Characterisation of Malaysian wood pellets and rubberwood using slow pyrolysis and microwave technology

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A series of biomass wastes from Malaysia known as Malaysian wood pellets, and rubberwood were employed in the present work. Using these materials as the feedstock, two different heating techniques; external heating by means of conventional slow pyrolysis (SP) and instanteneous volumetric heating by means of microwave pyrolysis (MP) were carried out. Two distinct temperatures; 500°C and 800°C were used. The main objective was to characterise both the microwave-pyrolysed products and slow pyrolysed products together including the influence of temperature so as to compare and contrast in terms of yield, and composition of the high-value fuel gas (H2) or syngas (H2+CO). The research found that the use of the microwave oven system to conduct pyrolysis boosted the production of oil but diminished the total gas yield. Char proportion also reduced when microwave heating method was applied. This research also revealed that the configuration of the microwave oven with mode stirrer and bottom-fed waveguide that produces a constant output power of 1000W at any set temperature has yielded different results when compared to previous studies and so provides a new insight to the microwave pyrolysis community. The results demonstrated that the microwave-pyrolysed chars were slightly porous than slow-pyrolysed chars at 500°C. However at higher temperature of 800°C, lower surface area was obtained from microwave pyrolysis which can be attributed to serious damage of char structure as the consequence of high power supplied into the cavity and high temperature used. SEM microphotographs revealed that microwave pyrolysis at 500°C led to the formation of char with clearly defined pore structure. In the case of gas product, both heating approaches were found to produce a comparable level of H2+CO content except to those produced by MP at higher temperature (800°C). Regarding bio-oil quality, the microwave-pyrolysed oil was found to present compounds with higher aliphatic content and contain less polycyclic aromatic hydrocarbon (PAH) content that is an added quality value as PAH is toxic to the environment.