Conversion of the lignin component of biomass into fuels and chemicals is one of the main challenges to the development of biorefineries. The recalcitrant structure of lignin presents many challenges to its decomposition that remain unresolved. In this context, hydropyrolysis is an option that offers important advantages: 1) the hydrogen environment promotes hydrogenation reactions that lead to the formation of hydrocarbons (drop-in fuels), 2) hydrogen radicals cap reactive intermediates from the thermal decomposition of lignin. These intermediates would otherwise recombine and produce significant amounts of char. In this work, we use bi-functional catalysts with a metal supported on a zeolite to carry out the direct conversion of lignin into a mixture of aromatic hydrocarbons and cycloalkanes. These are major components of drop-in fuels, with cycloalkanes being especially important for jet fuels. We hypothesize that the metal component catalyzes hydrogenation and deoxygenation reactions, and the zeolite component promotes deoxygenation reactions. The synergistic activity between the catalysts increases the hydrocarbon yields and is expected to decrease char formation. We have synthesized Pd/HZSM-5 catalysts and compared its activity to HZSM-5 under a variety of hydropyrolysis conditions. The effect of catalyst-to-lignin ratio, hydrogen partial pressure, and temperature were investigated. We observed thermodynamic limitations associated with the hydrogenation reactions at lower temperatures, and added an ex-situ upgrade downstream of the hydropyrolysis reactor to further increase the yield of hydrocarbons. Comparisons of the ex-situ upgrade with the in-situ upgrade have been performed and are a useful tool to elucidate the role of the metal and the zeolite. This presentation will discuss the roles identified for each catalyst on product yield, selectivity, and char formation. The catalyst activity will be discussed in combination to the effect of process variables and reactor configuration. The effect of sulfur from lignin on the catalyst deactivation will also be discussed.

Role of bifunctional catalysts in the hydropyrolysis of lignin

248th National Meeting (2014)

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