KOH活化木质碳纤维的孔隙结构及其成孔机理

Pores tructure and generation reaction path of wood-based activated carbon fibers by KOH activation

由于化石资源价格昂贵且面临着日益枯竭的危机,以木材等生物质资源代替化石资源生产活性炭纤维已势在必行。KOH活化制备的木质活性炭纤维孔隙结构较为单一,极大地限制了其应用领域,为了更好地对其孔隙进行调控,需对木质活性炭纤维的孔隙结构生成及其演变有一个全面的认知。笔者总结了原料以及KOH为活化剂处理木质活性炭纤维的工艺因子,如炭化温度、碱碳比、浸渍时间、活化时间对孔结构的生成、扩展的影响,并重点归纳了KOH活化木质活性炭纤维孔隙结构的生成及演变机制。在此基础上,凝炼出KOH活化木质活性炭纤维研究领域存在的诸如木质原料主化学成分是如何参与活性炭纤维孔隙构造,以及在KOH活化处理过程中孔隙结构的中间反应,即活化反应过程或生成路径的科学问题,同时指出了今后该领域应重点研究的几个方向。

Activated carbon fibers(ACFs)have unique characteristics compared with granular or powdered activated carbons(ACs)due to their welldeveloped pore structure and special surface reactivity.The application fields comprise adsorption and separation,electronic materials,catalyst support,and the storage of natural gas.The ACFs areusuallyprepared from polyacrylonitrile,pitch or phenolic resin fibers.Because fossil resources are expensive and facing increasingly depleted crises,it is imperative to use biomass resources as an alternative of fossil resources to prepare activated carbon fibers.Wood is the most abundant terrestrial biomass,containing up to threequarter of polysaccharides and around onequarter of lignin,which has been utilized for the preparation of the ACFs.Liquefied wood(Wliq)was also investigated for ACF production.This approach does not require the separation of chemical components of wood and leads to higher wood utilization ratio.However,regardless of high specific surface area and pore volume,wood basedACFs prepared by KOH activation has a single pore structure,which greatly restricts their application.In order to improve their pore structures,it is necessary to have a comprehensive cognition of the formation and evolution of pore structure of wood based ACFs.Therefore,this paper summarized the effect of raw material properties and process factors of preparing woodbased ACF(WACF)by using KOH as an activator on formation and extension of pore structure,such as carbonization temperature,ratio of Alkali to char,impregnating and activation time.This paper also was focused on the generation reaction paths of pore structure of the WACF activated by KOH.Based on those results,scientific problems in the research field of the WACF by KOH activation were refined,e.g.,the formation procedure of the WACF pore structure and intermediate reactions of the main chemical components of wood raw material during the activation,namely the process of activation reaction or generation path.Meanwhile,some specific recommendations about the research directions in this field were put forward.