A New Approach for Industrial-Scale Production of Carbon Single-Walled Nanotubes
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A New Approach for Industrial-Scale Production of Carbon Single-Walled Nanotubes A.R. Harutyunyan1, E. Mora2 and T. Tokune1 1 Honda Research Institute USA Inc., 1381 Kinnear Road, Columbus, Ohio 43212, U.S.A. 2 Department of Physics, The Ohio State University, 191 West Woodruff Ave. Columbus, Ohio 43210, U.S.A. ABSTRACT In the methods reported for continuous synthesis of carbon single-walled nanotubes (SWNTs), the typical production rates are less than 1 g h-1, after purification. Here we report the development of a new technique with higher production rates, up to 6 g h-1, and a scaling capability up to 220 g h-1. SWNTs are produced by vertical floating technique and continuous injection of pre-prepared supported catalyst powder. INTRODUCTION To exploit the unique properties of SWNTs to their fullest potential, it is necessary to realize the large-scale production of high quality material. In the literature there are two main approaches described for the continuous production of SWNTs. One is based upon the in situ formation of floating catalyst particles by thermal decomposition of corresponding organometallics [1-5], and another one is based on the continual injection of pre-prepared colloidal solution of metal catalyst particles into the reactor. The first approach has been successfully applied for the growth of multi-walled nanotubes [6-9]. However, in the case of SWNTs, problems arise due to the crucial role of the catalyst particles diameter in the synthesis. In this case, it is essential to have adequate and narrow distribution of diameters of the in situ formed clusters. This requisite may cause some restriction of the catalyst concentration, therefore limiting the production rate and yield. Production rates of ~0.5 g h-1 of high purity (up to 97 mol %) SWNTs have been achieved using this concept [2,3]. On the other hand, SWNTs synthesis by the most common methods, laser ablation and arc discharge, face the same problems, being also limited by the target/electrode size. Despite this, the production of carbon soot rich in SWNTs has been achieved at a rate of 1.5 g h-1 [10]. The use of a colloidal solution of catalyst particles with controlled diameters overcomes the problems mentioned above. However, the production yield is very low, only 0.01 % SWNTs in the soot [11]. This is due to the poisoning of the catalyst with the carbon formed in the pyrolysis of the surfactant, and the limitation of the catalyst concentration during the injection. Recently, the production of SWNTs at a rate of ~1 g h-1, using a fluidized bed for introducing the catalyst into the reactor, has been reported [12]. Despite all of the significant achievements, the price, purity and quantity of the SWNTs remain far from the needs of the industry, limiting their application into broad areas. In consequence, developing a method for producing cheap carbon SWNTs with high yield still remains a challenge. Here, we report the continuous synthesis of high purity SWNTs with a high production yield (up to 6 g h-1), by an enhanced c
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