Investigating molecular transformation processes of biodiesel components during long-term storage via high resolution mass spectrometry.

Biodiesel is an important building block in renewable energy transformation. The main culprit is that during storage biodiesel will undergo transformation processes that can lead to molecular changes, which then can cause applicational problems such as severe motor damage. To prevent this a detailed understanding of the involved molecules and the emerging aging products is necessary. Biodiesel samples were stored for up to 12 months to monitor molecular changes and all mixtures were investigated by using ultrahigh resolution mass spectrometry (HR-MS) with electrospray ionization (ESI). The data reveal that during storage large numbers of oxygen atoms are incorporated into the fatty acid methyl esters (FAMEs). This process is dominant for the first quarter of aging but then becomes overshadowed by dimerization of oxygenated FAMEs. This means that there are two main pathways for aging in biodiesel: polyoxygenation and oligomerization. These findings greatly pin down the possible causes for sedimentation giving a solid foundation for aging inhibition development.