Abstract
Cross-metathesis of ethylene and trans-2-butene is studied at multiple temperatures and reactant ratios. Optimal propylene yield is at 150°C and 35% C2H4. [Display omitted]
â–º WH/Al2O3 is highly active and selective for ethylene 2-butene cross-metathesis. â–º Temperature significantly affects catalyst deactivation rate and mechanism. â–º At low temperature, coking due to olefin polymerization is the dominant deactivation. â–º At high temperature, deactivation due to active site changes appear to dominate. â–º Substoichiometric ethylene is preferred for optimal yield of propylene.
A highly active and selective catalyst based on supported tungsten hydride for the cross-metathesis between ethylene and 2-butenes yielding propylene has been investigated at low pressure with various temperatures and feed ratios. At low temperature (120°C), the catalyst deactivates notably with time on stream. This phenomenon was extensively examined by DRIFTS, TGA, DSC, and solid-state NMR techniques. It was found that a large amount of carbonaceous species were formed due to a side-reaction such as olefin polymerization which took place simultaneously with the metathesis reaction. However, at 150°C, the catalyst was stable with time and thereby gave a high productivity in propylene. Importantly, the slight increase in temperature clearly disfavored the side reaction. The ratio of ethylene to trans-2-butene was also studied, and surprisingly, the W-H/Al2O3 catalyst is stable and highly selective to propylene even at substoichiometric ethylene ratios.