控制热分解条件下制备生物炭及其表征

Preparation and Characterization of Biochar under the Controlling Conditions of Pyrolysis

以稻杆为原料,以KOH溶液为浸渍剂,在控制热分解条件下制备生物炭。采用N2吸附、碘吸附、Boehm滴定、元素分析、XRD和FTIR等方法对生物炭进行了表征,并探讨了KOH浸渍和热分解条件对生物炭孔结构,尤其是表面化学性质的影响。结果表明:KOH浸渍处理后生物炭比表面积和总孔容积明显增大,有利于生成强酸性官能团和减少可挥发性有机碳以及生成更为稳定的表面含氧官能团;生物炭吸碘值随着炭化温度升高和时间延长总体呈先上升后下降的趋势;气氛组成对生物炭孔结构和化学性质有重要影响,N2-NH3混合气氛条件下制备生物炭的比表面积、总孔容积、中孔率和吸附性能都显著大于纯N2气氛下制备的生物炭,而表面酸性含氧官能团数量明显减少,同时引入含氮碱性基团,并使生物炭表面极性增强。

The straw based biochar was prepared under the controlling conditions of pyrolysis. The straw powder was treated by KOH intercalation prior to performing pyrolysis. Biochar samples prepared were characterized by N2 adsorption at 77 K,iodine adsorption, Boehem titration, elemental analysis, XRD and FTIR. The influences of KOH intercalation and conditions for pyrolysis on the development of the porous structure and surface chemistry of biochar was studied by changing the concentration of KOH and the constitution of the gas flow as well as the temperature. Results showed that the specific surface area and total volume of biochar increased by KOH intercalation. Regarding the iodine adsorption, biochars showed a peak value with elevating pyrolyzing temperature and extending the pyrolyzing time. The gaseous constituent displayed an important influence on development of porous structure and surface chemistry of biochar. The specific surface area, total pore volume, porosity and adsorption performance of biochar formed under N2-NH3 flow were significantly greater than those obtained under pure N2 flow. Nevertheless, the number of acidic surface oxygen groups decreased significantly, and basic surface nitrogen groups was detected at the same time, displaying an increased surface polarity of biochar.