The stability evaluation of lime mud as transesterification catalyst in resisting CO2 and H2O for biodiesel production

• Lime mud (LM) is pretreated with calcination, hydration and desiccation.
• The alkali solubility is the amount of alkali compounds dissolved in methanol.
• The soluble alkali amount in LM700-H is higher than that of CaO–H.
• LM700 possesses a stronger capability than CaO in resisting H2O and CO2.

The most outstanding property of the heterogeneous transesterification catalysts is recyclable, but their catalytic activity may be depressed for the absorption of moisture (H2O) and carbon dioxide (CO2) in air, especially for the basic ones. Lime mud (LM) is effective in catalyzing transesterification, yet its property in resisting H2O and CO2 is indistinct, which should be emphasized. In this study, the LM based transesterification catalyst is prepared through calcinations. Then, it is hydrated and desiccated to simulate the contamination by H2O and CO2. Further, the fresh and the contaminated catalysts are characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), Hammette indicator, Brunauer–Emmett–Teller (BET) surface area and soluble alkali examination, to reveal the mechanism of LM in resisting H2O and CO2. Meanwhile, the analytical grade calcium oxide (CaO) is chosen for comparison. Finally, to comprehensively investigate the influences of H2O and CO2 on LM in catalyzing transesterification, the factors of the catalyst addition percentage, molar ratio of methanol to oil and transesterification temperature are evaluated.