Uncovering self-catalytic and phase boundary-driven interactions in the pyrolysis kinetics of wasted printed circuit boards: co-existing materials and the atmosphere

Abstract

Waste printed circuit boards (WPCBs) are hazardous solid wastes that are composed of various metal and non-metal materials. Pyrolysis has long been regarded as an environmentally friendly and promising application technology for recovering organic and inorganic materials from the WPCBs. The pyrolysis atmosphere and co-existing materials are critical factors that significantly influence the pyrolysis behavior. To compare the specific effects of these factors on the pyrolysis characteristics of the WPCBs, a series of thermogravimetric and kinetics analyses has been conducted. It was then found that the apparent activation energy was reduced when pyrolyzed in CO₂ or co-pyrolyzed with glass fibers, which was supposed to result from the enhanced diffusion and phase boundary reactions. In contrast, an increase in the apparent activation energy was observed at the early stage of the co-pyrolysis with Cu, which was inferred to be associated with the Cu-catalyzed cross-linking effects. Specifically, the formed coke might adsorb pyrolysis products and inhibit the diffusion and reduce the reactive phase boundary. Previous studies have primarily focused on the catalysis of metals in the pyrolysis of WPCBs, while other interactions as well as the kinetic effects of glass fibers and pyrolysis atmospheres have received less discussion. The study presented a comprehensive investigation of the roles played by the pyrolysis atmosphere and co-existing materials in the pyrolysis of the WPCBs. It showed that these factors could alter the reaction-controlling mechanisms by complex interactions. These findings can provide new mechanistic insights and contribute to the use and optimization of pyrolysis-based recycling technologies.

Graphical abstract

Keywords

Waste printed circuit boards / Pyrolysis / Kinetics / Pyrolysis atmosphere / Co-existing materials

Highlight

	● Pyrolysis of WPCBs was facilitated under CO2 at the later stage.
	● Glass fibers in WPCBs can reduce the activation energy of pyrolysis.
	● The enhanced phase boundary and diffusion reactions facilitated the pyrolysis.
	● Cu catalyzed crosslinking reaction inhibited pyrolysis at the early stage.

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