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MTDP-3 (toluene disproportionation)

A new ZSM-5 catalyst formulation that’s highly selective and stable is the heart of the MTDP-3sm (toluene disproportionation) process. It’s designed to process toluene and limited amounts of C9 aromatics, and can allow for inexpensive debottlenecking of existing toluene disproportionation (TDP) facilities.

The MTDP-3 process also allows for the production of more high-value mixed xylenes and benzene at less cost. As part of an MTDP-3 license, ExxonMobil Chemical provides full support for licensees from initial consultation through technology transfer and ongoing improvements.

Companies licensing the MTDP-3 process, ExxonMobil’s third-generation TDP technology, have included retrofits as well as start-ups. All have experienced MTDP-3’s exceptional catalyst stability, with first cycle lengths typically in excess of seven years.

MTDP 3
Photo — MTDP-3 process can debottleneck operations and lower costs of producing mixed xylenes.

Advantages

Lower costs and debottlenecks

MTDP-3 can debottleneck operations and lower the costs of producing mixed xylenes. Its high space velocity and low H2/hydrocarbon mole ratio can permit increases in throughput without reactor and/or compressor replacement. Additionally, it can reduce operating costs by requiring less hydrogen than competing technologies.

Retrofits into existing reactors

MTDP-3 incorporates ExxonMobil's expertise in ZSM-5 technology and is readily adaptable into existing radial-flow and conventional-flow reactors.

High-purity benzene co-product

Another advantage of the MTDP-3 process is that benzene co-product does not have to be extracted to meet commercial benzene specifications. The MTDP-3 benzene co-product purity exceeds 99.90 wt% via simple fractionation.

Simple fixed-bed process

The process flow (shown) is typical for a vapor-phase reaction in a fixed-bed reactor. Toluene feed with a limited amount of C9 aromatics is combined with a hydrogen-rich recycle gas. It is preheated and passed through a catalyst bed. Disproportionation occurs here, at a moderate temperature and pressure, to produce equilibrium-mixed xylenes and benzene. By-product yields are small.

Reactor effluent is cooled by heat exchange and the liquid products are separated from the recycle gas. The separated liquid is stripped to remove the light ends and then fractionated to recover the benzene product and the mixed xylenes. Unreacted toluene is recycled to extinction.

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