| Special separation and concentration of high viscosity/high solid content systems are difficult point in the field of separation.The tubular membrane is suitable for high viscosity/high solid content systems due to its wide flow channel and non-clogging characteristics.However,there are many challenges in the research on the preparation of self-supporting organic tubular membranes.The difficulty lies in that the self-supporting properties of the membrane tubes depend on the relative thickness of tube wall.The larger the diameter of the capillary membrane,the greater the membrane thickness.Therefore,the more polymer solution is extruded in the spinning process,resulting in the delay of phase separation rate,and raises the requirements for equipment.Whereupon,the increase of membrane thickness will lead to the decrease of membrane permeability flux,so it is necessary to optimize the membrane structure to improve the membrane permeability.The preparation of self-supporting capillary membranes is challenging,due to these problems.Polysulfone（PSf）is a kind of polymer membrane material which has been widely used in membrane separation.However,due to the characteristics of low surface energy and hydrophobicity,PSf membrane fouling is serious in application.It is an inevitable phenomenon that membrane fouling will reduce the performance of membrane,increase the cost of operation and maintenance,and shorten the service life of membrane.Therefore,improving its resistance to pollution is a more effective and applicable method to control membrane fouling.The hydrophilic modification of membrane surface is generally considered to be effective in slowing down or preventing membrane fouling.Therefore,to explore a simple operation,stable properties of polysulfone membrane surface hydrophilic modification method,so as to enhance the membrane fouling resistance,is the key to the practical application of capillary membrane.This paper mainly includes two parts:（1）Solve the two problems existing in the preparation process of capillary membrane:self-supporting and membrane forming defects.Therefore,a self-supporting PSf capillary membrane with a diameter of 2.5/2 mm and a molecular weight cut off of 67,000 was prepared by NIPS method in one step.The composition of casting solution,membrane formation conditions and post-treatment conditions were adjusted to optimize the structure and performance of the capillary membrane,and the relationship between membrane formation conditions and membrane structure and membrane performance was explored,as well as the mechanism of NIPS membrane formation.The effects of preparation conditions,additives,temperature of external coagulation bath,bore liquid temperature and post-treatment temperature on the morphology,properties,hydrophilicity and mechanical properties of the self-supporting capillary membrane were discussed.The surface morphology and structure of the ultrafiltration membrane were characterized by SEM and FTIR.It was found that the temperature of coagulation bath and the molecular weight of polyethylene glycol affect the structure of separation membrane,and the performance of capillary membrane can be improved by increasing the temperature of coagulation bath.The hydrothermal treatment in the post-treatment process can eliminate the internal stress in the polymer matrix,speed up the elution process of additives and improve the membrane flux.The optimal conditions of capillary polysulfone ultrafiltration membrane are as follows:the external coagulation bath water,and the temperature of the coagulation bath 60℃;the bore liquid deionized water at 35℃;the dry path 5 cm and the hydrothermal treatment temperature 120℃,the pure water flux of the capillary membrane was about 488.2L/（m~2 h bar）,the BSA solution flux was about 320.2 L/（m~2 h bar）,and the BSA rejection rate was about 90%.（2）Feasibility study of anti-fouling PSf capillary ultrafiltration membrane.The anti-fouling of polysulfone flat membrane was studied using the following three methods to verify the feasibility of preparing anti-fouling capillary ultrafiltration membrane:1.Study on preparation of anti-fouling membranes by polyvinyl pyrrolidone（PVP）self-crosslinkingThe effects of two PVP self-crosslinking methods on membrane fouling resistance were studied.The self-crosslinking of PVP and the stability of the self-crosslinking product were verified.Two kinds of self-crosslinking membranes were prepared at different concentration ratios.Then,the performance of the two kinds of crosslinked membranes was compared,including membrane flux,rejection rate,anti-fouling and other aspects.Finally,the self-crosslinking method was applied to improve the fouling resistance of capillary ultrafiltration membrane.The results show that the application ability of PVP self-crosslinking in improving the fouling resistance of membrane is limited due to the small amount of PVP combined with water.2.Study on preparation of anti-fouling membranes by blending PVP-CNTs nanoparticlesIn order to further study the potential of PVP as an anti-fouling modification material and fix the residual additive PVP which is easy to lose in the membrane matrix.In this paper,PVP-CNTs hybrid membranes were prepared by preparing PVP-CNTs nanoparticles and blending with polymers.The covalent bond between PVP and CNTs fixed the surface segregation and elution of PVP,and at the same time solved the dispersion problem of CNTs nanoparticles in the solvent.Finally,the anti-fouling performance of hybrid membrane was explored.3.Study on preparation of anti-fouling membranes by blending block copolymer PSf-PEGIn this paper,in order to study the feasibility of preparing excellent fouling resistant membrane,the method of bulk modification was adopted.Firstly,PSF-PEG copolymer was synthesized by modifying PSf raw material.Then,anti-fouling membranes were prepared by blending different proportions of PSf/PSf-PEG,and the effects of different blending concentrations on membrane properties were studied. |
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