Abstract: The increasing rates of plastic production and waste plastic accumulation pose a serious challenge to the society, environment, and economy. Current mechanical recycling process is limited by the sorting/pretreatment of plastic waste and degradation of plastics during the process, which calls for more efficient recycling strategies. Catalytic microwaveassisted pyrolysis could serve as a feasible approach to chemical recycling of waste plastics and producing fuel and petrochemical feedstocks such as naphtha. This lecture presents a series of our recent work on the aspects of pyrolysis reactor design and catalyst development with the goal of advancing this technology towards industrial applications. A labscale continuous microwaveassisted pyrolysis system with a processing capacity of 200 kg plastics per day was developed, which features continuous downdraft operation and a mixing ball bed reactor. The incorporation of silicon carbide as microwave absorbents into the microwave heating process enabled fast, uniform and energyefficient heating for the process. A baseline test of the system using conventional ZSM5 catalyst obtained a 57 wt.% yield for C5C22 liquid hydrocarbons from polyolefinbased plastics. Energy saving of the process compared to production of similar products from virgin materials was estimated to be 32% by using the Materials Flows through Industry supply chain analysis tool. In order the improve the yield and quality of the liquid hydrocarbon products, a series of catalysts were tested and compared on a labscale setting. Notably, relay catalysis of Al2O3 followed by ZSM5 achieved up to 100% conversion into monoaromatics and C5C12 alkanes/olefins at a catalyst to plastic ratio of 4:1; Y5.1, F20 zeolites and Al2O3 promoted the production of alkanes and alkenes mainly in the C5C23 range; MCM41 led to the formation of C13C23 alkanes and alkenes with a selectivity of 86.6%; ZSM5 favored the production of aromatics with a selectivity of 70%. In addition to developing and selecting the proper catalyst material, the catalytic reactor also needs to be carefully designed such that sufficient heat and mass transfer within the catalyst bed is ensured during operation and the catalyst regeneration procedure can be conveniently practiced. Conventional designs such as the randomly packed bed could be problematic in the process since catalyst deactivation and coke/wax buildup is very likely. A probable solution to this issue is a structured catalytic reactor consisting of a structured packing with coated catalysts, e.g. ZSM5 coatings on a SiC foam support. This structured catalyst has been tested in a labscale setting for upgrading pyrolytic vapors and results showed that it outperformed many other catalytic reactor designs in terms of catalytic activity and stability. In addition, the composite catalysts could be regenerated and reused while well preserving its material properties and catalytic activity after multiple reactionregeneration cycles.

Keywords: Catalyst; microwaveassisted pyrolysis; chemical recycling; plastic waste

Full Article: https://www.proceedings.iaamonline.or...

0:00 Introduction
1:01 Catalytic MicrowaveAssisted Pyrolysis CMA Process for Chemical Recycling of Plastics
1:53 MicrowaveAssisted Pyrolysis (MAP)
2:30 Microwave Absorbent
3:49 A LabScale Continuous Fast MicrowaveAssi Pyrolysis (CMAP) System
7:07 Catalytic MAP of Waste Plastics
7:41 Catalytic MAP of Plastic Waste: Effect
8:44 Insitu vs. Exsitu Catalysis
10:31 Structured Catalytic Reactor: SiC Foam Supported ZSM5
14:50 Catalytic Pyrolysis for Naphtha Production for Plastics Upcycling
16:18 Catalytic Pyrolysis for Naphtha Product Catalyst Screening
17:23 Naphtha Product from Polyethylene
17:52 Naphtha Product from a Mixed Waste Plastic St (LDPE 41%; HDPE 24%; PP 35%)
18:23 Energy and Mass Balances from a Baseline Ana of the MAP System