The hydrogenation kinetics of 2,2-dimethylol-1-butanal (TMP-aldol) and 2,2-dimethylol-1-propanal (TME-aldol) over a supported nickel catalyst were determined with experiments carried out in a batchwise operating autoclave at 50-90 degreesC and 40-80 bar hydrogen. Water was used as the solvent. TMP- and TME-aldol were hydrogenated with 100% selectivity tu the corresponding triols. The effects of the catalyst activation procedure and the formaldehyde concentration on the hydrogenation kinetics were studied with thermogravimetry, X-ray photoelectron spectroscopy, and hydrogenation experiments. Catalyst reduction at a high temperature (400 degreesC) under hydrogen flow was favorable because of a more effective reduction of nickel oxides. Formaldehyde had a considerable retarding effect on the aldol hydrogenation: the hydrogenation rate was low until all of the formaldehyde was hydrogenated to methanol. The hydrogenation rate of TME-aldol was found to be significantly lower than that of TMP-aldol at low temperatures and pressures (60 degreesC and 40 bar), whereas equally high rates for both aldol molecules were observed at the highest temperature and pressure studied. A kinetic model including the inhibitory effect of formaldehyde as well as real hydrogen solubility data was proposed for the aldol hydrogenation. The model is comprised of adsorption, desorption, and surface reaction steps. the rate equations based on the model were able to describe the experimentally recorded hydrogenation kinetics of TMP- and TME-aldol.

Butyraldehyde was aldolized with formaldehyde over a weakly basic anion-exchange resin catalyst in aqueous solvent in a batch reactor operating at atmospheric pressure and at temperatures 50–70°C. The reaction mixture was a liquid–liquid–solid system, an emulsion, the phase equilibria of which were studied through chemical analysis of the organic and aqueous phase as well as of the mixed emulsion. Simplified rate equations were derived starting from molecular reaction mechanisms on the catalyst surface. A liquid–liquid reactor model for the fitting of the experimental results was developed on the basis of the rate equations and the phase equilibria. The model described very well the experimental data.

Aldols are important intermediates in the production of polyols, which are raw material for lubricants, surface coatings, and synthetic resins. The activities and selectivities of gel-type and macroporous anion-exchange resin catalysts in the aldolization of butyraldehyde with formaldehyde in an aqueous environment were investigated at 60 degreesC. The experiments were carried out batchwise in a stirred glass reactor, and the reaction products were analyzed with high performance liquid chromatography. Two main products were observed, 2-ethyl-3-hydroxy-2-hydroxy-methylpropanal (trimethylolpropane aldol) and 2-ethylpropenal (ethylacrolein). The product ratio was strongly dependent on the catalyst. The selectivity with respect to trimethylolpropane aldol varied within the range 2.7-7.3 for the catalysts investigated. Systematic kinetic experiments were carried out at 50-70 degreesC with the gel-type resin catalyst displaying the highest aldol selectivity. A kinetic model based on molecular mechanisms was able to describe the product distribution.

The hydrogenation kinetics of 2,2-dimethylol-1-butanal. (TMP-aldol) over a supported nickel catalyst was determined with experiments carried out in a batchwise operating autoclave at 50-90 degrees C and 40-80 bar hydrogen. The reaction mixture was analyzed with gas and liquid chromatography. It was found that TMP-aldol can be hydrogenated with a 100% selectivity to the corresponding triol, trimethylolpropane. The effects of the catalyst; activation procedure and the formaldehyde concentration on the hydrogenation kinetics were studied. The hydrogenation experiments revealed that catalyst reduction at a high temperature (400 degrees C) under hydrogen flow was favorable for the catalyst performance. The reason was a more effective reduction of nickel oxides which was confirmed with thermogravimetry and X-ray photoelectron spectroscopy. The presence of formaldehyde had a considerable retarding effect on the aldol hydrogenation kinetics: the hydrogenation rate was low until all of the formaldehyde was hydrogenated to methanol. The retarding effect was more prominent at higher temperatures than at lower temperatures, which indicates that formaldehyde forms oligomers on the catalyst surface as the temperature increases. A kinetic model was proposed for the aldol hydrogenation. The model includes adsorption, desorption, and surface reaction steps as well as the inhibitory effect of formaldehyde on the aldol hydrogenation kinetics. The model was able to describe the experimentally recorded hydrogenation kinetics of TMP-aldol in the presence and in the absence of formaldehyde.

Butyraldehyde was aldolized with formaldehyde at 40–80°C over an anion-exchange resin catalyst in aqueous and methanolic solutions. The reaction mixture was analyzed with gas and liquid chromatography as well as nuclear magnetic resonance (NMR) spectroscopy. Two main products were detected: 2-ethyl-3-hydroxy-2-hydroxymethylpropanal (trimethylolpropane aldol) and 2-ethylpropenal (ethylacrolein). The molar ratio of the main products was dependent on the formaldehyde-to-butyraldehyde ratio and the solvent composition but independent of the temperature. The yield of 2-ethyl-3-hydroxy-2-hydroximethylpropanal increased with increasing formaldehyde-to-butyraldehyde ratio and with increasing water-to-methanol content of the reaction mixture. Besides the main reactions, self-condensation and acetalization of butyraldehyde were detected as side reactions of minor importance. The self-condensation of butyraldehyde was suppressed in the presence of formaldehyde and the acetalization of butyraldehyde was minimized by the use of water as reaction solvent. Rate equations were derived starting from molecular reaction mechanisms and adsorption of formaldehyde on the catalyst structure. It turned out that the rate equations can predict the distribution of the main products.

An alternative clean production technology was developed for the synthesis of two triols, trimethylolpropane (2,2-di(hydroxymethyl)butan-1-ol) and trimethylolethane (2,2-di(hydroxymethyl)propan-1-ol) starting from formaldehyde, propionaldehyde and butyraldehyde; the technology is based on the use of solid heterogeneous catalysts in the key process steps, aldolization and aldol hydrogenation. Catalyst screening and kinetic experiments with propionaldehyde and butyraldehyde showed that the desired aldols can be obtained with a high yield and selectivity when anion exchangers with amine groups are used as heterogeneous catalysts and the reaction is carried out in aqueous environment. Suitable reaction temperatures are 50-80 degrees C with formaldehyde:propion or butyraldehyde ranging from 3:1 to 4:1. In the second process step, the excess of formaldehyde was separated from the reaction mixture with atmospheric distillation in the presence of excess of water. Catalyst screening and kinetic experiments showed that nickel-chromium and copper-chromium are the most suitable catalysts for the aldol hydrogenation. The experiments carried out at 50-80 degrees C and 40-80 bar hydrogen gave 100% yields of trimethylolpropane and trimethylolethane. A process scheme for the continuous production of trimethylolpropane and trimethylolethane was proposed.

Generalized mass balance models were derived for semibatch liquid–liquid reactors, which are frequently used in the production of fine and speciality chemicals. The model comprises the reaction kinetics, liquid–liquid equilibria as well as interfacial mass transfer effects. The reactor model was applied on a case study, homogeneously catalyzed synthesis of diols through aldol condensation and Cannizzaro reaction. Rate equations for the process were obtained by applying steady-state approximations on ionic reaction intermediates. The rate equation were incorporated into the mass balances and tested with experimental kinetic data. The model was able to imitate the experimental behaviour of the two-phase system.

The effect of alumina pretreatment on the performance of alumina supported nickel catalysts was demonstrated in gas phase hydrogenation of toluene to methylcyclohexane. The state of the alumina was changed from pure gamma to pure theta phase through various heat treatments in air. The catalysts were prepared from vapor phase by saturating the accessible binding sites on the pretreated alumina with the nickel precursor. The highest number of active sites for hydrogenation was observed for catalysts prepared on alumina having an incomplete phase transition and a theta/gamma alumina phase ratio between 0.5 and 10. Results from temperature programmed desorption (TPD) studies revealed that a maximum in weakly chemisorbed hydrogen as well as in total amount of desorbed hydrogen was found for the same catalysts. By hydrogen chemisorption studies the total hydrogen uptake was found to correlate with the observed hydrogenation maximum. It is suggested that both the chemical and physical properties of the alumina influence the activity. An optimal metal-support interaction and structural defects on the alumina due to the phase transition can explain the observed maximum in the number of active sites and in hydrogen uptake.

The Atomic Layer Epitaxy (ALE) technique was originally developed for thin film production.1 In this paper we present an extension of ALE to the production of atomically controlled surfaces on porous materials. For producing W/Al2O3, WOCl4 was chemisorbed from the vapor phase onto the support. In ALE, each surface reaction is allowed to proceed to saturation. The regulation of the metal content is based on different saturation levels. Saturation levels of tungsten between 3 and 12 wt-% were obtained by varying the alumina preheating temperature and the reaction temperature between 150 and 400-degrees-C. W/Al2O3 samples prepared by ALE and conventional impregnation were compared. It was observed that the tungsten species were evenly distributed throughout the porous alumina particles in both of the preparation methods used. In all samples tungsten was well dispersed, XRD amorphous and present as W(VI) compounds.

The gas phase hydrogenation of toluene to methylcyclohexane on a commercial Ni/Al2O3 catalyst was investigated in a differential reactor operating at atmospheric pressure and temperatures between 150 and 210°C. The results revealed that the hydrogenation kinetics is of the order 1–3 with respect to hydrogen at the actual temperature interval and that the reaction order increases with temperature. The reaction order with respect to toluene is negative. The reaction rate exhibited a maximum at approximately 170°C. The rate maximum is explained by the escape of catalytically active hydrogen from the Ni-surface at the highest reaction temperatures, which was confirmed by temperature-programmed desorption studies and chemisorption studies of hydrogen. The kinetics was modelled with an empirical power-law rate expression and with three mechanistic rate models. The latter were based on the assumption of rapid competitive adsorption steps of toluene and hydrogen and rate determining surface reaction steps involving addition of hydrogen atoms to adsorbed toluene and partially hydrogenated intermediate molecules. The best fit to the experimental data were provided by two models; one implying simultaneous addition of hydrogen atoms to adsorbed toluene and the other, being more probable from a mechanistic point of view, implying sequencial addition of hydrogen atoms to adsorbed toluene.

The gas-phase hydrogenation of toluene to methylcyclohexane was studied on a noncommercial supported nickel catalyst. The reaction kinetics was investigated in a differential reactor operating at atmospheric pressure and temperatures between 120 and 200-degrees-C. The results revealed that the hydrogenation kinetics is of the order 0.5-2 with respect to hydrogen and that the reaction order increases with temperature. The reaction order with respect to toluene increases from slightly negative values to zero order over the temperature domain studied. The kinetics was modeled with an empirical power-law rate expression and with two mechanistic rate models. The latter models were based on the assumption of rapid competitive adsorption steps of toluene and hydrogen and rate-determining surface reaction steps involving addition of hydrogen atom pairs to adsorbed toluene and partially hydrogenated intermediate molecules. The surface coverages, the activation energy, and the optimal reaction temperature giving the maximum reaction rate were estimated using parameter values obtained from one of the mechanistic models.