MOF Adsorbents for Flue Gas Separation: Comparison of Material Ranking Approaches

Adsorption Equilibrium and Transport of CO2, N2, and H2O in CALF-20

CALF-20 is a hydrophobic MOF adsorbent demonstrated at a pilot scale for the capture of CO2 from wet flue gas using a direct steam heating TSA cycle. It has been synthesized following a published protocol, and its XRD structure matches known results. Both crystals and particles are used to study single-component adsorption and the diffusion of CO2, N2, and H2O by using gravimetric, volumetric, and dynamic column breakthrough methods. Temperature and relative humidity ranges explored are 25-150 °C and 0-95% in helium, respectively, up to 1 bar pressure. A steam-helium mixture is used above 100 °C. Small pressure steps are used to determine (approximately) locally constant transport parameters. The Sips-Henry isotherm is the best-fit model, which correctly captures the dependence of the isosteric heat of adsorption on adsorbent loading, especially the complex shape for H2O. The pore diffusion model captures crystal uptakes. The micropore diffusivity is an increasing function of the adsorbed-phase concentration up to a certain level before showing reversal, which is consistent with the Darken equation, a function of isotherm curvature. Gas/moisture transport in CALF-20 particles is controlled by Knudsen diffusion in the macropores. The key features observed from the single-component adsorption and diffusion studies and their impact on process studies are demonstrated by applying them to predict breakthrough results.

Optimizing filters of activated carbons obtained from biomass residues for ethylene removal in agro-food industry devices

A series of adsorbents (activated carbons, ACs) were synthesized by physical and chemical activation of olive stones (OS) and their textural and chemical characteristics determined by complementary techniques such as N2 and CO2 physisorption, pH of the point zero of charge (pHPZC), HRSEM or XPS. Samples with a wide range of physicochemical properties were obtained by fitting the activation procedure. The performance of these adsorbents in filters working under dynamic conditions was studied by determining the corresponding breakthrough curves for the ethylene removal. The physicochemical transformations of OS during activation were related with the adsorptive performance of derivative ACs. Results were compared to those obtained using commercial carbons, in particular ACs, carbon black or carbon fibers, in order to identify the properties of these materials on influencing the adsorptive performance. In general, ACs from OS perform better than the commercial samples, being also easily regenerated and properly used during consecutive adsorption cycles. CO2-activation showed to be the best synthesis option, leading to granular ACs with a suitable microporosity and surface chemistry. These results could favour the integration of this type of inexpensive materials on devices for the preservation of climacteric fruits, in a clear example of circular economy by reusing the agricultural residues.

Covalent organic frameworks for CO2 capture: from laboratory curiosity to industry implementation

CO2 concentration in the atmosphere has increased by about 40% since the 1960s. Among various technologies available for carbon capture, adsorption and membrane processes have been receiving tremendous attention due to their potential to capture CO2 at low costs. The kernel for such processes is the sorbent and membrane materials, and tremendous progress has been made in designing and fabricating novel porous materials for carbon capture. Covalent organic frameworks (COFs), a class of porous crystalline materials, are promising sorbents for CO2 capture due to their high surface area, low density, controllable pore size and structure, and preferable stabilities. However, the absence of synergistic developments between materials and engineering processes hinders achieving the qualitative leap for net-zero emissions. Considering the lack of a timely review on the combination of state-of-the-art COFs and engineering processes, in this Tutorial Review, we emphasize the developments of COFs for meeting the challenges of carbon capture and disclose the strategies of fabricating COFs for realizing industrial implementation. Moreover, this review presents a detailed and basic description of the engineering processes and industrial status of carbon capture. It highlights the importance of machine learning in integrating simulations of molecular and engineering levels. We aim to stimulate both academia and industry communities for joined efforts in bringing COFs to practical carbon capture.

Application of Metal-Organic Frameworks (MOFs) in Environmental Biosystems

Metal-organic frameworks (MOFs) are crystalline materials that are formed by self-assembling organic linkers and metal ions with large specific areas and pore volumes. Their chemical tunability, structural diversity, and tailor-ability make them adaptive to decorate many substrate materials, such as biomass-derived carbon materials, and competitive in many environmental biosystems, such as biofuel cells, bioelectrocatalysts, microbial metal reduction, and fermentation systems. In this review, we surmised the recent progress of MOFs and MOF-derived materials and their applications in environmental biosystems. The behavior of MOFs and MOF-derived materials in different environmental biosystems and their influences on performance are described. The inherent mechanisms will guide the rational design of MOF-related materials and lead to a better understanding of their interaction with biocomponents.