基于响应曲面法优化氮掺杂活性炭的制备和CO_(2)吸附性能研究

Optimization of preparation of nitrogen-doped activated carbon and CO_(2) adsorption property based on response surface methodology

氮掺杂活性炭制备过程中影响其性能的因素极其复杂,单一因素的定性分析无法满足对制备条件的准确调控,而多因素耦合量化分析可以弥补不足。以煤焦油沥青为原料,采用KOH活化法,与尿素共热解制备氮掺杂活性炭,通过响应曲面法(RSM)进行建模,以量化分析多因素耦合作用对活性炭产率和不同温度下(25℃,50℃和75℃)对CO_(2)吸附性能的影响,同时优化制备工艺参数,并且在此实验设计基础上利用线性拟合方法预测不同温度下CO_(2)吸附量的相关性。结果表明:对活性炭产率的影响由大到小的单因素依次为掺氮比(尿素与煤沥青的质量比)、活化温度、碱碳比(KOH与煤沥青的质量比)、活化时间,活化温度和活化时间的耦合作用影响最显著,碱碳比是影响活性炭CO_(2)吸附量最为关键的因素,但随吸附温度升高其他因素影响显著性增强;不同温度下CO_(2)吸附量可以进行相互预测,且相邻温度下CO_(2)吸附量之间的预测效果更好;得到的最佳制备条件为活化温度650℃、活化时间1.25 h、碱碳比2.5、掺氮比0.3,相应的活性炭产率可达59.316%,在25℃,50℃和75℃下CO_(2)吸附量分别为3.474 mmol/g,2.355 mmol/g,1.358 mmol/g。

The factors affecting the performance of nitrogen-doped activated carbon during its preparation process are extremely complex.The qualitative analysis of a single factor cannot satisfy the accurate control of preparation conditions,while the multi-factor coupled quantitative analysis can make up for the deficiency.In this study,with the help of KOH activation method,nitrogen-doped activated carbon was prepared by co-pyrolysis with urea using coal tar pitch as raw material.The response surface methodology(RSM)was used for modeling to quantitatively analyze the coupled effects of multi-factor on the yield of activated carbon and its CO_(2) adsorption performance at different temperatures(25℃,50℃ and 75℃).Simultaneously,optimal preparation process parameters were determined.Based on the experimental design,linear fitting method was utilized to predict the correlation of CO_(2) adsorption capacities at different temperatures.The results show that the relative influence of single-factor on the yield of activated carbon follows the order from large to small:nitrogen doping ratio(mass ratio of urea to coal tar pitch),activation temperature,alkali-to-carbon ratio(mass ratio of KOH to coal tar pitch),activation time,and the coupled effect of activation temperature and time is the most significant.The alkali-to-carbon ratio is the most critical factor affecting the CO_(2) adsorption capacity of the activated carbon.However,the significance of other factors increases notably with rising adsorption temperatures.The CO_(2) adsorption capacities at different temperatures can be mutually predicted,and the predictive effect between the CO_(2) adsorption capacities at adjacent temperatures is better.The optimum preparation conditions obtained are as follows:activation temperature of 650℃,activation time of 1.25 h,alkali-to-carbon ratio of 2.5,and nitrogen doping ratio of 0.3.Accordingly,the yield of activated carbon is 59.316%,and the CO_(2) adsorption capacities at 25℃,50℃ and 75℃ are 3.474 mmol/g,2.355 mmol/g and 1.358 mmol/g,respectively.