Stanley Hartland

STUDY OF DEMULSIFICATION OF WATER-IN-CRUDE OIL EMULSION

ABSTRACT Demulsification of water-in-crude oil emulsion was studied at two different salinities, 0.5% and 10% sodium chloride, using five different nonionic surfactants. Equilibrium crude oil-water interfacial tension was measured with drop volume method. Low molecular weight surfactants were found to be completely ineffective as demulsifiers. Three surfactants which were effective demulsifiers, exhibited good interfacial activity, surface adsorption and surface pressure. The performance of the demulsifiers changed with change in salinity of aqueous phase. Surfactants effective as demulsifiers reduced surface tension of water by more than 25 dynes-cm-1. For a given crude oil-water system, the surfactant which developed surface pressure in excess of 15 dynes-cm-1 was found to be good demulsifier for that system. Based upon these studies, a physical model of demulsification has been proposed

Solubilities of theobromine and caffeine in supercritical carbon dioxide : correlation with density-based models

Abstract Li S., Varadarajan G.S. and Hartland S., 1991. Solubilities of theobromine and caffeine in supercritical carbon dioxide: correlation with density-based models. Fluid Phase Equilibria 68: 263-280. Solubilities of theobromine and caffeine in supercritical carbon dioxide at several different temperatures (40, 60, 80 and 95°C) and pressures from 80 to 300 bar were measured using a dynamic method. The solubilities of theobromine were two orders of magnitude less than those of caffeine even though both compounds are xanthines with very similar chemical structures. The reasons are considered from a thermodynamic viewpoint. The applicability and limitations of three density-based models used to correlate the data are discussed.

A new industrial process for extracting cocoa butter and xanthines with supercritical carbon dioxide

This research explores the feasibility of extracting cocoa butter and xanthines (theobromine and caffeine) from cocoa beans with supercritical CO2. It is difficult to carry out the extraction with CO2 alone in the temperature range 40–90°C at pressures between 80 to 300 bar. However, the addition of a polar cosolvent, such as ethanol, greatly enhances solubilities, especially that of cocoa butter. Based on experimental investigations and theoretical inference, the design of a potential industrial process for extracting cocoa butter and xanthines is proposed, in which ethanol is used as cosolvent, and distillation is used to separate and regenerate ethanol. The pressure required is much less than that for CO2 alone as specified in the patent literature.

Dynamic simulation of agitated liquid—liquid dispersions—II. Experimental determination of breakage and coalescence rates in a stirred tank

Abstract Using the theoretical procedure outlined in the first part of this work, breakage and coalescence rates were determined experimentally in a stirred tank. After reaching steady-state conditions, the intensity of agitation was suddenly changed and the variation in drop size distribution with time was monitored. The coalescence and breakage constants were evaluated by optimising the fit of the experimental results with the theoretical solution of the model equations. No a priori assumptions concerning the dependence of the interaction rates on drop size, system properties and operating conditions were made. Precise techniques for measuring the drop size distribution in turbulent dispersions were developed and tested. Empirical equations for dependence of breakage and coalescence constants on drop volume, holdup and system properties were derived.

Influence of co-solvents on solubility and selectivity in extraction of xanthines and cocoa butter from cocoa beans with supercritical CO2

Abstract The solubilities of xanthines (theobromine and caffeine) and cocoa butter in supercritical CO 2 in the temperature range 40 to 95 °C and at pressures from 80 to 300 bar were measured. It is difficult to extract either xanthines or cocoa butter from cocoa nibs with CO 2 alone. However, the addition of polar co-sol-vent ethanol greatly enhances their solubilities which markedly depend on the concentration of ethanol. The selectivity of supercritical CO 2 -ethanol for cocoa butter relative to xanthines is high. By combining traditional separation methods it is possible to extract and separate both cocoa butter and xanthines simultaneously, the pressure required being much less than that using CO 2 alone or combined with water.

Drop size and concentration profile determination in petroleum emulsion separation

Abstract Stable emulsions of brine in crude oil were destabilized using a polymeric surfactant demulsifier and were studied during mixing and settling. After emulsion preparation and aging, demulsifier was added and the drop growth was measured using photomicroscopy. Phase separation was monitored using gamma-ray absorption. Aged emulsions exhibited less drop growth during mixing and slow separation; however, the age of an emulsion cannot always be controlled. Increased demulsifier concentration and longer mixing time after demulsifier addition both lead to a larger final drop size and faster separation. Optimizing the mixing conditions under which demulsifier is added to an emulsion could reduce the separation time, although these conditions would be system-specific. The drop size after demulsifier addition was an important indicator of subsequent emulsion separation behaviour.

Prediction of dispersed phase hold-up in pulsed perforated-plate extraction columns

Abstract Published experimental results for the dispersed phase hold-up in pulsed perforated-plate extraction columns are considered. Based on 1574 data points in the absence of solute transfer for 14 liquid-liquid systems a single empirical correlation is developed which predicts the hold-up in the mixer-settler, transition and emulsion regions of operation to within 17% from the physical properties and operating variables. The same correlation with modified constants (but unchanged indices) can be used when solute transfer occurs in either direction. Futhermore, this correlation also predicts the boundary between mixer-settler and transition regions of operation.

Dynamic simulation of liquid-liquid agitated dispersions—I. Derivation of a simplified model

Abstract In turbulent liquid-liquid systems with high disperse phase holdup the drop size distribution is determined by the drop breakage and coalescence frequencies. To calculate the drop size distribution, both at the steady state and under transient conditions, the drop size spectrum is usually discretised and a set of population balance equations is solved under given initial and boundary conditions. Generally, this is a difficult and time-consuming task, even for a large computer. A new model is proposed in this work based on discretisation of the drop size spectrum using a geometrical grid. While maintaining good accuracy, the solution becomes so easy that even parameter estimations may be carried out. A transient behaviour experiment is proposed from which the breakage and coalescence functions can be obtained simultaneously, without assuming a priori the shape of their functional dependence on drop volume.

KINETICS OF COALESCENCE OF WATER DROPLETS IN WATER-IN-CRUDE OIL EMULSIONS

ABSTRACT Water from water-in-crude oil emulsions is separated by chemical demul-sification. Coalescence rates of water droplets have been studied in the presence of a demulsifier. Droplet size measurement was carried out by photomicrography. Fastest coalescence rate was observed during first one minute. Binary coalescence time during this period was 5·4 seconds when 50 mg/1 of demulsifier was added and 4·2 seconds in the presence of 100 mg/1 of demulsifier.

A model for an axisymmetric dimpled draining film

Abstract A model is presented for a dimpled draining film which is assumed to consist of two parabolas, joined at the point of inflection, with the radius of curvature at the apex varying with time in the central parabola and constant in the peripheral parabola. By considering drainage through these parabolas analytical equations are derived for drops of any volume, for the variation with time, t , of the film thickness at the center δ 0 and at the barrier ring δ c . Experimental results suggest that the dynamic pressure falls to zero just outside the barrier ring and the equations then become δ 0 = 0.117(n 2 μr c 4 fσ 2 t) 14 and δ c = 0.370(n 2 μr c 4 ft) 12 , where f is the force pressing on the film, n the number of immobile interfaces, r c the radial distance from the center to the barrier ring, σ the interfacial tension, and μ viscosity of the draining film. Film thicknesses predicted by these equations with n = 2 are about 10% higher than the experimental values at the center and about 40% lower at the periphery. For small drops the equations reduce algebraically to those of Frankel and Mysels (1). The film becomes less uniform as δ 0 increases but more uniform as δ c and r c increase, so a criterion, δ 0 2 δ c r c , is suggested as a measure of nonuniformity in film thickness. For the gravitational approach of a drop toward a horizontal plane, the criterion may be estimated from the drop volume, ν, the density difference, Δρ, and interfacial tension, σ, using δ 0 2 δ c r c = 0.13 (ν 0.42 (Δρg) 0.63 /σ 0.63 ). Broadly speaking, if δ 0 2 δ c r c is greater than 1 the film is nonuniform in thickness, and if less than 0.1 fairly uniform in thickness.