Monoaromatic hydrocarbons, such as benzene, toluene, ethylbenzene, and xylenes (BTEX), are widely used as additives to gasoline and precursors to polymers. Green aromatics from renewable biomass, as a substitute for aromatics from petroleum refining, are essential for reducing worldwide dependence on petroleum and carbon dioxide emissions. Catalytic fast pyrolysis of biomass potentially offers a green route to make BTEX. However, biomass’ high oxygen content is unfavorable for making aromatics as it reduces the efficiencies of transport and conversion. Furthermore, the low bulk density of biomass results in a high transport cost. Biomass upgrading technologies, such as torrefaction, partially removes the chemically bound oxygen in biomass, thus lowering subsequent transport and conversion costs. Pelletization, after torrefaction, further lowers transport costs by increasing the bulk density of biomass. This study investigates the integration of decentralized biomass upgrading depots with a centralized BTEX production facility. An economic analysis of this bioenergy system was conducted to examine BTEX yields, biomass costs and their sensitivities. Model predictions were verified experimentally using pyrolysis GC/MS to quantify BTEX yields for raw and torrefied biomass. A group of factors, including torrefaction temperature, residence time, upgrading depot capacity and biomass on-site drying time, were optimized using the minimum production cost as the objective function. This optimization study found conditions that justify torrefaction as a pretreatment for making BTEX provided that starting feedstock costs are below $58 per tonne.
Read
