Longer chain n-alkanes

Although the ability to cope with complex mixtures of fuels may be some way off, dealing with alkane mixtures is certainly within our grasp. However, there appears to be one key aspect that requires clarification. From the evidence in Section 6.4, it is clear that the longer chain n-alkanes, such as n-heptane, can undergo spontaneous ignition at very low-temperatures. This is in marked contrast to the lower reactivity of the shorter n-alkane chains such as n-butane, or of highly branched isomers... 

There is ample experimental evidence for the formation of alkyldihydro-peroxides, especially from the longer chain n-alkanes (Section 6.5) but, as noted in Chapter 1, the rate of chain branching which arises from the homolysis of molecular hydroperoxides, regardless of whether they are alkyl hydroperoxides or dihydroperoxides, is too slow to account for the short duration of ignition delays in high-pressure gases at low-temperature. There is also experimental evidence for the formation of alkylketohydro-peroxy radicals of the form... 

It might also be expected during lateral migration within the Chalk that the longer chain n-alkanes and other less mobile constituents would be retarded. This geochromatographic effect explains the slightly lower wax contents in the Joanne Chalk oils. 

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