不同热解温度下杨树各组分生物质炭的理化特性分析与评价

【目的】通过对不同热解温度下杨树树叶、树枝、树皮生物质炭和秸秆生物质炭的理化特性及结构进行分析,筛选出更适用于林地土壤改良的农林废弃物种类和热解温度。【方法】以杨树不同组分树叶、树枝、树皮和秸秆等4种农林废弃物为原料,分别在300、500和700 ℃温度下制备生物质炭,测定其产率、pH、全碳、全氮含量、阳离子交换量(CEC)、比表面积和表面官能团等指标。【结果】随着热解温度的升高,4种原料生物质炭的产率逐渐降低,灰分含量和pH升高。同一热解温度下,树枝和树皮生物质炭的全碳含量高于树叶和秸秆生物质炭的,而全氮(TN)、全磷(TP)和全钾(TK)含量均低于树叶和秸秆生物质炭的。4种生物质炭水溶性盐基离子含量和交换性盐基离子含量均随着热解温度的升高而增加,树叶生物质炭的阳离子交换量总体高于其他3种原料的生物炭。树叶和树皮生物质炭的比表面积和总孔容积总体大于树枝和秸秆生物质炭,树皮和树叶生物质炭在700 ℃时比表面积分别高达597.02和121.01 m²/g。4种原料生物质炭的表面官能团种类基本相同,以芳香骨架为主,表面官能团数量均随着热解温度的升高而减少,芳香化程度增强。【结论】在不同热解温度和原料制备的生物质炭中,树叶和秸秆生物质炭的灰分、pH、N、K和盐基离子含量较高,比较适用于改良酸性土壤,增加土壤养分;而杨树树枝和树皮生物质炭含碳量较高,则适用于土壤固碳,提高土壤有机质含量。其中,500 ℃热解的杨树树叶生物质炭综合性能最好,氮、磷、钾养分耗失最少,阳离子交换能力较强,比表面积大,更适用于土壤改良。

Analysis and evaluation on physicochemical properties of poplar biochar at different pyrolysis temperatures

【Objective】The characteristics and structure of polar leaf, twig, and bark and straw biochar at different pyrolysis temperatures were analyzed, the types and pyrolysis temperature of agricultural and forestry wastes which are more suitable for forest soil improvement were selected. 【Method】We selected four kinds of agricultural and forestry residues as raw materials, namely leaves, twigs, bark harvested from different components of poplar, and straw harvested from rice. Furnace temperatures were respectively set at 300, 500 and 700 ℃. We studied the properties of biochar, including yield, pH, total C content, total N content, cation exchange capacity (CEC), specific surface area, and surface functional group. 【Result】The results of this study showed that with an increase in pyrolysis temperature, the yield of biochar of the four selected materials gradually decreased, whereas the ash content and pH value continuously increased. At the same pyrolysis temperature, the total C content of twig biochar and bark biochar was evidently higher than that of leaf biochar and straw biochar, while the total N content, total P content, and total K content were lower than those of leaf biochar and straw biochar. The water-soluble and exchangeable base cations of the four kinds of biochar increased with an increase in pyrolysis temperature. The CEC of leaf biochar was higher than that of the other three feedstock biochar. The specific surface area and total pore volume of leaf biochar and bark biochar were generally larger than those of twig biochar and straw biochar. The specific surface area of bark biochar and leaf biochar at 700 ℃ was as high as 597.02 m²/g and 121.01 m²/g, respectively. The surface functional groups, particularly the aromatic skeleton, of the four kinds of biochar were almost the same. We found that with an increase in pyrolysis temperature, the type and number of surface functional groups decreased; however, the degree of aromatization increased. 【Conclusion】Through a comprehensive analysis, we found that among biochar of different raw materials and pyrolysis temperatures, ash content, pH, N, K and base ion content of leaf and straw biochar are relatively higher; the values are more suitable for improving acidic soil and increasing soil nutrients. However, the higher carbon content in poplar twigs and bark is suitable for soil carbon sequestration for improving soil organic matter content. Overall, poplar leaf biochar at 500 ℃ had the highest N, P, and K content, strong CEC, and large specific surface area, and is thus more suitable for soil improvement in woodlands.