Plastic Membrane Will Help Filter Toxic Chemicals

Plastic membranes are essential to gas or water separation projects and Commonwealth Scientific and Industrial Research Organisation (CSIRO) has announced a joint Australia-Korea-USA project that developed a new plastic membrane that allows select small particles to pass while targeted large molecules are left out.

This is of great importance in natural gas processing in which toxic carbon dioxide is separated from methane for the production of natural gas fuel. It is also of great importance in water desalination projects. There are places in the world where a heavy dependence on desalinated water may arise due to lowered water tables and increasing drought, as well as because of burgeoning populations.

Additionally, small-large molecule separation is important in landfill gas recovery projects. Landfills produce gasses like methane that can be captured and processed for energy recovery programs: processed to be used as natural gas energy. Landfill gas recovery projects will be of growing importance in light of the Kyoto carbon credits, which are credits used toward offsetting carbon gas emissions through funding non-carbon emission projects such as forestry and sustainable power generation like gas capturing from landfills.

"The ability of the new plastic to separate small molecules surpasses the limits of any conventional plastics. It can separate carbon dioxide from natural gas a few hundred times faster than current plastic membranes and its performance is four times better in terms of purity of the separated gas," said Dr. Anita Hill of CSIRO Materials Science and Engineering. The material, was initially engineered by Ho Bum Park at Hanyang University, Korea, and then analyzed at CSIRO by Anita Hill and her team.

The new plastic membrane was inspired by naturally occurring plant membrane within plant cells, the pores of which are called aquaporins. These aquaporins (aqua means water in Spanish) permit the in-and-out transportation of small water molecules while preventing the entrance of larger molecules such as salt. The most striking aspect about aquaporins is their hourglass shape; it is this hourglass shape that blocks large molecules at the narrow neck.

The technology for the new plastic membrane borrows the idea of the hourglass-shaped aquaporin pores so that the pores in the new plastic membrane are also an hourglass shape. As in the plant cell membranes, the plastic's hourglass-shaped pores allow for a faster separation of small and large molecules than do other pore shapes while using less energy for the separation.

This research also shows how the hourglass-pore plastics can be systematically adjusted to block or pass a variety of different molecules depending on the specific task application. The same membrane, with systematic adjustments, may provide a low energy method of desalination (removing water from saltwater), carbon dioxide separation from methane for natural gas energy, or hydrogen separation from nitrogen.

Dr. Hill further said: "The new plastic is durable and can withstand high temperature, which is needed for many carbon capture applications. Heat-stable plastics usually have very low gas transport rates, but this plastic surprised us by its heightened ability to transport gases."

The Director of the organization Water for a Healthy Country Flagship, Dr Tom Hatton, said: "This global partnership has the goal of generating scientific understanding...of new membrane technologies for energy and the environment.... It is also a demonstration of how collaboration across boundaries can produce transformational science with potential societal benefits."

The efficiency of the new plastic membrane, which has an efficacy rate so much higher than conventional plastic membranes, has "huge potential to reduce the environmental footprint of water recycling and desalination," as Dr. Hatton said. An environmental footprint is the measure of land and other resources consumed to provide one individual, endeavor, industry, or nation with their needs, wants and desires. Developing countries and the people in them have small footprints while developed countries and the people in them have very large footprints.

"Fantastic plastic could cut CO2 emissions and purify water," Commonwealth Scientific and Industrial Research Organisation (CSIRO).