CN113509846A - Method for preparing polydimethylsiloxane composite membrane by water surface spreading method and application - Google Patents
Method for preparing polydimethylsiloxane composite membrane by water surface spreading method and application Download PDFInfo
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- B01D67/0002—Organic membrane manufacture
- B01D67/0009—Organic membrane manufacture by phase separation, sol-gel transition, evaporation or solvent quenching
- B01D67/0013—Casting processes
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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- 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
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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- B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
- B01D69/12—Composite membranes; Ultra-thin membranes
- B01D69/125—In situ manufacturing by polymerisation, polycondensation, cross-linking or chemical reaction
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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- B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
- B01D71/06—Organic material
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Abstract
A method for preparing a polydimethylsiloxane composite membrane by a water surface spreading method and application thereof belong to the technical field of membrane separation. The crosslinked polydimethylsiloxane film is prepared by utilizing the principle that a polydimethylsiloxane film casting solution is immiscible with water and can be spread on the water surface and crosslinked into a solid film, and then the film and a porous support body are compounded to prepare the composite film. The water surface spreading method avoids the phenomenon of pore permeation, thins the thickness of the active layer at the top of the composite membrane, can select a macroporous porous support body to reduce the mass transfer resistance of the composite membrane, widens the selection range of the porous support body, reduces the surface defects of the composite membrane, and increases the flux and selectivity of pervaporation. The invention provides a two-step preparation method of polydimethylsiloxane by pre-filming on a liquid-liquid interface and compounding with a porous support body, and the method is simple and easy to operate, mild in preparation conditions and low in cost, and is expected to realize industrial production.
Description
Technical Field
The invention relates to a method for preparing a polydimethylsiloxane composite membrane for pervaporation preferential permeation of organic matters by a water surface spreading method and application, belonging to the technical field of membrane separation.
Background
Membrane separation techniques compare traditional separation methods such as: the method has the advantages of low energy consumption, environmental protection, high efficiency, simple and easily-amplified equipment, difficult generation of byproducts in the operation process and the like, and is widely applied to the fields of energy conservation and emission reduction, seawater desalination, food and medicine and the like. The membrane separation technology becomes an effective method for relieving resource shortage and solving the environmental crisis and energy consumption, and further promotes the development of society, economy and science and technology.
Pervaporation is an emerging membrane separation technology in recent years, is mainly used for separating liquid mixtures, and is particularly suitable for near-boiling mixtures and azeotropic mixtures which are difficult to separate by ordinary rectification. At present, a pervaporation membrane widely researched is polydimethylsiloxane, and in order to improve the operation stability and the industrial application value of the polydimethylsiloxane membrane, the polydimethylsiloxane is usually coated on the surface of a porous support to prepare a composite membrane, and the traditional method for preparing the composite membrane is as follows: dipping, knife coating, and the like.
The preparation of the polymer composite membrane by the blade coating method comprises the steps of pouring the membrane casting solution on one side of the base membrane, uniformly coating the membrane casting solution on the surface of the base membrane by a scraper, and volatilizing a solvent to form a membrane. The composite film prepared by the blade coating method has good film forming property, the contact between polymer molecules of the blade coating layer and the base film is tight, and the running stability of the film is enhanced. The effective thickness of the composite film prepared by the blade coating method is generally more than 10 mu m. The dipping-pulling method is a process of dipping a base film into a film liquid, forming a thin skin layer on the surface of the base film after pulling, and then forming a film after heating and evaporating a solvent for drying. The film forming method of the dipping-pulling method is simple and convenient, the thickness of a compact separation layer of a prepared film is generally lower than that of a composite film prepared by a blade coating method, the flux is improved on the premise of ensuring higher separation factors, the binding force between a macromolecule layer and a base film is stronger, and the running stability of the film is better. The spin coating method is a process of forming a liquid or solid thin film by applying a solution drop on a horizontal turntable rotating at a certain rotational speed by the action of centrifugal force, and is called a spin coating method. Through the spin coating method, undiluted polydimethylsiloxane can prepare a film with the thickness of less than 10 microns, and polydimethylsiloxane diluted by a solvent can prepare a film with the thickness of less than 100 nm.
However, when the composite film is prepared by the traditional method, a macromolecule layer on the surface of the composite film can be formed by self-flowing of a solution and evaporation of solvent droplets. The thickness and the uniformity of the formed film are not easy to control due to the gravity flow process, and the surface of the film is easy to generate defects due to the hole seepage phenomenon. Therefore, when the membrane liquid is less, a large number of defects are easily generated by permeation holes of the membrane liquid, and when the membrane liquid is more, the prepared composite membrane separation layer is thicker due to the permeation holes. Membrane flux is generally lower when the separation factor is higher; when the prepared film is thin, defects are easily generated, and a high separation factor cannot be ensured.
In summary, in the conventional preparation methods, liquid macromolecules are coated on the surface of a solid porous substrate, liquid casting is difficult to control, and a pore seepage phenomenon obviously exists, so that the prepared macromolecular composite membrane has high mass transfer resistance or has a macromolecular layer defect on the surface of the membrane, and therefore, the composite membrane cannot take the dual advantages of selectivity and permeability into consideration, and has an obvious Trade-off phenomenon. And the traditional method can not observe the film forming process, and has higher requirements on the aperture, porosity, surface appearance, chemical properties and the like of the substrate. Therefore, in order to prepare the composite membrane with a compact surface active layer and small mass transfer resistance, the polydimethylsiloxane composite membrane can be prepared by a water surface spreading two-step method.
The polydimethylsiloxane film casting solution is crosslinked into a semi-solid ultrathin film on the water surface in advance by a water surface spreading method, and then the semi-solid ultrathin film is combined with a porous support with large aperture and large porosity to form a composite film, so that the hole seepage phenomenon of the composite film can be effectively reduced, the mass transfer resistance is reduced, the surface defects of the film are reduced, the selectivity and the permeability of the composite film are improved, and the trade-off effect is reduced. And the method is simple, easy to operate, mild in condition and has great industrial popularization potential.
Disclosure of Invention
The invention aims to prepare a polydimethylsiloxane composite membrane which has adjustable surface active layer thickness, avoids pore seepage and can be prepared on a base membrane with large aperture and large porosity. The polydimethylsiloxane membrane casting solution is pre-crosslinked, then is dripped on the water surface to spread into a polydimethylsiloxane membrane, and the polydimethylsiloxane membrane is compounded with a porous support body to prepare the polydimethylsiloxane composite membrane after the polydimethylsiloxane membrane is crosslinked to a certain degree on the water surface. The prepared polydimethylsiloxane composite membrane is used for permeation of organic solvent in the organic solvent/water mixed liquor through pervaporation separation. The polydimethylsiloxane composite membrane prepared by the method has reduced mass transfer resistance in the pervaporation operation process, has good permeability and preferential selectivity to organic molecules, and can stably operate.
The invention relates to a method for preparing a polydimethylsiloxane composite membrane for permeating and vaporizing organic substances preferentially by a water surface spreading method, which is used for reducing mass transfer resistance and surface defects of the polydimethylsiloxane membrane in permeating and vaporizing organic substances.
A method for preparing a polydimethylsiloxane composite membrane for pervaporation preferential organic permeation by a water surface spreading method is characterized by comprising the following steps of:
(1) pre-crosslinking of polydimethylsiloxane casting solutions
Dissolving polydimethylsiloxane into n-heptane, stirring for 1-3 h, adding crosslinking agent ethyl orthosilicate, stirring for a period of time, adding dibutyltin dilaurate, stirring for 1-3 h in a water bath kettle at 30-80 ℃, and pre-crosslinking until the materials are uniform;
(2) water surface spreading method for preparing polydimethylsiloxane/porous substrate composite membrane
A. Washing the surface of the base membrane with deionized water for 1min-10min, and vacuum filtering in a vacuum filter flask filled with deionized water for 1h-5 h; pouring deionized water into a container, placing the pretreated porous base membrane at the bottom of the container to ensure that the surface of the base membrane is immersed in the water, and placing the whole container in a blast oven at 30-80 ℃; B. dripping the pre-crosslinked polydimethylsiloxane casting solution obtained in the step (1) on the water surface, and standing for 20min-3 h; C. rapidly pulling the base film out of the water surface to enable the cross-linked polydimethylsiloxane film to fall on the surface of the base film, and preparing a composite film; placing the composite membrane in a forced air oven at 30 ℃ for drying for 12 h; then placing the mixture in a vacuum drying oven at the temperature of 80-100 ℃ for continuous crosslinking and drying for 8-12 h.
In the further step (1), per 2g-10g of polydimethylsiloxane, 18g-90g of n-heptane, 0.05g-0.3g of ethyl orthosilicate and 0.005 g-0.01 g of dibutyltin dilaurate correspond.
The porous base film includes: polysulfone, polyacrylonitrile, polyvinylidene fluoride, polytetrafluoroethylene, polypropylene, polyethylene, polyethersulfone, polybenzimidazole, cellulose acetate.
Soaking the base film in the step (2) to fill the film holes with water, thereby playing a role in supporting the film holes.
And (3) standing the porous nano particle/polydimethylsiloxane casting solution in the step (2) in a blast oven, wherein the temperature of the blast oven is the same as that of the blast oven in the step (A), so that the crosslinking environment temperature of the porous nano particle/polydimethylsiloxane casting solution is constant.
Dropwise adding the pre-crosslinked polydimethylsiloxane casting solution on the water surface, wherein each square centimeter of horizontal plane corresponds to 2-100 mu L of the pre-crosslinked polydimethylsiloxane casting solution, standing for 20min-3h, spreading the casting solution on the water surface, and volatilizing the solvent to crosslink into a polydimethylsiloxane film with a certain thickness.
And (2) pulling the base film to enable the polydimethylsiloxane film to fall on the surface of the base film, and preparing the polydimethylsiloxane composite film.
The polydimethylsiloxane composite membrane prepared by the method is applied to pervaporation and preferential permeation of organic matters.
The technical principle of the invention is as follows:
in order to prepare the high-selectivity and high-permeability polydimethylsiloxane composite membrane, the high-molecular polydimethylsiloxane/porous support composite membrane is crosslinked and assembled on a liquid-liquid interface based on the principle that a polydimethylsiloxane membrane casting solution is immiscible with water and can be spread into a thin membrane on the water surface. The polydimethylsiloxane film is crosslinked into an elastomer based on a liquid-liquid interface, so that the degree of seepage of the polydimethylsiloxane film on the surface of a porous support body can be effectively reduced, the thickness of the film is reduced, and the mass transfer resistance is reduced; the defects formed on the surface of the membrane due to seepage hole casting are reduced, so that the selection range of the pore diameter of the porous support is enlarged; and the thickness of the separation layer at the top of the composite membrane can be accurately regulated and controlled by regulating and controlling the conditions of water crosslinking time, the volume of the membrane casting solution, the pre-crosslinking viscosity of the membrane casting solution and the like, so that the permeability and the selectivity of the membrane are improved.
Description of the drawings:
FIG. 1 is a flow chart of a process for preparing a polydimethylsiloxane composite membrane by a water surface spreading method;
FIG. 2 is SEM images of composite PDMS membranes of different thicknesses prepared on a PTFE substrate with a pore size of 100 nm.
The specific implementation mode is as follows:
the present invention will be described in detail below with reference to the accompanying drawings and specific examples, but the present invention is not limited to the following examples.
Example 1
The preparation method of the membrane comprises the following steps:
(1) pre-crosslinking of polydimethylsiloxane casting solutions
Dissolving 2g of polydimethylsiloxane into 18g of n-heptane, stirring for 3h, adding 0.2g of cross-linking agent ethyl orthosilicate, stirring for a period of time, adding 0.005g of dibutyltin dilaurate, and stirring for 3h in a 60 ℃ water bath kettle;
(2) water surface spreading method for preparing polydimethylsiloxane/porous substrate composite membrane
Washing the surface of the polytetrafluoroethylene-based membrane (aperture 100nm) with deionized water for 1min, and performing suction filtration in a vacuum filtration bottle filled with deionized water for 5 h; pouring 300ml of deionized water into a culture dish with the diameter of 18cm, putting the pretreated basement membrane at the bottom of the culture dish, and integrally placing the basement membrane in a blast oven at 30 ℃; dripping 500 mu L of pre-crosslinked polydimethylsiloxane membrane casting solution on the water surface, and standing for 1 h; pulling the base film to enable the cross-linked polydimethylsiloxane film to fall on the surface of the base film, and preparing a composite film; and then drying the composite membrane in a vacuum drying oven at 80 ℃ for 8h to prepare the composite membrane shown in the attached figure 2.
The prepared pervaporation composite membrane is used for evaluating pervaporation ethanol, the raw material liquid is 5 wt% ethanol/water mixed liquid,the vacuum degree of the downstream side of the membrane is 300Pa, the temperature of the feed liquid is 40 ℃, and the flux and the separation factor of the ethanol/water mixed liquid are 9000 g.m-2·h-1And 3.8.
Example 2
The preparation method of the membrane comprises the following steps:
(1) pre-crosslinking of polydimethylsiloxane casting solutions
Dissolving 2g of polydimethylsiloxane into 18g of n-heptane, stirring for 3h, adding 0.2g of cross-linking agent ethyl orthosilicate, stirring for a period of time, adding 0.005g of dibutyltin dilaurate, and stirring for 3h in a 60 ℃ water bath kettle;
(2) water surface spreading method for preparing polydimethylsiloxane/porous substrate composite membrane
Washing the surface of the polytetrafluoroethylene-based membrane (aperture 100nm) with deionized water for 1min, and performing suction filtration in a vacuum filtration bottle filled with deionized water for 5 h; pouring 300ml of deionized water into a culture dish with the diameter of 18cm, putting the pretreated basement membrane at the bottom of the culture dish, and integrally placing the basement membrane in a blast oven at 30 ℃; dripping 1000 mu L of pre-crosslinked polydimethylsiloxane membrane casting solution on the water surface, and standing for 1 h; pulling the base film to enable the cross-linked polydimethylsiloxane film to fall on the surface of the base film, and preparing a composite film; and then placing the film in a vacuum drying oven at 80 ℃ for drying for 8h to prepare the composite film.
The prepared pervaporation composite membrane is used for evaluating pervaporation ethanol, the raw material liquid is 5 wt% ethanol/water mixed liquid, the vacuum degree at the downstream side of the membrane is 300Pa, the temperature of the feeding liquid is 40 ℃, and the flux and the separation factor of the ethanol/water mixed liquid are 7000 g.m-2·h-1And 5.6.
Example 3
The preparation method of the membrane comprises the following steps:
(1) pre-crosslinking of polydimethylsiloxane casting solutions
Dissolving 2g of polydimethylsiloxane into 18g of n-heptane, stirring for 3h, adding 0.2g of cross-linking agent ethyl orthosilicate, stirring for a period of time, adding 0.005g of dibutyltin dilaurate, and stirring for 3h in a 60 ℃ water bath kettle;
(2) water surface spreading method for preparing polydimethylsiloxane/porous substrate composite membrane
Washing the surface of the polytetrafluoroethylene-based membrane (aperture 100nm) with deionized water for 1min, and performing suction filtration in a vacuum filtration bottle filled with deionized water for 5 h; pouring 300ml of deionized water into a culture dish with the diameter of 18cm, putting the pretreated basement membrane at the bottom of the culture dish, and integrally placing the basement membrane in a blast oven at 30 ℃; dripping 1500 mu L of pre-crosslinked polydimethylsiloxane casting solution on the water surface, and standing for 1 h; pulling the base film to enable the cross-linked polydimethylsiloxane film to fall on the surface of the base film, and preparing a composite film; and then placing the membrane in a vacuum drying oven at 80 ℃ for drying for 8h to finally obtain the pervaporation organic-substance-permselective composite membrane.
The prepared pervaporation composite membrane is used for evaluating pervaporation ethanol, the raw material liquid is 5 wt% ethanol/water mixed liquid, the downstream side vacuum degree of the membrane is 300Pa, the temperature of the feeding liquid is 40 ℃, and the flux and the separation factor of the ethanol/water mixed liquid are respectively 5000 g.m-2·h-1And 10.2.
Example 4
The preparation method of the membrane comprises the following steps:
(1) pre-crosslinking of polydimethylsiloxane casting solutions
Dissolving 2g of polydimethylsiloxane into 18g of n-heptane, stirring for 3h, adding 0.2g of cross-linking agent ethyl orthosilicate, stirring for a period of time, adding 0.005g of dibutyltin dilaurate, and stirring for 3h in a 60 ℃ water bath kettle;
(2) water surface spreading method for preparing polydimethylsiloxane/porous substrate composite membrane
Washing the surface of the polytetrafluoroethylene-based membrane (aperture 100nm) with deionized water for 1min, and performing suction filtration in a vacuum filtration bottle filled with deionized water for 5 h; pouring 300ml of deionized water into a culture dish with the diameter of 18cm, putting the pretreated basement membrane at the bottom of the culture dish, and integrally placing the basement membrane in a blast oven at 30 ℃; dripping 2000 mu L of pre-crosslinked polydimethylsiloxane casting solution on the water surface, and standing for 1 h; pulling the base film to enable the cross-linked polydimethylsiloxane film to fall on the surface of the base film, and preparing a composite film; and then placing the membrane in a vacuum drying oven at 80 ℃ for drying for 8h to finally obtain the pervaporation organic-substance-permselective composite membrane.
Vaporizing the obtained pervaporationThe composite membrane is used for evaluating ethanol permeation by pervaporation, a raw material liquid is 5 wt% of ethanol/water mixed liquid, the vacuum degree at the downstream side of the membrane is 300Pa, the temperature of a feed liquid is 40 ℃, and the flux and the separation factor of the ethanol/water mixed liquid are 2300 g.m-2·h-1And 10.4.
Example 5
The preparation method of the membrane comprises the following steps:
(1) pre-crosslinking of polydimethylsiloxane casting solutions
Dissolving 2g of polydimethylsiloxane into 18g of n-heptane, stirring for 3h, adding 0.2g of cross-linking agent ethyl orthosilicate, stirring for a period of time, adding 0.005g of dibutyltin dilaurate, and stirring for 3h in a 60 ℃ water bath kettle;
(2) water surface spreading method for preparing polydimethylsiloxane/porous substrate composite membrane
Washing the surface of the polytetrafluoroethylene-based membrane (aperture 100nm) with deionized water for 1min, and performing suction filtration in a vacuum filtration bottle filled with deionized water for 5 h; pouring 300ml of deionized water into a culture dish with the diameter of 18cm, putting the pretreated basement membrane at the bottom of the culture dish, and integrally placing the basement membrane in a blast oven at 30 ℃; dripping 2.5mL of pre-crosslinked polydimethylsiloxane casting solution on the water surface, and standing for 1 h; pulling the base film to enable the cross-linked polydimethylsiloxane film to fall on the surface of the base film, and preparing a composite film; and then placing the membrane in a vacuum drying oven at 80 ℃ for drying for 8h to finally obtain the pervaporation organic-substance-permselective composite membrane.
The prepared pervaporation composite membrane is used for evaluating pervaporation ethanol, the raw material liquid is 5 wt% ethanol/water mixed liquid, the vacuum degree at the downstream side of the membrane is 300Pa, the temperature of the feeding liquid is 40 ℃, and the flux and the separation factor of the ethanol/water mixed liquid are respectively 90 g.m-2·h-1And 9.5.
Example 6
The preparation method of the membrane comprises the following steps:
(1) pre-crosslinking of polydimethylsiloxane casting solutions
Dissolving 2g of polydimethylsiloxane into 18g of n-heptane, stirring for 3h, adding 0.2g of cross-linking agent ethyl orthosilicate, stirring for a period of time, adding 0.005g of dibutyltin dilaurate, and stirring for 3h in a 60 ℃ water bath kettle;
(2) water surface spreading method for preparing polydimethylsiloxane/porous substrate composite membrane
Washing the surface of the polytetrafluoroethylene-based membrane (aperture 100nm) with deionized water for 1min, and performing suction filtration in a vacuum filtration bottle filled with deionized water for 5 h; pouring 300ml of deionized water into a culture dish with the diameter of 18cm, putting the pretreated basement membrane at the bottom of the culture dish, and putting the whole culture dish in a forced air oven at 80 ℃; dripping 1000 mu L of pre-crosslinked polydimethylsiloxane membrane casting solution on the water surface, and standing for 1 h; pulling the base film to enable the cross-linked polydimethylsiloxane film to fall on the surface of the base film, and preparing a composite film; and then placing the membrane in a vacuum drying oven at 80 ℃ for drying for 8h to finally obtain the pervaporation organic-substance-permselective composite membrane.
The prepared pervaporation composite membrane is used for evaluating pervaporation ethanol, the raw material liquid is 5 wt% ethanol/water mixed liquid, the downstream side vacuum degree of the membrane is 300Pa, the temperature of the feeding liquid is 40 ℃, and the flux and the separation factor of the ethanol/water mixed liquid are respectively 5000 g.m-2·h-1And 7.88.
Example 7
The preparation method of the membrane comprises the following steps:
(1) pre-crosslinking of polydimethylsiloxane casting solutions
Dissolving 2g of polydimethylsiloxane into 18g of n-heptane, stirring for 3h, adding 0.2g of cross-linking agent ethyl orthosilicate, stirring for a period of time, adding 0.005g of dibutyltin dilaurate, and stirring for 1h in a 60 ℃ water bath;
(2) water surface spreading method for preparing polydimethylsiloxane/porous substrate composite membrane
Washing the surface of the polytetrafluoroethylene-based membrane (aperture 100nm) with deionized water for 1min, and performing suction filtration in a vacuum filtration bottle filled with deionized water for 5 h; pouring 300ml of deionized water into a culture dish with the diameter of 18cm, putting the pretreated basement membrane at the bottom of the culture dish, and integrally placing the basement membrane in a blast oven at 30 ℃; dripping 1000 mu L of pre-crosslinked polydimethylsiloxane membrane casting solution on the water surface, and standing for 1 h; pulling the base film to enable the cross-linked polydimethylsiloxane film to fall on the surface of the base film, and preparing a composite film; and then placing the membrane in a vacuum drying oven at 80 ℃ for drying for 8h to finally obtain the pervaporation organic-substance-permselective composite membrane.
The prepared pervaporation composite membrane is used for evaluating pervaporation ethanol, the raw material liquid is 5 wt% ethanol/water mixed liquid, the vacuum degree at the downstream side of the membrane is 300Pa, the temperature of the feeding liquid is 40 ℃, and the flux and the separation factor of the ethanol/water mixed liquid are 8000 g.m-2·h-1And 3.45.
Example 8
The preparation method of the membrane comprises the following steps:
(1) pre-crosslinking of polydimethylsiloxane casting solutions
Dissolving 2g of polydimethylsiloxane into 18g of n-heptane, stirring for 3h, adding 0.2g of cross-linking agent ethyl orthosilicate, stirring for a period of time, adding 0.005g of dibutyltin dilaurate, and stirring for 1h in a 60 ℃ water bath;
(2) water surface spreading method for preparing polydimethylsiloxane/porous substrate composite membrane
Washing the surface of the polytetrafluoroethylene-based membrane (aperture 100nm) with deionized water for 1min, and performing suction filtration in a vacuum filtration bottle filled with deionized water for 5 h; pouring 300ml of deionized water into a culture dish with the diameter of 18cm, putting the pretreated basement membrane at the bottom of the culture dish, and integrally placing the basement membrane in a blast oven at 30 ℃; dripping 1000 mu L of pre-crosslinked polydimethylsiloxane membrane casting solution on the water surface, and standing for 1 h; pulling the base film to enable the cross-linked polydimethylsiloxane film to fall on the surface of the base film, and preparing a composite film; and then placing the membrane in a vacuum drying oven at 80 ℃ for drying for 8h to finally obtain the pervaporation organic-substance-permselective composite membrane.
The prepared pervaporation composite membrane is used for evaluating pervaporation ethanol, the raw material liquid is 5 wt% ethanol/water mixed liquid, the vacuum degree at the downstream side of the membrane is 300Pa, the temperature of the feeding liquid is 40 ℃, and the flux and the separation factor of the ethanol/water mixed liquid are 8000 g.m-2·h-1And 3.45.
Example 9
The preparation method of the membrane comprises the following steps:
(1) pre-crosslinking of polydimethylsiloxane casting solutions
Dissolving 2g of polydimethylsiloxane into 18g of n-heptane, stirring for 3h, adding 0.2g of cross-linking agent ethyl orthosilicate, stirring for a period of time, adding 0.005g of dibutyltin dilaurate, and stirring for 1h in a 60 ℃ water bath;
(2) water surface spreading method for preparing polydimethylsiloxane/porous substrate composite membrane
Washing the surface of the polytetrafluoroethylene-based membrane (aperture 100nm) with deionized water for 1min, and performing suction filtration in a vacuum filtration bottle filled with deionized water for 5 h; pouring 300ml of deionized water into a culture dish with the diameter of 18cm, putting the pretreated basement membrane at the bottom of the culture dish, and integrally placing the basement membrane in a blast oven at 30 ℃; dripping 1000 μ L of pre-crosslinked polydimethylsiloxane membrane casting solution on water surface, and standing for 20 min; pulling the base film to enable the cross-linked polydimethylsiloxane film to fall on the surface of the base film, and preparing a composite film; and then placing the membrane in a vacuum drying oven at 80 ℃ for drying for 8h to finally obtain the pervaporation organic-substance-permselective composite membrane.
The prepared pervaporation composite membrane is used for evaluating pervaporation ethanol, the raw material liquid is 5 wt% ethanol/water mixed liquid, the downstream side vacuum degree of the membrane is 300Pa, the temperature of the feeding liquid is 40 ℃, and the flux and the separation factor of the ethanol/water mixed liquid are 2155 g.m-2·h-1And 7.97.
Example 10
The preparation method of the membrane comprises the following steps:
(1) pre-crosslinking of polydimethylsiloxane casting solutions
Dissolving 2g of polydimethylsiloxane into 18g of n-heptane, stirring for 3h, adding 0.2g of cross-linking agent ethyl orthosilicate, stirring for a period of time, adding 0.005g of dibutyltin dilaurate, and stirring for 1h in a 60 ℃ water bath;
(2) water surface spreading method for preparing polydimethylsiloxane/porous substrate composite membrane
Washing the surface of the polytetrafluoroethylene-based membrane (aperture 100nm) with deionized water for 1min, and performing suction filtration in a vacuum filtration bottle filled with deionized water for 5 h; pouring 300ml of deionized water into a culture dish with the diameter of 18cm, putting the pretreated basement membrane at the bottom of the culture dish, and integrally placing the basement membrane in a blast oven at 30 ℃; dripping 1000 mu L of pre-crosslinked polydimethylsiloxane membrane casting solution on the water surface, and standing for 3 h; pulling the base film to enable the cross-linked polydimethylsiloxane film to fall on the surface of the base film, and preparing a composite film; and then placing the membrane in a vacuum drying oven at 80 ℃ for drying for 8h to finally obtain the pervaporation organic-substance-permselective composite membrane.
The prepared pervaporation composite membrane is used for evaluating pervaporation ethanol, the raw material liquid is 5 wt% ethanol/water mixed liquid, the downstream side vacuum degree of the membrane is 300Pa, the temperature of the feeding liquid is 40 ℃, and the flux and the separation factor of the ethanol/water mixed liquid are 2559 g.m-2·h-1And 9.45.
Comparative example 1
The preparation method of the membrane comprises the following steps:
(1) pre-crosslinking of polydimethylsiloxane casting solutions
Dissolving 2g of polydimethylsiloxane into 18g of n-heptane, stirring for 3h, adding 0.2g of cross-linking agent ethyl orthosilicate, stirring for a period of time, adding 0.005g of dibutyltin dilaurate, and stirring for 3h in a 60 ℃ water bath kettle;
(2) method for preparing polydimethylsiloxane/porous substrate composite membrane by dipping and pulling method
Washing the surface of the polytetrafluoroethylene-based membrane (aperture 100nm) with deionized water for 1min, and performing suction filtration in a vacuum filtration bottle filled with deionized water for 5 h; pouring the feed liquid into a culture dish; and (3) immersing the pretreated polytetrafluoroethylene-based membrane (with the aperture of 100nm) in the membrane casting solution, performing ultrasonic treatment for 1min, quickly taking out, and drying in a vacuum drying oven for 8 h.
The prepared pervaporation composite membrane is used for evaluating pervaporation ethanol, the raw material liquid is 5 wt% ethanol/water mixed liquid, the vacuum degree at the downstream side of the membrane is 300Pa, the temperature of the feeding liquid is 40 ℃, and the flux and the separation factor of the ethanol/water mixed liquid are respectively 600 g.m-2·h-1And 8.8.
Claims (9)
1. A method for preparing a polydimethylsiloxane composite membrane for pervaporation preferential organic permeation by a water surface spreading method is characterized by comprising the following steps of:
(1) pre-crosslinking of polydimethylsiloxane casting solutions
Dissolving polydimethylsiloxane into n-heptane, stirring for 1-3 h, adding crosslinking agent ethyl orthosilicate, stirring for a period of time, adding dibutyltin dilaurate, stirring for 1-3 h in a water bath kettle at 30-80 ℃, and pre-crosslinking until the materials are uniform;
(2) water surface spreading method for preparing polydimethylsiloxane/porous substrate composite membrane
A. Washing the surface of the base membrane with deionized water for 1min-10min, and vacuum filtering in a vacuum filter flask filled with deionized water for 1h-5 h; pouring deionized water into a container, placing the pretreated porous base membrane at the bottom of the container to ensure that the surface of the base membrane is immersed in the water, and placing the whole container in a blast oven at 30-80 ℃; B. dripping the pre-crosslinked polydimethylsiloxane casting solution obtained in the step (1) on the water surface, and standing for 20min-3 h; C. rapidly pulling the base film out of the water surface to enable the cross-linked polydimethylsiloxane film to fall on the surface of the base film, and preparing a composite film; placing the composite membrane in a forced air oven at 30 ℃ for drying for 12 h; then placing the mixture in a vacuum drying oven at the temperature of 80-100 ℃ for continuous crosslinking and drying for 8-12 h.
2. The method for preparing a polydimethylsiloxane composite membrane for an pervaporation permselective organic substance by the water surface spreading method according to claim 1, wherein the step (1) comprises 18g to 90g of n-heptane, 0.05g to 0.3g of ethyl orthosilicate, and 0.005g to 0.01g of dibutyltin dilaurate per 2g to 10g of polydimethylsiloxane.
3. The porous base membrane of claim 1 comprising: polysulfone, polyacrylonitrile, polyvinylidene fluoride, polytetrafluoroethylene, polypropylene, polyethylene, polyethersulfone, polybenzimidazole, cellulose acetate.
4. The method for preparing a polydimethylsiloxane composite membrane for permeating and vaporizing preferentially organic matters through the water surface spreading method according to claim 1, wherein the base membrane is soaked through the step (2) to fill the pores with water, thereby playing a role of supporting the pores.
5. The method for preparing a polydimethylsiloxane composite membrane for pervaporation of a preferential organic substance by a water surface spreading method according to claim 1,
and (3) standing the porous nano particle/polydimethylsiloxane casting solution in the step (2) in a blast oven, wherein the temperature of the blast oven is the same as that of the blast oven in the step (A), so that the crosslinking environment temperature of the porous nano particle/polydimethylsiloxane casting solution is constant.
6. The method for preparing the polydimethylsiloxane composite membrane for the pervaporation priority organic matter through the water surface spreading method according to claim 1, wherein the pre-crosslinked polydimethylsiloxane membrane casting solution is dropwise added on the water surface in the step (2), 2-100 mul of the pre-crosslinked polydimethylsiloxane membrane casting solution is corresponding to each square centimeter of the horizontal plane, the standing is carried out for 20min-3h, and the membrane casting solution is spread on the water surface in a drop manner and is volatilized and crosslinked into the polydimethylsiloxane membrane with a certain thickness through a solvent.
7. The method for preparing a polydimethylsiloxane composite membrane for the pervaporation of the preferentially organic substance through the water surface spreading method according to claim 1, wherein the step (2) pulls the base membrane so that the polydimethylsiloxane membrane falls on the surface of the base membrane to prepare the polydimethylsiloxane composite membrane.
8. Polydimethylsiloxane composite membrane prepared according to the method of any one of claims 1 to 7.
9. The polydimethylsiloxane composite membrane prepared by the method of any one of claims 1 to 7 is applied to pervaporation with priority to organic substances.
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| CN114768560A (en) * | 2022-03-31 | 2022-07-22 | 大连理工大学 | Polydimethylsiloxane/polysulfone ultrathin composite membrane, preparation method and application |
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