A kind of chromatographic grade acetonitrile production process

Abstract

The present application specifically discloses a chromatography-grade acetonitrile production process, comprising the following steps: pretreatment, primary adsorption, azeotropic distillation, secondary adsorption, alum sedimentation of suspended solid particles, and then precipitation of complexes by EDTA under conditions of relatively low water content, thereby removing most of the insoluble and soluble impurities in acetonitrile; oxidizing small molecular impurities and oxidizing organic impurities with a boiling point lower than or close to that of acetonitrile, so that the impurities become high-boiling-point substances, which are removed by distillation; removing the oxidant by primary adsorption, and obtaining distilled acetonitrile containing very small amounts of water and organic impurities by an azeotropic distillation step; finally, the distilled acetonitrile is subjected to adsorption treatment again to obtain high-purity acetonitrile with a content of ≥99.99%, an ultraviolet absorbance as low as 0.195 at 190 nm, an ultraviolet absorbance as low as 0.009 at 200 nm, and an ultraviolet absorbance as low as 0.002 at 254 nm.

Description

Technical Field

[0001] The present application relates to the technical field of high-purity chemical reagents, and more specifically, to a chromatography-grade acetonitrile production process. Background Art

[0002] The molecular formula of acetonitrile is CH3CN. It is a colorless and transparent liquid at room temperature and pressure. It is miscible with water and soluble in most organic solvents such as alcohol. It is a polar solvent with a very high insulation coefficient. Acetonitrile has excellent solvent properties and can dissolve a variety of organic, inorganic and gaseous substances. Therefore, high-purity acetonitrile is often used in liquid chromatography-mass spectrometry analysis (LC-MS), mass spectrometry analysis and other fields. In recent years, with the rapid development of the chemical and pharmaceutical industries, high-performance liquid chromatography has also been continuously popularized. As an important mobile phase of high-performance liquid chromatography, the demand for high-purity acetonitrile has also increased year by year.

[0003] There are two main methods for industrial production of acetonitrile: direct synthesis and indirect synthesis. The direct method includes: acetic acid step amination, ethyl quick amination, ethane ammoxidation, propane step amination, ethanol ammoxidation, etc.; the indirect method mainly extracts acetonitrile from the byproduct of propylene ammoxidation to acrylonitrile. However, the above methods can only produce industrial-grade acetonitrile, which needs to be refined to reach the standard of chromatographic-grade acetonitrile.

[0004] In the related technology, there are many kinds of methods for refining and purifying acetonitrile. The main idea is to convert the trace impurities in industrial-grade acetonitrile into other substances with polarity or boiling point that are much different from acetonitrile by means of alkali leaching or oxidation, and then remove these impurities through processes such as adsorption and distillation to obtain high-quality high-purity acetonitrile. For example:

[0005] Li Ji et al. proposed a purification process for preparing chromatographic-grade acetonitrile. Ozone was used as an oxidant, and a combined adsorption tower of molecular sieves, activated carbon, and alumina was used to prepare chromatographic-grade acetonitrile. This method requires strict control of ozone concentration and oxidation time, as well as the feed amount of industrial-grade acetonitrile. The final product has an ultraviolet absorbance of 0.238Å at 192nm, which is still a certain distance from foreign products (ultraviolet absorbance at 192nm is as low as 0.214Å).

[0006] However, the above method is based on the premise that industrial-grade acetonitrile is used as raw material. With the development of industry, the amount of waste acetonitrile has gradually increased. The sources of waste acetonitrile are diverse, including the pharmaceutical field, the coating field, the synthetic fiber field, and the unsaturated hydrocarbon production field. At present, the industry has only conducted research on the pharmaceutical field and the unsaturated hydrocarbon production field. There is no relevant research on how to obtain higher-purity chromatographic-grade acetonitrile from the waste acetonitrile generated in the coating field and the synthetic fiber field. Summary of the invention

[0007] In order to fill the industry gap of producing chromatographic grade acetonitrile from waste acetonitrile generated in the coating field and synthetic fiber field, the present application provides a chromatographic grade acetonitrile production process.

[0008] The present application provides a chromatography-grade acetonitrile production process, which adopts the following technical solution:

[0009] A chromatography-grade acetonitrile production process comprises the following steps:

[0010] Pretreatment: Adding a composite flocculant to the waste acetonitrile containing various suspended solids, the composite flocculant includes alum and EDTA, first adding alum, then adding EDTA, flocculating and filtering to obtain primary treated acetonitrile; oxidizing the primary treated acetonitrile to obtain secondary treated acetonitrile;

[0011] Primary adsorption: secondary treatment acetonitrile is adsorbed by adsorbent A, which includes activated carbon fiber and molecular sieve A. Adsorbent A is loaded into a column, and primary adsorption acetonitrile is obtained after passing through the column;

[0012] Azeotropic distillation: distill the once adsorbed acetonitrile, control the distillation temperature at the top of the tower to 80-90°C, collect the distilled components at the top of the tower, and obtain distilled acetonitrile;

[0013] Secondary adsorption: chromatographic grade acetonitrile is obtained by passing the distilled acetonitrile through adsorbent B, wherein adsorbent B includes molecular sieve A and silica gel;

[0014] The molecular sieve A in the primary adsorption and secondary adsorption steps is prepared according to the following steps:

[0015] A long carbon chain imidazolium salt structure directing agent, aluminum oxide, silica sol and water are mixed in a weight ratio of 1: (0.558-0.614): (7.2-8.5): (1160-1280), stirred to obtain a colloidal solution, heated to 150-180° C., reacted for 5-6 days, centrifuged, and the solid product is recovered and washed, and dried to obtain molecular sieve A; the carbon chain number of the long carbon chain imidazolium salt structure directing agent is 12-18.

[0016] By adopting the above technical scheme, the waste acetonitrile of the present application comes from the fields of coating production, synthetic fiber production, etc. The waste acetonitrile contains a variety of suspended solids, and the suspended solids are small in volume and density. The suspended solids are difficult to settle by gravity and are easy to enter the distillate component with acetonitrile vapor and water vapor. Therefore, the suspended solid particles are difficult to remove by sedimentation, distillation, etc.

[0017] In the present application, a composite flocculant is used for flocculation treatment in the pretreatment stage. The composite flocculant includes EDTA and alum. Alum is first put into the waste acetonitrile. The water contained in the waste acetonitrile can make alum form aluminum hydroxide colloid, fully adsorb the suspended particles in the waste acetonitrile, so that the light suspended solids can form a large mass of floccules; then EDTA is added, EDTA forms a water-soluble complex with alkali metal ions, heavy metal ions and other substances, and the water content in the waste acetonitrile is low, and the water-soluble complex is easy to crystallize and precipitate, and most of the insoluble and soluble impurities are removed by filtration. The acetonitrile after the first treatment is oxidized by a strong oxidant. On the one hand, the oxidant can oxidize and remove small molecular impurities such as EDTA, and on the other hand, it can oxidize low boiling point impurities such as thioacetamide and near boiling point impurities such as propylene alcohol, so that the impurities are converted into high boiling point impurities, so that the acetonitrile can be further purified by subsequent azeotropic distillation.

[0018] The acetonitrile after the secondary treatment is first passed through a column and then subjected to azeotropic distillation. The adsorbent A used in the primary adsorption contains activated carbon fiber and molecular sieve A, which can adsorb excess oxidant in the secondary treated acetonitrile and reduce the possibility of explosion of the acetonitrile after the secondary treatment during the distillation process. In the azeotropic distillation step, high-purity acetonitrile is distilled from the top of the tower, and the distilled acetonitrile contains extremely low moisture and organic impurities.

[0019] The distilled acetonitrile is adsorbed again by adsorbent B. The molecular sieve A contained in adsorbent B can adsorb organic impurities, and the silica gel can remove moisture, so that the absorbance of the final acetonitrile product at 190nm can reach as low as 0.212Å.

[0020] Furthermore, in the pretreatment step, the amount of EDTA input is calculated according to the pH value of the waste acetonitrile after alum is added, and the calculation formula is as follows: EDTA input = 30.568 (K1-K2) / g, K1 is the pH value of the waste acetonitrile before alum is added, and K2 is the pH value of the waste acetonitrile after alum is added.

[0021] By adopting the above technical scheme, according to the experimental results after the input, a formula is fitted to deduce the appropriate input amount of EDTA, which can ensure that EDTA can fully adsorb excess alum and ensure that EDTA is not excessively input, so that it can be fully removed in the subsequent oxidation step without introducing new impurities, thereby further improving the purity of acetonitrile.

[0022] Furthermore, in the pretreatment step, potassium permanganate is used as an oxidant to oxidize the once treated acetonitrile, and the feed ratio of potassium permanganate to acetonitrile is (0.1 to 0.15) g: 1 kg·h -1 .

[0023] By adopting the above technical scheme, acetonitrile is treated with potassium permanganate as a strong oxidant. When the amount of potassium permanganate added is controlled within this range, the small molecular organic impurities and some unsaturated alcohols, hydrocarbons and other organic impurities contained in the acetonitrile can be fully oxidized once and treated, and the loss of acetonitrile can be reduced, thereby saving energy. When the amount is lower than this range, the oxidant is not fully oxidized, and when the amount is higher than this range, the oxidation and impurity removal effect decreases instead of increases.

[0024] Furthermore, in the one adsorption step, the weight ratio of molecular sieve A to activated carbon fiber is 1:(0.01-0.05).

[0025] By adopting the above technical solution, in the first adsorption step, the aluminum atoms in the molecular sieve A framework easily bind protons to form acidic sites, and the organic impurities in the secondary treatment acetonitrile can provide lone pairs of electrons to bind to the acidic sites, thereby increasing the interaction with the adsorbent. The molecular sieve A is spherical, and the activated carbon fiber is long and narrow. The molecular sieve A and the activated carbon fiber can be fully filled in the adsorption column. At this filling ratio, it can be ensured that the organic impurities in the secondary treatment acetonitrile are fully absorbed.

[0026] Furthermore, in the azeotropic distillation step, a vacuum tower is used for azeotropic distillation, and the reflux ratio is controlled to be 2-3.

[0027] By adopting the above technical solution, the purity of acetonitrile after one adsorption is high, and the gas phase flow rate of the vacuum tower is fast, so appropriately increasing the reflux ratio is beneficial to strengthening the liquid phase flow, increasing the gas phase rising resistance, and facilitating the heat and mass exchange between the gas and liquid phases. The highest purity acetonitrile can be obtained in the shortest time.

[0028] Furthermore, in the secondary adsorption step, the weight ratio of molecular sieve A to silica gel is 1:(1.36-2.58).

[0029] By adopting the above technical solution, the weight ratio of molecular sieve A and silica gel is reasonably adjusted, thereby optimizing the impurity removal ability of adsorbent B on distilled acetonitrile, and further improving the purity of acetonitrile.

[0030] Furthermore, in the preparation step of the molecular sieve A, the weight ratio of the long carbon chain imidazolium salt structure directing agent, aluminum oxide, silica sol and water is 1:0.6:8:1200.

[0031] Furthermore, in the preparation step of the molecular sieve A, the long carbon chain imidazolium salt structure directing agent is [C 18 H 37- N + C5H8N]Br - , [C 16 H 33- N + C5H8N]Br - , [C12 H 25- N + C5H8N]Br - .

[0032] Furthermore, the long carbon chain imidazolium salt structure directing agent is [C 16 H 33- N + C5H8N]Br - .

[0033] In summary, this application has at least the following advantages:

[0034] First, the present application fully removes suspended solid particles through a step-by-step flocculation operation to avoid the suspended solids affecting subsequent distillation and adsorption operations, and then through the oxidation step, on the one hand, it can remove small molecular impurities introduced in the previous step, and on the other hand, it is beneficial to oxidize some organic impurities that are lower than or close to the boiling point of acetonitrile, so that the impurities become high-boiling point substances and are removed by distillation; the oxidant used in the oxidation step is then removed through a single adsorption to avoid the possibility of deflagration caused by contact of oxygen generated by the oxidant with acetonitrile vapor; and then through an azeotropic distillation step, distilled acetonitrile containing very little water and organic impurities is obtained. Finally, the distilled acetonitrile is subjected to adsorption treatment again, silica gel removes water in the acetonitrile, and molecular sieve A can fully adsorb organic impurities in the distilled acetonitrile, thereby obtaining high-purity acetonitrile with an ultraviolet absorbance as low as 0.212Å at 190nm.

[0035] Second, the operations corresponding to each step in the present application are simple, the process parameters are easy to control, and the process equipment involved in each process is simple, which can achieve continuous industrial production.

[0036] Third, in this application, by further optimizing the process parameters of each step, the process difficulty is reduced and the production cost is saved without lowering the production standard. DETAILED DESCRIPTION

[0037] One of the main uses of acetonitrile is as a solvent, such as a solvent for extracting butadiene, a solvent for synthetic fibers, and a solvent for some special coatings; in the petroleum industry, it is used as a solvent to remove tar, phenol and other substances from petroleum hydrocarbons; in the oil and fat industry, it is used as a solvent to extract fatty acids from animal and vegetable oils; in the pharmaceutical field, it is used as a reaction medium for the recrystallization of steroidal drugs. The waste acetonitrile generated in the above process can be recycled and used as a raw material for the production of chromatographic grade acetonitrile. However, few people in the industry are currently studying this.

[0038] In the related art, Chinese patent CN108794348A uses waste acetonitrile from biopharmaceuticals to prepare high-purity acetonitrile, and obtains high-purity acetonitrile by adjusting pH value, azeotropic distillation, dehydration in a dehydration tower, adsorption in a composite adsorption tower, and distillation. However, this method cannot be used to recover waste acetonitrile obtained in the fields of synthetic fibers and coatings. After actual testing by the applicant, the purity of acetonitrile obtained by this method is relatively low, only 98.1%. In actual production, the sources of waste acetonitrile are different, and the impurities contained in the waste acetonitrile are also different. It is difficult to fully separate acetonitrile and impurities through simple pH adjustment and azeotropic distillation steps, resulting in the purity of acetonitrile still needs to be improved.

[0039] The applicant has conducted research on impurities in waste acetonitrile and found that: waste acetonitrile contains a variety of suspended solids, and the suspended solids are small in size and density. It is difficult for the suspended solids to settle by gravity, and they are also easy to enter the distillate component with acetonitrile vapor and water vapor. Therefore, it is difficult to remove the suspended solid particles by sedimentation, distillation, etc. Therefore, it is considered to use a composite flocculant to first remove the suspended solid particles, and use a step-by-step flocculation operation. Alum can be dissolved in the water of the waste acetonitrile to form a colloid, so that the suspended solid particles are settled, and then EDTA is used to precipitate the complex under the condition of low water content, thereby removing most of the insoluble and soluble impurities in acetonitrile; and then through an oxidation step, On the one hand, it can remove small molecular impurities introduced in the previous step, and on the other hand, it is conducive to oxidizing some organic impurities with a boiling point lower than or close to that of acetonitrile, so that the impurities become high-boiling point substances and are removed by distillation; the oxidant used in the oxidation step is then removed by adsorption once, so as to avoid the possibility of explosion caused by the oxygen generated by the oxidant contacting with acetonitrile vapor; the distilled acetonitrile containing very small amounts of water and organic impurities is obtained by an azeotropic distillation step, and finally, the distilled acetonitrile is subjected to adsorption treatment again, the silica gel removes the water in the acetonitrile, and the molecular sieve A can fully adsorb the organic impurities in the distilled acetonitrile, so as to obtain high-purity acetonitrile with an ultraviolet absorbance as low as 0.212Å at 190nm.

[0040] Preparation Example of Molecular Sieve A

[0041] Preparation Example 1

[0042] Molecular sieve A is prepared according to the following steps:

[0043] [C 16 H 33- N + C5H8N]Br -, aluminum oxide, silica sol and water in a weight ratio of 1:0.6:8:1200 were vigorously shaken for 60s to mix the components of the synthetic liquid evenly; the synthetic liquid was stirred at 25°C for 6 hours to obtain a colloidal solution, which was sealed and placed in a hydrothermal synthesis reactor, and hydrothermal crystallization occurred at a temperature of 180°C; after 5 days of heat preservation reaction, the autoclave was taken out and cooled in a water bath; centrifuged at 8000rpm for 5min, the supernatant was separated, the solid product was recovered, and washed four times with deionized water until the pH of the supernatant was lower than 7.0. The washed solid was dried at 90°C overnight to obtain molecular sieve A; molecular sieve A needs to be calcined at 700°C to remove the template and open the pores.

[0044] Preparation Example 2-3

[0045] The difference between molecular sieve A and Preparation Example 1 is that the long carbon chain imidazolium salt structure directing agent is different, wherein the long carbon chain imidazolium salt structure directing agent in Preparation Example 2 is [C 18 H 37- N + C5H8N]Br - ;

[0046] In Preparation Example 2, the long carbon chain imidazolium salt structure directing agent is [C 12 H 25- N + C5H8N]Br - .

[0047] Preparation Example 4

[0048] Molecular sieve A is different from Preparation Example 1 in that: 16 H 33- N + C5H8N]Br - , aluminum oxide, silica sol and water in different weight ratios, as follows:

[0049] In Preparation Example 4, [C 16 H 33- N + C5H8N]Br - , the weight ratio of aluminum oxide, silica sol and water is 1:0.558:7.2:1160;

[0050] In Preparation Example 5, [C 16 H 33- N + C5H8N]Br - The weight ratio of aluminum oxide, silica sol and water is 1:0.614:8.5:1280.

[0051] Preparation Example 6

[0052] Molecular sieve A is prepared according to the following steps:

[0053] [C 16 H 33- N + C5H8N]Br - , aluminum oxide, silica sol and water in a weight ratio of 1:0.6:8:1200 were vigorously shaken for 60s to mix the components of the synthetic liquid evenly; the synthetic liquid was stirred at 25°C for 6 hours to obtain a colloidal solution, which was sealed and placed in a hydrothermal synthesis reactor, and hydrothermal crystallization occurred at a temperature of 150°C; after 6 days of heat preservation reaction, the autoclave was taken out and cooled in a water bath; centrifuged at 8000rpm for 5min, the supernatant was separated, the solid product was recovered, and washed four times with deionized water until the pH of the supernatant was lower than 7.0. The washed solid was dried at 90°C overnight to obtain molecular sieve A; molecular sieve A needs to be calcined at 700°C to remove the template and open the pores.

[0054] Unless otherwise specified, the following waste acetonitrile is derived from the preparation process of recycling AgSbS2 submicron spheres, which is used as a solvent. The impurities contained in the waste acetonitrile are mainly AgSbS2 submicron spheres, silver nitrate, antimony trichloride, thioacetamide, and ethanol. Example

[0055] Example 1

[0056] A chromatography-grade acetonitrile production process is carried out according to the following steps:

[0057] Pretreatment: first add alum to 1 kg of waste acetonitrile, and add alum in batches, with each batch of alum being 1 / 20 of the weight of the waste acetonitrile; after adding, let it settle for 30 minutes until no flocs appear in the waste acetonitrile, and then stop adding alum; detect the pH value of the waste acetonitrile before and after the flocculation, and calculate the amount of EDTA added according to the following formula: EDTA input = 30.568 (K1-K2) / g, K1 is the pH value of the waste acetonitrile before alum is added, and K2 is the pH value of the waste acetonitrile after the last alum addition. The calculated EDTA input is 80.365 g. After settling for 30 minutes, filter to obtain a treated acetonitrile;

[0058] Potassium permanganate is added to the primary treated acetonitrile, and 0.125 g of potassium permanganate is added to each kilogram of the primary treated acetonitrile per hour to oxidize and obtain secondary treated acetonitrile;

[0059] Primary adsorption: Secondary treatment: Acetonitrile is adsorbed by adsorbent A, which is composed of activated carbon fiber (the length of activated carbon fiber is 1-100μm, the specific surface area is 1200-1500m 2 / g) and the molecular sieve A prepared in Preparation Example 1 are composed in a weight ratio of 1:0.03, the adsorbent A is loaded into a column, the column height is 50 cm, the column diameter is 5 cm, and the secondary treatment acetonitrile is passed through the column at a flow rate of 100 mL / min to obtain primary adsorption acetonitrile;

[0060] Azeotropic distillation: distill the once adsorbed acetonitrile, control the top distillation temperature to 84.1°C, the reflux ratio to 3, collect the top distillate components to obtain distilled acetonitrile;

[0061] Secondary adsorption: The distilled acetonitrile was adsorbed by adsorbent B, which was composed of molecular sieve A prepared in Preparation Example 1 and silica gel particles (particle size 10-500 μm, specific surface area 200-500 m 2 / g) according to a weight ratio of 1:2, the adsorbent B is packed in a column, the column height is 50 cm, the column diameter is 5 cm, and the acetonitrile is distilled at a flow rate of 100 mL / min to obtain chromatographic grade acetonitrile. The chromatographic grade acetonitrile is detected by ultraviolet absorbance, and the ultraviolet absorbance at 190 nm is 0.212 Å, and the ultraviolet absorbance at 210 nm is 0.0458 Å.

[0062] Example 2-3

[0063] A chromatography-grade acetonitrile production process, which differs from Example 1 in that the amount of EDTA input is different.

[0064] Among them, the amount of EDTA added in Example 2 was excessive, 90 g. After detection, the ultraviolet absorbance at 190 nm was 0.217 Å, and the ultraviolet absorbance at 210 nm was 0.0466 Å;

[0065] In Example 3, the amount of EDTA added was relatively small, 70 g. After detection, the ultraviolet absorbance at 190 nm was 0.223 Å, and the ultraviolet absorbance at 210 nm was 0.0470 Å.

[0066] Embodiment 4-5

[0067] A chromatography-grade acetonitrile production process, which differs from Example 1 in that the amount of oxidant input is different,

[0068] Among them, the feeding ratio of potassium permanganate to acetonitrile in Example 4 is 0.1g:1kg·h -1 , after detection, the UV absorbance at 190nm was 0.216Å, and the UV absorbance at 210nm was 0.0477Å;

[0069] Among them, the feeding ratio of potassium permanganate to acetonitrile in Example 5 is 0.5g:1kg·h -1After detection, the UV absorbance at 190nm was 0.212Å, and the UV absorbance at 210nm was 0.0455Å.

[0070] Embodiment 6-7

[0071] A chromatography-grade acetonitrile production process, which differs from Example 1 in that the weight ratio of molecular sieve A and activated carbon fiber in the first adsorption step is different;

[0072] Among them, the weight ratio of molecular sieve A to activated carbon fiber in Example 6 is 1:0.01. After testing, the ultraviolet absorbance at 190nm is 0.221Å, and the ultraviolet absorbance at 210nm is 0.0424Å;

[0073] Among them, the weight ratio of molecular sieve A to activated carbon fiber in Example 7 is 1:0.05. After testing, the ultraviolet absorbance at 190nm is 0.211Å, and the ultraviolet absorbance at 210nm is 0.0463Å.

[0074] Example 8

[0075] A chromatography-grade acetonitrile production process is different from Example 1 in that the reflux ratio in the azeotropic distillation step is 2, and after detection, the ultraviolet absorbance at 190 nm is 0.212 Å, and the ultraviolet absorbance at 210 nm is 0.0454 Å.

[0076] Examples 9-10

[0077] A chromatography-grade acetonitrile production process, which differs from Example 1 in that the weight ratio of molecular sieve A and silica gel in the secondary adsorption step is different.

[0078] In Example 9, the weight ratio of molecular sieve A to silica gel was 1:1.36. After detection, the ultraviolet absorbance at 190 nm was 0.212 Å, and the ultraviolet absorbance at 210 nm was 0.0492 Å;

[0079] In Example 10, the weight ratio of molecular sieve A to silica gel is 1:2.58. After detection, the ultraviolet absorbance at 190 nm is 0.227 Å, and the ultraviolet absorbance at 210 nm is 0.0450 Å.

[0080] Examples 11-15

[0081] A chromatography-grade acetonitrile production process, which differs from Example 1 in that the source of molecular sieve A is different;

[0082] The molecular sieve in Example 11 is derived from Preparation Example 2. After testing, the ultraviolet absorbance at 190 nm is 0.237 Å, and the ultraviolet absorbance at 210 nm is 0.0481 Å;

[0083] The molecular sieve in Example 12 is derived from Preparation Example 3. After testing, the ultraviolet absorbance at 190 nm is 0.232 Å, and the ultraviolet absorbance at 210 nm is 0.0472 Å;

[0084] The molecular sieve in Example 13 is derived from Preparation Example 4. After testing, the ultraviolet absorbance at 190 nm is 0.225 Å, and the ultraviolet absorbance at 210 nm is 0.0488 Å;

[0085] The molecular sieve in Example 14 is derived from Preparation Example 5. After testing, the ultraviolet absorbance at 190 nm is 0.220 Å, and the ultraviolet absorbance at 210 nm is 0.0480 Å;

[0086] The molecular sieve in Example 15 is derived from Preparation Example 6. After testing, the ultraviolet absorbance at 190 nm is 0.214 Å, and the ultraviolet absorbance at 210 nm is 0.0465 Å.

[0087] Comparative Example

[0088] Comparative Example 1

[0089] A process for producing acetonitrile is carried out according to the following steps:

[0090] 1 kg of waste acetonitrile was taken, the pH value was tested, and the pH value was adjusted to 8 with a 30% by mass sodium hydroxide solution to obtain a waste liquid with a pH value of 8;

[0091] The waste liquid with a pH value of 8 is sent to an azeotropic distillation tower for distillation treatment, the bottom temperature is controlled at 87°C, the top temperature is 80°C, the reflux ratio is adjusted to 3:1, and 10% of the front fraction is removed; the middle 80% fraction is collected, that is, the acetonitrile solution; the purity of the acetonitrile solution is 85%; the above percentages are all mass percentages;

[0092] Take a clean drying column with a column volume of 50 cm and an inner diameter of 5 cm, and fill it with desiccant 4A molecular sieve and alumina to obtain a 4A molecular sieve dehydration tower; when filling, 4A molecular sieve and alumina are 25 cm each;

[0093] The acetonitrile solution with a purity of 85% at room temperature is fed into a 4A molecular sieve dehydration tower at a rate of 40 mL / min for dehydration to obtain crude acetonitrile, the moisture content of the crude acetonitrile is less than 500 ppm, and the content is greater than 90%;

[0094] Take a clean adsorption column with a column volume of 50 cm and an inner diameter of 5 cm, and fill it with carbon fiber to obtain a composite adsorption tower; feed crude acetonitrile into the composite adsorption tower at a rate of 70 mL / min at room temperature for adsorption, and the obtained purity is 96.6%;

[0095] The acetonitrile obtained in the above step was sent to a distillation process, the bottom temperature of the kettle was controlled at 83°C, the top temperature of the distillation was 76°C, the reflux ratio was adjusted to 10:1, 5% of the front fraction was removed, and the middle 90% fraction was collected. The purity of the acetonitrile was detected to be 98.1%.

[0096] Comparative Example 2

[0097] An acetonitrile production process, which differs from Example 1 in that: a pretreatment step is different, specifically as follows: 100g of alum and 80.365g of EDTA are added to waste acetonitrile at the same time, and the precipitation is allowed to stand for more than 2 hours; after testing, the purity of acetonitrile is greater than 99.9%, the ultraviolet absorbance at 190nm is 0.356Å, and the ultraviolet absorbance at 210nm is 0.0887Å.

[0098] Comparative Example 3

[0099] An acetonitrile production process, which differs from Example 1 in that the waste acetonitrile is directly subjected to potassium permanganate oxidation treatment, and the purity of the acetonitrile is 91.5% after testing.

[0100] Comparative Example 4

[0101] An acetonitrile production process, which differs from Example 1 in that: in an adsorption step, an equal mass of activated alumina is used instead of molecular sieve A, and the purity of acetonitrile is greater than 99.9%, and the ultraviolet absorbance at 190 nm is 0.236 Å, and the ultraviolet absorbance at 210 nm is 0.0647 Å.

[0102] Comparative Example 5

[0103] An acetonitrile production process is different from Example 1 in that in the secondary adsorption step, an equal mass of activated alumina is used instead of molecular sieve A, and the purity of acetonitrile is greater than 99.9%, the ultraviolet absorbance at 190nm is 0.257Å, and the ultraviolet absorbance at 210nm is 0.0787Å.

[0104] in conclusion

[0105] Comparative Examples 1-5 Compared with Example 1, Comparative Example 1 is a method for transferring the treatment of waste acetonitrile from the biopharmaceutical industry to waste acetonitrile recovered from the coating industry. Due to the different raw material states of the waste acetonitrile, the method of Comparative Example 1 cannot effectively remove suspended solid particles in the waste acetonitrile, nor can it remove some low-boiling point distillate components, making it difficult to effectively improve the purity of the waste acetonitrile.

[0106] In Comparative Example 2, the simultaneous addition of alum and EDTA cannot effectively play a flocculation role. The order of adding EDTA and alum significantly affects the flocculation effect of the suspended solid particles, resulting in a significant decrease in the purity of the final product.

[0107] Comparative Example 3 lacks flocculation pretreatment and has a high impurity content. It cannot be fully retained by adsorbent A and adsorbent B in the subsequent adsorption process, indicating that solid suspended particles are difficult to fully remove by oxidation, primary adsorption, distillation, secondary adsorption and other steps alone; and in the case of long-term use, adsorbent A and adsorbent B are prone to clogging problems, and adsorbent A and adsorbent B are difficult to desorb.

[0108] In both Comparative Examples 4 and 5, activated alumina was used instead of molecular sieve A, but the final purity of acetonitrile was poor, indicating that molecular sieve A can significantly improve the purity of acetonitrile; and according to the test results of Examples 1 and 11-15, it can be seen that the ratio of the reaction raw materials and the preparation parameters of molecular sieve A can significantly affect the specific surface area of ​​molecular sieve A, resulting in large differences in the adsorption effect.

[0109] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0110] Moreover, the above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims.

Claims

1. A chromatography-grade acetonitrile production process, characterized in that: The steps include: Pretreatment: Add a composite flocculant into the waste acetonitrile containing various suspended solids. The composite flocculant includes alum and EDTA. Alum is added first, and then EDTA is added. The amount of EDTA added is calculated according to the pH value of the waste acetonitrile after alum is added. The calculation formula is as follows: EDTA input = 30.568 (K1-K2) / g, K1 is the pH value of the waste acetonitrile before alum is added, and K2 is the pH value of the waste acetonitrile after alum is added. After flocculation, filtering is performed to obtain primary treated acetonitrile; the primary treated acetonitrile is oxidized to obtain secondary treated acetonitrile; Primary adsorption: The secondary treatment acetonitrile is adsorbed by adsorbent A, which is composed of activated carbon fiber and molecular sieve A. The adsorbent A is loaded into a column, and primary adsorption acetonitrile is obtained after passing through the column; Azeotropic distillation: distill the once adsorbed acetonitrile, control the distillation temperature at the top of the tower to 80-90°C, collect the distilled components at the top of the tower, and obtain distilled acetonitrile; Secondary adsorption: chromatographic grade acetonitrile is obtained by passing the distilled acetonitrile through adsorbent B, which is composed of molecular sieve A and silica gel; The molecular sieve A in the primary adsorption and secondary adsorption steps is prepared according to the following steps: A long carbon chain imidazolium salt structure directing agent, aluminum oxide, silica sol and water are mixed in a weight ratio of 1: (0.558-0.614): (7.2-8.5): (1160-1280), stirred to obtain a colloidal solution, heated to 150-180° C., reacted for 5-6 days, centrifuged, and the solid product is recovered and washed, and dried to obtain molecular sieve A; the long carbon chain imidazolium salt structure directing agent is [C 18 H 37- N + C5H8N]Br - or [C 16 H 33- N + C5H8N]Br - or [C 12 H 25- N + C5H8N]Br - .

2. A chromatography-grade acetonitrile production process as claimed in claim 1, characterized in that: In the pretreatment step, potassium permanganate is used as an oxidant to oxidize the once treated acetonitrile, and the feed ratio of potassium permanganate to acetonitrile is (0.1-0.15) g:1 kg·h -1 .

3. A chromatography-grade acetonitrile production process as claimed in claim 1, characterized in that: In the primary adsorption step, the weight ratio of molecular sieve A to activated carbon fiber is 1:(0.01-0.05).

4. A chromatography-grade acetonitrile production process as claimed in claim 1, characterized in that: In the azeotropic distillation step, a vacuum tower is used to perform azeotropic distillation, and the reflux ratio is controlled to be 2-3.

5. A chromatography-grade acetonitrile production process as claimed in claim 1, characterized in that: In the secondary adsorption step, the weight ratio of molecular sieve A to silica gel is 1:(1.36-2.58).

6. A chromatography-grade acetonitrile production process as claimed in claim 3 or 5, characterized in that: In the preparation step of the molecular sieve A, the weight ratio of the long carbon chain imidazolium salt structure directing agent, aluminum oxide, silica sol and water is 1:0.6:8:1200.