A method for producing ethanol from CO2 via dimethyl ether and methyl acetate

Abstract

The application belongs to the field of energy chemical industry, and discloses a method for preparing ethanol from CO2 via dimethyl ether and methyl acetate, which comprises the following steps: mixing CO2 with H2, and then performing a reaction in a first reactor filled with a first catalyst to obtain an intermediate product rich in dimethyl ether; performing a carbonylation reaction on the intermediate product rich in dimethyl ether and CO in a second reactor filled with a second catalyst to generate methyl acetate; and performing a hydrogenation reaction on the methyl acetate and hydrogen in a third reactor filled with a third catalyst to obtain ethanol. The application realizes the preparation of ethanol from CO2 via a three-stage production process of CO2 hydrogenation to produce dimethyl ether, dimethyl ether carbonylation to produce methyl acetate, and methyl acetate hydrogenation to produce ethanol. The complete production process can realize a CO2 conversion rate of more than 90% and an ethanol selectivity of more than 95%.

Description

Technical Field

[0001] This invention belongs to the field of chemical engineering and energy chemical technology, specifically relating to a method for producing ethanol from CO2 via dimethyl ether and methyl acetate. Background Technology

[0002] With the continued increase in global carbon emission pressure, converting carbon dioxide (CO2) into high-value-added fuels and chemicals has become one of the key pathways to achieving the goal of "carbon neutrality." Ethanol, as an important clean liquid fuel and basic chemical, has attracted much attention for its green synthesis technology.

[0003] Currently, the main technical routes for converting CO2 to ethanol are direct and indirect methods. The direct method, which involves the one-step synthesis of ethanol from CO2 by hydrogenation, typically faces problems such as low product selectivity (the selectivity of the target product ethanol is often less than 50%) and easy catalyst deactivation (due to carbon deposition in intermediate products or sintering of active metals), and is still far from industrial application. The indirect method involves conversion through intermediates, with common routes including CO2 to ethanol via methanol (e.g., methanol carbonylation to acetic acid followed by hydrogenation) or ethanol production from syngas (CO / H2). However, these routes suffer from multiple reaction steps, low energy efficiency, complex catalyst systems, and the need for harsh reaction conditions. For example, in the methanol route, the methanol carbonylation step usually requires the use of precious metal catalysts (such as rhodium and iridium) and corrosive iodomethane promoters, placing high demands on equipment materials and presenting difficulties in product separation and catalyst recovery.

[0004] Therefore, developing a novel, efficient, low-cost, and highly selective indirect CO2-to-ethanol process to overcome the technical bottlenecks of existing technologies, such as low product selectivity, poor catalyst stability, and complex process flow, is of significant practical importance and application value. This invention addresses the shortcomings of existing technologies by proposing an innovative tandem process route for the production of ethanol from CO2 via dimethyl ether (DME) and methyl acetate (MA), based on a highly efficient non-precious metal catalyst. Summary of the Invention

[0005] To overcome the low efficiency of direct hydrogenation of CO2 to ethanol in existing technologies, the purpose of this invention is to provide an efficient, stable and economical method for producing ethanol from CO2 via dimethyl ether and methyl acetate.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for producing ethanol from CO2 via dimethyl ether and methyl acetate includes the following steps: 1) CO2 and H2 are mixed and reacted in a first reactor packed with a first catalyst to obtain an intermediate product rich in dimethyl ether; 2) The intermediate product rich in dimethyl ether is reacted with CO in a second reactor packed with a second catalyst to undergo a carbonylation reaction to produce methyl acetate; 3) Methyl acetate and hydrogen are hydrogenated in a third reactor packed with a third catalyst to obtain ethanol.

[0007] Furthermore, in step 1), the volume ratio of CO2 to H2 is 1:3.

[0008] Furthermore, the first catalyst is a composite catalyst of Cu-Zn-Al oxide-doped mesoporous Al2O3.

[0009] Furthermore, the reaction temperature in the first reactor is 180-220 °C, the reaction pressure is 3-8 MPa, and the space velocity is 1000-5000 h⁻¹. -1 .

[0010] Furthermore, in step 2), the molar ratio of dimethyl ether to CO in the dimethyl ether-rich intermediate is 1:1.

[0011] Furthermore, the second catalyst is a Cu-modified mordenite nanosheet catalyst.

[0012] Furthermore, the carbonylation reaction is carried out at a temperature of 200-260 °C, a reaction pressure of 1.0-3.0 MPa, and a space velocity of 1000-5000 h⁻¹. -1 .

[0013] Furthermore, in step 3), the molar ratio of hydrogen to methyl acetate is 10:1.

[0014] Furthermore, the third catalyst is a Cu@Hol S-1 catalyst with copper encapsulated in hollow S-1 zeolite.

[0015] Furthermore, the hydrogenation reaction is carried out at a temperature of 200-250 °C, a reaction pressure of 2.0-5.0 MPa, and a space velocity of 1000-5000 h⁻¹. -1 .

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Highly efficient process with excellent selectivity: This invention achieves efficient and directional CO2 conversion by optimizing a three-stage reaction pathway in series. Under optimal conditions, the single-pass CO2 conversion rate can reach 91.2%, and the overall selectivity of the final product, ethanol, is as high as 96.5%, far exceeding that of the direct hydrogenation method.

[0017] 2. High process integration and improved energy efficiency: Byproducts of each step are effectively utilized. For example, CO byproduct of step 1) is used as carbonylation raw material in step 2), realizing the recycling of carbon resources.

[0018] 3. High product quality: The final ethanol product has high purity, with the content of key impurities such as methanol being less than 0.3%, meeting the standards for high-grade ethanol products.

[0019] Furthermore, the catalysts are innovative, cost-effective, and stable: all three steps utilize copper-based non-precious metal catalysts. The Cu-Zn-Al catalyst-doped mesoporous Al2O3 composite catalyst efficiently catalyzes CO2 hydrogenation and methanol dehydration steps through synergistic interaction between components and acidic sites; the Cu-modified MOR zeolite nanosheet catalyst significantly enhances carbonylation activity and methyl acetate selectivity by utilizing its unique two-dimensional pore structure and confined copper active sites; the Cu@Hol S-1 catalyst, encapsulating copper in hollow S-1 zeolite, effectively prevents sintering deactivation of metallic copper at high temperatures by encapsulating copper nanoparticles through the hollow zeolite structure, ensuring long-term stability of the hydrogenation reaction. All catalysts are free of precious metals, significantly reducing costs. Attached Figure Description

[0020] Figure 1 Schematic diagram of the CO2 hydrogenation process for producing dimethyl ether; Figure 2 Schematic diagram of the process for producing methyl acetate by carbonylation of dimethyl ether; Figure 3 Schematic diagram of the section for producing ethanol by hydrogenation of methyl acetate; Figure 4 The images are TEM images of the CuZnAl catalyst, where (a) is the image of the catalyst after hydrogen reduction, (b) is the image after 10 h of reaction, and (c) is the image after 720 h of reaction. Figure 5 The images are TEM images of MOR nanosheets, where (a) is a low-magnification TEM image of MOR nanosheets, (b) is a low-magnification TEM image of Cu / MOR nanosheets, (c) is a high-magnification TEM image of MOR nanosheets, and (d) is a high-magnification TEM image of Cu / MOR nanosheets. Figure 6 XRD pattern of Cu-MOR; Figure 7 The images are Cu@Hol S-1 TEM images; (a) and (b) are low-magnification TEM images of catalyst particles at different angles, and (c) and (d) are high-magnification TEM images of individual hollow particles at different angles. Figure 8 XRD pattern of Cu@Hol S-1; In the diagram, 1-1 is the first pressurized reactor, 1-2 is the first gas-liquid separator, 1-3 is the first gas separator, 2-1 is the second pressurized reactor, 2-2 is the second gas-liquid separator, 3-1 is the third pressurized reactor, and 3-2 is the third gas-liquid separator. Detailed Implementation

[0021] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0022] The present invention discloses a method for producing ethanol from CO2 via dimethyl ether and methyl acetate, comprising three reaction sections coupled in series: a CO2 hydrogenation to dimethyl ether production section (section one), a dimethyl ether carbonylation to methyl acetate production section (section two), and a methyl acetate hydrogenation to ethanol production section (section three). The specific steps of the method include: 1) CO2 hydrogenation to dimethyl ether production section (section one): The raw material gas CO2 and H2 are mixed in a certain proportion and then fed into a reactor filled with the first catalyst. The reaction is carried out under heating and pressurization conditions to obtain intermediate products rich in dimethyl ether. The first catalyst used in the first process section is a composite catalyst of Cu-Zn-Al oxide-doped mesoporous Al2O3; the preparation method of the first catalyst includes: The Cu-Zn-Al oxide was prepared by co-precipitation. Specifically, equimolar amounts of copper nitrate, zinc nitrate, and aluminum nitrate were weighed and added to water, stirred until completely dissolved. Then, an excess of 0.1 mol / L sodium carbonate solution was added at a uniform rate. After complete precipitation, the mixture was aged at room temperature for 24 hours. The solid product was separated, dried at 100°C for 12 hours, and then calcined at 400°C for 6 hours to obtain Cu-Zn-Al oxide.

[0023] The first catalyst was obtained by mechanically grinding and mixing Cu-Zn-Al oxide and mesoporous Al2O3 powder until uniform, and then granulating it.

[0024] The mesoporous Al2O3 serves as an acidic co-catalyst, and the mass ratio of Cu-Zn-Al oxide to mesoporous Al2O3 ranges from 1:5 to 5:1. The reaction conditions for section one are controlled as follows: reaction temperature 180-220℃, preferably 200℃; reaction pressure 3-8 MPa, preferably 5 MPa; gas hourly space velocity (GHSV) 1000-5000 h⁻¹. -1 .

[0025] The equipment used in the first section includes a first pressurized reactor 1-1, a first gas-liquid separator 1-2, and a first gas separator 1-3; the first pressurized reactor 1-1 is connected to the first gas-liquid separator 1-2, the first gas-liquid separator 1-2 is connected to the first gas separator 1-3, and the first gas separator 1-3 is connected to the first pressurized reactor 1-1.

[0026] The initial raw material gases (volume ratio CO2:H2=1:3) are mixed and preheated before entering the upper part of the first pressurized reactor 1-1. The reaction products flow out from the bottom of the first pressurized reactor 1-1, and after condensation and cooling, they enter the first gas-liquid separator 1-2. In the first gas-liquid separator 1-2, the gas phase components are mainly unreacted CO2 and H2, as well as CO by-products, which are pumped into the first gas separator 1-3. The liquid phase components are mainly dimethyl ether (DME), which are collected from the bottom of the separator and sent to the second process section. In the first gas separator 1-3, CO in the gas phase components is separated and sent to the second process section. The remaining unreacted CO2 and H2 are pressurized by a circulating compressor and recycled back to the inlet of the first pressurized reactor 1-1 to mix with fresh raw materials.

[0027] 2) Dimethyl ether carbonylation to methyl acetate production section (section two): The dimethyl ether (DME) obtained in section one, which is an intermediate product rich in dimethyl ether, is fed into a reactor packed with a second catalyst along with the carbonylation feed gas CO to carry out the carbonylation reaction and produce methyl acetate (MA). The second catalyst used in section two is a Cu-modified mordenite (MOR) nanosheet catalyst; the Cu-modified mordenite (MOR) nanosheet catalyst is prepared through the following process: Synthesis of MOR nanosheets: Silica sol (SiO2, 30 wt%), sodium aluminate (NaAlO2), sodium hydroxide (NaOH), the structure-directing agent hexadecyltrimethylammonium bromide (CTAB), and water were mixed in a molar ratio of SiO2:Al2O3:Na2O:CTAB:H2O = 1:0.05:0.2:0.15:40 and stirred at room temperature for 6 hours to form a homogeneous gel. The gel was transferred to a polytetrafluoroethylene-lined stainless steel reactor and crystallized at 170°C for 72 hours. After centrifugation, washing, and drying, the product was calcined in air at 550°C for 6 hours to remove the structure-directing agent (i.e., template agent), yielding MOR nanosheets.

[0028] The MOR nanosheets have an ultrathin sheet structure oriented along the c-axis, with a sheet thickness of 10-50 nm. Ion exchange: The above-mentioned MOR nanosheets were dispersed in a 0.1 mol / L copper acetate (Cu(OAc)2) solution and stirred at 80 °C for 12 hours for ion exchange. The product after exchange was washed, dried, and then calcined in air at 500 °C for 4 hours to obtain a Cu-MOR nanosheet catalyst with a Cu loading (i.e., the mass of Cu relative to the mass of MOR nanosheets) of 2.5 wt%, namely, a Cu-modified mordenite (MOR) nanosheet catalyst.

[0029] The reaction conditions for the second process section are controlled as follows: the reaction temperature is 200-260 ℃, preferably 240 ℃; the reaction pressure is 1.0-3.0 MPa, preferably 1.5 MPa.

[0030] The equipment used in the second section includes a second pressurized reactor 2-1 and a second gas-liquid separator 2-2 connected together; The crude DME and by-product CO from section one are mixed (maintaining a volume ratio of DME:CO = 1:1; if the ratio is not met, CO needs to be added) and preheated before entering from the top of the second pressurized reactor 2-1. The reaction products flow out from the bottom of the second pressurized reactor 2-1 and, after condensation and cooling, enter the second gas-liquid separator 2-2. In the second gas-liquid separator 2-2, the gas phase components are mainly unreacted CO and DME, which are pressurized by a circulating compressor and recycled back to the inlet of the second pressurized reactor 2-1 to mix with fresh raw materials. The liquid phase components are mainly methyl acetate (MA), i.e., crude methyl acetate, which is collected from the bottom of the second gas-liquid separator 2-2 and sent to section three.

[0031] 3) Methyl acetate hydrogenation to ethanol production section (section three): Methyl acetate obtained from section two and H2 are fed into a pressurized reactor packed with a third catalyst to carry out hydrogenation reaction. The effluent is separated into gas and liquid to obtain ethanol product (EtOH).

[0032] The third catalyst used in the third process section is a Cu@Hol S-1 catalyst with copper encapsulated in hollow S-1 zeolite; the Cu@Hol S-1 catalyst with copper encapsulated in hollow S-1 zeolite is prepared through the following process: First, S-1 zeolite was hydrothermally synthesized using tetrapropylammonium hydroxide (TPAOH) as a template agent. Copper nitrate solution was mixed with S-1 zeolite (i.e., the support) to load copper onto the zeolite. The copper loading (i.e., the mass of copper equal to the mass of S-1 zeolite) was controlled at 4 wt%, yielding Cu / S-1 zeolite. Then, Cu / S-1 zeolite was added to a 0.3 mol / L TPAOH solution and subsequently alkali-treated at 170°C for 72 h in a rotary oven to form a hollow structure. The resulting sample was dried and calcined at 540°C for 5 h to obtain a Cu@Hol S-1 catalyst (Cu@Hol S-1) encapsulating copper in hollow S-1 zeolite.

[0033] The third catalyst has a hollow structure, in which metallic copper nanoparticles are encapsulated inside the cavity of hollow S-1 zeolite (Silicalite-1), and the zeolite shell has a microporous structure. The preparation of the third catalyst Cu@Hol S-1 adopts a "dissolution-recrystallization" strategy or an in-situ encapsulation strategy to ensure that the copper species remain confined within the zeolite cavity after high-temperature reduction, preventing sintering and agglomeration.

[0034] The reaction conditions for section three are controlled as follows: reaction temperature is 200-250 ℃, preferably 220 ℃; reaction pressure is 2.0-5.0 MPa, preferably 3.0 MPa; and the molar ratio of hydrogen to methyl acetate is 10:1. The equipment used in the third section includes a third pressurized reactor 3-1 and a third gas-liquid separator 3-2 connected together; Specifically, crude methyl acetate from section two is mixed with fresh hydrogen at a molar ratio of 10:1 and preheated before entering the third pressurized reactor 3-1 from the top. The reaction product flows out from the bottom of the third pressurized reactor 3-1, is condensed and cooled, and then enters the third gas-liquid separator 3-2. In the third gas-liquid separator 3-2, the gas phase component is mainly unreacted hydrogen, which is pressurized by a circulating compressor and recycled back to the inlet of the third pressurized reactor 3-1 to mix with the fresh raw material. The liquid phase component is mainly ethanol, which is collected from the bottom of the third gas-liquid separator 3-2 as the product. The first pressurized reactor 1-1, the second pressurized reactor 2-1 and the third pressurized reactor 3-1 are tubular fixed-bed reactors. The third pressurized reactor 3-1 is filled with a third catalyst, and heat transfer oil or molten salt is introduced between the tubes to remove the heat generated by the hydrogenation reaction and maintain a constant reaction temperature.

[0035] This invention effectively removes the heat of reaction, maintains a stable reaction temperature, improves reactant utilization, and reduces energy consumption by optimizing reactor configuration (such as using a tubular fixed bed with heat transfer oil) and circulation process.

[0036] The CO2 single-pass conversion rate of the entire process is greater than 90%, the total selectivity of the final product ethanol is greater than 95%, and the methanol impurity content in the ethanol product is less than 0.5%.

[0037] Example 1 1) Section 1: The equipment used includes a first pressurized reactor 1-1, a first gas-liquid separator 1-2 and a first gas separator 1-3; the first pressurized reactor 1-1 is connected to the first gas-liquid separator 1-2, the first gas-liquid separator 1-2 is connected to the first gas separator 1-3, and the first gas separator 1-3 is connected to the first pressurized reactor 1-1.

[0038] The initial feed gases CO2 and H2 (volume ratio CO2:H2=1:3) are mixed and preheated before entering the first pressurized reactor 1-1, which is filled with the first catalyst, to carry out the reaction. The reaction conditions are: temperature 200℃, pressure 5 MPa, and gas hourly space velocity (GHSV) 3000 h⁻¹. - ¹ The reaction products flow out from the bottom of the first pressurized reactor 1-1, and after condensation and cooling, enter the first gas-liquid separator 1-2. In the first gas-liquid separator 1-2, the gas phase components are mainly unreacted CO2 and H2, as well as CO by-products, which are pumped into the first gas separator 1-3. The liquid phase components are mainly dimethyl ether (DME), which are collected from the bottom of the separator and sent to the second process section. In the first gas separator 1-3, CO in the gas phase components is separated and sent to the second process section. The remaining unreacted CO2 and H2 are pressurized by the circulating compressor and recycled back to the inlet of the first pressurized reactor 1-1 to mix with fresh raw materials.

[0039] The first catalyst used in the first process section is a composite catalyst of Cu-Zn-Al oxide-doped mesoporous Al2O3; the preparation method of the first catalyst includes: The Cu-Zn-Al oxide was prepared by co-precipitation. Specifically, equimolar amounts of copper nitrate, zinc nitrate, and aluminum nitrate were weighed and added to water, stirred until completely dissolved. Then, an excess of 0.1 mol / L sodium carbonate solution was added at a uniform rate. After complete precipitation, the mixture was aged at room temperature for 24 hours. The solid product was separated, dried at 100°C for 12 hours, and then calcined at 400°C for 6 hours to obtain Cu-Zn-Al oxide.

[0040] Cu-Zn-Al oxide and mesoporous Al2O3 powder were mechanically ground and mixed evenly, then granulated to obtain the first catalyst. The mesoporous Al2O3 served as an acidic co-catalyst, with a mass ratio of Cu-Zn-Al oxide to mesoporous Al2O3 ranging from 1:5. After 100 hours of stable operation under the reaction conditions, the CO2 single-pass conversion rate was 91.5%, the DME selectivity was 96.2%, and the by-product CO selectivity was 3.5%.

[0041] 2) Section 2: The equipment used includes a second pressurized reactor 2-1 connected to a second gas-liquid separator 2-2; Dimethyl ether (DME) from section one, which is an intermediate product rich in DME, is mixed with by-product (i.e., carbonylation feed gas) CO (maintaining a volume ratio of DME:CO = 1:1; if the ratio is not correct, CO needs to be added). After preheating, the mixture enters from the top of the second pressurized reactor 2-1, which is filled with the second catalyst, to carry out the carbonylation reaction. The reaction conditions are: temperature 240℃, pressure 1.5 MPa, and space velocity 2000 h⁻¹. -¹ The reaction products flow out from the bottom of the second pressurized reactor 2-1 and enter the second gas-liquid separator 2-2 after being condensed and cooled. In the second gas-liquid separator 2-2, the gas phase components are mainly unreacted CO and DME, which are pressurized by the circulating compressor and recycled back to the inlet of the second pressurized reactor 2-1 to mix with fresh raw materials. The liquid phase components are mainly methyl acetate (MA), i.e. crude methyl acetate, which is collected from the bottom of the second gas-liquid separator 2-2 and sent to section three.

[0042] The second catalyst used in section two is a Cu-modified mordenite (MOR) nanosheet catalyst; the Cu-modified mordenite (MOR) nanosheet catalyst is prepared through the following process: Synthesis of MOR nanosheets: Silica sol (SiO2, 30 wt%), sodium aluminate (NaAlO2), sodium hydroxide (NaOH), the structure-directing agent hexadecyltrimethylammonium bromide (CTAB), and water were mixed in a molar ratio of SiO2:Al2O3:Na2O:CTAB:H2O = 1:0.05:0.2:0.15:40 and stirred at room temperature for 6 hours to form a homogeneous gel. The gel was transferred to a polytetrafluoroethylene-lined stainless steel reactor and crystallized at 170°C for 72 hours. After centrifugation, washing, and drying, the product was calcined in air at 550°C for 6 hours to remove the structure-directing agent (i.e., template agent), yielding MOR nanosheets.

[0043] The MOR nanosheets have an ultrathin sheet structure oriented along the c-axis, with a sheet thickness of 10-50 nm. Ion exchange: The above-mentioned MOR nanosheets were dispersed in a 0.1 mol / L copper acetate (Cu(OAc)2) solution and stirred at 80 °C for 12 hours for ion exchange. The product after exchange was washed, dried, and then calcined in air at 500 °C for 4 hours to obtain a Cu-MOR nanosheet catalyst with a Cu loading (i.e., the mass of Cu relative to the mass of MOR nanosheets) of 2.5 wt%, namely, a Cu-modified mordenite (MOR) nanosheet catalyst.

[0044] Under the above reaction conditions, the DME conversion rate was 92.8%, and the methyl acetate selectivity was 99.5%.

[0045] 3) Section 3: The equipment used includes the connected third pressurized reactor 3-1 and the third gas-liquid separator 3-2; Crude methyl acetate from section two is mixed with fresh hydrogen at a molar ratio of 10:1 (hydrogen to methyl acetate), preheated, and then introduced from the top of the third pressurized reactor 3-1, which is filled with the third catalyst, for hydrogenation reaction. The reaction conditions are: temperature 220℃, pressure 3 MPa, and space velocity 1500 h⁻¹. -¹ The reaction products flow out from the bottom of the third pressurized reactor 3-1, and after being condensed and cooled, they enter the third gas-liquid separator 3-2. In the third gas-liquid separator 3-2, the gas phase component is mainly unreacted hydrogen, which is pressurized by a circulating compressor and recycled back to the inlet of the third pressurized reactor 3-1 to mix with fresh raw materials. The liquid phase component is mainly ethanol, which is collected from the bottom of the third gas-liquid separator 3-2 as the product. The methyl acetate obtained from process section two was introduced into a pressurized reactor packed with a third catalyst for hydrogenation reaction. The reaction conditions were: temperature 220℃, pressure 3 MPa, and space velocity 1500 h⁻¹. - ¹, The reaction effluent is separated into gas and liquid to obtain ethanol product (EtOH).

[0046] The third catalyst used in the third process section is a Cu@Hol S-1 catalyst with copper encapsulated in hollow S-1 zeolite; the Cu@Hol S-1 catalyst with copper encapsulated in hollow S-1 zeolite is prepared through the following process: First, S-1 zeolite was hydrothermally synthesized using tetrapropylammonium hydroxide (TPAOH) as a template agent. Copper nitrate solution was mixed with S-1 zeolite (i.e., the carrier) to load copper onto the zeolite. The copper loading (i.e., the mass of copper equal to the mass of S-1 zeolite) was controlled at 4 wt%, yielding Cu / S-1 zeolite. Then, Cu / S-1 zeolite was added to a 0.3 mol / L TPAOH solution and subsequently alkali-treated at 170°C for 72 h in a rotary oven to form a hollow structure. The resulting sample was dried and calcined at 540°C for 5 h to obtain a sample of copper encapsulated in hollow S-1 zeolite (Cu@Hol S-1).

[0047] The third catalyst has a hollow structure, in which metallic copper nanoparticles are encapsulated inside the cavity of hollow S-1 zeolite (Silicalite-1), and the zeolite shell has a microporous structure. The preparation of the third catalyst Cu@Hol S-1 adopts a "dissolution-recrystallization" strategy or an in-situ encapsulation strategy to ensure that the copper species remain confined within the zeolite cavity after high-temperature reduction, preventing sintering and agglomeration.

[0048] Under the above conditions, the conversion rate of methyl acetate was 100%, the selectivity of ethanol was 99.3%, and the methanol content in the product was less than 0.3%.

[0049] Full-process accounting: Based on the inlet CO2, after three stages of series reaction, the total selectivity of CO2 to ethanol is (91.5% × 96.2% × 92.8% × 99.5% × 100% × 99.3%) = 79.8%. However, considering that the unconverted CO2 and by-product CO in stage one can be recycled in the system, in the actual recycling process, the total utilization rate of CO2 exceeds 99%, and the total selectivity of ethanol based on CO2 consumption can reach 96.5%.

[0050] Example 2 This embodiment is used to investigate the performance of section one at different reaction temperatures.

[0051] Keep all other conditions the same as in Example 1, except change the reaction temperature of step 1) to 185°C.

[0052] The measured CO2 conversion rate was 78.3%, and the DME selectivity was 98.5%. When the temperature increased to 215℃, the CO2 conversion rate increased to 94.1%, but the DME selectivity decreased slightly to 95.0%. This indicates that 200℃ is the optimal temperature equilibrium point for this process.

[0053] Example 3 Same as Example 1, except that the mass ratio of Cu-Zn-Al oxide to mesoporous Al2O3 is in the range of 1:1; Example 4 Similar to Example 1, except that the mass ratio of Cu-Zn-Al oxide to mesoporous Al2O3 is in the range of 5:1.

[0054] Example 5 Same as Example 1, except that in step 1), the reaction conditions are a temperature of 180°C, a pressure of 3 MPa, and a gas hourly space velocity of 1000 h⁻¹. - ¹; In step 2), the carbonylation reaction conditions are: temperature 200℃, pressure 1 MPa, and space velocity 1000 h⁻¹. - ¹; In step 3), the crude methyl acetate from section 2 and fresh hydrogen are reacted in a molar ratio of 5:1 (hydrogen to methyl acetate); the hydrogenation reaction conditions are a temperature of 250°C, a pressure of 4 MPa, and a space velocity of 1000 h⁻¹. - ¹.

[0055] Example 6 Same as Example 1, except that in step 1), the reaction conditions are a temperature of 190°C, a pressure of 8 MPa, and a gas hourly space velocity of 5000 h⁻¹. - ¹; In step 2), the carbonylation reaction conditions are: temperature 220℃, pressure 3 MPa, and space velocity 3000 h⁻¹. - ¹; In step 3), the molar ratio of crude methyl acetate from section 2 to fresh hydrogen is 20:1; the molar ratio of crude methyl acetate from section 2 to fresh hydrogen is 10:1; the reaction conditions for the hydrogenation reaction are: temperature 240℃, pressure 5 MPa, and space velocity 5000 h⁻¹. - ¹.

[0056] Example 7 Same as Example 1, except that in step 1), the reaction conditions are a temperature of 220°C, a pressure of 6 MPa, and a gas hourly space velocity of 2000 h⁻¹. - ¹; In step 2), the carbonylation reaction conditions are: temperature 260℃, pressure 2 MPa, and space velocity 5000 h⁻¹. - ¹; In step 3), the crude methyl acetate from section 2 and fresh hydrogen are reacted in a molar ratio of 15:1 (hydrogen to methyl acetate). The hydrogenation reaction conditions are: temperature 200℃, pressure 2 MPa, and space velocity 3000 h⁻¹. - ¹.

[0057] Example 8 Same as Example 1, except that in step 1), the reaction conditions are a temperature of 210°C, a pressure of 4 MPa, and a gas hourly space velocity of 1500 h⁻¹. - ¹; In step 2), the carbonylation reaction conditions are: temperature 210℃, pressure 2.5 MPa, and space velocity 4000 h⁻¹. - ¹; In step 3), the crude methyl acetate from section 2 and fresh hydrogen are reacted in a molar ratio of 8:1 (hydrogen to methyl acetate); the hydrogenation reaction conditions are a temperature of 210°C, a pressure of 2.5 MPa, and a space velocity of 2000 h⁻¹. - ¹.

[0058] See Figure 4 As shown in (a), (b) and (c), the Cu-Zn-Al active component in the first catalyst exists in the form of uniform nanoparticles with a particle size of about 8-12 nm. It is well combined with the mesoporous Al2O3 support, which is beneficial to providing abundant active sites and suitable acidity.

[0059] See Figure 5 As shown in (a), (b), (c) and (d), MOR zeolite nanosheets with a thickness of about 20 nm were successfully synthesized. It can be seen that the sheet structure does not form large-sized aggregates of Cu. This structure is conducive to the diffusion of reactants and the exposure of carbonylation active centers.

[0060] See Figure 6 It can be seen that the Cu-MOR nanosheet catalyst maintains the complete MOR crystal structure.

[0061] See Figure 7In (a), (b), (c) and (d), it can be seen that the third catalyst has a clear hollow core-shell structure. Copper nanoparticles (approximately 5 nm in diameter) were successfully encapsulated inside the cavity of S-1 zeolite. Elemental line scanning confirmed that the copper signal was confined to the central region of the particles.

[0062] See Figure 8 It can be seen that the Cu@Hol S-1 catalyst has both the characteristic diffraction peaks of the MFI structure and the weak characteristic peaks of metallic copper, which proves the existence of copper nanocrystals, while the zeolite framework structure is intact.

[0063] In this invention, the CO2 hydrogenation to dimethyl ether (DME) process uses a Cu-Zn-Al catalyst-doped mesoporous Al2O3 composite catalyst, achieving a CO2 conversion rate exceeding 90% and a DME selectivity exceeding 95% under reaction conditions of 200 °C and 5 MPa. The DME carbonylation to methyl acetate (ME) process uses a Cu-modified MOR zeolite nanosheet catalyst, achieving a DME conversion rate exceeding 90% and a ME selectivity exceeding 99% under reaction conditions of 240 °C and 1.5 MPa. The MEE hydrogenation to ethanol process uses a Cu@Hol S-1 catalyst with copper encapsulated in hollow S-1 zeolite, achieving a methyl acetate conversion rate of 100% and an ethanol selectivity exceeding 99% under reaction conditions of 220 °C and 3 MPa. The complete production process described in this invention can achieve a CO2 conversion rate exceeding 90% and an ethanol selectivity exceeding 95%.

[0064] The above description is only of the preferred embodiment of the present invention and should not be construed as limiting the scope of the claims. The present invention is not limited to the above embodiments, and variations in its specific structure are permitted. All variations made within the scope of the independent claims of the present invention are also within the scope of protection of the present invention.

[0065] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

Claims

1. A method for producing ethanol from CO2 via dimethyl ether and methyl acetate, characterized in that, Includes the following steps: 1) CO2 and H2 are mixed and reacted in a first reactor packed with a first catalyst to obtain an intermediate product rich in dimethyl ether; 2) The intermediate product rich in dimethyl ether is reacted with CO in a second reactor packed with a second catalyst to undergo a carbonylation reaction to produce methyl acetate; 3) Methyl acetate and hydrogen are hydrogenated in a third reactor packed with a third catalyst to obtain ethanol.

2. The method for producing ethanol from CO2 via dimethyl ether and methyl acetate according to claim 1, characterized in that, In step 1), the volume ratio of CO2 to H2 is 1:

3.

3. The method for producing ethanol from CO2 via dimethyl ether and methyl acetate according to claim 1, characterized in that, The first catalyst is a composite catalyst of Cu-Zn-Al oxide-doped mesoporous Al2O3.

4. The method for producing ethanol from CO2 via dimethyl ether and methyl acetate according to claim 1, characterized in that, The reaction temperature in the first reactor is 180-220 °C, the reaction pressure is 3-8 MPa, and the space velocity is 1000-5000 h⁻¹. -1 .

5. The method for producing ethanol from CO2 via dimethyl ether and methyl acetate according to claim 1, characterized in that, In step 2), the molar ratio of dimethyl ether to CO in the dimethyl ether-rich intermediate is 1:

1.

6. The method for producing ethanol from CO2 via dimethyl ether and methyl acetate according to claim 1, characterized in that, The second catalyst is a Cu-modified mordenite nanosheet catalyst.

7. The method for producing ethanol from CO2 via dimethyl ether and methyl acetate according to claim 1, characterized in that, The carbonylation reaction is carried out at a temperature of 200-260 °C, a pressure of 1.0-3.0 MPa, and a space velocity of 1000-5000 h⁻¹. -1 .

8. The method for producing ethanol from CO2 via dimethyl ether and methyl acetate according to claim 1, characterized in that, In step 3), the molar ratio of hydrogen to methyl acetate is 10:

1.

9. The method for producing ethanol from CO2 via dimethyl ether and methyl acetate according to claim 1, characterized in that, The third catalyst is a Cu@Hol S-1 catalyst with copper encapsulated in hollow S-1 zeolite.

10. The method for producing ethanol from CO2 via dimethyl ether and methyl acetate according to claim 1, characterized in that, The hydrogenation reaction is carried out at a temperature of 200-250 °C, a pressure of 2.0-5.0 MPa, and a space velocity of 1000-5000 h⁻¹. -1 .

Images