A method for removing metal ions from para-xylene

Abstract

The application provides a method for removing metal ions in p-xylene, which utilizes the characteristics that p-xylene and water form a heterogeneous azeotrope and metal ions are more soluble in water, adopts azeotropic distillation technology combined with a gas phase condensation process, and makes metal ions in p-xylene transfer from p-xylene to water under the extraction of water, so as to achieve the purpose of removing metal ions. Compared with traditional methods for removing metal ions, the method has the characteristics of simple operation and high efficiency of removing metal ions.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of organic reagent purification, and particularly relates to a method for removing metal ions from p-xylene organic solvent. BACKGROUND

[0002] In the process of integrated circuits and liquid crystal display, high-purity and high-cleanliness chemical reagents are mainly used for cleaning and etching of chip, silicon round and liquid crystal display surface, and the purity and cleanliness have a very significant influence on the yield, electrical properties and reliability. As an important electronic chemical, ultra-clean high-purity p-xylene has been widely used in semiconductor and liquid crystal display. As a solvent, p-xylene is widely used in the preparation process of ultraviolet negative photoresist, and can be used as a solvent in the process of photoresist adjusting, and can also be used as a developing solution in the negative developing process, and is a commonly used photoresist supporting reagent. With the continuous development of semiconductor technology, the purity requirement of wet electronic chemicals is also getting higher and higher, especially the trace metal impurities in the wet electronic chemicals will directly affect the quality and yield of related semiconductor products. Therefore, it is an extremely important task to remove trace metal ion impurities from p-xylene.

[0003] The current metal ion removal methods mainly include rectification, adsorption, membrane separation, ion exchange, chemical precipitation and the like. A method for removing metal ions in the synthesis of polyhydroxy benzophenone is disclosed in Chinese patent CN 101781185A. After the decolorization and purification of the synthesis product of polyhydroxy benzophenone, 0.1% to 5% of a metal ion chelating agent based on the total weight of the synthesis raw material is added, and then recrystallization and centrifugal filtration are performed to make the total amount of metal ions in the product less than 100 ppb. However, the process is relatively complicated, and the removal effect of alkali metal ions such as sodium and potassium is poor. Chinese patent CN 101613259A discloses a preparation method of electronic-grade propylene glycol methyl ether. The method reduces the metal ions in propylene glycol methyl ether from 250 to 1000 ppb to less than 5 ppb by using a 316L stainless steel rectification tower subjected to passivation and polishing treatment. The process flow is simple and easy to operate, but the equipment material requirement is high. From the perspective of boiling point difference, metal ions generally exist in the form of salt, and the boiling point is higher than that of organic solvents. The rectification operation can remove metal ions, but there will be liquid entrainment in the rectification process, which causes the trace metal ions to be collected from the top of the tower, resulting in the metal content exceeding the standard in the distillate. Chinese patent CN 106748652A discloses a method for removing trace metal impurities in industrial-grade isopropanol. The method uses chemically modified natural fibers as an adsorbent for trace metal ions in isopropanol, and then ion exchange is performed through a cation exchange column to obtain isopropanol with a metal impurity ion content of less than 0.1 ppb. The method has good effect in removing metal ions, but there are problems such as generation of a large amount of waste liquid in the ion exchange resin regeneration process and possible inactivation of the ion exchange resin caused by organic solvents. Therefore, it is necessary to invent a simple method for removing metal ions from organic solvents. SUMMARY

[0004] The purpose of the present application is to provide a method for removing metal ions in industrial-grade p-xylene by azeotropic rectification, so as to overcome the problems of high cost, complex operation and difficult removal of metal ions in the prior art.

[0005] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0006] A method for removing metal ions in p-xylene, comprising the following steps:

[0007] A. Raw material pre-mixing: the ultrapure water and the industrial-grade p-xylene are sent into the azeotropic rectification tower kettle in a certain proportion, and continuous stirring is performed to make the p-xylene and the water fully contact;

[0008] B. Azeotropic distillation: under normal pressure, the mixture of p-xylene and water in the azeotropic distillation column is heated to form the azeotrope steam of p-xylene and water, which is separated from the top of the azeotropic distillation column and sent to the upper gas phase inlet of the condenser; on the surface of the heat exchange tube of the condenser, the gas phase is condensed to form a liquid film, which is condensed and gathered along the heat exchange tube to form liquid drops, which flow out from the lower liquid phase outlet of the condenser;

[0009] C. Layering: the liquid phase material flowing out of the condenser is divided into two streams by the reflux ratio controller and sent to the layering tank, and after standing and layering, the upper layer of p-xylene is taken out as the product, and the lower layer of water phase is returned to the azeotropic distillation column as the azeotrope for recycling.

[0010] Further, the mass ratio of the ultra-pure water to p-xylene used in step A is 5:1 to 1:2; the resistivity of the ultra-pure water is greater than or equal to 18 MΩ·cm.

[0011] Further, the azeotropic distillation column in step A is a packed column or a plate column, the theoretical plate number is 20 to 40, and the reflux ratio is 3 to 10. Under a suitable reflux ratio, the vapor-liquid mass transfer effect in the distillation column is good, which is beneficial to the purification of p-xylene.

[0012] Further, the temperature at the top of the azeotropic distillation column in step B is 90 to 100 DEG C.

[0013] Further, the material taken out from the top of the azeotropic distillation column in step B accounts for 1 / 3 to 2 / 3 of the total mass of the feed.

[0014] Further, the shell of the condenser in step B runs the material, and the tube of the condenser runs the refrigerant, and the temperature difference between the shell and the tube is 5 to 8 DEG C. The heat exchange temperature difference is small, the p-xylene and water vapor slowly condense on the surface of the heat exchange tube, and the formed liquid film is relatively thin, which is beneficial to the extraction mass transfer process.

[0015] Further, the cross section of the heat exchange tube of the condenser in step B is in the shape of an inverted drop.

[0016] Further, the upper part of the inverted drop shape is a semicircle with a diameter a, and the lower part of the inverted drop shape is an elliptical arc with a short axis length a and a long axis length b, wherein the ratio of b to a is 10:6. In the condensation process of the steam on the surface of the heat exchange tube, a liquid film is formed on the wall surface of the heat exchange tube, and the cross section of the heat exchange tube in the shape of a drop is beneficial to reducing the thickness of the liquid film.

[0017] Further, the temperature for standing and layering in step C is 25 to 35 DEG C, and the standing time is 30 to 60 min.

[0018] The advantages of the present application compared with the prior art are:

[0019] 1. The present invention uses ultra-pure water and p-xylene to carry out batch azeotropic rectification. P-xylene can form a minimum azeotrope with water, and the relative volatility between p-xylene and possible high-boiling substances can be improved, so that further purification of p-xylene can be achieved.

[0020] 2. Metal ions in the solvent generally exist in the form of salt, and their boiling points are higher than that of p-xylene. Azeotropic rectification is essentially a rectification process, so it is difficult to remove high-boiling metal ion impurities from the top of the column, and the separation between p-xylene and metal ions can be achieved.

[0021] 3. Compared with p-xylene, metal ions are more soluble in water. P-xylene and water form a heterogeneous azeotrope, and are taken out from the top of the batch rectification column and enter the condenser. When the vapor undergoes phase change in the condenser, a liquid film is formed on the surface of the heat exchange tube. In this way, p-xylene and water droplets can be mixed and distributed more uniformly without the need for external mechanical stirring and other measures, which is conducive to the transfer of metal ion impurities from the p-xylene phase to the water phase, and achieves the purpose of deep removal of metal ions.

[0022] 4. The cross section of the heat exchange tube of the condenser used in the present invention is in the shape of an inverted drop, which helps to reduce the thickness of the liquid film formed when the vapor condenses on the surface of the heat exchange tube, increase the two-phase contact area of p-xylene and water, and improve the mass transfer efficiency of metal ions between p-xylene and water. Under the same conditions, the total metal ion removal rate using the condenser heat exchange tube with a limited cross-sectional shape according to the present invention can be 13% higher than that using ordinary heat exchange tubes, the maximum condensation capacity can be 15% higher than that using ordinary heat exchange tubes, and the time to obtain the same volume of product can be shortened by 15%-25% compared with using ordinary heat exchange tubes.

[0023] 5. The temperature difference between the inner shell material of the condenser used in the present invention and the refrigerant in the heat exchange tube is small, which can make the material vapor in the shell condense slowly on the surface of the heat exchange tube, and is conducive to further reducing the thickness of the liquid film formed by p-xylene and water, and promoting two-phase extraction mass transfer. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The structure of the azeotropic rectification column used in the present invention is shown in the figure, wherein 1 is the column, 2 is the column, 3 is the condenser, 4 is the reflux ratio controller, 5 is the column heater, and 6 is the layered tank.

[0025] Figure 2 The cross-sectional shape of the heat exchange tube in the condenser used in the present invention is shown in the figure. DETAILED DESCRIPTION

[0026] A method for removing metal ions from p-xylene, comprising the following steps:

[0027] A. Raw material pre-mixing: ultrapure water (resistivity ≥ 18 MΩ·cm) and industrial-grade p-xylene are sent into the bottom of the azeotropic distillation column at a mass ratio of 5:1~1:2, and continuous stirring is performed to allow the p-xylene and water to fully contact each other;

[0028] B. Azeotropic distillation: under normal pressure, the p-xylene and water mixture in the bottom of the azeotropic distillation column is heated to form azeotrope vapor of p-xylene and water, which is collected from the top of the column under the separation action of the azeotropic distillation column, and the top temperature is 90~100℃, and the collected material accounts for 1 / 3~2 / 3 of the total mass of the feed; the material is sent to the upper gas phase inlet of the condenser; on the surface of the heat exchange tube of the condenser, the gas phase is condensed to form a liquid film, which is condensed and gathered along the heat exchange tube to form liquid droplets, which flow out from the lower liquid phase outlet of the condenser;

[0029] C. Layering: the liquid phase material flowing out from the condenser is divided into two streams by the reflux ratio controller and then sent to the layering tank, and after layering at 25~35℃ for 30~60min, the upper layer p-xylene is collected as the product, and the lower layer water phase is returned to the azeotropic distillation column for recycling as the azeotrope.

[0030] The azeotropic distillation column used herein is a packed column or a plate column, with a theoretical plate number of 20~40 and a reflux ratio of 3~10.

[0031] The shell of the condenser carries the material, and the tube of the condenser carries the coolant, with a temperature difference of 5~8℃ between the shell and the tube. The cross section of the heat exchange tube of the condenser is in the shape of an inverted drop. The upper part of the inverted drop is a semicircle with a diameter a, and the lower part of the inverted drop is an elliptical arc with a short axis length a and a long axis length b, wherein the ratio of b to a is 10:6.

[0032] In order to make the content of the present application more convenient to understand, the technical solutions of the present application will be further described in conjunction with specific embodiments, but the present application is not limited thereto. Examples

[0033] The azeotropic distillation column used adopts precision packing, the number of theoretical plates is 25, and the reflux ratio is 5. During operation, 150 kg of industrial-grade p-xylene and 100 kg of ultrapure water (resistivity of 18.25 MΩ·cm) are put into the azeotropic distillation column, and continuous stirring is carried out to make the p-xylene and water fully contact. Then, under the condition that the operating pressure of the azeotropic distillation column is 0.1 MPa, the p-xylene and water mixture in the azeotropic distillation column is heated to form azeotrope vapor of p-xylene and water, the top temperature of the column is controlled at 95℃, and the azeotrope vapor is collected from the top of the azeotropic distillation column and sent to the condenser. The shell of the condenser carries the material, the tube of the condenser carries the coolant, and the temperature difference between the shell and the tube is 6℃. The material condenses on the surface of the heat exchange tube of the condenser to form a liquid film, which condenses and accumulates along the heat exchange tube to form droplets, which flow out from the lower liquid phase outlet of the condenser, and then the material is placed in the stratification tank after the reflux ratio controller, the stratification temperature is 30℃, the standing time is 40 min, the upper layer of the stratification tank is collected p-xylene product, and the lower layer of the stratification tank is collected water returned to the column. When 75 kg of p-xylene product is collected, the batch distillation is ended.

[0034] The industrial-grade p-xylene raw material used and the p-xylene product collected after different processes are detected by inductively coupled plasma mass spectrometer, and the detection results are shown in Table 1.

[0035] Table 1 Comparison of metal ion content of industrial-grade p-xylene before and after rectification

[0036]

[0037] As can be seen from Table 1, after azeotropic distillation treatment, the content of each metal ion is <10 ppb.

[0038] The above only describes the preferred embodiments of the present application, and any changes and modifications made within the scope of the present application should be included in the scope of the present application.

Claims

1. A method for removing metal ions from para-xylene, characterized in that: The method comprises the following steps: A. Raw material pre-mixing: send ultrapure water and industrial-grade p-xylene into the bottom of the azeotropic distillation column at a certain ratio, and continuously stir to make the p-xylene and water fully contact; B. Azeotropic distillation: heat the mixture of p-xylene and water in the bottom of the azeotropic distillation column under normal pressure to form azeotrope steam of p-xylene and water, and make it flow out from the top of the column and enter the condenser to form liquid droplets; C. Layering: the liquid phase material flowing out of the condenser is sent to the layering tank after being divided by the reflux ratio controller, and after layering, the upper layer p-xylene is taken out as the product, and the lower layer water phase is returned to the azeotropic distillation column for recycling; The shell layer of the condenser in step B carries the material, and the tube layer of the condenser carries the refrigerant, and the temperature difference between the shell layer and the tube layer is 5-8℃; the cross section of the heat exchange tube of the condenser is in the shape of an inverted drop.

2. The method for removing metal ions from para-xylene according to claim 1, characterized in that: The mass ratio of ultrapure water to p-xylene used in step A is 5:1-1:

2.

3. The method of removing metal ions from para-xylene according to claim 1, characterized in that: The resistivity of the ultrapure water in step A is ≥18MΩ·cm.

4. The method of claim 1, wherein the method is characterized by: The azeotropic distillation column in step A is a packed column or a plate column, the theoretical plate number is 20-40, and the reflux ratio is 3-10.

5. The method of claim 1, wherein the method is characterized by: The top temperature of the azeotropic distillation column in step B is 90-100℃.

6. The method of claim 1, wherein the method is characterized by: The material taken out from the top of the azeotropic distillation column in step B accounts for 1 / 3-2 / 3 of the total mass of the feed.

7. The method of removing metal ions from para-xylene according to claim 1, wherein: The upper part of the inverted drop shape is a semicircle with a diameter a, and the lower part of the inverted drop shape is an elliptical arc with a short axis length a and a long axis length b, wherein the ratio of b to a is 10:

6.

8. The method of removing metal ions from para-xylene according to claim 1, characterized in that: The temperature for standing and layering in step C is 25-35℃, and the standing time is 30-60min.

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