System for purifying and producing methyl methacrylate and method for purifying methyl methacrylate

Abstract

The present application relates to a purification process of methyl methacrylate, and provides a purification method of methyl methacrylate, which can remove water in the crude product containing formaldehyde, solvent, water, methyl propionate and methyl methacrylate through a first membrane separation membrane, so that the first concentrated liquid retains the product methyl methacrylate, unreacted raw material methyl propionate and formaldehyde, and solvent such as methanol; the second membrane separation is used for removing small molecules such as methanol and formaldehyde in the first concentrated liquid, and methyl propionate and methyl methacrylate are obtained. The system for preparing methyl methacrylate provided by the present application uses the membrane separation technology and the rectification technology, realizes the repeated recycling of unreacted raw materials and the purification, separation and recycling of methyl methacrylate by effective combination, has the advantages of simple process operation, small equipment investment, high separation efficiency and low energy consumption of recycling, improves the economic benefit, the recovery rate of methyl methacrylate is greater than or equal to 99%, and the purity is greater than or equal to 99.9%.

Description

Technical Field

[0001] This invention relates to the preparation process of fine chemicals, specifically to the purification process of methyl methacrylate, and more specifically to a system for purifying methyl methacrylate, a system for preparing methyl methacrylate, and a method for purifying methyl methacrylate. Background Technology

[0002] Methyl methacrylate (MMA) is an organic compound and an important chemical raw material. It is the monomer used to produce polymethyl methacrylate (PMMA), a transparent plastic. PMMA's high transparency, scratch resistance, weather stability, high tensile strength, and ease of processing make it widely used in automotive and transportation systems, optical devices and communication equipment, medical technology, and construction and lighting. In recent years, the strong demand for downstream polymethyl methacrylate has led to rapid growth in the production of its monomer, methyl methacrylate.

[0003] Currently, the mainstream industrial production processes for methyl methacrylate (MMA) mainly include the acetone-cyanohydrin (ACH) route, the isobutylene oxidation method, and the ethylene method. The ACH method was first industrialized in 1937. This method consists of three steps: 1. Under an alkaline environment of NaOH, hydrogen cyanide and acetone react to produce acetone cyanohydrin; 2. Sulfuric acid reacts with the product of the first step, ACH, to synthesize methacrylamide sulfate; 3. The product from the hydrolysis of the sulfate synthesized in the previous step reacts with methanol to synthesize the final product, MMA. This method is mature, but the use of hydrogen cyanide as a raw material makes transportation and storage inconvenient. The isobutylene oxidation method can be divided into three-step and two-step oxidation synthesis of MMA. It mainly uses C4 fraction isobutylene as the main raw material. The advantage of the three-step oxidation method is that the raw materials are relatively abundant and the environmental impact is small. The disadvantages are that the MMA yield is low, the process is complex, and more equipment is required. The advantage of the two-step synthesis method is the reduction of related by-products and the increase in MMA yield, but the disadvantage is that the catalyst conditions are more demanding. The ethylene process was first developed by BASF in Germany. Its advantages include a simple production process, but its disadvantages include the limited selectivity and lifespan of the catalysts used, which are detrimental to the reaction. Lucite in the UK upgraded the ethylene process with α-MMA technology, which does not produce highly toxic intermediates, has relatively mild process conditions, and can reduce investment and production costs by 40% compared to traditional routes, while also being safe and environmentally friendly.

[0004] The α-MMA technique involves reacting ethylene, carbon monoxide, and methanol to produce methyl propionate, which is then further reacted with formaldehyde to produce methyl methacrylate. To obtain the methyl methacrylate product, the products need to be separated. The mixture contains methyl methacrylate, unreacted methyl propionate, formaldehyde, methanol solvent, and water as a byproduct.

[0005] Separating the aforementioned mixed systems presents significant challenges. Methyl propionate-methanol, methyl propionate-water, paraformaldehyde-water, and formaldehyde-methanol systems all form binary azeotropic systems, while methyl methacrylate-methanol-water and methyl propionate-methanol-water systems form ternary azeotropic systems, rendering traditional distillation techniques ineffective. Existing research on the separation of these complex mixed systems is limited. Lucite employs a method of first washing with water to remove most of the formaldehyde and methanol, followed by distillation to separate the methyl propionate and methyl methacrylate products. The addition of large amounts of wash water significantly increases the difficulty and energy consumption of formaldehyde and methanol recovery, especially in formaldehyde-water mixtures.

[0006] Therefore, it is very meaningful to develop a simpler, greener, and lower-energy-consumption purification scheme for methyl methacrylate, especially a recovery scheme for existing mainstream MMA preparation technologies. Summary of the Invention

[0007] The purpose of this invention is to address the problem of difficult separation of methyl methacrylate products during the preparation of methyl methacrylate from methyl propionate, and to develop a simple, green, low-energy-consumption, and efficient purification method for methyl methacrylate. This purification method can effectively improve the conversion rate of methyl propionate, reduce energy consumption in the process, simplify the process flow, and achieve efficient utilization of the reaction raw materials.

[0008] To achieve the above objectives, a first aspect of the present invention provides a method for purifying methyl methacrylate, the method comprising:

[0009] I) The crude product containing formaldehyde, solvent, water, methyl propionate and methyl methacrylate is subjected to a first membrane separation to obtain a first permeate containing water and a first concentrate containing formaldehyde, solvent, methyl propionate and methyl methacrylate.

[0010] II) The first concentrate is subjected to second membrane separation to obtain a second permeate containing solvent and formaldehyde, and a second concentrate containing methyl propionate and methyl methacrylate;

[0011] III) The second concentrate was separated by distillation to obtain methyl propionate and methyl methacrylate.

[0012] A second aspect of the present invention provides a system for purifying methyl methacrylate, the system comprising:

[0013] The first membrane separation unit, the second membrane separation unit, and the distillation unit are connected in series in sequence.

[0014] The first membrane separation unit is used to separate the crude product containing formaldehyde, solvent, water, methyl propionate and methyl methacrylate using a first membrane to obtain a first permeate containing water and a first concentrate containing formaldehyde, solvent, methyl propionate and methyl methacrylate.

[0015] The second membrane separation unit is used to perform second membrane separation on the first concentrate to obtain a second permeate containing solvent and formaldehyde, and to obtain a second concentrate containing methyl propionate and methyl methacrylate;

[0016] The distillation unit is used to distill and separate the second concentrate to obtain methyl propionate and methyl methacrylate.

[0017] A third aspect of the present invention provides a system for preparing methyl methacrylate, the system comprising:

[0018] A reactor, a first membrane separation unit, a second membrane separation unit, a first distillation column, and a second distillation column are connected in series.

[0019] The reactor is used for the contact reaction of formaldehyde and methyl propionate in the presence of a solvent to obtain crude methyl methacrylate.

[0020] The first membrane separation unit is used to perform a first membrane separation on the crude methyl methacrylate product to remove the first permeate containing water, and obtain a first concentrate containing formaldehyde, solvent, methyl propionate and methyl methacrylate. Optionally, a portion of the first concentrate can be refluxed back to the inlet of the reactor.

[0021] The second membrane separation unit is used to perform second membrane separation on the remaining portion of the first concentrate to obtain a second permeate containing solvent and formaldehyde, and a second concentrate containing methyl propionate and methyl methacrylate; optionally, it is used to return the second permeate to the inlet of the reactor.

[0022] The first distillation column is used to perform a first distillation separation on the second concentrate to obtain methyl propionate from the top of the first distillation column, and optionally the obtained methyl propionate is returned to the reactor inlet;

[0023] The second distillation column is used to perform a second distillation separation on the product at the bottom of the first distillation column, and to obtain methyl methacrylate product from the top of the second distillation column.

[0024] The purification method for methyl methacrylate provided by the present invention removes water from the crude product containing formaldehyde, solvent, water, methyl propionate and methyl methacrylate through a first membrane separation, so that the first concentrate retains the product methyl methacrylate, methyl propionate and formaldehyde and solvent; a second membrane separation is used to remove solvent and small molecules such as formaldehyde from the first concentrate to obtain methyl propionate and methyl methacrylate.

[0025] The system for preparing / purifying methyl methacrylate provided by this invention is particularly designed for the process route of preparing methyl methacrylate from methyl propionate. It uses technologies including membrane separation and distillation, which are effectively combined to achieve repeated recycling of unreacted raw materials and purification and separation of methyl methacrylate. It has the advantages of simple operation, low equipment investment, high separation efficiency and low energy consumption, which greatly improves economic benefits. The recovery rate of methyl methacrylate is ≥99%, and the purity is ≥99.9%. Attached Figure Description

[0026] Figure 1 This is a flowchart of a preferred embodiment of the methyl methacrylate purification method of the present invention.

[0027] Explanation of reference numerals in the attached figures

[0028] ① — Reactor; ② — First membrane separation unit;

[0029] ③—Second membrane separation unit; ④—First distillation column;

[0030] ⑤—Second distillation column;

[0031] The specific stock information is as follows:

[0032] 1-Formaldehyde; 2-Methyl methacrylate crude product;

[0033] 3—First permeate; 4—First distillate;

[0034] 5—Second distillate;

[0035] 6—Second concentrate; 7—Second permeate;

[0036] 8—Product from the bottom of the first distillation column; 9—Product from the top of the first distillation column;

[0037] 10—Product from the bottom of the second distillation column; 11—Methyl methacrylate product;

[0038] 12—Added methyl propionate. Detailed Implementation

[0039] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0040] In this invention, unless otherwise specified, the "bottom" of a container (such as a distillation column, reactor, etc.) refers to the position of the container from top to bottom at 90-100%; the "top" of the container refers to the position of the container from top to bottom at 0-10%; the "upper part" of the container refers to the position of the container from top to bottom at 0-30%; and the "middle part" of the container refers to the position of the container from top to bottom at 30-70%.

[0041] According to a first aspect of the present invention, the present invention provides a method for purifying methyl methacrylate, the method comprising:

[0042] I) The crude product containing formaldehyde, solvent, water, methyl propionate and methyl methacrylate is subjected to a first membrane separation to obtain a first permeate containing water and a first concentrate containing formaldehyde, solvent, methyl propionate and methyl methacrylate.

[0043] II) The first concentrate is subjected to second membrane separation to obtain a second permeate containing solvent and formaldehyde, and a second concentrate containing methyl propionate and methyl methacrylate;

[0044] III) The second concentrate was separated by distillation to obtain methyl propionate and methyl methacrylate.

[0045] In this invention, the first membrane separation is mainly used to remove water from the crude product, completely removing the water generated in the reaction, so that the first concentrate retains the product methyl methacrylate, unreacted raw materials methyl propionate and formaldehyde, and solvents such as methanol. The second membrane separation is mainly used to remove small molecules such as solvents like methanol and formaldehyde. The molecules of formaldehyde and solvents such as methanol in the first concentrate are larger than those of methyl propionate and methyl methacrylate, allowing for separation and effectively removing formaldehyde and methanol products from the product.

[0046] According to the present invention, membrane separation technology has advantages such as low energy consumption and green process, and is an excellent separation and purification method. First membrane separation, such as using an inorganic membrane, can remove water completely, leaving the products methyl methacrylate, methyl propionate, and formaldehyde, as well as solvents such as methanol, in the first concentrate. Second membrane separation is mainly used to remove small molecules of solvent methanol and formaldehyde from the first concentrate. The second membrane separation unit, for example, uses an organic membrane to selectively remove formaldehyde and solvents such as methanol, thereby achieving separation.

[0047] According to a preferred embodiment of the present invention, the membrane used for the first membrane separation is an inorganic membrane. Any inorganic membrane in the art can achieve the purpose of the present invention. Preferably, the inorganic membrane is a 3A type molecular sieve membrane. In the present invention, there are no special requirements for the preparation method of the 3A type molecular sieve membrane; as long as it is formed into a membrane, the purpose of the present invention can be achieved.

[0048] According to a preferred embodiment of the present invention, the membrane used for the second membrane separation is an organic membrane; preferably, the organic membrane is a polyvinyl alcohol membrane.

[0049] According to a preferred embodiment of the present invention, the crude product containing formaldehyde, solvent, water, methyl propionate and methyl methacrylate contains 1-3% by weight of formaldehyde, 20-30% by weight of solvent, 2-3% by weight of water, 50-70% by weight of methyl propionate and 10-15% by weight of methyl methacrylate.

[0050] According to a preferred embodiment of the present invention, the solvent is methanol and / or ethanol, preferably methanol.

[0051] According to a preferred embodiment of the present invention, the crude product containing formaldehyde, solvent, water, methyl propionate and methyl methacrylate comes from a reactor for preparing methyl methacrylate from formaldehyde and methyl propionate, preferably a fixed-bed reactor.

[0052] When methyl propionate reacts with formaldehyde, in addition to producing the product methyl methacrylate, water is also generated. Since water forms an azeotropic system with many components in the reaction system, it significantly increases the difficulty of subsequent separation. Therefore, the water needs to be separated before methyl methacrylate purification to reduce the complexity of methyl methacrylate purification. According to a preferred embodiment of the present invention, the purification method for methyl methacrylate includes:

[0053] (a) The crude methyl methacrylate product after the reaction of formaldehyde and methyl propionate from the reactor is subjected to a first membrane separation to remove the first permeate containing water, and a first concentrate containing formaldehyde, solvent, methyl propionate and methyl methacrylate.

[0054] (b) A portion of the first concentrate is refluxed to the inlet of the reactor, and the remainder is subjected to second membrane separation to obtain a second permeate containing solvent and formaldehyde, and a second concentrate containing methyl propionate and methyl methacrylate.

[0055] (c) The second permeate is returned to the inlet of the reactor, and the second concentrate is subjected to a first distillation separation to obtain methyl propionate from the top of the first distillation column. Optionally, the obtained methyl propionate is returned to the inlet of the reactor.

[0056] (d) The product from the bottom of the column after the first distillation separation is subjected to a second distillation separation, and methyl methacrylate is obtained from the top of the column after the second distillation separation.

[0057] According to some embodiments of the present invention, the volumetric flow rate ratio of the portion of the first concentrate after the first membrane separation that is refluxed to the reactor and the portion undergoing the second membrane separation is 10:1 to 1:10. Compared with conventional separation processes, this process uniquely separates the dehydrated product into two streams: one stream re-enters the reactor for further reaction, and the other stream undergoes the second membrane separation. This process has the following advantages:

[0058] 1. Improve raw material conversion rate: The dehydrated product is fed back into the reaction unit. Due to the lack of water in the reaction product, the water concentration in the reaction unit is reduced, causing the reaction to proceed in the direction of methyl methacrylate formation, thereby improving the raw material conversion rate.

[0059] 2. Reduced Energy Consumption in Subsequent Separation: The reduction in energy consumption is due to two factors. Firstly, the partial recirculation to the reaction unit reduces the amount of material to be processed in subsequent separation units, thereby reducing separation energy consumption. Secondly, the increased raw material conversion rate reduces the amount of unreacted raw material processed in subsequent separation units, improving the energy utilization rate of the methyl methacrylate product. This invention also provides a preferred volumetric flow rate ratio between the recirculation to the reactor section and the section undergoing the second membrane separation: 10:1 to 1:10. Exceeding this range will result in an excessively large reactor volume, hindering further effective improvement in methyl propionate conversion, while a lower ratio will result in insignificant energy savings and reduced methyl propionate conversion efficiency.

[0060] According to some embodiments of the present invention, the second permeate obtained from the second membrane separation is returned to the reactor, while the second concentrate enters a distillation column. After the second membrane separation treatment, small molecule formaldehyde and solvents such as methanol in the first permeate can permeate through the membrane material to form the second permeate. Since formaldehyde is the reactant and solvents such as methanol are the reaction solvents, the second permeate can be directly returned to the reactor. The second concentrate, mainly composed of methyl propionate and the product methyl methacrylate, enters the distillation column for further separation.

[0061] According to the present invention, there are no special requirements for the first distillation column. Preferably, the first distillation column is a conventional packed column or a plate column, and the second concentrate obtained by the second membrane separation enters from the upper middle part of the first distillation column. The purpose of the first distillation column is to separate methyl propionate and methyl methacrylate, which have significant differences in boiling points. A conventional packed column or plate column can achieve effective separation. Simultaneously, the first distillation column also removes light components other than methyl propionate, such as small amounts of methanol that were not removed during the second membrane separation. The feed location is in the upper middle part of the first distillation column to ensure that methyl propionate and other light components are completely removed in the first distillation column.

[0062] According to the present invention, the product exiting from the top of the first distillation column is mainly unreacted methyl propionate, which can be returned to the reactor for further reaction.

[0063] According to a preferred embodiment of the present invention, the operating pressure of the first distillation column is 0.5–1 atm, the reflux ratio is 0.2–4, and the reboiler temperature of the first distillation column is controlled at 80°C–101°C. The first distillation column needs to be operated under negative or atmospheric pressure to reduce the overall operating temperature of the column. The reflux ratio needs to be controlled within a certain range; too high a ratio will significantly increase distillation energy consumption and will not effectively remove methyl propionate and some light components. Too low a reflux ratio will result in waste of the product methyl methacrylate. Therefore, the reflux ratio needs to be controlled within the optimal range of 0.2–4. To ensure the purity of methyl methacrylate in the reboiler product, the reboiler temperature needs to be controlled at 80°C–101°C depending on the operating pressure.

[0064] According to the present invention, there are no special requirements for the second distillation column. The second distillation column is a conventional packed column or a plate column, and the bottom product of the first distillation column enters from the lower middle part of the second distillation column. The purpose of the second distillation column is to remove heavy components from methyl methacrylate and obtain methyl methacrylate product at the top of the column. Conventional packed columns or plate columns can achieve the above separation purpose. The bottom product of the first distillation column, i.e., the crude methacrylic acid, needs to enter from the lower middle part of the second distillation column to increase the height of the separation and rectification section and improve the purity of the top product, methyl methacrylate.

[0065] According to one embodiment of the present invention, the operating pressure of the second distillation column is 0.5–1 atm, the reflux ratio is 2–10, and the top temperature of the second distillation column is controlled at 78°C–100°C, collecting the top product. The second distillation column also needs to be operated under negative or atmospheric pressure to reduce the overall operating temperature of the column. The reflux ratio should be controlled within a relatively high range to achieve high purity of the top product. A low reflux ratio will cause some heavy components to enter the top of the column, resulting in a decrease in the purity of methyl methacrylate, while an excessively high reflux ratio will significantly increase distillation energy consumption. The optimal reflux ratio should be controlled within the range of 2–10. Simultaneously, during the distillation process, the top temperature needs to be strictly controlled, and depending on the operating pressure, the top temperature needs to be maintained between 78°C and 100°C.

[0066] According to a second aspect of the present invention, the present invention provides a system for purifying methyl methacrylate, such as... Figure 1 As shown, the system includes:

[0067] The first membrane separation unit ②, the second membrane separation unit ③, and the distillation unit are connected in series in sequence.

[0068] The first membrane separation unit ② is used to separate the crude product containing formaldehyde, solvent, water, methyl propionate and methyl methacrylate using a first membrane to obtain a first permeate containing water and a first concentrate containing formaldehyde, solvent, methyl propionate and methyl methacrylate.

[0069] The second membrane separation unit ③ is used to perform second membrane separation on the first concentrate to obtain a second permeate containing solvent and formaldehyde, and to obtain a second concentrate containing methyl propionate and methyl methacrylate;

[0070] The distillation unit is used to distill and separate the second concentrate to obtain methyl propionate and methyl methacrylate.

[0071] According to a third aspect of the present invention, the present invention provides a system for preparing methyl methacrylate, such as... Figure 1 As shown, the system includes:

[0072] The reactor ①, the first membrane separation unit ②, the second membrane separation unit ③, the first distillation column ④, and the second distillation column ⑤ are connected in series.

[0073] The reactor ① is used for the contact reaction of formaldehyde and methyl propionate in the presence of a solvent to obtain crude methyl methacrylate product.

[0074] The first membrane separation unit ② is used to perform a first membrane separation on the crude methyl methacrylate product to remove the first permeate containing water, and obtain a first concentrate containing formaldehyde, solvent, methyl propionate and methyl methacrylate. Optionally, a portion of the first concentrate can be refluxed back to the inlet of the reactor.

[0075] The second membrane separation unit ③ is used to perform second membrane separation on the remaining portion of the first concentrate to obtain a second permeate containing solvent and formaldehyde, and a second concentrate containing methyl propionate and methyl methacrylate; optionally, it is used to return the second permeate to the inlet of the reactor.

[0076] The first distillation column ④ is used to perform a first distillation separation on the second concentrate to obtain methyl propionate from the top of the first distillation column, and optionally the obtained methyl propionate is returned to the reactor inlet;

[0077] The second distillation column ⑤ is used to perform a second distillation separation on the product at the bottom of the first distillation column, and to obtain methyl methacrylate product from the top of the second distillation column.

[0078] According to a preferred embodiment of the present invention, the first membrane separation unit ② is disposed above the top outlet of the reactor ①.

[0079] According to a preferred embodiment of the present invention, the feed inlet of the first membrane separation unit ② is connected to the top discharge outlet of the reactor ①.

[0080] The first membrane separation unit ② includes a first permeate outlet for removing the first permeate containing water, and a first concentrate outlet, which is connected to the bottom inlet of the reactor ① and the inlet of the second membrane separation unit ③.

[0081] The second permeate outlet of the second membrane separation unit ③ is connected to the bottom feed inlet of the reactor ①, and the second concentrate outlet of the second membrane separation unit ③ is connected to the upper middle feed inlet of the first distillation column.

[0082] The product outlet of the first distillation column is connected to the feed inlet of the lower middle part of the second distillation column;

[0083] The first and second distillation columns are each ordinary packed columns or plate columns.

[0084] According to a preferred embodiment of the present invention, the membrane used for the first membrane separation is an inorganic membrane. Any inorganic membrane in the art can achieve the purpose of the present invention. Preferably, the inorganic membrane is a 3A type molecular sieve membrane. In the present invention, there are no special requirements for the preparation method of the 3A type molecular sieve membrane; as long as it is formed into a membrane, the purpose of the present invention can be achieved.

[0085] According to a preferred embodiment of the present invention, the membrane used for the second membrane separation is an organic membrane; preferably, the organic membrane is a polyvinyl alcohol membrane.

[0086] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0087] The reagents and raw materials used in this invention are all commercially available.

[0088] In this invention, the purity of the products in all embodiments was obtained by HPLC detection.

[0089] In routine operation, methyl propionate, formaldehyde, and methanol returned to the reactor, along with added methyl propionate and formaldehyde, enter the reactor together. The products exiting the reactor mainly consist of methyl propionate, formaldehyde, methanol, water, and methyl methacrylate. After separation by the first membrane, the permeate, primarily water, is discharged for further treatment. The concentrate from the first membrane separation is split into two streams: one returns to the reactor inlet, and the other enters the second membrane separation. The resulting permeate, primarily a mixture of formaldehyde and methanol, is also returned to the reactor. The concentrate from the second membrane separation mainly contains methyl propionate and methyl methacrylate, and enters the first distillation column for separation. Methyl propionate is obtained from the top of the column and returned to the reactor, while crude methyl methacrylate is obtained from the bottom. The crude product is then sent to the second distillation column for deweighting treatment, ultimately yielding methyl methacrylate at the top of the second distillation column.

[0090] In this invention, such as Figure 1 As shown, the crude methyl methacrylate product 2 (composed of: formaldehyde 1-3 wt%, solvent 20-30 wt%, water 2-3 wt%, methyl propionate 50-70 wt%, methyl methacrylate 10-15 wt%) produced after reaction in reactor ① undergoes first membrane separation in the first membrane separation unit ②. The first permeate 3, water, is discharged from the boundary area. The second concentrate, mainly composed of formaldehyde, methanol, methyl propionate, and methyl methacrylate, is divided into two streams. The first stream 4 is refluxed back to reactor ①, and the second stream 5 enters the second membrane separation unit ③ for second membrane separation. The second permeate 7, separated by the second membrane, is a mixture of formaldehyde and methanol and is returned to reactor ①. The second concentrate 6, mainly composed of methyl propionate and methyl methacrylate, enters the first distillation column ④ for distillation. The top product 9 of the first distillation column ④, mainly composed of methyl propionate, is returned to reactor ①. The bottom product 8 of the first distillation column enters the second distillation column ⑤ for distillation, ultimately obtaining methyl methacrylate product 11 at the top of the column. The top product 9 of the first distillation column returned to reactor ①, the second permeate 7, and the added methyl propionate 12 and formaldehyde 1 enter reactor ① together. The membrane used in the first membrane separation unit is a type 3A molecular sieve membrane, and the membrane used in the second membrane separation unit is a polyvinyl alcohol membrane.

[0091] In this invention, the methyl methacrylate recovery rate refers to the ratio of the final mass of methyl methacrylate to the mass of methyl methacrylate entering the first distillation column.

[0092] The following embodiments employ the following methods: Figure 1 The process shown is used for recycling.

[0093] In the following embodiments, the membrane used for the first membrane separation is a 3A type molecular sieve membrane, and the membrane used for the second membrane separation unit is a polyvinyl alcohol membrane.

[0094] Example 1

[0095] The products from the reactor reaction, measured by mass, contain 2% formaldehyde, 25% methanol, 3% water, 55% methyl propionate, and 15% methyl methacrylate. After passing through the first membrane separator, the permeate (water) is discharged from the boundary area. The concentrate, mainly composed of formaldehyde, methanol, methyl propionate, and methyl methacrylate, is divided into two streams: one is refluxed back to the reactor, and the other enters the second membrane separator. The volumetric flow rate ratio of the refluxed portion to the portion undergoing the second membrane separator is 10:1. The permeate from the second membrane separator, a mixture of formaldehyde and methanol, is also returned to the reactor, while the concentrate, mainly composed of methyl propionate and methyl methacrylate, enters the first distillation column. The operating pressure of the first distillation column is 0.5 atm, the reflux ratio is 1, and the temperature of the bottom column is controlled at 80°C. The top product of the first distillation column, mainly methyl propionate, is returned to the reactor, while the bottom product enters the second distillation column. The second distillation column operates at a pressure of 1 atm, a reflux ratio of 4, and a top temperature of 100°C. Methyl methacrylate is finally obtained at the top of the column, and its purity is measured to be 99.96%. The overall methyl methacrylate recovery rate is 99.6%.

[0096] Example 2

[0097] The products from the reactor reaction, measured by mass, contain 2% formaldehyde, 25% methanol, 3% water, 55% methyl propionate, and 15% methyl methacrylate. After passing through the first membrane separator, the permeate (water) is discharged from the boundary area. The concentrate, mainly composed of formaldehyde, methanol, methyl propionate, and methyl methacrylate, is divided into two streams: one is refluxed back to the reactor, and the other enters the second membrane separator. The volumetric flow rate ratio of the refluxed portion to the portion undergoing the second membrane separator is 2:1. The permeate from the second membrane separator, a mixture of formaldehyde and methanol, is also returned to the reactor, while the concentrate, mainly composed of methyl propionate and methyl methacrylate, enters the first distillation column. The operating pressure of the first distillation column is 0.75 atm, the reflux ratio is 1, and the temperature of the bottom column is controlled at 92°C. The top product of the first distillation column, mainly methyl propionate, is returned to the reactor, while the bottom product enters the second distillation column. The second distillation column operates at a pressure of 1 atm, a reflux ratio of 4, and a top temperature of 100°C. Methyl methacrylate is finally obtained at the top of the column, and its purity is 99.94%, with an overall methyl methacrylate recovery rate of 99.4%.

[0098] Example 3

[0099] The products from the reactor reaction, measured by mass, contain 2% formaldehyde, 25% methanol, 3% water, 55% methyl propionate, and 15% methyl methacrylate. After passing through the first membrane separator, the permeate (water) is discharged from the boundary area. The concentrate, mainly composed of formaldehyde, methanol, methyl propionate, and methyl methacrylate, is divided into two streams: one is refluxed back to the reactor, and the other enters the second membrane separator. The volumetric flow ratio of the refluxed portion to the portion undergoing the second membrane separator is 1:1. The permeate from the second membrane separator, a mixture of formaldehyde and methanol, is also returned to the reactor, while the concentrate, mainly composed of methyl propionate and methyl methacrylate, enters the first distillation column. The first distillation column operates at a pressure of 1 atm, a reflux ratio of 1, and a bottom temperature of 101°C. The top product of the first distillation column, mainly methyl propionate, is returned to the reactor, while the bottom product enters the second distillation column. The second distillation column operates at a pressure of 1 atm, a reflux ratio of 4, and a top temperature of 100°C. Methyl methacrylate is finally obtained at the top of the column, and its purity is measured to be 99.93%. The overall methyl methacrylate recovery rate is 99.3%.

[0100] Example 4

[0101] The products from the reactor reaction, measured by mass, contain 2% formaldehyde, 25% methanol, 3% water, 55% methyl propionate, and 15% methyl methacrylate. After passing through the first membrane separator, the permeate (water) is discharged from the boundary area. The concentrate, mainly composed of formaldehyde, methanol, methyl propionate, and methyl methacrylate, is divided into two streams: one is refluxed back to the reactor, and the other enters the second membrane separator. The volumetric flow rate ratio of the refluxed portion to the portion undergoing the second membrane separator is 1:2. The permeate from the second membrane separator, a mixture of formaldehyde and methanol, is also returned to the reactor, while the concentrate, mainly composed of methyl propionate and methyl methacrylate, enters the first distillation column. The operating pressure of the first distillation column is 0.75 atm, the reflux ratio is 1, and the temperature of the bottom column is controlled at 92°C. The top product of the first distillation column, mainly methyl propionate, is returned to the reactor, while the bottom product enters the second distillation column. The second distillation column operates at a pressure of 0.75 atm, a reflux ratio of 4, and a top temperature of 90°C. Methyl methacrylate is finally obtained at the top of the column, and its purity is measured to be 99.92%. The overall methyl methacrylate recovery rate is 99.1%.

[0102] Example 5

[0103] The products from the reactor reaction, measured by mass, contain 2% formaldehyde, 25% methanol, 3% water, 55% methyl propionate, and 15% methyl methacrylate. After passing through the first membrane separator, the permeate (water) is discharged from the boundary area. The concentrate, mainly composed of formaldehyde, methanol, methyl propionate, and methyl methacrylate, is divided into two streams: one is refluxed back to the reactor, and the other enters the second membrane separator. The volumetric flow rate ratio of the refluxed portion to the portion undergoing the second membrane separator is 1:10. The permeate from the second membrane separator, a mixture of formaldehyde and methanol, is also returned to the reactor, while the concentrate, mainly composed of methyl propionate and methyl methacrylate, enters the first distillation column. The operating pressure of the first distillation column is 0.75 atm, the reflux ratio is 1, and the temperature of the bottom column is controlled at 92°C. The top product of the first distillation column, mainly methyl propionate, is returned to the reactor, while the bottom product enters the second distillation column. The second distillation column operates at a pressure of 0.5 atm, a reflux ratio of 4, and a top temperature of 78°C. Methyl methacrylate is finally obtained at the top of the column, and its purity is 99.90%, with an overall methyl methacrylate recovery rate of 99.0%.

[0104] Example 6

[0105] The products from the reactor reaction, measured by mass, contain 2% formaldehyde, 25% methanol, 3% water, 55% methyl propionate, and 15% methyl methacrylate. After passing through the first membrane separator, the permeate (water) is discharged from the boundary area. The concentrate, mainly composed of formaldehyde, methanol, methyl propionate, and methyl methacrylate, is divided into two streams: one is refluxed back to the reactor, and the other enters the second membrane separator. The volumetric flow rate ratio of the refluxed portion to the portion undergoing the second membrane separator is 2:1. The permeate from the second membrane separator, a mixture of formaldehyde and methanol, is also returned to the reactor, while the concentrate, mainly composed of methyl propionate and methyl methacrylate, enters the first distillation column. The operating pressure of the first distillation column is 0.75 atm, the reflux ratio is 0.2, and the temperature of the bottom column is controlled at 92°C. The top product of the first distillation column, mainly methyl propionate, is returned to the reactor, while the bottom product enters the second distillation column. The second distillation column operates at a pressure of 1 atm, a reflux ratio of 4, and a top temperature of 100°C. Methyl methacrylate is finally obtained at the top of the column, and its purity is measured to be 99.96%. The overall methyl methacrylate recovery rate is 99.2%.

[0106] Example 7

[0107] The products from the reactor reaction, measured by mass, contain 2% formaldehyde, 25% methanol, 3% water, 55% methyl propionate, and 15% methyl methacrylate. After passing through the first membrane separator, the permeate (water) is discharged from the boundary area. The concentrate, mainly composed of formaldehyde, methanol, methyl propionate, and methyl methacrylate, is divided into two streams: one is refluxed back to the reactor, and the other enters the second membrane separator. The volumetric flow rate ratio of the refluxed portion to the portion undergoing the second membrane separator is 2:1. The permeate from the second membrane separator, a mixture of formaldehyde and methanol, is also returned to the reactor, while the concentrate, mainly composed of methyl propionate and methyl methacrylate, enters the first distillation column. The operating pressure of the first distillation column is 0.75 atm, the reflux ratio is 2, and the temperature of the bottom column is controlled at 92°C. The top product of the first distillation column, mainly methyl propionate, is returned to the reactor, while the bottom product enters the second distillation column. The second distillation column operates at a pressure of 1 atm, a reflux ratio of 4, and a top temperature of 100°C. Methyl methacrylate is finally obtained at the top of the column, and its purity is 99.94%, with an overall methyl methacrylate recovery rate of 99.4%.

[0108] Example 8

[0109] The products from the reactor reaction, measured by mass, contain 2% formaldehyde, 25% methanol, 3% water, 55% methyl propionate, and 15% methyl methacrylate. After passing through the first membrane separator, the permeate (water) is discharged from the boundary area. The concentrate, mainly composed of formaldehyde, methanol, methyl propionate, and methyl methacrylate, is divided into two streams: one is refluxed back to the reactor, and the other enters the second membrane separator. The volumetric flow rate ratio of the refluxed portion to the portion undergoing the second membrane separator is 2:1. The permeate from the second membrane separator, a mixture of formaldehyde and methanol, is also returned to the reactor, while the concentrate, mainly composed of methyl propionate and methyl methacrylate, enters the first distillation column. The operating pressure of the first distillation column is 0.75 atm, the reflux ratio is 4, and the temperature of the bottom column is controlled at 92°C. The top product of the first distillation column, mainly methyl propionate, is returned to the reactor, while the bottom product enters the second distillation column. The second distillation column operates at a pressure of 1 atm, a reflux ratio of 4, and a top temperature of 100°C. Methyl methacrylate is finally obtained at the top of the column, and its purity is 99.91%, with an overall methyl methacrylate recovery rate of 99.6%.

[0110] Example 9

[0111] The products from the reactor reaction, measured by mass, contain 2% formaldehyde, 25% methanol, 3% water, 55% methyl propionate, and 15% methyl methacrylate. After passing through the first membrane separator, the permeate (water) is discharged from the boundary area. The concentrate, mainly composed of formaldehyde, methanol, methyl propionate, and methyl methacrylate, is divided into two streams: one is refluxed back to the reactor, and the other enters the second membrane separator. The volumetric flow rate ratio of the refluxed portion to the portion undergoing the second membrane separator is 2:1. The permeate from the second membrane separator, a mixture of formaldehyde and methanol, is also returned to the reactor, while the concentrate, mainly composed of methyl propionate and methyl methacrylate, enters the first distillation column. The operating pressure of the first distillation column is 0.75 atm, the reflux ratio is 1, and the temperature of the bottom column is controlled at 92°C. The top product of the first distillation column, mainly methyl propionate, is returned to the reactor, while the bottom product enters the second distillation column. The second distillation column operates at a pressure of 1 atm, a reflux ratio of 2, and a top temperature of 100°C. Methyl methacrylate is finally obtained at the top of the column, and its purity is 99.92%, with an overall methyl methacrylate recovery rate of 99.5%.

[0112] Example 10

[0113] The products from the reactor reaction, measured by mass, contain 2% formaldehyde, 25% methanol, 3% water, 55% methyl propionate, and 15% methyl methacrylate. After passing through the first membrane separator, the permeate (water) is discharged from the boundary area. The concentrate, mainly composed of formaldehyde, methanol, methyl propionate, and methyl methacrylate, is divided into two streams: one is refluxed back to the reactor, and the other enters the second membrane separator. The volumetric flow rate ratio of the refluxed portion to the portion undergoing the second membrane separator is 2:1. The permeate from the second membrane separator, a mixture of formaldehyde and methanol, is also returned to the reactor, while the concentrate, mainly composed of methyl propionate and methyl methacrylate, enters the first distillation column. The operating pressure of the first distillation column is 0.75 atm, the reflux ratio is 1, and the temperature of the bottom column is controlled at 92°C. The top product of the first distillation column, mainly methyl propionate, is returned to the reactor, while the bottom product enters the second distillation column. The second distillation column operates at a pressure of 1 atm, a reflux ratio of 6, and a top temperature of 100°C. Methyl methacrylate is finally obtained at the top of the column, and its purity is 99.95%, with an overall methyl methacrylate recovery rate of 99.2%.

[0114] Example 11

[0115] The products from the reactor reaction, measured by mass, contain 2% formaldehyde, 25% methanol, 3% water, 55% methyl propionate, and 15% methyl methacrylate. After passing through the first membrane separator, the permeate (water) is discharged from the boundary area. The concentrate, mainly composed of formaldehyde, methanol, methyl propionate, and methyl methacrylate, is divided into two streams: one is refluxed back to the reactor, and the other enters the second membrane separator. The volumetric flow rate ratio of the refluxed portion to the portion undergoing the second membrane separator is 2:1. The permeate from the second membrane separator, a mixture of formaldehyde and methanol, is also returned to the reactor, while the concentrate, mainly composed of methyl propionate and methyl methacrylate, enters the first distillation column. The operating pressure of the first distillation column is 0.75 atm, the reflux ratio is 1, and the temperature of the bottom column is controlled at 92°C. The top product of the first distillation column, mainly methyl propionate, is returned to the reactor, while the bottom product enters the second distillation column. The second distillation column operates at a pressure of 1 atm, a reflux ratio of 10, and a top temperature of 100°C. Methyl methacrylate is finally obtained at the top of the column, and its purity is measured to be 99.97%. The overall methyl methacrylate recovery rate is 99.1%.

[0116] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

[0117] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for purifying methyl methacrylate, characterized in that, a crude product containing formaldehyde, solvent, water, methyl propionate and methyl methacrylate is obtained from a reactor for preparing methyl methacrylate from formaldehyde and methyl propionate; the method comprises: (a) removing a first permeate containing water from the crude product of methyl methacrylate after the reaction of formaldehyde and methyl propionate from the reactor by a first membrane separation to obtain a first concentrate containing formaldehyde, solvent, methyl propionate and methyl methacrylate; (b) returning part of the first concentrate to the inlet of the reactor and subjecting the rest to a second membrane separation to obtain a second permeate containing solvent and formaldehyde and a second concentrate containing methyl propionate and methyl methacrylate; (c) returning the second permeate to the inlet of the reactor and subjecting the second concentrate to a first rectification separation to obtain methyl methacrylate product from the top of the first rectification separation, and optionally returning the obtained methyl propionate to the inlet of the reactor; (d) subjecting the column bottom product after the first rectification separation to a second rectification separation to obtain methyl methacrylate product from the top of the second rectification separation; the ratio of the volume flow rate of the part of the first concentrate returned to the reactor to the part subjected to the second membrane separation is 10:1 to 1:10; the operating conditions of the first rectification include a pressure of 0.5 to 1 atm, a reflux ratio of 0.2 to 4, and a column bottom temperature of 80°C to 101°C; the operating conditions of the second rectification include a pressure of 0.5 to 1 atm, a reflux ratio of 2 to 10, and a column top temperature of 78°C to 100°C; the membrane used in the first membrane separation is an inorganic membrane; the membrane used in the second membrane separation is an organic membrane; the inorganic membrane is a 3A molecular sieve membrane; and the organic membrane is a polyvinyl alcohol membrane.

2. The purification method according to claim 1, wherein, the crude product containing formaldehyde, solvent, water, methyl propionate and methyl methacrylate contains 1-3% by weight of formaldehyde, 20-30% by weight of solvent, 2-3% by weight of water, 50-70% by weight of methyl propionate, and 10-15% by weight of methyl methacrylate.

3. The purification method according to claim 1, wherein, the solvent is methanol and / or ethanol.

4. The purification method according to claim 3, wherein, the solvent is methanol.

5. The purification method according to claim 1, wherein, the second concentrate enters from the middle upper part of the first rectification unit; and / or 6. The purification method of claim 1, wherein, the column bottom product of the first rectification enters from the middle lower part of the second rectification unit. The method is carried out in a system for preparing methyl methacrylate, which comprises: a reactor (①), a first membrane separation unit (②), a second membrane separation unit (③), a first rectification column (④) and a second rectification column (⑤) connected in series; the reactor (①) is used for contacting formaldehyde and methyl propionate in the presence of a solvent to obtain a crude product of methyl methacrylate; the reactor (①) is used for contacting formaldehyde and methyl propionate in the presence of a solvent to obtain a crude product of methyl methacrylate; The first membrane separation unit (②) is used for removing the first permeate containing water from the crude methyl methacrylate product by first membrane separation to obtain the first concentrated liquid containing formaldehyde, solvent, methyl propionate and methyl methacrylate, and optionally used for returning part of the first concentrated liquid to the inlet of the reactor; The second membrane separation unit (③) is used for performing second membrane separation on the remaining part of the first concentrated liquid to obtain the second permeate containing solvent and formaldehyde, and to obtain the second concentrated liquid containing methyl propionate and methyl methacrylate, and optionally used for returning the second permeate to the inlet of the reactor; The first rectification column (④) is used for performing first rectification separation on the second concentrated liquid to obtain methyl propionate from the top of the first rectification column, and optionally used for returning the obtained methyl propionate to the inlet of the reactor; The second rectification column (⑤) is used for performing second rectification separation on the column bottom product of the first rectification column to obtain the methyl methacrylate product from the top of the second rectification column; The ratio of the volume flow rate of the part of the first concentrated liquid returned to the reactor to the volume flow rate of the part subjected to second membrane separation is 10:1-1:10; The operating conditions of the first rectification include: the pressure is 0.5-1 atm, the reflux ratio is 0.2-4, and the column bottom temperature is 80-101℃; The operating conditions of the second rectification include: the pressure is 0.5-1 atm, the reflux ratio is 2-10, and the top temperature is 78-100℃.

7. The purification method according to claim 6, wherein, The first membrane separation unit (②) is arranged above the top discharge port of the reactor (①); and / or The feed port of the first membrane separation unit (②) is communicated with the top discharge port of the reactor (①); and / or The first membrane separation unit (②) comprises a first permeate discharge port for removing the first permeate containing water, and a first concentrated liquid discharge port communicated with the bottom feed port of the reactor (①) and the feed port of the second membrane separation unit (③); The second permeate discharge port of the second membrane separation unit (③) is communicated with the bottom feed port of the reactor (①), and the second concentrated liquid discharge port of the second membrane separation unit (③) is communicated with the middle-upper feed port of the first rectification column; The column bottom product outlet of the first rectification column is communicated with the middle-lower feed port of the second rectification column; The first rectification column and the second rectification column are each a common packed column or a plate column.

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