Microwave digestion of petroleum products for elemental analysis using the SRC technology in compliance with the UOP 1005- 1006 methods

Elemental analysis of petroleum products is critical to the petroleum industry for several reasons, ranging from refining processes to environmental compliance, from R&D to troubleshooting and diagnostics, and is usually performed on a wide variety of samples at different stages of the petroleum lifecycle. Each type of organic matrix, including crude oils, refined products, fuel additives, heavy oils, residual oils, petrochemicals and catalysts, provides valuable insights into the processes and products related with petroleum. Especially during the digestion steps, several challenges can be encountered, mainly related to the complex nature of oily matrices and the low concentration levels of some analytes.
The Milestone Single Reaction Chamber (SRC) technology enables petroleum testing labs to increase the digested sample masses, limit the effective volume of reagents and improve the quality of digestion compared to conventional digestion systems by meeting the high temperatures and pressures required by most of these complex matrices. Based on a stainless-steel reactor with a highpurity PTFE-TFM liner and cover, the Milestone ultraWAVE 3 allows the simultaneous digestion even of dissimilar petroleum sample types with different reagents, using disposable glass, quartz or PTFE-TFM vials in a unique batch.

In this study, recovery studies were performed on various Certified Reference Materials to demonstrate the efficiency of Milestone’s SRC technology in the sample preparation of petrochemical matrices for elemental analysis and its compliance with UOP methods.

INSTRUMENT
The Milestone SRC technology maintains uniform temperature and pressure throughout the entire stainless steel chamber, ensuring that each vial undergoes identical digestion conditions even with widely varying samples and acid mixtures. This uniformity significantly increases productivity and digestion quality, eliminating the need to batch similar samples and improving overall turnaround times. In addition, operational safety is ensured by continuous control of the digestion process via the easyTEMP infrared sensor. It constantly monitors the internal temperature of the base load in which the vials are immersed. For the purposes of this study, the following configuration has been adopted:

• Milestone SRC ultraWAVE 3
• 7-positions and 20-positions racks with 40 mL and 15 mL PTFE-TFM and quartz vials
• Analytical balance
• ICP-MS

SAMPLE AND REAGENTS
The performances of ultraWAVE 3 were evaluated through a recovery study on various CRMs including SPEX CertiPrep (organometallic oil), standard Conostan S21 (crude oil), NIST RM 8505 (crude oil), SRM 2718 (green petroleum coke) and calcined petroleum Coke SRM 2719.

According to the UOP 1005-14 and 1006-14 methods, the sample is intially treated with water, then with nitric and hydrofluoric acids to reduce the volatility of some metals. After that, the sample is digested and the final digestate is quantitatively transferred to a separate flask using purified water. Internal monitoring standards are also added before final analysis by ICP-MS.
Silicon is typically present in petroleum matrices as soluble organic silicones, but the UOP 1006- 14 method is also designed to detect other forms of silicon, such as the insoluble inorganic silicon salts and silica. This method is primarily used to analyze reformer charge stock for silicones, but can also be used for refinery charge stocks as heavy as vacuum gas oil (VGO)3.

Sample preparation with ultraWAVE 3 consists of weighing the appropriate sample mass into the vial, adding the required acid mixture and setting the microwave-heating program in accordance with the working conditions reported in Table 1. The results obtained after ICP-OES and ICP-MS analysis can be found in the full document.

As shown during this study, the Milestone SRC ultraWAVE 3 offers a unique approach to handle the challenges related to the digestion of petroleum samples. It ensures a rugged approach for the processing of large numbers of samples, even with mixed batches, while ensuring fast and high-quality digestions.
Analytical data reported in this report demonstrate the robustness and efficiency of Milestone’s ultraWAVE 3 for sample preparation of petroleum matrices as well as its compliance with official UOP methods.