(424g) Alcohol Stabilization of Bio-Oils during High Temperature Treatment
Bio-oil produced by fast pyrolysis of biomass requires significant modification to become an acceptable transportation fuel. The presence of large amounts of oxygenated compounds, such as water, carboxylic acid, aldehyde and phenol, is the primary reason for the differences in physical and chemical properties between fossil fuels and bio-oils, which renders bio-oil incompatible with existing fossil fuel refinery processes. Two effective routes in upgrading bio-oils through chemical pathways (deoxygenation) are hydrotreating (~250-450 ºC) and catalytic cracking (~450 ºC). The processing of bio-oils in existing hydrotreatment and fluid catalytic cracking (FCC) facilities is appealing; however, the high acid content of crude bio-oil may lead to infrastructure corrosion. Additionally, severe aging reactions occur when bio-oil is heated to above 200 ºC. The low hydrocarbon yield, formation of undesirable products (e.g., coke, tar, char), catalyst deactivation, and reactor plugging are significant barriers to bio-oil commercialization. To address these issues, conversion of the carboxylic acids and reactive carbonyl compounds into esters, ethers and acetals via the addition of low-cost alcohols is promising as a method to pretreat bio-oil before hydrotreating and catalytic cracking. In this study, methanol, ethanol, 1-propanol, 2-propanol and 1-octanol were added to a crude bio-oil and the mixture were stored at 200 ºC for different periods (6-50 h) to investigate changes in bio-oil’s physicochemical properties. Treated bio-oils were characterized to by Karl Fisher titration, viscometer, FTIR, GPC, TGA, DSC and GC/MS. Alcohol additives instantly reduced the viscosity of bio-oil and significantly decreased the rate of aging. Methanol showed a unique stabilization effect—a ~10 wt% increase in high molecular mass lignin content was observed for methanol/bio-oil mixtures whereas only slight increases were observed for other alcohol treatments. A rapid decrease in FTIR peak intensity for unconjugated carbonyls for the methanol/bio-oil mixture indicated methanol was more reactive than other alcohols. The C/O ratio was significantly improved by 1-octanol addition, but it resulted in the lowest stabilization. Chemical reactions between bio-oil and the additive alcohols, as well as additional hydrogen-bonding, appears to inhibit or mitigate the aging reactions.