Cu2O is an efficient catalyst in the partial oxidation of propylene to acrolein, while propylene oxidation on CuO leads to complete combustion. The interaction of propylene at elevated temperature (>300 K) and elevated pressure (5 Torr) with cuprous and cupric oxide has been investigated with core level XPS, resonant photoemission, and temperature-programmed desorption. Reduction of the copper oxide surfaces was examined as a function of temperature and revealed that cupric oxide has a greater reactivity toward propylene oxidation than cuprous oxide (Ea = 5.9 versus 11.5 kcal/mol for cuprous oxide (24.7 and 48.1 kJ/mol)). This variable temperature oxidation of propylene was also monitored via core level and resonant photoemission and was found to occur by a similar mechanism on both surfaces. Reaction at lower temperature produces a surface intermediate which exhibits carbon 1s XPS peaks at 284.0 and 285.5 eV binding energy in a 2:1 intensity ratio. This is consistent with an allyl alkoxide surface specie...

Propylene Oxidation on Copper Oxide Surfaces: Electronic and Geometric Contributions to Reactivity and Selectivity

Solubility and mass transfer of CO and H2 in Fischer—Tropsch liquids and slurries

Contact angles of water at its boiling point, measured on surfaces of copper and polytetrafluoroethylene, are reported for pressures ranging from 10–770 torr. The results suggest that not only impurities and oxidation have been responsible for the wide range of angles reported in the literature but that inconsistencies may be created because of an adsorbed layer of water vapour on the solid surface.

Wettability of copper and polytetrafluoroethylene surfaces with water—the influence of environmental conditions

We introduce Monte Carlo simulation methods for determining interfacial properties of binary fluid mixtures The interface potential approach, in which the interfacial properties of a system are related to the surface excess free energy of a thin fluid film in contact with a surface, is utilized to deduce the wetting characteristics of a fluid mixture The strategy described here provides an effective means to obtain the evolution of interfacial properties with the chemical composition of the fluid This task is accomplished by implementing an activity fraction expanded ensemble technique, which allows one to obtain elements of the interface potential as a function of composition We also show how this technique can be utilized to calculate bulk coexistence properties of fluid mixtures in an efficient manner The computational strategies introduced here are applied to three model systems One includes an argon-methane fluid mixture that is known to display simple behavior in the bulk The second fluid model contains a size asymmetric mixture that exhibits azeotropy The third model fluid is the well-studied size symmetric mixture that displays liquid-liquid-vapor phase coexistence The techniques outlined here are used to compile the composition dependence of spreading and drying coefficients, liquid-vapor surface tension, and contact angle for these systems We also compare our surface tension results with values estimated from predictive-style models that provide the surface tension of a fluid mixture in terms of pure component properties Overall, we find that the general approach pursued here provides an efficient and precise means to calculate the bulk and wetting properties of fluid mixtures

Monte Carlo simulation strategies to compute interfacial and bulk properties of binary fluid mixtures.

This paper describes the effect of temperature on the surface tension and adsorption kinetics of 1-hexanol aqueous solutions. The experiments were performed in a closed chamber where both liquid and vapor phases coexisted, and the surface tension was influenced by a combination of liquid and vapor phase adsorption. The surface tension of 1-hexanol aqueous solutions at steady-state was found to decrease upon an increase in temperature, and a linear relationship was observed between them. The modified Langmuir equation of state and the modified kinetic transfer equation were used to model the experimental data of the steady-state and dynamic (time-dependent) surface tension, respectively. The equilibrium constants and adsorption rate constants were evaluated through nonlinear regression for temperatures ranging from 10 to 35 °C. From the steady-state modeling, the equilibrium constants for adsorption from vapor phase and liquid phase were found to increase with temperature. From the dynamic modeling, the adsorption rate constants for adsorption from vapor phase and liquid phase were found to increase with temperature too. Small deviations from the experimental data have been observed in the dynamic modeling. These deviations may be due to the experimental errors or more likely the limitations of the model used.

Effect of temperature on the surface tension of 1-hexanol aqueous solutions.

Prediction of Distillation Column Performance for Surface Tension Positive and Negative Systems

Contact angles are reported for the azeotropic systems n-propanol-water and benzene-cyclohexane measured under distillation conditions at total reflux over a pressure range 50 to 760 torr on both copper and polytetrafluoroethylene surfaces. The influences of the solid surfaces, the surface tension positive and negative nature of the liquids, together with the changes accompanying the azeotropic shift with pressure on the wettability, have been established and shown to conform with wetting theory.

Adrian P. Boyes

Papers

Prediction of Distillation Column Performance for Surface Tension Positive and Negative Systems

The wetting behavior of azeotropic systems at atmospheric and reduced pressures

Coalescence Phenomena and Marangoni Instabilities in Distillation