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Phsicochemical Treatment of Hazardous Wastes - Chapter 4

Bất kỳ quá trình oxy hóa trong đó hydroxyl gốc tự do là loài chiếm ưu thế được định nghĩa như là một quá trình oxy hóa tiên tiến (AOP). Đối với bất kỳ phản ứng oxy hóa, hai yếu tố xác định tốc độ phản ứng. Đầu tiên, nếu phản ứng có năng lượng cao miễn phí hoặc tiềm năng điện cao, phản ứng là rất có khả năng xảy ra và nó được coi là nhiệt động thuận lợi. Tiềm năng oxy hóa oxy hóa phổ biến phù hợp cho các ứng dụng môi trường được liệt kê. | 4 Advanced Oxidation Processes 4.1 Introduction Any oxidation process in which hydroxyl radical is the dominant species is defined as an advanced oxidation process AOP . For any oxidation reaction two factors determine the rate of reaction. First if a reaction has a high free energy or high electrical potential the reaction is very likely to occur and it is considered to be thermodynamically favorable. The oxidation potentials for common oxidants suitable for environmental applications are listed in Table 4.1. As can be seen in the table the hydroxyl radical has an oxidation potential of 2.80 V. The hydroxyl radical is a short-lived and extremely potent oxidizing agent according to its potential as shown in the table. Because they are extremely potent oxidizing agents hydroxyl radicals react with organic compounds by three mechanisms hydrogen abstraction electron transfer and hydroxylation Huang et al. 1993 . From a thermodynamic point of view the higher the oxidation potential is the stronger the oxidant species will be. Another factor is how fast the reaction is. The fundamental theory underlining the mechanisms involved in AOPs is the transition state theory TST which provides theoretical guidance for the search of the most efficient AOP. According to the TST hydroxyl radicals may accelerate the oxidation rates of an organic compound by several orders of magnitude compared with oxidation rates for common oxidants. This is because the radical reaction will have a much lower activation energy barrier than regular reactions do therefore oxidants such as oxygen hydrogen peroxide and ozone are combined with catalysts such as transition metals metal oxides photons and ultrasound to generate hydroxyl radicals. For each AOP the degradation rate is investigated to search for the most efficient process. We begin this chapter with basic chemical kinetics followed by discussion on the TST oxidants and catalysts used in AOPs. 2004 by CRC Press LLC TABLE 4.1 .