Experimental techniques continuous-flow reactor

The active site responsible for the aerobic oxidation of alcohols over Pd/AljO, catalysts has long been debated [96-lOOj. Many reports claim that the active site for this catalyst material is the metallic palladium based on electrochemical studies of these catalysts [100, 101]. On the contrary, there are reports that claim that palladium oxide is the active site for the oxidation reaction and the metalhc palladium has a lesser catalytic activity [96,97). In this section, we present examples on how in situ XAS combined with other analytical techniques such as ATR-IR, DRIFTS, and mass spectroscopic methods have been used to study the nature of the actual active site for the supported palladium catalysts for the selective aerobic oxidation of benzylic alcohols. Initially, we present examples that claim that palladium in its metallic state is the active site for this selective aerobic oxidation, followed by some recent examples where researchers have reported that ojddic palladium is the active site for this reaction. Examples where in situ spectroscopic methods have been utilized to arrive at the conclusion are presented here. For this purpose, a spectroscopic reaction cell, acting as a continuous flow reactor, has been equipped with X-ray transparent windows and then charged with the catalyst material. A liquid pump is used to feed the reactants and solvent mixture into the reaction cell, which can be heated by an oven. The reaction was monitored by a transmission flow-through IR cell. A detailed description of the experimental setup and procedure can be found elsewhere [100]. Figure 12.10 shows the obtained XAS results as well as the online product analysis by FTIR for a Pd/AljOj catalyst during the aerobic oxidation of benzyl alcohol. 

The use of IR pulse technique was reported for the first time around the year 2000 in order to study a catalytic reaction by transient mode [126-131], A little amount of reactant can be quickly added on the continuous flow using an injection loop and then introduce a transient perturbation to the system. Figure 4.10 illustrates the experimental system used for transient pulse reaction. It generally consists in (1) the gas flow system with mass flow controllers, (2) the six-ports valve with the injection loop, (3) the in situ IR reactor cell with self-supporting catalyst wafer, (4) the analysis section with a FTIR spectrometer for recording spectra of adsorbed species and (5) a quadruple MS for the gas analysis of reactants and products. 

Novel microreactors with immobilized enzymes were fabricated using both silicon and polymer-based microfabrication techniques. The effectiveness of these reactors was examined along with their behavior over time. Urease enzyme was successfully incorporated into microchannels of a polymeric matrix of polydimethylsiloxane and through layer-bylayer self-assembly techniques onto silicon. The fabricated microchannels had cross-sectional dimensions ranging from tens to hundreds of micrometers in width and height. The experimental results for continuous-flow microreactors are reported for the conversion of urea to ammonia by urease enzyme. Urea conversions of >90% were observed. 

Polystyrene can be easily prepared by emulsion or suspension techniques. Harkins (1 ), Smith and Ewart(2) and Garden ( ) have described the mechanisms of emulsTon polymerization in batch reactors, and the results have been extended to a series of continuous stirred tank reactors (CSTR)( o Much information on continuous emulsion reactors Ts documented in the patent literature, with such innovations as use of a seed latex (5), use of pulsatile flow to reduce plugging of the tube ( ), and turbulent flow to reduce plugging (7 ). Feldon (8) discusses the tubular polymerization of SBR rubber wTth laminar flow (at Reynolds numbers of 660). There have been recent studies on continuous stirred tank reactors utilizing Smith-Ewart kinetics in a single CSTR ( ) as well as predictions of particle size distribution (10). Continuous tubular reactors have been examined for non-polymeric reactions (1 1 ) and polymeric reactions (12.1 31 The objective of this study was to develop a model for the continuous emulsion polymerization of styrene in a tubular reactor, and to verify the model with experimental data. 

This study investigates the hydrodynamic behaviour of an aimular bubble column reactor with continuous liquid and gas flow using an Eulerian-Eulerian computational fluid dynamics approach. The residence time distribution is completed using a numerical scalar technique which compares favourably to the corresponding experimental data. It is shown that liquid mixing performance and residence time are strong functions of flowrate and direction. 

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