A process for the extraction and separation of methyl methacrylate and methanol

Abstract

The present application relates to a kind of methods for extracting and separating methyl methacrylate and methanol, which is: first, the raw material stream containing methyl methacrylate and methanol is mixed with water to obtain a mixture stream, then the mixture stream is extracted using a solvent to obtain a rich solvent stream containing methyl methacrylate and a methanol aqueous solution, then the rich solvent stream is washed using water to remove methanol, and after recovering the solvent, a crude methyl methacrylate product is obtained.Compared with the prior art, the present application uses a combination process of two extractants, alkane solvent and water, to separate methyl methacrylate and methanol, solving the problem of residual MMA in the aqueous phase of the extractant using only water as the extractant, and the adaptation range of the concentration ratio of MMA and methanol in the separation raw material is wider, the separation precision is better, and the energy saving is significant.The water content in the obtained crude MMA product is ≤100 mg / kg, which is much lower than the requirement for water content in the superior product of HG / T 2305-2017 Industrial Methyl Methacrylate.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of organic matter separation, and relates to a method for extracting and separating methyl methacrylate and methanol from a stream containing methyl methacrylate and methanol, in particular to a method for extracting and separating methyl methacrylate and methanol from a stream containing methyl methacrylate and methanol formed in the process of producing methyl methacrylate through methacrylate esterification or methacrolein oxidation esterification. BACKGROUND

[0002] Methyl methacrylate (MMA) is an important organic chemical raw material and chemical product, which is mainly used for producing organic glass (PMMA), polyvinyl chloride auxiliary ACR (acrylate copolymer), methyl methacrylate-styrene-butadiene copolymer (MBS) and used as the second monomer of acrylic, and also can be used as a resin, an adhesive, a coating, an ion exchange resin, a paper brightener, a textile printing and dyeing auxiliary, a leather treatment agent, a lubricating oil additive, a crude oil pour point depressant, a wood and softwood impregnating agent, a motor coil impregnating agent, an insulating impregnating material and a plastic emulsion plasticizer, etc., and has a very wide range of uses.

[0003] There are many process technologies for producing methyl methacrylate, which are mainly divided into acetone cyanohydrin method, isobutylene method and ethylene method according to raw materials.

[0004] At present, most of the MMA production capacity at home and abroad still adopts the acetone cyanohydrin technology route, but due to the serious pollution and environmental unfriendliness of this route, it has already belonged to the national restricted development industry. The isobutylene technology route which has been industrialized in China is a three-step method of isobutylene→methyl methacrylaldehyde (MAL)→methyl methacrylate (MMA), which has a long process and a complex process, and more equipment. The improved isobutylene technology route only needs two-step reaction, that is, isobutylene→MAL→MMA technology route, in which MAL is directly produced into MMA by one-step oxidation esterification using nano gold catalyst, which shortens the process flow, improves the product yield, avoids the corrosion of the device, and has a mild reaction condition and a low requirement for the reaction equipment, and is a very promising technology route.

[0005] The technical route of one-step oxidation esterification of MAL to produce MMA is also applicable to the ethylene method, and the technical route is a combination of the process of producing propyl aldehyde through ethylene hydroformylation and the process of producing MAL through the condensation of propyl aldehyde and formaldehyde and the process of one-step oxidation esterification to generate MMA.

[0006] In order to improve the yield of MMA product, methanol is required to be excessive in the oxidation esterification reaction of MAL, and the molar ratio of methanol to MAL (also called alcohol aldehyde ratio) is generally 2-6 times. After the oxidation esterification reaction product is removed from the unreacted MAL, methanol needs to be separated from MMA, and the obtained crude MMA is sent to the product refining unit to produce MMA product, and the crude methanol is sent to the methanol recovery column to recover methanol and recycle it to the oxidation esterification reactor.

[0007] Since methanol and MMA have azeotrope, the azeotrope temperature is 64.2℃ at normal pressure, and the azeotrope composition contains 77.3wt% of methanol, so they cannot be effectively separated by ordinary distillation. CN105683148A discloses a method for separating methanol and MMA. This technology separates methanol and MMA by azeotropic distillation of MAL and methanol. Since the content of methanol in the azeotrope of MAL and methanol is about 32wt%, a large amount of MAL needs to be added when methanol and MMA are separated, so this method is only suitable for very low alcohol aldehyde ratio conditions, and has the defect of high energy consumption. CN106588654A discloses a method for separating MMA and methanol by extraction. This method uses desalted water as an extractant to extract methanol from MMA. Although this method can effectively separate methanol and MMA, about 5-10wt% of MMA is still contained in the aqueous phase of the extractant, which will return to the esterification reactor or the oxidation esterification reactor with the recycled methanol. Since the esterification reaction is an equilibrium reaction, the recycled MMA not only reduces the conversion rate of MAA in the esterification reactor or MAL in the oxidation esterification reactor, but also reduces the recovery rate of MMA, because the MMA will be polymerized during the recycling process and cause loss. In addition, the recycled MMA also increases the energy consumption of the separation process. SUMMARY

[0008] The purpose of the present application is to provide a method for extracting and separating methyl methacrylate and methanol, which can extract and separate methyl methacrylate and methanol from a stream containing methyl methacrylate and methanol, solve the problem of MMA carried by recycled methanol, thereby improving the conversion rate of MAL in the oxidation esterification reactor, reducing the energy consumption of separation, and improving the recovery rate of MMA.

[0009] The purpose of the present application can be achieved by the following technical solutions:

[0010] A method for extracting and separating methyl methacrylate and methanol, which comprises: first mixing a raw material stream containing methyl methacrylate and methanol with water to obtain a mixed stream, then extracting the mixed stream with a solvent to obtain a rich solvent stream containing methyl methacrylate and a methanol aqueous solution, then washing the rich solvent stream with water to remove methanol, and then recovering the solvent to obtain a crude methyl methacrylate product.

[0011] Further, the raw material stream is from the product of methacrylate esterification reaction or methacrolein oxidation esterification reaction. The raw material stream containing methyl methacrylate and methanol is from a reaction process or separation process that can produce methyl methacrylate and methanol, such as a methacrylate esterification process or a methacrolein oxidation esterification process, and the raw material stream can also contain one or more of water, methacrylic acid, methyl isobutyrate, methacrolein, methacrolein dimethyl acetal, heavy components, etc. The content of methyl methacrylate in the raw material stream is 10-80 wt%, preferably 20-70 wt%.

[0012] Further, the solvent includes one or more of cyclohexane, n-hexane, methylcyclohexane or n-heptane.

[0013] Further, the solvent is recovered by rectification.

[0014] Further, when the raw material stream also contains methacrolein dimethyl acetal (the content of methacrolein dimethyl acetal in the raw material stream is 0.05-5 wt%, preferably 0.1-3 wt%), the solvent-rich stream containing methyl methacrylate obtained by extraction is first mixed with inorganic acid and water to perform acetal hydrolysis reaction, and then the acetal hydrolysis reaction product is washed with water to remove methanol, and then the solvent is recovered to obtain the crude methyl methacrylate product.

[0015] Further, the method is specifically:

[0016] In the first extraction column, the raw material stream containing methyl methacrylate and methanol is mixed with the washing water stream from the second extraction column column to enter the upper part of the first extraction column, or enters the middle and upper parts of the first extraction column respectively, while the lean solvent stream as the extractant enters the lower part of the first extraction column, and the extraction process is completed by countercurrent contact, and the methanol aqueous solution stream is obtained at the column bottom of the first extraction column;

[0017] In the second extraction column, the solvent-rich stream from the top of the first extraction column enters the lower part of the second extraction column, and the fresh water stream as the washing agent enters the upper part of the second extraction column, the methanol in the solvent-rich stream is removed by continuous countercurrent water washing, and the washed solvent-rich stream is obtained at the top of the second extraction column, and the washing water stream is obtained at the column bottom of the second extraction column;

[0018] The washed solvent-rich stream enters the solvent recovery column, the recovered lean solvent stream is obtained from the top of the solvent recovery column and returned to the lower part of the first extraction column, and the crude methyl methacrylate product stream is obtained from the column bottom of the solvent recovery column. The crude methyl methacrylate product stream enters the subsequent methyl methacrylate refining unit for refining.

[0019] Further, the first extraction column, the second extraction column and the solvent recovery column are independently selected from packed column or plate column. The packing is random packing or structured packing.

[0020] Further, the operating pressure of the first extraction column and the second extraction column is independently selected from 0.1-1.2 MPa (absolute pressure), preferably 0.15-0.8 MPa (absolute pressure), and the operating temperature is independently selected from 5-60℃, preferably 15-40℃; the operating pressure of the solvent recovery column is 0.008-0.1 MPa (absolute pressure), preferably 0.016-0.0.05 MPa (absolute pressure), and the operating temperature is 10-100℃, preferably 20-79℃.

[0021] Further, the content of methyl methacrylate in the lean solvent stream is ≤6wt%, preferably ≤3wt%, the mass ratio of the lean solvent stream to the raw material stream is (0.08-1.2):1, preferably (0.14-0.8):1, and the mass ratio of the fresh water stream to the raw material stream is (0.3-2):1, preferably (0.5-1.5):1.

[0022] Further, when the raw material stream further contains methyl methacrylaldehyde dimethyl acetal, a part of the washing water stream is extracted from the bottom of the second extraction column, mixed with inorganic acid, and then enters the acetal hydrolysis reactor together with the rich solvent stream from the top of the first extraction column to perform acetal hydrolysis reaction, and the acetal hydrolysis reaction product is introduced into the lower part of the second extraction column. The acetal hydrolysis reactor is composed of 1-6 reaction stages connected in series, and each reaction stage is provided with an independent stirring paddle for uniformly mixing the reaction materials. The inorganic acid concentration of the mixed materials is 0.01-1wt%, preferably 0.02-0.5wt%, and the reaction temperature is 5-60℃, preferably 15-40℃. The inorganic acid includes one or any mixture of sulfuric acid, sulfonic acid, nitric acid, hydrochloric acid or other protonic acid.

[0023] Preferably, the mass ratio of the part of the washing water stream extracted from the bottom of the second extraction column to the rich solvent stream from the top of the first extraction column is (0.3-3):1, preferably (0.5-1.8):1.

[0024] Alternatively, the above-mentioned first extraction column and the second extraction column can be combined into one extraction column, and the method is as follows:

[0025] In the extraction column, the raw material stream containing methyl methacrylate and methanol is introduced into the middle part of the extraction column, the lean solvent stream as the extraction agent is introduced into the lower part of the extraction column, and the fresh water stream as the washing agent is introduced into the upper part of the extraction column, and the extraction and water washing processes are completed through countercurrent contact, and the methanol aqueous solution stream is obtained from the bottom of the extraction column, and the rich solvent stream after washing is obtained from the top of the extraction column.

[0026] The solvent-rich stream after washing enters the solvent recovery column, a recovered lean solvent stream is obtained from the top of the solvent recovery column, and is returned to the lower part of the extraction column, while a crude methyl methacrylate product stream is obtained from the column bottom of the solvent recovery column.

[0027] Further, the alkane used as the extractant is azeotropic with water, and the azeotropic temperature is much lower than that of water and MMA, so in the solvent recovery column, a small amount of dissolved water in the solvent-rich stream after washing will be distilled to the top, condensed by the condenser, separated in the reflux tank, and then discharged from the system, so as to achieve the purpose of removing water from the crude MMA product discharged from the column bottom of the solvent recovery column, and reduce the difficulty of refining the crude MMA product. According to HG / T 2305-2017 Industrial Methyl Methacrylate, the water content in the superior product of MMA is required to be ≤400mg / kg. Through research, the water content in the crude MMA product discharged from the column bottom of the solvent recovery column can be less than 100mg / kg through the technical scheme of the present application.

[0028] Compared with the prior art, the present application has the following characteristics:

[0029] 1) Compared with the method for separating methyl methacrylate and methanol by desalination water in the prior art, the present application uses a combined process of alkane solvent and water extractant to separate methyl methacrylate and methanol, which solves the problem of a large amount of residual MMA in the water phase of the extractant when only water is used as the extractant. Through the technical scheme of the present application, the content of residual MMA in the water phase of the extractant (methanol aqueous solution) is less than 0.4wt%;

[0030] 2) Compared with the method for separating methyl methacrylate and methanol by azeotropic distillation of MAL and methanol in the prior art, the present application has a wider range of adaptability to the concentration ratio of MMA and methanol in the separation raw material, better separation precision, and significant energy saving;

[0031] 3) The present application creatively adds an acetal hydrolysis reactor between the two extraction columns, which is simple to operate and has high hydrolysis efficiency, and solves the separation problem of MMA and dimethyl acetal of methacrolein in the subsequent MMA refining process;

[0032] 4) The water content in the crude MMA product obtained by the present application is ≤100mg / kg, which is much lower than the requirement for the water content in the superior product in HG / T 2305-2017 Industrial Methyl Methacrylate;

[0033] 5) The purity of the refined crude MMA product obtained by the present application can reach the requirement of ≥99.9wt% for the superior product. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1A schematic diagram of the process for separating methyl methacrylate and methanol by extraction in Example 1 is shown in the figure;

[0035] Figure 2 A schematic diagram of the process for separating methyl methacrylate and methanol by extraction in Example 2 is shown in the figure;

[0036] Figure 3 A schematic diagram of the process for separating methyl methacrylate and methanol by extraction in Example 3 is shown in the figure;

[0037] Figure 4 A schematic diagram of the process for separating methyl methacrylate and methanol by extraction in Example 4 is shown in the figure;

[0038] Explanation of the figure:

[0039] T1 - first extraction column, T2 - second extraction column, T3 - solvent recovery column, R1 - acetal hydrolysis reactor;

[0040] 1 - raw material stream, 2 - rich solvent stream, 3 - aqueous methanol stream, 4 - inorganic acid stream, 5 - dilute inorganic acid solution stream, 6 - acetal hydrolysis reaction product, 7 - fresh water stream, 8 - washed rich solvent stream, 9 - washing water stream, 10 - washing water stream from acetal hydrolysis reactor, 11 - washing water stream from first extraction column, 12 - recovered lean solvent stream, 13 - solvent discharge stream, 14 - supplemented fresh solvent stream, 15 - lean solvent stream, 16 - crude MMA product stream. DETAILED DESCRIPTION

[0041] The present application will be described in detail below with reference to the accompanying drawings and specific examples. The present examples are implemented on the basis of the technical solutions of the present application, and detailed implementation modes and specific operation processes are given, but the protection scope of the present application is not limited to the following examples.

[0042] The present application provides a method for separating methyl methacrylate and methanol from a stream containing methyl methacrylate and methanol, which specifically comprises:

[0043] In the first extraction column, the raw material stream containing methyl methacrylate and methanol is mixed with the washing water stream from the column bottom of the second extraction column and enters the upper part of the extraction column, the lean solvent stream used as the extractant enters the lower part of the extraction column, and the two are countercurrently contacted to complete the extraction process, wherein the solvent used as the extractant is selected from cyclohexane, n-hexane, methylcyclohexane, n-heptane and mixtures thereof;

[0044] In the second extraction column, the solvent-rich stream from the top of the first extraction column enters the lower part of the second extraction column, the fresh water stream used as scrubbing agent enters from the upper part of the second extraction column, the methanol in the solvent-rich stream is removed by continuous countercurrent water washing, thus obtaining a scrubbed solvent-rich stream at the top of the second extraction column, the scrubbed water stream from the bottom of the second extraction column is mixed with the feed stream containing methyl methacrylate and methanol and enters the upper part of the first extraction column;

[0045] The scrubbed solvent-rich stream enters the solvent recovery column, a recovered solvent-lean stream is obtained from the top of the solvent recovery column and is returned to the lower part of the first extraction column, a crude methyl methacrylate product stream is obtained from the bottom of the solvent recovery column and enters a subsequent methyl methacrylate purification unit.

[0046] In the first extraction column, another feeding mode can also be used, i.e. the scrubbed water stream from the bottom of the second extraction column enters the upper part of the first extraction column, the feed stream containing methyl methacrylate and methanol enters the middle part of the first extraction column, and the solvent-lean stream used as extractant enters the lower part of the first extraction column, the three streams complete the extraction process in the first extraction column. As far as the extraction process is concerned, the extraction process is the same as the extraction process in which the feed stream containing methyl methacrylate and methanol and the scrubbed water stream from the bottom of the second extraction column are mixed and enter the upper part of the first extraction column, and there is no essential difference.

[0047] The first extraction column, the second extraction column and the solvent recovery column can be selected in the form of equipment according to the conventional operation in the art, e.g. each can independently be a packed column or a sieve tray column, wherein the packing can be random packing or structured packing.

[0048] The feed stream containing methyl methacrylate and methanol can come from a reaction process or a separation process which produces a stream containing methyl methacrylate and methanol, e.g. an esterification reaction process of methacrylic acid, the product of the reaction process contains, in addition to methyl methacrylate, unreacted methacrylic acid and methanol and other impurity components; or an oxidative esterification process of methacrolein, the product of the reaction contains, in addition to methyl methacrylate, unreacted methacrolein and methanol and impurities such as methyl isobutyrate (MIB), methacrolein dimethyl acetal (MDA) and heavy components.

[0049] As far as the feed stream containing methyl methacrylate and methanol is concerned, there is no substantial requirement for the content of MMA, and a relatively wide range of MMA content can be contained therein, i.e. the method of the present application is very adaptable to the MMA content of the feed stream, e.g. the MMA content in the feed stream can be 10-80 wt%, preferably 20-70 wt%.

[0050] In the process of separating MMA from methanol, the water stream from the second extraction column is mixed with the feed stream containing MMA and methanol, and then enters the upper part of the first extraction column. The water phase stream in the first extraction column is extracted with solvent to reduce the content of MMA in the water phase stream from the bottom of the first extraction column. The solvent used for extraction is generally an alkane with polarity less than MMA.

[0051] After comprehensive consideration of the polarity, density, cost and source of the alkane, the alkane can be selected from cyclohexane, n-hexane, methylcyclohexane, n-heptane and mixtures thereof. Preferably, the alkane is n-hexane and / or n-heptane.

[0052] In the second extraction column, the solvent-rich stream from the top of the first extraction column enters the lower part of the second extraction column, and the fresh water stream used as washing agent enters the upper part of the second extraction column. The methanol in the solvent-rich stream is removed by continuous countercurrent washing, and a washed solvent-rich stream is obtained at the top of the second extraction column. The washing water stream from the bottom of the second extraction column is mixed with the feed stream containing MMA and methanol, and then enters the upper part of the first extraction column.

[0053] The operating pressure and temperature of the first extraction column and the second extraction column can be determined and selected according to conventional operation in the art. Generally, the operating pressure of the first extraction column and the second extraction column can be independently 0.1-1.2 MPa (absolute pressure), preferably 0.15-0.8 MPa (absolute pressure), and the operating temperature can be independently 5-60°C, preferably 15-40°C.

[0054] The flow rate and relative flow rate of each stream can be determined and selected according to conventional operation in the art during the entire operation process. In principle, the liquid-liquid extraction process is effective and meets the corresponding separation requirements. Generally, the mass ratio of the solvent-lean stream to the feed stream containing MMA and methanol is (0.08-1.2):1, preferably (0.14-0.8):1, and the mass ratio of the fresh water stream to the feed stream containing MMA and methanol is (0.3-2):1, preferably (0.5-1.5):1.

[0055] The washed solvent-rich stream enters the solvent recovery column, and the recovered solvent-lean stream is obtained from the top of the column and recycled to the lower part of the first extraction column. The crude MMA product stream is obtained from the bottom of the column and enters the subsequent MMA refining unit.

[0056] The alkane used as the extraction agent is azeotropic with water, and the azeotropic temperature is much lower than that of water and MMA, so in the solvent recovery column, the small amount of dissolved water in the rich solvent stream after washing will be distilled to the top of the column, condensed by the condenser, separated by the reflux tank, and then discharged from the system, thereby achieving the purpose of removing water from the crude MMA product discharged from the bottom of the solvent recovery column, and reducing the difficulty of refining the crude MMA product. According to HG / T 2305-2017 Industrial Methyl Methacrylate, the water content in the superior product of MMA is required to be ≤400mg / kg, and through research, the water content in the crude MMA product discharged from the bottom of the solvent recovery column can be less than 100mg / kg through the technical scheme of the present application.

[0057] In order to reduce the content of MMA in the water phase stream discharged from the bottom of the first extraction column as much as possible, thereby reducing the circulation amount of MMA, it is required that the content of methyl methacrylate in the lean solvent stream used as the extraction agent is ≤6wt%, preferably ≤3wt%. Since MMA is easy to polymerize at high temperature, the solvent recovery column is preferably operated at a lower pressure, such as an operating pressure of the solvent recovery column of 0.008-0.1MPa (absolute pressure), preferably 0.016-0.0.05MPa (absolute pressure), and an operating temperature of 10-100℃, preferably 20-79℃.

[0058] Since the solvent will be lost in a small amount during the recycling process, only fresh solvent needs to be continuously or intermittently supplemented to the system to maintain the total amount of solvent in the system. If some unknown impurities accumulate in the solvent during the recycling process, only an appropriate amount of solvent needs to be continuously or intermittently discharged from the system.

[0059] The raw material stream containing methyl methacrylate and methanol contains one or more of water, methacrylic acid, methyl isobutyrate, methacrolein, methacrolein dimethyl acetal, heavy components, etc. in addition to the main components methyl methacrylate and methanol. It is found through experimental research that methacrolein dimethyl acetal will mainly enter the crude MMA product during the extraction separation of the technical solution, and the content is 0.05-5wt%, preferably 0.1-3wt%. Since the boiling point is very close to that of MMA, if the MMA is refined to a superior product (content ≥ 99.9wt%), a very large energy consumption cost and MMA loss cost will be incurred. Through detailed experimental research, it is found that methacrolein dimethyl acetal is easily hydrolyzed in dilute acid solution, and the hydrolysis products MAL and methanol can both be used as 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 also the yield of MMA product can be improved. The hydrolysis reaction of methacrolein dimethyl acetal is an equilibrium reaction, in order to make the reaction proceed towards the hydrolysis reaction, it is necessary to reduce the methanol content and MAL content in the hydrolysis raw material as much as possible. In particular, in the technical solution of the present application, the methanol content and MAL content in the solvent-rich stream leaving the top of the first extraction column are very low, which is very suitable for hydrolysis reaction, and the hydrolysis water can be the washing water leaving the bottom of the second extraction column. The solvent-rich stream and the washing water stream enter the acetal hydrolysis reactor together for hydrolysis reaction. Considering the hydrolysis efficiency, investment and operation convenience, the acetal hydrolysis reactor can be composed of 1-6 reaction stages connected in series. Since the acetal hydrolysis reaction is a heterogeneous reaction, in order to improve the hydrolysis efficiency, each reaction stage is provided with an independent stirring paddle for uniformly mixing the reaction materials.

[0060] The inorganic acid used for hydrolysis does not have a particular requirement for the type of acid, as long as it can effectively provide hydrogen ions, for example, the inorganic acid used can be selected from any one of sulfuric acid, sulfonic acid, nitric acid, hydrochloric acid or other protonic acids and any mixture thereof, and the inorganic acid concentration of the mixture is 0.01-1wt%, preferably 0.02-0.5wt%. The acetal hydrolysis reaction product discharged from the hydrolysis reactor is returned to the lower part of the second extraction column, and the residual inorganic acid in the solvent-rich stream after hydrolysis is washed clean by water washing through the second extraction column.

[0061] According to the content of methacrolein dimethyl acetal and the concentration of the inorganic acid added, the ratio of the part of the washing water stream drawn from the bottom of the second extraction column to the solvent-rich stream leaving the top of the first extraction column can be determined and selected according to the conventional operation in the field, in principle, as long as the hydrolysis reaction proceeds effectively and the desired hydrolysis rate is achieved. Generally, the mass ratio of the part of the washing water stream drawn from the bottom of the second extraction column to the solvent-rich stream leaving the top of the first extraction column is (0.3-3):1, preferably (0.5-1.8):1.

[0062] In addition to the above-mentioned two extraction columns, the first extraction column and the second extraction column can be combined into one extraction column, and the method is as follows:

[0063] In the extraction column, the raw material stream containing methyl methacrylate and methanol enters the middle part of the extraction column, the lean solvent stream as the extractant enters the lower part of the extraction column, and the fresh water stream as the washing agent enters the upper part of the extraction column. Through countercurrent contact, the extraction and water washing processes are completed, and the methanol aqueous solution stream is obtained at the bottom of the extraction column, and the washed rich solvent stream is obtained at the top;

[0064] The washed rich solvent stream enters the solvent recovery column, the recovered lean solvent stream is obtained from the top of the solvent recovery column, and is returned to the lower part of the extraction column. At the same time, the crude methyl methacrylate product stream is obtained from the bottom of the solvent recovery column.

[0065] Example 1:

[0066] A method for extracting and separating methyl methacrylate and methanol, the process flow is as follows Figure 1 , the extraction solvent is selected as n-hexane, which is used to treat the raw material stream 1 containing methyl methacrylate and methanol discharged from an oxidation esterification device. In addition to containing methyl methacrylate, methanol, the stream also contains a small amount of water, methyl methacrylate, methyl isobutyrate, methyl methacrylate dimethyl acetal, heavy components, etc. The stream is mixed with the washing water stream 11 of the first extraction column and then enters the upper part of the first extraction column T1. The lean solvent stream 15 enters the lower part of the extraction column. The two are countercurrently contacted in the column to complete the extraction process. The methanol aqueous solution stream 3 discharged from the bottom of the column is sent to the methanol recovery unit. The rich solvent stream 2 discharged from the top of the column is mixed with the dilute inorganic acid solution stream 5 obtained by mixing the washing water stream 10 of the acetal hydrolysis reactor and the inorganic acid stream 4, and then enters the acetal hydrolysis reactor R1 for hydrolysis reaction. The acetal hydrolysis reactor R1 is a first-stage stirred reactor. The acetal hydrolysis reaction product 6 leaving the acetal hydrolysis reactor R1 enters the lower part of the second extraction column T2, and the fresh water stream 7 enters the upper part of the column. Through continuous countercurrent water washing, the methanol and inorganic acid in the hydrolyzed rich solvent stream are removed. The washing water stream 9 is divided into two parts, which are the washing water stream 10 of the acetal hydrolysis reactor and the washing water stream 11 of the first extraction column, respectively. The washed rich solvent stream 8 is sent to the solvent recovery column T3 to recover the solvent. In the solvent recovery column T3, the recovered lean solvent stream 12 is obtained from the top, and the crude MMA product stream 16 is discharged from the bottom and sent to the MMA product refining unit. The material balance table of the process flow is shown in Table 1.

[0067] Table 1 Material balance table of Example 1

[0068]

[0069]

[0070] Example 2:

[0071] A process for the extraction separation of methyl methacrylate and methanol is shown in Figure 2. Figure 2 The extraction solvent is n-heptane which is used to treat a feed stream 1 containing methyl methacrylate and methanol from an esterification unit. The feed stream contains in addition to methyl methacrylate and methanol, small amounts of water, heavies and other components. The feed stream is mixed with a wash water stream 9 from the bottom of a second extraction column T2 and fed to the top of a first extraction column Tl. A lean solvent stream 15 is fed to the bottom of the column. The two streams contact countercurrently in the column to complete the extraction process. The column bottoms stream 3 is a methanol and water stream which is sent to a methanol recovery unit. The column overhead stream 2 is a rich solvent stream which is fed to the bottom of a second extraction column T2. A fresh water stream 7 is fed to the top of the column. The methanol in the rich solvent stream 2 is removed by continuous countercurrent water washing. The wash water stream 9 is mixed with the feed stream 1 and sent to the first extraction column Tl. The washed rich solvent stream 8 is sent to a solvent recovery column T3 to recover the solvent. In the solvent recovery column T3, the recovered lean solvent stream 12 is obtained from the top of the column and the column bottoms stream 16 is a crude MMA product stream which is sent to a MMA product purification unit. The material balance for this process is shown in Table 2.

[0072] Table 2 Material Balance for Example 2

[0073]

[0074]

[0075] Example 3:

[0076] A process for the extraction separation of methyl methacrylate and methanol is shown in Figure 2. Figure 3The extraction solvent is a mixture of n-hexane / n-heptane, which is used to treat a raw material stream 1 containing methyl methacrylate and methanol discharged from a certain oxidative esterification unit. In addition to methyl methacrylate and methanol, this stream also contains a small amount of water, methacrolein, methyl isobutyrate, methacrolein dimethyl acetal, heavy components, etc. This stream is mixed with the washing water stream 11 going to the first extraction tower and then enters the upper part of the first extraction tower T1. The lean solvent stream 15 enters the lower part of the extraction tower. The two are in countercurrent contact in the tower to complete the extraction process. The methanol-water solution stream 3 discharged from the tower kettle is sent to the methanol recovery unit, and the rich solvent discharged from the top of the tower is used as the solvent. Solvent stream 2, along with wash water stream 10 from the acetal hydrolysis reactor and inorganic acid stream 4, produces a dilute inorganic acid solution stream 5, which is then fed into acetal hydrolysis reactor R1 for hydrolysis. Acetal hydrolysis reactor R1 is a three-stage series stirred reactor. Acetal hydrolysis product 6 exiting acetal hydrolysis reactor R1 enters the lower portion of second extraction tower T2, while fresh water stream 7 enters the upper portion of this tower. Continuous countercurrent water washing removes methanol and inorganic acid from the hydrolyzed rich solvent stream. Wash water stream 9 is split into two streams: wash water stream 10 for the acetal hydrolysis reactor and wash water stream 11 for the first extraction tower. The washed rich solvent stream 8 is then fed into solvent recovery tower T3 for solvent recovery. Lean solvent stream 12 is recovered from the top of solvent recovery tower T3, and crude MMA product stream 16 exits the bottom portion of the tower for the MMA product refining unit. The material balance for this process is shown in Table 3.

[0077] Table 3 Material balance table of Example 3

[0078]

[0079]

[0080] Example 4:

[0081] A method for extracting and separating methyl methacrylate and methanol, the process flow is shown in Figure 4, the extraction solvent is a mixture of n-hexane, n-heptane, cyclohexane and methylcyclohexane, wherein n-hexane is 70wt%, n-heptane is 20wt%, cyclohexane is 5wt% and methylcyclohexane is 5wt%, which is used to treat a feed stream 1 containing methyl methacrylate and methanol discharged from an esterification unit, the stream contains a small amount of water, methyl methacrylate, methyl methacrylate dimethyl acetal, methyl isobutyrate and other components besides methyl methacrylate and methanol, the stream enters the middle of a first extraction column T1, a washing water stream 11 discharged from the first extraction column enters the upper part of the first extraction column T1, a lean solvent stream 15 enters the lower part of the column, and the two streams contact countercurrently in the column to complete the extraction process, a methanol aqueous solution stream 3 discharged from the column bottom is sent to a methanol recovery unit, a rich solvent stream 2 discharged from the column top is mixed with a dilute inorganic acid solution stream 5 obtained by mixing a washing water stream 10 discharged from an acetal hydrolysis reactor and an inorganic acid stream 4, and then the mixture is sent to the acetal hydrolysis reactor R1 to perform a hydrolysis reaction, the acetal hydrolysis reactor R1 is a five-stage series stirred reactor, an acetal hydrolysis reaction product 6 discharged from the acetal hydrolysis reactor R1 enters the lower part of a second extraction column T2, and a fresh water stream 7 enters the upper part of the column, and the methanol and inorganic acid in the rich solvent stream after hydrolysis are removed by continuous countercurrent water washing, the washing water stream 9 is divided into two parts, which are a washing water stream 10 sent to the acetal hydrolysis reactor and a washing water stream 11 sent to the first extraction column, respectively. The rich solvent stream 8 after washing is sent to a solvent recovery column T3 to recover the solvent, in the solvent recovery column T3, a recovered lean solvent stream 12 is obtained from the column top, and a crude MMA product stream 16 is discharged from the column bottom and sent to an MMA product refining unit.

[0082] Since a small amount of solvent is lost during the recycling process, only fresh solvent needs to be continuously or intermittently supplemented into the system, for example, the supplemented fresh solvent stream 14 is mixed with the lean solvent stream 15 and then enters the lower part of the first extraction column T1 to maintain the total amount of solvent in the system, if some unknown impurities accumulate in the solvent during the recycling process, only a proper amount of solvent needs to be continuously or intermittently discharged from the system, for example, an external solvent stream 13 is introduced into the lean solvent stream 12.

[0083] The material balance table of the process flow is shown in Table 4.

[0084] Table 4 Material balance table of Example 4

[0085]

[0086] The foregoing description of the embodiments has been presented for the purpose of illustration and description. It is not intended to be exhaustive or to limit the application to the precise form disclosed. Modifications and variations are possible in light of the above teachings or can be acquired from practice of the application. As well, the description is presented in the context of the preferred embodiments as a number of alternatives. It is not intended to limit the application to the precise form described.

Claims

1. A method for extracting and separating methyl methacrylate and methanol, characterized in that: The method comprises the following steps: firstly, mixing a raw material stream containing methacrolein dimethyl acetal, methyl methacrylate and methanol with water to obtain a mixed stream; then extracting the mixed stream with a solvent to obtain a rich solvent stream containing methyl methacrylate and a methanol aqueous solution; then, mixing the rich solvent stream with an inorganic acid and water to perform an acetal hydrolysis reaction; then, washing the acetal hydrolysis reaction product with water to remove methanol; and finally recovering the solvent to obtain a crude methyl methacrylate product. The solvent is selected from one or more of cyclohexane, n-hexane, methylcyclohexane or n-heptane; In the first extraction tower, the feed stream is mixed with the wash water stream from the bottom of the second extraction tower and then enters the upper part of the first extraction tower. At the same time, the lean solvent stream serving as the extractant enters the lower part of the first extraction tower. The extraction process is completed through countercurrent contact, and a methanol-water solution stream is obtained in the bottom of the first extraction tower. A portion of the washing water stream is extracted from the bottom of the second extraction tower and mixed with the inorganic acid, and then enters the acetal hydrolysis reactor together with the rich solvent stream leaving the top of the first extraction tower to undergo acetal hydrolysis reaction. The obtained acetal hydrolysis reaction product enters the lower part of the second extraction tower; In the second extraction tower, the acetal hydrolysis reaction product of the acetal hydrolysis reactor enters the lower part of the second extraction tower, and a fresh water stream serving as a detergent enters the upper part of the second extraction tower. Methanol in the rich solvent stream is removed by continuous countercurrent water washing, and a washed rich solvent stream is obtained at the top of the second extraction tower. A washing water stream is obtained in the bottom of the second extraction tower. After washing, the rich solvent stream enters the solvent recovery tower, and the recovered lean solvent stream is obtained from the top of the solvent recovery tower and returned to the lower part of the first extraction tower. At the same time, the crude methyl methacrylate product stream is obtained from the bottom of the solvent recovery tower.

2. The method for extracting and separating methyl methacrylate and methanol according to claim 1, wherein: The raw material stream comes from the methacrylic acid esterification reaction product or the methacrolein oxidative esterification reaction product.

3. The method for extracting and separating methyl methacrylate and methanol according to claim 1, characterized in that: The solvent is recovered by distillation.

4. The method for extracting and separating methyl methacrylate and methanol according to claim 1, wherein: The operating pressure of the first extraction tower and the second extraction tower are independently selected from 0.1-1.2 MPa, and the operating temperature is independently selected from 5-60°C; the operating pressure of the solvent recovery tower is 0.008-0.1 MPa, and the operating temperature is 10-100°C.

5. The method for extracting and separating methyl methacrylate and methanol according to claim 1, characterized in that: The content of methyl methacrylate in the lean solvent stream is ≤6wt%, the mass ratio of the lean solvent stream to the raw material stream is (0.08-1.2):1, and the mass ratio of the fresh water stream to the raw material stream is (0.3-2):1.

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