FeCl_3和空气预氧化对煤焦结构及活化过程中孔隙生成的影响

利用铁基催化剂(3%FeCl_3)并辅以200℃下空气预氧化方法制备具有低烧失、高比表面积的鸡西烟煤活性炭。使用FTIR,SEM,N_2吸附仪、XRD和Raman获得热解和活化过程中烟煤焦微观和宏观结构的变化,研究FeCl_3和空气预氧化对煤焦结构及活化过程中孔隙生成的影响。结果表明,随着预氧化时间的延长,含氧官能团的种类和数量增多,脂肪结构被移除。热解中含氧官能团的演变和FeCl_3的催化作用,促进煤焦微观结构向无序方向转变,并形成较多孔隙,然而具有不同热稳定性的含氧官能团的热脱附行为对煤焦结构的影响更为显著。酸洗煤焦(JX-800)和单独负载FeCl_3煤焦(JXFe-800)在活化中孔隙均为逐级生成。由于两者微观结构的差异及Fe基化合物的存在,JX-800和JXFe-800分别在烧失率为53.7%和43.7%形成分级孔结构并具有相近的比表面积(549.64和600.47 m~2/g),但JX-800-53.7颗粒表面已造成严重烧失;负载后经空气氧化(15h)的煤焦(JXFeO15-800)和单独氧化氧化(48 h)煤焦(JXO48-800)的颗粒均具有较多孔隙和无序微观结构,促进活化气体的扩散,由颗粒内部和表面同时进行炭烧失生成孔隙,且颗粒表面均未发生明显烧失;由于Fe基化合物促进了活化气体与芳香结构的反应,JXFeO15-800的烧失率为30.9%时,比表面积已达到906.05 m~2/g;JXO48-800的烧失率为32.5%时,比表面积为809.69 m~2/g。

Effects of FeCl3 and air pre oxidation on char structure and pore development during activation

A series of the activated carbon with low burn off and high specific surface area from Jixi bituminous coal were prepared by air pre oxidation at 200 ℃ and adding iron based compounds (3% FeCl3).The changes of macrostructure and microstructure of bituminous chars during pyrolysis and activation were obtained by FTIR，SEM (scanning electron microscope)，nitrogen adsorption，XRD (X ray diffraction) and Raman spectroscopy.The effects of FeCl3 and air pre oxidation on char structure and pore development during activation were investigated.Results show that the increase of the type and quantity of oxygen functional groups and the removal of aliphatic chains are observed gradually with the increase of oxidation time from 15 to 48 h.The evolution of different oxygen containing structures and the catalysis of FeCl3 result in the disordered conversion of microstructure and the formation of more porosity during pyrolysis，however，the thermal desorption behavior of oxygen containing structures with different thermal stabilities plays a more important role on the changes of char structure.The pore formation of JX-800 and JXFe-800 follow a hierarchical development from the surface to the core during activation.Because of the difference in microstructure and the existence of Fe based compounds，JX-800 and JXFe-800 have the hierarchical pores and similar specific surface area (549.64 and 600.47 m2/g) at the lower burn offs of 53.7% and 43.7%，respectively，and severe carbon loss at the particles’ surfaces is observed for JX-800-53.7.The pore formations of JXFeO15 and JXO48 with more pores and disordered microstructure which promote the diffusion of activated gas follow a non hierarchical development from the external and internal particles simultaneously，thereby hindering the severe carbon losses at the particle surface.Because of Fe based compounds which promote the reaction between activated gas and aromatic structure，JXFeO15 has a high value of SBET(906.05 m2/g) at a low value of burn off 30.9%，compared with the values of SBET(809.69 m2/g)of JXO48-800 char at a value of burn off 32.5%.