Stable carbon isotope fractionation data between H(2)CO(3)(*) and CO(2)(g) extended to 120 °C.
Stable carbon isotope fractionation data between H(2)CO(3)(*) and CO(2)(g) extended to 120 °C.
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DOI：
10.1002/rcm.6950
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发表时间：
2014-08
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通讯作者：
A. Myrttinen;V. Becker;Bernhard Mayer;Johannes A. C. Barth
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文献类型：
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作者：
A. Myrttinen;V. Becker;Bernhard Mayer;Johannes A. C. Barth
理论依据关于H2 CO 3（*）（H2 CO 3 + CO2（aq））和气态CO2（CO2（g））之间实验得出的平衡稳定碳同位素分馏（10（3）lnα（13）C）的文献数据迄今为止仅在高达60 °C下可用，并且通常在大气压或接近大气压下测定。在这里，我们通过实验将该数据集扩展到接近CO2超临界状态的温度和压力条件。其目的是提高稳定碳同位素作为示踪剂在环境中的适用性，在这种情况下盛行。方法在钢制容器中进行了18个稳定碳同位素实验。将用盐酸（HCl，1 N）酸化至pH为2.4的去离子水用CO2（g）在55巴的压力（pCO 2）下平衡2至188小时的持续时间。实验在20、60、80、100和120 °C下进行。H2、CO 3（*）和CO2（g）分别取样，用同位素比值质谱法测定其碳同位素比值。结果在20 °C下，观察到平均10（3）In α（13）CH 2CO 3 * -CO2（g）值为-1.0 ± 0.1 ‰，优先使用H2 CO 3中的（12）C（*）与之前的研究一致。在120 °C的高温下，10（3）lnα（13）CH 2CO 3 * -CO2（g）值降至平均值-0.7 ± 0.1 ‰。H2 CO 3（*）和CO2（g）之间碳同位素分馏的温度依赖关系为10（3）lnα（13）CH 2CO 3 * -CO2（g）=（0.0025 ± 0.0004）T（℃）-（1.0 ± 0.03）‰。H2 CO 3（*）和CO2（g）之间的碳同位素平衡在反应时间18 h内达到，大部分在5 h或更短时间内达到。结论10（3）lnα（13）CH 2CO 3 * -CO2（g）数据现在可用于温度高达120 °C和压力高达55 bar的情况。结果表明，较高的pCO 2水平可能缩短碳同位素平衡时间。这些数据对于使用δ（13）C值作为示踪剂至关重要，例如在地质CO2封存地点和相应的天然类似物中。
RATIONALE Literature data on experimentally derived equilibrium stable carbon isotope fractionation (10(3) lnα(13) C) between H2 CO3 (*) (H2 CO3 + CO2(aq) ) and gaseous CO2 (CO2(g) ) are so far only available up to 60 °C and were typically determined at or near atmospheric pressures. Here we experimentally expand this dataset to temperature and pressure conditions close to the supercritical state for CO2 . The objective is to improve the applicability of stable carbon isotopes as a tracer in environments where such conditions prevail. METHODS Eighteen stable carbon isotope laboratory experiments were conducted in a steel vessel. Deionised water that was acidified with hydrochloric acid (HCl, 1 N) to a pH of 2.4 was equilibrated with CO2(g) at pressures (pCO2 ) of 55 bar for durations between 2 and 188 h. The experiments were conducted at 20, 60, 80, 100 and 120 °C. H2 CO3 (*) and CO2(g) were sampled separately and their carbon isotope ratios were determined by isotope ratio mass spectrometry. RESULTS At 20 °C, average 10(3) lnα(13) CH2CO3 * -CO2(g) values of -1.0 ± 0.1 ‰ were observed with a preference for (12) C in H2 CO3 (*) consistent with previous research. At elevated temperatures of 120 °C, 10(3) lnα(13) CH2CO3 * -CO2(g) values decreased to an average value of -0.7 ± 0.1 ‰. The resulting temperature dependence for carbon isotope fractionation between H2 CO3 (*) and CO2(g) was 10(3) lnα(13) CH2CO3 * -CO2(g) = (0.0025 ± 0.0004) T(°C) - (1.0 ± 0.03) ‰. Carbon isotope equilibrium between H2 CO3 (*) and CO2(g) was reached within reaction times of 18 h and mostly within 5 h or less. CONCLUSIONS 10(3) lnα(13) CH2CO3 * -CO2(g) data are now available for temperatures up to 120 °C and for pressures of up to 55 bar. The results suggest that higher pCO2 levels possibly shorten carbon isotope equilibration times. These data are critically important for using δ(13) C values as tracers, for instance at geological CO2 sequestration sites and corresponding natural analogues.