Michael A. Matthews

Sterilization using high-pressure carbon dioxide

Sterilization using high-pressure carbon dioxide Jian Zhang a, Thomas A. Davis a, Michael A. Matthews a,∗, Michael J. Drews b, Martine LaBerge c, Yuehuei H. An d a Department of Chemical Engineering, University of South Carolina, Columbia, SC 29208, USA b School of Materials Science and Engineering, Clemson University, Clemson, SC 29634, USA c Department of Bioengineering, Clemson University, Clemson, SC 29634, USA d Orthopaedic Research Laboratories, Medical University of South Carolina, Charleston, SC 29403, USA

Production of hydrogen from chemical hydrides via hydrolysis with steam

The objective of this work is to develop a method of producing H2 for use in hand-portable fuel cells eliminating the bulkiness and high pressures associated with storage tanks. Water, either as liquid or vapor, will react with solid hydrides such as NaBH4 to produce pure hydrogen. However, a number of limitations are inherent in the liquid–solid reaction. The insoluble hydrolysis products are extremely basic and high pH inhibits the reaction. A large excess of acid must be added to the mixture in order to force the reaction to completion, but is detrimental to the equipment. Furthermore, the liquid–solid reaction is inefficient on a weight basis because a large excess of the water-acid mixture must be used to obtain acceptable yields of hydrogen. Exploiting the vapor–solid reaction overcomes some of these limitations. An isothermal semi-batch reactor was constructed to test the concept. In each experiment the reactor was loaded with one gram of hydride and ambient pressure steam was metered through the reactor. A GC analysis of the product gas detected only hydrogen and water. The yield of hydrogen was measured and compared to the theoretical yield. The pH of the condensed, unreacted steam was tested and the percentage of excess water used was measured. A statistical analysis was conducted on the results in order to determine interactions between the parameters of flow rate and temperature. For some hydrides, nearly 100% yield of hydrogen was obtained without addition of any acid. Hydrogen yield depended strongly on temperature and, to a lesser extent, on flow rate of steam. The results and thermodynamic analysis suggest a conceptual hydrogen generation system in which the exothermic hydrolysis reaction is linked to an endothermic dehydriding reaction for the purpose of producing additional hydrogen.

Electrochemical Generation of Superoxide in Room-Temperature Ionic Liquids

We have demonstrated that superoxide ion can be generated electrochemically in room-temperature ionic-liquid solvents. In the absence of impurities, cyclic voltammetry showed that the super oxide ion is stable in these solvents. Similar superoxide ion chemistry has previously been demonstrated in volatile and environmentally suspect aprotic solvents such as dimethyl formamide and acetonitrile. However, ionic liquids are nonvolatile and should minimize the problems of secondary solvent waste. It is proposed that the resultant superoxide ion can be used to perform low-temperature oxidation of wastes. Low-temperature oxidation of waste solvents can provide a much needed alternative to high-temperature waste incinerators, whose use is greatly complicated by regulatory requirements and locating suitable sites.

Production of hydrogen gas from novel chemical hydrides

Abstract Six ligand-stabilized complexes have been synthesized and tested for use as hydrogen storage media for portable fuel cell applications. The new hydrides are: [HC (3,5-Me2pz) 3] LiBH4 (1) , { [H2C (3,5-Me2pz) 2] Li (BH4) } 2 (2) (pz = pyrazolyl ) , [ (TMEDA) Li (BH4) ] 2 (3) (TMEDA = (CH3) 2NCH2CH2N (CH3) 2) , [HC (pz) 3] LiBH4 (4) , { [H2C (pz) 2] Li (BH4) } 2 (5) and Mg(BH4)·23THF (6) (THF = tetrahydrofuran) . Hydrolysis reactions of the compounds liberate hydrogen in quantities which range from 56 to 104 (±5%) percent of the theoretical yield. Gas chromatographic analysis of the product gases from these reactions indicate that hydrogen is the only gas produced. Thermally initiated reactions of the novel compounds with NH4Cl were unsuccessful. Although the amount of hydrogen energy which can be theoretically obtained per unit weight is lower than that of the classical hydrides such as LiBH4 and NaBH4, the reactions are less violent and hydrolysis of compounds 1, 2, 4, 5 and 6 releases less heat per mole of hydrogen generated.

Diffusion in supercritical mixtures: CO2+ cosolvent + solutes

Abstract Diffusion coefficients are measured for acridine, phenanthrene, and benzoic acid at infinite dilution in either supercritical carbon dioxide, or a mixture of supercritical carbon dioxide with 5.5 mol % methanol as entrainer. These data indicate that diffusion of acridine and benzoic acid are markedly reduced by the presence of small amounts of methanol. Phenanthrene is not affected to as great an extent. These observations are in qualitative agreement with equilibrium solubility and spectroscopic measurements for these same systems, indicating the formation of clusters of the entrainer (methanol) about benzoic acid and acridine. It is proposed that the size of the diffusing cluster, not the size of the solute molecule, should be considered when predicting diffusion rates.

Diffusion coefficients of model contaminants in dense CO2

Dense CO2 extraction is an emerging technology in cleaning and remediation. The successful design and implementation of processes based on this technology require the accurate determination of solute diffusivities in the systems. In this work, a Taylor dispersion apparatus was constructed for measuring binary diffusion coefficients of benzoic acid, biphenyl, and p-dichlorobenzene in dense CO2 at temperatures of 293.15, 298.15, 308.15, 318.15, and 323.15 K and pressures from approximately 71 to 171 bar. For correlation and prediction of binary diffusivity, the Enskog kinetic approach with density correction, the Liu–Silva–Macedo (LSM) model, and the Eaton–Akgerman (EA) model were evaluated. The Enskog approach gave satisfactory predictions in liquid CO2, but it may be inappropriate to extrapolate this correlation to the supercritical region. The LSM model based on the Lennard–Jones fluid theory gave poor diffusivity predictions in liquid CO2 but its accuracy was improved in the supercritical region. The EA correlation based on the rough hard sphere theory gave accurate predictions in both the liquid and supercritical CO2 regions.

Evaluation of CO2‐based cold sterilization of a model hydrogel

The purpose of the present work is to evaluate a novel CO2‐based cold sterilization process in terms of both its killing efficiency and its effects on the physical properties of a model hydrogel, poly(acrylic acid‐co‐acrylamide) potassium salt. Suspensions of Staphylococcus aureus and Escherichia coli were prepared for hydration and inoculation of the gel. The hydrogels were treated with supercritical CO2 (40°C, 27.6 MPa). The amount of bacteria was quantified before and after treatment. With pure CO2, complete killing of S. aureus and E. coli was achieved for treatment times as low as 60 min. After treatment with CO2 plus trace amounts of H2O2 at the same experimental conditions, complete bacteria kill was also achieved. For times less than 30 min, incomplete kill was noted. Several physical properties of the gel were evaluated before and after SC‐CO2 treatment. These were largely unaffected by the CO2 process. Drying curves showed no significant change between treated (pure CO2 and CO2 plus 30% H2O2) and untreated samples. The average equilibrium swelling ratios were also very similar. No changes in the dry hydrogel particle structure were evident from SEM micrographs. Biotechnol. Bioeng. 2008;101: 1344–1352.

Green electrochemistry. Examples and challenges

Electrochemical methods have been proposed for synthesis of organic compounds, including conversion of CO2. Such methods may provide a basis for environmentally friendly and sustainable methods for chemical production. Nevertheless, electrochemical syntheses are not widely utilized. Several examples of ongoing research are presented that illustrate both the opportunities as well as the challenges associated with the utilization of electrochemistry for green chemical manufacturing.

Thermodynamic considerations of the reversible potential for the nickel electrode

The thermodynamics of ideal and non-ideal solutions is applied to nickel hydroxide, the electrochemically active material in the positive electrode of a nickel battery, to provide theoretical insight into the reversible potential as a function of the state-of-discharge. The models were fit to experimental discharge curves to obtain the activity-coefficient parameters and the standard potential over a temperature range from 5 to 55°C. The two-parameter activity coefficient models perform significantly better than the Nernst equation and one-parameter Margules at all temperatures, thus suggesting that the insertion of the protons into the lattice occurs in an ordered, non-random fashion. The standard potential decreases linearly with temperature by 0.84 mV/K. The thermodynamic expressions and parameters given here enable one to predict the reversible potential of nickel hydroxide as a function of temperature and state-of-discharge.

Hard-Sphere Theory for Correlation of Tracer Diffusion of Gases and Liquids in Alkanes

The rough hard‐sphere (RHS) theory for transport properties has substantially improved understanding of diffusion, viscosity, and thermal conductivity. At present, however, quantitative predictions for polyatomic species are hampered by uncertainties in assigning the hard‐sphere diameter and the roughness factor, and by lack of molecular dynamics calculations. Because the qualitative features of the theory have proven correct for a variety of chemical systems, methods have been proposed for using rough hard‐sphere theory even when the exact parameters needed to apply the theory are unknown. One such approach is examined for tracer diffusion in alkane solvents for solutes ranging in size from hydrogen to hexadecane. Useful relations are shown which are simple, yet entirely consistent with hard‐sphere theory. The approach circumvents the difficulties in assigning roughness factor, diameter, and molecular dynamics results.