Supercritical Ethanol Liquefaction of Swine Manure for Bio-Oils Production

Abstract

Problem statement: Environmental problems associated with animal waste are the most critical challenges faced by the US intensive confinement livestock industries. There is an import and urgent need to develop an efficient way to reduce the pollution of animal waste while extracting valuable energy. Supercritical liquefaction processing of swine manure into a liquid fuel was considered as a cost-effective approach for reducing animal waste in swine farms while simultaneously increasing the farmer’s income. Approach: Swine manure was converted to bio-oils by using ethanol as a solvent in an autoclave in the reaction temperature range of 240-360°C without any catalyst. The effect of reaction temperatures on the bio-oil yield and properties was investigated. The oil product was evaluated by Fourier Transform Infrared spectroscopy (FTIR), elemental analyses, heating values, water content analyses, ash content and solids content. Results: The experimental results show that the yield of the liquefaction products was significantly influenced by the reaction temperature. The maximum oil yield of 26.7% (of dry matter) with low content of oxygen (11.48%) and heating value of 33.98 MJ kg^-1 was obtained at reaction temperature of 300°C. A low content of carbonyl and aliphatic groups and a high aromaticity in the bio-oil were found in the bio-oils from high temperature as determined by FTIR. The elemental composition of the bio-oil samples changes with reaction temperature. However, no particular trends in the elemental composition were found within the range of reaction temperature used. Conclusion: This research proved that supercritical ethanol liquefaction was an effective way to remove oxygen and utilize carbon and hydrogen in swine manure to produce energy condensed bio-fuel. Further work is needed to optimize the bio-oil production process in terms of oil yield and oil quality.