Post-Combustion CO2 Capture Using Structured Bed Loaded With Functionalized SBA-15 Sorbent

Post-combustion CO₂ Capture Using Structured Bed Loaded with Functionalized SBA-15 Sorbent

Nikhil Mittal¹, Arunkumar Samanta¹, J. Segura², Saeid Amiri³, Partha Sarkar², Rajender Gupta^1,*

¹Department of Chemical and Materials Engineering, University of Alberta

9107 - 116 St, ECERF, AB, T6G 2V4, Canada, Email: rajender@ualberta.ca, Tel: 780-492-6861, Fax: 780-49-2881

² Environment and Carbon Management Division, Alberta Innovates - Technology Futures, Edmonton, AB, Canada

³Wave Control Systems. Inc., Edmonton, Alberta, T6E 0C2, Canada

Abstract:

The conventional packed bed for post-combustion CO₂ capture suffers from significantly high pressure drop whereas the fluidized bed finds problems in sorbent attrition and loss. So, there is a need of more reliable and efficient bed configuration, which can offer a lower pressure drop, fast mass transfer kinetics, high working capacity and improved thermal management. An alternative configuration to packed bed is sorbents placed in structured bed reactor.  The major advantage of using structured bed for post-combustion CO₂ capture is low pressure drop because of its straight gas flow channels. The hydrodynamics and external mass transfer can be optimized in this structured bed by adjusting channel size and channel shape, whereas the sorbent loading and/or internal mass transfer can be controlled by the thickness and structure of sorbent channel wall. The objectives of this investigation was to study the adsorption of CO₂ from a flue gas in a structured bed loaded with amine functionalized SBA-15 sorbent and to understand the effect of various design variables such as sorbent bed diameter, channel spacing, membrane layer thickness, and flue gas volumetric flow rate etc.

In the proposed structured bed, the solid sorbent is contained inside a porous alumina tubular membrane reactor (OD ~ 4mm, ID ~ 3mm and average pore diameter ~0.8 micron) and CO₂ laden bulk gas flows through the annular region. CO₂ diffuses across the barrier layer and adsorbs preferentially on the solid sorbent.   The equipment was designed and built to host single and multi-tube reactors with different lengths with minimum modification. The concentration of CO₂ stream coming to and from the adsorption column was monitored as a function of time by a Pfeiffer mass spectroscopy (Model: OmniStar GSD 320). Each membrane tube was filled with approximately 0.2 g of 50 wt% PEI impregnated SBA-15 solid sorbent. Thermal swing adsorption cycles were initially tested at different temperatures for CO₂ adsorption using a simulated flue gas containing 10%CO₂ by vol in N₂. The breakthrough curves obtained for CO₂ adsorption from CO₂/N₂ mixture (10%CO₂ bal. N₂) on structured bed of 50 wt% PEI impregnated SBA-15 at 75 °C revealed that average CO₂ adsorption capacity was about 2.4 mmol.g^-1 after ten consecutive cycles. Each adsorption/desorption cycle involved a 10 min of CO₂ adsorption at 75 °C followed by regeneration for 15 min at 105 °C. For this sorbent, equilibrium CO₂ adsorption capacity measured in TGA under similar condition was 3.07 mmol/g adsorbent.  The thermogravimetric data also suggested that the CO₂ capture kinetics was also found to be fast and reached 90% of the total capacities within the first ten minutes. Finally, an optimum set of geometric parameters of the structured bed such as channel spacing and gas superficial velocity has been determined to improve adsorption kinetics and to reduce the pressure drop per unit length of bed.