Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/15/1996
Publication Date: N/A
Interpretive Summary: The production of many chemical compounds from agricultural starting materials is often accomplished using solvents that are flammable, toxic, and which contribute to environmental pollution. An alternative medium to these solvents is the use of compressed gases, such as benign carbon dioxide, as reaction solvents. Carbon dioxide under high pressures exhibits liquid-like behavior and can dissolve the oil contained in soybean seeds, allowing it to be transported into a high pressure reaction vessel where it is catalytically converted to useful compounds called monoglycerides, which are used by several industries as food additives, lubricants, etc. The use of compressed carbon dioxide as a reaction medium facilitates selective dissolution of the oils into the carbon dioxide by changing its pressure and temperature. This permits mechanical control of the reactant composition as well as the solubility and hence composition of products in the dense gas medium. These products can then recovered by lowering the pressure on the carbon dioxide, which causes the dissolved monoglycerides to precipitate, and the harmless carbon dioxide can be released into the environment with no adverse effect.
Technical Abstract: The transesterification of soybean oil with glycerol, 1,2 propanediol, and methanol by an immobilized lipase in flowing supercritical carbon dioxide for the synthesis of monoglycerides is described. A lipase from Candida antarctica was used to catalyze the reaction of soybean oil with glycerol, 1,2-propanediol, ethylene glycol, and methanol. Reactions are performed in supercritical carbon dioxide at a density of 0.72 g/L and at a flow rate of 6 L/min (expanded gas). The substrates are added at flows ranging from 2.5 to 100 uL/min. Monoglycerides were obtained at up to 87 wt.% and fatty acid methyl esters at nearly 100 wt. %. The reactivity of the alcohols paralleled the solubility of the substrate in liquid carbon dioxide. Glycerol has the slowest reaction rate, only 2% that of methanol.