Preparation Of ZSM-5 Supported PDMS/PVDF Pervaporation Membrane And Its Performance In Separating Polycyclic Aromatic Hydrocarbons From Water

Polycyclic aromatic hydrocarbons（PAHs）are a class of persistent organic pollutants（POPs）with a"tri-causal"effect,which can persist in the environment such as water,atmosphere and soil.Although the concentration of PAHs in the water environment is low,the detection rate is high and there is a certain potential hazard to the ecological environment and human health.Therefore,how to effectively remove PAHs from water and thus improve the water environment has become a hot issue to be solved nowadays.Due to the stable structure and hydrophobicity of PAHs,it is difficult to remove them by conventional treatment technology and there are many disadvantages in the treatment process.Therefore,there is an urgent need for a cost-effective means to remove PAHs from water.Permeation vaporization technology is considered to be one of the most promising membrane separation technologies for the removal of POPs,which can separate and remove toxic and harmful organic pollutants from water bodies and thus eliminate their potential hazards,which is of great importance to promote human health and ecological protection.In this study,zeolite molecular sieve（ZSM-5）loaded polydimethylsiloxane（PDMS）/polyvinylidene fluoride（PVDF）permeation vaporization composite membranes（ZSM-5@PDMS/PVDF MMMs）were prepared by a combination of non-solvent induced phase separation method and solution casting method,and their corresponding properties were characterized and applied to the permeation vaporization separation process of PAHs/water system.The permeation vaporization performance of the composite membrane was investigated by single factor test method,and the best combination of parameter levels for PAHs/water system was explored by response surface optimization method,and finally the mass transfer process of PAHs/water system by permeation vaporization of the composite membrane was analyzed,and the main conclusions were as follows.（1）In this study,three types of ZSM-5@PDMS/PVDF MMMs were prepared,namely 20wt%（mass fraction,same below）ZSM-5 unmodified composite film（U-ZSM-5@PDMS/PVDF MMMs）,20 wt%ZSM-5 n-octyltriethoxysilane（OTES）modified composite film（O-ZSM-5@PDMS/PVDF MMMs）and 20 wt%ZSM-5γ-aminopropyltriethoxysilane（KH550）modified composite film（K-ZSM-5@PDMS/PVDF MMMs）.PVDF MMMs)and 20wt%ZSM-5γ-aminopropyltriethoxysilane（KH550）modified composite films（K-ZSM-5@PDMS/PVDF MMMs）.According to the SEM and FTIR combined with water contact angle characterization,the increase of ZSM-5 zeolite loading was beneficial to enhance the hydrophobic properties of the composite membranes.Meanwhile,the XRD pattern showed that the composite membrane exhibited a crystalline state after loading ZSM-5 zeolite,which provided a possibility for the enhancement of the permeation vaporization performance of the composite membrane.It is noteworthy that the modification of the composite membrane with OTES can enhance the affinity of the composite membrane to PAHs/water system more than KH550.（2）The single-factor test of the membrane conditions showed that the prepared O-ZSM-5@PDMS/PVDF MMMs with a ZSM-5 loading of 20 wt%,PVDF concentration of 11 wt%,PVDF solvent of N-N dimethylformamide,non-solvent of water,and modifier of OTES had the best permeation vaporization performance compared to U-ZSM-5@PDMS/PVDF MMMs and K-ZSM-5@PDMS/PVDF MMMs,the permeation vaporization performance was the best,and the PAHs permeation flux and PAHs permeation rate reached 61.24 mg/（m²·h）and 66.67%,respectively.（3）The permeate vaporization separation of PAHs/water system was performed by O-ZSM-5@PDMS/PVDF MMMs,and the PAHs permeate flux and PAHs transmission rate of the membrane were 61.73 mg/（m²·h）and 69.89%,respectively,when the feed concentration was 15μg/L,the feed temperature was 40℃,the negative pressure downstream of the membrane was 45 k Pa,and the feed flow rate was 50 m L/min.The permeate flux and PAHs transmission rate of the membrane were 61.73 mg/（m²·h）and 69.89%,respectively,at which the combination level of separation parameters was better and the permeate vaporization performance of the composite membrane was better.（4）The response surface method was applied to optimize the permeate vaporization parameters of O-ZSM-5@PDMS/PVDF MMMs,and the complex correlation coefficients of the selected models were all greater than 0.99,and their fits were good.Meanwhile,the significant effects of each parameter on PAHs permeate flux and PAHs permeate rate were as follows:PAHs permeate flux:feed concentration>feed temperature>downstream negative pressure>feed flow rate;PAHs permeate rate:feed concentration>downstream negative pressure>feed flow rate>feed temperature.The model predicted that the best separation effect was achieved when the feed concentration was 24μg/L,the feed temperature was 50℃,the downstream negative pressure was 33 k Pa,and the feed flow rate was 47 m L/min,and the PAHs permeate flux and PAHs transmittance were 93.65 mg/（m²·h）and 70.84%,respectively.The measured values were 95.24 mg/（m²·h）and 71.82%,and the errors of the predicted values were 1.70%and 1.39%,which were better than some of the results reported in the literature.（5）Based on the dissolution-diffusion model,the dissolution coefficient S,diffusion coefficient D and permeation coefficient P of the composite membranes were analyzed to investigate their effects on the mass transfer mechanism during the permeation vaporization of PAHs/water system.The results showed that the high temperature conditions were favorable to the solubilization and diffusion of PAHs molecules when the composite membrane types were the same;the selected temperature was 60℃,and for different types of composite membranes,S,D and P showed the trend of O-ZSM-5@PDMS/PVDF MMMs>K-ZSM-5@PDMS/PVDF MMMs>U-ZSM-5@PDMS/PVDF MMMs The trend indicates that the permeation of the composite membrane was enhanced after modification,and there were differences in the degree of influence of the type of modifier on the permeation of the composite membrane.（6）A tandem resistance model was used to explore the effect of composite membranes on the mass transfer resistance during the permeate vaporization separation of PAHs/water system.The results showed that with the gradual increase of feed concentration,the total mass transfer coefficient K_i,t of the composite membrane showed a trend of increasing and then decreasing,and the corresponding K_i,t of 25μg/L reached the maximum value,which was consistent with the results of the permeate vaporization test;when the feed flow rate was greater than 12 cm/s,the membrane concentration polarization phenomenon was gradually eliminated,the boundary layer resistance R_i,b tended to be close to 0,and the membrane resistance R_i,m gradually controls the mass transfer process.Therefore,the high flow rate conditions are favorable for the permeate vaporization transfer process of PAHs/water system by the composite membrane.