High-purity acetonitrile and method for preparing high-purity acetonitrile by extracting, rectifying and separating mixture containing acetonitrile and water

Abstract

The invention relates to the technical field of rectification separation, in particular to high-purity acetonitrile and a method for preparing high-purity acetonitrile by extracting, rectifying and separating a mixture containing acetonitrile and water. The method comprises the following step: carrying out extractive distillation on a mixture containing acetonitrile and water by taking a eutectic solvent as an extracting agent. According to the method disclosed by the invention, the eutectic solvent is added into the mixed system of acetonitrile and water as the extracting agent for extractive distillation, so that the energy consumption required by separation can be effectively reduced, the acetonitrile separation efficiency is improved, and the acetonitrile product quality is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of rectification separation, and particularly relates to a method for preparing high-purity acetonitrile by rectifying and separating a mixture containing acetonitrile and water with extractive rectification to obtain high-purity acetonitrile. Background Art

[0002] Acetonitrile, also known as methyl cyanide, is widely used as an organic solvent in fields such as pharmaceuticals, organic synthesis, chromatographic analysis, and solvents for semiconductor material synthesis. During the industrial production of acetonitrile, a large amount of water is generated, and subsequently, acetonitrile and water form a minimum boiling azeotropic system, greatly increasing the difficulty of separating acetonitrile. Currently, the separation methods of acetonitrile and water mainly include extractive rectification, azeotropic rectification, pressure swing rectification, liquid-liquid extraction, pervaporation, and adsorption.

[0003] CN112851550A discloses a method and equipment for continuously extracting and separating acetonitrile-water azeotrope. A polyol is used as an extractant to perform secondary extraction on the acetonitrile-water azeotrope to obtain acetonitrile with a water content of less than 0.5%. However, the amount of the polyol extractant used in this method is large, and the extractant needs to be recycled repeatedly during the secondary extraction process. At the same time, the removal of trace impurities in acetonitrile is not described in detail. CN111574404A discloses a refining method and refining device for high-purity acetonitrile. Ethylenediamine and formaldehyde are sequentially added to acetonitrile after removing hydrocyanic acid for chemical impurity removal, and then vacuum impurity removal and purification are carried out to obtain high-purity acetonitrile. This method adds ethylenediamine and formaldehyde to react with hydrocyanic acid and acrylonitrile in acetonitrile to form high-boiling compounds, thereby removing trace impurities in acetonitrile. However, this method will introduce ethylenediamine and formaldehyde at the same time, which will make the subsequent separation process of acetonitrile more complex and difficult, and high-purity acetonitrile cannot be obtained. CN105968028A discloses an acetonitrile continuous negative pressure distillation extraction process. Using ethylene glycol as an extractant, water-containing acetonitrile is dehydrated and purified by vacuum extractive rectification, and then ethylene glycol is recovered by negative pressure distillation to obtain an acetonitrile product with a purity of 99%. However, the amount of ethylene glycol used in this method is large, and the product purity is also low. In the prior art, the process flow of acetonitrile refining is relatively complex, the separation efficiency is low, the operation is complex, and the energy consumption is high.

[0004] Deep eutectic solvents are a new type of solvent similar to ionic liquids. They are formed by mixing and dissolving a hydrogen bond donor compound and a hydrogen bond acceptor compound into a homogeneous liquid at low temperature. Deep eutectic solvents have high thermal stability, low saturated vapor pressure, weak volatility, simple synthesis process, and low cost, and are widely used in fields such as electrodeposition, extraction separation, gas collection, catalytic reaction, and nanomaterial synthesis. Summary of the Invention

[0005] The object of the present invention is to overcome the problems existing in the prior art, such as the relatively complex process flow of acetonitrile refining, low separation efficiency, complex operation, and high energy consumption. A method for preparing high-purity acetonitrile by extractive distillation to separate a mixture containing acetonitrile and water is provided. This method has the characteristics of high acetonitrile separation efficiency, reducing the impurity content in acetonitrile, improving the quality of acetonitrile products, and having a simple, environmentally friendly and sustainable process flow.

[0006] To achieve the above object, on the one hand, the present invention provides a method for preparing high-purity acetonitrile by extractive distillation to separate a mixture containing acetonitrile and water, the method comprising: using a deep eutectic solvent as an extractant to perform extractive distillation on the mixture containing acetonitrile and water.

[0007] On the second aspect, the present invention provides high-purity acetonitrile prepared by the method described above, the purity of the high-purity acetonitrile being ≥99.5%, the water content being ≤1.5%, and the propionitrile content being ≤400 ppm.

[0008] Through the above technical solutions, the present invention has the following advantages:

[0009] By adding a deep eutectic solvent as an extractant to perform extractive distillation in a mixed system of acetonitrile and water, the method of the present invention can effectively reduce the energy consumption required for separation, improve the acetonitrile separation efficiency, and improve the quality of acetonitrile products. Description of the Drawings

[0010] Figure 1 is a device and flow chart for preferably separating acetonitrile from a mixture containing acetonitrile and water by extractive distillation according to the present invention.

[0011] Description of the Reference Numerals

[0012] A - light removal tower, B - adsorption tower, C - extractive distillation tower, D - solvent recovery tower, 1 - raw material crude acetonitrile, 2 - light component impurities, 3 - bottom stream of the light removal tower, 4 - side stream of the light removal tower, 5 - overhead stream of the adsorption tower, 6 - fresh deep eutectic solvent, 7 - high-purity acetonitrile, 8 - bottom stream of the extractive distillation tower, 9 - overhead stream of the solvent recovery tower, 10 - recycled deep eutectic solvent. Detailed Embodiments

[0013] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0014] In the present invention, unless otherwise specified, the orientation terms such as "upper, lower, left, and right" generally refer to the upper, lower, left, and right shown in the reference drawings; "inner and outer" refer to the inner and outer of the contour of each component itself.

[0015] In the present invention, without special circumstances, "bottom of the column" refers to the position of 90 - 100% from top to bottom of the container; "top of the column" refers to the position of 0 - 10% from top to bottom of the container; "upper part" refers to the position of 0 - 30% from top to bottom of the container; "middle part" refers to the position of 30 - 70% from top to bottom of the container.

[0016] The present invention provides a method for preparing high - purity acetonitrile by extractive distillation of a mixture containing acetonitrile and water, and the method includes: using a deep eutectic solvent as an extractant to perform extractive distillation on the mixture containing acetonitrile and water.

[0017] The method of the present invention can effectively reduce the energy consumption required for separation, improve the separation efficiency of acetonitrile, and improve the quality of acetonitrile products by adding a deep eutectic solvent as an extractant to perform extractive distillation in a mixed system of acetonitrile and water.

[0018] According to a preferred embodiment of the present invention, the deep eutectic solvent contains a hydrogen - bond donor compound and a hydrogen - bond acceptor compound, and the molar ratio of the hydrogen - bond donor compound to the hydrogen - bond acceptor compound is 0.5 - 4, preferably 1 - 3. By adopting the foregoing preferred scheme, the energy consumption required for separation can be further effectively reduced, the separation efficiency of acetonitrile can be improved, and the quality of acetonitrile products can be improved.

[0019] According to a preferred embodiment of the present invention, the hydrogen - bond donor compound is selected from at least one of urea, ethylene glycol, glycerol, triethylene glycol, 2 - hydroxypropionic acid, malonic acid, hydroxybutanedioic acid, glycolic acid, levulinic acid, preferably glycolic acid and / or levulinic acid; and / or

[0020] The hydrogen - bond acceptor compound is selected from at least one of choline chloride, N,N,N - trimethylglycine, ethylammonium chloride, acetylcholine, tetraethylammonium bromide, tetraethylammonium chloride, tetrabutylammonium chloride, preferably N,N,N - trimethylglycine and / or acetylcholine.

[0021] According to a preferred embodiment of the present invention, the preparation method of the deep eutectic solvent includes: mixing the hydrogen - bond donor compound and the hydrogen - bond acceptor compound at 60 - 120 °C to form a transparent liquid.

[0022] According to a preferred embodiment of the present invention, the mass content of acetonitrile in the mixture containing acetonitrile and water is 40 - 80 wt%, and the mass content of water is 20 - 50 wt%.

[0023] According to a preferred embodiment of the present invention, the mixture containing acetonitrile and water is derived from the crude acetonitrile raw material by-produced in propylene ammoxidation.

[0024] According to a preferred embodiment of the present invention, the method further includes: before extractive distillation, pre-treating the mixture containing acetonitrile and water.

[0025] According to a preferred embodiment of the present invention, the method further includes: after extractive distillation, recovering the extractant and recycling it back to extractive distillation.

[0026] According to a preferred embodiment of the present invention, the pre-treatment includes: performing light component removal and (partial) heavy component removal, acid-base removal and (residual) heavy component removal on the mixture containing acetonitrile and water.

[0027] According to a preferred embodiment of the present invention, the light component removal and heavy component removal are carried out in a distillation column, and the conditions include: the top pressure is 10 - 80 kPa, the column pressure drop is 10 - 50 kPa, the bottom temperature is 70 - 130 °C, the number of theoretical plates is 15 - 60, the reflux ratio is 5 - 60, and the top condensation temperature is 5 - 40 °C.

[0028] According to a preferred embodiment of the present invention, the acid-base and heavy component removal is carried out by adsorption removal. Preferably, the packing for adsorption removal includes at least one of basic anion exchange resin, activated carbon, acidic anion exchange resin, and molecular sieve. More preferably, the molecular sieve is at least one of A-type, X-type, and Y-type molecular sieves.

[0029] According to a preferred embodiment of the present invention, the recovery of the extractant is carried out in a distillation column, and the conditions include: the top pressure is 20 - 100 kPa, the column pressure drop is 10 - 50 kPa, the bottom temperature is 50 - 120 °C, the number of theoretical plates is 10 - 50, the reflux ratio is 2 - 30, and the top condensation temperature is 5 - 20 °C.

[0030] According to a preferred embodiment of the present invention, the conditions for extractive distillation include: the top pressure is 30 - 150 kPa, the column pressure drop is 10 - 50 kPa, the bottom temperature is 80 - 160 °C, the number of theoretical plates is 15 - 70, the reflux ratio is 5 - 30, the top condensation temperature is 5 - 40 °C, and the mass flow rate of the extractant feed is 5 - 50% of the mass flow rate of the mixture containing acetonitrile and water feed.

[0031] In the present invention, the pressures are all gauge pressures.

[0032] The present invention provides high-purity acetonitrile prepared by the described method. The purity of the high-purity acetonitrile is ≥ 95.5%, preferably ≥ 99.9%, the water content is ≤ 1.5%, preferably ≤ 0.1%, and the propionitrile content is ≤ 400 ppm, preferably ≤ 100 ppm.

[0033] As shown Figure 1 in the figure, the present invention provides a preferred apparatus for separating acetonitrile from a mixture containing acetonitrile and water by extractive distillation and a corresponding process:

[0034] The apparatus includes: a light component removal tower A, an adsorption tower B, an extractive distillation tower C, and a solvent recovery tower D, which are connected in sequence through pipelines; the bottom feed port of the adsorption tower B is connected to the side line discharge port of the light component removal tower A, the acetonitrile raw material feed port of the extractive distillation tower C is connected to the top discharge port of the adsorption tower B, an extractant feed port is arranged above the acetonitrile raw material feed port, the feed port of the solvent recovery tower D is connected to the bottom outlet of the extractive distillation tower C, and the bottom discharge port of the solvent recovery tower D is connected to the extractant feed port of the extractive distillation tower C; a top condenser is also arranged at the top of the light component removal tower A, the extractive distillation tower C, and the solvent recovery tower D, forming a top product logistics circulation loop;

[0035] According to a preferred embodiment of the present invention, the light component removal tower A, the extractive distillation tower C, and the solvent recovery tower D are each a sieve tray tower or a packed tower. The sieve trays of the sieve tray tower are one of vertical sieve trays, bubble cap solid sieve trays, rectangular vertical sieve trays, and high-efficiency guiding sieve trays, and the packed tower is a random packing or a structured packing.

[0036] The process includes:

[0037] S1. The raw material crude acetonitrile 1 enters the light component removal tower A. The top product components are light component impurities such as hydrocyanic acid, oxazole, and a small amount of acrylonitrile 2. The bottom product components of the light component removal tower are water, a small amount of acetonitrile, and some other heavy component impurities 3. The side line product 4 of the light component removal tower is the acetonitrile discharge position;

[0038] S2. The side line product 4 of the light component removal tower enters the adsorption tower B from the bottom. After fully interacting with the bed adsorption packing, trace acids, alkalis, and some other heavy components in the feed stream are adsorbed and removed;

[0039] S3. The top product 5 of the adsorption tower enters the extractive distillation tower C. The fresh eutectic solvent 6 is fed into the rectifying section. The top product stream is high-purity acetonitrile 7. The bottom product 8 of the extractive distillation tower is a mixture of the eutectic solvent and water;

[0040] S4. The bottom product 8 of the extractive distillation tower enters the solvent recovery tower D. The top product is water and some heavy component impurities such as a small amount of propionitrile. The bottom product is recycled as the eutectic solvent 10 and returned to the extractive distillation tower.

[0041] The present invention will be described in detail below through examples.

[0042] In the following examples, the contents of organic substances such as acetonitrile, acetone, propionitrile, allyl alcohol, methanol, acrylonitrile, and oxazole in raw materials and products were determined by gas chromatography, the content of hydrocyanic acid was determined by titration method, the water content was determined by Karl Fischer method, and the content of deep eutectic solvent was determined by the method of weighing the difference after vacuum drying; without special instructions, the raw materials were all commercially available products and were all carried out under the device shown in Figure 1 Shown in the device.

[0043] Example 1

[0044] The light removal tower is a packed tower, and the packing is corrugated structured packing; the extractive distillation tower is a sieve plate tower, and the tower plates are vertical sieve plates; the solvent recovery tower is a packed tower, and the packing is corrugated structured packing.

[0045] The adsorption tower is four-stage packed, and from the bottom to the top of the tower are strongly basic anion exchange resin, activated carbon, strongly acidic anion exchange resin, and 4A molecular sieve respectively.

[0046] The synthesis method of the deep eutectic solvent is: mix the hydrogen bond donor compound glycolic acid and the hydrogen bond acceptor compound acetylcholine in a molar ratio of 2, and stir at a constant temperature of 80 °C for 4 hours until it becomes a homogeneous transparent liquid.

[0047] In Figure 1 Shown in the device for treatment:

[0048] The top pressure of the light removal tower is 30 kPa, the tower pressure drop is 15 kPa, the tower bottom temperature is 78 °C, the number of theoretical plates is 50, the feed position is the 18th plate, the side line discharge position is the 48th plate from the bottom, the reflux ratio is 30, and the top condensation temperature is 10 °C.

[0049] The liquid hourly space velocity of the adsorption tower is 2.5 h -1 .

[0050] The top pressure of the extractive distillation tower is 40 kPa, the tower pressure drop is 25 kPa, the tower bottom temperature is 115 °C, the number of theoretical plates is 55, the feed position is the 45th plate, the deep eutectic solvent feed position is the 8th plate, the reflux ratio is 12, the top condensation temperature is 5 °C, and the mass flow rate of the deep eutectic solvent feed is 20% of the mass flow rate of the top stream of the adsorption tower.

[0051] The top pressure of the solvent recovery tower is 22 kPa, the tower pressure drop is 25 kPa, the tower bottom temperature is 86 °C, the number of theoretical plates is 35, the feed position is the 20th plate, the reflux ratio is 15, and the top condensation temperature is 5 °C.

[0052] The composition of acetonitrile in the raw materials of this example and the composition of the acetonitrile product are shown in Table 1.

[0053] Example 2

[0054] The light removal column is a packed column with structured corrugated packing; the extractive distillation column is a sieve plate column with vertical sieve plates; the solvent recovery column is a packed column with structured corrugated packing.

[0055] The adsorption column has four sections of packing. From the bottom to the top of the column are strongly basic anion exchange resin, activated carbon, strongly acidic anion exchange resin, and 13X molecular sieve.

[0056] The method for synthesizing the deep eutectic solvent is as follows: The hydrogen bond donor compound levulinic acid and the hydrogen bond acceptor compound acetylcholine are mixed at a molar ratio of 1.5, and then stirred at a constant temperature of 85 °C for 4 hours until a homogeneous and transparent liquid is formed.

[0057] In Figure 1 the device shown for processing:

[0058] The top pressure of the light removal column is 30 kPa, the column pressure drop is 10 kPa, the bottom temperature of the column is 78 °C, the number of theoretical plates is 50, the feed position is 18, the reflux ratio is 30, and the top condensation temperature is 10 °C.

[0059] The liquid hourly space velocity of the adsorption column is 2.0 h -1 .

[0060] The top pressure of the extractive distillation column is 50 kPa, the column pressure drop is 30 kPa, the bottom temperature of the column is 109 °C, the number of theoretical plates is 50, the feed position is the 46th plate, the deep eutectic solvent feed position is the 7th plate, the reflux ratio is 10, the top condensation temperature is 5 °C, and the mass flow rate of the deep eutectic solvent feed is 20% of the mass flow rate of the top stream of the adsorption column.

[0061] The top pressure of the solvent recovery column is 25 kPa, the column pressure drop is 30 kPa, the bottom temperature of the column is 83 °C, the number of theoretical plates is 30, the feed position is the 17th plate, the reflux ratio is 10, and the top condensation temperature is 5 °C.

[0062] The raw material acetonitrile composition and the acetonitrile product composition in this example are shown in Table 1.

[0063] Example 3

[0064] The light removal column is a packed column with structured corrugated packing; the extractive distillation column is a sieve plate column with vertical sieve plates; the solvent recovery column is a packed column with structured corrugated packing.

[0065] The adsorption column has four sections of packing. From the bottom to the top of the column are strongly basic anion exchange resin, activated carbon, strongly acidic anion exchange resin, and 5A molecular sieve.

[0066] The extractant of the extractive distillation column is the deep eutectic solvent, and the extractant feed position is above the feed position of the rectification raw material in the extractive distillation column.

[0067] The method for synthesizing the deep eutectic solvent is as follows: The hydrogen bond donor compound levulinic acid and the hydrogen bond acceptor compound N,N,N-trimethylglycine are mixed at a molar ratio of 2, and then stirred at a constant temperature of 90 °C for 5 hours until a homogeneous and transparent liquid is formed.

[0068] It is processed in the Figure 1 device shown:

[0069] The top pressure of the light removal tower is 25 kPa, the tower pressure drop is 10 kPa, the bottom temperature of the tower is 82 °C, the number of theoretical plates is 40, the feed position is 16, the reflux ratio is 35, and the top condensation temperature is 5 °C.

[0070] The liquid hourly space velocity of the adsorption tower is 3.0 h -1 .

[0071] The top pressure of the extractive distillation tower is 30 kPa, the tower pressure drop is 20 kPa, the bottom temperature of the tower is 103 °C, the number of theoretical plates is 45, the feed position is the 38th plate, the deep eutectic solvent feed position is the 5th plate, the reflux ratio is 15, the top condensation temperature is 5 °C, and the mass flow rate of the deep eutectic solvent feed is 20% of the mass flow rate of the top stream of the adsorption tower.

[0072] The top pressure of the solvent recovery tower is 25 kPa, the tower pressure drop is 30 kPa, the bottom temperature of the tower is 82 °C, the number of theoretical plates is 30, the feed position is the 17th plate, the reflux ratio is 10, and the top condensation temperature is 5 °C.

[0073] The raw material acetonitrile composition and the acetonitrile product composition in this example are shown in Table 1.

[0074] Example 4

[0075] The light removal tower is a packed tower, and the packing is corrugated structured packing; the extractive distillation tower is a sieve plate tower, and the tower plates are vertical sieve plates; the solvent recovery tower is a packed tower, and the packing is corrugated structured packing.

[0076] The adsorption tower is four sections of packing. From the bottom to the top of the tower are strongly basic anion exchange resin, activated carbon, strongly acidic anion exchange resin, and 4A molecular sieve.

[0077] The method for synthesizing the deep eutectic solvent is as follows: The hydrogen bond donor compound 2-hydroxypropanoic acid and the hydrogen bond acceptor compound N,N,N-trimethylglycine are mixed at a molar ratio of 2.5, and then stirred at a constant temperature of 90 °C for 6 hours until a homogeneous and transparent liquid is formed.

[0078] It is processed in the Figure 1 device shown:

[0079] The top pressure of the light-removal tower is 30 kPa, the tower pressure drop is 15 kPa, the bottom temperature is 75 °C, the theoretical number of plates is 50, the feed position is the 18th plate, the side discharge position is the bottom 48 plates, the reflux ratio is 30, and the top condensation temperature is 10 °C.

[0080] The liquid phase space velocity of the adsorption tower is 2.5h -1 .

[0081] The top pressure of the extractive distillation tower is 30 kPa, the tower pressure drop is 15 kPa, the bottom temperature is 108°C, the theoretical plate number is 50, the feed position is the 42nd block, the low eutectic solvent feed position is the 7th block, the reflux ratio is 15, the top condensation temperature is 5°C, and the low eutectic solvent feed mass flow rate is 25% of the bottom logistics mass flow rate of the adsorption tower.

[0082] The top pressure of the solvent recovery tower is 20 kPa, the tower pressure drop is 15 kPa, the bottom temperature is 82 °C, the theoretical plate number is 38, the feed position is the 21st block, the reflux ratio is 16, and the top condensation temperature is 5 °C.

[0083] The composition of the raw material acetonitrile and the acetonitrile product of this embodiment are shown in Table 1.

[0084] Example 5

[0085] The lightness removal tower is a packed tower, and the packing is a corrugated structured packing; the extraction distillation tower is a sieve plate tower, and the tower plates are vertical sieve plates; the solvent recovery tower is a packed tower, and the packing is a corrugated structured packing.

[0086] The adsorption tower has four sections of fillers, with strong alkaline anion exchange resin, activated carbon, strong acid anion exchange resin and 4A molecular sieve respectively from the bottom to the top of the tower.

[0087] The synthesis method of the low eutectic solvent is as follows: after mixing the hydrogen bond donor compound ethylene glycol and the hydrogen bond acceptor compound choline chloride in a molar ratio of 2, the mixture is stirred at a constant temperature of 80° C. for 4 hours until a uniform transparent liquid is obtained.

[0088] exist Figure 1 The treatment is carried out in the apparatus shown:

[0089] The top pressure of the light-removal tower is 30 kPa, the tower pressure drop is 15 kPa, the bottom temperature is 78 °C, the theoretical number of plates is 50, the feed position is the 18th plate, the side discharge position is the bottom 48 plates, the reflux ratio is 30, and the top condensation temperature is 10 °C.

[0090] The liquid phase space velocity of the adsorption tower is 2.5h -1 .

[0091] The top pressure of the extractive distillation column is 40 kPa, the column pressure drop is 22 kPa, the bottom temperature of the column is 108 °C, the number of theoretical plates is 52, the feed location is the 43rd plate, the eutectic solvent feed location is the 7th plate, the reflux ratio is 10, the top condensation temperature is 5 °C, and the mass flow rate of the eutectic solvent feed is 10% of the mass flow rate of the top stream of the adsorption column.

[0092] The top pressure of the solvent recovery column is 22 kPa, the column pressure drop is 25 kPa, the bottom temperature of the column is 86 °C, the number of theoretical plates is 35, the feed location is the 20th plate, the reflux ratio is 15, and the top condensation temperature is 5 °C.

[0093] The raw material acetonitrile composition and the acetonitrile product composition in this example are shown in Table 1.

[0094] Example 6

[0095] The de-lighting column is a packed column with structured corrugated packing; the extractive distillation column is a sieve plate column with vertical sieve plates; the solvent recovery column is a packed column with structured corrugated packing.

[0096] The adsorption column has four sections of packing. From the bottom to the top of the column are strongly basic anion exchange resin, activated carbon, strongly acidic anion exchange resin, and 4A molecular sieve.

[0097] The synthesis method of the eutectic solvent is as follows: The hydrogen bond donor compound 2-hydroxypropionic acid and the hydrogen bond acceptor compound N,N,N-trimethylglycine are mixed in a molar ratio of 2.5, and then stirred at a constant temperature of 90 °C for 6 hours until a homogeneous transparent liquid is formed.

[0098] In Figure 1 the device shown is processed:

[0099] The top pressure of the de-lighting column is 30 kPa, the column pressure drop is 15 kPa, the bottom temperature of the column is 75 °C, the number of theoretical plates is 50, the feed location is the 18th plate, the side line discharge location is the 48th plate from the bottom, the reflux ratio is 30, and the top condensation temperature is 10 °C.

[0100] The liquid hourly space velocity of the adsorption column is 2.5 h -1 .

[0101] The top pressure of the extractive distillation column is 30 kPa, the column pressure drop is 15 kPa, the bottom temperature of the column is 108 °C, the number of theoretical plates is 50, the feed location is the 42nd plate, the eutectic solvent feed location is the 7th plate, the reflux ratio is 15, the top condensation temperature is 5 °C, and the mass flow rate of the eutectic solvent feed is 25% of the mass flow rate of the bottom stream of the adsorption column.

[0102] The top pressure of the solvent recovery tower is 20 kPa, the tower pressure drop is 15 kPa, the bottom temperature is 78 ° C, the theoretical plate number is 35, the feed position is the 16th block, the reflux ratio is 5, and the top condensation temperature is 5 ° C.

[0103] The composition of the raw material acetonitrile and the acetonitrile product of this embodiment are shown in Table 1.

[0104] Example 7

[0105] The lightness removal tower is a packed tower, and the packing is a corrugated structured packing; the extraction distillation tower is a sieve plate tower, and the tower plates are vertical sieve plates; the solvent recovery tower is a packed tower, and the packing is a corrugated structured packing.

[0106] The adsorption tower has four sections of fillers, with strong alkaline anion exchange resin, activated carbon, strong acid anion exchange resin and 4A molecular sieve from the bottom to the top of the tower respectively.

[0107] The synthesis method of the low eutectic solvent is as follows: after mixing the hydrogen bond donor compound glycolic acid and the hydrogen bond acceptor compound N,N,N-trimethylglycine in a molar ratio of 2.5, stirring at a constant temperature of 90° C. for 6 hours until a uniform transparent liquid is obtained.

[0108] exist Figure 1 The treatment is carried out in the apparatus shown:

[0109] The top pressure of the light-removal tower is 30 kPa, the tower pressure drop is 15 kPa, the bottom temperature is 75 °C, the theoretical number of plates is 50, the feed position is the 18th plate, the side discharge position is the bottom 48 plates, the reflux ratio is 30, and the top condensation temperature is 10 °C.

[0110] The liquid phase space velocity of the adsorption tower is 2.5h -1 .

[0111] The top pressure of the extractive distillation tower is 30 kPa, the tower pressure drop is 15 kPa, the bottom temperature is 108°C, the theoretical plate number is 50, the feed position is the 42nd block, the low eutectic solvent feed position is the 7th block, the reflux ratio is 15, the top condensation temperature is 5°C, and the low eutectic solvent feed mass flow rate is 25% of the top flow mass flow rate of the adsorption tower.

[0112] The top pressure of the solvent recovery tower is 20 kPa, the tower pressure drop is 15 kPa, the bottom temperature is 82 °C, the theoretical plate number is 38, the feed position is the 21st block, the reflux ratio is 16, and the top condensation temperature is 5 °C.

[0113] The composition of the raw material acetonitrile and the acetonitrile product of this embodiment are shown in Table 1.

[0114] Comparative Example 1

[0115] The light - removing tower is a packed tower, and the packing is corrugated structured packing; the extractive distillation tower is a sieve - plate tower, and the tower plates are vertical sieve plates; the solvent recovery tower is a packed tower, and the packing is corrugated structured packing.

[0116] The adsorption tower has four sections of packing. From the bottom to the top of the tower, they are strongly basic anion - exchange resin, activated carbon, strongly acidic anion - exchange resin, and 4A molecular sieve respectively.

[0117] The extractant is ethylene glycol.

[0118] In Figure 1 the device shown below for treatment:

[0119] The top pressure of the light - removing tower is 30 kPa, the tower pressure drop is 15 kPa, the bottom temperature of the tower is 78 °C, the number of theoretical plates is 50, the feed position is the 18th plate, the side - line discharge position is the 48th plate from the bottom, the reflux ratio is 30, and the top condensation temperature is 10 °C.

[0120] The liquid hourly space velocity of the adsorption tower is 2.5 h -1 .

[0121] The top pressure of the extractive distillation tower is 40 kPa, the tower pressure drop is 25 kPa, the bottom temperature of the tower is 115 °C, the number of theoretical plates is 55, the feed position is the 45th plate, the feed position of the extractant ethylene glycol is the 8th plate, the reflux ratio is 12, the top condensation temperature is 5 °C, and the mass flow rate of the eutectic solvent feed is 20% of the mass flow rate of the top stream of the adsorption tower.

[0122] The top pressure of the solvent recovery tower is 22 kPa, the tower pressure drop is 25 kPa, the bottom temperature of the tower is 86 °C, the number of theoretical plates is 35, the feed position is the 20th plate, the reflux ratio is 15, and the top condensation temperature is 5 °C.

[0123] The raw material acetonitrile composition and the acetonitrile product composition in this example are shown in Table 1.

[0124] Table 1 Raw material acetonitrile composition and acetonitrile product composition

[0125]

[0126] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A method for preparing high-purity acetonitrile by extractive distillation to separate a mixture containing acetonitrile and water, characterized in that, the method includes: using a deep eutectic solvent as an extractant to perform extractive distillation on the mixture containing acetonitrile and water.

2. The method according to claim 1, wherein, the deep eutectic solvent contains a hydrogen bond donor compound and a hydrogen bond acceptor compound, and the molar ratio of the hydrogen bond donor compound to the hydrogen bond acceptor compound is 0.5 - 4, preferably 1 - 3; more preferably, the hydrogen bond donor compound is selected from at least one of urea, ethylene glycol, glycerol, triethylene glycol, 2-hydroxypropionic acid, malonic acid, hydroxybutanedioic acid, glycolic acid, levulinic acid, preferably glycolic acid and / or levulinic acid; and / or the hydrogen bond acceptor compound is selected from at least one of choline chloride, N,N,N-trimethylglycine, ethylammonium chloride, acetylcholine, tetraethylammonium bromide, tetraethylammonium chloride, tetrabutylammonium chloride, preferably N,N,N-trimethylglycine and / or acetylcholine.

3. The method according to claim 1 or 2, wherein, the preparation method of the deep eutectic solvent includes: mixing the hydrogen bond donor compound and the hydrogen bond acceptor compound at 60 - 120 °C to form a transparent liquid.

4. The method according to any one of claims 1 - 3, wherein, the mass content of acetonitrile in the mixture containing acetonitrile and water is 40 - 80 wt%, and the mass content of water is 20 - 50 wt%; preferably, the mixture containing acetonitrile and water is from the crude acetonitrile raw material by-produced from propylene ammoxidation.

5. The method according to any one of claims 1 - 4, wherein, the method further includes: pre-treating the mixture containing acetonitrile and water before extractive distillation; and / or recovering the extractant after extractive distillation and recycling it back to extractive distillation; preferably, the pre-treatment includes: performing light and heavy component removal, acid-base and heavy component removal on the mixture containing acetonitrile and water.

6. The method according to claim 5, wherein, the light and heavy component removal is carried out in a distillation column, and the conditions include: the top pressure of the column is 10 - 80 kPa, the pressure drop of the column is 10 - 50 kPa, the bottom temperature of the column is 70 - 130 °C, the number of theoretical plates is 15 - 60, the reflux ratio is 5 - 60, and the top condensation temperature is 5 - 40 °C.

7. The method according to claim 5, wherein, the method of acid-base and heavy component removal is adsorption removal. Preferably, the packing for adsorption removal includes at least one of an alkaline anion exchange resin, activated carbon, an acidic anion exchange resin, and a molecular sieve. More preferably, the molecular sieve is at least one of A-type, X-type, and Y-type molecular sieves.

8. The method according to claim 5, wherein, the recovery of the extractant is carried out in a distillation column, and the conditions include: the top pressure of the column is 20 - 100 kPa, the pressure drop of the column is 10 - 50 kPa, the bottom temperature of the column is 50 - 120 °C, the number of theoretical plates is 10 - 50, the reflux ratio is 2 - 30, and the top condensation temperature is 5 - 20 °C.

9. The method according to any one of claims 1 - 8, wherein, The conditions for extractive distillation include: the top pressure of the column is 30 - 150 kPa, the pressure drop of the column is 10 - 50 kPa, the bottom temperature of the column is 80 - 160 °C, the number of theoretical plates is 15 - 70, the reflux ratio is 5 - 30, the condensation temperature at the top of the column is 5 - 40 °C, and the mass flow rate of the extractant feed is 5 - 50% of the mass flow rate of the feed of the mixture containing acetonitrile and water.

10. High-purity acetonitrile prepared by the method according to any one of claims 1 - 9, characterized in that the purity of the high-purity acetonitrile is ≥95.5%, preferably ≥99.9, the water content is ≤1.5%, preferably ≤0.1%, and the propionitrile content is ≤400 ppm, preferably ≤100 ppm.

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