Optimization of Acid Activation Conditions for Athi River Bentonite Clay and Application of the Treated Clay in Palm Oil Bleaching

Abstract

Athi River bentonite clay was activated using sulphuric acid at various acid concentrations, clayacid ratio, temperature and contact times. Optimization was based on palm oil bleaching performance. The chemical compositions of the raw clay and clay activated at different acid concentrations were analysed to investigate the extent of cation dissolution and exchange. From the results, the clay was classified as calcium bentonite. Both cation exchange capacity (CEC) and the apparent bulk density were found to decrease with increase in acid concentration. When palm oil was bleached at 90°C for 30 minutes using1% and 4% clay activated with 2M sulphuric acid , the bleaching performances obtained were 94.5 and 98% respectively. These results compared well with those of a commercial bleaching clay which was used as standard. The equilibrium data was analysed using Freundlich and Langmuir adsorption isotherms and the former was found to provide a better fit for the data. The calculated heat of adsorption indicated that palm oil bleaching by the activated clay was an exothermic reaction and a physico-chemical process. Sulphuric acid activation was found to be an effective method of improving adsorption performance of Athi River bentonite clay and the activated product is a viable alternative to imported commercial bleaching earth.

Adsorption Behavior of Acid-Leached Clays in Bleaching of Oil

“…The differences in bleaching efficiency of the clays used in this study appeared to be due to differences in the physical and chemical properties of the bleaching media developed as a result of leaching clays. And this is similar to what was advanced when cotton-seed oil was bleached using acid-activated montmorillonite [47].…”

“…Similarly, heterogeneity of Cyprus bentonite was attributed both to different active centres on the smectite surface (Broensted and Lewis centres) and to the different phases present in bentonite, such as illitic layers and clinoptilolite, which also have active centres on their surfaces as the clay was a mixture of illite and smectite [26] [47].…”

How Variation of Turbidity of Bleached Oils Characterizes Purity Oil and Bleaching Processes

“…. Although the values obtained are less than those obtained for adsorption from gaseous phase, the fact that energy is evolved confirms the applicability of the Freundlich isotherms to the decolorization of cotton and sunflower seed oils (Ujeneza et al, 2014). The values enthalpies of adsorption obtained in this study were less than 20kJ mol -1 , indicating physical adsorption process occurred.…”

“…In this study, the turbidity and sorption characteristics of color, chlorophyll and carotene pigments onto the clay adsorbents can be mainly discussed on the basis of Freundlich and Langmuir isotherms (Kaynak et al, 2004). The removal of the main coloring pigments (chlorophyll, β-carotene and red color) in neutralized sunflower and/or cotton oils with different types of bleaching earth materials has been examined in a pilot system at temperature of 105 ºC and pressure of 50 mmHg and bleaching earth dosage (Topallar, 1998;Ujeneza et al, 2014;Topkafa et al, 2013). Freundlich (1906) developed equation 1.1 relating adsorption to residual solute concentration.…”

“…Boki et al, (1992) have applied the Langmuir and Freundlich equations to the adsorption isotherms of  -carotenes on montmorillonite, activated clay and sepiolite from alkali-refined rapeseed and soybean oils. Application of Langmuir and Freundlich equations to adsorption isotherms for bleaching of crude sunflower seed oil with bentonite and showed that absorbance of bleached sunflower oil decreased as the concentrations of bentonite increased with increase in temperature between 60 and 90 o C (Kara et al, 2008;Topallar, 1998;Ujeneza et al, 2014). In this study we examine the use of variation of turbidity of bleached oils in describing Freundlich and Langmuir isotherms in bleaching of oils using Ugandan clays.…”