Electrochemical enhanced evaporation crystallization closed loop carbon dioxide recovery method and apparatus

Abstract

The present application relates to the technical field of carbon dioxide emission reduction, and relates to an electrochemical enhanced evaporation crystallization closed-loop carbon dioxide recovery method and device. A low electric field is applied to an electrochemical absorption unit containing alkali absorption liquid, so that carbon dioxide is accelerated to convert into carbonate or bicarbonate in potassium hydroxide / potassium carbonate solution. Subsequently, the carbonate-rich solution is introduced into an evaporation-interface crystallization unit composed of hydrophilic fibers, industrial waste gas waste heat is used to drive interface evaporation, and efficient crystallization of potassium carbonate is realized in the designated area of the fibers. The aqueous solution of solid potassium carbonate and / or the uncrystallized mother liquor is sent into an electrochemical regeneration unit, potassium hydroxide is regenerated by electrochemical method, and high-purity carbon dioxide is released, so that the closed-loop process of absorption-crystallization-regeneration is realized. The present application has the advantages of low regeneration energy consumption, avoidance of high-temperature calcination, efficient and controllable crystallization, and modulization and amplification, and is suitable for carbon dioxide-containing waste gas emission reduction and resource utilization in the steel, chemical, power and other industries.

Description

An electrochemically enhanced evaporation crystallization closed-loop carbon dioxide recovery method and apparatus Technical Field

[0001] This invention belongs to the field of carbon dioxide capture and resource utilization technology, and particularly relates to an electrochemically enhanced evaporation crystallization closed-loop carbon dioxide recovery method and apparatus. Background Technology

[0002] Industrial waste gases emitted from the steel, chemical, cement, and thermal power industries typically contain 5%-20% carbon dioxide, making them a significant anthropogenic source of carbon emissions. Therefore, carbon dioxide capture from industrial waste gases is crucial for carbon dioxide emission reduction. Existing carbon dioxide capture technologies mainly include amine absorption, traditional potassium carbonate methods, solid adsorbent methods, and some electrochemical absorption methods. The amine method is a mature process, but it suffers from high regeneration energy consumption, severe solvent evaporation and degradation, equipment corrosion, and significant environmental problems. The potassium carbonate method has good stability, but its absorption rate is limited, and regeneration usually requires high temperatures. Solid adsorbent methods are limited in large-scale applications due to mass transfer rates, adsorption / desorption rates, and material costs. While some electrochemical methods avoid high-temperature regeneration, their absorption rates are limited, and overall energy consumption remains high.

[0003] On the other hand, evaporation-driven interfacial crystallization technology can utilize waste heat to construct a highly supersaturated region at the gas-liquid interface, allowing carbon dioxide to directly react with alkaline solutions to form carbonate crystals, achieving partial "passive" carbon dioxide capture and possessing the potential for low regeneration energy consumption. However, existing evaporation crystallization systems are mostly open structures with uncontrollable absorption rates and random crystallization locations, easily leading to equipment scaling and clogging, and a closed-loop process integrating absorption and regeneration units has not yet been formed.

[0004] Therefore, there is a need for a carbon dioxide recovery method and device that can effectively couple electrochemical enhanced absorption, interfacial evaporation crystallization and electrochemical regeneration, so as to achieve efficient and low-energy closed-loop capture of carbon dioxide from industrial waste gas without relying on high-temperature calcination. Summary of the Invention

[0005] The purpose of this invention is to address the above-mentioned problems by proposing an electrochemically enhanced evaporation crystallization closed-loop carbon dioxide recovery method and apparatus. By applying a low-potential electric field in an alkaline absorbent to enhance carbon dioxide absorption and carbonate formation, and utilizing capillary evaporation to achieve rapid crystallization of potassium carbonate in a designated area, the potassium carbonate is then converted into potassium hydroxide and high-purity carbon dioxide is released through an electrochemical regeneration unit. This constructs a fully electrically driven carbon dioxide recovery technology system that is free from high-temperature calcination, has low energy consumption, and is suitable for modular scale-up.

[0006] The technical solution for achieving the objective of this invention is as follows:

[0007] This invention provides an electrochemically enhanced evaporation-crystallization closed-loop carbon dioxide recovery method, comprising the following steps:

[0008] (1) Electrochemical enhanced absorption: The industrial waste gas containing carbon dioxide is passed into an electrochemical absorption unit equipped with a pair of electrodes and a circulating absorption liquid channel. The absorption liquid is an aqueous solution of potassium hydroxide and / or an aqueous solution of potassium carbonate. The unit is operated under a potential difference of 0.1-1.0V to accelerate the conversion of carbon dioxide into carbonate and / or bicarbonate in the alkaline solution to obtain a carbonate-rich solution.

[0009] (2) Evaporation-interface crystallization: The carbonate-rich solution obtained in step (1) is introduced into the evaporation-interface crystallization unit. The crystallization unit is composed of several bundles of hydrophilic capillary fibers. The absorbent rises along the capillary fibers to form a liquid film. Under the residual heat of industrial waste gas or hot air, interfacial evaporation occurs. The concentration of potassium ions and carbonate ions in the liquid film locally increases to supersaturation and crystallizes in a designated area on the fiber surface to generate solid potassium carbonate.

[0010] (3) Electrochemical regeneration: The aqueous solution of solid potassium carbonate obtained in step (2) and / or the uncrystallized mother liquor are sent to the electrochemical regeneration unit. Under the action of an external electric field, potassium carbonate is converted into potassium hydroxide and high-purity carbon dioxide is released. The regenerated potassium hydroxide aqueous solution is returned to the electrochemical absorption unit in step (1) as an absorbent, thus forming a closed loop of absorption-crystallization-regeneration.

[0011] Preferably, the volume fraction of carbon dioxide in the industrial waste gas in step (1) is 5%-20%, and the temperature of the electrochemical absorption unit is 40-120℃.

[0012] Preferably, the concentration of the potassium hydroxide aqueous solution and / or potassium carbonate aqueous solution in step (1) is 1-4 mol / L.

[0013] Preferably, the solid potassium carbonate obtained in step (2) is peeled off from the fiber surface by mechanical vibration, scraping or air backflushing, and transported together with the uncrystallized mother liquor to the electrochemical regeneration unit in step (3).

[0014] Preferably, the hydrophilic capillary fiber in step (2) is at least one of polyester capillary fiber, polypropylene capillary fiber, polyvinylidene fluoride capillary fiber, and polyamide capillary fiber. The surface of the hydrophilic capillary fiber is modified by plasma treatment, chemical oxidation, or hydrophilic coating to enhance liquid film stability and interfacial evaporation capacity. The diameter of a single fiber is 50-500 μm, and the fiber bundle height is 5-50 cm.

[0015] Preferably, the operating current density of the electrochemical regeneration unit is 20-300 A / m. 2 The energy consumption for electrochemical regeneration of one mole of carbon dioxide (CO2) is 4-6 kJ / mol.

[0016] Preferably, the lower end of the hydrophilic capillary fiber of the evaporation-interface crystallization unit is immersed in a carbonate-rich solution, while the upper end is exposed to industrial waste gas or hot air. The interfacial evaporation increases the concentration of potassium ions and carbonate ions in the liquid film, forming a supersaturated state and creating continuous or discontinuous potassium carbonate crystallization bands on the fiber surface. A weak electric field can be applied by auxiliary electrodes around the fiber to further control the crystallization position and crystal morphology.

[0017] Another aspect of the present invention provides an apparatus for implementing the above-described electrochemically enhanced evaporation-crystallization closed-loop carbon dioxide recovery method, comprising:

[0018] An electrochemical absorption unit, comprising an absorbent storage tank, an absorber, and a carbonate-rich solution storage tank;

[0019] An evaporation-interface crystallization unit is provided, comprising a liquid tank and several bundles of hydrophilic capillary fibers connected to the liquid tank. The liquid tank has a carbonate-rich solution inlet and a solid potassium carbonate crystal outlet. The outlet of the carbonate-rich solution storage tank is connected to the carbonate-rich solution inlet of the liquid tank.

[0020] An electrochemical regeneration unit includes a regenerated potassium hydroxide solution storage tank and an electrolytic cell. The electrolytic cell is provided with a feed inlet, a regenerated potassium hydroxide solution outlet, and a carbon dioxide outlet. The solid potassium carbonate crystal outlet of the liquid storage tank is connected to the feed inlet of the electrolytic cell.

[0021] The circulation system includes an absorbent circulation pipeline and a circulation pump, which are used to transport the regenerated potassium hydroxide solution generated by the electrochemical regeneration unit back to the absorbent storage tank, forming a closed-loop circulation.

[0022] Preferably, the absorber has a shell, porous electrodes arranged on both sides inside the shell, and gas and liquid channels located between the electrodes. The shell is provided with an industrial waste gas inlet, a carbonate-rich solution outlet, an absorbent inlet, and an absorbent outlet. The electrodes are porous carbon electrodes or conductive ceramic electrodes, and the electrode spacing is 0.5-5 mm.

[0023] Preferably, the electrolytic cell has a parallel plate or narrow-pitch flow channel structure; more preferably, it is a three-chamber electrolytic cell or a two-chamber electrolytic cell using a bipolar membrane. In this case, the middle chamber or acidification side is used to release carbon dioxide, while the alkaline side outputs potassium hydroxide solution. By adjusting the pH and potential in different chambers, potassium carbonate is decomposed into carbon dioxide and potassium hydroxide.

[0024] Preferably, the evaporation-interface crystallization unit further includes auxiliary electrodes disposed on both sides or below the fiber and gas channels for introducing hot waste gas or hot air.

[0025] Preferably, it also includes a control system for controlling the potential, current, flow rate and temperature of each unit.

[0026] The advantages and beneficial effects of this invention are:

[0027] (1) By using a low potential electric field to regulate the ion hydration structure and distribution in the alkaline solution, the conversion rate of carbon dioxide in potassium hydroxide / potassium carbonate solution can be increased, thereby achieving efficient absorption;

[0028] (2) By utilizing capillary fiber interface evaporation to construct a local high supersaturation zone, potassium carbonate can be rapidly crystallized within a controllable area, reducing the risk of scaling and clogging;

[0029] (3) The electrochemical regeneration unit completes the regeneration of potassium carbonate and release of carbon dioxide under medium and low temperature conditions, avoiding the traditional high temperature calcination process and significantly reducing energy consumption;

[0030] (4) The whole process is driven by electricity and waste heat, which is easy to couple with renewable energy to realize the low-carbon capture and resource utilization of carbon dioxide in industrial waste gas.

[0031] In summary, this invention has the advantages of low regeneration energy consumption, avoidance of high-temperature calcination, efficient and controllable crystallization, and modular scale-up, and is suitable for emission reduction and resource utilization of carbon dioxide-containing waste gas in industries such as steel, chemical, and power. Attached Figure Description

[0032] Figure 1 is a schematic diagram of the apparatus for realizing the electrochemically enhanced evaporation crystallization closed-loop carbon dioxide recovery method of the present invention;

[0033] Figure 2 is a schematic diagram of the electrochemical absorption unit of the present invention;

[0034] Figure 3 is a schematic diagram of the evaporation-interface crystallization unit of the present invention;

[0035] Figure 4 is a schematic diagram of the electrochemical regeneration unit of the present invention. Detailed Implementation

[0036] The present invention will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.

[0037] Example 1: Under the baseline operating condition

[0038] An electrochemically enhanced evaporation-crystallization closed-loop carbon dioxide recovery method includes the following steps:

[0039] (1) The absorbent was a 2.0 mol / L potassium hydroxide aqueous solution, which was circulated in the electrochemical absorption unit at a rate of 1.2 L / min. The simulated industrial waste gas was a mixture of 15% CO2 and 85% N2 by volume, at a temperature of 70℃. The absorber used a 2 mm-spaced parallel plate porous carbon electrode, and a potential difference of 0.5 V was applied across the electrode to obtain a carbonate-rich solution. Compared with the control without an electric field, the carbonate / bicarbonate equilibrium concentration in the solution increased by 30%, and the CO2 concentration in the gas phase decreased significantly.

[0040] (2) A carbonate-rich solution was continuously fed into the evaporation-interface crystallization unit. Hydrophilically modified polyester (PET) capillaries, with a fiber bundle height of 20 cm and a single filament diameter of 150 μm, were used. The hot air temperature was 75 °C and the wind speed was 1.0 m / s. After running for 30 min to reach a steady state, a stable potassium carbonate crystallization zone was formed in the region 9-11 cm above the liquid surface. The collected solid potassium carbonate was dissolved to obtain a 2.0 mol / L potassium carbonate solution.

[0041] The hydrophilic modification steps for polyester (PET) capillary fibers include:

[0042] ① Pre-treatment cleaning

[0043] PET capillary fibers were ultrasonically cleaned in ethanol and deionized water for 10-20 minutes each to remove oil and processing aids from the fiber surface. After cleaning, they were dried at 60 ℃ for later use.

[0044] ② Alkaline hydrolysis roughening treatment

[0045] The cleaned PET capillary fibers are immersed in a 1-3% sodium hydroxide aqueous solution and treated at 40-60℃ for 10-30 minutes to induce a slight hydrolysis reaction on the fiber surface, introduce polar groups such as carboxyl groups, and form a micro-rough structure. After treatment, the fibers are repeatedly rinsed with a large amount of deionized water until the washing solution is neutral.

[0046] ③ Hydrophilic functionalization treatment

[0047] The alkali-treated PET capillary fibers are immersed in a hydrophilic modification solution for surface functionalization. The hydrophilic modification solution is a solution containing hydrophilic polymers or precursors of hydrophilic functional groups. A stable hydrophilic layer is formed on the fiber surface by immersion to further improve the wettability and liquid film spreading ability of the fiber surface.

[0048] ④ Curing and drying

[0049] The modified PET capillary fibers are dried at 60-80℃ for 1-3 hours to allow the hydrophilic modification layer to be stably attached to the fiber surface, thus obtaining hydrophilic modified PET capillary fibers.

[0050] (3) A 2.0 mol / L potassium carbonate solution was fed into a three-chamber electrolytic cell for regeneration at 80 A / m 2 Operating at current density.

[0051] The CO2 capture flux is 4.0 mol·m -2 ·h -1 The CO2 conversion rate is 30%, the concentration of the potassium carbonate solution after the crystals are dissolved is 2.0 mol / L, the electrochemical regeneration energy consumption per mole of CO2 is 5.0 kJ / mol, the purity of potassium carbonate crystals is 97%, and the device can operate stably for no less than 100 hours, during which the fluctuation of each key operating parameter is less than 5%.

[0052] Example 2: High-throughput operation at increased alkali concentration

[0053] An electrochemically enhanced evaporation-crystallization closed-loop carbon dioxide recovery method includes the following steps:

[0054] (1) The concentration of the absorbent was increased to 3.0 mol / L potassium hydroxide, while the rest of the structure remained the same as in Example 1. The simulated tail gas integral was 12% CO2 and 88% N2, the temperature was 75℃, a potential difference of 0.6V was applied across the electrodes, and the circulation flow rate was maintained at 1.2L / min to obtain a carbonate-rich solution. Compared with the condition without an electric field, the carbonate / bicarbonate equilibrium concentration in the carbonate-rich solution increased by 40%.

[0055] (2) The carbonate-rich solution enters the evaporation-interface crystallization unit. The hydrophilically modified polypropylene (PP) capillary fibers have a fiber bundle height of 25 cm and a single filament diameter of 150 μm. The hot air temperature is 80 °C and the wind speed is 1.3 m / s. In the steady state, a continuous potassium carbonate crystallization zone is formed in the region 13-16 cm from the liquid surface. The crystallization layer is significantly thicker than that in Example 1.

[0056] The hydrophilic modification steps of the above-mentioned polypropylene (PP) capillary fibers include:

[0057] ① Pre-treatment cleaning

[0058] PP capillary fibers were ultrasonically cleaned in ethanol and deionized water for 10-20 minutes each to remove oil and processing aids from the fiber surface. After cleaning, they were dried at 60 ℃ for later use.

[0059] ② Surface activation treatment

[0060] The cleaned PP capillary fibers are placed in a low-pressure plasma reaction chamber, and air or oxygen is introduced. The fiber is then discharged with a radio frequency power of about 50-100W for 1-5 minutes to introduce polar functional groups such as hydroxyl and carbonyl groups on the fiber surface and to slightly etch and roughen it, thereby improving the surface energy and wettability.

[0061] ③ Hydrophilic functionalization treatment

[0062] PP capillary fibers that have undergone surface activation treatment are immersed in a hydrophilic modification solution for surface functionalization. The hydrophilic modification solution is a solution containing hydrophilic polymers or precursors with hydrophilic functional groups. A stable hydrophilic modification layer is formed on the fiber surface by impregnation to improve the hydrophilicity and wettability of the fiber surface.

[0063] ④ Curing and drying

[0064] After being rinsed with deionized water, the modified PP capillary fibers are dried at 60-80℃ under vacuum for 1-3 hours to allow the hydrophilic modification layer to be stably attached to the fiber surface, thus obtaining hydrophilic modified PP capillary fibers.

[0065] (3) After dissolving the crystals, a 2.2 mol / L potassium carbonate solution was obtained and fed into a bipolar membrane electrolyzer at 100 A / m. 2 Regeneration is performed using the current density.

[0066] Under this operating condition, the CO2 capture flux is 5.0 mol·m⁻². -2 ·h -1 The CO2 conversion rate is 36%, the concentration of the product potassium carbonate solution is 2.2 mol / L, the regeneration energy consumption per mole of CO2 is 4.5 kJ / mol, the purity of potassium carbonate crystals is 97%, and the system can operate continuously and stably for at least 120 hours without significant performance degradation.

[0067] Example 3: Longitudinal weak electric field modulation of crystal zone position

[0068] An electrochemically enhanced evaporation-crystallization closed-loop carbon dioxide recovery method includes the following steps:

[0069] (1) The absorbent was still 2.0 mol / L potassium hydroxide, and the electrochemical absorption unit structure was the same as in Example 1. The tail gas containing 15% CO2 and 85% N2 was treated under a potential difference of 0.5 V and a circulation flow rate of 1.0 L / min to obtain a carbonate-rich solution. Compared with the condition without an electric field, the carbonate / bicarbonate equilibrium concentration in the carbonate-rich solution increased by 40%.

[0070] (2) A carbonate-rich solution was fed into the evaporation-interface crystallization unit. The fiber bundle was 25 cm high and made of hydrophilically modified polyester capillary fibers (the hydrophilic modification method was the same as in Example 1). Auxiliary electrodes were arranged at the lower and upper ends of the fibers to form a weak electric field gradient from bottom to top (0.3V at the lower end and grounded at the upper end). The hot air temperature was maintained at 75℃ and the wind speed was 1.0 m / s. After steady-state operation, the potassium carbonate crystallization band shifted from about 10 cm without an auxiliary electric field to 15 cm, the band width narrowed significantly, and the crystal size became more uniform.

[0071] (3) After dissolving the crystals, a 2.0 mol / L potassium carbonate solution was obtained and fed into a three-chamber electrolytic cell at 80 A / m 2 Current density regeneration.

[0072] Under this operating condition, the CO2 capture flux is 4.1 mol·m⁻¹. -2 ·h -1 The CO2 conversion rate is 30%, the concentration of the product potassium carbonate solution is 2.0 mol / L, the regeneration energy consumption per mole of CO2 is 5.2 kJ / mol, the purity of potassium carbonate crystals is 97%, the system can operate stably for no less than 90 hours, and the position and morphology of the crystallization zone maintain good reproducibility during operation.

[0073] Example 4: Hollow fiber dual-interface evaporation-enhanced crystallization

[0074] An electrochemically enhanced evaporation-crystallization closed-loop carbon dioxide recovery method includes the following steps:

[0075] (1) The absorbent was 2.5 mol / L potassium hydroxide. Using the same parallel-plate porous carbon electrode structure as in Example 1, tail gas with a volume fraction of 12% CO2 and 88% N2 was treated at a circulation flow rate of 1.5 L / min at a temperature of 70 °C. A potential difference of 0.6 V was applied across the electrode to obtain a carbonate-rich solution. Compared to the condition without an electric field, the carbonate / bicarbonate equilibrium concentration in the carbonate-rich solution increased by 35%.

[0076] (2) A carbonate-rich solution is continuously fed into the evaporation-interface crystallization unit, which uses hollow polypropylene capillary fibers with an outer diameter of 300 μm, a wall thickness of 50 μm, and a fiber bundle height of 22 cm. The solution forms a liquid film on both the inner and outer walls simultaneously. The hot air temperature is 75℃ and the wind speed is 1.0 m / s. Under steady state, a potassium carbonate crystallization zone is formed simultaneously in the region 12-15 cm from the liquid surface at both the inner and outer interfaces.

[0077] (3) Electrochemical regeneration: The crystals are dissolved to obtain a 2.3 mol / L potassium carbonate solution, which is then fed into a bipolar membrane electrolyzer at 120 A / m 2 Regeneration is performed at current density.

[0078] Under these conditions, the CO2 capture flux is 5.5 mol·m⁻¹. -2 ·h -1 The CO2 conversion rate is 38%, the concentration of the product potassium carbonate solution is 2.3 mol / L, the regeneration energy consumption per mole of CO2 is 4.8 kJ / mol, the purity of potassium carbonate crystals is 97%, and the system can operate stably and continuously for at least 96 hours.

[0079] Example 5: Operation under SO2-containing industrial exhaust gas conditions

[0080] An electrochemically enhanced evaporation-crystallization closed-loop carbon dioxide recovery method includes the following steps:

[0081] (1) The absorbent was 2.0 mol / L potassium hydroxide. The electrochemical absorption unit structure was the same as in Example 1. Simulated steel tail gas was treated in the electrochemical absorption unit at a circulation rate of 1.2 L / min. The tail gas composition was 12% CO2, 70 ppm SO2, and equilibrium N2 by volume, at a temperature of 90 °C. The absorber still used porous carbon electrodes with a 2 mm spacing. A potential difference of 0.5 V was applied across the electrodes to obtain a carbonate-rich solution. Compared to the condition without an electric field, the carbonate / bicarbonate equilibrium concentration in the carbonate-rich solution increased by 40%.

[0082] (2) The carbonate-rich solution was fed into the evaporation-interface crystallization unit. The hydrophilically modified polyvinylidene fluoride (PVDF) capillary fibers with a fiber bundle height of 20 cm, hot air temperature of 75 °C and wind speed of 1.0 m / s, formed a stable potassium carbonate crystallization zone in the area 10-12 cm from the liquid surface. No obvious scaling aggravation caused by SO2 was observed.

[0083] The hydrophilic modification steps of the above-mentioned polyvinylidene fluoride (PVDF) capillary fibers include:

[0084] ① Pre-treatment cleaning

[0085] PVDF capillary fibers were ultrasonically cleaned in ethanol and deionized water for 10-20 minutes each to remove oil and processing aids from the fiber surface. After cleaning, the fibers were dried at 60 °C for later use.

[0086] ② Surface activation treatment

[0087] The cleaned PVDF capillary fibers are placed in a low-pressure plasma reaction chamber, and an inert gas or oxygen-containing gas is introduced. The mixture is treated at 20-50 W for tens of seconds to several minutes to introduce polar groups on the fiber surface and improve surface wettability.

[0088] ③ Hydrophilic functionalization treatment

[0089] PVDF capillary fibers that have undergone surface activation treatment are immersed in a hydrophilic modification solution for surface functionalization treatment. The hydrophilic modification solution is a solution containing hydrophilic monomers, hydrophilic polymers or precursors of hydrophilic functional groups. A stable hydrophilic layer is formed on the fiber surface by grafting or coating to improve the hydrophilicity and wettability of the fiber surface.

[0090] ④ Curing and drying

[0091] After being rinsed with deionized water, the modified PVDF capillary fibers are dried at 60-80℃ under vacuum for 1-3 hours to allow the hydrophilic modification layer to be stably attached to the fiber surface, thus obtaining hydrophilic modified PVDF capillary fibers.

[0092] (3) After dissolving the crystals, a potassium carbonate solution of 1.9-2.0 mol / L is obtained and fed into a three-chamber electrolytic cell at 80 A / m 2 Current density regeneration.

[0093] Under these conditions, the CO2 capture flux is 3.8 mol·m⁻¹. -2 ·h -1 The CO2 conversion rate is 28%, the concentration of the product potassium carbonate solution is 1.9-2.0 mol / L, the regeneration energy consumption per mole of CO2 is 5.5 kJ / mol, the purity of potassium carbonate crystals is 95%-96%, and the system can operate stably for no less than 72 hours under conditions containing SO2.

[0094] Example 6: Crystallization of superhydrophilic fibers under high humidity conditions

[0095] An electrochemically enhanced evaporation-crystallization closed-loop carbon dioxide recovery method includes the following steps:

[0096] (1) The absorbent was 1.8 mol / L potassium hydroxide. The electrochemical absorption unit had the same structure as in Example 1. The gas was circulated at 1.0 L / min to treat a tail gas with a volume fraction of 10% CO2. The gas temperature was 70°C, and a potential difference of 0.5 V was applied between the electrodes to obtain a carbonate-rich solution. Compared to the condition without an electric field, the carbonate / bicarbonate equilibrium concentration in the obtained carbonate-rich solution was increased by 25%.

[0097] (2) The carbonate-rich solution is fed into the evaporation-interface crystallization unit. Polyamide (PA) capillary fibers with a superhydrophilic coating are used. The fiber height is 20 cm, the ambient air temperature is 70 °C, and the relative humidity is 80%. Under high humidity conditions, the superhydrophilic fiber can still form a uniform and stable thin liquid film. After running for a period of time, a stable crystallization zone is formed in the area 12-14 cm away from the liquid surface.

[0098] (3) After dissolving the crystals, a 1.9 mol / L potassium carbonate solution was obtained and fed into a three-chamber electrolytic cell at 80 A / m 2 Regeneration is achieved using current density.

[0099] Under this high humidity environment, the CO2 capture flux is 3.5 mol·m -2 ·h -1The CO2 conversion rate is 27%, the concentration of the product potassium carbonate solution is 1.9 mol / L, the regeneration energy consumption per mole of CO2 is 5.8 kJ / mol, the purity of potassium carbonate crystals is 96%, and the system maintains small performance fluctuations even after 48 hours of continuous operation.

[0100] Example 7: Double-layer fiber-reinforced crystallization under low-temperature exhaust gas waste heat conditions

[0101] An electrochemically enhanced evaporation-crystallization closed-loop carbon dioxide recovery method includes the following steps:

[0102] (1) The absorbent was 1.5 mol / L potassium hydroxide, which absorbed low-temperature tail gas with a temperature of only 50°C and a volume fraction of 10% CO2 at a flow rate of 1.2 L / min under a potential difference of 0.4 V. The electrochemical absorption unit structure was the same as in Example 1, resulting in a carbonate-rich solution. Compared with the condition without an electric field, the carbonate / bicarbonate equilibrium concentration in the carbonate-rich solution increased by 20%.

[0103] (2) The carbonate-rich solution was fed into the evaporation-interface crystallization unit, which adopted a double-layer fiber structure. The inner layer consisted of hydrophilically modified 120 μm diameter polyester (PET) fine fibers, and the outer layer consisted of hydrophilically modified 300 μm diameter polypropylene (PP) coarse fibers (the hydrophilic modification method was the same as in Example 1). The overall height was 20 cm, the hot air temperature was 50 °C, and the wind speed was 1.0 m / s. Under these low-temperature conditions, a continuous crystallization zone could still be formed in the region 8-10 cm from the liquid surface. The double-layer fiber structure increased the crystallization amount per unit area by 25% compared to the single-layer structure.

[0104] (3) After dissolving the crystals, a 1.7 mol / L potassium carbonate solution was obtained and fed into a three-chamber electrolytic cell at 70 A / m 2 Regeneration at current density.

[0105] Under this operating condition, the CO2 capture flux is 3.2 mol·m⁻¹. -2 ·h -1 The CO2 conversion rate is 25%, the regeneration energy consumption per mole of CO2 is 6.0 kJ / mol, the potassium carbonate crystal purity is 95%-96%, and the system can operate stably for more than 50 hours.

[0106] Example 8: High-throughput operation under high-concentration alkaline solution and high-temperature evaporation

[0107] An electrochemically enhanced evaporation-crystallization closed-loop carbon dioxide recovery method includes the following steps:

[0108] (1) The absorbent was 4.0 mol / L potassium hydroxide. The electrochemical absorption unit structure was the same as in Example 1. In the electrochemical absorption unit, tail gas with a volume fraction of 15% CO2 and 85% N2 was treated at a flow rate of 1.5 L / min and a temperature of 75 °C. A potential difference of 0.7 V was applied between the electrodes to obtain a carbonate-rich solution. Compared with the condition without an electric field, the carbonate / bicarbonate equilibrium concentration in the carbonate-rich solution was significantly increased, by 45%.

[0109] (2) The carbonate-rich solution enters the evaporation-interface crystallization unit composed of hollow fiber bundles. The modified fiber bundles of hollow polyvinylidene fluoride (PVDF) hydrophilic capillary fibers (the hydrophilic modification method is the same as in Example 5) are used. The height is 30cm, the hot air temperature is 80℃, the wind speed is 1.5m / s, and a wide crystallization zone is formed in the area 15-20cm away from the liquid surface in steady state.

[0110] (3) After dissolving the potassium carbonate crystals, a 2.4 mol / L potassium carbonate solution was obtained and fed into a bipolar membrane electrolyzer at 120 A / m. 2 Regeneration is achieved using current density.

[0111] Under this high-flux operating condition, the CO2 capture flux is 6.0 mol·m⁻¹. -2 ·h -1 The CO2 conversion rate is 40%, the concentration of the product potassium carbonate solution is 2.4 mol / L, the regeneration energy consumption per mole of CO2 is 4.2 kJ / mol, the purity of potassium carbonate crystals is 97%, and the system can operate stably for no less than 80 hours.

[0112] Example 9

[0113] As shown in Figure 1, an apparatus for implementing the methods described in Examples 1-8 includes an electrochemical absorption unit, an evaporation-interface crystallization unit, an electrochemical regeneration unit, a circulation system, and a control system.

[0114] The electrochemical absorption unit shown in Figure 2 is used to contact carbon dioxide-containing waste gas with potassium hydroxide / potassium carbonate solution under a low potential electric field to generate a carbonate-rich solution. It includes an absorbent storage tank, an absorber, and a carbonate-rich solution storage tank. The absorber has a shell, porous electrodes arranged on both sides inside the shell, and gas and liquid channels located between the electrodes. The shell is provided with an industrial waste gas inlet, a carbonate-rich solution outlet, an absorbent inlet, and an absorbent outlet. The electrodes are porous carbon electrodes or conductive ceramic electrodes, and the electrode spacing is 0.5-5 mm.

[0115] The evaporation-interface crystallization unit shown in Figure 3 is used to achieve potassium carbonate crystallization on the surface of capillary fibers via interfacial evaporation. The evaporation-interface crystallization unit includes a liquid tank and several bundles of hydrophilic capillary fibers connected to the liquid tank. The liquid tank has a carbonate-rich solution inlet and a solid potassium carbonate crystal outlet; the outlet of the carbonate-rich solution storage tank is connected to the carbonate-rich solution inlet of the liquid tank. The evaporation-interface crystallization unit also includes auxiliary electrodes disposed on both sides or below the fibers and gas channels for introducing hot waste gas or hot air.

[0116] The electrochemical regeneration unit shown in Figure 4 is used to convert potassium carbonate into potassium hydroxide and release carbon dioxide. The unit includes a regenerated potassium hydroxide solution storage tank and an electrolytic cell. The electrolytic cell is equipped with a feed inlet, a regenerated potassium hydroxide solution outlet, and a carbon dioxide outlet. The solid potassium carbonate crystal outlet of the liquid storage tank is connected to the feed inlet of the electrolytic cell. The electrolytic cell has a parallel plate or narrow-pitch flow channel structure, preferably a three-chamber electrolytic cell or a two-chamber electrolytic cell using a bipolar membrane. The middle chamber or acidification side is used to release carbon dioxide, and the alkaline side outputs potassium hydroxide solution. By adjusting the pH and potential in different chambers, potassium carbonate is decomposed into carbon dioxide and potassium hydroxide.

[0117] The circulation system returns the regenerated potassium hydroxide solution to the electrochemical absorption unit. The circulation system includes absorbent circulation pipelines and a circulation pump, used to transport the regenerated potassium hydroxide solution produced by the electrochemical regeneration unit back to the absorbent storage tank, forming a closed-loop circulation. The control system controls the potential, current, flow rate, and temperature of each unit.

[0118] Comparative Example 1

[0119] The only difference from Example 1 is step (1), where electrochemical absorption enhancement is omitted. The same absorbent composition, gas composition, temperature, and flow rate conditions as Example 1 are used, but no external potential difference is applied to the electrodes, maintaining 0V, allowing carbon dioxide absorption to rely entirely on the alkaline absorption reaction of the solution itself. At this point, the carbonate / bicarbonate equilibrium concentration in the carbonate-rich solution is significantly lower than in Example 1. After the carbonate-rich solution enters the evaporation-interface crystallization unit with the same structure and operating conditions, only a thin and discontinuous crystalline layer forms in the region 6-8 cm from the liquid surface, and localized salt blockage easily occurs at the fiber roots. The resulting crystals are dissolved and electrolyzed in a three-chamber electrolytic cell at 80 A·m -2 Current density regeneration.

[0120] The results showed that, without electrochemical absorption enhancement, the CO2 capture flux was only 2.0 mol·m⁻¹. -2 ·h -1The CO2 conversion rate is 15%-18%, the concentration of the product potassium carbonate solution is 1.3-1.5 mol / L, the regeneration energy consumption per mole of CO2 increases to 8.0 kJ / mol, the purity of potassium carbonate crystals is 94%-95%, and the system shows significant performance degradation and increased scaling after less than 40 hours of continuous operation.

[0121] Comparative Example 2

[0122] The only difference from Example 2 is step (2). Instead of using a fiber bundle interface evaporation structure, the carbonate-rich solution is placed in a shallow tank and evaporated on an open liquid surface under 80°C hot air. Due to the lack of a capillary liquid film and local supersaturation concentration effect, crystals randomly precipitate near the liquid surface and gradually form an irregular hard shell, making it difficult to form a spatially controllable crystallization band and hindering continuous peeling. The resulting crystals are dissolved and sent to a bipolar membrane electrolytic cell at 100 A / m 2 Regeneration is achieved using current density.

[0123] The results showed that when simple open evaporation was used instead of the interfacial crystallization structure, the CO2 capture flux was only 1.5-1.8 mol·m⁻¹. -2 ·h -1 The CO2 conversion rate is 12%-15%, the concentration of the product potassium carbonate solution is 1.0-1.2 mol / L, the regeneration energy consumption per mole of CO2 increases to 9-10 kJ / mol, the purity of potassium carbonate crystals is 92%-94%, and the system has to be shut down in less than 24 hours due to scaling and hard shell blockage.

[0124] Comparative Example 3

[0125] The only difference from Example 1 is step (3). In step (3), instead of using an electrochemical regeneration unit, the crystalline solid is calcined and regenerated in a high-temperature furnace at 850°C to release carbon dioxide and restore potassium hydroxide. The calcined solid dissolves again to form a 2.0 mol / L potassium carbonate solution. Based on heat balance and energy consumption calculations, the energy consumption per mole of CO2 for conventional high-temperature calcination regeneration is 350-450 kJ / mol, which is much higher than that of Example 1. Although the absorption and crystallization steps remain unchanged, the CO2 capture flux in this comparative example is still 4.0 mol·m³. -2 ·h -1 The CO2 conversion rate is 30%, the concentration of the product potassium carbonate solution is 2.0 mol / L, and the purity of potassium carbonate crystals is 97%. However, the regeneration energy consumption is extremely high, and the high temperature conditions cause equipment corrosion and salt sintering. The system usually needs to be shut down for maintenance in less than 30 hours.

[0126] The foregoing descriptions are merely exemplary embodiments or examples of the present invention and are not intended to limit the invention. Those skilled in the art will recognize that the present invention can be modified and varied in many ways. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention are included within the scope of the claims of this application.

Claims

1. A closed-loop electrochemical enhanced evaporation-crystallization method for carbon dioxide recovery, characterized in that, The process includes the following steps: (1) Electrochemical enhanced absorption: Industrial waste gas containing carbon dioxide is introduced into the electrochemical absorption unit, and the absorbent is an aqueous solution of potassium hydroxide. The process is operated at a potential difference of 0.4-1.0V to obtain a carbonate-rich solution; (2) Evaporation-interface crystallization: The carbonate-rich solution obtained in step (1) is introduced into the evaporation-interface crystallization unit. The crystallization unit is composed of several bundles of hydrophilic capillary fibers. The absorbent rises along the capillary fibers to form a liquid film. Under the residual heat of industrial waste gas or hot air, interfacial evaporation occurs. The concentration of potassium ions and carbonate ions in the liquid film locally increases to supersaturation and crystallizes in a designated area on the fiber surface to generate solid potassium carbonate; (3) Electrochemical regeneration: The aqueous solution of solid potassium carbonate obtained in step (2) and / or the uncrystallized mother liquor are sent into the electrochemical regeneration unit. Under the action of an external electric field, the aqueous solution of potassium carbonate is converted into an aqueous solution of potassium hydroxide and high-purity carbon dioxide is released. The regenerated aqueous solution of potassium hydroxide is returned to step (1) as the absorbent, thus forming a closed loop of absorption-crystallization-regeneration.

2. The electrochemically enhanced evaporation-crystallization closed-loop carbon dioxide recovery method according to claim 1, characterized in that, The volume fraction of carbon dioxide in the industrial waste gas in step (1) is 5%-20%, and the absorption temperature is 40-120℃.

3. The electrochemically enhanced evaporation-crystallization closed-loop carbon dioxide recovery method according to claim 1, characterized in that, The concentration of the potassium hydroxide aqueous solution in step (1) is 1-4 mol / L.

4. The electrochemically enhanced evaporation-crystallization closed-loop carbon dioxide recovery method according to claim 1, characterized in that, The solid potassium carbonate obtained in step (2) is peeled off from the fiber surface by mechanical vibration, scraping or air backflushing.

5. The electrochemically enhanced evaporation-crystallization closed-loop carbon dioxide recovery method according to claim 1, characterized in that, The hydrophilic capillary fiber mentioned in step (2) is at least one of polyester capillary fiber, hollow polypropylene capillary fiber, polyvinylidene fluoride capillary fiber, and polyamide capillary fiber. The surface of the hydrophilic capillary fiber is modified by plasma treatment, chemical oxidation or hydrophilic coating. The diameter of a single fiber is 50-500 μm and the height of the fiber bundle is 5-50 cm.

6. The electrochemically enhanced evaporation-crystallization closed-loop carbon dioxide recovery method according to claim 1, characterized in that, An auxiliary electrode is set in the evaporation-interface crystallization unit described in step (2) to apply a weak electric field of DC or AC of 0.1-1.0V to regulate the starting position and crystallization band width of potassium carbonate crystallization.

7. The electrochemically enhanced evaporation-crystallization closed-loop carbon dioxide recovery method according to claim 1, characterized in that, The operating current density of the electrochemical regeneration unit in step (3) is 20-300 A / m. 2 The energy consumption for electrochemical regeneration per mole of carbon dioxide is 4-6 kJ / mol.

8. The electrochemically enhanced evaporation-crystallization closed-loop carbon dioxide recovery method according to claim 1, characterized in that, The apparatus used in the recovery method includes: an electrochemical absorption unit, comprising an absorbent storage tank, an absorber, and a carbonate-rich solution storage tank; an evaporation-interface crystallization unit, comprising a liquid tank and several bundles of hydrophilic capillary fibers connected to the liquid tank, the liquid tank having a carbonate-rich solution inlet and a solid potassium carbonate crystal outlet; the outlet of the carbonate-rich solution storage tank being connected to the carbonate-rich solution inlet of the liquid tank; an electrochemical regeneration unit, comprising a regenerated potassium hydroxide solution storage tank and an electrolytic cell, the electrolytic cell having a feed inlet, a regenerated potassium hydroxide solution outlet, and a carbon dioxide outlet, the solid potassium carbonate crystal outlet of the liquid tank being connected to the feed inlet of the electrolytic cell; and a circulation system, comprising an absorbent circulation pipeline and a circulation pump, used to transport the regenerated potassium hydroxide solution generated by the electrochemical regeneration unit back to the absorbent storage tank, forming a closed-loop circulation.

9. The electrochemically enhanced evaporation-crystallization closed-loop carbon dioxide recovery method according to claim 8, characterized in that, The electrolytic cell is a three-chamber electrolytic cell or a two-chamber electrolytic cell using a bipolar membrane; the absorber has a shell, porous electrodes arranged on both sides inside the shell, and gas and liquid channels located between the electrodes. The shell is provided with an industrial waste gas inlet, a carbonate-rich solution outlet, an absorbent inlet, and an absorbent outlet; the electrodes are porous carbon electrodes or conductive ceramic electrodes, and the electrode spacing is 0.5-5 mm.

10. The electrochemically enhanced evaporation-crystallization closed-loop carbon dioxide recovery method according to claim 8, characterized in that, The device also includes a control system for controlling the potential, current, flow rate, and temperature of each unit.

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