(535d) 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.