Hydrocarbon bitumen is a dark brown to black material in solid, semi-solid, or viscous forms, with adhesive properties, of natural or refinery origin, mainly containing high molecular weight hydrocarbons. These materials are completely soluble in carbon disulfide (CS2), trichloroethylene (C2HCl3), and xylene (C6H4(CH3)2). Its vapor pressure is negligible at ambient temperature and almost odorless in this state.

Hydrocarbon bitumen is a dark brown-black compound in solid, semi-solid, or viscous forms, with adhesive properties, originating from natural or refinery sources, mainly containing high molecular weight hydrocarbons. These materials are completely soluble in carbon disulfide(CS2  ) , trichloroethylene (C2HCl3  ) , and xylene (C6H4(CH3)2  ) . Its vapor pressure at ambient temperature is negligible, and it is almost odorless in this state.

The most abundant and widely used type of bitumen is petroleum bitumen, which is physically a homogeneous substance ( and chemically a heterogeneous mixture of various chemical compounds. This hydrocarbon mixture generally contains 90% carbon and hydrogen atoms, with the remainder being nitrogen, sulfur, and oxygen, and small amounts of metals such as nickel, iron, magnesium, etc.

60/70 bitumen is a type of bitumen that is obtained through the air-blowing process on vacuum bottom (the raw material for bitumen production, which is taken from the residue of the vacuum distillation tower of oil refineries) in bitumen production units, and its penetration grade (determining the hardness of the bitumen) is between 60 and 70. Bitumen penetration grades are classified based on the results of penetration and softening point tests. The classification is based only on the penetration range; for example, 40/60 bitumen has a penetration grade between 40 and 60 and a softening point between 48 and 56 degrees Celsius. Note that the penetration unit is not stated during classification. The majority of penetration grade bitumens are used in road construction. In the last two decades of the twentieth century, there has been an increasing tendency in most road construction projects to use hard bitumens due to the production of asphalts with higher properties compared to soft bitumens.

Bitumen Production Process

Batch Process

In the batch process, the aeration tower is filled with a specific volume of feed, and after air is blown in under predetermined conditions (reaction temperature, time, feed amount) and the product reaches the desired specifications, the tower is emptied and the product is transferred to the desired tanks.
The main components of a batch aeration unit are:
Pre Heater
Blower or Compressor
Oxidizer Tower
A system for collecting and burning vapors
Continues Process

In the continuous process, the feed with a specific and controllable flow rate and a predetermined temperature continuously enters the aeration tower, and after the aeration operation is performed under constant operating conditions, it continuously exits the aeration tower. This method of bitumen production, which is used in refineries, is considered due to the following advantages:
Reduction of polluting vapors produced
Reduction of equipment and maintenance costs
Increased efficiency and production rate per unit time
Reduction of the thermal load of feed preheaters
Ease of control and process execution due to the continuous nature of the process
Reduced air consumption and shorter aeration time due to optimal use of blown air
Aeration can be performed in horizontal and vertical towers, with vertical towers being preferred due to their higher efficiency. Effective parameters in aeration mainly include feed viscosity, feed temperature, and tower geometry. Explaining these parameters, it can be said that if the feed viscosity, air flow rate, or process temperature, or the height-to-diameter ratio of the tower (up to a certain extent) is higher, the reaction rate will be higher. The oxidation reaction is an exothermic reaction; therefore, to control the temperature and remove excess heat, heat exchangers with a capacity proportional to the desired temperature must be used.
As previously stated, during the aeration or oxidation process, air passes through the bitumen, and its oxygen interacts with the bitumen molecules. The vapors resulting from this process (Process Fumes) contain less than 10% oxygen and various compounds such as water vapor, aldehydes, ketones,CO ,CO2 , nitrogen oxides, methane, nitrogen, sulfur compounds(H2S,SO2) , and finally, "petroleum oil hydrocarbons." These hydrocarbons, due to the strong flow of blown air, either as vapor or liquid along with the air(Entrainment) exit the tower, and some of them condense in later stages(Condense) . These hydrocarbons are called "process oils." These aeration process fumes (Process Fumes) are typically treated by a set of separation devices to separate the entrained (or later condensed) oils, and then the vapors are burned. The percentage of feed loss in the aeration process is usually between (0.5-2) % by weight, depending on several factors, including feed viscosity, temperature, aeration time, etc. The majority of process vapors include this loss. Overcoming the problems related to process vapors is a problem that usually does not have a 100% satisfactory solution. These vapors also have an unpleasant odor, which is due to the compounds created in the oxidation process. The entrained oils(Entrained Oils) include the more volatile hydrocarbons present in the feed. For partial degreasing of the exhaust gases from the aeration tower, a simple Knok Out Drumor Vapor Trap is required. In some cases, theKnok Out Drum is equipped with a water spray, which will result in greater degreasing, which is known as a contact condenser. In other cases, methods such as returning vapors to the blower are used. Another method, in cases where there is sufficient space, is to use the following simple system:
The vapors pass through a long, horizontal air condenser (heat exchanger), and in this path, most of the entrained oils are separated, and the remaining vapors are directed to a vertical furnace for burning.