Emulsion is a heterogeneous system, containing at least immiscible liquid intimately dispersed in another in the form of droplets with a diameter, in general, ranging between (0.1~20) microns, and it is stabilized by an emulsifying agent, asphaltenes, resins and finely divided solids. The dispersed droplets are known as the internal phase. The liquid surrounding the dispersed droplets is the external or continuous phase. The emulsifying agent separates the dispersed droplets from the continuous phase [1] . Water-in-oil emulsion is formed during the production of oil, which is often accompanied with water. The stability of the emulsion is ranging from a few minutes to years depending on the nature of the crude oil [2] . Crude oils consist of, in any case, a series of hydrocarbons such as alkenes, naphthenes, and aromatic compounds as well as phenols, carboxylic acids, and metals. A major fraction of sulfur and nitrogen compounds may be present as well. The carbon numbers of all these components range from 1 (methane) through 50 or more (asphaltenes). Some of these components (asphaltenes, resins, wax, and naphthenic acids) can form films at oil surfaces. So, the tendency to form stable or unstable emulsions of different kinds varies greatly among different oils [3] . The natural petroleum emulsion resulting from the secondary production consists of crude oil as dispersion medium and brine as dispersed phase, normally stabilized by natural chemicals such as asphaltenes, resins, and solids such as clays and waxes [2] .

Emulsions are undesirable because the volume of dispersed water occupies space in the processing equipment and pipelines, increased operating and capital costs. Moreover, the characteristics and physical properties of oil change significantly on emulsification. Emulsion resolution is therefore an important element in handling the petroleum, from the time it is produced until it enters the refining process. In order to minimize the production problems related with crude oil emulsions and environmental concerns, petroleum operators need to prevent emulsion formation or to break it [4] . The treatment of water-in-crude oil emulsions involves the application of mechanical, thermal, electrical, and chemical processes [5] . Chemical method of resolving crude oil emulsions are based on the addition of reagents (de-emulsifiers) which destroy the protective action of hydrophobic emulsifying agents and allow the water droplets to coalesce. There are anionic, cationic and nonionic surfactants that have been used as de-emul- sifiers [6] . Success of chemical de-emulsifying method is dependent upon the adequate quantity of a properly selected chemical that must be added into the emulsion, through mixing of the chemical with the emulsion, adequately heat may be required to facilitate or fully resolve an emulsion. De-emulsifiers permit agglomeration, coalescence and gravity settling of the water droplets [7] . The formulation of commercial de-emulsifiers is largely based on empirical approaches in an attempt to get the effective agent, which can work in shorter separation times and smaller dosages [6] . In the petroleum industry the usual emulsions encountered are water droplets dispersed in the oil phase and termed as water-in-oil emulsion (W/O), conversely, if the oil is the dispersed phase, it is termed oil-in-water (O/W) emulsion. In addition to the usual emulsion types, multiple emulsions for instance, water droplets dispersed in oil droplets that are in turn dispersed in a continuous water phase (W/O/W) can occur.

Emulsion Stability is widely used to refer to the persistence of an emulsion in the environment, and has been identified as an important characteristic of water-in-oil emulsions. Some emulsions quickly decompose into separate oil and water phases once removed from the sea surface, while more stable emulsions can persist for days to years. Recent work indicates that the viscosity of an emulsion is related to its stability [8] . Crude oil is found in the reservoir in association with gas and saline formation water. The numbers of wells now co-producing water with crude oil is steadily increasing, these immiscible fluids are readily emulsified by the simultaneous action of pressure drop at the well head [9] . The knowledge of the properties and characteristics of the emulsion and the mechanisms that are taking place during coalescence of water droplets are required for fast separation [10] .

De-emulsifiers are molecules that aid the separation of oil from water usually at low concentrations. They prevent formation of water in oil mixture. The structures of de-emulsifiers are not easily categorized as emulsifiers. Some de-emulsifiers are polymers; others have structures similar to non-ionic emulsifiers. De-emulsifiers are surfactants that are important in breaking the emulsion system [11] .

The best de-emulsifiers are one that can reduce the interfacial shear viscosity increases the interfacial mobility and destabilizing the water-oil emulsion. To ensure the high quality performance, a de-emulsifier should possess the following characteristics [12] : 1) The de-emulsifier should be able to partition into the water phase and oil phase 2) Dissolved in the oil phase 3) The concentration of the de-emulsifier in the droplet must be sufficient to ensure a high enough diffusion flux to the interface.

The de-emulsifier must be high enough to suppress the interfacial tension gradient, thus accelerating the rate of film drainage hence promoting coalescence. Dodd [13] in 1954, concluded that the de-emulsifiers that are soluble in both phases are effective in breaking crude oil emulsions, provided that very small amounts of hydrochloric or Sulfuric acid are also added. He suggested the use of Phenol and Sulfuric acid. Hanapi [14] in 2006, investigated that the combination of oil soluble de-emulsifiers and water-soluble de-emulsifiers produced great result in water separation. He also observed that the formulation de-emul- sifiers is better than other commercial de-emulsifier.

The aim is to experimentally investigate the effect of de-emulsifier concentration, separation time and modifier agent to break crude oil emulsion. The main purpose of the research is to know the degree of the effectiveness of methanol and ethanol to emulsion de-emulsifiers. Two commercial de-emulsifiers were used: RP6000 and Chimec 2439. Chemical method was applied in breaking crude oil emulsion.