HAA is formed as the most abundant linear carbonyl product from pyrolytic ring scission of holocellulose. It is the simplest aldehyde-alcohol or sugar, and can be used as an active meat-browning agent in food flavoring industry [39], or ingredient in cosmetic industry.

As been indicated above, during fast pyrolysis of biomass, the pyrolytic ring scission of holocellulose will be promoted by the small amounts of ash or alkaline cations [89], and hence, HAA can be formed with high yield in these conditions. Moreover, HAA could be further formed from the secondary cracking of the anhy — drosugar products. As a result, HAA is usually the most abundant single organic compound in crude bio-oils produced from raw biomass materials.

Similar as the LG, the difficulty for the preparation of HAA mainly lies in its recovery from pyrolysis liquids, due to its high reactivity. An efficient purification method was patented by Stradal and Underwood [90].