Paraxylene Recovery

CrystPX is GTC’s crystallization technology for production of paraxylene, offered through alliance with Lyondell Bassell.  This process separates paraxylene by slurry phase crystallization and separation of the paraxylene crystals from the remaining liquid.  CrystPX technology is applicable with high or low concentration paraxylene feedstocks, and is a lower-cost alternative to adsorption methods for paraxylene production.  GTC takes advantage of recent advances in crystallization techniques and improvements in equipment to create this attractive method for paraxylene recovery and purification.

Process Description

In the CrystPX Technology process, suspension crystallization of paraxylene (PX) in the xylene isomer mixture is used to produce paraxylene crystals. The technology utilizes an optimized arrangement of equipment to obtain the required recovery and product purity. Washing the paraxylene crystal with the final product in a high efficiency pusher-centrifuge system produces the paraxylene product.
When paraxylene content in the feed is enriched above equilibrium, such as streams originating from selective toluene conversion processes, the proprietary crystallization process technology is even more economical to produce high-purity paraxylene product at high recoveries. The process technology takes advantage of recent advances in crystallization techniques and improvements in equipment to create this cost effective method for paraxylene recovery and purification.
The design uses only crystallizers and centrifuges in the primary operation. This simplicity of equipment promotes low maintenance costs, easy incremental expansions, and controlled flexibility. High-purity paraxylene is produced in the front section of the process at warm temperatures, taking advantage of the high concentration of paraxylene already in the feed. At the back end of the process, high paraxylene recovery is obtained by operating the crystallizers at colder temperatures. This scheme minimizes the need for recycling excessive amounts of filtrate, thus reducing overall energy requirements.

Process Advantages

  • High paraxylene purity and recovery (99.8+ wt.% purity at up to 95% recovery)
  • Crystallization equipment is simple and operationally trouble free
  • Compact design requires small plot size and lowest capital investment
  • Operation is flexible to meet market requirements for paraxylene purity
  • System is easily amendable to future requirement for incremental capacity increases
  • Feed concentration of paraxylene is used efficiently
  • Technology is flexible to process a range of feed concentrations (75-95 wt. % paraxylene) in a 1-stage refrigeration system
  • Design variations are used to recover paraxylene efficiently from feedstocks (-22% PX) in a multi-stage system, competitive with adsorption-based systems