KMnO4改性活性炭对臭气中甲硫醇的吸附特性

Adsorption characteristics of methyl mercaptan in odor by KM n04 modified activated carbon

针对普通活性炭对污水厂臭气中甲硫醇吸附量低的问题,采用KMnO4浸渍改性以获得高甲硫醇吸附量的改性活性炭,通过低温氮吸附仪、扫描电子显微镜和Boehm滴定等表征揭示改性后活性炭吸附量提高的原因,并进行改性活性炭吸附甲硫醇的动力学和热力学研究。结果表明:在KMnO4浓度为1%、温度为25℃、活性炭与浸渍液质量比为8∶100的条件下浸渍6 h,改性活性炭对甲硫醇的静态吸附量最高,达到344.22 mg·g-1,是未改性前的4.04倍:改性活性炭对甲硫醇吸附量提高的原因主要是表面碱性基团的增加(是原来的2.53倍),以及微孔容积和比表面积的增加。改性活性炭对甲硫醇的吸附符合准二级动力学模型,同时粒子内扩散模型显示吸附过程由气相扩散和内扩散共同作用;符合Freundlich吸附等温方程,具有多层吸附特征,且吸附容易进行,属于优惠吸附,是一个自发、放热和熵减的过程,升温不利于对甲硫醇的吸附。

Aiming at low adsorption capacity of methyl mercaptan in odor emitted from wastewater treatment plant by the common activated carbon, KMnO4 was used to modify activated carbon and produce a modified activated carbon with high adsorption capacity of methyl mercaptan. Low temperature nitrogen adsorption apparatus, scanning electron microscope and Boehm titration analysis were used to characterize the modified activated carbon and reveal the reason for the increase of its adsorption capacity. At the same time, the adsorption kinetics and thermodynamics of methyl mercaptan by the modified activated carbon were also studied. The results showed that the modified activated carbon presented the highest static adsorption capacity of 344.22 mg·g-1 toward methyl mercaptan, which was 4.04 times of the common activated carbon, under the conditions of KMnO4 concentration of 1%, 25 ℃, the mass ratio of activated carbon to impregnation of 8∶100 and impregnation time of 6 h. The reasons for the increase of the adsorption capacity of the modified activated carbon were as follows: the increase of alkaline groups on surface, which was 2.53 times of the common activated carbon, microporous volume and pore specific surface area. The adsorption characteristics of modified activated carbon to methyl mercaptan were in accordance with the pseudo-second-order kinetics model. The weber and morris model indicated that above adsorption process was affected by joint actions of gas-phase diffusion and internal diffusion. The adsorption isotherm fitted Freundlich equation, and belonged to multiplayer adsorption, and was easily carried out as a type of preferential adsorption. Moreover, the adsorption was a spontaneous, exothermic and entropy reduction process, the increase of temperature was not conducive to methyl mercaptan adsorption.