Preparation method of composite nanofiltration membrane, prepared composite nanofiltration membrane and application thereof, and method for solvent separation and recovery

Abstract

The application relates to the chemical industry field and discloses a preparation method of a composite nanofiltration membrane, the prepared composite nanofiltration membrane and application thereof, and a solvent separation and recovery method. The preparation method of the composite nanofiltration membrane comprises the following steps: (1) performing a chemical cross-linking reaction on a polyimide membrane and a cross-linking modification solution to obtain a polyimide support layer; (2) contacting the polyimide support layer with a hydrocarbon solution of an acyl chloride mixture to perform an interfacial polymerization reaction, thereby obtaining a composite nanofiltration membrane comprising a polyimide support layer and a polyamide separation layer containing an aromatic sulfonyl group; wherein the cross-linking modification solution is an alcohol solution of a sulfonamide monomer and a short-chain aliphatic diamine monomer. The preparation method can greatly improve the solvent resistance of the composite nanofiltration membrane and prolong the service life of the composite nanofiltration membrane.

Description

Technical Field

[0001] The present invention relates to the field of chemical industry, and in particular to a method for preparing a composite nanofiltration membrane, the prepared composite nanofiltration membrane and its application, and a method for solvent separation and recovery. Background Art

[0002] Solvent dewaxing technology is one of the most commonly used techniques in lubricant production. The dewaxing solvent used is primarily a mixture of toluene and butanone. Currently, the solvent in ketone-benzene dewaxing and deoiling units in industry is generally recovered using evaporation and steam stripping. Due to the large amount of solvent used, solvent recovery is the most energy-intensive element in the entire process. Solvent-resistant nanofiltration technology is a membrane separation technology that can be used to recover organic solvents. Under pressure-driven conditions, solvent-resistant nanofiltration selectively allows the permeation of low-molecular-weight solvents while retaining high-molecular-weight, high-value-added products or impurities. Because the separation process does not involve phase change, solvent recovery can be achieved with relatively low energy consumption.

[0003] Regarding solvent recovery during lubricating oil dewaxing, US Patent No. 5429748A discloses a polyimide nanofiltration membrane for solvent recovery in ketone-benzene dewaxing. At -10°C and 600 psi, the membrane achieves a flux of 7.6 GSFD and a lubricating oil retention rate of 96%. However, this nanofiltration membrane suffers from membrane fouling during use and requires regular cleaning.

[0004] CN109694745B, CN109692572B, and CN109694746B disclose a series of methods for recovering dewaxing solvent from lubricating oil feedstock using P84 polyimide nanofiltration membranes. These methods yield a high average organic solvent content in the membrane permeate and achieve excellent dewaxing solvent recovery at room temperature. These methods utilize a modified P84 nanofiltration membrane (CN101678286A) produced by Evonik, Germany. This method prepares the P84 membrane via a phase inversion process, followed by a 24-hour soaking in a diamine solution for chemical crosslinking. This results in a lengthy membrane preparation process, and the long-term separation stability of the membranes has not been tested. The membrane's separation stability in ketone-benzene solvents is unknown.

[0005] CN100363094C discloses a method for preparing a polyimide nanofiltration membrane. This method involves first preparing a polyamic acid nanofiltration membrane and then subjecting it to an amidation treatment. The polyimide prepared by this method is used to recover the solvent from ketone-benzene dewaxing of lubricating oil. However, the lubricating oil retention rate is only about 90%, and the recovered solvent is of low purity.

[0006] CN103464012B discloses a method for preparing an organic solvent-resistant polyimide nanofiltration membrane using an inorganic salt porogen. This method involves adding an inorganic salt to the polyimide casting solution to control the number of finger-like pores in the membrane and the thickness of the dense separation layer. The polyimide prepared by this method was used to recover the solvent from ketone-benzene dewaxing of lubricating oils. While the lubricating oil retention rate reached 90%, data on solvent recovery was lacking.

[0007] CN107174971A discloses a method for preparing a solvent-resistant polyamide nanofiltration membrane. This method uses a porous carrier such as a cross-linked polyimide or cross-linked polybenzimidazole as a support layer, on which a polyamide layer is composited to form the membrane. This invention uses an aqueous solution of a polyamine and m-phenylenediamine with a monoacyl chloride, polyacyl chloride, or mixture thereof for interfacial polymerization to prepare the polyamide layer. The long-term solvent tolerance of this separation membrane is not mentioned.

[0008] Therefore, there is a need for a nanofiltration membrane that can tolerate solvents for a long time while ensuring good separation performance. Summary of the Invention

[0009] The purpose of the present invention is to overcome the problems of low separation stability and low purity of recovered solvents in the nanofiltration membranes used in the membrane separation technology in the prior art, and to provide a preparation method of a composite nanofiltration membrane, a prepared composite nanofiltration membrane and its application, and a method for solvent separation and recovery. The preparation method can greatly improve the solvent resistance of the composite nanofiltration membrane and extend the service life of the composite nanofiltration membrane by compositely forming a separation layer of polyamide containing aromatic sulfone groups on a polyimide support layer. Within 500 hours of operation, the recovery performance of the composite nanofiltration membrane for lubricating oil dewaxing solvent remains basically stable.

[0010] In order to achieve the above object, the first aspect of the present invention provides a method for preparing a composite nanofiltration membrane, wherein the method comprises the following steps:

[0011] (1) chemically cross-linking the polyimide membrane with a cross-linking modification solution to obtain a polyimide support layer;

[0012] (2) contacting the polyimide support layer with a hydrocarbon solution of an acyl chloride mixture to perform an interfacial polymerization reaction to obtain a composite nanofiltration membrane comprising a polyimide support layer and a polyamide separation layer containing an aromatic sulfone group;

[0013] The cross-linking modification solution is an alcohol solution of a sulfonyl-containing diphenylamine monomer and a short-chain aliphatic diamine monomer.

[0014] The second aspect of the present invention provides a composite nanofiltration membrane prepared by the preparation method described in the first aspect, wherein the composite nanofiltration membrane comprises a polyimide support layer and a polyamide separation layer containing aromatic sulfone groups.

[0015] The third aspect of the present invention provides an application of the composite nanofiltration membrane described in the second aspect in the field of organic solvent separation and recovery.

[0016] The fourth aspect of the present invention provides a method for solvent separation and recovery, wherein the method comprises: using the composite nanofiltration membrane described in the second aspect to separate the lubricating oil dewaxing solvent, wherein the separation conditions include: a separation temperature of 10-30°C and an operating pressure of 2-4MPa.

[0017] Through the above technical solution, the beneficial effects obtained are as follows:

[0018] (1) The preparation method provided by the present invention is simple. The prepared composite nanofiltration membrane comprises a separation layer of polyamide containing aromatic sulfone groups on a polyimide support layer. The polyamide and polyimide are cross-linked by covalent action, which can greatly improve the solvent resistance and lubricating oil retention performance of the nanofiltration membrane. After 500 hours of use, the solvent recovery performance can still be maintained stably.

[0019] (2) In the present invention, preferably, the preparation of the composite nanofiltration membrane can flexibly control the retention performance and flux of the composite nanofiltration membrane by changing the type of solvent used in the post-reaction treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is an infrared spectrum of the composite nanofiltration membrane prepared in Example 1;

[0021] Figure 2 These are scanning electron microscope cross-sectional views of the composite nanofiltration membrane prepared in Example 1 and a partially enlarged scanning electron microscope cross-sectional view of the polyamide separation layer, a being a scanning electron microscope cross-sectional view of the composite nanofiltration membrane, and b being a partially enlarged scanning electron microscope cross-sectional view of the polyamide separation layer. DETAILED DESCRIPTION

[0022] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0023] A first aspect of the present invention provides a method for preparing a composite nanofiltration membrane, wherein the method comprises the following steps:

[0024] (1) chemically cross-linking the polyimide membrane with a cross-linking modification solution to obtain a polyimide support layer;

[0025] (2) contacting the polyimide support layer with a hydrocarbon solution of an acid chloride mixture to perform an interfacial polymerization reaction to obtain a composite nanofiltration membrane comprising a polyimide support layer and a polyamide separation layer containing aryl sulfone groups;

[0026] The cross-linking modification solution is an alcohol solution of a sulfone group-containing diphenylamine monomer and a short-chain aliphatic diamine monomer.

[0027] In the present application, the preparation method is to chemically cross-link and modify the imine group of the polyimide film with a diamine monomer, and the modified product is further contacted with an acid chloride mixture to perform an interfacial polymerization reaction to obtain a composite nanofiltration membrane comprising a polyimide support layer and a polyamide separation layer containing aryl sulfone groups. The solvent resistance of the composite nanofiltration membrane can be greatly improved, and the service life of the composite nanofiltration membrane is prolonged. Within 500 hours of work, the recovery performance of the composite nanofiltration membrane to the dewaxing solvent of lubricating oil is basically stable.

[0028] According to the present application, preferably, in step (1), the polyimide film is prepared by the following method:

[0029] The polyimide powder is mixed with a solvent, and after the mixed solution is degassed, a polyimide casting solution is obtained. The polyimide casting solution is coated on a polypropylene non-woven fabric to form a film, and the film is immersed in water and an alcohol reagent to obtain a polyimide film.

[0030] In the present application, the degassing method of the mixed solution is not particularly limited, and the conventional degassing method in the art can be used. Preferably, the degassing is static degassing and / or ultrasonic degassing, and the degassing time is not particularly limited. According to a preferred embodiment of the present application, the static degassing method is used, and the static degassing includes: at room temperature, the mixed solution is left standing for 12-24h.

[0031] In the present application, the mixing method of the polyimide powder and the solvent is not particularly limited, as long as the polyimide powder is fully dissolved. Preferably, the stirring mixing method is used, and the stirring rate is 500-1200rpm / min, and the stirring time is 1-20h.

[0032] In the present application, the source of the polyimide powder can be commercially available or prepared by existing methods, and the skilled person in the art can adaptively select. In the present application, preferably, the polyimide powder is dried in vacuum before use, and the drying temperature is 60-100℃.

[0033] In the present application, the device for the film scraping is not particularly limited, and according to a preferred embodiment of the present application, the film scraping can be performed in a film scraping machine. The film scraping speed is not particularly limited, and is preferably 20-200 mm / s. The film scraping thickness is not particularly limited, and is preferably 150-300 µm, preferably 150-250 µm. According to a preferred embodiment of the present application, after the film scraping is completed, the film scraping product is quickly placed in deionized water for 1-3 h, and then transferred to an alcohol reagent for soaking for 12 h or more, to obtain a polyimide film.

[0034] According to the present application, preferably, the mass concentration of polyimide in the polyimide casting solution is 15-25 wt%, preferably 16-22 wt%.

[0035] According to the present application, preferably, the solvent is a mixed solvent of N,N-dimethylformamide and 1,4-dioxane.

[0036] According to the present application, preferably, the mass ratio of N,N-dimethylformamide to 1,4-dioxane in the solvent is 0.3-5:1, preferably 2-4:1. In the present application, preferably, the polyimide mixed solution casting solution is prepared by using the above-mentioned solvent combination, and the polyimide film prepared has a more uniform pore size distribution, and the composite nanofiltration membrane prepared further has better uniformity.

[0037] According to the present application, preferably, the alcohol reagent is selected from at least one of methanol, ethanol and isopropanol.

[0038] According to the present application, preferably, in the cross-linking modification solution, the total mass concentration of the sulfonamide-containing diphenylamine monomer and the short-chain aliphatic diamine monomer is 0.5-8 wt%, for example 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, or any range between any two of them, preferably 1-5 wt%.

[0039] In the present application, preferably, the cross-linking modification solution further comprises an activity aid. The activity aid can improve the activity of the subsequent interfacial polymerization reaction of the sulfonamide-containing diphenylamine monomer and the sulfuryl chloride monomer. Preferably, the activity aid is selected from at least one of triethylamine, potassium hydroxide, sodium hydroxide and sodium bicarbonate. The mass concentration of the activity aid in the cross-linking modification solution is 0.1-1 wt%, preferably 0.1-0.5 wt%.

[0040] According to the present application, preferably, the mass ratio of the sulfonamide-containing diphenylamine monomer to the short-chain aliphatic diamine monomer is 1-3:1, preferably 1-2:1.

[0041] According to the present invention, preferably, the crosslinking and modifying solution contains a solvent selected from at least one of methanol, ethanol, and isopropanol. In the present invention, preferably, the crosslinking and modifying solution contains a solvent that is consistent with the alcohol reagent used to prepare the polyimide membrane, thereby controlling the polyimide membrane to maintain the same swelling state as during modification, thereby promoting a better crosslinking reaction.

[0042] According to the present invention, preferably, in step (1), the volume of the cross-linking modification solution added per square meter of the polyimide membrane is 1-10 L, preferably 2-5 L.

[0043] According to the present invention, preferably, the conditions of the chemical cross-linking reaction include: a reaction temperature of 10-35° C., preferably 15-25° C.; and a reaction time of 5-30 min, preferably 10-30 min.

[0044] In the present invention, the polyimide membrane swells in alcoholic solvents, allowing some sulfonyl-containing diphenylamine monomers and short-chain aliphatic diamine monomers to enter the polyimide. Chemical crosslinking covalently connects the diamine to the imide groups on the polyimide, primarily occurring on the surface of the polyimide membrane. Due to their linear structure and low molecular weight, the short-chain aliphatic diamine monomers can more easily enter the polyimide membrane, crosslinking with the polyimide segments and improving the membrane's solvent resistance.

[0045] In the present invention, polyimide undergoes chemical crosslinking with a sulfonyl-containing diphenylamine monomer and a short-chain aliphatic diamine monomer. The imide ring of the polyimide opens, and the C=O bond connects to the NH group of the sulfonyl-containing diphenylamine monomer or the short-chain aliphatic diamine monomer, forming an amide group. Chemical crosslinking introduces S=O and CH groups onto the surface of the polyimide film, demonstrating the occurrence of crosslinking between the polyimide, the sulfonyl-containing diphenylamine monomer, and the short-chain aliphatic diamine monomer.

[0046] In the present invention, by infrared spectroscopy ( Figure 1 ) and X-ray photoelectron spectroscopy (Table 1) to characterize the polyimide film before and after diamine modification. The infrared spectrum characterization results show that after diamine modification, the 1711cm -1 and 1780cm -1 The C=O stretching vibration peak of the imide group at 1360 cm -1 The CN stretching vibration peak intensity of the imide group at 1540-1560 cm -1 The CN / NH peak of the amide group at 1620-1640 cm -1 The C=O peak intensity of the amide group at 3300 cm -1The stretching vibration peak of NH after diamine grafting was newly added at 1310-1360cm. The above results show that the imide ring on the polyimide is opened, in which the C=O bond is connected to the NH of the diamine monomer to form an amide group; -1 and 1135-1165cm -1 A new characteristic peak of S=O after cross-linking of diphenylamine monomer containing sulfonyl group was added at 3100-3200 cm -1 A new CH stretching vibration peak on the unsaturated carbon after cross-linking of the sulfonyl-containing diphenylamine monomer was added, indicating that the sulfonyl-containing diphenylamine monomer and polyimide were cross-linked; 2700-3000 cm -1 The CH stretching vibration peak at the saturated carbon at [a] showed a significant shift and increased intensity, indicating that the short-chain aliphatic diamine monomer and the polyimide were cross-linked, introducing new saturated CH bonds on the membrane surface. X-ray photoelectron spectroscopy revealed that after diamine modification, the S element appeared on the membrane surface, the C element content on the membrane surface decreased significantly, and the N and O element contents increased significantly, corresponding to the above-mentioned infrared spectroscopy results, indicating that the diamine monomer and the polyimide membrane were cross-linked.

[0047] According to the present invention, preferably, the sulfonyl diphenylamine monomer is 4,4'-sulfonyl diphenylamine and / or 3,3'-sulfonyl diphenylamine. In the present invention, the diphenylamine monomer is limited to the above-mentioned sulfonyl diphenylamine monomer. Cross-linking with polyimide can introduce aromatic sulfone groups into the polymer chain segment, thereby improving the solvent resistance of the membrane.

[0048] According to the present invention, preferably, the short-chain aliphatic diamine monomer is selected from at least one of ethylenediamine, 1,3-propylenediamine, 1,4-butylenediamine, 1,5-pentanediamine, and 1,6-hexanediamine, preferably ethylenediamine and / or 1,3-propylenediamine. In the present invention, if the molecular chain of the short-chain aliphatic diamine monomer is too long, the aliphatic diamine monomer will have difficulty diffusing into the interior of the polyimide film due to the short crosslinking time, resulting in poor crosslinking effect.

[0049] According to the present invention, the acid chloride mixture preferably comprises terephthaloyl chloride and an aromatic sulfonyl chloride compound. In the present invention, the terephthaloyl chloride and aromatic sulfonyl chloride compounds in the acid chloride mixture react with the imine groups generated by the cross-linking reaction on the polyimide membrane and the residual unreacted diamine monomers to form an interfacial polymerization reaction, thereby forming a dense polyamide separation layer containing aromatic sulfone groups.

[0050] In the present invention, by infrared spectroscopy ( Figure 1 ) and X-ray photoelectron spectroscopy (Table 1) were used to characterize the composite nanofiltration membrane prepared by adding the acyl chloride mixture for interfacial polymerization. The infrared spectroscopy results showed that after the addition of the acyl chloride mixture for interfacial polymerization, the 3300 cm -1The NH stretching vibration peak at 1540-1560 cm -1 The CN / NH peak intensity at 950-1000 cm -1 The SN stretching vibration peak appeared at , and the characterization results of X-ray photoelectron spectroscopy showed that after the interfacial polymerization reaction, the content of C and N elements on the membrane surface decreased, while the content of O and S elements increased. The above results indicate that the imine groups generated after the cross-linking reaction on the polyimide membrane and the residual unreacted diamine monomer and acyl chloride mixture underwent interfacial polymerization reaction to form a dense polyamide separation layer containing aromatic sulfone groups.

[0051] According to the present invention, preferably, in step (2), the volume of the acyl chloride mixture solution added per square meter of the polyimide support layer is 2-6 L, preferably 2.5-4 L.

[0052] According to the present invention, preferably, in the hydrocarbon solution of the acyl chloride mixture, the total mass concentration of the acyl chloride mixture is 0.05-2wt%, preferably 0.1-1wt%. In the present invention, the total mass concentration of the acyl chloride mixture is limited, the rate of interfacial polymerization reaction and the density of generated interfacial polymerization layer can be controlled. The concentration of acyl chloride mixture is too low, and interfacial polymerization reaction efficiency is low, and the polyamide layer generated is not dense enough, and the interception effect is not good; The concentration of acyl chloride mixture is too high, and interfacial polymerization reaction is too violent, and the polyamide layer may be caused to be too thick, and the thickness is uneven, resulting in low membrane flux, and interception performance is not significantly improved.

[0053] According to the present invention, preferably, the interfacial polymerization reaction conditions include: a reaction temperature of 10-35°C, preferably 15-25°C; and a reaction time of 0.5-5 minutes, preferably 1-5 minutes. In the present invention, the interfacial polymerization reaction is fast and the reaction temperature is low, which can avoid side reactions at high temperatures. There are no particular restrictions on the reaction equipment.

[0054] According to the present invention, preferably, the aromatic sulfonyl chloride compound is 1,3-benzenedisulfonyl chloride and / or biphenyl-4,4-disulfonyl chloride. In the present invention, the aromatic sulfonyl chloride compound is subjected to an interfacial polymerization reaction with a diamine monomer to introduce sulfonamide groups into the polyamide separation layer, further enhancing the solvent resistance of the membrane.

[0055] According to the present invention, preferably, the mass ratio of terephthaloyl chloride to aromatic sulfonyl chloride in the acid chloride mixture is 0.1-2:1, preferably 0.3-1.5:1. In the present invention, the simultaneous addition of terephthaloyl chloride and aromatic sulfonyl chloride to the interfacial polymerization reaction can improve the efficiency of the interfacial polymerization reaction, forming a denser polyamide separation layer containing aromatic sulfone groups, and enhancing the membrane's lubricant oil retention and solvent resistance.

[0056] According to the present invention, preferably, the solvent contained in the hydrocarbon solution of the acyl chloride mixture is at least one selected from n-pentane, n-hexane, n-heptane, n-octane, toluene and trimethylbenzene.

[0057] According to the present invention, preferably, in step (2), after the interfacial polymerization reaction is completed, a termination reaction treatment is further performed, wherein the termination reaction treatment process comprises: soaking the polymerization product obtained by the interfacial polymerization reaction at the interface in an organic solvent for 0.5 min-1 min, and then curing at 60-100°C for 2-10 min.

[0058] According to the present invention, preferably, the organic solvent is selected from at least one of n-hexane, isopropanol and formamide, preferably n-hexane. In the present invention, an organic solvent is used to carry out a termination reaction treatment, and the organic solvent reacts with the unreacted acyl chloride monomer remaining in the interfacial polymerization reaction to perform end-capping. The amount of the organic solvent is not particularly limited. The use of the organic solvent of the preferred embodiment for the termination reaction treatment contributes to the regulation of the retention performance and membrane flux of the composite nanofiltration membrane. After the interfacial polymerization reaction is completed, the organic solvent is used to terminate the reaction, and while removing the acyl chloride monomer remaining in the interfacial polymerization reaction, no carboxyl group is introduced.

[0059] The second aspect of the present invention provides a composite nanofiltration membrane prepared by the preparation method described in the first aspect, wherein the composite nanofiltration membrane comprises a polyimide support layer and a polyamide separation layer containing aromatic sulfone groups.

[0060] In the present invention, the polyamide separation layer containing aromatic sulfone groups is obtained by interfacial polymerization of a mixture of sulfonyl-containing diphenylamine monomers, short-chain aliphatic diamine monomers and acyl chlorides, wherein the aromatic sulfone groups in the polyamide segments are connected to sulfonamide groups or amide groups.

[0061] According to the present invention, preferably, the thickness of the polyimide support layer is 150-300µm, preferably 150-250µm. In the present invention, the polyimide support layer comprises a cross-linked modified polyimide film and a polypropylene non-woven fabric layer.

[0062] According to the present invention, the thickness of the polyamide separation layer containing aromatic sulfone groups is preferably 100-400 nm, preferably 150-300 nm. In the present invention, if the thickness of the polyamide separation layer containing aromatic sulfone groups is too great, the membrane flux of the composite nanofiltration membrane is low; if the thickness is too small, the membrane separation effect is poor.

[0063] In the present invention, the polyamide containing aromatic sulfone groups has a structure as shown in formula (I) or formula (II):

[0064] Formula (I);

[0065] Formula (II);

[0066] Among them, R is C or S=O group (S is connected to N), and R1 is H or polyimide polymer chain segment.

[0067] In the present invention, R1 is introduced by cross-linking a diamine monomer with a polyimide. When the aforementioned sulfonyl-containing diphenylamine monomer and the aforementioned short-chain aliphatic diamine monomer are not completely cross-linked with the polyimide polymer segment, R1 is the remaining H from the reaction of the uncross-linked diamine monomer with the acyl chloride monomer. According to a preferred embodiment of the present invention, the polyimide is a commercially available product of BASF, brand Matrimid 5218, with a weight-average molecular weight of 30,000-40,000 Da. The polyimide polymer segment obtained by the aforementioned chemical cross-linking of the short-chain diamine monomer with the polyimide has a structure represented by formula (III):

[0068] Formula (III).

[0069] In the present invention, R is introduced by the added terephthaloyl chloride and aromatic sulfonyl chloride compounds. When the sulfonyl-containing diphenylamine monomer reacts with terephthaloyl chloride, R is a carbon atom; when the sulfonyl-containing diphenylamine monomer reacts with the aromatic sulfonyl chloride compound, R is an S=O group. The aromatic sulfone-containing polyamide separation layer is obtained by polycondensing the sulfonyl-containing diphenylamine monomer with the acyl chloride monomer to remove H and Cl atoms, respectively.

[0070] In the present invention, the short-chain aliphatic diamine monomer can also undergo a condensation reaction with terephthaloyl chloride and an aromatic sulfonyl chloride compound to remove H and Cl atoms respectively, so that the two acyl chloride monomers in the aromatic sulfone group-containing polyamide separation layer can also be connected to the residue after the two H atoms of the short-chain aliphatic diamine monomer are removed.

[0071] The third aspect of the present invention provides an application of the composite nanofiltration membrane described in the second aspect in the field of organic solvent separation and recovery.

[0072] According to the present invention, the composite nanofiltration membrane is preferably used for separating and recovering butanone and toluene solvents from lubricating oil dewaxing solvents. In the present invention, the composite nanofiltration membrane has good recovery performance for lubricating oil dewaxing solvents, a high retention rate for lubricating oil base oils, and good solvent resistance.

[0073] The fourth aspect of the present invention provides a method for solvent separation and recovery, wherein the method comprises: using the composite nanofiltration membrane described in the second aspect to separate the lubricating oil dewaxing solvent, wherein the separation conditions include: a separation temperature of 10-30°C and an operating pressure of 2-4MPa.

[0074] In the present invention, the equipment for solvent separation and recovery is not particularly limited, and those skilled in the art may select conventional separation equipment. In the present invention, preferably, a small-scale cross-flow membrane separation device is used to verify the separation and recovery of lubricating oil dewaxing solvent using a composite nanofiltration membrane. In the present invention, the feed rate of the lubricating oil dewaxing solvent is 10-60 mL / min.

[0075] In the present invention, under the conditions of operating pressure of 4 MPa, separation temperature of 25 ° C and membrane permeability of 40%, the rejection rate of the composite nanofiltration membrane for lubricating oil base oil in ketone benzene solvent is maintained between 93% and 99%, and the membrane flux is between 15 and 30 kg / m 2 After 500 hours of solvent immersion, the composite nanofiltration membrane's recovery performance for lubricating oil dewaxing solvent remained basically stable, with good solvent resistance, and was able to meet the requirements of long-term use in organic solvents.

[0076] In the present invention, the raw materials of the lubricating oil dewaxing solvent include butanone, toluene and lubricating oil base oil, and the weight percentage of each component is not particularly limited. Preferably, the raw material composition of the lubricating oil dewaxing solvent includes 20-60wt% butanone, 20-60wt% toluene and 10-30wt% lubricating oil base oil.

[0077] According to a particularly preferred embodiment of the present invention, a method for preparing a composite nanofiltration membrane is characterized in that the method comprises the following steps:

[0078] (1) chemically cross-linking the polyimide membrane with a cross-linking modification solution to obtain a polyimide support layer;

[0079] (2) contacting the polyimide support layer with a hydrocarbon solution of an acyl chloride mixture to perform an interfacial polymerization reaction to obtain a composite nanofiltration membrane comprising a polyimide support layer and a polyamide separation layer containing an aromatic sulfone group;

[0080] Wherein, the cross-linking modification solution is an alcohol solution of a sulfonyl-containing diphenylamine monomer and a short-chain aliphatic diamine monomer;

[0081] In the cross-linking modification solution, the total mass concentration of the sulfonyl-containing diphenylamine monomer and the short-chain aliphatic diamine monomer is 1-5wt%;

[0082] The mass ratio of the sulfonyl-containing diphenylamine monomer to the short-chain aliphatic diamine monomer is 1-2:1;

[0083] In the hydrocarbon solution of the acyl chloride mixture, the total mass concentration of the acyl chloride mixture is 0.1-1wt%;

[0084] The acyl chloride mixture includes terephthaloyl chloride and aromatic sulfonyl chloride compounds;

[0085] The mass ratio of terephthaloyl chloride to aromatic sulfonic acid chloride in the acyl chloride mixture is 0.3-1.5:1.

[0086] The present application will be described in detail below by way of examples and comparative examples. In the following examples and comparative examples, room temperature refers to 25°C;

[0087] The thickness of the polyimide support layer was measured by a screw micrometer, and the thickness of the polyamide separation layer containing aryl sulfone groups was measured by a scanning electron microscope cross-section image;

[0088] The changes in the surface elemental composition and the functional group composition of the polyimide membrane, the cross-linked polyimide support layer, and the composite nanofiltration membrane were measured by X-ray photoelectron spectroscopy and infrared spectroscopy;

[0089] The polyimide raw material was a commercially available product from BASF with the trade name Matrimid 5218. The polyimide powder used was vacuum dried at 80°C for 1 h before being dissolved.

[0090] Example 1

[0091] (1-1) A mixed solvent of N,N-dimethylformamide (DMF) and 1,4-dioxane was prepared with a mass ratio of 3:1, 1.8 g of polyimide powder was added, and the mixture was stirred and blended at 800 rpm / min for 6 h to fully dissolve the polyimide, and then the solution was left to stand for more than 12 h to degas.

[0092] (1-2) The film thickness of the knife coater was set to 250 µm and the speed was 100 mm / s, then the degassed polyimide casting solution was poured onto the polypropylene non-woven fabric to start the film coating, and after the film coating was completed, it was quickly placed in deionized water for 3 h, then transferred to an alcohol reagent for 12 h to obtain a polyimide membrane.

[0093] (1-3) Cross-linking modification solution: 1,3-propanediamine with a mass concentration of 1 wt% and 4,4'-diaminodiphenyl sulfone with a mass concentration of 1 wt% were prepared with ethanol as the solvent, and 0.2 wt% of triethylamine was added to the solution;

[0094] Preparation of acyl chloride mixture solution: prepare 0.05 wt% terephthaloyl chloride and 0.1 wt% 1,3-benzenedisulfonyl chloride with n-hexane as the solvent.

[0095] (1-4) The 80 cm 2 long polyimide membrane was immersed in 25 mL of the cross-linking modification solution at room temperature for 20 min, then removed and blown to remove the residual solution on the membrane to obtain a polyimide support layer;

[0096] (2) Pour 25 mL of the acyl chloride mixture solution on the surface of the polyimide support layer, and allow the interfacial polymerization reaction to proceed at room temperature for 5 minutes before quickly removing the solution. Then pour n-hexane reagent on the membrane surface, soak it for 1 minute, remove the n-hexane, and place it in air for curing at 80°C for 5 minutes to obtain a composite nanofiltration membrane.

[0097] Figure 2 The SEM cross-sectional view of the composite nanofiltration membrane prepared in Example 1 and the partially enlarged SEM cross-sectional view of the polyamide separation layer are shown in Figure a, and the SEM cross-sectional view of the polyamide separation layer is shown in Figure b. The thickness of the polyimide support layer in the composite nanofiltration membrane is 240 μm. Figure 2 It can be observed that the thickness of the separation layer of polyamide containing aromatic sulfone groups is 225 nm.

[0098] Table 1 shows the elemental composition (X-ray photoelectron spectroscopy) of the surfaces of polyimide membrane, diamine-modified polyimide membrane and composite nanofiltration membrane.

[0099] Table 1

[0100]

[0101] Example 2

[0102] A composite nanofiltration membrane was prepared according to the method of Example 1, except that in step (1-3), the concentration of 1,3-propylenediamine was 1.2 wt % and the concentration of 4,4'-sulfonyldiphenylamine was 0.8 wt %.

[0103] Example 3

[0104] A composite nanofiltration membrane was prepared according to the method of Example 1, except that in steps (1-3), 1,3-propylenediamine was replaced with an equal mass of 1,4-butanediamine.

[0105] Example 4

[0106] The method of Example 1 was followed, except that the solution for preparing the acyl chloride mixture in steps (1-3) was changed to a solution of 0.15 wt% terephthaloyl chloride and 0.05 wt% 1,3-benzenedisulfonyl chloride, with n-hexane as the solvent. A composite nanofiltration membrane was prepared.

[0107] Example 5

[0108] (1-1) Prepare a 10 g mixed solvent of N,N-dimethylformamide (DMF) and 1,4-dioxane in a mass ratio of 2:1. Add 1.8 g of polyimide powder to the mixture, and stir at 800 rpm / min for 6 h to fully dissolve the polyimide. Then, let the solution stand for at least 12 h to degas.

[0109] (1-2) Set the doctor blade thickness of the film doctoring machine to 300 µm, and the speed to 100 mm / s, then pour the defoamed polyimide casting solution onto the polypropylene non-woven fabric to start film doctoring, and after film doctoring is completed, quickly place it in deionized water for 3 h, then transfer it to an alcohol reagent for 12 h of immersion, to obtain a polyimide film.

[0110] (1-3) Cross-linking modification solution: prepare a solution of 1,6-hexanediamine with a mass concentration of 0.8 wt% and 3,3'-sulfonyldianiline with a mass concentration of 1.2 wt%, and the solvent is ethanol;

[0111] Prepare a solution of the acid chloride mixture: prepare a solution of terephthaloyl chloride with a mass concentration of 0.05 wt% and 1,3-benzenedisulfonyl chloride with a mass concentration of 0.1 wt%, and the solvent is n-hexane.

[0112] (1-4) At room temperature, immerse an 80 cm 2 long polyimide film in 25 mL of the cross-linking modification solution for 20 min, then blow off the residual solution on the film to obtain a polyimide support layer;

[0113] (2) Pour 25 mL of the solution of the acid chloride mixture onto the surface of the polyimide support layer, and after 5 min of interfacial polymerization at room temperature, quickly remove the solution; then pour n-hexane reagent onto the surface of the film, immerse for 1 min, then remove the n-hexane, and place it in air at 80°C for 5 min of curing, to obtain a composite nanofiltration membrane.

[0114] Example 6

[0115] According to the method of Example 1, except that 1,3-benzenedisulfonyl chloride in step (2) is replaced by an equal mass of trimesoyl chloride. A composite nanofiltration membrane is prepared.

[0116] Example 7

[0117] According to the method of Example 1, except that the diamine modification time in step (1-4) is changed to 2 min, and the interfacial polymerization time in step (2) is changed to 1 min. A composite nanofiltration membrane is prepared.

[0118] Comparative Example 1

[0119] According to the method of Example 1, except that in step (1-3), the cross-linking modification solution only contains 2 wt% of 4,4'-sulfonyldianiline. A composite nanofiltration membrane is prepared.

[0120] Comparative Example 2

[0121] According to the method of Example 1, except that in step (1-3), the cross-linking modification solution only contains 2 wt% of 1,3-propanediamine. A composite nanofiltration membrane is prepared.

[0122] Comparative Example 3

[0123] The polyimide support layer was prepared by the same steps (1-1) to (1-4) as in Example 1, and the polyimide support layer was directly used for recovering the lubricating oil dewaxing solvent without performing the subsequent steps.

[0124] Test Example 1

[0125] In the present invention, the separation performance of the prepared solvent-resistant composite nanofiltration membrane is evaluated using a small cross-flow membrane separation device built in the laboratory. The raw material composition of the lubricating oil dewaxing solvent is 40wt% butanone + 40wt% toluene + 20wt% lubricating oil base oil. The effective area of ​​the composite nanofiltration membrane used for the test is 12.56cm 2 The raw material amount of lubricating oil dewaxing solvent is 60 g, the separation temperature is 20℃, the operating pressure is 4MPa, and the feed flow rate of lubricating oil dewaxing raw material solvent is 60mL / min. The results are shown in Table 2.

[0126] (1) The flux of the composite nanofiltration membrane for treating the lubricating base oil dewaxing solvent is calculated by the following formula:

[0127] J=Q / (A·t), where J is the membrane flux (kg / m 2 / h), Q is the amount of permeate collected (kg), A is the effective membrane area of ​​the composite nanofiltration membrane (m 2 ), t is time (h);

[0128] (2) The retention rate of the composite nanofiltration membrane for lubricating oil base oil is calculated by the following formula:

[0129] R=(C Y -C P ) / C Y ×100%, where R is the retention rate of lubricating oil base oil (%), C Y is the mass fraction of lubricating oil base oil in the raw material, C P is the mass fraction of lubricating base oil in the permeate;

[0130] (3) The membrane permeability of the composite nanofiltration membrane in the process of treating lubricating oil base oil is calculated by the following formula:

[0131] X = M P / M Y ×100%, where X is the transmittance (%), M Y is the mass of raw materials, M P is the mass of the collected permeate. The test results in Table 2 show that the membrane permeation rate is 40%;

[0132] Table 2

[0133]

[0134] From the results in Table 2, it can be seen that the composite nanofiltration membrane of the embodiment of the present invention has a higher membrane flux and a retention rate for lubricating oil base oil, can still maintain a high retention rate after 500 hours, and has good solvent resistance.

[0135] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A method for preparing a composite nanofiltration membrane, characterized in that: The method comprises the following steps: (1) chemically cross-linking the polyimide membrane with a cross-linking modification solution to obtain a polyimide support layer; (2) contacting the polyimide support layer with a hydrocarbon solution of an acyl chloride mixture to perform an interfacial polymerization reaction to obtain a composite nanofiltration membrane comprising a polyimide support layer and a polyamide separation layer containing an aromatic sulfone group; Wherein, the cross-linking modification solution is an alcohol solution of a sulfonyl-containing diphenylamine monomer and a short-chain aliphatic diamine monomer; The acyl chloride mixture comprises terephthaloyl chloride and aromatic sulfonyl chloride compounds.

2. The preparation method according to claim 1, wherein In step (1), the polyimide film is prepared by the following method: The polyimide powder is mixed with a solvent, and the mixed solution is degassed to obtain a polyimide film casting solution. The polyimide film casting solution is coated on a polypropylene non-woven fabric and scraped into a film. The film is immersed in water and an alcohol reagent to obtain a polyimide film.

3. The preparation method according to claim 2, wherein The mass concentration of polyimide in the polyimide casting solution is 15-25wt%; And / or, the solvent is a mixed solvent of N,N-dimethylformamide and 1,4-dioxane.

4. The preparation method according to claim 3, wherein The mass concentration of polyimide in the polyimide casting solution is 16-22 wt %.

5. The preparation method according to claim 2, wherein The mass ratio of N,N-dimethylformamide to 1,4-dioxane in the solvent is 0.3-5:1; And / or, the alcohol reagent is selected from at least one of methanol, ethanol and isopropanol.

6. The preparation method according to claim 5, wherein The mass ratio of N,N-dimethylformamide to 1,4-dioxane in the solvent is 2-4:

1.

7. The preparation method according to claim 1 or 2, wherein In the cross-linking modification solution, the total mass concentration of the sulfonyl-containing diphenylamine monomer and the short-chain aliphatic diamine monomer is 0.5-8 wt %.

8. The preparation method according to claim 7, wherein In the cross-linking modification solution, the total mass concentration of the sulfonyl-containing diphenylamine monomer and the short-chain aliphatic diamine monomer is 1-5 wt %.

9. The preparation method according to claim 7, wherein The mass ratio of the sulfonyl-containing diphenylamine monomer to the short-chain aliphatic diamine monomer is 1-3:

1.

10. The preparation method according to claim 9, wherein The mass ratio of the sulfonyl-containing diphenylamine monomer to the short-chain aliphatic diamine monomer is 1-2:

1.

11. The preparation method according to claim 7, wherein The cross-linking modification solution contains a solvent selected from at least one of methanol, ethanol and isopropanol; And / or, the conditions of the chemical cross-linking reaction include: reaction temperature of 10-35° C.; reaction time of 5-30 min.

12. The preparation method according to claim 11, wherein The conditions of the chemical cross-linking reaction include: reaction temperature of 15-25° C.; reaction time of 10-30 min.

13. The preparation method according to claim 7, wherein The sulfonyl-containing diphenylamine monomer is 4,4'-sulfonyl diphenylamine and / or 3,3'-sulfonyl diphenylamine; And / or, the short-chain aliphatic diamine monomer is at least one selected from ethylenediamine, 1,3-propylenediamine, 1,4-butylenediamine, 1,5-pentanediamine and 1,6-hexanediamine.

14. The preparation method according to claim 1, wherein In the hydrocarbon solution of the acyl chloride mixture, the total mass concentration of the acyl chloride mixture is 0.05-2wt%; And / or, the conditions of the interfacial polymerization reaction include: a reaction temperature of 10-35°C; The reaction time is 0.5-5min.

15. The preparation method according to claim 14, wherein In the hydrocarbon solution of the acyl chloride mixture, the total mass concentration of the acyl chloride mixture is 0.1-1wt%; And / or, the conditions of the interfacial polymerization reaction include: reaction temperature of 15-25° C.; reaction time of 1-5 min.

16. The preparation method according to claim 1, wherein The aromatic sulfonyl chloride compound is 1,3-benzenedisulfonyl chloride and / or biphenyl-4,4-disulfonyl chloride.

17. The preparation method according to claim 1, wherein In the acyl chloride mixture, the mass ratio of terephthaloyl chloride to aromatic sulfonyl chloride compound is 0.1-2:1; And / or, the solvent contained in the hydrocarbon solution of the acyl chloride mixture is at least one selected from n-pentane, n-hexane, n-heptane, n-octane, toluene and trimethylbenzene.

18. The preparation method according to claim 17, wherein In the acyl chloride mixture, the mass ratio of terephthaloyl chloride to aromatic sulfonyl chloride compounds is 0.3-1.5:

1.

19. The preparation method according to claim 1, wherein In step (2), after the interfacial polymerization reaction is completed, a termination reaction treatment is further performed, wherein the termination reaction treatment process includes: soaking the polymerization product obtained by the interfacial polymerization reaction in an organic solvent for 0.5 min-1 min, and then curing it at 60-100° C. for 2-10 min.

20. The preparation method according to claim 19, wherein The organic solvent is selected from at least one of n-hexane, isopropyl alcohol and formamide.

21. The preparation method according to claim 20, wherein The organic solvent is n-hexane.

22. A composite nanofiltration membrane obtained by the preparation method according to any one of claims 1 to 21, wherein: The composite nanofiltration membrane comprises a polyimide support layer and a polyamide separation layer containing aromatic sulfone groups.

23. The composite nanofiltration membrane according to claim 22, wherein The thickness of the polyimide support layer is 150-300 μm; And / or, the thickness of the polyamide separation layer containing aromatic sulfone groups is 100-400 nm.

24. The composite nanofiltration membrane according to claim 23, wherein The thickness of the polyimide support layer is 150-250 μm; And / or, the thickness of the polyamide separation layer containing aromatic sulfone groups is 150-300 nm.

25. Use of the composite nanofiltration membrane according to any one of claims 22 to 24 in the field of separation and recovery of organic solvents.

26. The use according to claim 25, wherein: The composite nanofiltration membrane is used for separating and recovering butanone and toluene solvents in lubricating oil dewaxing solvents.

27. A method for separating and recovering a solvent, characterized in that: The method comprises: using the composite nanofiltration membrane described in any one of claims 22 to 24 to separate the lubricating oil dewaxing solvent, wherein the separation conditions include: a separation temperature of 10-30° C. and an operating pressure of 2-4 MPa.

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