Determination of n-paraffinic structure in petroleum fraction by infrared spectroscopy

The characteristic strong absorption infrared band near 720–725 cm−1 of an open chain methylene group of the type (CH2) n (n = 4 or more) has been used to estimate the number of n-paraffinic methylene groups in an average molecule of saturates, urea adductables and non-adductables of various gas-oil and vacuum gas oil fractions. The method was developed by computing the average absorptivity at 725 cm−1 of several pure n-paraffins (C14-C32). Although the interference due to the aromatic C — H band at 740 cm−1 disturbs the estimation of shorter chains, it is seen from the data on adductables and non-adductables that the estimation can be done in long chain paraffins even in the presence of aromatics.