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  • 1.
    Narang, Kritika
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Tailoring of adsorptive properties of zeolites for biogas upgrading2019Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Biogas is a promising alternative fuel with low CO2 emissions and high market potential due to the abundance of organic biomass. Despite being a renewable form of energy, biogas consists of 40-45% CO2, which lowers its calorific value [1]. Various porous materials have been tailored to adsorb CO2 gas from the biogas stream to obtain 95-97% biomethane. Zeolites are one of the promising porous materials that can contribute remarkably in the upgrading process by selectively adsorbing the CO2 gas from biogas [2].

    The aim of this thesis is to develop hierarchical structures by novel approaches to enhance their CO2 adsorptive properties. The first part of the study addresses the tailoring of zeolites NaX and CaA binderless beads using the ion-exchange process to acquire high CO2 adsorption capacities of 5.1 mmol/g and 4.3 mmol/g at 298 K with the high mechanical strength of 2 MPa and 1.3 MPa respectively. The ion-exchange process was optimized for NaX and CaA zeolite to obtain high CO2-over-CH4 selectivity of 525 and 1775 respectively. The breakthrough experiments show that the partially ion-exchanged zeolite NaX has high mass transfer kinetics with a CO2 uptake rate of 2.8 mg of CO2/g/s as compared to the zeolite CaA binderless beads.

    The second part dealt with the structuring of zeolites using freeze granulation and electrospinning techniques. The freeze granulation process was optimized to form granules of 2-3 mm in diameter from NaX and CaA zeolite powder. The CO2-over-CH4 selectivities were investigated using Henry’s law and it shows that the NaX granules offer high selectivity of 214 than the CaA granule, 172 at 273 K and 100 kPa. No physical damage was observed when the granules were subjected to five cyclic breakthrough adsorption-desorption experiments at 4 bar. In addition, NaX granules offer a high uptake rate of 3.6 mg of CO2/g/s with a mass transfer coefficient of 1.3 m/s as compared to the CaA granules.

    To move further in structuring techniques, electrospinning was used to fabricate hierarchical porous structures. ZSM-5 nanofibers composites were developed from the ZSM-5 nanopowder and polyvinylpyrrolidone (PVP) polymer. Two-step post thermal treatments were carried out: Pre-oxidation and carbonization on ZSM-5 nanofibers composites to form mechanically strong composite structures. The post-carbonized structures showed a 30.4% increase in specific BET surface area than the ZSM-5 nanopowder with the CO2 uptake of 2.15 mmol/g. To investigate the CO2 separation properties, secondary pellet structures were developed with a tensile strength up to 6.46 MPa. The CO2 uptake rate for pellets was 2.3 mg of CO2/g/s without any performance decay after the first cycle with the simulated mass transfer coefficient of 1.24 m/s.

    [1] J Wang. Decentralized biogas technology of anaerobic digestion and farm ecosystem: Opportunities and challenges, Front.Energy Res. 2 (2014).

    [2] RV Siriwardane, M- Shen, EP Fisher, J Losch. Adsorption of CO 2 on zeolites at moderate temperatures, Energy Fuels. 19 (2005) 1153-1159.

  • 2.
    Narang, Kritika
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Fodor, Kristina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Kaiser, Andreas
    Department of Energy Conversion, Technical University of Denmark, Roskilde 4000, Denmark.
    Akhtar, Farid
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Optimized cesium and potassium ion-exchanged zeolites A and X granules for biogas upgrading2018In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 8, no 65, p. 37277-37285Article in journal (Refereed)
    Abstract [en]

    Partially ion-exchanged zeolites A and X binderless granules were evaluated for CO2 separation from CH4. The CO2 adsorption capacity and CO2-over-CH4 selectivity of binderless zeolites A and X granules were optimized by partial exchange of cations with K+ and Cs+, while retaining the mechanical strength of 1.3 MPa and 2 MPa, respectively. Single gas CO2 and CH4 adsorption isotherms were recorded on zeolites A and X granules and used to estimate the co-adsorption of CO2–CH4 using ideal adsorbed solution theory (IAST). The IAST co-adsorption analysis showed that the partially ion-exchanged binderless zeolites A and X granules had a high CO2-over-CH4 selectivity of 1775 and 525 respectively, at 100 kPa and 298 K. Optimally ion-exchanged zeolite X granules retained 97% of CO2 uptake capacity, 3.8 mmol g−1, after 5 breakthrough adsorption–desorption cycles while for zeolite A ion-exchanged granules the reduction in CO2 uptake capacity was found to be 18%; CO2uptake capacity of 3.4 mmol g−1. The mass transfer analysis of breakthrough experimental data showed that the ion-exchanged zeolite X had offered a higher mass transfer coefficient, (κ) through the adsorption column compared to zeolite A; 0.41 and 0.13 m s−1 for NaK4.5Cs0.3X and CaK2.5Cs0.2A, respectively

  • 3.
    Wenjing, Zhang
    et al.
    Department of Energy Conversion and Storage, Technical University of Denmark (DTU), Denmark.
    Narang, Kritika
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Salcedo, Alma Jasso
    Department of Materials and Environmental Chemistry, Stockholm University, Sweden.
    Dou, Yibo
    Department of Energy Conversion and Storage, Technical University of Denmark (DTU), Denmark.
    Simonsen, Søren Bredmose
    Department of Energy Conversion and Storage, Technical University of Denmark (DTU), Denmark.
    Sørensen, Mads Gudik
    Department of Energy Conversion and Storage, Technical University of Denmark (DTU), Denmark.
    Vinkel, Nadja Maria
    Department of Energy Conversion and Storage, Technical University of Denmark (DTU), Denmark.
    Akhtar, Farid
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Hedin, Niklas
    Department of Materials and Environmental Chemistry, Stockholm University, Sweden.
    Kaiser, Andreas
    Department of Energy Conversion and Storage, Technical University of Denmark (DTU), Denmark.
    Electrospun nanofiber materials for energy and environmental applications2019Conference paper (Refereed)
    Abstract [en]

    Electrospinning is the one of the most versatile techniques to design nanofiber materials with numerous applications in the fields of energy conversion, catalytic chemistry, liquid and gas filtration.1 By electrospinning, complex structures can be designed from a rich variety of materials including polymers, metals, ceramics and composite, with the ability to control composition, morphology and secondary structure and tailor performance and functionality for specific applications. Moreover, with recent developments in the design of electrospinning equipment and availability of industrial-scale electrospinning technologies with production rates of several thousands of square meters per day new opportunities for electrospinning are imminent. With this, the advanced research on materials performed in our labs is getting closer to the commercialization of new products for applications in fields of energy and environment.

    An overview will be given on electrospinning activities at DTU Energy that address the sizable challenges in energy and environmental applications by electrospinning: 1. Electrospun perovskite oxide nanofiber electrode for use in solid oxide fuel cells. In this application, a (La0.6Sr0.4)0.99CoO3-δ cathode was shaped into 3-dimensional thin-film by so-gel assisted electrospinning method combined with calcination and sintering; 2. Electrospun nanofiber materials for gas adsorption. Both the advantages and challenges of using electrospun nanofiber materials will be discussed, in terms of electrochemical performance, surface area, packing efficiency and mechanical stability.

  • 4.
    Zhang, Wenjing
    et al.
    Department of Environmental Engineering, Technical University of Denmark, Lyngby, Denmark.
    Narang, Kritika
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Simonsen, Søren Bredmose
    Department of Energy Conversion and Storage, Technical University of Denmark, Roskilde, Denmark.
    Vinkel, Nadja Maria
    Department of Energy Conversion and Storage, Technical University of Denmark, Roskilde, Denmark.
    Gudik-Sørensen, Mads
    Department of Energy Conversion and Storage, Technical University of Denmark, Roskilde, DenmarkDepartment of Energy Conversion and Storage, Technical University of Denmark, Roskilde, Denmark.
    Han, Li
    Department of Energy Conversion and Storage, Technical University of Denmark, Roskilde, DenmarkDepartment of Energy Conversion and Storage, Technical University of Denmark, Roskilde, Denmark.
    Akhtar, Farid
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Kaiser, Andreas
    Department of Energy Conversion and Storage, Technical University of Denmark, Roskilde, DenmarkDepartment of Energy Conversion and Storage, Technical University of Denmark, Roskilde, Denmark.
    Highly Structured Nanofiber Zeolite Materials for Biogas Upgrading2020In: Energy Technology, E-ISSN 2194-4296, Vol. 8, no 1, article id 1900781Article in journal (Refereed)
    Abstract [en]

    Hierarchical zeolite composite nanofibers are designed using an electrospinning technique with post‐carbonization processing to form mechanically strong pellets for biogas upgrading. A ZSM‐5 nanopowder (zeolite) and a polyvinylpyrrolidone (PVP) polymer are electrospun to form ZSM/PVP composite nanofibers, which are transformed into a ZSM and carbon composite nanofiber (ZSM/C) by a two‐step heat treatment. The ZSM/C nanofibers show a 30.4% increase in Brunauer–Emmett–Teller (BET) surface area compared with the non‐structured ZSM‐5 nanopowder. Using ideal adsorbed solution theory, CO2‐over‐CH4 selectivity of 20 and CO2 uptake of 2.15 mmolg−1 at 293 K at 1 bar for ZSM/C nanofibers are obtained. For the efficient use of adsorbents in pressure swing adsorption operation, the nanofibers are structured into ZSM/C pellets that offer a maximum tensile strength of 6.46 MPa to withstand pressure swings. In the breakthrough tests, the CO2 uptake of the pellets reach 3.18 mmolg−1 at 293 K at 4 bar after 5 breakthrough adsorption–desorption cycles, with a much higher mass transfer coefficient of 1.24 ms−1 and CO2 uptake rate of 2.4 mg of CO2 g−1s−1, as compared with other structured zeolite adsorbents.

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