Determination of Nitrogen in Petroleum Products by Fast-neutron Activation and Matrix Effects

Abstract

The nitrogen analysis of petroleum products by means of the ¹⁴N (n, 2n) ¹³N reaction with 14 Me V neutrons was investigated. In order to avoid the various errors caused by the variation of the neutron flux, a rotation method, in which both an unknown sample and a standard sample would be irradiated by the same neutron flux, was adopted.
For hydrocarbon samples, the ¹²C (p, r) ¹³N and ¹³C (p, n) ¹³N reactions with recoil protons, matrix effects, have prevented the determination of a small amount of nitrogen. By a series of experiments on the relation between the effects and the compositions of hydrocarbons, it was found that the effects depend only on the weight fraction of carbon (W_c) . Furthermore, it was found that, in the narrow range of the W_c, the effects may be expressed by a linear equation of the weight fraction. This relation has made it possible to obtain the fairly good results for the sample whose W_c-value is known and the nitrogen content is more than 0.1%.
This method is particularly suitable for the analysis of nitrogen in fuel oils because they contain some considerable amounts of nitrogen and have nearly equal W_c-value which is 85%.
About 25 minutes were required for an analysis in the present experiment, but the time will considerably be shortened by increasing the neutron flux and improving the counting technique.