WO2016187249A1

WO2016187249A1 - A process for the aromatization of a methane-containing gas stream using scandium hydrogen acceptor particles

Info

Publication number: WO2016187249A1
Application number: PCT/US2016/032980
Authority: WO
Inventors: Steven Sangyun LIM; Peter Tanev Tanev; Shaojun Miao; Anthony Tyler SIMPSON
Original assignee: Shell Oil Company; Shell Internationale Research Maatschappij B.V.
Priority date: 2015-05-21
Filing date: 2016-05-18
Publication date: 2016-11-24

Abstract

Implementations of the disclosed subject matter provide a process for the aromatization of a methane-containing gas stream that includes contacting the methane-containing gas stream in a reaction zone of an aromatization reactor comprising an aromatization catalyst and a scandium hydrogen acceptor under methane-containing gas aromatization conditions to produce a product stream comprising aromatics and hydrogen, wherein at least a portion of the produced hydrogen is bound by the scandium hydrogen acceptor in the reaction zone and removed from the product stream and the reaction zone.

Description

A PROCESS FOR THE AROMATIZATION OF A METHANE-CONTAINING GAS STREAM USING SCANDIUM HYDROGEN ACCEPTOR PARTICLES

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application Serial No. 62/164,625 filed May 21, 2015, the entire disclosure of which is hereby incorporated by reference. This application is also related to co-pending U.S. Patent Application Ser. No. 14/395,819, entitled "AROMATIZATION OF A METHANE-CONTAINING GAS STREAM", which claims priority to U.S. Provisional Application No. 61/636,915 filed on April 23, 2012, the disclosure of which is incorporated herein by reference. This application is also related to co-pending U.S. Patent Application Ser. No. 14/395,821, entitled "A PROCESS FOR THE AROMATIZATION OF A METHANE-CONTAINING GAS STREAM", which claims priority to U.S. Provisional Application No. 61/636,906 filed on April 23, 2012, the disclosure of which is incorporated herein by reference.

TECHNICAL FIELD OF THE INVENTION [0002] This invention relates to a process for the aromatization of a methane- containing gas stream to form aromatics and hydrogen in a reactor containing both catalyst and scandium hydrogen acceptor particles in a fluidized bed state wherein the removal of hydrogen from the reaction zone is accomplished insitu by the scandium hydrogen acceptor. BACKGROUND

[0003] The aromatic hydrocarbons (specifically benzene, toluene and xylenes) are the main high-octane bearing components of the gasoline pool and important petrochemical building blocks used to produce high value chemicals and a variety of consumer products, for example, styrene, phenol, polymers, plastics, medicines, and others. Since the late 1930's, aromatics are primarily produced by upgrading of oil-derived feedstocks via catalytic reforming or cracking of heavy naphthas. However, occasional severe oil shortages and oil price spikes result in severe aromatics shortages and aromatics price spikes. Therefore, there is a need to develop new, independent from oil, commercial routes to produce high value aromatics from highly abundant and inexpensive hydrocarbon feedstocks such as methane or stranded natural gas (which typically contains about 80-90 % vol. methane).

[0004] There are enormous proven reserves of stranded natural gas around the world. According to some estimates, the world reserves of natural gas are at least equal to those of oil. However, unlike the oil reserves that are primarily concentrated in a few oil-rich countries and are extensively utilized, upgraded and monetized, the natural gas reserves are much more broadly distributed around the world and significantly more underutilized. Many developing countries that have significant natural gas reserves lack the proper infrastructure to exploit them and convert or upgrade them to higher value products. Quite often, in such situations, natural gas is flared to the atmosphere and wasted. Because of the above reasons, there is enormous economic incentive to develop new technologies that can efficiently convert methane or natural gas to higher value chemical products, specifically aromatics.

[0005] In 1993, Wang et al., (Catal. Lett. 1993, 21, 35-41), discovered a direct, non- oxidative route to partially convert methane to benzene by contacting methane with a catalyst containing 2.0 % wt. Molybdenum on an H-ZSM-5 zeolite support at atmospheric pressure and a temperature of 700 °C. Since Wang's discovery, numerous academic and industrial research groups have become active in this area and have contributed to further developing various aspects of the direct, non-oxidative methane to benzene catalyst and process technology. Many catalyst formulations have been prepared and tested and various reactor and process conditions and schemes have been explored.

[0006] Despite these efforts, a direct, non-oxidative methane aromatization catalyst and process cannot yet be commercialized. Some important challenges that need to be overcome to commercialize this process include: (i) the very low, as dictated by thermodynamic equilibrium, per pass methane conversion and benzene yield (for example, 10 % wt. and 6 % wt., respectively at 700 °C); (ii) the fact that the reaction is favored by high temperature and low pressure; (iii) the need to separate the produced aromatics and hydrogen from unreacted (mainly methane) hydrocarbon off gas and (iv) the rapid coke formation and deposition on the catalyst surface and corresponding relatively fast catalyst deactivation. Among these challenges, overcoming the thermodynamic equilibrium limitations and significantly the conversion and benzene yield per pass has the potential to enable the commercialization of an efficient, direct, non-oxidative methane-containing gas aromatization process.

[0007] The methane aromatization reaction can be described as follows:

Mo/ZSM-5

6CH₄ - C₆H₆ + 9H₂

[0008] According to the reaction, 6 molecules of methane are required to generate a molecule of benzene. It is also apparent that, the production of a molecule of benzene is accompanied by the production of 9 molecules of hydrogen. Simple thermodynamic calculations revealed and experimental data have confirmed that, the methane

aromatization at atmospheric pressure is equilibrium limited to about 10 or 20 % wt. at reaction temperatures of 700 °C or 800°C, respectively. In addition, experimental data showed that the above conversion levels correspond to about 6 and 11.5 % wt. benzene yield at 700 °C and 800 °C, respectively. The aforementioned low (per pass) methane conversions and benzene yields are not very attractive to provide an economic justification for scale-up and commercialization of a methane-comprising gas aromatization process.

[0009] Therefore, there is a need to develop an improved direct, non-oxidative methane aromatization process that provides for significantly higher (than those allowed by the thermodynamic equilibrium) methane conversion and benzene yields per pass by implementing an insitu hydrogen removal from the reaction zone.

BRIEF SUMMARY

[0010] The invention provides a process for the aromatization of a methane-containing gas stream comprising contacting the methane-containing gas stream in a reaction zone of an aromatization reactor comprising an aromatization catalyst and a scandium hydrogen acceptor under methane-containing gas aromatization conditions to produce a product stream comprising aromatics and hydrogen, wherein at least a portion of the produced hydrogen is bound by the scandium hydrogen acceptor in the reaction zone and removed from the product stream and from the reaction zone. [0011] The invention further provides a novel process and reactor schemes that employ single or multiple catalysts and/or scandium hydrogen acceptor beds.

[0012] The invention also provides several catalyst and/or scandium hydrogen acceptor recycle and regeneration process schemes. According to these schemes, the catalyst and/or scandium hydrogen acceptor particles are regenerated simultaneously or separately in single or in separate vessels and then returned to the reactor for continuous (uninterrupted) production of aromatic s and hydrogen. The aforementioned insitu hydrogen removal in the reaction zone allows for overcoming the thermodynamic equilibrium limitations and for shifting the reaction equilibrium to the right. This results in significantly higher and economically more attractive methane-containing gas stream conversion and benzene yields per pass relative to the case without hydrogen removal, i.e. without scandium hydrogen acceptor in the reaction zone. Additional features, advantages, and embodiments of the disclosed subject matter may be set forth or apparent from consideration of the following detailed description, drawings, and claims. Moreover, it is to be understood that both the foregoing summary and the following detailed description are examples and are intended to provide further explanation without limiting the scope of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The accompanying drawings, which are included to provide a further understanding of the disclosed subject matter, are incorporated in and constitute a part of this specification. The drawings also illustrate embodiments of the disclosed subject matter and together with the detailed description serve to explain the principles of embodiments of the disclosed subject matter. No attempt is made to show structural details in more detail than may be necessary for a fundamental understanding of the disclosed subject matter and various ways in which it may be practiced. [0014] FIG. 1 shows an example aromatization reactor with catalyst and scandium hydrogen acceptor particles intermixed in a fluidized bed according to an embodiment of the disclosed subject matter.

[0015] FIG. 2 shows an example co-regeneration of both scandium hydrogen acceptor and catalyst particles in a single vessel according to an implementation of the disclosed subject matter. [0016] FIG. 3 shows an example of regeneration of scandium hydrogen acceptor and catalyst particles in separate vessels according to an embodiment of the disclosed subject matter.

[0017] FIG. 4 shows the relationship between methane conversion and time on stream based on various embodiments of the invention and comparative examples.

[0018] FIG. 5 shows the relationship between benzene yield and time on stream based on various embodiments of the invention and comparative examples.

[0019] FIG. 6 shows the relationship between naphthalene yield and time on stream based on various embodiments of the invention and comparative examples. DETAILED DESCRIPTION

[0020] The conversion of a methane-containing gas stream to aromatics is typically carried out in a reactor comprising a catalyst, which is active in the conversion of the methane-containing gas stream to aromatics. The methane-containing gas stream that is fed to the reactor comprises more than 50 % vol. methane, preferably more than 70 % vol. methane and more preferably of from 75 % vol. to 100 % vol. methane. The balance of the methane-containing gas may comprise other alkanes, for example, ethane, propane and butane. The methane-containing gas stream may be natural gas which is a naturally occurring hydrocarbon gas mixture consisting primarily of methane, with up to about 30 % vol. concentration of other hydrocarbons (usually mainly ethane and propane) as well as small amounts of other impurities such as carbon dioxide, nitrogen and others.

[0021] According to the present invention, the use of a scandium hydrogen acceptor in the reaction zone provides several advantages over the prior art. The present invention provides a scandium H2 acceptor and preferred operating conditions for the aromatization of methane-containing gas stream consisting of contacting the methane-containing gas stream in a reactor comprising methane aromatization catalyst and scandium hydrogen acceptor particles. The hydrogen acceptor material used in this reaction is a scandium metal H2 acceptor that has the ability, when subjected to aromatization operating conditions, to selectively accept or react with hydrogen to form a sufficiently strong hydrogen-scandium acceptor bond. The scandium H₂ acceptor reversibly binds the hydrogen in such a way that during operation in the reactor, the hydrogen is strongly bound to the scandium ¾ acceptor under the methane containing gas aromatization conditions. In addition, the scandium ¾ acceptor is able to release the hydrogen when subjected to regeneration conditions that favor release of the previously bound hydrogen and regeneration of the scandium ¾ acceptor. The present invention provides an efficient, high temperature scandium ¾ acceptor material that is capable of shifting the

thermodynamic equilibrium of the M2B reaction to significantly higher CH₄ conversion and benzene yields relative to the maximum allowable yields by the thermodynamic equilibrium in the absence of scandium ¾ acceptor material.

[0022] The conversion of a methane-containing gas stream is carried out at a gas hourly space velocity (GHSV) of from 100 to 60000 h^"1, a pressure of from 0.5 to 10 bar and a temperature of from 500 to 900 °C. More preferably, the conversion is carried out at gas hourly space velocity of from 300 to 30000 h^"1, a pressure of from 0.5 to 5 bar and a temperature of from 650 to 875 °C. Even more preferably, the conversion is carried out at gas hourly space velocity of from 500 to 10000 h^"1, a pressure of from 0.5 to 3 bar and a temperature of from 700 to 850 °C. The methane-containing gas aromatization is carried out until the methane conversion falls to values that are lower than those that are economically acceptable. At this point, the aromatization catalyst has to be regenerated to restore its aromatization activity to a level similar to its original activity. The regeneration of the catalyst could be carried out separately from the scandium ¾ acceptor or in the presence of the scandium ¾ acceptor. Also, the regeneration of the scandium ¾ acceptor may be carried out separately from the catalyst or in the presence of the catalyst.

Following the regeneration, the catalyst and the scandium ¾ acceptor are subjected to a methane-containing gas stream in the reaction zone of the aromatization reactor under aromatization conditions for continuous production of aromatics. [0023] Any catalyst suitable for methane-containing gas stream aromatization may be used in the process of this invention. The catalyst typically comprises one or more active metals deposited on an inorganic oxide support and may also include promoters or other beneficial compounds. The active metal or metals, promoters, compounds as well as the inorganic support all contribute to the overall aromatization activity, mechanical strength and performance of the aromatization catalyst. [0024] The active metal(s) component of the catalyst may be any metal that exhibits catalytic activity when contacted with a gas stream comprising methane under methane- containing gas aromatization conditions. The active metal may be selected from the group consisting of: vanadium, chromium, manganese, zinc, iron, cobalt, nickel, copper, gallium, germanium, niobium, molybdenum, ruthenium, rhodium, silver, tantalum, tungsten, rhenium, platinum and lead and mixtures thereof. The active metal is preferably molybdenum.

[0025] The promoter or promoters may be any element or elements that, when added in a certain preferred amount and by a certain preferred method of addition during catalyst synthesis, improve the performance of the catalyst in the methane-containing gas stream aromatization reaction.

[0026] The inorganic oxide support can be any support that, when combined with the active metal or metals and optionally the promoter or promoters contributes to the overall catalyst performance exhibited in the methane aromatization reaction. The support has to be suitable for treating or impregnating with the active metal compound or solution thereof and a promoter compound or solution thereof. The inorganic support preferably has a well-developed porous structure with sufficiently high surface area and pore volume and suitable for aromatization surface acidity. The inorganic oxide support may be selected from the group consisting of: zeolites, non-zeolitic molecular sieves, silica, alumina, zirconia, titania, yttria, ceria, rare earth metal oxides and mixtures thereof. The inorganic oxide support of this invention contains zeolite as the primary component. The zeolite is selected from the group consisting of ZSM-5, ZSM-22, ZSM-8, ZSM-11, ZSM-12 or ZSM-35 zeolite structure types. The zeolite is preferably a ZSM-5 zeolite. The ZSM-5 zeolite further may have a S1O₂/AI₂O₃ ratio of 10 to 100. Preferably, the S1O₂/AI₂O₃ ratio of the zeolite is in the range of 20-50. Even more preferably the S1O₂/AI2O₃ ratio is from 20 to 40 and most preferably about 30. The support may optionally contain about 15-70% wt of a binder that binds the zeolite powder particles together and allows for shaping of the catalyst in the desired form and for achieving the desired high catalyst mechanical strength necessary for operation in a commercial aromatization reactor. More preferably the support contains from 15-30 % wt. binder. The binder is selected from the group consisting of silica, alumina, zirconia, titania, yttria, ceria, rare earth oxides or mixtures thereof. [0027] The final shaped catalyst could be in the form of cylindrical pellets, rings or spheres. The preferred catalyst shape of this invention (for fluidized bed reactor operation) is spherical. The spherical catalyst of this invention could be prepared by any method known to those skilled in the art. Preferably, the spherical catalyst of this invention is prepared via spray drying of zeolite containing sols of appropriate concentration and composition. The zeolite containing sol may optionally contain binder. The spherical catalyst has particle size distribution and predominant particle size or diameter that makes it suitable for fluidization. The spherical particle diameter of the catalyst of this invention is preferably selected to be in the range of 20-500 microns. More preferably, the spherical catalyst of this invention has a particle diameter in the range of 50-200 microns. As an example, particle size may be based on the prevalent particle size measured from a particle size distribution. For example, if a particle size distribution is measured (e.g., using the light scattering method) of the spherical catalyst particles, the prevalent particle size may appear as a peak in a plot of the number of particles versus particle size. [0028] The usage of scandium hydrogen acceptor particles in a reactor when operating under aromatization conditions provides for the quick removal of the produced hydrogen from the reaction zone and for shifting the aromatization reaction equilibrium toward greater methane conversion and benzene yield per pass. The scandium hydrogen acceptor used in this reaction can be scandium metal, scandium-containing alloy or a scandium-containing compound that, when subjected to aromatization operating conditions, selectively accepts, absorbs or reacts with hydrogen to form a sufficiently strong scandium acceptor - hydrogen bond (such as for example in scandium hydride). In addition, the scandium hydrogen acceptor reversibly binds the hydrogen in such a way that during operation in the fluidized bed reactor the hydrogen is strongly bound to the scandium acceptor under the methane-containing gas stream aromatization conditions. Furthermore, the scandium hydrogen acceptor is preferably able to release the hydrogen when transported to the regeneration section where it is subjected to a different set of (regeneration) conditions that favor release of the previously bound hydrogen and regeneration of the scandium hydrogen acceptor. Additionally, the scandium hydrogen acceptor may include one or more other metals or elements that may enhance the ability of the scandium hydrogen acceptor to accept and/or release hydrogen and/or improve the physical properties of the scandium hydrogen acceptor in order to provide, for example, greater metal phase stability, mechanical rigidity and/or enhanced fluidization ability of the acceptor particles. For example, the scandium hydrogen acceptor may comprise one or more metals that are capable of selectively binding hydrogen under the methane-containing gas aromatization conditions in the reaction zone. The shaped scandium hydrogen acceptor particles may be in the form of irregular particles, cylindrical pellets, rings, tablets or spheres. The preferred scandium hydrogen acceptor particle shape for fluidized bed operation is spherical.

[0029] The aromatization reaction of this invention is carried out in a fluidized bed reactor. To enable this, suitably shaped and sufficiently robust catalyst and scandium hydrogen acceptor particles that are able to sustain the rigors of high severity fluidized-bed operation under methane aromatization reaction conditions are prepared and used for the reaction. According to the present invention, the use of the methane aromatization catalyst and scandium hydrogen acceptor in a fluidized bed reactor and configuration provides several important advantages over the prior art. The most significant advantage of the methane aromatization process of this invention is that it provides for insitu removal of hydrogen from the reaction zone and as a consequence, significant increase of both methane-containing gas stream conversion and benzene yield per pass to values that are significantly higher relative to these dictated by the methane aromatization reaction equilibrium. [0030] The process according to the present invention comprises contacting the methane-containing gas stream in a reaction zone of an aromatization reactor comprising an aromatization catalyst and a scandium hydrogen acceptor under methane-containing gas aromatization conditions to produce a product stream comprising aromatic s and hydrogen. Further, at least a portion of the produced hydrogen is bound by the scandium hydrogen acceptor in the reaction zone and removed from the product stream and from the reaction zone as a hydride comprising scandium. This is enabled by mixing and placing the catalyst and scandium hydrogen acceptor particles in a fluidized-bed state in the reaction zone or the aromatization reactor (see Figure 1). In Figure 1, a fluidized bed reactor 10 comprises a mixture 16 of spherical catalyst and scandium hydrogen acceptor particles in the fluidized bed 18. The methane-containing gas stream, the catalyst and scandium hydrogen acceptor particles are introduced via one or more inlets 20 and the products, unreacted gases, and optionally the catalyst and scandium hydrogen acceptor particles are removed from the bed via one or more outlets 22 or 12. The feed and products may flow upwards in the direction of arrows 20. The catalyst and scandium hydrogen acceptor may be introduced upwardly in the direction of arrows 20 or 14. The fluidized bed reactor could be operated in a bubbling bed or a rising bed (riser) configuration. In a bubbling fluidized bed configuration the freshly regenerated catalyst and the scandium acceptor particles may be continuously introduced through inlet 14 and spent (coked and deactivated) catalyst and scandium acceptor saturated with hydrogen could be withdrawn through outlet 22. In a rising fluidized bed (riser reactor) configuration the freshly regenerated catalyst and scandium acceptor are constantly introduced through inlet 20 and spent catalyst and saturated hydrogen acceptor particles are removed through outlet 12.

[0031] The mixing of both types of particles in a fluidized bed state provides for the quick removal of the produced hydrogen from the reaction zone and for shifting the aromatization reaction equilibrium toward greater methane-containing gas conversion and benzene yields per pass. Another advantage of the present invention is that it allows, under fluidized bed operating conditions, for volume expansion of the scandium hydrogen acceptor particles during the process of binding of hydrogen to take place without adverse effects on pressure drop.

[0032] Yet another advantage of the present invention is that, the particle shapes, sizes and mass of both scandium-comprising hydrogen acceptor and catalyst particles are designed and selected in such a way so that they could be co-fluidized in the reactor to form the desired bubbling or riser fluidized bed. Also, the invention provides for two or more different by chemical formula and/or physical properties (including scandium- comprising) hydrogen acceptors to be simultaneously used with the catalyst in the fluidized bed reactor to achieve the desired degree of hydrogen separation from the aromatization reaction zone, i.e. degree of thermodynamic equilibrium shift. Another important advantage of the process of this invention is that it provides for the reacted catalyst and the reacted scandium hydrogen acceptor particles to be simultaneously and continuously withdrawn from the reaction zone or the reactor, regenerated in separate vessel or vessels according to one of the schemes illustrated in Figures 2 and 3 and then continuously returned back to the reactor for continuous aromatics and hydrogen production. The scandium hydrogen acceptor particles and catalyst particles regeneration could be accomplished either simultaneously or stepwise in the same vessel as illustrated in Figure 2 or separately in separate vessels as illustrated in Figure 3. This later operation scheme provides for maximum flexibility to accomplish the hydrogen release or regeneration of the acceptor and catalyst under different and suitable for the purpose set of operating conditions. The regeneration of catalyst and scandium hydrogen acceptor could be accomplished in fixed, moving or fluidized bed reactor vessels schematically shown in Figures 2 and 3.

[0033] In Figure 2, regenerator vessel 100 is used to regenerate the reacted catalyst and scandium hydrogen acceptor particles mixture. The reacted catalyst and scandium hydrogen acceptor particles mixture may be introduced via either inlets 102 or 106 and are then removed via either outlets 104 or 108. The regeneration of the catalyst and scandium hydrogen acceptor particles may be carried out in fixed, moving or fluidized bed mode. The hydrogen removed from the scandium hydrogen acceptor particles during regeneration as well as the gases produced during catalyst particles regeneration are removed from the regenerator via one or more outlets (not shown). [0034] In Figure 3, regenerator system 200 comprises feeding of the reacted catalyst and scandium acceptor particles mixture from the reactor via line 204 to a separation step 202. The purpose of this separation step is to separate the reacted catalyst particles from the reacted scandium hydrogen acceptor particles. The separated catalyst particles are fed to catalyst regeneration vessel 206, and the separated scandium hydrogen acceptor particles are fed to the scandium hydrogen acceptor regeneration vessel 208. The catalyst and scandium hydrogen acceptor particles are then regenerated under appropriate regeneration conditions in their respective vessels and then mixed back together in mixing step 210. The regenerated and mixed catalyst and scandium acceptor particles are then fed back to the reactor via line 212. [0035] In the case of separate regeneration (see Figure 3), the scandium hydrogen acceptor particles could be separated from the catalyst on the basis of (but not limited to) differences in mass, particle size, density or on the basis of difference in magnetic properties between the acceptor and the catalyst particles. In the latter case, the scandium hydrogen acceptor of this invention could be selected from the group of materials exhibiting fero-, para-or diamagnetic properties and comprising, for example, elements such as Fe, Co or Ni. It is well known that, the methane-containing gas aromatization is accompanied with significant coke formation and deposition on the surface of the catalyst. Accumulation of coke on the surface of the catalyst gradually covers the active aromatization sites of the catalyst resulting in gradual reduction of its activity. Therefore, the coked catalyst has to be removed at certain carefully chosen frequency from the reaction zone of the aromatization reactor and regenerated in one of the regeneration vessels depicted in Figures 2 and 3. The regeneration of the catalyst can be carried out by any method known to those skilled in the art. For example, two possible regeneration methods are hot hydrogen stripping and oxidative burning at temperatures sufficient to remove the coke from the surface of the catalyst. If hot hydrogen stripping is used to regenerate the catalyst, then at least a portion of the hydrogen used for the catalyst regeneration may come from the hydrogen released from the scandium hydrogen acceptor. Additionally, fresh hydrogen may be fed to the catalyst regeneration vessel as needed to properly supplement the hydrogen released from the scandium hydrogen acceptor and to complete the catalyst regeneration. If the regeneration of the catalyst and scandium acceptor particles mixture is carried out in the same vessel (see Figure 2), then the hydrogen removed from the scandium hydrogen acceptor particles insitu could at least partially hydrogen strip and regenerate the catalyst particles. If the regeneration is carried out in different vessels (see Figure 3) the operating conditions of each vessel could be selected and maintained to favor the regeneration of the catalyst particles or the scandium hydrogen acceptor particles. Hydrogen removed from the scandium hydrogen acceptor particles could then again be used to at least partially hydrogen strip and regenerate the catalyst particles.

[0036] Yet another important advantage of the process of this invention over the prior art is that it provides for the release of the hydrogen that is bound to the scandium hydrogen acceptor particles when the hydrogen saturated acceptor particles are subjected to a specific set of conditions in the regeneration vessel(s). Furthermore, the released hydrogen could be utilized to regenerate the catalyst particles or subjected to any other suitable chemical use or monetized to improve the overall aromatization process economics. [0037] Another important advantage of the present invention is that it allows for different regeneration conditions to be used in the different regeneration vessel or vessels to optimize and minimize the regeneration time required for the catalyst and scandium hydrogen acceptor particles and to improve their performance in the methane aromatization reaction.

[0038] The aforementioned advantages of the process of the present invention provide for an efficient removal of hydrogen from the reaction zone of methane-containing gas aromatization reactor operating in fluidized bed mode and for shifting the reaction equilibrium towards higher methane-containing gas stream conversion and benzene yields per pass. Therefore, the present invention has the potential to allow for the

commercialization of an economically attractive direct, non-oxidative methane-containing gas stream aromatization process. EXAMPLES

[0039] In fixed bed methane aromatization performance tests, it was discovered that the operating conditions and homogeneity of catalyst and scandium acceptor particles mixing have a profound effect on the degree of methane aromatization thermodynamic equilibrium shift, i.e. on the increase of the CH₄ conversion and aromatics product yields beyond those dictated by the thermodynamic equilibrium.

[0040] Materials:

Scandium H? acceptor:

Pure scandium metal granule-shaped particles (made by American Elements, 1-2 mm granule size, PN# SC-M-0251M-GR.1T2MM) were used as a hydrogen acceptor material. Prior to use, the scandium metal particles were stored under inert gas atmosphere in order to prevent the formation of scandium oxide.

Methane Aromatization Catalyst:

An H-ZSM-5 zeolite powder (Zeolyst, ID# CBV3024) was pressed, crushed, and sieved to obtain a particle fraction of size 425-2000 μιη. The zeolite particles were then dried under a flow of dry air at 125°C for 1 hour, and subsequently calcined in a flow of dry air using a 3°C/min heating rate to 500°C and holding at this temperature for 4 hours. Two-hundred grams of the so calcined zeolite particle fraction were then impregnated with 160 mL of an aqueous solution of Μο(¾0₄)3 to afford an 8 wt% loading of Mo. The resulting impregnate was dried under a flow of dry air at 100°C for 2 hours, and then calcined in a flow of dry air using a 3°C/min heating rate to 300°C and held at this temperature for 2 hours. Following that, using the same heating atmosphere and rate the catalyst was heated to 500°C and held at this temperature for 3 hours. The obtained methane aromatization catalyst was found to contain 8% wt Mo/H-ZSM-5.

[0041] Catalyst Pretreatment and Reactor Loading Protocols:

Catalyst Pretreatment/Reduction:

[0042] Prior to activity testing, 10 cc (-6.8 g) of the dry methane aromatization catalyst were placed in a quartz reactor, purged with inert gas and then reduced insitu with a 20 L/hr (GHSV=2000 h^"1) flow of pure hydrogen. The temperature profile during the reduction was as follows: 0.5°C/min heating rate to 240°C (held at temperature for 5 hours), 2.0°C/min hearing rate to 480°C (held at temperature for 2 hours), 2.0°C/min heating rate to 700°C (held at temperature for 1.5 hours). The pre-reduced methane aromatization catalyst was then cooled in hydrogen to 400°C, and then cooled under 20 L/hr of argon (GHSV=2000 h^"1) to ambient temperature and kept sealed in the reactor.

Catalyst/Reactor Loading:

Following the reduction of the catalyst, specific amounts of the scandium H2-acceptor particles were loaded into the quartz reactor with the catalyst. The loading of the acceptor was accomplished while purging the catalyst bed with argon at a sufficiently high flow rate to fluidize the catalyst bed and to allow for good intermixing of the methane aromatization catalyst and the scandium H2-acceptor particles. The scandium acceptor particles were slowly dropped into the fluidized catalyst bed in order to allow for homogeneous intermixing of acceptor and catalyst particles. This was accomplished while gradually adding small portions of acceptor particles and gradually reducing the argon gas flow rate. Once all acceptor particles were added, the argon flow was stopped, and the reactor inlet and outlet immediately thereafter blocked to maintain an inert gas environment within the reactor, i.e. around the catalyst and acceptor particles. The reactor, with well-mixed methane aromatization catalyst and scandium H2-acceptor particles was then placed into a reactor furnace and connected to gas supply and outlet lines. [0043] Activity Testing:

Activity measurements were carried out using the following test conditions:

[0044] A sample was prepared as described above by mixing 6.8 g of scandium ¾- acceptor particles and 10 cc (-6.8 g) of pretreated methane aromatization catalyst particles to obtain a 1 : 1 scandium H2-acceptor / methane aromatization catalyst particles weight ratio. The sample was then tested as described above using a methane flow rate of 10 L/hr (GHSV=1000 h^"1). The sample was found to exhibit maximum CH₄ conversions of 33 wt% at 800°C, and maximum benzene yield of 18 wt% and maximum naphthalene yield of 9 wt%. [0045] Analytics:

The catalytic performance data were gathered by taking GC sample shots at 10-minute intervals via a fully-automated GC-sampling system. The CH₄ conversion, benzene, naphthalene, and ¾ yields were used as criteria for the evaluation of methane

aromatization activity. [0046] Results:

[0047] Figure 4 shows the methane conversion vs. time on stream (TOS) data obtained according to the process of the present invention. In particular, Figure 4 shows the CH₄ conversion vs. time on stream for different reaction temperatures. The GHSV is a measure of the volume of gas passing through volume of catalyst per unit of time and is obtained by dividing the feed gas flow rate through the reactor expressed in cubic centimeter per hour (cc/hr) by the catalyst volume also expressed in cubic centimeters. The test conditions were based on 100 % vol CH₄ feed, GHSV=1000 h^"1, 1 bara and 700- 800°C. As mentioned above, according to the process of the present invention, the obtained conversion of the methane-containing gas stream is at least 15 wt%, at least 19 wt%, and at least 33 wt%. CH₄ conversion in weight percent is calculated on the basis of experimental/test data by subtracting the CH₄ mass flow rate at reactor outlet from the CH₄ mass flow rate at reactor inlet and then dividing by the CH₄ mass flow rate at the reactor inlet and multiplying by 100, as shown below:

CH Conversion, wt% [CH Mass Flow Rate I n - CH Mass Flow Rate out] X 100

4 = 4 4

CH Mass Flow Rate In

4

[0048] The benzene yield (adjusted for coke) is calculated as the benzene mass produced (at reactor outlet) per unit of time divided by the total (including coke on catalyst) mass flow from the reactor outlet, as shown below:

Benzene yield, wt% Benzene Mass Out Per Unit of Time X 100

Total Adjusted Mass (Including Coke) Flow Rate Out

[0049] The naphthalene yield (adjusted for coke) is calculated as the naphthalene mass produced (at reactor outlet) per unit of time divided by the total (including coke on catalyst) mass flow from the reactor outlet, as shown below: Naphthalene yield, wt% Naphthalene Mass Out Per Unit of Time X 100

Total Adjusted Mass (Including Coke) Flow Rate Out

[0050] The data in Figure 4 shows that in the absence of the scandium acceptor, the lined-out methane aromatization catalyst affords approximately 11 % wt of methane conversion at 700°C , 16% wt of methane conversion at 750°C, and 21% wt of methane conversion at 800°C (see dashed lines in Figure 4). These experimentally obtained methane conversion values match the maximum allowed by M2B thermodynamic equilibrium methane conversion values at the respective temperatures. In contrast, the data for the scandium hydrogen acceptor and methane aromatization catalyst particles mixture shows that increasing the temperature from 700°C to 750°C to 800°C leads to a very significant increase in the methane conversion. Remarkably, the 1 : 1 mixture of scandium hydrogen acceptor and methane aromatization catalyst at GHSV= 1000 h^"1 and 800 °C (see curve in Figure 4 denoted with square shaped line markers) afforded approximately 33 %wt methane conversion. This represents significantly higher methane conversion relative to the maximum allowed methane conversion by the M2B thermodynamic equilibrium obtained at the same set of operating conditions without scandium hydrogen acceptor. [0051] Figure 5 shows the corresponding benzene yields obtained in the tests performed according to the present invention. In particular, Figure 5 shows benzene yield vs. time on stream for a 1: 1 scandium hydrogen acceptor/ M2B catalyst particles mixture and different temperatures. Test Conditions were 100 %vol CH₄ feed, GHSV=1000h^_1, 1 bara, and temperatures ranging from 700°C to 750°C to 800°C. Due to the M2B thermodynamic equilibrium limitations and the short duration (1 hr) of the test, the methane aromatization catalyst alone, i.e. in the absence of scandium acceptor (see dashed lines in Figure 5), afforded less than 6 % wt benzene yield at 700°C, less than 9%wt benzene yield at 750°C, and about 12 %wt of benzene yield at 800°C. In contrast, the data for the scandium acceptor and methane aromatization catalyst particles mixture shows again that a very significant increase in the benzene yield can be achieved by use of the scandium hydrogen acceptor. Specifically, increasing the temperature from 700°C to 750°C to 800°C leads to a very significant increase in the benzene yield beyond those expected by thermodynamic equilibrium. More specifically, at 700°C the scandium acceptor: catalyst mixture afforded, at GHSV=1000 h^"1, approximately 7% wt. benzene yield. Also, at 750°C the scandium acceptor: catalyst mixture afforded, at GHSV=1000 h^" ¹, approximately 12% wt. benzene yield. In addition, the mixture with the highest temperature of 800°C afforded 19% wt benzene yield (see curve in Figure 5 denoted with square shaped line markers). Therefore, in accord with the magnitude of the methane conversion advantage, the benzene yield advantage afforded by the methane aromatization catalyst and scandium acceptor mixtures is higher than the one observed for the methane aromatization catalyst alone. Furthermore, according to the process of the present invention, the obtained benzene yield per pass is at least 7 wt%, at least 12 wt%, and at least 19 wt%, as shown in Figure 5. These significantly higher yields of benzene relative to the ones dictated by the thermodynamic equilibrium and observed/reported in the prior art, indicate that the commercialization of the hydrogen acceptor assisted methane aromatization process of this invention would be a more attractive, than prior processes, from an economics perspective proposition.

[0052] Figure 6 shows the corresponding naphthalene yields obtained in the tests carried out according to the present invention. In particular, Figure 6 shows naphthalene yield vs. time on stream for scandium hydrogen acceptor/ M2B catalyst particle mixture at different temperatures. Test conditions were 100 %v CH₄ feed, GHSV=1000h^_1, 1 bara, and from 700°C to 800°C. Due to the low methane conversion dictated by the

thermodynamic equilibrium at these specific test conditions, the naphthalene yields afforded by the methane aromatization catalyst alone (see dashed lines in Figure 6) were found to be only approximately 3% wt at 700°C, 3.5% wt at 750°C and 4.5% wt at 800°C. However, the data for the scandium acceptor and methane aromatization catalyst mixture shows again that a very significant increase in the naphthalene yield can be achieved by the use of the scandium hydrogen acceptor. Furthermore, increasing the temperature from 700°C to 750°C to 800°C also leads to a very significant increase in the naphthalene yields beyond those expected by thermodynamic equilibrium. Specifically, at a temperature of 700°C, the mixture of scandium acceptor and methane aromatization catalyst afforded a naphthalene yield of about 7 %wt. Further, at a temperature of 750°C, the mixture of scandium acceptor and methane aromatization catalyst afforded a naphthalene yield of about 8 %wt. The largest increase was observed at a temperature of 800°C, the mixture of scandium acceptor and methane aromatization catalyst afforded a naphthalene yield of about 9% wt. This is a very significant increase in the naphthalene yields beyond the expected ones from thermodynamic equilibrium limitations. The significantly higher yields of naphthalene, relative to the ones allowed by equilibrium/afforded by the prior art, makes the commercialization of a (scandium) hydrogen acceptor assisted methane aromatization process of the present invention a more attractive proposition from an economics stand point. It should be noted that even higher CH₄ conversion and aromatics yields may be possible at different weight ratios of scandium acceptor to catalyst and different more optimal process conditions.

[0053] The foregoing description, for purpose of explanation, has been described with reference to specific embodiments. However, the illustrative discussions above are not intended to be exhaustive or to limit embodiments of the disclosed subject matter to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings. The embodiments were chosen and described in order to explain the principles of embodiments of the disclosed subject matter and their practical applications, to thereby enable others skilled in the art to utilize those embodiments as well as various embodiments with various modifications as may be suited to the particular use

contemplated.

Claims

C L A IM S

1. A process for the aromatization of a methane-containing gas stream comprising: contacting the methane-containing gas stream in a reaction zone of an

aromatization reactor comprising an aromatization catalyst and a scandium hydrogen acceptor under methane-containing gas aromatization conditions to produce a product stream comprising aromatics and hydrogen, wherein at least a portion of the produced hydrogen is bound by the scandium hydrogen acceptor in the reaction zone and removed from the product stream and the reaction zone.

2. The process of claim 1, wherein the methane-containing gas stream conversion and corresponding benzene yield per pass are higher than the conversion and yield obtained with the same aromatization catalyst and under the same methane-containing gas aromatization conditions, but in the absence of scandium hydrogen acceptor in the reaction zone of the aromatization reactor.

3. The process of claim 1, wherein the methane-containing gas stream also comprises lower alkanes selected from the group consisting of ethane, propane and butane.

4. The process of claim 1, wherein the methane-containing gas stream comprises at least 60 % vol. methane.

5. The process of claim 1, wherein the aromatization catalyst comprises a zeolite selected from the group consisting of ZSM-5, ZSM-22, ZSM-8, ZSM-11, ZSM-12 or ZSM-35.

6. The process of claim 1, wherein the aromatization catalyst comprises a metal selected from the group consisting of vanadium, chromium, manganese, zinc, iron, cobalt, nickel, copper, gallium, germanium, niobium, molybdenum, ruthenium, rhodium, silver, tantalum, tungsten, rhenium, platinum and lead and mixtures thereof.

7. The process of claim 1 wherein the scandium hydrogen acceptor comprises one or more metals.

8. The process of claim 1, wherein the methane aromatization conditions comprise a temperature in the range of from 500 °C to 900 °C.

9. The process of claim 1, wherein the aromatization reactor is a fluidized bed reactor.

10. The process of claim 1, further comprising continuously regenerating the catalyst to remove coke formed during the reaction and continuously regenerating the scandium hydrogen acceptor by releasing the hydrogen under regeneration conditions.

11. The process as claimed in claim 10, wherein the catalyst and scandium hydrogen acceptor are regenerated in a single regeneration vessel.

12. The process of claim 10, wherein the catalyst and scandium hydrogen acceptor are regenerated in separate vessels.

13. The process of claim 10, wherein the catalyst and scandium hydrogen acceptor are each regenerated under different regeneration conditions.

14. The process as claimed in claim 10, wherein the hydrogen released from the scandium hydrogen acceptor is used for catalyst regeneration.

15. The process of claim 14, wherein supplemental hydrogen is supplied from an external source in order to properly complete the catalyst regeneration.

16. The process of claim 10, wherein the regeneration of the scandium hydrogen acceptor is accomplished under regeneration conditions including: feed rate, temperature and pressure that are substantially different from the aromatization conditions.

17. The process of claim 10, wherein the regeneration of the scandium hydrogen acceptor is accomplished with regeneration gas comprising argon.

18. The process of claim 1, wherein the methane-containing gas stream is derived from biogas.

19. The process of claim 1, wherein the methane-containing gas stream is natural gas.