Mechanistic and kinetic aspects of furfural degradation in dilute acidic media

Steiner, Andrew Charles Dudley Pringle (2019-04)

Thesis (MEng)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: Furfural is a renewable platform chemical produced from lignocellulosic biomass. Many chemicals are derived from furfural including furfuryl alcohol, cosmetic ingredients & fragrances, flavour ingredients, nematocides & other agricultural chemicals, biofuels/fuel additives, solvents, resins, nylon, spandex (PolyTHF), etc. Furfural is mostly produced by an acid catalysed dehydration of the xylan in the biomass. The same acid catalyst also catalyses furfural degradation reactions which are known to convert furfural into formic acid and solid, insoluble, heterogeneous, carbonaceous, furan-rich macromolecules known as humins. In this study, furfural degradation was investigated, considering reaction temperatures of 140 °C - 200 °C, initial furfural concentrations of 1.5 wt% - 6 wt% and the sulfuric acid catalyst concentration of 0.5 wt% - 2 wt%. The reaction kinetics of degradation were established by fitting experimental data to the Arrhenius equation. The results showed formic acid as a significant product of furfural degradation. It was found that for each mol of degraded furfural, 0.86 mol formic acid was formed under the conditions of this study. Humins were primarily composed of bifurylic and trifurylic structures and the humins composition was independent of reaction conditions and was uniform under all reaction conditions in the present study. Combustion of humins provides a route to valorise humins but generates only 1.3% of the energy required for furfural production. In a scenario where furfural is produced from biorefinery pre-treatment stages or from pulp mill pre-hydrolysis liquor (not directly from biomass) combustion of humins is a viable application as it facilitates removal of humins which otherwise block up the system. In this study, it was found that initial furfural concentration was the most influential factor towards furfural degradation. Increasing the initial furfural concentration caused an increase in the rate of degradation, more humins were formed and more formic acid was formed. Increasing reaction temperature caused an increase in the amount of humins formed and an increase in the rate of degradation. Increasing the concentration of sulfuric acid caused an increase in the rate of degradation.

AFRIKAANSE OPSOMMING: Furforaal is ʼn hernubare platform chemikalie wat vervaardig word uit lignosellulosiese biomassa. Baie chemikalieë word geproduseer uit furforaal insluitend furfurielalkohol, skoonheidsbestanddele en geure, geurbestanddele, nematodedoder en ander landbouchemikalieë, biobrandstowwe of brandstof bymiddels, oplosmiddels, hars, nylon, spandeks (PolyTHF), etc. Furforaal word meestal vervaardig deur ʼn suur gekataliseerde dehidrasie van die xilaan in die biomassa. Dieselfde suurkatalis kataliseer ook furfuraal afbrekingsreaksies wat bekend is om furfuraal na metanoësuur en soliede, onoplosbare, heterogene, koolstofryke, furaanryke makromolekules, genaamd humien, om te sit. In hierdie studie is furforaal afbreking ondersoek met inagneming van reaksietemperature van 140–200 °C, aanvanklike furfuraalkonsentrasies van 1.5–6wt.% en die swawelsuur kataliskonsentrasie van 0.5–2 wt.%. Die reaksie kinetika van afbreking is bepaal deur eksperimentele data op die Arrhenius vergelyking te pas. Die resultate het gewys dat metanoësuur ʼn beduidende produk van furfuraal afbreking is. Dis gevind dat vir elke mol van afgebreekte furfuraal, 0.86 mol metanoësuur gevorm is onder die toestande van hierdie studie. Humien het hoofsaaklik bestaan uit bifurkaat en trifurkaat strukture en die humien samestelling was onafhanklik van reaksiekondisies en was uniform onder alle reaksiekondisies in die huidige studie. Verbranding van humien verskaf ʼn roete om humien te valoriseer, maar genereer slegs 1.3% van die energie benodig vir furfuraalproduksie. In ʼn scenario waar furfuraal vervaardig word uit bioraffinadery voorbehandelingstadia, of uit pulpmeul voorhidrolise vog (nie direk uit biomassa nie) is verbranding van humien ʼn haalbare toepassing as dit verwydering van humien fasiliteer wat andersins die sisteem sou blokkeer. In hierdie studie is gevind dat reaksietemperatuur die mees beduidende faktor tot furforaal-afbreking was. Verhoging van reaksietemperatuur het ʼn verhoging in die kwantiteit van furforaal wat afbreek, ʼn verhoging in die hoeveelheid humien gevorm en verhoging in die tempo van afbreking, tot gevolg gehad. Verhoging van die aanvanklike furforaal-konsentrasie het ʼn verhoging in die tempo van afbreking gehad, meer humien is gevorm en meer mieresuur is gevorm. Verhoging in die konsentrasie van swaelsuur het ʼn verhoging in die tempo van afbreking gehad en ʼn verhoging in die hoeveelheid furforaal wat gereageer het.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/106097
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