Pretreating bio-oil to increase yield and reduce char during hydrodeoxygenation to produce hydrocarbons

Abstract

Conversion of pyrolysis oil to hydrocarbons has been successfully performed under high hydrogen pressure in the presence of hydrodeoxygenation (HDO) catalysts at high heat. The high hydrogen pressures utilized are a more expensive application than for a lower hydrogen pressure. Development of a modified HDO method utilizing lower pressure hydrogen with the potential for reduction of hydrogen consumption would be economically beneficial to the process if equal or higher biofuel yields and quality are maintained. The method tested here is the oxidation pretreatment of raw bio-oil to increase carboxylic acids by conversion of aldehydes and ketones; phenols and other alcohols were also oxidized to some extent. This oxidation pretreatment of raw bio-oil allowed performance of the hydrotreating step with low hydrogen pressure and reduced hydrogen consumption. The hydrotreated oxidized bio-oil had a 30.5% higher organic fraction yield; char and water content were reduced by approximately 92.0% and 46.2%, respectively. The hydrotreated oxidized product was then hydrocracked at higher hydrogen pressure to produce mixed hydrocarbons found suitable for transportation fuels. The hydrocarbons produced had approximately a 181.9% HHV increase at 45.1MJ/kg compared to raw bio-oil (16.0MJ/kg). The acid value, water and oxygen contents of the hydrocarbons were reduced to approximately zero.