Energy Densification of Carbohydrate-Derived Chemical Platforms by Catalytic Hydrogenation and Esterification Reactions

Abstract

Biomass-derived abundant and non-food polymeric carbohydrates (e.g., cellulose) have been identified as suitable biogenic carbon to synthesize transportation fuels, organic chemicals, and polymers. Catalysis remains at the heart of biorefinery research, which ensures energy efficiency, affords high product selectivity and yield, lessens materials input, and minimizes waste generation. The acid-catalyzed hydrolysis and dehydration of heavily functionalized and oxygenated biopolymers like cellulose into 5- (hydroxymethyl)furfural (HMF) is an elegant chemocatalytic value addition pathway of biomass. Other carbohydrate-derived compounds formed under acid hydrolysis conditions include furfural (FF) and levulinic acid (LA). Isosorbide (IS) can be formed from cellulose by catalytic steps involving hydrolysis, hydrogenation, and dehydration reactions. HMF, FF, LA, and IS have been identified as renewable chemical platforms for synthesizing wide classes of compounds of commercial significance. The value addition pathways often involve removing oxygen atoms and adding more hydrogen and carbon atoms in the structure for higher energy density. Humin, a complicated furan-based polymer, is formed as a side product during the acid-catalyzed dehydration of carbohydrates. Significant research has focused on minimizing humin formation and developing value-addition pathways of this waste material. This work developed solid acid and noble metal-based catalysts supported on humin-derived activated carbon (HAC) for the synthetic value addition of FF, HMF, and LA. γ-Butyrolactone (GBL) and γ-valerolactone (GVL), with potential applications as fuel oxygenates and green solvents, have been produced by catalytic hydrogenation of their precursors (i.e., 2- furanone and angelica lactone) using the Pd/HAC catalyst. Ethyl levulinate (EL), a potential diesel additive, has been produced by the esterification of LA and ethanolysis of furfuryl alcohol, respectively, using phosphotungstic acid supported on HAC. Various mono- and diesters of IS, with potential applications as renewable surfactants and plasticizers, have been reported using the transesterification reaction in the presence of an anhydrous K2CO3 catalyst. All the catalysts and the synthesized products were characterized extensively.