(592e) Fast-Hydropyrolysis and Catalytic Hydrodeoxygenation for Conversion of Biomass to Liquid Fuel

The production of high volumetric energy density fuels from a sustainable carbon source, such as lignocellulosic biomass, to supply the liquid fuel needs of the transportation sector is a grand challenge to be addressed. As one of the plausible solutions, a novel process, H₂Bioil¹, based on biomass fast-hydropyrolysis and catalytic hydrodeoxygenation (HDO), has been proposed for conversion of lignocellulosic biomass to liquid fuel with high estimated energy and carbon efficiencies. The H₂Bioil process integrates fast-pyrolysis thermochemical conversion, involving rapid heating of biomass, in a high-pressure (up to 50 bar) hydrogen environment, to produce fast-hydropyrolysis vapors that are subsequently catalytically upgraded in the vapor phase and quenched to form a deoxygenated liquid product with high energy density.

This presentation summarizes our work on H₂Bioil process development, using laboratory-scale high-pressure fast-hydropyrolysis and catalytic hydrodeoxygenation with cellulose, as a model biomass feedstock, and lignocellulosic feedstocks. To identify and quantitatively compare major chemical species present in the liquid product, we have developed and utilized a novel liquid chromatography-mass spectrometry (LC-MS) analytical method which accounts for up to 95% by mass of the cellulose hydropyrolysis liquid products. We have also used gas chromatography-mass spectrometry (GC-MS) and other analytical techniques such as elemental (C, H, O) and Karl Fisher water content analysis to characterize the liquid product. The effects of process conditions such as pyrolysis temperature (480°C-580°C), hydrogen partial pressure (25 bar, 50 bar) were studied with a cellulose model feedstock. The major product of high-pressure fast-pyrolysis and fast-hydropyrolysis of cellulose is the monomer (levoglucosan), which accounts for ~35-40% of the starting mass of cellulose pyrolyzed. As the pyrolysis temperature is increased, the product distribution shifts towards the lower molecular weight compounds, like glycolaldehyde and formic acid, which is attributed to increased thermal cracking of pyrolysis vapors. The first stage cellulose fast-hydropyrolysis does not lead to significant deoxygenation, even up to 50 bar hydrogen partial pressure, but presence of HDO catalysts leads to improvements in deoxygenation in the liquid product. The results from testing of candidate Pt-based and Ru-based catalysts for on-stream vapor-phase catalytic hydrodeoxygenation suggests that a balance of metal and acid catalytic functions is necessary for improving the extent of deoxygenation along with high carbon recovery in the liquid product and avoiding coking on the catalyst. 

¹Agrawal R, Singh NR. Synergistic Routes to Liquid Fuel for a Petroleum-Deprived Future, AIChE J. 2009; 55: 1898-1905