(761f) Total Acid Number (TAN) Analysis of Bio-Oil and Tan Balance over Bio-Oil Neutralization

Authors: 
Tsouris, C., Oak Ridge National Laboratory
Yiacoumi, S., Georgia Institute of Technology
Borole, A. P., Oak Ridge National Laboratory
Bio-oil or pyrolysis oil has the potential to replace fossil fuels. However, its low pH or high acidity limits its applications. To overcome this challenging property of bio-oil, we investigated an approach to neutralize bio-oil by adding alkaline solutions or solids. To evaluate the neutralization of bio-oil, measuring the acidity of samples beyond a simple pH measurement is essential. While pH can represent the concentration of hydrogen ions, it cannot identify or quantify acidic components in samples. Thus, chemical analyses, such as high-performance liquid chromatography and gas chromatography-mass spectrometry, become necessary. Yet, there is lack of consistency among different laboratories from the round-robin testing. Moreover, chemical analysis often underestimates the amount of total acids. An analysis of the total acid number (TAN)â??the amount of potassium hydroxide needed to titrate one gram of an oil sampleâ??was initially developed for analyzing petroleum products but has also been used for analyzing the acidity of biofuels including biodiesel and bio-oil. The objectives of this study are to investigate the relationship between the total acid number and the concentrations of acidic components in bio-oil samples; to explore whether a variety of chemicals present in bio-oil have any influence on TAN analysis; and to verify whether TAN balance can be achieved over the neutralization of bio-oil, which was performed by adding different alkaline solutions and solids in batch and continuous-flow systems using a static mixer and a centrifugal contactor. The TAN values of standard solutions (e.g., acetic acid, propionic acid, phenol, vanillic acid) were analyzed according to the ASTM D664 standard method with a minor modification of the electrode cleaning procedure. Aqueous bio-oil samples with known amounts of acetic acid added were also analyzed. To examine the TAN balance, the aqueous bio-oil was neutralized by adding alkaline solutions or solids, and the TAN values of neutralized aqueous and organic phases formed were measured. The results showed that the molar concentrations of carboxylic acids (e.g., acetic acid and propionic acid) had the same linear relationship with the TAN values. However, a different linear relationship was found for a phenolic acid possibly due to the presence of functional groups that contribute to the TAN value. Also, bio-oil samples with added acetic acid showed a proportional increase in the TAN value, and demonstrated that the bio-oil components did not interfere with the TAN analysis. The results from the neutralization in batch systems were comparable with those from continuous-flow systems. The results of this study indicate that the TAN of a sample with the carboxylic acids without phenolic acid can be converted to the molar concentration of total acids. A sample with phenolic acid may not be converted to the molar concentration of total acids because the phenolic acid has a higher influence on the TAN values. The TAN balance on the neutralization of bio-oil did not close. This behavior may be due to the exothermic reaction during neutralization. Specifically, heat during the neutralization process may have accelerated the aging process of bio-oil, thus increasing the acidity and the water content of the system.