PTQ Q3 2026 Issue

a co-feed in a WCN HDT pro- cess, three main points must be handled with precaution: • Injection of pygas regard- ing naphtha (NP) splitter (if existing). • Introduction of benzene in LCN and HCN. • SHU inlet specifications.

C-cut

Separation zone

Compression zone

Separation zone

Rx zone

Heavy feed

C cut

WCN

SHU Rx Temp > 120˚C

LCO

WCN HDT units

Slurry oil

LCN Rich in C olens + iC Rich in C–C olens Rich in aromatics HCN MCN

LCO: Light cycle oil/LCN-MCN-HCN: Light-Medium-Heavy cracked naphtha/SHU: Selective Hydrogenation Unit

Based on the presence (or absence) of an NP splitter downstream of an FCC debu- taniser, three configurations exist, as shown in Figure 4 . Pygas integration in option A Considering an FCC with a high-sulphur feed, where the WCN HDT process is implemented without an NP splitter, only one option exists: injecting raw pygas from gas crack- ers upstream of the WCN SHU. All pygas diolefins and sty - renics will go through the SHU (see Figure 5 ). If pygas integration is involved, recycling LCN will reroute (on purpose) some benzene to the FCC riser, while the remaining benzene will end up in the LCN-HCN. Benzene is resistant to FCC cracking. Recycling LCN rich in benzene, after integrating raw pygas from gas crackers, may lead to benzene accumulation within the recycle loop. Introducing benzene into the FCC WCN through pygas from gas crack- ers would violate the benzene specification in gasoline. The market is being flooded with ethylene that is cheaper than that which older liquid crackers can produce. In addi- tion, the CO₂ emissions per ton of ethylene produced are significantly higher with older cracking technologies. Due to environmental legislation and current ethylene market con- ditions, many industrials have decided to shut down their liquid crackers. Consequently, benzene availability, recov- ered from pygas for petrochemicals, will become limited. Benzene in FCC WCN is formed through alkylated mono-aromatics side cracking, naphthene hydrogen trans- fer, and cyclisation of olefins. The benzene content in WCN without pygas integration is very limited, and its extraction is not economically justified. Many other heavy hydrocarbon streams, with significant alkylated mono-aromatic content, exist and are processed through hydrocrackers, such as heavy coker gas oil (HCGO) from delayed coker units. Some refiners process this HCGO on purpose to FCC. Could this alternative be a maximisa- tion route for benzene production through FCC alkylated mono-aromatic side cracking at the expense of LPG olefins? Integration of pygas with WCN in a hydrotreatment unit would increase benzene content, and generating an addi- tional cut rich in benzene could be feasible. The WCN unit would require a revamp to recover the C₆-benzene-rich cut. Table 1 shows a comparison between FCC and steam crackers in terms of cracked naphtha yields and benzene content. The WCN, pygas, and benzene values shown in the table are highly dependent on the type of feed and co-feed, catalyst composition, and operating parameters. For instance, in FCC operations, zeolite can be adapted

Figure 3 Simplified scheme of FCC showing recovery of WCN streams

Integration options (FCC WCN + Cracker pyg as)

in FCC Without naphtha splitter

in FCC With naphtha splitter

B 1

Figure 4 Pygas co-processing integration options in WCN HDT

Raw p y g as

LCN

SHU/HDS

WCN

MCN

HCN

Figure 5 WCN process without a naphtha splitter (option A)

Yields of cracked naphtha and benzene content in FCC and steam crackers

Cracked naphtha

WCN

Pygas

(VGO FCC)

(liquid crackers) (gas crackers)

Yield, wt%

35-40

20-30 30-40

[Benzene], wt%

30-40

Table 1

to limit hydrogen transfer and to generate fewer gasoline species. In steam crackers, with a lower furnace cracking temperature, pygas is favoured over light olefins. Having a naphtha feed type rich in naphthenes would increase pygas yield. Pygas integration in options B1-B2 Integration of pygas with WCN in the HDT process with a naphtha splitter can be done in two ways, as shown in Figure 6 : • Injecting raw pygas upstream from the NP splitter (option B1). • Injecting raw pygas downstream from the NP splitter (option B2). In option B1, injecting pygas upstream of the NP splitter means that C 5 naphthenes and light reactive diolefins will go to the FCC riser, which may promote gum formation. In addition, some benzene will go to the splitter overhead.

PTQ Q3 2026