响应面法优化海藻基活性炭制备工艺及其吸附机理

Optimizing the production of Ulva-based activated carbon through response surface methodology and its adsorption mechanism

将海藻石莼通过预炭化得到半焦,再用KOH活化制备高附加值产品活性炭。以亚甲基蓝吸附值、碘吸附值为吸附性能指标,探究碱炭比、活化时间、活化温度等单因素对活性炭吸附性能的影响。Box-Behnken设计-响应面法优化活化工艺,亚甲基蓝吸附模型和碘吸附模型的P值均小于0.0001表现出具有极高的显著性,两个模型方程的确定性系数均大于0.99。亚甲基蓝模型的各因素交互影响P值也都小于0.0001,影响极显著;碘模型中各因素对吸附值的影响,活化温度大于碱炭比大于活化时间。通过对模型优化确定最佳工艺参数:碱炭比为2.99、活化时间为44.47 min、活化温度为809.91℃;该条件下的理论亚甲基蓝吸附值为809.91 mg/g、碘吸附值为1 843.11 mg/g。活性炭吸附废水亚甲基蓝的吸附过程符合准二级动力学模型方程。吸附等温线更符合Langmuir模型方程,略优于Freundlich模型方程,随着温度升高活性炭的吸附能力和饱和吸附量下降。

High value-added activated carbon was prepared through pyrolysis of the semi-coke of Ulva using KOH.The effects of KOH/coke, activation time, and activation temperature on the adsorption performance of activated carbon were investigated via iodine adsorption and methylene blue adsorption. The Box-Behnken design and response surface methodology were adopted to optimize the activation process condition. P values of both the methylene blue adsorption and iodine adsorption models were less than 0.0001, thus presenting high significance. The R-squared values of both models were higher than 0.99. The interaction P value of all factors in the methylene blue model was also less than 0.0001, indicating a significant impact. In the iodine model, the influence of activation temperature on the adsorption value was greater than that of the basic carbon ratio and activation time. The iodine adsorption and methylene blue adsorption values of activated carbon were 809.91 and 1843.11 mg/g, respectively,under optimal conditions;these values were obtained using the model equation of mass ratio of KOH/coke, 2.99∶1,an activated time of 45 min, and an activated temperature at 800℃. The theoretical value was consistent with the measured value. The adsorption process of activated carbon adsorption using wastewater methylene blue conformed to the pseudo-second-order kinetic equation. The adsorption isotherm was more consistent with the Langmuir equation, which was slightly better than the Freundlich equation. The adsorption and saturation adsorption capacities of activated carbon decreased with increasing temperature.