Tailoring Molecular Sieves’ Dielectric and Electric Properties for Efficient Microwave and Resistive Heating Regeneration

• Author / Creator

  Shariaty, Pooya

• Adsorption onto molecular sieve adsorbents is a well-developed technique in the industry for gaseous pollutants emission control. Loaded adsorbents must then be regenerated for reuse in further adsorption cycles. Microwave and resistive heating have been introduced as potential alternatives to conventional thermal regeneration methods due to lower energy consumption, higher desorption rate, and shorter duration. Their performances mainly depend on adsorbent’s permittivity (dielectric properties) and electrical resistivity for microwave and resistive heating, respectively. In general, molecular sieves have relatively low permittivity and high resistivity which can pose challenges for microwave and resistive heating regeneration. However, tuning the dielectric and electric properties of molecular sieves, can allow for more effective microwave heating regeneration and possibility of implementing resistive heating regeneration. The objective of this thesis is to provide a suitable method to tune these properties in molecular sieves without compromising their adsorption properties. Firstly, the effect of ion-exchange of Engelhard Titanosilicate, ETS-10, (test molecular sieve), on its dielectric, adsorption and microwave regeneration properties was investigated using water (polar adsorbate). Monovalent and divalent cations (Li+, K+, Ca2+, Cu2+, Ba2+) were used for ion-exchanging. The analysis of ion-exchanged samples showed decreased dielectric properties, which reduced microwave absorbance during regeneration. This effect along with increased water adsorption capacity led to up to 27% more adsorbent regeneration efficiency, suggesting more effective process due to direct adsorbate heating. Li-ETS-10 was the most suitable candidate for microwave regeneration when loaded with polar adsorbate, based on adsorption capacity, desorption efficiency, and energy consumption. Secondly, effect of different methods for carbon addition to dealuminated zeolite Y (highly resistive molecular sieve) on its resistivity and adsorption properties was studied. Carbon was added by thermal decomposition of polyvinyl-alcohol, catalytic CH4 decomposition, ethanol/benzene chemical vapor deposition, and physical mixing with powdered carbon. Elemental analyses and scanning electron micrographs confirmed addition of carbon to the zeolite which reduced its resistivity by up to 8 orders of magnitude. Resistivity reduction was greatest when carbon was added directly to the zeolite’s surface. Catalyzed CH4 decomposition resulted in 31wt% carbon addition in the form of carbon nanotube (CNT) reduced its resistivity from >107Ω.m to 0.7Ω.m, but decreased its adsorption capacity by 32%. Optimum condition for CNT deposition on dealuminated zeolite Y was then investigated aiming for minimizing the effect on its adsorption properties while suitably reducing its resistivity. Different thermal conditions were tested for this purpose. CNT addition using low temperature (as low as 400°C) and short (1hour) duration was achieved. SEM images revealed lower temperature resulted in less and smaller CNT deposition minimizing the effect on adsorption properties, while effectively reduced resistivity (to 1.1 Ω.m). The results suggested potential use of low-temperature procedure to tailor the adsorbents resistivity with minor effect on their adsorption properties. Additionally, adsorption/thermal regeneration cycles were completed to evaluate the performance of resistive heating compared to conventional conduction-convention heating. The samples were completely regenerated using a constant power of 70 W and 4.25 W for conventional and resistive heating, respectively. Resistive heating regeneration demonstrated 94% less energy consumption, 4 times higher heating rate, and 4 times higher desorption rate compared to conventional heating. Finally, adsorption/microwave heating regeneration performance of the modified sample was evaluated, aiming for improved dielectric properties with respect to microwave and conventional heating regeneration of original zeolite. The modification increased (>1 order of magnitude) the dielectric constant and loss factor of the zeolite resulting in higher heating rate (~10 times) and power absorption (~3 times) during microwave heating. Faster heating (16 and 5 times) and desorption rate (4 and 8 times) were obtained for microwave regeneration of modified zeolite compared to microwave and conventional regeneration of original zeolite. Modified zeolite required less time (half) and energy (7.4 times) for complete microwave regeneration compared to original zeolite. Also, modified sample showed similar microwave regeneration performance for both polar and non-polar adsorbates. In summary, a method for tailoring the dielectric and electric properties of molecular sieves with low permittivity and high resistivity was developed. The method allows for enhanced microwave and resistive heating regeneration of molecular sieves which provides shorter regeneration duration, faster desorption, and lower energy consumption compared to conventional thermal regeneration.

• Subjects / Keywords

  • Microwave Regeneration
  • Dielectric Properties
  • Resistive Heating Regeneration
  • Electric Properties
  • Molecular Sieve
  • Adsorption

• Graduation date

  Spring 2018

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3736MH4F

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.