Rajib Bandyopadhyay

Vapour phase beckmann rearrangement of cyclohexanone oxime over SAPO-11 molecular sieve

Abstract SAPO-11 exhibited a high caprolactam yield for the vapour phase Beckmann rearrangement of cyclohexanone oxime to caprolactam. At 663 K, the oxime conversion is 99,9% with a caprolactam selectivity around 85.7%. The effect of silicon content of the SAPO-11 on the catalytic efficiency is compared with aluminosilicate having MFI structure. SAPO-11 is the best catalyst for the reaction among the investigated catalysts, ALPO 4 -11 on silica carrier, silynated zeolite and silynated SAPO-11. Acid sites with medium strength ( Si / Al > 10 000) are very active in the rearrangement reaction.

Synthesis of borosilicate zeolites by the dry gel conversion method and their characterization

Abstract Borosilicate zeolites, [B]-BEA, [B]-MFI and [B]-MTW, were synthesized by the dry gel conversion technique. Phase selection of the crystallization product depended on the gel composition, mainly upon the SiO 2 /B 2 O 3 and TEAOH/SiO 2 ratio. Nearly complete conversion of gel to zeolites was achieved by this synthesis method, and there was no phase change during the crystallization. It was observed from the 13 C CP MAS NMR of the as-synthesized samples that TEA + was fully intact in [B]-BEA, whereas partial decomposition of the template occurred in [B]-MFI and [B]-MTW. FTIR and 11 B MAS NMR analyses of the samples indicated that boron was located mainly in the tetrahedral framework position. Most of the tetrahedral boron could be removed and substituted by repeatedly refluxing the calcined sample with aluminum nitrate solution.

Catalytic performance of silicoaluminophosphate (SAPO) molecular sieves in the isopropylation of biphenyl

Abstract Silicoaluminophosphate (SAPO) molecular sieves, SAPO-5, SAPO-11, SAPO-20 and SAPO-34, were successfully synthesized by a novel dry-gel conversion method. The isopropylation of biphenyl (BP) with propylene to selectively produce 4,4′-diisopropylbiphenyl (4,4′-DIPB) was investigated over these molecular sieves, with more emphasis on SAPO-5. SAPO-5 exhibited high selectivity for 4,4′-DIPB (65%) with high BP conversion (89%). SAPO-11 showed high selectivity for 4,4′-DIPB with low conversion, whereas SAPO-20 and SAPO-34 had only low activities for the isopropylation of BP. The activity was influenced by the acidity of the catalysts and the selectivity by their structures. The selectivity for 4,4′-DIPB was influenced by reaction temperature and by reaction period in the isopropylation of BP over SAPO-5. With the increase in temperature, the selectivity decreased; such a decrease was compensated by the increase of thermodynamically more stable 3,3′- and 3,4′-DIPBs, whereas the isomerization of 4,4′-DIPB was observed when the period was prolonged. However, the composition of 4,4′-DIPB in the encapsulated products was always higher than that in the bulk products. Propylene pressure had less effect on activity and selectivity. The isomerization of 4,4′-DIPB to 3,3′- and 3,4′-DIPBs was also studied over SAPO-5, and considerable isomerization was observed at high temperature (300xa0°C). Ceria modification of SAPO-5 was effective for enhancement of the selectivity for 4,4′-DIPB because of the decrease in the undesirable non-regioselective reactions on external acid sites.

Transalkylation of cumene with toluene over zeolite Beta

The transalkylation of cumene with toluene over zeolite H-Beta is described. The influence of various reaction parameters on the cymene selectivity and cumene conversion are discussed. The optimum conditions for the selective transalkylation are found to be temperature 473–493 K, WHSV 4.2 h−1 and toluene-to-cumene molar ratio 14. The catalytic activity is compared with that of H-Y and H-ZSM-12 zeolites. Lower activities over these catalysts are attributed to their acidic and structural properties. Decrease in total activity with increase in the p-cymene formation is observed with time on stream in these catalysts due to coke induced shape selectivity and inhibition in the secondary isomerization process.

Synthesis of AlPO4 Molecular Sieves with AFI and AEL Structures by Dry-Gel Conversion Method and Catalytic Application of Their SAPO Counterparts on Isopropylation of Biphenyl

AlPO4-5 and AlPO4-11 were synthesized by dry-gel conversion (DGC) method. Steam-assisted conversion (SAC) and vapor-phase transport (VPT) techniques were applied for this purpose. The synthesis was successful in presence of a certain minimum amount of external bulk water, without which the crystallization failed. Crystallization by VPT method was slower than corresponding SAC and HTS method. SAPO analogs of the samples, SAPO-5 and SAPO-11 were also synthesized by DGC method. Samples made by DGC methods had higher yield than the conventional hydrothermal synthesis (HTS); otherwise the samples showed similar characteristics as that made by HTS. XRD, SEM and N2-adsorption results showed high crystallinity and purity of the samples made by DGC, and 27Al MAS NMR spectra indicated the tetrahedral framework nature of Al. SAPO-5 and SAPO-11 were tested for their catalytic activity in isopropylation of biphenyl, and in terms of conversion and selectivity, SAPO-5 was found to be suitable for this application.

Transalkylation reaction : An alternative route to produce industrially important intermediates such as cymene

Abstract Selective formation of cymene by transalkylation reaction of toluene with cumene and 1,4-diisopropylbenzene is described. The effect of various reaction parameters on the activity and selectivity is studied over H-Beta and results are compared with H-Y and H-ZSM-12. The performance and deactivation of the zeolites are attributed to their structural properties.

Aniline methylation over AEL type molecular sieves

Abstract ALPO-11, SAPO-11 and MAPSO-11 were prepared hydrothermally. These microporous solid catalysts could be used for the synthesis of industrially important N -alkylated products during aniline methylation. The activity of these catalysts was compared with aluminosilicates of high silica having MFI structure. A number of stronger acid sites enhance successive alkylation. Activity and selectivity of N , N -dialkylated product for SAPO-11 is higher at all temperatures as compared to that of ALPO-11. By introduction of Mg in SAPO-11, during hydrothermal synthesis, a decrease in total acid strength and an increase in basic strength, as compared to SAPO-11, is observed. This acidity-basicity function is correlated with the activity of the catalyst and product pattern of the methylation of aniline. C -alkylated products via direct alkylation of aniline with methanol are not enhanced during the alkylation reaction, catalysed by ALPO-11 and its derivatives, whereas the reaction catalysed by aluminosilicates and high silica aluminosilicates with MFI structure, some amount of C -alkylated products (toluidines) are formed.

Synthesis of high-silica [Al]-SSZ-31 by a steam-assisted conversion method and its catalytic performance in the isopropylation of biphenyl

Synthesis of high-silica [Al]-SSZ-31 zeolite by a dry-gel conversion method was performed and the catalyst was tested for the isopropylation of biphenyl with propylene. In the case of the small-scale synthesis, the product phase was found to be dependent on the alkali concentration of the initial gel, and a phase change from BEA to SSZ-31 to MFI was observed with time at the optimum alkali concentration. In the case of the large-scale synthesis, temperature had a profound effect on the crystallization of SSZ-31. A phase transformation from BEA to SSZ-31 was observed when the crystallization temperature was changed from 150°C to 175°C. [Al]-SSZ-31 was active in the isopropylation of biphenyl and selectively catalyzed the production of the least bulky isomers. Biphenyl conversion decreased with increasing silica to alumina ratio while selectivity remained nearly constant. Triisopropyl isomer nyields were high in the case of lower silica to alumina ratios.

Characterization of SAPO-11 synthesized conventionally and in the presence of fluoride ions

SAPO-11 samples have been synthesized by the conventional route and from an aqueous solution containing F– anions. Characterization of these samples by X-ray diffraction (XRD), chemical analysis, X-ray photoelectron spectroscopy (XPS), thermal analysis, NMR, adsorption measurements and catalytic test reaction reveals that the samples are highly crystalline, but differ in some physico-chemical properties. These differences in the properties of SAPO-11 obtained via different synthesis routes are correlated with different ordering of silicon substitution within the framework.

Direct hydrothermal synthesis of B-SSZ-31 from silica and sodium borate using 1,3,3,6,6-pentamethyl-6-azoniabicyclo[3.2.1]octane hydroxide as structure-directing agent

The direct synthesis of a borosilicate version of SSZ-31 was investigated starting from fumed silica and sodium borate as the silicon and boron source, respectively. As-synthesized boron Beta as a seed material was required for synthesizing fully crystalline material. The synthesis vessel has been observed to play a major role during the synthesis. Synthesis inside quartz tubes succeeded whereas that inside a teflon-lined stainless steel autoclave failed. Crystalline material was obtained inside the autoclave in presence of hollow quartz tubes. Part of the tetrahedral boron could be substituted by aluminum refluxing the as-calcined sample with aluminum nitrate solution.