Catalytic conversion of lignite pyrolysis volatiles for enriching light aromatics over B-ZSM-5

doi:10.11949/0438-1157.20210973

Abstract

Abstract:

Under different alkaline conditions, the B-HZSM-5 (B-H5) catalyst was hydrothermally synthesized to catalyze the pyrolysis of lignite volatiles to produce light aromatics in situ. X-ray diffraction (XRD), scanning electron microscope(Gemini SEM 500), temperature programmed desorption of ammonia (NH₃-TPD), and N₂ adsorption-desorption were used to characterize the morphology, acidity and textural properties of xB-HZSM-5. The higher weak acid content and the higher crystallinity of Na-xB-H5(added NaOH) were obtained under a stronger alkaline solution. Compared with parent ZSM-5, the weak acidity assigned to the B—OH—Si groups of Na-xB-H5 provided more active sites to absorb ethylene and propylene to promote methylation and alkylation processes. The highest alkylbenzene yield was obtained (11.4 mg/g) over Na-0.69B-H5 (B content was 0.69 g) with higher crystallinity, sufficient active sites and hierarchical micro/mesopore. However, the excess B also brought a negative effect on aromatization due to the reduced rate of stronger acid and weak acid. The Na-xB-H5 provided a great prospect to enhance the catalyticperformance of lignite vapors by the introduction of B in the framework of H5.

Key words: catalyst, zeolites, stability, mass transfer, aromatics, lignite pyrolysis, B-HZSM-5

摘要：

在不同碱性条件下水热合成了B-HZSM-5 （B-H5）催化剂用于原位催化褐煤热解挥发分制备轻质芳烃。通过X射线衍射仪、扫描电子显微镜、氨气程序升温脱附仪和N₂物理吸附脱附表征了合成条件对分子筛的形貌、酸性和质构特征的影响。在强碱性条件下合成的分子筛表面更光滑、结晶度更高，Na-xB-H5（合成过程加碱）弱酸明显增强。与母体H5相比，Na-xB-H5骨架硼形成的B—OH—Si提供更多的弱酸位点能够吸附乙烯丙烯等中间产物，增加甲基化和烷基化速率。在具有较高的结晶度、丰富的酸位点和微孔/介孔的Na-0.69B-H5（硼添加量为0.69 g）上得到了最高烷基苯产率11.4 mg/g。而过量引入硼则会使骨架Al流失，强弱酸比例减少，抑制芳构化反应，降低轻质芳烃产率。通过骨架硼的引入调控分子筛酸性为褐煤催化热解提高轻质芳烃产率提供了新思路。

关键词: 催化剂, 沸石, 稳定性, 传质, 芳烃, 褐煤热解, B-HZSM-5

CLC Number:

TQ 523

Zhen YANG, Jingpei CAO, Chen ZHU, Tianlong LIU, Xiaoyan ZHAO. Catalytic conversion of lignite pyrolysis volatiles for enriching light aromatics over B-ZSM-5[J]. CIESC Journal, 2021, 72(11): 5633-5642.

杨珍, 曹景沛, 朱陈, 刘天龙, 赵小燕. B-ZSM-5酸调控及催化褐煤热解挥发分制轻质芳烃研究[J]. 化工学报, 2021, 72(11): 5633-5642.

Figures/Tables 14

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Samples	S_BET^①/(m²/g)	S_micro^②/(m²/g)	S_ext^③/(m²/g)	V_t^④/(cm³/g)	V_micro^⑤/(cm³/g)	V_ext^⑥/(cm³/g)	D_ave^⑦/nm
Na-H5	389	343	46	0.29	0.16	0.13	2.9
Na-0.23B-H5	396	342	54	0.29	0.16	0.13	3.0
Na-0.46B-H5	403	346	57	0.30	0.15	0.15	2.9
Na-0.69B-H5	406	344	62	0.33	0.15	0.18	3.3
H5	427	386	41	0.48	0.16	0.32	4.1
0.23B-H5	447	397	50	0.35	0.17	0.18	3.1
0.46B-H5	438	389	49	0.36	0.16	0.20	3.4
0.69B-H5	436	393	43	0.41	0.16	0.25	3.8

Samples	S_BET^①/(m²/g)	S_micro^②/(m²/g)	S_ext^③/(m²/g)	V_t^④/(cm³/g)	V_micro^⑤/(cm³/g)	V_ext^⑥/(cm³/g)	D_ave^⑦/nm
Na-H5	389	343	46	0.29	0.16	0.13	2.9
Na-0.23B-H5	396	342	54	0.29	0.16	0.13	3.0
Na-0.46B-H5	403	346	57	0.30	0.15	0.15	2.9
Na-0.69B-H5	406	344	62	0.33	0.15	0.18	3.3
H5	427	386	41	0.48	0.16	0.32	4.1
0.23B-H5	447	397	50	0.35	0.17	0.18	3.1
0.46B-H5	438	389	49	0.36	0.16	0.20	3.4
0.69B-H5	436	393	43	0.41	0.16	0.25	3.8

Catalysts	Acid/(mmol NH₃/g)			Acidity density/ (mmol/m²)	Relative crystallinity^① /%	Al^②/%	B^②/%
Catalysts	Weak (150~300℃)	Strong (300~500℃)	Total	Acidity density/ (mmol/m²)	Relative crystallinity^① /%	Al^②/%	B^②/%
Na-H5	0.12	0.12	0.24	0.00062	100	—	—
Na-0.23B-H5	0.18	0.14	0.32	0.00081	99.3	—	—
Na-0.46B-H5	0.22	0.13	0.35	0.00087	99.3	—	—
Na-0.69B-H5	0.20	0.14	0.34	0.00084	98.9	—	—
Na-0.92B-H5	0.21	0.13	0.34	—	99.1	—	—
H5	0.09	0.16	0.25	0.00059	99.8	—	—
0.23B-H5	0.15	0.11	0.26	0.00058	99.3	0.7	0.1
0.46B-H5	0.11	0.07	0.18	0.00041	99.2	0.8	0.2
0.69B-H5	0.09	0.05	0.14	0.00032	99.3	0.7	0.1

Catalysts	Acid/(mmol NH₃/g)			Acidity density/ (mmol/m²)	Relative crystallinity^① /%	Al^②/%	B^②/%
Catalysts	Weak (150~300℃)	Strong (300~500℃)	Total	Acidity density/ (mmol/m²)	Relative crystallinity^① /%	Al^②/%	B^②/%
Na-H5	0.12	0.12	0.24	0.00062	100	—	—
Na-0.23B-H5	0.18	0.14	0.32	0.00081	99.3	—	—
Na-0.46B-H5	0.22	0.13	0.35	0.00087	99.3	—	—
Na-0.69B-H5	0.20	0.14	0.34	0.00084	98.9	—	—
Na-0.92B-H5	0.21	0.13	0.34	—	99.1	—	—
H5	0.09	0.16	0.25	0.00059	99.8	—	—
0.23B-H5	0.15	0.11	0.26	0.00058	99.3	0.7	0.1
0.46B-H5	0.11	0.07	0.18	0.00041	99.2	0.8	0.2
0.69B-H5	0.09	0.05	0.14	0.00032	99.3	0.7	0.1

催化剂	气体产率/(mmol/g)
催化剂	H₂	CH₄	C₂H₆	C₂H₄	C₃~C₄	CO	CO₂
Na-H5	1.37	0.95	0.10	0.40	0.01	1.10	1.41
Na-0.23B-H5	1.40	0.89	0.08	0.31	0.01	1.23	0.86
Na-0.46B-H5	1.22	0.75	0.06	0.25	0.01	1.12	0.76
Na-0.69B-H5	1.16	0.76	0.06	0.26	<0.01	1.16	0.62
Na-0.92B-H5	1.47	0.86	0.07	0.28	<0.01	1.28	0.79
H5	1.23	0.81	0.07	0.30	0.01	1.25	0.78
0.23B-H5	1.06	0.83	0.08	0.31	0.01	1.23	0.76
0.46B-H5	1.26	0.84	0.08	0.32	0.02	1.26	0.89
0.69B-H5	1.13	0.85	0.09	0.34	0.01	1.27	1.01