Purification of biodiesel by adsorption with acid activated bentonite

Abstract

The objective of this research is to activating bentonite with sulfuric acid for purification of biodiesel. In order to activating bentonite, the effects of sulfuric acid concentrations (0.1, 0.3 and 0.5 M), activating temperature (60 and 100 °C) and activating times (1-24 h) were studied. The optimal condition for activating bentonite was 0.1 M H2SO4 at 60 °C for 12 h. The characteristics of activated bentonite were characterized by BET, XRD and XRF methods. The specific surface area and average pore diameter of activated bentonite were 55.15 m2/g and 8 nm, respectively. The morphology of activated bentonite was unchanged. The chemical composition: MgO, CaO, Na₂O and K₂O, were slightly decreased from 3.68, 3.30, 0.83 and 0.75 to 3.42, 2.69, 0.10 and 0.65 %wt., respectively. In order to purify biodiesel, the effects of amounts of activated bentonite (1-10 %wt. of activated bentonite per g oil), mesh sizes (60-200 mesh) and contact times (10-30 min.) on soap removal were also studied. The optimal condition for removal of soap in biodiesel was 10%wt. of activated bentonite (80-100 mesh) per g oil at room temperature with stirring rate of 150 rpm for 20 min. The removal of soap in biodiesel was 72.30%. The adsorption isotherm was fit to Freundlich isotherm. The results showed that activated bentonite can be used for purifying biodiesel. The quality of biodiesel after purified by activated bentonite followed by water washing could meet the major specification of biodiesel standards.