V. Höller

Three-phase nitrobenzene hydrogenation over supported glass fiber catalysts: reaction kinetics study

The catalytic properties of Pd and Pt supported on woven glass fibers (GF) were investigated in the three-phase hydrogenation of nitrobenzene (NB). Over all catalysts, a 100 % yield of aniline was attained. The catalytic activity for the best catalysts was two times higher than the activity of commercial Pt/C catalyst traditionally used for liquid‐phase hydrogenation. The intrinsic reaction kinetics were studied and a reaction scheme is suggested. The direct formation of aniline from NB was observed over Pd/ GF with traces of intermediates. Four intermediate products were detected during aniline formation over Pt/GF: nitrosobenzene, phenylhydroxylamine, azoxybenzene, and azobenzene. The Eley-Rideal kinetic model fits the experimental data well. The parameters of the model were determined as a function of initial NB concentration and hydrogen pressure. Pt and Pd supported on GF in woven fabrics are suggested as suitable materials for reactors with a structured catalytic bed in multiphase reactor performance.

Supported glass fibers catalysts for novel multi-phase reactor design

The catalytic properties of Pd and Pt supported on woven glass fabrics were explored for liquid-phase hydrogenation of benzaldehyde as a model for three-phase catalytic reaction. The catalysts demonstrated high activity and are suitable materials to be used in reactors with structured catalytic bed. The main characteristics of catalytic bed are discussed.

Reduction of nitrite-ions in water over Pd-supported on structured fibrous materials

The catalytic hydrogenation of nitrite in water to nitrogen over Pd-supported on different woven fibrous materials is studied. Low porosity carbon fibers, low porosity D-type glass fibers and composite (glass covered by -aluminia) fibers are used. The dispersion of Pd is compared for different supports at various Pd-loadings and correlated with the catalytic activity. The ammonia as an undesired by-product was also observed and the main parameters suppressing its formation are discussed. A reactor concept based on woven fibrous catalysts is suggested and the main design parameters for the technical application are estimated.

Structured multiphase reactors based on fibrous catalysts: nitrite hydrogenation as a case study

A reactor concept designed as a bubble column staged with fibrous catalytic layers is tested on pilot-scale for the redn. of nitrite to N by H. CO2 is used to neutralize the hydroxide ions produced during hydrogenation of nitrite. The effective reaction rate was found to depend on the superficial gas velocity ug0. The fibrous catalysts demonstrated a high selectivity towards nitrogen. The influence of the mass transport on the effective kinetics is discussed and the volumetric liq.-solid mass transfer coeff. kSaS is estd. as a function of the superficial gas velocity ug0. The selectivity was found to be independent of the hydrodynamics.

Fibrous structured catalytic beds for three-phase reaction engineering Hydrodynamics study in staged bubble columns

Woven fibrous materials are proposed as structured catalysts for three-phase catalytic reactors. The design of a catalytic bed arranged as a plate bubble column is discussed. The hydrodynamic parameters, like pressure drop and liquid hold-up were found to depend on the woven structure of the fibrous layers and are shown to be a function of the distance between the threads in the fibres.

Acoustic and visual study of bubble formation processes in bubble columns staged with fibrous catalytic layers

High-speed images of bubbly flow coupled with simultaneous passive acoustic measurements were carried out in a bubble column staged with structured fibrous catalysts. Local observations made with a high-speed camera system allow a detailed understanding of the influence of fabric structure on bubble formation processes and the determination of the Sauter bubble diameter. With acoustic measurements, the building frequency of bubble swarm formation is identified to be a linear function of the superficial gas velocity. Due to bubble size and building frequency of bubble swarm the percentage of simultaneously operative sites (holes at which bubbles were formed simultaneously) is calculated.