Catalytic Pyrolysis of a Residual Plastic Waste Using Zeolites Produced by Coal Fly Ash

Marco Cocchi,Leone Mazzeo,Stefano Vecchio Ciprioti,Piergianni Nardozi,Doina De Angelis,Vincenzo Piemonte,Riccardo Tuffi

doi:10.3390/catal10101113

Abstract

The plastic film residue (PFR) of a plastic waste recycling process was selected as pyrolysis feed. Both thermal and catalytic pyrolysis experiments were performed and coal fly ash (CFA) and X zeolites synthesized from CFA (X/CFA) were used as pyrolysis catalysts. The main goal is to study the effect of low-cost catalysts on yields and quality of pyrolysis oils. NaX/CFA, obtained using the fusion/hydrothermal method, underwent ion exchange followed by calcination in order to produce HX/CFA. Firstly, thermogravimetry and differential scanning calorimetry (TG and DSC, respectively) analyses evaluated the effect of catalysts on the PFR degradation temperature and the process energy demand. Subsequently, pyrolysis was carried out in a bench scale reactor adopting the liquid-phase contact mode. HX/CFA and NaX/CFA reduced the degradation temperature of PFR from 753 to 680 and 744 K, respectively, while the degradation energy from 2.27 to 1.47 and 2.07 MJkg−1, respectively. Pyrolysis runs showed that the highest oil yield (44 wt %) was obtained by HX/CFA, while the main products obtained by thermal pyrolysis were wax and tar. Furthermore, up to 70% of HX/CFA oil was composed by gasoline range hydrocarbons. Finally, the produced gases showed a combustion energy up to 8 times higher than the pyrolysis energy needs.

Highlights

The packaging industry is the largest consumer of plastic material and in EU-27, plastic represents the second most used material for packaging after cardboard, accounting for about 19% of the total [1].Polyolefins with particular reference to high density polyethylene (HDPE), low density polyethylene (LDPE), and polypropylene (PP), represent the most used plastic polymers for this application, accounting for about 70 wt % of the total amount [2], being 12.3 Mt the polyolefin packaging production in 2018 [2]
As observed for the degradation temperatures, significant differences were observed only for HX/coal fly ash (CFA) (Table 1), where the use of the catalyst induces a remarkable decrease in the decomposition heat (Qd ). This decrease is probably due to different reaction mechanisms and different compounds produced caused by the strong catalytic action of HX/CFA, as it will be confirmed by the results reported in the Section 2.2, Section 2.3, and Section 2.4
CFA and CFA-derived zeolites have been successfully tested as catalysts for the conversion of a packaging plastic waste to valuable hydrocarbon products

Summary

Introduction

Polyolefins with particular reference to high density polyethylene (HDPE), low density polyethylene (LDPE), and polypropylene (PP), represent the most used plastic polymers for this application, accounting for about 70 wt % of the total amount [2], being 12.3 Mt the polyolefin packaging production in 2018 [2]. EU collects 17.8 million tons of plastic packaging waste, but only 7.5 million tons, i.e., 42 wt % of the total, are recycled, while the rest, i.e., 58 wt %, either goes to energy production or landfilling [3]. This low recycling rate and the short life of plastic packaging pose a big challenge for waste management. Catalysts 2020, 10, 1113 a new methodology to calculate the packaging recycling rate by measuring recycled quantities at a later stage of the recycling process, that would decrease the current 42 wt % recycling rate to about 29 wt %, still more than the required 22.5 wt % imposed by the Directive 2004/12/EC [5] but consistently far from the 50 wt % targeted by for 2025 [6].

Objectives

Methods

Conclusion