Preparation Of Eucalyptus Bark Based Activated Carbon Via KOH Activated Hydrochar And Its Adsorption Behavior Of Toluene

Guangxi is the main area of eucalyptus planting in China.A great amount of biomass waste of eucalyptus bark is produced in rural areas every year,which brings challenges and opportunities to environmental protection and resource utilization.However,at present,the waste eucalyptus bark is mostly disposed in the way of discarding or burning due to its huge quantity and land occupation,which not only causes the waste of biomass resources,but also brings great pressure to the natural environment.As a renewable,inexpensive and easily degradable biomass resource,eucalyptus bark has a high carbon content which is the one of the ideal raw materials for preparing activated carbon.To improve the resource utilization of the waste eucalyptus bark and reduce the environmental problems caused by disposal,in this paper,the eucalyptus bark was used as raw material and be transformed into hydrochar by hydrothermal carbonization technology.And the eucalyptus bark based activated carbon was prepared by the method of high temperature pyrolysis KOH activation hydrochar.At the same time,thermogravimetric analysis,elemental analysis,N₂adsorption-desorption experiment,XRD,Laman,FT-IR,Alkali titration method were used to characterize and analyze the composition,structure and surface chemical characteristics of eucalyptus bark based activated carbon.The adsorption performance and adsorption behavior of eucalyptus bark based activated carbon on gaseous volatile organic pollutants under different conditions were investigated by toluene static and dynamic adsorption experiments.This paper’s main conclusions are as follows:（1）In this paper,firstly,the waste eucalyptus bark was transformed into hydrochar by hydrothermal carbonization technology.By studying the effect of hydrothermal temperature（160℃～220℃）and hydrothermal time（5h～9h）on the carbon fixation and yield of hydrochar,the optimal preparation conditions of hydrochar was determined as 200℃,hydrothermal time was 7h.In this condition,the fixed carbon content of hydrochar was 37.06%,and the yield was71.27%.Characterization analysis showed that most of cellulose and hemicellulose were degraded and part of the structure of lignin was destroyed during the hydrothermal carbonization process.（2）Using hydrochar as precursor,high temperature pyrolysis KOH activated hydrochar to prepare eucalyptus bark based activated carbon.The method of single factor analysis was used to investigate the adsorption performance of activated carbon for gaseous toluene.The results showed that the maximum adsorption capacity of gaseous toluene was 425.61 mg·g^-1under the preparation conditions of heating rate was 10℃·min^-1,carbonization temperature was 700℃,KOH concentration was 3 mol·L^-1,retention time was60 min.Compared with the preparation of activated carbon directly from raw materials and hydrochar,the specific surface area increased from 329.66 m²·g^-1to 508.4 m²·g^-1,and the pore volume increased from 0.1881 cm³·g^-1to 0.3139cm³·g^-1.（3）Porous structure was formed on the surface of the activated carbon and the pore size distribution was mainly micropores after KOH activation.Due to the difference in KOH concentration and carbonization temperature,the pore structure and surface characteristics were different.With the increase of carbonization temperature and KOH concentration,the specific surface area and pore volume of eucalyptus bark based activated carbon are increasing,and the structure was mainly amorphous.Among them,BC-3-700-60 was prepared under the conditions of KOH concentration was 3 mol·L^-1,activation temperature was 700℃,residence time was 60min,which had the largest specific surface area(1242.36 m²·g^-1)and total pore volume(0.6939 cm³·g^-1)among all the samples.In addition,the types of functional groups on the surface of activated carbon have little effect on temperature and KOH concentration,and basically belong to specialization,but after activation by KOH,the acidity of activated carbon decreases,and the alkaline enhancement.（4）The results of dynamic adsorption experiments at 30℃shown that the adsorption capacity of toluene on different eucalyptus bark based activated carbon corresponds to the specific surface area and pore volume of eucalyptus bark based activated carbon;with the ambient temperature（20℃～40℃）and the relative humidity（RH=0%～70%）increases,the adsorption breakthrough curve shifted to the left,the penetration time decreases,and the adsorption capacity decreases.The adsorption capacity of eucalyptus bark based activated carbon to toluene under different conditions was affected by the physical and chemical characteristics of eucalyptus bark based activated carbon and the environmental factors.Meanwhile,the Yoon-Nelson model,Thomas model and BDST model were used to fit the adsorption breakthrough curve of toluene on eucalyptus bark based activated carbon,and the fitting effect is better which indicated that the three models could better predict the dynamic adsorption of toluene on eucalyptus bark based activated carbon.