Studies On Preparation Of Zeolite T Membranes

Separation of azeotrope or close-boiling liquid mixtures by membrane-based pervaporation (PV) technology has attracted increasing attention because of the energy-efficient and lower operating cost. This thesis is aimed at synthesis of zeolite membranes for the separation of water/organic mixtures by PV. Hydrophilic zeolite T membranes were synthesized on mullite supports using secondary growth method. Zeolite T membranes were characterized by scanning electron microscopy (SEM) and x-ray diffraction (XRD).The effects of synthesis conditions of membranes and the resulting membranes PV performance were investigated.Firstly, zeolite T powders were obtained by hydrothermal treatment as inductive seeds for membrane preparation. The effects of molar ratios of n(SiO2)/n(Al2O3), n(Na2O+K2O)/n(SiO2), n(Na)/n(K) and the synthesis conditions on crystallization of zeolite T resulting in the formation of zeolite T with different morphology, size and crystallinity were studied. The optimized synthesis conditions were as following:the molar composition of gel was 1SiO2:0.055Al2O3:0.33(Na2O+K2O):12H2O and the crystallization temperature and time were 100℃and 120 h, respectively. The synthesized zeolite powder with about 5μm is suitable to prepare zeolite T membrane as surface seeds.Zeolite T membranes were prepared on porous tubular supports by secondary growth method. The effects of synthesis conditions such as synthesis time, temperature, as well as the molar ratios of n(SiO2)/n(Al2O3) and n(H2O)/n(SiO2) on the formation and separation properties of zeolite T membranes were investigated. Zeolite T membrane prepared with nanosized seeds showed high pervaporation performance. For example, zeolite T membrane obtained under optimized conditions displayed high flux of 3.0 kg·m-2·h-1 with a separation factor of 1600 toward a feed of 90 wt% iso-propanol mixtures at 75℃.Furthermore, high reproducibility zeolite T membranes were obtained under above synthesis conditions.The synthesized membranes were applied to the PV-assisted esterification of acetic acid and alcohol at 75℃.Zeolite T membranes could effectively remove water from the reactant mixtures and improve the conversion of acetic acid to almost 100% without the loss of reactants or products during the synthesis period of 6.5 h. On the other hand, the conversion of acetic acid achieved at a balanceable one of 70% when the absent of PV process to the esterification under the similar reactive conditions.