Comparative kinetics analysis of furfural production from xylan and xylose

Lamptey, Irene Naa Odarley (2019-04)

Thesis (MEng)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: Furfural is a valuable platform chemical with a wide range of industrial applications. The replacement of petrochemicals with alternative bio furfural will reduce the overall carbon footprint of crude oil based products. The current industrial furfural production method is a direct catalyzed conversion of lignocellulosic biomass in a continuous or batch reactor system. The mechanism of the reaction is primarily a two-step reaction process comprising xylan hydrolysis and xylose dehydration along with the simultaneous conversion of other components of the lignocellulose biomass material. Examining the kinetics of furfural production using xylan and xylose as starting material will provide insights and fundamental knowledge on the furfural production reaction with little effect of the inhibitory components present in whole lignocellulose biomass. This study focuses on the kinetics of furfural formation from xylan and xylose at temperature ranges of 140 oC-170 oC, H2SO4 concentration of 0.5wt%-2wt % and solids loading of 4-14wt %. The solids loading for xylan experiments were determined by standardizing the xylan reaction against the xylose reaction considering only the xylose composition of xylan (xylose-equivalent). The range of conditions were selected with reference to literature to obtain data that were relevant to industrial processes. Statistical analysis of the results showed that temperature and acid concentrations demonstrated significant effect on the reaction. However, it was found that the effect of solids loading on the reaction was insignificant. Based on the results, it was determined that the xylan conversion process is described by a kinetic model consisting of a two-step first order reaction, whereas the conversion process for xylose consisted of a single step first order reaction model. The main difference in the models was found to be the xylan hydrolysis step that precedes xylose dehydration in the xylan conversion reaction. This hydrolysis step was found to be fast compared to the xylose dehydration resulting in xylose accumulation within 5minutes of the reaction. The dehydration reaction (in xylan conversion process) was found to be the rate determining step of the reaction relative to the fast hydrolysis step with 98kJ/mol and 55 kJ/mol activation energies, respectively. The xylose dehydration in both xylose and xylan conversion process can be described by a first order single step reaction without any side product formation and degradation reaction. Consequently, it was determined from the models that xylose condensation degradation reactions were negligible in the range of condition investigated in this study. The activation energies of xylose dehydration step for xylan and xylose feed were 98kJ/mol and 95kJ/mol, respectively. Comparing the xylan and xylose conversion to furfural processes, it was determined that the xylan conversion process was generally faster despite the two steps process. Finally, higher furfural yields were observed for xylan compared to xylose at all conditions investigated in this study.

AFRIKAANSE OPSOMMING: Furfuraal is ʼn waardevolle platform chemikalie met ʼn wye bestek van industriële toepassings. Die vervanging van petrochemikalieë met alternatiewe biofurfuraal sal die algehele koolstofspoor van produkte gebaseer op ru-olie, laat afneem. Die huidige industriële furfuraalproduksiemetode is ʼn direkte gekataliseerde omsetting van lignosellulosiese biomassa in ʼn kontinue of lotreaktor stelsel. Die meganisme van die reaksie is primêr ʼn twee-stap reaksie proses wat bestaan uit xilaan hidrolise en xilose dehidrasie saam met die gelyktydige omsetting van ander komponente van die lignosellulose biomassa materiaal. Deur die kinetika van furfuraalproduksie te ondersoek deur xilaan en xilose te gebruik as begin materiaal, sal insig en fundamentele kennis verskaf oor furfuraalproduksie met min effekte van die inhiberende komponente teenwoordig in heel lignosellulose biomassa. Hierdie studie fokus op die kinetika van furfuraal formasie van xilaan en xilose by ʼn temperatuurbestek van 140–170 °C, H2SO4-konsentrasie van 0.5–2 wt.% en vastestoflading van 4–14 wt.%. Die vastestoflading vir xilaan eksperimente is vasgestel deur die standaardisering van xilaan reaksie teen xilose reaksie met in agneming van die xilose komposisie van xilaan (xilose-ekwivalent). Die bestek van toestande is gekies met verwysing na literatuur om data te verkry wat relevant is tot industriële prosesse. Die data verkry is verder gepas tot kinetiese modelle voorheen voorgestel in literatuur om vas te stel watter model elke omsettingsproses die beste beskryf. Statistiese analise van die resultate het gewys dat temperatuur en suurkonsentrasies ’n beduidende effek op die reaksie het. Dit is egter gevind dat die effek van vastestoflading op die reaksie onbeduidend was. Gebaseer op hierdie resultate is dit vasgestel dat ʼn kinetiese model wat uit ’n twee-stap eerste orde-reaksie bestaan (xilaan hidrolise en xilose dehidrasie) die xilaan omsettingsproses kan beskryf, waar die omsettingsproses vir xilose uit ʼn enkel stap eerste orde-reaksie (xilose dehidrasie) model bestaan. Dis gevind dat die hoof verskil tussen die modelle die xilaan hidrolise stap is, wat die xilose dehidrasie stap voorgaan in die xilaan omsettingreaksie. Hierdie hidrolise-stap is bevind om vinniger te wees in vergelyking met die xilose dehidrasie wat xilose akkumulasie binne vyf minute van die reaksie tot gevolg het. Die dehidrasie reaksie (in xilaan omsettingsproses) is bevind om die tempo-bepalende stap van die reaksie te wees relatief tot die vinnige hidrolise stap met 98 kJ/mol en 55 kJ/mol aktiveringsenergieë, onderskeidelik. Die xilose dehidrasie in beide xilose en xilaan omsettingsprosesse kan beskryf word deur ʼn eerste orde enkel stap reaksie sonder enige newe- en afbrekingproduk formasie. Gevolglik is dit vasgestel uit die modelle dat xilose kondensasie afbrekingsreaksies weglaatbaar in die bestek van toestande ondersoek in hierdie studie is. Die aktiveringsenergieë van die xilose dehidrasie stap vir xilaan en xilose voer was 98 kJ/mol en 95 kJ/mol, onderskeidelik. Deur die xilaan en xilose omsetting met furfuraal prosesse te vergelyk, is dit vasgestel dat die xilaan omsettingsproses oor die algemeen vinniger was ten spyte van die twee-stap proses. Ten slotte, hoër furfuraalopbrengste is waargeneem vir xilaan in vergelyking met xilose by al die toestande in hierdie studie.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/105904
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