Determination of halogens and sulfur in pitch from crude oil by plasma-based techniques after microwave-induced combustion

Abstract

This work demonstrates the feasibility of halogen and sulfur determination in pitch produced from crude oil residues by inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectrometry (ICP-OES), respectively, after digestion by microwave-induced combustion (MIC). Using the proposed system, it was possible to achieve a very effective digestion of pitch (up to 400 mg) using 20 bar of oxygen and 50 mL of 6 mol L À1 of ammonium nitrate as an ignition aid. Water and NH 4 OH solutions (10 to 100 mmol L À1 ) were evaluated for analyte absorption and a reflux step was applied after combustion in order to ensure quantitative analyte absorption. The volume of absorbing solution (6, 8, 10 and 12 mL) was also evaluated and best results were obtained using 6 mL confirming the results of previous studies. Accuracy was evaluated by comparison of results with those obtained using a total Cl and S analyzer, X-ray fluorescence (XRF, for Cl and S determination) and pyrohydrolysis followed by ICP-MS determination (Br and I). By using 50 mmol L À1 NH 4 OH as the absorbing solution the agreement with reference values ranged from 95 to 103% for all analytes. The results obtained using MIC presented an agreement of 101 and 100% with those obtained using a total Cl and S analyzer, respectively. The results were also compared with XRF analysis (for Cl and S) and agreement was 102 and 92%, respectively. In the same way, the results obtained by MIC were in agreement with those obtained by the pyrohydrolysis method (agreement of 97 and 105% for Br and I, respectively). The residual carbon content of MIC digests was always below 1% showing the high efficiency of pitch digestion. Using 400 mg of sample mass and 6 mL of 50 mmol L -1 NH 4 OH as the absorbing solution, limits of detection were 3.1 mg g À1 for S by ICP-OES and 3.2, 0.02 and 0.002 mg g À1 for Cl, Br and I by ICP-MS, respectively.

A Rapid Acid Digestion Technique for the Simultaneous Determination of Bromine and Iodine in Fifty‐Three Chinese Soils and Sediments by ICP‐MS

“…, Pereira et al . ). However, it is difficult to quantitatively extract Br and I from geological materials for ICP‐MS analysis.…”

“…For example, Br and I signatures in serpentinites record progressive dehydration during subduction from shallow oceanic via increased pressure and temperature conditions to breakdown of antigorite (John et al 2011). ICP-MS has been widely used to determine Br and I in various matrices (Larsen and Ludwigsen 1997, Li et al 2002, Pereira et al 2015. However, it is difficult to quantitatively extract Br and I from geological materials for ICP-MS analysis.…”

Challenges and trends for halogen determination by inductively coupled plasma mass spectrometry: A review

“…25,37,81,82,109 Another relatively simple and inexpensive sample preparation Na 2 CO 3 , Na 2 SO 3 , NaOH, or TMAH), being converted into their ionic form. 39,42,113,115,152,153 The pyrohydrolysis system consists of a quartz or silica reactor tube enclosed in an electric furnace. Samples are introduced into a quartz or silica boat into the reactor through one of its extremities, along with water vapor and a carrier gas (air, O 2 , or an inert gas).…”

“…In order to minimize or remove the spectral interferences, a dynamic reaction cell (DRC) has been extensively used for halogen determination by ICP-MS, mainly for chlorine. The main polyatomic interferences 39 for this element are 16 [40][41][42][43] have studied the use of DRC with NH 3 as the reaction gas as an efficient strategy for reducing 35 Cl interferences, resulting in a significant improvement in LOD. 39 Furthermore, a mass-shift approach using DRC with H 2 as the reaction gas has been used to shift 35 Cl to 35 Cl 1 H 1 H + and 37 Cl 1 H 1 H + , leading to lower LODs.…”

Microwave-Induced Combustion of Coal for Further Sulfur Determination by Inductively Coupled Plasma Optical Emission Spectrometry or Ion Chromatography

“…The use of MIC as a method for digestion of organic samples has been demonstrated for many solid matrices such as petroleum coke, 29 pitch, 30 carbon nanotubes, 31 polymers, 32 food and biological materials, [33][34][35] among others. Even though MIC method can be considered simple and a general protocol can be proposed, 36 a careful optimization regarding sample mass and combustion behavior must be performed.…”