Department of Chemical Engineering

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Aqueous-phase reforming of n-BuOH over Ni/Al2O3 and Ni/CeO2 catalysts
(Elsiever, 2011-12-15) Roy, Banasri
The aqueous-phase reforming (APR) of n-butanol (n-BuOH) over Ni(20 wt%) loaded Al2O3 and CeO2 catalysts has been studied in this paper. Over 100 h of run time, the Ni/Al2O3 catalyst showed significant deactivation compared to the Ni/CeO2 catalyst, both in terms of production rates and the selectivity to H2 and CO2. The Ni/CeO2 catalyst demonstrated higher selectivity for H2 and CO2, lower selectivity to alkanes, and a lower amount of C in the liquid phase compared to the Ni/Al2O3 sample. For the Ni/Al2O3 catalyst, the selectivity to CO increased with temperature, while the Ni/CeO2 catalyst produced no CO. For the Ni/CeO2 catalyst, the activation energies for H2 and CO2 production were 146 and 169 kJ mol−1, while for the Ni/Al2O3 catalyst these activation energies were 158 and 175 kJ mol−1, respectively. The difference of the active metal dispersion on Al2O3 and CeO2 supports, as measured from H2-pulse chemisorption was not significant. This indicates deposition of carbon on the catalyst as a likely cause of lower activity of the Ni/Al2O3 catalyst. It is unlikely that carbon would build up on the Ni/CeO2 catalyst due to higher oxygen mobility in the Ni doped non-stoichiometric CeO2 lattice. Based on the products formed, the proposed primary reaction pathway is the dehydrogenation of n-BuOH to butaldehyde followed by decarbonylation to propane. The propane then partially breaks down to hydrogen and carbon monoxide through steam reforming, while CO converts to CO2 mostly through water gas shift. Ethane and methane are formed via Fischer–Tropsch reactions of CO/CO2 with H2.
Surface modification of solution combustion synthesized Ni/Al2O3 catalyst for aqueous-phase reforming of ethanol
(Elsiever, 2010-11) Roy, Banasri
The effect of surface modification of an alumina powder supported nano-scale nickel catalyst used in aqueous-phase reforming of ethanol has been explored in this paper. The Al2O3 powder was prepared by a solution combustion synthesis (SCS) route and the surface of the powder was modified by a non-thermal RF plasma treatment using nitrogen gas. Catalysts were coated by an impregnation method. The performances of the unmodified and modified Ni/Al2O3 catalysts have been compared from a catalytic activity, selectivity, and microstructural point of view. The catalytic activity results showed that while nature, relative ratio and selectivity of the products both in gas and liquid effluents did not change, catalytic activity (in terms of EtOH conversion and H2 yield per g) of the sample increased after plasma modification. Microstructural (XRD, surface area) analysis showed that phase content and surface area of unmodified and modified catalysts are similar, while TEM and H2-chemisorption showed higher metal surface area, higher metal dispersion and lower active metal particle size for the modified sample compared to the unmodified sample. The temperature programmed reduction (TPR) analysis demonstrated stronger support-metal interaction and smaller NiO particles for the modified catalyst at lower heat treatment temperature. The temperature programmed desorption (TPD) of ammonia analysis showed stronger acidity for the modified support, which can explain better dispersion of the metal particles on the modified catalyst compared to the unmodified sample.
Influence of Sodium Chloride and Dibasic Sodium Phosphate Salt Matrices on the Anatase–Rutile Phase Transformation and Particle Size of Titanium Dioxide Powder
(https://ceramics.onlinelibrary.wiley.com/doi/10.1111/j.1551-2916.2009.03415.x, 2010-01-27) Roy, Banasri
The influence of sodium chloride (NaCl) and dibasic sodium phosphate (Na2HPO4·2H2O, DSP) on the phase transformation and particle size of titanium dioxide powder had been investigated. The salt matrix was shown to suppress both the amorphous to anatase transition and the anatase to rutile transition. DSP was particularly effective. Irrespective of the additives, transformation versus time curves of the anatase to rutile conversion were observed to be sigmoidal, and were interpreted in terms of a first order, nucleation-growth controlled phenomenon. Analysis of these curves using appropriate rate laws yielded activation energies for nucleation of ∼4.3 eV for NaCl salt matrix and ∼8.6 eV for DSP salt matrix, compared with ∼3.2 eV for a sample with no salt. Activation energies for the growth or propagation stage were ∼5 and ∼8.9 eV for NaCl and DSP powders, respectively, compared with ∼3.8 eV for no salt. In the solid state, salt matrices suppressed the particle growth as well. These behaviors, in general are thought to be governed by the presence of salt impurities, especially anions chemisorbed at the surface.
Synthesis of cobalt-doped bismuth vanadate by combustion-synthesis: Influence of fuel on phase content and morphology
(CUP, 2011-01-31) Roy, Banasri
Cobalt (15 at.%) doped bismuth vanadate, Bi4(V0.85Co0.15)2O11-δ (BICOVOX0.15), is known to have high oxygen ion conduction in the medium temperature range (400–600 °C). Small grain size may be important in stabilizing the highly conductive and disordered γ-phase at lower temperature. In this article, we report for the first time the synthesis of highly porous nanoscale BICOVOX powders by a solution combustion technique. The effects of fuel-to-oxidizer ratio, and postcombustion heat treatment temperature and time on the phase content and microstructure of the powders were investigated. As-combusted powders were revealed to be a mixture of Bi2O3, BiVO4, and γ-BICOVOX phases that were converted to phase pure γ-BICOVOX during heat treatment.
Molten Salt Synthesis of Bi4(V0.85Co0.15)2O11−δ (BICOVOX) Ceramic Powders
(Wiley, 2009-02-13) Roy, Banasri
Cobalt (15 at.%)-doped bismuth vanadate, Bi4(V0.85Co0.15)2O11−δ (BICOVOX) is known to have high oxygen ion conduction. However, the conductivity is highly anisotropic due to its layered structure. In this paper, we report the synthesis of BICOVOX powders with platelet habit by molten salt synthesis using a NaCl–KCl eutectic mixture as the reaction medium. The effects of treatment temperature and time on the morphology and phase content of the BICOVOX powders were investigated. By this method, it is possible to synthesize powders with platelets of major face dimension ∼50 μm and aspect ratio (major face dimension to thickness) as high as 15.
Controlling the Size and Morphology of TiO2 Powder by Molten and Solid Salt Synthesis
(Wiley, 2008-08-12) Roy, Banasri
Nano and submicrometer scale titanium oxide (TiO2) powders were synthesized by solid and molten salt synthesis (SSS and MSS) from amorphous titanium hydroxide precipitate. Sodium chloride (NaCl) and dibasic sodium phosphate (Na2HPO4·2H2O, DSP) separately or as mixture with different weight ratios were used as the salts. At the eutectic salt composition (20% DSP/80% NaCl), the microstructure and phase composition of the TiO2 was changed from equiaxed nanoparticles of anatase with size ∼40–50 nm, to mixed microstructure of bundle and acicular particles of rutile with 0.05–0.2 μm diameter, 6–10 μm length, and aspect ratio 20–60 depending on treatment time and temperature. At high temperature (825°C) and long time (30 h), microstructural differences were significant for the powders treated with different salts. Particle morphologies ranged from equiaxed, to acicular, to bundles, to nanofibers with very high aspect ratio. At lower treatment temperature (725°C) for shorter time (3 h), the morphology of the products did not change with different salt compositions, but the crystallite sizes changed appreciably. Different starting titanium precursors influenced particle size at lower temperature and time. Titanium hydroxide heat treated without salt resulted in significant grain growth and fused secondary particles, as compared with more finely separated and lightly agglomerated powders resulting from SSS and MSS treatments.
Preparation and characterization of sol–gel derived copper–strontium–oxide thin films
(Elsiever, 2008-04-30) Roy, Banasri
P-type transparent conductive oxides have potential applications in photovoltaics, transparent electronics, and organic optoelectronics. In this paper, results are presented on the synthesis of Cu2SrO2 thin films, a p-type transparent conducting oxide by a sol–gel route. Cu(II)methoxide and Sr-metal dissolved in anhydrous isopropanol were used as precursor for the sol preparation. For potassium (K) doping, K-acetate dissolved in anhydrous isopropanol was used as the precursor. Films were spin-coated onto substrates and partially pyrolysed in air at 225°C. After partial pyrolization, a two stage annealing sequence was used to achieve the final film microstructure and composition. Although combinations of oxygen pressure, annealing time, and annealing temperature were used to obtain phase pure Cu2SrO2 thin films, X-ray diffraction consistently showed the presence of Cu2O as a second phase with Cu2SrO2−the desired phase. Microstructural studies showed similar phase separation in the films and confirmed the microcrystalline nature. The best conductivities obtained for the undoped and 1% K-doped films were 2 × 10− 3 and 1.2 × 10− 2 S/cm, respectively. Both films showed a broad optical absorption edge in the visible range.
Monitoring of crystallization and the effect of the deposition rate, hydrogen content and annealing process on the crystallization of hot wire chemical vapor deposited hydrogenated amorphous silicon (a-Si:H) films
(Elsiever, 2008-07-31) Roy, Banasri
The crystallization behavior of the a-Si:H films grown by hot wire chemical vapor deposition has been studied using X-ray diffraction (XRD) and reflectance spectroscopy. The surface morphology of the films does not change during annealing. It has been observed that the different deposition rates, hydrogen contents, or annealing processes do not affect the nucleation mechanism or orientation of the films differently. The full width at half maxima of the XRD (111) peak of high deposition rate (~ 100 Å/s) films is observed to decrease when the same completely crystallized films (at 650 °C) are treated at increased temperatures up to 900 °C. Furthermore, films with different hydrogen contents and grown at a lower deposition rate (~ 5 Å/s) showed similar crystal growth activation energies upon rapid thermal annealing.
Two-step annealing of hot wire chemical vapor deposited a-Si:H films
(Springer, 2008) Roy, Banasri
A two-step annealing process was used to investigate the effect of dehydrogenation on crystallization and grain growth of low and high hydrogen content hot wire chemical vapor deposited (HWCVD) a-Si:H films. A low temperature pre-annealing followed by a rapid thermal annealing step at 600 °C was carried out. For the high hydrogen content film XRD (111) peak narrowed quite a bit, while opposite effect was observed for the low hydrogen content film. According to the grain sizes as calculated from TEM images, grain sizes of both of the two-step annealed high and low hydrogen content films are smaller than that of the single stage annealed film.
Rapid thermal annealing of hot wire chemical-vapor-deposited a-Si:H films: The effect of the film hydrogen content on the crystallization kinetics, surface morphology, and grain growth
(AIP, 2006-01) Roy, Banasri
The ability to crystallize thin amorphous Si layers into large grain Si can lead to significant improvements in Si solar cells and thin-film transistors. Here we report on the effect of the hydrogen content in as-grown films on the crystallization kinetics, surface morphology, and grain growth for hot wire chemical-vapor-deposited a-Si:H films crystallized by rapid thermal annealing (RTA). At RTA temperatures >750°C for high-hydrogen-content films, we observe the explosive evolution of hydrogen, with a resultant destruction of the film. Little or no damage is observed for films containing low hydrogen content. At a lower RTA temperature (600°C), the films remain intact with similar morphologies. At this same lower RTA temperature, both the incubation time and crystallization time decrease, and the grain size as measured by x-ray diffraction increases with decreasing hydrogen film content. Measurements of the crystallization time versus H evolution time indicate that the vast majority of the hydrogen must evolve from both films before crystallization commences. To examine the relationship between hydrogen evolution and crystallization, a two-step annealing process was utilized. For the high hydrogen content films, the final grain size increases if a large portion of the hydrogen is driven out at temperatures well below the crystallization temperature
Effect of salt composition on photovoltaic performance of the dye-sensitized solar cells prepared from nano anatase TiO2 powder using NaCl–Na2HPO4·2H2O salt matrices
(Springer, 2011-12) Roy, Banasri
Photovoltaic performances of dye-sensitized solar cells based on mesoporous TiO2 coating of nanocrystalline anatase prepared by solid salt synthesis were investigated in this study. Three different salt compositions pure NaCl, NaCl and DSP 50–50 wt% mixture, and pure DSP have been used as the reaction mediums. The best photovoltaic performances were obtained for the device made using the powder from DSP matrix. The dye-sensitized solar cells built from DSP and NaCl50 powders showed 13.8 and 6.5% improvements in the short-circuit current density, and 34 and 20% improvement in overall efficiency, respectively, than those of the cell made from Degussa P-25 powder. These results have been explained from the microstructural point of view of the powders. Electron microscopy, XRD, Raman, and nitrogen adsorption–desorption studies showed that the coatings made from the powders obtained via NaCl 50 and DSP salt medium treatments were of smaller sizes and contained higher densities of narrower mesoporous distribution than that obtained by the coating from NaCl and no-salt-synthesized materials.
Effect of variable conditions on steam reforming and aqueous phase reforming of n-butanol over Ni/CeO2 and Ni/Al2O3 catalysts
(Elsiever, 2014-12-01) Roy, Banasri
A comparison of aqueous phase reforming (APR) and steam reforming (SR) of n-butanol (n-BuOH) over Ni(20 wt%) loaded Al2O3 and CeO2 catalysts has been discussed in this paper. The BuOH conversion increases as the system pressure decreases in APR and SR. For both catalysts, the H2 and CO2 selectivity increased as the pressure increased in SR, reached a maximum at the bubble point pressure, and then decreased in the APR region. The Ni/CeO2 catalyst demonstrated higher selectivity for H2 and CO2than the Ni/Al2O3 catalyst during SR, which are consistent with the results of our previous publication on APR of n-butanol (n-BuOH) over similar catalysts. Unlike in APR, the Ni/CeO2 catalyst produced CO in SR. For both of the catalysts, the activation energies for H2 and CO2 production and BuOH conversion were lower in SR than that in APR. The proposed primary reaction pathway for reforming of BuOH on both catalysts is the same for APR and SR. The n-BuOH dehydrogenated to butaldehyde followed by decarbonylation to propane. Then the propane is steam reformed to hydrogen and carbon monoxide. The CO converts to CO2 mostly through water gas shift.
Effect of preparation method on the performance of the Ni/Al2O3 catalysts for aqueous-phase reforming of ethanol: Part I-characterization
(INFOFNA, 2012) Roy, Banasri
Synthesis of TiO2 scaffold by a 2 step bi-layer process using a molten salt synthesis technique
(Elsiever, 2011-04-10) Roy, Banasri
TiO2 scaffolds of anisotropic rutile particles were grown from rutile seeds by using molten salt synthesis techniques. The rutile seeds were either in the form of a separate layer applied on a substrate or a sintered bulk pellet. Mixtures of amorphous titanium hydroxide and salt applied as coatings on the rutile seeds were heat treated. Depending on the morphology of the seed layer, heat treatment temperature, time and salt medium, rutile was grown with different morphologies and microstructures. For NaCl–KCl eutectic salt mixture and heat treatment at 700 °C for 5 h, nano-whiskers of 20–50 nm diameter and 0.5–1 μm length were obtained. For the NaCl salt sample treated at 850 ºC for 20 h, rutile platelets of 2–5 μm thick, 2–10 μm wide and 5–25 μm in length were produced. X-ray diffraction and Raman scattering were used to identify and characterize the rutile phase of the nanowhiskers.
Non-vacuum and PLD growth of next generation TCO materials
(Elsiever, 2003-12-15) Roy, Banasri
Transparent conducting oxides represent a key component in a number of important opto-electronic technologies. The demand for improved materials is increasing. It is increasingly important to develop improved materials and process techniques. We report on the PLD growth of both Mo doped In-O, an n-type material with enhanced mobilities, and p-type Ca–CuInO2 films with improved conductivity. In both cases, very high quality films have been obtained with improved opto-electronic properties. We also report on a solution based route to p-type Cu2SrO2 which has produced phase pure films.
Performance evaluation of activated neem bark for the removal of Zn(II) and Cu(II) along with other metal ions from aqueous solution and synthetic pulp & paper industry effluent using fixed-bed reactor
(Elsiever, 2016-05-20) Gupta, Suresh; Maheshwari, Utkarsh
The fixed-bed adsorption experiments are performed for the removal of copper [Cu(II)] and zinc [Zn(II)] by utilizing activated neem bark as an adsorbent. The present study demonstrated the effect of various parameters such as inlet concentration, adsorbent mass and inlet flowrate for the removal of Cu(II) and Zn(II) from aqueous solutions. Various kinetic parameters such as EBRT, stoichiometric capacity, breakthrough time, etc. are evaluated using the experimental data. Yoon–Nelson and Yan model available in the literature are also validated with the experimental data. The developed adsorbent is also tested for the simultaneous removal of multiple metal ions [Cr(VI), Cu(II), Zn(II), Pb(II), Ni(II) and Cd(II)] from the synthetically prepared pulp & paper industrial effluent
Efficient adsorbent for simultaneous removal of Cu(II), Zn(II) and Cr(VI): Kinetic, thermodynamics and mass transfer mechanism
(Elsiever, 2015-11) Gupta, Suresh; Maheshwari, Utkarsh
Present study deals with the development of a nano-porous adsorbent using neem bark for the simultaneous removal of Cu(II), Cr(VI) and Zn(II). The developed adsorbent is characterized using SEM, EDS and TGA. The effect of initial metal concentration, contact time, adsorbent dosage, temperature and pH are studied to see the performance of nANB for the metal ions removal. Various isotherm, kinetic and mass transfer models are validated with the experimental data and corresponding parameters are estimated. The maximum adsorption capacity of the developed adsorbent for Cu(II) and Zn(II) adsorption are found to be 21.23 and 11.904 mg g−1, respectively. The optimum parameter values for contact time, adsorbent dosage, temperature and pH are obtained as 48 h, 6 g L−1, 35 °C and 1.2, respectively, from the experimental results of Cu(II) and Zn(II) removal using nANB. The performance of nANB on the industrial effluent is evaluated by performing equilibrium batch experiments for the simultaneous removal of Cu(II), Cr(VI) and Zn(II) from an aqueous solution. The overall adsorption capacity of the nANB for the removal of multiple metal ions at 200 mg L−1 of each is obtained as 38.95 mg g−1 which is more than double for that obtained for individual metal ions.
Simultaneous sequestration of ternary metal ions (Cr6+, Cu2+ and Zn2+) from aqueous solution by an indigenous bacterial consortium
(Elsiever, 2016-07) Gupta, Suresh; Raghuvanshi, Smita; Majumder, Subhajit
Sequestration of single heavy metal contaminant from industrial wastewater using pure bacterial strains has received much attention. However, application of a bacterial consortium in multiple metals sequestration is scarce. The present study was aimed to develop a consortium from three bacterial strains for the simultaneous sequestration of ternary metal ions (Cr6+, Cu2+ and Zn2+) from aqueous solution. Kinetic studies showed that the individual strain, Pseudomonas taiwanensis; Acinetobacter guillouiae and Klebsiella pneumoniae were able to remove Cr6+, Cu2+ and Zn2+ respectively. These bacterial strains were utilized to develop an indigenous consortium based on metal removal affinities and positive interferences between them. Consortium showed improved performance over individual strains for the removal of single as well as simultaneous removal of three metal ions. Fourier transform infrared (FTIR) spectral analysis showed the possible involvement of carboxyl, amino, hydroxyl, methyl, phosphate and sulphonate groups in metal ions sequestration. Consortium exhibits greater adaptability in ternary metal ions mixture which indicates its robust growth mechanism over individual bacterial strains.
Application of a hybrid biofilter column for the removal of Cr(VI) from aqueous solution using an indigenous bacterial strain Pseudomonas taiwanensis
(Taylor & Francis, 2016-02-01) Gupta, Suresh; Raghuvanshi, Smita; Majumder, Subhajit
In the present study, a laboratory-scale biofilter column was designed and fabricated. It was packed with a mixture of coal and compost as a packing medium. The column was enriched with an indigenous bacterial strain Pseudomonas taiwanensis isolated from aerobic mixed culture of Sewage Treatment Plant, BITS-Pilani, Pilani campus. The removal of hexavalent chromium [Cr(VI)] from aqueous solution was investigated in the biofilter column. The entire biofiltration operation was divided into five phases (I to V) for a period of 63 days. Biofilter column was subjected to shock loading conditions for 20 days immediately after 63 days of operation. The maximum removal efficiency of 89.4% was obtained during phase V for Cr(VI) inlet concentration of 40 mg L−1. During shock loading, maximum removal efficiency was obtained as 90% for 48.5–50 mg L−1 of initial Cr(VI) concentration. Kinetic parameters of biofiltration process for Cr(VI) removal were also determined by fitting Michaelis-Menten kinetic model with experimental data. The Michaelis-Menten kinetic constants were obtained as 0.258 mg L−1 min−1 and 26.83 mg L−1. It was found that Ottengraf-Van den Oever model with zero-order diffusion limitation fit the experimental data quite well for phases III, IV, and V with coefficient of determination (R2) values .97, .99, and .984, respectively. A possible method for safe disposal of packing medium was also presented in this study.
Energetic assessment of fixation of CO2 and subsequent biofuel production using B. cereus SM1 isolated from sewage treatment plant
(Springer, 2016-04-13) Gupta, Suresh; Raghuvanshi, Smita; Mishra, Somesh
The ongoing work on global warming resulting from green house gases (GHGs) has led to explore the possibility of bacterial strains which can fix carbon dioxide (CO2) and can generate value-added products. The present work is an effort in this direction and has carried out an exhaustive batch experiments for the fixation of CO2 using B. Cereus SM1 isolated from sewage treatment plant (STP). The work has incorporated 5-day batch run for gaseous phase inlet CO2 concentration of 13 ± 1 % (%v/v). 84.6 (±5.76) % of CO2 removal was obtained in the gaseous phase at mentioned CO2 concentration (%v/v). Energetic requirement for CO2 fixation was assessed by varying Fe[II] ion concentration (0–200 ppm) on the per-day basis. The cell lysate obtained from CO2 fixation studies (Fe[II] ion = 100 ppm) was analyzed using Fourier transformation infrared spectroscopy (FTIR) and gas chromatography-mass spectroscopy (GC–MS). This analysis confirmed the presence of fatty acids and hydrocarbon as valuable products. The hydrocarbons were found in the range of C11–C22 which is equivalent to light oil. The obtained fatty acids were found in the range of C11–C19. The possibility of fatty acid conversion to biodiesel was explored by carrying out the transesterification reaction. The yield of biodiesel was obtained as 86.5 (±0.048) % under the transesterification reaction conditions. Results of this research work can provide the valuable information in the implementation of biomitigation of CO2 at real scenario.