Contents lists available at ScienceDirect Separation and Purification Technology journal homepage: www.elsevier.com/locate/seppur Upgrading and isolation of low molecular weight compounds from bark and softwood bio-oils through vacuum distillation Shofiur Rahman a , Robert Helleur a , Stephanie MacQuarrie b, ⁎ , Sadegh Papari c , Kelly Hawboldt c a Department of Chemistry, Memorial University of Newfoundland, St. John’s, Newfoundland and Labrador A1B 3X7, Canada b Department of Chemistry, Cape Breton University, Nova Scotia B1P 6L2, Canada c Department of Process Engineering, Memorial University of Newfoundland, St. John’s, Newfoundland and Labrador A1B 3X7, Canada ARTICLE INFO Keywords: Bio-oil Isolation Low MW compounds Heating value Short-path vacuum distillation ABSTRACT In this paper an analysis of short-path vacuum distillation for the isolation of low molecular weight compounds (C1–C3) from softwood and bark bio-oils is reported. The short-path vacuum distillation was performed at 60–100 °C under vacuum (10 kPa) for 0.5–1 h. Although methanol and acrolein distilled completely, acetic acid and acetol failed to do so after 1 h. The acetic acid content and the total acid number of the residual oils decreased and their heating values doubled (to 19.6 kJ/g). Short-path vacuum distillation is an efficient method to both isolate low molecular weight feedstocks/fuels, and improve the quality of the residual bio-oil for blending with petroleum or biofuels. 1. Introduction Forestry residues (e.g. saw chips, bark etc.) from the harvesting of timber and production of wood products are a potential source of bioproducts, ranging from fuels to biochemicals. Bark residue, for ex- ample, comprises 12–20 wt% of an average dried log, and represents potential bioproduct feedstock. However, the residues are traditionally treated as “waste” material due to challenges and costs associated with conversion and transport [1]. Fast pyrolysis bio-oil is a liquid produced by the pyrolysis (450–500 °C) of biomass. Fast pyrolysis has many advantages, including high oil yields (up to 70 wt%) and a higher energy density than the parent biomass [2,3]. However, the direct use of crude bio-oil as a re- placement fuel is challenging due to the high water content and acidity, high viscosity, limited thermal stability, and low heating value [4–12]. Further, the acidity of the bio-oil (pH in the range of 2–4) is problematic leading to corrosion and safety issues. The primary drivers of the high acid content are low molecular weight organic acids, such as acetic and formic acid. Removal of these acids and other light organic fractions could improve the bio-oil quality while simultaneously generating a valuable feedstock for high-end chemicals used in industry. Low molecular weight (LMW) compounds such as methanol, acro- lein, glycolaldehyde, acetic acid, and acetol are platform chemicals used in the chemical industry. Bio-methanol fuel cells are promising energy conversion devices with high power density electrical energy potential [13,14]. The global acetic acid market is forecasted to be worth USD 13.65 billion by 2021 [15]. Acetol, which contains both hydroxyl and carbonyl functional groups, is used as a reagent in organic chemical reactions and is an important intermediate used to produce propylene glycol via hydrogenation [16]. Atmospheric, vacuum, fractional, and molecular distillation tech- nologies have been used for the separation of bio-oil compounds [17–21]. However, in most cases where many compounds have been reported, there has been no focus upon the low MW compounds or their quantification. The value associated with this light fraction is important from a sustainability perspective. If the by-product of improving the bio-oil quality is in itself a valuable commodity, then the overall sus- tainability and cost effectiveness of the removal process is enhanced. A phenolic concentrate with a guaiacolic fraction of 48.3 wt% was produced via a multistep extraction technique by Wang et al. [17]. Zhang et al. [18] were able to generate ∼52 wt% separable carboxylic acids, furans, phenols, anhydrosugars, and carbonyl compounds by at- mospheric distillation from co-pyrolysis. Microalgae pyrolytic bio-oil was separated by Nam et al. [19] into three fractions, using either fractional or vacuum distillation, consisting of paraffins and olefins, with the middle bio-oil fraction having a higher heating value (HHV) of 41.2 MJ/kg and < 1.25 wt% moisture. Capunitan et al. [20] fractio- nated corn stover bio-oil with 73–84% yield under atmospheric and vacuum distillation. The low density fractions obtained by Capunitan et al. contained aromatics and oxygenated compounds, whereas the heaviest fraction contained phenolics. Their focus was fractionation of the oil into multiple fractions and therefore temperatures up to 280 °C https://doi.org/10.1016/j.seppur.2017.11.033 Received 2 August 2017; Received in revised form 13 October 2017; Accepted 12 November 2017 ⁎ Corresponding author. E-mail address: stephanie_macquarrie@cbu.ca (S. MacQuarrie). Separation and Purification Technology 194 (2018) 123–129 Available online 14 November 2017 1383-5866/ © 2017 Elsevier B.V. All rights reserved. T