(679c) The Effect of Torrefaction Pretreatment, Temperature, and Lignin Content of Hybrid Poplar on the Quality of Fast Pyrolysis Bio-Oil

Authors: 
Klemetsrud, B., University of North Dakota
Shonnard, D. R., Michigan Technological University
Introduction: Fast pyrolysis of woody biomass has been identified as a potential means for the production of advanced transportation fuels. During fast pyrolysis the three main components of biomass (cellulose, hemicellulose, and lignin) thermochemically breakdown to produce bio-oil. Several studies have isolated these individual components and looked at their bio-oil distributions. However the interactions between these three main components and how variations in feedstock composition affect product distribution are not well understood. The purpose of this work is to assess the quality of bio-oil as lignin content is varied in the hybrid poplar, how temperature of pyrolysis affects these results, and how the addition of a torrefaction pretreatment will affect the composition of bio-oil. The quality of bio-oil is assessed by calculating bio-oil yield relative to dry biomass and relative to char and gas, changes in relative abundance of oxygen in the bio-oil, and energy density of the bio-oil. Eight genetically different poplar samples with varying lignin content were pyrolyzed at 500ºC using a CDS 5200 HP micro-pyrolysis unit, which was directly connected to a ThermoFisher Trace GC coupled with a DSQII MS. Four of these hybrid poplar samples over a range of lignin content were then pyrolyzed at temperatures of 550ºC and 600ºC to determine effects of pyrolysis temperature. Finally, two of those samples, a high and low lignin concentration, were then torrefied at 300ºC for 30 minutes and then pyrolyzed at 550ºC for 20 seconds.

Results: An increase of lignin concentration, by approximately 10% relative to the low lignin content sample, decreased the abundance of phenolic species in bio-oil by 3% and decreased the relative abundance of oxygen by 8% at 500ºC. The bio-oil yield similarly decreased by 5%, due to an increase char yield at high lignin levels. With an increase in pyrolysis temperatures, there was an increase in phenolics produced overall, but with respect to increasing lignin content, it continued the trend of decreasing phenolic species in bio-oil. Again with respect to lignin content at higher temperatures, the bio-oil yield decreased as the char yield increased. The addition of torrefaction as a pretreatment step, decreased the overall yield of bio-oil produced by 10% and in agreement with previous literature, removed low molecular weight highly oxygenated species, thereby decreasing bio-oil yield but improving the quality of bio-oil produced. From these results over a limited range of lignin content, higher temperatures are needed to increase the recovery of phenolic species from pyrolysis of poplar.