A pore‐hindered diffusion and reaction model can help explain the importance of pore size distribution in enzymatic hydrolysis of biomass

Abstract

Until now, most efforts to improve monosaccharide production from biomass through pretreatment and enzymatic hydrolysis have used empirical optimization rather than employing a rational design process guided by a theory-based modeling framework. For such an approach to be successful a modeling framework that captures the key mechanisms governing the relationship between pretreatment and enzymatic hydrolysis must be developed. In this study, we propose a pore-hindered diffusion and kinetic model for enzymatic hydrolysis of biomass. When compared to data available in the literature, this model accurately predicts the well-known dependence of initial cellulose hydrolysis rates on surface area available to a cellulase-size molecule. Modeling results suggest that, for particles smaller than 5 × 10(-3) cm, a key rate-limiting step is the exposure of previously unexposed cellulose occurring after cellulose on the surface has hydrolyzed, rather than binding or diffusion. However, for larger particles, according to the model, diffusion plays a more significant role. Therefore, the proposed model can be used to design experiments that produce results that are either affected or unaffected by diffusion. Finally, by using pore size distribution data to predict the biomass fraction that is accessible to degradation, this model can be used to predict cellulose hydrolysis with time using only pore size distribution and initial composition data.

Mechanical pretreatment improving hemicelluloses removal from cellulosic fibers during cold caustic extraction

“…The presence of pores and their sizes in fiber walls are critical factors that can affect the hemicelluloses diffusion process (thus, hemicelluloses removal). Previous work showed that the fibers structure and morphology can strongly affect: (1) the removal of non-cellulosic constituents from pulp fibers, such as lignin (Kerr and Goring, 1975); (2) the accessibility of cellulose to chemicals, such as carbon disulfide Miao et al, 2015) during the cellulose xanthation process, or enzymes (Luterbacher et al, 2013) during cellulose enzymatic degradation.…”

Mechanistic kinetic models of enzymatic cellulose hydrolysis—A review

“…To minimize the computational intensity, the substrate‐centric kinetic models may collapse elementary enzyme‐substrate interaction steps into coarser steps. For example, Luterbacher et al (, ) described complexation and hydrolysis rates by a lumped rate constant while Hosseini and Shah (2011) and Huron et al () assumed that adsorption reached rapid equilibrium and that all adsorbed cellulases were active. Some models focused only on the changing substrate without explicitly modeling enzyme interaction steps, thus implicitly attributing reaction bottlenecks to substrate properties (Lebaz et al, ; Seo et al, ).…”

Insights into the effect of dilute acid, hot water or alkaline pretreatment on the cellulose accessible surface area and the overall porosity of Populus

“…36 Moreover, some volumes of nanopores between 50 and 100 nm were also observed on the distribution curves of all the pretreated samples, while no pores with a diameter lower than 100 nm were found for the untreated sample. 40 Chundawat et al reported that nanoporous tunnel-like networks as visualized by 3D-electron tomography can be formed within the cell wall after ammonia fiber expansion, and the shape, size (10 to 1000 nm), and spatial distribution of pores depended on their location within the cell wall and the pretreatment conditions. Indeed, 160°C DA pretreatment significantly increases the pore volume between 10 and 1000 nm, primarily due to its near complete removal of hemicellulose and redistribution of lignin.…”