Products from the flash pyrolysis of peat and pine bark

Dry powders prepared from fuel-grade medium-decomposed Carex peat and from bark of Scots pine (Pinus sylvestris) were pyrolyzed in a continuous bench-scale fluidized-bed reactor over a temperature range of 400–800° C. Gas-phase residence time within the heated zone was about 0.5 s. In addition to the determination of the yields of major product groups, the organic liquid products were separated and identified by gas chromatography/mass spectrometry and characterized by infrared spectroscopy and gel permeation chromatography.
The highest yields of organic liquids, more than 50 wt% of bark organic matter and over 40 wt% of peat organics were obtained at 500° C. The yields of liquid products decreased at 600° C because of thermal secondary reactions, and the yields of gaseous products, such as CO, C₂H₄, CH₄ and H₂ increased correspondingly. At the highest temperature nearly 60 wt% of peat and nearly 50 wt% of bark were degraded to gaseous products. The proportion of organic liquids analyzed by gas chromatography was, in all cases, less than 30 wt%. Even so, significant changes in chemical structures were detected. According to the gel permeation chromatography results, the liquid products formed at 800° C still contained high-molecular-weight substances. On the other hand, the high-temperature liquid products were, overall, of lower molecular weight than those obtained at lower temperatures.
The results can be utilized in the development of thermochemical conversion processes based on flash pyrolysis. In addition, they can be applied in basic research on gasification and combustion at high-heating rates.