Department of Chemical Engineering
Permanent URI for this collectionhttp://localhost:4000/handle/123456789/1923
Browse
5 results
Search Results
Item Reforming of model biogas using Ni/CeO2/γ-Al2O3 monolith catalyst(Elsevier, 2023) Roy, Banasri; Srinivas, AppariThis study aims to develop a Ni-Ce coated alumina cordierite monolith for reforming model biogas. Dry reforming of biogas (DRBG) experiments are carried out at 800 °C for various ratios of CH4/CO2, mainly 1.0, 1.5, and 2.0. A 2 × 2 cm monolith is wash-coated with alumina and loaded with Ni-Ce by the wet impregnation method. For improving metal support interactions, the monoliths are calcined at 800 °C for 20 h and reduced in the presence of H2. The catalysts exhibited a CH4 conversion of 91%, 60%, and 48% and CO2 conversions of 60%, 80%, and 81% for a feed ratio of 1.0, 1.5, and 2.0, respectively. The prepared catalysts are characterized by employing various techniques such as XRD and FESEM incombined with EDS and Raman analysis. XRD of calcined catalysts displayed the phases of CeO2, Al2O3, NiO, NiAl2O4, and the monolith peaks and catalysts showed a stable activity for 40 h time-on stream for all the ratios. The Raman and FESEM analysis of spent catalysts reveal the presence of carbon deposition. However, catalysts showed high activity due to active Ni particles present on the top of the carbon nanotubes.Item Study of preparation method and oxidization/reduction effect on the performance of nickel-cerium oxide catalysts for aqueous-phase reforming of ethanol(Elsevier, 2015-12) Roy, BanasriThe effect of preparation method and oxidation state of the active metal on the catalytic activity of Ni–Ce–O catalysts was studied for aqueous phase reforming of ethanol. A sol-gel (SG) route and a solution combustion synthesis (SCS) method were used for the preparation of 10 wt% Ni loaded catalysts. The catalytic activity of three groups of catalysts; reduced at 425 °C (HR, metallic Ni), reduced at 1000 °C (FR, metallic Ni), and not reduced (NR, as NiO) were tested at different operating conditions. The difference in the metal particle sizes, governed by the preparation method, affects the catalytic efficiency most, not the reduced or oxidized state of Ni. The SG samples were superior for ethanol conversion and selectivity for H2 and CO2 compared to the SCS samples. The X-ray photoelectron spectroscopy (XPS) analysis of the samples demonstrated that the relative ratio of Ce2O3 to CeO2 increased inside the reactor. While Ni doping increases oxygen mobility in the Ce–O lattice, Ce3+ converts Ni2+ to metallic Ni inside the reactor. This can explain why the reduction stage for Ni–Ce–O system in APR is irrelevant. Higher oxygen mobility through the support helps oxidation of CO to CO2 leading to improved catalytic performance.Item Predicting the temperature and reactant concentration profiles of reacting flow in the partial oxidation of hot coke oven gas using detailed chemistry and a one-dimensional flow model(Elsiever, 2015-04) Srinivas, AppariA numerical approach is presented for predicting the species concentrations and temperature profiles of chemically reacting flow in the non-catalytic partial oxidation of hot coke oven gas (HCOG) in a pilot-scale reformer installed on an operating coke oven. A detailed chemical kinetic model consisting of 2216 reactions with 257 species ranging in size from the hydrogen radical to coronene was used to predict the chemistries of HCOG reforming and was coupled with a plug model and one-dimensional (1D) flow with axial diffusion model. The HCOG was a multi-component gas mixture derived from coal dry distillation, and was approximated with more than 40 compounds: H2, CO, CO2, CH4, C2 hydrocarbons, H2O, aromatic hydrocarbons such as benzene and toluene, and polycyclic aromatic hydrocarbons up to coronene. The measured gas temperature profiles were reproduced successfully by solving the energy balance equation accounting for the heat change induced by chemical reactions and heat losses to the surroundings. The approach was evaluated critically by comparing the computed results with experimental data for exit products such as H2, CO, CO2, and CH4, in addition to the total exit gas flow rate. The axial diffusion model slightly improves the predictions of H2, CO, and CO2, but significantly improves those of CH4 and total exit flow rate. The improvements in the model predictions were due primarily to the improved temperature predictions by accounting for axial diffusion in the flow model.Item A detailed kinetic model for biogas steam reforming on Ni and catalyst deactivation due to sulfur poisoning(Elsiever, 2014-02) Srinivas, AppariThis paper deals with the development and validation of a detailed kinetic model for steam reforming of biogas with and without H2S. The model has 68 reactions among 8 gasphase species and 18 surface adsorbed species including the catalytic surface. The activation energies for various reactions are calculated based on unity bond index-quadratic exponential potential (UBI-QEP) method. The whole mechanism is made thermodynamically consistent by using a previously published algorithm. Sensitivity analysis is carried out to understand the influence of reaction parameters on surface coverage of sulfur. The parameters describing sticking and desorption reactions of H2S are the most sensitive ones for the formation of adsorbed sulfur. The mechanism is validated in the temperature range of 873–1200 K for biogas free from H2S and 973–1173 K for biogas containing 20–108 ppm H2S. The model predicts that during the initial stages of poisoning sulfur coverages are high near the reactor inlet; however, as the reaction proceeds further sulfur coverages increase towards the reactor exit. In the absence of sulfur, CO and elemental hydrogen are the dominant surface adsorbed species. High temperature operation can significantly mitigate sulfur adsorption and hence the saturation sulfur coverages are lower compared to low temperature operation. Low temperature operation can lead to full deactivation of the catalyst. The model predicts saturation coverages that are comparable to experimental observation.Item Numerical study of on-board fuel reforming in a catalytic plate reactor for solid-oxide fuel cells(Elsiever, 2011-02) Srinivas, AppariA pseudo-transient numerical model is used for the simulation of a multi-functional catalytic plate reactor (CPR). The work mainly addresses the problems associated with on-board reforming for solid-oxide fuel cells. Heat management is achieved by indirectly coupling partial oxidation with reforming. Water management is achieved by partially recycling the anode stream from a solid-oxide fuel cell. The model uses detailed heterogeneous chemistry for reforming and oxidation reactions occurring on the catalyst beds.