Flash distillation of bio-oils for simultaneous production of hydrocarbons and green coke

Authors: Elkasabi, Yaseen; Mullen, Charles; Boateng, Akwasi; BROWN, AVERY - Worcester Polytechnical Institute; TIMKO, MICHAEL - Worcester Polytechnical Institute

Submitted to: Industrial and Engineering Chemistry Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/17/2018
Publication Date: 2/6/2019
Publication URL: https://handle.nal.usda.gov/10113/6302386
Citation: Elkasabi, Y.M., Mullen, C.A., Boateng, A.A., Brown, A., Timko, M.T. 2019. Flash distillation of bio-oils for simultaneous production of hydrocarbons and green coke. Industrial and Engineering Chemistry Research. 58:1794-1802. https://doi.org/10.1021/acs.iecr.8b04556.
DOI: https://doi.org/10.1021/acs.iecr.8b04556

Interpretive Summary: Biofuels can be produced either through biological processes such as fermentation, or through high-temperature reactions. The latter (pyrolysis) involves heating dried biomass to high temperature in the absence of oxygen, producing an oil that resembles petroleum (“bio-oil”) but contains high levels of oxygen (33%) that are detrimental to fuel end products. Improvements to the pyrolysis process can produce bio-oils with low levels of oxygen (<15%) and allow petroleum refinery processes to be used on the bio-oils. Distillation of bio-oils is one such example; bio-oils with less oxygen can distill, producing liquids for further processing into fuels, as well as a residue for production of solid carbon products (“coke”). This work demonstrated that bio-oils can be distilled continuously over longer periods of time without harming the distillation equipment and without significant losses of product. It was found that, as the oxygen level increases, the distillation become more difficult to carry out, resulting in losses of product. However, for most oils produced from advanced pyrolysis techniques, the distillation process handled and separated the oil components efficiently. The solid residues underwent conversion into coke with better structural integrity, for use as electrically conductive materials in aluminum production.

Technical Abstract: Fast pyrolysis bio-oils from biomass can potentially integrate with petroleum refinery infrastructure for production of renewable fuels and chemicals. Besides hydrodeoxygenation, few feasible options exist for entry points. When considering advanced pyrolysis techniques such as catalytic and/or tail-gas reactive pyrolysis (TGRP), distillation for using both light and heavy ends becomes possible. Our goal was to demonstrate and optimize continuous production of liquid organic distillates and residual solids coke, both in appreciable yields for downstream conversion into renewable products. We fabricated a flash drum for continuous one-step distillations of four oils of varying oxygen content (range form 5 – 32 wt%). While a mesh demisting screen enhanced seprations, removal of the screen ultimately improved overall yields. The flash drum proceeded to distill lower-oxygen oils (~10 wt%) with 80 wt% time-on-stream yields over several hours, with steady-state reached within 30-40 minutes. Bio-oils with moderate oxygen levels (20 wt%) took a noticeably longer time to attain steady-state and gave 60 wt% yield. Under distillation conditions, oils from conventional pyrolysis (32 wt%) underwent condensation repolymerization due to reactive instabilities and produced only 6 wt% organic liquid yield. Solid coke residues were collected and converted into calcined coke, with Raman analysis indicating that turbostratic carbons were produced.