Fractionation Of Sulfite Pretreated Royal Palm Sheath For Producing Fermentable Sugar And Semichemical Pulp

Palms are widely cultivated as important agricultural crops or decoration plants intropical and subtropical areas where the moist and rainy climate faciliates their fast growthand high productivity. Due to natural defoliation and fruit harvest, hundreds of millions tonsof palm residues are generated every year, including palm frond, palm trunk, palm emptyfruit bunches. This abundant non-wood lignocellulosic biomass could be utilized to producepulps or biofuels though conversion efficiency was restrained because of its heterogeneousstructure. In this thesis, royal palm sheath （RPS） was used as raw material and a new strategyfor complete utilization of palm residue was proposed by separating fibers and parenchymacells for the respective purposes of producing semichemical pulp and fermentable sugarthrough sulfite pretreatment followed by fractionation. The cell-type-dependent enzymatichydrolysis was also validated after investigating the substrate factors of fibers fractions andparenchyma cells fractions.To develop an efficient bioconversion strategy for RPS, firstly anatomical structure andcellular morphology of RPS were analyzed and its chemical compositions as well as fibersize distribution were measured. The results showed that RPS was mainly comprised ofvascular bundles and parenchyma tissues showing significant heterogeneity. Vasular bundlecontained a large number of long and narrow fibers, while cells in parenchyma tissues had athin-wall and large-lumen structure and were distinctly shorter than fibers. The chemicalcompositions of RPS fitted the typical characteristics of non-wood feedstocks and weresimilar to those of other palm lignocellulosic biomass. The abundance of parenchyma cellsaccounted for the high fines content of32.5%which significantly reduced the average fiberlength. To improve the utilization values of RPS, it is necessary to remove parenchyma cellsand enrich cellulose via pretreatments.Through mimicking neutrual sulfite semichemical pulping process, a sulfite pretreatmentwas employed to RPS prior to fractionation. For different fractions, the mass ratios and SEMmorphologies were identified, and chemical compositions were analyzed. Meanwhile,digestibility of each fraction to cellulase hydrolysis for producing fermentable sugar （glucose）was investigated. Average fiber dimensions, dynamic retention and drainability and handsheet physical properties were measured to estimate the effects of parenchyma cells removal onpapermaking properties. Results indicated that sulfite pretreated RPS was mainly comprisedof vascular bundles fraction（R14） and parenchyma cells fraction（P200）,which accounted for61.5%and34.1%of total mass, respectively. Dimensional distinction between two fractionswas so large that sepereation could be achieved readily and completely. Vascular bundleswere subsequently defibrated to produce semichemical fibers fraction （DF-R14） by a diskrefiner. P200was richer in glucan than other fractions（about1.16times higher than that ofDF-R14） and the amounts of lignin and xylan were both less than10%. Silica bodies, mainlycomprised of SiO₂, deteched from vascular bundles during sulifte pretreatment and werecollected in P200resulting in the high ash content. P200was extremely ready to behydrolyzed by cellulase compared with other fractions.82%glucan of P200could behydrolyzed in12h with the final cellulose enzymatic digestility （CED） up to92%. ForDF-R14, CED barely reached50%. The CED of P200was still maintained around90%afterincreasing initial substrate consistency to12%. P200hydrolysate also showed wellfermentability via active dry yeast fermentation. Removing parenchyma cells, the weightaverage fiber length, retention and drainability of DF-R14were remarkably improved. Thephysical properties of DF-R14were better than those of NSSC pulps of sugarcane bagasseand chemical pulps of date rachis. Through the process of sulfite pretreatment followed byfractionation, parenchyma cellls which were extremely suitable to produce fermentablesugars and vascular bundles which could be applied to produce semichemical pulps wereseparated effectively, thus improving the utilization efficiency of RPS.To identify the effects of cell types on subsequent enzymatic hydrolysis, substratefactors such as size dimensions, surface characteristics, chemical compositions and cellulosecrystallinity were analyzed and enzymatic digestibility of fibers fractions and parenchymacells fractions was compared. Results showed that parenchyma cells fractions were smaller insize, more abundant in exposed surface microfibrils, richer in glucan, less in lignin and xylanand lower in cellulose crystallinity, all of which are positive to enhance the accessibility andsusceptibility of substrates to cellulase, compared with fibers fractions. As a result, the CEDof parenchyma cells fractions was about twice as high as fibers fractions, regardless of sulfitepretreatment conditions. Enzymatic hydrolysis of fiber fractions was inhibited by the dry induced hornification resulting in more than20%decrease in CED, while the digestibility ofparenchyma cells was barely affected.