Miroslav Stanković

The Influence of the Isomerization Reactions on the Soybean Oil Hydrogenation Process

Abstract Soybean oil has been partially hydrogenated in the presence of a synthesized nickel catalyst, in an industrial reactor, under the standard industrial working conditions. The GC measurements of fatty acids in the investigated oil and hydrogenated products have been performed. The total trans isomers content has been determined by the IR spectroscopy. The model is established, which could be useful for the characterization of hydrogenation and isomerization reactions of poly-unsaturated acids. Iteration procedure, incorporating numerical simulation in each step is used to calculate rate constants of the proposed model from the comparison of the experimental and calculated kinetic runs. By the simultaneous treatment of the kinetic runs for the fatty acids composition and trans -isomer content, the 12 rate constants of individual hydrogenation and isomerization reaction steps are obtained.

The state of nickel in the silver modified NiMg/SiO2 vegetable oil hydrogenation catalysts

Two series of silver modified Ni-Mg materials were synthesized by precipitation-deposition on SiO2 support derived from two silica sources: diatomite activated at 800°C (Series a; Mg/Ni = 0.1 and SiO2/Ni = 1.07) and synthetic water glass (Series b; Mg/Ni = 0.1 and SiO2/Ni = 1.15). The modification with silver was made at three molar Ag/Ni ratios, namely 0.0025, 0.025, and 0.1. The effects of the source of the silica support and the silver presence and content on the nickel state in the silver modified reduced-passivated NiMg/SiO2 precursors of the vegetable oil hydrogenation catalyst were established by X-ray diffraction and X-ray photoelectron spectroscopy techniques. The passivation procedure was applied in order to protect the metallic nickel particles from further oxidation. The crystallization of the formed nickel hydrosilicate phases depends on the source of the silica support, more expressed in the diatomite supported samples. It was shown that the silver modification of the NiMg/SiO2 precursors enhances the reduction of the nickel hydrosilicates accompanied by formation of relatively smaller metallic nickel particles, more pronounced in the water glass supported precursors. The increase of the silver content in the water glass deposited samples is responsible for the metallic nickel dispersion increase. The higher content of the Ni0 particles on the surface of the diatomite deposited samples is in accordance with the higher stability of the larger metallic nickel crystallites to oxidation during the passivation step. On contrary, higher dispersed Ni0 particles on the surface of the water glass supported samples are more susceptible to the oxida

Supported Nickel-Based Catalysts for Partial Hydrogenation of Edible Oils

Nickel-based catalysts, supported on diatomite, silica gel and perlite, with high nickel loadings, have been prepared by precipitation-deposition method. Various nickel precursor salts were used for the preparation of catalyst precursors. In the precursor state, the catalysts were characterized using nitrogen physisorption, mercury porosimetry, infrared, and X-ray diffraction spectroscopy. The reducibility of catalyst precursors was evaluated using hydrogen temperature programmed reduction. Hydrogen chemisorption and X-ray photoelectron spectroscopy measurements were performed with the aim of characterizing the chemical state of the catalyst precursors. This research was focused on the study of some major factors on the state, dispersion and reducibility of a deposited Ni phase by the combined use of mentioned experimental techniques. We have examined the influence of the nature of support and the use of modifiers on activity of nickel-based catalysts in the partial hydrogenation of sunflower and soybean oils. Nitrogen physisorption and mercury porosimetry data showed that synthesis operating conditions and pore structure of supports have a profound effect on the textural properties of catalyst precursors. The analysis of infrared and X-ray diffraction spectra showed the existence of chemical species and phases which indicate the different extent of interaction between the support and the active metal. Temperature programmed reduction study revealed that the reduction features depend on the identity of the nickel precursor salt and its interaction with the support. A stronger interaction of the supported Ni phase with support hinders the reduction of catalyst precursors. Hydrogen chemisorption results showed the presence of nickel crystallites varying from 5 to 47 nm in size. The X-ray photoelectron spectroscopy data confirmed the formation surface species with different strength of interaction and different nickel crystallite sizes. The hydrogenation results showed significant differences, depending on the support and the modifier, as well as structural characteristics of reduced catalyst precursors. The results show the importance of modifiers in the control of the activity and selectivity of the partial hydrogenation

Kinetic Analysis of Nonisothermal Reduction of Silica-Supported Nickel Catalyst Precursors in a Hydrogen Atmosphere

A series of silica-supported nickel catalyst precursors was synthesized with different SiO2/Ni molar ratios. Reduction of Ni catalyst precursors with different SiO2/Ni molar ratios under a hydrogen atmosphere was investigated at different heating rates. Kinetic parameters were determined using Kissinger–Akahira–Sunose isoconversional and invariant kinetic parameter methods. It was found that for all molar ratios, the apparent activation energy (Ea) is practically constant in the conversion range of 0.20 ≤ α ≤ 0.80. In the considered conversion range, following values of Ea were found: 134.5 kJ mol−1 (SiO2/Ni = 0.20), 139.6 kJ mol−1 (SiO2/Ni = 0.80), and 128.3 kJ mol−1 (SiO2/Ni = 1.15). It was established that the reduction of Ni catalyst precursors with different SiO2/Ni molar ratios is a complex process and can be described by the Šesták–Berggren autocatalytic model. It was found that the reaction is more Langmuir–Hinshelwood type, as hydrogen dissociates rapidly on surface nuclei and the dissociated hydrogen reacts with the Ni–O active system. It was concluded that the reduction process proceeds through bulk nucleation, which is a dominant mechanism, where three-dimensional growth of crystals with polyhedron-like morphology exists. It was found that the Ni/Si ratio decreases after the reduction process. This has been explained by low Ni and higher Si surface concentrations. It has been disclosed that Ni dispersion decreases.

Perlite as a potential support for nickel catalyst in the process of sunflower oil hydrogenation

Investigation was conducted in order to elucidate the possibility of using perlite as support for preparation of nickel based precursor catalyst, potentially applicable in vegetable oil hydrogenation process. On three differently prepared expanded perlite, nickel catalyst precursors with identical Ni/SiO2 = 1.1 and Ni/Mg = 10/1 ratios were synthesized by precipitation-deposition method. Different techniques, SEM micrography, He-pycnometry, calcimetry, Hg-porosimetry, N2-physisorption, H2-chemisorption and temperature programmed reduction, were used for characterization of obtained samples. Determining the precursor texture, morphology and reducibility shows a successfully deposited nickel phase on perlite support with promising properties for vegetable oil hydrogenation. Chosen precursor was reduced and passivated in paraffin oil and the obtained catalyst showed significant catalytic activity in the test of sunflower oil hydrogenation.

Hydrogenation of Soybean Oil over Ag-Ni/Diatomite Catalysts. Effect of Silver Content on the Cis/Trans Isomerization Selectivity

Silver promoted nickel catalysts supported on diatomite were prepared by precipitation method. Characterization of the catalysts prepared with different silver contents (0.1-4.0 wt%) included AAS, XRD, Hg porosimetry, BET and H2 chemisorption measurements. The catalytic activity and selectivity were tested by soybean oil (SBO) hydrogenation under pressure of hydrogen of 0.16 MPa at 160 °C. Fatty acids (FA) contained in hydrogenated SBO were analysed by gas chromatography. Trans fatty acid (TFA) content in hydrogenated SBO varied considerably depending of the silver content in prepared catalysts.

Nickel Catalysts on Porous Ceramic Supports for the Reaction of Partial Oxidation of Propane to CO and H2

In this paper synthesis, textural and structural properties as well as selectivity of Ni based catalysts for partial oxidation of propane to CO and H2 are given. The influence of aluminosilicate and magnesia based porous ceramic supports on catalyst performance is emphasized. The influence of concentration of impregnation solution, number of successive impregnations and nature of modifier was investigated. The catalytic test was performed in order to define the catalyst with the highest selectivity toward CO and H2 while the presence of side-products like CO2, CH4, and coke as well as unreacted C3H8 are reduced to minimum. All synthesized catalysts samples were dominantly macroporous. The selectivity of catalysts increased with presence of modifiers in the following order: CaO < MgO < Al2O3. The selectivity of studied catalysts is governed mainly by two structural parameters: nickel loading and nickel crystallite size. The comparison of the best performing aluminosilicate and magnesia supported catalysts with Al as modifier revealed that the latter express somewhat lower selectivity particularly toward CO.