Deactivation and Regeneration of Zeolite Catalysts Used in Pyrolysis of Plastic Wastes—A Process and Analytical Review

Abstract

In catalytic industrial processes, coke deposition remains a major drawback for solid catalysts use as it causes catalyst deactivation. Extensive study of this phenomenon over the last decades has provided a better understanding of coke behavior in a great number of processes. Among them, catalytic pyrolysis of plastics, which has been identified as a promising process for waste revalorization, is given particular attention in this paper. Combined economic and environmental concerns rose the necessity to restore catalytic activity by recovering deactivated catalysts. Consequently, various regeneration processes have been investigated over the years and development of an efficient and sustainable process remains an industrial challenge. Coke removal can be achieved via several chemical processes, such as oxidation, gasification, and hydrogenation. This review focuses on oxidative treatments for catalyst regeneration, covering the current progress of oxidation treatments and presenting advantages and drawbacks for each method. Molecular oxidation with oxygen and ozone, as well as advanced oxidation processes with the formation of OH radicals, are detailed to provide a deep understanding of the mechanisms and kinetics involved (direct and indirect oxidation, reaction rates and selectivity, diffusion, and mass transfer). Finally, this paper summarizes all relevant analytical techniques that can be used to characterize deactivated and regenerated solid catalysts: XRD, N2 adsorption-desorption, SEM, NH3-TPD, elemental analysis, IR. Analytical techniques are classified according to the type of information they provide, such as structural characteristics, elemental composition, or chemical properties. In function of the investigated property, this overall tool is useful and easy-to-use to determine the adequate analysis.

Production of Hydrocarbon Liquid Fuels from waste Personal Protective Equipment (PPEs) through Pyrolysis

“…The peaks in the range of 1000 and 1800 cm and again somewhere in the range of 1350 and 1450 cm address C−H distortions and shows the CH, −CH, and C−H groups presence which feature the aliphatic behaviour of the oils. The chemical construction of waste plastics and model polymers before and after the reusing technique was affirmed by recording their infra‐red spectrum [10,12,38,39] . The spectra of FTIR of all the pyrolytic fluids produced somewhere in range of 500–700 °C which shows that elevated temperature significantly affects the resultant oil [12] .…”

“…The maximum oil yield of higher volume and low boiling point was recorded as 77.03 % in 2 hours. [12,36] Liquid Fuel distillation shows all the lighter parts at higher temperature and longer time. Nonetheless, further analysis is important to use this oil as a fuel or feeding processes.…”

“…The chemical construction of waste plastics and model polymers before and after the reusing technique was affirmed by recording their infra-red spectrum. [10,12,38,39] The spectra of FTIR of all the pyrolytic fluids produced somewhere in range of 500-700 °C which shows that elevated temperature significantly affects the resultant oil. [12] The FTIR spectrum of the products pre and post the recycling and the estimations of the ductile mechanical characteristics is at most similar from the raw polymer.…”

“…[10,12,38,39] The spectra of FTIR of all the pyrolytic fluids produced somewhere in range of 500-700 °C which shows that elevated temperature significantly affects the resultant oil. [12] The FTIR spectrum of the products pre and post the recycling and the estimations of the ductile mechanical characteristics is at most similar from the raw polymer. Moreover, pyrolysis was found to be a potential strategy for thermo-chemical recycling of the waste polymers.…”

“…However, the catalytic pyrolysis process relies on many factors like residence time, temperature, feedstock composition, heating rates and presence of moisture or harmful components [11] . Catalytic pyrolysis is a substitute to incineration and recycling of materials [12] . The pyrolytic matter can be generally separated into gas, fluid, and solid remains.…”