Upgrading of bio-oil distillation bottoms into biorenewable calcined coke

Abstract

Depleting fossil fuel sources necessitate renewable substitutes for petroleum-based co-products. Fast pyrolysis of biomass generates a hydrocarbon liquid (“bio-oil”) amenable to distillation and/or hydrotreatment into hydrocarbon blendstocks. Biorefineries must add value through parallel generation of co-products. We demonstrated a straightforward conversion of bio-oil distillate bottoms into calcined coke. The solid residue was subjected to calcination at 1200 °C for 1 h under N2 atmosphere. The dry calcined product contained 96–99% carbon, was free from sulfur (<0.05% mass fraction), and contained a mass fraction of 0.2–1.1% ash. XRD confirmed steady increases in crystallite size with both devolatilization and calcination. FTIR spectroscopy indicated a loss of functional groups after calcination, except two broad peaks representing C–C and C–O. Temperature programmed oxidation (TPO) of the bottoms before and after calcination illustrates an increasing structural order via the increasing temperature(s) necessary to oxidize the samples. SEM images reveal bubbly morphologies similar to the industrially-favored sponge coke. The electrical resistivity of calcined coke samples measured to be < 1.6 mΩ-m, which closely falls in line with specifications for carbon anodes. Due to the aforementioned qualities and biomass origin, biorenewable calcined coke is an improved alternative to petroleum coke and can find application in carbon anodes, steel carburization, and graphite synthesis.