2020 CATALYST HANDBOOK INDUSTRY CATEGORIES PROCESS CATEGORIES COMPANY INDEX PETROCHEMICAL Disproportionation PxMax catalyst Recycle toluene - C5 Application: Selective conversion of toluene to high-purity (90%+), paraxylene-rich xylenes and benzene. Description: Dry toluene feed and hydrogen-rich recycle gas are pumped into the reactor through feed/effluent exchangers and the charge heater (Fig. 1, step 1). Selective toluene disproportionation (STDP) occurs in the vapor phase to produce the paraxylene-rich xylene and benzene coproduct. Byproduct yields are small. Reactor effluent is cooled by heat exchange, and liquid products are separated from the recycle gas. Hydrogen-rich gas from the separator (2) is recycled back to the reactor together with makeup hydrogen. Liquid product is stripped of remaining light gas in the stabilizer (3) and sent to product fractionation. Unconverted toluene is recycled to extinction. The PxMax technology uses catalyst that is permanently selectivated by ex-situ pretreatment during catalyst manufacture. PxMax technology provides significantly higher selectivity and longer operating cycles than other STDP technologies. Operating costs associated with downstream recovery are also reduced by the high paraxylene purity from the process. Products: Paraxylene and benzene. Paraxylene Paraxylene-enriched xylenes Paraxylene recovery 99.9+% benzene H2 Stabilizer Toluene PxMAX process Benzene column Toluene column Xylene column Paraxylene-depleted mixed xylenes C9+ aromatics Fig. 1. The PxMax process. ExxonMobil has led the development and application of technologies for xylenes and benzene production since the discovery of ZSM-5 in the late 1960s. As part of our license, we provide full support from initial consultation through technology transfer and ongoing improvements to ensure that operators achieve full value. Advantages: The PxMax process operates at lower start-of-cycle temperature and lower hydrogen-to-hydrocarbon recycle ratios than other STDP technologies, resulting in longer cycles and lower utilities. By eliminating the in-situ selectivation step, the PxMax technology offers simplified operation and lower capital costs. The catalyst has long operating cycles and is regenerable. Installations: Two MSTDP units (predecessor technology to PxMax) and 12 PxMax units are in operation. Development/delivery: The first two units running the PxMax process were started up in 1996 and 1997 at Chalmette Refining's Louisiana refinery and Mobil Chemical's Beaumont, Texas plant, respectively. Contact: https://www.exxonmobilchemical.com/en/resources/contact-us Licensor: ExxonMobil Catalysts and Licensing LLC; Axens Website: www.catalysts-licensing.com Copyright © 2020 Gulf Energy Information. All rights reserved.https://www.hydrocarbonprocessing.com/ http://www.catalysts-licensing.com https://www.exxonmobilchemical.com/en/resources/contact-us