Department of Chemical Engineering
Permanent URI for this collectionhttp://localhost:4000/handle/123456789/1923
Browse
6 results
Search Results
Item Dual reforming of model biogas for syngas production on Ni/γ-Al2O3 and Ni-C/ZSM-5 cordierite monolith catalysts(Elsevier, 2023) Roy, Banasri; Srinivas, AppariThis work attempts to convert the model biogas on Ni/γ-Al2O3 and Ni-C/ZSM-5 into syngas using a dual-bed catalytic monolith reactor. The monolith is wash-coated with alumina and ZSM-5, respectively, followed by Ni and glucose-assisted Ni (Ni-C) loading using the wet impregnation technique. These two monoliths are loaded in an Inconel reactor and placed in a two-zone heating furnace. In dual reforming, either Ni/γ-Al2O3 or Ni-C/ZSM-5 monolith is used for dry reforming, and then Ni/γ-Al2O3 is used for steam reforming. A distance of ∼ 10 cm is maintained between these two monoliths. The exhaust gases from the first monolith are combined with steam before passing to the second monolith. The biogas reforming is carried out for a feed ratio (CH4:CO2) 1.5, GHSV of 1440 h−1 and 2880 h−1, at 800℃ and 1 atm pressure. The steam to CH4 ratio (S/C) is optimized to maximize the conversions (greater than80 %) of both CH4 and CO2. It was observed that the CH4 conversions increase with an increased S/C ratio due to the steam reforming in the second monolith. The TGA results show 7.6 % carbon formation on Ni-C/ZSM-5 and 35 % on Ni/γ-Al2O3 in dry reforming on the first monolith bed.Item Effect of Calcination Time on the Catalytic Activity of Ni/γ-Al2O3 Cordierite Monolith for Dry Reforming of Biogas(Elsevier, 2021-02) Roy, Banasri; Srinivas, AppariNi/γ-Al2O3 wash coated cordierite monolith catalysts are calcined in air at 800 °C for 4, 10, and 20 h in order to study the effect of calcination time on the activity of the catalysts for dry reforming of model biogas. Catalytic activity studies are performed at 800 °C with three different CH4/CO2 ratios of 1.0, 1.5, and 2.0. The catalyst calcined for the longest time (C-20) displays higher stability and activity in terms of CH4 and CO2 conversion compared to those calcined for 4 h (C-4) and 10 h (C-10). XRD data and TPR analysis detect the maximum amount of NiAl2O4/MgAl2O4 phases and strongest metal-support interaction, respectively, for the C-20 sample. FESEM reveals the particle size of the calcined and reduced C-20 sample to be smaller than that of the C-4 and C-10 samples. Whereas, H2 pulse-chemisorption characterization demonstrates the highest metal surface area, metal dispersion, and smallest Ni particle size for the C-20 catalyst. While, no carbon deposition on any catalyst occurs for the CH4/CO2 ratio of one, lowest amount of carbon nanotubes is formed on the C-20 sample for the CH4/CO2 ratio of 1.5 and 2.0, as observe by DTA-TGA. EDX reveals concentration variation of Mg and Si from the cordierite monolith wall along the thickness of the coating for all the samples. In addition, the maximum amount of these elements is observed for the calcined C-20 catalyst coating. These implies that the diffusion of Mg and Si from the cordierite monolith to the catalyst coating during calcination contribute significantly in controlling the physicochemical properties of the catalysts. As a result, the higher stability and activity of the C-20 could be attributed to the formation of higher amount of the Ni– Mg- alumina spinel complex in the catalyst coating during longer calcination time, which leads to the improved metal-support interaction and higher nickel dispersion over monolith.Item Recent advances and perspectives of perovskite-derived Ni-based catalysts for CO2reforming of biogas(Elsevier, 2022-11) Srinivas, Appari; Roy, BanasriCO2 reforming of biogas (CRBG) is a promising renewable energy source to tackle the global energy demands and environmental challenges. Biogas (BG) is reformed to produce syngas on numerous catalysts, including transitional (Ni, Co, Fe, and Mo) and precious (Pt, Pd, Rh, and Ru) metals over various supports. However, catalyst deactivation due to the carbon deposition and trace amounts of H2S in BG is a significant barrier to commercializing the CRBG. Recently, perovskite oxide catalysts have gained interest due to their unique structural characteristics and articulating properties that favor CRBG for carbon-free operation. This review discusses the perovskite oxide catalysts in CO2 reforming, emphasizing structural stability, activity, and carbon deposition. The exsolved perovskite catalysts are reviewed as potential alternatives to the conventional LaNiO3, which suffers the structure break-down during the dry reforming. The exsolution of the catalysts offers numerous benefits such as structural stability, strong metal support interaction, oxygen storage capacity, and active small particle size with good dispersion, thus leading to better catalyst stability without deactivation in CRBG. However, catalyst reduction conditions dictate the particle size and activity of the catalysts. This review extensively covers the studies on different Ni-derived perovskites, the effect of partial doping of various metals (Ni, Co, Fe, Pt, Pd, and Rh), and mechanisms and related mixed-oxide systems.Item Effect of Calcination Time on the Catalytic Activity of Ni/γ-Al2O3 Cordierite Monolith for Dry Reforming of Biogas(Elsiever, 2020) Srinivas, Appari; Roy, BanasriNi/γ-Al2O3 wash coated cordierite monolith catalysts are calcined in air at 800 °C for 4, 10, and 20 h in order to study the effect of calcination time on the activity of the catalysts for dry reforming of model biogas. Catalytic activity studies are performed at 800 °C with three different CH4/CO2 ratios of 1.0, 1.5, and 2.0. The catalyst calcined for the longest time (C-20) displays higher stability and activity in terms of CH4 and CO2 conversion compared to those calcined for 4 h (C-4) and 10 h (C-10). XRD data and TPR analysis detect the maximum amount of NiAl2O4/MgAl2O4 phases and strongest metal-support interaction, respectively, for the C-20 sample. FESEM reveals the particle size of the calcined and reduced C-20 sample to be smaller than that of the C-4 and C-10 samples. Whereas, H2 pulse-chemisorption characterization demonstrates the highest metal surface area, metal dispersion, and smallest Ni particle size for the C-20 catalyst. While, no carbon deposition on any catalyst occurs for the CH4/CO2 ratio of one, lowest amount of carbon nanotubes is formed on the C-20 sample for the CH4/CO2 ratio of 1.5 and 2.0, as observe by DTA-TGA. EDX reveals concentration variation of Mg and Si from the cordierite monolith wall along the thickness of the coating for all the samples. In addition, the maximum amount of these elements is observed for the calcined C-20 catalyst coating. These implies that the diffusion of Mg and Si from the cordierite monolith to the catalyst coating during calcination contribute significantly in controlling the physicochemical properties of the catalysts. As a result, the higher stability and activity of the C-20 could be attributed to the formation of higher amount of the Ni– Mg- alumina spinel complex in the catalyst coating during longer calcination time, which leads to the improved metal-support interaction and higher nickel dispersion over monolith.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 Deactivation and regeneration of Ni catalyst during steam reforming of model biogas: An experimental investigation(Elsiever, 2014-01) Srinivas, AppariThis paper presents detailed study of biogas reforming. Model biogas with different levels of H2S is subjected to reforming reaction over supported Ni catalyst in a fixed bed reactor at 700 °C and 800 °C. In order to understand the poisoning effects of H2S the reactions have been initially carried out without H2S in the feed stream. Three different H2S concentrations (20, 50 and 100 ppm) have been considered in the study. The H2O to CH4 ratio is maintained in such as way that CO2 also participates in the reforming reaction. After performing the poisoning studies, regeneration of the catalyst has been studied using three different techniques i) removal of H2S from the feed stream ii) temperature enhancement and iii) steam treatment. Poisoning at low temperature is not recoverable just by removal of H2S from the feed stream. However, poisoning at high temperature is easily reversed just by removal of H2S from the feed stream. Unlike some previous reports by Li et al. (2010) and Rostrup-nielsen (1971) [1,2], catalyst regeneration is achieved in shorter time frames for all the regeneration techniques attempted.