A process for the production of propylene glycol monomethyl ether acetate by continuous catalytic rectification transesterification

Abstract

The present application relates to a kind of continuous catalytic rectification ester exchange production propylene glycol monomethyl ether acetate processes, including PO catalytic rectification tower, PM catalytic rectification tower, MeOAc recovery tower, PMA refining tower, PO catalytic rectification tower is generated using PO and methanol reaction PM;PM is sent into PM catalytic rectification tower and occurs ester exchange reaction with MeOAc, and PMA is generated;The MeOAc, MeOH mixture obtained from PM catalytic rectification tower top is sent into MeOAc recovery tower and is separated, and the MeOAC and MeOH azeotrope of recovery tower top is recycled to PO catalytic rectification tower and is fully utilized MeOH, and the MeOAc of column bottom is recycled to PM catalytic rectification tower and participates in reaction;PMA refining tower separates the PMA obtained from PM catalytic rectification tower bottom and a small amount of PM, and the PM of refining tower top is recycled to PM catalytic rectification tower, and the PMA product of column bottom is obtained with high purity.Process operation is simple, process conversion rate and selectivity are high, catalyst can be recycled, post-treatment separation is simple, and have good industrial application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to a process for producing propylene glycol monomethyl ether acetate by continuous catalytic distillation transesterification. BACKGROUND

[0002] Propylene glycol monomethyl ether acetate (PMA) is a colorless transparent liquid with special aromatic odor. At normal pressure, its melting point is -87 ℃, boiling point is 149 ℃, and relative density to water is 0.966. Propylene glycol monomethyl ether acetate is an industrial solvent with multiple functional groups. There are both polar and non-polar functional groups in the molecule, which are mutually restricted and repelled. It has good solubility for both polar and non-polar substances, and its solubility is higher than that of ethylene glycol ether compounds and general solvents. Due to its excellent solubility and non-pollution, propylene glycol monomethyl ether acetate is widely used in printing, coating, fuel additive, photosensitive material and electronic chemicals, etc.

[0003] In the research of synthesis methods of propylene glycol monomethyl ether acetate, there are mainly one-step method of propylene oxide, esterification method of propylene glycol monomethyl ether and transesterification method of propylene glycol monomethyl ether.

[0004] The one-step method of propylene oxide uses alkylene oxide and ester compounds as raw materials, and a catalyst with Lewis acid sites such as Al-Mg oxide to catalyze the alkoxylation reaction to generate a certain polymer. This method has the advantage of high atom utilization rate, but a series of side reactions occur in the alkoxylation process, resulting in poor selectivity. In addition, this synthesis method requires high temperature and pressure, and has high requirements for reaction equipment, which limits the development of the synthesis of propylene glycol monomethyl ether acetate by one-step method of propylene oxide.

[0005] In the traditional synthesis process of propylene glycol monomethyl ether acetate, propylene glycol monomethyl ether esterification method is adopted, propylene glycol monomethyl ether and acetic acid are used as raw materials, concentrated sulfuric acid, benzene sulfonic acid and other liquid acids are usually used as catalysts to generate propylene glycol monomethyl ether acetate and water. Although liquid acid has strong catalytic performance, liquid acid has strong corrosive property, and it is easy to corrode equipment and pipeline during transportation and use; there are many side reactions, and the separation and purification of the product are difficult; the catalyst is difficult to separate from the product and cannot be reused; a large amount of "three wastes" is generated in the production process, which is harmful to the environment, and increases the cost of treating "three wastes". In related research, solid acid catalyst is usually used instead of liquid acid, and solid acid is beneficial to the separation of catalyst and the reuse of catalyst. Because water is generated in the esterification process, water will form azeotrope with propylene glycol monomethyl ether acetate, which is not conducive to the refining of propylene glycol monomethyl ether acetate. In order to avoid the generation of this azeotrope and promote the separation of water, a water-carrying agent needs to be added to separate the water generated in the system, and the water-carrying agent is usually benzene, toluene and other organic matters with certain toxicity, which is harmful to human body and environment and also increases the cost of the process.

[0006] The ester exchange synthesis process of propylene glycol monomethyl ether acetate is to generate propylene glycol monomethyl ether acetate and methanol by ester exchange reaction of propylene glycol monomethyl ether and methyl acetate under the action of alkaline or acidic catalyst. The advantage of this process is that it does not use acetic acid as raw material to avoid the problem of too high acid value of propylene glycol monomethyl ether acetate product, and the by-product is methanol which can be recycled to the propylene glycol monomethyl ether production process. It is a low-cost, clean and efficient synthesis method. CN109265314A discloses a preparation method and device of propylene glycol methyl ether acetate, which uses sodium methoxide as catalyst to catalyze the ester exchange reaction of propylene glycol monomethyl ether and methyl acetate in a batch reaction rectifying tower. After separating the mixture of propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate and catalyst obtained from the bottom of the batch reaction rectifying tower, the conversion rate of propylene glycol monomethyl ether is 75.2%, and the yield of propylene glycol monomethyl ether acetate is 96.5%. Since sodium methoxide cannot be dissolved in the reaction system, sodium methoxide will precipitate on the surface of the packing in the reaction rectifying tower, which will hinder the gas-liquid mass transfer in the packing. Only batch reaction rectification can be carried out, and complete conversion of propylene glycol monomethyl ether cannot be achieved. Sodium methoxide has strong corrosive property and can easily corrode equipment during use; it is insoluble in propylene glycol monomethyl ether and propylene glycol monomethyl ether acetate, and precipitates in the tower kettle, generating a large amount of solid waste, which cannot be reused, increasing the production cost and seriously polluting the environment. SUMMARY

[0007] The present application improves the prior art, i.e., the technical problem to be solved by the present application is to provide a process for producing propylene glycol monomethyl ether acetate by continuous catalytic rectification ester exchange based on a metal oxide catalyst, which is reasonable in design, easy to operate in process flow, and high in raw material conversion rate and product selectivity.

[0008] To achieve the above object, the technical scheme adopted by the present application is as follows: a process for producing propylene glycol monomethyl ether acetate by continuous catalytic rectification ester exchange, comprising an epoxypropane catalytic rectification tower, a propylene glycol monomethyl ether catalytic rectification tower, a methyl acetate recovery tower, and a propylene glycol monomethyl ether acetate refining tower; the epoxypropane catalytic rectification tower and the propylene glycol monomethyl ether catalytic rectification tower each have a rectification section, a reaction section, and a stripping section; the rectification section and the stripping section use cyclone trays or are filled with stainless steel packing; the reaction section uses cyclone trays and a composite metal oxide as a solid alkaline catalyst, which is fixed on the cyclone trays in the form of a catalytic element; and the process comprises the following steps:

[0009] Step S1: in the epoxypropane catalytic rectification tower, epoxypropane reacts with methanol to generate propylene glycol monomethyl ether, and then the propylene glycol monomethyl ether is sent to the propylene glycol monomethyl ether catalytic rectification tower to react with methyl acetate to generate propylene glycol monomethyl ether acetate;

[0010] Step S2: the mixture of methyl acetate and methanol obtained from the top of the propylene glycol monomethyl ether catalytic rectification tower is sent to the methyl acetate recovery tower for separation; the methyl acetate and methanol azeotrope from the top of the methyl acetate recovery tower is recycled to the epoxypropane catalytic rectification tower to fully utilize the methanol; and the methyl acetate from the bottom of the methyl acetate recovery tower is recycled to the propylene glycol monomethyl ether catalytic rectification tower to participate in the reaction;

[0011] Step S3: the propylene glycol monomethyl ether acetate and a small amount of propylene glycol monomethyl ether obtained from the bottom of the propylene glycol monomethyl ether catalytic rectification tower are separated in the propylene glycol monomethyl ether acetate refining tower; the propylene glycol monomethyl ether from the top of the propylene glycol monomethyl ether acetate refining tower is recycled to the propylene glycol monomethyl ether catalytic rectification tower; and the high-purity propylene glycol monomethyl ether acetate product is obtained from the bottom of the propylene glycol monomethyl ether acetate refining tower.

[0012] Further, in step S1, in the epoxypropane catalytic rectification tower, the epoxypropane and the methanol are respectively fed from the lower end and the upper end of the reaction section of the epoxypropane catalytic rectification tower, and the epoxypropane and the methanol perform ring-opening reaction to generate propylene glycol monomethyl ether under the action of the metal oxide catalyst in the reaction section.

[0013] Further, in step S2, in the propylene glycol monomethyl ether catalytic rectification tower, propylene glycol monomethyl ether and methyl acetate raw materials are respectively fed from the upper end and the lower end of the reaction section of the propylene glycol monomethyl ether catalytic rectification tower, the raw material propylene glycol monomethyl ether is sent into the propylene glycol monomethyl ether catalytic rectification tower together with the propylene glycol monomethyl ether obtained by separating the propylene glycol monomethyl ether acetate refining tower, and the raw material methyl acetate is sent into the tower together with the methyl acetate obtained by separating the methyl acetate recovery tower, under the action of the metal oxide catalyst in the reaction section, the propylene glycol monomethyl ether and the methyl acetate perform ester exchange reaction to generate propylene glycol monomethyl ether acetate and methanol.

[0014] Further, in step S1, in the propylene glycol monomethyl ether catalytic rectification tower, propylene glycol monomethyl ether and methyl acetate raw materials are respectively fed from the upper end and the lower end of the reaction section of the propylene glycol monomethyl ether catalytic rectification tower, the raw material propylene glycol monomethyl ether is sent into the propylene glycol monomethyl ether catalytic rectification tower together with the propylene glycol monomethyl ether obtained by separating the propylene glycol monomethyl ether acetate refining tower, and the raw material methyl acetate is sent into the tower together with the methyl acetate obtained by separating the methyl acetate recovery tower, under the action of the metal oxide catalyst in the reaction section, the propylene glycol monomethyl ether and the methyl acetate perform ester exchange reaction to generate propylene glycol monomethyl ether acetate and methanol.

[0015] Further, in step S3, the methyl acetate recovery tower is used to separate the components at the top of the propylene glycol monomethyl ether catalytic rectification tower, after separation, the methyl acetate and methanol azeotrope obtained at the top of the methyl acetate recovery tower is recycled to the propylene glycol monomethyl ether catalytic rectification tower to continue to participate in the reaction, so as to fully utilize the methanol, and the methyl acetate obtained at the tower bottom is recycled to the propylene glycol monomethyl ether catalytic rectification tower to continue to participate in the reaction.

[0016] Further, the loading mode in the reaction section of the propylene glycol monomethyl ether catalytic rectification tower and the propylene glycol monomethyl ether catalytic rectification tower is that the composite metal oxide solid alkaline catalyst particles are loaded in the catalytic packing elements and are fixed horizontally on the cyclone tray.

[0017] Further, the composite metal oxide solid alkaline catalyst includes one or more of metal oxide, supported metal oxide, and composite metal oxide.

[0018] Further, the carrier of the supported metal oxide includes activated carbon, aluminum oxide, silicon oxide, molecular sieve, and hydrotalcite; the metal oxide-based catalyst is a solid particle with a size of 1-10 mm, and the active ingredient includes an oxide of at least one metal element selected from Be, Mg, Ca, Sr, and Ba.

[0019] Further, the feed mode of the propylene glycol monomethyl ether catalytic rectification tower satisfies that the molar ratio of methyl acetate to propylene glycol monomethyl ether is within 1:1-8:1, and the reaction section temperature is 80-100 DEG C.

[0020] Further, the reflux ratio of the propylene oxide catalytic rectification tower is 5, the operating pressure is normal pressure, the tower top temperature is 53.0-54.5 DEG C, and the tower bottom temperature is 145.5-147.5 DEG C.

[0021] Compared with the prior art, the present application has the following effects: the present application is reasonable in design, uses a composite metal oxide as a catalyst to realize continuous production of propylene glycol monomethyl ether acetate in a catalytic rectification process, and simultaneously improves the conversion rate of raw materials and the selectivity of products, the conversion rate of propylene glycol monomethyl ether can reach more than 99.9%, and the selectivity of propylene glycol monomethyl ether acetate can reach more than 99%; the catalytic rectification process is simple in operation, high in conversion rate and selectivity, and the catalyst can be recycled and utilized, and the post-treatment separation is simple, and has a good industrial application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0022] Fig. 1 is a process flow chart of the embodiment of the present application;

[0023] Fig. 2 is a structural schematic diagram of a cyclone tray in the embodiment of the present application;

[0024] Fig. 3 is a distribution mode, an opening form and a liquid flow direction of a catalytic element on the cyclone tray in the embodiment of the present application.

[0025] In the drawings:

[0026] 1-propylene oxide catalytic rectification tower; 2-propylene glycol monomethyl ether catalytic rectification tower; 3-methyl acetate recovery tower; 4-propylene glycol monomethyl ether acetate refining tower; 5-catalytic element; 6-tongue-shaped hole. DETAILED DESCRIPTION

[0027] The present application will be further described in detail below in combination with the drawings and specific embodiments.

[0028] In the description of the present application, it should be understood that the terms "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0029] AsFigs. 1-3 As shown, the process for producing propylene glycol monomethyl ether acetate by continuous catalytic rectification ester exchange of the present application comprises a propylene oxide (PO) catalytic rectification column 1, a propylene glycol monomethyl ether (PM) catalytic rectification column 2, a methyl acetate (MeOAc) recovery column 3, and a propylene glycol monomethyl ether acetate (PMA) refining column 4. The propylene oxide catalytic rectification column 1 and the propylene glycol monomethyl ether catalytic rectification column 2 each have a rectification section, a reaction section, and a stripping section. The rectification section and the stripping section use cyclone trays or stainless steel θ ring packing to achieve separation. In the reaction section, instead of the traditional tray or catalyst packing in the catalytic rectification column, a catalytic element combined with a cyclone tray is used. The use of the cyclone tray can strengthen the mass transfer process between the vapor and liquid phases in the reaction section, promote uniform gas distribution while reducing the liquid gradient on the tray, improve the tray efficiency of the reaction section, and use a composite metal oxide as a solid alkaline catalyst, which is fixed on the cyclone tray in the form of a catalytic element. The process uses a solid base as a catalyst to achieve continuous catalytic rectification for the ester exchange synthesis of propylene glycol monomethyl ether acetate, and has the advantages of easy catalyst recovery and utilization, simple process operation, high raw material utilization rate, and high product selectivity.

[0030] The specific process comprises the following steps:

[0031] Step S1: In the propylene oxide catalytic rectification column 1, propylene glycol monomethyl ether is generated by the reaction of propylene oxide and methanol, and then the propylene glycol monomethyl ether is sent to the propylene glycol monomethyl ether catalytic rectification column 2 to react with methyl acetate to generate propylene glycol monomethyl ether acetate;

[0032] Step S2: The methyl acetate and methanol mixture obtained from the top of the propylene glycol monomethyl ether catalytic rectification column 2 is sent to the methyl acetate recovery column for separation. The methyl acetate and methanol azeotrope from the top of the methyl acetate recovery column 3 is recycled to the propylene oxide catalytic rectification column 1 to fully utilize the methanol, and the methyl acetate from the bottom of the methyl acetate recovery column 3 is recycled to the propylene glycol monomethyl ether catalytic rectification column 2 to participate in the reaction;

[0033] Step S3: The propylene glycol monomethyl ether acetate refining column 4 separates the propylene glycol monomethyl ether acetate and a small amount of propylene glycol monomethyl ether obtained from the bottom of the propylene glycol monomethyl ether catalytic rectification column 2. The propylene glycol monomethyl ether from the top of the propylene glycol monomethyl ether acetate refining column 4 is recycled to the propylene glycol monomethyl ether catalytic rectification column 2, and the high-purity propylene glycol monomethyl ether acetate product is obtained from the bottom of the propylene glycol monomethyl ether acetate refining column 4.

[0034] In the step S1, in the propylene oxide catalytic rectifying tower, propylene oxide and methanol are fed into the lower end and upper end of the reaction section of the propylene oxide catalytic rectifying tower respectively, wherein the raw material methanol and methyl acetate obtained by separating the azeotrope of methyl acetate and methanol in the methyl acetate recovery tower are fed into the propylene oxide catalytic rectifying tower, and the propylene oxide and methanol are subjected to ring-opening reaction under the action of the metal oxide catalyst in the reaction section to generate propylene glycol monomethyl ether.

[0035] In the step S2, in the propylene glycol monomethyl ether catalytic rectifying tower, the raw material propylene glycol monomethyl ether and methyl acetate are fed into the upper end and lower end of the reaction section of the propylene glycol monomethyl ether catalytic rectifying tower respectively, the raw material propylene glycol monomethyl ether and the propylene glycol monomethyl ether acetate obtained by separating the propylene glycol monomethyl ether in the propylene glycol monomethyl ether acetate refining tower are fed into the propylene glycol monomethyl ether catalytic rectifying tower, and the raw material methyl acetate and the methyl acetate obtained by separating the methyl acetate in the methyl acetate recovery tower are fed into the tower, and the propylene glycol monomethyl ether and the methyl acetate are subjected to ester exchange reaction under the action of the metal oxide catalyst in the reaction section to generate propylene glycol monomethyl ether acetate and methanol.

[0036] In the step S1, in the propylene oxide catalytic rectifying tower, propylene oxide and methanol are subjected to reaction by countercurrent contact in the reaction section to generate propylene glycol monomethyl ether, the light component propylene oxide is totally refluxed at the top of the tower, and the propylene glycol monomethyl ether generated by reaction and the methyl acetate not participating in the reaction are taken out from the tower bottom and transported to the propylene glycol monomethyl ether PM catalytic rectifying tower; in the propylene glycol monomethyl ether catalytic rectifying tower, the propylene glycol monomethyl ether is subjected to reaction by countercurrent and sufficient contact with the methyl acetate in the reaction section to generate propylene glycol monomethyl ether acetate and methanol, the methyl acetate and the methanol form an azeotrope, the azeotrope and excess methyl acetate are obtained at the top of the propylene glycol monomethyl ether catalytic rectifying tower, and the propylene glycol monomethyl ether acetate and a small amount of unreacted propylene glycol monomethyl ether are obtained at the tower bottom.

[0037] In the step S3, the methyl acetate recovery tower is used to separate the components at the top of the propylene glycol monomethyl ether catalytic rectifying tower, and the azeotrope of the methyl acetate and the methanol obtained at the top of the methyl acetate recovery tower is recycled to the propylene oxide catalytic rectifying tower to continue participating in the reaction so as to fully utilize the methanol, and the methyl acetate obtained at the tower bottom is recycled to the propylene glycol monomethyl ether catalytic rectifying tower to continue participating in the reaction. The propylene glycol monomethyl ether acetate and the unreacted propylene glycol monomethyl ether taken out from the tower bottom of the propylene glycol monomethyl ether catalytic rectifying tower are separated by using the propylene glycol monomethyl ether acetate refining tower. After the separation, the propylene glycol monomethyl ether acetate product with high purity (>99.9%) is obtained at the tower bottom of the refining tower, and a small amount of unreacted propylene glycol monomethyl ether is obtained at the top of the tower and recycled to the propylene glycol monomethyl ether catalytic rectifying tower to participate in the reaction.

[0038] In this embodiment, the loading mode in the reaction section of the propylene oxide catalytic rectification tower and the propylene glycol monomethyl ether catalytic rectification tower is that the composite metal oxide solid alkaline catalyst particles are loaded in the catalytic packing elements and are fixed horizontally on the cyclone tray.

[0039] In this embodiment, the composite metal oxide solid alkaline catalyst includes one or more of metal oxides, supported metal oxides, and composite metal oxides. The support of the supported metal oxide includes activated carbon, aluminum oxide, silicon oxide, molecular sieve, and hydrotalcite. The metal oxide-based catalyst is a solid particle with a particle size of 1-10 mm, and the active ingredient includes an oxide of at least one metal element selected from Be, Mg, Ca, Sr, and Ba. The composite metal oxide catalyst has the advantages of high catalyst activity, high product selectivity, simple preparation process, low cost, easy separation after reaction, and repeated use after simple treatment.

[0040] In this embodiment, the feeding mode of the propylene glycol monomethyl ether catalytic rectification tower is normal temperature feeding, and a certain ester-ether molar ratio should also be met. The excess methyl acetate is introduced to promote the forward reaction, so as to realize the complete conversion of the propylene glycol monomethyl ether as much as possible. The molar ratio of methyl acetate to propylene glycol monomethyl ether is within 1:1-8:1, and the reaction section temperature is 80-100 ℃.

[0041] In this embodiment, the reflux ratio of the propylene oxide catalytic rectification tower is 5, the operating pressure is normal pressure, the reaction section temperature is 80-100 ℃, the tower top temperature is 53.0-54.5 ℃, and the tower bottom temperature is 145.5-147.5 ℃.

[0042] Specific implementation process: The process includes a propylene oxide (PO) catalytic rectification tower, a propylene glycol monomethyl ether (PM) catalytic rectification tower, a methyl acetate (MeOAc) recovery tower, and a propylene glycol monomethyl ether acetate (PMA) refining tower. The propylene glycol monomethyl ether catalytic rectification tower is divided into a rectification section, a reaction section, and a stripping section from top to bottom. The rectification section is 0.4 m long, the reaction section is 1.2 m long, and the stripping section is 0.6 m long. The metal oxide catalyst in the reaction section is a shaped alkaline earth metal oxide particle (with a particle size of 1-10 mm), which is loaded in the tower in the form of a catalytic element. The rectification section and the stripping section are loaded with bulk-packed stainless steel θ ring packing.

[0043] For the propylene glycol monomethyl ether catalytic rectification tower, the propylene glycol monomethyl ether is transported to the upper end of the propylene glycol monomethyl ether catalytic rectification tower reaction section by a delivery pump, and the methyl acetate is transported to the lower end of the catalytic rectification tower reaction section by a delivery pump. The propylene glycol monomethyl ether and the methyl acetate are fully contacted in the reaction section in countercurrent to generate propylene glycol monomethyl ether acetate and methanol through ester exchange reaction. The overhead material of the propylene glycol monomethyl ether catalytic rectification tower is a mixture of methyl acetate and methanol, which is sent to a methyl acetate recovery tower. The overhead of the recovery tower is azeotrope of methyl acetate and methanol, and the bottom is methyl acetate. The methyl acetate is recycled to the propylene glycol monomethyl ether catalytic rectification tower for repeated use, and the azeotrope of methyl acetate and methanol is recycled to the propylene catalytic rectification tower to participate in the synthesis of propylene glycol monomethyl ether, thereby effectively utilizing methanol and improving the atomic economy of the process. The bottom material of the propylene glycol monomethyl ether catalytic rectification tower is propylene glycol monomethyl ether acetate and a small amount of unreacted propylene glycol monomethyl ether, which is sent to a propylene glycol monomethyl ether acetate refining tower. A small amount of unreacted propylene glycol monomethyl ether is obtained at the top of the tower, and high-purity propylene glycol monomethyl ether acetate is obtained at the bottom of the tower.

[0044] Example 1

[0045] Under the condition that the molar ratio of propylene glycol monomethyl ether to methyl acetate is 1:5, the propylene glycol monomethyl ether enters the tower from the upper end of the reaction section and the methyl acetate enters the tower from the lower end of the reaction section at room temperature. The pressure of the catalytic rectification tower is atmospheric pressure, the reaction section temperature is 108 ℃, the overhead temperature is 53.1 ℃, the bottom temperature is 145.2 ℃, and the reflux ratio is 5:1. After the reaction, the composition of the catalytic rectification tower overhead and the bottom is analyzed by gas chromatography, and the analysis results are shown in Table 1. Through calculation, the conversion rate of propylene glycol monomethyl ether can reach 95.03%, and the selectivity of propylene glycol monomethyl ether acetate is 100%.

[0046] Table 1

[0047]

[0048] Example 2

[0049] Under the condition that the molar ratio of propylene glycol monomethyl ether to methyl acetate is 1:6, the propylene glycol monomethyl ether enters the tower from the upper end of the reaction section and the methyl acetate enters the tower from the lower end of the reaction section at room temperature. The pressure of the catalytic rectification tower is atmospheric pressure, the reaction section temperature is 105 ℃, the overhead temperature is 53.5 ℃, the bottom temperature is 147.2 ℃, and the reflux ratio is 5:1. After the reaction, the composition of the catalytic rectification tower overhead and the bottom is analyzed by gas chromatography, and the analysis results are shown in Table 2. Through calculation, the conversion rate of propylene glycol monomethyl ether can reach 99.95%, and the selectivity of propylene glycol monomethyl ether acetate is 100%.

[0050] Table 2

[0051]

[0052] Example 3:

[0053] The propylene glycol monomethyl ether and methyl acetate are fed at room temperature with a molar ratio of 1:7, the propylene glycol monomethyl ether is fed into the tower from the upper end of the reaction section, and the methyl acetate is fed into the tower from the lower end of the reaction section. The pressure of the catalytic rectification tower is atmospheric pressure, the reaction section temperature is 100 DEG C, the tower top temperature is 53.9 DEG C, the tower bottom temperature is 147.2 DEG C, and the reflux ratio is 5:1. After the reaction, the compositions of the catalytic rectification tower top and tower bottom are analyzed by gas chromatography, and the analysis results are shown in Table 3. Through calculation, the conversion rate of the propylene glycol monomethyl ether can reach 99.95%, and the selectivity of the propylene glycol monomethyl ether acetate is 100%.

[0054] Table 3

[0055]

[0056] The advantages of the present application are that the propylene glycol monomethyl ether and methyl acetate raw materials with significant boiling point difference are fed from the upper end and the lower end of the reaction section respectively, the reaction area is fully utilized by adopting the form of combination of catalytic elements and cyclone trays, the reaction products are continuously separated from the reaction system through the continuous catalytic rectification process, the complete conversion of the propylene glycol monomethyl ether raw material is realized, and the conversion rate of the propylene glycol monomethyl ether can reach more than 99.9%. The advantages of using a solid base as a catalyst are that the problems of serious equipment corrosion and the inability to recycle the catalyst caused by the homogeneous catalyst are overcome; compared with the solid acid, the metal oxide catalyst has a large treatment capacity and high selectivity, the selectivity of the propylene glycol monomethyl ether acetate can reach 100%, the steps of subsequent product purification and refining are reduced, and the production cost of the process is reduced. The process is easy to operate, the raw material conversion rate and the product selectivity are high, there is no byproduct impurity, the process is green, clean and efficient, and the industrialized production is easy.

[0057] If the present application discloses or involves mutually fixed connecting parts or structural parts, unless otherwise stated, the fixed connection can be understood as: detachable fixed connection (for example, connected by using bolts or screws), and can also be understood as: non-detachable fixed connection (for example, riveting, welding), of course, the mutual fixed connection can also be replaced by an integral structure (for example, manufactured by using a casting process to form integrally) (except for obviously unable to use an integral forming process).

[0058] In addition, the terms used to represent the position relationship or shape in any of the technical solutions disclosed in the present application include the approximate, similar or close state or shape, unless otherwise stated.

[0059] Any component provided by the present application can be assembled from multiple individual components, or can be a single component manufactured by an integral forming process.

[0060] It should be noted that the above examples are only used to illustrate the technical solutions of the present application but not to limit the present application; although the present application has been described in detail with reference to the preferred embodiments, it is understood by those skilled in the art that the specific embodiments of the present application can be modified or some technical features can be replaced by equivalent ones; without departing from the spirit of the technical solutions of the present application, all of them should be covered in the technical solution range of the present application claimed by the present application.

Claims

1. A process for the continuous catalytic rectification ester interchange production of propylene glycol monomethyl ether acetate, characterized by: The process comprises the following steps: Step S1: In the propylene oxide catalytic rectification tower, propylene oxide reacts with methanol to produce monomethyl ether glycol, and then the monomethyl ether glycol is sent to the monomethyl ether glycol catalytic rectification tower to react with methyl acetate to produce monomethyl ether glycol acetate; Step S2: The mixture of methyl acetate and methanol obtained from the top of the monomethyl ether glycol catalytic rectification tower is sent to the methyl acetate recovery tower for separation, the methyl acetate and methanol azeotrope from the top of the methyl acetate recovery tower is recycled to the propylene oxide catalytic rectification tower to fully utilize the methanol, and the methyl acetate from the bottom of the methyl acetate recovery tower is recycled to the monomethyl ether glycol catalytic rectification tower to participate in the reaction; Step S3: The monomethyl ether glycol acetate and a small amount of monomethyl ether glycol obtained from the bottom of the monomethyl ether glycol catalytic rectification tower are separated in the monomethyl ether glycol acetate refining tower, the monomethyl ether glycol from the top of the monomethyl ether glycol acetate refining tower is recycled to the monomethyl ether glycol catalytic rectification tower, and the monomethyl ether glycol acetate product with high purity is obtained from the bottom of the monomethyl ether glycol acetate refining tower; The loading method in the reaction section of the propylene oxide catalytic rectification tower and the monomethyl ether glycol catalytic rectification tower is that the composite metal oxide solid alkaline catalyst particles are loaded in the catalytic element and are fixed horizontally on the cyclone tray.

2. A process for the production of propylene glycol monomethyl ether acetate by continuous catalytic rectification interesterification as claimed in claim 1, wherein: In step S1, in the propylene oxide catalytic rectification tower, propylene oxide and methanol are respectively fed from the lower end and the upper end of the reaction section of the propylene oxide catalytic rectification tower, and the ring-opening reaction of propylene oxide and methanol is carried out under the action of the metal oxide catalyst in the reaction section to produce monomethyl ether glycol.

3. A process for the production of propylene glycol monomethyl ether acetate by continuous catalytic rectification interesterification as claimed in claim 1, wherein: In step S2, in the monomethyl ether glycol catalytic rectification tower, monomethyl ether glycol and methyl acetate are respectively fed from the upper end and the lower end of the reaction section of the monomethyl ether glycol catalytic rectification tower, the monomethyl ether glycol obtained from the separation of the monomethyl ether glycol acetate refining tower is sent into the monomethyl ether glycol catalytic rectification tower together with the monomethyl ether glycol, and the methyl acetate obtained from the separation of the methyl acetate recovery tower is sent into the tower together with the methyl acetate, and the transesterification reaction of monomethyl ether glycol and methyl acetate is carried out under the action of the metal oxide catalyst in the reaction section to produce monomethyl ether glycol acetate and methanol.

4. A process for the production of propylene glycol monomethyl ether acetate by continuous catalytic rectification interesterification as claimed in claim 1, wherein: In step S1, in the propylene oxide catalytic rectification tower, propylene oxide and methanol are countercurrently contacted in the reaction section to generate propylene glycol monomethyl ether PM, the light component propylene oxide is totally refluxed at the top of the tower, the reaction generated propylene glycol monomethyl ether and the acetic acid methyl ester not participating in the reaction are taken out from the tower bottom and transported to the propylene glycol monomethyl ether catalytic rectification tower; in the propylene glycol monomethyl ether catalytic rectification tower, the propylene glycol monomethyl ether is countercurrently contacted with the acetic acid methyl ester in the reaction section to generate propylene glycol monomethyl ether acetate and methanol, the acetic acid methyl ester and the methanol form an azeotrope, the azeotrope and the excess acetic acid methyl ester are obtained at the top of the propylene glycol monomethyl ether catalytic rectification tower, and the propylene glycol monomethyl ether acetate and a small amount of unreacted propylene glycol monomethyl ether are obtained at the tower bottom.

5. A process for the production of propylene glycol monomethyl ether acetate by continuous catalytic rectification interesterification as claimed in claim 1, wherein: In step S3, the acetic acid methyl ester recovery tower is used to separate the components at the top of the propylene glycol monomethyl ether catalytic rectification tower, after the separation, the acetic acid methyl ester and methanol azeotrope obtained at the top of the acetic acid methyl ester recovery tower is recycled to the propylene oxide catalytic rectification tower to continue participating in the reaction to fully utilize the methanol, and the acetic acid methyl ester obtained at the tower bottom is recycled to the propylene glycol monomethyl ether catalytic rectification tower to continue participating in the reaction.

6. A process for the production of propylene glycol monomethyl ether acetate by continuous catalytic rectification interesterification as claimed in claim 1, wherein: The composite metal oxide solid alkali catalyst comprises one or more of a metal oxide, a supported metal oxide and a composite metal oxide.

7. A process for the production of propylene glycol monomethyl ether acetate by continuous catalytic rectification interesterification as claimed in claim 6, wherein: The carrier of the supported metal oxide comprises activated carbon, alumina, silicon oxide, molecular sieve and hydrotalcite; the metal oxide catalyst is a solid particle with a size of 1-10 mm, and the active component thereof is selected from oxides of at least one metal element selected from Be, Mg, Ca, Sr and Ba.

8. A process for the production of propylene glycol monomethyl ether acetate by continuous catalytic rectification interesterification as claimed in claim 1, wherein: The feeding mode of the propylene glycol monomethyl ether catalytic rectification tower satisfies that the molar ratio of the acetic acid methyl ester to the propylene glycol monomethyl ether is within 1:1-8:1, and the temperature of the reaction section is 80-100 ℃.

9. A process for the production of propylene glycol monomethyl ether acetate by continuous catalytic rectification interesterification as claimed in claim 1, wherein: The reflux ratio of the propylene oxide catalytic rectification tower is 5, the operating pressure is normal pressure, the top temperature is 53.0-54.5 ℃, and the bottom temperature is 145.5-147.5 ℃.

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