Slurry reactors classified

Figure 1. Slurry reactors classified by the contacting pattern and mechanical devices (a) slurry (bubble) column (b) countercurrent column (c) co-current upflow (d) co-current downflow (e) stirred vessel (C) draft tube reactor (g) tray column (h) rotating disc or multi-agitated column reactor (i) three-phase spray column — liquid flow —> gas flow.

Table II,Slurry reactors classified according to the chemical system...

In terms of industrial use, each of the aforementioned reactors and their contacting modes offer different advantages and disadvantages. Therefore, the reactor selection for a particular chemistry or process needs to be done after careful consideration of the operating factors and contacting options that the different reactor configurations provide. Table 6.2 provides some qualitative ratings to these factors for some of the important and industrially common reactors from the list presented in Table 6.1. Clearly, the three-phase slurry reactor types classified within the box, which are the scope of this chapter, represent a class of reactors... 

As listed in Tables 6.1 and 6.2, reactors classified as three-phase slurry reactors broadly fall under the following categories ... 

Slurry reactors can be classified according to the phases where the reactants are present. Table II gives an overview. The most important distinction is whether the solid phase is a reactant or a catalyst. In principle, the solids could also be inert and only present to increase mass transfer between phases as is often the case, e.g., in trickle flow reactors. In slurry reactors the introduction of solids for this purpose only is not worthwhile, with the exception of solids like zeolites and activated carbon for enhancement of mass transfer or improvement of selectivity [21, 22] but in such a system the solid is not really inert. Another example is the turbulent contactor in which large but light balls are moved by a gas flow and irrigated by a liquid phase. However, this regime falls outside the scope of the present presentation. If the solid is a reactant as well as the gas phase and liquid phase, the situation becomes rather complex nevertheless, it corresponds to many practical situations (see e.g. Shah [2]). A rather exceptional... 

Fig. 1 Slurry reactors as classified by the contacting pattern and mechanical...

Polymerization reactions can also be classified in terms of the reaction medium, and the principal types are bulk, solution, slurry, emulsion, and gas-phase. In bulk polymerization, the reactor initially contains only monomer, and the product is a viscous melt. This is the type of system usually used for step (condensation) polymers. In solution polymerization, both the monomer and the polymer are soluble in the solvent, while in emulsion and slurry reactors, the polymer is not soluble in the reaction medium, which is called a diluent. The principal monomers polymerized by means of emulsion polymerization are vinyl acetate, methyl methacrylate, and vinyl chloride. In a gas-phase reactor or slurry reactor, the gaseous monomer is polymerized on the surface of catalyst particles, which are supported either by stirring in a horizontal reactor, or by fluidization in a vertical reactor. Slurry and gas-phase reactors are used primarily to make polyolefins. 

A control technique based on high-frequency pressure measurements was developed and implemented to avoid hydrodynamic instabilities in continuous olefin slurry-loop reactors [ 186]. The obtained high-frequency pressure patterns are compared to typical process responses and then used to classify the status of the plant operation. The idea is that pressure fluctuations that do not follow the standard pattern indicate some sort of process instabiUty. When hydrodynamic instabilities are detected, monomer flow rates and/or reactor temperatures are manipulated to reduce the polymer density and the reaction rates and reduce the risks of plant shutdown. Similar procedures can be used for detection and correction of abnormal plant operation in suspension [ 187] and emulsion [188] polymerizations with the help of Raman and near infrared spectroscopy techniques. 

Initially it was studied the effect of various factors on the total volume of the reactor.Results showed that the main factors influencing its value were linear mixing velocity and suspension physical properties These variables were classified in form of impeller Reynolds number of the slurry (Re ).Its effect upon the reactor volume is illustrated in Fig.. The experimental values in the figure are interconnected by dotted lines.They were found to be represented well by a correlation of the Darcy type ... 

The polymerization of olefins with coordination catalysts is performed in a large variety of polymerization processes and reactor configurations that can be classified broadly into solution, gas-phase, or slurry processes. In solution processes, both the catalyst and the polymer are soluble in the reaction medium. These processes are used to produce most of the commercial EPDM rubbers and some polyethylene resins. Solution processes are performed in autoclave, tubular, and loop reactors. In slurry and gas-phase processes, the polymer is formed around heterogeneous catalyst particles in the way described by the multigrain model. Slurry processes can be subdivided into slurry-diluent and slurry-bulk. In slurry-diluent processes, an inert diluent is used to suspend the polymer particles while gaseous (ethylene and propylene) and liquid (higher a-olefins) monomers are fed into the reactor. On the other hand, only liquid monomer is used in the slurry-bulk pro-... 

The techniques actually available for SO2 removal from flue gases may be broadly classified into wet and dry systems. The wet methods employ a slurry or solution of some absorbent for SO2, whereas the dry systems use dry particles of absorbent in such gas-solid contacting devices as fluidized beds, packed beds, and entrainment reactors. It is with these latter methods that we are concerned here, although wet methods appear to be at least as satisfactory as the dry systems. 

---