BBUs, ABUs, and oxidizers produce oxidized bitumen, commonly known as blown asphalt.
In the oxidized bitumen production, to modify the physical qualities of the products, air at a rate of 85-140 cubic meters per minute is continually passed through the bitumen feed at high temperature. The primary goal is to harden the bitumen, raise the softening point, and alter the bitumen’s thermal viscosity qualities. The mechanisms for achieving these objectives include varying degrees of chemical reactions that result in a rise in the average weight of bitumen molecules, which leads to an increase in bitumen’s maximum viscosity.
Air cooling, or mild air blowing, is often used to change the physical qualities of injected feed to generate materials used in the manufacturing of roofing insulation (Bituminous Membranes) products and other industrial operations. To soften the feed in the BBU unit, fluid oils might be employed. Catalysts can also be used to speed up the reaction and enhance temperature sensitivity. Catalysts include ferric chloride, hydrochloric acid, phosphorus pentoxide, and phosphoric acid.
The BBU unit in the oxidized bitumen production comprises essentially of a reactor, air blower, gas removal or combustion equipment, and temperature control equipment. The reactor is typically a vacuum vessel, but it can also contain blades or a mechanical stirring device to guarantee full bitumen-air mixing. Because the oxidation process is often exothermic, the reactor can be outfitted with a water jacket or water spray apparatus on top to regulate the bitumen temperature. To regulate and limit the danger of fire or explosion, steam or water injection into the reactor’s top area is utilized to lower the quantity of oxygen. The graphic below depicts the schematic diagram of the oxidized bitumen unit.
Despite the complicated reaction mechanism and kinetics in the blown unit, the overall reaction pathway in the oxidized bitumen production is characterized as the transformation and conversion of cyclic structures to resins (polar aromatics), which are then condensed to create asphaltene. The principal oxidation mechanism in blown bitumen is the creation of carbon-carbon bonds by condensation oxidation and, to a lesser degree, the formation of ester groups.
The basic goal of oxidized bitumen production is to harden, raise the softening point, and modify the thermal viscosity.
Depending on the strength of the oxidation process, the chemical changes that occur cause variations in the physical qualities of the BBU unit feed. As a consequence of the interaction between the rings and the resins, an oily maltene phase forms, which covers the asphaltenes and causes the bitumen to harden, lose permeability, and soften. When the concentration of asphaltenes is increased above a specific amount, the flow characteristics of bitumen at ambient temperature shift from viscoelastic to almost pure elastic.
The temperature sensitivity of goods is determined by the degree of oxidation. The qualities of air-refined (moderate oxidation) products are comparable to those of vacuum-distilled straight-run bitumen. As a result, air-modified bitumens and vacuum distillation residuals are employed directly or in combination to generate final products. Because of the largest proportion of asphaltene, oxidised bitumens exhibit considerable variances in temperature sensitivity values and a high and significant softening point. These qualities cannot be combined by ordinary distillation or air reforming.
The rate and speed of the oxidation reaction that occurs in the oxidized bitumen production are influenced by the properties of the feed and the conditions in the blown unit, such as the viscosity or permeability of the feed, reactivity of the feed, temperature, air flow rate, degree of stimulation, pressure, air feeding ratio, and whether or not it is used. It is determined by the catalyst.
The oxidized bitumen production, the main purpose is to harden the bitumen, elevate the softening point, and change the thermal viscosity properties of the bitumen.