Preparation Of Walnut Shell-Based Activated Carbon And Its Adsorption Performance For Toluene By Potassium Hydroxide Ultrasonic Method

Recently,there was a dramatic increase in volatile organic compounds(VOCs)emissions as a result of the continuous industrial developments,which cause environmental problems such as photochemical smog,haze smog and so on.Adsorption technique has been widely applied in the treatment of VOCs due to its low cost and efficient characteristics.There are some problems in adsorption activity of activated carbon,such as low adsorption capacity,high transfer resistance and poor stability.In order to solve these problems,KOH horn-based ultrasonic method was used to prepare walnut shell-based activated carbon,and the physical and chemical properties of the product were investigated.The main contents and conclusions are as follows:(1)Walnut shell was used as raw material,and potassium hydroxide(KOH)activation was carried out.The effects of activation ratio,activation temperature and activation time on the surface physicochemical properties and toluene adsorption performance of adsorbent were systematically investigated.The results show that The best performing adsorbent(KAC-1:3/800/1.0)adsorbent with the activation ratio of Walnut shell precursor(WC):KOH of 1:3,activation temperature of 800℃and activation time of 1 h has the largest specific surface area,pore volume and the largest adsorption capacity for toluene.After 4 cycles of adsorption and desorption experiments,the adsorption efficiency was still maintained at95%.(2)Further activation of KAC-1:3/800/1.0 activated carbon was carried out using a variable amplitude ultrasonic method,and the effects of ultrasonic time and power on activated carbon were studied.The results showed that the activated carbon(UAC-T1W30)with the best performance after ultrasonic treatment had an increase in specific surface area and micropore proportion,a greater degree of disorder,and an increase in oxygen-containing groups,greatly improving the toluene adsorption performance.The simulation coefficients R~2of Yoon-Nelson,Thomas and isothermal adsorption models are all above 95%,and the simulation results are good.After high temperature treatment,the horn-based ultrasonic activated carbon UAC-T10W30 also showed good thermal stability,and the adsorption efficiency remained at 95%after 4 cycles of adsorption and desorption experiments.(3)In order to explore the applicability of KOH horn-based ultrasonic activation method to different biomass,litchi shell,araucaria leaves and pine cones were used as biomass to prepare activated carbon under the optimum preparation conditions of KOH activation and horn-based ultrasonic activation,respectively.The toluene adsorption capacity of the three biomass was investigated.The results showed that the toluene adsorption capacity was increased by 37.3%,39.7%and 18.5%after horn ultrasonic activation.