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Generic Pygas Process
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Generic Pygas Process

General Process Description

Pyrolysis Gasoline or Pygas (C5+ cut) is a Naphtha-range liquid product with high Aromatics content produced in an Ethylene plant that processes Naphtha, Butane or Gasoil
This C5+ cut, if left in its raw form, has little commercial value owing to its high reactivity and low stability. However, the stream contains many high-value components, such as Isoprene, Benzene, Toluene and Xylenes. Extracting these components can be highly economical and typically requires hydrotreating in a Pygas Hydrogenation Unit (PHU). The stream can be treated in various ways, depending on the required product slate. Products derived from Pygas treatment are used either for Gasoline blending or as a feedstock for a BTX extraction unit. The following description is an example of an existing Pygas hydrotreating complex that includes a HydroDealkylation Unit (HDU)[1,2].    


The Pygas is separated in a first column (depentanizer) into Raw-C5 and C6+ Pygas,

Hydrogenation Unit

The C6+ Pygas is sent to the two-stage hydrogenation unit, that successively hydrogenates the double-bond compounds to make saturated compounds, and removes sulfur compounds and turn them into feedstock suitable for the extraction unit.


The hydrotreated Pygas is separated in the Deoctanizer into a hydrogenated HEART CUT (mixed C6~C8) that is sent to the extraction unit, and the C9+ Raffinate that is used as feedstock for the HydroDealkylation Unit (HDA).

Extraction Unit

The Extraction Unit selectively extracts Aromatic Compounds from the C6~C8 Heart Cut, that dissolve well in Sulfolane. The extracted Aromatic Compounds are sent to the Fractionation Unit. The remainer lighter fraction from the extraction process is a Non-Aromatic Raffinate

Hyrodealkylation Unit

The Hydrodealkylation Unit turns the C9+ mixture fractionated in the Hydrogenation Unit into a Benzene-rich Aromatic Mixture through Hydrocracking and Hydrodealkylation.

Fractionation Unit

The Fractionation Unit uses the difference in boiling points of Aromatic Mixtures coming from the Extraction Unit and Hydrodealkylation Unit to produce high-purity Benzene, Toluene and Xylene.


  1. enggcyclopedia, Jun 2012, Typical Process Flow Diagram (PFD) – Pygas Processing
  2. YEOCHUN NCC, Intro to Plants, Aromatic Plant 2.
System Info

Updated by
UserPic  Kokel, Nicolas
5/7/2024 7:55 AM
Added by
UserPic  Kokel, Nicolas
2/5/2022 7:55 PM



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Simplified Pygas Processing Block Flow Diagram https://www.enggcyclopedia.com/2012/06/pygas-processing-pfd-process-flow-diagram/
Simplified Pygas Processing Block Flow Diagram https://www.enggcyclopedia.com/2012/06/pygas-processing-pfd-process-flow-diagram/
Yeochun Aromatic Plant 2 https://www.yncc.co.kr/en/product/factory/2/persimmon.do
Entity Site (Country) Asset (Plant)
Sadara Sadara Aromatics Facility
YNCC Yeosu Pygas Plant 1
YNCC Yeosu Pygas Plant 2
YNCC Yeosu Pygas Plant 3