Pyrolysis bio-oil upgrading to renewable liquid fuels by catalytic hydrocracking: Effect of operating conditions on the process

Abstract

This work analyses the influence of operating conditions during the catalytic hydrocracking of a bio-oil obtained from the fast pyrolysis of pinewood. The original liquid has a 39 wt.% of water and the following elemental composition in dry basis: 54 wt.% C, 3.3 wt.% H, 41.3 wt.% O, 0.8 wt.% N and 0.6 wt.% S. Experiments were carried out in a batch microbomb reactor employing a co-precipitated Ni-Co/Al-Mg catalyst. They were planned according to a full factorial design of experiments with a statistical analysis of the results in order to analyse the effects of temperature (350-450 °C), hydrogen pressure (70-150 bar), catalyst/bio-oil mass ratio (0-0.25 g catalyst/g organics), reaction time (0-60 min) and all interactions between these operating variables on the process. Statistical analysis of the results indicates that the operating conditions have a statistically significant effect on the results. Specifically, the yields to upgraded bio-oil (liquid), gas and solid vary in ranges of 3-97 %, 0-86% and 3-41% respectively. Depending on the operating conditions, the amount of C, H and O (wt.%) in the upgraded bio-oil varies in ranges of 50-82, 3.5-8.3 and 9-44 respectively. This represents an increase of up to 52 and 150% in the proportion of C and H respectively, as well as a decrease of up to 78% in the proportion of O. The higher heating value of the treated bio-oil varies from 19 to 37 MJ/kg, which is considerably higher than that of the original bio-oil.