Preparation of cancrinite-type zeolite from diatomaceous earth as transesterification catalysts for biodiesel production

A new type of solid catalyst prepared from hydrothermal reaction of natural diatomaceous earth in NaOH solution was studied for biodiesel production through the transesterification of soybean and palm oil in excess methanol. Explicitly, the natural diatomite was transformed into efficacious catalysts, sequentially, by dispersion and activation in NaOH solutions for 30 min at 30 °C, followed by hydrothermal treatments at 180 °C or 220 °C for 12 h, and finally by calcination at 500 °C for 6 h. Coincidently, the physicochemical characteristics of these as-prepared catalysts were shown to bear a good resemblance with those of zeolite CAN. Under suitable conditions, the conversion efficiencies of soybean and palm oils to biodiesel in presence of these zeolite CAN catalysts at 63 °C and 70 °C could be obtained as high as 98.0% and 98.4%, respectively. Furthermore, the activation energies of the transesterification reactions of soybean and palm oils in excess methanol were found as 64.1 kJ/mol and 122.5 kJ/mol, respectively.