TOLUENE METHYLATION TO PARA-XYLENE

This design project explores the economic viability of a novel technology for the production of para-xylene via the methylation of toluene. Current production processes yield an unsatisfactory equilibrium mixture of xylene isomers only 23% pure in para-xylene. This low yield of para-xylene necessitates the use of prohibitively expensive separation processes such as the absorptive separation process, Parex, licensed at a whopping $57 million – not including utilities. A new process patented by Breen et al. makes use of an oxide-modified ZSM-5 catalyst and short catalyst contact times to achieve a 99.9% para-xylene selectivity. This design allows for the production of 99.9% pure para-xylene by use of conventional decantation and distillation. This project investigates the economic and environmental feasibility of converting 400 million lb/yr of toluene to para-xylene. The methylation reactor is designed according to patent specifications to reproduce operating conditions that yield a 99.9% para-xylene selectivity and a 100% single-pass methanol conversion. Conserving resources is prioritized through extensive recycling of reactants and through introduction of an intricate heat exchanger network that capitalizes upon the high exothermic nature of the reaction. The Total Capital Investment for the process is $63,170,900 with a projected Net Present Value in 15 years of $60,468,500 and an Investor’s Rate of Return of 28.80%. In light of the economic profitability of the process and the projected increase in demand for para-xylene, it is recommended that the design be considered for further implementation.