RICE HUSKS AS ADSORBENT TO REMOVE ACIDITY AND PEROXIDES FROM WASTE COOKING OIL

Lower percentages of residual oil compared to other raw materials in biodiesel synthesis are linked to low and inconsistent quality, which is considered an obstacle to its use in a homogeneous alkaline transesterification. In this context, the present study aimed to evaluate the adsorbent potential of rice husks, a widely available agroindutrial residue, in reducing acidity and peroxides of waste cooking oils, and compare it to the results obtained with the use of commercial activated carbon. The chemical and morphological characterization of the adsorbents was carried out by means of nitrogen physisorption, scanning electron microscope, energy dispersive spectroscopy and X-ray diffraction, for property identification that could provide information regarding adsorbent and adsorbate interactions. The adsorbent potential of the materials was investigated evaluating different operating conditions of temperature, adsorbent mass and agitation. After establishing the best operating conditions in the intervals tested and perform kinetic adsorption tests, it was observed that activated carbon as an adsorbent reduced acidity and peroxide indexes by 47 and 29% respectively, using 25°C, 200 rpm and with 4.95 g of adsorbent, knowing the untreated waste cooking oil had an acidity of 4 mg KOH g-1 and peroxide index of 36.21 meq kg-1. By its turn, the rice husks reduced by 40% and 24% the acidity and peroxides indexes, using 17ºC, 200 rpm and 4.95 g of adsorbent, which corresponds to 15% of the oil mass. The results obtained prove the use of rice husk as an adsorbent agent is an advantageous alternative for the treatment of waste cooking oil, since it is a by-product of residual character and low added value and that provided similar results to those obtained with the use of the commercial adsorbent material also evaluated.