process

Abstract

A process for producing carbon nanotube products is described, comprising: (a) sequentially or simultaneously introducing a metal catalyst precursor, a carbon source, and a sulfur-containing additive into a continuous flow of hydrogen-containing carrier gas in a temperature-controlled flow once-through reactor; (b) exposing the metal catalyst precursor in the flow of hydrogen-containing carrier gas to a first temperature zone at a temperature sufficient to generate particulate metal catalysts; (c) exposing the particulate metal catalyst, a carbon source, and a sulfur-containing additive to a second temperature zone downstream of the first temperature zone, the second temperature zone being at a temperature sufficient to generate carbon nanotube aggregates; (d) discharging the carbon nanotube aggregates as continuous emissions from the outlet of the temperature-controlled flow once-through reactor; (e) collecting the continuous emissions in the form of carbon nanotube products; and (f) continuously recirculating the discharge flow of hydrogen by-products discharged from the outlet back to step (a) to gradually replace the continuous flow of hydrogen-containing carrier gas. Furthermore, a temperature-controlled flow once-through reactor for the production of carbon nanotube products is also described.

Description

[Technical field]

[0001] The present invention relates to a process for producing carbon nanotube (CNT) products and a temperature-controlled flow-through reactor. [Background technology]

[0002] There is an increasing demand for lightweight products with high strength and stiffness, especially those that combine high electrical and thermal conductivity. Floating catalytic chemical vapor deposition (FCCVD) is a widely studied process that has been used to produce CNT products (e.g., fibers) by agglomerating CNTs to form a continuous network of entangled (or interconnected) CNTs, like an aerogel. The FCCVD process, typically carried out in a temperature-controlled flow-through reactor (e.g., a furnace), involves the catalysis of CNT growth reactions by nanoparticle-generated iron in a hydrocarbon-rich atmosphere excited by the presence of sulfur. Different reaction mixtures and conditions to vary and improve the quantity and quality of CNT products are being investigated. However, the cost-effective and continuous production of aligned CNTs at microscopic scales for engineering applications by FCCVD remains challenging. Summary of the Invention

[0003] The present invention relates to a process that can advantageously utilize hydrogen, a by-product of hydrocarbon reactions, to continuously produce CNT products (eg, fibers, films, or sheets), and a temperature-controlled, flow-through reactor to accomplish this.

[0004] Thus, in a first aspect, the present invention provides a process for producing a carbon nanotube product, the process comprising: (a) sequentially or simultaneously introducing a metal catalyst precursor, a carbon source, and a sulfur-containing additive into a continuous flow of a hydrogen-containing carrier gas in a temperature-controlled, flow-through reactor; (b) exposing the metal catalyst precursor in the flow of the hydrogen-containing carrier gas to a first temperature zone at a temperature sufficient to generate a particulate metal catalyst; (c) exposing the particulate metal catalyst, the carbon source, and the sulfur-containing additive to a second temperature zone downstream of the first temperature zone, the second temperature zone being at a temperature sufficient to produce carbon nanotube aggregates; (d) discharging the carbon nanotube aggregates as a continuous discharge from an outlet of the temperature-controlled flow-through reactor; (e) collecting said continuous output in the form of carbon nanotube products; (f) continuously recycling the hydrogen by-product exhaust stream discharged from said outlet to step (a) to progressively replace the continuous flow of said hydrogen-containing carrier gas; Equipped with.

[0005] Surprisingly, the process achieves a high level of efficient recycle requiring only the addition of metal catalyst precursors, carbon sources, or sulfur-containing additives, which significantly reduces raw material costs and leads to reduced energy usage through hot gas recycle.

[0006] The hydrogen by-product exhaust stream may be purified or filtered.

[0007] Preferably, the temperature controlled flow once-through reactor comprises: an elongated heat resistant housing (e.g., a furnace) extending from an upstream end to a downstream end; a thermal enclosure surrounding an elongated, heat-resistant housing configured to provide a temperature variation in an axial direction between temperature zones within the elongated, heat-resistant housing, the temperature zones including a first temperature zone and a second temperature zone; Equipped with.

[0008] In step (a), the metal catalyst precursor may be introduced axially or radially into the temperature controlled flow-through reactor. The metal catalyst precursor may be introduced with a probe or injector. The metal catalyst precursor may be introduced at various locations.

[0009] The metal catalyst precursor may be a suspension of solid particles, preferably solid nanoparticles.

[0010] The metal catalyst precursor may be a compound of at least one metal selected from the group consisting of Fe, Ru, Co, W, Cr, Mo, Rh, Ir, Os, Ni, Pd, Pt, Ru, Y, La, Ce, Mn, Pr, Nd, Tb, Dy, Ho, Er, Lu, Hf, Li, and Gd.

[0011] Typically, the metal catalyst precursor is a metal compound of iron.

[0012] The metal catalyst precursor may be a metal complex or an organometallic compound.

[0013] Preferably, the metal catalyst precursor is ferrocene.

[0014] Typically, the fine particle metal catalyst is a nanoparticle metal catalyst. Preferably, the nanoparticles of the nanoparticle metal catalyst have an average diameter (e.g., the average diameter value in the volume or surface) of 1 to 50 nm (preferably 1 to 10 nm). Preferably, 80% or more of the particles of the nanoparticle metal catalyst have a diameter of less than 30 nm. Particularly preferably, 80% or more of the particles of the nanoparticle metal catalyst have a diameter of less than 12 nm. The concentration of the nanoparticle metal catalyst is 10 6 ~10 10 particles / cm 3 may be also possible.

[0015] The sulfur-containing additive may be elemental sulfur, thiophene, iron sulfide, a sulfur-containing ferrocenyl derivative (eg, ferrocenyl sulfide), hydrogen sulfide, or carbon disulfide.

[0016] Preferably, the sulfur-containing additive is a thiophene.

[0017] In step (a), the carbon source may be discharged axially or radially into the temperature-controlled flow-through reactor. The carbon source may be introduced with a probe or injector. The carbon source may be introduced at various locations.

[0018] Typically, the carbon source is a hydrocarbon.

[0019] The carbon source may be an aromatic hydrocarbon, which may be substituted and / or hydroxylated, or an aliphatic acyclic hydrocarbon (e.g., an alkyne, alkane, or alkene) or an aliphatic cyclic hydrocarbon (e.g., an alkyne, alkane, or alkene), which may be interrupted by one or more heteroatoms (e.g., oxygen). 1-6 Hydrocarbons (e.g. methane, propane, ethylene, acetylene or tetrachloroethylene), optionally mono-, di- or tri-substituted benzene derivatives (e.g. toluene), C 1-6 Alcohols (eg ethanol, or butanol), or aromatic hydrocarbons (eg benzene or toluene) are preferred.

[0020] Typically, the carbon source consists essentially of (preferably consists of) methane gas.

[0021] Preferably, the carbon source is biogenerated methane, optionally diluted with hydrogen (e.g., 50% hydrogen), natural gas, industrial waste methane (e.g., containing high levels of H2S), or biogas-derived methane (e.g., high levels of CO and / or CO2).

[0022] The generation of the particulate metal catalyst may begin in step (b) by thermal decomposition or ionization of the metal catalyst precursor into metal species (e.g., atoms, radicals, or ions). The generation of the particulate metal catalyst in step (b) may include nucleation of the metal species into nucleated metal species (e.g., clusters). The generation of the particulate metal catalyst may include growth of the nucleated metal species into the particulate metal catalyst.

[0023] The first and second temperature zones may range from 600 to 1300° C. (or higher).

[0024] The hydrogen-containing carrier gas typically consists essentially of hydrogen gas (preferably consists of hydrogen gas). The flow rate of the hydrogen-containing carrier gas may be 1000 to 50000 sccm (eg, 30000 sccm).

[0025] The carbon aggregates may include multi-walled carbon nanotubes (eg, double-walled carbon nanotubes) and / or single-walled carbon nanotubes.

[0026] The carbon aggregates may be in the form of a 3D continuous network (eg, an aerogel).

[0027] Preferably, the carbon aggregate is an aerogel.

[0028] The carbon nanotube article may have substantially aligned carbon nanotubes.

[0029] The carbon nanotube product may be a powder, fiber, wire, film, ribbon, thread, sheet, plate, mesh, or mat.

[0030] In a further aspect, the present invention provides a temperature-controlled once-through reactor for producing carbon nanotube products, the temperature-controlled once-through reactor comprising: an elongated heat resistant housing extending from an upstream end to a downstream end; a delivery system that sequentially or simultaneously releases a metal catalyst precursor, a carbon source, and a sulfur-containing additive into a continuous flow of a hydrogen-containing carrier gas; an inlet at or near the upstream end of the elongated, heat-resistant housing for introducing a continuous flow of hydrogen-containing carrier gas flowing from the upstream end to the downstream end; a thermal enclosure surrounding the elongated, heat-resistant housing configured to provide a temperature variation in an axial direction between temperature zones within the elongated, heat-resistant housing, the temperature zones including a first temperature zone at a temperature sufficient to generate a particulate metal catalyst and a second temperature zone at a temperature sufficient to generate carbon nanotube aggregates; a collector for collecting a continuous output of carbon nanotube aggregates from the downstream end in the form of carbon nanotube products; a piping recirculation system for continuously feeding an exhaust stream of hydrogen by-product discharged from the downstream end to the delivery system to progressively replace the continuous flow of hydrogen-containing carrier gas; Equipped with.

[0031] In a preferred embodiment, the piping recirculation system includes a primary pipeline incorporating a recirculation pump between a downstream end and the delivery system. Particularly preferably, the primary pipeline incorporates a flow meter (e.g., an area-based flow meter such as a rotameter) or a control valve upstream of the recirculation pump. More preferably, the primary pipeline incorporates a filter (e.g., upstream of the flow meter).

[0032] Preferably, the piping recirculation system includes a secondary pipeline branching off from the primary pipeline (e.g., at an upstream location in the pipe), the secondary pipeline incorporating the auxiliary equipment. Particularly preferably, the secondary pipeline incorporates a flow meter (e.g., a volumetric flow meter such as a rotameter) or a control valve that apportions the flow of the hydrogen by-product exhaust stream between the auxiliary equipment and the delivery system.

[0033] The auxiliary equipment may be one or more of a gas purification column, a separator, a spectrometer (eg, an infrared spectrometer), a storage tank, a compressor, or a vent.

[0034] A purification column or separator may be used to separate pure hydrogen (which may then be stored, sold, and / or used in many other processes) from other gases (e.g., methane, heavier hydrocarbons from the partial cracking of methane, or H2S). Concentrated stocks of process gas can be reused in the process of the invention.

[0035] The delivery system may include an injection nozzle, a lance, a probe, or a multi-orifice injector (eg, a showerhead injector).

[0036] In a preferred embodiment, the delivery system includes a controller for controlling (eg, timing and metering) the release of the metal catalyst precursor, the carbon source, and the sulfur-containing additive into a continuous flow of the hydrogen-containing carrier gas.

[0037] Preferably, the controller further controls the delivery (eg, timing and metering) of the hydrogen by-product exhaust stream to the delivery system to progressively replace the continuous flow of hydrogen-containing carrier gas.

[0038] The elongated, heat resistant housing may be generally cylindrical (eg, tubular).

[0039] The elongated heat resistant housing may be a furnace.

[0040] Typically, the thermal enclosure is electrically insulating.

[0041] The axial temperature change need not be uniform (eg, stepwise).The temperature of a temperature-controlled flow-through reactor may be controlled by resistive heating, plasma, or laser.

[0042] The temperature controlled flow-through reactor may be substantially vertical or horizontal.

[0043] The collector is typically electrically conductive (e.g., made of a metal) and may be a rotating spindle, a reel, a winder, or a drum.

[0044] In another further aspect, the present invention provides a method for producing a carbon nanotube product, the method comprising: (1) sequentially or simultaneously introducing a particulate metal catalyst, a carbon source, and a sulfur-containing additive into a continuous flow of a hydrogen-containing carrier gas in a temperature-controlled, flow-through reactor; (2) exposing a particulate metal catalyst, a carbon source, and a sulfur-containing additive to a temperature zone at a temperature sufficient to produce carbon nanotube aggregates; (3) discharging the carbon nanotube aggregates as a continuous discharge from an outlet of the temperature-controlled flow-through reactor; (4) collecting the continuous output in the form of carbon nanotube products; (5) continuously recycling the exhaust stream of hydrogen by-product discharged from the outlet to step (a) to progressively replace the continuous flow of hydrogen-containing carrier gas.

[0045] Particulate metal catalysts may be prepared (for example) from elemental metals (or metal alloys) by ablation (eg laser ablation, plasma ablation, or electric arc ablation). [Brief description of the drawings]

[0046] The invention is herein described in a non-limiting sense with reference to the accompanying drawings. [Figure 1] 1 shows a schematic of a temperature-controlled flow-through reactor embodiment of the present invention, equipped with a recycle gas line and a water trap. [Diagram 2] 1 shows a schematic piping and instrumentation diagram (P&ID) of a further embodiment of a temperature-controlled flow-through reactor of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0047] A research-based, temperature-controlled, flow-through reactor, diagrammatically shown in Figure 1, was configured to continuously produce CNT product on a winder and to emit an exhaust stream of excess hydrogen gas that could be collected and purified for use as a process gas. The reactor involved connecting a pump to a branch of the exhaust line to extract hydrogen gas and feed it to a gas purification column and an infrared spectrometer. The branch and pump allowed for gas lines to be fed to the injector and back into the reactor to explore gas recirculation.

[0048] Following experimental and plumbing changes, the system was modified so that the recirculated gas would carry the reagents (thiophene and ferrocene) instead of fresh hydrogen from a bottled source, with re-metering of the recirculated gas at a stationary control panel rather than downstream. It was anticipated that low levels of recirculation would be possible. A secondary branch line to the gas purification column and spectrometer was retained and used to restore line pressure if it built up (e.g. due to gas purification or fresh input of methane).

[0049] Due to the need to feed non-recirculated reagents and the potential for build-up of impurities, it was anticipated that a minimal amount of fresh hydrogen would be required to run the system continuously. However, to our surprise, we found that the system would function with 100% recirculation (with only a small amount of fresh methane added) and re-metered exhaust gas. Furthermore, the process was found to be stable and to have continuously wound fiber for up to an hour with minimal manual intervention, and was only limited by the accumulation of CNT product on the take-up spool.

[0050] This work presents a novel process to optimize CNT production using hydrogen exhaust gas instead of a fresh hydrogen gas source, and using methane and small amounts of thiophene and ferrocene as fresh inputs.

[0051] (Equipment and process overview) FIG. 1 shows a schematic of CNT aerogel growth in sock form and where the exhaust gas goes. In the control tower, mass flow controllers meter hydrogen and methane gas from the bottles, and a heated ferrocene puck and a cooled thiophene bubbler manage the gas flow ratios to deliver small amounts of ferrocene and thiophene vapors, respectively, to the furnace. CNT formation occurs in the furnace, and the outlet of the furnace tube is connected directly to a small collection box that houses a motorized winder that collects the solid CNT product. The exhaust gas typically passes through a water trap that keeps the system at near atmospheric pressure. Once the recirculation loop is secured, the pump is turned on and the flow control rotameter is opened to allow enough gas to escape so that substantially no exhaust gas escapes through the water trap. The pumped exhaust gas may be diverted to an infrared spectrometer for analysis and / or a gas column for purification. The remaining gas is returned to the control tower panel and pumped back to the mass flow controller to begin the cycle again. As 100% circulation is gradually established, the flow from the hydrogen bottle supply is shut off and the rotameter adjusted as necessary. Fresh methane is then injected into the furnace and the reaction continues as the thiophene and ferrocene are introduced (usually ferrocene last).

[0052] Figure 2 shows a schematic piping and instrumentation diagram (P&ID) of a further embodiment of a temperature-controlled flow-through reactor according to the invention. Separate mass flow controllers and gas supplies are shown. This embodiment features an additional small rotameter (R) in a branch from the recycle line used to limit the exiting exhaust gases for purification, analysis or pressure relief. In practice, the rotameter (R) sets the recycle rate. Theoretically, this flow is equal to the fresh flow of methane to the furnace plus the gases released in the reaction minus the methane consumed.

[0053] (Experiment overview) Single pass CNT socks formation was demonstrated using a collection box setup. After ensuring a 100% gas recirculation loop, fresh methane was added at only 30ml / min (normally 100ml / min or higher) to the re-metered gas flow of 1.08L / min along with reduced thiophene runoff (20ml / min down from 60ml / min) and normal ferrocene runoff (100ml / min) to demonstrate sock formation. Collection continued for 51 minutes with near high continuity / minimal manual intervention until it was clear the winder was completely full. After collection of the first sample, the run was repeated with reduced methane (20ml / min) and collection continued for 60 minutes until the winder was completely full. Further experiments were carried out to test gas purification in parallel with gas recirculation at higher total flow rates, maximum throughput and continuous single pass conditions (with minimal manual intervention to collect socks) with less than 100% recirculation.

[0054] (Practical findings from experiments) First, it was necessary to ensure a recirculation loop by starting with only hydrogen flowing through the furnace barrel. Starting with a single pass reaction condition would result in excessive soot formation, clogging, and a shorter safe time to balance the fresh input vs. recirculation pump vs. water trap discharge flows (backsuction can occur if the pump draws too much). To grow a strong aerogel sock that self-extrudes and wraps around the winder roller, the initial delivery rate of methane needs to be faster (e.g., 2x normal speed in 5 min) to deliver the ferrocene and finally the nanoparticles to a reagent-rich environment. Due to the low fresh gas input (~30 ml / min) compared to the equipment volume (~14 L), it takes longer for the reagents to accumulate in the recirculating gas stream (carbon species and H2S) up to the point of aerogel formation (~10 min for initial weak sock formation and >30 min for proper stabilization). However, the higher methane flow cannot be sustained for longer because soot formation can occur. · Continuous winding from the start of the run is very beneficial to keep the end of the furnace barrel clean of soot and CNT sock debris. Soot buildup can cause material blockages that prevent continuous winding. Additional heating elements can be deployed around the end of the furnace barrel to keep the barrel hot enough to not clog all the way to the collection box. Gas mixtures may be used instead of pure methane. Mixtures used in tests include (re-synthesized) waste methane with high H2S concentration, methane-derived biogas with high CO and CO2 concentration (~50%), and biogas-derived methane diluted with hydrogen (~50% hydrogen, ~30% CO). These mixtures have been successfully used to produce CNT films in a single pass setup, with simple adjustment of the amount of methane injected to supplement the mixture. · Difficulties in cycling with some gas mixtures may be improved by diluting the gas mixture with pure methane. Alternatives to dilute (pure) methane may result in higher amounts of unreacted species in the gas loop, which may create additional complications. In this case, it may be necessary to increase the dilution feed gas with purer methane, or to continuously inject fresh hydrogen to dilute the contaminants. Additional purification techniques may be employed to remove the contaminants.

Claims

1. 1. A process for producing a carbon nanotube product, comprising: (a) sequentially or simultaneously introducing a metal catalyst precursor, a carbon source, and a sulfur-containing additive into a continuous flow of a hydrogen-containing carrier gas in a temperature-controlled, flow-through reactor; (b) exposing the metal catalyst precursor in the flow of the hydrogen-containing carrier gas to a first temperature zone at a temperature sufficient to generate a particulate metal catalyst; (c) exposing the particulate metal catalyst, the carbon source, and the sulfur-containing additive to a second temperature zone downstream of the first temperature zone, the second temperature zone being at a temperature sufficient to produce carbon nanotube aggregates; (d) discharging the carbon nanotube aggregates as a continuous discharge from an outlet of the temperature-controlled flow-through reactor; (e) collecting said continuous output in the form of carbon nanotube products; (f) continuously recycling the hydrogen by-product effluent stream discharged from said outlet to step (a) to progressively replace said continuous flow of hydrogen-containing carrier gas; A process comprising:

2. 10. The process of claim 1, wherein the carbon source comprises methane.

3. 10. The process of claim 1, wherein the carbon source is biogenerated methane, natural gas, industrial waste methane, or biogas-derived methane, optionally diluted with hydrogen.

4. 1. A temperature-controlled flow-through reactor for producing carbon nanotube products, comprising: an elongated heat resistant housing extending from an upstream end to a downstream end; a delivery system that sequentially or simultaneously releases a metal catalyst precursor, a carbon source, and a sulfur-containing additive into a continuous flow of a hydrogen-containing carrier gas; an inlet at or near the upstream end of the elongated, heat-resistant housing for introducing the continuous flow of the hydrogen-containing carrier gas flowing from the upstream end to the downstream end; a thermal enclosure surrounding the elongated, heat-resistant housing configured to provide a temperature variation in an axial direction between temperature zones within the elongated, heat-resistant housing, the temperature zones including a first temperature zone at a temperature sufficient to generate a particulate metal catalyst and a second temperature zone at a temperature sufficient to generate carbon nanotube aggregates; a collector for collecting the continuous output of the carbon nanotube aggregates from the downstream end in the form of carbon nanotube products; a piping recirculation system that continuously delivers an exhaust stream of hydrogen by-product discharged from the downstream end to the delivery system to gradually replace the continuous flow of the hydrogen-containing carrier gas; A temperature-controlled flow-through reactor comprising:

5. 5. The temperature-controlled flow-through reactor of claim 4, wherein the piping recirculation system includes a primary pipeline incorporating a recirculation pump between the downstream end and the feed system.

6. 6. The temperature-controlled flow-through reactor of claim 5, wherein the primary pipeline incorporates a flow meter upstream of the recirculation pump.

7. 7. A temperature-controlled once-through flow reactor according to claim 5 or 6, wherein the primary pipeline incorporates a filter.

8. 6. The temperature-controlled flow-through reactor according to claim 4 or 5, wherein the piping recirculation system includes a secondary pipeline branching off from the primary pipeline, the secondary pipeline incorporating auxiliary equipment.

9. 10. The temperature-controlled flow-through reactor of claim 8, wherein the secondary pipeline incorporates a flow meter, the flow meter apportioning the flow of the exhaust stream of hydrogen by-product between the auxiliary equipment and the delivery system.

10. 6. The temperature-controlled once-through flow reactor of claim 4, wherein the delivery system includes a controller for controlling the release of the metal catalyst precursor, the carbon source, and the sulfur-containing additive into the continuous flow of the hydrogen-containing carrier gas.

11. 11. The temperature-controlled flow-through reactor of claim 10, wherein the controller further controls the delivery of the effluent stream of hydrogen by-product to the delivery system to gradually replace the continuous flow of the hydrogen-containing carrier gas.

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