The Use of WDXRF in the Petroleum and Oil Industry

WDXRF stands for Wavelength Dispersive X-ray Fluorescence. It is an analytical technique that uses primary X-rays to excite atoms in a sample, causing them to emit fluorescent X-rays with specific wavelengths and energies characteristic of each element. By measuring the intensity of these fluorescent X-rays, the elemental composition and concentration of a sample can be determined. In the petroleum and petrochemical industries, WDXRF is a valuable tool used throughout the entire process, from exploration and exploitation to refining and quality control of end products. It's used to analyze rock structures, the quality of materials used in wells (steel, cement), crude oil composition, refined products (gasoline, lubricating oils), and even petrochemical products like plastics and polymers.

Why is WDXRF analysis important in the petroleum and petrochemical industries?

WDXRF is crucial for several reasons. It helps determine the elemental composition of various materials encountered at different stages, aiding in exploration decisions, ensuring the quality of materials used in infrastructure, and monitoring contaminants and additives in crude oil, refined products, and lubricating oils. This analysis supports quality control, process optimization, and compliance with various industry standards (like ASTM and ISO methods for sulfur and chlorine). Rigaku highlights that WDXRF can analyze mineral elements at every step of the refining and petrochemical processes.

• Qualitative Analysis: Simply identifies which elements are present in a sample based on the positions of peaks in a spectrum.
• Semi-Quantitative Analysis (SQX): Quantifies element concentrations based on peak heights and a database of intensities from pure standards. It's suitable when the matrix (the main component) of the sample is more or less known and calculated to sum to 100%.
• Semi-Quantitative X-ray Scatter FP Method (SQX ScatterFP): An advanced semi-quantitative method that uses scattered X-ray tube lines (specifically the Compton peak) to estimate the influence of light elements (hydrogen to oxygen) that are difficult to measure directly with XRF. This method is particularly useful for samples with unknown matrices, such as sludges, waste oils, or organic samples.
• Quantitative Analysis: The most accurate method, which uses calibration curves generated from certified reference materials (CRMs) to determine precise element concentrations.

The oil solidification method is a unique approach to analyzing liquid oil samples by converting them into a solid form. This is achieved by mixing the oil with a solidification agent (like stearic acid), melting, homogenizing, and then cooling the mixture in a mold. The advantages of this method include eliminating leakage risks during analysis, preventing settling of compounds in heavy fuels, allowing analysis in a vacuum atmosphere (reducing or eliminating the need for helium, which can be expensive or difficult to obtain), and improving sensitivity and detection limits for light elements (like sodium and magnesium) by avoiding absorption from sample films.

The SQX Scatter FP method utilizes the scattered X-ray tube lines, particularly the incoherent scattering (Compton effect), to gain information about the average matrix composition, especially the influence of light elements that cannot be directly measured with XRF. When primary photons from the X-ray tube interact with a sample, some are scattered. The Compton peak, which is always present in a WDXRF spectrum, arises from incoherent scattering where photons lose some energy. The position and height of this Compton peak vary depending on the sample matrix. For example, a hydrocarbon sample (light matrix) shows a higher Compton peak than an inorganic sample (heavy matrix). By measuring and analyzing the Compton peak, the software can estimate the contribution of light elements and correct for their influence on the measured intensities of other elements, improving the accuracy of the analysis for samples with unknown or variable matrices

OIL-MULTI-PAK is a pre-calibrated method offered by Rigaku, specifically designed for their ZSX Primus IVi spectrometer, to provide screening analysis for 27 elements in a wide range of petroleum and petrochemical products. It's a comprehensive package that includes integrated correction methods for matrix effects (like varying carbon, hydrogen, and oxygen content), sample weight variations, and sample film absorption. This allows for the analysis of diverse sample types with a single calibration, including crude oil, heavy fuels (for natural catalyst elements and mineral elements), refined/distillation products (contaminants), lubricating oils (additives and wear metals), and biofuels. The method aims to provide good accuracy, relatively short measurement times (around 20 minutes for 27 elements), and good detection limits with simple sample preparation.

The OIL-MULTI-PAK incorporates several automatic correction methods to ensure accurate analysis across different petroleum products and sample conditions:

• CHO (Hydrocarbon and Oxygen) correction: Uses information from scattered X-rays (the Compton peak) to automatically correct for the varying concentrations of carbon, hydrogen, and oxygen in different oil matrices.
• Sample weight correction: Utilizes the integrated intensity of the Rhodium Compton peak (from the X-ray tube anode) to correct for variations in sample weight, allowing analysis even with less than the standard amount of sample.
• Sample film correction: Accounts for the absorption of X-rays by the sample film used to hold liquid samples. Different film materials and thicknesses absorb X-rays to varying degrees, especially for light elements. This correction allows the use of different films while still applying the same fundamental parameter calibration.
• Geometry effect correction: Corrects for the fact that WDXRF analyzes a specific area or volume of the sample, which can vary depending on the sample amount, rather than the entire volume, especially in liquid samples.

Selecting the right WDXRF spectrometer is crucial and requires careful consideration of several factors:

• Analytical Task and Objectives: What specific applications and analyses are needed?
• Matrices and Materials: What types of samples will be analyzed (liquids, solids, powders, etc.)?
• Elements and Concentration Ranges: Which elements are of interest, and what are their expected concentration levels?
• Detection Limits: What level of sensitivity and detection limits are required?
• Software Usability: Is the software user-friendly and suitable for the intended applications?
• Sample Preparation Tools: Are the necessary sample preparation tools (like presses, fusion machines, solidification kits) available or budgeted for?
• Budget: What is the available budget for the spectrometer and associated equipment?
• Support: Is adequate service and application support available from the manufacturer or vendor?
• Future Needs: Consider potential future analytical needs that may require different capabilities. Rigaku offers various models tailored to specific applications and elemental ranges. The ZSX Primus IVi, with its tube-below geometry and ability to handle diverse methods and analysis types, is highlighted as a model of significant importance for petroleum analysis.