New Rapid Method for the Determination of Total Acid Number (Tan) of Bio-Oils

Fast pyrolysis oils are one source of renewable liquid fuels, which could be used as green fuels in a sustainable manner. The ASTM D664 method used to determine the acidic constituents in petroleum products, lubricants, and biodiesel requires mixtures of isopropyl alcohol (IPA) and toluene as solvent. The ASTM method also uses large quantities of solvents for the total acid number (TAN) determination. The ASTM D664 method has been adopted for the determination of TAN for bio-oils data published in literature. However, the properties of bio-oils are different from those of petroleum products and biodiesel, because biooils are soluble in polar solvents and partially soluble in water whereas petroleum products and biodiesel are insoluble in water and are more non-polar. An alternative method which is more suitable for TAN determination of bio-oil has been developed and validated. Aqueous potassium hydroxide (0.1 M KOH) was used as standard titrant instead of 0.1M KOH in alcoholic solution, and acetone was used as titration solvent instead of mixtures of toluene and IPA as specified in the ASTM method. Four bio-oil samples were analyzed for their TAN using the new method and the ASTM method for comparison. The results showed that TAN of bio-oil samples determined by the new method were in good agreement with those determined by the ASTM method. It was confirmed that the new method was simpler and relatively cheaper and more suitable for TAN determination of the pyrolysis oils than the ASTM D664 method.