Oxidized bitumen, often known as blown bitumen, is produced in a production unit known as a blown bitumen unit (BBU) or an air blowing unit (ABU), or an oxidizer. Depending on the feed concentration and processing conditions, the BBU produces two types of products with different concentrations and properties, including air-corrected bitumen, often known as semi-blown bitumen, and oxidized bitumen, known as blown bitumen.
The process involves the passage of air at a rate of 140-85 cubic meters per minute regularly through the bitumen feed at high temperatures to change the physical properties of the products. The main purpose is to harden the bitumen, increase the softening point and change the thermal viscosity properties of the bitumen. The process of achieving these goals is through various degrees of chemical reactions that result in an increase in the average weight of bitumen molecules leading to an increase in the maximum viscosity of the bitumen.
The medium degree of air blowing, known as air correction, is commonly used to adjust the physical properties of injected feed to produce materials used in the manufacture of roof insulation products and other industrial activities. Fluid oils may be used to soften the feed in the BBU. Catalysts may also be used to increase the reaction rate and improve temperature sensitivity. Catalysts include substances such as ferric chloride, hydrochloric acid, phosphorus pentoxide, or phosphoric acid.
The BBU unit primarily consists of a reactor, air blower, exhaust or combustion equipment, and temperature control equipment. The reactor is usually an empty source but may have blades or a mechanical excitation system to ensure complete mixing of the bitumen with the air.
The oxidation reaction is usually heat-generating, so the reactor may be equipped with a Water Jacket or water spray equipment on top to control the temperature of the bitumen. Injection of steam or water into the upper space of the reactor is used to reduce the amount of oxygen to manage and control the risk of fire or explosion. The schematic diagram of the blown bitumen unit is presented in Figure 5.
Despite the complex reaction mechanism and kinetics in the blown unit, the overall reaction path is summarized as the transformation of ring structures into resins (polar aromatics) that have been concentrated to form asphaltene. In blown bitumen, the initial oxidation process is the formation of a carbon-carbon bond through compression oxidation and to a lesser extent the formation of ester groups.
The chemical changes that occur during oxidation make changes to the physical properties of the BBU unit feed depending on the intensity of the oxidation process.
As a result of the reaction of the rings and resins, an oily maltene phase is formed, which covers the asphaltene and makes the bitumen harder, reduces the permeability, and increases the softening point. Increasing the concentration of asphaltenes beyond a certain point changes the flow properties at the ambient temperature of bitumen from viscoelastic behavior to practically pure elastic behavior.
Oxidation intensity determines the temperature sensitivity of products Is. Air-modified products (medium oxidation) have properties similar to vacuum-distilled Stright-run bitumen. For this reason, aerated bitumen and residual vacuum distillation are used directly or in combination to produce the final products. Oxidized bitumens have significant differences in temperature sensitivity values as a result of the maximum amount of asphaltene and have a high and remarkable softening point. The combination of these properties can not be achieved by simple distillation or air correction.
The rate and speed of the oxidation reaction that occurs under the influence of feed characteristics and conditions in the blown unit such as viscosity or permeability of feed, feed reactivity, temperature, airflow velocity, degree of excitation, pressure, air feed ratio, and use or not Catalyst depends.
The products obtained from the process of air correction and oxidation can be different using the following characteristics:
The feed enters the blown bitumen unit
- Permeability
- Characterization change: Feed input versus blown bitumen output from the unit
- Change at the soft spot
- Permeability rate
- Bitumen output blown
- Influence index
- Soft spot
