Energy Efficient Styrene Process: Design and Plantwide Control

The paper deals with conceptual design and simulation of an energy efficient process for manufacturing styrene by ethylbenzene dehydrogenation in adiabatic reactors using superheated steam as inert. A high performance catalyst is employed with selectivity of 95% at conversion of 70%. An innovative solution leads to a spectacular energy saving. The idea is running the steam generation under vacuum, followed by mechanical vapor recompression (MVR). The resulting pressure allows matching the temperature–enthalpy profiles of cold and hot streams in an evaporation/condensation zone that concentrates 40% from the hot energy input. In addition, effective heat transfer is ensured by high transfer coefficients. An efficient network of five feed-effluent-heat-exchanger (FEHE) units diminishes the utility consumption by 73% with respect to the base-case. The economic analysis demonstrates that the cost of energy dominates over the cost of equipment. Despite the investment in the compressor, the MVR alternative brings a reduction in the total annual cost by 36%. The feasibility of the proposed solution is validated by dynamic simulation. The plantwide control adopts the strategy of keeping constant the flow rate of ethylbenzene to the reaction section proportional to the required production rate. The process can handle disturbances of ±10% in throughput while keeping the purity of styrene over 99.5%.