The acidic groups in FPBO might be esterified with an alcohol to reduce acidity. The university of Groningen tested the esterification of FPBO with an excess of butanol in the presence of a catalysts . The reactions are shown in the figure below. A strong reduction in acidity was obtained by the researchers.
BTG explored the possibility of Fast pyrolysis oil treatment with butanol in a reactive distillation process and in the presence of a catalyst, resulting in upgraded fast pyrolysis oil with lower acidity, lower water content and higher energy content. The operating pressure was 300 mbar (typically) at a reactor temperature of 85 °C, with a solid acid catalyst (Nafion SEC13). During the process the butanol reacts with the acids in the fast pyrolysis oil to form esters and water is removed via the vapour phase. On a weight basis the pyrolysis oil:butanol ratio is around 10. A sample of fast pyrolysis oil was subject to an esterification process and tested in a diesel engine. 
- Mahfud FH, Melian-Cabrera IV, Manurung R, Heeres HJ. Biomass to fuels: upgrading flash pyrolysis oil by reactive distillation using a high boiling alcohol and acid catalysts. Process safety and environmental protection 2007;85(5):466–72
- Bioliquids-CHP - Power generation from biomass, Main project results 2011, brochure