Elemental Analysis of Crude and Lubricating Oils by Energy Dispersive X-Ray Fluorescence

Abstract

Most aspects of petroleum research, exploration, and refining require elemental analysis from trace to minor elemental concentrations. Numerous elements ranging from atomic numbers 15 to 92 can be found in many crudes. Elements such as vanadium, iron, nickel, copper, and arsenic can have deleterious effects on the catalysts utilized in the catalytic cracking process. Other elements purposely introduced as additives into finished lubricating oils must also be measured and controlled. Typically elements such as phosphorus, sulphur, calcium, zinc, and molybdenum are in the range of 0.00 to 5.00 wt%. In addition to crude oils and finished lubricating oils, engine and turbine bearing wear analysis are often performed by X-ray fluorescence. In these cases, typical bearing and piston ring elements such as copper, chromium, zinc, lead, tin, and silver are usually quantified. The techniques for preparing samples of crude oil, finished lubricating oils, and used engine oils are basically identical. The sample is transferred into a polypropylene sample cup with a 6.3 μm polypropylene support film. Errors in volume or sample depth can produce significant intensity deviations for higher energy X-rays. The error for lead, for example, is approximately 1.5% relative per 0.1 mL error at volumes of 3 mL. Minimum detectable limits or several tenths of parts per million for atomic numbers 30 to 92 from a range of 5 to 800 parts per million can be expected.