Novel Nanosheet allows for efficient ‘Molecular Sieving’ – Zeolite Membranes have enormous potential in Energy and Chemical industries


Zeolites have played an important role in the chemical industry in past decades. These microporous, aluminosilicate materials are well-known catalysts and adsorbents for catalytic reforming and separation of petrochemicals. More recently, zeolites have also been used to remove radioactive cesium from seawater following the Fukushima Daiichi nuclear disaster. Now, recent work from the University of Cincinnati, has opened even more doors for the material by tweaking its geometry and surface chemistry.

Zishu Cao and her colleagues fabricated membranes by tiling with 6-nanometre-thick zeolite flat sheets, they synthesized by a modified hydrothermal crystallization procedure. The resultant membrane was much thinner than a conventional zeolite membrane, with a thickness of less than 500 nanometres versus a traditional membrane’s thickness of several micrometres.

Tiling enhancements

Cao’s adviser, Junhang Dong of the Department of Chemical and Environmental Engineering, says Cao’s two-dimensional zeolite sheets overcome the major transport issues the conventional thicker zeolite membranes typically experience when they are several microns thick.

Fukushima 1 Infographic jpg

“The potential for zeolite membranes in the energy and chemical industries is enormous,” says Dong, “but the practical realization of their use is hindered by two serious issues caused by intercrystalline spaces in the films and their randomly oriented polycrystalline structure.”

These intercrystalline spaces, or gaps between the randomly oriented crystals that comprise the films, undermine the separation selectivity by causing nonselective permeation of molecules and ions. In addition, the random orientation of the crystals in the films results in longer and un-preferred diffusion paths making the membrane permeation inefficient.

The two-dimensional, zeolite nanosheet tiled membranes synthesized by Cao, however, provide an oriented straight channel structure that provides both reduced intercrystalline spaces and shortened diffusion lengths for enhanced selectivity and membrane flux.

“Imagine you are using blocks to waterproof a roof. Now we are using tiles or shingles to construct the roof,” says Dong.

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Petrochemical inspiration

Their readily scalable membrane fabrication by zeolite nanosheet lamination was inspired by recent work from the University of Minnesota, where researchers synthesized organophilic pure-silica zeolite nanosheets suitable for petrochemical separations. In Cao’s work, they incorporated aluminium ions into the silica-based zeolite framework to make the surface ionic and strongly hydrophilic – both favorable properties for water and ion separations. To the group’s knowledge, the ionic zeolite nanosheet laminated membrane is the first of its kind.

In their recently published paper, Cao displayed its potential for water desalination. The group chose to study this application because of its relevance to a wide range of needs in treating high salinity wastewaters, from industrial activities such as oil and gas drilling and power plant desulphurization and cooling. They reported high water flux with high salt rejection rates for brines containing up to 24% dissolved sodium chloride by weight.

The group says many routes are possible – desalination was just an example of the membrane’s capabilities. From here, they are exploring high-performance battery ion separators, catalysts, adsorbents, and thin-film sensors.

More details can be found in Science Advances.

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Lockheed Martin Tests Nanofilters for Oil and Gas Wastewater Management


The company states that the ultimate goal is water desalination, but more feasible and immediate uses can be found in the oil and gas industry, where the requirements in terms of the quality of the graphene and hole sizes are less challenging.

Lockheed simulated-nanoporous-graphene-filtering-salt-ionsLockheed Martin is working with two firms in the oil and gas industry to assess the feasibility of using Perforene filters to clean drilling wastewater. The aim is not the total elimination of contaminants but targeting the worst of them, making the problem more manageable. This goal only requires 50-100 nanometer sized holes, compared to 1 nanometer holes required for desalination.

The company claims that commercialization of Perforene filters could begin in the next five years, possibly with some sort of medical device that would only require small amounts. Finding a way to produce graphene with single nanometer-sized holes on a commercial scale for desalination would probably take five or more years. The company has tested it only on a small scale, but the results were promising.

Lockheed is not ready to commercialize this technology yet. They are still refining the process for making the holes in graphene, and also the production process of the graphene itself. They had expected to have a prototype filter by the end of 2013. This prototype will be a drop-in replacement for current filters used in reverse osmosis (RO) plants. They hope to commercialize this technology by 2014-2015 and are looking for partners in the filter manufacturing arena.

This is not the first time we hear of water desalination using graphene membranes. In June 2012 MIT scientists have shown (in simulations) that nanoporous graphene can filter salt from water at a rate that is 2-3 orders of magnitude faster than today’s best commercial RO desalination technology. Back in October 2010 researchers from Australia and Shanghai have developed a Capacitive Deionization (CDI) application that uses graphene-like nanoflakes as electrodes (CDI is a relatively new way to purify water). Earlier in 2010 Korean researchers have made a new type of composite material made from reduced graphene oxide and magnetite that could effectively remove arsenic from drinking water.

In 2013, Lockheed Martin developed a water desalination technology with nanometer-sized holes, with hopes of commercialization around 2014-2015.

Source: reuters

Nano Filter Cleans Dirty Industry


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Prototypes of nano-cellulose based filters with high purification capacity towards environmentally hazardous contaminants from industrial effluents eg. process industries, have been developed by researchers at Luleå University of Technology. The research, conducted in collaboration with Imperial College in the UK has reached a breakthrough with the prototypes and they will now be tested on a few industries in Europe.

The bio-based filter of nano-cellulose is to be used for the first time in real-life situations and tested within a process industry and in municipal wastewater treatment in Spain. Other industries have also shown interest in this technology and representatives of the mining industry have contacted me and I have even received requests from a large retail chain in the UK, says Aji Mathew Associate Professor, Division of Materials Science at Luleå University.

Researchers have combined a cheap residue from the cellulose industry, with functional nano-cellulose to prepare adsorbent sheets with high filtration capacity. The sheets have since been constructed to different prototypes, called cartridges, to be tested. They have high capacity and can filter out heavy metal ions from industrial waters, dyes residues from the printing industry and nitrates from municipal water. Next year, larger sheets with a layer of nano-cellulose can be produced and formed into cartridges, with higher capacity.

nanotechfilt

– Each such membrane can be tailored to have different removal capability depending on the kind of pollutant, viz., copper, iron, silver, dyes, nitrates and the like, she says.

Behind the research, which is funded mainly by the EU, is a consortium of research institutes, universities, small businesses and process industries. It is coordinated by Luleå University led by Aji Mathew. She thinks that the next step is to seek more money from the EU to scale up this technology to industrial level.

– Alfa Laval is very interested in this and in the beginning of 2015, I go in with a second application to the EU framework program Horizon 2020 with goals for full-scale demonstrations of this technology, she says.

Two of Aji Mathews graduate students Peng Liu and Zoheb Karim are also deeply involved in research on nano-filters.

– I focus on how these membranes can filter out heavy metals by measuring different materials such as nanocrystals and nano-fibers to determine their capacity to absorb and my colleague focuses on how to produce membranes, says Peng Liu PhD student in the Department of Materials Science and Engineering at Luleå University of Technology.