A method and device for separating and recovering acetonitrile waste liquid

Abstract

The present application relates to acetonitrile recovery field, in particular to a kind of acetonitrile waste liquid separation and recovery method and device. The method includes steps: the pH of the acetonitrile waste liquid is adjusted to 6 8; the acetonitrile waste liquid having a pH adjusted to 6 8 is sent to the first distillation tower, and rectification obtains one-level separation acetonitrile; the one-level separation acetonitrile is sent to a gas-liquid separator, and secondary separation acetonitrile is obtained after separation; the secondary separation acetonitrile is sent to a permeation vaporization membrane assembly, and tertiary separation acetonitrile is obtained after separation; the tertiary separation acetonitrile is sent to the second distillation tower, and rectification obtains acetonitrile. The present application removes the water in acetonitrile-water azeotrope by a gas-liquid separator and a permeation vaporization membrane assembly, and two kinds of equipment have low working energy consumption, and water content can be reduced to less than 0.1% after being used in combination; in addition, only two rectifications need to be carried out before and after, and the equipment used is less than that of existing separation method, and structure is simple and compact, and whole process does not need to introduce new substances (such as extractants, adsorbents, etc.), effectively reducing recovery cost.

Description

Technical Field

[0001] The present invention relates to the field of acetonitrile recovery, and in particular to a method and device for separating and recovering acetonitrile waste liquid. Background Art

[0002] Liquid chromatography solvents are divided into mobile phase solvents and blank solvents. Selected solvents generally should have low viscosity, high purity, good chemical stability, appropriate polarity and good selectivity for the sample, strong detector compatibility, and low toxicity. Mobile phase solvents are generally binary or polybasic solvents, allowing for flexible adjustment of mobile phase polarity and selectivity, thereby improving separation and adjusting peak elution time.

[0003] Acetonitrile is a commonly used solvent in liquid chromatography. After use, the resulting acetonitrile waste liquid generally contains a small amount of acetonitrile and a large amount of water. Acetonitrile forms an azeotrope with water, making it difficult to separate. Current methods for recovering high-purity acetonitrile from acetonitrile waste liquid have the problems of complex equipment and high cost. Summary of the Invention

[0004] The main purpose of this application is to provide a method for separating and recovering acetonitrile waste liquid, aiming to solve the problems of complex equipment and high cost in the existing method for recovering high-purity acetonitrile from acetonitrile waste liquid.

[0005] In order to solve the above technical problems, the present application provides a method for separating and recovering acetonitrile waste liquid, comprising the following steps:

[0006] The pH of the acetonitrile waste liquid is adjusted to 6-8;

[0007] The acetonitrile waste liquid with a pH adjusted to 6-8 is sent to the first distillation tower for distillation to obtain primary separated acetonitrile;

[0008] The first-stage separated acetonitrile is sent to a gas-liquid separator to obtain the second-stage separated acetonitrile after separation;

[0009] sending the secondary separated acetonitrile to a pervaporation membrane assembly to obtain tertiary separated acetonitrile after separation;

[0010] The acetonitrile separated in the three stages is sent to a second distillation tower for distillation to obtain acetonitrile.

[0011] Optionally, the acetonitrile waste liquid is a solvent used for liquid chromatography analysis, and its components include acetonitrile and water.

[0012] Optionally, before adjusting the pH of the acetonitrile waste liquid to 6-8, the method further comprises the step of preheating the acetonitrile waste liquid, wherein the preheating heat source is the hot water extracted from the bottom of the first distillation tower.

[0013] Optionally, the pressure of the first distillation tower is 130-170 KPa, the bottom temperature of the first distillation tower is 120° C.-130° C., and the top temperature of the first distillation tower is 100° C.-107° C.

[0014] Optionally, the pressure of the second distillation tower is atmospheric pressure, and the temperature of the bottom and top of the second distillation tower is 75°C-80°C.

[0015] Optionally, the pressure of the gas-liquid separator is normal pressure and the temperature is 85°C-95°C.

[0016] Optionally, the pressure of the pervaporation membrane assembly is 70Kpa-95Kpa, and the temperature is 100°C-110°C.

[0017] Based on the same inventive concept, the present application also provides an acetonitrile waste liquid separation and recovery device, comprising a pH adjustment tank, a first distillation tower, a gas-liquid separator, a pervaporation membrane assembly, and a second distillation tower connected in sequence;

[0018] The acetonitrile waste liquid separation and recovery device is used to implement the acetonitrile waste liquid separation and recovery method according to any one of claims 1 to 7.

[0019] Optionally, the pH adjustment tank is also connected to a mobile phase outlet of a liquid chromatograph.

[0020] Optionally, both the first distillation tower and the second distillation tower are packed towers.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The separation and recovery method of the present application is mainly aimed at acetonitrile solvent waste liquid from liquid chromatography. After the acetonitrile waste liquid is distilled in a first distillation tower, acetonitrile gas is extracted from the tower top and then separated by a gas-liquid separator. The liquid is retained, and the acetonitrile gas is allowed to pass through. The acetonitrile is then sent through a pervaporation membrane assembly. Smaller water molecules pass through the pervaporation membrane assembly, while larger acetonitrile molecules are retained. The acetonitrile is then sent to a second distillation tower for a second distillation to remove a small amount of impurities (such as methanol or ethanol, etc.), and acetonitrile with a purity of 99.9% is obtained in the bottom of the second distillation tower.

[0023] The present application removes water from the acetonitrile-water azeotrope through a gas-liquid separator and a pervaporation membrane assembly. The two devices have low operating energy consumption and can reduce the water content to below 0.1% when used in combination. In addition, only two distillations are required before and after, which requires less equipment than existing separation methods, has a simple and compact structure, and does not require the introduction of new substances (such as extractants, adsorbents, etc.), effectively reducing recovery costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the solutions shown in these drawings without any creative work.

[0025] Figure 1 This is a flow chart of a method for separating and recovering acetonitrile waste liquid in one embodiment of the present application;

[0026] Figure 2 This is a schematic structural diagram of an acetonitrile waste liquid separation and recovery device in one embodiment of the present application.

[0027] Explanation of symbols: 1-pH adjustment tank, 2-first distillation tower, 3-gas-liquid separator, 4-pervaporization membrane module, 5-second distillation tower.

[0028] The realization of the objectives, functional features and advantages of this application will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0030] In the description of the present invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, features specified as "first" or "second" may explicitly or implicitly include one or more of the specified features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0031] In this application, the word "as an example" is used to mean "used as an example, illustration or illustration". Any embodiment described in this application as "as an example" is not necessarily to be construed as preferred or advantageous over other embodiments. The following description is given to enable any person skilled in the art to make and use the invention. In the following description, details are listed for the purpose of explanation. It should be understood that one of ordinary skill in the art can recognize that the invention can be practiced without using these specific details. In other instances, well-known structures and processes are not elaborated in detail to avoid obscuring the description of the invention with unnecessary details. Therefore, the present invention is not intended to be limited to the embodiments shown, but is to be consistent with the widest scope consistent with the principles and features disclosed in this application.

[0032] Acetonitrile, also commonly known as methyl cyanide and methyl nitrile, is a colorless, transparent liquid at room temperature. It is highly volatile with a distinctive ether-like odor and is flammable, burning with a bright flame. It is miscible with water, methanol, carbon tetrachloride, methyl acetate, ethyl acetate, ethylene dichloride, and many unsaturated hydrocarbon solvents. Acetonitrile has excellent solvent properties and is an important organic intermediate. It is widely used as a highly chemically active aprotic solvent. Its primary use is as a solvent, used in the synthesis of vitamin A, cortisone, and amine drugs and their intermediates. It is also used as an active medium solvent in the manufacture of vitamin B1 and amino acids. Acetonitrile is also widely used in chromatographic analysis, using acetonitrile or a mixture of acetonitrile and water as the mobile phase. The mobile phase contains some acetonitrile and some water, and may also contain small amounts of other impurities. Directly disposing this acetonitrile as wastewater results in significant waste and high analytical costs. Therefore, it is necessary to separate and recover acetonitrile wastewater to recycle it.

[0033] Acetonitrile and water form an azeotropic system, making it difficult to separate via simple distillation. Current methods for separating and recovering acetonitrile wastewater include extractive distillation, a combination of distillation-evaporation-adsorption, or chemical treatment followed by distillation. These methods require extensive and complex equipment and result in high recovery costs.

[0034] The present application provides a method for separating and recovering acetonitrile waste liquid, comprising the following steps:

[0035] The pH of the acetonitrile waste liquid is adjusted to 6-8;

[0036] The acetonitrile waste liquid with a pH of 6-8 is sent to the first distillation tower 2 for distillation to obtain primary separated acetonitrile;

[0037] The first-stage separated acetonitrile is sent to a gas-liquid separator 3 to obtain the second-stage separated acetonitrile after separation;

[0038] The secondary separated acetonitrile is sent to the pervaporation membrane module 4 to obtain the tertiary separated acetonitrile after separation;

[0039] The acetonitrile separated in the three stages is sent to the second distillation tower 5 for distillation to obtain acetonitrile.

[0040] The separation and recovery method of the present application is mainly for acetonitrile waste liquid of liquid chromatography. After the acetonitrile waste liquid is rectified by a first distillation tower 2, acetonitrile gas is extracted from the tower top, which also contains a small amount of water. It is then separated by a gas-liquid separator 3, and the liquid is retained. The acetonitrile gas is allowed to pass through and then passes through a pervaporation membrane module 4. Smaller water molecules pass through the pervaporation membrane module 4, while larger acetonitrile molecules are retained. The acetonitrile is then sent to a second distillation tower 5 for a single distillation. This distillation is to remove a small amount of impurities (such as methanol or ethanol, etc.) therein, and acetonitrile with a purity of 99.9% is obtained in the second distillation tower 5 bottom. The obtained high-purity acetonitrile can be used as a mobile phase for liquid chromatography, realizing the renewable recycling of acetonitrile and effectively reducing the analysis cost.

[0041] The present application removes water from the acetonitrile-water azeotrope through a gas-liquid separator 3 and a pervaporation membrane assembly 4. The two devices have low operating energy consumption and can reduce the water content to below 0.1% when used in combination. In addition, only two distillations are required before and after, which requires less equipment than existing separation methods, has a simple and compact structure, and does not require the introduction of new substances (such as extractants, adsorbents, etc.) during the entire process, effectively reducing recovery costs.

[0042] As an optional embodiment of the present application, the acetonitrile waste liquid is a solvent used for liquid chromatography analysis, and is composed of acetonitrile and water, wherein the water accounts for 50 wt% to 85 wt%, and the balance is acetonitrile and a small amount of impurities.

[0043] As an optional embodiment of the present application, before adjusting the pH of the acetonitrile waste liquid to 6-8, the method further includes the step of preheating the acetonitrile waste liquid, wherein the preheating heat source is the hot water in the bottom of the first distillation tower 2. The remaining water in the bottom of the first distillation tower 2 has a high heat content, and using it to preheat the acetonitrile waste liquid can fully utilize energy and significantly reduce the energy consumption of the first distillation tower 2.

[0044] As an optional embodiment of the present application, the pressure of the first distillation tower 2 is 130-170 KPa, the bottom temperature is 120° C.-130° C., and the top temperature is 100° C.-107° C. The process parameters of the first distillation tower 2 are set so that acetonitrile is produced from the top of the tower and water remains in the bottom of the tower.

[0045] As an optional embodiment of the present application, the pressure of the second distillation tower 5 is atmospheric pressure, and the bottom and top temperatures are 75-80° C. The process parameters of the first distillation tower 2 are set in such a way that impurities are extracted from the top and acetonitrile remains in the bottom.

[0046] As an optional embodiment of the present application, the gas-liquid separator 3 operates at atmospheric pressure and a temperature of 85°C-95°C. The gas-liquid separator 3 effectively separates gaseous and liquid components. In this application, the primary acetonitrile separation is a mixture of acetonitrile gas and a small amount of water. The gas-liquid separator 3 separates and removes the majority of the liquid water. After passing through the gas-liquid separator 3, the acetonitrile gas enters the pervaporation membrane module 4. The retained water is returned to the first distillation tower 2 for further distillation.

[0047] As an optional embodiment of the present application, the pressure of the pervaporation membrane module 4 is 70 kPa-95 kPa, and the temperature is 100°C-110°C. When passing through the pervaporation membrane module 4, the components need to remain in a gaseous state, so the temperature needs to be maintained at 100°C or above. The pervaporation membrane module 4 specifically uses a molecular sieve membrane to preferentially allow water molecules to pass through.

[0048] Pervaporation membrane separation technology is a novel membrane separation technology. Used for separating liquid mixtures, its key advantage is its ability to achieve separations difficult to accomplish with traditional methods such as distillation, extraction, and adsorption, using low energy consumption. It is particularly suitable for separating near-boiling and azeotropic mixtures that are difficult or impossible to separate with conventional distillation. It offers significant economic and technical advantages for removing trace amounts of water from organic solvents and mixed solvents, and for separating small amounts of organic pollutants from wastewater. It can also be coupled with chemical reactions to continuously remove reaction products, significantly improving reaction conversion rates. Operating results from both domestic and international industrial plants indicate that pervaporation can save 1 / 3-1 / 2 of energy compared to traditional azeotropic distillation and extractive distillation.

[0049] Based on the same inventive concept, the present application also provides an acetonitrile waste liquid separation and recovery device, which includes a pH adjustment tank 1, a first distillation tower 2, a gas-liquid separator 3, a permeation vaporization membrane assembly 4 and a second distillation tower 5 connected in sequence along the material flow direction;

[0050] The acetonitrile waste liquid separation and recovery device is used to implement the above-mentioned acetonitrile waste liquid separation and recovery method.

[0051] As an optional embodiment of the present application, the pH adjustment tank 1 is also connected to the mobile phase outlet of the liquid chromatograph. That is, the mobile phase can be directly sent to the pH adjustment tank 1 after exiting the chromatograph for separation and recovery. Alternatively, a temporary storage tank can be provided to temporarily store the acetonitrile waste liquid from the chromatograph, and then be separated and recovered when the waste liquid reaches a certain amount.

[0052] As an optional embodiment of the present application, the temporary storage tank is provided with an interlayer. The high-temperature water from the bottom of the first distillation tower 2 is collected and then passed through the interlayer of the temporary storage tank to preheat the waste liquid in the temporary storage tank. This fully utilizes energy and effectively reduces the energy consumption of the first distillation tower 2.

[0053] The gas-liquid separator 3 includes a liquid storage tank for storing the intercepted liquid, and the liquid collection tank is connected to the first distillation tower 2 to return the stored liquid to the first distillation tower 2 for distillation. The gas-liquid separator 3 can also remove most of the inorganic impurities and solid impurities.

[0054] As an optional embodiment of the present application, the first distillation tower 2 and the second distillation tower 5 are both packed towers. A packed tower is a type of tower equipment. The tower is filled with packing of appropriate height to increase the contact surface between the two fluids. The liquid enters the tower through a distributor from the top and descends along the surface of the packing. The gas flows upstream from the bottom of the tower through the pores of the packing, interacting with the liquid in close contact. The structure is relatively simple and maintenance is relatively convenient. It is widely used in operations such as gas absorption, distillation, and extraction.

[0055] The above technical solutions of the present application are described in detail below in conjunction with specific embodiments. The methods of the following embodiments are all implemented based on the above-mentioned acetonitrile waste liquid separation and recovery device.

[0056] Example 1

[0057] A method for separating and recovering acetonitrile waste liquid comprises the following steps:

[0058] Step S10, adjusting the pH of the acetonitrile waste liquid to 6-8;

[0059] Specifically, the contents of the components in the acetonitrile waste liquid are 70 wt% water, 26 wt% acetonitrile, 2% methanol, and 2 wt% ethanol;

[0060] Generally, after flowing out of the chromatograph, the acetonitrile waste liquid is acidic and the pH of the acetonitrile waste liquid needs to be adjusted to neutral. Therefore, sodium hydroxide solution is used for pH adjustment until the pH reaches 6-8.

[0061] Step S20, sending the pH-adjusted acetonitrile waste liquid to the first distillation tower 2 for distillation to obtain primary separated acetonitrile;

[0062] Specifically, the acetonitrile waste liquid material flow rate is 1000.0 kg / h, the pressure in the first distillation tower 2 is 150 kPa, the tower bottom temperature is 125° C., and the tower top temperature is 105° C. Acetonitrile has a lower boiling point than water, and a higher concentration of acetonitrile is extracted from the tower top, thus obtaining primary separated acetonitrile.

[0063] The contents of the components at the top of the first distillation tower 2 are: 13.72 wt% water, 74.78 wt% acetonitrile, 5.75 wt% methanol, and 5.75 wt% ethanol;

[0064] The contents of the components in the bottom of the first distillation tower 2 are: 99.95 wt% of water, 0.05 wt% of acetonitrile, 0.00 wt% of methanol, and 0.00 wt% of ethanol.

[0065] Step S30, sending the primary separated acetonitrile to the gas-liquid separator 3 to obtain secondary separated acetonitrile after separation;

[0066] Specifically, the pressure of the gas-liquid separator 3 is normal pressure, and the temperature is set to 90° C. The gas passing through the gas-liquid separator 3, i.e., the content of each component in the secondary separated acetonitrile is: 7.03 wt % water, 80.57 wt % acetonitrile, 6.20 wt % methanol, and 6.20 wt % ethanol;

[0067] The contents of the components in the liquid intercepted by the gas-liquid separator 3 are: 95.03 wt% water, 4.97 wt% acetonitrile, 0.00 wt% methanol, and 0.00 wt% ethanol. This portion of liquid is sent back to the first distillation tower 2 for distillation.

[0068] Step S40, sending the secondary separated acetonitrile to the pervaporation membrane module 4 to obtain tertiary separated acetonitrile after separation;

[0069] Specifically, the pervaporation membrane material is a molecular sieve membrane, the operating pressure inside the membrane is 80 KPa, and the temperature is 105°C.

[0070] After permeation, the contents of the components in the three-stage separated acetonitrile were: 0.07 wt% water, 86.06 wt% acetonitrile, 6.62 wt% methanol, and 6.62 wt% ethanol;

[0071] The permeate of the pervaporation membrane is basically water, which can be recycled for cooling (containing a very small amount of acetonitrile, which needs to be cooled before storage to prevent acetonitrile from volatilizing). This water can also be used to prepare the mobile phase of liquid chromatography for recycling.

[0072] Step S50: sending the tertiary separated acetonitrile to the second distillation tower 5 for distillation to obtain acetonitrile.

[0073] Specifically, the acetonitrile separated in the tertiary stage is in a gaseous state when entering the second distillation tower 5. The pressure of the second distillation tower 5 is atmospheric pressure, and the temperatures at the bottom and top of the tower are both 80° C. Methanol and ethanol impurities are extracted from the top of the second distillation tower 5, and acetonitrile with a concentration of greater than 99.9 wt% is extracted from the bottom of the tower.

[0074] Example 2

[0075] A method for separating and recovering acetonitrile waste liquid comprises the following steps:

[0076] Step S10, adjusting the pH of the acetonitrile waste liquid to 6-8;

[0077] Specifically, the contents of the components in the acetonitrile waste liquid are 62.5 wt% of water, 31.1 wt% of acetonitrile, 3% of methanol, and 3.4 wt% of ethanol;

[0078] Generally, after flowing out of the chromatograph, the acetonitrile waste liquid is acidic and the pH of the acetonitrile waste liquid needs to be adjusted to neutral. Therefore, sodium hydroxide solution is used for pH adjustment until the pH reaches 6-8.

[0079] Step S20, sending the pH-adjusted acetonitrile waste liquid to the first distillation tower 2 for distillation to obtain primary separated acetonitrile;

[0080] Specifically, the acetonitrile waste liquid material flow rate is 800.0 kg / h, the pressure in the first distillation tower 2 is 145 kPa, the tower bottom temperature is 120° C., and the tower top temperature is 100° C. Acetonitrile has a lower boiling point than water, and a higher concentration of acetonitrile is extracted from the tower top, thus obtaining primary separated acetonitrile.

[0081] The contents of the components at the top of the first distillation tower 2 are: 12.08 wt% of water, 70.22 wt% of acetonitrile, 8.25% of methanol, and 9.45 wt% of ethanol;

[0082] The contents of the components in the bottom of the first distillation tower 2 are: 99.97 wt% of water, 0.03 wt% of acetonitrile, 0.00 wt% of methanol, and 0.00 wt% of ethanol.

[0083] Step S30, sending the primary separated acetonitrile to the gas-liquid separator 3 to obtain secondary separated acetonitrile after separation;

[0084] Specifically, the pressure of the gas-liquid separator 3 is normal pressure, and the temperature is set to 85° C. The gas passing through the gas-liquid separator 3, i.e., the content of each component in the secondary separated acetonitrile is: 4.30 wt % water, 76.95 wt % acetonitrile, 9.04 wt % methanol, and 9.71 wt % ethanol;

[0085] The contents of the components in the liquid intercepted by the gas-liquid separator 3 are: 97.21 wt% water, 2.79 wt% acetonitrile, 0.00 wt% methanol, and 0.00 wt% ethanol. This portion of liquid is sent back to the first distillation tower 2 for distillation.

[0086] Step S40, sending the secondary separated acetonitrile to the pervaporation membrane module 4 to obtain tertiary separated acetonitrile after separation;

[0087] Specifically, the pervaporation membrane material is a molecular sieve membrane, the operating pressure inside the membrane is 70 KPa, and the temperature is 105°C.

[0088] After permeation, the contents of the components in the three-stage separated acetonitrile were: 0.05 wt% water, 82.78 wt% acetonitrile, 8.01% methanol, and 9.16 wt% ethanol;

[0089] The permeate of the pervaporation membrane is basically water, which can be recycled for cooling (containing a very small amount of acetonitrile, which needs to be cooled before storage to prevent acetonitrile from volatilizing). This water can also be used to prepare the mobile phase of liquid chromatography for recycling.

[0090] Step S50: sending the tertiary separated acetonitrile to the second distillation tower 5 for distillation to obtain acetonitrile.

[0091] Specifically, the acetonitrile separated in the tertiary stage is in a gaseous state when entering the second distillation tower 5. The pressure of the second distillation tower 5 is atmospheric pressure, and the temperatures at the bottom and top of the tower are both 80° C. Methanol and ethanol impurities are extracted from the top of the second distillation tower 5, and acetonitrile with a concentration of greater than 99.9 wt% is extracted from the bottom of the tower.

[0092] Example 3

[0093] A method for separating and recovering acetonitrile waste liquid comprises the following steps:

[0094] Step S10, adjusting the pH of the acetonitrile waste liquid to 6-8;

[0095] Specifically, the contents of the components in the acetonitrile waste liquid are 80 wt% of water, 18 wt% of acetonitrile, and 2 wt% of ethanol;

[0096] Generally, after flowing out of the chromatograph, the acetonitrile waste liquid is acidic and the pH of the acetonitrile waste liquid needs to be adjusted to neutral. Therefore, sodium hydroxide solution is used for pH adjustment until the pH reaches 6-8.

[0097] Step S20, sending the pH-adjusted acetonitrile waste liquid to the first distillation tower 2 for distillation to obtain primary separated acetonitrile;

[0098] Specifically, the acetonitrile waste liquid material flow rate is 900.0 kg / h, the pressure in the first distillation tower 2 is 160 kPa, the bottom temperature is 125° C., and the top temperature is 105° C. Acetonitrile has a lower boiling point than water, and a higher concentration of acetonitrile is extracted from the top of the tower to obtain primary separated acetonitrile.

[0099] The contents of the components at the top of the first distillation tower 2 are: 14.21 wt% water, 78.16 wt% acetonitrile, and 7.63 wt% ethanol;

[0100] The contents of the components in the bottom of the first distillation tower 2 are: 99.96 wt% of water, 0.04 wt% of acetonitrile, and 0.00 wt% of ethanol.

[0101] Step S30, sending the primary separated acetonitrile to the gas-liquid separator 3 to obtain secondary separated acetonitrile after separation;

[0102] Specifically, the pressure of the gas-liquid separator 3 is normal pressure, and the temperature is set to 90° C. The gas passing through the gas-liquid separator 3, i.e., the content of each component in the secondary separated acetonitrile is: 4.1 wt % water, 86.37 wt % acetonitrile, and 9.53 wt % ethanol;

[0103] The contents of the components in the liquid intercepted by the gas-liquid separator 3 are: 98.60 wt% water, 1.40 wt% acetonitrile, and 0.00 wt% ethanol. This portion of liquid is sent back to the first distillation tower 2 for distillation.

[0104] Step S40, sending the secondary separated acetonitrile to the pervaporation membrane module 4 to obtain tertiary separated acetonitrile after separation;

[0105] Specifically, the pervaporation membrane material is a molecular sieve membrane, the operating pressure inside the membrane is 80 KPa, and the temperature is 105°C.

[0106] After permeation, the contents of the components in the three-stage separated acetonitrile were: 0.04 wt% water, 90.09 wt% acetonitrile, and 9.87 wt% ethanol;

[0107] The permeate of the pervaporation membrane is basically water, which can be recycled for cooling (containing a very small amount of acetonitrile, which needs to be cooled before storage to prevent acetonitrile from volatilizing). This water can also be used to prepare the mobile phase of liquid chromatography for recycling.

[0108] Step S50: sending the tertiary separated acetonitrile to the second distillation tower 5 for distillation to obtain acetonitrile.

[0109] Specifically, the acetonitrile separated in the tertiary stage is in a gaseous state when entering the second distillation tower 5. The pressure of the second distillation tower 5 is atmospheric pressure, and the temperatures of the bottom and top of the tower are both 80° C. Ethanol impurities are extracted from the top of the second distillation tower 5, and acetonitrile with a concentration greater than 99.9 wt% is extracted from the bottom of the tower.

[0110] Example 4

[0111] A method for separating and recovering acetonitrile waste liquid comprises the following steps:

[0112] Step S10, adjusting the pH of the acetonitrile waste liquid to 6-8;

[0113] Specifically, the contents of the components in the acetonitrile waste liquid are 55 wt% water, 44 wt% acetonitrile, and 1 wt% carbon tetrachloride;

[0114] Generally, after flowing out of the chromatograph, the acetonitrile waste liquid is acidic and the pH of the acetonitrile waste liquid needs to be adjusted to neutral. Therefore, sodium hydroxide solution is used for pH adjustment until the pH reaches 6-8.

[0115] Step S20, sending the pH-adjusted acetonitrile waste liquid to the first distillation tower 2 for distillation to obtain primary separated acetonitrile;

[0116] Specifically, the acetonitrile waste liquid material flow rate is 850.0 kg / h, the pressure in the first distillation tower 2 is 135 kPa, the tower bottom temperature is 120° C., and the tower top temperature is 107° C. Acetonitrile has a lower boiling point than water, and a higher concentration of acetonitrile is extracted from the tower top, thus obtaining primary separated acetonitrile.

[0117] The contents of the components at the top of the first distillation tower 2 are: 16.55 wt% of water, 81.79 wt% of acetonitrile, and 1.66 wt% of carbon tetrachloride;

[0118] The contents of the components in the bottom of the first distillation tower 2 are: 99.97 wt% of water and 0.03 wt% of acetonitrile.

[0119] Step S30, sending the primary separated acetonitrile to the gas-liquid separator 3 to obtain secondary separated acetonitrile after separation;

[0120] Specifically, the pressure of the gas-liquid separator 3 is normal pressure, and the temperature is set to 95° C. The gas passing through the gas-liquid separator 3, i.e., the content of each component in the secondary separated acetonitrile is: 6.28 wt % of water, 91.64 wt % of acetonitrile, and 2.08 wt % of carbon tetrachloride;

[0121] The contents of the components in the liquid intercepted by the gas-liquid separator 3 are: 98.87 wt% water, 1.13 wt% acetonitrile. This portion of liquid is sent back to the first distillation tower 2 for distillation.

[0122] Step S40, sending the secondary separated acetonitrile to the pervaporation membrane module 4 to obtain tertiary separated acetonitrile after separation;

[0123] Specifically, the pervaporation membrane material is a molecular sieve membrane, the operating pressure inside the membrane is 70 KPa, and the temperature is 102°C.

[0124] After permeation, the contents of the components in the three-stage separated acetonitrile were as follows: 0.07 wt% water, 97.63 wt% acetonitrile, and 2.3 wt%;

[0125] The permeate of the pervaporation membrane is basically water, which can be recycled for cooling (containing a very small amount of acetonitrile, which needs to be cooled before storage to prevent acetonitrile from volatilizing). This water can also be used to prepare the mobile phase of liquid chromatography for recycling.

[0126] Step S50: sending the tertiary separated acetonitrile to the second distillation tower 5 for distillation to obtain acetonitrile.

[0127] Specifically, the acetonitrile separated in the tertiary stage is in a gaseous state when entering the second distillation tower 5. The pressure of the second distillation tower 5 is atmospheric pressure, and the temperatures of the bottom and top of the tower are both 75° C. Carbon tetrachloride impurities are extracted from the top of the second distillation tower 5, and acetonitrile with a concentration greater than 99.9 wt% is extracted from the bottom of the tower.

[0128] Example 5

[0129] A method for separating and recovering acetonitrile waste liquid comprises the following steps:

[0130] Step S10, adjusting the pH of the acetonitrile waste liquid to 6-8;

[0131] Specifically, the contents of the components in the acetonitrile waste liquid are 60 wt% water, 38 wt% acetonitrile, and 2 wt% ethanol;

[0132] Generally, after flowing out of the chromatograph, the acetonitrile waste liquid is acidic and the pH of the acetonitrile waste liquid needs to be adjusted to neutral. Therefore, sodium hydroxide solution is used for pH adjustment until the pH reaches 6-8.

[0133] Step S20, sending the pH-adjusted acetonitrile waste liquid to the first distillation tower 2 for distillation to obtain primary separated acetonitrile;

[0134] Specifically, the acetonitrile waste liquid material flow rate is 700.0 kg / h, the pressure in the first distillation tower 2 is 130 kPa, the bottom temperature is 130° C., and the top temperature is 100° C. Acetonitrile has a lower boiling point than water, and a higher concentration of acetonitrile is extracted from the top of the tower, thus obtaining primary separated acetonitrile.

[0135] The contents of the components at the top of the first distillation tower 2 are: 13.23 wt% water, 82.47 wt% acetonitrile, and 4.3 wt% ethanol;

[0136] The contents of the components in the bottom of the first distillation tower 2 are: 99.95 wt% of water, 0.05 wt% of acetonitrile, and 0.00 wt% of ethanol.

[0137] Step S30, sending the primary separated acetonitrile to the gas-liquid separator 3 to obtain secondary separated acetonitrile after separation;

[0138] Specifically, the pressure of the gas-liquid separator 3 is normal pressure, and the temperature is set to 85° C. The gas passing through the gas-liquid separator 3, i.e., the content of each component in the secondary separated acetonitrile is: 5.65 wt % water, 89.69 wt % acetonitrile, and 4.66 wt % ethanol;

[0139] The contents of the components in the liquid intercepted by the gas-liquid separator 3 are: 96.71 wt% water, 3.29 wt% acetonitrile, and 0.00 wt% ethanol. This portion of liquid is sent back to the first distillation tower 2 for distillation.

[0140] Step S40, sending the secondary separated acetonitrile to the pervaporation membrane module 4 to obtain tertiary separated acetonitrile after separation;

[0141] Specifically, the pervaporation membrane material is a molecular sieve membrane, the operating pressure inside the membrane is 95 KPa, and the temperature is 110°C.

[0142] After permeation, the contents of the components in the three-stage separated acetonitrile were: 0.06 wt% water, 94.25 wt% acetonitrile, and 5.69 wt% ethanol;

[0143] The permeate of the pervaporation membrane is basically water, which can be recycled for cooling (containing a very small amount of acetonitrile, which needs to be cooled before storage to prevent acetonitrile from volatilizing). This water can also be used to prepare the mobile phase of liquid chromatography for recycling.

[0144] Step S50: sending the tertiary separated acetonitrile to the second distillation tower 5 for distillation to obtain acetonitrile.

[0145] Specifically, the acetonitrile separated in the tertiary stage is in a gaseous state when entering the second distillation tower 5. The pressure of the second distillation tower 5 is atmospheric pressure, and the temperatures of the bottom and top of the tower are both 78° C. Ethanol impurities are extracted from the top of the second distillation tower 5, and acetonitrile with a concentration greater than 99.9 wt% is extracted from the bottom of the tower.

[0146] The acetonitrile waste liquid recovery method that prior art provides generally needs to use sorbent or other treatment agents, as Chinese patent CN117361697A and CN117923690A, then need to use multiple rectifying towers or evaporators in other traditional separation processes, equipment complexity and energy consumption are higher.The application separates most of water by the first rectifying tower 2, then is combined with the use of gas-liquid separator 3 and pervaporation membrane by low-energy consumption, when realizing efficient dehydration, can also effectively remove inorganic impurities and particulate impurities therein, finally remove light component impurities therein through a rectification again.The application's recovery process reduces the use of rectifying tower, can not introduce new material (sorbent or other treatment agents are all consumables, can increase cost) simultaneously, reduces recovery cost, and the acetonitrile purity of recovery can reach 99.9% (chromatographic grade), can act as liquid chromatography mobile phase and reuse.

[0147] The above description is merely an optional embodiment of the present application and does not limit the patent scope of the present application. All equivalent structural transformations made using the contents of the present application specification and drawings under the inventive concept of the present application, or direct / indirect application in other related technical fields are included in the patent protection scope of the present application.

Claims

1. A method for separating and recovering acetonitrile waste liquid, characterized in that, The acetonitrile waste liquid is a solvent waste liquid used for liquid chromatography analysis, wherein water accounts for 50wt%-85wt% and the remainder is acetonitrile and a small amount of impurities; The method comprises the following steps: Adjust the pH of the acetonitrile waste liquid to 6-8; The acetonitrile waste liquid with a pH adjusted to 6-8 is sent to a first distillation tower for distillation to obtain primary separated acetonitrile and withdrawn from the top of the tower; wherein the pressure of the first distillation tower is 130-170KPa, the bottom temperature of the first distillation tower is 120°C-130°C, and the top temperature of the tower is 100°C-107°C; The first-stage separated acetonitrile is sent to a gas-liquid separator to obtain the second-stage separated acetonitrile after separation; the pressure of the gas-liquid separator is normal pressure and the temperature is 85°C-95°C; The secondary separated acetonitrile is sent to a pervaporation membrane assembly to obtain tertiary separated acetonitrile after separation; the pressure of the pervaporation membrane assembly is 70KPa-95KPa, and the temperature is 100°C-110°C. The pervaporation membrane assembly adopts a molecular sieve membrane to allow water molecules to pass through preferentially; The tertiary separated acetonitrile is sent to a second distillation tower, the pressure of the second distillation tower is normal pressure, the bottom temperature of the second distillation tower is 75°C-80°C, and the top temperature is 75°C-80°C, and acetonitrile is obtained by distillation in the bottom of the tower.

2. A method for separating and recovering acetonitrile waste liquid according to claim 1, characterized in that, Before adjusting the pH of the acetonitrile waste liquid to 6-8, the method further comprises the step of preheating the acetonitrile waste liquid, wherein the preheating heat source is the hot water extracted from the bottom of the first distillation tower.

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