Experimental Investigation of Entrapped Water Droplets in Wax Deposition from Water-in-Oil Emulsion Considering Wax Crystals Adsorption at the Oil–Water Interface

Abstract

The presence of water in wax deposition from water-in-oil emulsion for petroleum transportation in pipelines has received much attention in recent years. This study investigated the formation of wax deposition with water droplets, considering interfacial adsorption by wax crystals. The prepared 20 vol % water-in-oil emulsion was used for the wax deposition experiment with an analysis of deposition mass/thickness and water volume fraction in deposition, determining that the water content in deposition during the whole deposition duration was constant and equaled to the water content in emulsion. Moreover, a polarizing microscope was employed to observe the microstructure of wax deposition, revealing that some water droplets were covered with wax crystals due to interfacial adsorption, while some droplets were enclosed by the network of wax crystals. Depending on these findings, two kinds of entrapment of water droplets in deposition were proposed. One contained the formation and growth of a crystal network accompanied with these wax-covered water droplets themselves; another one indicated that water droplets were surrounded by a crystal network, resulting in the movement of these droplets being limited and therefore the droplets settling in deposition. Furthermore, a comparison of the distribution of water droplets in deposition using a microscope and that in emulsion by focused-beam reflectance measurement was presented. It was observed that these small droplets were more likely to be incorporated into deposition in contrast with these large ones. The largest size measured for an entrapped water droplet was 115 μm, which was in accordance with the previous research claiming that the general diameter of water droplets incorporated into deposition was no more than ∼100 μm. Interfacial adsorption of wax crystals provides an additional insight to investigate water droplets in wax deposition.

Effect of the Ethylene Vinyl Acetate Copolymer on the Induction of Cyclopentane Hydrate in a Water-in-Waxy Oil Emulsion System

“…Moreover, the induction time further increases to 3 h 14 min and 3 h 44 min when the wax to oil phase mass ratio is 5:100 (wax content = 4.72 wt %) and 7:100 (wax content = 6.48 wt %), respectively. Wax crystals are reported to be adsorbed at the oil and water interface through a synergistic effect with surfactant molecules. , The more the wax crystals absorbed at the interface, the less the mass transfer between cyclopentane and water molecules, and the formation of hydrate would be hindered.…”

“…Wax crystals are reported to be adsorbed at the oil and water interface through a synergistic effect with surfactant molecules. 53,54 The more the wax crystals absorbed at the interface, the less the mass transfer between cyclopentane and water molecules, and the formation of hydrate would be hindered.…”

Wax and Wax–Hydrate Deposition Characteristics in Single-, Two-, and Three-Phase Pipelines: A Review

“…Because of the shearing force of pumps or valves and the presence of natural emulsifiers such as glial and asphaltene in crude oil, the medium in the pipe can easily form emulsions in the oil–water transportation, and the most common one is the oil-in-water (W/O) emulsion. , Therefore, for the wax deposition process in oil–water flow, its influencing factors are more complicated than the single-phase pipeline wax deposition process. According to the related research, the existence of a dispersed phase will obviously change the wax deposition characteristics and make it difficult to predict the deposition process. , …”

Characterization of the Precipitation Modes of Paraffin Wax in Water-in-Model-Oil Emulsions

“…The stabilization by the combination of the above two mechanisms has received more and more attention recently. The optical microscopic observation performed by many researchers found the existence of wax particles both at the interface and in the oil phase. ,− Ma et al proposed that there are two kinds of entrapment of water droplets in one emulsion. The first kind is the growth of a crystal network accompanying the wax-covered Pickering droplets, while the second is simply the network stabilization .…”

“…The optical microscopic observation performed by many researchers found the existence of wax particles both at the interface and in the oil phase. ,− Ma et al proposed that there are two kinds of entrapment of water droplets in one emulsion. The first kind is the growth of a crystal network accompanying the wax-covered Pickering droplets, while the second is simply the network stabilization . According to Macierzanka et al and Visintin et al, the wax crystals adsorb at the interface of water droplets initially (Pickering stabilization).…”