Characterization of fast-pyrolysis bio-oil distillation residues and their potential applications

Authors: Elkasabi, Yaseen; Mullen, Charles; Jackson, Michael - Mike; Boateng, Akwasi

Submitted to: Journal of Analytical and Applied Pyrolysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/27/2015
Publication Date: 6/1/2015
Publication URL: http://handle.nal.usda.gov/10113/61111
Citation: Elkasabi, Y.M., Mullen, C.A., Jackson, M.A., Boateng, A.A. 2015. Characterization of fast-pyrolysis bio-oil distillation residues and their potential applications. Journal of Analytical and Applied Pyrolysis. 114:179-186.

Interpretive Summary: Bio-oil is the liquid crude product which comes from pyrolysis, the high-temperature breakdown of agricultural byproducts in the absence of oxygen. As a fuel intermediate, bio-oil is extremely unstable. However, bio-oil from a modified pyrolysis process (tail-gas reactive pyrolysis, or TGRP) holds promise for processing bio-oil into finished fuels, in a similar manner to traditional fossil-derived petroleum. While past studies have investigated the feasibility of removing light compounds via distillation, the heavy residue that is left over (termed “bottoms”) must be converted into an end product in order for the whole process to be economical. This study investigated the physical and chemical properties associated with bio-oil bottoms, in relation to the desired end products. It was found that all bottoms samples could serve as a source of solid fuel much like coal. TGRP-based bottoms lacked the chemical structures necessary for most chemical reactions to take place, which hinders their use in materials applications. However, a repeated higher-temperature pyrolysis of the TGRP bottoms indicates that the bottoms can potentially break down further and release more fuel-grade chemicals.

Technical Abstract: A typical petroleum refinery makes use of the vacuum gas oil by cracking the large molecular weight compounds into light fuel hydrocarbons. For various types of fast pyrolysis bio-oil, successful analogous methods for processing heavy fractions could expedite integration into a petroleum refinery for fuel production. This paper investigated the applicability of bio-oil distillation residues (i.e. ‘bottoms’) towards end-use and/or post-processing through the use of various physical and chemical characterization methods including FTIR, NMR and their decomposition in a micropyrolyzer (py-GC/MS). We compared distillate bottoms from both the recently developed tail-gas reactive pyrolysis (TGRP) and traditional pyrolysis bio-oils, emanating from switchgrass and horse manure feedstocks. Based on the FTIR and NMR measurements, we found the traditional bio-oil bottoms to contain more reactive functional groups, whereas TGRP bottoms are highly aromatic and exhibit a lack of functional groups. Manure-based bottoms consistently contained more aliphatic carbons than those of switchgrass origin. However, irrespective of the origin of the feedstock, all bottoms samples possessed high HHVs making them suitable for solid fuel application such as direct combustion (30 MJ/kg for traditional bio-oil bottoms; 37 MJ/kg for TGRP bottoms). A preliminary evaluation using py-GC/MS to test their suitability for use in refinery cracking processes revealed that the TGRP-based bottoms all produced significant yields of pyrolyzate (20 – 50%), with nearly all comprising of alkyl benzenes and alkyl phenols. However, the manure-based TGRP bottoms produced a higher proportion of C8 – C18 paraffin compounds.