Transesterification of Vegetable Oils’ Triglycerides by the Head Fraction of Ethyl Alcohol

Abstract

The regularities of sunflower, rapeseed and flaxseed oils’ triglycerides transesterification by the head fraction of ethyl alcohol in the presence of various catalysts have been investigated. The cation exchange resin KU-2-8 in H+-form and cation exchange resin KU-2-8 containing an immobilized Cu2+-ions (untreated and treated by 0,1 M sodium hydroxide solution for 90 min and for 7 days) were used as catalyst. It was shown that the all investigated catalysts except the untreated cation exchange resin KU-2-8 containing an immobilized Cu2+-ions allow to achieve of triglycerides conversion over 90 % under the reaction conditions. It was found that the catalyst KU-2-8 containing an immobilized Cu2+-ions treated by 0.1 M sodium hydroxide solution for 90 min shows the highest activity. Also it was found that this catalyst allows to achieve triglyceride conversion all of studied vegetable oils over 99.5% in 180 min of reaction. Simultaneously it was found that the highest rate of transesterification reaction in its presence is observed. The influence of these catalysts on the esterification reaction of free fatty acids, present in vegetable oils, by ethyl alcohol, present in the head fraction, was studied. It was established that the influence of the investigated catalysts on the esterification reaction is different. It was shown that cation exchange resin KU-2-8 containing an immobilized Cu2+-ions treated by 0.1 M sodium hydroxide solution for 90 min catalyzes the esterification reaction of free fatty acids of all investigated oils. Their conversion is from 21.6 % (in sunflower oil) up to 74.1 % (in rapeseed oil). At the same time, it was found that long-term treatment of cation exchange resin KU-2-8 containing an immobilized Cu2+-ions by sodium hydroxide solution leads to a sharp decrease or loss of catalyst activity in the esterification reaction of free fatty acids by ethyl alcohol. It was shown that the use of this catalyst for the transesterification of rapeseed and sunflower oils’ triglycerides even increases the acid number of the reaction mixture, namely to the partial hydrolysis of triglycerides. The obtained results show that the short-term treatment the cation exchange resin KU-2-8 containing an immobilized Cu2+-ions by 0.1 M alkali solution is one of the ways that allow to increase its catalytic activity in the transesterification process of vegetable oils by head fraction of ethyl alcohol. It is assumed that such treatment affects the catalytic activity of Cu2+-ions due to changes in the electron density on the catalyst cation caused the coordination of part of the OH–-anions. The long-term treatment of the cation exchange resin containing an immobilized Cu2+-ions by alkali solution causes a maximum saturation of the cation coordination sphere. This obviously creates steric problem of a reagents access to the catalyst and reduces the catalytic activity cation exchange resin.