Optimum Cycle for a Catalytic Dehydrogenation-Regeneration Process

In dehydrogenation of n-butane over alumina-chromia catalyst, a decrease in reaction rate with increase in time of reaction process is due mainly to the catalyst fouling caused by the accumulation of coke on the catalyst pellets. Such cyclic operation in which a catalytic reaction and catalyst regeneration are performed alternately is necessary from economic onsiderations. It. is deduced from the experimental result that in a complete mixed type reactor the rate of coke formation is proportional to the mole fraction of n-butene in the reactor, and the time required for complete generation of the fouled catalyst is proportional to the total amount of n-butene produced. The objective functions are expressed in terms of the amount of n-butene produced, the time of reaction, and the time required for complete regeneration. Criteria for predicting the optimum switching time are associated with maximizing the average production rate of n-butene, minimizing the direct production costs per mole of n-butene, and maximizing the gross profit in one cyclic operation. By expressing the desired substance in the reactor effluent in terms of its mole fraction, these criteria have the advantage in that the optimum switching time can be determined not by the activity of the catalyst, but by the mole fraction of n-butene in the effluent.