模板法调控多级孔ZSM-5催化褐煤挥发分制备轻质芳烃的研究

doi:10.11949/0438-1157.20210799

摘要/Abstract

摘要：

在相同的水热合成条件下，以氧化炭黑为硬模板和十六烷基三甲基溴化铵（CTAB）为软模板，经一步结晶法分别制得了一系列以晶内介孔为主和以无定形介孔为主的多级孔ZSM-5分子筛。通过采用次氯酸钠、双氧水和硝酸来氧化改性商业炭黑，以增加其亲水性及分散性，进而促进了ZSM-5在晶化过程中分子筛前体与炭粒之间的相互作用。重点阐述了不同碳源和CTAB对合成的多级孔ZSM-5物化结构特性的影响，并将该催化剂用于褐煤热解挥发分催化重整制备轻质芳烃的反应中。结果表明，成功构筑的孔径均一的微-介孔梯度的ZSM-5在催化重整褐煤热解挥发分提质过程中有效地解决了催化剂的扩散传质问题，抑制了催化剂失活。引入硝酸氧化改性炭黑晶化合成的ZSM-5分子筛在褐煤热解挥发分的催化重整反应中表现出了很好的催化性能，其中轻质芳烃含量达到27.0 mg/g，选择性为81.7%。此外，在氢气气氛下，该催化剂能够有效降低积炭的碳含量。

关键词: 多级孔ZSM-5, 热解, 催化活性, 轻质芳烃, 失活

Abstract:

Under the same hydrothermal synthesis conditions, using oxidized carbon black as the hard template and cetyltrimethylammonium bromide (CTAB) as the soft template, a series of intracrystalline mesopores were prepared by one-step crystallization method. And the multi-porous ZSM-5 zeolite dominated by amorphous mesopores. The commercial carbon black was oxidized by sodium hypochlorite, hydrogen peroxide and nitric acid to increase its hydrophilicity and dispersion, thus promoting the interaction between ZSM-5 precursor and carbon particles in the crystallization process. The effects of different carbon sources and CTAB on the physicochemical properties of the hierarchical ZSM-5 were discussed. Meanwhile, these catalysts were used in the catalytic reforming of lignite-derived volatiles to prepare light aromatics. The results show that the micro-mesoporous gradient ZSM-5 with uniform pore size can effectively solve the diffusion and mass transfer problem and inhibit the deactivation of the catalyst. ZSM-5 zeolite synthesized by oxidized carbon black with nitric acid showed good catalytic performance in the catalytic reforming of lignite-derived volatiles, in which the content of light aromatics was 27.0 mg/g and the selectivity was 81.7%. In addition, the catalyst can effectively reduce the coke content in hydrogen atmosphere.

Key words: hierarchical ZSM-5, pyrolysis, catalyst activation, light aromatics, deactivation

中图分类号:

TQ 530

任雪宇, 曹景沛, 姚乃瑜, 赵小燕, 冯晓博, 刘天龙, 赵云鹏. 模板法调控多级孔ZSM-5催化褐煤挥发分制备轻质芳烃的研究[J]. 化工学报, 2021, 72(11): 5620-5632.

Xueyu REN, Jingpei CAO, Naiyu YAO, Xiaoyan ZHAO, Xiaobo FENG, Tianlong LIU, Yunpeng ZHAO. Turning hierarchical ZSM-5 by template methods and its application in catalyzing lignite-derived volatiles to light aromatics[J]. CIESC Journal, 2021, 72(11): 5620-5632.

图/表 15

图1 下坠床快速催化热解反应装置示意图

Fig.1 Schematic diagram of catalytic fast pyrolysis of the drop bed reactor

图2 CB和氧化改性炭黑的N2等温吸-脱附曲线和孔径分布(DFT法)

Fig.2 N2 adsorption-desorption isotherms and pore size distribution (using the DFT method) of CB and oxidated CB

表1 氧化改性炭黑和多级孔ZSM-5的结构特性

Table 1 The textural properties of oxidation modified CB and hierarchical ZSM-5

Sample	Surface area/(m²/g)			Pore volume/(cm³/g)			D_ave^⑤/nm
Sample	S_BET^①	S_micro^②	S_ext^②	V_total^④	V_micro^②	V_ext^③	D_ave^⑤/nm
CB	1351	890	461	3.35	0.41	2.94	10.00
NaClO-CB	1026	654	372	2.54	0.31	2.23	9.91
H₂O₂-CB	450	101	349	1.47	0.05	1.42	13.00
HNO₃-CB	1232	838	394	1.97	0.39	1.58	6.38
HeZ5	386	350	36	0.23	0.14	0.09	2.43
HeZ5-Ⅰ	345	312	33	0.21	0.15	0.06	2.44
HeZ5-Ⅱ	364	312	52	0.23	0.16	0.07	2.56
HeZ5-Ⅲ	377	347	30	0.21	0.16	0.05	2.27
HeZ5-Ⅳ	344	264	80	0.19	0.16	0.03	2.23
HZSM-5	422	376	46	0.23	0.16	0.07	3.70

图3 CB和氧化改性炭黑的SEM图、接触角、FT-IR谱图和XRD谱图

Fig.3 SEM images, contact angles on the surface layer, FT-IR spectra and XRD patterns of CB and oxidated CB

图4 CB和HNO3-CB的表面C 1s和O 1s的XPS光谱

Fig.4 XPS spectra of C 1s and O 1s on CB and HNO3-CB

表2 XPS光谱中各官能团的相对含量

Table 2 The relative content of functional groups in XPS spectra

Sample	C 1s				O 1s			C/O（atomic ratio）
Sample	C—C	C—O	CO	OC—O	—CO	C—O	OC—O	C/O（atomic ratio）
CB	35.10	24.15	19.64	21.11	34.42	33.23	32.35	10.10
HNO₃-CB	36.18	22.31	19.44	22.07	35.04	33.15	31.81	3.85

图5 硬模板和软模板合成多级孔ZSM-5的N2等温吸-脱附曲线

Fig.5 N2 adsorption-desorption isotherms of hierarchical ZSM-5 via “hard” and “soft” template methods

图6 硬模板合成多级孔ZSM-5的SEM图、XRD谱图和孔径分布(DFT法)

Fig.6 SEM images, XRD patterns and pore size distribution curves (using the DFT method) of hierarchical ZSM-5 via “hard” template method

图7 HeZ5-Ⅲ分子筛Si 2p和Al 2p的XPS光谱

Fig.7 XPS spectra of Si 2p and Al 2p on HeZ5-Ⅲ

图8 软模板法合成HeZ5-Ⅳ的SEM图、XRD图和孔径分布(DFT法)

Fig.8 SEM images, XRD pattern and pore size distribution curves (using the DFT method) of HeZ5-Ⅳ via “soft” template method

图9 硬模板和软模板法合成多级孔ZSM-5的NH3-TPD谱图

Fig.9 NH3-TPD profiles of hierarchical ZSM-5 via “hard” and “soft” template methods

表3 硬模板和软模板法合成多级孔ZSM-5的酸量

Table 3 The acidic amount of hierarchical ZSM-5 via “hard” and “soft” template methods

Catalysts	Acidity/(mmol/g)
Catalysts	Strong acid	Weak acid	Total acid
HeZ5	—	0.57	0.57
HeZ5-Ⅰ	0.11	0.18	0.29
HeZ5-Ⅱ	0.06	0.12	0.18
HeZ5-Ⅲ	0.11	0.18	0.29
HeZ5-Ⅳ	—	0.11	0.12
HZSM-5^[32]	0.36	0.83	1.19

图10 挥发分经多级孔ZSM-5催化重整产物的碳产率、碳转化率和气体组成分布

Fig.10 Products carbon yields, carbon conversion yield and gaseous components distribution from catalytic reforming of volatiles over hierarchical ZSM-5

图11 挥发分经多级孔ZSM-5催化重整产生的BTEXN碳产率及其碳选择性

Fig.11 BTEXN carbon yields and its carbon selectivity during catalytic reforming of volatiles over hierarchical ZSM-5

图12 使用后的多级孔ZSM-5的TG和DTG曲线

Fig.12 TG and DTG curves of spent hierarchical ZSM-5

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