Extraction and Upgrading of Bio-crude and Bio-residue from Hydrothermal Liquefaction of Agricultural Biomass

Abstract

Fossil-based sources of energy have conventionally driven the human civilization till date. However, in the wake of an unprecedented population explosion, these conventional sources of energy are falling short of meeting the increased global demand due to the finite nature of their reserves. Moreover, they have increasingly caused the environment to deteriorate due to the pollutants that are released into the atmosphere as a result of their utilization. This has caused researchers to look for alternative renewable sources of energy which would also be environmentally benign. Bio-crude is one such alternative which can potentially substitute the use of fossil-based fuels such as petroleum crude. Bio-crude can be produced via two main processes: fast pyrolysis and hydrothermal liquefaction (HTL). Due to certain inherent drawbacks of the pyrolysis process, the focus is currently on producing bio-crude from the HTL process. In the present study, three different solvents – ethyl acetate, tetrahydrofuran and petroleum ether – were used to extract bio-crude from a hydrothermal liquefaction product mixture obtained from canola meal and waste wheat flour. The bio-crude yields and the ease of extraction were compared for each of the solvents to evaluate the efficacy of the solvent-extraction process and to determine the most suitable solvent for the same. The extracted bio-crude and bio-residue fractions were characterized in detail so as to determine their physicochemical properties and identify the samples that would be ideal for further upgrading processes. The bio-crude thus produced has a high percentage of oxygen and thus, needs to be upgraded to make it comparable with diesel fuel for utilization in different applications. Therefore, the report further focusses on decreasing the amount of oxygen present in HTL bio-crude via catalytic hydrodeoxygenation (HDO). To serve the purpose, carbon-supported molybdenum carbide catalysts were synthesized via Carbothermal Hydrogen Reduction (CHR) method using three different carbon supports – commercial activated carbon, commercial multi-walled carbon nanotubes and bio-residue obtained during solvent-extraction. The catalysts were screened for their oxygen reduction efficiency using a blend of bio-crude in hydrotreated heavy gas oil and the efficiency of the best-performing catalyst was compared with that of commercial hydrotreating catalysts. The synthesized catalysts were characterized in order to explain their oxygen reduction percentages and a parametric study was carried out for the best-performing catalyst to determine the effects of process parameters such as temperature, pressure, reaction time and catalyst loading on oxygen reduction efficiency.