Synthesis and characterization of H-ZSM-5 zeolites and their catalytic performance in CH3Br conversion to aromatics

Abstract

Described in this paper are the synthesis, characterization and catalytic application of H-ZSM-5 zeolites for the conversion of CH 3 Br into aromatics. The H-ZSM-5 zeolites were fabricated by hydrothermal crystallization using n-butylamine (BTA) as a template and characterized by XRD, SEM and NH 3 -TPD techniques. The effects of batch SiO 2 /Al 2 O 3 ratio, alkalinity, NaCl/Al 2 O 3 ratio, seed crystals, and crystallization time on the yield, structure/texture and catalytic performance were systematically studied. Adopting the optimum sol (SiO 2 /Al 2 O 3 = 70, BTA/SiO 2 = 0.2847, Na 2 O/SiO 2 = 0.1237, H 2 O/SiO 2 = 37.4, NaCl/Al 2 O 3 = 60, and seed/SiO 2 = 5 wt%) and under the most preferable crystallization conditions of 100°C/24 h-170°C/24 h, H-ZSM-5 zeolites of high crystallinity and small size (300-700 nm) were obtained. Good catalytic performance was observed over the H-ZSM-5 zeolites (aromatic yield up to 44.2%). However, unlike the modification of large commercial HZSM-5, the use of MoO 3 or PbO as modifying agents for the small-size H-ZSM-5 zeolites results in a decline of catalytic performance. The relationship between the structure and the catalytic efficiency of as-synthesized H-ZSM-5 samples were investigated. It was found that with crystallinity enhancement and/or decline in crystal size, there is improvement of catalytic performance.

A new catalytic process for high‐efficiency synthesis of p‐xylene by methylation of toluene with CH3Br

“…The para ‐selectivity in CH 3 Br catalytic conversion (90.1%) is close to that in toluene methylation (93.1%). In view of the product distribution, we consider that the mechanism of side reactions is similar to those reported elsewhere, caused only by CH 3 Br in toluene methylation.…”

“…One can see that the change of CH 3 Br conversion in the catalytic reaction is similar to that in toluene methylation. In both reactions the conversion of CH 3 Br is stable in the first 3 h, and declines significantly in the next 5 h. The results of CH 3 Br conversion, aromatics yield as well as products distribution in the liquid and gas phases in CH 3 Br catalytic conversion over Si—P/HZSM‐5 are somewhat different from those reported before . In addition, the distribution of gas phase products in CH 3 Br catalytic conversion is also different from those (shown in Table ) in the reaction of toluene methylation with CH 3 Br.…”

“…The different results may be attributed to the variation of surface acidity across the catalysts. We found that CH 3 Br conversion needs an appropriate ratio of strong and weak acid sites . Based on the overall results of these two reactions (toluene methylation and CH 3 Br catalytic conversion in this study), one comes to the awareness that the conversion of CH 3 Br has much to do with the catalytic activity (toluene conversion) of the catalyst.…”

“…Although with increase of CH 3 Br/toluene molar ratio, there is reduction in CH 3 Br conversion (shown in Figure ), there is however increase in terms of total CH 3 Br conversion. Our previous study demonstrated that CH 3 Br conversion requires moderate surface acidity over HZSM‐5. Therefore, with increase of CH 3 Br/toluene molar ratio, more strong acid sites on Si—P/HZSM‐5 would be involved in CH 3 Br activation, and there is relatively less participation of strong acid sites in p ‐xylene isomerization.…”

Highly Enhanced Aromatics Selectivity by Coupling of Chloromethane and Carbon Monoxide over H‐ZSM‐5

“…[11] Studies on methyl halide to olefins, in particular, were carried out over SAPO-34 at 723 K, 0.1 MPa, obtaining up to 95 % ethylene and propylene selectivity. [11,12] However, few investigations on the synthesis of aromatics by methyl halide have been published, with the majority of them focusing on CH 3 Br-toaromatics over HZSM-5 [13] or modified ZSM-5 zeolites. [14] It is apparent that under the conditions of < 673 K and 0.1 MPa, 100 % conversion of CH 3 Br was achieved.…”