阅读说明：本技术 一种聚苯硫醚生产过程中产生混盐回收氯化锂的方法 (Method for recovering lithium chloride from mixed salt generated in polyphenylene sulfide production process ) 是由 侯永生 李盼盼 朱素娟 徐淑强 马华青 吴国军 冯雁金 于 2021-04-06 设计创作，主要内容包括：本发明公开了一种聚苯硫醚生产过程中产生混盐回收氯化锂的方法,取含有氯化钠和氯化锂混盐的混合水溶液,蒸馏,高温过滤,得到氯化钠固体和滤液；滤液浓缩得到氯化锂。本发明针对含有氯化钠和氯化锂的水溶液提出的,通过先分离氯化钠再分离氯化锂的顺序实现这两者的分离和回收。该方法将氯化钠与氯化锂进行了有效的分离回收,氯化锂的回收率可以达到99%以上,氯化钠的纯度也可以达到99%以上。(The invention discloses a method for recovering lithium chloride by producing mixed salt in the production process of polyphenylene sulfide, which comprises the steps of taking mixed aqueous solution containing sodium chloride and lithium chloride mixed salt, distilling, and filtering at high temperature to obtain sodium chloride solid and filtrate; and concentrating the filtrate to obtain lithium chloride. The invention provides a method for separating and recovering sodium chloride and lithium chloride from an aqueous solution containing the sodium chloride and the lithium chloride by sequentially separating the sodium chloride and the lithium chloride. The method effectively separates and recovers the sodium chloride and the lithium chloride, the recovery rate of the lithium chloride can reach more than 99 percent, and the purity of the sodium chloride can also reach more than 99 percent.)

1. A method for producing mixed salt and recovering lithium chloride in the production process of polyphenylene sulfide is characterized by comprising the following steps:

(1) taking an aqueous solution containing mixed salt of sodium chloride and lithium chloride, distilling, and filtering at high temperature to obtain sodium chloride solid and filtrate;

(2) and concentrating the filtrate to obtain lithium chloride.

2. The method for producing mixed salt and recovering lithium chloride in the polyphenylene sulfide production process as claimed in claim 1, wherein the sodium chloride solid in step (1) is washed with saturated aqueous solution of sodium chloride, and the water washing solution is returned to the aqueous solution containing the mixed salt of sodium chloride and lithium chloride, and the separation of the sodium chloride solid and the lithium chloride is continued.

3. The method for producing mixed salt and recovering lithium chloride in the polyphenylene sulfide production process as claimed in claim 1 or 2, wherein the concentration of lithium chloride during the high temperature filtration in the step (1) is 40-45%.

4. The method for producing mixed salt and recovering lithium chloride in the polyphenylene sulfide production process as claimed in claim 1, wherein the temperature of the high-temperature filtration in the step (1) is 70-100 ℃.

5. The method for producing mixed salt to recover lithium chloride in the polyphenylene sulfide production process according to claim 1, 2 or 4, wherein in the step (2), the concentration is performed by evaporation or distillation.

Technical Field

The invention relates to the technical field of polyphenylene sulfide catalyst recovery, in particular to a method for recovering lithium chloride from mixed salt generated in the production process of polyphenylene sulfide.

Background

Polyphenylene sulfide is a novel high-performance thermoplastic resin, has the advantages of high mechanical strength, high temperature resistance, chemical resistance, flame retardancy, good thermal stability, excellent electrical property and the like, and is widely applied to the fields of electronics, automobiles, machinery and chemical industry.

Lithium chloride is generally used as a catalyst in the production process of polyphenylene sulfide, the market unit price of the lithium chloride is 70000 yuan/ton, and the unit price is higher, so the recovery rate of the lithium chloride is directly related to the production cost of the polyphenylene sulfide. Therefore, it is necessary to develop a method for recovering lithium chloride with high efficiency.

Sodium chloride is generated in the production process of polyphenylene sulfide, lithium chloride and sodium chloride which are finally added as catalysts are discharged out of the system in the form of mixed salt, and at present, Chinese patents disclose that a plurality of ways (for example, patent CN 107983393A) for recovering lithium chloride are that sodium carbonate is added after salt is dissolved, lithium chloride and sodium carbonate react to generate lithium carbonate precipitate and sodium chloride, then lithium carbonate is recovered in a filtration way, hydrochloric acid is added into lithium carbonate, and lithium carbonate and hydrochloric acid react to generate lithium chloride, water and carbon dioxide. This recovery method has the following disadvantages: 1) lithium carbonate has certain solubility in water, so that the recovery rate of lithium chloride is low, and the recovery rate of lithium chloride in the method is generally 80 percent and is up to 85 percent; 2) sodium chloride contains a certain amount of lithium chloride, which affects the downstream use of sodium chloride.

Patent CN108586746A provides a method for separating and recovering by-products in polyphenylene sulfide production, which comprises removing residual NMP, inputting the residual water solution after extracting NMP into an evaporator for evaporation and concentration, crystallizing and precipitating sodium chloride at the bottom of the evaporator, monitoring the concentration of lithium chloride in the mother solution to approach saturation, transferring out the mother solution, performing partition wall type cooling to 40-60 ℃, and crystallizing and precipitating lithium chloride. This method requires that the concentration of lithium chloride is saturated by crystallization, and it is known from the solubility of lithium chloride in water that the solubility of lithium chloride in water is high at high temperatures, and when the concentration of lithium chloride in the mother liquor approaches saturation, the sodium chloride precipitated at this time contains a large amount of lithium chloride (because sodium chloride contains water, lithium chloride is dissolved in water), which affects not only the quality of sodium chloride but also the recovery rate of lithium chloride is lowered.

Patent CN111057239A discloses a method for recovering lithium salt auxiliary agent in the production process of polyphenylene sulfide, which comprises subjecting the byproduct dry salt of polyphenylene sulfide with organic by-product and lithium salt auxiliary agent to incineration treatment with a flue gas treatment system, dissolving again and removing impurities, and finally evaporating and concentrating to recover lithium salt as polyphenylene sulfide synthesis auxiliary agent. The purification of impurities is finished through the processes of acid regulation and filtration, and finally LiCl can be directly recovered through evaporation and concentration. However, the method has the following disadvantages that (1) solid salt is directly incinerated, a large amount of nitrogen oxides are generated in the incineration process due to the large amount of NMP contained in the solid salt, the tail gas treatment measures are complex, and the treatment cost is high; (2) organic matters are removed and then dissolved, so that the energy consumption is high; (3) this method cannot obtain high purity sodium chloride and lithium chloride, and the separation of mixed salts is not thorough.

In the method for recycling the lithium salt and the solvent in the preparation of the polyphenylene sulfide of patent CN 103965476A, sodium chloride is separated from an NMP solvent, and lithium chloride has higher solubility in NMP, so that the sodium chloride contains a large amount of NMP, and the quality of the salt is poor.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides a method for recovering lithium chloride by producing mixed salt in the production process of polyphenylene sulfide, the method effectively separates and recovers sodium chloride and lithium chloride, the recovery rate of lithium chloride can reach more than 99%, and the purity of sodium chloride can also reach more than 99%.

The invention provides a method for separating and recovering sodium chloride and lithium chloride from an aqueous solution containing the sodium chloride and the lithium chloride by sequentially separating the sodium chloride and the lithium chloride. Heating an aqueous solution containing mixed salt of sodium chloride and lithium chloride, filtering at high temperature to obtain sodium chloride solid and filtrate, continuously heating and distilling the filtrate, filtering at normal temperature to obtain lithium chloride monohydrate, and evaporating and dehydrating the lithium chloride monohydrate by using equipment such as a rake dryer and the like according to requirements to obtain the anhydrous lithium chloride. The sodium chloride solid containing a small amount of lithium chloride can be recovered by washing. The lithium chloride recovered by the method has the recovery rate of over 99 percent and the purity of sodium chloride of over 99 percent.

The specific technical scheme of the invention is as follows:

a method for producing mixed salt and recovering lithium chloride in the production process of polyphenylene sulfide comprises the following steps:

(1) taking a mixed aqueous solution containing mixed salt of sodium chloride and lithium chloride, distilling and dehydrating, and filtering at high temperature to obtain sodium chloride solid and filtrate;

(2) and concentrating the filtrate to obtain lithium chloride.

The method is characterized in that the solubility of sodium chloride in water is small along with the change of temperature, and the solubility of lithium chloride in water is large along with the change of temperature; and at the same temperature, the solubility of lithium chloride in water is higher than that of sodium chloride; and the sodium chloride and the lithium chloride have the characteristics of the same ion effect and the like in the solution, so that after the water in the solution is removed by distillation, the sodium chloride is firstly separated out, and the lithium chloride in the solution is controlled at a certain concentration (the concentration of the lithium chloride is more than 41 percent), so that the complete separation of the sodium chloride can be ensured. At this time, high-temperature filtration is selected to recover sodium chloride. Since the sodium chloride contains a small amount of water and dissolves lithium chloride, the sodium chloride contains a small amount of lithium chloride.

Further, the sodium chloride solid described in the step (1) is washed with a saturated aqueous solution of sodium chloride, and the water-washed liquid is returned to the aqueous solution containing a mixed salt of sodium chloride and lithium chloride, and the separation of the both is continued. Since sodium chloride and lithium chloride have the same ion effect, when a small amount of lithium chloride is contained in the sodium chloride, the lithium chloride can be recovered by a salt washing mode. The solid sodium chloride was washed with a saturated aqueous solution of sodium chloride, lithium chloride was dissolved in water, and sodium chloride was precipitated.

Further, the distillation in the step (1) is carried out under normal pressure or negative pressure.

Further, the concentration of lithium chloride in the high-temperature filtration in the step (1) is 40-45%, the sodium chloride and the lithium chloride have the same ion effect in the solution, and the content of the lithium chloride in the solution is controlled to be a certain concentration (the concentration of the lithium chloride is more than 40%), so that the sodium chloride can be ensured to be completely separated out.

Further, the temperature of the filtration in the step (1) is 70-100 ℃. High-temperature filtration is selected to ensure that the precipitated sodium chloride contains lithium chloride as little as possible, and because the solubility of the lithium chloride in water is increased along with the increase of the temperature, the lithium chloride is dissolved in the water when the sodium chloride is filtered, so the filtration is carried out at the high temperature of 70-100 ℃.

Further, in the step (2), concentration is carried out by means known in the art such as evaporation, distillation, and the like. The lithium chloride obtained by distillation is lithium chloride monohydrate, and if anhydrous lithium chloride is needed in the production process, high-temperature drying equipment such as a rake dryer can be adopted for reprocessing, and crystal water in the lithium chloride monohydrate is evaporated and removed to obtain the anhydrous lithium chloride. The lithium chloride product obtained by the method is white crystal, and the purity can reach more than 99.0 percent through determination.

The invention provides a method for effectively separating lithium chloride and sodium chloride mixed salt generated in the production process of polyphenylene sulfide, which has the following beneficial effects:

(1) can realize the rate of recovery more than 99% of lithium chloride through this patent, compare traditional technology 80% lithium chloride rate of recovery, improve nearly 20% rate of recovery of lithium chloride.

(2) The purity of the sodium chloride obtained by the method is more than 99%, and after organic matters in the sodium chloride are removed by other processes such as a high-temperature melting oxidation technology, the sodium chloride can be utilized to a chlor-alkali device to meet the index requirement of cyclic utilization of the sodium chloride.

Drawings

FIG. 1 is a process flow diagram.

Detailed Description

The present invention will be described in further detail with reference to specific embodiments. The following description is exemplary only, and is not intended to limit the scope thereof. In the following examples, unless otherwise specified, the concentrations or contents are mass concentrations.

In the following examples, the analysis method of lithium chloride employs a sodium phosphate method, sodium phosphate reacts with lithium chloride to generate lithium phosphate precipitate, and the content of lithium chloride is inversely deduced according to the quality of lithium phosphate precipitate. Of particular note is the excess of sodium phosphate, which ensures that all of the lithium chloride is reacted to form lithium phosphate.

Example 1

1069.1g of mixed salt solution of sodium chloride and lithium chloride (wherein the concentration of the sodium chloride is 9.36 percent and the concentration of the lithium chloride is 4.64 percent) is taken to be put into a distillation device for normal pressure distillation, when 851g of fraction is extracted, high-temperature filtration is carried out, the filtration temperature is 70 ℃, and 116.04g of filtrate and 102.06g of solid sodium chloride salt are obtained, and the concentration of the lithium chloride in the filtrate is 42.03 percent; the atmospheric distillation experiment was continued on the filtrate to obtain 47.61g of solid lithium chloride salt (solid dried to constant weight at 105 ℃).

Through analysis, the sodium chloride content in the solid sodium chloride salt is 93.62 percent, the lithium chloride content is 1.95 percent, and the water content is 4.43 percent; the lithium chloride content in the solid lithium chloride salt is 100%, and sodium chloride is not contained.

The obtained sodium chloride salt was washed with a saturated aqueous sodium chloride solution, and then with a saturated aqueous sodium chloride solution, sodium chloride was precipitated, and the lithium chloride aqueous solution was returned to the mixed salt separation step.

The sodium chloride content of the solid sodium chloride salt at this point was 99.8% by analysis.

Example 2

1073.8g of mixed salt solution of sodium chloride and lithium chloride (wherein the concentration of the sodium chloride is 9.36 percent and the concentration of the lithium chloride is 4.64 percent) is taken to be put into a distillation device for normal pressure distillation, when 862.4g of fraction is extracted, high-temperature filtration is carried out, the filtration temperature is 80 ℃, 108.6g of filtrate and 102.8g of solid sodium chloride salt are obtained, and the concentration of the lithium chloride in the filtrate is 44.93 percent; the atmospheric distillation experiment was continued on the filtrate to obtain 47.56g of solid lithium chloride salt (solid dried to constant weight at 105 ℃).

Through analysis, the content of sodium chloride in the solid sodium chloride salt is 92.8 percent, the content of lithium chloride is 2.2 percent, and the water content is 5 percent; the lithium chloride content in the solid lithium chloride salt is 100%, and sodium chloride is not contained.

The obtained sodium chloride salt was washed with a saturated aqueous sodium chloride solution, and then with a saturated aqueous sodium chloride solution, sodium chloride was precipitated, and the lithium chloride aqueous solution was returned to the mixed salt separation step.

The sodium chloride content of the solid sodium chloride salt at this point was 99.7% by analysis.

Example 3

Taking 1173 g of mixed salt solution of sodium chloride and lithium chloride (wherein the concentration of the sodium chloride is 9.36 percent, and the concentration of the lithium chloride is 4.64 percent) into a distillation device, distilling at normal pressure, and when 943g of fraction is extracted, filtering at high temperature, wherein the filtering temperature is 75 ℃, so that 117.55g of filtrate and 112.45g of solid sodium chloride salt are obtained, and the concentration of the lithium chloride in the filtrate is 45.28 percent; the atmospheric distillation experiment was continued on the filtrate to obtain 51.77g of solid lithium chloride salt (solid dried to constant weight at 105 ℃).

Through analysis, the sodium chloride content in the solid sodium chloride salt is 92.28%, the lithium chloride content is 2.37%, and the water content is 5.35%; the lithium chloride content in the solid lithium chloride salt is 100%, and sodium chloride is not contained.

The obtained sodium chloride salt was washed with a saturated aqueous sodium chloride solution, and then with a saturated aqueous sodium chloride solution, sodium chloride was precipitated, and the lithium chloride aqueous solution was returned to the mixed salt separation step.

The sodium chloride content of the solid sodium chloride salt at this point was 99.8% by analysis.

Comparative example 1

Adding 1198g of mixed salt solution of sodium chloride and lithium chloride (wherein the concentration of the sodium chloride is 9.36 percent, and the concentration of the lithium chloride is 4.64 percent) into a distillation device, distilling at normal pressure, and filtering at high temperature when 951g of distillate is extracted, wherein the filtering temperature is 65 ℃, so that 129.19g of filtrate and 117.81g of solid sodium chloride salt are obtained, and the concentration of the lithium chloride in the filtrate is 41.22 percent; the atmospheric distillation experiment was continued on the filtrate to obtain 45.98g of solid lithium chloride salt (solid dried to constant weight at 105 ℃).

Through analysis, the sodium chloride content in the solid sodium chloride salt is 89%, the lithium chloride content is 5.65%, and the water content is 5.35%; the lithium chloride content in the solid lithium chloride salt is 100%, and sodium chloride is not contained.

The obtained sodium chloride salt was washed with a saturated aqueous sodium chloride solution, and then with a saturated aqueous sodium chloride solution, sodium chloride was precipitated, and the lithium chloride aqueous solution was returned to the mixed salt separation step.

The sodium chloride content of the solid sodium chloride salt at this point was 98.35% by analysis.

Comparative example 2

Putting 1123g of mixed salt solution of sodium chloride and lithium chloride (wherein the concentration of the sodium chloride is 9.36 percent and the concentration of the lithium chloride is 4.64 percent) into a distillation device, distilling at normal pressure, and when 876g of fraction is extracted, filtering at high temperature and the filtering temperature is 70 ℃, so as to obtain 145g of filtrate and 102g of solid sodium chloride salt, wherein the concentration of the lithium chloride in the filtrate is 36.72 percent; the atmospheric distillation experiment was continued on the filtrate to obtain 53.18g of solid lithium chloride salt (solid dried to constant weight at 105 ℃).

Through analysis, the sodium chloride content in the solid sodium chloride salt is 92.63 percent, the lithium chloride content is 2 percent, and the water content is 5.37 percent; the solid lithium chloride salt contained 82.49% lithium chloride and 17.51% sodium chloride.

Comparative example 3

Taking 1654g of mixed salt solution of sodium chloride and lithium chloride (wherein the concentration of the sodium chloride is 9.36 percent and the concentration of the lithium chloride is 4.64 percent) into a distillation device, distilling at normal pressure, and when 1336g of fraction is extracted, filtering at high temperature and 70 ℃ to obtain 101.9g of filtrate and 216.1g of solid sodium chloride salt, wherein the concentration of the lithium chloride in the filtrate is 47.03 percent; the atmospheric distillation experiment was continued on the filtrate to obtain 19.9g of solid lithium chloride salt (solid dried to constant weight at 105 ℃).

Through analysis, the sodium chloride content in the solid sodium chloride salt is 71.64%, the lithium chloride content is 23%, and the water content is 5.36%; the lithium chloride content in the solid lithium chloride salt is 100%, and sodium chloride is not contained.

It should be noted that the above-mentioned embodiments are only for illustrating the technical solutions of the present invention and not for limiting, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions may be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, which should be covered by the claims of the present invention.