Hydrogenation of Vegetable Oils Using Mixtures of Supercritical Carbon Dioxide and Hydrogen

摘要

Hydrogenation of vegetable oils under supercriti-cal conditions can involve a homogeneous one-phase system, or alternatively two supercritical components in the presence of acondensed phase consisting of oil and a solid catalyst. The for-mer operation is usually conducted in flow reactors while the lat-ter mode is more amenable to stirred, batch-reactor technology. Although many advantages have been cited for the one-phase hy-drogenation of oils or oleochemicals using supercritical carbon dioxide or propane, its ultimate productivity is limited by the oil solubility in the supercritical fluid phase as well as unconven-tional conditions that affect the hydrogenation. In this study, a dead-end reactor has been utilized in conjunction with a head-space consisting of either a binary fluid phase consisting of varying amounts of carbon dioxide mixed with hydrogen or neat hydro-gen for comparison purposes. Reaction pressures upto 2000 psi and temperatures in the range of 120—1 400C have been utilized with a conventional nickel catalyst to hydrogenate soybean oil. Depending on the chosen reaction conditions, a wide variety of end products can be produced having different iodine values, percentage trans fatty acid content, and dropping points or solid fat indices. Although addition of carbon dioxide to the fluid phase containing hydrogen retards the overall reaction rate in most of the studied cases, the majority of products have low trans fatty acid content, consistent with a nonselective mode of hydrogena-tion.