Abstract
The effect of SiO2/MgO molar ratios of magnesium silicate on adsorption of free fatty acid (FFA), soap and glycerine in biodiesel was studied. The magnesium silicate adsorbent was prepared by the precipitation of magnesium sulfate and sodium metasilicate. The molar ratios of SiO2/MgO in synthetic magnesium silicate, i.e., 0.31:1, 0.76:1 and 2.04:1 were obtained by varying concentrations of Na2SiO3:MgSO4. The element analysis, crystal structures and surface area and pore size of the adsorbents were characterized by X-ray fluorescence method (XRF), X-ray diffraction method (XRD) and Brunauer-Emmett-Teller technique (BET), respectively. FTIR technique was used to confirm the chemical characteristics of the adsorbents. The adsorption efficiency of synthesized magnesium silicate in biodiesel containing different amount of SiO2 / MgO molar ratios was studied by varying dosage amount of adsorbents (1, 2 and 3 g) for 150 g of biodiesel at 60°C for 5 hours. The results showed that the magnesium silicate at 2.04:1 SiO2/MgO molar ratio and 3 g of adsorbent showed the highest efficiency in adsorption of FFA, soap and glycerine at 77.39%, 77.11% and 82.92%, respectively. While the adsorption capacity was 52.57 mg/g of FFA adsorption, 1.37 mg/g of soap adsorption and 155.06 mg/g of glycerine adsorption. The 2.04:1 molar ratio of SiO2/MgO in magnesium silicate had the biggest pore size, 105 A°, that was proportional to the contaminates adsorbed. Noticeably, the structure size of concerned contaminates were large, so the pore size of adsorbents could play a significant role on adsorptivity of adsorbate.
