Alkaline pretreatment mainly includes ammonium hydroxide, sodium hydroxide, potassium hydroxide and lime pretreatment. Among these, ammonium hydroxide is widely popular due to its ease in recovering ammonium hydroxide after the pretreatment process by evaporation method. Ammonium hydroxide can be used in its native form or diluted with solvents such as water. Ammonia fiber explosion (AFEX) is performed using ammonia in a pressurized vessel (Dale et al. US Patent 2009/0053771 A1). Aqueous ammonia can be used in different ways to achieve delignification of lignocellulosic biomass. Recycle percolation and soaking in aqueous ammonia (SAA) pretreatments are widely in use. SAA pretreatment operates at moderate temperatures ranging from 30-80°C with less formation of inhibitory compounds compared to other pretreatments (Kim and Lee 2007). In addition, SAA pretreatment preserves cellulose and hemicellulose in a solid state; the use of ammonium hydroxide potentially makes the SAA process more economical than other pretreatment methods because of its relative ease of recovery, ability to reduce enzyme loading in subsequent steps and its abundance as a commodity chemical (Mosier et al. 2005; Kim and Holtzapple 2006; Kim et al. 2006, 2008; Kim and Lee 2007). SAA pretreatment has been effective for herbaceous crops such as switchgrass. However, the recalcitrance of softwood (primarily due to the higher lignin content and crystallinity) would be ineffective using aqueous ammonium hydroxide pretreatment. Gupta (2008) mentioned in his dissertation, "In alkaline pretreatment using sodium hydroxide/potassium hydroxide, lignin degradation occurs mainly due to the breakage of aryl ether linkages which constitute approximately 50-70% of total lignin linkages. However, diaryl ethers and carbon-carbon bonds of the lignin are relatively stable, and thus present barriers to complete degradation. In addition, hydroxyl ions catalyze the cleavage of ether linkages in the lignin and can result in the formation of byproducts that can inhibit microbial fermentation such as soluble sodium phenolates."