Optimization Of Process Variables In The Synthesis Of Butyl Butyrate Using Amino Acid-Functionalized Heteropolyacids As Catalysts

Response surface methodology was successfully applied to optimize esterification of butanol with butyric acids over amino acid-functionalized heteropolyacids, namely, [GlyH](x)H3-x PW12O40 (x = 1.0-3.0). A series of catalysts were prepared by incorporating tungstophosphoric acid (TPA) with varied amounts of glycine (Gly). The [GlyH](1.0)H2.0PW12O40 catalyst was found to exhibit the best activity with an optimal butyl butyrate yield of 97.9%, which was in excellent agreement with the predicted value by the Box-Behnken design (BBD) model. These superior esterification activities observed for the organic TPA salt catalysts might be due to their highly acidic nature, weak molecular transport resistance, and "pseudo-liquid" catalysis modes. Furthermore, the catalytic activity of [GlyH](1.0)H2.0PW12O40 catalyst was observed to have no appreciable change in the conversion after five consecutive runs. A kinetic study for the esterification was also performed under optimal reaction conditions. The results revealed that the reaction followed second-order kinetics, and the activation energy was found to be 81.90 kJ/mol.