In this study, we prepared calcium silicate at different molar ratios (Ca:Si=1:3, 1:6, and 1:9 refer to CAS-30S, CAS-60S, and CAS-90S, respectively) with water addition. The adsorbent characteristics (specific surface area, pore volume, mean pore diameter, and elemental analysis) were measured and the effect of water addition on the adsorbent surface for the prevention of deterioration was evaluated. In addition, the deterioration of soybean oil (SO) subjected to heating and aeration was investigated based on the acid value (AV) and carbonyl value (CV). The specific surface area increased in the order CAS-60S (160.51 m2/g) < CAS-30S (182.61 m2/g) < CAS-90S (204.19 m2/g). Deterioration of SO could be induced by heating and aeration with AV and CV of 1.4 mg/g and 102.9 µmol/g, respectively. The adsorbent (CAS-30S and CAS-90S) with water addition (25% and 50%) was found to decrease the AV, indicating that a small amount of water addition to adsorbent surface is important for the decreasing of AV. In addition, the correlation between the decrease in AV and the specific surface area is strongly positive (R value: 0.968). The adsorption mechanism is thought to involve interactions between the polar compounds (free fatty acids) in the SO (nonaqueous phase) and the water layer (containing calcium ions released from the adsorbent) on the adsorbent surface. In summary, the data obtained in this study provide useful information for preventing the deterioration of SO and prolonging the oil life cycle.
Keywords: adsorption; calcium silicate; deterioration; soybean oil; water addition.