Challenges in biofuels downstream processing: separation of the 1,3-propanediol + water mixture

Current effort to reduce consumption of fossil fuels and to increase the use of renewable energy sources has raised a great interest in biofuels. Specifically, alcohols deriving from renewable sources (e.g., bio-ethanol and bio-butanol) can be regarded as excellent fuel substitutes or additives to raise the octane number, ensure a better combustion and, thus, reduce harmful exhaust pipe emissions. Nevertheless, even tiny amounts of water in the blend can lead to phase splitting, which in turn can cause engine troubles. Thus, alcohol dehydration is essential and advanced separation methods have to be applied for an efficient purification, which is made complex by the formation of low-boiling azeotropes. Moreover, heavy by-products, such as 1,3-propanediol, are often present in the aqueous mixture: their separation from water by distillation techniques is challenging due to the high energy consumption, leading to a high cost of the target product. This work focuses on the separation of the 1,3-propanediol + water mixture (required also in 1,3 propanediol production processes), which, to our knowledge, is poorly investigated in the literature. Different technologies may be applied for this separation, the major ones being reactive extraction , liquid-liquid extraction, evaporation, distillation, membrane permeation and ion exchange chromatography. The aim of this work is to simulate the removal of water and purification of 1,3-propanediol by distillation using the commercial process simulator ASPEN Plus® and, by means of a sensitivity analysis on different operating variables, to determine the optimal solution, which allows minimizing the energy requirements of the separation process.