Pore Structure, Pore Reaction Path And Properties Of Activated Carbon Fiber From Windmill Palm Fiber

This study was devoted to clarifying the evolution and formation reaction path of wind palm (Trachycarpus fortunei) fiber during physical and chemical activation, providing the theoretical basis and data for preparation of windmill palm-based activated carbon fiber (ACF) with high value and high properties. WPF were activated by steam or phosphoric acid.The basic properites of WPF was illustrated, and the effect of activation parameters on the microstructure of ACF was investigated, including their special surface area, adsorption capactity and pore size distribution. According to the variations of physical and chemical microstructure, the formation process of pore structure was concluded. Moreover, the electrochemistry performance and adsorption performance of methylene blue (MB) were detected and the relationship between these properties and the pore structure were also explored.The main results of this study as follows:1. Wind palm fiber had natural pore structure, abundant carbon content(48.07%), high ratio of lignin(34.78%) and low content of ash(<1%), which proved to be one kind of promising materials for activated carbon fiber.2. SACF prepared from steam activation had both micropores and mesopores, which was comparable to commercial ACF. With increasing temperatures, the specific surface area, volume of micropores and mesopores, MP-ratio and the average pore diameter increased. One step method was more efficient than two step method.3. HACF prepared from phosphoric acid activation had both micropores and mesopores, which possessed lower specific surface area but higher yield than SACF. The most obvious impact on HACF pore structure was activation temperature, and after that could be activation concentration and time. High temperature contributed to micropores generation, longer activation time contributed to mesopores generation, higher activation concentration contributed to high micropore ratio.4. The ACF pore structure reaction path could be divided into five phases. In the first stage(<200 ℃), the original pores did not change. In the second stage(200-400℃), the pyrolysis of cellulose, hemicellulose promoted mesopores generation.In the third stage(400-800℃), the carbon net structure continually developed led to new micropore generation, the second rearrangement of molecule led to the increase of mesopores.In the fourth stage(800 ℃,0-20 min), steam as active agent could widen the pore size distribution, and the elements of H and O left with gases, leading to a huge number generation of micropores and mesopores.In the fifth stage(800 ℃, 20-80 min), the consistent steam activation could not change pore size distribution but could widen original pore size. While the speed of regenerated micropores overcame the speed of converted micropores, the micropore specific surface area decreased, and eventually leading to the decrease of total specific surface area.5. The specific capacitance of WACF reached 60-142 F/g in 1 mol/L H2SO4 electrolyte, with 0.75 of retention ratio at 10 A/g. The retention ratio after 2000 charging-discharging cycles at 10 A/g reached up to 0.96.6. The methylene blue adsorption capacity of SACF was 177-1522 mg/g. One step method was better than two step method. The methylene blue adsorption capacity of HACF was 91-135mg/g. Better capacity could be got by lower activation temperature, shorter activation time and lower activation concentration.7. High specific surface area and plenty micropores could be the key factors for high specific capacitance for ACF, and the ratio of micropore to mesopore contributed to the retention ratio. The specific capacitance for ACF do not had directly relationship with mesopore volume and average pore diameter.The methylene blue adsorption capacity mainly increased with the increaseing mesopore volume.