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The activity of a catalyst in transestrification reaction usually declines with repeated uses and this limits the possibility to use it many times. This paper presents a review of various techniques used to evaluate the activity changes, the recycling processes for calcium and magnesium oxides based heterogeneous catalysts for biodiesel production. The activity of calcium and magnesium oxides based catalysts declines due to leaching, surface or active sites poisoning by reactant or product molecules and modification of physical aspects. Physico-chemical methods (AAS, BET, CO2-TPD, EDS, FTIR, ICP-AES, SEM, TG/DTA and XRD were used to check the catalyst modification and to confirm the deactivation. When separated from the reaction mixture by filtration, the catalyst could be reused without any treatment or recycled by washing, drying or/and recalcination. Between various recycling processes for calcium and magnesium oxides based catalysts, mixed oxides showed less leaching and performed FAME or FAEE yield >90% with reusability.

Deactivation Processes, Regeneration Conditions and Reusability Performance of CaO or MgO Based Catalysts Used for Biodiesel Production—A Review