Membrane separation process and system for recycling mercaptoacetic acid

Abstract

The invention relates to the technical field of membrane separation, in particular to a membrane separation process and system for recycling mercaptoacetic acid, and the membrane separation process comprises the following steps: step S102, adjusting the pH value of tail liquid containing mercaptoacetic acid to 0-1; step S104, enabling tail liquid containing mercaptoacetic acid to be in contact with an extraction membrane; step S106, adjusting the vacuum degree of the other side of the extraction membrane to 0.04-0.06 MPa, cooling the extracted mercaptoacetic acid by using liquid nitrogen, and collecting the mercaptoacetic acid; wherein the extraction membrane comprises a hydrophobic membrane and a hydrophilic membrane, the hydrophobic membrane is in contact with tail liquid containing mercaptoacetic acid, the hydrophilic membrane is attached to the hydrophobic membrane, and an extraction agent is arranged in membrane holes of the hydrophobic membrane. According to the method, the advantages of the membrane extraction process and the membrane distillation process are fully utilized, the using amount of the extracting agent is small, the evaporation speed is high, and the high-value utilization process of the thionocarbamate production tail liquid can be improved. Compared with a traditional process, the method has obvious advantages in safety and economy, and cost increase and safety risks caused by equipment requirements are reduced.

Description

Technical Field

[0001] The invention relates to the technical field of membrane separation, and in particular to a membrane separation process and system for recovering thioglycolic acid. Background Art

[0002] Thiocarbamate is one of the most widely used copper-sulfur separation collectors in the world. Compared with traditional collectors, thiocarbamate not only has good selectivity for minerals, but also has lower toxicity and better biodegradability. The domestic thiocarbamate industry is dominated by small and medium-sized enterprises, and the monochloroacetic acid esterification process is generally adopted, which has the advantages of high efficiency and high yield, and can quickly produce a large amount of high-quality thiocarbamate. However, this process also has some problems that need to be solved, especially in the treatment of tail liquid containing thioglycolate. The monochloroacetic acid esterification method is used to produce thiocarbamate. For every ton of thiocarbamate produced, about 4 tons of tail liquid are produced as a by-product. The content of thioglycolate in the tail liquid is about 8% to 20%, which is a widely used fine chemical raw material. Most companies use extraction technology to recover thioglycolic acid in the tail liquid. It can be said that the recovery process of thioglycolic acid is the key to the high-value utilization of the tail liquid.

[0003] Currently, the recovery of thioglycolic acid generally adopts the following steps: first, the tail liquid is acidified to reduce its pH value to below 1.0, so that the thioglycolate salt exists mainly in the form of undissociated thioglycolic acid; second, a suitable extractant is selected and the thioglycolic acid is extracted using an extraction centrifuge; third, the extractant and thioglycolic acid are separated by distillation to obtain a thioglycolic acid product.

[0004] Based on cost considerations, enterprises generally use low-priced ester or ether extractants, but the expensive extraction centrifuge and the distillation separation of the extractant and thioglycolic acid make the cost of the process high. In addition, since the flash point of commonly used extractants is very low (such as the flash point of commonly used isopropyl acetate is only 2°C), the explosion-proof requirements for equipment are very high, which not only increases the cost of equipment, but also brings greater safety risks. For example, patent CN103360291A discloses a method for producing high-concentration thioglycolic acid using the tail liquid of O-alkyl-N-alkylthiocarbamate. In this patent, ester and ether mixed extractants are used. The crude acid is flashed at a vacuum degree of -0.01MPa and a temperature of 90-130°C to obtain a thioglycolic acid product with a purity of more than 99.5wt%.

[0005] Patent CN115627368A discloses a method for efficiently enriching hafnium using advanced membrane separation technology. It uses an ionic liquid-supported liquid membrane to efficiently enrich hafnium from a zirconium-hafnium mixture, realizing a combination of extraction and stripping. Although the process completes the stripping, the product obtained is a hafnium solution with a solvent, and further separation processes (distillation or centrifugation, etc.) are still required to obtain a pure product.

[0006] Patent CN103816804B discloses a method for in-situ separation of low-concentration organic matter in an aqueous phase, which combines membrane extraction with membrane distillation, uses a porous membrane as the outer shell of the membrane assembly to realize the membrane extraction process, and the internal membrane filaments are used to realize the membrane distillation process. This patent requires the use of more extractants during the extraction process, and the contact area between the porous membrane shell and the feed liquid is too small, resulting in low extraction efficiency. Summary of the invention

[0007] In order to solve the deficiencies in the prior art, the present invention provides a membrane separation process and system for recovering thioglycolic acid.

[0008] To achieve the above object, the technical solution of the present invention is: a membrane separation process for recovering thioglycolic acid, comprising the following steps:

[0009] Step S102, adjusting the pH value of the tail liquid containing thioglycolic acid to 0-1;

[0010] Step S104, contacting the tail liquid containing thioglycolic acid with an extraction membrane;

[0011] Step S106, adjusting the vacuum degree on the other side of the extraction membrane to 0.04-0.06 MPa, and using liquid nitrogen to cool the extracted thioglycolic acid, and collecting the thioglycolic acid;

[0012] The extraction membrane comprises a hydrophobic membrane in contact with the tail liquid containing thioglycolic acid and a hydrophilic membrane in contact with the hydrophobic membrane, and an extractant is arranged in the membrane pores of the hydrophobic membrane.

[0013] Furthermore, step S103 is included between step S102 and step S104, and step S103 includes preheating the tail liquid containing thioglycolic acid to 40-60°C.

[0014] Furthermore, the extractant is one of alcohols, ethers, esters, ketones and ionic liquids.

[0015] Furthermore, the extractant is one of isopropyl acetate and 1-octyl-3-methylimidazole trifluoromethanesulfonate.

[0016] Furthermore, the material of the hydrophilic membrane is one of polyethersulfone and polyethylene terephthalate; and the material of the hydrophobic membrane is polytetrafluoroethylene.

[0017] Furthermore, the pore size of the hydrophilic membrane is 0.02-0.5 μm; the pore size of the hydrophobic membrane is 0.1-0.3 μm.

[0018] Furthermore, the hydrophilic membrane and the hydrophobic membrane in the extraction membrane are an integrated composite membrane structure.

[0019] Furthermore, the extraction time in step S106 is 4 to 8 hours.

[0020] A membrane separation process for recovering thioglycolic acid comprises an extraction chamber, wherein an extraction membrane is arranged in the extraction chamber, a liquid inlet pipe and a liquid outlet pipe of the extraction chamber are arranged above the extraction membrane, a liquid collecting port of the extraction chamber is arranged below the extraction membrane, a collection chamber is arranged below the extraction chamber, a condenser is arranged in the collection chamber, and a vacuum pump is arranged on one side of the top of the collection chamber.

[0021] Furthermore, a heat exchanger is provided on the liquid inlet pipe.

[0022] The beneficial effects achieved by the present invention are:

[0023] The invention fully utilizes the advantages of the two processes of membrane extraction and membrane distillation through the coupling of membrane separation and membrane distillation, uses a small amount of extractant and has a fast evaporation rate, can improve the high-value utilization process of the tail liquid of thiocarbamate production, realizes the direct recovery of thioglycolic acid, does not require subsequent distillation or centrifugal separation steps, and reduces energy consumption. Compared with traditional processes, the invention has obvious advantages in safety and economy, reduces the cost increase and safety risks caused by equipment requirements, and meets the development trend and requirements of modern chemical production. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the overall structure of a membrane separation system for recovering thioglycolic acid;

[0025] Figure 2 yes Figure 1 The enlarged structural diagram at A in the middle;

[0026] Figure 3 This is the curve of extraction rate changing with time of ordinary membrane extraction.

[0027] Explanation of the markings in the figure: 1. heat exchanger; 2. liquid inlet pipe; 3. extraction chamber; 4. extraction membrane; 5. liquid outlet pipe; 6. liquid collecting port; 7. condenser; 8. collecting chamber; 9. vacuum pump; 401. hydrophobic membrane; 402. hydrophilic membrane; 403. extractant. DETAILED DESCRIPTION

[0028] In order to better understand the purpose, structure and function of the present invention, the following is a further detailed description of a membrane separation process and system for recovering thioglycolic acid of the present invention in conjunction with the accompanying drawings.

[0029] like Figure 1 to Figure 2As shown, a membrane separation system for recovering thioglycolic acid comprises an extraction chamber, wherein an extraction membrane is arranged in the extraction chamber, the extraction membrane divides the extraction chamber into two parts, an upper part and an lower part, a liquid inlet pipe is arranged on one side of the upper part of the extraction chamber, and a liquid outlet pipe is arranged on the other side, a heat exchanger for heating tail liquid containing thioglycolic acid is arranged on the liquid inlet pipe, a liquid collecting port is arranged at the bottom of the extraction chamber, a collecting chamber is arranged below the extraction chamber, the collecting chamber is used to collect the extracted thioglycolic acid, a condenser is arranged in the collecting chamber, the condenser cools the thioglycolic acid by liquid nitrogen, a vacuum pump is arranged on one side of the collecting chamber, and the vacuum pump is used to adjust the vacuum degree below the extraction membrane.

[0030] Example 1 Extraction Agent Comparison

[0031] The liquid phase was the tail liquid of thiocarbamate production, provided by Qingdao Liantuo Chemical Co., Ltd., wherein the concentration of thioglycolic acid was 0.1428 g / mL, the pH of the liquid phase was 0.44, the temperature of the liquid phase was 20° C., and the volume of the liquid phase was 10 mL.

[0032] The extractant phases were isopropyl acetate (≥99%) and ionic liquid (1-octyl-3-methylimidazolium trifluoromethanesulfonate) (≥99%), and the volumes of the extractant phases were 10 mL and 100 mL, respectively. After mixing with the feed liquid phase, the mixture was vigorously stirred for 10 minutes. After standing and stratifying for 1 hour, the extractant phase was taken to determine the concentration of thioglycolic acid. The results are shown in Table 1.

[0033] The extraction rate of thioglycolic acid is calculated according to formula (1):

[0034]

[0035] In the formula,

[0036] C0——mass concentration of thioglycolic acid in the liquid phase, g / mL;

[0037] C t ——Mass concentration of thioglycolic acid in the extractant, g / mL;

[0038] V E ——The volume of the extractant, mL;

[0039] V0——the system of liquid phase, mL;

[0040] Table 1 Comparison of extraction rates of different extractants

[0041]

[0042] The experiment found that when the extraction ratio was 1:1, the extraction rates of the ionic liquid (1-octyl-3-methylimidazolium trifluoromethanesulfonate) and isopropyl acetate were close, and when the extraction ratio was 10:1, the extraction rate of the ionic liquid (1-octyl-3-methylimidazolium trifluoromethanesulfonate) was 10 times that of isopropyl acetate. It can be seen that thioglycolic acid has a higher solubility and distribution coefficient in the ionic liquid (1-octyl-3-methylimidazolium trifluoromethanesulfonate).

[0043] Example 2 Conventional membrane extraction

[0044] The liquid phase is the tail liquid of thiocarbamate production, provided by Qingdao Liantuo Chemical Co., Ltd., wherein the concentration of thioglycolic acid is 0.1428 g / mL, the pH of the liquid phase is 0.44, the temperature of the liquid phase is 20°C, and the volume of the liquid phase is 150 mL; the extractant is 99% pure isopropyl acetate, the temperature of the extractant is 20°C, and the volume of the extractant is 300 mL; the magnetic stirring rate of the liquid phase and the extractant is 220 rpm. In the middle is a polytetrafluoroethylene membrane, which is round, 40 mm in diameter, 0.1 μm in pore size, 56% in porosity, and 20 μm in thickness.

[0045] like Figure 3 As shown, this example verifies the feasibility of membrane extraction. According to the experimental results, the mass transfer coefficient can be calculated to be about 8.91*10 4 The raw material contained 18.72 g of thioglycolic acid. After the extraction was completed, the obtained extract contained 7.05 g of thioglycolic acid. The obtained product was distilled to finally obtain 6.82 g of thioglycolic acid with a purity of 98%.

[0046] Example 3: Coupling process of membrane extraction and membrane distillation, double-layer membrane stacking

[0047] The feed liquid phase is the tail liquid of thiocarbamate production, provided by Qingdao Liantuo Chemical Co., Ltd., wherein the concentration of thioglycolic acid is 0.1428 g / mL, the pH of the feed liquid phase is 0.44, and the volume of the feed liquid phase is 150 mL; the extractant is 1-octyl-3-methylimidazole trifluoromethanesulfonate with a purity of 99%, and the extractant is immersed in the membrane pores with a volume of about 0.08 mL.

[0048] There are two layers of membranes stacked in the middle. One layer is a polytetrafluoroethylene membrane filled with extractant, which is circular, 40 mm in diameter, 0.1 μm in pore size, 56% in porosity, and 20 μm in thickness. The other layer is a hydrophilic polyethersulfone membrane, which is circular, 40 mm in diameter, 0.02 μm in pore size, 66% in porosity, and 20 μm in thickness.

[0049] The vacuum degree on the stripping side was 0.05 MPa, liquid nitrogen was added for cooling, the product was collected, and the extraction continued for 6 hours.

[0050] When the feed liquid phase temperature was 20°C, no product was obtained. When the feed liquid phase temperature was raised to 45°C, the product appeared. This example verifies the feasibility of the membrane extraction and membrane distillation coupling process. According to the experimental results, the mass transfer coefficient can be calculated to be about 3.71*10 4 m / min, which is lower than that of ordinary membrane extraction. This process can directly obtain 5.93 grams of thioglycolic acid product with a purity of 99% without extractant.

[0051] Example 4 Hydrophilic-Hydrophobic Integrated Composite Membrane

[0052] The feed liquid phase is the tail liquid of thiocarbamate production, provided by Qingdao Liantuo Chemical Co., Ltd., wherein the concentration of thioglycolic acid is 0.1428 g / mL, the pH of the feed liquid phase is 0.44, the volume of the feed liquid phase is 150 mL, and the temperature is 45°C; the extractant is 1-octyl-3-methylimidazole trifluoromethanesulfonate with a purity of 99%, and the extractant is immersed in the membrane pores.

[0053] In the middle is a hydrophilic-hydrophobic integrated composite membrane, which is round, 40 mm in diameter, 60% in porosity and 30 μm in thickness. The bottom membrane is hydrophilic polyethylene terephthalate with a pore size of 0.45 μm, and the upper layer is polytetrafluoroethylene with a pore size of 0.1 μm.

[0054] The vacuum degree on the stripping side was 0.05 MPa, liquid nitrogen was added for cooling, the product was collected, and the extraction continued for 6 hours.

[0055] According to the experimental results, the mass transfer coefficient can be calculated to be about 5.22*10 4 m / min, which is higher than the superposition of double-layer membranes and slightly lower than ordinary membrane extraction. This process can directly obtain 6.24 grams of thioglycolic acid product with a purity of 99% without extractant.

[0056] Example 5 Raising the temperature

[0057] The other conditions were the same as those in Example 4. The temperature of the liquid phase was further increased to 60°C. The extraction was carried out for 4 hours until equilibrium was reached. According to the experimental results, the mass transfer coefficient was calculated to be about 5.62*10 4 m / min, and 6.35 g of thioglycolic acid product with a purity of 99% without extractant was directly obtained.

[0058] It is to be understood that the present invention is described by some embodiments, and it is known to those skilled in the art that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the scope of protection of the present invention.

Claims

1. A membrane separation process for recovering thioglycolic acid, characterized in that: The following steps are involved: Step S102, adjusting the pH value of the tail liquid containing thioglycolic acid to 0-1; Step S104, contacting the tail liquid containing thioglycolic acid with an extraction membrane; Step S106, adjusting the vacuum degree on the other side of the extraction membrane to 0.04-0.06 MPa, and using liquid nitrogen to cool the extracted thioglycolic acid, and collecting the thioglycolic acid; The extraction membrane comprises a hydrophobic membrane in contact with the tail liquid containing thioglycolic acid and a hydrophilic membrane in contact with the hydrophobic membrane, and an extractant is arranged in the membrane pores of the hydrophobic membrane.

2. A membrane separation process for recovering thioglycolic acid according to claim 1, characterized in that: The step S103 is further included between the step S102 and the step S104. The step S103 includes preheating the tail liquid containing thioglycolic acid to 40-60°C.

3. A membrane separation process for recovering thioglycolic acid according to claim 1, characterized in that: The extractant is one of alcohols, ethers, esters, ketones and ionic liquids.

4. A membrane separation process for recovering thioglycolic acid according to claim 3, characterized in that: The extractant is one of isopropyl acetate and 1-octyl-3-methylimidazole trifluoromethanesulfonate.

5. A membrane separation process for recovering thioglycolic acid according to claim 1, characterized in that: The material of the hydrophilic membrane is one of polyethersulfone and polyethylene terephthalate; the material of the hydrophobic membrane is polytetrafluoroethylene.

6. A membrane separation process for recovering thioglycolic acid according to claim 1, characterized in that: The pore size of the hydrophilic membrane is 0.02-0.5 μm; the pore size of the hydrophobic membrane is 0.1-0.3 μm.

7. A membrane separation process for recovering thioglycolic acid according to claim 1, characterized in that: The hydrophilic membrane and the hydrophobic membrane in the extraction membrane are an integrated composite membrane structure.

8. A membrane separation process for recovering thioglycolic acid according to claim 1, characterized in that: The extraction time in step S106 is 4 to 8 hours.

9. A system for a membrane separation process for recovering thioglycolic acid according to any one of claims 1 to 8, characterized in that: It comprises an extraction chamber, wherein an extraction membrane is arranged in the extraction chamber, the liquid inlet pipe and the liquid outlet pipe of the extraction chamber are arranged above the extraction membrane, the liquid collecting port of the extraction chamber is arranged below the extraction membrane, a collection chamber is arranged below the extraction chamber, a condenser is arranged in the collection chamber, and a vacuum pump is arranged on one side of the top of the collection chamber.

10. A membrane separation system for recovering thioglycolic acid according to claim 9, characterized in that: A heat exchanger is arranged on the liquid inlet pipeline.

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