NO在活性炭表面的吸附平衡和动力学研究

Adsorption Equilibrium and Kinetics of NO Removal on Activated Carbons

利用石英固定床反应器研究了程序升温反应(temperature programmed reaction,TPR)中NO在活性炭表面的转化率变化和等温条件下的NO吸附平衡和动力学。活性炭-NO的TPR结果和等温实验结果相一致。TPR(30～600℃)呈现3个温度区,分别对应化学吸附、过渡温度区和还原反应。用Langmuir、Freundlich和Temkin等温线方程分别拟合吸附数据,发现Langmuir方程能够很好地预测NO在活性炭表面的吸附平衡。使用颗粒内扩散方程、Langmuir速率方程和Elovich方程分别拟合动力学数据,结果表明低温时活性炭-NO的动力学符合Elovich方程,其机制由化学吸附控制,起始吸附速率随着温度升高而降低,吸附活化能随着吸附量增加而线性增大。高温时等温实验结果表明,活性炭-NO由还原反应机制控制。

The adsorption equilibrium and kinetics of NO removal on activated carbons （ACs） were investigated based on a quartz fixed bed reactor by temperature programmed reaction （TPR） and isothermal reaction. The results of TPR were in good agreement with that of isothermal reaction. ACs-NO in TPR （30~600 ℃） showed three temperature regions, corresponding to chemisorption, transition and reduction reaction respectively with increasing temperature. Compared with Freundlich and Temkin isotherm equation, Langmuir isotherm equation presented better fitted results for NO adsorption equilibrium. Three kinetic models including intra-particle diffusion equation, Langmuir rate equation and Elovich equation were applied in describing the reaction of ACs-NO at low temperatures. The correlation efficient from the three kinetic models revealed that Elovich equation was the most suitable one. Therefore, NO removal on AC at low temperature was controlled by chemisorption rate. The initial adsorption rate varied inversely with temperature. The activation energy of chemisorption increased with the increase of NO uptakes from an initial negative value. The kinetics of ACs-NO at high temperatures was controlled by reduction reaction.