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What strategies can be considered to meet the expanding paraxylene market?

Apr-2025

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Keith Couch, 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-chemicals 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 C7-C10 molecules out of the gasoline pool so it can be reformed into aromatics. This strands a lot of C4s and light naphtha that can no longer be soaked up into a residual gasoline pool. The result is typically another set of investments to alkylate the C4s 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 bottles and shirts. As economy of scale and crude-to-chemicals have taken off, there needs to be an integrated value chain to truly compete.
• Embrace the latest tech: While PX technology has been in the market since the early 1970s, large advancements in the technology have driven step-change lower coefficient of performance (COP) and economy of scale since 2014 to date. Latest designs, catalysts, and adsorbents have reduced the energy footprint by more than 30%, and equipment tonnage and cost by 25% per tonne of PX. UOP’s Light Desorbent PX (LDPX) technology was launched in 2015 and now accounts for about 35% of the world’s total PX production. Older tech can be revamped but often faces the challenges of limited feedstock to take advantage of scale.
• High-yield reforming catalysts: Catalyst technologies have advanced over the past five years, improving aromatics selectivity and hydrogen production. These are easy to change out ‘on the fly’ and provide significant PX production improvements.

Apr-2025
Danny Verboekend, 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 (biomass) 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 (C9+) with toluene and/or benzene represents an attractive option. Finally, within the aromatic C8 fraction, isomerisation reactions may be executed to maximise the PX yield at the expense of ethylbenzene and the lesser desired xylene isomers.

Importantly, the preferred catalysts for this reaction are zeolite-based, giving rise to a relatively high shape selectivity 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), hydrocracking, 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.

Apr-2025