Homogenizing microwave pyrolysis of oily sludge using nano-Fe₃O₄: volatile gas product analysis

To improve the homogeneity of heating, the magnetic absorbing material Fe₃O₄ is considered to use in microwave pyrolysis of oily sludge. Therefore, the effect of Fe₃O₄ on the microwave pyrolysis of oily sludge is investigated based on gas volatile products. Thermogravimetric mass spectrometry result certifies that Fe₃O₄ will increase the weight-loss ratio from 13.0% to 14.1%. Also, the characteristic peak intensity of CO in gas products decreases from 5.41 × 10^-10 A/g to 1.95 × 10^-10 A/g, while H₂O increases from 3.57 × 10^-10 A/g to 7.32 × 10^-10 A/g and CO₂ increases from 6.87 × 10^-10 A/g to 8.92 × 10^-10 A/g. This is caused by the esterification of alcohols and esters and the reduction of Fe₃O₄ by CO. Based on the decrease in activation energy and enthalpy values of Stage II and IV, it infers that Fe₃O₄ catalyzes the pyrolysis process of oily sludge to some extent. Similarly, gas chromatography-mass spectrometry results show that Fe₃O₄ can make the types of gas products increase. Especially, the number of molecular species increases from 5 to 46 under 200-300 °C. Finally, a simple molecular dynamics simulation model is conducted, and the results are in agreement with the experimental results. This study shows that Fe₃O₄ improves the pyrolysis homogeneity and the pyrolysis efficiency also improves.