suitable for quantifying styrene and its derivatives, as they are not considered conjugated diolefins. Careful attention must be given to unit design and the dilution effect. While MAV of WCN values are lower than 20 mg/g, raw pygas has values above 80 mg/g. Summary and conclusion Refineries must be able to switch between fuels and pet - rochemicals according to market demand. Integration between the FCC and steam cracker is essential to opti- mise value streams, particularly for benzene and propylene. However, each integration scenario carries specific techni - cal challenges (such as reactive diolefins, gum formation, benzene content, and catalyst selectivity) that need to be carefully addressed and assessed. Benzene is a highly marketable petrochemical intermedi- ate needed in several industries. Co-processing raw pygas in the WCN process offers certain benefits but also comes with some limitations and drawbacks. To compensate for benzene loss and satisfy market demand, integration of pygas could be used as an alternative but requires further evaluation and assessment by licensors. The impact of C5 naphthenes must be evaluated by FCC catalyst manufac- turers to assess the potential benefits and limitations. Values discussed in the article are derived from real industrial sampling and operating observations from commercial units. Certain data have been normalised for confidentiality purposes. References 1 Castaño, P., Pawelec, B., Fierro, J.L.G., Arandes, J.M., Bilbao, J., Enhancement of pyrolysis gasoline hydrogenation over Pd-promoted Ni/SiO 2 -Al 2 O 3 catalysts, Fuel , Vol 86, Issue 15, 2007, pp. 2,262-2,274. 2 Hoffer, B.W., Bonné, R.L.C., van Langeveld, A.D., Griffiths, C., Lok, C.M., Moulijn, J.A. Enhancing the start-up of pyrolysis gasoline hydro- genation reactors by applying tailored ex situ presulfided Ni/Al2 O 3 cat- alysts, Fuel , Vol 83, Issue 1, 2004, pp.1-8. 3 Nijhuis, T.A., Dautzenberg, F.M., Moulijn, J.A., Modeling of monolithic and trickle-bed reactors for the hydrogenation of styrene, Chemical Engineering Science, Vol 58, Issue 7, 2003, pp.1,113-1,124. 4 Gonzalez, R.C., Chau, C., Nogales, J.L., Lopez-Aranguren, B.A., Larraz Mora, R.D., FCC catalyst for maximum propylene, PTQ Q4, 2016. 5 De Graaf, B., Allahverdi, M., Evans, M., Diddams, P., How ZSM-5 works on FCC gasoline composition, PTQ Q4, 2015. 6 Ohayon, D., Le Van Mao, R., Ciaravino, D., Hazel, H., Cochennec, A., Rolland, N., Methods for pore size engineering in ZSM-5 zeolite. Applied Catalysis A: General, Vol 217, Issues 1-2, 2001, pp.241-251. 7 Buchanan, J.S., The chemistry of olefins production by ZSM-5 addi - tion to catalytic cracking units, Catalysis Today , Vol 55, Issue 3, 2000, pp.207-212. Abdul Rahman Noah Abou Einein is a senior expert in process technologies at OMV, with more than 10 years in the refining and petrochemical industries. He is part of OMV Downstream GmbH, sup - porting joint venture assets in the Middle East. Throughout his work across diverse technical positions, he has developed a proficiency in troubleshooting chemical processes. A graduate of French Petroleum Institute, Ecole Normale Supérieure de Lyon, and Lebanese University, he has extensive expertise in cracking, olefins, pyrolysis gasoline, and water chemistry.
Raw p y g as (Option B 1 )
Lights to recycle
LCN
SHU/HDS
WCN
MCN
HCN
Raw p y g as (Option B2) Heavy aromatics
As pygas from gas crackers is a raw stream, it requires the separation of the heavy-end tail. Injecting it upstream from the NP splitter would allow removal of pygas heavies (C₉+) to avoid violating HCN specifications. In all steam crackers, pygas is frequently used as a wash- ing stream for pumps and filters. In liquid crackers, pygas washing effluents are mixed with raw pygas, where the heavies will be later processed through the heavy-end split- ter and rerouted to pyrolysis fuel oil (PyFO). In gas crackers, pygas is the heaviest fraction; there is no PyFO recovery stream. All pygas washing effluents are then mixed with raw pygas. In option B2, injecting pygas downstream of the NP split- ter will not allow C₅ naphthenes, light reactive diolefins, and benzene to be recycled to the FCC riser; they will all be pro- cessed through the WCN SHU. On the other hand, pygas heavies would not be removed and will end in HCN, which will impact final specifications, unless partial co-processing is applied and dilution is prevailing. SHU inlet specifications When raw pygas is integrated with WCN, careful attention must be given to SHU inlet specifications. Pygas SHU oper - ating conditions and catalyst differ from the those in the WCN SHU process. The main difference is having milder conditions. At the end of run, the pygas SHU process tem - perature must not go beyond 110-120°C. If it does, it is essential to switch to the spare reactor. Otherwise, gum formation and uncontrolled polymerisation reactions may occur due to the reactive conjugated C 5 diolefins and sty - renics in the SHU reactor and heat exchangers. On the other hand, WCN in FCC SHU normally operates at a temperature above 140-150°C. Exposing untreated pygas to a high temperature in the WCN SHU must be avoided, and dilution may be insufficient. A careful evalua - tion with the SHU licensor must be done. HCN is very well known for its content in C₈ aromatics (mainly xylenes). In addition to xylenes, among C₈ aromat - ics, pygas is widely recognised for its content in styrene and its derivatives. If raw pygas from gas crackers is inte- grated with the WCN HDT process, introducing styrenic derivatives may lead to gum formation and plugging when exposed to high temperature in the WCN HDT process, similar to C 5 conjugated diolefins. Maleic acid value (MAV) measures only conjugated diole - fins that react with maleic acid. MAV measurement is not Figure 6 WCN process with a naphtha splitter (options B1-B2)
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PTQ Q3 2026
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