Multi-Scale Simulation of Propane Valorization to BTX as a Co-Product from Algal Oil Hydroprocessing

Abstract

Microalgae are a very promising and appealing feedstock for biofuels production. In fact, it is reported that some algal strains have very high oil content, even exceeding the 50 % of the dry weight. After growing and harvesting, algae require to be dewatered and the lipid fraction has to be separated. The obtained algal oil can be converted into alkyl esters by means of transesterification with an alcohol to produce biodiesel or may be treated with hydrogenation/cracking processes for the production of hydrocarbons, whose chemical structure is close to that of diesel fuels. Second generation processes for the production of drop-in biofuels from vegetable oils are based on hydrogenation reactions, which lead to the production of green diesel, and selective cracking reactions that maximize the production of bio-jet fuels C10-C15 fractions. These catalytic processes involve the cracking of triglycerides, saturation of double bonds, heteroatoms rejection (especially deoxygenation) and isomerization. Moreover, while glycerol is the low added value co-product for oils transesterification, propane represents more than 30 % of the final product in the hydrotreatment of the lipid fraction. Propane can be upgraded by selective conversion to aromatics, as additives for jet-fuels and versatile feedstocks for the chemical industry. The low selectivity to aromatics is the drawback of this process, resulting in a large production of cracking gases. In general, zeolites with MFI pore structure are used due to their high resistance to deactivation with metal components, such as gallium, added to enhance the dehydrogenation function. Kinetic studies of propane aromatization over H- ZSM-5 at 500 °C in a wide range of conversions are reported in the literature (Nguyen et al., 2006). Based on these and similar results (Bhan et al., 2005), a general kinetic model for propane aromatization has been developed. In this work the revised kinetic model is presented and embedded in a multi-scale simulation of a propane aromatization process, performed with the commercial code Invensys PRO/II (Kansha et al., 2009). Several technologies have been designed to directly convert LPG into aromatics (BTX). In this study the Cyclar process (Giannetto et al., 1994) developed by UOP and BP was selected.