Experimental Study On Upgrading Of Bio-oil By Catalytic Esterification

The liquid product from fast pyrolysis of biomass, called bio-oil, has aroused widespread attention as a potential substitute for fossil fuels. Nonetheless, the drawbacks including high acidity, low heating value, high corrosiveness, high viscosity and poor stability of bio-oil limit its usage as a high grade/transportation fuel. Consequently, upgrading of bio-oil before utilization is desirable to give a liquid product that can be used in a wider variety of applications. The catalytic esterification of bio-oil was investigated in order to convert the organic acids in bio-oil to their corresponding neutral esters and to reduce the content of organic acids in bio-oil. The stability, corrosion property and other qualities were also expected to be improved after bio-oil upgrading.The concept of acid number was introduced and method of potentiometric titration was proposed to quantify the content of organic acids in bio-oil. The influence of solvent, concentration of titrant and bio-oil sample size on measurement precision was studied. Experiments of adding standard sample into bio-oil were conducted to calibrate the method. It was proven that acid number determination by potentiometric titration is simple and accurate for measuring the total content of organic acids in bio-oils. This method can also be employed for evaluating esterification degree of bio-oil in the follow-up process of upgrading.The performances of 732, D072 and NKC-9 type cation exchange resins were investigated by model reaction of acetic acid and methanol. Effects of catalyst amount, acetic acid/methanol molar ratio and temperature on reaction rate and acetic acid conversion were also explored. All the three catalysts showed high catalytic activities with the sequence of 732>D072>NKC-9, and conversions of acetic acid were close to or more than 80%. After recycling, the catalysts can be repeatedly used.Methanol was added into bio-oil and esterification of bio-oil was investigated. Model mixture which comprised of several typical componenets in bio-oil was used to study the esterification activity of resin catalysts in a complex system similar to bio-oil. 732 and NKC-9 type resins were choosed as catalysts for bio-oil esterificaiton wchih was conducted in a batch reactor. After bio-oil was upgraded over 732 and NKC-9, the heating values increased by 32.26% and 31.64%, respectively; the moisture contents decreased by 27.74% and 30.87%, respectively; the densities were both lowered by 21.77% and the viscosities were lowered by 97% approximately; Acid numbers of bio-oil were significantly decreased by 88.54% and 85.95%, which represents the conversion of organic acids to neutral esters. Besides, fixed bed reactor was employed for continuous catalytic esterification of bio-oil by 732 resin and the acid number also remarkably decreased by 92.61%. The stability of upgraded bio-oil was proved to be impoved in the accelerated ageing test. Compared to the original bio-oil, upgraded bio-oil was less corrosive on aluminum in the Laboratory Immersion Corrosion Testing. It could be concluded that catalytic esterification is promising method to upgrade bio-oil.