(24g) Fast Hydropyrolysis and Catalytic Hydrodeoxygenation of Cellulose in a Micro-Scale Batch Reactor

Development of high energy density fuel for the transportation sector in a sustainable manner poses a significant challenge.  The H₂Bioil¹ process proposed high pressure fast hydropyrolysis of biomass followed by catalytic vapor phase hydrodeoxygenation (HDO) and subsequent quenching to generate hydrocarbon-like fuel. Fast hydropyrolysis of biomass generates a complex mixture of oxygenated compounds which requires upgrading to reduce the oxygen content of the condensed bio-oil.  Understanding the mechanism of fast pyrolysis of biomass and biomass model compounds is the key for tailoring the pyrolysis product distribution, thereby making it suitable for final downstream catalytic upgrading.

A micro-scale batch reactor, a modified commercial pyrolyzer, was used to study the pyrolysis of cellulose. A novel design allowed online sampling of pyrolysis vapor product composition under high pressure hydrogen (up to 350 psi) directly into the gas chromatograph and mass spectrometer (GC-MS) for analysis. An inline fixed-bed catalytic reactor was used to study the catalytic hydrodeoxygenation (HDO) of the pyrolysis products. Quantification of the pyrolysis products using the GC-MS accounted for 80-85% of the starting mass of the cellulose. Pyrolysis of cellulose was conducted in a temperature range 350°C-700°C. The major product observed was levoglucosan (~40%). The average molecular weight of the pyrolysis vapors decreased with an increase in the temperature of pyrolysis. Catalytic hydrodeoxygenation is required for upgrading pyrolysis vapors since fast hydropyrolysis alone did not lead to significant deoxygenation. Cellulose pyrolysis products were upgraded here over 2%Pt /ZrO₂ and 2%Ru/ZrO₂ catalyst at 300°C and 350 psi partial pressure of hydrogen. Complete hydrodeoxygenation of the pyrolysis products of biomass was observed under conditions of high catalyst to feed ratio (~20:1). The product distribution obtained over the two catalysts showed a lower degree of C-C bond hydrogenolysis over the 2%Pt/ZrO₂ catalyst versus 2%Ru/ZrO₂, with C4 and higher molecular weight hydrocarbons accounting for 40% of the carbon from the feed. The implications of these findings on the mechanism of cellulose pyrolysis and catalyst development for maximizing carbon conversion to fuel range molecules will be discussed.

1)      R. Agrawal, N. R. Singh, Synergistic Routes to Liquid Fuel for a Petroleum Deprived Future, AIChE Journal,55,7,1898-1905, 2009.