Method for recovering acetonitrile from mixed waste liquid containing acetonitrile, triethylamine and water

Abstract

The invention provides a method for recovering acetonitrile from a mixed waste liquid containing acetonitrile, triethylamine and water, which comprises the following steps: (1) carrying out reduced pressure distillation on the mixed waste liquid containing acetonitrile, triethylamine and water to obtain an acetonitrile-triethylamine-water mixed liquid; (2) mixing an acid with the acetonitrile-triethylamine-water mixed solution obtained in the step (1), and rectifying to obtain an acetonitrile-water mixed solution; and (3) carrying out membrane separation on the acetonitrile-water mixed solution obtained in the step (2) to obtain an acetonitrile product. Other organic matters do not need to be added in the process flow for separating acetonitrile, triethylamine and water, so that the introduction of new organic matters in the system can be effectively avoided, the recycling of acetonitrile can be realized, and compared with a multi-rectification system or a rectification extraction system, the energy consumption is lower, and the operability is stronger.

Description

Technical Field

[0001] The present invention relates to the technical field of organic pharmaceutical waste liquid treatment, and particularly to a method for recovering acetonitrile from a mixed waste liquid containing acetonitrile, triethylamine and water. Background Art

[0002] Acetonitrile is an important chemical raw material, a colorless transparent liquid, extremely volatile, with a special smell similar to ether. During the production of organic drugs, an acetonitrile-triethylamine-water mixed waste liquid is generated. This waste liquid is difficult to treat and easily causes waste of acetonitrile resources.

[0003] Due to the existence of multiple azeotropes in the acetonitrile-triethylamine-water mixed waste liquid system, it is difficult to recover and treat it by ordinary distillation methods.

[0004] CN115850091A discloses a method for separating acetonitrile, triethylamine and water by azeotropic distillation. The specific process flow is as follows: Step A: Feed the waste liquid containing acetonitrile, triethylamine and water into the azeotropic tower T1. After azeotropic distillation, a ternary homogeneous azeotrope of acetonitrile-triethylamine-water is obtained at the top of the azeotropic tower T1, and a mixture of acetonitrile and water is obtained at the bottom of the azeotropic tower T1. The bottom mixture of the azeotropic tower T1 is dehydrated through a NaA molecular sieve membrane to obtain a qualified acetonitrile product; Step B: The acetonitrile-triethylamine-water ternary azeotrope is fed into the azeotropic tower T2 for further separation. Using n-hexane as the azeotropic agent, after azeotropic distillation, a ternary heterogeneous azeotrope of acetonitrile-water-n-hexane is obtained at the top of the azeotropic tower T2. After the overhead material of the azeotropic tower T2 is stratified by a phase separator, the oil phase containing n-hexane is returned to the azeotropic tower T2 as the azeotropic agent and reflux liquid for continued use, and the aqueous phase is dehydrated through a NaA molecular sieve membrane to obtain an acetonitrile product with a purity of more than 99%, and a qualified triethylamine product is obtained at the bottom of the azeotropic tower T2.

[0005] CN113461544B also discloses a method for separating a triethylamine and acetonitrile mixture by azeotropic distillation using n-hexane as the azeotropic agent.

[0006] However, in the above methods, cyclohexane needs to be added as the azeotropic agent, which will lead to the introduction of organic substances such as n-hexane into the entire pharmaceutical project system. The trace or trace residues caused by the introduction of new organic substances may affect the subsequent drugs.

[0007] At present, there is no suitable method for treating the acetonitrile-triethylamine-water mixed waste liquid without introducing organic substances. Therefore, it is necessary to develop a new process to recover the acetonitrile resources in the acetonitrile-triethylamine-water mixed waste liquid. Summary of the Invention

[0008] In view of the problems existing in the prior art, the present invention provides a method for recovering acetonitrile from a mixed waste liquid containing acetonitrile, triethylamine and water. By vacuum distillation, high-boiling organic substances and salts in the original mixed waste liquid containing acetonitrile, triethylamine and water are removed. Then, after reacting the acid with triethylamine in the acetonitrile-triethylamine-water mixture and rectifying, the finally obtained acetonitrile-water mixture is subjected to membrane separation, that is, the acetonitrile product is recovered. No new organic substances need to be added throughout the process, and no new organic substances are introduced into the overall pharmaceutical production project. There is no need for multiple rectification, extractive rectification or azeotropic rectification, with low energy consumption and high-efficiency recovery of acetonitrile achieved.

[0009] To achieve this purpose, the present invention adopts the following technical solutions:

[0010] The present invention provides a method for recovering acetonitrile from a mixed waste liquid containing acetonitrile, triethylamine and water, and the method comprises the following steps:

[0011] (1) The mixed waste liquid containing acetonitrile, triethylamine and water is subjected to vacuum distillation to obtain an acetonitrile-triethylamine-water mixture;

[0012] (2) A mixed acid is mixed with the acetonitrile-triethylamine-water mixture obtained in step (1) and subjected to rectification to obtain an acetonitrile-water mixture;

[0013] (3) The acetonitrile-water mixture obtained in step (2) is subjected to membrane separation to obtain an acetonitrile product.

[0014] The present invention first adopts vacuum distillation, and an acetonitrile-triethylamine-water mixture is obtained at the upper part of the vacuum distillation, thereby removing high-boiling organic substances and salts in the original mixed waste liquid; subsequently, the method of acid reaction and rectification is adopted to remove triethylamine, and the finally obtained acetonitrile-water mixture can be recovered to obtain an acetonitrile product through membrane separation.

[0015] It is worth noting that the mixed waste liquid of acetonitrile, triethylamine and water in the present invention comes from an organic pharmaceutical production project. Those skilled in the art understand that in the process of organic pharmaceutical production, the substances used in the whole project need to be strictly controlled, especially the introduction of organic substances, which is a basic requirement in pharmaceutical production. In the present invention, there is an azeotrope among acetonitrile, triethylamine and water, and it is difficult to separate them by ordinary rectification. Currently, generally, methods such as extractive rectification or azeotropic rectification separation are adopted. However, these methods all need to introduce new organic substances. In the present invention, it is desired to recover acetonitrile in the mixed waste liquid without adding extra organic substances. After restricting the addition of organic substances, the recovery of acetonitrile becomes more difficult. Based on this, the present invention creatively develops a technological process of vacuum distillation - acid addition rectification - membrane separation. These three steps interact with each other to achieve high-efficiency recovery of acetonitrile, and the recovered acetonitrile has a low water content and can be preferably recycled to the original pharmaceutical production project.

[0016] Preferably, the content of acetonitrile in the mixed waste liquid containing acetonitrile, triethylamine and water in step (1) ranges from 30 to 40 wt%, for example, it can be 30 wt%, 32 wt%, 33 wt%, 34 wt%, 35 wt%, 36 wt%, 37 wt%, 38 wt%, 39 wt% or 40 wt%, etc., but is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0017] Preferably, the content of triethylamine in the mixed waste liquid containing acetonitrile, triethylamine and water ranges from 3 to 5 wt%, for example, it can be 3 wt%, 3.3 wt%, 3.5 wt%, 3.7 wt%, 3.9 wt%, 4.2 wt%, 4.4 wt%, 4.6 wt%, 4.8 wt% or 5 wt%, etc., but is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0018] Preferably, the content of water in the mixed waste liquid containing acetonitrile, triethylamine and water ranges from 40 to 55 wt%, for example, it can be 40 wt%, 42 wt%, 44 wt%, 45 wt%, 47 wt%, 49 wt%, 50 wt%, 52 wt%, 54 wt% or 55 wt%, etc., but is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0019] It should be noted that from the composition of the above-mentioned mixed waste liquid of acetonitrile, triethylamine and water, it can be seen that the content of acetonitrile in the mixed waste liquid targeted by the present invention is high, while the content of triethylamine is low. Therefore, the method of acid + rectification is selected for removal, which can effectively avoid the large loss of acetonitrile caused by azeotropic rectification.

[0020] Preferably, the mixed waste liquid containing acetonitrile, triethylamine and water in step (1) further contains salt.

[0021] Preferably, the salt includes any one or a combination of at least two of sodium sulfite, triethylamine trimethylbenzenesulfonate or sodium sulfate. Typical but non-limiting combinations are combinations of sodium sulfite and triethylamine trimethylbenzenesulfonate, combinations of sodium sulfate and triethylamine trimethylbenzenesulfonate, and combinations of sodium sulfite and sodium sulfate.

[0022] Preferably, the content of salt in the mixed waste liquid containing acetonitrile, triethylamine and water ranges from 5 to 10%, for example, it can be 5%, 5.6%, 6.2%, 6.7%, 7.3%, 7.8%, 8.4%, 8.9%, 9.5% or 10%, etc., but is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0023] Preferably, the mixed waste liquid containing acetonitrile, triethylamine and water further contains high-boiling organic substances with a boiling point ≥ 130 °C. For example, it can be 130 °C, 131 °C, 132 °C, 133 °C, 135 °C, 140 °C, 145 °C or 150 °C, etc., but is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0024] Preferably, the high-boiling organic substances include project materials and piperidinol.

[0025] The high-boiling organic substances in the present invention are prone to entrainment of foams during subsequent rectification. Therefore, the high-boiling organic substances and salts are first removed by vacuum distillation to provide a material basis for the subsequent rectification and separation of triethylamine.

[0026] It should be noted that the project materials in the present invention refer to the materials in the production of organic drugs, which will not be elaborated here.

[0027] The mixed waste liquid containing acetonitrile, triethylamine and water in the present invention is derived from the mixed waste liquid generated during the production of the product with the following molecular formula.

[0028]

[0029] Preferably, the temperature range of the vacuum distillation in step (1) is 55 - 65 °C. For example, it can be 55 °C, 57 °C, 58 °C, 59 °C, 60 °C, 61 °C, 62 °C, 63 °C, 64 °C or 65 °C, etc., but is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0030] Preferably, the pressure range of the vacuum distillation is ≤ -0.80 MPa. For example, it can be -0.80 MPa, -0.82 MPa, -0.85 MPa, -0.90 MPa, -0.95 MPa, -1.0 MPa, -1.05 MPa or -1.1 MPa, etc., but is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0031] Preferably, the acid in step (2) includes sulfuric acid.

[0032] The acid selected in the present invention is sulfuric acid, which can react with triethylamine to form triethylamine sulfate, so that it will no longer form an azeotrope with the mixed liquid of acetonitrile and water during subsequent rectification, realizing the separation of triethylamine from acetonitrile and water. At the same time, in this step, acetonitrile and water are obtained as an acetonitrile-water mixed liquid in the form of an azeotropic composition, reducing the pressure for subsequent membrane separation.

[0033] Preferably, the concentration of the acid is 25-35 wt%, for example, it can be 25 wt%, 27 wt%, 28 wt%, 29 wt%, 30 wt%, 31 wt%, 32 wt%, 33 wt%, 34 wt% or 35 wt%, etc., but not limited to the listed values, and other unlisted values within this range are equally applicable.

[0034] Preferably, the pH of the system after mixing the mixed acid and the acetonitrile-triethylamine-water mixture in step (1) is 2.5-3.0, for example, it can be 2.5, 2.6, 2.7, 2.8, 2.9 or 3.0, etc., but not limited to the listed values, and other unlisted values within this range are equally applicable.

[0035] It should be noted that the selection of this pH value is very crucial. Triethylamine sulfate is prone to gradual overflow of triethylamine after heating in a weakly acidic, neutral or alkaline environment, that is, triethylamine sulfate is prone to decomposition. Therefore, the present invention strictly controls the pH to be 2.5-3.0, which can ensure the effective removal of triethylamine in the subsequent rectification.

[0036] Preferably, the bottom temperature of the rectification in step (2) is ≤100 °C, for example, it can be 100 °C, 99 °C, 98 °C, 97 °C, 95 °C, 90 °C, 89 °C, 85 °C or 80 °C, etc., but not limited to the listed values, and other unlisted values within this range are equally applicable.

[0037] Preferably, the top temperature of the rectification is 73-83 °C, for example, it can be 73 °C, 75 °C, 76 °C, 77 °C, 78 °C, 79 °C, 80 °C, 81 °C, 82 °C or 83 °C, etc., but not limited to the listed values, and other unlisted values within this range are equally applicable.

[0038] Preferably, the pressure of the rectification is atmospheric pressure.

[0039] Preferably, the rectification obtains an acetonitrile-water mixture at ≤80 °C, for example, it can be 80 °C, 79 °C, 78 °C, 75 °C or 70 °C, etc., but not limited to the listed values, and other unlisted values within this range are equally applicable.

[0040] Preferably, the temperature of the membrane separation in step (3) is 110-130 °C, for example, it can be 110 °C, 113 °C, 115 °C, 117 °C, 119 °C, 122 °C, 124 °C, 126 °C, 128 °C or 130 °C, etc., but not limited to the listed values, and other unlisted values within this range are equally applicable.

[0041] Preferably, the pressure of the membrane separation is 200-230 kPa. For example, it can be 200 kPa, 204 kPa, 207 kPa, 210 kPa, 214 kPa, 217 kPa, 220 kPa, 224 kPa, 227 kPa or 230 kPa, etc., but is not limited to the listed values. Other unlisted values within this range are equally applicable.

[0042] Preferably, the inorganic gasification permeation membrane for the membrane separation in step (3).

[0043] Preferably, the yield of the acetonitrile product in step (3) is above 75%. For example, it can be 75%, 75.6%, 76.2%, 76.7%, 77.3%, 77.8%, 78.4%, 78.9%, 79.5% or 80%, etc., but is not limited to the listed values. Other unlisted values within this range are equally applicable.

[0044] Preferably, the purity of the acetonitrile product is ≥99.5%. For example, it can be 99.5%, 99.6%, 99.6%, 99.7%, 99.7%, 99.8%, 99.8%, 99.9%, 99.9% or 99.9%, etc., but is not limited to the listed values. Other unlisted values within this range are equally applicable.

[0045] Preferably, the water content in the acetonitrile product is ≤0.2 wt%. For example, it can be 0.2 wt%, 0.19 wt%, 0.18 wt%, 0.17 wt%, 0.16 wt%, 0.15 wt%, 0.14 wt%, 0.13 wt%, 0.10 wt%, 0.08 wt%, 0.05 wt% or 0.04 wt%, etc., but is not limited to the listed values. Other unlisted values within this range are equally applicable.

[0046] As a preferred technical solution of the present invention, the method includes the following steps:

[0047] (1) The mixed waste liquid containing acetonitrile, triethylamine and water is subjected to vacuum distillation under the conditions of ≤ -0.80 MPa and 55-65 °C. The content range of acetonitrile in the mixed waste liquid containing acetonitrile, triethylamine and water is 30-40 wt, the content range of triethylamine is 3-5 wt%, the content range of water is 40-55 wt%, the content range of salt is 5-10%, and the content of high-boiling organic substances with a boiling point ≥130 °C is 2-4 wt%, to obtain an acetonitrile-triethylamine-water mixed liquid;

[0048] (2) Mix sulfuric acid and the acetonitrile-triethylamine-water mixed liquid obtained in step (1) to make the pH 2.5-3.0, and carry out rectification at 73-83 °C and atmospheric pressure. The bottom temperature of the rectification is ≤100 °C to obtain an acetonitrile-water mixed liquid with a distillate ≤80 °C;

[0049] (3) The acetonitrile-water mixture described in step (2) is subjected to membrane separation under the conditions of 110-130 °C and 200-230 kPa to obtain an acetonitrile product with a water content ≤ 0.2 wt% and a purity ≥ 99.5%.

[0050] Compared with the prior art, the present invention has at least the following beneficial effects:

[0051] (1) The method for recovering acetonitrile from a mixed waste liquid containing acetonitrile, triethylamine and water provided by the present invention does not require the addition of other organic substances, and can effectively avoid the introduction of new organic substances into the system;

[0052] (2) The method for recovering acetonitrile from a mixed waste liquid containing acetonitrile, triethylamine and water provided by the present invention does not require a multi-distillation process, and has lower energy consumption;

[0053] (3) The method for recovering acetonitrile from a mixed waste liquid containing acetonitrile, triethylamine and water provided by the present invention can realize the recycling of acetonitrile, wherein the recovery rate of acetonitrile is above 70%, preferably above 80%, the purity ≥ 99.5%, preferably ≥ 99.8%, the content of triethylamine ≤ 0.05 wt%, the water content ≤ 0.2 wt%, and even the water content ≤ 0.02 wt%, which is more conducive to recycling and using in the drug preparation project. Description of the Drawings

[0054] Figure 1 is a flow chart of the method for recovering acetonitrile from a mixed waste liquid containing acetonitrile, triethylamine and water provided by the specific embodiment of the present invention. Specific Embodiment

[0055] The technical solution of the present invention will be further described below in conjunction with the drawings and through specific embodiments.

[0056] The present invention will be further described in detail below. However, the following examples are only simple examples of the present invention, and do not represent or limit the scope of the protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0057] As a specific embodiment of the present invention, a method for recovering acetonitrile from a mixed waste liquid containing acetonitrile, triethylamine and water is provided, and the flow chart is as Figure 1 shown, and the method includes the following steps:

[0058] (1) The mixed waste liquid containing acetonitrile, triethylamine and water is subjected to vacuum distillation, and an acetonitrile-triethylamine-water mixture is obtained at the top, and high-boiling organic impurities are obtained at the bottom. The high-boiling organic impurities enter the waste treatment process;

[0059] (2) Mix sulfuric acid with the acetonitrile - triethylamine - water mixture described in step (1) to make the pH 2.5 - 3.0, and then carry out rectification. Draw out the acetonitrile - water mixture with a distillate fraction ≤ 80°C, and obtain the residue of triethylamine sulfate in the bottom of the column. The residue of triethylamine sulfate is processed separately;

[0060] (3) The acetonitrile - water mixture described in step (2) is subjected to membrane separation to obtain acetonitrile product and water.

[0061] Example 1

[0062] This example provides a method for recovering acetonitrile from a mixed waste liquid containing acetonitrile, triethylamine and water. The method includes the following steps:

[0063] (1) The mixed waste liquid containing acetonitrile, triethylamine and water (acetonitrile content is 35 wt%, triethylamine content is 4 wt%, water content is 50 wt%, salt content is 6%, and the content of high - boiling organic substances with a boiling point ≥ 130°C is 3 wt%) is subjected to vacuum distillation under the conditions of - 0.90 MPa and 60°C. An acetonitrile - triethylamine - water mixture is obtained at the top, and high - boiling organic impurities are obtained at the bottom. The high - boiling organic impurities enter the waste treatment process;

[0064] (2) Mix sulfuric acid with a concentration of 30 wt% and the acetonitrile - triethylamine - water mixture described in step (1) to make the pH 2.8, and then carry out rectification at 80°C and under normal pressure (1 atm.). The temperature at the bottom of the rectification column is 90°C. Draw out the acetonitrile - water mixture with a distillate fraction ≤ 80°C, and obtain the residue of triethylamine sulfate in the bottom of the column. The residue of triethylamine sulfate is processed separately;

[0065] (3) The acetonitrile - water mixture described in step (2) is subjected to membrane separation under the conditions of 120°C and 220 kPa (the membrane is a Na - ion type inorganic vapor permeation membrane, Jiangsu Jiutian High - Tech Co., Ltd.) to obtain acetonitrile product.

[0066] Example 2

[0067] This example provides a method for recovering acetonitrile from a mixed waste liquid containing acetonitrile, triethylamine and water. The method includes the following steps:

[0068] (1) The mixed waste liquid containing acetonitrile, triethylamine and water (acetonitrile content is 40 wt%, triethylamine content is 3 wt%, water content is 45 wt%, salt content is 8%, and the content of high - boiling organic substances with a boiling point ≥ 130°C is 2 wt%) is subjected to vacuum distillation under the conditions of - 0.85 MPa and 65°C. An acetonitrile - triethylamine - water mixture is obtained at the top, and high - boiling organic impurities are obtained at the bottom. The high - boiling organic impurities enter the waste treatment process;

[0069] (2) Mix sulfuric acid with a concentration of 35 wt% and the acetonitrile - triethylamine - water mixture described in step (1) to make the pH 3.0, and then perform rectification at 83°C and atmospheric pressure (1 atm.). The bottom temperature of the rectification column is 95°C. Draw out the acetonitrile - water mixture with a distillate temperature ≤ 80°C, and obtain the residue of triethylamine sulfate in the bottom of the column. The residue of triethylamine sulfate is processed separately;

[0070] (3) The acetonitrile - water mixture described in step (2) is subjected to membrane separation under the conditions of 130°C and 230 kPa (the membrane is a Na - ion type inorganic vapor permeation membrane, Jiangsu Jiutian High - Tech Co., Ltd.) to obtain acetonitrile products.

[0071] Example 3

[0072] This example provides a method for recovering acetonitrile from a mixed waste liquid containing acetonitrile, triethylamine, and water. The method includes the following steps:

[0073] (1) The mixed waste liquid containing acetonitrile, triethylamine, and water (acetonitrile content is 30 wt, triethylamine content is 5 wt%, water content is 55 wt%, salt content is 5%, and the content of high - boiling organic substances with a boiling point ≥ 130°C is 4 wt%) is subjected to vacuum distillation under the conditions of - 1.0 MPa and 55°C. An acetonitrile - triethylamine - water mixture is obtained at the top, and high - boiling organic impurities are obtained at the bottom. The high - boiling organic impurities enter the waste treatment process;

[0074] (2) Mix sulfuric acid with a concentration of 25 wt% and the acetonitrile - triethylamine - water mixture described in step (1) to make the pH 2.5, and then perform rectification at 73°C and atmospheric pressure (1 atm.). The bottom temperature of the rectification column is 85°C. Draw out the acetonitrile - water mixture with a distillate temperature ≤ 80°C, and obtain the residue of triethylamine sulfate in the bottom of the column. The residue of triethylamine sulfate is processed separately;

[0075] (3) The acetonitrile - water mixture described in step (2) is subjected to membrane separation under the conditions of 110°C and 200 kPa (the membrane is a Na - ion type inorganic vapor permeation membrane, Jiangsu Jiutian High - Tech Co., Ltd.) to obtain acetonitrile products.

[0076] Example 4

[0077] This example provides a method for recovering acetonitrile from a mixed waste liquid containing acetonitrile, triethylamine, and water. Except that the pH is 4.0 in step (2), the rest are the same as in Example 1 and will not be elaborated here. Example 5

[0078] This example provides a method for recovering acetonitrile from a mixed waste liquid containing acetonitrile, triethylamine, and water. Except that the pH is 2.0 in step (2), the rest are the same as in Example 1 and will not be elaborated here. Example 6

[0079] This embodiment provides a method for recovering acetonitrile from a mixed waste liquid containing acetonitrile, triethylamine and water. Except that sulfuric acid is replaced by nitric acid in step (2), the rest are the same as those in Embodiment 1 and will not be elaborated here. Comparative Example 1

[0080] This comparative example provides a method for recovering acetonitrile from a mixed waste liquid containing acetonitrile, triethylamine and water. Except that step (1) is not carried out, the rest are the same as those in Embodiment 1 and will not be elaborated here.

[0081] Comparative Example 2

[0082] This comparative example provides a method for recovering acetonitrile from a mixed waste liquid containing acetonitrile, triethylamine and water. Except that membrane separation is not used in step (3) and extractive distillation separation in Example 2 of CN103601653A is used instead, the rest are the same as those in Embodiment 1 and will not be elaborated here.

[0083] Testing method: The Karl Fischer method is used to test the water content in the acetonitrile product, the gas chromatography method is used to test the triethylamine content in the acetonitrile product, and the gas chromatography is used to test the purity of acetonitrile. At the same time, the recovery rate of acetonitrile is calculated.

[0084] The test results of the above examples and comparative examples are shown in Table 1.

[0085] Table 1

[0086]

[0087] It can be seen from Table 1 as follows:

[0088] (1) From Examples 1 to 3, it can be seen that the method for recovering acetonitrile from a mixed waste liquid containing acetonitrile, triethylamine and water provided by the present invention can achieve efficient recovery of acetonitrile without introducing new organic substances. The purity of the acetonitrile product is as high as 99.8 wt%, the content of triethylamine therein is ≤ 0.04 wt%, the water content is less than or equal to 0.02 wt%, and the recovery rate of acetonitrile is above 77%;

[0089] (2) From Examples 1 and 4 to 5, it can be seen that after adding sulfuric acid in Example 1, the pH of the system is adjusted to 2.8. Compared with adjusting the pH to 4.0 and 2.0 in Examples 4 to 5 respectively, in Example 4, due to the too high pH, the fixation of triethylamine is unstable during the rectification process, and the content of triethylamine in the finished acetonitrile increases to 0.3 wt%, and the purity of the acetonitrile product decreases. In Example 5, due to excessive addition of sulfuric acid, the corrosion resistance of the equipment is significantly increased, and the waste of sulfuric acid is serious. At the same time, the purity and recovery rate of the acetonitrile product do not increase further;

[0090] (3) It can be seen from the comprehensive comparison of Example 1 and Example 6 that in Example 1, sulfuric acid is used. Compared with nitric acid used in Example 6, nitric acid has too strong oxidizing property and high danger. At the same time, the fixing effect of nitric acid on triethylamine is lower than that of sulfuric acid, resulting in an increase in the content of triethylamine in the final product and a decrease in the yield of acetonitrile product. This shows that by choosing sulfuric acid as the acid for adjusting acidity in the present invention, the purity and yield of acetonitrile product can be further improved;

[0091] (4) It can be seen from the comprehensive comparison of Example 1 and Comparative Example 1 that in Comparative Example 1, the reduced-pressure distillation in step (1) is not carried out, resulting in a significant decrease in the purity of the acetonitrile product and the yield dropping to only 75%. This shows that by choosing to use reduced-pressure distillation first in the present invention, the purity and yield of the acetonitrile product can be improved;

[0092] (5) It can be seen from the comprehensive comparison of Example 1 and Comparative Example 2 that the scheme of using extractive distillation to separate water and acetonitrile in Comparative Example 2 not only reduces the purity of the acetonitrile product, there is a trace amount of extractant remaining in the acetonitrile product, and the yield is only 69%, but also organic substances such as ethylene glycol and 1-ethyl-3-methylimidazolium chloride are introduced during the extraction process, which has a greater negative impact on the entire pharmaceutical project. This shows that by comprehensively using the method of reduced-pressure distillation - acid-adjusting rectification - membrane separation in the present invention, not only no organic substances need to be introduced, but also the purity and recovery rate of the acetonitrile product are high.

[0093] The present invention uses the above-mentioned examples to illustrate the detailed structural features of the present invention. However, the present invention is not limited to the above-mentioned detailed structural features, that is, it does not mean that the present invention must rely on the above-mentioned detailed structural features to be implemented. Those skilled in the art should understand that any improvement to the present invention, the equivalent replacement of the components selected by the present invention, the addition of auxiliary components, and the selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for recovering acetonitrile from a mixed waste liquid containing acetonitrile, triethylamine and water, characterized in that, The method includes the following steps: (1) The mixed waste liquid containing acetonitrile, triethylamine and water is subjected to vacuum distillation to obtain an acetonitrile-triethylamine-water mixture; (2) Mix the mixed acid with the acetonitrile-triethylamine-water mixture obtained in step (1) and subject it to rectification to obtain an acetonitrile-water mixture; (3) The acetonitrile-water mixture obtained in step (2) is subjected to membrane separation to obtain an acetonitrile product.

2. The method according to claim 1, wherein In step (1), the content of acetonitrile in the mixed waste liquid containing acetonitrile, triethylamine and water ranges from 30 to 40 wt%; Preferably, the content of triethylamine in the mixed waste liquid containing acetonitrile, triethylamine and water ranges from 3 to 5 wt%; Preferably, the content of water in the mixed waste liquid containing acetonitrile, triethylamine and water ranges from 40 to 55 wt%.

3. The method according to claim 1 or 2, characterized in that The mixed waste liquid containing acetonitrile, triethylamine and water in step (1) also contains salts; Preferably, the salt includes any one or a combination of at least two of sodium sulfite, triethylamine trimethylbenzenesulfonate or sodium sulfate; Preferably, the salt content in the mixed waste liquid containing acetonitrile, triethylamine and water ranges from 5 to 10%; Preferably, the mixed waste liquid containing acetonitrile, triethylamine and water also contains high-boiling organic substances with a boiling point ≥ 130°C; Preferably, the high-boiling organic substances include project materials and piperidinol.

4. The method according to any one of claims 1 to 3, characterized in that, In step (1), the temperature range of the vacuum distillation is 55 to 65°C; Preferably, the pressure range of the vacuum distillation is ≤ -0.80 MPa.

5. The method according to any one of claims 1 to 4, characterized in that, In step (2), the acid includes sulfuric acid; Preferably, the concentration of the acid is 25 to 35 wt%.

6. The method according to any one of claims 1 to 5, characterized in that, The pH of the system after mixing the mixed acid with the acetonitrile-triethylamine-water mixture obtained in step (1) is 2.5 to 3.

0.

7. The method according to any one of claims 1 to 6, characterized in that, In step (2), the bottom temperature of the rectification is ≤ 100°C; Preferably, the top temperature of the rectification is 73 to 83°C; Preferably, the pressure of the rectification is atmospheric pressure; Preferably, the acetonitrile-water mixture obtained by rectification has a temperature ≤ 80°C.

8. The method according to any one of claims 1 to 7, characterized in that, In step (3), the temperature of the membrane separation is 110 to 130°C; Preferably, the pressure of the membrane separation is 200 to 230 kPa.

9. The method according to any one of claims 1 to 8, characterized in that, In step (3), the inorganic gasification permeable membrane for membrane separation.

10. The method according to any one of claims 1 to 9, characterized in that, In step (3), the yield of the acetonitrile product is more than 75%; Preferably, the purity of the acetonitrile product ≥ 99.5%; Preferably, the water content in the acetonitrile product ≤ 0.2 wt%.

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