Modeling and analysis of the enzymatic hydrolysis of lignocellulosic substrates

Abstract

Simultaneous saccharification and fermentation (SSF) and simultaneous saccharification and cofermentation (SSCF) are two process options for production of ethanol from lignocellulosic substrates that are superior to separate hydrolysis and fermentation (SHF). The principal benefits of performing the enzymatic hydrolysis together with the fermentation, instead of in a separate step after the hydrolysis as SHF does, are the reduced end-product inhibition of the enzymatic hydrolysis, and the reduced investment costs. The principal drawbacks, on the other hand, are the need to find favorable conditions (e.g. temperature and pH) for both the enzymatic hydrolysis and the fermentation and the difficulty to recycle the fermenting organism and the enzymes. In order to enhance the efficiency of the lignocellulose-to-ethanol conversion, optimization of the hydrolysis (also called saccharification) process step to achieve an optimal conversion of crystalline domains of cellulose is crucial. Towards this end, a few existing models with respect to the kinetics of enzymatic hydrolysis are analyzed and compared for biochemical conversion of lignocellulosic substrates. The work is focused on selecting, enhancing and redeveloping an appropriate model for enzymatic hydrolysis. Therefore, a few models are simulated and fitted to a set of experimental data, which are taken from literature, in order to compare the accuracy and the applicability of the models. Based on this, a new kinetic model for enzymatic hydrolysis of lignocellulosic substrates is also proposed and analyzed.