Effect of Steam Explosion Pretreatment on the Pyrolysis Properties of Pineapple (Ananas Comosus) Crown Waste

Abstract

The use of biomass as a substitute for fossil fuel has gained attention due to its renewability and availability. Biomass can be converted into fossil fuel equivalents through processes such as gasification, pyrolysis or hydrothermal liquefaction. However, before conversion into valuable fuel forms, several pre-treatment activities are carried out to make biomass amenable to the conversion process. One such pre-treatment approach is steam explosion where biomass components are broken down by high-pressure saturated steam. Pineapple crown waste is a typical biomass source that requires attention regarding disposal. During harvesting and processing activities, a lot of waste is generated from peels to crowns which may end up in landfills or burnt in the open. This can contribute to environmental problems and thus, exploitation of this waste's valuable uses is imperative. Therefore, this study seeks to determine the effect of steam explosion pre-treatment on thermal decomposition behaviour during the pyrolysis of pineapple crown waste. Three pre-treatment pressures of 6 bar, 8 bar and 10 bar were used for the process in a reactor. Each pre-treatment pressure had residence times varied at 5 min,10 min, and 15 min. Compositional analysis revealed the potential of pineapple crown waste biomass as a valuable resource for thermochemical applications. After the steam explosion pre-treatment, the pyrolysis study was done through thermogravimetric analysis (TGA) at a heating rate of 20 ˚C min-1. TGA curves and derivative thermogravimetry (DTG) curves showed the decomposition pattern of the pineapple crown waste biomass components. Thermal degradation of the pineapple crown waste happened in four different stages. Moisture was released in the early stage, followed by the degradation of weak cellulose and hemicelluloses in the second stage. The third stage is where cellulose mainly decomposes and pyrolysis primarily occurs to produce bio-oil and gas. The final stage decomposed the remaining biomass components which were not degraded during the previous stages, forming char. Lignin is mostly degraded at this stage. Pronounced peaks were observed for each pre-treatment pressure at 15 min residence time. Calculation of kinetic parameters according to the Coats and Redfern model depicted an increase in frequency factor and a slight significant decrease in activation energy, especially for pre-treatment pressure at 10 bar. This shows that the thermal reactivity of the pineapple crown waste was improved with steam explosion pre-treatment. Also, higher pressure and increased residence time during pre-treatment contributed to the better decomposition of pineapple crown biomass during pyrolysis, and thus yield good products for biofuel utilization.