Effect of modified montmorillonite on the pyrolysis behavior of Xinjiang Hefeng coal

doi:10.11949/0438-1157.20211298

Abstract

Abstract:

A serial of Zr modified montmorillonites were prepared by mechanical ball milling and their characteristics were depicted by X-ray diffractometer (XRD), N₂ adsorption-desorption instrument (BET), temperature-programmed desorption of ammonia (NH₃-TPD). Then, the effect of Zr catalysts on tar quality and product distribution during coal pyrolysis was investigated in a fixed bed reactor. Finally, the pyrolysis performance of phenyl benzyl ether (BPE), bibenzyl and biphenyl model compounds of coal, were carried out to explore the breakage mechanism of covalent bonds in coal. The results show that in comparison with raw montmorillonite, the specific surface area of acid leaching sample increases, while a first decrease and then an increase trend is observed with increasing Zr content. In view of total acid sites and strong acid sites, the maximum value appears when ZrO₂ content is 24%(mass) (24ZrAM). Under the action of xZrAM, both the tar yield and pitch content decrease to a certain degree. Specially, 24ZrAM shows the highest catalytic activity, resulting in the highest light fraction of 53.2%(mass), the content of long-chain hydrocarbon decreases by 22.1% and phenolic compounds increases by 22.5%. The conversion rates of BPE, dibenzyl and biphenyl were 87.2%, 63.2% and 31.3% higher than those without catalyst, respectively, indicating that 24ZrAM can promote the cleavage of long-chain hydrocarbons and the cleavage of C_al—O, C_al—C_al and C_ar—C_ar bonds.

Key words: Zr modified montmorillonite, Xinjiang Hefeng coal, model compound, catalytic pyrolysis, tar quality

摘要：

采用机械球磨法制得不同Zr含量的改性蒙脱土催化剂，通过X射线衍射仪(XRD)、物理吸附仪(BET)和化学吸附仪(NH₃-TPD)表征其结构特征，在固定床中考察催化剂对煤热解产物分布和焦油品质的影响规律，基于模型化合物苄基苯基醚(BPE)、联苄和联苯的热解行为分析，探讨了催化剂对煤中共价键断裂规律的作用机制。结果表明：酸洗可增加蒙脱土的比表面积，添加Zr后该值先减小后增加，酸性与之相反，当Zr含量为24%(质量)(24ZrAM)时，催化剂的酸量与强酸强度达最高。在xZrAM的作用下，热解焦油产率和沥青含量均下降，特别是24ZrAM对焦油的提质活性最好，轻油组分分率最高，为53.2%(质量)，长链烃含量降低了22.1%，酚类化合物增加了22.5%。BPE、联苄和联苯的转化率分别比无催化剂时提高了87.2%、63.2%和31.3%，说明24ZrAM可促进长链烃裂解和C_al—O、C_al—C_al和C_ar—C_ar键的断裂。

关键词: Zr改性蒙脱土, 新疆和丰煤, 模型化合物, 催化热解, 焦油品质

CLC Number:

TQ 530.2

Zhaoxi ZHANG,Mei ZHONG,Jian LI, YALKUN·Tursun. Effect of modified montmorillonite on the pyrolysis behavior of Xinjiang Hefeng coal[J]. CIESC Journal, 2022, 73(1): 402-410.

张照曦,钟梅,李建,亚力昆江?吐尔逊. 改性蒙脱土对新疆和丰煤热解行为的影响[J]. 化工学报, 2022, 73(1): 402-410.

Figures/Tables 13

Table 1 Analysis of coal samples

Sample	Proximate analysis/%(mass)			Ultimate analysis/%(mass,daf)
Sample	A_d	V_daf	FC_daf^①	C	H	O^①	N	S
raw coal	22.83	47.47	52.53	72.06	5.64	19.07	3.00	0.23
DC	1.10	44.98	55.02	61.17	4.93	30.86	2.83	0.21

Fig.1 Schematic of coal pyrolysis setup

Fig.2 XRD patterns of modified catalysts

Fig.3 N2 adsorption-desorption isotherms (a) and pore size distributions of catalysts (b)

Table 2 Pore texture properties of the catalysts

Sample	BET surface area /(m²/g)	Pore volume / (cm³/g)	Average pore size /nm
RM	55	0.09	7.73
AM	113	0.17	3.02
8ZrAM	80	0.14	8.04
16ZrAM	81	0.13	8.12
24ZrAM	93	0.12	6.58
32ZrAM	100	0.12	6.14

Fig.4 NH3-TPD profiles of catalysts (a) and Gaussian fitting results of NH3-TPD (b)

Fig.5 Products distribution (a) and gas components (b) from Hefeng coal pyrolysis over catalysts

Fig.6 Simulated distillate fractions (a) and yields (b) of tar

Table 3 Composition analysis of tar

Components	Relative content/%
Components	DC	24ZrAM
aliphatic hydrocarbons	52.71	52.01
b.p. above 300℃	40.74	31.74
aromatic hydrocarbons	35.10	39.73
benzenes	5.98	6.19
phenols	18.27	22.74
naphthalenes	8.65	8.79
indenes	2.20	2.01
other heteroatom compounds beyond phenol derivatives	12.19	9.26

Fig.7 Products distribution and BPE conversion (a) and gas components (b) from MeOH-BPE pyrolysis over catalysts

Fig.8 GCMS spectra of products (a) and aromatic compound yields (b) from MeOH-BPE pyrolysis over catalysts

Fig.9 Reaction mechanism for BPE (a), bibenzyl (b) and biphenyl pyrolysis (c)

Fig.10 Relative content of bibenzyl (a) and biphenyl (b) pyrolysis products

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