V. Dossat et al., Continuous enzymatic transesterification of high oleic sunflower oil in a packed bed reactor: influence of the glycerol production, ENZYME MICR, 25(3-5), 1999, pp. 194-200
The transesterification of high oleic sunflower oil with butanol by the imm
obilized Lipozyme(R) in n-hexane was carried out in a continuous packed bed
reactor, oleic acid, butyl ester, and glycerol being formed as the main pr
oducts. It was found that glycerol, insoluble in n-hexane, remained in the
reactor adsorbed onto the enzymatic support, leading to a drastic decrease
in enzymatic activity. The phenomenon involved in this loss of activity was
attributed to the formation of an hydrophilic hindrance around the enzyme
resulting in diffusion limitations of the hydrophobic substrate from the or
ganic phase to the enzyme. To recover enzymatic activity, several solutions
are proposed. The addition of silica gel into the enzymatic bed to adsorb
the produced glycerol did not enable this loss of activity to be avoided. I
n order to enhance the solubility of glycerol in the reaction medium as soo
n as it was produced, n-hexane amended acetone was used as solvent, but hig
h conversion of sunflower oil was not restored. Finally, by intermittent ri
nsing of the catalyst bed with a solution of tertiary alcohol amended with
water to obtain the optimal thermodynamic water activity of 0.54, glycerol
was eliminated from the reactor, and high conversion was maintained. This s
emi-continuous process allowed not only the synthesis of oleic acid butyl e
ater but also the two products to be recovered separately. (C) 1999 Elsevie
r Science Inc. All rights reserved.