Continuous removal of metallic ions from soybean oil

Removal of metallic ions like copper, nickel and sodium from vegetable oils is important to edible oil processors. Continuous washing of soybean oil with acidic water, followed by ion exchange treatment of the aqueous solution to remove metallic cations and permit reuse of the water, is an effective and economical method for metal removal. Several types of washing apparatus were studied: A Podbielniak countercurrent centrifugal contactor, a rotating disc countercurrent contactor and a contactor-centrifuge system. Equipment for the third system is already available for the continuous washing of refined oil in modern refineries. With a contactor-centrifuge ion-exchange system, copper in soybean oil was reduced by washing from 1.5 to 0.03 ppm; nickel, from 0.4 to 0.04 ppm; sodium, from 20 to <1 ppm. The effects of pH and type of acid (anion) were studied. The cost of washing soybean oil by this method is estimated to be about 0.06 cent/lb, and there is no loss of oil. One of 28 papers presented at the Symposium, “Metal-Catalyzed Lipid Oxidation,” ISF-AOCS World Congress, Chicago, September 1970. No. Utiliz. Res. Dev. Div., ARS, USDA.