Lyles School of Civil Engineering , Purdue University , 550 Stadium Mall Drive , West Lafayette , Indiana 47907 , United States.
Department of Chemistry , Towson University , 8000 York Road , Towson , Maryland 21252 , United States.
Environ Sci Technol. 2019 Jul 16;53(14):8167-8176. doi: 10.1021/acs.est.9b01446. Epub 2019 Jun 20.
Aromatic polyamide thin-film composite membranes are widely used in reverse osmosis (RO) and nanofiltration (NF) due to their high water permeability and selectivity. However, these membranes undergo biofouling and can degrade and eventually fail during free chlorine exposure. To better understand this effect, the reactivity of the polyamide monomer (benzanilide (BA)) with free chlorine was tested under varying pH and chloride (Cl) conditions. The kinetic results indicated that the current existing mechanisms, especially the Orton rearrangement, were invalid. Revised reaction pathways were proposed where BA chlorination was driven by two independent pathways involving the anilide ring and amide nitrogen moieties. The ability for one moiety to be chosen over the other was highly dependent on the pH, Cl concentration, and the resulting chlorinating agents (e.g., Cl, HOCl, OCl, and ClO) generated. Species-specific rate constants for BA with Cl, OCl, and HOCl equaled (7.6 ± 0.19) × 10, (1.7 ± 1.5) × 10, (2.1 ± 0.71) × 10 M s, respectively. A similar value for ClO could not be accurately estimated under the tested conditions. The behavior of these chlorinating agents differed for each reactive site such that OCl > HOCl for -chlorination and Cl > HOCl > OCl for anilide ring chlorination. Experiments with modified monomers indicated that substituent placement largely affected which reactive site was kinetically favorable. Overall, such findings provide a predictive model of how the polyamide monomer degrades during chlorine exposure and guidance on how chlorine-resistant polyamide membranes should be designed.
芳香族聚酰胺薄膜复合膜由于其高水透过率和选择性，广泛应用于反渗透（RO）和纳滤（NF）中。然而，这些膜会发生生物污染，并在暴露于游离氯时降解，最终失效。为了更好地理解这种效应，测试了聚酰胺单体（苯甲酰苯胺（BA））在不同 pH 和氯（Cl）条件下与游离氯的反应性。动力学结果表明，目前现有的机制，特别是 Orton 重排，是无效的。提出了修订后的反应途径，其中 BA 的氯化由两个独立的途径驱动，涉及酰亚胺环和酰胺氮部分。一个部分被选择而不是另一个部分的能力高度依赖于 pH、Cl 浓度以及生成的氯化剂（例如 Cl、HOCl、OCl 和 ClO）。BA 与 Cl、OCl 和 HOCl 的特定于物种的速率常数分别为（7.6±0.19）×10、（1.7±1.5）×10 和（2.1±0.71）×10 M s。在测试条件下，无法准确估计 ClO 的速率常数。这些氯化剂的行为因每个反应性位点而异，对于 -氯化，OCl > HOCl；对于酰亚胺环氯化，Cl > HOCl > OCl。用改性单体进行的实验表明，取代基的位置很大程度上影响了哪个反应性位点在动力学上是有利的。总的来说，这些发现为聚酰胺单体在暴露于氯时的降解提供了一个预测模型，并为如何设计耐氯聚酰胺膜提供了指导。
