聚丙烯定向转化制芳烃：金属-分子筛协同催化机制

doi:10.11949/0438-1157.20250196

摘要/Abstract

摘要：

废弃塑料中聚丙烯约占25%，将其选择性转化为高值芳烃原料对于推动循环经济和实现碳中和目标具有重要意义。尽管金属-分子筛催化剂已被证明能够促进聚烯烃催化转化为芳烃，但聚丙烯在分子筛外表面裂化的反应路径及金属对该裂化反应的影响仍不明确。本研究通过构筑选择性暴露外表面位点的金属-分子筛催化剂，研究了聚丙烯转化过程中主要中间物种2，4-二甲基-1-庚烯在催化剂外表面的催化裂化行为，揭示金属能够显著增强富含甲基取代基的烯烃中间物种在分子筛外表面的裂化深度，生成的小分子烯烃物种扩散至分子筛微孔中，进一步发生芳构化反应，从而提高微孔内芳构化位点的利用效率。在优化条件下，聚丙烯催化转化制芳烃的总收率为73.5%，其中三苯收率为65.6%。本研究建立了金属-分子筛催化剂结构与多步反应性能之间的关联机制，为化学回收聚丙烯制芳烃的高效催化剂设计提供了理论依据和技术支持。

关键词: 聚丙烯, 分子筛, 催化剂, 金属酸催化, 芳烃, 多相反应

Abstract:

Polypropylene accounts for about 25% of plastic waste, and its selective conversion into high-value aromatic feedstocks is crucial for promoting a circular economy and achieving carbon neutrality. Although metal-zeolite catalysts have been shown to promote the catalytic conversion of polyolefins to aromatics, the reaction path of polypropylene cracking on the outer surface of molecular sieves and the effect of metals on the cracking reaction are still unclear. Here, metal-zeolite catalysts with selectively exposed external surface sites were designed to investigate the catalytic cracking behavior of the key intermediate 2,4-dimethyl-1-heptene on the catalyst's external surface. The results show that metals can significantly enhance the cracking degree of branched olefin intermediates on the zeolite external surface, leading to the diffusion of small olefin molecules into the zeolite micropores, where further aromatization occurs. This process improves the utilization of aromatization sites within the micropores. Under optimized conditions, the yield of aromatics from the catalytic conversion of polypropylene reaches 73%, with a sum yield of benzene, toluene, and xylene of 65%. This study establishes a relationship between the structure of metal-zeolite catalysts and the cascade polypropylene-to-aromatics process, offering valuable insights for designing highly efficient catalysts for the chemical recycling of polypropylene into aromatics.

Key words: polypropylene, zeolite, catalyst, metal-acid catalysis, aromatics, multiphase reaction

中图分类号:

TQ 032.4

钱慧慧, 王文婕, 陈文尧, 周兴贵, 张晶, 段学志. 聚丙烯定向转化制芳烃：金属-分子筛协同催化机制[J]. 化工学报, 2025, 76(9): 4838-4849.

Huihui QIAN, Wenjie WANG, Wenyao CHEN, Xinggui ZHOU, Jing ZHANG, Xuezhi DUAN. Synergistic metal-zeolite catalysis for conversion of polypropylene into aromatics[J]. CIESC Journal, 2025, 76(9): 4838-4849.

图/表 11

图1 催化剂性能评价装置图

Fig.1 Schematic diagram of the catalyst performance evaluation apparatus

图2 催化剂的N2吸脱附等温线和孔径分布曲线

Fig.2 N2 adsorbtion-desorption isotherms and pore size distributions curves of catalysts

表1 催化剂的孔结构参数

Table 1 Pore structure parameters of catalysts

催化剂	SiO₂/Al₂O₃	孔结构性质
催化剂	SiO₂/Al₂O₃	比表面积/(m²·g^-1)	孔容/(cm³·g^-1)	微孔孔容/(cm³·g^-1)
ZSM-5（25）	25	284.5	0.190	0.131
ZSM-5（38）	38	333.5	0.178	0.161
ZSM-5（50）	50	246.3	0.134	0.123
ZSM-5（70）	70	285.2	0.175	0.133
Pt-ZSM-5（38）	38	314.3	0.171	0.149
ZSM-5-B	40	16.3	0.066	0.002
Pt-ZSM-5-B	40	12.0	0.048	0.001

图3 催化剂的XRD谱图

Fig.3 XRD patterns of catalysts

图4 催化剂的NH3-TPD和Py-FTIR谱图

Fig.4 NH3-TPD and Py-FTIR profiles of the catalysts

表2 基于NH3-TPD分析的催化剂酸位数量

Table 2 The number of acid sites of the catalyst based on NH3-TPD analysis

催化剂	酸位数量/(mmol·g^-1)
催化剂	弱酸	强酸
ZSM-5（38）	0.5	0.6
Pt-ZSM-5（38）	0.6	0.9

图5 催化剂的元素分布和形貌分析

Fig.5 Elemental distribution and morphological analysis of the catalysts

图6 模型化合物在堵孔催化剂上的裂解产物碳数分布与非堵孔催化剂上三苯收率

Fig.6 The carbon number distribution of cracking products from the model compound on the pore-blocking catalyst and the BTX yield on the conventional catalyst

图7 聚丙烯催化裂解反应条件筛选

Fig.7 Screening of reaction conditions for PP catalytic cracking

图8 聚丙烯在堵孔催化剂上的裂解产物碳数分布

Fig.8 The carbon number distribution of cracking products from PP on the pore-blocking catalyst

图9 聚丙烯热裂解和催化热裂解产物收率碳数分布

Fig.9 Carbon number distribution diagram of yield of PP pyrolysis and catalytic pyrolysis products

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