Total Acid Value Titration of Hydrotreated Biomass Fast Pyrolysis Oil: Determination of Carboxylic Acids and Phenolics with Multiple End-Point Detection

摘要

Total acid value titration has long been used to estimate the corrosive potential of petroleum crude oil and fuel oil products. A natural application of this method is the titration of pyrolysis-derived bio-oil, which is a candidate for refinery upgrading to produce drop-in renewable fuels, but which can have high oxygen content and high acidity.1 Determining the total acid value of hydrotreated (low oxygen content) pyrolysis-derived bio-oil has proven challenging and not necessarily amenable to the methodology employed for petroleum products due to the different nature of acids present. We previously presented an acid value titration for bio-oil products that utilizes potentiometry with an alkylammonium hydroxide titrant and an alkylammonium bromide reference electrolyte.2 This titration detected weak acid end points in bio-oil samples that were not detected by ASTM method D664. These extra end points were attributed to phenolic compounds based on the results of high-performance liquid chromatography and gas chromatograph/mass spectroscope studies. To demonstrate the accuracy of this titration, we conducted analyses with model compounds that have shown that this titration can be used to differentiate and quantify weak acid species in bio-oil. Titrimetric measurement of phenolics in bio-oil was found to be subject to a relatively high limit of detection, which may limit the utility of titrimetric methodology for characterizing the acidity of pyrolysis oil and its products.