Study Of Aqueous Ammonia Pretreatment Of Lignocellulosic Materials And Its Enzymatic Hydrolysis Performance

Study of pretreatment technology and hemicellulase in hydrolysis of lignocellulosicmaterials, can provide important basis for the efficient use of lignocelluloses for makingbioethanol and other high value chemicals.In this paper, firstly, start with cellulose and xylan as the raw materials to study the effectof carbohydrates substances dissolution in ammonia pretreatment liquid. The impact ofaqueous ammonia pretreatment on the structural properties, delignifiability, andhydrolysability of pretreated wheat straw and corn stover was also investigated. In addition,the function of xylanase in lignocelluloses hydrolysis process was monitored.After soaking in ammonia for an extent period (6-96h) at different temperature,cellulose substrates had no sugar loss in spend ammonia liquid (SAL), whereas, a portion ofxylan substrates were solublized in SAL and the oat spelt xylan had the largest xylan lossyields among three substrates. Xylan solubilization was comfirmed by ESI-MS analysis. Theexperimental results showed that solubilized xylooligosaccharides (XOS) of oat spelt xylan,beechwood xylan and wheat straw xylan were all composed by4-O-glucuronic acid groupand xylose. Ammonia pretreatment retained nearly100%of the xylan and removed4%of theglucan of wheat straw and corn stover.The results showed that the aqueous ammonia pretreatment had excellent delignificationability and that the corn stover exhibited higher susceptibility to an aqueous ammonia attackthan wheat straw. In total,40.9%and80.0%of the lignin in wheat straw and corn stover wereremoved, respectively, by the aqueous ammonia pretreatment at75℃with21%ammoniaand a solid:liquid ratio of1:10for50h. Chemical structure of substrates after aqueousammonia pretreatment were analyzed using Fourier transform infrared spectroscopy, scanningelectron microscopy, and X-ray diffraction and the results supported that ammoniapretreatment broke ester bonds between lignin and hemicelluloses, increased specific surfacearea and crystallinity index. The result of enzymatic hydrolysis was showed that, aqueousammonia pretreatment clearly increase the hydroylysis yield. In the experiment of mechanism of hemicellulase enzyme hydrolysis, the effect ofadding xylanase into lignocelluloses enzymatic hydrolysis process was also investigated. Acertain degree of synergistic effect was showed after adding xylanase in the cellulasehydrolysis of lignocellulose materials. The synergy factors for glucose release of wheat strawand corn stover were1.20and1.18, respectively, by the aqueous ammonia pretreatment at75oC with21%ammonia and a solid:liquid (S:L) ratio of1:10for50h. The synergy factors forxylose release of wheat straw and corn stover were1.99and1.80respectively, under thecondition of21%ammonia, S:L1:10, room temperature and20h. The conversion ofenzymatic hydrolysis was different with different orders of adding enzymes. The glucanconversion was improved under the pattern of delay6h adding xylanase into the cellulasehydrolysis process, while the xylan conversion reached the highest yield when added xylanaseinto cellulase hydrolysis process at the same time.