Preparation Of Inorganic/Organic Hybrid Pervaporation Membranes And Effectiveness In Phenol Separation

Pervaporation(PV)is an energy-saving and cost-effective membrane separation technique,especially suitable for separating isotrope,isomers with the same boiling point and thermo-sensitive substances.This paper focuses on the fabrication of composite membranes suitable for PV separation of phenol in phenolcontaining wastewater,with which the concentration of phenol in the wastewater could be reduced to a range that the microorganisms in the biochemical tr eatment stage could tolerate.To separate phenols from the phenol-containing wastewater using PV,silanization modified ZSM-5 zeolite/polydimethylsiloxane/polyvinylidene fluoride(S-ZSM-5/PDMS/PVDF)hollow fiber composite membranes were fabricated using dynamic negative pressure.The influence of ZSM-5 silanization reaction,coating time and concentration of ZSM-5 on the PV performance of composite membranes was investigated.The water contact angle of the membrane was increased significantly from 99 ° to 132 ° when the concentration of ZSM-5 increased from 0 wt% to 50 wt%.SEM images illustrated that the thickness of the separating layer had distinct differences at varying coating times and when the coating time was extended from 10 min to 60 min,both the phenol flux and the water flux decreased,while the separation factor increased.Considering the flux and separation factor comprehensively,ZSM-5 was selected to have a filling concentration of 40 wt% and a coating time of 60 min.The effects of phenol concentration,feed temperature,and permeate pressure on PV performance were studied,using permeation flux and separation factor as evaluation indicators.When phenol concentration was 1 g/L,feed liquid temperature was at 80 ? and permeation side pressure was 5 k Pa,the phenol flux reached 5.78 g/(m2·h)and the separation factor reached 4.56.The separation factor decreased by 13.2 %,and the PV performance of the composite membrane decreased after operating under those conditions for 20 cycles.In order to improve the mechanical properties of the composite membrane and the stability of the PV system,a new type of inorganic/organic hybrid membrane material was designed that combined the mechanical properties,heat resistance an d chemical stability of ceramic membranes,as well as the selectivity of polymers.Considering the weak interaction forces between ceramic membranes and organic materials,it is necessary to choose a functional substance that connects the two-phase interface of organic and inorganic materials,and so vinyl trimethoxysilane(VTMS)containing two chemical functional groups that can simultaneously connect an organic material and an inorganic material been used as coupling agent.An alumina-supported Zirconia(ASZ)ceramic membrane as the base membrane,the structure and micro-morphology and surface elements of VTMS modified ASZ ceramic membranes were analyzed,using XRD and SEM-EDS as characterization methods.According to the XPS,FTIR and TG-DSC results,it was shown that the VTMS chemically reacted with the hydroxyl group on the surface of the ASZ ceramic membrane to form a stable chemical bond,namely(Si-O-Zr).In order to construct a new ceramic support polymer(CSP)composite membrane with good chemical stability,separation performance,non-swelling and uncompressible characteristics,the polymer layer(Polyvinyl acetate(PVAc)or Polydimethylsiloxane(PDMS)layers)was successfully prepared on the VTMS silylated ASZ membrane by free radical graft polymerization of vinyl acetate(VAc)or Si-H bond addition reaction of PDMS.Then XRD,SEM-EDS and contact angle characterization methods were used to analyze the structure,micro-morphology and hydrophobicity of PVAc/VTMS/ASZ and PDMS/VTMS/ASZ ceramic composite membranes.The grafting mechanism of the polymer and the VTMS/ASZ ceramic membranes was studied by FTIR,TG and XPS characterization methods.After comparing the PV performances of the two CSP composite membranes,the PDMS/VTMS/ASZ composite membrane with better performance was selected to investigate the PV performance under varying conditions,such as feed liquid temperature,permeation side pressure,feed liquid circulation fl ow rate.When the phenol concentration in the feed solution was at 1458-1561 mg/L,the feed solution temperature at 80 ?,the permeate side pressure at 3 k Pa,and the circulation flow rate was 190 m L/min,the PDMS/VTMS/ASZ ceramic membrane had the best PV performance.The phenol flux was 10.09 g/(m2·h)and the separation factor was 3.9.The mass transfer process of PV was studied,and the relationship between the total mass transfer coefficient K and the Re in the tube was scaled exponentially.As the feed liquid velocity increased,the mass transfer coefficient kl of the liquid membrane boundary layer increased,and the mass transfer coefficient km in the membrane was almost unaffected.After the PDMS/VTMS/ASZ composite membrane PV system had been operated for 43 h,the concentration of phenol in the phenol-containing wastewater decreased from 1690 mg/L to a concentration of 206.64 mg/L,meaning the removal rate reached 87.78 %.At this level,the phenol concentration was able to meet the phenol concentration requirements in the biochemical treatment stage.