Investigations on bitumen

Data from colloid analysis show that the concentration of the dispersion medium may be related to the distillable fraction AG400, whereas the concentration of asphaltenes, or the total of asphaltenes and petroleum resins, determines the quantity of coke residue after pyrolysis. That portion of the sample which can be cracked, CR, will usually be determined from die concentration of petroleum resins. The aliphatic side chains of the alkylaromatic system of the asphaltenes have a small influence. The coke residue can be related to the data from structural group analysis which describe the aromatic character of the samples. 

Thermogravimetry in air only shows the correlation of data describing the molecule size with those index numbers which are relevant to the evaporation behavior. 

The reaction kinetic constants activation energy E and frequency factor A, can only be correlated with the concentration of paraffinic carbon, CP (from structural group analysis) with the concentration of dispersion medium (fiom colloid analysis) and with the H/C ratio (from elemental analysis). These functions show correlation coefficients of an acceptable magnitude. Examination of the correlation of the concentration of maltenes revealed a similar tendency but with very low coefficients of correlation. It is well known that the dispersion medium contains the highest concentration of chemical bonds, which can be cracked under the chosen reaction conditions [4-20]. In the pyrolysis experiments from distillation residues, about 92 % of the dispersion medium was converted, whereas conversion of the petroleum resins was only 83 %, despite the fact that the kinetic coefficients are of nearly the same magnitude for the two components. 

Bitumens are residues of the vacuum distillation of suitable crude oils (distillation bitumen). Residues of less suitable crudes must be partially oxidized by blowing to achieve the desired technical properties (semi-blown bitumen). Blown bitumens for special purposes can also be produced from vacuum residues. The process is executed by blowing a stream of finely distributed air through the molten bitumen (sometimes reduced in viscosity by addition of flux oil) at temperatures of 250-290 C. 

These data are subject to relative wide tolerance ranges therefore, individual testing of the penetration and the softening point R B is advisable if eventual correlation with other values is attempted, 

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Some overlapping of the evaporation and pyrolysis reactions was observed, due to the content of low boiling flux oils, especially in the experiments with separated components of the colloid system. In order to avoid such overlapping as much as possible and to simulate the technical conditions of the crack processes, further investigations on bitumens and their colloid components were carried out in a hydrocarbon atmosphere (methane) at 10 bar pressure. 

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