(132b) Conversion of Biomass Derived Sugars to 2,5-Dihydroxymethyltetrahydrofuran
The key obstacle in the production of chemicals from biomass derived sugars is the selective removal of excess oxygen functionality. We have studied the solid-acid catalyzed dehydration of six-carbon sugars to 5-hydroxymethylfurfural (HMF) and the subsequent hydrogenation of HMF to 2,5-dihydroxymethyltetrahydrofuran (DHMTHF). DHMTHF can be used as a monomer for the production of biopolymers or can be further converted to 1,6-hexanediol, a specialty intermediate chemical.
HMF undergoes undesirable degradation reactions in the presence of an acid catalyst, which has led researchers to explore the use of biphasic systems to extract the product. To further increase the yield of furan species we have explored the conversion of HMF to the more stable molecule DHMTHF. A major challenge in this process is the hydrogenation of HMF in the presence of fructose, the latter of which can be hydrogenated to polyols, eliminating the ability to recycle unreacted fructose. To limit the hydrogenation of fructose, we have synthesized a series of hydrophobic heterogeneous catalysts composed of ruthenium on functionalized supports. Through this functionalization, we have been able to decrease the rate of fructose hydrogenation in the absence of HMF. Furthermore, kinetic studies of the hydrogenation of fructose and HMF in a biphasic system have shown that fructose hydrogenation is inhibited by HMF site blocking. This leads to slower rates of fructose hydrogenation while HMF is in the system, followed by faster rates once the HMF has been consumed.
The observation that fructose hydrogenation is inhibited by HMF site blocking has led to the design of a double reactor system for the production of DHMTHF. The first reactor would consist of a solid acid catalyst to dehydrate fructose to HMF. The effluent of this reactor would be fed to a second reactor containing a metal catalyst to hydrogenate HMF, while preserving the fructose for recycle. To test the feasibility of recycle, we have explored the effect of DHMTHF as a phase modifier in the dehydration reaction. This approach allows for the selective production of target molecules from biomass derived sugars through reactor design and novel functionalized hydrogenation catalysts.