纳米ZSM-5在高硅铝比料液中的再生长机制及其甲醇制芳烃性能

doi:10.16085/j.issn.1000-6613.2022-0363

摘要/Abstract

摘要：

芳烃选择性低是ZSM-5催化甲醇制芳烃反应的难点问题，调变ZSM-5酸性质是提升选择性的重要方法。本研究将SiO₂/Al₂O₃为50的纳米ZSM-5分别置于硅铝比为50、110、220、440和660的料液中继续水热生长，优化其表面酸性，以提高轻质芳烃选择性。采用X射线衍射（XRD）、透射电子显微镜（TEM）、X射线荧光光谱（XRF）、吡啶红外（Py-IR）、氨气程序升温脱附（NH₃-TPD）等手段分析所得ZSM-5形貌、织构和酸性质，研究其水热再生长规律。发现生长过程中原粉部分溶解，包围在其表面的料液先形成小晶粒，经逐步堆积完成对原粉的包覆，最终形成孔道贯通性良好的单晶。在较低硅铝比料液中样品粒径分布不均匀，然而随着料液硅铝比的增加，包覆趋向均匀且表面呈现凸起结构。二次生长显著改变了表面酸性质及芳构化性能，在硅铝比为220的料液中生长后总酸量增加到194.9μmol/g，高于原粉的169.7μmol/g。值得注意的是，催化剂表面的强酸占比由原粉的37%显著增加至53%，B/L值也由原粉的0.56增加至3.19。该酸性的变化在促进甲醇芳构化的同时，还能强化芳烃的脱烷基化而提高BTX选择性，使总芳烃选择性和BTX选择性分别由16.1%和8.2%提高到23.8%和13.5%。

关键词: 沸石, 水热, 制备, 催化, 选择性, 甲醇制芳烃

Abstract:

Low selectivity is the main issue in methanol to aromatics (MTA) reaction catalyzed by ZSM-5. Rational design and control of the acid properties of ZSM-5 catalysts is an effective strategy to promote highly selective generation of aromatic hydrocarbons. In this study, nano ZSM-5 with SiO₂/Al₂O₃ ratio of 50 was placed in ZSM-5 synthesis system with different SiO₂/Al₂O₃ ratios (50, 110, 220, 440 and 660) for secondary growth to prepare a series of samples to optimize the surface acidities and improve the selectivity of light aromatics. The morphology, texture properties and acid properties of the ZSM-5 zeolites were characterized by using X-ray diffraction (XRD), transmission electron microscope (TEM), X-ray fluorescence (XRF), pyridine adsorption Fourier-transform infrared (Py-IR) and temperature-programmed desorption of ammonia (NH₃-TPD), and the crystal growth mechanism was studied accordingly. During the crystal growth, the parent powder was partially dissolved and small crystals were formed firstly, surrounding the surface of the parent ZSM-5. The crystals grown over N50 to form nanosized single-crystal coated ZSM-5. The particle size distribution of the sample was not uniform after secondary growth in the feed solution with low SiO₂/Al₂O₃ ratio. But on the whole, with the increase of SiO₂/Al₂O₃ ratio, the crystal particles tended to be uniform and zeolites with rough protrusions structure. The secondary growth significantly changed the acid properties of the zeolite surface and aromatization properties. The total acid amount increased to 194.9μmol/g, after secondary growing in the feed solution with a higher SiO₂/Al₂O₃ ratio (220), which was significantly higher than that of the parent powder (169.7μmol/g). It is worth noting that the proportion of strong acid on the catalyst surface also increased significantly from 37% of the parent powder to 53%, and B/L ratio also increased from 0.56 to 3.19. The acidity modulation not only facilitated the conversion of methanol to aromatics, but also strengthened the dealkylation conversion of aromatics and BTX selectivity increased accordingly. Thus, the selectivities of aromatics and BTX were increased from 16.1% and 8.2% to 23.8% and 13.5%, respectively.

Key words: zeolite, hydrothermal, preparation, catalysis, selectivity, methanol to aromatics

中图分类号:

O643.3

惠燕, 付廷俊, 马倩, 李忠. 纳米ZSM-5在高硅铝比料液中的再生长机制及其甲醇制芳烃性能[J]. 化工进展, 2022, 41(12): 6364-6376.

HUI Yan, FU Tingjun, MA Qian, LI Zhong. Secondary growth mechanism of nano-ZSM-5 in solution of high SiO₂/Al₂O₃ratio and its performance of methanol to aromatics[J]. Chemical Industry and Engineering Progress, 2022, 41(12): 6364-6376.

图/表 15

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样品	比表面积/m²·g^-1			体积/cm³·g^-1
样品	总比表面积（S_BET^①）	外比表面积（S_Exter^②）	微孔比表面积（S_Micro^②）	总体积（V_Total^③）	介孔体积（V_Meso^④）	微孔体积（V_Micro^②）
N50	408	53	355	0.49	0.31	0.18
N50@N50	383	31	352	0.30	0.13	0.17
N50@N110	394	32	362	0.32	0.14	0.18
N50@N220	401	37	364	0.42	0.25	0.17
N50@N440	431	44	387	0.48	0.29	0.19
N50@N660	434	44	390	0.46	0.28	0.18

样品	比表面积/m²·g^-1			体积/cm³·g^-1
样品	总比表面积（S_BET^①）	外比表面积（S_Exter^②）	微孔比表面积（S_Micro^②）	总体积（V_Total^③）	介孔体积（V_Meso^④）	微孔体积（V_Micro^②）
N50	408	53	355	0.49	0.31	0.18
N50@N50	383	31	352	0.30	0.13	0.17
N50@N110	394	32	362	0.32	0.14	0.18
N50@N220	401	37	364	0.42	0.25	0.17
N50@N440	431	44	387	0.48	0.29	0.19
N50@N660	434	44	390	0.46	0.28	0.18

样品	SiO₂/Al₂O₃^①	SiO₂/Al₂O₃^②	酸量^③/μmol·g^-1				强酸/弱酸	酸量^④/μmol·g^-1		B/L
样品	SiO₂/Al₂O₃^①	SiO₂/Al₂O₃^②	总量	弱酸	中强酸	强酸	强酸/弱酸	B酸	L酸	B/L
N50	72	21	169.7	84.0	22.5	63.2	0.75	26.8	47.6	0.56
N50@N50	70	—	247.5	100.1	41.8	105.6	1.06	—	—	—
N50@N110	77	27	194.9	85.2	33.8	75.9	0.89	37.1	19.8	1.87
N50@N220	87	46	194.9	70.4	21.0	103.4	1.47	38.2	12.0	3.19
N50@N440	94	—	142.6	41.9	19.6	81.1	1.93	—	—	—
N50@N660	106	50	125.6	42.3	15.4	67.9	1.61	4.0	15.6	0.25

样品	SiO₂/Al₂O₃^①	SiO₂/Al₂O₃^②	酸量^③/μmol·g^-1				强酸/弱酸	酸量^④/μmol·g^-1		B/L
样品	SiO₂/Al₂O₃^①	SiO₂/Al₂O₃^②	总量	弱酸	中强酸	强酸	强酸/弱酸	B酸	L酸	B/L
N50	72	21	169.7	84.0	22.5	63.2	0.75	26.8	47.6	0.56
N50@N50	70	—	247.5	100.1	41.8	105.6	1.06	—	—	—
N50@N110	77	27	194.9	85.2	33.8	75.9	0.89	37.1	19.8	1.87
N50@N220	87	46	194.9	70.4	21.0	103.4	1.47	38.2	12.0	3.19
N50@N440	94	—	142.6	41.9	19.6	81.1	1.93	—	—	—
N50@N660	106	50	125.6	42.3	15.4	67.9	1.61	4.0	15.6	0.25

样品	选择性/%							氢转移指数^①	丙烯/乙烯（P/E）
样品	甲烷	乙烷	丙烷	丁烷	乙烯	丙烯	丁烯	氢转移指数^①	丙烯/乙烯（P/E）
N50	0.7	0.4	4.4	17.1	8.5	21.5	16.3	0.17	2.53
N50@N50	1.8	0.3	6.0	17.4	9.5	19.9	13.5	0.23	2.09
N50@N110	1.3	0.2	5.3	16.9	8.8	19.9	14.0	0.21	2.27
N50@N220	1.7	0.3	6.9	15.6	8.4	18.8	13.1	0.27	2.23
N50@N440	1.4	0.3	5.6	13.4	8.2	22.3	16.7	0.20	2.72
N50@N660	1.7	0.3	5.2	12.8	9.0	24.3	18.3	0.18	2.71