Study of Intermediates in the Acetylation of Glycerol

OKULIK NORA; PADRÓ, C.; BEDOGNI, G.

Santiago de Chile

Congreso; WATOC 2014; 2014

Pontificia Universidad Católica de Chile

The manufacture of first generation biodiesels by transesterification processes has been growing continuously, mainly due to the renewable source of this fuel in comparison with the conventional fuels derived from petroleum. Consequently a large amount of glycerol is produced (accounts for 10 wt% of the total product) which has to be revaluated in order to make the bio-fuel industry economically and environmentally viable. The esterification of glycerol into acetins is quite attractive due to the versatile in. ustrial application of the final products, going from cosmetic to fuel additives. The products of glycerol esterification with acetic acid are: monoacetins, MAG: 1-monoacetin, 1-MAG and 2-monoacetin, 2-MAG, diacetins, DAG: 1,2-diacetin,1,2-DAG and 1,3-diacetin, 1,3-DAG and triacetin, TAG. In order to explain experimental results on the glycerol esterification with acetic acid reaction on Amberlyst 36 wet we carried out a theoretical study of those reactions. Nevertheless many questions remain unanswered so we accomplished a detailed theoretical study address to gain in-depth on transformation of glycerol into acetins. This work describes density functional theory calculations on level of M06-2X/6-311+G(d,p) carried out on glycerol esterification simulating acetic acid environment using the Polarizable Continuum Model. The most stable structures of the reactants, intermediates and products were located by considering a large amount of conformers. The thermodynamics is discussed in terms of the calculated reaction Gibbs free energy and the atoms-in-molecules theory was used to characterize the structures. The obtained results allow us to explain the experimental findings. Indeed, we obtained an experimental 1-MAG/2-MAG and 1,3-DAG/1,2-DAG ratios (18 and 2, respectively) close to the calculated (19 and 3.7, respectively). The transformation of glycerol into 1-MAG and then into 1,3-DAG to produce TAG seems to be the appropriate path for the reaction via few intermediates.