Kitami Institute of Technology, Graduate School of Engineering, 165 Koen-cho, Kitami 090-8507, Japan.
National Metrology Institute of Japan (NMIJ), National Institute of Advanced Industrial Science and Technology (AIST), Central 5, Higashi 1-1-1, Tsukuba 305-8565, Japan.
Molecules. 2021 Jul 11;26(14):4215. doi: 10.3390/molecules26144215.
Knowledge of carbon isotope fractionation is needed in order to discuss the formation and dissociation of naturally occurring CO hydrates. We investigated carbon isotope fractionation during CO hydrate formation and measured the three-phase equilibria of CO-HO and CO-HO systems. From a crystal structure viewpoint, the difference in the Raman spectra of hydrate-bound CO and CO was revealed, although their unit cell size was similar. The δC of hydrate-bound CO was lower than that of the residual CO (1.0-1.5‰) in a formation temperature ranging between 226 K and 278 K. The results show that the small difference between equilibrium pressures of ~0.01 MPa in CO and CO hydrates causes carbon isotope fractionation of ~1‰. However, the difference between equilibrium pressures in the CO-HO and CO-HO systems was smaller than the standard uncertainties of measurement; more accurate pressure measurement is required for quantitative discussion.
为了讨论天然 CO 水合物的形成和分解，需要了解碳同位素分馏的知识。我们研究了 CO 水合物形成过程中的碳同位素分馏，并测量了 CO-HO 和 CO-HO 体系的三相平衡。从晶体结构的角度来看，尽管它们的晶胞大小相似，但水合 CO 和 CO 的拉曼光谱存在差异。在 226 K 至 278 K 的形成温度范围内，水合 CO 中 δC 的值低于剩余 CO（1.0-1.5‰）。结果表明，CO 和 CO 水合物之间约 0.01 MPa 的平衡压力差导致了约 1‰的碳同位素分馏。然而，CO-HO 和 CO-HO 体系之间的平衡压力差小于测量的标准不确定度；需要更准确的压力测量来进行定量讨论。
