Hydrodeoxygenation of Black Liquor HTL-Oil Model Compounds in Supercritical Water

A very promising and currently underutilized abundant non-food feedstock for biofuels is black liquor (BL), a side stream of chemical pulping industry. The lignin and other organics present in black liquor contain circa half of the energy of wood chips, and currently most of it is burnt in pulp mills. EU project Black Liquor to Fuel (BL2F) aims to develop a feasible route from black liquor to drop-in biofuels for aviation and shipping. In the first step, black liquor is treated under hydrothermal conditions to separate the cooking chemicals and produce HTL-oil from the organics. The HTL-oil is then further upgraded using catalytic hydrotreating using an integrated hydrothermal hydrodeoxygenation process. The aim of the hydrothermal HDO is to remove most of the oxygen and sulfur present in the feed and to stabilise the oil for easier transport and further upgrading at oil refineries.

In this work, we have studied hydrodeoxygenation of HTL-oil model compounds in aqueous conditions in a batch reactor. Isoeugenol, 4-methylcatechol and diphenylmethane were selected as model compounds representing different functionalities in HTL-oil. The studied catalysts were selected based on stability of the catalysts and support materials under supercritical water conditions. The HDO experiments were carried out both in subcritical and supercritical conditions using hydrogen gas; the effect of the catalyst and reaction conditions on the product distribution will be discussed in detail.