Microwave susceptor positional configuration for palm empty fruit bunch and waste tire co-pyrolytic oil yield and selectivity of value-added chemicals

Abstract

The co-pyrolysis of the palm empty fruit bunch (EFB) and waste tire (WT) was conducted at a constant microwave power of 600 W, a reaction temperature of 500 °C, and EFB-to-WT ratio of 65:35 using activated carbon as a carbonaceous microwave susceptor (CMS). The study investigated the effect of CMS positional configuration on heating rates, pyrolytic oil yield, and chemical selectivity. Nine CMS positions were tested, and the results showed that the CMS located at the bottom of the feedstock (P1) produced the highest average heating rate (80.45 °C.min−1) with the fewest hotspots. In contrast, the feedstock sandwiching the CMS (P3) had the lowest average heating rate (45.86 °C.min−1), leading to an inconsistent heating profile due to hotspot formation. The study also found that faster heating rates (>70 °C.min−1) significantly affected pyrolytic oil yield, with position P1 producing a higher yield (39.53 wt%). The properties of the pyrolytic oil were characterised using GCMS, which revealed that higher average heating rates favoured the formation of d-limonene, with position P1 containing a higher fraction of this compound (35.24%). Slower average heating rates (<60 °C.min−1) favoured phenolic selectivity. Surprisingly, the CMS position with significant hotspots promoted the formation of monoaromatic hydrocarbons, resulting in a higher relative content of these compounds. Furthermore, moderate average heating rates (60–70 °C.min−1) favoured benzene, toluene, ethylene, and xylene (BTEX) selectivity, with toluene and xylene being the most prevalent compounds. Notably, CMS positions had no discernible effect on the heating value (HHV) of the pyrolytic oil produced, which had an average value of 42.00 MJ.kg−1 ± 1.0.