A method for preparing high-purity vinyl methyl ether by gas phase cracking of acetaldehyde dimethyl acetal

Abstract

The present invention provides a method for preparing high-purity vinyl methyl ether by gas-phase cracking of acetaldehyde dimethyl acetal, and relates to the technical field of preparation of vinyl methyl ether. The present invention adopts a solid inorganic acid catalyst for cracking reaction, and the catalyst is prepared by a mixing method. The cracking reaction is carried out in a fixed bed reactor. After being gasified and preheated, acetaldehyde dimethyl acetal passes through the reaction bed and, under the action of the catalyst, is cracked into vinyl methyl ether and methanol gas. Vinyl methyl ether with higher purity is obtained by step-by-step cooling and separation. The catalyst preparation process of the present invention is simple, low in cost, high in catalytic activity, strong in selectivity, and has few cracking product components. It also has good preparation process stability, mild reaction conditions, can be continuously produced and operated for a long period of time, has simple equipment, low investment, high product purity, less three wastes, and high energy efficiency, and has good application prospects.

Description

Technical Field

[0001] The invention relates to the technical field of vinyl methyl ether preparation, and in particular to a method for preparing high-purity vinyl methyl ether by gas-phase cracking of acetaldehyde dimethyl acetal. Background Art

[0002] Methyl vinyl ether (MVE) is an important organic synthesis intermediate and polymer monomer. Its homopolymers and copolymers are widely used in adhesives, coatings, cosmetics, oral care products, lubricants, plasticizers, pesticides, and surface protection materials. Vinyl ether monomers are increasingly valued for their low volatility, odorlessness, low toxicity, rapid UV or electron beam curing, and low solid viscosity, enabling spray application and improving application efficiency.

[0003] The active double bond properties of vinyl methyl ether have led to its widespread application in organic synthesis, such as in the Diels-Alder reaction and in the preparation of compounds such as glutaraldehyde, γ-pyran, and γ-pyridine. Vinyl methyl ether is also used in the synthesis of β-lactams, which are important intermediates in the backbone structure of numerous antibiotics and play a crucial role in the synthesis of β-amino acid drugs. Furthermore, due to the excellent properties of vinyl ether monomers, vinyl methyl ether / maleic anhydride copolymers are used in the pharmaceutical field as adhesives for anastomosis, dental and dental tray fixatives, and as coating agents for enteric-coated drugs. In agriculture, maleic anhydride / methyl vinyl ether copolymers are important ingredients in many pesticides, herbicides, and fungicides. In the light chemical industry, maleic anhydride / methyl vinyl ether copolymers are used as surfactants, thickeners for water-soluble materials, active ingredients in detergents and adhesives, and additives in skin care and beauty products.

[0004] However, vinyl ether compounds cannot be prepared using conventional methods for preparing ethers. The reason is that vinyl alcohol does not exist, so potassium and sodium vinyl alcoholate cannot be used to react with alkyl halides; and alkyl halides show almost no nucleophilic substitution activity, so they cannot be prepared using vinyl chloride and sodium alcoholate. Currently, the main methods for preparing vinyl methyl ether are the acetylene method and the acetal cracking method. Vinyl methyl ether is synthesized using acetylene and methanol in the presence of a strong alkaline catalyst. This method has a short catalyst life and poor safety. GB616197 reports an improved method using high-boiling-point ether as a solvent and an alkali metal acetylene compound at normal pressure as a catalyst. However, this method has a very short start-up cycle and cannot be used for large-scale production. R. Rigamont et al. studied the nucleophilic addition reaction of acetylene and methanol in the presence of a superbase KOH-DMSO catalyst system. The yield of vinyl ether can reach 90%, and the reaction can be carried out at normal pressure. US Patent No. 3,341,606.1967 reports a method for preparing vinyl ether compounds by directly reacting CaC2 with alcohols, achieving a reaction yield of 15.4%. However, the calcium carbide method currently suffers from significant safety risks, a short catalyst cycle, and low product purity. Regarding acetal liquid-phase cracking, KC Drannock, Soc. 81.3382.1959 proposed heating acetal with a small amount of 85% phosphoric acid as a catalyst to obtain vinyl ethers by fractional distillation. Under these conditions, the reactants produced a large amount of black, tarry material, and the yield of vinyl ethers remained very low. Chinese Patent No. CN.10066.649.1992 proposes a solution using diethyl acetal as the raw material, a high-boiling-point, highly chemically stable liquid silyl ether compound as the liquid phase medium, p-toluenesulfonic acid as the catalyst, and a nitrogen-containing heterocyclic compound as the retarder. At a reaction temperature of 200°C to 280°C, heptanal diethyl acetal undergoes liquid-phase decomposition to produce 1-n-pentyl-2-ethoxyethylene with a conversion rate of 96% and a selectivity of 85%. This liquid-phase pyrolysis method utilizes relatively simple catalysts and easily controlled conditions; however, post-processing is complex and poses significant environmental challenges. Furthermore, early vapor-phase pyrolysis methods used metal catalysts such as silver, gold, and palladium-platinum, which are difficult to prepare and expensive. Later improvements employed inorganic acid catalysts. Unsaturated ethers (British Patent No. 681,059, 1952) uses BaO deposited on a silica gel surface as a catalyst. Vinyl ethyl ether can be produced at a reaction temperature of 290-305°C and a space velocity of 0.2-2.0 through the catalyst bed. The reaction has a conversion rate of 71% and a selectivity of 95%. U.S. Patent No. 4,014,941, 1977, describes a method using calcium phosphate as a cracking catalyst, achieving a conversion rate of 98.1% and a selectivity of 96.5%.

[0005] It can be seen that the current preparation of vinyl ether products still has problems such as low catalyst efficiency, high energy consumption, high cost, environmental unfriendliness, poor process stability or insufficient product purity. Summary of the Invention

[0006] To solve the above problems, the present invention provides a method for preparing high-purity vinyl methyl ether by gas-phase cracking of acetaldehyde dimethyl acetal. The method achieves low-cost and efficient preparation of high-purity vinyl methyl ether by using a specific cracking catalyst in combination with a specific cracking process.

[0007] The method for preparing high-purity vinyl methyl ether by gas-phase cracking of acetaldehyde dimethyl acetal of the present invention comprises the following steps:

[0008] (1) The acetaldehyde dimethyl acetal liquid is first preheated, wherein the preheating treatment is to first pass the acetaldehyde dimethyl acetal liquid through a cracking gas cooler, exchange heat with the cracking gas generated by catalytic cracking, and vaporize it, raising the temperature to 80-90° C., and then enter a preheater to raise the temperature to 260-280° C., and then enter a cracking reactor for catalytic cracking;

[0009] (2) the preheated acetaldehyde dimethyl acetal gas undergoes a cracking reaction under the action of a catalyst to obtain cracked gas; the cracking reaction temperature is 260 to 400° C.;

[0010] (3) The cracked gas is first cooled to 100-110°C, then cooled to 58-62°C, and finally cooled to 20-30°C. The unliquefied methanol is cooled and liquefied to obtain purified vinyl methyl ether.

[0011] Furthermore, in the step (1), the content of acetaldehyde dimethyl acetal in the acetaldehyde dimethyl acetal gas is greater than 75%.

[0012] Furthermore, in the step (1), the liquid hourly space velocity of the acetaldehyde dimethyl acetal gas is 0.6 to 2.0 h -1 .

[0013] Furthermore, the present invention fills the catalyst into a fixed bed reactor and divides the filling into three sections on average. Active porcelain balls with a particle size of 3 mm are filled between each section, and the height of the porcelain balls is 1 / 5 to 1 / 4 of the height of the catalyst.

[0014] Furthermore, the catalytic cracking temperature is 300-350°C.

[0015] Preferably, the catalytic cracking temperature is 300°C to 320°C.

[0016] Furthermore, the part above the catalyst in the fixed-bed reactor is filled with inert porcelain balls with a particle size of 6 mm, and the height is 1 / 2 to 2 / 3 of the catalytic cracking section. The part below the catalyst in the fixed-bed reactor is filled with active supporting porcelain balls with a particle size of 3 mm, and the height is 1 / 3 to 1 / 2 of the catalytic cracking section. By filling porcelain balls in the upper and lower sections of the reactor catalyst, the present invention can fix the catalyst while the upper section can supply energy to the raw gas to maintain the temperature, and the lower section can also prevent the generation of trace polymers in the cracking reaction.

[0017] Furthermore, the catalyst is an inorganic acid catalyst.

[0018] Furthermore, the inorganic acid catalyst consists of a main component and an auxiliary agent.

[0019] Furthermore, the weight ratio of the main component to the auxiliary agent is 10:1 to 1.5.

[0020] Furthermore, the main component is composed of inorganic salt or phosphoric acid and acid-washed diatomaceous earth in a weight ratio of 1:0.2-0.4.

[0021] Furthermore, the inorganic salt is one or more of phosphate, acid phosphate, and sulfite.

[0022] Furthermore, the phosphate is one or more of calcium phosphate, magnesium phosphate, aluminum phosphate, zinc phosphate, and barium phosphate; the acid phosphate is one or more of calcium hydrogen phosphate, sodium hydrogen phosphate, and magnesium hydrogen phosphate; and the sulfite is one or both of potassium sulfite and calcium sulfite.

[0023] Furthermore, the auxiliary agent is a metal oxide or a halide.

[0024] Furthermore, the metal oxide is one or more of sodium oxide, calcium oxide, barium oxide, and magnesium oxide, and the halide is one or more of sodium chloride, calcium chloride, magnesium chloride, and barium chloride.

[0025] Furthermore, the catalyst further comprises 1 wt% to 3 wt% of a porogen.

[0026] Furthermore, the porogen is sesbania powder.

[0027] Furthermore, the catalyst further comprises 10 wt% to 15 wt% of a silica sol adhesive, and the content of the silica sol adhesive is calculated based on 30% silicon dioxide.

[0028] Furthermore, the preparation method of the catalyst is as follows: after the main component, auxiliary agent and porogen are evenly mixed, water is added to form a mass, which is extruded into a strip, dried at 120°C for 2 to 4 hours, and then cut into particles with a diameter of 2 to 3 mm, and calcined at 550 to 600°C for 4 hours to form.

[0029] Furthermore, the content of the purified vinyl methyl ether of the present invention is ≥98.0%, and the methanol content is <1%. The quality of the product is higher than that of the vinyl methyl ether produced by the acetylene process.

[0030] Compared with the prior art, the present invention has the following beneficial technical effects:

[0031] (1) The catalyst preparation process of the present invention is simple, low in cost, high in catalytic activity, strong in selectivity, and has a small number of cracking product components. The main components of the cracking products have a large boiling point difference under normal pressure and are easy to separate;

[0032] (2) The present invention combines cracking and purification, and achieves separation and purification of products by cooling the cracking gas in steps;

[0033] (3) The present invention fully utilizes the thermal energy of the cracking gas, effectively reduces energy consumption, and achieves the goal of low-carbon cleaning;

[0034] (4) The preparation method of high-purity vinyl methyl ether of the present invention has the characteristics of good process stability, mild reaction conditions, continuous long-term production operation, simple equipment, low investment, high product purity, less three wastes, and high energy efficiency, and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The present invention will be further described below with reference to the accompanying drawings.

[0036] Figure 1 The present invention is a process flow chart for preparing high-purity vinyl methyl ether by gas-phase cracking of acetaldehyde dimethyl acetal. DETAILED DESCRIPTION

[0037] The technical solution provided by the present invention is further described below in conjunction with embodiments.

[0038] Example 1

[0039] Preparation of catalyst:

[0040] 90g of aluminum phosphate, 30g of diatomaceous earth, and 10g of magnesium hydrogen phosphate were mixed thoroughly, and then 3.0wt% of sesbania powder, 6wt% of calcium chloride, and 10wt% of silica sol (calculated as 30% of silicon dioxide) were added in sequence. The mixture was thoroughly mixed, and an appropriate amount of distilled water was added to form a mass. The mass was extruded into strips, dried at 120°C for 2h, and then sheared into cylindrical particles of 2-3mm. The catalyst was calcined at 550°C for 4h to obtain a catalyst with a strength of 380N / cm 2 .

[0041] Example 2

[0042] A method for preparing high-purity vinyl methyl ether by gas-phase cracking of acetaldehyde dimethyl acetal, comprising the following steps:

[0043] (1) Acetaldehyde dimethyl acetal gas with a purity of 98% was pumped from a storage tank and heated to 85° C. by heat exchange with catalytic cracking reaction gas in a cracking gas cooling heat exchanger. The heat source of the cracking gas cooling heat exchanger was provided by the cracking gas in the cracking reactor. The liquid hourly space velocity of the acetaldehyde dimethyl acetal gas was set to a specific value, as shown in Table 1.

[0044] (2) The material is vaporized by the cracking gas cooling heat exchanger and then enters the preheater and is heated to 280°C for preheating. In the initial operation, acetaldehyde dimethyl acetal directly enters the preheater and the outlet temperature is controlled by the flow rate;

[0045] (3) The preheated acetaldehyde dimethyl acetal enters the catalytic cracking reactor, and the material is heated to 320°C in the upper section of the reactor. The heated material in the upper section of the reactor flows into the catalytic cracking section, and the catalyst prepared in Example 1 is loaded on the fixed bed reactor to catalytically crack and generate vinyl methyl ether and methanol. The catalytic cracking reactor is powered by molten salt, and the molten salt has a uniform heating effect, which can prevent local overheating caused by electric heating. The catalyst in the fixed bed reactor is evenly loaded in three sections, and active porcelain balls with a particle size of 3 mm are filled between each section. The height of the porcelain balls is 1 / 5 of the height of the catalyst. The part above the catalyst in the reactor is loaded with inert porcelain balls with a particle size of 6 mm, and the height is 2 / 3 of the catalytic cracking section. The part below the catalyst in the reactor is loaded with active supporting porcelain balls with a particle size of 3 mm, and the height is 1 / 3 of the catalytic cracking section. The present invention can fix the catalyst by filling porcelain balls in the upper and lower sections of the reactor catalyst, while the upper section can supply energy to the raw gas to maintain the temperature, and the lower section can also prevent the generation of trace addition polymers in the cracking reaction;

[0046] (4) The cracking product passes through the reaction temperature control section and then passes through a buffer tank. A baffle is installed in the tank, and a trace amount of polymer in the cracking gas is deposited in the tank. The cracking gas enters the cracking gas cooler. The cracking gas cooling heat exchanger adopts a spiral plate heat exchanger, and heat is exchanged with the cracking raw material acetaldehyde dimethyl acetal. The outlet temperature of the cracking gas after heat exchange is 100°C, and the temperature of acetaldehyde dimethyl acetal after heat exchange is 85°C;

[0047] (5) The 100°C cracked gas is temperature-controlled and cooled to 60°C to liquefy the methanol. The heat exchanger adopts a shell-and-tube heat exchanger to liquefy the methanol. The liquefied part flows into the liquid storage tank for redistribution and returns to the acetaldehyde dimethyl acetal synthesis section through the liquid storage tank to prepare acetaldehyde dimethyl acetal; the separated uncondensed gas passes through the vinyl methyl ether purification heat exchanger to cool the 60°C cracked gas to 25°C, and the unliquefied methanol is fully cooled and liquefied. The purified vinyl methyl ether is liquefied and collected by a compressor to achieve the preparation of high-purity vinyl methyl ether. The liquefied methanol contains a certain amount of acetaldehyde dimethyl acetal and flows into the heat exchanger liquid storage tank. It returns to the cracking outlet through the liquid storage tank to merge with the cracked gas, and is cooled and separated again. The hot water generated during the heat exchange process is sent to the acetaldehyde dimethyl acetal synthesis process for heating acetaldehyde dimethyl acetal.

[0048] The cooling components were collected separately and the analysis results are shown in Table 1.

[0049] Table 1

[0050]

[0051]

[0052] Example 3

[0053] Same as Example 2, with a fixed air velocity of 1 h -1 The difference is that the content of acetaldehyde dimethyl acetal in the raw gas is changed, and the other processes are the same as those in Example 2. The cooling components are collected separately, and the analysis results are shown in Table 2.

[0054] Table 2

[0055]

[0056] This shows that acetaldehyde dimethyl acetal is synthesized from acetaldehyde and methanol in the presence of an acidic catalyst. Methanol is in excess during the reaction, so the content of acetaldehyde dimethyl acetal decreases. The main component that increases is methanol, and the amount of acetaldehyde changes very little. Therefore, the total amount of methanol recovered by cracking increases, but its content does not change much with the raw material content. For the same reason, the product composition and material content do not change much.

[0057] Example 4

[0058] Same as Example 2, with a fixed air velocity of 1 h -1 The difference is that the catalytic cracking temperature is changed, and the other processes are the same as in Example 2. The cooling components were collected separately, and the analysis results are shown in Table 3.

[0059] Table 3

[0060]

[0061] Example 5

[0062] Same as Example 2, with a fixed air velocity of 1 h -1 The difference is that the running time is changed, and the other processes are the same as Example 2. The cooling components at different times are collected and the analysis results are shown in Table 4.

[0063] Table 4

[0064]

[0065] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only intended to help understand the method and core concept of the present invention. At the same time, those skilled in the art will find that the specific implementation methods and application scopes may vary based on the concept of the present invention. In summary, the contents of this specification should not be construed as limiting the present invention.

Claims

1. A method for preparing high-purity vinyl methyl ether by gas phase cracking of acetaldehyde dimethyl acetal, characterized in that: The following steps are involved: (1) The acetaldehyde dimethyl acetal liquid is first preheated to 80-90°C, then enters a preheater to be heated to 260-280°C, and then enters a cracking reactor for catalytic cracking, wherein the liquid hourly space velocity of the acetaldehyde dimethyl acetal gas is 1.0h -1 ; (2) the preheated acetaldehyde dimethyl acetal gas undergoes a cracking reaction under the action of a catalyst to obtain cracked gas; the cracking reaction temperature is 310° C. or 330° C.; The cracking reaction is carried out in a cracking reactor, which includes a fixed bed reactor. The catalyst in the fixed bed reactor is evenly loaded in three sections. Active porcelain balls with a particle size of 3 mm are filled between each section, and the height of the porcelain balls is 1 / 5 of the height of the catalyst. The part above the catalyst in the reactor is loaded with inert porcelain balls with a particle size of 6 mm, and the height is 2 / 3 of the catalytic cracking section. The section below the catalyst in the reactor is loaded with active support porcelain balls with a particle size of 3 mm, and the height is 1 / 3 of the catalytic cracking section. (3) first cooling the cracked gas to 100-110° C., then cooling it to 58-62° C., and finally cooling it to 20-30° C., cooling and liquefying the unliquefied methanol to obtain purified vinyl methyl ether; The catalyst is prepared as follows: 90 g of aluminum phosphate, 30 g of diatomaceous earth, and 10 g of magnesium hydrogen phosphate are thoroughly mixed, and then 3.0 wt% of sesbania powder, 6 wt% of calcium chloride, and 10 wt% of silica sol (calculated as 30% of silicon dioxide) are added in sequence, and the mixture is thoroughly mixed. An appropriate amount of distilled water is added to knead the mixture into a mass, which is extruded into strips, dried at 120° C. for 2 h, and then sheared into cylindrical particles of 2 to 3 mm. The particles are calcined at 550° C. for 4 h to obtain the catalyst.

2. The method for preparing high-purity vinyl methyl ether by gas phase cracking of acetaldehyde dimethyl acetal according to claim 1, characterized in that: The purified vinyl methyl ether content is ≥98.0%, and the methanol content is <1%.

Images