Abstract
Fossil fuels are finite, cause anthropogenic climate change and are often points of conflicts in geopolitical crises. The process of transformation to renewable energy carriers has already started, but is still in an early stage. Especially in the fields of travel and transportation, there has been much resistance. The implementation of electrically powered motors is not only late and slow, it also is not a feasible option for many less wealthy countries. Biodiesel (fatty acid methyl esters, FAME) and biofuels produce far less CO2 than traditional fuel and are easily adaptable for existent motor systems. Therefore, they bear the potential as a fast and easily accessible interim technology for the reduction of CO2 emissions, using existing infrastructure.
One major challenge for a widespread use of biodiesel is its susceptibility for aging. During aging substances emerge that are harmful to motors or can form precipitates, especially in blends of petro- and biodiesel. Thorough knowledge of these aging products and the processes leading to them could help to inhibit their formation and thus massively increase the employment of biodiesel.
The aim of this work is to reach a detailed molecular analysis of aging products of biodiesel as well as bio/petrodiesel blends. To this end, ultra-high resolution mass spectrometry is used to monitor different samples over a storage period of twelve months. Furthermore, to simplify these complex mixtures, different variants of liquid chromatography were evaluated to separate the samples into petrodiesel compounds, biofuel components and aging-products. Tandem mass spectrometry has been employed for structural elucidation, to verify findings and to obtain information of molecular structures, which can ultimately deliver information of reaction processes.
After a storage period of twelve months, more than 1500 oxygen containing compounds were found in a biodiesel sample. These can be classified into five major groups. Aside from the unaltered esters, the most important group consists of (poly-)oxygenated esters, which have incorporated up to six additional oxygen atoms into their molecular structure. Furthermore, covalent dimers and trimers of oxygenated esters can be detected. Another diverse group of compounds is formed by oxygenated esters, with alkyl chains partly cleaved off and oligomers thereof. Sediments, only occurring in blends during the storage experiment, mainly consist of cross products from aged petro- and biodiesel components.
