活性炭孔径分布对吸附CH_4性能的影响

Effects of activated carbon pore distribution on CH_4 adsorption

为了分离和浓缩煤矿瓦斯中的CH_4,以太西无烟煤为原料、水蒸气为活化介质,研究了在添加剂作用下工艺条件对活性炭孔隙结构及吸附CH_4性能的影响.实验结果表明:影响CH_4吸附量的关键因素是0.6~0.8nm孔的孔容大小,无论工艺条件如何变化,只要能提高该范围的孔容积,活性炭的CH_4吸附量也随之增大.添加NH_4Cl和KNO3时,活化程度(烧失率)、炭化终温、炭化升温速率、活化温度等工艺条件对活性炭的微孔率影响不大,微孔率均在91%左右,但对微孔分布有明显影响,NH_4Cl和KNO3的添加有利于小微孔的生成,特别是有利于孔径0.6~0.8nm孔隙的形成,能有效提高活性炭CH_4吸附量的增大.活性炭的烧失率过低或过高都不利于0.6~0.8nm孔隙的形成,适宜的烧失率为30%~40%;较高的炭化升温速率不利于0.6~0.8nm之间孔容积的提高,适宜的炭化升温速率为3~5℃/min;过低或过高的炭化终温不利于0.6~0.8nm之间孔容积的提高,适宜的炭化终温为650℃;总体来说,活化温度的影响相对较小,适宜的活化温度为880℃.在最优条件下制备的活性炭CH_4吸附量达到24.31mL/g.

To separate and concentrate CH_4 in coal mine gas,Taixi anthracite was used as raw material and steam as activation medium to explore the effects of technological conditions under the action of additive on the pore structure of the activated carbon and its CH_4 adsorption performances.The results show that the key factor influencing the CH_4 adsorption capacity is the pore volume with the pore diameter between 0.6 and 0.8 nm,and no matter how technological condition changes,as long as the pore volume within the range of 0.6—0.8 nm rises,the CH_4 adsorption capacity increases.Taking NH_4 Cl and KNO_3 as additives,the technological conditions such as activation degree,carbonization heating rate,carbonization temperature,activation temperature and so on have little influence on the microporosities of the activated carbons,which maintain at about 91%,but have great influence on the micropore distribution.NH_4 Cland KNO3 can increase the formation of small micropores(<1 nm),especially the micropores within 0.6—0.8 nm,which can improve the CH_4 adsorption capacity effectively.Too low or too high burn off of the activated carbon does harm to the formation of the pores within 0.6—0.8 nm,the suitable burn off is 30%—40%.High carbonization heating rate is not helpful to improve the pore volume within the range of 0.6—0.8 nm,and the suitable heating rate is 3 to5 ℃/min.Too low or too high carbonization temperature hinders the formation of the pores within the range of 0.6—0.8 nm,and the suitable carbonization temperature is 650℃.Generally,activation temperature has little influence on forming the pores within the range of 0.6 to0.8 nm,the suitable activation temperature is 880℃.The activated carbon prepared under the optimum conditions mentioned above can reach a CH_4 adsorption capacity of 24.31 mL/g.