PTQ Q2 2025 Issue

pt q&a

More answers to these questions can be found at www.digitalrefining.com/qanda

Q What strategies can be considered to meet the expanding paraxylene market? A Danny Verboekend, CSO, Zeopore, danny.verboeend@ zeopore.com Many methods to maximise the supply of paraxylene (PX) involve molecular conversions of refinery streams using heterogeneous catalysts (see Figure 1 ). Diverse raw and waste streams, based on either fossil or biomass origin, can be converted to aromatics (and therefore paraxylene) using thermo-catalytic processes in an aromatisation step. These can be currently available streams such as lights or naphtha and crude oil, but also upcoming streams of natural (bio - mass) and synthetic polymers (waste plastics). Secondly, an opportunity exists to maximise PX yields by upgrading the obtained aromatic-rich feeds, such as that done on the pyoil obtained from naphtha cracking. Herein, the trans-alkylation of heavy aromatics (C 9 +) with toluene and/or benzene represents an attractive option. Finally, within the aromatic C 8 fraction, isomerisation reactions may be executed to maximise the PX yield at the expense of eth- ylbenzene and the lesser desired xylene isomers. Importantly, the preferred catalysts for this reaction are zeolite-based, giving rise to a relatively high shape selec - tivity to xylenes based on the tight fit of such aromatics in the very narrow zeolite pores (diameter of 0.5 nm, which is a similar size to a xylene molecule). Strikingly, this tight fit also gives rise to transport and access limitations, which implies that only the external surface of the zeolite crystals, hence about 10%, is effectively used in catalysis. One way to overcome such limitations is to use more

accessible (mesoporous) zeolites, which feature either much smaller crystals and/or intra-crystalline mesopores (size range 2-50 nm), increasing the zeolite’s external surface and, importantly, giving rise to sizable benefits in catalytic applications in terms of activity, selectivity, and lifetime. Yet, similar to fluid catalytic cracking (FCC), hydrocrack - ing, and dewaxing, syntheses of the required accessible zeolites are typically executed in the persistent presence of unscalable unit operations and/or the use of costly (organic) ingredients, hampering their widespread implementation. Based on the apparent and urgent need for commercially viable, accessible (mesoporous) zeolites, Zeopore was founded. A Keith Couch, Sr. Director, Business Development & Integrated Projects, Honeywell UOP, keith.couch@ honeywell.com The PX market continues to grow with increased demand for beverage bottles, food packing, and textured polyester yarns, a market truly driven by bottles and shirts. China has driven much of the growth in PX to feed its fibre production. Whereas a single train PX unit was ~600 kMTA as recently as 2010, as PET trains have increased in size, single train PX complexes are now ~2,400 kMTA. This has driven an economy of scale that almost requires a crude-to-chemi - cals complex to feed it. Around 2011, the investment wave of PX units built in Korea consumed most of the world’s remaining merchant heavy naphtha. This put an end to the historical cycle in the aromatics market. Since then, most PX complexes have been integrated with either a dedicated new refinery or associated with a firm intentionally reducing its exposure to gasoline markets. The latter takes a committed move. The production of PX from refinery feedstocks pulls much of the C 7-C10 molecules out of the gasoline pool so it can be reformed into aromatics. This strands a lot of C 4s and light naphtha that can no longer be soaked up into a residual gasoline pool. The result is typically another set of invest - ments to alkylate the C 4s or shedding these materials to the merchant market that could involve the following options: • Go big: Economy of scale matters in the PX world. Most firms will need to fill up at least a world-scale PET plant to be competitive. • Controlling feedstock supply: The days of competing with merchant mixed-aromatics feedstocks are over. These plants have the highest cost, followed by those that buy merchant heavy naphtha. These are the assets that have the hardest time to compete. • Integrating the value chain: The PX market is about bot- tles and shirts. As economy of scale and crude-to-chemi - cals have taken off, there needs to be an integrated value chain to truly compete. • Embrace the latest tech: While PX technology has been

Lights and naphtha

Synthetic or natural polymers

Crude oil

Aromatisation

C+ aromatics

C+ trans- alkylation

Ethylbenzene isomerisation

Benzene, Toluene, Xylenes

MX + OX to PX isomerisation

Figure 1 Catalytic conversions (in green) to convert streams to paraxylene-containing aromatic streams. Each conver - sion involves a zeolite-based catalyst

PTQ Q2 2025