3.2. Quantification of the model compounds in bio-oil
To demonstrate the validity of our non-aqueous titration technique,
the titration of acetic acid and phenol, two main kinds of
acidic compounds in the bio-oil, was conducted in the mixed
non-aqueous medium which is the same as that used in the titration
of bio-oils. Fig. 2 showed the titration curve of the mixture of
acetic acid and phenol. Two distinguishable inflection points were
identified. With adding titrant, the acids with relative big dissociation
constants were neutralized firstly, followed by the acidic
compounds with relative small dissociation constants. Theoretically,
every gram of acetic acid will produce 16.67 mmol of hydrogen
ion during titration, calculated by Eq. (1), which is in a good
agreement with experimental result, 16.44 mmol. The experimental
acid number of phenol is also quite close to the theoretical one.
The isolation effect of target compounds was remarkable with two
different voltage ranges. Our titration method is sensitive and reliable
to identify and distinguish acetic acid and phenol.