School of Chemical Engineering Seminar: Breaking the Chemical and Engineering Barriers to Lignocellulosic Biofuels
|Event Date:||May 21, 2008|
|Speaker:||Dr. George Huber|
|Speaker Affiliation:||Armstrong Professional Development Professor, Department of Chemical Engineering, University of Massachusetts, Amherst|
|Time:||10:30 - 11:30 am
Concerns about global warming and national security, 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 plant biomass is the only sustainable feedstock that can be used for production of renewable liquid fuels. Currently cellulosic biomass is significantly cheaper than petroleum (at $15 per barrel of oil energy equivalent) and abundant. However, the chief impediment to the utilization of our lignocellulosic biomass resources is the lack of economical processes. Heterogeneous catalysis allows us to convert our petroleum resources into fuels and chemicals. In the future heterogeneous catalysts will also be used for conversion of biomass feedstocks into fuels and chemicals.
In this presentation we will discuss two strategies for production of biofuels and chemicals with heterogeneous catalysis: aqueous-phase processing and catalytic fast pyrolysis. Biomass-derived oxygenates typically have a high degree of functionality and a low thermal stability making aqueous-phase processing advantageous in that it is possible to convert thermally unstable compounds without high levels of coke. Hydrogen, a range of alkanes, and chemicals can be produced by aqueous-phase processing. Aqueous-phase reforming (APR) of carbohydrates creates hydrogen at low temperatures (423-538 K) in a single reactor over supported mono and bimetallic catalysts. While high yields of undesirable methane occur with APR on Ni-based catalysts, we have discovered that the addition of Sn to Ni decreases the rate of methane production, while still maintaining high rates of H2 production. Alkanes ranging from C1 to C6 are produced by aqueous phase dehydration/hydrogenation (APD/H) of sorbitol (hydrogenated glucose) by a bi-functional pathway. Sorbitol is repeatedly dehydrated by a solid acid (SiO2-Al2O3) or a mineral acid (HCl) catalyst and then hydrogenated on a metal catalyst (Pt or Pd). The biorefining of sugars to alkanes plus CO2 and water is an exothermic process in which the products retain approximately 95 % of the heating value and only 30 % of the mass of the reactant. Larger straight diesel fuel range liquid alkanes (ranging from n-C7-C15) can be produced from carbohydrate-derived species by combining the dehydration/hydrogenation process with an aldol condensation step.
Catalytic fast pyrolysis produces gasoline range aromatics from solid biomass (including cellulose, sugars and sugar alcohols) in a single catalytic reactor at short residence times (less than 60 s) by a process we call catalytic fast pyrolysis. This process involves rapidly heating (500-900oC/s) the biomass to intermediate temperatures (400-600oC) in the presence of zeolite based catalysts. The fast heating rates are essential in that they allow the thermally unstable compounds to be introduced into the zeolite material prior to thermal decomposition. The solid biomass-derived compounds undergo thermal decomposition reactions to intermediates that are then catalytically converted to aromatics, CO2 and water. The reactions involved for catalytic fast pyrolysis include dehydration, hydrogen transfer, decarbonylation, C-C bond forming reactions, isomerization, and aromatic production. These reactions must be properly balanced by using the proper catalytic material and reaction conditions to produce the desired products.