(404d) Biofuel Production By Catalytic Fast Pyrolysis

Concerns about national security, global warming, combined with the diminishing supply and increased cost of fossil fuels are causing our society to search for new sources of transportation fuels. In this respect the only sustainable source of renewable carbon is plant biomass. Cellulosic biomass is both inexpensive ($15 per barrel of oil energy equivalent) and abundant (the US can sustainably produce 4 billion barrels of oil energy equivalent per year). Fast pyrolysis is one of the most promising methods for biofuel production. Fast pyrolysis involves rapidly heating the biomass (500oC/sec) to intermediate temperatures (400-600oC) followed by rapid cooling (residence times 1-2 s). These reaction conditions allow the conversion of thermally unstable biomass compounds to a liquid product called bio-oils while minimizing undesired reactions (i.e. coke and gas formation). The bio-oils are an acidic combustible liquid containing more than 300 compounds that degrade with time. It would be desirable to improve the characteristics of the bio-oils produced in the fast pyrolysis process. As we will show in this presentation addition of heterogeneous catalysis to fast pyrolysis (catalytic fast pyrolysis) significantly changes the products produced. The fast heating rates used in fast pyrolysis allow the conversion of thermally unstable compounds allows us to convert these compounds before they produce undesired coke.

We have tested a wide range of catalysts (including SiO2-Al2O3, Pt/ SiO2-Al2O3, WOx/ZrO2, SOx/ZrO2, HY-zeolite, â-zeolite, and HZSM-5) for feedstock-derived from cellulosic (xylose, glucose, xylitol, cellobiose, cellulose) and lignin (organosolv and benzyl phenyl ether) fractions of biomass in a microscale flash pyrolysis reactor. The reactions involved for catalytic fast pyrolysis include dehydration, hydrogen transfer, decarbonylation and aromatic production. These reactions must be properly balanced to produce the desired reaction. Shape selectivity appears to be very important for these reactions as zeolite catalysts produce more aromatics than amorphous catalysts.

We have used xylitol as a feed to study the effects of different catalysts. Coke, dehydrated products (including furan, methyl furan and furfural), CO and CO2 were the primary products for SiO2-Al2O3, Pt/ SiO2-Al2O3, WOx/ZrO2, and SOx/ZrO2. Coke, aromatics and CO were the primary products for HZSM-5. The products for HY-Zeolite and â-Zeolite include coke, dehydrated products, aromatics, CO and CO2. The aromatics produced in order of decreasing concentration include: alkyl substituted Naphthalenes >> Toluene > Xylenes > Naphthalene > Benzene > alkyl substituted Indanes >> Indane. These aromatics could be used as a gasoline blend. Other cellulosic feeds (including cellulose, cellobiose-glucose dimer, and glucose) gave similar product selectivities with a â-Zeolite catalyst suggesting that catalytic fast pyrolysis can be used for conversion of polysaccharides to aromatics.

We also tested catalytic fast pyrolysis of organosolv lignin and benzyl phenyl ether (BPE-a model lignin compound). Pyrolysis of BPE produced phenol, benzene and toluene as the major products. Pyrolysis of neat BPE resulted in phenol (80% selectivity) as the main product whereas in presence of Silica-Alumina or HZSM-5 as catalyst phenol and benzene were the major products with about 40% selectivity The selectivity changes from phenol to benzene as the catalyst to BPE ratio increases. Catalytic fast pyrolysis of organsolv lignin with HZSM-5 and â-zeolite produced aromatics (40 % selectivity) and CO (45 % selectivity).

In summary heterogeneous catalysts can significantly change the reaction chemistry that is occurring in the fast pyrolysis process. It is likely that future advances in understanding the reaction mechanism combined with new material synthesis and theoretical chemistry will help improve the reaction chemistry further and make catalytic fast pyrolysis an efficient reaction for biofuel production.