Method for two-stage semi-continuous synthesis of n,n-dimethylbenzylamine

Abstract

The present invention relates to the field of organic synthesis and particularly relates to a method for synthesis of N,N-dimethylbenzylamine. The method comprises the following steps: 1) first-stage reaction: enabling mixed raw material solution I composed of benzyl chloride, aqueous phase II resulting from liquid separation in phase separator V-4, and alkali solution I to react in tube reactor R-1, and collecting a first-stage reaction solution at phase separator V-3 for standing and liquid separation to obtain organic phase I and aqueous phase I, respectively; 2) second-stage reaction: enabling mixed raw material solution II composed of dimethylamine, organic phase I resulting from liquid separation in phase separator V-3, and alkali solution II to react in tube reactor R-2, and collecting a second-stage reaction solution at phase separator V-4 for standing and liquid separation to obtain organic phase II and aqueous phase II, respectively; and 3) post-treatment: distilling organic phase II to obtain N,N-dimethylbenzylamine. The method of the present invention does not involve the use of a catalyst and has the advantages of small wastewater discharge, high product yield, and low production cost.

Description

A two-stage semi-continuous method for the synthesis of N,N-dimethylbenzylamine Technical Field

[0001] This invention belongs to the field of organic synthesis, specifically relating to a method for synthesizing N,N-dimethylbenzylamine. Background Technology

[0002] N,N-Dimethylbenzylamine, abbreviated as BDMA, has the molecular formula C9H. 13 N,N-dimethylbenzylamine, with a molecular weight of 135.2 and CAS number 103-83-3, has the structural formula shown in Formula 1. In the polyurethane industry, N,N-dimethylbenzylamine is a catalyst for polyester-type polyurethane block foam, rigid polyurethane foam, and adhesive coatings. Primarily used in rigid foams, it imparts good initial flowability and uniform cell structure, resulting in better adhesion between the foam and the substrate. In epoxy resins, N,N-dimethylbenzylamine promotes curing 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 mainly used in the synthesis of organic drugs (such as benzalkonium chloride), dehalogenation catalysts, acid neutralizers, preservatives, and accelerators for electron microscope section embedding. N,N-dimethylbenzylamine is also used to synthesize quaternary ammonium salts and produce cationic surfactants.

[0003] The main synthetic methods for N,N-dimethylbenzylamine are as follows:

[0004] Patent CN106748800B describes a method that mixes and heats benzyl chloride with a 20-40 wt% dimethylamine aqueous solution at a molar ratio of 1:(1.2-2.2) using a feed pump within a glass module of a microchannel reactor. The resulting oil-water mixture is collected, cooled, and separated; the upper oil layer is the reaction product, N,N-dimethylbenzylamine. This method offers a short reaction time and safe reaction control, but it fails to treat the generated hydrogen chloride, resulting in significant wastewater pollution. Using a 1:1 molar ratio in this method leads to the formation of N,N-dimethylbenzylamine hydrochloride, thereby reducing the yield of the target product.

[0005] Patent CN115850087A describes the synthesis of N,N-dimethylbenzylamine from benzaldehyde and dimethylamine. A catalyst is added to a jet-loop reactor, dimethylamine is fed in, and the reaction temperature is controlled. The material is kept circulating within the jet-loop reactor. Hydrogen is then introduced, and benzaldehyde is continuously pumped into the reactor under controlled reaction pressure until the feed is complete, thus synthesizing N,N-dimethylbenzylamine. This method utilizes a recycled catalyst, resulting in stable product quality. However, because benzaldehyde is used as a raw material, the hydrogenation reaction generates numerous byproducts that are difficult to separate.

[0006] The literature (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 with dimethyl carbonate to synthesize N,N-dimethylbenzylamine. This method is novel and environmentally friendly, but the product selectivity is low and N-methylbenzylamine is generated as a byproduct.

[0007] Patent CN114436851A proposes a method for synthesizing N,N-dimethylbenzylamine using molybdenum trioxide as a catalyst, metal chloride as an additive, N,N-dimethylformamide as the N-methyl group source and reaction solvent, and benzyl alcohol as a raw material. This invention prepares N,N-dimethylbenzylamine through the N-alkylation reaction of benzyl alcohol and DMF via the synergistic catalysis of molybdenum trioxide and chloride. The reaction conditions are mild and the process route is simple, but the production cost is relatively high, making large-scale production difficult.

[0008] Current methods for synthesizing N,N-dimethylbenzylamine all have certain drawbacks, such as large wastewater discharge, poor product selectivity, and high production costs. Therefore, this invention proposes a new process route for synthesizing N,N-dimethylbenzylamine. Summary of the Invention

[0009] 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 catalyst.

[0010] To solve the above-mentioned technical problems, the present invention provides a two-stage semi-continuous synthesis method for N,N-dimethylbenzylamine, comprising the following steps:

[0011] 1) First stage reaction:

[0012] Benzyl chloride, aqueous phase II obtained from phase separator V-4, and alkaline solution I are pumped into static mixer S-1 for combined mixing. The resulting raw material mixture 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 of reaction liquid is collected at phase separator V-3 for static separation to obtain organic phase I (upper layer) and aqueous phase I (lower layer).

[0013] Note: The aqueous phase I mainly consists of sodium chloride and water; the organic phase I mainly consists of unreacted benzyl chloride and N,N-dimethylbenzylamine produced by the reaction.

[0014] 2) Two-stage reaction:

[0015] Dimethylamine, organic phase I obtained from phase separator V-3, and alkaline solution II are pumped into static mixer S-2 for merging and mixing. The resulting raw material mixture II is reacted in pipeline reactor R-2 at a pressure of 0.1-2.0 MPa and a temperature of 20-120°C. The two reaction liquids are collected at phase separator V-4 for static separation to obtain organic phase II (upper layer) and aqueous phase II (lower layer).

[0016] The reaction temperature of pipeline reactor R-1 is equal to the reaction temperature of pipeline reactor R-2.

[0017] Note: Aqueous phase II mainly consists of unreacted dimethylamine, sodium chloride, and water; organic phase II mainly consists of N,N-dimethylbenzylamine produced in the reaction, i.e., organic phase II is the product phase (crude N,N-dimethylbenzylamine);

[0018] 3) Post-processing:

[0019] Organic phase II was distilled to obtain N,N-dimethylbenzylamine.

[0020] As an improvement to the two-stage semi-continuous synthesis method of N,N-dimethylbenzylamine of the present invention, step 3) is as follows: the organic phase II obtained by separation in phase separator V-4 is subjected to atmospheric distillation, and the fore fraction is obtained by distillation at a kettle temperature of 120-180°C, and N,N-dimethylbenzylamine (N,N-dimethylbenzylamine fraction with purity ≥99.5%) is obtained by distillation at a kettle temperature of 180°C.

[0021] The fore-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 for distillation, thus achieving reuse.

[0022] As a further improvement to the two-stage semi-continuous synthesis method of N,N-dimethylbenzylamine of the present invention, in step 1), the residence time of the mixture I in the pipeline reactor R-1 is 10 to 600 s (preferably 29 to 120 s);

[0023] In step 2), the residence time of mixture II in the pipeline reactor R-2 is 10 to 600 s (preferably 29 to 120 s).

[0024] Note: The residence time of raw material mixture I in pipeline reactor R-1 can be set to the same as the residence time of raw material mixture II in pipeline reactor R-2.

[0025] As a further improvement to the two-stage semi-continuous synthesis method of N,N-dimethylbenzylamine of the present invention:

[0026] The molar ratio of benzyl chloride to dimethylamine is 1:(1~1.05).

[0027] The molar ratio of benzyl chloride to sodium hydroxide is 1:1 to 1.5.

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

[0029] In step 1): the reaction solution in section 1 is collected at phase separator V-3 and allowed to stand for separation for 0.5–4 hours (preferably 1–1.5 hours).

[0030] In step 2): the reaction solution from the two stages is collected at phase separator V-4 and allowed to stand for separation for 0.5–4 hours (preferably 1–1.5 hours).

[0031] illustrate:

[0032] When the pipeline reactor R-1 no longer produces new reaction liquid, the phase separator V-3 begins to perform settling and separation (i.e., the settling and separation time begins to be counted).

[0033] When the pipeline reactor R-2 no longer produces new reaction liquid, the phase separator V-4 begins to settle and separate the liquid (i.e., the settling and separating time begins to be counted).

[0034] As a further improvement to the two-stage semi-continuous synthesis method of N,N-dimethylbenzylamine of the present invention:

[0035] Alkali solution I and alkali solution II are both obtained by adding sodium hydroxide solid alkali to aqueous phase I obtained from phase separator V-3 and filtering to obtain an aqueous sodium hydroxide solution with a mass concentration of 5% to 40%. Aqueous phase I obtained from phase separator V-3 in each batch is filtered with alkali and then recycled to the next batch, that is, the aqueous phase can be recycled.

[0036] As a further improvement to the two-stage semi-continuous synthesis method of N,N-dimethylbenzylamine of the present invention:

[0037] Pipeline reactors R-1 and R-2 have the same pipe length and inner diameter. They are both made of 316L stainless steel pipe, with a pipe length of 60±6m and an inner diameter of 3±0.3mm.

[0038] As a further improvement to the two-stage semi-continuous synthesis method of N,N-dimethylbenzylamine of the present invention:

[0039] In the first stage of the reaction in step 1), the volumetric flow rate of benzyl chloride is 0.5–10.0 mL / s (preferably 1.3–5.4 mL / s), the volumetric flow rate of aqueous phase II is 0.5–10.0 mL / s (preferably 1.4–5.8 mL / s), and the volumetric flow rate of alkaline solution I is 0.5–10.0 mL / s (preferably 0.7–3 mL / s).

[0040] In the two-stage reaction of step 2), the volumetric flow rate of the 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 alkaline solution II is 0.5–10.0 mL / s (preferably 1.3–5.2 mL / s).

[0041] The synthetic reaction formula of the present invention is as follows: Formula 2:

[0042] This invention synthesizes N,N-dimethylbenzylamine using a two-stage semi-continuous method, which has the following technical advantages:

[0043] 1. The total molar ratio of the reaction raw materials is close to 1:1. The online molar ratio is increased by the countercurrent process of the two-stage reaction, which promotes the forward reaction and results in high material utilization (the materials are basically completely reacted), which can reduce production costs.

[0044] 2. The entire reaction process is semi-continuous, resulting in high production efficiency;

[0045] 3. This reaction device features reaction-separation coupling, material recovery and reuse, and minimal wastewater discharge;

[0046] Specifically, in this invention, the organic phase I (located in the upper layer, containing unreacted benzyl chloride) obtained from the first stage reaction separation participates in the second stage reaction; the aqueous phase II (located in the lower layer, containing unreacted dimethylamine) obtained from the second stage reaction separation can participate in the first stage reaction; and the aqueous phase I (located in the lower layer) obtained from the first stage reaction separation, after adding sodium hydroxide to prepare alkali and filtering, can be used as the alkali solution required for the first and second stage reactions, thereby achieving recycling.

[0047] 4. The entire synthetic route can be carried out under relatively mild conditions, the operation is simple, and the requirements for reaction equipment are low;

[0048] 5. The present invention consumes the hydrogen chloride generated in the reaction by adding the acid-binding agent sodium hydroxide (hydrogen chloride reacts with sodium hydroxide to produce sodium chloride and water), that is, the product yield is improved by adding the acid-binding agent to regulate the reaction;

[0049] 6. Only the theoretical amount of newly generated aqueous phase is discharged, and the remaining aqueous phase is still prepared with alkali, filtered, and recycled for the next batch.

[0050] In summary, this synthesis route features high material utilization, low wastewater discharge, and low production cost, thus it has good application prospects and is suitable for large-scale production. Attached Figure Description

[0051] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0052] Figure 1 shows a diagram of a two-stage semi-continuous reaction apparatus. Detailed Implementation

[0053] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto:

[0054] Example 1: A two-stage semi-continuous reaction device, as shown in Figure 1, includes a storage tank V-1 for storing benzyl chloride, a storage tank V-2 for storing dimethylamine, a phase separator (with level gauge) V-3 for collecting the first stage reaction liquid, a phase separator (with level gauge) V-4 for collecting the second stage reaction liquid, pumps P-1, P-2, P-3, P-4, P-5, and P-6, static mixers S-1 and S-2, constant temperature heating devices H-1 and H-2, pipelined reactors R-1 and R-2, back pressure valves B-1 and B-2, alkali preparation and water conditioning tanks A-1 and A-2, and a storage tank L-1.

[0055] Each of the following locations has a corresponding valve installed at the inlet and outlet of storage tank V-1, the inlet and outlet of storage tank V-2, the two outlets (aqueous phase outlet and organic phase outlet) of phase separator V-3, the two outlets (aqueous phase outlet and organic phase outlet) of phase separator V-4, the drain outlet, the inlet and outlet of alkali preparation and water conditioning tank A-1, the inlet and outlet of alkali preparation and water conditioning tank A-2, and the two outlets of storage tank L-1. These valves are used to regulate the on / off state of the components. This valve installation is a conventional technique.

[0056] The outlet of storage tank V-1 is connected to the inlet of static mixer S-1 via pump P-1; the water phase outlet of phase separator V-4 is connected to the inlet of static mixer S-1 via pump P-6.

[0057] The aqueous phase outlet of phase separator V-3 is divided into three paths. One path connects to the drain outlet (equipped with a valve). The other two paths connect to the inlets of alkali preparation tank A-1 and A-2, respectively. The outlets of alkali preparation tank A-1 and A-2 are connected to the inlets of storage tank L-1. Outlet one of storage tank L-1 is connected to the inlet of static mixer S-1 via pump P-4. Outlet two of storage tank L-1 is connected to the inlet of static mixer S-2 via pump P-5. The organic phase outlet of phase separator V-3 is connected to the inlet of static mixer S-2 via pump P-3.

[0058] The outlet of static mixer S-1, pipelined reactor R-1, back pressure valve B-1, and inlet of phase separator V-3 are connected in sequence. Pipeline reactor R-1 is placed inside a constant temperature heating device H-1, which controls the reaction temperature within R-1. A back pressure valve B-1 is located at the outlet of pipelined reactor R-1; its function is to regulate the pressure within R-1.

[0059] The outlet 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, pipelined reactor R-2, back pressure valve B-2, and the inlet of phase separator V-4 are connected in sequence. Pipeline reactor R-2 is placed inside a constant temperature heating device H-2, which controls the reaction temperature within pipelined reactor R-2. A back pressure valve B-2 is installed at the outlet of pipelined reactor R-2; its function is to regulate the pressure within pipelined reactor R-2.

[0060] Each of the pipeline reactors R-1 and R-2 is equipped with a pressure gauge to display the pressure inside their respective pipeline reactors. Both pipeline reactors R-1 and R-2 are made of 316L stainless steel pipes, with a length of 60m, an inner diameter of 3mm, and a volume of 423.9mL.

[0061] In this invention, the inlet valves of alkali mixing and water conditioning tank A-1 and alkali mixing and water conditioning tank A-2 are first closed, and the valve at the drain outlet is opened. After the theoretical amount of newly generated water obtained by the phase separator V-3 is discharged from the drain outlet (controlled by weighing the amount of water phase discharged from the drain outlet), the valve at the drain outlet is closed, and then the inlet valve of alkali mixing and water conditioning tank A-1 or alkali mixing and water conditioning tank A-2 is opened.

[0062] In this invention, the alkali preparation tank A-1 and the alkali preparation tank A-2 are used alternately. When the aqueous phase I obtained from the phase separator V-3 is introduced into the alkali preparation tank A-1, the alkali preparation tank A-2 is kept in reserve (the valve at the inlet of the alkali preparation tank A-1 is open, and the valve at the inlet of the alkali preparation tank A-2 is closed). Sodium hydroxide is added to the alkali preparation tank A-1 for alkali preparation and filtration. Since sodium chloride in the aqueous phase I will precipitate, after filtering to remove sodium chloride, a sodium hydroxide aqueous solution of the required concentration can be obtained. Then, the valve at the outlet of the alkali preparation tank A-1 is opened, and the sodium hydroxide aqueous solution flows into the storage tank L-1 as the alkali solution I / alkali solution II required by this invention. The working mode of the alkali preparation tank A-2 is similar. The aqueous phase I obtained from the previous batch of phase separator V-3 is alkali-prepared and filtered in alkali preparation and water conditioning tank A-1. The aqueous phase I obtained from the next batch of phase separator V-3 is then alkali-prepared and filtered in alkali preparation and water conditioning tank A-2. At this time, alkali preparation and water conditioning tank A-1 is used to remove sodium chloride, and is ready for the next batch of alkali preparation and filtration.

[0063] The working process of this invention is as follows:

[0064] 1. According to the set dosage ratio, set the required amount of benzyl chloride in storage tank V-1 and the required amount of dimethylamine in storage tank V-2;

[0065] 2. After the product from the previous batch of the pipeline reactor R-2 is allowed to stand in the phase separator V-4 for a set time, organic phase II and aqueous phase II have been formed. Therefore, the valves of the aqueous phase outlet and the organic phase outlet of the phase separator V-4 are opened respectively. Organic phase II is discharged from the system through the organic phase outlet of the phase separator V-4. Aqueous phase II is transported to the static mixer S-1 by pump P-6. At the same time, the valve of the discharge port of storage tank V-1 and the valve of the outlet of storage tank L-1 are opened, so that benzyl chloride, aqueous phase II obtained from the phase separator V-4, and alkaline solution I are pumped into the static mixer S-1 for merging and mixing. The resulting mixed liquid I is reacted in the pipeline reactor R-1.

[0066] The reaction liquid produced by the pipeline reactor R-1 continuously flows into the phase separator V-3. When the pipeline reactor R-1 no longer produces new reaction liquid, the phase separator V-3 begins to settle and separate the liquid (i.e., the settling and separating time begins to be counted).

[0067] 3. After the set set time for settling and separation in phase separator V-3, organic phase I and aqueous phase I have formed in phase separator V-3. Therefore, open the valves at the aqueous phase outlet and the organic phase outlet of phase separator V-3 respectively. Organic phase I enters the static mixer S-2 through pump P-3. Aqueous phase I first discharges the theoretical amount of newly generated water (the total amount of water generated by the reactions in pipeline reactors R-1 and R-2) through the drain outlet, and then enters the alkali preparation and water conditioning tank A-1 or A-2. At the same time, open the valve at the discharge port of storage tank V-2 and the valve at outlet II of storage tank L-1, so that dimethylamine, organic phase I obtained from phase separator V-3, and alkali solution II are combined and mixed in static mixer S-2. The resulting mixture II reacts in pipeline reactor R-2. The reaction liquid produced by the pipeline reactor R-2 continuously flows into the phase separator V-4. When the pipeline reactor R-2 no longer produces new reaction liquid, the phase separator V-4 begins to settle and separate the liquid (i.e., the set set time for settling and separating the liquid is started). When the set set time for settling and separating the liquid is reached, organic phase II and aqueous phase II will be formed in the phase separator V-4.

[0068] Then, repeat step 2) above to perform subsequent operations.

[0069] In this invention, since the liquid separation of phase separator V-3 and phase separator V-4 both require time, this invention belongs to a semi-continuous operation.

[0070] 4. It should be noted that during the initial reaction, since there is no aqueous phase II obtained from phase separator V-4, nor is there an alkaline solution prepared from organic phase I obtained from phase separator V-3, the benzyl chloride, dimethylamine, and sodium hydroxide aqueous solution are mixed according to the set dosage ratio and reacted in the tubular reactor R-1. Then, the process described in "3" above is repeated to obtain the reaction product in the tubular reactor R-2, preparing for the next batch of reactions.

[0071] Example 1: A two-stage semi-continuous synthesis method for N,N-dimethylbenzylamine, wherein the molar ratio of benzyl chloride (provided by storage tank V-1) in step 1) to dimethylamine (provided by storage tank V-2) in step 2) is set to 1:1; the molar ratio of (NaOH in alkaline solution I + NaOH in alkaline solution II) to benzyl chloride (provided by storage tank V-1) in step 1) is set to 1:1.

[0072] 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;

[0073] The following steps are performed sequentially:

[0074] 1) First stage reaction:

[0075] 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 aqueous phase II (containing unused dimethylamine from the second stage of reaction) obtained by phase separator V-4 is 2.9 mL / s, and the flow rate of alkaline solution I (20% sodium hydroxide solution) is 1.5 mL / s. At this time, the molar ratio of benzyl chloride: dimethylamine in aqueous phase II: sodium hydroxide in alkaline solution I is approximately 1:0.4:0.4.

[0076] The three components are combined and mixed in static mixer S-1 to form raw material mixture I. Raw material mixture I enters pipeline reactor R-1 and reacts at a reaction temperature of 60°C and a pressure of 0.1MPa. The residence time of raw material mixture I in pipeline reactor R-1 is 59.7s. The first stage of reaction liquid is collected at phase separator V-3 for static separation (static separation for 1h).

[0077] The aqueous phase I (located in the lower layer) obtained by phase separator V-3 contains sodium chloride and water; 400g (10mol) NaOH is added to aqueous phase I to obtain a sodium hydroxide solution with a mass concentration of about 20%.

[0078] The organic phase I (located in the upper layer) obtained by phase separator V-3 contains unreacted benzyl chloride and N,N-dimethylbenzylamine generated by the reaction;

[0079] 2) Two-stage reaction:

[0080] Adjust the flow rates of pumps P-2, P-3, and P-5 so that the flow rate of dimethylamine (provided by storage tank V-2) is 1.8 mL / s, the flow rate of organic phase I obtained by phase separator V-3 is 2.7 mL / s, and the flow rate of alkaline solution II (approximately 20% mass concentration sodium hydroxide solution) is 2.6 mL / s. At this time, the molar ratio of dimethylamine: benzyl chloride in organic phase I: sodium hydroxide in alkaline solution II is approximately 1:0.6:0.6.

[0081] 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 pipeline 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 pipeline reactor R-2 is 59.7 s. The two stages of reaction liquid are collected at phase separator V-4 for static separation (static separation for 1 h).

[0082] The aqueous phase II (located in the lower layer) obtained by phase separator V-4 consists of unreacted dimethylamine, sodium chloride, and water, while the organic phase II (located in the upper layer) consists of crude N,N-dimethylbenzylamine produced by the reaction.

[0083] 3) Post-processing:

[0084] The organic phase II (crude N,N-dimethylbenzylamine) obtained from phase separator V-4 was subjected to atmospheric distillation. The fore fraction was obtained by distillation at a still temperature of 120-180℃, and 1258.8g of N,N-dimethylbenzylamine fraction with a purity ≥99.5% was obtained by distillation at a still temperature of 180℃, with a product yield of 93.1%.

[0085] Product yield = Amount of N,N-dimethylbenzylamine obtained by actual atmospheric distillation / Amount of N,N-dimethylbenzylamine obtained theoretically.

[0086] Note: The above yields are obtained by combining the forefra of the previous batch with the organic phase II of this batch. The yields for the following cases are explained in the same way.

[0087] Examples 2-9: Compared to Example 1, the following changes are made:

[0088] Examples 2-4 differed from Example 1 by varying the reaction temperature.

[0089] Examples 5 and 6 differed in that the residence time of raw material mixture I in pipeline reactor R-1 and the residence time of raw material mixture II in pipeline reactor R-2 were changed; otherwise, they were the same as in Example 1.

[0090] Example 7: The concentration of the alkali solution was changed; that is, the amount of NaOH added to aqueous phase I was changed to 15 mol, and the rest was the same as in Example 1.

[0091] In Example 8, the flow rate was adjusted to change the molar ratio of the materials in the two-stage reaction to 1:0.3:0.3 and 1:0.7:0.7, respectively; all other aspects were the same as in Example 1.

[0092] Example 9: The flow rate was adjusted to change the molar ratio of the materials in the two reaction stages to 1:0.5:0.5 and 1:0.5:0.5, respectively; all other aspects were the same as in Example 1.

[0093] The specific conditions and their corresponding results are shown in Table 1 below.

[0094] Note: In Examples 1 to 9, the reaction temperature of the pipeline reactor R-1 is equal to that of the pipeline reactor R-2, the residence time of raw material mixture I in the pipeline reactor R-1 is equal to that of raw material mixture II in the pipeline reactor R-2, and alkaline solution I and alkaline solution II are the same type of alkaline solution (i.e., the alkaline solution concentrations are equal).

[0095] Table 1. Effects of different reaction conditions on the results of BDMA synthesis.

[0096] Therefore, in Examples 2 to 9, the total molar ratio of benzyl chloride to dimethylamine in the two-stage reaction was close to 1:1, and the molar ratio of benzyl chloride to base was 1:1 in all cases except Example 7, which was 1:1.5.

[0097] Comparative Example 1, compared to Example 1, the following changes were made:

[0098] The two-stage semi-continuous reaction device of the present invention is modified into a single batch reactor, and the rest is the same as in Example 1. The specific operation is as follows:

[0099] 2000g of a 20% NaOH aqueous solution (containing 400g NaOH) and 450.8g (10.0mol) of dimethylamine were added to a 5L reactor. The mixture was stirred and heated to 60℃. Benzyl chloride was then pumped into the reactor, totaling 1265.8g (10.0mol) over 3 hours. After pumping, the reaction was maintained at this temperature for another 2 hours. The reaction was then stopped, cooled to room temperature, and the reactor was opened. The reaction solution was allowed to stand for 2 hours to separate the layers, yielding a lower aqueous phase and an upper product phase. The upper product phase was distilled to obtain N,N-dimethylbenzylamine, with a yield of 84.3%.

[0100] Comparative Example 2, compared to Example 1, makes the following changes:

[0101] In steps 1) and 2), the amount of sodium hydroxide used when preparing alkali from the aqueous phase I obtained by the phase separator V-3 is changed from 400g to 0g. That is, the aqueous phase I is directly used to replace the alkali solution I and alkali solution II in Example 1, and the rest is the same as in Example 1.

[0102] The yield of N,N-dimethylbenzylamine obtained in step 3) was 71.3%.

[0103] Finally, it should be noted that the above examples are merely some specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments and many variations are possible. All variations that can be directly derived or conceived by those skilled in the art from the disclosure of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A two-stage semi-continuous synthesis method for N,N-dimethylbenzylamine, characterized in that... Includes the following steps: 1) First stage reaction: Benzyl chloride, aqueous phase II obtained from phase separator V-4, and alkaline solution I are pumped into static mixer S-1 for combined mixing. The resulting raw material mixture I is reacted in pipeline reactor R-1 at a pressure of 0.1-0.5 MPa and a temperature of 20-120°C. The first stage of reaction liquid is collected at phase separator V-3 for static separation to obtain organic phase I and aqueous phase I respectively. 2) Two-stage reaction: Dimethylamine, organic phase I obtained from phase separator V-3, and alkaline solution II are pumped into static mixer S-2 for merging and mixing. The resulting raw material mixture II is reacted in pipeline reactor R-2 at a pressure of 0.1-2.0 MPa and a temperature of 20-120°C. The two reaction liquids are collected at phase separator V-4 for static separation to obtain organic phase II and aqueous phase II, respectively. The reaction temperature of pipeline reactor R-1 is equal to the reaction temperature of pipeline reactor R-2. 3) Post-processing: Organic phase II was distilled to obtain N,N-dimethylbenzylamine.

2. The method for the two-stage semi-continuous synthesis of N,N-dimethylbenzylamine according to claim 1, characterized in that... Step 3) is as follows: the organic phase II obtained by the phase separator V-4 is subjected to atmospheric pressure distillation, and the fore fraction is obtained by distillation at a kettle temperature of 120-180℃, and N,N-dimethylbenzylamine is obtained by distillation at a kettle temperature of 180℃.

3. The method for the two-stage semi-continuous synthesis of N,N-dimethylbenzylamine according to claim 1 or 2, characterized in that: In step 1): the residence time of mixture I in the tubular reactor R-1 is 10–600 s; In step 2), the residence time of mixture II in the pipeline reactor R-2 is 10 to 600 s.

4. The method for the two-stage semi-continuous synthesis of N,N-dimethylbenzylamine according to claim 3, characterized in that: The molar ratio of benzyl chloride to dimethylamine is 1:1 to 1.05; the molar ratio of benzyl chloride to sodium hydroxide is 1:1 to 1.

5.

5. The method for the two-stage semi-continuous synthesis of N,N-dimethylbenzylamine according to claim 4, characterized in that: In step 1): the reaction solution in section 1 is collected at phase separator V-3 and allowed to stand for separation for 0.5–4 hours. In step 2), the reaction solution from the two stages is collected at phase separator V-4 and allowed to stand for 0.5 to 4 hours for separation.

6. The method for the two-stage semi-continuous synthesis of N,N-dimethylbenzylamine according to any one of claims 1 to 5, characterized in that: Alkali solution I and alkali solution II are both obtained by adding sodium hydroxide solid alkali to aqueous phase I obtained from phase separator V-3 and filtering to obtain an aqueous sodium hydroxide solution with a mass concentration of 5% to 40%. Aqueous phase I obtained from phase separator V-3 in each batch is filtered with alkali and then recycled to the next batch.

7. The method for the two-stage semi-continuous synthesis of N,N-dimethylbenzylamine according to any one of claims 1 to 6, characterized in that: Pipeline reactors R-1 and R-2 have the same pipe length and inner diameter. They are both made of 316L stainless steel pipe, with a pipe length of 60±6m and an inner diameter of 3±0.3mm.

8. The method for the two-stage semi-continuous synthesis of N,N-dimethylbenzylamine according to claim 7, characterized in that: In the first stage of the reaction in step 1), the volumetric flow rate of benzyl chloride is 0.5–10.0 mL / s, the volumetric flow rate of aqueous phase II is 0.5–10.0 mL / s, and the volumetric flow rate of alkaline solution I is 0.5–10.0 mL / s. In the two-stage reaction of step 2), the volumetric flow rate of dimethylamine is 0.5–10.0 mL / s, the volumetric flow rate of organic phase I is 0.5–10.0 mL / s, and the volumetric flow rate of alkaline solution II is 0.5–10.0 mL / s.

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