Hydroxyethyl sulfonic acid alkali metal salt solution and preparation method thereof

Abstract

The invention relates to the technical field of organic synthesis, in particular to a hydroxyethyl sulfonic acid alkali metal salt solution and a preparation method thereof. According to the preparation method provided by the invention, 50-65wt% of an isethionic acid alkali metal salt solution can be directly obtained, and the content of sulfate is not higher than 0.2 wt%; the content of sulfite is not higher than 0.015 wt%; the ethylene glycol content is not higher than 0.25 wt%. The solution can be directly used for preparing surfactants such as N-methyl taurine alkali metal salt and coconut oil acyl isethionate alkali metal salt, and the obtained product is high in yield and good in quality.

Description

Technical Field

[0001] The present invention relates to the technical field of organic synthesis, and in particular to an alkali metal isethionate solution and a preparation method thereof. Background Art

[0002] Alkali metal isethionate, also known as alkali metal 2-hydroxyethanesulfonate, is an important chemical product. It is commonly used as an intermediate in the production of taurine and surfactants. It is widely used in fine chemical fields such as electroplating, daily chemicals (such as shampoo and high-end soaps), cosmetics, and pharmaceuticals. It is also a precursor for the production of surfactants such as alkali metal N-methyl taurine, alkali metal cocoyl isethionate, and alkali metal lauroyl isethionate.

[0003] Alkali metal isethionate stock solutions are typically prepared by reacting ethylene oxide with bisulfite. During the preparation process, impurities such as sulfate, sulfite (including bisulfite), and ethylene glycol (including polyethylene glycol) are generated. Sulfite is gradually converted to sulfate through oxidation in the reaction system, during transportation, and during storage. Downstream products of alkali metal isethionate have relatively high requirements for the presence of sulfate impurities. For example, in taurine production, residual sulfate can significantly affect the taste of the finished taurine. In the reaction of coconut acid with alkali metal isethionate to produce alkali metal cocoyl isethionate and alkali metal lauroyl isethionate, residual sulfate in the final product can reduce the foam stability of the surfactant. High levels of sulfate ions in surfactants can also cause dry skin.

[0004] In order to remove sulfite and sulfate from isethionate, common methods include barium method and membrane separation method. 2+ With SO3 in solution 2- 、SO4 2- The reaction generates BaSO3 and BaSO4 precipitation. However, this method is not only easy to cause Ba 2+ Exceeding the standard, and it is difficult to filter BaSO4 in industry; on the other hand, if BaCl2 is added, the Cl introduced - It will cause accelerated equipment corrosion, high operating costs, difficulty in recovering by-products, and bring great difficulties to production and on-site management.

[0005] The key to membrane separation is that a single NF membrane layer can effectively separate polyvalent anions from monovalent anions in aqueous solution. However, this method has certain requirements for feed concentration, requiring relatively low feed concentrations. Furthermore, it produces a large amount of wastewater. Furthermore, the relatively low membrane treatment capacity per unit area results in relatively high equipment investment costs.

[0006] Therefore, there is an urgent need to develop a method for preparing alkali metal isethionate with low sulfate and sulfite content, low cost, and without introducing new cations. Summary of the Invention

[0007] The present invention aims to at least partially address one of the technical problems in the related art. To this end, one object of the present invention is to provide an alkali metal isethionate salt and a method for preparing the same. The alkali metal isethionate salt solution prepared by the method has a high yield and high quality, with a sulfate content of no more than 0.2 wt%, a sulfite content (including bisulfite) of no more than 0.015 wt%, and an ethylene glycol (including polyethylene glycol) content of no more than 0.25 wt%. The product purification process is simple, with a high purification yield and low cost. No new cations are introduced, and the product meets the high sulfate content requirements of downstream products of the alkali metal isethionate salt. Furthermore, due to the low bisulfite content in the product, the quality of the alkali metal isethionate salt can be maintained during transportation and storage.

[0008] To this end, the first aspect of the present invention provides a method for preparing an alkali metal isethionate solution. According to an embodiment of the present invention, the method comprises:

[0009] S1: In the reaction stage, ethylene oxide is contacted with bisulfite and an alkali metal hydroxide catalyst is added. When the residual concentration of bisulfite in the reaction solution is 0.075 mol / L to 0.1 mol / L and the pH value of the reaction solution is 6-7, the addition of ethylene oxide and bisulfite is stopped;

[0010] S2: During the adjustment stage, ethylene oxide is continuously introduced into the reaction solution. When the residual concentration of bisulfite in the reaction solution is 0.005 mol / L to 0.0125 mol / L, the introduction of ethylene oxide is stopped to obtain a stock solution of alkali metal isethionate.

[0011] The method for preparing an alkali metal isethionic acid salt solution provided by the present invention has a high conversion rate of ethylene oxide, an ethylene glycol (including polyethylene glycol) impurity content not higher than 0.25 wt%, a sulfate content not higher than 0.2 wt%, and a sulfite content not higher than 0.015 wt%.

[0012] According to an embodiment of the present invention, in steps S1 and S2, the total feed molar ratio of ethylene oxide to bisulfite is 1:(1.03-1.08).

[0013] According to an embodiment of the present invention, the alkali metal hydroxide is selected from sodium hydroxide or potassium hydroxide.

[0014] According to an embodiment of the present invention, the alkali metal hydroxide is sodium hydroxide, and in the reaction stage, the molar ratio of sodium hydroxide to ethylene oxide is (0.05-0.15):1.

[0015] According to an embodiment of the present invention, in step S1, the residual content of bisulfite is indicated by measuring the number of iodine drops. The higher the number of iodine drops, the more residual bisulfite. The feeding of ethylene oxide and the circulating absorption can be appropriately increased. When the residual concentration of sodium bisulfite is 0.075 mol / L to 0.1 mol / L and the pH value is 6 to 7, the feeding of ethylene oxide and bisulfite can be stopped, and the reaction solution is transferred to the adjustment stage.

[0016] In step S2, ethylene oxide is continuously introduced into the reaction solution, and the number of iodine drops is measured to indicate the residual content of bisulfite. When the residual concentration of bisulfite is 0.005 mol / L to 0.0125 mol / L, the addition of ethylene oxide is stopped to obtain a stock solution of an alkali metal isethionate.

[0017] By measuring the number of iodine drops, the feed can be added according to the actual reaction conditions, thereby improving the conversion rate of ethylene oxide and controlling the residual bisulfite and the production of by-product ethylene glycol.

[0018] According to an embodiment of the present invention, the preparation method further comprises:

[0019] S3: adding an oxidizing agent to the isethionate alkali metal salt stock solution to obtain an oxidized solution having at least partially reduced sulfite content;

[0020] S4: Adsorbing the oxidized solution with an anion exchange resin to obtain a purified alkali metal isethionate solution.

[0021] After the preparation of alkali metal isethionate, a small amount of bisulfite will remain. The addition of an oxidant can oxidize the bisulfite into sodium sulfate. The use of anion exchange resin for adsorption can further remove sulfate and improve the purity of the alkali metal isethionate product.

[0022] Common oxidants in the chemical industry include sodium hypochlorite and sodium chlorate. Extensive experiments have shown that using chlorine-containing compounds as oxidants can, on the one hand, cause excessive sodium chloride content in the product, and, on the other hand, chloride ions can corrode metal equipment. Therefore, according to embodiments of the present invention, a preferred oxidant includes at least one selected from oxygen, ozone, and hydrogen peroxide.

[0023] According to an embodiment of the present invention, in step S3, the mass ratio of the oxidant to the isethionate alkali metal salt stock solution is not less than 1:1000.

[0024] According to an embodiment of the present invention, the anion exchange resin column is selected from D285 or D301 anion exchange resin column.

[0025] In the preparation method provided by the present invention, by using a specific anion exchange resin column, the purity of the alkali metal isethionate can be further improved and the content of sodium sulfate can be reduced.

[0026] A second aspect of the present invention provides an alkali metal isethionate solution. According to an embodiment of the present invention, the alkali metal isethionate solution is prepared by the preparation method described in the first aspect.

[0027] The third aspect of the present invention provides an alkali metal isethionate solution. According to an embodiment of the present invention, the alkali metal isethionate solution comprises: an alkali metal isethionate salt, a sulfate, a sulfite (including hydrogen sulfite), and ethylene glycol (including polyethylene glycol).

[0028] Wherein, the content of the alkali metal isethionate is 50% to 65% by weight,

[0029] The content of the sulfate is not higher than 0.2wt%;

[0030] The content of the sulfite is not higher than 0.015wt%;

[0031] The content of the ethylene glycol (including polyethylene glycol) is not higher than 0.25 wt %.

[0032] According to an embodiment of the present invention, the pH of the alkali metal isethionate solution is 8-11.

[0033] The alkali metal isethionate solution provided by the present invention is not only of good quality and can be directly used in the production of downstream products to meet the requirements of downstream high-end customers, but also convenient to transport and store for a long time without exceeding the sulfate standard.

[0034] The preparation method provided by the present invention can directly produce a 50% to 65% by weight alkali metal isethionate solution, wherein the sulfate content is no more than 0.2% by weight, the sulfite content is no more than 0.015% by weight, and the ethylene glycol (including polyethylene glycol) content is no more than 0.25% by weight. This solution can be directly used to prepare surfactants such as alkali metal N-methyl taurine, alkali metal cocoyl isethionate, and alkali metal lauroyl isethionate, with high yield, high quality, and low sulfate content.

[0035] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. DETAILED DESCRIPTION

[0036] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be understood as limiting the present invention.

[0037] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, features defined as "first" or "second" may explicitly or implicitly include one or more of such features. Furthermore, in the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0038] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0039] In order to make the present invention more easily understood, certain technical and scientific terms are specifically defined below. Unless otherwise clearly defined elsewhere in this document, all other technical and scientific terms used herein have the meaning commonly understood by those skilled in the art to which the present invention belongs.

[0040] In this document, the terms “include” or “comprising” are open expressions, that is, including the contents specified in the present invention, but not excluding other contents.

[0041] As used herein, the terms "optionally," "optional," or "optionally" generally mean that the subsequently described event or circumstance may but need not occur, and that the description includes instances where the event or circumstance occurs and instances where it does not.

[0042] Alkali metal isethionates are typically prepared by reacting ethylene oxide with bisulfite. During this process, sulfate is produced as an intermediate impurity. In some fine chemical industries, when preparing downstream products of alkali metal isethionates, strict requirements are placed on the presence of the sulfate impurity. Sulfate can affect catalyst activity and reduce the efficiency of the esterification of alkali metal isethionates with coconut oil. Furthermore, residual sulfate in the final product can reduce foam stability.

[0043] In order to remove sulfite and sulfate from isethionate, common methods include barium method and membrane separation method. 2+ With SO3 in solution 2- 、SO4 2-The reaction generates BaSO3 and BaSO4 precipitation. However, this method is easy to cause Ba 2 + Exceeding the standard, and it is difficult to filter BaSO4 in industry; on the other hand, if BaCl2 is added, the Cl introduced - It will cause accelerated equipment corrosion, high operating costs, difficulty in recovering by-products, and bring great difficulties to production and on-site management.

[0044] The key to membrane separation is that a single NF membrane layer can effectively separate polyvalent anions from monovalent anions in aqueous solution. However, this method has certain requirements for feed concentration, requiring relatively low feed concentrations and wastewater treatment. The low membrane treatment capacity per unit area results in relatively high equipment investment costs.

[0045] Based on this, the inventors have developed a method for preparing an alkali metal isethionate salt that contains a low content of sulfate as an impurity, is low-cost, and does not introduce new cations. The preparation method provided by the present invention has low processing costs and does not introduce new cations. The resulting alkali metal isethionate salt product has a sulfate content of no more than 0.2 wt%, a bisulfite content of no more than 0.015 wt%, and an ethylene glycol content of no more than 0.25 wt%.

[0046] According to a specific embodiment of the present invention, the present invention provides a method for preparing an alkali metal isethionate solution, comprising:

[0047] S1: In the reaction stage, ethylene oxide is contacted with bisulfite and an alkali metal hydroxide catalyst is added. When the residual concentration of bisulfite in the reaction solution is 0.075 mol / L to 0.1 mol / L and the pH value of the reaction solution is 6 to 7, the addition of ethylene oxide and bisulfite is stopped;

[0048] S2: During the adjustment stage, ethylene oxide is continuously introduced into the reaction solution. When the residual concentration of bisulfite in the reaction solution is 0.005 mol / L to 0.0125 mol / L, the introduction of ethylene oxide is stopped to obtain a stock solution of alkali metal isethionate.

[0049] According to a specific embodiment of the present invention, in steps S1 and S2, the total feed molar ratio of ethylene oxide to bisulfite is 1:(1.03-1.08).

[0050] According to a specific embodiment of the present invention, the alkali metal hydroxide is selected from sodium hydroxide or potassium hydroxide.

[0051] According to a specific embodiment of the present invention, the alkali metal hydroxide is sodium hydroxide, and in the reaction stage, the molar ratio of sodium hydroxide to ethylene oxide is (0.05-0.15):1.

[0052] According to a specific embodiment of the present invention, the preparation method further comprises:

[0053] S3: adding an oxidizing agent to the isethionate alkali metal salt stock solution to obtain an oxidized solution having at least partially reduced sulfite content;

[0054] S4: Adsorbing the oxidized solution with an anion exchange resin to obtain a purified alkali metal isethionate solution.

[0055] In the preparation method, an oxidant is added to convert sulfite into sulfate, which is then adsorbed by an anion resin to control the sulfate content and remove inorganic salts, thereby further improving the purity of the product.

[0056] According to a specific embodiment of the present invention, the oxidant includes but is not limited to oxygen, ozone, hydrogen peroxide, etc.

[0057] According to a specific embodiment of the present invention, in step S3, the mass ratio of the isethionate alkali metal salt stock solution to the oxidant is not less than 1:1000.

[0058] According to a specific embodiment of the present invention, the anion exchange resin column is selected from D285 or D301 anion exchange resin column.

[0059] According to an embodiment of the present invention, the anion exchange resin column is selected from D285 or D301 anion exchange resin column.

[0060] The alkali metal isethionate solution obtained by the preparation method provided by the present invention can be directly used in the preparation of downstream products such as N-methyl taurate alkali metal salt and cocoyl isethionate alkali metal salt. The obtained alkali metal isethionate solution can also be used in the preparation of N-methyl taurate alkali metal salt and cocoyl isethionate alkali metal salt after recrystallization and drying.

[0061] It should be noted that there are many methods for determining the residual bisulfite concentration, and all methods known in the art are encompassed by the scope of protection of the present invention. According to a specific embodiment of the present invention, iodine titration can be used to control the sulfite concentration during the preparation of the alkali metal isethionate.

[0062] According to a specific embodiment of the present invention, the preparation process of the alkali metal salt of isethionate includes two reaction stages: a reaction stage and a reaction adjustment stage. In the reaction stage, ethylene oxide and bisulfite react under the catalysis of an alkali metal hydroxide. During the reaction, the reaction liquid is sampled and analyzed. When the residual concentration of bisulfite in the reaction liquid is 0.075 mol / L to 0.1 mol / L and the pH value of the reaction liquid is 6 to 7, the introduction of ethylene oxide and bisulfite is stopped.

[0063] During the reaction adjustment stage, ethylene oxide is continuously introduced into the reaction solution. When the residual concentration of bisulfite in the reaction solution is 0.005 mol / L to 0.0125 mol / L, the introduction of ethylene oxide is stopped to obtain a stock solution of alkali metal isethionate.

[0064] It should be noted that during the reaction of ethylene oxide and bisulfite, the consumption of bisulfite is controlled by monitoring the number of iodine drops, pH value, and the flow rate of circulating ethylene oxide absorption; by controlling the residual amount of bisulfite, the conversion rate of ethylene oxide is increased, and the residual sulfite and the production of by-product ethylene glycol are reduced.

[0065] According to a specific embodiment of the present invention, the present invention provides a method for preparing an alkali metal isethionate, comprising:

[0066] S1: During the reaction stage, the ratio of ethylene oxide to bisulfite is controlled. When the residual bisulfite concentration in the reaction solution is 0.075 mol / L to 0.1 mol / L and the pH is maintained at 6 to 7, the reaction mixture enters the adjustment stage, where only ethylene oxide is introduced to control the residual bisulfite concentration to 0.005 mol / L to 0.0125 mol / L, thereby obtaining a stock solution of an alkali metal isethionate.

[0067] S2: introducing oxygen or other oxidizing agent into the alkali metal salt of isethionate solution and stirring for a period of time to remove bisulfite;

[0068] S3: The liquid obtained in S2 is treated with an anion exchange resin (D285 or D301) to remove sodium sulfate, thereby obtaining a 50% to 65% by weight alkali metal isethionate solution, wherein the sulfate content is no more than 0.2% by weight and the sulfite content is no more than 0.015% by weight.

[0069] According to a specific embodiment of the present invention, the present invention provides an alkali metal isethionate solution, which is prepared by the above-mentioned preparation method.

[0070] According to a specific embodiment of the present invention, the present invention provides an alkali metal isethionate solution, wherein the alkali metal isethionate solution comprises an alkali metal isethionate, a sulfate, a sulfite and ethylene glycol.

[0071] Wherein, the content of the alkali metal isethionate is 50% to 65% by weight,

[0072] The content of the sulfate is not higher than 0.2wt%;

[0073] The content of the sulfite is not higher than 0.015wt%;

[0074] The content of the ethylene glycol is not higher than 0.25 wt%.

[0075] It should be noted that, in the alkali metal salt of isethionate solution described herein, the "sulfite content" refers to the total content of sulfite and bisulfite contained in the alkali metal salt of isethionate solution; and the "ethylene glycol content" refers to the total content of ethylene glycol and ethylene glycol obtained by hydrolysis of polyethylene glycol contained in the alkali metal salt of isethionate solution.

[0076] According to a specific embodiment of the present invention, the pH of the alkali metal isethionate solution is 8-11.

[0077] The scheme of the present disclosure will be explained below in conjunction with the examples. Those skilled in the art will understand that the following examples are only used to illustrate the present disclosure and should not be considered to limit the scope of the present disclosure. Where specific techniques or conditions are not specified in the examples, they are carried out according to the techniques or conditions described in the literature in this area or according to the product instructions. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be obtained commercially.

[0078] Example 1 Preparation of Alkali Metal Isethionate Stock Solution by Two-Step Sulfite Content Control Method

[0079] The preparation method of the alkali metal salt of isethionate according to one embodiment of the present invention comprises the following steps:

[0080] S1: During the hydroxylation reaction stage, the flow rates of ethylene oxide (content above 99.9%) and sodium bisulfite solution (0.48 g / mL) were controlled to 275 g / h and 1900 g / h, respectively. The initial molar ratio of ethylene oxide to sodium bisulfite was 1:1.08. In the initial stage of the reaction, 195 g of NaOH solution (32 wt%) was introduced, and the reaction temperature was controlled to be 60-70°C. After reacting for 2 hours, the flow rates of ethylene oxide and bisulfite solution were controlled, and samples were taken. The sulfite content was indicated by measuring the number of iodine drops. When the sulfite content was 0.075 mol / L-0.1 mol / L and the pH value was maintained at 6-7, the introduction of ethylene oxide and bisulfite solution was stopped.

[0081] S2: The reaction solution in S1 is transferred to the adjustment stage, and sampling is performed. The sulfite content is indicated by measuring the number of iodine drops. When the sulfite content is 0.005 mol / L to 0.0125 mol / L (reaching the end point in about 1.5 hours), the reaction is stopped to obtain the alkali metal salt of isethionate stock solution 1. The total amount of ethylene oxide fed is 588 g, the total amount of sodium bisulfite solution fed is 3803 g, and the total molar ratio of ethylene oxide to sodium bisulfite is 1:1.05.

[0082] The yield of alkali metal isethionate (calculated as ethylene oxide), the content of alkali metal isethionate stock solution, and the product purity test are shown in Table 1 below:

[0083] Table 1

[0084]

[0085] Comparative Example 1 Preparation of alkali metal isethionate stock solution by quantitative feeding method

[0086] The preparation method of an alkali metal isethionate of a comparative example of the present invention comprises the following steps:

[0087] S1: Ethylene oxide (content 99.9% or more) and sodium bisulfite solution (0.48 g / mL) were added at a molar ratio of 1:1.08. The actual amount of ethylene oxide added was 44 g, and the actual amount of sodium bisulfite solution added was 293 g (the pure amount of sodium bisulfite was 112.32 g). At the initial stage of the reaction, 12.5 g of NaOH (32 wt%) was added. The reaction temperature was controlled at 60-70° C., and the reaction was allowed to proceed for 2.5 hours to obtain a stock solution of alkali metal isethionate 1-1.

[0088] The yield of alkali metal isethionate (calculated as ethylene oxide), the content of alkali metal isethionate stock solution, and the purity of the product are shown in Table 2 below:

[0089] Table 2

[0090]

[0091] Comparative Example 2: Preparation of hydroxyethyl sulfonic acid alkali metal salt stock solution by one-step sulfite content control method

[0092] The preparation method of an alkali metal isethionate of a comparative example of the present invention comprises the following steps:

[0093] The flow rates of ethylene oxide (content above 99.9%) and sodium bisulfite solution (0.48 g / mL) were controlled to be 275 g / h and 1900 g / h, respectively. The initial molar ratio of ethylene oxide to sodium bisulfite was 1:1.08. In the initial stage of the reaction, 195 g of NaOH solution (32 wt%) was introduced with an initial molar ratio of ethylene oxide to sodium bisulfite of 1:1.08. The reaction temperature was controlled to be 60-70°C. After reacting for 2 hours, the flow rate ratio of ethylene oxide to sodium bisulfite solution was reduced and controlled. Sampling was performed. The reaction mixture was stirred for 2 hours. The reaction mixture was stirred for 2 hours. The reaction mixture was stirred for 3 hours. The reaction mixture was stirred for 3 hours. The reaction mixture was stirred for 3 hours. The number was determined to indicate the sulfite content. The reaction was planned to be stopped when the sulfite content was 0.005 mol / L to 0.0125 mol / L. However, after 2.5 hours of reaction, the endpoint was still not reached. Therefore, the reaction was stopped when the sulfite content was approximately 0.025 mol / L to obtain alkali metal isethionate stock solution 2-1. The total amount of ethylene oxide charged was 612 g, the total amount of sodium bisulfite charged was 3993 g, and the total molar ratio of ethylene oxide to sodium bisulfite was 1:1.06.

[0094] The yield of alkali metal isethionate (calculated as ethylene oxide), the content of alkali metal isethionate stock solution, and the purity of the product are shown in Table 3 below:

[0095] Table 3:

[0096]

[0097] The experimental results of Example 1, Comparative Example 1, and Comparative Example 2 indicate that by using the number of iodine drops to monitor the bisulfite content in the hydroxylation reaction in real time, the process of preparing alkali metal isethionate by the ethylene oxide process is divided into two stages, thereby regulating the feed amount of the reaction raw materials. This can increase the ethylene oxide conversion rate (from 95.3% to 98.5%), improve production efficiency, reduce the formation of the byproduct ethylene glycol (not more than 0.5 wt %), and reduce the sulfate and sulfite contents in the product.

[0098] Example 2 Adding an oxidizing agent to the isethionic acid alkali metal salt stock solution to remove sulfite

[0099] Three 500g samples of the alkali metal isethionate solution prepared in Example 1 were taken, numbered 2-A, 2-B, and 2-C, and the effects of different oxidants on the sulfate and sulfite content of the products were investigated. The specific steps were as follows:

[0100] S3: adding an oxidant to the isethionic acid alkali metal salt stock solution and stirring for a period of time to remove bisulfite; taking a sample and detecting the content of sulfate and sulfite in the solution after adding the oxidant;

[0101] The experimental results corresponding to different oxidants are shown in Table 4:

[0102] Table 4

[0103]

[0104] The experimental results of Example 2 indicate that the addition of an oxidizing agent such as oxygen, ozone, or hydrogen peroxide to the isethionate alkali metal salt stock solution can significantly reduce the sulfite content (not exceeding 0.15 wt %) in the isethionate alkali metal salt stock solution without introducing new impurity ions.

[0105] In the chemical industry, commonly used oxidants include sodium hypochlorite and sodium chlorate. After a large number of experiments, we found that using chlorine-containing compounds as oxidants will, on the one hand, cause the sodium chloride content in the product to exceed the standard, and on the other hand, chloride ions will corrode metal equipment.

[0106] Example 3: Removal of Sulfate from an Alkali Metal Isethionate Solution Treated with an Oxidant Using an Anion Exchange Resin

[0107] The reaction products obtained in Example 2 were sampled separately. Two 200g samples of each product were taken. Each sample was diluted with 800g of water and labeled 2-AP-1, 2-AP-2, 2-BP-1, 2-BP-2, 2-CP-1, and 2-CP-2. The effects of treating the alkali metal isethionic acid salt solution obtained in Example 2 with different anion exchange resins were investigated to determine the effects of sulfate and sulfite content in the products. The specific steps were as follows:

[0108] S4: passing the raw materials numbered 2-AP-1, 2-AP-2, 2-BP-1, 2-BP-2, 2-CP-1, and 2-CP-2 through six resin columns filled with 100 ml of anionic resin for adsorption treatment, respectively, collecting the products, and performing reduced pressure distillation on the products at 80° C. and 0.08 MPa. When the concentration of the alkali metal isethionate solution is 0.5 g / mL to 0.65 g / mL, the concentration is stopped to obtain a surfactant precursor solution;

[0109] The corresponding resin models and the content data of sulfate, sulfite and ethylene glycol in the surfactant precursor solution after treatment with the anion exchange resin column are shown in Table 5:

[0110] Table 5

[0111]

[0112] Note: When the periodate oxidation method is used to determine the ethylene glycol content, what is actually being determined is the total ethylene glycol content of ethylene glycol and polyethylene glycol decomposed into ethylene glycol.

[0113] The experimental results of Example 3 indicate that the D285 and D301 anion exchange resins can adsorb sulfate in an alkali metal isethionate solution and have a certain adsorption capacity for ethylene glycol. After treatment with the anion resin, the sulfate content, sulfite content, and ethylene glycol content of the alkali metal isethionate solution are no more than 0.2 wt %, no more than 0.15 wt %, and no more than 0.25 wt %.

[0114] The alkali metal isethionate solution obtained in Example 3 has a high concentration, low sulfite and sulfate contents, and a weakly alkaline pH value. It can be directly used in the synthesis of the surfactant N-methyltaurine alkali metal salt and is a good surfactant precursor.

[0115] Comparative Example 3: Removal of sulfate from an alkali metal isethionate solution not treated with an oxidant using an anion exchange resin

[0116] Two 200g samples of the isethionic acid alkali metal salt stock solution prepared in Example 1 were taken, each sample being diluted with 800g of water and numbered 2-D and 2-E. The changes in sulfate and sulfite content in the products of the isethionic acid alkali metal salt solution obtained in Example 1 were investigated by treating the isethionic acid alkali metal salt solution with different anion exchange resins. The specific steps were as follows: The raw materials numbered 2-D and 2-E were respectively passed through two resin columns containing 100ml of anion resin for adsorption treatment. The products were collected and subjected to reduced pressure distillation at 80°C and 0.08 MPa. Concentration was stopped when the isethionic acid alkali metal salt solution had a concentration of 0.5g / mL to 0.65g / mL, thereby obtaining a surfactant precursor solution.

[0117] The corresponding resin models and the content data of sulfate, sulfite and ethylene glycol in the surfactant precursor solution after treatment with the anion exchange resin column are shown in Table 6:

[0118] Table 6:

[0119]

[0120] Note: When the periodate oxidation method is used to determine the ethylene glycol content, what is actually being determined is the total ethylene glycol content of ethylene glycol and polyethylene glycol decomposed into ethylene glycol.

[0121] The experimental results of Example 3 and Comparative Example 3 indicate that D285 and D301 anion exchange resins have good adsorption for sulfate, some adsorption for ethylene glycol, and poor adsorption for sulfite. Therefore, if the alkali metal isethionate solution is not oxidized with an oxidizing agent and adsorption is performed solely on an anion resin, it is not possible to effectively remove sulfite from the alkali metal isethionate solution. Due to residual sulfite, sulfite is gradually converted to sulfate during long-term transportation and storage, resulting in excessive sulfate levels.

[0122] Example 4 Preparation of solid alkali metal isethionate

[0123] 100 g of each of the six product solutions obtained in Example 3 was concentrated (heated to 80°C, distilled under reduced pressure at 0.08 MPa, and stopped when the concentration of the alkali metal isethionate solution reached 70 wt %), crystallized (cooled to 30°C-40°C, crystallized), and centrifuged and dried until no more crystals precipitated to obtain high-purity solid alkali metal isethionate. The solid products were then numbered. The contents of alkali metal isethionate, sulfate, and sulfite in the solid products are shown in Table 7 below.

[0124] Table 7

[0125]

[0126] The solid alkali metal isethionate obtained in Example 4 has high purity, a sulfite content of no more than 10 ppm, and a sulfate content of no more than 200 ppm. It can be directly used in the synthesis of surfactants such as alkali metal cocoyl isethionate and alkali metal lauroyl isethionate. It is a good surfactant precursor that can meet the needs of high-end customers.

[0127] Comparative Example 4 Preparation of solid alkali metal isethionate using the alkali metal isethionate stock solution prepared by prior art

[0128] 100 mL of the stock solution of the alkali metal isethionate obtained in Comparative Example 1 was concentrated (heated to 80° C., distilled under reduced pressure at 0.08 MPa, and the concentration was stopped when the concentration of the alkali metal isethionate solution reached 70 wt %), crystallized (cooled to 30° C. to 40° C., and then centrifuged and dried until no more crystals precipitated) to obtain a solid alkali metal isethionate (No. 4-1-P). The contents of alkali metal isethionate, sulfate, and sulfite in the solid product are shown in Table 8 below.

[0129] Table 8

[0130]

[0131] Comparative Example 4 shows that it is difficult to obtain high-quality solid alkali metal isethionate by using conventional technology to prepare alkali metal isethionate stock solution and treating the alkali metal isethionate stock solution only by recrystallization.

[0132] Example 5: Preparation of surfactant N-methyltaurine alkali metal salt

[0133] 50 mL of the sodium isethionate solution (product number 3-A-1-P) from Example 3 was added to a 500 mL reactor. 30 mL of water was added to the reactor, and the reactor temperature was maintained at approximately 25°C. 15.8 g of methylamine was slowly introduced into the reactor over 30 minutes. After the methylamine was introduced, the reaction system was heated to 230°C and the pressure maintained at approximately 8 MPa. After the reaction had proceeded for 1 hour, the reaction was stopped. The temperature was then lowered to 50°C, and unreacted methylamine was removed from the reaction solution at 0.05 MPa. After removal, the reaction solution was cooled to room temperature, the total reaction volume was measured, and a sample was taken to determine the content of alkali metal N-methyltaurine. The yield was then calculated. The product was concentrated and recrystallized once, and the sodium sulfate and bisulfite contents were determined. The experimental data are shown in Table 9.

[0134] Table 9

[0135]

[0136] Comparative Example 5: Preparation of surfactant N-methyltaurine alkali metal salt using isethionic acid alkali metal salt stock solution prepared by existing technology

[0137] 50 mL each of the isethionic acid alkali metal salt stock solution (product 3-D) from Comparative Example 1 and the isethionic acid alkali metal salt solution (product 3-D) from Comparative Example 3 were added to two 500 mL reactors, designated reaction numbers 5-1 and 5-3. 30 mL of water was added to each reactor, maintaining the reactor temperature at approximately 25°C. Over 30 minutes, 15.8 g of methylamine was slowly introduced into each reactor. After the methylamine was introduced, the reaction system was heated to 230°C and the pressure maintained at approximately 8 MPa. After 1 hour of reaction, the reaction was terminated. The temperature was then lowered to 50°C, and unreacted methylamine was removed from the reaction solution at 0.05 MPa. After removal, the reaction solution was cooled to room temperature, the total reaction volume was measured, and a sample was taken to determine the content of N-methyltaurine alkali metal salt, and the yield was calculated. The product was concentrated and recrystallized once, and the sodium sulfate and bisulfite contents were determined. The experimental data are shown in Table 10.

[0138] Table 10

[0139]

[0140] As can be seen from the experimental results of Example 5 and Comparative Example 5, the purity of the reaction raw materials will affect the yield of N-methyltaurine and directly affect the product quality of N-methyltaurine. Since the raw material purity used in Example 5 is relatively high, the sulfate content of the product can be reduced to 50ppm after a single concentration and recrystallization, and there is essentially no sulfite in the product. The sulfate content is also relatively low. This surfactant is suitable for long-term storage and transportation and can be directly used in high-end products. However, the raw material purity used in Comparative Example 5 is relatively low. After the product is recrystallized once, the sulfate and sulfite contents in the 5-1 product are still at a relatively high level and cannot meet the quality requirements required for application in surfactants; the sulfite content in the 5-3 product is at a relatively high level, which is not suitable for long-term storage and long-distance transportation.

[0141] Example 6: Preparation of surfactant cocoyl isethionate alkali metal salt

[0142] 30 g of solid alkali metal isethionate (product number 4-A-1) from Example 4 was added to a 250 mL three-necked flask. 50 g of coconut oil acid was added to the flask. The temperature was raised to 180°C under nitrogen, followed by the addition of 1.7 g of zinc oxide catalyst. The reaction was incubated for 6 hours to obtain an alkali metal isethionate surfactant. Samples were taken to determine the residual content of the alkali metal isethionate, and the conversion rate was calculated. The product was concentrated and recrystallized once, and the sodium sulfate and bisulfite contents were determined. The experimental data are shown in Table 11.

[0143] Table 11

[0144]

[0145] Comparative Example 6: Preparation of Cocoyl Isethionate Alkali Metal Salt Surfactant Using Isethionate Alkali Metal Salt Solid Prepared by Existing Technology: 30 g of the isethionate alkali metal salt solid produced in Comparative Example 4 was added to a 250 mL three-necked flask. 50 g of coconut acid was added to the flask, and the temperature was raised to 180°C under nitrogen. 1.7 g of zinc oxide catalyst was then added, and the reaction was maintained at this temperature for 6 hours to obtain the cocoyl isethionate alkali metal salt surfactant. Samples were taken to determine the residual isethionate alkali metal salt content, and the conversion rate was calculated. The product was concentrated and recrystallized once, and the sodium sulfate and bisulfite contents in the product were determined. The experimental data are shown in Table 12.

[0146] Table 12

[0147]

[0148] The experimental results of Example 6 and Comparative Example 6 indicate that sulfates and sulfites in the reaction raw materials affect the conversion rate of alkali metal isethionate and directly impact the quality of the product, alkali metal cocoyl isethionate. Because the raw materials used in Example 6 were relatively pure, the sulfate content of the product was reduced to 45 ppm after a single concentration and recrystallization, and the product was essentially sulfite-free. This surfactant is suitable for long-term storage and transportation and can be directly used in high-end products. However, the raw materials used in Comparative Example 6 were of moderate purity, and the sulfate and sulfite contents of the product remained high after a single recrystallization, failing to meet the quality requirements of high-end products.

[0149] Comparative Example 7: The isethionic acid alkali metal salt stock solution prepared by the prior art was treated with a cationic resin and an anionic resin.

[0150] A 20g sample of the alkali metal isethionate solution prepared in Comparative Example 1 was diluted with 80g of water and designated 7-A. The alkali metal isethionate solution obtained in Comparative Example 1 was treated with cation and anion exchange resins to investigate changes in the sulfate and sulfite content of the product. The specific steps were as follows: The raw material, designated 7-A, was sequentially passed through two series-connected cation exchange resin columns (filled with 10ml of 732 cation exchange resin) and anion exchange resin column (filled with 10ml of D285 anion exchange resin). The product with a sulfate content below 500ppm was collected and subjected to reduced pressure distillation at 80°C and 0.08 MPa. The product was concentrated to a concentration of 0.5g / mL to 0.65g / mL. Concentration was then stopped to obtain a surfactant precursor solution (Product No. 7-B).

[0151] The content data of sulfate, sulfite and ethylene glycol in the surfactant precursor solution after treatment with the cation and anion exchange resin columns are shown in Table 13:

[0152] Table 13:

[0153]

[0154] Note: When the periodate oxidation method is used to determine the ethylene glycol content, what is actually being determined is the total ethylene glycol content of ethylene glycol and polyethylene glycol decomposed into ethylene glycol.

[0155] As can be seen from Comparative Example 7, when a cationic resin and an anionic resin are used in combination to treat a stock solution of an alkali metal isethionate prepared by the prior art, only a solution with a sulfate content of less than 500 ppm is collected. While sulfate can be effectively removed from the product, sulfite cannot be effectively removed, and the purification yield of the alkali metal isethionate is only 79%.

[0156] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", "some implementation plans" or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0157] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A method for preparing an alkali metal isethionate solution, characterized in that: include: S1: In the reaction stage, ethylene oxide is contacted with bisulfite and an alkali metal hydroxide catalyst is added. When the residual concentration of bisulfite in the reaction solution is 0.075 mol / L to 0.1 mol / L and the pH value of the reaction solution is 6 to 7, the addition of ethylene oxide and bisulfite is stopped; S2: During the adjustment stage, ethylene oxide is continuously introduced into the reaction solution. When the residual concentration of bisulfite in the reaction solution is 0.005 mol / L to 0.0125 mol / L, the introduction of ethylene oxide is stopped to obtain a stock solution of alkali metal isethionate.

2. The preparation method according to claim 1, characterized in that In steps S1 and S2, the total molar ratio of ethylene oxide to bisulfite is 1:(1.03-1.08).

3. The preparation method according to claim 1, characterized in that The alkali metal hydroxide is selected from sodium hydroxide or potassium hydroxide; Optionally, the alkali metal hydroxide is sodium hydroxide, and in the reaction stage, the molar ratio of sodium hydroxide to ethylene oxide is (0.05-0.15):

1.

4. The preparation method according to claim 1, characterized in that The preparation method further comprises: S3: adding an oxidizing agent to the isethionate alkali metal salt stock solution to obtain an oxidized solution having at least partially reduced sulfite content; S4: Adsorbing the oxidized solution with an anion exchange resin to obtain a purified alkali metal isethionate solution.

5. The preparation method according to claim 4, characterized in that The oxidant includes at least one selected from oxygen, ozone, and hydrogen peroxide.

6. The preparation method according to claim 4, characterized in that In step S3, the mass ratio of the oxidant to the isethionate alkali metal salt stock solution is not less than 1:1000.

7. The preparation method according to claim 4, characterized in that The anion exchange resin column is selected from D285 or D301 anion exchange resin column.

8. An alkali metal isethionate solution, characterized in that The alkali metal isethionate solution is prepared by the preparation method according to any one of claims 1 to 7.

9. An alkali metal isethionate solution, characterized in that include: Alkali metal isethionates, sulfates, sulfites and ethylene glycol, Wherein, the content of the alkali metal isethionate is 50% to 65% by weight, The content of the sulfate is not higher than 0.2wt%; The content of the sulfite is not higher than 0.015wt%; The content of the ethylene glycol is not higher than 0.25 wt%.

10. The alkali metal isethionate solution according to claim 9, wherein The pH of the alkali metal isethionate solution is 8-11.

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