Co-pyrolysis of waste plastics and brown coal upgraded under hydrothermal condition

Added Title

Annual International Pittsburgh Coal Conference (24th : 2007)
PCC 2007


Gokongwei College of Engineering


Chemical Engineering

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Conference Proceeding

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24th Annual International Pittsburgh Coal Conference 2007, PCC 2007



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Brown coals contain large amount of water (~60%) in general, and they show high spontaneous combustibility when dried. Therefore, it is essential to upgrade as well as to dewater for storage and transportation of brown coal. We have recently presented a hydrothermal extraction method that not only removes water from brown coal but also upgrades the coal and extracts low molecular mass compounds simultaneously. The upgraded coal contained much less oxygen than the raw coal. However, it still needs to be further upgraded to be utilized as a substitute for bituminous coal. In this study co-pyrolysis of the upgraded coals and waxes formed from waste plastics was investigated for this purpose. Waxes were prepared through pyrolysis of polyethylene, polypropylene, and polyethylene terephtalate. Upgraded coals were then impregnated with the waxes in an autoclave at 200°C under pressure. The mixtures of coal and wax were rapidly heated up to 1040°C at about 3000°C/s using a Curie point pyrolyzer in an inert atmosphere. The char yield was greatly enhanced by a factor of 1.1 to 1.3 compared to the char yield obtained when the upgraded coals and waxes were pyrolyzed independently. Even under a slower heating rate (0.17°C/s) the char yields increased by a factor of 1.2 for the all mixtures of the upgraded coal and waxes. Since no such effect was found when the raw brown coal was impregnated with waxes, it was suggested that the modification of the structure of brown coal by the hydrothermal extraction could enhance interactions between the coal and the wax when co-pyrolyzed. Effect of wax mixing ratio on co-pyrolysis behavior was also examined. The enhancement of char yield was small when the wax content was smaller than 0.3 g/g-upgraded coal. On the other hand, the char yield dramatically increased when the wax content exceeded about 0.3 g/g-upgraded coal for the pyrolysis of both under slow and rapid heating rates. This trend coincided with that of the swelling ratio of the upgraded coal impregnated with wax, indicating that some physical change by wax-impregnation affected the co-pyrolysis behavior. Co-pyrolysis mechanism was also examined in detail for the pyrolysis under a slower heating rate.



Chemical Engineering


Lignite; Pyrolysis

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