Professor Somenath Mitra works in his lab. Credit: NJIT. |
A faster, better, and cheaper desalination process enhanced by
carbon nanotubes has been developed by NJIT Professor Somenath Mitra.
The process creates a new architecture for the membrane
distillation process by immobilizing carbon nanotubes in the membrane pores.
Conventional approaches to desalination are thermal distillation and reverse
osmosis.
“Unfortunately the current membrane distillation method is too
expensive for use in countries and municipalities that need potable water,”
said Mitra. “Generally only industry, where waste heat is freely available,
uses this process. However, we’re hoping our new work will have far-reaching
consequences bringing good, clean water to the people who need it.”
The process is outlined in “Water Desalination Using Carbon
Nanotube Enhanced Membrane Distillation,” by Mitra and his research team in Applied
Materials & Interfaces. Doctoral students Ken Gethard and Ornthida
Sae-Khow worked on the project.
Membrane distillation is a water purification process in which
heated salt water passes through a tube-like membrane, called a hollow fiber. Membrane
distillation allows only water vapor to pass through the walls of the hollow
tube, but not the liquid. When the system works, potable water emerges from the
net flux of water vapor which moves from the warm to the cool side. At the same
time, saline or salt water passes through the fiber.
Membrane distillation offers several advantages. It’s a clean,
non-toxic technology and can be carried out at 60ºC to 90ºC. This temperature
is lower than conventional distillation which uses higher temperatures. Reverse
osmosis uses relatively high pressure.
However, membrane distillation is not trouble free. It is costly
and getting the membrane to work properly and efficiently can be difficult. “The
biggest challenge,” said Mitra, “is finding appropriate membranes that
encourage high water vapor flux but prevent salt from passing through.”
Mitra’s new method creates a better membrane by immobilizing
carbon nanotubes in the pores. The architecture not only increases vapor
permeation, but also prevents liquid water from clogging the membrane pores. Test
outcomes show increases in both reductions in salt and water production.
Another advantage is that the new process can facilitate
membrane distillation at a relatively lower temperature, higher flow rate, and
higher salt concentration. Compared to a plain membrane, this new distillation
process demonstrates the same level of salt reduction at a 20°C lower
temperature, and at a flow rate six times greater.
“Together these benefits lead to a greener process which could
make membrane distillation economically competitive with existing desalination
technologies and we hope could provide potable water where it is most needed,”
said Mitra.
