Energy Consumption of Nanofiltration Diafiltration Process: Identifying the Optimal Conditions of Continuous and Intermittent Feed Diafiltration

The demand for the separation of small molecules (ions and small organics) is expanding with the development of various industries. The nanofiltration (NF) diafiltration process was developed to make up for the deficiencies of NF membrane performance to realize the separation of small molecules, but NF diafiltration is operated with high energy consumption. Therefore, optimizing the NF diafiltration process to reduce the required separation energy is inevitable. In this work, the minimum required separation energies (MRSEs) of continuous feed diafiltration (CFD) and intermittent feed diafiltration (IFD) under the reversible thermodynamic process and constant applied pressure mode are calculated and compared. Additionally, a reverse osmosis (RO) unit was designed to recycle the solvent, and the energy consumption of the integrated NF-RO process is evaluated and compared. Finally, based on the variation of osmotic pressure with solutes composition, the NF-RO process with various solute composition is modeled to calculate the MRSE. This work aims to provide guidance for the industrialization of NF diafiltration-RO concentration process, with potential application for small molecule separation.