CN111763143A

CN111763143A - Method for synthesizing acrylic acid

Info

Publication number: CN111763143A
Application number: CN201911154730.6A
Authority: CN
Inventors: 王峰; 张志鑫; 王业红; 李书双; 张健
Original assignee: Dalian Institute of Chemical Physics of CAS
Current assignee: Dalian Institute of Chemical Physics of CAS
Priority date: 2019-11-22
Filing date: 2019-11-22
Publication date: 2020-10-13

Abstract

The invention relates to a synthesis method of acrylic acid, in particular to a process method for preparing acrylic acid by catalytic conversion of acetic acid and formaldehyde aqueous solution. Comprises a reaction process of obtaining acrylic acid through contact reaction of acetic acid and formaldehyde in the presence of an aldol condensation catalyst and a separation process; the product of said reaction process is subjected to said separation process to obtain at least acetic acid, acrylic acid, water. Wherein the acetic acid obtained in the separation process is recycled for the reaction process. The yield of the acrylic acid in the method can reach more than 95 percent.

Description

Method for synthesizing acrylic acid

Technical Field

The invention relates to a process method for synthesizing acrylic acid, in particular to a process method for synthesizing acrylic acid by acetic acid and formaldehyde or a formaldehyde precursor reagent under the action of a catalyst.

Background

Acrylic acid is an important organic compound that readily polymerizes on its own or with other polymer monomers to form polymers. The polymers are widely applied to the fields of super absorbent materials, dispersing agents, flocculating agents, thickening agents and the like. The synthesis of acrylic acid has attracted considerable attention from the industry and academia due to its important commercial value.

The production method of the acrylic acid mainly comprises the following steps: ethylene process (ethylene, CO and O)₂Reaction), the ethylene oxide process (reaction of ethylene oxide with CO), the ketene process (reaction of ketene with formaldehyde), the acetylene carbonylation process (Reppe process), the chlorohydrin process, the cyanoethanol process, the propane oxidation process, the propylene oxidation process, and the acrylonitrile hydrolysis process. Among the above methods, the ethylene process, the ethylene oxide process and the propane oxidation process are still under development, and no large-scale production apparatus is available, and the ketene process, the acetylene carbonylation process, the chlorohydrin process, the cyanoethanol process and the acrylonitrile hydrolysis process have been eliminated due to low efficiency, large consumption and high cost. To date, propylene oxidation is used in all large-scale acrylic acid production facilities in the world. Companies possessing propylene oxidation production technologies mainly include japanese catalytic chemical company, mitsubishi chemical company, BASF company, and ohio standard petroleum Sohio company. With the increasing exhaustion of fossil resources, the cost of producing acrylic acid from propylene as a raw material will gradually increase.

The 20 th century and 70 th era have increased the price of petroleum, and a route for synthesizing acrylic acid from non-petroleum raw materials, namely acetic acid and formaldehyde, has been produced. Both acetic acid and formaldehyde can be generated from methanol, and the methanol is from synthesis gas and has rich raw material sources. With the development of the modern coal chemical industry, the route is widely concerned by researchers.

Among the reported catalysts, VPO-based catalysts are an effective class of catalysts, whose surface is mainly medium-strong Lewis acid sites and basic sites, which synergistically catalyze the process. Mamoru Ai and the like take acetic acid or methyl acetate and formaldehyde as raw materials and utilize V₂O₅-P₂O₅Acrylic acid or methyl acrylate is prepared by aldol condensation of catalysts such as binary acid oxide, vanadium-titanium binary phosphate (V-Ti-P-O) and the like. In recent years, researchers have focused on how to expose more catalytically active sites, with a series of efforts being directed to the preparation of VPO-based catalysts and their catalyzed aldol condensation to acrylic acids and esters. For example, the PEG6000 is used as a template to prepare the VPO catalyst with high specific surface areaOr loading VPO on SiO₂SBA-15 and Al₂O₃On the carriers, the concentration of active sites on the surface of the catalyst is effectively improved, so that the yield of target products of acrylic acid and esters thereof is improved. Acidic molecular sieve catalyst such as HZSM-5, HZSM-35 and the like, and Cs/SiO₂Or Cs/SBA-15 and other catalysts are also applied to catalyzing condensation of acetic acid or methyl acetate and formaldehyde to prepare acrylic acid or methyl acrylate, but compared with a VPO catalyst, the catalysts are easier to deposit carbon, and the catalysts need to be regenerated frequently to maintain the catalytic activity. In addition, acetic acid and acrylic acid on the strong basic catalyst are easy to generate decarboxylation side reaction to generate a large amount of CO_xAnd carbon deposition, which is not favorable for the generation of target products.

Celanese corporation disclosed a combined process of methanol carbonylation to produce acetic acid and reaction of acetic acid with formaldehyde to produce acrylic acid (US20140073812), where acetic acid conversion can reach 50% and acrylic acid selectivity can reach 70%. The advantage of this process is that formaldehyde is easily removed from the crude acrylic acid. BASF corporation discloses a combined process for preparing acetic acid by oxidizing ethanol and preparing acrylic acid by condensing acetic acid and formaldehyde (CN 104817450). The process for preparing acrylic acid by using methanol and acetic acid as raw materials is also protected in the granted patent CN201180054828.X, and a new patent CN201580053093.7 is newly applied to protect the process after the patent right is ended. Eastman discloses a process for preparing acrylic acid from aqueous acetic acid and formaldehyde solutions (US20130237724) in which the mixed oxides of V, Ti and P are used as catalysts and which have a relatively good space-time yield. The southwest institute of chemical engineering design Co., Ltd discloses TiO₂、SiO₂Or the catalyst of active components such as V, Ti, Zr, P and the like loaded by the molecular sieve catalyzes formaldehyde aqueous solution or paraformaldehyde and acetic acid to synthesize acrylic acid (and methyl acrylate), or catalyzes methylal and methyl acetate to synthesize methyl acrylate, and the catalyst has higher activity and selectivity (CN20140795266, CN201210502752 and CN 201210491886). Asahi chemical technology research institute Limited company reported a method for preparing a catalyst for the synthesis of methyl acrylate and co-production of methyl methacrylate from methyl acetate and formaldehyde, wherein SiO is used as the catalyst₂As a catalyst carrier, further comprises CsAnd metal salts of Zr, and oxides of Sb (CN 201410022889). A Yangjiang research team, Zhang-Jordan institute of Process engineering, of the Chinese academy of sciences, reports a catalyst for synthesizing acrylic acid from formaldehyde aqueous solution and acetic acid, and a preparation and application method thereof (CN201310566202), wherein the catalyst is prepared from activated carbon and Al₂O₃、SiO₂Or one or more than two of the molecular sieves are used as carriers to load phosphorus pentoxide and one or more than two alkaline earth metal oxides. The Nanjing Daichi-Chongji team reported a VPO catalyst and its application in the preparation of acrylic acid (esters) by reacting acetic acid (esters) with formaldehyde (CN201410103826), in which the active VPO catalyst was prepared by refluxing V in a mixed alcohol solution₂O₅The preparation method comprises the steps of adding polyethylene glycol (PEG6000) as a surfactant, and activating the prepared active catalyst in a butane-air mixed atmosphere of 1.5 percent (volume fraction).

In summary, in the literature and patents of acrylic acid synthesis reported in the prior art, the molar ratio of acetic acid to formaldehyde is ensured to be in the most suitable range by controlling the reaction process, so that formaldehyde is basically and completely converted, the yield of the target product is improved, and the separation cost is reduced.

Disclosure of Invention

The object of the present invention is to provide a process for synthesizing acrylic acid which is different from the prior art and which is effective in increasing the yield of acrylic acid.

The invention provides a device for implementing the method for synthesizing acrylic acid, which comprises a reaction device of a process and a device for separating the process, wherein the reaction device of the process comprises an acetic acid feeding port and a formaldehyde water solution feeding port, the device for separating the process at least comprises a device for separating acetic acid, a device for separating acrylic acid and a device for separating formaldehyde water solution, the device for separating acetic acid is connected with the reaction device of the process through a pipeline, the device for separating formaldehyde water solution is connected with the reaction device of the process through a pipeline, and the reaction device of the process is connected with the device for separating acrylic acid to separate acrylic acid.

The apparatus of the present invention wherein said process I reaction apparatus is comprised of a plurality of individual reactors connected in series, the first reactor having an acetic acid feed and each individual reactor having a formaldehyde feed.

The apparatus provided by the invention, wherein the equipment capable of separating the obtained acetic acid and the equipment capable of separating the obtained acrylic acid can be expressed as an acetic acid tower and an acrylic acid tower. In the apparatus for the separation process, in addition to the three separation columns described above, an acetogenic column following the acetogenic column may be included to remove water and other non-acetic acid products therefrom, the acetogenic column being connected to the reaction apparatus of the reaction process.

The technical scheme is as follows:

a process for synthesizing acrylic acid, in the presence of condensation catalyst, in the fixed bed reactor, acetic acid or its aqueous solution contacts reaction process and separation process of getting acrylic acid with aqueous solution of formaldehyde, the products of said reaction process get acetic acid, acrylic acid, water at least through said separation process, wherein, the acetic acid that said separation process gets is recycled and used in the reaction process, said reaction process is carried on in a plurality of fixed bed reactors connected in series, said acetic acid or its aqueous solution enters from the entrance of the first reactor, said aqueous solution of formaldehyde divides into multiple strands and enters each reactor separately sequentially.

The condensation catalyst comprises: a VPO catalyst comprising a metal-doped VPO catalyst, a metal phosphate catalyst, a metal pyrophosphate catalyst, a hydrogen-type molecular sieve catalyst, an alkali metal or alkaline earth metal oxide catalyst; the metals in the metal-doped VPO catalyst, the metal phosphate catalyst and the metal pyrophosphate catalyst include: sc, Y, La, Ce, Pr, Hf, Nb, Ta, Mo, W, Fe, Co, Ni, Cu, Sn, Bi; the catalyst can also contain a carrier, and the content of the carrier is 5-95%; the carrier is selected from: SiO 2₂,Al₂O₃SiC, a mixture of one or more of MgO;

in the reaction process, the molar ratio of acetic acid to formaldehyde in each reactor is (5-20): 1; the reaction temperature is 280-450 ℃; the reaction pressure is 0.05-5 MPa; the liquid hourly space velocity of the acetic acid and the formaldehyde is 0.5-5.0h < -1 >; the mass fraction of acetic acid in the acetic acid aqueous solution is 30-99.9%; the mass fraction of formaldehyde in the formaldehyde aqueous solution is 5-99.9%;

providing a scheme that:

in the reaction process, the molar ratio of acetic acid to formaldehyde in each reactor is (10-20): 1; the reaction temperature is as follows: 280 ℃ and 400 ℃; the reaction pressure is as follows: 0.05-3 MPa; the liquid hourly space velocity of acetic acid and formaldehyde is: 0.5-5.0h^-1(ii) a The mass fraction of acetic acid in the acetic acid aqueous solution is 30-80%; the mass fraction of formaldehyde in the formaldehyde aqueous solution is 5-60%;

the device for implementing the method comprises a reaction device of the process I and a device for separating the process, wherein the reaction device of the reaction process is a fixed bed reactor and comprises an acetic acid feeding port and a formaldehyde water solution feeding port, the device for separating the process at least comprises a device for separating acetic acid and a device for separating acrylic acid, and the device for separating acetic acid is connected with the reaction device of the reaction process through a pipeline. Wherein, the reaction equipment in the reaction process is formed by connecting a plurality of independent reactors in series, the first reactor is provided with an acetic acid feeding port, and each independent reactor is provided with a formaldehyde feeding port.

Wherein said means for separating acetic acid is followed by an acetic acid treatment column to remove water and other non-acetic acid products from the acetic acid, and the acetic acid treatment column is connected to the process reaction means.

Wherein, in the apparatus for the separation process, a rectifying column is further provided to remove impurity components having boiling points lower than that of acrylic acid.

The invention has the advantages that: the proportion of the two raw materials in the reaction is carefully controlled, and the process of the fixed bed reactor connected in series is combined, so that the reaction of the latter reactant in the reactor is ensured to be complete, the separation process is simplified, and the energy consumption of the separation process is reduced.

Drawings

FIG. 1 is a schematic flow chart of the method of the present invention.

FIG. 2 is a schematic diagram showing a specific flow of the process provided by the present invention, wherein the reaction process is carried out in a plurality of reactors connected in series.

FIG. 3 is a gas chromatogram of the product of example 8, with a retention time of 14.15min being the product acrylic acid.

Detailed Description

A process for synthesizing acrylic acid, which comprises a reaction step of contacting acetic acid or its aqueous solution with an aqueous solution of formaldehyde in the presence of a condensation catalyst to obtain acrylic acid and a separation step of the reaction step and the product obtained by the separation step to obtain at least acetic acid, acrylic acid and water, wherein the acetic acid obtained by the separation step is recycled to the reaction step.

In the method provided by the invention, in the reaction process, the molar ratio of acetic acid to formaldehyde is preferably (5-20): 1, more preferably (10-20): 1. the reaction process is carried out in 4 reactors connected in series. Raw material acetic acid or aqueous solution thereof enters a reactor from an inlet of a first reactor and sequentially passes through the reactors which are connected in series, the formaldehyde aqueous solution is divided into a plurality of strands and sequentially enters the reactors, and the concentration and the feeding amount of the formaldehyde aqueous solution are controlled at a feeding hole of each reactor, so that the molar ratio of the acetic acid to the formaldehyde in each reactor is (5-20): 1.

in the method provided by the invention, the mass fraction of acetic acid in the acetic acid aqueous solution in the reaction process is 30-99.9%, and preferably 30-80%; the mass fraction of formaldehyde in the formaldehyde aqueous solution is 5-99.9%, preferably 5-60%; the reaction temperature of the acetic acid and the formaldehyde is 280-450 ℃, and preferably 280-400 ℃; the reaction pressure is 0.05-5 MPa, and the preferable pressure is 0.05-3 MPa; the liquid hourly space velocity of the acetic acid and the formaldehyde is 0.5-5.0h^-1Preferably 0.5 to 3.0h^-1。

In the method provided by the invention, when a plurality of reactors are connected in series in the reaction process, a heat exchanger is arranged between the reactors to ensure that the temperature of the material is adjusted to the temperature required by the inlet of the next reactor.

In the method provided by the invention, the reaction fluid flow direction of the reaction of the process I can be an ascending type or a descending type, wherein the descending type fluid flow direction is preferred, namely, the reaction materials flow through the catalyst from top to bottom for reaction. The reaction in the process I can adopt an isothermal fixed bed reactor (such as a tubular reactor), also can select an adiabatic fixed bed reactor, and preferably adopts an isothermal fixed bed reactor.

In the method provided by the invention, the reaction in the reaction process is carried out in the presence of a condensation catalyst. The condensation catalyst is a VPO catalyst, and contains a metal-doped VPO catalyst, a metal phosphate catalyst, a metal pyrophosphate catalyst, a hydrogen type molecular sieve catalyst and an alkali metal or alkaline earth metal oxide catalyst; the metals in the metal-doped VPO catalyst, the metal phosphate catalyst and the metal pyrophosphate catalyst include: sc, Y, La, Ce, Pr, Hf, Nb, Ta, Mo, W, Fe, Co, Ni, Cu, Sn, Bi; the catalyst can also contain a carrier, and the content of the carrier is 5-95%; the carrier is selected from: SiO 2₂,Al₂O₃SiC, MgO.

In the method provided by the invention, after acetic acid and formaldehyde react in a reactor in the reaction process, reaction products are separated to obtain acetic acid, acrylic acid, water and the like. The acetic acid is recycled after being pressurized, and the acrylic acid is the target product. The purity of the acetic acid to be recycled is preferably 80% or more, more preferably 90% or more.

In order to further explain the present invention in detail, several specific embodiments are given below, but the present invention is not limited to these embodiments.

Example 1

The fixed bed reactor of the reaction process shown in FIG. 2 was charged with VPO catalyst and was packed with inert material up and down, respectively. Firstly, heating a reactor to 280 ℃ in an inert atmosphere, controlling the pressure to be 0.05MPa, and pumping acetic acid and 99.9% formaldehyde aqueous solution into the reactor after the temperature and the device are stable; at a liquid hourly space velocity of 0.5h^-1Under the condition of (1), raw materials are added into a reactor to continuously react according to the molar ratio of acetic acid to formaldehyde of 5. The bottom effluent of the reactor was taken for chromatographic analysis. The reaction results are shown in Table 1.

Example 2

In the fixed bed reactor of the reaction process shown in FIG. 2, a Ti-doped VPO catalyst (5% by mass of the catalyst) was charged, and the upper and lower sides of the reactor were filled with inert materials, respectively. Firstly, heating a reactor to 300 ℃ in an inert atmosphere, controlling the pressure at 0.1MPa, and pumping 90% acetic acid and 80% formaldehyde aqueous solution into the reactor after the temperature and the device are stable; at a liquid hourly space velocity of 1h^-1Under the condition of (1), raw materials are added into a reactor to continuously react according to the molar ratio of acetic acid to formaldehyde of 10. The bottom effluent of the reactor was taken for chromatographic analysis. The reaction results are shown in Table 1.

Example 3

In the fixed bed reactor of the reaction process shown in FIG. 2, a Nb-doped VPO catalyst (10% by mass of the catalyst) was charged, and the upper and lower sides of the reactor were filled with inert materials, respectively. Firstly, heating a reactor to 400 ℃ in an inert atmosphere, controlling the pressure to be 1MPa, and pumping 60% acetic acid and 60% formaldehyde aqueous solution into the reactor after the temperature and the device are stable; at a liquid hourly space velocity of 2h^-1Under the condition of (1), raw materials are added into a reactor to continuously react according to the molar ratio of acetic acid to formaldehyde of 20. The bottom effluent of the reactor was taken for chromatographic analysis. The reaction results are shown in Table 1.

Example 4

In the fixed bed reactor of the reaction process shown in FIG. 2, a Sn-doped VPO catalyst (the mass doping amount is 20% of the catalyst) was charged, and the reactor was filled with inert substances at the upper and lower sides, respectively. Firstly, heating a reactor to 450 ℃ in an inert atmosphere, controlling the pressure to be 5MPa, and pumping 30% acetic acid and 60% formaldehyde aqueous solution into the reactor after the temperature and the device are stable; at a liquid hourly space velocity of 5h^-1Under the condition of (1), raw materials are added into a reactor to continuously react according to the molar ratio of acetic acid to formaldehyde of 20. The bottom effluent of the reactor was taken for chromatographic analysis. The reaction results are shown in Table 1.

Example 5

In the fixed bed reactor of the reaction process shown in FIG. 2, W-doped VPO catalyst (mass doping amount: 1% of the catalyst) was charged, and the reactor was filled with inert materials at the upper and lower sides, respectively. Firstly, in an inert atmosphere, the temperature of a reactor is raised to 350 ℃, the pressure is controlled to be 0.1MPaPumping acetic acid and 5% formaldehyde water solution into the reactor after the temperature and the device are stable; at a liquid hourly space velocity of 3h^-1Under the condition of (1), raw materials are added into a reactor to continuously react according to the molar ratio of acetic acid to formaldehyde of 20. The bottom effluent of the reactor was taken for chromatographic analysis. The reaction results are shown in Table 1.

Example 6

The fixed bed reactor of the reaction process shown in FIG. 2 was charged with a Ce-doped VPO catalyst (30% by mass of the catalyst), and the reactor was filled with inert materials from top to bottom. Firstly, heating a reactor to 350 ℃ in an inert atmosphere, controlling the pressure at 0.1MPa, and pumping 80% acetic acid and 60% formaldehyde aqueous solution into the reactor after the temperature and the device are stable; at a liquid hourly space velocity of 3h^-1Under the condition of (1), raw materials are added into a reactor to continuously react according to the molar ratio of acetic acid to formaldehyde of 10. The bottom effluent of the reactor was taken for chromatographic analysis. The reaction results are shown in Table 1.

Example 7

In the fixed bed reactor of the reaction process shown in FIG. 2, a Bi-doped VPO catalyst (mass doping amount: 15% of the catalyst) was charged, and the upper and lower sides of the reactor were filled with inert materials, respectively. Firstly, heating a reactor to 350 ℃ in an inert atmosphere, controlling the pressure at 0.1MPa, and pumping 80% acetic acid and 60% formaldehyde aqueous solution into the reactor after the temperature and the device are stable; at a liquid hourly space velocity of 3h^-1Under the condition of (1), raw materials are added into a reactor to continuously react according to the molar ratio of acetic acid to formaldehyde of 10. The bottom effluent of the reactor was taken for chromatographic analysis. The reaction results are shown in Table 1.

Example 8

In the fixed bed reactor of the reaction process shown in FIG. 2, cerium phosphate was charged, and the upper and lower sides of the reactor were filled with inert substances, respectively. Firstly, heating a reactor to 350 ℃ in an inert atmosphere, controlling the pressure at 0.1MPa, and pumping 80% acetic acid and 60% formaldehyde aqueous solution into the reactor after the temperature and the device are stable; at a liquid hourly space velocity of 3h^-1Under the condition of (1), raw materials are added into a reactor to continuously react according to the molar ratio of acetic acid to formaldehyde of 10. The bottom effluent of the reactor was taken for chromatographic analysis. The reaction results are shown in Table 1.

Example 9

In the reaction shown in FIG. 2, praseodymium phosphate was charged into a fixed bed reactor, and the reactor was filled with inert materials at the upper and lower sides, respectively. Firstly, heating a reactor to 350 ℃ in an inert atmosphere, controlling the pressure at 0.1MPa, and pumping 80% acetic acid and 60% formaldehyde aqueous solution into the reactor after the temperature and the device are stable; at a liquid hourly space velocity of 3h^-1Under the condition of (1), raw materials are added into a reactor to continuously react according to the molar ratio of acetic acid to formaldehyde of 10. The bottom effluent of the reactor was taken for chromatographic analysis. The reaction results are shown in Table 1.

Example 10

In the fixed bed reactor of the reaction process shown in FIG. 2, lanthanum phosphate was charged, and the upper and lower sides of the reactor were filled with inert substances, respectively. Firstly, heating a reactor to 350 ℃ in an inert atmosphere, controlling the pressure at 0.1MPa, and pumping 80% acetic acid and 60% formaldehyde aqueous solution into the reactor after the temperature and the device are stable; at a liquid hourly space velocity of 3h^-1Under the condition of (1), raw materials are added into a reactor to continuously react according to the molar ratio of acetic acid to formaldehyde of 10. The bottom effluent of the reactor was taken for chromatographic analysis. The reaction results are shown in Table 1.

Example 11

In the fixed bed reactor in the reaction process shown in FIG. 2, nickel pyrophosphate was charged, and the upper and lower sides of the reactor were filled with inert materials, respectively. Firstly, heating a reactor to 350 ℃ in an inert atmosphere, controlling the pressure at 0.1MPa, and pumping 80% acetic acid and 60% formaldehyde aqueous solution into the reactor after the temperature and the device are stable; at a liquid hourly space velocity of 3h^-1Under the condition of (1), raw materials are added into a reactor to continuously react according to the molar ratio of acetic acid to formaldehyde of 10. The bottom effluent of the reactor was taken for chromatographic analysis. The reaction results are shown in Table 1.

Example 12

Cobalt pyrophosphate was charged into a fixed bed reactor in the reaction process shown in FIG. 2, and the upper and lower sides of the reactor were filled with inert materials, respectively. Firstly, heating a reactor to 350 ℃ in an inert atmosphere, controlling the pressure at 0.1MPa, and pumping 80% acetic acid and 60% formaldehyde aqueous solution into the reactor after the temperature and the device are stable; at a liquid hourly space velocity of 3h^-1Under the conditions of (1) acetic acid/formaldehydeThe raw materials are added into the reactor in a molar ratio of 10 for continuous reaction. The bottom effluent of the reactor was taken for chromatographic analysis. The reaction results are shown in Table 1.

Example 13

In the fixed bed reactor of the reaction process shown in FIG. 2, HZSM-5 was charged, and the upper and lower sides of the reactor were filled with inert materials, respectively. Firstly, heating a reactor to 350 ℃ in an inert atmosphere, controlling the pressure at 0.1MPa, and pumping 80% acetic acid and 60% formaldehyde aqueous solution into the reactor after the temperature and the device are stable; at a liquid hourly space velocity of 3h^-1Under the condition of (1), raw materials are added into a reactor to continuously react according to the molar ratio of acetic acid to formaldehyde of 10. The bottom effluent of the reactor was taken for chromatographic analysis. The reaction results are shown in Table 1.

Example 14

HY was charged into the fixed bed reactor in the reaction process shown in FIG. 2, and the reactor was filled with inert materials at the upper and lower sides. Firstly, heating a reactor to 350 ℃ in an inert atmosphere, controlling the pressure at 0.1MPa, and pumping 80% acetic acid and 60% formaldehyde aqueous solution into the reactor after the temperature and the device are stable; at a liquid hourly space velocity of 3h^-1Under the condition of (1), raw materials are added into a reactor to continuously react according to the molar ratio of acetic acid to formaldehyde of 10. The bottom effluent of the reactor was taken for chromatographic analysis. The reaction results are shown in Table 1.

Example 15

H β is filled into a fixed bed reactor in the reaction process shown in figure 2, the upper part and the lower part of the reactor are respectively filled with inert substances, firstly, the reactor is heated to 350 ℃ in inert atmosphere, the pressure is controlled to be 0.1MPa, 80 percent of acetic acid and 60 percent of formaldehyde aqueous solution are pumped into the reactor after the temperature and the device are stable, and the liquid hourly space velocity is 3H^-1Under the condition of (1), raw materials are added into a reactor to continuously react according to the molar ratio of acetic acid to formaldehyde of 10. The bottom effluent of the reactor was taken for chromatographic analysis. The reaction results are shown in Table 1.

Example 16

The fixed bed reactor of the reaction process shown in FIG. 2 was charged with 5 wt% Cs₂O/SiO₂The reactor was filled with inert material from top to bottom. Firstly, in an inert atmosphere, the temperature of a reactor is raised to 350 ℃, and the pressure is controlledPreparing under 0.1MPa, and pumping 80% acetic acid and 60% formaldehyde water solution into the reactor after the temperature and the device are stable; at a liquid hourly space velocity of 3h^-1Under the condition of (1), raw materials are added into a reactor to continuously react according to the molar ratio of acetic acid to formaldehyde of 10. The bottom effluent of the reactor was taken for chromatographic analysis. The reaction results are shown in Table 1.

Example 17

The fixed bed reactor of the reaction process shown in FIG. 2 was charged with 95 wt% MgO/Al₂O₃The reactor was filled with inert material from top to bottom. Firstly, heating a reactor to 350 ℃ in an inert atmosphere, controlling the pressure at 0.1MPa, and pumping 80% acetic acid and 60% formaldehyde aqueous solution into the reactor after the temperature and the device are stable; at a liquid hourly space velocity of 3h^-1Under the condition of (1), raw materials are added into a reactor to continuously react according to the molar ratio of acetic acid to formaldehyde of 10. The bottom effluent of the reactor was taken for chromatographic analysis. The reaction results are shown in Table 1.

Example 18

A fixed bed reactor in the reaction process shown in FIG. 2 was charged with 60 wt% BaO/SiC, and the upper and lower sides of the reactor were filled with inert substances, respectively. Firstly, heating a reactor to 350 ℃ in an inert atmosphere, controlling the pressure at 0.1MPa, and pumping 80% acetic acid and 60% formaldehyde aqueous solution into the reactor after the temperature and the device are stable; at a liquid hourly space velocity of 3h^-1Under the condition of (1), raw materials are added into a reactor to continuously react according to the molar ratio of acetic acid to formaldehyde of 10. The bottom effluent of the reactor was taken for chromatographic analysis. The reaction results are shown in Table 1.

Example 19

In the fixed bed reactor of the reaction process shown in FIG. 2, 30 wt% SrO/MgO was charged, and the upper and lower sides of the reactor were filled with inert materials, respectively. Firstly, heating a reactor to 350 ℃ in an inert atmosphere, controlling the pressure at 0.1MPa, and pumping 80% acetic acid and 60% formaldehyde aqueous solution into the reactor after the temperature and the device are stable; at a liquid hourly space velocity of 3h^-1Under the condition of (1), raw materials are added into a reactor to continuously react according to the molar ratio of acetic acid to formaldehyde of 10. The bottom effluent of the reactor was taken for chromatographic analysis. The reaction results are shown in Table 1.

Example 20

The fixed bed reactor of the reaction process shown in FIG. 2 was charged with 30 wt% K₂O/SiO₂-Al₂O₃The reactor was filled with inert material from top to bottom. Firstly, heating a reactor to 350 ℃ in an inert atmosphere, controlling the pressure at 0.1MPa, and pumping 80% acetic acid and 60% formaldehyde aqueous solution into the reactor after the temperature and the device are stable; at a liquid hourly space velocity of 3h^-1Under the condition of (1), raw materials are added into a reactor to continuously react according to the molar ratio of acetic acid to formaldehyde of 10. The bottom effluent of the reactor was taken for chromatographic analysis. The reaction results are shown in Table 1.

Comparative example 1:

HZSM-5 was charged into a single fixed bed reaction, and the reactor was filled with inert materials at the top and bottom, respectively. Firstly, heating a reactor to 350 ℃ in an inert atmosphere, controlling the pressure at 0.1MPa, and pumping 80% acetic acid and 60% formaldehyde aqueous solution into the reactor after the temperature and the device are stable; at a liquid hourly space velocity of 3h^-1Under the condition of (1), raw materials are added into a reactor to continuously react according to the molar ratio of acetic acid to formaldehyde of 3. The bottom effluent of the reactor was taken for chromatographic analysis. The reaction results are shown in Table 1. The formaldehyde can not be completely reacted, and a formaldehyde separation device is required to be added to the separation part, so that the separation energy consumption is increased.

Comparative example 2:

HZSM-5 was charged into a single fixed bed reaction, and the reactor was filled with inert materials at the top and bottom, respectively. Firstly, heating a reactor to 350 ℃ in an inert atmosphere, controlling the pressure at 0.1MPa, and pumping 80% acetic acid and 60% formaldehyde aqueous solution into the reactor after the temperature and the device are stable; at a liquid hourly space velocity of 3h^-1Under the condition of (1), raw materials are added into a reactor to continuously react according to the molar ratio of acetic acid to formaldehyde of 25. The bottom effluent of the reactor was taken for chromatographic analysis. The reaction results are shown in Table 1. Although formaldehyde can be basically completely reacted, a large amount of acetic acid enters a separation device, and the circulating energy consumption is remarkably increased.

Comparative example 3:

a single fixed bed reaction was charged with Ti-doped VPO catalyst and the reactor was filled up and down with inert material, respectively. Firstly, in an inert atmosphere, the temperature of the reactor is raised to 300 ℃ and the pressure is increasedControlling the pressure to be 0.1MPa, and pumping 90% acetic acid and 80% formaldehyde water solution into the reactor after the temperature and the device are stable; at a liquid hourly space velocity of 1h^-1Under the condition of (1), raw materials are added into a reactor to continuously react according to the molar ratio of acetic acid to formaldehyde of 4. The bottom effluent of the reactor was taken for chromatographic analysis. The reaction results are shown in Table 1. The formaldehyde can not be completely reacted, and a formaldehyde separation device is required to be added to the separation part, so that the separation energy consumption is increased.

Comparative example 4:

a single fixed bed reaction was charged with Ti-doped VPO catalyst and the reactor was filled up and down with inert material, respectively. Firstly, heating a reactor to 300 ℃ in an inert atmosphere, controlling the pressure at 0.1MPa, and pumping 90% acetic acid and 80% formaldehyde aqueous solution into the reactor after the temperature and the device are stable; at a liquid hourly space velocity of 1h^-1Under the condition of (1), raw materials are added into a reactor to continuously react according to the molar ratio of acetic acid to formaldehyde of 30. The bottom effluent of the reactor was taken for chromatographic analysis. The reaction results are shown in Table 1. Although formaldehyde is completely reacted, a large amount of acetic acid enters a separation device, and the circulating energy consumption is remarkably increased.

TABLE 1 reaction evaluation results

Claims

1. A method for synthesizing acrylic acid, characterized by:

acetic acid and formaldehyde react in more than 2 fixed bed reactors connected in series in sequence, a formaldehyde aqueous solution raw material is introduced into each fixed bed reactor, and the formaldehyde aqueous solution is divided into more than 2 strands and sequentially enters each reactor respectively; only introducing acetic acid raw material into the first fixed bed reactor; the method comprises the following steps of firstly introducing an acetic acid raw material and a formaldehyde aqueous solution raw material into a first fixed bed reactor for reaction, introducing a product of the last fixed bed reactor and the formaldehyde aqueous solution raw material into a next-stage fixed bed reactor for reaction, introducing a product of the last fixed bed reactor into a gas-liquid separation tower for gas-liquid separation, introducing a separated liquid-phase product into an azeotropic dehydration tower for dehydration, separating the dehydrated product by an acetic acid separation tower to obtain acrylic acid and a feed liquid containing acetic acid, and returning the feed liquid containing acetic acid as the acetic acid raw material into the first fixed bed reactor for reaction for synthesizing the acrylic acid;

an aldol condensation catalyst is filled in the fixed bed reactor; the acetic acid raw material is acetic acid or aqueous solution thereof;

in the presence of an aldol condensation catalyst, in a fixed bed reactor, an acetic acid raw material and a formaldehyde aqueous solution are in contact reaction to obtain a product containing acrylic acid.

2. The method of claim 1, wherein:

the condensation catalyst comprises: VPO catalyst, which contains one or more than two of metal-doped VPO catalyst, metal phosphate catalyst, metal pyrophosphate catalyst, hydrogen type molecular sieve catalyst and alkali metal or alkaline earth metal oxide catalyst;

the VPO catalyst is VPxOy, x is 0.5 to 3, y is a suitable value to satisfy the valency of each element (V and P);

the metals in the metal-doped VPO catalyst, metal phosphate catalyst or metal pyrophosphate catalyst include: sc, Y, La, Ce, Pr, Hf, Nb, Ta, Mo, W, Fe, Co, Ni, Cu, Sn, Bi; the mass doping amount is 1-30% of the metal-doped VPO catalyst;

the catalyst except the hydrogen type molecular sieve catalyst does not contain or can also contain a carrier, and the content of the carrier is 5-95 wt%; the carrier is selected from: SiO 2₂,Al₂O₃SiC, MgO.

3. A method according to claim 1 or 2, characterized in that:

in the process I, the molar ratio of acetic acid to formaldehyde in each fixed bed reactor is (5-20): 1;

the reaction temperature is 280-450 ℃;

the reaction pressure is 0.05-5 MPa;

the mass space velocity of the sum of the acetic acid and the formaldehyde is 0.5 to 5.0h^-1；

The mass fraction of acetic acid in the acetic acid or the acetic acid aqueous solution is 30-99.9%;

the mass fraction of formaldehyde in the formaldehyde aqueous solution is 5-99.9%.

4. A method according to claim 1 or 2, characterized in that:

in the process I, the molar ratio of acetic acid to formaldehyde in each fixed bed reactor is (10-20): 1;

the reaction temperature is as follows: 280 ℃ and 400 ℃;

the reaction pressure is as follows: 0.05-3 MPa;

the mass space velocity of the sum of acetic acid and formaldehyde is as follows: 0.5-3.0 h^-1；

The mass fraction of acetic acid in the acetic acid aqueous solution is 30-80%;

the mass fraction of formaldehyde in the formaldehyde aqueous solution is 5-60%.

5. An apparatus for carrying out the process according to any one of claims 1 to 4, comprising reaction means and means for separation, said reaction means being a fixed bed reactor, said means for separation comprising at least means for gas-liquid separation, dehydration and separation to acrylic acid, the de-acrylated mass of said means for separation to acrylic acid being connected to said reaction means via a line.

6. The apparatus of claim 5, wherein said reaction means for reacting comprises a plurality of separate reactors connected in series, the first reactor having an acetic acid feed and each separate reactor having a formaldehyde feed.

7. The apparatus according to claim 5, wherein said means for separating acetic acid is followed by an acetic acid treatment column to remove water and other non-acetic acid products from the acetic acid, and wherein the acetic acid treatment column is connected to the process reaction means.

8. The apparatus according to claim 5, wherein said means for the separation process further comprises a rectifying column for removing impurity components having boiling points lower than that of acrylic acid.