Conversion of Sugars Into Monomers for Bio-based Polymers Via Lewis Acid Molecular Sieves

Chemocatalytic routes for the conversion of sugars into monomers that can be used to create known and new polymers have significant potential to enable large-scale production of bio-based polymers. Starting from glucose, reaction pathways that lead to the synthesis of terephthalic acid (PTA) and racemic lactic acid (LA), that can be used to prepare bio-based polyethylene terephthalate (PET) and polylactic acid and/or polyacrylates (dehydration of lactic acid to acrylic acid), respectively, will be discussed. For each of the reaction pathways, molecular sieve catalysts that have isolated Lewis acid sites (via insertion of elements such as Sn, Ti, Zr, into the silica frameworks) have been synthesized and shown to accomplish reactions heretofore unexplored with these types of solid catalysts. For example, a large pore molecular sieve that contains Sn (Sn-Beta) is able to isomerize glucose to fructose in aqueous media with high activity and selectivity. With isotopically labeled glucose, it is demonstrated that the isomerization reaction catalyzed by Sn-Beta proceeds by way of an intramolecular hydride shift, confirming that framework tin centers in Sn-Beta act as Lewis acids. The same large pore molecular sieve containing Zr (Zr-Beta) can selectively catalyze Diels-Alder-dehydration reactions with ethylene and oxidized variants of 5-hydroxymethylfurfural (HMF: prepared from glucose) to give new routes to PTA. Additionally, some of the reaction pathways employ conversions that involve combining the Lewis acid molecular sieves with other catalysts in one-pot systems, e.g., glucose to HMF and fructose to lactates. These examples illustrate the potential of exploiting new chemocatalytic pathways to produce valued chemicals from biomass.

Speaker: Mark Davis, California Institute of Technology