Amino acid-functionalized heteropolyacids as efficient and recyclable catalysts for esterification of palmitic acid to biodiesel

Abstract

The organic–inorganic hybrid catalysts, namely [GlyH]xH3−xPW12O40 (x=1.0–3.0), prepared by mixing varied amounts of glycine (Gly) and tungstophosphoric acid (TPA), were characterized by different analytical and spectroscopic techniques such as TGA, XRD, FT-IR, and 1H and 13C NMR. In particular, their acidic properties were probed by solid-state 31P MAS NMR of adsorbed trimethylphosphine oxide. The catalytic performances of various Gly–TPA catalysts during esterification reaction of palmitic acid with methanol for production of methyl palmitate were illustrated and examined. The catalyst system revealed self-separation characteristics, forming biphasic product/catalyst layers to render facile product separation and catalyst recycling. The [GlyH]1.0H2.0PW12O40 catalyst was found to exhibit the best activity with an optimal biodiesel yield of 93.3%.