Catalytic Pyrolysis of Waste Polyethylene Using Combined CaO and Ga/ZSM-5 Catalysts for High Value-Added Aromatics Production

Abstract

Amidst the global focus on recycling and treatment of waste plastics for resource sustainability, it is a huge challenge to convert waste plastics into aromatics, especially high value-added monocyclic aromatic hydrocarbons (MAHs). In this work, catalytic pyrolysis experiments of linear low-density polyethylene (LLDPE) indicated that the selectivity to aromatics increased from 70.35% when using pure HZSM-5 to 94.02% with 7 wt % Ga-modified HZMS-5. Further, the cracking catalyst CaO was utilized to increase the proportion of MAHs in aromatics. Three different catalytic modes, CaO sequential with Ga/ZSM-5 mode, Ga/ZSM-5 sequential with CaO mode, and the mixed mode, were conducted for the combined catalytic pyrolysis of polyethylene. Under such three modes, the selectivities to benzene, toluene, ethylbenzene, and xylene (BTEX) were 45.18%, 52.29%, and 56.21%, respectively. MAHs were inhibited under CaO sequential with the Ga/ZSM-5 mode and facilitated under the other two modes. By contrast, the mixed mode showed the best catalytic synergistic effect involving Ga/ZSM-5 and CaO, where LLDPE pyrolytic gas was randomly and repeatedly exposed to Ga/ZSM-5 and CaO, creating more chances to form shuttle catalysis involving aromatization and cracking. The present study is expected to provide some reference value for recycling and utilizing liquid products via catalytic pyrolysis of waste plastics.

Understanding the Structure–Activity Relationships in Catalytic Conversion of Polyolefin Plastics by Zeolite-Based Catalysts: A Critical Review

“…Some relevant works have reported that the LAS of zeolite could be enhanced by a dopant of heteroatoms. The reaction showed remarkable selectivity to aromatics, − which will be fully discussed in section 4.1.…”

Chemical Recycling of Waste Polypropylene via Thermocatalytic Pyrolysis over HZSM‐5 Catalysts

“…Moreover, the inorganic additives present in some samples might have some synergistic effects during catalytic pyrolysis that led to different product distribution than in the case of VPP. More recently, Fu et al [17] described the synergistic effect of CaO when using HZSM-5based catalysts for the pyrolysis of polyethylene.…”

“…In this context, zeolites are interesting catalytic materials due to their remarkable properties, e.g., acidity and porosity, which Amer Inayat can be exploited in cracking, olefination as well as aromatization during thermocatalytic pyrolysis of plastics. Recently, there has been a growing interest in using zeolite-based catalysts for the thermocatalytic pyrolysis of plastics in general and polyolefin plastics in particular and several reports in open literature on this topic can be found [6,10,12,[14][15][16][17][18]. However, studies showing the influence of different types of waste polyolefins in conjunction with different reactor configuration/ operation mode are rather scarce.…”

Heterogeneous Photocatalytic Oxidative Cleavage of Polystyrene to Aromatics at Room Temperature

“…Polystyrene (PS) is often used in packaging, appliances, automotive, and insulation, which undergoes slow natural environmental degradation. , The incineration of PS produces heat, while toxic polycyclic aromatic hydrocarbons are inevitably generated . Pioneering oxidation methods have been developed to decompose PS into carbon dioxide that can efficiently decrease the plastic residue in the environment. , Catalytic pyrolysis is another common method to convert waste plastics into small molecules, aromatics, and aviation oil. − Besides, the upgrading of PS to value-added chemicals will motivate the sorting and recovery of plastic. − …”