Preparation Of Microporous And Mesoporous Carbon From Wood Sawdust By Chemical Agent Activation

In this dissertation, the sawdust of poplar etc. from the remainder of wood manufacture in North area was activated separately by KOH and H₃PO₄ to obtain mesoporous and microporous activated carbon (AC) with superior adsorption property. The effect of the compositions of these raw materials on the yield, specific surface area, adsorption values and ash of AC were systematically investigated. The effect of activation conditions, such as ratio, activation time and activation temperature which are controlled, on the specific-surface-area (SSA), pore structure and adsorption values was investigated to obtain the optimal activation condition. And the activation mechanism was simply researched accordingly in this paper. The main researches and achievements are comprised of the following aspects:1. The effect of the compositions of those raw materials on the yield, specific surface area, adsorption values and ash of AC were investigated. The yield and ash of the AC obtained from the extracted larch and the larch are 22.8% and 10.7%, respectively. The result showed that at the same condition as the ratio of KOH to sawdust 4:1, temperature 700℃and retention time 1 hour, the content of lignin was the most important factor for the specific surface area. The higher lignin content is, the smaller specific surface area is but the yields vary contrarily in the wood material. The effect on the yield of the ash contents in the material is less than the lignin contents.2. Microporous carbon was obtained through the activation of KOH. The optimal activation condition was ratio 1:1, activation time 60 min, and activation temperature 700℃. The activated carbon from poplar sawdust possesses specific surface area of 1748.82m²/g, the iodine adsorption value of 1147.88mg/g and the yield of 13.08%. The average pore volume and diameter were 0.562cm³/g and 23.43 A. The width of pore relating to highest pore volume distribution was 4.17 A. The proportion of micropores was about 70%.3. Mesoporous carbon was obtained through the activation of H₃PO₄. The optimal activation condition was ratio around 1:2, activation time 60 to 90 min, and activation temperature 400℃to 500℃. The activated carbon from poplar sawdust possesses specific surface area of 1609.43 m²/g, the methylene adsorption value of 192.45 mg/g, caramel decoloring value of 118 %, VB₁₂ adsorption value of 73.46mg/g. The BJH Method Cumulative Desorption Pore Volume was 1.72 cm³/g. The average pore diameter was 38.69A. The result of SF Method Pore Diameter was 28.05A. The proportion of mesopores was about 60%. 4. The activation process and mechanism activated by KOH and H₃PO₄ were analyzed and concerned respectively. The activation process activated by KOH took place at a relatively high temperature about 600℃. The main productions in the activated carbon of activation processes were K₂CO₃ and KOH, and the proportion of KOH was enhanced obviously with the increase of ration. The activation process activated by H₃PO₄ took place from room temperature. Before 450℃, phosphate esters were formed as the impregnation of phosphate acid. The ideal activation temperature of mesoporous carbon was produced between 400℃to 500℃. The mesopores were destroyed and decreased sharply at more than 550℃.