Department of Environmental Science and Engineering, Fudan University, Shanghai, China; Shanghai Institute of Pollution Control and Ecological Security, Shanghai, China.
Department of Civil and Environmental Engineering, Stanford University, Stanford, CA, United States.
Water Res. 2020 Mar 1;170:115299. doi: 10.1016/j.watres.2019.115299. Epub 2019 Nov 9.
The formation of carcinogenic N-nitrosamines from reactions between solvent amines and flue gas NO is an important concern for the application of amine-based processes to capture CO post-combustion. Using an advanced test rig with interconnected absorber and desorber units, we evaluated the importance for N-nitrosamine formation of the desorber relative to the absorber, and any synergism between the two units. Variations in desorber temperature and in flue gas composition indicated that N-nitrosamine formation from fresh monoethanolamine (MEA) occurred predominantly in the absorber. N-nitrosamine formation was driven by high NO and O flue gas concentrations, although NO also contributed. In contrast, N-nitrosamine formation from piperazine (PZ) was driven by reactions with nitrite in the heated desorber, and accelerated concurrent with nitrite accumulation. A complementary experiment simulating aged MEA solvent (high nitrite, 1.5% sarcosine as a proxy of secondary amine degradation products) suggested the desorber becomes an order of magnitude more important than the absorber for N-nitrosamine formation. For fresh MEA solvent, increasing the desorber temperature from 110 °C to 130 °C promoted thermal decomposition of N-nitrosamines, reducing N-nitrosamine accumulation rates two-fold. Compared to the test rig, the prevailing practice of using separate absorber columns and autoclave-like treatments to mimic desorber units predicted the direction, but underestimated the magnitude of N-nitrosamine formation. Because N-nitrosamine accumulation rates are the net result of competing formation and thermal decomposition processes, use of continuously cycling test rigs may be necessary to understand the impacts of different operating conditions.
胺类溶剂与烟道气中的 NO 发生反应生成致癌性 N-亚硝胺，这是胺基工艺用于捕集燃烧后 CO 的一个重要关注点。我们使用带有相互连接的吸收器和解吸器单元的先进测试设备，评估了解吸器相对于吸收器以及两个单元之间的协同作用对 N-亚硝胺形成的重要性。解吸器温度和烟道气成分的变化表明，新鲜单乙醇胺（MEA）中的 N-亚硝胺主要在吸收器中形成。尽管 NO 也有贡献，但高浓度的 NO 和 O 烟道气是 N-亚硝胺形成的驱动力。相比之下，哌嗪（PZ）中的 N-亚硝胺形成是由加热解吸器中的亚硝酸盐与 PZ 反应驱动的，且随着亚硝酸盐的积累而加速。一项模拟老化 MEA 溶剂的补充实验（高亚硝酸盐，1.5%肌氨酸作为二级胺降解产物的替代品）表明，解吸器对于 N-亚硝胺形成比吸收器重要一个数量级。对于新鲜的 MEA 溶剂，将解吸器温度从 110°C 升高到 130°C 会促进 N-亚硝胺的热分解，使 N-亚硝胺积累率降低两倍。与测试设备相比，目前使用单独的吸收器柱和类似于高压锅的处理方法来模拟解吸器单元的做法虽然预测了方向，但低估了 N-亚硝胺形成的程度。由于 N-亚硝胺积累率是形成和热分解过程竞争的净结果，因此可能需要使用连续循环测试设备来了解不同操作条件的影响。
