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    Investigation of mixed matrix membranes of graphene and acid-treated graphene fillers in cellulose acetate and polyetherimide polymers for CO2 separation from biogas
    (Wiley, 2024-10) Kuncharam, Bhanu Vardhan Reddy
    Gas separation membranes are crucial for upgrading biogas by separating carbon dioxide (CO2) from biogas, thereby enhancing its calorific value and reducing greenhouse gas emissions. This study aims to improve CO2/CH4 separation using mixed-matrix membranes (MMMs) by incorporating graphene (Gr) and acid-treated graphene (AGr) fillers in a cellulose acetate (CA) polymer matrix. Similarly, polyetherimide (PEI) MMMs were also prepared with Gr and AGr fillers to draw a comparison. Various characterization techniques, including Fourier transform infrared spectroscopy, differential scanning calorimetry, field emission scanning electron microscopy, Raman spectroscopy, and X-ray diffraction, were employed to investigate the structural and morphological properties of the membranes and fillers. Gas permeation tests using a model biogas mixture (40% CO2 and 60% CH4) revealed that the 0.1%AGr/CA membrane achieved the highest CO2 permeability of 43 Barrers, which is approximately 307% more than that of the pure CA membrane, and showed a CO2/CH4 selectivity of 14.80. The 0.5%Gr/PEI membrane demonstrated the best performance among PEI-based MMMs, with a CO2 permeability of 17.48 Barrers and a CO2/CH4 selectivity of 8.96. These results indicate that the incorporation of Gr and AGr significantly enhances the gas separation performance over pure CA and PEI membranes.
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    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, Appari
    This 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.
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    Investigation of Ba doping in A-site deficient perovskite Ni-exsolved catalysts for biogas dry reforming
    (Elsevier, 2024-08) Roy, Banasri
    This work presents the development of an A-site deficient La0.9−xBaxAl0.85Ni0.15O3 (x = 0, 0.02, 0.04, and 0.06) perovskite oxide catalyst for dry reforming of model biogas. The catalysts are prepared using a citrate sol-gel method and used for biogas dry reforming at 800 °C for feed ratios (CH4/CO2) of 1.5 and 2.0. The fresh and spent catalysts are analyzed using XRD, FTIR, TPD, XPS, FESEM, TEM, TPR, TGA-DTA, and Raman analysis. The XRD analysis exhibits the host perovskite oxide structure and the exsolved Ni phase for all prepared catalysts. The partial doping of Ba improves the metal support interaction and oxygen vacancies that enhance catalytic activity and stability, as revealed by the TPR and XPS analysis. The stability experiment on La0.9−xBaxAl0.85Ni0.15O3, for x = 0 catalyst resulted in reduced activity due to the catalyst deactivation by sintering, as confirmed by XRD and FE-SEM. Among all the catalysts studied, La0.84Ba0.06Al0.85Ni0.15O3 (LB6AN-15) exhibited the highest catalytic stability with CH4, and CO2 conversions are 60% and 93%, respectively, for 40 h time-on-stream due to the strong metal support interactions, high oxygen vacancies, and anti-sintering of exsolved Ni nanoparticles in biogas dry reforming.
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    Study of mixed matrix membranes with in situ synthesized zeolite imidazolate frameworks (ZIF-8, ZIF-67) in polyethersulfone polymer for CO2/CH4 separation
    (RSC, 2024-08) Kuncharam, Bhanu Vardhan Reddy
    Biogas, produced from anaerobic digestion, is a sustainable and renewable energy source. To upgrade biogas to Bio-CNG, CO2 must be removed from the raw mixture. Membrane separation is an economical process for the removal of CO2, and mixed matrix membranes (MMMs) are being explored for CO2/CH4 separation. MMMs are fabricated using techniques such as in situ techniques to overcome research gaps, such as in filler agglomeration and filler–polymer interfaces. In this work, MMMs were fabricated using the in situ growth of ZIF-8 and ZIF-67 in polyethersulfone (PES) and compared with traditional filler dispersion of ZIF-8 and ZIF-67. The fabricated MMMs were characterized and tested for gas permeation using a model biogas. Fourier-transform infrared (FTIR) spectroscopy and Field Emission Scanning Electron Microscopy (FESEM) analysis were conducted to confirm in situ synthesis of ZIF-8 and ZIF-67. CO2 permeability of in situ ZIF-8 and ZIF-67-based MMMs have enhanced to 84.5 Barrer and 78.8 Barrer, respectively, compared to pure PES membrane, which is around 25 Barrer. Similarly, ZIF-8 and ZIF-67-based traditional MMMs have shown an increase in the CO2 permeability of 75.6 Barrer and 68 Barrer, respectively. Additionally, the selectivity for CO2/CH4 separation increased for some of the prepared MMMs, demonstrating the effectiveness of the in situ fabrication method.
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    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, Appari
    Ni/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.
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    Recent advances and perspectives of perovskite-derived Ni-based catalysts for CO2reforming of biogas
    (Elsevier, 2022-11) Srinivas, Appari; Roy, Banasri
    CO2 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.
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    An experimental study on gas-to-liquids and biogas dual fuel operation of a diesel engine
    (Inder Science, 2021-10) Verma, Saket
    In the present configuration, GTL replaces diesel, and biogas is used as gaseous fuel in the dual fuel (DF) operations. The effects of this substitution have been evaluated from the perspectives of second-law of thermodynamics. The results are compared with the diesel single-fuel, GTL single-fuel and GTL-biogas DF operations. Also, engine out emissions have been compared to understand the environmental impact of these fuel combinations. The results show that DF operation offers up to 80% pilot liquid fuel replacement by biogas, however, some reductions in energy and exergy efficiencies are observed.
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    Advances in the Utilization of Biogas in Diesel Engines: An Exergy Based Approach
    (Springer, 2022-01) Verma, Saket
    In order to reduce the use of fossil fuels in the transportation sector, various alternatives have been explored in the past. Biogas is an interesting candidate in this context with its large potential in countries like India, which can be utilized for vehicular as well as decentralized power generation applications. Biogas is a renewable fuel that is produced from organic waste materials through anaerobic digestion process. The produced raw biogas contains methane as the fuel; however, carbon dioxide is also present in considerable amount. This inert gas reduces the flame speed and heating value of biogas and eventually deteriorates engine performances. The auto-ignition temperature of biogas is high enough that it cannot be directly utilized in the diesel engines. One of the easiest and flexible ways to utilize biogas in diesel engines is through ‘Dual Fuel (DF)’ technique. In this technique biogas is used as the main gaseous fuel and another liquid fuel (commonly diesel) is used as the pilot fuel. In this way, existing diesel engines can use biogas as the fuel with minimum engine modifications. Nevertheless, the performance of biogas DF engine has been found to be much poor than the standard diesel engine, especially at the low loads. It has been shown that there are many engine parameters, e.g. engine load, type and quantity of biogas, injection timing of the pilot fuel etc., which can affect the performance and emission characteristics of a DF engine. This article presents an overview of these effects on a biogas operated DF engine and suggests various techniques to enhance the performance of the engine.
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    An Experimental Comparison of Enriched Biogas and CNG on Dual Fuel Operation of a Diesel Engine
    (IOP, 2019) Verma, Saket
    In the present work CNG and enriched biogas (93% CH4 by vol.) have been experimentally compared for performance and emission characteristics in a dual fuel diesel engine. The diesel is used as the pilot fuel, which is directly injected into the engine cylinder. The CNG and biogas are used as the main fuels, which are inducted with the intake air in the intake manifold. The experimental observations are taken for steady state conditions at varying engine loads for maximum pilot fuel substitution conditions. The performance of the engine is evaluated based on energy and exergy analyses. The emission characteristics are shown for oxides of nitrogen (NOx), hydrocarbon (HC), carbon monoxide (CO) and smoke emissions. It was found that enriched biogas showed the performance similar to that with CNG, whereas slight variations in the emissions were observed. The exergy efficiencies of 27.8% and 26.9% were calculated for CNG and biogas dual fuel operations respectively at the full load. Similarly, maximum pilot fuel substitutions were found 73.4% and 71.4% for the above conditions respectively
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    An experimental investigation of biodiesel-biogas dual-fuel engine based on energy and exergy analysis
    (Inder Science, 2018-06) Verma, Saket
    In the present work, exergy analysis has been performed on the biodiesel-biogas dual fuel (DF) engine. The DF operation has been studied with biodiesel (Jatropha curcas) as the pilot fuel to ignite the main fuel (biogas). The experiments were performed at a constant engine speed of 1500 rpm with varying engine loads and optimised injection timings for both diesel and DF modes. The results indicate that DF operation at low load produces poor performance and emission characteristics, however, no significant variations were observed between diesel-DF and biodiesel-DF operations. At 23% of engine load, exergy efficiencies were found to be 8.53% and 8.4% for diesel-DF and biodiesel-DF operations respectively; compared to 12.57% for pure diesel operation. Nevertheless, at higher loads, exergetic performances of DF operations were significantly improved. Furthermore, oxides of nitrogen (NOx) emissions from DF operations were significantly reduced compared to that with diesel operation.