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Bitumen can be found in the natural state, but the bitumen used nowadays for the surfacing of roads and a variety of industrial uses is produced in refineries from special qualities of crude oil.
Natural bitumen
In its natural state, bitumen is found oozing out onto the surface of the earth (USA, Israel, Mexico, Venezuela).
Not far from Los Angeles (USA), accumulations of natural bitumen have been found, resulting from oozing of oil from the remains of numerous herbivorous animals, of something like a thousand smilodons (a genus of sabre-toothed tigers with prominent canine teeth alive in the Pleistocene period) and of more than one thousand five hundred wolves. The carnivorous animals, attracted by the presence of their prey bogged down in this natural trap, became prisoners of the sticky viscous bitumen in their turn. Dating the remains has shown that some of these animals lived fifteen thousand years ago.
Archaeologists have found traces of the use of natural bituminous materials dating from 5 000 BC. Bitumen as caulking for Noah’s Ark and Moses’ cradle is mentioned in the Old Testament.
More recently, particularly in the XIXth century, painters used asphalt or bitumen on their canvasses to obtain blacks with a brown tint. For example, in his celebrated painting, The Raft of the Medusa, Géricault made use of bitumen of Judea to obtain the brownish tones and a violent chiaroscuro. (Source : Bitumen Info n°10, GPN )
A special distillation
Nowadays, natural deposits are no longer sufficient for our requirements. The greater part of the bitumen used to meet the demands of civil engineering and construction is extracted from crude oil. Scientists agree today on the animal origin of crude oil. Over geological ages, the transformation of marine micro-organisms (plankton), deposited in the sedimentary layers of rocks, led to the formation and accumulation of numerous varieties of crude.
Bitumen is obtained essentially by distillation of a blend of crudes containing at least one bitumen crude. The others, which are lighter, go to satisfy requirements for different types of fuel and combustibles. Contrary to a common but mistaken idea, bitumen is not an oil residue that the petroleum industry wants to get rid of at little cost. In reality, to produce bitumen of good quality with constant properties, refiners meticulously select one or more bitumen crudes, following very strict internal approval procedures.
Of the 1 300 types of crude oil classified worldwide, only 10 % are suitable for producing bitumen capable of meeting the specifications for use. These types are known as bitumen crudes (in practice, about 30 are usable in Europe).
In a nutshell, bitumen is a blend of hydrocarbons, solid and semi-solid and brown or black in colour. |