Adsorptive Properties of Vanadium Substituted ETS-10

• Author / Creator

  Mani, Farnaz

• High purity microporous vanadosilicate (EVS-10/AM-6) has been hydrothermally synthesized by a simple template-free, reducing agent-free method in the absence of titanosilicate ETS-10 seeds. Direct comparison between EVS-10 and ETS-10 showed successful isomorphous substitution of titanium with vanadium in the framework. The existence of vanadium is confirmed by energy dispersive X-ray spectroscopy and inductively coupled plasma mass spectrometry. The scan electron microscopy and the X-ray diffractometer show similar crystal morphology and structure. The structural and adsorptive characteristics of EVS-10 with ETS-10 have been compared. The Henry Law constants and heats of adsorption were calculated for both adsorbents from low pressure adsorption data using CH4, C2H6, C2H4, N2, O2, and CO2 for pressures up to 100 kPa and temperatures of 303, 323, and 343 K. The adsorption data were fit using Langmuir, Toth, and Redlich-Peterson isotherms. The best model was selected based on the quality of fit to the data and how closely the model predicted the saturation concentration. The structural properties for EVS-10 are almost indistinguishable from ETS-10. The adsorption data reflects this similarity in that both adsorbents have similar heats of adsorption and selectivities for a wide range of gases. These results suggest that heteroatom substitution in ETS-10 does not necessarily affect its adsorption properties if the framework dimensions and composition remain similar. A proposal for the differences in the adsorption characteristic for ETS-10 is created by contrasting the adsorption properties of as-synthesized ETS-10 with 13X and high siliceous ZSM-5. To determine whether adsorption on Na-ETS-10 is driven predominately by cationic or van der Waals effects, the adsorption affinity for several gases was measured on all three adsorbents. The adsorption mechanism was probed by using the isotherms to calculate both the enthalpy and entropy of adsorption as a function of loading and by contrasting the behaviour of ETS-10 against both 13X and ZSM-5. The results of the analysis indicate that ETS-10 has, simultaneously, a high affinity for molecules both with and without strong quadrupole moments. This behaviour is believed to result from a sparse number of highly deshielded cations that exist in the otherwise non-polar channels. The phenomenon associated with the ion-exchange of silver ions into the microporous vanadosilicate EVS-10 is explored. The divalent charge on the vanadium is offset by mobile and exchangeable cationic counter-ions. It was found that silver replaces sodium quantitatively and that, unexpectedly, the silver ions are spontaneously reduced to silver metal which appear as nano-scale metal clusters in the TEM images. The reduction of the silver ions is accompanied by an oxidation of the framework vanadium and this redox pair is established through XPS and Raman spectroscopy. The mechanism for this unique behaviour is believed to be explained by a galvanic reaction between the incoming Ag+ and the framework V4+. Separation of ethane from methane from a binary gas mixture was conducted by adsorption on EVS-10. In this study a feed consisted of 80% methane and 20% ethane was used. The bed selectivity resulted from adsorptive separation on EVS-10 was 36 at room temperature and atmospheric pressure. This study suggested that EVS-10 could be an effective candidate for separation of ethane from the gas streams highly enriched in methane. In other words, EVS-10 could be potentially used in cases such as natural gas purification.

• Subjects / Keywords

  • ETS-10
  • AM-6
  • Vanadium
  • EVS-10
  • Adsorption
  • Isotherm
  • Separations

• Graduation date

  Fall 2015

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3416T94M

• 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.