Experimental Study On Activated Carbon Preparation By Coal And Biomass Co-carbonization,and Activation

Although China has abundant reserves of low-rank coal,it has poor direct combustion economy.Pyrolysis is an efficient and clean way to utilize low-rank coal,but the tar from solely-coal pyrolysis holds a high content of heavy components that are not conducive for future use.Biomass has a high H to C ratio,co-pyrolysis of biomass and coal can convert heavy aromatic and naphthenic molecules in tar into lighter aliphatic and aromatic molecules,which is significant for the realization of coal and biomass upgrade utilization at the same time.For the solid product from co-pyrolysis,which we called char,can be modified to prepare activated carbon with excellent adsorption properties and stable chemical properties.The activated carbon can be used in many fields,like collaborative removal of gaseous pollutant,capture and storage of CO2,soil remediation and water treatment.The adsorption performance of activated carbon is related to its pore structure and surface functional groups,which depend strongly on the raw materials and preparation condition.In this investigation,Zhundong coal and poplar bark were used as raw materials,CO2 and steam were used as activation agents,and "one-step method" is used to prepare activated carbon in an experimental horizontal tube furnace.This paper mainly focuses on the influences of raw material's mixing ratio,reaction conditions during carbonization and activation on the yield,specific surface area,pore structure,iodine sorption value and surface functional group of activated carbon.We first did the carbonization experiments to determine the optimal carbonization condition for "one-step method" activated carbon preparation,because there are many variables need to be investigated.Carbonization process mainly concentrated on the influences of Zhundong coal and poplar bark mixing ratio and carbonization temperature on the yields and specific surface area of char.It was found that the char yields decrease with the increase of carbonization temperature and mixture of poplar bark,while the specific surface area show an opposite trend.The optimal carbonization condition appears when the mixing ratio of coal and biomass is 2:1,and carbonization temperature is 600?,at which the char yield is 52.24%,surface area is 196.56m2/g,and micropore ratio is 90.83%.A mixing ratio of 2:1 and temperature of 600? are used as carbonization condition,and "one-step method" is used to prepare activated carbon,we investigated the influences of activation temperature,duration time and concentration of activation agents on the yield,iodine sorption value,specific surface area and pore structure of activated carbon.When all the yield,surface area and iodine sorption value were considered together,800?was chosen as activation temperature,90min and 60min were chosen as activation time for single activation agent and mixed activation agent,respectively.When investigating the influence of activation agent,it was found that with the increase of activation agent,the reaction rates between steam and CO2 molecules and carbon atoms are accelerated.which aggravated the erosion of carbon atoms,and then result in the decline of activated carbon yield.When steam is used as activation agent,the iodine sorption value and specific surface area both reach their peak point at steam concentration of 30%,which are 1093.66mg/g and 708.69m2/g,respectively.When CO2 is used as activation agent,the peak point of iodine sorption value appears at 100%concentration,which is 909.65mg/g,corresponding with surface area of 667.7m2/g.When the mixture of steam and CO2 is used as activation agent,the iodine sorption value reaches its peak point(911.83mg/g)at steam and CO2 concentration both of 20%,the specific surface area reaches its maximum value(662.59m2/g)at steam concentration of 10%and CO2 concentration of 40%Furthermore,the scanning electron microscope(SEM)and Fourier transform infrared spectroscopy(FTIR)of Zhundong coal,poplar bark and activated carbons were analyzed to investigate the evolution mechanism of surface morphology and functional group.It was found that,after activation,the number of-OH and C-H reduced because they are released in the form of volatile;and the S-H band disappeared due to the formation and release of H2S and SO2 gases;the number of oxygen-containing functional group decreased.CO2 and steam play different roles during activation process,steam mainly accelerates the radial growth of pores,which increases the diameter of pores to facilitate the formation of mesopore,while CO2 mainly promotes the growth of pores in lengthwise direction,which develops the microporous structure.