Catalytic Pyrolysis of Waste Electrical and Electronic Equipment (WEEE)
Cleaner Pathways to Resource Recovery
Time: Fri 2025-11-28 10.00
Location: D 37, Lindstedtsvägen 5
Language: English
Subject area: Materials Science and Engineering
Doctoral student: Samina Gulshan , Processer, KTH Royal Institute of Technology, Energy and Furnace Technology
Opponent: Professor Tobias Richards, Faculty of Textiles, Engineering and Business, University of Borås, Borås, Sweden
Supervisor: Docent Weihong Yang, ; Professor Pär Jönsson, Processer; Dr Panagiotis Evangelopoulos, RISE
QC 20241107
Abstract
As one of the fastest-growing waste streams worldwide, waste electrical and electronic equipment (WEEE) poses major challenges for environmental sustainability and resource management. Existing practices, such as landfilling and incineration, release toxic emissions, while recycling and other recovery methods are often constrained by technical and economic limitations. In this context, pyrolysis combined with catalytic upgrading offers a promising thermochemical pathway to convert complex WEEE into valuable hydrocarbons, energy carriers, and recyclable residues, thereby supporting circular economy objectives.
This thesis aims to develop feasible thermochemical processes to enhance material circularity through catalytic pyrolysis of WEEE. To achieve this, fundamental studies were carried out involving both experimental investigations and process developments at the lab scale. This thesis is written based on the results from five interconnected studies, which together examine the decomposition kinetics of WEEE polymers, catalytic upgrading strategies, and process optimization in both batch and continuous systems. Particular emphasis is placed on understanding how feedstock properties, catalyst design, and operating conditions influence the performance of pyrolysis and in line catalytic upgrading, as well as on advancing process configurations that improve product quality and environmental outcomes.
The first part of the work investigates the pyrolysis behavior of low-grade (LGE) and medium-grade (MGE) WEEE fractions using kinetic modeling, thermogravimetric analysis and micro-scale pyrolyzer coupled with GC-MS/FID, revealing complex multi-stage decomposition associated with PVC, PE, PET, PP, PS, and ABS in feedstock fractions. Catalytic studies showed that acidic zeolites, especially HBeta and HZSM-5, promoted a selective production of benzene, toluene, and xylene (BTX). TiO2 and HZSM-5 reduced activation energies for pseudo 3 and 4 reactions, while higher pyrolysis temperatures in the range of 500-600 oC promoted styrene intermediates that enhanced BTX formation. Importantly, pyrolysis configuration influenced outcomes, with ex-situ catalysis favoring BTX production in LGE and in-situ catalysis proving more effective for MGE.
The second part focuses on the ex-situ catalytic pyrolysis of engineered WEEE fractions (LGEW and MGEW) using HZSM-5 and modified catalysts in both single and dual configurations to optimize system performance. HZSM-5 at 450 oC achieved the highest organic fraction (28.5 wt.%), improved monoaromatic selectivity, and enhanced syngas composition while lowering CO2 emissions and total acid number. Higher catalyst-to-feedstock ratios improved gas yield and aromatic selectivity. The use of Fe-modified HZSM-5 catalyst further enhanced the BTXE production via hydrogen transfer and β-scission pathways but suffered from higher coke deposition, whereas CaO was effective for deoxygenation and CO2 adsorption. A dual CaO/HZSM-5 configuration balancing cracking and deoxygenation activities, yielding higher oil production, improved aromatic selectivity, and reduced CO2 emissions.
The third part demonstrates continuous catalytic pyrolysis of waste electronic circuit boards (WECB) in an auger reactor using a dual HZSM-5/CaO system. This setup improved aromatic yields, reduced oxygenates, generated hydrogen-rich syngas, and stabilized bromine as inorganic bromides in solid residues. Operating at lower weight hourly space velocity (WHSV) further enhanced deoxygenation efficiency, increased H2 production, and minimized CO2 emissions, highlighting the industrial promise of dual-catalyst strategies.
Overall, this thesis demonstrates that catalytic pyrolysis, particularly with dual HZSM-5/CaO systems, provides a feasible and scalable pathway for WEEE valorization. By fulfilling the defined objectives from kinetic assessment to pilot-scale validation, the work enhanced aromatic hydrocarbon recovery, improved syngas quality, and achieved bromine stabilization in solid residues. These outcomes confirm that the central aim of developing thermochemical processes to enhance material circularity through catalytic pyrolysis has been substantially achieved, offering both scientific insight and practical solutions for sustainable e-waste recycling.