Hydrotreatment of straw bio-oil from ablative fast pyrolysis to produce suitable refinery intermediates

To meet the expected requirements of the proposed EU Renewable Energy Directive for the next decade (RED II), it is necessary to increase the availability of second-generation biofuels. One promising way of doing this involves using ablative fast pyrolysis units to transform an agricultural by-product, for example straw, into bio-oil. To obtain straw bio-oil suitable for processing in a typical refinery, we optimized the key parameters of its hydrotreatment. For the upgrading, a continuous flow reactor with a fixed bed of a commercial sulphide NiMo/Al2O3 catalyst was used. The reaction temperature and pressure were tested at 240-360 degrees C and 2-8 MPa, respectively. The reaction off-gas was analysed by GC-FID/TCD. A detailed physicochemical analysis of the products was carried out. Under most conditions tested, the product was separated into an aqueous and an organic phase. For the best products, > 85% of the feed energy content remained in the organic phase and a significant decrease in viscosity and acidity was achieved. The product prepared at 360 degrees C and 8 MPa was the only one completely miscible with straight-run gas oil and, thus, appears to be the most suitable for co-processing in a refinery.