Bitumen is primarily obtained by vacuum distillation of carefully selected crude oil or blends of crude oil. It comprises the non-distillable fraction? oftentechnically reffered to as vacuum residue. In its simplest form bitumen production processes separated the lighter, low bololing pointfractions from cruide oil resulting in product with high bolling point, high molecular weight with very low volatility. Properties and quality of bitumen depend mainly on the crude oil (s) used in its manufacture. It is produced to grade specification ither directly by renining or by blending. Bitumen can be further processed to after its physical properties in order meet certain specifications. Experience of the world bitumen production industry shows that the following processes are viable for bitumen production:
- concentration of oil residue for vacuum distillation. Inert gas or steam are used in the process. Atmospheric distillation is used for production of residual bitumen from asphalt-resinous oil;
- oxidation of various oil residue with air oxygen at 180-300ºС. Such residue can include flux oil, tar, oil pitch, deasphalting asphalts, cracking residue etc;
- desaphalting of oil tar with selective solvents;
- mixing (compounding) of oil residue with distillates, as well as oxidized or residual bitumens.
In practice, the methods above can also be combined.
The most common raw material for bitumen production is oil tar or deasphalting asphalts (asphalt and resinous substances). In some literature they are referred to as “deposited bitumens”. It should be noted that sometimes extracts of selective oil refining, thermal cracking residue or pyrolysis resins can be used for bitumen production.
Production of highly plastic bitumen with good thermal stability and binding properties, raw materials of consistent composition and quality is required.
Usually, heavy oil tar with high resin and asphalt content has the required properties. In the general case, the following is true: the higher the “asphaltene:resin” ratio, the better the structure and properties of bitumen produced. In heavy crude, this ratio is 1.0-1.3.
In countries with short supply of such oil, regular crude is used, which makes the product properties fall short of the quality standards.
