selective toluene

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.

Key benefits

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

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

PxMax flowscheme

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