Queen’s University Belfast researchers synthesize “porous liquid”; applications in more efficient chemical processes
Scientists at Queen’s University Belfast, Northern Ireland, UK, have synthesized a porous liquid with the potential for application in a wide range of new, more efficient and greener chemical processes including carbon capture.
The researchers in the School of Chemistry and Chemical Engineering at Queen’s, along with colleagues at the University of Liverpool, UK, and other international partners, found that the new liquid can dissolve unusually large amounts of gas, which are absorbed into “holes” in the liquid. The results of their research are published in the journal Nature.
Porous solids such as zeolites and metal–organic frameworks are useful in molecular separation and in catalysis, but their solid nature can impose limitations. For example, liquid solvents, rather than porous solids, are the most mature technology for post-combustion capture of carbon dioxide because liquid circulation systems are more easily retrofitted to existing plants. Solid porous adsorbents offer major benefits, such as lower energy penalties in adsorption–desorption cycles, but they are difficult to implement in conventional flow processes. Materials that combine the properties of fluidity and permanent porosity could therefore offer technological advantages, but permanent porosity is not associated with conventional liquids. Here we report free-flowing liquids whose bulk properties are determined by their permanent porosity.—Giri et al.
To prepare the porous liquid, the researchers took rigid organic cage molecules—each of which defines a molecular pore space—and dissolved them at high concentration in a solvent that is too large to enter the pores. As a result, the pores in the cages remain empty and available to solutes.
The concentration of unoccupied cages can thus be around 500 times greater than in other molecular solutions that contain cavities, resulting in a marked change in bulk properties, such as an eightfold increase in the solubility of methane gas, they found.
The results provide the basis for development of a new class of functional porous materials for chemical processes. The team also presented a one-step, multigram scale-up route for highly soluble scrambled porous cages prepared from a mixture of commercially available reagents. The unifying design principle for these materials is the avoidance of functional groups that can penetrate into the molecular cage cavities.
Materials which contain permanent holes, or pores, are technologically important. They are used for manufacturing a range of products from plastic bottles to petrol. However, until recently, these porous materials have been solids. What we have done is to design a special liquid from the “bottom-up”—we designed the shapes of the molecules which make up the liquid so that the liquid could not fill up all the space. Because of the empty holes we then had in the liquid, we found that it was able to dissolve unusually large amounts of gas. These first experiments are what is needed to understand this new type of material, and the results point to interesting long-term applications which rely on dissolution of gases.
A few more years’ research will be needed, but if we can find applications for these porous liquids they could result in new or improved chemical processes. At the very least, we have managed to demonstrate a very new principle – that by creating holes in liquids we can dramatically increase the amount of gas they can dissolve. These remarkable properties suggest interesting applications in the long term.—Professor Stuart James of Queen’s School of Chemistry and Chemical Engineering
Queen’s University Belfast led the research which also involved the University of Liverpool and universities in France, Germany and Argentina. The study was mainly funded by the Leverhulme Trust and the Engineering Physical Science Research Council (EPSRC).
Nicola Giri, Mario G. Del Pópolo, Gavin Melaugh, Rebecca L. Greenaway, Klaus Rätzke, Tönjes Koschine, Laure Pison, Margarida F. Costa Gomes, Andrew I. Cooper & Stuart L. James (2015) “Liquids with permanent porosity” Nature 527, 216–220 doi: 10.1038/nature16072