Valorization of low concentration sugar side-stream from dissolving pulp production

Among the platform chemicals that can be produced from lignocellulosic biomass, furfural (FUR) constitutes a promising intermediate that can be processed into a variety of advanced end products. In this thesis, the catalytic dehydration of C5-sugars was first developed and optimized using aqueous xylose solutions before the prehydrolysate of birch wood was used as a real substrate. Initially, the use of various metal oxides, such as sulphated zirconium dioxide (SZ) on cordierite and aluminium oxide on cordierite, as catalysts for the conversion of xylose to FUR was investigated and optimized, as they were considered relatively stable under hydrothermal conditions and also exhibit a relatively high proton activity. The maximum FUR yields from xylose were 41 mol% when using SZ on cordierite after 2 min at 210 °C, 43 mol% when using alumina on cordierite for 30 min at 210 °C and 48 mol% using autocatalysis for 60 min at 210 °C. After five reusability cycles with SZ on cordierite, this catalyst can be regenerated with similar performance and FUR yield in the 6th cycle. In addition to heterogeneously catalyzed xylose dehydration into FUR in a monophasic, aqueous system, FUR formation in a biphasic system under auto-catalyzed conditions was also investigated. With water-immiscible organic solvents such as isophorone, cy-clopentyl methyl ether (CPME), 2-methyltetrahydrofuran and 2-sec-butylphenol (SBP) FUR was immediately extracted from the aqueous phase to avoid degradation as far as possible. The maximum FUR yields reached from xylose were 48 mol% when using isophorone, 78 mol% when using CPME and 59% when employing SBP. The use of birch prehydrolysate as a source of C5-sugars led to a yield of 68% FUR at 190 °C when using CPME. When using SBP as organic solvent, a FUR yield of 54% was reached at 190 °C under optimized conditions. In the second phase of the dissertation, Starbon®, a carbonaceous sulfonated acid catalyst, was used in a two-phase system to produce furfural from xylose. A maximum FUR yield and selectivity of 70 mol% was achieved at complete xylose conversion under optimum experimental conditions. This work suggests that functionalized Starbon® can be used as solid acid catalyst for the conversion of C5-sugars into FUR that has significant hydrothermal stability and can be reused for several cycles. Finally, a techno-economic analysis was completed for a FUR plant with a production capacity of 5 kt/a with a minimum selling price to be 1.33 EUR/kg.