Process for preparing acetic acid by anaerobic fermentation coupled with fixed bed thermal catalysis in series

Abstract

The application discloses a process for preparing acetic acid by anaerobic fermentation and fixed bed thermal catalysis in series coupling, and belongs to the technical field of new energy and chemical industry. Fe and Pt are used as metal centers, TiO2 and MMT are used as carriers, active metals are deposited on the carriers by a hydrothermal method, a Pt-Fe / TiO2-MMT bimetallic composite carrier catalyst is prepared, organic waste is used as raw material, biogas is prepared by anaerobic fermentation, methane and carbon dioxide are obtained by purification, the methane and carbon dioxide are used as substrates, and acetic acid is prepared by fixed bed reactor thermal catalysis. The application realizes that the gas fermented from the organic waste is directly used for synthesizing acetic acid, 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 in a certain proportion in the prior art, simplifies a process flow, has high resource utilization, reaction byproducts can be recycled, environmental pollution is reduced, and the application accords with the environmental protection concept.

Description

TECHNICAL FIELD

[0001] The present application relates to a process for preparing acetic acid by anaerobic fermentation and fixed-bed thermal catalysis in series coupling, belonging to the field of new energy and chemical technology. BACKGROUND

[0002] With the development of global economy, the demand for energy is increasing, and traditional fossil energy is facing exhaustion and causing serious environmental pollution problems. Therefore, it is urgent to develop renewable and clean energy. Biogas, as a kind of biomass energy, has the advantages of being renewable and widely distributed, and its development and utilization have attracted widespread attention. A large amount of organic waste, such as crop straw, livestock manure, municipal sludge, etc., is generated in agriculture, industry and daily life. Improper disposal of these wastes will cause environmental pollution and waste of resources. Biogas fermentation is a biochemical process centered on anaerobic microorganisms. By converting organic waste such as crop straw, livestock manure, kitchen waste, etc. into renewable energy biogas (mainly composed of methane CH4 and carbon dioxide CO2), it can also produce organic fertilizer such as biogas slurry and biogas residue, achieving waste reduction, resource utilization and harmless treatment, and improving resource recycling rate.

[0003] Acetic acid is an important organic chemical raw material, which is widely used in PTA (terephthalic acid), vinyl acetate, acetate, and acetic anhydride production fields, and is an important raw material for synthetic fibers, adhesives, medicines, dyes and pesticides. In the food industry, acetic acid is the main component of edible vinegar, and is also used to make yogurt, salad dressing and other foods, and as a food additive for pickled foods. In addition, with the development of technology, the application of acetic acid in the fields of medicine, agriculture and cleaning products is also expanding. The production of acetic acid mainly relies on steam reforming process and carbonylation process derived from petroleum chemical raw materials. The traditional industrial synthesis of acetic acid includes methane reforming to synthesis gas, synthesis gas to methanol, and methanol carbonylation to acetic acid. However, such processes have problems such as difficulty in recovering noble metal catalysts, high energy consumption, and high carbon emissions. Direct use of methane and carbon dioxide to produce acetic acid can consume CH4 and CO2, reduce the emission of two kinds of greenhouse gases, and reduce carbon emissions. However, the selectivity of the existing acetic acid preparation method is low, and the existing technology for direct synthesis of acetic acid from methane and carbon dioxide requires the input of pure carbon dioxide and methane gas, and the input amount of carbon dioxide should be greater than or equal to the input amount of methane, which has strict reaction conditions.

[0004] Therefore, by anaerobic fermentation of organic waste to produce biogas, and then efficiently utilizing the main components of biogas, methane (CH4) and carbon dioxide (CO2), to directly convert them into high-value chemical acetic acid, the energy utilization can be optimized, which is an important direction for current technical process research. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application aims to provide an anaerobic fermentation series coupling fixed bed thermal catalysis process for preparing acetic acid, which realizes efficient conversion of acetic acid and has mild reaction conditions, is green and environmentally friendly, and has high resource utilization rate.

[0006] To solve the above technical problems, the technical scheme provided by the present application is:

[0007] An anaerobic fermentation series coupling fixed bed thermal catalysis process for preparing acetic acid comprises the following steps:

[0008] (1) anaerobic fermentation of organic waste to obtain biogas;

[0009] (2) purification of the biogas to obtain a purified methane / carbon dioxide mixed gas;

[0010] (3) passing the purified methane / carbon dioxide gas into a reactor to perform thermal catalysis under the action of a Pt-Fe / TiO2-MMT catalyst to obtain an acetic acid mixture;

[0011] (4) condensation and separation of the acetic acid mixture to obtain acetic acid and recover reaction by-products and unreacted gas.

[0012] Further, in step (1), the organic waste comprises crop straw, kitchen waste and livestock manure.

[0013] Further, in step (1), the pH value of the anaerobic fermentation is 6.8-7.5, the temperature of the anaerobic fermentation is 35-55℃, the stirring speed of the anaerobic fermentation is 1000rmp, and the time of the anaerobic fermentation is 15-25 days.

[0014] Further, in step (1), the content of methane in the biogas is 55-62%, and the content of carbon dioxide is 35-40%.

[0015] Further, in step (2), the purification uses a purification device, which comprises desulfurization, dehydration and separation treatment.

[0016] Further, the desulfurization and dehydration treatment is as follows: iron oxide or activated carbon adsorption is used to reduce the concentration of H2S to below 5ppm, and then a condensing device is used to reduce the humidity of the gas; an evaporator is used to reduce the temperature to below the dew point (10℃ lower than the minimum ambient temperature) to make the water vapor in the mixed gas begin to condense into liquid water, which is discharged through a water guide pipe to complete humidity separation and control the humidity of the gas to be 40-60%; the dehumidified gas is warmed to room temperature by a condenser to avoid excessively low air temperature;

[0017] The separation treatment is: separating methane and carbon dioxide by membrane separation or pressure swing adsorption (PSA) process, and increasing the content of methane and carbon dioxide to more than 95%; wherein, the membrane separation process selects a selective permeation membrane material, the molecular size of CO2 is smaller than that of methane, and the diffusivity is high, that is, carbon dioxide will preferentially permeate the membrane, and methane will be intercepted; the pressure swing adsorption process will preferentially adsorb carbon dioxide at a high pressure of 3-5 MPa, and methane will be excluded from the top of the adsorption. Through desulfurization and dehydration treatment, H2S and water are removed, and the mixed gas of methane and carbon dioxide is retained, which is directly used for the synthesis of acetic acid subsequently.

[0018] Further, in step (3), the thermal catalytic reaction is divided into a preheating section and a reaction section, and the reaction section and the preheating section are independently controlled in temperature; and the reactor is a fixed bed reactor.

[0019] Further, in step (3), the active metal component of the Pt-Fe / TiO2-MMT catalyst is a Pt-Fe bimetal, the carrier is TiO2 and modified MMT, and the active metal content is 5-6 wt.%.

[0020] 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 noble metal and has good catalytic activity, Pt can effectively promote the activation of the C-H bond of CH4 to generate methyl radicals (-CH3) in photocatalysis, Pt can significantly reduce the activation energy barrier of C-H, promote dehydrogenation, Pt and Fe produce a synergistic effect, which can adjust the adsorption strength of the intermediate, inhibit excessive dehydrogenation, enhance the activity of CO2, and thus inhibit the excessive reaction of the intermediate product. At the same time, Pt is used to modify TiO2, which can form a metal-semiconductor interface, enhance the separation efficiency of photo-generated electrons and holes, and Pt and TiO2 can form Pt-O and Pt 2+ , which produces more B acid sites, and these unique structures can optimize the adsorption of CO2 and promote the generation of -COOH. Methane and CO2 selectively generate acetic acid at the Pt-O site, and Pt is reduced to efficiently release acetic acid at the same time, which can effectively avoid the problem of excessive oxidation.

[0021] The photo-generated electron-hole pairs of TiO2 can promote the decomposition of H2O to generate -OH, the thermal stability and chemical stability of MMT are good, and the modification using the cation exchange property has great advantages in metal loading. The modification of MMT by gradient treatment with mixed acid can avoid excessive damage to the crystal structure of MMT, make the acid sites of MMT more uniform, and enable Pt and Fe to be more uniformly dispersed and loaded; concentrated sulfuric acid can etch the impurities on the surface of MMT, and then the strong acidity of phosphoric acid is used to expand the interlayer oxygen density of montmorillonite to form a porous structure, and the high interlayer oxygen density is conducive to adjusting the adsorption and activation efficiency of CO2; at the same time, dilute nitric acid is used to improve the cation exchange performance of MMT to enhance the catalytic performance of MMT as a carrier.

[0022] Therefore, the synergistic effect of Pt-Fe bimetal and TiO2-MMT composite carrier can improve the activity of the catalyst and the selectivity of acetic acid, realize efficient conversion of biogas resources, reduce the dependence on traditional fossil energy, reduce carbon emissions, and has significant economic benefits and environmental value.

[0023] Further, the preparation steps of the Pt-Fe / TiO2-MMT catalyst are:

[0024] (a) In the presence of deionized water or an organic solvent, a soluble Pt salt, a soluble Fe salt, and TiO2 powder are reacted by hydrothermal induction to generate a Pt-Fe / TiO2 solution;

[0025] (b) The sodium-based montmorillonite MMT is stirred with mixed acid at a constant temperature of 90℃ for 6h, washed by centrifugation until neutral, and then placed in a nitric acid solution for ultrasonic treatment for 1h to obtain modified MMT;

[0026] (c) The modified MMT is completely immersed in the Pt-Fe / TiO2 solution to form a catalyst, and a Pt-Fe / TiO2-MMT catalyst is obtained.

[0027] Further, in step (a), the preparation steps of the Pt-Fe / TiO2 solution are: weighing a soluble Pt salt and a soluble Fe salt into a container, adding TiO2 powder, adding deionized water or an organic solvent, mixing thoroughly, then transferring to a polytetrafluoroethylene hydrothermal kettle, and hydrothermal reaction at 160-180℃ in an oven for 5-8h to obtain a Pt-Fe / TiO2 solution.

[0028] Further, 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 5mg:11mg:50mg:(1-2)g:(10-15)mL.

[0029] Further, in step (a), the soluble Pt salt is at least one of chloroplatinic acid, tetraammine platinum nitrate, potassium chloroplatinite; the soluble Fe salt is at least one of ferric nitrate, ferric chloride, ferric sulfate; the TiO2 is nanoscale anatase hydrophilic type; and the organic solvent is one of dimethylformamide and ethylene glycol.

[0030] Further, in step (b), the particle size of the MMT is 0.5-0.8 μm, 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 the MMT to the mixed acid is 1:15; and the nitric acid solution is a dilute nitric acid solution with a concentration of 6 wt.%, and the ratio of the MMT to the dilute nitric acid is 1 g:20 mL.

[0031] Further, in step (c), the specific steps of forming the catalyst are as follows: the acid-treated MMT is completely immersed in a Pt-Fe / TiO2 solution, continuously stirred at a constant temperature of 80℃ and a rotation speed of 300-500 rpm in a water bath, then placed in an oven at 80℃ for drying overnight, then transferred to a muffle furnace for calcination, heated to 400-450℃ at a heating rate of not more than 5℃ / min, kept at a constant temperature of 150-180 min, naturally cooled, ground, sieved and stored.

[0032] Further, in step (3), the temperature of the thermal catalytic reaction is 400-550℃, 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 rotation speed of the thermal catalytic reaction is 800-2000 rpm. Under the conditions of high temperature and high pressure, the direct oxidative coupling reaction of methane and carbon dioxide is realized to generate acetic acid. In the prior art, methane and carbon dioxide are directly used to synthesize acetic acid, and the amount of carbon dioxide introduced is required to be greater than or equal to the amount of methane introduced. However, in the present application, the biogas after fermentation is directly used, the content of methane is 55-62%, the content of carbon dioxide is 35-40%, and the ratio of carbon dioxide to methane is not the optimal ratio. However, the catalyst prepared by the present application still has high selectivity and high synthesis efficiency of acetic acid.

[0033] Further, in step (4), the purity of the acetic acid is >99%. The acetic acid is stored in a corrosion-resistant storage tank.

[0034] Further, in step (4), the condensation separation is carried out by a condensation separation device to separate acetic acid, and the condensation separation temperature is 20-25℃. During the reaction, byproducts including unreacted gas or H2O are generated, which can be recycled and returned to the reactor for repeated use or further treatment through a recycling pipeline.

[0035] Compared with the prior art, the present application has the following advantages:

[0036] (1) The present application uses agricultural and forestry biomass waste as raw material to produce biogas through anaerobic fermentation, and then uses the biogas to prepare acetic acid through a heat catalytic process, so as to realize the resource utilization of waste, and has the advantages of green environmental protection, high resource utilization rate, low energy consumption, and high selectivity of target product.

[0037] (2) The present application provides a preparation method of a new type of Pt-Fe / TiO2-MMT catalyst, which is prepared by loading metals on TiO2 and MMT through hydrothermal induction, and is used for preparing acetic acid through biogas fermentation coupled heat catalysis, and has high acetic acid yield and selectivity, and can improve the efficiency of acetic acid preparation.

[0038] (3) The preparation process of the catalyst is simple, the prepared catalyst has the characteristics of uniform particle dispersion, small size, good activity and stability, and the carrier and organic solvent used are widely available and low in price, which can effectively reduce the production cost of noble metal catalyst in the acetic acid preparation experiment process.

[0039] (4) The process route for preparing acetic acid provided by the present application realizes the direct use of gas fermented from organic waste for synthesizing acetic acid, without the need of separating methane and carbon dioxide, or without the need of introducing carbon dioxide and methane in a certain proportion, so that the process flow is simplified, the reaction by-products can be recycled, the pollution to the environment is reduced, and the environmental protection concept is met.

[0040] (5) The present application directly uses organic waste as raw material, the content of methane in the obtained biogas is 55-62%, the content of carbon dioxide is 35-40%, and the mixed gas of methane and carbon dioxide obtained by fermenting the above biogas is catalytically synthesized into acetic acid by using the catalyst prepared by the present application, which can realize a liquid yield of 40% and an acetic acid selectivity of 50%. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 is a process route for preparing acetic acid through anaerobic fermentation coupled fixed bed heat catalysis;

[0042] Figure 2 is a process route for heat catalytically synthesizing acetic acid from methane and carbon dioxide under the action of a Pt-Fe / TiO2-MMT catalyst. DETAILED DESCRIPTION

[0043] Example 1

[0044] Take 50mg TiO2, 5mg Pt(NH3)4(NO3)2, 11mg Fe(NO3)3 in a polytetrafluoroethylene liner, and drop 10-15mL of deionized water drop by drop, stir and mix evenly; then transfer to a stainless steel reaction kettle, hydrothermal at 170°C in an oven for 6h, get Pt-Fe / TiO2 solution; take 1g of MMT with a particle size of 0.5μm and a specific surface area of 500m 2 / g, mix with 7.5g of concentrated sulfuric acid and 7.5g of phosphoric acid, stir at constant temperature 90°C for 6h, then centrifugal wash to neutral, then put into 20mL of dilute nitric acid with a concentration of 6wt.% and treat with ultrasonic for 1h, get modified MMT; immerse the modified MMT in the Pt-Fe / TiO2 solution completely, continuously stir at constant temperature 80°C and rotation speed 300rmp in a water bath, then put in an oven at 80°C and dry overnight, then transfer to a muffle furnace for calcination, heat to 400°C at a heating rate of 5°C / min, keep constant temperature for 180min, natural cooling, finally grind and seal the obtained sample, get Pt-Fe / TiO2-MMT catalyst with active metal content of 5wt.%.

[0045] Example 2

[0046] Take 50mg TiO2, 5mg Pt(NH3)4(NO3)2, 11mg Fe(NO3)3 in a polytetrafluoroethylene liner, and drop 10-15mL of deionized water drop by drop, stir and mix evenly; then transfer to a stainless steel reaction kettle, hydrothermal at 170°C in an oven for 6h, get Pt-Fe / TiO2 solution; take 1g of MMT with a particle size of 0.5μm and a specific surface area of 500m 2 / g, mix with 7.5g of concentrated sulfuric acid and 7.5g of phosphoric acid, stir at constant temperature 90°C for 6h, then centrifugal wash to neutral, then put into 20mL of dilute nitric acid with a concentration of 6wt.% and treat with ultrasonic for 1h, get modified MMT; immerse the modified MMT in the Pt-Fe / TiO2 solution completely, continuously stir at constant temperature 80°C and rotation speed 300rmp in a water bath, then put in an oven at 80°C and dry overnight, then transfer to a muffle furnace for calcination, heat to 400°C at a heating rate of 5°C / min, keep constant temperature for 180min, natural cooling, finally grind and seal the obtained sample, get Pt-Fe / TiO2-MMT catalyst with active metal content of 5wt.%.

[0047] Example 3

[0048] Take 50 mg TiO2, 5 mg Pt(NH3)4(NO3)2, 11 mg Fe(NO3)3 in a polytetrafluoroethylene liner, and drop 10-15 mL of deionized water drop by drop, stir and mix evenly; then transfer to a stainless steel reaction kettle, hydrothermal at 170°C in an oven for 6h, get Pt-Fe / TiO2 solution; take 1 g of MMT with a particle size of 0.8 μm and a specific surface area of 650 m 2 / g, mix with 11.25 g of concentrated sulfuric acid and 3.75 g of phosphoric acid, stir at constant temperature 90°C for 6h, then centrifugal wash to neutral, then put into 20 mL of dilute nitric acid with a concentration of 6wt.% and treat with ultrasonic for 1h, get modified MMT; immerse the modified MMT in the Pt-Fe / TiO2 solution completely, continuously stir at constant temperature 80°C and rotation speed 300rmp in a water bath, then place in an oven at 80°C and dry overnight, then transfer to a muffle furnace for calcination, heat to 400°C at a heating rate of 5°C / min, keep constant temperature for 180 min, natural cooling, finally grind and seal the obtained sample, get Pt-Fe / TiO2-MMT catalyst with active metal content of 5wt.%.

[0049] Example 4

[0050] Take 50 mg TiO2, 5 mg Pt(NH3)4(NO3)2, 11 mg Fe(NO3)3 in a polytetrafluoroethylene liner, and drop 10-15 mL of deionized water drop by drop, stir and mix evenly; then transfer to a stainless steel reaction kettle, hydrothermal at 170°C in an oven for 6h, get Pt-Fe / TiO2 solution; take 1 g of MMT with a particle size of 0.8 μm and a specific surface area of 650 m 2 / g, mix with 11.25 g of concentrated sulfuric acid and 3.75 g of phosphoric acid, stir at constant temperature 90°C for 6h, then centrifugal wash to neutral, then put into 20 mL of dilute nitric acid with a concentration of 6wt.% and treat with ultrasonic for 1h, get modified MMT; immerse the modified MMT in the Pt-Fe / TiO2 solution completely, continuously stir at constant temperature 80°C and rotation speed 300rmp in a water bath, then place in an oven at 80°C and dry overnight, then transfer to a muffle furnace for calcination, heat to 400°C at a heating rate of 5°C / min, keep constant temperature for 180 min, natural cooling, finally grind and seal the obtained sample, get Pt-Fe / TiO2-MMT catalyst with active metal content of 5wt.%.

[0051] Example 5

[0052] Take 50 mg TiO2, 5 mg Pt(NH3)4(NO3)2, 11 mg Fe(NO3)3 in a polytetrafluoroethylene liner, and drop 10-15 mL of deionized water drop by drop, stir and mix evenly, then transfer to a stainless steel reaction kettle, hydrothermal at 180℃ in an oven for 6h, get Pt-Fe / TiO2 solution; take 2g of MMT with a particle size of 0.6μm and a specific surface area of 600m 2 / g, mix with 20g concentrated sulfuric acid and 10g phosphoric acid, stir at constant temperature 90℃ for 6h, then centrifugal wash to neutral, then put into 20mL of dilute nitric acid with a concentration of 6wt.% and treat with ultrasonic for 1h, get modified MMT; immerse the modified MMT in the Pt-Fe / TiO2 solution completely, continuously stir at constant temperature 80℃ and rotation speed 400rmp in a water bath, then place in an oven at 80℃ and dry overnight, then transfer to a muffle furnace for calcination, heat to 420℃ at a heating rate of 3℃ / min, keep constant temperature for 150min, naturally cool down, finally grind and seal the obtained sample, get Pt-Fe / TiO2-MMT catalyst with active metal content of 5wt.%.

[0053] Example 6

[0054] Take 50 mg TiO2, 5 mg Pt(NH3)4(NO3)2, 11 mg Fe(NO3)3 in a polytetrafluoroethylene liner, and drop 10-15 mL of deionized water drop by drop, stir and mix evenly, then transfer to a stainless steel reaction kettle, hydrothermal at 180℃ in an oven for 6h, get Pt-Fe / TiO2 solution; take 2g of MMT with a particle size of 0.6μm and a specific surface area of 600m 2 / g, mix with 20g concentrated sulfuric acid and 10g phosphoric acid, stir at constant temperature 90℃ for 6h, then centrifugal wash to neutral, then put into 20mL of dilute nitric acid with a concentration of 6wt.% and treat with ultrasonic for 1h, get modified MMT; immerse the modified MMT in the Pt-Fe / TiO2 solution completely, continuously stir at constant temperature 80℃ and rotation speed 400rmp in a water bath, then place in an oven at 80℃ and dry overnight, then transfer to a muffle furnace for calcination, heat to 420℃ at a heating rate of 3℃ / min, keep constant temperature for 150min, naturally cool down, finally grind and seal the obtained sample, get Pt-Fe / TiO2-MMT catalyst with active metal content of 5wt.%.

[0055] Example 7

[0056] An anaerobic fermentation series coupling fixed bed thermal catalytic process for preparing acetic acid, comprising the following steps:

[0057] (1) the organic waste kitchen garbage is anaerobically fermented under the conditions of pH 7.1, temperature 40℃ and stirring speed 1000rmp for 20 days to produce biogas, the methane content in the obtained biogas is 55%, and the carbon dioxide content is 40%;

[0058] (2) the biogas is adsorbed by using iron oxide or activated carbon to reduce the concentration of H2S to below 5ppm, then the gas humidity is reduced by a condensing device, then the methane and carbon dioxide are separated by using a membrane separation or pressure swing adsorption (PSA) process, the content of methane and carbon dioxide is increased to above 95%, and the purified methane / carbon dioxide mixed gas is obtained;

[0059] (3) the purified methane / carbon dioxide mixed gas is introduced into a reactor, and under the action of a Pt-Fe / TiO2-MMT catalyst, thermal catalytic reaction is carried out at a temperature of 450℃, a pressure of 3MPa and a rotating speed of 1000rmp for 10h to produce an acetic acid mixture;

[0060] (4) the acetic acid mixture is separated by a condensing separation device to separate acetic acid, the cooling temperature is 23℃, the purity of the obtained acetic acid is above 99%, the reaction byproducts and unreacted gas are recovered and returned to the reactor through a circulating pipeline for continuous utilization or further treatment.

[0061] Example 8

[0062] A process for preparing acetic acid by anaerobic fermentation and coupling fixed bed thermal catalysis in series, comprising the following steps:

[0063] (1) the organic waste crop straw is anaerobically fermented under the conditions of pH 6.8, temperature 55℃ and stirring speed 1000rmp for 25 days to produce biogas, the methane content in the obtained biogas is 62%, and the carbon dioxide content is 35%;

[0064] (2) the biogas is adsorbed by using iron oxide or activated carbon to reduce the concentration of H2S to below 5ppm, then the gas humidity is reduced by a condensing device, then the methane and carbon dioxide are separated by using a membrane separation process, the content of methane and carbon dioxide is increased to above 95%, and the purified methane / carbon dioxide mixed gas is obtained;

[0065] (3) the purified methane / carbon dioxide mixed gas is introduced into a reactor, and under the action of a Pt-Fe / TiO2-MMT catalyst, thermal catalytic reaction is carried out at a temperature of 550℃, a pressure of 2MPa and a rotating speed of 800rmp for 18h to produce an acetic acid mixture;

[0066] (4) The acetic acid mixture is separated into acetic acid by a condensation separation device, the cooling temperature is 20℃, acetic acid with purity of more than 99% is obtained, reaction by-products and unreacted gas are recovered, and returned to the reactor through a circulation pipeline for continuous utilization or further treatment.

[0067] Example 9

[0068] A process for preparing acetic acid by anaerobic fermentation and fixed-bed thermal catalysis in series coupling, comprising the following steps:

[0069] (1) The livestock manure is subjected to anaerobic fermentation under the conditions of pH 7.5, temperature 35℃ and stirring speed 1000rmp for 15 days to produce biogas, wherein the methane content in the obtained biogas is 60% and the carbon dioxide content is 35%;

[0070] (2) The biogas is adsorbed by iron oxide or activated carbon to reduce the concentration of H2S to less than 5ppm, then the gas humidity is reduced by a condensation device, and 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;

[0071] (3) The purified methane / carbon dioxide mixed gas is introduced into a reactor, and under the action of a Pt-Fe / TiO2-MMT catalyst, thermal catalytic reaction is carried out under the conditions of temperature 400℃, pressure 5MPa and rotation speed 2000rmp for 6h to produce an acetic acid mixture;

[0072] (4) The acetic acid mixture is separated into acetic acid by a condensation separation device, the cooling temperature is 25℃, acetic acid with purity of more than 99% is obtained, reaction by-products and unreacted gas are recovered, and returned to the reactor through a circulation pipeline for continuous utilization or further treatment.

[0073] Comparative Example 1

[0074] Take 50mg TiO2, 5mg Pt(NH3)4(NO3)2, place them in a polytetrafluoroethylene liner, and drop 10-15mL of deionized water drop by drop, stir and mix uniformly, then transfer to a stainless steel reaction kettle, hydrothermal at 170℃ in an oven for 6h to obtain a Pt / TiO2 solution; dry the Pt / TiO2 solution at 80℃ overnight, then heat to 400℃ at a temperature rising rate of 5℃ / min, keep constant temperature for 180min, naturally cool down, finally grind and seal the obtained sample to obtain a Pt / TiO2 catalyst with active metal content of 5wt.%.

[0075] Comparative Example 2

[0076] Take 50 mg TiO2, 11 mg Fe(NO3)3, and add 10-15 mL of deionized water drop by drop in a polytetrafluoroethylene liner, mix well, then transfer to a stainless steel reactor, hydrothermal at 170°C in an oven for 6h, to obtain a Fe / TiO2 solution; dry the Fe / TiO2 solution at 80°C overnight, then heat to 400°C at a rate of 5°C / min, and keep constant temperature for 180 min, natural cooling, finally grind and seal the obtained sample, to obtain a Fe / TiO2 catalyst with an active metal content of 5wt.%.

[0077] Comparative Example 3

[0078] Take 50 mg TiO2, 5 mg Pt(NH3)4(NO3)2, and add 10-15 mL of deionized water drop by drop in a polytetrafluoroethylene liner, mix well, then transfer to a stainless steel reactor, hydrothermal at 170°C in an oven for 6h, to obtain a Pt / TiO2 solution; take 1 g of MMT with a particle size of 0.5 μm and a specific surface area of 500 m 2 / g, mix with 7.5 g of concentrated sulfuric acid and 7.5 g of phosphoric acid, stir at constant temperature of 90°C for 6h, then centrifuge and wash to neutral, then put into dilute nitric acid with a concentration of 6wt.% and treat with ultrasonic for 1h, to obtain modified MMT; immerse the modified MMT completely in the Pt / TiO2 solution, continuously stir at constant temperature of 80°C and rotation speed of 300rmp in a water bath, then dry in an oven at 80°C overnight, then transfer to a muffle furnace for calcination, heat to 400°C at a rate of 5°C / min, keep constant temperature for 180 min, natural cooling, finally grind and seal the obtained sample, to obtain a Pt / TiO2-MMT catalyst with an active metal content of 5wt.%.

[0079] Comparative Example 4

[0080] Take 50 mg TiO2, 11 mg Fe(NO3)3, and add 10-15 mL of deionized water drop by drop in a polytetrafluoroethylene liner, mix well, then transfer to a stainless steel reactor, hydrothermal at 170°C in an oven for 6h, to obtain a Fe / TiO2 solution; take 1 g of MMT with a particle size of 0.5 μm and a specific surface area of 500 m 2MMT with 7.5 g of concentrated sulfuric acid and 7.5 g of phosphoric acid, centrifuged and washed to neutral after stirring at a constant temperature of 90 °C for 6 h, then placed in dilute nitric acid with a concentration of 6 wt.% and treated by ultrasonic for 1 h, to obtain modified MMT; the modified MMT was completely immersed in the Fe / TiO2 solution, continuously stirred at a constant temperature of 80 °C and a rotation speed of 300 rpm in a water bath for 5 h, then placed in an oven at 80 °C for drying overnight, and then transferred to a muffle furnace for calcination, heated to 400 °C at a heating rate of 5 °C / min, kept at a constant temperature for 180 min, naturally cooled, and finally ground and sealed to obtain the Fe / TiO2-MMT catalyst with an active metal content of 5 wt.%.

[0081] Comparative Example 5

[0082] 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 uniformly; then transferred to a stainless steel reaction kettle, and hydrothermally treated at 170 °C in an oven for 6 h to obtain a Pt-Fe / TiO2 solution; 1 g of MMT with a particle size of 0.5 μm and a specific surface area of 500 m 2 / g was completely immersed in the Pt-Fe / TiO2 solution, continuously stirred at a constant temperature of 80 °C and a rotation speed of 300 rpm in a water bath for 5 h, then placed in an oven at 80 °C for drying overnight, and then transferred to a muffle furnace for calcination, heated to 400 °C at a heating rate of 5 °C / min, kept at a constant temperature for 180 min, naturally cooled, and finally ground and sealed to obtain the Pt-Fe / TiO2-MMT catalyst with an active metal content of 5 wt.%.

[0083] Comparative Example 6

[0084] 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 uniformly; then transferred to a stainless steel reaction kettle, and hydrothermally treated at 170 °C in an oven for 6 h to obtain a Pt-Fe / TiO2 solution; 1 g of MMT with a particle size of 0.5 μm and a specific surface area of 500 m 2MMT, 7.5 g of concentrated sulfuric acid and 7.5 g of phosphoric acid were mixed, and after stirring at a constant temperature of 90°C for 6 h, the mixture was centrifuged and washed to neutral to obtain modified MMT; the modified MMT was completely immersed in the Pt-Fe / TiO2 solution, and after continuous stirring at a constant temperature of 80°C and a rotation speed of 300 rpm in a water bath for 5 h, the mixture was dried in an oven at 80°C overnight, then transferred to a muffle furnace for calcination, and heated to 400°C at a heating rate of 5°C / min, kept at a constant temperature for 180 min, and naturally cooled down, finally the obtained sample was ground and sealed to obtain a Pt-Fe / TiO2-MMT catalyst with an active metal content of 5 wt.%.

[0085] Comparative Example 7

[0086] 50 mg of TiO2, 5 mg of Pt(NH3)4(NO3)2and 11 mg of Fe(NO3)3were placed in a polytetrafluoroethylene liner, and 10-15 mL of deionized water was added dropwise, and the mixture was stirred and mixed uniformly; then transferred to a stainless steel reaction kettle, and hydrothermally treated at 170°C in an oven for 6 h to obtain a Pt-Fe / TiO2 solution; 1 g of MMT with a particle size of 0.5 μm and a specific surface area of 500 m 2 / g was treated with 20 mL of dilute nitric acid with a concentration of 6 wt.% for 1 h under ultrasonic treatment to obtain modified MMT; the modified MMT was completely immersed in the Pt-Fe / TiO2 solution, and after continuous stirring at a constant temperature of 80°C and a rotation speed of 300 rpm in a water bath for 5 h, the mixture was dried in an oven at 80°C overnight, then transferred to a muffle furnace for calcination, and heated to 400°C at a heating rate of 5°C / min, kept at a constant temperature for 180 min, and naturally cooled down, finally the obtained sample was ground and sealed to obtain a Pt-Fe / TiO2-MMT catalyst with an active metal content of 5 wt.%.

[0087] Experimental Example 1

[0088] The catalysts obtained in Examples 1-6 were used to prepare acetic acid according to the process of Example 7, and the reaction results were evaluated, with liquid yield and acetic acid selectivity as the evaluation indexes, and the results are shown in Table 1.

[0089] Table 1. Reaction evaluation of catalysts for preparing acetic acid

[0090]

[0091] The process route of thermal catalytic synthesis of acetic acid from methane and carbon dioxide in the presence of a Pt-Fe / TiO2-MMT catalyst is shown in Figure 1. Figure 2As shown in the figure, a small amount of oxygen is introduced, and under the action of oxygen, Pt and TiO2 can form more Pt-O sites on the Pt-Fe / TiO2-MMT catalyst, and methane and carbon dioxide can be more effectively converted into acetic acid on the Pt-O sites. At the same time, Pt 2+ is reduced to Pt; meanwhile, the byproduct water can be hydrolyzed to -OH under the action of the catalyst, promote the carboxylation of CO2 to generate -COOH, and have a positive promoting effect on the generation of acetic acid. The acetic acid is separated through a condensing device, and the remaining byproducts enter the circulation pipeline. Therefore, the Pt-Fe / TiO2-MMT catalyst prepared by the present application can promote the generation of acetic acid in multiple ways under the process conditions of the present application, avoid the generation of other impurities, and more effectively prepare acetic acid.

[0092] As can be seen from Table 1, the Pt-Fe / TiO2-MMT catalyst prepared by the method of the present application has high liquid yield and acetic acid selectivity, and can significantly improve the conversion efficiency of acetic acid preparation. Among them, when 2g of MMT with a particle size of 0.6μm and a specific surface area of 600m 2 / g is selected, the MMT is modified with concentrated sulfuric acid and phosphoric acid at a ratio of 2:1, and the preparation conditions of the Pt-Fe / TiO2-MMT catalyst are optimized, the liquid yield can reach 40%, and the acetic acid selectivity can reach 50%.

[0093] Experimental Example 2

[0094] The catalysts obtained in Comparative Examples 1-7 were used to prepare acetic acid according to the process method of Example 7, and the reaction results were evaluated with liquid yield and acetic acid selectivity as the evaluation indexes, and the results are shown in Table 2.

[0095] Table 2. Reaction evaluation of acetic acid prepared by different catalysts

[0096]

[0097] The liquid yield of the catalyst prepared in Example 5 can be up to 40%, and the acetic acid selectivity can reach 50%. As can be seen from Table 2, the catalysts of Comparative Example 1 and Comparative Example 2 do not contain MMT and are single-metal (Pt or Fe) / TiO2 catalysts, and when the catalysts are used to catalyze the preparation of acetic acid, the liquid yield and the acetic acid selectivity are both low, and the catalytic acetic acid efficiency is low; the catalysts of Comparative Example 3 and Comparative Example 4 contain modified MMT and are single-metal (Pt or Fe) / TiO2 catalysts, and when the catalysts are used to catalyze the preparation of acetic acid, the catalytic performance is improved, but the liquid yield and the acetic acid selectivity are still low, which shows that the bimetallic center of the application can effectively improve the catalytic activity of the catalyst; the catalysts of Comparative Example 5, Comparative Example 6 and Comparative Example 7 are not modified by the gradient acid treatment, which shows that the gradient acid treatment of MMT can effectively improve the catalytic activity of the catalyst.

[0098] Experimental Example 3

[0099] The Zn-Fe / MMT catalyst prepared by using the patent CN118767922A, the single-atom magnesium catalyst prepared by using the patent CN118527129A and the Pt-Fe / TiO2-MMT catalyst prepared in Example 5 of the application are used to prepare acetic acid according to the process method of Example 7, and the liquid yield, the acetic acid selectivity, the methane conversion rate and the acetic acid generation rate are determined, and the results are shown in Table 3.

[0100] Table 3. Reaction evaluation of different catalysts for preparing acetic acid

[0101]

[0102] As can be seen from Table 3, under the process conditions of the application, the amount of carbon dioxide does not meet the amount of methane, but the catalyst prepared by using the application can still achieve high selectivity. Compared with the catalyst prepared by using the prior art, the Pt-Fe / TiO2-MMT catalyst prepared by using the application has very good catalytic performance for directly synthesizing acetic acid from carbon dioxide and methane, the acetic acid selectivity is 50.0%, the methane conversion rate is 12.3%, the liquid yield is 40.0%, and the acetic acid generation rate is 204.6 μmol·g cat -1 ·h -1 .

[0103] Experimental Example 4

[0104] The process conditions and the acetic acid preparation efficiency of Examples 7-9 are determined, and the results are shown in Table 4.

[0105] Table 4. Process conditions and acetic acid preparation efficiency

[0106]

[0107] As can be seen from Table 4, the present application uses crop stalks, kitchen waste, livestock and poultry manure and other organic waste as raw materials to ferment to obtain biogas, the content of methane in the obtained biogas is 55-62%, the content of carbon dioxide is 35-40%, and the mixed gas of methane and carbon dioxide obtained by fermentation is used for preparing acetic acid through a thermal catalytic process in series coupling, so that higher liquid yield and acetic acid selectivity can be achieved, the step of separating and purifying methane and carbon dioxide to purified gas is reduced, the production cost is effectively reduced, and the present application realizes resource utilization of waste, has the advantages of green environmental protection, high resource utilization rate, low energy consumption and high selectivity of target product.

Claims

1. A process for the anaerobic fermentation coupled with a fixed-bed thermocatalytic process to prepare acetic acid, characterized in that: Includes the following steps: (1) Organic waste is anaerobicly fermented to produce biogas; (2) Purify the biogas to obtain purified methane / carbon dioxide mixture; (3) The purified methane / carbon dioxide mixture is introduced into the reactor and subjected to a thermocatalytic reaction under the action of Pt-Fe / TiO2-MMT catalyst to obtain an acetic acid mixture; (4) The acetic acid mixture is condensed and separated to obtain acetic acid, and the unreacted gas is recovered; In step (1), the biogas contains 55-62% methane and 35-40% carbon dioxide. In step (3), the active metal component of the Pt-Fe / TiO2-MMT catalyst is Pt-Fe bimetal, the support is TiO2 and modified MMT, and its active metal content is 5-6 wt.%; The preparation steps of the Pt-Fe / TiO2-MMT catalyst are as follows: (a) In the presence of deionized water or organic solvent, soluble Pt salt, soluble Fe salt, and TiO2 powder are converted into Pt-Fe / TiO2 solution through a hydrothermal induced reaction. (b) Sodium-based montmorillonite MMT was stirred with mixed acid at a constant temperature of 90°C for 6 hours, centrifuged and washed until neutral, and then placed in nitric acid solution and sonicated for 1 hour to obtain modified MMT. (c) The modified MMT was completely immersed in a Pt-Fe / TiO2 solution to form the catalyst, thus obtaining the Pt-Fe / TiO2-MMT catalyst.

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

4. The process for preparing acetic acid by anaerobic fermentation coupled in series with fixed-bed thermocatalysis according to claim 3, characterized in that: In step (a), the soluble Pt salt is at least one of chloroplatinic acid, tetraammineplatinum nitrate, and potassium chloroplatinate; the soluble Fe salt is at least one of ferric nitrate, ferric chloride, and ferric sulfate; the TiO2 is nano-sized anatase hydrophilic type; and the organic solvent is dimethylformamide or ethylene glycol.

5. The process for preparing acetic acid by anaerobic fermentation coupled in series with fixed-bed thermocatalysis according to claim 4, 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 m². 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.

6. The process for preparing acetic acid by anaerobic fermentation coupled in series with fixed-bed thermocatalysis according to claim 5, characterized in that: In step (c), the specific steps for catalyst formation are as follows: the acid-treated MMT is completely immersed in a Pt-Fe / TiO2 solution, stirred continuously for 4-6 hours under a constant temperature of 80-100℃ and a rotation speed of 300-500 rpm in a water bath, then dried overnight in an oven at 80℃, and then transferred to a muffle furnace for calcination. The temperature is raised to 400-450℃ at a heating rate not exceeding 5℃ / min, held at a constant temperature for 180 min, cooled naturally, ground, sieved, and sealed.

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

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