Department of Energy, Environmental & Chemical Engineering, Washington University in St. Louis, St. Louis, Missouri 63130, United States.
Environ Sci Technol. 2021 Feb 2;55(3):1545-1554. doi: 10.1021/acs.est.0c03685. Epub 2021 Jan 15.
In hydraulic fracturing fluids, the oxidant persulfate is used to generate sulfate radical to break down polymer-based gels. However, sulfate radical may be scavenged by high concentrations of halides in hydraulic fracturing fluids, producing halogen radicals (e.g., Cl, Cl, Br, Br, and BrCl). In this study, we investigated how halogen radicals alter the mechanisms and kinetics of the degradation of organic chemicals in hydraulic fracturing fluids. Using a radical scavenger (i.e., isopropanol), we determined that halogenated products of additives such as cinnamaldehyde (i.e., α-chlorocinnamaldehyde and α-bromocinnamaldehyde) and citrate (i.e., trihalomethanes) were generated via a pathway involving halogen radicals. We next investigated the impact of halogen radicals on cinnamaldehyde degradation rates. The conversion of sulfate radicals to halogen radicals may result in selective degradation of organic compounds. Surprisingly, we found that the addition of halides to convert sulfate radicals to halogen radicals did not result in selective degradation of cinnamaldehyde over other compounds (i.e., benzoate and guar), which may challenge the application of radical selectivity experiments to more complex molecules. Overall, we find that halogen radicals, known to react in advanced oxidative treatment and sunlight photochemistry, also contribute to the unintended degradation and halogenation of additives in hydraulic fracturing fluids.
在水力压裂液中，过硫酸盐氧化剂被用于生成硫酸根自由基以分解基于聚合物的凝胶。然而，硫酸根自由基可能会被水力压裂液中高浓度的卤化物猝灭，生成卤基自由基（如 Cl、Cl、Br、Br 和 BrCl）。在这项研究中，我们研究了卤基自由基如何改变水力压裂液中有机化学品降解的机制和动力学。我们使用自由基清除剂（异丙醇），确定了肉桂醛（如α-氯肉桂醛和α-溴肉桂醛）和柠檬酸盐（如三卤甲烷）等添加剂的卤代产物是通过涉及卤基自由基的途径生成的。我们接下来研究了卤基自由基对肉桂醛降解速率的影响。硫酸根自由基向卤基自由基的转化可能导致有机化合物的选择性降解。令人惊讶的是，我们发现，向体系中添加卤化物将硫酸根自由基转化为卤基自由基，并不会导致肉桂醛相对于其他化合物（如苯甲酸酯和瓜尔胶）的选择性降解，这可能会对基于自由基选择性实验的更复杂分子的应用提出挑战。总的来说，我们发现，卤基自由基已知会在高级氧化处理和阳光光化学中发生反应，也会导致水力压裂液中添加剂的非预期降解和卤化。
