Method for synthesizing lemon yellow through micro-channel continuous flow

Abstract

The invention provides a method for synthesizing lemon yellow through micro-channel continuous flow, and belongs to the technical field of food pigment synthesis. The method for synthesizing lemon yellow by taking sodium sulfanilate, sodium nitrite, a hydrochloric acid solution, dimethyl acetylsuccinate and a sodium carbonate solution as raw materials is carried out in a plurality of micro-reactors and micro-mixers according to different reaction types, so that full-continuous reaction of diazotization, condensation and coupling is realized; the method has the advantages of simple operation, short reaction time, few byproducts, high product purity and overall yield, and greatly improved production safety and stability.

Description

Technical Field

[0001] The invention relates to the technical field of food pigment synthesis, in particular to a method for synthesizing tartrazine through a microchannel continuous flow. Background Art

[0002] Lemon yellow is a water-soluble synthetic pigment, also known as tartrate yellow, acid light yellow, and hydrazine yellow. Its chemical name is 1-(4-sulfonate phenyl)-4-(4-sulfonate phenylazo)-5-pyrazolone-3-carboxylic acid trisodium salt. It can be safely used for coloring food, beverages, medicines, cosmetics, feed, tobacco, toys, food packaging materials, etc. It is the most stable colorant.

[0003] At present, the production process of tartrazine is to carry out diazotization reaction of aminobenzenesulfonic acid to obtain two diazonium salts, and then add DMAS (dimethyl acetyl succinate) to one of the diazonium salts, and carry out condensation reaction by adjusting the pH value of the solution. The obtained condensation liquid is coupled with the other diazonium salt, and then the product is obtained through hydrolysis, salting out, filtration and drying.

[0004] However, the production process of lemon yellow involves the diazotization reaction of sodium p-aminobenzenesulfonate. The diazonium salt is unstable and may decompose or even explode under high temperature, friction, impact, etc. Therefore, the traditional intermittent diazotization process usually slows down the reaction speed of diazotization, which greatly increases the reaction time and still has certain risks. In addition, two portions of diazonium salt need to be prepared and used separately during production, and the two diazotization reactions are more risky. It is difficult to keep the raw material amount and output material concentration of the two reactions consistent, which affects the product quality.

[0005] The condensation reaction of diazonium salt and dimethyl acetosuccinate also has some problems. The pH value of the condensation liquid needs to be adjusted during the condensation reaction. The intermittent process is prone to self-coupling reaction due to reasons such as long residence time and insufficient material mixing, resulting in lower purity of the condensation liquid, affecting the next coupling reaction and lowering the final product yield.

[0006] Based on this, there is an urgent need to provide a method for synthesizing tartrazine with high purity, high yield and high safety. Summary of the invention

[0007] The object of the present invention is to provide a method for synthesizing tartrazine by microchannel continuous flow, so as to solve the technical problems of low purity and yield of tartrazine, high risk in the production process and long reaction time in the prior art.

[0008] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0009] The present invention provides a method for synthesizing tartrazine by microchannel continuous flow, comprising the following steps:

[0010] (1) dissolving sodium p-aminobenzenesulfonate and sodium nitrite in water to obtain a mixed solution, and then passing the mixed solution and hydrochloric acid solution into a micro mixer 1 for diazotization reaction, and after passing through the tubular reactor 1, obtaining a diazotization reaction solution A;

[0011] (2) introducing the diazotization reaction solution A and dimethyl acetyl succinate into a micro mixer 2 for mixing, and then continuously introducing the mixture with a soda ash solution into n microreactors connected in series, adjusting the pH value of the mixed solution step by step to alkaline, and performing a condensation reaction to obtain a condensation reaction solution, wherein n≥3;

[0012] (3) dissolving sodium p-aminobenzenesulfonate and sodium nitrite in water to obtain a mixed solution, then passing the mixed solution and hydrochloric acid solution into a micro mixer 3 for diazotization reaction, and after passing through a tubular reactor 2, obtaining a diazotization reaction liquid B, and then passing the condensation reaction liquid and the diazotization reaction liquid B into a micro mixer 4 for coupling reaction, and after passing through a tubular reactor 3, obtaining a coupling liquid;

[0013] (4) The coupling liquid and solid soda ash are mixed and heated to hydrolyze to obtain tartrazine.

[0014] Further, the micromixer 1, micromixer 2, micromixer 3 and micromixer 4 are independently T-type microchannel mixers or Y-type microchannel mixers;

[0015] The inner diameters of the tubular reactor 1, tubular reactor 2 and tubular reactor 3 are independently 1 to 3 mm, and the lengths are independently 1 to 3 m.

[0016] Further, the microreactor 1, microreactor 2, microreactor 3, microreactor 4 and microreactor n are plate-type microreactors, wherein the flow rate ratio of the nitriding reaction solution A and the soda ash solution in the microreactor is 15 to 20:1;

[0017] The residence time of each microreactor is independently 5 to 20 seconds, and the temperature of the condensation reaction is 10 to 30°C.

[0018] Further, the micro-mixer 1, tubular reactor 1, micro-mixer 2, micro-reactor 1, micro-reactor 2, micro-reactor 3, micro-reactor 4 and micro-reactor n are sequentially connected in series in a closed manner;

[0019] The micro mixer 3, tubular reactor 2, micro mixer 4 and tubular reactor 3 are sequentially connected in series in a closed manner;

[0020] The microreactor n, micromixer 4 and tubular reactor 3 are connected in series in a closed manner.

[0021] Furthermore, in the step (1) and the step (3), the feed rate of the mixed solution is independently 20 to 30 mL / min, and the feed rate of the hydrochloric acid solution is independently 7 to 12 mL / min;

[0022] The concentration of sodium p-aminobenzenesulfonate in the mixed solution is independently 3-12 wt %, and the concentration of sodium nitrite in the mixed solution is independently 1-4 wt %;

[0023] The concentration of the hydrochloric acid solution before dilution is independently 37%, and the concentration after dilution is independently 3-8%; the molar ratio of the hydrochloric acid solution to sodium p-aminobenzenesulfonate is 2-3:1.

[0024] Furthermore, the purity of the dimethyl acetyl succinate is 97.5-99.5 wt %, and the feed rate is 0.5-1.5 mL / min;

[0025] The molar ratio of dimethyl acetylsuccinate to sodium p-aminobenzenesulfonate is 0.95-1.05:1.

[0026] Furthermore, in the steps (2) and (4), the concentration of the soda ash solution is independently 5 to 20 wt%, and the feed rate is independently 1.8 to 2.5 mL / min;

[0027] The feed molar ratio of sodium p-aminobenzenesulfonate in the condensation reaction solution and the diazonium salt solution B is 0.5-2:0.5-2.

[0028] Furthermore, in the step (1) and the step (3), the time of the diazotization reaction is independently 5 to 30 seconds, and the temperature of the diazotization reaction is independently 5 to 45°C.

[0029] Furthermore, the mass ratio of the coupling liquid to solid soda ash is 4 to 6:1.

[0030] Furthermore, the temperature of the heating hydrolysis is 60-80° C., the time of the heating hydrolysis is 1-2 hours, and the pH of the heating hydrolysis is 8-9.

[0031] Beneficial effects of the present invention:

[0032] (1) The present invention utilizes microreactor continuous flow reaction technology. The amount of chemical raw materials remaining in the microreactor is very small, and the volume of the reactants is very small. Even if the reaction is out of control, the degree of harm is greatly reduced.

[0033] (2) The microreactor used in the method of the present invention has extremely high heat exchange efficiency. During the diazotization reaction, even if a large amount of reaction heat is suddenly released, it can be quickly discharged, thereby ensuring the stability of the reaction temperature, reducing the possibility of safety and quality accidents, and achieving safe and efficient production;

[0034] (3) The method of the present invention can accurately and quickly mix the materials according to the material ratio, and the properties of the two prepared diazonium salt solutions are basically the same, thereby avoiding the formation of by-products;

[0035] (4) The method of the present invention connects diazotization reaction, condensation reaction and coupling reaction in series, which can realize continuous production, greatly shorten the reaction time, save manpower, improve reaction efficiency and increase production capacity;

[0036] (5) In the method of the present invention, in the condensation reaction step, the method of using microreactors in series to gradually increase the pH value of the condensation liquid can effectively avoid the self-coupling reaction of the condensation liquid, improve the purity of the condensation liquid, and further improve the yield of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 The present invention is a process flow chart for synthesizing tartrazine. DETAILED DESCRIPTION

[0038] The present invention provides a method for synthesizing tartrazine by microchannel continuous flow, comprising the following steps:

[0039] (1) dissolving sodium p-aminobenzenesulfonate and sodium nitrite in water to obtain a mixed solution, and then passing the mixed solution and hydrochloric acid solution into a micro mixer 1 for diazotization reaction, and after passing through the tubular reactor 1, obtaining a diazotization reaction solution A;

[0040] (2) introducing the diazotization reaction solution A and dimethyl acetyl succinate into a micro mixer 2 for mixing, and then continuously introducing the mixture with a soda ash solution into n microreactors connected in series, adjusting the pH value of the mixed solution step by step to alkaline, and performing a condensation reaction to obtain a condensation reaction solution, wherein n≥3;

[0041] (3) dissolving sodium p-aminobenzenesulfonate and sodium nitrite in water to obtain a mixed solution, then passing the mixed solution and hydrochloric acid solution into a micro mixer 3 for diazotization reaction, and after passing through a tubular reactor 2, obtaining a diazotization reaction liquid B, and then passing the condensation reaction liquid and the diazotization reaction liquid B into a micro mixer 4 for coupling reaction, and after passing through a tubular reactor 3, obtaining a coupling liquid;

[0042] (4) The coupling liquid and solid soda ash are mixed and heated to hydrolyze to obtain tartrazine.

[0043] In the present invention, the number n of microreactors is preferably 3, 4, 5, 6 or 7, and more preferably 5.

[0044] In the present invention, when n is 3, the pH values ​​of the condensation reaction solution are controlled at 3.0-4.0, 4.0-5.0 and 7.5-8.5 in microreactor 1, microreactor 2 and microreactor 3, respectively.

[0045] In the present invention, when n is 5, the pH values ​​of the condensation reaction liquid are controlled at 2.0-2.5, 3.0-3.5, 3.5-4.0, 4.5-5.0, and 7.5-8.5 in microreactor 1, microreactor 2, microreactor 3, microreactor 4, and microreactor 5, respectively.

[0046] In the present invention, when n is 7, the pH value of the condensation reaction liquid is controlled at 2.0-2.5, 2.5-3.0, 3.0-3.5, 3.5-4.0, 4.0-4.5, 4.5-5.0, and 7.5-8.5 in microreactor 1, microreactor 2, microreactor 3, microreactor 4, microreactor 5, microreactor 6, and microreactor 7, respectively.

[0047] In the present invention, the micromixer 1, micromixer 2, micromixer 3 and micromixer 4 are independently T-type microchannel mixers or Y-type microchannel mixers, preferably T-type microchannel mixers.

[0048] In the present invention, the inner diameters of the tubular reactor 1, tubular reactor 2 and tubular reactor 3 are independently 1 to 3 mm, preferably 1.5 to 2.5 mm, and more preferably 2 mm; the lengths are independently 1 to 3 m, preferably 1.2 to 2.8 m, and more preferably 1.5 to 2.5 m.

[0049] In the present invention, the microreactor 1, microreactor 2, microreactor 3, microreactor 4 and microreactor n are respectively plate-type microreactors, wherein the flow rate ratio of the nitriding reaction liquid A and the soda ash solution in the microreactor is 15 to 20:1; and the plate-type microreactor is a heart-shaped structure.

[0050] In the present invention, the residence time of each microreactor is independently 5 to 20 s, preferably 8 to 18 s, and more preferably 10 to 15 s; the temperature of the condensation reaction is 10 to 30°C, preferably 12 to 28°C, and more preferably 15 to 25°C.

[0051] In the present invention, the micro-mixer 1, tubular reactor 1, micro-mixer 2, micro-reactor 1, micro-reactor 2, micro-reactor 3, micro-reactor 4 and micro-reactor n are sequentially connected in series in a closed manner;

[0052] The micro mixer 3, tubular reactor 2, micro mixer 4 and tubular reactor 3 are sequentially connected in series in a closed manner;

[0053] The microreactor n, micromixer 4 and tubular reactor 3 are connected in series in a closed manner.

[0054] In the present invention, in step (1) and step (3), the feed rate of the mixed solution is independently 20 to 30 mL / min, preferably 22 to 28 mL / min, and more preferably 25 mL / min; the feed rate of the hydrochloric acid solution is independently 7 to 12 mL / min, preferably 8 to 11 mL / min, and more preferably 9 to 10 mL / min.

[0055] In the present invention, the concentration of sodium p-aminobenzenesulfonate in the mixed solution is independently 3 to 12 wt%, preferably 4 to 10 wt%, and more preferably 5 to 8 wt%; the concentration of sodium nitrite in the mixed solution is independently 1 to 4 wt%, preferably 1.5 to 3.5 wt%, and more preferably 2 to 3 wt%;

[0056] The concentration of the hydrochloric acid solution before dilution is independently 37%, and the concentration after dilution is independently 3-8%, preferably 3.5-7.5%, and more preferably 4-7%; the molar ratio of the hydrochloric acid solution to sodium p-aminobenzenesulfonate is 2-3:1, preferably 2.1-2.8:1, and more preferably 2.2-2.5:1.

[0057] In the present invention, the purity of dimethyl acetyl succinate is 97.5-99.5wt%, preferably 98-99wt%, and more preferably 98.5wt%; the feed rate is 0.5-1.5mL / min, preferably 0.7-1.2mL / min, and more preferably 0.9-1mL / min.

[0058] In the present invention, the molar ratio of dimethyl acetylsuccinate to sodium p-aminobenzenesulfonate is 0.95-1.05:1, preferably 0.98-1.03:1, and more preferably 1:1.

[0059] In the present invention, in step (2) and step (4), the concentration of the soda ash solution is independently 5 to 20 wt%, preferably 8 to 15 wt%, and more preferably 10 wt%; the feed rate is independently 1.8 to 2.5 mL / min, preferably 1.9 to 2.4 mL / min, and more preferably 2 to 2.3 mL / min.

[0060] In the present invention, the molar ratio of the sodium p-aminobenzenesulfonate in the condensation reaction solution and the diazonium salt solution B is 0.5-2:0.5-2, preferably 0.8-1.5:0.8-1.5, and more preferably 1:1.

[0061] In the present invention, in the step (1) and the step (3), the time of the diazotization reaction is independently 5 to 30 seconds, preferably 7 to 25 seconds, and more preferably 10 to 20 seconds; the temperature of the diazotization reaction is independently 5 to 45°C, preferably 10 to 40°C, and more preferably 15 to 35°C.

[0062] In the present invention, the mass ratio of the coupling liquid to solid soda ash is 4-6:1, preferably 4.5-5.5:1, and more preferably 5.2:1.

[0063] In the present invention, the temperature of the heating hydrolysis is 60-80°C, preferably 65-75°C, and more preferably 70°C; the time of the heating hydrolysis is 1-2h, preferably 1.2-1.8h, and more preferably 1.5h; the pH of the heating hydrolysis is 8-9, preferably 8.2-8.9, and more preferably 8.5-8.8.

[0064] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0065] Example 1

[0066] 37.5 g of sodium p-aminobenzenesulfonate and 11.36 g of sodium nitrite are dissolved in 700 g of water to obtain a mixed solution, 36 g of hydrochloric acid with a concentration of 37% is added to 230 g of water for dilution to obtain a diluted hydrochloric acid solution, and then the mixed solution and the diluted hydrochloric acid solution are passed into a micro mixer 1 (micro mixer 1 is a T-type microchannel mixer) for diazotization reaction, and passed through a tubular reactor 1 (tubular reactor 1 has an inner diameter of 2 mm and a length of 2 m), wherein the mixed solution feed rate is 25 mL / min, the hydrochloric acid solution feed rate is 9 mL / min, the diazotization reaction time is 13 s, and the diazotization reaction temperature is 20° C. to obtain a diazotization reaction solution A;

[0067] The diazotization reaction liquid A and dimethyl acetyl succinate with a purity of 98.5% are introduced into a micromixer 2 (micromixer 2 is a T-type microchannel mixer) for mixing, wherein the feeding rate of dimethyl acetyl succinate is 0.9 mL / min, and the molar ratio of dimethyl acetyl succinate to sodium para-aminobenzenesulfonate is 1:1, and then continuously introduced into three microreactors in series with a soda ash solution with a concentration of 10 wt% for condensation reaction, wherein the feeding rates of the soda ash solution in microreactor 1, microreactor 2, and microreactor 3 are 2.0 mL / min, 1.8 mL / min, and 2.5 mL / min, respectively, the residence time of the condensation reaction liquid in microreactors 1, 2, and 3 are 20 s, 20 s, and 10 s, respectively, and the pH value of the condensation reaction liquid is controlled at 3.5, 4.5, and 8 in microreactors 1, 2, and 3, respectively, and finally the condensation reaction liquid is obtained through microreactor 3;

[0068] 37.5 g of sodium p-aminobenzenesulfonate and 11.36 g of sodium nitrite are dissolved in 700 g of water to obtain a mixed solution, 36 g of hydrochloric acid with a concentration of 37% is added to 230 g of water for dilution to obtain a diluted hydrochloric acid solution, and then the mixed solution and the diluted hydrochloric acid solution are passed into a micro mixer 3 (micro mixer 3 is a T-type microchannel mixer) for diazotization reaction, and passed through a tubular reactor 2 (the tubular reactor 2 has an inner diameter of 2 mm and a length of 2 m), wherein the mixed solution feed rate is 25 mL / min, the hydrochloric acid solution feed rate is 9 mL / min, the diazotization reaction time is 13 s, and the diazotization reaction temperature is 20° C. to obtain a diazotization reaction solution B;

[0069] The condensation reaction liquid and the diazotization reaction liquid B are introduced into a micro mixer 4 (the micro mixer 4 is a T-type microchannel mixer) for coupling reaction, and after passing through a tubular reactor 3 (the tubular reactor 3 has an inner diameter of 2 mm and a length of 2 m), the coupling reaction temperature is 20° C., the coupling reaction time is 12 s, and a coupling liquid is obtained;

[0070] The coupling liquid and solid soda ash were mixed, the pH of the solution was adjusted to 8.8, and then heated to hydrolyze at 75°C for 1 h to obtain lemon yellow.

[0071] The tartrazine prepared in Example 1 was subjected to HPLC liquid phase analysis to determine the content of the hydrolyzate, and the yield was calculated. The yield was calculated as follows: (hydrolyzate content % × hydrolyzate mass g / tartrazine molecular weight) / (mass of sodium p-aminobenzenesulfonate / molecular weight of sodium p-aminobenzenesulfonate) × 100%, and the yield of tartrazine in Example 1 was 96.5%.

[0072] Example 2

[0073] Compared with Example 1, the difference is that Example 2 uses 5 microreactors connected in series, wherein the feed rates of soda ash solution in microreactors 1, 2, 3, 4, and 5 are 1.5 mL / min, 0.8 mL / min, 0.8 mL / min, 1.2 mL / min, and 2.5 mL / min, respectively, and the residence time of the condensation reaction liquid in microreactors 1, 2, 3, 4, and 5 are 20 s, 20 s, 20 s, 20 s, and 10 s, respectively, and the pH value of the condensation reaction liquid is controlled at 2.0, 3.2, 3.8, 4.8, and 7.8 in microreactors 1, 2, 3, 4, and 5, respectively.

[0074] The yield of lemon yellow in Example 2 was calculated in the same manner as in Example 1. The yield of lemon yellow prepared in Example 2 was 97.3%.

[0075] Example 3

[0076] Compared with Example 1, the difference is that Example 3 uses 7 microreactors connected in series, wherein the feed rates of soda ash solution in microreactors 1, 2, 3, 4, 5, 6, and 7 are 1.5 mL / min, 0.4 mL / min, 0.4 mL / min, 0.6 mL / min, 0.5 mL / min, 0.5 mL / min, and 2.5 mL / min, respectively, and the residence time of the condensation reaction liquid in microreactors 1, 2, 3, 4, 5, 6, and 7 are 20 s, 20 s, 20 s, 20 s, 20 s, 20 s, and 10 s, respectively, and the pH value of the condensation reaction liquid is controlled at 2.0, 2.5, 3.2, 3.8, 4.2, 4.8, and 7.8 in microreactors 1, 2, 3, 4, 5, 6, and 7, respectively.

[0077] The yield of lemon yellow in Example 3 was calculated in the same manner as in Example 1. The yield of lemon yellow prepared in Example 3 was 97%.

[0078] Example 4

[0079] Compared with Example 2, the difference is that the temperature of the diazotization reaction in Example 4 is 45°C.

[0080] The yield of lemon yellow in Example 4 was calculated in the same manner as in Example 1. The yield of lemon yellow prepared in Example 4 was 96.2%.

[0081] Example 5

[0082] Compared with Example 2, the difference is that the coupling reaction temperature in Example 5 is 45°C.

[0083] The yield of lemon yellow in Example 5 was calculated in the same manner as in Example 1. The yield of lemon yellow prepared in Example 5 was 95.5%.

[0084] Comparative Example 1

[0085] Comparative Example 1: Tartrazine was prepared using a conventional batch process.

[0086] 37.5 g of sodium p-aminobenzenesulfonate was added to 100 g of water, and the temperature was raised to 40°C to fully dissolve it. Then 36 g of 37% hydrochloric acid was slowly added dropwise, and the temperature was lowered to 10°C after stirring for 30 min. 11.36 g of sodium nitrite was dissolved in 25 g of water, and the mixture was slowly added dropwise to the above reaction solution, and the temperature was controlled at 15°C. After the addition was completed, the mixture was kept warm and stirred for 1 hour to obtain diazotization reaction solution A.

[0087] Add 30.7 g of dimethyl acetosuccinate to the diazotization reaction solution A, stir evenly, and then slowly add a 15% soda ash solution, control the pH to be less than 5, and the temperature to be between 20°C. After the liquid is clarified, control the pH to be between 4.5-5.0. After keeping the temperature for 1 hour, add soda ash to adjust the solution pH to 8.0.

[0088] Add 37.5g of sodium p-aminobenzenesulfonate to 100g of water, heat to 40°C to fully dissolve it, then slowly drop 36g of 37% hydrochloric acid, stir for 30min and cool to 10°C; dissolve 11.36g of sodium nitrite in 25g of water, slowly drop into the previous reaction solution, control the temperature at 15°C, keep warm and stir for 1h after dropping, and diazotize reaction solution B;

[0089] The diazotization reaction liquid B was dropped into the condensation reaction liquid. The temperature was controlled at 30°C during the dropping process. After the dropping was completed, the mixture was kept warm and stirred for 2 hours to obtain a coupling liquid. 21.5 g of solid soda ash was added to the coupling liquid, the pH of the solution was adjusted to 8.7, and then heated and hydrolyzed at 75°C for 1 hour to obtain lemon yellow.

[0090] The yield of lemon yellow in Comparative Example 1 was calculated in the same manner as in Example 1. The yield of lemon yellow prepared in Comparative Example 1 was 92.1%.

[0091] Comparative Example 2

[0092] Compared with Example 1, the difference is that Comparative Example 2 uses 2 microreactors connected in series, the feed rates of the soda ash solution are 2.5 mL / min and 3.5 mL / min, respectively, the residence time of the condensation reaction liquid in each microreactor is 20 s and 15 s, respectively, and the pH value of the condensation reaction liquid is controlled at 3.5 and 7.8, respectively.

[0093] The yield of lemon yellow in Comparative Example 2 was calculated in the same manner as in Example 1. The yield of lemon yellow prepared in Comparative Example 2 was 92.8%.

[0094] It can be seen from Examples 1 to 3 and Comparative Example 2 that in the process of adjusting the pH value of the condensation liquid, the more the number of microreactors, the smaller the pH value rising gradient, and under the appropriate residence time, the more stable the condensation reaction, the higher the purity of the condensation liquid. In the intermittent condensation reaction process, the condensation liquid that has completed the condensation reaction in the same reactor is easy to self-couple with the unreacted diazonium salt solution, causing the purity of the condensation liquid to decrease, and the microchannel continuous flow process can be efficiently mixed in the microreactor, quickly complete the condensation reaction and immediately pass it to the next reactor, which can effectively avoid its self-coupling reaction. However, when the number of micro-mixers n = 7, compared with n = 5, the purity of the condensation liquid is not further improved, and the final yield of the lemon yellow hydrolyzate is also relatively low. This is because the increase in the number of reactors causes the condensation liquid residence time to become longer, and there are by-products generated. Considering that the increase in the number of microreactors will cause an increase in production costs, therefore, in the process of adjusting the pH value of the condensation liquid, the number of microreactors n = 5 is the optimal process.

[0095] It can be seen from Examples 2 and 4-5 that temperature has an effect on both the diazotization reaction and the coupling reaction. Although a higher temperature can accelerate the reaction rate, by-products will be generated, affecting the final product yield.

[0096] As can be seen from the above embodiments, the present invention provides a method for synthesizing lemon yellow by microchannel continuous flow. The yield of lemon yellow synthesized by the microchannel continuous flow method of the present invention is significantly higher than that of the batch process. Thanks to the large heat exchange area of ​​each reactor in the microchannel continuous process, the reaction temperature can be accurately controlled, the reaction hot spots are eliminated, and the reaction is always in a stable state, while the intermittent drip method has a local temperature over-high phenomenon, and a small amount of by-products are generated, thereby affecting the product purity. In addition, in the process of diazotization and coupling reaction, the microchannel process can accurately and quickly mix the materials, effectively avoiding the generation of by-products, thereby improving the product purity and the yield. Compared with the batch process of the batch process, the present invention is not only improved in the final yield of the product, but more importantly, for the strongly exothermic diazotization reaction, the extremely large specific surface area of ​​the microchannel equipment gives the microreactor a great heat exchange efficiency, and the temperature of the reaction system is timely regulated, and the total liquid holding capacity is less, reducing the possibility of safety and quality accidents, and realizing safe and efficient production; in addition, the microreactor is small in size, the supporting equipment occupies a small area, saves space, and the continuous process can be equipped with an intelligent control system to realize online operation and save manpower.

[0097] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for synthesizing tartrazine by microchannel continuous flow, characterized in that: The following steps are involved: (1) dissolving sodium p-aminobenzenesulfonate and sodium nitrite in water to obtain a mixed solution, and then passing the mixed solution and hydrochloric acid solution into a micro mixer 1 for diazotization reaction, and after passing through the tubular reactor 1, obtaining a diazotization reaction solution A; (2) introducing the diazotization reaction solution A and dimethyl acetyl succinate into a micro mixer 2 for mixing, and then continuously introducing the mixture with a soda ash solution into n microreactors connected in series, adjusting the pH value of the mixed solution step by step to alkaline, and performing a condensation reaction to obtain a condensation reaction solution, wherein n≥3; (3) dissolving sodium p-aminobenzenesulfonate and sodium nitrite in water to obtain a mixed solution, then passing the mixed solution and hydrochloric acid solution into a micro mixer 3 for diazotization reaction, and after passing through a tubular reactor 2, obtaining a diazotization reaction liquid B, and then passing the condensation reaction liquid and the diazotization reaction liquid B into a micro mixer 4 for coupling reaction, and after passing through a tubular reactor 3, obtaining a coupling liquid; (4) The coupling liquid and solid soda ash are mixed and heated to hydrolyze to obtain tartrazine.

2. The method for synthesizing lemon yellow by microchannel continuous flow according to claim 1, characterized in that: The micromixer 1, micromixer 2, micromixer 3 and micromixer 4 are independently T-type microchannel mixers or Y-type microchannel mixers; The inner diameters of the tubular reactor 1, tubular reactor 2 and tubular reactor 3 are independently 1 to 3 mm, and the lengths are independently 1 to 3 m.

3. The method for synthesizing lemon yellow by microchannel continuous flow according to claim 1 or 2, characterized in that: The microreactor 1, microreactor 2, microreactor 3, microreactor 4 and microreactor n are plate-type microreactors, wherein the flow rate ratio of the nitriding reaction solution A and the soda ash solution in the microreactor is 15-20:1; The residence time of each microreactor is independently 5 to 20 seconds, and the temperature of the condensation reaction is 10 to 30°C.

4. The method for synthesizing lemon yellow by microchannel continuous flow according to claim 1, characterized in that: The micro-mixer 1, tubular reactor 1, micro-mixer 2, micro-reactor 1, micro-reactor 2, micro-reactor 3, micro-reactor 4 and micro-reactor n are connected in series in a closed manner in sequence; The micro mixer 3, tubular reactor 2, microreactor 4 and tubular reactor 3 are connected in series in a closed manner; The microreactor n, micromixer 4 and tubular reactor 3 are connected in series in a closed manner.

5. The method for synthesizing lemon yellow by microchannel continuous flow according to claim 4, characterized in that: In the steps (1) and (3), the feed rate of the mixed solution is independently 20 to 30 mL / min, and the feed rate of the hydrochloric acid solution is independently 7 to 12 mL / min; The concentration of sodium p-aminobenzenesulfonate in the mixed solution is independently 3-12 wt %, and the concentration of sodium nitrite in the mixed solution is independently 1-4 wt %; The concentration of the hydrochloric acid solution before dilution is independently 37%, and the concentration after dilution is independently 3-8%; the molar ratio of the hydrochloric acid solution to sodium p-aminobenzenesulfonate is 2-3:

1.

6. The method for synthesizing lemon yellow by microchannel continuous flow according to claim 1, characterized in that: The purity of the dimethyl acetyl succinate is 97.5-99.5 wt %, and the feed rate is 0.5-1.5 mL / min; The molar ratio of dimethyl acetylsuccinate to sodium p-aminobenzenesulfonate is 0.95-1.05:

1.

7. The method for synthesizing lemon yellow by microchannel continuous flow according to claim 6, characterized in that: In the steps (2) and (4), the concentration of the soda ash solution is independently 5 to 20 wt %, and the feed rate is independently 1.8 to 2.5 mL / min; The feed molar ratio of sodium p-aminobenzenesulfonate in the condensation reaction solution and the diazonium salt solution B is 0.5-2:0.5-2.

8. The method for synthesizing lemon yellow by microchannel continuous flow according to claim 7, characterized in that: In the step (1) and the step (3), the time of the diazotization reaction is independently 5 to 30 seconds, and the temperature of the diazotization reaction is independently 5 to 45°C.

9. The method for synthesizing tartrazine by microchannel continuous flow according to claim 8, characterized in that: The mass ratio of the coupling liquid to solid soda ash is 4-6:

1.

10. The method for synthesizing tartrazine by microchannel continuous flow according to claim 8, characterized in that: The temperature of the heating hydrolysis is 60-80° C., the time of the heating hydrolysis is 1-2 hours, and the pH of the heating hydrolysis is 8-9.

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