Preparation method of chromatographic grade acetonitrile

Abstract

The invention provides a preparation method of chromatographic grade acetonitrile, and belongs to the field of chromatographic grade acetonitrile. The preparation method of the chromatographic grade acetonitrile comprises the following steps: pretreatment, low-temperature plasma oxidation impurity removal, adsorption impurity removal and rectification refining. According to the preparation method of the chromatographic-grade acetonitrile, a strong oxidant and an alkaline neutralizer do not need to be additionally added, the problem of secondary pollution caused by introduction of additional chemical reagents is effectively avoided, and high-efficiency impurity removal can be performed on the industrial-grade acetonitrile under mild conditions on the premise of ensuring the refining efficiency.

Description

Technical Field

[0001] The present invention relates to the field of chromatographic grade acetonitrile, and particularly to a preparation method of chromatographic grade acetonitrile. Background Art

[0002] Acetonitrile (CH3CN), also known as methyl cyanide, is the simplest saturated aliphatic nitrile compound. It is a colorless transparent liquid under normal temperature and pressure and has a special smell similar to ether. Acetonitrile has excellent solvent properties and can dissolve a variety of inorganic, organic and gaseous compounds. At the same time, acetonitrile is a relatively stable nitrile compound and is not prone to oxidation or reduction reactions. In the pharmaceutical industry, acetonitrile can be used as a synthetic intermediate for vitamins B1, the antihypertensive drug moxonidine, cortisone, sulfonamide drugs and other drugs. In petrochemical industry, acetonitrile can be used as an extractant for extracting butadiene and isoprene, and can also be used as a synthetic raw material for fine chemicals such as dyes, surfactants, pesticides, spices and organic synthesis. In instrumental analysis, acetonitrile can be used as the mobile phase solvent for thin layer chromatography, paper chromatography, spectroscopy, polarography and high performance liquid chromatography (HPLC), and can also be used as a DNA synthesis / purification solvent, a solvent for organic material synthesis, a cleaning solvent for electronic components, etc. With the continuous development of technologies in high-end application fields, the purity requirements for acetonitrile are also constantly increasing, and chromatographic grade acetonitrile is often required to meet the application requirements.

[0003] Chromatographic grade acetonitrile refers to an acetonitrile product with a purity of not less than 99.9% and having no absorption or only extremely weak absorption in the near ultraviolet band. Due to its lack of absorption or only extremely weak absorption in the near ultraviolet band, it can be used as an organic modifier and solvent for thin layer chromatography, paper chromatography, gas chromatography, especially high performance liquid chromatography. At the same time, as a highly pure solvent with relatively strong polarity, chromatographic grade acetonitrile has good solubility for compounds such as oils and fats, and can be used as a semiconductor cleaning agent to clean off oils, fingerprints, etc. on silicon wafers.

[0004] The existing chromatographic grade acetonitrile is prepared by using industrial grade acetonitrile as raw material and refining to remove impurities. For the industrial grade acetonitrile obtained by the acetic acid ammoniation method, its impurities generally include acetaldehyde, acetone, acrolein, acrylonitrile, methanol, isopropanol, etc. The existing preparation methods of chromatographic grade acetonitrile mainly use a combination of methods such as adding strong oxidants or photocatalysts for oxidative impurity removal, multi-stage distillation for impurity removal, and multi-stage adsorption for impurity removal. However, for the method of oxidative impurity removal using oxidants, strong oxidants such as potassium permanganate and concentrated sulfuric acid are required, and an alkaline neutralizing agent is needed to adjust the pH, which will introduce additional chemical reagents, not only causing secondary pollution to acetonitrile, but also increasing the pressure of subsequent rectification and adsorption treatment, and reducing the efficiency and effect of subsequent refining; for the method of multi-stage distillation for impurity removal, there are risks of thermal decomposition or polymerization in the high-temperature distillation environment of industrial grade acetonitrile, and the impurity removal efficiency is low, and it is impossible to achieve efficient impurity removal of acetonitrile under mild conditions. Summary of the Invention

[0005] To solve the technical problems existing in the prior art, the present invention provides a preparation method of chromatographic grade acetonitrile, which does not require additional addition of strong oxidants and alkaline neutralizing agents, effectively avoids the problem of secondary pollution caused by the introduction of additional chemical reagents, and can efficiently remove impurities from industrial grade acetonitrile under mild conditions while ensuring the refining efficiency.

[0006] To solve the above technical problems, the technical solutions adopted by the present invention are as follows: A preparation method of chromatographic grade acetonitrile, which consists of the following steps: pretreatment, low-temperature plasma oxidative impurity removal, adsorption impurity removal, and rectification and refining.

[0007] For the pretreatment, after the industrial grade acetonitrile flows through the adsorption column filled with 3A molecular sieve, a pretreatment solution is obtained; For the low-temperature plasma oxidative impurity removal, after the pretreatment solution and the supported catalyst are mixed evenly, they are placed in the treatment chamber of the low-temperature plasma treatment device. Under the protection of an argon atmosphere, a mixed gas of argon and oxygen is used as the reaction gas. The discharge voltage of the low-temperature plasma treatment is controlled at 25 - 27 KV, the discharge frequency is 55 - 60 Hz, and the discharge power is 220 - 250 W. After the reaction gas is activated by low-temperature plasma discharge at room temperature, it is continuously introduced below the liquid level of the pretreatment solution for bubbling; after the bubbling is completed, filtration is carried out to obtain the oxidative impurity removal solution; The supported catalyst is prepared by impregnating a carboxylated multi-walled carbon nanotube as a carrier into a metal salt loading solution containing manganese and lanthanum, followed by drying and calcination; For the adsorption impurity removal, after the oxidative impurity removal solution flows through the adsorption columns filled with mesoporous activated carbon and 5A molecular sieve in sequence, an adsorption impurity removal solution is obtained; The adsorption impurity removal solution is subjected to rectification and refining to obtain chromatographic grade acetonitrile.

[0008] Preferably, in the pretreatment, the flow rate of industrial-grade acetonitrile is 200-220 mL / min, and the residence time of industrial-grade acetonitrile in the adsorption column is 17-26 min.

[0009] Preferably, in the low-temperature plasma oxidation and impurity removal, the volume ratio of argon to oxygen in the reaction gas is 100:7-8; The total volume of the reaction gas introduced is 5-6 times the total volume of the pretreatment liquid; The weight ratio of the supported catalyst to the pretreatment liquid is 1.2-1.5:100.

[0010] Preferably, in the low-temperature plasma oxidation and impurity removal, after the reaction gas is activated by low-temperature plasma discharge, it is bubbled into the pretreatment liquid through a microporous aeration head or a gas distributor arranged at the bottom of the treatment chamber; The bubbling time is controlled to be 420-480 s.

[0011] Furthermore, the preparation method of the supported catalyst is as follows: dissolve manganese nitrate and lanthanum nitrate in deionized water to obtain a metal salt loading solution; immerse carboxylated multi-walled carbon nanotubes in the metal salt loading solution, after immersion at 40-45 °C, separate to obtain a solid; the dried solid is calcined at 320-330 °C to obtain the supported catalyst.

[0012] Preferably, in the preparation of the supported catalyst, the metal salt concentration of the metal salt loading solution is 0.2-0.3 mol / L; The molar ratio of manganese nitrate to lanthanum nitrate is 2-2.3:0.4-0.5.

[0013] Preferably, in the preparation of the supported catalyst, the weight ratio of carboxylated multi-walled carbon nanotubes to the metal salt loading solution is 1:8-10; The calcination time at 320-330 °C is 3-4 h.

[0014] In the adsorption and impurity removal, the flow rate of the oxidation and impurity removal liquid is 100-110 mL / min; The residence time of the oxidation and impurity removal liquid in each adsorption column is 35-55 min.

[0015] Preferably, in the adsorption and impurity removal, the average particle size of the mesoporous activated carbon is 80-100 μm, the specific surface area is 1200-1300 m 2 / g, and the average pore diameter is 3-8 nm.

[0016] Preferably, for the rectification and refining, the adsorption and impurity removal liquid is introduced into a rectification column, and the rectification column is controlled to have a bottom temperature of 85-87 °C, a top temperature of 80-83 °C, and a reflux ratio of 5-6:1 for rectification and refining to obtain chromatographic-grade acetonitrile.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) In the preparation method of chromatographic grade acetonitrile of the present invention, first, through a pretreatment step, an adsorption column filled with 3A molecular sieve is used to remove most of the moisture in industrial grade acetonitrile to obtain a pretreatment solution, so as to avoid the problem of interfering with plasma treatment due to excessive moisture content in acetonitrile during the subsequent low-temperature plasma oxidation and impurity removal process, and improve the treatment efficiency and performance of subsequent low-temperature plasma oxidation and impurity removal. Then, in the low-temperature plasma oxidation and impurity removal step, by using reaction gases with a specific composition and ratio, under specific plasma treatment process parameters (discharge voltage, discharge frequency, discharge power), the reaction gases are discharged and activated and then bubbled into the pretreatment solution. At the same time, with the selective catalysis of the supported catalyst on the impurity components, the impurity components in the pretreatment solution are oxidatively degraded with high controllable selectivity; and by precisely controlling the above-mentioned reaction gas ratio, plasma treatment process parameters, and bubbling time, over-oxidation of acetonitrile is avoided, and the acetonitrile component in the pretreatment solution is retained to obtain an oxidation and impurity removal solution. Then, in the adsorption and impurity removal step, the oxidation and impurity removal solution is successively passed through adsorption columns filled with mesoporous activated carbon and 5A molecular sieve for adsorption and impurity removal, and the impurity components remaining in the oxidation and impurity removal solution are targeted for adsorption to obtain an adsorption and impurity removal solution. Finally, the adsorption and impurity removal solution is refined by distillation to obtain chromatographic grade acetonitrile. The above-mentioned technical means cooperate with each other and work synergistically, without the need to additionally add strong oxidants and alkaline neutralizing agents, effectively avoiding the problem of secondary pollution caused by the introduction of additional chemical reagents, and being able to efficiently remove impurities from industrial grade acetonitrile under mild conditions while ensuring the refining efficiency, providing a new process route for the preparation of chromatographic grade acetonitrile.

[0018] (2) Through experiments, using the preparation method of chromatographic grade acetonitrile of the present invention, the purity of the obtained chromatographic grade acetonitrile exceeds 99.98 wt%, the moisture content is 0.0027 - 0.0031 wt%, the acidity is 0.0002 - 0.0003 mmol / g, the alkalinity is not detected, the evaporation residue is 0.8 - 0.9 ppm, and the yield is 99.1 - 99.4%; the absorbance of the obtained chromatographic grade acetonitrile at 200 nm is 0.012 - 0.015, at 210 nm is 0.004 - 0.005, at 220 nm is 0.001 - 0.003, at 230 nm is 0.001, at 240 nm is 0, and at 250 nm is 0.

[0019] (3) Through experiments, using the preparation method of chromatographic grade acetonitrile of the present invention, the quality of the obtained chromatographic grade acetonitrile is stable; the fluctuations in its yield, moisture content, acidity, evaporation residue, absorbance at 200 nm, and absorbance at 210 nm are all within the allowable threshold range, and the batch consistency is good. Detailed implementation manners

[0020] For a clearer understanding of the technical features, objectives, and effects of the present invention, the specific embodiments of the present invention will now be described. It should be noted that the following detailed descriptions are all exemplary and are intended to provide further explanations of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0021] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, "first", "second", etc. are used to distinguish similar objects and are not used to describe a specific order or sequence. In addition, it should also be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0022] An embodiment of the present invention provides a method for preparing chromatographic grade acetonitrile, which consists of the following steps: pretreatment, low-temperature plasma oxidation for impurity removal, adsorption for impurity removal, and rectification and purification.

[0023] The method of the pretreatment is that at room temperature, industrial grade acetonitrile flows through an adsorption column filled with 3A molecular sieve at a flow rate of 200 - 220 mL / min, and the residence time of industrial grade acetonitrile in the adsorption column is controlled to be 17 - 26 min to obtain a pretreatment solution.

[0024] In the pretreatment, the height of the adsorption column filled with 3A molecular sieve is 1 - 1.1 m, and the inner diameter is 7 - 8 cm; the filling height of 3A molecular sieve is 80 - 85% of the height of the adsorption column.

[0025] The method of low-temperature plasma oxidation for impurity removal is as follows: The supported catalyst is put into the pretreatment solution, ultrasonically dispersed for 10 - 20 min, and then placed in the treatment chamber of the low-temperature plasma treatment device. The air in the treatment chamber is completely replaced with argon, and a mixed gas of argon and oxygen (volume ratio of 100:7 - 8) is used as the reaction gas. The discharge voltage of the low-temperature plasma treatment is controlled to be 25 - 27 KV, the discharge frequency is 55 - 60 Hz, and the discharge power is 220 - 250 W. At room temperature, the reaction gas continuously passes between the two discharge electrodes of the low-temperature plasma treatment device and is discharged and activated, and then continuously introduced below the liquid level of the pretreatment solution for uniform bubbling, so that the impurity components in the pretreatment solution are controllably oxidized and degraded, and the oxidation and degradation of acetonitrile are avoided; the bubbling time is controlled to be 420 - 480 s. After the bubbling is completed, the low-temperature plasma oxidation for impurity removal is completed. After filtering and recovering the solids, an oxidation impurity removal solution is obtained; at the same time, during the low-temperature plasma oxidation for impurity removal, the generated waste gas is collected and discharged to the waste gas treatment device for treatment.

[0026] In the low-temperature plasma oxidation for impurity removal, bubbling is preferably evenly distributed into the pretreatment liquid through a microporous aeration head or a gas distributor with an average pore size of 50-60 μm arranged at the bottom of the treatment chamber, so as to achieve sufficient gas-liquid contact.

[0027] In the low-temperature plasma oxidation for impurity removal, the total volume of the reaction gas introduced is 5-6 times the total volume of the pretreatment liquid.

[0028] In the low-temperature plasma oxidation for impurity removal, the weight ratio of the supported catalyst to the pretreatment liquid is 1.2-1.5:100.

[0029] The supported catalyst is prepared by impregnating carboxylated multi-walled carbon nanotubes into a loading solution, followed by drying and calcination. Specifically, manganese nitrate and lanthanum nitrate are put into deionized water, stirred and dissolved to prepare a metal salt loading solution with a concentration of 0.2-0.3 mol / L. The carboxylated multi-walled carbon nanotubes are put into the metal salt loading solution, kept at 40-45 °C with stirring for 3-4 h, and then centrifuged to obtain a solid. The solid is dried at 110-120 °C for 10-12 h, calcined at 320-330 °C for 3-4 h, and ground evenly to obtain the supported catalyst.

[0030] In the preparation of the supported catalyst, the molar ratio of manganese nitrate to lanthanum nitrate is 2-2.3:0.4-0.5; The weight ratio of the carboxylated multi-walled carbon nanotubes to the metal salt loading solution is 1:8-10.

[0031] The method for adsorption and impurity removal is that at room temperature, the oxidation impurity removal liquid flows through adsorption columns filled with mesoporous activated carbon and 5A molecular sieve in sequence at a flow rate of 100-110 mL / min, and the residence time of the oxidation impurity removal liquid in each adsorption column is controlled to be 35-55 min to obtain the adsorption impurity removal liquid.

[0032] In the adsorption and impurity removal, the height of the adsorption column filled with mesoporous activated carbon is 1-1.1 m, and the inner diameter is 7-8 cm; the filling height of the mesoporous activated carbon is 80-85% of the height of the adsorption column; the height of the adsorption column filled with 5A molecular sieve is 1-1.1 m, and the inner diameter is 7-8 cm; the filling height of the 5A molecular sieve is 80-85% of the height of the adsorption column.

[0033] In the adsorption and impurity removal, the average particle size of the mesoporous activated carbon used is 80-100 μm, the specific surface area is 1200-1300 m 2 / g, and the average pore diameter is 3-8 nm.

[0034] The method for rectification and purification is to introduce the adsorption impurity removal liquid into a rectification column, control the bottom temperature of the rectification column to be 85-87 °C, the top temperature to be 80-83 °C, and the reflux ratio to be 5-6:1, and carry out rectification and purification to obtain chromatographic grade acetonitrile.

[0035] The present invention will be further described below in conjunction with some specific embodiments.

[0036] Example 1 This example provides a method for preparing chromatographic grade acetonitrile. Industrial grade acetonitrile with a purity of 99.53 wt%, a water content of 0.18 wt%, an acidity (calculated as acetic acid) of 0.005 mmol / g, an alkalinity (calculated as OH - -) of 0.0003 mmol / g, and an evaporation residue of 0.008 wt% is processed. The specific steps are as follows: 1. Pretreatment At room temperature, industrial grade acetonitrile flows through an adsorption column filled with 3A molecular sieve at a flow rate of 200 mL / min, and the residence time of industrial grade acetonitrile in the adsorption column is controlled to be 19.2 min to obtain a pretreatment solution.

[0037] Among them, the height of the adsorption column filled with 3A molecular sieve is 1 m, and the inner diameter is 7 cm; the filling height of 3A molecular sieve is 80% of the height of the adsorption column.

[0038] 2. Low-temperature plasma oxidation for impurity removal The supported catalyst is put into the pretreatment solution. After ultrasonic dispersion for 10 min, it is placed in the treatment chamber of a low-temperature plasma treatment device. The air in the treatment chamber is completely replaced with argon. A mixed gas of argon and oxygen (volume ratio of 100:7) is used as the reaction gas. The discharge voltage of the low-temperature plasma treatment is controlled to be 25 KV, the discharge frequency is 60 Hz, and the discharge power is 220 W. At room temperature, the reaction gas continuously passes between the two discharge electrode plates of the low-temperature plasma treatment device and is activated by discharge. Then, it continuously bubbles into the pretreatment solution through a microporous aeration head with an average pore diameter of 50 μm arranged at the bottom of the treatment chamber to achieve full gas-liquid contact, so that the impurity components in the pretreatment solution are controllably oxidized and degraded, and the oxidation and degradation of acetonitrile are avoided; the bubbling time is controlled at 480 s. After the bubbling is completed, the low-temperature plasma oxidation for impurity removal is completed. After filtering and recovering the solid (supported catalyst), an oxidation and impurity removal solution is obtained; at the same time, during the low-temperature plasma oxidation for impurity removal, the generated waste gas is collected and discharged to a waste gas treatment device for treatment.

[0039] During the low-temperature plasma oxidation for impurity removal, the total volume of the reaction gas introduced is 5 times the total volume of the pretreatment solution.

[0040] The weight ratio of the supported catalyst to the pretreatment solution is 1.2:100.

[0041] The preparation method of the supported catalyst is as follows: Manganese nitrate and lanthanum nitrate are put into deionized water and stirred to dissolve to obtain a metal salt supported solution with a concentration of 0.2 mol / L; The carboxylated multi-walled carbon nanotubes are put into the metal salt supported solution, and after being kept at 40 °C with stirring for 3 h, solid substances are obtained by centrifugation; The solid substances are dried at 110 °C for 10 h, calcined at 320 °C for 3 h, and ground evenly to obtain the supported catalyst loaded with copper oxide, cobalt oxide, and lanthanum oxide.

[0042] In the preparation of the supported catalyst, the molar ratio of manganese nitrate to lanthanum nitrate used is 2:0.4.

[0043] The weight ratio of the carboxylated multi-walled carbon nanotubes to the metal salt supported solution is 1:8.

[0044] 3. Adsorption and impurity removal At room temperature, the oxidation impurity removal solution flows through the adsorption columns filled with mesoporous activated carbon and 5A molecular sieve at a flow rate of 100 mL / min in sequence, and the residence time of the oxidation impurity removal solution in each adsorption column is controlled to be 38.5 min to obtain the adsorption impurity removal solution.

[0045] Among them, the height of the adsorption column filled with mesoporous activated carbon is 1 m, and the inner diameter is 7 cm; The filling height of the mesoporous activated carbon is 80% of the height of the adsorption column.

[0046] The height of the adsorption column filled with 5A molecular sieve is 1 m, and the inner diameter is 7 cm; The filling height of the 5A molecular sieve is 80% of the height of the adsorption column.

[0047] The average particle size of the mesoporous activated carbon is 100 μm, the specific surface area is 1300 m 2 / g, and the average pore diameter is 5 nm.

[0048] 4. Rectification and purification The adsorption impurity removal solution is introduced into the rectification column, and the rectification column is controlled with the bottom temperature of 85 °C, the top temperature of 80 °C, and the reflux ratio of 5:1 for rectification and purification to obtain chromatographic grade acetonitrile.

[0049] Example 2 This example provides a preparation method of chromatographic grade acetonitrile, which is used to process industrial grade acetonitrile with a purity of 99.53 wt%, a water content of 0.18 wt%, an acidity (calculated as acetic acid) of 0.005 mmol / g, an alkalinity (calculated as OH - -) of 0.0003 mmol / g, and an evaporation residue of 0.008 wt%. The specific steps are as follows: 1. Pretreatment At room temperature, the industrial grade acetonitrile flows through the adsorption column filled with 3A molecular sieve at a flow rate of 210 mL / min, and the residence time of the industrial grade acetonitrile in the adsorption column is controlled to be 18.3 min to obtain the pretreatment solution.

[0050] Among them, the height of the adsorption column filled with 3A molecular sieve is 1 m, and the inner diameter is 7 cm; the filling height of the 3A molecular sieve is 80% of the height of the adsorption column.

[0051] 2. Impurity removal by low-temperature plasma oxidation Put the supported catalyst into the pretreatment liquid, ultrasonically disperse it for 15 min, then place it in the treatment chamber of the low-temperature plasma treatment device. Use argon to completely displace the air in the treatment chamber, and use a mixed gas of argon and oxygen (volume ratio of 100:7.5) as the reaction gas. Control the discharge voltage of the low-temperature plasma treatment to be 26 KV, the discharge frequency to be 60 Hz, and the discharge power to be 240 W. At room temperature, the reaction gas continuously passes between the two discharge electrode plates of the low-temperature plasma treatment device and is activated by discharge, and then continuously bubbles into the pretreatment liquid through a microporous aeration head with an average pore diameter of 50 μm set at the bottom of the treatment chamber to achieve full gas-liquid contact, so that the impurity components in the pretreatment liquid are controllably oxidized and degraded, and the oxidation and degradation of acetonitrile are avoided; the bubbling time is controlled at 450 s. After the bubbling is completed, the low-temperature plasma oxidation impurity removal is completed. After filtering and recovering the solid (supported catalyst), the oxidation impurity removal liquid is obtained; at the same time, during the low-temperature plasma oxidation impurity removal process, the generated waste gas is collected and discharged to the waste gas treatment device for treatment.

[0052] During the low-temperature plasma oxidation impurity removal process, the total volume of the reaction gas introduced is 5.7 times the total volume of the pretreatment liquid.

[0053] The weight ratio of the supported catalyst to the pretreatment liquid is 1.4:100.

[0054] The preparation method of the supported catalyst is as follows: Put manganese nitrate and lanthanum nitrate into deionized water, stir and dissolve to prepare a metal salt supported liquid with a concentration of 0.25 mol / L; put carboxylated multi-walled carbon nanotubes into the metal salt supported liquid, keep stirring at 42 °C for 3.5 h, and then centrifuge to obtain a solid; the solid is dried at 115 °C for 11 h, calcined at 325 °C for 3.5 h, and ground evenly to prepare the supported catalyst.

[0055] In the preparation of the supported catalyst, the molar ratio of manganese nitrate to lanthanum nitrate used is 2.1:0.43.

[0056] The weight ratio of the carboxylated multi-walled carbon nanotubes to the metal salt supported liquid is 1:9.

[0057] 3. Adsorption impurity removal At room temperature, the oxidation impurity removal liquid flows through the adsorption columns filled with mesoporous activated carbon and 5A molecular sieve at a flow rate of 105 mL / min, and the residence time of the oxidation impurity removal liquid in each adsorption column is controlled at 36.7 min to obtain the adsorption impurity removal liquid.

[0058] Among them, the height of the adsorption column filled with mesoporous activated carbon is 1 m, and the inner diameter is 7 cm; the filling height of the mesoporous activated carbon is 80% of the height of the adsorption column.

[0059] The height of the adsorption column filled with 5A molecular sieve is 1 m, and the inner diameter is 7 cm; the filling height of the 5A molecular sieve is 80% of the height of the adsorption column.

[0060] The average particle size of the mesoporous activated carbon is 100 μm, the specific surface area is 1300 m 2 / g, and the average pore diameter is 5 nm.

[0061] 4. Rectification and purification The adsorption and impurity-removing liquid is introduced into the rectification column, and the temperature of the column kettle of the rectification column is controlled at 86 °C, the temperature at the top of the column is 82 °C, and the reflux ratio is 5.8:1 for rectification and purification to obtain chromatographic grade acetonitrile.

[0062] Example 3 This example provides a method for preparing chromatographic grade acetonitrile, which is used to treat industrial grade acetonitrile with a purity of 99.53 wt%, a water content of 0.18 wt%, an acidity (calculated as acetic acid) of 0.005 mmol / g, an alkalinity (calculated as OH - -) of 0.0003 mmol / g, and an evaporation residue of 0.008 wt%. The specific steps are as follows: 1. Pretreatment At room temperature, the industrial grade acetonitrile flows through the adsorption column filled with 3A molecular sieve at a flow rate of 220 mL / min, and the residence time of the industrial grade acetonitrile in the adsorption column is controlled at 17.5 min to obtain a pretreatment liquid.

[0063] Among them, the height of the adsorption column filled with 3A molecular sieve is 1 m, and the inner diameter is 7 cm; the filling height of the 3A molecular sieve is 80% of the height of the adsorption column.

[0064] 2. Low-temperature plasma oxidation for impurity removal The supported catalyst was put into the pretreatment solution. After ultrasonic dispersion for 20 min, it was placed in the treatment chamber of the low-temperature plasma treatment device. The air in the treatment chamber was completely replaced with argon. Using a mixed gas of argon and oxygen (volume ratio of 100:8) as the reaction gas, the discharge voltage of the low-temperature plasma treatment was controlled at 27 KV, the discharge frequency was 60 Hz, and the discharge power was 250 W. At room temperature, the reaction gas continuously passed between the two discharge electrodes of the low-temperature plasma treatment device and was activated by discharge. Then, it continuously bubbled into the pretreatment solution through a gas distributor with an average pore size of 50 μm set at the bottom of the treatment chamber to achieve full gas-liquid contact, enabling the impurity components in the pretreatment solution to undergo controllable oxidative degradation and avoiding the oxidative degradation of acetonitrile. The bubbling time was controlled at 420 s. After the bubbling was completed, the low-temperature plasma oxidation for impurity removal was completed. After filtering and recovering the solid (supported catalyst), the oxidation impurity removal solution was obtained. At the same time, during the low-temperature plasma oxidation for impurity removal, the generated waste gas was collected and discharged to the waste gas treatment device for treatment.

[0065] During the low-temperature plasma oxidation for impurity removal, the total volume of the reaction gas introduced was 6 times the total volume of the pretreatment solution.

[0066] The weight ratio of the supported catalyst to the pretreatment solution was 1.5:100.

[0067] The preparation method of the supported catalyst was as follows: Manganese nitrate and lanthanum nitrate were put into deionized water and stirred to dissolve to prepare a metal salt loading solution with a concentration of 0.3 mol / L. The carboxylated multi-walled carbon nanotubes were put into the metal salt loading solution. After maintaining the temperature at 45 °C and stirring for 4 h, solid substances were obtained by centrifugal separation. The solid substances were dried at 120 °C for 12 h, calcined at 330 °C for 4 h, and ground evenly to obtain the supported catalyst.

[0068] In the preparation of the supported catalyst, the molar ratio of manganese nitrate to lanthanum nitrate used was 2.3:0.5.

[0069] The weight ratio of the carboxylated multi-walled carbon nanotubes to the metal salt loading solution was 1:10.

[0070] 3. Adsorption for impurity removal At room temperature, the oxidation impurity removal solution flowed through the adsorption columns filled with mesoporous activated carbon and 5A molecular sieve at a flow rate of 110 mL / min, and the residence time of the oxidation impurity removal solution in each adsorption column was controlled at 35 min to obtain the adsorption impurity removal solution.

[0071] Among them, the height of the adsorption column filled with mesoporous activated carbon was 1 m, and the inner diameter was 7 cm; the filling height of the mesoporous activated carbon was 80% of the height of the adsorption column.

[0072] The height of the adsorption column filled with 5A molecular sieve was 1 m, and the inner diameter was 7 cm; the filling height of the 5A molecular sieve was 80% of the height of the adsorption column.

[0073] The average particle size of the mesoporous activated carbon is 100 μm, the specific surface area is 1300 m 2 / g, and the average pore diameter is 5 nm.

[0074] 4. Rectification and purification Introduce the adsorption and impurity removal liquid into the rectification column, control the bottom temperature of the rectification column to be 87 °C, the top temperature to be 83 °C, and the reflux ratio to be 6:1, and carry out rectification and purification to obtain chromatographic grade acetonitrile.

[0075] Comparative example 1 Adopt the technical scheme of Example 2, the difference is that: the supported catalyst used in the low-temperature plasma oxidation and impurity removal step is omitted.

[0076] Comparative example 2 Adopt the technical scheme of Example 2, the differences are that: 1) Omit the pretreatment step and directly carry out low-temperature plasma oxidation and impurity removal on industrial grade acetonitrile; 2) In the adsorption and impurity removal step, 3A molecular sieve is used to replace mesoporous activated carbon.

[0077] Detect and count the purity, water content, acidity (calculated as acetic acid), alkalinity (calculated as OH - ), evaporation residue, and yield of the acetonitrile products prepared in Examples 1-3 and Comparative Examples 1-2 respectively; and detect the absorbance of each acetonitrile product at 200 nm, 210 nm, 220 nm, 230 nm, 240 nm, and 250 nm respectively. The specific results are shown in the following table:

[0078] It can be seen that in the preparation method of chromatographic-grade acetonitrile of the present invention, first, through a pretreatment step, most of the moisture in industrial-grade acetonitrile is removed by an adsorption column filled with 3A molecular sieve to obtain a pretreatment solution, so as to avoid the problem of interfering with plasma treatment due to too high moisture content in acetonitrile during the subsequent low-temperature plasma oxidation and impurity removal process, and improve the treatment efficiency and performance of subsequent low-temperature plasma oxidation and impurity removal. Then, in the low-temperature plasma oxidation and impurity removal step, by using reaction gases with a specific composition and ratio, under specific plasma treatment process parameters (discharge voltage, discharge frequency, discharge power), the reaction gases are discharged and activated and then bubbled into the pretreatment solution. At the same time, with the selective catalysis of the supported catalyst on the impurity components, the impurity components in the pretreatment solution are oxidatively degraded with controllable high selectivity; and by precisely controlling the above-mentioned reaction gas ratio, plasma treatment process parameters, and bubbling time, over-oxidation of acetonitrile is avoided, and the acetonitrile component in the pretreatment solution is retained to obtain an oxidation and impurity removal solution. Then, in the adsorption and impurity removal step, the oxidation and impurity removal solution is successively passed through adsorption columns filled with mesoporous activated carbon and 5A molecular sieve for adsorption and impurity removal, and the impurity components remaining in the oxidation and impurity removal solution are specifically adsorbed to obtain an adsorption and impurity removal solution. Finally, the adsorption and impurity removal solution is refined by distillation to obtain chromatographic-grade acetonitrile.

[0079] It can be seen from Comparative Example 1 that after omitting the supported catalyst in the low-temperature plasma oxidation and impurity removal step, due to the lack of selective catalysis of the supported catalyst on the impurity components in the pretreatment solution, under the conditions of the same composition and ratio of reaction gases, the same plasma treatment process parameters, and the same bubbling time, the oxidation and impurity removal effect on the impurity components in the pretreatment solution is reduced; moreover, the impurity components remaining in the obtained oxidation and impurity removal solution cannot be effectively removed through the subsequent adsorption and impurity removal and distillation and refining processes. Specifically, the purity, acidity, alkalinity, and yield of the acetonitrile product obtained in Comparative Example 1 all show obvious deterioration, and the absorbance of the acetonitrile product at 200 nm, 210 nm, 220 nm, 230 nm, 240 nm, and 250 nm all shows obvious increase, which also indicates that its refining and impurity removal effect on industrial-grade acetonitrile is reduced.

[0080] It can be seen from Comparative Example 2 that after omitting the pretreatment step, the problem of interfering with plasma treatment due to too high moisture content in industrial-grade acetonitrile during the low-temperature plasma oxidation and impurity removal process cannot be avoided, which directly leads to the treatment efficiency and performance of low-temperature plasma oxidation and impurity removal; at the same time, using 3A molecular sieve to replace mesoporous activated carbon in the adsorption and impurity removal step cannot achieve specific adsorption of the residual impurity components in the oxidation and impurity removal solution. Specifically, the purity, acidity, and alkalinity of the acetonitrile product obtained in Comparative Example 2 all show a certain degree of deterioration, and the absorbance of the acetonitrile product at 200 nm, 210 nm, 220 nm, 230 nm, 240 nm, and 250 nm all shows a certain degree of increase.

[0081] Further, the technical solutions of Example 2 and Comparative Example 1 were respectively used to repeat the preparation of chromatographic grade acetonitrile 5 times to verify its batch consistency; during this process, the supported catalyst used in Example 2 was not replaced and was continuously reused 5 times. The yields, water contents, acidities, evaporation residues, absorbances at 200 nm, and absorbances at 210 nm of the acetonitrile products obtained in each batch were respectively measured and statistically analyzed; the above-mentioned indicators were compared with the corresponding indicators of the acetonitrile product obtained in the first batch to determine whether the indicator fluctuations exceeded the threshold value.

[0082] Specifically, the judgment standard for the yield of the acetonitrile product is: whether the difference between the acetonitrile yield (%) of the current batch and the acetonitrile yield (%) of the first batch is within the range of ±1.5%; fluctuations within the threshold range are acceptable production index fluctuations, and those exceeding the threshold range are unacceptable production index fluctuations.

[0083] The judgment standard for the water content of the acetonitrile product is: whether the difference between the water content (wt%) of the acetonitrile in the current batch and the water content (wt%) of the acetonitrile in the first batch is within the range of ±0.0005 wt%; fluctuations within the threshold range are acceptable production index fluctuations, and those exceeding the threshold range are unacceptable production index fluctuations.

[0084] The judgment standard for the acidity of the acetonitrile product is: whether the difference between the acidity (mmol / g) of the acetonitrile in the current batch and the acidity (mmol / g) of the acetonitrile in the first batch is within the range of ±0.0001 mmol / g; fluctuations within the threshold range are acceptable production index fluctuations, and those exceeding the threshold range are unacceptable production index fluctuations.

[0085] The judgment standard for the evaporation residue of the acetonitrile product is: whether the difference between the evaporation residue (ppm) of the acetonitrile in the current batch and the evaporation residue (ppm) of the acetonitrile in the first batch is within the range of ±0.5 ppm; fluctuations within the threshold range are acceptable production index fluctuations, and those exceeding the threshold range are unacceptable production index fluctuations.

[0086] The judgment standard for the absorbance at 200 nm of the acetonitrile product is: whether the difference between the absorbance at 200 nm of the acetonitrile in the current batch and the absorbance at 200 nm of the acetonitrile in the first batch is within the range of ±0.002; fluctuations within the threshold range are acceptable production index fluctuations, and those exceeding the threshold range are unacceptable production index fluctuations.

[0087] The determination criterion for the absorbance at 210 nm of the acetonitrile product is as follows: whether the difference between the absorbance at 210 nm of the acetonitrile in the current batch and the absorbance at 210 nm of the acetonitrile in the first batch is within the range of ±0.001; the production index fluctuations within the threshold range are acceptable, and those exceeding the threshold range are unacceptable production index fluctuations.

[0088] The specific results are shown in the following table:

[0089] It can be seen that for the method for preparing chromatographic grade acetonitrile of the present invention, the quality of the chromatographic grade acetonitrile prepared from industrial grade acetonitrile as the raw material is stable, the fluctuations of each index are within the allowable threshold range, and the batch consistency is good; at the same time, the reusable performance of the supported catalyst used in the low-temperature plasma oxidation and impurity removal step is good, and it can still maintain good catalytic performance after being reused many times. It can be seen from Comparative Example 1 that after omitting the supported catalyst in the low-temperature plasma oxidation and impurity removal step, the batch consistency of the prepared acetonitrile product is reduced, and the quality stability of the acetonitrile product cannot be maintained. Specifically, the fluctuations of the yield, acidity, absorbance at 200 nm, and absorbance at 210 nm of the prepared acetonitrile product exceed the allowable threshold range.

[0090] Unless otherwise specified, the percentages used in the present invention are all mass percentages.

[0091] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing chromatographic grade acetonitrile, characterized in that, It consists of the following steps: pretreatment, low-temperature plasma oxidation for impurity removal, adsorption for impurity removal, and rectification for purification; For the said pretreatment, industrial-grade acetonitrile flows through an adsorption column filled with 3A molecular sieve to obtain a pretreated liquid; For the said low-temperature plasma oxidation for impurity removal, after mixing the pretreated liquid and the supported catalyst evenly, they are placed in the treatment chamber of a low-temperature plasma treatment device. Under the protection of an argon atmosphere, a mixed gas of argon and oxygen is used as the reaction gas. The discharge voltage of the low-temperature plasma treatment is controlled at 25 - 27 KV, the discharge frequency is 55 - 60 Hz, and the discharge power is 220 - 250 W. After the reaction gas is activated by low-temperature plasma discharge at room temperature, it is continuously introduced below the liquid level of the pretreated liquid for bubbling; after the bubbling is completed, filtration is carried out to obtain an oxidized impurity-removed liquid; The said supported catalyst is prepared by impregnating carboxylated multi-walled carbon nanotubes into a metal salt loading solution containing manganese and lanthanum, followed by drying and calcination; For the said adsorption for impurity removal, the oxidized impurity-removed liquid flows through adsorption columns filled with mesoporous activated carbon and 5A molecular sieve in sequence to obtain an adsorbed impurity-removed liquid; The said adsorbed impurity-removed liquid is subjected to rectification for purification to obtain chromatographic-grade acetonitrile.

2. The preparation method of chromatographic grade acetonitrile according to claim 1, characterized in that, In the said pretreatment, the flow rate of industrial-grade acetonitrile is 200 - 220 mL / min, and the residence time of industrial-grade acetonitrile in the adsorption column is 17 - 26 min.

3. The preparation method of chromatographic grade acetonitrile according to claim 1, characterized in that, In the said low-temperature plasma oxidation for impurity removal, the volume ratio of argon to oxygen in the reaction gas is 100:7 - 8; The total volume of the introduced reaction gas is 5 - 6 times the total volume of the pretreated liquid; The weight ratio of the supported catalyst to the pretreated liquid is 1.2 - 1.5:

100.

4. The preparation method of chromatographic grade acetonitrile according to claim 1, characterized in that, In the said low-temperature plasma oxidation for impurity removal, after the reaction gas is activated by low-temperature plasma discharge, it is bubbled into the pretreated liquid through a microporous aeration head or a gas distributor arranged at the bottom of the treatment chamber; The bubbling time is controlled at 420 - 480 s.

5. The preparation method of chromatographic grade acetonitrile according to claim 1, characterized in that, The preparation method of the said supported catalyst is as follows: dissolve manganese nitrate and lanthanum nitrate in deionized water to prepare a metal salt loading solution; impregnate carboxylated multi-walled carbon nanotubes into the metal salt loading solution, after impregnation at 40 - 45 °C, separate to obtain a solid; the dried solid is calcined at 320 - 330 °C to obtain the supported catalyst.

6. The preparation method of chromatographic grade acetonitrile according to claim 5, wherein, In the preparation of the said supported catalyst, the metal salt concentration of the metal salt loading solution is 0.2 - 0.3 mol / L; The molar ratio of manganese nitrate to lanthanum nitrate is 2 - 2.3:0.4 - 0.

5.

7. The preparation method of chromatographic grade acetonitrile according to claim 5, characterized in that, In the preparation of the said supported catalyst, the weight ratio of carboxylated multi-walled carbon nanotubes to the metal salt loading solution is 1:8 - 10; The calcination time at 320 - 330 °C is 3 - 4 h.

8. The preparation method of chromatographic grade acetonitrile according to claim 1, characterized in that, In the said adsorption for impurity removal, the flow rate of the oxidized impurity-removed liquid is 100 - 110 mL / min; The residence time of the oxidized impurity-removed liquid in each adsorption column is 35 - 55 min.

9. The preparation method of chromatographic grade acetonitrile according to claim 1, wherein, In the adsorption and impurity removal, the average particle size of the mesoporous activated carbon is 80-100 μm, the specific surface area is 1200-1300 m 2 / g, and the average pore diameter is 3-8 nm.

10. The preparation method of chromatographic grade acetonitrile according to claim 1, characterized in that, For the said rectification for purification, the adsorbed impurity-removed liquid is introduced into a rectification column, and the column bottom temperature of the rectification column is controlled at 85 - 87 °C, the top temperature is 80 - 83 °C, and the reflux ratio is 5 - 6:1 for rectification for purification to obtain chromatographic-grade acetonitrile.

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