Heterogeneous esterification of free fatty acids using ion exchanged ETS-10 base catalyst

Abstract

Engelhard titanosilicate-10 (ETS-10) was synthesized via hydrothermal crystallization in the absence of organic template and seed. The influence of SiO₂/TiO₂ mole ratio of the initial gel on the formation of ETS-10 was examined in system 5SiO2: xTiO2: 3NaOH: KF: 75H₂O, where x was varied between 0.5-1.0. In addition, base-modified ETS-10 could be prepared by ion-exchange method with various alkali cation i.e. NaOH, KOH, RbOH and CsOH•H₂O in order to increase basic site of catalyst. The synthesized materials were characterized by powder X-ray diffraction (XRD), N₂-adsorption/desorption, DR-UV spectroscopy, scanning electron microscopy (SEM), inductively coupled plasma-atomic emission spectroscopy (ICP-AES) and atomic absorption spectrophotometry (AAS) techniques. The synthetic materials are mainly cubic-like particle ETS-10 phase with pore size around 0.6 nm. All synthesized materials were tested their activities in esterification of oleic, palmitic and linoleic acid with methanol to produce fatty acid methyl ester (biodiesel). The various reaction conditions such as catalyst amount, methanol to oil mole ratio including reaction time and temperature were studied. From this study, Rb-ETS-10 was distinguishable in both oleic acid and palmitic acid esterification. The optimum condition is methanol to acid mole ratio 9 to 1, reaction temperature 110-120℃, reaction time 18-24 h, amount of catalyst 10 wt% with stirring speed 200 rpm. The maximum methyl ester yield reached 100% when reaction was carried out under the optimum condition. Moreover, catalytic activities of reused and regenerated Rb-ETS-10 catalysts were also investigated.