Catalysis of Carbon-Carbon Coupling Reactions for the Formation of Liquid Hydrocarbon Fuels from Biomass and Shale Gas Resources

Richard Caulkins, Purdue University

Abstract

Biomass and shale gas have been proposed as alternate sources of hydrocarbon fuels, but traditional petroleum refining is not capable of directly converting either the highly oxygenated molecular structure of lignocellulosic biomass or the low molecular weight alkanes of shale gas into liquid fuels. Here, we investigate aspects of aldol condensation and oligomerization to perform C-C coupling of low molecular weight species in biomass pyrolysis vapors and shale gas. Pyrolysis of woody biomass into C1-C9 molecules has demonstrated significant carbon losses away from fuel-range hydrocarbons to C1-C3 species following hydrodeoxygenation [1]. Aldol condensation has been proposed as a means of leveraging oxygen functional groups present in the pyrolysis product distribution prior to hydrodeoxygenation in order to couple low molecular weight species such as glycolaldehyde to transform the C1-C3 fraction into C4+ species. Here, we demonstrate that glycolaldehyde coupling has only a minor effect on aldol condensation of cellulose pyrolysis vapors, and that higher molecular weight species undergo significant reaction over the aldol condensation catalyst. We demonstrate a pathway by which levoglucosan can be converted into levoglucosenone, which then forms higher molecular weight species over the aldol condensation catalyst Cu/TiO2. Ni cation sites exchanged onto microporous materials catalyze ethene oligomerization to butenes and heavier oligomers but also undergo rapid deactivation. The use of mesoporous supports has been reported previously to alleviate deactivation in regimes of high ethene pressures and low temperatures that cause capillary condensation of ethene within mesoporous voids. Here, we reproduce these prior findings on mesoporous Ni-MCM-41 and report that, in sharp contrast, reaction conditions that nominally correspond to ethene capillary condensation in microporous NiBeta or Ni-FAU zeolites do not mitigate deactivation, likely because confinement within microporous voids restricts the formation of condensed phases of ethene that are effective at solvating and desorbing heavier intermediates that are precursors to deactivation. Deactivation rates are found to transition from a first-order to a second-order dependence on Ni site density in Ni-FAU zeolites with increasing ethene pressure, suggesting a transition in the dominant deactivation mechanism involving a single Ni site to one involving two Ni sites, reminiscent of the effects of increasing H2pressure on changing the kinetic order of deactivation in our prior work on Ni-Beta zeolites.

Degree

Ph.D.

Advisors

Ribeiro, Purdue University.

Subject Area

Alternative Energy|Energy|Polymer chemistry

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