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Posted: March 15, 2008

Fullerenes: produce and divide

(Nanowerk News) The unique complex designed and built from several units by specialists of the Closed Joint-Stock Company “Innovations of the Leningrad Institutes and Enterprises” (St. Petersburg) enables to produce kilograms of fullerenes per day – amazing hollow “globules”, “ellipsoids of rotation” – molecules consisting of several dozens of carbon atoms each. And most importantly, the complex allows, if necessary, to divide them by the molecular mass, i.e., to single out the most investigated and often used fullerenes, molecules of which consist of 60 and 70 carbon atoms, as well as a fraction consisting of a mixture of heavier fullerene modifications – containing 76, 78, 84, 90 and more atoms of carbon.
It should be noted that relatively not long ago, fullerenes were rather exotic objects, which were actively studied but which were not practically used. But, as the scientists often put it, fullerenes are too perfect to be useless. Indeed, it has turned out that fullerenes per se and materials based on them or even the materials that contain a relatively small quantity of fullerenes or their derivatives in their composition possess various interesting and sometimes exceptionally useful properties. Fullerenes can act as catalysts and cocatalysts in a wide class of organic synthesis reactions, they are able to increase durability and elasticity of materials, fullerenes help to change optical properties of materials – their thermal and electroconductivity.
However, industrial processes require large-scale quantities of these surprising compounds, but the most well-known methods for obtaining fullerenes allow to produce very little of them, and in the mixture with other carbon retrofits – in the so-called fullerene soot along with graphite, amorphous carbon, carbonic nanotubes and other structures. Besides, properties of different fullerenes vary, consequently, to control the final material properties, it is necessary to use only fullerenes of a certain kind. It means that specialists should know how to divede them, this being also done in large-scale quantities, not in laboratory amounts.
The complex designed by the authors from St. Petersburg enables to produce fullerenes in significant quantities and to single out their target types, which are practically not contaminated by other carbonic products. The complex contains several basic units. The first unit is a 25-liter reactor per se for obtaining the primary product of fullerene mixture of particularly pure graphite rods – up to 120 grams per hour. This is the so-called fullerene soot, but fullerenes already make 12% to 14% of the mass. For the time being, it is still a mixture, but it mainly consists of the C60 fullerenes (65% to 70%), 23% to 27% - are the C70 fullerenes, and the rest is the mixture of heavier fullerenes.
The next unit is an extractor. Its task is to isolate the fullerene mixture from soot, the extractor productivity being about 400 grams of fullerene per one five-hour cycle (the extractor useful capacity is 1.8 l). The authors have designed an exclusively productive extractor – it enables to isolate practically all fullerenes from soot (more than 98%).
And finally, the closing unit of the complex is the separator system for obtaining individual fullerenes, first of all, the most demanded and the lightest type of fullerenes – C60. With the capacity of 10 l, it enables to produce 100 grams of fullerene per day, the product purity being rather high – 99.5% to 99.9%. Besides, there are special separators for isolation of heavier fractions, if needed. Thus, the complex allows to get absolutely exotic kinds of fullerenes, such as C84 and C90, they are also very pure but are obtained in lower quantities – however, the demand for them is significantly lower. As for the C70 fullerene, the complex manages to produce up to 20 grams of it per cycle, the cycle making two days in this case.
Certainly, this is only a list of main stages of the process developed by the researchers and, accordingly, only main types of required equipment. However, the authors did not only develop, patent and design the entire complex and all fundamental processes, but they even built real, production prototypes, not laboratory samples. The complex is operating, so as much fullerene as needed can be produced now. So far, kilograms of fullerenes are required, but most probably more will be needed in near future.
Source: InformNauka