Balan Venkatesh, Bals Bryan, Chundawat Shishir P S, Marshall Derek, Dale Bruce E
Department of Chemical Engineering and Materials Science, Michigan State University, Lansing, MI, USA.
Methods Mol Biol. 2009;581:61-77. doi: 10.1007/978-1-60761-214-8_5.
Although cellulose is the most abundant organic molecule, its susceptibility to hydrolysis is restricted due to the rigid lignin and hemicellulose protection surrounding the cellulose micro fibrils. Therefore, an effective pretreatment is necessary to liberate the cellulose from the lignin-hemicellulose seal and also reduce cellulosic crystallinity. Some of the available pretreatment techniques include acid hydrolysis, steam explosion, ammonia fiber expansion (AFEX), alkaline wet oxidation, and hot water pretreatment. Besides reducing lignocellulosic recalcitrance, an ideal pretreatment must also minimize formation of degradation products that inhibit subsequent hydrolysis and fermentation. AFEX is an important pretreatment technology that utilizes both physical (high temperature and pressure) and chemical (ammonia) processes to achieve effective pretreatment. Besides increasing the surface accessibility for hydrolysis, AFEX promotes cellulose decrystallization and partial hemicellulose depolymerization and reduces the lignin recalcitrance in the treated biomass. Theoretical glucose yield upon optimal enzymatic hydrolysis on AFEX-treated corn stover is approximately 98%. Furthermore, AFEX offers several unique advantages over other pretreatments, which include near complete recovery of the pretreatment chemical (ammonia), nutrient addition for microbial growth through the remaining ammonia on pretreated biomass, and not requiring a washing step during the process which facilitates high solid loading hydrolysis. This chapter provides a detailed practical procedure to perform AFEX, design the reactor, determine the mass balances, and conduct the process safely.
尽管纤维素是最丰富的有机分子，但由于纤维素微纤丝周围存在坚硬的木质素和半纤维素保护，其水解敏感性受到限制。因此，需要进行有效的预处理，以从木质素 - 半纤维素密封中释放纤维素，并降低纤维素的结晶度。一些可用的预处理技术包括酸水解、蒸汽爆破、氨纤维膨胀（AFEX）、碱性湿式氧化和热水预处理。除了降低木质纤维素的抗降解性外，理想的预处理还必须尽量减少抑制后续水解和发酵的降解产物的形成。AFEX是一种重要的预处理技术，它利用物理（高温和高压）和化学（氨）过程来实现有效的预处理。除了增加水解的表面可及性外，AFEX还能促进纤维素的去结晶化和部分半纤维素的解聚，并降低处理后生物质中木质素的抗降解性。对AFEX处理的玉米秸秆进行最佳酶水解时，理论葡萄糖产率约为98%。此外，与其他预处理相比，AFEX具有几个独特的优势，包括预处理化学品（氨）几乎完全回收、通过预处理生物质上残留的氨为微生物生长添加营养，以及在过程中不需要洗涤步骤，这有利于高固含量水解。本章提供了执行AFEX、设计反应器、确定质量平衡以及安全进行该过程的详细实际操作程序。
