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91.
Parameters are developed for a practical application of the empirical van der Waals (vdW) correction infrastructure available in the CPMD density functional theory (DFT) code. The binding energy, geometry, and potential energy surface (PES) are examined for methane, ethane, ethylene, formaldehyde, ammonia, three benzene dimer geometries, and three benzene–water geometries. The vdW corrected results compare favorably with MP2 and CCSD(T) calculations near the complete basis set limits, and with experimental results where they are available. 相似文献
92.
Apparent equilibrium constants and calorimetric enthalpies of reaction have been measured for the reaction L-tryptophan(aq) + H2O(l) = indole(aq) + pyruvate(aq) + ammonia(aq) which is catalyzed by L-tryptophanase. High-pressure liquid-chromatography and microcalorimetery were used to perform these measurements. The equilibrium measurements were performed as a function of pH, temperature, and ionic strength. The results have been interpreted with a chemical equilibrium model to obtain thermodynamic quantities for the reference reaction: L-tryptophan(aq) + H2O(l) = indole(aq) + pyruvate–(aq) + NH
4
+
(aq). At T=25°C and Im=O the results for this reaction are: Ko=(1.05±0.13)×10–4,
G°=(22.71±0.33) kJ-mol–1,
H°=(62.0±2.3) kJ-mol–1, and
S°=(132±8) J-K–1-mol–1. These results have been used together with thermodynamic results from the literature to calculate standard Gibbs energies of formation, standard enthalpies of formation, standard molar entropies, standard molar heat capacities, and standard transformed formation properties for the substances participating in this reaction.Presented at the Symposium, 76th CSC Congress, Sherbrooke, Quebec, May 30–June 3, 1993, honoring Professor Donald Patterson on the occasion of his 65th birthday. 相似文献
93.
94.
Modified modeling of the effect of pH and viscosity on the mass transfer in hydrophobic hollow fiber membrane contactors 总被引:3,自引:0,他引:3
This paper studied the effect of pH and the viscosity of feed solution on the mass transfer in two different specifications of hydrophobic hollow fiber membrane contactors. Experimental results showed that the pH of the feed had a significant effect on the rate of mass transfer, the flux and the removal efficiency of easily ionized volatile compounds (VCs), such as ammonia. In unbuffered feed solutions, both the resistance of membrane and the resistance of feed side were affected by the pH of feed and both of them had contributions to the overall mass transfer. A model, , was proposed to predict the effect of pH and gave good agreement with the experimental data for the two contactors. The relationship between viscosities and the mass transfer coefficient could be described by . Based on our experiments, the change of the viscosities in the concentration range of ammonia from 50 to 10,000 mg l−1 caused about 3–4% variation of the mass transfer coefficients. Moreover, it may be more suitable to use the equilibrium concentrations of volatile species instead of the total concentrations of VCs to estimate mass transfer coefficients, removal efficiency and flux. Experimental results also revealed that the choice of the pH of feed might be one of the most crucial factors for removing easily ionized VCs, such as ammonia, from water and wastewater. 相似文献
95.
96.
97.
Grand canonical Monte Carlo simulation is used to study the adsorption of nitrogen at 77 K and ammonia at 240 K to represent weakly polar and polar molecules, respectively, on infinite and finite graphite surfaces. These graphite surfaces were modeled with different percentages of carbons removed (defects) from the top graphite layer. Increasing the number of defects increases the adsorption and the isosteric heat of nitrogen at low pressure. At moderate pressures the amount adsorbed is less due to the disruption in the packing of the nitrogen in the first layer. In contrast, the adsorption of ammonia at all pressures is reduced as the percentage of defects is increased. This is due to the disruption in ammonia bonding caused by the defects. The condensation-like step change in the ammonia isotherm on the perfect graphite surface is not observed for any of these surfaces with defects even for the case of only 10% defects. At high percentage of defects the adsorption isotherm is close to Henry law behavior for much of the pressure range. The adsorption on finite surfaces shows that the amount adsorbed for both molecules decreases compared with that of the infinite surfaces, resulting from interaction potentials with the surface and other fluid molecules at the edge. The decrease is much greater for the ammonia adsorption because the bonding between ammonia molecules is disrupted, meaning that the adsorption cannot follow the mechanism of condensation seen for the infinite surface. 相似文献
98.
PVA固定化脲酶电极的制作及电极特性的研究 总被引:2,自引:0,他引:2
利用PVA低温下的物理交联固定酶,制成酶电极并在不同尿素浓度、pH值、温度等条件下进一步研究这种酶电极的响应特性. 相似文献
99.
The results detail a novel methodology for the electrochemical determination of ammonia based on its interaction with hydroquinone in DMF. It has been shown that ammonia reversibly removes protons from the hydroquinone molecules, thus facilitating the oxidative process with the emergence of a new wave at less positive potentials. The analytical utility of the proposed methodology has been examined with a linear range from 10 to 95 ppm and corresponding limit-of-detection of 4.2 ppm achievable. Finally, the response of hydroquinone in the presence of ammonia has been examined in the room temperature ionic liquid 1-ethyl-3-methylimidazolium bis(trifluormethylsulfonyl)imide, [EMIM][N(Tf)2]. Analogous voltammetric waveshapes to that observed in DMF were obtained, thereby confirming the viability of the method in either DMF or [EMIM][N(Tf)2] as solvent. 相似文献
100.