Removal of Carbon Dioxide from Light Gas Mixtures using a Porous Strontium(II) Silicoaluminophosphate Fixed Bed: Closed Volume and Portable Applications

Abstract

A Sr 2+ -SAPO-34 bed was assembled to study CO 2 dynamic adsorption under conditions that emulate those found in closed volume and portable applications. Although the surface area was reduced by 7% during pelletization, adsorption capacities estimated from breakthrough curves compared well with static volumetric adsorption data. Modeling of the breakthrough adsorption was achieved using a Linear Driving Force mass transfer rate model, showing good agreement with the experimental data and confirming fast kinetics and efficient use of the bed. Fast kinetics were also evidenced by the length of the unused section of the bed as calculated from a Mass Transfer Zone model. Adsorption capacity degradation was not observed after multiple regeneration cycles. Apparent and equilibrium adsorption isotherm data estimated from the bed and static volumetric experiments at 25 C were compared to that of 5A Zeolite. These showed that Sr 2+ -SAPO-34 is a superior adsorbent for CO 2 removal in the low partial pressure range (<1500 ppm). CO 2 and H 2 O multicomponent adsorption breakthrough curves were also gathered for a CO 2 inlet concentration of 1000 ppm and dew points of −5 and 8 C. The addition of moisture resulted in a decrease in total processed gas volume by 31 and 47%, respectively.

A Fine-Tuned Fluorinated MOF Addresses the Needs for Trace CO2 Removal and Air Capture Using Physisorption

“…Considerately, the aerospace industry recognized the advantages of the physisorption-based separation and recently shifted their efforts to the utilization of recyclable physical adsorbents, such as the zeolite 5A (Ca 2+ ) and the SAPO-34 (Sr 2+ ), for the capture of CO 2 in confined spaces. 18,19 Typically, the aforementioned physical adsorbents exhibit a moderate CO 2 heat of adsorption of 45-50 kJ/mol and a recyclable CO 2 uptake of 9-15 cm 3 (STP)/g (1.7-2.9 wt%) at 1300 ppm. Nonetheless, their overall performance is inadequate and ineffective in the presence of water vapor due to their relative low tolerance to water.…”

“…Markedly, there is a need to develop a new generation of highly CO 2 -selective physical adsorbent materials with a moderate CO 2 heat of adsorption, i.e., below 60 kJ/mol. ,− Consequently, such a looked-for adsorbent will pave the way to affordable, effective, and energy-efficient recovery of CO 2 and will render the DAC competitive and self-sustainable. Considerately, the aerospace industry recognized the advantages of the physisorption-based separation and recently shifted their efforts to the utilization of recyclable physical adsorbents, such as the zeolite 5A (Ca 2+ ) and the SAPO-34 (Sr 2+ ), for the capture of CO 2 in confined spaces. , Typically, the aforementioned physical adsorbents exhibit a moderate CO 2 heat of adsorption of 45–50 kJ/mol and a recyclable CO 2 uptake of 9–15 cm 3 (STP)/g (1.7–2.9 wt %) at 1300 ppm. Nonetheless, their overall performance is inadequate and ineffective in the presence of water vapor due to their relatively low tolerance to water.…”

The potential of direct air capture using adsorbents in cold climates

“…In addition, zeolites have high adsorption capacities at cold temperatures and low heats of adsorption when compared to other key benchmark and novel materials ( Figure 8 ). 28 , 29 , 34 , 35 , 41 , 42 As discussed, lower CO 2 heats of sorption reduce the energy required to regenerate the sorbent, and higher sorption capacities reduce operating and capital costs. Although Na-X and Li-X have low heats of sorption, they become more promising materials for DAC application at colder temperatures due to their increased adsorption capacities.…”

Carbon Dioxide Removal from Humid Atmosphere by a Porous Hierarchical Silicoaluminophosphate/Carbon Composite Adsorbent

“…Among zeolitic adsorbents, silicoaluminophosphates (SAPOs), particularly Sr 2+ -SAPO-34, have shown efficacy in the removal of CO 2 at very low concentrations due to physisorption enhancement from overlapping surface electrostatic potential fields generated in combination with the extra-framework Sr 2+ and their interaction with the adsorbate; this is possible in part due to the relative sizes of the adsorbate (kinetic diameter, σ = 3.30 Å), the adsorbent pore (∼ 4–5 Å), and the actual distances between the active Sr 2+ adsorption sites within the SAPO structure. , It was also determined that the Sr 2+ active sites were located in exposed locations within the framework main cage (see Scheme ), occupying unique preferential positions (near sites II’ and III) that are connected to the enhancement in adsorption capacity at low CO 2 concentrations . Sr 2+ -SAPO-34 adsorbents can also be easily regenerated using a vacuum swing with or without a thermal intervention, which helps to minimize or plausibly eliminate any significant energy expenditure . Nevertheless, although the Sr 2+ -SAPO-34 framework is tolerant to water, its adsorptive capacity is limited due to the competitive adsorption of water since a CO 2 roll-up behavior was observed during fixed-bed adsorption tests .…”

“…Sr 2+ -SAPO-34 adsorbents can also be easily regenerated using a vacuum swing with or without a thermal intervention, which helps to minimize or plausibly eliminate any significant energy expenditure . Nevertheless, although the Sr 2+ -SAPO-34 framework is tolerant to water, its adsorptive capacity is limited due to the competitive adsorption of water since a CO 2 roll-up behavior was observed during fixed-bed adsorption tests . Generally, for systems where the hydrophilicity limits the removal efficiency, the design of hierarchical composites with tailored hydrophobicity could be an alternative − and confined space synthesis procedures can be used to create a core/shell arrangement where advantages of different adsorbent material phases can be synergistically combined .…”