Conversion of carbohydrates to alpha-hydroxy-acids over Lewis acidic HF-, SN- and ZR- beta zeolite catalysts using gamma-valerolactone and water as solvent
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The incorporation of Sn, Hf and Zr in the structure of Beta zeolite using a post-synthetic method gives catalysts with Lewis acidity that are effective for the conversion of C6 sugars to alpha-hydroxy acids (AHAs), such as lactic acid. Sn-Beta zeolite with a Si/Sn of 561 has the best catalytic performance both in water and in a 9:1 mixture of gamma-valerolactone (GVL) and water. The use of GVL as cosolvent with water improves the activity, selectivity and stability of the catalysts for the conversion of C6 carbohydrates to AHAs. Glucose conversion in GVL:water 9:1 is a viable pathway for AHAs production. The use of toluene at room temperature is an effective method for the extraction of the products from GVL. At room temperature the combination forms a bi-phasic solvent system giving an organic phase rich in GVL and toluene and an aqueous phase rich in AHAs and water.