Carbon dioxide capture-related gas adsorption and separation in metal-organic frameworks

Metal–organic frameworks have received significant attention as a new class of adsorbents for natural gas storage; however, inconsistencies in reporting high-pressure adsorption data and a lack of comparative studies have made it challenging to evaluate both new and existing materials. Here, we briefly discuss high-pressure adsorption measurements and review efforts to develop metal–organic frameworks with high methane storage capacities. To illustrate the most important properties for evaluating adsorbents for natural gas storage and for designing a next generation of improved materials, six metal–organic frameworks and an activated carbon, with a range of surface areas, pore structures, and surface chemistries representative of the most promising adsorbents for methane storage, are evaluated in detail. High-pressure methane adsorption isotherms are used to compare gravimetric and volumetric capacities, isosteric heats of adsorption, and usable storage capacities. Additionally, the relative importance of increasing volumetric capacity, rather than gravimetric capacity, for extending the driving range of natural gas vehicles is highlighted. Other important systems-level factors, such as thermal management, mechanical properties, and the effects of impurities, are also considered, and potential materials synthesis contributions to improving performance in a complete adsorbed natural gas system are discussed.

https://pubs.rsc.org/en/content/articlepdf/2014/SC/C3SC52633J

Evaluating metal–organic frameworks for natural gas storage

This Review focuses on research oriented toward elucidation of the various aspects that determine adsorption of CO2 in metal–organic frameworks and its separation from gas mixtures found in industrial processes. It includes theoretical, experimental, and combined approaches able to characterize the materials, investigate the adsorption/desorption/reaction properties of the adsorbates inside such environments, screen and design new materials, and analyze additional factors such as material regenerability, stability, effects of impurities, and cost among several factors that influence the effectiveness of the separations. CO2 adsorption, separations, and membranes are reviewed followed by an analysis of the effects of stability, impurities, and process operation conditions on practical applications.

CO2 Capture and Separations Using MOFs: Computational and Experimental Studies

Metal-organic frameworks (MOFs) represent the largest known class of porous crystalline materials ever synthesized Their narrow pore windows and nearly unlimited structural and chemical features have made these materials of significant interest for membrane-based gas separations In this comprehensive review, we discuss opportunities and challenges related to the formation of pure MOF films and mixed-matrix membranes (MMMs) Common and emerging separation applications are identified, and membrane transport theory for MOFs is described and contextualized relative to the governing principles that describe transport in polymers Additionally, cross-cutting research opportunities using advanced metrologies and computational techniques are reviewed To quantify membrane performance, we introduce a simple membrane performance score that has been tabulated for all of the literature data compiled in this review These data are reported on upper bound plots, revealing classes of MOF materials that consistently demonstrate promising separation performance Recommendations are provided with the intent of identifying the most promising materials and directions for the field in terms of fundamental science and eventual deployment of MOF materials for commercial membrane-based gas separations

MOF-Based Membranes for Gas Separations.

The zeolite imidazolate framework ZIF-8 is shown for the first time to be able to catalyze transesterification of vegetable oil with significant activity. Rationalization of this behavior at the atomic scale is provided by combining CO adsorption monitored by FTIR and DFT calculations (clusters and periodic models). We demonstrate that the acido-basic sites are located at the external surface of the material or at defects, but not in the microporosity of ZIF-8. A great variety of sites are found the surface: OH and NH groups, hydrogenocarbonates, low-coordinated Zn atoms, and free N(-) moieties belonging to linkers. Their proportions depend on the operating conditions (temperature and pressure). The acido-basicity of the surface is then probed by adsorption of CO at low temperature. In parallel, the species present are mapped by DFT calculations combined with a thermodynamic model. An assignment of the CO region of the FTIR spectra can thus be proposed. The complex infrared spectrum is attributed to the coexistence of classical C-adducts of CO with acid sites and other modes on basic sites (O-adducts and side-on adducts). Adsorption energies and CO frequency shifts show that some strong Lewis sites exist (in particular Zn(II) species), as well as strong Bronsted acid sites (NH groups), together with basic sites (OH groups and N(-) moieties). By calculating the co-adsorption of a model ester (methyl acetate) and methanol, we show the prevailing role of Zn(II) species as acid sites, combined with N(-) moieties and OH groups as basic ones, in determining the catalytic properties of ZIF-8. This work opens new perspectives on the use of MOFs in catalysis and, more generally, on the properties of their external surface.

Catalysis of transesterification by a nonfunctionalized metal-organic framework: acido-basicity at the external surface of ZIF-8 probed by FTIR and ab initio calculations.

Experimental measurements and molecular simulations were conducted for two zeolitic imidazolate frameworks, ZIF-8 and ZIF-76. The transferability of the force field was tested by comparing molecular simulation results of gas adsorption with experimental data available in the literature for other ZIF materials (ZIF-69). Owing to the good agreement observed between simulation and experimental data, the simulation results can be used to identify preferential adsorption sites, which are located close to the organic linkers. Topological mapping of the potential-energy surfaces makes it possible to relate the preferential adsorption sites, Henry constant, and isosteric heats of adsorption at zero coverage to the nature of the host-guest interactions and the chemical nature of the organic linker. The role played by the topology of the solid and the organic linkers, instead of the metal sites, upon gas adsorption on zeolite-like metal-organic frameworks is discussed.

Adsorption of CO2, CH4, and N2 on Zeolitic Imidazolate Frameworks: Experiments and Simulations

The invention describes a method for separating paraxylene from an aromatic hydrocarbon feedstock containing isomers with 8 carbon atoms by liquid-phase or gas-phase adsorption. The adsorbent used belongs to the family of ZIFs of SOD structure, containing an inorganic network of metal centres based on Zn 2+ cations connected to one another by organic imidazolate ligands substituted in position 2.

Method for separating paraxylenes using an adsorbent from the family of zifs of sod structure.

The invention relates to a novel hybrid solid having a structural zeolite framework. CHA belongs to the ZIF family containing an inorganic network of Zn 2+ cation metal centers connected together by two organic ligands, 2-methylimidazolate, and a benzimidazolate. The invention also relates to the preparation and use of said adsorbent solid in a method for separating multi-branched paraffins included in a hydrocarbon feedstock containing linear paraffins, single-branched paraffins, and multi-branched paraffins having 5 to 7 carbon atoms per molecule, wherein said method includes placing said filler in contact with said adsorbent solid so as to produce at least a first stream enriched with multi-branched paraffins, and a second stream enriched with linear and single-branched paraffins.

Novel hybrid organic/inorganic im-22 solid, and use thereof in the separation of multi-branched paraffins from linear and single-branched paraffins

A novel crystallized hybrid solid with an organic-inorganic mixed matrix is described that has a three-dimensional structure containing an inorganic lattice of zinc-based metal centres connected together by deprotonated organic ligands constituted by the species -O 2 C-C 6 H 2 -(O) 2 -CO 2 . This novel solid is called IM-21 and has an X-ray diffraction diagram as given below.

Novel im-21 organic-inorganic hybrid solid and process for preparing same

On decrit un procede de separation du paraxylene d'une charge d'hydrocarbures aromatiques contenant des isomeres a 8 atomes de carbone par adsorption en phase liquide ou en phase gaz L'adsorbant utilise appartient a la famille des ZIFs de type structural SOD, contenant un reseau inorganique de centres metalliques a base de cations Zn connectes entre eux par des ligands organiques imidazolates substitues en position 2

David Peralta

Papers

Adsorption of CO2, CH4, and N2 on Zeolitic Imidazolate Frameworks: Experiments and Simulations

Method for separating paraxylenes using an adsorbent from the family of zifs of sod structure.

Novel hybrid organic/inorganic im-22 solid, and use thereof in the separation of multi-branched paraffins from linear and single-branched paraffins

Novel im-21 organic-inorganic hybrid solid and process for preparing same

Procede de separation de paraxylenes utilisant un adsorbant de la famille des zif de type structural sod