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Batch and continuous extraction of free glycerol from biodiesel with deep eutectic solvent

After biodiesel synthesis, it is necessary to purify it since it contains various impurities that adversely affect its properties, its storage properties as well as engine performance and engine lifetime. One promising alternative method for purification of biodiesel is extraction with deep eutectic solvents (DES). Some studies on vegetable oils have shown that the use of DESs reduces the content of all impurities present in crude biodiesel. Biodiesel was synthesized from waste sunflower oil by means of chemical transesterification catalyzed by alkali catalyst. Deep eutectic solvent, choline-chloride/ethylene- glycol (molar ratio 1:2.5), was prepared and used as extraction media in batch and continuous Karr column. The influence of hydrodynamic conditions, solvent to biodiesel ratio and duration of extraction on its efficiency were tested during batch experiments. Continuous experiments were conducted under constant solvent and biodiesel flowrates with different pulsation rate. The results have demonstrated that hydrodynamic conditions, solvent to biodiesel ratio and extraction duration have a largely negligible impact on the efficiency of free glycerol removal in the tested range of conditions and that the efficiency is relatively high for all conducted experiments. The efficiency was only slightly lower during continuous extraction. Free glycerol content was below the limit, but the total glycerol and glycerides content was too high to comply with the standard. Choline- chloride/ethylene-glycol (molar ratio 1:2.5) has proved to be successful for free glycerol extraction, but further modification of methods for raw material and biodiesel processing will be needed to fully comply with the standard.

biodiesel; deep eutectic solvents; glycerol; liquid-liquid extraction

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