Catalytic Upgrading of Kraft Black Liquor-Derived Ketones to Bio-lubricant Blendstocks

Abstract

Biomass is a sustainable, renewable feedstock that could be used for producing lubricant-grade hydrocarbons. Prior studies have demonstrated the condensation of simplified biomass-derived model ketones, but the condensation of structurally diverse ketone mixtures obtained from real biomass-derived feeds remains largely unexplored. This study establishes a mechanistic framework for the condensation of a structurally diverse ketone mixture derived from kraft black liquor (KBL) and applies it to the synthesis of lubricant-range hydrocarbons. Using representative terminal, internal, and branched ketones, we show that mixed Mg/Al oxide (MgxAlyOz) rapidly converts terminal methyl ketones to cyclic trimers but is largely ineffective for internal ketones, whereas niobium(V) oxide (Nb2O5) activates both ketone classes and promotes dimerization, secondary condensation, and aromatization through strong Lewis acid sites. Pyridine and ketone adsorption followed by FTIR spectroscopy, adsorption measurements, and selective poisoning experiments suggest that these Lewis acid sites as the catalytically relevant centers for carbonyl activation and deeper C–C coupling. Unexpectedly, 3-pentanone adsorbs more strongly on Nb2O5 than 2-pentanone but condenses more slowly because of its higher intrinsic barriers for C–C bond formation, demonstrating that stronger adsorption does not necessarily translate to higher reactivity. Residual carboxylic acids also strongly suppress condensation, highlighting the importance of effective and complete upstream ketonization. Guided by these insights, a real ketone stream derived from KBL hydroxy acids is condensed over Nb2O5 to generate oxygenated products spanning mainly 15 to 33 carbon atoms (C15–C33) and these products are subsequently hydrotreated over 2 wt % Pt/Nb2O5, giving an estimated overall liquid-hydrocarbon carbon yield of ∼58%. To our knowledge, this is the first demonstration of catalytic upgrading of a real KBL-derived ketone stream to potential lubricant-range hydrocarbon blendstocks, supporting further development of KBL-derived hydroxy acids as a renewable feedstock for hydrocarbon production.