Continuous mass production in fluidized-bed reactors now appears feasible.
A continuing program of research and development has been directed toward improvement of a prior batch process in which single-walled carbon nanotubes are formed by catalytic disproportionation of carbon monoxide in a fluidized-bed reactor. The overall effect of the improvements has been to make progress toward converting the process from a batch mode to a continuous mode and to scaling of production to larger quantities. Efforts have also been made to optimize associated purification and dispersion post processes to make them effective at large scales and to investigate means of incorporating the purified products into composite materials. The ultimate purpose of the program is to enable the production of high-quality single-walled carbon nanotubes in quantities large enough and at costs low enough to foster the further development of practical applications.
The fluidized bed used in this process contains mixed-metal catalyst particles. The choice of the catalyst and the operating conditions is such that the yield of single-walled carbon nanotubes, relative to all forms of carbon (including carbon fibers, multi-walled carbon nanotubes, and graphite) produced in the disproportionation reaction is more than 90 weight percent. After the reaction, the nanotubes are dispersed in various solvents in preparation for end use, which typically involves blending into a plastic, ceramic, or other matrix to form a composite material.
Notwithstanding the batch nature of the unmodified prior fluidized-bed process, the fluidized-bed reactor operates in a continuous mode during the process. The operation is almost entirely automated, utilizing mass flow controllers, a control computer running software specific to the process, and other equipment. Moreover, an important inherent advantage of fluidized-bed reactors in general is that solid particles can be added to and removed from fluidized beds during operation. For these reasons, the process and equipment were amenable to modification for conversion from batch to continuous production.
The improvements include the following:
- A provision has been made for continuous addition of catalyst particles by entraining them in a stream of helium that is fed into the reactor.
- Progress has been made toward implementation of a purification/suspension post-process.
- Progress has also been made toward implementation of an alternative purification process that involves the use of hydrofluoric acid.
- A post-purification drying method was invented. This method increases the probability of success of subsequent efforts to re-disperse lyophilized samples of purified product material.
- Techniques of in-situ polymerization were explored. The findings may lead to development of strong, lightweight carbon-nanotube/polymer composites.
This work was done by Leandro Balzano and Daniel E. Resasco of SouthWest Nano Technologies, Inc., for Johnson Space Center. For more information, see www.swnano.com.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:
Leandro Balzano, SWeNT Development
SouthWest NanoTechnologies Inc.
2501 Technology Place
Norman, OK 73071-1102
Phone No.: (405) 217-8388
Refer to MSC-23706-1, volume and number of this NASA Tech Briefs issue, and the page number.