The distribution of ethyl esters, triglycerides, diglycerides, monoglycerides, and glycerol between the ester and glycerol phase was investigated after the ethanolysis of rapeseed oil at various reaction conditions. The determination of these substances in the ester and glycerol phases was carried out by the GC method. The amount of ethyl esters in the glycerol phase was unexpectedly high and therefore the possibility of the reduction of this amount was investigated. The distribution coefficients and the weight distributions of each investigated substance were calculated and compared mutually. The distribution coefficients between the ester and glycerol phase increase in this sequence: glycerol, monoglycerides, diglycerides, ethyl esters, and triglycerides. Soaps and monoglycerides in the reaction mixture cause a worse separation of ethyl esters from the reaction mixture. The existence of a non-separable reaction mixture was observed also, and its composition was determined.

Various effects on the separation of raw reaction mixture after the ethanolysis of rapeseed oil were investigated. Water addition, initial temperature of separation, centrifugation, ionic compound addition and time effects affecting concentrations of potassium, free glycerol and yield of the ester phase were found out. Centrifugation has the most positive effect. Finally, correlation between concentrations of potassium and free glycerol was found out.

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Many samples of rapeseed oil ethyl ester were prepared by alkaline-catalyzed transesterification at various conditions (reaction time, temperature, amount of catalyst, the molar ratio of ethanol to oil, the rotations of a disperser and the purification by water). The concentrations of the key impurities for biodiesel quality (the concentrations of monoglycerides, diglycerides, triglycerides, free glycerol, ethanol, free fatty acids, water) and some qualitative parameters (flash point, carbon residue, kinematics viscosity at 40 °C) were determined and then the relationships among them were found out. The relationships were characterized by the linear or non-linear statistical models.The found models enable the better understanding of the significance of the qualitative parameters and estimate them from the concentrations of impurities. The temperature 2 dependence was also measured in the case of the viscosity of ethyl ester and used rapeseed oil.