Characterization of rare earths obtained from monazite concentrate processing and their application in esterification for biodiesel production

Rare earths namely lanthanum (La), neodymium (Nd) and cerium (Ce) obtained from the monazite concentrate processing were comprehensively characterized using XRF, XRD, FTIR, N2 adsorption–desorption, CO2/NH3-TPD and SEM to reveal their catalytic performance in esterification of oleic acid for biodiesel production. The effect of calcination temperatures (500–1000 °C) on the catalyst properties and biodiesel conversion was also investigated. The catalytic performances of the catalysts were tested under the conditions of catalyst loading 3 wt%, molar ratio of oil to methanol 1:20, reaction temperature 200 °C, stirring rate 600 rpm for 5 h. It is interesting that the Ce catalyst calcined at 1000 °C showed the best performance and the highest FAME content of 78.54% could be achieved, even its acid sites was very low, which is probably associated to the availability of oxygen vacancies at high calcination temperature. The La catalysts calcined at 600 °C exhibited the balancing of strong Lewis acid and Lewis basic sites, which is related to the catalytic activity with FAME content of 74.44%. For the catalytic performance of Nd catalysts, the FAME content of 63.60% was obtained at calcination temperature of 500 °C, which was lower than those La and Ce catalysts. [Display omitted] •La, Nd and Ce catalysts are utilized as catalyst for esterification of oleic acid.•The maximum conversion of 78.54% was achieved over Ce catalyst calcined at 1000 °C.•More oxygen vacancies forming on surface of Ce may promote the esterification activity.•The high activity of La and Nd could attributed to the balancing of strong acid-basic sites.