(476b) Dehydration of Fructose to 5-Hydroxymethylfurfural Using Solid Acid Catalysts Modified with Polyvinylpyrroldine

The
use of carbohydrates, a key component of biomass, presents one route towards
the production of renewable fuel and chemicals such as 5-hydroxymethylfurfural
(HMF), levulinic acid, gamma-valerolactone, furfuryl alcohol, ethylene glycol,
and polyols. HMF, a high value added chemical derived from biomass, can be
produced from the acid-catalyzed dehydration of fructose. Research on HMF
production has primarily focused on homogenous systems using mineral acids or
ionic liquids reaching yields above 80%. However, such systems are limited by
costs associated with corrosion, separation, and/or water sensitivity. Solid
acid catalysts can provide an efficient route for the production of biomass
derived HMF. One of the most significant challenges in the fructose dehydration
chemistry is the development of solid acid catalysts that can reach yields
comparable to those of the classical homogeneous systems.

We
report a new solid acid catalyst based on using the amphiphilic polymer polyvinylpyrroldine
(PVP) as a surface modifier for the selective production of HMF. PVP was impregnated
onto commercial silica spheres modified with propylsulfonic acid groups (SS). PVP
is soluble in polar solvents and has shown to play an important role in increasing
the selectivity to HMF for fructose dehydration in biphasic liquid phase systems.
PVP was crosslinked onto the SS catalyst surface to minimize polymer leaching. The
catalyst preparation was optimized by varying the concentration and type of crosslinking
agent and both the overall PVP weight loading and PVP molar weight distribution.

Under
optimal conditions, 8 wt% of insoluble PVP was impregnated onto SS. This
catalyst, named SS/PVP, was studied in the dehydration of fructose to HMF, and it
achieved 63%selectivity to HMF, which is 30% higher than unmodified SS at
similar conversions. If homogeneous PVP is added to a reaction using SS as
catalyst, the selectivity of the reaction is still lower than that observed for
SS/PVP, indicating that the interaction between the acid sites and PVP on the
silica surface in the SS/PVP catalyst has an important role in its enhanced
performance. Replacing PVP with a different polymer, such as polyvinylalcohol, did
not result in a significant increase in the selectivity to HMF, indicating that
the functionality of PVP accounts for the increased selectivity to HMF.

Catalysts
were also prepared by impregnating PVP onto mesoporous silicas modified with
propylsulfonic acid groups. SBA-15 impregnated with PVP reaches selectivities for
HMF that are higher than 80%, which is comparable to the selectivities observed
in homogeneous systems using mineral acids or ionic liquids. This class of
materials presents a new route for the production of chemicals from
carbohydrates with high selectivities.