Investigation into long-term stability of C1-oxygenate blends

The C1-oxygenates methanol (MeOH), dimethyl carbonate (DMC) and methyl formate (MeFo) which, due to their absence of C-C bonds, show a significant decrease in particle emission during combustion, were investigated in the NAMOSYN project on long-term and decomposition stability. The tested systems were blends consisting of MeOH or DMC and MeFo in varying compositions to adjust the vapour pressure. To investigate potential decompositions of MeFo to MeOH and formic acid, caused by hydrolysis, long-term measurements with NMR spectroscopy were carried out. Here, the focus was on the blends C65F35 (DMC 65 V%, MeFo 35 V%), M86F14 (MeOH 86 V%, MeFo 14 V%) and M70F30 (MeOH 70 V%, MeFo 30 V%) including varying amounts of H2O. It was proven that the water content has a significant influence on the decomposition of MeFo and the equilibrium concentration of formic acid. Furthermore, it was shown that the M86F14 blend is stable in the long term without additives up to a maximum H2O amount of 2000 ppm. In addition, using the ILSB-setup [1] (ideal ionic liquid salt bridge), pH measurements were conducted in the above blends to establish a new method for the direct determination of formed formic acid. First promising results were accomplished even though a more precise measurement setup requires additional refinement.