Upgrading of Bio-oil by Catalytic Esterification and Determination of Acid Number for Evaluating Esterification Degree

Bio-oil was upgraded by catalytic esterification over the selected catalysts of 732- and NKC-9-type ion-exchange resins. The determination of the acid number by potentiometric titration was recommended by the authors to quantify the total content of organic acids in bio-oil and also to evaluate the esterification degree of bio-oil in the process of upgrading. We analyzed the measurement precision and calibrated the method of potentiometric titration. It was proven that this method is accurate for measuring the content of organic acids in bio-oil. After bio-oil was upgraded over 732 and NKC-9, acid numbers of bio-oil were lowered by 88.54 and 85.95%, respectively, which represents the conversion of organic acids to neutral esters, the heating values increased by 32.26 and 31.64%, and the moisture contents decreased by 27.74 and 30.87%, respectively. The accelerated aging test and aluminum strip corrosion test showed improvement of stability and corrosion property of bio-oil after upgrading, respectively.