Optimization of a Commercial p-Xylene-Simulated Moving-Bed Process with Extended Langmuir Isotherms.

This study reports a new commercial simulated moving-bed (SMB) process for separating ~620 kt/year of p-xylene (PX) with 99.7% purity from the C8 aromatic mixture. An extended Langmuir isotherm was used to consider the binary interaction among six components. The binary interaction parameters were estimated from single and binary adsorptions experimentally measured on a faujasite X-type zeolite at 177 °C and 10 atm. Because the PX-SMB system included 24 bed lines connecting one rotary valve and 24 beds, three flushing sequences were necessary to prevent the deterioration of purity caused by the bed lines. An SMB dynamic model with port switching was created, and its solution for concentration profiles was compared to the plant data. The three flushing flow rates and the tertiary flushing port location were optimized by the parametric study. The PX production rate increased by 0.8% under the optimized condition, which corresponded to the growth of 5.1 kt/year of PX. [ABSTRACT FROM AUTHOR]