Understanding the factors that contribute to extractive ammonia (EA) pretreatment performance

Extractive Ammonia (EA) is a pretreatment technology for lignocellulosic biomass that uses anhydrous liquid ammonia to convert native cellulose I_β to highly digestible cellulose III (allomorph of crystalline cellulose), while simultaneously extracting up to about 50 % of the lignin from lignocellulosic biomass. EA pretreatment is highly effective on grasses when using ammonia-to-biomass ratios between 3:1 and 6:1, temperatures around 120 ˚C and residence times between 30 and 60 minutes. Under such conditions, EA pretreatment can reduce the enzyme loading by half compared with optimally AFEX™ pretreated biomass and generating a separate lignin stream for valorization.

Preliminary experimental results showed that enzymatic hydrolysis yields can vary quite significantly with EA processing conditions. Therefore, it is important to understand how pretreatment conditions can impact physicochemical modifications of the plant cell wall, which in turn affect the recalcitrance of the pretreated substrate. To improve our fundamental understanding of the mechanism of EA pretreatment, we have applied statistical design of experiments to evaluate how EA conditions impact ester-bond cleavage due to ammonolysis and hydrolysis reactions. Also, we have evaluated how EA conditions impact cellulose III conversion and lignin extraction and how these key physicochemical modifications affect the enzymatic digestibility of the pretreated biomass.

AFEX is a trademark of MBI International, Lansing, Michigan.