Demulsifiers selection

The major problem in demulsifying crude oil emulsions is the extreme sensitivity to demulsifier composition. There have been attempts (2, 3) to correlate demulsifier effectiveness with some of the physical properties governing emulsion stability. However, our understanding in this area is still limited. Consequently, demulsifier selection has been traditionally based on a trial and error method with hundreds of chemicals in the field. 

Work on the characterization of oil-field emulsions coupled with chemical characterization of commercially available demulsifier formulations has shown that physical processes (temperature, pumping, and dispersed water size distribution) can be at least as important as the chemical effects associated with demulsifiers themselves in determining demulsifier effectiveness [468,469].In fact, there are so many variables involved in industrial demulsification that, to a large degree, demulsifier selection and performance evaluation are still conducted using simple test procedures developed for use in the plant or field. These tests, usually bottle or centrifuge tests, can be good indicators of performance trends, and are usually carried out for selected suites of commercial demulsifier formulations. 

Several excellent reviews of demulsifier chemistry and properties can be found in the literature [J ]. For this chapter, the important factors in demulsifier selection and characterization will be discussed, accompanied with specific examples. 

Chemical demulsification is commonly used to separate water from heavy oils in order to produce a fluid suitable for pipelining (typically less than 0.5% solids and water). A wide range of chemical demulsifiers are available in order to effect this separation. In order to develop the fundamental understanding necessary to optimize demulsifier selection for a particular emulsion, it should be sufficient, in principle, to obtain a complete chemical and physical characterization of both the emulsion to be separated and the demulsifier to be used. 

In practice, however, this is not possible because of the wide range of factors that can affect demulsifier performance. Aside from demulsifier chemistry, factors such as oil type, the presence and wettability of solids, oil viscosity, and the size distribution of the dispersed water phase can all influence demulsifier effectiveness. As a result, demulsifier selection for a... 

Determining the best demulsifier for resolution of a given water-in-oil emulsion, given a variety of process variables, is not a task that lends itself to solutions based on analysis of the fundamental principles involved. A series of bottle tests are generally performed in order to determine the most effective demulsifier or combination of demulsifiers for a given emulsion. In spite of the difficulties involved, however, several attempts have been made to put demulsifier selection on a solid scientific... 

An Empirical Approach to Demulsifier Selection. Research into emulsion fundamentals added greatly to our understanding of the factors that determine emulsion stability and the surface-active chemicals that can be used to manipulate those factors. In spite of these advances, the requirement for blending demulsifiers in order to achieve acceptable field performance means that empirical approaches are often required for demulsifier selection. In fact, complete characterization of emulsion properties, including process residence times, temperatures, and product requirements still only provides guidance in the selection of process demulsifiers. The costs and time involved in achieving the level of characterization required for a fundamental approach can also be... 

The demulsifier selection should be made with the process system in mind. If the treating process is a settling tank, a relatively slow-acting compoimd can be applied with good results. On the other hand, if the system is a chemical-electric process where some of the flocculation and coalescing action is accomplished by an electric field, there is need for a quick-acting compound, but not one that must complete the droplet-building action. 

In the production of crude oil, the greatest part of the crude oil occurs as a water-in-oil emulsion. The composition of the continuous phase depends on the water/oil ratio, the natural emulsifier systems contained in the oil, and the origin of the emulsion. The natural emulsifiers contained in crude oils have a complex chemical structure, so that, to overcome their effect, petroleum-emulsion demulsifiers must be selectively developed. As new oil fields are developed, and as the production conditions change at older fields, there is a constant need for demulsifiers that lead to a rapid separation into water and oil, as well as minimal-residual water and salt mixtures. 

The dielectric constant can be used as a criterion for screening, ranking, and selecting demulsifiers for emulsion breaking. In a study, the dielectric constants of emulsions and demulsifiers were measured using a portable capacitance meter, and bottle tests were conducted according to the API specification [18]. The results showed that the dielectric constants can be used effectively to screen and rank demulsifiers, whereas a confirmatory bottle test should be conducted... 

Berger, P.D., Hsu, C., and Arendell, J.P. "Designing and Selecting Demulsifiers for Optimum Field Performance on the Basis of Production Fluid Characteristics," SPE Prod. Eng.. November 1988, 522-526. 

As a general rule, the addition of ethylene oxide to a resin backbone will tend to increase the water solubility of the compound. The addition of propylene oxide or butylene oxide to the resin will tend to increase the hydrocarbon solubility of the compound. Often, the dehazer or demulsifier can be made to perform selectively in oil-water systems by adding both ethylene oxide and propylene oxide to the same molecule. Performance and solubility of the alkoxylated compound can then be finely tuned by closely controlling the amount and order of epoxide addition. A random EO-PO based fuel demulsifier is shown in FIGURE 6-6. 

Experience is a very useful teacher in selecting demulsifiers. The man who is familiar with the history of treating m an area, the demands of the treating plants, and the performance of the chemicals can do a pretty good job ot picking compounds. However, this approach fails when changes occur in emulsion characteristics, new emulsions are encountered, or new chemicals become available. 

A number of parameters are used to select demulsifiers [68,465,467], including ... 

The more common emulsion formed in the petroleum industry is the water-in-oil type. The sensitivity of electrokinetic sonic analysis to coagulation-coalescence processes in water-in-oil media is of great importance. It allows for rapid selection and optimization of different chemical demulsifiers. In addition, as a research tool, it supports the development of a fundamental understanding of chemical treatment of water-in-oil emulsions. 

In some cases, minimal effort is required for the demulsification process. For example, in field tests, adequate separation of a bitumen emulsion could be achieved without the use of demulsifiers by raising the temperature of the emulsion to 190 T and providing 24 to 48 h of residence time in quiescent storage tanks. However, proper selection of demulsification chemicals is essential when treating the emulsions in conventional equipment on a continuous-flow basis. 

Selection of a suitable chemical emulsion breaker and dosage is crucial. A particular demulsifier may be effective and efficient for one emulsion yet entirely unsatisfactory for another. Contemporary demulsifiers are formulated with polymeric chains of ethylene and propylene oxides of alcohol, alkyl phenols, amino compounds, and resinous materials that have hydroxy acceptor groups. Each of these polymers is carefully formulated to yield a molecule with a particular affinity for water. Demulsifier dosage is also important excessive demulsifier addition can inhibit the efficiency of emulsion breakdown. 

Retention Time. To effectively demulsify an oil-in-water emulsion, it must be held at a suitable treating temperature for a specific time period. In the absence of experimental data, 20-30 min is usually a realistic estimate for retention time for conventional oil projects for heavy-oil recovery operations, retention times could be several hours. Nonetheless, the vessel geometry and specifications required for a specific retention time may not necessarily be the same as those dictated by the settling requirements. The solution is to select the larger geometry and dimensions determined by either of the two criteria. The retention time is determined as follows (3). For horizontal vessels. 

In samples with low-water volume, or those with more than normal residence time, the speed of water dropout may be of lesser significance in selecting the best demulsifier. Nonetheless, in all cases the speed of water dropout and volume should be recorded. 

Recently, we have shown that sulfonated PHP can act as a demulsifier for highly stable emulsions like crud and water-in-crude oil emulsions. The mechanism of demulsification is that sulfonated PHP removes selectively surface active species in the emulsion, causing destabilization. At the same time, it also adsorbs metal ions, thus achieving two functions at the same time. As a result, these materials are called demulsifier adsorbers. In highly stable emulsions where neither electric field nor demulsifier adsorbers are effective, the combination of these two methods appears to create synergy for separation. 

Encapsulation of enzymes in LMs offers further improvements for immobilization of complex enzyme systems, as the enzymes / cofactors, etc. are situated in aqueous droplets surrounded by a stable liquid hydrocarbon film (Figure 1). Instead of the physical pores present in microcapsules, the HC barrier, which has a diffusion thickness of about 0.1-1.0 p, effectively blocks all molecules except those which are oil-soluble or transportable by the selected carriers. Encapsulation of enzymes in LMs is accomplished simply by emulsifying aqueous enzyme solutions. Hence, LMs offer many advantages over other systems used for separation and eirzyme immobilization they are inexpensive and easy to prepare they promote rapid mass transport they are selective for various chemical species they can be disrupted (demulsified) for recovery of internal aqueous solutions gradients of pH and concentration (even of small molecules) can be maintained across the HC barrier multiple enzyme / cofactor systems can be coencapsulated and enzymatic reaction and separation can be combined. Some of the potential disadvantages of LMs for enzyme encapsulation have been discussed earlier. 

It is often said that the skill of formulating a demulsifier is a black art , selection of an effective product relying on a trial and error approach, supplemented by the selector s knowledge of what worked before. The test procedure requires the production of an emulsion under reproducible conditions. The rate of water coalescence is taken as a measure of the effectiveness of the product. 

In practice considerable difficulties are encountered in selecting both demulsifiers and demulsification methods. Thermal, electric and chemical demulsification methods are listed in [241]. The latter is discussed very briefly and includes commonly known conditions 1) choice of demulsifier and its optimum concentration 2) effective stirring at a certain temperature 3) optimum period of time to allow the phases to separate and to obtain a clear-cut boundary between the phases. Besides, 2 examples of rather well-known formulations are given, which... 

J.P. (1987) Designing and selecting demulsifiers for optimum field performance based on production fluid characteristics, in Proceedings-SPE Annual Technical Conference, Society of Petroleum Engineers, Richardson, TX, SPE paper 16285. 

This is followed by a description of the chemicals used as demulsifiers in practice and in research. The agricultural and petroleum sourees of the basic chemical building blocks are indicated. The typical responses for selected types of ehemicals are discussed, in terms of published research findings to date. 

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