Bench-Scale Fluidized-Bed Pyrolysis of Switchgrass for Bio-Oil Production ² Akwasi A. Boateng,* ,‡ Daren E. Daugaard, § Neil M. Goldberg, ‡ and Kevin B. Hicks ‡ Eastern Regional Research Center, Agricultural Research SerVice, U.S. Department of Agriculture, 600 East Mermaid Lane, Wyndmoor, PennsylVania 19038, and Department of Mechanical Engineering, The UniVersity of Texas at San Antonio, One UTSA Circle, San Antonio, Texas 78249 The U.S. biomass initiative is counting on lignocellulosic conversion to boost the quantities of biofuels currently produced from starches in order to achieve much needed energy security in the future. However, with current challenges in fermentation of lignocellulosic material to ethanol, other methods of converting biomass to usable energy have received consideration nationally. One thermochemical technique, fast pyrolysis, is being considered by the Agricultural Research Service (ARS) researchers of the USDA for processing energy crops such as switchgrass and other agricultural residues, e.g., barley hulls and alfalfa stems for bio-oil (pyrolysis oil or pyrolysis liquids) production. A 2.5 kg/h biomass fast pyrolyzer has been developed at ARS and tested for switchgrass conversion. The unit has provided useful data such as energy requirements and product yields that can be used as design parameters for larger systems based on the processing of perennial energy crops. Bio-oil yields greater than 60% by mass have been demonstrated for switchgrass, with energy conversion efficiencies ranging from 52 to 81%. The results show that char yielded would suffice in providing all the energy required for the endothermic pyrolysis reaction process. The composition of the noncondensable gas produced has been initially characterized. Initial mass and energy balances have been calculated based on this system, yielding useful parameters for future economic and design studies. 1. Introduction Switchgrass is being considered as a biomass feedstock for the renewable fuel biorefining industry. Several varieties are being cultivated with the aim of finding the best yielding varieties with maximum fuel potential. Genetic engineering is also being applied to develop improved cultivars of switchgrass. Because enzymatic and fermentative conversion of lignocellu- losic feedstock to ethanol is still not economically feasible, thermochemical conversion is considered a potential alternative method for converting biomass into useful forms of energy. Thermal conversion of switchgrass includes combustion, gas- ification, and pyrolysis. Direct combustion of switchgrass to fuel power plants has been investigated. Thus far only cofiring with coal has been demonstrated to be economical, with switchgrass replacing only up to 20% of pulverized coal boiler energy requirements. 1 With fossil fuel prices skyrocketing, industries such as fuel ethanol producers are looking at dedicated crops like switchgrass to fulfill their energy needs. Gasification of switchgrass in which the organic matter is converted into combustible gas (syngas) has been demonstrated in the com- bined heat and power (CHP) industry. 2 Pyrolysis, a rapid decomposition of organic materials in the absence of oxygen, yields char, gas, and pyrolysis oil. The latter has potential to be used to power stationary engines or be upgraded to transportation fuels. Several demonstrations of pyrolysis oil combustion have been carried out, including applications such as boilers, diesel engines, and gas turbines. 3 Much of these works have been concentrated in Europe and Canada. Also, pyrolysis oils can be cost-effectively transported to centralized refineries and can be used as feedstock for the production of Fischer-Tropsch fuels from syngas when the liquids are used as the gasifier feedstock. 4 This notwithstanding, several issues including changes in composition during aging, phase separation, and corrosiveness due to excessive water content are some of the storage stability problems that plague bio-oil as a transporta- tion fuel. 5 With regard to production, a number of different approaches have been researched to achieve fast pyrolysis conditions using high heating rates and short residence times that have resulted in several reactor designs. Reactors of choice have included fluidized-bed, circulating fluidized bed, ablative, and auger type systems. 6 Most of these designs have used wood sawdust as the primary feedstock. Extensive testing on herba- ceous grasses has been rare. Previous work at the Department of Energy’s National Renewable Energy Laboratory (NREL) produced and characterized pyrolysis oils from oak and pine wood along with switchgrass in an ablative reactor and investigated droplet combustion characteristics of these oils. 3 Boateng et al. 7 investigated pyrolysis of Cave-in-Rock switch- grass in an analytical pyrolysis probe coupled with a gas chromatograph-mass spectrometer (PY-GC/MS), but only a qualitative measure of the condensable gas (pyrolysis liquids) * To whom correspondence should be addressed. Tel.: (215) 233- 6493. Fax: (215) 233-6406. E-mail: akwasi.boateng@ars.usda.gov. ² Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture. ‡ Eastern Regional Research Center, Agricultural Research Service. § The University of Texas at San Antonio. Figure 1. Reactor design and layout. 1891 Ind. Eng. Chem. Res. 2007, 46, 1891-1897 10.1021/ie0614529 CCC: $37.00 © 2007 American Chemical Society Published on Web 03/01/2007