Continuous production of carbon nanomaterials using a high temperature inductively coupled plasma

Abstract

High-power inductively coupled plasma technology is used for thermal cracking and vaporization of continuously fed carbonaceous materials into elemental carbon, for reaction with separate and continuously fed metal catalysts inside a gas-phase high-temperature reactor system operating at or slightly below atmospheric pressures. In one particularly preferred embodiment, in-flight growth of carbon nanomaterials is initiated, continued, and controlled at high flow rates, enabling continuous collection and product removal via gas/solid filtration and separation methods, and/or liquid spray filtration and solid collection methods suitable for producing industrial-scale production quantities. In another embodiment, the reaction chamber and/or filtration/separation media include non-catalytic or catalytic metals to simultaneously or separately induce on-substrate synthesis and growth of carbon nanomaterials. The on-substrate grown carbon nanomaterials are produced in secondary chambers that are selectively isolated for periodic removal of the product.

1 . A method for producing carbon nanomaterials (CNMs) in-flight within a gas flow in a reactor using an inductively coupled plasma (ICP), comprising the steps of:
 (a) establishing a gas flow within the reactor, the reactor being configured to inhibit growth of CNMs on internal surfaces of the reactor;   (b) introducing the ICP into the reactor;   (c) introducing a carbonaceous material into the reactor, such that the ICP heats and reacts with the carbonaceous material to produce free carbon;   (d) introducing a catalyst into the gas flow within the reactor, the catalyst having been selected to enhance the production of CNMs from the free carbon within the gas flow, such that the CNMs thus produced are entrained within the gas flow;   (e) directing the gas flow and entrained CNMs out of the reactor; and   (f) separating the CNMs from the gas flow outside of the reactor.   
     
     
         2 . The method of  claim 1 , wherein the step of separating the CNMs from the gas stream outside of the reactor comprises the step of sorting the CNMs into different groups of CNMs based on size. 
     
     
         3 . The method of  claim 1 , further comprising the step of producing the CNMs continuously, continuous production being facilitated by separating the CNMs from the gas stream outside of the reactor, as the reactor need not be shut down periodically to remove CNMs accumulated within the reactor. 
     
     
         4 . The method of  claim 1 , wherein the step of introducing the ICP into the reactor comprises the step of using an inert gas to generate the ICP. 
     
     
         5 . The method of  claim 1 , wherein the step of introducing the ICP into the reactor comprises the step of using carbon monoxide to generate the ICP. 
     
     
         6 . The method of  claim 1 , wherein the step of introducing the catalyst into the reactor comprises one step selected from the group consisting of:
 (a) introducing the catalyst into the reactor such that relatively smaller catalytic particles are achieved, thereby favoring the production of single wall carbon nanotubes;   (b) introducing the catalyst into the reactor such that relatively larger catalytic particles are achieved, thereby favoring the production of multi-walled carbon nanotubes;   (c) introducing a metal powder; and   (d) introducing a metal salt.   
     
     
         7 . The method of  claim 1 , further comprising the step of filtering the gas flow exiting the reactor to recover the catalyst, and recycling the catalyst by reintroducing the catalyst into the reactor. 
     
     
         8 . The method of  claim 1 , further comprising the step of directing the gas flow exiting the reactor into a secondary chamber, before separating the CNMs from the gas flow, the secondary chamber providing additional residence time to promote the growth of longer CNMs. 
     
     
         9 . The method of  claim 8 , further comprising at least one step selected from the group consisting of:
 (a) using supplemental heat to maintain the temperature conditions in the secondary chamber above a threshold value required to facilitate the additional growth of the CNMs;   (b) introducing additional carbonaceous materials into the secondary chamber to provide additional carbon to facilitate the additional growth of the CNMs; and   (c) directing the gas flow over a substrate in the secondary chamber, such that CNMs are formed on the substrate, as well as being formed in-flight in the gas flow.   
     
     
         10 . The method of  claim 1 , further comprising at least one step selected from a group consisting of:
 (a) providing a reactor that does not include structures that would inhibit a free flow of gas within the reactor, such that a deposition of CNMs on internal surfaces of the reactor is minimized; and   (b) providing a reactor whose internal surfaces are non-metallic, such that a deposition of CNMs on internal surfaces of the reactor is minimized.   
     
     
         11 . The method of  claim 1 , further comprising the step of establishing a negative pressure condition within the reactor, such that the gas flow is pulled through the reactor. 
     
     
         12 . The method of  claim 1 , wherein the step of introducing the carbonaceous material into the reactor comprises the step of introducing the carbonaceous material into the reactor at more than one location, in order to prevent carbon concentrations in any one part of the reactor to favor the formation of soot. 
     
     
         13 . A method for producing carbon nanomaterials (CNMs) both in-flight and on a substrate, using an inductively coupled plasma, comprising the steps of:
 (a) using the ICP to establish a gas flow in a reactor, the reactor being configured to inhibit growth of CNMs on surfaces within the reactor;   (b) introducing a carbonaceous material into the reactor, such that the ICP reacts with the carbonaceous material to produce free carbon in the reactor;   (c) introducing a catalyst into the gas flow, such that the catalyst stimulates the combination of free carbon to form CNMs in-flight within the gas flow in the reactor; and   (d) directing the gas flow from the reactor into a secondary chamber including a substrate configured to encourage growth of CNMs on the substrate, such that CNMs are formed on the substrate in the secondary chamber.   
     
     
         14 . The method of  claim 13 , further comprising the steps of:
 (a) collecting a process gas including CNMs entrained in the process gas from at least one of the reactor and the secondary chamber; and   (b) separating the CNMs from the process gas, such that the CNMs are sorted into different groups of CNMs based on size.   
     
     
         15 . The method of  claim 13 , wherein the step of introducing the catalyst into the reactor comprises one step selected from the group consisting of:
 (a) introducing the catalyst into the reactor such that relatively smaller catalytic particles are achieved, thereby favoring the production of single wall carbon nanotubes; and   (b) introducing the catalyst into the reactor such that relatively larger catalytic particles are achieved, thereby favoring the production of multi-walled carbon nanotubes.   
     
     
         16 . The method of  claim 13 , further comprising at least one step selected from the group consisting of:
 (a) using supplemental heat to maintain the temperature conditions in the secondary chamber above a threshold value required to facilitate the additional growth of the CNMs; and   (b) introducing additional carbonaceous materials into the secondary chamber to provide additional carbon to facilitate the additional growth of the CNMs.   
     
     
         17 . The method of  claim 13 , wherein the step of introducing the carbonaceous material into the reactor comprises the step of introducing the carbonaceous material into the reactor at more than one location, in order to prevent carbon concentrations in any one part of the reactor to favor the formation of soot. 
     
     
         18 . A system for using an inductively coupled plasma (ICP) to generate carbon nanomaterials (CNMs), comprising:
 (a) a plasma generator capable of a sustained production of the ICP, the plasma generator being coupled to a source of electrical power;   (b) a reactor configured to receive the ICP and a carbonaceous material, the carbonaceous material being reformed in a gas stream in the reactor into free carbon, which in the presence of a suitable catalyst that is provided in the reactor, combine to produce CNMs in-flight; and   (c) a filter unit configured to remove the CNMs from the gas stream exiting the reactor.   
     
     
         19 . The system of  claim 18 , wherein the reactor is configured to operate under at least one set of conditions selected from a group consisting of:
 (a) substantially atmospheric pressure; and   (b) a pressure that is sufficiently negative such that the gas stream is pulled through the reactor.   
     
     
         20 . The system of  claim 18 , wherein internal surfaces of the reactor are configured to inhibit the formation of CNMs on the internal surfaces, the internal surfaces comprising at least one element selected from a group consisting of:
 (a) substantially smooth surfaces that do not inhibit gas flow through the reactor;   (b) substantially non-metallic surfaces;   (c) glass surfaces;   (d) ceramic surfaces; and   (e) quartz surfaces.   
     
     
         21 . The system of  claim 18 , wherein the filter unit is configured to separate the CNMs into different products according to size. 
     
     
         22 . The system of  claim 18 , further comprising at least one additional process unit selected from a group consisting of:
 (a) a secondary reaction unit having an inlet and an outlet, and configured to receive the gas stream exiting the reactor, the secondary reaction unit being disposed between the reactor and the filter unit, the secondary reaction unit increasing a residence time of the gas stream and thereby providing additional time for formation of the CNMs;   (b) a catalyst recovery unit configured to remove a catalyst entrained within the gas stream; and   (c) a product integration unit configured to receive CNMs from the filter unit and to incorporate the CNMs into a product.   
     
     
         23 . The system of  claim 22 , wherein the secondary reaction chamber comprises at least one member selected from the group consisting of:
 (a) a substantially tubular chamber such that the gas stream is not required to change direction while traversing the secondary reaction chamber;   (b) a substantially tubular chamber including a plurality of bends, such that the gas stream is required to change direction while traversing the secondary reaction chamber;   (c) a plurality of ports, the plurality of ports enabling at least one of an introduction of additional process materials, and a collection of a product; and   (d) a substrate configured to encourage formation of CNMs on the substrate.