Comparison of Soybean and Cottonseed Oils upon Hydrogenation with Nickel, Palladium and Platinum Catalysts

Abstract

There is current interest in reducing the trans fatty acids (TFA) in hydrogenated vegetable oils because consumption of foods high in TFA has been linked to increased serum cholesterol content. In the interest of understanding the TFA levels, hydrogenation was carried out in this work on soybean oil and cottonseed oil at two pressures (2 and 5 bar) and 100°C using commercially available Ni, Pd, and Pt catalysts. The TFA levels and the fatty acid profiles were analyzed by gas chromatography. The iodine value of interest is *70 for all-purpose shortening and 95-110 for pourable oil applications. In all cases, higher hydrogen pressures produced lower levels of TFA. In the range of 70-95 iodine values for the hydrogenated products, the Pt catalyst gave the least TFA, followed closely by Ni, and then Pd, for both oils. For all three catalysts at 2-and 5-bar pressures and 70-95 iodine values, cottonseed oil contained noticeably less TFA than soybean oil; this is probably because cottonseed oil contains a lower total amount of olefin-containing fatty acids relative to soybean oil. Approximate kinetic modeling was also done on the hydrogenation data that provided additional confirmation of data consistency.

Modifications of Plant Oils for Value-Added Uses

“…Pt catalysts converted linoleic and oleic acids more slowly to TFA and quickly hydrogenated TFA, thereby leading to low TFA levels. Furthermore, in a direct comparison of hydrogenated soybean oil and cottonseed oil, lower TFA and stearic levels were found with hydrogenated cottonseed oil (28).…”

The Influence of the Hydrogen Pressure on Kinetics of the Canola Oil Hydrogenation on Industrial Nickel Catalyst

“…The results revealed that for cis/trans isomerization reactions the rate constants are comparably small except for the rate constant for the isomerization of oleic acid to elaidic acid. Only recently Chang et al proposed a model where linolenic acid is excluded and the hydrogenation reaction of oleic acid positional isomers, 9c-C18:1 and 12c-C18:1 proceeds independently via two different pathways [25]. Based on further studies, it was revealed that the rates of hydrogenation for this mechanism were pseudo first-order in triglycerides [16][17][18][19].…”

The Persistence of Exploded Myths

“…Accordingly, the ratios of the rate constants k 25 and k 52 and the ratios of the rate constants k 36 and k 63 should be the same for all catalysts and both oils. Checking whether that is the case only requires elementary arithmetic, the outcome of which is given in the table below; the rate constants in the table below are those given in Table 2 of [1]:…”

“…To the readers of the journal it is a comforting thought that all articles published in the journal have been read by several editors and studied in depth by at least two reviewers who have been selected for their expert knowledge of the subject. It is therefore most unexpected to find that a layman with just a basic knowledge of chemistry and arithmetic could show that an article that recently appeared in the journal [1] makes no sense. The article reports on the partial hydrogenation of two oils (soybean oil and cottonseed oil) with three different metal catalysts (Ni, Pd and Pt).…”

“…In their earlier publication [3], in which the authors did not distinguish between the 9 and the 12 positions in the oleic acid, they arrive at equilibrium constants of 150 for the nickel catalyst, 20 for the palladium catalyst and 33 for the platinum catalyst. They do not provide error ranges for the rate constants so that I could not estimate error ranges for the equilibrium constants like I did for their later publication [1] but given the hydrogenation temperature used, these values should again have been close to 4.0. Again, the sad conclusion has to be reached that all kinetic parameters reported by the authors in their earlier publication [3] are equally meaningless.…”