A method for purifying inositol

Abstract

The present invention relates to the technical field of purification of organic chemicals, and specifically relates to a method for purifying inositol. The inositol solution obtained after neutralization and filtration of the phytic acid hydrolysis solution in the present invention is subjected to desalting treatment to remove the metal salts in the inositol solution. During the process, a continuous circulation desalting process is adopted, so that the desalting efficiency reaches more than 99%. The purified solution obtained by desalting is concentrated and then added to a crystallization kettle containing low-temperature ethanol by spraying. The concentrated solution quickly crystallizes in the crystallization kettle to obtain inositol crystals, with high crystallization efficiency and high product purity. The ethanol mother liquor obtained after distillation is recycled, and the residue obtained is returned to the front end of the desalting section, thereby keeping the metal salt content in the system at a relatively low level all the time, which is of great significance for ensuring the stable operation of the system and the quality of the inositol product. The method of the present invention has low energy consumption, greatly improved product purity, and less waste liquid volume, which helps to improve the economic benefits of enterprises, save resources and protect the environment.

Description

Technical Field

[0001] The present invention relates to the technical field of purification of organic chemicals, and particularly relates to a method for purifying inositol. Background Art

[0002] Inositol, also known as cyclohexanehexol, has the molecular formula C6H 12 O6, with a molecular weight of 180. It is a white crystalline powder, with a melting point of 224 °C - 227 °C. It is soluble in water, slightly soluble in ethanol, and almost insoluble in ether, chloroform, and absolute acetone. Inositol is widely distributed in organisms and is a growth factor for animals and microorganisms. Inositol belongs to the vitamin B group and has many significant physiological and pharmacological activities. It has good curative effects especially on mental and neurological diseases, cancer, and lipid metabolism diseases. In addition, inositol is also widely used in the food and feed industry, playing a good role in promoting the growth and health of humans and animals.

[0003] The existing relatively mature inositol production process generally includes steps such as hydrolysis of phytic acid (a double salt formed by inositol hexaphosphate and metal calcium, magnesium ions, etc.), concentration, crystallization of crude products, centrifugal separation, dissolution and recrystallization, secondary centrifugal separation, drying and packaging, etc. There are the following disadvantages in the whole process: 1. High energy consumption for multiple dissolution and crystallization; 2. Even after two crystallizations, the obtained product, although with qualified purity, still cannot prepare high-purity products, resulting in low economic benefits. Continuing dissolution and crystallization will increase costs and is not worthwhile; 3. A large amount of crystallization mother liquor is generated. Disposing of it will result in a low final yield of inositol products, while recycling it to the system will cause the salt content in the solution to become higher and higher, ultimately affecting product quality and being difficult to handle.

[0004] Therefore, in view of the defects in the prior art, the present invention proposes an inositol purification method that can effectively reduce energy consumption while obtaining high-purity and high-yield inositol products, improving the economic benefits of enterprises and reducing the amount of waste liquid, which is beneficial to environmental protection. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for purifying inositol to solve the problems of high energy consumption, low product yield and purity, and large amount of crystallization mother liquor and difficult treatment in the existing purification process.

[0006] To achieve the above purpose, the present invention adopts the following technical scheme: A method for purifying inositol, based on phytic acid hydrolysis solution, is characterized by including the following steps:

[0007] S1. Add an alkali solution to the phytic acid hydrolysis solution and adjust the pH to alkaline. After filtering the obtained solution, an inositol solution is obtained;

[0008] S2. Feed the inositol solution obtained in S1 to a desalting section for desalting to obtain a purified solution after desalting;

[0009] S3. Concentrate the purified liquid obtained in S2 to obtain a concentrated liquid.

[0010] S4. Introduce the concentrated liquid obtained in S3 into a crystallization kettle containing low-temperature ethanol by spraying. The concentrated liquid crystallizes in the crystallization kettle, and inositol crystals are obtained after centrifugal separation.

[0011] S5. Dry and package the inositol crystals obtained in S4 to obtain an inositol product.

[0012] Furthermore, in S1, the lye is calcium hydroxide emulsion, the pH of the phytic acid hydrolysis solution is adjusted to 9 - 11, and the obtained solution is filtered using a plate and frame filter press.

[0013] Furthermore, in S2, the desalination section includes multiple desalination units connected in series and a regeneration unit. During the cycle, the primary desalination unit stops working first and enters the regeneration stage to obtain a new regeneration unit. The secondary desalination unit serves as the new primary desalination unit, and the original regeneration unit serves as the new final desalination unit to start working. After the new regeneration unit is regenerated, it waits to enter the cycle again.

[0014] Furthermore, in S2, the removal rate of metal salts in the purified liquid is greater than 99.9%.

[0015] Furthermore, in S2, the number of desalination units is not less than two. The desalination units and the regeneration unit each include a cation exchanger and an anion exchanger connected in series, filled with H + -type strongly acidic cation exchange resin and OH - -type strongly basic anion exchange resin respectively.

[0016] Furthermore, in S2, the cation exchanger is rinsed and regenerated with hydrochloric acid solution, and then washed with water to neutrality; the anion exchanger is rinsed and regenerated with sodium hydroxide solution, and then washed with water to neutrality.

[0017] Furthermore, in S3, evaporation and concentration are carried out using a vacuum evaporator. The temperature of the concentrated liquid obtained after concentration is 70 - 80°C, and the mass fraction of inositol in the concentrated liquid is 25 - 30%.

[0018] Furthermore, in S4, the ratio of the amount of the concentrated liquid to the amount of ethanol is controlled at 1:5 - 10, the temperature in the crystallization kettle is controlled at 10 - 15°C, and inositol crystal seeds are added to the crystallization kettle.

[0019] Furthermore, in S4, the time for single crystallization is 5 - 8 h, and the yield of inositol in single crystallization is greater than 95%.

[0020] Further, in step S4, the purity of the inositol crystals obtained by centrifugation is greater than 99%. After centrifugal separation, mother liquor of ethanol is also obtained. The obtained mother liquor of ethanol is distilled in a distillation column. The obtained ethanol is returned to the crystallization kettle in S4 for recycling, and the obtained residue liquid is returned to the front end of the desalination section in S2 to achieve recycling.

[0021] Advantages of the present invention:

[0022] 1. The process flow of the present invention is simple. Compared with the existing process, the energy consumption is reduced, and at the same time, the purity of the obtained product is greatly improved, and the generation of production waste liquid is greatly reduced, which is helpful for the improvement of the economic benefits of enterprises and the protection of the environment;

[0023] 2. The inositol solution is desalted by a continuous desalting process. During the process, the desalting unit is a series connection of a cation exchanger and an anion exchanger, and a plurality of desalting units and regeneration units are connected in series and circulated. The desalting effect reaches more than 99%. While realizing continuous desalting, the desalting system also operates stably, which is beneficial to the simplification of the process and the guarantee of the product quality. There is less regeneration waste liquid during the operation process, which is helpful for cost reduction and environmental protection;

[0024] 3. The desalted and purified liquid is evaporated and concentrated. On the one hand, the concentration of inositol is increased, and on the other hand, the temperature is increased, so as to increase the solubility of inositol. Finally, the concentration of inositol is further increased, so that more inositol crystals can be obtained in a single batch, which is beneficial to the reduction of production equipment costs and the improvement of production efficiency;

[0025] 4. The method of spraying the concentrated liquid into low-temperature ethanol and adding crystal seeds is adopted, so that the inositol in the concentrated liquid can be quickly precipitated. Compared with the existing process, the efficiency is nearly doubled, the production efficiency is greatly improved, and at the same time, the single batch yield is above 95% and the purity is above 99%, and the effect is remarkable;

[0026] 5. After the mother liquor of ethanol separated from the crystallization kettle passes through the evaporation tower, the obtained ethanol is used for recycling, realizing the recycling of ethanol, and the obtained residue liquid is returned to the front end of the desalination process and re-enters the system. On the one hand, desalination ensures the stable operation of the system, and on the other hand, it also ensures that the produced inositol has no loss. In theory, the yield of inositol can reach 100%. Description of the drawings

[0027] Figure 1 is a schematic diagram of the process flow of the present invention;

[0028] Figure 2 is a schematic diagram of the desalination process of the present invention.

[0029] Names corresponding to each mark in the figure:

[0030] 1. Inositol solution pipeline; 11. Liquid inlet branch pipe; 111. First-stage liquid inlet control valve; 2. Desalination unit; 21. Inter-column pipeline; 211. First-stage inter-column control valve; 212. Second-stage inter-column control valve; 22. Liquid outlet branch pipe; 221. Third-stage liquid outlet control valve; 222. On-line conductivity measuring instrument; 3. Purified liquid pipeline; 4. Regeneration pipeline; 41. Regeneration control valve. Specific embodiments

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0032] As Figure 1 shown, phyticin (a double salt formed by inositol hexaphosphate and metal calcium, magnesium and other ions) is hydrolyzed under pressure to obtain a phyticin hydrolysis solution. The phyticin hydrolysis solution is neutralized with calcium hydroxide emulsion and then filtered. During the process, phosphate ions are removed in the form of calcium phosphate, so as to obtain an inositol solution. There are still a certain amount of anions and cations in the inositol solution, such as Ca 2+ , OH - etc. Therefore, desalination is required during the process. Desalination is carried out by using anion and cation exchange resins. After desalination of the inositol solution, a pure purified solution is obtained. However, at this time, the inositol content in the solution is low. Therefore, the purified solution is further concentrated by evaporation. During the process, a vacuum evaporator etc. can be used. The concentrated solution obtained by concentration is sprayed into a crystallization kettle by spraying. And ethanol has been introduced and seeds have been added to the crystallization kettle in advance. At this time, inositol in the concentrated solution crystallizes in the crystallization kettle, so that inositol crystals are obtained after centrifugal separation. The inositol crystals are dried and packaged to be inositol products. And the ethanol mother liquor separated by centrifugation during the process is distilled by a distillation column to realize the recovery and recycling of ethanol, and the residue liquid is returned to the front end of the desalination process and re-fed into the system.

[0033] As Figure 2 shown, in the desalination process of the present invention, a continuous desalination mode is adopted, in which a circulating mode of multiple desalination units 2 connected in series is adopted. Each desalination unit 2 includes a cation exchanger and an anion exchanger connected in series, and is respectively filled with H + -type strongly acidic cation exchange resin and OH -The strongly basic anion exchange resin adopts a method of coordinating multi-stage desalination and regeneration standby to achieve a continuous desalination process. Each desalination unit 2 is arranged in a ring shape. The inositol solution pipeline 1 is distributed to each desalination unit 2 through the liquid inlet branch pipe 11. For the convenience of description and understanding, a state of the illustrated desalination process is described as follows. As shown in the figure, at this time, the first-stage liquid inlet control valve 111 is opened, and the other liquid inlet control valves are kept closed. In each state, only one liquid inlet control valve needs to be opened. At the same time, the first-stage inter-column control valve 211 and the second-stage inter-column control valve 212 are opened, and the other inter-column control valves are kept closed. The third-stage liquid outlet control valve 221 is opened, and the other liquid outlet control valves are kept closed. The liquid outlet control valve is installed on the liquid outlet branch pipe 22 to discharge the purified liquid to the next process section. During the cyclic operation, only the first-stage desalination unit needs to stop feeding and then be regenerated. The original second-stage unit serves as the new first-stage unit, and the subsequent units are connected in sequence, while the original regeneration unit serves as the third-stage unit. A regeneration pipeline 4 is equipped on each ion exchanger, and a regeneration control valve 41 is installed. Among them, the cation exchanger is regenerated by introducing acid, and the anion exchanger is regenerated by introducing an alkali solution. When automated control is connected, an on-line conductivity measuring instrument 222 is installed on the liquid outlet branch pipe 22 to detect the desalination effect through the on-line conductivity measuring instrument 222. When the desalination effect is not good, it can be automatically cycled and switched.

[0034] The principle of the present invention is as follows:

[0035] The existing relatively mature inositol production process is the pressurized hydrolysis method. The general process is: phytic acid (hydrolysis) - hydrolysis solution (neutralization, filtration) - inositol solution (impurity removal, concentration, crystallization and centrifugation) - crude inositol (dissolution for impurity removal, crystallization and centrifugation) - refined product. During the whole process, since the inositol solution contains metal salts, it needs to be dissolved and crystallized many times to obtain a qualified product. However, there are many defects in the process: 1. The energy consumption of multiple dissolution and crystallization is high; 2. Even after two crystallizations, the obtained product has a qualified purity, but still cannot be used to prepare high-purity products, resulting in low economic benefits. Continuing to dissolve and crystallize will increase costs and is not worth it; 3. A large amount of crystallization mother liquor is generated. Disposing of it will result in a low final yield of inositol products, while recycling it to the system will cause the salt content in the solution to become higher and higher, ultimately affecting the product quality and being difficult to handle.

[0036] Therefore, the present invention explores and optimizes the existing process to solve these drawbacks.

[0037] First, the present invention adds an alkali to the phytic acid hydrolysis solution for neutralization, aiming to adjust the pH and precipitate phosphate ions. In the process, calcium hydroxide emulsion is generally the best choice for the alkali solution. During the process, not only can phosphate ions be removed, but also the low solubility of calcium hydroxide itself can adjust the pH of the solution to weakly alkaline, around 9 - 11. At this time, filtration is carried out, and the introduced anions and cations in the finally obtained inositol solution are also less, which can reduce the treatment burden of the subsequent desalination section.

[0038] The obtained inositol solution is desalted through a desalination process. In the desalination process of the present invention, a continuous desalination process is adopted. Through the cooperation of a three - stage desalination unit and a first - stage regeneration unit, continuous regeneration and desalination are realized. In the desalination process of the present invention, a unique design is made for the continuous desalination system. After the inositol solution undergoes three - stage desalination, a purified solution is obtained. When the on - line conductivity meter 222 at the purified solution outlet detects a decrease in the desalination effect, at this time, the first - stage desalination unit is separated from the system. The previous second - stage desalination unit serves as the new first - stage desalination unit, and the previous regeneration unit serves as the new third - stage desalination unit and is incorporated into the system. The separated previous first - stage desalination unit enters regeneration and waits for the next cycle. The advantages of this are as follows: on the one hand, the desalination process is cycled, which is beneficial to the continuous and stable production and the improvement of production efficiency; on the other hand, taking the regeneration unit as the new third - stage desalination unit is equivalent to a counter - current desalination method (the first stage is the first to contact the feed liquid and its function declines the fastest, and incorporating it into the new third stage is equivalent to further refining), making the desalination effect of the entire system better. In actual production operation, automatic control can be adopted. When the on - line conductivity meter 222 detects that the conductivity of the outlet liquid is greater than 20 μS / cm, it is considered that the desalination effect begins to decline, and at this time, automatic cycle switching can start. The automatic control involved in the process is the existing mature PLC control, and the control principle is relatively mature and simple, which is not difficult for those skilled in the art to understand and will not be elaborated here. Finally, the removal rate of metal salts in the obtained purified solution is above 99.9%.

[0039] Cation - anion resins need to be regenerated after being used for a period of time. Regeneration is carried out by flushing with a regeneration solution. The cation resin is regenerated by flushing with about 5% hydrochloric acid and then washed with water to neutrality. The anion resin is regenerated with about 5% sodium hydroxide solution and then washed with water to neutrality. In actual production, regeneration is generally switched once every half month or so, and the generated waste liquid is less, which helps to save resources and protect the environment.

[0040] The concentration of inositol in the purified liquid after desalination is relatively low. At this time, for subsequent processing, concentration is required. There are two purposes for concentration. One is to increase the concentration of inositol, and the other is to increase the temperature to improve the solubility of inositol, and ultimately further increase the concentration of inositol. The concentration process can use a vacuum evaporator, etc. to improve the evaporation efficiency. The evaporation temperature can be carried out at a relatively high temperature. The temperature of the finally obtained inositol solution is controlled at 70-80 °C, and the mass fraction of the solution is controlled at 25-30%.

[0041] The concentrated liquid obtained above is sprayed into the crystallization kettle by spraying. The crystallization kettle is a common existing device and will not be elaborated here. Before spraying, ethanol is stored in the crystallization kettle. The purity of this ethanol is relatively high, reaching more than 98%, and the temperature is about 10 °C. At the same time, crystal seeds are added. Then, after the concentrated liquid is sprayed into the crystallization kettle, crystals quickly precipitate in the ethanol aqueous solution, thus obtaining inositol crystals. In the actual production process, the ratio of the amount of the concentrated liquid to the amount of ethanol is controlled at 1:5-10, which can precipitate inositol crystals quickly and efficiently. The single crystallization process takes 5-8 hours. Compared with the existing crystallization method, the efficiency is nearly doubled. The single-pass yield of inositol during the process is above 95%, and the purity of a single crystallization is above 99%. The effect is very obvious.

[0042] The ethanol mother liquor obtained after crystallization separation is a mixed liquid of ethanol and water, and still contains a small amount of inositol during the process. The ethanol in this ethanol mother liquor is recovered by distillation and then returned to the crystallization kettle for recycling to realize the recycling of ethanol. The residue liquid during the process is mainly water and contains a small amount of inositol, as well as a small amount of cations and anions. At this time, the residue liquid is returned to the front end of the desalination process to realize recycling within the system. There is no waste liquid generated during the whole process, and theoretically there is no inositol loss. The yield of inositol can reach 100%. At the same time, only one crystallization and one distillation are carried out in the whole process, and there is no excessive cooling process. Compared with the existing process, the energy consumption is reduced, but the effect is very obvious. On the one hand, there is no excessive waste liquid, and on the other hand, the process is optimized, the product purity is greatly improved, and the economic benefit is significantly improved, which is of great significance for improving the production efficiency of enterprises and environmental protection.

[0043] Example 1

[0044] An organic chemical synthesis enterprise used to prepare inositol by the process of phytic acid pressurized hydrolysis, concentration, crude product crystallization, centrifugal separation, dissolution and recrystallization, secondary centrifugal separation, drying and packaging. The purity of the inositol finally obtained was about 95-98%. In actual production, one or two additional dissolution and recrystallization processes were often required to make the product purity reach about 99% to meet customer requirements. The whole process had high energy consumption and low economic benefits. At the same time, a large amount of crystallization mother liquor was produced. Since the mother liquor contained metal salts, the enterprise often treated it as wastewater and sent it to the wastewater treatment section. Finally, in the whole inositol production process, the yield of inositol was only about 70-80%, which not only caused a large amount of waste but also increased the cost of wastewater treatment.

[0045] The company carried out technical transformation on the production workshop through the process method of the present invention. During the transformation process, a new desalination process (tertiary desalination + primary regeneration) was added, a distillation column was newly added, and the layout of the pipelines of the new process was also carried out. The whole transformation took about 3 months. The equipment, labor and electrical control costs of the whole transformation project were about 1 million yuan. After the transformation was completed, after commissioning, the system was formally put into production after stable operation.

[0046] After the process system was stably operating, laboratory staff measured and recorded the process parameters during the production process, including the metal content in the inositol solution before and after desalination to evaluate the performance of the desalination system, and the purity of the obtained inositol product to evaluate the performance and stability during the whole process operation, as follows:

[0047] Table 1 Desalination effect table of metal salt content in inositol solution

[0048]

[0049] In Table 1, in order to accurately monitor the desalination effect, sampling was carried out once every week, and then a salt content measuring instrument was used to measure the salt content before and after desalination. The obtained results were calculated in terms of NaCl. It can be seen that the desalination effect of metal salts was obvious before and after desalination. The desalination rate of sample No. 3 was relatively low during the process because the desalination unit was about to switch to regeneration during the sampling period. This sample was taken when the desalination capacity of the desalination section was the weakest, so it was lower. When sampling next time, the desalination unit had carried out cyclic switching, and the desalination effect further recovered. Generally speaking, the metal salt desalination rate could reach more than 99.9%, indicating that the desalination process was stably operating and beneficial to the stable production.

[0050] Table 2 Inositol product purity table

[0051]

[0052] Randomly select 5 batches of samples before the transformation of the laboratory process and compare them with those after the transformation. Use gas chromatography to determine the inositol content in the samples. As can be seen from Table 2, the purity of the products before the transformation generally fluctuated between 95% and 98%. The purity of Sample 4# reached 99.1%, which was obtained by three crystallizations. Therefore, the purity was relatively high, but the corresponding energy consumption was also higher. After the transformation, the purity of each batch of products was relatively stable, all stable above 99%. The highest reached 99.24%, meeting the pharmaceutical standard. The price of pharmaceutical-grade inositol is 40,000 - 50,000 yuan / ton, while the price of ordinary specifications is 5,000 - 15,000 yuan / ton. The price difference is obvious, bringing higher economic benefits to the enterprise.

[0053] It can be seen that after the enterprise uses the process method of the present invention for transformation, the process runs stably. At the same time, the obtained products have high purity and stable quality, bringing good economic benefits. During the production operation process, the original crystallized mother liquor wastewater no longer generates, reducing the enterprise's wastewater treatment cost. The newly generated residual liquid realizes circulation in the system, not only causing no pollution, but also achieving an increase in the inositol recovery rate, improving the enterprise's economic benefits and contributing to environmental protection.

[0054] During the operation process of the transformed process, some wastewater is also generated, namely the resin regeneration wastewater. However, this wastewater can be basically discharged after neutralization and pH adjustment, with low treatment cost. At the same time, during the production process, the resin needs to be replaced after the end of its service life. The service life of the ion exchange resin is relatively long, 2 - 3 years, with a low replacement frequency and relatively low price, and low production cost. Generally speaking, the process method of the present invention is superior to the existing process, with great improvements in terms of energy consumption, cost, product yield, product quality, etc., playing an important role in promoting the development of the enterprise.

[0055] The present invention is not limited to the above best implementation mode. Anyone can obtain other various forms of products under the inspiration of the present invention. However, no matter what changes are made in its shape or structure, as long as it has the same or similar technical solutions as the present application, it falls within the protection scope of the present invention.

Claims

1. A method for purifying inositol, based on phytic acid hydrolysis solution, characterized in that, It includes the following steps: S1. Add lye to the phytic acid hydrolysis solution and adjust the pH to alkaline. After filtering the obtained solution, inositol solution is obtained; S2. Feed the inositol solution obtained in S1 to the desalting section for desalting to obtain the purified solution after desalting; The desalting section includes multiple desalting units connected in series and a regeneration unit. During the circulation process, the primary desalting unit stops working first and enters the regeneration stage to obtain a new regeneration unit. The secondary desalting unit serves as the new primary desalting unit, and the original regeneration unit serves as the new final desalting unit to start working. After the new regeneration unit is regenerated, it waits to enter the circulation again; The number of desalination units is not less than two. Both the desalination units and the regeneration units include a cation exchanger and an anion exchanger connected in series, filled with strong acid cation exchange resin of H + type and strong base anion exchange resin of OH - type respectively; S3. Concentrate the purified solution obtained in S2 to obtain a concentrated solution; S4. Feed the concentrated solution obtained in S3 into a crystallization kettle containing low-temperature ethanol by spraying. The concentrated solution crystallizes in the crystallization kettle, and inositol crystals are obtained after centrifugal separation; S5. Dry and package the inositol crystals obtained in S4 to obtain inositol products.

2. The purification method of inositol according to claim 1, characterized in that: In the above S1, the lye is calcium hydroxide emulsion, the pH of the phytic acid hydrolysis solution is adjusted to 9 - 11, and a plate and frame filter press is used to filter the obtained solution.

3. The purification method of inositol according to claim 1, wherein: In the above S2, the removal rate of metal salts in the purified solution is greater than 99.9%.

4. The purification method of inositol according to claim 1, characterized in that: In the above S2, the cation exchanger is rinsed and regenerated with hydrochloric acid solution and then washed with water to neutrality; the anion exchanger is rinsed and regenerated with sodium hydroxide solution and then washed with water to neutrality.

5. The purification method of inositol according to claim 1, characterized in that: In the above S3, concentration is carried out by vacuum evaporation. The temperature of the concentrated solution obtained after concentration is 70 - 80 °C, and the mass fraction of inositol in the concentrated solution is 25 - 30%.

6. The purification method of inositol according to claim 1, characterized in that: In the above S4, the ratio of the amount of the concentrated solution to the amount of ethanol is controlled at 1:5 - 10, the temperature in the crystallization kettle is controlled at 10 - 15 °C, and inositol crystal seeds are added to the crystallization kettle.

7. A method for purifying inositol according to claim 6, characterized in that: In the above S4, the time for single crystallization is 5 - 8 h, and the yield of inositol in single crystallization is greater than 95%.

8. The purification method of inositol according to claim 6, characterized in that: In the above S4, the purity of the inositol crystals obtained by centrifugation is greater than 99%. After centrifugal separation, ethanol mother liquor is also obtained. The obtained ethanol mother liquor is distilled in a distillation column, and the obtained ethanol is returned to the crystallization kettle in S4 for recycling, and the obtained residue liquid is returned to the front end of the desalting section in S2 to achieve recycling.

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