Mobile Low-Field 1H NMR Spectroscopy for on-line monitoring transesterification reactions and biodiesel analysis.

YAMILA GARRO LINCK; MARIO H. M. KILLNER; ERNESTO DANIELI; J. ROHWEDDER; BERNHARD BLÜMICH

Rio de Janeiro

Congreso; 18 ISMAR Meeting; 2013

Biodiesel has gained importance in recent decades because of its favorable properties. It is defined as alkyl esters of vegetable oils or animal fats, by means of transesterification with an alcohol. The quality control of biodiesel is important to the successful commercialization of this fuel and its blends1. We show the use of a new mobile low-field 1H NMR device, based on permanent magnets arranged in a modified Halbach geometry2, for the real time study of transesterification reactions. Low-field 1H NMR spectra of the compounds coexisting in a typical transesterification reaction are first discussed. Then, the online monitoring of the reaction through NMR spectroscopy is presented, which allows the determination of the conversion rate of the product. This was determined by a partial least squares (PLS) calibration model, validated with high field experiments. Additionally, the relative concentration values of hydroxilic protons were also analyzed, giving a quantitative idea of the alcohols partitioning between the two phases during the reaction. These results are useful to understand the reaction mechanism of biodiesel production. A strong shift in the spectral position of the hydroxilic protons was observed, which shows good correlation with the conversion ratio of the reaction. Moreover, the degree of saturation of different biofuel samples was estimated by low-field NMR spectroscopy measurements3, which is of great importance because of its direct relation with biodiesel properties such as viscosity, density and higher heating values. 1. G. Knothe, J. Van Gerpen, J. Krahl (eds.), The biodiesel handbook (AOCS Press, Champaign, 2005). 2. E. Danieli et al. Angew. Chem. Int. Ed. 49, 4133 (2010). 3. Y. Garro Linck, M. H. Killner, E. Danieli and B. Blümich. Appl. Magn. Reson. 44, 41 (2013).