PTQ Q3 2026 Issue

Synergies between FCC naphtha and pygas

Maximising integration between the FCC and steam cracker to its fullest extent involves specific technical challenges, all needing careful assessment

Abdul Rahman Noah Abou Einein OMV Downstream GmbH

T he global refining market is experiencing instability. Future demand for fuels remains uncertain. Refiners must be prepared to transition to petrochemical pro - duction depending on economic drivers and market demand. A key challenge in the petrochemical industry is the shut - down of liquid steam crackers, impacting not only olefins markets but also aromatic industries. The switch to ethane crackers reduces the production of pyrolysis gasoline (pygas), disrupting the petrochemical balance. To compen - sate, industrials must explore alternatives through potential integration routes between refineries and petrochemical complexes. Pygas Raw pyrolysis gasoline (untreated pygas) is a C₅+ hydro - carbon fraction from steam crackers. It contains notable concentrations of olefins, diolefins, and aromatics. It serves various purposes in industry, primarily for recovering C₅ naphthenes, benzene, toluene, and xylenes. Both gas and liquid crackers generate similar hydro - carbon species in pygas. Selective pygas hydrogenation units (SHUs) are mainly installed in liquid crackers and are designed for the selective hydrogenation of reactive diole - fins and vinyl groups in styrenics. While liquid crackers produce a yield between 20-30 wt% pygas, gas crackers exhibit a lower yield, less than 5 wt%. In a steam cracker, pygas is generally withdrawn at two points, as shown in Figure 1 : the bottom of the quench water tower (hot zone) and the bottom of the debutaniser (cold zone). Pygas processing configurations Two main process configura - tions exist for pygas:

further cracking. Liquid steam crackers are considered one of the main contributors to the C₅ naphthenes industry. • Medium pygas (C₆ benzene-rich cut): Used for benzene extraction. Liquid steam crackers are a main contributor to the benzene market. • Heavy pygas (C₇+ cut): Used for gasoline blending or sold as a cut rich in toluene and xylenes for extraction. v Two-stage hydrogenation (full saturation): All olefins and diolefins are fully saturated, producing an olefin/diole - fin-free pygas. This approach is found in applications where aromatics extraction is the main purpose. The key C₅ species in pygas are olefins, diolefins, and naph - thenes. Conjugated diolefins in the C₅ cut, such as 1,3-pen - tadiene, isoprene, and cyclopentadiene, are unstable, highly reactive, and may lead to gum formation1 , 2 if untreated (through Diels-Alder and polymerisation reactions). The C₅ unsaturated species in light cuts of whole cracked naphtha (WCN) and pygas are displayed in Figure 2 . In addition to C₅ reactive diolefins that must be at least partially hydrogenated, styrene and its derivatives act sim - ilarly to unstable diolefins. They are not considered as con - jugated diolefins; the vinyl group is highly stabilised by the aromatic ring. This bond could initiate easily uncontrolled radical polymerisation reactions. If untreated, styrenics may lead to gum formation.³ Pygas C₅ cut Integration in FCC In fluidised catalytic cracking units (FCC), when a high- sulphur feed is processed, WCN, known as FCC naphtha, requires hydrotreatment (WCN-HDT process). The process typically includes SHU and HDS (hydrodesulphurisation). These units mainly target the conversion of WCN diolefins

C- cut

u Limited to a SHU, after con - version of diolefins and styren - ics, three cuts are produced and can be used for different purposes: • Light pygas (C₅-rich cut): Used as gasoline blending or sold for C₅ naphthenes recov - ery or recycled to furnaces for

C cut

Compression zone

Hot zone

Cold zone

Naphtha

C cut

SHU Rx Temp< 120˚C

P y g as

Pygas SHU

Py o il

C cut Rich in C olens + CC + iC Rich in olens and aromatics (BTX) C- cut C cut

Py o il: Pyrolysis oil or Fuel oil pyrolysis/CC: C Naphthenes/ BTX: Benzene, Toluene, Xylene

Figure 1 Simplified scheme of a liquid steam cracker showing pygas recovery

PTQ Q3 2026