Impact of Co-Fed Hydrogen on High Conversion Propylene Aromatization on H-ZSM-5 and Ga/H-ZSM-5

Abstract

The expanded production of shale gas has increased the desire for developing methods for converting light alkanes, especially propane and ethane, into aromatic compounds (i.e., benzene, toluene, and xylene) for petrochemicals and fuels. The Cyclar process is one example of an industrial process that has been demonstrated for the conversion of butane to aromatics; however, the conversion of lower molecular weight alkanes remains elusive. A multi-step process for the conversion of light alkanes to aromatics may be developed, where the first stage converts light alkanes into olefins and hydrogen, and the second stage converts olefins into aromatics. However, to determine the viability of this process, a better understanding of the performance of olefin aromatization in the presence of equimolar hydrogen is necessary. Herein, H-ZSM-5 and Ga-modified H-ZSM-5 are compared for propylene aromatization in the presence and absence of equimolar hydrogen at 1.9 kPa and 50 kPa partial pressures. The presence of H2 has no impact on the product distribution with H-ZSM-5 at either pressure. At 1.9 kPa with Ga/H-ZSM-5, similar product distributions are observed regardless of the presence or absence of H2 since Ga is not sufficiently active for hydrogenation to inhibit aromatics formation. However, at 50 kPa of H2 with Ga/H-ZSM-5, there is an increased selectivity to C4 products and a decrease in toluene and xylene selectivities at high conversions (i.e., χ > 80%), suggesting that aromatic dehydrogenation of cyclic hydrocarbons has been suppressed.