Organic compounds -- part of the class 532-570 series – Organic compounds – Fatty compounds having an acid moiety which contains the...
Reexamination Certificate
1996-11-12
2001-04-17
Wong, Edna (Department: 1741)
Organic compounds -- part of the class 532-570 series
Organic compounds
Fatty compounds having an acid moiety which contains the...
C554S141000, C554S147000, C205S413000, C205S462000, C205S695000, C205S696000, C204S167000
Reexamination Certificate
active
06218556
ABSTRACT:
BACKGROUND OF THE INVENTION
The hydrogenation of the unsaturated fatty acid constituents of an edible oil's triglycerides is carried out to produce a more oxidatively stable product and/or change a normally liquid oil into a semi-solid or solid fat with melting characteristics designed for a particular application. Most commercial oil hydrogenation plants use Raney or supported nickel catalyst, where the chemical catalytic reaction is carried out at a high temperature (typically 150-225 C.) and a hydrogen gas pressure in the range of 10-60 psig. These conditions are required to solubilize sufficiently high concentrations of hydrogen gas in the oil/catalyst reaction medium so that the hydrogenation reaction can proceed at acceptably high rates. The hydrogenation rate and fatty acid product distribution has been shown to be dependent mainly on temperature, pressure, agitation rate, and catalyst type and loading. Unfortunately, high reaction temperatures promote a number of deleterious side-reactions including the unfavorable production of trans isomers and the formation of cyclic aromatic fatty acids.
An alternative method to edible and nonedible oil and fatty acid hydrogenation by a traditional chemical catalytic reaction scheme is a low temperature electrocatalytic (electrochemical) route, where an electrically conducting catalyst (e.g., Raney nickel or platinum black) is used as the cathode in an electrochemical reactor. Atomic hydrogen can be generated on the catalyst surface by the electrochemical reduction of protons from the adjacent electrolytic solution. The electro-generated hydrogen then reacts chemically with unsaturated fatty acids in solution or in the oil's triglycerides. The overall oil hydrogenation reaction sequence is as follows:
2H
+
+2e
−
→2H
ads
(1)
2H
ads
+R—CH═CH—R→R—CH
2
—CH
2
—R (2)
where R—CH═CH—R denotes an unsaturated fatty acid. An unwanted side reaction that consumes electro-generated H
ads
(i.e., current) but does not effect the organic product yield is the formation of H
2
gas by the combination of two adsorbed hydrogen atoms,
2H
ads
→H
2
(gas) (3)
All electrochemical reactors must contain two electrodes, a cathode for reduction reactions such as that given by Equation 1 and an anode at which one or more oxidation reactions occur. For a water-based electrolytic solution, the anode reaction is often the oxidation of H
2
O to O
2
gas,
H
2
O→½O
2
+2H
+
2e
−
(4)
In organic electrochemical syntheses where two or more reactions occur at the same electrode, the effectiveness of the primary electrode reaction is often gauged by the reaction current efficiency. During the electrochemical hydrogenation of edible or non-edible oils, this quantity is a measure of the amount of electro-generated hydrogen which combines with an oil's unsaturated fatty acids (according to Equation 2), as opposed to the amount of atomic hydrogen lost as H
2
gas (Equation 3). The current efficiency is computed from the change in total moles of double bonds in the oil or fatty acid (as determined from the gas chromatography fatty acid profiles of initial and final samples of the reaction medium) and the total charge passed in an electrolysis, as noted by the product of the current density (A/cm
2
), the geometric electrode area (cm
2
), and the time of current passage (seconds),
Current Efficiency(%)=(_moles of double bonds)(2 equiv/mole)F/C (5)
where F is Faraday's constant (96,487 C/equiv.) and C is the total coulombs passed in electrolysis (the total coulombs is given by the arithmetic product of the current density, geometric electrode area, and time). For the cathodic reaction system where electro-generated H either adds to the oil or two hydrogen atoms combine to form H
2
, a current efficiency below 100% provides a direct measure of the fraction of current consumed by the H
2
gas evolution reaction (cf. Equation 3).
The hydrogenation of the fatty acid constituents of an edible oil's triglycerides is a particularly attractive reaction to examine in an electrocatalytic scheme for the following reasons: (1) low reactor operating temperatures minimize unwanted side reactions and the deleterious thermal degradation of the oil, (2) normally, only 25%-50% of the double bonds in an oil are hydrogenated, thus, eliminating the common problem in electrochemical reactors of low hydrogenation current efficiencies when the unsaturated starting material is nearly depleted, (3) the high molecular weight of the starting oil (892 g/mole for refined soybean oil) means that the electrical energy consumption per pound of hydrogenated product will be low even though the saturation of a double bond requires 2 F/mole of electron charge, and (4) when water is used as the anode reactant and source of H (according to Equation 4), the electrochemical oil hydrogenation method circumvents the need to produce, store, compress, and transport H
2
gas.
Since hydrogen is generated in-situ directly on the catalyst surface in an electrocatalytic reaction scheme, high operating temperatures and pressures are not required. By maintaining a low reaction temperature, it may be possible to minimize unwanted isomerization reactions, thermal degradation of the oil, and other deleterious reactions. By passing a high current through the catalyst (i.e., by maintaining a high concentration of atomic hydrogen on the catalyst surface), the hydrogenation rate of the oil may be kept high, even at atmospheric pressure and a low or moderate reaction temperature.
Numerous studies have shown that low hydrogen overpotential electrically conducting catalysts (e.g., Raney nickel, platinum and palladium on carbon powder, and Devarda copper) can be used to electrocatalytically hydrogenate a variety of organic compounds including benzene and multi-ring aromatic compounds, phenol, ketones, nitro-compounds, dinitriles, and glucose [see, for example, T. Chiba, M. Okimoto, H. Nagai, and Y. Takata,
Bulletin of the Chemical Society of Japan,
56, 719, 1983; L. L. Miller and L. Christensen,
Journal of Organic Chemistry,
43, 2059, 1978; P. N. Pintauro and J. Bontha,
Journal of Applied Electrochemistry,
21, 799, 1991; and K Park, P. N. Pintauro, M. M. Baizer, and K. Nobe,
Journal of the Electrochemical Society,
16, 941, 1986]. These reactions were carried out in both batch and semi-continuous flow reactors containing a liquid-phase electrolytic solution. In most cases the reaction products were similar to those obtained from a traditional chemical catalytic scheme at elevated temperatures and pressures.
Pintauro [U.S. Pat. No., 5,225,581 Jul. 6, 1993] and Yusem and Pintauro [
Journal of the American Oil Chemists Society,
69, 399, 1992] showed that soybean oil can be hydrogenated electrocatalytically at a moderate temperature, without an external supply of pressurized H
2
gas. Experiments were carried out at 70 C. using an undivided flow-through electrochemical reactor operating in a batch recycle mode. The reaction medium was a two-phase substance of soybean oil in a water/t-butanol solvent containing tetraethylammonium p-toluenesulfonate (hereafter denoted as TEATS) as the supporting electrolyte. In the experiments the reaction was allowed to continue for sufficient time in order to synthesize a commercial-grade “brush” hydrogenation product (25% theoretical conversion of double bonds). Hydrogenation current efficiencies in the range of 50-80% were obtained for apparent current densities of 0.010-0.020 A/cm
2
with an oil concentration between 20 and 40 wt/vol % in the water/t-butanol/TEATS electrolyte. The electro-hydrogenated oil was characterized by a somewhat higher stearic acid content, as compared to that produced in a traditional hydrogenation process. The total trans isomer content of the electrochemically saturated oil product, typically in the range of 8%-12% was lower than the 20%-30% trans product from a high-temperature chem
Carbo Michael D.
Carbo, P.L.C. Michael D.
The Administrators of the Tulane Educational Fund
Ventola II Ronald J.
Wong Edna
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