Upgrading of hydrothermal liquefaction biocrudes from mono- and co-liquefaction of cow manure and wheat straw through hydrotreating and distillation

Abstract

Liquid hydrocarbons from agricultural wet wastes can serve as a strategy to greatly reduce CO2 emissions. This study presents the upgrading via catalytic hydrotreatment of hydrothermal liquefaction (HTL) biocrudes derived from cow manure, wheat straw and their combined liquefaction (co-HTL). Four different temperatures were tested (340, 360, 380 and 400 °C) at constant hydrogen and biocrude flowrate. The co-HTL biocrude contained more recalcitrant nitrogen-containing molecules towards hydrotreatment, which caused decreased hydrogen consumption and overall lower quality of upgraded products. Generally, upgraded products were obtained with >80 wt% carbon yields based on biocrude input. Products of hydrotreatment at 400 °C were distilled into four cuts. Increased hydrotreatment temperature improved physicochemical properties of upgraded products, leading to generally higher yields of gasoline and kerosene through significant cracking of bottom residues. Bottom residues derived from single feedstock HTL biocrudes were totally miscible with fossil-derived vacuum gas oil at room temperature, while the co-HTL derived one required increased temperature for total solubility. We show that the co-HTL approach leads to a higher production of the diesel and bottom residue fractions. Overall, single feedstock HTL resulted in a carbon yield from biomass to upgraded oils of 34 and 38 % respectively for wheat straw and cow manure, while the co-HTL approach increased this value to 43 %. The combination of agribusiness waste for HTL processing is shown here to be an attractive solution for wet waste processing and carbon recovery towards advanced biofuels.