Bitumen, as a black-colored hydrocarbon material, has numerous industrial and non-industrial applications, and due to its unique characteristics such as excellent adhesiveness and high water impermeability, it can have various uses. This material easily dissolves in carbon disulfide and tetrachloromethane and exists in different forms such as solid, liquid, and plasma. Bitumen can come in various types, including gilsonite, petroleum bitumen, natural bitumen, blown bitumen, cut-back or emulsified bitumen, and others. Emulsified bitumen is also one of the types of bitumen, which has multiple applications.
What is Emulsified Bitumen?
Emulsified bitumen is essentially a type of dissolved bitumen, where bitumen is combined with water and an emulsifying agent. The main components of this bitumen are pure or polymer-modified bitumen, pure water, acid, emulsifier, calcium chloride, and a hydrocarbon solvent (if required and depending on the type of emulsion produced). The emulsifying agent constitutes around 0.3 to 0.5 percent by weight of the bitumen and can be an alkaline salt of organic acids or ammonium salt.
These substances can charge the bitumen particles and create a repulsive force, which causes the bitumen particles to float in water as spheres with a diameter of one-hundredth to one-thousandth of a millimeter. Emulsified bitumen has lower polluting power and, unlike other types of bitumen, has a lower risk of ignition. Essentially, each type of bitumen can have multiple capabilities and applications based on factors such as softening point, penetration grade, tensile strength, breaking point, the effect of heat and air on bitumen, viscosity, specific gravity, solubility or purity of bitumen, flash point, and others.
Process and Formula for Producing Emulsified Bitumen
Each type of bitumen can be produced through different methods and processes, and have unique characteristics. Emulsified bitumen is no exception to this rule. In general, the formula for producing bitumen can be done in two ways: batch process or continuous process, as described below:
Batch Process
The production of bitumen in the batch or "Batching" method is divided into two phases: the water phase and the bitumen phase. The water phase is carried out in a covered tank, where the water is preheated to the required amount, and then the emulsifier and other necessary chemicals are added to create a homogeneous mixture. The quantity and amount of each material in this mixture must be precisely calculated to ensure the final quality of the emulsified bitumen is satisfactory. The discharge of materials and their combination is done by automated equipment and systems to minimize the rate of errors.
Most bitumen emulsions are produced through a continuous process using a colloid mill (a device used to reduce the particle size of a solid suspended in a liquid or to reduce the droplet size of a liquid suspended in other liquids). The colloid mill consists of a high-speed rotor that rotates in a stator at 1,000 to 6,000 revolutions per minute. The gap between the rotor and stator can be adjusted, although the standard size is 0.25-0.50 millimeters.
The hot bitumen solutions, emulsifier, and other additives mentioned are separately but simultaneously fed into the colloid mill at a specific temperature. The bitumen entering the colloid mill must have a defined density (no more than 0.2 Pa·s (2 poises)) and the bitumen temperature is set between 100 to 140 degrees. To prevent boiling and evaporation of water, the temperature of the water phase must be adjusted so that the temperature of the resulting emulsion is less than 90 degrees Celsius.
The bitumen solutions and emulsifier are simultaneously fed into the colloid mill and subjected to intense shear forces, which causes the bitumen to break down into small droplets. The separated bitumen droplets are coated with the emulsifier, and an electrical charge is induced on the surface of each droplet. The electrostatic forces resulting from the accumulation and agglomeration of the droplets prevent them from rejoining.
Use of Hard Bitumen in Batch Process
The type and quality of the bitumen used in the batch process is of utmost importance. When bitumen with a lower softening point (not penetration-grade) or polymer-modified bitumen is used, the process becomes more challenging. In such cases, higher temperature and pressure are required to inject the bitumen into the pump and disperse it in the mill. For bitumens with high density, pressure-operated mills at normal emulsion temperatures are used, which allows for greater efficiency with regular bitumens. The emulsions are produced at a maximum temperature of 130 degrees Celsius under high pressure, and the emulsion output must be cooled to below 100 degrees Celsius before being discharged into the storage tanks.
Continuous Process
The second formula for producing emulsified bitumen is the Continuous process, which, unlike the batch method, does not have separate tanks for bitumen and emulsifier solution. Instead, the bitumen and emulsifier solution are directly fed from the main storage tanks. This is essentially a continuous process for producing small volumes of emulsion, and can even use natural bitumen. The type of mixer used in this method is selected based on the desired consistency of the final product. For low-viscosity road emulsions, a high-speed propeller can be used, while a slow Z-blade mixer can be used for industrial emulsions like pastes. Key parameters in this process include bitumen dispersion, emulsion formation, bitumen particle size, and others that must be controlled based on the desired product.
Price of Emulsified Bitumen
As mentioned earlier, emulsified bitumens possess multiple characteristics and can have various applications depending on their degree of purity, softening point, flammability, and other factors. The price of these bitumens, similar to the price of gilsonite, can be influenced by various factors such as the production formula, technical specifications, applications and intended use, physical and chemical properties of the bitumen, brand and manufacturer, global oil and bitumen prices, and so on.
Final Summary
Emulsified bitumen is a type of cutback bitumen produced by combining bitumen with water, a hydrocarbon solvent, and an emulsifying agent. This bitumen can be produced through different methods such as the batch process and the continuous process, and can have various industrial and non-industrial applications.
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