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Extraction and recovery of precursor chemicals from sugarcane bagasse, bamboo and triticale bran using conventional, advanced and fractionation pretreatment technologies

Diedericks, Danie (2013-03)

Thesis (PhD)--Stellenbosch University, 2013.


ENGLISH ABSTRACT: Conventional, advanced and fractionation pretreatment technologies were employed to recover and/or enhance the efficacy of the main constituents present in lignocellulosic biomass. Bamboo and triticale bran are novel feedstocks and hence their response towards treatment is unknown. Thus, to assist with the characterisation of these feedstock, in terms of the amount of sugar released during acid and enzymatic hydrolysis, use were made of conventional pretreatment technologies. Pretreatment involved the use of either the conventional single-stage dilute-acid or the conventional acid-catalysed steam-explosion process at times, temperatures and acid concentration ranging between 5 to 40 min, 120 to 214°C, and 0.002 to 0.055 (H3O+) gmol/L, respectively. For additional comparison, results were also obtained from an established feedstock namely sugarcane bagasse, by subjecting it to the single-stage dilute-acid process, at similar pretreatment conditions employed during the treatment of the other feedstocks. Sugarcane bagasse and bamboo, upon pretreatment and enzymatic hydrolysis, both yielded a similar combined sugar recovery yield of 78.0% and 81.2%, respectively. Alternatively, only 55.3% (w/w) of the total sugar content in triticale bran could be recovered. Triticale bran consists predominantly of hemicellulose which, compared to cellulose, the main constituent in sugarcane bagasse and bamboo, is more susceptible to degradation. Thus, to enhance the combined sugar recovery yield, it is recommended that triticale bran be treated at less severe pretreatment conditions, in order to preserve the hemicellulose. To further enhance the amount of sugar (i.e. cellulose and hemicellulose) that can be recovered from sugarcane bagasse, the use of a two- rather than one-stage dilute acid process was proposed. The single-stage dilute acid process, despite being the subject of many research efforts, failed to recover more than 83% (w/w) of the total sugar content in sugarcane bagasse. Following an extensive literature study, it was concluded that sugarcane bagasse comprises a hemicellulose and cellulose fraction which dictates the use of different pretreatment conditions in order to ensure their effective recovery. The use of a more advance two-step dilute acid process was therefore proposed as it allows for multiple-sets of pretreatment conditions which accommodate the requirements set forth by each of the polysaccharides present in sugarcane bagasse. With the assistance of response surface methodology, a 4.8% (w/w) improvement over the single-stage method was calculated for the two-stage process, by assuming both pretreatment technologies operated at optimum pretreatment conditions. This improvement, which is similar to the 7.7% (w/w) obtained with substrates other than sugarcane bagasse, was accredited to the use of multiple-sets of pretreatment conditions. Both low and high severity pretreatment conditions were applied to maximise the recovery of hemicellulose and cellulose, respectively. In the case of bamboo however, little can be gained by using the two- in lieu of the one-stage method, as similar pretreatment conditions are required to maximise both hemicellulose and cellulose recovery. Alternatively, a three- rather than a two-stage process needs to be applied, when treating triticale bran, to accommodate for an additional set of pretreatment conditions required to recover arabinan, a third polysaccharide. In order to realise the full potential of sugarcane bagasse, use was made of a fractionation method, which in addition to the recovery of polysaccharide (i.e. cellulose and hemicellulose), also allowed for the recovery of the polyphenolic content (i.e. lignin) thereof. Limited by the complexity of the fractionation process, sugarcane bagasse was selected as the preferred substrate to be subjected to fractionation, mainly because of its availability in the South African (established sugar milling industry), and ease of treatment using both conventional (e.g. single-stage) and advanced (e.g. two-stage) pretreatment technologies. A novel fractionation technology, involving the use of the ionic liquid 1-butyl-3- mehylimidazolium methyl sulphate ([BMiM]MeSO4), was devised to separate the main constituents of sugarcane bagasse. Although other ionic liquid fractionation examples also exist in literature, processes used caused production of multi-component product streams with 34% (w/w) of the original lignin and hemicellulose being recovered in the same product stream. Tests conducted during the present study confirmed these results and further indicated that the production of multi-constituent product streams could not be avoided by using acetone, an acetone-water mixture or a sodium hydroxide solution as the solvent in a subsequent solvent extraction step. Hence, to avoid the production of multi-component product streams, a hemicellulose pre-extraction step, comprising the single-stage dilute acid process, was introduced to extract and recover 75% (w/w) of the hemicellulose content. The remaining solid was subjected to ionic liquid treatment whereafter it was effectively separated into cellulose and lignin enriched product streams through solvent extraction. Up to 73% (w/w) of the original lignin and cellulose content was recovered using optimum operating conditions (120 min; 125°C). Comparison of the novel ionic liquid ([BMiM]MeSO4) with 1-ethyl-3-methylimidazolium acetate, an established ionic liquid, identified the former to be the superior delignification solvent whereas the latter contributed more towards the digestibility of the residual solids. In conclusion, methods for the effective recovery of polysaccharides and polyphenol units from established (i.e. sugarcane bagasse) and novel (i.e. bamboo, triticale bran) lignocellulosic feedstocks have been demonstrated through the application of conventional (single-stage), advanced (two-stage) and fractionation pretreatment technologies. Economic improvement is promised through the application of these constituents as they may serve as precursor chemicals for the production of value-added products that may replace the fuel and chemicals currently derived from fossil carbon resources.

AFRIKAANSE OPSOMMING: Konvensionele, gevorderde en fraksionering voorafbehandeling tegnologieë is gebruik om die herwinning en gebruiksaamheid van die hoofbestanddele wat in lignosellulose biomassa aanwesig is, te verbeter. Bamboes en tritikale semels is nuwe rou materiale en dus is hul reaksie op behandeling onbekend. Ten einde die karaktereienskappe van hierdie rou materiale, in terme van die hoeveelheid suiker wat gedurende die suur- en suiker ensimatiese-hidrolise vrygestel word, te bepaal, is gebruik gemaak van konvensionele voorbehandeling tegnologieë. Voorbehandeling behels die gebruik van óf die konvensionele enkelstadium vedunde-suur óf die konvensionele suur-gekataliseerde stoomontploffingsproses; by tye, temperature en suurladings wat wissel tusen 5 en 40 minute, 120 tot 214°C, en 0.002 tot 0.055 (H3O+)gmol/L, onderskeidelik. Vir verdere vergelykings is resultate vanaf ’n gevestigde rou materiaal, naamlik suikerriet reste, verkry, deur dit te onderwerp aan ’n enkelstadium verdunde suur proses met dieselfde voorbehandeling toestande wat gegeld het gedurende die behandeling van die ander roumateriale. Tydens voorbehandeling en ensimaties-hidrolise het suikerriet reste en bamboes ’n gelyke gekombineerde terugwinnings opbrengs van 78.0% en 81.2% suiker, onderskeidelik, gelewer. Daar kon egter net 55.3% (w/w) van die totale suikerinhoud van tritikale semels herwin word. Tritikale semels bestaan hoofsaaklik uit hemisellulose, wat meer vatbaar is vir degradasie ten opsigte van sellulose, die hoof bestanddeel van suikerriet reste en bamboes. Om dus die gekombineerde suikerherwinnings-opbrengs te verbeter, word daar voorgestel dat tritikale semels aan minder strawwe toestande onderwerp word, om sodoende die hemisellulose te bewaar. Om verder die hoeveelheid suiker (d.w.s glukose en xilose) wat vanuit suikerriet reste herwin kan word, te verbeter, is die gebruik van ’n twee- in plaas van ’n eenstadium verdunde suur proses, voorgestel. Die enkelstadium verdunde suur proses het, ten spyte daarvan dat dit al die onderwerp van verskillende navorsing projekte was, nie daarin geslaag om meer as 83% (w/w) van die totale suikerinhoud vanuit die suikerriet reste te herwin nie. Na ’n uitgebreide literatuurstudie is daar tot die slotsom gekom dat suikerriet reste bestaan uit ’n hemisellulose deel en ’n sellulose deel wat die gebruik van verskillende voorbehandeling toestande noodsaak, om sodoende effektiewe herwinning daarvan te verseker. Die aanwending van ’n meer gevorderde twee-stap verdunde suur proses is dus voorgestel, aangesien dit van veelvoudige-stelle voorbehandelings toestande, soos vereis deur die polisakkariedes in suikerriet reste, gebruik maak. Deur die toepassing van reaksie oppervlakte metodologie, is ’n 4.2% verbetering op die enkel-stadium metode vir die twee-stadium proses behaal deur aan te neem dat beide van hierdie prosesse, by optimum kondisies vir maksimale suiker herwinning, uitgevoer is. Hierdie verbetering is soortgelyk aan die 7.7% (w/w) verbetering wat voorheen met andersoortige substrate (uitgesonder suikerriet reste) verkry is. Sodanige verhoging word toegeskryf aan die gebruik van veelvoudige stelle van voorbehandeling toestande, wat beide meer en minder strawwe toestande insluit, om sodoende die herwinning van xilose en glukose onderskeidelik te maksimeer. In die geval van bamboes, is die twee-stadium metode nie superieur tot die een-stadium metode nie, aangesien soortgelyke voorbehandeling-toestande benodig word om beide die herwinning van xilose en glukose te maksimeer. Alternatiewelik moet ’n drie-stadium in plaas van ’n twee-stadium proses gebruik word wanneer tritikale semels behandel word aangesien ’n bykomende stel voorbehandeling toestande benodig word om arabinan, ’n derde polisakkaried, te herwin. Om sodoende die volle potensiaal van suikerriet reste te ontgin, is gebruik gemaak van ʼn fraksioneringstegnologie. Waar konvensionele voorbehandeling metodes slegs fokus op die herwinning van polisakkariedes (naamlik sellulose en hemisellulose), kan die fraksioneringsproses ook die poli-fenoliese inhoud (naamlik lignien) in lignosellulose, herwin. Weens die ingewikkeldheid van die fraksioneringsproses, is suikerriet reste gekies as die mees geskikte substraat vir fraksionering, hoofsaaklik omdat dit veral in die Suid- Afrikaanse konteks, maklik beskikbaar is en omdat dit ook maklik is om met beide die konvensionele (bv. die enkel-stadium) en die gevorderde (bv. die twee-stadium) voorbehandeling proses behandel te word. ʼn Nuut ontwikkelde fraksionering tegnologie wat gebruik maak van die ioniese vloeistof 1-butiel-3-metielimidazolium metielsulfaat ([BMiM]MeSO4) is ontwikkel, om die hoofbestanddele in suikerriet reste van mekaar te skei. Literatuur bevat verskeie voorbeelde waar ioniese vloeistowe gebruik word vir fraksionering. Die doeltreffendheid van hierdie prosesse is egter deur die produksie van multi-komponent produkstrome, waartydens tot en met ekwivalente hoeveelhede hemisellulose en lignien in dieselfde produkstrome herwin is, beperk. Hierdie resultate is tydens die studie deur middel van toetse bevestig. Sodanige toetse het ook aangedui dat die produksie van multi-komponent produkstrome nie deur die gebruikmaking van asetoon, ʼn asetoon-water mengsel of ʼn natrium hidroksied oplosmiddel, wat deel maak van ʼn opvolgende oplossing-ekstraksie-stap, vermy kon word nie. Om gevolglik die vervaardiging van multi-komponent produkstrome te vermy, is ʼn hemisellulose vooraf-ekstraksie stap, bestaande uit die enkel-stap verdunde suur proses, gebruik, om sodoende 75% (w/w) van die hemisellulose inhoud in suikerriet reste, te herwin. Die oorblywende vastestof was onderwerp aan ioniese vloeistof behandeling waarna dit effektiewelik geskei is in onderskeidelik, sellulose en lignien verrykte produkstrome, verkry deur gebruikmaking van ʼn oplossing-ekstraksie-stap. Tot en met 73% (w/w) van die oorspronklike lignien en sellulose inhoud was herwin deur gebruik te maak van optimale behandelingskondisies (120 min, 125°C). ʼn Vergelyking tussen die nuut-geïdentifiseerde ioniese vloeistof ([BMiM]MeSO4) en 1-etiel-3-metielimidazolium asetaat, ʼn gevestigde ioniese vloeistof, het aangetoon dat eersgenoemde ʼn superieure delignifikasie oplosmiddel is terwyl laasgenoemde ʼn groter bydra tot die verteerbarheid van die oorblywende reste lewer. Ten slotte het hierdie studie, metodes vir die effektiewe herwinning van polisakkariedes en poli-fenoliese eenhede, vanaf gevestigde (bv. Suikerriet reste) en nuwe (bv. bamboes en tritikale semels) lignosellulose rou materiale, gedemonstreer, deur telkens van konvensionele (enkel-stadium), gevorderde (twee-stadium) en fraksionerings voorbehandeling tegnologieë gebruik te maak. Ekonomiese verbetering kan dus verwag word indien hierdie bestanddele as voorloper chemikalieë vir die produksie van waarde toegevoegde produkte aangewend word, aangesien sodanige produkte die plek kan inneem van brandstof en chemikalieë wat tans vanuit fossielbronne vervaardig word.

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