Molecular dynamics modeling of nano-porous centrifuge for reverse osmosis desalination

Abstract

A concept of the porous graphene membrane centrifuge is proposed aiming at fabrication of large scale, fouling-free desalination machine with nanomaterial-based reverse osmosis modules. The concept as well as strategy of such porous rotating graphene membrane device is approved through molecular dynamics (MD) modeling and simulation of a nano-fluidic device that in order to make a quantitative evaluation. First, an analytical formulation is derived for the critical angular velocity above which the centrifugal force is able to counter-balance osmosis pressure, so that the reverse osmosis (RO) desalination process can proceed. The critical angular velocity derived from this formulation is compared with MD simulated critical angular velocity.Based on MD simulation results, it is shown that the rotating porous membrane device may significantly improve desalination efficiency by combining the centrifugal separation and and the selectivity of porous graphene membrane to achieve reverse-osmosis desalination. Furthermore, we have shown that the proposed desalination device has an intrinsic anti-fouling mechanism, and then we have studied the effect of pore size on the flux rate by conducting simulations with the applied rotating speed. Moreover, we have conducted energy and efficiency analysis for the proposed desalination device model, and we obtained the relationship between fresh water flux rate and the angular velocity, at the same time, with the pore size. By choosing the most efficient angular velocity and the pore size that ensures salt rejection, an optimal nano-fluidic device design is achieved.