Pretreatment ammonia fiber explosion

Ammonia fiber explosion (AFEX) is another physicochemical pretreatment in which lignocellulosic materials are exposed to liquid ammonia at high temperature and pressure for a period of time, and then the pressure is swiftly reduced. A typical dosage is 1-2 kg ammonia/kg dry biomass at 90 °C and residence time of 30 min. To reduce the cost and protect the environment, ammonia must be recycled after the pretreatment. 

AFEX [Ammonia Fiber Explosion (or Expansion)] A pretreatment process for ligno-cellulose prior to enzymatic conversion to ethanol. The wood is exposed to liquid ammonia at 60 to 100°C for a short time, and the pressure suddenly released. Invented in 1998 by B.E. Dale and M. Moniruzzaman at Texas A M University and further developed by Dale at Michigan State University. In 2006, AFEX was regarded as the leading nonenzymatic biomass pretreatment process. 

Com stover used for this study was harvested in 2003 at the Kramer Farm in Wray, Colorado. The stover was pretreated either in-house at the National Renewable Energy Laboratory or received via subcontract fiom the CAFI [12] pretreatment group members. The samples selected for this study were pietreated by alkaline peroxide (NREL), sulfite steam explosion (UBC), ammonia fiber explosion (MSU), and dilute sulfuric acid (NREL) methods. The composition of the pretreated stover was determined by a two-stage sulfuric acid hydrolysis treatment according to the NREL Laboratory Analytical Procedure titled Determination of Stmctural Carbohydrates and Lignin in Biomass [13]. The pretreatment conditions and compositional information for each substrate are listed in Table 2. 

The pretreatment of any lignocellulosic biomass is cmcial before enzymatic hydrolysis. The objective of pretreatment is to decrease the crystallinity of cellulose which enhances the hydrolysis of cellulose by cellulases (17). Various pretreatment options are available to fractionate, solubilize, hydrolyze and separate cellulose, hemicellulose and lignin components (1,18-20). These include concentrated acid (27), dilute acid (22), SOj (25), alkali (24, 25), hydrogen peroxide (26), wet-oxidation (27), steam explosion (autohydrolysis) (28), ammonia fiber explosion (AFEX) (29), CO2 explosion (30), liquid hot water (31) and organic solvent treatments (52). In each option, the biomass is reduced in size and its physical structure is opened. Some methods of pretreatment of Lignocellulose is given in Table I. 

In order to implement the process steps into the Aspen Plus simulator, the stoichiometric reactor unit was used when the process involved a reaction system, and the flash unit was used for the LIME and ammonia fiber explosion (AFEX) pretreatments (in which there are no reactions). The operation conditions specified in these units, for each process, are shown in Table 2.6. 

Alizadeh, H., Teymouri, F., Gilbert, T.I., Dale, B.E., 2005. Pretreatment of switchgrass by ammonia fiber explosion (AFEX). Applied Biochemistry and Biotechnology — Part A Enzyme Engineering and Biotechnology 124 (1—3), 1133—1141. 

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