Preparation method of high-purity acetonitrile

Abstract

The present invention relates to the technical field of acetonitrile purification, and in particular to a method for preparing high-purity acetonitrile. The present invention first puts crude acetonitrile into a distillation bottle, then distills the solution, controls the system temperature to maintain between 80 and 90°C, leaves propionitrile as a heavy component at the bottom of the flask, and steams acrylonitrile and acetonitrile from the top, and then passes through a functional membrane component, which is composed of a polyacrylonitrile membrane and activated alumina, so that acrylonitrile and acetonitrile are separated, the purity of acetonitrile is increased to 99.99%, and then collected, and the ultraviolet absorption photometric value at a wavelength of 200nm to 250nm is tested. The present invention is scientifically and reasonably designed, easy to operate, not only improves the purity of acetonitrile, but also simplifies the process flow, and has the advantages of low energy consumption and no three wastes.

Description

Technical Field

[0001] The present invention relates to the technical field of acetonitrile purification, and in particular to a method for preparing high-purity acetonitrile. Background Art

[0002] Acetonitrile can be used as a chemical reaction solvent, particularly as a mobile phase solvent for the synthesis and purification of pharmaceutical intermediates and high performance liquid chromatography, and these applications require the use of higher purity acetonitrile (>99.9%). Commonly available acetonitrile at present is mainly obtained by reclaiming and purifying crude acetonitrile (purity ≥99%), which is obtained as a by-product when manufacturing acrylonitrile through the contact ammoxidation of propylene, ammonia, and molecular oxygen. The crude acetonitrile obtained from this by-product contains impurities such as water, acrylonitrile, and propionitrile.

[0003] The most important technical specification for acetonitrile (99.99% purity), a mobile phase solvent for high-performance liquid chromatography (HPLC), is its ultraviolet absorption light intensity value of ≤0.05 at a wavelength of 200nm to 250nm. In order to enable chromatographic analysis under conditions where the wavelength is lower and the sensitivity is higher, acetonitrile is required to have a low absorbance of ultraviolet light absorption at a wavelength of 200nm to 250nm. Therefore, even if the acetonitrile is highly purified, if there are trace amounts of compounds with absorbance in the ultraviolet range as impurities, its absorbance becomes larger, causing it to fail to meet the requirements of being a mobile phase solvent for HPLC. For this reason, the impurities in the acetonitrile must be removed as much as possible before it can be used as a chromatographic reagent in the biological and pharmaceutical fields.

[0004] Currently, the main methods for purifying acetonitrile reagents include distillation-adsorption purification, alkali washing-adsorption purification, oxidation-adsorption purification, oxidation-distillation-adsorption purification, etc.

[0005] CN 104744299A introduces a method for purifying a high-purity organic solvent, acetonitrile. This method first treats the acetonitrile with a strong acid and a strong base, then uses activated carbon and a molecular sieve for adsorption, and finally purifies it by distillation.

[0006] In CN 111960966A, fuming sulfuric acid is first used for oxidation, and then a peroxide is used for distillation oxidation, and then distillation is performed.

[0007] CN 104744300A first uses potassium permanganate or an oxidant to treat acetonitrile, then uses activated carbon and ion exchange resin for adsorption, and finally purifies it by distillation.

[0008] Although these methods can obtain acetonitrile with higher purity, the entire process is complicated and energy consumption is high. At the same time, the use of acid, alkali and strong oxidant will produce a large amount of waste acid, waste alkali and waste oxidant, and the yield of acetonitrile is also low. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a method for preparing high-purity acetonitrile. The method has a scientific and reasonable design and is easy to operate, which not only improves the purity of the acetonitrile but also simplifies the process flow and has the advantages of low energy consumption and no generation of three wastes.

[0010] The method for preparing high-purity acetonitrile of the present invention comprises the following steps: firstly, placing crude acetonitrile in a distillation flask, then rectifying the solution, controlling the system temperature to maintain between 80 and 90° C., leaving propionitrile as a heavy component at the bottom of the flask, and distilling acrylonitrile and acetonitrile from the top. The solution is then passed through a functional membrane assembly composed of a polyacrylonitrile membrane and activated alumina to separate acrylonitrile and acetonitrile, thereby increasing the purity of the acetonitrile to 99.99%. The solution is then collected and tested for ultraviolet absorption light value at a wavelength of 200 nm to 250 nm.

[0011] Preferably, the purity of crude acetonitrile is ≥99%.

[0012] Preferably, the acrylonitrile content in the crude acetonitrile is ≤100 mg / kg, the propionitrile content is ≤1000 mg / kg, and the density is 0.780-0.785 g / cm 3 .

[0013] Preferably, the filler used in the rectification column is spring glass with a diameter of 2 mm, and the preferred filler height is 70-90 cm.

[0014] Preferably, during distillation, the system temperature is controlled to be maintained at 82-92° C., more preferably 86° C., and the distillation reflux ratio is 0.2-0.4, more preferably 0.3.

[0015] The functional membrane component comprises a support layer and a separation layer, wherein the separation layer is located on the support layer.

[0016] The support layer is activated alumina with a pore structure of 0.01 to 0.2 μm, and a thickness of 0.5 to 5 mm, preferably 0.05 μm, and a thickness of 1 to 3 mm.

[0017] The separation layer is a polyacrylonitrile membrane, the weight average molecular weight of the polyacrylonitrile powder is 150,000-400,000, preferably 200,000-300,000. The total thickness of the separation layer is 10-100 μm, and the total number of separation layers is 4-8, preferably 5-6.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] (1) The present invention passes the acrylonitrile by-product acetonitrile through a distillation column filled with a spring glass filler with a diameter of 2 mm to completely remove the heavy component propionitrile, and then removes a small amount of acrylonitrile in the acetonitrile through a functional membrane assembly, so that the purity of the acetonitrile is increased to more than 99.99%, while satisfying the ultraviolet absorption light value of ≤0.05 at a wavelength of 200nm to 250nm.

[0020] (2) The acetonitrile yield of the present invention reaches more than 90%, and it also has the advantages of low energy consumption, simple production process, and no generation of three wastes. DETAILED DESCRIPTION

[0021] The present invention is further described below with reference to the examples.

[0022] Example 1

[0023] Take 350 mL of 99% pure acetonitrile (containing 90 mg / kg of acrylonitrile and 900 mg / kg of propionitrile) and add it to a 500 mL distillation flask. Then, the solution is distilled with a packing height of 80 cm. The system temperature is controlled to be maintained at 84°C, the reflux ratio is 0.3, and reflux is performed for 60 minutes.

[0024] The top material was passed through a functional membrane assembly. The separation layer used polyacrylonitrile powder had a weight-average molecular weight of 250,000, a total thickness of 50 μm, and six layers. The support layer consisted of activated alumina with a 0.04 μm pore structure and a thickness of 3 mm. The material was collected below the membrane and tested for purity and UV absorbance at a wavelength of 200 to 250 nm.

[0025] Example 2

[0026] Take 350 mL of 99% pure acetonitrile (containing 70 mg / kg of acrylonitrile and 800 mg / kg of propionitrile) and add it to a 500 mL distillation flask. Then, the solution is distilled with a packing height of 70 cm. The system temperature is controlled to be maintained at 83°C, the reflux ratio is 0.25, and reflux is performed for 60 minutes.

[0027] The top material was passed through a functional membrane assembly. The separation layer used polyacrylonitrile powder had a weight-average molecular weight of 300,000, a total thickness of 40 μm, and five layers. The support layer consisted of 2 mm thick activated alumina with a 0.05 μm pore structure. The material was collected below the membrane and tested for purity and UV absorbance at a wavelength of 200 to 250 nm.

[0028] Example 3

[0029] Take 350 mL of 99% pure acetonitrile (containing 60 mg / kg acrylonitrile and 900 mg / kg propionitrile) and add it to a 500 mL distillation flask. Then, the solution is distilled with a packing height of 60 cm. The system temperature is controlled to be maintained at 85°C, the reflux ratio is 0.4, and reflux is performed for 60 minutes.

[0030] The top material was passed through a functional membrane assembly. The separation layer used polyacrylonitrile powder had a weight-average molecular weight of 200,000, a total thickness of 60 μm, and four layers. The support layer consisted of activated alumina with a 0.03 μm pore structure and a thickness of 4 mm. The material was collected below the membrane and tested for purity and UV absorbance at a wavelength of 200-250 nm.

[0031] Example 4

[0032] Take 350 mL of 99% pure acetonitrile (containing 50 mg / kg acrylonitrile and 600 mg / kg propionitrile) and add it to a 500 mL distillation flask. Then, the solution is distilled with a packing height of 70 cm. The system temperature is controlled to be maintained at 86°C, the reflux ratio is 0.2, and reflux is performed for 60 minutes.

[0033] The top material was passed through a functional membrane assembly. The polyacrylonitrile powder used in the separation layer had a weight-average molecular weight of 350,000, a total thickness of 30 μm, and four layers. The support layer was 5 mm thick activated alumina with a 0.06 μm pore structure. The material was collected below the membrane and tested for purity and UV absorbance at a wavelength of 200 to 250 nm.

[0034] Example 5

[0035] Take 350 mL of 99% pure acetonitrile (containing 30 mg / kg acrylonitrile and 1000 mg / kg propionitrile) and add it to a 500 mL distillation flask. Then, the solution is distilled with a packing height of 75 cm. The system temperature is controlled to be maintained at 87°C, the reflux ratio is 0.3, and reflux is performed for 60 minutes.

[0036] The top material was passed through a functional membrane assembly. The separation layer used polyacrylonitrile powder had a weight-average molecular weight of 300,000, a total thickness of 60 μm, and five layers. The support layer was 2 mm thick activated alumina with a 0.05 μm pore structure. The material was collected below the membrane and tested for purity and UV absorbance at a wavelength of 200 to 250 nm.

[0037] Example 6

[0038] Take 350 mL of 99% pure acetonitrile (containing 100 mg / kg acrylonitrile and 500 mg / kg propionitrile) and add it to a 500 mL distillation flask. Then, the solution is distilled with a packing height of 65 cm. The system temperature is controlled to be maintained at 88°C, the reflux ratio is 0.4, and reflux is carried out for 60 minutes.

[0039] The top material was passed through a functional membrane assembly. The separation layer used polyacrylonitrile powder had a weight-average molecular weight of 250,000, a total thickness of 70 μm, and five layers. The support layer consisted of activated alumina with a 0.09 μm pore structure and a thickness of 4 mm. The material was collected below the membrane and tested for purity and UV absorbance at a wavelength of 200 to 250 nm.

[0040] Comparative Example 1

[0041] Take 350 mL of 99% pure acetonitrile (containing 300 mg / kg of acrylonitrile and 900 mg / kg of propionitrile) and add it to a 500 mL distillation flask. Then, the solution is distilled. The packing height is 60 cm, the packing diameter is 5 mm, the system temperature is controlled to be maintained at 83°C, the reflux ratio is 0.3, and reflux is carried out for 60 minutes. The material is collected from the top and its purity and ultraviolet absorption light value at a wavelength of 200 nm to 250 nm are tested.

[0042] Comparative Example 2

[0043] 350 mL of 99% pure acetonitrile (containing 50 mg / kg acrylonitrile and 300 mg / kg propionitrile) was passed through a functional membrane assembly. The polyacrylonitrile powder used in the separation layer had a weight-average molecular weight of 250,000, a total thickness of 60 μm, and five layers. The support layer consisted of activated alumina with a 0.05 μm pore structure and a thickness of 5 mm. The material was collected below the membrane and tested for purity and UV absorbance at wavelengths of 200 to 250 nm.

[0044] Comparative Example 3

[0045] Take 350 mL of 99% pure acetonitrile (containing 150 mg / kg acrylonitrile and 800 mg / kg propionitrile) and add it to a 500 mL distillation flask. Then, the solution is distilled with a packing height of 50 cm. The system temperature is controlled to be maintained at 87°C, the reflux ratio is 0.4, and reflux is performed for 60 minutes.

[0046] The top material was passed through a functional membrane assembly. The separation layer used polyacrylonitrile powder had a weight-average molecular weight of 90,000, a total thickness of 40 μm, and five layers. The support layer consisted of activated alumina with a 0.2 μm pore structure and a thickness of 2 mm. The material was collected below the membrane and tested for purity and UV absorbance at a wavelength of 200 to 250 nm.

[0047] Table 1 Purity and yield of acetonitrile obtained by different treatment methods

[0048] sample Acetonitrile purity, % Acetonitrile yield, % Example 1 99.991 91 Example 2 99.992 90 Example 3 99.991 92 Example 4 99.993 91 Example 5 99.992 91 Example 6 99.992 92 Comparative Example 1 99.100 86 Comparative Example 2 99.300 87 Comparative Example 3 99.970 89

[0049] Table 2 Ultraviolet absorption light values ​​of acetonitrile obtained by different treatment methods at 200nm~250nm

[0050]

[0051]

[0052] Note: The membrane in Comparative Example 3 was damaged to a certain extent.

Claims

1. A method for preparing high-purity acetonitrile, characterized in that: The following steps are involved: (1) placing crude acetonitrile in a distillation flask for distillation, controlling the system temperature to maintain at 80-90° C., with propionitrile remaining at the bottom of the distillation flask, and acrylonitrile and acetonitrile distilled from the top; the purity of the crude acetonitrile is ≥99%; the acrylonitrile content in the crude acetonitrile is ≤100 mg / kg, the propionitrile content is ≤1000 mg / kg, and the density is 0.780-0.785 g / cm 3 ; (2) passing the evaporated mixture through a functional membrane assembly, and then collecting acetonitrile; The functional membrane component is composed of a polyacrylonitrile membrane and activated alumina; the functional membrane component includes a support layer and a separation layer, and the separation layer is located on the support layer; the support layer is activated alumina with a pore structure of 0.01 to 0.2 μm, and the thickness of the support layer is 0.5 to 5 mm; the separation layer is a polyacrylonitrile membrane, the weight-average molecular weight of the polyacrylonitrile powder is 150,000 to 400,000, the total thickness of the separation layer is 10 to 100 μm, and the total number of separation layers is 4 to 8.

2. The method for preparing high-purity acetonitrile according to claim 1, wherein: The filling material used in the distillation column is spring-type glass with a diameter of 2 mm and a filling height of 70-90 cm.

3. The method for preparing high-purity acetonitrile according to claim 1, wherein: During distillation, the system temperature is controlled to be maintained at 82-92°C, and the distillation reflux ratio is 0.2-0.

4.

4. The method for preparing high-purity acetonitrile according to claim 1, wherein: The supporting layer is activated alumina with a pore structure of 0.05 μm, and the thickness of the supporting layer is 1 to 3 mm.

5. The method for preparing high-purity acetonitrile according to claim 1, wherein: The separation layer is a polyacrylonitrile membrane, the weight average molecular weight of the polyacrylonitrile powder is 200,000-300,000, and the total number of separation layers is 5-6.

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