A membrane technology breakthrough

Imperial College London

RESEARCHERS from the Livingston Group at Imperial College London, UK, in collaboration with BP, have made breakthrough insights into membrane technology. The study findings could lead to improved membrane technologies.

Ultrathin polyamide nanofilters are an important component used in water purification processes such as desalination, filtering impurities, and creating clean drinking water. They are made up of a polyamide film separating layer and a porous mechanical support layer.

The Livingston Group developed a novel method of production allowing them to create nanofilters thinner and smoother than those produced by conventional methods. They produced nanofilters as thin as 6 nm, the thinnest usable nanofilters ever reported. These very thin nanofilters allowed water to pass through faster than conventional nanofilters. This research could help increase the efficiency of membrane-based separation for use in processes such as desalination.

Separation processes, such as distillation, account for 10–15% of global energy consumption, according to figures from a paper in Nature. Creating improved membranes, with the potential for novel use in industry, could help to cut energy consumption considerably. The same study said alternative separation processes that don’t require heat could make 80% of separations in the US ten times more energy efficient.   

Though reverse osmosis using nanofilters is a well-established process, little research has investigated the properties and function of these nanofilters. The BP International Centre for Advanced Material (BP-ICAM) has funded research that could improve understanding of the fundamental science of membranes, which could potentially lead to further research and industrial applications.

Andrew Livingston, professor of chemical engineering at Imperial, spoke to a university reporter about his group’s work: “It’s fundamental research but with clear industrial applications in mind. This work is only possible because of the people on my team and BP’s vision to understand the properties of the materials they use.”

The group is in the early stages of development of a project aiming to create membranes that allow for more accurate separation between molecules.

A sister project at the University of Illinois, US is investigating new membranes for wastewater treatment.

Membranes

Conventionally, ultrathin polyamide nanofilters are produced using relatively uncontrolled interfacial polymerisation onto a porous support. This typically results in crumpled nanofilms, with separating layers that have been reported as being around 50–200 nm thick.

In conventional methods, the separating layer cannot be made independently of the porous support. The inability to study these layers separately has confounded efforts to understand the independent effects of thickness, permeation mechanism, and support material.

In this study, the Livingston Group was able to produce composite nanofilms layer-by-layer with subsequent attachment. The developed nanofilms had increased permeance, and levels of salt rejection were maintained.

The group was also able to further investigate the effects of the support layer, which had previously been considered to have little impact on nanofilter efficiency. They found that the support layer does in fact have a noticeable impact on performance, as it acts as another barrier which water has to pass through. The group found that water permeance increased as more porous supports were employed. Livingston considered this finding to be the most significant finding for the membrane industry. Zhiwei Jiang, a research associate in the department of chemical engineering, said: “After penetrating through the active [separating] layer, water has to seek pores on the support for further transport. The more porous the support is, the shorter the distance water has to travel laterally. As a result, the overall permeance is enhanced.”

Livingston said: “We managed to improve the flux by about 50%.” He then added: “There would be other constraints on the system…but, you might be looking at a decent reduction in the amount of membrane required if you could take this technology and implement it.”

The oil and gas industry

During oil extraction, water is injected into reservoirs to help extract reserves. Typically, seawater is used, which requires treatment prior to injection. One such treatment is desalination.

When studies showed that using low salinity water can lead to significant increases in oil production, the industry bolstered efforts to improve desalination processes.

Dale Williams, senior process engineer at BP, said: “Membranes give us the opportunity to take seawater, and to generate the low salinity water that we need.”

This research helped make breakthroughs in membrane technology that could increase the efficiency and reduce costs and energy requirements of oil production.

Advanced Materials: http://doi.org/gc35bq