Acid Treated Attapulgite Functionalized with Sodium Compounds as Novel Bifunctional Heterogeneous Solid Catalysts for Biodiesel Production

Abstract

In this study, catalytic transesterification of Parkia seed oil with methanol to biodiesel was studied. Attapulgite clay, treated with HCl and then functionalized with C₄H₆O₄KNa and Na₂C₂O₄ was used as a solid base catalyst. Having screened the catalytic action of attapulgite treated with HCl and functionalized with C₄H₆O₄KNa at different concentrations, 4 M solution C₄H₆O₄KNa was chosen for the functionalization and the results were compared with data obtained with 4 M Na₂C₂O₄. Impregnation method was applied to prepare catalysts. Functionalized catalysts dried and calcined at 450°C for 4 h were characterized by Hammett indicators, nitrogen adsorption isotherms, Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy and thermogravimetric analyses. The performance of HCl treated attapulgite and functionalized with 4 M C₄H₆O₄KNa (4NK/HCl-Atta-4) was superior both to HCl treated attapulgite functionalized with Na₂C₂O₄ (4NC/HCl-Atta-4) and to HCl treated attapulgite (HCl-Atta-4, reference). Maximum yields of biodiesels of 94.7 and 92.2% were obtained by using 4NK/HCl-Atta-4 and 4NC/HCl-Atta-4, respectively. The optimum reaction conditions were: ratio methanol : oil = 9 : 1; catalyst amount, 6 wt %; and reaction temperature, 60°C; reaction time, 6 h. The catalysts preserved catalytic activity after 5 runs of reuse. The properties of the biodiesels were comparable with those required by American and European Union standards and they could be considered as a realistic alternative fuel to diesel.