Conversion of lignocellulosic feedstocks to renewable fuels

The increased worldwide demand for energy has led to the search for a long-term solution of a reliable source of clean energy. The major possible additions to the current energy portfolio include ethanol, butanol and bio-oils produced from lignocellulosic biomass. A great deal of research is being made in the fields of biomass conversion through biochemical and thermochemical pathways to biofuels. Much attention is focused on identifying a suitable biomass species that can provide high energy outputs to replace the fossil fuels. The current study focuses on some commonly available waste biomasses in Canada originating from forests (pinewood), energy crop systems (timothy grass) and agriculture (wheat straw) for their usage towards next generation biofuel production. The biomasses were examined physico-chemically to understand their chemistry through various analytical, structural and spectroscopic approaches. Pinewood, timothy grass and wheat straw contained 34-39 wt.% cellulose, 24-30 wt.% hemicellulose and 16-20 wt.% lignin. In order to have a comparative evaluation of bio-oil, biochar and gas yields, the feedstocks were pyrolyzed at 450°C with slow (2°C/min) and high (450°C/min) heating rates. The slow heating rate pyrolysis generated 41-44 wt.% biochars, 18-24 wt.% biooils and 24-27 wt.% gases, whereas high heating rate pyrolysis produced 21-24 wt.% biochars, 40-48 wt.% bio-oils and 17-24 wt.% gases from the three feedstocks. Lignin acts as a barrier for biomass conversion to alcohols. Moreover, its chemistry and distribution in the plant cell wall is least understood. With this objective, the in-situ characterization of lignin arrangement in untreated, hydrothermally pretreated and delignified biomasses was performed through chemical maps generated from Raman spectroscopy. Furthermore, the biomass conversion to ethanol and butanol was evaluated using Saccharomyces cerevisiae and Clostridium beijerinckii, respectively. The highest ethanol and butanol concentrations reached in the range of 22.6-24.1 and 10.8-11.6 g/L from biomass hydrolysates, respectively. As a result of biomass pretreatment, significant amount of hydrolysis residues were generated. The pyrolysis of these hydrolysis residues at 600°C produced bio-oils (18.6-22.3 wt.%), biochars (38.9-41.7 wt.%) and gases (24.9-28.8 wt.%) that demonstrated remarkable energy and environmental benefits.