Department of Chemical and Environmental Engineering , Yale University , New Haven , Connecticut 06520 , United States.
Department of Civil and Environmental Engineering , Massachusetts Institute of Technology , Cambridge , Massachusetts 02139 , United States.
Environ Sci Technol. 2019 Jul 16;53(14):8216-8226. doi: 10.1021/acs.est.9b01896. Epub 2019 Jul 5.
A number of flowback samples derived from horizontally drilled hydraulic fracturing (HDHF) operations reveal consistent detections of halogenated organic species , yet the source of these compounds remains uncertain. Studies simulating subsurface conditions have found that oxidative "breakers" can halogenate certain additives, but these pathways are unverified in the presence of cross-linked-gels, common features of HDHF operations. Using a high-throughput custom reactor system, we implemented a reaction matrix to test the capacity for halogenation of two frequently disclosed compounds with demonstrated halogenation pathways (cinnamaldehyde and citric acid) across guar gels with varied types and concentrations of cross-linkers and oxidative breakers. Cinnamaldehyde halogenation proceeded most readily in borate cross-linked gels at high ammonium persulfate dosages. Citric acid formed trihalomethanes (THMs) broadly across the matrix, generating brominated THMs at higher levels of hypochlorite breaker. Isolated removals of cross-linker or guar enhanced or diminished certain product formations, highlighting additional capacities for relevant ingredients to influence halogenation. Finally, we analyzed flowback samples from the Denver-Julesberg Basin, finding that additions of oxidant enhanced halogenation. As a more realistic subsurface simulation, this work demonstrates strict criteria for the subsurface halogenation of cinnamaldehyde and the broad capacity for THM formation due to systematic oxidant usage as gel breakers in HDHF operations.
许多来自水平定向水力压裂（HDHF）作业的返排样品都显示出卤代有机物质的一致检测，但这些化合物的来源仍不确定。模拟地下条件的研究发现，氧化“破胶剂”可以卤化某些添加剂，但在交联凝胶（HDHF 作业常见的特征）存在的情况下，这些途径尚未得到验证。我们使用高通量定制反应器系统，实施了一个反应矩阵，以测试两种经常披露的具有证明卤化途径的化合物（肉桂醛和柠檬酸）在具有不同类型和浓度交联剂和氧化破胶剂的瓜尔胶凝胶中的卤化能力。在高过硫酸铵剂量下，硼酸交联凝胶中肉桂醛的卤化最容易进行。柠檬酸在基质中广泛形成三卤甲烷（THM），在较高次氯酸盐破胶剂水平下生成溴化 THM。交联剂或瓜尔胶的单独去除增强或减弱了某些产物的形成，突出了相关成分对卤化影响的其他能力。最后，我们分析了丹佛-朱尔斯堡盆地的返排样品，发现氧化剂的添加增强了卤化作用。作为更现实的地下模拟，这项工作证明了肉桂醛在地下卤化的严格标准，以及由于系统氧化剂作为 HDHF 作业中的凝胶破胶剂的使用而广泛形成三卤甲烷的能力。
