Heterogeneously under continuous-flow conditions

Strecker reaction A robust heterogeneous self-supported chiral titanium cluster (SCTC) catalyst applied both in batch and continuous mode [44] enabled imine cyanation as well as a three-component Strecker reaction using the corresponding aldehydes and amines under continuous flow conditions in a PBR giving aminonitriles enantiomeric excess values of up to 98%. 

As mentioned above, the vast majority of examples of EPR spectroscopy in catalysis comprise heterogeneous catalytic reactions, mostly performed at elevated temperatures and under continuous flow of reactant gas mixtures. To realize these conditions, heatable flow reactors have to be placed directly into the cavity of the spectrometer. The design can be accomplished in various ways. 

The key issue in effective catalytic oxidation of organics is finding a suitable catalyst. Oxidation of aqueous phenol solutions by using different transition metal oxides as heterogeneous catalysts is already known [4-6]. On the other hand, the potential of molecular sieves to catalyze oxidative phenol destruction has not been examined yet. The objective of this contribution is to provide kinetic and mechanistic data on the catalytic liquid-phase oxidation of aqueous phenol solutions obtained in the presence of various transition metal oxides and molecular sieves. The reaction was studied in a semibatch slurry as well as two-and three-phase continuous-flow reactors. Another matter of concern was the chemical stability of catalysts under the reaction conditions. 

Microwave-assisted esterification by a heterogeneous acid catalyst has been studied in a low dielectric constant medium (see Scheme 35) [64]. A continuous-flow setup has been devised in the system and the heterogeneous acid catalyst (Amberlyst A15 sulphonic acid cation-exchange resin) 61 localized in a polyethylene active flow cell. Use of a low dielectric constant medium (hexane) ensured absorption of microwave radiation only to the reacting species. In this case, the findings suggest a comparable esterification reaction under both microwave and thermal conditions. Furthermore, the presence of water in the catalytic resin resulted in a reduction of the reaction rate irrespective of the type... 

Today parallel reactor systems for rapid catalyst testing under real process conditions are state-of-the-art. An example of an integrated system is the 48-parallel high-throughput reactor, which can be apphed to discover and to optimize new heterogeneous catalysts. It provides continuous flow of the reactants through separate... 

The power feed addition strategy is also conducted under monomer starved conditions but aiming at producing a copolymer with varying composition, see Basset and Hoy (1981). In this case a heterogeneous copolymer composition distribution, that is, a copolymer product with a predefined composition distribution, is sought. This is obviously achieved by varying the ratio of the monomer flow rates into the reactor continuously with time. 

Industrial reactors generally operate at very high velocities (of order 1 m/s) much in excess of terminal falling velocity for at least the finest powder fractions. Powder is continually elutriated and returned to the bed via cyclones. Under these conditions there is disagreement as to whether or not bubbles retain their identity and such beds have been described as "turbulent" or "fast fluidised". What little evidence there is supports the continued existence of bubbles but now in a much disturbed or heterogeneous dense phase and with a less definite shape. Until more is known about this physical situation it is not easy to see how the bubbling bed reactor models should be modified correctly to describe this flow regime. 

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