酸洗预处理对纤维素热裂解的影响研究

Experimental study of the influence of acid wash on cellulose pyrolysis

为获得液体产量的最大化和提高产物中糖类的质量分数,采用盐酸(3%、5%、7%)、磷酸(7%)和硫酸(7%)对纤维素进行酸洗预处理。不同酸洗预处理下纤维素的微观结构和聚合度变化表明,酸处理损坏了纤维素的物理结构,并使聚合度大幅度降低。在“┣”形石英玻璃反应器的快速热裂解试验装置上进行了不同酸处理前后的纤维素热裂解试验,发现酸浸泡处理后,生物油产率下降,相应的气体和焦炭产率提高,并且随着酸浓度的提高,该趋势逐渐增强。与盐酸和磷酸相比,硫酸对生物油的生成具有更强的抑制作用,这表明,酸对纤维素交联和脱水反应的催化效果。通过GC-MS色质联机分析技术对生物油成分进行分析,发现酸的存在并没有改变生物油成分的种类,但使化合物之间的相对质量分数发生了变化。左旋葡聚糖的质量分数随稀酸溶液浓度的增加呈下降趋势,原因是残留在物料中的微量酸以催化脱水和交联反应的方式,对其生成起抑制作用。

In order to maximize the liquid yield and glucide content in biomass pyrolysis products, acid wash pretreatment was usually adopted. The analysis of microstructure and polymerization degree shows that the acid wash can alter the cellulose morphology and decrease the polymerization degree largely. A series of experiments were carded out to study the effect of acid wash on the cellulose rapid pyrolysis. Experimental results indicate that under the acid pretreatment the yield of bio-oil decreases, while the yield of gas and char increases. The effect would be greater with the increase of acid concentration. Sulphuric acid has a stronger restraint on the formarion of bio-oil than hydrochloric acid and phosphoric acid. It is suggested that the acid has a catalysis to the cross linking and dehydration reaction of cellulose. According to the GC-MS analysis of bio-oil, the existence of acid would not alter the bio-oil components, but change the relative contents of bio-oil compounds. High-concentration acid wash can restrain the formation of levoglucosan by catalyzing the dehydration and cross linking reaction.