A heat-effective 'integrated' process of C2H4 production, incorporating exothermic oxidative coupling of methane (OCM) carried out in the catalytic section of a flow tubular reactor, and endothermic pyrolysis of naphtha carried out in the postcatalytic section of the same reactor, studied earlier in a small silica reactor, was examined now in a scaled-up unit with a stainless-steel (1H18N9T) reactor (volume 400 cm(3), Li/MgO catalyst bed 165 cm(3)). It was demonstrated that depending on the operating conditions, such an integrated process could be realized over a wide range of the relative contribution of the two component processes, leading always to an increase in the C2H4 yield, as compared with OCM or pyrolysis alone. A high degree of additivity of the yields of all products was observed in all cases, independently of the relative contribution of OCM and pyrolysis. Such results indicated that in the scaled-up unit with a stainless-steel reactor, the interactions between the component processes and products were only negligible under experimental conditions. The overall balance of CH4, being consumed in OCM and formed in pyrolysis, was negative, equal to zero, or positive, depending on the relative contribution of the component processes. The integrated process could be based, therefore, either on CH4 and naphtha as raw materials or exclusively on naphtha, with the recirculation of the excess of CH4 to the OCM section. (C) 2004 Society of Chemical Industry.