| Popis: |
Homogenous catalysts are generally more active than their heterogeneous counterparts because the solubility in the reaction medium contributes to access of reactants to all active sites. However, heterogeneous catalysts are commonly preferred because catalysts can be easily recovered from the medium and be reused. Poly(styrenesulfonic acid) (PSSA) combines the advantages of both homogeneous and heterogeneous catalysis. PSSA is soluble in polar solvents, therefore all sulfonic acid sites are readily accessible. In addition, the catalyst cannot be deactivated through coking because there is no surface for the carbonaceous species to be deposited. At the same time, PSSA, due to its high molecular weight, can be easily recovered by ultrafiltration and be reused. PSSA has shown to be effective in reactions that require Brønsted acid sites, e.g., production of biodiesel from vegetable oil, dehydration of xylose to furfural, and oxidation of furfural to maleic and succinic acids.The first part of this thesis focuses on the use of PSSA in the dehydration of fructose to hydroxymethylfurfural (HMF) in a biphasic medium consisting of water and 2-sec-butylphenol. HMF can be effectively obtained from fructose, but its production from glucose is more convenient due to the higher availability and lower cost of this substrate. The synthesis of HMF from glucose proceeds through a tandem reaction consisting of an isomerization step followed by dehydration. The second part of this thesis focuses on the synthesis of a soluble polymer catalyst containing both Lewis acid sites (for isomerization) and Brønsted acid sites (for dehydration). This catalyst was obtained by the incorporation of AlCl3 into PSSA by ion exchange in liquid medium. |
