Method and device for continuous catalytic synthesis of tetramethylpiperidone

Abstract

The invention provides a method and a device for continuous catalytic synthesis of tetramethyl piperidone, and belongs to the field of tetramethyl piperidone. The method for continuous catalytic synthesis of tetramethyl piperidone comprises the following steps: premixing, synthesizing, curing, continuously neutralizing and refining. According to the method and device for continuous catalytic synthesis of tetramethylpiperidone, side reactions in the reaction process are effectively reduced, the refining difficulty and energy consumption are effectively reduced, and the purity of the prepared tetramethylpiperidone product exceeds 99.9%.

Description

Technical Field

[0001] The present invention relates to the field of preparation of heterocyclic compounds, and particularly to a method and device for continuously catalytically synthesizing tetramethylpiperidone. Background Art

[0002] Tetramethylpiperidone, also known as triacetoneamine, with the chemical name 2,2,6,6 - tetramethylpiperidone, is an important synthetic intermediate and can be used to synthesize hindered amine light stabilizers such as tetramethylpiperidinol, oxidants, and polymerization regulators.

[0003] Among them, hindered amine light stabilizers based on tetramethylpiperidinol have the advantages of effectively improving the anti - ultraviolet performance and anti - γ - radiation performance of polymers. Their light - stabilizing effect is 2 - 4 times that of traditional absorption - type light stabilizers, has good compatibility with many resins, and does not change with the thickness of the product. Currently, it has been widely used in fields such as agricultural films, mechanical engineering plastics, and polymer coatings. With the continuous increase in the demand for tetramethylpiperidinol, the demand for tetramethylpiperidone as its intermediate is also increasing.

[0004] In the prior art, the main synthesis methods of tetramethylpiperidone can be divided into: indirect method and direct method.

[0005] The indirect method uses acetone and ammonia as raw materials to synthesize intermediates such as diacetone alcohol, acetonine, and phorone, and then uses the intermediates, acetone, and ammonia as raw materials to synthesize triacetoneamine. For example, US Patent US3943139 - Method for Preparing Triacetoneamine and US Patent US3960875 - Method for Preparing 2,2,6,6 - Tetramethyl - 4 - oxopiperidine respectively disclose methods for synthesizing triacetoneamine using the synthesis of acetonine, phorone, and diacetone alcohol as raw materials, and the yields are relatively good. However, due to the difficulty in the synthesis and separation of acetonine, phorone, and diacetone alcohol, there are defects such as a long process flow, high preparation cost, and difficulty in large - scale industrialization.

[0006] The direct method uses acetone and ammonia as raw materials and directly synthesizes triacetoneamine under the action of a catalyst. Compared with the aforementioned indirect method, the direct method can avoid the steps of separating and purifying intermediate products, greatly saving manpower and material resources and reducing production costs. The main reaction mechanism of the direct method is as follows: First, acetone reacts with ammonia under the action of a catalyst to form imine intermediate 1; imine intermediate 1 then undergoes an aldol condensation reaction with acetone to form imine intermediate 2. In addition, acetone can also undergo an aldol condensation reaction under the action of a catalyst to form isopropylideneacetone. A part of the isopropylideneacetone undergoes a nucleophilic addition-dehydration reaction with ammonia and also generates imine intermediate 2; another part of the isopropylideneacetone will first undergo a Michael addition reaction with ammonia to form diacetoneamine, and diacetoneamine will further undergo a nucleophilic addition-elimination reaction with ammonia to form diamine intermediate 3. After the formation of diamine intermediate 3, it will react with acetone to remove one molecule of water to form acetonine, and the formed acetonine can react with acetone again to generate triacetoneamine when acetone is in excess.

[0007] Furthermore, imine intermediate 2 undergoes a rearrangement reaction under the action of a catalyst to form an enamine intermediate, and the formed enamine intermediate further undergoes an aldol condensation reaction with acetone to form 2,2-dimethyl-2,5-heptadiene-4-imine. The 2,2-dimethyl-2,5-heptadiene-4-imine is the key to the synthesis of triacetoneamine. After the formation of this compound, it will undergo a Michael addition reaction with ammonia to form a β-amino compound. The β-amino compound further undergoes an intramolecular Michael addition reaction under the action of a catalyst to form imine intermediate 4. After the formation of imine intermediate 4, it will undergo a nucleophilic addition-deamination reaction with water to form the target product triacetoneamine. And, each of the aforementioned reaction processes is a reversible reaction. The specific reaction route is as Figure 1 shown.

[0008] However, the inventors have found through research that although the reaction yield of this method is acceptable, a strong base such as sodium hydroxide needs to be added during the post-treatment process to neutralize a large amount of ammonium nitrate used as a catalyst during the reaction process, which will generate a large amount of wastewater. On the one hand, it brings difficulties to the enterprise in treating a large amount of wastewater; on the other hand, improper treatment of the wastewater also poses a major safety hazard.

[0009] Therefore, providing a device and method for 4-methylpiperidone that can solve the aforementioned problems is of great significance for the safe production, cost saving, environmental protection, etc. of enterprises. Summary of the Invention

[0010] To solve the technical problems existing in the prior art, the present invention provides a method and device for continuously catalytically synthesizing tetramethylpiperidone to achieve the following invention objectives: to overcome the problems in the prior art that in the post-treatment process of the process for preparing tetramethylpiperidone using a large amount of ammonium nitrate as a catalyst, a strong base such as sodium hydroxide needs to be added to neutralize ammonium nitrate, resulting in a large amount of wastewater generation, difficult wastewater treatment, and major potential safety hazards if not properly treated.

[0011] To solve the above technical problems, the technical solutions adopted by the present invention are as follows: A method for continuously catalytically synthesizing tetramethylpiperidone, which consists of the following steps: premixing, synthesis, aging, continuous neutralization, and refining; The method for premixing is to put acetone and a modified sulfonic acid type resin catalyst into a premixing kettle, mix them evenly to obtain a premixed material; The modified sulfonic acid type resin catalyst is prepared by the following steps: activation and modification; The method for activation is to put the sulfonic acid type resin into thionyl chloride, heat it to reflux, keep it stirring under heat preservation, then separate to obtain a solid, and the solid is washed and dried to obtain the activated sulfonic acid type resin; The method for modification is to put the activated sulfonic acid type resin into absolute ethanol, disperse it evenly, then add (1R,2R)-(+)-1,2-diphenylethylenediamine, triethylamine, and ammonium nitrate aqueous solution, and stir at room temperature; separate to obtain a solid, and the solid is washed and dried to obtain the modified sulfonic acid type resin catalyst; The synthesis consists of the following steps: primary synthesis and secondary synthesis; The method for primary synthesis is to continuously feed the premixed material and liquid ammonia into a primary synthesis kettle; control the reaction pressure to be 0.1 - 0.3 MPa and the reaction temperature to be 60 - 65 °C for primary synthesis, and obtain a primary reaction liquid and continuously introduce it into a secondary synthesis kettle; The method for secondary synthesis is that the secondary synthesis kettle continuously receives the primary reaction liquid, controls the reaction pressure to be 0.1 - 0.3 MPa and the reaction temperature to be 60 - 65 °C for secondary synthesis, and obtains a secondary reaction liquid and continuously introduces it into a primary aging kettle; After the secondary reaction liquid undergoes primary aging in the primary aging kettle, a primary aged liquid is obtained and introduced into a secondary aging kettle. After secondary aging, a secondary aged liquid is obtained; the secondary aged liquid is continuously neutralized and then refined to obtain tetramethylpiperidone.

[0012] Further, the method for primary aging is that the primary aging kettle filled with a composite catalyst continuously receives the secondary reaction liquid; control the temperature of the primary aging kettle to be 60 - 63 °C and the pressure to be 0.1 - 0.3 MPa for primary aging, and obtain a primary aged liquid and continuously introduce it into a secondary aging kettle; The method of secondary aging is that the secondary aging kettle continuously receives the primary aging liquid; the temperature of the secondary aging kettle is controlled at 60-63 °C and the pressure is 0.1-0.3 MPa for secondary aging to obtain the secondary aging liquid, which is continuously introduced into the continuous neutralizer; The method of continuous neutralization is to continuously introduce sodium hydroxide solution into the continuous neutralizer to continuously neutralize the secondary aging liquid to a pH value of 14; the organic phase after continuous neutralization is refined to obtain tetramethylpiperidone.

[0013] Further, the refining method is to heat the organic phase after continuous neutralization to 70-90 °C, keep it warm and distill until no gas phase is generated to obtain the rectified liquid phase; the rectified liquid phase is subjected to crystallization, separation and distillation to obtain tetramethylpiperidone.

[0014] Further, the composite catalyst is prepared by the following steps: carrier pretreatment and loading; The method of carrier pretreatment is to put ZSM-5 molecular sieve into the first phosphate buffer solution, heat it to 30-35 °C, keep it warm and drop in epichlorohydrin, and then keep it warm and stir; the solid is separated, washed to neutrality, put into the second phosphate buffer solution, heated to 30-35 °C, put in β-cyclodextrin, and keep it warm and stir; the solid is separated, washed and dried to obtain the carrier; The loading method is to put the carrier into the loading solution, keep it warm and stir at 25-30 °C, separate the solid and dry it to obtain the composite catalyst; The loading solution is deionized water dispersed with ammonium chloride, calcium chloride, magnesium chloride and copper chloride.

[0015] Preferably, in the premixing, the weight ratio of acetone to the modified sulfonic acid type resin catalyst is 100-200:1; In the primary aging, the weight of the composite catalyst is 1-6 wt% of the total weight of the materials in the primary aging kettle within 1 h of residence time; In the continuous neutralization, the concentration of the sodium hydroxide solution used is 80 wt%, and the continuous neutralization temperature is 50-55 °C.

[0016] Preferably, in the activation, the heat preservation and reflux time of the sulfonic acid type resin in thionyl chloride is 12-16 h; the weight ratio of the sulfonic acid type resin to thionyl chloride is 1:15-20; In the modification, the weight ratio of the activated sulfonic acid type resin, (1R,2R)-(+)-1,2-diphenylethylenediamine, triethylamine, ammonium nitrate aqueous solution and absolute ethanol is 3-5:6-8:1.5-2.5:9-11:26.5-29.

[0017] Preferably, in the carrier pretreatment, the dropping rate of epichlorohydrin is 0.2 - 0.5 mL / min, the heat preservation and stirring time after the dropping of epichlorohydrin is completed is 1 - 2 h; the stirring time after the addition of β-cyclodextrin is completed is 2 - 3 h; The weight ratio of ZSM-5 molecular sieve, epichlorohydrin, and β-cyclodextrin is 1:0.05 - 0.08:0.1 - 0.2;

[0018] Preferably, in the carrier pretreatment, the first phosphate buffer solution is a deionized aqueous solution of potassium dihydrogen phosphate and dipotassium hydrogen phosphate, and the weight ratio of potassium dihydrogen phosphate, dipotassium hydrogen phosphate, and deionized water in the first phosphate buffer solution is 8.3 - 8.5:0.86 - 0.88:1000; the second phosphate buffer solution is a deionized aqueous solution of potassium dihydrogen phosphate and dipotassium hydrogen phosphate, and the weight ratio of potassium dihydrogen phosphate, dipotassium hydrogen phosphate, and deionized water in the second phosphate buffer solution is 5.4 - 5.6:0.4 - 0.45:1000; In the loading process, the weight ratio of ammonium chloride, calcium chloride, magnesium chloride, copper chloride, and deionized water in the loading solution is 12 - 18:4 - 6:4 - 6:1 - 3:120 - 150.

[0018] A device for continuously catalytically synthesizing tetramethylpiperidone to implement the foregoing method, which consists of the following: a premixing unit, a synthesis unit, a ripening unit, a neutralization unit, and a refining unit; The premixing unit includes: a premixing kettle and a preheater; The synthesis unit includes: a first-stage synthesis kettle and a second-stage synthesis kettle; The ripening unit includes: a first-stage ripening kettle and a second-stage ripening kettle; The neutralization unit includes: a continuous neutralizer; An acetone feed port and a catalyst feeding port are arranged at the top of the premixing kettle, and a discharge port is arranged at the bottom of the premixing kettle; the discharge port of the premixing kettle is connected to the feed port of the preheater through a pipeline; The discharge port of the preheater is connected to the feed port of the first-stage synthesis kettle through a pipeline; The discharge port of the first-stage synthesis kettle is connected to the feed port of the second-stage synthesis kettle through a charging pump and a pipeline; The discharge port of the second-stage synthesis kettle is connected to the feed port of the first-stage ripening kettle through a charging pump and a pipeline; The discharge port of the first-stage ripening kettle is connected to the feed port of the second-stage ripening kettle through a charging pump and a pipeline; The discharge port of the second-stage ripening kettle is connected to the tangential inlet pipeline of the continuous neutralizer through a charging pump; The organic phase outlet of the continuous neutralizer is connected to the refining unit; The refining unit is used to carry out rectification, crystallization, separation, and distillation on the organic phase from the continuous neutralizer to obtain tetramethylpiperidone.

[0019] Furthermore, the continuous neutralizer is provided with an automatic control module, including a temperature sensor, an alkali liquor flow sensor, a controller, an automatic control valve, and a pH on-line detector; The temperature sensor is interlocked with the alkali liquor flow sensor and the automatic control valve, and is used to maintain the temperature in the continuous neutralizer at 50 - 55 °C by adjusting the flow rate of the sodium hydroxide solution under the action of the controller; the alkali liquor flow sensor is interlocked with the pH on-line detector and the automatic control valve, and is used to adjust the addition amount of the sodium hydroxide solution under the action of the controller to control the pH value of the material in the continuous neutralizer to be 14.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The method and device for continuously catalytically synthesizing tetramethylpiperidone of the present invention, while achieving the continuous production of tetramethylpiperidone in a breakthrough manner, by using different catalysts in the synthesis step and the aging step, the catalysts can be reused, and can effectively match the continuous production conditions and pressure, effectively improve the continuous reaction efficiency, inhibit the generation of by-products, and reduce the production cost.

[0021] (2) The method for continuously catalytically synthesizing tetramethylpiperidone of the present invention adopts a modified sulfonic acid type resin catalyst in the synthesis step, which can effectively improve the conversion rate of acetone, can promote the reaction of acetone with ammonia to generate an imine intermediate, and then be converted into triacetoneamine; at the same time, it can also effectively inhibit the aldol condensation reaction between acetones, thereby inhibiting the generation of isopropylideneacetone and effectively reducing the generation of by-products; (3) The method for continuously catalytically synthesizing tetramethylpiperidone of the present invention adopts a modified sulfonic acid type resin catalyst with a low dosage in the synthesis step, which can effectively match the continuous production conditions and pressure, has good continuous catalytic performance, and is conducive to large-scale industrial production.

[0022] (4) The method for continuously catalytically synthesizing tetramethylpiperidone of the present invention adopts a composite catalyst in the aging step, effectively reducing the aging reaction time, can effectively meet the requirements of continuous production, and at the same time, in cooperation with the device for continuously catalytically synthesizing tetramethylpiperidone of the present invention, effectively improves the production efficiency and increases the product yield.

[0023] (5) The method and device for continuously catalytically synthesizing tetramethylpiperidone of the present invention effectively reduce the side reactions in the reaction process, the obtained intermediate product has high purity, simple rectification and purification, effectively reduces the refining difficulty and energy consumption, and the purity of the obtained tetramethylpiperidone product exceeds 99.9%.

[0024] (6)The method and device for continuously catalytically synthesizing tetramethylpiperidone of the present invention, the modified sulfonic acid type resin catalyst and the composite catalyst adopted can be reused, have high catalytic activity, an effective catalytic life exceeding 2500 h, and can greatly reduce the generation amount of by-product salts during the reaction process, further ensuring the product purity.

[0025] (7)The method and device for continuously catalytically synthesizing tetramethylpiperidone of the present invention have a low wastewater generation amount, effectively solve the problems in the traditional process, such as a large amount of wastewater generation, difficult wastewater treatment, and potential safety hazards during the treatment process.

[0026] (8)The method and device for continuously catalytically synthesizing tetramethylpiperidone of the present invention produce a tetramethylpiperidone product with stable quality, which can meet the requirements of high-efficiency and large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the reaction mechanism for directly synthesizing triacetoneamine in the background art; Figure 2 It is a schematic diagram of the device for continuously catalytically synthesizing tetramethylpiperidone in Example 1; In the figure, 1 - premixing kettle; 2 - preheater; 3 - first-stage synthesis kettle; 4 - second-stage synthesis kettle; 5 - first-stage aging kettle; 6 - second-stage aging kettle; 7 - continuous neutralizer. DETAILED DESCRIPTION OF THE INVENTION

[0028] In order to have a clearer understanding of the technical features, objectives, and effects of the present invention, the specific embodiments of the present invention are now described.

[0029] Example 1 This example provides a method for continuously catalytically synthesizing tetramethylpiperidone, which is as follows: 1. Premixing Put a predetermined amount of acetone and a modified sulfonic acid type resin catalyst into the premixing kettle 1, and heat to 45 °C under stirring at 30 rpm to obtain a premixed material.

[0030] Among them, the weight ratio of acetone to the modified sulfonic acid type resin catalyst is 100:1.

[0031] The modified sulfonic acid type resin catalyst is prepared by the following method: 1) Activation Put the sulfonic acid type resin into thionyl chloride, heat to reflux, keep stirring for 12 h; then filter out the solid, wash it with 5 times the volume of dichloromethane, and place it in an environment with a vacuum degree of 0.03 MPa and dry at 80 °C for 4 h to obtain the activated sulfonic acid type resin.

[0032] Among them, the weight ratio of the sulfonic acid type resin to thionyl chloride is 1:15.

[0033] The sulfonic acid resin has the trade name NKC-9.

[0034] 2) Modification Put the activated sulfonic acid resin into absolute ethanol and stir for 2 h at room temperature; then successively add (1R,2R)-(+)-1,2-diphenylethylenediamine, triethylamine, and ammonium nitrate aqueous solution. After the addition is completed, stir for 48 h at room temperature; filter out the solid, wash the solid with 8 times the weight of absolute ethanol and then with 10 times the weight of deionized water; then place the washed solid in an environment with a vacuum of 0.07 MPa and dry at 45 °C for 8 h to obtain the modified sulfonic acid resin catalyst.

[0035] Among them, the weight ratio of the activated sulfonic acid resin, (1R,2R)-(+)-1,2-diphenylethylenediamine, triethylamine, ammonium nitrate aqueous solution, and absolute ethanol is 3:6:1.5:9:26.5.

[0036] In the ammonium nitrate aqueous solution, the mass fraction of ammonium nitrate is 50%.

[0037] The (1R,2R)-(+)-1,2-diphenylethylenediamine is obtained by purchasing through the market.

[0038] 2. Synthesis 1) Primary synthesis The premix is preheated by the preheater 2 and then fed continuously into the primary synthesis kettle 3 from the top; liquid ammonia is fed into the primary synthesis kettle 3 from the lower part by a feed pump; control the reaction pressure at 0.1 MPa and the reaction temperature at 60 °C for primary synthesis; the primary reaction liquid of the primary synthesis reaction is continuously introduced from the top of the primary synthesis kettle 3 into the secondary synthesis kettle 4 by a feed pump for secondary synthesis.

[0039] 2) Secondary synthesis The secondary synthesis kettle 4 receives the primary reaction liquid introduced from the primary synthesis kettle 3, controls the reaction pressure at 0.1 MPa and the reaction temperature at 60 °C for secondary synthesis; the reaction liquid of the secondary synthesis reaction is continuously introduced from the top of the secondary synthesis kettle 4 into the primary aging kettle 5 by a feed pump for primary aging.

[0040] 3. Aging 1) Primary aging The first-stage aging kettle 5 receives the reaction solution introduced from the second-stage synthesis kettle 4; a predetermined amount of composite catalyst is contained in the first-stage aging kettle 5; by controlling the flow rate of the cooling water in the jacket of the first-stage aging kettle 5, the temperature in the first-stage aging kettle 5 is adjusted to 60 °C; the pressure in the first-stage aging kettle 5 is controlled to be 0.1 MPa for the first-stage aging; the first-stage aging solution of the first-stage aging reaction is continuously introduced from the top of the first-stage aging kettle 5 into the second-stage aging kettle 6 through a feeding pump for the second-stage aging.

[0041] Among them, the weight of the composite catalyst is 2 wt% of the total weight of the materials in the first-stage aging kettle 5 within a residence time of 1 h.

[0042] The composite catalyst is prepared by the following steps: ① Carrier pretreatment Put the ZSM-5 molecular sieve into a first phosphate buffer solution with a volume 2 times that of the ZSM-5 molecular sieve, heat it up to 30 °C, and then drop epichlorohydrin at a dropping rate of 0.2 mL / min; after the dropping is completed, keep stirring for 1 h, and filter out the solid; wash the solid with deionized water until the pH value is neutral, and then put it into a second phosphate buffer solution with a volume 2 times that of the solid, heat it up to 30 °C, add β-cyclodextrin, and stir at 200 rpm for 2 h, and filter out the solid; wash the solid with deionized water until the pH value is neutral; then under the conditions of a vacuum degree of 0.02 MPa and 90 °C, dry it until the weight is constant to obtain the carrier.

[0043] Among them, the weight ratio of the ZSM-5 molecular sieve, epichlorohydrin, and β-cyclodextrin is 1:0.05:0.1.

[0044] The preparation method of the first phosphate buffer solution is to put a predetermined amount of potassium dihydrogen phosphate and dipotassium hydrogen phosphate into deionized water and stir at 50 rpm for 10 min to obtain the first phosphate buffer solution.

[0045] The weight ratio of potassium dihydrogen phosphate, dipotassium hydrogen phosphate, and deionized water is 8.3:0.86:1000.

[0046] The preparation method of the second phosphate buffer solution is to put a predetermined amount of potassium dihydrogen phosphate and dipotassium hydrogen phosphate into deionized water and stir at 50 rpm for 100 min to obtain the second phosphate buffer solution.

[0047] The weight ratio of potassium dihydrogen phosphate, dipotassium hydrogen phosphate, and deionized water is 5.4:0.4:1000.

[0048] ② Loading Put the carrier into a loading solution with a volume 3 times that of the carrier, heat it up to 25 °C under the condition of stirring at 20 rpm, keep stirring for 2 h, and filter out the solid; place the solid in a temperature environment of 90 °C and let it stand and dry for 5 h to obtain the composite catalyst.

[0049] Among them, the loading solution is composed of the following components: ammonium chloride, calcium chloride, magnesium chloride, copper chloride, and deionized water. The weight ratio of ammonium chloride, calcium chloride, magnesium chloride, copper chloride, and deionized water is 12:4:4:1:120.

[0050] 2) Secondary aging The secondary aging kettle 6 receives the primary aging solution introduced from the primary aging kettle 5. By controlling the flow rate of the cooling water in the jacket of the secondary aging kettle 6, the temperature inside the secondary aging kettle 6 is adjusted to 60 °C; the pressure inside the secondary aging kettle 6 is controlled to be 0.1 MPa for secondary aging; the secondary aging solution from the secondary aging reaction is continuously fed into the continuous neutralizer 7 by a feeding pump for continuous neutralization.

[0051] 4. Continuous neutralization An 80 wt% sodium hydroxide solution is continuously pumped into the continuous neutralizer 7 by a centrifugal pump for continuous neutralization; during the continuous neutralization process, the real-time flow rate of the sodium hydroxide solution is controlled by temperature-flow interlock control, and the temperature inside the continuous neutralizer 7 is controlled to be 50 °C; at the same time, the total input amount of the sodium hydroxide solution is controlled according to the pH value of the neutralized solution inside the continuous neutralizer 7, and the pH value of the neutralized solution is controlled to be 14; the organic phase (i.e., crude tetramethylpiperidone) from the continuous neutralization continuously flows out from the top discharge pipe of the continuous neutralizer 7 under the action of centrifugation to the refining process; the aqueous phase from the continuous neutralization settles to the bottom of the continuous neutralizer 7 and is discharged to sewage treatment.

[0052] 5. Refining The crude tetramethylpiperidone obtained in the continuous neutralization step is heated to 70 °C and kept warm for distillation until no gas phase is generated to obtain the rectified liquid phase; the rectified liquid phase is subjected to crystallization, separation, and distillation treatment to obtain tetramethylpiperidone with a purity of 99.93%.

[0053] As Figure 2 shown, this embodiment also provides a device for continuously catalytically synthesizing tetramethylpiperidone to implement the foregoing method, which is provided with a premixing unit, a synthesis unit, an aging unit, a neutralization unit, and a refining unit.

[0054] A premixing kettle 1 and a preheater 2 are arranged inside the premixing unit.

[0055] The premixing kettle 1 is provided with a premixing kettle heating module, a premixing kettle cooling module, and a premixing kettle stirring module; and a premixing kettle acetone inlet and a premixing kettle catalyst feeding port are arranged at the top of the premixing kettle 1, and a premixing kettle discharge port is arranged at the bottom of the premixing kettle 1.

[0056] The preheater 2 is provided with a preheater inlet and a preheater outlet; the preheater inlet is connected to the premixing kettle discharge port for preheating the premixed material; the preheater outlet is connected to the first-stage synthesis kettle inlet.

[0057] The synthesis unit is provided with a primary synthesis kettle 3 and a secondary synthesis kettle 4.

[0058] The primary synthesis kettle 3 is provided with a primary synthesis kettle cooling module, a primary synthesis kettle automatic control module; and a primary synthesis kettle feed inlet, a primary synthesis kettle overflow discharge outlet, and a primary synthesis kettle liquid ammonia outlet provided at the top, and a primary synthesis kettle liquid ammonia inlet provided at the bottom. Among them, the primary synthesis kettle feed inlet is connected to the outlet of the preheater, and the primary synthesis kettle feed inlet is provided below the outlet of the preheater so that the pre-mixed material after preheating can enter the primary synthesis kettle 3 under the action of gravity.

[0059] The secondary synthesis kettle 4 is provided with a secondary synthesis kettle cooling module, a secondary synthesis kettle automatic control module; and a secondary synthesis kettle feed inlet, a secondary synthesis kettle discharge outlet provided at the top, and a secondary synthesis kettle liquid ammonia inlet provided at the bottom; among them, the secondary synthesis kettle feed inlet is connected to the primary synthesis kettle overflow discharge outlet via a pumping pump so that the material in the primary synthesis kettle 3 can be continuously introduced into the secondary synthesis kettle 4.

[0060] The aging unit is provided with a primary aging kettle 5 and a secondary aging kettle 6.

[0061] The primary aging kettle 5 is provided with a primary aging kettle cooling module; and a primary aging kettle feed inlet, a primary aging kettle overflow discharge outlet, and a primary aging kettle catalyst addition port provided at the top; among them, the primary aging kettle feed inlet is connected to the primary synthesis kettle overflow discharge outlet via a pumping pump so that the material in the secondary synthesis kettle 4 can be continuously introduced into the primary aging kettle 5.

[0062] The secondary aging kettle 6 is provided with a secondary aging kettle cooling module; and a secondary aging kettle feed inlet, a secondary aging kettle overflow discharge outlet provided at the top; among them, the secondary aging kettle feed inlet is connected to the primary aging kettle overflow discharge outlet via a pumping pump so that the material in the primary aging kettle 5 can be continuously introduced into the secondary aging kettle 6.

[0063] The neutralization unit is provided with a continuous neutralizer 7. The continuous neutralizer 7 adopts a rotary sedimentation separation device and is provided with a continuous neutralizer automatic control module; and an alkali liquid inlet and a material tangential inlet provided in the middle of the continuous neutralizer 7, an organic phase outlet provided at the upper part of the continuous neutralizer 7, and an aqueous phase outlet provided at the lower part of the continuous neutralizer 7. Among them, the material tangential inlet is connected to the secondary aging kettle overflow discharge outlet via a pumping pump so that the material in the secondary aging kettle 6 can be continuously introduced into the continuous neutralizer 7. The upper organic phase outlet of the continuous neutralizer 7 is connected to the refining unit, and the lower aqueous phase outlet goes to sewage treatment.

[0064] Further, the continuous neutralizer automatic control module includes a temperature sensor, an alkali liquor flow sensor, a controller, an automatic control valve, and a pH on-line detector. Among them, the temperature sensor, the alkali liquor flow sensor, and the automatic control valve are interlocked to keep the temperature in the continuous neutralizer 7 at 50-55°C by adjusting the alkali liquor flow under the action of the controller. At the same time, the alkali liquor flow sensor, the pH on-line detector, and the automatic control valve are interlocked to adjust the total amount of liquid alkali added to control the pH value of the material in the continuous neutralizer 7 to 14.

[0065] The refining unit is used to carry out distillation, crystallization, separation, and distillation on the organic phase from the continuous neutralizer 7 to finally obtain tetramethylpiperidone.

[0066] Example 2 This example provides a method for continuously catalytically synthesizing tetramethylpiperidone, which is as follows: 1. Premixing Put a predetermined amount of acetone and a modified sulfonic acid type resin catalyst into the premixing kettle 1, heat to 50°C under stirring at 40 rpm to obtain a premixed material.

[0067] Among them, the weight ratio of acetone to the modified sulfonic acid type resin catalyst is 150:1.

[0068] The modified sulfonic acid type resin catalyst is prepared by the following method: 1) Activation Put the sulfonic acid type resin into thionyl chloride, heat to reflux, keep stirring for 14 h; then filter out the solid, wash it with 8 times the volume of dichloromethane, and place it in an environment with a vacuum degree of 0.05 MPa and dry at 85°C for 6 h to obtain the activated sulfonic acid type resin.

[0069] Among them, the weight ratio of the sulfonic acid type resin to thionyl chloride is 1:17.

[0070] The sulfonic acid type resin has the brand number NKC-9.

[0071] 2) Modification Put the activated sulfonic acid type resin into absolute ethanol, stir at room temperature for 3 h; then add (1R,2R)-(+)-1,2-diphenylethylenediamine, triethylamine, and ammonium nitrate aqueous solution in sequence. After the addition is completed, stir at room temperature for 50 h; filter out the solid, wash the solid with 9 times the weight of absolute ethanol, and then wash the solid with 11 times the weight of deionized water; then place the washed solid in an environment with a vacuum degree of 0.08 MPa and dry at 50°C for 9 h to obtain the modified sulfonic acid type resin catalyst.

[0072] Among them, the weight ratio of the activated sulfonic acid resin, (1R,2R)-(+)-1,2-diphenylethylenediamine, triethylamine, ammonium nitrate aqueous solution, and absolute ethanol is 4:7:2:10:28.

[0073] In the ammonium nitrate aqueous solution, the mass fraction of ammonium nitrate is 60%.

[0074] The (1R,2R)-(+)-1,2-diphenylethylenediamine is obtained by purchasing through the market.

[0075] 2. Synthesis 1) Primary synthesis After being preheated by the preheater 22, the premix is fed into the primary synthesis kettle 3 continuously from the top of the primary synthesis kettle 3; liquid ammonia is fed into the primary synthesis kettle 3 from the lower part of the primary synthesis kettle 3 through a feeding pump; the reaction pressure is controlled at 0.2 MPa and the reaction temperature is 62 °C for primary synthesis; the primary reaction liquid of the primary synthesis reaction is continuously introduced into the secondary synthesis kettle 4 from the top of the primary synthesis kettle 3 through a feeding pump for secondary synthesis.

[0076] 2) Secondary synthesis The secondary synthesis kettle 4 receives the primary reaction liquid introduced from the primary synthesis kettle 3, controls the reaction pressure at 0.2 MPa and the reaction temperature at 62 °C for secondary synthesis; the reaction liquid of the secondary synthesis reaction is continuously introduced into the primary aging kettle 5 from the top of the secondary synthesis kettle 4 through a feeding pump for primary aging.

[0077] 3. Aging 1) Primary aging The primary aging kettle 5 receives the reaction liquid introduced from the secondary synthesis kettle 4; a predetermined amount of composite catalyst is contained in the primary aging kettle 5; by controlling the flow rate of the cooling water in the jacket of the primary aging kettle 5, the temperature in the primary aging kettle 5 is adjusted to 62 °C; the pressure in the primary aging kettle 5 is controlled at 0.2 MPa for primary aging; the primary aging liquid of the primary aging reaction is continuously introduced into the secondary aging kettle 6 from the top of the primary aging kettle 5 through a feeding pump for secondary aging.

[0078] Among them, the weight of the composite catalyst is 2.8 wt% of the total weight of the materials in the primary aging kettle 5 within a residence time of 1 h.

[0079] The composite catalyst is prepared by the following steps: ① Carrier pretreatment Put the ZSM-5 molecular sieve into 3 times the volume of the first phosphate buffer solution, heat it up to 32 °C, and then add epichlorohydrin dropwise at a dropping rate of 0.3 mL / min. After the dropping is completed, keep it warm and stir for 1.5 h, and filter out the solid. Wash the solid with deionized water until the pH value is neutral, and then put it into 3 times the volume of the second phosphate buffer solution, heat it up to 32 °C, add β-cyclodextrin, and stir at 250 rpm for 2.5 h, and filter out the solid. Wash the solid with deionized water until the pH value is neutral; then dry it at a vacuum degree of 0.03 MPa and 92 °C until the weight is constant to obtain the carrier.

[0080] Among them, the weight ratio of the ZSM-5 molecular sieve, epichlorohydrin, and β-cyclodextrin is 1:0.06:0.13.

[0081] The preparation method of the first phosphate buffer solution is to put a predetermined amount of potassium dihydrogen phosphate and dipotassium hydrogen phosphate into deionized water and stir at 80 rpm for 15 min to obtain the first phosphate buffer solution.

[0082] The weight ratio of potassium dihydrogen phosphate, dipotassium hydrogen phosphate, and deionized water is 8.4:0.87:1000.

[0083] The preparation method of the second phosphate buffer solution is to put a predetermined amount of potassium dihydrogen phosphate and dipotassium hydrogen phosphate into deionized water and stir at 80 rpm for 15 min to obtain the second phosphate buffer solution.

[0084] The weight ratio of potassium dihydrogen phosphate, dipotassium hydrogen phosphate, and deionized water is 5.5:0.43:1000.

[0085] ② Loading Put the carrier into 4 times the volume of the loading solution, heat it up to 28 °C under stirring at 30 rpm, keep it warm and stir for 2.5 h, and filter out the solid. Place the solid in a temperature environment of 92 °C and let it stand and dry for 6 h to obtain the composite catalyst.

[0086] Among them, the loading solution is composed of the following components: ammonium chloride, calcium chloride, magnesium chloride, copper chloride, and deionized water. The weight ratio of ammonium chloride, calcium chloride, magnesium chloride, copper chloride, and deionized water is 16:5:5:2:130.

[0087] 2) Secondary aging The secondary aging kettle 6 receives the primary aging liquid introduced from the primary aging kettle 5, and adjusts the temperature in the secondary aging kettle 6 to 62 °C by controlling the flow rate of the jacket cooling water of the secondary aging kettle 6; control the pressure in the secondary aging kettle 6 to 0.2 MPa for secondary aging; the secondary aging liquid of the secondary aging reaction is continuously fed into the continuous neutralizer 7 by a feeding pump for continuous neutralization.

[0088] 4. Continuous Neutralization A sodium hydroxide solution with a concentration of 80 wt% is continuously pumped into the continuous neutralizer 7 by a centrifugal pump for continuous neutralization. During the continuous neutralization process, the real-time flow rate of the sodium hydroxide solution is controlled by temperature-flow interlock, and the temperature in the continuous neutralizer 7 is controlled at 52 °C. At the same time, the total input amount of the sodium hydroxide solution is controlled according to the pH value of the neutralized liquid in the continuous neutralizer 7, and the pH value of the neutralized liquid is controlled at 14. The organic phase (i.e., crude tetramethylpiperidone) after continuous neutralization continuously flows out from the top discharge pipe of the continuous neutralizer 7 to the refining process under the action of centrifugation; the aqueous phase after continuous neutralization settles to the bottom of the continuous neutralizer 7 and is discharged to sewage treatment.

[0089] 5. Refining The crude tetramethylpiperidone obtained in the continuous neutralization step is heated to 80 °C and kept warm for distillation until no gas phase is generated to obtain a rectified liquid phase; the rectified liquid phase is subjected to crystallization, separation, and distillation treatments to obtain tetramethylpiperidone with a purity of 99.96%.

[0090] The device for continuously catalytically synthesizing tetramethylpiperidone used in this example is the same as that in Example 1.

[0091] Example 3 This example provides a method for continuously catalytically synthesizing tetramethylpiperidone, which is as follows: 1. Premixing Predetermined amounts of acetone and a modified sulfonic acid type resin catalyst are put into the premixing kettle 1 and heated to 55 °C under stirring at 60 rpm to obtain a premixed material.

[0092] Among them, the weight ratio of acetone to the modified sulfonic acid type resin catalyst is 200:1.

[0093] The modified sulfonic acid type resin catalyst is prepared by the following method: 1) Activation The sulfonic acid type resin is put into thionyl chloride and heated to reflux, and kept warm and stirred for 16 h; then the solid matter is filtered out, washed with 10 times the volume of dichloromethane, and placed in an environment with a vacuum degree of 0.08 MPa and dried at 90 °C for 8 h to obtain an activated sulfonic acid type resin.

[0094] Among them, the weight ratio of the sulfonic acid type resin to thionyl chloride is 1:20.

[0095] The sulfonic acid type resin has the brand number NKC-9.

[0096] 2) Modification Put the activated sulfonic acid resin into absolute ethanol and stir for 4 h at room temperature. Then, add (1R,2R)-(+)-1,2-diphenylethylenediamine, triethylamine, and ammonium nitrate aqueous solution in sequence. After the addition is completed, stir for 52 h at room temperature. Filter out the solid, wash the solid with absolute ethanol 10 times its weight and then wash the solid with deionized water 12 times its weight. Then, place the washed solid in an environment with a vacuum of 0.09 MPa and dry at 55 °C for 10 h to obtain the modified sulfonic acid resin catalyst.

[0097] Among them, the weight ratio of the activated sulfonic acid resin, (1R,2R)-(+)-1,2-diphenylethylenediamine, triethylamine, ammonium nitrate aqueous solution, and absolute ethanol is 5:8:2.5:11:29.

[0098] In the ammonium nitrate aqueous solution, the mass fraction of ammonium nitrate is 70%.

[0099] The (1R,2R)-(+)-1,2-diphenylethylenediamine is obtained by purchasing through the commercial channel.

[0100] 2. Synthesis 1) Primary synthesis After being preheated by the preheater 22, the premix is fed into the primary synthesis kettle 3 continuously from the top of the primary synthesis kettle 3. Liquid ammonia is fed into the primary synthesis kettle 3 from the lower part of the primary synthesis kettle 3 through a feeding pump. Control the reaction pressure at 0.3 MPa and the reaction temperature at 65 °C for primary synthesis. The primary reaction liquid of the primary synthesis reaction is continuously introduced into the secondary synthesis kettle 4 from the top of the primary synthesis kettle 3 through a feeding pump for secondary synthesis.

[0101] 2) Secondary synthesis The secondary synthesis kettle 4 receives the primary reaction liquid introduced from the primary synthesis kettle 3. Control the reaction pressure at 0.3 MPa and the reaction temperature at 65 °C for secondary synthesis. The reaction liquid of the secondary synthesis reaction is continuously introduced into the primary aging kettle 5 from the top of the secondary synthesis kettle 4 through a feeding pump for primary aging.

[0102] 3. Aging 1) Primary aging The primary aging kettle 5 receives the reaction liquid introduced from the secondary synthesis kettle 4. A predetermined amount of composite catalyst is contained in the primary aging kettle 5. By controlling the flow rate of the cooling water in the jacket of the primary aging kettle 5, the temperature in the primary aging kettle 5 is adjusted to 63 °C. Control the pressure in the primary aging kettle 5 at 0.3 MPa for primary aging. The primary aging liquid of the primary aging reaction is continuously introduced into the secondary aging kettle 6 from the top of the primary aging kettle 5 through a feeding pump for secondary aging.

[0103] Among them, the weight of the composite catalyst is 6 wt% of the total weight of the materials in the primary aging kettle 5 within a residence time of 1 h.

[0104] The said composite catalyst is prepared by the following steps: ① Carrier pretreatment Put the ZSM-5 molecular sieve into a first phosphate buffer solution with 4 times the volume, heat up to 35 °C, and then drop epichlorohydrin at a dropping rate of 0.5 mL / min; after the dropping is completed, keep stirring for 2 h, and filter out the solid; wash the solid with deionized water until the pH value is neutral, then put it into a second phosphate buffer solution with 4 times the volume, heat up to 35 °C, add β-cyclodextrin, stir at 300 rpm for 3 h, and filter out the solid; wash the solid with deionized water until the pH value is neutral; then dry it at a vacuum degree of 0.05 MPa and 95 °C until the weight is constant to obtain the carrier.

[0105] Among them, the weight part ratio of the ZSM-5 molecular sieve, epichlorohydrin, and β-cyclodextrin is 1:0.08:0.2.

[0106] The preparation method of the first phosphate buffer solution is to put a predetermined number of parts of potassium dihydrogen phosphate and dipotassium hydrogen phosphate into deionized water and stir at 100 rpm for 20 min to obtain the first phosphate buffer solution.

[0107] The weight part ratio of potassium dihydrogen phosphate, dipotassium hydrogen phosphate, and deionized water is 8.5:0.88:1000.

[0108] The preparation method of the second phosphate buffer solution is to put a predetermined number of parts of potassium dihydrogen phosphate and dipotassium hydrogen phosphate into deionized water and stir at 100 rpm for 20 min to obtain the second phosphate buffer solution.

[0109] The weight part ratio of potassium dihydrogen phosphate, dipotassium hydrogen phosphate, and deionized water is 5.6:0.45:1000.

[0110] ② Loading Put the carrier into a loading solution with 5 times the volume, heat up to 30 °C under stirring at 40 rpm, keep stirring for 3 h, and filter out the solid; place the solid in a temperature environment of 95 °C and let it stand and dry for 8 h to obtain the composite catalyst.

[0111] Among them, the loading solution consists of the following components: ammonium chloride, calcium chloride, magnesium chloride, copper chloride, and deionized water. The weight part ratio of ammonium chloride, calcium chloride, magnesium chloride, copper chloride, and deionized water is 18:6:6:3:150.

[0112] 2) Secondary aging The secondary aging kettle 6 receives the primary aging liquid introduced from the primary aging kettle 5, and adjusts the temperature inside the secondary aging kettle 6 to 63°C by controlling the flow rate of the jacket cooling water of the secondary aging kettle 6; controls the pressure inside the secondary aging kettle 6 to 0.3 MPa for secondary aging; the secondary aging liquid from the secondary aging reaction is continuously fed into the continuous neutralizer 7 by a feeding pump for continuous neutralization.

[0113] 4. Continuous Neutralization Sodium hydroxide solution with a concentration of 80 wt% is continuously pumped into the continuous neutralizer 7 by a centrifugal pump for continuous neutralization; during the continuous neutralization process, the real-time flow rate of the sodium hydroxide solution is controlled by temperature-flow interlock, and the temperature inside the continuous neutralizer 7 is controlled to 55°C; meanwhile, the total input amount of the sodium hydroxide solution is controlled according to the pH value of the neutralized liquid inside the continuous neutralizer 7, and the pH value of the neutralized liquid is controlled to 14; the organic phase (i.e., crude tetramethylpiperidone) from the continuous neutralization continuously flows out from the top discharge pipe of the continuous neutralizer 7 under the action of centrifugation to the refining process; the aqueous phase from the continuous neutralization settles to the bottom of the continuous neutralizer 7 and is discharged to sewage treatment.

[0114] 5. Refining The crude tetramethylpiperidone obtained in the continuous neutralization step is heated to 90°C and kept for distillation until no gas phase is produced to obtain the rectified liquid phase; the rectified liquid phase is subjected to crystallization, separation, and distillation treatments to obtain tetramethylpiperidone with a purity of 99.95%.

[0115] The device for continuously catalytically synthesizing tetramethylpiperidone used in this example is the same as that in Example 1.

[0116] Comparative Example 1 The method and device for continuously catalytically synthesizing tetramethylpiperidone in Example 2 are adopted, and the differences are as follows: 1) In the method, the secondary synthesis and secondary aging steps are omitted, and the secondary synthesis kettle and secondary aging kettle are correspondingly omitted in the device; 2) A conventional organic sulfonic acid catalyst is used to replace the modified sulfonic acid type resin catalyst; 3) Ammonium nitrate is used to replace the composite catalyst.

[0117] After detection, the purity of the tetramethylpiperidone obtained in Comparative Example 1 is 95.62%, and the catalyst cannot achieve continuous catalysis. The product quality of the tetramethylpiperidone obtained after continuous production for 2 h is significantly reduced, and the continuous large-scale production of tetramethylpiperidone cannot be maintained.

[0118] Test Example 1 The effective catalytic life of the modified sulfonic acid resin catalyst and the composite catalyst prepared in Examples 1-3 was tested. Specifically, the method for continuously catalytically synthesizing tetramethylpiperidone described in Example 2 was adopted to continuously produce tetramethylpiperidone; during the continuous catalytic production process, the continuous and stable supply of each raw material was maintained, and the temperature and pressure of each reaction device were kept stable. After each catalyst was continuously catalytically reacted for 2500 h, the purity of the prepared tetramethylpiperidone was detected, and the test results are as follows:

[0119] It can be seen that after continuous catalytic reaction for 2500 h, the modified sulfonic acid resin catalyst and the composite catalyst can still maintain ideal catalytic performance, can meet the requirements of large-scale continuous production, and are beneficial to large-scale production.

[0120] Unless otherwise specified, the percentages used in the present invention are all mass percentages.

[0121] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for continuously catalytically synthesizing tetramethyl piperidone, characterized in that: It consists of the following steps: premixing, synthesis, aging, continuous neutralization, and refining; The premixing method comprises: adding acetone and a modified sulfonic acid resin catalyst into a premixing kettle (1), mixing them evenly, and obtaining a premix; The modified sulfonic acid resin catalyst is prepared by the following steps: activation and modification; The activation method comprises the following steps: putting the sulfonic acid resin into thionyl chloride, heating to reflux, keeping the temperature and stirring, separating and obtaining a solid, and washing and drying the solid to obtain an activated sulfonic acid resin; The modification method comprises the following steps: putting the activated sulfonic acid resin into anhydrous ethanol, uniformly dispersing the resin, adding (1R, 2R)-(+)-1,2-diphenylethylenediamine, triethylamine and ammonium nitrate aqueous solution, and stirring the mixture at room temperature; separating and obtaining a solid, washing and drying the solid to obtain a modified sulfonic acid resin catalyst; The synthesis is composed of the following steps: primary synthesis, secondary synthesis; The method for the primary synthesis is as follows: the premix and liquid ammonia are continuously fed into the primary synthesis reactor (3); the reaction pressure is controlled to be 0.1-0.3 MPa and the reaction temperature is controlled to be 60-65° C., the primary synthesis is performed, and the primary reaction liquid is obtained and continuously introduced into the secondary synthesis reactor (4); The secondary synthesis method comprises: the secondary synthesis reactor (4) continuously receives the primary reaction liquid, controls the reaction pressure to be 0.1-0.3 MPa, and the reaction temperature to be 60-65° C., performs the secondary synthesis, obtains the secondary reaction liquid and continuously introduces it into the primary aging reactor (5); The secondary reaction liquid is subjected to primary aging in the primary aging kettle (5) to obtain a primary aging liquid, which is continuously introduced into the secondary aging kettle (6) to obtain a secondary aging liquid after secondary aging. The secondary aging liquid is continuously neutralized and refined to obtain tetramethylpiperidone.

2. The method for continuous catalytic synthesis of tetramethyl piperidone according to claim 1, characterized in that: The primary aging method comprises: a primary aging kettle (5) filled with a composite catalyst continuously receives the secondary reaction liquid; the temperature of the primary aging kettle (5) is controlled to be 60-63° C. and the pressure to be 0.1-0.3 MPa, primary aging is performed, and the primary aging liquid is obtained and continuously introduced into the secondary aging kettle (6); The secondary aging method comprises: the secondary aging kettle (6) continuously receives the primary aging liquid; the temperature of the secondary aging kettle (6) is controlled to be 60-63° C. and the pressure is controlled to be 0.1-0.3 MPa to perform secondary aging, and the secondary aging liquid is obtained and continuously introduced into the continuous neutralizer (7); The continuous neutralization method comprises: continuously introducing a sodium hydroxide solution into a continuous neutralizer (7) to continuously neutralize the secondary aging liquid until the pH value reaches 14; and the organic phase of the continuous neutralization is subjected to a refining treatment to obtain tetramethylpiperidone.

3. The method for continuous catalytic synthesis of tetramethyl piperidone according to claim 2, characterized in that: The refining method comprises the following steps: heating the continuously neutralized organic phase to 70-90° C., distilling the phase at this temperature until no gas phase is generated, thereby obtaining a distillation liquid phase; and crystallizing, separating and distilling the distillation liquid phase to obtain tetramethyl piperidone.

4. The method for continuous catalytic synthesis of tetramethyl piperidone according to claim 2, characterized in that: The composite catalyst is prepared by the following steps: carrier pretreatment and loading; The carrier pretreatment method comprises the following steps: putting ZSM-5 molecular sieve into a first phosphate buffer solution, heating the solution to 30-35° C., dripping epichlorohydrin while keeping the solution warm, and stirring the solution while keeping the solution warm; separating and obtaining solid matter, washing the solid matter to neutrality, and then putting the solid matter into a second phosphate buffer solution, heating the solution to 30-35° C., adding β-cyclodextrin, and stirring the solution while keeping the solution warm; separating and obtaining solid matter, and washing and drying the solid matter to obtain a carrier; The loading method is to put the carrier into the loading liquid, keep it warm at 25-30°C and stir it, separate the solid matter and then dry it to obtain the composite catalyst; The loading liquid is deionized water dispersed with ammonium chloride, calcium chloride, magnesium chloride and copper chloride.

5. The method for continuous catalytic synthesis of tetramethyl piperidone according to claim 2, characterized in that: In the premix, the weight ratio of acetone to modified sulfonic acid resin catalyst is 100-200:1; In the primary aging, the weight of the composite catalyst is 1-6wt% of the total weight of the materials in the primary aging reactor within a residence time of 1h; In the continuous neutralization, the concentration of the sodium hydroxide solution used is 80wt%, and the continuous neutralization temperature is 50-55°C.

6. The method for continuous catalytic synthesis of tetramethyl piperidone according to claim 1, characterized in that: During the activation, the sulfonic acid resin is kept in thionyl chloride for 12-16 hours under reflux; the weight ratio of the sulfonic acid resin to the thionyl chloride is 1:15-20; In the modification, the weight ratio of activated sulfonic acid resin, (1R, 2R)-(+)-1,2-diphenylethylenediamine, triethylamine, ammonium nitrate aqueous solution and anhydrous ethanol is 3-5:6-8:1.5-2.5:9-11:26.5-29.

7. The method for continuous catalytic synthesis of tetramethyl piperidone according to claim 4, characterized in that: In the carrier pretreatment, the drop rate of epichlorohydrin is 0.2-0.5 mL / min, and the heat preservation and stirring time after the drop of epichlorohydrin is 1-2 h; the stirring time after the addition of β-cyclodextrin is 2-3 h; The weight ratio of ZSM-5 molecular sieve, epichlorohydrin and beta-cyclodextrin is 1:0.05-0.08:0.1-0.

2.

8. The method for continuous catalytic synthesis of tetramethyl piperidone according to claim 4, characterized in that: In the carrier pretreatment, the first phosphate buffer is a deionized water solution of potassium dihydrogen phosphate and dipotassium hydrogen phosphate, and the weight ratio of potassium dihydrogen phosphate, dipotassium hydrogen phosphate and deionized water in the first phosphate buffer is 8.3-8.5:0.86-0.88:1000; the second phosphate buffer is a deionized water solution of potassium dihydrogen phosphate and dipotassium hydrogen phosphate, and the weight ratio of potassium dihydrogen phosphate, dipotassium hydrogen phosphate and deionized water in the second phosphate buffer is 5.4-5.6:0.4-0.45:1000; In the load, the weight ratio of ammonium chloride, calcium chloride, magnesium chloride, copper chloride and deionized water in the load liquid is 12-18:4-6:4-6:1-3:120-150.

9. A device for continuously catalytically synthesizing tetramethylpiperidone according to any one of claims 1 to 8, characterized in that: It consists of the following: premixing unit, synthesis unit, aging unit, neutralization unit, and refining unit; The premixing unit comprises: a premixing kettle (1) and a preheater (2); The synthesis unit comprises: a primary synthesis reactor (3) and a secondary synthesis reactor (4); The maturation unit comprises: a primary maturation kettle (5) and a secondary maturation kettle (6); The neutralization unit comprises: a continuous neutralizer (7); The top of the premixing kettle (1) is provided with an acetone feed port and a catalyst feed port, and the bottom of the premixing kettle (1) is provided with a discharge port; the discharge port of the premixing kettle (1) is connected to the feed port pipeline of the preheater (2); The discharge port of the preheater (2) is connected to the feed port pipeline of the first-stage synthesis reactor (3); The discharge port of the first synthesis reactor (3) is connected to the feed port pipeline of the second synthesis reactor (4) via a feed pump; The discharge port of the secondary synthesis kettle (4) is connected to the feed port pipeline of the primary aging kettle (5) via a feed pump; The discharge port of the first-stage aging kettle (5) is connected to the feed port pipeline of the second-stage aging kettle (6) via a feed pump; The discharge port of the secondary aging kettle (6) is connected to the material tangential inlet pipeline of the continuous neutralizer (7) via a feed pump; The organic phase outlet of the continuous neutralizer (7) is connected to the refining unit; The refining unit is used to carry out rectification, crystallization, separation and distillation treatment on the organic phase from the continuous neutralizer (7) to obtain tetramethylpiperidone.

10. The device for continuous catalytic synthesis of tetramethyl piperidone according to claim 9, characterized in that: The continuous neutralizer (7) is provided with an automatic control module, including a temperature sensor, an alkali solution flow sensor, a controller, an automatic control valve, and a pH online detector; The temperature sensor is interlocked with the alkali solution flow sensor and the automatic control valve, and is used to adjust the flow rate of the sodium hydroxide solution under the action of the controller to maintain the temperature in the continuous neutralizer (7) at 50-55°C; the alkali solution flow sensor is interlocked with the pH online detector and the automatic control valve, and is used to adjust the amount of sodium hydroxide solution added under the action of the controller to control the pH value of the material in the continuous neutralizer (7) to 14.

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