Batch mode catalysis

The first role of agitation is to keep the catalyst particles uniformly suspended in the reaction medium. When gas and liquid reactants are simultaneously used, agitation plays an essential role in facilitating the gas to liquid mass transfer.1201 Moreover, an efficient stirring is needed to avoid external (i.e. from the organic phase to the external surface of the catalyst particles) mass and heat transfer limitations.1113-151 

A simple experimental method can be used to specify the minimum stirring rate to be chosen in order to avoid external mass transfer limitation (provided, however, there is no large temperature gradient between the bulk and surface of the catalyst). Indeed the reaction rate first increases with the stirring rate, then becomes constant, indicating that the rate is then limited by chemical steps. This type of experiment 

The simplest method is to pelletize the zeolite under low pressure then to crush the pellets into small particles (0.02-0.04 mm). This treatment causes no significant agglomeration of the small crystals and the organic molecules continue to enter easily the zeolite micropores through interparticular mesopores. 

Before their use, zeolite catalysts have always to undergo activation treatments. Part of these treatments depends on the nature of the active sites (e.g. metals supported over zeolites have to be reduced before reaction). However, the elimination of moisture from hygroscopic solids, as zeolites are, has always to be carried out. 

The strong affinity of zeolites for water is well known and some of them (Na and K LTA also called 4A and 3A, NaX or 13X) are furthermore used for drying gases or liquid organic compounds both in industrial units and in academic laboratories. Zeolites can also be used as water scavenger to displace thermodynamic equilibrium 

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Recent mechanistic studies using HP infrared equipment, as well as HP-NMR measurements involving the use of CO and CH3I, have allowed the iridium intermediates which are present in solution as methyl acetate and water, and are consumed to produce acetic acid [.12, 34, 41-43], to be followed. All of these observations can be rationalized by a single catalytic cycle (see Figure 8.5), in which equilibria exist between the neutral and anionic complexes for all species. The main species involved in the carbonylation, which are detected in batch mode under carbonylation conditions [34], and correspond to the slower steps of catalysis, are the methyl—iridium and acetyl-iridium complexes [Ir(CH3)l3(CO)2] and [Ir(COCH3)l3(CO)2] respectively. 

The reaction engineering aspects of these polymerizations are similar. Excellent heat transfer makes them suitable for vinyl addition polymerizations. Free radical catalysis is mostly used, but cationic catalysis is used for non-aqueous dispersion polymerization (e.g., of isobutene). High conversions are generally possible, and the resulting polymer, either as a latex or as beads, is directly suitable for some applications (e.g., paints, gel-permeation chromatography beads, expanded polystyrene). Most of these polymerizations are run in the batch mode, but continuous emulsion polymerization is common. 

Kr/Xe-fine-purification plants are available in numerous designs, combining the separation techniques cryogenic rectification, catalysis, adsorption, chemisorption or membrane separation. They may be operated continuously or, due to the small capacities, in batch mode. 

A hst of polyol producers is shown in Table 6. Each producer has a varied line of PPO and EOPO copolymers for polyurethane use. Polyols are usually produced in a semibatch mode in stainless steel autoclaves using basic catalysis. Autoclaves in use range from one gallon (3.785 L) size in research faciUties to 20,000 gallon (75.7 m ) commercial vessels. In semibatch operation, starter and catalyst are charged to the reactor and the water formed is removed under vacuum. Sometimes an intermediate is made and stored because a 30—100 dilution of starter with PO would require an extraordinary reactor to provide adequate stirring. PO and/or EO are added continuously until the desired OH No. is reached the reaction is stopped and the catalyst is removed. A uniform addition rate and temperature profile is required to keep unsaturation the same from batch to batch. The KOH catalyst can be removed by absorbent treatment (140), extraction into water (141), neutralization and/or crystallization of the salt (142—147), and ion exchange (148—150). 

Then, a survey of micro reactors for heterogeneous catalyst screening introduces the technological methods used for screening. The description of microstructured reactors will be supplemented by other, conventional small-scale equipment such as mini-batch and fixed-bed reactors and small monoliths. For each of these reactors, exemplary applications will be given in order to demonstrate the properties of small-scale operation. Among a number of examples, methane oxidation as a sample reaction will be considered in detail. In a detailed case study, some intrinsic theoretical aspects of micro devices are discussed with respect to reactor design and experimental evaluation under the transient mode of reactor operation. It will be shown that, as soon as fluid dynamic information is added to the pure experimental data, more complex aspects of catalysis are derivable from overall conversion data, such as the intrinsic reaction kinetics. 

Obviously, it is very desirable to substitute these modes of benzylic ether preparation by an heterogeneous catalysis process. Clays (50) and resins (51, 52) which were the first solid acid catalysts used have given low or moderate yields. The first experiments with zeolites were carried out by Rhodia (53, 54) on the etherification of vanillic alcohol (A) in a batch reactor over a HBEA zeolite with a Si/Al ratio of 12.5 ... 

It is important to note that most reactions using homogeneous catalysts are run in the liquid phase in a batch-wise mode. Especially in academic research laboratories, homogeneous catalysis is attributed to batch reactions using organic solvents. However, in large-scale industrial processes, e.g., carbonyl-ation reactions, oxidations are performed in a continuous mode. 

Various processes exist, combining adsorption, catalysis, partial condensation and rectification for the isolation of neon. For example, the process applied by the Linde AG either in batch or continuous mode combines these unit operations in the following way [3.5] ... 

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