XRecent advances in canola oil hydrogenations

Rapeseed oil has been the source of edible oils in many parts of the world. In the last decade, Canadian plant breeders have developed new rapeseed cultivars which yield oil low in erucic acid and meal low in glucosinolates. These cultivars were named “canola” by the Canadian rapeseed industry. Literature on the hydrogenation characteristics of canola oil is limited; however, in recent years, several aspects of canola oil hydrogenations with commercial nickel catalysts have been reported including the formation ofrans-isomers, trisaturated glycerides and physical properties. In addition, as the methods for determination of sulfur compounds in canola oil developed, the effect of some isothiocyanates on the hydrogenation rate was further investigated to determine the relative catalyst poisoning ability of serveral of these sulfur compounds. However, during the last few years, most of the efforts were directed towards development of novel, selective and active catalysts for canola oil hydrogenations. These studies cover a wide range of homogeneous and heterogeneous catalysts including sulfur poisoned nickel, gold supported on silica, arene-Cr(CO)₃, RuCl₂(CO)₂(PPh₃)₂, palladium on carbon, palladium black and nickel and arene-Cr(CO)₃ mixtures. Effects of temperature, pressure, catalyst concentration and catalyst preparation procedure on the hydrogenation rate, selectivity, catalyst life and quality of the oil were examined and compared with that of commercial nickel catalysts. A brief discussion about continous hydrogenations of canola oil with commerical fixed bed catalysts is also included.     

Behavior of hydrogenation catalysts. I. Hydrogenation of soybean oil with palladium

A statistical method for evaluation of catalysts was used to determine the behavior of palladium catalyst for soybean oil hydrogenation. Empirical models were developed that predict the rate,trans-isomer formation, and selectivity over a range of practical reaction conditions. Two target iodine value (IV) ranges were studied: one range for a liquid salad oil and the other for a margarine basestock. Although palladium has very high activity, it offered no special advantage intrans-isomer formation or selectivity. Palladium can substitute for nickel catalyst, at greatly reduced temperature and catalyst concentrations, for production of salad oil or margarine basestock from soybean oil. Presented at the AOCS meeting, Chicago, May 1983.     

Supported gold catalysis in the hydrogenation of canola oil

The catalytic activity of gold supported on silica orγ-alumina has been studied in the hydrogenation of canola oil. In the hydrogenation of butadiene and pentene using these catalysts, high stability, low yield oftrans-isomers and high monoene selectivity have been reported in the literature. Catalysts containing 1% and 5% Au w/w on porous silica andγ-alumina were active in hydrogenating canola oil in the range of 150 to 250 C and 3550 to 5620 kPa. The activity level of these catalysts was about 30 times lower than that shown by the standard AOCS Ni catalyst based on the concentration of metal (g Au/L oil). Up to 91% monoene content was obtained using these catalysts in comparison with a maximum of 73% for the AOCS standard Ni catalysts. Gold catalysts can be recovered easily by filtration and reused several times without a decrease in activity. The hydrogenated oil was nearly colorless. No gold was detectable in the oil. Contrary to claims in the patent literature, the gold catalyst produces higher concentrations oftrans-isomers than does nickel. However, using gold catalysts the complete reduction of linolenic acid in canola oil can be achieved at a lowertrans-isomer content in the products than that obtained by using the AOCS standard nickel catalyst.     

Heterogeneous catalytic hydrogenation of canola oil using palladium

The hydrogenation of canola oil was studied using palladium black as a potential catalyst for producing partially hydrogenated fats with lowtrans-isomer content. Pressure (150\s-750 psig) appeared to have the largest effect ontrans-isomer formation. At 750 psig, 90 C and 560 ppm metal concentration, a maximum of 18.7%trans isomers was obtained at IV 53. A nickel catalyst produces about 50%rans isomers at the same IV. For palladium black, the linolenate and linoleate selectivities were 1.2 and 2.7, respectively. The maximum level oftrans isomers observed ranged from 18.7% to 42.8% (150 psig). Temperature (30\s-90 C) and catalyst concentration (80\s-560 ppm) affected the reaction rate with little effect ontrans-isomer formation and selectivities. At 250 psig and 50 C, supported palladium (5% Pd/C) appeared to be twice as active as palladium black. At 560 ppm Pd, 5% Pd/C produced 30.2%trans (IV 67.5), versus 19.0%trans for palladium black (IV 68.9). Respective linoleate selectivities were 15 and 6.6, while linolenate selectivities were approximately unity. Analysis of the oil samples by neutron activation showedapproximately a 1 ppm, Pdresidue after filtration.     

Electrochemical hydrogenation of canola oil using a hydrogen transfer agent

A novel low-temperature process for the electrochemical hydrogenation of canola oil is described. An emulsion of oil and water containing formic acid and a nickel hydrogenation catalyst, placed in the cathode compartment of an electrolysis cell and subjected to an electrical current, underwent hydrogenation at temperatures as low as 45°C. At these low temperatures of hydrogenation, the trans FA content of the hydrogenated canola oil was very low as compared with that of the edible oils hydrogenated by commercial processes using high temperature and high partial pressure of hydrogen gas. Because of its adverse health effects, a high trans FA content in edbile oils is viewed as undesirable. In addition to the commercially available nickel supported on silica, amorphous nickelphosphorus alloys supported on a variety of substrates were also used. Amorphous alloys are generally very corrosion resistant because of the absence of grain boundaries. A mechanism for hydrogenation using the hydrogen transfer agent of formic acid and its continuous regeneration at the cathode was evoked to explain the experimental data.     

High Oleic and Low <Emphasis Type="Italic">Trans</Emphasis> Fatty Acid Formation by an Electrochemical Process

Electrochemical hydrogenation employing a mediator of formate/formic acid resulted in partial hydrogenation of vegetable and soybean oil at 20–40 °C and ambient pressure when palladium supported on alumina was employed as a catalyst. An oleic acid content of 48% with a corresponding iodine value of 81 for the vegetable oil hydrogenated at 20 °C was obtained. The total trans fatty acid content and especially the 18:1 trans fatty acid were found to increase with the reaction temperature and time. Nonetheless, relatively low total trans and 18:1 trans fatty acid (7 and 3.8%, respectively) contents were found when the vegetable oil was partially hydrogenated to achieve an iodine value of 112.     

Catalytic behavior of palladium in the hydrogenation of edible oils II. Geometrical and positional isomerization characteristics

The geometrical isomerization characteristics of 5% Pd/alumina were investigated using response surface methodology. From the response surface, it was observed as expected that moretrans isomers were formed at lower pressures and higher temperatures. A doubling of the metal concentration from 50 to 100 ppm resulted in a small increase in isomerization in soybean oil, while for canola oil the same increase had a larger effect, especially at lower pressures. Similarly, an increase in temperature increases geometrical isomerization, especially at lower pressures, but the effect is more pronounced for canola than for soybean oil. Positional isomers were determined by oxidative ozonolysis in BF₃-MeOH and subsequent GLC analysis. Higher pressures suppressed positional isomerization. The effect of various catalyst supports on positional isomerization was also investigated.     

Degradation and Nutritional Quality Changes of Oil During Frying

The changes in regular canola oil as affected by frying temperature were studied. French fries were fried intermittently in canola oil that was heated for 7 h daily over seven consecutive days. Thermo-oxidative alterations of the oil heated at 185 ± 5 or 215 ± 5 °C were measured by total polar components (TPC), anisidine value (AV), color components formation, and changes in fatty acid composition and tocopherols. Results showed that TPC, AV, color and trans fatty acid content increased significantly (P < 0.05) as a function of frying temperature and time. The oil polyunsaturated fatty acids (PUFA) decreased in direct proportion to frying temperature and time. After 7 days of frying, the amount of PUFA was reduced by half and the trans isomers contribution increased 2.5 times during frying at 215 °C. Of the parameters assessed, total polar component and color had the highest correlation, with correlation coefficients of 0.9650 and 0.9302 for frying at 215 and 185 °C, respectively. TPC formation correlated inversely with the reduction of tocopherols.     

The hydrogenation of fatty oils with palladium catalyst. III. Hydrogenation of fatty oils for shortening stock

Summary Palladium-on-carbon catalysts are exceedingly active for the hydrogenation of natural unsaturated oils when very mild conditions are used. Selectivity is usually good, andtrans content can be adequately controlled by the proper choice of conditions. In the range of operating variables used in this work,trans formation is lessened with increased agitation and pressure, decreased catalyst activity, decreased concentration of metal in oil and on carrier, and with decreased temperature. Some shortening stocks were obtained which have good physical properties, as expressed by their dilatometric curves.     

Catalytic behavior of ruthenium in soybean oil hydrogenation

Soybean oil was hydrogenated with a carbon‐supported ruthenium catalyst (Ru/C) at 165 °C, 2 bar H₂ and 500 rpm stirring speed. Reaction rates, trans isomer formation, selectivity ratios and melting behaviors of the samples were monitored. No catalytic activity was found for the application of 10 ppm of the catalyst, and significant catalytic activity appeared at >50 ppm of active catalyst. The catalyst concentration had an effect on the reaction rate of hydrogenation, but the weight‐normalized reaction rate constant (k_c) was almost independent of the catalyst concentration at lower iodine values. Ru/C generated considerable amounts of trans fatty acids (TFA), including high amounts of trans 18:2, and also stearic acid, due to its very non‐selective nature. The selectivity ratios were found to be low and varied between 1.12 and 4.32 during the reactions. On the other hand, because of the low selectivity, higher slip melting points and solid fat contents at high temperatures were obtained than those for nickel and palladium catalysts. Another different characteristic of this catalyst was the formation (max 1.67%) of conjugated linoleic acid (CLA) during hydrogenation. Besides, CLA formation in the early stages of the reactions did not change very much with the lower iodine values.     

Hydrogenation of fatty oils with palladium catalysts. V. Products of the tall oil industry

Conditions were found for reducing tall oil distillate to an iodine number of 22 with a sufficiently small amount of palladium catalyst to make the process commereially feasible. The operating conditions were 200°C and 2,600 psi. Tall oil fatty acids were reduced with palladium and the concentration of linoleic acid,cis-oleic acid, saturated acid, andtrans isomers were determined as a function of iodine number. The five-platinum group metals (Pt, Pd, Ir, Rh, Ru) were compared as to activity, selectivity of partial hydrogenation, and tendeney to formtrans-isomers.     

Deodorization of vegetable oils. Part I: Modelling the geometrical isomerization of polyunsaturated fatty acids

Laboratory-scale treatments of canola oils similar to deodorization were carried out by applying the following conditions: reduced pressure with nitrogen or steam stripping at different temperatures ranging from 210 to 270°C for 2–65 h. The formation of the group of trans linolenic acid isomers follows a first-order reaction and the kinetic constant varies according to the Arrhenius’ law. Similar results were observed for the trans isomerization of linoleic acid. Based on these experiments, a mathematical model was developed to describe the isomerization reaction steps occurring in linoleic and linolenic acids during deodorization. The calculated degrees of isomerization are independent of the composition of the oil but related to both time and temperature of deodorization. The degree of isomerization of linolenic acid is unaffected by the decrease of this acid content observed during the deodorization. Deodorization at about 220–230°C appears to be a critical limit beyond which the linolenic isomerization increases very strongly. The newly established model can be a tool for manufacturers to reduce the total trans isomer content of refined oils, and was applied to produce a special selectively isomerized oil for a European Nutritional Project.     

Effect of some isothiocyanates on the hydrogenation of canola oil

Sulfur compounds were added to refined and bleached canola oil before hydrogenation in the form of allyl, heptyl and 2-phenethyl isothiocyanates, and the effects on hydrogenation rate, solid fat content and percentagetrans fatty acids were determined. The poisoning effect was most pronounced with allyl isothiocyanate and least with phenethyl isothiocyanate. As the amount of added sulfur increased, the hydrogenation rate decreased. Of the three isothiocyanates used, allyl isothiocyanate caused formation of larger amounts oftrans isomers. An increased sulfur level in the oil resulted in increased solid fat content andtrans isomer level. Allyl isothiocyanate also caused formation of larger amounts of solid fat than other isothiocyanates at all levels of sulfur addition.     

Conversion of canola oil to various hydrocarbons over Pt/HZSM-5 bifunctional catalyst

Canola oil conversion was studied at atmospheric pressure over Pt/HZSM-5 catalyst (0.5 mass% Pt) in a fixed bed micro-reactor. The operating conditions were: temperature range of 400?500°C, weight hourly space velocity (WHSV) of 1.8 and 3.6 h^?1 and steam/oil ratio of 4. The objective was to optimize the amount of gasoline range hydrocarbons in the organic liquid product (OLP) and the selectivity towards olefins and isohydrocarbons in the gas product. The gas yields varied between 22–65 mass% and were higher in the presence of steam compared to the operation without steam. The olefin/paraffin mass ratio of C₂-C₄ hydrocarbon gases varied between 0.31–0.79. The isohydrocarbons/n-hydrocarbons ratio was higher with Pt/HZSM-5 (1.6–4.8) compared with pure HZSM-5 catalyst (0.2–1.0). The OLP yields with Pt/HZSM-5 (20–55 mass% of canola oil) were slightly lower compared to HZSM-5 (40–63 mass% of canola oil) under similar conditions. The major components of OLP were aliphatic and aromatic hydrocarbons. A scheme postulating the reaction pathways for the conversion of canola oil over Pt/HZSM-5 catalyst is also presented.     

Empirical modeling of soybean oil hydrogenation

Empirical hydrogenation models were generated from statistically designed laboratory experiments. These models, consisting of a set of polynomial equations, relate the operating variables of soybean oil hydrogenation to properties of the reaction and of the fat produced. These properties include reaction rate,trans-isomer content and melting point. Operating variables included in the models were temperature, hydrogen pressure, catalyst concentration, agitation rate and iodine value. The effects of catalyst concentration and agitation rate were found to be significant in determiningtrans-isomer content, which in turn influences the melting characteristics of the hydrogenated oil. Pressures above 30 psig were found to have little effect ontrans-isomer content, although pressure was very important in determining reaction rate. Reaction temperature was observed as the most important factor in determining thetrans-isomer content for a given iodine value. Generally, 50 to 60%trans isomer content is predicted by the model for the iodine value range and operating conditions used in this study. Thus, these predictive models can assist in scaling up hydrogenation processes and in determining the optimum operating parameters for running commercial hydrogenation. Presented at the AOCS Meeting, Chicago, May 1983.     

Hydrogenation of methyl oleate in solvents

The hydrogenation of the oleic acid group was investigated with the objective of determining the effect of solvents on the reaction rate and the formation of positional and geometrical isomers. Methyl oleate, either alone or dissolved in one of several solvents, hexane, ethanol,n-butyl ether, or acetic acid, was hydrogenated to an iodine value of about 50 under atmospheric pressure and at 30°C, with palladium-on-carbon and the W-5 form of Raney nickel as catalysts. Hydrogenation with palladium catalyst, with or without solvents, produced 76.6 to 79.1%trans bonds, based on the total double bonds. This is significantly greater than the 67% obtained previously. Hydrogenation products obtained with Raney nickel and solvents contained as little as 20.7%trans bonds at an iodine value of about 50. In two cases thetrans bonds were equal to about one-third the positional isomers. Positional isomers formed extensively when the Raney nickel was used in the absence of solvents and when the palladium catalyst was used. When the Raney nickel and solvents were used large proportions of double bonds were found in the original 9-position. Presented at the 51st Annual Meeting of the American Oil Chemists’ Society, Dallas, Tex., April 4–6, 1960. One of the laboratories of the Southern Utilization Research and Development Division, Agricultural Research Service, U. S. Department of Agriculture.     

Laboratory-scale continuous hydrogenation: Effect of pressure

A laboratory-scale, high-pressure, continuous reactor was used to partially hydrogenate soybean oil with copper catalysts. Effects of pressure on the kinetics of the reaction were studied by conducting experiments in a central composite design. The interaction of pressure (75\s-200 psig) with the other independent variables of temperature (155\s-255 C) and copper concentration (0.15\s-1.85%) was evaluated. Dependent variables studied were linolenate selectivity and formation of trans isomers and conjugated dienes. in addition, effects of pressure up to 500 psig, use of experimental and commercial copper catalysts and comparison of continuous with high-pressure batch rections were investigated. Linolenate selectivity (8\s-10) and trans-isomer formation were not significantly affected by any of the independent variables. Conjugated dienes were eliminated as products of the reaction when pressure was above 200 psig. Experimental copper-silica catalyst gave a 1.6-fold increase in reaction rate over commercial copper catalysts. Presented at ISF-AOCS meeting, New York, April 1980.     

Reuse of copper catalyst in continuous hydrogenation

Continuous hydrogenation of soybean oil using copper catalyst can be improved economically by reusing the catalyst. A hydrogenated oil with an approximate iodine value drop of 25 was attained by regulating the conditions and size of the reactor. Catalyst was removed by centrifuge and recycled. Reaction products were evaluated to determine catalyst activity, linolenate selectivity andtrans formation. By adding 0.2–0.4% fresh catalyst each time, the activity was retained. Linolenate selectivity ranged from 6 to 11 andtrans formation, expressed as specific isomerization, ranged from 0.63 to 0.78.     

Deodorization of vegetable oils: Prediction of trans polyunsaturated fatty acid content

Kinetics of the formation of trans linoleic acid and trans linolenic acid were compared. Pilot plant-scale tests on canola oils were carried out to validate the laboratory-scale kinetic model of geometrical isomerization of polyunsaturated fatty acids described in our earlier publication. The reliability of the model was confirmed by statistical calculations. Formation of the individual trans linoleic and linolenic acids was studied, as well as the effect of the degree of isomerization on the distribution of the trans fatty acid isomers. Oil samples were deodorized at temperatures from 204 to 230°C from 2 to 86 h. Results showed an increase in the relative percentage of isomerized linolenic and linoleic acid with an increase in either the deodorization time or the temperature. The percentage of trans linoleic acid (compared to the total) after deodorization ranged from <1 to nearly 6%, whereas the percentage of trans linolenic acid ranged from <1 to >65%. Applying this model, the researchers determined the conditions required to produce a specially isomerized oil for a nutritional study. The practical applications of these trials are as follows: (i) the trans fatty acid level of refined oils can be predicted for given deodorization conditions, (ii) the conditions to meet increasingly strict consumer demands concerning the trans isomer content can be calculated, and (iii) the deodorizer design can be characterized by the deviation from the theoretical trans fatty acid content of the deodorized oil.     

Control of the product distribution in the hydrogenation of vegetable oils over nickel on silica catalysts

Several nickel on silica catalysts, prepared by impregnation or precipitation/deposition, and a commercial catalyst were tested for activity and selectivity in the sunflower seed oil hydrogenation. An average turn-over frequency of 2.57 s^?1 was found for the catalysts, assuming inaccessibility of nickel in pores smaller than 2 nm and a constant nickel surface concentration poisoned by the reaction mixture. After studying the mass-transfer steps, the effect of temperature (373-453 K) and pressure (101-608 kPa) on reaction rates in the kinetic regime was analyzed, and the corresponding apparent activation energies and reaction orders were obtained. Conclusions on the effect of temperature and pressure on the selectivity to the preferential hydrogenation of polyunsaturates (S_o) and to the formation of trans-isomers ((S_trans)₀) in the kinetic regime were derived from the results. Finally, a similar analysis was carried out when diffusion limitations were known to be present.