Diesel production via standalone and co-hydrotreating of catalytic fast pyrolysis oil

Abstract

Hydrotreating catalytic fast pyrolysis (CFP) oil is a promising technology for producing diesel fuel from lignocellulosic biomass to reduce greenhouse gas emissions. Compared to fast pyrolysis oil, CFP oils exhibit a low oxygen content and high stability and can be processed in a single hydrotreater. Two strategies were evaluated for biogenic carbon-incorporation into the diesel production: co-hydrotreating of CFP oil with straight run diesel (SRD) and standalone hydrotreating of CFP oil. Co-hydrotreating 80 vol% SRD and 20 vol% CFP oil at typical conditions of SRD hydrotreating employed at petroleum refineries (325 °C, 55 bar) over sulfided NiMo and CoMo catalysts led to products with desirable fuel properties, including indicated cetane numbers (ICNs) of 42–45. While oxygen was efficiently removed from products by co-hydrotreating over both catalysts, NiMo resulted in a higher formation of cycloalkanes and a higher ICN. Over 90% of the carbon in CFP oil was incorporated into the hydrotreated product as determined by C-14 analysis. Standalone hydrotreating of CFP oil was performed at 385 °C, 125 bar over NiMo in a single hydrotreating reactor with a two-zone configuration consisting of an initial zone from 150 °C to the hydrotreating temperature followed by an isothermal zone. Compared to previously reported isothermal hydrotreating, the new hydrotreating configuration resulted in a similar carbon efficiency but a higher fraction (95 vs. 84 wt%) boiling in the fuel range and significantly improved fuel properties (cetane number of 45 vs. 24). Both co-hydrotreating and standalone hydrotreating of CFP oil strategies showed great potential to produce sustainable diesel fuel with properties meeting standard diesel specifications in an existing petroleum refinery and a customized biorefinery, respectively.