Methods and apparatus for carbon capture combined with hydrogen production

Abstract

The present invention provides a method and apparatus for carbon capture combined with hydrogen production. The method includes the steps of collecting low-concentration CO2 using a solution of an alkali metal hydroxide to obtain a low-concentration CO2 absorbent, collecting high-concentration CO2 using a first partial low-concentration CO2 absorbent to obtain a high-concentration CO2 absorbent, and performing electrolysis using a second partial low-concentration CO2 absorbent as the catholyte and the high-concentration CO2 absorbent as the anolyte, with a non-ionic separator as the separator. The method according to the present invention can achieve the capture of CO2 in a wide concentration range, realize the regeneration of the absorbent by performing electrolysis using a non-ionic separator, and combine it with hydrogen production, reduce the CO2 capture cost in a wide concentration range, obtain by-products of H2 and O2, and also reduce the hydrogen production cost.

Description

Technical Field

[0001] The present invention relates to the field of carbon capture technology, and specifically to a method and apparatus for carbon capture combined with hydrogen production.

Background Art

[0002] Global warming is currently one of the main environmental problems in the world, and carbon dioxide is the main greenhouse gas. Conventional carbon capture, utilization, and storage technologies (CCUS), especially direct air capture technology, and water electrolysis hydrogen production are too costly, and the storage, transportation, and consumption technologies are immature, so their development is severely restricted. Currently, the carbon dioxide capture method is mainly the adsorption method using liquid amine solvents. Conventional liquid amine solvents have high renewable energy consumption, strong corrosivity, high toxicity, are easy to volatilize, and are costly, so they are currently the main obstacles restricting the development of this capture technology. In addition, the above method can only achieve the capture of carbon dioxide with a high concentration such as flue gas, and cannot be applied to the capture of carbon dioxide with a low concentration such as air. The carbon dioxide capture technology in air developed in recent years can adsorb carbon dioxide using liquid alkaline solutions and solid amine membranes to achieve the capture of CO2 in a wide concentration range.

[0003] However, the above carbon dioxide capture technology in air has the problem of high renewable energy consumption of the carbon dioxide adsorbent. When capturing carbon dioxide in air using a solid amine membrane as an adsorbent, the amine adsorbent is costly and has a high economic cost for commercial use. In another technical route, a liquid alkaline solution is adopted as an absorbent, and the adsorbent is regenerated by a two-step chemical reaction. That is, in the first step, carbon dioxide is combined with the alkaline solution to form a carbonate solution and the absorbent is regenerated. Then, calcium hydroxide is reacted with the carbonate solution obtained in the first step to form calcium carbonate precipitate, which is further calcined to form high-purity carbon dioxide and regenerate calcium hydroxide. In this technical route, the energy consumption required for calcining calcium carbonate is high, the device investment is large, and the economic cost is high.

[0004] In Patent WO2011123817A3 and Patent CN102605383A, carbon capture is carried out using an alkaline ion exchange film, but its use conditions are strict, the film cost is high, and it lacks commercial utilization value. In Patent AU2009290161B2, an alkaline ion exchange membrane is adopted, and its carbon dioxide is introduced into the electrolytic cell in a gaseous state and combined with the alkaline solution in the cell through the gas diffusion layer to form a NaOH-NaHCO3-Na2CO3 mixed solution, but it is impossible to form and regenerate a high-purity alkaline solution, and it is necessary to supplement a high concentration of carbon dioxide, and it is impossible to carry out capture and electrolysis using carbon dioxide in the air. In Patent US9095813B2, an alkaline solution adsorption technology is adopted, and a two-stage chemical circuit is required to realize the reduction of the gas adsorbent, the system design is complex, the manufacturing cost is high, the control system is difficult to realize, and the regeneration chemical circuit requires heat supply by combustion at 900°C, which greatly increases its energy loss and carbon emissions. Furthermore, since the calcium oxide adsorbent is easily deactivated, it is necessary to supplement a large amount of calcium carbonate. The air CO2 capture devices according to Patent US20170113184A1 and Patent EP2160234A1 are also solid film capture technologies. Since steam is required for the reduction of the absorbent, CO2 emissions increase, and only the CO2 capture problem can be solved, and the CO2 utilization problem cannot be solved.

[0005] In the prior art, there is a technology in which potassium hydroxide is used to absorb CO2 to obtain potassium carbonate, and then potassium carbonate is electrolyzed by an ion membrane. Potassium carbonate generates a mixed solution of potassium bicarbonate and potassium carbonate, O2 and CO2 gas at the anode, and H2 and KOH solution are obtained at the cathode to realize the regeneration of the absorbent. However, first, in order to prevent the reaction between potassium bicarbonate at the anode and potassium hydroxide at the cathode during the electrolysis process, an ion exchange membrane is often used to separate the cathode liquid chamber and the anode liquid chamber. However, the ion membrane is expensive and has strict usage conditions, so the cost is high and its application range is limited by complex purification processes. Second, when KOH absorbs low-concentration CO2 such as CO2 in the air, generally only a KOH-K2CO3 mixed solution can be obtained, and it is difficult to obtain completely converted K2CO3, so the utilization rate of KOH is too low. If we try to completely convert KOH into potassium carbonate, it is necessary to increase the air passage volume, but both the later CO2 absorption rate and CO2 utilization efficiency are extremely low. Third, when a potassium carbonate mixed solution containing a predetermined amount of potassium hydroxide is introduced into the anode liquid, the efficiency of acidifying potassium carbonate at the anode will decrease.

Summary of the Invention

Problems to be Solved by the Invention

[0006] The main object of the present invention is to provide a carbon capture method and device combined with hydrogen production to solve the problems that the capture costs of CO2 in a wide concentration range and the hydrogen production costs in the prior art are both high.

Means for Solving the Problems

[0007] To achieve the above object, one aspect of the present invention provides a method for carbon capture combined with hydrogen production. The method for carbon capture combined with hydrogen production includes step S1 of collecting low-concentration CO2 using a solution of an alkali metal hydroxide to obtain a low-concentration CO2 absorption solution, where the low-concentration CO2 absorption solution contains an alkali metal carbonate and an alkali metal hydroxide; step S2 of dividing the low-concentration CO2 absorption solution into a first-part low-concentration CO2 absorption solution and a second-part low-concentration CO2 absorption solution, and collecting high-concentration CO2 using the first-part low-concentration CO2 absorption solution to obtain a high-concentration CO2 absorption solution, where the high-concentration CO2 absorption solution contains an alkali metal carbonate and an alkali metal bicarbonate; and step S3 of using the second-part low-concentration CO2 absorption solution as the catholyte, the high-concentration CO2 absorption solution as the anolyte, and a non-ionic separator as the separator to perform electrolysis, obtaining H2 and a cathode effluent at the electrolysis cathode, obtaining O2, CO2, and an anode effluent at the electrolysis anode, and returning the cathode effluent to step S1, where the cathode effluent contains an alkali metal carbonate and an alkali metal hydroxide, and the anode effluent contains an alkali metal carbonate and an alkali metal bicarbonate.

[0008] Furthermore, the alkali metal hydroxide is KOH, the alkali metal carbonate is K2CO3, and the alkali metal bicarbonate is KHCO3, or the alkali metal hydroxide is NaOH, the alkali metal carbonate is Na2CO3, and the alkali metal bicarbonate is NaHCO3.

[0009] Furthermore, in step S2, in terms of volume percentage, the first-part low-concentration CO2 absorption solution is 10% to 90% of the low-concentration CO2 absorption solution.

[0010] Furthermore, step S3 further includes performing electrolysis using the anode discharge liquid as the anolyte. Preferably, in the catholyte, the concentration of carbonate is 0.1 to 6 M, and the concentration of hydroxide is 0.1 to 10 M. More preferably, in the catholyte, the concentration of carbonate is 0.5 to 3 M, and the concentration of hydroxide is 3 to 7 M. Preferably, in the anolyte, the concentration of carbonate is 0.1 to 6.5 M, and the concentration of bicarbonate is 0.1 to 3 M. More preferably, in the anolyte, the concentration of carbonate is 2 to 5 M, and the concentration of bicarbonate is 0.6 to 1.5 M.

[0011] Furthermore, the nonionic separator is one or more of a porous polymer separator, a Zirfon film, a polyphenylene sulfide film, a polysulfone film, and a polyethersulfone film. Preferably, the nonionic separator is a porous polymer separator. More preferably, the surface polymer layer of the porous polymer separator is one or more of a carboxylic acid ion resin layer, polyphenylene sulfide, polysulfone, and polyethersulfone.

[0012] Another aspect of the present invention provides an apparatus for carbon capture combined with hydrogen production. The apparatus for carbon capture combined with hydrogen production includes a low-concentration CO2 absorption unit, a high-concentration CO2 absorption unit, and an electrolysis unit. The low-concentration CO2 absorption unit has an alkali metal hydroxide solution inlet, a first capture target raw material inlet containing low-concentration CO2, a first partial low-concentration CO2 absorption liquid outlet, a second partial low-concentration CO2 absorption liquid outlet, and a first waste gas outlet. The low-concentration CO2 absorption unit is configured to capture low-concentration CO2 with an alkali metal hydroxide solution to obtain a low-concentration CO2 absorption liquid, and the low-concentration CO2 absorption liquid contains an alkali metal carbonate and an alkali metal hydroxide. The high-concentration CO2 absorption unit has a first partial low-concentration CO2 absorption liquid inlet, a second capture target raw material inlet containing high-concentration CO2, a high-concentration CO2 absorption liquid outlet, and a second waste gas outlet, and the first partial low-concentration CO2 absorption liquid inlet is connected to the first partial low-concentration CO2 absorption liquid outlet. The high-concentration CO2 absorption unit is configured to capture high-concentration CO2 using the first partial low-concentration CO2 absorption liquid to obtain a high-concentration CO2 absorption liquid. The high-concentration CO2 absorption liquid contains an alkali metal carbonate and an alkali metal bicarbonate. The electrolysis unit has a cathode liquid inlet, a non-ionic separator, an anode liquid inlet, a cathode discharge liquid outlet, an anode discharge liquid outlet, an H2 outlet, and an O2 / CO2 mixed gas outlet. The cathode liquid inlet is connected to the second partial low-concentration CO2 absorption liquid outlet, the cathode liquid outlet is connected to the alkali metal hydroxide solution inlet, and the anode liquid inlet is connected to the high-concentration CO2 absorption liquid outlet. The electrolysis unit is configured to electrolyze the second partial low-concentration CO2 absorption liquid and the high-concentration CO2 absorption liquid to obtain H2 and a cathode discharge liquid at the electrolysis cathode, and to obtain O2, CO2, and an anode discharge liquid at the electrolysis anode. The cathode discharge liquid contains an alkali metal carbonate and an alkali metal hydroxide, and the anode discharge liquid contains an alkali metal carbonate and an alkali metal bicarbonate.

[0013] Furthermore, the low-concentration CO2 absorption unit includes a low-concentration absorption tower. The top of the low-concentration absorption tower has an alkali metal hydroxide solution inlet and a first waste gas outlet. The bottom of the low-concentration absorption tower has a first capture target raw material inlet containing low-concentration CO2, a first partial low-concentration CO2 absorption liquid outlet, and a second partial low-concentration CO2 absorption liquid outlet. The high-concentration CO2 absorption unit includes a high-concentration absorption tower. The top of the high-concentration absorption tower has a first partial low-concentration CO2 absorption liquid inlet and a second waste gas outlet. The bottom of the high-concentration absorption tower has a second capture target raw material inlet containing high-concentration CO2 and a high-concentration CO2 absorption liquid outlet.

[0014] Furthermore, the electrolysis unit includes an electrolytic cell. The electrolytic cell has a cathode chamber and an anode chamber. A non-ionic separator is installed between the cathode chamber and the anode chamber. An electrolytic cathode is installed in the cathode chamber, and an electrolytic anode is installed in the anode chamber. The cathode chamber has a cathode liquid inlet, a cathode discharge liquid outlet, and an H2 outlet. The anode chamber has an anode liquid inlet, an anode discharge liquid outlet, and an O2 / CO2 mixed gas outlet.

[0015] Furthermore, the high-concentration CO2 absorption unit further includes a high-concentration CO2 absorption liquid tank. The high-concentration CO2 absorption liquid tank is installed in a pipeline connecting the anode liquid inlet and the high-concentration CO2 absorption liquid outlet and is located on the high-concentration CO2 absorption liquid outlet side.

[0016] Furthermore, the electrolysis unit further includes a cathode feed liquid tank installed in a pipeline connecting the cathode liquid inlet and the second partial low-concentration CO2 absorption liquid outlet, and / or a cathode discharge liquid tank installed in a pipeline connecting the cathode liquid outlet and the alkali metal hydroxide solution inlet, and / or an anode storage liquid tank installed in a pipeline connecting the anode liquid inlet and the high-concentration CO2 absorption liquid outlet and located on the anode liquid inlet side.

Advantages of the Invention

[0017] According to the technical solution of the present invention, by using an alkaline solution as an absorbent, the absorption and capture of CO2 in a wide concentration range for low / high concentration CO2 can be realized. On the other hand, by electrolyzing the absorption products of low / high concentration CO2 with a non-ionic separator and coupling hydrogen production, the regeneration of the absorbent liquid can be realized, high-concentration CO2 can be obtained, and by-products H2 and O2 can be obtained. The present invention employs a low-concentration CO2 absorbent as the cathode electrolyte and a high-concentration CO2 absorbent as the anode electrolyte. Under the condition of not using an ion exchange membrane, the increase in the concentration of CO3 2- at the electrolysis cathode can suppress the mass diffusion caused by the concentration difference. Therefore, the diffusion of HCO3 - and CO3 2- at the electrolysis anode to the cathode can be reduced. At the same time, since CO3 2- with a high charge amount generates electromigration earlier than OH - , the electromigration of OH - to the anode can be reduced. By electrolyzing the working medium liquid after collecting the above carbon dioxide, the regeneration of the alkaline absorbent liquid can be realized, high-purity product gas can be obtained, and the recycling use of the collected liquid can be realized to reduce the regeneration cost of the absorbent liquid. In addition, the use of a non-ionic separator can greatly reduce the cost of the electrolyzer, avoid the strict restrictions of the ion membrane on the electrolyte and the electrolyzer, further simplify the impurity removal process of the CO2 absorbent liquid, and further reduce the collection cost of CO2. From the above, the method according to the present invention can realize the collection of CO2 in a wide concentration range, realize the regeneration of the absorbent liquid by electrolyzing with a non-ionic separator and coupling hydrogen production, reduce the CO2 collection cost in a wide concentration range, obtain by-products H2 and O2, and reduce the hydrogen production cost.

Brief Description of the Drawings

[0018] The drawings forming a part of this disclosure are for providing a further understanding of the present invention. The schematic embodiments and their descriptions of the present invention are for interpreting the present invention and do not unduly limit the present invention.

Figure 1

DETAILED DESCRIPTION OF THE INVENTION

[0019] Note that, as long as there is no contradiction, the embodiments in this application and the configurations in the embodiments can be combined with each other. Hereinafter, the present invention will be described in detail in relation to the embodiments with reference to the drawings.

[0020] Note that the terms such as "first" and "second" in the specification and claims of the present invention are merely for distinguishing similar objects and do not necessarily explain a specific order or priority. The data used in this way can be appropriately exchanged to facilitate the description of the embodiments of the present invention described herein. Also, the terms "comprising" and "having" and any variations thereof are intended to inclusively include, for example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those steps or units explicitly listed, and may include those not explicitly listed or other things specific to these processes, methods, products or devices. Also, the terms "high, low, medium, low concentration, high concentration" related to the solution in the specification and claims of the present invention represent the relative high concentration, relative low concentration and relative intermediate concentration in different steps of the related solution, and do not limit the specific magnitude of the concentration.

[0021] Note that the terms "low-concentration CO2" and "high-concentration CO2" in the description and claims of the present invention are only used to distinguish CO2-containing materials under different CO2 concentrations. For example, "low-concentration CO2" may refer to a situation where the volume concentration of carbon dioxide is 1% or less (e.g., CO2 in air), and "high-concentration CO2" may refer to a situation where the volume concentration of carbon dioxide is 1% or more (e.g., CO2 in flue gas). Here, "1%" is only an exemplary value rather than an absolute value for distinguishing low-concentration CO2 and high-concentration CO2, and it can be adjusted according to the actual situation in the actual operation process.

[0022] Note that in the present invention, the "solution" means an aqueous solution unless otherwise specified.

[0023] As described in the background art of the present invention, in the prior art, there is a problem that both the CO2 capture cost and the hydrogen production cost in a wide concentration range are high. To solve the above problems, one typical embodiment of the present invention provides a method for carbon capture combined with hydrogen production. The method for carbon capture combined with hydrogen production includes step S1 of capturing low-concentration CO2 with an alkali metal hydroxide solution to obtain a low-concentration CO2 absorption solution, where the low-concentration CO2 absorption solution contains an alkali metal carbonate and an alkali metal hydroxide; step S2 of dividing the low-concentration CO2 absorption solution into a first partial low-concentration CO2 absorption solution and a second partial low-concentration CO2 absorption solution, and capturing high-concentration CO2 with the first partial low-concentration CO2 absorption solution to obtain a high-concentration CO2 absorption solution, where the high-concentration CO2 absorption solution contains an alkali metal carbonate and an alkali metal bicarbonate; step S3 of using the second partial low-concentration CO2 absorption solution as the catholyte, the high-concentration CO2 absorption solution as the anolyte, and performing electrolysis with a non-ionic separator as the separator to obtain H2 and a cathode discharge solution at the electrolysis cathode, and obtaining O2, CO2, and an anode discharge solution at the electrolysis anode, and returning the cathode discharge solution to step S1, where the cathode discharge solution contains an alkali metal carbonate and an alkali metal hydroxide, and the anode discharge solution contains an alkali metal carbonate and an alkali metal bicarbonate.

[0024] The present invention first collects low-concentration CO2 with an alkali metal hydroxide solution to obtain a low-concentration CO2 absorbent containing alkali metal carbonate-alkali metal hydroxide, and the alkali metal hydroxide is not fully converted into alkali metal hydroxide. Then, high-concentration CO2 is collected with the first part of the low-concentration CO2 absorbent to obtain a high-concentration CO2 absorbent containing alkali metal carbonate-alkali metal bicarbonate with a small amount of alkali metal bicarbonate, realizing the absorption and collection of CO2 in a wide range including low and high concentrations. Another part of the low-concentration CO2 absorbent is used as the cathode electrolyte, the high-concentration CO2 absorbent is used as the anode electrolyte, and a non-ionic separator is used as the electrolytic separator for electrolysis, so that the low-concentration CO2 absorbent containing alkali metal carbonate-alkali metal hydroxide generates a hydrogen evolution reaction at the cathode to produce H2. At the same time, the alkali metal ions in the anolyte enter the electrolytic cathode through the separator under the action of the electric field force and form OH - and regenerated alkali metal hydroxide to obtain a mixed solution of alkali metal carbonate-alkali metal hydroxide with an improved alkali metal hydroxide concentration at the electrolytic cathode, and obtain O2, CO2, and an alkali metal carbonate-alkali metal bicarbonate regeneration solution at the anode of the electrolytic cell.

[0025] On the one hand, by using an alkaline solution as the absorbent, the absorption and collection of CO2 in a wide concentration range for low / high-concentration CO2 can be realized. On the other hand, by electrolyzing the absorption products of low / high-concentration CO2 with a non-ionic separator and coupling hydrogen production, the regeneration of the absorbent can be realized, high-concentration CO2 can be obtained, and by-products H2 and O2 can be obtained. The present invention employs a low-concentration CO2 absorbent as the cathode electrolyte and a high-concentration CO2 absorbent as the anode electrolyte. Under the condition of not using an ion exchange membrane, the increase in the concentration of CO3 2- at the electrolytic cathode can suppress the mass diffusion caused by the concentration difference. Therefore, the diffusion of HCO3 - , CO3 2- at the electrolytic anode to the cathode is reduced. At the same time, since CO3 2- with a high charge amount undergoes electromigration earlier than OH - , OH -It is possible to reduce the electromigration to the anode. By electrolyzing the working medium liquid after collecting the carbon dioxide, the regeneration of the alkaline absorbent can be realized, a high-purity product gas can be obtained, and the recycling use of the collecting liquid can be realized to reduce the regeneration cost of the absorbent. In addition, the use of a non-ionic separator can greatly reduce the cost of the electrolytic cell, avoid the strict restrictions of the ion-exchange membrane on the electrolytic solution and the electrolytic cell, and further simplify the impurity removal process of the CO2 absorbent to further reduce the collection cost of CO2. From the above, the method according to the present invention can realize the collection of CO2 in a wide concentration range, realize the regeneration of the absorbent by electrolyzing with a non-ionic separator, and can be carried out in combination with hydrogen production, reduce the collection cost of CO2 in a wide concentration range, obtain by-products H2 and O2, and reduce the hydrogen production cost.

[0026] The alkali metal of the present invention may use Li, Na, K, or Rb. For the purpose of further improving the CO2 absorption and the electrolysis effect of the absorbent and further reducing the cost, the alkali metal is preferably K or Na. In a preferred embodiment, the alkali metal hydroxide is KOH, the alkali metal carbonate is K2CO3, the alkali metal bicarbonate is KHCO3, or the alkali metal hydroxide is NaOH, the alkali metal carbonate is Na2CO3, and the alkali metal bicarbonate is NaHCO3. Taking the case where the alkali metal hydroxide is KOH as an example, the reaction formula of the operation of the method according to the present invention is as follows.

[0027] In the collection of low-concentration CO2, it is CO2 + 2KOH → K2CO3 + H2O, and KOH is not completely converted, and a KOH-K2CO3 mixed solution is obtained.

[0028] In the collection of high-concentration CO2, it is CO2 + KOH → KHCO3, and the residual KOH is completely converted, and a K2CO3-KHCO3 mixed solution is obtained.

[0029] <Electrolysis> The cathode reaction is 4H2O + 4K + + 4e- → 2H2 + 4KOH. The anodic reaction is 2K2CO3 - 4e - → 4K + + O2 + 2CO2. The overall electrolytic reaction is 2K2CO3 + 4H2O → 4KOH + 2H2 + O2 + 2CO2.

[0030] In order to more reasonably distribute the low-concentration CO2 absorbent, in a preferred embodiment, in step S2, in terms of volume percentage, the first part of the low-concentration CO2 absorbent is 10 to 90% of the low-concentration CO2 absorbent. By collecting high-concentration CO2 with a solution containing an appropriate amount of unreacted alkali metal hydroxide, the high-concentration CO2 absorbent as the anolyte and the low-concentration CO2 absorbent as the catholyte have more compatible electrolytic volumes.

[0031] In a preferred embodiment, step S3 further includes performing electrolysis using the anodic effluent as the anolyte. Thereby, the recycling of the anodic effluent is realized. Preferably, in the catholyte, the concentration of carbonate is 0.1 to 6 M, and the concentration of hydroxide is 0.1 to 10 M. More preferably, in the catholyte, the concentration of carbonate is 0.5 to 3 M, and the concentration of hydroxide is 3 to 7 M. Preferably, in the anolyte, the concentration of carbonate is 0.1 to 6.5 M, and the concentration of bicarbonate is 0.1 to 3 M. More preferably, in the anolyte, the concentration of carbonate is 2 to 5 M, and the concentration of bicarbonate is 0.6 to 1.5 M. This further contributes to the collection of CO2 in a wide concentration range by the alkali metal hydroxide solution and the rapid progress of the electrolysis process, while avoiding the increase in viscosity and electrolysis energy consumption due to too high ionic concentration.

[0032] As described above, in the method for carbon capture combined with hydrogen production of the present invention, since the catholyte and anolyte of the electrolysis are CO2 absorption liquids with different concentrations, a good electrolysis effect can be achieved without using a high-cost ion exchange membrane, and the limitation due to the strict use conditions of the ion membrane can be avoided. In a preferred embodiment, the non-ionic separator is one or more of a porous polymer separator, a Zirfon membrane, a polyphenylene sulfide film, a polysulfone film, and a polyethersulfone film. Preferably, the non-ionic separator is a porous polymer separator, and more preferably, the surface polymer layer of the porous polymer separator is one or more of a carboxylic acid ion resin layer, polyphenylene sulfide, polysulfone, and polyethersulfone. Negative charges such as carboxylate can - assist in suppressing the diffusion of OH at the cathode to the anode, contributing to the improvement of the current efficiency. The above non-ionic separator can further reduce the cost when the electrolysis efficiency is guaranteed.

[0033] Another typical embodiment of the present invention further provides an apparatus for carbon capture combined with hydrogen production. As shown in FIG. 1, the apparatus for carbon capture combined with hydrogen production includes a low-concentration CO2 absorption unit 1, a high-concentration CO2 absorption unit 2, and an electrolysis unit 3. The low-concentration CO2 absorption unit 1 has an alkali metal hydroxide solution inlet, a first capture target raw material inlet containing low-concentration CO2, a first partial low-concentration CO2 absorption liquid outlet, a second partial low-concentration CO2 absorption liquid outlet, and a first waste gas outlet. The low-concentration CO2 absorption unit 1 is configured to capture low-concentration CO2 with an alkali metal hydroxide solution to obtain a low-concentration CO2 absorption liquid, and the low-concentration CO2 absorption liquid contains an alkali metal carbonate and an alkali metal hydroxide. The high-concentration CO2 absorption unit 2 has a first partial low-concentration CO2 absorption liquid inlet, a second capture target raw material inlet containing high-concentration CO2, a high-concentration CO2 absorption liquid outlet, and a second waste gas outlet. The first partial low-concentration CO2 absorption liquid inlet is connected to the first partial low-concentration CO2 absorption liquid outlet. The high-concentration CO2 absorption unit 2 is configured to capture high-concentration CO2 with the first partial low-concentration CO2 absorption liquid to obtain a high-concentration CO2 absorption liquid, and the high-concentration CO2 absorption liquid contains an alkali metal carbonate and an alkali metal bicarbonate. The electrolysis unit 3 has a cathode liquid inlet, a non-ionic separator, an anode liquid inlet, a cathode discharge liquid outlet, an anode discharge liquid outlet, an H2 outlet, and an O2 / CO2 mixed gas outlet. The cathode liquid inlet is connected to the second partial low-concentration CO2 absorption liquid outlet, the cathode liquid outlet is connected to the alkali metal hydroxide solution inlet, the anode liquid inlet is connected to the high-concentration CO2 absorption liquid outlet. The electrolysis unit 3 is configured to electrolyze the second partial low-concentration CO2 absorption liquid and the high-concentration CO2 absorption liquid to obtain H2 and a cathode discharge liquid at the electrolysis cathode, and obtain O2, CO2 and an anode discharge liquid at the electrolysis anode. The cathode discharge liquid contains an alkali metal carbonate and an alkali metal hydroxide, and the anode discharge liquid contains an alkali metal carbonate and an alkali metal bicarbonate.

[0034] In the using process, low-concentration CO₂ is captured in the low-concentration CO₂ absorption unit 1 by using an alkali metal hydroxide solution to obtain a low-concentration CO₂ absorption liquid containing an alkali metal carbonate-alkali metal hydroxide. A part of it is introduced into the electrolytic cathode, and the other part is introduced into the high-concentration CO₂ absorption unit 2 for absorbing high-concentration CO₂. Therefore, a high-concentration CO₂ absorption liquid of an alkali metal carbonate-alkali metal bicarbonate containing a small amount of alkali metal bicarbonate is obtained, and this is introduced into the electrolytic anode for electrolysis. The alkali metal carbonate-alkali metal bicarbonate mixed solution generates an oxygen evolution reaction at the anode to obtain O₂, CO₂ and a low-concentration alkali metal carbonate-medium-concentration alkali metal bicarbonate mixed solution, which is mixed with the high-concentration CO₂ absorption liquid and introduced into the anode feed device, and then circulated and introduced into the electrolysis unit 3. The alkali metal carbonate-alkali metal hydroxide mixed solution generates a hydrogen evolution reaction at the cathode to obtain H₂ and a cathode discharge liquid of an alkali metal carbonate-alkali metal hydroxide with an increased alkali metal hydroxide concentration, which is then introduced into the low-concentration CO₂ absorption unit 1 to continuously capture low-concentration CO₂. In the low-concentration CO₂ absorption unit, the mixed solution of alkali metal carbonate (with a relatively low content)-alkali metal hydroxide (with a relatively high content) is consumed by CO₂, and a mixed solution of alkali metal carbonate (with a relatively high content)-alkali metal hydroxide (with a relatively low content) is obtained. A part of it is introduced into the electrolytic cathode, and a part of it is introduced into the high-concentration CO₂ absorption unit 2. The above is continuously carried out in a cycle as described above.

[0035] When using the above device, gradient absorption of CO₂ in a wide concentration range can be realized, electrolysis can be carried out with a non-ionic separator to realize the regeneration of the absorption liquid KOH, and at the same time, the CO₂ capture cost in a wide concentration range can be reduced. By combining hydrogen production, by-products of H₂ and O₂ can be obtained, and the hydrogen production cost can be reduced. Among them, the flow rate of the first part of the low-concentration CO₂ absorption liquid can be adjusted by a flow rate regulating valve.

[0036] Specifically, as shown in FIG. 1, in a preferred embodiment, the low-concentration CO2 absorption unit 1 includes a low-concentration absorption tower 11. The top of the low-concentration absorption tower 11 has an alkali metal hydroxide solution inlet and a first waste gas outlet. The bottom of the low-concentration absorption tower 11 has a low-concentration CO2-containing first raw material inlet to be captured, a first partial low-concentration CO2 absorption liquid outlet, and a second partial low-concentration CO2 absorption liquid outlet. The high-concentration CO2 absorption unit 2 includes a high-concentration absorption tower 21. The top of the high-concentration absorption tower 21 has a first partial low-concentration CO2 absorption liquid inlet and a second waste gas outlet. The bottom of the high-concentration absorption tower 21 has a high-concentration CO2-containing second raw material inlet to be captured and a high-concentration CO2 absorption liquid outlet.

[0037] In a preferred embodiment, the electrolysis unit 3 includes an electrolytic cell 31. The electrolytic cell 31 has a cathode chamber 311 and an anode chamber 312. A non-ionic separator 313 is installed between the cathode chamber 311 and the anode chamber 312. An electrolytic cathode is installed in the cathode chamber 311, and an electrolytic anode is installed in the anode chamber 312. The cathode chamber 311 has a cathode liquid inlet, a cathode discharge liquid outlet, and an H2 outlet. The anode chamber 312 has an anode liquid inlet, an anode discharge liquid outlet, and an O2 / CO2 mixed gas outlet.

[0038] In a preferred embodiment, the high-concentration CO2 absorption unit 2 further includes a high-concentration CO2 absorption liquid tank 22. The high-concentration CO2 absorption liquid tank 22 is installed in a pipeline connecting the anode liquid inlet and the high-concentration CO2 absorption liquid outlet and is located on the high-concentration CO2 absorption liquid outlet side.

[0039] In a preferred embodiment, the electrolysis unit 3 further includes a cathode feed liquid tank 33 installed in a pipeline connecting the cathode liquid inlet and the second partial low-concentration CO2 absorption liquid outlet, and / or a cathode discharge liquid tank 34 installed in a pipeline connecting the cathode liquid outlet and the alkali metal hydroxide solution inlet, and / or an anode storage liquid tank 32 installed in a pipeline connecting the anode liquid inlet and the high-concentration CO2 absorption liquid outlet and located on the anode liquid inlet side.

[0040] Here, the first raw material A1 containing low-concentration CO2 is introduced into the absorption tower 11, collected by the alkali metal hydroxide solution fed therein, the first waste gas B1 is discharged, and a low-concentration CO2 absorption solution containing alkali metal carbonate-alkali metal hydroxide is obtained. A part of it is introduced into the cathode feed liquid tank 33, and then introduced into the cathode chamber 311 for electrolysis. Another part is introduced into the absorption tower 22 to collect the second raw material A2 containing high-concentration CO2, the second waste gas B2 is discharged, and a high-concentration CO2 absorption solution containing a small amount of alkali metal bicarbonate, that is, alkali metal carbonate-alkali metal bicarbonate, is obtained. This is introduced into the high-concentration CO2 absorption solution tank 22, then introduced into the anode liquid tank 32, and finally introduced into the anode chamber 312 for electrolysis.

[0041] Here, in the cathode chamber 311, a hydrogen evolution reaction occurs to obtain a cathode discharge liquid of alkali metal carbonate-alkali metal hydroxide with increased H2 and alkali metal hydroxide concentrations. It is introduced into the cathode liquid tank 34 and returned to the absorption tower 11 to continuously collect low-concentration CO2. In the anode chamber 312, an oxygen evolution reaction occurs to obtain O2, CO2, and a mixed solution of low-concentration alkali metal carbonate-medium-concentration alkali metal bicarbonate. It is introduced into the anode liquid tank 32, circulated, and introduced into the anode chamber 312 for electrolysis.

[0042] The cathode liquid and the anode liquid can be further controlled to appropriate concentrations by replenishing water and / or adjusting the mixing ratio, thereby further improving the electrolysis efficiency. In addition, the cathode liquid contains K2CO3 (>0.5M) at a predetermined concentration, and the presence of cathode CO3 2- can reduce and / or suppress the diffusion of HCO3 - and CO3 2- at the anode to the cathode, but it cannot be completely avoided. Therefore, in a preferred embodiment, when not electrolyzing, the cathode liquid and the anode liquid are pumped out of the electrolytic cell. In the anode storage liquid tank, the ratio of the anode discharge liquid to the high-concentration CO2 absorption solution may be (0.2~2):1, which further contributes to the circulation execution during the electrolysis process.

[0043] The method and apparatus for carbon capture combined with hydrogen production of the present invention have high future application potential. The application fields include the fields of CO2 capture and utilization, hydrogen energy, etc. The possible application scenarios include, but are not limited to, the following. In Scenario 1, in areas rich in renewable energy such as wind energy and solar energy, and areas suitable for the construction of nuclear power plants, electricity is generated with the above energy to capture CO2 in the air, making full use of various types of energy and reducing the CO2 content in the atmosphere. In Scenario 2, industrial flue gases from power plants, cement plants, metallurgical plants, etc. contain a large amount of CO2 and medium and low temperature waste heat. Applying the present invention to the above industrial fields, the flue gas waste heat can be used as the regeneration heat source of the alkaline solution absorbent, and CO2 capture can be carried out without the need for additional heat sources, realizing the dual goals of industrial energy conservation and CO2 emission reduction, and obtaining by-product hydrogen gas. In Scenario 3, it is used in the energy storage field of renewable energy such as wind energy and solar energy. The gas products of the present invention contain CO2 and H2 and can be used for the synthesis of secondary fuels such as methanol. When the present invention is used in the energy storage field, renewable energy can be converted into fuel chemical energy for storage, and problems such as the stability, timeliness and transportation of renewable energy storage can be solved.

[0044] Hereinafter, the present application will be described in more detail in connection with specific examples, which should not be understood as a limitation to the protection scope claimed by the present application.

[0045] [Example 1] The CO2 capture device combined with hydrogen production in Example 1 is shown in Figure 1. Air containing low-concentration CO₂ is introduced into the absorption tower 11, collected with the KOH solution fed therein, the first waste gas B1 is discharged, a low-concentration CO₂ absorption solution containing K₂CO₃-KOH is obtained, a part of it is introduced into the cathode feed liquid tank 33, and then introduced into the cathode chamber 311 for electrolysis. Another part is introduced into the absorption tower 22 to collect high-concentration CO₂-containing flue gas, the second waste gas B2 is discharged, a high-concentration CO₂ absorption solution of K₂CO₃-KHCO₃ containing a small amount of KHCO₃ is obtained, this is introduced into the high-concentration CO₂ absorption solution tank 22, and then introduced into the anode storage liquid tank 32, and finally introduced into the anode chamber 312 for electrolysis.

[0046] In the cathode chamber 311, a hydrogen evolution reaction occurs to obtain H₂ and a K₂CO₃-KOH cathode discharge solution with increased KOH concentration, which is introduced into the cathode liquid tank 34 and returned to the absorption tower 11 to continue collecting low-concentration CO₂. In the anode chamber 312, an oxygen evolution reaction occurs to obtain O₂, CO₂ and a low-concentration K₂CO₃-medium-concentration KHCO₃ mixed solution, which is introduced into the anode storage liquid tank 32, circulated and introduced into the anode chamber 312 for electrolysis. The electrolytic separator is a porous polymer separator with a surface polymer carboxylic acid ion resin layer.

[0047] Here, the first partial low-concentration CO₂ absorption solution is 50% of the low-concentration CO₂ absorption solution, the cathode liquid is a mixed solution of 2M K₂CO₃ and 5M KOH, and the anode liquid is a mixed solution of 3M K₂CO₃ and 1M KHCO₃.

[0048] [Example 2] Examples 2 to 6 are different from Example 1 in that the ion concentrations in the cathode liquid and the anode liquid are different, and the details are shown in Table 1.

Table 1

[0049] [Example 7] Example 7 is different from Example 1 in that the first partial low-concentration CO₂ absorption solution is 10% of the low-concentration CO₂ absorption solution.

[0050] [Example 8] Example 8 is different from Example 1 in that the first partial low-concentration CO2 absorbent is 90% of the low-concentration CO2 absorbent.

[0051] [Comparative Example 1] CO2 in a wide concentration range was collected with an aqueous KOH solution, K2CO3 was obtained and electrolysis was carried out. As the electrolysis separator, an ion exchange resin membrane was used. At the anode, a mixed solution of KHCO3 and K2CO3, and a CO2 / O2 mixed gas were generated, and at the cathode, H2 and a regenerated KOH solution were obtained.

[0052] Examples 1 to 8 and Comparative Examples 1 to 2 were all electrolyzed at a current density of 2000 A / m 2 (Faraday efficiency was 100%). When the CO2 collection amount was 1 kg, the H2 yield, O2 yield, KOH regeneration amount, and electrolysis energy consumption are shown in Table 2.

Table 2

[0053] From the above, compared with the comparative examples, in the examples, since the method and apparatus for CO2 collection combined with hydrogen production according to the present invention were used, by using an alkaline solution as an absorbent, absorption and collection of CO2 in a wide concentration range of low / high-concentration CO2 were realized. Also, by electrolyzing the absorption product of low / high-concentration CO2 with a non-ionic separator and combining hydrogen production, regeneration of the absorbent was realized, high-concentration CO2 was obtained, and by-products H2 and O2 could be obtained. The present invention employs a low-concentration CO2 absorbent as the cathode electrolyte and a high-concentration CO2 absorbent as the anode electrolyte, and the increase in the CO3 2- concentration at the electrolysis cathode can suppress the substance diffusion caused by the concentration difference. Therefore, the diffusion of HCO3 - , CO3 2- at the electrolysis anode to the cathode is reduced, and also, since CO3 2- with a higher charge amount generates electromigration preferentially over OH - , OH -It is possible to reduce the electromigration to the anode. It is not necessary to use an ionic separator, which can significantly reduce the cost of the electrolytic cell, avoid strict restrictions on the ion-exchange membrane for the electrolytic solution and the electrolytic cell, realize the recycling of the collected liquid and the regeneration of the alkaline absorbent, and further reduce the CO2 capture cost. In summary, the method of the present invention can achieve the capture of CO2 in a wide concentration range, perform electrolysis using a non-ionic separator, realize the regeneration of the absorbent while coupling hydrogen production, reduce the CO2 capture cost in a wide concentration range, obtain by-products H2 and O2, and reduce the hydrogen production cost.

[0054] The above are only preferred embodiments of the present invention and do not limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should all be included within the protection scope of the present invention.

Description of Reference Numerals

[0055] 1 Low-concentration CO2 absorption unit 2 High-concentration CO2 absorption unit 3 Electrolysis unit 11 Low-concentration absorption tower 21 High-concentration absorption tower 22 High-concentration CO2 absorbent tank 31 Electrolytic cell 32 Anode liquid storage tank 33 Cathode feed liquid tank 34 Cathode discharge liquid tank 311 Cathode chamber 312 Anode chamber 313 Non-ionic separator

Claims

1. A method for carbon capture combined with hydrogen production, comprising: Using a solution of an alkali metal hydroxide to collect low-concentration CO ２ and obtaining a low-concentration CO ２ absorbent solution in step S1, wherein the low-concentration CO ２ absorbent solution contains an alkali metal carbonate and the alkali metal hydroxide in step S1, the low-concentration CO ２ The absorbent is divided into a first-part low-concentration CO ２ absorbent and a second-part low-concentration CO ２ absorbent, and in step S2 of obtaining a high-concentration CO ２ absorbent by collecting high-concentration CO ２ using the first-part low-concentration CO ２ absorbent, the high-concentration CO ２ absorbent includes the alkali metal carbonate and the alkali metal bicarbonate in step S2 the second part of low-concentration CO ２ using the absorbent solution as the cathode solution, and the high-concentration CO ２ using the absorbent solution as the anode solution, and performing electrolysis using a nonionic separator as the separator, so that H is obtained at the electrolytic cathode ２ and the cathode effluent is obtained, and O is obtained at the electrolytic anode ２ , CO ２ and the anode effluent are obtained, and step S3 of returning the cathode effluent to step S1, wherein the cathode effluent contains the alkali metal carbonate and the alkali metal hydroxide, and the anode effluent contains the alkali metal carbonate and the alkali metal hydrogen carbonate, including step S3 A method for carbon capture combined with hydrogen production, characterized in that.

2. The alkali metal hydroxide is KOH, and the alkali metal carbonate is K ２ CO ３ and the alkali metal bicarbonate is KHCO ３ or Or The alkali metal hydroxide is NaOH, and the alkali metal carbonate is Na ２ CO ３ and the alkali metal hydrogen carbonate is NaHCO ３ . The method for carbon capture combined with hydrogen production according to claim 1, characterized in that.

3. In the step S2, the first partial low-concentration CO in terms of volume percentage ２ absorbent liquid is the low-concentration CO ２ in an amount of 10% to 90% of the absorbent liquid. The method for carbon capture combined with hydrogen production according to claim 1 or 2, characterized in that.

4. Step S3 further includes performing electrolysis using the anode effluent as the anode solution. Preferably, in the cathode solution, the concentration of carbonate is 0.1 to 6 M, and the concentration of hydroxide is 0.1 to 10 M. More preferably, in the cathode solution, the concentration of carbonate is 0.5 to 3 M, and the concentration of hydroxide is 3 to 7 M. Preferably, in the anode solution, the concentration of carbonate is 0.1 to 6.5 M, and the concentration of bicarbonate is 0.1 to 3 M. More preferably, in the anode solution, the concentration of carbonate is 2 to 5 M, and the concentration of bicarbonate is 0.6 to 1.5 M. The method for carbon capture combined with hydrogen production according to any one of claims 1 to 3, characterized in that.

5. The non-ionic separator is one or more of a porous polymer separator, a Zirfon film, a polyphenylene sulfide film, a polysulfone film, and a polyethersulfone film. Preferably, the non-ionic separator is a porous polymer separator. More preferably, the surface polymer layer of the porous polymer separator is one or more of a carboxylic acid ion resin layer, polyphenylene sulfide, polysulfone, and polyethersulfone. The method for carbon capture combined with hydrogen production according to any one of claims 1 to 4, characterized in that.

6. An apparatus for carbon capture combined with hydrogen production, with low-concentration CO ２ an absorption unit (1), high-concentration CO ２ an absorption unit (2), and an electrolysis unit (3), and comprising the low-concentration CO ２ The absorption unit (1) has an alkali metal hydroxide solution inlet, a low-concentration CO ２ containing first target raw material inlet, a first partial low-concentration CO ２ absorbing liquid outlet, a second partial low-concentration CO ２ absorbing liquid outlet, and a first waste gas outlet, and the low-concentration CO ２ The absorption unit (1) uses a solution of an alkali metal hydroxide to collect low-concentration CO ２ to obtain a low-concentration CO ２ absorbing liquid, and the low-concentration CO ２ absorbing liquid contains an alkali metal carbonate and the alkali metal hydroxide, The high-concentration CO ２ The absorption unit (2) has a first partial low-concentration CO ２ absorbent inlet, a high-concentration CO ２ containing second target raw material inlet, a high-concentration CO ２ absorbent outlet, and a second waste gas outlet, and the first partial low-concentration CO ２ absorbent inlet is connected to the first partial low-concentration CO ２ absorbent outlet, and the high-concentration CO ２ The absorption unit (2) uses the first partial low-concentration CO ２ absorbent to collect high-concentration CO ２ and obtain a high-concentration CO ２ absorbent, and the high-concentration CO ２ absorbent contains the alkali metal carbonate and the alkali metal bicarbonate, The electrolysis unit (3) has a cathode liquid inlet, a non-ionic separator, an anode liquid inlet, a cathode discharge liquid outlet, an anode discharge liquid outlet, an H ２ outlet, and an O ２ / CO ２ mixed gas outlet. The cathode liquid inlet is connected to the second partial low-concentration CO ２ absorbent liquid outlet. The cathode liquid outlet is connected to the alkali metal hydroxide solution inlet. The anode liquid inlet is connected to the high-concentration CO ２ absorbent liquid outlet. The electrolysis unit (3) is configured to electrolyze the second partial low-concentration CO ２ absorbent liquid and the high-concentration CO ２ absorbent liquid to obtain H ２ and cathode discharge liquid at the electrolysis cathode and obtain O ２ , CO ２ and anode discharge liquid at the electrolysis anode. The cathode discharge liquid contains the alkali metal carbonate and the alkali metal hydroxide, and the anode discharge liquid contains the alkali metal carbonate and the alkali metal bicarbonate. An apparatus for carbon capture combined with hydrogen production, characterized in that.

7. the low-concentration CO ２ The absorption unit (1) includes a low-concentration absorption tower (11). The top of the low-concentration absorption tower (11) has the alkali metal hydroxide solution inlet and the first waste gas outlet. The bottom of the low-concentration absorption tower (11) has the low-concentration CO ２ containing the first capture target raw material inlet, the first partial low-concentration CO ２ absorption liquid outlet and the second partial low-concentration CO ２ absorption liquid outlet, and The high-concentration CO ２ The absorption unit (2) includes a high-concentration absorption tower (21). The top of the high-concentration absorption tower (21) has the first partial low-concentration CO ２ absorbent liquid inlet and the second waste gas outlet. The bottom of the high-concentration absorption tower (21) has the high-concentration CO ２ containing second collection target raw material inlet and the high-concentration CO ２ absorbent liquid outlet, The apparatus for carbon capture combined with hydrogen production according to claim 6, characterized in that.

8. The electrolysis unit (3) includes an electrolytic cell (31). The electrolytic cell (31) has a cathode chamber (311) and an anode chamber (312). An anionic separator (313) is installed between the cathode chamber (311) and the anode chamber (312). An electrolytic cathode is installed in the cathode chamber (311), and an electrolytic anode is installed in the anode chamber (312). The cathode chamber (311) has the cathode liquid inlet, the cathode discharge liquid outlet, and the H ２ outlet. The anode chamber (312) has the anode liquid inlet, the anode discharge liquid outlet, and the O ２ / CO ２ mixed gas outlet. The apparatus for carbon capture combined with hydrogen production according to claim 6 or 7, characterized in that.

9. the high-concentration CO ２ The absorption unit (2) contains high-concentration CO ２ and further includes an absorption liquid tank (22), and the high-concentration CO ２ The absorption liquid tank (22) is installed in a pipeline connecting the anolyte inlet and the high-concentration CO ２ absorption liquid outlet, and is located on the absorption liquid outlet side of the high-concentration CO ２ ​ The apparatus for carbon capture combined with hydrogen production according to any one of claims 6 to 8, characterized in that.

10. The electrolysis unit (3) The cathode liquid inlet and the second partial low-concentration CO ２ A cathode liquid supply tank (33) installed in a pipeline connecting the absorption liquid outlet, and / or A cathode effluent tank (34) installed in a pipeline connecting the cathode solution outlet and the alkali metal hydroxide solution inlet, and / or The anolyte inlet and the high-concentration CO ２ An anolyte storage tank (32) installed in a pipeline connecting the absorption liquid outlet and located on the anolyte inlet side is further included. The apparatus for carbon capture combined with hydrogen production according to any one of claims 6 to 9, characterized in that...

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