The pyrolysis of ethane is a complex reaction involving six individual reactions in a reactant mixture of thirteen components. It is further complicated by the deposition of carbon along the reactor walls. The carbon buildup eventually necessitates reactor shutdown, During the intermediate stages the reactor experiences a gradual increase in inlet pressure which affects the reaction conditions, Optimum temperature profiles exist because the yield goes up with increasing temperature, but, consequently, the reactor must be shut down and cleaned out with increasing frequency. The combined effect causes the yearly production of ethylene to go through an optimum.
To find this optimum a computer program was developed with the ability of handling 25 simultaneous reactions involving up to 25 components, It calculates the carbon deposition profile and the changing pressure profiles, as a function of a predetermined reaction gas temperature profile. The reactor will remain in production until the inlet pressure exceeds eight atmospheres. The average yearly production rate is calculated, assessing a reactor shut down penalty of 24 and 48 hours required for the cleaning of the clogged pyrolysis tubes.
The optimum exit temperature for the 24 hour penalty was 1127°K with a corresponding 57% one pass ethane conversion. The 48 hour penalty lowers the optimum exit temperature to 1124°K and a 50.5% ethane conversion.
The practice of increasing pressure to compensate for carbon buildup results in accelerated carbon deposition and is detrimental to overall production scheme.
The program given here is immediately applicable to any plug flow system, the only additional requirement being the physical and thermodynamic constants for the additional components. The program could, for example, be used to calculate the production of acetylene.
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