Progress on Biobased Industrial Carbons as Thermochemical Biorefinery Coproducts
Yaseen Elkasabi, Charles A. Mullen
Abstract
Industrial carbons are a category of high purity carbon (>95 wt %) materials that are solid at room temperature, produced in bulk as refinery byproducts, and subsequently used in a wide variety of applications. The most dominant industrial carbons are calcined coke, coal tar pitch, carbon black, and graphite. The manufacturing sector consumes a large majority of industrial carbons as electrode materials, carbon binders, tire reinforcement fillers, and ink components and constitutes one of the largest contributors to greenhouse gas emissions worldwide. Thermochemical conversion of biomass offers promising pathways for both the integration of drop-in fuels with refinery infrastructure and for the production of carbonaceous solid materials. Conversely, over the past two decades, most biofuels efforts focused on fuel production technologies with high-value small molecule chemicals as coproducts. This review summarizes recent progress toward developing biobased industrial carbons, particularly as coproducts from thermochemical conversions of biomass. Pyrolysis and gasification produce liquid and solid products in varying yields; biocarbons from either stream currently must compromise between adequate yield and adequate quality. While metals can be removed post-synthesis, there exist opportunities for improvement of biocarbon quality, including using deashed biomass and/or process modification beyond standard pyrolysis conditions. Improving calcined coke and tar pitch properties (density/porosity and softening point/coking value, respectively) will likely follow by departing from standard biomass conversion parameters. Although markets exist for biobased graphite, current products of high quality will require significant research into scale-up strategies.