不同炭化–活化过程杉木液化物碳纤维微晶结构演变及孔结构形成路径

Microcrystalline structure evolution and pore structure formation of liquefied Chinese fir carbon fibers during different carbonization-activation processes

【目的】为进一步揭示木材液化物活性碳纤维(ALWCFs)孔结构形成机制,探讨了不同炭化–活化过程杉木液化物碳纤维(LWCFs)微晶结构演变及孔结构形成路径。【方法】通过控制炭化温度(500~900℃)获得具有不同微晶结构的LWCFs,在800℃进行水蒸气活化,采用元素分析仪、X射线衍射仪和氮气吸附仪分别考察了不同炭化–活化过程中LWCFs的元素组成、微晶结构和孔结构的变化。【结果】随着炭化温度的升高,LWCFs中碳元素质量分数逐渐升高,氢、氧元素质量分数减少,ALWCFs碳元素质量分数逐渐增加,氢、氧元素质量分数逐渐减少。炭化温度的升高使LWCFs乱层石墨微晶轴向尺寸逐渐增大,结构更加致密,900℃时横向微晶发生了生长。在活化过程中,高的炭化温度显著促进了水蒸气对轴向微晶的侵蚀,且随着活化时间的延长,侵蚀程度加重。活化20 min时,微晶横向尺寸显著增大,900℃炭化样品增长最为明显,进一步延长活化时间横向微晶结构无显著变化。孔结构数据表明:炭化温度的升高提高了ALWCFs的比表面积和总孔容,对微孔结构的形成有明显促进作用,且活化时间越长,微孔结构增加越显著。低的炭化温度有利于活化初期中孔结构的形成,而900℃炭化样品初期中孔结构较少,但随着活化时间延长,微孔结构的逐步扩大导致了中孔结构明显增多。【结论】水蒸气对乱层石墨轴向微晶内部的侵蚀是形成ALWCFs微孔结构的主要途径,中孔结构在活化初期主要来源于水蒸气对晶体缺陷或初始孔隙处的活化作用,活化后期主要来自于初期微孔的逐步扩大。

[Objective]To further reveal the pore structure formation mechanism of liquefied wood activated carbon fibers(ALWCFs),the microcrystalline structure evolution and pore structure formation of liquefied Chinese fir carbon fiber(LWCFs)during different carbonization-activation processes were investigated.[Method]By controlling carbonization temperature(500-900℃),LWCFs with different microcrystalline structures were obtained and activated by water vapor at 800℃.The changes of elemental composition,microcrystalline structure and pore structure of LWCFs during different carbonization-activation processes were investigated by elemental analyzer,X-ray diffractometer and nitrogen adsorption analyzer.[Result]With the increase of carbonization temperature,the mass fraction of carbon increased gradually,and the mass fractions of hydrogen and oxygen decreased for LWCFs,while for ALWCFs the mass fraction of carbon increased gradually,and the mass fractions of hydrogen and oxygen decreased gradually.With the increase of carbonization temperature,the axial size of turbostratic graphite-like microcrystals from LWCFs gradually increased and the structure became more densely.Furthermore,the transverse microcrystals began to grow at 900℃.During the activation process,the high carbonization temperature significantly promoted the erosion of axial microcrystals by water vapor,which became more seriously with increasing activation time.When activated for 20 min,the transverse size of the microcrystals increased significantly,and grew most obviously when carbonized at 900℃,while it did not change significantly with further activation.The pore structure data showed that the specific surface area and total pore volume of ALWCFs were enhanced with the increase of carbonization temperature,and the micropore structure significantly increased with the increase of activation time.For mesoporous structure,low carbonization temperature was beneficial to the formation of mesoporous structure in the initial activation stage.When carbonized at 900℃,less mesoporous structure was formed in the initial activation stage,but the mesoporous structure significantly increased with the increase of activation time,due to the gradual expansion of microporous structure.[Conclusion]The erosion of the interior of the turbostratic graphiticlike axial microcrystals by water vapor is the main way to form the microporous structure for ALWCFs,while the mesoporous structure is mainly derived from the activation of water vapor on the crystal defect or the original crack in the initial activation stage,and from the expansion of the initial micropores in the later activation stage.