Overview to Ammonia Pretreatments for Lignocellulosic Biorefineries

Development of environmentally sustainable and economically viable technologies for plant cell wall deconstruction to fermentable sugars has been impeded due to native plant cell wall recalcitrance to thermochemical and biological based processing. Lower severity alkaline-based pretreatment processes like Ammonia Fiber Expansion (AFEX™) can overcome several limitations of traditional pretreatment approaches (e.g., acidic pretreatments) to producing cellulosic biofuels and biochemicals. Here, we give an overview of chemical reactions taking place during alkaline pretreatments including reactions between ammonia and polysaccharides/lignin (e.g., ammonolysis, hydrolysis and Maillard-type reactions). AFEX™ based pretreatments enhance enzymatic digestibility and fermentability of lignocellulosic biomass through various chemical and ultra-structural modifications within the cell wall. An improved mechanistic understanding of the AFEX™ process has led to the development of novel alkaline pretreatments that are briefly discussed in this review.Peer reviewed