Asphalt pentane-insoluble constituents

Another method (ASTM D-893) covers the determination of pentane-and toluene-insoluble constituents in used lubricating oils and can be applied to asphalt. Pentane-insoluble constituents include oil-insoluble materials, and toluene-insoluble constituents can come from external contamination and highly carbonized materials from degradation. A significant change in pentane- or toluene=insoluble constituents indicates a change in asphalt properties that could lead to problems in service. The insoluble constituents measured can also assist in evaluating the performance characteristics of asphalt. 

In procedure A, a sample is mixed with pentane and centrifuged, after which the resid or asphalt solution is decanted and the precipitate is washed twice with pentane, dried, and weighed. For toluene-insoluble constituents, a separate sample of the resid or asphalt is mixed with pentane and centrifuged. The precipitate is washed twice with pentane, once with toluene-alcohol solution, and once with toluene. The insoluble material is then dried and weighed. In procedure B, procedure A is followed except that instead of pentane, a pentane-coagulant solution is used. 

Generally, asphalt can be fractionated into four important fractions saturates, aromatics, resins, and asphaltenes . The classic definition of fractions of asphalts is based on the solution properties of petroleum residuum in various solvents. A complete fractionation scheme is given in Figure 1 (1) the oil constituents are propane soluble (2) resins are n-pentane soluble but propane insoluble (3) asphaltenes are toluene soluble but n-pentane insoluble and (4) preasphaltenes are insoluble both in n-pentane and toluene. The fractionated part of oil is generally considered to be a combination of saturates and aromatics. The polarity of these four fractions increases from saturates, to aromatics, to resins, to asphdtenes. 

Crude oil has been characterized as a colloid (1,2) in which high molecular weight, asphaltic particles are dispersed. Such particulates—known as asphaltenes—are held in solution via peptization by lower molecular weight components—classified as resins. This association forms a micellar type structure (3-5). Classification of the asphaltic constituents in crude oil is based primarily upon each component s solubility in various solvents (e.g., the pentane soluble, propane insoluble resin or maltene fraction and the benzene soluble, pentane insoluble asphaltene fraction) (6,7). 

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