Transport emulsions

Oil-in-water emulsions provide a cost-effective alternative to the methods mentioned previously, namely, heating or diluting. A typical transport emulsion is composed of 70% crude oil, 30% aqueous phase, and 500 to 2000 ppm of a stabilizing surfactant formulation [1497]. Nonionic surfactants are relatively insensitive to the salt content of the aqueous phase ethoxylated alkylphenols have been used successfully for the formation of stable emulsions that resist inversion. 

Emulsions may be encountered throughout all stages of the process industries. For example, in the petroleum industry (see Chapter 11) both desirable and undesirable emulsions permeate the entire production cycle, including emulsion drilling fluid, injected or in situ emulsions used in enhanced oil-recovery processes, wellhead production emulsions, pipeline transportation emulsions, and refinery process emulsions [2], Such emulsions may contain not just oil and water, but also solid particles and even gas, as occur in the large Canadian oil sands mining and processing operations [2-4],... 

Once a transportation emulsion reaches its destination, it has to be broken. The demulsification techniques used are similar to those discussed in Section 7.2.1, and typically include any or all of raising the temperature of the emulsion, adding demulsifiers, and adding diluents. 

Emulsion Preparation. Preparing a transport emulsion is a fundamentally simple operation that includes the steps of forming a water-brine solution of the emulsion-stabilizing composition followed by a shearing process in which the crude oil and aqueous phases are metered to a specific mixing device. 

Each developer of transport emulsion technology selects specific surfactant formulations for particular applications. The primary functions of the surfactant are to reduce the interfacial tension between the crude oil and aqueous phases, to provide stability to the individual oil droplets formed during the shearing process, and to prevent subsequent coalescence of the droplets. The surfactant molecules collect at the phase boundaries and provide resistance to coalescence of the oil droplets by establishing mechanical, steric, and electrical barriers (5). 

A wide range of surfactant types may be used to form and stabilize transport emulsions. Nonionic surfactants have the advantage of relative insensitivity to the salt content of the aqueous phase being employed (6). The group of surfactants known as ethoxylated alkylphenols, represented by the formula,... 

Crude oil and brine pumps may be centrifugal or positive displacement, but must be capable of providing steady flow to the mixing device because emulsion properties are highly dependent on the resulting crude-oil-brine ratio. Surfactant may be dissolved in the brine phase on a batch or continuous basis. Static mixers provide a simple method for the preparation step because they require no moving parts, are easy to scale up, and provide an mixing intensity that is suited to preparation of transport emulsions. 

Emulsion Pipeline Operations. Prediction of pipeline pressure gradients is required for operation of any pipeline system. Pressure gradients for a transport emulsion flowing in commercial-size pipelines may be estimated via standard techniques because chemically stabilized emulsions exhibit rheological behavior that is nearly Newtonian. The emulsion viscosity must be known to implement these methods. The best way to determine emulsion viscosity for an application is to prepare an emulsion batch conforming to planned specifications and directly measure the pipe viscosity in a pipe loop of at least 1-in. inside diameter. Care must be taken to use the same brine composition, surfactant concentration, droplet size distribution, brine-crude-oil ratio, and temperature as are expected in the field application. In practice, a pilot-plant run may not be feasible, or there may be some disparity between pipe-loop test conditions and anticipated commercial pipeline conditions. In these cases, adjustments may be applied to the best available viscosity data using adjustment factors described later to compensate for disparities in operating parameters between the measurement conditions and the pipeline conditions. 

Monitoring Emulsion Aging. The surfactants used in transport emulsions may gradually lose their ability to stabilize the oil droplets. As the oil droplets coalesce, a two-phase mixture is formed, and it remains pumpable with no significant change in effective viscosity. This process is referred to as emulsion failure. An alternative to this process is inversion of the emulsion, in which a water-in-oil emulsion is formed with a potentially very high viscosity. Proper selection of the surfactant formulation can prevent the occurrence of emulsion inversion. 

The techniques used for demulsification of a transport emulsion may include raising the temperature of the emulsion, addition of emulsionbreaking additives, addition of diluents to reduce the viscosity of the heavy crude oil, and the use of equipment designed to promote coalescence of the crude-oil droplets. Raising the temperature of the emulsion increases the... 

The basic procedure for demulsification of a heavy-crude-oil transport emulsion then consists of the following steps ... 

Johnson OL, Washington G, Davis SS. Long-term stability studies of fluorocarbon oxygen transport emulsions. Int J Pharm 1990 63 65-72. 

The physical transport of the reactor products may also need sufficient processing. Bulk polymerizations in high-pressure extruders may be followed by dicing the product into small pellets suitable for pneumatic transport. Emulsion and solution products are usually transported as obtained and frequently used in the same mode. The design of suitable containers and transportation protocols is very important to avoid harming the product during transportation and storage. For example, special containers may be required for air-sensitive materials, or to avoid solvent or water loss from solutions and emulsions, respectively. 

Explosive emulsions are minute droplets of ammonium nitrate solution emulsified to the texture of margarine in a fuel (often diesel). Because the ammonium nitrate remains in solution, it is not an explosive and maintains an inherent high degree of safety during transportation. Emulsions are sensitized just prior to use by the introduction of gas bubbles or glass microballoons which create voids around which ammonium nitrate solidifies (the explosive form). Initiation is caused by the shockwave of a high explosive detonator. 

Emulsifieation as a low-viseosity vehicle for pipeline transportation shares some requirements with the OAV fuel emulsion, but differs in others. In effect, the transported emulsion should be stable during the pipeline pumping, but should be easy to break at the pipeline end. 

Transportation Emulsions. Some emulsions are made to reduce viscosity so that an oil can be made to flow. Emulsions of asphalt, a semi-solid variety of bitumen dispersed in water, are formulated to be both less viscous than the original asphalt and stable so that they can be transported and handled. In application, the emulsion should shear thin and break to form a suitable water-repelling roadway coating material. Another example of emulsions that are formulated for lower viscosity with good stability are those made from heavy oils and intended for economic pipeline transportation over large distances. Here again the emulsions should be stable for transport but will need to be broken at the end of the pipeline. It is desirable for the dispersion to possess poor stability under static conditions to permit easy separation of the oil and water. In addition, the oil that has undergone separation is often re-emulsified for further treatment/application. 

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