Preparation Of Activated Carbons By Pyrolysis Gas And Their Adsorption Application

As a great agricultural country,China produces a large amount of biomass every year.According to statistics from National Bureau of Statistics of China,the amount of crop residues had exceeded 800 million by 2016,accounting for 60% of renewable biomass energy.It has been considered as an effective measure to take biomass as raw materials for the preparation of activated carbons(ACs),which can effectively reduce pollution,carbon emissions and material cost of ACs.The biomass activated carbons have been widely used in the field of water and air treatment.In general,conventional preparation methods of activated carbons usually require additional activators such as ZnCl2,H3PO4,KOH,K2CO3,CO2 and steam,which may generate secondary pollution or extra energy consumption.If the activated carbons could be prepared without extra activators,the pollution and cost would be obviously decreased.The study untilized mixed biomass compression particles to prepare activated carbons by pyrolysis gas activation.The impacts of pyrolysis gas and activation temperature were investigated for the properties of ACs.Batch experiments were performed to study the adsorption properties of ACs for carbaryl,Cu(II)and Cr(VI)in solution.The carbons were characterized by elemental analysis,N2 adsorption–desorption isotherms,scanning electron microscopy(SEM),Fourier transform infrared spectroscopy(FT-IR)and X-ray diffraction analysis(XRD)to investigate the elemental composition,pore structure,surface morphology,and surface functional groups of ACs.Static adsorption experiments were designed at different conditions to study the adsorption properties of ACs,such as dosage,initial concentration,pH and adsorption time.Compared to the pyrolytic carbon without activation process by pyrolysis gas,the aromaticity of activated carbons increased,polarity and surface oxygen functional group decreased,SBET increased from 207.40 m2?g-1 to 515.10 m2?g-1,DP decreased from 5.908 nm to 2.710 nm,and the surface of carbons became coarser.All the changes indicated the pyrolysis gas had obviously promoted the development of pore structure.As for the different physicochemical properties of ACs at virious activation temperatures,with the increase of temperature,the carbon content,hydrophobicity and aromaticity of carbons increased,the “soft carbon” of raw materials gradually became “hard carbon”.When the activation temperature was controlled from 600 °C to 900 °C,higher temperature promoted the production of microporous structure,SBET increased from 239.00 m2?g-1 to 629.20 m2?g-1 and DP decreased from 5.438 nm to 3.005 nm.For the adsorption of carbaryl,the adsorption capacity of activated carbons could exceed 300 mg?g-1.Freundlich model well described adsorption isotherms,the adsorption capacity of ACs increased with activation temperature.Pseudo-second order model was fitter for the adsorption kinetics and adsorption basically reached equilibrium within 60 h.The adsorption capacity yield(mgcarbaryl?g-1feedstock)attained maximum when the activation temperature was 800 °C.For the adsorption of Cu(II)and Cr(VI),the pH of solutions had weak effect on the adsorption of Cu(II),while the removal rate of Cr(VI)significantly dropped with the decrease of pH.Pseudo-second order model was fitter for the adsorption kinetics of Cu(II)and Cr(VI)and the adsorption process basically reached equilibrium within 6 h.Langmuir model well described adsorption isotherms and the qm calculated could reach 6.8 mg?g-1 and 4.9 mg?g-1 for Cu(II)and Cr(VI),respectively.