Pyrolysis of Woody Residue Feedstocks: Upgrading of Bio-oils from Mountain-Pine-Beetle-Killed Trees and Hog Fuel

Liquid transportation fuel blendstocks were produced by pyrolysis and catalytic upgrading of woody residue biomass. Mountain-pine-beetle-killed (MPBK) wood and hog fuel from a saw mill were pyrolyzed in a 1 kg/h fluidized bed reactor and, subsequently, upgraded to hydrocarbons in a continuous fixed bed hydrotreater. Upgrading was performed by catalytic hydrotreatment in a two-stage bed at 170 and 405 °C with a per bed liquid hourly space velocity between 0.17 and 0.19. The overall yields from biomass to upgraded fuel were similar for both feeds (24-25%), despite the differences in bio-oil (intermediate) mass yield. The pyrolysis bio-oil mass yield was 61% from MPBK wood, and subsequent upgrading of the bio-oil gave an average mass yield of 41% to liquid fuel blend stocks. Hydrogen was consumed at an average of 0.042 g/g of bio-oil fed, with a final oxygen content in the product fuel ranging from 0.3 to 1.6% over the course of the test. Comparatively, for hog fuel, the pyrolysis bio-oil mass yield was lower at 54% because of inorganics in the biomass, but subsequent upgrading of that bio-oil had an average mass yield of 45% to liquid fuel, resulting in a similar final mass yield to fuel compared to the cleaner MPBK wood. Hydrogen consumption for the hog fuel upgrading averaged 0.041 g/g of bio-oil fed, and the final oxygen content of the product fuel ranged from 0.09 to 2.4% over the run. While it was confirmed that inorganic-laden biomass yields less bio-oil, this work demonstrated that the resultant bio-oil can be upgraded to hydrocarbons at a higher yield than bio-oil from clean wood. Thus, the final hydrocarbon yield from clean or residue biomass pyrolysis/upgrading was similar.