Polymerization of soybean oil via permanganate oxidation with sub/supercritical CO2

The reaction of soybean oil with aqueous KMnO4 solution, in the presence of dense CO2, is investigated by monitoring the amount of carbon-carbon double bonds and the fatty acid distribution of soybean oil. Experiments are performed with soybean oil and a model compound (methyl oleate) at 25 and 50degreesC and 70, 120 and 130 bar. Reactor configuration (batch and semi-batch), reaction time, and product-storage period on the extent of the reaction are studied. With the semi-batch configuration, water feed rates ranging from 0.023 to 0.250 ml/min are studied. Effect of reaction time is investigated with batch periods of 1, 3, 8, 12, 16, 24, 32 and 40 h. Physical inspections and tests, as well as instrumental analysis are carried out on the soybean-oil-derived products, which are observed to change their characteristics in time in storage vials. The consumption of soybean triglyceride double bonds (STDB) are observed to increase from 23.5 to 32.6%, when the water feed rate in the semi-batch experiments was increased from 0.023 to 0.250 ml/min. A saturation behavior is observed for the consumption of STDB with increasing batch reaction time. STDB consumption is 8% for one-hour reaction time, increasing to 30.1% for 16 h and 42% for 40 h. The samples obtained continued to react during storage, losing more than 80% of their carbon-carbon double bonds and attaining a rubber-like structure. Since there is no permanganate remaining in the collected samples, the change in the remaining fatty acid distribution and the observations about the product physical properties suggest that the depletion of STDB is due to air-oxidation polymerization, possibly initiated at the oil-water interface and accelerated by permanganate in the presence of dense CO2. (C) 2003 Elsevier B.V. All rights reserved.