(671b) Polar Aprotic Solvent and Alkali Metal Ion Effects on the Conversion of C6 Carbohydrates to Alpha-Hydroxy Acids Using Lewis Acid Beta Zeolites

The growing concerns about the limited reserves and adverse environmental impacts of fossil fuels caused increased research efforts for the development of green routes to produce chemicals from biomass. One family of such chemicals obtained from lignocellulosic raw materials includes α-hydroxy acids(AHAs), such as lactic acid(LA). Those platform molecules are promising monomers for the manufacture of biodegradable polymers.

Currently, LA is manufactured using a biochemical route. The process generates high quantities of gypsum waste and has pH and temperature control issues. The use of a catalytic pathway using Lewis acid Beta zeolites, for example Sn-Beta, may overcome those limitations.

Low reaction rates and the generation of undesirable humins limits the conversion of C6 carbohydrates to AHAs using Sn-Beta in water. The conversion decreased from 58% to 29%, after using the same catalyst for three reaction cycles and the AHAs yields also decrease after each cycle, indicating catalyst deactivation. After the regeneration, the initial values were only partially recovered (53%conversion) evidencing an irreversible modification of the zeolite framework.

The use of a polar aprotic cosolvent such as gamma-valerolactone(GVL), increased the catalytic activity as compared to the behavior in water. The use of GVL:water(9:1) also reduced the formation of furans and humins. After three reaction cycles, the conversion only decreased from 88% to 84% and the initial conversion and yields were recovered after calcination in flowing air at 150mL/min. The catalyst is more stable in GVL:water 9:1 compared to the use of only water as solvent.

We also found that the addition of K₂CO₃ to the reactive media improves AHAs production decreasing furans formation in GVL but not in water. This is probably because of the neutralization of Brønsted acids.