CN101574629B - Preparation method of polyvinyl alcohol/polyether sulfone pervaporation composite membrane - Google Patents

Abstract

The invention relates to a preparation method of a polyvinyl alcohol/polyether sulfone pervaporation composite membrane, which comprises the steps of placing polyether sulfone in a 0.05-5 wt% borax water solution for soaking for 6-12 hours; dissolving polyvinyl alcohol in deionized water at 80-95 ℃ to prepare a casting solution with the mass concentration of the polyvinyl alcohol of 1-7 wt%, and cooling to 20-25 ℃; placing the treated polyether sulfone in a polyvinyl alcohol membrane casting solution, preparing a polyvinyl alcohol separation layer with the thickness of 1-8 microns on a polyether sulfone base membrane, and drying at 20-25 ℃ to obtain a composite membrane; placing the prepared composite membrane in acetone solution containing 5-20 vol% of glutaraldehyde and 0.1-0.15 vol% of HCl, wherein the treatment temperature is 20-50 ℃, and the treatment time is 0.5-5 hours; the preparation method has simple process and easily controlled conditions, the membrane is suitable for separating water/glycol mixture, and the permeation flux of the composite membrane can reach 445 g/²h)。

Description

A kind of preparation method of polyvinyl alcohol/polyethersulfone pervaporation composite membrane

technical field

The invention relates to a preparation method of a polyvinyl alcohol/polyethersulfone pervaporation composite membrane for separating water/organic (water/ethylene glycol) mixture.

Background technique

In order to develop high-flux pervaporation permeable membranes, many researchers have reduced the membrane thickness by preparing asymmetric membrane structures. This membrane is composed of an ultra-thin and dense active separation layer and a porous support layer. The active skin layer and the support layer can be made of different materials, so each layer of its material can be optimized individually, and the active skin layer can be optimized to the ideal selection. The support layer can achieve the best strength and pressure tightness. As a result, the composite membrane has high selectivity and permeation flux while maintaining good chemical and thermal stability.

Usually the support layer of the composite membrane is an asymmetric ultrafiltration membrane made by phase inversion technology, in which polysulfone, polyethersulfone, sulfonated polysulfone, polyacrylonitrile, polyimide and polyvinylidene fluoride membrane materials are used The formed support layer is the most common. The active separation layer material of the pervaporation dehydration composite membrane is a hydrophilic polymer material such as polyvinyl alcohol, chitosan, polyacrylic acid, etc. The existing problem is that the ultrafiltration membrane material of the support layer is relatively hydrophilic, and the ultrafiltration membrane material has strong hydrophobicity, resulting in a low interfacial force between the hydrophilic active separation layer and the hydrophobic support layer, resulting in hydrophilic It is difficult for the water-based active separation layer to be evenly applied to the surface of the support layer, and it is easy to form defects between the active separation layer and the support layer interface, which affects the separation performance of the membrane. Thus improving the hydrophilicity and cohesiveness of the support layer to enhance the interfacial force between the active separation layer and the support layer has become the focus of people's research. The main methods are: (1) using a hydrophilic active separation layer and a hydrophobic support Coupling agent or surfactant modification with affinity for both layers; (2) bulk or surface hydrophilic modification of the support layer to increase its surface energy.

One of the key points of the pervaporation dehydration composite membrane is the structural stability of the composite membrane, because the hydrophilic active separation layer is easy to swell in aqueous solution. If the active separation layer and the support layer swell differently, stress will be generated at the interface. When the stress exceeds a certain critical value, the active layer and the support layer will separate. Therefore, the control of the interfacial force between the active separation layer and the support layer is the key to the preparation of pervaporation composite membranes and ultrathin active separation layers.

Contents of the invention

The purpose of the present invention is to provide a kind of interfacial reaction cross-linking agent that introduces the polyethersulfone support layer to have reactivity with the active separation layer after treatment, increase the interfacial force between the composite membrane support layer and the active separation layer, thereby improve the polyethersulfone support layer. A preparation method of polyvinyl alcohol/polyethersulfone pervaporation composite membrane for pervaporation performance and stability of vinyl alcohol pervaporation membrane.

The preparation method of the polyvinyl alcohol/polyethersulfone pervaporation composite membrane of the present invention is realized through the following steps:

(1) support layer modification: the polyethersulfone support layer with a molecular weight cut off of 20000-30000 is placed in 0.05-5wt% interface reaction cross-linking agent borax aqueous solution, soaked for 6-12 hours, taken out, and dried;

(2) Preparation of active separation layer casting solution: dissolve polyvinyl alcohol with a degree of polymerization of 1650 to 2500 in deionized water at 80-95°C to make a casting solution with a mass concentration of polyvinyl alcohol of 1-7wt%, and cool to 20-25°C, filter with a sieve to remove impurities, and set aside after defoaming;

(3) Preparation of composite membrane: the polyethersulfone support layer (PES) treated in step (1) is placed in the active separation layer membrane solution prepared in step (2), and prepared on the polyethersulfone base membrane by dip coating method. Obtain a polyvinyl alcohol (PVA) active separation layer with a thickness of 1-8 μm, and dry it at 20-25° C. to form the prepared composite membrane;

(4) Surface cross-linking treatment of composite membrane active separation layer: the composite membrane prepared by step (3) is placed in an acetone solution containing 5-20vol% glutaraldehyde (GA) and 0.1-0.15vol% HCl in total volume In the process, the treatment temperature is 20-50° C., and the treatment time is 0.5-5 hours to obtain a surface cross-linked polyvinyl alcohol/polyethersulfone pervaporation composite membrane.

The invention has the advantages that the process of preparing the composite membrane is simple and the conditions are easy to control. The prepared surface cross-linked polyvinyl alcohol/polyethersulfone composite membrane can separate water and ethylene glycol mixture by pervaporation, and has high permeation flux. The permeation flux of the existing surface-crosslinked polyvinyl alcohol homogeneous membrane to water and ethylene glycol mixture is only 211g/(m ² h), while the surface-crosslinked polyvinyl alcohol/polyethersulfone composite prepared by the present invention The permeation flux of the membrane to the mixture of water and ethylene glycol can reach 445g/(m ² h).

Detailed ways

Example 1

Preparation of polyvinyl alcohol/polyethersulfone pervaporation composite membrane (membrane 1)

Weigh 7.5g of polyvinyl alcohol (PVA) with a degree of polymerization of 1750 and 492.5g of deionized water into a three-neck flask, heat in a constant temperature water bath at 90°C, and dissolve for 1 hour while stirring at 900r/min. After completely dissolving, lower the temperature to 25° C., remove the insoluble matter by filtration, and let stand for defoaming to prepare a polyvinyl alcohol active separation layer casting solution with a mass concentration of 1.5%.

A polyethersulfone membrane with a molecular weight cut-off of 25000 is used as a support layer (10cm×10cm) and soaked in deionized water for 2 days to remove glycerin in the membrane and dry at 20-25°C. The dried polyethersulfone membrane is soaked and adsorbed in 0.1 wt% borax aqueous solution for 12 hours, taken out and dried at 20-25°C. Fix the treated PES support layer on a glass plate, seal it with tape around it, then place it in the prepared 1.5wt% PVA active separation layer casting solution for reaction adsorption for 5min, take it out, and dry it at 20-25°C for 12 hours. After the active separation layer is completely dry, place it in an acetone solution containing 15 vol% glutaraldehyde and 0.12 vol% HCl in the total volume, cross-link at 40°C for 3 hours, and take out the composite membrane after cross-linking. Rinse with distilled water three times to obtain a surface-crosslinked polyvinyl alcohol/polyethersulfone composite membrane (membrane 1). The average thickness of the PVA active separation layer is 1 μm through scanning electron microscope observation of the composite membrane section. The composite membrane is used to separate water and ethylene glycol mixture with a water mass concentration of 20%, which can make the mass concentration of the permeate side water reach more than 91.45%, and the total permeate flux can reach more than 756g/(m ² h).

Example 2

Preparation of polyvinyl alcohol/polyethersulfone pervaporation composite membrane (membrane 2)

The experimental process and conditions are the same as in Example 1. In this example, only the concentration of the PVA active separation layer casting solution is changed to 2 wt%, and the resulting surface crosslinked polyvinyl alcohol/polyethersulfone composite membrane (membrane 2) passes The scanning electron microscope observation shows that the average thickness of the PVA active separation layer is 1.5 μm. The composite membrane is used to separate the mixture of water and ethylene glycol with a water mass concentration of 20%, which can make the mass concentration of the permeate side water reach more than 99.09%, and the total permeate flux can reach more than 427g/(m ² h).

Example 3

Preparation of polyvinyl alcohol/polyethersulfone pervaporation composite membrane (membrane 3)

The experimental process and conditions are the same as in Example 1. This example only changes the PVA active separation layer casting solution concentration to 3wt%, and the resulting surface crosslinked polyvinyl alcohol/polyethersulfone composite membrane (membrane 3) passes The scanning electron microscope observation shows that the average thickness of the PVA active separation layer is 2.5 μm. The composite membrane is used to separate the mixture of water and ethylene glycol with a water mass concentration of 20%, so that the mass concentration of the permeate side water can reach more than 98.50%, and the total permeation flux can reach more than 412g/(m ² h).

Example 4

Preparation of polyvinyl alcohol/polyethersulfone pervaporation composite membrane (membrane 4)

The experimental process and conditions are the same as in Example 1. This example only changes the PVA active separation layer casting solution concentration to 5wt%, and the resulting surface crosslinked polyvinyl alcohol/polyethersulfone composite membrane (membrane 4) passes through the composite membrane section. The scanning electron microscope observation shows that the average thickness of the PVA active separation layer is 4.0 μm. The composite membrane is used to separate the mixture of water and ethylene glycol with a water mass concentration of 20%, so that the mass concentration of the permeate side water can reach more than 97.72%, and the total permeation flux can reach more than 281g/(m ² h).

Example 5

Preparation of polyvinyl alcohol/polyethersulfone pervaporation composite membrane (membrane 5)

The experimental process and conditions are the same as in Example 1. This example only changes the PVA active separation layer casting solution concentration to 7wt%, and the resulting surface crosslinked polyvinyl alcohol/polyethersulfone composite membrane (membrane 5) passes The scanning electron microscope observation shows that the average thickness of the PVA active separation layer is 7.0 μm. The composite membrane is used to separate the mixture of water and ethylene glycol with a water mass concentration of 20%, which can make the mass concentration of the permeate side water reach more than 94.78%, and the total permeate flux can reach more than 218g/(m ² h).

Comparative example 1

Preparation of polyvinyl alcohol/polyethersulfone pervaporation composite membrane (membrane 6)

Weigh 10 g of polyvinyl alcohol with a degree of polymerization of 1750 and 490 g of deionized water into a three-neck flask, heat in a constant temperature water bath at 90°C, and dissolve for 1 hour while stirring at 900 r/min. After completely dissolving, lower the temperature to 25° C., remove the insoluble matter by filtration, and let it stand for defoaming to prepare a polyvinyl alcohol active separation layer casting solution with a mass concentration of 2.0 wt%.

A polyethersulfone membrane with a molecular weight cut-off of 25000 is used as a support layer (10cm×10cm) and soaked in deionized water for 2 days to remove glycerin in the membrane and dry at 20-25°C. The dried polyethersulfone membrane was soaked and adsorbed in 5vol% glutaraldehyde aqueous solution for 12 hours, taken out and dried at 20-25°C. Fix the treated PES support layer on a glass plate, seal it with tape around it, then place it in the prepared 2.0wt% PVA active separation layer casting solution for reaction adsorption for 5 minutes, take it out, and dry it at 20-25°C for 12 hours. After the active separation layer is completely dry, place it in an acetone solution containing 15 vol% glutaraldehyde and 0.12 vol% HCl in the total volume, cross-link at 40°C for 3 hours, take it out and rinse it with distilled water after cross-linking Three times, the surface cross-linked polyvinyl alcohol/polyethersulfone composite membrane (membrane 6) can be prepared, and the average thickness of the PVA active separation layer is 3.5 μm according to the scanning electron microscope observation of the composite membrane section. The composite membrane is used to separate the mixture of water and ethylene glycol with a water mass concentration of 20%, which can make the mass concentration of the permeate side water reach more than 95.45%, and the total permeate flux can reach more than 393g/(m ² h).

Comparative example 2

Preparation of Surface Crosslinked Polyvinyl Alcohol Homogeneous Membrane (Membrane 7)

Weigh 5 g of polyvinyl alcohol with a degree of polymerization of 1750 and 50 g of deionized water into a three-neck flask, heat in a constant temperature water bath at 90°C, and dissolve for 1 hour while stirring at 900 r/min. After all the solution is dissolved, it is lowered to 25°C, filtered to remove insoluble matter, left to defoam, and made into a polyvinyl alcohol aqueous solution with a mass concentration of 10wt%, scraped on a glass plate to form a film, and dried at 20-25°C for 24 hours. Remove the membrane and place it in an acetone solution containing 15 vol% glutaraldehyde and 0.12 vol% HCl in the total volume, cross-link at 40°C for 3 hours, take it out and rinse it with distilled water three times, and place Acetone solution was used to further remove residual glutaraldehyde on the membrane surface. It is used to separate the mixture of water and ethylene glycol with a water mass concentration of 20%, so that the mass concentration of the permeate side water can reach more than 99.58%, and the total permeate flux can reach more than 211g/(m ² h).

Table 1 shows the membrane 1 that embodiment makes, membrane 2, membrane 3, membrane 4, membrane 5 and the membrane 6 that comparative example makes, the permeation of the pervaporation of membrane 7 separates water and ethylene glycol mixture. Quantity and Separation Factor Results.

Table 1

Claims (1)

1. a preparation method of polyvinyl alcohol/polyethersulfone pervaporation composite membrane, is characterized in that: realize by following steps: (1) support layer modification: the polyethersulfone support layer with a molecular weight cut off of 20000-30000 is placed in 0.05-5wt% interface reaction cross-linking agent borax aqueous solution, soaked for 6-12 hours, taken out, and dried; (2) Preparation of active separation layer casting solution: dissolve polyvinyl alcohol with a degree of polymerization of 1650 to 2500 in deionized water at 80-95°C to make a casting solution with a mass concentration of polyvinyl alcohol of 1-7wt%, and cool to 20-25°C, filter with a sieve to remove impurities, and set aside after defoaming; (3) Preparation of the composite membrane: the polyethersulfone support layer treated in step (1) is placed in the active separation layer casting solution prepared in step (2), and the thickness is obtained on the polyethersulfone base membrane by dip coating. It is a 1-8μm polyvinyl alcohol active separation layer, which is the composite membrane obtained after drying at 20-25°C; (4) Composite membrane active separation layer surface crosslinking treatment: the composite membrane prepared by step (3) is placed in an acetone solution containing 5-20vol% glutaraldehyde and 0.1-0.15vol% HCl that accounts for the total volume. The temperature is 20-50° C., and the treatment time is 0.5-5 hours to obtain a surface cross-linked polyvinyl alcohol/polyethersulfone pervaporation composite film.