Specialized Reactors

In the literature, examples are given of bench-scale equipment designed for special fields such as for polymerizations [186] and for kinetic studies of catalytic reactions [187]. 

The polymerization reactor is of the heat-balance type because of the change in the heat transfer characteristics of the reaction mass during the polymerization. As the viscosity increases, the rate of heat dissipation by mixing will generally decline, which must be taken into consideration in setting up the equipment and in taking the appropriate measurements. 

The bench-scale unit for the study of catalytic reactions has been designed with features such as accessibility, isothermal operation, and catalyst pretreatment. The use for catalytic screening tests makes easy accessibility a necessity, while the study of kinetics prescribes isothermal operation. 

Reaction Vessel Calibration Heater Foil Heater 

The advantage of such specially designed calorimetric reactors is that optimal results can be obtained for the designated reaction systems. Use for other types of systems, however, is limited. 

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Oxidants commonly used include ozone, permanganate, chlorine, chlorine dioxide, and ferrate, often in combination with catalysts. Standard-type mixed reactors are used with contact times of several minutes to an hour. Special reactors for use with ultraviolet light have been developed. 

These materials can only be cured at relatively high temperatures (typically, 130-300°C). Therefore, the process is normally carried out at works. With the use of special reactors, it can be accomplished on-site but the operation is difficult. In all cases, the application is critical, and variations in temperature and cure time will result in different film-forming properties. The application should always be left to specialists. 

Post-column on-line derivatisation is carried out in a special reactor situated between the column and detector. A feature of this technique is that the derivatisation reaction need not go to completion provided it can be made reproducible. The reaction, however, needs to be fairly rapid at moderate temperatures and there should be no detector response to any excess reagent present. Clearly an advantage of post-column derivatisation is that ideally the separation and detection processes can be optimised separately. A problem which may arise, however, is that the most suitable eluant for the chromatographic separation rarely provides an ideal reaction medium for derivatisation this is particularly true for electrochemical detectors which operate correctly only within a limited range of pH, ionic strength and aqueous solvent composition. 

Special reactors are required to conduct biochemical reactions for the transformation and production of chemical and biological substances involving the use of biocatalysts (enzymes, immobilised enzymes, microorganisms, plant and animal cells). These bioreactors have to be designed so that the enzymes or living organisms can be used under defined, optimal conditions. The bioreactors which are mainly used on laboratory scale and industrially are roller bottles, shake flasks, stirred tanks and bubble columns (see Table 1). 

As is the case with pure bubble columns and gas-operated loop reactors, most bioreactors in technical use are aerated with oxygen or air. Reactors with pure surface aeration, such as roller bottles, shake flasks and small stirred reactors or special reactors with membrane aeration, are exceptions. The latter are used for the cultivation of cells and organisms which are particularly sensitive to shearing (see e. g. [28 - 29]). The influence of gas bubbles in increasing stress has been described in many publications (see e.g. [4, 27, 29, 30]). In principle it can be caused by the following processes ... 

Table 5. Special reactors used with model particle systems...

OS 89] [R 19] [P 69] Using a special reactor configuration with an interdigital micro-mixer array with pre-reactor, subsequent tubing and a quench, a yield of 95% at 0 °C was obtained [127]. The industrial semi-batch process had the same yield at -70 °C. 

The silicon chip reactor was compressed between a top plate, for direct observation of the flows, gaskets with punched holes and a base plate with all fluid connections [13,14]. Thermocouples inserted between the two plates were located next to the micro reactor. A third inlet served for reaction quenching by introducing an inert gas such as nitrogen. Generally, heat removal is facilitated by the special reactor arrangement acting as a heat sink. 

The reaction mechanism of SCR of NOx with decane on acid and iron-exchanged MFI-type zeolite was also investigated by operando FTIR spectroscopy and a special reactor cell enabling the use of water-containing gas mixtures. Brosius et al. found that water has a dramatic influence on the reaction pathway, while the formation of organic nitro and nitrite compounds does not proceed via chemisorbed states of NO, as observed in SCR with dry gases [174],... 

Other microwave-assisted parallel processes, for example those involving solid-phase organic synthesis, are discussed in Section 7.1. In the majority of the cases described so far, domestic multimode microwave ovens were used as heating devices, without utilizing specialized reactor equipment. Since reactions in household multimode ovens are notoriously difficult to reproduce due to the lack of temperature and pressure control, pulsed irradiation, uneven electromagnetic field distribution, and the unpredictable formation of hotspots (Section 3.2), in most contemporary published methods dedicated commercially available multimode reactor systems for parallel processing are used. These multivessel rotor systems are described in detail in Section 3.4. 

BIOKOP A process for treating liquid effluents containing wastes from organic chemical manufacture. It combines aerobic fermentation, in special reactors known as BIOHOCH reactors, with treatment by powdered activated carbon. Developed originally for treating the effluent from the Griesheim works of Hoechst, it was engineered by Uhde and is now offered by that company. See also PACT. 

SRU A variation of the Claus process, for use in the presence of ammonia. It uses a special reactor, designed to avoid plugging by compounds of ammonia with sulfur trioxide. Designed by JGC Corporation. Thirty one units were in operation as of 1992. 

Carbon tetrachloride represents an example of the change to petroleum raw materials in this field. The traditional source of this widely used product has been the chlorination of carbon disulfide, either directly or through the use of sulfur dichloride. Military requirements in World War II caused an increase in demand, and in addition to expansion of the older operations, a new process (28) was introduced in 1943 it involved direct chlorination of methane at 400° to 500° C. and essentially atmospheric pressure. This apparently straight-forward substitution of halogen for hydrogen in the simplest paraffin hydrocarbon was still a difficult technical accomplishment, requiring special reactor construction to avoid explosive conditions. There is also the fact that disposal of by-product hydrochloric acid is necessary here, though this does not enter the carbon disulfide picture. That these problems have been settled successfully is indicated by the report (82) that the chlorination of methane is the predominant process in use in the United States today, and it is estimated that more than 100,000,000 pounds of carbon tetrachloride were so produced last year. 

Mass Spectroscopy. Thermal decomposition of CH2N2 in a special reactor attached to a mass spectrometer has enabled Eltenton29-30 to detect CH2 by its mass spectrum. No evidence of CH2 in the thermal decomposition of CH4 was found by this method. 

Several fluorinated diols 6 have been synthesized from highly fluorinated alkanols 5 via mercury-photosensitized dehydrodimerization in the vapor phase163 in a special reactor.164 In almost all cases, the corresponding dl- and meso-diols are obtained in a 50 50 ratio.163... 

For electrochemical reactions, special reactors electrolysis cells) are required. Fortunately, today a large number of electrolysis cells are commercially available for many types of electrochemical reactions. For laboratory use or small-and medium-scale technical applications, no cell construction is necessary. 

I Electroorganic syntheses require special reactors the cells used in inorganic electrochemistry are not suitable for electroorganic syntheses in general. 

Von Hippel et al. [104] patented a special reactor head, which allows for a distribution of the two gas flows through each individual channel. Even at a 1 200 °C monolith temperature the heads did not heat up to more than 200 °C, hence silicone rubber was applied for sealing the heads. This concept was applied for coupling methane combustion and steam reforming in separate flow paths [105],... 

Oxidative fluorination Water only HF Very high temperatures Special reactors Energy HF handling One step with recycling of fluoride 80%... 

Direct fluorination Salt (neutralised HF) F2, HF Cooling Special reactors F2 generation and handling One step 70%... 

Balz-Schiemann Salt Lost solvent BF3 Unstable intermediate HF, BF3 Cooling Special reactors Anilines Two steps (omitting aniline manufacture) 44% (omitting aniline manufacture)... 

Handling of caking coals has proved to be a serious obstacle to the development of hydrocarbonization processes and was, in fact, one of the principal factors contributing to the failure of the Coalcon project. However, a number of technologically successful approaches to handling of caking coals have now been demonstrated. The most common approach is through special reactor... 

In this lecture, the development of the MTG process will be reviewed. First, the unique aspects of MTG — the catalyst, chemistry, and its special reactor design aspects — will be discussed. Next, the choices for the conversion system will be presented along with the dual-pronged strategy for development of both the fixed- and fluid bed processes. Finally, our future development plans for this general area of technology will be highlighted. 

The Chemical Development Drug Evaluation branch of Johnson Johnson Pharmaceutical Research Development LLC in Raritan, USA, tested microreactors for processes at elevated temperatures above the limit of most multipurpose conventional reactors, which is above 140°C [34], Operation above this limit is only possible by means of special reactors equipped with heat transfer units. 

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