Process intensification in the demulsification of water-in-crude oil emulsions via crossflow microfiltration through a hydrophilic polyHIPE polymer (PHP)

Abstract

In petroleum industry, highly stable water-in-oil (w/o) emulsions are formed during extraction process and these emulsions are stabilized by the indigenous surface active species in the oil. The recovery of crude oil through emulsion breakdown and subsequent separation (demulsification) should be carried out at source in order to avoid costly pumping and cooling of emulsion which enhances emulsion stability. Although conventional methods available for emulsion breakdown using demulsifiers and electric field separation, in the case of viscous crude oils with large amounts of indigenous surfactants, such methods are not satisfactory to achieve on-site oil-water separation. Therefore, such emulsions may have to be chemically treated. It was previously shown that when hydrophilic micro-porous polymers, known as PolyHIPE Polymers (PHPs) were added to the emulsion, it caused emulsion to separate as a result of selective removal of surfactants. This separation process was further enhanced in the presence of electric field. This current study focuses on cross-flow microfiltration of w/o emulsions through a sulphonated hydrophilic microporous polymeric material in the absence or presence of electric field. However, sulphonated PHPs used in the experiments do not have an active membrane layer with pores at micron- or nano- scale. The thickness of the separation layer is ca. 4 mm and pore size is in 10 micrometer range. We used either 50 or 70 vol. % oil phase in the w/o emulsions. Effect of: pore size, crossflow velocity and electric field strength on permeate flux rate decay and separation efficiency of emulsions which are stable for more than 70 days otherwise was investigated. It was found that the permeate flux rate decayed rapidly with crossflow filtration time before the flux reached steady state. The application of electric field enhanced the permeate flux rate. Under steady state conditions, permeate flux rate was not significantly affected by the PHP pore size. Permeate from the crossflow filtration was collected in glass cylinders and allowed to separate under gravity as a function of time. It was found that the demulsification time was affected primarily by the applied electric field, emulsion water content, crossflow velocity and PHP pore size. Demulsification rate increased with increasing electric field and water fraction of emulsion and with decreasing pore size of PHP. Demulsification was achieved within 6-7 hr. The results were interpreted in terms of ‘confinement phenomenon’ in which it was postulated that the PHP filtration media selectively retained the surface active agents and; thus, causing the demulsification of the emulsions. The surface active agents were deposited within the pores of the separation media and; thus, causing flux decay. Although the deposits of surface active agents could break-up due to permeate flow through the separation media, they could not be re-distributed at the oil-water interface to re-stabilize the emulsion. However, some water can be trapped within the oil as oil-in-water-in-oil multiple emulsion which would be more resistant to demulsification.