针对SO2脱除的煤基活性炭结构及表面优化调控

Optimization of the structural and surface characteristics of activated carbon for SO2 removal

以神华褐煤为原料,ZnCl2为活化剂,采用化学活化法制备煤基活性炭,并通过NaOH溶液改性调控活性炭表面的化学官能团,进行烟气中SO2吸附的研究。利用扫描电镜观察活性炭的表观形貌,利用低温N2吸附法表征活性炭的比表面积及孔隙结构,利用红外光谱和Boehm滴定法考察活性炭的表面化学官能团。基于响应曲面法(RSM),对煤基活性炭的制备工艺参数进行了详细探究,建立了炭化温度、炭化时间、升温速率对活性炭比表面积的预测模型。通过响应曲面法得到的煤基活性炭制备实验优化工艺条件为:炭化温度700℃,升温速率15℃/min,炭化时间3h。得到活性炭的BET比表面积为599m^2/g,微孔比表面积为269m2/g。考察NaOH溶液浓度对煤基活性炭的孔隙结构、表面化学官能团及SO2吸附量的影响机制。结果表明,NaOH改性后活性炭的表面更加凹凸不平,孔结构被剧烈破坏,活性炭的孔径主要分布在0.5~0.6,0.7~0.9和1.0~4.0nm范围。在20%NaOH浓度改性时,活性炭具有最高的比表面积(681m2/g)和微孔比表面积(292m^2/g)。说明低浓度的碱处理对活性炭有扩孔的效果,而碱浓度过高会导致孔结构破坏,比表面积和孔容下降。随着NaOH浓度的增加,活性炭表面的羧基、羟基等酸性基团的含量下降,而羰基等碱性基团的含量则明显增加。30%NaOH浓度处理样品的碱性基团含量最高,可达到0.557mmol/g。进一步对活性炭的微孔比表面积、碱性官能团含量与SO2吸附量的相关性进行分析,发现SO2吸附量与微孔比表面积和碱性官能团含量都呈现正线性相关关系,且碱性官能团含量的相关性高于微孔比表面积。因此,表面碱性官能团和微孔结构有利于SO2在活性炭表面的吸附。

Coal-based activated carbons (ACs) were prepared from Shenhua lignite by chemical activation of ZnCl 2 .The surface functional groups of ACs were modified by NaOH to study the adsorption of SO 2 in flue gas.Scanning electron microscope (SEM) was used to observe the surface morphologies,N 2 adsorption was used to characterize the pore structures,Fourier transform infrared spectroscopy (FTIR) and Boehm titration were used to investigate the functional groups.The preparation parameters of ACs were discussed based on the response surface methodology (RSM) method,and a prediction model for the surface area was established based on carbonization temperature,carbonization time and heating rate.The optimum conditions for preparation of ACs by RSM were as follows:carbonization temperature of 700 ℃,heating rate of 15 ℃/min,and carbonization time of 3 h.The BET surface area and microporous surface area of the obtained AC were 599 m^2 /g and 269 m 2 /g,respectively.The effects of NaOH concentration on the pore structures,surface functional groups and SO 2 adsorption capacities of ACs were investigated.Results showed that the pore structures were severely damaged after NaOH modification,and the pores were mainly distributed in the range of 0.5-0.6 nm,0.7-0.9 nm and 1.0-4.0 nm.Highest BET surface area (681 m 2/g) and microporous surface area (292 m^2 /g) was reached with treatment by 20% NaOH.This illustrated that low concentration of alkali treatment could expand pores in ACs,while high concentration of alkali might destroy the pore structures,leading to the decrease in surface area and pore volume.The amount of acidic groups decreased with the increasing of alkali concentration,while the basic functional groups increased.AC treated with 30% NaOH exhibited the highest content of basic groups (0.557 mmol/g).The correlations between the microporous surface area and the content of basic groups with the SO 2 adsorption amount were further analyzed.The adsorption capacities of SO 2 were positively linearly correlated with the amount of basic groups and microporous surface areas,and the correlation coefficient of basic groups was higher than the microporous surface area.Therefore,the surface basic functional groups and microporous structure were beneficial to the adsorption of SO 2 on activated carbon.