Catalytic pyrolysis for the production of refinery-ready biocrude oils from six different biomass sources

Abstract

This study focused on understanding the impact of catalytic pyrolysis and biomass feedstock on the physicochemical properties of upgraded bio-oils. Results from catalytic conversion of different types of biomass feedstocks (woody: pine, hybrid poplar and pinyon-juniper; herbaceous: switchgrass; agricultural residue: corn stover; and forest residue: pine bark) with HZSM-5 zeolite to biocrude oils are presented. The study showed that the source of biomass plays an important role in catalytic pyrolysis products. Significant differences were observed in product distribution, selectivity to aromatic hydrocarbons and physicochemical properties of the biocrude oils. The pyroprobe-GC/MS experiment showed that pine and pinyon-juniper produced the highest carbon yield of monoaromatic hydrocarbons. ¹³C NMR analysis revealed that aromatic hydrocarbon content of the oils followed this order: pinyon-juniper > corn stover > pine > poplar > switchgrass > pine bark. The chemical composition and the physicochemical properties indicated that it is critical to reduce carbonyls to achieve stable oils. Also, it was found that elimination of sugars (levoglucosan) and phenolics would improve oil specific gravity and viscosity. Furthermore, reducing the acidity of oils by catalytic pyrolysis appeared to be very challenging. Hence, phenols (weak acids) may have to be minimized in addition to other acids to increase the pH. The nitrogen contents correlated with pH values. Thus, feedstocks with high nitrogen content produced less acidic oils. Nonetheless, high content of nitrogenous compounds could make the biocrude oil highly unstable. The effects of the bio-oil chemical composition on the physicochemical properties are discussed as well as opportunities and challenges of utilizing biocrude oil as feed for standard refinery units.