Preparation method of long-chain alkyl succinic amide disodium sulfonate

Abstract

The invention discloses a preparation method of long-chain alkyl succinic amide disodium sulfonate.The preparation method comprises the steps that after long-chain primary amine is molten, a composite catalyst is added into the long-chain primary amine, the composite catalyst comprises a component 1 and a component 2, the component 1 is composed of one or more of triethylamine, pyridine, imidazole and N-methylimidazole, and the component 2 is composed of one or more of triethylamine, pyridine, imidazole and N-methylimidazole; the component 2 is composed of one or more of the following substances: sodium acetate, sodium carbonate and trisodium phosphate; the preparation method comprises the following steps: firstly, adding maleic anhydride into a reaction kettle, slowly adding a maleic anhydride solid into the reaction kettle, violently stirring, slowly adding a sodium sulfite aqueous solution into the reaction kettle after the reaction is completed, and obtaining the long-chain alkyl succinic amide disodium sulfonate after the reaction is completed, and the system temperature in the whole reaction process does not exceed 90 DEG C. By adding the composite catalyst, the reaction activity of reactants is enhanced, the reaction temperature is reduced, the sublimation problem of maleic anhydride is avoided, side reactions and high-melting-point compounds are inhibited, and the reaction selectivity and the purity and yield of the product are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of organic synthesis, and more specifically to a method for preparing disodium long-chain alkyl succinamide sulfonate. Background Art

[0002] The preparation of long-chain alkyl succinamide sulfonic acid disodium is mainly divided into two steps. The first step is the amidation reaction, and the reaction equation is: CH3(CH2) R NH2+C4H2O3→CH3(CH2) R -NH-CO-CH=CH-COOH; Where R = 13 to 19, the reaction has the following characteristics: (1) Both long-chain primary amines and maleic anhydride are solids with melting points of 50 to 60°C. The reaction requires the addition of a solvent or is carried out in a molten state, and maleic anhydride has a strong sublimation property; (2) A large amount of heat is released instantaneously after the two are mixed; (3) The reaction product is a solid with a melting point of around 80°C; (4) When the long-chain primary amine is in excess, a hard waxy solid with a melting point exceeding 120°C is generated.

[0003] The second step is an addition reaction, and the reaction equation is as follows: CH3(CH2) R -NH-CO-CH=CH-COOH+Na2SO3→CH3(CH2) R -NH-CO-CHSO3 - Na + -CH3-COO - Na + ; Wherein R=13~19, the reaction has the following characteristics: (1) a small amount of heat is released when the two are just mixed, and the reaction is heated in the later stage; (2) the product is a stable white to light yellow suspension. If the reaction conversion rate is not high or the impurity content is high, water will precipitate and stratification will occur.

[0004] According to the characteristics of the preparation reaction of long-chain alkyl succinamide sulfonic acid disodium, the reaction in the first step has the greatest impact on product quality. The existing processes mainly include the solvent method and the melting method. Among them, the solvent method mainly uses acetone or toluene as a solvent to dissolve the two solid raw materials and then conduct a homogeneous reaction. After the reaction is completed, the solvent is removed and the second step reaction is carried out. The reaction conditions of this method are mild, generally below 80°C, which can prevent the occurrence of side reactions. At the same time, the final product has a good color, generally white. However, this method requires the use of flammable, toxic and volatile solvents such as acetone and toluene, which poses a great safety hazard during production. At the same time, after the reaction is completed, the acetone, toluene and other solvents need to be removed, which requires additional energy and time. In addition, the organic solvents will remain in the product because they are difficult to completely remove, which will not only produce odor but also limit the application range of the product.

[0005] The melting method does not require the use of a solvent. After melting two solid raw materials, a long-chain primary amine is slowly added dropwise to maleic anhydride. The reaction is carried out at a high temperature of 100-120°C. After the reaction is completed, the temperature is lowered to proceed to the second step. For example, Chinese patent CN105037219A discloses a method for synthesizing disodium alkyl succinamic acid sulfonate. The method uses maleic anhydride, primary amine, and sodium metabisulfite as the reaction raw materials. Maleic anhydride is first added to a reactor, and then the pre-melted primary amine is poured into a dropping funnel. Stirring is started, and the primary amine is slowly added to the reactor. The temperature is controlled not to exceed 110°C. The reaction is maintained for 2-4 hours to obtain an intermediate. The sodium metabisulfite is then dissolved in water, adjusted to pH 7-8 with caustic soda, and heated to 70-80°C to obtain a sodium metabisulfite solution. Finally, the intermediate is heated to 110-120°C and stirred and added to the sodium metabisulfite solution. The temperature is controlled at 85-95°C and the stirring reaction is maintained for 3-5 hours to obtain the target product.

[0006] However, this method also has some defects: (1) Maleic anhydride has a significant sublimation effect at high temperature, so a large excess is required, and the impurity content in the product will be higher; (2) Excessively high reaction temperature will induce side reactions such as self-polymerization and oxidation of maleic anhydride; (3) The final product has a poor color, mostly yellow; (4) A hard solid with a high melting point may be generated during the reaction, which poses a risk of stirring jam. Summary of the Invention

[0007] In view of the deficiencies in the prior art, the present invention provides a method for preparing disodium long-chain alkyl succinamide sulfonate, which allows the reaction to be carried out at a relatively low temperature, avoids the sublimation problem of maleic anhydride and the generation of high-melting-point compounds, and improves product quality and yield.

[0008] The present invention provides a method for preparing disodium long-chain alkyl succinamide sulfonate, comprising the following steps: (1) adding a long-chain primary amine into a reactor and melting it, and then adding a composite catalyst thereto after the long-chain primary amine is melted, wherein the composite catalyst comprises component 1 and component 2, wherein component 1 is composed of one or more of the following substances: triethylamine, pyridine, imidazole, and N-methylimidazole, and component 2 is composed of one or more of the following substances: sodium acetate, sodium carbonate, and trisodium phosphate; (2) Then, slowly add maleic anhydride solid to the reactor and stir vigorously. The system temperature does not exceed 90°C during the whole process. After the maleic anhydride is added, keep it at 80-90°C for 3-5 hours; (3) Then, slowly add the sodium sulfite aqueous solution to the reactor, and keep the system temperature below 90° C. during the whole process. After the sodium sulfite aqueous solution is added, keep the temperature at 80-90° C. for 6-9 hours to obtain long-chain alkyl succinamide sulfonic acid disodium.

[0009] The present invention prepares long-chain alkyl succinamide sulfonic acid disodium by a melting method, does not use an organic solvent, does not require additional removal of the organic solvent, and does not cause organic solvent residues in the product. At the same time, the preparation of long-chain alkyl succinamide sulfonic acid disodium is divided into two steps. The first step is an amidation reaction to generate an amide intermediate. Before the reaction begins, the present invention adds a composite catalyst to the melted long-chain primary amine, wherein component 1 in the composite catalyst is a strong proton acceptor, which can capture hydrogen ions generated by the reaction to prevent them from affecting the reaction activity after combining with the raw materials, thereby improving the yield of the amide intermediate. Component 2 in the composite catalyst is a stabilizer, which can reduce the color change and property change of the product caused by the strong proton acceptor. In addition, the composite catalyst captures the protons generated in the reaction, and also avoids the reaction of excess long-chain primary amine with the amide intermediate to generate a high melting point compound, ensuring that the entire reaction process is carried out in a homogeneous state, solving the risk problem of stuck stirring during the reaction and the problem of uneven reaction caused by it.

[0010] At the same time, the addition of the composite catalyst enables the reaction to proceed better at a relatively low temperature, and the reaction temperature does not exceed 90°C, thereby avoiding the sublimation of maleic anhydride at high temperature and the occurrence of side reactions such as self-polymerization and oxidation of maleic anhydride, inhibiting the formation of impurities, and improving the purity and yield of the product.

[0011] Moreover, maleic anhydride is easy to sublime, while long-chain primary amines are not easy to volatilize. The conventional method is to drop the melted long-chain primary amine into the melted maleic anhydride to avoid the excessive long-chain primary amine and amide intermediate from forming a high-melting-point compound, but this will lead to severe sublimation of the maleic anhydride. The present invention first adds a composite catalyst to the melted long-chain primary amine, and then slowly adds maleic anhydride solid. This not only allows the composite catalyst to fully exert its role in enhancing the reactivity of the reactants and inhibiting the formation of impurities such as high-melting-point compounds, but also provides a stable liquid-phase reaction environment for maleic anhydride. Maleic anhydride is wrapped by the long-chain primary amine and rapidly undergoes an amidation reaction. Maleic anhydride and the long-chain primary amine are continuously and stably consumed during the reaction, so that the number of free maleic anhydride molecules in the system is continuously reduced by reaction, and it is difficult for the free maleic anhydride molecules to leave the system, thereby inhibiting the sublimation of maleic anhydride.

[0012] In the composite catalyst of the present invention, component 1 is a strong proton acceptor, and the amount of the component 1 accounts for 20% to 50% of the amount of the composite catalyst. If the amount is less than 20%, the protons cannot be completely captured, and if the amount is greater than 50%, the color, viscosity and other properties will be changed. Component 2 is a stabilizer, and the amount of the component 2 accounts for 50% to 80% of the amount of the composite catalyst. If the amount is less than 50%, the stabilizer may not fully play its role and effectively reduce the color change and property change of the product caused by the strong proton acceptor. If the amount is greater than 80%, some active sites of the strong proton acceptor may be covered, thereby inhibiting the effect of the strong proton acceptor.

[0013] The amount of the composite catalyst added is 0.5 to 1.1 times the amount of maleic anhydride. If the amount of the composite catalyst added is too small, the reaction activity of the reactants cannot be effectively enhanced, and side reactions and the generation of high-melting-point compounds cannot be suppressed, resulting in low product purity and yield. If the amount of the composite catalyst added is too large, some side reactions may be triggered, resulting in the generation of impurities, thereby reducing product purity and affecting product yield. Therefore, an appropriate amount of catalyst can fully absorb the protons generated in the reaction, improve the reaction conversion rate, and avoid the generation of high-melting-point compounds, thereby improving product purity and yield. The melting point of the long-chain primary amine is 50 to 70°C.

[0014] The molar ratio of the long-chain primary amine to the maleic anhydride is 1:1-1.15.

[0015] The amount of sodium sulfite added is 1 to 1.2 times the amount of maleic anhydride.

[0016] The present invention adds a composite catalyst composed of a strong proton acceptor and a stabilizer to the melted long-chain primary amine before the reaction begins, which can capture protons generated by the reaction and improve the reaction activity. At the same time, it also avoids the reaction of excessive long-chain primary amine with the amide intermediate to generate a high-melting-point compound, ensures that the entire reaction process is carried out in a homogeneous state, solves the risk of stuck stirring during the reaction process and the problem of uneven reaction caused by the problem, improves the yield and quality of the amide intermediate, and thus improves the yield and quality of the long-chain alkyl succinamide sulfonic acid disodium; the addition of the composite catalyst also makes the reaction The process is carried out at a relatively low temperature, thereby avoiding the sublimation of maleic anhydride and the occurrence of side reactions such as self-polymerization and oxidation of maleic anhydride at high temperatures, suppressing the generation of impurities, and improving the selectivity of the reaction as well as the purity and yield of the product. At the same time, the slow addition of maleic anhydride solid to the molten long-chain primary amine can further avoid the sublimation problem of maleic anhydride, thereby ensuring the utilization rate of the reactants and the product yield. In addition, the method of the present invention adopts a melting method to prepare long-chain alkyl succinamide sulfonic acid disodium, does not use an organic solvent, does not require additional removal of the organic solvent, and does not cause residual organic solvent in the product. DETAILED DESCRIPTION

[0017] The embodiments of the present application will be described in more detail below. The present application can be implemented in various forms and should not be construed as being limited to the embodiments set forth herein. Instead, these embodiments are provided for a more thorough and complete understanding of the present application. It should be understood that the embodiments of the present application are intended for exemplary purposes only and are not intended to limit the scope of protection of the present application.

[0018] Example 1: Long-chain alkyl succinamide sulfonic acid disodium salt is prepared according to the following technical scheme, and the specific steps include: (1) 128 kg of hexadecylamine was added to a reactor and heated to 60° C. to melt. After the hexadecylamine was melted, a composite catalyst was added thereto, wherein component 1 of the composite catalyst was triethylamine, the amount of which accounted for 20% of the amount of the composite catalyst, and component 2 was trisodium phosphate, the amount of which accounted for 60% of the amount of the composite catalyst. The amount of the composite catalyst added was 0.5 times the amount of maleic anhydride. (2) Then, 52 kg of maleic anhydride was slowly added to the reactor. During the whole process, the system temperature was kept below 90°C while stirring vigorously. After the addition of maleic anhydride, the system temperature was kept below 90°C for 3 h while stirring vigorously. (3) Then, 767 kg of an 11% sodium sulfite aqueous solution was slowly added to the reactor. The system was stirred vigorously during the entire process and the temperature was kept below 90° C. After the sodium sulfite aqueous solution was added, the system was stirred vigorously and kept warm at 80° C. for 9 h to obtain disodium long-chain alkyl succinamide sulfonate.

[0019] Example 2: Long-chain alkyl succinamide sulfonic acid disodium salt is prepared according to the following technical scheme, and the specific steps include: (1) 135 kg of octadecylamine was added to a reactor and heated to 60° C. to melt. After the octadecylamine was melted, a composite catalyst was added thereto, wherein component 1 of the composite catalyst was triethylamine, the amount of which accounted for 20% of the amount of the composite catalyst, and component 2 was sodium acetate, the amount of which accounted for 80% of the amount of the composite catalyst. The amount of the composite catalyst added was 1.0 times the amount of maleic anhydride. (2) Then, 52 kg of maleic anhydride was slowly added to the reactor. The system temperature was kept below 90°C during the whole process while stirring vigorously. After the addition of maleic anhydride, the system temperature was kept below 80°C for 5 h while stirring vigorously. (3) Then, 767 kg of an 11% sodium sulfite aqueous solution was slowly added to the reactor. The system was stirred vigorously during the entire process and the temperature was kept below 90° C. After the sodium sulfite aqueous solution was added, the system was stirred vigorously and kept warm at 85° C. for 8 h to obtain disodium long-chain alkyl succinamide sulfonate.

[0020] Example 3: Long-chain alkyl succinamide sulfonic acid disodium salt is prepared according to the following technical scheme, and the specific steps include: (1) 142 kg of icosamine was added to a reactor and heated to 60° C. to melt. After the icosamine was melted, a composite catalyst was added thereto, wherein component 1 of the composite catalyst was pyridine, the amount of which accounted for 40% of the amount of the composite catalyst, and component 2 was sodium acetate, the amount of which accounted for 60% of the amount of the composite catalyst. The amount of the composite catalyst added was 1.1 times the amount of maleic anhydride. (2) Then, 52 kg of maleic anhydride was slowly added to the reactor. During the whole process, the system temperature was kept below 90°C while stirring vigorously. After the addition of maleic anhydride, the system temperature was kept below 90°C for 3 h while stirring vigorously. (3) Subsequently, 767 kg of an 11% sodium sulfite aqueous solution was slowly added to the reactor. The system temperature was kept below 90° C. while stirring vigorously during the entire process. After the sodium sulfite aqueous solution was added, the system was kept stirring vigorously and kept at 90° C. for 7 h to obtain disodium long-chain alkyl succinamide sulfonate.

[0021] Example 4: Long-chain alkyl succinamide sulfonic acid disodium salt is prepared according to the following technical scheme, and the specific steps include: (1) 135 kg of octadecylamine was added to a reactor and heated to 60° C. to melt. After the octadecylamine was melted, a composite catalyst was added thereto, wherein component 1 of the composite catalyst was a mixture of imidazole and N-methylimidazole, the amount of imidazole and N-methylimidazole respectively accounting for 20% of the amount of the composite catalyst, component 2 was trisodium phosphate, the amount of which accounted for 60% of the amount of the composite catalyst, and the amount of the composite catalyst added was 0.8 times the amount of maleic anhydride; (2) Then, 52 kg of maleic anhydride was slowly added to the reactor. The system temperature was kept below 90°C while stirring vigorously during the entire process. After the addition of maleic anhydride, the system temperature was kept below 85°C for 4 h while stirring vigorously. (3) Then, 767 kg of an 11% sodium sulfite aqueous solution was slowly added to the reactor. The system was stirred vigorously during the entire process and the temperature was kept below 90° C. After the sodium sulfite aqueous solution was added, the system was stirred vigorously and kept warm at 80° C. for 9 h to obtain disodium long-chain alkyl succinamide sulfonate.

[0022] Example 5: Long-chain alkyl succinamide sulfonic acid disodium salt is prepared according to the following technical scheme, and the specific steps include: (1) 135 kg of octadecylamine was added to a reactor and heated to 60° C. to melt. After the octadecylamine was melted, a composite catalyst was added thereto, wherein component 1 of the composite catalyst was a mixture of triethylamine, pyridine, imidazole and N-methylimidazole, and the amounts of triethylamine, pyridine, imidazole and N-methylimidazole accounted for 10%, 10%, 5% and 5% of the amount of the composite catalyst, respectively; component 2 was a mixture of trisodium phosphate, sodium carbonate and sodium acetate, and the amounts of trisodium phosphate, sodium carbonate and sodium acetate accounted for 40%, 10% and 20% of the amount of the composite catalyst, respectively; and the amount of the composite catalyst added was 0.8 times the amount of maleic anhydride; (2) Then, 52 kg of maleic anhydride was slowly added to the reactor. The system temperature was kept below 90°C while stirring vigorously during the entire process. After the addition of maleic anhydride, the system temperature was kept below 85°C for 4 h while stirring vigorously. (3) Then, 767 kg of an 11% sodium sulfite aqueous solution was slowly added to the reactor. The system was stirred vigorously during the entire process and the temperature was kept below 90° C. After the sodium sulfite aqueous solution was added, the system was stirred vigorously and kept warm at 80° C. for 9 h to obtain disodium long-chain alkyl succinamide sulfonate.

[0023] Comparative Example 1: Disodium long-chain alkyl succinamide sulfonate was prepared by a solvent method: 135 kg of octadecylamine and 52 kg of maleic anhydride were added to 382 kg of acetone, mixed and dispersed, vigorously stirred, and kept at 90°C for 3 hours. After the reaction was completed, the acetone was distilled off; then, 767 kg of an 11% sodium sulfite aqueous solution was slowly added to the mixture, with vigorous stirring throughout the process, keeping the system temperature below 90°C. After the addition of the sodium sulfite aqueous solution, vigorous stirring was maintained and the system was kept at 80°C for 9 hours to obtain disodium long-chain alkyl succinamide sulfonate.

[0024] Comparative Example 2: Long-chain alkyl succinamide sulfonic acid disodium salt was prepared by a conventional melt method: 135 kg of octadecylamine and 52 kg of maleic anhydride were melted at 60°C, and the molten octadecylamine was slowly added to the molten maleic anhydride with vigorous stirring throughout the process, and the system temperature did not exceed 120°C. After the addition was completed, vigorous stirring was maintained and the temperature was kept at 120°C for 3 hours. Then, 767 kg of an 11% by weight sodium sulfite aqueous solution was slowly added to the solution with vigorous stirring throughout the process, and the system temperature did not exceed 90°C. After the addition of the sodium sulfite aqueous solution, vigorous stirring was maintained and the temperature was kept at 80°C for 9 hours to obtain long-chain alkyl succinamide sulfonic acid disodium salt.

[0025] Comparative Example 3: Long-chain alkyl succinamide sulfonic acid disodium salt is prepared according to the following technical scheme, and the specific steps include: (1) 135 kg of octadecylamine was added to a reactor and heated to 60° C. to melt. After the octadecylamine was melted, triethylamine was added thereto as a catalyst. The amount of the catalyst added was 1.0 times the amount of maleic anhydride. (2) Then, 52 kg of maleic anhydride was slowly added to the reactor. The system temperature was kept below 90°C while stirring vigorously during the entire process. After the addition of maleic anhydride, the system temperature was kept below 85°C for 4 h while stirring vigorously. (3) Then, 767 kg of an 11% sodium sulfite aqueous solution was slowly added to the reactor. The system was stirred vigorously during the entire process and the temperature was kept below 90° C. After the sodium sulfite aqueous solution was added, the system was stirred vigorously and kept warm at 80° C. for 9 h to obtain disodium long-chain alkyl succinamide sulfonate.

[0026] Table 1 shows the properties and yields of the long-chain alkyl succinamide sulfonic acid disodium products obtained in the examples and comparative examples. It can be seen that the long-chain alkyl succinamide sulfonic acid disodium products obtained in Examples 1 to 5 are milky white, indicating high purity and few impurities. At the same time, the yields of the active substances and products contained therein are significantly improved relative to the products obtained in the comparative examples. Comparative Example 1 is a solvent method for preparing long-chain alkyl succinamide sulfonic acid disodium. Although the product obtained is milky white, it not only has the disadvantage of using an organic solvent, but also has a low product yield and a low active substance content. The method of the present invention makes up for the shortcomings of the solvent method. It does not have an organic solvent and significantly improves the product yield and active substance content. Comparative Example 2 is a conventional melting method for preparing long-chain alkyl succinamide sulfonic acid disodium. No composite catalyst is added. Obviously, its reaction temperature is higher, resulting in a more obvious sublimation effect of maleic anhydride at high temperature, which makes the yield and active substance content of the product very low. At the same time, side reactions will also occur, which will increase the impurity content in the product, resulting in a low purity of the product and a yellow color. Experiments have fully demonstrated that the method of the present invention enables the reaction to proceed under relatively mild conditions, while enhancing the reactivity of the raw materials, avoiding the sublimation of maleic anhydride and the generation of side reactions, inhibiting the formation of high-melting-point compounds, and improving the high activity, high purity and high yield of the product.

[0027] In addition, in Comparative Example 3, only triethylamine was added as a catalyst. The active ingredient content and yield of the product were similar to those of the composite catalyst. However, the color of the product was brown, indicating that the strong proton acceptor catalyst would affect the color and other properties of the final product, and a stabilizer needed to be added to avoid this effect.

[0028] Table 1: Properties and yields of the products obtained in Examples and Comparative Examples. Case Active ingredient content of the product Product color Product weight Product yield Example 1 23.3％ Milky white suspension 987kg 96.0％ Example 2 23.9％ Milky white suspension 1001kg 97.1％ Example 3 23.7％ Milky white suspension 1010kg 94.4％ Example 4 23.7％ Milky white suspension 1011kg 97.2％ Example 5 23.3％ Milky white suspension 1007kg 95.2％ Comparative Example 1 20.3％ Milky white suspension 959kg 79.0％ Comparative Example 2 15.8％ Yellow suspension 952kg 61.0％ Comparative Example 3 23.2％ Brown suspension 1004kg 94.5％

[0029] The above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of changes or replacements within the technical scope disclosed in this application, which should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for preparing disodium long-chain alkyl succinamide sulfonate, characterized in that: The following steps are involved: (1) adding a long-chain primary amine into a reactor and melting it, and then adding a composite catalyst thereto after the long-chain primary amine is melted, wherein the composite catalyst comprises component 1 and component 2, wherein component 1 is composed of one or more of the following substances: triethylamine, pyridine, imidazole, and N-methylimidazole, and component 2 is composed of one or more of the following substances: sodium acetate, sodium carbonate, and trisodium phosphate; (2) Then, slowly add maleic anhydride solid to the reactor and stir vigorously. The system temperature does not exceed 90°C during the whole process. After the maleic anhydride is added, keep it at 80-90°C for 3-5 hours; (3) Then, slowly add the sodium sulfite aqueous solution to the reactor, and keep the system temperature below 90° C. during the whole process. After the sodium sulfite aqueous solution is added, keep the temperature at 80-90° C. for 6-9 hours to obtain long-chain alkyl succinamide sulfonic acid disodium.

2. The method for preparing a long-chain alkyl succinamide sulfonic acid disodium according to claim 1, wherein In the composite catalyst, the amount of component 1 accounts for 20% to 50% of the total amount of the composite catalyst, and the amount of component 2 accounts for 50% to 80% of the total amount of the composite catalyst.

3. The preparation method of a long-chain alkyl succinamide sulfonic acid disodium according to any one of claims 1 and 2, wherein: The added amount of the composite catalyst is 0.5 to 1.1 times the amount of maleic anhydride.

4. The preparation method of a long-chain alkyl succinamide sulfonic acid disodium according to claim 1, wherein The melting temperature of long-chain primary amines is 50-70°C.

5. The preparation method of a long-chain alkyl succinamide sulfonic acid disodium according to claim 1, wherein The molar ratio of the long-chain primary amine to the maleic anhydride is 1:1 to 1.

15.

6. The preparation method of a long-chain alkyl succinamide sulfonic acid disodium according to claim 1, wherein The amount of sodium sulfite added is 1 to 1.2 times the amount of maleic anhydride.