改性活性炭吸附甲苯废气的研究进展

Toluene Removal from Waste Gas by Modified Activated Carbon: a Review

甲苯是一种有毒的挥发性有机物,会对环境造成严重危害。活性炭吸附法是处理甲苯的经典工艺,但普通活性炭通常存在灰分高、吸附选择性差、孔径分布不均匀及表面官能团限制等问题。为了更高效、更有针对性地吸附目标物质,需要对活性炭进行改性处理。研究人员从选择合适的改性物质、处理工艺、操作条件及改性物剂量等方面不断尝试来确定最佳改性方法。目前活性炭的改性方法主要有酸碱改性法、负载杂原子和化合物改性法、低温等离子体改性法、微波改性法等。酸碱改性法通过去除活性炭中酸碱可溶性物质来降低灰分含量,从而扩大其比表面积和孔道容积。相较酸改性,碱改性可提高活性炭表面碱性官能团数量,增强其表面π-π色散力,使活性炭整体的非极性提升,有利于其吸附弱极性的甲苯。负载杂原子和化合物改性法是利用负载的杂原子和化合物与甲苯之间的络合作用来提高活性炭的吸附性能,但引入的杂原子和化合物含量过高时易堵塞孔道,降低活性炭对甲苯的吸附容量。低温等离子改性法具有能耗低、使用范围广和效率高等优点,是一项去除污染物的环保新技术,不仅可改变活性炭表面的化学性质,也会对其界面物性产生影响,在活性炭表面处理方面显示出广阔的应用前景。微波改性法利用微波能量在活性炭表面产生更多的活性位点,配合通入的还原性气体还能分解活性炭表面的酸性官能团,增强其碱性。微波加热可以去除活性炭孔道内部的杂质,但随着温度的升高,会造成炭骨架收缩,不利于吸附的进行。其中微波辐照功率、改性物的浓度及辐照时间是微波改性法中需要控制的关键因素。本文综述了活性炭及各种改性活性炭吸附甲苯的研究进展,通过吸附等温模型对比分析了不同改性活性炭对甲苯的吸附性能及吸附机理。研究表明,活性炭的比表面积、孔道结构及表面化学性质等是影响吸附性能的主要原因。本文还探讨了不同改性方法对活性炭理化性质的影响,对于提高活性炭的吸附效率具有重要意义,也为研制高效吸附甲苯的改性活性炭奠定了理论基础。最后,提出了活性炭研究中亟待解决的问题与其今后的发展方向,为后续研究和工业生产应用提供参考。

As a toxic volatile organic compound,toluene can cause serious harm to the environment.Activated carbon adsorption is a classic process for toluene removal,nevertheless,common ordinary activated carbon usually suffered from high ash content,poor adsorption selectivity,uneven pore size distribution and limited surface functional groups.For the sake of acquiring higher efficiency and selectivity in adsorption of target substances,modification of activated carbon should be conducted inevitably.Numerous attempts have been made by researchers to figure out the optimal modification method,which concern the selection of the appropriate modification substance,processing technology,operating conditions and the dosage of modifier.At present,the primary modification methods of activated carbon mainly include acid and alkali modification,loading ofheteroatoms and compounds,low temperature plasma modification,and microwave modification etc.In terms of acid and alkali modification,it can reduce the ash content by removing the acid and alkali soluble substances in activated carbon,thus enlarging the specific area and pore volume of activated carbon.Different from acid modification,alkali modification can increase the number of basic functional groups on the surface of activated carbon,enhance the surfaceπ-πdispersion force to further improve the overall non-polarity,which is beneficial to the adsorption of weakly polar toluene.Considering the loading of heteroatoms and compounds,it utilizes the complexation between heteroatoms/compounds and toluene to significantly improve the adsorption ability of activated carbon.However,excessive loading of heteroatoms and compounds will be likely to block the pore channels and reduce the adsorption capacity of activated carbon for toluene.The low temperature plasma modification features low energy consumption,higher efficiency and wide application range,which is regarded as a novel environment-friendly technique for toluene removal.It can not only improve the surface chemistry properties,but also affect the interfacial physical properties.Therefore,low temperature plasma modification exhibits a promising prospect in the field of toluene removal.Regarding to microwave modification,more active sites can be generated on the surface of activated carbon thanks to the microwave energy.With the introduction of reducing gas,the acidic functional groups on the surface of activated carbon could also be decomposed and the alkalinity can be enhanced as well.Microwave heating can remove impurities in the pores of activated carbon,whereas,with the increase of temperature,the carbon skeleton will shrink,which is not conducive to the adsorption.In particular,the power of microwave irradiation,the concentration of the modifier and the irradiation duration are the key factors to be controlled in microwave modification.In this article,the research progress of adsorption of toluene by activated carbon and modified activated carbon is reviewed.The adsorption performances and mechanisms of various modified activated carbon for toluene are investigated by comparing and analyzing their isothermal adsorption models.It is demonstrated that the specific surface area,channel structure and surface chemistry properties are the main factors that affect the adsorption performances.The influence of various modification methods on the physical and chemical properties of activated carbon are discussed,which is of great significance to improve the adsorption efficiency and lay a theoretical foundation for developing more efficient modified activated carbon in toluene removal.Finally,the problems remain to be solved and future trend for activated carbon modification are put forward,which provided a valuable information for further study and industrial application.