Selective toluene disproportionation (PxMax℠)

ExxonMobil’s PxMax℠ process is the industry benchmark Selective Toluene Disproportionation (STDP) process. The technology, based on the ex-situ selectivated EM-2300 catalyst, offers unmatched paraxylene selectivity and product yields, as well as exceptionally long and stable cycles. The PxMax℠ process is also licensed by our alliance partner, Axens, as part of the ParamaX® technology suite for grassroots aromatics complexes. ExxonMobil’s Dividing-Wall Column (DWC) technology is also available for licensing in combination with the PxMax℠ process.

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Key benefits

- Ultra-high PX selectivity
- Higher total xylene yields
- Superior xylenes/benzene ratio
- Benzene product with greater than 99.9% purity
- No in-situ regeneration need (cycles > 15 years)
- Performance improves over the catalyst cycle
- Reduced size of reactor and PX recovery unit
- Lower metallurgy cost
- Lower operating costs

Ultra-high paraxylene selectivity, superior yields, extremely long catalyst cycles

The EM-2300 catalyst is at the heart of the unique performance and superior yields of the PxMax℠ process. The catalyst is manufactured using a proprietary ex-situ selectivation technique which increases the relative diffusivity rate of paraxylene versus those of the larger isomers. As a result, the PxMax℠ process yields ultra-high paraxylene selectivity at SOC (> 96%). Paraxylene selectivity further increases as the cycle progresses making the PxMax℠ process by far the most paraxylene selective STDP process on the market.

Life cycle support

Initial discussions to confirm client objectives and tailor the solution

Detailed yield estimate

Feasibility study

Commercial proposal

Process design package

Technology transfer, training, catalyst loading and startup support

Technology improvement

Performance monitoring and technical assistance throughout the life of the catalyst

PxMax flowscheme

Compared with traditional STDP processes requiring in-situ coke selectivation, the PxMax process offers the following advantages:

Ultra-high paraxylene selectivity (>96%) which increases throughout the cycle
Higher total xylenes yield
Superior xylenes/benzene ratio
Benzene product with greater than 99.9% purity
Very stable catalyst yielding extremely long cycles (more than 15 years)
No in-situ selectivation requirement, resulting in:

- Simplified operation (no lost time for selectivation)

- Easier retrofit into existing equipment

- Lower metallurgy investment cost and operating cost

High weight hourly space velocity (WHSV)
Very low H₂ consumption
Reduced size for associated paraxylene separation unit resulting in lower investment and operating costs due to the very high paraxylene content in the C₈ aromatic product

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