Fractionation of Lignocellulosic Biomass for production of materials and chemicals

Makhetha, Mannyalleng Relebohile Alice (2016-03)

Thesis (MEng)--Stellenbosch University, 2017.

Thesis

ENGLISH ABSTRACT: The development and application of biorefineries is the promising effective use of lignocellulose in the substitution of fossil fuel-based chemicals, materials and fuels. The biorefineries are attractive as they will utilise all lignocellulose components (cellulose, hemicellulose and lignin) for production of various products. The biorefineries require efficient lignocellulose fractionation methods, which are able to overcome the recalcitrance of lignocellulose to dissolution and chemical conversion, giving high yield, purity and preferably polymeric forms of all three major fractions. The aim of the study was to compare organosolv and ionic liquid fractionation methods on sugarcane bagasse (SCB) and Eucalyptus grandis (E. grandis), in terms of extraction and separation efficiencies, as well as operational challenges. Effects of alkaline extraction of hemicellulose on efficiencies of organosolv and ionic liquid fractionation methods were also studied. The choice of feedstocks was based on the availability and industrial processing in the Southern Hemisphere. Alkaline pre- and extractions of hemicelluloses were carried out using sodium hydroxide solutions. Organosolv fractionation of both SCB and E. grandis was carried out using aqueous ethanol and conditions adapted from Huijgen et al. (2012). The ionic liquid used was 1-ethyl-3-methylimidazolium acetate, [EMIM]OAc. Central composite design of experiments was used to optimise aqueous ionic liquid fractionation, and obtained desirable conditions were used for comparison study. The mass balances and quality of fractions were used to compare organosolv and ionic liquid fractionations in terms of extraction and separation efficiencies. The results obtained showed that alkaline pre-extraction method extracted and preserved hemicellulose (xylan) in polymeric form. Alkaline pre-extraction solubilised significant amount of hemicelluloses, and that preserved reasonable amount of hemicellulose from degradation by either organosolv or ionic liquid process. When alkaline post-extraction was coupled with organosolv and ionic liquid fractionation methods, the recovered hemicelluloses had lower molecular weight, and were accompanied by very low xylan balances. The alkaline pre-extraction combinations with organosolv and ionic liquid fractionation methods outweighed alkaline post-extraction combinations. Ionic liquid fractionation yielded highly digestible solid residues (≥98 %), while organosolv yielded less digestible solid residues (≤63 %). Both organosolv and ionic liquid fractionation methods resulted in high quality lignin. Ionic liquid fractionation outweighed organosolv process in terms of hemicellulose preservation. In terms of robustness to different feedstocks, ionic liquid fractionation was more robust than organosolv process. In terms of separation efficiencies, ionic liquid fractionation produced fractions which were easily separated than organosolv process (particularly hemicellulose-lignin mixture). Although ionic liquid fractionation outweighed organosolv process, ionic liquid fractionation has the challenge/limitation of scalability due to high cost of ionic liquids. In order to address this challenge, several scale-up tests, as well as optimisation studies for recovery and recycling of ionic liquids have to be carried out. Following that, techno-economic models can be developed for ionic liquid fractionation process, and be compared to organosolv techno-economic models.

AFRIKAANSE OPSOMMING: Die ontwikkeling en ingebruikstelling van bioraffineerders is ’n belowende en effektiewe gebruik van lignosellulose as plaasvervanger vir fossiel-gebaseerde chemiese stowwe, materiaal en brandstowwe. Die bioraffineerders is aantreklik aangesien hulle alle lignosellulose komponemte (sellulose, hemisellulose en lignien) in die produksie van verskillende produkte gebruik. Die bioraffineerders vereis doeltreffende metodes vir die afbreking van die lignosellulose wat moeilik oplos en nie maklik chemies omsitbaar is nie. Die opbrengs moet hoog en suiwer wees en verkieslik in polimeer vorm. Daar is tydens die studie gepoog om die doeltreffendheid van afbrekingsmetodes op saamgepersde suikerriet (SCB) en Eucalyptus grandis (E. grandis), in ten die operasienele uitdagings en terme van ektraksie en en die doeltreffendheid van skeiding te toets. of extraction and separation efficiencies, as well as operational challenges. Effects of alkaline extraction of hemicellulose on efficiencies of organosolv and ionic liquid fractionation methods were also studied. Die keuse van voerstowwe is baseer op die beskikbaarheid en industriële prossessering in die Suidelike Halfrond. Alkaliese pre- en post-ektraksie van hemiselluloses is uitgevoer met die gebruik van natrium hidroksied oplossings. Organosolv afbreking van SCB and E. grandis is met die gebruik van wateragtige etanol en volgens die metodes van Huijgen et al. (2012) uitgevoer. Die ioniese vloeistof wat gebruik is, is 1-etiel-3-metilimidazolium asetaat, [EMIM]OAc. Die Sentraal saamgestelde ontwerp van eksperimente is gebruik om die afbreking van die ionise vloeistof te optimeer en die toestande wat verkry is, is vir die vergelyking gebruik. Die balans van die massa en die gehalte van die breuke is gebruik om organosolv en ionise vloeistof afbreking in terme van ekstraksie en die doeltreffendheid van skeiding te vergelyk. Daar is gevind dat die alkaliese voor-ekstraksie metode die hemisellulose (Xylan) en polemeer vorm bewaar, Tydens alkaliese pre-ekstraksie is groot hoeveelhede hemisellulose opgelos en dus nie tydens die organodolve of die ionise vloeistof proses degradeer nie. Toe alkalise post-ektraksie tesame met organosolv en ionise vloiestof afbrekingsmetodes gebruik is, het die hemisellulose ’n laer gewig gedra en was die oorblywende houtweefsel baie laer, die alkalise pre-ektraksie kombinasies en die ionise vloeistof afbrekings metodes is verkieslik bo die alkalisee post-ekstraksie metodes. Ioniese vloeistof afbrekingsmetodes het hoogs verteerbare oorkiet (≥98 %) tot gevolg gehad terwyl organosolv minder verteerbare oorskiet (≤63 %) tot gevolg gehad het. Albei organosolv en ionise vloeistof afbreking het gelei tot ’n hoë gehalte lignien. Hemisellulose is egter beter bewaar tydens die organosolv proses. In terme van robuustheid teenoor voerstowwe is ionise vloeistof afbreking meer robuust as die organosolv proses. Ioniese vloeistof afbreking het gelei tot dele wat makliker skeibaar is as die wat gevolg het op organosolv (veral die hemisellulose-lignien mengsel). Alhoewel die ionise vloeistof metode die organosolv proses oortref het, is die ionise vloeistowwe baie duur. As gevolg van hierdie probleem is baie toetse en studies gedoen wat betref die verhaal en hergebruik van ionise vloeistowwe. Tegno- ekenomiese modelle van die ionise vloeistof afbrekingsmetode kan ontwikkel word en met die organosolv tegno-ekonomiese modelle vergelyk word.

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