Microporous SiO 2 /Vycor membranes for gas separation
- PDF / 421,046 Bytes
- 10 Pages / 612 x 792 pts (letter) Page_size
- 4 Downloads / 255 Views
MATERIALS RESEARCH
Welcome
Comments
Help
Microporous SiO2yVycor membranes for gas separation R. A. Levy, E. S. Ramos, L. N. Krasnoperov, A. Datta, and J. M. Grow New Jersey Institute of Technology, University Heights, Newark, New Jersey 07102 (Received 13 March 1996; accepted 4 September 1996)
˚ initial pore diameter were modified In this study, porous Vycor tubes with 40 A using low pressure chemical vapor deposition (LPCVD) of SiO2 . Diethylsilane (DES) in conjunction with O2 or N2 O were used as precursors to synthesize the SiO2 films. Both “single side” (reactants flowing on the same side of porous membrane) and “counterflow” (reactants flowing on both sides of porous membrane) reactant geometries have been investigated. The flow of H2 , He, N2 , Ar, and toluene (C7 H8 ) was monitored in situ after each deposition period. Membranes modified by the “single side” reactants geometry exhibited good selectivities between small and large molecules. However, cracking in these membranes after prolonged deposition limited the maximum achievable selectivity values. Higher selectivities and better mechanical stability were achieved with membranes produced using the “counterflow” reactants geometry. Pore narrowing rate was observed to increase with oxidant flow (O2 or N2 O). For membranes prepared using both oxidants, selectivities on the order of 1000 : 1 were readily attained for H2 and He over N2 , Ar, and C7 H8 . As compared to O2 , the use of N2 O caused improvements in both the pore narrowing rate and N2 : C7 H8 selectivity. Membranes prepared using the “counterflow” geometry showed no signs of degradation or cracking after thermal cycling.
I. INTRODUCTION
Gas separation is important in processes involving oxygen enrichment, inert gas generation, as well as hydrogen, helium, and hydrocarbon recovery.1,2 It is also a subject of growing interest in studies concerned with the emission reduction of volatile organic compounds (VOC’s).3,4 Although there are a number of methods, such as adsorption and absorption, available to achieve gas separation, the use of membranes offers an attractive alternative because of the associated low capital investments, high processing flexibility, and simple operation.5,6 This study examines the use of porous Vycor membranes modified by low pressure chemical vapor deposition (LPCVD) of silicon dioxide (SiO2 ) films for gas separation. Such a structure was favored due to the matched coefficients of thermal expansion between film and substrate, which would minimize film cracking during thermal cycling.7 Ceramic membranes of that type offer the potential of handling gas streams at high pressures without breakage, and the added advantages of operating under corrosive environments at elevated temperatures where organic membranes usually disintegrate.5,8–10 Currently available ceramic membranes possess pore ˚ in size. Such memdiameters that are no less than 40 A branes separate gases primarily by Knudsen and surface diffusions, thus resulting in low selectivity. Through a reduction of the
Data Loading...
