碱/碱土金属浸渍对酸洗生物质热解影响研究

为研究碱/碱土金属(AAEM)浸渍预处理对酸洗生物质热解特性的影响,本文选用稻壳、橡木和秸秆3种生物质为原样,对酸洗及酸洗后5种金属硝酸盐(KNO3,Ca(NO3)2,Mg(NO3)2,Fe(NO3)3,Ni(NO3)2)溶液浸渍样进行热重分析。结果表明:酸洗使得生物质中金属含量降低,而浸渍预处理使生物质中金属含量增加;经酸洗后生物质的TG和DTG曲线向高温方向移动,最大热解速率明显增加,焦炭产量下降;AAEM盐浸渍预处理可以促进生物质的热解过程,使生物质的TG和DTG曲线向低温移动;Fe、K、Ni盐的反应活性稍高于Ca、Mg盐。从动力学方面看,Coats-Redfern法对150~340℃范围内生物质热解均有很好的相关性,反应级数为一级,金属的添加使生物质热解所需活化能降低,对热解具有催化作用。

The effects of alkali/alkaline earth metal impregnation pretreatment on the pyrolysis characteristics of biomass

In order to understand the catalytic effect of alkali and alkaline earth metal (AAEM) salts on the pyrolysis characteristics of biomass, three typical biomass samples, namely rice husks, oak and corn stalks, were washed by acid and subsequently impregnated with different metal nitrate salts, including KNO3, Ca(NO3)2, Mg(NO3)2, Fe(NO3)3 and Ni(NO3)2. The products were investigated by thermogravimetric analysis. The results showed that acid washing could reduce the metal content of the biomass. After acid washing, the TG and DTG curves of the biomass were shifted to higher temperature, the maximum pyrolysis rate increased significantly, and the char yield decreased. AAEM salts could catalyze the pyrolysis process and shifted the TG and DTG curves of the biomass to lower temperature. Fe, K, and Ni salts showed higher reactive activities than Ca and Mg salts. In terms of pyrolysis kinetics, the Coats-Redfern method applied to biomass pyrolysis at 150-340℃ had a high correlation and the pyrolysis process can be described by a first-order reaction kinetics model. The adding of AAEM salts can lower the activation energy of biomass in pyrolysis and catalyze the pyrolysis process, and is thus beneficial to biomass pyrolysis.