不同秸秆生物炭的孔隙结构及其差异

基于低温氮气吸附的研究方法，对水稻秸秆、玉米秸秆、小麦秸秆制备的生物炭进行了孔结构研究，用BET方程、BJH方程和t-plot方法分别计算得到生物炭的比表面积、孔径分布和微孔数据，利用FHH模型计算了孔隙分形维数。研究表明：不同温度不同材料都对生物炭的孔结构有较大影响，随着热解温度的升高水稻秸秆生物炭和小麦秸秆生物炭的BET比表面积和总孔容呈先增加后降低的趋势，而玉米秸秆生物炭的孔隙度随着热解温度升高持续增加；3种秸秆生物炭的孔径分布均以中孔为主，孔隙内部以Ⅱ型孔为主；水稻秸秆、玉米秸秆、小麦秸秆制备的生物炭都具有很好的分形特征，分形维数(D)分别为2.545 4~2.669 3、2.629 7~2.689 5、2.577 3~2.597 2，表明这3种生物炭孔隙结构比较复杂，非均质性强，其中水稻秸秆生物炭和小麦秸秆生物炭均在500 ℃条件下有较高的分形维数，分别是2.669 3和2.597 2,玉米秸秆生物炭则在700 ℃条件下有较高的分形维数，为2.689 5。

Pore Structure and Fractal Characteristics of Biochars From Different Straw

Based on the cryogenic nitrogen gas adsorption method, the pore characteristics of biochars made from farmland waste including rice straw, corn stalk and wheat straw were studied. The BET equation, BJH equation and t-plot method were used to caculate the specific surface area, pore size distribution and microporous parameters, and FHH model was used to obtain the fractal dimension(D) of pore. Results showed that different temperature and different materials all had larger effects on the pore characteristics of biochar. With the increase of pyrolysis temperature, the BET specific surface area and pore volume of rice-straw-biochar and wheat-straw-biochar increased firstly and then decreased, whereas, the porosity of corn-stalk-biochar always increased. It was concluded that the mesopores were the main type of pores in three kinds of biochars and the pores mainly consisted of the second pores. It was found that rice-straw-biochar, corn-stalk-biochar and wheat-straw-biochar all had good fractal characteristics, and the pore fractal dimensions were 2.545 4-2.669 3, 2.629 7-2.689 5 and 2.577 3-2.597 2, respectively, which reflected the complexity and heterogeneity of the biochar porosity. Both rice-straw-biochar and wheat-straw-biochar had higher fractal dimension at 500 ℃(2.669 3 and 2.597 2), but corn-stalk-biochar had higher fractal dimension at 700 ℃(2.689 5).