Theoretical predictions of compatibility of polyoxymethylene dimethyl ethers with diesel fuels and diesel additives

Polyoxymethylene dimethyl ethers (PODEn) is an emerging biofuel that has a great potential to become one of the competitive alternative fuels for diesel engine due to their capability of reducing soot formation during combustion. The reliable methods for calculation/prediction of the miscibility of PODEn with diesel and the compatibility of PODEn with diesel additives are essential for the utilization of PODEn. The methods for accurate calculation/prediction of the liquid-liquid equilibrium (LLE) in the systems of PODEn, water and extractants are essential for the reliable design of the production process of PODEn. However, these methods are seldom reported. Here, the COSMO-RS is used to predict the LLE in the systems (PODEn + H2O + extractant), and good agreements with experimental results are achieved. Then, the COSMO-RS is used to predict the solubilities of neat PODE1-8 in six diesel hydrocarbons and three model diesel fuels at different temperatures. The results show that the solubilities of neat PODE1-8 in the diesel hydrocarbons and the model diesel fuels considered decrease with increasing the oxygen content and n value of PODEn. The miscibility of PODE3-4/PODE3-5 with diesel is also predicted. The results show that the miscibility of PODEn mixtures with diesel decreases with increasing the proportion of long-chain PODEn of the PODEn mixture. Meanwhile, the effect of other types of diesel additives on the miscibility of the PODEn mixtures with diesel is predicted. The results show that the anti-wear agent, CN improver, stabilizer and emulsifier considered can promote the miscibility of PODEn with diesel, while the pour point depressant considered decreases the miscibility of PODEn with diesel.