Nowadays, bitumen obtained mainly from oil. There are two general ways to earn bitumen from oil.
In the first method, depends on food and way of refining, after distillation in vacuum condition, bitumen with suitable physical characteristics for making roads and industrial applications obtained.
In the second method, obtained vacuum residue, usually has very low viscosity and high degree of penetration of 300-400 mm. The product has low asphaltene, so it is not suitable for making roads in tropical and temperate regions.
To convert bitumen shaped residue to bitumen with suitable physical properties, during a process, heavy molecules like asphaltenes should be added. To do this, air that is combined from different types of gases like: oxygen, nitrogen, co2 etc been pressed by a compressor and it has been injected to a tower containing molten bitumen upper than oc200. The process can be continuous or batch. The so called semi-aeration process causes production of semi-blown bitumen with suitable penetration degree and softening point 100/85 or 70/60 which is used in road making and moisture barrier of houses.
If in that unit or next unit, the process of aeration being continued, gradually, penetration degree of bitumen is decreased and its softening point increases. Result is blown firm bitumen with very low penetration and so high softening point like 10/110, 15/90, 25/85. These types of bitumen are used in buildings and additives in moisture barriers.