High Pressure Carbon Monoxide HiPco Process

The high-pressure carbon monoxide (HiPco) process (603 Kb) was developed at Rice University to create single-walled carbon nanotubes (SWCNT) from the gas-phase reaction of iron carbonyl with high-pressure carbon monoxide gas. Iron pentacarbonyl is used to produce iron nanoparticles that provide a nucleation surface for the transformation of carbon monoxide into carbon during the growth of the nanotubes. Experiments use in the range of milligrams to grams of material. Waste material is regularly picked up by a professional waste disposal company, and the waste material is incinerated, avoiding environmental release.

Description of the Material The CNT produced in the HiPco reactor is a fluffy-fibrous material. This raw material can become airborne if it is not contained. Shortly after the reactor was installed, Rick Smalley provided large quantities of material to NASA for safety testing, and also had NIOSH conduct tests at Rice where they generated aerosols of the raw product. The overall conclusion was that CNT tend to strongly aggregate into clusters of hundreds of microns or larger, so that the product does not behave as airborne nano-particulates, and are not readily respired into the lungs. needed Vacuum cleaners with HEPA filters effectively trap the material and are suitable for cleanup. In toxicology studies elsewhere, respiring this particular CNT material into the lungs of mice proved to be so difficult that it was necessary to make a slurry and introduce this by syringe into the lungs of mice for study, or the CNT were blown into the lungs. Injection of such slurries has caused granulomas in the lungs of mice. needed

Subsequent use — The CNT material is usually purified before experimental use, which considerably compacts the material and it essentially becomes a fibrous or granular solid. In experimental use in the other laboratories, CNT material is normally either in solution, suspension, or solid. It does not return to the fluffy state of the original material, and since it is non-volatile, the risk of airborne exposure is minimal.

HiPco Raw Product Exposure Assessment

Risk of exposure to airborne CNT clusters and to skin contact: Material is normally contained within the closed cycle reactor and collection system. Material is transferred to buckets or other appropriate containers at the full height fume hood. For gas phase purification, the material is loaded into a fine mesh basket for exposure to processing gases. Then this is wet processed with acid to remove residual iron.

The iron catalyst particles are bound to the CNT and hence do not constitute a separate exposure hazard.

HiPco Raw Product Exposure Control

When the CNT are confined in fully enclosed containers, standard laboratory hygiene is observed. During raw product transfer, wear full protection:

Lab coat, HEPA filtration respirator mask, chemical safety goggles or face shield, chemical gloves. Keep laboratory doors closed and locked during transfer. Promptly use HEPA vacuum cleaner to pick any stray material and/or use wet wipe methods for any CNT material settled on surfaces.

For trace amounts of bound material to container surfaces, use wet wipe methods. At present, the numerous studies indicate that CNT has the potential as a moderately hazardous material for respiration. The transfer process is short term, for free/unbound material, so we believe this corresponds to control band #2. Skin contact does not appear to be a route for uptake into the body, and standard laboratory hygiene practices should be adequate here.

Hazard group B: Potential release, short term exposure, control band 2 Good chemical hygiene as spelled out in the Chemical Hygiene Manual provided by the Rice University Chemistry Department will be maintained. Loose CNT materials will be promptly be cleaned up by HEPA vacuum or wet wipe, as appropriate. New employees will be trained by experienced staff in the specific procedures of the HiPco laboratory after they receive general training from the University EH&S. University Facilities, Engineering and Planning will routinely inspect fume hoods, and certify proper operation. Use of conventional vacuum cleaners is prohibited as this may re-suspend CNT particles (This hazard was verified by OSHA personnel). Waste material is labeled for content, and is removed by the University chemical waste disposal service.

New information from the literature as to hazards of CNT will be discussed to determine if procedures need to be modified to reduce risk of exposure. Such changes will be incorporated into the protocol and training.

The University EHS and/or the Chemistry Department maintains records on employee training and overall safety procedures. The HiPco laboratory will maintain records of personnel properly trained in handling the CNT material, production and use of material, and any unusual incidents or deviations from the normal protocol.