Carbon dioxide pretreatment method for ethylene carbonate synthesis

Abstract

The application provides a carbon dioxide pretreatment method for ethylene carbonate synthesis, comprising the following steps: passing the carbon dioxide to be treated into a desulfurization and dealkylation device for desulfurization and dealkylation treatment to obtain a first product; and passing the first product into a dehydration device for dehydration treatment to obtain purified carbon dioxide; the desulfurization and dealkylation device is provided with a modified composite adsorbent, the modified composite adsorbent comprises a chemical adsorption component and a physical adsorption component; the chemical adsorption component comprises at least one of a main group metal oxide and a transition metal oxide; and the physical adsorption component comprises at least one of activated carbon and a molecular sieve. The pretreatment method provided by the application has high adsorption capacity and strong selectivity, and can completely remove sulfur and hydrocarbons, thereby meeting the demand of high-purity EC synthesis for batteries, eliminating the problem of catalyst sulfur poisoning from the source of raw materials, significantly inhibiting the synthesis of by-products, and reducing the generation of ester by-products.

Description

Technical Field

[0001] This invention belongs to the field of ethylene carbonate preparation technology, specifically relating to a carbon dioxide pretreatment method for ethylene carbonate synthesis. Background Technology

[0002] Ethylene carbonate (EC) is the core solvent of lithium-ion battery electrolytes. High-purity EC used in batteries requires a main content of ≥99.99%, a metal impurity content of ≤0.1ppm, and an impurity count of ≤8. However, CO2 is a key raw material for synthesizing EC. The sulfides, hydrocarbons, and trace amounts of water contained in the raw material CO2 can poison and deactivate ionic liquid catalysts, reduce catalytic activity, decrease reaction selectivity, and introduce byproducts. This directly leads to an increased load on subsequent distillation and crystallization purification processes, making it difficult for the purity of the finished ethylene carbonate product to consistently reach the high-end battery-grade standard of ≥99.99%.

[0003] Existing CO2 pretreatment technologies suffer from the following drawbacks: poor desulfurization and dehydrocarbonization effects; commercial pressure swing adsorption (PSA) systems mostly use single activated carbon or 13X molecular sieves, removing sulfides and hydrocarbons solely through physical adsorption; low adsorption capacity and weak selectivity result in CO2 with sulfide content ≥0.1ppm and hydrocarbon content ≥5ppm, failing to meet the high-purity EC synthesis requirements for batteries; and relying solely on physical adsorption for desulfurization and dehydrocarbonization leads to incomplete desulfurization, making impurities prone to secondary desorption under high-pressure swing conditions. Summary of the Invention

[0004] To address the problems of existing methods for preparing high-purity ethylene carbonate for batteries, which rely solely on physical adsorption for desulfurization and dehydrocarbonation, resulting in low adsorption capacity, weak selectivity, incomplete desulfurization, easy secondary desorption of impurities under high-voltage transformer conditions, and high sulfide and hydrocarbon content in the treated CO2, thus failing to meet the requirements for high-purity EC synthesis for batteries, this application provides a carbon dioxide pretreatment method for ethylene carbonate synthesis.

[0005] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: This application provides a carbon dioxide pretreatment method for the synthesis of ethylene carbonate, comprising the following steps: The carbon dioxide to be treated is passed into a desulfurization and dehydrocarbonization unit for desulfurization and dehydrocarbonization treatment to obtain the first product; the first product is then passed into a dehydration unit for dehydration treatment to obtain purified carbon dioxide. The desulfurization and dehydrocarbonization device is equipped with a modified composite adsorbent, which includes a chemical adsorption component and a physical adsorption component; the chemical adsorption component includes at least one of main group metal oxides and transition metal oxides; the physical adsorption component includes at least one of activated carbon and molecular sieves.

[0006] Preferably, the mass ratio of the chemical adsorption component to the physical adsorption component is (1~3):(6~10).

[0007] Preferably, the mass ratio of the activated carbon, the molecular sieve, and the chemical adsorption component is (4~6):(2~4):(1~3).

[0008] Preferably, the chemisorption component is selected from group A metal oxides and transition metal oxides; The main group metal oxides include at least one of γ-Al2O3 and MgO; The transition metal oxide includes at least one of CuO, MnO2, ZnO, Fe2O3, TiO2, and Co3O4; The transition metal oxide is loaded in the main group metal oxide, and the mass ratio of the transition metal oxide to the main group metal oxide is (3~8):100.

[0009] Preferably, the pressure of the carbon dioxide to be treated is 2.5 MPa to 3.5 MPa, and the pressure of the first product is 2.0 MPa to 2.2 MPa.

[0010] Preferably, the first product is passed into a dehydration device for dehydration treatment to obtain purified carbon dioxide, including the following steps: The first product is passed into a first dehydration device to remove free water, resulting in a second product; the second product is then passed into a second dehydration device to remove free water and bound water, resulting in the purified carbon dioxide. The first dehydration device is equipped with a hybrid pervaporation membrane; The second dehydration device is equipped with a primary cryogenic device and a secondary cryogenic device. The primary cryogenic device removes free water, and the secondary cryogenic device removes bound water.

[0011] Preferably, the hybrid pervaporation membrane comprises a modified inorganic filler and a polyimide, wherein the polyimide is bonded to the modified inorganic filler via chemical bonds; the surface of the modified inorganic filler contains hydrophilic groups. The modified inorganic filler includes a modifier and an inorganic filler, wherein the modifier includes a silane coupling agent.

[0012] Preferably, the hybrid pervaporation membrane is provided with channels, and the average pore size of the channels is 0.3 nm to 0.5 nm; The thickness of the hybrid pervaporation membrane is 30 μm to 100 μm.

[0013] Preferably, the temperature of the primary cryogenic device is -20℃ to -10℃; The temperature of the secondary cryogenic device is -40℃ to -30℃.

[0014] Preferably, the preparation of the hybrid pervaporation membrane includes the following steps: A mixed solution is obtained by uniformly mixing modified inorganic filler, polyimide and organic solvent. The mixed solution is coated on the surface of a substrate and then subjected to a third drying and crosslinking process to obtain a hybrid pervaporation membrane. The organic solvent includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide; The third drying process is carried out at a temperature of 60℃~100℃ for 1h~4h. The cross-linking temperature is 120℃~180℃, and the time is 2h~6h.

[0015] The carbon dioxide pretreatment method for ethylene carbonate synthesis provided in this application has the following advantages: 1) The chemical adsorption component includes at least one of main group metal oxides and transition metal oxides, which can chemically react with carbonyl sulfide, hydrogen sulfide, and other sulfides in CO2, deeply locking in sulfides through chemical fixation. It has high adsorption capacity, strong selectivity, and thorough desulfurization, and will not desorb with pressure changes, solving the problems of incomplete physical adsorption desulfurization, low adsorption capacity, weak selectivity, and easy secondary desorption of impurities under high-pressure and variable-pressure conditions. 2) By utilizing the physical adsorption component to adsorb hydrocarbon impurities, it can selectively remove hydrocarbon impurities from carbon dioxide, with high adsorption capacity and thorough hydrocarbon removal. 3) The chemical adsorption component in the modified composite adsorbent is used for desulfurization, and the physical adsorption component is used for dehydrocarbonation. It has high adsorption capacity and strong selectivity, and the desulfurization and dehydrocarbonation are thorough. The sulfides in the treated CO2 can be removed to ≤0.20ppm, which is about 50% lower than the existing physical adsorption process. It meets the requirements of high-purity EC synthesis for batteries, eliminates the problem of catalyst sulfur poisoning from the source of raw materials, significantly inhibits the synthesis side reaction, reduces the generation of ester by-products, and makes the purity of ethylene carbonate product stably reach the high-end standard requirement of battery grade above 99.99%. Detailed Implementation

[0016] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0017] This invention provides a carbon dioxide pretreatment method for the synthesis of ethylene carbonate, comprising the following steps: The carbon dioxide to be treated is passed into a desulfurization and dehydrocarbonization unit for desulfurization and dehydrocarbonization treatment to obtain the first product; the first product is then passed into a dehydration unit for dehydration treatment to obtain purified carbon dioxide. The desulfurization and dehydrocarbonization device is equipped with a modified composite adsorbent, which includes a chemical adsorption component and a physical adsorption component; the chemical adsorption component includes at least one of main group metal oxides and transition metal oxides; the physical adsorption component includes at least one of activated carbon and molecular sieves.

[0018] The carbon dioxide pretreatment method for ethylene carbonate synthesis provided in this application has the following advantages: 1) The chemical adsorption component includes at least one of main group metal oxides and transition metal oxides, which can chemically react with carbonyl sulfide, hydrogen sulfide, and other sulfides in CO2, deeply locking in sulfides through chemical fixation. It has high adsorption capacity, strong selectivity, and thorough desulfurization, and will not desorb with pressure changes, solving the problems of incomplete physical adsorption desulfurization, low adsorption capacity, weak selectivity, and easy secondary desorption of impurities under high-pressure and variable-pressure conditions. 2) By utilizing the physical adsorption component to adsorb hydrocarbon impurities, it can selectively remove hydrocarbon impurities from carbon dioxide, with high adsorption capacity and thorough hydrocarbon removal. 3) The chemical adsorption component in the modified composite adsorbent is used for desulfurization, and the physical adsorption component is used for dehydrocarbonation. It has high adsorption capacity and strong selectivity, and the desulfurization and dehydrocarbonation are thorough. The sulfides in the treated CO2 can be removed to ≤0.20ppm. Compared with the existing physical adsorption process, the sulfide removal effect can be improved by more than 50%, which meets the requirements of high-purity EC synthesis for batteries. It eliminates the problem of catalyst sulfur poisoning from the source of raw materials, significantly inhibits the synthesis side reaction, reduces the generation of heteroester by-products, and makes the purity of ethylene carbonate finished product stably reach the high-end standard requirement of battery grade of more than 99.99%.

[0019] In some embodiments, the mass ratio of chemical adsorption component to physical adsorption component is (1~3):(6~10).

[0020] Specifically, the mass ratio of chemical adsorption components to physical adsorption components is in the range of (1~3):(6~10). The chemical adsorption components react chemically with carbonyl sulfide, hydrogen sulfide and other sulfides to deeply lock in the sulfides through chemical fixation, resulting in thorough desulfurization. The physical adsorption components adsorb hydrocarbon impurities, perform directional dehydrocarbonization, have high adsorption capacity and strong selectivity, and achieve thorough desulfurization and dehydrocarbonization, avoiding catalyst sulfur poisoning. This ensures that the purity of the finished ethylene carbonate product consistently meets the high-end battery-grade standard requirement of over 99.99%.

[0021] In specific embodiments, the mass ratio of the chemically adsorbed component to the physically adsorbed component can be 1:6, 1:7, 1:8, 1:9, 1:10, 2:6, 2:7, 2:8, 2:9, 2:10, 3:6, 3:7, 3:8, 3:9, 3:10, etc.

[0022] In some embodiments, the physical adsorption component is selected from activated carbon and molecular sieves.

[0023] Specifically, activated carbon can adsorb large molecular hydrocarbons with ≥3 carbon atoms, while molecular sieves adsorb small molecular hydrocarbons with less than 3 carbon atoms, achieving synergistic removal of hydrocarbon impurities from all components.

[0024] In some embodiments, the mass ratio of the activated carbon, the molecular sieve, and the chemical adsorption component is (4~6):(2~4):(1~3).

[0025] Specifically, the mass ratio of activated carbon, molecular sieve, and chemical adsorption components is within the range of (4~6):(2~4):(1~3), which is conducive to the effective adsorption of large molecular hydrocarbon impurities with ≥3 carbon atoms by activated carbon, the adsorption of small molecular hydrocarbon impurities by molecular sieve, and the removal of sulfide impurities by chemical adsorption components, thus effectively removing sulfide and hydrocarbon impurities from carbon dioxide.

[0026] In a more specific embodiment, the mass ratio of activated carbon, molecular sieve, and chemical adsorption component can be 4:2:1, 5:2:1, 6:2:1, 4:3:1, 5:3:1, 6:3:1, 4:4:1, 5:4:1, 6:4:1, 4:3:2, 5:3:3, 6:4:3, 4:4:3, etc. If the activated carbon content is too low, the ability to adsorb large molecular hydrocarbon impurities with ≥3 carbon atoms will be low, and the hydrocarbon impurity content of carbon dioxide will be high; if the molecular sieve content is too low, the ability to adsorb large molecular hydrocarbon impurities with less than 3 carbon atoms will be low, and the hydrocarbon impurity content of carbon dioxide will be high; if the content of chemical adsorption components is low, the sulfide impurity content in carbon dioxide will be high; none of the above can ensure that the purity of the finished ethylene carbonate product can stably reach above 99.99%, and thus cannot meet the battery usage standards.

[0027] In some embodiments, the molecular sieve includes at least one of 13X molecular sieve, 5A molecular sieve, 4A molecular sieve, and 3A molecular sieve.

[0028] In some embodiments, the chemisorption components are selected from group A metal oxides and transition metal oxides; The main group metal oxides include at least one of γ-Al2O3 and MgO; The transition metal oxide includes at least one of CuO, MnO2, ZnO, Fe2O3, TiO2, and Co3O4; The transition metal oxide is loaded in the main group metal oxide, and the mass ratio of the transition metal oxide to the main group metal oxide is (3~8):100.

[0029] Specifically, the chemical adsorption components are selected from main group metal oxides and transition metal oxides. The main group metal oxides and transition metal oxides are selected from the above types. The mass ratio of the transition metal oxide to the main group metal oxide is in the range of (3~8):100. The two work together effectively to react chemically with carbonyl sulfide, hydrogen sulfide and other sulfides in CO2. The sulfides are deeply locked in by chemical fixation and will not desorb with pressure changes, thus effectively removing sulfide impurities in carbon dioxide.

[0030] In specific embodiments, the mass ratio of the transition metal oxide to the main group metal oxide can be 3:100, 4:100, 5:100, 6:100, 7:100, 8:100, etc.

[0031] If the content of transition metal oxides is too low, the removal effect on impurities such as hydrogen sulfide and carbonyl sulfide will be reduced. If the content of transition metal oxides is too high, the pretreatment cost will increase.

[0032] In some embodiments, the pressure of the carbon dioxide to be treated is 2.5 MPa to 3.5 MPa, and the pressure of the first product is 2.0 MPa to 2.2 MPa.

[0033] Specifically, the pressure of the carbon dioxide to be treated is in the range of 2.5MPa to 3.5MPa. The high pressure of the carbon dioxide to be treated before desulfurization and dehydrocarbonization increases the adsorption capacity of sulfides and hydrocarbons on the surface of the modified composite adsorbent, increases the reaction rate between the chemical adsorption components and sulfides, and improves the desulfurization and dehydrocarbonization efficiency.

[0034] The pressure of the first product is controlled within the range of 2.0MPa to 2.2MPa to facilitate the dehydration efficiency of the subsequent dehydration process and ensure the stability of the sulfide and hydrocarbon content in the treated CO2.

[0035] In specific embodiments, the pressure of the carbon dioxide to be treated can be 2.5MPa, 2.6MPa, 2.7MPa, 2.8MPa, 2.9MPa, 3.0MPa, 3.2MPa, 3.3MPa, 3.4MPa, 3.5MPa, etc.

[0036] The pressure of the first product can be 2.0 MPa, 2.03 MPa, 2.05 MPa, 2.07 MPa, 2.1 MPa, 2.15 MPa, 2.2 MPa, etc.

[0037] It should be noted that the pressure of the first product can be controlled by valves in the desulfurization and dehydrocarbonization unit, thereby keeping the pressure of the first product flowing out of the desulfurization and dehydrocarbonization unit within the range of 2.0 MPa to 2.2 MPa.

[0038] In some embodiments, the temperature of the first product is 25°C to 35°C.

[0039] Specifically, the temperature of the first product is between 25℃ and 35℃, and the pressure of the first product is between 2.0MPa and 2.2MPa. Under these temperature and pressure conditions, the desorption of impurities due to excessive temperature can be avoided, while maintaining a stable gas state and providing stable feeding conditions for the subsequent membrane dehydration process, thereby ensuring the stability of the sulfide and hydrocarbon content in the treated CO2.

[0040] In specific embodiments, the temperature of the first product can be 25°C, 27°C, 28°C, 30°C, 32°C, 33°C, 35°C, etc.

[0041] In some embodiments, the adsorption time of the carbon dioxide to be treated in the desulfurization and dehydrocarbonization device is 10 min to 30 min.

[0042] Further preferred, the adsorption time is 10 min to 20 min.

[0043] In some embodiments, the space velocity of the carbon dioxide to be treated introduced into the desulfurization and dehydrocarbonization unit is 500 h⁻¹. -1 ~2000h -1 .

[0044] Specifically, space velocity is a key parameter for measuring feedstock processing efficiency in catalytic reactions, defined as the amount of feedstock passing through a unit volume of catalyst per unit time, and measured in hours (h). -1 In this process, the space velocity needs to be determined comprehensively based on the loading volume of the modified composite adsorbent and the target treatment efficiency to ensure that sulfides and hydrocarbon impurities have sufficient contact reaction time.

[0045] More preferably, the space velocity of the carbon dioxide to be treated when introduced into the desulfurization and dehydrocarbonization unit is 1000 h⁻¹. -1 ~1500h -1 scope.

[0046] In some embodiments, the method further includes desorbing the modified composite adsorbent, comprising the following steps: The modified composite adsorbent was purged with nitrogen gas.

[0047] The volumetric flow rate of nitrogen is 5% to 8% of the volumetric flow rate of carbon dioxide to be treated.

[0048] The modified composite adsorbent is purged with nitrogen gas to desorb it, and the desorbed modified composite adsorbent can be repeatedly treated for desulfurization and dehydrocarbonization.

[0049] It should be noted that nitrogen gas is only introduced during the desorption stage of the modified composite adsorbent, does not participate in the adsorption process, and will not follow the first product into the subsequent dehydration process.

[0050] In some embodiments, the preparation method of the modified composite adsorbent includes the following steps: subjecting molecular sieves and activated carbon to a first drying process; obtaining a chemisorption component; Molecular sieves, activated carbon, and chemical adsorption components are mixed evenly, a binder is added for granulation, and then subjected to a second drying and a first calcination to obtain the modified composite adsorbent.

[0051] In some embodiments, the particle size of the modified composite adsorbent obtained by granulation is 2 mm to 5 mm.

[0052] In some embodiments, the binder includes at least one of alumina sol, silica sol, bentonite, kaolin, and boehmite.

[0053] In some embodiments, the modified composite adsorbent is obtained by a second drying and a first calcination. The second drying temperature is 100℃~150℃ and the second drying time is 2h~6h. The first calcination temperature is 400℃~600℃ and the first calcination time is 2h~4h.

[0054] In some embodiments, obtaining the chemically adsorbed component includes the following steps: A carrier for transition metal oxides loaded onto main group metal oxides was obtained by an equal-volume impregnation method. The carrier was then calcined at 300℃-600℃ for 2-4 hours to obtain the chemisorbed component.

[0055] In some embodiments, a transition metal oxide-supported main group metal oxide carrier is obtained by an equal-volume impregnation method, comprising the following steps: drying the main group metal oxide and measuring the saturated water absorption rate of the main group metal oxide; obtaining a transition metal oxide precursor solution by the equal-volume impregnation method and adding it dropwise to the main group metal oxide, stirring until the main group metal oxide is completely and uniformly wetted and there is no remaining free solution in the beaker; after standing for 2-4 hours, drying to remove the solvent, thereby obtaining a transition metal oxide-supported main group metal oxide carrier.

[0056] The saturated water absorption rate of a main group metal oxide is measured by the following steps: Weigh the main group metal oxide by mass m1, add deionized water dropwise to the main group metal oxide, stir until the main group metal oxide is completely and uniformly wetted and clumps together, and there is no free liquid flowing at the bottom, stop adding water, and record the total volume of deionized water consumed V1. The saturated water absorption rate of the main group metal oxide is W = V1 / m1.

[0057] The transition metal oxide precursor solution is obtained by the equal volume impregnation method, including the following steps: the mass m2 of the transition metal oxide is 0.03m1~0.08m1; the mass m3 of the transition metal oxide precursor is calculated based on m2; the mass m3 of the transition metal oxide precursor and the volume V1 of deionized water are mixed evenly to obtain the transition metal oxide precursor solution.

[0058] In some preferred embodiments, the precursor of the transition metal oxide is selected from transition metal nitrates.

[0059] In some embodiments, the molecular sieve and activated carbon undergo a first drying process, which includes the following steps: pulverizing the molecular sieve and activated carbon to 130 mesh to 270 mesh, and then performing a first drying process at a temperature of 100°C to 120°C for a time of 10 to 14 hours.

[0060] Pulverizing activated carbon and molecular sieves to a mesh size of 130-270 is to obtain powders with uniform particle size, facilitating subsequent mixing and molding with other components and avoiding problems such as uneven mixing and poor molding strength caused by uneven particle size. Pulverizing to a mesh size of 130-270 ensures a sufficiently fine specific surface area and uniform mixing, while avoiding excessive dust and filtration difficulties due to excessive fineness.

[0061] The first drying temperature is 100-120℃, which is conducive to removing physically adsorbed water; the first drying time is 10-14 hours to ensure complete removal of moisture.

[0062] In some embodiments, the first product is passed into a dehydration device for dehydration treatment to obtain purified carbon dioxide, including the following steps: The first product is passed into a first dehydration device to remove free water, resulting in a second product; the second product is then passed into a second dehydration device to remove free water and bound water, resulting in the purified carbon dioxide. The first dehydration device is equipped with a hybrid pervaporation membrane; The second dehydration device is equipped with a primary cryogenic device and a secondary cryogenic device. The primary cryogenic device removes free water, and the secondary cryogenic device removes bound water.

[0063] The carbon dioxide pretreatment method for ethylene carbonate synthesis provided in this application has the following effects: 1) The modified composite adsorbent is used for desulfurization and dehydrocarbonation. The first dehydration unit is equipped with a hybrid pervaporation membrane, which selectively removes free water through pervaporation. The first-stage cryogenic unit removes free water, and the second-stage cryogenic unit removes bound water, achieving precise removal of three types of harmful impurities step by step. It strictly follows the physicochemical principles of physical adsorption, chemical reaction, molecular sieving, phase change condensation, and gas-liquid separation. The impurity removal logic is clear, and the purification is carried out step by step, with a removal depth far exceeding that of traditional single pretreatment processes. 2) The second dehydration unit uses a first-stage cryogenic unit and a second-stage cryogenic unit. Both stages of cryogenic separation are equipped with gas-liquid separation, solving the industry pain point of incomplete removal of trace water. Compared with direct cryogenic treatment with liquid nitrogen, energy consumption is significantly reduced. The refrigeration source system is clearly defined and fully conforms to the configuration of continuous industrial production. The process is feasible and can be scaled up. 3) Eliminate the problems of catalyst sulfur poisoning and hydrolysis deactivation from the source of raw materials, protect the catalytic system from the raw material end, significantly inhibit the synthesis side reaction, reduce the generation of heteroester by-products, greatly reduce the purification load of subsequent distillation and melting crystallization, reduce the purification pressure at the back end, and stably ensure that the purity of ethylene carbonate finished product is stable at ≥99.99%, meeting the requirements of continuous industrial production of high-purity ethylene carbonate.

[0064] In some embodiments, the hybrid pervaporation membrane comprises a modified inorganic filler and a polyimide, wherein the polyimide is bonded to the modified inorganic filler via chemical bonds; the surface of the modified inorganic filler contains hydrophilic groups. The modified inorganic filler includes a modifier and an inorganic filler, wherein the modifier includes a silane coupling agent.

[0065] Specifically, the hybrid pervaporation membrane includes modified inorganic fillers and polyimide. The surface of the modified inorganic fillers contains hydrophilic groups, which generate strong hydrogen bond adsorption for water molecules, allowing the hybrid pervaporation membrane to preferentially adsorb water.

[0066] The modified inorganic filler includes a modifier and an inorganic filler. The modifier includes a silane coupling agent. The silane coupling agent hydrolyzes to generate Si-OH. The surface of the inorganic filler contains -OH. Si-OH and -OH undergo a dehydration condensation reaction to form Si-O bonds, thereby achieving chemical bonding of the silane coupling agent to the surface of the inorganic filler.

[0067] In some embodiments, the hybrid pervaporation membrane is provided with channels, the average pore size of which is 0.3 nm to 0.5 nm.

[0068] Specifically, the dynamic diameter of a water molecule is 0.26 nm, while that of a carbon dioxide molecule is 0.33 nm. The dynamic diameter of a water molecule is smaller than that of a carbon dioxide molecule. The hybrid pervaporation membrane contains channels with an average pore size of 0.3 nm to 0.5 nm. The membrane contains hydrophilic groups that adsorb water molecules. Under this force, water molecules can quickly permeate through the membrane, while carbon dioxide is retained. By controlling the pore size, the difference in permeation rates between water molecules and CO2 is amplified. This, combined with preferential adsorption by hydrophilic molecules and dissolution-diffusion, achieves the effect of "preferential water permeation and CO2 retention."

[0069] Based on the characteristics of CO2 gas, the pore size distribution of the hybrid pervaporation membrane was optimized to form a precise permeation channel with an average pore size in the range of 0.3nm to 0.5nm. This allows only water molecules to pass through while creating a sieving effect on CO2 molecules, thus reducing CO2 permeation loss.

[0070] In specific embodiments, the average aperture of the channel can be 0.3nm, 0.32nm, 0.35nm, 0.37nm, 0.4nm, 0.42nm, 0.45nm, 0.48nm, 0.5nm, etc.

[0071] If the average pore size is greater than 0.5 nm, the diffusion resistance of CO2 will decrease significantly, the permeation rate will increase, leading to a decrease in the dehydration selectivity of the hybrid pervaporation membrane, making it impossible to stably control the outlet water content, and causing CO2 product gas loss. If the average pore size is less than 0.3 nm, even if water molecules can pass through the hybrid pervaporation membrane, the permeation and diffusion resistance of water molecules will increase, the water permeation rate will decrease, the membrane permeability will be low, and the water content of the carbon dioxide product will be high.

[0072] The average pore size of the channel can be measured by using the nitrogen adsorption-desorption method (BET method) to test the specific surface area and pore size distribution of the membrane and calculate the average pore size; or by using an atomic force microscope (AFM) to directly observe the membrane surface and statistically analyze the pore size to obtain the average pore size.

[0073] It removes most of the free moisture from the gas, retains and produces carbon dioxide, and removes free moisture. At the same time, the inorganic packing material inhibits the swelling of the hybrid pervaporation membrane under high pressure, ensuring long-term separation stability.

[0074] Traditional polyimide pervaporation membranes have limited hydrophilicity, poor dehydration selectivity, are prone to swelling under high-pressure CO2 environments, exhibit poor resistance to CO2 swelling, insufficient separation precision, low efficiency in removing trace amounts of water, and difficulty in reducing the water content after treatment to below 5 ppm. Furthermore, membrane flux tends to decrease over time. To address these issues, this application provides a hybrid pervaporation membrane. This membrane improves mechanical strength and anti-swelling properties, preventing softening, deformation, and enlarged pore size under high CO2 pressure, thus ensuring stable dehydration performance and maintaining a water content consistently below 2 ppm over the long term. It also ensures stable separation precision under high-pressure conditions, preventing excessively high CO2 water content due to membrane deformation, which could negatively impact subsequent EC synthesis.

[0075] The hybrid pervaporation membrane can operate stably for a long time under high-pressure CO2 conditions of 1.8MPa~2.2MPa. The hybrid pervaporation membrane has a free water removal efficiency that is more than 40% higher than that of ordinary polyimide membranes, and the flux decay rate is ≤5% after 1000 hours of continuous operation. This solves the problems of easy swelling and rapid flux decay of existing polyimide membranes under high-pressure CO2 environment.

[0076] In some embodiments, the first product is heated to 40°C to 50°C before being fed into the dehydration apparatus.

[0077] Furthermore, the temperature of the first product flowing out of the desulfurization and dehydrocarbonization unit is 25~35℃. Before entering the dehydration unit, the temperature of the first product is heated to prevent low-temperature CO2 from condensing on the surface of the hybrid pervaporation membrane, which would affect the separation effect of water and carbon dioxide.

[0078] Heating the first product to 40℃~50℃ can significantly increase the saturated vapor pressure of water vapor and increase the water vapor partial pressure difference across the hybrid pervaporation membrane, thereby greatly improving the dehydration efficiency.

[0079] In some embodiments, the pressure of the second product is 1.8 MPa to 2.0 MPa, the temperature is 35°C to 45°C, and the water content is ≤10 ppm.

[0080] In the first dehydration unit, the pressure of the second product exiting the first dehydration unit is controlled within the range of 1.8MPa to 2.0MPa by a pressure reducing valve, so as to ensure the pressure of the second product in the second dehydration unit is stable and to avoid carbon dioxide liquefaction loss.

[0081] In some preferred embodiments, the silane coupling agent contains an amino group.

[0082] Specifically, the silane coupling agent forms covalent bonds with the polyimide molecular chain through amino groups, rather than through simple physical doping. This significantly improves the mechanical strength and anti-swelling properties of the hybrid pervaporation membrane, preventing the membrane from softening, deforming, or becoming larger under high CO2 pressure. This ensures stable dehydration and maintains a water content of ≤10ppm over a long period. Furthermore, it ensures stable separation accuracy under high pressure conditions, preventing excessively high carbon dioxide water content due to deformation of the hybrid pervaporation membrane, which could affect subsequent EC synthesis.

[0083] In some embodiments, the inorganic filler includes at least one of silicon dioxide, titanium dioxide, and aluminum oxide.

[0084] In some embodiments, the silane coupling agent includes at least one of γ-aminopropyltriethoxysilane (KH-550), γ-aminopropyltrimethoxysilane (KH-540), γ-glycidoxypropyltrimethoxysilane (KH-560), γ-mercaptopropyltriethoxysilane (KH-580), vinyltriethoxysilane (A151), and methyltriethoxysilane (MTES).

[0085] In some embodiments, the first dehydration device is provided with a vacuum negative pressure environment, which is located outside the hybrid pervaporation membrane; The absolute pressure of the vacuum negative pressure environment is 0.09MPa~0.095MPa.

[0086] Specifically, a vacuum negative pressure environment is set on the outside of the hybrid pervaporation membrane. The absolute pressure of the vacuum negative pressure environment is in the range of 0.09MPa~0.095MPa, which can form a water vapor partial pressure difference mass transfer force, making it easier to extract and condense the water molecules adsorbed by the hybrid pervaporation membrane, thereby improving the efficiency of the hybrid pervaporation membrane in adsorbing water molecules.

[0087] In specific embodiments, the absolute pressure of the vacuum negative pressure environment can be 0.09MPa, 0.091MPa, 0.092MPa, 0.093MPa, 0.094MPa, 0.095MPa, etc.

[0088] In some embodiments, the mass of the modified inorganic filler accounts for 5% to 15% of the mass of the polyimide.

[0089] Specifically, the modified inorganic filler accounts for 5% to 15% of the mass of the polyimide membrane, which not only ensures the continuity of the hydrophilic channels but also avoids the membrane pore blockage caused by particle agglomeration, effectively improving the efficiency of the hybrid pervaporation membrane in adsorbing free water.

[0090] In some embodiments, the thickness of the hybrid pervaporation membrane is 30 μm to 100 μm.

[0091] Specifically, the thickness of the hybrid pervaporation membrane is in the range of 30μm to 100μm, which takes into account both the mechanical strength and dehydration efficiency of the hybrid pervaporation membrane, and improves the efficiency of the hybrid pervaporation membrane in adsorbing free water.

[0092] If the thickness of the hybrid pervaporation membrane is too thin, defects are likely to occur, leading to a decrease in selectivity and a reduction in the efficiency of the hybrid pervaporation membrane in adsorbing free water. If the thickness of the hybrid pervaporation membrane is too large, it will increase the mass transfer resistance and reduce the carbon dioxide transport flux.

[0093] In some preferred embodiments, the thickness of the hybrid pervaporation membrane is 40 μm to 60 μm.

[0094] Specifically, hybrid pervaporation membranes with a thickness within the aforementioned range exhibit better mechanical strength, effectively improving their efficiency in adsorbing free water.

[0095] In some embodiments, the preparation of the hybrid pervaporation membrane includes the following steps: A mixed solution is obtained by uniformly mixing modified inorganic filler, polyimide and organic solvent. The mixed solution is then coated on the surface of a substrate and subjected to a third drying and crosslinking process to obtain a hybrid pervaporation membrane.

[0096] The third drying temperature is 60℃~100℃, and the third drying time is 1h~4h.

[0097] In some embodiments, the crosslinking temperature is 120℃~180℃ and the crosslinking time is 2h~6h.

[0098] Specifically, the mixed solution is coated onto the substrate surface, and a third drying process is performed to remove the organic solvent. After the third drying, a crosslinking reaction is carried out. Crosslinking temperature and time within the aforementioned ranges are beneficial for the crosslinking of the silane coupling agent and polyimide, allowing the amino groups in the silane coupling agent to form covalent bonds with the polyimide molecular chains.

[0099] The substrate material can be ceramic, glass, metal, alloy, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene fluoride, etc.

[0100] In some embodiments, the organic solvent includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide.

[0101] The preparation of modified inorganic filler includes the following steps: mixing silane coupling agent, inorganic filler and alcohol solvent evenly and refluxing reaction, filtering, washing and drying to obtain solid product after the reaction, calcining the solid product a second time, and obtaining the modified inorganic filler after the second calcination.

[0102] In some embodiments, the reflux reaction temperature is 60°C to 80°C and the reflux reaction time is 2h to 4h.

[0103] Specifically, a reflux reaction is carried out at a temperature of 60~80℃, which is the hydrolysis of the siloxane of the silane coupling agent to generate Si-OH. At the above temperature, Si-OH undergoes dehydration condensation with -OH on the surface of the inorganic filler, so that the silane coupling agent and the inorganic filler are bonded together.

[0104] In specific embodiments, the reflux reaction temperature can be 60℃, 62℃, 65℃, 67℃, 69℃, 70℃, 73℃, 75℃, 78℃, 80℃, etc.

[0105] In some embodiments, the temperature of the fourth drying is 100°C to 120°C, and the drying time is 10h to 14h.

[0106] Specifically, the fourth drying temperature and time are within the above range to remove alcohol solvent and water.

[0107] In the washing process, it is preferable to use water for washing.

[0108] In some embodiments, the temperature of the second calcination is 300°C to 500°C, and the time of the second calcination is 2 hours to 3 hours.

[0109] Specifically, the second calcination temperature and time are within the above range, and high-temperature curing heat treatment is carried out to further deepen the condensation and form a more dense and structurally stable modified inorganic filler.

[0110] In some embodiments, mixing the silane coupling agent, inorganic filler, and alcohol solvent uniformly includes the following steps: mixing the silane coupling agent and alcohol solvent uniformly to obtain a second mixed solution, adding the inorganic filler to the second mixed solution, ultrasonically dispersing for 30 min to 60 min, and mixing uniformly.

[0111] Alcohol solvents include ethanol solvents.

[0112] In some embodiments, the temperature of the primary cryogenic device is -20°C to -10°C; The temperature of the secondary cryogenic device is -40℃ to -30℃.

[0113] Single cryogenic drying requires cooling CO2 to below -60°C, consuming 40% more energy than conventional processes. It also fails to distinguish between free and bound water, resulting in incomplete dehydration. To address these issues, this application provides a second dehydration device comprising a primary cryogenic unit and a secondary cryogenic unit. The primary unit removes free water, while the secondary unit removes bound water. Both stages are equipped with gas-liquid separation, ensuring thorough dehydration by removing water in stages. This solves the industry pain point of incomplete removal of trace amounts of water. The refrigeration system is clearly defined, perfectly suited for continuous industrial production, and the process is feasible and scalable. The two-stage cryogenic system employs a gradient cooling source configuration, combining intermediate and deep cooling, significantly reducing energy consumption compared to direct liquid nitrogen cryogenic drying.

[0114] Specifically, the second product flowing out of the first dehydration unit enters the second dehydration unit to remove free water and bound water. The temperature of the first-stage cryogenic unit is in the range of -20℃ to -10℃, which is conducive to the rapid condensation of free liquid water mist and large particulate water vapor, and then the product is discharged by cooling.

[0115] The temperature range of the secondary cryogenic unit is -40℃ to -30℃, which is conducive to the condensation of gaseous bound water and trace amounts of saturated water vapor; these are then discharged through cooling. If the temperature of the secondary cryogenic unit is above -30℃, some bound water cannot be removed, resulting in a high moisture content in the carbon dioxide, which can easily cause catalyst hydrolysis and deactivation. If the temperature of the secondary cryogenic unit is below -40℃, energy consumption and costs increase.

[0116] In specific embodiments, the temperature of the primary cryogenic device can be -10℃, -12℃, -13℃, -14℃, -15℃, -16℃, -17℃, -18℃, -19℃, -20℃, etc. The temperature of the secondary cryogenic device can be -30℃, -32℃, -33℃, -35℃, -37℃, -38℃, -39℃, -40℃, etc. The cooling medium for the first-stage cryogenic unit is at least one of the following: a 40wt%~60wt% aqueous solution of ethylene glycol, pure ethylene glycol, or a mixed solution of 40wt%~60wt% ethylene glycol-salt water. Indirect heat exchange is achieved through a shell-and-tube heat exchanger, controlling the cooling range to -20 to -10°C. Further preferably, a vertical wire mesh demister-type gas-liquid separator is installed after the first-stage cryogenic unit to directly separate and discharge condensate.

[0117] Specifically, the ethylene glycol-salt solution, also known as frozen brine, is the refrigerant used in cryogenic devices. With a concentration range of 40-60 wt%, the corresponding freezing point temperature is around -25℃ to -40℃, which can fully meet the cooling requirements of the first-stage cryogenic device from -20℃ to -10℃. Furthermore, it will not cause an increase in viscosity or a decrease in heat exchange efficiency due to excessively high concentration, nor will it cause the solution to freeze due to excessively low concentration.

[0118] The cooling medium for the secondary cryogenic unit is at least one of liquid nitrogen, ethylene glycol, and carbon dioxide; indirect heat exchange is achieved through a plate-fin heat exchanger, controlling the cooling range to -40 to -30°C. A high-efficiency gas-liquid separator is installed after the secondary cryogenic unit to completely separate and remove trace amounts of moisture.

[0119] In the second dehydration unit, carbon dioxide flows in the gas phase throughout the process, is cooled step by step, and does not liquefy; water changes from a gaseous state to a liquid state and condenses out, with gas-liquid separation in both stages, and is removed cleanly step by step.

[0120] In a further preferred embodiment, the second product first enters a primary cryogenic unit to remove free water, and the product exiting the primary cryogenic unit then enters a secondary cryogenic unit to remove bound water.

[0121] In some embodiments, the temperature fluctuation of the primary cryogenic device is in the range of ±0.2℃ to ±0.5℃, and the temperature fluctuation of the secondary cryogenic device is in the range of ±0.2℃ to ±0.5℃.

[0122] The temperature fluctuations of the primary cryogenic device and the secondary cryogenic device are within the above-mentioned ranges, which ensures effective removal of free water and bound water while also effectively reducing energy consumption.

[0123] In some embodiments, the preprocessing method further includes the following steps: The purified carbon dioxide is detected using an online detection device, and the detection results are transmitted to the control system. The control system is electrically connected to the online detection device, the desulfurization and dehydrogenation device, and the dehydration device, respectively.

[0124] Specifically, the purified carbon dioxide after desulfurization, dehydrogenation, and dehydration is monitored using an online detection device to determine its sulfide content, water content, and carbon dioxide purity. The results are transmitted to the control system, which then determines whether the results meet the process requirements. If the sulfide content is high, the control system instructs the desulfurization and dehydrogenation unit (electrically connected to the control system) to extend the adsorption time of the modified composite adsorbent, allowing it to adsorb impurities for a longer period. If the water content exceeds the standard, the control system instructs the secondary cryogenic unit (electrically connected to the control system) to lower its temperature and simultaneously increase the vacuum level in the vacuum environment of the primary dehydration unit, making it easier for water to be extracted, condensed, and removed.

[0125] The carbon dioxide pretreatment method for ethylene carbonate synthesis provided in this application uses an online detection device to monitor the purified carbon dioxide and transmits the detection results to the control system. The control system automatically adjusts the process parameters in the dehydration and desulfurization / dehydrocarbonation units based on the detection results, without manual intervention, ensuring long-term stability of the output CO2 impurity levels. This integrated design retains the bulk carbon dioxide throughout the process while selectively removing sulfides, hydrocarbons, and moisture, creating a complementary advantage between each step. It solves the industry pain point that a single process cannot simultaneously achieve the synergistic and deep removal of sulfides, hydrocarbons, and trace amounts of water, achieving unexpected technical results. Each step can be linked and automatically controlled, exhibiting strong resistance to raw material fluctuations, stable continuous operation, and significant industrial applicability and economic benefits.

[0126] In some embodiments, the online detection device is selected from an online infrared spectroscopy analyzer.

[0127] The online detection device has a detection frequency of 1 time per minute.

[0128] Compared with existing processes, the carbon dioxide pretreatment method for ethylene carbonate synthesis provided in this application can remove sulfides to ≤0.20ppm and water content to ≤2ppm; more preferably, sulfides can be removed as low as ≤0.03ppm and water content can be removed to ≤1.4ppm; the energy consumption of the whole process is 76~90kWh / tonCO2, which is more than 30% lower than the single cryogenic process, and the purity fluctuation of the finished product CO2 is ≤±0.001%, which has clear innovation and industrial promotion value.

[0129] The present invention will be further illustrated by the following examples.

[0130] Example 1 This embodiment illustrates a carbon dioxide pretreatment method for the synthesis of ethylene carbonate disclosed in this invention.

[0131] S1: Preparation of modified composite adsorbent S11: Pulverize activated carbon and 13X molecular sieve to 200 mesh and dry at 110℃ for 12 hours.

[0132] S12: Dry the γ-Al2O3 support and measure the saturated water absorption rate of the γ-Al2O3 support, including the following steps: Weigh the γ-Al2O3 support mass as m1, add deionized water dropwise to the γ-Al2O3 support, stir until the γ-Al2O3 support is completely and uniformly wetted and clumps together, and there is no free liquid flowing at the bottom, stop adding water, and record the total volume of deionized water consumed V1. The saturated water absorption rate of the γ-Al2O3 support is W=V1 / m1.

[0133] S13: Obtaining CuO and MnO2 precursor solutions using the equal-volume impregnation method includes the following steps: The mass of CuO is 0.02m1, and the mass of MnO2 is 0.03m1, so the corresponding m2 = 0.02m1 + 0.03m1 = 0.05m1. Based on m2, the mass of copper nitrate (m31) and the mass of manganese nitrate (m32) are calculated. The copper nitrate (m31), manganese nitrate (m32), and deionized water (volume V1) are mixed evenly to obtain a precursor solution containing copper nitrate and manganese nitrate.

[0134] S14: The precursor solution containing copper nitrate and manganese nitrate obtained in step S13 is added dropwise to the γ-Al2O3 support and stirred until the γ-Al2O3 support is completely and uniformly wetted and there is no remaining free solution in the beaker. After standing for 2 hours, the solvent is removed by drying to obtain the CuO-MnO2 / γ-Al2O3 support. The mass ratio of CuO-MnO2 to γ-Al2O3 in the CuO-MnO2 / γ-Al2O3 support is 5:100.

[0135] S15: The CuO-MnO2 / γ-Al2O3 support obtained in step S14 is calcined at 450℃ for 6 hours to obtain the chemically adsorbed component.

[0136] S16: Activated carbon, 13X molecular sieve powder, and CuO-MnO2 / γ-Al2O3 carrier are mixed in a mass ratio of 5:3:2. The binder, boehmite, is added to granulate the mixture into 3mm spherical particles. After drying and calcination, the modified composite adsorbent is obtained, which has a particle size of 3mm.

[0137] S2: Preparation of hybrid pervaporation membrane S21: The silane coupling agent is γ-aminopropyltriethoxysilane. The inorganic filler is selected from silica.

[0138] The preparation method of modified nano-silica includes the following steps: A silane coupling agent and an alcohol solvent are mixed evenly to obtain a second mixed solution. An inorganic filler is added to the second mixed solution, and the mixture is ultrasonically dispersed for 40 minutes until homogeneous. Then, the mixture is stirred and refluxed at 70°C for 3 hours. After the reflux reaction, the mixture is filtered and washed, and then dried for a fourth time at 110°C for 12 hours. Finally, a second calcination is performed at 400°C for 2 hours to obtain modified nano-silica.

[0139] S22: The modified nano-silica, polyimide, and N,N-dimethylformamide obtained in step S21 are mixed evenly to obtain a mixed solution. The mixed solution is coated on the surface of a ceramic substrate, and then subjected to a third drying and crosslinking process to obtain a hybrid pervaporation membrane. The third drying temperature is 80℃ and the third drying time is 2 hours. The crosslinking temperature is 150℃ and the crosslinking time is 4 hours.

[0140] The mass ratio of polyimide to modified nano-silica is 100:5. The hybrid pervaporation membrane has a thickness of 50 μm and contains channels. The average pore size of the tested channels is 0.4 nm.

[0141] The average pore size of the channel is tested by using the nitrogen adsorption-desorption method (BET method) to test the specific surface area and pore size distribution of the membrane, and then calculating the average pore size.

[0142] S3: A carbon dioxide pretreatment method for the synthesis of ethylene carbonate, comprising the following steps: S31: Before being introduced into the desulfurization and dehydrocarbonization unit, the carbon dioxide gas to be treated is pressurized to 2.5 MPa and then sent into the three-tower series pressure swing adsorption tower group of the desulfurization and dehydrocarbonization unit. The adsorption time is 12 min. After the adsorption is completed, the first product flows out from the three-tower series pressure swing adsorption tower group.

[0143] The carbon dioxide space velocity introduced into the desulfurization and dehydrocarbonization unit is 1000 h⁻¹. -1 The three-tower series pressure swing adsorption array is equipped with the modified composite adsorbent prepared in step S1. The modified composite adsorbent is desorbed using 5% high-purity nitrogen gas at an industrial-grade carbon dioxide gas volume flow rate.

[0144] The pressure of the first product is 2.2 MPa and the temperature is 25 °C.

[0145] S32: The first product obtained in step S31 is first heated to 45°C in a preheater, and then enters the first dehydration device for free water removal treatment; after the dehydration treatment is completed, the second product flows out from the first dehydration device.

[0146] The first dehydration device is equipped with a hybrid pervaporation membrane prepared in step S2, and a vacuum negative pressure environment is set outside the hybrid pervaporation membrane. The absolute pressure of the vacuum negative pressure environment is 0.09 MPa.

[0147] The pressure of the second product is 1.8 MPa, and the temperature is 40℃.

[0148] S33: The second product obtained in step S32 is fed into the second dehydration unit. First, free water is removed by a primary cryogenic unit, and then bound water is removed by a secondary cryogenic unit. The product coming out of the secondary cryogenic unit is purified carbon dioxide.

[0149] The temperature of the first-stage cryogenic unit is -20℃, with a temperature fluctuation of ±0.3℃; the temperature of the second-stage cryogenic unit is -40℃, with a temperature fluctuation of ±0.3℃. A vertical wire mesh demister-type gas-liquid separator is installed after the first-stage cryogenic unit to directly separate and discharge condensate. A high-efficiency gas-liquid separator is installed after the second-stage cryogenic unit to completely separate and discharge trace amounts of moisture.

[0150] The first-stage cryogenic unit uses ethylene glycol as the cooling medium, while the second-stage cryogenic unit uses liquid nitrogen as the cooling medium.

[0151] S34: An online infrared spectrometer is installed at the outlet of the secondary cryogenic unit to test the purified carbon dioxide obtained in step S33. As the purified CO2 gas flows through, the water and sulfur content and purity are directly measured via spectral analysis, with data taken every minute. The test results are transmitted to the control system, which sets a sulfide threshold of 0.18 ppm and a water threshold of 6.5 ppm. If the sulfur content exceeds the standard, the control system adjusts the desulfurization and dehydrocarbonization unit to increase the adsorption time. If the water content exceeds the standard, the control system lowers the temperature of the secondary cryogenic unit while simultaneously increasing the absolute pressure in the vacuum negative pressure environment of the first dehydration unit.

[0152] The purified carbon dioxide was tested to have a purity of 99.9992%, a sulfide content of 0.08 ppm, a hydrocarbon content of 3 ppm, and a water content of 1.5 ppm. The energy consumption for the above pretreatment was 80 kWh / ton CO2.

[0153] Examples 2-5, 22-26 Examples 2-5, 22-26 are largely the same as Example 1, with the following differences: the mass ratio of transition metal oxides to main group metal oxides in step S1 is different, as are the mass ratios of activated carbon, molecular sieves, and chemisorption components, as detailed in Table 1; in Example 2, the mass of CuO in step S13 is 0.04 ml, and the mass of MnO2 is 0.04 ml; in Example 5, the mass of CuO in step S13 is 0.02 ml, and the mass of MnO2 is 0.01 ml; in Example 25, the mass of CuO in step S13 is 0.01 ml, and the mass of MnO2 is 0.01 ml; in Example 26, the mass of CuO in step S13 is 0.04 ml, and the mass of MnO2 is 0.05 ml; the rest is the same as in Example 1, and the purity of purified carbon dioxide, sulfide content, hydrocarbon content, water content, and energy consumption are detailed in Table 1.

[0154] Table 1 Examples 6-9, 27 Most of the steps in Examples 6-9 and 27 are the same as those in Example 1. The difference is that some parameters in step S31 are different, as shown in Table 2. The rest are the same as in Example 1. The purity of purified carbon dioxide, sulfide content, hydrocarbon content, water content, and energy consumption are shown in Table 2.

[0155] Table 2 Examples 10-11, 28-31 Most of the steps in Examples 10-11, 28-31 are the same as those in Example 1, except that the mass ratio of polyimide to modified inorganic filler is different, the thickness of the hybrid pervaporation membrane is different, and the average pore size of the channel is different, as detailed in Table 3; the rest are the same as in Example 1, and the purity of purified carbon dioxide, sulfide content, hydrocarbon content, water content, and energy consumption are detailed in Table 3.

[0156] Table 3 Examples 12-14 Most of the steps in Examples 12-14 are the same as those in Example 1. The differences are: the absolute pressure of the vacuum negative pressure environment in step S32 is different, the pressure of the second product is different, and the crosslinking temperature and time are different. See Table 4 for details. The rest are the same as in Example 1. The purity of the purified carbon dioxide, sulfide content, hydrocarbon content, water content, and energy consumption are shown in Table 4.

[0157] Table 4 Examples 15-18 Most of the steps in Examples 15-18 are the same as those in Example 1. The differences are: the temperatures of the primary cryogenic device and the secondary cryogenic device in step S33 are different, the temperature fluctuations are different, and the cold medium is different. See Table 5 for details. The rest are the same as in Example 1. The purity of purified carbon dioxide, sulfide content, hydrocarbon content, water content, and energy consumption are shown in Table 5.

[0158] Table 5 Example 19 Most of the steps in this embodiment are the same as those in Embodiment 1. The difference is that in step S2, there is no hybrid pervaporation membrane and a polyimide membrane is used instead. Correspondingly, the hybrid pervaporation membrane in step S32 of Embodiment 1 is replaced with a polyimide membrane. The pressure of the second product is 2.0 MPa. The rest is the same as in Embodiment 1.

[0159] The purified carbon dioxide prepared in this embodiment has a purity of 99.9950%; sulfide content of 0.08 ppm; hydrocarbon content of 3 ppm; water content of 5 ppm; and energy consumption of 85 kWh / ton CO2.

[0160] Example 21 Most of the steps in this embodiment are the same as those in Embodiment 1, except that step S34 is omitted, while the rest are the same as in Embodiment 1.

[0161] Sampling and testing were conducted every minute. The purified carbon dioxide prepared in this embodiment had a purity of 99.998%~99.999%; sulfide content of 0.05~0.15ppm; hydrocarbon content of 3.0~5.8ppm; water content of 1.5~3ppm; and energy consumption of 80kWh / ton CO2.

[0162] Comparative Example 1 Most of the steps in this comparative example are the same as those in Example 1, except that: in step S1, there is no preparation of the modified composite adsorbent; the adsorbent used in Comparative Example 1 is a mixture of activated carbon and 13X molecular sieve, with a mass ratio of activated carbon to 13X molecular sieve of 5:3; correspondingly, the modified composite adsorbent in step S31 of Example 1 is replaced with an adsorbent; the industrial-grade carbon dioxide gas pressure in step S31 is 3.0 MPa, and the adsorption time is 15 min, with the rest being the same as in Example 1.

[0163] The purified carbon dioxide prepared in Comparative Example 1 had a purity of 99.9911%; sulfide content of 0.20 ppm; hydrocarbon content of 8 ppm; water content of 1.5 ppm; and energy consumption of 110 kWh / ton CO2.

[0164] Comparative Example 2 Most steps in this comparative example are the same as in Example 1, with the following differences: Step S1 does not involve the preparation of a modified composite adsorbent; the adsorbent used in Comparative Example 1 is a mixture of activated carbon and 13X molecular sieve, with a mass ratio of 5:3. Correspondingly, the modified composite adsorbent in Step S31 of Example 1 is replaced with an adsorbent; the industrial-grade carbon dioxide gas pressure in Step S31 is 3.0 MPa, and the adsorption time is 15 min. Step S2 does not use a hybrid pervaporation membrane; a polyimide membrane is used. Correspondingly, the hybrid pervaporation membrane in Step S32 of Example 1 is replaced with a polyimide membrane, and the pressure of the second product is 2.0 MPa. Step S33 only has a primary cryogenic device, without a secondary cryogenic device; the temperature of the primary cryogenic device is -60°C. The rest is the same as in Example 1.

[0165] The purified carbon dioxide prepared in this comparative example has a purity of 99.9812%; sulfide content of 0.30 ppm; hydrocarbon content of 10 ppm; water content of 8 ppm; and energy consumption of 130 kWh / ton CO2.

[0166] By comparing the above embodiments and comparative examples, it can be seen that, compared with Comparative Examples 1 and 2, the desulfurization and dehydrocarbonation devices of Comparative Examples 1 and 2 only use physical adsorption components and have no chemical adsorption components. The purified carbon dioxide prepared by Comparative Examples 1 and 2 has low purity, high sulfide content, high hydrocarbon content, and high energy consumption. This shows that the carbon dioxide pretreatment method for ethylene carbonate synthesis of this application, in which the chemical adsorption component in the modified composite adsorbent is used for desulfurization and the physical adsorption component is used for dehydrocarbonation, has high adsorption capacity, strong selectivity, and thorough desulfurization and dehydrocarbonation. The sulfide content, hydrocarbon content, and water content are low, which meets the requirements of high-purity EC synthesis for batteries. It eliminates the problem of catalyst sulfur poisoning from the source of raw materials, significantly reduces synthesis side reactions, reduces the generation of heteroester by-products, and makes the purity of the finished ethylene carbonate product stably reach the high-end standard requirement of battery grade above 99.99%.

[0167] Comparing Examples 1, 19, 20, and 2, the first dehydration device in Example 19, which contains only a polyimide membrane and no hybrid pervaporation membrane, yields purified carbon dioxide with a high water content. The second dehydration device in Example 20 contains only a primary cryogenic device. Although the temperature of the primary cryogenic device is lower than that of the primary and secondary cryogenic devices in Example 1, the water content in Example 20 is still higher, and the energy consumption is significantly greater than in Example 1. Comparative Example 2 lacks both a hybrid pervaporation membrane and a secondary cryogenic device, resulting in low carbon dioxide purity, high water content, and high energy consumption. This demonstrates that using the first and second dehydration devices provided in this application, with the first dehydration device containing a hybrid pervaporation membrane that selectively removes free water through pervaporation, and the primary cryogenic device removing free water and the secondary cryogenic device removing bound water, effectively removes water from carbon dioxide.

[0168] Comparing Example 1 and Example 21, Example 21 lacks step S34 and an online infrared spectrometer, making it impossible to detect the purity, sulfide content, water content, and hydrocarbon content of carbon dioxide in real time. This results in significant fluctuations in the purity of the obtained carbon dioxide and poor stability in the sulfide, water, and hydrocarbon content. This demonstrates that installing an online infrared spectrometer after the secondary cryogenic unit allows for the detection of these parameters in the purified carbon dioxide. The results are transmitted to the control system, which automatically adjusts the process parameters in the dehydration and desulfurization / dehydrocarbonization units based on the results, eliminating the need for manual intervention and ensuring long-term stability of the output CO2 impurity levels. This integrated design retains the bulk carbon dioxide throughout the process while selectively removing sulfides, hydrocarbons, and water, creating a complementary advantage between processes. It addresses the industry pain point that a single process cannot simultaneously achieve the synergistic deep removal of sulfides, hydrocarbons, and trace amounts of water, achieving unexpected technical results. The processes are interconnected and automatically controlled, exhibiting strong resistance to raw material fluctuations, stable continuous operation, and significant industrial practicality and economic benefits.

[0169] Comparing Examples 1, 3-4, 22 and Examples 23, 24, Example 23 showed that the chemical adsorption component added was too small, resulting in low purity carbon dioxide and high sulfide content; Example 24 showed that the activated carbon and molecular sieve added were too small, resulting in low purity carbon dioxide and high hydrocarbon content. This indicates that a mass ratio of activated carbon, molecular sieve and chemical adsorption component within the range of (4~6):(2~4):(1~3) can effectively remove sulfide and hydrocarbon impurities from carbon dioxide and improve the purity of purified carbon dioxide.

[0170] Comparing Examples 1, 2, and 5 with Examples 25 and 26, in Example 25, the mass ratio of transition metal oxide to main group metal oxide was lower than (3~8):100, indicating insufficient transition metal oxide content, which could not effectively remove carbonyl sulfides, resulting in a high sulfide content in carbon dioxide. In Example 26, the mass ratio of transition metal oxide to main group metal oxide was higher than (3~8):100, indicating excessive transition metal oxide content, increased energy consumption, and increased cost. This demonstrates that a mass ratio of transition metal oxide to main group metal oxide within the range of (3~8):100 allows for chemical reactions with carbonyl sulfides, hydrogen sulfide, and other sulfides in CO2, deeply locking in sulfides through chemical fixation, preventing desorption with pressure changes, and effectively removing sulfide impurities from carbon dioxide. In Example 2, the change in the content of transition metal oxide in the chemical adsorption component affected the removal of hydrocarbon impurities by the physical adsorption component.

[0171] Comparing Examples 1 and 6-7, it is evident that the pressure of the carbon dioxide to be treated is in the range of 2.5 MPa to 3.5 MPa, and the pressure of the first product is in the range of 2.0 MPa to 2.2 MPa, which is beneficial for removing sulfides and hydrocarbon impurities, while also ensuring good impurity stability. Comparing Examples 1, 8-9 and Example 27, the adsorption time in Example 27 is short, indicating that the modified composite adsorbent cannot effectively remove sulfides and hydrocarbon impurities, and the purified carbon dioxide has high hydrocarbon and sulfide content; this suggests that the space velocity of carbon dioxide introduced into the desulfurization and dehydrocarbonization unit in step S31 is 1000 h⁻¹. -1 ~1500h -1 The adsorption time is within the range of 10 min to 20 min, and it can effectively remove sulfides and hydrocarbon impurities.

[0172] Comparing Examples 1, 10, 11 and Examples 28, 29, in Example 28, the modified inorganic filler accounted for less than 5% of the polyimide mass, resulting in reduced water adsorption and dehydration capacity. The resulting hybrid pervaporation membrane had an average pore size greater than 0.5 nm, significantly reducing CO2 diffusion resistance and increasing permeation rate. However, this led to decreased dehydration selectivity, inability to stably control outlet water content, and CO2 product gas loss. In Example 29, the modified inorganic filler accounted for more than 15% of the polyimide mass, resulting in a hybrid pervaporation membrane with an average pore size less than 0.3 nm. This increased water molecule diffusion resistance, decreased water permeation, low membrane permeability, and excessively high water content in carbon dioxide. The comparison demonstrates that an average pore size in the range of 0.3 nm to 0.5 nm and a modified inorganic filler mass in the range of 5% to 15% of the polyimide mass effectively reduces the water content in carbon dioxide. Comparing Examples 1, 10-11, and Examples 30-31, the hybrid pervaporation membrane in Example 30 was thicker, increasing mass transfer resistance and increasing the water content of the purified carbon dioxide; the hybrid pervaporation membrane in Example 31 was thinner, reducing the efficiency of adsorbing free water and increasing the water content of the purified carbon dioxide. This indicates that a thickness of 30μm to 100μm for the hybrid pervaporation membrane improves the efficiency of adsorbing free water and effectively reduces the water content of carbon dioxide.

[0173] Comparing Examples 1, 12, 13, and 14, it is shown that the absolute pressure of the vacuum negative pressure environment, within the range of 0.09 MPa to 0.095 MPa, can generate a water vapor partial pressure difference mass transfer force, which facilitates the extraction and condensation of water molecules adsorbed by the hybrid pervaporation membrane, thereby improving the water molecule adsorption of the hybrid pervaporation membrane and reducing the water content of carbon dioxide. The crosslinking temperature, within the range of 120℃ to 180℃, and the crosslinking time, within the range of 2h to 6h, are conducive to the crosslinking of silane coupling agent and polyimide, allowing the amino groups in the silane coupling agent to form covalent bonds with the polyimide molecular chains. The resulting hybrid pervaporation membrane adsorbs water molecules, reducing the water content of carbon dioxide.

[0174] Comparing Examples 1, 15, and 16, although the higher temperature of the secondary cryogenic device in Example 16 resulted in lower water content in the carbon dioxide, it also increased energy consumption. This indicates that the temperature of the primary cryogenic device is in the range of -20℃ to -10℃, and the temperature of the secondary cryogenic device is in the range of -40℃ to -30℃. The primary cryogenic device removes free water, and the secondary cryogenic device removes bound water. Both stages of cryogenic treatment are equipped with gas-liquid separation, which removes water in stages and cleans it step by step. At the same time, it ensures that the production requirements for carbon dioxide for the synthesis of ethylene carbonate are met while using lower energy consumption.

[0175] Comparing Examples 1, 15-17, and Example 18, the temperature fluctuation range of the primary cryogenic device in Example 18 is large, and the temperature fluctuation range of the secondary cryogenic device is also large. Although the energy consumption is low, the water content of the corresponding carbon dioxide is increased. This indicates that the temperature fluctuation range of the primary cryogenic device is ±0.2℃ to ±0.5℃, and the temperature fluctuation range of the secondary cryogenic device is ±0.2℃ to ±0.5℃, which can effectively remove water from carbon dioxide while ensuring low energy consumption.

[0176] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A carbon dioxide pretreatment method for the synthesis of ethylene carbonate, characterized in that, Includes the following steps: The carbon dioxide to be treated is passed into a desulfurization and dehydrocarbonization unit for desulfurization and dehydrocarbonization treatment to obtain the first product; the first product is then passed into a dehydration unit for dehydration treatment to obtain purified carbon dioxide. The desulfurization and dehydrocarbonization device is equipped with a modified composite adsorbent, which includes a chemical adsorption component and a physical adsorption component; the chemical adsorption component includes at least one of main group metal oxides and transition metal oxides; the physical adsorption component includes at least one of activated carbon and molecular sieves.

2. The carbon dioxide pretreatment method for ethylene carbonate synthesis according to claim 1, characterized in that, The mass ratio of the chemical adsorption component to the physical adsorption component is (1~3):(6~10).

3. The carbon dioxide pretreatment method for the synthesis of ethylene carbonate according to claim 1 or 2, characterized in that, The mass ratio of the activated carbon, the molecular sieve, and the chemical adsorption component is (4~6):(2~4):(1~3).

4. The carbon dioxide pretreatment method for ethylene carbonate synthesis according to claim 1, characterized in that, The chemical adsorption components are selected from group A metal oxides and transition metal oxides; The main group metal oxides include at least one of γ-Al2O3 and MgO; The transition metal oxide includes at least one of CuO, MnO2, ZnO, Fe2O3, TiO2, and Co3O4; The transition metal oxide is loaded in the main group metal oxide, and the mass ratio of the transition metal oxide to the main group metal oxide is (3~8):

100.

5. The carbon dioxide pretreatment method for ethylene carbonate synthesis according to claim 1, characterized in that, The pressure of the carbon dioxide to be treated is 2.5 MPa to 3.5 MPa, and the pressure of the first product is 2.0 MPa to 2.2 MPa.

6. The carbon dioxide pretreatment method for ethylene carbonate synthesis according to claim 1, characterized in that, The first product is passed into a dehydration device for dehydration treatment to obtain purified carbon dioxide, including the following steps: The first product is passed into a first dehydration device to remove free water, resulting in a second product; the second product is then passed into a second dehydration device to remove free water and bound water, resulting in the purified carbon dioxide. The first dehydration device is equipped with a hybrid pervaporation membrane; The second dehydration device is equipped with a primary cryogenic device and a secondary cryogenic device. The primary cryogenic device removes free water, and the secondary cryogenic device removes bound water.

7. The carbon dioxide pretreatment method for ethylene carbonate synthesis according to claim 6, characterized in that, The hybrid pervaporation membrane comprises a modified inorganic filler and a polyimide, wherein the polyimide is bonded to the modified inorganic filler via chemical bonds; the surface of the modified inorganic filler contains hydrophilic groups. The modified inorganic filler includes a modifier and an inorganic filler, wherein the modifier includes a silane coupling agent.

8. The carbon dioxide pretreatment method for ethylene carbonate synthesis according to claim 6, characterized in that, The hybrid pervaporation membrane has channels provided inside, and the average pore size of the channels is 0.3nm~0.5nm; the thickness of the hybrid pervaporation membrane is 30μm~100μm.

9. The carbon dioxide pretreatment method for ethylene carbonate synthesis according to claim 6, characterized in that, The temperature of the primary cryogenic device is -20℃ to -10℃; The temperature of the secondary cryogenic device is -40℃ to -30℃.

10. The carbon dioxide pretreatment method for ethylene carbonate synthesis according to claim 7, characterized in that, The preparation of the hybrid pervaporation membrane includes the following steps: The modified inorganic filler, the polyimide, and the organic solvent are mixed evenly to obtain a mixed solution. The mixed solution is coated on the surface of the substrate, and after a third drying and crosslinking process, a hybrid pervaporation membrane is obtained. The organic solvent includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide; The third drying process is carried out at a temperature of 60℃~100℃ for 1h~4h. The cross-linking temperature is 120℃~180℃, and the time is 2h~6h.

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