Abstract
Levulinic acid (LA) is considered to be one of the promising organic bio-platform chemicals and intermediates for the synthesis of fuels, chemicals, and polymers. In the present study, heterogeneous catalytic dehydration of hexose sugars, fructose and glucose, using a strong cation exchange resin (hydrogen form) as an acid catalyst, was performed to produce LA in an aqueous medium. The effect of salts such as NaCl, KCl, CaCl2, Na2CO3, and Na2SO4 in the medium on the rate of sugar conversion and LA yield was evaluated. Under optimum reaction conditions, 10% (w/w) fructose was dehydrated to LA (with 74.6% yield) in 10% (w/w) NaCl aqueous solution in 24 h at 110 °C using the catalyst at 30% (w/w sugar). Even 10% (w/w) glucose monohydrate was directly dehydrated to LA (with 70.7% yield) under similar conditions but at 145 °C. This study shows that the salts enhance the rate of catalytic dehydration in the order of Cl– > CO32– > SO42–. Thus, the combination of high sugar concentration and heterogeneous catalysis in an aqueous system under relatively mild conditions could provide a high-yielding and sustainable process for bio-based LA production.
Highlights
As the main source of functional carbon-building blocks for the fuel, chemical, and polymer industries is still based on fossil resources, one of the greatest challenges of the 21st century is to enable transition to an economy based on renewable resources
This paper reports a study performed on the effect of salts on the conversion of fructose and glucose to Levulinic acid (LA) in an aqueous medium using an ion exchange resin, Dowex DR-2030, as the catalyst
Our preliminary studies on using the catalyst in an aqueous solution for dehydration of fructose and glucose showed the formation of LA and formic acid
Summary
As the main source of functional carbon-building blocks for the fuel, chemical, and polymer industries is still based on fossil resources, one of the greatest challenges of the 21st century is to enable transition to an economy based on renewable resources. Production of LA from monosaccharides (e.g. glucose and fructose), polysaccharides, and lignocellulosic biomass has been extensively investigated using homogeneous or heterogeneous catalysts (Scheme 1). 83 and 51% yields of LA were obtained from fructose and glucose using 0.25 M HCl at 130 °C, respectively.[13] In general, lower yields of LA have been reported when using glucose as the starting material with HCl/H2SO4 as a catalyst as compared to that obtained with fructose.[13] production of LA directly from polysaccharides results in comparable yields as that from monosaccharides, longer reaction times or higher amounts of acid catalysts are needed.[13]
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