A method for separating acetonitrile-water with low energy consumption

Abstract

The application discloses a method for separating acetonitrile-water with low energy consumption, comprising the following steps: first, a hydrophobic filter paper is prepared by performing silanization hydrophobic modification on the surface of the filter paper by using a silanization reagent; then, an acetonitrile-water mixed solution is induced to be separated into an acetonitrile-rich phase and a water-rich phase by using inorganic salt; and finally, the acetonitrile-rich phase and the water-rich phase are separated by using the hydrophobic filter paper for filtering. The application provides a simple and rapid salt-induced phase separation (SIPS) and hydrophobic filtration (HF) combined strategy (SIPS-HF) for separating the acetonitrile-water mixed solution, the acetonitrile-water mixed solution is induced to be separated into the acetonitrile-rich phase and the water-rich phase by using inorganic salt, and then the hydrophobic filter paper is selected as a matrix for separating the water-rich phase and the acetonitrile-rich phase. The method is simple, rapid and low in energy consumption, the separation efficiency is more than 95% under the premise of maintaining high throughput, the separation method is only driven by gravity and does not consume other energy, and is suitable for industrial application.

Description

Technical Field

[0001] This invention belongs to the field of chemical reagent separation technology, and particularly relates to a low-energy-consumption method for separating acetonitrile-water. Background Technology

[0002] Acetonitrile (ACN) is an excellent solvent, extractant, and important chemical raw material, but it is also a toxic chemical that is difficult to degrade. Acetonitrile is widely used in the chemical industry, but it inevitably generates high concentrations of toxic industrial wastewater. Because acetonitrile is highly harmful to humans, animals, and plants, the direct discharge of high-concentration acetonitrile wastewater into the environment without treatment will cause pollution. Therefore, pretreatment of acetonitrile wastewater to meet discharge standards or the standards for use in subsequent processes is crucial.

[0003] Acetonitrile and water form a miscible binary azeotropic system (16% water and 84% acetonitrile, v / v, azeotropic point 76℃). Common distillation methods are limited by the azeotropic point, making complete separation of acetonitrile and water difficult. Pervaporation is a commonly used membrane separation technology with advantages such as energy saving, environmental friendliness, and small footprint, and is widely used in the separation of low-concentration acetonitrile. For the separation of high-concentration acetonitrile wastewater, distillation is first used to obtain an 84% acetonitrile azeotrope, and then dehydrating agents such as calcium chloride or sodium hydroxide are added during azeotropic distillation to obtain high-purity acetonitrile. While these technologies are relatively mature, they suffer from drawbacks such as high equipment investment, low separation efficiency, complex operation, high energy consumption, and significant expenditure of manpower and resources.

[0004] Salt-induced phase separation (SIPS) is a novel separation method that utilizes the induction of phase change by adding salt as an inducer to a homogeneous miscible solvent to achieve two-phase separation. In homogeneous systems formed by organic solvents and water, the presence of high concentrations of salt in the aqueous solution reduces the solubility of the organic solvent or low-polarity analytes, promoting phase separation. For azeotropic systems, adding a small amount of salt can achieve two-phase separation. Salt-induced phase separation offers advantages such as reduced production costs and resource conservation, and possesses superior separation efficiency, making it widely used in solvent extraction and separation.

[0005] For acetonitrile-containing wastewater, after salt-induced phase separation forms an acetonitrile-water solution consisting of an upper acetonitrile-rich phase (ARP) and a lower aqueous-rich phase (WRP), further separation of the aqueous and acetonitrile-rich phases is necessary to achieve water and acetonitrile recycling. For treating small amounts of acetonitrile wastewater in the laboratory, salt-induced phase separation can be performed in a separatory funnel. The lower aqueous phase is first discharged from the drain pipe at the bottom of the funnel, and then the remaining acetonitrile-rich phase is poured out from the mouth of the separatory funnel. However, in industrial applications, separating the acetonitrile-rich and aqueous phases after induced phase separation presents challenges. Summary of the Invention

[0006] The technical problem this invention aims to solve is to overcome the shortcomings and defects mentioned in the background art, and to address the problems of high investment, low separation efficiency, complex operation, and high energy consumption in existing acetonitrile-water mixed solution separation equipment, by providing a low-energy-consumption method for separating acetonitrile-water. This invention provides a simple and rapid combined strategy of salt-induced phase separation (SIPS) and hydrophobic filtration (HF) (SIPS-HF) to separate acetonitrile-water mixed solutions. Inorganic salts are used to induce the acetonitrile-water mixed solution to separate into an acetonitrile-rich phase and a water-rich phase, and then hydrophobic filter paper is selected as the matrix for separating the water-rich and acetonitrile-rich phases. This separation method is driven solely by gravity and does not consume other energy sources.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0008] A low-energy-consumption method for separating acetonitrile-water includes the following steps:

[0009] (1) Hydrophobic filter paper was prepared by silanizing and hydrophobic modification of the filter paper surface using silanizing reagent;

[0010] (2) Inorganic salts were used to induce the acetonitrile-water mixed solution to separate into an acetonitrile-rich phase and a water-rich phase;

[0011] (3) After phase separation, the hydrophobic filter paper is used for filtration to separate the acetonitrile-rich phase and the water-rich phase.

[0012] This invention systematically studies the phase separation behavior of the water-acetonitrile-salt (WAS) system, obtains ternary phase diagrams of different salts in the WAS system, and investigates the salt selection and separation efficiency of the WAS system. It demonstrates that efficient phase separation of acetonitrile-water mixed solutions can be achieved through salt-induced phase separation, resulting in two-phase acetonitrile-water solutions.

[0013] Preferably, the silanizing agent includes any one or more of methyltrichlorosilane, butyltrichlorosilane, octyltrichlorosilane, dodecyltrichlorosilane, and octadecyltrichlorosilane.

[0014] Preferably, the silanizing agent is butyltrichlorosilane or octyltrichlorosilane.

[0015] More preferably, the volume concentration of butyltrichlorosilane is 0.3-1.5%, and the volume concentration of octyltrichlorosilane is 0.3-1.0%.

[0016] The retention capacity of hydrophobic filter paper for acetonitrile-aqueous mixed solutions of different concentrations depends on the hydrophobicity of the paper base, which is related to the carbon chain length and concentration of the silanizing agent. Hydrophobic filter paper needs to intercept the water-rich phase while allowing the acetonitrile-rich phase to pass through, while also possessing good separation efficiency and throughput. This invention has shown that selecting the aforementioned silanizing agent and concentration results in the optimal retention capacity.

[0017] Preferably, the method for preparing the hydrophobic filter paper specifically includes the following steps:

[0018] S1. Prepare a silanizing reagent-n-hexane solution, sonicate for 8-10 min, immerse filter paper in the silanizing reagent-n-hexane solution, and sonicate for 4-6 min at room temperature to perform silanization hydrophobic modification on the surface of the filter paper.

[0019] S2. Take out the filter paper and rinse its surface with hexane, ethanol and methanol in sequence. Then, let it air dry in a fume hood for 10-12 hours to obtain hydrophobic filter paper.

[0020] Hydrophobic membranes, such as polydimethylsiloxane membranes, polypropylene membranes, and microporous polymer membranes, exhibit permeability selectivity. Hydrophobic organic compounds can permeate through these membranes, while water cannot. Based on this, hydrophobic membranes have demonstrated superior performance in the removal of volatile organic compounds (VOCs) from water and in oil-water separation research. However, used organic hydrophobic membranes are difficult to degrade and can easily cause secondary pollution. Filter paper, composed of cotton fibers, has a highly networked hydroxyl molecular structure and excellent water permeability. Compared with other matrices, filter paper has advantages such as low cost, recyclability, good biocompatibility, and ease of modification, and is widely used in sample processing and solvent separation. If filter paper is modified to be hydrophobic, it holds promise as a replacement for hydrophobic membranes in oil-water separation.

[0021] Preferably, the volume fraction of acetonitrile in the acetonitrile-water mixed solution is 20%-90%.

[0022] Preferably, the inorganic salt includes one or more selected from LiCl, NaCl, KCl, NH4Cl, K2CO3, Na2CO3, Li2SO4, Na2SO4, and MgSO4. More preferably, the inorganic salt is NaCl.

[0023] Preferably, the amount of inorganic salt added is based on exceeding the saturation dose in the acetonitrile-water mixture.

[0024] Preferably, the filtration is natural gravity filtration.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] 1. The method for separating acetonitrile-water using the present invention is simple, rapid, and energy-efficient, achieving a separation efficiency of over 95% while maintaining high throughput. Furthermore, this separation method is driven solely by gravity and does not consume other energy sources, making it suitable for industrial applications.

[0027] 2. Even after being stored for 3 months or soaked in an acetonitrile-water mixture for 12 hours, the hydrophobic filter paper used in this invention still exhibits strong hydrophobicity and a high acetonitrile interception concentration. After continuously separating the solution to its maximum volume 25 times, it can still maintain a high separation flux and separation efficiency, and no water-rich phase was found to pass through the hydrophobic filter paper. The separation effect is stable during the separation process, and the hydrophobic filter paper can be directly incinerated after use without causing secondary pollution, which is environmentally friendly. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a flowchart of the salt-induced phase separation-hydrophobic filtration combined strategy in this invention;

[0030] Figure 2 This is a schematic diagram illustrating the principle of silanization modification.

[0031] Figure 3 The images show the scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) spectra of unmodified filter paper and hydrophobic filter paper; where: (a) SEM image of unmodified filter paper at 100x magnification; (b) SEM image of unmodified filter paper at 500x magnification; (c) EDS spectrum of unmodified filter paper; (d) SEM image of hydrophobic filter paper at 100x magnification; (e) SEM image of hydrophobic filter paper at 500x magnification; (f) EDS spectrum of hydrophobic filter paper.

[0032] Figure 4 XPS images of unmodified filter paper and hydrophobic filter paper: (a) full spectrum scan; (b) C 1s scan; (c) O 1s scan; (d) Si 2p scan.

[0033] Figure 5 The static water contact angle and static acetonitrile contact angle of hydrophobic filter paper modified with different silanizing agents at five different concentrations;

[0034] Figure 6 The interception concentration of the acetonitrile-aqueous mixed solution by the hydrophobic filter paper modified with C4 and C8;

[0035] Figure 7 The actual separation behavior of hydrophobic filter papers modified with C4 and C8;

[0036] Figure 8 Figure showing the stability of hydrophobic filter paper;

[0037] Figure 9 The graph shows the effect of different types of inorganic salts on the phase separation induced by the acetonitrile-aqueous mixture.

[0038] Figure 10 This is a diagram showing the acetonitrile volume fraction distribution after phase separation of acetonitrile-water mixed solutions with different acetonitrile volume fractions induced by NaCl. Detailed Implementation

[0039] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0040] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0041] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0042] Throughout the text, "acetonitrile-water mixed solution" represents the solution before salt-induced phase separation; "acetonitrile-water solution" represents the solution after salt-induced phase separation, and this is used as a distinction. The acetonitrile-water solution includes both acetonitrile-rich and water-rich phases.

[0043] Example 1:

[0044] A low-energy-consumption method for separating acetonitrile-water: First, an inorganic salt is used to induce the separation of the acetonitrile-water mixture into an acetonitrile-rich phase and a water-rich phase. Then, hydrophobic filter paper is selected as the matrix for separating the acetonitrile-rich and water-rich phases, such as... Figure 1 The specific steps are as follows:

[0045] (1) Preparation of hydrophobic filter paper using silanizing reagents: Preparation of different volume fractions The silanizing reagent-n-hexane solution (Table 1) was used. After ultrasonic mixing for 10 min, filter paper was immersed in the solution and ultrasonically reacted for 5 min at room temperature to silanize and hydrophobically modify the surface of ordinary filter paper. The filter paper was then removed and washed sequentially with n-hexane, ethanol, and methanol, and then naturally dried in a fume hood for 12 hours to obtain hydrophobic filter paper for subsequent separation of acetonitrile-rich and water-rich phases. The principle of silanization modification is as follows: Figure 2 As shown.

[0046] (2) Inducing phase separation of acetonitrile-water mixture with inorganic salt: Add an amount of inorganic salt exceeding the saturation dose of water to acetonitrile-water mixtures with different volume ratios at once, shake vigorously until the inorganic salt is fully dissolved, and let stand for 4-6 minutes to separate the acetonitrile-water mixture into two phases. The solution after phase separation is represented as acetonitrile-water solution, wherein the upper phase is the acetonitrile-rich phase and the lower phase is the water-rich phase.

[0047] (3) Separation of acetonitrile-rich and water-rich phases using hydrophobic filter paper: Fold a circular hydrophobic filter paper twice to form a cone. Invert this cone into a conical glass funnel to form a hydrophobic filter paper conical funnel (referred to as the hydrophobic filter paper funnel). Take 10 mL of acetonitrile-water solution (the volume ratio of the acetonitrile-rich phase to the water-rich phase is 1:1) and pour it into the hydrophobic filter paper funnel, controlling the upper liquid level of the solution to be less than 0.5 cm from the upper edge of the filter paper. Observe the separation performance of hydrophobic filter papers modified with different reagents. The entire process is carried out under gravity only.

[0048] Table 1. Volume fraction of five silanizing reagent solutions

[0049]

[0050]

[0051] The experimental methods and results of this embodiment are as follows:

[0052] 1. Calculation of acetonitrile recovery rate after salt-induced phase separation

[0053] In acetonitrile-aqueous mixed solutions of different volume ratios, an inorganic salt exceeding the saturation level in the water is added in a single batch. The mixture is then vigorously shaken until the inorganic salt is fully dissolved. After standing for 5 minutes, the acetonitrile-aqueous mixed solutions are separated into two phases. The separated solution is represented as an acetonitrile-water solution, where the upper phase is acetonitrile-rich and the lower phase is water-rich. The recovery rate (R) of acetonitrile is calculated as follows:

[0054]

[0055] Where m a denoted as , where is the number of moles of acetonitrile in the acetonitrile-rich phase after salt-induced phase separation, and m0 is the number of moles of acetonitrile in the acetonitrile-water mixed solution before phase separation.

[0056] 2. Calculation of separation flux and separation efficiency of acetonitrile-rich phase through hydrophobic filter paper

[0057] After pouring the aqueous phase and the acetonitrile-rich phase into the hydrophobic filter paper funnel, only the acetonitrile-rich phase can pass through the funnel, while the aqueous phase is retained by the hydrophobic filter paper. The equations for calculating the separation efficiency (E) and separation flux (Flux) are as follows:

[0058]

[0059] Where V is the volume of the acetonitrile-rich phase that passes through the hydrophobic filter paper after separation, and V0 is the volume of the original acetonitrile-rich phase after phase separation.

[0060]

[0061] Where S0 is the surface area of ​​the acetonitrile-rich phase in contact with the hydrophobic filter paper, and t is the time it takes for the acetonitrile-rich phase to permeate through the hydrophobic filter paper. Mathematically, when a semicircle is folded into a cone (with a vertex angle of 60°), the relationship between the area (S') of the semicircle and the volume (V') of the cone formed by the folding is as follows:

[0062]

[0063] Since the density of the acetonitrile-rich phase is lower than that of the water-rich phase, when the acetonitrile-water solution is poured into the hydrophobic filter paper funnel, if the contact area between the acetonitrile-rich phase and the hydrophobic filter paper is S0 and S1 respectively, and the volumes of the acetonitrile-rich phase and the water-rich acetonitrile phase in the funnel are V0 and V1 respectively, the separation flux of the acetonitrile-rich phase can be derived from equations (3) and (4):

[0064]

[0065] Where V2 is the total volume of the acetonitrile-rich phase and the water-rich phase, i.e., V2 = V0 + V1. For separation experiments with accurate volumes of the water-rich and acetonitrile-rich phases, t, V0, and V1 can be accurately measured, and therefore the separation flux can be easily calculated.

[0066] 3. Determination of acetonitrile content in water-rich and acetonitrile-rich phases

[0067] Preparation of standard series solutions: Transfer 1.00 mL of acetonitrile, dissolve it in an appropriate amount of water, quantitatively transfer it to a 100 mL volumetric flask, dilute to volume, and shake thoroughly to obtain an acetonitrile solution with a volume fraction of 1.0%. Dilute the 1.0% acetonitrile solution sequentially to obtain a standard series of solutions with acetonitrile volume fractions of 0.01%, 0.03%, 0.05%, 0.07%, 0.09%, and 0.1%, respectively. Determine the calibration curve based on the acetonitrile volume fraction and obtain the calibration curve equation.

[0068] After salt-induced phase separation, 0.1 mL of each of the acetonitrile-rich and aqueous-rich phase solutions were precisely transferred, diluted with water to 100 mL, and filtered through a 0.22 μm water film before gas chromatography analysis. The volume fraction of acetonitrile in the acetonitrile-rich and aqueous-rich phase solutions was calculated using the calibration curve equation.

[0069] The acetonitrile content was determined using gas chromatography with a flame ionization detector (GC-FID). The GC conditions were as follows: column: 30m × 0.25mm × 0.25μm Omegawax 250 capillary column; injection port temperature: 220℃; FID temperature: 250℃; carrier gas flow rate: 1mL / min; injection volume: 1.0μL; split ratio: 100:1; hydrogen flow rate: 40mL / min; air flow rate: 400mL / min; make-up gas flow rate: 30mL / min. The column temperature program was 40℃ for 12 min.

[0070] 4. Characterization of hydrophobic filter paper

[0071] The changes in the surface microstructure of quantitative filter paper before and after silanization modification were observed using scanning electron microscopy (SEM). The results are as follows: Figure 3 As shown. Figure 3 Figures a and 3b show that the filter paper has a porous structure. Figure 3 Figures d and 3e show that after silanization modification, the fiber structure of the filter paper did not differ significantly from that before modification. However, a thin film formed on the surface of the silanized filter paper, making the surface smoother than that of the unmodified filter paper. In the EDS image, all elements are characteristic spectral lines of the K electron shell. Figure 3 c shows that the elemental composition of the unmodified filter paper is mainly C and O (H is undetectable), compared to Figure 3 c, Figure 3 The f-value shows that the Si peak intensity of the filter paper increases after silanization modification, indicating that the filter paper was successfully silanized.

[0072] To further investigate the changes in the surface chemical composition of the filter paper before and after silanization modification, XPS characterization was performed on the quantitative filter paper before and after silanization modification. The results are as follows: Figure 4 As shown. In Figure 4 In sample a, the broadband scan of the quantitative filter paper showed only two peaks: a C1s peak at 286.5 eV and an O1s peak at 532.8 eV, indicating that the sample contained only C and O elements besides H (H was undetectable). However, the filter paper modified with C8 silanization showed a Si 2s peak at 153.8 eV and a Si 2p peak at 102.5 eV. Peak separation was performed on the XPS spectra of the quantitative filter paper before and after silanization modification, and the C1s (…) peaks were compared. Figure 4 b) O 1s( Figure 4c) and Si 2p( Figure 4 From the XPS spectrum of d), three important changes can be observed before and after silanization modification: (1) Due to the long aliphatic chain of the silanizing agent molecule at the C1s peak, the peak response of the C-C bond increases while the peak response of the CO-C bond decreases (e.g., Figure 4 (b) The decrease in the COC peak value in the O 1s peak indicates a decrease in the content of alcohols (as shown in b). Figure 4 (as shown in c), (3) the Si 2p peak showed responses of Si-C and Si-O bonds (as shown in c). Figure 4 (As shown in d). XPS analysis further showed that the modified silanized groups replaced the hydroxyl groups on the paper surface, reducing the number of C-OH groups, indicating that the filter paper surface was successfully modified.

[0073] Unmodified quantitative filter paper can filter both water and acetonitrile. To enable selective acetonitrile filtration while retaining water, it is crucial to impart hydrophobicity and acetonitrile affinity to the filter paper. The affinity of the filter paper for water and acetonitrile can be expressed by the static water contact angle and the static acetonitrile contact angle. This invention uses five silanizing agents: C1, C4, C8, and C6. 12 and C 18 Filter paper was modified to be hydrophobic, and five concentrations of each reagent, from low to high, were selected for the study. The concentrations of the silanizing reagents are listed in Table 3. The contact angle measurement results of the modified hydrophobic filter paper are shown in... Figure 5 middle. Figure 5 The results show that modifying filter paper with the five investigated silanizing agents can impart a certain degree of hydrophobicity. For the same silanizing agent, the static water contact angle of the modified paper substrate gradually increases with increasing silanizing agent concentration. Compared to the silanizing agent C1 containing a short carbon chain, the silanizing agent containing a longer carbon chain achieves a higher static water contact angle at a lower concentration, indicating that the hydrophobicity of the modified paper substrate increases with increasing carbon chain length within a certain range when the carbon chain length of the hydrophobic modifying agent increases. When C8, C... 12 and C 18 When the concentrations of the modified paper were greater than 0.5%, 0.2%, and 0.02%, respectively, a static water contact angle greater than 140° could be obtained. However, comparing the static acetonitrile contact angles, it can be seen that when C1, C4, and C8 were used as modifying agents, the static acetonitrile contact angles of the modified paper base were close to 0°, indicating that the modified paper base exhibited good wettability to acetonitrile; while when C8 was used... 12 and C 18When C4 or C8 is used as the modifying reagent, the static acetonitrile contact angle of the modified paper base gradually increases with the increase of the modifying reagent concentration. The static acetonitrile contact angle corresponding to the modifying solvent concentration that is greater than 140° also reaches about 80°. This indicates that the hydrophobic filter paper modified with a silanizing reagent with a longer carbon chain exhibits acetonitrile-repellent properties when the hydrophobic effect is strong. In summary, using C4 or C8 as the modifying reagent can yield modified paper bases with both good hydrophobicity and good acetonitrile wettability, which are expected to demonstrate good separation performance for acetonitrile-water solutions.

[0074] 5. Investigate the retention capacity of different hydrophobic filter papers for acetonitrile-water mixed solutions.

[0075] For an acetonitrile-water mixture, after salt-induced phase separation, two phases are separated: an acetonitrile-rich phase and a water-rich phase. Both phases contain acetonitrile and water, but the acetonitrile-rich phase has a larger volume fraction of acetonitrile, while the water-rich phase has a relatively smaller volume fraction of acetonitrile. The modified hydrophobic filter paper of this invention separates the two phases through hydrophobic filtration, allowing the acetonitrile-rich phase with a higher volume fraction of acetonitrile to pass through, while intercepting the water-rich phase with a lower volume fraction of acetonitrile. The surface wettability of the hydrophobic filter paper is a crucial factor for the successful separation of the acetonitrile-rich and water-rich phases.

[0076] This invention uses the "intercepted concentration" of hydrophobic filter paper to describe the interception ability of different hydrophobic filter papers for acetonitrile-aqueous mixed solutions. The "intercepted concentration" of the hydrophobic filter paper refers to the minimum volume fraction of acetonitrile in the acetonitrile-aqueous mixed solution that can pass through the hydrophobic filter paper. When the volume fraction of acetonitrile is less than the intercepted concentration, it will not pass through the hydrophobic filter paper and will be intercepted. Therefore, separation of the acetonitrile-rich phase and the water-rich phase can only be achieved when the volume fraction of acetonitrile in the water-rich phase is less than the intercepted concentration of the hydrophobic filter paper, and the volume fraction of acetonitrile in the acetonitrile-rich phase is greater than the intercepted concentration of the hydrophobic filter paper (i.e., volume fraction of acetonitrile in the water-rich phase < intercepted concentration of the hydrophobic filter paper < volume fraction of acetonitrile in the acetonitrile-rich phase). The intercepted concentration is determined by preparing a series of acetonitrile-aqueous mixed solutions with different volume fractions, arranged from highest to lowest acetonitrile volume fraction (…). Acetonitrile-water mixed solutions were added dropwise onto hydrophobic filter paper in the following order: 1.0, 0.95, 0.9, 0.85, 0.8, 0.75, 0.7, 0.65, 0.6, 0.55, 0.5, 0.45, 0.4, 0.35, 0.3, 0.25, 0.2, 0.15, 0.1, 0.05, 0.0. When the added acetonitrile-water mixed solution remained impermeable to the hydrophobic filter paper after standing for 10 minutes, the volume fraction of acetonitrile in the acetonitrile-water mixed solution at that point was considered the interception concentration of the hydrophobic filter paper. The interception concentrations of hydrophobic filter papers prepared with five different concentrations of C4 and C8 reagents were investigated, and the results are as follows: Figure 6 . Figure 6 The results show that, within the investigated concentration range, the interception concentration of hydrophobic filter paper modified with both C4 and C8 reagents initially increases and then tends to plateau with increasing silanizing reagent concentration. Furthermore, at the same modification concentration, the interception concentration of hydrophobic filter paper modified with C8 reagent is higher than that modified with C4 reagent. When the C4 concentration is between 0.3% and 1.5% and the C8 concentration is between 0.1% and 1.0%, the interception concentration of the prepared hydrophobic filter paper is between 0.16 and 0.92, indicating that both silanizing reagents can produce satisfactory hydrophobic filter paper within a relatively wide range of modification reagent concentrations.

[0077] 6. Separation flux and separation efficiency of hydrophobic filter paper

[0078] To further investigate the separation behavior of hydrophobic filter paper in practical applications, 10 mL of an acetonitrile-water solution with a volume ratio of 1:1 (rich acetonitrile phase and rich water phase) was used as a model solution and poured into a hydrophobic filter paper funnel. The separation of acetonitrile-water solution by hydrophobic filter paper modified with five different concentrations of C4 and C8 reagents was examined. The results are as follows: Figure 7 In the actual separation process, the separation performance of the hydrophobic filter papers modified with 0.1% C4 and 0.1% C8 was as follows. Figure 7 As shown in Figure a, the red acetonitrile-rich phase rapidly permeates through the hydrophobic filter paper under gravity. Simultaneously, some colorless aqueous-rich phase also permeates through the hydrophobic filter paper, making acetonitrile-aqueous solution separation impossible. The separation results of hydrophobic filter papers modified with 0.3%-1.5% C4 and 0.3%-1.0% C8 are similar. Figure 7 As shown in b, the red acetonitrile-rich phase quickly passes through the hydrophobic filter paper, while the colorless water-rich phase is retained in the upper funnel, thus achieving the separation requirements of acetonitrile-water solution.

[0079] Based on the above separation results, the separation efficiency and separation flux of the acetonitrile-rich phase through hydrophobic filter paper modified with 0.3%-1.5% C4 and 0.3%-1.0% C8 were investigated to evaluate the separation performance of the filter paper. The calculation results are listed in Table 2.

[0080] Table 2 Separation efficiency and flux of hydrophobic filter paper for separating acetonitrile-rich phases

[0081]

[0082]

[0083] As shown in the table above, both C4 and C8 modified hydrophobic filter papers exhibit high separation fluxes, ranging from 420 to 485 L·m⁻¹. -2 ·h -1 and 345-415 L·m -2 ·h -1Meanwhile, the separation efficiency of the hydrophobic filter paper is also above 95%. Therefore, hydrophobic filter papers modified with 0.3%-1.5% C4 and 0.3%-1.0% C8 can separate the acetonitrile-rich phase and the water-rich phase with high throughput and high efficiency. The separation throughput of the C4-modified hydrophobic filter paper is higher than that of the C8-modified hydrophobic filter paper. The porosity and pore size of the hydrophobic filter paper surface decrease with the increase of the carbon chain length of the silanizing reagent, resulting in a decrease in separation throughput. The separation throughput of hydrophobic filter papers modified with different concentrations of C4 and C8 is affected by both the modification concentration and the interception concentration. Overall, the separation throughput shows a decreasing trend with the increase of the concentration of the modifying reagent and the interception concentration.

[0084] 7. Stability Study of Hydrophobic Filter Paper

[0085] In practical applications, durable and stable separation performance is of great significance for the treatment of WAS systems. This invention takes 0.5% C8 modified hydrophobic filter paper as an example to investigate the stability of the hydrophobic filter paper. The results are as follows: Figure 8 . Figure 8 The results show that after storing the hydrophobic filter paper at room temperature for 15 days, the static water contact angle of the filter paper changes very little, and the interception concentration does not change significantly. After storing it at room temperature for 90 days, the static water contact angle of the hydrophobic filter paper remains above 137°, decreasing by only 1.0%, and the interception concentration decreases from 0.50 to 0.35. According to the aforementioned research results, this interception concentration is still within the usable interception concentration range. After storing the hydrophobic filter paper at room temperature for 180 days, the static water contact angle of the hydrophobic filter paper still remains above 127°, and the interception concentration is approximately 0.30, still usable for the separation of acetonitrile-water solutions. The results demonstrate that the hydrophobic filter paper has superior hydrophobic stability and separation stability.

[0086] To simulate the application of hydrophobic filter paper in actual separation processes, 0.5% C8 modified hydrophobic filter paper was immersed in a series of acetonitrile-water mixed solutions with different volume fractions of acetonitrile for a certain period of time. The results are as follows: Figure 8 b. Figure 8 b shows that when hydrophobic filter paper was soaked in acetonitrile-aqueous mixed solutions with volume fractions of 10%, 30%, 50%, 70%, and 90% for 3 hours, the static water contact angle of the filter paper only decreased slightly by 0.3%-1.5%. When the soaking time was increased to 12 hours, the static water contact angle decreased by 2.0%-3.0%, indicating that the tested hydrophobic filter paper has good tolerance to acetonitrile-aqueous mixed solutions with volume fractions between 10% and 90%. Meanwhile, Figure 8c shows that the soaking time of the hydrophobic filter paper in the acetonitrile-water mixed solution has a certain impact on the interception concentration of the hydrophobic filter paper. When the hydrophobic filter paper is soaked in the acetonitrile-water mixed solution with the volume fraction of acetonitrile under investigation for 12 hours, the interception concentration of the hydrophobic filter paper decreases by 0.05-0.15. Moreover, as the volume fraction of acetonitrile in the soaking solution increases, the interception concentration of the hydrophobic filter paper gradually decreases. When the volume fraction of acetonitrile is as high as 90%, the interception concentration of the hydrophobic filter paper decreases from the initial 0.50 to 0.35 after soaking for 12 hours, but the interception concentration is still within the applicable range.

[0087] A circular filter paper with a diameter of 90 mm can hold a maximum of about 20 mL of solution when folded into a cone. Therefore, 20 mL of acetonitrile-water solution (with a volume ratio of acetonitrile-rich phase to water-rich phase of 1:1) was used as the model solution for the separation experiment. Figure 8 Figure d shows the relationship between the separation flux and separation efficiency of the hydrophobic filter paper and the number of separation cycles. During 25 consecutive separation cycles, the separation flux of the hydrophobic filter paper was approximately 240 L·m⁻¹. -2 ·h -1 -280L·m -2 ·h -1 The separation efficiency remained above 95% throughout the 25 separations, with no hydrophobic phase permeating the hydrophobic filter paper. These results indicate that the prepared hydrophobic filter paper exhibits good stability during the separation process.

[0088] 8. Investigate the phase separation induced by different salts.

[0089] In salt-induced phase separation, a suitable salt-inducing reagent is crucial for the separation of miscible systems. This invention investigates the acetonitrile-water phase separation induced by nine inorganic salts: LiCl, NaCl, KCl, NH4Cl, K2CO3, Na2CO3, Li2SO4, Na2SO4, and MgSO4. The nine inorganic salts were added to 10 mL (1:1, v / v) of an acetonitrile-water mixture at doses exceeding the saturation level in water. The volumes of the acetonitrile-rich and water-rich phases after phase separation were recorded. The volume fraction of acetonitrile in the acetonitrile-rich and water-rich phases was determined by gas chromatography. and The recovery rate R of acetonitrile in the separated acetonitrile-rich phase was calculated according to equation (1), and the results are as follows: Figure 9 As shown. Figure 9The results showed that all nine inorganic salts investigated could induce phase separation in the acetonitrile-water mixture. The volume fraction of acetonitrile in the acetonitrile-rich phases obtained after phase separation induced by chloride salts, K₂CO₃, and Na₂SO₄ was greater than 0.84 (the volume fraction of acetonitrile in the acetonitrile-water azeotrope). Among these, the volume fraction of acetonitrile in the acetonitrile-rich phases induced by LiCl, NaCl, NH₄Cl, and K₂CO₃ was greater than 0.9. The volume fraction of acetonitrile in the acetonitrile-rich phases induced by different anions was as follows: Cl - SO4 2- CO3 2- Of the six inorganic salts mentioned above that can increase the volume fraction of acetonitrile in the acetonitrile-rich phase solution to greater than 0.84%, although Na₂SO₄ and K₂CO₃ can achieve higher acetonitrile recovery rates, K₂CO₃ releases a large amount of heat during dissolution, which is not conducive to practical application. Furthermore, the volume fraction of acetonitrile in the acetonitrile-rich phase after Na₂SO₄ phase separation is only 0.86, and the wastewater containing Na₂SO₄ will cause environmental pollution. Therefore, considering both the cost and environmental friendliness of the salts, and while ensuring good phase separation capability, we chose NaCl as the salt-inducing reagent, which can guarantee the highest acetonitrile volume fraction in the induced phase separation phase and a near 80% acetonitrile recovery rate.

[0090] 9. Phase separation induced by NaCl in acetonitrile-water mixed solutions under different acetonitrile-water volume ratios.

[0091] In actual industrial production and laboratory research, the acetonitrile content in the obtained acetonitrile-water mixed solutions is usually unknown. To study the phase separation behavior of NaCl in acetonitrile-water mixed solutions with different volume ratios, samples were prepared at the same volume and different acetonitrile volume fractions. Salt-induced phase separation was studied using NaCl as an inducing agent in acetonitrile-aqueous mixed solutions with acetonitrile volume fractions of 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, and 0.85. The results of NaCl-induced phase separation in acetonitrile-aqueous mixed solutions with different acetonitrile volume fractions are shown below. Figure 10 .from Figure 10 An interesting phenomenon was observed: for the acetonitrile-water mixed solution under investigation, regardless of the change in the volume fraction of acetonitrile, after NaCl-induced phase separation, the volume fraction of acetonitrile in the resulting acetonitrile-rich phase was consistently approximately 0.92, while the volume fraction of acetonitrile in the resulting water-rich phase was consistently approximately 0.16. These results indicate that the initial volume fraction of acetonitrile in the acetonitrile-water mixed solution does not affect the phase separation induction ability of NaCl. For acetonitrile-water mixed systems with acetonitrile volume fractions increasing from 0.2 to 0.85, NaCl can efficiently induce phase separation, and in all cases, an acetonitrile-rich phase with a volume fraction as high as 0.92 can be obtained. This is crucial for the efficient recovery of acetonitrile from acetonitrile wastewater.

[0092] 10. Method Comparison

[0093] To compare the differences between our established method and the distillation separation effect, a constant-temperature magnetic stirrer with a rated power of 300W and a glass distillation apparatus were used to distill and separate the acetonitrile-water mixture. 100 mL of the acetonitrile-water mixture (acetonitrile to water volume ratio of 1:1, acetonitrile and water volume fractions of 50%) and 100 mL of the acetonitrile-water azeotropic mixture (acetonitrile to water volume ratio of 84:16, acetonitrile volume fraction of 84%, water volume fraction of 16%) were distilled at atmospheric pressure at 80℃. The distillation time was recorded, and the energy consumption of the distillation process was estimated. The energy consumption was calculated using equation (6):

[0094] W = P·t (6)

[0095] Where P is the rated power of the thermostatic magnetic stirrer integrating heating and stirring during normal operation, and t is the total time required for the distillation process. After diluting the separated sample solution, the volume fraction of acetonitrile in the solution was determined by GC-FID, and the results are listed in Table 3.

[0096] Table 3. Comparison of separation performance between distillation and SIPS-HF methods

[0097]

[0098] Note: "\" indicates that this method consumes very little energy, almost zero.

[0099] As shown in Table 3, distilling 100 mL of an acetonitrile-water mixture with a volume ratio of 50:50 to reach an azeotropic composition requires 100 minutes, while the SIPS-HF method only requires 20 minutes to separate the same mixture, which is 1 / 5 of the distillation time. Distillation not only suffers from high energy consumption and large water consumption, but the cost of laboratory distillation equipment is also almost 50 times that of the SIPS-HF method. The acetonitrile-water mixture is an infinitely miscible solution; atmospheric distillation can only obtain an acetonitrile-water mixture with a volume fraction of approximately 83%. Salt induction can disrupt the azeotropic point of the acetonitrile-water mixture, yielding an acetonitrile-rich phase with a volume fraction greater than 90%.

[0100] In summary, the low-energy-consumption method for separating acetonitrile-water according to this invention is simple, rapid, and energy-efficient, achieving a separation efficiency of over 95% while maintaining high throughput. Furthermore, this separation method is driven solely by gravity, consuming no other energy sources, making it suitable for industrial applications. The hydrophobic filter paper used in this invention retains strong hydrophobicity and a high acetonitrile interception concentration even after storage for 3 months or soaking in an acetonitrile-water mixture for 12 hours. Even after 25 consecutive separations of the solution at its maximum volume, it maintains high separation throughput and efficiency, with no aqueous phase observed passing through the hydrophobic filter paper. The separation process is stable, and the used hydrophobic filter paper can be directly incinerated without causing secondary pollution, making it environmentally friendly.

Claims

1. A low-energy-consumption method for separating acetonitrile-water, characterized in that, Includes the following steps: (1) Prepare a silanizing reagent-n-hexane solution, mix it by sonication, immerse filter paper in the silanizing reagent-n-hexane solution, and sonicate it at room temperature to modify the surface of the filter paper by silanization and hydrophobicity. Take out the filter paper and rinse the surface of the filter paper with n-hexane, ethanol and methanol in sequence, and then let it dry naturally to obtain hydrophobic filter paper; the silanizing reagent is butyltrichlorosilane or octyltrichlorosilane; in the silanizing reagent-n-hexane solution, the volume concentration of butyltrichlorosilane is 0.3-1.5% and the volume concentration of octyltrichlorosilane is 0.3-1.0%; (2) An inorganic salt is used to induce the acetonitrile-water mixed solution to separate into an acetonitrile-rich phase and a water-rich phase; the inorganic salt is NaCl; (3) After phase separation, the hydrophobic filter paper is used for filtration to separate the acetonitrile-rich phase and the water-rich phase.

2. The method for low-energy separation of acetonitrile-water according to claim 1, characterized in that, The volume fraction of acetonitrile in the acetonitrile-aqueous mixed solution is 20%-90%.

3. The method for low-energy separation of acetonitrile-water according to claim 1, characterized in that, The amount of inorganic salt added should exceed the saturation dose in the acetonitrile-water mixture.

4. The low-energy-consumption method for separating acetonitrile-water according to any one of claims 1-3, characterized in that, The filtration method is natural gravity filtration.

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