Application of sodium carbonate prevents sulphur poisoning of catalysts in automated total mercury analysis

• Published in: Spectrochimica acta. Part B: Atomic spectroscopy Vol. 133; pp. 60 - 62
• Main Authors: McLagan, David S., Huang, Haiyong, Lei, Ying D., Wania, Frank, Mitchell, Carl P.J.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.07.2017
• Subjects: Atomic absorption spectroscopy (AAS); Sodium carbonate additive; Sulphur catalyst poisoning; Thermal decomposition; Total mercury (THg) analysis; Total mercury (THg) analysis; Atomic absorption spectroscopy (AAS); Sodium carbonate additive; Thermal decomposition; Sulphur catalyst poisoning
• ISSN: 0584-8547; 1873-3565
• DOI: 10.1016/j.sab.2017.04.014

Analysis of high sulphur-containing samples for total mercury content using automated thermal decomposition, amalgamation, and atomic absorption spectroscopy instruments (USEPA Method 7473) leads to rapid and costly SO2 poisoning of catalysts. In an effort to overcome this issue, we tested whether the addition of powdered sodium carbonate (Na2CO3) to the catalyst and/or directly on top of sample material increases throughput of sulphur-impregnated (8–15wt%) activated carbon samples per catalyst tube. Adding 5g of Na2CO3 to the catalyst alone only marginally increases the functional lifetime of the catalyst (31±4g of activated carbon analyzed per catalyst tube) in relation to unaltered catalyst of the AMA254 total mercury analyzer (17±4g of activated carbon). Adding ≈0.2g of Na2CO3 to samples substantially increases (81±17g of activated carbon) catalyst life over the unaltered catalyst. The greatest improvement is achieved by adding Na2CO3 to both catalyst and samples (200±70g of activated carbon), which significantly increases catalyst performance over all other treatments and enables an order of magnitude greater sample throughput than the unaltered samples and catalyst. It is likely that Na2CO3 efficiently sequesters SO2, even at high furnace temperatures to produce Na2SO4 and CO2, largely negating the poisonous impact of SO2 on the catalyst material. Increased corrosion of nickel sampling boats resulting from this methodological variation is easily resolved by substituting quartz boats. Overall, this variation enables an efficient and significantly more affordable means of employing automated atomic absorption spectrometry instruments for total mercury analysis of high-sulphur matrices. [Display omitted] •Sulphur-impregnated activated carbon poisons catalysts in total mercury analysis.•Addition of powdered Na2CO3 increases catalyst life by an order of magnitude.•Best catalyst performance when Na2CO3 is added to sample boats and catalyst tube.•Quartz boats preferable to nickel as nickel is corroded by Na2CO3 and SO2 reaction.