Characterization of Petroleum Industry Emulsions And Suspensions Using Microscopy
Authors: Munoz V.A. , Mikula R.J. 
Published: March 2010

Confocal microscopy and cryogenic scanning electron microscopy are common characterization techniques in biological, pharmaceutical, and food sciences. Although these techniques are less common in the petroleum industry, there are many similarities in the samples found there and those in the life sciences. Cryogenic scanning electron microscopy (cryo-SEM) and confocal laser scanning microscopy (CLSM) are ideally suited to elucidate the fundamental interactions that ultimately determine the bulk behaviour of oil emulsions and suspensions. Both water-in-oil and oil-in-water emulsions are found in oil processing and resolving or separating the phases is important for both environmental and economic reasons. Whether or not the dispersed phase is stabilized by solid particles, the nature of the particle surface, and the size distribution of the dispersed phase are all important factors in determining emulsion stability or the degree of difficulty in separating the components. Microscopy is an important first step in determining whether a chemical or physical separation method would be the most efficient.

Introduction

Emulsion separation can be broadly divided into chemical and physical methods, or combinations of the two. Typically, the approach to chemical separation is an empirical one involving many bottle tests to determine demulsifier effectiveness. The purpose of the demulsifier is to destabilize the oil-in-water or water-in-oil emulsion, resulting in coalescence and separation of the dispersed phase. If a significant amount of solids are present, whether they are associated with the oil or water phases has an impact on the effectiveness of the separation, either because of the hindered movement of the dispersed phase, or because of interactions of the solids at the emulsion interface, preventing coalescence.

Physical separation relies on the density differences between the dispersed and continuous phases. Settling vessel or centrifuge performance is a function of this density difference and the size distribution of the emulsion. Combinations of chemical and physical separation methods are most commonly used and these include the use of demulsifiers to enhance free water knock out vessel performance, and/or centrifugation, as well as chemical process aids to separate solids or to enhance flotation.

Microscopic characterization of the emulsion system can be an important first step in determining whether chemical or physical separation techniques are most likely to be successful and to provide guidelines as to their ultimate efficiency. A series of microscopic methods are available to characterize both oil-in-water and water-in-oil emulsions(1–4). The three most common techniques will be discussed with examples of their use in oil industry emulsion separation problems.

Methods

Light microscopy (LM)

This technique has been used extensively at the Fuel Processing Laboratory (FPL) to study a variety of samples, particularly in the reflectance and fluorescence modes. The optical parameters characterizing the organic and inorganic particles are the isotropic or anisotropic character, fluorescence properties, morphology, colour, and reflectivity. Reflected light is more commonly used than transmitted light because of the opaque nature of most oil emulsion samples. Creating a sample thin enough for transmitted light observation usually distorts the original sample and in some cases can even invert a water-in-oil emulsion into an oil-in-water emulsion when it is squeezed between two glass slides.