Conversion of carbonyl compounds in bio-oil during the acid/base-catalysed reactive distillation at high pressure

Abstract

The carbonyl compounds are mainly responsible for the instability and corrosiveness of a bio-oil. To upgrade or utilise a bio-oil, it is important to stabilise the carbonyl compounds. This study mainly investigates the conversion of carbonyl compounds in bio-oil via high-pressure reactive distillation in the presence of acid and base catalysts. It is found that high pressure could affect the distribution of carbonyl compounds in the bio-oil to accelerate the reaction of light carbonyl compounds and inhibit the reaction of heavy carbonyl compounds. The acid could not remove the carbonyl compounds significantly because it can not only catalyse the aldol condensation of carbonyl compounds but also help produce more carbonyl compounds by accelerating the hydrolysis of sugar compounds. The base (e.g. NaOH) could remove carbonyl compounds by acting as a catalyst to the aldol condensation reaction of aldehydes and ketones and neutralising the carboxylic acids during the high-pressure reactive distillation. Even though the based-catalysed aldol condensation could lead to the increase of the average molecular weight, the average boiling point of the distillation product is still in the acceptable range for fuels.