Zero-Discharge Process for Recycling of Tetrahydrofuran–Water Mixtures


The sustainable design of separation and polymer synthesis processes is of great importance. Therefore, an energy-efficient process for the purification of tetrahydrofuran (THF)–water (H2O) solvent mixtures from an upstream polymer synthesis process in pilot scale was developed with the aim to obtain high purity separation products. The advantages and limitations of a hybrid process in the pilot scale were studied utilizing an Aspen Plus Dynamics® simulation at different pressures to prove the feasibility and energy efficiency. For the rough separation of the two components, distillation was chosen as the first process step. In this way, a separation of a water stream of sufficient quality for further precipitations after polymer synthesis could be achieved. In order to overcome the limitations of the distillation process posed by the azeotropic point of the mixture, a vapor permeation is used, which takes advantage of the heat of evaporation already used in the distillation column. For the purpose of achieving the required low water contents, an adsorption column is installed downstream for final THF purification. This leads to a novel hybrid separation process that is energy efficient and thus allows also the use of the solvents again for upstream polymer synthesis achieving the high purity requirements in a closed-loop process.
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