Biodiesel production over lithium modified lime catalysts: Activity and deactivation

• Biodiesel from rapeseed oil was produced over lithium modified CaO catalysts.
• Lithium improve the surface basicity by formation of electron defects.
• The calcination temperature plays an important role on the catalyst performances.
• Calcium diglyceroxide formation is enhanced by catalyst basicity.
• Leaching of Ca seems to be due to calcium glyceroxide formed during reaction.

Biodiesel production by methanolysis of semi-refined rapeseed oil was studied over lime based catalysts. In order to improve the catalysts basicity a commercial CaO material was impregnated with aqueous solution of lithium nitrate (Li/Ca = 0.3 atomic ratio). The catalysts were calcined at 575 °C and 800 °C, for 5 h, to remove nitrate ions before reaction.The XRD patterns of the fresh catalysts, including the bare CaO, showed lines ascribable to CaO and Ca(OH)2. The absence of XRD lines belonging to Li phases confirms the efficient dispersion of Li over CaO.In the tested condition (wcat/woil = 5%; CH3OH/oil = 12 molar ratio) all the fresh catalysts provided similar biodiesel yields (FAME >93% after 4 h) but the bare CaO catalyst was more stable. The activity decay of the Li modified samples can be related to the enhanced, by the higher basicity, calcium diglyceroxide formation during methanolysis which promotes calcium leaching. The calcination temperature for Li modified catalysts plays an important role since encourages the crystals sinterization which appears to improve the catalyst stability.

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