Enzymatic Enhancement And Deconstruction Of Arundo Donax Linn. By Amberlyst 35 Catalyzed Ionic Liquid Pretreatment

The world's ever-growing energy demands and concerns over the detrimental effects of oil on environment have garnered interest in the research for alternative rich and renewable lignocellulose sources for the sustainable production of fuels and petroleum based products.In order to improve the conversion efficiency of Arundo donax Linn.(one of energy crops),the dissertation proposed novel Amberlyst 35 catalyzed ionic liquid pretreatments and the mechanisms of enzymatic enhancement including the deconstruction of plant structures and lignin of A.donax were investigated.Facile isothermal pretreatments and a new anti-solvent were established.Firstly,the major recalcitrant components,lignin and lignin chemical linked lignin carbohydrate complex preparations were subsequently isolated from A.donax,and chemically characterized by using GPC,HPAEC,FT-IR,FT-Raman,and 2D HSQC NMR spectroscopy.Results indicated that the lignin and LCC preparations have molecular weights ranging from 1940 to 5260 g/mol.Lignins in these fractions were GSH type lignins with S/G ratio of 0.55-0.88.A predominance of ?-O-4' aryl ether linkages among lignin units was demonstrated.Moreover,the carbohydrate,hydrocinnamic acids and lignin constituents in each lignin and LCC preparation were chemically bonded.The hydrocinnamic acids especially p-coumaric acid in lignin were fast identified by FT-Raman spectra at peaks of 1 173 cm-1.A clean and efficient pretreatment of solid acid Amberlyst 35 catalyzed less expensive ionic liquid(IL)1-butyl-3-methylimidazolium chloride([C4mim]C1)was developed.Results indicated that the IL-Amberlyst 35 pretreatment was effective,evidenced by the reduction in cellulose crystallinity,increasing porosity and partial removal of lignin.Consequently,a high glucose yield of 92.8%was obtained after 72 h of enzymatic hydrolysis,which was 2.17-fold higher than that of single[C4mim]C1 pretreatment and 5.21-fold higher than that of untreated biomass.In addition,the cost of the pretreatment was cut down by about 2-10 times when compared to other IL pretreatments that had similar results for cellulose digestibility.To simplify the abovementioned method,facile isothermal pretreatments using Amberlyst 35 catalyzed[C4mim]CI at mild conditions were proposed on A.donax to enhance the combined sugars(sugars in both cellulase hydrolysate and pretreatment liquor)released.It was found that the structural features and pretreatment efficiency were dependent on pretreatment conditions since the liberation of H3O into lL were temperature-and time-dependent.Under the optimal condition of IL pretreated at 110? for 3.0 h and sequently acid reacted for 1.0 h,24.2 g glucose and 5.4 g xylose in enzymatic hydrolysate and 28.8 g TRS in pretreatment liquor were produced.This process could potentially recover 85.0%of the total reducing glycan in the untreated A.donax.Relatively high combined sugars yields still can be achieved after reusing the IL and acid for twice.A new aqueous ethanol regeneration method was developed to change the structural characteristics to further improve the efficiency of IL-Amberlyst 35 pretreatment.Obvious porous and surface coverage reduction were observed as a result of the competition between ethanol and water anti-solvents.The cellulose digestibility of acid-IL pretreated A.donax was significantly enhanced to about 100%and approximately 11-fold and 2-fold higher than that of untreated and conventional water regenerated pretreated samples,respectively.More importantly,a giant leap in the initial rate of enzymatic hydrolysis was detected in 50%aqueous ethanol regenerated samples and only about 10 h was needed to convert 80%of cellulose to glucose due to the appearance of cellulose ? hydrate-like and porous structure.The mechanisms of structural features and lignin structure changes during the pretreatment were exposed.Progressive deconstruction of crop cell wall was occurred with increased catalysis time by gradual releasing of H3O+ of Ainberlyst 35.During the pretreatment,hemicelluloses were gradually removed and cellulose crystal transformation from cellulose I to II was progressively occurred.When acid reaction was 34 min,cellulose ? was totally transformed to cellulose ? and lignin re-deposited polymers began to deposite on fibres.However,vast lignin re-deposited polymers on fibres could hinder further enzymatic hydrolysis when further prolong the acid reaction time.Regarding to the lignin chemical structural changes,it was determined that the depolymerisation of(3-0-4' linkage,lignin re-condensation,and the cleavage of ferulate-lignin ether linkages were took place during the pretreatment.Apart from chemical structural changes,the tree branch like aggregates supramolecular structure of lignin were destroyed to monodisperse particles after the pretreatment.Moreover,lignin particles exhibited a more oblate ellipsoid morphology with some collapsed structures on the surface.