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Emulsion bitumen production process

Emulsion bitumen production process
Bitumen is used in the asphalt pavement process for several purposes:
1. Adhesion between asphalt stone materials and binders
2. Sealing and impermeability of asphalt overlays
3. Sealcoating (pavement sealing) and building a consistent surface for asphalt pavement retention
The pure bitumen is solid naturally at ambient temperature. The process of converting the pure bitumen into liquid bitumen for use in road construction is done through the three following approaches:
1. Heating the pure bitumen that is applicable for manufacturing hot mixed asphalts (HMAs)
2. Bitumen Cutback or Asphalt Cutbacks using petroleum solvents, which is used to manufacture protective asphalts and overlay plates in road construction. (This technique is not recommended under the current situation and due to environmental issues.)
3. Using water to make emulsion bitumen. This technique is also used for the preparation and application of protective asphalts and overlay plates in road construction.
This report focuses on the third technique, i.e., emulsion bitumen, which are categorized as liquid bitumen.
Emulsion bitumen is a two-phase mixture of two immiscible liquids (i.e., bitumen and water), where the inner phase is bitumen and is suspended in the form of very fine particles inside the outer phase (i.e., water).
The advantages of this type of liquid bitumen include the following:
No environmental pollution
Operability under humid circumstances
No need for heating during operation
No requirement for expensive petroleum solvents
High safety in transportation and storage and no risk of firing
Emulsion bitumen is divided into two main categories, i.e., anionic and cationic bitumen. Today, cationic emulsion bitumen is used for national applications in Iran, which is discussed in this report. Cationic emulsion bitumen is defined in terms of setting time (rapid, moderate, slow) and classified into the three categories as follows:
Components of cationic emulsion bitumen
1. Pure or polymer bitumen
2. Purified water
3. Acid
4. Emulsifier
5. Calcium Chloride
6. Hydrocarbon solvent (if required and depending on the type of emulsion produced)
The manufacturing process of liquid emulsion bitumen
This type of bitumen is manufactured according to a predefined process and protocol in the emulsion bitumen manufacturing plant, using either batch or flow (linear) manufacturing processes.
Batch manufacturing process
The batch manufacturing process is divided into the water phase and the bitumen phase. In the water phase, which is done in a covered tank, first, the water that has already been heated to a given temperature is drained with an emulsifier and other chemicals and mixed thoroughly. The volume of each ingredient shall be precisely calculated and added. This is a leading factor in the quality of the final emulsion bitumen and a minor violation of the workshop protocol will come with undesirable outcomes.
Ingredients should be added to the tank and mixed by automatic devices and systems to avoid the least error.
Most bitumen emulsions are manufactured by a continuous process using a colloidal mill (i.e., a device to decrease the particle size of a solid suspended in one liquid or to diminish the droplet size of a suspended liquid in other liquids). The system is equipped with a high-speed rotor that rotates in a stator at 1000 to 6000 rpm. The distance between the rotor and the stator is usually from 0.25 to 0.50 mm and is adjustable.
Hot bitumen solutions and emulsifiers and other additives are fed separately but simultaneously in the colloidal mill, where the temperature of these two components is a leading factor in the manufacturing process. The viscosity of the bitumen fed into the colloidal mill should not exceed 0.2 Pa/s (or 2 P) and its temperature shall be from 100 ℃ to 140 ℃. This viscosity is achievable by utilizing bitumen with a degree of penetration that is usually used in emulsions. To avoid water boiling, the temperature of the aqueous phase is adjusted so that the temperature of the resulting emulsion is less than 90 °C.
When bitumen and emulsifier solutions are simultaneously fed into the colloidal mill, they undergo intense shear forces that cause the bitumen to break into small globules. Separated bitumen globules are coated with an emulsifier, which induces an electric charge on the surface of each droplet. The resulted electrostatic forces prevent the globules from shrinking and aggregating.
The process is more complex to proceed when the bitumen is not soft enough (i.e., of penetration-grade bitumen type) or when a polymer-modified bitumen (PMB) is utilized. A higher temperature is required to allow the bitumen to be injected into the pump and dispersed in the mill. Furthermore, the bitumen dispersion requires more force to enter the mill, which raises the temperature of the product as well. For bitumen with a high viscosity, pressured mills are employed at normal emulsion temperatures, which provides more power with conventional bitumen. Emulsions are manufactured at temperatures up to 130 °C under high pressure, but the outlet emulsion should be cooled to below 100 °C before discharging it into conventional storage tanks.
Continuous manufacturing process
In this technique, there are no batch tanks of bitumen and emulsifier solutions, and both bitumen and emulsifier solutions are used directly from the main storage tanks.
A continuous process can be used to manufacture a small volume of the emulsion. The type of mixer is determined to match the consistency of the final product, which may vary from a high-speed impeller for low-viscosity road emulsions to a slow Z-blade mixer for industrial emulsions (e.g., paste).
The process of grinding and forming emulsions in the mill and the diameter of bitumen particles are influencing factors in the manufacture of emulsion bitumen. In this step, bitumen is suspended in the form of very fine particles in the aqueous phase solution. All the necessary precautions shall be taken during and after manufacturing to prevent the re-adhesion (aggregating) of fine bitumen particles.
The diameter of particles, mill rotor velocity, the distance between rotor and stator (fixed part), the duration of passing within the mill, the volume and type of emulsifier utilized, and manufacturing temperature are critical factors to consider in this process. Ultimately, the manufactured emulsion bitumen is stored in the relevant tanks and ready for loading and use.

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