Organic-Inorganic Hybrid Prevaporation Membranes With Reversal Trade-off Effect

In this work, the theories for designing the organic-inorganic hybrid membranes were tentatively proposed. The orgnaic-inorganic interface morphology theory was presented for the first time and the ideal orgnaic-inorganic interface morphologies were summarized. The theory of network pore and aggregate pore was presented firstly, and pointed out that the size and number of network pore and aggregate pore affected dominantly the fractional free volume of organic-inorganic hybrid membranes. In this dissertation, in order to solve the Trade-off effect of polymer membranes tentatively, we chose the poly(vinyl alcohol) (PVA)-based membrane and benzene/cyclohexane mixtures as the model system, and prepared two classes of organic-inorganic hybrid membranes, which included the"class I"hybrid membranes such as PVA-CG, PVA-CNT, PVA-CMS, PVA-SiOx and PVA-SiNT hybrid membranes, and the"class II"hybrid membranes such as PVA-GPTMS hybrid membranes. These organic-inorganic hybrid membranes were characterized by FTIR, 29Si NMR, SEM/EDX, TEM, XRD, DMA and TGA/DTA ect., and their swelling and sorption properties, diffusion properties, and pervaporation properties were investigated detailedly.The PVA-CG hybrid membranes and PVA-GPTMS hybrid membranes with reversal Trade-off effect was studied and theoretical analysis was given according to the organic-inorganic interface morphology theory, free volume theory, network pore and aggregate pore theory. The permeation flux and separation factor of PVA-CG hybrid membrane (CG particle size 2μm, content 6wt%) to benzene/cyclohexane (50/50, wt) mixtures were 90.7 g/(m2 h) and 100.1 respectively. The enhanced permeation flux and separation factor simutaneously were ascribed to the creation of ideal interface morphology, the increase of free volume, and the appropriate adjustment of size and number of network pore. The formation mechanism, physical and chemical structure of PVA-GPTMS hybrid membranes were studied. The effect of GPTMS content, annealing temperature and annealing time on apparent factional free volume, the size and number of network pore and aggregate pore were investigated, and the affecting factors on the swelling and sorption properties, diffusion properties, and pervaporation properties of PVA-GPTMS hybrid membranes were also investigated. Based on these results, the theoretical explanation of the reversal Trade-off effect of PVA-GPTMS hybrid membranes was described detailedly. Thepermeation flux and separation factor of PVA-GPTMS-28 hybrid membrane could be to 137.1 g/(m2 h) and 46.9 respectively when annealing temperature was 393K and annealing time was 1h, which was the highest results among the literatures related to PVA-based pervaporation membranes. The effect of operating conditions such as feed concentration, operating temperature and feed flow rate on the swelling and sorption properties, diffusion properties, and pervaporation properties were investigated.The interaction between PVA and graphites with different chemical structure, the free volume properteis of PVA and PVA-CG hybrid membranes were studied through molecular dynamics simulation. The calculation results indicated that incorporation of hydroxyl and carboxyl groups into graphites decreased hydrogen bonding energy , and the stronger hydrogen bonding interaction between PVA and graphite is, the more ideal free volume cavity size is. In case no hydrogen bonding formed between PVA and graphite, the probability of forming large nonselective voids increased.The inherent relationship between the microstructure of pervaporation membranes and the macroscopical separation properties was studied. The results showed that the apparent fractional free volume could be directly used to predict the peremability of organic-inorganic hybrid membranes. In this work, the mathematical model on correlating the relationship between permeation flux and apparent fractional free volume was firstly presented. The relationship between the network pore size and separation factor of organic-inorganic hybrid membranes was firstly correlated, the results indicated that separation factor of organic-inorganic hybrid membranes became bigger when the network pore radius lay between 0.26-0.28nm. The inherent relationship between interface morphology and separation properties indicated that the weak interaction between organic and inorganic components could lead to more ideal interface morphology. Finally, we tentatively presented the criterion for designing and selecting organic-inorganic hybrid membrane materials.