Noncatalytic solid-gas

Structural Variations as a Tool to Analyze the Mechanism of Noncatalytic Solid-Gas Reactions... 

Ishida, M. and C.Y. Wen. Effect of Solid Mixing on Noncatalytic Solid-Gas Reactions in a Fluidized Bed. 

Nonbulking sludge, 25 899 Nonbulk packages, of hazardous materials, 25 338, 342-343 Noncatalytic cracking, 18 648 Noncatalytic gas-solid reactions, 21 331 Noncatalytic solid-fluid reactions, 21 343-344 categories of, 21 344... 

Costa, E. Smith, J. Kinetics of noncatalytic, nonisothermal gas-solid reactions hydrofluori-nation of uranium dioxide. AIChE J. 1971, 17, 947-958. 

We now consider 12 case studies that include simple homogeneous liquid-phase reactions, complex homogeneous gas-phase reactions, gas-solid catalytic and noncatalytic reactions, gas-liquid simple and complex reactions, gas-liquid-solid (noncatalytic) reactions, gas-liquid-solid (catalytic) reactions, and solid-solid reactions. The scope and coverage of each case study are summarized in Table 11.27. In the first, homogeneous reactions are considered. For these relatively simple reactions, the possibility of optimum design is discussed. 

If the catalyst consists of particles, one has a fixed or mobile stationary particles reactor. The flow is no longer nniform and the reaction is considered heterophasic. In this case, the catalyst consists of solid particles, but the reactants and products are gas or liquid and may flow through the particle bed in the concurrent or counter current direction. The reaction may be catalytic or noncatalytic and takes place on the particle surface and/or within the pores of the catalyst. In this case, the system is heterophasic and may be solid-gas type, solid-liquid, or solid-liquid-gas taking place in the respective reactors fixed or mobile-bed, trickle bed, and slurry bed. 

Fixed-bed noncatalytic reactors. Fixed-bed reactors can be used to react a gas and a solid. For example, hydrogen sulfide can be removed from fuel gases by reaction with ferric oxide ... 

Fluidized bed noncatalytic reactors. Fluidized heds are also suited to gas-solid noncatalytic reactions. All the advantages described earlier for gas-solid catalytic reactions apply. As an example. 

Heterogeneous reactions of industrial significance occur between all combinations of gas, liquid, and solid phases. The solids may be inert or reac tive or catalysts in granular form. Some noncatalytic examples are listed in Table 7-11, and processes with solid catalysts are listed under Catalysis in Sec. 23. Equipment and operating conditions of heterogeneous processes are covered at some length in Sec. 23 only some highlights will be pointed out here. 

Although they are termed homogeneous, most industrial gas-phase reactions take place in contact with solids, either the vessel wall or particles as heat carriers or catalysts. With catalysts, mass diffusional resistances are present with inert solids, the only complication is with heat transfer. A few of the reactions in Table 23-1 are gas-phase type, mostly catalytic. Usually a system of industrial interest is liquefiea to take advantage of the higher rates of liquid reactions, or to utihze liquid homogeneous cat ysts, or simply to keep equipment size down. In this section, some important noncatalytic gas reactions are described. 

Two fixed-bed reactors can be used in parallel, one reacting and the other regenerating. However, there are many disadvantages in carrying out this type of reaction in a packed bed. The operation is not under steady state conditions, and this can present control problems. Eventually, the bed must be taken off line to replace the solid. Fluidized beds (to be discussed later) are usually preferred for gas-solid noncatalytic reactions. 

In this chapter, we consider multiphase (noncatalytic) systems in which substances in different phases react. This is a vast field, since the systems may involve two or three (or more) phases gas, liquid, and solid. We restrict our attention here to the case of two-phase systems to illustrate how the various types of possible rate processes (reaction, diffusion, and mass and heat transfer) are taken into account in a reaction model, although for the most part we treat isothermal situations. 

Homogeneous reactions Homogeneous noncatalytic reactions are normally carried out in a fluidized bed to achieve mixing of the gases and temperature control. The solids of the bed act as a heat sink or source and facilitate heat transfer from or to the gas or from or to heat-exchange surfaces. Reactions of this type include chlorination of hydrocarbons or oxidation of gaseous fuels. 

Pore-diffusion resistance Reactions involve solid particle size greater than about 1.6 mm All fast, noncatalytic gas-solid (G/S) reactions such as combustion and gasification Reactors with particle size lower than 100 pm to 0.1 mm Catalytic bubbling fluidized beds (BFB) Slurry reactors... 

CSTR for most reactions. These conditions are best met for short residence times where velocity profiles in the tubes can be maintained in the turbulent flow regime. In an empty tube this requires high flow rates for packed columns the flow rates need not be as high. Noncatalytic reactions performed in PFRs include high-pressure polymerization of ethylene and naphtha conversion to ethylene. A gas-liquid noncatalytic PFR is used for adipinic nitrile production. A gas-solid PFR is a packed-bed reactor (Section IV). An example of a noncatalytic gas-solid PFR is the convertor for steel production. Catalytic PFRs are used for sulfur dioxide combustion and ammonia synthesis. 

All of these roasting furnace reactors operate continuously. They are noncatalytic gas-solid heterogeneous reactors. The multiple hearth has characteristics similar to plug flow operation. The flash roaster approaches CSTR, and the third option is a fluidized bed configuration. 

G. Uhde, U. Hoffmann, Noncatalytic Gas-Solid Reactions Modelling of Simultaneous Reaction and Formation of Surface with a Nonisothermal Crackling Core Model, Chem. 

There are a number of references on gas-solid noncatalytic reactions, e.g., Brown, Dollimore, and Galwey ["Reactions in the Solid State, in Bamford and Tipper (eds.), Comprehensive Chemical Kinetics, vol. 22, Elsevier, 1980], Galwey (Chemistry of Solids, Chapman and Hall, 1967), Sohn and Wadsworth (eds.) (Rate Processes of Extractive Metallurgy, Plenum Press, 1979), Szekely, Evans, and Sohn (Gas-Solid Reactions, Academic Press, 1976), and Ullmann (Enzyk-lopaedie der technischen Chemie, Uncatalyzed Reactions with Solids, vol. 3, 4th ed., Verlag Chemie, 1973, pp. 395-464). 

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