Biomimetic Catalysis for Hemicellulose Hydrolysis in Corn Stover

Yulin Lu, LORRE/Ag and Bio Engineering, Purdue University, 500 Central Drive, Potter Building, W. Lafayette, IN 47907 and Nathan Mosier, LORRE / Agricultural and Biological Engineering, Purdue University, 500 Central Drive, Potter Building, W. Lafayette, IN 47907.

Efficient and economical hydrolysis of plant cell wall polysaccharides into monomeric sugars is a significant technical hurdle in biomass processing for renewable fuels and chemicals. One possible approach to overcoming this hurdle is a biomimetic approach with dicarboxylic acid catalyst mimicking the catalytic core microenvironment in natural enzymes. This paper reports developments in the use of a biomimetic catalysis, maleic acid, for hemicellulose hydrolysis in corn stover. Hemicellulose hydrolysis and xylose degradation kinetics in the presence of maleic acid was compared to sulfuric acid. At the selected reaction conditions, maleic acid hydrolysis results in minimal xylose degradation, while sulfuric acid causes 3 - 10 times more xylose degradation. This underlying mechanism sets the basis for optimization of hydrolysis of hemicellulose from corn stover using maleic acid. At 40 g/L dry corn stover solid loading, both acid catalysts can achieve near-quantitative monomeric xylose yield, though xylose degradation is much higher at prolonged reaction times compared to maleic acid. At higher solids loadings (150-200 g dry stover per liter), sulfuric acid catalyzed hydrolysis results in more than 30% degradation of the xylose, even under optimized conditions. However, due to minimized xylose degradation, optimized biomimetic hydrolysis of hemicellulose by maleic acid can reach ~ 95% monomeric xylose yields with trace amounts of furfural. Fermentation of the resulting unconditioned hydrolysate by recombinant S. cerevisiae show 87% of theoretical ethanol yield. Enzyme digestibility experiments on the residual corn stover solids show that > 90% yields of glucose can be produced from the remaining cellulose with 15 FPU / g-glucan in 160 h.