Richard Chahine

Low-pressure adsorption storage of hydrogen

Abstract The amount of gas that can be stored in an adsorption system is dictated by the nature of the adsorbent material and the operating conditions of the storage system, namely the storage pressure and temperature. This paper describes the impact of these factors on H2 storage. The discussion is based on measurements of hydrogen adsorption on commercially available and densified adsorbents. The measurements were carried out in the pressure range 1–80 atm and at different storage temperatures using a high-pressure volumetric method. The results show that the adsorption technique could provide a viable method for hydrogen storage.

Hydrogen adsorption in carbon nanostructures

Abstract Hydrogen adsorption, (BET) specific surface area and X-ray diffraction (XRD) measurements have been performed on carbon nanofibers, intercalated and exfoliated carbon materials. Excess adsorption capacity was evaluated at equilibrium pressures and temperatures ranging from 0.1 to 10.5MPa and 77 to 295K, respectively. We find that at room temperature, carbon nanofibers can adsorb up to 0.7wt% at 10.5MPa. We observed that the presence of different nickel–copper ratios in the catalyst particles leads to change in crystalline structure and specific surface area. Furthermore, we noted that the latter can be increased by the addition of hydrogen in the organic gas during the synthesis of the nanofibers. Finally, we will discuss the hydrogen coverage per unit surface area which is substantially larger on nanostructures than on activated carbon.

The Influence of the Range of Electroactivity and Capacitance of Conducting Polymers on the Performance of Carbon Conducting Polymer Hybrid Supercapacitor

Hybrid electrochemical supercapacitors based on carbon and conducting polymers as negative and positive electrodes, respectively, have been investigated. Poly-(3-fluorinatedphenyl)thiophene and poly(ethylenedioxythiophene) derivatives showing various ranges of electrochemical activity and capacitance values were evaluated as positive electrodes. It was shown that the mass and capacitance of the polymers have a significant effect on the charge/discharge characteristics and performance of such hybrid electrochemical supercapacitors. The experimental conditions that should be used to obtain specific charge/discharge curves are presented. A linear charge/discharge curve can be obtained between 0 and 3 V when the weight of conducting polymer is larger than that of the negative carbon electrode. In contrast, a battery-like charge/discharge curve is recorded when a smaller conducting polymer weight, relative to that of the carbon electrode, is used.

Volumetric hydrogen sorption capacity of monoliths prepared by mechanical densification of MOF-177

Bulk powdered MOF-177 is mechanically compressed to prepare monoliths with bulk densities more than three times its crystallographic density, and their excess and total gravimetric and volumetric hydrogen storage capacities are measured over a pressure range of 0–13 MPa at 77 K and room temperature. The maximum excess volumetric hydrogen storage capacity of these monoliths at ∼6 MPa and 77 K is 25.8 ± 1.2 g L−1, which is a 78% increase of that of powdered bulk MOF-177 and 80% of the theoretical maximum excess volumetric hydrogen storage capacity predicted on the basis of the materials crystallographic density. The monoliths show diminishing excess gravimetric capacity with increasing density which is attributed to their decreasing micropore volume, which in turn stems from the progressive collapse of MOF-177 crystals to an amorphous phase when they are subjected to densification. A modified Dubinin–Astakhov (DA) model is adapted to describe the excess gravimetric adsorption of samples with varying bulk densities. The total volumetric capacity of monoliths prepared from MOF-177 is 48.0 ± 2.1 g L−1 at 13 MPa and 77 K; if a complete storage system that does not reduce this capacity by more than 20% is designed, it can then meet the DOE 2015 volumetric system target at 77 K. Under the same conditions, it is easier to meet the DOE 2015 gravimetric system target of 5.5 wt% as the materials total gravimetric storage capacity is ∼10.3 ± 0.3 wt%.

The catalytic effect of single-wall carbon nanotubes on the hydrogen sorption properties of sodium alanates

Single-wall carbon nanotubes (SWNTs) were examined as catalysts for improving the hydrogen absorption and desorption properties of Ti/Zr-doped NaAlH4 hydride, proposed as a reversible hydrogen storage material. We studied the hydrogen charge and discharge characteristics and stability of sodium aluminium composites ball milled with carbon additives such as SWNTs, graphite or activated carbon (AX-21). The SWNT–NaAlH4 system was tested at 160 °C for up to 200 cycles, and the sorption kinetics were enhanced by a factor of four. Also, the catalyzed NaAlH4 hydride with graphite and activated carbon additives shows fast absorption and desorption kinetics. Our results indicate that by creating new hydrogen transition sites, the structure of carbon in the composites plays an important role in enhancing the hydrogen absorption and release rates.

Measurement of Small Dielectric Loss by Time-Domain Spectroscopy: Application to Water/Oil Emulsions

Total reflection time-domain spectroscopic method as applied to moderate to strongly polar liquids is described. A difference method based on total reflection is applied to the study of dielectric properties of water/oil emulsions. Measurement of maximum dielectric loss as small as Emax = 0.005 is discussed.

Development of a dipole probe for the study of dielectric properties of biological substances in radiofrequency and microwave region with time-domain reflectometry

A time-domain reflectometric (TDR) technique with a needle-like dipole probe is described for dielectric measurements of biological substances. The probe is tested by measuring some known liquids. The dielectric measurements made on beef muscle and fat compare favorably with existing literature values of human muscle and fat.

IMPORTANCE OF THE DIELECTRIC PROPERTIES OF MATERIALS FOR MICROWAVE HEATING

ABSTRACT In this paper, we show the importance of having a good knowledge of the dielectric properties of a material when it is intended to heat or dry this material by microwaves. We study the frequency, temperature and composition dependence of the dielectric permittivity in order to see how these dependences can affect the microwave heating process. We also study the non-uniform absorption of energy in a sample due to dielectric or conductive losses.

Simulation of binary CO 2 /CH 4 mixture breakthrough profiles in MIL-53 (Al)

MIL-53 (Al) aluminum terephthalate, a commercial metal-organic framework, has been studied as a potential candidate for pressure swing adsorption separation of CO2/CH4 binary mixtures. Pure gas isotherms of CH4 and CO2 measured over 0-6MPa and at room temperature are fitted with the Dubinin-Astakhov (D-A) model. The D-A model parameters are used in the Doong-Yang Multicomponent adsorption model to predict the binary mixture isotherms. A one-dimensional multicomponent adsorption breakthrough model is then used to performa parametric study of the effect of adsorbent particle diameter, inlet pressures, feed flow rates, and feed compositions on the breakthrough performance. Commercial MIL-53 with a particle diameter of 20 µm renders high tortuous flow; therefore it is less effective for separation. More effective separation can be achieved if MIL-53 monoliths of diameters above 200 µm are used. Faster separation is possible by increasing the feed pressure or if the starting compositions are richer in CO2. More CH4 is produced per cycle at higher feed pressures, but the shortened time at higher pressures can result in the reduction of the CH4 purity.

Computer-Based Permittivity Measurements and Analysis of Microwave Power Absorption in Conductive Dielectrics

The time domain reflectometer technique is applied to measure the dielectric properties of a pure Debye dielectric mixed with various amounts of salt. The effect of ohmic conductivity on a Debye dielectric is studied as a function of temperature and frequency. A computer simulation technique is used to compare the heating pattern in a conductive dielectric for two microwave absorption frequencies of 2.45 GHz and 915 MHz.