Salvilla John Nikko V, Yang Sasha, Liu Qianqian, Xie Zongli, Chen Zhenyu, Song Haitao, Zhang Lian
Department of Chemical and Biological Engineering, Monash University, Wellington Road, Clayton, Melbourne, Victoria, 3800, Australia.
Research Institute of Petroleum Processing, SINOPEC, Beijing, 100083, PR China.
J Environ Manage. 2025 Aug;389:126165. doi: 10.1016/j.jenvman.2025.126165. Epub 2025 Jun 14.
The emission of hydrogen cyanide (HCN) from the industrial fluid catalytic cracking (FCC) catalyst regenerator is a concerning pollutant that is highly toxic. Yet, the underpinning rationale particularly the role of carbon dioxide (CO) and its competition with O, remains poorly understood. Through the tests of three industrial spent FCC catalysts via temperature-programmed oxidation and Chemkin simulation, this study revealed a dual role of CO in the transformation of HCN. At high temperatures (e.g. >700C), the presence of CO is in favor of promoting the thermal cracking of coke via the Boudourad reaction, which subsequently accelerates the cracking of the associated N-bearing species for an enhanced formation of HCN. Meanwhile, a high CO partial pressure >10 % was found to benefit the generation of OH and O radicals, which are the chain carriers for the oxidation of HCN into NO and/or N. This is distinct from an environment containing only O in N in which an optimum O partial pressure of ∼1 % maximises the HCN oxidation rate. Higher O partial pressure above 1 % leads to an early release of HCN before its ignition temperature, resulting in significant emission of unreacted HCN in the outlet gas. In an O-CO-N environment, where O and CO coexist, CO can promote additional coke conversion, leading to increased initial HCN formation when the available O is insufficient to fully oxidize the coke. During the subsequent gas-phase oxidation of HCN, CO competes with O for H radicals, reducing the production of OH and O which in turn diminishes the HCN oxidation rates. Additionally, heightened CO formation from the Bouoduard reaction reduced the NO formed into N. From a practical implication perspective, these findings underscore the importance of gas conditions and maintaining temperature uniformity across the regenerator to effectively manage the emissions of HCN and other pollutant gases.
工业流化催化裂化（FCC）催化剂再生器中氰化氢（HCN）的排放是一种令人担忧的剧毒污染物。然而，其背后的原理，尤其是二氧化碳（CO）的作用及其与氧气（O）的竞争关系，仍知之甚少。通过对三种工业废FCC催化剂进行程序升温氧化测试和Chemkin模拟，本研究揭示了CO在HCN转化过程中的双重作用。在高温下（如>700℃），CO的存在有利于通过布多阿尔德反应促进焦炭的热裂解，随后加速相关含氮物种的裂解，从而增强HCN的生成。同时，发现高CO分压>10%有利于OH和O自由基的生成，这些自由基是将HCN氧化为NO和/或N的链载体。这与仅含N中的O的环境不同，在该环境中，约1%的最佳O分压可使HCN氧化速率最大化。高于1%的较高O分压会导致HCN在其着火温度之前提前释放，从而导致出口气体中大量未反应的HCN排放。在O-CO-N环境中，O和CO共存时，当可用的O不足以完全氧化焦炭时，CO可促进额外的焦炭转化，导致初始HCN生成增加。在随后的HCN气相氧化过程中，CO与O竞争H自由基，减少了OH和O的生成，进而降低了HCN的氧化速率。此外，布多阿尔德反应中CO生成的增加减少了生成的NO转化为N。从实际意义的角度来看，这些发现强调了气体条件以及保持再生器内温度均匀性对于有效控制HCN和其他污染气体排放的重要性。
