In this study a non-aqueous potentiometric titration method has been developed to quantify the carboxylic
acids and phenolics in bio-oil. Quarternary ammonium hydroxide was used as the titrant and a mixture
of tert-butanol and acetone was used as the solvent to differentiate the acidic components with
distinct acidities. The heavy carboxylic acids, which cannot be identified with GC–MS, account for ca.
29–45% (mol basis) of all the carboxylic acids in the bio-oil from mallee wood. In addition, both the heavy
and light phenolic components could be identified with the titration method developed, while GC–MS
can only identify some light phenolic compounds (3% mol basis). The titration method was further
applied to the determination of the concentrations of acidic components in the bio-oils from mallee
wood, bark and leaves. The pyrolysis of mallee wood produced the highest yields of acidic components
while that of leaves produce the lowest. The successful development of the titration method for quanti-
fication of these heavy carboxylic acids and phenolics provides useful information for the further upgrading
of bio-oil.
2013 Elsevier Ltd. All rights reserved.
1. Introduction
Bio-oil produced from renewable biomass has many potential
applications such as the feedstock for production of value-added
chemicals and bio-fuels [1–3]. However, bio-oil has many undesirable
properties such as corrosiveness and high tendency to polymerisation,
resulting from the abundance of organics in bio-oil
including acids, aldehydes, ketones and oligomers [4–10]. Among
these organics the acidic compounds such as carboxylic acid and
phenolics deserve special attention as they are the origin of the
corrosiveness of bio-oil and catalysts for polymerisation reactions
[11–14].
Several analytical approaches have been applied to quantify
acids and phenolic groups in bio-oil. For example, GC–MS can detect
the volatile compounds