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Kinetic characterization for dilute sulfuric acid hydrolysis of timber varieties and switchgrass

Yat, Shu Chiang, Berger, Alan, Shonnard, David R.
Bioresource technology 2008 v.99 no.9 pp. 3855-3863
Panicum virgatum, hemicellulose, Abies balsamea, Acer rubrum, furfural, galactose, glucose, arabinose, models, activation energy, mannose, particle size, sulfuric acid, xylose, acid hydrolysis, temperature, biomass
Hydrolysis of four timber species (aspen, balsam fir, basswood, and red maple) and switchgrass was studied using dilute sulfuric acid at 50g dry biomass/L under similar conditions previously described as acid pretreatment. The primary goal was to obtain detailed kinetic data of xylose formation and degradation from a match between a first order reaction model and the experimental data at various final reactor temperatures (160-190°C), sulfuric acid concentrations (0.25-1.0% w/v), and particle sizes (28-10/20mesh) in a glass-lined 1L well-mixed batch reactor. Reaction rates for the generation of xylose from hemicellulose and the generation of furfural from xylose were strongly dependent on both temperature and acid concentration. However, no effect was observed for the particle sizes studied. Oligomer sugars, representing incomplete products of hydrolysis, were observed early in the reaction period for all sugars (xylose, glucose, arabinose, mannose, and galactose), but were reduced to low concentrations at later times (higher hemicellulose conversions). Maximum yields for xylose ranged from 70% (balsam) to 94% (switchgrass), for glucose from 10.6% to 13.6%, and for other minor sugars from 8.6% to 58.9%. Xylose formation activation energies and the pre-exponential factors for the timber species and switchgrass were in a range of 49-180kJ/mol and from 7.5x10⁴ to 2.6x10²⁰ min⁻¹, respectively. In addition, for xylose degradation, the activation energies and the pre-exponential factors ranged from 130 to 170kJ/mol and from 6.8x10¹³ to 3.7x10¹⁷ min⁻¹, respectively. There was a near linear dependence on acid concentration observed for xylose degradation. Our results suggest that mixtures of biomass species may be processed together and still achieve high yields for all species.