Methodology for the determination of minor and trace elements in petroleum cokes by wavelength-dispersive X-ray fluorescence (WD-XRF)

Abstract

This article describes a methodology for the analysis of minor and trace elements in petroleum cokes by wavelength-dispersive X-ray fluorescence (WD-XRF) spectrometry. The methodology was developed in order to have a rapid and reliable control method of these elements, because they determine coke end uses. There are a number of standard methods of chemical analysis by WD-XRF or inductively coupled plasma atomic emission spectrometry (ICP-OES) techniques. However, the standards that use WD-XRF measurement give detection limits (LD) above 10 mg·kg−1 and only analyse a few elements of interest, whereas the ICP-OES method requires extensive sample handling and long sample preparation times, with the ensuing errors. In order to improve the method described in the standard ASTM D6376 and reach the LD and quantification limits (LQ) required, the different stages of the process, ranging from sample preparation to measurement conditions: analytical line, detector, crystal, tube power, use of primary beam filters, and measurement time, were optimised. The samples were prepared in the form of pressed pellets, under conditions of high cleanliness of the mills, crushers, presses, and dies, and of the laboratory itself. The following reference materials were used in measurement calibration and validation: SRM 1632c, SRM 2718, SRM 2719, SRM 2685b, AR 2771, AR 2772, SARM 18, SARM 19, and CLB-1. In addition, a series of materials were analysed by WD-XRF and ICP-OES, and the results were compared. The developed methodology, which uses WD-XRF, is rapid and accurate, and very low LD and measurement uncertainties were obtained for the following elements: Al, Ba, Ca, Cr, Cu, Fe, Ge, K, Mg, Mn, Mo, Na, Ni, P, Pb, S, Sb, Se, Si, Sn, Sr, Ti, V, and Zn. Copyright © 2010 John Wiley & Sons, Ltd.