Methanol-to-aromatics conversion over H-Gallosilicate (MFI): influence of Si/Ga ratio, degree of H<SUP>+</SUP> exchange, pretreatment conditions, and poisoning of strong acid sites

The conversion of methanol to aromatics over H-gallosilicate (H-GaMFI) zeolite with different Si/Ga ratios and degrees of H+ exchange, calcined at different temperatures (600-1,100&#176;C), and pretreated hydrothermally at different temperatures and partial pressures of steam, has been investigated in a pulse microreactor at 400&#176;C. The aromatization activity and product distribution in the methanol-to-aromatics conversion are found to be influenced strongly by the above zeolite factors and calcination/pretreatment parameters. The aromatization activity of the zeolite shows a close relationship with its strong acidity (measured in terms of pyridine chemisorbed at 400&#176;C). H-GaMFI and H-ZSM-5 zeolites (having almost the same Si/(Ga or Al) ratio and degree of H+ exchange and pretreated under similar conditions) have been compared for their catalytic activity/selectivity in the methanol-to-aromatics conversion and also for the poisoning of their strong acid sites by pyridine chemisorption at 400&#176;C. H-GaMFI shows much higher aromatization activity. Unlike H-ZSM-5, H-GaMFI shows appreciable aromatization activity even after the poisoning of its strong acid sites or in the presence of only weak acid sites because of its higher dehydrogenation activity

Effect of silica binder on acidity, catalytic activity and deactivation due to coking in propane aromatization over H-gallosilicate (MFI)

Influence of the addition of silica, as a binder at a concentration of 10 or 50 wt%, to H- gallosilicate (MFI) zeolite on its inter- and intracrystalline acidity, initial activity, product selectivity and distribution of aromatics formed in the propane amortization (at 550&#176;C) and also on its deactivation due to coking in the aromatization process has been thoroughly investigated. Silica binder caused an appreciable decrease in the zeolitic acidity (both external and intracrystalline acid sites) and also in the propane conversion/aromatization activity. Because of it, the deactivation due to coking of the zeolite in the propane aromatization is, however, decreased. The deactivation rate constant for the initial fast deactivation is decreased but that for the later slow deactivation is increased because of the binder. The aromatics selectivity for aromatics and para shape selectivity of the zeolite, particularly at lower conversions, are increased but the propylene selectivity and dehydrogenation/cracking activity ratio are decreased due to the presence of binder in the zeolite catalyst

Simultaneous aromatization of propane and higher alkanes or alkenes over H-GaAlMFI zeolite

Conversion of propane in its aromatization over H-GaAlMFI zeolite can be enhanced by a factor of about two by carrying out the aromatization simultaneously with that of higher alkanes or alkenes; this is mostly due to hydrogen-transfer reactions between propane and higher alkenes

H.Na-Gallosilicate (MFI) propane aromatization catalyst: influence of H<SUP>+</SUP> exchange on acidity, activity, and deactivation due to coking

The effect of H+ exchange of H.Na-GaMFI (bulk Si/Ga = 33 and framework Si/Ga = 48 &#177; 3) on its external acidity (measured in terms of the activity in iso-octane cracking at 400&#176;C), and the overall acidity (measured in terms of the pyridine chemisorbed at 400&#176;C and also in terms of the activity in o-xylene isomerization at 400&#176;C and in toluene disproportionation at 500&#176;C) has been investigated. The initial activity and product selectivity (at the same conversion) and time-on-stream activity (or deactivation due to coking) in propane aromatization (at 550&#176;C) over the zeolite with different degrees of H+ exchange has also been thoroughly investigated. Both the external and overall acid sites and the initial activity and selectivity for aromatics in the propane aromatization are increased with increasing H+ exchange. The dehydrogenation/cracking activity ratio and aromatics/(methane + ethane) mass ratio are also increased with increasing the I-T exchange. However, the rate of catalyst deactivation due to coking is higher for the zeolite with higher H+ exchange because of its higher activity. The shape selectivity of the zeolite is increased with its deactivation due to coking, the effect being stronger for the lower H+ exchange. The selectivity for cracking products (C1 + C2) is increased, and consequently dehydrogenation/cracking and aromatization/cracking activity ratios are decreased due to the catalyst deactivation. The initial activity and selectivity for aromatics in propane aromatization shows a strong dependence on the zeolite acidity

Direct aromatization of natural gas over H-gallosilicate (MFI), H-galloaluminosilicate (MFI) and Ga/H-ZSM-5 zeolites

Direct Conversion of the C2+ hydrocarbons from natural gas to aromatics over H-Gallosilicate (MFI), H-Galloaluminosilicate (MFI) and Ga/H-ZSM-5 zeolites has been investigated at different temperatures (500-600C) and space velocities (500-6660 cm3 g-1 h-1). The zeolites are compared for their activity/selectivity and distribution of aromatics formed in the natural gas-to-aromatics conversion at different process conditions. The performance shown by the zeolites is in the following order: H-Galloaluminosilicate (MFI)H-Gallosilcate (MFI)Ga/H-ZSM-5. Natural gas, containing 27.3 wt% C2+ hydrocarbons, can be converted to aromatics with very high selectivity (90%) at a high conversion (70%) of C2+ hydrocarbons over H-Galloaluminosilicate (MFI) zeolite at 600°C and space velocity of 3000 cm3 g-1 h-1

Influence of binder on the acidity and performance of H-Gallosilicate (MFI) zeolite in propane aromatization

Influence of the addition of alumina or kaolin, as a binder at a concentration of 10 or 50 wt% to H-Gallosilicate (MFI) zeolite on its inter- and intracrystalline acidity, initial activity, product selectivity and distribution of aromatics formed in the propane aromatization (at 550&#176;C) and also on its deactivation due to coking in the aromatization process has been thoroughly investigated. Kaolin binder caused an appreciable decrease in the acidity (both inter- and intracrystalline) and propane aromatization activity of the zeolite. Whereas, alumina binder has no significant effect on the intracrystalline acidity and propane aromatization activity but caused a significant increase in the intercrystalline acidity. The catalyst deactivation and coke deposition on the zeolite are increased due to the alumina binder. But when kaolin binder is used, the coke deposition is not changed significantly. However, the deactivation rate constant for the initial fast deactivation is decreased but for the later slow deactivation is increased by kaolin binder. The selectivity for aromatics and para selectivity of the zeolite are increased by both the binders. The product selectivity, dehydrogenation/cracking and aromatization/cracking activity ratios and para selectivity, particularly for the zeolite with alumina (50 wt%) binder, are strongly influenced by the catalyst deactivation. However, the influence of binder and/or catalyst deactivation on the distribution of aromatics is very small

Influence of O<SUB>2</SUB> and H<SUB>2</SUB> pretreatments on acidity/acid strength distribution and acid functions of Ga/H-ZSM-5, H-GaMFI and H-GaAl MFI zeolites

H-gallosilicate (H-GaMFI), H-galloaluminosilicate (H-GaAlMFI) and Ga, impregnated H-ZSM-5 (Ga/H-ZSM-5) zeolites pretreated with O<SUB>2</SUB> and H2 (at 600° C for 10 h) have been characterized for their acidity/acid strength distribution (by chemisorption and stepwise thermal desorption of pyridine from 100° -400° C) and also for their acid functions by acid catalysed reactions [viz. isooctane cracking (at 400°C) (for characterizing external acid sites) and toluene disproportionation (at 500° C) and methanol-to-aromatics conversion (400°C)] using a pulse microreactor. The catalysts were also characterized by XPS,<SUP>29</SUP>Si,<SUP>27</SUP>Al and<SUP>71</SUP>Ga MAS NMR. The acidity/acid strength distribution, activity in the acid catalyzed reactions, frame-work Si/Ga ratio and surface Ga/Si ratio of the zeolites are significantly affected by their pretreatment by O<SUB>2</SUB> or H<SUB>2</SUB>

Acidity, catalytic activity, and deactivation of H-Gallosilicate (MFI) in propane aromatization: influence of hydrothermal pretreatments

Effect of various hydrothermal pretreatments [at different temperatures (400-800&#176;C) and concentrations of steam (13-80 mol%) or with liquid water at 150&#176;C under autogenous pressure] to H-gallosilicate (MFI) zeolite (bulk Si/Ga = 33 and Na/Ga = 0.1) on its acidity/acid strength distribution (determined by chemisorption and step-wise thermal desorption of pyridine from 100-400&#176;C), acid function (studied by acid catalyzed model reactions viz. isooctane cracking for external acidity ando-xylene isomerization and toluene disproportionation for internal or intracrystalline acidity), and deactivation due to coking in propane aromatization (at 550&#176; and time-on-stream of 8.5 &#177; 0.5) has been thoroughly investigated. With the increase in the severity of hydrothermal treatment to the zeolite, its crystallinity, framework (FW) Ga (observed by <SUP>71</SUP>Ga and <SUP>29</SUP>Si MAS NMR and FTIR), acidity (measured in terms of the pyridine chemisorbed at 400&#176;C and activity in the model reactions), and catalytic activity in the propane aromatization are decreased, but its deactivation due to coking and shape selectivity are increased appreciably. These effects are attributed to the extensive degalliation of the zeolite due its hydrothermal treatments. Its product selectivity, dehydrogenation/cracking (D/C) activity ratio, and aromatics/(methane + ethane) mass ratio in the propane aromatization are also influenced by its hydrothermal treatments, depending upon the conversion. The product and shape selectivity of the zeolite are also affected by its deactivation due to coking. The influence of hydrothermal treatments on the activity/selectivity and catalyst deactivation are attributed to a combined/complex effect produced by the decreased zeolitic acidity (i.e., FW Ga) and increased non-FW Ga oxide species in the zeolite channels, depending upon the severity of hydrothermal treatment. The hydrothermal stability of H-gallosilicate (MFI) is much lower than that H-ZSM-5

Initial activity/selectivity of H-Gallosilicate (MFI) in propane aromatization: influence of H<SUP>+</SUP> exchange and thermal/hydrothermal pretreatments

Initial activity/selectivity of H-gallosilicate (MFI) zeolite with different degrees of H<SUP>+</SUP> exchange and pretreated under different thermal and hydrothermal conditions in propane aromatization (at 500&#8800; C) has been determined using a pulse microreactor connected to GC. It is found to be strongly influenced by the degree of H<SUP>+</SUP> exchange, calcination temperature and hydrothermal treatment at different temperatures and concentrations of steam. There exists a close relationship between the acidity (measured in terms of pyridine chemisorbed at 400&#8800;C) of the gallosilicate and its initial propane conversion and aromatization activity. Presence of strong acidic sites (attributed to FW Ga) at high concentration is essential for the well dispersed non-FW Ga oxide species to be active for dehydrogenation in the propane aromatization over the zeolite

H-Gallosilicate (MFI) propane aromatization catalyst: influence of calcination temperature on acidity and deactivation due to coking

H-Gallosilicate (MFI) (bulk Si/Ga = 33) calcined at different temperatures (600-1100° C) has been characterized for its acidity/acid strength distribution (by step wise thermal desorption and chemisorption of pyridine at 100-400° C), acid function by acid catalyzed model reactions (viz. isooctane cracking (at 400° C) for external acid sites and o-xylene isomerization (at 400° C) and toluene disproportionation (at 500° C) for overall acid sites), crystallinity by XRD, incorporation of Ga in the zeolite framework by 71Ga MAS NMR and FTIR, and framework and non-framework Ga by 29Si MAS NMR and bulk chemical analysis. Influence of the calcination temperature on the catalytic activity/selectivity and catalyst deactivation due to coking in the propane aromatization process (at 550° C) has also been thoroughly investigated. The acidity, framework Ga, crystallinity and catalytic activity and catalyst deactivation in the propane aromatization are found to be strongly influenced by the calcination temperature, mostly because of the extensive degalliation of the zeolite, depending upon the calcination temperature. The product selectivity, shape selectivity and dehydrogenation activity relative to cracking activity, of the zeolite in the propane aromatization are influenced strongly by the calcination temperature and also by the catalyst deactivation due to coking