Seashell-derived mixed compounds of Ca, Zn and Al as active and stable catalysts fore the transesterification of palm oil with methanol to biodiesel

摘要

Heterogeneous base catalysts, composed of mixed calcium, zinc and aluminium compounds (ZSA), for the transesterification of palm oil with methanol to produce biodiesel as fatty acid methyl esters (FAME) were prepared from waste mixed seashells in the presence of zinc nitrate and alumina via dissolution precipitation method. The effects of the catalyst calcination temperature on the physicochemical and catalytic properties were studied. Calcination of ZSA at 300 degrees C generated calcium hydroxide as the main active phase, while the formation of CaO at higher calcination temperatures contributed to the catalyst basicity and catalytic activity. The catalyst calcined at 500 degrees C (ZSA-500) possessed a calcium-rich surface on which nanocrystallites of CaO were dispersed. The ZSA-500 catalyst showed the highest stability to ambient air (relative humidity of 73%) exposure for 3 d. The loss of catalytic activity at the higher calcination temperatures of 700 and 900 degrees C was related to the formation of Ca12Al14O33 and the transformation of CaO to calcium carbonate during air exposure. The ZSA-500 catalyst had the highest surface area and basicity and gave the highest FAME yield (98.0 +/- 1.60 wt%). Suitable conditions for transesterification over ZSA-500 at 60 degrees C were a catalyst loading of 10 wt%, methanol:oil molar ratio of 30:1 and reaction time of 3 h. Moreover, the ZSA-500 catalyst could be reused after methanol washing to give a FAME yield more than 96% for at least five uses. (C) 2016 Elsevier Ltd. All rights reserved.