The influence of heat dispersion on the performance of adiabatic industrial-scale membrane reactors is studied in this work. The results presented are from the application of the model to a membrane reactor that is introduced in an IGCC plant, to control carbon dioxide emissions. The performance of this reactor equipped with highly selective membranes is studied in detail. The thermal phenomena that take place in the interior of the membrane reactor have a considerable influence on the operation of the reactor thus the assumption of isothermal operation is not valid. The omission of thermal dispersion results on the underestimation of the system operation and the total gaseous fluxes that permeate through the membrane. The temperature distribution in the membrane reactor differs significantly from the calculated distribution, predicted from the model that ignores thermal dispersion effects.