Design of a comprehensive teaching experiment on the preparation of PVA/SAPO-34 mixed-matrix membranes and pervaporation performance
[Objective]Fuel ethanol is a promising form of biomass energy with wide-ranging applications.During its production,an azeotrope forms when the ethanol concentration reaches 93 wt％.In this respect,pervaporation offers distinct advantages over other dehydration methods as it effectively removes water from ethanol solutions.Currently,pervaporation is extensively employed in organic solvent dehydration,primarily using polyvinyl alcohol(PVA)membranes.Although PVA exhibits strong stability and suitable separation factors,its low permeation flux necessitates large membrane areas for practical implementation,resulting in high investment costs that somewhat hinder its widespread adoption and application.It is a commonly employed technique to fabricate mixed-matrix membranes(MMMs)through the construction of a Turing structure on the surface,modification of the membrane surface,and incorporation of powder.[Methods]In this study,a PVA/polyacrylonitrile(PAN)composite membrane was prepared using PVA as the separation material,glutaraldehyde as the crosslinking agent,and PAN ultrafiltration membrane as the supporting layer.By incorporating SAPO-34 molecular sieve powders into PVA,PVA/SAPO-34/PAN MMMs were fabricated.On the one hand,the well-defined pore channels of the SAPO-34 molecular sieve served as preferential pathways for penetrants.On the other hand,incorporating the SAPO-34 molecular sieve increased the roughness of the membrane surface and thus enhanced its specific surface area.Both factors contributed to improving membrane permeability.The physicochemical properties of these films were characterized using scanning electron microscopy(SEM),Fourier transform infrared(FT-IR)spectroscopy,and contact angle measurements.The pervaporation performance of these MMMs was evaluated using an ethanol/water system.The effects of varying amounts of molecular sieve addition and operation temperature on pervaporation performance were investigated.[Results]The experimental results demonstrated that the addition of SAPO-34 powder led to an increase in membrane surface roughness and surface area.However,when the amount of SAPO-34 powder reached 15 wt％,noticeable agglomeration occurred.Infrared analysis revealed a C—O—C stretching vibration peak at 1 080 cm-1,indicating a crosslinking reaction between PVA and glutaraldehyde within the membrane.The water contact angle on the composite film surface slightly decreased with increasing filling amount,dropping from 56.8° to 54.1° at a SAPO-34 filling amount of 1 wt％.Subsequently,as the filling amount increased further,the contact angle significantly rose.The incorporation of SAPO-34 greatly enhanced membrane separation performance.The permeation flux for the unfilled PVA/PAN composite membrane was 480 g/m2·h-1;however,with a filling amount of 1 wt％,it rapidly increased to 2 529 g/m2 h-1,more than five times that of the PVA/PAN composite membrane.Although the separation factor decreased from 148 to 55,PSI remained nearly one time higher than the PVA/PAN composite film,resulting in significantly improved overall separation performance.As the SAPO-34 filling amount continued to increase,both permeation flux and separation factor began to decline.Temperature also exerted a pronounced effect on the MMMs.As the temperature increased,the permeation flux rapidly rose,whereas the separation factor reached its peak value of 80 at 60 ℃.Subsequently,further temperature increases caused a decline in the separation factor.When SAPO-34 was incorporated into a PVA/SAPO-34/PAN MMM,the separation performance exhibited significant enhancement,leading to a substantial increase in the flux of the composite membrane.[Conclusions]The synthetic film-making process for this experiment was straightforward and easily practiced by students.By using advanced analytical methods such as SEM,FT-IR,water contact angle,and gas chromatography,students'understanding and proficiency in modem analytical techniques were effectively enhanced.By conducting performance experiments and analyzing characterization results alongside performance test outcomes,students'ability to integrate theory with practice and apply their knowledge effectively can be greatly improved.The practical results indicate that this experiment helps students understand the research frontiers of chemical separation technology,which can stimulate their research enthusiasm and interest,cultivate their innovative spirit,and promote the improvement of their comprehensive practical abilities.
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