Rectification, with chemical reaction

P. E. Cuille and G. V. Reklaitis. Dynamic simulation of multicomponent batch rectification with chemical reactions. Comp. Chem. Eng., 10(4) 389-398, 1986. 

Very often the mass transfer processes in the packed bed columns in case of absorption, as well as in rectification are accompanied 1 different chemical reactions. In this chapter their influence on die mass transfer process and also the methods for calculation of these apparatuses accounting for the chemical reactions are shortly considered. The basic theory of the mass transfer accompanied with chemical reaction is presented in the books of Astarita [1] Dancli eits [2] and Zai cki and Chacuki [3]. Principally the diemical reacticm can take place in each of the phases, gas and liquid. Because it is usually in fte liquid phase, lat we craisider more detailed this case. 

The use of the top part of the packed tower as the chlorinator will also ensure good mass exchange between chlorination and rectification zones this will allow to quickly withdraw chlorination products from the reaction zone and continuously send back the unreacted dimethyldichlorosilane as a result of the rectification of the mixture in the lower part of the tower. However, this chlorination technique can be possible only with chemical initiators, not UV rays, since in the latter case the effect of light will be screened by the head. 

In mass transfer apparatus one of two processes can take place. Multicomponent mixtures can either be separated into their individual substances or in reverse can be produced from these individual components. This happens in mass transfer apparatus by bringing the components into contact with each other and using the different solubilities of the individual components in the phases to separate or bind them together. An example, which we have already discussed, was the transfer of a component from a liquid mixture into a gas by evaporation. In the following section we will limit ourselves to mass transfer devices in which physical processes take place. Apparatus where a chemical reaction also influences the mass transfer will be discussed in section 2.5. Mass will be transferred between two phases which are in direct contact with each other and are not separated by a membrane which is only permeable for certain components. The individual phases will mostly flow countercurrent to each other, in order to get the best mass transfer. The separation processes most frequently implemented are absorption, extraction and rectification. 

In reactive rectification a rectification process is coupled with a chemical reaction. A simple example is the combination of a stirred tank in which an esterification takes place with a column for separation of the water of reaction [Stichlmair 1998, Frey 1998a],... 

Semicontinuous rectification processes are of practical importance for vapor mixtures generated in a discontinuous chemical reaction. These then have to be separated into a component continuously fed back to the reactor and a discharging fraction. For example, the main task during the transesterification of dimethyl teraphthalate with ethylene glycol is to continuously separate methanol from the reaction mixture. The reaction equilibrium is then shifted toward the product. Methanol is the top product of the column which is connected directly to the transesterification reactor. The high-boiling, or heavy, bottom product. 

Metallothermic reduction of silicon tetrachloride with zinc. Silicon tetrachloride, SiCl, is preliminarily obtained as a byproduct from the carbochlorination of zircon and, to a lesser extent, from that of pure silica sand with carbon and chlorine. Afterward a high-purity silicon tetrachloride is produced by rectification (i.e., fractional distillation). Simultaneously, zinc is purified by vaporization. Then both chemicals are added to the heated quartz-reaction-heated vessel. Needlelike polycrystalline silicon is grown inside the furnace as a result of the following chemical reaction ... 

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