Tseng-Chang Tsai

Disproportionation and transalkylation of alkylbenzenes over zeolite catalysts

Disproportionation and transalkylation are important processes for the interconversion of mono-, di-, and tri-alkylbenzenes. In this review, we discuss the recent advances in process technology with special focus on improvements of para-isomer selectivity and catalyst stability. Extensive patent search and discussion on technology development are presented. The key criteria for process development are identified. The working principles of para-isomer selectivity improvements involve the reduction of diffusivity and the inactivation of external surface. In conjunction with the fundamental research, various practical modification aspects particularly the pre-coking and the silica deposition techniques, are extensively reviewed. The impact of para-isomer selective technology on process economics and product recovery strategy is discussed. Furthermore, perspective trends in related research and development are provided.

Base treated H-mordenite as stable catalyst in alkylbenzene transalkylation

The effect of post treatment methods on the pore structure of hierarchical mordenite and its catalytic performance in transalkylation of heavy alkylbenzenes were studied. While the catalytic stability of H-mordenite deteriorated with dealumination by acid or steam treatment, it was improved with desilication by base post treatment. Comparing to the state-of-the-art Pt/mordenite catalysts, the desilicated H-mordenite showed comparable stability giving the best benzene product purity at lower hydrogen and energy consumption and presented the greenest solution. The improved stability is attributed to an enhanced diffusion behavior in the meso-micro hierarchical structure. As confirmed by NMR and sorption data, base treatment can preferentially remove framework silica and re-insert octahedral aluminium into the mordenite structure simultaneously, through which it created enlarged mesopores and defected 12-MR micropores to form a hierarchical porous structure.

Effects of binder, coking and regeneration on acid properties of H-mordenite during TDP reaction

The effects of binder, coking and regeneration on the acid properties of H-mordenite zeolite during toluene disproportionation reaction (TDP) have been investigated by solid-state 31P-MAS-NMR of various adsorbed phosphorous probe molecules in conjunction with elemental analysis by ICP-MS technique. A series of fresh, spent and regenerated mordenite-based commercial catalysts were examined and the results were also compared with binder-free H-mordenite zeolite and unformulated γ-alumina binder. It is found that parent H-mordenite zeolite possessed only Brønsted acidity, which is responsible for the observed catalytic activity. In contrast, the γ-Al2O3 binder exhibited only Lewis acidity and plays a minor role during the catalytic reaction. While the amount of strong Brønsted acid sites decreased rapidly during initial coking, it reached a plateau at a total coke content of ca. 7 wt%, corresponding to ca. 80% decrease in total acidity. That the catalyst remained active even under deep coke deposition (>7 wt%) condition indicated catalytic activity may be invoked by subsequent coking taking place on the external surface rather than intracrystalline channels of the zeolite catalyst. Furthermore, upon catalyst regeneration treatment, ca. 75% of the total acidity could be effectively recovered.

Synergism of acidic zeolite and Pt/zeolite in aromatics transalkylation

Abstract The synergism of a dual-catalyst system comprising of Pt/ZSM-12 and H-Beta aiming to improve the benzene product purity during transalkylation of aromatics has been studied. Catalyst compositions of the dual-catalyst system were optimized at various reaction temperatures in terms of benzene product purity and premium product yields. Accordingly, a notable improvement in benzene purity at 683 K that meets the industrial specification was achieved using the cascade dual-bed catalyst.

Benzene hydrogenation over Pt/siliceous zeolites

A comprehensive study has been made on benzene hydrogenation over several zeolite and alumina supported platinum catalysts. It was found that the hydrogenation activity of the supported Pt depends strongly on the support structure, reaction temperature, and Pt content and deposition procedures. For Pt/ZSM-5 (Si/Al=150), a higher activity was observed for supported Pt prepared by impregnation than ion-exchange method. Consequently, a reverse trend was observed for the methylcyclopentane-to-cyclohexane product ratio, which serves as an indicator for bifunctional catalysis. Selective modifications of Pt/ZSM-5 catalysts using various phosphines as Pt-poisoning agents have been made to identify the locations of the supported Pt. The results correlate well with rate constants and activation energies derived from the zeroth order kinetics model. Furthermore, a highly active Pt/silicalite catalyst has been developed, its potential applications in catalyzing benzene saturation reaction of light reformate in gasoline is also discussed.