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German team produces hydrocarbons from thermal degradation of free fatty acids and animal fat in water and sodium carbonate; ultimately 43% diesel-range and 14% gasoline-range fractions

Researchers in Germany have produced a hydrocarbon-based bio-crude and non-condensable gases from the thermal degradation of free fatty acids and animal fat in the presence of water and sodium carbonate (Na2CO3, a sodium salt of carbonic acid commonly used as a water softener). Ultimately, they achieved a total yield of 43% diesel-range and 14% gasoline-range fractions from animal fat. They report on their work in a paper in the journal Fuel.

The process was carried out in a moving bed of sodium carbonate at 5 wt% water at 430± 20 °C at a pilot-scale plant. During start-up the loading rates for a 60:40 mixture of oleic and stearic acids were 10 kg/h resulting in a 69 ± 5% of bio-crude. The loading rates for animal fat were increased from 10 to 40 kg/h corresponding to a weight hourly space velocity of 0.03–0.1 h−1 over a period of 6 months.

Heat transfer into the reactor was the limiting criterion. The main product with a yield of 65 ± 5% was bio-crude showing an acidity index of 0.5–1.8 mg KOH/g. The mean value for kinematic viscosity at 40 °C was 1.78 mm2/s. The net calorific value of bio-crude was 41.6 MJ/kg. Coke deposits on sodium carbonate were determined to be 5 ± 1%. The gaseous products ranged from 25 wt% to 30 wt%. The presence of CO2, H2, CH4, C2H6, C2H4 and C3 to C5 hydrocarbons as major components was established by gas chromatography.

The gases were directly fed into an on-site gas line and used for heating purposes. The distillation curve of bio-crude from animal fat showed hydrocarbon based bio-fuels in the boiling ranges of gasoline and diesel. Upon rectification 66% of bio-diesel and 21% of bio-gasoline were obtained. This corresponds to a total yield of 43% bio-diesel and 14% bio-gasoline from animal fat.

The bio-diesel had favorable low-temperature properties (cold filter plugging point = −18 °C) with oxidation stability between that of mineral oil based diesel and fatty acid methyl ester fuels. The gasoline fraction lacked low-boiling hydrocarbons as indicated by a vapor pressure of 26 kPa instead of 60-90 kPa (DIN EN 228). Thus, water-cooled condensers need to be improved for a full-scale plant.

Resources

  • Bernd Weber, Ernst A. Stadlbauer, Sabrina Stengl, Mohammad Hossain, Andreas Frank, Diedrich Steffens, Elmar Schlich, Gerhard Schilling (2011) Production of hydrocarbons from fatty acids and animal fat in the presence of water and sodium carbonate: Reactor performance and fuel properties. Fuel DOI: 10.1016/j.fuel.2011.08.04

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