Production of hydrocarbons from fatty acids and animal fat in the presence of water and sodium carbonate: Reactor performance and fuel properties

Abstract

The thermal degradation of free fatty acids and animal fat in a moving bed of sodium carbonate and 5wt% of water were carried out 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 10kg/h resulting in a 69±5% of bio-crude. The acidity index was remarkably low within a range of 0.64–0.80mg KOH/g during 3weeks of operation. The loading rates for animal fat were increased from 10 to 40kg/h corresponding to a weight hourly space velocity of 0.03–0.1h−1 over a period of 6months. 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 0.5–1.8mg KOH/g. The mean value for kinematic viscosity at 40°C was 1.78mm2/s. The net calorific value of bio-crude was 41.6MJ/kg. Coke deposits on sodium carbonate were determined to be 5±1%. The gaseous products ranged from 25wt% to 30wt%. 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 26kPa instead of 60-90kPa (DIN EN 228). Thus, water-cooled condensers need to be improved for a full-scale plant. The results are discussed in terms of German specifications for standard fuels.