5:15 PM - 7:15 PM
[PCG21-P07] Mass spectroscopy of thermal decomposition of macromolecular organic matter under low gas pressure environment
Organic matter is mainly composed of C, H, N, O, which are volatile and abundant elements in space. Due to their volatile nature, the abundances of those elements in meteorites and returned asteroid samples (Ryugu and Bennu) [e.g., 1-4] are depleted compared to the solar abundance. Such deficits are sometimes attributed to the irreversible thermal decomposition of organic matter at the soot (tar) line of protoplanetary disks prior to planetesimal formation.
Previous studies [e.g., 5, 6] have evaluated the soot line temperature from experiments of the thermal decomposition of terrestrial kerogen in an Ar gas flow [7, 8] or molecular cloud organic matter simulants in vacuum [6]. However, no systematic experiments have been conducted on the thermal decomposition of various macromolecular organic matter under more plausible conditions. We have begun thermal decomposition of insoluble organic matter (IOM) from Murchison carbonaceous chondrite (CM2) and molecular cloud organic matter simulants in vacuum to investigate the thermal decomposition behaviors of macromolecular organic matter under protoplanetary disk conditions.
IOM was extracted from Murchison chondrite at Kyushu University. Molecular cloud organic matter simulants with the same composition as [6] were prepared by mixing chemical reagents in a nitrogen-filled glove box. In our preliminary experiment, the IOM sample was heated in a gold mirror vacuum furnace [e.g., 9], and released gases were monitored during heating using quadrupole mass spectrometer (QMS; MKS Microvision 2; m/z 1-100). For identifying gases specifically released from each sample, each QMS data was compared with a blank experiment and normalized to the weight of sample.
When the Murchison IOM was heated up to 1000°C at the rate of 20 K/min, H2O (m/z 18), CO (m/z 28), and CO2 (m/z 44) were the dominant released gases during heating. A total gas release pattern from IOM has two peaks, at ~220°C and ~430°C, where H2O, CO, and CO2 were also released significantly. At higher temperature (>600°C), H2 (m/z 2) and HCN/C2H3 (m/z 27) became dominant released gases. About 64% of the initial mass was left as a residue after heating to 1000°C (heated up from room temperature at 20 K/min), which is consistent with the observation by [10], where the Murchison IOM was heated in a He-flow at 10 K/min. At the meeting, we will also discuss the gas release patterns from molecular cloud organic matter simulants.
References: [1] Yokoyama T. et al. (2023) Science 379, eabn7850. [2] Lauretta D. S., Connolly H. C., Jr. et al. (2024) MaPS. 59(9), 2453. [3] Naraoka H. et al. (2023) Science 379, eabn9033. [4] Oba Y. et al. (2023) Nat. Commun. 14, 1. [5] Li J. et al. (2021) Sci. Adv. 7, eabd3632. [6] Nakano H. et al. (2003) ApJ. 592, 1252. [7] Burnham A. K. et al. (1987) Energy Fuels 1, 452. [8] Chyba C. F. et al. (1990) Science 249(4967), 366. [9] Yamamoto D. and Tachibana S. (2018) ACS Earth Space. Chem. 2(8), 778. [10] Komiya M. and Shimoyama A. (1996) Bul. Chem. Soc. Jpn. 69, 53.
Previous studies [e.g., 5, 6] have evaluated the soot line temperature from experiments of the thermal decomposition of terrestrial kerogen in an Ar gas flow [7, 8] or molecular cloud organic matter simulants in vacuum [6]. However, no systematic experiments have been conducted on the thermal decomposition of various macromolecular organic matter under more plausible conditions. We have begun thermal decomposition of insoluble organic matter (IOM) from Murchison carbonaceous chondrite (CM2) and molecular cloud organic matter simulants in vacuum to investigate the thermal decomposition behaviors of macromolecular organic matter under protoplanetary disk conditions.
IOM was extracted from Murchison chondrite at Kyushu University. Molecular cloud organic matter simulants with the same composition as [6] were prepared by mixing chemical reagents in a nitrogen-filled glove box. In our preliminary experiment, the IOM sample was heated in a gold mirror vacuum furnace [e.g., 9], and released gases were monitored during heating using quadrupole mass spectrometer (QMS; MKS Microvision 2; m/z 1-100). For identifying gases specifically released from each sample, each QMS data was compared with a blank experiment and normalized to the weight of sample.
When the Murchison IOM was heated up to 1000°C at the rate of 20 K/min, H2O (m/z 18), CO (m/z 28), and CO2 (m/z 44) were the dominant released gases during heating. A total gas release pattern from IOM has two peaks, at ~220°C and ~430°C, where H2O, CO, and CO2 were also released significantly. At higher temperature (>600°C), H2 (m/z 2) and HCN/C2H3 (m/z 27) became dominant released gases. About 64% of the initial mass was left as a residue after heating to 1000°C (heated up from room temperature at 20 K/min), which is consistent with the observation by [10], where the Murchison IOM was heated in a He-flow at 10 K/min. At the meeting, we will also discuss the gas release patterns from molecular cloud organic matter simulants.
References: [1] Yokoyama T. et al. (2023) Science 379, eabn7850. [2] Lauretta D. S., Connolly H. C., Jr. et al. (2024) MaPS. 59(9), 2453. [3] Naraoka H. et al. (2023) Science 379, eabn9033. [4] Oba Y. et al. (2023) Nat. Commun. 14, 1. [5] Li J. et al. (2021) Sci. Adv. 7, eabd3632. [6] Nakano H. et al. (2003) ApJ. 592, 1252. [7] Burnham A. K. et al. (1987) Energy Fuels 1, 452. [8] Chyba C. F. et al. (1990) Science 249(4967), 366. [9] Yamamoto D. and Tachibana S. (2018) ACS Earth Space. Chem. 2(8), 778. [10] Komiya M. and Shimoyama A. (1996) Bul. Chem. Soc. Jpn. 69, 53.