Relaxation Kinetics of an Expanded Oil-Water Interface in the Presence of Oil-Soluble Polyethers

Abstract

Relaxation kinetics were recorded for a homologous series of polypropylene glycols and triols upon rapid expansion of a water droplet suspended in a heptane or toluene solution. The polypropylene oxide (PPO) and polypropylene oxide-polyethylene oxide polymers (PPO-PEO) used are oil-soluble and are prototypical of polymers used in industry to demulsify crude oil. Relaxation data were exponential in nature. This and the time frames of the relaxations are indicative of a non-diffusion-controlled relaxation mechanism at the interface. The effect of changing from an aliphatic solvent (heptane) to an aromatic solvent (toluene) on relaxation rate was found to be minimal for the PPO-type polyethers, but significant when hydrophilic polyethylene oxide (PEO) segments were present in the structure. Increasing the percentages of PEO resulted in slower relaxation kinetics, possibly due to intra- or intermolecular associations of the PEO segments in the oil phase. This data suggests that for light, waxy crude oil emulsions the best performance should be from demulsifiers with minimal PEO content, consistent with empirical observation.