Alkaline Clay Deacidification Processes And Dynamics Research In Soybean Oil

The presence of free fatty acids in soybean oil affects the flavor, food security and storage stability of the oil. Traditional deacidification methods have their own limitations. New deacidification methods mostly have been in the laboratory research stage. Assay deacidification has been the research hotspot resently, since it is easy operation, low energy consumption and no pollution. Our team used bentonite as raw materials to make solid base adsorbent-alkaline clay. It has a high adsorption capacity and inexpensive, but there is a difficulty in solid-liquid separation and no comparison of deacidification processes and dynamics have been researched. This article is just based on the above work to resolve the shortcomings.Considering both deacidification effects and filter performance, the optimum process conditions are as follows:alkali content of alkaline clay is33.3%; water content of alkaline clay is11%; the dosage of alkaline clay is3%; the temperature is variable. The process coupling of deacidification and bleaching can simplify the process and reduce energy consumption. Firstly, add3%alkaline clay in soybean oil (AV=2.02) at room temperature and remain stirring for90min. Then, add2%active clay and rise the temperature to75℃.Lastly, filter the oil-soil mixture at75℃. The comparation of traditional intermittent alkali refining and alkaline clay adsorption deacidification in the laboratory showed that both the two methods could satisfy the basic deacidification requirements, but the latter shortened10hours during each batch of oil processing and the refined oil yield increased3.3%. Therefore, alkaline clay adsorption has significant economic and social benefits compared with conventional alkali deacidification.The kinetics study showed that the adsorption of oleic acid from soybean oil onto alkaline clay was well described by the pseudo-second-order model. At low temperatures, chemisorption was the main rate determining step while physisorption played a key role at high temperatures. The activation energy of system (Ea) was calculated as70.7kJ·mol-1. The water content of alkaline clay influenced the affinity of adsorbent with soybean oil and the adsorption rate constant increased with higher water contents. The SEM pictures of clay before and after adsorbing oleic acid as well as their organic ignition loss showed that the force among the alkaline clay particles was weak. To maintain the integrity of the absorbent, the water content of alkaline clay should not exceed13%; the adsorption temperature should be controlled at30-50℃; initial acid volue should not exceed4; the rate of stir is150rpm.The presence of water molecules reduced the contact angle between alkaline clay and oil and enhanced their affinity, accelerating the adsorption rate and improving the adsorption effect. The surface of alkaline clay will be covered by the long carbon chain of oleic acid and form an organic layer with the reaction. Oleic acid molecules diffused across the organic layer is belonged to physical adsorption, while the oleic acid molecules were adsorbed by the inorganic active sites (-OH) in the inner layer is chemical adsorption. The strong chemical action between alkaline clay and oleic acid would weaken the van der Waals force and coulomb force among particles, leading the breakage of adsorbent and adding the difficulty to be filtered. Therefore, the rate and adsorption amount of oleic acid should be controlled within a reasonable range.