Insight into microwave heating patterns for sustainable decomposition of plastic wastes into hydrogen

Abstract

The manufacture of sustainable fuels from renewable resources has become a prospective technology towards the waste-to-resource concept. In this paper, the rapid microwave-driven method was proposed, and two microwave heating patterns of volumetric heating and localized heating were revealed through experimental and numerical methods. On the one hand, the microwave energy was consumed and transformed into heat volumetrically via dielectric loss and magnetic loss. The temperature distribution inside the particle was consistent with the microwave power dissipation density, simultaneously influenced by the electric field and magnetic field. On the other hand, a considerable portion of microwave energy in the multiparticle system was expended by local plasma discharging with massive heat bursts. The temperature enhancement of about 3 times was achieved by the microwave plasma, indicating the intensified conversion of microwave energy. This localized heating pattern induced the concentrated hotspot and led to the radical temperature rise inwards with a temperature gradient of over 180 °C·s⁻¹. The coupling of volumetric heating by dissipation and localized heating by plasma facilitated the distinctive and efficient performance of plastic decomposition with the H₂ yield of 280 mmol·g⁻¹H_plastic. Altogether, this work promoted the insight into the microwave heating patterns and temperature distribution, which provided guidance for the further optimization of microwave catalysts for efficient and sustainable valorization.