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ARS Home » Research » Publications at this Location » Publication #114990
Title: HYDROGENATION OF VEGETABLE OILS USING MIXTURES OF SUPERCRITICAL CARBON DIOXIDE AND HYDROGEN

Author
item King, Jerry
item HOLLIDAY, RUSSELL - FORMER ARS EMPLOYEE
item List, Gary
item SNYDER, JANET - RETIRED, ARS EMPLOYEE

Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/4/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: The hardening of vegetable oils to produce solid-like fat compositions for use in shortenings and margarines utilizes a process called hydrogenation in which hydrogen gas is added to a slurry of vegetable oil plus catalyst. A major factor in achieving the desired degree of hydrogenation is the dissolving and contact of the hydrogen gas with the oil and catalyst surface, respectively. In this study, the addition of pressurized carbon dioxide to pressurized hydrogen was studied to see what beneficial effects would accrue on the factors effecting hydrogenation and the resultant end products. Carbon dioxide addition was actually found to slow down the rate of hydrogenation at one temperature while accelerating it at a slightly higher temperature. In general, addition of the second gas (carbon dioxide) to hydrogen resulted in hydrogenated products that had a low trans fatty acid content and a variable quantity of solids, both desirable characteristics for use in food products. The described approach offers oil and fat processors an alternative production method for generating margarine and shortening basestocks and provides insight into the mechanism of hydrogenating fats and oils.

Technical Abstract: Hydrogenation of vegetable oils under supercritical conditions can involve a homogeneous one phase system, or alternatively two supercritical components in the presence of a condensed phase consisting of oil and a solid catalyst. The former operation is usually conducted in flow reactors while the latter mode is more amenable to stirred, batch reactor technology. Although many advantages have been cited for the one phase hydrogenation 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 unconventional conditions for affecting the hydrogenation. In this study, a dead end reactor has been utilized in conjunction with a headspace consisting of either a binary fluid phase consisting of varying amounts of carbon dioxide mixed with hydrogen or neat hydrogen for comparison purposes. Reaction pressures up to 2000 psi and temperatures in the range of 120-140 deg C 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, % 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 synthesized products have low trans fatty acid content, consistent with a non-specific mode of hydrogenation.