Method for extracting thiodiglycolic acid from isooctyl thioglycolate raffinate

Abstract

The invention discloses a method for extracting thiodiglycolic acid from isooctyl thioglycolate raffinate, and relates to the field of industrial by-product recovery. According to the method for extracting thiodiglycolic acid from the isooctyl thioglycolate raffinate, an alkaline hydrolysis water phase is put into a reaction kettle, hydrochloric acid is dropwise added into the reaction kettle, so that main thiodiglycolic acid sodium salt and dithiodiglycolic acid sodium salt in the water phase react with hydrochloric acid to generate thiodiglycolic acid and sodium chloride, and the thiodiglycolic acid and sodium chloride are extracted by utilizing a mode of cooling after distilling and draining water. The method comprises the following steps: adding sodium chloride into a sodium chloride solution, carrying out crystal precipitation after the sodium chloride forms a supersaturated solution, removing most of sodium chloride, carrying out cooling crystallization in the later stage, carrying out synchronous crystallization precipitation on thiodiglycolic acid and sodium chloride, carrying out recrystallization after dissolution, and carrying out crystallization discharge on most of thiodiglycolic acid by utilizing the water solubility difference between thiodiglycolic acid and sodium chloride. Therefore, pure thiodiglycolic acid crystals are obtained, recycling of the isooctyl thioglycolate raffinate is achieved, industrial pollution is reduced, and the product recycling efficiency is improved.

Description

Technical Field

[0001] The invention relates to the technical field of industrial by-product recovery, in particular to a method for extracting thiodiglycolic acid from isooctyl thioglycolate residual liquid. Background Art

[0002] In the production process of isooctyl thioglycolate, in addition to the desired reaction, some side reactions will occur, and the side reactions mainly produce diisooctyl thiodiglycolate and diisooctyl dithiodiglycolate. Diisooctyl dithiodiglycolate can be reduced to obtain the main product of isooctyl thioglycolate, so the remaining residual liquid is mainly diisooctyl thiodiglycolate.

[0003] In actual industrial treatment, this part of the material is mainly recovered by alkaline hydrolysis to recover isooctyl alcohol, which is continuously used as the raw material of mercaptoethyl isooctyl ester, and the alkaline hydrolysis aqueous phase is discharged to a sewage treatment system. The aqueous phase after the alkaline hydrolysis reaction contains a high content of sodium thiodiglycolic acid salt, which is usually discharged to the sewage treatment system after the pH value is adjusted to neutral. On the one hand, it is easy to cause serious industrial pollution, and on the other hand, there is a situation in which the product recovery is incomplete and causes material waste. Therefore, a method for extracting thiodiglycolic acid from isooctyl thioglycolate residual liquid is provided, which is used for reacting the sodium thiodiglycolic acid salt in the alkaline hydrolysis aqueous phase to generate thiodiglycolic acid for recycling. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a method for extracting thiodiglycolic acid from isooctyl thioglycolate residual liquid, which solves the problem that in the existing industrial preparation process of isooctyl thioglycolate, the final product of the reaction contains a high content of sodium thiodiglycolic acid in the aqueous phase after alkaline hydrolysis, and is usually discharged into a sewage treatment system after pH is adjusted to neutral, which, on the one hand, easily causes serious industrial pollution, and on the other hand, there is a problem of material waste caused by incomplete product recovery.

[0005] To achieve the above object, the present invention is implemented by the following technical scheme: a method for extracting thiodiglycolic acid from isooctyl thioglycolate residual liquid, comprising the following steps;

[0006] Step 1: Adding materials, the aqueous phase after the alkaline hydrolysis reaction of the isooctyl thioglycolate residual liquid is added into the reactor;

[0007] Step 2, synthesis, add hydrochloric acid to the reaction kettle and adjust to strong acidity so that the pH is less than 1, then the reaction starts, and the reaction formula is:

[0008]

[0009] After the reaction is completed, it is concentrated to remove the sodium chloride crystals;

[0010] The mother liquor is put into a crystallization kettle and cooled again to generate thiodiglycolic acid crystals, which are then centrifuged to obtain a wet thiodiglycolic acid product;

[0011] Step 3, refining and purification, putting the wet thiodiglycolic acid into a reactor, adding water and heating it to reflux, then cooling it for crystallization, so that a small amount of sodium chloride is dissolved in water to generate pure thiodiglycolic acid crystals, taking out the crystals and drying them to obtain solid thiodiglycolic acid.

[0012] Preferably, the aqueous phase after the alkaline hydrolysis reaction of the isooctyl thioglycolate residual liquid contains sodium thiodiglycolic acid, sodium dithiodiglycolic acid and sodium mercaptopropionate. By weighing 200g of the alkaline hydrolysis aqueous phase, it contains 23% sodium thiodiglycolic acid, 1% sodium dithiodiglycolic acid and 0.5% sodium mercaptopropionate.

[0013] Preferably, the concentration of hydrochloric acid is 31%, and the dropping process adopts a method of dropping while stirring, the total amount of dropping is 80g, continuous stirring is performed during the dropping process, and the dropping is stopped when the pH value is measured to be less than 1 after the dropping is completed, and then continuous stirring is performed to allow the alkaline hydrolysis aqueous phase to fully react with the hydrochloric acid, and then the mixture is allowed to stand.

[0014] Preferably, removing sodium chloride in step 2 comprises the following steps:

[0015] S1, the mother liquor after the reaction in the reactor is subjected to atmospheric distillation, and the amount of water distilled is 100g, so that the concentration of sodium chloride in the mother liquor is increased, and then the concentrated mother liquor is poured into a centrifuge and cooled to 50°C. At this time, supersaturated crystals of sodium chloride appear, and the sodium chloride is removed by centrifugation;

[0016] S2. The mother liquor after centrifugation is put back into the reactor and distilled at room temperature again. The amount of water distilled is 20-30g. The concentrated mother liquor is poured into the centrifuge again and cooled to 70°C. At this time, a small amount of supersaturated crystals of sodium chloride appear here, and the sodium chloride is removed by centrifugation.

[0017] Preferably, in the step 2, after the mother liquor is put into the crystallization kettle, the temperature is lowered to 25-30 degrees, at which time thiodiglycolic acid begins to crystallize, and after the crystallization is completed, centrifugation is performed to obtain about 50g of thiodiglycolic acid, which is a wet product. In addition to the mother liquor containing sodium chloride adhering to the surface, a small amount of sodium chloride crystals also exist in the crystals, waiting for refining and purification, and the mother liquor after centrifugation is retained for standby use.

[0018] Preferably, in the refining and purification process, the wet thiodiglycolic acid is put into a reactor, 30g of pure water is added, the temperature is raised and refluxed to form a mixed solution of thiodiglycolic acid and a small amount of sodium chloride, and then the temperature is lowered to about 55°C again, at which time thiodiglycolic acid begins to crystallize, and sodium chloride is dissolved in water. At this time, centrifugation is performed again to obtain solid crystals of thiodiglycolic acid, and then the obtained crystals are placed at 80-90°C for drying to finally obtain about 43g of thiodiglycolic acid finished product, and the recovery rate of thiodiglycolic acid in a single process reaches 93.5%, and the mother liquor containing sodium chloride and trace amounts of thiodiglycolic acid remains in the reactor.

[0019] Preferably, the mother liquor after multiple crystallizations of thiodiglycolic acid in the crystallization kettle is enriched, and then distilled to remove water for concentration, and then sodium chloride is crystallized by cooling to remove sodium chloride, and a mother liquor without sodium chloride is obtained.

[0020] Preferably, the mother liquor containing sodium chloride and trace thiodiglycolic acid remaining in the reactor after refining and purification is mixed with the mother liquor removed from sodium chloride obtained by secondary removal of sodium chloride in the crystallization kettle for enrichment and enters the next round of thiodiglycolic acid recovery process.

[0021] The present invention discloses a method for extracting thiodiglycolic acid from isooctyl thioglycolate residual liquid, which has the following beneficial effects:

[0022] 1. The method for extracting thiodiglycolic acid from isooctyl thioglycolate residual liquid comprises the following steps: putting the aqueous phase after alkaline hydrolysis reaction of isooctyl thioglycolate residual liquid into a reactor, then dripping hydrochloric acid into the reactor, so that sodium thiodiglycolic acid, sodium dithiodiglycolic acid and sodium mercaptopropionate in the aqueous phase react with the hydrochloric acid to generate thiodiglycolic acid and sodium chloride; in the early stage, the sodium chloride forms a supersaturated solution and crystallizes after cooling by distillation and drainage; then the sodium chloride crystals are removed by centrifugation; when a large amount of sodium chloride is precipitated, the thiodiglycolic acid and sodium chloride are crystallized and precipitated synchronously by cooling and crystallization; then the mixed crystals are dissolved and recrystallized; and the difference in water solubility between thiodiglycolic acid and sodium chloride is utilized to crystallize and discharge most of the thiodiglycolic acid, so as to obtain pure thiodiglycolic acid crystals, thereby realizing the recycling of isooctyl thioglycolate residual liquid, reducing industrial pollution and improving product recovery efficiency.

[0023] 2. The method for extracting thiodiglycolic acid from the residual liquid of isooctyl thioglycolate comprises the following steps: enriching the mother liquor after the thiodiglycolic acid is crystallized in the crystallization kettle for multiple times, and then distilling and removing water to achieve concentration; then cooling to achieve sodium chloride crystallization, removing sodium chloride, and obtaining the sodium chloride-removed mother liquor, thereby further reducing the sodium chloride content in the mother liquor remaining in the crystallization kettle after multiple enrichments; then mixing the mother liquor containing sodium chloride and trace thiodiglycolic acid in the reactor after refining and purification with the sodium chloride-removed mother liquor obtained by secondary sodium chloride removal in the crystallization kettle for enrichment, and entering the next round of thiodiglycolic acid recovery process, thereby achieving infinite recycling of thiodiglycolic acid; in the whole process, by continuously adding hydrochloric acid, the target product thiodiglycolic acid and the byproducts sodium chloride and distilled water are prepared; the distilled water and sodium chloride can be used for industrial recycling, and the enriched mother liquor is infinitely recycled to achieve the effect of zero pollution discharge in a true sense.

[0024] 3. In the method for extracting thiodiglycolic acid from isooctyl thioglycolate residual liquid, the product input in the whole operation process is hydrochloric acid solution, and the equipment input is a reactor, distillation and centrifugation equipment, all of which are industrial basic equipment. There is no need to add additional complex equipment and complex operating steps, so that the thiodiglycolic acid in the isooctyl thioglycolate residual liquid can be extracted and recovered using the existing industrial basic equipment, and the equipment cost, material cost and process difficulty required for recovery are greatly reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0026] Figure 1 It is the overall process flow chart of the present invention;

[0027] Figure 2 This is a schematic diagram of the reaction formula for generating thiodiglycolic acid of the present invention;

[0028] Figure 3 The figure is a curve diagram showing the solubility of thiodiglycolic acid and sodium chloride and temperature. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] The embodiment of the present application provides a method for extracting thiodiglycolic acid from isooctyl thioglycolate residual liquid, thereby solving the problem that in the existing industrial production process of isooctyl thioglycolate, the final product of the reaction contains a high content of sodium thiodiglycolic acid in the aqueous phase after alkaline hydrolysis, and is usually discharged into a sewage treatment system after adjusting the pH to neutral, which on the one hand easily causes serious industrial pollution, and on the other hand, there is a problem of incomplete product recovery causing material waste.

[0031] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0032] The embodiment of the invention discloses a method for extracting thiodiglycolic acid from isooctyl thioglycolate residual liquid.

[0033] Embodiment 1, according to the attached Figure 1-3 As shown, the following steps are included;

[0034] Step 1: Adding materials, the aqueous phase after the alkaline hydrolysis reaction of the isooctyl thioglycolate residual liquid is added into the reactor;

[0035] Step 2, synthesis, add hydrochloric acid to the reaction kettle and adjust to strong acidity so that the pH is less than 1, then the reaction starts, and the reaction formula is:

[0036]

[0037] After the reaction is completed, it is concentrated to remove the sodium chloride crystals;

[0038] The mother liquor is put into a crystallization kettle and cooled again to generate thiodiglycolic acid crystals, which are then centrifuged to obtain a wet thiodiglycolic acid product;

[0039] Step 3, refining and purification, putting the wet thiodiglycolic acid into a reactor, adding water and heating it to reflux, then cooling it for crystallization, so that a small amount of sodium chloride is dissolved in water to generate pure thiodiglycolic acid crystals, taking out the crystals and drying them to obtain solid thiodiglycolic acid.

[0040] Example 2: A certain amount of alkaline hydrolysis aqueous phase is weighed as an experiment, and hydrochloric acid is added dropwise to carry out a replacement reaction, thereby preparing thiodiglycolic acid using thiodiglycolic acid sodium salt;

[0041] First, the mother liquor is a byproduct of the production process of isooctyl thioglycolate. After the residual liquor is subjected to alkaline hydrolysis, the aqueous phase contains sodium thiodiglycolate, sodium dithiodiglycolate and sodium mercaptopropionate.

[0042] In this embodiment, 200 g of the alkaline hydrolysis aqueous phase was weighed, which contained 23% sodium thiodiglycolic acid, 1% sodium dithiodiglycolic acid, and 0.5% sodium mercaptopropionate. The mother liquor was then added to a reaction kettle and dripped with 31% hydrochloric acid. The dripping process was performed while stirring. The test data of the amount of hydrochloric acid dripped and the reaction residual amount of 23% sodium thiodiglycolic acid were as follows;

[0043] Hydrochloric acid drop amount 40g 50g 60g 70g 80g 90g Residual concentration of sodium thiodiglycolate 12％ 9％ 6％ 3％ 0 0 Residual concentration of hydrochloric acid 0 0 0 0 0.5％ 6％

[0044] Through the above-mentioned multiple groups of control hydrochloric acid amount drop test, it was found that in the case of 200g of the alkaline hydrolysis aqueous phase, the total amount of 31% hydrochloric acid dropwise added was optimally 80g, at which time the sodium thiodiglycolic acid salt was completely reacted, and there was substantially no residual hydrochloric acid in the mixed mother liquor, and continuous stirring was performed during the dropwise addition. After 80g of 31% hydrochloric acid was added dropwise, the pH value at this time was measured to be less than 1, and then continuous stirring was performed to allow the alkaline hydrolysis aqueous phase to fully react with the hydrochloric acid, and then allowed to stand, so that the sodium thiodiglycolic acid salt, the sodium dithiodiglycolic acid salt and the sodium mercaptopropionate in the original mother liquor were fully reacted, and all the reaction formulas are as follows;

[0045] Main reaction: NaOOC-CH2-S-CH2-COONa+2HCL=2NaCL+HOOC-CH2-S-CH2-COOH;

[0046] Side reaction 1; HSCH2CH2COONa+HCL=HSCH2CH2COOH+NaCL;

[0047] Side reaction 2: Na00C-CH2-SS-CH-COONa+2HCl=2NaCl+HOOC-CH-SS-CH2-COOH;

[0048] Thereby, the sodium thiodiglycolate, sodium dithiodiglycolate and sodium mercaptopropionate in the original mother liquor are basically consumed.

[0049] Removing sodium chloride in step 2 comprises the following steps:

[0050] S1, the mother liquor after the reaction in the reactor is subjected to atmospheric distillation, and the amount of water distilled is 100g, so that the concentration of sodium chloride in the mother liquor is increased, and then the concentrated mother liquor is poured into a centrifuge and cooled to 50°C. At this time, supersaturated crystals of sodium chloride appear, and the sodium chloride is removed by centrifugation;

[0051] S2. The mother liquor after centrifugation is put back into the reactor and distilled at room temperature again. The amount of water distilled is 20-30g. The concentrated mother liquor is poured into the centrifuge again and cooled to 70°C. At this time, a small amount of supersaturated crystals of sodium chloride appear here, and the sodium chloride is removed by centrifugation.

[0052] In the above process, since the hydrochloric acid is basically consumed after the reaction between the original mother liquor and the hydrochloric acid, the total mass of the mixed solution is 280g at this time. Assuming that the hydrochloric acid is completely consumed, since the concentration of the hydrochloric acid added is 31% and the total amount is 80g, it can be calculated that the concentration of sodium chloride generated after the reaction in the mixed solution is 15.96%, and then the temperature is increased to 100°C and then distilled and drained, so that the concentration of sodium chloride increases to form a supersaturated sodium chloride solution, and then the temperature is lowered to form sodium chloride crystals and precipitate, and then the sodium chloride is crystallized and separated from the mixed mother liquor by centrifugation, and the sodium chloride crystallization is performed twice by gradient concentration reduction, and finally 70% of the sodium chloride is removed, and the temperature is 70 degrees during the second cooling to avoid the crystallization of thiodiglycolic acid caused by too low a temperature and being separated;

[0053] In step 2, after the mother liquor is put into the crystallization kettle, the temperature is reduced to 25-30 degrees, at which time thiodiglycolic acid begins to crystallize. After the crystallization is completed, centrifugation is performed to obtain about 50g of thiodiglycolic acid, which is a wet product. In addition to the mother liquor containing sodium chloride adhering to the surface, a small amount of sodium chloride crystals also exist in the crystals, waiting for refining and purification, and the mother liquor after centrifugation is retained for standby use.

[0054] In the above process, the temperature is greatly reduced so that thiodiglycolic acid and sodium chloride are crystallized simultaneously. The crystals obtained at this time are mixed crystals of thiodiglycolic acid and sodium chloride. The crystals are then separated by centrifugation and the crystals are then separated.

[0055] During the refining and purification process, wet thiodiglycolic acid (containing a small amount of sodium chloride crystals) is put into a reactor, 30g of pure water is added, and the temperature is raised and refluxed to form a mixed solution of thiodiglycolic acid and a small amount of sodium chloride, and then the temperature is lowered to about 55°C again. At this time, thiodiglycolic acid begins to crystallize, and sodium chloride is dissolved in water. The crystallization of thiodiglycolic acid and sodium chloride in this process is affected by temperature. The test data are as follows;

[0056] Temperature (Celsius) 90 80 70 60 55 50 40 Residual thiodiglycolic acid concentration in solution 15％ 11％ 8％ 5.5％ 2.8％ 2％ 1.2％ Residual sodium chloride concentration in solution 19％ 19％ 19％ 19％ 19％ 18.5％ 15％

[0057] According to the test data in the above table, when the temperature drops below 55°C, sodium chloride begins to crystallize. Therefore, in order to avoid the subsequent crystallization product still containing sodium chloride crystals, the crystallization temperature is controlled at 55°C to obtain pure thiodiglycolic acid crystals.

[0058] At this time, centrifugation is performed again to obtain pure solid crystals of thiodiglycolic acid, and then the obtained crystals are placed at 80-90°C for drying to finally obtain about 43g of thiodiglycolic acid finished product. The recovery rate of thiodiglycolic acid in a single process reaches 93.5%. At the same time, the mother liquor containing sodium chloride and trace amounts of thiodiglycolic acid remains in the reactor.

[0059] The mother liquor after multiple crystallizations of thiodiglycolic acid in the crystallization kettle is enriched, and then distilled to remove water for concentration, and then sodium chloride is crystallized by cooling to remove sodium chloride, and at the same time, a sodium chloride-free mother liquor is obtained, thereby further reducing the sodium chloride content in the remaining mother liquor in the crystallization kettle after multiple enrichments.

[0060] The mother liquor containing sodium chloride and trace thiodiglycolic acid remaining in the reactor after refining and purification is mixed with the mother liquor obtained by removing sodium chloride twice in the crystallization kettle for enrichment, and enters the next round of thiodiglycolic acid recovery process, thereby realizing infinite recycling of thiodiglycolic acid. In this way, during the whole process, by continuously adding hydrochloric acid, the target product thiodiglycolic acid and the by-products sodium chloride and distilled water are prepared. The distilled water and sodium chloride can be used for industrial recycling, and the enriched mother liquor is infinitely recycled to achieve zero pollution discharge and high proportion of product recovery. In addition, the product input in the whole operation process is hydrochloric acid solution, and the equipment input is reactor, distillation and centrifugation equipment, all of which are industrial basic equipment. There is no need to add additional complex equipment and complex operating steps, so that the existing industrial basic equipment is used to realize the extraction and recovery of thiodiglycolic acid in the residual liquid of isooctyl thioglycolate, avoiding industrial pollution and material waste caused by incomplete product recovery.

[0061] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for extracting thiodiglycolic acid from isooctyl thioglycolate residual liquid, characterized in that: The steps include: Step 1: Adding materials, the aqueous phase after the alkaline hydrolysis reaction of the isooctyl thioglycolate residual liquid is added into the reactor; Step 2, synthesis, add hydrochloric acid to the reaction kettle and adjust to strong acidity so that the pH is less than 1, then the reaction starts, and the reaction formula is: After the reaction is completed, it is concentrated to remove the sodium chloride crystals; The mother liquor is put into a crystallization kettle and cooled again to generate thiodiglycolic acid crystals, which are then centrifuged to obtain a wet thiodiglycolic acid product; Step 3, refining and purification, putting the wet thiodiglycolic acid into a reactor, adding water and heating it to reflux, then cooling it for crystallization, so that a small amount of sodium chloride is dissolved in water to generate pure thiodiglycolic acid crystals, taking out the crystals and drying them to obtain solid thiodiglycolic acid.

2. The method for extracting thiodiglycolic acid from isooctyl thioglycolate residual liquid according to claim 1, characterized in that: The aqueous phase after the alkaline hydrolysis reaction of the isooctyl thioglycolate residual liquid contains sodium thiodiglycolic acid, sodium dithiodiglycolic acid and sodium mercaptopropionate. 200g of the alkaline hydrolysis aqueous phase is weighed, which contains 23% sodium thiodiglycolic acid, 1% sodium dithiodiglycolic acid and 0.5% sodium mercaptopropionate.

3. The method for extracting thiodiglycolic acid from isooctyl thioglycolate residual liquid according to claim 2, characterized in that: The concentration of the hydrochloric acid is 31%, and the dropping process adopts a method of dropping while stirring. The total amount of dropping is 80g. Continuous stirring is performed during the dropping process, and the dropping is stopped when the pH value is measured to be less than 1 after the dropping is completed. Then, continuous stirring is performed to allow the alkaline hydrolysis water phase to fully react with the hydrochloric acid, and then the mixture is allowed to stand.

4. The method for extracting thiodiglycolic acid from isooctyl thioglycolate residual liquid according to claim 2, characterized in that: The step 2 of removing sodium chloride comprises the following steps: S1, the mother liquor after the reaction in the reactor is subjected to atmospheric distillation, and the amount of water distilled is 100g, so that the concentration of sodium chloride in the mother liquor is increased, and then the concentrated mother liquor is poured into a centrifuge and cooled to 50°C. At this time, supersaturated crystals of sodium chloride appear, and the sodium chloride is removed by centrifugation; S2. The mother liquor after centrifugation is put back into the reactor and distilled at room temperature again. The amount of water distilled is 20-30g. The concentrated mother liquor is poured into the centrifuge again and cooled to 70°C. At this time, a small amount of supersaturated crystals of sodium chloride appear here, and the sodium chloride is removed by centrifugation.

5. The method for extracting thiodiglycolic acid from isooctyl thioglycolate residual liquid according to claim 2, characterized in that: In the step 2, after the mother liquor is put into the crystallization kettle, the temperature is lowered to 25-30 degrees, at which time thiodiglycolic acid begins to crystallize. After the crystallization is completed, centrifugation is performed to obtain about 50g of thiodiglycolic acid. The thiodiglycolic acid is a wet product. In addition to the mother liquor containing sodium chloride adhering to the surface, a small amount of sodium chloride crystals also exist in the crystals, waiting for refining and purification. At the same time, the mother liquor after centrifugation is retained for standby use.

6. The method for extracting thiodiglycolic acid from isooctyl thioglycolate residual liquid according to claim 5, characterized in that: In the refining and purification process, wet thiodiglycolic acid is put into a reactor, 30g of pure water is added, and the temperature is raised and refluxed to form a mixed solution of thiodiglycolic acid and a small amount of sodium chloride, and then the temperature is lowered to about 55°C again, at which time thiodiglycolic acid begins to crystallize, and sodium chloride is dissolved in water, and centrifugation is performed again to obtain solid crystals of thiodiglycolic acid, and then the obtained crystals are placed at 80-90°C for drying to finally obtain about 43g of thiodiglycolic acid finished product, and the recovery rate of thiodiglycolic acid in a single process reaches 93.5%, and at the same time, mother liquor containing sodium chloride and trace amounts of thiodiglycolic acid remains in the reactor.

7. The method for extracting thiodiglycolic acid from isooctyl thioglycolate residual liquid according to claim 6, characterized in that: The mother liquor after multiple crystallizations of thiodiglycolic acid in the crystallization kettle is enriched, and then distilled to remove water for concentration, and then sodium chloride is crystallized by cooling to remove sodium chloride, and at the same time, a sodium chloride-removed mother liquor is obtained.

8. The method for extracting thiodiglycolic acid from isooctyl thioglycolate residual liquid according to claim 7, characterized in that: The mother liquor containing sodium chloride and trace thiodiglycolic acid remaining in the reactor after refining and purification is mixed with the mother liquor removed from sodium chloride obtained by secondary removal of sodium chloride in the crystallization kettle for enrichment and enters the next round of thiodiglycolic acid recovery process.

Images