Журнал химической инженерии и технологических процессов
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Microwave Pyrolysis of Plastic

Elham Khaghanikavkani, Mohammed M. Farid, John Holdem and Allan Williamson

Microwave heating has been used in the chemical industry for many years for diverse applications due to advantages, such as volumetric heating, high power density, and fast and easier temperature control. The motivation of this work is to develop a methodology to use potential benefits of microwave as a heat source in plastic pyrolysis. A goal was to use the available knowledge to design and build a rotating microwave reactor, to attain homogeneous temperature distribution in anticipation of producing pyrolysis products with uniform molecular hydrocarbon distribution. Also, it was sought to investigate the effect of process parameters on products’ yield and composition, and examine their suitability as fuel and useful chemicals. A rotating microwave reactor was designed and fabricated using a coaxial transmission structure without the limitations of the commonly-used enclosed glass quartz reactor, which made the design appealing for any future industrial-sized microwave reactor.

The optimum pyrolysis operating condition led to the production of a suitable product for a fuel application. However these products cannot be used directly as phase change materials due to their low latent heat and very broad melting range. Fractionation of the products may also be used as phase change materials, capable of storing/releasing heat at suitable application temperature. The microwave heating provided a more uniform heating distribution, although it did not alter product composition in comparison to the conventional pyrolysis of plastic. In the small microwave reactor used in this project, microwave benefit was not evident with regards to its effect in creating uniform temperature distribution. The benefit may be clearer in an industrial-sized reactor in which heat penetration in conventional thermal reactor can be a serious problem.

The pyrolysed products (oil/waxes) were quantitatively analysed using GC/FID. The results of microwave pyrolysis showed 73% oil/wax yield, with silicon carbide used as a microwave absorbent.