Extractive Ammonia (ea): a Novel Ammonia-based Pretreatment Technology for Lignocellulosic Biomass

Large scale production of economically viable biofuels can only be achieved from widely available resources, notably lignocellulosic biomass. This feedstock is largely composed by complex carbohydrates, which can be enzymatically hydrolyzed and converted to fuels and chemicals by fermentative organisms. Lignocellulosic biomass is recalcitrant to enzymatic degradation and therefore, a pretreatment step is required for achieving acceptable sugar yields. Recent research has improved our fundamental understanding about the physico-chemical events occurring during ammonia pretreatment of biomass that correlate with enzymatic hydrolysis yields. From this understanding, a novel Extractive Ammonia (EA) pretreatment was developed and is presented herein for the first time. This technology allows the conversion of naturally occurring cellulose I (CI) to cellulose III (CIII) and the selective extraction of lignin from the plant cell wall with liquid ammonia. These extractives are collected in a separate stream as a valuable byproduct. While CIII is known to improve enzymatic hydrolysis rates up to two fold compared to native CI, lignin is acknowledged as a major inhibitor for both enzymes and microbes. Other key events include ester-bonds cleavage via ammonolysis and hydrolysis reactions during EA. Ester bonds play an important role in cross-linking lignin and carbohydrates and therefore, their cleavage disrupts the complex cell wall architecture, allowing carbohydrates to be more easily accessible by enzymes.