Meosporous MTW zeolites modified by secondary crystallization and their catalytic properties in alkylation reaction of benzene and cyclohexene

doi:10.11949/0438-1157.20250125

Abstract

Abstract:

In this study, the MTW zeolite was modified by the secondary crystallization method, and its catalytic performance and mechanisms in the alkylation reaction of benzene and cyclohexene were deeply explored. The structural parameters and acid site concentration of the prepared MTW zeolite samples were systematically explored by various characterization methods such as XRD, ICP-OES, N₂adsorption-desorption isotherm, SEM and Py-IR. At the same time, the catalytic performance of MTW zeolite samples in the alkylation of benzene and cyclohexene was evaluated by fixed bed reactor. The characterization results show that the secondary crystallization method successfully introduced mesoporous structures into the MTW zeolite. Without changing the crystal configuration, the total Brønsted acid amount and the external-surface Brønsted acid amount were significantly increased. The catalytic performance results of the alkylation reaction of benzene and cyclohexene indicate that the activity of the MTW zeolite after the secondary crystallization treatment is significantly improved. Among them, MTW-Ⅱ exhibits the most excellent conversion rate, reaching 41.74%. At the same time, the modified MTW zeolite performs outstandingly in terms of selectivity, all remaining above 75%. In addition, through a clear analysis of the components of the reaction mixture, the reaction network of the alkylation reaction of benzene and cyclohexene was successfully deduced. This study demonstrates that the secondary crystallization method is an efficient modification method for MTW zeolites, providing a solid theoretical support for the industrial production of cyclohexylbenzene and opening up a new path for the design and optimization of zeolite catalysts.

Key words: MTW zeolite, the secondary crystallization, cyclohexylbenzene, catalysis, multiphase reaction

摘要：

采用二次晶化法对MTW分子筛进行改性，并深入探究其在苯和环己烯烷基化反应中的催化性能和机理。通过XRD、ICP-OES、N₂吸附-脱附等温线、SEM 以及Py-IR等多种表征手段，系统探究了所制备MTW分子筛样品的结构参数以及酸性位点浓度，同时，采用固定床反应器对MTW分子筛样品在苯和环己烯烷基化反应中的催化性能展开评价。表征结果表明，二次晶化法成功为MTW分子筛引入介孔结构，在不改变晶体构型的前提下，显著提高了总B酸量及外表面B酸量。苯和环己烯烷基化反应的催化性能结果表明，经二次晶化处理后的MTW分子筛的活性得到显著提高，其中MTW-Ⅱ表现出最优异的转化率，达到41.74%。同时，改性后的MTW分子筛在选择性方面表现出色，均维持在75%以上。此外，通过对反应混合物成分的明确分析，推测出了苯和环己烯烷基化反应的反应网络，为环己基苯工业化生产提供了理论支撑。

关键词: MTW分子筛, 二次晶化, 环己基苯, 催化, 多相反应

CLC Number:

TQ 426

Mei ZHOU, Haojie ZENG, Huoyan JIANG, Ting PU, Xingxing ZENG, Baoyu LIU. Meosporous MTW zeolites modified by secondary crystallization and their catalytic properties in alkylation reaction of benzene and cyclohexene[J]. CIESC Journal, 2025, 76(8): 4071-4080.

周媚, 曾浩桀, 蒋火炎, 蒲婷, 曾星星, 刘宝玉. 二次晶化法改性合成MTW分子筛及其在苯和环己烯烷基化反应中的催化性能[J]. 化工学报, 2025, 76(8): 4071-4080.

Figures/Tables 17

Fig.1 The process of treating MTW zeolite by the secondary crystallization method

Fig.2 Fixed-bed reaction device

Fig.3 XRD patterns of different MTW zeolites

Table 1 The elemental content of MTW zeolite

催化剂	元素含量（质量）/ %		Si/Al
催化剂	Si	Al	Si/Al
MTW-P	45.44	0.76	60
MTW-I	44.76	1.76	25
MTW-Ⅱ	44.98	1.72	26
MTW-Ⅲ	44.81	1.75	26

Table 2 The pore structure parameters of MTW zeolite

催化剂	S_BET/(m²/g)	S_ext/(m²/g)	S_micro/(m²/g)	V_tol/(cm³/g)	V_micro/(cm³/g)	V_meso/(cm³/g)	S_ext/S_BET	V_meso/V_tol
MTW-P	367	56	311	0.191	0.123	0.068	0.153	0.356
MTW-I	389	97	292	0.248	0.119	0.129	0.249	0.520
MTW-Ⅱ	434	106	328	0.273	0.133	0.140	0.244	0.513
MTW-Ⅲ	372	92	280	0.242	0.113	0.129	0.247	0.533

Table 3 The acidity of MTW zeolite

催化剂	总Brønsted酸量^①/(mmol/g)	外表面Brønsted酸量^②/(mmol/g)
MTW-P	0.0154	0.0079
MTW-Ⅰ	0.0409	0.0208
MTW-Ⅱ	0.0741	0.0219
MTW-Ⅲ	0.0868	0.0324

Fig.4 N2 adsorption-desorption isotherms and BJH pore size distributions of different MTW zeolites

Fig.5 The changes of different MTW zeolites after modification treatment

Fig.6 SEM images of MTW-P (a), MTW-Ⅰ(b), MTW-Ⅱ(c) and MTW-Ⅲ(d) zeolites

Fig.7 The modification mechanism during the secondary crystallization of MTW zeolite

Fig.8 The adsorption infrared spectra of different MTW zeolites

Fig.9 The conversion rate of cyclohexene and the selectivity of cyclohexylbenzene on different MTW zeolites

Fig.10 The product distribution during the reaction process of benzene and cyclohexene

Fig.11 Thermogravimetric analysis of the MTW zeolite after the reaction

Table 4 The coke deposition of different MTW zeolites

催化剂	样品质量/mg	软焦炭^①/mg	硬焦炭^②/mg	焦炭沉积速率^③/(mg/h)
MTW-P	6.19	0.116	0.273	0.091
MTW-Ⅱ	5.83	0.233	0.164	0.0082

Fig.12 GC-MS of the alkylation reaction mixture of benzene and cyclohexene

Fig.13 The reaction process of benzene and cyclohexene

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