Isothermal reactors summary

This you cannot do in an adiabatic reactor unless you go to extremely high mixing ratios of fresh feed and recycle gas. In summary, it is a question of selectivity, which is the reason for using the isothermal reactor for Fischer-Tropsch. An adiabatic reactor with a waste heat boiler is cheaper than an isothermal feactor, and hence it is used for methanation. 

SUMMARY OF FUNDAMENTAL DESIGN RELATIONS—COMPARISON OF ISOTHERMAL STIRRED TANK AND PLUG FLOW REACTORS... 

A summary of reactor models used by various authors to interpret trickle-bed reactor data mainly from liquid-limiting petroleum hydrodesulfurization reactions (19-21) is given in Table I of reference (37). These models are based upon i) plug-flow of the liquid-phase, ii) the apparent rate of reaction is controlled by either internal diffusion or intrinsic kinetics, iii) the reactor operates isothermally, and iv) the intrinsic reaction rate is first-order with respect to the nonvolatile liquid-limiting reactant. Model 4 in this table accounts for both incomplete external and internal catalyst wetting by introduction of the effectiveness factor r)Tg developed especially for this situation (37 ). 

In summary, the operation of commercial reactors falls into three categories isothermal, adiabatic, and the broad division of nonadiabatic, where attempts are made to approach isothermal conditions, but the magnitude of the heat of reaction or the temperature level prevents attaining this objective. Quantitative calculations for isothermal and nonisothermal homogeneous reactors are given in Chaps. 4 and 5. 

Laboratory experiments can in principle be carried out in all kinds of continuous and discontinuous reactors. In practice, however, the simple, isothermal BR is the most common choice for a test reactor in kinetic experiments. The reactor vessel is filled with a reaction mixture, and the concentrations of the reactants—and preferably even those of the products—are recorded by chemical analysis. The concentrations are measured either online by a continuous analysis method or via sampling from the reactor vessel and off-line analysis. Various analytical methods are used nowadays, a brief summary of which is given in Table A 10.1. 

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