Preparation method of 3-methylthiopropionaldehyde

Abstract

The present invention relates to the field of 3-methylthiopropionaldehyde production, and in particular to a method for preparing 3-methylthiopropionaldehyde. By introducing water in the synthesis of 3-methylthiopropionaldehyde, on the one hand, due to the absorption of acrolein by water, AC in MMP is retained in the upper layer of the system, and water has an extraction effect, and MMP and MC in the system are layered, so that MC is also retained in the upper layer of the system; on the other hand, due to the solvation effect of water, the dissociation degree of the catalyst is enhanced, and the amount of the catalyst used can be reduced to less than half of the original level while still maintaining the same reaction rate. At the same time, the catalyst of the present invention can be recovered / partially recovered, saving costs, and in the subsequent refining process of MMP, MMP will also reduce the degree of polymerization due to the reduced content of the catalyst; the light components removed in the refining process of MMP are condensed and absorbed, and MC and MMP are recovered, further reducing production costs.

Description

Technical Field

[0001] The invention relates to the field of 3-methylmercaptopropionaldehyde production, and in particular to a method for preparing 3-methylmercaptopropionaldehyde. Background Art

[0002] 3-Methylthiopropionaldehyde (MMP) is used in food flavors, and in larger quantities as a raw material for 2-hydroxy-4-methylthiobutyric acid (MHA) and 2-amino-4-methylthiobutyric acid (Met). MMP is conventionally prepared from acrolein (AC) and methyl mercaptan (MC).

[0003] The method for preparing AC in large quantities is partial oxidation of propylene. In addition to the target component AC, there are also secondary by-product components such as acrylic acid, formic acid, acetic acid, acetaldehyde, propane, formaldehyde, carbon dioxide, carbon monoxide, allyl alcohol and allyl alcohol derivatives, as well as diluent components such as nitrogen and water. The method for preparing MC in large quantities is high-temperature dehydration of hydrogen sulfide and methanol. In addition to the main component methyl mercaptan, the secondary components include hydrogen sulfide, methanol, dimethyl sulfide, and dimethyl disulfide. The refining process of AC and MC cannot completely remove by-products, and further removal is required after the synthesis of MMP, otherwise it will cause trouble for subsequent use.

[0004] The known MMP purification method is to first remove the low-boiling-point secondary components (light removal) at a certain temperature and negative pressure and then evaporate the MMP (heavy removal) to meet the quality requirements for subsequent use.

[0005] The reaction of AC and MC to prepare MMP is carried out in a molar ratio of 1:1. AC can continue to react with MMP to form hemithioacetal, and the hemithioacetal can also react with another molecule of MMP. CN108218749A uses this reaction to store AC and MMP below 15°C for up to 14 weeks. CN108884027A uses the reversibility of the reaction to compensate for the amount of MC in the reaction of AC and MC.

[0006] CN1096779A points out that the use of hemithioacetal to replace MC and AC to produce MMP has slow conversion reaction kinetics, so the presence of a large amount of hemithioacetal should be avoided as much as possible during the synthesis of MMP. However, the generation of hemithioacetal is inevitable, and the molar amounts of AC and MC added are fixed and close. The closer the reaction is to the end point, the lower the concentration of the two, the slower the reaction rate, and MC is more likely to react with high-concentration MMP. After the reaction is completed, AC and MC remain in the system and need to be removed in the subsequent refining process.

[0007] The addition reaction of AC and MC requires the addition of a catalyst. CN1705641A uses a combination of N-alkylmorpholine / lower fatty acids, especially N-methylmorpholine / acetic acid, to prepare MMP at 30-50°C. Compared with the combination of pyridine or acetic acid, imidazole or acetic acid, the MMP prepared by the combination of N-methylmorpholine / acetic acid has the best reaction rate, yield and stability. CN101857560A uses a combination of triallylamine / acetic acid to prepare MMP.

[0008] CN104230771A points out that low-boiling-point catalysts such as pyridine and acetic acid cannot be completely evaporated in the subsequent refining process, and studies have shown that a small amount of acid and base substances can also cause instability of MMP. A relatively high temperature is used in the refining process of MMP, so acid and base substances can also cause instability of MMP during the refining process, thereby affecting the yield.

[0009] The existing disclosed technologies have the following problems: one is the one-way use of the catalyst, and the other is that the light components are not effectively recovered. The one-way use of the catalyst is a waste of resources, which leads to instability in the subsequent refining and storage of MMP, thereby affecting the yield of polymer production; the light components still contain beneficial components including MMP, AC and MC, which have recycling value, and direct waste treatment increases costs and affects benefits. Summary of the invention

[0010] In order to solve the problems mentioned in the background technology, the purpose of the present invention is to provide a method for preparing 3-methylthiopropionaldehyde, which solves the problem that the one-way use of the catalyst leads to waste of resources and instability in the subsequent refining and storage of MMP, thereby affecting the yield of polymer production; on the other hand, it solves the problem that the beneficial components MMP, AC and MC light components in the light components are not effectively recovered, thereby increasing costs.

[0011] The present invention provides a method for preparing 3-methylthiopropionaldehyde, which mainly comprises the following steps:

[0012] S1. Acrolein, methyl mercaptan and a catalyst are formed into a reaction system with a water content of 2 to 20 wt %, and the reaction is stirred at 30 to 50° C. for 30 to 360 min. After the reaction is completed, a crude 3-methylmercaptopropionaldehyde is obtained, and the crude 3-methylmercaptopropionaldehyde is allowed to stand and separate. The water in the reaction system can be directly added, introduced through acrolein, introduced through a catalyst, or introduced through MMP backflow. Due to the absorption of AC by water, AC in MMP is retained in the upper layer of the system, and water has an extraction effect, separating MMP and MC in the system, so that MC is also retained in the upper layer of the system.

[0013] S2. The upper liquid is returned to S1 to participate in the synthesis of crude 3-methylthiopropionaldehyde;

[0014] S3. The lower layer liquid is firstly subjected to removal of low boiling point substances at 90-110°C and -0.01 to 0 bar, and then distilled to obtain 3-methylthiopropionaldehyde.

[0015] Since the molar ratio of MC to MC is 0.95 to 1.05 in the synthesis of MMP, in the final stage of the reaction, the low concentrations of AC and MC will cause the reaction rate of the two to be basically 0, and MC will continue to react with MMP to form hemithioacetal. It is very difficult to completely react AC and MC. Not only the by-products introduced by AC and MC in MMP are called impurities, but the two substances that are not completely reacted are also impurities, which need to be removed in the subsequent refining. The catalyst is often a combination of organic amines and organic carboxylic acids. When MMP is evaporated, it will not be completely retained in the residual liquid. Acids and alkalis will cause the instability of MMP. This scheme can save catalysts and recover / partially recover the catalyst after the MMP synthesis reaction is completed, which has beneficial results for subsequent refining.

[0016] Preferably, the water content of the reaction system in S1 is 5 to 15 wt %.

[0017] Preferably, the standing time in S1 is 5 to 100 minutes.

[0018] Preferably, the standing time in S1 is 5 to 30 minutes.

[0019] Preferably, the standing time in S1 is 10 to 30 minutes.

[0020] Preferably, the standing temperature in S1 is 10-50°C.

[0021] Preferably, the standing temperature in S1 is 30-40°C.

[0022] Preferably, the low-boiling point substances removed in S3 are condensed at 10 to 60° C., and the condensate is circulated and absorbed. The low-boiling point substances are steam. After condensation at 10 to 60° C., dimethyl sulfide, dimethyl disulfide, methanol, water, acrolein, methyl mercaptan, allyl alcohol, acetic acid, formic acid, and MMP are dissolved in the condensate. The non-condensable gas in the low-boiling point substances reacts with 3-methylthiopropionaldehyde to form hemithioacetal, and then returns to S1 to participate in the synthesis of 3-methylthiopropionaldehyde crude product. Since the low-boiling point substances include dimethyl sulfide, dimethyl disulfide, methanol, water, acrolein, methyl mercaptan, allyl alcohol, acetic acid, and formic acid, a small amount of MMP will also be evaporated when the low-boiling point substances are evaporated. This solution can effectively recover the beneficial components MMP, AC, and MC in the low-boiling point substances.

[0023] Preferably, when the conversion rate of 3-methylthiopropionaldehyde reacting with the non-condensable gas is ≤80%, the reaction is terminated. Since the non-condensable gas contains methyl mercaptan, this solution can achieve more thorough recovery of methyl mercaptan in the non-condensable gas, thereby increasing the recovery value of methyl mercaptan.

[0024] Preferably, during the condensate circulation absorption process, the condensate portion that has accumulated some low-boiling point substances is transferred out, and after standing and stratification, the bottom layer of liquid is taken out and returned to S1 to participate in the synthesis of crude 3-methylmercaptopropionaldehyde or returned to S3 to participate in the distillation of 3-methylmercaptopropionaldehyde.

[0025] Beneficial effects: Compared with the prior art, the preparation method of 3-methylthiopropionaldehyde of the present invention introduces water in the synthesis of 3-methylthiopropionaldehyde. On the one hand, due to the absorption of acrolein by water, AC in MMP is retained in the upper layer of the system, and water has an extraction effect, which separates MMP and MC in the system, so that MC is also retained in the upper layer of the system; on the other hand, due to the solvation effect of water, the dissociation degree of the catalyst is enhanced, and the amount of the catalyst used can be reduced to less than half of the original level while maintaining the same reaction rate. At the same time, the catalyst of the present invention can be recovered / partially recovered, saving costs. In the subsequent refining process of MMP, the polymerization degree of MMP will also be reduced due to the reduction of the catalyst content; the light components removed in the refining process of MMP are condensed and absorbed, and MC and MMP are recovered, further reducing production costs. DETAILED DESCRIPTION

[0026] The present invention is described in detail below by specific examples. It is pointed out that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above invention content. Unless otherwise specified, the parts described in the present invention are all weight parts, the percentages described are all mass percentages, and the concentrations described are mass percentage concentrations.

[0027] Example 1

[0028] Take 1000g of crude MMP prepared by a conventional production method, add 100g of water, keep warm at 30°C, prepare 10 groups, stir for 10min at the same time until the system turns white, start timing from stopping stirring, take out two groups of lower layer MMP samples at 5, 10, 20, 30, and 60min, for a total of 10 groups, each with a mass of 400g; add 100g of 99wt% AC and 88.6g of 97.6wt% MC to the remaining 10 groups of upper layer samples, respectively, and react at 30°C. Start timing from the addition of MC until the sum of the mass fractions of MC and AC in the system is less than 1%, stop timing, and record the standing separation time and addition reaction time of each group, as shown in Table 1.

[0029]

[0030] Table 1

[0031] Example 2

[0032] Take 1000g of refined MMP (wherein, the MMP content is 99.4wt%, the methyl mercaptan content is 0.13wt%, and the acrolein content is 0.05wt%), add 1g of glacial acetic acid and 0.67g of pyridine, prepare 10 groups, add 0, 10, 50, 100, and 200g of water to each two groups, respectively, then add 100g of 99wt% AC and 88.6g of 97.6wt% MC, react at 30°C, and stir at a speed of 500r / min. Start timing from the addition of MC, and stop timing when the sum of the mass fractions of MC and AC in the system is less than 1%. Record the standing separation time and addition reaction time of each group, as shown in Table 2.

[0033]

[0034] Table 2

[0035] Example 3

[0036] Take 10 groups of MMP prepared by conventional method, each group has a mass of 1000g, add 0, 50, 100, 150, 200g of water to every two groups, keep warm and stir at 30℃ for 15min until emulsified, let it stand for 30min, take all the MMP in the lower layer, remove low boiling point substances at 90℃ and relative pressure of -0.01bar until the total mass fraction is less than 1wt%, detect the content of heavy components in the residue, and use gas chromatography to detect low boiling point substances. Substances with boiling points lower than MMP are classified as light components. The test results are shown in Table 3.

[0037]

[0038] Table 3

[0039] Example 4

[0040] Ten groups of 1000 g MMP prepared by conventional method were prepared, each group had a mass of 1000 g. 0, 50, 100, 150, and 200 g of water were added to every two groups. The mixture was stirred at 30°C for 15 min until emulsified. The mixture was allowed to stand for 30 min, and all the MMP in the lower layer was taken out. The contents of water, MMP, AC, and MC were detected, and the contents of MMP, AC, and MC after deducting water were calculated. The test results are shown in Table 4.

[0041]

[0042] Table 4

[0043] Example 5

[0044] Take 5000g of MMP prepared by the conventional method, remove low-boiling point substances at 90°C and -0.01bar, evaporate the low-boiling point substances and condense them at 30°C first, and pass the non-condensable gas into 500g of MMP prepared by the conventional method at 35°C. When the sum of the mass fractions of light components in the residual liquid is less than 1wt%, terminate the reaction, and let the condensate stand to separate.

[0045] Test results: 1. The composition and content of the bottom layer were detected, where the mass of MMP in the lower layer of the condensate was 71g, of which the MMP content was 94.7wt%, the AC content was 1.36wt%, the MC content was 0.45wt%, and the water content was 2.3wt%.

[0046] 2. Take 500gMMP to detect the increase in MC. The increase in AC in 500g of MMP absorption liquid is 10.4g.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. 3-methylthiopropionaldehyde preparation method, characterized in that The following steps are involved: S1. Acrolein, methyl mercaptan, an organic amine and an organic carboxylic acid are mixed to form a reaction system having a water content of 5 to 15 wt%, and the reaction is stirred at 30-50 ° C for 30-360 min. After the reaction is completed, a crude 3-methylthiopropionaldehyde product is obtained, and the crude 3-methylthiopropionaldehyde product is allowed to stand for 30-100 min and then separated; S2. The upper liquid is returned to S1 to participate in the synthesis of crude 3-methylthiopropionaldehyde; S3. The lower layer liquid is firstly subjected to removal of low boiling point substances at 90-110°C and -0.01 to 0 bar, and then distilled to obtain 3-methylthiopropionaldehyde.

2. The method for preparing 3-methylthiopropionaldehyde according to claim 1, characterized in that: The standing temperature in S1 is 10-50°C.

3. The method for preparing 3-methylthiopropionaldehyde according to claim 1, characterized in that: The standing temperature in S1 is 30-40°C.

4. The method for preparing 3-methylthiopropionaldehyde according to claim 1, characterized in that: The low-boiling point substances removed in S3 are condensed at 10-60° C., and the condensate is circulated and absorbed. Dimethyl sulfide, dimethyl disulfide, methanol, water, acrolein, methyl mercaptan, allyl alcohol, acetic acid, formic acid, and 3-methylmercaptopropionaldehyde in the low-boiling point substances are dissolved in the condensate. The non-condensable gas in the low-boiling point substances reacts with 3-methylmercaptopropionaldehyde to form hemithioacetal, and then returns to S1 to participate in the synthesis of crude 3-methylmercaptopropionaldehyde.

5. The method for preparing 3-methylthiopropionaldehyde according to claim 4, characterized in that: When the conversion rate of 3-methylthiopropionaldehyde reacting with the non-condensable gas is ≤80%, the reaction is terminated.

6. The method for preparing 3-methylthiopropionaldehyde according to any one of claims 4-5, characterized in that: During the condensate circulation absorption process, part of the condensate with accumulated low-boiling point substances is transferred out. After standing and stratification, the bottom layer of liquid is taken out and returned to S1 to participate in the synthesis of crude 3-methylmercaptopropionaldehyde or returned to S3 to participate in the distillation of 3-methylmercaptopropionaldehyde.

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