Surface area of pretreated lignocellulosics as a function of the extent of enzymatic hydrolysis

Abstract

The distribution of surface area as a function of pore size in the pores of hardwood, pretreated by mild acid hydrolysis, was estimated from the pore volume distribution, as a function of the extent of enzymatic hydrolysis. Pore volume distributions were obtained using the solute exclusion technique. Throughout the reaction, the total surface area of the substrate was mostly in pores too small to be accessible to the enzyme, which has been estimated to be 51–90 A in diameter. For wood pretreated at 200°C, the surface area of pores large enough to be accessible to cellulase decreases rapidly as the enzymatic hydrolysis proceeds. The surface area in pores too small to be accessible to the enzyme decreases more slowly, presumably because the substrate containing these small pores reacts only at the external surface. In wood pretreated at 220°C, a more gradual decrease in the accessible pore surface area occurs. It is hypothesized that this occurs because of the increase of external surface as the size of the substrate particle decreases by more severe pretreatment. This external surface is thought to adsorb more of the enzyme, leaving less for the surface in the pores. For the more severely pretreated hardwood, more enzyme is adsorbed throughout the course of reaction.