Integrated production of thiophenes and carbon nanotubes

Abstract

The present invention provides integrated production systems and methods of thiophenes (and / or substituted thiophenes) and carbon nanotubes. The product effluent of the thiophene synthesis may include thiophene, sulfur-containing organic compounds, and unreacted hydrocarbons during the thiophene synthesis. This product effluent can be used as a feed for the synthesis of carbon nanotubes. The effluent provides hydrocarbons for pyrolysis to form H2 and carbon. In addition, the thiophene provides sulfur, which can be used for in situ catalyst formation for forming carbon nanotubes.

Description

Related Applications

[0001] This application claims priority to U.S. Provisional Application No. 63 / 349,738, filed on June 7, 2023, which is incorporated herein by reference in its entirety. Field of the Invention

[0002] Systems and methods are provided for the integrated production of thiophene and / or substituted thiophenes and carbon nanotubes. Background of the Invention

[0003] Currently, thiophene and alkyl-substituted thiophenes are commercially produced by the gas phase reaction of an alcohol with a sulfur source (e.g., carbon disulfide) in the presence of an oxide catalyst. An example of an oxide catalyst is Cr2O3 supported on a matrix including Al2O3 and K2CO3. Although this can be used for the production of thiophene, the alcohol required as a reagent corresponds to a specialty chemical. This significantly increases the production cost of thiophene, thereby limiting the potential applications of products made from such thiophenes.

[0004] It is desirable to have alternative methods that can produce thiophenes at lower cost. This could potentially increase the number and / or types of applications for thiophenes. For example, polythiophenes correspond to conjugated polymers. Conjugated polymers (e.g. ) generally have favorable tensile strength and / or other properties that are favorable for use as structural materials. Therefore, if thiophene (and therefore polythiophene) can be produced at a lower cost, then applications using polythiophene as a structural material may become attractive. In addition, oxidized and / or doped polythiophene can potentially be used as a conductive polymer.

[0005] Another method that is gaining increasing attention is the pyrolysis of hydrocarbons to form hydrogen. Hydrocarbon pyrolysis to form hydrogen provides a way to convert hydrocarbons into H2, a clean-burning fuel, and solid carbon. In terms of CO2 emissions, the use of hydrocarbon pyrolysis to generate H2 may provide a way to reduce or minimize CO2 emissions without deploying carbon capture technology in every process that requires fuel combustion. However, there are still various challenges to implementing hydrocarbon pyrolysis to generate H2 as a fuel on a commercial scale.

[0006] One of the difficulties with using pyrolysis to generate H2 as a fuel is that a large amount of solid carbon is also produced as a byproduct. Solid carbon is a relatively low value material and if the option of using the solid carbon as a combustion fuel is eliminated, the value of the solid carbon is generally negative (i.e., the carbon is disposed of rather than sold as a valuable product). In order to make the generation of H2 by pyrolysis of hydrocarbons a commercially viable technology, it would be desirable to have a system or method that would allow the pyrolysis reaction to form a carbon product with a positive value rather than a negative value.

[0007] One option for forming carbon products with positive values ​​is to combine the hydrocarbon pyrolysis process with the pyrolysis for carbon nanotube formation. Carbon nanotubes have a variety of commercially beneficial properties, so even low yields of carbon nanotubes can greatly improve the economics of the hydrocarbon pyrolysis process. However, carbon nanotube formation is currently a laboratory-scale process carried out in reactors that produce grams of carbon nanotubes per day. Although existing small-scale reactors may be used in parallel to produce large quantities of carbon nanotubes, such expansion will pose significant engineering challenges. First, various complex manifolds may be required to manage input flows, output H2 flows, and extraction of carbon nanotubes. In addition, the difficulty of providing the heat required for pyrolysis to a large number of individual reactors at the same time needs to be addressed. The equipment footprint required to handle this expanded configuration may also be large. Therefore, it would be beneficial if there were available systems and / or methods that could achieve commercial production of carbon nanotubes and H2 while avoiding the significant engineering challenges associated with the use of a large number of small reactors.

[0008] An example of an alternative process for thiophene production is to use n-butane (or another alkane) instead of alcohol. U.S. Patent 3,939,179 describes an example of a catalytic process for converting n-butane and H2S to thiophene. Various metal oxides supported on refractory oxides are described as catalyst precursors, including a combination of potassium oxide and chromium oxide supported on alumina.

[0009] Another option is to operate at elevated temperatures without the use of a catalyst. An example of this type of process is described in U.S. Patent 2,450,658. While this type of process can produce thiophene, the single-pass conversion of n-butane is limited, meaning that a large number of cycles are required to achieve high net conversions. In addition, the thiophene synthesis conditions result in the formation of large amounts of tarry products. It is further noted that the results reported for the thiophene synthesis example based on mass balance appear to be missing a large amount of carbon in the input stream. Based on the relatively thorough characterization of the other products, this may indicate that a large amount of coke is produced, which is consistent with the higher temperature operation required to achieve large conversions of n-butane in the absence of a catalyst.

[0010] US Patent No. 9,061,913 describes an apparatus for producing carbon nanotubes. The apparatus provides a method for introducing a reactive input stream in the form of droplets.

[0011] A journal article titled “Mapping the Parameter Space for Direct-Spun Carbon Nanotube Aerogels” (Weller et al., Carbon, Vol. 146, p. 789 (2019)) describes conditions that can be used to form single-walled carbon nanotubes and multi-walled carbon nanotubes.

[0012] A journal article titled “Initial Competing Chemical Pathways during Floating Catalyst Chemical Vapor Deposition Carbon Nanotube Growth” (McLean et al., J. Appl. Phys. Vol. 129, p. 044302 (2021)) describes simulations of the initial formation of carbon nanotube structures using a floating catalyst-chemical vapor deposition type catalyst.

[0013] A journal article titled “Catalytic Decomposition of Methane into Hydrogen and High-Value Carbons: Combined Experimental and DFT Computational Study” (Wang et al., Cat. Sci. Technol. Vol. 11, p. 4911 (2021)) describes a method for recovering metals from carbon nanotubes for use as a catalyst for forming additional carbon nanotubes. SUMMARY OF THE INVENTION

[0014] In one aspect, a method for producing carbon nanotubes is provided. The method comprises: preparing a carbon nanotube containing one or more C4 to C 16 A first feedstock of alkanes and a second feedstock containing a gas-phase sulfur source are exposed to a synthesis catalyst to form a synthesis effluent containing thiophene, alkylated thiophene or a combination thereof. The method also includes heating the gas stream to a temperature of 1000°C or higher to form a heated gas stream. The method also includes passing the heated gas stream into a reactor including a pyrolysis zone, the pyrolysis zone having an average cross-sectional area available for the gas stream. The method also includes mixing i) a catalytic metal precursor containing a catalytic metal and ii) at least a portion of the synthesis effluent with the heated gas stream to form a heated gas stream mixture, the heated gas stream mixture containing 10% by volume or less hydrocarbons, thiophene and alkylated thiophene. The method also includes maintaining the heated gas stream mixture in the pyrolysis zone at a temperature of 1000°C or higher for a continuous pyrolysis residence time to form an intermediate product stream containing H2, carbon and a catalyst including a catalytic metal. The method also includes cooling the intermediate product stream to a temperature of 800°C or lower. In addition, the method includes conveying the intermediate product stream to an array of gas stream tubes in the reactor to form a carbon nanotube product stream. In some aspects, the ratio of the average cross-sectional area of ​​the pyrolysis zone available for gas flow to the average cross-sectional area of ​​the gas flow tube array is 1.1 or greater. Additionally or alternatively, in some aspects, the ratio of the average cross-sectional area of ​​the pyrolysis zone available for gas flow to the average cross-sectional area of ​​the tubes in the gas flow tube array is 10 or greater. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 An example of a reaction system for synthesizing thiophene is shown.

[0016] Figure 2 An example of a reaction system for forming carbon nanotubes is shown.

[0017] Figure 3 Transmission electron micrograph of the layered chromium sulfide phase of the sulfided catalyst is shown.

[0018] Figure 4 Examples of compounds produced during thiophene synthesis are shown. Detailed description of implementation plan

[0019] All numerical values ​​in this detailed description and claims are modified by indicating the value "about" or "approximately", and take into account experimental error and variations that would be expected by a person of ordinary skill in the art. Overview

[0020] In various aspects, systems and methods for the integrated production of thiophene (and / or substituted thiophene) and carbon nanotubes are provided. The product effluent of thiophene production can include thiophene (and / or substituted thiophene), sulfur-containing organic compounds, and unreacted hydrocarbons from the thiophene synthesis process. This product effluent can be used as a feed for carbon nanotube synthesis. The effluent provides hydrocarbons for pyrolysis to form H2 and carbon. In addition, thiophene provides sulfur, which can be used for in-situ catalyst formation for the formation of carbon nanotubes.

[0021] The metal components required for the in-situ catalyst formation can be provided in any convenient manner. In some aspects, a metal-containing precursor (e.g., ferrocene) can be used as a reagent for the in-situ catalyst formation. Additionally or alternatively, the metal used for the in-situ catalyst formation can be provided based on a metal recovery process that includes using a portion of carbon nanotubes to form the catalyst. The carbon nanotubes can correspond to a recovered portion of nanotubes and / or fresh nanotubes made in a different process.

[0022] In some aspects, thiophene can be synthesized using a catalyst that provides improved results when producing thiophene by converting n-butane (and / or other alkanes) and a gas phase sulfur-containing compound (e.g., CS , H , S , or another form of sulfur). The catalyst can correspond to a chromium sulfide supported on a zeolite carrier, such as a zeolite carrier in the form of an alkali metal or an alkaline earth metal. A method for producing a catalyst and a corresponding catalyst precursor is also provided. In addition, a method for producing thiophene and / or alkylated thiophene is also provided. definition

[0023] In this discussion, zeolite is defined as a crystalline material having a porous framework structure consisting of tetrahedral atoms connected by bridging oxygen atoms. The example of a known zeolite framework is in "Zeolite Framework Atlas" (published on behalf of the International Zeolite Association Structure Committee) 6th edition revised edition, Ch.Baerlocher, LBMcCusker, DH Olson edited, Elsevier, New York (2007) and the corresponding website http: / / www.iza-structure.org / databases / Provided. In this discussion, zeolite generally refers to the crystalline structure of a zeolite framework with an oxide containing only silicon and aluminum. In this discussion, zeolite generally refers to the crystalline structure with a zeolite framework, which is a zeolite or may also include an oxide of heteroatoms different from silicon and aluminum. Such heteroatoms may include any heteroatoms generally known to be suitable for inclusion in a zeolite framework, such as gallium, boron, germanium, phosphorus, zinc and / or other transition metals that may replace silicon and / or aluminum in a zeolite framework. It is worth noting that according to this definition, zeolite can include materials such as silicoaluminophosphate (SAPO) materials, silicophosphate (SiPO) materials or aluminophosphate (AlPO) materials.

[0024] A support material that includes a zeolite framework structure (ie, a crystal structure corresponding to a zeolite framework) may be referred to as a zeolite support. Optionally, a zeolite support (eg, a zeolite support) may include one or more oxides as a binder material in the support.

[0025] In this discussion, alkali metals include metals of Group 1 of the IUPAC Periodic Table, including lithium, sodium, potassium, rubidium, and cesium. In this discussion, alkaline earth metals include metals of Group 2 of the IUPAC Periodic Table, including magnesium, calcium, strontium, and barium.

[0026] In the present discussion, alkylated thiophenes are defined as thiophenes that include one or more alkyl chains attached to the thiophene ring.

[0027] In this discussion, the Alpha value is a measure of the cracking activity of the catalyst and is described in U.S. Pat. No. 3,354,078 and Catalysis Journal, Vol. 4, p. 527 (1965); Vol. 6, p. 278 (1966); and Vol. 61, p. 395 (1980), each of which is incorporated herein by reference. The experimental conditions for the tests used herein include a constant temperature of 538° C. and a variable flow rate, as described in detail in Catalysis Journal, Vol. 61, p. 395.

[0028] In this discussion, "substituted thiophene" is defined as any derivative containing at least one thiophene ring. Thus, substituted thiophenes include alkylated thiophenes in which one or more alkyl carbon chains are attached to the thiophene ring. Substituted thiophenes also include oligomers of thiophene, such as compounds that may contain multiple thiophene rings and / or fused thiophene rings (e.g., benzothiophene). Substituted thiophenes also include other types of fused ring structures, such as benzothiophene. Thiophene synthesis conditions

[0029] In various aspects, thiophene synthesis can be performed by exposing a plurality of gas phase feedstocks to a thiophene synthesis catalyst. At least one feedstock can correspond to a thiophene containing C 4+ Alkane feedstocks such as n-butane, butane mixtures, n-pentane, mixtures of n-butane and n-pentane, mixtures of butane and pentane, n-hexane, and / or any other convenient combination of alkanes containing 4 or more carbon atoms. 4+ Alkanes can correspond to any convenient combination of normal alkanes and branched alkanes (i.e., alkanes containing at least one branch but not comprising a ring structure). In some aspects, branched alkanes can correspond to 25 wt % or less of the total weight of alkanes in the gas phase feedstock, or 10 wt % or less, or 5.0 wt % or less, or 1.0 wt % or less, such as being as low as substantially free of branched alkanes. In some aspects, a variety of gas phase feedstocks can include 10 wt % or less of the total weight of alkanes in the gas phase feedstock. 5+ hydrocarbons, or 5.0 wt % or less, or 1.0 wt % or less, such as down to substantially free of C 5+ In some aspects, C 4+ Alkanes can correspond to C4 to C 16 Alkanes, C4 to C 12 Alkanes or C4 to C8 alkanes.

[0030] In some aspects, a plurality of gas phase feedstocks may include 50 wt % or more of alkanes, or 75 wt % or more, or 90 wt % or more, or 95 wt % or more, or 99 wt % or more relative to the total weight of hydrocarbons in the gas phase feedstock, for example, until alkanes are substantially the only hydrocarbons in the gas phase feedstock. Additionally or alternatively, in some aspects, a plurality of gas phase feedstocks may include 50 wt % or more of normal alkanes, or 75 wt % or more, or 90 wt % or more, or 95 wt % or more, or 99 wt % or more relative to the total weight of hydrocarbons in the gas phase feedstock, for example, until normal alkanes are substantially the only hydrocarbons in the gas phase feedstock. In addition, additionally or alternatively, in some aspects, a plurality of gas phase feedstocks may include 50 wt % or more of normal butane, or 75 wt % or more, or 90 wt % or more, or 95 wt % or more, or 99 wt % or more relative to the total weight of hydrocarbons in the gas phase feedstock, for example, until normal butane is substantially the only hydrocarbon in the gas phase feedstock.

[0031] Optionally, the plurality of raw materials may also include C 4+ In some aspects, relative to the total hydrocarbons in the input stream, C 4+ The olefins may correspond to 25 wt % or less, or 10 wt % or less, or 5.0 wt % or less, or 1.0 wt % or less of the input stream, for example, until there are substantially no olefins in the gas phase feed. 4+ The olefin may correspond to n-butene (corresponding to 1-butene, cis-2-butene, trans-2-butene or a combination thereof), isobutene, n-pentene, isopentane, n-hexene and / or any other convenient combination of n-olefins and branched olefins. 4+ The olefin may include a diene.

[0032] In addition, at least one feedstock may correspond to a gaseous source of sulfur. The gaseous source of sulfur may include, but is not limited to, H2S, CS2, S2, and / or other forms of sulfur that may be present in a gaseous stream at temperatures close to the thiophene synthesis reaction temperature.

[0033] Multiple gaseous raw materials can be introduced into the reactor as a single stream, or gaseous raw materials can be introduced as multiple streams. Reactor volume (or a part thereof) can be used as the reaction environment of thiophene synthesis reaction. Optionally, when multiple streams are introduced into the reaction environment, different input streams can have different compositions. For example, a selection can be to have a first feed stream comprising one or more alkanes and a second feed stream comprising one or more gaseous sulfur sources. Any convenient type of container can be used as a reactor, as long as the container is suitable for the reactant in the reaction environment to be maintained under synthesis conditions and to keep the average synthesis residence time.

[0034] In various aspects, the molar ratio of sulfur atoms in the reaction environment to hydrocarbons in the reaction environment can be from 0.9 to 30 (i.e., ranging from 0.9 moles of sulfur atoms per mole of hydrocarbon to 30 moles of sulfur atoms per mole of hydrocarbon). In some aspects, the molar ratio of sulfur atoms in the reaction environment to hydrocarbons can be from 0.9 to 30, or from 0.9 to 15, or from 0.9 to 10, or from 1.0 to 30, or from 1.0 to 15, or from 1.0 to 10, or from 1.5 to 30, or from 1.5 to 15, or from 1.5 to 10, or from 2.5 to 30, or from 2.5 to 15, or from 2.5 to 10. Additionally or alternatively, the molar ratio of H2S to hydrocarbon in the reaction environment can be from 0.9 to 15, or from 0.9 to 10, or from 1.0 to 15, or from 1.0 to 12, or from 1.0 to 10, or from 1.5 to 15, or from 1.5 to 10, or from 2.5 to 15, or from 2.5 to 10.

[0035] In the reaction environment, the average residence time can be 0.01 second to 100 seconds, or 0.1 second to 100 seconds, or 1.0 second to 100 seconds, or 0.01 second to 50 seconds, or 0.1 second to 50 seconds, or 1.0 second to 50 seconds, or 0.01 second to 10 seconds, or 0.1 second to 10 seconds, or 1.0 second to 10 seconds. The temperature in the reaction environment can be 450°C to 750°C, or 450°C to 650°C, or 450°C to 600°C, or 450°C to 550°C, or 500°C to 750°C, or 500°C to 650°C, or 500°C to 600°C, or 550°C to 750°C, or 550°C to 650°C. The pressure in the reaction environment can range from 0 kPa-g to 1750 kPa-g, or 0 kPa-g to 1050 kPa-g, or 0 kPa-g to 350 kPa-g, or 15 kPa-g to 1750 kPa-g, or 15 kPa-g to 1050 kPa-g, or 15 kPa-g to 350 kPa-g, or 150 kPa-g to 1750 kPa-g, or 150 kPa-g to 1050 kPa-g, or 150 kPa-g to 350 kPa-g.

[0036] Exposure of a feedstock corresponding to a gas phase sulfur source and a feedstock including an alkane (e.g., n-butane) to a thiophene synthesis catalyst may result in the production of thiophene along with byproducts and / or unreacted reagents. The reaction products may include, but are not limited to, thiophene and / or alkylated thiophene; coke; 4- or C 3- Hydrocarbon purge stream; C4 to C 10 Hydrocarbons (including unreacted C 4+ hydrocarbons); one or more sulfur compounds (e.g., H2S, CS2, S2 and / or other forms of gas phase sulfur; and C 10+ Hydrocarbon. C 10+ The hydrocarbons may, for example, be sent to a hydrotreater to produce fuels.10 The hydrocarbons may be used, for example, as light alkane products; may be recycled back to the reactor; or may be separated before recycling to the reactor to at least partially separate the olefins from C4 to C 10 It is worth noting that other choices can be made as to which hydrocarbons are recycled rather than sent to hydroprocessing to form fuel. For example, the intermediate hydrocarbon stream (optionally for recycling) can correspond to a C4 to C6 stream, or a C4 to C8 stream, or a C4 to C 10 Flow, or C4 to C 12 Flow, or C4 to C 16 Depending on the hydrocarbons selected for inclusion in the lighter hydrocarbon stream, the hydrocarbons used for fuel production may correspond to C 6+ Hydrocarbons, or C 8+ Hydrocarbons, or C 10+ Hydrocarbons, or C 12+ Hydrocarbons, or C 16+ Yet another option is to separate the hydrocarbons into more fractions. In some aspects, depending on the separation efficiency, the "heavy" stream sent to hydroprocessing to produce fuels may not have any overlap in composition with the recycle stream. For example, if the recycle stream corresponds to a C4 to C8 stream, the "heavy" stream may optionally correspond to a C4 to C8 stream. 9+ The flow of compounds, where C 8- The content is 5.0 wt% or less, or 1.0 wt% or less, for example, as low as substantially free of C 8- hydrocarbon.

[0037] During the thiophene synthesis reaction, some sulfur is consumed to produce thiophene and / or alkylated thiophene. Since thiophene synthesis conditions generally include a stoichiometric excess of sulfur, at least a portion of the reaction products (including unreacted reagents) may generally correspond to certain types of sulfur-containing compounds. For example, in the reaction product streams identified above, one or more purge or light hydrocarbon streams (e.g., C 4- ), intermediate hydrocarbons (e.g. C4-C 10 ) and heavy hydrocarbon streams (e.g. C 10+ ) may include sulfided organic compounds. Due to the atomic weight of sulfur, this may result in some mixing of the carbon numbers present in the stream. For example, C8 sulfided compounds may correspond to separation into C 10+ Fraction of compounds. Reaction products and further processing

[0038] After thiophene synthesis is performed, various portions of the reaction products may be subjected to some type of further processing. One type of further processing may be to perform one or more separations to recover thiophene and / or alkylated thiophene from the remaining reaction products and / or unreacted reagents. The separation may also produce one or more additional streams, such as light hydrocarbons (C 3-) streams, intermediate hydrocarbons (e.g. C4-C 10 hydrocarbons) streams, heavier hydrocarbons (such as C 10+ CS2 may also be a reaction byproduct. A large amount of coke is also formed.

[0039] Another type of further processing can be to use the reaction product effluent as a feed for carbon nanotube synthesis. In some aspects, the separated thiophene and / or alkylated thiophene fractions can be used. In other aspects, intermediate hydrocarbons (C4-C 10 ) and / or heavier hydrocarbons (C 10+ ) as part of the feed for carbon nanotube synthesis. It should be noted that the separation of thiophene, substituted thiophene and hydrocarbons only needs to be carried out to such an extent that these compounds are not contained in the feed for carbon nanotube synthesis. Configuration Example

[0040] Figure 1 An example of a reaction system configuration for producing thiophene is shown. Figure 1 In the reactor 20, a feedstock 11 containing alkanes (e.g., n-butane or normal alkanes) and a gas phase sulfur feedstock 12 corresponding to S2 (and / or other gas phase molecules containing only sulfur) may be introduced. Figure 1 In the illustrated configuration, feedstock 11 and vapor-phase sulfur feedstock 12 are shown as separate input streams. In other aspects, any convenient number of input streams may be used to introduce feedstock 11 and vapor-phase sulfur feedstock 12 into reactor 20. In addition to feedstock 11 and vapor-phase sulfur feedstock 12, one or more recycle streams may optionally be introduced into reactor 20. Figure 1 In the configuration shown, the circulating stream includes the H2S circulating stream 39, the H2S supplementary stream 19 and the C 4+ Hydrocarbon recycle stream 31 .

[0041] Reactor 20 may be used to carry out a thiophene synthesis reaction. The effluent 25 from the reaction may then be sent to one or more separation stages. Figure 1 In the embodiment of the present invention, one or more separation stages are represented by a fractionator 30. Figure 1 In the example configuration shown, a fractionator 30 may be used to separate the effluent 25 into a plurality of streams. This may include a hydrocarbon recycle stream 31, an H2S recycle stream 39, light hydrocarbons (C 4- or C 3- ) a purge stream 33, a product stream 35 comprising thiophene and / or alkylated thiophene, and a heavy hydrocarbon stream 37 containing hydrocarbons having a boiling point (on average) higher than that of the hydrocarbons in the hydrocarbon recycle stream 31.

[0042] Reaction system configuration (e.g. Figure 1The configuration shown in Figure 1 can be integrated with a larger overall synthesis scheme. For example, the reaction system for thiophene synthesis can be integrated with the reaction system for methane pyrolysis and carbon nanotube production.

[0043] Figure 2 An example of a system for methane pyrolysis and carbon nanotube production is shown. Figure 2 , reactor 100 corresponds to a reactor for forming carbon nanotubes. Reactor 100 may include a pyrolysis zone or portion 110 and a carbon nanotube formation zone or portion 120. During operation, a heated gas stream 175 may be introduced into the beginning of the pyrolysis zone 110 of reactor 100 via a hot gas flow conduit. The temperature of heated gas stream 175 may be 1000°C or higher, or 1100°C or higher, or 1200°C or higher. Reactant stream 170 may be added to heated gas stream 175 before entering reactor 100 (i.e., in the heated gas flow conduit) or after entering reactor 100. Figure 2 In the example shown, the reaction stream 170 includes a catalyst precursor for a catalyst for forming carbon nanotubes and a portion of hydrocarbons for pyrolysis. Alternatively, the catalyst precursor and the hydrocarbons for pyrolysis can be introduced as separate streams. Optionally, a secondary heated gas stream 176 can be used to introduce hydrocarbons 180 for pyrolysis at a downstream position within the pyrolysis zone 110. In some aspects, substantially all of the hydrocarbons introduced into the reactor can be used as part of the secondary heated gas stream 176. In some aspects, an additional hydrocarbon stream 185 for generating free radicals in the reactor can be added to the hydrocarbons 180.

[0044] In various aspects, at least a portion of the organic compounds in reactant stream 170 can correspond to thiophenes, substituted thiophenes, and / or hydrocarbons from the reaction product effluent of thiophene synthesis. Using the reaction product effluent (or a portion thereof) of thiophene synthesis can provide a variety of benefits. For example, the reaction product effluent contains thiophenes and / or substituted thiophenes and, therefore, contains sulfur required to form an in situ catalyst for carbon nanotube synthesis.

[0045] In some aspects, the metal used to form the in-situ catalyst can be introduced as part of a recovery process, which involves recovering the metal previously used to form the carbon nanotube. When using a method involving a catalyst (e.g., FC-CVD catalyst) to synthesize carbon nanotubes, the synthesized carbon nanotubes can contain metal nanoparticles within and / or as part of the nanotube structure. Acid treatment can be used to recover these metal nanoparticles from the nanotubes. For example, the nanotubes can be refluxed with nitric acid in a series of stages while increasing the nitric acid concentration to separate the carbon nanotubes from the incorporated metal. This metal recovery process keeps the carbon nanotubes substantially intact during the separation process. Solid metals can then be recovered from the nitric acid. After the metal is recovered, the metal can be ground into a powder and then mixed with a portion of the carbon nanotubes in a convenient solvent (e.g., acetone). The solutions can be mixed and then heated in a closed container to form a metal catalyst supported on the nanotubes. The supported catalyst can then be used as at least a portion of a metal precursor to form an in-situ FC-CVD catalyst. An example of such a metal recovery and recycling procedure is described in Wang et al., Cat. Sci. Technol. Vol. 11, pg 4911 (2021). More generally, any convenient similar method can be used to recover metals from carbon nanotubes and form a recycled catalyst involving recovered metals and carbon nanotubes. Additionally or alternatively, the metal can be introduced as a reagent, for example by adding ferrocene to a heated gas stream.

[0046] Once in the reactor, the reactants in the heated gas stream can react. The catalyst precursor can react to form a catalyst for carbon nanotube formation. The hydrocarbons can be pyrolyzed to form H2 and carbon atoms. These can be carried from the pyrolysis zone 110 to the carbon nanotube formation zone 120 by the gas stream within the reactor 100. Figure 2 In the example shown, quench stream 130 is introduced to cool the gas stream prior to entering carbon nanotube formation zone 120. In this example, the location of quench stream 130 defines the end of pyrolysis zone 110 and the beginning of quench zone 135. Optionally, steam 140 may be introduced after quench stream 130 to assist in gasifying amorphous carbon present in the gas stream.

[0047] exist Figure 2 In the example shown, the carbon nanotube region 120 corresponds to at least a portion of the shell of a shell and tube heat exchanger. The tubes 122 of the shell and tube heat exchanger include a heat transfer fluid 150 for cooling the gas flow in the carbon nanotube formation zone to a temperature of 800° C. or less. Figure 2In the example shown, the heat transfer fluid 150 can be a gas used in heating the gas stream 175, such as nitrogen and / or hydrogen. For example, when hydrogen is used as the gas for heating the gas stream 175, the use of hydrogen as the heat transfer fluid 150 can heat the hydrogen to a temperature between 500° C. and 700° C. to form partially heated hydrogen 155. Optionally, the hydrogen used for the heat transfer fluid 150 can correspond to hydrogen recovered from the product 115. The partially heated hydrogen 155 can then be transferred to the heater 160 to form heated hydrogen 165. The heated hydrogen 165 can then be used to form the heated gas stream 175 and the optional secondary heated gas stream 176.

[0048] As Figure 2 As an alternative to the type of configuration shown in , in certain aspects, the heat transfer fluid of the heat exchanger can be used to provide recovered heat energy to generate steam and / or generate electricity.

[0049] exist Figure 2 In the example shown, the array of tubes for reducing gas flow turbulence may correspond to the tubes 112 interspersed between the tubes 122 of the shell and tube heat exchanger. After passing through the tubes, various products 115 may exit the reactor. The products 115 may include H2 formed during the pyrolysis process, carbon nanotubes, gases from the heated gas stream 175 that has passed through the reactor 110, and unreacted hydrocarbons.

[0050] It is worth noting that Figure 2 The elements shown in can also be described with respect to the ability of a fluid to pass from one element to the next. Such fluid communication between elements in a reaction system and / or reactor is defined as the ability of a fluid to pass from a first element to a second element. Fluid communication can correspond to direct fluid communication or indirect fluid communication. Figure 2 In the example shown in FIG. 1 , the pyrolysis zone 110 is in direct fluid communication with the quench zone 135. The pyrolysis zone 110 is in indirect fluid communication with the array of tubes 112 through the quench zone 135.

[0051] Thiophene synthesis reaction system (e.g. Figure 1 The configuration shown) and the carbon nanotube synthesis reactor (eg Figure 2 There are various options for integration of the thiophene product (e.g. Figure 1 The thiophene product 35) is used as Figure 2 The thiophene source in the reactant stream 170. The thiophene can be used in combination with ferrocene and / or recycled nanotubes and / or additional carbon nanotubes to form a floating catalyst-chemical vapor deposition (FC-CVD) catalyst for catalyzing the formation of nanotubes. More generally, at least a portion of the thiophene product 35 and / or heavy hydrocarbons 37 and / or light hydrocarbon purge 33 can be used as Figure 2The light hydrocarbon purge can provide a carbon source for the pyrolysis reaction prior to nanotube formation. In addition, in some alternative aspects, heat integration between thiophene synthesis and carbon nanotube formation can be provided by forming thiophene in situ in a reactor for forming carbon nanotubes. Carbon Nanotube Formation - Initial Heating and Catalyst Formation

[0052] In various aspects, systems and methods for producing carbon nanotubes and H2 using a reaction system configuration suitable for large-scale production are provided. In the reaction system, most of the heat of the reaction can be provided by using a heated gas stream. Optionally, the heated gas stream can correspond to a heated H2 gas stream. By using a heated gas stream, when a catalyst precursor of a floating catalyst-chemical vapor deposition (FC-CVD) type catalyst is added to the gas stream, the temperature of the gas stream can reach 1000°C or higher. This can reduce or minimize the loss of catalyst precursor material and / or the deposition of coke on the sidewall of the reactor. In addition, the downstream portion of the reactor can include a plurality of reduced-size flow channels that pass through a heat exchanger environment, such as a shell and tube heat exchanger. This can provide cooling of the gas stream after the catalyst is formed to allow the formation of carbon nanotubes, while also fully reducing the Reynolds number of the flow to provide laminar flow in the region where the carbon nanotubes are formed.

[0053] In various aspects, reactors, reaction systems, and methods of operating reactors / reaction systems are provided that can overcome various challenges of forming carbon nanotubes in larger scale reactors. With respect to managing the addition of heat to achieve a temperature for pyrolysis of methane (or other hydrocarbons), a heated gas stream can be used to heat the reactor. The gas stream can be heated to a desired temperature before being introduced into the reactor. Then, various reactants (e.g., thiophene, substituted thiophenes, and / or hydrocarbons (for pyrolysis) and catalyst precursors (e.g., thiophene, substituted thiophenes, carbon nanotubes used as metal supports recovered from previously synthesized nanotubes, and / or reagents such as ferrocene) can be introduced into the gas stream at a location within the reactor, or close enough to the starting location of the reactor so that catalyst formation and / or methane pyrolysis occurs substantially within the reactor. It is noteworthy that after the reactants are introduced using one or more gas streams, the gas stream volume of the reactants (e.g., thiophene, hydrocarbons, catalyst precursors) is about a few percent relative to the total volume of the heated gas stream and reactants. Therefore, even if the reactant gas stream is not heated or only slightly heated before introduction into the reactor, the much larger volume of the heated gas stream can quickly heat the reactants. In some aspects, the heated gas stream can correspond to a hydrogen gas stream, such as hydrogen produced by the pyrolysis process. In other aspects, at least a portion of the heated gas stream can correspond to a gas that is substantially non-reactive under pyrolysis conditions, such as N2 or Ar. Optionally, the walls of the reactor can also be heated to supplement the thermal energy of the heated gas stream.

[0054] Using a heated gas stream to heat the reactor can also provide unexpected benefits. By heating the heated gas stream to a temperature above 1000°C before entering the reactor, the gas stream is at a temperature above 700°C-900°C when it contacts the catalyst precursor. Since the volume of the catalyst precursor is small relative to the volume of the heated gas stream, the catalyst precursor can be quickly heated to a temperature of 1000°C or more. Due to this rapid heating, the catalyst precursor experiences a temperature of 700°C to 900°C in a few milliseconds or less. Therefore, metal deposition of the catalyst precursor on the upstream portion of the reactor wall is reduced or minimized because the catalyst precursor does not stay at a temperature between 700°C and 900°C for a sufficient time to promote such deposition. This also has the additional benefit of reducing or minimizing any carbon deposition because there are no metal deposits that nucleate carbon deposition.

[0055] With regard to managing the removal of heat after pyrolysis is performed so that the pyrolysis products and the in-situ catalyst can react to form carbon nanotubes, a heat exchanger can be used to reduce the temperature of the pyrolysis product gas stream. An example of a suitable heat exchanger design is a shell and tube heat exchanger. In this design, multiple conduits can pass through the shell of the reactor. This can reduce the temperature within the shell to the level required for carbon nanotube formation.

[0056] With respect to flow management, the reactant stream is injected into the reactor in such a manner that the fluid in the initial portion of the reactor is turbulent, with a Reynolds number of 2000 or more, or 5000 or more, or 8000 or more, such as up to 20,000 or possibly higher. Depending on the design of the reactor, this initial turbulent flow can be converted to essentially laminar flow (Reynolds number less than 2000) in subsequent portions of the reactor. In areas where the fluid needs to be cooled to allow the formation of carbon nanotubes, the fluid can be passed to a shell and tube heat exchanger section. The "shell" portion of the heat exchanger is the portion of the heat exchanger that receives the internal reactor flow. The shell portion can be divided into a large number of flow channels. Dividing the fluid into multiple flow channels can provide several advantages. First, the diameter of each flow channel can be greatly reduced. Second, the total cross-sectional area available in the reactor to receive the fluid can be reduced, resulting in a net increase in flow rate. The combination of forcing the fluid into a smaller pipe at a higher velocity can greatly reduce the Reynolds number of the fluid so that the initial turbulent flow can be converted into multiple laminar flows in the flow channels.

[0057] It is important to note that the calculation of the Reynolds number is a well-known procedure based on a few pieces of data that are usually readily available. Equation (1) shows the calculation method for determining the Reynolds number. (1)

[0058] In formula (1), ρ is the density of the fluid, v is the velocity of the fluid, l is the characteristic distance (in this case, the diameter of the pipe), μ is the dynamic viscosity of the fluid, and ν is the kinematic viscosity of the fluid. As shown in formula (1), the Reynolds number can be calculated using either the dynamic or kinematic viscosity, depending on which method is more convenient.

[0059] In various aspects, the Reynolds number can be calculated at a convenient location in the reactor based on the following method. First, the flow rate in the reactor can be determined using a mass balance. The velocity at any given location can then be determined based on the mass flow rate, the pressure in the reactor, and the average diameter of the flow path in the reactor at that location. It is worth noting that in the second half of the reactor, the average diameter of the flow path corresponds to the diameter of each tube in the shell and tube section. The average diameter also corresponds to the characteristic length "l" of formula 1. For viscosity, the average composition of the gas flow in the reactor can be determined based on the input flow. The required viscosity of the average composition can then be determined based on standard values ​​(and based on the temperature at a given location in the reactor). Based on the calculation of the Reynolds number at each location, the mass flow rate entering the reactor can be determined so that the initial stage has sufficient turbulence, and the subsequent stage can have sufficient laminar flow.

[0060] In this discussion, a reactor is described that includes a pyrolysis section or zone and a carbon nanotube formation section or zone. In this discussion, the beginning of the carbon nanotube formation section or zone is defined as the location where the gas flow in the reactor enters the array of smaller diameter gas flow tubes located within the shell and tube heat exchanger portion of the reactor. It is worth noting that the smaller diameter gas flow tubes are located within the "shell" portion of the heat exchanger. The "tube" portion of the heat exchanger in this design contains a heat transfer fluid and is not part of the gas flow path for carbon nanotube formation. The end of the pyrolysis zone is defined as a) the beginning of the carbon nanotube formation section or zone, or b) if one or more quench streams are introduced into the heated gas flow, the gas flow is located downstream of exposing the hydrocarbons to 1000°C or higher temperatures, but upstream of the beginning of the carbon nanotube formation section or zone, then the location of the quench stream corresponds to the end of the pyrolysis zone. If the quench stream is introduced to multiple locations, the farthest upstream location is the end of the pyrolysis zone. It is worth noting that if a quench stream is present, the quench zone can exist between the end of the pyrolysis zone and the beginning of the carbon nanotube formation zone. The length of this quench zone can be selected to control the size and / or distribution of the nucleation catalyst particles that promote carbon nanotube growth.

[0061] The reaction system for carbon nanotube formation can perform at least three types of reactions. One reaction is the in situ formation of a catalyst for forming carbon nanotubes. The second reaction is the pyrolysis of thiophene, substituted thiophenes and / or other hydrocarbons (such as methane) to provide H2 and carbon for forming carbon nanotubes. It is worth noting that thiophene also provides sulfur for in situ catalyst formation. The third reaction is the formation of carbon nanotubes on re-nucleation catalyst particles formed in situ. The various reactions can be managed by controlling the temperature of various regions of the reactor.

[0062] The catalyst for forming the carbon nanotubes may correspond to a floating catalyst-chemical vapor deposition (FC-CVD) type catalyst. Some examples of suitable FC-CVD catalysts are catalysts formed in situ by decomposing appropriate precursors. For example, one option for forming a FC-CVD catalyst is to use ferrocene and thiophene precursors. Another option may be to use thiophene (and / or substituted thiophene) to provide sulfur and use carbon nanotubes as a metal source for the catalyst. Thiophene is at least partially decomposed at about 500°C, while ferrocene is decomposed at about 750°C. Carbon nanotubes are decomposed at about 900°C. Iron sulfide and Fe(CO)5 are other examples of iron-based precursors that can be used to form FC-CVD catalysts. More generally, FC-CVD catalysts may include iron, cobalt, nickel and / or palladium. General examples of metal precursors may include acetylene precursors, cyclopentadiene precursors and catalytic metals supported on (optionally recycled) carbon nanotubes. In order to form the catalyst, the precursors are decomposed and mixed to form the catalyst. Mixing can be performed in any convenient manner. This can include, for example, injecting the precursor stream at an angle relative to the direction of flow in the reactor to assist in mixing; inserting internal structures to help create turbulence to promote mixing; using various types of nozzles to disperse the precursor stream in the gas flow within the reactor; and / or any other convenient method. The catalyst is then cooled to a temperature of about 600°C to 800°C to allow carbon nanotubes to form. Within such a temperature range, the catalyst can serve as a nucleation site for the formation of carbon nanotubes. It is worth noting that the term "catalyst" is used to describe the FC-CVD catalyst because it facilitates the formation of carbon nanotubes. However, it is understood that at least a portion of the FC-CVD catalyst is consumed during the formation process because at least a portion of the iron is incorporated into the nanotube structure during the synthesis process. In this discussion, the term "catalyst" is defined to include materials that function in the manner of a FC-CVD catalyst.

[0063] To avoid adverse side effects, such as deposition of metals and / or coke on the sidewalls of the reactor, catalyst precursors (e.g., thiophene and ferrocene) can be injected into the heated gas stream after the gas stream is already at a temperature of 1000°C or higher. This can avoid the difficulty in controlling the decomposition of the catalyst precursor when the catalyst precursor is heated from a temperature of 500°C or less to 1000°C or higher. By injecting the precursor into the heated gas stream at a temperature of 1000°C or higher, the time that the catalyst precursor is at a temperature between 500°C and 1000°C can be reduced or minimized. During the injection of the catalyst precursor, the temperature of the heated gas stream can be 1000°C or higher, or 1100°C or higher, or 1200°C or higher, such as up to 1600°C or possibly higher.

[0064] In other aspects, when methane or another hydrocarbon stream is used as at least a portion of the hydrocarbons for forming carbon nanotubes, substantially all of the methane / other hydrocarbon can be introduced into the reactor downstream of the catalyst formation zone. This can allow the FC-CVD catalyst (or other catalyst) to be present when methane pyrolysis begins to occur, thereby reducing or minimizing the amount of pyrolysis that occurs in the absence of the catalyst. This can increase the likelihood of carbon nanotube formation because any methane that is pyrolyzed in the absence of the FC-CVD catalyst is more likely to result in coke formation rather than carbon nanotube formation. Alternative Thiophene Synthesis and Catalyst Formation - In situ Thiophene Synthesis in a Reactor for Nanotube Formation

[0065] One option to integrate thiophene synthesis and carbon nanotube formation is by having separate reaction vessels for thiophene synthesis and nanotube formation. Another option is to synthesize thiophene in situ. This can improve thermal integration in combination with the use of metals supported on nanotubes as the catalyst metal source.

[0066] The above-mentioned thiophene synthesis conditions include a temperature range of about 450°C to 750°C. Although this is an effective range for thiophene synthesis, the limitation on the upper limit of this temperature range is partly due to considerations related to how to construct the reactor. In particular, limiting the temperature to 750°C or lower can allow the use of typical metal types for reactor construction in refinery or chemical plant environments to synthesize thiophene. However, thiophene synthesis can still be carried out at higher temperatures, such as temperatures of 750°C to 1200°C, or 900°C to 1200°C, or 950°C to 1200°C, or 1000°C to 1200°C, or 750°C to 1100°C, or 900°C to 1100°C.

[0067] In some aspects, rather than forming thiophene in a separate vessel and then feeding the thiophene-containing reaction product into the vessel used for carbon nanotube formation, thiophene can be synthesized in the vessel used for carbon nanotube formation. The thiophene synthesis reaction is exothermic. By performing thiophene synthesis in the same reactor vessel as carbon nanotube synthesis, the heat generated by thiophene synthesis can be used as part of the heat required for the subsequent pyrolysis reaction to form carbon and H2.

[0068] In terms of thiophene synthesis and carbon nanotube formation being carried out in the same reactor, similar methods can still be used. Figure 2 configuration, but modifies the flow into the reactor vessel. Therefore, reference can be made to Figure 2 This alternative synthesis approach with improved heat integration is illustrated.

[0069] In aspects where thiophene synthesis is performed in the same reactor as carbon nanotube formation, reactant stream 170 may include a catalytic metal supported on carbon nanotubes as a support, plus at least a portion of the hydrocarbon for pyrolysis. However, thiophene need not be included in reactant stream 170. Instead, a thiophene-forming precursor may be added to reactor 100 at a location (not shown) downstream of where reactant stream 170 enters reactor 100 but upstream of pyrolysis zone 110. As described above, the thiophene-forming precursor may include at least one vapor-phase sulfur source and C 4+ The thiophene synthesis catalyst may be located at or near the location where the thiophene precursor is introduced into the reactor 100. The thiophene synthesis reaction may then be conducted in the presence of the heated gas stream 175 mixed with the reactant stream 170.

[0070] By performing thiophene synthesis within reactor 100, the heat generated during thiophene formation can be at least partially consumed by the surrounding gas phase environment, thereby increasing the temperature of the mixture of heated gas stream 175 and reactant stream 170 passing through reactor 100. Thus, the heat generated by thiophene synthesis can be at least partially used to provide heat for subsequent hydrocarbon pyrolysis in region 110 of reactor 100. After thiophene is formed, thiophene (or at least sulfur from thiophene) can combine with catalytic metals in reactant stream 170 to form a catalyst for carbon nanotube formation.

[0071] In some aspects, by integrating thiophene synthesis with carbon nanotube formation, additional heat generated in situ in the reactor can reduce the amount of heat that needs to be added using heater 160 while still maintaining a target temperature for heated gas stream 170. In these aspects, the temperature of heated gas stream 170 after thiophene synthesis but before entering pyrolysis zone 110 can be 20° C. or more, or 40° C. or more, or 60° C. or more, such as up to 100° C. or possibly higher, than the temperature of heated gas stream 170 before entering reactor 110. After synthesizing thiophene, reactant stream 170 can enter pyrolysis zone 110. Carbon Nanotube Formation - Hydrocarbon Pyrolysis and Reactor Heating

[0072] Although the pyrolysis of some hydrocarbons can occur at temperatures below 1000°C, in order to achieve a conversion rate (pyrolysis) of more than 50% of methane and / or other hydrocarbons in the reactor, the temperature in the pyrolysis environment can be 1000°C or higher, or 1100°C or higher, or 1200°C or higher, such as up to 1600°C or possibly higher. As described above, this temperature can be achieved in the reactor by using a heated gas stream. Optionally, some supplementary heating of the reactor wall can also be performed. In these optional aspects, the amount of this supplementary heating can be characterized relative to the thermal energy content of the heated gas stream. In this discussion, the thermal energy content of the heated gas stream is defined as the thermal energy required to heat the gas stream composition from 25°C to the temperature of the heated gas stream when entering the reactor. Based on this definition of the thermal energy content of the heated gas stream, the thermal energy (i.e., power) added to the reactor per unit time can be determined. The average thermal energy per unit time added to the reactor by heating the sidewalls can correspond to 20% or less, or 10% or less, or 5% or less of the thermal energy content of the heated gas stream per unit time, for example, until there is substantially no thermal energy added to the reactor by the reactor sidewalls. In aspects where reactor wall heating is used, such supplemental heating can further reduce or minimize the formation of deposits on the reactor walls.

[0073] In some aspects, the heated gas stream for heating the reactor can correspond to a substantially non-reactive gas stream relative to the catalyst precursor and the hydrocarbon for pyrolysis. The example of substantially non-reactive gas can include N2 and Ar. In other aspects, the hydrogen produced by the pyrolysis process (or optionally another hydrogen source) can be used at least in part as the heated gas stream. In these aspects, the H2 in the heated gas stream can be 20 volume % or more of the heated gas stream, or 40 volume % or more, or 60 volume % or more, or 80 volume % or more, such as up to a heated gas stream (95 volume % or more, such as up to 100 volume %) consisting essentially of hydrogen.

[0074] Optionally, when a H2-containing gas is used, the H2-containing gas may also include CO, such that the H2-containing gas corresponds to synthesis gas. The synthesis gas may also optionally contain water and / or CO2. Optionally, CO, CO2 and / or ethanol may be added to the H2-containing gas, depending on the type of FC-CVD catalyst formed in situ.

[0075] In some aspects, using a H2-containing gas as a heating gas stream can provide additional advantages to further reduce or minimize carbon deposition within the reactor. Under pyrolysis conditions, both carbon atoms and H2 are formed. Carbon atoms may tend to deposit on the surface of the reactor. However, having a H2-rich gas phase environment can reduce or minimize the tendency of carbon atoms to deposit on the surface and / or can promote the removal of carbon atoms that may be deposited on the surface. In such an environment, the increased amount of carbon can be retained in the gas phase in some form until the gas stream reaches a lower temperature in the carbon nanotube formation region.

[0076] One option for heating the gas stream may be to use multiple heating stages. For example, the initial heating stage may correspond to a furnace for heating the reactor, such as a furnace type used in a steam cracking reaction system. Conventional furnaces can be used to heat the gas stream (e.g., a gas stream containing H2) to a temperature of about 1000°C or possibly higher. Additional heating can be provided by a variety of methods to further increase the temperature to 1100°C or higher, or 1200°C or higher. One option may be to use electrical heating to heat the walls of the pipe containing the gas stream. Although the reactor size is large, the pipe used to heat the gas stream before entering the reactor can be appropriately sized to allow effective heat transfer. Other options may include induction heating or plasma heating. Since pyrolysis is an endothermic process, the temperature of the gas stream can be reduced as the pyrolysis reaction proceeds. Therefore, it is ideal to heat the gas stream to a temperature above 1000°C so that when the endothermic pyrolysis process cools the gas stream, there is enough volume in the reactor above 1000°C. After the gas stream is cooled below 1000°C, some additional pyrolysis will still occur, but the reaction rate is slower.

[0077] Another option is to include an electric heating element in the gas flow. Silicon carbide is an example of a suitable material for forming an electric heating element. Examples of silicon carbide heating elements are manufactured by Sandvik Materials Technology of Hallstahammar, Sweden. Examples of other materials that may be used to form the heating element may include, but are not limited to, Fe / Cr / Al alloys; molybdenum; tungsten; silicon carbide; and combinations thereof.

[0078] After the gas stream is heated, the catalyst precursor and hydrocarbons for pyrolysis (e.g., a portion of the thiophene synthesis effluent, or methane / natural gas) can be added to the gas stream and / or reactor. Preferably, the catalyst precursor and hydrocarbons for pyrolysis can be added to the reactor. The flow rate of hydrocarbons for pyrolysis can correspond to 10 volume % or less of the total gas flow rate entering the reactor, or 5.0 volume % or less, or 3.0 volume % or less, such as as low as 1.0 volume %, wherein the total gas stream includes the heated gas stream, the hydrocarbons for pyrolysis, and the stream for the catalyst precursor. The volume of the stream of the catalyst precursor can correspond to 1.0 volume % or less of the total gas stream volume entering the reactor.

[0079] The stream of methane, a portion of the thiophene synthesis effluent, and / or other hydrocarbon / organic compounds entering the reactor may also be partially preheated to maintain the desired temperature in the reactor after the methane is mixed with the heated gas stream. In some aspects, the methane may be preheated to a temperature of 200°C to 500°C or 200°C to 400°C. If the catalyst precursor is mixed with the methane / thiophene synthesis effluent before entering the reactor, preheating the methane (or other hydrocarbon stream) to 500°C or less will reduce or minimize the decomposition of the catalyst precursor before mixing with the heated gas stream. Alternatively, if the catalyst precursor is introduced into the heated gas stream alone, the methane / thiophene synthesis effluent may be preheated to 200°C to 800°C, or 200°C to 600°C, or 400°C to 800°C.

[0080] In certain aspects, a portion of the methane stream / thiophene synthesis effluent can be supplemented with hydrocarbons that form free radicals under pyrolysis conditions. By forming free radicals, the temperature required for the pyrolysis of methane can be reduced. One option can be to introduce propane and / or butanes together with the methane feed. Propane and butane are typically provided as part of the "condensate" stream at a natural gas production site. Another option can be to use a free radical precursor that provides free radicals with a longer lifespan. Toluene is an example of a hydrocarbon that can provide stable free radicals in a pyrolysis environment. When additional hydrocarbons are used to provide free radicals in a pyrolysis environment, the amount of the additional hydrocarbons can be equivalent to 0.1 mol % to 5.0 mol % of the amount of methane introduced into the reactor.

[0081] In some aspects, hydrocarbons and / or catalyst precursors for pyrolysis can be mixed with the heated gas stream in the reactor. In other aspects, at least one of the hydrocarbons and catalyst precursors for pyrolysis can be mixed with the heated gas stream before entering the reactor. Optionally, a portion of the heated gas stream and / or a portion of the hydrocarbons for pyrolysis can be introduced into the reactor at a downstream position of the reactor relative to the flow direction. Introducing different portions of the gas stream at different positions in the reactor can help manage the reaction curve in the reactor. For example, by adding a portion of methane at a downstream position of the reactor, the amount of methane available for pyrolysis in the early part of the reactor can be reduced or minimized to further reduce the possibility of early carbon nanotube formation and / or early deposition of carbon on the reactor surface.

[0082] It is noteworthy that the gas velocity within the reactor can be relatively high. The velocity within the reactor can determine the residence time of the reactants in the pyrolysis zone. By combining high velocity, low concentration of hydrocarbons in the total flow (approximately 10 volume % or less) and temperatures above 1000°C, high conversion rates can be achieved with low residence times. Having a low residence time in the pyrolysis zone of the reactor can reduce or minimize carbon deposition on the reactor surface before the product reaches the carbon nanotube formation zone. In addition, since turbulence is conducive to the formation of in-situ FC-CVD catalysts in the early part of the reactor, having a relatively high velocity can reduce or minimize the possibility of any partial flow staying in the pyrolysis zone for a long time due to backmixing. In various aspects, the average residence time of the heated gas flow in the pyrolysis zone can range from 0.05 seconds to 5.0 seconds, or from 0.05 seconds to 1.0 seconds, or from 0.1 seconds to 5.0 seconds. Creating a Cooling Laminar Flow for Carbon Nanotube Formation

[0083] After the pyrolysis zone in the reactor, the gas stream containing the carrier gas (which may be H2), the pyrolysis products (including carbon atoms), and the catalyst for forming carbon nanotubes can have a Reynolds number of 2000 or more, or 4000 or more, such as up to 20,000 or possibly more. This indicates turbulence. The temperature can also still be close to the pyrolysis temperature of 800°C or more, or 900°C or more, or 1000°C or more. In order to effectively form carbon nanotubes, the temperature of the gas stream can be reduced to 750°C or less, or 700°C or less, and the Reynolds number of the flow can be reduced to less than 2000, so that the gas stream has laminar properties.

[0084] One option for cooling the gas stream can be to configure the carbon nanotube region of the reactor as a shell and tube heat exchanger. In a shell and tube heat exchanger, the gas stream enters the "shell" portion of the heat exchanger. A heat transfer fluid is passed through the tubes to allow rapid cooling of the gas stream containing the carrier gas, pyrolysis products, and a catalyst for forming carbon nanotubes. This can cool the gas stream to a temperature that is favorable for carbon nanotube formation, such as a temperature of 600°C to 800°C. In addition, within the heat exchanger, there can be a temperature gradient so that the gas stream continues to cool as the gas flows within the heat exchanger. Due to this variation, the temperature at the beginning of the tube array can be between 600°C and 800°C, while the temperature at the end of the tube array can be 10°C to 150°C, or 50°C to 150°C, or 10°C to 100°C, or 50°C to 100°C lower.

[0085] In some aspects, further cooling can be performed by adding a quenching stream to the gas stream. The quenching stream can correspond to H2, CH4, or another convenient stream. Preferably, the quenching stream can include a reduced or minimized amount of H2O. Adding a quenching stream can help cool the gas stream to the temperature required for nanotube production.

[0086] In terms of using a quench flow, a steam flow can be injected at a downstream location. Adding steam after the gas flow temperature is reduced to 800°C or less, or 750°C or less can allow the amorphous carbon to be gasified with little effect on any nanotubes. It is believed that amorphous carbon can be gasified in the presence of steam at 700°C or higher. In contrast, it is believed that temperatures of 900°C or higher are required to gasify carbon nanotubes using steam. Adding steam to gasify amorphous carbon can provide several benefits. First, amorphous carbon formed on catalyst particles can be removed, thereby providing additional clean nucleation sites for forming additional carbon nanotubes. In addition, to the extent that amorphous carbon may be formed as part of the carbon nanotube structure, such amorphous carbon can be removed. This can allow the production of carbon nanotubes with improved morphology.

[0087] In addition to cooling the airflow, the turbulence of the airflow can also be fully reduced to provide laminar flow. This can correspond to a Reynolds number of less than 2000, or 1950 or less, or 1500 or less, or 1000 or less, or 600 or less, for example, as low as Reynolds number 1. Turbulence can be reduced by providing a smaller flow tube array in the shell portion of the heat exchanger for receiving the airflow. The use of a smaller flow tube array can provide two separate methods to reduce turbulence in the airflow. First, the turbulence of the flow can be reduced by transferring the airflow from a larger diameter volume to a smaller diameter volume. Secondly, the flow cross-sectional area of ​​the flow tube array can be less than the cross-sectional area of ​​the pyrolysis portion of the reactor. This reduction in cross-sectional area means that the airflow velocity will increase because the net flow velocity in the reactor remains unchanged. By increasing the velocity while reducing the diameter of a single pipe through which the airflow passes, a significant reduction in the Reynolds number can be achieved.

[0088] Regarding tube size, the diameter of a single tube in the flow tube array can be smaller than the diameter of the pyrolysis reactor. The ratio of the average cross-sectional area available for gas flow in the reactor pyrolysis portion to the average diameter of a single tube in the flow tube array can be 10 or greater (i.e., 10:1 or greater), or 20 or greater, or 30 or greater, such as up to 100 or possibly greater. Regarding available cross-sectional area, the average cross-sectional area available for gas flow in the pyrolysis section of the reactor to the average cross-sectional area available for gas flow in the flow tube array can be 1.1 or greater (i.e., 1.1:1 or greater), or 1.5 or greater, or 2.0 or greater, or 3.0 or greater, such as up to 10 or possibly higher. It is worth noting that the increase in gas velocity will be substantially similar to the ratio of the cross-sectional area available for gas flow. In this discussion, the cross-sectional area available for gas flow at a certain position refers to the portion of the total cross-sectional area of ​​a pipeline or reactor that is open to gas flow and is connected to the volume fluid containing gas flow. Any internal structure in the reactor corresponds to the cross-sectional area / volume that is not available for gas flow.

[0089] It is worth noting that the total cross-sectional area of ​​the shell and tube heat exchanger portion of the reactor may be larger than the pyrolysis zone of the reactor. However, since the gas flow is delivered to the array of flow tubes within the shell and tube heat exchanger, the cross-sectional area of ​​the shell and tube heat exchanger is not as critical to the overall configuration.

[0090] After passing through the flow tube array, the product of the carbon nanotube formation process can be collected. In this final product recovery area, the flow leaving the reactor can be cooled to a temperature of about 100°C or less. The hydrogen formed by the pyrolysis reaction can be taken out as a gas phase product, together with any hydrogen originally present in the heated gas flow. The carbon nanotubes can be recovered in any convenient way. For example, the carbon nanotubes can form an aerogel, and a spinning process can be used to pull out macroscopic carbon fibers. As another example, a conveyor belt with a support or collection matrix can be provided in the carbon nanotube formation area. The nanotubes can be deposited on the collection matrix and then taken out of the nanotube formation area by the conveyor belt. The carbon nanotubes can then be recovered from the collection matrix, for example by scraping. A portion of iron can be incorporated into the carbon nanotubes. Any excess iron can form a deposit in the product recovery area.

[0091] From the perspective of yield, 90% by volume or more (or 95% by volume or more, such as up to 100% by volume) of the hydrocarbons entering the reactor can be converted into carbon and H2. For the carbon formed by pyrolysis, 90 mol% or more of the carbon atoms can enter the product recovery zone. For the iron in the ferrocene catalyst, 50% by weight or more (or 65% by weight or more, or 75% by weight or more, such as up to 100% by weight) of the iron can be transferred to the product recovery zone in the form of iron in the carbon nanotubes or a bulk iron-containing phase in the product recovery zone. As described above, the iron and / or other metals incorporated into the nanotubes can then be recovered for subsequent synthesis cycles, for example by separating the metals from the carbon nanotubes using acid treatment. Thiophene catalyst and synthesis method

[0092] In various aspects, thiophene synthesis can be carried out using a catalyst prepared by impregnating a zeolite support with chromium, calcining the impregnated support to form a catalyst precursor comprising chromium oxide, and then sulfiding the catalyst precursor to form a catalyst corresponding to the chromium sulfide supported on the zeolite support. In some aspects, if the zeolite support is substantially a zeolite in the form of an alkali metal and an alkaline earth metal before adding Cr, additional benefits can be achieved. Based on the presence of such a metal in the synthesis solution for forming a zeolite framework structure, such an alkali metal and / or an alkaline earth metal can be associated with the zeolite framework structure. After synthesis, ion exchange with an alkali metal is an example of this type of acid site neutralization, which can provide enhanced catalyst performance. Additionally or alternatively, an alkali metal can also be added during and / or after the Cr impregnation to neutralize the acid sites.

[0093] Without being bound by any particular theory, it is believed that the improved activity of the thiophene synthesis catalyst is related to the formation of chromium-sulfur compounds and / or complexes within the zeolite framework structure. Alkali metals and / or alkaline earth metals are associated with nearly all of the acid sites (90% or more) in the zeolite framework structure and appear to form Cr2S3 and / or Cr3S4 phases, which do not appear to form when chromium is simply deposited on an oxide substrate. Cr2S3 and Cr3S4 phases can be observed by XRD. In addition, after thiophene synthesis using the catalyst, layered chromium sulfide phases can be observed by transmission electron microscopy (TEM). These layered phases are believed to correspond to Cr2S3. In addition or alternatively, neutralization of the acid sites with alkali metals can provide stability to chromium sulfides with higher chromium oxidation states. Cr2S3 and Cr3S4 are examples of chromium sulfides with higher chromium oxidation states.

[0094] In various aspects, the unexpectedly improved activity for thiophene (including alkylated thiophene) synthesis and / or the reduction in coke production during thiophene synthesis may be attributed in part to a catalyst having an average stoichiometric ratio of sulfur to chromium in the catalyst of greater than 1.0:1. In other words, in stoichiometric terms, the chromium sulfide in the catalyst can be described as having the formula CrS x , where "x" is greater than 1.0. In this definition, the value of "x" is not limited to an integer. In this discussion, the average stoichiometry of chromium sulfide on a catalyst sample can be determined by using X-ray diffraction (XRD) on the sulfided catalyst. This can correspond to the catalyst before use in thiophene synthesis, or the catalyst after use. Although XRD cannot be used to quantitatively determine the relative amounts of the various chromium sulfide phases, the lowest sulfur-chromium ratio known to exist in chromium sulfide is 1.0:1 (CrS). All other phases of chromium sulfide have sulfur-chromium ratios greater than 1.0:1. Therefore, if XRD detects any other chromium sulfide phase, such as Cr2S3 or Cr3S4, the average stoichiometry of the sample will correspond to a sulfur-chromium ratio greater than 1.0 (i.e., CrS x , x is greater than 1.0). Therefore, even though XRD cannot make quantitative comparisons of phases, XRD can be used to determine whether only CrS is present (x=1.0) or whether chromium sulfide phases other than CrS are present (x>1.0).

[0095] In some aspects, it is believed that the presence of alkali metals and / or alkaline earth metals associated with the zeolite framework structure can allow for improved production of thiophenes (including alkylated thiophenes) and / or can allow for reduced coke formation. x The formation of phases increases, in which the stoichiometric ratio of Cr to S is greater than 1. Chromium is able to form various CrS x phase, including (but not limited to) CrS, Cr2S3 and Cr3S4. x In the phase, the oxidation state of sulfur is usually understood to be -2. Therefore, in CrS, the oxidation state of Cr is usually understood to be +2. In Cr2S3, the oxidation state of Cr is usually understood to be +3, and in Cr3S4, the oxidation state is usually understood to be a mixture of +2 and +3.

[0096] Without being bound by any particular theory, it is believed that the combination of chromium sulfide comprising high oxidation state chromium, the presence of the zeolite framework structure to provide a "cage-like" environment, and the presence of alkali metals and / or alkaline earth metals associated with the zeolite framework structure can act synergistically to provide improved activity and / or selectivity for thiophene production while reducing or minimizing the selectivity for coke production.

[0097] With respect to chromium sulfides, it is believed that the presence of higher oxidation state chromium can promote the donation of sulfur atoms from the chromium sulfide phase to combine with alkane precursors to form thiophenes and / or alkylated thiophenes. It is believed that the removal of sulfur from chromium sulfides leads to CrS x The oxidation state of the Cr atom in the compound changes. When only CrS is available, the removal of the sulfur atom requires the Cr atom to change from the +2 oxidation state to metallic Cr. In contrast, when phases such as Cr2S3 or Cr3S4 are present, the sulfur atom can be removed from the chromium sulfide while the oxidation state of the Cr atom only changes from +3 to +2.

[0098] It is further believed that the cage-like structure of the pore network of the zeolite framework may limit the rate of formation of materials with a large number of carbon-carbon bonds. By limiting the formation of larger carbon complexes, this can increase the chance of carbon-sulfur bonds forming as part of complexes containing eight or fewer atoms, seven or fewer atoms, six or fewer atoms, five or fewer atoms. These small complexes can then have an increased chance of forming thiophene rings, rather than adding further carbon-carbon bonds and forming coke or coke precursors.

[0099] Additionally or alternatively, it is believed that the catalyst comprising a zeolite carrier can promote the formation of layered domains of carbon sulfide. These layered domains can be observed in the transmission electron microscope image of the sulfided catalyst. It is believed that when loaded on a zeolite carrier, these layered domains can contribute to the activity of improving chromium sulfide. It is believed that this layered domain corresponds to the Cr2S3 phase.

[0100] It is also believed that the presence of the alkali metal and / or alkaline earth metal associated with the zeolite framework structure can help form thiophene and / or alkylated thiophene in many ways. First, the presence of the alkali metal and / or alkaline earth metal associated with the zeolite framework structure can allow the formation of a sulfide phase corresponding to a mixture of chromium and alkali metal or alkaline earth metal. These mixed sulfides can further promote the ability of the sulfide phase to participate in the reaction of forming thiophene or alkylated thiophene. Additionally or alternatively, alkali metal and / or alkaline earth metal can be associated with the acidic site in the zeolite framework structure. The presence of such metals can neutralize the acidic site (contrary to having a hydrogen atom). It is believed that this neutralization of the acidic site can reduce or minimize the formation of coke in the thiophene building-up process.

[0101] A variety of zeolite frameworks can be used as supports for thiophene synthesis catalysts. Suitable zeolite frameworks can include "large pore" zeolites and "medium pore" zeolites. Large pore zeolites have maximum pore channels with an average pore size of ~0.65nm or greater, or ~0.70nm or greater, for example, up to ~1.0nm. In some aspects, such large pore zeolites may have maximum pore channels corresponding to 12-membered rings in the zeolite framework. Medium pore zeolites may have maximum pore channels with an average pore size of less than ~0.70nm, for example, ~0.50nm to ~0.70nm. In some aspects, such medium pore zeolites may have maximum pore channels corresponding to 10-membered rings in the zeolite framework.

[0102] Some examples of large pore zeolite frameworks can include FAU, which includes zeolites such as USY and faujasite, and MWW, which includes zeolites such as MCM-22 and MCM-49. Other large pore zeolites that can be used according to the present invention include natural and synthetic large pore zeolites. Non-limiting examples of natural large pore zeolite frameworks include sodium zeolite, chabazite, dachia zeolite, clinoptilolite, faujasite, heulandite, analcime, chlorite, erionite, sodalite, cancrinite, nepheline, celestite, analcime, sodium zeolite, chabazite, mesogenite, mordenite, lumberstone and ferrierite. Non-limiting examples of synthetic large pore zeolite frameworks are zeolite X, Y, A, L, ZK-4, ZK-5, B, E, F, H, J, M, Q, T, W, Z, α, β, ω, REY and USY, and MSE framework materials (e.g., MCM-68). In some aspects, the large pore zeolite support can correspond to a zeolite support (ie, having only oxides of silicon and aluminum in the zeolite framework structure).

[0103] Medium pore size zeolite materials may include, but are not limited to, crystalline materials with MFI, MFS, MEL, MTW, EUO, MTT, HEU, FER and TON zeolite frameworks. The non-limiting examples of such medium pore size zeolites include ZSM-5, ZSM-12, ZSM-22, ZSM-23, ZSM-34, ZSM-35, ZSM-38, ZSM-48, ZSM-50, silicalite and silicalite 2. The example of suitable medium pore size zeolite may be ZSM-5, for example, described in U.S. Patent Nos. 3,702,886 and 3,770,614. Other suitable zeolite types may include ZSM-11, ZSM-12, ZSM-21, ZSM-38, ZSM-23 and ZSM-35. As described above, SAPO, such as SAPO-11, SAPO-34, SAPO-41 and SAPO-42, may also be used herein. Non-limiting examples of other mesoporous zeolite-type frameworks that can be used herein include chromosilicates; gallosilicates; ferrosilicates; aluminophosphates (AlPO), such as AlPO-11; titanoaluminosilicates (TASO), such as TASO-45; borosilicates; titanoaluminophosphates (TAPO), such as TAPO-11, and ferroaluminosilicates.

[0104] As used herein, the large pore zeolite framework structure and / or the medium pore zeolite framework structure may include a "crystalline mixture", which is believed to be the result of a failure in a crystal or crystalline region during the zeolite synthesis process. Examples of ZSM-5 and ZSM-11 crystalline mixtures can be found in U.S. Patent No. 4,229,424, which is incorporated herein by reference. The crystalline mixture itself is a zeolite, as opposed to a physical mixture of zeolites, in which different crystals of crystallites of different zeolites are physically present in the same catalyst composite or hydrothermal reaction mixture.

[0105] Optionally, the zeolite framework can be combined with a binder before Cr is added to the zeolite framework material. Any convenient weight ratio of the zeolite framework to the binder can be used. The amount of binder in the combined zeolite and binder composition can correspond to 10% to 90% by weight of the composition, based only on the weight of the zeolite and binder.

[0106] In some aspects, before Cr is added to the zeolite carrier, the zeolite carrier can be in a form where the acid sites in the zeolite framework structure are substantially neutralized. This can be achieved in any convenient manner. In some aspects, the initial synthesis of the zeolite material can allow the formation of a zeolite material with neutralized acid sites. For example, some zeolite synthesis methods use alkali metal hydroxides (e.g., NaOH) and / or alkaline earth metal hydroxides (e.g., CaOH) as part of the synthesis mixture forming the zeolite. This results in a zeolite in which almost all of the acid sites (90% or more) in the zeolite framework structure are neutralized by ions of alkali metals (e.g., Na or K) and / or alkaline earth metals (e.g., Mg or Ca). In other aspects, ion exchange can be performed on the zeolite to exchange the acid sites (usually terminated with hydrogen) with alkali metals. In other aspects, alkali metal ion exchange can be performed during and / or after the zeolite carrier is impregnated with Cr. While this may be at least partially effective, it is believed that unexpectedly improved activity / selectivity for thiophene production may be achieved when neutralization with alkali / alkaline earth metals is performed prior to impregnation with Cr.

[0107] It is believed that further unexpectedly improved activity / selectivity for thiophene production can be achieved when sufficient alkali metal and / or alkaline earth metal is present in the synthesis solution to form a zeolite that is substantially in the form of alkali metal and alkaline earth metal. This is in contrast to "H-type" zeolites, in which a large portion of the acidic sites of the zeolite framework structure are terminated by hydrogen. Such H-type zeolites may have higher Alpha values ​​based on this increased acidity. Due to the nature of the thiophene synthesis reaction conditions, it is believed that such higher acidity zeolites contribute to the formation of coke. This is also in contrast to zeolites whose counterions to the acidic sites are amine or ammonium type counterions or some other type of counterion that does not correspond to an alkali metal or alkaline earth metal.

[0108] In this discussion, a "zeolite in substantially alkali metal form" or a "zeolite framework structure in substantially alkali metal form" is defined as a zeolite in which the majority of acid sites in the zeolite framework structure are associated with / exchanged with / occupied by alkali metal ions. In this discussion, a "zeolite in substantially alkaline earth metal form" or a "zeolite framework structure in substantially alkaline earth metal form" is defined as a zeolite in which the majority of acid sites in the zeolite framework structure are associated with / exchanged with / occupied by alkaline earth metal ions. In this discussion, a "substantially alkali and alkaline earth metal-exchanged zeolite" or a "substantially alkali and alkaline earth metal-exchanged zeolite framework structure" is defined as a zeolite in which the majority of acid sites in the zeolite framework structure are associated with / exchanged with / occupied by alkali metal ions and / or alkaline earth metal ions. It is worth noting that, according to these definitions, a "zeolite in substantially alkali and alkaline earth metal form" is broad enough to cover zeolites containing only alkali metals or only alkaline earth metals.

[0109] One option of forming a zeolite that is substantially in the form of alkali metal / alkaline earth metal is based on the initial synthesis of zeolite. For many zeolites, the typical synthesis solution that forms the zeolite framework structure includes adding alkali to achieve the required pH in the synthesis mixture. One option of forming a zeolite that is substantially in the form of alkali metal / alkaline earth metal is to include alkali metal and / or alkaline earth metal as the counter ion of at least a part of the alkali contained in the synthesis mixture. This can correspond to, for example, including sodium hydroxide (alkali metal counter ion) or calcium hydroxide (alkaline earth metal counter ion) as a base. In this discussion, if the synthesis mixture includes a hydroxide base (such as sodium hydroxide or calcium hydroxide), and if 50 weight % or more of the hydroxide base corresponds to an alkali metal hydroxide, the zeolite produced by the synthesis mixture is defined as a zeolite that is substantially in the form of alkali metal. In this discussion, if the synthesis mixture includes a hydroxide base, and if 50 weight % or more of the hydroxide base corresponds to an alkaline earth metal hydroxide, the zeolite produced by the synthesis mixture is defined as a zeolite that is substantially in the form of alkaline earth metal. In the present discussion, a zeolite produced from a synthesis mixture is defined as being substantially in the alkali and alkaline earth metal form if the synthesis mixture includes a hydroxide base and if 50% by weight or more of the hydroxide base corresponds to at least one of an alkali metal hydroxide and an alkaline earth metal hydroxide. It is worth noting that a "substantially alkali or alkaline earth metal form of zeolite" may be formed directly from the initial synthesis mixture used to form the zeolite if the synthesis mixture includes a suitable alkali and / or alkaline earth metal source.

[0110] Another option for forming a zeolite in substantially alkali metal form / alkaline earth metal form is to combine alkali metal / alkaline earth metal with zeolite after synthesis but before impregnation / otherwise adding chromium to the zeolite support. This can be achieved by, for example, ion exchange, initial wetness impregnation and / or any other convenient method for exposing the zeolite to a solution containing alkali metal ions and / or alkaline earth metal ions. For this type of ion exchange, there should be an excess of alkali metal ions / alkaline earth metal ions. There are many methods for determining whether there is an excess. If the number of acid sites available per gram of zeolite is known, a stoichiometric calculation can be performed. If the number of acid sites is unknown, one of various types of alternative methods can be used to provide an excess of alkali metal ions / alkaline earth metal ions. An alternative method is that if the zeolite is exposed to a metal salt in a soluble form (e.g., a water-soluble form), wherein a) 50 mol % or more of the metal in the solution corresponds to an alkali metal and / or alkaline earth metal, and b) the weight of the alkali metal salt and / or alkaline earth metal salt in the solution is equal to or greater than the weight of the zeolite in contact with the solution.

[0111] In addition to having essentially alkali and alkaline earth zeolites, the zeolite support can also be impregnated with Cr. This can be done in any convenient manner, such as by initial wetting. For example, a Cr salt solution can be formed, such as a solution of chromium (III) nitrate nonahydrate in water. A material containing a zeolite framework structure (such as USY, MCM-49 or ZSM-5) can be exposed to a solution containing a Cr salt. The resulting material can then be optionally dried to remove water while leaving Cr. An example of a drying step can include exposing the resulting material to a temperature of 80° C. to 200° C. Drying can be carried out for a convenient period of time, such as 0.5 hours to 24 hours. Since the temperature during the drying process is relatively low, an inert atmosphere or an oxygen-containing atmosphere (such as air) can be used during the drying process.

[0112] In various aspects, the amount of Cr loaded on the zeolite support can be from 1.0 wt% to 20 wt%, or from 1.0 wt% to 12 wt%, or from 1.0 wt% to 8.0 wt%, or from 3.0 wt% to 20 wt%, or from 3.0 wt% to 12 wt%, or from 3.0 wt% to 8.0 wt%, or from 5.0 wt% to 20 wt%, or from 5.0 wt% to 12 wt%, or from 5.0 wt% to 8.0 wt%. In aspects where the zeolite support includes a zeolite framework structure and a binder, the amount of Cr on the zeolite support corresponds to the amount of Cr on the total weight of the zeolite plus the binder.

[0113] Optionally, after impregnation of the zeolite support with Cr, an additional ion exchange / initial wetness procedure may be performed using an alkali metal salt and / or an alkaline earth metal salt. This optional addition of an alkali metal and / or an alkaline earth metal after impregnation with Cr may help to further neutralize acidic sites after impregnation with Cr.

[0114] After impregnation of the zeolite support with Cr (and after any other metal impregnation / ion exchange, such as addition of alkali metals and / or alkaline earth metals to neutralize acidic sites), the resulting Cr-impregnated zeolite support can be exposed to a calcination step in an oxygen-containing environment to form a catalyst precursor comprising chromium oxide. Calcination can be carried out at a temperature of 300° C. to 650° C. Air (e.g., flowing air) is an example of a suitable oxygen-containing atmosphere. Calcination can be carried out for a convenient period of time, such as 0.5 hour to 24 hours.

[0115] After forming the catalyst precursor, the catalyst precursor can be sulfided to form a thiophene synthesis catalyst. For example, the catalyst precursor can be exposed to a gas phase sulfiding agent, such as H2S for a period of time at a sulfiding temperature. During the sulfiding process, H2S can be mixed with one or more diluent gases, such as N2, to allow control of the sulfiding rate. The sulfiding of the catalyst precursor can be carried out at a temperature of 400°C to 600°C or 500°C to 600°C. The catalyst precursor can be sulfided for a period of 1.0 hours to 8.0 hours. Examples of sulfiding agents can include, but are not limited to, H2S, CS2, S2, dimethyl disulfide, and tert-butyl polysulfide.

[0116] Sulfidation of the catalyst precursor results in the formation of a catalyst comprising a chromium sulfide supported on a zeolite support. The sulfide on the zeolite support, as detectable by X-ray diffraction (XRD), may include, but is not limited to, Cr2S3, CrS, Cr3S4, and combinations thereof. Alternative catalysts for thiophene synthesis

[0117] In addition to chromium sulfides supported on zeolite supports, various other types of catalysts may also be useful for thiophene formation based on the gas phase reaction of alkanes with gas phase sulfur compounds.

[0118] An example of an alternative catalyst may be formed from a catalyst precursor comprising Sm2O3. Sm2O3 may be supported on a refractory oxide (e.g., silica or alumina) and / or a zeolite support. Optionally, an alkali metal may also be impregnated on such a catalyst precursor. The catalyst precursor may be converted into a catalyst by gas phase sulfidation.

[0119] Another example of an alternative catalyst corresponds to a catalyst comprising chromium sulfide and an alkali metal oxide supported on alumina (or another refractory oxide). This is the type of catalyst currently used for thiophene production when alcohols (instead of alkanes) are used as starting reagents.

[0120] Other examples of alternative catalysts may be catalysts comprising Ni, Co, Mo, W, V or combinations thereof supported on a support. The support may correspond to a refractory oxide and / or a zeolite support. Optionally, an alkali metal may also be impregnated on a catalyst precursor for forming such a catalyst prior to sulfidation. Example - Initial Preparation of Thiophene Synthesis Catalyst

[0121] Three groups of potential catalyst precursors for thiophene synthesis catalysts were prepared. The first group of catalyst precursors corresponded to transition metal oxides, optionally in combination with alkali metal oxides, supported on alumina or silica supports. The second group of catalyst precursors corresponded to chromium or molybdenum oxides, optionally in combination with alkali metal oxides, supported on a zeolite support. The third group of catalyst precursors corresponded to catalyst precursors based on Sm2O3.

[0122] After forming the catalyst precursor, the precursor was sulfided at 550°C in the presence of H2S. Examples 1 to 5 Catalyst Precursors with Alumina or Silica Supports

[0123] For the first group of catalysts, the general synthesis method is to start with a support corresponding to Versal 300 alumina. The transition metal reagent is dissolved in water and then impregnated on the alumina. The resulting solid is then dried at 120°C for 3 to 4 hours and calcined at 550°C for 6 hours under a continuous air flow with a heating rate of 3°C per minute. If an alkali metal oxide is also added, the alkali metal oxide is dissolved in water, impregnated on the support (after impregnation with the transition metal), dried at 120°C for 4 hours, and then calcined at 350°C for 6 hours under a continuous air flow.

[0124] Catalyst precursors prepared according to the method are 20 wt% Cr2O3 supported on alumina (Example 1); 1.5 wt% K2O / 20 wt% Cr2O3 supported on alumina (Example 2); 20 wt% V2O5 supported on alumina (Example 3); 1.5 wt% K2O / 20 wt% V2O5 supported on alumina (Example 4); 20 wt% molybdenum oxide supported on alumina (Example 5); and CoMo (about 20 wt% CoMo, Co to Mo molar ratio of 4:3) supported on silica. Examples of reagents used for catalyst synthesis include Versal 300 alumina; chromium (III) nitrate nonahydrate; and ammonium molybdate tetrahydrate. Examples 6 to 10 - Catalyst Precursors with Zeolite Supports

[0125] Example 6: 10 wt% Cr2O3 supported on ZSM-5. ZSM-5 was synthesized according to a conventional synthesis method, using ammonium hydroxide as a base to adjust the pH of the synthesis mixture. 16.6 g of chromium (III) nitrate nonahydrate was dissolved in 24 ml of deionized water. The solution was impregnated onto 30.6 g of ZSM-5. The resulting solid was dried at 120°C for 6 hours and calcined at 550°C for 6 hours under air flow.

[0126] Example 7: 5.0 wt% MoO3 supported on ZSM-5. 1.84 g of ammonium heptamolybdate tetrahydrate was dissolved in 30 ml of deionized water. The solution was impregnated onto 30 g of ZSM-5. Due to the presence of sodium in the synthesis environment, the ZSM-5 corresponds to a substantially complete sodium metal form. The resulting solid was dried at 120°C for 4 hours and calcined at 550°C for 6 hours under a continuous air flow.

[0127] Example 8: 5.0 wt% Cr2O3 supported on ZSM-5. 7.9 g of chromium (III) nitrate nonahydrate was dissolved in 30 ml of deionized water. The solution was impregnated onto 30 g of ZSM-5. Due to the presence of sodium in the initial ZSM-5 synthesis environment, the ZSM-5 corresponds to a form that is essentially sodium metal. The resulting solid was dried at 120°C for 4 hours and calcined at 550°C for 6 hours under a continuous air flow.

[0128] Example 9: 5.0 wt% Cr2O3 supported on USY. 30 g of USY was impregnated in 7.9 g of chromium (III) nitrate nonahydrate dissolved in 30 cc of deionized water. USY is a low acidity version, essentially in sodium metal form due to the presence of sodium in the initial USY synthesis environment. The resulting solid was dried at 120°C for 4 hours. 1.3 g of potassium nitrate was dissolved in 30 cc of deionized water and impregnated onto the dried sample. It was dried at 120°C for 6 hours and calcined at 550°C for 6 hours under a continuous air flow.

[0129] Example 10: 5.0 wt% Cr2O3 supported on MCM-49. 30 grams of MCM-49 were impregnated in 7.9 grams of chromium (III) nitrate nonahydrate dissolved in 30 cc of deionized water. Due to the nature of the MCM-49 synthesis, the MCM-49 was partially hydrogen terminated before the chromium oxide impregnation because no alkali or alkaline earth metals were included in the synthesis mixture. The resulting solid was dried at 120°C for 4 hours and calcined at 550°C for 6 hours under continuous airflow. After the chromium oxide impregnation, the resulting solid was further impregnated in 1.3 grams of KNO3 dissolved in 30 cc of deionized water. The same drying and calcination procedure was repeated. Test equipment

[0130] The catalyst was loaded into a quartz reactor as a bed and sulfided as described above to form a sulfided catalyst. After sulfidation, the resulting catalyst was exposed to a 5.0% N2, 14.0% C4H 10 , 14.0% S2 and 66.5% H2S in a gas stream. S2 was added to the feed at a temperature of 150°C using H2S as a purge gas over liquid S2. H2S and S2 were then mixed with the remainder of the feed and the feed was heated to 350°C before exposure to the catalyst. During exposure to the feed, the quartz reactor was maintained at 550°C. The feed was exposed to the catalyst at approximately atmospheric pressure (approximately 100 kPa-a). The reaction system did not include recycle, so the results produced corresponded to "single pass" reactivity.

[0131] Table 1 shows the results of exposing the feed to various catalysts corresponding to Examples 1 to 5. In Table 1, "% Conversion" is the amount of n-butane converted in the feed; "% Thiophene Selectivity" is the weight percentage of the conversion product corresponding to thiophene; "% Thiophene Yield" corresponds to the weight percentage of thiophene relative to the weight of the feed; "% Coke Yield" is the weight percentage of the conversion product corresponding to coke. It is worth noting that in Tables 1, 2 and 3, when the thiophene yield plus the coke yield is less than 100%, the remaining yield corresponds to the light fraction (C 3- ) or liquid (optionally sulphurized) products. Apart from coke formation on the catalyst, no tarry or solid products were observed after testing any of the examples. Table 1 - Thiophene Synthesis of Examples 1 to 5

[0132] As shown in Table 1, Example 2 provides the best overall combination of thiophene selectivity, thiophene yield, and coke yield. Notably, the conversion of Example 2 is lower than that of Example 1. However, even with recycle, the coke yield of the catalyst in Example 2 will be significantly lower than any other catalyst. The addition of alkali metals in Examples 4 and 5 also appears to mitigate coke formation, but the baseline levels are higher.

[0133] Table 2 shows the test results of Examples 6-10. Table 2 - Thiophene Synthesis of Examples 6 to 10

[0134] Table 2 shows the unexpected benefit of using chromium sulfide loaded on a zeolite carrier that is substantially in alkali metal form (and / or substantially in alkaline earth metal form). As shown in Table 2, acid neutralization (Example 6) using a zeolite carrier that does not contain alkali metal and / or alkaline earth metal results in low thiophene yield and high coke selectivity. In Example 7, a zeolite carrier of the same type as used in Example 8 is used to load a molybdenum catalyst. This also results in a large amount of coke formation and low thiophene yield. However, by using a zeolite carrier that is substantially in alkali metal form and chromium as a combination of catalytic metals (Examples 8 and 9), it is unexpectedly found that high butane conversion and high thiophene selectivity and low coke yield are achieved. It is noteworthy that treatment with alkali metals (Example 10) after impregnation with chromium provides unexpectedly low coke selectivity, but alkane conversion is low. Therefore, it is shown that the additional advantage of combining high alkane conversion and low coke yield is provided for the zeolite carrier to achieve substantially alkali metal and / or alkaline earth metal form before chromium impregnation.

[0135] Based on the favorable results of Examples 8-9, the catalyst in Example 9 was further analyzed using transmission electron microscopy (TEM). Figure 3 TEM micrographs of the sulfided catalyst are shown. Figure 3 As shown, regions 310, 320, and 330 correspond to examples of regions showing layered structures separated from the crystal structure of the USY support. It is believed that layered structures (such as the structures in regions 310, 320, and 330) are indicative of a layered chromium sulfide phase, which can unexpectedly promote improved thiophene synthesis results. This phase can be formed when a zeolite support that is substantially in the form of an alkali metal and / or alkaline earth metal is used as a support for a chromium sulfide catalyst. Example 11 - Characterization of Liquid Products

[0136] As described above, liquid products including at least hydrocarbons and sulfided hydrocarbons are formed under the synthesis conditions.The liquid products produced by the catalyst testing in Example 8 were further characterized using gas chromatography-mass spectrometry (GC-MS) to identify compounds in the liquid products.

[0137] Figure 4 Examples of compounds detected in the liquid product by GC-MS are shown. It is worth noting that some larger compounds may also be formed, but the compounds detected are limited to those that are volatile in the gas chromatograph. Figure 4 As shown, a variety of 1-ring and 2-ring sulfur-containing compounds are formed, including thiophene, various alkylated thiophenes, benzothiophene, various alkylated benzothiophenes, bithiophene, and bithiophene (two fused thiophene rings). Figure 4 As shown in the chemical structures at the bottom, a variety of alkylated benzenes (as well as unsubstituted benzene) were also detected. Additional Implementation

[0138] Embodiment 1. A method for producing carbon nanotubes, comprising: reacting a carbon nanotube containing one or more C4 to C 16 A first feedstock of alkanes and a second feedstock comprising a vapor-phase sulfur source are exposed to a synthesis catalyst to form a synthesis effluent comprising thiophene, alkylated thiophene, or a combination thereof; the gas stream is heated to a temperature of 1000° C. or higher to form a heated gas stream; the heated gas stream is fed into a reactor comprising a pyrolysis zone, the pyrolysis zone comprising an average cross-sectional area available for the gas stream; i) a catalytic metal precursor comprising a catalytic metal and ii) at least a portion of the synthesis effluent are mixed with the heated gas stream to form a heated gas stream mixture, the heated gas stream mixture comprising 10% by volume or less of hydrocarbons, thiophene, and alkylated thiophenes; the heated gas stream in the pyrolysis zone is mixed with a catalytic metal precursor comprising a catalytic metal and ii) at least a portion of the synthesis effluent to form a heated gas stream mixture; the heated gas stream mixture comprises 10% by volume or less of hydrocarbons, thiophene, and alkylated thiophenes; The mixture is maintained at a temperature of 1000°C or higher and continued for a pyrolysis residence time to form an intermediate product stream comprising H2, carbon and a catalyst, wherein the catalyst comprises a catalytic metal; the intermediate product stream is cooled to a temperature of 800°C or lower; and the intermediate product stream is conveyed to a gas flow tube array within a reactor to form a carbon nanotube product stream, wherein the ratio of the average cross-sectional area of ​​the pyrolysis zone available for the gas flow to the average cross-sectional area of ​​the gas flow tube array is 1.1 or higher, or wherein the ratio of the average cross-sectional area of ​​the pyrolysis zone available for the gas flow to the average cross-sectional area of ​​the tubes in the gas flow tube array is 10 or higher, or a combination thereof.

[0139] Embodiment 2. The method of Embodiment 1, wherein the catalytic metal comprises Fe, Co, Ni, Pd or a combination thereof.

[0140] Embodiment 3. The method of any of the above embodiments, wherein the catalytic metal precursor comprises a catalytic metal recovered from carbon nanotubes, optionally recovered from at least a portion of a carbon nanotube product stream.

[0141] Embodiment 4. The method of Embodiment 3, wherein the catalytic metal precursor comprises a catalytic metal precursor formed from catalytic metal recovered from at least a portion of the carbon nanotube product stream and a recycled portion of the carbon nanotube product stream.

[0142] Embodiment 5. A method according to any of the above embodiments, wherein the synthesis effluent is mixed with a heated gas stream by exposing the first feedstock and the second feedstock to a synthesis catalyst in the presence of a heated gas stream, and the thiophene synthesis conditions include a temperature of 900°C or higher; or wherein the thiophene synthesis conditions include a temperature of 450°C to 750°C.

[0143] Embodiment 6. A method according to any of the above embodiments, i) wherein the heated gas stream contains 80 vol% or more H2; ii) wherein the heated gas stream also contains CO, CO2, ethanol or a combination thereof; iii) wherein the intermediate product stream also contains CO, CO2, ethanol or a combination thereof; or iv) a combination of two or more of i), ii) and iii).

[0144] Embodiment 7. The method of any of the above embodiments, wherein at least a portion of the synthetic effluent is mixed with a heated gas stream after entering the reactor, or wherein substantially all of the synthetic effluent is mixed with a heated gas stream after entering the reactor.

[0145] Embodiment 8. The method of any of the above embodiments, wherein cooling the product stream to a temperature of 800° C. or less comprises passing the product stream to a shell and tube heat exchanger, the tube array being located within the shell and tube heat exchanger.

[0146] Embodiment 9. The method of any of the above embodiments, wherein the shell and tube heat exchanger further comprises heat exchanger tubes, and wherein at least a portion of the gas stream comprises a heat transfer fluid passed through the heat exchanger tubes.

[0147] Embodiment 10. The method of any of the above embodiments, wherein one or more C4 to C 16 Alkanes include n-butane.

[0148] Embodiment 11. The method of any of the above embodiments, wherein the first feedstock further comprises one or more C4 to C 10 Olefins, wherein the synthesis effluent also contains C 4- alkanes, and wherein the first feedstock comprises C 4+ Recycled portion of the alkanes.

[0149] Embodiment 12. The method of any of the above embodiments, wherein the synthetic catalyst comprises a support, the support comprising a) a zeolite framework structure in substantially alkali metal form, b) a zeolite framework structure in substantially alkaline earth metal form, or c) a zeolite framework structure in substantially alkali metal and alkaline earth metal form, the zeolite framework structure having 10-membered ring pore channels or 12-membered ring pore channels as the largest pore channels; and 1.0 wt% to 10 wt% of chromium sulfide, relative to the weight of the sulfided catalyst, the chromium sulfide having CrS x The average stoichiometry of , where x is greater than 1.0.

[0150] Embodiment 13. The method of Embodiment 12, wherein the zeolite framework structure is synthesized in a) substantially alkali metal form, b) substantially alkaline earth metal form, or c) substantially alkali metal and alkaline earth metal form.

[0151] Embodiment 14. The method of Embodiment 12 or 13, wherein prior to adding the chromium to the support, the zeolite framework structure is in a) substantially alkali metal form, b) substantially alkaline earth metal form, or c) substantially alkali metal and alkaline earth metal form.

[0152] Embodiment 15. The method of any one of Embodiments 12 to 14, a) wherein the zeolite framework structure comprises a zeolite framework of FAU, MFI, MWW or a combination thereof; b) wherein the support comprises a zeolite framework structure substantially in the form of an alkali metal, the alkali metal comprising sodium, potassium or a combination thereof; c) wherein the support comprises a zeolite framework structure substantially in the form of an alkaline earth metal, the alkaline earth metal comprising magnesium, calcium or a combination thereof; or d) a combination of two or more of a), b) and c).

[0153] Additional Embodiments A. The method of any one of Embodiments 1 to 2 or 5 to 15, wherein the catalytic metal precursor comprises ferrocene.

[0154] While the present invention has been described and illustrated by reference to particular embodiments, those skilled in the art will appreciate that the invention lends itself to variations not necessarily illustrated herein. Accordingly, reference should be made solely to the appended claims to determine the true scope of the present invention.

Claims

1. A method for producing carbon nanotubes, comprising: Under thiophene synthesis conditions, one or more C4 to C 16 exposing a first feedstock of an alkane and a second feedstock comprising a vapor-phase sulfur source to a synthesis catalyst to form a synthesis effluent comprising thiophene, alkylated thiophene, or a combination thereof; heating the gas stream to a temperature of 1000° C. or higher to form a heated gas stream; passing a heated gas stream into a reactor comprising a pyrolysis zone comprising an average cross-sectional area available for the gas stream; mixing i) a catalytic metal precursor comprising a catalytic metal and ii) at least a portion of the synthesis effluent with a heated gas stream to form a heated gas stream mixture comprising 10% by volume or less of hydrocarbons, thiophenes, and alkylated thiophenes; maintaining the heated gas stream mixture in the pyrolysis zone at a temperature of 1000° C. or greater for a pyrolysis residence time to form an intermediate product stream comprising H 2 , carbon, and a catalyst comprising a catalytic metal; cooling the intermediate product stream to a temperature of 800° C. or less; and The intermediate product stream is conveyed to a gas flow tube array in the reactor to form a carbon nanotube product stream, wherein the ratio of the average cross-sectional area of ​​the pyrolysis zone available for gas flow to the average cross-sectional area of ​​the gas flow tube array is 1.1 or greater, or wherein the ratio of the average cross-sectional area of ​​the pyrolysis zone available for gas flow to the average cross-sectional area of ​​the tubes in the gas flow tube array is 10 or greater, or a combination thereof.

2. The method of claim 1, wherein the catalytic metal comprises Fe, Co, Ni or a combination thereof.

3. The method of claim 1, wherein the catalytic metal precursor comprises a catalytic metal recovered from carbon nanotubes.

4. The method of claim 3, wherein the catalytic metal recovered from the carbon nanotubes comprises catalytic metal recovered from at least a portion of the carbon nanotube product stream.

5. The method of claim 3, wherein the catalytic metal precursor comprises a catalytic metal precursor formed from catalytic metal recovered from at least a portion of the carbon nanotube product stream and a recycled portion of the carbon nanotube product stream. The method of claim 1 , wherein the catalytic metal precursor comprises ferrocene.

7. The method of claim 1, wherein the synthesis effluent is mixed with a heated gas stream by exposing the first feedstock and the second feedstock to a synthesis catalyst in the presence of a heated gas stream, the thiophene synthesis conditions comprising a temperature of 900°C or greater.

8. The method of claim 1, wherein the thiophene synthesis conditions include a temperature of 450°C to 750°C.

9. The method of claim 1, i) wherein the heated gas stream comprises 80 vol% or more H2; ii) wherein the heated gas stream further comprises CO, CO2, ethanol or a combination thereof; iii) wherein the intermediate product stream further comprises CO, CO2, ethanol or a combination thereof; or iv) a combination of two or more of i), ii) and iii).

10. The method of claim 1, wherein at least a portion of the synthetic effluent is mixed with a heated gas stream after entering the reactor, or wherein substantially all of the synthetic effluent is mixed with a heated gas stream after entering the reactor.

11. The method of claim 1, wherein cooling the product stream to a temperature of 800°C or less comprises passing the product stream into a shell and tube heat exchanger, the tube array being located within the shell and tube heat exchanger.

12. The method of claim 1, wherein the shell and tube heat exchanger further comprises heat exchanger tubes, and wherein at least a portion of the gas stream comprises a heat transfer fluid passing through the heat exchanger tubes.

13. The method of claim 1, wherein the one or more C4 to C 16 Alkanes include n-butane.

14. The method according to claim 1, wherein the first feedstock further comprises one or more C4 to C 10 Olefins.

15. The method of claim 14, wherein the synthetic effluent further comprises C 4+ alkanes, and wherein the first feedstock comprises C 4+ Recycled portion of the alkanes.

16. The method according to claim 1, wherein the synthetic catalyst comprises A carrier comprising a) a zeolite framework structure substantially in the form of an alkali metal, b) a zeolite framework structure substantially in the form of an alkaline earth metal, or c) a zeolite framework structure substantially in the form of an alkali metal and an alkaline earth metal, the zeolite framework structure having a 10-membered ring pore channel or a 12-membered ring pore channel as the largest pore channel; and 1.0 wt % to 10 wt % of a chromium sulfide, relative to the weight of the sulfided catalyst, wherein the chromium sulfide has a CrS x The average stoichiometry of , where x is greater than 1.

0.

17. The method of claim 16, wherein the zeolite framework is synthesized in a) substantially alkali metal form, b) substantially alkaline earth metal form, or c) substantially alkali metal and alkaline earth metal form.

18. The method of claim 11, wherein prior to adding chromium to the support, the zeolite framework is in a) substantially alkali metal form, b) substantially alkaline earth metal form, or c) substantially alkali metal and alkaline earth metal form.

19. The method of claim 11, wherein the zeolite framework structure comprises a zeolite framework of FAU, MFI, MWW, or a combination thereof.

20. The method of claim 11, wherein the support comprises a zeolite framework structure substantially in the form of an alkali metal, the alkali metal comprising sodium, potassium, or a combination thereof; or wherein the support comprises a zeolite framework structure substantially in the form of an alkaline earth metal, the alkaline earth metal comprising magnesium, calcium, or a combination thereof.

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