Abstract

Advanced oxidation processes, specifically catalytic wet air oxidation (CWAO), are considered as useful and robust methods for the treatment of refractory organic compounds such as phenol in wastewater. This paper reviews reaction mechanisms, kinetics and computational fluid dynamics (CFD) modeling of CWAO of phenol. Different reaction mechanisms have been proposed by various researchers to account for possible intermediates during phenol oxidation. These mechanisms can be either direct or indirect; with the indirect path resulting in the formation of intermediates, while with the direct mechanism, no intermediates are formed, the reaction proceeds straight to carbon dioxide and water. Acetic acid is considered as the most stable intermediate of phenol oxidation. Power law and Langmuir–Hinshelwood models were used to account for the adsorption/desorption of the reactants on the surface of the catalyst. The reviewed studies show that phenol conversion increases with increased temperature, pressure, gas velocity and decreases with increasing liquid space velocity. The formation of hot spots next to the walls of the reactor leads to safety issues and may cause catalyst deactivation and reactor thermal run away. This prompted a review of liquid mal-distribution and the formation of hot spots inside the reactor using the CFD modeling technique. In most cases, liquid channeling was observed, resulting in the formation of hot spots and catalyst deactivation.

摘要

高级氧化工艺，特别是催化湿空气氧化 (CWAO)，被认为是处理废水中的难降解有机化合物（如苯酚）的有用且可靠的方法。本文回顾了苯酚 CWAO 的反应机理、动力学和计算流体动力学 (CFD) 建模。不同的研究人员提出了不同的反应机制来解释苯酚氧化过程中可能的中间体。这些机制可以是直接的，也可以是间接的；间接途径导致中间体的形成，而直接机制则不形成中间体，反应直接进行到二氧化碳和水。乙酸被认为是苯酚氧化最稳定的中间体。使用幂律和 Langmuir-Hinshelwood 模型来解释反应物在催化剂表面的吸附/解吸。审查的研究表明，苯酚转化率随着温度、压力、气体速度的增加而增加，并随着液体空间速度的增加而降低。靠近反应器壁形成热点会导致安全问题，并可能导致催化剂失活和反应器热失控。这促使我们使用 CFD 建模技术对液体分布不均和反应器内部热点的形成进行审查。在大多数情况下，观察到液体窜流，导致形成热点和催化剂失活。气体速度并随着液体空间速度的增加而减小。靠近反应器壁形成热点会导致安全问题，并可能导致催化剂失活和反应器热失控。这促使我们使用 CFD 建模技术对液体分布不均和反应器内部热点的形成进行审查。在大多数情况下，观察到液体窜流，导致形成热点和催化剂失活。气体速度并随着液体空间速度的增加而减小。靠近反应器壁形成热点会导致安全问题，并可能导致催化剂失活和反应器热失控。这促使我们使用 CFD 建模技术对液体分布不均和反应器内部热点的形成进行审查。在大多数情况下，观察到液体窜流，导致形成热点和催化剂失活。