Heat Effects of Industrial Reactions

The precetUug sections have dealt with the standard heat of reaction. Industrial reactions 05 rarely carried out under standard-state conditions. Furthermore, in actual reactions the reactants may not bn present in stoichiocnetric proportions, the reaction may not go to completion, and the final temperatiu-e may diiffer from the initial temperature. Moreover, inert species may bn present, and several reactions may occur simultaneously. Nevertheless, calculations or the heat effects of actuM reactions oxe based on the principle.s already considered and are best illustrated by example. 

In the foregoing examples of reactions that occur at approximately 1 bar, we have tacitly assumed that the heat effects of reaction are the same whether gases are mixed or pure, an acceptable procedure for low pressures. For reactions at elevated pressures, this may not be the case, and it may be necessary to account for the effects of pressure and of mixing on the heat of reaction. However, these effects are usually small. 

For steady flow in a heat exchanger at approximately atmospheric pressure, wliat is the final temperature  

How much heat is required when 10 000 kg of CaCOs is heated at atmospheric pressure from323.15 to 1153.15K (50°Cto 880°C)  

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Chapter 1 reviews the concepts necessary for treating the problems associated with the design of industrial reactions. These include the essentials of kinetics, thermodynamics, and basic mass, heat and momentum transfer. Ideal reactor types are treated in Chapter 2 and the most important of these are the batch reactor, the tubular reactor and the continuous stirred tank. Reactor stability is considered. Chapter 3 describes the effect of complex homogeneous kinetics on reactor performance. The special case of gas—solid reactions is discussed in Chapter 4 and Chapter 5 deals with other heterogeneous systems namely those involving gas—liquid, liquid—solid and liquid—liquid interfaces. Finally, Chapter 6 considers how real reactors may differ from the ideal reactors considered in earlier chapters. 

In heterogeneous catalysis reactants have to be transported to the catalyst and (if the catalyst is a porous, solid particle) also through the pores of the particle to the active material. In this case all kinds of transport resistance s may play a role, which prevent the catalyst from being fully effective in its industrial application. Furthermore, because appreciable heat effects accompany most reactions, heat has to be removed from the particle or supplied to it in order to keep it in the appropriate temperature range (where the catalyst is really fully effective). Furthermore, heterogeneous catalysis is one of the most complex branches of chemical kinetics. Rarely do we know the compositions, properties or concentrations of the reaction intermediates that exist on the surfaces covered with the catalytically effective material. TTie chemical factors that govern reaction rates under these conditions are less well known than in homogeneous catalysis. Yet solid catalysts display specificities for particular reactions, and selectivity s for desired products, that in most practical cases cannot be equaled in other ways. Thus use of solid catalysts and the proper (mathematical) tools to describe their performance are essential. 

When applied to the synthesis of ethers the reaction is effective only with primary alcohols Elimination to form alkenes predominates with secondary and tertiary alcohols Diethyl ether is prepared on an industrial scale by heating ethanol with sulfuric acid at 140°C At higher temperatures elimination predominates and ethylene is the major product A mechanism for the formation of diethyl ether is outlined m Figure 15 3 The individual steps of this mechanism are analogous to those seen earlier Nucleophilic attack on a protonated alcohol was encountered m the reaction of primary alcohols with hydrogen halides (Section 4 12) and the nucleophilic properties of alcohols were dis cussed m the context of solvolysis reactions (Section 8 7) Both the first and the last steps are proton transfer reactions between oxygens... 

Petroleum refining, also called petroleum processing, is the recovery and/or generation of usable or salable fractions and products from cmde oil, either by distillation or by chemical reaction of the cmde oil constituents under the effects of heat and pressure. Synthetic cmde oil, produced from tar sand (oil sand) bitumen, and heavier oils are also used as feedstocks in some refineries. Heavy oil conversion (1), as practiced in many refineries, does not fall into the category of synthetic fuels (syncmde) production. In terms of Hquid fuels from coal and other carbonaceous feedstocks, such as oil shale (qv), the concept of a synthetic fuels industry has diminished over the past several years as being uneconomical in light of current petroleum prices. 

The predictive power of tendency models is obviously limited. However, the models can be useful in evaluation of the effect of changing heat-transfer conditions upon scale-up of reactors. Tendency models can be extremely useful for improvement and optimization of existing industrial reactors/reactions, especially for the improvement of the time-temperature policy and the policy of addition of component(s) to the reaction mixture. 

Heat, See also High temperature entries Hot entries Temperature entries Therm- entries effect on rubber aging, 27 785 in ethylene oxidation, 70 650 exponents of dimensions, 8 585t external resistance to, 25 312-316 in industrial hygiene, 74 221 wood reaction to, 26 348-351 Heat aging, of polychloroprene polymers, 79 844-845... 

The activity calculated from (7) comprises both film and pore diffusion resistance, but also the positive effect of increased temperature of the catalyst particle due to the exothermic reaction. From the observed reaction rates and mass- and heat transfer coefficients, it is found that the effect of external transport restrictions on the reaction rate is less than 5% in both laboratory and industrial plants. Thus, Table 2 shows that smaller catalyst particles are more active due to less diffusion restriction in the porous particle. For the dilute S02 gas, this effect can be analyzed by an approximate model assuming 1st order reversible and isothermal reaction. In this case, the surface effectiveness factor is calculated from... 

In this paper only isothermal simulations have been conducted to show the important features of the model to describe mass transfer with chemical reaction. In many industrial processes, distillation, reactive distillation and some absorption processes, heat effects play an important role and therefore cannot be neglected. These effects will be discussed in Part II. 

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