Results of the last decade with respect to the selective hydrogenation of hydrocarbons with multiple unsaturation (dienes and alkynes) over heterogeneous palladium catalysts are reviewed. Factors such as metal dispersion, carbon deposits, and the use of promoters and additives controlling catalytic activities and chemo-, regio- and stereo-selectivity are discussed. A detailed treatment of the status of the selective removal of hydrocarbon impurities with multiple unsaturation from industrial feedstocks is also given.

Hydrogenation of carbon–carbon multiple bonds: chemo-, regio- and stereo-selectivity

Applications Rosaria Ciriminna,† Alexandra Fidalgo,‡ Valerica Pandarus, Franco̧is Beĺand, Laura M. Ilharco,*,‡ and Mario Pagliaro*,† †Istituto per lo Studio dei Materiali Nanostrutturati, CNR, via U. La Malfa 153, 90146 Palermo, Italy ‡Centro de Química-Física Molecular and IN-Institute of Nanoscience and Nanotechnology, Instituto Superior Tećnico, Complexo I, Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal SiliCycle Inc., 2500, Parc-Technologique Boulevard, Quebec City, Quebec G1P 4S6, Canada

The Sol–Gel Route to Advanced Silica-Based Materials and Recent Applications

Catalysis is a multidisciplinary science that serves a broad range of industries covering specialty, fine, intermediate, commodity and life science chemicals. Catalysts are commonly used for the hydrogenation of alkenes, alkynes, aromatics, aldehydes, ketones, esters, carboxylic acids, nitro groups, nitriles and imines. These materials may be in the form of bio-, homogeneous, heterogeneous and heterogenised homogeneous catalysts where each type has its own special properties that can be adjusted for their optimal use. Heterogeneous catalysts are commonly used in the form of powders for slurry and fluidized bed reactions or as formed bodies for fixed bed hydrogenations. The addition of promoters and adjustments in particle size and porosity allow these catalysts to be fine tuned for specific reactions. Homogeneous catalysts are also very flexible where the choice of active metal, ligands and reaction conditions can lead to highly selective hydrogenations. The separation problems associated with homogeneous catalysts have led to the development of heterogenised homogeneous catalysts via the fixation of the active complexes on organic or inorganic supports or via application in biphasic systems. While there have been some successes in this area, there still remains a considerable amount of work to be done. Biocatalysts are of particular interest for the formation of enantiopure compounds. New developments in cofactor regeneration and raised substrate tolerance help to implement enzymatic reduction reaction on industrial scale. Efficient reductases are still needed to broaden this technology for further applications. It is expected that the development of these catalysts will be accelerated through the use of high throughput screening and that the testing of catalyst libraries will allow for the rapid selection of both catalyst and conditions for targeted processes. Reactor technology will also change as continuous processes slowly replace the workhorse batch ones for the manufacture of large-scale chemicals. This paper provides an overview of the above-mentioned topics for the industrially relevant hydrogenations that have been brought on stream over the last 20 years, as well as, the upcoming processes that will set the future trends in chemical industry.

New developments in hydrogenation catalysis particularly in synthesis of fine and intermediate chemicals

Hardening of vegetable oils is reviewed from an engineering point of view. The present review focuses on kinetics of the hydrogenation and relevant transport and adsorption steps. It aims to contribute to accelerate new research to improve substantially on selectivities in general and a decrease of trans fatty acid content in particular. From a comprehensive literature review, we concluded the absence of reliable, mechanistically based kinetic rate expression. Moreover, transport limitations, both intraparticle and interfacial, cannot be excluded from the vast majority of available experimental data. Therefore, future research should focus on the development of intrinsic kinetic rate expressions, which may subsequently contribute to develop new and improved hydrogenation catalysts.

Heterogeneous hydrogenation of vegetable oils: A literature review

Hydrogenated vegetable oils contain of trans fatty acids. Because of the increased health concern about trans fatty acids, new hydrogenations have been studied to seek ways for substantial reduction of the trans fatty acids in the hydrogenated vegetable oils. This paper reviews new hydrogenation processes such as electrocatalytic hydrogenation, precious catalyst hydrogenation, and supercritical fluid state hydrogen, which have shown promising results for the reduction of trans fatty acids below the level of 8%. This paper also reviews the recently introduced hydeogenation technique for high accumulation of conjugated linoleic acids, beneficiary functional components. The hydrogenated vegetable oils with high quantity conjugated linoleic acid might provide the possibility for the utilization of hydrogenated oils as health-prompting food ingredients.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1541-4337.2005.tb00069.x

Hydrogenation for Low Trans and High Conjugated Fatty Acids

Palladium supported on alumina was used to hydrogenate soybean and canola oil. Previous literature reports indicated that palladium forms moretrans isomers than nickel. At 750 psig, 50 ppm palladium, and at 70 C, only 9.4%trans were formed when canola oil was hydrogenated to IV 74. In general, high pressure and low temperature favored lowtrans formation with no appreciable loss in catalyst activity. The effect of pressure, temperature and catalyst concentration on reaction rate,trans formation and selectivity is presented. A survey of various catalyst supports is discussed. Apparent activation energies of 6.3 to 8.9 kcal/mol were obtained; they are in good agreement with values reported in the literature.

Catalytic behavior of palladium in the hydrogenation of edible oils

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.

Heterogeneous catalytic hydrogenation of canola oil using palladium

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.

N. Hsu

Papers

Catalytic behavior of palladium in the hydrogenation of edible oils

Heterogeneous catalytic hydrogenation of canola oil using palladium

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