James E. Atwater

Complex permittivities and dielectric relaxation of granular activated carbons at microwave frequencies between 0.2 and 26 GHz

Carbonaceous materials are amenable to microwave heating to varying degrees. The primary indicator of susceptibility is the complex permittivity (e*), of which the real component correlates with polarization and the imaginary term represents dielectric loss. For a given material, the complex permittivity is dependent upon both frequency and temperature. Here we report the complex permittivities of three activated carbons of diverse origin over the frequency range from 0.2 to 26 GHz. Dielectric polarization-relaxation phenomena for these materials are also characterized. Measurements were made using a coaxial dielectric probe and vector network analyzer based system across the temperature region between 22 and 190 8C.  2003 Elsevier Science Ltd. All rights reserved.

LOW TEMPERATURE AQUEOUS PHASE CATALYTIC OXIDATION OF PHENOL

Abstract Low temperature aqueous phase heterogeneous catalytic oxidation of dissolved organic compounds is a potential means for remediation of contaminated ground and surface waters, industrial effluents, and other wastewater streams. The capability for operation at substantially milder conditions of temperature and pressure, in comparison to those required for supercritical water oxidation and closely related wet air oxidation processes, is made possible through the use of an extremely active bi-metallic noble metal catalyst. Phenol degradation studies were conducted using continuous flow packed bed microreactors configured to minimize the deviation from plug flow. Reaction rate constants for the disappearance of phenol were determined using a pseudo first order plug flow kinetic model over the temperature range between 35–65°C. These data were used to derive Arrhenius activation energies and pre-exponential factors. Reactor operating conditions required for mineralization of phenol have been determined.

Aqueous phase heterogeneous catalytic oxidation of trichloroethylene

Abstract Aqueous phase heterogeneous catalytic oxidation of dissolved organic compounds has been demonstrated as a potential means for the remediation of contaminated ground waters, industrial effluents, and other wastewater streams under comparatively mild conditions of temperature and pressure. Dissolved molecular oxygen is used as oxidant over a platinum-ruthenium catalyst on a high surface area carbon support at temperatures to 130°C and pressures to 6 atm. Studies were conducted using packed catalyst beds in tubular continuous plug flow microreactors. Reaction rate constants for the oxidation of trichloroethylene were determined using a pseudo first-order plug flow kinetic model over the temperature range between 90–120°C. Reactor operating conditions required for deep oxidation of aqueous trichloroethylene at 90°C are reported.

A urease bioreactor for water reclamation aboard manned spacecraft

Development of a fixed bed continuous flow bioreactor, utilizing urease immobilized on diatomaceous earth, for decomposition of aqueous urea in a spacecraft closed loop environmetital life support system is described. The results of small scale bioreactor experiments investigating the effects of throughput, temperature, pH and conductivity are reported. The design and performance of a full scale bioreactor are also presented.

A continuous alcohol oxidase bioreactor for regenerative life support

The development of a composite fixed-bed continuous-flow immobilized alcohol oxidase bioreactor is described for use in the production of drinking water from humidity condensates collected aboard manned spacecraft. The principal organic contaminants of this wastewater stream are low molecular weight alcohols and organic acids. Alcohol oxidase catalyzes the oxidation of short chain primary alcohols to aldehydes at ambient temperatures. The resulting aldehydes are subjected to a second oxidation via the action of a heterogeneous noble metal catalyst to form carboxylic acids which are removed by sorption onto ion exchange resins. Inactivation of the enzyme by hydrogen peroxide has been significantly reduced by coimmobilization of metallic platinum onto the support. The results of ground-based testing using model contaminant solutions and true humidity condensates are reported.

Enzymatic Determination of Ethanol Using ‘Reagentless’ Electrocatalyzed Luminol Chemiluminescence

Abstract Flow analysis methodology is presented for the determination of aqueous ethanol in concentrations between 3–340 μM. Alcohol oxidase catalyzes the production of hydrogen peroxide which is detected by luminol chemiluminescence. Adjustment of the pH to alkaline conditions and addition of the luminophore are implemented using in-line flow-through beds containing crystalline media. The requirement for a homogeneous catalyst is eliminated by electrochemical initiation of luminescence. Traditional laboratory reagents are replaced by packed beds containing immobilized enzyme, solid phase basification media, and crystalline luminol. The methodology is suitable for application in both continuous flow and flow injection analysis configurations.

Porous cobalt spheres for high temperature gradient magnetically assisted fluidized beds.

Porous metallic cobalt spheres have been prepared as high temperature capable media for employment in gradient magnetically assisted fluidization and filtration technologies. Cobalt impregnated alginate beads are first formed by extrusion of an aqueous suspension of Co3O4 into a Co(II) chloride solution. The organic polymer is thermally decomposed yielding cobalt oxide spheres, followed by reduction to the metallic state, and densification. Cobalt beads have been produced with porosities ranging between 10 and 50%, depending upon sintering conditions. The product media have been characterized by scanning electron microscopy (SEM), nitrogen adsorption porosimetry, and vibrating sample magnetometry.

“Reagentless” Flow Analysis Determination of Hydrogen Peroxide by Electrocatalyzed Luminol Chemiluminescence

Flow analysis methodology is presented for the determination of micromolar levels of aqueous hydrogen peroxide by luminol chemiluminescence. Adjustment of the pH to alkaline conditions and addition of the luminophore are implemented using in-line flow-through beds containing crystalline media. The requirement for a homogeneous catalyst is eliminated by electrochemical initiation of luminescence. Traditional laboratory reagents are replaced by packed beds containing solid phase basification media, and crystalline luminol. The methodology is suitable for application in both continuous flow and flow injection analysis configurations.

Regenerable Microbial Check Valve: Life Cycle Tests Results

Life cycle regeneration testing of the Microbial Check Valve (MCV) that is used on the Shuttle Orbiter to provide microbial control of potable water is currently in progress. Four beds are being challenged with simulated reclaimed waters and repeatedly regenerated. Preliminary results indicate that contaminant systems exhibit unique regeneration periodicities. Cyclic throughput diminishes with increasing cumulative flow. It is considered to be feasible to design a regenerable MCV system which will function without human intervention and with minimal resupply penalty for the 30 year life of the Space Station.

Numerical simulation of iodine speciation in relation to water disinfection aboard manned spacecraft I. Equilibria

Elemental iodine (I2) is currently used as the drinking water disinfectant aboard the Shuttle Orbiter and will also be incorporated into the water recovery and distribution system for the International Space Station Alpha. Controlled release of I2 is achieved using the Microbial Check Valve (MCV), a flow-through device containing an iodinated polymer which imparts a bacteriostatic residual concentration of approximately 2mg/L to the aqueous stream. During regeneration of MCV canisters, I2 concentrations of approximately 300 mg/L are used. Dissolved iodine undergoes a series of hydrolytic disproportionation and related reactions which result in the formation of an array of inorganic species including: I-, I3-, HOI, OI-, IO3-, HIO3, I2OH-, I2O(-2), and H2OI+. Numerical estimation of the steady-state distribution of inorganic iodine containing species in pure water at 25 degrees C has been achieved by simultaneous solution of the multiple equilibrium expressions as a function of pH. The results are reported herein.