A process for the separation of a methacrolein oxidation esterification reaction product

Abstract

The present application relates to a kind of methyl methacrolein oxidation esterification reaction product separation method, comprising: (1) the methyl methacrolein oxidation esterification reaction product of pretreatment is sent to demethyl methacrolein tower, and removes most of the unreacted methyl methacrolein therein;(2) the demethyl methacrolein tower tank product is mixed with water, and after obtaining mixture stream, it is entered into extraction tower, is extracted with lean solvent stream, and from the top, it is obtained that the solvent stream is rich, and from the tank, it is obtained that the aqueous phase stream;(3) the solvent stream is rich and is sent to washing tower, and after being washed with water, it is obtained that the solvent stream is washed after being washed and is sent to solvent recovery tower;(4) the solvent recovery tower top is obtained that the recovered lean solvent stream is used as extraction solvent in step (2) and is recycled, and the crude methyl methacrylate product is obtained from the tank of solvent recovery tower;(5) the crude methyl methacrylate product is refined and is obtained that the methyl methacrylate product;(6) the aqueous phase stream of step (2) is sent to methanol recovery tower, and the obtained methanol is recovered and returned to methyl methacrylate reaction unit.

Description

Technical Field

[0001] This invention belongs to the field of chemical product separation technology, and in particular relates to a method for separating products of methacrolein oxidation esterification reaction. Background Technology

[0002] Methyl methacrylate (MMA) is an important organic chemical raw material and chemical product, mainly used in the production of acrylic glass (PMMA), polyvinyl chloride additive ACR (acrylate copolymer), methyl methacrylate-styrene-butadiene copolymer (MBS), and as a second monomer for acrylic fibers. It can also be used as a resin, adhesive, coating, ion exchange resin, paper varnish, textile printing and dyeing auxiliary agent, leather treatment agent, lubricant additive, crude oil pour point depressant, impregnating agent for wood and softwood, impregnating agent for motor coils, insulating potting material, and plasticizer for plastic emulsions, etc., with a wide range of applications.

[0003] There are many technologies for producing methyl methacrylate, which can be mainly classified by raw materials as the acetone cyanohydrin method, the isobutylene method, and the ethylene method.

[0004] Currently, most domestic and international MMA production capacity still uses the acetone cyanohydrin (ACE) technology route. However, due to its severe pollution and environmental unfriendliness, this route is classified as a restricted industry by the state. The domestically industrialized isobutylene technology route involves a three-step process: isobutylene → methacrolein (MAL) → methacrylic acid (MAA) → MMA. This process is lengthy, complex, and requires numerous pieces of equipment. In contrast, the improved isobutylene technology route only requires two steps: isobutylene → MAL → MMA. In this route, MAL is directly oxidized and esterified in a single step using a nano-gold catalyst to produce MMA. This shortens the process, increases product yield, avoids equipment corrosion, and provides milder reaction conditions with lower requirements for reaction equipment. Therefore, this technology route has great development potential.

[0005] The one-step oxidation esterification process for MAL to produce MMA is also applicable to the ethylene process. This process combines the hydroformylation of ethylene to produce propionaldehyde and the condensation of propionaldehyde and formaldehyde to produce MAL with the one-step oxidation esterification process to produce MMA.

[0006] To improve the selectivity of MMA products, methanol is required in excess during the MAL oxidative esterification reaction. The molar ratio of methanol to MAL (also called the alcohol-aldehyde ratio) is generally 2-8 times. Furthermore, to improve the economic efficiency of the oxidative esterification reaction, the single-pass conversion rate of methacrolein is generally controlled between 70% and 95%. Therefore, the reaction products of MAL oxidative esterification, in addition to methyl methacrylate and water, include unreacted methanol and methacrolein. Depending on the raw materials used in MAL production, small amounts of one or more impurities may also be present, such as methacrylic acid, acetone, ethanol, methyl propionate (MP), methyl isobutyrate, methacrolein dimethyl acetal, and other heavy components.

[0007] Because the MAL oxidative esterification reaction products contain multiple binary or multi-component azeotropic components, such as methanol and methacrolein azeotropic components, methanol and methyl methacrylate azeotropic components, water and methacrolein azeotropic components, and water and methyl methacrylate azeotropic components, the separation of MAL oxidative esterification products is extremely challenging. In addition to refining the methyl methacrylate product to meet the requirements of the superior grade in "HG / T 2305-2017 Industrial Methyl Methacrolein". Unreacted methanol and methacrolein must also be separated and returned to the oxidative esterification reactor. At the same time, an outlet must be found for the impurities that may accumulate in these recycled materials.

[0008] CN105683148B discloses a method for separating products from the oxidative esterification reaction of methacrolein (MAL). This method separates methanol and MMA through azeotropic distillation of MAL and methanol, followed by extraction with water. After phase separation, an organic phase and an aqueous phase are obtained. These are then purified by an MMA heavy phase removal column and an MMA light phase removal column to obtain pre-purified MMA for further purification. However, since methanol accounts for approximately 32 wt% of the azeotropic composition of MAL and methanol, a large amount of MAL needs to be added during the separation of methanol and MMA. Therefore, this method is only suitable for conditions with a very low alcohol-aldehyde ratio and suffers from high energy consumption. Furthermore, this separation process only yields pre-purified MMA, requiring further purification to obtain the final MMA product. Summary of the Invention

[0009] To address the problems of high energy consumption, unreasonable separation process, and inability to obtain high-quality MMA products during the separation of products from the oxidative esterification reaction of methacrolein, this invention provides a method for separating products from the oxidative esterification reaction of methacrolein.

[0010] The objective of this invention can be achieved through the following technical solutions:

[0011] This invention provides a method for separating products from the oxidative esterification reaction of methacrolein, comprising the following steps:

[0012] (1) The pretreated methacrolein oxidation esterification reaction product is sent to the demethylacrolein tower, where most of the unreacted methacrolein is removed by azeotropic distillation.

[0013] (2) The product from the bottom of the demethyl acrolein tower is mixed with water to obtain a mixture stream, which is then fed into an extraction tower. Extraction is performed using a lean solvent stream, and a rich solvent stream is obtained from the top of the tower, while an aqueous stream is obtained from the bottom of the tower.

[0014] (3) The rich solvent stream is sent to the washing tower, washed with water to obtain the washed rich solvent stream, and then sent to the solvent recovery tower.

[0015] (4) The recovered lean solvent stream is obtained from the top of the solvent recovery tower and returned to step (2) for recycling as an extraction solvent, and crude methyl methacrylate product is obtained from the bottom of the solvent recovery tower.

[0016] (5) The crude methyl methacrylate product is refined to obtain the methyl methacrylate product;

[0017] (6) The aqueous phase stream from step (2) is sent to the methanol recovery tower, and the recovered methanol is returned to the methyl methacrylate reaction unit.

[0018] In one embodiment of the present invention, the pretreated methacrylaldehyde oxidative esterification reaction product refers to the methacrylaldehyde oxidative esterification reaction product that has undergone treatments including but not limited to filtration and degassing.

[0019] Because the oxidative esterification reaction product is obtained by oxidizing methacrolein with methanol and oxygen under an absolute pressure of 0.5-1.2 MPa, a temperature of 50-100°C, and in the presence of a heterogeneous catalyst containing precious metals, the reaction product needs to first be filtered to recover the lost precious metal catalyst, and then the solvent oxygen and dissolved nitrogen are removed by vacuum flash evaporation before entering the subsequent product separation process.

[0020] In one embodiment of the present invention, if the methacrylic acid content in the methacrolein oxidative esterification reaction product is high, the pretreated methacrolein oxidative esterification reaction product further includes a methacrolein oxidative esterification reaction product treated with alkali. If the methacrylic acid content in the reaction product is high, to avoid corrosion of pipelines and equipment in subsequent processes, an appropriate amount of alkali solution, such as sodium hydroxide solution, can be added to the reaction product stream to make the stream nearly neutral or weakly alkaline.

[0021] In one embodiment of the present invention, the components of the pretreated methacrolein oxidative esterification reaction product, in addition to the main product methyl methacrylate (MMA) and the byproduct water, also contain unreacted methacrolein (MAL), methanol, and other impurity components, which vary depending on the raw materials used to synthesize MAL, wherein the content of methyl methacrylate is 10-80 wt%.

[0022] In one embodiment of the present invention, the pretreated methacrolein oxidative esterification product further contains one or more impurity components such as methacrylic acid, acetone, ethanol, methyl propionate, methyl acetate, methyl isobutyrate, methacrolein dimethyl acetal, and heavy components. Since the raw material MAL for the oxidative esterification reaction can be derived from ethylene or isobutylene, the impurities generated from MAL from two different sources are different.

[0023] In one embodiment of the present invention, the pretreated methacrolein oxidative esterification reaction product is first sent to a demethylacrolein tower, where unreacted methacrolein is removed by azeotropic distillation. Azeotropic distillation refers to the process where the lowest azeotropic temperature formed by methanol and MAL at atmospheric pressure is 58.0°C, which is lower than the azeotropic temperature of methanol and MMA (64.2°C). Therefore, the MAL can be separated from the pretreated oxidative esterification reaction product by distillation in the demethylacrolein tower. The top product of the demethylacrolein tower is returned to the oxidative esterification reactor, while the bottom product enters the subsequent separation process.

[0024] In one embodiment of the present invention, the top product of the demethylacrolein tower in step (1) is sent to the demethylacrolein light removal tower, and then the bottom product of the tower is returned to the methyl methacrylate reaction unit, while the top product is discharged.

[0025] According to the method of the present invention, it was found in the study that under certain operating conditions, some impurity components in the top product of the MAL removal tower, such as acetone and methyl acetate, accumulate during the recycling process. Therefore, it is necessary to maintain the stability of the content of these components by appropriately discharging the recovered MAL stream. However, when the content of these components in the oxidative esterification reaction product is high, direct discharge will cause a large loss of MAL. In order to reduce the loss of MAL, the MAL recovered from the top product of the MAL removal tower in step (1) can be sent to the MAL light component removal tower. This tower will further concentrate the components that accumulate during the MAL recycling process and discharge them from the top of the tower. Then, the bottom product of this tower is returned to the methyl methacrylate reaction unit.

[0026] In one embodiment of the present invention, the water flow in step (2) is selected from the washing water flow discharged from the bottom of the washing tower.

[0027] In one embodiment of the present invention, in the extraction tower, the wash water stream from the bottom of the washing tower enters the upper part of the extraction tower, the product from the bottom of the demethylacrolein tower enters the middle part of the extraction tower, and the lean solvent stream used as the extraction solvent enters the lower part of the extraction tower. The three streams complete the extraction process in the extraction tower.

[0028] In terms of the extraction process, this extraction process achieves the same effect as the extraction process in which the product from the bottom of the demethylacrolein tower is mixed with the washing water stream before entering the extraction tower, and there is no essential difference. The only difference is the mixing position of the product from the bottom of the demethylacrolein tower and the washing water stream.

[0029] In one embodiment of the present invention, after taking into account the polarity, density, cost and source of the extraction solvent, the extraction solvent may be selected from any one of cyclohexane, n-hexane, methylcyclohexane or n-heptane and mixtures thereof, preferably, the extraction solvent is n-hexane and / or n-heptane.

[0030] In one embodiment of the present invention, the extraction solvent needs to be recycled after being recovered by the solvent recovery tower. Depending on the MMA content in the extraction solvent, the solvent stream that has been recovered by the solvent recovery tower and has a low MMA content can be called the lean solvent stream, and the stream that will be discharged from the top of the extraction tower and has a high MMA content can be called the rich solvent stream.

[0031] In the washing tower, the rich solvent stream leaving the top of the extraction tower enters the lower part of the tower, while the water stream used as a washing agent enters from the top of the tower. The methanol in the rich solvent stream is removed by continuous countercurrent water washing, thereby obtaining the washed rich solvent stream at the top of the washing tower. The wash water stream leaving the tower is mixed with the MAL removal tower bottom stream and then enters the upper part of the extraction tower.

[0032] In one embodiment of the present invention, experimental research revealed that methacrolein dimethyl acetal, during the extraction and separation process of this technical solution, mainly enters the crude MMA product, with a content of 0.05-5 wt%, preferably 0.1-3 wt%. Since its boiling point is very close to that of MMA, refining MMA to a superior grade (content ≥99.9 wt%) requires significant energy consumption and MMA loss costs. Detailed experimental research showed that methacrolein dimethyl acetal is easily hydrolyzed in dilute acid solution, and both the hydrolysis products MAL and methanol can be used as reaction raw materials for methyl methacrylate. Therefore, if methacrolein dimethyl acetal can be effectively hydrolyzed, not only can the separation problem of MMA and methacrolein dimethyl acetal be solved, but the yield of MMA product can also be improved. The hydrolysis reaction of methacrolein dimethyl acetal is an equilibrium reaction; to promote the reaction in the direction of hydrolysis, it is necessary to minimize the methanol and MAL content in the hydrolysis raw materials. In particular, in the technical solution of this invention, the methanol and MAL content in the solvent-rich stream leaving the top of the extraction tower is very low, making it highly suitable for hydrolysis. The hydrolysis water can be the wash water leaving the washing tower bottom. The solvent-rich stream, wash water stream, and inorganic acid are fed together into the acetal hydrolysis reactor for hydrolysis. Considering hydrolysis efficiency, investment, and ease of operation, the acetal hydrolysis reactor can be composed of 1-6 reaction stages connected in series.

[0033] In one embodiment of the present invention, since the acetal hydrolysis reaction is a heterogeneous reaction, each reaction stage is equipped with a device for mixing or improving the mixing effect in order to improve the hydrolysis efficiency. For example, in some preferred embodiments of the present invention, each reaction stage may be equipped with an independent stirring paddle for uniformly mixing the reactants. The choice of stirring paddles is a preferred mixing method considering both mixing effect and economy.

[0034] In one embodiment of the present invention, the inorganic acid used in the acetal hydrolysis reactor is not particularly required to be of a specific type, as long as it can effectively provide hydrogen ions. For example, the inorganic acid used can be any one of sulfuric acid, sulfonic acid, nitric acid, hydrochloric acid, or other protic acids and any mixture thereof. The concentration of the inorganic acid in the mixture is 0.01-1 wt%, preferably 0.02 wt%-0.5 wt%. The acetal hydrolysis product discharged from the hydrolysis reactor is returned to the lower part of the washing tower, where water washing removes the residual inorganic acid and methanol from the solvent-rich stream after the hydrolysis reaction.

[0035] According to the method of the present invention, the ratio of the washing water stream drawn from the bottom of the washing tower to the solvent-rich stream leaving the top of the extraction tower can be determined and selected according to the different contents of methacrolein dimethyl acetal and the concentration of the added inorganic acid, in accordance with conventional operation in the art. In principle, the hydrolysis reaction can be carried out effectively and the desired hydrolysis rate can be achieved.

[0036] In one embodiment of the present invention, when the content of methacrolein dimethyl acetal in the oxidative esterification reaction is low and there is no need to use an acetal hydrolysis reactor, the extraction tower in step (2) and the washing tower in step (3) can be combined into one tower, wherein the aqueous stream enters the upper part of the tower, the product from the bottom of the demethylacrolein tower enters the middle part of the tower, and the lean solvent stream used as the extraction solvent enters the lower part of the tower. The three streams complete the extraction process in the extraction tower, and then the washed and rich solvent stream is obtained from the top of the tower and sent to the solvent recovery tower, while the aqueous phase stream from the bottom of the tower is sent to the methanol recovery tower.

[0037] In one embodiment of the present invention, the washed rich solvent stream enters a solvent recovery tower, from which a recovered lean solvent stream is obtained and returned to the lower part of the extraction tower for recycling. From the bottom of the tower, a crude MMA product stream is obtained and enters the subsequent MMA refining unit.

[0038] In one embodiment of the present invention, the alkane used as the extraction solvent forms an azeotrope with water, and the azeotropic temperature is much lower than that of water and MMA. Therefore, in the solvent recovery tower, a small amount of dissolved water in the solvent-rich stream after washing is distilled to the top of the tower, condensed by a condenser, and then discharged from the system after phase separation in a reflux tank, thereby achieving the purpose of removing moisture from the crude MMA product and reducing the refining difficulty of the crude MMA product. According to "HG / T 2305-2017 Industrial Methyl Methacrylate", the moisture content requirement for superior grade MMA is ≤400mg / kg. Through research, the technical solution of the present invention shows that the moisture content in the crude MMA product discharged from the bottom of the solvent recovery tower can be less than 100mg / kg.

[0039] In one embodiment of the present invention, in order to minimize the MMA content in the aqueous stream discharged from the bottom of the extraction column, thereby reducing the amount of MMA circulating in the system, the MMA content in the lean solvent stream is required to be ≤6wt%, preferably ≤3wt%.

[0040] In one embodiment of the present invention, since the extraction solvent will be slightly lost during the recycling process, it is only necessary to continuously or intermittently replenish the system with fresh extraction solvent to maintain the total solvent balance in the system; if some trace amounts of unknown impurities accumulate during the recycling process, it is only necessary to continuously or intermittently discharge an appropriate amount of recovered solvent from the system.

[0041] In one embodiment of the present invention, the purification of methyl methacrylate (MMA) product comprises a methyl methacrylate (MMA) light component removal tower and a methyl methacrylate (MMA) product tower. Light components and a small amount of methyl methacrylate are discharged from the top of the methyl methacrylate light component removal tower, while the remaining methyl methacrylate and heavy components are discharged from the bottom of the tower and enter the methyl methacrylate product tower. The purified methyl methacrylate product is obtained from the top of the methyl methacrylate product tower, while the heavy components and a small amount of methyl methacrylate from the bottom of the tower are discharged externally. The purpose of the MMA light component removal tower is to remove most of the components lighter than MMA from the crude MMA product through distillation. Thus, most of the light components and a small amount of MMA are discharged from the top of the crude MMA light component removal tower, while the remaining MMA, heavy components, and trace amounts of light components are discharged from the bottom of the tower and enter the MMA product tower. In the MMA product column, qualified MMA product is obtained at the top through distillation. This MMA product meets the quality requirements of superior grade in "HG / T2305-2017 Methyl Methacrylate for Industrial Use". Most of the components heavier than MMA and a small amount of MMA are discharged from the bottom of the column.

[0042] In one embodiment of the present invention, the purification of methyl methacrylate (MMA) product consists of a methyl methacrylate light component removal tower, a methyl methacrylate product tower, and a methyl methacrylate recovery tower. Light components and a small amount of methyl methacrylate are discharged from the top of the methyl methacrylate light component removal tower. The remaining methyl methacrylate and heavy components are discharged from the bottom of the tower and enter the methyl methacrylate product tower. Refined methyl methacrylate product is obtained from the top of the methyl methacrylate product tower. The heavy components and a small amount of methyl methacrylate from the bottom of the tower enter the methyl methacrylate recovery tower. The recovered methyl methacrylate obtained from the top of the methyl methacrylate recovery tower is returned to the methyl methacrylate product tower. The heavy components and an even smaller amount of methyl methacrylate from the bottom of the tower are discharged.

[0043] This implementation method aims to further improve the recovery rate of MMA. Therefore, the stream discharged from the bottom of the MMA product tower enters the MMA recovery tower for further MMA recovery. The recovered MMA is returned to the MMA product tower, and the recombinant stream from the bottom of the tower is discharged externally.

[0044] In one embodiment of the invention, the aqueous phase stream discharged from the bottom of the extraction tower is sent to a methanol recovery tower. The recovered methanol stream is obtained from the top of this tower and returned to the oxidative esterification reaction unit. The wastewater from the bottom of the tower is cooled and then discharged or partially reused. Since trace amounts of fusel oils such as ethanol are generated during the MAL oxidative esterification reaction, to prevent the accumulation of these fusel oils in the system, the methanol recovery tower needs to be equipped with one or more side-collection fusel oil ports. Small amounts of side-collected fusel oils are intermittently or continuously discharged to avoid the accumulation of fusel oils and ensure the purity of the methanol at the top of the tower.

[0045] In one embodiment of the present invention, if the aqueous phase stream discharged from the bottom of the extraction tower contains corrosive substances such as inorganic or organic acids before being sent to the methanol recovery tower, an appropriate amount of alkaline solution, such as sodium hydroxide solution, can be added to the stream to make it close to neutral or weakly alkaline in order to avoid corrosion of the methanol recovery tower and related pipeline equipment.

[0046] In one embodiment of the present invention, in order to avoid the polymerization of components such as MAL or MMA, the temperature of the bottom of the MAL stripping tower, MAL light component stripping tower, solvent recovery tower, MMA light component stripping tower, and MMA product tower should not exceed 90°C, preferably not exceeding 80°C. Therefore, the temperature of the methanol vapor at the top of the methanol recovery tower can be increased by increasing the operating pressure of the methanol recovery tower, and the methanol vapor can be used as the heat source for all or part of the reboilers of one or more of the equipment such as the MAL stripping tower, MAL light component stripping tower, solvent recovery tower, MMA light component stripping tower, and MMA product tower. Through thermal coupling, the energy consumption for the separation of oxidative esterification reaction products can be reduced.

[0047] In one embodiment of the present invention, during the entire operation, the equipment form of each tower can be determined and selected in accordance with conventional practices in the art, such as each being an independent packed tower or a sieve plate tower, wherein the packing can be random packing or structured packing.

[0048] In one embodiment of the present invention, since components such as MAL and MMA are prone to polymerization at high temperatures, causing blockages in equipment or pipelines, distillation tower equipment containing MAL or MMA components, such as MAL removal towers, MAL light component removal towers, solvent recovery towers, MMA light component removal towers, MMA product towers, and MMA recovery towers, should preferably be operated at lower temperatures. The operating temperature of these distillation tower equipment can be selected from 15-100°C, preferably 25°C-80°C. Each distillation tower can meet the preferred temperature requirements by reducing the operating pressure of the distillation tower equipment according to the preferred operating temperature.

[0049] In one embodiment of the present invention, since components such as MAL and MMA are prone to polymerization at high temperatures, it is preferable to add one or more polymerization inhibitors to the process, particularly to the condenser inlet and top of the distillation column. The polymerization inhibitors include hydroquinone, hydroquinone ether, phenothiazine, Topanol A (polymerization inhibitor TBX), NAUGARD I-4701, p-phenylenediamine, etc., which are well known in the art. Furthermore, polymerization-inhibiting air can be added to the reboiler inlet and outlet of the distillation column to achieve a better polymerization inhibition effect.

[0050] Compared with existing separation methods that use azeotropic distillation and water extraction to separate products from the oxidation esterification reaction of methacrolein, this invention achieves significant technological progress, specifically including the following aspects:

[0051] 1. This invention removes most of the unreacted MAL from the MAL oxidation esterification reaction products through azeotropic distillation and returns them to the MMA reaction unit. The process is reasonable and has low energy consumption.

[0052] 2. This invention uses a combination of alkane solvent and water as extraction solvents to separate methyl methacrylate and methanol. Compared with using only desalinated water as extraction solvent, this solves the problem of a large amount of residual MMA in the aqueous stream. With this technical solution, the residual MMA content in the aqueous stream is less than 0.6 wt%.

[0053] 3. This invention creatively adds an acetal hydrolysis reactor between the extraction tower and the washing tower, which is simple to operate, has high hydrolysis efficiency, and solves the problem of separating MMA and methacrolein dimethyl acetal in the subsequent MMA purification process.

[0054] 4. The extraction solvent of this invention can form a minimum azeotrope with water. While recovering the solvent, the water in the crude MMA product is removed. The water content in the crude MMA product is ≤100mg / kg, which is far lower than the requirement of ≤400mg / kg for the superior grade in "HG / T2305-2017 Industrial Methyl Methacrylate".

[0055] 5. According to the present invention, the purity of the crude MMA product obtained after refining can meet the requirement of ≥99.9wt% for superior grade products;

[0056] 6. This invention organically combines various functional steps to form a complete whole. It not only has a reasonable process, low separation energy consumption, and high product purity, but also has good adaptability to the composition of oxidative esterification reaction products, meeting the requirements of continuous large-scale industrial production. Attached Figure Description

[0057] Figure 1This is a schematic diagram of the separation process of the methacrolein oxidative esterification reaction product in Example 1 of the present invention;

[0058] Figure 2 This is a schematic diagram of the separation process of the methacrolein oxidative esterification reaction product in Example 2 of the present invention;

[0059] Figure 3 This is a schematic diagram of the separation process of the methacrolein oxidative esterification reaction product in Example 3 of the present invention;

[0060] Figure 4 This is a schematic diagram of the separation process of the product from the oxidative esterification reaction of methacrolein in Example 4 of the present invention.

[0061] In the accompanying drawings, identical equipment and logistics materials with the same function are represented by the same reference numerals, the specific meanings of which are as follows:

[0062] T201-MAL-removing tower

[0063] T202-MAL Lightweight Tower

[0064] T301-Extraction Tower

[0065] T302-Scrubber Tower

[0066] R301-Acetal Hydrolysis Reactor

[0067] T401 Solvent Recovery Tower

[0068] T501-MMA Lightweight Tower

[0069] T502-MMA Product Tower

[0070] T503-MMA Recycling Tower

[0071] T601-Methanol Recovery Tower

[0072] 201 - Pretreated MAL oxidation esterification product stream; 202 - Top product stream from the MAL removal column; 203 - Light MAL component stream; 204 - Bottom product stream from the MAL removal column; 205 - Bottom product stream from the MAL removal column; 301 - Heavy phase feed stream from the extraction column; 302 - Solvent-rich stream; 303 - Aqueous phase stream; 304 - Acetal hydrolysis product stream; 305 - Water stream; 306 - Solvent-rich stream after washing; 307 - Total wash water stream; 308 - Deacetal hydrolysis... Streams of the following materials are listed: 309 - Wash water from the reactor; 310 - Wash water from the extraction tower; 401 - Inorganic acid stream; 402 - Lean solvent stream; 403 - Crude MMA product stream; 404 - Fresh extraction solvent replenishment stream; 501 - Light MMA component stream; 502 - MMA removal tower bottom stream; 503 - MMA product stream; 504 - MMA product tower bottom stream; 505 - Recovered MMA stream; 506 - Heavy MMA component stream; 601 - Recovered methanol stream; 602 - Wastewater stream. Detailed Implementation

[0073] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0074] Example 1

[0075] In this embodiment, because the content of methacrolein dimethyl acetal in the oxidative esterification reaction product is low, there is no need to use an acetal hydrolysis reactor, and n-heptane is selected as the extraction solvent.

[0076] The process flow diagram of this embodiment is shown below. Figure 1The pretreated MAL oxidation esterification product stream 201 is sent to the MAL removal tower T201, the top product stream 202 is sent to the MAL light component removal tower T202, and the bottom product stream 205 is mixed with the wash water stream 309 from the extraction tower and sent to the extraction tower T301. In the MAL light component removal tower T202, the MAL light component stream 203 is discharged from the top of the tower, and the bottom product stream 204 is sent to the MMA reaction unit for MAL recovery. In extraction column T301, lean solvent stream 401 enters the lower part of the column, while heavy phase feed stream 301 enters the upper part. This heavy phase feed stream 301 is a mixture of the MAL stripping column bottom product stream 205 and the wash water stream 309 from the extraction column. From the top of extraction column T301, a rich solvent stream 302 is obtained and sent to washing column T302. The aqueous stream 303 from the bottom of extraction column T301 is sent to methanol recovery column T601. In washing column T302, water stream 305 is fed from the upper part of the column, while the rich solvent stream 302 enters the lower part. Through continuous countercurrent washing, a washed rich solvent stream 306 is obtained from the top and sent to solvent recovery column T401. The total wash water stream discharged from the bottom of washing column T302 is the wash water stream 309 sent to the extraction column. In solvent recovery tower T401, the recovered solvent after phase separation and dehydration is obtained from the top of the tower. This solvent is mixed with the replenished fresh extraction solvent stream 403 and sent as lean solvent stream 401 to extraction tower T301. The crude MMA product stream 402 obtained from the bottom of solvent recovery tower T401 is sent to MMA light component removal tower T501. In MMA light component removal tower T501, the MMA light component stream 501 is discharged from the top of the tower. The bottom stream 502 of the MMA light component removal tower is sent to MMA product tower T502. Then, MMA product stream 503 is obtained from the top of MMA product tower T502, and the bottom stream 504 of the MMA product tower is sent to MMA recovery tower T503. In MMA recovery tower T503, the recovered MMA stream 505 from the top of the tower is returned to the lower part of MMA product tower T502, and the heavy MMA component stream 506 from the bottom of MMA recovery tower T503 is discharged. In methanol recovery tower T601, the aqueous phase stream 303 flowing out of the bottom of extraction tower T301 enters the middle of methanol recovery tower T601. The top of methanol recovery tower T601 is the recovered methanol stream 601, which goes to the MMA reaction unit. The bottom of methanol recovery tower T601 is the wastewater stream 602, which is discharged or partially reused.

[0077] The material balance sheet for this embodiment is shown in Table 1.

[0078] Table 1 Material Balance Sheet for Example 1

[0079]

[0080]

[0081] Example 2

[0082] In this embodiment, because the content of light components such as acetone and methyl acetate in the oxidative esterification reaction products is low, it is not necessary to use a MAL light component removal tower to further concentrate these impurity components in the recovered MAL. The extraction solvent is n-hexane, and the acetal hydrolysis reactor is a single-stage stirred tank.

[0083] The process flow diagram of this embodiment is shown below. Figure 2 The pretreated MAL oxidation esterification reaction product stream 201 is sent to the MAL removal tower T201. A small portion of the top product of the MAL removal tower is discharged as the light MAL component stream 203, and most of the remaining stream 204 is returned to the MMA reaction unit. The bottom product stream 205 of the MAL removal tower is mixed with the wash water stream 309 from the extraction tower and then sent to the extraction tower T301.

[0084] In extraction tower T301, lean solvent stream 401 enters the lower part of the tower, and heavy phase feed stream 301 enters the upper part of the tower. The heavy phase feed stream 301 is the stream after the product stream 205 from the bottom of the MAL removal tower is mixed with the wash water stream 309 from the extraction tower. The rich solvent stream 302 obtained from the top of extraction tower T301, together with the wash water stream 308 from the acetal hydrolysis reactor and the inorganic acid stream 310, enters the acetal hydrolysis reactor R301. The aqueous phase stream 303 from the bottom of extraction tower T301 goes to methanol recovery tower T601.

[0085] The acetal hydrolysis reactor R301 is a single-stage stirred reactor, and its acetal hydrolysis product stream 304 enters the lower part of the washing tower T302.

[0086] In washing tower T302, water stream 305 is fed from the top of the tower, and acetal hydrolysis product stream 304 enters the bottom of the tower. After continuous countercurrent water washing, a solvent-rich stream 306 is obtained from the top of the tower and sent to solvent recovery tower T401. The washing water stream 307 in the tower bottom is divided into two parts. One part is the washing water stream 308 from the acetal hydrolysis reactor, and the other part is the washing water stream 309 from the extraction tower. The washing water stream 308 from the acetal hydrolysis reactor goes to the acetal hydrolysis reactor R301, and the remaining washing water stream 309 going to the extraction tower is mixed with the MAL removal tower bottom stream 205 and then sent to the extraction tower T301.

[0087] In solvent recovery tower T401, the recovered solvent after phase separation and dehydration is obtained from the top of the tower. This solvent is mixed with the replenished fresh extraction solvent stream 403 and sent as lean solvent stream 401 to extraction tower T301. The crude MMA product stream 402 obtained from the bottom of solvent recovery tower T401 is sent to MMA light component removal tower T501. In MMA light component removal tower T501, the MMA light component stream 501 is discharged from the top of the tower. The bottom stream 502 of the MMA light component removal tower is sent to MMA product tower T502. Then, MMA product stream 503 is obtained from the top of MMA product tower T502, and the bottom stream 504 of the MMA product tower is sent to MMA recovery tower T503. In MMA recovery tower T503, the recovered MMA stream 505 from the top of the tower is returned to the lower part of MMA product tower T502, and the heavy MMA component stream 506 from the bottom of MMA recovery tower T503 is discharged. In methanol recovery tower T601, the aqueous phase stream 303 flowing from the bottom of extraction tower T301 enters the middle of methanol recovery tower T601. The top of methanol recovery tower T601 contains recovered methanol stream 601, which goes to the MMA reaction unit. The bottom of methanol recovery tower T601 contains wastewater stream 602, which is either discharged or partially reused. The material balance table for this embodiment is shown in Table 2.

[0088] Table 2 Material Balance Sheet for Example 2

[0089]

[0090]

[0091] Example 3

[0092] In this embodiment, the extraction solvent is a mixture of n-hexane and n-heptane, and the acetal hydrolysis reactor is a three-stage stirred tank in series.

[0093] The process flow diagram of this embodiment is shown below. Figure 3 The pretreated MAL oxidation esterification product stream 201 is sent to the MAL removal tower T201, the top product stream 202 is sent to the MAL light component removal tower T202, and the bottom product stream 205 is mixed with the wash water stream 309 from the extraction tower and sent to the extraction tower T301. In the MAL light component removal tower T202, the MAL light component stream 203 is discharged from the top of the tower, and the bottom product stream 204 is sent to the MMA reaction unit for MAL recovery.

[0094] In extraction tower T301, lean solvent stream 401 enters the lower part of the tower, and heavy phase feed stream 301 enters the upper part of the tower. The heavy phase feed stream 301 is the stream after the product stream 205 from the bottom of the MAL removal tower is mixed with the wash water stream 309 from the extraction tower. The rich solvent stream 302 obtained from the top of extraction tower T301, together with the wash water stream 308 from the acetal hydrolysis reactor and the inorganic acid stream 310, enters the acetal hydrolysis reactor R301. The aqueous phase stream 303 from the bottom of extraction tower T301 goes to methanol recovery tower T601.

[0095] The acetal hydrolysis reactor R301 is a three-stage stirred reactor connected in series, and its acetal hydrolysis product stream 304 enters the lower part of the washing tower T302.

[0096] In washing tower T302, water stream 305 is fed from the top of the tower, and acetal hydrolysis product stream 304 enters the bottom of the tower. After continuous countercurrent water washing, a solvent-rich stream 306 is obtained from the top of the tower and sent to solvent recovery tower T401. The washing water stream 307 in the tower bottom is divided into two parts. One part is the washing water stream 308 from the acetal hydrolysis reactor, and the other part is the washing water stream 309 from the extraction tower. The washing water stream 308 from the acetal hydrolysis reactor goes to the acetal hydrolysis reactor R301, and the remaining washing water stream 309 going to the extraction tower is mixed with the MAL removal tower bottom stream 205 and then sent to the extraction tower T301.

[0097] In solvent recovery tower T401, the recovered solvent after phase separation and dehydration is obtained from the top of the tower. This solvent is mixed with the replenished fresh extraction solvent stream 403 and sent as lean solvent stream 401 to extraction tower T301. The crude MMA product stream 402 obtained from the bottom of solvent recovery tower T401 is sent to MMA light component removal tower T501. In MMA light component removal tower T501, the MMA light component stream 501 is discharged from the top of the tower. The bottom stream 502 of the MMA light component removal tower is sent to MMA product tower T502. Then, MMA product stream 503 is obtained from the top of MMA product tower T502, and the bottom stream 504 of the MMA product tower is sent to MMA recovery tower T503. In MMA recovery tower T503, the recovered MMA stream 505 from the top of the tower is returned to the lower part of MMA product tower T502, and the heavy MMA component stream 506 from the bottom of MMA recovery tower T503 is discharged. In methanol recovery tower T601, the aqueous phase stream 303 flowing out of the bottom of extraction tower T301 enters the middle of methanol recovery tower T601. The top of methanol recovery tower T601 contains recovered methanol stream 601, which goes to the MMA reaction unit. The bottom of methanol recovery tower T601 contains wastewater stream 602, which is either discharged or partially reused. The material balance table for this embodiment is shown in Table 3.

[0098] Table 3 Material Balance Sheet for Example 3

[0099]

[0100] Example 4

[0101] In this embodiment, the extraction solvent is a mixture of n-hexane, n-heptane, cyclohexane, and methylcyclohexane, wherein n-hexane is 70 wt%, n-heptane is 20 wt%, cyclohexane is 5 wt%, and methylcyclohexane is 5 wt%. The acetal hydrolysis reactor is a five-stage stirred tank in series.

[0102] The process flow diagram of this embodiment is shown below. Figure 4 The pretreated MAL oxidation esterification product stream 201 is sent to the MAL removal tower T201, the top product stream 202 is sent to the MAL light component removal tower T202, and the bottom product stream 205 is mixed with the wash water stream 309 from the extraction tower and sent to the extraction tower T301. In the MAL light component removal tower T202, the MAL light component stream 203 is discharged from the top of the tower, and the bottom product stream 204 is sent to the MMA reaction unit for MAL recovery.

[0103] In extraction tower T301, lean solvent stream 401 enters the lower part of the tower, and heavy phase feed stream 301 enters the upper part of the tower. The heavy phase feed stream 301 is the stream after the product stream 205 from the bottom of the MAL removal tower is mixed with the wash water stream 309 from the extraction tower. The rich solvent stream 302 obtained from the top of extraction tower T301, together with the wash water stream 308 from the acetal hydrolysis reactor and the inorganic acid stream 310, enters the acetal hydrolysis reactor R301. The aqueous phase stream 303 from the bottom of extraction tower T301 goes to methanol recovery tower T601.

[0104] The acetal hydrolysis reactor R301 is a five-stage series stirred tank, and its acetal hydrolysis product stream 304 enters the lower part of the washing tower T302.

[0105] In washing tower T302, water stream 305 is fed from the top of the tower, and acetal hydrolysis product stream 304 enters the bottom of the tower. After continuous countercurrent water washing, a solvent-rich stream 306 is obtained from the top of the tower and sent to solvent recovery tower T401. The washing water stream 307 in the tower bottom is divided into two parts. One part is the washing water stream 308 from the acetal hydrolysis reactor, and the other part is the washing water stream 309 from the extraction tower. The washing water stream 308 from the acetal hydrolysis reactor goes to the acetal hydrolysis reactor R301, and the remaining washing water stream 309 going to the extraction tower is mixed with the MAL removal tower bottom stream 205 and then sent to the extraction tower T301.

[0106] In solvent recovery tower T401, the recovered solvent after phase separation and dehydration is obtained from the top of the tower. This solvent is mixed with the replenished fresh extraction solvent stream 403 and sent to extraction tower T301 as lean solvent stream 401. The crude MMA product stream 402 obtained from the bottom of solvent recovery tower T401 is sent to MMA light component removal tower T501. In MMA light component removal tower T501, the MMA light component stream 501 is discharged from the top of the tower. The MMA light component removal tower bottom stream 502 is sent to MMA product tower T502. Then, the MMA product stream 503 is obtained from the top of MMA product tower T502. The MMA heavy component stream 506 from the bottom of the tower is discharged. In methanol recovery tower T601, the aqueous phase stream 303 flowing out of the bottom of extraction tower T301 enters the middle of methanol recovery tower T601. The top of methanol recovery tower T601 contains recovered methanol stream 601, which goes to the MMA reaction unit. The bottom of methanol recovery tower T601 contains wastewater stream 602, which is either discharged or partially reused. The material balance table for this embodiment is shown in Table 4.

[0107] Table 4 Material Balance Sheet for Example 4

[0108]

[0109]

[0110] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for separating products from the oxidative esterification reaction of methacrolein, characterized in that, Includes the following steps: (1) The pretreated methacrolein oxidation esterification reaction product is sent to the demethylacrolein tower, where most of the unreacted methacrolein is removed by azeotropic distillation; (2) The product from the bottom of the demethylated acrolein tower is mixed with water to obtain a mixture stream, which is then fed into an extraction tower. Extraction is performed using a lean solvent stream, and a rich solvent stream is obtained from the top of the tower, while an aqueous stream is obtained from the bottom of the tower. (3) The solvent-rich stream is hydrolyzed in an acetal hydrolysis reactor and then sent to a washing tower. After washing with water, the washed solvent-rich stream is sent to a solvent recovery tower. (4) The recovered lean solvent stream is obtained from the top of the solvent recovery tower and returned to step (2) for recycling as an extraction solvent, and crude methyl methacrylate product is obtained from the bottom of the solvent recovery tower; (5) The crude methyl methacrylate product is purified to obtain the methyl methacrylate product; (6) The aqueous phase stream from step (2) is sent to the methanol recovery tower, and the recovered methanol is returned to the methyl methacrylate reaction unit; In step (2), the water is selected from the washing water stream discharged from the bottom of the washing tower; After the extraction solvent is recovered by the solvent recovery tower, the solvent stream with a low methyl methacrylate content after being recovered by the solvent recovery tower is called the lean solvent stream, and the stream with a high methyl methacrylate content that will be discharged from the top of the extraction tower is called the rich solvent stream, depending on the different contents of methyl methacrylate in the extraction solvent. The methyl methacrylate content in the lean solvent stream is ≤6 wt%; The solvent-rich stream and a portion of the washing water stream are introduced into the acetal hydrolysis reactor, and inorganic acid is added for hydrolysis. The acetal hydrolysis reactor consists of 1-6 reaction stages connected in series. The concentration of inorganic acid in the mixture in the acetal hydrolysis reactor is 0.01-1 wt%. The products of acetal hydrolysis are returned to the bottom of the scrubbing tower; The pretreated methacrolein oxidative esterification reaction product, in addition to the main product methyl methacrylate and the byproduct water, also contains unreacted methacrolein, methanol, and other impurities, wherein the content of methyl methacrylate is 10-80 wt%. The extraction solvent used in the extraction tower is selected from any one of cyclohexane, n-hexane, methylcyclohexane, or n-heptane, or a mixture thereof.

2. The method for separating the products of the oxidative esterification reaction of methacrolein according to claim 1, characterized in that, The pretreated methacrylaldehyde oxidation esterification reaction product refers to the methacrylaldehyde oxidation esterification reaction product that has undergone filtration and degassing treatment.

3. The method for separating the products of the oxidative esterification reaction of methacrolein according to claim 1, characterized in that, The top product of the demethylacrolein tower in step (1) is sent to the demethylacrolein light removal tower, and then the bottom product of the tower is returned to the methyl methacrylate reaction unit, while the top product is discharged.

4. The method for separating the products of the oxidative esterification reaction of methacrolein according to claim 1, characterized in that, In step (2), water flows into the upper part of the extraction tower, the product from the bottom of the demethylated acrolein tower enters the middle part of the extraction tower, and the lean solvent stream used as the extraction solvent enters the lower part of the extraction tower. The three streams complete the extraction process in the extraction tower.

5. The method for separating the products of the oxidative esterification reaction of methacrolein according to claim 1, characterized in that, The extraction solvent used in the extraction tower is n-hexane and / or n-heptane.

6. The method for separating the products of the oxidative esterification reaction of methacrolein according to claim 1, characterized in that, The methyl methacrylate content in the lean solvent stream is ≤3wt%.

7. The method for separating the products of the oxidative esterification reaction of methacrolein according to claim 1, characterized in that, The concentration of inorganic acid in the mixture in the acetal hydrolysis reactor is 0.02wt%-0.5wt%.

8. The method for separating the products of the oxidative esterification reaction of methacrolein according to claim 1, characterized in that, The purification of crude methyl methacrylate consists of a methyl methacrylate removal tower and a methyl methacrylate product tower. The light components and a small amount of methyl methacrylate are discharged from the top of the methyl methacrylate removal tower, while the remaining methyl methacrylate and heavy components are discharged from the bottom of the tower and enter the methyl methacrylate product tower. The purified methyl methacrylate product is obtained from the top of the methyl methacrylate product tower, while the heavy components and a small amount of methyl methacrylate in the bottom of the tower are discharged.

9. The method for separating the products of the oxidative esterification reaction of methacrolein according to claim 1, characterized in that, The purification of crude methyl methacrylate consists of a methyl methacrylate removal tower, a methyl methacrylate product tower, and a methyl methacrylate recovery tower. Light components and a small amount of methyl methacrylate are discharged from the top of the methyl methacrylate removal tower. The remaining methyl methacrylate and heavy components are discharged from the bottom of the tower and enter the methyl methacrylate product tower. Refined methyl methacrylate product is obtained from the top of the methyl methacrylate product tower. The heavy components and a small amount of methyl methacrylate from the bottom of the tower enter the methyl methacrylate recovery tower. The recovered methyl methacrylate obtained from the top of the methyl methacrylate recovery tower is returned to the methyl methacrylate product tower. The heavy components and an even smaller amount of methyl methacrylate from the bottom of the tower are discharged externally.

10. The method for separating the products of the oxidative esterification reaction of methacrolein according to claim 1, characterized in that, The methanol recovery tower is equipped with one or more side sampling ports for fusel oil.

11. The method for separating the products of the oxidative esterification reaction of methacrolein according to claim 1, characterized in that, The temperature of the bottom of the demethylated acrolein tower, the methacrolein light component removal tower, the solvent recovery tower, the methyl methacrylate light component removal tower, and the methyl methacrylate product tower shall not exceed 90°C. The methanol vapor at the top of the methanol recovery tower can be used as a heat source for all or part of the reboilers in one or more of the following: a demethylacrolein tower, a methacrolein light component removal tower, a solvent recovery tower, a methyl methacrylate light component removal tower, and a methyl methacrylate product tower.

12. The method for separating the products of the oxidative esterification reaction of methacrolein according to claim 11, characterized in that, The temperature of the bottom of the demethylated acrolein tower, the methacrolein light component removal tower, the solvent recovery tower, the methyl methacrylate light component removal tower, and the methyl methacrylate product tower shall not exceed 80℃.

13. The method for separating the products of the oxidative esterification reaction of methacrolein according to claim 1, characterized in that, One or more polymerization inhibitors are added to the separation process of the products of the oxidative esterification reaction of methacrolein.

14. The method for separating the products of the oxidative esterification reaction of methacrolein according to claim 13, characterized in that, Added to the condenser inlet and top of the distillation column; Add polymerization-inhibiting air to the inlet and outlet of the reboiler in the distillation column.

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