It has been known for a long time that sulfonated active-carbon acid can catalyze both esterification and transesterification to produce biodiesel fuels from oils with high acid value without pretreatment. However, the separation of such catalysts requires filtration or centrifugation, which are energy intensive and time consuming. In order to enable the magnetic separation of this type of catalyst, professor Fang Zhen and his team at the Xishuangbanna Tropical Botanical Garden of the Chinese Academy of Sciences (Menglun, Yunnan Province; ) have synthesized magnetic carbonaceous acid catalysts with high acidity and strong magnetism for biodiesel production from oils with high acid value. The catalyst allows production of biodiesel from crude Jatropha oil with high acid value (17.2 mg KOH/g) and high yields, a slight reduction in total acid density and high catalyst recovery rate of 96.3%. With the catalyst, the team has achieved a Jatropha diesel fuel yield of 90.5% at 200°C with three cycles.

To make the catalyst, the researchers used a five-step process involving double hydrothermal precipitation at 180°C and pyrolysis at 400 to 800°C, and subsequent sulfonation at 150°C. A pyrolysis temperature of 600°C was found to give a catalyst with high acid density (2.79 mmol/g) and strong magnetization (14.4 Am²/kg). The magnetic catalyst directly esterifies and transesterifies high-acid-value oil without pretreatment, with high biodiesel yield and the catalyst was easily separated for three recycles with little deactivation. The team believes the catalyst could also find application in the pretreatment of oils with high acid value and in the hydrolysis of biomass.

URL:  http://www.chemengonline.com/attractive-catalyst-making-biodiesel-fuels/