Conversion of heavy reformate into xylenes over mordenite-based catalysts

Liquid-phase xylene isomerization on nano-sized ZSM-5

The isomerization process of xylene in the liquid phase has garnered significant attention due to its low energy consumption and high selectivity. However, conventional ZSM-5 zeolites have exhibited significantly diminished activity in this process, primarily attributed to diffusion barriers. To address this issue, Nano-ZSM-5 zeolite was synthesized using tetrapropylammonium hydroxide (TPAOH) as a structure direct agent (SDA) and introducing silicate-1 (S-1) as a crystallization seed. The impact of OH-/SiO2 molar ratio on the sample morphology was investigated. The structure of Nano-ZSM-5 zeolite was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N2 physical -sorption analysis. The results demonstrate that the addition of S-1 crystal seeds enables the formation of ZSM-5 crystallites with diminutive particle sizes (∼20 nm). Furthermore, variations in the OH-/SiO2 molar ratio within the synthetic system impact crystallite aggregation, excessively high or low ratios result in severe aggregation, leading to decreased specific surface area and mesoporous volume. By optimizing the OH-/SiO2 molar ratio to 0.2, the sample exhibits exceptional dispersibility with a specific surface area of 420 m2 g-1 and a mesoporous volume extending to 0.57 cm3 g-1. When utilized as a catalyst for liquid-phase xylene isomerization, nano-ZSM-5 demonstrates superior catalytic performance compared to traditional zeolite.

Friedel-Crafts Acylation for Accessing Multi-Bridge-Functionalized Large Pillar[n]arenes

Pillar[n]arenes can be constructed using a Friedel-Crafts alkylation process. However, due to the reversible nature of the alkylation, mixture of large pillar[n]arenes (n≥7) are obtained as minor products, and thus laborious purification are necessary to isolate the larger pillar[n]arenes. Moreover, inert methylene bridges are introduced during the alkylation process, and the multi-functionalization of the bridges has never been investigated. Herein, an irreversible Friedel-Crafts acylation is used to prepare pillar[n]arenes. Due to the irreversible nature of the acylation, the reaction of precursors bearing carboxylic acids and electron-rich arene rings results in a size-exclusive formation of pillar[n]arenes, in which the ring-size is determined by the precursor length. Because of this size-selective formation, laborious separation of undesired macrocycles is not necessary. Moreover, the bridges of pillar[n]arenes are selectively installed with reactive carbonyl groups using the acylation method, whose positions are determined by the precursor used. The carbonyl bridges can be easily converted into versatile functional groups, leading to various laterally modified pillar[n]arenes, which cannot be accessed by the alkylation strategy.

Dealkylation in Fluid Catalytic Cracking Condition for Efficient Conversion of Heavy Aromatics to Benzene-Toluene-Xylene

Based on the characteristics of typical C₉ ⁺ aromatics in naphtha fractions, the effects of key process parameters and heavy aromatic composition on product distribution of fluid catalytic cracking (FCC) of heavy aromatics (HAs) were investigated. The results show that catalysts with large pore size and strong acid sites are favorable for the conversion of HAs to benzene-toluene-xylene (BTX) at higher reaction temperatures and moderate catalyst-oil ratios (C/O). With a Y zeolite-based catalyst which was hydrothermally pretreated for 4 h, the conversion of Feed 1 at 600 °C and C/O of 10 may reach 64.93%. Meanwhile, the yield and selectivity of BTX are 34.80 and 53.61%, respectively. The proportion of BTX can be adjusted within a certain range. The HAs from different sources show high conversion and good BTX selectivity, which provides strong support for the technological development of HAs to light aromatics in FCC operation.

Synergistic interaction of metal loaded multifactorial nanocatalysts over bifunctional transalkylation for environmental applications

A feasible and cost-effective process for utilization of toluene and heavy reformate is the conversion of its streams by transalkylation reaction into highly valuable xylenes. The process is usually catalysed by zeolites and the challenges to overcome in transalkylation of heavy reformate with toluene over zeolites are their selectivity, activity, long-term stability, and coke formation. Current study aimed to investigate xylenes production by transalkylation reaction on the synthesized metal-doped zeolite catalysts and to characterize prepared catalysts by FTIR, SEM, EDS and BET analysis. Toluene/heavy reformate modelled mixture was utilized as a feed. For the first time Beta and ZSM-5 catalysts with 10% (w/w) cerium and 0.1% (w/w) palladium were synthesized by calcination and wet impregnation method. Catalytic tests were performed by continuous-flow gas/solid catalytic fixed bed reactor at atmospheric pressure, 2 h^-1 and 5 h^-1 and 250, 300, 350 and 400 °C. Experimental results revealed that the highest heavy reformate conversion (98.94%) and toluene conversion (9.82%) were obtained over H-ZSM-5, at 400 °C and 2 h^-1 WHSV. The highest xylene selectivity (11.53) was achieved over H-ZSM-5, and the highest p-xylene percentage (62.40%), using Ce-ZSM-5 catalyst. ZSM-5 catalysts showed more resistance to coke deposition than Beta zeolites. The present study delivers novel approach and catalysts, which have immense potential for developing safer and inexpensive transalkylation process in industry.

Effect of zeolite pore structure on the diffusion and catalytic behaviors in the transalkylation of toluene with 1,2,4-trimethylbenzene

The effect of zeolite pore structure on catalytic properties in the transalkylation of toluene with 1,2,4-trimethylbenzene is investigated by studying the diffusion process and reaction mechanism.