Selective production of phenolics from waste printed circuit boards via microwave assisted pyrolysis

Abstract

Abstract In this study, microwave assisted pyrolysis of waste printed circuit boards (PCBs) using carbonaceous susceptors like graphite and activated carbon was conducted to devise an efficient technique to treat the electronic wastes. Pyrolysis experiments were conducted in a batch microwave reactor, and the effects of PCB to susceptor mass ratio and the type of susceptor on the yields and composition of char, tar and gas were evaluated. The effect of increasing the initial mass of PCB from 10 to 100 g on product yield and quality was also assessed. Different analytical techniques were adopted to determine the composition of (a) tar compounds like phenols and oxygenated compounds, (b) non-condensable gases like H2, CO2 and CH4, and (c) metals in char. Char constituted a major fraction of the products (ca. 58 wt.%). High amount of susceptor resulted in low yield of tar and high yield of gases. The mass and energy yields of tar were high when graphite was used as the susceptor. Tar fraction contained phenolic compounds and phenyl phosphates in significant amounts. Higher amount of susceptor, i.e. 10:50 g/g of PCB:susceptor, resulted in >90% selectivity of phenol in the tar fraction. Average heating value of the tar fraction was 31.8 MJ kg−1. CO2 was the major component in the gas fraction, and the production of H2 was more when activated carbon was used as the susceptor. The major metals present in char were Cu, Pb, Ti, and other metals present in minor amounts included Bi, Fe and Ca. The average heating value of char was 19 MJ kg−1.