Loading...

Synthesis and Characterization of Nano-zeolite Membranes for Natural Gas Sweetening

Maghsoudi, Hafez | 2013

1082 Viewed
  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 45148 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Soltanieh, Mohammad
  7. Abstract:
  8. Zeolite membranes are of interest due to their special properties; thermal and mechanical resistances and non-plasticization property in gas separations. Therefore, separation of H2S from natural gas by these membranes is the main goal of this thesis which is not investigated in the world. After some theoretical investigations including diffusion mechanisms of gases in the zeolites and adsorption mechanism of H2S on the zeolites, pure silica CHA-type (Si-CHA) zeolite was selected. After successful synthesis of Si-CHA zeolite, adsorption isotherms of H2S, CO2, and CH4 on the Si-CHA zeolite were measured over pressure range of 0-190 kPa and temperatures of 25 °C, 50 °C, and 75 °C. Acid gases adsorption isotherms on this type of zeolite are reported for the first time. The isotherms follow a typical Type-I shape according to the Brunauer classification. Both Langmuir and Toth isotherms describe well the adsorption isotherms of methane and acid gases over the experimental conditions tested. Plateau behavior of isosteric heats of adsorption versus adsorbate loading indicates that the adsorption system is energetically homogeneous. Si-CHA zeolite showed high adsorption selectivity for acid gases over methane. Si-CHA zeolite showed high ideal selectivities for acid gases over methane at 100 kPa (6.15 for H2S and 4.06 for CO2 at 25 °C). Furthermore, FTIR spectra of the Si-CHA zeolite powder showed that H2S adsorption mechanism is physical, and hence, Si-CHA can be utilized in pressure swing adsorption processes (PSA) or as a zeolite membrane for H2S separation from natural gas.
    In this thesis, Si-CHA zeolite membranes were synthesized by two methods: in-situ crystallization and dry gel conversion. According to their separation characteristics for pure gases CO2, CH4, N2 and O2, in-situ crystallization method led to a better membrane with CO2 permeability of 3.39×10-8 mol/m2.s.Pa and CO2/CH4 ideal selectivity of 21.6 at 30 °C and 1 bar pressure difference over the membrane. Then the separation properties of that membrane were analyzed in some binary CO2/CH4 mixtures and a ternary H2S/CO2/CH4 mixture. The results are remarkable because it can selectively separate H2S from CH4. To best of our knowledge, this is the first zeolite membrane in the world that can be utilized in H2S/CH4 separation. The membrane showed selectivities of CO2/CH4=5.3 and H2S/CH4=3.24 for H2S/CO2/CH4 ternary mixture with a molar composition of 0.3/2.13/97.57 at 25 °C and 4 bar pressure difference over the membrane. At that conditions, CO2 and H2S permeabilities were 2.765×10-8 mol/m2.s.Pa and 1.70×10-8 mol/m2.s.Pa, respectively
  9. Keywords:
  10. Zeolite Membrane ; Gases Separation ; Hydrogen Sulfide ; Gas Sweetening ; CHA Zeolite

 Digital Object List

 Bookmark

No TOC