溶融塩の腐食作用の低減(Reducing molten salt’s corrosive effect)

2022-10-04

2022-10-03 オークリッジ国立研究所(ORNL)

科学者たちは最近、溶融塩化物塩を精製するための低温で安全な方法を実証し、金属を腐食させる能力を最小限に抑えることに成功した。この方法により、塩化物溶融塩が太陽の熱から生成されるエネルギーを貯蔵するのに役立つ可能性がある。
実験では、塩化チオニルを使って、溶融塩から腐食の原因となる不純物を除去している。塩化チオニルを使用しないと、塩がパイプや貯蔵タンクを腐食させるからだ。
研究チームは、太陽熱エネルギー貯蔵用に検討されている豊富な鉱石である市販のカルナライトを溶かし、塩化チオニルを飽和させた不活性ガスに接触させて反応させた。塩の温度を測定し、赤外分光法で放出されるガスを分析することで、反応状況を監視した。

＜関連情報＞

塩化チオニル蒸気との反応による酸素、酸素含有化合物、水酸化物の除去による塩化物塩の精製法
Chloride Salt Purification by Reaction With Thionyl Chloride Vapors to Remove Oxygen, Oxygenated Compounds, and Hydroxides

Joanna McFarlane, Guillermo D. Del Cul, Jordan R. Massengale, Richard T. Mayes, Kevin R. Robb and Dino Sulejmanovic
Frontiers of Chemical Engineering Published:25 April 2022
DOI:https://doi.org/10.3389/fceng.2022.811513

Molten chloride salts (including MgCl₂, KCl, NaCl, and ZnCl₂) are being considered for heat transfer media for renewable (solar) and nuclear power generators, as fuel carrier for nuclear reactors, and as thermal energy storage media. Impurities such as oxygen, hydroxides, moisture, and sulfur are known to negatively influence the corrosion of materials in contact with the salt (e.g., structural metals). Commercially available chloride salts come with a range of impurities. Before using the chloride salts at high temperature, it is desirable to remove the impurities to increase the performance of the salt and reduce corrosion. In this study, we tested the use of thionyl chloride vaporized into a stream of argon to react with oxygenated impurities in a mixture of MgCl₂-KCl-NaCl, removing them as HCl and SO₂. The reagent was bubbled through the salt when both above and below the melting point. The reaction was followed using thermocouple data from the salt and by Fourier transform infrared (FTIR) spectroscopy on the exhaust of the reactor. The reaction kinetics were followed by comparing the peaks from SO₂ product to SOCl₂ reagent in the FTIR spectra. The purity of the salt was assessed at the end of the purification process by x-ray diffraction and inductively coupled plasma analysis. Although the process was effective in removing the oxygen content of the mixture, ternary compounds were formed in the process, including KNiCl₃ and KMgCl₃. The nickel in KNiCl₃ came from the reaction between the salt and the nickel vessel. Thus, these experiments suggest that improvements to the process must be made before using SOCl₂ vapors for the purification of chloride salts.