Two-stage semi-continuous synthesis method of N,N-dimethylbenzylamine

Abstract

The present invention belongs to the field of organic synthesis, and specifically relates to a method for synthesizing N,N-dimethylbenzylamine, which comprises the following steps: 1) First-stage reaction: A raw material mixture I composed of benzyl chloride, aqueous phase II obtained by liquid separation in phase separator V-4, and alkali solution I is reacted in a tubular reactor R-1. The first-stage reaction solution is collected at phase separator V-3 for static liquid separation to obtain organic phase I and aqueous phase I respectively; 2) Second-stage reaction: A raw material mixture II composed of dimethylamine, organic phase I obtained by liquid separation in phase separator V-3, and alkali solution II is reacted in a tubular reactor R-2. The second-stage reaction solution is collected at phase separator V-4 for static liquid separation to obtain organic phase II and aqueous phase II respectively; 3) Post-treatment: The organic phase II is distilled to obtain N,N-dimethylbenzylamine. The method of the present invention does not involve the use of a catalyst, and has the advantages of less wastewater discharge, high product yield, and low production cost.

Description

Technical Field

[0001] The invention belongs to the field of organic synthesis, and particularly relates to a method for synthesizing N,N-dimethylbenzylamine. Background Art

[0002] N,N-dimethylbenzylamine, referred to as BDMA, has a molecular formula of C9H 13 N, with a molecular weight of 135.2, a CAS number of 103-83-3, and a structural formula shown in Formula 1. In the polyurethane industry, N,N-dimethylbenzylamine is a catalyst for polyester-type polyurethane block flexible foam, polyurethane rigid foam, and adhesive coatings. Primarily used in rigid foam, it imparts good initial fluidity and uniform pores to polyurethane foam, ensuring good adhesion between the foam and the substrate. In epoxy resins, N,N-dimethylbenzylamine can accelerate the curing of epoxy resins and is widely used in epoxy resin electronic potting materials, encapsulation materials, epoxy floor coatings, and marine paints. In organic synthesis, N,N-dimethylbenzylamine is primarily used in the synthesis of organic pharmaceuticals (such as chlorhexidine), dehydrohalogenation catalysts, acidic neutralizers, preservatives, and accelerators for embedding electron microscope sections. N,N-dimethylbenzylamine is also used in the synthesis of quaternary ammonium salts and the production of cationic surfactants.

[0003]

[0004] Formula 1N,N-dimethylbenzylamine structural formula

[0005] The main synthesis methods of N,N-dimethylbenzylamine are as follows:

[0006] Patent CN10674880B introduces benzyl chloride and a 20-40 wt% aqueous dimethylamine solution into a glass module of a microchannel reactor at a molar ratio of 1:1 (1.2-2.2) using a feed pump. The mixture is then heated and reacted. The resulting oil-water mixture is collected, cooled, allowed to stand, and then separated. The upper oil layer is the reaction product, N,N-dimethylbenzylamine. This method has a short reaction time and safe reaction control, but the untreated hydrogen chloride generated by the reaction can cause significant wastewater pollution. Using a 1:1 molar ratio in this method can result in the formation of N,N-dimethylbenzylamine hydrochloride, thereby reducing the yield of the target product.

[0007] Patent CN115850087A synthesizes N,N-dimethylbenzylamine using benzaldehyde and dimethylamine as raw materials. A catalyst is added to a jet loop reactor, dimethylamine is fed, and the reaction temperature is controlled. The materials circulate in the jet loop reactor, and hydrogen is then introduced. After controlling the reaction pressure, benzaldehyde is continuously pumped into the reactor until the feed is complete. This method utilizes recycled catalysts and produces stable product quality. However, the use of benzaldehyde as a raw material results in the formation of numerous byproducts during the hydrogenation reaction, which are difficult to separate.

[0008] Reference (Synthesis of N,N-dimethylbenzylamine by Methylation of Benzylamine Catalyzed by Aluminum Phosphate Molecular Sieve) uses aluminum phosphate molecular sieve as a catalyst to catalyze the reaction of benzylamine and dimethyl carbonate to synthesize N,N-dimethylbenzylamine. This method has a novel process route and is green and environmentally friendly, but the product selectivity is low and N-methylbenzylamine is produced as a by-product.

[0009] Patent CN114436851A proposes the synthesis of N,N-dimethylbenzylamine using molybdenum trioxide as a catalyst, metal chlorides as additives, N,N-dimethylformamide as a nitrogen methyl source and reaction solvent, and benzyl alcohol as a raw material. This invention uses the synergistic catalysis of metal molybdenum oxide and chloride to achieve the N-alkylation reaction of benzyl alcohol with DMF to produce N,N-dimethylbenzylamine. The reaction conditions are mild and the process is simple, but the production cost is relatively high, making large-scale production difficult.

[0010] The current methods for synthesizing N,N-dimethylbenzylamine have certain defects to a greater or lesser extent, such as large wastewater discharge, poor product selectivity, and high production costs. Therefore, the present invention proposes a new process route for synthesizing N,N-dimethylbenzylamine. Summary of the Invention

[0011] The technical problem to be solved by the present invention is to provide a method for synthesizing N,N-dimethylbenzylamine with low wastewater discharge, high product yield and low production cost, and the method of the present invention does not involve the use of a catalyst.

[0012] To solve the above technical problems, the present invention provides a two-stage semi-continuous synthesis method of N,N-dimethylbenzylamine, comprising the following steps:

[0013] 1) 1st stage reaction:

[0014] Benzyl chloride, aqueous phase II obtained by separation in phase separator V-4, and alkali solution I are respectively pumped into static mixer S-1 for merging and mixing. The resulting raw material mixed solution I is reacted in pipeline reactor R-1 at a pressure of 0.1-0.5 MPa and a temperature of 20-120°C (preferably 40-100°C). The first stage reaction solution is collected in phase separator V-3 for static separation to obtain organic phase I (located in the upper layer) and aqueous phase I (located in the lower layer).

[0015] Note: The components of aqueous phase I are mainly sodium chloride and water; the components of organic phase I are mainly unreacted benzyl chloride and N,N-dimethylbenzylamine generated by the reaction;

[0016] 2) Two-stage reaction:

[0017] Dimethylamine, the organic phase I obtained by separation in the phase separator V-3, and the alkali solution II are respectively pumped into the static mixer S-2 for merging and mixing. The resulting raw material mixed solution II is reacted in the pipeline reactor R-2 at a pressure of 0.1-2.0 MPa and a temperature of 20-120°C. The two stages of reaction liquid are collected in the phase separator V-4 for static separation to obtain the organic phase II (located in the upper layer) and the aqueous phase II (located in the lower layer).

[0018] The reaction temperature of the pipeline reactor R-1 = the reaction temperature of the pipeline reactor R-2;

[0019] Note: The aqueous phase II mainly contains unreacted dimethylamine, sodium chloride, and water; the organic phase II mainly contains N,N-dimethylbenzylamine generated by the reaction, that is, the organic phase II is the product phase (crude N,N-dimethylbenzylamine);

[0020] 3) Post-processing:

[0021] The organic phase II is distilled to obtain N,N-dimethylbenzylamine.

[0022] As an improvement to the two-stage semi-continuous synthesis method of N,N-dimethylbenzylamine of the present invention, step 3) is: the organic phase II obtained by separation in the phase separator V-4 is subjected to atmospheric distillation, distilled at a kettle temperature of 120-180°C to obtain a fore-fraction, and distilled at a kettle temperature of 180°C to obtain N,N-dimethylbenzylamine (N,N-dimethylbenzylamine fraction with a purity of ≥99.5%).

[0023] The front fraction consists of a small amount of water, a small amount of dimethylamine and N,N-dimethylbenzylamine product; it can be added to the next batch of organic phase II and distilled together, thereby achieving application.

[0024] As a further improvement of the two-stage semi-continuous synthesis method of N,N-dimethylbenzylamine of the present invention, in step 1):

[0025] The residence time of the mixed solution I in the pipeline reactor R-1 is 10 to 600 seconds (preferably 29 to 120 seconds);

[0026] In step 2), the residence time of the mixed solution II in the pipeline reactor R-2 is 10 to 600 seconds (preferably 29 to 120 seconds).

[0027] Note: The residence time of the raw material mixed liquid I in the pipeline reactor R-1 can be set to be the same as the residence time of the raw material mixed liquid II in the pipeline reactor R-2.

[0028] As a further improvement of the two-stage semi-continuous synthesis method of N,N-dimethylbenzylamine of the present invention:

[0029] Benzyl chloride: dimethylamine = 1: (1 to 1.05) molar ratio;

[0030] Benzyl chloride: sodium hydroxide = 1:1 to 1.5 molar ratio.

[0031] As a further improvement of the two-stage semi-continuous synthesis method of N,N-dimethylbenzylamine of the present invention:

[0032] In step 1), the time for the 1st stage reaction solution to be collected at the phase separator V-3 for static liquid separation is 0.5 to 4 h (preferably 1 to 1.5 h),

[0033] In step 2), the time for the 2nd stage reaction solution to be collected at the phase separator V-4 for static liquid separation is 0.5 to 4 h (preferably 1 to 1.5 h),

[0034] Note:

[0035] When no new reaction solution is generated in the tubular reactor R-1, the phase separator V-3 starts static liquid separation (i.e., starts to count the static liquid separation time);

[0036] When no new reaction solution is generated in the tubular reactor R-2, the phase separator V-4 starts static liquid separation (i.e., starts to count the static liquid separation time).

[0037] As a further improvement of the two-stage semi-continuous synthesis method of N,N-dimethylbenzylamine of the present invention:

[0038] Both lye I and lye II are obtained by adding solid sodium hydroxide to the aqueous phase I obtained from the phase separator V-3 for alkali preparation and filtration, obtaining a sodium hydroxide aqueous solution with a mass concentration of 5% to 40%; the aqueous phase I obtained from the phase separator V-3 in each batch is recycled and applied in the next batch after alkali preparation and filtration, that is, the aqueous phase can be recycled.

[0039] As a further improvement of the two-stage semi-continuous synthesis method of N,N-dimethylbenzylamine of the present invention:

[0040] The tubular reactor R-1 and the tubular reactor R-2 have the same tube length, the same inner diameter, and the material is 316L stainless steel tube, and the tube length is 60 ± 6 m and the inner diameter is 3 ± 0.3 mm.

[0041] As a further improvement of the two-stage semi-continuous synthesis method of N,N-dimethylbenzylamine of the present invention:

[0042] In the 1st stage reaction of step 1), the volume flow rate of the benzyl chloride is 0.5 to 10.0 mL / s (preferably 1.3 to 5.4 mL / s), the volume flow rate of the aqueous phase II is 0.5 to 10.0 mL / s (preferably 1.4 to 5.8 mL / s), and the volume flow rate of the lye I is 0.5 to 10.0 mL / s (preferably 0.7 to 3 mL / s);

[0043] In the two-stage reaction of step 2), the volumetric flow rate of dimethylamine is 0.5 - 10.0 mL / s (preferably 0.9 - 3.6 mL / s), the volumetric flow rate of organic phase I is 0.5 - 10.0 mL / s (preferably 1.3 - 5.4 mL / s), and the volumetric flow rate of lye II is 0.5 - 10.0 mL / s (preferably 1.3 - 5.2 mL / s).

[0044] The synthesis reaction formula of the present invention is as follows: Formula 2

[0045]

[0046] Synthesis reaction formula of N,N-dimethylbenzylamine in Formula 2

[0047] The present invention synthesizes N,N-dimethylbenzylamine by a two-stage semi-continuous method, having the following technical advantages:

[0048] 1. The total molar ratio of reaction raw materials is close to 1:1. By the countercurrent process of the two-stage reaction, the on-line molar ratio is increased to promote the forward progress of the reaction. The material utilization rate is high (the materials basically react completely), and the production cost can be reduced.

[0049] 2. The whole reaction process is carried out semi-continuously, with high production efficiency.

[0050] 3. The reaction device of this reaction couples reaction and separation, recovers and utilizes materials, and has less wastewater discharge.

[0051] Specifically: In the present invention, the organic phase I separated in the first-stage reaction (located in the upper layer and containing unreacted benzyl chloride) participates in the second-stage reaction; the aqueous phase II separated in the second-stage reaction (located in the lower layer and containing unreacted dimethylamine) can participate in the first-stage reaction; and the aqueous phase I separated in the first-stage reaction (located in the lower layer) can be used as the lye required for the first-stage reaction and the second-stage reaction after adding sodium hydroxide for alkali preparation and filtration, thus realizing recycling.

[0052] 4. The whole synthesis route can be carried out under relatively mild conditions, with simple operation and low requirements for reaction equipment.

[0053] 5. The present invention adds a deacidifying agent, sodium hydroxide, to consume the hydrogen chloride generated in the reaction (hydrogen chloride reacts with sodium hydroxide to form sodium chloride and water), that is, the reaction is regulated by adding a deacidifying agent to improve the product yield.

[0054] 6. Only the newly generated aqueous phase in the theoretical amount of the reaction is discharged, and the remaining aqueous phase is still used for alkali preparation and filtration and then recycled for the next batch.

[0055] In summary, this synthesis route has the characteristics of high material utilization rate, less wastewater discharge, and low production cost. Therefore, it has good application prospects and is suitable for large-scale production. Description of the Drawings

[0056] The following further describes in detail the specific embodiments of the present invention with reference to the accompanying drawings.

[0057] Figure 1 It is a two-stage semi-continuous reaction device diagram. Specific Embodiments

[0058] The following further describes the present invention with reference to specific embodiments, but the protection scope of the present invention is not limited thereto:

[0059] Example 1. A two-stage semi-continuous reaction device, as Figure 1 shown, includes a storage tank V-1 for storing benzyl chloride, a storage tank V-2 for storing dimethylamine, a phase separator (with a liquid level gauge) V-3 for collecting the reaction liquid in the first stage, a phase separator (with a liquid level gauge) V-4 for collecting the reaction liquid in the second stage, pumps P-1, P-2, P-3, P-4, P-5, P-6, static mixers S-1, S-2, a constant temperature heating device H-1, a constant temperature heating device H-2, a tubular reactor R-1, a tubular reactor R-2, back pressure valves B-1, B-2, an alkali preparation and adjustment water tank A-1, an alkali preparation and adjustment water tank A-2, and a liquid storage tank L-1.

[0060] At the inlet and outlet of the storage tank V-1, the inlet and outlet of the storage tank V-2, the two outlets (aqueous phase outlet and organic phase outlet) of the phase separator V-3, the two outlets (aqueous phase outlet and organic phase outlet) of the phase separator V-4, the drain outlet, the inlet and outlet of the alkali preparation and adjustment water tank A-1, the inlet and outlet of the alkali preparation and adjustment water tank A-2, and the two outlets of the liquid storage tank L-1, respective corresponding valves are provided to adjust the on-off state of the component. The setting of this valve belongs to conventional technology.

[0061] The outlet of the storage tank V-1 is connected to the inlet of the static mixer S-1 through the pump P-1; the aqueous phase outlet of the phase separator V-4 is connected to the inlet of the static mixer S-1 through the pump P-6;

[0062] The aqueous phase outlet of the phase separator V-3 is divided into three paths. One path is connected to the drain outlet (a valve is provided at the drain outlet), and the other two paths are respectively connected to the inlet of the alkali preparation and adjustment water tank A-1 and the inlet of the alkali preparation and adjustment water tank A-2; the outlets of the alkali preparation and adjustment water tank A-1 and the alkali preparation and adjustment water tank A-2 are respectively connected to the inlet of the liquid storage tank L-1. One outlet of the liquid storage tank L-1 is connected to the inlet of the static mixer S-1 through the pump P-4. The second outlet of the liquid storage tank L-1 is connected to the inlet of the static mixer S-2 through the pump P-5. The organic phase outlet of the phase separator V-3 is connected to the inlet of the static mixer S-2 through the pump P-3.

[0063] The outlet of static mixer S-1, pipeline reactor R-1, backpressure valve B-1, and the inlet of phase separator V-3 are sequentially connected. Pipeline reactor R-1 is housed within a constant temperature heating device H-1, which controls the reaction temperature within pipeline reactor R-1. A backpressure valve B-1 is installed at the outlet of pipeline reactor R-1 to regulate the pressure within pipeline reactor R-1.

[0064] The discharge port of storage tank V-2 is connected to the inlet of static mixer S-2 via pump P-2. The outlet of static mixer S-2, pipeline reactor R-2, backpressure valve B-2, and the inlet of phase separator V-4 are sequentially connected. Pipeline reactor R-2 is housed within a constant temperature heating device H-2, which controls the reaction temperature within pipeline reactor R-2. A backpressure valve B-2 is installed at the outlet of pipeline reactor R-2 to regulate the pressure within pipeline reactor R-2.

[0065] The pipeline reactors R-1 and R-2 are each provided with a pressure gauge for displaying the pressure inside the respective pipeline reactors. The pipeline reactors R-1 and R-2 are both made of 316L stainless steel pipes with a length of 60m, an inner diameter of 3mm and a volume of 423.9mL.

[0066] In the present invention, the inlet valves of the alkali preparation and water adjustment tank A-1 and the alkali preparation and water adjustment tank A-2 are first closed, and the valve at the drain outlet is opened. After the water phase I obtained by the phase separator V-3 separation discharges the theoretical amount of newly generated water from the reaction from the drain outlet (controlled by weighing the amount of the water phase discharged from the drain outlet), the valve at the drain outlet is closed, and then the inlet valve of the alkali preparation and water adjustment tank A-1 or the alkali preparation and water adjustment tank A-2 is opened.

[0067] In the present invention, alkali preparation and water conditioning tank A-1 and alkali preparation and water conditioning tank A-2 are used alternately. When the aqueous phase I obtained by separation in phase separator V-3 is introduced into alkali preparation and water conditioning tank A-1, alkali preparation and water conditioning tank A-2 is on standby (the valve at the inlet of alkali preparation and water conditioning tank A-1 is open, and the valve at the inlet of alkali preparation and water conditioning tank A-2 is closed). Sodium hydroxide is added to alkali preparation and water conditioning tank A-1 for alkali preparation and filtration. Since sodium chloride in aqueous phase I will precipitate, after filtering and removing the sodium chloride, the desired concentration of sodium hydroxide aqueous solution can be obtained. Then, the valve at the outlet of alkali preparation and water conditioning tank A-1 is opened, and the sodium hydroxide aqueous solution flows into liquid storage tank L-1 as the alkali solution I / alkali solution II required by the present invention. The operating mode of alkali preparation and water conditioning tank A-2 is similar. The aqueous phase I obtained by the phase separator V-3 separation of the previous batch is subjected to alkali preparation and filtration in the alkali preparation and water conditioning tank A-1, and the aqueous phase I obtained by the phase separator V-3 separation of the next batch is subjected to alkali preparation and filtration in the alkali preparation and water conditioning tank A-2. At this time, the alkali preparation and water conditioning tank A-1 is subjected to the sodium chloride removal operation and is used as a standby for the next batch of alkali preparation and filtration operations.

[0068] The working process of the present invention is as follows:

[0069] 1. According to the set dosage ratio relationship, benzyl chloride with the required dosage is set in storage tank V-1, and dimethylamine with the required dosage is set in storage tank V-2;

[0070] 2. After the reaction product from the tubular reactor R-2 obtained in the previous batch enters the phase separator V-4 and stands for the set time, an organic phase II and an aqueous phase II have been formed. Therefore, the valves at the aqueous phase outlet and the organic phase outlet of the phase separator V-4 are opened respectively. The organic phase II is discharged out of the system through the organic phase outlet of the phase separator V-4; the aqueous phase II is transported to the static mixer S-1 by the pump P-6. At the same time, the valves at the discharge port of the storage tank V-1 and the first outlet of the storage tank L-1 are opened, so that benzyl chloride, the aqueous phase II separated from the phase separator V-4, and the lye I are respectively pumped into the static mixer S-1 for merging and mixing, and the obtained mixed liquid I reacts in the tubular reactor R-1;

[0071] The reaction liquid generated by the tubular reactor R-1 continuously flows into the phase separator V-3. When no new reaction liquid is generated in the tubular reactor R-1, the phase separator V-3 starts to stand for liquid separation (i.e., starts to count the standing liquid separation time).

[0072] 3. When the set standing liquid separation time of the phase separator V-3 arrives, an organic phase I and an aqueous phase I have been formed in the phase separator V-3; therefore, the valves at the aqueous phase outlet and the organic phase outlet of the phase separator V-3 are opened respectively. The organic phase I enters the static mixer S-2 through the pump P-3; the aqueous phase I first discharges the theoretically generated water (the total amount of water generated by the reactions in the tubular reactor R-1 and the tubular reactor R-2) through the drain port, and then enters the alkali preparation and adjustment water tank A-1 or the alkali preparation and adjustment water tank A-2. At the same time, the valves at the discharge port of the storage tank V-2 and the second outlet of the storage tank L-1 are opened, so that dimethylamine, the organic phase I separated from the phase separator V-3, and the lye II are merged and mixed in the static mixer S-2, and the obtained mixed liquid II reacts in the tubular reactor R-2. The reaction liquid generated by the tubular reactor R-2 continuously flows into the phase separator V-4. When no new reaction liquid is generated in the tubular reactor R-2, the phase separator V-4 starts to stand for liquid separation (i.e., starts to count the standing liquid separation time). When the set standing liquid separation time of the phase separator V-4 arrives, an organic phase II and an aqueous phase II will be formed in the phase separator V-4;

[0073] Then, repeat the above step 2) for subsequent operations.

[0074] In the present invention, since the liquid separation of the phase separator V-3 and the liquid separation of the phase separator V-4 both require time, the present invention belongs to semi-continuous operation.

[0075] 4. It should be noted that: during the first reaction, since there is no aqueous phase II separated by the phase separator V-4 and there is also no lye prepared from the organic phase I separated by the phase separator V-3, therefore, according to the set dosage ratio relationship, benzyl chloride, dimethylamine and aqueous sodium hydroxide solution are mixed and then reacted in the tubular reactor R-1. Then, the operation is carried out according to the above "3" to obtain the reaction product of the tubular reactor R-2, preparing for the reaction of the next batch.

[0076] Example 1. A method for two-stage semi-continuous synthesis of N,N-dimethylbenzylamine, setting the molar ratio of benzyl chloride (provided by storage tank V-1) in step 1): dimethylamine (provided by storage tank V-2) in step 2) = 1:1; setting (NaOH in lye I + NaOH in lye II): benzyl chloride (provided by storage tank V-1) in step 1) = 1:1 molar ratio;

[0077] That is, benzyl chloride (provided by storage tank V-1) is 10 mol, dimethylamine (provided by storage tank V-2) is 10 mol, and NaOH is 10 mol;

[0078] The following steps are carried out in sequence:

[0079] 1). Stage 1 reaction:

[0080] Adjust the flow rates of pumps P-1, P-6, and P-4 so that the flow rate of benzyl chloride (provided by storage tank V-1) is 2.7 mL / s, the flow rate of the aqueous phase II separated by the phase separator V-4 (containing unreacted dimethylamine from the stage 2 reaction) is 2.9 mL / s, and the flow rate of lye I (20% mass concentration sodium hydroxide solution) is 1.5 mL / s. At this time, the molar ratio of benzyl chloride: dimethylamine in the aqueous phase II: sodium hydroxide in lye I is approximately 1:0.4:0.4;

[0081] The three are combined and mixed in the static mixer S-1 to form the raw material mixture I. The raw material mixture I enters the tubular reactor R-1 and reacts at a reaction temperature of 60 °C and a pressure of 0.1 MPa. The residence time of the raw material mixture I in the tubular reactor R-1 is 59.7 s. The stage 1 reaction solution is collected at the phase separator V-3 for static liquid separation (static liquid separation for 1 h).

[0082] The aqueous phase I (located at the lower layer) separated by the phase separator V-3 contains sodium chloride and water; 400 g (10 mol) of NaOH is added to the aqueous phase I to obtain a sodium hydroxide solution with a mass concentration of approximately 20%.

[0083] The organic phase I (located at the upper layer) separated by the phase separator V-3 contains unreacted benzyl chloride and the reaction-generated N,N-dimethylbenzylamine;

[0084] 2) Two-stage reaction:

[0085] Adjust the flow rates of pumps P-2, P-3, and P-5 so that the flow rate of dimethylamine (supplied by storage tank V-2) is 1.8 mL / s, the flow rate of organic phase I separated by phase separator V-3 is 2.7 mL / s, and the flow rate of caustic solution II (sodium hydroxide solution with a mass concentration of about 20%) is 2.6 mL / s. At this time, the molar ratio of dimethylamine: benzyl chloride in organic phase I: sodium hydroxide in caustic solution II is approximately 1:0.6:0.6.

[0086] Dimethylamine, benzyl chloride, and sodium hydroxide are combined and mixed in static mixer S-2 to form raw material mixture II. Raw material mixture II enters tubular reactor R-2 and reacts at a reaction temperature of 60°C and a pressure of 0.5 MPa. The residence time of raw material mixture II in tubular reactor R-2 is 59.7 s. The two-stage reaction liquid is collected at phase separator V-4 for static separation (static separation for 1 h).

[0087] The aqueous phase II (located at the lower layer) separated by phase separator V-4 is unreacted dimethylamine, sodium chloride, and water, and the organic phase II (located at the upper layer) is the crude product of N,N-dimethylbenzylamine formed by the reaction;

[0088] 3) Post-treatment:

[0089] The organic phase II (crude product of N,N-dimethylbenzylamine) obtained from phase separator V-4 is subjected to atmospheric distillation. The pre-fraction is distilled at a kettle temperature of 120 - 180°C, and the N,N-dimethylbenzylamine fraction with a purity ≥ 99.5% is distilled at a kettle temperature of 180°C, obtaining 1258.8 g. The product yield is 93.1%.

[0090] Product yield = Amount of N,N-dimethylbenzylamine actually obtained by atmospheric distillation / Amount of N,N-dimethylbenzylamine theoretically obtained.

[0091] Note: The above yield is the yield obtained after combining the pre-fraction of the previous batch with organic phase II of this batch. The yields in the following cases are the same as this note.

[0092] Examples 2 - 9: Compared with Example 1, the following changes are made:

[0093] In Examples 2 - 4, the reaction temperature is changed; the rest is the same as Example 1.

[0094] In Examples 5 - 6, the residence time of raw material mixture I in tubular reactor R-1 and the residence time of raw material mixture II in tubular reactor R-2 are changed; the rest is the same as Example 1.

[0095] Example 7: Change the concentration of the lye; that is, change the amount of NaOH added to the aqueous phase I to 15 mol, and the rest is the same as in Example 1.

[0096] Example 8: Adjust the flow rate to change the molar ratios of the materials in the two-stage reaction to 1:0.3:0.3 and 1:0.7:0.7 respectively; the rest is the same as in Example 1.

[0097] Example 9: Adjust the flow rate to change the molar ratios of the materials in the two-stage reaction to 1:0.5:0.5 and 1:0.5:0.5 respectively; the rest is the same as in Example 1.

[0098] The corresponding relationships between the specific conditions and the obtained results are shown in Table 1 below.

[0099] Note: In Examples 1 to 9, the reaction temperature of the tubular reactor R-1 = that of the tubular reactor R-2, the residence time of the raw material mixture I in the tubular reactor R-1 = the residence time of the raw material mixture II in the tubular reactor R-2, and the lye I and lye II are the same lye (that is, the lye concentrations are equal).

[0100] Table 1 Influence of different reaction conditions on the results when synthesizing BDMA

[0101]

[0102] Therefore, in Examples 2 to 9, the total molar ratio of benzyl chloride to dimethylamine in the two-stage reaction is close to 1:1, and the molar ratio of benzyl chloride to lye is 1:1 in all cases except 1:1.5 in Example 7.

[0103] Comparative Example 1: Compared with Example 1, the following changes are made:

[0104] Change the two-stage semi-continuous reaction device of the present invention into a single batch reactor, and the rest refers to Example 1. The specific operation is as follows:

[0105] Add 2000 g of 20% mass concentration NaOH aqueous solution (containing 400 g of NaOH) and 450.8 g (10.0 mol) of dimethylamine into a 5 L reaction kettle, start stirring and heating to 60 °C, then pump benzyl chloride into the kettle. A total of 1265.8 g (10.0 mol) of benzyl chloride is pumped in 3 h, and after pumping, continue to keep the temperature for reaction for 2 h. Then stop the reaction, cool to room temperature and open the kettle. The reaction solution is allowed to stand and separate for 2 h to obtain the lower aqueous phase and the upper product phase. The upper product phase is distilled to obtain N,N-dimethylbenzylamine product, and its yield is 84.3%.

[0106] Comparative Example 2: Compared with Example 1, the following changes are made:

[0107] The amount of sodium hydroxide used in preparing the alkali in the aqueous phase I obtained by separation in the phase separator V-3 in step 1) and step 2) was changed from 400 g to 0 g, that is, the alkali solution I and alkali solution II in Example 1 were directly replaced by the aqueous phase I, and the rest was the same as Example 1.

[0108] The yield of N,N-dimethylbenzylamine obtained in step 3) is 71.3%.

[0109] Finally, it should be noted that the above examples are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above examples and is subject to numerous variations. All variations that can be directly derived or conceived by a person of ordinary skill in the art from the disclosure of the present invention are considered to be within the scope of protection of the present invention.

Claims

1. A method for synthesizing N,N-dimethylbenzylamine in a two-stage semi-continuous manner, characterized in that It includes the following steps: 1). First-stage reaction: Benzyl chloride, aqueous phase II obtained by liquid-liquid separation in phase separator V-4, and lye I are respectively pumped into static mixer S-1 for merging and mixing. The obtained raw material mixture I reacts in tubular reactor R-1 at a pressure of 0.1 - 0.5 MPa and a temperature of 20 - 120 °C. The first-stage reaction liquid is collected at phase separator V-3 for static liquid-liquid separation to obtain organic phase I and aqueous phase I respectively; The residence time of mixture I in tubular reactor R-1 is 10 - 600 s; 2). Second-stage reaction: Dimethylamine, organic phase I obtained by liquid-liquid separation in phase separator V-3, and lye II are respectively pumped into static mixer S-2 for merging and mixing. The obtained raw material mixture II reacts in tubular reactor R-2 at a pressure of 0.1 - 2.0 MPa and a temperature of 20 - 120 °C. The second-stage reaction liquid is collected at phase separator V-4 for static liquid-liquid separation to obtain organic phase II and aqueous phase II respectively; The reaction temperature of tubular reactor R-1 = the reaction temperature of tubular reactor R-2; The residence time of mixture II in tubular reactor R-2 is 10 - 600 s; Both lye I and lye II are obtained by adding solid sodium hydroxide to aqueous phase I obtained from phase separator V-3 for alkali preparation and filtration, obtaining a sodium hydroxide aqueous solution with a mass concentration of 5% - 40%. The aqueous phase I obtained from phase separator V-3 in each batch is recycled in the next batch after alkali preparation and filtration; The molar ratio of benzyl chloride to dimethylamine is 1:1 - 1.05; the molar ratio of benzyl chloride to sodium hydroxide is 1:1 - 1.5; 3). Post-treatment: The organic phase II is distilled to obtain N,N-dimethylbenzylamine.

2. The method for synthesizing N,N-dimethylbenzylamine in a two-stage semi-continuous manner according to claim 1, wherein The step 3) is: The organic phase II obtained by liquid-liquid separation in phase separator V-4 is subjected to atmospheric distillation. The pre-fraction is distilled at a kettle temperature of 120 - 180 °C, and N,N-dimethylbenzylamine is distilled at a kettle temperature of 180 °C.

3. According to the method for two-stage semi-continuous synthesis of N,N-dimethylbenzylamine described in claim 2, it is characterized in that: In step 1): The time for the first-stage reaction liquid to be collected at phase separator V-3 for static liquid-liquid separation is 0.5 - 4 h, In step 2): The time for the second-stage reaction liquid to be collected at phase separator V-4 for static liquid-liquid separation is 0.5 - 4 h.

4. The method for synthesizing N,N-dimethylbenzylamine in a two-stage semi-continuous manner according to claim 3, characterized in that: Tubular reactor R-1 and tubular reactor R-2 have the same tube length, the same inner diameter, and the material is 316L stainless steel tube, and the tube length is 60 ± 6 m and the inner diameter is 3 ± 0.3 mm.

5. According to the method for two-stage semi-continuous synthesis of N,N-dimethylbenzylamine described in claim 4, it is characterized in that: In the first-stage reaction of step 1): The volume flow rate of benzyl chloride is 0.5 - 10.0 mL / s, the volume flow rate of aqueous phase II is 0.5 - 10.0 mL / s, and the volume flow rate of lye I is 0.5 - 10.0 mL / s; In the second-stage reaction of step 2): The volume flow rate of dimethylamine is 0.5 - 10.0 mL / s, the volume flow rate of organic phase I is 0.5 - 10.0 mL / s, and the volume flow rate of lye II is 0.5 - 10.0 mL / s.

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