• Sreedevi Upadhyayula

      Articles written in Journal of Chemical Sciences

    • Alkylation of toluene with isopropyl alcohol over SAPO-5 catalyst

      Sreedevi Upadhyayula

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      Isopropylation of toluene with isopropyl alcohol was studied over the large pore silicon alumino phosphate molecular sieves (SAPO-5) with varying Si content. Toluene conversion was found to increase with increase in the Si of the catalysts. The effect of temperature on yields of cymene was studied in the range of 453 to 553 K. The highest yield and selectivity for cymene was observed at 513 K. Good cymene selectivity was confirmed with the absence of 𝑛-propyl toluene in the product. The catalyst activity, in terms of 𝑝-cymene selectivity, remained almost stable during a nine hour time on stream run. Enhanced cymene selectivity and decreased 𝑝-cymene selectivity was observed with increase in the toluene to isopropyl alcohol feed mole ratio from 2 to 8. Power law model and L-H-H-W model fitted the experimental data well and are used to explain the kinetics of this reaction.

    • Gas phase toluene isopropylation over high silica mordenite

      Sreedevi Upadhyayula

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      Mordenite (HM) catalysts with three different Si/Al ratios were compared for their activity and selectivities in gas phase toluene isopropylation with isopropanol. Catalyst with Si/Al ratio 44.9 offered better cumene selectivity, hence, it was chosen for detailed kinetic investigations. The influence of various process parameters like temperature, time-on-stream, weight hourly space velocity (WHSV), reactant mole ratio on this catalyst activity are discussed. The cymene selectivity was found to increase with reaction temperature and passed through a maximum at 473 K. The deactivation with time-onstream is almost negligible. Lower isopropyl alcohol concentration in the feed improved cymene selectivity. The conversion and selectivity to cymenes were compared with those of the large pore beta catalyst. The rate constant and activation energy were found to be 7.34 m3/kg h and 41.84 kJ/mol, respectively using homogeneous kinetic model.

    • Efficient utilization of bimetallic catalyst in low H₂/CO environment syngas for liquid fuel production


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      Application of Fischer-Tropsch synthesis (FTS) in the utilization of low H ₂/CO ratio (0.5–1.5) gas obtained from coal and biomass gasification can be done by selecting a catalyst system active for both FTS and WGS reaction. The enhancement of H ₂ content depends on the extent of water gas shift (WGS) reaction and can be quantified by measuring usage ratio define as a mole of H₂ to CO converted. With an attempt to utilize low H ₂/CO ratio syngas bimetallic (Fe/Co/SiO ₂) were prepared and compared with monometallic (Fe/SiO ₂ and Co/SiO ₂) catalysts. The catalysts were tested in fixed bed reactor at industrial relevant FTS conditions(T: 220−260 ◦C, P: 2.0 MPa, GHSV-1.2 SL/gcat-h, H ₂/CO: 1–1.5). The incorporation of Fe-Co bimetallic catalyst facilitates both FT and WGS reaction because of the presence of iron and cobalt phases. Compared to monometallic catalyst there is a significant increase in CO conversion over the bimetallic catalyst. Also, the yield of C ₅+ was significantly higher over bimetallic catalyst compared to iron catalyst, where olefin was the major product. Selected catalyst (Fe/Co/SiO ₂) was tested for their activity toward WGS reaction. Effects of temperature, pressure, and feed composition on WGS reaction over bimetallic catalyst were studied. Lower value usage ratio (1.62 and 1.58) reveals the occurrence WGS reaction Fe-Co bimetallic catalyst at 240 ◦C and 260 ◦C. At 240 ◦C, 72% CO conversion, and 60% C ₅ + selectivity show that the catalyst efficiently utilizes the increased H ₂/CO ratio in the production of liquid hydrocarbon.

    • Non-oxidative methane dehydroaromatization reaction over highly active α-MoC1−x ZSM-5 derived from pretreatment


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      The catalytic active-phase of reduced Mo species plays a vital role in non-oxidative methane dehydroaromatization (MDA) reaction. Pretreatment effect of one of the gases containing N2, H2 and (90 vol%) CH4 + H2 over 15% Mo-loaded HZSM-5 catalyst has been investigated in the present work. Various spectroscopic investigations viz., XRD, TPR, TPO, XPS, etc., show that the pretreatment of 15% Mo-HZSM-5 catalyst with (90 vol%) CH4 + H2 gas stream exclusively leads to the formation of MoOxCyHzwhich acts as precursor moieties for the formation of highly active metastable fcc (α-MoC1-x) and MoOxCy phases during the induction period. Comparatively, H2 and N2-pretreated catalysts showed major formation of hcp (β-Mo2C) species that are found to be a less-active phase inMDA reaction. The active fcc (α-MoC1-x) phases are immuneto inert coking and assist primary ethylene products formed on carbonized Mo associated Brønsted acid sites to travel in the zeolite channels which is further aromatized over Brønsted acid sites deep inside the channels.XPS analysis of the catalyst shows that α-MoC1-x and β-Mo2C are major catalytic phases that are covered with graphitic carbon and amorphous carbon present on the surface. The active phases α-MoC1-x and MoOxCy,associated with Brønsted acid sites along with the vacant Brønsted acid sites in catalyst pretreated with (90 vol%) CH4 + H2 mixture are responsible for high activity in methane conversion (∼13%), excellent aromatic selectivity (38%), and high stability of the catalyst

    • Evaluation of materials of construction for the sulfuric acid decomposition section in the sulfur–iodine (S–I) cycle for hydrogen production: Some preliminary studies on selected materials


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      Water splitting by Sulfur–Iodine (S–I) cycle is one of the promising thermochemical processes for hydrogen production due to its high efficiency. The decomposition of H2SO4 to produce SO2 is the reaction with the highest energy demand in the S–I cycle and it shows a large kinetic barrier. Sulfuric acid ishighly corrosive and its endothermic decomposition needs elevated temperatures (>800 ºC). Henceforth, before the scale-up of the process plant there is a need to explore various materials of construction under very harsh acidic environments and phase changing conditions. Corrosion studies on some of the possible materials of construction (SS-304, SS-310, SS-316, Inconel-800, Alloy-20, Inconel-600, Incoloy-800H, Hastelloy C-276) were performed in detail and the most corrosion resistant material is suggested for the construction of sulfuric acid decomposition unit. The studies were performed at low temperatures (60ºC and 120ºC) as well as at high temperatures (700ºC, 800ºC and 900ºC). The corrosion rates were determined using weight loss method at low as well as high temperature and by using electrochemical method at low temperature (80ºC). The phase changing condition was more severe and resulted in higher corrosion rate. Hastelloy C-276 showed the least corrosion rate.

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