Method for preparing methyl methacrylate and methylacrolein from methyl propionate

Abstract

The present disclosure relates to a method for preparing methyl methacrylate and methylacrolein from methyl propionate, the method comprising: contacting a first stream comprising methyl propionate and a formaldehyde source with a catalyst and performing an aldol condensation reaction to obtain a second stream comprising methyl methacrylate and methylacrolein; the catalyst comprises a molecular sieve with metal elements, the metal elements comprise skeleton metal elements and non-skeleton metal elements, and the molar ratio of the non-skeleton metal elements to the skeleton metal elements in the molecular sieve is less than 0.1; the skeleton metal element comprises Sn; on the basis of the total mole number of all metal elements in the molecular sieve, the content of framework tin is greater than 90 mol%; the molar ratio of the framework tin to the silicon element in the molecular sieve is (0.001-0.05): 1. According to the method disclosed by the invention, the conversion rate of methyl propionate can be effectively improved, and the selectivity of methyl methacrylate and methylacrolein is improved.

Description

Technical Field

[0001] The present disclosure relates to the technical field of aldol condensation, and in particular, to a method for preparing methyl methacrylate and methacrolein from methyl propionate. Background Art

[0002] Methacrolein is mainly used in the manufacture of copolymers and resins, and is an important intermediate product in the production of methyl methacrylate by the ethylene carbonyl process. In addition, methacrolein can also be used to produce higher methacrylate esters, acrylic second monomers, acrylic adhesives, unsaturated polyester crosslinkers and polymer concrete.

[0003] In 1989, BASF of Germany developed a production process of ethylene-propionaldehyde-methyl methacrylate route and built a plant with an annual output of 40,000 tons of methyl methacrylate in Germany. The first step of this method is to synthesize propionaldehyde using ethylene, carbon monoxide and hydrogen; the second step is to react propionaldehyde with formaldehyde under the catalysis of secondary amine to produce methacrolein. Finally, methacrolein is oxidized and esterified to produce methyl methacrylate. The key product of this method is methacrolein. BASF used secondary amine ionic liquids for the first time to catalyze the synthesis of methacrolein from formaldehyde and propionaldehyde, but the catalyst is a homogeneous catalyst and has the disadvantage of being difficult to separate.

[0004] Methyl methacrylate (MMA) is an important organic chemical material stream, mainly used to produce polymethyl methacrylate and acrylic resin materials, and is also widely used in the manufacture of other resins, plastics, coatings, adhesives, lubricants, sizing agents, glazing agents, printing and dyeing auxiliaries, and insulating filling materials, etc. Wierzchowsky and Zatorski, Catalysis Letters 9 (1991), pages 411 to 414, record the aldol condensation of in-situ prepared formaldehyde and methyl propionate in the gas phase over a variety of zeolite catalysts, with a methyl propionate conversion rate of less than 20% and a methyl methacrylate selectivity of up to 74.1%. MamoruAi reported in Bull.Chem.Soc.Jpn., 63, 3722-3724 (1990) that V-Si-P ternary oxide was used as a catalyst in the reaction of methyl propionate and formaldehyde aldol condensation to prepare methyl methacrylate, the molar ratio of the reaction raw materials methyl propionate, formaldehyde, and methanol was 1:1:1, the reaction temperature was 320°C, the atomic ratio of V-Si-P ternary oxide was 1:16:3.2, the conversion rate of methyl propionate was about 35%, and the total yield of methyl methacrylate and methacrylic acid was 53 mol%. CN103551148B improves selectivity by adding an active additive, the main active ingredient includes one or more oxides or salts of Cs, the active additive is one or more oxides or salts of Sb, Nb, Ag, Al, and Zr, and the carrier includes SiO2 and a carrier additive. Although the product selectivity is improved, the conversion rate of methyl propionate is also low.

[0005] Although many methods for preparing methyl methacrylate have been developed, a catalyst capable of simultaneously preparing the above two high value-added products has never been reported. Summary of the invention

[0006] The purpose of the present disclosure is to provide a method for preparing methyl methacrylate and methacrolein from methyl propionate, wherein the method uses a molecular sieve having a tin element in the framework as a catalyst, and can catalyze the aldol condensation reaction of methyl propionate with a formaldehyde source to generate a second material stream containing both methyl methacrylate and methacrolein.

[0007] In order to achieve the above-mentioned object, the present disclosure provides a method for preparing methyl methacrylate and methacrolein from methyl propionate, the method comprising: contacting a first stream containing methyl propionate and a formaldehyde source with a catalyst and performing an aldol condensation reaction to obtain a second stream containing methyl methacrylate and methacrolein; the catalyst comprises a molecular sieve having metal elements, the metal elements comprising a skeleton metal element and a non-skeleton metal element, the molar ratio of the non-skeleton metal element to the skeleton metal element being less than 0.1; wherein the skeleton metal element comprises Sn; based on the total molar number of all metal elements in the molecular sieve, the content of skeleton tin is greater than 90 mol%; the molar ratio of skeleton tin to silicon element in the molecular sieve is (0.001-0.05):1; the skeleton tin is calculated as SnO2, the silicon element is calculated as SiO2, and the metal element is calculated as metal oxide.

[0008] Optionally, the molar ratio of the non-framework metal element to the framework metal element is less than 0.08, preferably less than 0.05; based on the total molar number of all metal elements in the molecular sieve, the content of the framework tin is more than 91 mol%, preferably more than 95 mol%; the molar ratio of the framework tin to the silicon element in the molecular sieve is (0.001-0.02):1; wherein the framework metal element also includes one or more of Zr, Hf, Zn, Mn, Fe, Co, V, Ni and Al, and the non-framework metal element is selected from one or more of Sn, Zr, Hf, Zn, Mn, Fe, Co, V and Al, preferably Sn.

[0009] Optionally, the total acid content of B acid of the catalyst measured by pyridine adsorption infrared method at 50°C is 50 μmol·g -1 Below, preferably 30 μmol·g -1 Below, more preferably 0 μmol·g -1 ; L acid total acid content is 20~800μmol·g -1 , preferably 100 to 600 μmol·g -1 .

[0010] Optionally, the molar ratio of methyl propionate to formaldehyde source in the first material stream is (0.5-10):1, preferably (0.5-8):1, and more preferably (0.5-5):1; based on the total weight of the second material stream, the content of methyl methacrylate in the second material stream is 40-60% by weight, and the content of methacrolein is 40-60% by weight.

[0011] Optionally, the formaldehyde source is selected from one or more of formaldehyde, trioxymethylene and polyoxymethylene; the polyoxymethylene has a structure as shown in the following formula (1): R1-O-(CH2-O) i-R2 formula (1); wherein R1 and R2 are independently selected from one or more of an alkyl group having 1 to 12 carbon atoms, a substituted or unsubstituted aryl group having 6 to 14 carbon atoms, and a substituted or unsubstituted cycloalkyl group having 3 to 12 carbon atoms, and at most one of R1 and R2 is selected from hydrogen; i is selected from any integer from 1 to 100; the alkyl group having 1 to 12 carbon atoms is selected from one or more of methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, sec-pentyl, neopentyl, 1,2-dimethylpropyl, isopentyl, n-hexyl, isohexyl, sec-hexyl, n-heptyl, isoheptyl, n-octyl, n-nonyl, n-decyl and n-dodecyl, preferably methyl; the unsubstituted aryl group is selected from one or more of phenyl, naphthyl, anthracenyl and phenanthrenyl, wherein the substituent on the substituted aryl group is selected from one or more of carbon atoms The alkyl group having 1 to 8 carbon atoms is preferably one or more selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl and tert-butyl; more preferably, the substituted or unsubstituted aryl group having 6 to 14 carbon atoms is selected from one or more selected from phenyl, benzyl, propylphenyl and butylphenyl, and is further preferably phenyl or benzyl; the unsubstituted cycloalkyl group is selected from one or more selected from cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, cyclodecyl, cycloundecyl and cyclododecyl; wherein the substituent on the substituted cycloalkyl group is selected from alkyl groups having 1 to 9 carbon atoms, and is preferably one or more selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl and tert-butyl; more preferably, the substituted or unsubstituted cycloalkyl group having 3 to 12 carbon atoms is selected from one or more selected from cyclopentyl, cyclohexyl and cycloheptyl.

[0012] Optionally, the first material stream also includes a diluent, which is selected from one or more of alcohols, ethers, alkanes and aromatic hydrocarbons, preferably one or more of alcohols with carbon atoms of 1 to 6, ethers with carbon atoms of 1 to 6, alkanes with carbon atoms of 1 to 6 and aromatic hydrocarbons with carbon atoms of 6 to 10, more preferably one or more of methanol, ether, cyclohexane and toluene; the molar ratio of the diluent to the carbonyl compound raw material is (0.5 to 10):1, preferably (0.5 to 5):1, and more preferably (1 to 3):1.

[0013] Optionally, the reaction temperature is 200-500°C, preferably 250-450°C, more preferably 300-400°C; the reaction time is 0.1-24h, preferably 2-12h; and the pressure is 0.01-2.5MPa, preferably 0.5-1.0MPa.

[0014] Optionally, the aldol condensation reaction is carried out in a reactor, the reactor is a fixed bed reactor, and the mass liquid hourly space velocity of the reaction is 0.1 to 5 h-1 , preferably 0.1 to 2 hours -1 , more preferably 0.1 to 1 h -1 ; Alternatively, the reactor is a fluidized bed reactor, and the weight ratio of the mixture of methyl propionate and the formaldehyde source to the catalyst is (1-500):1, preferably (1-200):1; Alternatively, the reactor is a kettle reactor, and the weight ratio of the mixture of methyl propionate and the formaldehyde source to the catalyst is (1-200):1, preferably (1-50):1.

[0015] Optionally, the reaction is carried out in an inert atmosphere or an oxygen-containing compound atmosphere, wherein the inert atmosphere includes one or more of nitrogen, helium and argon, and the oxygen-containing compound atmosphere includes carbon monoxide and / or carbon dioxide.

[0016] Optionally, the molecular sieve is one or more selected from MFI type molecular sieve, MEL type molecular sieve, BEA type molecular sieve, MWW type molecular sieve, FAU type molecular sieve and MOR type molecular sieve, preferably one or more selected from MFI type molecular sieve, MEL type molecular sieve and BEA type molecular sieve.

[0017] Through the above technical scheme, on the one hand, due to the strong electron-withdrawing effect of the framework tin atoms in the molecular sieve, the oxygen-containing functional groups of methyl propionate and formaldehyde source have higher adsorption and activation capabilities, promote the generation of products, and the highly dispersed framework tetracoordinated tin has stronger intrinsic catalytic activity. On the other hand, the tin silicon molecular sieve has abundant L acid sites, which can effectively accelerate the occurrence of the aldol condensation reaction, so that the reaction has a high raw material conversion rate and product selectivity, and can simultaneously prepare two products, methyl methacrylate and methacrolein. Compared with the prior art, the method disclosed in the present invention is simple to operate and has a short reaction process. It can not only prepare two products at the same time, but also has good industrial application prospects. Moreover, the two products prepared are easy to separate, avoiding further reaction of methyl methacrylate and avoiding rapid deactivation of the catalyst.

[0018] Other features and advantages of the present disclosure will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The accompanying drawings are used to provide a further understanding of the present disclosure and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present disclosure but do not constitute a limitation of the present disclosure. In the accompanying drawings:

[0020] Figure 1 is the UV-visible spectrum of the catalyst 1 prepared in Preparation Example 1 of the present disclosure;

[0021] Figure 2 is the pyridine acid infrared spectrum of catalyst 1 prepared in Preparation Example 1 of the present disclosure;

[0022] Figure 3 It is the ultraviolet-visible spectrum of comparative catalyst 5 prepared in comparative example 5 of the present disclosure. DETAILED DESCRIPTION

[0023] The specific implementation of the present disclosure is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described herein is only used to illustrate and explain the present disclosure, and is not used to limit the present disclosure.

[0024] The present disclosure provides a method for preparing methyl methacrylate and methacrolein from methyl propionate, the method comprising: contacting a first stream containing methyl propionate and a formaldehyde source with a catalyst and performing an aldol condensation reaction to obtain a second stream containing methyl methacrylate and methacrolein; the catalyst comprises a molecular sieve having a metal element, the metal element comprises a skeleton metal element and a non-skeleton metal element, the molar ratio of the non-skeleton metal element to the skeleton metal element is less than 0.1; wherein the skeleton metal element comprises Sn; based on the total molar number of all metal elements in the molecular sieve, the content of skeleton tin is greater than 90 mol%; the molar ratio of skeleton tin to silicon element in the molecular sieve is (0.001-0.05):1; the skeleton tin is calculated as SnO2, the silicon element is calculated as SiO2, the metal element is calculated as metal oxide, wherein the silicon element includes all silicon in the molecular sieve.

[0025] The skeleton metal element disclosed herein refers to a metal element located in the molecular sieve lattice framework and replacing a part of the silicon atoms in the molecular sieve lattice framework, and the non-skeleton metal element refers to a metal element located in the molecular sieve pores and existing in the form of an octahedral oxide. The tetracoordinated Si on the molecular sieve framework disclosed herein is replaced by a part of the skeleton metal element, but the molecular sieve still maintains the original topological structure. The content of the metal element in the molecular sieve can be measured by the conventional XRF method in the art, and the state of the metal species in the molecular sieve can be measured by ultraviolet-visible spectroscopy (UV-Vis). For example, when using ultraviolet-visible spectroscopy to analyze the states of different tin species in the molecular sieve, it is generally believed that the absorption peak appearing near a wavelength of 215 ± 5nm is a characteristic peak of a skeleton tetracoordinated tin species; the absorption peak appearing near a wavelength of 283 ± 3nm is a characteristic peak of a non-skeleton hexacoordinated tin species (Journal of Molecular Catalysis A: Chemical, 105 (1996), 149-158).

[0026] The inventors of the present disclosure have found in their research that when a molecular sieve with a skeleton metal element tin is used as a catalyst to catalyze the aldol condensation reaction, the content of the skeleton metal element tin is greater than 90 mol% to improve the efficiency of the aldol condensation reaction. On the one hand, due to the strong electron-withdrawing effect of the skeleton tin atoms in the molecular sieve, it has a higher adsorption and activation ability for the oxygen-containing functional groups of methyl propionate and formaldehyde sources, promoting the generation of products, and the highly dispersed skeleton tetracoordinated tin has a stronger intrinsic catalytic activity. On the other hand, the tin silicon molecular sieve has abundant L acid sites, which can effectively accelerate the occurrence of the aldol condensation reaction, so that the reaction has a higher raw material conversion rate and product selectivity, and can simultaneously prepare two products, methyl methacrylate and methacrolein. Compared with the prior art, the method disclosed in the present disclosure is simple to operate and has a short reaction process. The catalyst can not only inhibit the hydrolysis of methyl propionate and reduce the generation of propionic acid, but also can generate two high value-added products, methyl methacrylate and methacrolein, in situ, and reduce the generation of heavy substances; the two products prepared at the same time are easy to separate, avoiding the further reaction of methyl methacrylate to generate macromolecular substances and avoiding the rapid deactivation of the catalyst. The method disclosed in the present invention has excellent raw material conversion rate and high product selectivity, and has good industrial application prospects.

[0027] In one embodiment of the present disclosure, the molar ratio of the non-framework metal element to the framework metal element is less than 0.08, preferably less than 0.05; based on the total molar number of all metal elements in the molecular sieve, the content of the framework tin is more than 91 mol%, preferably more than 95 mol%; the molar ratio of the framework tin to the silicon element in the molecular sieve is (0.001-0.02): 1; wherein the framework metal element also includes one or more of Zr, Hf, Zn, Mn, Fe, Co, V, Ni and Al, and the non-framework metal element is selected from one or more of Sn, Zr, Hf, Zn, Mn, Fe, Co, V and Al, preferably Sn. In the above embodiment, by selecting the preferred content of the framework metal element and the non-framework metal element, the synergistic effect between the two can be further improved; selecting the preferred content of the framework tin can improve the selectivity of the catalyst.

[0028] In one embodiment of the present disclosure, the total acid content of B acid of the catalyst measured by pyridine adsorption infrared method at 350°C is 50 μmol·g -1 Below, preferably 30 μmol·g -1 Below, more preferably 10 μmol·g -1 Below, more preferably 0 μmol·g -1 ; L acid total acid content is 20~800μmol·g -1 , preferably 100 to 600 μmol·g -1 , more preferably 300 to 600 μmol·g -1, more preferably 450 to 580 μmol·g -1 In the above embodiment, the catalytic activity of the catalyst can be further improved by selecting a preferred acid strength. The pyridine adsorption infrared spectrum is 1540cm -1 The peak at 1450±5cm -1 The peak at reflects the L-acid characteristic of the molecular sieve, and the B-acid characteristic is provided by other impurity metal elements of the molecular sieve, such as metal aluminum; the L-acid characteristic is provided by the framework tin.

[0029] In one embodiment of the present disclosure, the molar ratio of methyl propionate to formaldehyde source in the first stream is (0.5-10):1, preferably (0.5-8):1, and more preferably (0.5-5):1; based on the total weight of the second stream, the content of methyl methacrylate in the second stream is 40-60% by weight, and the content of methacrolein is 40-60% by weight. In the above embodiment, the second stream contains a specific content of methyl methacrylate and methacrolein, which is beneficial to reduce the generation of by-products such as propionic acid and methyl isobutyrate, and avoids further reaction of methyl methacrylate to generate heavy substances (such as polymethyl methacrylate), thereby avoiding deactivation of the catalyst.

[0030] The formaldehyde source that can be used in the present disclosure is in principle any suitable formaldehyde source, including but not limited to one or more selected from formaldehyde, trioxymethylene, polyoxymethylene and a balance component that can provide a formaldehyde source; the polyoxymethylene has a structure as shown in the following formula (1): R1-O-(CH2-O) i -R2 formula (1); wherein R1 and R2 are each independently selected from one or more of an alkyl group having 1 to 12 carbon atoms, a substituted or unsubstituted aryl group having 6 to 14 carbon atoms, and a substituted or unsubstituted cycloalkyl group having 3 to 12 carbon atoms, and at most one of R1 and R2 is selected from hydrogen; i is selected from any integer from 1 to 100, preferably any integer from 1 to 5, and more preferably any integer from 1 to 3; the balance component capable of providing a source of formaldehyde, such as formalin (a mixture comprising formaldehyde, methanol and water) or a mixture comprising formaldehyde, methanol and methyl propionate. Formalin refers to a mixture of formaldehyde:methanol:water in a weight ratio of (25-65):(0.01-25):(25-70), preferably a mixture of formaldehyde:methanol:water in a weight ratio of (30-60):(0.03-20):(35-60), and more preferably a mixture of formaldehyde:methanol:water in a weight ratio of (35-55):(0.05-18):(42-53).

[0031] The alkyl group having 1 to 12 carbon atoms is selected from one or more of methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, sec-pentyl, neopentyl, 1,2-dimethylpropyl, isopentyl, n-hexyl, isohexyl, sec-hexyl, n-heptyl, isoheptyl, n-octyl, n-nonyl, n-decyl and n-dodecyl, and is preferably methyl.

[0032] The unsubstituted aryl group is selected from one or more of phenyl, naphthyl, anthracenyl and phenanthrenyl, wherein the substituent on the substituted aryl group is selected from an alkyl group having 1 to 8 carbon atoms, preferably one or more of methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl and tert-butyl; more preferably, the substituted or unsubstituted aryl group having 6 to 14 carbon atoms is selected from one or more of phenyl, benzyl, propylphenyl and butylphenyl, further preferably phenyl or benzyl.

[0033] The unsubstituted cycloalkyl group is selected from one or more of cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, cyclodecyl, cycloundecyl and cyclododecyl; the substituent on the substituted cycloalkyl group is selected from one or more of alkyl groups having 1 to 9 carbon atoms, preferably one or more of methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl and tert-butyl; more preferably, the substituted or unsubstituted cycloalkyl group having 3 to 12 carbon atoms is selected from one or more of cyclopentyl, cyclohexyl and cycloheptyl.

[0034] In the present disclosure, "substituted or unsubstituted aryl" refers to an aryl with a substituent or an unsubstituted aryl, and a substituted aryl may be one or more hydrogen atoms in the aryl replaced by a substituent; "substituted or unsubstituted cycloalkyl" refers to a cycloalkyl with a substituent or an unsubstituted cycloalkyl, and a substituted cycloalkyl may be one or more hydrogen atoms in the cycloalkyl replaced by a substituent; the number of carbon atoms of a substituted or unsubstituted group refers to the total number of carbon atoms. For example, if the aryl group is selected from a substituted phenyl group having 10 carbon atoms, the total number of carbon atoms of the phenyl group and the substituents thereon is 10.

[0035] In a preferred embodiment, the formaldehyde source is selected from one or more of formaldehyde, trioxymethylene, formaldehyde benzyl alcohol hemiacetal and dimethanol formal, more preferably formaldehyde.

[0036] In the present disclosure, the second material stream also contains other components in addition to methyl methacrylate and methacrolein, for example, the second material stream contains unreacted methyl propionate, a formaldehyde source, and / or contains propionic acid (a decomposition product of methyl propionate), methyl formate and dimethyl ether (a decomposition product of the formaldehyde source); based on the total weight of the second material stream, the content of the other components is 1 to 3 weight %.

[0037] In one embodiment of the present disclosure, the first material stream also includes a diluent, and the diluent is selected from one or more of alcohols, ethers, alkanes and aromatic hydrocarbons, preferably one or more of alcohols with carbon atoms of 1 to 6, ethers with carbon atoms of 1 to 6, alkanes with carbon atoms of 1 to 6 and aromatic hydrocarbons with carbon atoms of 6 to 10, and more preferably one or more of methanol, diethyl ether, cyclohexane and toluene; the molar ratio of the diluent to the carbonyl compound raw material is (0.5-10):1, preferably (0.5-5):1, and more preferably (1-3):1.

[0038] In one embodiment of the present disclosure, the reaction temperature is 200-500°C, preferably 250-450°C, more preferably 300-400°C; the reaction time is 0.1-24h, preferably 2-12h; the pressure is 0.01-2.5MPa, preferably 0.5-1.0MPa. The method of the present disclosure does not limit the heat source, and in principle any heat source can be used.

[0039] The reaction of the present disclosure is carried out in a conventional reactor, and the present disclosure does not impose any special restrictions. In one embodiment of the present disclosure, the reactor is a fixed bed reactor, and the mass liquid hourly space velocity of the reaction is 0.1 to 5 h based on the total volume of the first stream. -1 , preferably 0.1 to 2 hours -1 , more preferably 0.1 to 1 h -1 ; Alternatively, the reactor is a fluidized bed reactor, and the weight ratio of the mixture of methyl propionate and formaldehyde source to the catalyst is (1-500):1, preferably (1-200):1; Alternatively, the reactor is a kettle reactor, and the weight ratio of the mixture of methyl propionate and formaldehyde source to the catalyst is (1-200):1, preferably (1-50:1); wherein the mass liquid hourly space velocity refers to the mass of the first stream passing through a unit mass of the catalyst per unit time.

[0040] It will be appreciated by those skilled in the art that, depending on the different reactors used, the catalyst disclosed herein may be a molecular sieve raw powder or a molded catalyst after the molecular sieve is mixed and molded with a carrier. The separation of the product and the catalyst may be achieved in a variety of ways. For example, when the original powdered skeleton contains a tetravalent metal element molecular sieve as a catalyst, the separation of the product and the recycling of the catalyst may be achieved by sedimentation, filtration, centrifugation, evaporation, membrane separation, etc. Alternatively, the catalyst may be molded and loaded into a fixed bed reactor, and the catalyst may be recovered after the reaction is completed. The separation and recovery methods of various catalysts are widely involved in existing literature and will not be described here. The specific operation of the reactor is well known to those skilled in the art.

[0041] In one embodiment of the present disclosure, the reaction is carried out in an inert atmosphere or an oxygen-containing compound atmosphere, wherein the inert atmosphere includes one or more of nitrogen, helium and argon, and the oxygen-containing compound atmosphere includes carbon monoxide and / or carbon dioxide. The atmosphere can be supplied to the reaction process of the present disclosure from the outside, or the gas can be circulated in the reaction process by means of one or more circulation steps.

[0042] In one embodiment of the present disclosure, the molecular sieve is selected from one or more of MFI type molecular sieve, MEL type molecular sieve, BEA type molecular sieve, MWW type molecular sieve, FAU type molecular sieve and MOR type molecular sieve, preferably one or more of MFI type molecular sieve, MEL type molecular sieve and BEA type molecular sieve.

[0043] In one embodiment of the present disclosure, the molecular sieve is a product of metal elements replacing part of the framework silicon of molecular sieves of various topological structures. The topological structure of the molecular sieve can be referenced from the website of the International Zeolite Association. For example, the molecular sieve can be selected from one or more of MFI type molecular sieves, MEL type molecular sieves, BEA type molecular sieves, MWW type molecular sieves, FAU type molecular sieves and MOR type molecular sieves, preferably one or more of MFI type molecular sieves, MEL type molecular sieves and BEA type molecular sieves. In one embodiment, when the skeleton metal element and the non-skeleton metal element are both Sn, the molecular sieve is a tin silicon molecular sieve, and the tin silicon molecular sieve is selected from one or more of MFI type tin silicon molecular sieve, MEL type tin silicon molecular sieve, BEA type tin silicon molecular sieve, MWW type tin silicon molecular sieve, FAU type tin silicon molecular sieve and MOR type tin silicon molecular sieve, MFI type tin silicon molecular sieve is, for example, Sn-MFI molecular sieve, MEL type tin silicon molecular sieve is, for example, Sn-MEL molecular sieve, BEA type tin silicon molecular sieve is, for example, Sn-Beta molecular sieve, MWW type tin silicon molecular sieve is, for example, Sn-MCM-22 molecular sieve, FAU type tin silicon molecular sieve is, for example, Sn-FAU molecular sieve, MOR type tin silicon molecular sieve is, for example, Sn-MOR molecular sieve. Further preferably, the tin silicon molecular sieve is an MFI type tin silicon molecular sieve. The source of the molecular sieve is not limited, and it can be obtained by commercial purchase, or it can be prepared by conventional technical methods in the art.

[0044] The present disclosure is further illustrated by the following examples, but the present disclosure is not limited thereto. Unless otherwise specified, the raw materials used in the examples and comparative examples of the present disclosure are purchased through commercial channels and are pure reagents.

[0045] The embodiments and comparative examples of the present disclosure adopt ultraviolet-visible spectroscopy to analyze framework metal elements and non-framework metal elements. The instrument model is Cary300 ultraviolet spectrophotometer, the manufacturer is Agilent, and the test conditions are: room temperature, normal pressure, the sample is tested after tabletting, and the scanning range is 190-800nm.

[0046] The types and contents of all metal elements and the content of silicon were determined using a ZSX100E X-ray fluorescence spectrometer produced by Rigaku Corporation of Japan. Test conditions: The samples were pressed into tablets and tested using tungsten palladium, an excitation voltage of 40 kV, and an excitation current of 250 mA. The B acid and L acid contents were measured using the 2,6-di-tert-butylpyridine adsorption infrared acid method and the Vertex 70 instrument produced by Bruker Instruments was used for the determination. The specific method was as follows: the catalyst was pressed into a 10 mg / cm 2 The thin slice was placed in an infrared cell with a CaF2 window, first evacuated at 400°C, then lowered to 150°C to adsorb 2,6-di-tert-butylpyridine for 15 minutes, then evacuated for 1 hour, lowered to room temperature to collect spectra, and calculated the acid amounts of B acid and L acid. See Applied Catalysis A: General, 294, 2005: 92.

[0047] The composition of the reaction product was analyzed by gas chromatography, and the analysis results were quantified by external standard method. The chromatographic analysis conditions were: Agilent-6890 chromatograph, HP-5 capillary column, injection volume 0.5 μL, injection port temperature 280°C; column temperature was maintained at 100°C for 2 min, then increased to 200°C at a rate of 15°C / min and maintained for 3 min. FID detector, detector temperature 300°C.

[0048] The particle size unit "mesh" in the present disclosure refers to the number of holes per inch on the screen used to screen different particle sizes. For example, 20 mesh means that there are 20 holes per inch on the screen, and 20-40 mesh refers to the particle size that can pass through the 20 mesh screen and be retained by the 40 mesh screen.

[0049] The preparation examples and the preparation comparative examples are used to provide catalysts used in the examples and comparative examples.

[0050] Preparation Example 1

[0051] Tetraethyl orthosilicate (TEOS), tin tetrachloride (SnCl4·5H2O) and tetrapropylammonium hydroxide (TPAOH, 26.5wt%) solutions were mixed in a molar ratio of SiO2: 0.015SnO2: 0.36TPAOH: 35H2O, and then stirred for 15 minutes to obtain a clear liquid. Finally, water was added to the clear liquid, and stirred at 348-353K for about 3 hours to obtain a clear sol, which was then crystallized at 443K for 3 days. The obtained solid was then filtered, washed with distilled water, dried at 373K for 5 hours, and then calcined at 823K for 10 hours to obtain Sn-MFI molecular sieve raw powder. The molecular sieve raw powder was pressed into sheets at a pressure of 20MPa, and particles of 20-40 mesh (i.e., an average particle size of 0.63-0.85mm) were screened as catalyst 1, denoted as C1, and its composition is shown in Table 1. The amount of TEOS used is 208.3 g, the amount of SnCl4·5H2O used is 5.25 g, the amount of TPAOH used is 286 g, and the amount of water used is 417.5 g.

[0052] The UV-visible spectrum of the prepared catalyst C1 is shown in Figure 1 As shown, from Figure 1 It can be seen that C1 has framework tin, which shows a characteristic peak of framework tetracoordinated tin species at around 215 nm.

[0053] The pyridine acid infrared spectrum of catalyst C1 is as follows Figure 2 As shown, from Figure 2 It can be seen that C1 is at 1540cm -1 There is no peak at the position of C1, indicating that C1 has no B acid site and its B acid content is 0 μmol·g -1 ; at 1446cm -1 The peak at 147.3° indicates that C1 has an L-acid site, and its L-acid content is 485.6 μmol·g -1 The L acid site is beneficial to promote the aldol condensation reaction and improve the raw material conversion rate and product selectivity.

[0054] Preparation Example 2

[0055] The same as Preparation Example 1, the only difference is: tetrapropylammonium hydroxide solution (TPAOH, 26.5wt%) is replaced by tetrabutylammonium hydroxide solution (TBAOH, 20wt%), the amount of TBAOH is 259.5g, so that the materials are mixed according to the molar ratio of SiO2: 0.015SnO2: 0.20TBAOH: 35H2O to obtain Sn-MEL molecular sieve raw powder, the molecular sieve raw powder is pressed into tablets at a pressure of 20MPa, and particles of 20-40 mesh (i.e., the average particle size is 0.63-0.85mm) are screened as catalyst 2, denoted as C2, and its composition is shown in Table 1.

[0056] Preparation Example 3

[0057] 60 g of BEA molecular sieve with a silicon-aluminum ratio of 11 after calcination was mixed with a 13 mol / L nitric acid aqueous solution, and the mixed solution was stirred at 90°C for 24 h, washed with deionized water, dried and calcined to obtain a dealuminated molecular sieve; the dealuminated molecular sieve was mixed with 5.25 g of SnCl4·5H2O and stirred, filtered and dried, and calcined at 550°C for 3 h to obtain Sn-BEA molecular sieve raw powder, which was pressed into tablets under a pressure of 20 MPa, and particles of 20 to 40 mesh (i.e., an average particle size of 0.63 to 0.85 mm) were screened as catalyst 3, denoted as C3, and its composition is shown in Table 1.

[0058] Preparation Example 4

[0059] The same as Preparation Example 1, the only difference is that the amount of SnCl4·5H2O added is 7.0 g, so that the materials are mixed according to the molar ratio of SiO2: 0.020SnO2: 0.36TPAOH: 35H2O to obtain Sn-MFI molecular sieve raw powder, which is pressed into tablets at a pressure of 20 MPa, and particles of 20 to 40 mesh (i.e., an average particle size of 0.63 to 0.85 mm) are screened as catalyst 4, denoted as C4, and its composition is shown in Table 1.

[0060] Preparation Comparative Example 1

[0061] This comparative preparation example is prepared according to the method of the literature M.Ai.Applied Catalysis A: General 288 (2005) 211-215 to prepare Cs-loaded amorphous silica molecular sieve. The specific preparation method is as follows:

[0062] The excess water in the aqueous SiO2 colloid (20%) is evaporated to obtain a silica dry gel; the dry gel is ground and sieved to obtain a solid with a size of 20 to 40 mesh. The obtained solid is calcined at 400°C for 4 hours, and then impregnated with an aqueous solution (2 mol / L) containing the required amount of cesium hydroxide. The wet gel is dried in an oven and calcined again at 400°C in an air flow for 6 hours to obtain Cs / SiO2 molecular sieve raw powder, which is pressed into tablets at a pressure of 20 MPa, and particles of 20 to 40 mesh (i.e., an average particle size of 0.63 to 0.85 mm) are screened as comparative catalyst 1, denoted as D1, and its composition is shown in Table 1.

[0063] Preparation Comparative Example 2

[0064] The same as the preparation of comparative example 1, the only difference is that the cesium hydroxide aqueous solution is replaced by the same amount of SnCl4·5H2O to obtain Sn / SiO2 molecular sieve raw powder, the molecular sieve raw powder is pressed into tablets under a pressure of 20 MPa, and particles of 20 to 40 mesh (i.e., an average particle size of 0.63 to 0.85 mm) are screened as comparative catalyst 2, denoted as D2, and its composition is shown in Table 1.

[0065] Preparation Comparative Example 3

[0066] A measured solution of tetrapropylammonium hydroxide (TPAOH, 26.5wt%) was added to a solution of tetraethyl orthosilicate (TEOS) to obtain a liquid mixture with a pH of about 13, and then stirred for 3 hours under vigorous stirring to obtain a clear liquid, and then stirred for about 3 hours at 348-353K to obtain a sol with a chemical composition of SiO2: 0.36TPAOH: 35H2O, and then crystallized at 443K for 3 days, after which the obtained solid was filtered, washed with distilled water, dried at 373K for 5 hours, and then calcined at 823K for 10 hours to obtain a full-silicon S-MFI molecular sieve. Among them, the amount of TEOS used is 208.3g, the amount of TPAOH used is 286g, and the amount of water used is 417.5g;

[0067] 7.0 g SnCl4·5H2O was dissolved in ethanol, then impregnated with an equal volume of S-MFI molecular sieve and dried at 110°C for 2 h. After the mixture was dried, it was placed in a muffle furnace and calcined at 400°C for 4 h to obtain an impregnated supported D-Sn-MFI molecular sieve raw powder. The molecular sieve raw powder was pressed into sheets at a pressure of 20 MPa, and particles of 20 to 40 mesh (i.e., an average particle size of 0.63 to 0.85 mm) were screened as comparative catalyst 3, denoted as D3, and its composition is shown in Table 1.

[0068] Preparation Comparative Example 4

[0069] The same as Preparation Example 1, the only difference is that the amount of SnCl4·5H2O used is 10.5g, so that the materials are mixed in a molar ratio of SiO2: 0.03SnO2: 0.36TPAOH: 35H2O to obtain D-Sn-MFI molecular sieve raw powder, the molecular sieve raw powder is pressed into tablets at a pressure of 20MPa, and particles of 20 to 40 mesh (i.e., an average particle size of 0.63 to 0.85mm) are screened as comparative catalyst 4, denoted as D4, and its composition is shown in Table 1.

[0070] Preparation Comparative Example 5

[0071] The same as Preparation Example 1, the only difference is that the amount of SnCl4·5H2O used is 35.0 g, so that the materials are mixed in a molar ratio of SiO2:0.1SnO2:0.36TPAOH:35H2O to obtain D-Sn-MFI molecular sieve raw powder, which is pressed into tablets at a pressure of 20 MPa, and particles of 20 to 40 mesh (i.e., an average particle size of 0.63 to 0.85 mm) are screened as comparative catalyst 5, denoted as D5, and its composition is shown in Table 1.

[0072] The UV-visible spectrum of the prepared catalyst D5 is shown in Figure 3 As shown, from Figure 3 It can be seen that D5 has framework metallic tin and non-framework metallic tin, wherein a characteristic peak of a framework tetracoordinated tin species appears near a wavelength of 215 nm, and a characteristic peak of a non-framework hexacoordinated tin species appears near a wavelength of 280 nm.

[0073] Table 1

[0074]

[0075]

[0076] “-” means that the species is not contained or the content of the species is 0.

[0077] The examples and comparative examples are used to illustrate the method of preparing methyl methacrylate and methacrolein by catalyzing carbonyl compound raw materials with different catalysts.

[0078] Example 1

[0079] The catalyst 1 prepared in Preparation Example 1 was loaded into a fixed bed reactor and preactivated. The preactivation conditions were as follows: the N2 flow rate was 30 mL / min, the temperature was raised to 400°C at a rate of 2°C / min, and the temperature was kept constant at 400°C for 5 hours, and then the temperature was lowered to the desired reaction temperature of 360°C in a nitrogen atmosphere. Formaldehyde, methyl propionate and methanol were fed into the bed of the reaction section through N2, wherein the reaction temperature was 360°C, the reaction time was 1 hour, the reaction pressure was 0.5 MPa, the molar ratio of formaldehyde to methyl propionate was 1:1, the molar ratio of methanol to methyl propionate was 1.5:1, and the mass liquid hourly space velocity was 0.5 h based on the total volume of formaldehyde, methyl propionate and methanol. -1 The results of the aldol condensation reaction are shown in Table 2. The conversion rate of methyl propionate, the selectivity of methyl methacrylate and the selectivity of methacrolein were calculated according to the following formulas (1) to (3):

[0080]

[0081]

[0082]

[0083] Embodiments 2 to 4

[0084] The aldol condensation reaction was carried out according to the method and reaction conditions of Example 1, and the catalysts prepared in Preparation Examples 2 to 4 were used to catalyze the aldol condensation reaction. The reaction results are shown in Table 2.

[0085] Embodiments 5 to 7

[0086] The aldol condensation reaction was carried out according to the method of Example 1. The catalyst and reaction conditions used are shown in Table 3.

[0087] Comparative Examples 1 to 5

[0088] The aldol condensation reaction was carried out according to the method and reaction conditions of Example 1, and the aldol condensation reaction was catalyzed by the comparative catalysts prepared in Comparative Preparation Examples 1 to 5. The reaction results are shown in Table 2.

[0089] Table 2

[0090]

[0091] Table 3

[0092]

[0093] It can be seen from the results of the above embodiments and comparative examples that when methyl methacrylate and methacrolein are prepared by the method of the present invention, and the molar ratio of non-framework metal elements to framework metal elements in the molecular sieve is limited to less than 0.1, and the total molar number of all metal elements in the molecular sieve is used as a benchmark, when the content of framework tin is greater than 90 mol%, the conversion rate of methyl propionate can be effectively improved, and the selectivity of methyl methacrylate and methacrolein can be improved, while the decomposition of methyl propionate can be avoided, the selectivity of propionic acid can be reduced, and the occurrence of side reactions can be reduced.

[0094] The preferred embodiments of the present disclosure are described in detail above in conjunction with the accompanying drawings; however, the present disclosure is not limited to the specific details in the above embodiments. Within the technical concept of the present disclosure, a variety of simple modifications can be made to the technical solution of the present disclosure, and these simple modifications all fall within the protection scope of the present disclosure.

[0095] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present disclosure will not further describe various possible combinations.

[0096] In addition, various embodiments of the present disclosure may be arbitrarily combined, and as long as they do not violate the concept of the present disclosure, they should also be regarded as the contents disclosed by the present disclosure.

Claims

1. A method for preparing methyl methacrylate and methacrolein from methyl propionate, characterized in that: The method comprises: contacting a first stream comprising methyl propionate and a formaldehyde source with a catalyst and performing an aldol condensation reaction to obtain a second stream comprising methyl methacrylate and methacrolein; The catalyst comprises a molecular sieve having a metal element, wherein the metal element comprises a skeleton metal element and a non-skeleton metal element, and a molar ratio of the non-skeleton metal element to the skeleton metal element is less than 0.1; Among them, the skeleton metal elements include Sn; based on the total molar number of all metal elements in the molecular sieve, the content of skeleton tin is greater than 90 mol%; the molar ratio of skeleton tin to silicon element in the molecular sieve is (0.001~0.05):1; the skeleton tin is calculated as SnO2, the silicon element is calculated as SiO2, and the metal elements are calculated as metal oxides.

2. The method according to claim 1, characterized in that: The molar ratio of the non-framework metal element to the framework metal element is less than 0.08, preferably less than 0.05; Based on the total molar number of all metal elements in the molecular sieve, the content of the framework tin is 91 mol% or more, preferably 95 mol% or more; The molar ratio of framework tin to silicon in the molecular sieve is (0.001-0.02):1; Among them, the skeleton metal elements also include one or more of Zr, Hf, Zn, Mn, Fe, Co, V, Ni and Al, and the non-skeleton metal elements are selected from one or more of Sn, Zr, Hf, Zn, Mn, Fe, Co, V and Al, preferably Sn.

3. The method according to claim 1, characterized in that The total acid content of B acid of the catalyst measured by pyridine adsorption infrared method at 50°C is 50 μmol·g -1 Below, preferably 30 μmol·g -1 Below, more preferably 0 μmol·g -1 ; L acid total acid content is 20~800μmol·g -1 , preferably 100 to 600 μmol·g -1 .

4. The method according to claim 1, characterized in that The molar ratio of methyl propionate to formaldehyde source in the first stream is (0.5-10):1, preferably (0.5-8):1, and more preferably (0.5-5):1; Based on the total weight of the second material stream, the content of methyl methacrylate in the second material stream is 40 to 60% by weight, and the content of methacrolein is 40 to 60% by weight.

5. The method according to claim 1, characterized in that: The formaldehyde source is selected from one or more of formaldehyde, trioxymethylene and polyoxymethylene; the polyoxymethylene has a structure as shown in the following formula (1): R1-O-(CH2-O) i -R2 formula (1); wherein R1 and R2 are independently selected from one or more of an alkyl group having 1 to 12 carbon atoms, a substituted or unsubstituted aryl group having 6 to 14 carbon atoms, and a substituted or unsubstituted cycloalkyl group having 3 to 12 carbon atoms, and at most one of R1 and R2 is selected from hydrogen; i is selected from any integer from 1 to 100; The alkyl group having 1 to 12 carbon atoms is one or more selected from the group consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, sec-pentyl, neopentyl, 1,2-dimethylpropyl, isopentyl, n-hexyl, isohexyl, sec-hexyl, n-heptyl, isoheptyl, n-octyl, n-nonyl, n-decyl and n-dodecyl, and is preferably methyl; The unsubstituted aryl group is selected from one or more of phenyl, naphthyl, anthracenyl and phenanthrenyl, wherein the substituent on the substituted aryl group is selected from an alkyl group having 1 to 8 carbon atoms, preferably one or more of methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl and tert-butyl; more preferably, the substituted or unsubstituted aryl group having 6 to 14 carbon atoms is selected from one or more of phenyl, benzyl, propylphenyl and butylphenyl, further preferably phenyl or benzyl; The unsubstituted cycloalkyl group is selected from one or more of cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, cyclodecyl, cycloundecyl and cyclododecyl; the substituent on the substituted cycloalkyl group is selected from one or more of alkyl groups having 1 to 9 carbon atoms, preferably one or more of methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl and tert-butyl; more preferably, the substituted or unsubstituted cycloalkyl group having 3 to 12 carbon atoms is selected from one or more of cyclopentyl, cyclohexyl and cycloheptyl.

6. The method according to claim 1, characterized in that The first stream also includes a diluent, which is selected from one or more of alcohols, ethers, alkanes and aromatic hydrocarbons, preferably one or more of alcohols with 1 to 6 carbon atoms, ethers with 1 to 6 carbon atoms, alkanes with 1 to 6 carbon atoms and aromatic hydrocarbons with 6 to 10 carbon atoms, more preferably one or more of methanol, ether, cyclohexane and toluene; The molar ratio of the diluent to the carbonyl compound raw material is (0.5-10):1, preferably (0.5-5):1, and more preferably (1-3):

1.

7. The method according to claim 1, characterized in that The reaction temperature is 200-500° C., preferably 250-450° C., more preferably 300-400° C.; the reaction time is 0.1-24 h, preferably 2-12 h; and the pressure is 0.01-2.5 MPa, preferably 0.5-1.0 MPa.

8. The method according to claim 1, characterized in that: The aldol condensation reaction is carried out in a reactor, which is a fixed bed reactor. The mass liquid hourly space velocity of the reaction is 0.1 to 5 h based on the total volume of the first stream. -1 , preferably 0.1 to 2 hours -1 , more preferably 0.1 to 1 h -1 ; or, The reactor is a fluidized bed reactor, and the weight ratio of the mixture of methyl propionate and formaldehyde source to the catalyst is (1-500):1, preferably (1-200):1; or, The reactor is a kettle reactor, and the weight ratio of the mixture of methyl propionate and formaldehyde source to the catalyst is (1-200):1, preferably (1-50):

1.

9. The method according to claim 1, characterized in that: The reaction is carried out in an inert atmosphere or an oxygen-containing compound atmosphere, wherein the inert atmosphere includes one or more of nitrogen, helium and argon, and the oxygen-containing compound atmosphere includes carbon monoxide and / or carbon dioxide.

10. The method according to claim 1, characterized in that The molecular sieve is one or more selected from MFI type molecular sieve, MEL type molecular sieve, BEA type molecular sieve, MWW type molecular sieve, FAU type molecular sieve and MOR type molecular sieve, preferably one or more selected from MFI type molecular sieve, MEL type molecular sieve and BEA type molecular sieve.

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