Hydrogenation of vegetable oils using mixtures of supercritical carbon dioxide and hydrogen

Hydrogenation of vegetable oils under supercritical conditions can involve a homogeneous one-phase system, or alternatively two supercritical componen ts in the presence of a condensed phase consisting of oil and a solid catal yst. The former operation is usually conducted in flow reactors while the l atter mode is more amenable to stirred, batch-reactor technology. Although many advantages have been cired for the one-phase hydrogenation of oils or oleochemicals using supercritical carbon dioxide or propane, its ultimate p roductivity is limited by the oil solubility in the supercritical fluid pha se as well as unconventional conditions that affect the hydrogenation. In t his study, a dead-end reactor has been utilized in conjunction with a heads pace consisting of either a binary fluid phase consisting of varying amount s of carbon dioxide mixed with hydrogen or neat hydrogen for comparison pur poses. Reaction pressures up to 2000 psi and temperatures in the range of 1 20-140 degreesC have been utilized with a conventional nickel catalyst to h ydrogenate soybean oil. Depending on the chosen reaction conditions, a wide variety of end products can be produced having different iodine values, pe rcentage trans fatty acid content, and dropping points or solid fat indices . Although addition of carbon dioxide to the fluid phase containing hydroge n retards the overall reaction rate in most of the studied cases, the major ity of products have low trans fatty acid content, consistent with a nonsel ective mode of hydrogenation.