A critical review on BTEX adsorption by activated carbon
Background,aim,and scope With the development of urbanization and industrialization,volatile organic compounds(VOCs)emitted by human activities exhibit serious impacts on environment and human health.Therefore,it is essential to control the excessive emission of VOCs.Benzene series are the typical components of indoor VOCs and possess the characteristics of complex source,low concentration and long emission period.Taking into account the advantages and disadvantages of various VOCs control technologies,adsorption technology is an economical and effective method for indoor benzene series control.Activated carbon is one of the most promising adsorbents because of its low cost,acid and alkali resistance,good thermal stability,large specific surface area,and fast adsorption rate.However,activated carbon shows limited adsorption capacity and needs modifications to improve VOCs purification performance.This article summarizes relative influencing factors and modification methods.In addition,the interaction between activated carbon and benzene series has been elaborated in depth,which provides a more in-depth understanding for the study of activated carbon adsorption of benzene series.Materials and methods This article first reviews the sources of benzene series and their physical and chemical properties.Subsequently,the preparation process of activated carbon and its physical indexes,chemical indexes and adsorption indexes are introduced.Then the adsorption performance of activated carbon toward benzene series is summarized.Finally,the factors influencing activated carbon adsorption performance toward benzene series and the regeneration method of activated carbon are discussed.Results Both the specific surface area and pore structure of activated carbon can affect their adsorption performance.Generally,large specific surface area can provide abundant adsorption sites,thereby improving the adsorption performance.The macropores and mesoporou serve as a channel for the adsorption and transport of benzene series,and the micropores are the final trap pores for benzene series.Additionally,the oxygen-containing functional groups on the surface of activated carbon not only affect the surface polarity,but also affect the hydrophilic and hydrophobic properties.The surface of activated carbon loaded with heteroatoms or compounds can also change the polarity and hydrophobicity and physical structure,which improve the pore selectivity and electrostatic adsorption between benzene series and activated carbon.Moreover,the molecular characteristics of VOCs,such as size and shape,also play a significant role in the adsorption process.In addition,during the adsorption reaction process,the initial pollutant concentration,humidity,and fixed bed depth affect the adsorption performance of benzene series.In the regeneration process of activated carbon,in addition to conventional heating and desorption,there are also microwave heating and Joule heating regeneration technologies.Discussion The physical structure of activated carbon is adjusted by acid-base modification to obtain large specific surface area and different pore size distribution.Reducing the number of oxygen-containing functional groups on the surface of activated carbon can decrease the surface polarity and hydrophilicity of activated carbon.In addition,the introduction of Si—O and Si—OH groups can improve the hydrophobicity of the activated carbon surface.The introduction of pyridine N can enhance the π—π electron adsorption capacity of activated carbon toward benzene series.Introducing metal oxides on the surface of activated carbon is conducive to the reduction part of the oxygen-containing functional groups,the increase of the pore size,and the regulation of adsorption energy.Moreover,high concentrations of pollutants and water vapor,high adsorption temperature,and short fixed bed have a negative impact on adsorption.In the regeneration process of activated carbon with saturated adsorption,the microwave heating and Joule heating regeneration methods are energy-saving and efficient than conventional heating.Conclusions The research on activated carbon adsorption of benzene series mainly focuses on regulating the physical structure of activated carbon and the modification of surface chemical properties.In addition,it is necessary to match the adsorption reaction conditions(flow rate,humidity and temperature)with the usage and pad length of activated carbon in order to obtain the best adsorption performance of modified activated carbon in the practical application.Attention should also be paid to the regeneration technology of activated carbon.Recommendations and perspectives Significant progress have been made in the study of activated carbon materials for adsorbing benzene series.However,there are still many problems need to be solved,including the following aspects:(1)chemical modifiers should be used appropriately to avoid secondary pollution;(2)modifier chemicals should be introduced during the preparation of activated carbon to reduce energy loss and simplify the modifying process;(3)in the face of the coexistence of multiple benzene series,the adsorption mechanism of activated carbon should be unveiled to improve adsorption selectivity;(4)clarifying the regeneration mechanism of activated carbon after adsorption saturation and developing appropriate treatment methods which can transform desorption products to harmless resource.
activated carbonadsorptionBTEXsurface physical and chemical propertiesregeneration technology
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