2025 AIChE Annual Meeting

Desalinating Saltwater with a Reverse Osmosis Membrane Apparatus

Separation processes use fundamental chemical engineering principles including thermodynamics and heat, mass, and momentum transport to enable the production of valuable products in chemical, pharmaceutical, biotechnology, and food applications. These operations are essential for optimizing plant costs and efficiency. When learning separations in chemical engineering coursework, it is often beneficial to apply the knowledge in hands-on laboratory work to better understand the concepts. This project introduces a reverse osmosis (RO) membrane separation system designed for an academic laboratory to provide a practical demonstration of membrane desalination. RO separation is driven by an induced pressure difference to force the freshwater through a semipermeable membrane. Unlike osmosis, RO is not spontaneous and requires external work. The osmotic pressure of the system is the pressure required for freshwater to travel through the membrane and is dependent on the concentration of the initial saltwater solution. Two high pressure pumps were used to create a pressure gradient that pushes water through a semi-permeable RO membrane. This experiment investigates the effects of changing the starting saltwater concentration and pressure through the membrane. Students will be able to use this system to create conductivity calibration curves for both distilled and filtered water and to learn how to separate different saltwater solutions and contaminate levels into purified water and concentrated saltwater. The system constructed here successfully removed 95.78% of salt from a 0.2% mass starting saltwater solution, effectively demonstrating the principles and efficiency of reverse osmosis in a practical educational setting.