Methyl methacrylate separation method

Abstract

The invention provides a methyl methacrylate (MMA) separation method. The method comprises the steps of pretreatment, pre-rectification, water phase extraction and phase separation, oil phase ionic liquid extractive distillation, refining and the like. According to the method, light components are removed through pre-rectification, water and water-soluble impurities are removed through water-phase extraction, impurity components difficult to separate are removed through an ionic liquid extractive distillation technology, and finally a high-purity MMA product is obtained. According to the method, the energy consumption in the separation process is effectively reduced, the operation process is simplified, the equipment investment cost is reduced, and the purity and yield of the MMA product are improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of chemical separation technology, and particularly relates to a separation method for producing methyl methacrylate (MMA) by adopting an Alpha-MMA technology. BACKGROUND

[0002] Methyl methacrylate (MMA) is an important organic chemical raw material, which is widely used in the production of polymethyl methacrylate (PMMA), acrylic resin material, and the manufacture of other resins, plastics, paints, adhesives, lubricants, impregnating agents, polishing agents, printing and dyeing auxiliaries, and insulating filling materials, etc. In the production of polymethyl methacrylate (PMMA), methyl methacrylate with high purity is required, and even a low content of impurities may cause appearance defects such as turbidity, no light or discoloration of PMMA products, and may change its structural properties. Therefore, it is crucial to provide methyl methacrylate monomer with high purity.

[0003] At present, the production methods of methyl methacrylate mainly include acetone cyanohydrin (ACH) method, isobutene oxidation method and ethylene method (Alpha-MMA). The ethylene method MMA process has gradually become a research hotspot due to its environmental friendliness, mild reaction conditions, no generation of toxic intermediate products and other advantages. The process includes the generation of methyl propionate through the carbonyl synthesis reaction of ethylene, carbon monoxide and methanol, and the generation of methyl methacrylate through the aldol condensation reaction of methyl propionate and formaldehyde. However, the crude methyl methacrylate reaction solution synthesized by the ethylene method MMA process has complex components, including methyl methacrylate, formaldehyde, methanol, water, methyl propionate and other impurities. Among them, methyl methacrylate forms multiple binary or ternary azeotropic systems with methanol, water and the like, which is difficult to separate by ordinary distillation. The conventional distillation method is difficult to effectively separate these by-products, especially the impurities with boiling points close to methyl methacrylate, such as methyl isobutyrate (MIB) and diethyl ketone (DEK), which have boiling points very close to methyl methacrylate, increasing the difficulty of separation.

[0004] The existing separation methods have many deficiencies:

[0005] The MMA purification method proposed in patent CN102256926B removes aldehydes, unsaturated ketones and olefins and other impurities from MMA products of the acetone cyanohydrin method or C4 method route, and uses a sulfonic acid ion exchange resin to remove impurities, but the sulfonic acid ion exchange resin needs to be regenerated regularly, and the operation is complex.

[0006] Patent CN11303331C uses a fractional crystallization method to separate impurities, which has problems such as large product loss and high impurity content in the final product.

[0007] Patent CN108689812A proposes a method for removing methanol and water by ionic liquid extractive distillation, which has certain effect on industrial materials containing methanol and water, but the method has limited effect on the separation of complex multi-component system in ethylene method MMA separation, and the ionic liquid recycling process is complex.

[0008] In summary, the existing methyl methacrylate production technology has many challenges in the separation and purification link, and it is urgent to develop a new methyl methacrylate separation method to reduce the generation of impurities close to the boiling point of methyl methacrylate, simple operation, reduce energy consumption, and finally obtain high-purity methyl methacrylate product. SUMMARY

[0009] The purpose of the present application is to provide a methyl methacrylate separation method, which combines water phase extraction and phase separation and ionic liquid extraction technology, realizes efficient separation of each component in the crude MMA reaction liquid, simple operation, low impurity content, and high purity of the obtained methyl methacrylate.

[0010] In order to achieve the above application purposes, the technical solutions adopted by the present application are as follows:

[0011] A methyl methacrylate separation method, comprising the following steps:

[0012] (1) Pre-distillation: The methyl methacrylate reaction liquid is sent into the pre-distillation column for distillation to remove light components;

[0013] (2) Water phase extraction and phase separation: The reaction liquid after pre-distillation is introduced into the extraction column for extraction, and the oil phase and the water phase are separated;

[0014] (3) Oil phase ionic liquid extractive distillation: The oil phase after extraction is sent from the column to the extractive distillation column, and ionic liquid extractant is added from the top of the column.

[0015] (4) Refining: The light components collected from the top of the extractive distillation column are further refined to obtain methyl methacrylate.

[0016] Preferably, the methyl methacrylate reaction liquid is obtained by an ethylene method.

[0017] Preferably, the ethylene method refers to the carbonyl synthesis reaction of ethylene, carbon monoxide and methanol under the catalysis of a catalyst to produce methyl propionate, the hydroxy aldehyde condensation reaction of methyl propionate and formaldehyde to produce methyl methacrylate and water.

[0018] Generally, the methyl methacrylate reaction liquid includes 4-20wt% of methyl methacrylate, and may also include formaldehyde, methyl methacrylate, other acrylates, alcohols, etc.

[0019] Further, the methyl methacrylate reaction liquid is filtered to remove impurities before pre-distillation.

[0020] Further preferably, the methyl methacrylate reaction liquid is cooled to 40-60℃, and a filter with a filtering precision of 1-5 μm is used to remove mechanical impurities to prevent subsequent equipment from being blocked.

[0021] Preferably, the pre-distillation is carried out at normal pressure, and the pre-distillation temperature is 40-70℃, and the reflux ratio is 2-5. Through pre-distillation, light components such as methanol and methyl propionate can be removed, and the light components collected at the top of the column can be recycled to the reactor.

[0022] Preferably, in the water phase extraction, water is used as the extractant, and the amount of water added is 0.5-1.5 times the mass of the reaction liquid, and the operation condition is normal pressure, and the extraction temperature is 30-60℃. Through water phase extraction, water and part of the water-soluble impurities are preferentially separated, reducing the load of the subsequent ionic liquid extractive distillation. After the extraction is completed, separation by static layering or a separatory funnel is used.

[0023] Preferably, in step (3), the operation condition of the extractive distillation column is normal pressure, the temperature is 50-150℃, and the reflux ratio is 2-5. The ionic liquid interacts with the MMA in the oil phase, effectively breaking the azeotrope system of the MMA and the impurities, and further separating the MMA and the remaining impurities. The MMA light component containing a small amount of impurities is collected at the top of the column, and the heavy component containing the ionic liquid and heavy impurities is collected at the bottom of the column.

[0024] Preferably, the mass ratio of the ionic liquid to the oil phase is 0.5-2:1.

[0025] Preferably, the ionic liquid includes one or more of 1-ethyl-3-methylimidazolium acetate (EMIM O2CCH3), 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM PF6), 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM BF4), 1-butyl-3-methylimidazolium trifluoromethanesulfonate (BMIM CF3SO3), 1-hexyl-3-methylimidazolium hexafluorophosphate (HMIM PF6), 1-ethyl-3-methylimidazolium dicyanamide (EMIM dca), 1-butyl-3-methylimidazolium chloride (BMIM Cl), 1-ethyl-3-methylimidazolium sulfate (EMIM SO4), 1-butyl-3-methylimidazolium acetate (BMIM O2CCH3), and 1-hexyl-3-methylimidazolium tetrafluoroborate (HMIM BF4); preferably, two or more combinations.

[0026] Preferably, the ionic liquid is one or more of the following combinations of ionic liquids: 1-ethyl-3-methylimidazolium acetate (EMIM O2CCH3) and 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM PF6), 1-butyl-3-methylimidazolium trifluoromethanesulfonate (BMIM CF3SO3) and 1-hexyl-3-methylimidazolium hexafluorophosphate (HMIM PF6), 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM BF4) and 1-butyl-3-methylimidazolium acetate (BMIM O2CCH3)

[0027] The ionic liquid used in the present application not only has good hydrophobicity, which can reduce the influence of water on the extraction process, but also has high thermal stability and chemical stability, ensuring high extraction performance during repeated recycling.

[0028] When the ionic liquid is a combination of two ionic liquids, the mass ratio is 1:0.5-2;

[0029] When more than three ionic liquids are combined, the mass ratio of each component is 1:0.5-2:0.5-2:…;

[0030] Preferably, the total amount of ionic liquid added is 0.5-2 times the mass of the oil phase.

[0031] Preferably, the operating pressure of the extractive distillation column is atmospheric pressure, the temperature of the extractive distillation column is 50-150℃, and the reflux ratio is 1-3.

[0032] Preferably, after ionic liquid extractive distillation, the light components at the top of the column are refined to obtain methyl methacrylate. The refinement can be carried out by distillation to remove light components, and the methyl methacrylate component is obtained from the column bottom.

[0033] The heavy components containing ionic liquid obtained from the column bottom after ionic liquid extractive distillation can be purified by distillation to obtain ionic liquid, which is then recycled back to the extractive distillation column for use. The efficient recovery of ionic liquid reduces production costs while ensuring the continuity and stability of the separation process.

[0034] Preferably, the water content in the ionic liquid is not more than 500 ppm (mass content).

[0035] Preferably, the purity of the ionic liquid is more than 98%.

[0036] To ensure the performance and separation efficiency of the ionic liquid, the ionic liquid needs to be dried and purified by distillation during recycling.

[0037] The optional drying method includes but is not limited to: in the ion liquid recovery tower, the recovered ion liquid is dried by using on-site drying technology, the water content in the ion liquid is controlled to be not more than 500 ppm, and the interference of water on the subsequent extraction process is prevented.

[0038] The methyl methacrylate separation method of the present application has significant advantages. By water phase extraction, water is preferentially removed, reducing the water interference in the subsequent ion liquid extraction, improving the separation efficiency, and reducing the loss of methyl methacrylate. At the same time, the recycling of impurities is realized, which has good application prospect. Compared with the traditional separation method, the method of the present application not only effectively reduces the energy consumption in the separation process, but also simplifies the operation process, reduces the equipment investment cost, and performs well in separation efficiency and product purity, which has broad industrial application prospect. DETAILED DESCRIPTION

[0039] In order to facilitate the understanding of the present application, the present application will be further described below in combination with examples. It should be understood that the following examples are only for better understanding of the present application, and do not mean that the present application is limited to the following examples only.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0041] In some preferred embodiments of the present application, the composition of the crude MMA reaction liquid is as follows: MMA: 5%-15%; formaldehyde: 1%-3%; methanol: 30%-35%; methyl propionate: 50%-58%; water: 2%-4%; methacrylic acid: 0.02%-0.3%; other components: 0.1%-5.0%.

[0042] In the examples of the present application, two batches of MMA reaction liquid prepared by ethylene method were selected, and the composition of the crude MMA reaction liquid is shown in Table 1:

[0043] Table 1

[0044] Material Reaction 1 wt% Reaction 2 wt% Water 3.142 2.942 Formaldehyde 2.008 1.384 Methylal 0.018 0.009 Methanol 30.767 32.919 Methyl propionate 56.789 52.96 Methyl isobutyrate 0.104 0.098 Methyl acrylate 0.067 0.044 3-pentanone 0.013 0.015 MMA 5.585 7.948 Propionic acid 0.547 0.728 Methacrylic acid 0.074 0.163 Ethyl acetate 0.533 0.568 Methacrolein 0.018 0.022 Ethyl butyrate 0.030 0.043 Other 0.305 0.157

[0045] In the following examples, examples 1 and 2 use reaction liquid 1, and the MMA reaction liquid used in example 3 is reaction liquid 2.

[0046] Example 1

[0047] (1) Pretreatment: cool the crude MMA reaction liquid (reaction liquid 1) to 50℃, and filter it using a 3μm filter to remove mechanical impurities and prevent subsequent equipment blockage.

[0048] (2) Pre-distillation: The pretreated reaction liquid is sent into a pre-distillation column, and the operating conditions are normal pressure, temperature 50-60°C, and reflux ratio 3. Light components such as methanol and methyl propionate are removed, and the light components collected at the top of the column are returned to the reactor for recycling.

[0049] (3) Water phase extraction and phase separation: The reaction liquid after pre-distillation is sent into a water phase extraction column, and water with a mass of 0.7 times that of the reaction liquid is added as an extractant. The operating conditions are normal pressure and temperature 40-50°C. Through water phase extraction, water and part of water-soluble impurities are preferentially separated, reducing the load of subsequent ionic liquid extractive distillation. After extraction, the oil phase and the water phase are separated by static layering, and the water phase mainly contains water, a small amount of methanol and methyl propionate and other impurities, which can be returned to the reactor for recycling.

[0050] (4) Oil phase ionic liquid extractive distillation: The oil phase after water phase extraction is sent from the column bottom into an ionic liquid extractive distillation column, and an ionic liquid extractant with a mass ratio of 1:1 to the oil phase is added at the top of the column. The ionic liquid extractant is a combination of 1-ethyl-3-methylimidazole acetate (EMIM O2CCH3) and 1-butyl-3-methylimidazole hexafluorophosphate (BMIM PF6) with a mass ratio of 1:1. The operating conditions of the extractive distillation column are normal pressure, temperature 100°C, and reflux ratio 3. The ionic liquid interacts with MMA in the oil phase, effectively breaking the azeotropic system of MMA and impurities, and further separating MMA and remaining impurities. The MMA light component containing a small amount of impurities is collected at the top of the column, and the heavy component containing ionic liquid and heavy impurities is collected at the column bottom.

[0051] (5) Ionic liquid recovery: The material at the column bottom of the extractive distillation column is sent into an ionic liquid recovery column, and the operating conditions are normal pressure, temperature 120°C, and reflux ratio 2. The ionic liquid is recovered by distillation, and its purity reaches more than 98%, and then it is recycled to the extractive distillation column.

[0052] (6) Refining: The light component collected at the top of the extractive distillation column is further refined by two-stage distillation. The first stage removes light impurities, and the second stage removes heavy impurities, and finally MMA products with a purity of >99.9% are obtained.

[0053] Example 2

[0054] The same method as in Example 1 is used, and the main process conditions are as follows:

[0055] (1) Pretreatment: The reaction liquid is cooled to 45°C and filtered using a 2 μm filter.

[0056] (2) Pre-distillation: The operating conditions are normal pressure and temperature 45°C.

[0057] (3) Water phase extraction and phase separation: The operating conditions are normal pressure, temperature 45°C, and reflux ratio 3.5.

[0058] (4) Oil phase ionic liquid extractive distillation: the ionic liquid extractant is a combination of 1-butyl-3-methylimidazolium trifluoromethanesulfonate (BMIM CF3SO3) and 1-hexyl-3-methylimidazolium hexafluorophosphate (HMIM PF6) with a mass ratio of 1:0.8. The mass ratio of ionic liquid to oil phase is 0.6:1. The operating conditions of the extractive distillation column are normal pressure, a temperature of 120°C, and a reflux ratio of 2.5.

[0059] (5) Ionic liquid recovery: the operating conditions are normal pressure, a temperature of 120°C, and a reflux ratio of 1.5. The purity of the recovered ionic liquid is >97.5%.

[0060] (6) Refining: the final MMA product has a purity of >99.85%.

[0061] Example 3

[0062] The same method as in Example 1 is used, and the main process conditions are as follows:

[0063] (1) Pretreatment: the reaction solution is reaction solution 2, which is cooled to 55°C and filtered using a 4 μm filter.

[0064] (2) Pre-distillation: the operating conditions are normal pressure, a temperature of 55-65°C, and a reflux ratio of 4.

[0065] (3) Water phase extraction and phase separation: the operating conditions are normal pressure and a temperature of 50°C.

[0066] (4) Oil phase ionic liquid extractive distillation: the ionic liquid extractant is a combination of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM BF4) and 1-butyl-3-methylimidazolium acetate (BMIM O2CCH3) with a mass ratio of 1:1.5. The mass ratio of ionic liquid to oil phase is 1.5:1. The operating conditions of the extractive distillation column are normal pressure, a temperature of -100°C, and a reflux ratio of 4.

[0067] (5) Ionic liquid recovery: the operating conditions are normal pressure, a temperature of 140°C, and a reflux ratio of 2.5. The purity of the recovered ionic liquid is >98.5%.

[0068] (6) Refining: the final MMA product has a purity of >99.95%.

[0069] Comparative Example 1

[0070] The same method as in Example 1 is used, and the main process conditions are as follows:

[0071] (1) Pretreatment: the reaction solution is cooled to 50°C and filtered using a 3 μm filter.

[0072] (2) Azeotropic distillation: the pretreated reaction liquid was separated in an azeotropic distillation column under the conditions of normal pressure, 90°C and reflux ratio of 4. The MMA content in the material collected from the column bottom was 88%, and the material collected from the column top contained more methanol, water, formaldehyde, methyl propionate and other impurities.

[0073] (3) Refining: the material collected from the column top was further refined in a common distillation column under the conditions of normal pressure, 60°C and reflux ratio of 3. The final MMA product had a purity of 98.2%.

[0074] Comparative Example 2

[0075] The same method as in Example 1 was used, and the main process conditions were as follows:

[0076] (1) Pretreatment: the reaction liquid was cooled to 45°C and filtered using a 2 μm filter.

[0077] (2) Pre-distillation: the operation conditions were normal pressure, 45-55°C and reflux ratio of 2.5.

[0078] (3) Water phase extraction and phase separation: the operation conditions were normal pressure, 35-55°C and reflux ratio of 3.5.

[0079] (4) Oil phase azeotropic distillation: the oil phase reaction liquid after water extraction was separated in an azeotropic distillation column under the conditions of normal pressure, 90°C and reflux ratio of 4. The MMA content in the material collected from the column bottom was 88%, and the material collected from the column top contained more methanol, water, methyl propionate and other impurities.

[0080] (5) Refining: the material collected from the column top was further refined in a common distillation column under the conditions of normal pressure, 60°C and reflux ratio of 3. The final MMA product had a purity of 98.7%. The impurities contained were mainly 3-pentanone, methyl isobutyrate and other difficult-to-separate substances.

[0081] It is easily understood that the above examples are merely illustrative and do not mean that the present application is limited to them. Other different forms of changes or variations can be made on the basis of the above description by those skilled in the art. It is not necessary or possible to exhaust all the embodiments. The obvious changes or variations derived therefrom are still within the protection scope of the present application.

Claims

1. A method for separating methyl methacrylate, characterized by, The method comprises the following steps: (1) Pre-distillation: the methyl methacrylate reaction liquid is sent into a pre-distillation column for distillation to remove light components; (2) Water phase extraction and phase separation: the reaction liquid after pre-distillation is sent into an extraction column for extraction, and oil phase and water phase are separated; (3) Oil phase ionic liquid extractive distillation: the oil phase after extraction is sent from the column bottom into an extractive distillation column, and ionic liquid extractant is added from the top of the column; (4) Refining: the light components collected from the top of the extractive distillation column are further refined to obtain methyl methacrylate.

2. The separation method according to claim 1, characterized in that, The methyl methacrylate reaction liquid is obtained by an ethylene method; Preferably, the ethylene method refers to that methyl propionate is produced by carbonylation of ethylene, carbon monoxide and methanol under the catalysis of a catalyst, and the methyl propionate and formaldehyde are subjected to aldol condensation to produce methyl methacrylate and water; Preferably, the methyl methacrylate reaction liquid comprises 4-20 wt% of methyl methacrylate, and further comprises formaldehyde, methyl methacrylate, other acrylates and alcohols.

3. The separation method of claim 1, wherein, The methyl methacrylate reaction liquid is filtered to remove impurities before pre-distillation; Further preferably, the methyl methacrylate reaction liquid is cooled to 40-60℃, and a filter with a filtering precision of 1-5 μm is used to remove impurities.

4. The separation method according to any one of claims 1 to 3, characterized in that, The pre-distillation is carried out at normal pressure, and the pre-distillation temperature is 40-70℃ and the reflux ratio is 2-5.

5. The separation method according to any one of claims 1 to 4, characterized in that, In the water phase extraction, water is used as the extractant, and the water is added in an amount of 0.5-1.5 times the mass of the reaction liquid, and the operation condition is normal pressure and the extraction temperature is 30-60℃.

6. The separation method according to any one of claims 1 to 5, characterized in that, In step (3), the operation condition of the extractive distillation column is normal pressure, the temperature is 50-150℃, and the reflux ratio is 2-5.

7. The separation method according to any one of claims 1 to 6, characterized in that, The mass ratio of the ionic liquid to the oil phase is 0.5-2:1; Preferably, the ionic liquid comprises one or more of the following: 1-ethyl-3-methylimidazolium acetate (EMIM O2CCH3); 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM PF6); 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM BF4); 1-butyl-3-methylimidazolium trifluoromethanesulfonate (BMIM CF3SO3); 1-hexyl-3-methylimidazolium hexafluorophosphate (HMIM PF6); 1-ethyl-3-methylimidazolium dicyanamide (EMIM dca); 1-butyl-3-methylimidazolium chloride (BMIM Cl); 1-ethyl-3-methylimidazolium sulfate (EMIM SO4); 1-butyl-3-methylimidazolium acetate (BMIM O2CCH3); 1-hexyl-3-methylimidazolium tetrafluoroborate (HMIM BF4); and preferably a combination of two or more thereof; Preferably, the ionic liquid is one or more of the following combinations of ionic liquids: 1-ethyl-3-methylimidazolium acetate (EMIM O2CCH3) and 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM PF6), 1-butyl-3-methylimidazolium trifluoromethanesulfonate (BMIM CF3SO3) and 1-hexyl-3-methylimidazolium hexafluorophosphate (HMIM PF6), 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM BF4) and 1-butyl-3-methylimidazolium acetate (BMIM O2CCH3); Preferably, when the ionic liquid is a combination of two ionic liquids, the mass ratio is 1:0.5-2; Preferably, when more than three ionic liquids are combined, the mass ratio of each component is 1:0.5-2:0.5-2:….

8. The separation method according to any one of claims 1 to 7, characterized in that, The total amount of the ionic liquid added is 0.5-2 times the mass of the oil phase; Preferably, the extractive distillation column operates at atmospheric pressure, the temperature is 50-150℃, and the reflux ratio is 1-3; Preferably, the light components from the top of the ionic liquid extractive distillation column are refined to obtain methyl methacrylate. The refinement can be distillation to remove light components, and the methyl methacrylate component is obtained from the column bottom.

9. The separation method according to any one of claims 1 to 8, characterized in that, The heavy components containing ionic liquid from the column bottom after ionic liquid extractive distillation can be purified by distillation to obtain ionic liquid, which is then recycled back to the extractive distillation column.

10. The separation method according to any one of claims 1 to 9, characterized in that, The mass content of water in the ionic liquid is not more than 500 ppm; Preferably, the purity of the ionic liquid is more than 98%.