Substitution of liquid methanol with methanol vapour increases the activity and stability of carbon-based solid acid catalysts in biodiesel production process

Abstract

The effect of methanol vapour esterification (MVE) on the catalyst activity and reusability was investigated using methanol vapour (MV) instead of liquid methanol for the esterification reaction of oleic acid catalysed by a carbon-based solid acid catalyst (CSAC) S150-4. The conversion yield for the MVE was 98.8 % at a catalyst loading of 4 wt%, methanol/oleic acid molar ratio of 40:1, reaction temperature of 76 °C and reaction time of 4 h. When the catalyst loading is increased to 10 wt%, S150-4 repeatedly catalysed MVE up to the eighth batch, while still achieving 83.4 % conversion. The turnover frequency and number of catalyst reuses were twice as high for MVE as in liquid methanol esterification (LME) under the optimal esterification conditions for both modalities. When compared to LME, MVE achieved a combination of a large amount of methanol and oleic acid in a short time, increasing the conversion yield while reducing the average contact time between methanol and the acidic groups on the surface of the CSAC, resulting in less leaching and chemical derivatization of the sulphonic acid groups from the catalyst in MVE. The production cost of methyl oleate in MVE was 19.1 % lower than that for LME. Therefore, the application of MVE as an alternative to conventional esterification is an effective way to extend the life of CSACs.