Hydrogenation Of Linolenate Research Articles

Shunt reactions in methyl linolenate hydrogenation using a supported Ni catalyst

A study of the kinetics of methyl linolenate catalytic hydrogenation in liquid phase with a Ni catalyst at 398–443 K and 370–645 kPa, focusing on the proper modelling of the shunt reactions in the network—simultaneous cohydrogenation of double bonds—is presented. A reliable estimation of the corresponding kinetic parameters using pseudo first order rate expressions is made, based on the strategy of analysing subsystems with increasing degress of complexity. The study demonstrates that the linear, consecutive sequence of irreversible hydrogenations from tri-unsaturated to linear methyl esters does not provide a correct description of the kinetic process. Bulk and surface shunt reactions contribute significantly to the net hydrogenation of tri- and di-unsaturates.

Continuous slurry hydrogenation of soybean oil with nickel catalysts

AbstractSoybean oil was hydrogenated continuously in the presence of nickel catalysts. The iodine value of the products was varied by changing the oil flow rate and temperature of the reaction. Sulfur‐promoted nickel catalyst increased the selectivity for linolenate hydrogenation, but formed much higher proportions oftrans isomers. Linoleate selectivity improved with temperature with both nickel and sulfur‐promoted nickel catalysts, buttrans isomerization also increased. The feasibility of this continuous reactor system was demonstrated as a practical means to prepare hydrogenated stocks of desired composition and physical characteristics at high throughput.

Ultrasonic hydrogenation of soybean oil

AbstractThe rate of hydrogenation of soybean oil with either copper chromite or nickel catalysts increased more than a hundredfold with the aid of ultrasonication. In a continuous reaction system, the selectivity with copper catalyst for linolenate reduction was somewhat lower when ultrasonic energy was applied than when not applied. With ultrasonic energy, 87% hydrogenation of linolenate in soybean oil was obtained in 9 sec at 115 psig H2 with 1% copper chromite at 181 C and 77% linolenate hydrogenation with 0.025% nickel. Without ultrasonic energy, only 59% linolenate hydrogenation was obtained in 240 sec with copper chromite at 198 C and 500 psig H2 and 68% linolenate hydrogenation in 480 sec with nickel at 200 C and 115 psig H2. This innovation may offer an important advantage in increasing the activity of commercial catalysts, particularly copper chromite, for fats and oil hydrogenation.

Selective conjugation of soybean esters to increase hydrogenation selectivity

AbstractPolyunsaturated fatty acid methyl esters of soybean oil (MeSBO) were selectively conjugated as a means of increasing the linolenate selectivity of various homogeneous and heterogeneous hydrogenation catalysts. Kinetics of the conjugation reaction in various solvents indicated that linolenate conjugated 5–8 times faster than linoleate. Selective conjugation of MeSBO with potassiumt‐butoxide in dipolar solvents resulted in an increase in linolenate hydrogenation selectivity to 7–8 with Ni and Pd heterogeneous catalysts, and to 7–10 with homogeneous and heterogeneous chromium carbonyl catalysts.Trans‐unsaturation in the hydrogenated products was only 1–3% with the chromium carbonyl catalysts, in contrast to 30–39% with the heterogeneous metal catalysts. Triglycerides were readily converted to partial glycerides andt‐butyl esters with the potassiumt‐butoxide reagent.

Selective hydrogenation with copper catalysts: V. Kinetics and mechanism at high pressure

AbstractThe mechanism of hydrogenation at 900~950 psi with copper‐chromite catalyst was investigated with pure methyl esters as well as their mixtures. A comparison of double bond distribution intrans‐monoenes formed during hydrogenation of linoleate and alkali‐conjugated linoleate revealed that 85~95% of the double bonds in linoleate conjugated prior to hydrogenation. The mode of hydrogen addition to conjugated triene and diene at high pressure is similar to that at low pressure but positional and geometric isomerizations of unreduced conjugated esters were less at high pressure. Geometric isomerization of methyl linoleate and linolenate was considerable at high pressure whereas it was negligible at low pressure. The absence of conjugated products during hydrogenation of polyunsaturated fatty acid esters resulted from their high reactivity. Conjugated dienes are 12 times more reactive than the triene, methyl linolenate, and 31 times more reactive than the diene, methyl linoleate. The products of methyl linolenate hydrogenation were the same as those predicted by the conjugation mechanism.

Selective homogeneous hydrogenation of triunsaturated fats catalyzed by tricarbonyl chromium complexes

AbstractThe need for a selective catalyst to hydrogenate linolenate in soybean oil has prompted our continuing study of various model triunsaturated fats. Hydrogenation of methylβ‐eleostearate (methyltrans,trans,trans‐9,11,13‐octadecatrienoate) with Cr(CO)3 complexes yielded diene products expected from 1,4‐addition (trans‐9,cis‐12‐ andcis‐10,trans‐13‐octadecadienoates). Withα‐eleostearate (cis,trans,trans‐9,11,13‐octadecatrienoate), stereoselective 1,4‐reduction of thetrans,trans‐diene portion yielded linoleate (cis,cis‐9,12‐octadecadienoate). However,cis,trans‐1,4‐dienes were also formed from the apparent isomerization ofα‐ toβ‐eleostearate. Hydrogenation of methyl linolenate (methylcis,cis,cis‐9,12,15‐octadecatrienoate) produced a mixture of isomeric dienes and monoenes attributed to conjugation occurring as an intermediate step. The hydrogenation ofα‐eleostearin in tung oil was more stereoselective in forming thecis,cis‐diene than the corresponding methyl ester. Hydrogenation of linseed oil yielded a mixture of dienes and monoenes containing 7%trans unsaturation. We have suggested how the mechanism of stereoselective hydrogenation with Cr(CO)3 catalysts can be applied to the problem of selective hydrogenation of linolenate in soybean oil.

Hydrogenation of unsaturated fatty esters with copper‐chromite catalyst: Kinetics, mechanism and isomerization

AbstractHydrogenation of linolenate with copper chromite produced a large amount of conjugated diene and minor amounts of nonconjugatable dienes. The double bonds in conjugated dienes and monoenes were scrambled all along the chain. This product distribution can be explained if it is assumed that conjugation of the double bonds is followed by hydrogenation. In competitive hydrogenation, fatty esters with conjugated double bonds were reduced preferentially over fatty esters with methylene‐interrupted double bonds. Isomerization of conjugated double bonds (geometric and positional) occurred more rapidly than reduction. Reduction of conjugated double bonds in the presence of deuterium resulted in a majority of the products containing no deuterium. Most of the added deuterium was incorporated into the unreacted material. Mechanisms are proposed to account for the products formed during the hydrogenation of linolenate, linoleate and their isomers.

Selective hydrogenation with copper catalysts: II. Kinetics

AbstractTo explain the unusually high selectivity of copper catalysts toward linolenate, model compounds were hydrogenated (150 C and atmospheric pressure) and the reaction products analyzed. Products varied depending upon location of the double bonds. Monoenes were not reduced by copper chromite except when the double bond was next to a carboxyl group. Dienes with isolated double bonds also were not reduced. Binary mixtures of model compounds were hydrogenated with copper chromite. From the composition of the initial and final products, a competitive rate ratio of the two compounds was determined. Esters with conjugated double bonds reacted faster than esters containing methylene interrupted double bonds. Kinetic data on the hydrogenation of linolenate indicated conjugation of the double bonds. Simulation of the kinetic data gave competitive reaction rates for the different isomers formed.

Selective hydrogenation with copper catalysts: I. Isolation and identification of isomers formed during hydrogenation of linolenate

AbstractMethyl linolenate was hydrogenated with 10% copper chromite catalyst at 150 C and atmospheric hydrogen pressure. The product was separated into monoene, diene and triene fractions by countercurrent distribution. These fractions were further separated into various geometrical isomers. The double bond location in the various fractions was determined by reductive ozonolysis. Double bonds in bothcis andtrans monoene fractions, as well as incis,trans andtrans,trans conjugated dienes, were extensively isomerized. A monoene containing vinylic unsaturation was one of the major products. The nonconjugated dienes were mostly dienes whose double bonds were widely separated. Results are explained on the basis of conjugation of the double bonds in linolenate followed by hydrogen addition.

Homogeneous catalytic hydrogenation of unsaturated fats: Metal acetylacetonates

AbstractHydrogenation of linseed and soybean methyl esters was achieved at 100舑180C, 100舑1000 psi H2 and 0.05舑0.25 moles catalyst per mole of ester. The relative activity of metal acetylacetonates in decreasing order was: nickel (III), cobalt (III), copper (II) and iron (III). Reduction occurred readily in methanol solution but only slowly in dimethylformamide and acetic acid. No reduction occurred in the absence of solvents. Soybean oil was also hydrogenated rapidly with nickel (III) acetylacetonate in methanol, but in this system the triglycerides were converted to methyl esters. Nickel (III) acetylacetonate was the most selective catalyst toward linolenate hydrogenation. Methyl linoleate and linolenate hydrogenated with nickel(III) acetylacetonate were fractionated into monoenes, dienes and trienes. Thecis monoenes separated in 62 to 68% yield had double bonds in the original position. The remainingtrans monoenes had extensively scattered unsaturation. The dienes and trienes showed no conjugation, but some of the double bonds in the dienes were not conjugatable with alkali. Little stearate was formed.

Hydrogenation of linolenate. XII. Effect of solvents on selectivity.

AbstractSelectivity of heterogeneous catalysts for hydrogenation of linolenate over linoleate is increased by the presence of certain polar solvents. A ratio of specific reaction rate constants for linolenate to linoleate of 4 was obtained with a 5% palladium‐on‐alumina catalyst when dimethyl formamide (DMF) was used as the solvent. This high selectivity of DMF was independent of temperature and catalyst concentration. Other solvents that improved selectivity include furfural, acetonitrile, tetramethyl urea and trimethyl phosphate.

Hydrogenation of linolenate. XI. Nuclear magnetic resonance investigation

AbstractNuclear magnetic resonance (NMR) spectra have been obtained during the hydrogenation of methyl linolenate with platinum, nickel and sulfur‐poisoned‐nickel catalysts and during the reduction of linolenic acid with hydrazine. Structural changes have been studied by 舠proton counting舡 techniques and include those for the total unsaturation (olefinic protons), 15,16‐double bond (ॆ‐olefinic methyl protons), 1,4‐pentadienes (di‐ॅ‐olefinic methylene protons) and allylic methylene (ॅ‐olefinic methylene protons).The number of olefinic protons is inversely related to the degree of saturation as determined by iodine value, GLC and hydrogen absorption. Amounts of double bonds in the 15,16‐position and in the 1,4‐pentadiene structures decrease linearly with increasing saturation, but the slopes of lines differ for specific catalysts. Sulfur‐poisoned pickel has the most negative slope, followed by electrolytic nickel, and then platinum and hydrazine. Amounts of ॅ‐olefinic structures with increasing saturation are roughly constant for hydrazine and platinum during reduction with the first mole of hydrogen; they fall to zero at complete saturation. For the two nickel catalysts, the ॅ‐olefinic structures increase during absorption of the first mole and a half of hydrogen before dropping to zero. The possibility of substituting NMR measurements for iodine value, alkali‐isomerization spectrophotometric determination and other structural analyses is discussed.

Hydrogenation of linolenate. X. Comparison of products formed with platinum and nickel catalysts

AbstractOne mole of hydrogen/mole of ester was added to methyl linolenate over a platinum catalyst at 20C and atmospheric pressure. The product was separated into trienoic, dienoic and monenoic esters by countercurrent distribution (CCD) with acetonitrile and hexane. Bach of these ester fractions was further separated by CCD with methanolic silver nitrate and hexane. Comparison with hydrogȳnations, in which a commercial nickel catalyst at 140C and atmos‐pheric pressure was used, shows that with plati‐num more stȳarate is formed; i.e., the platinum hydrogȳnation was less selective. Also, a smaller amt oftrans esters was formed with platinum, and there was less shift of double bonds from the original 9, 12 and 15 positions.

Hydrogenation of linolenate. VIII. Effects of catalyst concentration and of temperature on rate, selectivity, andtrans formation

AbstractThe effects of catalyst concentration and of temperature on linolenate selectivity,trans formation, and rate of hydrogenation have been studied for a commercial electrolytic nickel catalyst. Results obtained with an equimixture of linoleate and linolenate, following the procedure previously described, are presented as isometric drawings, which cover the experimentally practicable temperature ranges from 70舑230C and nickel concentration from 0.05舑10%. Whereas the rate of hydrogenation depends upon both temperature and catalyst concentration,trans formation is essentially a function of temperature while selectivity is little influenced by either parameter.

Hydrogenation of Linolenate. Fractionation of Isomeric Ester by Countercurrent Distribution with an Argentation System.

Hydrogenation of Linolenate. Fractionation of Isomeric Ester by Countercurrent Distribution with an Argentation System.

Hydrogenation of linolenate. VII. Separation and identification of isomeric dienes and monoenes

AbstractIsomeric dienes and monoenes produced by partial hydrogenation of linolenic acid have been separated by the combined use of low‐temp crystallization and countercurrent distribution.Cis, trans dienes have been separated fromcis, cis dienes.Cis, cis conjugatable dienes have been partially separated fromcis,cis nonconjugatable dienes. Dienes with onetrans double bond were separated by gas chromatography into two groups:cis, trans andtrans, cis. Individual positional isomers could not be separated.Cis‐9 monoene was separated fromcis‐12,cis‐15, andtrans monoenes by low‐temp crystallization. Countercurrent distribution at 3,000 transfers only partially separated this mixture ofcis‐12,cis‐15, andtrans monoenes. The double bond in bothcis andtrans monoenes was found in all carbon positions, 7 through 16, showing for the first time that the 15, 16 bond of linolenic acid had moved away from the carboxyl. The majorcis bonds remained at carbons 9, 12, and 15.Combination of countercurrent distribution fractions has produced samples containing 95%cis, cis dienes; 90%cis, trans ortrans, cis dienes; 95%cis monoenes; and 90%trans monoenes.

Kinetics of linolenate hydrogenation

Kinetics of linolenate hydrogenation

Hydrogenation of linolenate. VI. Survey of commercial catalysts

AbstractA survey of commercially available hydrogenation catalysts has been made in a search for high‐selectivity and low‐isomerizing characteristics. Selectivity舒the ratio of hydrogenation rates for linolenate to linoleate舒was determined on a linoleate‐linolenate equimixture under standardized conditions. Ratios of reaction rate constants for nickel catalysts at 140C ranged between 1.48 and 2.71; for palladium catalysts at 25C, 1.68 to 1.99; and for platinum catalysts at 25C, 1.33 to 1.61.Trans contents of ester mixtures reduced with these three metal catalysts ranged from 18.0 to 22.8, 16.7 to 20.5, and 6.3 to 8.4%, respectively. Although platinum catalysts produced the lowest isomerization, their selectivities were also low.

Hydrogenation of linolenate. V. Procedure of evaluating hydrogenation catalysts for selectivity

AbstractEquations for determining the ratio of hydrogenation rates for linolenate and linoleate acyl groups are derived from kinetic theory. They are based upon the analysis for linolenate after absorption of 0.5 mole of hydrogen by an equal mixture of linoleate and linolenate. This method finds routine application in the evaluation of hydrogenation catalysts for selectivity.

Hydrogenation of linolenate. IV. Kinetics of catalytic and homogeneous chemical reduction

AbstractKinetics for consecutive reactions of octadecatrienoate to octadecadienoate to octadecenoate have been studied with the aid of radioisotopic tracers and gas chromatography. Evidence for a triene to monoene shunt has been obtained. Similarly, the chemical reduction with hydrazine has been studied, but no evidence for this anomalous behavior was obtained. Methods to determine reaction rates from these kinetic measurements are discussed.