Removal of catalyst poisons for the production of sugar alcohols from a real biomass molasses using a heterogeneous Ni catalyst

Abstract

Molasses is an abundant biomass waste that remains after the manufacture of sucrose in sugar industries. This material still contains a large amount of sucrose, which is an attractive feedstock for the production of renewable chemicals. However, such real biomass often contains impurities that work as catalyst poisons in the chemical conversion, and thus the study on the effect of catalyst poisons and their removal is crucial to establish biorefinery. Herein, we report the pretreatment and catalytic conversion of sugarcane molasses to synthesize sugar alcohols (sorbitol and mannitol) that are versatile precursors to chemicals. In the adsorption pretreatment of molasses, Montmorillonite K10 selectively reduced organosulfur and organonitrogen compounds with no adsorption of sugars. Pristine molasses gives a low yield of sugar alcohols with low selectivity in the presence of a sponge nickel catalyst, but the pretreated sample provides up to 84% yield after optimization of reaction conditions. The correlation between the content of impurities and hydrogenation activity, controlled experiments, and density functional theory calculations show that organosulfur compounds are the main catalyst poisons due to the strong adsorption on nickel by the electron donation from S 3s3p hybrid orbitals to Ni unoccupied ones predominantly consisting of 4p.