CN116712873A - Polyvinyl alcohol doped modified carbon nano tube pervaporation membrane and preparation method thereof - Google Patents

Polyvinyl alcohol doped modified carbon nano tube pervaporation membrane and preparation method thereof Download PDF

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CN116712873A
CN116712873A CN202310849910.6A CN202310849910A CN116712873A CN 116712873 A CN116712873 A CN 116712873A CN 202310849910 A CN202310849910 A CN 202310849910A CN 116712873 A CN116712873 A CN 116712873A
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polyvinyl alcohol
modified carbon
pervaporation membrane
carbon nanotubes
mwcnt
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薛闯
戴相承
康巍
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Dalian University of Technology
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Dalian University of Technology
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/06—Organic material
    • B01D71/38—Polyalkenylalcohols; Polyalkenylesters; Polyalkenylethers; Polyalkenylaldehydes; Polyalkenylketones; Polyalkenylacetals; Polyalkenylketals
    • B01D71/381—Polyvinylalcohol
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/36—Pervaporation; Membrane distillation; Liquid permeation
    • B01D61/362—Pervaporation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/36—Pervaporation; Membrane distillation; Liquid permeation
    • B01D61/366—Apparatus therefor
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
    • B01D67/0079—Manufacture of membranes comprising organic and inorganic components
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/02—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor characterised by their properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/02—Inorganic material
    • B01D71/021—Carbon
    • B01D71/0212—Carbon nanotubes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/06—Organic material
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2325/00—Details relating to properties of membranes
    • B01D2325/24—Mechanical properties, e.g. strength
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2325/00—Details relating to properties of membranes
    • B01D2325/36—Hydrophilic membranes

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  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Water Supply & Treatment (AREA)
  • Inorganic Chemistry (AREA)
  • Materials Engineering (AREA)
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  • Separation Using Semi-Permeable Membranes (AREA)

Abstract

The invention discloses a polyvinyl alcohol doped modified carbon nanotube pervaporation membrane and a preparation method thereof, wherein the pervaporation membrane is obtained by coating polyvinyl alcohol base casting solution, modified carbon nanotubes are doped in the casting solution, and chitosan molecules are non-covalently modified on carboxylated carbon nanotubes to obtain the modified carbon nanotubes; solves the problem that the separation performance of the existing polyvinyl alcohol pervaporation membrane on short-chain alcohol and water needs to be improved.

Description

Polyvinyl alcohol doped modified carbon nano tube pervaporation membrane and preparation method thereof
Technical Field
The invention relates to the technical field of membrane separation, in particular to a polyvinyl alcohol pervaporation membrane and a preparation method thereof.
Background
When Pervaporation (PV) is a membrane-based separation process, it was proposed in 1917 by p.a. kober (Philip Adolph Kober, PERVAPORATION, PERSTILLATION AND percrystalllination.1, journal of the American Chemical Society 1917 39 (5), 944-948), the pervaporation process uses the pressure difference across the separation membrane as the mass transfer driving force, AND is used for separation of near boiling mixtures, azeotropes or temperature sensitive components according to the difference in dissolution AND diffusion properties of the separated liquid mixture within the membrane, because of its high separation efficiency, low energy consumption, stability AND safety, AND easy operation advantages are favored in the fields of chemical industry, energy, environment AND food industry. The separation process of pervaporation can be generally divided into two categories, based on the hydrophilicity and hydrophobicity of the membrane, respectively: solvent dehydration and solute concentration. Meanwhile, according to a dissolution-diffusion model applied in the pervaporation process, the intrinsic properties of membrane materials, such as free volume differences in the membrane caused by different membrane materials, such as an inorganic membrane, an organic membrane, a mixed matrix membrane and the like, and whether the surface of the membrane is modified with functional groups and the like determine the separation effect. The hydrophilic organic polymers currently used for pervaporation include polyvinyl alcohol (polyvinyl alcohol, PVA), polyamide (PA), polyimide (PI) and the like, and in contrast, the number of hydrophobic membranes directly used for pervaporation is smaller than that of hydrophilic membranes, and Polydimethylsiloxanes (PDMS) and the like (Liu G, jin W.Pervanporation membrane materials: recent trends and perspectives [ J ]. Journal of Membrane Science,2021,636: 119557.) are more commonly used.
Among the water-removing membranes, polyvinyl alcohol (PVA) is a hydrophilic organic material which is inexpensive and easy to prepare, and is also the earliest commercialized pervaporation membrane, and researchers still use PVA as the reference polymer for solvent dehydration in pervaporation (Vane, L.M., review: membrane materials for the removal of water from industrial solvents by pervaporation and vapor permeation.J.chem.technology.Biotechnol., (2019) 94:343-365.). PVA has a main structure of long 1, 3-propanediol chains, and the hydrophilicity of PVA is mainly derived from side chain hydroxyl groups. However, the polyvinyl alcohol film has low mechanical properties and strength, and is susceptible to swelling during separation, which results in reduced separation effect and is not usable for a long period of time. Early studies focused mainly on changing the molecular structure of PVA by cross-linking, but simple polymer blending still failed to overcome the tradeoff between permeability and selectivity of the polymer film, so researchers have been trying to fill higher performance materials into PVA to overcome this conjugation effect in the last decade.
Carbon Nanotubes (CNTs) are a novel carbon structure discovered in 1991, and have extremely high specific surface area and extremely smooth inner and outer walls of graphite, so that the transmission resistance of molecules on the inner and outer surfaces of the carbon nanotubes is far lower than that of other organic high polymer materials. Filling CNTs into pervaporation membranes and modulating their structure and permeation pathways can thus be very good at facilitating the transport of fluid molecules (e.g., water or small molecule alcohols). CNTs have also been one of the important fillers used by researchers to improve PVA separation performance, however due to the nature of CNTs themselves that are surface hydrophobic and readily agglomerate in aqueous dispersions, membranes tend not to achieve higher permeate fluxes, for example, PVA/MWCNT membranes developed by Jae-Hyun Choi et al have permeate fluxes of 90 g/(m 2. H) for separation of 90wt% ethanol-water mixtures at 60 degrees Celsius (Choi, J.—H., jegal, J., kim, W.—N.and Choi, H.—S, incorporation of multiwalled carbon nanotubes into poly (vinyl alcohol) membranes for use in the pervaporation of water/ethanol minerals J.Appl.Polym.Sci.,. 2009, 111:2186-2193); PVA-X (X is the loading content of CNT in the membrane) prepared by Yaser Shirazi et al has a permeation flux of 79 g/(m 2. H) of 90wt% isopropyl alcohol-water mixture separated at 30 degrees Celsius (Yaser Shirazi, maryam Ahmadzadeh Tofighy, toray Mohammadi, synthesis and characterization of carbon nanotubes/poly vinyl alcohol nanocomposite membranes for dehydration of isopropanol, journal of Membrane Science, volume 378, issues 1-2,2011, pages 551-561). It has been found that the free volume of molecules in the PVA film increases less due to agglomeration of carbon tubes which readily occurs during filling (Peng F, pan F, sun H, et al, novel nanocomposite pervaporation membranes composed of poly (vinyl alcohol) and chitosan-wrapped carbon nanotube [ J ]. Journal of Membrane Science,2007,300 (1-2): 13-19 ]), and that "carbon particles" formed by agglomeration deposit on the film surface to cause roughness thereof, thereby making it difficult for the raw material liquid to wet the film as it passes through the film surface, and causing a decrease in film selectivity.
Thus, researchers have tried many methods of modifying the surface of CNTs, one is to functionally modify different chemical groups on CNTs, such as hydrophilic groups hydroxyl (-OH) or carboxyl (-COOH) to increase the solubility of CNTs in PVA aqueous solutions; the second is to wrap CNTs, non-covalently modify a layer of hydrophilic compound on the outer wall of CNTs by utilizing the unique property of the graphene layer on the outer wall, shadpour Mallakpour and the like, so as to modify L-phenylalanine on the outer wall of CNTs, further improve the dispersity of CNTs in PVA aqueous solution, and the prepared film has extremely strong thermal stability (Malakpore S, abdolmulalpeki A, borandeh S.l-Phenylalanine amino acid functionalized Multi Walled Carbon Nanotube (MWCNT) as a reinforced filler for improving mechanical and morphological properties of poly (vinyl alcohol)/MWCNT composition [ J ]. Progress in Organic Coatings,2014,77 (11): 1966-1971).
At present, many different kinds of surface-modified CNTs have been applied to the modification strategy for PVA films, however, most of these materials focus on the stability and conductivity of the materials themselves, and there has been no study on the improvement of the separation performance of short-chain alcohols with great difficulty in separation from water.
Disclosure of Invention
In view of the above, the invention provides a polyvinyl alcohol doped modified carbon nanotube pervaporation membrane, which solves the problem that the separation performance of the existing polyvinyl alcohol pervaporation membrane on short-chain alcohol and water needs to be improved.
In addition, the invention also provides a preparation method of the polyvinyl alcohol doped modified carbon nano tube pervaporation membrane.
In order to achieve the above object, the polyvinyl alcohol doped modified carbon nanotube pervaporation membrane is obtained by coating a polyvinyl alcohol-based casting solution, wherein the casting solution contains modified carbon nanotubes, and is characterized in that:
non-covalent modification of chitosan molecules on carboxylated carbon nanotubes to obtain the modified carbon nanotubes.
In the present disclosure and possible embodiments, the method of non-covalent modification comprises:
dispersing chitosan powder and carboxylated carbon nanotubes in an acetic acid solution, regulating the pH value of the system to 9.0-9.4 by using ammonia water, adding glutaraldehyde to carry out a system crosslinking reaction, and carrying out post-treatment on a solid after the crosslinking reaction to obtain the modified carbon nanotubes.
In the present disclosure and possible embodiments, the mass ratio of the chitosan powder to the carboxylated carbon nanotubes is 0.6:1.
In the present disclosure and possible embodiments, the system is stirred after the pH is adjusted to 9.0-9.4 and glutaraldehyde is added while stirring.
In the present disclosure and possible embodiments, the post-processing method includes: and washing the solid with acetic acid solution and deionized water in sequence, centrifuging, performing vacuum freeze drying, and grinding the dried particles into powder.
In a second aspect, the preparation method of the polyvinyl alcohol doped modified carbon nanotube pervaporation membrane comprises the following steps:
adding modified carbon nano-tubes obtained by non-covalent modification of chitosan molecules on carboxylated carbon nano-tubes into acetic acid solution of polyvinyl alcohol to obtain a uniformly dispersed mixture, adding glutaraldehyde into the mixture to carry out crosslinking reaction to obtain the casting film solution,
in the present disclosure and the possible embodiments, the mass concentration of the modified carbon nanotubes in the casting solution is (0.05 to 0.3%).
In the disclosed and possible embodiments, the mass concentration of the modified carbon nanotubes in the casting solution is 0.1% -0.3%; and/or the number of the groups of groups,
the polyvinyl alcohol was dissolved with a 1wt% acetic acid solution to prepare a 7.5wt% acetic acid solution of polyvinyl alcohol.
In the present disclosure and possible embodiments, the modified carbon nanotubes are dispersed in deionized water and then added to a 7.5wt% acetic acid solution of polyvinyl alcohol.
In the present disclosure and the possible embodiments, the dispersion is performed by ultrasonic dispersion, and the crosslinking reaction is performed in a stirred state.
The invention has the following beneficial effects:
according to the polyvinyl alcohol doped modified carbon nanotube pervaporation membrane, a PVA pervaporation membrane is constructed, and meanwhile, non-covalent modified carbon nanotube CNTs wrapped by chitosan CS are introduced, so that the agglomeration effect of the original CNTs when the original CNTs enter a hydrophilic PVA polymer is reduced, the uniform and flat membrane is ensured, and meanwhile, the mass transfer speed of water molecules in the membrane is enhanced, and the separation performance of the membrane is improved; PVA is a pervaporation membrane material with low cost, strong hydrophilicity and good film forming property, and the non-covalent modified CNTs wrapped by CS are mixed to effectively improve the permeation flux of PVA and enhance the mechanical property of PVA, and simultaneously can obviously reduce the swelling effect of PVA.
Drawings
The above and other objects, features and advantages of the present disclosure will become more apparent from the following description of embodiments thereof with reference to the accompanying drawings in which:
FIG. 1 is a HRTEM image of CS@f-MWCNT in 60mg CS reaction of example 1, with a white dotted line to the outermost tube wall bordered by f-MWCNT, showing that the prepared CS@f-MWCNT has been successfully modified on the outer wall of the carbon tube;
FIG. 2 is a FESEM image of the CS@f-MWCNT under dry conditions at 60mg CS reaction in example 1, at 60000 magnification, showing that the agglomeration effect of the carbon tubes under dry conditions is reduced due to successful modification of the carbon tubes;
FIG. 3 is a FESEM image of CS@f-MWCNT under dry conditions at 60mg CS reaction in example 1, showing free carbon tubes at a magnification of 300000, with a roughened surface on the carbon tubes indicating successful modification of the carbon tubes;
FIG. 4 is a FTIR result of different amounts of CS coated CS@f-MWCNT of example 1, showing that the content of nitrogen-containing functional groups in chitosan increases with increasing chitosan addition;
FIG. 5 is a surface FESEM image of PVA/CS@f-MWCNT of example 1 showing the overall flatness of the film surface after CS@f-MWCNT incorporation;
FIG. 6 is an XRD pattern for PVA/CS@f-MWCNT of example 1 at different loading levels of modified carbon tubes. As the addition amount of cs@f-MWCNT gradually increased, a surface crystallization peak of 2 theta=14 degrees appeared in the XRD spectrum except for the peak of 2 theta=19 degrees, indicating that the modified carbon tube was deposited on the surface of the carbon tube as the cs@f-MWCNT content increased.
Detailed Description
The present disclosure is described below based on embodiments, but it is worth noting that the present disclosure is not limited to these embodiments. In the following detailed description of the present disclosure, certain specific details are set forth in detail. However, for portions not described in detail, those skilled in the art can also fully understand the present disclosure.
Furthermore, those of ordinary skill in the art will appreciate that the drawings are provided solely for purposes of illustrating the objects, features, and advantages of the disclosure and that the drawings are not necessarily drawn to scale.
Meanwhile, unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise", "comprising", and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is, it is the meaning of "including but not limited to".
According to the pervaporation membrane, in order to reduce the aggregation phenomenon of hydrophobic carbon nanotubes in hydrophilic polymer polyvinyl alcohol and increase the dispersity of CNTs in the hydrophilic polymer polyvinyl alcohol, a layer of Chitosan (CS) molecules is wrapped on the surface of the carbon tube by non-covalent modification of carboxylated carbon nanotubes (f-MWCNTs), and amino groups on the CS molecules can form hydrogen bonds with hydroxyl oxygen in PVA, so that CNTs are better dispersed in PVA; meanwhile, f-MWCNT wrapping CS is wrapped by CS molecules, so that CNTs are less likely to agglomerate in the system and can be better dispersed through a physical method of ultrasonic and mechanical stirring.
After filling the modified CNTs, more molecular-grade pore channels with smooth surfaces of carbon tubes can be opened in the PVA film, so that the mass transfer speed of water molecules in the film is faster; the modified CNTs are not easy to agglomerate in the membrane to form larger particles, so that the physical properties of the membrane are not greatly affected, and the structure in the membrane is compact and the surface is smooth and flat; the hydroxyl in PVA and the amino on the surface of modified CNTs have better hydrophilicity, so that water molecules selectively pass through the PVA, thereby improving the separation performance of the membrane.
The preparation process of the modified carbon nanotube (CS@f-MWCNT) adopted by the embodiment of the invention is as follows:
adding 60mg of CS powder (low viscosity of less than 200 mPa.s, deacetylation degree of 99%) and 0.1mg/mL of f-MWCNT (Nanjing Xianfeng nanometer, 5-15 nm) dispersion aqueous solution into 1wt% acetic acid solution according to the mass ratio of chitosan powder to carboxylated carbon nano tube of 0.6:1, adding 50vt% ammonia water into the solution until the pH reaches 9.0-9.4 at room temperature, performing ultrasonic treatment at 60 ℃ and 35kHz power for 1h, adding 100 mu L of 25vt% Glutaraldehyde (GA) solution at 65-70 ℃ for crosslinking, centrifugally collecting solids at 8000rpm, washing with 1wt% acetic acid solution and deionized water respectively, centrifuging at 12000rpm, collecting the solids, and performing vacuum freeze drying for 48h; grinding the particles after complete drying and sieving the particles by a 200-mesh sieve, and collecting powder to obtain CS@f-MWCNT.
The preparation process of the polyvinyl alcohol-based casting film liquid provided by the embodiment of the invention comprises the following steps:
selecting 1797 type PVA, wherein the alcoholysis degree is 96% -98%, preparing PVA acetic acid solution with the concentration of 7.5wt%, dispersing f-MWCNT in 2ml deionized water at the temperature of 30 ℃ under 35kHz ultrasonic, and adding the F-MWCNT into 18g PVA solution according to the mass ratio of the dispersed modified carbon nano tube to the total mass of the mixed casting solution of 0.0005-0.003:1 (namely, the mass fraction of the dispersed modified carbon nano tube to the total mass of 0.05% -0.3 percent); the polyvinyl alcohol-based casting film liquid is obtained by adding 60 mu L of Glutaraldehyde (GA) solution for crosslinking reaction for 20min at the temperature of 65 ℃ under high-speed stirring after the system is subjected to ultrasonic treatment for 1h at the power of 35kHz at the temperature of 30 ℃.
In the following implementation process, an ethanol-water mixed system is used as a separation raw material, the mass ratio of the ethanol-water mixed system to the separation raw material is 9:1, and a permeation flux (J, the unit is g.m is used -2 ·h -1 ) The permeability of the pervaporation membrane is evaluated, the selectivity of the pervaporation membrane is evaluated by the separation factor (alpha), and the overall separation performance of the pervaporation membrane is generally measured by the separation index (PSI), wherein the PSI is used as a first judgment basis, and the higher the value is, the better the overall separation performance of the membrane is. The calculation formulas of the three factors are respectively as follows:
J＝M/(S·t)
α＝(y w /y e )/(x w /x e )
PSI＝J·α
wherein M is the mass (g) of the permeate obtained by the separation, S is the effective area (M -2 ) T is the separation time (h), x w ，y w Represents the mass fraction (g.L) of the feed liquid and the permeate water respectively -1 )，x e ，y e Representing the mass fractions of feed liquid and permeate ethanol respectively.
Example 1
1. Preparation of modified carbon nanotubes CS@f-MWCNT
60mg of CS powder (low viscosity less than 200 mPas, degree of deacetylation 99%) and 1000mL of 0.1mg/mL of f-MWCNT (Nanj Xianfeng nanometer, 5-15 nm) dispersion aqueous solution are added and dissolved into 1wt% acetic acid solution, 50vt% ammonia water is added thereto under room temperature condition until pH reaches 9.0, ultrasonic treatment is carried out at 60 ℃ at 35kHz power for 1h and 100 μl of 25vt% Glutaraldehyde (GA) solution is added at 65-70 ℃ for crosslinking, centrifugation is carried out at 8000rpm to collect solids, the solids are respectively washed with 1wt% acetic acid solution and deionized water, centrifugation is carried out at 12000rpm and then vacuum freeze drying is carried out for 48h; grinding the particles after complete drying, sieving the particles with a 200-mesh sieve, and collecting powder to obtain CS@f-MWCNT
2. Casting solution for preparing PVA/CS@f-MWCNT pervaporation membrane
Dispersing 0.01g of CS@f-MWCNT in 2ml of deionized water at 30 ℃ under 35kHz ultrasonic, and adding the dispersed CS@f-MWCNT into 18g of 7.5wt% PVA solution containing 1wt% of acetic acid to obtain a mixed solution with the mass concentration of CS@f-MWCNT of 0.05 wt%; and then carrying out ultrasonic treatment on the mixed solution at the power of 35kHz for 1 hour at the temperature of 30 ℃, stirring at a high speed, and adding 60 mu L of 25vt percent GA solution at the temperature of 65 ℃ for carrying out crosslinking reaction for 30 minutes to obtain the casting solution.
3. Preparation of PVA/CS@f-MWCNT pervaporation Membrane
Spreading 6-8ml of casting film liquid under 35cm x 35cm glass plate; the glass plate is dried for 1h under a blowing drying oven at 65 ℃, and the thin film on the glass plate is carefully removed by a needle point to obtain the PVA/CS@f-MWCNT pervaporation membrane with the CS@f-MWCNT content of 0.05 wt%.
4. Separation of PVA/CS@f-MWCNT pervaporation membrane on ethanol water mixed system
PVA/CS@f-MWCNT pervaporation membrane was used to separate the ethanol water system, the ethanol concentration used was 90wt% and the feed side temperature was 65 ℃. The pervaporation water is preferentially permeated, and the average permeation flux J of the membrane is 81.88 g.m through calculation -2 ·h -1 The mass concentration of ethanol on the permeate side was about 0.13g/mL, the average separation factor α was 50.91, and the separation index PSI was 4168.51.
Example 2
Using cs@f-MWCNT of example 1, 0.016g of cs@f-MWCNT was dispersed in 2ml of deionized water at 30 ℃,35kHz ultrasound, and added to 18g of 7.5wt% pva solution containing 1wt% acetic acid to obtain a mixed solution with a cs@f-MWCNT mass concentration of 0.08 wt%; and then, the mixed solution is subjected to ultrasonic treatment at the power of 35kHz for 1 hour at the temperature of 30 ℃, and then, 60 mu L of 25vt percent GA solution is added at the temperature of 65 ℃ for crosslinking reaction for 30 minutes, so as to obtain the casting solution.
Spreading 6-8ml of casting film liquid under 35cm x 35cm glass plate; the glass plate is dried for 1h under a blowing drying oven at 65 ℃, and the thin film on the glass plate is carefully removed by a needle point to obtain the PVA/CS@f-MWCNT pervaporation membrane with the CS@f-MWCNT content of 0.08 wt%.
PVA/CS@f-MWCNT pervaporation membrane was used to separate the ethanol water system. The ethanol concentration used was 90wt% and the feed side temperature was 65 ℃. The pervaporation water preferentially permeates, and the average permeation flux is 90.76 g.m -2 ·h -1 The mass concentration of ethanol on the permeate side was about 0.12g/mL, and the average separation factor was 62.36. The separation index was 5659.79.
Comparative example 1
Adding 60 mu L of GA solution into 7.5wt% PVA acetic acid solution under high-speed stirring at 65 ℃ for crosslinking reaction for 30min to obtain casting solution, and scraping and coating 6-8ml of casting solution under 35cm x 35cm glass plates; the mixture is placed under a blowing drying oven at 65 ℃ for drying for 1h, and the thin film on the glass plate is carefully removed by using a needle point to obtain the pure PVA pervaporation membrane.
The pure PVA pervaporation membrane obtained above was used for separating an ethanol water system, the concentration of ethanol used was 90wt%, and the temperature of the feed side was 65 ℃. The infiltration vaporized water is preferentially permeated, and the infiltration flux is 62.38 g.m -2 ·h -1 The separation factor was 50.91 and the permeate side ethanol mass concentration was about 0.17g/mL. The separation index was 3175.77.
In examples 1 and 2, the permeation flux of the pervaporation membrane was increased as compared to the comparative example, but the increase in the separation factor was not significant. The filled CS@f-MWCNT can still be used as a dopant to destroy the original structure of a PVA high polymer chain when the content is low, so that a new molecular runoff pore canal is opened, however, under the condition of low content of CS@f-MWCNT, the content of a CS coating is also low, so that the coating effect of the carbon tube is not obvious after the carbon tube enters a PVA matrix, slight agglomeration still occurs, the selectivity of the opened molecular runoff pore canal is lower, and the overall selectivity is slightly reduced. The membranes of examples 1 and 2 had much higher permeation fluxes than the comparative examples, so the final separation index was also higher than the comparative examples, and the PVA/CS@f-MWCNT pervaporation membranes of examples 1 and 2 had better short-chain alcohol and water separation properties than the conventional pure PVA pervaporation membranes, according to the principle that the overall separation performance of the membranes was better the higher the separation index.
Example 3
Using the cs@f-MWCNT of example 1, 0.02g of cs@f-MWCNT was dispersed in 2ml of deionized water at 30 ℃,35kHz ultrasound, and added to 18g of a 7.5wt% pva solution containing 1wt% acetic acid to obtain a mixed solution having a cs@f-MWCNT mass concentration of 0.1 wt%; and then the mixed solution is subjected to ultrasonic treatment at the power of 35kHz for 1 hour at the temperature of 30 ℃, and then 60 mu L of 25vt percent GA solution is added at the temperature of 65 ℃ for crosslinking reaction for 30 minutes to obtain the casting solution.
Spreading 6-8ml of casting film liquid under 35cm x 35cm glass plate; the glass plate is dried for 1h under a blowing drying oven at 65 ℃, and the thin film on the glass plate is carefully removed by a needle point to obtain the PVA/CS@f-MWCNT pervaporation membrane with the CS@f-MWCNT content of 0.1 wt%.
The above-mentioned materials are obtainedThe PVA/CS@f-MWCNT pervaporation membrane obtained was used for separating an ethanol water system, the ethanol concentration used was 90wt%, and the feed side temperature was 65 ℃. The pervaporation water preferentially permeates, and the average permeation flux is 99.73 g.m -2 ·h -1 The average separation factor was 67.23, the mass concentration of ethanol on the permeate side was about 0.11g/mL, and the separation index was 6704.85.
Example 4
Using the cs@f-MWCNT of example 1, 0.03g of cs@f-MWCNT was dispersed in 2ml of deionized water at 30 ℃,35kHz ultrasound, and added to 18g of 7.5wt% pva solution containing 1wt% acetic acid to obtain a mixed solution having a cs@f-MWCNT mass concentration of 0.1 wt%; and then, the mixed solution is subjected to ultrasonic treatment at the power of 35kHz for 1 hour at the temperature of 30 ℃, and then, 60 mu L of 25vt percent GA solution is continuously added for crosslinking reaction for 30 minutes under the conditions of high-speed stirring and 65 ℃ to obtain the casting solution.
Spreading 6-8ml of casting film liquid under 35cm x 35cm glass plate; the glass plate is dried for 1h under a blowing drying oven at 65 ℃, and the thin film on the glass plate is carefully removed by a needle point to obtain the PVA/CS@f-MWCNT pervaporation membrane with the CS@f-MWCNT content of 0.15 wt%.
The PVA/CS@f-MWCNT pervaporation membrane obtained above was used for separating an ethanol water system, the ethanol concentration used was 90wt%, and the feed side temperature was 65 ℃. The pervaporation water is preferentially permeated, and the average permeation flux is 122.97 g.m -2 ·h -1 The average separation factor was 76.79, the mass concentration of ethanol on the permeate side was about 0.10g/mL, and the separation index was 9442.87.
Example 5
Using CS@f-MWCNT of example 1, 0.06g of CS@f-MWCNT was dispersed in 2ml of deionized water at 30℃under 35kHz ultrasonic, and added to 18g of 7.5wt% PVA solution containing 1wt% acetic acid to obtain a mixed solution having a mass concentration of CS@f-MWCNT of 0.3wt%, after which the mixed solution was subjected to ultrasonic treatment at 30℃under 35kHz power for 1 hour, and then 60. Mu.L of 25vt% GA solution was continuously added at 65℃with high-speed stirring, and the crosslinking reaction was carried out for 30 minutes to obtain a casting solution.
Spreading 6-8ml of casting film liquid under 35cm x 35cm glass plate; the glass plate is dried for 1h under a blowing drying oven at 65 ℃, and the thin film on the glass plate is carefully removed by a needle point to obtain PVA/CS@f-MWCNT with the CS@f-MWCNT content of 0.3 wt%.
The PVA/CS@f-MWCNT obtained above was used for separating an ethanol aqueous system, the ethanol concentration used was 90wt%, and the feed side temperature was 65 ℃. The infiltration vaporization water is preferentially permeated, and the infiltration flux is 149.87 g.m -2 ·h -1 The separation factor was 83.80, the mass concentration of ethanol on the permeate side was about 0.09g/mL, and the separation index was 12559.11.
To investigate the separation stability of the membranes filled with modified carbon tubes of different concentrations, the membrane swelling ratios mentioned in examples 1-4 above were determined, the membrane was cut into strips of 2cm x 1cm, the mass was measured on a ten-thousandth balance and immersed in 90wt% ethanol at 65 ℃ for 48h, removed, carefully wiped dry with filter paper and the mass was again measured and recorded. The calculation formula of the swelling ratio is as follows:
SD＝(m t -m o )/m o
wherein SD represents the swelling ratio (%), m of the film o For the original mass of the film sample, m t For mass of film samples after ethanol soak and wiped dry, all film samples were taken from three different locations on the same film, and the results were calculated as follows:
TABLE 2 swelling Rate of PVA at different CS@f-MWCNT loadings
Examples CS@f-MWCNT mass concentration Average swelling ratio
Comparative example 0wt％ 17.72％
Example 1 0.05wt％ 13.16％
Example 2 0.08wt％ 16.15％
Example 3 0.1wt％ 5.44％
Example 4 0.15wt％ 5.12％
Example 5 0.3wt％ 5.23％
The result shows that the swelling rate of the pervaporation membrane filled with more CS@f-MWCNT is lower, and the volume of the membrane cannot be increased due to the absorption of the raw material liquid in the separation process, so that the reduction of the separation performance of the membrane is avoided. It was found that at a packing concentration of greater than 0.1wt%, the PVA/CS@f-MWCNT had better separation performance and separation stability.
The above examples are merely representative of embodiments of the present disclosure, which are described in more detail and are not to be construed as limiting the scope of the present disclosure. It should be noted that modifications, equivalent substitutions, improvements, etc. can be made by those skilled in the art without departing from the spirit of the present disclosure, which are all within the scope of the present disclosure. Accordingly, the scope of protection of the present disclosure should be determined by the following claims.

Claims (10)

1. The polyvinyl alcohol doped modified carbon nanotube pervaporation membrane is obtained by coating a polyvinyl alcohol-based casting solution, wherein the casting solution contains modified carbon nanotubes and is characterized in that:
non-covalent modification of chitosan molecules on carboxylated carbon nanotubes to obtain the modified carbon nanotubes.
2. The polyvinyl alcohol doped modified carbon nanotube pervaporation membrane of claim 1, wherein the non-covalent modification method comprises:
dispersing chitosan powder and carboxylated carbon nanotubes in an acetic acid solution, regulating the pH value of the system to 9.0-9.4 by using ammonia water, adding glutaraldehyde to carry out a system crosslinking reaction, and carrying out post-treatment on a solid after the crosslinking reaction to obtain the modified carbon nanotubes.
3. The polyvinyl alcohol-doped modified carbon nanotube pervaporation membrane according to claim 2, wherein:
the mass ratio of the chitosan powder to the carboxylated carbon nanotubes is 0.6:1.
4. The polyvinyl alcohol-doped modified carbon nanotube pervaporation membrane according to claim 3, wherein:
after the pH is adjusted to 9.0-9.4, the system is stirred and glutaraldehyde is added in a stirred state.
5. The polyvinyl alcohol-doped modified carbon nanotube pervaporation membrane according to claim 4, wherein:
the post-processing method comprises the following steps: and washing the solid with acetic acid solution and deionized water in sequence, centrifuging, performing vacuum freeze drying, and grinding the dried particles into powder.
6. The method for preparing the polyvinyl alcohol doped modified carbon nanotube pervaporation membrane according to any one of claims 1 to 5, characterized in that the method comprises the steps of:
adding modified carbon nano tubes obtained by non-covalent modification of chitosan molecules on carboxylated carbon nano tubes into acetic acid solution of polyvinyl alcohol to obtain a mixture with uniform dispersion, and adding glutaraldehyde into the mixture to carry out a crosslinking reaction to obtain the casting film liquid.
7. The method of manufacturing according to claim 6, wherein:
the mass concentration of the modified carbon nano tube in the film casting liquid is (0.05-0.3)%.
8. The method of manufacturing according to claim 7, wherein:
the mass concentration of the modified carbon nano tube in the film casting liquid is 0.1-0.3%; and/or the number of the groups of groups,
the polyvinyl alcohol was dissolved with a 1wt% acetic acid solution to prepare a 7.5wt% acetic acid solution of polyvinyl alcohol.
9. The method of manufacturing according to claim 8, wherein:
the modified carbon nanotubes were dispersed in deionized water and then added to a 7.5wt% acetic acid solution of polyvinyl alcohol.
10. The method of manufacturing according to claim 9, wherein:
the dispersion adopts an ultrasonic dispersion mode, and the crosslinking reaction is carried out in a stirring state.
CN202310849910.6A 2023-07-11 2023-07-11 Polyvinyl alcohol doped modified carbon nano tube pervaporation membrane and preparation method thereof Pending CN116712873A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN117771947A (en) * 2024-01-03 2024-03-29 西陇科学股份有限公司 Preparation method of polyvinyl alcohol mixed matrix pervaporation membrane

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN117771947A (en) * 2024-01-03 2024-03-29 西陇科学股份有限公司 Preparation method of polyvinyl alcohol mixed matrix pervaporation membrane

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