Effect Of The Component From Lignocellulosic Materials On Pore Structure Of Activated Carbon Produced By H₃PO₄ Activation

Activated carbon (AC) with high surface area and developed pore structure which is a versatile adsorbent and special microcrystalline structure. Significant researches have been devoted to the production of activated carbons from waste materials of agricultural origin and based on lignocellulosic materials. Choosing suitable raw materials for preparation activated carbon with particular pore structure is an interesting and forefront issues in the research field. Prepareing AC from lignocellulosic materials become an hot topic.Hemicellulose, cellulose and lignin are the main three components of lignocellulosic materials. During the carbonization of the lignocellulosic precursors, hemicellulose, cellulose and lignin decompose at different rates and within distinct temperature ranges. Due to the differences inreactivity between those three basic components during the pyrolysis step, as well as the competition of the reactions involved during their decompositions, the study of their carbonization is rather complex.The present study is focused on the effect of lignin on the porous properties of activated carbon produced by H3PO4. activation has been investigated using sawdust of poplar, larch and flax as starting materials. Lignin was removed by acetic acid-sodium chlorite method. The surface area and porosity analyzer (N2,77K) together with iodine and methylene blue adsorption were used to characterize the pore structure. Thermal behavior of the raw material before and after lignin removal was investigated by TG/DTG analysis. The results showed that after the removal of lignin, the BET surface area, total pore volume, external surface area decreased. Removal of lignin from wood materials was beneficial for the development of micropore and detrimental for mesopore structure. The result of iodine and methylene blue adsorption further demonstrated this. Thermogravimetric result showed that after the removal of lignin, the thermostability of wood reduced.In a second part, these results are compared to the effect of cellulose on the porous properties of AC by H3PO4, activation has been studied using sawdust of birch and larch as raw materials. The surface area and porosity analyzer (N2,77 K) together with iodine and methylene blue adsorption were used to characterize the pore structure. Thermal behavior of the raw material before and after lignin removal was investigated by TG/DTG analysis. The results showed after removing cellulose micropore pore volume decread. The adsorbent amount of iodine and methylene blue adsorption also proved the conclusion.In the third part, Activated carbons were prepared from birch sawdust and pine sawdust by phosphoric acid activation under same operation conditions. Characteristics of raw materials and activated carbons were examined by adsorption experiment, and N2-adsorption isotherm method. The results showed that lignin is the main factor for mesospore structure. Mesopore and macrospore volume of larch sawdust-based activated carbon was always higher than that of birch sawdust-based carbon due to the higher content of lignin. Moreover, the SBET exhibited a similar tendency.It has been already extensively demonstrated that the microporous properties of activated carbons depend not only on the experimental conditions of the carbonization and activation steps but also preponderantly on the original nature and structure of the involved precursor. Nowadays, choosing suitable raw materials for preparation activated carbon with particular pore structure is an interesting and forefront issues in the research field. Biomass materials with natural pore structure and low ash composition, become important raw materials for preparing activated carbon. In this paper, the effect of composition of biomass materials on activated carbon pore structures were studied.