Application of a silicalite-1 membrane reactor in metathesis reactions Original Research Article

A silicalite-1 membrane was used in a membrane enclosed catalytic reactor to study the effect of selective product removal in the equilibrium limited metathesis of propene to ethene and 2-butene and of cis-2-butene to trans-2-butene. Based on a simple model of the membrane reactor, the goals for membrane performance, in terms of permeability and selectivity, were predetermined.The metathesis reactions were carried out at 296 K using a 16.4 wt% Re2O7/γ-Al2O3 catalyst, which was activated ex situ using tetraethyltin as a promoter. The membrane was able to separate trans-2-butene from propene (αC4/C3=5) and from cis-2-butene (αtrans/cis=1.6). In both reactions trans-2-butene is a product, so the effect of product removal on the conversion could be studied. Depending on the operating conditions, the propene conversion was 13% higher than the thermodynamic equilibrium conversion obtained in a conventional packed bed reactor. The ratio between trans-2-butene and cis-2-butene formed, increased with 34% compared to the thermodynamic equilibrium. The trans-2-butene yield from the geometrical isomerization of cis-2-butene increased with 4% compared to the thermodynamic equilibrium. Comparison of the areal time yield of the silicalite-1 membrane with the space time yield of catalytic reactors revealed that the current permeability of the membrane is not far from realistic for industrial application.