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

doi:10.11949/0438-1157.20211697

Abstract

Abstract:

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.

Key words: catalyst, pyrolysis, catalysis, tar, coke

摘要：

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。

关键词: 催化剂, 热解, 催化, 焦油, 积炭

CLC Number:

TQ 530.2

Yong LI, Lunjing YAN, Xiaorong LI, Xin JIN, Ting LI, Qian LIU, Meijun WANG, Jiao KONG, Liping CHANG, Weiren BAO. Study on the mechanism of acid/base catalyst on the release behavior of volatiles during low rank coal pyrolysis[J]. CIESC Journal, 2022, 73(3): 1173-1183.

李勇, 闫伦靖, 李晓荣, 靳鑫, 李挺, 刘倩, 王美君, 孔娇, 常丽萍, 鲍卫仁. 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[J]. 化工学报, 2022, 73(3): 1173-1183.

Figures/Tables 16

Table 1 Proximate analysis and ultimate analysis of NMH coal

Proximate analysis/%(mass)				Ultimate analysis /%(mass, daf)
M_ad^①	A_d^②	V_daf^③		C	H	N	S	O^④
19.5	5.8	50.12		74.35	5.13	0.72	0.31	19.49

Fig.1 Downer-bed continuous pyrolysis experimental device and filling method of catalyst

Fig.2 XRD patterns of different types of catalysts before and after experiment (F－before experiment, S－after experiment)

Fig.3 N2 isothermal adsorption desorption curves of different types of catalysts

Table 2 Pore structure parameters of different types of catalysts before and after reaction

Sample	S_BET / (m²/g)	S_mic/ (m²/g)	V_toal/ (cm³/g)	V_micro/ (cm³/g)	V_meso/ (cm³/g)
Al-MCM-41 (F)	759.34	295.98	0.8995	0.2310	0.6686
Al-MCM-41 (S)	542.43	306.70	0.7087	0.2168	0.4919
USY (F)	686.64	628.24	0.4385	0.2374	0.2010
USY (S)	283.96	246.42	0.2550	0.0941	0.1609
HZSM-5 (F)	320.88	241.42	0.3044	0.0982	0.2062
HZSM-5 (S)	271.31	203.93	0.2558	0.0826	0.1732
Ca-Al (F)	0.56	0.40	0.0013	0.0002	0.0012
Ca-Al (S)	0.23	0.13	0.0007	0.0001	0.0006

Fig.4 NH3-TPD and CO2-TPD curves of different types of catalysts

Fig.5 Distribution of coal pyrolysis products from coal pyrolysis under different types of catalysts

Fig.6 Yield of gases from coal pyrolysis under different types of catalysts

Fig.7 Distribution of coke in catalytic pyrolysis of coal

Fig.8 Fractions distribution of tar from coal pyrolysis with different types of catalysts

Fig.9 Components distribution of tar from coal pyrolysis with different types of catalysts

Fig.10 Distribution of products from coal pyrolysis products under combined catalysts

Fig.11 Yield of gases from coal pyrolysis products under combined catalysts

Fig.12 Distribution of coke in coal pyrolysis with combined catalysts

Fig.13 Fractions distribution of tar from coal pyrolysis over combined catalysts

Fig.14 Components distribution of tar from coal pyrolysis over combined catalysts

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