Selective Toluene Disproportionation process.
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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.
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.
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 C? aromatic product
Life cycle support
Initial discussions to confirm client objectives and tailor the solution
Detailed yield estimate
Process design package
Technology transfer, training, catalyst loading and startup support
Performance monitoring and technical assistance throughout the life of the catalyst
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