A method and system for continuous separation of an acetonitrile and methanol mixture

Abstract

The application belongs to the field of acetonitrile and methanol homogeneous azeotrope separation, and particularly relates to a method and system for continuously separating acetonitrile and methanol mixture. The separation method comprises raw material pretreatment, extraction, methanol recovery and acetonitrile product refining process, so that acetonitrile, methanol and water can be efficiently separated. The separation system cooperating with the above separation method comprises a pretreatment unit, an extraction unit, a methanol recovery unit and an acetonitrile product refining unit. The pretreatment unit is used for removing impurities in the raw material. The extraction unit is used for extracting the raw material treated by the pretreatment unit, and separating an extraction phase and a raffinate phase. The methanol recovery unit is used for rectifying the extraction phase to obtain product methanol. The acetonitrile product refining unit is used for rectifying the raffinate phase to obtain product acetonitrile. In the application, inorganic salt extraction liquid is used to absorb methanol and water, and acetonitrile and methanol are efficiently rectified and purified. The application has the advantages of high product purity, high recovery rate, easy recovery of extraction agent, flexible process flow, economy and environmental protection, etc.

Description

Technical Field

[0001] This invention belongs to the field of homogeneous azeotropic material separation technology, specifically relating to a method and system for the continuous separation of a mixture of acetonitrile and methanol. Background Technology

[0002] Acetonitrile and methanol are common raw materials in organic synthesis and widely used solvents in the chemical and pharmaceutical industries. Methanol and acetonitrile form an azeotrope at atmospheric pressure with an azeotropic temperature of 63.45℃ and an azeotropic composition of 81 wt% methanol and 19 wt% acetonitrile. Similarly, acetonitrile and water form an azeotrope at atmospheric pressure with an azeotropic temperature of 76℃ and an azeotropic composition of 85 wt% acetonitrile and 15 wt% water. Water-acetonitrile and methanol-acetonitrile mixtures are typical azeotropic systems, and ordinary distillation methods cannot separate these mixtures.

[0003] Most commercially available materials containing acetonitrile and methanol also contain a certain amount of water, other organic solvents with high and low boiling points, and insoluble solids. These are often obtained through simple crude distillation to obtain an acetonitrile-methanol-water mixture, which is then used as an alcohol-based fuel. However, this type of acetonitrile-containing alcohol-based fuel emits strong odors and exceeds ammonia and nitrogen limits during combustion, restricting its use in the fuel industry. Studies on the separation of acetonitrile-methanol-water azeotropes have shown that special distillation methods can be used to separate acetonitrile azeotropes, including azeotropic distillation, extractive distillation, salt extraction distillation, and reactive distillation. If azeotropic distillation is used to separate the acetonitrile-methanol-water azeotrope, an entrainer is required. The azeotrope formed by the entrainer, methanol, water, and acetonitrile needs to be separated by adding water or by cooling and stratifying the resulting ternary or multi-component azeotropic mixture to finally obtain the final products of acetonitrile and methanol. This method is lengthy, requires significant investment, and involves high energy consumption due to the reuse of entrainer and water. Furthermore, the acetonitrile product contains entrainer residues, resulting in poor economic efficiency. Extractive distillation of acetonitrile azeotropes requires the addition of an extractant. The presence of the extractant eliminates the azeotropic point between acetonitrile and methanol or water. Similar to azeotropic distillation, extractant residue remains in the acetonitrile product, affecting product quality. Extractive distillation methods have certain limitations in producing high-purity acetonitrile. Pressure distillation of acetonitrile azeotropes uses a combination of atmospheric pressure, reduced pressure, and pressurization to separate azeotropes. It utilizes the differences in azeotropic temperature and component content under different pressure conditions to separate acetonitrile and methanol. This method yields high-quality acetonitrile, but the relative volatility of components decreases during pressurization, increasing energy consumption. It requires thermal integration of high and low heat sources, making the process more complex. The pressure distillation column has relatively high temperature and pressure, necessitating a higher safety level. In summary, existing methods for separating acetonitrile azeotropes by distillation suffer from problems such as long process flow, high investment, high energy consumption, high safety requirements, poor distillation efficiency, and extractant residue in acetonitrile. Summary of the Invention

[0004] To address the shortcomings of the existing technology, this invention provides a method for the continuous separation of a mixture of acetonitrile and methanol. The aim is to achieve efficient separation of acetonitrile, methanol, and water. The separation process is simple, operates under mild conditions, consumes little energy, and is economical and environmentally friendly. The separated methanol and acetonitrile are of good quality, and the separated water has good biodegradability. To implement the above separation method, this invention also provides a corresponding separation system.

[0005] The present invention provides a first technical solution, which is a method for continuous separation of a mixture of acetonitrile and methanol, the specific technical solution of which is as follows:

[0006] A method for the continuous separation of a mixture of acetonitrile and methanol includes the following steps:

[0007] S1, Pretreatment: Acetonitrile-methanol mixed feedstock is continuously fed into a distillation kettle to remove impurities, the evaporated gas is fed into a crude distillation tower for rectification, and crude acetonitrile is collected from the top of the crude distillation tower;

[0008] S2, Extraction: The crude acetonitrile is continuously fed into the extraction vessel for extraction and then into the phase separation tank. After phase separation, the extract phase and the raffinate phase are obtained.

[0009] S3, Methanol Recovery: The preheated extract phase enters the methanol tower, and the top and bottom products after distillation are returned to the extraction vessel; the product methanol is obtained by condensing the product in the tower.

[0010] S4, Acetonitrile product refining: The raffinate phase is processed in an evaporator, and the resulting gas phase is processed by a condenser before entering the acetonitrile light phase removal tower. After distillation, the material collected from the top of the tower is returned to the extraction vessel, and the material collected from the bottom of the tower is continuously fed into the acetonitrile tower for distillation to obtain the product acetonitrile.

[0011] Preferably, in step S1, the impurities are solid waste and heavy components; the acetonitrile-methanol mixed raw material comprises 30-95% acetonitrile, 5-20% methanol, 20-50% moisture, and 2-5% residue; the distillation kettle parameters are set as follows: temperature 80-90℃, pressure 70-110 kPa; the crude distillation tower parameters are set as follows: top temperature 55-70℃, bottom temperature 80-110℃, top pressure 70-110 kPa, bottom pressure 80-120 kPa, and operating reflux ratio 1.0-2.5; the crude acetonitrile comprises 70-80% acetonitrile, 10-15% methanol, and 5-15% moisture.

[0012] Preferably, in step S2, the extractant in the extraction vessel is an inorganic salt aqueous solution, which comprises 25-40% chlorinated inorganic salt and 60-75% water. The chlorinated inorganic salt is one or more of magnesium chloride, calcium chloride, barium chloride, manganese chloride, and nickel chloride. In the extraction vessel, the ratio of organic phase to inorganic salt solution is 1:3-5, and the operating temperature is 10-25℃. The extractant phase is a methanol-containing salt aqueous solution, which comprises 15-20% inorganic salt, 5-20% methanol, 1-5% acetonitrile, and 60-80% water. The raffinate phase comprises 95-98% acetonitrile, 0.5-3% methanol, and 0.5-2% water.

[0013] Preferably, the extractant is combined with ethanolamine and other acid inhibitors and antioxidants to form an extract solution. The addition of ethanolamine can prevent the formation of peroxides, enabling the extract solution to be used continuously for a long period of time and ensuring stable quality.

[0014] Preferably, in step S3, the process parameters of the methanol tower are set as follows: raw material preheating temperature 70℃, tower top temperature 63.5℃, methanol vapor phase temperature collected in the middle of the tower 65℃, and tower bottom temperature 110-125℃; tower top pressure is atmospheric pressure, and tower bottom pressure is 110 kPa; the reflux ratio of the methanol tower top azeotrope is 1.0-2.0, and the reflux ratio of the methanol product is 1.0-1.5; the top product is an acetonitrile-methanol binary azeotrope, which comprises 19% acetonitrile and 81% methanol.

[0015] Preferably, in step S4, the process parameters of the acetonitrile removal tower are set as follows: top temperature 63.5℃, bottom temperature 84-88℃; top pressure atmospheric pressure, bottom pressure 101-110 kPa, and reflux ratio 3-20; the ratio of liquid flow rate to feed flow rate in the condenser is 0-1; the top product is a mixture of acetonitrile-methanol-water, comprising 20-30% methanol, 60-70% acetonitrile, and 5-10% water; the bottom product is heavy acetonitrile liquid, which is returned to the distillation vessel along with the feed. The acetonitrile heavy liquid comprises 99.0-99.99% acetonitrile and 0.001-0.01% water. The process parameters of the acetonitrile tower are set as follows: top temperature 81.6℃, side stream temperature 82.0-82.5℃, bottom temperature 84-88℃; top pressure is atmospheric pressure, bottom pressure is 101-110 kPa, and reflux ratio is 2-5. The product acetonitrile includes ordinary grade acetonitrile and premium grade acetonitrile. The ordinary grade acetonitrile is collected from the top of the acetonitrile tower and has an acetonitrile content ≥99.5%. The premium grade acetonitrile is collected from the bottom of the acetonitrile tower and has an acetonitrile content ≥99.95%.

[0016] The present invention also provides a second technical solution: a system for the continuous separation of a mixture of acetonitrile and methanol, used in conjunction with the first technical solution: a method for the continuous separation of a mixture of acetonitrile and methanol. The specific technical solution is as follows:

[0017] A system for continuous separation of a mixture of acetonitrile and methanol includes a pretreatment unit, an extraction unit, a methanol recovery unit, and an acetonitrile product refining unit. The pretreatment unit is used to remove impurities from the raw materials. The extraction unit is used to extract the raw materials after pretreatment to separate an extract phase and a raffinate phase. The methanol recovery unit is used to distill the extract phase to obtain methanol. The acetonitrile product refining unit is used to distill the raffinate phase to obtain acetonitrile.

[0018] Preferably, the pretreatment unit includes a distillation kettle, a crude distillation column, a first reboiler, a first top condenser, and a first top cooler; the distillation kettle is connected to the crude distillation column, the inlet and outlet of the first reboiler are both connected to the lower part of the crude distillation column, and the top of the crude distillation column is connected to the first top cooler through the first top condenser; the theoretical plate number of the rectification section and the theoretical plate number of the stripping section of the crude distillation column are both 20-30.

[0019] Preferably, the distillation vessel is a stirred distillation vessel, employing a paddle or anchor stirrer.

[0020] Preferably, the crude distillation tower is equipped with a thermosiphon reboiler at the bottom and a condenser and cooler at the top.

[0021] Preferably, the extraction unit includes an extraction vessel, a phase separation tank, an extractant storage tank, and a raffinate storage tank; the extraction vessel is connected to the pretreatment unit, and the extraction vessel is connected to the extractant storage tank and the raffinate storage tank respectively through the phase separation tank.

[0022] Preferably, the methanol recovery unit includes a methanol tower, a reboiler, a preheater, a second reboiler, a second top condenser, a second top cooler, a first intermediate condenser, and a first intermediate cooler. The methanol tower is connected to the extraction unit via the preheater. The lower part of the methanol tower is connected to the reboiler. The inlet and outlet of the second reboiler are both connected to the reboiler, and the bottom of the reboiler is connected to the bottom of the preheater. The upper part of the methanol tower is connected to the second top cooler via the second top condenser, and the middle part of the methanol tower is connected to the first intermediate condenser via the first intermediate cooler. The theoretical plate number of the upper section of the rectification section and the lower section of the stripping section of the methanol tower are both 10-15. The methanol tower is a partitioned wall distillation tower. In the partitioned wall distillation tower, the theoretical plate number of the upper and lower sections of the feed section are both 10-15, and the theoretical plate number of the upper section of the methanol section is 20-30.

[0023] Preferably, the acetonitrile product refining unit includes an evaporator, a condenser, an acetonitrile light-weight removal tower, a third reboiler, a third top condenser, a third top cooler, an acetonitrile tower, a fourth reboiler, a fourth top condenser, a fourth top cooler, and a side-stream cooler; the top of the evaporator is connected to the extraction unit and the acetonitrile light-weight removal tower respectively; the upper part of the acetonitrile light-weight removal tower is connected to the third top cooler via the third top condenser; the inlet and outlet of the condenser are both connected to the middle of the acetonitrile light-weight removal tower; and the inlet and outlet of the third reboiler are both connected to the acetonitrile light-weight removal tower. The lower part of the column is connected, and the bottom of the acetonitrile removal column is connected to the acetonitrile column; the inlet and outlet of the fourth reboiler are both connected to the lower part of the acetonitrile column, the upper part of the acetonitrile column is connected to the fourth top cooler through the fourth top condenser, and the upper part of the acetonitrile column is connected to the side stream cooler; in the acetonitrile removal column, the theoretical plate number of the rectifying section is 20-30, and the theoretical plate number of the stripping section is 30-40; the acetonitrile column is a side stream column, and the theoretical plate number of both the rectifying section and the stripping section of the side stream column is 30-50, and the distance from the side stream to the top of the column is 10-15 theoretical plates.

[0024] Preferably, the acetonitrile product refining unit adopts a two-tower continuous distillation method, which can remove heavy components from the acetonitrile product, resulting in a high rate of superior acetonitrile, controllable quality, and high economic benefits.

[0025] This invention obtains a stable extract by selecting an inorganic salt solution and compounding it with acid inhibitors and antioxidants such as ethanolamine, which enables the separation of aqueous acetonitrile and methanol mixtures, while the extractant can be recycled. The principle is that methanol can form crystals with chlorides in inorganic salt solutions. For example, methanol can form crystalline substances with calcium chloride, such as CaCl2·3CH3OH, which dissolves in an aqueous methanol solution. Similar compounds include MgCl2·6CH3OH, CuSO4·2CH3OH, AlCl3·4CH3OH, AlCl3·6CH3OH, and AlCl3·10CH3OH. Chlorides are less effective adsorbents for non-polar substances such as acetonitrile. Under high concentration and low temperature conditions, inorganic salts have a high extraction rate for methanol and water. The extract of this invention differs from drying adsorption. If a desiccant is used to adsorb methanol and water, the solid desiccant needs to be regenerated afterward. The solid drying process is complicated, environmentally unfriendly, and poses safety hazards. The extract used in this invention can remove methanol and water from the acetonitrile-methanol mixture and exists in liquid form without undergoing a solid-liquid phase change.

[0026] The present invention offers the following advantages: A method and system for the continuous separation of a mixture of acetonitrile and methanol is provided. By selecting an inorganic salt solution, a stable extract is obtained, resulting in efficient separation of the acetonitrile and methanol mixture. The separated methanol and acetonitrile products are of good quality, and the extract can be recycled. Furthermore, the present invention employs a continuous four-tower distillation ternary extraction process system for acetonitrile, methanol, and water. This process is simple, produces stable product quality, and operates under mild conditions, avoiding adverse factors such as high temperature and high pressure. This improves production safety, reduces manufacturing costs, and achieves good economic benefits. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the method and system for separating acetonitrile and methanol according to the present invention.

[0028] In the diagram: R1 - Distillation kettle, T1 - Crude distillation column, E1 - First reboiler, E2 - First column top condenser, E3 - First column top cooler, R2 - Extraction kettle, M1 - Phase separation tank, V1 - Extract storage tank, V2 - Raffinate storage tank, T2 - Methanol column, V3 - Column bottom, E4 - Preheater, E5 - Second reboiler, E6 - Second column top condenser, E7 - Second column top cooler, E8 - First column intermediate condenser, E9 - First column intermediate cooler, R3 - Evaporation kettle, E11 - Separator, T3 - Acetonitrile light component removal column, E12 - Third reboiler. E13 - Third column top condenser, E14 - Third column top cooler, T4 - Acetonitrile column, E15 - Fourth reboiler, E16 - Fourth column top condenser, E17 - Fourth column top cooler, E18 - Side stream cooler; 101 - Acetonitrile-methanol mixed feedstock, 201 - Crude acetonitrile, 202 - Extract liquid, 203 - Extract phase, 204 - Raffinate phase, 301 - Product methanol, 302 - Acetonitrile-methanol azeotrope, 401 - Acetonitrile-methanol-water mixture, 402 - Ordinary grade acetonitrile, 403 - Premium grade acetonitrile, 404 - Heavy acetonitrile liquid. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the present invention clearer, specific embodiments are described below, with reference to the appendix. Figure 1 The present invention will be further described in detail below.

[0030] This invention provides a method for the continuous separation of a mixture of acetonitrile and methanol, the specific scheme of which is as follows:

[0031] A method for the continuous separation of a mixture of acetonitrile and methanol includes the following steps:

[0032] S1, Pretreatment: Acetonitrile-methanol mixed feedstock 101 is continuously fed into distillation kettle R1 to remove impurities. The evaporated gas enters crude distillation tower T1 for rectification. Crude acetonitrile 201 is collected from the top of the crude distillation tower.

[0033] S2, Extraction: Crude acetonitrile 201 is continuously fed into the extraction vessel R2 for extraction and then enters the phase separation tank M1. After phase separation, extract phase 203 and raffinate phase 204 are obtained.

[0034] S3, Methanol Recovery: After preheating, the extract phase 203 enters the methanol tower T2. After distillation, the top and bottom products are returned to the extraction vessel R2. The product methanol 301 is obtained after condensation of the product collected in the tower.

[0035] S4, Acetonitrile product refining: Raffinate phase 204 enters the evaporator R3 for treatment, and the resulting gas phase is treated by the condenser E11 before entering the acetonitrile light phase removal tower T3. After distillation, the material collected from the top of the tower is returned to the extraction vessel R2, and the material collected from the bottom of the tower is continuously fed into the acetonitrile tower T4 for distillation to obtain the product acetonitrile.

[0036] Based on the above separation method, the present invention also provides a system for the continuous separation of a mixture of acetonitrile and methanol, such as... Figure 1 As shown, it mainly includes: a pretreatment unit, an extraction unit, a methanol recovery unit, and an acetonitrile product refining unit; the pretreatment unit is used to remove impurities from the raw materials, the extraction unit is used to extract the raw materials after the pretreatment unit, separating the extract phase 203 and the raffinate phase 204, the methanol recovery unit is used to distill the extract phase to obtain product methanol 301, and the acetonitrile product refining unit is used to distill the raffinate phase 204 to obtain product acetonitrile.

[0037] The pretreatment unit includes a distillation kettle R1, a crude distillation column T1, a first reboiler E1, a first top condenser E2, and a first top cooler E3. The distillation kettle R1 is connected to the crude distillation column T1. The inlet and outlet of the first reboiler E1 are both connected to the lower part of the crude distillation column T1. The top of the crude distillation column T1 is connected to the first top cooler E3 through the first top condenser E2.

[0038] The extraction unit includes an extraction vessel R2, a phase separation tank M1, an extractant storage tank V1, and a raffinate storage tank V2. The extraction vessel R2 is connected to the pretreatment unit, and the extraction vessel R2 is connected to the extractant storage tank V1 and the raffinate storage tank V2 through the phase separation tank M1.

[0039] The methanol recovery unit includes a methanol tower T2, a tower bottom V3, a preheater E4, a second reboiler E5, a second top condenser E6, a second top cooler E7, a first intermediate condenser E8, and a first intermediate cooler E9. The methanol tower T2 is connected to the extraction unit through the preheater E4. The lower part of the methanol tower T2 is connected to the tower bottom V3. The inlet and outlet of the second reboiler E5 are both connected to the tower bottom V3, and the bottom of the tower bottom V3 is connected to the bottom of the preheater E4. The upper part of the methanol tower T2 is connected to the second top cooler E7 through the second top condenser E6, and the middle part of the methanol tower T2 is connected to the first intermediate cooler E9 through the first intermediate condenser E8.

[0040] The acetonitrile product refining unit includes an evaporator R3, a condenser E11, an acetonitrile light-weight removal tower T3, a third reboiler E12, a third top condenser E13, a third top cooler E14, an acetonitrile tower T4, a fourth reboiler E15, a fourth top condenser E16, a fourth top cooler E17, and a side-stream cooler E18. The top of the evaporator R3 is connected to both the extraction unit and the acetonitrile light-weight removal tower T3. The upper part of the acetonitrile light-weight removal tower T3 is connected to the third top condenser E13. Cooler E14 is connected, and the inlet and outlet of condenser E11 are both connected to the middle of acetonitrile removal tower T3. The inlet and outlet of the third reboiler E12 are both connected to the lower part of acetonitrile removal tower T3, and the bottom of acetonitrile removal tower T3 is connected to acetonitrile tower T4. The inlet and outlet of the fourth reboiler E15 are both connected to the lower part of acetonitrile tower T4. The upper part of acetonitrile tower T4 is connected to the fourth top cooler E17 through the fourth top condenser E16, and the upper part of acetonitrile tower T4 is connected to the side stream cooler E18.

[0041] Table 1 shows the composition of the mixture of acetonitrile and methanol in various embodiments of the present invention, and Table 2 shows the composition of crude acetonitrile. The main components were determined by gas chromatography.

[0042] Table 1 Composition of the raw material mixture of acetonitrile and methanol

[0043]

[0044] Table 2. Composition of Crude Acetonitrile

[0045]

[0046] Example 1

[0047] Raw material 1 in Table 1 was pretreated by first neutralizing it to a slightly acidic state, then removing high-boiling impurities through a distillation kettle, and finally distilling it in a crude distillation column to obtain crude acetonitrile. The acetonitrile content in the raw material was much higher than that in methanol. The parameters of the crude distillation column were set as follows: top temperature 55℃, bottom temperature 80℃, top pressure 70kPa, bottom pressure 80kPa; operating reflux ratio 2.0. Crude acetonitrile was collected from the top of the crude distillation column. The composition of the crude acetonitrile is shown in the data of raw material 1 in Table 2. Pretreatment removed some water and solid waste.

[0048] The crude acetonitrile was extracted, with ethanolamine and other acid inhibitors and antioxidants added to the extract. The inorganic salt content of the extract was 25%, with magnesium chloride being the selected inorganic salt. The extraction temperature was 10°C. The raffinate consisted of 96.7% acetonitrile, 1.5% methanol, and 1.2% water. Other solvents and water from the crude product were present in the extract. The extract was regenerated and reused.

[0049] The extract phase undergoes methanol recovery treatment. The feed preheating temperature is 70℃, the methanol tower top temperature is 63.5℃, the methanol vapor phase temperature collected in the middle of the tower is 65℃, and the tower bottom temperature is 125℃. The tower top pressure is atmospheric pressure, and the tower bottom pressure is 110 kPa. The methanol tower top azeotrope operating reflux ratio is 2.0, and the methanol product operating reflux ratio is 1.0. The methanol vapor phase collected in the tower is condensed to obtain qualified product methanol.

[0050] The raffinate phase is purified by acetonitrile product refining. The process parameters for the acetonitrile light phase removal tower are set as follows: top temperature 63.5℃, bottom temperature 88℃, top pressure atmospheric pressure, bottom pressure 110 kPa, and operating reflux ratio 3. The process parameters for the acetonitrile tower are set as follows: top temperature 81.6℃, side stream temperature 82.5℃, bottom temperature 88℃, top pressure atmospheric pressure, bottom pressure 110 kPa, and operating reflux ratio 2. Ordinary grade acetonitrile with an acetonitrile content ≥99.5% is collected from the top of the acetonitrile tower, and premium grade acetonitrile with an acetonitrile content ≥99.95% is collected from the middle of the acetonitrile tower.

[0051] Example 2

[0052] Raw material 2 in Table 1 was pretreated by neutralizing it to a slightly acidic state, removing high-boiling impurities through a distillation kettle, and then distilling it in a crude distillation column to obtain crude acetonitrile. The acetonitrile content in the raw material was much higher than that in methanol. The parameters of the crude distillation column were set as follows: top temperature 65℃, bottom temperature 90℃, top pressure 110 kPa, bottom pressure 120 kPa; operating reflux ratio 2.5; crude acetonitrile was collected from the top of the crude distillation column, and the composition of the crude acetonitrile is shown in the raw material 2 data in Table 2.

[0053] The crude acetonitrile was extracted, and the inorganic salt content of the extract was 35%, with calcium chloride being selected as the inorganic salt. The extraction temperature was 20°C. The raffinate consisted of 98.1% acetonitrile, 0.6% methanol, and 0.8% water. Other solvents and water from the crude product were contained in the extract phase. The extract was regenerated and reused.

[0054] The extract phase undergoes methanol recovery treatment. The feed preheating temperature is 70℃, the methanol tower top temperature is 63.5℃, the methanol vapor phase temperature collected in the middle of the tower is 65℃, and the tower bottom temperature is 110℃. The tower top pressure is atmospheric pressure, and the tower bottom pressure is 110 kPa. The methanol tower top azeotrope operating reflux ratio is 1.0, and the methanol product operating reflux ratio is 1.5. The methanol vapor phase collected in the tower is condensed to obtain qualified product methanol.

[0055] The raffinate phase is purified by acetonitrile product refining. The process parameters for the acetonitrile light phase removal tower are set as follows: top temperature 63.5℃, bottom temperature 88℃, top pressure atmospheric pressure, bottom pressure 110 kPa, and operating reflux ratio 10. The process parameters for the acetonitrile tower are set as follows: top temperature 81.6℃, side stream temperature 82℃, bottom temperature 84℃, top pressure atmospheric pressure, bottom pressure 105 kPa, and operating reflux ratio 5. Ordinary grade acetonitrile with an acetonitrile content ≥99.5% is collected from the top of the acetonitrile tower, and premium grade acetonitrile with an acetonitrile content ≥99.95% is collected from the middle of the acetonitrile tower.

[0056] Other separation methods were the same as in Example 1, and qualified finished products methanol and acetonitrile were finally obtained. The distillation energy consumption was reduced compared with Example 1.

[0057] Example 3

[0058] Raw material 3 in Table 1 was pretreated by neutralizing it to a slightly acidic state, removing high-boiling impurities through a distillation kettle, and then distilling it in a crude distillation column to obtain crude acetonitrile. The acetonitrile content in the raw material was much higher than that in methanol. The parameters of the crude distillation column were set as follows: top temperature 65℃, bottom temperature 90℃, top pressure 110 kPa, bottom pressure 120 kPa; operating reflux ratio 2.5; crude acetonitrile was collected from the top of the crude distillation column, and the composition of the crude acetonitrile is shown in the raw material 3 data in Table 2.

[0059] The crude acetonitrile was extracted, and the inorganic salt content of the extract was 40%, with barium chloride being selected as the inorganic salt. The extraction temperature was 25°C. The raffinate consisted of 95.4% acetonitrile, 2% methanol, and 1.8% water. Other solvents and water from the crude product were contained in the extract phase. The extract was regenerated and reused.

[0060] The extract phase is treated with methanol recovery, the bottom temperature of the column is 115℃, the top pressure of the column is atmospheric pressure, and the bottom pressure of the column is 110kPa. The reflux ratio of the methanol column top azeotrope is 1.5, and the reflux ratio of the methanol product is 1.3. The methanol vapor phase collected in the column is condensed to obtain qualified product methanol.

[0061] The raffinate phase is purified by acetonitrile product refining. The process parameters for the acetonitrile light phase removal tower are set as follows: tower bottom pressure is 110 kPa, and the operating reflux ratio is 10; the process parameters for the acetonitrile tower are set as follows: tower top temperature is 81.6℃, side stream temperature is 82℃, and tower bottom temperature is 86℃; the tower top pressure is atmospheric pressure, the tower bottom pressure is 101 kPa, and the operating reflux ratio is 20. Ordinary grade acetonitrile with an acetonitrile content ≥99.5% is collected from the top of the acetonitrile tower, and premium grade acetonitrile with an acetonitrile content ≥99.95% is collected from the middle of the acetonitrile tower.

[0062] Other separation methods were the same as in Example 2, and qualified finished products methanol and acetonitrile were finally obtained. The distillation energy consumption was increased compared with Example 2.

[0063] Example 4

[0064] Raw material 4 in Table 1 was pretreated by neutralizing it to a slightly acidic state, removing high-boiling impurities through a distillation kettle, and then distilling it in a crude distillation column to obtain crude acetonitrile. The acetonitrile content in the raw material was much higher than that in methanol. The parameters of the crude distillation column were set as follows: top temperature of 60℃, bottom temperature of 100℃, top pressure of 90 kPa, bottom pressure of 100 kPa, and reflux ratio of 2. Crude acetonitrile was collected from the top of the crude distillation column. The composition of the crude acetonitrile is shown in the data of raw material 4 in Table 2.

[0065] The crude acetonitrile was extracted, and the inorganic salt content of the extract was 33%, with manganese chloride being selected as the inorganic salt. The extraction temperature was 15°C. The raffinate consisted of 96.1% acetonitrile, 2.1% methanol, and 1.5% water. Other solvents and water from the crude product were present in the extract phase. The extract was regenerated and reused.

[0066] The extract phase is treated with methanol recovery, the bottom temperature of the column is 115℃, the top pressure of the column is atmospheric pressure, and the bottom pressure of the column is 110kPa. The reflux ratio of the methanol column top azeotrope is 2.0, and the reflux ratio of the methanol product is 1.1. The methanol vapor phase collected in the column is condensed to obtain qualified product methanol.

[0067] The raffinate phase was purified by acetonitrile product refining. The process parameters for the acetonitrile light phase removal tower were set as follows: tower bottom pressure 105 kPa, operating reflux ratio 5; acetonitrile tower process parameters were set as follows: tower top temperature 81.6℃, side stream temperature 82℃, tower bottom temperature 86℃; tower top pressure was atmospheric pressure, tower bottom pressure 101 kPa, operating reflux ratio 15. Ordinary grade acetonitrile with an acetonitrile content ≥99.5% was collected from the top of the acetonitrile tower, and premium grade acetonitrile with an acetonitrile content ≥99.95% was collected from the middle of the acetonitrile tower. Other separation methods were the same as in Example 3, ultimately yielding qualified finished methanol and acetonitrile products.

[0068] Example 5

[0069] Raw material 5 in Table 1 was pretreated by first neutralizing it to a slightly acidic state, then removing high-boiling impurities through a distillation kettle, and finally distilling it in a crude distillation tower to obtain crude acetonitrile. The composition of the crude acetonitrile is shown in Table 2, which contains data on raw material 5.

[0070] The crude acetonitrile is extracted, and the inorganic salt content of the extract is 35%. The inorganic salts selected are manganese chloride and nickel chloride. The temperature of the extract is 15℃. The raffinate phase includes 97.5% acetonitrile, 1.3% methanol, and 0.9% water. Other solvents and water in the crude product are in the extract phase. The extract is regenerated and reused.

[0071] The extract phase is treated with methanol recovery, and the methanol vapor phase collected in the tower is condensed to obtain qualified product methanol.

[0072] The raffinate phase was purified by acetonitrile product refining. Ordinary grade acetonitrile with a content ≥99.5% was collected from the top of the acetonitrile tower, while premium grade acetonitrile with a content ≥99.95% was collected from the middle of the acetonitrile tower. Other separation methods were the same as in Example 2, ultimately yielding qualified finished products of methanol and acetonitrile.

[0073] Example 6

[0074] Raw material 6 in Table 1 was pretreated by first neutralizing it to a slightly acidic state, then removing high-boiling impurities through a distillation kettle, and finally distilling it in a crude distillation tower to obtain crude acetonitrile. The composition of the crude acetonitrile is shown in the data of raw material 6 in Table 2.

[0075] The crude acetonitrile is extracted, and the inorganic salt content of the extract is 30%. The inorganic salts selected are manganese chloride and magnesium chloride. The temperature of the extract is 15℃. The raffinate phase includes 97.5% acetonitrile, 1.3% methanol, and 0.9% water. Other solvents and water in the crude product are in the extract phase. The extract is regenerated and reused.

[0076] The extract phase is treated with methanol recovery, and the methanol vapor phase collected in the tower is condensed to obtain qualified product methanol.

[0077] The raffinate phase was purified by acetonitrile product refining. Ordinary grade acetonitrile with a content ≥99.5% was collected from the top of the acetonitrile tower, while premium grade acetonitrile with a content ≥99.95% was collected from the middle of the acetonitrile tower. Other separation methods were the same as in Example 4, ultimately yielding qualified finished products of methanol and acetonitrile.

[0078] Example 7

[0079] Raw material 7 in Table 1 was pretreated by first neutralizing it to a slightly acidic state, then removing high-boiling impurities through a distillation kettle, and finally distilling it in a crude distillation tower to obtain crude acetonitrile. The composition of crude acetonitrile is shown in the data of raw material 7 in Table 2.

[0080] The crude acetonitrile is extracted, and the inorganic salt content of the extract is 40%. The inorganic salts selected are calcium chloride and magnesium chloride. The temperature of the extract is 20°C. The raffinate phase includes 95.0% acetonitrile, 2.5% methanol, and 2.1% water. Other solvents and water in the crude product are in the extract phase. The extract is regenerated and reused.

[0081] The extract phase is treated with methanol recovery, and the methanol vapor phase collected in the tower is condensed to obtain qualified product methanol.

[0082] The raffinate phase was purified by acetonitrile product refining. Ordinary grade acetonitrile with a content ≥99.5% was collected from the top of the acetonitrile tower, while premium grade acetonitrile with a content ≥99.95% was collected from the middle of the acetonitrile tower. Other separation methods were the same as in Example 6, ultimately yielding qualified finished products of methanol and acetonitrile.

[0083] Example 8

[0084] Raw material 8 in Table 1 was pretreated by first neutralizing it to a slightly acidic state, then removing high-boiling impurities through a distillation kettle, and finally distilling it in a crude distillation tower to obtain crude acetonitrile. The composition of the crude acetonitrile is shown in the data of raw material 8 in Table 2.

[0085] The crude acetonitrile is extracted, and the inorganic salt content of the extract is 40%. The inorganic salts selected are calcium chloride and magnesium chloride. The temperature of the extract is 20°C. The raffinate phase includes 95.0% acetonitrile, 2.5% methanol, and 2.1% water. Other solvents and water in the crude product are in the extract phase. The extract is regenerated and reused.

[0086] The extract phase is treated with methanol recovery, and the methanol vapor phase collected in the tower is condensed to obtain qualified product methanol.

[0087] The raffinate phase was purified by acetonitrile product refining. Ordinary grade acetonitrile with a content ≥99.5% was collected from the top of the acetonitrile tower, while premium grade acetonitrile with a content ≥99.95% was collected from the middle of the acetonitrile tower. Other separation methods were the same as in Example 7, ultimately yielding qualified finished products of methanol and acetonitrile.

[0088] In summary, the method and system for continuous separation of acetonitrile and methanol mixtures provided by this invention removes impurities from the raw materials through a pretreatment unit, resulting in crude acetonitrile free of solid waste, thus initially increasing the organic content of methanol and acetonitrile. By selecting an inorganic salt solution, the acetonitrile and methanol mixture is separated efficiently. The addition of acid-suppressing agents such as ethanolamine and antioxidants makes the extract more stable, allowing for long-term use and recycling. Furthermore, this invention employs a continuous four-tower distillation ternary extraction process system for acetonitrile, methanol, and water, which features a simple separation process, stable product quality, and mild separation conditions, avoiding adverse factors such as high temperature and high pressure, improving production safety, reducing manufacturing costs, and achieving good economic benefits.

[0089] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. The present invention is not limited to the examples described above. Any changes, modifications, additions, or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for continuous separation of a mixture of acetonitrile and methanol, characterized in that, Includes the following steps: S1, Pretreatment: Acetonitrile-methanol mixed feedstock (101) is continuously fed into distillation kettle (R1) to remove impurities. The evaporated gas enters crude distillation tower (T1) for rectification. Crude acetonitrile (201) is collected from the top of crude distillation tower (T1). S2, Extraction: The crude acetonitrile (201) is continuously fed into the extraction vessel (R2) for extraction and then into the phase separation tank (M1). After phase separation, the extract phase (203) and the raffinate phase (204) are obtained. S3, Methanol Recovery: The preheated extraction phase (203) enters the methanol tower (T2), and the top and bottom products after distillation are returned to the extraction vessel (R2); the product methanol (301) is obtained after condensation of the product in the tower. S4, Acetonitrile product refining: The raffinate (204) is processed in an evaporator (R3), and the resulting gas phase is processed by a condenser (E11) and then enters the acetonitrile light removal tower (T3). After distillation, the material collected from the top of the tower is returned to the extraction vessel (R2), and the material collected from the bottom of the tower is continuously fed into the acetonitrile tower (T4) for distillation to obtain the product acetonitrile. In step S1, the acetonitrile-methanol mixed feedstock (101) comprises 30-95% acetonitrile, 5-20% methanol, 20-50% moisture, and 2-5% residue; the parameters of the distillation vessel (R1) are set as follows: temperature 80-90℃, pressure 70-110 kPa; the parameters of the crude distillation tower (T1) are set as follows: top temperature 55-70℃, bottom temperature 80-110℃, top pressure 70-110 kPa, bottom pressure 80-120 kPa, and operating reflux ratio 1.0-2.5; the crude acetonitrile (201) comprises 70-80% acetonitrile, 10-15% methanol, and 5-15% moisture. In step S2, the extractant in the extraction vessel (R2) is an inorganic salt aqueous solution, which includes 25-40% chlorinated inorganic salt and 60-75% water. The chlorinated inorganic salt is one or more of magnesium chloride, calcium chloride, barium chloride, manganese chloride, and nickel chloride. In the extraction vessel (R2), the ratio of organic phase to inorganic salt solution is 1:3-5, and the operating temperature is 10-25℃. The extract phase (203) is a methanol-containing salt aqueous solution, which includes 15-20% inorganic salt, 5-20% methanol, 1-5% acetonitrile, and 60-80% water. The raffinate phase (204) includes 95-98% acetonitrile, 0.5-3% methanol, and 0.5-2% water. In step S3, the process parameters of the methanol tower (T2) are set as follows: raw material preheating temperature 70℃, tower top temperature 63.5℃, methanol vapor phase temperature collected in the middle of the tower 65℃, and tower bottom temperature 110-125℃; tower top pressure is atmospheric pressure, and tower bottom pressure is 110 kPa; the reflux ratio of the azeotrope at the top of the methanol tower (T2) is 1.0-2.0, and the reflux ratio of the methanol product is 1.0-1.5; the material collected at the top of the tower is acetonitrile-methanol azeotrope (302), which includes 19% acetonitrile and 81% methanol; In step S4, the process parameters of the acetonitrile light component removal tower (T3) are set as follows: top temperature 63.5℃, bottom temperature 84-88℃; top pressure atmospheric pressure, bottom pressure 101-110 kPa, and reflux ratio 3-20; the ratio of liquid flow rate to feed flow rate in the condenser (E11) is 0-1; the top product is an acetonitrile-methanol-water mixture (401), which includes 20-30% methanol, 60-70% acetonitrile, and 5-10% water; the bottom product includes 99.0-99.99% acetonitrile and 0.99% water. 0.01-0.01%; the process parameters of the acetonitrile tower (T4) are set as follows: top temperature 81.6℃, side stream temperature 82.0-82.5℃, bottom temperature 84-88℃; top pressure is atmospheric pressure, bottom pressure is 101-110 kPa, and reflux ratio is 2-5; the product acetonitrile includes ordinary grade acetonitrile (402) and premium grade acetonitrile (403). The ordinary grade acetonitrile (402) is collected from the top of the acetonitrile tower (T4) and has an acetonitrile content ≥99.5%; the premium grade acetonitrile (403) is collected from the acetonitrile tower (T4) and has an acetonitrile content ≥99.95%.

Images