An investigation on synergistic effects and kinetic characteristics of pyrolysis of kitchen waste components: Starch, protein and lipid

The large volume and complex composition of kitchen waste necessitate environmentally sound treatment methods. Pyrolysis emerges as a promising way in treatment and utilization of kitchen waste. However, due to the complex composition and structure of kitchen waste, its pyrolysis characteristics remain unclear. Herein, thermogravimetric analysis was used to compare the pyrolysis characteristics of starch, protein, and lipid in kitchen waste as well as their synergistic interactions at various heating rates. Activation energy and reaction mechanisms were explored using the model-free and model methods. Evolved vapors were analyzed with thermogravimetric-mass spectrometry. The results showed that the presence of lipid slowed down the escape of volatile fractions when co-pyrolyzing with starch, protein or their mixtures (250-420 degrees C), but promoted the overall conversion with lower solid residual rates (Delta W > 1.6 wt%) and higher generation of gaseous products (mainly C2H4/CO and H2O). The increased activation energies led by lipid addition during co-pyrolysis were mainly because of the liquid phase formation over starch and protein, thereby preventing the deep degradation of organics. Contrary to the pyrolysis of starch, protein and lipid, distinct reaction mechanisms were revealed during the co-pyrolysis, with starch/lipid, starch/protein, protein/lipid and starch/protein/lipid following reaction models of F1.5, R1, ZH and F2, respectively. This study provides theoretical support for the development of advanced pyrolysis-based technologies for kitchen waste treatment.