Understanding high-solids enzymatic liquefaction and hydrolysis kinetics of biomass via in situ MRI rheological measurements

Worldwide need for alternatives to fossil fuels has driven significant research effort toward the development and scale-up of sustainable forms of energy. Second generation biofuels, obtained from the breakdown of the lignocellulosic components of, for instance, agricultural waste, present a promising alternative for biofuel production. Enzymatic hydrolysis is currently one of the most costly steps in the biochemical breakdown of lignocellulosic biomass, and economic considerations for large-scale implementation of the process demand operation in the high solids regime. In this regime, the biomass is processed at concentrations of 15% (w/w) or higher, forming a high viscosity slurry which introduces processing challenges especially in the initial stages of hydrolysis (liquefaction). During liquefaction, dramatic changes in the rheological properties of biomass occur. We performed in situ rheological studies using magnetic resonance imaging (MRI) velocimetry on biomass undergoing hydrolysis in batch and fed-batch mode to develop a fundamental understanding of the bulk-scale physicochemical changes during high-solids biomass hydrolysis. By performing hydrolysis at high solids with a variety of cellulases and modes of enzyme addition, key aspects that affect enzyme kinetics at high solids (e.g., substrate morphological changes, end-product inhibition, synergy and anti-synergy) were studied. These fundamental rheological studies, in turn, improved our understanding of the high-solids biomass hydrolysis process for better utilization of agricultural waste.