Multifunctional Beta zeolites for the production of methyl lactate from glucose

Carbohydrates represent a huge resource of already functionalized molecules from which it is possible to obtain a large range of bio-fuels and bio-chemicals, e.g bio-based polymers. Currently, the processing of the biomass feedstock is still dominated by bio-fermentative approaches with several drawbacks in terms of waste generation and costly product purification. Chemo-catalytic processes can overcome most of these problems, opening the way to a more intense exploitation of biomasses. Sn-Beta zeolites are promising catalysts for the rearrangement of simple sugars into valuable chemicals, such as lactic acid, the monomer for polylactic acid (PLA) production. In work, Sn-Beta was used as catalyst for the isomerization of glucose into fructose and the transformation of the latter into methyl lactate in methanol as solvent. This catalyst allows to perform both the reactions in the same reactor at temperatures above 150°C. Different multifunctional zeolites were synthetized and characterized with NH3-TPD, XRD, XRF and BET techniques. We demonstrated that the addition of co-metals incorporated in the zeolite framework increases the selectivity into methyl lactate and the rate of its production. The presence of added metals favors the retro-aldol cleavage leading to methyl lactate and inhibits the dehydration of fructose to furanic by-products. While the positive effect of alkali metals was already studied in previous studies, the benign effect of also bivalent cations such as manganese, calcium and magnesium was investigated. Using manganese, the effect was observed to be as positive as that with potassium, and it is the first example of the use of this metal for this reaction. Kinetic and stability tests were performed for the catalysts giving the best results in order to understand the catalytic activity of the multifunctional materials and to underline the differences between having conventional Sn-Beta zeolites rather than multifunctional systems.