Y.S. Bhat

Transalkylation and disproportionation of toluene and C9 aromatics over zeolite beta

Transalkylation and disproportionation (TADP) of toluene and C9 aromatics from a commercial stream have been studied over a zeolite possessing a three-dimensional, 12-membered ring pore system. The study encompassed the effect of C9 aromatics content in feed on TADP. Formation of xylenes was maximum with a feed containing 50 ∶ 50 toluene and C9 aromatics. In order to understand the role of different C9 aromatics in TADP, experiments using individual C9 aromatics with and without toluene mixture as feed were carried out. An interesting observation of these experiments was that ethyltoluenes produced xylenes through disproportionation of toluene generated from their deethylation. The total yield of xylenes was much less than that obtained from trimethyl benzenes. A reaction scheme accounting all the reactions taking place during TADP is proposed.

Toluene isopropylation over zeolite β and metallosilicates of MFI structure

Abstract The industrially important para -cymene synthesis has been carried out by toluene isopropylation on medium pore MFI zeolites and large pore zeolite β. The roles of crystal size and change in acidity by isomorphous substitution on para -cymene selectivity are discussed. The external surface passivation by silica deposition was done to differentiate the reactions taking place on the external surface and inside the zeolite channels during alkylation. This has helped to enhance the fraction of para -cymene among cymenes to nearly 100%.

Effect of extrusion and silylation of ZSM-5 onpara selectivity of diethylbenzenes

Abstract Zeolite extrusion using an alumina binder in different proportions and its effect on the selectivity for the para isomer in diethylbenzenes during ethylbenzene ethylation with ethanol is reported. The study also includes the silylation of extrudates of zeolites with different Si/Al ratios to enhance the para selectivity. It was observed that in the presence of binder the diethylbenzenes fraction contained less para isomer due to increased isomerization of primary product of alkylation. As compared to pure zeolite, the extrudates required a higher amount of silica deposition to enhance the para selectivity.

Zeolite beta catalyzed C7 and C9 aromatics transformation

Abstract Transformation of commercial C 7 and C 9 aromatic streams to xylenes over zeolite beta have been studied. These results have been compared with those obtained on other zeolites like ZSM-5 and mordenite. The effect of variations in reaction parameters like temperature, weight hourly space velocity (WHSV) and feed composition on xylene formation was considered. The trimethylbenzenes became disproportionated, while ethyltoluenes underwent de-ethylation followed by disproportionation of product toluene. The highest yield of xylenes was obtained with a feed consisting of nearly equal proportions of toluene and 1,3,5-trimethylbenzene. Lower WHSV and higher temperature enhanced the formation of xylenes.

Selective ethylation of ethylbenzene in the presence of other aromatics

Abstract The alkylation of ethylbenzene in the presence of other aromatic compounds has been studied over a pore size regulated MFI zeolite. The aromatic compounds chosen were of various kinetic diameter, hence they were expected to hinder the movement of reactant molecules both on the external surface and within zeolite channels. It was observed that some of the aromatic compounds got alkylated along with ethylbenzene. The effects of varying the concentration of aromatic compounds in the feed on ethylbenzene conversion and product distribution have been discussed.

Microwave rehydrated Mg–Al-LDH as base catalyst for the acetalization of glycerol

Acetalization of glycerol with aldehydes to form cyclic acetals is an industrially important reaction and is generally carried out using acid catalysts. Base catalysts such as LDH can bring about microwave-assisted acetalization of glycerol and aldehydes to form 5-membered and 6-membered cyclic acetals. Among the different LDHs used, Mg–Al-LDH was found to exhibit maximum conversion of glycerol into 5-membered cyclic acetal. Modification of Mg–Al-LDH involving calcination at 450 °C and subsequent microwave-assisted rehydration showed improved glycerol conversion rate under similar reaction conditions. Rehydration of calcined Mg–Al-LDH by microwave irradiation was found to result in LDH regaining its layered structure with higher basicity possibly exposing more hydroxyl ions responsible for basicity. Multiple use of methanol washed spent catalyst showed good repeatability for conversion up to three cycles which subsequently showed a marginal decrease in the conversion. Further dehydration followed by rehydration of the spent LDH catalyst under microwave irradiation was found to rejuvenate the catalytic activity to its initial level.

Reactions of ethylbenzene in the presence of toluene over external surface passivated MFI zeolite

The reactions of ethylbenzene in the presence of toluene were studied over external surface passivated MFI zeolite. With increase in extent of external surface passivation the para selectivity of both transalkylation and disproportionation reactions enhanced. The effects of mole ratio of ethylbenzene to toluene, reaction temperature and WHSV on the performance of the modified zeolite are discussed. It was observed that the high para selectivity feature of the modified zeolite is not influenced by changes in reaction conditions.

Microwave-activated p-TSA dealuminated montmorillonite – a new material with improved catalytic activity

Abstract We report a montmorillonite material with enhanced surface area but with very little alteration in cation exchange capacity (CEC) upon dealumination with para toluene sulphonic acid (p-TSA). The new material shows higher catalytic activity in comparison with mineral-acid-treated clay. Montmorillonite clay was treated with p-TSA for 10 minutes under microwave irradiation. The resulting clay was characterized by CEC, X-ray diffraction (XRD), BET analysis, Fourier transform infrared spectroscopy (FT-IR), temperature programmed desorption (TPD) of ammonia and cyclic voltametry (CV) techniques. XRD patterns show an unchanged structure of pristine matrix after the acid action. BET analysis revealed an increase in the surface area and pore volume on p-TSA treatment, indicating formation of voids in the octahedral layer which suggests dealumination. Nitrogen adsorption-desorption curves showed the creation of new micro porous regions, possibly in the octahedral sheets. In contrast to mineral acid treatment, p-TSA treated clay samples showed similar CEC which shows the absence of dissolution of isomorphously substituted Mg and Fe ions present in the octahedral layer. CV studies confirm the formation of an Al-p-TSA complex, suggesting dissolution of aluminium octahedral sheets. The complex subsequently hydrolyses, replacing interlayer cations with Al3+ ions. Similar treatment with mineral acid resulted in clay with enhanced surface area but with reduced CEC, evidently due to the removal of isomorphously substituted Fe and Mg. Further, the p-TSA treated clays showed relatively higher esterification activity under solvent-free microwave irradiation. The p-TSA treated clay retained its activity even after three subsequent runs and thus can be exploited for practical applications.

Toluene ethylation over metallosilicates of MFI structure. Effects of acidity and crystal size on para-selectivity

Toluene ethylation with ethanol over Al-MFI and B-, Fe-, Ga-isomorphously substituted zeolites of MFI structure was carried out. The acid properties of the metallosilicates increased in the order B < Fe < Ga < Al. This order is reflected in the activity of the zeolites in terms of toluene conversion. The separate effects of crystal size variation and acidity change by isomorphous substitution on para product selectivity have been established.

The active site accessibility aspect of montmorillonite for ketone yield in ester rearrangement

The removal of Al from the octahedral layer of montmorillonite by organic acid treatment results in increased microporosity generating a material with different surface features from the virgin clay. The micropores thus generated are found to be responsible for ester to ketone transformation. Various parameters of the newly generated pores such as the pore diameter, pore structure, pore volumes and acidity by pyridine-FTIR were evaluated with respect to ester to ketone formation. The best correlation was found between the volume accessibility factors (VAF) and the ketone yield. The VAF reflects the extent of volume space available around the acid site for the reactant to orient in a specific way for the transformation to occur within the pore to form a specific product. This acid site accessibility aspect was further verified by extending to micropores with large VAF generated by treatment with phenoldisulfonic acid (PDSA).