MOBILE high-resolution NMR sensor for biodiesel transesterification monitoring and quality control.

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

Dublin

Conferencia; Euromar 2012. Magnetic Resonance Conference; 2012

In the last decades, the request for alternative and renewable sources of energy to diminish the dependence on fossil fuel has caused fuels derived from biological sources to be increasingly scrutinized and utilized. Biodiesel [1], defined as the mono-alkyl esters of vegetable oils or animal fats [2], derived from these feedstocks by transesterification, is probably the most commonly used biofuel as a replacement for petroleum-derived diesel fuel. High-field NMR spectroscopy has been employed in the past for monitoring the transesterification reaction and the quality control of biodiesel. However, the use of conventional high-resolution NMR relies on expensive and sophisticated superconducting magnets. The development towards the highest achievable magnetic fields has pulled NMR spectrometers away from the chemistry hoods in the synthesis laboratories and restricts the use of NMR to experimental conditions more demanding, than those acceptable in industrial environments, where cryogenic liquids often cannot be used. In these cases, small and robust magnets that provide a good share of the performance of large magnets could be installed in chemistry labs to monitor reactions in real time, or mounted in the production line of chemical plants to improve the product quality. During the last years important progress has been achieved in the development of small, robust magnets [3, 4]. Today it is possible to obtain proton NMR spectra of different compounds contained in a 5mm NMR tube with resolutions better than 0.15 ppm using a magnet that is shorter than the sample tube [3]. In this work we show the performance of this new generation of magnets, working at a magnetic field strength of 1 Tesla. These high-resolution systems allow us to follow the rate of conversion during the biodiesel transesterification process and to quantify the concentration via line integration. We also show the application of this small magnet to determine physical properties of the biofuel such as the self-diffusion coefficient from which the viscosity can be determined. The diffusion coefficient was measured with pulsed field gradients benefiting from the excellent switching times of the magnet.