Tailoring the Composition of Bio-oil by Vapor-Phase Removal of Organic Acids

Selective removal of organic acids from biomass pyrolysis vapors was demonstrated. A broad adsorbent range was tested with CaCO3 showing the best selectivity. Extensive material characterization demonstrated that the acid removal occurred through monolayer adsorption on CaCO3. Adsorbent regeneration was achieved by in situ heat treatment of the post-reaction adsorbent where the adsorbed acid was converted into a ketone. The mitigation of the loss of other products was achieved by using surface modified CaCO3 materials, resulting in a significant improvement in the selectivity toward organic acid removal. The surface modification appeared to lead to formation of a metal-carboxylate intermediate consisting of both acetate and carbonate groups. Acetate group on the CaCO3 surface resulted in the suppression of side reactions. Generally, a higher acid removal was accompanied with a greater loss of other compounds, which could be tuned by using CaCO3 with different surface modification.