A majority of the propylene produced currently is a co- or by-product of ethylene and gasoline production. However, due to the shift from naphtha to lighter feedstocks, propylene production via steam cracking is expected to decrease in the coming years. As a result, manufacturers are gravitating to on-purpose production strategies to address the expected production gap. Olefin metathesis is one approach that has been utilized by the industry successfully for propylene production. Various research approaches using metathesis have been investigated because of the adaptability of the process to produce the desired alkenes based on the choice of starting materials.<br/><br/>The primary objective of this research study is to provide a method for the valorization of low-value C4 raffinate streams, for example, from an FCC refinery stream, to propylene. Self-metathesis allows for the production of propylene without the need of ethylene as a feedstock. A key challenge in this research effort is developing a robust catalyst that (1) allows for appropriate isomerization of the butenes mixture (2) produces considerable amounts of propylene and minimizes heavies production and (3) displays long lifetime and stability.<br/><br/>In the quest for developing a novel catalyst which has the optimal blend of acidity and the appropriate loading of tungsten oxide on the non-reducible support, we report a method in which silica and alumina blends are used as a support for tungsten oxide. The modified catalyst support in the form of a mixture of silica and alumina can lead to the creation of both highly acidic Lewis and Brönsted acid sites, which aid in controlling isomerization of the 2-butenes stream to the desired level while also allowing metathesis to occur at lower temperatures. We speculate that the mixture of silica and alumina provides better flexibility in enabling tungsten oxide to change its oxidation states which in turn enhances metathesis activity while simultaneously allowing the metal particles to disperse better. Results of a thorough investigation to optimizing metal dispersion and the silica to alumina ratio has been reported using three different synthesis techniques.

Isomerization and self-metathesis of raffinate butenes to propylene on a W/Si-Al catalyst

251st National Meeting (2016)

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