A method for characterizing and predicting the performance of emulsion breakers has been developed which involves the relationship between the preferred alkane carbon number (PACN) of the demulsifier to the equivalent alkane carbon number (EACN) of the crude oil and the salinity of the emulsified aqueous phase. This procedure can be used both to chose the proper emulsifier for field use and to develop effective new compounds by determining the effect of changes in molecular architecture and interfacial properties on performance. Parameters which have been studied include chemical type, molecular weight, degree of branching, partition coefficient between the water and oil phases, interfacial tension reduction and interfacial viscosity changes. The importance of each of these properties to performance will be discussed. Introduction The design and application of oilfield demulsifier compounds has historically involved the evaluation of numerous products and the bottle testing of even more numerous blends in order to arrive at a product giving acceptable performance. Since demulsifiers are surfactants this work was initiated in an attempt to apply surface chemical principals to emulsion breakers. Early in the work it was found that although much had been published about the stability of oil-in-water emulsions, very little was available about water-in-oil emulsions.

Summary A method for characterizing and predicting the performance of emulsion breakers has been developed that involves the relationship between the preferred alkane carbon number (P ACN) of the demulsifier and the equivalent alkane carbon number (EACN) of the crude oil and the salinity of the emulsified aqueous phase. This procedure can be used both to choose the proper demulsifier for field use and to develop effective new compounds by determining the effect of changes in molecular architecture and interfacial properties on performance. Parameters studied include chemical type, molecular weight, degree of branching, partition coefficient between the water and oil phases, interfacial-tension (1FT) reduction, and interfacial-viscosity changes. The importance of each of these properties to performance is discussed. Introduction The design and application of oilfield demulsifier compounds have historically involved evaluation of numerous products and the bottle testing of even more numerous blends to arrive at a product that gives acceptable performance. Because demulsifiers are surfactants, this work was initiated in an attempt to apply surface chemical principles to emulsion breakers. Early in the work, it was found that although much had been published about the stability of oil-in-water emulsions, very little was available about water-in-oil emulsions. We therefore decided to determine which factors were important in predicting the stability and instability of these neglected types of emulsions. The investigation we pursued took three main paths. The first involved a look at the surface chemistry of water-in-oil systems to determine which properties at the interface or in the bulk phases were responsible for emulsion stability. The primary factors of interest were1FT,interfacial transport,interfacial viscosity, andpartition coefficient. The second main path was the structural chemistry of the demulsifier molecule itself. Here we looked atmolecular weight,molecular configuration,chemical type, andmolecular distribution. The third path involved the emulsion system itself. Here we tried to isolate the most important characteristics of the three phases involved: the external oil phase, the internal aqueous phase, and any dispersed solids. Surface Chemistry of Demulsifiers IFT. A great deal of misconception exists about the relative importance of IFT to emulsion stability and surfactant performance in general. Several investigators1–4 have shown that lowering 1FT is conducive to emulsion stability. They have also shown, however, that if the 1FT becomes too low, the emulsion becomes unstable and in some cases an emulsion cannot be formed at all. Rosano et al.2 state that "a sufficiently low positive value of ? is always better for emulsion formation. Nevertheless, below a certain value of ? phase separation, sol or gel formation will be produced but not emulsification. Moreover, emulsion stability is, in turn, not dependent on the value of the interfacial tension but solely on the structure of the interfacial film surrounding the individual droplet." Fig. 1 shows the effect of changing the hydrophilic/lipophilic balance (HLB) of a series of polypropylene glycol ethoxylates on the 1FT and the emulsion stability, with white mineral oil as the oil phase and 2.0% sodium chloride and 2.0% surfactant as the aqueous phase. Equal volumes of the two phases were mixed and the emulsion stability was measured by determining the time required for complete separation. 1FT measurements were also taken on the various mixtures before emulsification with a Cahn RG 2000™ electronic balance fitted with a platinum ring or a U. of Texas Model 500™ spinning drop interfacial tensiometer. The data show that as the HLB is increased from 9.6 to 9.8, the stability of the emulsion (water-in-oil) increases and the 1FT decreases. Further increase in HLB results in a less stable emulsion; however, the 1FT continues to decrease, reaching a minimum at an HLB of 10.5 where the emulsion is least stable. Further increase in HLB results in the formation of an increasingly stable oil-in-water emulsion and an increasing 1FT. These results confirm the facts that a low 1FT is required for emulsion stability but too Iowan 1FT results in unstable emulsions. Unpublished work in our laboratory has shown that the rate at which surfactants attain equilibrium or orient themselves at interfaces is an important factor in determining their effectiveness. Plans are currently being formulated to apply recently developed dynamic surface and interfacial techniques to determine the contribution of interfacial transport and dilational interfacial viscosity to demulsifier effectiveness. Interfacial Viscosity. Fig. 2 shows the measurement of the interfacial viscosity between the aqueous and oil phases of an east Texas crude oil containing 200 ppm of a series of demulsifiers. The coalescence rate was measured by determining the amount of water separated from the emulsion after 15 minutes compared with the total amount of water known to be present. The interfacial viscosity was measured with a deep-channel, viscous-traction interfacial shear viscometer developed by the Dept. of Chemical Engineering, Illinois Inst. of Technology.5,6 The data show a direct relationship between the interfacial viscosity of the oil and aqueous phases and the emulsion stability. As the viscosity at the interface is reduced, the emulsion stability is reduced. Demulsifier F resolved almost 90% of the water in 15 minutes and gave the lowest interfacial viscosity. Demulsifier A gave the lowest amount of water (< 15 %) and had the highest interfacial viscosity except for the untreated blank sample. These results indicate that interfacial-viscosity reduction is important for demulsification. IFT. A great deal of misconception exists about the relative importance of IFT to emulsion stability and surfactant performance in general. Several investigators1–4 have shown that lowering 1FT is conducive to emulsion stability. They have also shown, however, that if the 1FT becomes too low, the emulsion becomes unstable and in some cases an emulsion cannot be formed at all. Rosano et al.2 state that "a sufficiently low positive value of ? is always better for emulsion formation. Nevertheless, below a certain value of ? phase separation, sol or gel formation will be produced but not emulsification. Moreover, emulsion stability is, in turn, not dependent on the value of the interfacial tension but solely on the structure of the interfacial film surrounding the individual droplet." Fig. 1 shows the effect of changing the hydrophilic/lipophilic balance (HLB) of a series of polypropylene glycol ethoxylates on the 1FT and the emulsion stability, with white mineral oil as the oil phase and 2.0% sodium chloride and 2.0% surfactant as the aqueous phase. Equal volumes of the two phases were mixed and the emulsion stability was measured by determining the time required for complete separation. 1FT measurements were also taken on the various mixtures before emulsification with a Cahn RG 2000™ electronic balance fitted with a platinum ring or a U. of Texas Model 500™ spinning drop interfacial tensiometer. The data show that as the HLB is increased from 9.6 to 9.8, the stability of the emulsion (water-in-oil) increases and the 1FT decreases. Further increase in HLB results in a less stable emulsion; however, the 1FT continues to decrease, reaching a minimum at an HLB of 10.5 where the emulsion is least stable. Further increase in HLB results in the formation of an increasingly stable oil-in-water emulsion and an increasing 1FT. These results confirm the facts that a low 1FT is required for emulsion stability but too Iowan 1FT results in unstable emulsions. Unpublished work in our laboratory has shown that the rate at which surfactants attain equilibrium or orient themselves at interfaces is an important factor in determining their effectiveness. Plans are currently being formulated to apply recently developed dynamic surface and interfacial techniques to determine the contribution of interfacial transport and dilational interfacial viscosity to demulsifier effectiveness. Interfacial Viscosity. Fig. 2 shows the measurement of the interfacial viscosity between the aqueous and oil phases of an east Texas crude oil containing 200 ppm of a series of demulsifiers. The coalescence rate was measured by determining the amount of water separated from the emulsion after 15 minutes compared with the total amount of water known to be present. The interfacial viscosity was measured with a deep-channel, viscous-traction interfacial shear viscometer developed by the Dept. of Chemical Engineering, Illinois Inst. of Technology.5,6 The data show a direct relationship between the interfacial viscosity of the oil and aqueous phases and the emulsion stability. As the viscosity at the interface is reduced, the emulsion stability is reduced. Demulsifier F resolved almost 90% of the water in 15 minutes and gave the lowest interfacial viscosity. Demulsifier A gave the lowest amount of water (< 15 %) and had the highest interfacial viscosity except for the untreated blank sample. These results indicate that interfacial-viscosity reduction is important for demulsification.