酸/碱催化剂对低阶煤热解挥发分转化行为的作用机制研究

Study on the mechanism of acid/base catalyst on the release behavior of volatiles during low rank coal pyrolysis

利用下行床连续热解实验装置,采用催化剂原位填充方式考察了三种孔道结构,不同酸量的酸性催化剂HZSM-5、Al-MCM-41、USY和一种碱性催化剂铝酸钙(Ca-Al)及酸碱催化剂的不同组合方式对挥发分转化行为的影响。结果表明,Al-MCM-41因具有适宜酸性及较大的比表面积和丰富的介孔结构,降低了焦油中重质组分含量,增加了轻质组分含量,在降低积炭和减少焦油损失方面优于酸性较强的HZSM-5和USY催化剂。Ca-Al促进烃类物质脱氢产生富氢小分子,抑制了大分子物质的缩聚,显著降低了积炭产率。结合酸碱催化剂对热解挥发分各自作用的优势,将其进行不同方式的组合,探究了在组合催化剂作用后热解挥发分产物的组成和产率变化情况,结果显示热解挥发分先通过具有脱氢性能的Ca-Al、然后再通过裂解作用适中的Al-MCM-41的Ca-Al/Al催化剂组合,表现出较强的调控挥发分组分间转化行为的能力,有效地降低了积炭的产率。

The effects of three acidic catalysts HZSM-5,Al-MCM-41,USY and a base catalyst of calcium aluminate(Ca-Al)with different pore structures and acid contents on volatiles conversion were investigated by in-situ filling method in a downer-bed continuous pyrolysis experiment.The results show that Al-MCM-41 catalysts with suitable acidity,large specific surface areas and rich mesoporous structures can reduce the content of heavy components in tar and increase the content of light components,which is superior to HZSM-5 and USY catalysts with stronger acidity in reducing coke and tar loss.Ca-Al promotes the dehydrogenation of hydrocarbons to generate hydrogen-rich small molecules,inhibits the polycondensation of macromolecules,and significantly reduces the yield of carbon deposition.Integrated with the advantages of acid-base catalysts in their respective effects on pyrolytic volatiles,they were combined in different ways to explore the composition and yield changes of pyrolytic volatiles after the combined catalyst.The results show that when the pyrolytic volatiles are first dehydrogenated by Ca-Al and then cracked moderately by Al-MCM-41,the combination catalyst of Ca-Al/Al has a strong ability to regulate the conversion behaviors between components in volatiles and reduce the yield of coke effectively.