Feasibility of Microwave-Induced Combustion for Digestion of Crude Oil Vacuum Distillation Residue for Chlorine Determination

Abstract

The microwave-induced combustion (MIC) method was applied for digestion of crude oil vacuum distillation residue for further chlorine determination. Ignition was performed by microwave radiation using a microwave oven designed for conventional pressurized wet digestion. Combustion was carried out using 20 bar of oxygen and NH 4 NO 3 as the igniter. Water or H 2 O 2 , Na 2 CO 3 , and (NH 4 ) 2 CO 3 solutions were investigated for analyte absorption as well as the necessity of a reflux step. Digests were suitable to be analyzed by inductively coupled plasma optical emission spectrometry and ion chromatography. Accuracy was evaluated using spiked samples and certified reference materials of coal (BCR 181) and fuel oil (NIST 1634c). Recoveries for Cl were in the range of 98.4-100.2% for all investigated solutions using the reflux step. The agreement with certified values was better than 95% using 25 mmol L -1 (NH 4 ) 2 CO 3 as the absorbing solution and reflux step. Poor recoveries for Cl were observed using microwave-assisted wet digestion and water extraction procedures. Residual carbon content for MIC was below 1%, whereas it was about 20% using microwave-assisted wet digestion. Using MIC, up to 400 mg of sample could be decomposed and digestion was complete in less time (5 min for combustion and 20 min for cooling) in comparison to other conventional procedures (more than 1 h). Up to eight samples could be digested simultaneously, making the proposed procedure suitable for further routine Cl determination in oil refineries.

Bromine and chlorine determination in cigarette tobacco using microwave-induced combustion and inductively coupled plasma optical emission spectrometry

“…A reflux step can be applied after combustion, assuring an effective washing of vessel walls and holder surface, which is a great advantage over the classic combustion systems, where the cleaning step of the vessel must be performed manually. This method has been successfully applied for digestion of biological samples, 24,25 elastomers, 26 coal 27 and crude oil products [28][29][30][31][32][33] for subsequent metal and halogens determinations. In this work different cigarette tobacco samples were digested by MIC and further Br and Cl determination was performed by ICP OES.…”

Analytical methods for the determination of halogens in bioanalytical sciences: a review

“…A few microliters of ammonium nitrate is added to the filter paper to aid combustion [58,118]. MIC has been applied for many analytes and matrices such as food [58,111,120,121], botanical samples [83,86,122,123], soil [124], and petroleum-related matrices [125][126][127][128][129][130][131]. Dilute alkaline solutions are required to ensure quantitative recoveries for halogens when using MIC and to avoid losses, especially for bromine and iodine [58,91].…”

Microwave-Induced Combustion

“…Several works published in literature regarding to halogens analysis in many types of matrices have proposed the use of diluted alkaline solution for analytes retention, as ammonium carbonate [23,27,38,43,47,49,50] or ammonium hydroxide [31] or even water [56]. In most cases for halogens absorption, ammonium carbonate is preferred as absorbing solution.…”