Reactor examples of

The second type of solution polymerization concept uses mixtures of supercritical ethylene and molten PE as the medium for ethylene polymerization. Some reactors previously used for free-radical ethylene polymerization in supercritical ethylene at high pressure (see Olefin POLYMERS,LOW DENSITY polyethylene) were converted for the catalytic synthesis of LLDPE. Both stirred and tubular autoclaves operating at 30—200 MPa (4,500—30,000 psig) and 170—350°C can also be used for this purpose. Residence times in these reactors are short, from 1 to 5 minutes. Three types of catalysts are used in these processes. The first type includes pseudo-homogeneous Ziegler catalysts. In this case, all catalyst components are introduced into a reactor as hquids or solutions but form soHd catalysts when combined in the reactor. Examples of such catalysts include titanium tetrachloride as well as its mixtures with vanadium oxytrichloride and a trialkyl aluminum compound (53,54). The second type of catalysts are soHd Ziegler catalysts (55). Both of these catalysts produce compositionaHy nonuniform LLDPE resins. Exxon Chemical Company uses a third type of catalysts, metallocene catalysts, in a similar solution process to produce uniformly branched ethylene copolymers with 1-butene and 1-hexene called Exact resins (56). 

Liquid-liquid reactors. Examples of liquid-liquid reactions are the nitration and sulfonation of organic liquids. Much of the discussion for gas-liquid reactions also applies to liquid-liquid reactions. In liquid-liquid reactions, mass needs to be transferred between two immiscible liquids for the reaction to take place. However, rather than gas-and liquid-film resistance as shown in Figure 7.2, there are two liquid-film resistances. The reaction may occur in one phase or both phases simultaneously. Generally, the solubility relationships are such that the extent of the reactions in one of the phases is so small that it can be neglected. 

A continuous bulk polymerization process with three reaction zones in series has been developed. The degree of polymerization increases from the first reactor to the third reactor. Examples of suitable reactors include continuous stirred tank reactors, stirred tower reactors, axially segregated horizontal reactors, and pipe reactors with static mixers. The continuous stirred tank reactor type is advantageous, because it allows for precise independent control of the residence time in a given reactor by adjusting the level in a given reactor. Thus, the residence time of the polymer mixtures can be independently adjusted and optimized in each of the reactors in series (8). 

Donnet, M., Bowen, P., Jongen, N., Lemaitre, J., Hofmann, H., Schreiner, A., Jones, A. G., Schenk, R., Hofmann, C., Successful scale-up from millilitre batch optimization to a small scale continuous production using the segmented flow tubular reactor example of calcium carbonate precipitation, Chem. Eng. Trans. 2002, 1,1353-1358. 

Another classification of chemical reactors is according to the phases being present, either single phase or multiphase reactors. Examples of multiphase reactors are gas liquid, liquid-liquid, gas solid or liquid solid catalytic reactors. In the last category, all reactants and products are in the same phase, but the reaction is catalysed by a solid catalyst. Another group is gas liquid solid reactors, where one reactant is in the gas phase, another in the liquid phase and the reaction is catalysed by a solid catalyst. In multiphase reactors, in order for the reaction to occur, components have to diffuse from one phase to another. These mass transfer processes influence and determine, in combination with the chemical kinetics, the overall reaction rate, i.e. how fast the chemical reaction takes place. This interaction between mass transfer and chemical kinetics is very important in chemical reaction engineering. Since chemical reactions either produce or consume heat, heat removal is also very important. Heat transfer processes determine the reaction temperature and, hence, influence the reaction rate. 

Miachon S, Perez V, Crehan G, Torp EG, Raeder H, Bredesen R, and Dalmon JA. Comparison of a contactor catalytic membrane reactor with a conventional reactor Example of wet air oxidation. Catal Today 2003 82(1 ) 75-81. 

Selectivity may also be difierent in stirred-tank and tubular-flow reactors. It has been shown that, depending on the kinetics and nature of the multiple reactions, selectivity obtained in a stirred-tank reactor may be less, the same as, or greater than that for a tubular-flow reactor. Examples of reaction systems for each result are given in Table 4-12. The order of... 

Supported Ti02 photocatalysts can be implemented in fluidized beds, fixed powder layer reactors, annulai- reactors and monolith reactors. Examples of these reactors ai e described in the following section ... 

For example, alcohol dehydrogenase has been immobilized into nanotubes of Ti02, which were prepared by sol-gel template synthesis. This enzyme retained its ability to oxidize ethanol for more than 4 days (NAD" cofactor, phosphate bulfer, pH Since these Ti02 nanotubes were open at both ends, this configuration allowed their use as a flow reactor. Examples of boimd enzymes acting as bioreactor are large in number. They also involve covalent binding of antibodies to functionalize sol-gel films. ... 

Figure 4.11.3 Evaluation of kinetic data by the differential method from data of an integral reactor (example of batch reactor).

Heat transfer. A number of options exist for the heat exchanger/chemical reactor. Examples of alternative interfaces include traditional heat exchangers, radiation heat transfer (thermal infrared between tube banks), duplex tubes (tubes constructed of two metals), and intermediate heat exchanger loops. It is not clear what the preferred option is. The very high temperatures does create new options such as the use of a heat exchanger that operates on radiation heat transfer (Fig. 5). Such options provide very high degrees of separation between the nuclear and chemical facilities. 

The results are relevant to a number of practical situations. The most important applications will be found in the development of chemical reactors for liquid phase reactions which are not very fast, such as we often encounter in the synthesis of organic products. For this type of syntheses, we can easily design, e.g., large scale continuous stirred tank reactors on the basis of data obtained with small scale batch-reactors. Examples of these are discussed in Chapter 10. 

Salts Used in Reactors. Examples of fluoride salts with lower melting points Li-Na-Be (22-44-33) 300 C Na-Rb-Zr (6-46-48) 380 C... 

Novel reactor configurations are discussed in terms of micro and monolith reactors. Examples of gas and liquid phase reactions and appropriate reactor configmations and process details are presented with a focus on PI. Structured reactors are discussed with their advantages compared to conventional reactors. Process aspects of monolith reactors including their applications in some industrially important reactions are discussed. A brief mention is made about novel devices for heat, mass and momentum transfer. The achievement of PI... 

With regard to the ability to isolate products stereo-chemically, the ability to use microreactors for chiral resolutions has also been shown. In addition to packed-bed reactors, examples of polymeric monoliths being used to... 

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