The release and transformation of typical chemical forms of sodium (i.e., H2O-soluble salts and carboxylates) in kitchen waste during torrefaction at 200–300 °C was investigated in this study. It was found that sodium release is negligible (<2%) at 200 °C after torrefaction for 15 min, but the release increases to ∼10% when the temperature is increased to 300 °C. Because of the high concentration of water-soluble sodium in raw noodles, the release of sodium during torrefaction is mainly in the form of NaHCO3 or Na2CO3, as NaCl is relatively stable at torrefaction temperatures. The transformation of Na from a water-soluble form to a CH3COONH4-soluble form during torrefaction was found to be an important factor in the release of sodium from raw noodles, since sodium release occurs much more readily from a Na-exchanged sample during torrefaction. CH3COONH4-soluble sodium is also found to transform back into a water-soluble form during torrefaction. For example, ∼18% of the sodium in a Na-exchanged sample transforms to a water-soluble form (i.e., Na2CO3) at 300 °C, indicating the existence of an interconversion mechanism between the water-soluble and CH3COONH4-soluble forms. A small amount of water-soluble or CH3COONH4-soluble sodium could also transform to acid-soluble and stable forms during torrefaction at high temperatures (i.e., 300 °C).

Experiments were performed to determine the effects of alkali and alkaline earth metallic (AAEM) species on the ignition behavior of char under O2/N2 conditions. The char ignition temperatures of a Loy Yang brown coal were investigated using a wire-mesh reactor, where the secondary reactions of the evolved volatiles were minimized. Water, ammonium acetate, and sulfuric acid sequential extractions were employed to prepare the coal samples of different chemical forms of AAEM compounds from raw coal. In comparison to that of raw coal, the increases in the average char ignition temperature of 33 and 55 °C were observed for ammonium-acetate-extracted coal and sulfuric-acid-extracted coal (H-form coal), respectively, indicating the strong catalytic effects of various chemical forms of AAEM species on the char ignition behavior of brown coal. To find out which chemical form of sodium has a higher catalytic effect on the char ignition behavior, combustion experiments were also carried out for Na-exchanged coals and NaCl-loaded coals, which were prepared from H-form coal. The average char ignition temperature of 0.05 M Na-exchanged coal is 48 °C lower than that of 0.05 M NaCl-loaded coal in air, although those two samples have a close content but different chemical forms of sodium. It was found that sodium in char as carboxylates (−COONa) or NaCl can both improve the ignition characteristics of coal samples but carboxylates (−COONa) show a more significant catalytic effect on the average char ignition temperature in air combustion.

Pyrolysis experiments of polyvinylchloride (PVC) were performed to investigate the effects of peak temperature, holding time, and heating rate on the formation of nascent tar. The nascent tar samples were collected using a wire-mesh reactor where the secondary reactions of the evolved volatiles were minimized. The small compounds, such as benzenes and alkanes, were not detected in nascent tar in wire-mesh reactor, whose components are quite different from those of other tars in tube type reactor and vacuum reactor. At a heating rate of 1000 K/s, the quasi-3 rings and 3 rings group aromatics were the major components in nascent tar; while the content of 2 rings group aromatics increased from 7.02% to 31.75% with increasing peak temperature from 500 to 800 °C. At a longer holding time of 300 s, an increase of 2 rings group aromatics from 7.02% to 50.33% was also observed for the nascent tar at 500 °C, indicating that the tar composition significantly changed at different stages of PVC pyrolysis. It seems that 3–4 rings compounds form in the early stage and then 2 rings compounds release in the later stage of PVC pyrolysis. Based on the experimental results in this work, a new four-stage mechanism, including (1) dechlorination accompanied with inner cyclization, (2) aromatic chain scission, (3) release of quasi-3 rings or 3 rings group, and (4) release of 2 rings group, of the PVC tar formation was proposed.