|OMOLAYO, YETUNDE - Drexel University
|SPATARI, SABRINA - Drexel University
Submitted to: ACS Sustainable Chemistry & Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/28/2020
Publication Date: 1/18/2021
Citation: Elkasabi, Y.M., Omolayo, Y., Spatari, S. 2021. Continuous calcination of biocoke/petcoke blends in a rotary tube furnace. ACS Sustainable Chemistry & Engineering. 9:695-703. https://doi.org/10.1021/acssuschemeng.0c06307?ref=pdf.
Interpretive Summary: The aluminum industry relies on electrically conductive carbon materials to produce aluminum. Oil refineries usually create these materials as solid waste, but these solid wastes contain much more metals, which increases production costs and still puts more carbon dioxide into the atmosphere, which is a major contributor to global warming. Our process for making renewable oils converts agricultural wastes into a crude oil that is similar to petroleum, with significant chemical differences. However, we can separate the oil into valuable liquids and waste carbon solids, similar to what is done with petroleum. In this work, we blended the refinery fossil-based carbon wastes with biofuels solid waste and used that to make a better electrically-conductive carbon material. Our process imitates on a smaller scale what the aluminum industry does on a large scale. The blended product contains less metals and is strong enough for processes that make aluminum metal, which requires temperatures more than 1200 degree C. If this method is adopted by the aluminum industry – even blending just 10% - it would decrease non-renewable CO2 by 7.5 million tons per year.
Technical Abstract: The aluminum industry relies on calcined petroleum coke as an anode material for smelting of aluminum oxide into aluminum metal. While distillate residues from biomass pyrolysis oils can convert into calcined coke with promising elemental and physical properties, no studies have produced calcined biocoke continuously from rotary kilns. Using a solids feeder and rotary tube furnace, blends of green petroleum coke and biocoke underwent calcination continuously. Biocoke from pyrolysis bio-oil distillation residues contained ~13 wt% O. In control experiments without biocoke, the furnace converted green petroleum coke into calcined petroleum coke within industry specifications. Properties measured include % anisotropy (homogeneity indicated by polarized light microscopy), porosity, crystallite thickness (Lc), and trace elements concentrations. With biocoke blends (10 wt% and 27 wt%), the effects on properties increased with respect to the blend concentration. Microscopy indicated blends to be mostly anisotropic with some amorphous domains remained in the blended product. Steady-state sulfur concentrations decreased from 3.2 wt% to 2.7 wt%. Nickel and vanadium successfully decreased to acceptable limits, especially when 27% biocoke was used. Adding biocoke increased phosphorous concentrations by 5-7 ppm. The average crystallite height (Lc) decreased from 26.5 to 25.6 Å, which still remains within typical specifications. Slight increases to blending of biocoke (beyond 27 wt%) is possible, though Lc and phosphorous values will govern the blending limit.