Naslov
The effect of microvave heating on the esterification of lactie acid in ionic liquid

Autori
Major, Brigitta ; Vrsalović Presečki, Ana ; Kelemenné Horváth, Ilona ; Vass, András1 ; Gubicza Láslo

Vrsta, podvrsta i kategorija rada
Radovi u zbornicima skupova, cjeloviti rad (in extenso), znanstveni

Izvornik
Muszaki Kemiai Napok '08 Conference of Chemical Engineering '08 / Endre, Nagy ; Ferenc, Simon ; Katalin, Kiss ; Imre, Hegedus - Veszprém : Pannon Egyetem, 2008, 127-132

ISBN
978-963-9696-36-5

Skup
Muszaki Kemiai Napok '08 Conference of Chemical Engineering

Mjesto i datum
Veszprém, Mađarska, 22.04.2008. - 24.04.2008

Vrsta sudjelovanja
Poster

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
esterification; ionic liquid; lipase

Sažetak
The esterification of lactic acid has a grate industrial importance because this is the onli purification process, which separates other organic acids. In addition, ethyl lactate is a natural flavouring compound and can be used as a ''green'' solvent as well. Microwave heating is widely used in organic chemistry because it usally shortens the reaction time and enhances the reaction rate but the question is what kind of effect it has on enzymatic esterification reactions in ionic liquid media. That is why the production of ethyl lactate in non-conventional media was studied and results of conventional and microwave heating were compared. A concentrated solution of lactic acid was used in the esterification experiments in order to avoid the inhibitory effect of the water but this resulted the presence of lactic acid oligomers which amount were determined by titration. The accurate composition of the lactic acid solution was 14 w% water, 53 w% lactic acid, 26 w% lactoyllactic acid, and 7 w% other oligomers. The ester yield was calculated from the monomer contents of the reaction mixtures. In the first step reaction were carried out in organic solvents and the best results were received in toluene using 250mg immobilised Candida antarctica lipase enzyme. After that 20 different ionic liquids were tested, but reaction could be carried out with measurable yield only in 7 media: Cyphos 202, Cyphos 163, Cyphos 166, Cyphos 102, Cyphos 106, and Cyphos 110 ionic liquids. These media could be divided into 3 groups. In the first group (Cyphos 104) only the enzyme had catalytic effect. In the second one (Cyphos 163, Cyphos 166, Cyphos 102, Cyphos 106 and Cyphos 110), the reaction was catalysed by the ionic liquid as well and a similar ester yield was observed without enzyme. Finally, Cyphos 202 was situated between the two previous groups, because it slightly catalysed the reaction. The enantioselectivity of the reaction was tested as well and Cyphos 104 was the only medium where a slight excess (e.e. 19%) of ethyl-L lactate was observed. The ethyl lactate production was optimized in Cyphos 104 and highest yield was achieved using the following parameters: 0.8 mmol ionic liquid, a lactic acid solution containing 2 mmol monomer acid, 7 times ethanol excess, 1 w% initial water content, 25 mg enzyme. The reusability of the enzyme was also tested and compared with the results in toluene. We found that in organic solvent the ethyl lactate yield decreased completely after four cycles, but in ionic liquid it decreased only 20 % after 6 cycles. By these experiments it can be said that in ionic liquid not only smaller amount enzyme is needed but its stability is much better. Reactions were carried out under microwave heating in Cyphos 104, 202, 106, and 110 but positive effect was observed only in two media (Cyphos 202 and 106) where the achieved yield was higher and the reaction time shorter. The optimal initial water content was also tested and the best result was observed at 1 w% initial water content in Cyphos 106, and at 3 w% in Cyphos 202. The obtained yield was77 % and 105 %, respectively. In some cases ester yield exceeded the monomer lactic acid content of the reaction mixture which can be only possible if the dimers are able to decompose to monomers and form ethyl lactate. This theory could be verified by HPLC analysis because if can separate the different oligomers. The result of the analysis was that in the reaction mixture there is an equilibrium between the lactic acid oligomers which is stable during the reaction. It means 46 w% lactic acid, 44 w% lactoyllactic acid, and 10 w% other oligomers in Cyphos 202 while the ethyl ester yield increased 98 w% so the dimers has to decompose to keep the equilibrium.

Izvorni jezik
Engleski

Znanstvena područja
Biotehnologija

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