Hydrogenation Kinetics of 2,2-Dimethylol-1-butanal to Trimethylolpropane over a Supported Nickel Catalyst

Abstract

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 °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 °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.

Parallel hydrogenation of 2,2‐dimethylol‐1‐butanal and formaldehyde over supported NiCr and CuCr catalysts

“…The product desorption step is assumed to be irreversible and very rapid. The details are described in a previous paper 9. The resulting model describes the data well, but should probably be regarded as empirical, rather than truly mechanistic, since it requires a rare termolecular rate determining step, and is based on an equilibrium coverage of the formaldehyde species.…”

“…The adsorption equilibrium constants were assumed to diminish as a function of the coverage of formaldehyde. By assuming further that the adsorption equilibrium constants obey the law of van't Hoff and the rate constants that of Arrhenius, the lumped rate parameters become 9 …”

“…The mass balance of hydrogen was not included, since its pressure was kept constant and the value of the saturation concentration of hydrogen in liquid phase was used in kinetic modelling 9…”

Catalytic Synthesis of Trimethylolpropane in the Presence of Basic Ionic Liquid

“…1 Generally, TMP Vol.31 is synthesized via a two-step process, namely, an Aldol condensation of formaldehyde and butyraldehyde followed by a Cannizzaro condensation 2 or catalytic hydrogenation. 3,4 The catalytic hydrogenation method usually suffers from high reaction temperatures and high H2 pressure, requiring robust equipment for the dangerous operating conditions. In contrast, the Cannizzaro condensation is more popular because of its gentle reaction conditions and efficient product separation.…”

Hydrogenation of 2,2-Dimethylol-1-butanal and 2,2-Dimethylol-1-propanal to Trimethylolpropane and Trimethylolethane over a Supported Nickel Catalyst

“…Previous studies of our group − have shown that it is possible to replace the conventional synthesis route based on a soluble alkali catalyst by weakly basic ion-exchange resins and Ni catalysts. In the first step, aldol condensation takes place on the ion exchanger and the Cannizzaro reaction, in which yield of sodium formate is completely prevented.…”