Nanofiltration Membrane 2D: Pore-Scale Diffusion &…

What is Nanofiltration?

Nanofiltration is a pressure-driven membrane separation process used to remove small molecules from solutions while allowing larger molecules or particles to pass through. It operates in the size range of microfiltration and ultrafiltration, but with a higher rejection rate for ions compared to these processes.

In nanofiltration, solute particles are subjected to Brownian motion and electrostatic interactions as they attempt to pass through nanopores in the membrane.

Pore-Scale Dynamics

At the pore scale, the behavior of solute particles is governed by Brownian dynamics and convective drift. The Stokes-Einstein equation describes how particle diffusion is affected by their size and the viscosity of the surrounding fluid.

Particles must navigate through the membrane's nanopores, where they encounter steric sieving (Ferry effect) and Donnan charge exclusion, which determine whether they are retained or allowed to pass.

live demo · related simulation● LIVE

Governing Principles

The movement of solute particles in nanofiltration is described by the Stokes-Einstein equation: D = kT / (6πηr), where D is the diffusion coefficient, k is the Boltzmann constant, T is temperature, η is viscosity, and r is particle radius. This equation quantifies how Brownian motion influences particle transport.

Electrostatic interactions are governed by Donnan equilibrium, which describes the distribution of ions in a solution near a charged membrane surface.

Real-World Applications

Nanofiltration is widely used in water treatment to remove contaminants such as arsenic and fluoride from drinking water.

It also finds applications in food processing, pharmaceuticals, and wastewater treatment, where it can selectively retain or reject specific ions based on their size and charge.

Frequently asked questions

What is the difference between nanofiltration and reverse osmosis?

Nanofiltration uses a less restrictive membrane than reverse osmosis, allowing larger molecules to pass through while retaining smaller ions such as divalent cations. Reverse osmosis membranes are more selective and remove even monovalent ions.

How does temperature affect nanofiltration performance?

Temperature increases the kinetic energy of particles, enhancing their Brownian motion and diffusion rate. However, higher temperatures can also increase membrane permeability, potentially reducing selectivity in nanofiltration processes.

Can nanofiltration be used for desalination?

Nanofiltration is not typically used for desalination due to its lower rejection rate compared to reverse osmosis. However, it can be effective in removing specific ions from seawater or brackish water.

What factors influence the selectivity of nanofiltration membranes?

Selectivity is influenced by membrane pore size, surface charge density, and the electrostatic interactions between solute particles and the membrane. The Ferry effect and Donnan charge exclusion play crucial roles in determining which ions are retained or allowed to pass.

Try it live

Everything above runs in your browser — open Nanofiltration Membrane 2D: Pore-Scale Diffusion & Rejection and change the parameters while it is running. Nothing is installed, nothing is uploaded, the whole model lives in one tab.

▶ Open Nanofiltration Membrane 2D: Pore-Scale Diffusion & Rejection simulation