Study of catalysts for the conversion of alcohols to olefins and diesel-range hydrocarbons

Abstract

Given the current ecological concerns, such as global warming and environmental degradation inconnection to fossil fuels consumption, the search for alternative and renewable energy sourced is becoming a pressing matter. Among the most challenging areas is aviation, where the high energy density required for long-distance flights cannot be met by batteries and traditional biofuels.Another challenge is to find and alternative, for which the already existing infrastructure does not have to be altered. For this, Sustainable Aviation Fuels (SAFs) offer a promising route,as they can be applied as "drop-in" fuels, meaning they can directly substitute fossil fuels without any further adjustments in the operating system. SAFs are non-fossil jet-fuels, derived fromoils or agricultural waste materials. But because these sources are limited, further alternatives are required.1 Also, finding new routes for SAF production would lead to a general increase inthe share of SAFs in total energy use.The aim of this project is to convert alcohols, derived from organic matter, to jet-fuel range hydrocarbons, in two steps. Both reactions catalyzed over zeolite based catalysts. The alcohol synthesis is performed at pilot scale at BEST - Bioenergy and Sustainable Technology GmbH,using CO2, CO, and H2 stemming from the classification of wood chips.The first step involves converting the alcohols into light olefins (C2–C5) through reaction over zeolite catalysts, following the already well established alcohol to olefin (ATO) reaction. To evaluate the relevant system parameters, methanol was used as feedstock and reacted over acommercially obtained H-ZSM-5 catalyst with a Si/Al ratio of 45 and compared to results of previous experiments with a Si/Al ratio of 30. The results showed that increasing the Si/Al ratio enhanced selectivity towards C2–C4 olefins, while simultaneously suppressing by-product formation caused by hydrogen transfer reactions.In the second step, the obtained light olefins are intended to further oligomerize to form heavy hydrocarbons in jet-fuel range. In homogeneous catalysis, Ni(II)-based systems are already established for the selective transformation of light olefins into heavy hydrocarbons. However, to be able to combine the advantages of heterogeneous catalysis, such as ease of product separation, and the benefits of zeolite-based systems, including enhanced selectivity, thermal- and chemical stability, Ni-loaded zeolites are a promising alternative.