SO2 Saturation of the Room Temperature Ionic Liquid [C(2)mim][NTf2] Much Reduces the Activation Energy for Diffusion

The physical effect of high concentrations of reversibly dissolved SO2 on [C(2)mim][NTf2] was examined using cyclic voltammetry, chronoamperometry, and ESR spectroscopy. Cyclic voltammetry of the oxidation of solutions of ferrocene, N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD), and chloride in the room temperature ionic liquid (RTIL) 1-ethyl-3-methylimidazolium bis(trifluoromethanesufonyl)imide ([C(2)mim][NTf2]) reveals an increase in limiting current of each species corresponding to the addition of increasing concentrations of sulfur dioxide. Quantitative chronoamperometry reveals an increase in each species' diffusion coefficient with SO2 concentration. When chronoamperometric data were obtained for ferrocene in [C(2)mim][NTf2] at a range of temperatures, the translational diffusion activation energy (29.0 +/- 0.5 kJ mol(-1)) was found to be in good agreement with previous studies. Adding SO2 results in apparent near-activationless translational diffusion. A significant decrease in the activation energy of rotational diffusion with the SO2 saturation of a 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO) solution in [C(2)mim][NTf2] (29.9 +/- 2.0 to 7.7 +/- 5.3 kJ mol(-1)) was observed using electron spin resonance (ESR) spectroscopy. The reversible physical absorption Of SO2 by [C(2)mim][NTf2] should have no adverse effect on the ability of that ionic liquid to be employed as a solvent in an electrochemical gas sensor, and it is possible that the SO2-mediated reduction of RTIL viscosity could have intrinsic utility.

Measuring the solubility of benzoic acid in room temperature ionic liquids using chronoamperometric techniques

The electrochemical reduction of benzoic acid (BZA) has been studied at platinum micro-electrodes (10 and 2 mu m diameters) in acetonitrile (MeCN) and six room temperature ionic liquids (RTILs): [C(2)mim][NTf2], [C(4)min][NTf2], [C(4)mpyrr][NTf2], [C(4)mim][BF4], [C(4)mim][NO3] and [C(4)mim][PF6] (where [C(n)mim](+)=1-alkyl-3-methylimidazolium, [NTf2](-)=bis(trifluoromethylsulphonyl)imide, [C(4)mpyrr](+)=N-butyl-N-methylpyrrolidinium, [BF4](-)=tetrafluoroborate, [NO3](-)=nitrate and [PF6] = hexafluorophosphate). Based on the theoretical fitting to experimental chronoamperometric transients in [C4mpyrr][NTf2] and MeCN at several concentrations and on different size electrodes, it is suggested that a fast chemical step preceeds the electron transfer step in a CE mechanism (given below) in both RTILs and MeCN, leading to the appearance of a simple one-electron transfer mechanism.

Electrochemical Determination of Manganese Solubility in Mercury via Amalgamation and Stripping in the Room Temperature Ionic Liquid n-Hexyltriethylammonium Bis(trifluoromethanesulfonyl)imide, [N-6,N-2,N-2,N-2][NTf2]

The solubility of manganese in mercury was determined electrochemically via amalgamation and stripping in the room temperature ionic liquid n-hexyltriethylammonium bis(trifluoromethanesulfonyl)imide, [N-6,N-2,N-2,N-2][NTf2]. A hemispherical mercury electrode was made by electrodepositing mercury onto a planar platinum microelectrode. Cyclic voltammetry of Mn2+ in [N-6,N-2,N-2,N-2][NTf2] at the mercury microhemisphere electrode was investigated at temperatures of 298, 303 and 313 K. The solubility of Mn in Hg was determined on the basis of the charge under the reduction peak (Mn2+ --> Mn-0) and the corresponding reoxidation.

Effect of Water on the Electrochemical Window and Potential Limits of Room-Temperature Ionic Liquids

The effect of water content on room-temperature ionic liquids (RTILs) was studied by Karl Fischer titration and cyclic voltammetry in the following ionic liquids: tris(P-hexyl)tetradecylphosphonium trifluorotris(pentafluoroethyl)phosphate [P-14,P-6,P-6,P-6][NTf2], N-butyl-N-methyl-pyrrolidinium bis(trifluoromethylsulfonyl)imide [C(4)mpyrr][NTf2], 1-hexyl-3-methylimidazolium tris(perfluoroethyl)trifluorophosphate [C(6)mim][FAP], 1-butyl3-methylimidazolium bis(trifluoromethylsulfonyl)imide [C(4)mim][NTf2], 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [C(4)dmim][NTf2], N-hexyltriethylammonium bis(trifluoromethylsolfonyl)imide [N-6,N-2,N-2,N-2][NTf2], 1-butyl-3-methylirnidazolium hexafluorophosphate [C(4)mim][PF6], F6], 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [C(2)mim][NTf2], 1-butyl-3-methylimidazolium tetrafluoroborate [C(4)mim][BF4], 1-hexyl-3-methylimidazolium iodide [C(4)mim][I], 1-butyl-3-methylimidazolium trifluoromethylsulfonate [C(4)mim][OTf], and 1-hexyl-3-methylimidazolium chloride [C(6)mim][Cl]. In addition, electrochemically relevant properties such as viscosity, conductivity, density, and melting point of RTILs are summarized from previous literature and are discussed. Karl Fisher titrations were carried out to determine the water content of RTILs for vacuum-dried, atmospheric, and wet samples. The anion in particular was found to affect the level of water uptake. The hydrophobicity of the anions adhered to the following trend: [FAP](-) > [NTf2](-) > [PF6](-) > [BF4](-) > halides. Cyclic voltammetry shows that an increase in water content significantly narrows the electrochemical window of each ionic liquid. The electrochemical window decreases in the following order: vacuum-dried > atmospheric > wet at 298 K > 318 K > 338 K. The anodic and cathodic potentials vs ferrocene internal reference are also listed under vacuum-dried and atmospheric conditions. The data obtained may aid the selection of a RTIL for use as a solvent in electrochemical applications.

A Hybrid Evolutionary Approach to the Nurse Rostering Problem

Nurse rostering is a difficult search problem with many constraints. In the literature, a number of approaches have been investigated including penalty function methods to tackle these constraints within genetic algorithm frameworks. In this paper, we investigate an extension of a previously proposed stochastic ranking method, which has demonstrated superior performance to other constraint handling techniques when tested against a set of constrained optimisation benchmark problems. An initial experiment on nurse rostering problems demonstrates that the stochastic ranking method is better in finding feasible solutions but fails to obtain good results with regard to the objective function. To improve the performance of the algorithm, we hybridise it with a recently proposed simulated annealing hyper-heuristic within a local search and genetic algorithm framework. The hybrid algorithm shows significant improvement over both the genetic algorithm with stochastic ranking and the simulated annealing hyper-heuristic alone. The hybrid algorithm also considerably outperforms the methods in the literature which have the previously best known results.

Room-temperature ionic liquids as replacements for organic solvents in multiphase bioprocess operations

Organic solvents are widely used in a range of multiphase bioprocess operations including the liquid-liquid extraction of antibiotics and two-phase biotransformation reactions. There are, however, considerable problems associated with the safe handling of these solvents which relate to their toxic and flammable nature. In this work we have shown for the first time that room-temperature ionic liquids, such as 1-butyl-3-methylimidazolium hexafluorophosphate, [bmim][PF6], can be successfully used in place of conventional solvents for the liquid-liquid extraction of erythromycin-A and for the Rhodococcus R312 catalyzed biotransformation of 1,3-dicyanobenzene (1,3-DCB) in a liquid-liquid, two-phase system. Extraction of erythromycin with either butyl acetate or [bmim][PF6] showed that values of the equilibrium partition coefficient, K, up to 20-25 could be obtained for both extractants. The variation of K with the extraction pH was also similar in the pH range 5-9 though differed significantly at higher pH values. Biotransformation of 1,3-DCB in both water-toluene and water-[bmim][PF6] systems showed similar profiles for the conversion of 1,3-DCB initially to 3-cyanobenzamide and then 3-cyanobenzoic acid. The initial rate of 3-cyanobenzamide production in the water-[bmim][PF6] system was somewhat lower, however, due to the reduced rate of 1,3-DCB mass transfer from the more viscous [bmim] [PF,] phase. it was also shown that the specific activity of the biocatalyst in the water-[bmim][PF6] system was almost an order of magnitude greater than in the water-toluene system which suggests that the rate of 3-cyanobenzamide production was limited by substrate mass transfer rather than the activity of the biocatalyst. (C) 2000 John Wiley & Sons, Inc.

Uncertainty and Sensitivity Analysis in Aircraft Operating Costs in Structural Design Optimization

The paper focuses on the development of an aircraft design optimization methodology that models uncertainty and sensitivity analysis in the tradeoff between manufacturing cost, structural requirements, andaircraft direct operating cost.Specifically,ratherthanonlylooking atmanufacturingcost, direct operatingcost is also consideredintermsof the impact of weight on fuel burn, in addition to the acquisition cost to be borne by the operator. Ultimately, there is a tradeoff between driving design according to minimal weight and driving it according to reduced manufacturing cost. Theanalysis of cost is facilitated withagenetic-causal cost-modeling methodology,andthe structural analysis is driven by numerical expressions of appropriate failure modes that use ESDU International reference data. However, a key contribution of the paper is to investigate the modeling of uncertainty and to perform a sensitivity analysis to investigate the robustness of the optimization methodology. Stochastic distributions are used to characterize manufacturing cost distributions, andMonteCarlo analysis is performed in modeling the impact of uncertainty on the cost modeling. The results are then used in a sensitivity analysis that incorporates the optimization methodology. In addition to investigating manufacturing cost variance, the sensitivity of the optimization to fuel burn cost and structural loading are also investigated. It is found that the consideration of manufacturing cost does make an impact and results in a different optimal design configuration from that delivered by the minimal-weight method. However, it was shown that at lower applied loads there is a threshold fuel burn cost at which the optimization process needs to reduce weight, and this threshold decreases with increasing load. The new optimal solution results in lower direct operating cost with a predicted savings of 640=m2 of fuselage skin over the life, relating to a rough order-of-magnitude direct operating cost savings of $500,000 for the fuselage alone of a small regional jet. Moreover, it was found through the uncertainty analysis that the principle was not sensitive to cost variance, although the margins do change.