Methanol synthesis temperature profil

Fig ure 6-12. Profiles of equilibrium oonversion Xg versus temperature T for methanol synthesis. (Source Schmidt, L. D., The Engineering of Chemioal Reaotions, Oxford University Press, New York, 1998.)... 

This is illustrated by the TPD spectra of formate adsorbed on Cu(lOO). To prove that formate is a reaction intermediate in the synthesis of methanol from CO2 and H2, a Cu(lOO) surface was subjected to methanol synthesis conditions and the TPD spectra recorded (lower traces of Fig. 7.13). For comparison, the upper traces represent the decomposition of formate obtained by dosing formic acid on the surface. As both CO2 and H2 desorb at significantly lower temperatures than those of the peaks in Fig. 7.13, the measurements represent decomposition-limited desorptions. Hence, the fact that both decomposition profiles are identical is strong evidence that formate is present under methanol synthesis conditions. 

Temperature profiles, reactors ammonia synthesis, 582, 584 cement kiln, 590 cracking of petroleum, 595 endo- and exothermic processes, 584 jacketed tubular reactor, 584 methanol synthesis, 580 phosgene synthesis, 594 reactor with internal heat exchange, 584 sulfur dioxide oxidation, 580... 

Fig. 2 shows the I.C.I. warm-shot methanol synthesis loop. The adiabatic methanol reactor has multiple catalyst beds which cure quenched with warm reactant gas that control the methanol converter s temperature profile and methanol outlet concentration as portrayed in Fig. 3.. In this adiabatic quench redctor methanol loop scheme, the main features are ...

This figure clearly illustrates that the range within which multiple steady states can occur is very narrow. It is true that, as Hlavacek and Hofmann calculated, the adiabatic temperature rise is sufficiently high in ammonia, methanol and oxo-synthesis and in ethylene, naphthalene, and o-xylene oxidation. None of the reactions are carried out in adiabatic reactors, however, although multibed adiabatic reactors are sometimes used. According to Beskov (mentioned in Hlavacek and Hofmann) in methanol synthesis the effect of axial mixing would have to be taken into account when Pe < 30. In industrial methanol synthesis reactors Pe is of the order of 600 and more. In ethylene oxidation Pe would have to be smaller than 200 for axial effective transport to be of some importance, but in industrial practice Pe exceeds 2500. Baddour et al. in their simulation of the TVA ammonia synthesis converter found that the axial diffusion of heat altered the steady-state temperature profile by less than 0.6°C. Therefore, the length of... 

Exothermic equilibrium reactions like methanol or ammonia synthesis have the disadvantage that a low temperature is needed to reach a favorable high equUibrium conversion of the reactants. Conversely, a sufficiently high temperature is required with respect to kinetics to carry out the reaction at an acceptable rate. Unfortunately, the temperature increases towards the exit of the fixed bed due to the exothermicity of the reaction (if we do not use intensive cooling), which additionally lowers the obtainable equilibrium conversion. Thus, the temperature profile is exactly the wrong way round, and the feed has to be preheated and the product stream has to be cooled, usually by feed-effluent heat exchangers. In addition, heat has to be removed between reaction stages, if the reaction temperature increases too much. 

Examples of a simultaneous numerical solution of molar and energy balance equations for the gas bulk and catalyst particles are introduced in Figure 5.27, in which the concentration and temperature profiles in a methanol synthesis reactor are analyzed. The methanol synthesis reaction, CO -F 2H2 CH3OH, is a strongly exothermic and diffusion-limited reaction. This implies that concentration gradients emerge in the catalyst particles, whereas the heat conductivity of the particles is so good that the catalyst particles are practically isothermal. 

Methanol Synthesis. Form of Temperature Profile with 3 lypes of Reactors. 

After the input has been read and sorted, heat transfer coefficients and other thermodunamic data are calculated at the beginning of each catalyst zone. Temperature and conversion profile in the catalyst bed is then calculated by an axial integration. The mathematical model used in the integrations is described in. This model allows in principle the determination of diffusion restrictions and calculation of effectiveness factors for each reaction in cases where several reactions take place simultaneously. In such cases the concept of effectiveness factor may become rather dubious as shown below for the methanol synthesis, and this may be reflected in difficulties in the calculations. 

Fig. 6.9 Energy profile for the synthesis of DMC from methanol and CO2 under DCC catalysis lower part) at 330 K. Increasing the temperature above 340 K the selectivity of the process is decreased as new compounds (carbamates and isocyanates) are formed upper part). Reprinted with permission from [74]. Copyright (2014) Springer...

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