Jyrki Kuusisto

Solvent effects in enantioselective hydrogenation of 1-phenyl-1,2-propanedione

Abstract Solvent effects in enantioselective hydrogenation of 1-phenyl-1,2-propanedione ( A ) were investigated in a batch reactor over a cinchonidine modified Pt/Al 2 O 3 catalyst. The effect of different solvents, binary solvent mixtures and solvent dielectric constant on regio- and enantioselectivity as well as on the hydrogenation rate were studied. The hydrogen solubility in different solvents and the dielectic constants of solvent mixtures were measured. The highest enantiomeric excesses (ee) of ( R )-1-hydroxy-1-phenylpropanone ( B ) (65%) were obtained in toluene. The ee decreased non-linearly with an increasing solvent dielectric constant being close to zero in methanol. The role of the reactant conformation in different solvents was evaluated by quantum chemical calculations and the role of the Open(3) conformer of the modifier, cinchonidine was discussed. The dependence of ee on the dielectric constant could not solely be attributed to the abundance of the Open(3) conformer of cinchonidine in the liquid phase. A possible involvement of additional factors was proposed and discussed. The non-linear dependence of the ee on the dielectric constant was included in a kinetic model to describe quantitatively the variation of the ee in different solvents.

Modelling of kinetic and transport effects in aldol hydrogenation over metal catalysts

Abstract This work concerned the pathway from intrinsic kinetics to diffusion-affected kinetics in catalytic hydrogenation. Kinetics and mass transfer effects in the liquid-phase hydrogenation process of an aldol (2,2-dimethylol-1-butanal) to the corresponding triol (trimethylolpropane) were studied in a semibatchwise operating autoclave, where finely dispersed and large catalyst particles were used. The intrinsic hydrogenation kinetics was determined with the crushed catalyst particles at 40– 80 bar H 2 and 50–90°C in isobaric experiments. A kinetic model based on competitive adsorption and surface reaction between the aldol and hydrogen was successfully fitted to the experimental data. Physical measurements of the density, viscosity as well as hydrogen solubility in the reaction mixture were carried out. The measurements revealed that the governing factor in the physical data is the temperature dependence, while the composition dependence during the hydrogenation is a minor factor under the actual experimental conditions. The models for intrinsic kinetics, physical properties and mass transfer effects were combined to describe the behaviour of large catalyst particles. It turned out that the theoretically developed model agreed well with experimental observations made with large-size catalyst particles. The approach is suitable for the scale-up of catalytic hydrogenation processes.

Residence time distributions from CFD in monolith reactors-combination of avant-garde and classical modelling

Abstract Computational fluid dynamics (CFD) was used to investigate the flow pattern and flow distribution in a recirculating monolith reactor system designed for catalytic three-phase processes. The information from the CFD model was transferred to a simplified simulation model, where the monolith and the mixing system were described by parallel tubular reactors coupled to a mixing space. The model was based on the following principles: the mixing space and the monoliths were in fully dynamic states, but the concept of differential reactors was applied on the monolith channels. Thus the simplified model consisted of ordinary differential equations for the gas and liquid phases. The modelling concept was successfully illustrated by a case study involving complex reaction kinetics: hydrogenation of citral to citronellal, citronellol and 3,7-dimethyloctanol over cordeorite-supported nickel on alumina washcoat. A comparison of experimental results with the model predictions revealed that the proposed approach is reasonable for the description of three-phase monolith reactors.

Studies on The Ultrasonic Enhancement of The Catalytic Activity in The Hydrogenation of Citral

Acoustic energy is mechanical by its nature. Cavitation bubbles are formed, provided that the intensity of ultrasonic field is sufficiently high. Cavitation close to the liquid-solid interface differs from that in pure liquid. Different mechanisms for the effects of cavitation close to the surfaces have been proposed: microjet impact and Shockwave damage (Suslick, 1990, Suslick et al. 1987). Heterogeneous catalysis involving suspended solid particles in liquid is accelerated by the use of acoustic irradiation. However, studies in the regenerating effect of acoustic irradiation in catalysts are sparse. The localized erosion and grinding caused by these phenomena are responsible for ultrasonic cleaning, generating newly exposed, highly active surface. In this work, we studied on-line acoustic irradiation in batchwise, three-phase hydrogenation of citral to citronellal and citronellol over a Raney nickel catalyst. Citral can be used in the preparation of citronellol (referred as OL hereafter) or citronellal (referred as AL hereafter), to be utilized by parfume industry etc. due to their pleasant odor (Maki-Arvela et al, 1997; Salmi et al, 2000).

Hydrogenation of 2,2-dimethylol-1-butanal and 2,2-dimethylol-1-propanal to trimethylolpropane and trimethylolethane over a supported nickel catalyst

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 °C and 40−80 bar hydrogen. Water was used as the solvent. TMP- and TME-aldol were hydrogenated with 100% selectivity to 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 °C) 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 ...