Reaction heat effects

Taskin, M.E. et al. (2008) CFD study of the influence of catalyst particle design on steam reforming reaction heat effects in narrow packed tubes. Ind. Eng. Chem. Res., 47 (16), 5966-5975. 

Energy balances are needed whenever temperature changes are important, as caused by reaction heating effects or by cooling and heating for temperature control. For example, such a balance is needed when the heat of reaction causes a change in reactor temperature. This is seen in the information flow diagram for a non-isothermal continuous reactor as shown in Fig. 1.19. 

Fig. 33. Comparison of temperature fields in WS midplane for particles with active outer shell (95% inactive, left diagram) and particles with no reaction heat effects (100% inactive, right diagram). 

If a process involves chemical reactions, heat effects will invariably be present. The amount of heat produced in a chemical reaction... 

The amount of heat required for a specific chemical reaction depends on the temperatures of both the reactants and products. A consistent basis for treatment of reaction heat effects results when the heat of reaction is defined as the heat effect that results when all products and reactants are at the same temperature. 

The problem of heat effects in gas liquid reactions was first analyzed by Danckwerts.38,41 He showed that for the absorption of C02 in amine solutions, the heat- effects are negligible. Carberry25 showed that, in many gas-liquid reactions, heat effects are small because of the low activation energy for the reactions. 

Indications for the reaction enthalpy are also derived from the continuous pilot installations, both at Shell Research (1984-1986) and the present one at TNO-MEP. Here one measures the steady state electric energy supply required for heating the reaction mixture to the desired temperature. By comparing this with a blank experiment where only water is heated one concludes that the overall reaction heat effect is exothermic, and its value is consistent with the result from the autoclave work. 

Adiabatic or nonisothermal operation of a stirred tank reactor presents a different physical situation from that for plug flow, since spatial variations of concentration and temperature do not exist. Rather, reaction heat effects manifest themselves by establishing a temperature level within the CSTR that differs from that of the feed. Thus, when we use the terms adiabatic or nonisothermal in reference to CSTR systems, it will be understood to imply analysis where thermal effects are included in the conservation equations but not to imply the existence of thermal gradients. 

R = a constant endothermic volumetric reaction heat effect, cal/hr... 

The circulating bed media may be coal ash particles or limestone particles, depending on the process desulfurization needs—the limestone reaction conversions in this cyclic oxidizing-reducing environment may have reaction heat effects that influence the process performance. 

Here p is density, kg m, and Cp is specific heat capacity of the reaction mixture, J (kgK) AH is the reaction heat effect (taking the sing into account), J moP To be specific, these parameters depend on temperature. In addition, heat capacity and density can change as the reaction goes. One should account for that when performing important calculations. In order not to overcomplicate, we assume that these values are constant. We will define an additional parameter J = AH/pCp. One can see that ... 

Direct fluorination with elemental fluorine is not practical for commercial synthesis of fluorinated surfactants. Elemental fluorine is extremely reactive and difficult to handle. The heat of formation of the C—bond (about 460 kJ/mol or 110 kcal/mol) and the H—F bond (566 kJ/mol or 135 kcal/mol) exceeds that of the C—C bond (about 348 kJ/mol or 83 kcal/mol) [1]. Hence, the fluorination with elemental fluorine leads to a violent fragmentation of the substrate unless the reaction is carefully controlled and the reaction heat effectively dissipated [2,3]. Commercially important pathways to fluorinated surfactants are electrochemical fluorination, telomerization, and oligomerization of tetrafluoroethylene [4-6]. 

Suspension polymerization is a polymerization process in which dispersed monomer droplets are stabilized by surfactant and mechanical agitation in a liquid phase such as water. As in emulsion polymerization, the monomers used for suspension polymerization are usually insoluble in water. Advantages of suspension polymerization compared with other polymerization methods include easy removal of reaction heat, effective temperature control, low viscosity of the reaetion system, simple polymerization mechanism, high purity of the produet, easy separation and purifieation of the produet and shaped product in particle form. Polymers prepared by suspension polymerization inelude... 

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