微波加热核桃壳制取活性炭及孔结构表征

Preparation and characterazation of activated carbon from walnut shells by microwave heating

以核桃壳为原料,采用微波加热-水蒸汽活化法制备了活性炭。研究了微波功率、活化时间和水蒸汽流量等因素对吸附性能的影响。最佳工艺条件为：微波功率600 W、活化时间7 min、水蒸汽流量5 mL/min,活性炭产品的碘吸附值1076．57 mg/g,亚甲基蓝吸附值195 mg/g,得率25．11%。该工艺将常规加热方法的炭化和活化简化为一个过程,所需加热时间仅为传统方法的1/21,产品活性炭的亚甲基蓝吸附值为国家一级品标准的1．44倍。同时测定了该活性炭的氮吸附等温线,通过BET计算了活性炭的比表面积,并通过H—K方程和密度函数理论表征了活性炭的孔结构。结果表明,该活性炭为微孔型,BET 比表面积1 154．91 m^2/g,总孔体积0．564 9 mL/g,微孔占总孔体积(体积分数,下同) 79．86%,中孔体积分数19．97%,大孔占0．17%。

The activated carbon is prepared from walnut shells by microwave heating-steam activating.The effects of microwave power,activation time and flow rate of steam on the yield and ad sorption properties of the resultant activated carbon are investigated. Through primary study of the reaction mechanism of activated car- bon preparation,the optimum conditions have been obtained as fol- lows:flow rate of steam is 5 mL/min,while microwave power is 700 W with activation time being 7 min.Under above conditions,the yield of the activated carbon is 25.11% when the methylene blue ad- sorption reached 195 mg/g and the iodine number is 1076.57 mg/g. The activation time by microwave heating is only 1/21 times as large as that of the conventional process.The methylene blue adsorption is 1.44 times of that specified for the first grade product in the Na- tional Standard.Furthermore,the activated carbon manufactured in optimum technology is tested by nitrogen adsorption at 77 K.The specific surface area of activated carbon is 1 154. 91m^2/g by BET method.The porous structures of the activated carbon are investiga- ted by Horvath-Kawazoe equations and Density Function Theory.It is shown that the activated carbon has micro-porous characteristic in structure with 0.564 9 mL/g for total pore volume,of which 79.86% is micropore volume,19.97% is mecropore volume and 0. 17% is macropore volume.