M. Douglas LeVan

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.

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.

Adsorption, science and technology

I. Characterization of Adsorbents and Tthermodynamics of Adsorption.- Characterization of adsorbents.- Theories of adsorption in micropores.- The statistical thermodynamic approach to the correlation of equilibrium data.- A two-patch heterogeneous model with surface phase transition for benzene adsorption on silicalite.- Interpretation of low temperature gas adsorption and desorption using stochastic pore networks.- Adsorption of n-hexane and 3-methylpentane on zeolites Y and ZSM 20.- II. Kinetics of Adsorption and Fixed-Bed Processes.- Adsorption kinetics.- Dynamics of fixed-bed adsorbers. Isothermal adsorption of single components.- Asymptotic fixed-bed behavior: proportionate and constant patterns.- Pore scale hydrodynamics.- Separation processes based on electrosorption phenomena.- Adsorptive reactors.- Design aspects of fixed-bed adsorption processes.- Numerical methods for the solution of adsorption models.- III. Cyclic Processes and Simulated Moving Beds.- Gas separation by pressure swing adsorption using carbon molecular sieves.- Pressure swing adsorption technology.- Modeling and simulation of rate induced PSA separations.- Thermal swing adsorption.- On countercurrent adsorption separation processes.- Sorbex: continuing innovation in liquid phase adsorption.- IV. Applications in Biotechnology and Environmental Engineering.- The use of granular activated carbon for potable water treatment as an example of liquid phase applications of activated carbon.- Breakthrough time of organic vapours in activated carbon filters as a function of the air flow pattern.- Continuous adsorption in biotechnology.- Continuous chromatographic processes.- Biochemical reaction and separation in chromatographic columns.- Some factors involved in scale-up of industrial biotechnological adsorption processes.- Development of physical and mathematical modelling for scale-up of batch stirred tank and packed-bed column adsorption and chromatographic units.- Optimisation of adsorption techniques for the purification of biomolecules.- Gel filtration chromatography.- Adsorption chromatography for protein purification.- List of Lecturers and Participants.

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.

Mesoporous silica–metal organic composite: synthesis, characterization, and ammonia adsorption

A novel composite adsorbent composed of an inorganic silica phase impregnated with a metal organic phase is synthesized and characterized. Specifically, MCM-41 is impregnated with copper active sites, which are then functionalized with benzene-1,3,5-tricarboxylic acid, which is the linker in the metal organic framework CuBTC. X-ray diffraction, nitrogen adsorption isotherms, thermogravimetric analysis, scanning electron microscopy, X-ray photoelectron spectroscopy, and equilibrium ammonia capacities are used to characterize the composite and control materials. Properties of the composite and control samples after conditioning at 85 °C in saturated water vapor for 5 h are also evaluated. Results show that the silica phase of the composite material provides an engineered phase that enhances the hydrothermal stability of the metal organic phase and the metal organic phase provides active sites for chemisorption. The composite material has a high ammonia capacity of 5.2 mol kg−1 and remains stable after conditioning. In comparison, the CuBTC structure degrades and shows low ammonia capacity after conditioning.

Metal–Organic Frameworks for Oxygen Storage

We present a systematic study of metal-organic frameworks (MOFs) for the storage of oxygen. The study starts with grand canonical Monte Carlo simulations on a suite of 10,000 MOFs for the adsorption of oxygen. From these data, the MOFs were down selected to the prime candidates of HKUST-1 (Cu-BTC) and NU-125, both with coordinatively unsaturated Cu sites. Oxygen isotherms up to 30 bar were measured at multiple temperatures to determine the isosteric heat of adsorption for oxygen on each MOF by fitting to a Toth isotherm model. High pressure (up to 140 bar) oxygen isotherms were measured for HKUST-1 and NU-125 to determine the working capacity of each MOF. Compared to the zeolite NaX and Norit activated carbon, NU-125 has an increased excess capacity for oxygen of 237% and 98%, respectively. These materials could ultimately prove useful for oxygen storage in medical, military, and aerospace applications.

Adsorption heat pump modeling: the thermal wave process with local equilibrium

Abstract This paper describes a model for a thermal-wave adsorption heat pump cycle. Local equilibrium is assumed, providing the asymptotic best-case performance. The model is utilized to examine the performance of adsorption refrigeration cycles powered by low temperature waste heat sources of 373–393 K. The impact of varying system temperatures, bed cycling frequency, valve positioning, and sectioning of the bed are examined. Cycle coefficients of performance (COPs) were greater than 1.2 for the base case of a 393 K heat source, 303 K condenser temperature, and 278 K evaporator temperature for a cycle utilizing a water/NaX zeolite adsorbate/adsorbent pair. As an effect of the small temperature changes during the cycle, for some regions of the bed, the loading change was opposite of that expected; i.e., from the start to the end of the entire heating process some portions of the bed experienced loading increases. The location of the inlet/outlet valves in the bed was found to have an impact on the shape of the temperature and loading fronts. The introduction of partitions within the bed was found to have only a small impact on the performance of the cycle for the temperatures examined, with sections of the bed undergoing pressurization in a non-sequential order.

Frequency Response Method for Measuring Mass Transfer Rates in Adsorbents via Pressure Perturbation

A new apparatus for the measurement of equilibria and dynamics for gas-phase adsorption systems is utilized to examine the adsorption of carbon dioxide on BPL activated carbon. The apparatus has a flow-through configuration. For dynamics, with constant inlet flow, pressure within the adsorbent-containing section is varied sinusoidally, and the time-dependent outlet flow rate is measured to determine an amplitude ratio and phase lag. Studies are made of temperature effects and particle size effects. Results are compared with several mathematical models. Frequency response data show that the BPL system follows surface (or micropore) diffusion kinetics. The rate of adsorption for the activated carbon is found to be only weakly dependent on the bulk particle size.

A Novel Adsorption Cycle for CO2 Recovery: Experimental and Theoretical Investigations of a Temperature Swing Compression Process

Abstract A novel adsorption cycle is examined experimentally and theoretically for recovering carbon dioxide from a 50 mol% mixture with carbon monoxide. Several adsorbents are considered, and zeolite NaY is chosen for the process due to its high capacity and selectivity for CO2 in the presence of CO. The process consists of three steps. The bed is fed the gas mixture at 273 K until CO2 breakthrough occurs. The bed then undergoes countercurrent blowdown of CO2 while heating at 391 K and is finally cooled to the initial feed temperature once the bed has been depleted of CO2. Results are presented from laboratory scale experiments and are described using numerical simulations. This novel cycle provides a method for capturing and producing CO2 without the need for a purge gas and has low energy requirements if waste heat is available.

Periodic states of adsorption cycles III. Convergence acceleration for direct determination

Abstract This paper describes several enhancements to accelerate the direct determination of the periodic states of fixed-bed adsorption cycles. The new methods make it possible to calculate the periodic states up to 40 times faster than our original formulation (Croft & LeVan, Chem. Eng. Sci. 49 (1994) 1821) and in many cases 100–1000s of times faster than by just running cycle after cycle. We have tested the methods on several examples and have obtained fast, stable, robust convergence. The enhancements are (i) the use of a hybrid Newton–Broyden method to reduce some of the Jacobian matrix calculation processes required by Newtons method, (ii) the initial application of a novel iterative-secant approach to increase stability and to avoid the calculation of the first Jacobian matrix for the hybrid Newton–Broyden method, (iii) the implementation of a sensitivity interpolation technique with dynamic grid allocation, and (iv) the dynamic specification of integration error tolerances.