Document Type : Original Article

Author

• Jafar Azamat

Department of Chemistry Education, Farhangian University, P.O. Box 14665-889, Tehran, Iran

Abstract

Methanol-water separation is a major energy-requiring step in the chemical industry, where up to 70% of the energy demand is met using azeotropic distillation. The separation of Methanol-water mixture using BNNTs with a (5,5) and (6,6) structure embedded between impermeable graphene sheets was carried out using molecular dynamics (MD) simulations. The separation was done using an external pressure gradient (5-100 Mpa) at 298K. An analysis of permeation properties, density profiles, radial distribution functions, and H-bond analysis was done. The presence of a 0.69 nm (5,5) BNNT resulted in 100% rejection with a flux rate of 21.3 molecules/ns at 100 MPa for water, allowing it to pass through; for the (6,6) BNNT, the rate increased to 40.2 molecules/ns at 100 MPa, though a certain amount of methanol also permeated. The water flux had a linear dependence on the applied pressure given by the formula J = 0.76P+33.10 for (5,5) BNNTs and J = 1.58P+47.65 for (6,6) BNNTs. Rejection of the former was due to steric or kinetic diameters larger than 0.38 nm above the effective pore size and the dipole misalignment. The radial distribution functions show that the H-bond network is destroyed upon confinement, with gr peak values increasing from 2.85 Å for bulk molecules to 3.66 Å for (5,5) BNNTs and 4.45 Å for (6,6) BNNTs. The coordination number decreased from 4.2 for bulk molecules to 2.8. The results show that BNNT membranes have the design rules with 90% energy savings during a distillation process for biofuel cleaning.

Graphical Abstract

Keywords

• Boron nitride nanotubes
• Molecular dynamics
• Methanol-water separation
• Nanofiltration
• Size exclusion