Biomass Pyrolysis Study on the Aging Mechanism of Pyrolysis Bio-oil The unstable nature of pyrolysis oil produced from biomass fast pyrolysis is one of the key issues that limit its application and upgrading , as aged bio-oil typically shows increased water content , viscosity , and phase separation. The aging phenomena are considered due to the polymerization of bio-oil components under acidic and thermal conditions catalyzed by the mineral compounds contained in char particles in the bio-oil. Current research on bio-oil aging is focused on characterizing the behavior together with seeking methods to slow down the aging speed. However , little research was reported on investigating the molecular-level polymerization mechanism of pyrolysis bio-oil during the aging. In this study , accelerated aging of the bio-oil produced from loblolly pine was performed with different aging time and temperature and with or without additives to access the bio-oil thermal stability by measuring water content , viscosity , acidity , molecular weight distribution , and chemical composition. With the chemical analysis of aged bio-oils , it was found that ether soluble fraction of the bio-oil was significantly reduced during the aging process and glycolaldehyde is the most reactive compound in that fraction. The pyrolytic lignin fraction , especially high molecular weight lignin , was found to gradually increase , which suggests the reaction between the compounds of ether soluble fraction and the lignin fraction. Because of the great reduction of glycolaldehyde concentration during the aging , synthetic bio-oil with different concentration of glycolaldehyde was mixed with pyrolytic lignin and aged at 80 °C to further study the role of glycolaldehyde on bio-oil aging chemistry. To elucidate the polymerization chemistry between ether soluble fraction and pyrolytic lignin fraction , model compounds , such as 13C labeled glycolaldehyde and 13C labeled phenolic compounds (phenol and guaiacol type) , were reacted in a similar condition to that of accelerated aging. In addition , other suggested mechanisms of bio-oil aging will be reviewed and discussed in detail.
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