Chemical vapor deposition of silica on silicalite crystals and shape-selective adsorption of paraffins

Chemical vapor deposition (CVD) of Si(OCH3)(4) was carried out on silicalit e crystals in order to control the pore-opening size. Due to the non-acidit y, relatively high temperature such as 773 K was required to deposit thicke r silica layers sufficient for obtaining selective adsorbents. Adsorption o f linear and branched alkanes on silicalite and CVD-silicalites was perform ed gravimetrically and chromatographically at about 298 K. Both methods sho wed that adsorption behavior was almost unchanged for hexane and butane on CVD-silicalites but the adsorption for 2-methylpentane and 2-methylpropane was suppressed with the increase of the silica amount on silicalite. The ex tent of suppression depended upon the length of paraffins and the amount of deposited silica on silicalite. Thus. linear and branched paraffins can be separated by choosing the extent of silica deposition on silicalite. (C) 2 001 Elsevier Science B.V. All rights reserved.