Preparation method of 2-hydroxy-4-methylthio butyronitrile and reaction device

Abstract

The invention provides a preparation method of 2-hydroxy-4-methylthio-butyronitrile and a reaction device, and relates to the technical field of chemical synthesis, and the preparation method comprises the following steps: a material mixing stage: introducing 2-hydroxy-4-methylthio-butyronitrile as a solvent into the reaction device, firstly absorbing hydrocyanic acid, and then sequentially mixing methyl mercaptan and acrolein; in the reaction stage, the mixture obtained in the material mixing stage generates 2-hydroxy-4-methylthio-butyronitrile under the action of a mixed catalyst of organic acid and organic alkali, and the prepared 2-hydroxy-4-methylthio-butyronitrile partially refluxes to serve as a solvent and is introduced into the reaction device again. According to the method, the 2-hydroxy-4-methylthio butyronitrile is used as a solvent for reaction, addition of water is avoided, the 2-hydroxy-4-methylthio butyronitrile is used as the solvent for reflux absorption of the hydrocyanic acid, the 2-hydroxy-4-methylthio butyronitrile can be in contact with the acrolein in an acid environment, and the polymerization degree of the acrolein is reduced; by adopting the method, equivalent reaction can be realized, and formic acid generation caused by excessive use of hydrocyanic acid is avoided.

Description

Technical Field

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

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

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

[0004] The US patent with publication number US4225516A discloses a method for producing β-methylthiopropionaldehyde, which comprises using methylthiopropionaldehyde to absorb acrolein for reaction, and methylthiopropionaldehyde enters the upper part of a tower at a temperature of -10°C. The mixture of methylthiopropionaldehyde and acrolein obtained at the bottom of the tower passes through a reactor, in which acrolein and methyl mercaptan react in the presence of a catalyst. In this method, methyl mercaptan is continuously added to the reactor, and a large amount of water is contained in the product.

[0005] The Chinese invention patent with publication number CN85108505A discloses a method for synthesizing 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 hydrocyanic acid aqueous solution and ammonium bicarbonate aqueous solution, 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, it is equivalent to acrolein and methyl mercaptan first contacting and reacting to obtain methylthiopropionaldehyde, and then introducing hydrocyanic acid and an esterifying agent. In 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 will 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 excessively to ensure that the acrolein reacts completely; 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 the present application is a method for preparing 2-hydroxy-4-methylthiobutyronitrile, comprising the following steps: Mixing stage: 2-hydroxy-4-methylthiobutyronitrile is introduced into the reaction device as a solvent to first absorb hydrocyanic acid, and then methyl mercaptan and acrolein are mixed 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 part of the prepared 2-hydroxy-4-methylthiobutyronitrile is refluxed and reintroduced into the reaction device as a solvent.

[0008] 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, the acidity coefficient of the organic acid and organic base mixed catalyst is 2-6 by mixing an organic acid and an organic base; the refluxed 2-hydroxy-4-methylthiobutyronitrile is cooled by a heat exchanger, and then the organic acid and organic base mixed catalyst is added, and then the organic acid and organic base mixed catalyst is introduced into a reaction device through a circulation pipeline by spraying, 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.

[0009] 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 amine macroporous resin, wherein the amine 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, 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 alkaline functional group of the macroporous resin in the fixed bed is 1-1.5:1 of the molar number of the acidic functional group, 2-hydroxy-4-methylthiobutyronitrile is discharged from the upper end of the fixed bed, and part of the reflux is cooled in a heat exchanger and then sprayed into a reaction device through a circulation pipeline, and the reflux ratio is 500-1200:1.

[0010] Optionally, 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.

[0011] 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.

[0012] 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.

[0013] Optionally, the hydrocyanic acid is hydrocyanic acid gas after deammoniation, the hydrocyanic acid gas is obtained by Angle method or BMW process, and the hydrocyanic acid content is 9.4%±2%, and the acrolein is acrolein gas after deacrylic acid, and the acrolein content is 7.0%±2%.

[0014] 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 comprising a feed zone and a gas-liquid separation zone, the feed zone being provided with a hydrocyanic acid feeder, a methyl mercaptan feeder and an acrolein feeder in sequence from top to bottom, a 2-hydroxy-4-methylthiobutyronitrile spraying device being provided on the top of the reaction device, the reaction device being provided with a circulation pipeline, and the circulation pipeline being provided with a heat exchanger.

[0015] Optionally, the gas-liquid separation zone includes a gas-liquid separation tank and a droplet catcher. When 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 first venturi feed pipe and the second venturi feed pipe are arranged in sequence from top to bottom inside the reaction device. Flow regulators are arranged 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.

[0016] 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.

[0017] The beneficial effects of the preparation method and reaction device of 2-hydroxy-4-methylthiobutyronitrile provided in the present application are: Using 2-hydroxy-4-methylthiobutyronitrile as a solvent for reaction avoids the addition of water, reduces the subsequent separation process, simplifies the post-processing steps, thereby reducing the process complexity and time cost, and the product quality is high, the product purity is higher than 99.6%, and the yield is higher than 99%; using 2-hydroxy-4-methylthiobutyronitrile as a solvent for reflux absorption of hydrocyanic acid can contact acrolein in an acidic environment and reduce the polymerization degree of acrolein; the method can achieve an equivalent reaction and avoid excessive use of hydrocyanic acid to generate formic acid, which consumes system capacity for subsequent separation and treatment; unrefined hydrocyanic acid and acrolein can be used as raw materials to prepare 2-hydroxy-4-methylthiobutyronitrile in one pot, reduce process steps and reaction equipment, reduce production costs, and shorten the storage time of hydrocyanic acid and acrolein in the system to reduce safety risks. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] 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.

[0019] 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.

[0020] Figure 2 This is a schematic diagram of a reaction device for preparing 2-hydroxy-4-methylthiobutyronitrile provided in Example 7 of the present application; Figure 3 This is the liquid phase spectrum of the 2-hydroxy-4-methylthiobutyronitrile product prepared in Example 8 of the present application; Figure 4 This is the liquid phase spectrum of the 2-hydroxy-4-methylthiobutyronitrile product prepared in Example 9 of the present application.

[0021] Explanation of the accompanying drawings: 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

[0022] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0023] Example 1 A method for preparing 2-hydroxy-4-methylthiobutyronitrile, 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 to first absorb hydrocyanic acid as a solvent, and then methyl mercaptan and acrolein are mixed in sequence to generate 2-hydroxy-4-methylthiobutyronitrile under the action of a mixed catalyst of an organic acid and an organic base, and then falls into the gas-liquid separation zone 12, and 2-hydroxy-4-methylthiobutyronitrile is obtained through gas-liquid separation.

[0024] The reaction device is provided with a hydrocyanic acid feeder 1 capable of feeding hydrocyanic acid in gaseous state, a methyl mercaptan feeder capable of feeding methyl mercaptan in liquid state, and an acrolein feeder 4 capable of feeding acrolein in gaseous state from top to bottom, a 2-hydroxy-4-methylthiobutyronitrile spraying device 19 is provided on the top of the reaction device, and the reaction device is provided with a circulation pipeline 18, and the circulation pipeline 18 is provided with a heat exchanger 8.

[0025] 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 incompletely reacted gas.

[0026] A first venturi feed pipe 15 and a second venturi feed pipe 16 are arranged inside the reaction device. The feed port of the hydrocyanic acid feeder 1 is arranged at the throat of the first venturi feed pipe 15, and the feed port of the acrolein feeder 4 is arranged at the throat of the second venturi feed pipe 16. The width of the throat of the first venturi feed pipe 15 and the second venturi feed pipe 16 is 1 / 4 of the inner diameter of the tower of the feed zone 17 (Note: Figure 1 and Figure 2 The diagram only represents a schematic diagram of the 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.

[0027] 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 arranged at the end of the external pipeline so that the droplets of methyl mercaptan liquid sprayed by the sprayer 3 are ≤10 μm, and the residence time of methyl mercaptan in the tower is ≥2s.

[0028] 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.

[0029] Hydrocyanic acid comes from hydrogen cyanide gas after deamination, and the hydrogen cyanide gas is obtained by Angle method or BMW process, and the content of hydrogen cyanide is 9.4%±2%. Acrolein comes from acrolein gas after deacrylic acid, and the content of acrolein is 7.0%±2%.

[0030] 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%.

[0031] 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%.

[0032] As indicated by the reflux diagram 10 of 2-hydroxy-4-methylthiobutyronitrile and the discharge diagram 11 of 2-hydroxy-4-methylthiobutyronitrile product, the 2-hydroxy-4-methylthiobutyronitrile preparation product is discharged from the bottom of the reaction device, and part of it refluxes through the circulation pipeline 18 and the heat exchanger 8 into the feed zone 17. After cooling through the heat exchanger 8, it is introduced from 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 organic acid and organic base mixed catalyst 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 organic acid and organic base mixed catalyst is added at the catalyst feed schematic position 13, and is introduced into the reaction device through the circulation pipeline 18 and the 2-hydroxy-4-methylthiobutyronitrile spray device 19. The molar ratio of the added catalyst to the hydrocyanic acid is 1:10000.

[0033] Venturi feed pipes are arranged below the feed ports of the hydrocyanic acid feeder 1 and the acrolein feeder 4. The width of the throat of the venturi feed pipe is 1 / 4 of the inner diameter of the reaction zone tower. A flow regulator is arranged below the throat of the venturi feed pipe. A first flow regulator 2 is arranged below the hydrocyanic acid feeder 1, and a second flow regulator 5 is arranged below the acrolein feeder 4, which is used to control the instantaneous flow rate of the material and break up the material particles. The shape of the first flow regulator 2 and the second flow regulator 5 is set to be cylindrical or spherical according to the shape of the throat. In this embodiment, the throat shape of the venturi feed pipe is a downwardly contracted cone, and the flow regulator is spherical. Hydrocyanic acid is fed from the throat of the first venturi feed pipe 15 in a gaseous state and enters the feed zone 17 from the outside. Acrolein is fed from the throat of the second venturi feed pipe 16 in a gaseous state and enters the feed zone 17 from the outside.

[0034] As shown in the tail gas flow diagram 9, the unreacted gas is discharged through the droplet catcher 6 in the gas-liquid separation zone 12, and an online detection device is set at the tail gas outlet, requiring the content of acrolein in the tail gas to be less than 200ppm, hydrocyanic acid to be less than 5ppm, and methyl mercaptan to be less than 10ppm. The unreacted raw materials in the tail gas are used as an indicator for adjusting the reaction speed. When the unreacted raw materials in the tail gas exceed the above standards, the introduction speed of each raw material is reduced to extend the reaction time.

[0035] The purity of the prepared 2-hydroxy-4-methylthiobutyronitrile product was 99.72% and the yield was 99.3%.

[0036] Example 2 The difference from Example 1 is that, in this embodiment, the flow rate of hydrocyanic acid passing through the throat of the first venturi feed pipe is 30 m / s, the flow rate of acrolein passing 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 organic acid and organic base mixed catalyst is morpholine, 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 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 1:5000.

[0037] The purity of the prepared product of 2-hydroxy-4-methylthiobutyronitrile is 99.78%, and the yield is 99.5%.

[0038] Example 3 The difference from Example 1 is that, in this embodiment, the flow rate of hydrocyanic acid passing through the throat of the first venturi feed pipe is 35 m / s, the flow rate of acrolein passing through the throat of the second venturi feed pipe is 25 m / s, the reflux ratio is 400, the organic base in the organic acid and organic base mixed catalyst is propylamine (i.e., RNH2, R is C3), the organic acid is 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 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.

[0039] The purity of the prepared 2-hydroxy-4-methylthiobutyronitrile product is 99.85% and the yield is 99.7%.

[0040] Example 4 The difference from Example 1 is that in this embodiment, the flow rate of hydrocyanic acid passing through the throat of the first venturi feed pipe is 40 m / s, the flow rate of acrolein passing 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 mixed catalyst of the organic acid and the organic base is 2-6, and the molar ratio of the added amount of the catalyst to the hydrocyanic acid is 1:1000.

[0041] The purity of the prepared 2-hydroxy-4-methylthiobutyronitrile product was 99.92% and the yield was 99.7%.

[0042] Example 5 The difference from Example 1 is that, in this embodiment, the flow rate of hydrocyanic acid passing through the throat of the first venturi feed pipe is 45 m / s, the organic base in the mixed catalyst of organic acid and organic base is pyridine and morpholine, the organic acid is formic acid, the addition ratio of 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 catalyst to hydrocyanic acid is 1:1000.

[0043] The purity of the prepared product of 2-hydroxy-4-methylthiobutyronitrile is 99.66%, and the yield is 99.6%.

[0044] Example 6 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.

[0045] The purity of the prepared product of 2-hydroxy-4-methylthiobutyronitrile is 99.66%, and the yield is 99.6%.

[0046] Example 7 like Figure 2 As shown, the difference from Example 1 is that this embodiment uses macroporous resin as a catalyst, the circulation pipeline 18 is provided with a fixed bed 14, the macroporous resin is loaded inside the fixed bed 14, and the macroporous resin is a mixed loading of benzenesulfonic acid macroporous resin and tertiary amine macroporous resin. In this embodiment, the benzenesulfonic acid macroporous resin is DuPont's Amberlyst 35 model resin, and the type is a sulfonic acid type strong acid cation exchange resin. The functional group is benzenesulfonic acid, the appearance is opaque spherical particles, the particle size is 0.7-0.95mm, the surface area is 50m² / g, the total acid concentration is>5.0eq / kg, and the temperature resistance is up to 150°C. The tertiary amine macroporous resin is Tulsimer® A-8X MP resin of Kehaisi (Beijing) Technology Co., Ltd., the type is a macroporous weakly basic anion exchange resin, and the functional group is a tertiary amine. Wet spherical particles, particle size distribution 0.3-1.2mm. The total exchange capacity is ≥1.3meq / ml, the applicable pH range is 0-9, and the temperature resistance is 80℃.

[0047] In order to satisfy the requirement that the molar number of basic functional groups is 1 times 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 upper end of the fixed bed 14, and part of the reflux enters the reaction device after cooling through the heat exchanger 8, and is introduced from the top of the reaction device as a solvent, with a reflux ratio of 500.

[0048] The purity of the prepared product of 2-hydroxy-4-methylthiobutyronitrile is 99.78%, and the yield is 99.5%.

[0049] Example 8 The difference from Example 7 is that the macroporous resin in this embodiment is a mixed filling 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, which is 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 volume total exchange capacity is ≥10.8 mmol / g (dry). The tertiary amine-based macroporous resin is the same as in Example 7.

[0050] In order to satisfy 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.

[0051] The purity of the prepared product of 2-hydroxy-4-methylthiobutyronitrile is 99.75%, and the yield is 99.7%.

[0052] Example 9 The difference from Example 7 is that, in order to satisfy the requirement that the molar number of the basic functional group is 1.5 times that of the acidic functional group, 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.

[0053] The purity of the prepared 2-hydroxy-4-methylthiobutyronitrile product is 99.85% and the yield is 99.7%.

[0054] Example 10 The difference from Example 7 is that the macroporous resin in this embodiment is a mixed filling of a benzenesulfonic acid macroporous resin and a quaternary amine macroporous resin, the benzenesulfonic acid macroporous resin is Tulsimer® T-62 MPDRY resin of Cohais (Beijing) Technology Co., Ltd., the main structure is a polystyrene copolymer, the functional group is a sulfonic acid group, the particle size is 0.42-1.2 mm, and the H+ concentration is 4.8 meq / dry gm; the quaternary amine macroporous resin is DuPont's Amberlyst A26 resin catalyst, the main structure is styrene-divinylbenzene, the functional group is a quaternary amine group, the base site concentration is greater than or equal to 4.20 eq / kg, and the particle size is 560-700 μm. In order to meet the requirement that the molar number of the basic functional group is 1 times that of the acidic functional group, the mass ratio of Amberlyst A26 to Tulsimer T-62MP DRY is 4.8:1. The reflux ratio is 1200.

[0055] The purity of the prepared 2-hydroxy-4-methylthiobutyronitrile product was 99.91% and the yield was 99.7%.

[0056] Test method: Thermo Fisher Scientific high performance liquid chromatography U3000 was selected, and the conditions involved were: Chromatographic column: C18 chromatographic column; the column length is 250 mm and the inner diameter is 4.6 mm; the column temperature is 40°C; the mobile phase is 80% (v / v) acetonitrile / water; the mobile phase flow rate is 0.8 mL / min; the detector is an ultraviolet detector with a detection wavelength of 210 nm; the peak 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 They are respectively the liquid phase spectra of the 2-hydroxy-4-methylthiobutyronitrile product prepared in Example 8 and Example 9 of the present application.

[0057] Table 1 Reaction parameters and product statistics of Example 1-Example 6

[0058] 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%.

[0059] Table 2 Reaction parameters and product statistics of Example 7-Example 10

[0060] 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%.

[0061] 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 embodiments of the present application, and should all be included in the protection scope 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 to first absorb hydrocyanic acid, and then methyl mercaptan and acrolein are mixed 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 part of the prepared 2-hydroxy-4-methylthiobutyronitrile is refluxed and reintroduced into the reaction device as a solvent.

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 includes one or two of formic acid and acetic acid, and the organic base includes one or more of pyridine, morpholine and RNH2, and 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; the refluxed 2-hydroxy-4-methylthiobutyronitrile is cooled by a heat exchanger, and then the organic acid and organic base mixed catalyst is added, and then the organic acid and organic base mixed catalyst is introduced into the reaction device through a circulation pipeline by spraying, 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 amine macroporous resin, wherein the amine 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 group of the macroporous resin in the fixed bed is 1-1.5:1 of the molar number of the acidic functional group, and the 2-hydroxy-4-methylthiobutyronitrile is discharged from the upper end of the fixed bed, and part of the reflux is 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 as claimed in claim 2, characterized in that: 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, characterized in that: The hydrocyanic acid and acrolein enter the reaction device in gaseous form, and the 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.

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

1.

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

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

9. The reaction device of 2-hydroxy-4-methylthiobutyronitrile according to claim 8, 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. A first venturi feed pipe and a second venturi feed pipe are arranged in sequence from top to bottom inside the reaction device. Flow regulators are arranged below the throats of the first venturi feed pipe and the second venturi feed pipe. The methyl mercaptan feeder is provided with a sprayer.

10. The reaction device of 2-hydroxy-4-methylthiobutyronitrile according to claim 8, 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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