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The model-based optimization of the cooling system of an industrial tubular reactor for the production of lowdensity polyethylene (LDPE) is studied in this paper. First a detailed reactor simulator is presented. Second, a series of wellposed optimization problems are formulated and solved. To this end, the optimization problems are presented with an increasing number of degrees of freedom. Moreover, economic cost functions consisting of conversion and energy terms are derived and constraints due to operational and safety reasons are added. The degrees of freedom involve parameters such as the initiator feed rates, the cooling water temperatures, and the switching position between hot and cold cooling water. The optimization results indicate that a dual water circuit operating at a low and a high temperature allows significant improvements in conversion with respect to the reference case of a single temperature circuit, while maintaining similar molecular characteristics.