Macro-and micromixing in a continuous flow Taylor-vortex reactor with novel ribbed rotors were investigated and compared to the features of a classical cylindrical rotor. The characterisation was performed in a wide hydrodynamic range (40 < Ta < 2500 and 0.03 < Re < 0.51) through tracer experiments and the analysis of the rotor power consumption. Additionally, the flow patterns were visualised by using a rheoscopic fluid. The results show that the novel rotors equipped with ribs immobilise and stabilise the vortices. As compared to cylindrical rotors, micromixing is clearly enhanced while axial dispersion can be simultaneously reduced. Through the use of ribbed rotors, the operational window can be broadened considerably, in which the reactor runs at very low or moderate extent of macromixing.

A series of (azidomethyl)silanes [Me 3 SiCH 2 N 3 (1b), Me 2 Si(CH 2 N 3 ) 2 (2b), MeSi(CH 2 N 3 ) 3 (3b), (CH 2 ) 4 Si(CH 2 N 3 ) 2 (4b), and (CH 2 ) 5 Si(CH 2 N 3 ) 2 (5b)] was synthesized, starting from the corresponding (chloromethyl)silanes 1a-3a or (iodomethyl)silanes 4a and 5a. Compounds 1b-5b were characterized by NMR, IR, and Raman

The single-stage self-condensation and subsequent hydrogenation of acetone to methyl isobutyl ketone (MIBK) in the gas phase was carried out using catalysts consisting of hydrogenating metals supported on active carbon (Me/C). The reaction was conducted in a continuously operated, ideally backmixed Berty reactor at 1 MPa and 623 K. Platinum, palladium, nickel, and copper were applied as metal components, and their hydrogenation activity decreased in the order Pt > Pd > Ni > Cu. The impact of the hydrogenation reactions in the reaction network can also be enhanced by increasing the molar ratio of hydrogen to acetone in the feed, and by raising the metal content of the Me/C catalysts. A low hydrogenation activity negatively affects the acetone conversion and promotes the production of mesityl oxide. Hydrogenation conditions being too severe may favor the unwanted hydrogenation of acetone to 2-propanol and of MIBK to methyl isobutyl carbinol, but this effect is less detrimental to the MIBK selectivity than an unsufficient hydrogenation activity. The best performance showed a Pt/C catalyst with 0.5% m/m Pt and a Ni/C catalyst with a higher Ni loading (2.71% m/m); the optimum H 2 /acetone feed ratio was 0.5, which is the stoichiometric value for the idealized formation of MIBK from acetone. Despite the higher metal content required, the Ni/C catalyst allows for a considerable reduction of the costs for catalyst production.

No abstract

An unusual temporal behavior of the by-product spectrum, as well as the temperature profiles of a commercial phthalic anhydride reactor, indicated a non-typical change of the incumbent catalyst. In order to understand these observations, catalyst samples were taken from this reactor and analyzed by standard physico-chemical methods. Catalyst samples from another commercial reference reactor with most similar operating conditions and catalyst lifetime were also taken for comparison. The detailed physical analysis did not indicate unusual thermal stress leading to catalyst deactivation by rutilisation or sintering of the titania phase. The chemical analysis did not reveal significant amounts of any of the known catalyst poisons, which would also contribute to an untypical catalyst deactivation/behavior. Quantitative X-ray diffraction measurements on the other hand revealed an unusually high degree of reduction of the vanadium species in the final polishing catalyst layer. Such an abnormal degree of catalyst reduction, and hence, irreversible damaging, was concluded to likely originate from a unit shutdown without sufficient air purging of the catalyst bed. Combustion analysis of the deactivated catalyst confirmed unusually high carbon contents in the finishing catalyst bed (L4) accompanied with a significant loss in the specific surface area by plugging the catalyst pores with high-molecular carbon deposits. According to the well-known Mars–van-Krevelen-mechanism, o-xylene and reaction intermediates remain adsorbed on the catalyst surface in case of a shutdown without air purging and will continue to consume lattice oxygen, accordingly reducing the catalytic species. This systematic investigation of used catalyst samples demonstrated the importance of sufficient air purging during and after a unit shutdown to avoid abnormal, irreversible damage and thus negative impact to catalyst performance.