Process for preparing acetic acid through series connection of anaerobic fermentation and fixed bed thermocatalysis

Abstract

The invention discloses a process for preparing acetic acid through anaerobic fermentation series coupling fixed bed thermocatalysis, and belongs to the technical field of new energy and chemical engineering. According to the method, Fe and Pt serve as metal centers, TiO2 and MMT serve as carriers, active metal is deposited on the carriers through a hydrothermal method, a Pt-Fe / TiO2-MMT bimetallic composite carrier catalyst is prepared, organic waste serves as a raw material, biogas is prepared through anaerobic fermentation, then methane and carbon dioxide are obtained through purification, the methane and the carbon dioxide serve as substrates, and acetic acid is prepared through thermocatalysis of a fixed bed reactor. The method realizes direct synthesis of acetic acid from organic waste fermentation gas, has a liquid yield of 40% and acetic acid selectivity of 50%, solves the problem that carbon dioxide and methane need to be respectively introduced according to a certain ratio in the prior art, simplifies the process flow, has a high resource utilization rate, realizes cyclic utilization of reaction by-products, and is suitable for industrial production. The pollution to the environment is reduced, and the environmental protection concept is met.

Description

Technical Field

[0001] The invention relates to a process for preparing acetic acid by anaerobic fermentation in series coupled with fixed-bed thermal catalysis, and belongs to the technical field of new energy and chemical industry. Background Art

[0002] With the development of the global economy, the demand for energy is increasing. Traditional fossil energy sources are facing depletion and causing serious environmental pollution. Therefore, the development of renewable and clean energy has become a top priority. Biogas, as a biomass energy source, has the advantages of being renewable and widely distributed, and its development and utilization has attracted widespread attention. Agriculture, industry, and daily life generate a large amount of organic waste, such as crop straw, livestock manure, and municipal sludge. Improper disposal of these wastes can cause environmental pollution and waste resources. Biogas fermentation is a biochemical process centered on anaerobic microorganisms. It converts organic waste such as crop straw, livestock manure, and food waste into renewable biogas (primarily methane CH4 and carbon dioxide CO2). It also produces organic fertilizers such as biogas slurry and biogas residue, thereby reducing waste, recycling it, and rendering it harmless, thereby improving resource recycling rates.

[0003] Acetic acid is an important organic chemical raw material, widely used in the production of PTA (terephthalic acid), vinyl acetate, acetate esters, and acetic anhydride. It is also a key raw material for synthetic fibers, adhesives, pharmaceuticals, dyes, and pesticides. In the food industry, acetic acid is the main ingredient in edible vinegar and is also used in foods such as yogurt and salad dressing, and as a food additive in pickled foods. Furthermore, with technological advancements, the application of acetic acid in fields such as medicine, agriculture, and cleaning products is also expanding. The production of acetic acid primarily relies on steam reforming and carbonylation processes derived from petrochemical feedstocks. Traditional industrial acetic acid synthesis involves methane reforming to syngas, syngas to methanol, and methanol carbonylation to acetic acid. However, these processes pose challenges such as difficulty recovering precious metal catalysts, high energy consumption, and high carbon emissions. Directly utilizing methane and carbon dioxide to prepare acetic acid consumes both CH4 and CO2, while simultaneously reducing emissions of both greenhouse gases and carbon emissions. However, the selectivity for acetic acid in the existing technology is low. Furthermore, in the existing technology, the direct synthesis of acetic acid from methane and carbon dioxide requires the introduction of purified carbon dioxide and methane gases, respectively, and requires that the amount of carbon dioxide introduced be ≥ the amount of methane introduced, resulting in relatively harsh reaction conditions.

[0004] Therefore, using organic waste to generate biogas through anaerobic fermentation, and then efficiently utilizing the main components of biogas, methane (CH4) and carbon dioxide (CO2), to achieve direct conversion into high-value-added chemical acetic acid, can optimize energy utilization and become an important direction of current technical and process research. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a process for preparing acetic acid by anaerobic fermentation in series coupled with fixed-bed thermal catalysis, which can achieve efficient conversion of acetic acid, mild reaction conditions, environmental protection and high resource utilization.

[0006] In order to solve the above technical problems, the technical solution provided by the present invention is: A process for preparing acetic acid by anaerobic fermentation in series coupled with fixed-bed thermal catalysis comprises the following steps: (1) Anaerobic fermentation of organic waste to produce biogas; (2) Purifying the biogas to obtain a purified methane / carbon dioxide mixed gas; (3) The purified methane / carbon dioxide gas is introduced into a reactor and subjected to a thermal catalytic reaction under the action of a Pt-Fe / TiO2-MMT catalyst to produce an acetic acid mixture; (4) Condensing and separating the acetic acid mixture to obtain acetic acid, and recovering reaction by-products and unreacted gases.

[0007] Furthermore, in step (1), the organic waste includes crop straw, kitchen waste, and livestock and poultry manure.

[0008] Furthermore, in step (1), the pH value of the anaerobic fermentation is 6.8-7.5, the temperature of the anaerobic fermentation is 35-55° C., the stirring speed of the anaerobic fermentation is 1000 rpm, and the time of the anaerobic fermentation is 15-25 days.

[0009] Furthermore, in step (1), the methane content in the biogas is 55-62%, and the carbon dioxide content is 35-40%.

[0010] Furthermore, in step (2), the purification adopts a purification device including desulfurization, dehydration and separation treatment.

[0011] Furthermore, the desulfurization and dehydration treatment includes: using iron oxide or activated carbon adsorption to reduce the H2S concentration to below 5ppm, and then reducing the gas humidity through a condenser; using an evaporator to reduce the temperature to below the dew point (below the minimum ambient temperature by 10°C) so that the water vapor in the mixed gas begins to condense into liquid water, which is discharged through a water pipe to complete humidity separation and control the gas humidity to 40-60%; the dehumidified gas is returned to room temperature through a condenser to avoid the exhaust air temperature being too low; The separation process involves using membrane separation or pressure swing adsorption (PSA) to separate methane and carbon dioxide, increasing their content to over 95%. Membrane separation uses selectively permeable membrane materials. CO2 molecules are smaller than methane and have high diffusivity, meaning that CO2 preferentially permeates the membrane, retaining methane. At high pressures of 3-5 MPa, PSA preferentially adsorbs CO2, while methane is removed from the top of the adsorption process. Desulfurization and dehydration remove H2S and water, leaving a methane and CO2 mixture that can be directly used in acetic acid synthesis.

[0012] Furthermore, in step (3), the thermal catalytic reaction is divided into a preheating section and a reaction section, and the temperatures of the reaction section and the preheating section are independently controlled; and the reactor is a fixed bed reactor.

[0013] Furthermore, in step (3), the active metal component of the Pt-Fe / TiO2-MMT catalyst is Pt-Fe bimetallic, the carrier is TiO2 and modified MMT, and the active metal content is 5-6 wt.%.

[0014] Fe can improve the redox ability and form oxygen vacancies to promote the activation of CO2. CO2 is adsorbed on the oxygen vacancies of Fe or MMT and dissociates into CO or formic acid intermediates. Pt is a precious metal with good catalytic activity. Pt can effectively promote the activation of CH bonds of CH4 to generate methyl radicals (-CH3) during photocatalysis. Pt can significantly reduce the activation energy barrier of CH and promote dehydrogenation. Pt and Fe produce a synergistic effect, which can adjust the adsorption strength of intermediates, inhibit excessive dehydrogenation, enhance the activity of CO2, and thus inhibit excessive reaction of intermediate products. At the same time, Pt is used to modify TiO2 to form a metal semiconductor interface, enhance the separation efficiency of photogenerated electrons and holes, and Pt and TiO2 can form Pt-O and Pt 2+ , producing more B acid sites. These unique structures optimize CO2 adsorption and promote the formation of -COOH. Methane and CO2 selectively generate acetic acid at the Pt-O site, and the simultaneous reduction of Pt efficiently releases acetic acid, effectively avoiding the problem of excessive oxidation.

[0015] Photogenerated electron-hole pairs in TiO2 promote the decomposition of H2O to form -OH. MMT has excellent thermal and chemical stability, and its cation exchange properties can be used to modify it, which has great advantages for metal loading. Modifying MMT with a mixed acid gradient treatment can avoid excessive damage to the MMT crystal structure, making the MMT acid sites more uniform and allowing for a more even dispersion of metal Pt and Fe. Concentrated sulfuric acid can etch impurities on the MMT surface, and the strong acidity of phosphoric acid is then used to expand the interlayer oxygen density of montmorillonite, forming a porous structure. This high interlayer oxygen density is beneficial for regulating CO2 adsorption and activation efficiency. At the same time, dilute nitric acid is used to improve the cation exchange properties of MMT, thereby enhancing the catalytic performance of MMT as a carrier.

[0016] Therefore, the synergistic effect of Pt-Fe bimetallic and TiO2-MMT composite support can improve the activity of the catalyst and the selectivity of acetic acid, while achieving efficient conversion of biogas resources, reducing dependence on traditional fossil energy and lowering carbon emissions, which has significant economic benefits and environmental value.

[0017] Furthermore, the preparation steps of the Pt-Fe / TiO2-MMT catalyst are as follows: (a) In the presence of deionized water or an organic solvent, a soluble Pt salt, a soluble Fe salt, and TiO2 powder undergo a hydrothermal reaction to generate a Pt-Fe / TiO2 solution. (b) Sodium montmorillonite (MMT) was stirred with mixed acid at a constant temperature of 90°C for 6 h, washed by centrifugation until neutral, and then placed in a nitric acid solution for ultrasonic treatment for 1 h to obtain modified MMT; (c) The modified MMT was completely immersed in the Pt-Fe / TiO2 solution to form the catalyst and obtain the Pt-Fe / TiO2-MMT catalyst.

[0018] Furthermore, in step (a), the preparation steps of the Pt-Fe / TiO2 solution are specifically as follows: weighing a soluble Pt salt and a soluble Fe salt and placing them in a container, adding TiO2 powder, and then adding deionized water or an organic solvent and mixing them thoroughly, and then transferring them to a polytetrafluoroethylene hydrothermal reactor, and performing a hydrothermal reaction in an oven at 160-180°C for 5-8h to obtain a Pt-Fe / TiO2 solution. Furthermore, in step (a), the ratio of the soluble Pt salt, the soluble Fe salt, the TiO2 powder, the MMT and the deionized water or the organic solvent is 5 mg:11 mg:50 mg:(1-2) g:(10-15) mL.

[0019] Furthermore, in step (a), the soluble Pt salt is at least one of chloroplatinic acid, tetraammineplatinum nitrate, and potassium chloroplatinite; the soluble Fe salt is at least one of ferric nitrate, ferric chloride, and ferric sulfate; the TiO2 is a nano-scale anatase hydrophilic type; and the organic solvent is one of dimethylformamide and ethylene glycol.

[0020] Furthermore, in step (b), the particle size of the MMT is 0.5-0.8 μm, and the specific surface area of the MMT is 500-650 m 2 / g; the mixed acid is a mixed solution of concentrated sulfuric acid and phosphoric acid in a mass ratio of (1-3):1; the mass ratio of MMT to the mixed acid is 1:15; the nitric acid solution is a dilute nitric acid solution with a concentration of 6wt.%, and the ratio of MMT to dilute nitric acid is 1g:20mL.

[0021] Furthermore, in step (c), the specific steps of forming the catalyst are: completely immersing the acid-treated MMT in a Pt-Fe / TiO2 solution, continuously stirring for 4-6 hours in a water bath at a constant temperature of 80°C and a rotation speed of 300-500 rpm, then placing it in an oven at 80°C to dry overnight, and then transferring it to a muffle furnace for calcination, heating it to 400-450°C at a heating rate not exceeding 5°C / min, keeping the temperature constant for 150-180 minutes, cooling it naturally, grinding and sieving it, and sealing it.

[0022] Furthermore, in step (3), the temperature of the thermal catalytic reaction is 400-550°C, the pressure of the thermal catalytic reaction is 2-5 MPa, the time of the thermal catalytic reaction is 6-18 hours, and the stirring speed of the thermal catalytic reaction is 800-2000 rpm. Under high temperature and high pressure conditions, a direct oxidative coupling reaction of methane and carbon dioxide is achieved to produce acetic acid. Currently, in the prior art, acetic acid is directly synthesized from methane and carbon dioxide by introducing purified gases of carbon dioxide and methane, respectively, and requiring the amount of carbon dioxide introduced to be greater than the amount of methane introduced. However, the present invention directly uses fermented biogas, which has a methane content of 55-62% and a carbon dioxide content of 35-40%. Although the ratio of carbon dioxide to methane is not optimal, the catalyst prepared by the present invention can still achieve high selectivity and high efficiency in the synthesis of acetic acid.

[0023] Furthermore, in step (4), the purity of the acetic acid is greater than 99%. The acetic acid is stored in a corrosion-resistant storage tank.

[0024] Furthermore, in step (4), the condensation separation is performed by separating acetic acid using a condensation separation device, and the condensation separation temperature is 20-25°C. While the reaction generates acetic acid, by-products including unreacted gas or H2O are generated. The by-products can be recycled and returned to the reactor through a circulation pipeline for reuse or further treatment.

[0025] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention uses agricultural and forestry biomass waste as raw materials to carry out anaerobic fermentation to produce biogas, which is then used in a thermal catalytic process to prepare acetic acid through series coupling, thereby realizing waste resource utilization. It has the advantages of being green and environmentally friendly, high resource utilization rate, low energy consumption, and high selectivity for target products.

[0026] (2) The present invention provides a method for preparing a novel Pt-Fe / TiO2-MMT catalyst, wherein a metal is loaded on TiO2 and MMT by hydrothermal induction to prepare a Pt-Fe / TiO2-MMT catalyst, which is used for preparing acetic acid by coupled thermal catalysis of biogas fermentation. The catalyst has a high acetic acid yield and selectivity, and can improve the efficiency of acetic acid preparation.

[0027] (3) The preparation process of the catalyst of the present invention is simple. The prepared catalyst has the characteristics of uniform particle dispersion, small size, good activity and stability. In addition, the carrier and organic solvent used are widely available and inexpensive, which can effectively reduce the production cost of precious metal catalysts in the acetic acid preparation experiment.

[0028] (4) The process route for preparing acetic acid provided by the present invention realizes that the gas fermented from organic waste can be directly used to synthesize acetic acid. There is no need to separate methane and carbon dioxide, nor is there a need to introduce carbon dioxide and methane in a certain ratio. This simplifies the process flow, and the reaction by-products can be recycled, reducing pollution to the environment, which is in line with the concept of environmental protection.

[0029] (5) The present invention directly uses organic waste as raw material, and the methane content in the fermented biogas is 55-62%, and the carbon dioxide content is 35-40%. The mixed gas of methane and carbon dioxide obtained from the fermented biogas is catalyzed by the catalyst prepared by the present invention to synthesize acetic acid, which can achieve a liquid yield of 40% and an acetic acid selectivity of 50%. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a process for producing acetic acid by anaerobic fermentation in series coupled with fixed-bed thermal catalysis; Figure 2 It is a process route for thermally catalytically synthesizing acetic acid from methane and carbon dioxide in the presence of a Pt-Fe / TiO2-MMT catalyst. DETAILED DESCRIPTION

[0031] Example 1 Take 50mg TiO2, 5mg Pt(NH3)4(NO3)2, and 11mg Fe(NO3)3 and place them in a polytetrafluoroethylene liner, and add 10-15mL deionized water dropwise and stir to mix evenly; then transfer them to a stainless steel reactor and heat them in an oven at 170℃ for 6h to obtain Pt-Fe / TiO2 solution; take 1g of a particle size of 0.5μm and a specific surface area of 500m 2 / g of MMT was mixed with 7.5g of concentrated sulfuric acid and 7.5g of phosphoric acid, stirred at a constant temperature of 90℃ for 6h, and then centrifuged and washed until neutral. Then, it was placed in 20mL of dilute nitric acid with a concentration of 6wt.% and ultrasonically treated for 1h to obtain modified MMT; the modified MMT was completely immersed in Pt-Fe / TiO2 solution, continuously stirred for 5h in a water bath at a constant temperature of 80℃ and a speed of 300rmp, then placed in an oven at 80℃ to dry overnight, and then transferred to a muffle furnace for calcination, heated to 400℃ at a heating rate of 5℃ / min, kept at this temperature for 180min, and cooled naturally. Finally, the obtained sample was ground and sealed to obtain a Pt-Fe / TiO2-MMT catalyst with an active metal content of 5wt.%.

[0032] Example 2 Take 50mg TiO2, 5mg Pt(NH3)4(NO3)2, and 11mg Fe(NO3)3 and place them in a polytetrafluoroethylene liner, and add 10-15mL deionized water dropwise and stir to mix evenly; then transfer them to a stainless steel reactor and heat them in an oven at 170℃ for 6h to obtain Pt-Fe / TiO2 solution; take 1g of a particle size of 0.6μm and a specific surface area of 600m 2 / g of MMT was mixed with 10g of concentrated sulfuric acid and 5g of phosphoric acid, stirred at a constant temperature of 90℃ for 6h, and then centrifuged and washed until neutral. Then, it was placed in 20mL of dilute nitric acid with a concentration of 6wt.% and ultrasonically treated for 1h to obtain modified MMT; the modified MMT was completely immersed in Pt-Fe / TiO2 solution, continuously stirred for 5h in a water bath at a constant temperature of 80℃ and a speed of 300rmp, then placed in an oven at 80℃ to dry overnight, and then transferred to a muffle furnace for calcination, heated to 400℃ at a heating rate of 5℃ / min, kept at this temperature for 180min, and cooled naturally. Finally, the obtained sample was ground and sealed to obtain a Pt-Fe / TiO2-MMT catalyst with an active metal content of 5wt.%.

[0033] Example 3 50 mg of TiO2, 5 mg of Pt(NH3)4(NO3)2, and 11 mg of Fe(NO3)3 were placed in a polytetrafluoroethylene liner, and 10-15 mL of deionized water was added dropwise and stirred to mix evenly. The mixture was then transferred to a stainless steel reactor and heated in an oven at 170 ° C for 6 h to obtain a Pt-Fe / TiO2 solution. 1 g of a 0.8 μm particle size and a specific surface area of 650 m 2 / g of MMT was mixed with 11.25g of concentrated sulfuric acid and 3.75g of phosphoric acid, stirred at a constant temperature of 90℃ for 6h, and then centrifuged and washed until neutral. Then, it was placed in 20mL of dilute nitric acid with a concentration of 6wt.% and ultrasonically treated for 1h to obtain modified MMT; the modified MMT was completely immersed in Pt-Fe / TiO2 solution, continuously stirred for 5h in a water bath at a constant temperature of 80℃ and a speed of 300rpm, then placed in an oven at 80℃ to dry overnight, and then transferred to a muffle furnace for calcination, heated to 400℃ at a heating rate of 5℃ / min, kept at this temperature for 180min, and cooled naturally. Finally, the obtained sample was ground and sealed to obtain a Pt-Fe / TiO2-MMT catalyst with an active metal content of 5wt.%.

[0034] Example 4 50 mg TiO2, 5 mg Pt(NH3)4(NO3)2, and 11 mg Fe(NO3)3 were placed in a polytetrafluoroethylene liner, and 10-15 mL deionized water was added dropwise and stirred to mix evenly; then the mixture was transferred to a stainless steel reactor and heated in an oven at 180 ° C for 6 h to obtain a Pt-Fe / TiO2 solution; 2 g of a 0.6 μm particle size and a specific surface area of 600 m 2 / g of MMT was mixed with 15g of concentrated sulfuric acid and 15g of phosphoric acid, stirred at a constant temperature of 90℃ for 6h, and then centrifuged and washed until neutral. Then, it was placed in 20mL of dilute nitric acid with a concentration of 6wt.% and ultrasonically treated for 1h to obtain modified MMT; the modified MMT was completely immersed in Pt-Fe / TiO2 solution, stirred continuously for 6h in a water bath at a constant temperature of 80℃ and a speed of 300rmp, then placed in an oven at 80℃ to dry overnight, and then transferred to a muffle furnace for calcination, heated to 450℃ at a heating rate of 5℃ / min, kept at this temperature for 180min, and cooled naturally. Finally, the obtained sample was ground and sealed to obtain a Pt-Fe / TiO2-MMT catalyst with an active metal content of 5wt.%.

[0035] Example 5 50 mg TiO2, 5 mg Pt(NH3)4(NO3)2, and 11 mg Fe(NO3)3 were placed in a polytetrafluoroethylene liner, and 10-15 mL deionized water was added dropwise and stirred to mix evenly; then the mixture was transferred to a stainless steel reactor and heated in an oven at 180 ° C for 6 h to obtain a Pt-Fe / TiO2 solution; 2 g of a 0.6 μm particle size and a specific surface area of 600 m 2 / g of MMT was mixed with 20g of concentrated sulfuric acid and 10g of phosphoric acid, stirred at a constant temperature of 90℃ for 6h, and then centrifuged and washed until neutral. Then, it was placed in 20mL of dilute nitric acid with a concentration of 6wt.% and ultrasonically treated for 1h to obtain modified MMT; the modified MMT was completely immersed in Pt-Fe / TiO2 solution, continuously stirred for 6h in a water bath at a constant temperature of 80℃ and a speed of 400rpm, then placed in an oven at 80℃ to dry overnight, and then transferred to a muffle furnace for calcination, heated to 420℃ at a heating rate of 3℃ / min, kept at this temperature for 150min, and cooled naturally. Finally, the obtained sample was ground and sealed to obtain a Pt-Fe / TiO2-MMT catalyst with an active metal content of 5wt.%.

[0036] Example 6 Take 50mg TiO2, 5mg Pt(NH3)4(NO3)2, and 11mg Fe(NO3)3 and place them in a polytetrafluoroethylene liner, and add 10-15mL deionized water dropwise, stir and mix evenly, then transfer to a stainless steel reactor, and heat at 180℃ in an oven for 6h to obtain Pt-Fe / TiO2 solution; take 2g of 0.6μm particle size and 600m 2 / g of MMT was mixed with 20g of concentrated sulfuric acid and 10g of phosphoric acid, stirred at a constant temperature of 90℃ for 6h, and then centrifuged and washed until neutral. Then, it was placed in 20mL of dilute nitric acid with a concentration of 6wt.% and ultrasonically treated for 1h to obtain modified MMT; the modified MMT was completely immersed in Pt-Fe / TiO2 solution, continuously stirred for 5h in a water bath at a constant temperature of 100℃ and a speed of 500rpm, then placed in an oven at 80℃ to dry overnight, and then transferred to a muffle furnace for calcination. The temperature was raised to 450℃ at a heating rate of 3℃ / min, kept constant for 150min, and cooled naturally. Finally, the obtained sample was ground and sealed to obtain a Pt-Fe / TiO2-MMT catalyst with an active metal content of 5wt.%.

[0037] Example 7 A process for preparing acetic acid by anaerobic fermentation in series coupled with fixed-bed thermal catalysis comprises the following steps: (1) Organic waste food waste was anaerobically fermented at a pH of 7.1, a temperature of 40°C, and a stirring speed of 1000 rpm for 20 days to produce biogas. The methane content of the obtained biogas was 55% and the carbon dioxide content was 40%. (2) Using iron oxide or activated carbon to adsorb biogas, reduce the H2S concentration to below 5 ppm, then reduce the gas humidity through a condenser, and then use membrane separation or pressure swing adsorption (PSA) process to separate methane and carbon dioxide, increase the content of methane and carbon dioxide to more than 95%, and obtain a purified methane / carbon dioxide mixed gas; (3) The purified methane / carbon dioxide mixed gas was introduced into the reactor and subjected to a thermal catalytic reaction at a temperature of 450°C, a pressure of 3 MPa, and a rotation speed of 1000 rpm for 10 h to produce an acetic acid mixture; (4) The acetic acid mixture is separated into acetic acid by a condensation separation device at a cooling temperature of 23°C to obtain acetic acid with a purity of more than 99%. The reaction by-products and unreacted gases are recovered and returned to the reactor through a circulation pipeline for continued use or further treatment.

[0038] Example 8 A process for preparing acetic acid by anaerobic fermentation in series coupled with fixed-bed thermal catalysis comprises the following steps: (1) Organic waste crop straw was anaerobically fermented at a pH of 6.8, a temperature of 55°C, and a stirring speed of 1000 rpm for 25 days to produce biogas. The methane content of the obtained biogas was 62% and the carbon dioxide content was 35%; (2) The biogas is adsorbed with iron oxide or activated carbon to reduce the H2S concentration to below 5 ppm, and then the gas humidity is reduced by a condensation device. Then, a membrane separation process is used to separate methane and carbon dioxide, and the content of methane and carbon dioxide is increased to more than 95%, thereby obtaining a purified methane / carbon dioxide mixed gas; (3) The purified methane / carbon dioxide mixed gas was introduced into the reactor and subjected to a thermal catalytic reaction at a temperature of 550°C, a pressure of 2 MPa, and a rotation speed of 800 rpm for 18 hours under the action of a Pt-Fe / TiO2-MMT catalyst to produce an acetic acid mixture; (4) The acetic acid mixture is separated into acetic acid by a condensation separation device at a cooling temperature of 20°C to obtain acetic acid with a purity of more than 99%. The reaction by-products and unreacted gases are recovered and returned to the reactor through a circulation pipeline for continued use or further treatment.

[0039] Example 9 A process for preparing acetic acid by anaerobic fermentation in series coupled with fixed-bed thermal catalysis comprises the following steps: (1) The organic waste livestock and poultry manure was anaerobically fermented at a pH of 7.5, a temperature of 35°C, and a stirring speed of 1000 rpm for 15 days to produce biogas. The methane content of the obtained biogas was 60% and the carbon dioxide content was 35%; (2) The biogas is adsorbed with iron oxide or activated carbon to reduce the H2S concentration to below 5 ppm, and then the gas humidity is reduced by a condensation device. Then, the methane and carbon dioxide are separated by a pressure swing adsorption (PSA) process to increase the content of methane and carbon dioxide to more than 95%, thereby obtaining a purified methane / carbon dioxide mixed gas; (3) The purified methane / carbon dioxide mixed gas was introduced into the reactor and subjected to a thermal catalytic reaction at a temperature of 400°C, a pressure of 5 MPa, and a rotation speed of 2000 rpm for 6 hours under the action of a Pt-Fe / TiO2-MMT catalyst to produce an acetic acid mixture; (4) The acetic acid mixture is separated into acetic acid by a condensation separation device at a cooling temperature of 25°C to obtain acetic acid with a purity of more than 99%. The reaction by-products and unreacted gases are recovered and returned to the reactor through a circulation pipeline for continued use or further treatment.

[0040] Comparative Example 1 Take 50mg TiO2 and 5mg Pt(NH3)4(NO3)2, place them in a polytetrafluoroethylene liner, and add 10-15mL deionized water dropwise, stir and mix evenly, then transfer to a stainless steel reactor, hydroheat in an oven at 170℃ for 6h to obtain a Pt / TiO2 solution; dry the Pt / TiO2 solution at 80℃ overnight, then heat it to 400℃ at a heating rate of 5℃ / min, keep it at a constant temperature for 180min, cool it naturally, and finally grind and seal the obtained sample to obtain a Pt / TiO2 catalyst with an active metal content of 5wt.%.

[0041] Comparative Example 2 Take 50mg TiO2 and 11mg Fe(NO3)3 and place them in a polytetrafluoroethylene liner, and add 10-15mL deionized water dropwise, stir and mix evenly, then transfer to a stainless steel reactor, hydroheat in an oven at 170℃ for 6h to obtain Fe / TiO2 solution; dry the Fe / TiO2 solution at 80℃ overnight, then heat it to 400℃ at a heating rate of 5℃ / min, keep the temperature constant for 180min, cool it naturally, and finally grind and seal the obtained sample to obtain a Fe / TiO2 catalyst with an active metal content of 5wt.%.

[0042] Comparative Example 3 Take 50mg TiO2 and 5mg Pt(NH3)4(NO3)2 and place them in a polytetrafluoroethylene liner, and add 10-15mL deionized water dropwise, stir and mix evenly, then transfer to a stainless steel reactor, and heat in an oven at 170℃ for 6h to obtain Pt / TiO2 solution; take 1g of a particle size of 0.5μm and a specific surface area of 500m 2 / g of MMT was mixed with 7.5g of concentrated sulfuric acid and 7.5g of phosphoric acid, stirred at a constant temperature of 90℃ for 6h, and then centrifuged and washed until neutral. Then, it was placed in dilute nitric acid with a concentration of 6wt.% and ultrasonically treated for 1h to obtain modified MMT; the modified MMT was completely immersed in Pt / TiO2 solution, continuously stirred for 5h in a water bath at a constant temperature of 80℃ and a speed of 300rmp, then placed in an oven at 80℃ to dry overnight, and then transferred to a muffle furnace for calcination, heated to 400℃ at a heating rate of 5℃ / min, kept at this temperature for 180min, and cooled naturally. Finally, the obtained sample was ground and sealed to obtain a Pt / TiO2-MMT catalyst with an active metal content of 5wt.%.

[0043] Comparative Example 4 Take 50mg TiO2 and 11mg Fe(NO3)3, place them in a polytetrafluoroethylene liner, and add 10-15mL deionized water dropwise, stir and mix evenly, then transfer to a stainless steel reactor, and heat in an oven at 170℃ for 6h to obtain Fe / TiO2 solution; take 1g of Fe / TiO2 with a particle size of 0.5μm and a specific surface area of 500m 2 / g of MMT was mixed with 7.5g of concentrated sulfuric acid and 7.5g of phosphoric acid, stirred at a constant temperature of 90℃ for 6h, and then centrifuged and washed until neutral. Then, it was placed in dilute nitric acid with a concentration of 6wt.% and ultrasonically treated for 1h to obtain modified MMT; the modified MMT was completely immersed in Fe / TiO2 solution, continuously stirred for 5h in a water bath at a constant temperature of 80℃ and a speed of 300rmp, then placed in an oven at 80℃ to dry overnight, and then transferred to a muffle furnace for calcination, heated to 400℃ at a heating rate of 5℃ / min, kept at this temperature for 180min, and cooled naturally. Finally, the obtained sample was ground and sealed to obtain a Fe / TiO2-MMT catalyst with an active metal content of 5wt.%.

[0044] Comparative Example 5 Take 50mg TiO2, 5mg Pt(NH3)4(NO3)2, and 11mg Fe(NO3)3 and place them in a polytetrafluoroethylene liner, and add 10-15mL deionized water dropwise and stir to mix evenly; then transfer them to a stainless steel reactor and heat them in an oven at 170℃ for 6h to obtain Pt-Fe / TiO2 solution; take 1g of a particle size of 0.5μm and a specific surface area of 500m 2 / g of MMT was completely immersed in Pt-Fe / TiO2 solution, stirred continuously for 5 hours in a water bath at a constant temperature of 80℃ and a rotation speed of 300rpm, then placed in an oven at 80℃ to dry overnight, and then transferred to a muffle furnace for calcination. The temperature was raised to 400℃ at a heating rate of 5℃ / min, kept constant at this temperature for 180min, and cooled naturally. Finally, the obtained sample was ground and sealed to obtain a Pt-Fe / TiO2-MMT catalyst with an active metal content of 5wt.%.

[0045] Comparative Example 6 Take 50mg TiO2, 5mg Pt(NH3)4(NO3)2, and 11mg Fe(NO3)3 and place them in a polytetrafluoroethylene liner, and add 10-15mL deionized water dropwise and stir to mix evenly; then transfer them to a stainless steel reactor and heat them in an oven at 170℃ for 6h to obtain Pt-Fe / TiO2 solution; take 1g of a particle size of 0.5μm and a specific surface area of 500m 2 / g of MMT was mixed with 7.5g of concentrated sulfuric acid and 7.5g of phosphoric acid, stirred at a constant temperature of 90℃ for 6h, and then centrifuged and washed until neutral to obtain modified MMT; the modified MMT was completely immersed in Pt-Fe / TiO2 solution, stirred continuously for 5h in a water bath at a constant temperature of 80℃ and a speed of 300rpm, then placed in an oven at 80℃ to dry overnight, and then transferred to a muffle furnace for calcination, heated to 400℃ at a heating rate of 5℃ / min, kept at this temperature for 180min, and cooled naturally. Finally, the obtained sample was ground and sealed to obtain a Pt-Fe / TiO2-MMT catalyst with an active metal content of 5wt.%.

[0046] Comparative Example 7 Take 50mg TiO2, 5mg Pt(NH3)4(NO3)2, and 11mg Fe(NO3)3 and place them in a polytetrafluoroethylene liner, and add 10-15mL deionized water dropwise and stir to mix evenly; then transfer them to a stainless steel reactor and heat them in an oven at 170℃ for 6h to obtain Pt-Fe / TiO2 solution; take 1g of a particle size of 0.5μm and a specific surface area of 500m 2 / g of MMT was placed in 20mL of 6wt.% dilute nitric acid and ultrasonically treated for 1h to obtain modified MMT; the modified MMT was completely immersed in Pt-Fe / TiO2 solution, stirred continuously for 5h in a water bath at a constant temperature of 80℃ and a speed of 300rmp, then placed in an oven at 80℃ to dry overnight, and then transferred to a muffle furnace for calcination, heated to 400℃ at a heating rate of 5℃ / min, kept at a constant temperature for 180min, and cooled naturally. Finally, the obtained sample was ground and sealed to obtain a Pt-Fe / TiO2-MMT catalyst with an active metal content of 5wt.%.

[0047] Experimental Example 1 The catalysts obtained in Examples 1-6 were used to prepare acetic acid according to the process of Example 7. The reaction results were evaluated using liquid yield and acetic acid selectivity as evaluation indicators. The results are listed in Table 1.

[0048] Table 1. Catalyst evaluation for acetic acid production The process of thermal catalytic synthesis of acetic acid from methane and carbon dioxide over Pt-Fe / TiO2-MMT catalyst is shown in the attached figure. Figure 2 As shown in the figure, it can be seen that when a small amount of oxygen is introduced, Pt and TiO2 can form more Pt-O sites under the action of oxygen. Methane and carbon dioxide can more effectively generate acetic acid at the Pt-O sites. While generating acetic acid, Pt 2+ The catalyst also hydrolyzes the byproduct water to generate -OH, which promotes the carboxylation of CO2 to generate -COOH, positively promoting the production of acetic acid. The acetic acid is then separated by a condenser, and the remaining byproduct enters a circulation pipeline. Therefore, the Pt-Fe / TiO2-MMT catalyst prepared in the present invention can promote the production of acetic acid in many aspects under the process conditions of the present invention, avoid the formation of other impurities, and more efficiently produce acetic acid.

[0049] As shown in Table 1, the Pt-Fe / TiO2-MMT catalyst prepared by the method of the present invention has a high liquid yield and acetic acid selectivity, which can significantly improve the conversion efficiency of acetic acid preparation. 2 / g of MMT was modified with concentrated sulfuric acid and phosphoric acid in a ratio of 2:1. At the same time, the preparation conditions of Pt-Fe / TiO2-MMT catalyst were optimized. The liquid yield could reach up to 40% and the acetic acid selectivity reached 50%.

[0050] Experimental Example 2 The catalysts obtained in Comparative Examples 1-7 were used to prepare acetic acid according to the process of Example 7. The reaction results were evaluated using liquid yield and acetic acid selectivity as evaluation indicators. The results are listed in Table 2.

[0051] Table 2. Evaluation of the reaction of different catalysts for preparing acetic acid The catalyst prepared in Example 5 achieved a liquid yield of up to 40% and an acetic acid selectivity of 50%. As shown in Table 2, the catalysts in Comparative Examples 1 and 2, both of which did not contain MMT and were single metal (Pt or Fe) / TiO2 catalysts, exhibited very low liquid yields and acetic acid selectivities when used to prepare acetic acid, indicating low catalytic efficiency. The catalysts in Comparative Examples 3 and 4, single metal (Pt or Fe) / TiO2 catalysts containing modified MMT, exhibited improved catalytic performance when used to prepare acetic acid, but the liquid yield and acetic acid selectivity remained low, demonstrating that the bimetallic center of the present invention can effectively enhance the catalytic activity of the catalyst. The catalytic performance of the catalysts obtained in Comparative Example 5, which did not modify MMT, in Comparative Example 6, which modified MMT only with a mixed acid, and in Comparative Example 7, which modified MMT only with dilute nitric acid, all underperformed that of the catalyst prepared in the present invention, demonstrating that the gradient acidification modification of MMT in the present invention effectively enhances the catalytic activity of the catalyst.

[0052] Experimental Example 3 Acetic acid was prepared according to the process of Example 7 using the Zn-Fe / MMT catalyst prepared in patent CN118767922A, the monatomic magnesium catalyst prepared in patent CN118527129A, and the Pt-Fe / TiO2-MMT catalyst prepared in Example 5 of the present invention. The liquid yield, acetic acid selectivity, methane conversion, and acetic acid production rate were measured, and the results are listed in Table 3.

[0053] Table 3. Reaction evaluation of different catalysts for preparing acetic acid As shown in Table 3, under the process conditions of the present invention, the requirement that the amount of carbon dioxide fed must be ≥ the amount of methane fed is not satisfied. However, the catalyst prepared by the present invention can still achieve high selectivity. Compared with the catalyst prepared in the prior art, the Pt-Fe / TiO2-MMT catalyst prepared by the present invention has excellent catalytic performance for the direct synthesis of acetic acid from carbon dioxide and methane, with an acetic acid selectivity of 50.0%, a methane conversion of 12.3%, a liquid yield of 40.0%, and an acetic acid production rate of 204.6 μmol·g cat -1 ·h -1 .

[0054] Experimental Example 4 The process conditions and acetic acid production efficiency of Examples 7-9 were measured, and the results are listed in Table 4.

[0055] Table 4. Process conditions and acetic acid preparation efficiency As can be seen from Table 4, the present invention uses organic waste such as crop straw, kitchen waste, and livestock and poultry manure as raw materials to ferment and produce biogas. The methane content of the fermented biogas is 55-62%, and the carbon dioxide content is 35-40%. The mixed gas of methane and carbon dioxide obtained from the fermentation of the biogas is used in a series-coupled thermal catalytic process to prepare acetic acid. This can achieve a high liquid yield and acetic acid selectivity, reduce the steps of separating methane and carbon dioxide and purifying them to purified gas, and effectively reduce production costs. In addition, the present invention realizes waste resource utilization and has the advantages of being green and environmentally friendly, having high resource utilization, low energy consumption, and high selectivity for the target product.

Claims

1. A process for preparing acetic acid by anaerobic fermentation in series coupled with fixed-bed thermal catalysis, characterized by: The following steps are involved: (1) Anaerobic fermentation of organic waste to produce biogas; (2) Purifying the biogas to obtain a purified methane / carbon dioxide mixed gas; (3) The purified methane / carbon dioxide mixed gas is introduced into the reactor and subjected to a thermal catalytic reaction under the action of a Pt-Fe / TiO2-MMT catalyst to produce an acetic acid mixture; (4) Condensing and separating the acetic acid mixture to obtain acetic acid and recovering the unreacted gas.

2. The process for preparing acetic acid by anaerobic fermentation in series coupled with fixed-bed thermal catalysis according to claim 1, characterized in that: In step (1), the pH value of the anaerobic fermentation is 6.8-7.5, the temperature of the anaerobic fermentation is 35-55° C., the stirring speed of the anaerobic fermentation is 1000 rpm, and the time of the anaerobic fermentation is 15-25 days.

3. The process for preparing acetic acid by anaerobic fermentation in series coupled with fixed-bed thermal catalysis according to claim 1, characterized in that: In step (1), the methane content in the biogas is 55-62%, and the carbon dioxide content is 35-40%.

4. The process for preparing acetic acid by anaerobic fermentation in series coupled with fixed-bed thermal catalysis according to claim 1, characterized in that: In step (3), the active metal component of the Pt-Fe / TiO2-MMT catalyst is Pt-Fe bimetallic, the carrier is TiO2 and modified MMT, and the active metal content is 5-6 wt.%.

5. The process for preparing acetic acid by anaerobic fermentation in series coupled with fixed-bed thermal catalysis according to claim 1 or 4, characterized in that: The preparation steps of the Pt-Fe / TiO2-MMT catalyst are as follows: (a) In the presence of deionized water or an organic solvent, a soluble Pt salt, a soluble Fe salt, and TiO2 powder undergo a hydrothermal reaction to generate a Pt-Fe / TiO2 solution. (b) Sodium montmorillonite (MMT) was stirred with mixed acid at a constant temperature of 90°C for 6 h, washed by centrifugation until neutral, and then placed in a nitric acid solution and ultrasonicated for 1 h to obtain modified MMT; (c) The modified MMT was completely immersed in the Pt-Fe / TiO2 solution to form the catalyst and obtain the Pt-Fe / TiO2-MMT catalyst.

6. The process for preparing acetic acid by anaerobic fermentation in series coupled with fixed-bed thermal catalysis according to claim 5, characterized in that: In step (a), the ratio of the soluble Pt salt, the soluble Fe salt, the TiO2 powder, the MMT and the deionized water or the organic solvent is 5 mg:11 mg:50 mg:(1-2) g:(10-15) mL.

7. The process for preparing acetic acid by anaerobic fermentation in series coupled with fixed-bed thermal catalysis according to claim 5, characterized in that: In step (a), the soluble Pt salt is at least one of chloroplatinic acid, tetraammineplatinum nitrate, and potassium chloroplatinite; the soluble Fe salt is at least one of ferric nitrate, ferric chloride, and ferric sulfate; the TiO2 is nano-scale anatase hydrophilic type; and the organic solvent is dimethylformamide or ethylene glycol.

8. The process for preparing acetic acid by anaerobic fermentation in series coupled with fixed-bed thermal catalysis according to claim 5, characterized in that: In step (b), the particle size of the MMT is 0.5-0.8 μm, and the specific surface area of the MMT is 500-650 m 2 / g; the mixed acid is a mixed solution of concentrated sulfuric acid and phosphoric acid in a mass ratio of (1-3):1; the mass ratio of MMT to the mixed acid is 1:

15.

9. The process for preparing acetic acid by anaerobic fermentation in series coupled with fixed-bed thermal catalysis according to claim 5, characterized in that: In step (c), the specific steps of forming the catalyst are: completely immersing the acid-treated MMT in a Pt-Fe / TiO2 solution, continuously stirring for 4-6 hours in a water bath at a constant temperature of 80-100°C and a rotation speed of 300-500 rpm, then placing it in an oven at 80°C to dry overnight, and then transferring it to a muffle furnace for calcination, heating it to 400-450°C at a heating rate of no more than 5°C / min, keeping the temperature constant for 180 minutes, cooling it naturally, grinding and sieving it, and sealing it.

10. The process for preparing acetic acid by anaerobic fermentation in series coupled with fixed-bed thermal catalysis according to claim 1, characterized in that: In step (3), the temperature of the thermal catalytic reaction is 400-550° C., the pressure of the thermal catalytic reaction is 2-5 MPa, the time of the thermal catalytic reaction is 6-18 h, and the stirring speed of the thermal catalytic reaction is 800-2000 rpm.

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