The main challenge is separating the m-xylene isomer from the other isomers (o-xylene and p-xylene) and ethylbenzene due to their similar boiling points.
Process Flow Information
The overall process involves production of a mixed C8 aromatic stream and subsequent separation:
Feedstock & Reaction: The primary feedstock is naphtha, which undergoes catalytic reforming to produce a mixture rich in BTX aromatics.
Separation: The C8 aromatic stream (containing ethylbenzene, p-, m-, and o-xylenes) is sent to separation units.
Distillation: Initial distillation separates lighter and heavier components. A xylene splitter may be used, with the top stream containing about 40% m-xylene, 20% p-xylene, and 40% ethylbenzene.
Specialized Separation: Because the boiling points are close, standard distillation is energy-intensive and often insufficient for high purity. Specialized methods are used for selective separation:
Crystallization: This process is often used to first remove para-xylene, which has a much higher melting point than the other isomers (-47.9°C for m-xylene vs. 13.3°C for p-xylene). The remaining mother liquor is enriched in m-xylene.
Adsorption: Adsorption processes, often using zeolites as adsorbents, are a common industrial method for separating specific xylene isomers, including m-xylene.
Isomerization & Recycle: The non-desired isomers (e.g., in the mother liquor from crystallization) are typically sent to an isomerization unit. This unit converts them into an equilibrium mixture of all isomers, which is then recycled back to the separation unit to maximize the yield of the target product.
Visual Examples
While a specific, detailed PFD for a standalone m-xylene plant is complex and often proprietary, the images below illustrate related process components and general xylene structures.
For detailed process flow diagrams (PFDs) used in industry, engineering resources like those mentioned in the search results provide comprehensive information.
source : Fernando Romo Sanchez
