MEASUREMENTS OF TRANSPORT RATES OF C-4 HYDROCARBONS ACROSS A SINGLE-CRYSTAL SILICALITE MEMBRANE

A 'direct' macroscopic experimental technique has been used to measure the rates of transport of C4 hydrocarbons in a silicalite crystal. A silicalite membrane was fabricated by embedding a large (300 x 100 x 1 00 mum) silicalite crystal in an epoxy resin. The membrane was subject ed to a known adsorbate pressure on the inflow side and the rates of t ransport of C4 hydrocarbons across the membrane were determined by mea suring the increase in pressure on the outflow side as a function of t ime. The data were analysed to determine the micropore diffusivities o f the hydrocarbons in silicalite. This method is an attractive alterna tive to other macroscopic techniques such as chromatographic, gravimet ric and zero-length chromatography which are commonly employed to dete rmine the micropore diffusivities. It eliminates many of the extraneou s mass-transfer resistances that may be present in these other methods . However, the membrane method also has several shortcomings. As prese ntly formulated, it can provide only an order of magnitude estimate of the micropore diffusivities and it can measure only integral diffusiv ity and not the differential diffusivity which is a more important fun damental quantity of interest. Experimental modifications and refineme nts of the mathematical model are presently being pursued to overcome these shortcomings.