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Continuous Upgrading of Fast Pyrolysis Oil by Simultaneous Esterification and Hydrogenation

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journal contribution
posted on 08.09.2016, 00:00 by Roger Hilten, Justin Weber, James R. Kastner
A mixture of fast pyrolysis oil (FPO) and methanol (1/1 v/v) was continuously converted to methyl levulinate (ML), methyl acetate (MA), and C3 or greater methyl esters using metal-acid functionalized zeolites (Ni and Ru/HZSM-5) and an iron oxide catalyst with both acid and base sites (250 °C, 600 psig). Fractional conversion of FPO components was 60% or greater using the iron oxide catalyst, and space time yields approached 150 and 30–50 g/L cat/h for MA and C3 methyl esters, respectively, at 250 °C (W/F = 0.4 h, liquid hourly space velocity = 5–11.2 h–1). Product yield and concentration using the iron oxide catalyst were comparable to those of the Ni and Ru/HZM-5 catalysts and achieved performance levels higher than those of SiO2‑Al2O3 and HZSM-5. Two potential pathways for acetic acid conversion (ketonization and esterification) and ML formation from levoglucosan were observed. Using the bifunctional catalysts in the presence of hydrogen resulted in significant coke reduction (60–80%) and the production of esters of carboxylic acids C3 or greater (e.g., pentanoic and hexanoic acid methyl esters) and MA from the mixture. More interestingly, contrary to the other catalysts, an increase in phenolic levels (e.g., 2-methoxy phenol) was observed using the iron oxide catalyst with H2 and isopropanol (replacing H2), indicating the presence of undetected lignin oligomers in the feed and their subsequent hydrogenolysis. Simultaneous esterification and hydrogenation resulted in percent reduction in total acid numbers ranging from 66 to 76%.