Dehydrogenation of ethylbenzene using CO₂ - A process design study

The scope in this project is the design of a dehydrogenation process for ethylbenzene using CO₂ as mild oxidant including a technical and economical evaluation. Compared to the conventional process this process has a more favorable equilibrium and can therefore be operated at a lower temperature and lower energy consumption. The design is based on the data of the most promising catalyst investigated which is Fe/Al/Zn (1/2/6) reported by Mimura (2002). Laboratory results show a single pass conversion of 26% with a selectivity to styrene of 91% for a CO₂/ethylbenzene ratio of 11. The process is designed according to the systematic process synthesis techniques. Results show that the low conversion and especially the high CO ₂/ethylbenzene ratio results in an unfeasible recycle flow. It is decided to reduce the CO₂/ethylbenzene ratio to 2. The economic evaluation shows that the current margin of $200 between the product and raw material is too low and should be minimal $250. An alternative would be to increase the selectivity to minimal 93%. The available catalyst data such as selectivity, conversion and lifetime is limited and should be subject of further research especially at low CO₂/ethylbenzene ratios.