Bitumen Specification

Distillation

Bitumen is produced by fractional distillation of crude oil. Usually, distillation is done in two steps. First the crude oil is heated up to 300-350°C and introduced into an atmospheric distillation column. Lighter fractions like naphtha, kerosene and gas oil are separated from the crude oil at different heights in the column. The heaviest fractions left at the bottom of the column are called heavy residue.

The long residue is heated up to 350-400°C and introduced into a vacuum distillation column. By using reduced pressure it is possible to further distillate lighter products from the residue because the equivalent temperature (temperature under atmospheric conditions) is much higher. If second distillation were carried out under atmospheric conditions and by increasing the temperature above 400°C, thermal decomposition/cracking of the heavy residue would occur. The residue at the bottom of the column is called short residue and is the feedstock for the manufacture of bitumen.

The viscosity of the short residue depends on the origin of the crude oil, the temperature of the long residue, the temperature and pressure in the vacuum column and the residence time. Usually, the conditions are such that short residue is produced with a Penetration between 100 and 300 dmm. The amount of short residue decreases and the relative amount of asphaltenes increases with increasing viscosity of the short residue.

Bitumen manufactured from the short residue is called straight run bitumen. The differences in properties between high and low penetration grade bitumen are mainly caused by different amounts of molecule structures with strong interactions. Low penetration grade bitumen contains more of these molecule structures. This is the main reason why their viscosity, Fraass breaking point, Softening point, etc., is so much higher than for high penetration grade bitumen. The fact that they contain less low viscosity products is of less significance.

Propane Deasphalting

Bitumen is also produced by propane deasphalting and there are differences in the properties of bitumen prepared by propane deasphalting and those prepared by vacuum distillation from the same feed stock. Propane deasphalting also has the ability to reduce a residuum even further and to produce a bituminous product with lower viscosity, higher ductility, and higher temperature susceptibility than other bitumen, although such properties might be anticipated to be very much crude oil dependent. Propane deasphalting is conventionally applied to low-bitumen-content crude oils, which are generally different in type and source from those processed by distillation of higher-yield crude oils.

Air Blowing

The properties of bitumen can be modified by air blowing in batch and continuous processes. On the other hand, the preparation of bitumen in liquid form by blending (cutting back) bitumen with a petroleum distillate fraction is customary and is generally accomplished in tanks equipped with coils for air agitation or with a mechanical stirrer or a vortex mixer. Air is heated up to 150–250°C and introduced at the bottom of a blowing column. It then migrates through the bitumen to the top of the column. The chemical reactions result in bitumen with a different mixture of molecular structures. Catalysts can influence this process.

Blown bitumen has more and stronger molecular interactions than the original bitumen and is therefore more cohesive. Blowing causes the softening point to increase and the penetration to decrease. However, the increase in softening point is usually more than the decrease in penetration. This means that blowing reduces the temperature susceptibility of bitumen. The effectiveness of blowing depends largely on the original bitumen (i.e. the original mixture of molecular structures).

With respect to the composition, generally the amount of saturates do not change, the amount of aromates decreases because some oxidized aromates behave like resins, the amount of asphaltenes increases due to trans-formation of some resins and the total amount of resins stays the same.

When bitumen is strongly blown it becomes so cohesive that the adhesive properties become so poor that it is not suited for asphalt applications anymore. Therefore, only semi-blown bitumen is suited for asphalt applications. Semi-blown bitumen can have both improved cohesion and improved adhesion.

Visbreaking

Light products have a higher selling value than heavy products like bitumen. Visbreaking is a way to break heavy products (e.g. the residue from crude oil distillation or even very heavy crude oils) into lighter products. Hereto, the crude oil or residue is heated up to 450 °C and kept at that temperature for 1 to 20 minutes. During this period a large amount of molecular structures are broken into smaller structures. The product from the visbreaking process (VB product) is further normally distilled.

Bitumen production from VB products age very fast. This is because these products contain very reactive constituents (olefins). Even blends of straight run bitumen with bitumen from VB products have the same ageing problems. This makes them unsuitable for most asphalt applications. The properties may be somewhat improved by blowing.

Bitumen 60/70 :

Definition: It is a kind of bitumen, which is provided during the process of oxidation of vacuum bottom (the bitumen production feedstock that derives from distillation tower residue in vacuum oil refineries) at bitumen production units. In a manner that its penetration point (kind of test to indicate the hardness of bitumen) becomes between 60-70.

Usage: The main common usage of this product is in road making at temperate regions.

Characteristics:

Bitumen 85/100:

Definition: It`s kind of bitumen which is provided during the process of oxidation of vacuum bottom (the bitumen production feedstock that derives from distillation tower residue in vacuum oil refineries) at bitumen production units. In which its penetration point (kind of test to indicate the hardness of bitumen) becomes between 85-100.

Usage: The main common usage of this product is in road making at cold regions.

Characteristics: 

 Bitumen 40/50

Definition:

It is a kind of bitumen, which is provided during the process of oxidation of vacuum bottom (the bitumen production feedstock that derives from distillation tower residue in vacuum oil refineries) at bitumen production units. In a manner that its penetration point (kind of test to indicate the hardness of bitumen) becomes between 40-50.

Usage:

The main common usage of this product is to use in road making at tropical regions.

Characteristics: