Submitted to: ACS Sustainable Chemistry & Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/11/2014
Publication Date: 6/30/2014
Citation: Elkasabi, Y.M., Mullen, C.A., Boateng, A.A. 2014. Distillation and isolation of commodity chemicals from Bio-oil made by tail-gas reactive prolysis. ACS Sustainable Chemistry & Engineering. 2(8):2042-2052.
Interpretive Summary: Bio-oil is the name of the liquid product that is made by rapidly heating agricultural products, such as switchgrass, horse manure, and other types of biomass, in the absence of oxygen. While bio-oil possesses many properties that are similar to petroleum and make it a promising fuel alternative, bio-oil also is chemically unstable and difficult to process due to its high levels of water and oxygen-rich chemical compounds. A traditional oil refinery is unable to accept bio-oil as-is without significant upgrading and preprocessing. Distillation, the process of separating bio-oil based on boiling points, is the first step in a petroleum refinery. However, the distillation of bio-oil has been regarded as impossible due to the highly reactive and unpredictable nature of bio-oil. Using an enhanced pyrolysis process which exploits the reactive nature of recycling gas products from pyrolysis, we have demonstrated the distillation of tail-gas reactive pyrolysis (TGRP) bio-oil into fuels and petrochemicals. The efficiency of TGRP bio-oil distillation is at least 3 times greater than the distillation of traditional bio-oil. This information will be valuable to those interested in developing an economical process to convert various types of biomass and other agricultural materials into liquid fuels.
Technical Abstract: Owing to instabilities, very little has been accomplished with regards to simple cost-effective separations of fast-pyrolysis bio-oil. However, recent developments in the use of tail-gas reactive pyrolysis (TGRP) (Mullen and Boateng 2013) provide higher quality bio-oils that are thermally stable. We used fractional distillation to isolate compounds from bio-oil produced by TGRP. All bio-oils produced from TGRP contained significantly less acid (0.2 – 4% total), trace amounts of aldehydes, and significantly higher concentrations of hydrocarbons and phenolics (5 – 20% each). One TGRP bio-oil rich in naphthalenes yielded the greatest mass of distillates (close to 65%). Using atmospheric distillation alone, we recovered the most distillates from another phenol-rich TGRP oil. Compared to traditional bio-oils, distillation of TGRP oils yielded three times more organic compounds; the yield improvement increases to a factor of ten when the contribution of acetic acid is removed from consideration. Greater deficiencies in distillation yield occur with higher acids content (4 wt% acid). We categorized distillates according to boiling temperature and chemical components: benzene-toluene-xylenes (BTX), styrene, indene, pyridine, phenols, naphthalenes, acetic acid, and fluorene/anthracene. The relatively narrow product distributions allowed for the isolation of pure naphthalene by recrystallization from a naphthalene-rich fraction. Thermodynamic computation of the TGRP distillation profiles correctly predicted the experimental results, except when acid content equaled 4 wt%. The quality of the TGRP pyrolysis oils allows for insertion into existing refineries, as well as the required modeling and scale-up.