The effect of naphtha to bitumen ratio on properties of water in diluted bitumen emulsions

Properties of water in naphtha-diluted bitumen emulsion depend on naphtha to bitumen ratio. There is a critical dilution ratio, at which the system properties change abruptly. The critical dilution ratio coincides with an onset of asphaltene precipitation. The critical diluted ratio for the bitumen and naphtha used in this study is 4. At N/B<4, when diluted bitumen was contacted with water, micron-sized water droplets were found in the oil phase close to the oil–water interface without any agitation. This phenomenon was especially noticeable at N/B<1.5. The precipitation of asphaltene was detected at N/B≥4. If the precipitation took place in the presence of water, some of the precipitated particles showed optical anisotropy when observed under cross polarizers. The stability of water in diluted bitumen emulsion depended on the order of emulsion preparation. If water was emulsified into already diluted bitumen, the stability decreased with dilution as expected. If, however, water and naphtha were added at the same time, the stability first decreased until about N/B=1.5, then increased again, leveling of at N/B of about 4. Possible explanations for this behaviour are that it is due to the state of asphaltenes in the oil phase when water is emulsified or to yet unknown phase transition in the organization of the stabilizing layer present at the water–oil interface.