Measurements of 13C/12C Methane from Anaerobic Digesters: Comparison of Optical Spectrometry with Continuous-Flow Isotope Ratio Mass Spectrometry

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• 作者：Frank Keppler ; Stephan Laukenmann ; Jennifer Rinne ; Hauke Heuwinkel ; Markus Greule ; Michael Whiticar ; Jos Lelieveld
• 刊名：Environmental Science & Technology
• 出版年：2010
• 出版时间：July 1, 2010
• 年：2010
• 卷：44
• 期：13
• 页码：5067-5073
• 全文大小：220K
• 年卷期：v.44,no.13(July 1, 2010)
• ISSN：1520-5851

文摘

Methane production by anaerobic digestion of biomass has recently become more attractive because of its potential for renewable energy production. Analytical tools are needed to study and optimize the ongoing processes in biogas reactors. It is considered that optical methods providing continuous measurements at high temporal resolution of carbon isotope ratios of methane (δ¹³C_CH4) might be of great help for this purpose. In this study we have tested near-infrared laser optical spectrometry and compared it with conventional continuous-flow isotope ratio mass spectrometry (CF-IRMS) using several methane carbon isotope standards and a large number of biogas samples from batch anaerobic reactors. Results from measurements on these samples were used to determine and compare the precision of the two techniques and to quantify for systematic offsets. With pure standards analytical precision of measurements for δ¹³C_CH4 was found to be in the range of 0.33 and 0.48‰, and 0.09 and 0.27‰ for the optical method and CF-IRMS, respectively. Biogas samples showed an average mean deviation of δ¹³C_CH4 of 0.38‰ and 0.08‰ for the optical method and CF-IRMS, respectively. Although the tested laser optical spectrometer showed a dependence of δ¹³C_CH4 on CH₄ mixing ratio in the range of 500 to 8000 ppm this could be easily corrected. After correction, the δ¹³C_CH4 values usually varied within 0.7‰ from those measured by conventional CF-IRMS and thus results from both methods agreed within the given analytical uncertainties. Although the precision of the conventional CF-IRMS is higher than the tested optical system, both instruments were well within the acceptable δ¹³C_CH4 precision required for biogas methane measurements. The advantages of the optical system are its simplicity of operation, speed of analysis, good precision, reduced costs in comparison to IRMS, and the potential for field applications.