Study On The Pretreatments Based On Integrated Dissolving Pulp Biorefinery And Structure Of Eulaliopsis Binata

More and more attention has been put to the renewable biomass energy due to the energycrisis and environmental pollution around the world. It is an important way to improve thecompetitiveness of the pulp and paper-making industry by integrating it with biorefinery.Based on the integrated dissolving pulp biorefinery of Eulaliopsis binata, the pretreatmentsand the effects of pretreatments on the structure of Eulaliopsis binata, as well ascharacterization of pretreatment liquor were studied systematically in this thesis.The chemical components of Eulaliopsis binata were analyzed in detail, and the resultsshowed that there is less lignin and more holocellulose in Eulaliopsis binata than those ofother raw materials widely used in pulp and paper-making industry. As well, the three mainchemical constituents in Eulaliopsis binata, namely cellulose, hemicellulose, and lignin wereeffectively isolated. The Ion Chromatography （IC）, High Performance Liquid Chromatography（HPLC） and other conventional chemical analysis methods were employed to analyze thechemical components of the isolated cellulose, hemicellulose and lignin. The molecular weightof the three main constituents was determined by Gel Permeation Chromatography （GPC）. TheFourier Transform Infrared Spectroscopy （FT-IR）, X-Ray Diffraction（XRD）,¹3C-NMR,2D-HSQC NMR、Thermal Gravimetric Analysis（TGA）were employed for the detailedcharacterization for the structures and properties of the cellulose, hemicellulose and lignin ofEulaliopsis binata. The results demonstrated that the weight average degree of polymerizationand the number average degree of polymerization of cellulose from Eulaliopsis binata were2317and311, and the crystallinity of cellulose was56.7%, respectively. The main thermaldegradation temperature of cellulose of Eulaliopsis binata was in the range from300to400°C. For the hemicellulose isolated from Eulaliopsis binata, the weight average molecularweight （M_w） and number average molecular weight （M_n） were30890Da and25010Da,respectively. The main thermal degradation temperature of hemicellulose ranged from200to300°C. The main structure of hemicellulose of Eulaliopsis binata was L-arabinose-（4-O-methyl-D-glucuronic acid）-D-xylan. The Mwand M_nof the lignin of Eulaliopsis binata were8017Da and4004Da, respectively. The lignin of Eulaliopsis binata is composed of guaiacyl（G）, syringyl （S）, and p-hydroxyl phenyl （H） units and considerable proportion of cinnamicacid. The content of aliphatics hydroxyl groups was3.05mmol/g, which was the dominanthydroxyl groups in lignin of Eulaliopsis binata. The condensed phenolic hydroxyl groupscontent in lignin was relatively low at0.10mmol/g, while the content of hydroxyl groupsfrom carboxyl groups was comparatively high at0.74mmol/g. The contents of phenolic hydroxyl groups from G and H units in lignin were0.62mmol/g and0.43mmol/g,respectively. And the main thermal degradation temperature of lignin of Eulaliopsis binataranged from200to500°C.By simulating the diluted acid pretreatment process in industry, the correlationsbetween the dissolution rates of pentaose and hexose with prehydrolysis factor （P factor） andthe initial mass concentration of dilute sulfuric acid during the dilute sulfuric acid-aidedpretreatment of Eulaliopsis binata were investigated. Based on the experimental results, twoempirical models respectively describing the dissolution laws of pentaose and hexose wereestablished. During the dilute sulfuric acid-aided pretreatment of Eulaliopsis binata,dissolution laws of pentaose and hexose could be expressed asU=100(1-e^{-0.00111P（ρv+1）2})andY=0.0333（ρv+1）²lnP, respectively.Three pretreatments including dilute sulfuric acid pretreatment, auto-hydrolysispretreatment and dilute acetic acid pretreatment were conducted with Eulaliopsis binata,respectively. Effects of pretreatments on the pretreatment yield, pentosans removal ratio,-cellulose and lignin content were investigated in detail and the pretreatment conditions wereoptimized as well. Among the three pretreatments of Eulaliopsis binata based on integrateddissolving pulp biorefinery, dilute sulfuric acid pretreatment was the optimal one with theconditions listed as follows, pretreatment temperature at160°C，pretreatment time for60min，and the dilute sulfuric acid concentration at0.2%. Based on these pretreatmentconditions, the pretreatment yield was72.39%and the pentosans removal ratio reached75.83%. After pretreatment, the contents of acid-insoluble lignin, acid-soluble lignin and-cellulose were17.84%,0.66%and42.81%（based on the oven dry raw material）,respectively.The pretreatment liquors from dilute sulfuric acid pretreatment, auto-hydrolysispretreatment and dilute acetic acid pretreatment of Eulaliopsis binata were carefully analyzed.The filtration/concentration of dilute sulfuric acid pretreatment liquor was completed using ananofiltration membrane, and further analysis for the liquor after filtration was also carriedout. Among the three pretreatment liquors, dilute sulfuric acid pretreatment liquor was themost suitable for producing bioethanol because lignin and furfural contents were low, and88.79%of sugars were in the form of monosaccharide. Therefore, the process of enzymolysisof oligomer sugars could be avoided when the dilute sulfuric acid pretreatment liquor is usedfor producing bioethanol, As such, the cost of bioethanol production could be dramaticallyreduced. The dilute sulfuric acid pretreatment liquor could be concentrated with a100Da membrane filtration and the substances with small molecular weight such as furfural, aceticacid and so on could be removed after filtration. The permeate stream could be recycled intothe pretreatment process with adding some fresh water and a little amount of acid. Here, a“zero release” for the dilute sulfuric acid pretreatment liquor could be achieved.The structures and properties of cellulose, hemicellulose and lignin in the dilute sulfuricacid pretreated, auto-hydrolysis pretreated, dilute acetic acid pretreated and untreatedEulaliopsis binata were also studied. The results showed that the degree of polymerization ofcellulose decreased while the crystallinity of cellulose increased as a result of the pretreatment.For the dilute sulfuric acid pretreatment, the auto-hydrolysis pretreatment and the dilute aceticacid pretreatment, the degree of polymerization of cellulose was decreased from2317to1849,1624,1985, respectively; the crystallinity was increased from56.7%to65.9%,58.8%and61.5%, respectively. The molecular weights of hemicelluloses of Eulaliopsis binata weredecreased while the polydispersity indexes were increased due to the pretreatment. For thedilute sulfuric acid pretreatment, the auto-hydrolysis pretreatment and the dilute acetic acidpretreatment, the molecular weight of hemicellulose of Eulaliopsis binata was decreased from30890Da to7818Da,16729Da and9924Da, respectively. The content of arabinose branchin L-arabinose-（4-O-methyl-D-glucuronic acid）-D-xylan decreased significantly, the4-O-methyl-D-glucuronic acid linkage disappeared and the xylan remained after pretreatment.The aliphatic hydroxyl groups of lignin of Eulaliopsis binata decreased while the condensedphenolic hydroxyl groups increased due to the pretreatment. For the dilute sulfuric acidpretreatment, the auto-hydrolysis pretreatment and the dilute acetic acid pretreatment, theβ-O-4linkage dropped by30%,19%and38%, respectively, and the syringyl units contentdecreased as well. With the dilute sulfuric acid pretreatment, the auto-hydrolysis pretreatmentand the dilute acetic acid pretreatment, the molecular weight of lignin changed from8017Dato7053Da,623Da and5129Da, respectively.The pretreated and untreated Eulaliopsis binata were subjected to soda pulping, and theeffects of different pulping technics on the pulp properties of pretreated Eulaliopsis binatawere studied. Moreover, the Total Chloride Free （TCF） bleaching was applied in order tominimize the pollution during the bleaching process, and further to improve the quality of thedissolving pulp from Eulaliopsis binata. The results showed that the pretreatment processcontributed much to ease the cooking conditions for Eulaliopsis binata. The optimumconditions were concluded as, liquor ratio at1:5，dosage of NaOH at14.00%，dosage of greenoxygen chemical at0.05%，maximum cooking temperature at135°C，heating-up time60min and soaking time45min. The whiteness reached as high as88.7%ISO，-cellulose contentwas97.52%after TCF bleaching. Compared to the standard of viscose fiber from wood pulp,the Eulaliopsis binata pulp obtained after pretreatment met the quality standards of dissolvingpulp.