黑液的热失重特性及其动力学分析

采用热重分析法对黑液固形物样品的热解行为进行了研究,分析了黑液在不同升温速率时的热解特性,并与纯碱木素的热解特性进行对比.结果表明:黑液的热解过程可以分为4个阶段,且在低温区和高温区各有一个强烈失重峰,黑液中糖、有机酸以及碱金属盐对黑液热解特性存在一定的影响;而纯碱木素的热解过程由脱水、保持、剧烈失重和缓慢失重4个区域组成,热解开始较早,但持续时间较长.黑液的热解特性与纯碱木素的有一定差别.在实验的基础上,根据Coats-Redfern法描述了热解过程,计算了黑液和纯碱木素样品在不同升温速率下的热解动力学参数.动力学研究结果表明:黑液有机物热解的主要区域的反应级数为4,活化能和频率因子随加热速率的提高而轻微上升.

Thermogravimetric Properties of Black Liquor and Corresponding Kinetic Analysis

The pyrolysis characteristics of black liquor solid were studied via thermogravimetric analysis,and the effect of heating rate on the pyrolysis characteristics was investigated,followed by a comparison with that of alkali lignin.The results show that(1) the pyrolysis of black liquor consists of 4 stages,with two peaks of rapid weight loss respectively in the lowand high-temperature ranges;(2) the polysaccharides,aliphatic carboxylic acids and alkali metal salts in black liquor have certain effects on the pyrolysis characteristics of black liquor;(3) the pyrolysis of alkali lignin,which begins early and lasts for a long period,includes 4 stages,namely,the dehydration,the water holding,the rapid weight loss and the slow weight loss stages;and(4) there are some differences in the pyrolysis characteristics between black liquor and alkali lignin.Moreover,according to the analysis of pyrolysis process by means of Coats-Redferen method and based on the calculated kinetic parameters of black liquor and alkali lignin pyrolysis at different heating rates,it is found that the reaction order of black liquor pyrolysis is 4 at the organic pyrolysis region,and that the activation energy and frequency factor in the decomposition increase slightly with the heating rate.