A low-cost synthesis of biodiesel at room temperature and purification of by-product glycerol for reuse

Biodiesel has been synthesized from used frying oil at room temperature (35°C) using NaOH and CH₃ONa as homogeneous catalyst and methanol as reactant. Glycerol has been obtained as a by-product which comprised of impurities such as unreacted methanol, inorganic metals, and traces of triglycerides. The inorganic materials present in glycerol were adsorbed on the surface of activated carbon derived from rice husk. Glycerol is then acidified with 1.2 M H₂SO₄ to form two layers. The upper layer comprised of free fatty acids, and the bottom layer comprised of a glycerol-rich layer. The bottom layer was decanted and neutralized with an aqueous solution of 10 M NaOH and heated at 110°C for 2.5 h to remove the residual water in the glycerol. Further extraction of glycerol with ethanol gives glycerol of high purity. For removal of ethanol from the glycerol, the solution was heated up to 80°C for 30 min. The purity of glycerol was verified by analysis on ¹³C-NMR. The upper free fatty acid layer is confirmed with the help of the treatment of this layer with base solution (NaOH) to give soap. Formation of soap is confirmed with the help of Fourier transform infrared spectroscopy.