Supercritical Ethanol Liquefaction of Swine Manure to Produce Bio-oils

Researchers from North Carolina A and T State University have converted swine manure to bio-oils by using ethanol as a solvent in an autoclave in the reaction temperature range of 240-360 °C without any catalyst. Bio-oils can be upgraded to transportation fuels.

Animal waste has tremendous energy potential. It can be viewed as an underutilized renewable energy resource. Within the US approximately 250 million tons of dry fecal materials are produced yearly, with an energy value comparable to wood (on a dry matter basis). If this energy could be harvested, it would be equivalent to 21 billion gallons of gasoline (ThePigSite, 2004).

In the case of swine manure, an estimated 5.3 Million Tons (MT) is produced annually in the US, which could supply biomass for the production of biofuels equivalent to 6.0 Million Barrels (MB) of petroleum-based fuels (USDA, 2005). The energy content of these biofuels is equivalent to 2.1% annual consumption of petroleum oil in the US.

—Xiu et al.

Their study showed 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 (Fourier Transform Infrared spectroscopy). Although the elemental composition of the bio-oil samples changes with reaction temperature,the team found no particular trends in the elemental composition within the range of reaction temperature used.

In a paper published in the American Journal of Engineering and Applied Sciences, the authors conclude 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.


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