Anhydrous formaldehyde generation method and preparation method of unsaturated olefine acid ester

Abstract

The invention relates to an anhydrous formaldehyde generation method and an unsaturated olefine acid ester preparation method. The anhydrous formaldehyde generation method comprises the following steps: under a continuous reaction condition, a raw material containing a polyformaldehyde alcohol solution enables polyformaldehyde to be depolymerized into anhydrous formaldehyde under a depolymerization condition, and the anhydrous formaldehyde alcohol solution is discharged in real time. According to the anhydrous formaldehyde generation method, the problem of in-situ generation of monomer anhydrous formaldehyde is solved, the problem of coking and carbon deposition of formaldehyde in a high-temperature non-catalytic area is solved, and the formaldehyde utilization rate is greatly increased. The anhydrous formaldehyde prepared by the method is used for preparing unsaturated olefine acid ester, and has the advantages of high formaldehyde utilization rate, high reaction selectivity, long catalyst life and the like.

Description

Technical Field

[0001] The invention relates to a method for generating anhydrous formaldehyde and a method for preparing unsaturated olefin ester. Background Art

[0002] Formaldehyde is an important chemical raw material. With formaldehyde as a raw material, it can be used for addition, condensation, polymerization, carbonylation, decomposition, oxidation-reduction and other reactions to synthesize a variety of products. Among them, anhydrous formaldehyde is widely used in the synthesis of polymer materials, new drug intermediates, advanced spices, dyes, etc., such as methyl methacrylate (MMA), urea-formaldehyde resin, melamine formaldehyde resin, phenolic resin, urotropine, neopentyl glycol, trimethylolpropane, polyoxymethylene resin (POM), pyridine, etc. Anhydrous formaldehyde cannot exist stably at room temperature and pressure, and will slowly polymerize into polyformaldehyde at temperatures below 100°C. Therefore, formaldehyde usually exists in the form of aqueous solution or polyformaldehyde. At present, the industrial preparation of anhydrous formaldehyde is obtained by separating and purifying the formaldehyde aqueous solution. This process is difficult to operate and expensive. Summary of the invention

[0003] Since anhydrous formaldehyde cannot exist stably at room temperature and pressure, in the prior art, the mainstream practice of fixed bed reaction is to use formaldehyde aqueous solution or trioxymethylene solution for feeding reaction. The catalysts used in most reactions cannot work for a long time in a high-temperature hydrothermal environment, and water will cause a large amount of by-products to be generated. Therefore, it is not suitable to use formaldehyde aqueous solution as raw material. Trioxymethylene has the disadvantages of difficult depolymerization, low selectivity of depolymerization reaction (by-product CO2, etc.), and high price.

[0004] The purpose of the present invention is to overcome the technical problems of complicated operation and high cost of the anhydrous formaldehyde preparation technology in the prior art, and to provide an anhydrous formaldehyde generation method and a method for preparing unsaturated olefin esters, which solve the problem of in-situ generation of monomeric formaldehyde and the problem of coking and carbon deposition of formaldehyde in a high-temperature non-catalytic zone, thereby improving the utilization rate of formaldehyde.

[0005] In order to achieve the above object, the first aspect of the present invention provides a method for generating anhydrous formaldehyde, the method comprising:

[0006] Under continuous reaction conditions, the raw material containing the alcohol solution of polyoxymethylene is depolymerized into anhydrous formaldehyde under depolymerization conditions and the alcohol solution of anhydrous formaldehyde is discharged in real time.

[0007] A second aspect of the present invention provides a method for preparing an unsaturated olefinic acid ester, the method comprising:

[0008] According to the anhydrous formaldehyde generation method of the present invention, depolymerization is carried out; in the presence of a catalyst, the anhydrous formaldehyde alcohol solution discharged in real time is contacted with a saturated ester substance for reaction.

[0009] Through the above technical scheme, the anhydrous formaldehyde generation method of the present invention can achieve continuous and stable generation of formaldehyde under relatively mild conditions without using any catalyst to assist the depolymerization of polyoxymethylene.

[0010] The anhydrous formaldehyde generation method of the present invention solves the problem of in-situ generation of monomeric anhydrous formaldehyde and the problem of coking and carbon deposition of formaldehyde in high-temperature non-catalytic zones, thereby greatly improving the utilization rate of formaldehyde.

[0011] The method for preparing unsaturated olefin esters of the present invention has the advantages of high formaldehyde utilization rate, high reaction selectivity, long catalyst life and the like (when the amount of formaldehyde generated is controllable, the catalyst charring regeneration cycle can be extended). BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a schematic diagram of an anhydrous formaldehyde in-situ generation system provided by a preferred embodiment of the present invention.

[0013] Description of Reference Numerals

[0014] 1—Reaction tower 2—Reaction tube

[0015] 3—Jacket 4—Temperature measuring device

[0016] 5—first feed pipe 6—first discharge pipe

[0017] 7—Second feeding pipe 8—Second discharging pipe

[0018] 9—Reaction Bed DETAILED DESCRIPTION

[0019] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0020] In the present invention, unless otherwise specified, directional words such as "up, down, left, right" generally refer to up, down, left, right as shown in the reference drawings; "inside, outside" refer to inside and outside relative to the outline of each component itself.

[0021] The first aspect of the present invention provides a method for generating anhydrous formaldehyde, the method comprising:

[0022] Under continuous reaction conditions, the raw material containing the alcohol solution of polyoxymethylene is depolymerized into anhydrous formaldehyde under depolymerization conditions and the alcohol solution of anhydrous formaldehyde is discharged in real time.

[0023] According to a preferred embodiment of the present invention, the depolymerization conditions include: temperature of 50-300°C; pressure of 0-10MPa; depolymerization time of 0.1-10s; in the alcohol solution of polyformaldehyde, the mass concentration of polyformaldehyde is 0.1%-50%; by adopting the anhydrous formaldehyde generation method of the present invention, continuous and stable generation of formaldehyde can be achieved under relatively mild conditions, without the need to use any catalyst to assist the depolymerization of polyformaldehyde.

[0024] According to a preferred embodiment of the present invention, the depolymerization conditions include: a temperature of 100-200°C.

[0025] According to a preferred embodiment of the present invention, the depolymerization conditions include: a pressure of 0-2 MPa.

[0026] According to a preferred embodiment of the present invention, the depolymerization conditions include: the depolymerization time is 1-5s.

[0027] In the present invention, the depolymerization time can be controlled by adjusting the flow rate of the carrier gas, thereby controlling the residence time of the solution in the depolymerization process.

[0028] In the present invention, there is no particular requirement for the type of the carrier gas, as long as it does not react with the raw materials or does not dissolve with each other, etc. For example, it can be an inert gas, preferably nitrogen.

[0029] According to a preferred embodiment of the present invention, the depolymerization conditions include: in the alcohol solution of polyoxymethylene, the mass concentration of polyoxymethylene is 5%-30%.

[0030] In the present invention, there is no special requirement for the alcohol in the alcohol solution of polyoxymethylene. The following is an exemplary description of the embodiments of the present invention, but the present invention is not limited to this scope.

[0031] According to one embodiment of the present invention, in the alcohol solution of polyoxymethylene, the alcohol is selected from C1-C4 alcohols, preferably at least one of methanol, ethanol, n-propanol, isopropanol, n-butanol and isobutanol.

[0032] A second aspect of the present invention provides a method for preparing an unsaturated olefinic acid ester, the method comprising:

[0033] According to the method of the present invention, the depolymerization is prepared; in the presence of a catalyst, the alcohol solution of anhydrous formaldehyde discharged in real time is contacted with a saturated ester substance for reaction.

[0034] In the present invention, there is no special requirement for the concentration of the anhydrous formaldehyde alcohol solution. The following is an exemplary description of the implementation of the present invention, but the present invention is not limited to this scope.

[0035] According to one embodiment of the present invention, in the anhydrous formaldehyde-alcohol solution, the mass fraction of alcohol is 0.1-80 wt %, preferably 5-60 wt %.

[0036] In the present invention, the choice of alcohol in the anhydrous formaldehyde alcohol solution depends on the product. If the product is a methyl ester, methanol is selected as the alcohol; if other alcohols are used, ester exchange will occur, and the choice of alcohol needs to be combined with the product.

[0037] In the present invention, there is no special requirement for the type of saturated ester substances. The following is an exemplary description of the implementation of the present invention, but the present invention is not limited to this scope.

[0038] According to a preferred embodiment of the present invention, the saturated ester substance is selected from at least one of the substances represented by formula (I);

[0039]

[0040] Wherein, R1 is selected from C1-C4 alkyl group; R2 is selected from C1-C3 alkyl group.

[0041] According to a preferred embodiment of the present invention, the saturated ester substance is selected from at least one of methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate and ethyl butyrate.

[0042] In the present invention, any catalyst used in the art for preparing unsaturated olefinic acid esters from formaldehyde and saturated esters can be used in the present invention. There is no special requirement for the type of catalyst. The following is an exemplary description of the implementation of the present invention, but the present invention is not limited to this scope.

[0043] According to a preferred embodiment of the present invention, the catalyst comprises: a carrier and an alkali metal oxide and / or an alkaline earth metal oxide supported on the carrier.

[0044] In the present invention, there is no special requirement for the type of the carrier. The following is an exemplary description of the implementation mode of the present invention, but the present invention is not limited to this scope.

[0045] According to a preferred embodiment of the present invention, the carrier is selected from at least one of alumina, silica, molecular sieve and activated carbon.

[0046] According to a preferred embodiment of the present invention, the alkali metal is selected from at least one of K, Ru and Cs.

[0047] According to a preferred embodiment of the present invention, the alkaline earth metal is selected from at least one of Mg, Ca, Ba and Sr.

[0048] According to a preferred embodiment of the present invention, in the catalyst, the mass fraction of the alkali metal oxide and / or alkaline earth metal oxide is 0.1-60wt%, preferably 2-10wt%.

[0049] In the present invention, the optional range of the usage ratio of the saturated ester substance to the anhydrous formaldehyde is relatively wide. According to a preferred embodiment of the present invention, the molar ratio of the saturated ester substance to the anhydrous formaldehyde is 0.05-50, preferably 0.5-20.

[0050] In the present invention, the conditions for the contact reaction of the anhydrous formaldehyde alcohol solution with the saturated ester substance can be selected in a wide range. According to a preferred embodiment of the present invention, the contact conditions include: reaction temperature: 200-500°C, preferably 250-400°C; pressure: 0-5MPa, preferably 0.05-1MPa; feed space velocity: 0.01-2h -1 , preferably 0.05-1h -1 .

[0051] According to a preferred embodiment of the present invention, the method for preparing the unsaturated olefinic acid ester is carried out in an unsaturated olefinic acid ester preparation system, and the unsaturated olefinic acid ester preparation system comprises:

[0052] The reaction tower includes a low-temperature reaction zone and a high-temperature reaction zone along the material flow direction;

[0053] The anhydrous formaldehyde generating unit is arranged in the low temperature reaction zone, and is used for depolymerizing the raw materials containing the formaldehyde source to generate anhydrous formaldehyde;

[0054] The high temperature reaction zone is used for continuously feeding the anhydrous formaldehyde output from the anhydrous formaldehyde generating unit to contact and react with the saturated ester compound; the preparation method of the unsaturated olefinic acid ester comprises:

[0055] (1) In an anhydrous formaldehyde generating unit, under continuous reaction conditions, a raw material containing a polyoxymethylene alcohol solution depolymerizes the polyoxymethylene into anhydrous formaldehyde under depolymerization conditions and discharges the anhydrous formaldehyde alcohol solution in real time;

[0056] (2) In the presence of a catalyst, the anhydrous formaldehyde alcohol solution discharged in real time is contacted with a saturated ester substance for reaction.

[0057] According to a preferred embodiment of the present invention, the time for anhydrous formaldehyde to be transported from the anhydrous formaldehyde generating unit to the high-temperature reaction zone is 0.1-1 s, preferably 0.2-0.5 s.

[0058] According to a preferred embodiment of the present invention, the anhydrous formaldehyde generating unit comprises an anhydrous formaldehyde generating device and a temperature control device;

[0059] The anhydrous formaldehyde generating device is used to depolymerize raw materials containing a formaldehyde source to generate an anhydrous formaldehyde alcohol solution;

[0060] The temperature control device is used to control the temperature of the anhydrous formaldehyde generating unit so as to control the temperature of the anhydrous formaldehyde generating device;

[0061] The reaction bed arranged in the high temperature reaction zone is used for the contact reaction between the anhydrous formaldehyde outputted from the anhydrous formaldehyde generating unit and the saturated ester compound.

[0062] According to a preferred embodiment of the present invention, the anhydrous formaldehyde generating device comprises a reaction tube for depolymerizing a raw material containing a formaldehyde source to generate an anhydrous formaldehyde alcohol solution;

[0063] The temperature control device comprises at least one temperature measuring device arranged on the reaction tube and a jacket arranged outside the reaction tube;

[0064] The temperature measuring device is used to monitor the temperature of the reaction tube;

[0065] The jacket is used to contain and circulate cooling medium to cool the reaction tube and regulate the temperature of the reaction tube.

[0066] According to a preferred embodiment of the present invention, the system for preparing unsaturated olefinic acid ester further comprises:

[0067] A first feeding pipe, connected to the inlet of the reaction tube, for feeding the raw material containing the polyoxymethylene alcohol solution;

[0068] A first discharge pipe, connected to the outlet of the reaction tube, for discharging anhydrous formaldehyde alcohol solution;

[0069] a second feed pipe connected to the jacket inlet and used to feed the cooling medium into the jacket;

[0070] The second discharge pipe is connected to the outlet of the jacket and is used for discharging the cooling medium from the jacket.

[0071] In the present invention, there is no particular limitation on the type of the temperature measuring device, as long as it can monitor the temperature of the reaction tube in real time. According to a preferred embodiment of the present invention, the temperature measuring device is selected from at least one of a temperature measuring thermocouple and a thermometer, preferably a temperature measuring thermocouple.

[0072] In the present invention, there is no particular limitation on the type of the reaction, as long as the raw material containing the formaldehyde source can be depolymerized. According to a preferred embodiment of the present invention, the reaction tube is at least one of a coil and a U-shaped tube, preferably a coil.

[0073] According to a preferred embodiment of the present invention, the anhydrous formaldehyde in-situ generation system comprises:

[0074] The reaction tower includes a low-temperature reaction zone and a high-temperature reaction zone along the material flow direction;

[0075] The reaction tube and jacket are arranged from the inside to the outside in the low temperature reaction zone;

[0076] The reaction tube is used for depolymerizing the raw material containing polyoxymethylene alcohol solution to generate anhydrous formaldehyde alcohol solution;

[0077] The reaction tube is provided with at least one temperature measuring device for monitoring the temperature of the reaction tube so as to control the temperature of the reaction tube by the inflow and outflow flow of the cooling medium;

[0078] The jacket is used to contain and circulate cooling medium to cool the reaction tube;

[0079] A first feeding pipe, connected to the inlet of the reaction tube, for feeding a raw material containing a formaldehyde source;

[0080] A first discharge pipe, connected to the outlet of the reaction tube, for discharging anhydrous formaldehyde alcohol solution;

[0081] a second feed pipe connected to the jacket inlet and used to feed the cooling medium into the jacket;

[0082] A second discharge pipe is connected to the outlet of the jacket and is used to discharge the cooling medium from the jacket;

[0083] The reaction device arranged in the high temperature reaction zone is used to react the anhydrous formaldehyde alcohol solution output from the first discharge pipe with the saturated ester compound. The above-mentioned anhydrous formaldehyde in-situ generation system is adopted. Along the material flow direction, the interior of the reaction tower includes a low temperature reaction zone and a high temperature reaction zone. The anhydrous formaldehyde generation unit arranged in the low temperature reaction zone includes a reaction tube, a jacket, a cooling medium inlet and outlet pipe, and a temperature measuring device on the reaction tube. The temperature of the reaction tube is monitored in real time by the temperature measuring device, and the temperature in the reaction tube is controlled by the feed rate of the cooling medium through the temperature heating of the low temperature reaction zone of the reaction tower. The temperature in the reaction tube is controlled to be a temperature range in which the raw material containing the formaldehyde source (such as polyoxymethylene) can be fully depolymerized. The depolymerized formaldehyde and other gasified raw materials quickly reach the reaction device in the high temperature reaction zone through the first discharge pipe to react with other raw materials.

[0084] In the present invention, the temperature of the low temperature reaction zone is set to 100-200°C, so that the reaction tube is heated by the temperature of the low temperature reaction zone, and the temperature in the reaction tube is controlled by the feed rate of the cooling medium.

[0085] In the present invention, the temperature of the high temperature reaction zone is set to 250-400° C. After the anhydrous formaldehyde is introduced into the reaction device, it can react with other raw materials.

[0086] According to a preferred embodiment of the present invention, the low-temperature reaction zone and the high-temperature reaction zone are arranged in the same reactor in the direction of gravity, and the low-temperature reaction zone is located above the direction of gravity so as to realize the rapid transportation of anhydrous formaldehyde from the anhydrous formaldehyde generating unit to the high-temperature reaction zone.

[0087] According to a preferred embodiment of the present invention, the present invention provides an anhydrous formaldehyde in-situ generation system, as shown in the schematic diagram Figure 1As shown, the generating system comprises:

[0088] Reaction tower 1, along the material flow direction, the interior of the reaction tower includes a low-temperature reaction zone and a high-temperature reaction zone;

[0089] The reaction tube 2 and the jacket 3 are arranged from the inside to the outside in the low temperature reaction zone;

[0090] The reaction tube 2 is used for depolymerizing the raw materials containing the formaldehyde source to generate anhydrous formaldehyde alcohol solution;

[0091] The reaction tube 2 is provided with at least one temperature measuring device 4 for monitoring the temperature of the reaction tube;

[0092] The jacket 3 is used to contain and circulate a cooling medium so as to control the temperature of the reaction tube 2 by the inflow and outflow flow of the cooling medium;

[0093] A first feed pipe 5, connected to the inlet of the reaction tube 2, for feeding a raw material containing a formaldehyde source;

[0094] A first discharge pipe 6, connected to the outlet of the reaction tube 2, for discharging anhydrous formaldehyde alcohol solution;

[0095] A second feed pipe 7, connected to the inlet of the jacket 3, for feeding the cooling medium into the jacket 3;

[0096] A second discharge pipe 7, connected to the outlet of the jacket 3, for discharging the cooling medium from the jacket 3;

[0097] The reaction bed 9 arranged in the high temperature reaction zone is used to load the catalyst and react the anhydrous formaldehyde alcohol solution output from the first discharge pipe 6 with the saturated ester compound.

[0098] The present invention will be described in detail below through examples.

[0099] In the following examples, the product compositions were measured by gas chromatography;

[0100] Saturated ester compounds, alcohols, and polyformaldehyde were all analytically pure drugs commercially available from Sinopharm Group.

[0101] The following examples are Figure 1 The anhydrous formaldehyde in-situ generation system shown in the figure is carried out, wherein the reaction tube 2 is a coil; the temperature measuring device 4 is a temperature measuring thermocouple; the anhydrous formaldehyde in-situ generation method includes:

[0102] A plunger pump is used to feed a raw material containing a formaldehyde source from a first feed pipe 5 into a coil 2, so that the formaldehyde source is depolymerized into anhydrous formaldehyde to obtain an anhydrous formaldehyde alcohol solution, which is then transported from a first discharge pipe 6 to a reaction bed 9;

[0103] The temperature of the reaction tube 2 is monitored in real time by the temperature measuring device 4 , and the temperature inside the reaction tube 1 is controlled by heating the low-temperature reaction zone of the reaction tower 1 and the feeding rate of the cooling medium in the jacket 3 .

[0104] Example 1

[0105] (1) The coil temperature is 150° C. and the pressure is 0.1 MPa. A methanol solution containing 10% polyoxymethylene is prepared and transported to the coil at a flow rate of 0.05 mL / min. The residence time of the solution in the coil is controlled to be 2 s by adjusting the flow rate of the carrier gas. The concentration of anhydrous formaldehyde in the anhydrous formaldehyde methanol solution at the outlet of the coil is analyzed by chromatography (the formaldehyde content in the anhydrous formaldehyde methanol solution is 10 wt %). The depolymerization rate of polyoxymethylene is 99.7%;

[0106] (2) Anhydrous formaldehyde methanol solution is transported from the coil outlet to the reaction bed, the transport time is 0.3 s, the catalyst is 5 wt% Cs2O / SiO2, and the catalyst loading amount is 10 mL; the saturated ester compound is methyl propionate, the ester feed rate is 0.05 mL / min (the molar ratio of methyl propionate to anhydrous formaldehyde is 3.4), the reaction temperature is 320°C, the reaction pressure is 0.1 MPa, and the space velocity is 0.6 h -1 The product was analyzed by gas chromatography, and it was calculated that the conversion rate of methyl propionate was 20%, and the selectivity of methyl methacrylate was 95%.

[0107] Example 2

[0108] (1) The coil temperature is 200° C. and the pressure is 0 MPa. An ethanol solution containing 30% polyoxymethylene is prepared and transported to the coil at a flow rate of 0.1 mL / min. The residence time of the solution in the coil is controlled to be 1 s by adjusting the flow rate of the carrier gas. The concentration of anhydrous formaldehyde in the anhydrous formaldehyde ethanol solution at the outlet of the coil is analyzed by chromatography (the formaldehyde content in the anhydrous formaldehyde ethanol solution is 29.6 wt %). The depolymerization rate of polyoxymethylene is 99.6%;

[0109] (2) Anhydrous formaldehyde ethanol solution is transported from the coil outlet to the reaction bed, the transport time is 0.5 s, the catalyst is 8 wt% SrO / Al2O3, and the catalyst loading is 10 mL; the saturated ester compound is ethyl acetate, the ester feed rate is 0.03 mL / min (the molar ratio of ethyl acetate to anhydrous formaldehyde is 1.7), the reaction temperature is 400°C, the reaction pressure is 0.5 MPa, and the space velocity is 0.3 h -1 The product was analyzed by gas chromatography, and it was calculated that the conversion rate of ethyl acetate was 19.7% and the selectivity of ethyl acrylate was 94.6%.

[0110] Example 3

[0111] (1) The coil temperature is 100° C. and the pressure is 2 MPa. A methanol solution containing 5 wt% polyoxymethylene is prepared and transported to the coil at a flow rate of 0.02 mL / min. The residence time of the solution in the coil is controlled to be 5 s by adjusting the flow rate of the carrier gas. The concentration of anhydrous formaldehyde in the anhydrous formaldehyde methanol solution at the outlet of the coil is analyzed by chromatography (the formaldehyde content in the anhydrous formaldehyde methanol solution is 5 wt%). The depolymerization rate of polyoxymethylene is 99.6%;

[0112] (2) Anhydrous formaldehyde methanol solution is transported from the coil outlet to the reaction bed, the transport time is 0.2 s, the catalyst is 6 wt% MgO / molecular sieve, and the catalyst loading amount is 10 mL; the saturated ester compound is methyl propionate, the ester feed rate is 0.02 mL / min (the molar ratio of methyl propionate to anhydrous formaldehyde is 1.4), the reaction temperature is 250° C., the reaction pressure is 1 MPa, and the space velocity is 0.7 h -1 The product was analyzed by gas chromatography, and it was calculated that the conversion rate of methyl propionate was 19.1%, and the selectivity of methyl methacrylate was 93.3%.

[0113] Example 4

[0114] The method of Example 1 is followed, except that the coil temperature is 260° C.; the concentration of anhydrous formaldehyde in the anhydrous formaldehyde methanol solution at the outlet of the coil is analyzed by chromatography (the formaldehyde content in the anhydrous formaldehyde methanol solution is 8.8 wt %), and the depolymerization rate of polyoxymethylene is 99.8%;

[0115] In step (2), the molar ratio of methyl propionate to anhydrous formaldehyde is 3.9.

[0116] The product was analyzed by gas chromatography, and calculation showed that the conversion rate of methyl propionate was 14%, and the selectivity of methyl methacrylate was 94%.

[0117] Example 5

[0118] The method of Example 1 is used, except that the polyoxymethylene concentration in the polyoxymethylene methanol solution is 35 wt %; the other conditions are the same as those of Example 1; the concentration of anhydrous formaldehyde in the anhydrous formaldehyde methanol solution at the outlet of the coil is analyzed by chromatography (the formaldehyde content in the anhydrous formaldehyde methanol solution is 32.9 wt %), and the depolymerization rate of polyoxymethylene is 97.2%;

[0119] In step (2), the molar ratio of methyl propionate to anhydrous formaldehyde is 1.0.

[0120] The product was analyzed by gas chromatography, and calculation showed that the conversion rate of methyl propionate was 17%, and the selectivity of methyl methacrylate was 91%.

[0121] Example 6

[0122] The method of Example 1 is used, except that the residence time of the solution in the coil is controlled to be 7 seconds by adjusting the flow rate of the carrier gas; the other conditions are the same as those of Example 1; the concentration of anhydrous formaldehyde in the anhydrous formaldehyde methanol solution at the outlet of the coil is analyzed by chromatography (the formaldehyde content in the anhydrous formaldehyde methanol solution is 9.7wt%), and the depolymerization rate of polyoxymethylene is 99.5%;

[0123] In step (2), the molar ratio of methyl propionate to anhydrous formaldehyde is 3.5.

[0124] The product was analyzed by gas chromatography, and calculation showed that the conversion rate of methyl propionate was 15%, and the selectivity of methyl methacrylate was 89%.

[0125] Example 7

[0126] The method of Example 1 is used, except that the residence time of the solution in the coil is controlled to be 0.5 s by adjusting the flow rate of the carrier gas; the other conditions are the same as those of Example 1; the concentration of anhydrous formaldehyde in the anhydrous formaldehyde methanol solution at the outlet of the coil is analyzed by chromatography (the formaldehyde content in the anhydrous formaldehyde methanol solution is 8.3 wt %), and the depolymerization rate of polyoxymethylene is 85.2%;

[0127] In step (2), the molar ratio of methyl propionate to anhydrous formaldehyde is 4.1.

[0128] The product was analyzed by gas chromatography, and calculation showed that the conversion rate of methyl propionate was 14%, and the selectivity of methyl methacrylate was 92%.

[0129] Comparative Example 1

[0130] In a fixed bed reaction device (inner diameter 35mm, length 1500mm), the catalyst is Cs2O / SiO2 (Cs2O content is 5wt%), the catalyst loading is 10mL, the raw material ratio is: methyl propionate / trioxymethylene / methanol=5 / 1 / 8.5, the feed rate is 0.1mL / min, the reaction temperature is 320°C, and the reaction pressure is 0.1MPa. The product is analyzed by gas chromatography, and it is calculated that the conversion rate of methyl propionate is 13%, and the selectivity of methyl methacrylate is 94%.

[0131] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for generating anhydrous formaldehyde, characterized in that: The method includes: Under continuous reaction conditions, the raw material containing the alcohol solution of polyoxymethylene is depolymerized into anhydrous formaldehyde under depolymerization conditions and the alcohol solution of anhydrous formaldehyde is discharged in real time.

2. The anhydrous formaldehyde generating method according to claim 1, wherein: Depolymerization conditions include: temperature of 50-300°C; The pressure is 0-10MPa; Depolymerization time is 0.1-10s; In the alcohol solution of polyoxymethylene, the mass concentration of polyoxymethylene is 0.1%-50%; Preferably, Depolymerization conditions include: temperature of 100-200°C; and / or The pressure is 0-2MPa; and / or The depolymerization time is 1-5s; and / or In the alcohol solution of polyoxymethylene, the mass concentration of polyoxymethylene is 5%-30%.

3. The anhydrous formaldehyde generating method according to claim 1 or 2, wherein: In the alcohol solution of polyoxymethylene, the alcohol is selected from C1-C4 alcohols, preferably at least one of methanol, ethanol, n-propanol, isopropanol, n-butanol and isobutanol.

4. A method for preparing an unsaturated olefinic acid ester, characterized in that: The method includes: Depolymerization according to any one of claims 1 to 3; in the presence of a catalyst, the alcohol solution of anhydrous formaldehyde discharged in real time is contacted with a saturated ester substance for reaction.

5. The method according to claim 4, wherein: The alcohol solution of anhydrous formaldehyde has an alcohol content of 0.1-80 wt %, preferably 5-60 wt %; and / or The saturated ester substance is selected from at least one of the substances shown in formula (I); Wherein, R1 is selected from C1-C4 alkyl; R2 is selected from C1-C3 alkyl; Preferably, the saturated ester substance is selected from at least one of methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate and ethyl butyrate; and / or The catalyst comprises: a carrier and an alkali metal oxide and / or an alkaline earth metal oxide supported on the carrier; Preferably, The carrier is selected from at least one of alumina, silica, molecular sieve and activated carbon; and / or The alkali metal is at least one selected from K, Ru and Cs; and / or The alkaline earth metal is at least one selected from the group consisting of Mg, Ca, Ba and Sr.

6. The preparation method according to claim 4 or 5, wherein: The molar ratio of the saturated ester substance to the anhydrous formaldehyde is 0.05-50, preferably 0.5-20; and / or Contact conditions include: Reaction temperature: 200-500°C, preferably 250-400°C; and / or Pressure: 0-5MPa, preferably 0.05-1MPa; Feed air velocity: 0.01-2h -1 , preferably 0.05-1h -1 .

7. The preparation method according to any one of claims 4 to 6, wherein: The preparation method is carried out in an unsaturated olefinic acid ester preparation system, and the unsaturated olefinic acid ester preparation system comprises: The reaction tower includes a low-temperature reaction zone and a high-temperature reaction zone along the material flow direction; The anhydrous formaldehyde generating unit is arranged in the low temperature reaction zone, and is used for depolymerizing the raw materials containing the formaldehyde source to generate anhydrous formaldehyde; A high temperature reaction zone, used for continuously feeding anhydrous formaldehyde output from an anhydrous formaldehyde generating unit to contact and react with saturated ester compounds; The preparation method of the unsaturated olefinic acid ester comprises: (1) In an anhydrous formaldehyde generating unit, under continuous reaction conditions, a raw material containing a polyoxymethylene alcohol solution depolymerizes the polyoxymethylene into anhydrous formaldehyde under depolymerization conditions and discharges the anhydrous formaldehyde alcohol solution in real time; (2) In the presence of a catalyst, the anhydrous formaldehyde alcohol solution discharged in real time is contacted with a saturated ester substance for reaction.

8. The preparation method according to claim 7, wherein: The time for anhydrous formaldehyde to be transported from the anhydrous formaldehyde generating unit to the high-temperature reaction zone is 0.1-1 s, preferably 0.2-0.5 s.

9. The preparation method according to claim 7, wherein: The unsaturated olefin ester preparation system includes: The anhydrous formaldehyde generating unit comprises an anhydrous formaldehyde generating device and a temperature control device; The anhydrous formaldehyde generating device is used to depolymerize raw materials containing a formaldehyde source to generate anhydrous formaldehyde; The temperature control device is used to control the temperature of the anhydrous formaldehyde generating unit; The reaction bed arranged in the high temperature reaction zone is used for the contact reaction between the anhydrous formaldehyde outputted from the anhydrous formaldehyde generating unit and the saturated ester compound.

10. The preparation method according to claim 9, wherein: The anhydrous formaldehyde generating device comprises a reaction tube, which is used for depolymerizing raw materials containing a formaldehyde source to generate anhydrous formaldehyde; The temperature control device comprises at least one temperature measuring device arranged on the reaction tube and a jacket arranged outside the reaction tube; The temperature measuring device is used to monitor the temperature of the reaction tube; The jacket is used to contain and circulate cooling medium to cool the reaction tube and regulate the temperature of the reaction tube.

Images