Steady-State Example No. 2 Thermal Cracking of Acetaldehyde

Steady-State Example No. 2 Thermal Cracking of Acetaldehyde [10] 

This next example is not quite perfect because it gives a solution with a leftover radical unaccounted for. However, it is shown here as an example of what to expect in research. Suppose we want to understand the thermal decomposition of acetaldehyde. Rice and Herzfeld [10] studied the thermal cracking of hydrocarbons as part of a very important study related to petroleum processing. Here, we present the thermal cracking of acetaldehyde. Consider the following scheme for the thermal decomposition reaction [11]  

The third steady-state species ( CHO) is apparently constant and only depends on the amount of acetaldehyde, so that is a dead end as far as the steady-state substitution process goes. There may be some other steps leading to H2CO but here CHO does not contribute to the production of CH4. However, from the second equation, we find that 

Then from the first steady-state equation, we have by substitution of the [ CH2CHO]ss expression  

even though we are not given the values of the A constants, we can estimate the E energy. There are many other such free radical mechanisms in thermal cracking of hydrocarbons and these have been in use in designing petroleum refining operations for many years. 

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