the cooler is sent to a filtration membrane, such as a nanofiltration (NF) membrane. An exemplary NF membrane is NTR-729HF, available from Nitto Denko (Teaneck, NJ).

[0040] The permeate (219), which contains the amine in water, is sent to the contactor (201). In some embodiments, the contactor is a falling film column, a packed column, a bubble column, a spray tower, or a gas-liquid stirred vessel.

[0041] The present disclosure also provides a method for direct CO2 capture. The method includes the use of a catalyst containing a Group 2 element of the periodic table. The method is an energy-efficient process for direct carbon dioxide capture. In some embodiments, the process includes the use of natural energy sources, such as heat from the sun, cooling from the ocean or sea, or both. A description of process (300) is shown in FIG. 4. An air (or gas) stream (309) is passed through a filter (301) to remove solid particles (e.g., dust) suspended in the air (or gas) stream. The stream (309) is then injected into the bottom of a contactor (303). A cooled aqueous absorption liquid stream containing a regenerated catalyst (315) absorbs CO2 from the air (or gas) stream (309) within the contactor (303). The carbon dioxide-depleted air stream exits the top of the contactor (303) (312). The aqueous bicarbonate stream (311) is heated using a solar concentrator (305) and sent via 313 to a flash column (306). The hot aqueous solution (313) separates a CO2 stream (314), which is recovered at the top of the flash column (306). A CO2 lean aqueous stream (315) is sent via pump (307) to a cold source (308) for cooling. The liquid stream (315) is sent to a contactor (303).

[0042] The air (or gas) stream (309) can be an air or gas stream containing carbon dioxide, hydrogen sulfide, or both. In some embodiments, the air or gas stream contains carbon dioxide. In some embodiments, the air or gas stream contains hydrogen sulfide. In some embodiments, the air or gas stream contains carbon dioxide and hydrogen sulfide. In some embodiments, the air or gas stream is natural gas. In some embodiments, the air or gas stream is an acid gas.

[0043] A cooled aqueous absorption liquid stream (315) containing regenerated catalyst absorbs CO from the air (or gas) stream (309) in the contactor (303). In some embodiments, the regenerated catalyst is a catalyst of the present disclosure. In some embodiments, the regenerated catalyst comprises a Group 2 element of the periodic table. In some embodiments, the regenerated catalyst comprises magnesium or calcium. In some embodiments, the regenerated catalyst is magnesium carbonate. In some embodiments, the concentration of the regenerated catalyst in the aqueous carbonate (or amine) stream is from about 0.01 mg / L to about 400 mg / L.

[0044] The aqueous bicarbonate stream (311) is heated using a solar concentrator (305) and sent to a flash column (306). In some embodiments, the flash column is selected from a demister, a packed column, and a stirred vessel. The aqueous solution is heated in the solar concentrator. In some embodiments, the solution is heated to about 45°C to less than about 100°C, e.g., about 45°C, about 50°C, about 55°C, about 60°C, about 65°C, about 70°C, about 75°C, about 80°C, about 85°C, about 90°C, about 95°C, about 96°C, about 97°C, about 98°C, or about 99°C. In some embodiments, the low heat is renewable heat, such as heat from the sun. In some embodiments, the low heat is renewable heat, such as from the sun in tropical climates.

[0045] The dilute CO2 aqueous solution stream (315) is sent to a cold source (308). The cold source can be any cold source capable of cooling the aqueous solution stream to the desired temperature. In some embodiments, the cold source is the ocean or sea.

[0046] The liquid stream (315) from the cold source is sent to a contactor (303). In some embodiments, the contactor is a falling film column, a packed column, a bubble column, a spray tower, or a gas-liquid agitated vessel.

[0047] Accordingly, provided herein is a method for removing carbon dioxide (CO) from an air or gas stream, the method comprising contacting the air or gas stream containing CO with a regenerated catalyst comprising a Group 2 element of the periodic table, heating the resulting composition to about 45°C to less than about 100°C, e.g., about 50°C to about 55°C, separating a CO-containing gas stream from the composition, and recovering the CO. In some embodiments, the resulting composition is heated to about 50°C to about 55°C. In some embodiments, the contacting of the air or gas stream with the regenerated catalyst occurs under absorber conditions. As used herein, "absorber conditions" refers to the temperature of the absorbent and the presence or absence of the regenerated catalyst in the absorbent solution. In some embodiments, the regenerated catalyst is in the absorbent solution, and the absorber has a temperature below about 40°C (see, e.g., Figures 2 and 4). In some embodiments, the regenerated catalyst is removed from the absorbent solution by a selective membrane, and the absorber has a temperature between about 30°C and about 80°C (see, e.g., Figure 3). Also provided herein is a method for removing hydrogen sulfide (HS) from a gas stream, the method comprising contacting an air or gas stream containing HS with a regenerated catalyst comprising a Group 2 element of the periodic table; heating the resulting composition to about 60°C to less than about 100°C, e.g., about 60°C to about 65°C; separating the HS-containing gas stream from the composition; and recovering the HS. In some embodiments, the resulting composition is heated to about 60°C to about 65°C. In some embodiments, the catalyst comprises magnesium. In some embodiments, the air or gas is an acid gas. In some embodiments, the heat source is a renewable or recoverable heat source.

[0048] Also provided in this disclosure is a method for treating acid gas, the method including contacting an acid stream with a regenerated catalyst comprising an element from Group 2 of the periodic table, heating the resulting composition to about 45°C to less than about 100°C, e.g., about 60°C to about 65°C, separating a gas stream containing HS, CO, or both from the composition, and recovering the HS, CO, or both. In some embodiments, the resulting composition is heated to about 60°C to about 65°C.

[0049] The disclosed process is more cost-effective and energy efficient than similar processes that do not use the disclosed regenerated catalyst, in part due to the lower regeneration temperatures required in the disclosed process and the opportunity to use renewable or recovered heat sources.

[0050] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The methods and materials used in this application are described herein; however, other suitable methods and materials known in the art can also be used. The materials, methods, and examples are illustrative only and are not intended to be limiting. All publications, patent applications, patents, sequences, database entries, and other references mentioned in this document are incorporated herein by reference in their entirety. In case of conflict, the present specification, including definitions, will control.

[0051] Values ​​expressed in range format should be interpreted flexibly to include not only the numerical values ​​explicitly stated as the limits of the range, but also all individual numerical values ​​and subranges within that range, as if each individual numerical value and subrange were expressly stated. For example, a range such as "about 0.1% to about 5%" or "about 0.1% to 5%" should be interpreted to include not only about 0.1% to about 5%, but also individual values ​​(e.g., 1%, 2%, 3%, 4%) and subranges within the indicated range (e.g., 0.1% to 0.5%, 1.1% to 2.2%, 3.3% to 4.4%). Unless otherwise specified, the phrase "about X to Y" has the same meaning as "about X to about Y." Similarly, unless otherwise specified, the phrase "about X, Y, or about Z" has the same meaning as "about X, about Y, or about Z."

[0052] As used in this disclosure, the term "about" allows for a degree of variation in a value or range, for example, within 10%, within 5%, or within 1% of a stated value or the limits of a stated range.

[0053] As used in this disclosure, the terms "a," "an," and "the" are used to include one or more unless the context clearly dictates otherwise. The term "or" refers to a non-exclusive "or" unless otherwise specified. The phrase "at least one of A and B" has the same meaning as "A, B, or A and B." Additionally, unless otherwise specified, it should be understood that the words or terms used in this disclosure are for purposes of description only and not limitation. The use of section headings is intended to aid in the reading and comprehension of the document and should not be construed as limiting. Information associated with a section heading may be found within or outside of that particular section.

[0054] As used herein, an "acid gas absorbent" is a base (pKa>7) that reacts with acid gases to form a salt and chemisorbs the acid gases in solution.

[0055] As used herein, "acid gas stream" is used broadly to refer to a gas stream that forms an acidic solution when combined with water. For example, in some embodiments, the air or gas stream of the present disclosure comprises one or more of carbon dioxide gas, hydrogen sulfide gas, mercaptans, and carbonyl sulfide.

[0056] As used herein, "sour gas" refers to a gaseous fluid containing hydrogen sulfide. In some embodiments, sour gas contains more than about 500 ppm hydrogen sulfide, although any amount may be considered sour if it is undesirable.

[0057] As used herein, "sweet gas" refers to a gaseous fluid that contains small amounts of hydrogen sulfide or is substantially free of hydrogen sulfide. In some embodiments, sweet gas contains less than about 500 ppm, e.g., less than about 20 ppm, of hydrogen sulfide.

[0058] In the methods described herein, acts may be performed in any order unless a temporal or operational order is explicitly recited. Furthermore, certain acts may be performed simultaneously unless an explicit claim recitation clearly states that they be performed separately. For example, a claimed act of performing X and a claimed act of performing Y may be performed simultaneously in a single operation, and the resulting process would fall within the literal scope of the claimed process. [Example]

[0059] Example 1 - Non-catalytic CO2 regeneration

[0060] In a two-neck round-bottom flask, 34.0725 g of sodium bicarbonate (0.4055 mol) was added to 100.0142 g of distilled water at room temperature. The aqueous suspension was stirred and heated to 55°C. Gas evolution was collected in an inverted 250 mL graduated cylinder, which was first filled with water and then charged into a 500 mL crystallizer. The volume evolved was recorded as a function of time. As shown in Figure 5, a small volume of 33 mL was evolved, which was due to an increase in vapor within the flask as well as a slight initial decarbonation of the sodium bicarbonate. A plateau was reached after 20 minutes.

[0061] Example 2 - Catalytic CO2 Regeneration

[0062] In a two-necked round-bottom flask, add magnesium carbonate (0.4601 × 10 -3 0.0388 g of 0.4055 mol of sodium bicarbonate was added to 100.0748 g of distilled water at room temperature. After the catalyst was dissolved, 34.0646 g of sodium bicarbonate (0.4055 mol) was added to the aqueous solution at room temperature. Initial carbon dioxide bubbles were barely observed. The aqueous suspension was stirred and heated to 55°C. Gas evolution was collected in an inverted 250 mL graduated cylinder, which was first filled with water and then charged into a 500 mL crystallizer. The volume discharged was recorded as a function of time. As shown in Figure 5, a large volume of 220 mL was discharged, which was primarily due to the decarboxylation of bicarbonate (plus a negligible effect of steam buildup in the flask). After 45 minutes, no plateau was reached compared to Example 1 (no catalyst).

[0063] Other embodiments While the present invention has been described in conjunction with its detailed description, it is to be understood that the foregoing description is intended to be illustrative, but not limiting, of the scope of the invention, which is defined by the appended claims. Other aspects, advantages, and modifications are within the scope of the following claims.

Claims

1. Carbon dioxide (CO ２ ) a method for removing the To form the aqueous bicarbonate composition, ２ contacting said air or gas stream containing CO ２ heating the aqueous bicarbonate composition to about 45° C. to less than about 100° C. to separate a gas stream comprising CO ２ recovering said gas stream comprising: Including, The regenerated catalyst comprises an element from Group 2 of the periodic table; method.

2. The method of claim 1 , wherein the regenerated catalyst comprises magnesium or calcium.

3. 10. The method of claim 1, wherein the regeneration catalyst is magnesium carbonate.

4. 10. The method of claim 1, wherein the concentration of the regenerated catalyst in the aqueous composition is from about 0.01 mg / L to about 400 mg / L.

5. The method of claim 1 , wherein the heat source is a recovered or renewable heat source.

6. 6. The method of claim 5, wherein the heat source is selected from low pressure steam recovered from another process, hot water recovered from another process, or the sun.

7. from the aqueous bicarbonate composition ２ 10. The method of claim 1, further comprising recycling the aqueous carbonate composition after separating a gas stream comprising:

8. before recycling the aqueous carbonate composition and removing CO from the aqueous bicarbonate composition. ２ 8. The method of claim 7, further comprising cooling the aqueous carbonate composition after separating the gas stream comprising:

9. 9. The method of claim 8, wherein the cooling source is ambient air or the sea or ocean.

10. 10. The method of claim 1, wherein the air or gas stream is an acid gas.

11. Hydrogen sulfide (H ２ S), comprising the steps of: To form an aqueous hydrosulfide composition, H ２ contacting the S-containing gas stream under conditions with an aqueous composition comprising an aqueous carbonate (or amine) solution and a regenerated catalyst; H ２ heating the aqueous hydrosulfide composition to about 60° C. to less than about 100° C. to separate the S-containing gas stream from the aqueous hydrosulfide composition and obtain an aqueous hydroxide composition; and H ２ recovering said gas stream containing S; Including, The regenerated catalyst comprises an element from Group 2 of the periodic table; method.

12. The method of claim 11 , wherein the regenerated catalyst comprises magnesium or calcium.

13. 12. The method of claim 11, wherein the regeneration catalyst is magnesium hydroxide.

14. 12. The method of claim 11, wherein the concentration of the regenerated catalyst in the aqueous composition is from about 0.01 mg / L to about 400 mg / L.

15. The method of claim 11 , wherein the heat source is a recovered or renewable heat source.

16. 16. The method of claim 15, wherein the heat source is selected from low pressure steam recovered from another process, hot water recovered from another process, or the sun.

17. H from aqueous hydrosulfide compositions ２ 12. The method of claim 11, further comprising recycling the aqueous hydroxide composition after separating the S-containing gas stream.

18. before recycling the aqueous hydroxide composition and removing CO from the aqueous hydrosulfide composition. ２ 20. The method of claim 17, further comprising cooling the aqueous hydroxide composition after separating the gas stream comprising:

19. 20. The method of claim 18, wherein the cooling source is ambient air or the sea or ocean.

20. 12. The method of claim 11, wherein the air or gas stream is an acid gas.

21. 12. The method of claim 11, wherein the air or gas stream is sour gas.

22. 1. A method for treating acid gas, comprising: contacting the acid gas stream with an aqueous composition comprising an aqueous carbonate (or amine) solution and a regenerated catalyst to form a combined gas-liquid composition; CO ２ , H ２ heating the gas-liquid composition to about 60° C. to less than about 100° C. to separate a gas stream containing S, or both from the gas-liquid composition; and The CO ２ , H ２ recovering said gas stream containing S, or both; Including, The regenerated catalyst comprises an element from Group 2 of the periodic table; method.

23. 23. The method of claim 22, wherein the regenerated catalyst comprises magnesium.

24. 24. The method of claim 23, wherein the regeneration catalyst is magnesium carbonate or magnesium hydroxide.

25. 23. The method of claim 22, wherein the concentration of the regenerated catalyst in the aqueous composition is from about 0.01 mg / L to about 400 mg / L.

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