PTQ Q2 2025 Issue

Exemplary Steam Cracker naphtha specs

Exemplary catalytic reformer naphtha specs

Property

Method

Specs < 750

Property

Method

Specs <750

Density @ 15°C, kg/m3

ASTM D4052 ASTM D2887 UOP 326-82 ASTM D5622 ASTM D5762 ASTM D5453 ASTM D7359

Density @ 15°C, kg/m3

ASTM D4052 ASTM D2887 UOP 326-82 ASTM D5622 ASTM D5762 ASTM D5453 ASTM D7359

FBP, °C

193

FBP, °C

180-205

Diene value (DV), g I2/100 g Total elemental oxygen, wppm

none

Diene Value (DV), g I2/100 g Total elemental oxygen, wppm

none

<50

Nitrogen, wppm

<0.5

Total sulphur, wppm

<500

Total sulphur, wppm

<1 <1 <1

Organic halides (Cl, Br, F), wppm

Metals As, ppbwt Pb, ppbwt Na, ppbwt Si, wppm

Metals

ICP-AES ICP-AES ICP-AES ICP-AES

<10 <50

Si, wppm

ICP-AES

<0.1

< 100

Table 2

normally represents an integrated sequence of adsorption and hydrogenation process steps. Catalytic reforming unit (CRU) Catalytic reforming is a primary technology that produces aromatics, a high-octane component for gasoline and a key source of BTX, responsible for about 68% of a global vol- ume. As the base platform molecules, BTX stands at the very beginning of important value chains that lead to versatile plastics and resins such as polyurethanes, polycarbonates, nylon, and polyester fibres. The feedstock for the catalytic reforming process is a straight-run heavy naphtha typically supplied from the atmospheric distillation unit of the refinery. The naphtha is hydrotreated to remove sulphur and nitrogen impurities upstream of the CRU. The cracked naphthas from processes like fluid catalytic cracking (FCC), visbreaking, or delayed coking can be pro- cessed in the CRU, but only after deep hydroprocessing, which typically involves stabilisation (diolefin saturation and hydrodesulphurisation, and hydrodenitrogenation steps). Replacing a fossil-based with a pyoil-derived naphtha in catalytic reforming presents an opportunity to at least par- tially transition to circularity in the production of non-poly- olefin polymers. While there are multiple benefits to putting pyoil-derived naphtha into a catalytic reformer, a thorough assessment is required, which should encompass detailed feedstock purity, composition, and boiling range evaluation. It is recognised that CRU feedstock must be of exceptional purity. The reason for that is high poison sensitivity of plat- inum (Pt)-based catalysts almost exclusively used across all variations of catalytic reforming technology.10 To reach the required purity levels, commercial reformers rely on an upstream hydrotreating step that removes most sulphur, nitrogen, and other components that would otherwise poi- son the catalyst, leading to rapid activity loss. In this regard, the naphtha specifications for reforming are very stringent, which leads to extra purity requirements if the feedstock is pyoil-based (see Table 2 ). An additional aspect that needs to be considered while assessing the use of a pyoil-derived naphtha as the feed- stock for catalytic reforming is the content of cycloalkanes (naphthenes and paraffins). Unlike straight-chain hydrocar- bons, naphthenes readily convert to aromatics, increasing the yields of valuable BTX and maximising overall process

Table 1

The effect appears to be related to certain differences in hydrocarbon speciation of plastics and fossil-derived naphtha,8 , 9 which directly affects ethylene and propylene yields. Consulting with a correspondent licensing com- pany is essential for an operator to assess those effects. Nevertheless, from an ease-of-use perspective, liquid-fed crackers are optimal to accept pyoil-based feeds. The respective amounts of circular ethylene, propylene or, if desired, butadiene and aromatics are calculated using a mass balance principle. The situation is more complicated in the case of ethane or LPG-fed crackers if those are to be used in producing cir- cular monomers. Although pyrolysis of waste plastics does generate an off-gas stream that contains C2-C4 hydrocar- bons, the amounts are minor and typically do not warrant an effort to enrich and purify these components. In addition, most pyrolysis units are not integrated into the respective pipeline infrastructure that would be needed to transport the gas feedstock even if a certain pyrolysis technology does produce high C2-C4 gas product stream. Nevertheless, some potentially viable workarounds are being discussed in the industry. These would rely on feed- ing pyoil-based stocks into processes that already copro- duce LPG, such as catalytic reforming of naphtha (typically 5-15% LPG yield) or, under certain conditions, atmospheric distillation of crude oil (1-4% LPG yield). A mass balance approach is then utilised to calculate the quantity of circular LPG that is available to feed a gas cracker. While in theory doable, these routes are likely cost prohibitive unless used as part of a wider strategy to make circular chemicals. For example, putting the focus on claiming circular BTX from catalytic reforming. Upgrading needs (steam crackers) Due to stringent purity specifications imposed on naphtha used in steam crackers, thorough upgrading of pyoil-de- rived naphtha is required. The key impurities to address are halogens, nitrogen, oxygen, and metals, predominantly silicon (Si) and alkali metals (see Table 1 ). Using effective catalysts and absorbents, it is possible to process raw pyoil naphtha or the blend after pyoil has been mixed with the conventional feedstock. The optimal configuration of the purification train is a function of pyoil composition and

PTQ Q2 2025