Driving a Reaction by Chemical Coupling

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1,3-Butadiene can be produced by the gas-phase catalytic dehydrogenation of 1-Butene by the reaction . To suppress the reverse reaction, an inert gas (e.g. steam) can be added to the feed stream of the reactor. Instead, we choose here to add to the reactor. Assume a suitable catalyst is present for the water-gas shift reaction ; this second reaction consumes . Therefore, in accordance with Le Chatelier's principle, higher conversion for the dehydrogenation should be achieved. This Demonstration illustrates how one can drive a chemical reaction (i.e. the dehydrogenation reaction) by coupling to a second reaction.


The coupling factor is equal to the number of moles of carbon dioxide added per mole of 1-Butene. The Demonstration computes the equilibrium conversion versus the coupling factor using the Gibbs free energy minimization method. You can set values of the temperature in kelvin as well as the pressure in atm. Here, only low to moderate values of pressure are allowed. Thus, the gas mixture can be assumed to be ideal.

In accordance with Le Chatelier's principle, you can verify that:

1. The conversion is greater when more carbon dioxide is added to the reactor.

2. The conversion is greater when you increase the temperature. Indeed, this reaction is endothermic (, where is the enthalpy).

3. The forward reaction is favored by low pressures. Indeed, there are more moles of product than reactant (, where is the stoichiometric coefficient of species ).


Contributed by: Housam Binous, Mohammad Mozahar Hossain, and Ahmed Bellagi (January 2016)
(King Fahd University of Petroleum & Minerals, KSA; ENIM, University of Monastir, Tunisia)
Open content licensed under CC BY-NC-SA




[1] J. R. Elliott and C. T. Lira, Introductory Chemical Engineering Thermodynamics, 2nd ed., Englewood Cliffs, NJ: Prentice Hall International Editions, 2012.

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