Optimal Inlet Temperature Profile Strategies for Decaying Fixed Bed Reactor

Kamleshkumar Ghodasara and Robin Smith. Centre for Process Integration, The University of Manchester, PO BOX 88, Manchester, M601QD, United Kingdom

Inefficient use of raw materials in most catalytic processes can be attributed mainly to the deactivation of catalysts in chemical reactors. Also, the economics of the catalytic reactor, which is prone to coking, depends on the relative rates of the reactions and deactivation of catalyst. Optimization of the operational variables of the catalytic reactors mainly depends on the downstream processing requirements. Also, optimization of temperature profiles in reactors is one of the key problems for the synthesis catalytic reactors. s. In order to achieve efficient use of raw materials, this paper addresses mitigation of deactivation through optimization of inlet temperature-time trajectories.

In this work, simulation of the transformation of methanol into olefins and light gasoline has been carried out in an isothermal fixed bed reactor. Optimum performance, measured in terms of olefin yield, has been achieved by decreasing the inlet temperature with time. This is in contrast to perception prevailing in industry that increase of inlet temperature with respect to time results in constant performance of the reactor. Maintenance of constant performance results in lower impact on the separation networks. To elaborate on this, two types of objectives in terms of reactor yield have been considered, (a) maintaining constant average yield through a single operating cycle which, results in increasing inlet temperature profile through time, (b) optimizing for the maximum overall yield which, results in decreasing inlet temperature profile through time.

In this work, higher average yield has been achieved; however, it decreases through cycle time. In common practice, performance of the reactor is usually maintained constant or nearly constant in order to reduce the impact on down stream processing; however, with an inefficient use of raw materials. Simulations have also been made to keep constant olefin yield at predetermined values by optimising inlet temperature profiles through cycle time. In these simulations, inlet temperature profile has been found increasing for lower values of olefin yields and maintains constant performance through cycle time. Also, a profile based synthesis has been used to develop a temperature profile and parameters determining the size and shape of it in order to establish optimizing variables at different times. The resulting dynamic optimization problem has been solved using a nonlinear optimization algorithm.