Adsorber heat exchanger using Al-fumarate beads for heat-pump applications - a transport study.

Metal-Organic Frameworks (MOFs), thanks to their type V water adsorption isotherms ("S-Shape") and large water capacities, are considered as potential breakthrough adsorbents for heat-pump applications. In particular, Al(OH)-fumarate could enable efficient regeneration at a lower temperature than silica-gel which would allow us to address the conversion of waste heat at low temperature such as found in data centers. Despite its greater adsorption capacity features, heat and mass transport limitations could jeopardize the potential performance of Al(OH)-fumarate. Heat and mass transport depend on the size of the bodies (mm range), their packing and on the pore structures, i.e. macro-mesopore volumes and sizes. This paper describes the cost-efficient and scalable synthesis and shaping processes of Al(OH)-fumarate beads of various sizes appropriate for use in water Adsorption Heat-Pumps (AHPs). The objective was to study transport limitations (i.e. mass and heat) in practical e beads which meet mechanical stability requirements. Dynamic data at the grain scale was obtained by the Large Temperature Jump method while dynamic data at the adsorber scale was obtained on a heat exchanger filled with more than 1 kg of Al(OH)-fumarate beads. Whereas the binder content had little impact on mass and heat transfer in this study, we found that Knudsen diffusion in mesopores of the grain may be the main limiting factor at the grain scale. At the adsorber scale, heat-transfer within the bed packing as well as to the heat exchanger is likely responsible for the slow adsorption and desorption kinetics which have been observed for very low desorption temperature. Finally, the dynamic aspects of the observed water adsorption isotherm shift with temperature are discussed in light of reported reversible structure modification upon temperature triggered water adsorption-desorption.

Absolute molecular sieve separation of ethylene/ethane mixtures with silver zeolite A.

Absolute ethylene/ethane separation is achieved by ethane exclusion on silver-exchanged zeolite A adsorbent. This molecular sieving type separation is attributed to the pore size of the adsorbent, which falls between ethylene and ethane kinetic diameters.

An operando DRIFTS investigation into the resistance against CO2 poisoning of a Rh/alumina catalyst during toluene hydrogenation.

CO(2) is a major contaminant of renewable H(2) derived from biomass fermentation. The effect of the presence of CO(2) on the activity of alumina-supported Pt and Rh catalysts used for the hydrogenation of toluene at 348 K was investigated. The use of operando diffuse reflectance spectroscopy (DRIFTS) was crucial in unravelling the changes in the nature and abundance of species adsorbed at the sample surface and relating those to the changes of catalytic activity. Rhodium supported on alumina was only partly deactivated by the introduction of CO(2) during the hydrogenation of toluene, contrary to the case of Pt/alumina. Rh was only partially covered by carbonyl species derived from CO(2) and it was shown that toluene could successfully compete with some of the linearly adsorbed carbonyls for adsorption. The alumina support stored many CO(2)-derived adsorbates (carbonates, hydrogenocarbonates, carboxylates) that could spill over to the metal and form carbonyl species even after the removal of CO(2) from the feed.

Direct volumetric measurement of gas oversolubility in nanoliquids: beyond Henry's law.

The properties of condensed matter are strongly affected by confinement and size effects at the nanoscale. Herein, we measured by microvolumetry the increased solubility of H(2) in a series of solvents (CHCl(3), CCl(4), n-hexane, ethanol, and water) when confined in the cavities of mesoporous solids (gamma-alumina, silica, and MCM-41). Gas/liquid solubilities are enhanced by up to 15 times over the corresponding bulk values for nanoliquid sizes smaller than 15 nm as long as gas/liquid interfaces are mesoconfined in a porous network. Although Henry's law constant apparently no longer applies under these confinement, the concentration of dissolved H(2) still increases linearly with increasing pressure in the range 1-5 bar. We discuss the role and main implications of surface excess concentrations at mesoconfined gas/liquid interfaces in enhancing gas solubility.

Heats of adsorption for seven gases in three metal-organic frameworks: systematic comparison of experiment and simulation.

The heat of adsorption is an important parameter for gas separation and storage applications in porous materials such as metal-organic frameworks (MOFs). There are, however, few systematic studies available in the MOF literature. Many papers report results for only one MOF and often only for a single gas. In this work, systematic experimental measurements by TAP-2 are reported for the heats of adsorption of seven gases in three MOFs. The gases are Kr, Xe, N2, CO2, CH4, n-C4H10, and i-C4H10. The MOFs studied are IRMOF-1, IRMOF-3, and HKUST-1. The data set provides a valuable test for molecular simulation. The simulation results suggest that structural differences in HKUST-1 experimental samples may lead to differing heats of adsorption.

Enantioseparation of new nucleoside analogs, related to d4T and acyclovir, by chiral capillary electrophoresis using highly sulfated beta-cyclodextrins.

Baseline separation of some new acyclic nucleosides which are potential antiviral agents was achieved using cyclodextrin capillary zone electrophoresis (CD-CZE). A method for the enantiomeric resolution of these compounds and determination of their enantiomeric purity was developed using anionic CDs (highly sulfated-CD or highly S-CD) as chiral selectors and capillaries, which were dynamically coated with polyethylene oxide (PEO). Operational parameters including (i) the nature and concentration of the chiral selectors, (ii) organic modifiers, (iii) temperature, and (iv) applied voltage were investigated. The use of charged CDs provides (i) a supplementary driving force for the compounds in a running buffer and (ii) enantiomeric resolution by inclusion of compounds in the CD cavity. The highly S-CD was found to be the most effective complexing agent and allowed good enantiomeric resolution. The complete resolution of five nucleoside analogs was obtained using 25 mM phosphate buffer, pH 2.5, containing either highly S-alpha-CD, S-beta-CD or S-gamma-CD at 30 degrees C with an applied field of 0.30 kV/cm. The apparent association constants of the inclusion complexes were calculated. The enantiomer migration order for the molecules investigated was determined and the detection limit of enantiomeric impurities was found to vary between 0.34 to 3.56 ng.mL(-1) for the first enantiomer.