Measurement of competitive $$\text {CO}_{2}$$ and $$\text {H}_{2}\text {O}$$ adsorption on zeolite 13X for post-combustion $$\text {CO}_{2}$$ capture

The Challenge of Water Competition in Physical Adsorption of CO2 by Porous Solids for Carbon Capture Applications - A Short Perspective

With ever-increasing efforts to design sorbent materials to capture carbon dioxide from flue gas and air, this perspective article is provided based on nearly a decade of collaboration across science, engineering, and industry partners. A key point learned is that a holistic view of the carbon capture problem is critical. While researchers can be inclined to value their own fields and associated metrics, often, key parameters are those that enable synergy between materials and processes. While the role of water in the chemisorption of CO2 is well-studied, in this perspective, it is hoped to highlight the often-overlooked but critical role of water in assessing the potential of a physical adsorbent for CO2 capture. This is a challenge that requires interdisciplinarity. As such, this document is written for a general audience rather than experts in any specific discipline.

Aluminum formate, Al(HCOO)3: An earth-abundant, scalable, and highly selective material for CO2 capture

A combination of gas adsorption and gas breakthrough measurements show that the metal-organic framework, Al(HCOO)3 (ALF), which can be made inexpensively from commodity chemicals, exhibits excellent CO2 adsorption capacities and outstanding CO2/N2 selectivity that enable it to remove CO2 from dried CO2-containing gas streams at elevated temperatures (323 kelvin). Notably, ALF is scalable, readily pelletized, stable to SO2 and NO, and simple to regenerate. Density functional theory calculations and in situ neutron diffraction studies reveal that the preferential adsorption of CO2 is a size-selective separation that depends on the subtle difference between the kinetic diameters of CO2 and N2. The findings are supported by additional measurements, including Fourier transform infrared spectroscopy, thermogravimetric analysis, and variable temperature powder and single-crystal x-ray diffraction.

CO 2 Capture by Hybrid Ultramicroporous TIFSIX‐3‐Ni under Humid Conditions Using Non‐Equilibrium Cycling

Although pyrazine‐linked hybrid ultramicroporous materials (HUMs, pore size <7 Å) are benchmark physisorbents for trace carbon dioxide (CO₂) capture under dry conditions, their affinity for water (H₂O) mitigates their carbon capture performance in humid conditions. Herein, we report on the co‐adsorption of H₂O and CO₂ by TIFSIX‐3‐Ni—a high CO₂ affinity HUM—and find that slow H₂O sorption kinetics can enable CO₂ uptake and release using shortened adsorption cycles with retention of ca. 90 % of dry CO₂ uptake. Insight into co‐adsorption is provided by in situ infrared spectroscopy and ab initio calculations. The binding sites and sorption mechanisms reveal that both CO₂ and H₂O molecules occupy the same ultramicropore through favorable interactions between CO₂ and H₂O at low water loading. An energetically favored water network displaces CO₂ molecules at higher loading. Our results offer bottom‐up design principles and insight into co‐adsorption of CO₂ and H₂O that is likely to be relevant across the full spectrum of carbon capture sorbents to better understand and address the challenge posed by humidity to gas capture.

CO2 /N2 Separation on Highly Selective Carbon Nanofibers Investigated by Dynamic Gas Adsorption

The development of highly selective adsorbents for CO₂ is a key part to advance separation by adsorption as a viable technique for CO₂ capture. In this work, polyacrylonitrile (PAN) based carbon nanofibers (CNFs) were investigated for their CO₂ separation capabilities using dynamic gas adsorption. The CNFs were prepared by electrospinning and subsequent carbonization at various temperatures ranging from 600 to 1000 °C. A thorough investigation of the CO₂ /N₂ selectivity resulted in measured values of 53-106 at 1 bar and 25 °C on CNFs carbonized at 600, 700, or 800 °C. Moreover, the selectivity increased with lower measurement temperatures and lower CO₂ partial pressures, reaching values up to 194. Further analysis revealed high long-term stability with no degradation over 300 cycles and fast adsorption kinetics for CNFs carbonized at 600 or 700 °C. These excellent properties make PAN-based CNFs carbonized at 600 or 700 °C promising candidates for the capture of CO₂ .

Experimental Study on the Kinetics of CO2 and H2O Adsorption on Honeycomb Carbon Monoliths under Cement Flue Gas Conditions

The main challenge of adsorption consists in the production of materials that can be used in real situations. This study comprehensively describes the CO₂ and H₂O adsorption behavior of honeycomb-shaped sorbents commonly used in rapid pressure swing adsorption cycles (RPSA). With this purpose, the kinetics and equilibrium of adsorption of CO₂/H₂O/N₂ mixtures on three honeycomb carbon monoliths (793, 932, and AM03) were assessed in a thermogravimetric analyzer (TGA) under different postcombustion capture scenarios (temperature of 50 °C and several concentrations of CO₂). The kinetics study exhibited that the single adsorption of CO₂ and H₂O can be adequately described by the Avrami and exponential decay-2 models, respectively. As expected, the three carbon monoliths presented fast adsorption of CO₂ from a CO₂/H₂O mixture. Furthermore, when humid flue gas was considered, overall adsorption kinetics were governed by CO₂. Besides, the experimental data fitting to the intraparticle diffusion model showed that gradual CO₂ and H₂O diffusion toward the micropores was the rate-limiting stage. The obtained results give a better insight into the selective adsorption of CO₂ and the potential of honeycomb carbon monoliths to separate CO₂ from humid flue gas in the context of the cement industry. Carbon monolith 793 is the best carbon monolith candidate to capture CO₂ under the evaluated conditions: a capacity of adsorption of 1 mmol of CO₂ g^-1 and favorable kinetics in 32 vol % CO₂ and 4 vol % H₂O_(v), at 50 °C and 101.3 kPa.

Carbon dioxide capture with zeotype materials

This review describes the application of zeotype materials for the capture of CO2 in different scenarios, the critical parameters defining the adsorption performances, and the challenges of zeolitic adsorbents for CO2 capture.

A scalable metal-organic framework as a durable physisorbent for carbon dioxide capture

[Figure: see text].

Zinc Containing Small-Pore Zeolites for Capture of Low Concentration Carbon Dioxide

The capture of low concentration CO₂ presents numerous challenges. Here, we report that zinc containing chabazite (CHA) zeolites can realize high capacity, fast adsorption kinetics, and low desorption energy when capturing ca. 400 ppm CO₂ . Control of the state and location of the zinc ions in the CHA cage is critical to the performance. Zn²⁺ loaded onto paired anionic sites in the six-membered rings (6MRs) in the CHA cage are the primary sites to adsorb ca. 0.51 mmol CO₂ /g-zeolite with Si/Al=ca. 7, a 17-fold increase compared to the parent H-form. The capacity is increased further to ca. 0.67 mmol CO₂ /g-zeolite with Si/Al=ca. 2 due to more paired sites for zinc exchange. Zeolites with double six-membered rings (D6MRs) that orient 6MRs into the cages give enhanced uptakes for CO₂ adsorption with zinc exchange. The results reveal that zinc exchanged CHA and several other small pore, cage containing zeolites merit further investigation for the capture of low concentration CO₂ .

MUF-16: A Robust Metal-Organic Framework for Pre- and Post-Combustion Carbon Dioxide Capture

One of the most critical environmental issues of our age is the escalating release of CO₂ into the atmosphere. Separation technologies with low energy footprints may be an effective way to capture CO₂ and prevent its accumulation. Metal-organic frameworks (MOFs) can meet separation challenges due to their tailored structures and tunable pore surfaces. However, obstacles to their deployment can include the energy consumed by regeneration, a lack of long-term structural stability, and their production on large scales. Herein, we report on MUF-16 ([Co(Haip)₂], H₂aip = 5-aminoisophthalic acid), a hydrogen-bonded water-stable microporous material that combines high CO₂ adsorption with a low affinity for other gases. MUF-16 is built up from inexpensive starting reagents in a scalable process. It can be easily regenerated at room temperature by purging with inert gas, and it maintains its performance over multiple adsorption/desorption cycles. MUF-16 features one-dimensional channels that trap CO₂ guest molecules by a raft of attractive electrostatic interactions and size complementarity. It rejects H₂ and N₂ molecules around room temperature. This was verified by simulated and experimental breakthrough separation measurements on CO₂/N₂ and CO₂/H₂ mixtures. MUF-16 can be pelletized by coating with polymeric poly(vinylidene difluoride) (PVDF) to render it compatible with large-scale applications.