A kind of continuous purification method of crude acetonitrile

Abstract

The present invention provides a continuous purification method for crude acetonitrile, belonging to the field of acetonitrile purification. The continuous purification method for crude acetonitrile comprises the following steps: distillation to remove light substances, membrane separation to remove impurities, adsorption to remove impurities, and distillation purification. The continuous purification method for crude acetonitrile of the present invention can achieve continuous purification of crude acetonitrile while avoiding the problems of introducing new impurities due to side reactions caused by treating the distillate with sodium hydroxide and formaldehyde, affecting distillation efficiency and stability, and the excessive alkalinity of the treated secondary distillate affecting the equipment. By continuously purifying the crude acetonitrile, an acetonitrile product with a purity that meets the requirements is obtained.

Description

Technical Field

[0001] The present invention relates to the field of acetonitrile purification, in particular to a continuous purification method for crude acetonitrile. Background Art

[0002] Acetonitrile is a colorless, transparent liquid. Its primary use is as a solvent, such as for the extraction of butadiene and in organic synthesis. It is also an important raw material for pharmaceuticals (vitamin B1) and fragrance intermediates. High-purity acetonitrile can be used as a mobile phase in liquid chromatography and as a key solvent in the preparation and purification of drugs such as insulin and paclitaxel. While industrial-grade acetonitrile currently has a relatively high purity, it still contains numerous trace impurities, making it insufficient for applications in high-end fields such as fine chemicals, biopharmaceuticals, biosynthesis, electronic component cleaning, and scientific research.

[0003] The main methods for synthesizing acetonitrile in the prior art include: propylene ammoxidation to produce acrylonitrile as a by-product of acetonitrile, acetylene amination, ethanol amination, acetic acid amination, etc. Among them, acetonitrile as a by-product of propylene ammoxidation to produce acrylonitrile is an important source of industrial acetonitrile production; during its preparation process, the crude acetonitrile obtained is still a very complex aqueous solution mixture, its main components being water and acetonitrile, while also containing impurities such as hydrocyanic acid, acrylonitrile, oxazole, propionitrile, allyl alcohol, acetone, acrylic acid, etc. Purification of crude acetonitrile is relatively difficult, and the purification process is mostly intermittent, making it impossible to achieve stable continuous purification.

[0004] The prior art discloses a continuous purification process for crude acetonitrile, which comprises performing a primary distillation on the crude acetonitrile to remove light impurities to obtain a primary distillate containing cyanide impurities, water, and acetonitrile; then, intermittently treating the primary distillate with sodium hydroxide solution and formaldehyde to convert the cyanide impurities therein into high-boiling substances; then performing a secondary distillation to remove water and high-boiling impurities; and finally, performing a tertiary distillation to obtain a secondary distillate to obtain a high-purity acetonitrile product.

[0005] However, in the process of using sodium hydroxide solution and formaldehyde to treat the primary distillate, the treatment effect is unstable, and side reactions (such as formaldehyde self-polymerization, acetonitrile condensation, etc.) are prone to occur, which introduce new impurities, thereby increasing the difficulty of subsequent separation and purification; moreover, the cyanohydrin and cyanomethyl polymers produced in the process are relatively viscous, and are easy to adhere to or coke on the inner wall or tower plate of the equipment during the secondary distillation process, seriously affecting the distillation efficiency and distillation stability; at the same time, the alkalinity of the treated secondary distillate will also accelerate the corrosion of the distillation equipment, affecting the service life and operational stability of the device. Summary of the Invention

[0006] In order to solve the technical problems existing in the prior art, the present invention provides a continuous purification method for crude acetonitrile. The method can achieve continuous purification of crude acetonitrile while avoiding the problems of introducing new impurities due to side reactions caused by treating a distillate with sodium hydroxide and formaldehyde, affecting distillation efficiency and stability due to the treated product, and affecting the device due to excessive alkalinity of a secondary distillate after treatment. By continuously purifying the crude acetonitrile, an acetonitrile product with a purity that meets the requirements is obtained.

[0007] In order to solve the above technical problems, the technical solutions adopted by the present invention are as follows:

[0008] A continuous purification method for crude acetonitrile, comprising the following steps: distillation to remove light substances, membrane separation to remove impurities, adsorption to remove impurities, and distillation purification;

[0009] In the distillation and light removal, crude acetonitrile is continuously fed into the distillation and light removal tower to remove light component impurities, and is withdrawn through the side line to continuously obtain the distillation and light removal product;

[0010] The membrane separation and impurity removal, the distillation and light product are fed into a pervaporation membrane separation device provided with a polyvinyl alcohol membrane assembly, and the pervaporation membrane is used for separation and impurity removal to obtain a membrane separation product with a moisture content of less than 0.5wt%;

[0011] In the adsorption impurity removal, the membrane separation product is continuously fed into a tubular reactor filled with an adsorption impurity removal agent, and after adsorption impurity removal, an adsorption impurity removal liquid is continuously obtained;

[0012] The adsorption impurity remover is composed of a composite adsorbent and mesoporous activated carbon;

[0013] The composite adsorbent is prepared by combining a zirconium-based metal organic framework UiO-66-NH2 with a lanthanum-doped Mg / Al hydrotalcite-like compound;

[0014] The distillation and purification process continuously feeds the adsorption and impurity removal liquid into a distillation and purification tower for distillation and purification treatment, and the purified acetonitrile is continuously obtained by withdrawing it from the side line.

[0015] Preferably, in the distillation de-lightening process, the bottom temperature of the distillation de-lightening tower is controlled to be 98-102°C, the top temperature is 75-80°C, the top pressure is 0.002-0.003MPa, the bottom pressure is 0.025-0.030MPa, and the reflux ratio is 3.2-3.5:1.

[0016] Preferably, in the distillation and light removal process, the number of plates of the distillation and light removal tower is 28-31, the crude acetonitrile feed position is the 7th to 8th plate of the distillation and light removal tower, and the side line extraction position is the 19th to 20th plate of the distillation and light removal tower.

[0017] Preferably, in the membrane separation and impurity removal, the feed temperature for distillation to remove light products is 105-110°C;

[0018] The pervaporation membrane separation device is provided with 7-8 polyvinyl alcohol membrane modules connected in series, and the membrane area of ​​each polyvinyl alcohol membrane module is 8.5-9m 2 ;

[0019] The gauge pressure on the retentate side of the permeation membrane separation is 0.2-0.25 MPa, and the absolute pressure on the permeate side is 9-10 KPa.

[0020] Preferably, in the adsorption impurity removal, the temperature of the tubular reactor is controlled to be 45-50° C., and the residence time of the membrane separation product in the tubular reactor is 500-600 s;

[0021] The loading amount of the adsorption impurity remover in the tubular reactor is 6-6.5% of the total weight of the membrane separation product fed into the tubular reactor within 1 hour.

[0022] Preferably, in the adsorption impurity removal, the mass ratio of the composite adsorbent to the mesoporous activated carbon in the adsorption impurity remover is 1:1.5-1.8;

[0023] The average particle size of mesoporous activated carbon is 180-200 μm, and the specific surface area is 1100-1200 m 2 / g, the average pore diameter is 3-8nm, and the graphitization degree measured by XDR method is 55-57%.

[0024] Furthermore, the preparation method of the composite adsorbent is as follows: magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, lanthanum nitrate hexahydrate, and urea are added to deionized water and dispersed evenly, zirconium-based metal organic framework UiO-66-NH2 is added and dispersed evenly, and then the mixture is transferred to a high-pressure reactor and sealed, heated to 110-115°C, kept warm for reaction for 22-26 hours, and then cooled to obtain a reaction mass; solid matter is separated and collected, and the solid matter is washed and dried to obtain a composite adsorbent.

[0025] Preferably, in the preparation of the composite adsorbent, the heating rate to 110-115°C is 0.3-0.5°C / min;

[0026] The molar ratio of magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, lanthanum nitrate hexahydrate, and urea is 2.5-3:1:0.2-0.25:0.15-0.2;

[0027] The total molar concentration of magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, and lanthanum nitrate hexahydrate in deionized water is 1.8-2 mol / L;

[0028] The weight of the zirconium-based metal-organic framework UiO-66-NH2 is 8-9% of the total weight of magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, and lanthanum nitrate hexahydrate.

[0029] Preferably, in the distillation purification, the bottom temperature of the distillation purification tower is controlled to be 145-148° C., the top temperature is 130-133° C., the top pressure is 0.45-0.50 MPa, and the bottom pressure is 0.49-0.55 MPa;

[0030] During the distillation purification process, part of the condensate of the light components at the top of the tower is refluxed into the distillation purification tower, and the other part is introduced into the tubular reactor for further adsorption and impurity removal, with a reflux ratio of 6-6.5:1.

[0031] Preferably, in the distillation purification, the number of plates of the distillation purification tower is 24-26, the adsorption and impurity removal liquid is fed at the 4th to 5th plates of the distillation purification tower, and the side line extraction position is at the 16th to 17th plates of the distillation purification tower.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) The continuous purification method of crude acetonitrile of the present invention is based on the characteristics of crude acetonitrile. First, distillation is performed to remove most of the light component impurities to obtain a distillation-delighted product; then, a pervaporation membrane separation device equipped with a polyvinyl alcohol membrane assembly is used to perform membrane separation and impurity removal on the distillation-delighted product. While removing water, some impurities are further removed to obtain a membrane separation product with a moisture content of less than 0.5wt%; then, an adsorption impurity removal agent is used to continuously adsorb and remove the small amount of water and cyanide impurities present in the membrane separation product to obtain a product with a moisture content of less than 100pp m, an adsorption impurity removal liquid with a cyanide content of less than 0.2ppm; wherein the adsorption impurity removal agent used is composed of a composite adsorbent and mesoporous activated carbon, and the water and residual hydrocyanic acid in the membrane separation product are specifically adsorbed by the mesoporous activated carbon of specific specifications; at the same time, in the preparation of the composite adsorbent, the zirconium-based metal organic framework UiO-66-NH2 is composited with lanthanum-doped Mg / Al-type hydrotalcite, and the CN in the membrane separation product is separated by the high specific surface area and chemical adsorption performance of UiO-66-NH2 and the ion exchange performance of the lanthanum-doped Mg / Al-type hydrotalcite. - Targeted adsorption; finally, the adsorbed impurity-removed liquid is subjected to distillation and purification to produce purified acetonitrile. The aforementioned technical means work together to achieve continuous purification of crude acetonitrile while avoiding the problems of introducing new impurities due to side reactions caused by treating the distillate with sodium hydroxide and formaldehyde, affecting distillation efficiency and stability, and the excessive alkalinity of the treated secondary distillate affecting the equipment. Through the continuous purification of crude acetonitrile, an acetonitrile product with the required purity is produced.

[0034] (2) The continuous purification method of crude acetonitrile of the present invention has a purity of 99.97-99.98 wt %, a moisture content of 65-73 ppm, a cyanide content of 0.11-0.15 ppm, an oxazole content of 0.6-0.8 ppm, an acidity of 0.0002-0.0004 mmol / g, a basicity of 0.0001-0.0002 mmol / g, an evaporation residue content of 4-5 ppm, and an acetonitrile yield of 93.8-94.1%. DETAILED DESCRIPTION

[0035] In order to provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention are now described. It should be noted that the following detailed description is illustrative and is intended to further illustrate the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0036] It should be noted that the terms used herein are intended only to describe specific embodiments and are not intended to limit the exemplary embodiments of the present invention. As used herein, "first," "second," and the like are used to distinguish similar objects and are not used to describe a specific order or precedence. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0037] The embodiment of the present invention provides a continuous purification method for crude acetonitrile, which comprises the following steps: distillation to remove light substances, membrane separation to remove impurities, adsorption to remove impurities, and distillation purification.

[0038] The distillation and light-removal method comprises the following steps: continuously feeding crude acetonitrile into a distillation and light-removal tower (theoretical number of tower plates is 28-31) from the 7th to 8th tower plates; controlling the bottom temperature of the distillation and light-removal tower to be 98-102° C., the top temperature to be 75-80° C., the top pressure to be 0.002-0.003 MPa, and the bottom pressure to be 0.025-0.030 MPa, to perform distillation and light-removal treatment; and continuously extracting a side stream fraction from the 19th to 20th tower plates of the distillation and light-removal tower to continuously obtain a distillation and light-removal product.

[0039] During the distillation and light removal process, the overhead light components are discharged from the top of the distillation and light removal tower to a condenser for condensation. Part of the condensate is refluxed back into the distillation and light removal tower, and the remaining part is discharged to wastewater treatment, with a reflux ratio of 3.2-3.5:1. Non-condensable gases are discharged to the tail gas treatment plant for treatment and then vented. High-boiling products at the bottom of the tower are discharged from the bottom of the distillation and light removal tower and collected in a waste liquid tank, and wastewater treatment is performed regularly.

[0040] The membrane separation and impurity removal method is to heat the distillation light product to 105-110°C and then introduce it into a pervaporation membrane separation device composed of 7-8 polyvinyl alcohol (PVA) membrane modules connected in series, with each polyvinyl alcohol (PVA) membrane module having a membrane area of ​​8.5-9m 2 , control the pressure on the retention side of the permeation membrane device to 0.2-0.25MPa (gauge pressure), and the pressure on the permeation side to 9-10KPa (absolute pressure) to perform membrane separation and impurity removal; the material that passes through the permeation membrane and enters the permeation side is condensed by the permeation side condenser, discharged and collected in the waste liquid tank, and the wastewater is treated regularly; the material on the retention side is subjected to membrane separation and impurity removal treatment, and then condensed by the retention side condenser to obtain a membrane separation product with a moisture content of <0.5wt%.

[0041] The adsorption impurity removal method comprises the following steps: continuously feeding the membrane separation product into a tubular reactor filled with an adsorption impurity removal agent, controlling the temperature of the tubular reactor to be 45-50° C., and allowing the membrane separation product to reside in the tubular reactor for 500-600 seconds. After the adsorption impurity removal, an adsorption impurity removal liquid (with a water content of less than 100 ppm and a cyanide content of less than 0.2 ppm) is continuously obtained.

[0042] In the adsorption impurity removal, the loading amount of the adsorption impurity remover in the tubular reactor is 6-6.5% of the total weight of the membrane separation product fed into the tubular reactor within 1 hour.

[0043] In the adsorption impurity removal, the adsorption impurity removal agent is a mixture of a composite adsorbent and mesoporous activated carbon; the mass ratio of the composite adsorbent to the mesoporous activated carbon is 1:1.5-1.8.

[0044] The average particle size of mesoporous activated carbon is 180-200 μm, and the specific surface area is 1100-1200 m 2 / g, the average pore diameter is 3-8nm, and the graphitization degree measured by XDR method is 55-57%.

[0045] The preparation method of the composite adsorbent comprises the following steps: adding magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, lanthanum nitrate hexahydrate and urea into deionized water, stirring and dissolving the mixture, then adding a zirconium-based metal organic framework UiO-66-NH2, ultrasonically dispersing the mixture for 20-30 minutes, transferring the mixture into a polytetrafluoroethylene high-pressure reactor, sealing the reactor, heating the mixture to 110-115°C at a heating rate of 0.3-0.5°C / min, keeping the temperature for reaction for 22-26 hours, and naturally cooling the mixture to room temperature to obtain a reaction mass; centrifuging the reaction mass, collecting a solid, washing the solid 2-3 times with deionized water, placing the solid in a constant temperature box, and drying the mixture at 70-75°C to a constant weight to obtain the composite adsorbent.

[0046] In the preparation of the composite adsorbent, the molar ratio of magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, lanthanum nitrate hexahydrate, and urea is 2.5-3:1:0.2-0.25:0.15-0.2;

[0047] The total molar concentration of magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, and lanthanum nitrate hexahydrate in deionized water is 1.8-2 mol / L;

[0048] The weight of the zirconium-based metal-organic framework UiO-66-NH2 is 8-9% of the total weight of magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, and lanthanum nitrate hexahydrate.

[0049] The distillation purification method comprises the following steps: continuously feeding the adsorption impurity removal liquid into a distillation purification tower (theoretical number of plates is 24-26) from the 4th to 5th tower plates; controlling the bottom temperature of the distillation purification tower to be 145-148° C., the top temperature to be 130-133° C., the top pressure to be 0.45-0.50 MPa, and the bottom pressure to be 0.49-0.55 MPa for distillation purification treatment; and continuously extracting a side stream fraction from the 16th to 17th tower plates of the distillation purification tower; and continuously obtaining a purified acetonitrile product after condensing the side stream fraction through a condenser.

[0050] During the distillation and purification process, the overhead light fraction is discharged from the top of the distillation and purification tower to a condenser for condensation. A portion of the condensate is then refluxed back into the distillation and purification tower, while the remaining portion is introduced into a tubular reactor for further adsorption and impurity removal. The reflux ratio is 6-6.5:1. Non-condensable gases are discharged to an exhaust gas treatment facility for treatment and then vented. High-boiling products at the bottom of the tower are regularly discharged from the bottom of the distillation and purification tower to a waste liquid tank for regular wastewater treatment.

[0051] The present invention will be further described below with reference to some specific embodiments.

[0052] Example 1

[0053] This embodiment provides a method for continuously purifying crude acetonitrile, wherein the crude acetonitrile contains the following components by mass fraction: 51.3 wt % acetonitrile, 44.2 wt % water, 1.63 wt % hydrocyanic acid, 2.3 wt % acrylonitrile, 0.5 wt % oxazole, and 0.07 wt % propionitrile; the specific method is as follows:

[0054] 1. Distillation to remove light

[0055] Crude acetonitrile was continuously fed into a distillation and light-removal tower (theoretical number of plates was 30) from the 7th tray, and the bottom temperature, top temperature, top pressure and bottom pressure of the distillation and light-removal tower were controlled at 98°C, 75°C, 0.002MPa and 0.025MPa, respectively, for distillation and light-removal treatment. A side stream fraction was continuously withdrawn from the 19th tray of the distillation and light-removal tower to continuously obtain a distillation and light-removal product.

[0056] During the distillation and de-lightening process, overhead light components are discharged from the top of the distillation and de-lightening tower to a condenser for condensation. A portion of the condensate is refluxed back into the distillation and de-lightening tower, while the remainder is discharged to wastewater treatment, with a reflux ratio of 3.2:1. Non-condensable gases are discharged to the tail gas treatment facility for treatment and then vented. High-boiling products at the bottom of the tower are discharged from the bottom of the distillation and de-lightening tower and collected in a waste liquid tank, where they are regularly treated.

[0057] 2. Membrane separation and impurity removal

[0058] The distillation light product was heated to 105°C and then introduced into a pervaporation membrane separation device consisting of 8 polyvinyl alcohol (PVA) membrane modules connected in series. The membrane area of ​​each polyvinyl alcohol (PVA) membrane module was 9m 2 , the pressure on the retention side of the permeation membrane device is controlled to be 0.2MPa (gauge pressure), and the pressure on the permeation side is controlled to be 9KPa (absolute pressure) to perform membrane separation and impurity removal; the material that passes through the permeation membrane and enters the permeation side is condensed by the permeation side condenser, discharged and collected in the waste liquid tank, and the wastewater is treated regularly; the material on the retention side is subjected to membrane separation and impurity removal treatment, and then condensed by the retention side condenser to obtain a membrane separation product with a moisture content of 0.42wt%.

[0059] 3. Adsorption and impurity removal

[0060] The membrane separation product was continuously fed into a tubular reactor filled with an adsorption impurity removal agent. The temperature of the tubular reactor was controlled at 45°C, and the residence time of the membrane separation product in the tubular reactor was 500s. After adsorption impurity removal, an adsorption impurity removal liquid (water content of 81 ppm, cyanide content of 0.17 ppm) was continuously obtained.

[0061] The loading amount of the adsorption impurity remover in the tubular reactor is 6% of the total weight of the membrane separation product fed into the tubular reactor within 1 hour.

[0062] The adsorption impurity remover consists of a composite adsorbent and mesoporous activated carbon, and the mass ratio of the composite adsorbent to the mesoporous activated carbon is 1:1.5.

[0063] The average particle size of mesoporous activated carbon is 200 μm and the specific surface area is 1200 m 2 / g, the average pore diameter is 6nm, and the graphitization degree measured by XDR method is 56.4%.

[0064] The preparation method of the composite adsorbent comprises the following steps: adding magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, lanthanum nitrate hexahydrate, and urea into deionized water, stirring and dissolving the mixture, then adding a zirconium-based metal organic framework UiO-66-NH2, ultrasonically dispersing the mixture for 20 minutes, transferring the mixture into a polytetrafluoroethylene high-pressure reactor, sealing the reactor, heating the mixture to 110°C at a heating rate of 0.3°C / min, keeping the temperature for reaction for 22 hours, and naturally cooling the mixture to room temperature to obtain a reaction mass; centrifuging the reaction mass, collecting a solid, washing the solid three times with deionized water, placing the solid in a constant temperature box, and drying the mixture at 70°C to a constant weight to obtain a composite adsorbent.

[0065] The molar ratio of magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, lanthanum nitrate hexahydrate and urea is 2.5:1:0.2:0.15.

[0066] The total molar concentration of magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, and lanthanum nitrate hexahydrate in deionized water is 1.8 mol / L.

[0067] The weight of the zirconium-based metal-organic framework UiO-66-NH2 is 8% of the total weight of magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, and lanthanum nitrate hexahydrate; the zirconium-based metal-organic framework UiO-66-NH2 is purchased from commercial sources.

[0068] 4. Distillation and purification

[0069] The adsorption and impurity removal liquid was continuously fed into a distillation purification tower (theoretical number of plates was 26) from the 5th tower plate, and the bottom temperature, top temperature, top pressure and bottom pressure of the distillation purification tower were controlled at 145°C, 130°C, 0.45 MPa and 0.49 MPa, respectively, for distillation and purification treatment. A side stream fraction was continuously withdrawn from the 16th tower plate of the distillation purification tower, and the side stream fraction was condensed in a condenser to continuously obtain a purified acetonitrile product.

[0070] During the distillation and purification process, the overhead light fraction is discharged from the top of the distillation and purification tower to a condenser for condensation. Part of the condensate is refluxed back into the distillation and purification tower, while the remaining portion is introduced into a tubular reactor for further adsorption and impurity removal. The reflux ratio is 6:1. Non-condensable gases are discharged to the tail gas treatment plant for treatment and then vented. High-boiling substances at the bottom of the tower are regularly discharged from the bottom of the distillation and purification tower to a waste liquid tank for regular wastewater treatment.

[0071] After testing, the purity of the purified acetonitrile obtained in this example was 99.97 wt %, the moisture content was 73 ppm, the cyanide content was 0.15 ppm, the oxazole content was 0.8 ppm, the acidity was 0.0004 mmol / g, the alkalinity was 0.0002 mmol / g, the evaporation residue content was 5 ppm, and the acetonitrile yield was 93.8%; wherein, the purity and oxazole content of the purified acetonitrile were obtained by gas chromatography-mass spectrometry (GC-MS), the cyanide content was obtained by spectrophotometry, the moisture content was obtained by Karl Fischer coulometric method, and the acidity and alkalinity were obtained by potentiometric titration.

[0072] Example 2

[0073] This embodiment provides a method for continuously purifying crude acetonitrile, wherein the crude acetonitrile contains the following components by mass fraction: 51.3 wt % acetonitrile, 44.2 wt % water, 1.63 wt % hydrocyanic acid, 2.3 wt % acrylonitrile, 0.5 wt % oxazole, and 0.07 wt % propionitrile; the specific method is as follows:

[0074] 1. Distillation to remove light

[0075] Crude acetonitrile was continuously fed into a distillation and light-removal tower (theoretical number of plates was 30) from the 7th tray. The bottom temperature, top temperature, top pressure and bottom pressure of the distillation and light-removal tower were controlled at 100°C, 78°C, 0.0025 MPa and 0.027 MPa, respectively, for distillation and light-removal treatment. A side stream fraction was continuously withdrawn from the 19th tray of the distillation and light-removal tower to continuously obtain a distillation and light-removal product.

[0076] During the distillation and de-lightening process, overhead light components are discharged from the top of the distillation and de-lightening tower to a condenser for condensation. A portion of the condensate is refluxed back into the distillation and de-lightening tower, while the remainder is discharged to wastewater treatment, with a reflux ratio of 3.4:1. Non-condensable gases are discharged to the tail gas treatment facility for treatment and then vented. High-boiling products at the bottom of the tower are discharged from the bottom of the distillation and de-lightening tower and collected in a waste liquid tank, with regular wastewater treatment.

[0077] 2. Membrane separation and impurity removal

[0078] The distillation light product was heated to 108°C and then introduced into a pervaporation membrane separation device consisting of 8 polyvinyl alcohol (PVA) membrane modules connected in series. The membrane area of ​​each polyvinyl alcohol (PVA) membrane module was 9m 2 , the pressure on the retention side of the permeation membrane device is controlled to be 0.22MPa (gauge pressure), and the pressure on the permeation side is controlled to be 9.5KPa (absolute pressure) to perform membrane separation and impurity removal; the material that passes through the permeation membrane and enters the permeation side is condensed by the permeation side condenser, discharged and collected in the waste liquid tank, and the wastewater is treated regularly; the material on the retention side is subjected to membrane separation and impurity removal treatment, and then condensed by the retention side condenser to obtain a membrane separation product with a moisture content of 0.39wt%.

[0079] 3. Adsorption and impurity removal

[0080] The membrane separation product was continuously fed into a tubular reactor filled with an adsorption impurity removal agent. The temperature of the tubular reactor was controlled at 48°C, and the residence time of the membrane separation product in the tubular reactor was 570s. After adsorption impurity removal, an adsorption impurity removal liquid (water content of 75ppm, cyanide content of 0.15ppm) was continuously obtained.

[0081] The loading amount of the adsorption impurity remover in the tubular reactor is 6.4% of the total weight of the membrane separation product fed into the tubular reactor within 1 hour.

[0082] The adsorption impurity remover consists of a composite adsorbent and mesoporous activated carbon, and the mass ratio of the composite adsorbent to the mesoporous activated carbon is 1:1.65.

[0083] The average particle size of mesoporous activated carbon is 200 μm and the specific surface area is 1200 m 2 / g, the average pore diameter is 6nm, and the graphitization degree measured by XDR method is 56.4%.

[0084] The preparation method of the composite adsorbent comprises the following steps: adding magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, lanthanum nitrate hexahydrate, and urea into deionized water, stirring and dissolving the mixture, then adding a zirconium-based metal organic framework UiO-66-NH2, ultrasonically dispersing the mixture for 25 minutes, transferring the mixture into a polytetrafluoroethylene high-pressure reactor, sealing the reactor, heating the mixture to 112°C at a heating rate of 0.4°C / min, keeping the temperature for reaction for 24 hours, and naturally cooling the mixture to room temperature to obtain a reaction mass; centrifuging the reaction mass, collecting a solid, washing the solid three times with deionized water, placing the solid in a constant temperature box, and drying the mixture at 72°C to a constant weight to obtain a composite adsorbent.

[0085] The molar ratio of magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, lanthanum nitrate hexahydrate and urea is 2.8:1:0.23:0.16.

[0086] The total molar concentration of magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, and lanthanum nitrate hexahydrate in deionized water is 1.9 mol / L.

[0087] The weight of the zirconium-based metal-organic framework UiO-66-NH2 is 8.4% of the total weight of magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, and lanthanum nitrate hexahydrate; the zirconium-based metal-organic framework UiO-66-NH2 is purchased from commercial sources.

[0088] 4. Distillation and purification

[0089] The adsorption and impurity removal liquid was continuously fed into a distillation purification tower (theoretical number of plates was 26) from the 5th tower plate, and the bottom temperature, top temperature, top pressure and bottom pressure of the distillation purification tower were controlled at 146°C, 131°C, 0.46 MPa and 0.51 MPa, respectively, for distillation and purification treatment. A side stream fraction was continuously withdrawn from the 16th tower plate of the distillation purification tower, and the side stream fraction was condensed in a condenser to continuously obtain a purified acetonitrile product.

[0090] During the distillation and purification process, the overhead light fraction is discharged from the top of the distillation and purification tower to a condenser for condensation. Part of the condensate is refluxed back into the distillation and purification tower, while the remaining portion is introduced into a tubular reactor for further adsorption and impurity removal. The reflux ratio is 6.2:1. Non-condensable gases are discharged to the tail gas treatment plant for treatment and then vented. High-boiling substances at the bottom of the tower are regularly discharged from the bottom of the distillation and purification tower to a waste liquid tank for regular wastewater treatment.

[0091] After testing, the purity of the purified acetonitrile prepared in this example was 99.98 wt %, the moisture content was 65 ppm, the cyanide content was 0.11 ppm, the oxazole content was 0.6 ppm, the acidity was 0.0002 mmol / g, the alkalinity was 0.0001 mmol / g, the evaporation residue content was 4 ppm, and the acetonitrile yield was 94.1%. The purity and oxazole content of the purified acetonitrile were determined by gas chromatography-mass spectrometry (GC-MS), the cyanide content was determined by spectrophotometry, the moisture content was determined by Karl Fischer coulometry, and the acidity and alkalinity were determined by potentiometric titration.

[0092] Example 3

[0093] This embodiment provides a method for continuously purifying crude acetonitrile, wherein the crude acetonitrile contains the following components by mass fraction: 51.3 wt % acetonitrile, 44.2 wt % water, 1.63 wt % hydrocyanic acid, 2.3 wt % acrylonitrile, 0.5 wt % oxazole, and 0.07 wt % propionitrile; the specific method is as follows:

[0094] 1. Distillation to remove light

[0095] Crude acetonitrile was continuously fed into a distillation and light-removal tower (theoretical number of plates was 30) from the 7th tray, and the bottom temperature, top temperature, top pressure and bottom pressure of the distillation and light-removal tower were controlled at 102°C, 80°C, 0.003 MPa and 0.030 MPa, respectively, for distillation and light-removal treatment. A side stream fraction was continuously withdrawn from the 19th tray of the distillation and light-removal tower to continuously obtain a distillation and light-removal product.

[0096] During the distillation and degassing process, overhead light components are discharged from the top of the distillation and degassing tower to a condenser for condensation. A portion of the condensate is refluxed back into the distillation and degassing tower, while the remaining portion is discharged to wastewater treatment, with a reflux ratio of 3.5:1. Non-condensable gases are discharged to the tail gas treatment plant for treatment and then vented. High-boiling products at the bottom of the tower are discharged from the bottom of the distillation and degassing tower and collected in a waste liquid tank, with regular wastewater treatment.

[0097] 2. Membrane separation and impurity removal

[0098] The distillation light product was heated to 110°C and then introduced into a pervaporation membrane separation device consisting of 8 polyvinyl alcohol (PVA) membrane modules connected in series. The membrane area of ​​each polyvinyl alcohol (PVA) membrane module was 9m 2 , control the pressure on the retention side of the permeation membrane device to 0.25MPa (gauge pressure), and the pressure on the permeation side to 10KPa (absolute pressure) to perform membrane separation and impurity removal; the material that passes through the permeation membrane and enters the permeation side is condensed by the permeation side condenser, discharged and collected in the waste liquid tank, and the wastewater is treated regularly; the material on the retention side is subjected to membrane separation and impurity removal treatment, and then condensed by the retention side condenser to obtain a membrane separation product with a moisture content of 0.40wt%.

[0099] 3. Adsorption and impurity removal

[0100] The membrane separation product was continuously fed into a tubular reactor filled with an adsorption impurity removal agent. The temperature of the tubular reactor was controlled at 50°C, and the residence time of the membrane separation product in the tubular reactor was 600s. After adsorption impurity removal, an adsorption impurity removal liquid (water content of 79 ppm, cyanide content of 0.16 ppm) was continuously obtained.

[0101] The loading amount of the adsorption impurity remover in the tubular reactor is 6.5% of the total weight of the membrane separation product fed into the tubular reactor within 1 hour.

[0102] The adsorption impurity remover consists of a composite adsorbent and mesoporous activated carbon, and the mass ratio of the composite adsorbent to the mesoporous activated carbon is 1:1.8.

[0103] The average particle size of mesoporous activated carbon is 200 μm and the specific surface area is 1200 m 2 / g, the average pore diameter is 6nm, and the graphitization degree measured by XDR method is 56.4%.

[0104] The preparation method of the composite adsorbent comprises the following steps: adding magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, lanthanum nitrate hexahydrate, and urea into deionized water, stirring and dissolving the mixture, then adding a zirconium-based metal organic framework UiO-66-NH2, ultrasonically dispersing the mixture for 30 minutes, transferring the mixture into a polytetrafluoroethylene high-pressure reactor, sealing the reactor, heating the mixture to 115°C at a heating rate of 0.5°C / min, keeping the temperature for reaction for 26 hours, and naturally cooling the mixture to room temperature to obtain a reaction mass; centrifuging the reaction mass, collecting a solid, washing the solid three times with deionized water, placing the solid in a constant temperature box, and drying the mixture at 75°C to a constant weight to obtain a composite adsorbent.

[0105] The molar ratio of magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, lanthanum nitrate hexahydrate and urea is 3:1:0.25:0.2.

[0106] The total molar concentration of magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, and lanthanum nitrate hexahydrate in deionized water is 2 mol / L.

[0107] The weight of the zirconium-based metal-organic framework UiO-66-NH2 is 9% of the total weight of magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, and lanthanum nitrate hexahydrate; the zirconium-based metal-organic framework UiO-66-NH2 is purchased from commercial sources.

[0108] 4. Distillation and purification

[0109] The adsorption and impurity removal liquid was continuously fed into a distillation purification tower (theoretical number of plates was 26) from the 5th tower plate, and the bottom temperature, top temperature, top pressure and bottom pressure of the distillation purification tower were controlled at 148°C, 133°C, 0.50 MPa and 0.55 MPa, respectively, for distillation and purification treatment. A side stream fraction was continuously withdrawn from the 16th tower plate of the distillation purification tower, and the side stream fraction was condensed in a condenser to continuously obtain a purified acetonitrile product.

[0110] During the distillation and purification process, the overhead light fraction is discharged from the top of the distillation and purification tower to a condenser for condensation. Part of the condensate is refluxed back into the distillation and purification tower, while the remaining portion is introduced into a tubular reactor for further adsorption and impurity removal. The reflux ratio is 6.5:1. Non-condensable gases are discharged to the tail gas treatment plant for treatment and then vented. High-boiling substances at the bottom of the tower are regularly discharged from the bottom of the distillation and purification tower to a waste liquid tank for regular wastewater treatment.

[0111] After testing, the purity of the purified acetonitrile prepared in this example was 99.98 wt %, the moisture content was 70 ppm, the cyanide content was 0.14 ppm, the oxazole content was 0.8 ppm, the acidity was 0.0003 mmol / g, the alkalinity was 0.0002 mmol / g, the evaporation residue content was 4 ppm, and the acetonitrile yield was 93.9%; wherein, the purity and oxazole content of the purified acetonitrile were obtained by gas chromatography-mass spectrometry (GC-MS), the cyanide content was obtained by spectrophotometry, the moisture content was obtained by Karl Fischer coulometric method, and the acidity and alkalinity were obtained by potentiometric titration.

[0112] Comparative Example 1

[0113] Comparative Example 1 adopts the technical solution of Example 2, with the following changes: in the preparation of the composite adsorbent, the addition of lanthanum nitrate hexahydrate and the zirconium-based metal-organic framework UiO-66-NH2 is omitted.

[0114] Comparative Example 1: After the membrane separation product was subjected to adsorption and impurity removal treatment, the water content of the adsorption and impurity removal liquid obtained was 77 ppm, and the cyanide content was 7.1 ppm. The purity of the purified acetonitrile finally obtained was 99.96 wt%, the water content was 69 ppm, the cyanide content was 7.0 ppm, the oxazole content was 1.1 ppm, the acidity was 0.0008 mmol / g, the alkalinity was 0.0002 mmol / g, the evaporation residue content was 7 ppm, and the acetonitrile yield was 91.9%; wherein, the purity and oxazole content of the purified acetonitrile were obtained by gas chromatography-mass spectrometry (GC-MS), the cyanide content was obtained by spectrophotometry, the water content was obtained by Karl Fischer coulometry, and the acidity and alkalinity were obtained by potentiometric titration.

[0115] It can be seen that the continuous purification method of crude acetonitrile of the present invention is based on the characteristics of crude acetonitrile. It is first subjected to distillation to remove most of the light component impurities to obtain a distillation-delighted product; then a pervaporation membrane separation device provided with a polyvinyl alcohol membrane assembly is used to perform membrane separation and impurity removal on the distillation-delighted product. While removing water, some impurities are further removed to obtain a membrane separation product with a moisture content of less than 0.5wt%; then, for a small amount of water and cyanide impurities present in the membrane separation product, an adsorption impurity remover is used to perform continuous adsorption impurity removal to obtain a membrane separation product with a moisture content of less than 100wt%. ppm, and an adsorption impurity removal liquid with a cyanide content of less than 0.2ppm; wherein, the adsorption impurity removal agent used is composed of a composite adsorbent and mesoporous activated carbon, and the water and residual hydrocyanic acid in the membrane separation product are specifically adsorbed by the mesoporous activated carbon of specific specifications; at the same time, in the preparation of the composite adsorbent, the zirconium-based metal organic framework UiO-66-NH2 is composited with lanthanum-doped Mg / Al-type hydrotalcite, and the CN in the membrane separation product is separated by the high specific surface area and chemical adsorption performance of UiO-66-NH2 and the ion exchange performance of the lanthanum-doped Mg / Al-type hydrotalcite. - Targeted adsorption; finally, the adsorbed impurity-removed liquid is subjected to distillation and purification to produce purified acetonitrile. The aforementioned technical means work synergistically to achieve continuous purification of crude acetonitrile while avoiding the problems of introducing new impurities due to side reactions caused by treating the distillate with sodium hydroxide and formaldehyde, affecting distillation efficiency and stability, and the excessive alkalinity of the treated secondary distillate affecting the equipment. Through the continuous purification of crude acetonitrile, an acetonitrile product with the required purity is produced.

[0116] It can be seen from Comparative Example 1 that after omitting the addition of lanthanum nitrate hexahydrate and zirconium-based metal organic framework UiO-66-NH2 in the preparation of the composite adsorbent, the membrane separation product is subjected to adsorption and impurity removal treatment. - The adsorption performance of the product was significantly deteriorated, which was manifested in a significant increase in the cyanide content in the obtained adsorption and impurity removal liquid and purified acetonitrile.

[0117] Furthermore, the recycling performance test was conducted on the adsorption impurity removers used in Example 2 and Comparative Example 1. Specifically, when the adsorption impurity removers used in Example 2 and Comparative Example 1 reached adsorption equilibrium, the adsorption impurity removers were regenerated and reused in the adsorption impurity removal step; after 15 consecutive cycles, the moisture content and cyanide content of the adsorption impurity removal liquids obtained in the adsorption impurity removal step of Example 2 and Comparative Example 1 were respectively tested; and the adsorption capacity retention rate of the composite adsorbent in the adsorption impurity removers of Example 2 and Comparative Example 1 was measured. The specific results are shown in the following table:

[0118]

[0119] It can be seen that in the preparation of the composite adsorbent, the present invention combines the zirconium-based metal-organic framework UiO-66-NH2 with the lanthanum-doped Mg / Al-type hydrotalcite, which can also effectively improve the stability of the Mg / Al-type hydrotalcite for continuous purification of membrane separation products, and improve the recycling performance and adsorption capacity retention performance of the composite adsorbent. Comparative Example 1 shows that after omitting the addition of lanthanum nitrate hexahydrate and the zirconium-based metal-organic framework UiO-66-NH2 in the preparation of the composite adsorbent, the recycling performance and adsorption capacity retention performance of the composite adsorbent show a significant decrease, specifically manifested in a decrease in cyanide adsorption performance and a decrease in adsorption capacity retention after 15 cycles.

[0120] Unless otherwise specified, all percentages used in the present invention are by mass.

[0121] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will be able to modify the technical solutions described in the aforementioned embodiments or substitute equivalents for some of the technical features. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A continuous purification method for crude acetonitrile, characterized in that, The process includes the following steps: distillation to remove light substances, membrane separation to remove impurities, adsorption to remove impurities, and distillation purification; In the distillation and light removal, crude acetonitrile is continuously fed into the distillation and light removal tower to remove light component impurities, and is withdrawn through the side line to continuously obtain the distillation and light removal product; The membrane separation and impurity removal, the distillation and light product are fed into a pervaporation membrane separation device provided with a polyvinyl alcohol membrane assembly, and the pervaporation membrane is used for separation and impurity removal to obtain a membrane separation product with a moisture content of less than 0.5wt%; In the adsorption impurity removal, the membrane separation product is continuously fed into a tubular reactor filled with an adsorption impurity removal agent, and after adsorption impurity removal, an adsorption impurity removal liquid is continuously obtained; The adsorption impurity remover is composed of a composite adsorbent and mesoporous activated carbon; the mass ratio of the composite adsorbent to the mesoporous activated carbon in the adsorption impurity remover is 1:1.5-1.8; The average particle size of the mesoporous activated carbon is 180-200 μm, and the specific surface area is 1100-1200 m 2 / g, the average pore size is 3-8nm, and the degree of graphitization measured by XDR method is 55-57%; The composite adsorbent preparation method comprises the following steps: adding magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, lanthanum nitrate hexahydrate, and urea into deionized water, uniformly dispersing the mixture, adding a zirconium-based metal organic framework UiO-66-NH2, uniformly dispersing the mixture, transferring the mixture into a high-pressure reactor, sealing the reactor, heating the reactor to 110-115° C., maintaining the temperature for reaction for 22-26 hours, and cooling the reactor to obtain a reaction mass; separating and collecting a solid matter, washing the solid matter, and drying the solid matter to obtain a composite adsorbent; The distillation and purification process continuously feeds the adsorption and impurity removal liquid into a distillation and purification tower for distillation and purification treatment, and the purified acetonitrile is continuously obtained by withdrawing it from the side line.

2. the continuous purification method of crude acetonitrile according to claim 1, is characterized in that, In the distillation de-lightening process, the bottom temperature of the distillation de-lightening tower is controlled to be 98-102° C., the top temperature is controlled to be 75-80° C., the top pressure is controlled to be 0.002-0.003 MPa, the bottom pressure is controlled to be 0.025-0.030 MPa, and the reflux ratio is controlled to be 3.2-3.5:

1.

3. The continuous purification method of crude acetonitrile according to claim 1, wherein In the distillation and de-lightening process, the number of plates of the distillation and de-lightening tower is 28-31, the crude acetonitrile feeding position is the 7th to 8th plate of the distillation and de-lightening tower, and the side line extraction position is the 19th to 20th plate of the distillation and de-lightening tower.

4. the continuous purification method of crude acetonitrile according to claim 1, is characterized in that, In the membrane separation and impurity removal, the feed temperature for distillation to remove light products is 105-110°C; The pervaporation membrane separation device is provided with 7-8 polyvinyl alcohol membrane modules connected in series, and the membrane area of ​​each polyvinyl alcohol membrane module is 8.5-9m 2 ; The gauge pressure on the retentate side of the permeation membrane separation is 0.2-0.25 MPa, and the absolute pressure on the permeate side is 9-10 KPa.

5. The continuous purification method of crude acetonitrile according to claim 1, wherein In the adsorption impurity removal, the temperature of the tubular reactor is controlled to be 45-50° C., and the residence time of the membrane separation product in the tubular reactor is 500-600 s; The loading amount of the adsorption impurity remover in the tubular reactor is 6-6.5% of the total weight of the membrane separation product fed into the tubular reactor within 1 hour.

6. The continuous purification method of crude acetonitrile according to claim 1, wherein In the preparation of the composite adsorbent, the heating rate to 110-115°C is 0.3-0.5°C / min; The molar ratio of magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, lanthanum nitrate hexahydrate, and urea is 2.5-3:1:0.2-0.25:0.15-0.2; The total molar concentration of magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, and lanthanum nitrate hexahydrate in deionized water is 1.8-2 mol / L; The weight of the zirconium-based metal-organic framework UiO-66-NH2 is 8-9% of the total weight of magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, and lanthanum nitrate hexahydrate.

7. The continuous purification method of crude acetonitrile according to claim 1, wherein During the distillation purification, the bottom temperature of the distillation purification tower is controlled to be 145-148° C., the top temperature is controlled to be 130-133° C., the top pressure is controlled to be 0.45-0.50 MPa, and the bottom pressure is controlled to be 0.49-0.55 MPa; During the distillation purification process, part of the condensate of the light components at the top of the tower is refluxed into the distillation purification tower, and the other part is introduced into the tubular reactor for further adsorption and impurity removal, with a reflux ratio of 6-6.5:

1.

8. The continuous purification method of crude acetonitrile according to claim 1, wherein In the distillation purification, the number of plates of the distillation purification tower is 24-26, the adsorption and impurity removal liquid is fed at the 4th to 5th plates of the distillation purification tower, and the side line extraction position is at the 16th to 17th plates of the distillation purification tower.

Images