Cyclic regeneration method for metal oxide catalyst

Abstract

The invention discloses a cyclic regeneration method for a metal oxide catalyst. The device comprises at least two sections of reactors, the upper part of each section of reactor controls the switching of reaction raw materials and regenerated gas through valve switching, the lower part of each section of reactor is provided with an outlet, and the outlet is connected with a gas-liquid separation device. And when the activity of the catalyst in the reactor is reduced by 5-20%, a valve cutting device at the upper part of the reactor is switched to regenerated gas to regenerate the catalyst. The process takes cyclic regeneration of an oxide catalyst for preparing acrylic acid through aldol condensation as an example. The process is carried out in a fixed bed reactor, the production is continuous through a cyclic regeneration method, the variation amplitude of a reaction product in the reaction process is effectively reduced, and the stable quality of the product is ensured. The process has the advantages that the regenerated catalyst is stable in performance, and heat released in the regeneration process can be used for a reaction heat source to reduce energy consumption.

Description

Technical Field

[0001] The invention relates to a cyclic regeneration process for metal oxide catalysts, and in particular to a method for in-situ regeneration and activation of catalysts in a fixed bed reactor by alternating switching. Background Art

[0002] Acrylic acid is an important monomer used to produce homopolymers and copolymers. It plays a very important role in the field of fine chemicals. Most of it is esterified with alcohols to produce corresponding esters, such as methyl acrylate, ethyl acrylate, butyl acrylate, etc. A small amount is used to produce highly absorbent resins, detergent aids and water treatment agents, etc. At present, with the rapid development of related industries, the market potential of acrylic acid is gradually optimistic.

[0003] Since the industrial production of acrylic acid was realized in the 1930s, it has gone through the cyanohydrin process, the Rep process, the ketene process, the acrylonitrile hydrolysis process and the propylene oxidation process currently used in industry. The first four processes have been eliminated due to technical and economic reasons. The propylene oxidation process currently used in industry is a new method developed in the 1960s. It mainly involves the oxidation of propylene to acrylic acid in two steps using a heterogeneous catalyst. First, propylene is partially oxidized to produce acrolein and then further oxidized to produce acrylic acid.

[0004] Since propylene mainly comes from petroleum cracking, with the increasing shortage of petroleum resources and the characteristics of my country's energy structure, the propylene oxidation method has certain resource limitations in my country. Based on my country's coal-rich energy characteristics and the stable market conditions of coal-based methanol and acetic acid in recent years, especially the oversaturation of the acetic acid market, there is a serious overcapacity. Therefore, the development of the condensation of formaldehyde and acetic acid to prepare acrylic acid is of great significance to my country.

[0005] In recent years, many domestic scientific research institutions have also conducted certain research on the preparation of acrylic acid by condensation of formaldehyde and acetic acid. According to the type of reactor, it is mainly divided into fixed bed reactor and fluidized bed reactor. The use of fixed bed reactors has the disadvantages of rapid catalyst deactivation and insufficient raw material reaction, such as Dalian Institute of Chemical Physics, Chinese Academy of Sciences (patents: CN111763144A, CN114605252A), Shandong Coal Chemical Research Institute (DOI: 10.3969 / j.issn.1008-021X.2014.04.056), Southwest Institute of Chemical Technology (patent: CN 102962052A, Doi:10.3969 / j.issn.1003-2673.2011.12.011) and other technologies; the process using a fluidized bed reactor has problems of low selectivity and conversion rate, such as Xuyang Coking's technology (patents: CN102775302A and CN103435483A) and the technology of the Institute of Process Engineering of the Chinese Academy of Sciences (patent: CN104926644A); and the fluidized bed process for directly preparing acrylic acid from formaldehyde and acetic acid has not been reported. Summary of the invention

[0006] The purpose of the present invention is to provide a catalyst recycling process for metal oxides. The method is characterized in that a fixed bed reactor is used to regenerate and activate the catalyst in situ by alternating switching, so that the production is continuous, the variation range of the reaction product during the reaction is effectively reduced, and the quality of the product is guaranteed to be stable.

[0007] A recycling process for a metal oxide catalyst, specifically:

[0008] The recycling and regeneration process of the metal oxide catalyst is as follows: taking the preparation of acrylic acid by aldol condensation reaction as an example, a mixed solution of formaldehyde aqueous solution and acetic acid is used as a raw material, passes through a preheating device under the condition of no carrier gas, and then enters a fixed bed reactor in a gaseous form for condensation reaction; wherein, by adjusting the switching sequence of control valves 1-4, the reactor a and the reactor b are alternately in the condensation reaction and regeneration process according to the set time, and the heat released in the regeneration process is transferred to the condensation reaction process for reaction heat source, and the product and unreacted raw materials are condensed by a cooling device and enter a product collection tank;

[0009] The catalyst includes one or more of a VPO catalyst, a metal-doped VPO catalyst, and a metal phosphate catalyst;

[0010] The catalyst is a non-supported catalyst or a supported catalyst; the catalyst is supported on a carrier, the carrier includes one or more of γ-Al2O3, SiO2, ZSM-5, HY, and the content of the carrier in the supported catalyst is 5-95wt%, preferably 5-30wt%.

[0011] The molar ratio of acetic acid to formaldehyde in the mixed solution of formaldehyde aqueous solution and acetic acid is 1:1-10:1 (preferably 1.5:1-6:1); the water content in the mixed solution is 0-65wt%, preferably 0-30wt%;

[0012] The formaldehyde source is one or more of formalin, methylal, trioxymethylene and polyformaldehyde.

[0013] The control valve 1-4 (such as Figure 1 The switching sequence of the control valves on the same reactor is to ensure that they are opened and closed alternately. When the catalyst reaction activity decreases by 5-20%, the switch is performed, and the switching actions of the control valves are performed simultaneously. The heat released during regeneration needs to be transferred to the condensation reaction for reaction heat.

[0014] The regeneration gas is one of air, oxygen, carbon dioxide, nitrogen, argon and helium, or a mixture of two or more thereof.

[0015] In the fixed bed reactor, the catalyst prepared in the above process is filled in the middle of the bed (the catalyst after molding is selected to be 40-60 mesh), and the upper and lower sections are filled with quartz sand; the reaction temperature is 240-400°C, the regeneration temperature is 300-600°C, and the GHSV is 900-2000h -1 The final product is a mixed solution with acrylic acid as the main product.

[0016] The process of the present invention takes the cyclic regeneration of the oxide catalyst for preparing acrylic acid by aldol condensation as an example. The process is carried out in a fixed bed reactor, and the production is continuous through the cyclic regeneration method, which effectively reduces the variation range of the reaction product during the reaction process and ensures the stability of the product quality. The advantage of this process is that the performance of the catalyst after regeneration is stable, and the heat released during the regeneration process can be used as a reaction heat source to reduce energy consumption.

[0017] Beneficial technical effects of the present invention

[0018] 1. The recycling process of the metal oxide catalyst used in the present invention has a good reference significance for the recycling of other metal oxide catalysts, avoiding the problems of catalyst pulverization and loss, complex fluidized bed structure and high equipment cost in the fluidized bed process.

[0019] 2. The heat released in the regeneration process is transferred to the condensation reaction process through heat transfer means such as heat transfer oil, thereby improving the utilization rate of waste heat and reducing energy consumption. The entire process is simple and easy to industrialize. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a process flow chart of the present invention.

[0021] Figure 2 This is the thermogravimetric comparison curve before and after the catalyst reaction. DETAILED DESCRIPTION

[0022] The following is a detailed description of the preferred embodiments of the present invention so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more definite definition of the protection scope of the present invention.

[0023] like Figure 1 As shown, a recycling method for a metal oxide catalyst is a recycling method for a metal oxide catalyst used in the preparation of acrylic acid by the condensation reaction of formaldehyde and acetic acid aldol, which is specifically as follows:

[0024] A mixed solution of formaldehyde aqueous solution and acetic acid is used as a raw material (in the absence of carrier gas) and then gasified and introduced into one of two parallel fixed bed reactors respectively filled with metal oxide catalysts in gaseous form for condensation reaction. A regeneration gas is introduced into the other fixed bed reactor filled with metal oxide catalysts to regenerate the metal oxide catalyst. The two fixed bed reactors alternately carry out the condensation reaction and the regeneration process of the metal oxide catalyst, so that the metal oxide catalysts in the two fixed bed reactors alternately carry out the cyclic regeneration and cyclic catalytic aldol condensation reaction process.

[0025] The two parallel fixed bed reactors are reactor a and reactor b, which are connected to a mixed solution storage tank of formaldehyde aqueous solution and acetic acid and a regeneration gas source by adjusting the first, second, third and fourth control valves (1-4), respectively. By adjusting the switching sequence of the first, second, third and fourth control valves (1-4), reactor a and reactor b are alternately in a condensation reaction and a regeneration process according to a set time, and the product and unreacted raw materials are condensed by a cooling device and enter a product collection tank.

[0026] The heat released during the regeneration process is transferred to the condensation reaction process to be used as a heat source for gasifying the reaction raw materials; the heat released during the regeneration process needs to be transferred to the condensation reaction for reaction heat;

[0027] A flow pump is provided at the discharge port of the mixed solution storage tank of the formaldehyde aqueous solution and acetic acid, a flow meter is provided at the gas outlet of the regeneration gas source; and an exhaust port is provided at the upper part of the product collecting tank.

[0028] The first, second, third and fourth control valves (1-4 as Figure 1 The switching sequence of the reactor is as follows: two control valves connected to the mixed solution storage tank of the formaldehyde aqueous solution and acetic acid and the regeneration gas source respectively on the same reactor should be opened and closed alternately, and one of the two reactors should be connected to the mixed solution storage tank of the formaldehyde aqueous solution and acetic acid, and the other should be connected to the regeneration gas source at the same time;

[0029] The metal oxide catalyst (the catalyst after molding is 40-60 mesh) is filled in the middle section of the fixed bed reactor, and the upper and lower sections (the upper and lower parts of the middle catalyst bed) are filled with quartz sand (40-60 mesh).

[0030] When the catalyst reaction activity in the condensation reactor decreases by 5-20% from the initial activity of the condensation reaction after switching, the condensation and regeneration process in the second reactor is switched again, and the switching actions of the first, second, third and fourth control valves are carried out simultaneously.

[0031] Example 1

[0032] The condensation catalyst is prepared according to the method in patent CN111763143A. VPO oxide, P / V = 1 / 1.2 (atomic number ratio), the catalyst size is 40-60um, the formaldehyde source in the raw material is formalin, n 醋酸 :n 甲醛 =1:1 (molar ratio, water content 29.8%), reaction temperature 280°C, GHSV = 1250h -1 When the formaldehyde conversion rate drops from 50% to 40%, switching regeneration is performed; the control valve switch status is: the first and fourth control valves 1 and 4 are open, and the second and third control valves 2 and 3 are closed; the regeneration gas is a mixture of nitrogen and oxygen in a volume ratio of 1:1, the regeneration temperature is 300℃, and GHSV=1250h -1 ; After each valve cut operation for 30 minutes, the gas product and liquid product analysis were carried out. The gas product was monitored online by gas chromatography, and the liquid product was analyzed offline. The molar selectivity of acrylic acid was 90%, CO X The molar selectivity is 4%.

[0033] Example 2

[0034] Ti-doped condensation catalyst VTiPO oxide was prepared according to the method in patent CN111763143A, P / V=1:1.2 (atomic ratio), the doping amount of Ti was 5% of the mass of the condensation catalyst, the catalyst size was 40-60um, the formaldehyde source in the raw material was trioxymethylene, n 醋酸 :n 甲醛 =1.5:1 (molar ratio, water content 0%), reaction temperature 340°C, WHSV = 1580h -1 When the molar conversion rate of formaldehyde drops from 68% to 50%, switching regeneration is performed; the switch state of the control valve is: the first and fourth control valves 1 and 4 are open, and the second and third control valves 2 and 3 are closed; the regeneration gas is air, the regeneration temperature is 340℃, and GHSV=1580h -1; After each valve cut operation for 30 minutes, the gas product and liquid product analysis were carried out. The products were monitored online by gas chromatography, and the liquid products were analyzed offline. The molar selectivity of acrylic acid was 95%, CO X The molar selectivity was 3.5%.

[0035] Example 3

[0036] The condensation catalyst is VPO oxide prepared according to the method in patent CN111763143A, P / V=1:1.2 (atomic ratio), and then loaded on γ-Al2O3, the VPO oxide mass loading is 5%, the catalyst size is 40-60um, the formaldehyde source in the raw material is methylal, n 醋酸 :n 甲醛 =1:1 (molar ratio, water content 3.6%), reaction temperature 200°C, GHSV = 1450h -1 , when the molar conversion rate of formaldehyde drops from 40% to 35%, switching is performed; the switch state of the control valve is: the first and fourth control valves 1 and 4 are open, and the second and third control valves 2 and 3 are closed; the regeneration gas is a mixture of argon and air in a volume ratio of 1:3, the regeneration temperature is 600℃, and GHSV=1450h -1 ; After each valve cut operation for 30 minutes, the gas product and liquid product analysis were carried out. The gas product was monitored online by gas chromatography, and the liquid product was analyzed offline. The molar selectivity of acrylic acid was 80%, CO X The molar selectivity was 6.2%.

[0037] Example 4

[0038] The Ti-doped condensation catalyst VTiPO oxide is prepared according to the method in patent CN111763143A, P / V=1:1.2 (atomic ratio), and the mass doping amount of Ti in VTiPO oxide is 5%; then it is loaded on γ-Al2O3, the mass loading amount of VTiPO oxide is 20%, the catalyst size is 40-60um, the formaldehyde source in the raw material is polyformaldehyde, n 醋酸 :n 甲醛 =10:1 (molar ratio, water content 4.6%), reaction temperature 320°C, GHSV = 2000h -1 , when the molar conversion rate of formaldehyde drops from 90% to 85%, the switch is performed; the control valve switch state is: control valves 1 and 4 are open, control valves 2 and 3 are closed; the regeneration gas is oxygen, the regeneration temperature is 400℃, GHSV=2000h -1After each valve cut operation for 30 minutes, the gas product and liquid product analysis were carried out. The gas product was monitored online by gas chromatography, and the liquid product was analyzed offline. The molar selectivity of acrylic acid was 92%, and the CO X The molar selectivity was 4.7%.

[0039] Example 5

[0040] The condensation catalyst is VPO oxide prepared according to the method in patent CN111763143A, P / V=1:5 (atomic ratio), and then loaded on SiO2, the VPO oxide mass loading is 50%, the catalyst size is 40-60um, the formaldehyde source in the raw material is formalin, n 醋酸 :n 甲醛 =2:1 (molar ratio, water content 20.3%), reaction temperature 300°C, GHSV = 1800h -1 , when the molar conversion rate of formaldehyde drops from 40% to 33%, switching is performed; the switch status of the control valve is: control valves 1 and 4 are open, control valves 2 and 3 are closed; the regeneration gas is a mixture of carbon dioxide and oxygen, the regeneration temperature is 450℃, GHSV=1800h -1 After each valve cut operation for 30 minutes, the gas product and liquid product analysis were carried out. The gas product was monitored online by gas chromatography, and the liquid product was analyzed offline. The molar selectivity of acrylic acid was 91%, and the CO X The molar selectivity was 3.2%.

[0041] Example 6

[0042] Ti-doped condensation catalyst VTiPO oxide was prepared according to the method in patent CN111763143A, P / V=1:1.2 (atomic ratio), Ti mass doping amount was 5%, and then loaded on SiO2, VTiPO oxide mass loading amount was 95%, catalyst size was 40-60um, formaldehyde source in raw material was methylal, n 醋酸 :n 甲醛 =6:1 (molar ratio, water content 3.2%), reaction temperature 400°C, GHSV = 1950h -1 , when the molar conversion rate of formaldehyde drops from 90% to 60%, switching is performed; the switch status of the control valve is: control valves 1 and 4 are open, control valves 2 and 3 are closed; the regeneration gas is a mixture of air and helium, the regeneration temperature is 400℃, GHSV=1950h -1 After each valve cut operation for 30 minutes, the gas product and liquid product analysis were carried out. The gas product was monitored online by gas chromatography, and the liquid product was analyzed offline. The molar selectivity of acrylic acid was 90%, CO X The molar selectivity was 5.6%.

[0043] Example 7

[0044] The condensation catalyst is VPO oxide prepared according to the method in patent CN111763143A, P / V=1:0.5 (atomic ratio), and then loaded on ZSM-5, the VPO oxide mass loading is 5%, the catalyst size is 40-60um, the formaldehyde source in the raw material is methylal, n 醋酸 :n 甲醛 =1.5:1 (molar ratio, water content 7.7%), reaction temperature 250°C, GHSV = 1450h -1 , when the molar conversion rate of formaldehyde drops from 75% to 52.5%, the switch is performed; the switch state of the control valve is: control valves 1 and 4 are open, control valves 2 and 3 are closed; the regeneration gas is carbon dioxide, the regeneration temperature is 500℃, and GHSV=1450h -1 After each valve cut operation for 30 minutes, the gas product and liquid product analysis were carried out. The gas product was monitored online by gas chromatography, and the liquid product was analyzed offline. The molar selectivity of acrylic acid was 89%, CO X The molar selectivity was 7.0%.

[0045] Example 8

[0046] The condensation catalyst is VPO oxide prepared according to the method in patent CN111763143A, P / V=1:2 (atomic ratio), and then loaded on HY, the VPO oxide mass loading is 5%, the catalyst size is 40-60um, the formaldehyde source in the raw material is methylal, n 醋酸 :n 甲醛 =1:1 (molar ratio, water content 33.3%), reaction temperature 380°C, GHSV = 900h -1 , when the molar conversion rate of formaldehyde drops from 60% to 30%, switching is performed; the switch status of the control valve is: control valves 1 and 4 are open, control valves 2 and 3 are closed; the regeneration gas is a mixture of air and oxygen, the regeneration temperature is 340℃, GHSV=900h -1 After each valve cut operation for 30 minutes, the gas product and liquid product analysis were carried out. The gas product was monitored online by gas chromatography, and the liquid product was analyzed offline. The molar selectivity of acrylic acid was 85%, CO X The molar selectivity was 8.1%.

[0047] Example 9

[0048] The Nb-doped condensation catalyst VNbPO oxide was prepared according to the method in patent CN111763143A, P / V = 1:1.4 (atomic ratio), the Nb doping amount was 15%, the catalyst size was 40-60um, the formaldehyde source in the raw material was trioxymethylene, n醋酸 :n 甲醛 =1:1 (molar ratio, water content 7.7%), reaction temperature 320°C, GHSV = 1670h -1 When the molar conversion rate of formaldehyde drops from 50% to 38%, switching regeneration is performed; the control valve switch state is: control valves 1 and 4 are open, control valves 2 and 3 are closed; the regeneration gas is a mixture of air and helium, the regeneration temperature is 400℃, and GHSV=1670h -1 After each valve cut operation for 30 minutes, the gas product and liquid product analysis were carried out. The gas product was monitored online by gas chromatography, and the liquid product was analyzed offline. The molar selectivity of acrylic acid was 80%, CO X The molar selectivity was 7.8%.

[0049] Example 10

[0050] Ni-doped condensation catalyst VNiPO oxide was prepared according to the method in patent CN111763143A, P / V=1:3 (atomic ratio), Ni doping amount was 10%, catalyst size was 40-60um, formaldehyde source in raw material was trioxymethylene, n 醋酸 :n 甲醛 =1.5:1 (molar ratio, water content 14.3%), reaction temperature 300°C, GHSV = 1570h -1 When the molar conversion rate of formaldehyde drops from 50% to 38%, switching regeneration is performed; the control valve switch state is: control valves 1 and 4 are open, control valves 2 and 3 are closed; the regeneration gas is carbon dioxide, the regeneration temperature is 450℃, and GHSV=1570h -1 After each valve cut operation for 30 minutes, the gas product and liquid product analysis were carried out. The gas product was monitored online by gas chromatography, and the liquid product was analyzed offline. The molar selectivity of acrylic acid was 86%, CO X The molar selectivity was 4.9%.

[0051] Embodiment 11

[0052] The Bi-doped condensation catalyst VBiPO oxide was prepared according to the method in patent CN111763143A, P / V = 1:2.5 (atomic ratio), the Bi doping amount was 20%, the catalyst size was 40-60um, the formaldehyde source in the raw material was trioxymethylene, n 醋酸 :n 甲醛 =2:1 (molar ratio, water content 16.7%), reaction temperature 250°C, GHSV = 1900h -1When the molar conversion rate of formaldehyde drops from 70% to 54%, switching regeneration is performed; the control valve switch state is: control valves 1 and 4 are open, control valves 2 and 3 are closed; the regeneration gas is carbon dioxide, the regeneration temperature is 500℃, GHSV=1900h -1 After each valve cut operation for 30 minutes, the gas product and liquid product analysis were carried out. The gas product was monitored online by gas chromatography, and the liquid product was analyzed offline. The molar selectivity of acrylic acid was 80%, CO X The molar selectivity was 7.6%.

[0053] Example 12

[0054] Sn-doped condensation catalyst VSnPO oxide was prepared according to the method in patent CN111763143A, P / V=1:4 (atomic ratio), Sn doping amount was 25%, catalyst size was 40-60um, formaldehyde source in raw material was trioxymethylene, n 醋酸 :n 甲醛 =6:1 (molar ratio, water content 0.9%), reaction temperature 320°C, GHSV = 1950h -1 When the molar conversion rate of formaldehyde drops from 90% to 60%, switching regeneration is performed; the control valve switch state is: control valves 1 and 4 are open, control valves 2 and 3 are closed; the regeneration gas is air, the regeneration temperature is 400℃, GHSV=1950h -1 After each valve cut operation for 30 minutes, the gas product and liquid product analysis were carried out. The gas product was monitored online by gas chromatography, and the liquid product was analyzed offline. The molar selectivity of acrylic acid was 76%, CO X The molar selectivity was 3.0%.

[0055] Embodiment 13

[0056] W-doped condensation catalyst VWPO oxide was prepared according to the method in patent CN111763143A, P / W=1:4.5 (atomic ratio), W doping amount was 30%, catalyst size was 40-60um, formaldehyde source in raw material was trioxymethylene, n 醋酸 :n 甲醛 =3:1 (molar ratio, water content 5.8%), reaction temperature 340°C, GHSV = 1670h -1 When the molar conversion rate of formaldehyde drops from 90% to 75%, switching regeneration is performed; the control valve switch state is: control valves 1 and 4 are open, control valves 2 and 3 are closed; the regeneration gas is air, the regeneration temperature is 340℃, GHSV=1670h -1 After each valve cut operation for 30 minutes, the gas product and liquid product analysis were carried out. The gas product was monitored online by gas chromatography, and the liquid product was analyzed offline. The molar selectivity of acrylic acid was 82%, COX The molar selectivity was 6.2%.

[0057] Embodiment 14

[0058] The Ce-doped condensation catalyst VCePO oxide was prepared according to the method in patent CN111763143A, P / W = 1:1.5 (atomic ratio), Ce doping amount was 5%, catalyst size was 40-60um, formaldehyde source in the raw material was trioxymethylene, n 醋酸 :n 甲醛 =2:1 (molar ratio, water content 64.3%), reaction temperature 280°C, GHSV = 1400h -1 When the molar conversion rate of formaldehyde drops from 84% to 64%, switching regeneration is performed; the control valve switch state is: control valves 1 and 4 are open, control valves 2 and 3 are closed; the regeneration gas is air, the regeneration temperature is 300℃, GHSV=1400h -1 After each valve cut operation for 30 minutes, the gas product and liquid product analysis were carried out. The gas product was monitored online by gas chromatography, and the liquid product was analyzed offline. The molar selectivity of acrylic acid was 85%, CO X The molar selectivity was 6.9%.

[0059] Comparative Example 1

[0060] Ti-doped condensation catalyst VTiPO oxide was prepared according to the method in patent CN111763143A, P / V=1:1.2 (atomic ratio), the doping amount of Ti was 5% of the mass of the condensation catalyst, the catalyst size was 40-60um, the formaldehyde source in the raw material was trioxymethylene, n 醋酸 :n 甲醛 =1.5:1, reaction temperature is 340℃, GHSV=900h -1 , when the molar conversion rate of formaldehyde drops from 70% to 43%, switching is performed; the control valve switch status is: control valves 1 and 3 are open, control valves 2 and 4 are closed; the regeneration gas is air, the regeneration temperature is 340℃, GHSV=900h -1 After each valve cut operation for 30 minutes, the gas product and liquid product analysis were carried out. The gas product was monitored online by gas chromatography, and the liquid product was analyzed offline. The molar selectivity of acrylic acid was 80%, CO X The molar selectivity was 10.6%.

[0061] Comparative Example 2

[0062] Ti-doped condensation catalyst VTiPO oxide was prepared according to the method in patent CN111763143A, P / V=1:1.2 (atomic ratio), the doping amount of Ti was 5% of the mass of the condensation catalyst, the catalyst size was 40-60um, the formaldehyde source in the raw material was trioxymethylene, n 醋酸 :n 甲醛 =1.5:1, reaction temperature is 340℃, GHSV=1580h -1 , the switch status of the control valves is: control valves 1 and 2 are open, control valves 3 and 4 are closed, no regeneration is performed, and sampling is performed every 2 hours; the gas product is monitored online by gas chromatography, and the liquid product is analyzed offline; after 20 hours of continuous operation, the molar conversion rate of formaldehyde is reduced from the initial 68% to 20%, the molar selectivity of acrylic acid is reduced from the initial 95% to 73%, and the CO X The molar selectivity was 15.3%.

[0063] Under the same condensation catalyst and the same evaluation conditions, by comparing Comparative Example 1 with Example 2, it is found that the introduction of regeneration gas during the reaction process will increase the conversion rate of formaldehyde and decrease the selectivity of acrylic acid, indicating that this process will cause the oxidation of raw materials and products to generate by-products such as CO X The selectivity of acrylic acid decreased. Comparison between Comparative Example 2 and Example 2 shows that if the catalyst is not regenerated, the catalyst gradually deactivates after a long period of continuous operation. The activity of the catalyst further decreases with prolonged reaction time. DTG also shows that the catalyst without regeneration loses weight significantly after a long period of operation. Figure 2 As shown, it indicates that there is a large amount of carbon deposits on the catalyst surface, which leads to a decrease in the activity of the catalyst.

[0064] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for recycling a metal oxide catalyst, characterized in that: The invention relates to a recycling method for a metal oxide catalyst used in the preparation of acrylic acid by the condensation reaction of formaldehyde and acetic acid, which is specifically as follows: A mixed solution of formaldehyde aqueous solution and acetic acid is used as a raw material and is gasified and then introduced into one of two parallel fixed bed reactors respectively filled with metal oxide catalysts in gaseous form for condensation reaction. A regeneration gas is introduced into the other fixed bed reactor filled with metal oxide catalysts to regenerate the metal oxide catalyst. The two fixed bed reactors alternately carry out the condensation reaction and the regeneration process of the metal oxide catalyst, so that the metal oxide catalysts in the two fixed bed reactors alternately carry out the cyclic regeneration and cyclic catalytic aldol condensation reaction process.

2. The method according to claim 1, characterized in that: The two parallel fixed bed reactors are reactor a and reactor b, which are connected to a mixed solution storage tank of formaldehyde aqueous solution and acetic acid and a regeneration gas source by adjusting the first, second, third and fourth control valves (1-4), respectively. By adjusting the switching sequence of the first, second, third and fourth control valves (1-4), reactor a and reactor b are alternately in a condensation reaction and a regeneration process according to a set time, and the product and unreacted raw materials are condensed by a cooling device and enter a product collection tank.

3. The method according to claim 2, characterized in that: The heat released during the regeneration process is transferred to the condensation reaction process to be used as a heat source for gasifying the reaction raw materials; the heat released during the regeneration process needs to be transferred to the condensation reaction for reaction heat; A flow pump is provided at the discharge port of the mixed solution storage tank of the formaldehyde aqueous solution and acetic acid, a flow meter is provided at the gas outlet of the regeneration gas source; and an exhaust port is provided at the upper part of the product collecting tank.

4. The method according to claim 1 or 2, characterized in that: The catalyst includes one or more of a VPO catalyst, a metal-doped VPO catalyst, and a metal phosphate catalyst; The catalyst is a non-supported catalyst or a supported catalyst; the catalyst is supported on a carrier, the carrier includes one or more of γ-Al2O3, SiO2, ZSM-5, HY, and the content of the carrier in the supported catalyst is 5-95wt%, preferably 5-30wt%.

5. The method according to claim 4, characterized in that: The atomic ratio of P to V in the VPO catalyst is 1:0.5-1:5, preferably 1:0.5-1:2; The metal-doped VPO catalyst, the doped metal M includes: one or more of Ti, Sc, Y, La, Ce, Pr, Hf, Nb, Ta, Mo, W, Fe, Ti, Co, Ni, Cu, Sn, Bi; the mass doping amount of the doped metal M is 1-30wt% of the metal-doped VPO catalyst, preferably 5-30wt%; wherein the atomic ratio of P to V is 1:0.5-1:5, preferably 1:0.5-1:

2.

6. The method according to claim 1, 2 or 3, characterized in that: The molar ratio of acetic acid to formaldehyde in the mixed solution of formaldehyde aqueous solution and acetic acid is 1:1-10:1 (preferably 1.5:1-6:1); the water content in the mixed solution is 0-65wt%, preferably 0-30wt%; The formaldehyde source is one or more of formalin, methylal, trioxymethylene and polyformaldehyde.

7. The method according to claim 2, characterized in that: The switching sequence of the first, second, third and fourth control valves (1-4 as shown in FIG1 ) is that the two control valves connected to the mixed solution storage tank of the formaldehyde aqueous solution and acetic acid and the regeneration gas source on the same reactor are ensured to be opened and closed alternately, and one of the two reactors is connected to the mixed solution storage tank of the formaldehyde aqueous solution and acetic acid, and the other is connected to the regeneration gas source at the same time; When the catalyst reaction activity in the condensation reactor decreases by 5-20% from the initial activity of the condensation reaction after switching, the condensation and regeneration process in the second reactor is switched again, and the switching actions of the first, second, third and fourth control valves are carried out simultaneously.

8. The method according to claim 1 or 2, characterized in that: The regeneration gas is one of air, oxygen, carbon dioxide, nitrogen, argon and helium, or a mixture of two or more thereof.

9. The method according to claim 1, characterized in that: The middle section of the fixed bed reactor is filled with a metal oxide catalyst (the catalyst after molding is selected to be 40-60 mesh), and the upper and lower sections (the upper and lower parts of the middle catalyst bed) are filled with quartz sand (40-60 mesh); the reaction temperature is 200-400°C, the regeneration temperature is 300-600°C, and the GHSV of the condensation reaction and regeneration process is 900-2000h -1 ; The final product is a mixed solution with acrylic acid as the main product.

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