The Parex unit for industrial-scale purification of p-xylene was studied through detailed simulation and the accuracy of the developed model tested against real industrial data. Starting from a comprehensive analysis of the construction and operation of the industrial unit, a simulation model was developed that incorporates the existing three major types of dead volumes: bed lines, which connect the beds to the rotary valve, circulation lines, which connect adjacent adsorbent chambers, and bed-head dead volumes, which are located upstream of each bed due to the existence of internals. By gathering operation data and surveys in the pumparound line and in the extract stream, three case studies were defined and compared with simulation results. The model is capable of predicting the performance of the industrial unit. Further simulations were made and compared with plant data to assess the effect of adsorbent capacity loss on the long-term performance of the unit. (C) 2015 American Institute of Chemical Engineers