Integrated device and method for synthesizing acrylic acid from methanol and acetic acid

Abstract

The invention discloses an integrated device and method for synthesizing acrylic acid from methanol and acetic acid, and belongs to the technical field of preparation and application of energy and chemical catalytic materials. The device comprises a fixed bed reactor, two reaction bed layers are arranged in the fixed bed reactor, a methanol and air feed port is formed in the top of the fixed bed reactor, and a dehydrogenation catalyst is arranged on the upper reaction bed layer; a liquid feeding hole is formed between the upper-section reaction bed layer and the lower-section reaction bed layer; an aldol condensation catalyst is arranged on the lower-section reaction bed layer; the bottom of the fixed bed reactor is connected with a gas-liquid separator. Methanol enters the upper-section reaction bed layer for oxidative dehydrogenation to generate formaldehyde, and then formaldehyde and acetic acid are subjected to condensation reaction on the lower-section reaction bed layer to generate acrylic acid. The single fixed bed reactor is adopted to directly synthesize acrylic acid from methanol and acetic acid, the process route is simple, the acrylic acid with high purity can be obtained, and the separation cost is effectively reduced; the catalyst is filled in two sections of the single fixed bed, the temperature is controlled respectively, and the production energy consumption is low.

Description

Technical Field

[0001] The present invention relates to an integrated device and method for synthesizing acrylic acid from methanol and acetic acid, and particularly to a method for directly synthesizing acrylic acid from methanol and acetic acid by loading catalysts with special functions in two stages in a single fixed-bed reactor, belonging to the technical field of preparation and application of energy and chemical catalytic materials. Background Art

[0002] Acrylic acid is an important chemical monomer, which can be used to prepare superabsorbent resins and is widely used in the fields of diapers, hygiene products, agriculture and forestry horticulture, chemical fibers, papermaking, etc. The production of acrylic acid mainly goes through methods such as the chloroethanol method, the cyanoethanol method, the Reppe method, and the propylene hydrolysis method. With the progress of technology and the emphasis on environmental protection, most of these methods have been phased out. Currently, acrylic acid is mainly obtained by the propylene oxidation method based on the petroleum route. Due to the fluctuation of oil prices, the market supply and demand of acrylic acid are greatly affected. In recent years, some other methods have also been developed, such as the propane oxidation method. Although certain progress has been made in this process, the selectivity and yield of the target product are not ideal, and there are also problems such as the harsh preparation conditions of the catalysts used and poor reproducibility. Considering China's "rich in coal, poor in oil, and scarce in gas" energy structure, it is of great significance to develop a new technical route for coal-based acrylic acid.

[0003] For the coal-based route, the process routes for preparing acrylic acid from formaldehyde and acetic acid have been studied extensively. As early as 1990, Ai et al. first reported the route for synthesizing acrylic acid using formaldehyde and acetic acid as raw materials [M. Ai, J. Catal. 124(1990) 293-296. M. Ai, J. Catal., 124 (1990) 293-296]. After decades of research, acidic catalysts represented by VPO [X.Z. Feng, et, al. 314 (2014) 132-141] and basic catalysts represented by Cs-based catalysts [M. Ai, et al. Appl. Catal. A-Gen., 288 (2005) 211-215; T. He et al., Ind. Eng. Chem. Res., 57(2018) 2773-2786] have been mainly developed. This route has achieved good indicators in terms of both the selectivity of acrylic acid and the catalytic efficiency [J. Liu, et al. Chem. Commun., 56(2020) 1022-1025]. However, in this route, the raw material formaldehyde is chemically active and prone to polymerization. Generally, 9-15 wt% of methanol needs to be added to the formaldehyde solution as a stabilizer. On the one hand, when synthesizing acrylic acid using aqueous formaldehyde as the raw material, a large amount of water in the system will cause the VPO catalyst to pulverize and block the reactor. On the other hand, the stabilizer methanol will also react with the raw material acetic acid and the generated acrylic acid to form ester products: methyl acetate and methyl acrylate, which brings problems such as high separation costs in the subsequent process, and this has limited its large-scale application to a certain extent.

[0004] In contrast, if acrylic acid can be synthesized from methanol and acetic acid as raw materials, the safety and stability of methanol are superior to those of formaldehyde. Moreover, the water in the product is basically generated during the reaction process, and its relative content is significantly reduced. On the one hand, the problem of catalyst pulverization is avoided, and on the other hand, the waste water is less, reducing the cost, so it has obvious advantages. Judging from the existing reports, the synthesis of acrylic acid from methanol and acetic acid generally includes a one-step process and a two-step process. The one-step process directly uses methanol and acetic acid as raw materials to synthesize acrylic acid through a single fixed-bed reactor. This route has a short process flow and simple equipment. At present, there are many literature and patent reports on this process [[M. Ai, etal. Bull. Chem. Soc. Jpn., 63(1990), 199-202; L.Q.Shen, et,al (97) 2019 2699-2707]. In the current one-step process, the catalyst used needs to have the bifunctional characteristics of dehydrogenating methanol to formaldehyde and condensing formaldehyde with acetic acid to acrylic acid. Moreover, there are dehydrogenation and esterification competitive reactions during the reaction process, resulting in the formation of methyl acetate and methyl acrylate in the product. If these problems can be solved well, this route will have good application prospects. In recent years, the researchers of the Institute of Coal Chemistry, Chinese Academy of Sciences have developed a new type of sodium superionic conductor catalyst, which can directly convert methanol and acetic acid into acrylic acid and its methyl ester [CN109364967A; CN115090308A; CN117599818A]. Chinese Patent CN116640060A discloses a method for loading catalysts in a double-bed layer to realize a catalyst system and process for directly synthesizing esters such as methyl acrylate and methyl methacrylate from methanol and methyl acetate. Among them, the double-bed layer is respectively loaded with Cu-based and Cs-based catalysts. This process shows great superiority in the condensation conversion of esters, but there are still problems such as a wide product distribution and low selectivity of the target product. The two-step process refers to the preparation of acrylic acid by using two fixed-bed reactors for methanol and acetic acid. One reactor is used for dehydrogenating methanol to prepare formaldehyde, and the other reactor is responsible for catalytically converting formaldehyde and acetic acid to synthesize acrylic acid. This process can avoid the direct contact of methanol and acetic acid to generate by-product methyl acetate, obtain a higher-purity acrylic acid monomer, and reduce the separation energy consumption, so it has good application prospects. Chinese Patent CN114605249A discloses a process for synthesizing acrylic acid by two-stage reaction of methanol and acetic acid. An anaerobic dehydrogenation catalyst supported by metal or oxide is used in the first-stage reactor, and phosphate catalysts such as VPO are loaded in the second-stage reactor. As can be seen from the above, compared with the one-step process, although the two-step process uses two fixed-bed reactors, the subsequent product separation will significantly reduce the separation cost and obtain a high-purity target product, acrylic acid.Considering both catalytic efficiency and environmental protection, continuous improvement of the catalyst preparation method or exploration of new catalytic systems, development of low-toxic and highly efficient combined catalytic systems, and optimization of related processes are of great significance for realizing the clean, efficient, and low-carbon method of synthesizing acrylic acid from methanol and acetic acid. Summary of the Invention

[0005] The present invention aims to provide an integrated device and method for synthesizing acrylic acid from methanol and acetic acid. By using two different catalysts in a single fixed-bed reactor for synthesizing acrylic acid from methanol and acetic acid, the generation of ester products can be significantly reduced, the wastewater is less, the products are easy to separate, the cost is greatly reduced, and good economic benefits are brought.

[0006] The present invention provides an independently developed single fixed-bed reactor. By segmentally loading highly active catalysts in the single fixed-bed reactor and realizing the process of producing formaldehyde by dehydrogenating methanol and further preparing acrylic acid by aldol condensation of formaldehyde and acetic acid through segmented temperature control. Among them, the dehydrogenation catalyst is a Mo-based catalyst, and the aldol condensation catalyst is a modified NASICON catalyst (sodium superionic conductor catalyst). The catalyst preparation process is simple, low in cost, and has good activity and stability. In this process, an integrated reaction system with methanol fed in the upper section and acetic acid fed in the middle section is designed according to the reaction characteristics to achieve a step-by-step synthesis process. The equipment is simple and the manufacturing cost is low.

[0007] The present invention provides an integrated device for synthesizing acrylic acid from methanol and acetic acid, including a fixed-bed reactor. There are two reaction bed layers in the fixed-bed reactor. A methanol feed port and an air feed port are provided at the top of the fixed-bed reactor, which are connected to the upper reaction bed layer. A dehydrogenation catalyst is provided in the upper reaction bed layer, and the rest is filled with magnetic rings; a liquid feed port (a liquid feed port is left between the oxidative dehydrogenation reaction section and the condensation reaction section) is provided between the upper reaction bed layer and the lower reaction bed layer, which is connected to the lower reaction bed layer; an aldol condensation catalyst is provided in the lower reaction bed layer, and the rest is filled with magnetic rings; the bottom of the fixed-bed reactor is connected to a gas-liquid separator, and a stop valve is provided at the bottom of the gas-liquid separator to control the outflow of the liquid-phase product.

[0008] The reactor described is a fixed-bed reactor with separately controllable temperatures for the upper and lower reaction beds, including an oxidative dehydrogenation reaction section in the upper layer and a condensation reaction section in the lower layer; a liquid feed pump is provided at the methanol feed inlet, and an air compressor is provided at the air feed inlet. The feed flow rate is controlled by a flow meter. Methanol is vaporized through magnetic ring packing and reacts on an oxidative dehydrogenation catalyst; a liquid sampling pump is provided at the middle liquid feed inlet to control the acetic acid liquid feed. The acetic acid is mixed with the gas after the oxidative dehydrogenation reaction section in the lower reaction bed; a heating furnace is provided outside the fixed-bed reactor, and the heating furnace can perform three-stage temperature control to achieve separate temperature control for feed preheating, the upper reaction bed, and the lower reaction bed. Specifically, the heating furnace uses thermocouples for temperature control, and sleeves into which thermocouples can be inserted are installed in the preheating section, the upper reaction bed, and the lower reaction bed to monitor the reaction temperature.

[0009] The present invention provides an integrated method for synthesizing acrylic acid from methanol and acetic acid, comprising the following steps: The methanol and air raw materials are respectively fed from the methanol feed inlet and the air feed inlet at the top of the reactor. Methanol is introduced into the system through a liquid feed pump, and air is injected through an air compressor. Flow meters are provided at the feed inlets to control the flow rate; the gas and liquid phases enter the upper reaction bed of the fixed-bed reactor. Methanol is vaporized through magnetic ring packing and undergoes an oxidative dehydrogenation reaction on an oxidative dehydrogenation catalyst to generate formaldehyde; a liquid sampling pump is provided at the middle liquid feed inlet to control the acetic acid liquid feed. The introduced acetic acid and formaldehyde are fully mixed and then contact and react with a condensation catalyst. The obtained tail gas is separated on a gas-liquid separator, and the collected liquid enters the subsequent process for further separation and purification to obtain an acrylic acid product; during the reaction process, the feed is preheated, and the upper reaction bed and the lower reaction bed are respectively temperature-controlled through a heating furnace.

[0010] The temperature of the preheating section is controlled at 180 °C.

[0011] In the oxidative dehydrogenation reaction, the volume ratio of methanol to air is 1:2.5 - 5, acetic acid enters from the middle liquid feed inlet, and the molar ratio of methanol to acetic acid is 0.5 - 3.

[0012] Furthermore, the oxidative dehydrogenation catalyst is a Mo-based catalyst. The preparation method of the Mo-based catalyst is as follows: Tetraethyl orthosilicate (TEOS) is dissolved in an isopropanol solvent, and a certain concentration of ammonia water (0.5 - 3 mol / L) is added dropwise. Stirring is continued at room temperature until the hydrolysis of TEOS is complete, and then the temperature is raised for reflux for 4 - 6 h; subsequently, ammonium molybdate (Mo content is 56.5 wt%) and iron nitrate (FeNO3·9H2O) are added in proportion, and stirring is continued for 2 - 4 hours. The isopropanol solvent is evaporated and dried overnight at 120 °C; the collected sample is calcined at 400 - 600 °C to obtain the Mo-based catalyst raw powder. The mass sum of Mo and Fe components in the above Mo-based catalyst accounts for 8 - 30% of the mass of the catalyst.

[0013] When preparing the above oxidative dehydrogenation catalyst, the mass ratio of each synthesis raw material is: TEOS∶isopropanol∶ammonia (NH3)∶ammonium molybdate∶iron nitrate = 100∶120 - 300∶0.5 - 1.36∶3.44 - 11.2∶2.72 - 16.8. Among them, the Mo / Fe atomic ratio is preferably 1.5 - 3.

[0014] Furthermore, during the oxidative dehydrogenation process, the liquid hourly space velocity of methanol on the Mo-based catalyst is 0.5 - 3.0 mL / (g cat h); the temperature of the oxidative dehydrogenation reaction is 200 - 280 °C; the reaction pressure of the oxidative dehydrogenation is atmospheric pressure.

[0015] Furthermore, in the condensation reaction section, the condensation catalyst is a single NASICON (sodium superionic conductor) catalyst or a phosphate-modified NASICON catalyst; the preparation method of the condensation catalyst is as follows: The single NASICON catalyst material is prepared by the sol-gel method: First, dissolve the weighed titanium oxysulfate or titanium sulfate in deionized water, then sequentially add hydrogen peroxide and polyethylene glycol surfactant (PEG, molecular weight 15 - 20 kDa), and stir vigorously for 2 - 4 h; then dropwise add concentrated phosphoric acid (85%), and continue to stir for 2 - 4 h; place the obtained suspension in an oil bath at 40 - 60 °C for static aging for 48 - 96 h; place the obtained dry gel in a muffle furnace and calcine at 550 - 700 °C for 6 - 8 h to obtain the single NASICON catalyst material.

[0016] When preparing the above single NASICON catalyst, the molar ratio of each raw material in the synthesis mother liquor is titanium source∶hydrogen peroxide∶polyethylene glycol∶concentrated phosphoric acid = 0.6 - 1.2∶1.1 - 2.0∶0.0025 - 0.008∶1.

[0017] The phosphate-modified NASICON catalyst is realized by the equal-volume impregnation method. Specifically: at room temperature, impregnate the single NASICON material prepared above with equal volume into a solution containing phosphate, and ultrasonically treat until most of the water volatilizes; the obtained sample is calcined at 500 - 700 °C for 2 - 4 h to obtain the phosphate-modified NASICON catalyst raw powder.

[0018] Further, for the phosphate-modified NASICON catalyst, the modifying component phosphate is an ammonium salt, a sodium salt, a potassium salt or a cesium salt, including ammonium phosphate ((NH4)3PO4), diammonium hydrogen phosphate ((NH4)2HPO4), ammonium dihydrogen phosphate (NH4H2PO4), sodium phosphate (Na3PO4), disodium hydrogen phosphate (Na2HPO4), sodium dihydrogen phosphate (NaH2PO4), potassium phosphate (K3PO4), dipotassium hydrogen phosphate (K2HPO4), potassium dihydrogen phosphate (KH2PO4), cesium phosphate (Cs3PO4), or any combination of any two of them. In the obtained catalyst, the mass percentage of phosphate in the catalyst is 0.1-10 wt%.

[0019] Further, during the condensation reaction process, the liquid hourly space velocity of the raw material acetic acid is 0.5-2 mL / (g cat h), the condensation reaction temperature is 340-400 °C, and the condensation reaction pressure is atmospheric pressure; Using the above process, calculated based on acetic acid, the conversion rate of acetic acid is more than 50%, the selectivity for acrylic acid reaches more than 80%, and can reach up to 94.7% at most, and the selectivity of the ester products is less than 5%.

[0020] The beneficial effects of the present invention are as follows: (1) Based on the reaction characteristics of the synthesis of acrylic acid from methanol and acetic acid and the deficiencies of the existing processes, the present invention uses a single fixed-bed reactor to directly synthesize acrylic acid from methanol and acetic acid. The reaction tail gas of the upper reaction bed layer in the reaction process does not need to be separated and directly enters the lower reaction bed layer for reaction to produce the target product. The reaction operating conditions are mild, the process route is simple, high-purity acrylic acid can be obtained, and the separation cost is effectively reduced; the single fixed-bed two-stage loading catalyst and the reaction device with separately controlled temperature developed by the present invention have significant advantages such as low equipment investment and low production energy consumption.

[0021] (2) The oxidative dehydrogenation Mo-based catalyst used in the upper reaction bed layer has a larger specific surface area, highly dispersed active site centers, and better oxidation performance compared with the traditional MoFe catalyst. It can achieve complete and highly selective oxidation of methanol to formaldehyde at a lower temperature, reducing energy consumption. The catalyst raw materials are easy to obtain, the synthesis method is simple, the pollution is small, the requirements for equipment are low, the synthesis cost is low, and it is easy to produce in batches.

[0022] (3) The NASICON condensation catalyst in the lower reaction bed layer has a simple synthesis method, easy-to-obtain raw materials, low cost, and is easy to produce in batches; the surface acidity and basicity of this condensation catalyst are further regulated, which can not only efficiently convert the formaldehyde generated in the upper reaction bed layer and the acetic acid introduced in the lower reaction bed layer into acrylic acid, with the conversion rate of acetic acid being more than 50% and the selectivity for acrylic acid reaching up to 94.7% at most, and the formation of ester products is greatly inhibited, with the corresponding selectivity being less than 3%, but also the stability of the catalyst is significantly improved.

[0023] (4) The present invention provides a new catalytic reaction system and route for converting methanol and acetic acid into high-value-added acrylic acid. The reaction conditions in the whole process are mild, the equipment requirements are low, the products are relatively single, and they are easy to separate and purify, with broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of an integrated device for synthesizing acrylic acid from methanol and acetic acid.

[0025] In the figure: 1 is a fixed-bed reactor, 2 is a methanol feed port, 3 is an air feed port, 4 is the upper reaction bed layer, 5 is a dehydrogenation catalyst, 6 is the lower reaction bed layer, 7 is a liquid feed port, 8 is an aldol condensation catalyst, 9 is a gas-liquid separator, 10 is a stop valve, 11 is a heating furnace, A is methanol, B is air, C is acetic acid, D is cooling water, E is tail gas, and F is a liquid-phase product. DETAILED DESCRIPTION OF THE INVENTION

[0026] The present invention will be further described below through examples, but is not limited to the following examples.

[0027] As Figure 1 shown, this embodiment provides an integrated device for synthesizing acrylic acid from methanol and acetic acid, including a fixed-bed reactor 1. There are two reaction bed layers in the fixed-bed reactor 1. A methanol feed port 2 and an air feed port 3 are provided at the top of the fixed-bed reactor 1, which are connected to the upper reaction bed layer 4. A dehydrogenation catalyst 5 is provided in the upper reaction bed layer, and the rest is filled with magnetic rings; a liquid feed port 7 (a liquid feed port is left between the oxidative dehydrogenation reaction section and the aldol condensation reaction section) is provided between the upper reaction bed layer 4 and the lower reaction bed layer 6, which is connected to the lower reaction bed layer 6; an aldol condensation catalyst 8 is provided in the lower reaction bed layer 6, and the rest is filled with magnetic rings; the bottom of the fixed-bed reactor 1 is connected to a gas-liquid separator 9, and a stop valve 10 is provided at the bottom of the gas-liquid separator 9 to control the outflow of the liquid-phase product.

[0028] The reactor is a fixed-bed reactor with separately controllable temperatures for the upper and lower reaction bed layers, including an oxidative dehydrogenation reaction section in the upper layer and an aldol condensation reaction section in the lower layer; a liquid feed pump is provided at the methanol feed port, and an air compressor is provided at the air feed port. The feed flow rate is controlled by a flow meter. Methanol is gasified through the magnetic ring packing and reacts on the oxidative dehydrogenation catalyst; a liquid sampling pump is provided at the middle liquid feed port to control the liquid feed of acetic acid. Acetic acid is mixed with the gas after the reaction in the oxidative dehydrogenation reaction section in the lower reaction bed layer; a heating furnace 11 is provided outside the fixed-bed reactor. The heating furnace can perform three-stage temperature control to realize separate temperature control for feed preheating, the upper reaction bed layer, and the lower reaction bed layer. Specifically, the heating furnace 11 uses a thermocouple for temperature control, and sleeves into which thermocouples can be inserted are installed in the preheating section, the upper reaction bed layer, and the lower reaction bed layer to monitor the reaction temperature.

[0029] The following method for synthesizing acrylic acid from methanol and acetic acid is implemented using the Figure 1 device shown below. The specific embodiments are as follows: Example 1

[0030] (1) Preparation of Mo-based catalyst Dissolve 50 g of tetraethyl orthosilicate (TEOS) in 100 mL of isopropanol solution, and add 10 mL of ammonia water with a concentration of 2 mol / L dropwise. Continuously stir at room temperature until the hydrolysis of TEOS is complete, and then raise the temperature to reflux for 6 h. Subsequently, add 2 g of ammonium molybdate and 2 g of iron nitrate (FeNO3·9H2O) (the Mo / Fe atomic ratio is about 2.4), continue to stir for 3 h, heat and evaporate to remove the isopropanol solvent, and continue to dry overnight at 120 °C. The collected sample is calcined at 400 °C to obtain the Mo-based catalyst raw powder, where the mass fraction of MoFe is 9.75%.

[0031] (2) Preparation of ammonium dihydrogen sulfate-modified NASICON condensation catalyst a. The single NASICON material is prepared by the sol-gel method. First, dissolve 20 g of weighed titanium sulfate in 40 g of deionized water, then add 16 g of hydrogen peroxide (30 wt%), sonicate for 1 h, add 6.1 g of polyethylene glycol (DA.10000) surfactant (PEG, molecular weight 15 - 20 kDa), and then stir vigorously for 4 h. Subsequently, add 6 g of concentrated phosphoric acid (85%) dropwise and continue to stir for 3 h. The obtained suspension is placed in an oil bath at 60 °C for static aging for 72 h; the obtained dry gel is calcined in a muffle furnace at 600 °C for 7 h to obtain the single NASICON material.

[0032] b. The ammonium dihydrogen phosphate-modified NASICON catalyst is realized by the equal-volume impregnation method. At room temperature, impregnate 6 g of the single NASICON material prepared in step a above with equal volume into a solution containing 0.3 g of ammonium dihydrogen phosphate (NH4H2PO4)) (the initial mass fraction of NH4H2PO4 in the NASICON carrier is 5.0 wt%), and sonicate until most of the water has evaporated. The obtained sample is calcined in the range of 400 °C for 2 h to obtain the condensation catalyst raw powder.

[0033] (3) Catalytic performance test The obtained Mo-based catalyst and the condensation catalyst were respectively tableted and sieved into 20-40 mesh particles. 2 g of each was weighed and filled into the upper oxidation dehydrogenation bed and the lower condensation reaction bed of the reactor, and the rest was filled with magnetic rings. After the reactor and other equipment were installed, the temperatures of the upper and lower reaction beds were respectively raised to 240 °C and 360 °C in an air atmosphere (50 mL / min). Methanol and acetic acid were respectively injected into the reactor using a liquid piston pump. Methanol was injected from the upper feed port, and acetic acid was injected from the middle feed port. The feed space velocity of methanol relative to the Mo-based catalyst was 0.75 mL / (g cat h) (methanol vapor: air = 1:3.6), and the liquid space velocity of acetic acid relative to the condensation catalyst was 1.06 mL / (g cat h). The products were separated by a gas-liquid separator, and the liquid and gas products after 2 h of reaction were analyzed using a chromatographic analyzer. Based on acetic acid, the conversion rate of acetic acid was calculated to be 65.3%, the selectivity of acrylic acid was 87.3%, the selectivity of methyl acetate was 1.3%, the selectivity of methyl acrylate was 0.67%, and other products were 10.73%. Other products mainly included hydrocarbons and CO x .

[0034] The ammonium molybdate (NH4)2MoO4 was commercially available. In the ammonium molybdate used in this example, the Mo content accounted for 56.5 wt%. Example 2

[0035] (1) Preparation of Mo-based catalyst 50 g of tetraethyl orthosilicate (TEOS) was dissolved in 120 mL of isopropanol solution, and 30 mL of ammonia water with a concentration of 0.5 mol / L was added dropwise. Stirring was continued at room temperature until the hydrolysis of TEOS was complete, and then the temperature was raised for reflux for 4 h. Subsequently, 4.2 g of ammonium molybdate (Mo content accounted for 56.5 wt%) and 4 g of iron nitrate (FeNO3·9H2O) (the Mo / Fe atomic ratio was about 2.5) were added, and stirring was continued for 4 h. The isopropanol solvent was removed by heating and evaporation, and drying was continued overnight at 120 °C. The collected sample was calcined at 600 °C to obtain the Mo-based catalyst raw powder, in which the MoFe mass fraction was about 20.3%.

[0036] (2) Preparation of NASICON condensation catalyst modified with sodium dihydrogen phosphate a. The single NASICON material was prepared by the sol-gel method. First, 20 g of weighed titanium sulfate was dissolved in 30 g of deionized water, then 16 g of hydrogen peroxide (30 wt%) was added, ultrasonicated for 1 h, and 5.1 g of polyethylene glycol (DA.10000) surfactant (PEG, molecular weight 15 - 20 kDa) was added, followed by strong stirring for 3 h; subsequently, 6 g of concentrated phosphoric acid (85%) was added dropwise, and stirring continued for 2 h. The resulting suspension was placed in an oil bath at 50 °C for static aging for 72 h; the obtained xerogel was calcined in a muffle furnace at 650 °C for 8 h to obtain the single NASICON material.

[0037] b. The NASICON catalyst modified with sodium dihydrogen phosphate was achieved by the equal-volume impregnation method. At room temperature, 6 g of the single NASICON material prepared in step a above was impregnated in an equal volume into a solution containing 0.6 g of sodium dihydrogen phosphate (NaH2PO4) (the initial mass fraction of NaH2PO4 in the NASICON support was 10.0 wt%), and ultrasonicated until most of the moisture had evaporated. The obtained sample was calcined at 500 °C for 4 h to obtain the condensed catalyst raw powder.

[0038] (3) Catalytic performance test The obtained Mo-based catalyst and condensed catalyst were respectively pressed and sieved into 20 - 40 mesh particles. 1 g and 2 g were respectively weighed and loaded into the upper oxidation dehydrogenation bed layer and the lower condensation reaction bed layer of the reactor, and the rest was filled with magnetic rings. After the reactor and other equipment were installed, the upper bed layer and the lower bed layer were respectively heated to 260 °C and 350 °C in an air atmosphere (50 mL / min). Methanol and acetic acid were respectively injected into the reactor using a liquid piston pump, where methanol was injected from the upper inlet and acetic acid was injected from the middle feed port. The feed space velocity of methanol relative to the Mo-based catalyst was 1.05 mL / (g cat h) (methanol vapor: air = 1:3.6), and the liquid space velocity of acetic acid relative to the condensed catalyst was 1.26 mL / (g cat h). The products were separated by a gas-liquid separator, and the liquid and gas products after 2 h of reaction were analyzed by chromatography. Based on acetic acid, the calculated conversion rate of acetic acid was 50.1%, the selectivity of acrylic acid was 90.6%, the selectivity of methyl acetate was 2.2%, the selectivity of methyl acrylate was 0.87%, and other products were 6.33%, mainly including hydrocarbons and CO x . Example 3

[0039] (1) Preparation of Mo-based catalyst Dissolve 50 g of tetraethyl orthosilicate (TEOS) in 77 mL of isopropanol solution, and dropwise add 10 mL of ammonia water with a concentration of 3 mol / L. Continuously stir at room temperature until the hydrolysis of TEOS is complete, and then raise the temperature to reflux for 4 h. Subsequently, add 1.72 g of ammonium molybdate (Mo content is 56.5 wt%) and 1.36 g of iron nitrate (FeNO3·9H2O) (the Mo / Fe atomic ratio is about 3.0), continue to stir for 2 h, heat and evaporate to remove the isopropanol solvent, and continue to dry overnight at 120 °C. The collected sample is calcined at 400 °C to obtain the original Mo-based catalyst powder, where the mass fraction of MoFe is about 8.0%.

[0040] (2) Preparation of sodium phosphate-modified NASICON condensation catalyst a. The single NASICON material is prepared by the sol-gel method. First, dissolve 20 g of weighed titanium sulfate in 30 g of deionized water, then add 16 g of hydrogen peroxide (30 wt%), ultrasonicate for 1 h, add 5.1 g of polyethylene glycol (DA.10000) surfactant (PEG, molecular weight 15 - 20 kDa), and then stir vigorously for 3 h. Subsequently, dropwise add 6 g of concentrated phosphoric acid (85%), and continue to stir for 2 h. The obtained suspension is placed in an oil bath at 60 °C for static aging for 48 h; the obtained dry gel is calcined in a muffle furnace at 700 °C for 8 h to obtain the single NASICON material.

[0041] b. The sodium phosphate-modified NASICON catalyst is realized by the equal-volume impregnation method. At room temperature, impregnate 6 g of the single NASICON material prepared in step a above with equal volume into a solution containing 0.18 g of sodium phosphate (Na3PO4) (the initial mass fraction of Na3PO4 in the NASICON support is 3.0 wt%), and ultrasonicate until most of the water volatilizes. The obtained sample is calcined at 400 °C for 2 h to obtain the original condensation catalyst powder.

[0042] (3) Catalytic performance test Tablet and screen the above-obtained Mo-based catalyst and condensation catalyst into 20 - 40 mesh particles. Weigh 1 g and 2 g respectively and load them into the upper oxidation dehydrogenation bed layer and the lower condensation reaction bed layer of the reactor, and fill the rest with magnetic rings. After installing the reactor and other equipment, heat the upper bed layer and the lower bed layer to 260 °C and 360 °C respectively in an air atmosphere (30 mL / min). Use a liquid piston pump to inject methanol and acetic acid into the reactor respectively, where methanol is injected from the upper inlet and acetic acid is injected from the middle feed port. The feed space velocity of methanol relative to the Mo-based catalyst is 1.05 mL / (g cath) (Methanol vapor:Air = 1:3.2), the liquid hourly space velocity of acetic acid relative to the condensation catalyst is 0.75 mL / (g cat h). The product is separated by a gas-liquid separator, and the liquid and gas products after 2 h of reaction are analyzed by chromatography. Based on acetic acid, the calculated conversion rate of acetic acid is 70.3%, the selectivity of acrylic acid is 86.6%, the selectivity of methyl acetate is 2.5%, the selectivity of methyl acrylate is 0.93%, and other products are 9.97%, mainly including hydrocarbons and CO x . Example 4

[0043] (1) Preparation of Mo-based catalyst Dissolve 50 g of tetraethyl orthosilicate (TEOS) in 150 mL of isopropanol solution, and add dropwise 20 mL of ammonia water with a concentration of 1.0 mol / L. Continuously stir at room temperature until TEOS is completely hydrolyzed, and then heat to reflux for 6 h; subsequently, add 5.6 g of ammonium molybdate (Mo content accounts for 56.5 wt%), 8.4 g of iron nitrate (FeNO3·9H2O) (the Mo / Fe atomic ratio is about 1.6), continue to stir for 3 h, heat and evaporate to remove the isopropanol solvent, and continue to dry overnight at 120 °C. The collected sample is calcined at 500 °C to obtain the Mo-based catalyst raw powder, in which the mass fraction of MoFe is about 30.0%.

[0044] (2) Preparation of sodium dihydrogen phosphate condensation catalyst a. The single NASICON material is prepared by the sol-gel method. Dissolve 20 g of titanium oxysulfate-sulfuric acid hydrate (TiOSO4, TiO2 content ≥ 29 wt%) in 20 g of deionized water, and add dropwise 25 g of hydrogen peroxide with a concentration of 30 wt%, 5 g of polyethylene glycol (DA.10000) surfactant, and stir evenly. Then, add 18.44 g of 85 wt% concentrated phosphoric acid and 10 g of deionized water to this solution at one time, and continue to stir strongly for 2 h. The obtained solution is left standing at 60 °C and aged for 72 h to form a dry gel; subsequently, the dry gel is placed in a tube furnace, and under a flowing air atmosphere, it is heated to 600 °C at a rate of 2 °C / min and calcined for 6 h to obtain the NASICON material raw powder synthesized from titanium oxysulfate.

[0045] b. The NASICON catalyst modified with sodium dihydrogen phosphate is prepared by the incipient wetness impregnation method. At room temperature, more than 6 g of the single NASICON material prepared in step a is impregnated with the same volume into a solution containing 0.3 g of sodium dihydrogen phosphate (NaH2PO4) (the initial mass fraction of Na4H2PO4 in the NASICON support is 5.0 wt%). Ultrasonic treatment is carried out until most of the moisture has evaporated. The obtained sample is calcined at 400 °C for 2 h to obtain the original powder of the condensation catalyst.

[0046] (3) Catalytic performance test The Mo-based catalyst and the condensation catalyst obtained above are respectively tableted and sieved into 20-40 mesh particles. Weigh 2 g and 2 g respectively and load them into the upper oxidation dehydrogenation bed layer and the lower condensation reaction bed layer of the reactor, and the rest is filled with magnetic rings. After the installation of the reactor and other equipment is completed, the upper bed layer and the lower bed layer are heated to 220 °C and 340 °C respectively in an air atmosphere (70 mL / min). Methanol and acetic acid are respectively injected into the reactor by a liquid piston pump. Methanol is injected from the upper inlet, and acetic acid is injected from the middle feed port. The feed space velocity of methanol relative to the Mo-based catalyst is 1.5 mL / (g cat h) (methanol vapor: air = 1:2.53), and the liquid space velocity of acetic acid relative to the condensation catalyst is 1.5 mL / (g cat h). The products are separated by a gas-liquid separator, and the liquid and gas products after 2 h of reaction are analyzed by chromatography. Based on acetic acid, the conversion rate of acetic acid is calculated to be 55.4%, the selectivity of acrylic acid is 92.6%, the selectivity of methyl acetate is 1.2%, the selectivity of methyl acrylate is 0.37%, and other products are 6.43%, mainly including hydrocarbons and CO x . Example 5

[0047] (1) Preparation of Mo-based catalyst Dissolve 50 g of tetraethyl orthosilicate (TEOS) in 90 mL of isopropanol solution, and add 20 mL of ammonia water with a concentration of 1.5 mol / L dropwise. Continuously stir at room temperature until the hydrolysis of TEOS is complete, and then heat to reflux for 4 h; then add 3.1 g of ammonium molybdate (Mo content accounts for 56.5 wt%) and 4.9 g of iron nitrate (FeNO3·9H2O) (the Mo / Fe atomic ratio is about 1.5), continue to stir for 2 h, heat and evaporate to remove the isopropanol solvent, and continue to dry overnight at 120 °C. The collected sample is calcined at 400 °C to obtain the original powder of the Mo-based catalyst, and the mass fraction of MoFe is about 16.8%.

[0048] (2) Preparation of NASICON condensation catalyst modified with dipotassium hydrogen phosphate a. The single NASICON material is prepared by the sol-gel method. The NASICON carrier raw powder is prepared by the preparation method of step a in Example 2.

[0049] b. The NASICON catalyst modified with dipotassium hydrogen phosphate is realized by the equal-volume impregnation method. At room temperature, 6 g or more of the single NASICON material prepared in step a above is impregnated into a solution containing 0.12 g of dipotassium hydrogen phosphate (K2HPO4) (the initial mass fraction of K2HPO4 in the NASICON carrier is 2.0 wt%). Ultrasonic until most of the moisture evaporates completely. The obtained sample is calcined at 500 °C for 2 h to obtain the condensation catalyst raw powder.

[0050] (3) Catalytic performance test The obtained Mo-based catalyst and condensation catalyst above are respectively tableted and sieved into 20-40 mesh particles. 1 g and 2 g are respectively weighed and filled into the upper oxidation dehydrogenation bed layer and the lower condensation reaction bed layer of the reactor, and the rest is filled with magnetic rings. After the reactor and other equipment are installed, the upper bed layer and the lower bed layer are respectively heated to 280 °C and 350 °C in an air atmosphere (70 mL / min). Methanol and acetic acid are respectively injected into the reactor by a liquid piston pump, where methanol is injected from the upper inlet and acetic acid is injected from the middle feed port. The feed space velocity of methanol relative to the Mo-based catalyst is 2.5 mL / (g cat h) (methanol vapor: air = 1:3.0), and the liquid space velocity of acetic acid relative to the condensation catalyst is 0.5 mL / (g cat h). The products are separated by a gas-liquid separator, and the liquid and gas products after 2 h of reaction are analyzed by chromatography. Based on acetic acid, the calculated conversion rate of acetic acid is 85.3%, the selectivity of acrylic acid is 94.7%, the selectivity of methyl acetate is 2.1%, the selectivity of methyl acrylate is 0.87%, and other products are 2.33%, mainly including hydrocarbons and CO x . Example 6

[0051] (1) Preparation of Mo-based catalyst The Mo-based catalyst is prepared by the method in Example 4.

[0052] (2) Preparation of NASICON condensation catalyst modified with potassium phosphate a. The single NASICON material is prepared by the sol-gel method. The NASICON carrier raw powder is synthesized by the preparation method of step a in Example 4.

[0053] b. The NASICON catalyst modified with potassium phosphate was prepared by the incipient wetness impregnation method. The preparation method was the same as that of Example 4, and the initial mass fraction of potassium phosphate (K2HPO4) in the NASICON support was 4.0 wt%.

[0054] (3) Catalytic performance test The above-obtained Mo-based catalyst and the condensation catalyst were respectively tableted and sieved into 20-40 mesh particles. 2 g and 2 g were respectively weighed and loaded into the upper oxidation dehydrogenation bed layer and the lower condensation reaction bed layer of the reactor, and the rest was filled with magnetic rings. After the reactor and other equipment were installed, the upper bed layer and the lower bed layer were respectively heated to 200 °C and 350 °C in an air atmosphere (30 mL / min). Methanol and acetic acid were respectively injected into the reactor by a liquid piston pump. Methanol was injected from the upper inlet, and acetic acid was injected from the middle feed inlet. The feed space velocity of methanol relative to the Mo-based catalyst was 0.5 mL / (g cat h) (methanol vapor: air = 1:2.5), and the liquid space velocity of acetic acid relative to the condensation catalyst was 0.5 mL / (g cat h). The products were separated by a gas-liquid separator, and the liquid and gas products after 2 h of reaction were analyzed by chromatography. Based on acetic acid, the conversion rate of acetic acid was calculated to be 68.3%, the selectivity of acrylic acid was 87.1%, the selectivity of methyl acetate was 0.85%, the selectivity of methyl acrylate was 0.13%, and other products were 11.92%, mainly including hydrocarbons and CO x . Example 7

[0055] (1) Preparation of Mo-based catalyst 50 g of tetraethyl orthosilicate (TEOS) was dissolved in 190 mL of isopropanol solution, and 20 mL of ammonia water with a concentration of 2 mol / L was added dropwise. Stirring was continued at room temperature until TEOS was completely hydrolyzed, and then the temperature was raised to reflux for 6 h; then 4.0 g of ammonium molybdate (Mo content accounted for 56.5 wt%) and 4.5 g of iron nitrate (FeNO3·9H2O) (the Mo / Fe atomic ratio was about 2.1) were added, and stirring was continued for 4 h. The isopropanol solvent was removed by heating and evaporation, and drying was continued overnight at 120 °C. The collected sample was calcined at 450 °C to obtain the Mo-based catalyst raw powder, in which the MoFe mass fraction was about 20.0%.

[0056] (2) Preparation of NASICON condensation catalyst modified with cesium phosphate a. The single NASICON material was prepared by the sol-gel method. First, 20 g of weighed titanium sulfate was dissolved in 25 g of deionized water, then 10 g of hydrogen peroxide (30 wt%) was added, and it was ultrasonicated for 1 h. Then, 5.5 g of polyethylene glycol (DA.10000) surfactant (PEG, with a molecular weight of 15 - 20 kDa) was added, and then it was vigorously stirred for 3 h. Subsequently, 6.5 g of concentrated phosphoric acid (85%) was added dropwise, and stirring was continued for 4 h. The resulting suspension was placed in an oil bath at 50 °C and allowed to stand and age for 96 h. The obtained xerogel was calcined in a muffle furnace at 550 °C for 8 h to obtain the single NASICON material.

[0057] b. The cesium phosphate modified NASICON catalyst was prepared by the incipient wetness impregnation method. At room temperature, 6 g of the single NASICON material prepared in step a above was impregnated in an equal volume into a solution containing 0.09 g of cesium phosphate (Cs3PO4) (the initial mass fraction of CsH2PO4 in the NASICON support was 1.5 wt%), and it was ultrasonicated until most of the water had evaporated. The obtained sample was calcined at 500 °C for 2 h to obtain the condensed catalyst raw powder.

[0058] (3) Catalytic performance test The Mo-based catalyst and the condensed catalyst obtained above were respectively pressed and sieved into 20 - 40 mesh particles. 1 g and 2 g were respectively weighed and loaded into the upper oxidation dehydrogenation bed and the lower condensation reaction bed of the reactor. After the equipment was installed, the upper bed and the lower bed were respectively heated to 270 °C and 350 °C in an air atmosphere (30 mL / min). Methanol and acetic acid were respectively injected into the reactor using a liquid piston pump. Among them, methanol was injected from the upper inlet, and acetic acid was injected from the middle feed inlet. The feed space velocity of methanol relative to the Mo-based catalyst was 0.84 mL / (g cat h) (methanol vapor: air = 1:3.9), and the liquid space velocity of acetic acid relative to the condensed catalyst was 0.90 mL / (g cat h). The liquid and gas products after 2 h of reaction were analyzed by chromatography. Based on acetic acid, the calculated conversion rate of acetic acid was 64.3%, the selectivity of acrylic acid was 89.3%, the selectivity of methyl acetate was 1.33%, the selectivity of methyl acrylate was 0.63%, and other products were 8.74%, mainly including hydrocarbons and CO x . Example 8

[0059] (1) Catalysts used The Mo-based catalyst prepared in Example 4 above was used as the oxidation dehydrogenation catalyst, and the single NASICON material prepared in Example 1 was used as the condensation catalyst.

[0060] (2) Catalytic performance evaluation Take 2 g of each of the above catalysts and place them in the upper oxidation dehydrogenation bed and the lower condensation reaction bed of the reactor, respectively. The Mo-based catalyst is placed in the upper bed, and the NASICON material is placed in the lower bed. The air flow rate is 50 ml / min, and the temperatures of the upper and lower beds of the reactor are controlled at 240 °C and 340 °C, respectively. The feed space velocity of methanol relative to the Mo-based catalyst is 1.0 mL / (g cat ·h) (methanol vapor: air = 1:2.7), and the feed space velocity of acetic acid relative to the condensation catalyst is 1.0 mL / (g cat ·h). The liquid-phase products are analyzed by chromatography for 2 h, and the gas products are analyzed online. Based on acetic acid, the calculated conversion rate of acetic acid is 63.2%, the selectivity of acrylic acid is 85.1%, the selectivity of methyl acetate is 2.8%, the selectivity of methyl acrylate is 2.0%, and the rest are by-products such as acrolein, acetaldehyde, CO x , hydrocarbons, etc., and their selectivity is 10.2%. Example 9

[0061] (1) Catalyst preparation a. The oxidation dehydrogenation catalyst uses the Mo-based catalyst prepared in Example 7.

[0062] b. Preparation of the condensation catalyst Using the single NASICON material prepared in Example 4 as the carrier, disodium hydrogen phosphate (Na2HPO4) is introduced onto its surface by the impregnation method to prepare the condensation catalyst. The preparation parameters or methods are as in Example 4, where the mass fraction of disodium hydrogen phosphate in the NASICON material is 7.0%.

[0063] (2) Catalytic performance evaluation Take 1 g and 2 g of the above Mo-based catalyst and condensation catalyst, respectively, and load them into the upper oxidation dehydrogenation bed and the lower condensation reaction bed of the reactor, respectively. The air flow rate is 90 ml / min, and the temperatures of the upper and lower beds of the reactor are controlled at 250 and 340 °C, respectively. The feed space velocity of methanol relative to the oxidation dehydrogenation catalyst is 3.0 mL / (g cat ·h) (methanol vapor: air = 1:3.2), and the feed space velocity of acetic acid relative to the condensation catalyst is 3.0 mL / (g cat ·h). The gas phase and the liquid-phase products collected for 2 h are analyzed by chromatography. Based on acetic acid, the calculated conversion rate of acetic acid is 50.1%, the selectivity of acrylic acid is 88.2%, the selectivity of methyl acetate is 2.1%, the selectivity of methyl acrylate is 1.3%, and the rest are CO x and hydrocarbons, and the selectivity is 8.4%. Example 10

[0064] The dehydrogenation catalyst and the condensation catalyst prepared in Example 5 were used to test the long-term operation of the catalytic reaction. After the reaction ran for 100 h, the conversion rate of acetic acid decreased from the initial 85.3% to 82.9%, and the selectivity of acrylic acid decreased from the initial 94.7% to 93.1%. The reaction was further run for 100 h, the conversion rate of acetic acid decreased to 80.4%, and the selectivity of acrylic acid decreased to 91.6%. At this time, the selectivity of methyl acetate was 2.6%, and the selectivity of methyl acrylate was 1.2%. It shows that this catalytic system deactivates slowly. The condensation catalyst in the lower bed was calcined in situ at 400 °C in an air atmosphere for 5 h, and then the reaction of synthesizing acrylic acid by methanol-acetic acid condensation was carried out again. The results showed that the conversion rate of acetic acid could be restored to 85.2%, and the selectivity of acrylic acid was 94.1%, indicating that this catalytic system has good regeneration activity.

[0065] Comparative Example 1 Two fixed-bed series reaction devices were used to evaluate the direct synthesis of acrylic acid from methanol and acetic acid. The dehydrogenation Mo-based catalyst prepared in Example 4 and the NASICON condensation catalyst modified with sodium dihydrogen sulfate were respectively loaded into two series-connected fixed-bed reactors for acrylic acid synthesis reaction. The loading amount of the catalyst in both fixed beds was 2 g, and the temperatures of the first stage and the second stage were controlled at 220 °C and 340 °C respectively. First, methanol and air were introduced into the first fixed-bed reactor filled with the Mo-based catalyst through the feed port, and an acetic acid raw material feed system was incorporated at the tail gas end of the first fixed-bed reactor. The mixed raw materials were preheated by a magnetic ring and then entered the second fixed-bed reactor filled with the condensation catalyst for condensation reaction. Among them, the feed space velocity of methanol relative to the Mo-based catalyst was 1.5 mL / (g cat h) (methanol vapor: air = 1:2.53), and the liquid space velocity of acetic acid relative to the condensation catalyst was 1.5 mL / (g cat h). After the products were analyzed, the calculated conversion rate of acetic acid was 53.7%, the selectivity of acrylic acid was 86.3%, the selectivity of methyl acetate was 1.1, the selectivity of methyl acrylate was 0.41, and the selectivity of other products was 8.19%, mainly including hydrocarbons, CO x etc.

[0066] Comparing Example 4 with Comparative Example 1 shows that: the single fixed-bed reactor provided by the present invention realizes the reaction of directly synthesizing acrylic acid from methanol and acetic acid in one reactor, not only realizes the generation of relatively pure acrylic acid products, but also has low energy consumption and small equipment investment compared with using two fixed-bed reactors.

[0067] In addition, under the same reaction conditions as Example 4, the conversion rate of acetic acid in Comparative Example 1 is slightly lower than the data in Example 4, but the selectivity of acrylic acid is significantly lower than the result of 92.6% in Example 4. This shows that the formation of ester products can also be suppressed by using two fixed bed reactors, but the implementation effect of the present invention (Example 4) is better. In actual production, the use of two fixed bed reactors invisibly increases the equipment investment, and the energy consumption of the two fixed bed reactors is also higher than that of a single fixed bed reactor, resulting in an increase in the total production cost. Therefore, the single fixed bed two-stage loading and temperature control reaction device mentioned in the present invention has obvious advantages such as low equipment investment and low production energy consumption.

[0068] Comparative Example 2: Comparison of catalyst advantages In Example 7 of Chinese Patent 114605249A, a two-step fixed bed device is used to synthesize acrylic acid. The dehydrogenation reaction uses MgO-Al2O3-Li2O catalyst, oxygen-free dehydrogenation is used, and the dehydrogenation temperature is 600°C; the condensation reaction stage uses VPO / Al2O3 catalyst, the reaction temperature is 350°C, and the pressure is 10atm. According to calculations, the acetic acid conversion rate is 83% and the acrylic acid selectivity is 92%.

[0069] In Example 5 of the present invention, the reaction adopts an integrated reaction device, and the intermediate product formaldehyde is obtained by using the oxidative dehydrogenation catalyst designed by the present invention, the reaction temperature is 280°C, the condensation reaction temperature is 350°C, and the reaction pressure is normal pressure, and an acetic acid conversion rate of 85.3% and an acrylic acid selectivity of 94.7% can be obtained. This shows that the catalytic effect obtained by using the catalyst and reaction system designed by the present invention is better than the result in Chinese Patent 114605249A.

[0070] Comparative Example 3: The traditional methanol oxidative dehydrogenation catalyst is a MoFe two-component catalyst, so in the experiment, a Mo-based catalyst with a Mo / Fe atomic ratio of 2.0 was prepared according to the method reported in Chinese invention patent CN113877612A. The traditional condensation catalyst has the best effect with VPO, so in the experiment, a VPO / Al2O3 catalyst was prepared according to the method in Chinese invention patent 114605249A. The above two catalysts are loaded in a fixed bed reactor of the present invention in different beds, and the loading amount and loading method are the same as in Example 10. The feed space velocity of raw material methanol, acetic acid and carrying gas and the reaction parameters are the same as in Example 10. After the reaction, chromatographic analysis was performed to obtain a conversion rate of acetic acid of 33.2%, a selectivity of acrylic acid of 75%, a selectivity of methyl acetate of 14.3%, a selectivity of methyl acrylate of 6.2%, and the remaining products of 4.5%.

[0071] In contrast, in Example 10 of the present invention, the acetic acid conversion rate is 50.1%, the acrylic acid selectivity is 88.2%, the selectivity of methyl acetate is 2.1%, and the selectivity of methyl acrylate is 1.3%, which is significantly better than the operation effect of the above existing catalysts in this reaction device.

[0072] The above proves that the catalyst prepared in the present invention and the device of the present invention have specificity. Using the catalyst and reaction device of the present invention can achieve good synergistic effects and achieve the purpose of efficiently synthesizing acrylic acid from methanol and acetic acid.

[0073] Comparative Example 4: The Mo-based catalyst prepared in Example 7 was used for the oxidative dehydrogenation of methanol to prepare formaldehyde. The catalyst loading was 1 g, the reaction temperature was controlled at 220 °C, and the liquid hourly space velocity of methanol was 3.0 mL / (g cat h) -1 ; the air flow rate was; 138 mL / min, and the reaction pressure was atmospheric pressure. The reaction tail gas was absorbed by distilled water and analyzed by chromatography. The conversion rate of methanol was 95%, and the selectivity of formaldehyde was 95%.

[0074] A MoFe catalyst without SiO2 was prepared by a traditional precipitation method. The preparation process was as described in Chinese Patent (CN113877612A). The atomic ratio of Mo and Fe was the same as that in this example (the Mo / Fe atomic ratio was about 2.1). This catalyst was used for the dehydrogenation of methanol to prepare formaldehyde. Under the same reaction conditions, on the traditional MoFe catalyst, the methanol conversion rate was 72%, and the selectivity of formaldehyde was 87%. The above results show that the doped SiO2 MoFe catalyst prepared by the present invention has better low-temperature catalytic performance than the MoFe catalyst prepared by the traditional method, and both the methanol conversion rate and the formaldehyde selectivity are superior.

Claims

1. An integrated device for synthesizing acrylic acid from methanol and acetic acid, characterized in that: It includes a fixed-bed reactor. There are two reaction bed layers inside the fixed-bed reactor. At the top of the fixed-bed reactor, there are a methanol feed inlet and an air feed inlet, which are connected to the upper reaction bed layer. A dehydrogenation catalyst is provided in the upper reaction bed layer, and the rest is filled with magnetic rings; there is a liquid feed inlet between the upper reaction bed layer and the lower reaction bed layer, which is connected to the lower reaction bed layer; a aldol condensation catalyst is provided in the lower reaction bed layer, and the rest is filled with magnetic rings; the bottom of the fixed-bed reactor is connected to a gas-liquid separator, and a stop valve is provided at the bottom of the gas-liquid separator to control the outflow of the liquid phase product.

2. The integrated device for synthesizing acrylic acid from methanol and acetic acid according to claim 1, wherein: The reactor is a fixed-bed reactor with separately controllable temperatures for the upper and lower reaction bed layers, including an oxidative dehydrogenation reaction section in the upper layer and a condensation reaction section in the lower layer; a liquid feed pump is provided at the methanol feed inlet, and an air compressor is provided at the air feed inlet. The feed flow rate is controlled by a flow meter. Methanol is gasified through the magnetic ring packing and reacts on the oxidative dehydrogenation catalyst; a liquid injection pump is provided at the middle liquid feed inlet to control the acetic acid liquid feed. Acetic acid is mixed with the gas after the oxidative dehydrogenation reaction section and reacts in the lower reaction bed layer; a heating furnace is provided outside the fixed-bed reactor. The heating furnace can perform three-stage temperature control to achieve separate temperature control of the feed preheating, the upper reaction bed layer, and the lower reaction bed layer. The heating furnace uses a thermocouple for temperature control.

3. An integrated method for synthesizing acrylic acid from methanol and acetic acid, using the integrated device for synthesizing acrylic acid from methanol and acetic acid according to claim 1 or 2, characterized in that It includes the following steps: Methanol and air raw materials are fed respectively from the methanol feed inlet and the air feed inlet at the top of the reactor. Methanol is introduced into the system through a liquid feed pump, and air is injected through an air compressor. Flow meters are provided at the feed inlets to control the flow rate; the gas and liquid phases enter the upper reaction bed layer of the fixed-bed reactor. Methanol is gasified through the magnetic ring packing and undergoes an oxidative dehydrogenation reaction on the oxidative dehydrogenation catalyst to generate formaldehyde; a liquid injection pump is provided at the middle liquid feed inlet to control the acetic acid liquid feed. The introduced acetic acid and formaldehyde are fully mixed and then contact and react with the condensation catalyst. The obtained tail gas is separated on the gas-liquid separator. The collected liquid enters the subsequent process for further separation and purification to obtain acrylic acid products; during the reaction process, the feed preheating, the upper reaction bed layer, and the lower reaction bed layer are respectively temperature-controlled through the heating furnace.

4. The integrated method for synthesizing acrylic acid from methanol and acetic acid according to claim 3, characterized in that: The volume ratio of methanol to air is 1∶2.5 - 5, and acetic acid enters from the middle liquid feed inlet. The molar ratio of methanol to acetic acid is 0.5 - 3.

5. The integrated method for synthesizing acrylic acid from methanol and acetic acid according to claim 3, characterized in that: In the oxidative dehydrogenation reaction, the oxidative dehydrogenation catalyst is a Mo-based catalyst. The preparation method of the Mo-based catalyst is as follows: Tetraethyl orthosilicate (TEOS) is dissolved in an isopropanol solvent, and ammonia water with a concentration of 0.5 - 3 mol / L is added dropwise. Stir continuously at room temperature until TEOS is completely hydrolyzed, and then heat to reflux for 4 - 6 h; then add ammonium molybdate and iron nitrate in proportion and continue to stir for 2 - 4 hours. Evaporate and remove the isopropanol solvent and dry overnight at 120 °C; the collected sample is calcined at 400 - 600 °C to obtain the Mo-based catalyst raw powder; When preparing the oxidative dehydrogenation catalyst, the mass ratio of each synthesis raw material is: TEOS∶isopropanol∶ammonia water (calculated as NH3)∶ammonium molybdate∶iron nitrate = 100∶120 - 300∶0.5 - 1.36∶3.44 - 11.2∶2.72 - 16.

8.

6. The integrated method for synthesizing acrylic acid from methanol and acetic acid according to claim 5, characterized in that: The temperature of the preheating section is controlled at 180 °C; during the oxidative dehydrogenation process, the liquid hourly space velocity of methanol on the Mo-based catalyst is 0.5 - 3.0 mL / (g cat h); the temperature of the oxidative dehydrogenation reaction is 200 - 280 °C; the reaction pressure of the oxidative dehydrogenation is atmospheric pressure.

7. The integrated method for synthesizing acrylic acid from methanol and acetic acid according to claim 3, characterized in that: The condensation catalyst is a single NASICON catalyst or a phosphate-modified NASICON catalyst; The preparation method of the single NASICON catalyst is as follows: Prepared by the sol-gel method: First, dissolve the weighed titanium oxysulfate or titanium sulfate in deionized water, then sequentially add hydrogen peroxide and polyethylene glycol surfactant, and stir vigorously for 2 - 4 h; Subsequently, add 85% concentrated phosphoric acid dropwise and continue stirring for 2 - 4 h; The obtained suspension is placed in an oil bath at 40 - 60 °C and left to stand and age for 48 - 96 h; The obtained dry gel is calcined in a muffle furnace at 550 - 700 °C for 6 - 8 h to obtain a single NASICON catalyst material; The preparation method of the phosphate-modified NASICON catalyst is as follows: Achieved by the equal-volume impregnation method, specifically: At room temperature, impregnate the single NASICON material prepared above with an equal volume into a solution containing phosphate, and ultrasonicate until most of the water has evaporated; The obtained sample is calcined in the range of 500 - 700 °C for 2 - 4 h to obtain the original powder of the phosphate-modified NASICON catalyst.

8. The integrated method for synthesizing acrylic acid from methanol and acetic acid according to claim 7, characterized in that: When preparing the single NASICON catalyst, the molar ratio of each raw material in the synthesis mother liquor is titanium source∶hydrogen peroxide∶polyethylene glycol∶concentrated phosphoric acid = 0.6 - 1.2∶1.1 - 2.0∶0.0025 - 0.008∶1; For the phosphate-modified NASICON catalyst, the modifying component phosphate is an ammonium salt, sodium salt, potassium salt or cesium salt, including one or any two combinations of ammonium phosphate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, sodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, potassium phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, cesium phosphate; In the obtained catalyst, the mass percentage of phosphate in the catalyst is 0.1 - 10 wt%.

9. The integrated method for synthesizing acrylic acid from methanol and acetic acid according to claim 3, wherein: During the condensation reaction process, the liquid hourly space velocity of the raw material acetic acid is 0.5 - 2 mL / (g cat h), the condensation reaction temperature is 340 - 400 °C, and the condensation reaction pressure is atmospheric pressure.

10. The integrated method for synthesizing acrylic acid from methanol and acetic acid according to claim 3, characterized in that: Calculated based on acetic acid, the conversion rate of acetic acid is above 50%, the selectivity for acrylic acid reaches above 80%, and the selectivity for ester products is below 5%.

Images