Molecular ‘sieves’ provide greener power generation

New research shows that exposing polymer molecular sieve membranes to ultraviolet (UV) irradiation in the presence of oxygen produces highly permeable and selective membranes.

These membranes could prove valuable for more efficient molecular-level separation, an essential process in everything from water purification to controlling gas emissions.

Scientists believe such research is an important step towards more energy efficient and environmentally friendly gas-separation

Published in the journal Nature Communications, researchers have now demonstrated that the ‘selectivity’ of these newly modified membranes could be enhanced to a remarkable level for practical applications.

It is estimated that the permeability could increase between anywhere from a hundred to a thousand times greater than the current commercially-used polymer membranes.

Scientists believe such research is an important step towards more energy efficient and environmentally friendly gas-separation applications in major global energy processes.

These can range from purification of natural gases and hydrogen for sustainable energy production, the production of enriched oxygen from air for cleaner combustion of fossil fuels and more-efficient power generation, and the capture of carbon dioxide and other harmful greenhouse gases.

“Our discoveries lead to better understandings of physics of the novel materials, so we will be able to develop better membranes in the future” said Qilei Song, a researcher in Dr Easan Sivaniah’s group and the paper’s lead author.

Conventional separation technologies, such as cryogenic distillation and amine absorption, are significantly energy-intensive processes.

Membrane separation technology is highly attractive to industry, as it has the potential to replace conventional technologies with higher energy efficiency and lower environmental impacts.

But gas separation performance of current commercially-available polymer membranes are subject to what scientists describe as “a poor trade-off” between low permeability levels and high degree of selective molecular separation.

The next generation membranes - such as polymers of intrinsic microporosity (PIMs) - being studied at the Cavendish are based on tuning the pore size and interaction with specific molecules to achieve both high permeability and, critically, high selectivity.

Currently, these flat-sheet membranes show great separation performance and are mechanically robust for clean cylinder gases.

“We are working on ways to further improve these membranes and our next step is to develop large scale and more practical industrial modules such as thin film composite membranes or hollow fibers with selective layer as thin as possible,” said Dr Easan Sivaniah.

“We are also exploring many other applications of these fascinating polymer materials, such as liquid and vapour separation, water treatment by desalination, sensor devices and photolithography technology, and energy storage applications”.