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This article reports on the influence of elevated pressure and catalyst particle lyophobicity at particle concentrations up to 3 vol % on the hydrodynamics and the gasto-liquid mass transfer in a slurry bubble column. The study was done with demineralized water (aqueous phase) and Isopar-M oil (organic phase) slurries in a 0.15 m internal diameter bubble column operated at pressures ranging from 0.1 to 1.3 MPa. The overall gas hold-up, the flow regime transition point, the average large bubble diameter, and the centerline liquid velocity were measured along with the gas-liquid mass transfer coefficient. The gas hold-up and the flow regime transition point are not influenced by the presence of lyophilic particles. Lyophobic particles shift the regime transition to a higher gas velocity and cause foam formation. Increasing operating pressure significantly increases the gas hold-up and the regime transition velocity, irrespective of the particle lyophobicity. The gas-liquid mass transfer coefficient is proportional to the gas hold-up for all investigated slurries and is not affected by the particle lyophobicity, the particle concentration, and the operating pressure. A correlation is presented to estimate the gas-liquid mass transfer coefficient as a function of the measured gas hold-up: k l a l =e g ¼ 3:0

The selectivity and conversion of the sulfuric acid-catalyzed Beckmann rearrangement of cyclohexanone oxime, dissolved in cyclooctane, to e-caprolactam are determined in a microreactor for conditions with a high concentration of e-caprolactam. The microreactor consists of a low-temperature mixing zone followed by a high-temperature reaction zone. The mixing is conducted in a splitand-recombine micromixer and a microchannel at 65°C, followed immediately by a second microchannel at 100-127°C to obtain complete conversion. Under these conditions a selectivity of 99 % is achieved. The residence time of the reactants in the microreactor setup is about 10 s. In literature, a selectivity of about 95 % for the same reaction in a similar setup is reported, but at a uniform temperature of 120-130°C for mixing and reaction. So, suppressing the reaction during mixing is a major tool to enhance the selectivity to e-caprolactam.

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Reaction kinetics of the gas-phase Beckmann rearrangement of cyclohexanone oxime to ε-caprolactam was studied over a NbO x /SiO2 catalyst in a fixed-bed reactor. Kinetic measurements were carried out by variation of cyclohexanone oxime partial pressure and reactor temperature in the range of 5 to 80 hPa and 360 to 420 °C, respectively. It was found that ethanol, used as solvent in addition to toluene, is essential for high catalytic performance. Reaction rates as a function of cyclohexanone oxime partial pressure display Langmuir-type behavior, but the results could not be interpreted satisfactorily on the basis of a Langmuir–Hinshelwood mechanism. Another kinetic scheme is proposed, involving a kinetic adsorption step for cyclohexanone oxime instead of an adsorption equilibrium. Activation energies for the adsorption step and for the Beckmann rearrangement reaction were found to be 154 and 68 kJ·mol–1, respectively. Substitution of ethanol by alcohols with longer chain length (e.g., n-hexanol) resulted in significantly higher ε-caprolactam selectivities.