Search

Production of bioethanol, a renewable energy source, is limited by the costly, energy-consuming concentration processes involved. Membrane separation techniques have emerged as promising alternatives to overcome these limitations. In this study, silicalite-1 zeolite membranes with high pervaporation (PV) performance were prepared on porous tubular silica supports by a secondary growth method. The effects of the deposited seed amount on the support and synthesis parameters, namely, the tetra- n -propylammonium concentration (TPA + /Si), alkalinity (OH − /Si), and crystallization time, were investigated. A dense zeolite layer was formed between the typical columnar crystal layer of silicalite-1 membranes and the silica support. The PV performance was mainly dependent on the thickness of the dense layer: as the thickness increased, the separation factor increased. The silicalite-1 membrane prepared using a synthesis solution with a molar composition of 1SiO 2 :0.05TPABr:0.08NaOH:75H 2 O at 433 K for 8 h exhibited the highest separation performance with a separation factor of 92 and a flux of 3.00 kg m −2 h −1 for 10 wt% ethanol/water mixtures at 323 K, which is the best result reported to date for tubular supports. Thus, silica supports proved to be suitable for the preparation of high-performance silicalite-1 membranes for ethanol/water mixture separation.

A MFI zeolite membrane was synthesized on a porous silica substrate. The defect-free MFI zeolite membrane was synthesized via a secondary growth method using seed crystals (Si/Al = 20) on a silica substrate in a parent gel of Si/Al = 100. The silica substrate prevented the dissolution of the seed crystals during the synthesis to promote the MFI zeolite membrane synthesis. The MFI zeolite membranes were employed for a contactor-type reactor for methanol-to-olefins (MTO) reactions to produce olefins, such as propylene. The methanol conversion was 99.9% with the selectivity of ethylene - pentene at 91.5% for the permeate side of the membrane contactor. The propylene selectivity was high at 48.5% with the C3H6/C3H8 ratio at 236.

A hydrophobic pure-silica *BEA-type zeolite membrane was prepared using the steam-assisted conversion (SAC) method on a seeded tubular silica support coated with dilute synthetic gel. This study systematically investigates the effects of the synthetic conditions on the membrane formation process and separation performance. Under the optimized conditions, when using a dilute synthetic gel with a H2O/SiO2 ratio of 500, a dense and continuous membrane layer was formed in 24 h. This was attributed to dissolution of the surface of the silica support during the steaming process, which functions as a silica source for the growth of a seed crystal layer. An increase in silica the concentration on the support surface locally enabled the formation of a membrane under the dilute synthetic gel composition. The obtained membrane exhibited selectivity toward n-butanol, in addition to a high flux with a separation factor of 132 and a flux of 1.00 kg m−2h−1 for a 1 wt% n-butanol/water mixture at 318 K. This novel simple membrane formation method combines a dilute synthesis gel with SAC, takes advantage of the dissolution of a silica support, and reduces the consumption and cost of chemical raw materials used for membrane synthesis.