Comparative study of the chemical, structural and adsorptive properties of local thermally activated clay and an imported commercial clay for the depigmentation of crude palm oil

The present study investigated the performance of raw kaolinite clay (Ao), thermally activated local kaolinite clay and an imported commercial clay (AIC) for the depigmentation of crude palm oil. The local clay was thermally activated at 400 °C/1 h (A1), 600 °C/1 h (A2) and 600 °C/2 h (A3). Standard analytical methods such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) surface analysis were used to characterize the different materials. Batch adsorption was used to carry out experiments on the decolorization of crude palm oil. During this process, the effect of parameters such as contact time, adsorbent dose, acidity and stirring speed were evaluated. The physicochemical characteristics revealed that the A3 clay has a larger variety of functional groups and active sites (Si/Al ˂ 1) and a higher specific surface area (28.62 m2/g) than the A1 and A2 clays. The active sites in A3 activated by calcination compensate for the functional group deficit compared with the commercial clay AIC as evidenced by the comparable depigmentation efficiency of crude palm oil. The characteristics of the oil decolorized with A3 and AIC clays revealed negligible impurities, water content and volatile matter, and indistinguishable coloration of 15.8 R30Y for an optimum depigmentation time of 30 min. The acid, iodine and peroxide values of the oils treated with A3 and AIC show that the oils are not deteriorated by the clays during the depigmentation process. Since the performance of the materials are indistinguishable, the tradeoff between importation costs and costs of thermal treatment indicates that the use of local kaolinite clay of Njinon, is plausible alternative for use in the palm oil refining process with higher potential of trickle-down economics effect to the local economy relative to adsorbent importation.