Feedstocks Thermodynamic and Kinetic Feasibility

The interplay between temperature and equilibrium conversion provides a useful guide as to the appropriate temperature window under which to operate a chemical process. Clearly there is little point in operating a process at temperatures where the equilibrium conversion is negligible, as the higher the equilibrium conversion the better from a practical and cost point of view. In cases where the equilibrium conversion reduces with increasing temperature a compromise has to be struck between the temperatures required for a decent equilibrium conversion of reactants and that for a commercially viable rate of reaction. 

A clear illustration of this occurs in the manufacture of methanol from CO and hydrogen (Section 4.7.1), where the first industrial process (commercialized 

The enthalpy of reaction, AH, is the other important thermodynamic parameter to consider. On its own, whether a reaction is exothermic or endothermic will not determine if a reaction is industrially feasible or not. Both exothermic and endothermic processes are known in industry, methanol carbonylation to acetic acid (Equation 3 AH —123 kJ/mol at 200°C), being an example of the former and the steam reforming of methane to synthesis gas, (Equation 4 AH + 227 kJ/mol at 800°C), being an example of the latter. 

The AHj. does however have an important bearing on plant design and costs. An endothermic reaction requires energy to drive it, which is an additional cost. The energy has to be supplied efficiently to the reaction section of the plant, which has a significant impact on reactor design and cost. 

In the case of an exothermic reaction the energy generated needs to be efficiently removed otherwise a runaway reaction could occur with potentially disastrous consequences. The catalyst itself may also be sensitive to even small increases in reaction temperature which may shorten its lifetime or result in a loss in reaction selectivity. The energy generated in an exothermic reaction may be recovered, often as steam, and used as a cost credit that energy has to be efficiently removed from the reaction section of the plant, again with impact on reactor design and cost. 

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