Talk in Chemistry: Ultrafast Transport of Organic Solvents through Carbon Nanosheet Membranes: Viscous Flow in 1 nm Pore

Dr. Santanu Karan, a Post Doctoral Research Associate at  National Institute for Material Science (NIMS), Tsukuba, Japan is visiting the Department of Chemistry on 18th June, 2012 for a seminar. He obtained his PhD from Department of Spectroscopy, Indian Association for the Cultivation of Science (IACS).

Seminar Title: Ultrafast Transport of Organic Solvents through Carbon Nanosheet Membranes: Viscous Flow in 1 nm Pore 

 Venue: L3

 Date & Time:  18th June, 2012: 12.00 - 1:00 pm

 Speaker: Dr. Santanu Karan, Post Doctoral Research Associate at  National Institute for Material Science (NIMS).

 Abstract:  Ultrafast solvent transport through the size-exclusion filtration membrane is strongly demanded in chemical and petrochemical industries to separate highly-purified products from reaction mixtures and natural resources. Fabrication of thin filtration membranes has been examined by using carbon nanotubes, block polymers, porous silicon, and other inorganic materials. However, the real challenge was to make the membranes mechanically robust at the thickness of a few tens of nanometers, since the solvent flux increases inversely proportional to the thickness of the membrane. We have succeeded in developing extremely thin (10 – 40 nm thick) porous carbon nanosheet membranes with pores having a diameter of about 1 nm. Such carbon membranes are very stable in organic solvents and exhibits ultrafast viscous flow of solvents. In contrast, conventional commercial membranes show extremely low solvent flow according to the diffusion of solvent through the membrane material. The technique to form a rigid porous path of few nanometers in diameter within the polymer film is not well established in the present technology. On the other hand, carbon film is used for a long as a gas or vapor separation membranes, high-speed flow has not been achieved for organic solvents. To achieve this, extremely rigid porous structure of the carbon film was necessary to pass the solvent molecules through the porous channel without any swelling of the membrane. Such carbon membranes have diamond-like mechanical strength (Young’s modulus of 170 GPa, about one seventh of diamond). The porous structure is stable in organic solvents and never collapses even when 2.0 MPa (roughly 20 atmospheres) pressure difference was applied across the membrane. Because a very large number of flow channels with diameters of about 1 nm are formed in the interior of the carbon nanosheet, ultrafast flow of organic solvents was possible. The flow rate of hexane, which is one constituent of fossil fuel oil, exceeded 380 L/m2h when 80 kPa pressure difference was applied, and the rejection of azobenzene (molecular weight: 182.2), which was used as a model impurity, was more than 90%. Processing speed was approximately three orders faster than that of commercial filters with similar performance. Such high-performance carbon membranes can be applied for the removal of molecular sulfur compounds from diesel to produce low sulfur diesel oil and to reduce the urban pollution.