(108b) Effect of Biomass Type, Heating Rate, and Sample Size on Microwave Enhanced Fast Pyrolysis Product Yields and Qualities

Authors: 
Westover, T. L., Idaho National Laboratory
Klinger, J., Michigan Technological University
Emerson, R., Idaho National Laboratory
Williams, C. L., Idaho National Laboratory
Hernandez, S., Idaho National Laboratory
Using fast pyrolysis processes, renewable biomass resources can be converted to bio-oils that retain more than 60% of the original energy content, and these oils can then be upgraded to motor fuels or other commodity chemicals. The products from fast pyrolysis of biomass are variable and highly dependent upon biomass composition, particle size and geometry, and operating conditions. To better understand the interconnection of biomass characteristics and fast pyrolysis products, a microwave-enhanced fast pyrolysis (MEFP) reactor was constructed. The use of microwave heating under consistent reaction conditions can help to elucidate the primary effects of the original material’s composition on the product yield. This work tested the MEFP conversion of fifteen biomass materials and blends, including woody feedstock, with and without bark, agricultural residues, and herbaceous energy crops, including some of the materials at different final temperatures and different heating rates. The highest liquid yield was obtained from tulip poplar (64.9 wt%), while the lowest yield was obtained from corn stover (48.5 wt%). The liquid yields obtained from the reactor were repeatable with an average standard deviation of 1.1 wt% (average 1.9% relative standard deviation). The reactor was able to achieve heating rates up to 200 °C/s, although greater product yield was not observed beyond a threshold of approximately 10 °C/s. Multivariate linear regression indicates that >85% of the convertibility of the different feedstocks can be explained using the measured properties of alkali and alkaline earth metals, volatile matter, and lignin contents. Reasonable qualitative agreement was achieved between MEFP yields and yields from a circulating fluidized bed reactor using the same biomass samples (R2 between 0.78 and 0.85, depending upon how the results are weighted), suggesting that the MEFP can be used as a screening device to select samples and conditions that will maximize the impact from tests performed in larger, continuous conversion systems. MEFP tests have a further advantage in that the microwave heating, which is internal to the particles, facilitates separating the effects of physical heat transfer from those of chemical reaction kinetics for improved understanding of the fundamental polymer deconstruction mechanisms that produce oils from solid feedstocks.