A method of making nanocarbon structures from cashew nut shell pyrolysis vapours
Due to their fascinating broad range of electronic, thermal and structural properties, carbon nanotubes (CNTs), the tubular fullerenes, are envisaged as the key to potentially revolutionary technologies and have attracted a lot of attention from the industries and research communities. They are highly versatile, with a range of applications, which extend from super strong composites to nanoelectronics. Carbon nanotubes are seamless tubes of graphite sheets with full fullerene caps, which were first synthesised in 1991 as multilayer concentric tubes called as multi-walled carbon nanotubes and were later synthesised in 1993 as single walled carbon nanotubes. Since then, numerous attempts have been made to synthesise such products on a large scale and at low cost. Carbon nanotubes are synthesised by methods like arc discharge, laser ablation or catalytic chemical vapour deposition (CVD). Among the various methods, CVD has become more popular and is considered to be the best method for low cost and large scale synthesis of high quality nanotube materials. The inventors in IIT have attempted to synthesize a nanocarbon structures from cashew nut shell pyrolysis vapours. On heating the cashew nut shells (CNS), an agroindustrial residue, upto about 100oC, the pericardium fluid present in the shells oozes out and is collected (about 14-16% by weight). This is generally used for making resins and adhesives. The partially de-oiled cashew nut shells are further heated upto about 280oC to remove gases like carbon dioxide, carbon monoxide and water vapour. Subsequent heating of the shells upto about 500oC produces pyrolysis vapours which are condensed to recover oil rich in cardanol.