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USGS · 70184977

Carbon and oxygen isotopic composition of coal and carbon dioxide derived from laboratory coal combustion: A preliminary study

Peter D. Warwick·Leslie F. Ruppert
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Abstract

The concentration of carbon dioxide (CO 2 ) in the atmosphere has dramatically increased from the start of the industrial revolution in the mid-1700s to present levels exceeding 400 ppm. Carbon dioxide derived from fossil fuel combustion is a greenhouse gas and a major contributor to on-going climate change. Carbon and oxygen stable isotope geochemistry is a useful tool to help model and predict the contributions of anthropogenic sources of CO 2 in the global carbon cycle. Surprisingly few studies have addressed the carbon and oxygen isotopic composition of CO 2 derived from coal combustion. The goal of this study is to document the relationships between the carbon and oxygen isotope signatures of coal and signatures of the CO 2 produced from laboratory coal combustion in atmospheric conditions. Six coal samples were selected that represent various geologic ages (Carboniferous to Tertiary) and coal ranks (lignite to bituminous). Duplicate splits of the six coal samples were ignited and partially combusted in the laboratory at atmospheric conditions. The resulting coal-combustion gases were collected and the molecular composition of the collected gases and isotopic analyses of δ 13 C of CO 2 , δ 13 C of CH 4 , and δ 18 O of CO 2 were analysed by a commercial laboratory. Splits (~ 1 g) of the un-combusted dried ground coal samples were analyzed for δ 13 C and δ 18 O by the U.S. Geological Survey Reston Stable Isotope Laboratory. The major findings of this preliminary work indicate that the isotopic signatures of δ 13 C (relative to the Vienna Pee Dee Belemnite scale, VPDB) of CO 2 resulting from coal combustion are similar to the δ 13 C VPDB signature of the bulk coal (− 28.46 to − 23.86 ‰) and are not similar to atmospheric δ 13 C VPDB of CO 2 (~ − 8 ‰, see http://www.esrl.noaa.gov/gmd/outreach/isotopes/c13tellsus.html ). The δ 18 O values of bulk coal are strongly correlated to the coal dry ash yields and appear to have little or no influence on the δ 18 O values of CO 2 resulting from coal combustion in open atmospheric conditions. There is a wide range of δ 13 C values of coal reported in the literature and the δ 13 C values from this study generally follow reported ranges for higher plants over geologic time. The values of δ 18 O (relative to Vienna Standard Mean Ocean Water) of CO 2 derived from atmospheric combustion of coal and other high-carbon fuels (peat and coal) range from + 19.03 to + 27.03‰ and are similar to atmospheric oxygen δ 18 O VSMOW values which average + 23.8‰. Further work is needed on a broader set of samples to better define the relationships between coal composition and combustion-derived gases.

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Peter D. Warwick, Leslie F. Ruppert. 2016. Carbon and oxygen isotopic composition of coal and carbon dioxide derived from laboratory coal combustion: A preliminary study. https://doi.org/10.1016/j.coal.2016.06.009

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