Study On Preparation Technology Of Biomass Activated Carbon For Toluene Adsorption

Waste Zanthoxylum bungeanum branches was a kind of carbon-rich biomass and widely distributed resource.Improper treatment of Zanthoxylum bungeanum branches would cause serious pollution to the environment.Preparing carbon materials from the waste Zanthoxylum bungeanum branches can effectively solve the disposal problem of Zanthoxylum bungeanum branches.The prepared activated carbon materials can be widely used in adsorption,catalysis,energy storage,electrochemistry and other fields,so converting the Zanthoxylum bungeanum branches into activated carbons has broad application prospects.In order to study the effect of pore structures and surface oxygen-containing functional groups of Zanthoxylum bungeanum branches activated carbons on the toluene adsorption,Zanthoxylum bungeanum branches activated carbons were prepared by various preparation methods using waste Zanthoxylum bungeanum branches as raw materials.The physical and chemical properties of Zanthoxylum bungeanum branches activated carbons were studied by N₂adsorption-desorption（BET）,scanning electron microscope（SEM）,X-ray diffraction（XRD）and fourier transform infrared spectroscopy（FT-IR）.Through toluene adsorption-desorption test and kinetic fitting,the relationship between the physicochemical properties and the toluene adsorption-desorption performance of the prepared activated carbons was studied,and the renewable property of the prepared activated carbons was studied by circular test.The conclusions are as follows:1.The Zanthoxylum bungeanum activated carbons with mesoporous structures were prepared by HNO₃assisted H₃PO₄activation method.The surface oxygen-containing functional groups of the prepared activated carbons were rich.At the same time,with the increase the HNO₃addition,the specific surface area,mesoporous specific surface area and pore volume of the prepared biomass activated carbons showed a"volcanic"trend.Excessive HNO₃addition would cause excessive hydrolysis of biomass cell wall structures,which was not conducive to the formation of pore structure.The specific surface area,mesoporous specific surface area and pore volume of NAC3 activated carbon prepared with 3.0%HNO₃addition were the largest,reaching 1334.7 m²/g,1053.9 m²/g and 2.3 cm³/g respectively,and the pore volume of NAC3 increased from 1.3 cm³/g of NAC0 to 2.3 cm³/g.The toluene adsorption capacity of NAC3 adsorbent was 490.0 mg/g,and NAC3 adsorbent has good low-temperature renewable performance.2.The Zanthoxylum bungeanum biomass activated carbon with rich microporous structure was prepared by low-temperature hydrothermal pretreatment of Zanthoxylum bungeanum branches with H₃PO₄as activator.With the increase of hydrothermal pretreatment temperature,the specific surface area and micropore contents of the biomass activated carbons increased,and the toluene adsorption performance of the activated carbon became stronger with the increase of micropore contents.The HT180activated carbon prepared at 180°C hydrothermal pretreatment temperature had the largest specific surface area（1290.9 m²/g）and the highest micropore proportion,and the micropore proportion increased from 30.6%of NHT000 to 63.6%of HT180.The HT180 with highest micropore ratio showed the best toluene adsorption performance,and the toluene adsorption capacity increased from 309.8 mg/g of NHT000 to 532.9mg/g of HT180.However,the high micropore ratio of activated carbon adsorbents was not conducive to the desorption of adsorbed toluene.3.Microporous biomass activated carbon with rich oxygen-containing functional groups was prepared by HNO₃assisted H₃PO₄activation and hydrothermal pretreatment technology.With the increase of HNO₃addition,the specific surface area and micropore contents of the biomass activated carbons showed a"volcanic"trend.The specific surface area of the HTNAC1 adsorbent prepared by 1.0%HNO₃addition assisted H₃PO₄hydrothermal pretreatment was up to 1547.8 m²/g,and the micropore ratio of the HTNAC2 adsorbent prepared by 2.0%HNO₃addition assisted H₃PO₄hydrothermal pretreatment was up to 73.0%.Excessive HNO₃addition caused activated carbons to be excessively oxidized and etched,so the specific surface area of micropores was reduced.In addition,HNO₃assisted H₃PO₄hydrothermal pretreatment of waste Zanthoxylum bungeanum branches significantly increased the contents of surface oxygen-containing functional groups of the prepared activated carbons.HTNAC2 adsorbent had the best adsorption performance for toluene,and its adsorption capacity of toluene was up to669.8 mg/g,and HTNAC2 adsorbent could be regenerated at a higher heat treatment temperature.