Michael J. Hey

Emulsions of water in asphaltene-containing oils 1. Droplet size distribution and emulsification rates

Abstract Emulsions of simulated sea water in three crude oils and in a model oil consisting of n-heptane, m-xylene and asphaltenes were examined by optical microscopy to obtain droplet diameters which were found to fit the log-normal distribution function. The rate of formation of interfacial area with respect to stirring time in the crude oil emulsions was first order. Values of Sm, the limiting area stabilised, increased with increasing asphaltene content while k, the rate constant, decreased. Addition of surfactants to either the oil phase or to the aqueous phase before mixing slowed the formation of Kuwait crude emulsions and increased Sm. This effect could result from a decrease in the oil/water interfacial tension causing a change in the equilibrium contact angle between asphaltene particles and the interface.

Effect of temperature on poly(ethylene oxide) chains in aqueous solution. A viscometric, 1H NMR and Raman spectroscopic study

A combination of viscometry, Raman scattering and 1H NMR measurements has been used to study the effect of temperature changes on the properties of solutions of poly(ethylene oxide) in H2O or D2O. The viscosity data show that the overall dimensions of the polymer chains decrease with increasing temperature, while the Raman spectra indicate a simultaneous decrease in chain helicity. Polymer 1H NMR spin–lattice relaxation times in D2O are consistent with a mechanism in which small segments of the chain reorient at a rate controlled by the solvent viscosity up to a temperature of ca. 80 °C.

Surface tensions of aqueous solutions of some 1:1 electrolytes

Measurements of the surface tension of aqueous solutions of NaF, KF, NaNO3 and KNO3 have been made by means of the ring detachment method. The data were obtained for a range of concentrations and temperatures and analysed using the Gibbs equation. A simple model is proposed which explains the correlation found between the surface-tension data and the standard hydration enthalpies of the salts.

Poly(ethylene oxide) hydration studied by differential scanning calorimetry

Differential scanning calorimetry has been used to investigate the melting behaviour of mixtures of poly(ethylene oxide) and deuterium oxide. The phase diagram shows that a eutectic mixture is formed with a weight fraction of D2O of 0.57 and a melting point of 264 K. A change in the curvature of the polymer liquidus curve occurs when the ratio of D2O to EO repeat unit is 1.2. For higher water contents the liquidus curves can be fitted by the Flory–Huggins theory. Enthalpies of fusion have been used to calculate the enthalpy of mixing of the two components at 264 K. A maximum exothermicity is found for a D2O/EO ratio of 1.3 ± 0.1. Quenching of mixtures with either high or low water contents in liquid nitrogen produces glassy polymer which undergoes devitrification and cold crystallization on heating. Plots of the enthalpies of cold crystallization against weight fraction of D2O indicate that the maximum amount of glass is formed at a D2O/EO ratio of 0.9 ± 0.3. It is concluded that the average hydration number of the EO group is approximately one.

Water in poly(ethylene oxide): differential scanning calorimetry and nuclear magnetic resonance experiments

Non-freezable D2O in partially crystalline poly(ethylene oxide) shows residual deuterium quadrupolar splitting. Extrapolation of enthalpies of eutectic melting to zero yields an average hydration number of 0.9.

Enthalpies of mixed-micelle formation

Critical micelle concentrations have been measured for binary mixtures of an anionic and a polyoxyethylenated non-ionic surfactant in aqueous solution. The data were used to calculate the molecular interaction parameter β in the Rubingh theory of mixed-micelle formation. Enthalpies of mixed-micelle formation determined calorimetrically were then compared with theoretical values based on β. Differences found between expected and observed enthalpies are attributed to deficiencies in the theory with respect to the temperature dependence of β and the variation of counterion binding as the micelle composition changes.

The effect of acid treatment on the properties of dealuminated Y zeolite

Dealuminated Y zeolite has been prepared by treatment of the hydrogen form with SiCl4 vapour at 720 K. Measurements of aluminium content, pore volume, crystallinity and infrared spectra, together with 27Al and 29Si magic-angle spinning nuclear magnetic resonance spectra, have been used to characterize the product following controlled acid treatments between pH 4.8 and 0.0. Extrastructural aluminium was progressively extracted with increasing acidity between pH 4.8 and 1.3, whilst the Si/Al ratio of the framework structure increased only slightly from its initial value of ca. 16. With acid treatment below pH 1.0 extraction of both extrastructural and structural aluminium was accompanied by loss of porosity and crystallinity. Measurements of the catalytic activity for dehydration of propan-2-ol at 380 K confirmed that mineral acid at ca. pH 1.0 provides the optimum pretreatment for moderately dealuminated Y zeolite. The investigation emphasizes the need to control activation procedures for dealuminated zeolite catalysts.

Attenuated total reflection FT–IR study of hydrogen bonding in water/ether mixtures

Abstract A FTIR–ATR study of hydrogen bonding in binary aqueous mixtures containing tetrahydrofuran, 1,4-dioxane or poly(ethylene oxide) is reported. Observed spectra were converted to linear absorption coefficient spectra using the Bertie–Eysel procedure. The frequency of the OH stretching mode in isotopically dilute HOD was found to increase with ether concentration, implying a continuous reduction in average hydrogen-bond strength. In water-rich mixtures, the initial gradients were proportional to the number of oxygen atoms in the cyclic ether molecules or in the polymer subunit.

Emulsions of water in asphaltene-containing oils 2. Rheology

Abstract Emulsions of simulated sea water in crude oils or in model oils containing dispersed asphaltenes have been studied using a Couette viscometer. Non-Newtonian behavior was observed for the model oil emulsions and for some of the crude oil emulsions with high water contents and small droplet diameters. Viscosities of the crude oil emulsions have been related to water volume fractions by the use of an Eilers-type equation which allows estimates to be made of maximum packing fractions and intrinsic viscosites. The latter were found to be greater than 2.5 and to increase as average droplet size decreased. For the model emulsions, flow curves became linear above minimum shear rates which were used to calculate flocculated droplet separations according to the theory of Albers and Overbeek.

Enthalpies of adsorption of sodium dodecyl sulphate and O-n-octyltetraethylene glycol from aqueous solutions onto graphitised carbon

A comparison has been made of the adsorption of a non-ionic and an ionic surfactant from aqueous solution on to graphitised carbon. Adsorption enthalpies determined calorimetrically have been combined with adsorption isotherms to yield differential heats of adsorption. The ionic compound was found to adsorb with a negative differential heat at all coverages studied, whereas the non-ionic compound adsorbed in three clearly distinguishable stages which corresponded to exothermic, athermal and endothermic processes. A model is suggested to account for these observations.