Fenton reaction tower

Chapter 1 Introduction

Advanced Oxidation Processes are defined as processes that generate a large amount of • OH free radicals, which use highly active free radicals to attack and react with large organic molecules, thereby disrupting the molecular structure of the oil agent and achieving the goal of oxidizing and removing organic matter, achieving efficient oxidation treatment.
The Fenton method exhibits significant selectivity in treating wastewater containing hydroxyl organic compounds. The type of hydroxyl substituent, the number of hydroxyl groups, the position of hydroxyl substitution, the length of the main chain, and the saturation of the main chain all have varying degrees of influence on the treatment effect of Fenton method. The experimental results indicate that monophenolic hydroxyl groups have a promoting effect on the Fenton reaction, while monophenolic hydroxyl groups have a strong inhibitory effect on it; When the number of carbon atoms is the same but the number of hydroxyl groups is different, the effect on the Fenton reaction gradually decreases with the increase of the number of hydroxyl groups; The more carbon atoms in the main chain of a saturated monoalcohol, the more pronounced its inhibitory effect on the Fenton reaction; The effect of the unsaturation of the main chain on the Fenton reaction is also different. The Fenton treatment of aliphatic unsaturated hydroxyl compounds is very poor, while it has a good oxidation treatment effect on benzene ring hydroxyl compounds; When the chain length and the number of hydroxyl groups in the alcohol are different, the inhibitory effect on the Fenton reaction decreases with the increase of the main chain and the number of hydroxyl groups, showing a good oxidative degradation effect. The amount of hydroxyl radicals produced in different systems can be used to directly determine the inhibitory effect and degree of substrate on Fenton reagent. Pulse heating has a promoting effect on the oxidation of Fenton reagent at room temperature, and the higher the heating frequency, the more significant the effect.

Chapter 2 Fenton's Principle

When Fenton discovered the Fenton reagent, it was still unclear what oxidant was generated by the reaction between hydrogen peroxide and divalent iron ions, which had such strong oxidizing ability. More than 20 years later, some people hypothesize that radical free radicals may have been generated during the reaction. Due to the presence of catalyst Fe3+(Fe2+), H2O2 can efficiently decompose into radical free radicals (· OH) with strong oxidizing ability and high electronegativity or electrophilicity (electron affinity 569.3KJ). · OH can oxidize and degrade organic pollutants in water, ultimately mineralizing them into small molecules such as CO2, H2O, and inorganic salts. According to calculations, in a solution with a pH of 4, the oxidation potential of - OH is as high as 2.73 V, and its oxidation ability is second only to hydrofluoric acid in the solution. Therefore, conventional reagents are difficult to oxidize persistent organic compounds, especially aromatic compounds and some heterocyclic compounds. Fenton reagents can selectively oxidize and degrade the vast majority of them.
Regarding the reaction mechanism of Fenton reagent, one study suggests that it is a reaction between inorganic substances, such as Fe2+, Fe3+, H202, · OH, HO2 ·, and 02- ·, which are present in general Fenton reaction systems. The mechanism research of this part of the reaction is mainly completed through chemical capture agents and advanced analytical instruments. The research mainly focuses on whether oxidation species mainly composed of 9-radical or alkoxy radicals are generated, or whether high valence transient oxidation species centered on iron are generated. In recent years, researchers have found that Pizha can be used as a free radical scavenger to capture HO2 · radicals. Meanwhile, the competitive reaction of - OH radicals does not affect the capture of HO2 · radicals. Based on this discovery, researchers have proposed a mechanism for the generation of high-energy free radicals and oxidants, which is also a mature mechanism for the Fenton reaction. However, until now, there are still many issues that need to be studied regarding the forms and other aspects that exist in the reaction after iron oxidation. In response to this phenomenon, some scholars have proposed many intermediate processes, which can be summarized into several types: when the pH value is between 2.5 and 4.5, low concentrations of Fe2+mainly exist in the form of Fe (OH) (H20) 52+. This reaction occurs when H2O2 undergoes coordination exchange on the first ligand of Fe2+, followed by a transfer reaction of two electrons in the body to form Fe complexes. The intermediate Fe (oH) 3 (H2O) 4+continues to react and produce · OH, while Fe (oH) (H2O) 52+continues to react with H2O2:, allowing Fe2+to circulate.

Chapter 3 Fenton Oxidation Tower

In recent years, our company has been committed to studying the reaction patterns between Fenton and organic compounds and their intermediate products; Studied the kinetics of Fenton on different organic compounds and established different kinetic models. This research has promoted the maturity of our Fenton oxidation technology. Our company has developed Fenton oxidation tower equipment. This device can treat most difficult to degrade organic wastewater, such as cyanide, phenolic, dye wastewater, dye intermediate or dye additive wastewater, pesticide (glyphosate) wastewater, coking wastewater, landfill leachate, etc.
Here is an example to illustrate our company's research on using Fenton oxidation tower to treat recalcitrant chlorophenol wastewater. Our company focuses on the reaction characteristics of Fenton oxidation of chlorophenol, mainly studying the effects of pH, H202, and Fe2+on the reaction. In the study, it was found that if the acidity is too strong and the concentration of H+in the solution is too high, hydrogen peroxide can exist stably as H3O2+, and organic matter is not easily decomposed in a strongly acidic environment. Fe3+cannot be smoothly reduced to Fe2+, and the catalytic reaction is hindered. Experimental results have shown that the reaction is influenced by the concentration of free Fe2+, which is a key factor in the generation of · OH. Some of the small molecule organic compounds decomposed by Fenton will accelerate their decomposition, while the other part will form stable compounds with Fe2+, which are difficult to further degrade. As long as H+is present, the degradation reaction of organic compounds will continue. According to the experimental results, the degradation rate of organic matter occurs within a few minutes at pH 2-4. This degradation rate is a first-order reaction relative to the concentration of chlorophenol, and its reaction rate constant is proportional to the initial concentrations of Fe2+and H202. The experiment found that the reaction is greatly influenced by intermediate organic products, so the study of kinetics should consider the influence of intermediate products. Our technicians conducted a study on the kinetics of m-nitroaniline, examining the changes in H2O2 concentration, Fe2+concentration, pH value, and temperature over time. This study used univariate linear regression to quantitatively analyze the correlation between the residual concentration of m-nitroaniline and reaction time after different oxidation degradation times. It was found that the oxidation degradation of m-nitroaniline follows a first-order kinetic pattern, and the apparent rate constant and activation energy of the reaction were obtained. Using UV spectroscopy to study the mechanism, it was found that the main intermediate product in the catalytic oxidation process of meta nitroaniline should be pentanedioic acid. Due to the fact that the reaction rate constant between free radicals and m-nitroaniline is greater than that of organic acids, according to chemical kinetics theory, in the Fenton reagent catalyzed degradation reaction, when the dosage of Fenton reagent added is not sufficient to completely oxidize m-nitroaniline, m-nitroaniline can be preferentially oxidized and removed, causing the degradation reaction to terminate in the acid production stage. Therefore, in the actual treatment of difficult to degrade industrial wastewater, Fenton reagent oxidation method can be used as a pretreatment method for difficult to degrade wastewater such as meta nitroaniline as needed, providing good reaction conditions for subsequent biochemical treatment. However, when the dosage of Fenton reagent is large, it can further degrade the intermediate organic acids, generating small molecule compounds until they are degraded into carbon dioxide and water. Studying the kinetics of the reaction between Fenton reagent and organic compounds can help understand the reaction process of organic compounds in Fenton reagent, search for suitable reaction residence time, reaction order and rate constant, and provide solid basis and experience for the treatment effect of our Fenton oxidation tower equipment.

Chapter 4: Advantages of Fenton Oxidation Tower

(1). The intermediate state active species hydroxyl radicals (· OH) generated by the Fenton system have a higher oxidation electrode potential compared to other oxidants. It has stronger oxidation ability, no toxicity of reagents, no obstacles to mass transfer in homogeneous systems, simple operation, and low investment.
(2) The intermediate state active species hydroxyl radicals (· OH) generated by the Fenton system are strong oxidants, with an oxidation electrode potential (E) of 2.80V, second only to F2 among known oxidants.
(3) The intermediate state active species hydroxyl radicals (· OH) generated by the Fenton system have high electronegativity or electron affinity (569.3kj), making them easy to attack high electron cloud density points. At the same time, the attack of hydroxyl radicals has a certain selectivity.
(4) The intermediate active species hydroxyl radicals (· OH) generated by the Fenton system also have addition effects. When there is a carbon carbon double bond present, unless the attacked molecule has highly active carbon hydrogen bonds, an addition reaction will occur.