The Research On Polyethersulfone Hollow Fiber Membrane-Based Extraction Of Organic Pollutants From Aqueous Solution

Membrane extraction is a new separation technology which combines membrane process with liquid-liquid extraction.It is a new membrane-based separation process for the removal of azeotropic compounds,volatile organic compounds,thermosensitive and low boiling point matters from aqueous solution.In contrast with traditional ones,it has many advantages,such as high efficiency,low energy consumption,simpleness,conveniency,extraction process only happens on the surface of extraction phase and being extracted phase without difficult separation for emulsification between two phases.In recent years,membrane extraction has obtained extensive attention in the field of wastewater treatment,particularly utilized in treating high salty and high concentrated organic wastewater.In this dissertation,a hollow fiber membrane-based extraction(HFME) method was developed to extract target organic pollutants(benzene,toluene,ethyibenzene,p-xylene, nitrobenzene and nitrobenzene) from aqueous solution,n-heptanol,n-octanol,n-undecane and n-dodecane were used as organic extractants,and the microporous hydrophobic polyethersulfone(PES) hollow fiber membrane which was made in our laboratory was used as the solid support for HFME.A new approach for choosing the organic extractants which was based on Godfery's data-based method and Hansen Solubility Parameters(HSP) theory was proposed.The validity of the method was verified by the distribution coefficients and permeability coefficients of organic pollutants and hollow fiber membrane-based extraction, which is expected to be reliable.Due to unique predictive capability of this method,it is universally useful for all kinds of solvent-sensitive process,thus eliminating expensive trial and error testing.The effect of different parameters such as initial concentration of organic pollutants, operation temperature,fluxes of aqueous phase and organic phase,and pH value in aqueous phase was also studied in order to find out the most optimal operation conditions.With the increase of the initial organic pollutants in the aqueous phase,the total mass-transfer coefficients do not have significant change.When the concentrations of the initial organic pollutants are very high,the problem of the HFME process can be solved by reducing the flux of aqueous phase,increasing the membrane area or circulation extraction process and so on.It is found that the extraction rates and extraction efficiencies increase when the operation temperature increases,and high temperature improve the HFME process.But the viscosity of organic extractants decreases with the increase of operation temperature,causing the instability of organic phase,and the organic phase flows out easily from the membrane pores and mixed with the aqueous phase.Unfortunately,higher operation temperature is not a good operation condition in a real system.When PES hydrophobic membrane was used in the HFME process, aqueous phase mass-transfer resistance accounts for the proportion in the total mass-transfer resistance to be very big,and the proportion of organic phase mass-transfer resistance is small. Therefore,the flux of aqueous phase plays an important role in the HFMS process,and the flux of organic phase is not a main parameter to accelerate the extraction performance.When the range of the pH value in the aqueous phase is between 7 and 8,that is,neutral or weak basic medium,the optimal operation can be reached.The pH value in the aqueous phase is too high or too low,the extraction efficiencies of target organic pollutants will decline.The research results of this paper have provided theoretical foundation for the industrialization of hollow fiber membrane-based extraction of organic pollutants from aqueous solution.