Use of lime mud from paper mill as a heterogeneous catalyst for transesterification

Lime mud (LM), a solid waste from the paper mill, is used as an economic and environmental friendly heterogeneous basic catalyst for transesterification, which is accompanied by characterization of X-ray fluorescence, thermogravimetric-differential thermal analysis, X-ray diffraction, N₂ adsorption, and Hammett indicator method. To investigate the performance of the achieved catalyst, which is activated through calcination, the aspects of calcination temperature, reaction time, mole ratio of methanol to oil, catalyst addition percentage, and reaction temperature are concerned. Characterization of catalyst reveals that LM could be activated through calcination to transform the carbonate and hydrate of calcium into the oxide forms and higher calcination temperature could lead to stronger basic strength. However, N₂ adsorption results indicate that higher temperature causes the sintering of the catalyst and shrinkage of the catalyst grains. When LM is activated at 800°C (LM-800) and the reaction is carried out at 64°C with a methanol to oil mole ratio of 15:1, catalyst addition percentage of 6%, and reaction time of 2 h, the maximum transesterification conversion of 94.35% could be achieved. Reusability of LM-800 is also investigated compared with laboratory grade CaO in five reaction cycles and the results indicate that the catalysts derived from LM can be used as an economic and efficient catalyst for biodiesel production.