Richard R. Willis

Screening of Metal−Organic Frameworks for Carbon Dioxide Capture from Flue Gas Using a Combined Experimental and Modeling Approach

A diverse collection of 14 metal-organic frameworks (MOFs) was screened for CO(2) capture from flue gas using a combined experimental and modeling approach. Adsorption measurements are reported for the screened MOFs at room temperature up to 1 bar. These data are used to validate a generalized strategy for molecular modeling of CO(2) and other small molecules in MOFs. MOFs possessing a high density of open metal sites are found to adsorb significant amounts of CO(2) even at low pressure. An excellent correlation is found between the heat of adsorption and the amount of CO(2) adsorbed below 1 bar. Molecular modeling can aid in selection of adsorbents for CO(2) capture from flue gas by screening a large number of MOFs.

Virtual high throughput screening confirmed experimentally: porous coordination polymer hydration.

Hydrothermal stability is a pertinent issue to address for many industrial applications where percent levels of water can be present at temperatures ranging from subambient to several hundred degrees. Our objective is to understand relative stabilities of MOF materials through experimental testing combined with molecular modeling. This will enable the ultimate design of materials with improved hydrothermal stability, while maintaining the properties of interest. The tools that we have employed for these studies include quantum mechanical calculations based upon cluster models and combinatorial steaming methods whereby a steam stability map was formulated according to the relative stability of different materials. The experimental steaming method allows for high throughput screening of materials stability over a broad range of steam levels as well as in-depth investigation of structural transformations under more highly resolved conditions, while the cluster model presented here yields the correct trends in hydrothermal stability. Good agreement was observed between predicted relative stabilities of materials by molecular modeling and experimental results. Fundamental information from these studies has provided insight into how metal composition and coordination, chemical functionality of organic linker, framework dimensionality, and interpenetration affect the relative stabilities of PCP materials. This work suggests that the strength of the bond between the metal oxide cluster and the bridging linker is important in determining the hydrothermal stability of the PCP. Although the flexibility of the framework plays a role, it is not as important as the metal-linker bond strength. This demonstration of alignment between experimental and calculated observations has proven the validity of the method, and the insight derived herein insight facilitates direction in designing ideal MOF materials with improved hydrothermal stability for desired applications.

CO2/H2O Adsorption Equilibrium and Rates on Metal−Organic Frameworks: HKUST-1 and Ni/DOBDC

Metal-organic frameworks (MOFs) have recently attracted intense research interest because of their permanent porous structures, huge surface areas, and potential applications as novel adsorbents and catalysts. In order to provide a basis for consideration of MOFs for removal of carbon dioxide from gases containing water vapor, such as flue gas, we have studied adsorption equilibrium of CO(2), H(2)O vapor, and their mixtures and also rates of CO(2) adsorption in two MOFs: HKUST-1 (CuBTC) and Ni/DOBDC (CPO-27-Ni or Ni/MOF-74). The MOFs were synthesized via solvothermal methods, and the as-synthesized products were solvent exchanged and regenerated before experiments. Pure component adsorption equilibria and CO(2)/H(2)O binary adsorption equilibria were studied using a volumetric system. The effects of H(2)O adsorption on CO(2) adsorption for both MOF samples were determined, and the results for 5A and NaX zeolites were included for comparison. The hydrothermal stabilities for the two MOFs over the course of repetitive measurements of H(2)O and CO(2)/H(2)O mixture equilibria were also studied. CO(2) adsorption rates from helium for the MOF samples were investigated by using a unique concentration-swing frequency response (CSFR) system. Mass transfer into the MOFs is rapid with the controlling resistance found to be macropore diffusion, and rate parameters were established for the mechanism.

Stability effects on CO2 adsorption for the DOBDC series of metal-organic frameworks.

Metal-organic frameworks with unsaturated metal centers in their crystal structures, such as Ni/DOBDC and Mg/DOBDC, are promising adsorbents for carbon dioxide capture from flue gas due to their high CO(2) capacities at subatmospheric pressures. However, stability is a critical issue for their application. In this paper, the stabilities of Ni/DOBDC and Mg/DOBDC are investigated. Effects of steam conditioning, simulated flue gas conditioning, and long-term storage on CO(2) adsorption capacities are considered. Results show that Ni/DOBDC can maintain its CO(2) capacity after steam conditioning and long-term storage, whereas Mg/DOBDC does not. Nitrogen isotherms for Mg/DOBDC show a drop in surface area after steaming, corresponding to the decrease in CO(2) adsorption, which may be caused by a reduction of unsaturated metal centers in its structure. Conditioning with dry simulated flue gas at room temperature only slightly affects CO(2) adsorption in Ni/DOBDC. However, introducing water vapor into the simulated flue gas further reduces the CO(2) capacity of Ni/DOBDC.

The effect of pyridine modification of Ni–DOBDC on CO2 capture under humid conditions

The metal-organic framework Ni-DOBDC was modified with pyridine molecules to make the normally hydrophilic internal surface more hydrophobic. Experiments and molecular simulations show that the pyridine modification reduces H2O adsorption while retaining substantial CO2 capacity under the conditions of interest for carbon capture from flue gas.

UZM-13, UZM-17, UZM-19 and UZM-25: synthesis and structure of new layered precursors and a zeolite discovered via combinatorial chemistry techniques

Abstract A combinatorial chemistry investigation screening the abilities of the diethyldimethylammonium (DEDMA), ethyltrimethylammonium (ETMA), and [Me 3 N(CH 2 ) 4 NMe 3 ] 2+ (diquat-4, DQ-4) cations to form zeolites over a range of conditions was carried out. Each of the templates formed a layered precursor; UZM-13, UZM-17, and UZM-19 forming in the DEDMA, ETMA, and DQ-4 systems, respectively. The layered materials are distinct from, but similar to MCM-47 by XRD. The structure of UZM-13 was solved from powder data and was confirmed to contain MCM-47-like aluminosilicate layers. Calcination of these layered materials led to condensation along the b-axis, forming similar 3-dimensional zeolitic species designated UZM-25. However, the UZM-25 derived from the UZM-13 material was superior in crystallinity and had the only XRD pattern that could be indexed. The structure of UZM-25 was determined to be of the CDO structure type, which contains 2-dimensional intersecting 8-ring pores, from both powder and single crystal data.

Toward commercialization of nanozeolites

Many reagents, parameters, and outcomes which are typical in the laboratory are not acceptable at the commercial scale, or are simply not scaleable. Several of these are addressed here. Significant pressure generated via organic template decomposition during BEA zeolite synthesis was addressed with a continuous venting processing scheme. The selection of a less expensive silica raw material source and the development of diafiltration as a product purification method, allowed for significant product cost reduction. Microcalorimetry was shown to be an effective at pinpointing synthesis events in situ. Comparison of nano BEA to a commercial BEA revealed significant differences in external surface area, particle morphology, and activity in a pilot plant catalyst evaluation.

Scaling Up of Catalysts Discovered from Small-Scale Experiments

The chemical industry faces a challenging business climate due to difficult economic conditions in much of the world, strong international competition, and worldwide environmental concern. In addition, innovation in this industry has slowed as catalyst and process technology has matured. The need for a methodology that can increase catalyst innovation while continuing to decrease cycle times has been recognized by the Council for Chemical Research (Catalysis Roadmap, Vision 2020) [1]. In the 1980s, the pharmaceutical industry faced similar circumstances. Downward pressure on drug prices became incompatible with the high cost of drug discovery. Combinatorial chemistry, based on advances in laboratory automation, high-throughput synthesis, and activity screening, allowed the pharmaceutical companies to break the innovation impasse [2, 3].

Carbon dioxide separation with novel microporous metal organic frameworks

The goal of this program was to develop a low cost novel sorbent to remove carbon dioxide from flue gas and gasification streams in electric utilities. Porous materials named metal-organic frameworks (MOFs) were found to have good capacity and selectivity for the capture of carbon dioxide. Several materials from the initial set of reference MOFs showed extremely high CO{sub 2} adsorption capacities and very desirable linear isotherm shapes. Sample preparation occurred at a high level, with a new family of materials suitable for intellectual property protection prepared and characterized. Raman spectroscopy was shown to be useful for the facile characterization of MOF materials during adsorption and especially, desorption. Further, the development of a Raman spectroscopic-based method of determining binary adsorption isotherms was initiated. It was discovered that a stronger base functionality will need to be added to MOF linkers in order to enhance CO{sub 2} selectivity over other gases via a chemisorption mechanism. A concentrated effort was expended on being able to accurately predict CO{sub 2} selectivities and on the calculation of predicted MOF surface area values from first principles. A method of modeling hydrolysis on MOF materials that correlates with experimental data was developed and refined. Complimentary experimental data were recorded via utilization of a combinatorial chemistry heat treatment unit and high-throughput X-ray diffractometer. The three main Deliverables for the project, namely (a) a MOF for pre-combustion (e.g., IGCC) CO{sub 2} capture, (b) a MOF for post-combustion (flue gas) CO{sub 2} capture, and (c) an assessment of commercial potential for a MOF in the IGCC application, were completed. The key properties for MOFs to work in this application - high CO{sub 2} capacity, good adsorption/desorption rates, high adsorption selectivity for CO{sub 2} over other gases such as methane and nitrogen, high stability to contaminants, namely moisture, and easy regenerability, were all addressed during this program. As predicted at the start of the program, MOFs have high potential for CO{sub 2} capture in the IGCC and flue gas applications.