Separation and purification process of ultrahigh purity p-xylene

Abstract

The application discloses a separation and purification process of ultrahigh-purity p-xylene, and the main impurities contained in industrial-grade p-xylene are isomer impurities, such as m-xylene and o-xylene; the isomer impurities are difficult to be completely separated through common rectification due to the similar boiling points; the separation and purification difficulty is greatly reduced through a combined process of azeotropic rectification and normal-pressure rectification and with the aid of liquid-liquid layering; and the industrial-grade p-xylene with a purity of 99.5% can be purified to ultrahigh-purity 99.99% p-xylene. The application has the characteristics of simple process, simple operation and low material consumption.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of chemical separation, and particularly relates to a separation and purification method of ultrahigh-purity p-xylene. BACKGROUND

[0002] P-xylene (PX) is the most widely used C8 aromatic hydrocarbon in industry, which is the raw material for producing terephthalic acid (PTA). PTA is an important raw material for polyester and plastic industries. More than 80% of the PX is used to produce PTA in the global consumption structure of PX. P-xylene is also widely used in the fields of medicine, pesticide, dye and solvent.

[0003] As a solvent, p-xylene is widely used in the preparation process of ultraviolet negative photoresist. It can be used as a solvent in the photoresist adjusting process, and can also be used as the main organic solvent of the developing solution in the developing process of ultraviolet negative photoresist. With the continuous development of semiconductor technology, the requirements for wet electronic chemicals are also becoming higher and higher. Therefore, it is of great economic value to develop a separation and purification technology of ultraclean high-purity electronic-grade p-xylene.

[0004] The traditional process for producing p-xylene in industry mainly includes two kinds: one is mixed xylene isomerization, and the other is the disproportionation and transalkylation of toluene and C9 aromatic hydrocarbons. According to the differences in the physical and chemical properties of mixed xylene, currently, technologies such as adsorption separation, zeolite membrane separation, complex extraction, crystallization separation, and adsorption-crystallization integrated separation are mainly used to separate mixed xylene to obtain p-xylene.

[0005] Crystallization method takes advantage of the large difference in melting points of C8 aromatic hydrocarbons: p-xylene 13.3℃, o-xylene-25.2℃, m-xylene-47.9℃, and ethylbenzene-94.95℃. Therefore, p-xylene with the highest melting point can be separated by crystallization method. This method is also the only practical method for separating p-xylene before the emergence of molecular sieve adsorption separation method, and it is still adopted by many devices in the world so far. In order to improve the crystallization efficiency, US3177265A and US3467724A introduce a two-stage crystallization separation method. The crystallization separation method generally consists of two-stage crystallization process. The first-stage crystallization temperature is controlled at the low eutectic temperature of-62~-68℃ to improve the recovery rate of p-xylene. In the second-stage crystallization process, the first-stage crystallization crude product is melted and the crystallization temperature is controlled at-20~-10℃ for recrystallization to improve the purity of the product, so that p-xylene with purity >98% can be obtained. The secondary crystallization product can be washed with toluene to remove the m- and o-isomers intercalated between the p-xylene crystals. After the crystals are melted, toluene is removed through a rectification tower, and the purity of the obtained p-xylene product can reach 99.9%, greatly improving the purity of the product. However, due to the extremely low temperature requirement of xylene crystallization, the energy consumption of crystallization method is large, the cost is expensive, and it is mostly operated intermittently.

[0006] Adsorption separation is to separate isomers by using the selectivity of adsorbent to xylene. The kinetic diameter of p-xylene is 0.67 nm, the kinetic diameter of o-xylene is 0.74 nm, and the kinetic diameter of m-xylene is 0.71 nm. In industry, zeolite is often used as an adsorbent, and simulated moving bed adsorption separation technology is adopted. The desorbent is p-diethylbenzene or toluene. After desorption, the desorbent is removed by rectification. The key to adsorption separation is to prepare a highly selective adsorbent to achieve precise adsorption. US3558730 discloses a BaKX molecular sieve, which has a selectivity to PX significantly higher than BaX and KX. CN109529764A discloses a method for modifying a ten-membered ring pore molecular sieve to obtain a new high-selectivity adsorbent. CN108525641A discloses a method for preparing a small ball adsorbent for adsorption separation of p-xylene, which obtains a small ball with X molecular sieve as a matrix and Silicalite-1 molecular sieve as a shell layer, and has high p-xylene adsorption selectivity. CN108262004A modifies the molecular sieve, so that the cation sites are occupied by Ba ions or Ba ions and K ions. A small ball adsorbent with X / ZSM-5 core / shell molecular sieve as an active component is obtained. However, the production cost of adsorption technology is high, the equipment requirements are strict, and it is difficult to obtain ultra-high purity p-xylene by adsorption.

[0007] In summary, the traditional p-xylene separation and purification process has high energy consumption, high equipment requirements, and the purity is generally 99.5%, and it is difficult to meet the purity requirement of 4 9 for electronic chemicals. Therefore, it is necessary to study a high-efficiency ultra-high purity p-xylene separation and purification process. SUMMARY

[0008] To solve the above problems, the application discloses a method for purifying p-xylene by combining azeotropic rectification with atmospheric rectification.

[0009] In order to achieve the above purpose, the application provides the following technical scheme:

[0010] A method for purifying p-xylene by combining azeotropic rectification with atmospheric rectification, as shown in the flowchart Figure 1 The method comprises the following steps:

[0011] A) Azeotropic rectification: industrial-grade p-xylene raw material is mixed with ultrapure water in a certain proportion, and S1 is sent into the azeotropic rectification tower ① from the feed inlet. Under the heating action of the reboiler, the azeotrope vapor formed by p-xylene and water is taken out from the top of the tower, and the liquid phase S2 formed after condensation by the condenser is sent into the first layer separator ④. The water phase S3 taken out from the lower layer of the first layer separator is returned to the azeotropic rectification tower ① as reflux. The oil phase S4 taken out from the upper layer of the first layer separator is sent to the subsequent tower. The p-xylene containing impurities and water S5 is discharged from the azeotropic rectification tower.

[0012] B) Rectification purification: The oil phase distillate S4 from the first separator in step A is sent to the rectification purification column ②. Under the heating action of the reboiler, vapor-liquid mass transfer is carried out in the rectification purification column, and xylene and trace amounts of water and light components are enriched at the top of the column. The gas phase material collected at the top is condensed by the condenser to form a liquid phase S7, which is returned to the rectification purification column as reflux, and a small amount of light components S6 accumulated at the top of the column are collected periodically. High-purity p-xylene is collected from the upper side of the column S8, and p-xylene containing heavy impurities S9 is collected from the column bottom periodically.

[0013] C) Solvent dehydration: The material S5 collected from the bottom of the azeotropic rectification column in step A is sent to the second separator ⑤, and the oil phase material S10 from the second separator is sent to the solvent dehydration column ③. Under the heating action of the reboiler, vapor-liquid mass transfer is carried out in the dehydration column, and the xylene and water azeotrope is enriched at the top of the column. The gas phase material collected at the top is condensed by the condenser to form a liquid phase, part of which is returned to the solvent dehydration column as reflux S12, and part S13 is sent to the second separator ⑤. The water phase S11 from the second separator is discharged as waste water to the sewage treatment device, and the industrial-grade p-xylene product S14 is collected from the bottom of the solvent dehydration column.

[0014] Further, the raw material used in step A is industrial-grade p-xylene, with a purity of more than 99.5wt%, and the single impurity content requirements are toluene ≤0.1wt%, ethylbenzene ≤0.2wt%, m-xylene ≤0.2wt%, and o-xylene ≤0.1wt%.

[0015] Further, the mass ratio of the feed p-xylene to ultrapure water in step A is 3~5:2, and the resistivity of the ultrapure water is greater than 18 MΩ*cm.

[0016] Further, the azeotropic rectification column in step A uses a packed column, with a theoretical plate number of 15~20. The feed inlet is located at 2 / 5~3 / 5 of the column height, the water phase reflux feed ratio at the top of the column is 2~4, the column is operated at atmospheric pressure, the operating temperature at the top of the column is 95~96℃, and the operating temperature at the bottom of the column is 105~110℃.

[0017] Further, the rectification purification column in step B has a theoretical plate number of 20~30, the feed inlet is located at 3 / 5~4 / 5 of the column height (close to the column bottom), the side draw inlet is located at 1 / 4~2 / 5 of the column height (close to the column top), the column is operated at atmospheric pressure, the reflux ratio is 3~5, and the side draw temperature is 138~139℃.

[0018] Further, the solvent dehydration column in step C has a theoretical plate number of 15~30, the feed inlet is located at 2 / 5~1 / 2 of the column height, the reflux ratio is 2~5, the feed inlet is located at 2 / 5~1 / 2 of the column height, and the column bottom temperature is 138~140℃.

[0019] Further, the temperature of the first and second delaminators is 35-40℃, and the residence time of the material in the delaminators is 30-60min.

[0020] Compared with the prior art, the present application has the following beneficial effects:

[0021] 1) The introduction of water in the azeotropic distillation and the formation of the minimum azeotrope with p-xylene increase the relative volatility between p-xylene and other impurities, greatly reducing the difficulty of distillation separation, thereby realizing the separation and purification of industrial-grade p-xylene;

[0022] 2) Since p-xylene is insoluble in water, preliminary separation can be achieved by standing and delamination, which is simple to operate and greatly reduces the separation energy consumption of the purification column;

[0023] 3) The dehydration column uses atmospheric distillation, and a small amount of p-xylene-water azeotrope is collected at the top, which can remove a small amount of water and further improve the purity of p-xylene, and the material at the bottom of the column can be sold as industrial-grade p-xylene product. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The figure is a flow diagram of the system of the present application. ① is the azeotropic distillation column, ② is the purification column, ③ is the dehydration column, ④ is the first delaminator, and ⑤ is the second delaminator. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical scheme and advantages of the present application clearer and more apparent, the present application will be further described in detail below in combination with the drawings and examples. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0026] Example 1

[0027] The azeotropic distillation column ① uses metal packing, and the theoretical plate number from top to bottom is 18, and the feeding position is at the 12th theoretical plate. The purification column ② uses metal packing, and the theoretical plate number from top to bottom is 24, and the feeding position is at the 19th theoretical plate, and the side sampling position is at the 8th theoretical plate. The dehydration column ③ uses metal packing, and the theoretical plate number from top to bottom is 28, and the feeding position is at the 10th theoretical plate.

[0028] The purity of the industrial grade p-xylene is 99.7wt%, containing 0.03wt% of light component toluene, 0.12wt% of heavy component ethylbenzene, 0.10wt% of isomer dimethylbenzene, and 0.05wt% of o-xylene. After mixing 100kg / hr of the industrial grade p-xylene and 40kg / hr of ultrapure water, the mixture is fed into the azeotropic rectification tower ①, and operated under normal pressure, with a water phase reflux feed ratio of 2.5, a tower top temperature of 95.3℃, and a tower bottom temperature of 106.2℃. The oil phase is taken out from the first layer separator ④ at a rate of 59.91kg / hr, and the tower bottom is taken out at a rate of 80.09kg / hr.

[0029] The material taken out from the top of the azeotropic rectification tower ① is fed into the rectification purification tower ②, and operated under normal pressure, with a reflux ratio of 3.5, a side taking temperature of 138.1℃, a tower top taking out at a rate of 5.12kg / hr, and a tower bottom taking out at a rate of 3.55kg / hr. The side taking obtains 51.23kg / hr of p-xylene with a purity of 99.99%.

[0030] The material taken out from the bottom of the azeotropic rectification tower ① is fed into the second layer separator ⑤, and the oil phase material of the second layer separator ⑤ is fed into the dehydration tower ③. The dehydration tower ③ is operated under normal pressure, with a reflux ratio of 3, a tower bottom temperature of 138.6℃, and a tower bottom taking out at a rate of 40.06kg / hr of industrial grade p-xylene. A part of the material taken out from the top is also fed into the second layer separator ⑤, and the water phase is taken out from the second layer separator ⑤ at a rate of 40.03kg / hr of waste water.

[0031] The compositions of the partial streams are shown in the following table. The purity of the p-xylene obtained by the above process is 99.993%, and the yield is 51.23%.

[0032] Table 1 Partial stream table

[0033]

[0034] The above only describes the preferred embodiments of the present application, and any equivalent changes and modifications made within the scope of the patent application of the present application shall be included in the scope of the present application.

Claims

1. A process for the separation and purification of ultrahigh purity para-xylene, characterized in that, Comprising the following steps: A) azeotropic distillation: the industrial-grade para-xylene raw material is mixed with ultrapure water in a proportion, and then sent into the azeotropic distillation column from the feed inlet. Under the heating action of the reboiler, the azeotrope vapor of para-xylene and water is taken out from the top of the column, and then condensed by the condenser to form a liquid phase which is sent into the first layer separator. The water phase taken out from the lower layer of the first layer separator is returned to the azeotropic distillation column as reflux, and the oil phase taken out from the upper layer of the first layer separator is sent to the subsequent column separation. The para-xylene containing impurities and water is discharged from the bottom of the azeotropic distillation column; B) rectification and purification: the oil phase distillate of the first layer separator in step A) is sent into the rectification and purification column. Under the heating action of the reboiler, vapor-liquid mass transfer is carried out in the rectification and purification column. Para-xylene and a small amount of water and light components are enriched at the top of the column. The gaseous phase material taken out from the top of the column is condensed by the condenser to form a liquid phase, most of which is returned to the rectification and purification column as reflux, and a small amount is periodically taken out. High-purity para-xylene is taken out from the upper side of the column, and para-xylene containing heavy impurities is periodically taken out from the bottom of the column; C) solvent dehydration: the material taken out from the bottom of the azeotropic distillation column in step A) is sent to the second layer separator. The oil phase material in the upper layer of the second layer separator is sent to the solvent dehydration column. Under the heating action of the reboiler, vapor-liquid mass transfer is carried out in the dehydration column. The azeotrope of para-xylene and water is enriched at the top of the column. The gaseous phase material taken out from the top of the column is condensed by the condenser to form a liquid phase, part of which is returned to the solvent dehydration column as reflux, and part of which is sent to the second layer separator. The water phase in the lower layer of the second layer separator is discharged as waste water to the sewage treatment device. The industrial-grade para-xylene product is taken out from the bottom of the solvent dehydration column.

2. The separation and purification process of ultrahigh purity p-xylene according to claim 1, characterized in that: The raw material used in step A) is industrial-grade para-xylene with a purity of ≥99.5wt%, and the single impurity content requirements are toluene content ≤0.1wt%, ethylbenzene content ≤0.2wt%, m-xylene ≤0.2wt%, and o-xylene ≤0.1wt%.

3. The process for separating and purifying ultrahigh purity para-xylene according to claim 1, characterized in that: The mass ratio of para-xylene to ultrapure water in step A) is 3-5:2, and the resistivity of ultrapure water is greater than 18 MΩ*cm.

4. The process for separating and purifying ultrahigh purity para-xylene according to claim 1, wherein the process is characterized by: The azeotropic distillation column in step A) uses a packed column, the number of theoretical plates from top to bottom is 15-20, the feed inlet is at 2 / 5-3 / 5 of the column, the water phase reflux feed ratio at the top of the column is 2-4, it is operated at atmospheric pressure, the operating temperature at the top of the column is 95-96℃, and the operating temperature at the bottom of the column is 105-110℃.

5. The process for separating and purifying ultrahigh purity para-xylene according to claim 1, wherein the process is characterized by: The temperature of the first layer separator in step A) is 35-40℃, and the layering time is 30-60min.

6. The process of claim 1, wherein the process is a process for separating and purifying ultra-high purity p-xylene, characterized in that: The number of theoretical plates of the rectification and purification column in step B) from top to bottom is 20-30, the feed inlet is at 3 / 5-4 / 5 of the column near the column bottom, the side draw port is at 1 / 4-2 / 5 of the column near the column top, the reflux ratio is 3-5, and the side draw temperature is 138-139℃.

7. The separation and purification process for ultra-high purity p-xylene as described in claim 1, characterized in that: The number of theoretical plates of the solvent dehydration column in step C) is 15-30, the feed inlet is at 2 / 5-1 / 2 of the column, the reflux ratio is 2-5, and the operating temperature at the bottom of the column is 138-140℃.

8. The process of claim 1, wherein the process is a process for separating and purifying ultra-high purity para-xylene, characterized in that: The temperature of the second layer separator is 35-40℃, and the residence time of the material in the layer separator is 30-60min.

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