Preparation method and reaction device of 2-hydroxy-4-methylthiobutyronitrile

Abstract

The present invention provides a kind of preparation method and reaction unit of 2-hydroxy-4-methylthiobutyronitrile, relate to the field of chemical synthesis technology, comprise the following steps: mixing stage: using 2-hydroxy-4-methylthiobutyronitrile as solvent to pass into reaction unit, first absorb hydrocyanic acid, and then sequentially mix methyl mercaptan and acrolein;Reaction stage: the mixture obtained by mixing stage generates 2-hydroxy-4-methylthiobutyronitrile under the action of organic acid and organic base mixed catalyst, and the prepared 2-hydroxy-4-methylthiobutyronitrile part refluxes and is passed into reaction unit again as solvent. The application uses 2-hydroxy-4-methylthiobutyronitrile as solvent to react, avoids the addition of water, uses 2-hydroxy-4-methylthiobutyronitrile as solvent reflux to absorb hydrocyanic acid, can contact acrolein under acidic environment, reduce the degree of polymerization of acrolein;Using this method, equivalent reaction can be achieved, avoids the use of hydrocyanic acid to generate excessive formic acid.

Description

Technical Field

[0001] The present application relates to the technical field of chemical synthesis, and more specifically, to a preparation method and reaction device of 2-hydroxy-4-methylthiobutyronitrile. Background Art

[0002] 2-Hydroxy-4-methylthiobutyronitrile (MMCN) is an important intermediate in the production of DL-methionine and methionine hydroxy analogs. Methionine or liquid methionine is an essential supplemental additive in animal feed. In the prior art, MMCN is obtained via a two-step process: methylthiopropionaldehyde is prepared from acrolein and methyl mercaptan, which is then reacted with hydrocyanic acid. In the traditional process for preparing methylthiopropionaldehyde, liquid acrolein and methyl mercaptan react in a reactor containing the liquid methylthiopropionaldehyde product, using purified liquid acrolein and methyl mercaptan. Acrolein is highly toxic, flammable, and polymerizable, requiring high safety requirements and high investment in post-processing. Furthermore, the existing process uses pyridine as a catalyst in the reaction of acrolein and methyl mercaptan, which can easily generate difficult-to-remove high-boiling-point impurities that remain in the product.

[0003] Chinese invention patent publication number CN103347854A discloses a method for preparing 2-hydroxy-4-(methylthio)butyronitrile from 3-(methylthio)propionaldehyde and hydrocyanic acid. This method includes using a trialkylamine as a catalyst. By selecting appropriate additives and storage conditions, methylthiopropionaldehyde-CN with high storage stability is obtained. The patent specification states that after removing ammonia from the crude HCN gas mixture by acid washing, other purification steps prior to the synthesis of methylthiopropionaldehyde-CN can be omitted. However, acrolein and the methylthiopropionaldehyde generated in the early stages of the reaction have very low solubility in water. If water is used as a solvent, the reaction gradually becomes homogeneous as it proceeds, which not only reduces the reaction rate but also causes side reactions such as polymerization during the heterogeneous reaction.

[0004] U.S. Patent Publication No. US4225516A discloses a method for producing β-methylthiopropionaldehyde. The method involves using methylthiopropionaldehyde to absorb acrolein for a reaction. The methylthiopropionaldehyde enters the upper portion of a tower at a temperature of -10°C. The mixture of methylthiopropionaldehyde and acrolein obtained at the bottom of the tower is passed through a reactor, where acrolein and methyl mercaptan react in the presence of a catalyst. In this method, methyl mercaptan is continuously added to the reactor, and the product contains a large amount of water.

[0005] The Chinese invention patent with publication number CN85108505A discloses a method for synthesizing the methionine intermediate 5-(β-methylthioethyl)hydantoin in one step from acrolein, methyl mercaptan, hydrocyanic acid, and ammonium bicarbonate. The method comprises first adding acrolein and a catalyst into a reactor, then introducing gaseous methyl mercaptan, heating the reaction, then introducing an aqueous solution of hydrocyanic acid and an aqueous solution of ammonium bicarbonate, and reacting at 60-80°C for 2-3 hours. The catalyst used in the patent is a mixture of one or two neutral amino acids and organic carboxylic acids. After repeated experiments, it was found that in the actual reaction process, acrolein and methyl mercaptan first contact and react to obtain methylthiopropionaldehyde, and then introduce hydrocyanic acid and an esterifying agent. During the long reaction process, acrolein and hydrocyanic acid are more likely to polymerize.

[0006] In summary, water is used as a solvent in the process adopted in the prior art. Water, hydrocyanic acid and acrolein consume a lot of energy in the subsequent separation process, and hydrocyanic acid and acrolein are prone to self-polymerization during the treatment process; in the methylthiopropionaldehyde reaction, in order to ensure that the self-polymerization of acrolein is reduced, methyl mercaptan is added in excess to ensure that the acrolein reaction is complete; in the MMCN reaction, excessive hydrocyanic acid is also added to ensure that the methylthiopropionaldehyde reacts fully, and finally formic acid is generated, which increases the cost of subsequent processing. Summary of the Invention

[0007] To solve the above problems, the technical solution adopted in this application is a method for preparing 2-hydroxy-4-methylthiobutyronitrile, comprising the following steps:

[0008] Mixing stage: 2-hydroxy-4-methylthiobutyronitrile is introduced into the reaction device as a solvent, first absorbing hydrocyanic acid, and then mixing methyl mercaptan and acrolein in sequence;

[0009] Reaction stage: the mixture obtained in the mixing stage generates 2-hydroxy-4-methylthiobutyronitrile under the action of a mixed catalyst of an organic acid and an organic base, and a portion of the prepared 2-hydroxy-4-methylthiobutyronitrile is refluxed and reintroduced into the reaction device as a solvent.

[0010] Optionally, the organic acid in the mixed catalyst of organic acid and organic base includes one or both of formic acid and acetic acid, the organic base includes one or more of pyridine, morpholine and RNH2, and R represents C3-C 10 In one embodiment, an organic acid and an organic base are mixed to adjust the acidity coefficient of the organic acid and organic base mixed catalyst to 2-6; the refluxed 2-hydroxy-4-methylthiobutyronitrile is cooled in a heat exchanger, and then the organic acid and organic base mixed catalyst is added, and then the mixed catalyst is sprayed into a reaction device through a circulation pipeline, and the molar ratio of the organic acid and organic base mixed catalyst to the hydrocyanic acid is 1:1000-10000.

[0011] Optionally, the organic acid in the mixed catalyst of organic acid and organic base is one or both of benzenesulfonic acid macroporous resin and carboxylic acid macroporous resin, and the organic base is amino macroporous resin, wherein the amino group is RNH2, R2NH, R3N and R4N + One of them, R represents C3-C 10 In one method, a macroporous resin is loaded inside a fixed bed. An organic acid macroporous resin and an organic base macroporous resin are mixed and loaded in the fixed bed so that the molar number of the basic functional groups of the macroporous resin in the fixed bed is 1-1.5:1 of the molar number of the acidic functional groups. 2-Hydroxy-4-methylthiobutyronitrile is discharged from the upper end of the fixed bed, and a portion of the reflux is cooled in a heat exchanger and then sprayed into a reaction device through a circulation pipeline. The reflux ratio is 500-1200:1.

[0012] Optionally, the reflux ratio is 200-500:1, the temperature in the reaction device is 30-70° C., and the pressure is 0.1 MPa-0.15 MPa.

[0013] Optionally, hydrocyanic acid and acrolein enter the reaction device in gaseous form, and methyl mercaptan enters the reaction device in droplet form. When feeding, the methyl mercaptan droplets are controlled to be ≤10 μm, and the residence time of the methyl mercaptan droplets in the mixing stage is ≥2 s.

[0014] Optionally, a first venturi feed pipe and a second venturi feed pipe are sequentially arranged inside the reaction device from top to bottom, the flow rate of hydrocyanic acid passing through the throat of the first venturi feed pipe is 25-45 m / s, the flow rate of acrolein passing through the throat of the second venturi feed pipe is 15-30 m / s, and the molar ratio of the feed amounts of hydrocyanic acid, methyl mercaptan and acrolein entering the reaction device is 1:1:1.

[0015] Optionally, the hydrocyanic acid is deaminated hydrocyanic acid gas, which is obtained by Angle method or BMW process, and has a hydrocyanic acid content of 9.4%±2%. The acrolein is deacrylic acid-free acrolein gas, and has an acrolein content of 7.0%±2%.

[0016] The present application also provides a reaction device for 2-hydroxy-4-methylthiobutyronitrile, which is suitable for implementing any of the aforementioned methods for preparing 2-hydroxy-4-methylthiobutyronitrile. The reaction device includes a feed area and a gas-liquid separation area. The feed area is provided with a hydrocyanic acid feeder, a methyl mercaptan feeder and an acrolein feeder from top to bottom. A 2-hydroxy-4-methylthiobutyronitrile spray device is provided on the top of the reaction device. The reaction device is provided with a circulation pipeline, and the circulation pipeline is provided with a heat exchanger.

[0017] Optionally, the gas-liquid separation zone includes a gas-liquid separation tank and a droplet catcher. During the preparation of 2-hydroxy-4-methylthiobutyronitrile, the liquid level in the gas-liquid separation tank is controlled to be below 2 / 3. The droplet catcher is arranged above the gas-liquid separation tank. The first venturi feed pipe and the second venturi feed pipe are sequentially arranged inside the reaction device from top to bottom. Flow regulators are provided below the throats of the first venturi feed pipe and the second venturi feed pipe, and the methyl mercaptan feeder is provided with a sprayer.

[0018] Optionally, the feed port of the hydrocyanic acid feeder is set at the throat of the first venturi feed pipe, and the feed port of the acrolein feeder is set at the throat of the second venturi feed pipe. The width of the throats of the first venturi feed pipe and the second venturi feed pipe are both 1 / 6-1 / 4 of the inner diameter of the feed zone tower.

[0019] The beneficial effects of the preparation method and reaction device of 2-hydroxy-4-methylthiobutyronitrile provided in this application are:

[0020] Using 2-hydroxy-4-methylthiobutyronitrile as a solvent for the reaction avoids the addition of water, reduces subsequent separation processes, simplifies post-processing steps, thereby reducing process complexity and time costs, and achieving high product quality, with a product purity exceeding 99.6% and a yield exceeding 99%. Using 2-hydroxy-4-methylthiobutyronitrile as a solvent for reflux absorption of hydrocyanic acid allows it to contact acrolein under an acidic environment, thereby reducing the polymerization degree of acrolein. The method enables an equivalent reaction to be achieved, avoiding the excessive use of hydrocyanic acid to generate formic acid, which consumes system capacity for subsequent separation and processing. Unrefined hydrocyanic acid and acrolein can be used as raw materials to prepare 2-hydroxy-4-methylthiobutyronitrile in a one-pot process, reducing process steps and reaction equipment, lowering production costs, and simultaneously shortening the storage time of hydrocyanic acid and acrolein in the system, thereby reducing safety risks. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments or descriptions of the prior art.

[0022] Figure 1 This is a schematic diagram of the reaction apparatus for preparing 2-hydroxy-4-methylthiobutyronitrile provided in Example 1 of the present application.

[0023] Figure 2 This is a schematic diagram of the reaction apparatus for preparing 2-hydroxy-4-methylthiobutyronitrile provided in Example 7 of the present application;

[0024] Figure 3 This is a liquid chromatography spectrum of the 2-hydroxy-4-methylthiobutyronitrile product prepared in Example 8 of the present application;

[0025] Figure 4This is the liquid phase spectrum of the 2-hydroxy-4-methylthiobutyronitrile product prepared in Example 9 of the present application.

[0026] Explanation of the accompanying symbols: 1. Hydrocyanic acid feeder; 2. First flow regulator; 3. Sprayer; 4. Acrolein feeder; 5. Second flow regulator; 6. Droplet catcher; 7. Gas-liquid separation tank; 8. Heat exchanger; 9. Schematic diagram of exhaust gas flow direction; 10. Schematic diagram of 2-hydroxy-4-methylthiobutyronitrile reflux; 11. Schematic diagram of 2-hydroxy-4-methylthiobutyronitrile product discharge; 12. Gas-liquid separation zone; 13. Schematic diagram of catalyst feed; 14. Fixed bed; 15. First Venturi feed pipe; 16. Second Venturi feed pipe; 17. Feed zone; 18. Circulation pipeline; 19. Spraying device. DETAILED DESCRIPTION

[0027] In order to make the technical problems, technical solutions and beneficial effects to be solved by this application more clearly understood, this application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0028] Example 1

[0029] A preparation method of 2-hydroxy-4-methylthiobutyronitrile, such as Figure 1 As shown, the reaction device includes a feed zone 17 and a gas-liquid separation zone 12. 2-hydroxy-4-methylthiobutyronitrile liquid is introduced from the top of the feed zone 17, and first absorbs hydrocyanic acid as a solvent, and then methyl mercaptan and acrolein are mixed in sequence. Under the action of a mixed catalyst of an organic acid and an organic base, 2-hydroxy-4-methylthiobutyronitrile is generated, and falls into the gas-liquid separation zone 12. After gas-liquid separation, 2-hydroxy-4-methylthiobutyronitrile is obtained.

[0030] The reaction device is provided with a hydrocyanic acid feeder 1 capable of feeding hydrocyanic acid in a gaseous state, a methyl mercaptan feeder capable of feeding methyl mercaptan in a liquid state, and an acrolein feeder 4 capable of feeding acrolein in a gaseous state in sequence from top to bottom. A 2-hydroxy-4-methylthiobutyronitrile spraying device 19 is provided at the top of the reaction device. The reaction device is provided with a circulation pipe 18, and the circulation pipe 18 is provided with a heat exchanger 8.

[0031] The gas-liquid separation zone 12 includes a gas-liquid separation tank 7 and a droplet catcher 6. During the preparation of 2-hydroxy-4-methylthiobutyronitrile, the liquid level in the gas-liquid separation tank 7 is controlled below 2 / 3. The droplet catcher 6 is arranged above the gas-liquid separation tank 7 to remove droplets entrained in the unreacted gas.

[0032] A first venturi feed pipe 15 and a second venturi feed pipe 16 are provided inside the reaction device. The feed port of the hydrocyanic acid feeder 1 is provided at the throat of the first venturi feed pipe 15, and the feed port of the acrolein feeder 4 is provided at the throat of the second venturi feed pipe 16. The width of the throats of the first venturi feed pipe 15 and the second venturi feed pipe 16 are both 1 / 4 of the inner diameter of the feed zone 17 (Note: Figure 1 and Figure 2 The diagram only represents a schematic structure and does not represent the actual scale). Flow regulators are provided below the throats of the first venturi feed pipe 15 and the second venturi feed pipe 16. Hydrocyanic acid is fed in a gaseous state from the throat of the first venturi feed pipe 15 and passed into the feed zone 17 from the outside. Acrolein is fed in a gaseous state from the throat of the second venturi feed pipe 16 and passed into the feed zone 17 from the outside.

[0033] The methyl mercaptan feeder can allow methyl mercaptan to enter the feed zone 17 in liquid form from an external pipeline. A sprayer 3 is provided at the end of the external pipeline so that the droplets of methyl mercaptan liquid sprayed by the sprayer 3 are ≤10μm, and the residence time of methyl mercaptan in the tower is ≥2s.

[0034] The flow rate of hydrocyanic acid through the throat of the first venturi feed pipe 15 is 25 m / s, the flow rate of acrolein through the throat of the second venturi feed pipe 16 is 15 m / s, and the molar ratio of the feed amounts of hydrocyanic acid, methyl mercaptan and acrolein entering the reaction device is 1:1:1.

[0035] Hydrocyanic acid is derived from hydrocyanic acid gas after deamination, which is obtained by Angle method or BMW process, and has a hydrocyanic acid content of 9.4%±2%. Acrolein is derived from acrolein gas after deacrylic acid removal, and has an acrolein content of 7.0%±2%.

[0036] The hydrocyanic acid gas after deammoniation is composed of the following components in mass percentage: hydrocyanic acid 9.4%±2%, hydrogen 1.6%±2%, nitrogen 79.4%±2%, oxygen 1.7%±1%, carbon monoxide 5.8%±1%, carbon dioxide 1.5%±1%, and methane 0.6%±0.2%.

[0037] The acrolein gas after removal of acrylic acid is composed of the following components in mass percentage: acrolein 7.0%±2%, oxygen 5.2%±2%, nitrogen 83.4%±2%, carbon monoxide 0.5%±0.2%, carbon dioxide 1.2%±0.5%, propylene 0.2%±0.2%, and others 2.3%±1%.

[0038] As shown in the reflux diagram 10 of 2-hydroxy-4-methylthiobutyronitrile and the discharge diagram 11 of 2-hydroxy-4-methylthiobutyronitrile product, the product of 2-hydroxy-4-methylthiobutyronitrile is discharged from the bottom of the reaction device, and part of it refluxes through the circulation pipe 18 and the heat exchanger 8 into the feed zone 17. After cooling through the heat exchanger 8, it is introduced into the top of the reaction device as a solvent. The reflux ratio is 200, the temperature in the reaction device is 30-70°C, and the pressure is 0.1MPa-0.15MPa (measured by gauge pressure rather than absolute pressure). The pressure is provided by the feed. When the pressure is higher than The feed rate is reduced when the pressure is within this pressure range, and the feed rate is increased when the pressure is lower than this pressure range. The organic acid in the mixed catalyst of organic acid and organic base is formic acid, the organic base is pyridine, and the acidity coefficient (pKa) is 2-6. After the refluxed 2-hydroxy-4-methylthiobutyronitrile preparation product passes through the heat exchanger 8, the mixed catalyst of organic acid and organic base is added at the catalyst feed schematic position 13, and is introduced into the reaction device through the circulation pipe 18 and the 2-hydroxy-4-methylthiobutyronitrile spray device 19. The molar ratio of the added catalyst to the hydrocyanic acid is 1:10000.

[0039] Venturi feed pipes are located below the feed openings of both the hydrocyanic acid feeder 1 and the acrolein feeder 4. The width of the throat of the Venturi feed pipe is ¼ of the inner diameter of the reaction tower. Flow regulators are located below the throats of the Venturi feed pipes. A first flow regulator 2 is located below the hydrocyanic acid feeder 1, and a second flow regulator 5 is located below the acrolein feeder 4. These flow regulators are used to control the instantaneous flow rate of the material and break up the material particles. The first and second flow regulators 2 and 5 are cylindrical or spherical depending on the shape of the throat opening. In this embodiment, the throat openings of the Venturi feed pipes are both conical, converging downward, and the flow regulators are spherical. Hydrocyanic acid is fed in a gaseous state from above the throat of the first Venturi feed pipe 15 and introduced into the feed zone 17 from the outside. Acrolein is fed in a gaseous state from above the throat of the second Venturi feed pipe 16 and introduced into the feed zone 17 from the outside.

[0040] As shown in the tail gas flow diagram 9, unreacted gas is discharged through the droplet catcher 6 in the gas-liquid separation zone 12. An online monitoring device is installed at the tail gas outlet to ensure that the acrolein content in the tail gas is less than 200 ppm, the hydrocyanic acid content is less than 5 ppm, and the methyl mercaptan content is less than 10 ppm. The unreacted raw materials in the tail gas are used as indicators for adjusting the reaction rate. When the unreacted raw materials in the tail gas exceed the above standards, the introduction rate of each raw material is reduced, and the reaction time is extended.

[0041] The purity of the prepared product of 2-hydroxy-4-methylthiobutyronitrile was 99.72% and the yield was 99.3%.

[0042] Example 2

[0043] The difference from Example 1 is that, in this embodiment, the flow rate of hydrocyanic acid through the throat of the first Venturi feed pipe is 30 m / s, the flow rate of acrolein through the throat of the second Venturi feed pipe is 20 m / s, the ratio of the throat size of the Venturi feeder to the inner diameter of the reaction zone tower is 1 / 6, the reflux ratio is 300, the organic base in the mixed catalyst of organic acid and organic base is morpholine, and the organic acid is acetic acid. The addition ratio of the organic acid and organic base is controlled so that the acidity coefficient (pKa) of the mixed catalyst of organic acid and organic base is 2-6, and the molar ratio of the added amount of the catalyst to the hydrocyanic acid is 1:5000.

[0044] The purity of the product prepared from 2-hydroxy-4-methylthiobutyronitrile was 99.78% and the yield was 99.5%.

[0045] Example 3

[0046] The difference from Example 1 is that in this embodiment, the flow rate of hydrocyanic acid through the throat of the first venturi feed pipe is 35 m / s, the flow rate of acrolein through the throat of the second venturi feed pipe is 25 m / s, the reflux ratio is 400, the organic base in the mixed catalyst of organic acid and organic base is propylamine (i.e., RNH2, R is C3), the organic acids are formic acid and acetic acid, the addition ratio of the organic acid and organic base is controlled so that the acidity coefficient (pKa) of the mixed catalyst of organic acid and organic base is 2-6, and the molar ratio of the added amount of the catalyst to the hydrocyanic acid is 1:1000.

[0047] The purity of the product prepared from 2-hydroxy-4-methylthiobutyronitrile was 99.85% and the yield was 99.7%.

[0048] Example 4

[0049] The difference from Example 1 is that in this embodiment, the flow rate of hydrocyanic acid through the throat of the first venturi feed pipe is 40 m / s, the flow rate of acrolein through the throat of the second venturi feed pipe is 30 m / s, the reflux ratio is 500, and the organic base in the mixed catalyst of organic acid and organic base is decylamine (i.e., RNH2, R is C 10 ), the organic acid is formic acid, the addition ratio of the organic acid and the organic base is controlled so that the acidity coefficient (pKa) of the organic acid and organic base mixed catalyst is 2-6, and the molar ratio of the added amount of the catalyst to the hydrocyanic acid is 1:1000.

[0050] The purity of the product prepared from 2-hydroxy-4-methylthiobutyronitrile was 99.92% and the yield was 99.7%.

[0051] Example 5

[0052] The difference from Example 1 is that in this embodiment, the flow rate of hydrocyanic acid through the throat of the first venturi feed pipe is 45 m / s, the organic bases in the mixed catalyst of organic acid and organic base are pyridine and morpholine, the organic acid is formic acid, the addition ratio of the organic acid and organic base is controlled so that the acidity coefficient (pKa) of the mixed catalyst of organic acid and organic base is 2-6, and the molar ratio of the added amount of the catalyst to the hydrocyanic acid is 1:1000.

[0053] The purity of the product prepared from 2-hydroxy-4-methylthiobutyronitrile was 99.66%, and the yield was 99.6%.

[0054] Example 6

[0055] The difference from Example 1 is that in this embodiment, the organic base in the mixed catalyst of organic acid and organic base is propylamine (i.e., RNH2, R is C3), the organic acid is formic acid, the addition ratio of the organic acid and organic base is controlled so that the acidity coefficient (pKa) of the mixed catalyst of organic acid and organic base is 2-6, and the molar ratio of the added amount of the catalyst to the hydrocyanic acid is 1:1000.

[0056] The purity of the product prepared from 2-hydroxy-4-methylthiobutyronitrile was 99.66%, and the yield was 99.6%.

[0057] Example 7

[0058] like Figure 2 As shown, this embodiment differs from Example 1 in that a macroporous resin is used as the catalyst. A fixed bed 14 is provided in the circulation conduit 18, and the macroporous resin is loaded within the fixed bed 14. The macroporous resin is a mixture of benzenesulfonic acid-based macroporous resin and tertiary amine-based macroporous resin. In this embodiment, the benzenesulfonic acid-based macroporous resin is DuPont's Amberlyst 35 resin, a sulfonic acid-type strongly acidic cation exchange resin. The functional group is benzenesulfonic acid. The particles appear as opaque spherical particles with a particle size of 0.7-0.95 mm, a surface area of 50 m² / g, a total acid concentration of >5.0 eq / kg, and a temperature resistance of up to 150°C. The tertiary amine-based macroporous resin is Tulsimer® A-8X MP resin from Cohis (Beijing) Technology Co., Ltd., a macroporous weakly basic anion exchange resin with a tertiary amine functional group. The particles are wet spherical with a particle size distribution of 0.3-1.2 mm. The total exchange capacity is ≥1.3meq / ml, the applicable pH range is 0-9, and the temperature resistance is 80℃.

[0059] To ensure that the molar number of basic functional groups is twice that of acidic functional groups, the mass ratio of Tulsimer® A-8X MP to Amberlyst 35 is 4:1. 2-Hydroxy-4-methylthiobutyronitrile is discharged from the top of fixed bed 14, and a portion of the reflux is cooled through heat exchanger 8 before entering the reaction unit. It is introduced from the top of the reaction unit as the solvent, with a reflux ratio of 500.

[0060] The purity of the product prepared from 2-hydroxy-4-methylthiobutyronitrile was 99.78% and the yield was 99.5%.

[0061] Example 8

[0062] The difference from Example 7 is that the macroporous resin in this embodiment is a mixed packing of a carboxylic acid-based macroporous resin and a tertiary amine-based macroporous resin. In this embodiment, the carboxylic acid-based macroporous resin is DuPont's Amberlite IRC50 resin, a macroporous weakly acidic cation exchange resin. The functional group is a carboxylic acid group, the matrix is a macroporous polypropylene copolymer, the appearance is light yellow opaque particles, the main particle size is 280-700 μm, and the volumetric total exchange capacity is ≥10.8 mmol / g (dry). The tertiary amine-based macroporous resin is the same as in Example 7.

[0063] In order to meet the requirement that the molar number of basic functional groups is 1.2 times that of acidic functional groups, the mass ratio of Tulsimer® A-8X MP resin to Amberlite IRC50 resin is 2.4:1. The reflux ratio is 750. The test results are as follows Figure 3 shown.

[0064] The purity of the product prepared from 2-hydroxy-4-methylthiobutyronitrile was 99.75% and the yield was 99.7%.

[0065] Example 9

[0066] The difference from Example 7 is that, in order to satisfy the requirement that the molar number of basic functional groups is 1.5 times that of acidic functional groups, the mass ratio of Tulsimer® A-8X MP to Amberlyst 35 is 6:1, and the reflux ratio is 1000. The test results are as follows: Figure 4 shown.

[0067] The purity of the product prepared from 2-hydroxy-4-methylthiobutyronitrile was 99.85% and the yield was 99.7%.

[0068] Example 10

[0069] The difference from Example 7 is that the macroporous resin in this example is a mixed packing of a benzenesulfonic acid macroporous resin and a quaternary ammonium macroporous resin. The benzenesulfonic acid macroporous resin is Tulsimer® T-62 MPDRY resin from Cohis (Beijing) Technology Co., Ltd., which has a main structure of polystyrene copolymer, sulfonic acid functional groups, a particle size of 0.42-1.2 mm, and an H+ concentration of 4.8 meq / dry gm. The quaternary ammonium macroporous resin is DuPont's Amberlyst A26 resin catalyst, which has a main structure of styrene-divinylbenzene, quaternary ammonium functional groups, a basic site concentration of greater than or equal to 4.20 eq / kg, and a particle size of 560-700 μm. To ensure that the molar number of basic functional groups is twice that of acidic functional groups, the mass ratio of Amberlyst A26 to Tulsimer T-62 MP DRY is 4.8:1. The reflux ratio is 1200.

[0070] The purity of the product prepared from 2-hydroxy-4-methylthiobutyronitrile was 99.91% and the yield was 99.7%.

[0071] Test method:

[0072] The Thermo Fisher Scientific high performance liquid chromatography U3000 was selected, wherein the conditions involved are:

[0073] Chromatographic column: C18 chromatographic column; column length: 250 mm, inner diameter: 4.6 mm; column temperature: 40°C; mobile phase: 80% (v / v) acetonitrile / water; mobile phase flow rate: 0.8 mL / min; detector: UV detector, detection wavelength: 210 nm; the elution time of 2-hydroxy-4-methylthiobutyronitrile in the liquid phase spectrum was 3.793 min after comparison with standard analysis. Figure 3 and Figure 4 The liquid phase spectra of the 2-hydroxy-4-methylthiobutyronitrile product prepared in Examples 8 and 9 of the present application are respectively.

[0074] Table 1 Reaction parameters and product statistics of Examples 1 to 6

[0075]

[0076] As shown in Table 1, after testing, the purity of the product of each embodiment is higher than 99.6%, and the yield is higher than 99%.

[0077] Table 2 Reaction parameters and product statistics of Examples 7-10

[0078]

[0079] As shown in Table 2, after testing, the purity of the product of each embodiment is higher than 99.7%, and the yield is higher than 99%.

[0080] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present application, and should all be included in the scope of protection of the present application.

Claims

1. A method for preparing 2-hydroxy-4-methylthiobutyronitrile, characterized in that: The following steps are involved: Mixing stage: 2-hydroxy-4-methylthiobutyronitrile is introduced into the reaction device as a solvent, first absorbing hydrocyanic acid, and then mixing methyl mercaptan and acrolein in sequence; Reaction stage: the mixture obtained in the mixing stage generates 2-hydroxy-4-methylthiobutyronitrile under the action of a mixed catalyst of an organic acid and an organic base, and a portion of the prepared 2-hydroxy-4-methylthiobutyronitrile is refluxed and reintroduced into the reaction device as a solvent; The hydrocyanic acid and acrolein enter the reaction device in gaseous form, and the methyl mercaptan enters the reaction device in the form of droplets. When feeding, the methyl mercaptan droplets are controlled to be ≤10 μm, and the residence time of the methyl mercaptan droplets in the mixing stage is ≥2 s. The first venturi feed pipe and the second venturi feed pipe are sequentially arranged in the reaction device from top to bottom; The organic acid in the organic acid and organic base mixed catalyst comprises at least one or two of formic acid and acetic acid, and the organic base comprises at least one or more of pyridine, morpholine and RNH2, wherein R represents C3-C 10 One of them is to mix an organic acid and an organic base so that the acidity coefficient of the organic acid and organic base mixed catalyst is 2-6; Alternatively, the organic acid in the organic acid and organic base mixed catalyst is one or both of benzenesulfonic acid macroporous resin and carboxylic acid macroporous resin, and the organic base is an amino macroporous resin, wherein the amino group is RNH2, R2NH, R3N and R4N + One of them, R represents C3-C 10 One of them.

2. The method for preparing 2-hydroxy-4-methylthiobutyronitrile according to claim 1, wherein: The organic acid in the organic acid and organic base mixed catalyst comprises at least one or two of formic acid and acetic acid, and the organic base comprises at least one or more of pyridine, morpholine and RNH2, wherein R represents C3-C 10 In one embodiment, an organic acid and an organic base are mixed to make the acidity coefficient of the organic acid and organic base mixed catalyst 2-6; the refluxed 2-hydroxy-4-methylthiobutyronitrile is cooled in a heat exchanger, the organic acid and organic base mixed catalyst is added, and then the organic acid and organic base mixed catalyst is sprayed into the reaction device through a circulation pipe, and the molar ratio of the feed amount of the organic acid and organic base mixed catalyst to the hydrocyanic acid is 1:1000-10000.

3. The method for preparing 2-hydroxy-4-methylthiobutyronitrile according to claim 1, wherein: The organic acid in the organic acid and organic base mixed catalyst is one or both of benzenesulfonic acid macroporous resin and carboxylic acid macroporous resin, and the organic base is amino macroporous resin, wherein the amino group is RNH2, R2NH, R3N and R4N. + One of them, R represents C3-C 10 In one embodiment, the macroporous resin is loaded inside a fixed bed, and an organic acid macroporous resin and an organic base macroporous resin are mixed and loaded in the fixed bed so that the molar number of the basic functional groups of the macroporous resin in the fixed bed is 1-1.5:1 of the molar number of the acidic functional groups. The 2-hydroxy-4-methylthiobutyronitrile is discharged from the upper end of the fixed bed, partially refluxed, cooled in a heat exchanger, and then sprayed into the reaction device through a circulation pipeline, and the reflux ratio is 500-1200:

1.

4. The method for preparing 2-hydroxy-4-methylthiobutyronitrile according to claim 2, wherein: The reflux ratio is 200-500:1, the temperature in the reaction device is 30-70°C, and the pressure is 0.1MPa-0.15MPa.

5. The method for preparing 2-hydroxy-4-methylthiobutyronitrile according to claim 1, wherein: The flow rate of the hydrocyanic acid passing through the throat of the first venturi feed pipe is 25-45 m / s, the flow rate of the acrolein passing through the throat of the second venturi feed pipe is 15-30 m / s, and the molar ratio of the feed amounts of the hydrocyanic acid, methyl mercaptan and acrolein entering the reaction device is 1:1:

1.

6. The method for preparing 2-hydroxy-4-methylthiobutyronitrile according to claim 1, wherein: The hydrocyanic acid is hydrocyanic acid gas obtained after deamination, and the hydrocyanic acid gas is obtained by Angle method or BMW process, and the hydrocyanic acid content is 9.4%±2%. The acrolein is acrolein gas obtained after deacrylic acid, and the acrolein content is 7.0%±2%.

7. A reaction device for 2-hydroxy-4-methylthiobutyronitrile, characterized in that: The method is suitable for implementing the preparation method of 2-hydroxy-4-methylthiobutyronitrile according to any one of claims 1 to 6, wherein the reaction apparatus comprises a feeding zone and a gas-liquid separation zone, the feeding zone is sequentially provided with a hydrocyanic acid feeder, a methyl mercaptan feeder and an acrolein feeder from top to bottom, and a 2-hydroxy-4-methylthiobutyronitrile spray device is provided on the top of the reaction apparatus, the reaction apparatus is provided with a circulation pipeline, and the circulation pipeline is provided with a heat exchanger.

8. The reaction device of 2-hydroxy-4-methylthiobutyronitrile according to claim 7, characterized in that: The gas-liquid separation zone includes a gas-liquid separation tank and a droplet catcher. When the 2-hydroxy-4-methylthiobutyronitrile is prepared, the liquid level in the gas-liquid separation tank is controlled to be below 2 / 3. The droplet catcher is arranged above the gas-liquid separation tank. The inside of the reaction device is sequentially provided with a first venturi feed pipe and a second venturi feed pipe from top to bottom. A flow regulator is provided below the throat of the first venturi feed pipe and the second venturi feed pipe, and the methyl mercaptan feeder is provided with a sprayer.

9. The reaction device of 2-hydroxy-4-methylthiobutyronitrile according to claim 7, characterized in that: The feed port of the hydrocyanic acid feeder is arranged at the throat of the first venturi feed pipe, and the feed port of the acrolein feeder is arranged at the throat of the second venturi feed pipe. The width of the throats of the first venturi feed pipe and the second venturi feed pipe are both 1 / 6-1 / 4 of the inner diameter of the feed zone tower.

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