Determination of Sulfur in Petroleum Coke Combining Closed Vessel Microwave-Induced Combustion and Inductively Coupled Plasma-Optical Emission Spectrometry

Abstract

A new procedure based on closed vessel Microwave-Induced Combustion (MIC) technique is proposed for the decomposition of petroleum coke and further determination of sulfur by Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES). The procedure is based on sample ignition by microwave radiation using closed quartz vessels pressurized with oxygen and use of NH₄NO₃ as an ignition aid. The nature and concentration of absorbing/refluxing solution were studied, as well as the operational parameters related to MIC technique. Results were compared with those obtained by conventional wet digestion in closed vessels, certified reference materials (agreement was better than 98%), and also using ion chromatography for S determination.

Keywords:

• Inductively coupled plasma-optical emission spectrometry
• ion chromatography
• microwave-induced combustion
• petroleum coke
• sulfur determination

The authors are grateful to CNPq, CAPES, and FAPERGS for supporting this study and also to CENPES/PETROBRAS S.A. for financial support and for supplying the petroleum coke samples.

Notes

∗initial O₂ pressure = 20 bar, 6 mL H₂O as absorbing solution, n ≥ 10.

^a 150 mg of sample, initial O₂ pressure = 20 bar, 6 mL of absorbing solution.

^b certified value for sulfur in CRM NIST 2718 (green petroleum coke) = 47030±79 µg g⁻¹.

∗150 mg of sample mass, initial O₂ pressure = 20 bar, 6 mL 0.05 mol L⁻¹ (NH₄)₂CO₃ as absorbing solution, 50 µL of 6 mol L⁻¹ NH₄NO₃.