WO2022166540A1 - Process method for preparing glycol maleate - Google Patents

Abstract

Disclosed in the present invention is a process method for preparing glycol maleate. The process method comprises the following steps: (1) performing a pre-esterification reaction on maleic anhydride and lower aliphatic alcohol in a pre-esterification reactor, so as to obtain a mixture of corresponding water, alcohol, monoalcohol maleate, glycol maleate and a small amount of maleic anhydride; and (2) performing flash evaporation and rectification on the reaction mixture generated by the pre-esterification reaction, then performing reactive rectification on the reaction mixture and corresponding lower aliphatic alcohol under the catalysis of acidic resin, and completing esterification, so as to obtain the desired glycol maleate. Compared with the prior art, the process method for preparing glycol maleate of the present invention has less process pollution, low energy consumption, high product yield and stable operation of the whole process, avoids the over-temperature on a tray of a reaction rectification column, and prolongs the service life of a catalyst.

Description

A kind of technological method of preparing maleic acid glycol ester technical field

The invention relates to the technical field of fine chemicals and polymer monomer synthesis, in particular to a synthetic process method and route for preparing maleic acid glycol ester.

Background technique

Dimethyl maleate (DMM), Diethyl Maleate (DEM) and Dipropyl Maleate (DPM) are the most representative of maleic acid glycol esters. ), the first two are important fine chemical raw materials. The production process and methods of other maleic acid glycol esters are basically similar to the first two. In existing articles and patents, DMM and DEM are basically used as representatives to introduce their process routes and methods. Dimethyl maleate (DMM) is a colorless viscous liquid with a boiling point (1.0bar) of 200.4°C, a melting point of 19.0°C and a relative density (25°C) of 1.1462g/cm ³ . It is used for the production of paints, coatings and adhesives. , pesticides, water purifiers, optical materials, anti-shrinkage finishing agents and anti-rust additives and other important chemical raw materials, the domestic and foreign demand for dimethyl maleate is increasing.

The traditional production method of dimethyl maleate mostly adopts maleic anhydride as raw material, and carries out esterification reaction with methanol under the catalysis of sulfuric acid or p-toluenesulfonic acid. Although the production process has high catalytic activity and low price of the catalyst , but there are many side reactions, the product is easily isomerized into dimethyl fumarate DMF, the equipment is seriously corroded, and the follow-up treatment is complicated. The traditional process is semi-continuous, generally a reaction kettle and a matching reactive distillation column are used as the reaction device, and the water and excess alcohol produced by the reaction are distilled off while the reaction is completed, and the corresponding dimethyl maleate and the catalyst are obtained. The mixture, distilled water and excess alcohol are rectified to recover valuable methanol. The mixed solution is then subjected to alkaline washing or water extraction to obtain an intermediate product after removing the catalyst. The intermediate product is further subjected to double-column rectification to achieve light and weight removal to obtain pure dimethyl maleate. This traditional production process will lose a considerable amount of dimethyl maleate during water washing or alkali washing; at least four rectification processes are involved in the traditional process, and the energy consumption is also quite high. Even so, this traditional process is still the mainstream process for the production of DMM in China because of its low technological difficulty and small equipment investment.

Dimethyl maleate is also an important organic chemical raw material, especially through catalytic hydrogenation, it can be used to produce 1,4-butanediol, tetrahydrofuran and γ-butyrolactone, so that maleic anhydride and methanol can react to produce maleic acid. The method of dimethyl acid has received great attention. This has been described in detail in many patents, such as CN87105388A, CN200410032595.5, CN87105338A, CN87105388A, EU0255399A2, WO90/08127, US4795824, US4751334, WO88/00937, US4584419, etc.

Davy Mckee has developed a maleic anhydride esterification process using methanol as an esterification agent. The advantages of this process are: the use of catalyst reactive distillation process, the separation of methanol and water after esterification becomes easy; the volatility of dimethyl maleate is increased, and the operating range of gas-phase hydrogenation is widened; The esterification conversion rate of enedioic anhydride is as high as 99.5%, no need to recycle unreacted maleic anhydride and monomethyl maleate, only methanol is recycled; the process is simplified, and the total project investment is reduced by about 15%. Since 1987, a series of patents have been published for the aforementioned route developed by the British company Davy Mckee. Although this technology has certain advanced nature, it also has its limitations. Specifically, the British Davy Mckee Company transferred several sets of equipment from several Chinese companies, none of which are still driving. In addition to market changes and the reasons for the loss of competitiveness of the process, the defects of some of the technology are also one of the reasons for its failure. The specific reasons are: the process of the esterification process of maleic anhydride (MAH) and methanol is not described in depth, and the reaction process and heat release of the two-step esterification reaction are not deeply understood, resulting in the operation of the equipment during the operation. Poor performance; local hot spots in the catalyst bed due to reaction exotherm cannot be effectively controlled, acid resin catalysts are easily deactivated due to over-temperature deacidification, and the acid resin catalysts used are short-lived (4-5 months); The high temperature sulfuric acid will cause strong corrosion to the column internals and catalyst mesh packaging bags of the reactive distillation column, resulting in major problems in the quality of the final product. When a company in China used Davy Mckee's technology on the device, it was found that due to the unreasonable design of part of the process, the temperature of the reactive distillation column was extremely difficult to control, resulting in the overheating of the catalyst tray, and the acidic resin on the tray. The sulfuric acid was removed, and then the sulfuric acid corroded the catalyst packaging mesh bag and the subsequent filter screen made of 316L stainless steel, causing the acidic resin with polystyrene as the skeleton to enter the next section, causing tens of millions of economic losses to the factory within a week. .

Represented by patent EU0255399A2, this patent describes their process route in detail by taking maleic anhydride (MAH) esterification to produce diethyl maleate as a specific example. The purpose is to produce diethyl maleate by esterification of maleic anhydride, and then hydrogenation to produce BDO, tetrahydrofuran and γ-butyrolactone. In this process, maleic anhydride and excess ethanol are mixed to carry out esterification reaction to first generate maleic acid monoethyl ester. The monoesterification reaction is carried out under the conditions of 0.1 MPa and 50-80° C. without catalyst, and the yield is 99%. The monoethyl ester is further reacted with ethanol for diesterification to generate diethyl maleate. In this step, a catalyst distillation process is adopted, and a solid acid ion exchange resin is used as a catalyst. Excess ethanol and water are removed from the reactor by rectification, and the generated diethyl maleate gas is further purified by distillation, and the unreacted monoethyl ester is removed and recycled to the reactor. By-products, which account for 1% of the total product, can be removed by combustion. The excess ethanol recovered from the reaction part is rectified to remove water, and then mixed with the ethanol recycled from the product rectification and returned to the esterification reactor. Although the technology is somewhat advanced, it also has the same limitations as the company's other series of patents.

The Chinese patent has CN103360252B, and the first paragraph of its technology is modeled on the technology of Davy Mckee Company of the United Kingdom. The first monoester reactor has a temperature of 110-130° C., a pressure of 0.85-0.95 Mpa, the feeding molar ratio of maleic anhydride/methanol is 2-3, and the residence time is 0.01-0.09h. This process route is in fact inappropriate and cannot solve the most fundamental and fatal problems accompanying the Davy process. The double esterification reactor proposed in this patent is divided into multiple sections, 1-4 fixed beds, the top temperature is 80-130°C, the pressure is 0.15-0.25Mpa; the bottom temperature is 160-180°C, the pressure is 0.2-0.4Mpa, and the residence time is 0.02 ~0.08h. The fixed bed reaction temperature is 80～180℃, and the pressure is 0.1～0.5Mpa. The second stage seems reasonable and is different from the British Davy Mckee company, but for a two-stage reversible esterification dehydration reaction, this design is not practical at all: only a four-stage reaction equilibrium is impossible achieve its stated reaction progress (conversion rate) and effect. The patent does not have a practical case of industrialization in China or even in the world.

The patent CN102908955B and the patent CN102911053B of a Chinese company have also been authorized in China, but the process and reaction conditions described in this patent are far from the real reaction between maleic anhydride and methanol. Neither of these two patents mentions that the first and second steps of the esterification reaction of maleic anhydride and methanol do not exist in isolation, and both have their specific equilibrium. The design of the monoesterification reactor is unreasonable, and the calculation and design of the heat release of the reaction are inconsistent with the actual situation, and it is unavoidable that excessive heat release of the esterification reaction occurs too much on the tray of the reactive distillation column containing the acid resin. Therefore, it is unavoidable that the acid resin catalyst is deactivated due to over-temperature deacidification, and the dilute sulfuric acid removed from the catalyst will strongly corrode the column internals and the catalyst mesh stainless steel packaging bag in the reactive distillation column at high temperature. Both of these two patents propose new improvements to the tray design of the reactive distillation column, the catalyst and the catalyst filling, but their applications are also limited due to the unresolved fundamental problems. The fact is: the patent does not have an actual industrialized case of industrialization in China or even in the world.

The Chinese patent CN107473966A proposes to absorb the maleic anhydride in the middle of the n-butane process and the benzene process maleic anhydride reaction mixture with DMM, the final reaction product of maleic anhydride and methanol, and then learn from the technology of Davy Mckee Company in the United Kingdom, with its mixture and Methanol and other alcohols react to generate dimethyl maleate, DMM, etc. The technology described in this patent seems reasonable, but in fact there is a fatal problem: in traditional processes, dibutyl phthalate DBP (or dibutyl cyclohexanedioate) is used as an absorbent in the production of maleic anhydride. The biggest feature of DBP is that it can dissolve the maleic anhydride produced by the partial oxidation of n-butane and benzene, and is incompatible with the by-product water. Because the production of maleic anhydride, n-butane and benzene are also partially oxidized to generate a large amount of water. The DMM and water used as the absorbent in this patent are partially miscible. Although DMM will be layered with the water phase, the DMM dissolved in the water layer is not only difficult to recover, but also increases the system wastewater discharge and treatment difficulty. DMM oil The phase also contains water, which increases the difficulty of rectification. Therefore, the patent is not engineering feasible.

Chinese patent CN102070448B, "a method for preparing dimethyl succinate", the process of their first step of synthesizing the DMM section of dimethyl maleate basically imitated the process of Davy Mckee Company. But what they changed was that the first step pre-esterification used a fixed bed and an acidic resin catalyst. Different from Davy Mckee's process, its second step reactive distillation section was basically the same as the Davy process. We repeated their experiments according to their examples and found that the results of the examples were not reproducible. In addition: in the first step pre-esterification reaction of maleic anhydride and methanol, the equilibrium ratio is also inconsistent with the example; and the first step of maleic anhydride and methanol pre-esterification exothermic heat is very large. In this patent, a fixed bed reactor is used for the first stage of pre-esterification, and it is described that the reaction temperature is 60～90℃, the pressure is 0.2～0.8Mpa, the acid anhydride/methanol (molar ratio)=2～6, and the maleic anhydride space velocity is 0.5 ~1h ^-1 ; the conversion rate of maleic anhydride reaches over 95%, and the conversion rate of DMM, the representative product of the reaction process, is over 87%. According to our experimental data and theoretical simulations, such conversion and selectivity are not only impossible, but the adiabatic temperature rise of the reactor in the fixed bed will also be above 120 °C, and the temperature of the reaction mixture will be in the absence of heat transfer and material vaporization. The temperature will fly above 180°C. According to the several acidic resins mentioned in the patent and used in its examples, none of them can withstand temperatures above 140°C. Therefore, it can be determined that the process described in its patent, producing dimethyl maleate DMM from maleic anhydride and methanol, and then selectively hydrogenating it is not feasible.

The applicant of the present patent proposed the use of maleic anhydride (MAH), hydrogen (H ₂ ) and 1, 4 butanediol in the application publication number "CN110563933 A" of the original application of "a kind of ultra-high molecular weight PBS and its preparation method" (BDO) is a new route for the three-step production of polybutylene succinate PBS as the main raw material. The route is (1) esterification of maleic anhydride and lower aliphatic alcohol to obtain diol maleate; (2) selective hydrogenation of the diol maleate obtained in step (1), obtaining diol succinate; (3) performing transesterification and polycondensation of the diol succinate obtained in step (2) and aliphatic diol to obtain the desired ultra-high molecular weight PBS. Maleic anhydride and BDO are in a state of overcapacity in China and even in the world, and there are abundant sources of raw materials. Therefore, the process route of producing PBS with maleic anhydride, hydrogen and BDO as raw materials is the most feasible and can solve the white pollution caused by traditional plastics in China and even the world, and is the most promising process route. In this process route, maleic anhydride and lower aliphatic alcohol are used for esterification to obtain diol maleate, which is the first stage of the latter two-step reaction and the basis of the latter two steps. Optimized for large-scale industrial production.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide a process method for preparing diol maleate with little process pollution, low energy consumption and high product yield, aiming at the current situation of the prior art.

The technical scheme adopted by the present invention to solve the technical problem is "a process method for preparing diol maleate", which is characterized in that it comprises the following steps:

(1) maleic anhydride and lower fatty alcohol carry out pre-esterification reaction in the pre-esterification reactor to obtain the mixture of corresponding water, alcohol, maleic acid monoalcohol ester, maleic acid glycol ester and a small amount of maleic anhydride;

(2) flashing and rectifying the mixture produced by the pre-esterification reaction, and then complete the esterification with the corresponding lower aliphatic alcohol by reactive distillation under the catalysis of the acidic resin to obtain the desired diol maleate .

Wherein, taking the reaction of maleic anhydride and methanol as an example, the reaction equation that above-mentioned maleic anhydride and lower aliphatic alcohol carry out monoesterification and diesterification are as follows:

(1)

(2)

Both the two steps of the esterification reaction are reversible reactions, in which both the reaction (1) and the reaction (2) can occur without a catalyst, but usually the reaction (2) is performed with a catalyst and a reactive distillation process. It can be done quickly and thoroughly. Reaction (2) needs to use the process of reactive distillation to distill out the water and remaining alcohol produced by the reaction to obtain a higher content of dimethyl maleate (DMM). The esterification of alcohols such as ethanol and propanol with maleic anhydride and methanol is similar to the esterification reaction of maleic anhydride and methanol, and the corresponding maleic diol esters such as diethyl maleate (DEM) and dipropyl maleate (DPM) can also be obtained. Wait. The traditional processes of these esterification reactions generally use sulfuric acid, p-toluenesulfonic acid and other acid catalysts, the reaction temperature is 90-140 ° C, the reaction pressure is 0.1-1.6 Mpa absolute pressure, and the reaction device includes an esterification pre-reactor, an intermediate flash evaporation Rectification column, reactive rectification column, alcohol-water separation rectification column and product rectification column, etc.

The traditional process generally takes sulfuric acid or p-toluenesulfonic acid as a catalyst, and takes a reaction kettle and a reaction distillation column that is allocated as a reaction device to complete the reaction (1) and the reaction (2), and simultaneously steam the reaction (2) to produce The water and excess alcohol are obtained to obtain the corresponding mixture of diol maleate and catalyst, and the mixture of distilled water and excess alcohol is rectified to recover valuable fatty alcohol. The mixed solution is then subjected to alkaline washing or water extraction, and then an intermediate product is obtained. The intermediate product is further de-lighted and de-weighted by double-column rectification to obtain pure maleic acid glycol ester. This traditional production process generally uses more polluting and corrosive sulfuric acid or p-toluenesulfonic acid as a catalyst; a considerable amount of maleic acid glycol will be lost during water washing or alkali washing; at least four catalysts are involved in the traditional process. Distillation process, energy consumption is quite high. Although the traditional process can obtain pure products, it is obviously not the optimal process path. While learning from and summarizing traditional processes, we developed a new process path for the production of diol maleate through experiments and process simulation, realizing the continuous production of diol maleate and solving the pollution of traditional processes. Large, high energy consumption and low product yield problems.

In order to reduce the temperature of the material and prevent the material from continuing to react and exothermic damage to the resin catalyst due to overheating on the next tray, it is necessary to flash the product of the pre-esterification reaction first. The first solution is: in the step (2) A reactive distillation column with a flash section is used for flash distillation and reactive distillation. The reactive distillation column is divided into three sections. The upper section is a stripping section for methanol and water, and the temperature is controlled between 80 and 100 °C. The middle section is the flashing section of the reaction mixture, the temperature is controlled and distributed between 220 and 100 ° C from top to bottom, and the lower section is a plurality of trays arranged in sequence from top to bottom, and the temperature is controlled and distributed between 100 and 130 ° C, At least 6 trays are filled with macroporous acid resin catalyst, in this reactive distillation column, the mixture produced by pre-esterification flows from top to bottom, and the water produced by lower aliphatic alcohol and diesterification is in gaseous state from the bottom. And upstream flow. The second scheme is: in the step (2), a flash distillation column and a reactive distillation column are used to carry out flash distillation and reactive distillation respectively, and the reactive distillation column is divided into two sections, and the lower section is composed of a plurality of The lower trays are arranged in sequence, and the temperature is controlled between 100 and 130°C. At least 6 trays are filled with macroporous acidic resin catalysts. In the reactive distillation column, the pre-esterification reaction mixture flows from top to bottom. , the lower aliphatic alcohol and the water produced by the further esterification reaction flow countercurrently from bottom to top in a gaseous state. The operating pressure of the flash distillation column is 0.1-0.5Mpa, and the temperature is controlled between 90-130°C.

Both schemes are beneficial to make the whole process simple and easy to operate in the process of producing diol maleate, and further enable each section of the process to operate smoothly and avoid uncontrollable fluctuations. Compared with the first scheme, the second scheme adds a flash distillation column. Although the investment is increased, the total number of trays of the reactive distillation column is reduced, the height of the column is reduced, and the reaction concentration is reduced. The cost and difficulty of making the distillation column. At the same time, due to the low temperature of the material entering the reactive distillation column, the difficulty of operation is reduced, the operation of the entire column is simpler and more stable, the possibility of over-temperature of the catalyst tray is reduced, and the deacidification of the catalyst due to over-temperature is further reduced. risk, which is beneficial to prolong the life of the catalyst.

In order to facilitate the reaction and heat exchange between the upper superheated methanol vapor and the liquid material mainly composed of maleic acid glycol ester in the lower part, and avoid the overheating of the tray to damage the catalyst, in the tray, at least two trays located at the bottom are not filled with catalyst.

Preferably, the operating pressure of the reactive distillation column is 0.1-0.5Mpa.

In order to recover the lower aliphatic alcohol, the corresponding lower aliphatic alcohol and the water produced by the diesterification reaction are distilled from the top of the reactive distillation column, and then separated in the alcohol recovery column, and the obtained lower aliphatic alcohol is recycled.

In order to further purify the product, the reactant obtained at the bottom of the reactive rectification tower is subjected to double-column rectification to achieve delight and weight removal to obtain maleic acid glycol ester with a purity of more than 99.5%.

In order to make full use of the heat released by the pre-esterification reaction, the pre-esterification reactor is a shell-and-tube reactor, and the tube side of the shell-and-tube reactor is used for the pre-esterification reaction. The process is used for the passage of lower aliphatic alcohols. The mixture produced by the pre-esterification reaction in the tube process of the shell-and-tube reactor is sent to the upper part of the reactive distillation column, or after flash distillation and then enters the corresponding reactive distillation column. The lower aliphatic alcohol in the shell side of the shell reactor is vaporized to remove the heat released by the pre-esterification reaction and then sent to the lower part of the reactive distillation column.

Preferably, the molar ratio of maleic anhydride and fatty alcohol in the tube side of the shell-and-tube reactor is 1:1.5-4, the reaction temperature is 60-220°C, the reaction pressure is 0.1-1.6MPa, and the reaction time is 0.1-8h; The temperature of the shell fatty alcohol of the shell-and-tube reactor is 80-200°C, the reaction pressure is 0.1-1.6Mpa, and the vapor-liquid equilibrium vaporization of the corresponding alcohol at this temperature can be maintained, and the corresponding amount is sufficient to remove the reaction generated The heat shall prevail.

Preferably, the lower aliphatic alcohol is at least one of methanol, ethanol, propanol and butanol.

Compared with the prior art, the advantages of the present invention are:

(1) The technical route of the present invention is to use maleic anhydride as the initial raw material to produce diol maleate, and the raw material of maleic anhydride can be n-butane or pure benzene, and the source of raw materials is abundant, and now maleic anhydride is already a hundred and one in China. The current production capacity of 10,000-ton-level bulk chemicals in China is over 2 million tons per year, and the annual output is over 1 million tons. Various large companies are actively expanding production; their sources are also very rich; The DMM demand required for PBS with more than one million tons provides a basic guarantee;

(2) by technological process optimization, let pre-esterification reaction exotherm carry out pre-heating and vaporization to the alcohols that follow-up esterification reaction needs, be conducive to the comprehensive utilization of energy into the whole process, realize the maximum utilization of energy;

(3) in the operational route of the present invention, the addition ratio of alcohol in the maleic anhydride first esterification section is improved, the reaction temperature and the reaction pressure are improved, the reaction time is prolonged, and the two-step reaction is carried out lower, so as to be beneficial to reach as far as possible In its equilibrium state, it is possible to avoid the excessive occurrence of the monoesterification reaction with a large exothermic heat and the diesterification reaction with the same exothermic heat on the trays in the subsequent reactive distillation column, reducing the excess heat caused by the reaction in the later stage. The possibility of deacidification of the acid resin on the tray caused by the temperature reduces the deactivation of the catalyst, which is beneficial to prolong the life of the catalyst, and at the same time reduces the corrosion of the equipment by the sulfuric acid removed by the catalyst overheating.

Description of drawings

Fig. 1 is the structural representation of the reaction device of the maleic acid glycol ester adopted in the embodiment of the present invention C2;

FIG. 2 is a schematic structural diagram of the reaction device of the maleic acid glycol ester adopted in Example C1 of the present invention.

Detailed ways

The present invention will be further described in detail below with reference to the embodiments of the accompanying drawings.

As shown in Figure 1, the present invention uses maleic anhydride and methanol as reaction raw materials to produce dimethyl maleate (DMM) as an example to introduce our newly invented process route.

Taking the reaction of maleic anhydride and methanol as an example, the reaction is divided into two steps; the pre-esterification of the first step includes the monoesterification reaction (1) and the diesterification reaction (2), both of which are exothermic and reversible reactions, The reaction equation is:

(1)

(2)

Pipeline 1 is the liquid maleic anhydride from the production system, the temperature is 60℃～220℃, the pipe 2 is the methanol recovered by the alcohol recovery tower, the temperature is 35～60℃, the mixed material 4, the temperature is 60～160℃, The pressure is 0.1-1.6Mpa, and the molar ratio of maleic anhydride and methanol is between 1:1.5-4, preferably 1:2-3. The initial stage of the reaction uses methanol from the methanol storage tank via the pump 10 via the branch line 7 of the line 5 . The methanol used in this system is all methanol with purity >99.5% and water content <0.5%, including methanol after rectification in alcohol recovery rectification column. The material 4 enters the tubular reactor 9, and the mixture of maleic anhydride and methanol is carried on the tube side; the shell side is methanol, and the pressure is 0.3-1.6Mpa. The two-step reaction of producing dimethyl maleate with maleic anhydride and methanol as reaction raw materials is an exothermic and reversible reaction, and the exothermic heat is removed by the vaporization of methanol in the shell side. After the material enters the 9th tube pass of the reactor, the reaction temperature is 60-220°C, the pressure is 0.1-1.6Mpa, and the reaction residence time is 0.1-8h, in order to facilitate the reaction to proceed completely and consume as much maleic anhydride as possible, and the reaction (2) is also As close as possible to the chemical reaction equilibrium point.

Excessive methanol is added in this process section, which increases the reaction temperature and reaction pressure, and prolongs the reaction time, in order to make the reaction proceed faster and more thoroughly. Therefore, excessive occurrence of the monoesterification reaction (1) with a large exothermic heat and the diesterification reaction (2) with the same exothermic heat in the subsequent reactive distillation column can be avoided. This further reduces the possibility of deacidification of the acidic resin caused by the reaction exotherm and over-temperature when the catalyst is used later, reduces the deactivation of the catalyst, and is beneficial to prolong the life of the catalyst. Because the catalyst used in the reactive distillation column is generally a sulfonic acid resin catalyst, when the temperature is above 130 °C, the sulfonic acid resin catalyst will react with water to remove some sulfonic acid groups to generate sulfuric acid. A large amount of sulfuric acid is removed from the inside, causing the catalyst to deactivate, and the removed sulfuric acid will also corrode the equipment. The flow rates of the reaction lines 2, 3, 5, 6 and 7 in this process section are controlled cooperatively to facilitate the adjustment of the molar ratio of maleic anhydride and methanol and the required amount of vaporized methanol for the reaction exotherm.

Via the reaction mixture after the reactor 9, the mixture containing water, methanol, monomethyl maleate and dimethyl maleate and a small amount of maleic anhydride enters the upper part of the reactive distillation column 12 via the pipeline 8, and the vaporized methanol passes through the pipeline 11. After adiabatic expansion, it enters the lower part of the reactive distillation column 12 . The reactive distillation column is divided into three sections, the upper section is the stripping section for methanol and water, the middle section is the flashing section of the reaction mixture in pipeline 8, and the lower section is a plurality of catalyst trays filled with macroporous acid resin catalysts. The liquids whose main components are monomethyl maleate and dimethyl maleate flow down from the top, methanol and the water produced by the reaction flow countercurrently from bottom to top in a gaseous state, and the reaction of the second step occurs on each tray, The residence time of the liquid reaction is 0.5-4h, and the specific time is determined according to the type of the macroporous acid resin catalyst, the relevant reaction kinetic data and the design of the reactive distillation column. When the reaction solution reaches the tray at the bottom of the column 12 that is not loaded with the catalyst, it contacts pure methanol vapor. The reaction progress of the entire reactive distillation column material under the action of the catalyst reaches more than 99.5%, the content of the liquid material dimethyl maleate is more than 95%, and the rest are methanol, reaction by-products and traces of maleic anhydride and malic acid. Monomethyl methanoate.

The pressure of the reactive distillation column 12 is controlled at 0.1～0.5Mpa, the temperature of the stripping section of methanol and water is controlled at 80～100°C, and the top distillate contains 10～20% of water, 80～90% of methanol and a small amount of The reaction by-products of dimethyl ether and traces of dimethyl maleate. The distillate is condensed in the heat exchanger 18 through the pipeline 14, and then sent to the liquid collection tank 19. Part of the distillate is refluxed to the column 12 through the pump 20, and the rest is passed through the pump 21 and then through the pipeline 22 to the methanol recovery column 23. The middle of the reactive distillation column 12 is the flashing section of the reaction mixture on several trays, and the temperature is controlled to be distributed at 220-100°C. The lower section of reactive distillation tower 12 is a catalyst tray, and the temperature is controlled at 100 to 130° C. The 2 to 4 trays at the bottom are not loaded with catalysts, so as to facilitate the upward flow of superheated methanol steam and maleic acid glycol esters in the lower part. The liquid material reacts and exchanges heat to avoid damage to the catalyst due to overheating of the tray. The bottom of the reactive distillation column 12 is equipped with a reboiler 17 (temperature 130-150° C.), which uses medium-pressure steam to control the temperature of the entire column body. The bottom liquid is the main mixture of dimethyl maleate, the molar content of DMM is more than 95%, and the rest are dissolved methanol, reaction by-products and trace amounts of maleic anhydride and monomethyl maleate. The mixed liquor is pumped out of the system via line 13 to heat exchanger 15 and then to pump 16. The mixture is subjected to classic double-column rectification (not shown in the figure) to obtain dimethyl maleate DMM with a purity of >99.5%. The light components are returned to the methanol recovery tower through pipeline 36. After the heavy components are taken and partially discarded, Partial reuse is returned to the system via pipe 1.

The materials in pipeline 36 and pipeline 22 enter methanol recovery tower 23, the temperature is controlled at 60～120℃, and the pressure is controlled at 0.1～0.2Mpa. The top of the tower is the steam of methanol and by-product dimethyl ether DME, which is sent to the heat exchanger 29 through the pipeline 25 and to the sump 30, and part of the reflux liquid is formed through the pump 31, and the non-condensable gas (mainly dimethyl ether and tetrahydrofuran, etc.) ), recovered through 32 after freezing and condensing. The methanol at the top of the column is extracted through the pipeline 26, and is further divided into the pipeline 2 and the pipeline 3 through the heat exchanger 27 to the pump 28 to form the methanol reuse. There is a reboiler 33 at the bottom of the tower, which uses low-pressure steam; the liquid at the bottom of the kettle is waste water with a concentration of more than 99.5%, and contains <0.5% of dimethyl maleate DMM, after the heat exchanger 34, the pump 35 is sent to the biochemical treatment pool. Dimethyl maleate DMM is a biodegradable organic matter, and the wastewater treatment pressure is small.

Fig. 2 also utilizes maleic anhydride and methanol as reaction raw materials to produce dimethyl maleate process route, and the difference from Fig. 1 is that Fig. 2 adds a flash distillation column 37. The reaction mixture containing water, methanol, monomethyl maleate and dimethyl maleate and a small amount of maleic anhydride after the tube-pass reaction of the tubular reactor 9, the flash distillation column 37 entering through the pipeline 8 is flashed. Steam and rectification. The water and methanol mixture at the top of the flash distillation column 37 is mixed with the water and methanol mixture from the pump 21 through the pipeline 39, and then enters the methanol recovery column through the pipeline 22. The content of water and methanol in the pipeline 39 varies according to the ratio of maleic anhydride and methanol in the tubular reactor 9 and the reaction progress, and contains 20 to 35% of water, 65 to 80% of methanol and a trace amount of maleic anhydride. Dimethyl acid. The flash distillation column 37 has the dual properties of flash distillation and rectification. The insufficient heat is provided by the low pressure steam of the bottom reboiler 40. The pressure of the flash distillation column 37 is 0.1-0.5Mpa, and the temperature of each tray is 0.1-0.5Mpa. The change is large, and the entire tower is controlled between 100 and 220 °C. The bottom material of the flash distillation column 37, after passing through the cooler 41, enters the line 38 to the reactive distillation column 12.

The reactive distillation column 12 of the process shown in Fig. 2 and the process shown in Fig. 1 is also different in structure from Fig. 1: the reactive distillation column 12 of Fig. 2 is divided into two sections, and the upper section is the stripping section of methanol and water, The lower section is a plurality of catalyst trays filled with macroporous acidic resin. The material composition of pipeline 38 entering into reactive distillation column 12 is also different from that in the flow process of Fig. 1. In Fig. 2, the pipeline 38 entering the middle and upper part of the tower is a mixture of monomethyl maleate, dimethyl maleate and a small amount of maleic anhydride. mixture at a temperature of 100-120°C.

In Figure 2, the pressure of the reactive distillation column 12 is controlled at 0.1 to 0.5 Mpa, the temperature of the stripping section of methanol and water is controlled at 80 to 100°C, and the overhead distillate contains 10 to 20% of water and 80 to 90% of methanol. And a small amount of reaction by-products dimethyl ether and traces of dimethyl maleate. The temperature of the multiple catalyst trays in the lower section of the reactive distillation column 12 is controlled at 100-130°C, and the 2-4 trays at the bottom are not loaded with catalysts, so as to facilitate the upper part of the superheated methanol steam and the maleic acid glycol ester as the catalyst. The main liquid material reacts and exchanges heat to avoid damage to the catalyst due to overheating of the tray. Compared with the process of FIG. 1, the process of FIG. 2 adds a flash distillation column 37, although the investment is increased, the total number of trays of the reactive distillation column 12 is reduced, the height of the column is reduced, and the The manufacturing cost and difficulty of the reactive distillation column 12. At the same time, due to the low temperature of the material 38 entering the reactive distillation column 12, the difficulty of operation is reduced, the operation of the entire tower is simpler and more stable, the possibility of overheating of the catalyst tray is reduced, and the overtemperature of the catalyst is further reduced. The risk of deacidification is beneficial to further prolong the life of the catalyst.

Embodiments A1-A5: Exploration of maleic anhydride/methanol molar ratio

In a 2.5L autoclave, add 4mol (392g) of maleic anhydride MAH, then add 6mol (192g) of methanol, after 3 times of 5kg nitrogen replacement, increase the reaction temperature to 110°C and maintain stirring, sampling at intervals , and detected by gas chromatography. After 8 hours of reaction, the composition of each component in the system no longer changes, which can prove that the reaction has reached an equilibrium state. Under the same reaction conditions, the reaction proceeded three times, but the molar ratio of maleic anhydride and methanol changed from 1:1.2 to 1:1.5, 1:2, 1:2.5 and 1:3, respectively, that is, the added The amount of methanol was 4.8mol (153.6g), 58mol (256g), 10mol (320g) and 12mol (384g) respectively, the reaction process was the same, and finally reached an equilibrium state. The above different MAH/methanol ratios and the equilibrium composition of the reaction (w %) see Table 1.

Table 1: Equilibrium composition (w%) of reactants with different maleic anhydride/methanol molar ratios

Example	A1	A2	A3	A4	A5
Component/molar ratio	1/1.2	1/1.5	1/2.0	1/2.5	1/3.0
Methanol (%)	5.31	4.56	5.23	14.5	22.67
water(%)	2.03	6.8	7.57	7.8	6.33
Maleic anhydride (%)	12.49	6.57	4.01	0.30	0.55
Monomethyl maleate (%)	63.89	29.12	36.50	14.8	19.76
Dimethyl maleate (%)	16.27	54.4	56.63	62.4	50.69
other(%)	0	0	0	0.20	0

As can be seen from the above table, when the molar ratio of maleic anhydride and methanol is 1:2.5, the conversion rate of dimethyl maleate is the best.

Examples B1-B5: Exploration of the first-stage esterification reaction conditions

The first-step esterification reaction is carried out in a shell-side Φ108X4 (SS304) and 7 Φ25X3 (SS316L) tubular reactors. The tube-side is filled with Φ5X5 ceramic Raschig rings (bulk density 1.2, pores rate 0.46), the circulating heat transfer oil with a fixed temperature is used as the heat transfer medium on the shell side; the maleic anhydride is melted and kept at a constant temperature of 90 °C, the feeding pump head and the pipeline are heated at 110 °C with electric tracing; methanol is kept at 50 °C, The methanol pump head and pipeline are also kept at 50°C; the pressure of the two product collection tanks of the product collection system is maintained at 1.0Mpa in the mode of nitrogen back pressure, so that the reaction can be carried out continuously. The molar ratio of maleic anhydride and methanol to be fed is 1:2.5; the reaction was carried out at 110°C and 130°C, respectively; the residence time of the reactants in the shell-and-tube reactor was 1h, 2h and 4h, and the compositions of the reaction products were listed in Table 2 together;

Table 2: Reactant composition (w%) of maleic anhydride/methanol under different temperature conditions and times

implement

condition\composition

methanol

water

maleic anhydride

MMM

DMM

other

example	(w%)	(%)	(%)	(%)	(%)	(%)	(%)
B1	110℃-1h	19.74	5.55	0.39	29.75	44.41	0.16
B2	110℃-2h	14.9	6.73	0.36	23.93	53.82	0.26
B3	110℃-4h	15.62	7.74	0.33	16.60	59.74	0.24
B4	130℃-1h	13.77	7.26	0.96	19.62	58.12	0.27
B5	130℃-2h	11.52	7.71	0.97	17.86	61.64	0.30
B6	130℃-4h	12.28	8.01	0.84	14.50	64.06	0.20

Example C1: Synthesis of Dimethyl Maleate DMM

(1) first-stage esterification reaction: with embodiment B3;

(2) flash distillation: carry out flash distillation of 4000 g of the reaction mixture obtained in the previous step under the condition of 110°C-4h; the flash distillation column used is continuous feed in the middle, the total length is one meter, and the inner diameter is one meter. It is a 25mm glass rectification column with Φ5 titanium ring wire mesh packing inside. The bottom of the flash distillation column is equipped with a 2500ml three-necked flask, which is heated by an oil bath; the whole flash distillation column is equipped with upper reflux and extraction, The feed in the middle and the discharge at the bottom are carried out by a peristaltic pump equipped with a silicone tube; the entire flash distillation column is operated at a slight positive pressure, and the temperature of the column body is 80-120 ° C. The temperature was controlled at 140°C. After steaming most of the water and methanol in the reaction mixture, finally obtaining the mixture 3100g that the main component is monomethyl maleate and dimethyl maleate is for subsequent use, and its composition is shown in Table 3;

Table 3: Composition (w%) of the product after flash distillation at 110°C-4h

Composition (w%)	Methanol (%)	water(%)	Maleic anhydride (%)	MMM(%)	DMM(%)	other(%)
110℃-4h after rectification	0.13	2.28	0.42	21.06	75.80	0.30

(3) second-stage esterification reaction: 3100 g of product after 110 ℃-4h product rectification gained in the previous step is sent into a reactive distillation column, which is a self-made, two-stage rectifying column, and the total A glass rectification tower with a length of 1.5 meters and an inner diameter of 25 mm, and a three-necked flask of 2500 ml at the bottom of the kettle, which is heated by an oil bath; the entire reactive distillation tower is equipped with upper reflux and extraction, middle and upper second section feed and bottom three-necked flask The discharge port, feeding and discharging are all carried out by a peristaltic pump equipped with a silicone tube; the DZH acid sulfonic acid resin used is first soaked and replaced with methanol for 4 times, and then wrapped tightly with 80 mesh 316 stainless steel wire mesh to make a diameter of about Columnar bag of about 25mm and height of 25mm; glass rectification column is divided into sections, and the upper section is filled with Φ5 titanium ring wire mesh packing; DZH acid sulfonic acid resin bag is filled into the lower section of rectification column, and the middle of each catalyst bag is filled with Φ5mm ceramic Raschia Ring 25mm; the bottom 100mm of the rectification column is filled with a Φ5mm ceramic Raschig ring to replace the tray without catalyst; the two sections of the rectification column are heated with electric heating belts for heat preservation and temperature control, and the upper and lower temperatures are 80 to 100 °C, respectively. 110～130℃; 3100g of the mixture of monomethyl maleate and dimethyl maleate was added dropwise from the upper part of the second-stage rectifying tower at a speed of 3ml/min; the lower part was pumped into methanol through a long glass dropper At the bottom of the three-necked flask, the flow rate is 1.2ml/min; the temperature in the three-necked flask is maintained between 130-140°C, and the entire tower is maintained in a slightly positive pressure state; through the experiment, the ratio of the material content in the 2500ml three-necked flask is tested, and then passed Fine-tune the temperature of the rectifying column and the flow rate of the upper and lower feeds to ensure that the reaction that monomethyl maleate is converted into dimethyl maleate is completed more than 99.9%; after 20 hours of reaction, the reactant of 3200g is finally obtained, wherein The content of dimethyl maleate is 97%;

(4) Refinement: the above-mentioned reaction mixture of 3200g is divided into two times, in the there-necked flask of 2500ml equipped with a simple distillation column, heated with an oil bath; first, the reaction solution is heated to 120° C. and kept stirring to steam out the light components ; Raise the temperature to 180-200 ° C again, and distill out 3000 g of dimethyl maleate DMM with a purity of > 99.7% under reduced pressure.

Example C2: Synthesis of Dimethyl Maleate DMM

(1) first-stage esterification section reaction: with embodiment B5;

(2) second-stage esterification reaction: the 130 ℃-2h gained in the above-mentioned steps is sent into the reactive distillation column without rectifying product 4000g; the reaction conditions are basically the same as the step (3) of embodiment C1, and different places There are: the reactive distillation column is divided into three sections, the second section of the rectification column is not filled with catalyst, and the ceramic Raschig ring of Φ5mm is filled with 100mm; 4000g of methanol, water, monomethyl maleate and dimethyl maleate mixture Add dropwise from the top of the second section of the rectifying column at a speed of 4ml/min, and the methanol is pumped into the bottom of the three-necked flask at the bottom of the rectifying column through a long glass dropper with a flow rate of 1.2ml/min; after 20 hours of reaction, This embodiment also obtains the reactant of 3200g at last, and wherein dimethyl maleate content is 96%;

(3) Refining: the same as step (4) in Example C1, after delighting and deweighting, 3000 g of dimethyl maleate DMM with a purity of >99.8% was also obtained.

Example D: Synthesis of Dipropyl Maleate DPM

(1) first-stage esterification reaction: select the same shell-and-tube reactor with embodiment B, the molar ratio of maleic anhydride and n-propanol is 1:2.5, and the temperature of reaction is 140 ℃, and the dual product of the product collection system The pressure of the collection tank is maintained at 0.8Mpa with the mode of nitrogen back pressure, and the retention time of the material in the reactor is 3h; finally, 5000g of product is obtained, and the composition is shown in Table 4;

Table 4: Composition (w%) of the first-stage esterification section reaction product of DPM synthesis at 140℃-3h

Composition (w%)	Propanol (%)	water(%)	Maleic anhydride (%)	MPM(%)	DPM(%)	other(%)
140℃-3h product	16.44	5.91	0.19	12.46	64.81	0.18

(2) flash distillation: the flash distillation of the first-stage esterification section reaction product of DPM synthesis is also carried out in the rectifying device of embodiment C1, and the difference is that the temperature required for the rectification is different: the tower body temperature The temperature in the bottom three-necked flask is controlled at 155°C; after steaming most of the water and propanol in the reaction mixture, the main components are monopropyl maleate and dipropyl maleate. The mixture 3950g is standby, its composition is shown in Table 5;

Table 5: Composition (w%) of DPM synthesis product after rectification at 140℃-3h

Composition (w%)	Propanol (%)	water(%)	Maleic anhydride (%)	MPM(%)	DPM(%)	other(%)
140℃-3h after rectification	0.31	2.39	0.24	15.66	81.48	0.23

(3) second-stage esterification reaction: product 3950g after the above-mentioned 110 ℃-4h product rectification of gained is realized the second-step esterification of product in the reactive distillation column used in embodiment C1; the temperature of the two-stage rectifying column 80～100℃ and 110～130℃ respectively from top to bottom, the reaction mixture was added dropwise at a rate of 5ml/min from the upper part of the second-stage rectifying column, and the inflow rate of the propanol pump was 2ml/min; the temperature in the three-necked flask was maintained Between 150 and 160 ° C, the entire tower is maintained in a slightly positive pressure state; through the experiment, the ratio of the material content in the 2500ml three-necked flask is tested, and then the temperature of the rectifying column and the flow rate of the upper and lower feeds are fine-tuned. The reaction of converting monopropyl lylate to dipropyl maleate is over 99.9% complete, and after 20 hours of reaction, 4100 g of reactant is finally obtained, wherein the content of dipropyl maleate is about 98%.

(4) Refining: the same as step (4) in Example C1, after delighting and deweighting, 4000 g of product dipropyl maleate DPM with a purity of >99.9% were also obtained.

Claims (9)

1. A kind of processing method of preparing maleic acid glycol ester is characterized in that comprising the following steps:

   (1) carry out pre-esterification reaction with maleic anhydride and lower aliphatic alcohol in pre-esterification reactor, obtain the mixture of corresponding water, alcohol, maleic acid monoalcohol ester, maleic acid glycol ester and a small amount of maleic anhydride;

   (2) flashing and rectifying the reaction mixture produced by the pre-esterification reaction, then complete esterification with corresponding lower aliphatic alcohol by reactive distillation under the catalysis of the acidic resin to obtain the desired maleic acid diol ester.
2. The process method for preparing maleic acid diol ester according to claim 1 is characterized in that: in the step (2), a reactive distillation column with a flash section is used to further react to complete the esterification, and the reactive distillation The tower is divided into three sections, the upper section is the stripping section for methanol and water, and the temperature is controlled between 80 and 100 °C; The lower section is a plurality of trays arranged in sequence from top to bottom, the temperature is controlled between 100 and 130 ° C, and at least 6 trays are filled with macroporous acid resin catalysts, and the pre-esterification reaction is carried out in the reactive distillation column. The resulting mixture flows from top to bottom, and the lower aliphatic alcohol and water from further esterification flow countercurrently from bottom to top in gaseous state.
3. The method for preparing diol maleate according to claim 1, characterized in that: in the step (2), a flash distillation column and a reactive distillation column are adopted, and the reaction is further carried out after the flash distillation is carried out. Rectification, the reactive rectification tower is divided into two sections, the lower section is a plurality of trays arranged in sequence from top to bottom, the temperature is controlled between 100 and 130 ° C, and at least 6 trays are filled with macroporous acid resin catalysts , in this reactive distillation column, the mixture produced by the pre-esterification reaction flows from top to bottom, and the water produced by the lower aliphatic alcohol and the further esterification reaction flows countercurrently from bottom to top in a gaseous state. The operating pressure is 0.1～0.5Mpa, and the temperature is controlled between 90～130℃.
4. The process method for preparing diol maleate according to claim 2 or 3, characterized in that: in the column tray, at least two column trays located at the bottom are not filled with catalyst.
5. The process method for preparing diol maleate according to claim 2 or 3, characterized in that: the operating pressure of the reactive distillation column is 0.1-0.5Mpa.
6. The method for preparing diol maleate according to claim 2 or 3, characterized in that: the reactant obtained at the bottom of the reactive distillation column is subjected to double-column rectification to realize delighting and deweighting to obtain purity Above 99.5% maleic acid glycol ester.
7. The process method for preparing diol maleate according to claim 2 or 3, wherein the pre-esterification reactor is a shell-and-tube reactor, and the tube side of the shell-and-tube reactor is used for supplying The pre-esterification reaction is carried out, the shell side of the shell-and-tube reactor is used for the passage of lower fatty alcohols, and the mixture produced by the pre-esterification reaction in the tube side of the shell-and-tube reactor is sent to the upper part of the reactive distillation column, or is flashed After rectification, it enters the corresponding reactive rectification tower, and the lower fatty alcohol in the shell side of the shell-and-tube reactor is vaporized to remove the heat released by the pre-esterification reaction and then sent to the lower part of the reactive rectification tower.
8. The process method for preparing diol maleate according to claim 7, wherein the molar ratio of maleic anhydride and fatty alcohol in the tube side of the shell-and-tube reactor is 1:1.5-4, and the reaction temperature is 60 °C ～220℃, the reaction pressure is 0.1～1.6MPa, and the reaction time is 0.1～8h; the temperature of the fatty alcohol in the shell layer of the shell-and-tube reactor is 80～200℃, the reaction pressure is 0.3～1.6MPa, and the corresponding temperature is maintained. The vapor-liquid equilibrium vaporization of the alcohol at this temperature is sufficient, and the corresponding amount is sufficient to remove the heat generated by the reaction.
9. The method for preparing diol maleate according to claim 1, wherein the lower aliphatic alcohol is at least one of methanol, ethanol, propanol and butanol.

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