Evaluation of Novel Metal-Organic Framework Materials for Adsorptive Post-Combustion CO2 Capture

  • Author / Creator
    Baboolal,Johan D
  • The mitigation of CO2 emissions from large anthropogenic sources such as coal-fired power plants by CO2 capture is a challenging engineering problem. Due to the large scale of energy generation, post-combustion CO2 capture processes must be very low-cost for practical
    implementation. The current industry standard technology for CO2 capture, absorption, separates CO2 from post-combustion flue gas by scrubbing with a liquid amine solvent, and is very energy intensive. Pressure swing adsorption (PSA) uses a porous, solid adsorbent
    material to separate CO2 and N2, and is a potentially lower energy alternative to absorption, due to the regeneration simply requiring a reduction in pressure.
    The benchmark or standard adsorbent which has been considered and evaluated in literature for post-combustion CO2 capture is zeolite 13X. Recently, several novel metal-organic framework (MOF) materials have been reported in literature to have potential as alternatives to zeolite 13X, however evaluation of these MOFs in a PSA process has not been done.
    This research will be focused on the evaluation of two types of MOFs in a PSA process using simulated flue gas as a feed, and comparing their performance to zeolite 13X. The first type of MOF evaluated, called SiF6 or SIFSIX, was reported in literature to not
    be significantly affected by the presence of water. Zeolite 13X, however, has a significantly reduced CO2 capacity when water vapor is present in flue gas. Two types of SIFSIX materials were investigated, SIFSIX-2-Cu-i and SIFSIX-3-Zn. The experimental adsorption
    isotherms of these materials were fitted to a Langmuir model, and this was incorporated into a full PSA model. Optimization of the SIFSIX adsorbents and zeolite 13X under feed of 15% CO2 and 85% N2 showed that both SIFSIX adsorbents have similar purity and
    recovery performance when compared to 13X. An energy and productivity analysis was also performed, and SIFSIX-2-Cu-i had a similar energy requirement compared to Zeolite 13X, with a minimum energy of 155 kWh/t CO2 captured. The minimum energy for SIFSIX-3-Zn was 140 kWh/t CO2, however the very sharp isotherm of SIFSIX-3-Zn results
    in a productivity of 0.18 mol/m3 adsorbent/s, which is significantly lower than that for 13X, at 0.42 mol/m3 adsorbent/s and SIFSIX-2-Cu-i at 0.75 mol/m3 adsorbent/s. These results indicate that in a dry case, Zeolite 13X is a better adsorbent than SIFSIX-3-Zn, and
    SIFSIX-2-Cu-i has performance which is only marginably better.
    The second type of MOF evaluated for post-combustion capture is a diamine-appended MOF, mmen-Fe2. This type of adsorbent was reported in the literature to have an S shaped or type V adsorption isotherm. A quadratic-langmuir isotherm model was employed to fit
    the adsorption isotherm of mmen-Fe2 at a temperature of 30C. The performance of mmen-Fe2 and Zeolite 13X was then compared by an optimization study, which revealed that the minimum energy for the mmen-Fe2 adsorbent was 110kWh/t CO2, compared to that of 13X which was 135 kWh/t CO2. The reduction in energy was due to a higher blowdown pressure
    being possible in the mmen-Fe2 adsorbent due to its capacity for N2 being significantly less than Zeolite 13X. The S-shaped CO2 isotherm was also beneficial, as the increased working
    capacity of CO2 resulted in a productivity for mmen-Fe2 which was 1 mol/m3 adsorbent/s, almost twice that of Zeolite 13X, at 0.55 mol/m3 adsorbent/s. Therefore, the mmen-Fe2 adsorbent is a good candidate for CO2 capture by VSA considering its better performance
    than zeolite 13X in terms of both energy and productivity.

  • Subjects / Keywords
  • Graduation date
    Fall 2015
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
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