The Mechanism Of The Degradation Of Dns And Its Kinetics

The oxidative coupling reactions of substituted toluenes to the corresponding substituted stilbenes by oxygen have been widely applied in the industry for many years . Among these reactions, the oxidation of p-nitrotoluene-o-sulfonic acid (NTS) to 4,4'-dinitrostilbene- 2,2'disulfonic acid (DNS) is representative. However, the complicated side reactions of this oxidative coupling will significantly reduce the yield of DNS. In order to optimize the reaction conditions and reduce the side reactions, detailed studies on the side reaction mechanisms during this oxidation process are necessary. Conventional mechanisms concerning the formation of by-products thought 4-nitro-2-sulfobenzonic acid (NSBA) as the main by-product, and all the by-products were regarded from the oxidation of NTS or DNS by oxygen. While some surprising findings cannot be explained by the conventional side reaction mechanisms. Therefore, a new mechanism based on degradation of DNS under oxygen free conditions was proposed to explain the presence of all the by-products during the oxidation process. In addition, dynamic experiments were also done to help optimizing the reaction conditions and increasing the yield of the oxidation process.To optimize the oxidation of NTS, kinetic experiments were performed to evaluate the effects of oxygen rate, temperature and concentration of NaOH and DNS on the rate of degradation of DNS. An empirical rate equation for the degradation of DNS wae established.By the systemic analysis of oxidation products, we proposed a new mechanism based on tht decomposition of DNS without oxygen under the alkaline conditions. This new mechanism can explain the existence of all the by-products during the oxidation process.The classical Double-membrane model was described in this paper, which includes diffusion-reaction equation for the degradation of DNS with oxygen. Through preliminary experiments, we found that the gas-liquid mass transfer was improved with the existence of activated carbon, and the results showed that the existence of activated carbon would decrease the rate of this side reaction and increase the yield of DNS.