Crystallization provides an energy efficient separation process.


Xylene exists in the form of three isomers:
1,2 dimethylbenzene (ortho-Xylene)
1,3 dimethylbenzene (meta-Xylene)  Download our brochure
1,4 dimethylbenzene (para-Xylene)   Download our brochure


There are many uses for solutions of mixed Xylene isomers including solvent in the printing, rubber, electronics and leather industries. The most commercially important product is the 1,4 isomer (p-Xylene) since it is used as a feedstock in the production of terephthalic acid, which is a monomer used in the production of the polymer (PET) widely used in the production of bottles, films and fibers.

Due to their similar boiling points it is difficult to completely separate the Xylene isomers by distillation. The most common technique used today is adsorption. This occurs when one isomer is preferentially attracted to an adsorbent. The mixed isomer solution is pumped through a column that is loaded with a specially developed resin that will become loaded with the para-Xylene isomer. After a period of time the adsorbent is flushed to extract the para-Xylene and so provides an increase in the purity of the para-isomer. Repeating this process will provide high purity para-Xylene.

The low viscosity and rapid crystal growth in para-xylene purification systems allow use of the high capacity screw type wash columns.
The low viscosity and rapid crystal growth in para-xylene purification systems allow use of the high capacity screw type wash columns.


Melt crystallization can also be used to effectively separate the mixed Xylenes. This accounts for 25-30% of the world’s production of para-Xylene. The melting temperature of the pure para- isomer is much higher (+13°C) than the ortho- (-25 °C) or meta- (-48°C) isomers. It is possible to form high purity para-Xylene crystals in mixed Xylene solutions even down to its eutectic (±13wt% para-Xylene). When this solid is separated from the remaining liquid high purity para-Xylene can be recovered.

A hybrid system utilizing adsorption and crystallization can provide high purity para-Xylene and is an energy efficient method to expand the capacity of existing adsorption systems.