Study On The Preparation Of PDMS Perstraction Membranes And Their Application In Phenol Wastewater Treatment

Recently,the large amounts of discharge of phenol-containing wastewater from the petrochemical and phenolic resins industries aggravates the environmental deterioration and threatens the human health seriously.However,it is not economical with conventional methods to treat phenol-containing wastewater due to their severe backmixing and solvent loss.Perstraction is a technology combining with pervaporation and membrane exetraction process.It is adequate for the separation of VOCs using polydimethysiloxane(PDMS) as the separation membrane due to its low energy consumption and easy operation.Considering its low mass flux,the mass transport process of the perstraction should be improved by the development of new membrane materials and contactors.In this study,simulation phenol wastewater and sodium hydroxide(NaOH) solution were chosen as the research object and the stripping solution,respectively.The initial phenol concentration of simulation phenol wastewater is 8.0g·L^-1.The effects of membrane materials,membrane contactors,and operation conditions of perstraction on the overall mass transfer coefficient(OMTC) of phenol were investigated with the use of silicon rubber,home-made PDMS flat membrane,and PDMS composite membrane.Firstly,the tubular membrane contactor made from home-made PDMS flat membrane was used in treatment of simulation phenol wastewater.The comparison between the tubular contactor and two other membrane contactors made from silicon tube,including spirally wound contactor and tubular contactor was made.In comparison with the silicon tube,the membrane resistance decreased and the OMTC of phenol increased in the phenol wastewater treatment by the PDMS flate membrane.The removal efficiency,OMTC and permeation flux of phenol with PDMS flate membrane were 97.3%,1.77×10^-7m·s^-1,6.97×10^-7g·m^-2·s^-1, respectively.Comparing with the spirally wound contactor,the concentration polarization decreased and the utilization ratio of the membrane area increased with the tubular contactor made from silicon tube.The OMTC of phenol with the tubular perstraction contactor and spirally wound perstraction contactor were 1.25×10^-7m·s^-1 and 5.11×10^-8m·s^-1,respectively.In order to improve the OMTC of phenol,the PDMS/polysulfone with single hole(PS-1), PDMS/polysulfone with four holes(PS-4),PDMS/polyacrylonitrile(PAN), PDMS/polyvinylidene fluoride(PVDF) and PDMS/ployetherimide(PEI) composite membranes were made by dipping coating method.The effects of the preparation parameters on the separation performance of the composite membranes were investigated,which was used to test the coating integrity of PDMS layer.The optimal coating concentration of PDMS of five composite membrane were 5.0wt.%,5.0wt.%,3.0wt.%,3.5wt.%and 5.0wt.%, respectively.The optimal coating layers of the five composite membranes were 2,2,2,3 and 1,respectively.On this basis,according to the membrane separation performance and the operation complexity,the PDMS/PS-1 composite membrane was chosen to analyze the effects of operation conditions on the OMTC of phenol.In addition,a comparison between PDMS/PS-1 composite membrane and four other composite membranes on the OMTC was made.The experimental results showed that the optimal flux and temperature of the feed solution,the flux and pH of the stripping solution were 82.8L·h^-1,323.15K,45.0L·h^-1 and 13.0, respectively.On this condition,the removal efficiency and the OMTC of phenol was 99.9% and 3.90×10^-6m·s^-1 with the PDMS/PS-1 composite membrane.And the OMTC of phenol was 0.50,0.45,5.37 and 7.00 times as high as thoes of PDMS/PS-4,PDMS/PAN,PDMS/PVDF, PDMS/PEI composite membranes,respectively.