Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C2/00—Preparation of hydrocarbons from hydrocarbons containing a smaller number of carbon atoms
  • C07C2/76—Preparation of hydrocarbons from hydrocarbons containing a smaller number of carbon atoms by condensation of hydrocarbons with partial elimination of hydrogen
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C2529/00—Catalysts comprising molecular sieves
  • C07C2529/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites, pillared clays
  • C07C2529/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
  • C07C2529/40—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the pentasil type, e.g. types ZSM-5, ZSM-8 or ZSM-11
  • C07C2529/48—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the pentasil type, e.g. types ZSM-5, ZSM-8 or ZSM-11 containing arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium

Definitions

• This invention relates to a process for the aromatization of a methane-containing gas stream in a reactor containing both catalyst and hydrogen acceptor particles, wherein at least the hydrogen acceptor particles are in a moving bed state and the removal of hydrogen from the reaction zone is accomplished insitu by the hydrogen acceptor.
• aromatic hydrocarbons 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 price spikes result in severe aromatics shortages and 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 containing about 80-90 vol. methane).
• hydrocarbon feedstocks such as methane or stranded natural gas (which typically containing about 80-90 vol. methane).
• 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 underutilized. Many developing countries that have significant natural gas reserves lack the proper
• thermodynamic equilibrium, per pass conversion and benzene yield for example, 10 % wt. and 6 % wt., respectively at 700 °C
• thermodynamic equilibrium, per pass conversion and benzene yield for example, 10 % wt. and 6 % wt., respectively at 700 °C
• the fact that the reaction is favored by high temperature and low pressure for example, 10 % wt. and 6 % wt., respectively at 700 °C
• the fact that the reaction is favored by high temperature and low pressure
• the need to separate the produced aromatics and hydrogen from unreacted (mainly methane) hydrocarbon off gas and the rapid coke formation and deposition on the catalyst surface and corresponding relatively fast catalyst deactivation.
• overcoming the thermodynamic equilibrium limitations and significantly improving 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.
• the methane aromatization reaction can be described as follows:
• aromatization at atmospheric pressure is equilibrium limited to about 10 and 20 % wt. at reaction temperature of 700 or 800°C, respectively.
• experimental data showed that the above conversion levels correspond to about 6 and 11.5 % wt. benzene yield at 700 and 800 °C, respectively.
• the generation of 9 molecules of hydrogen per molecule of benzene during the reaction leads to significant volume expansion that suppresses the reaction to proceed to the right, i.e. it suppresses methane conversion and formation of reaction products, i.e. benzene yield.
• the aforementioned low per pass conversions and benzene yields are not very attractive to provide an economic justification for scale -up and commercialization of methane containing gas aromatization process.
• 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 with a moving bed comprising an aromatization catalyst and a hydrogen acceptor under methane- containing gas aromatization conditions to produce a product stream comprising aromatics and hydrogen wherein at least a portion of the hydrogen is bound by the hydrogen acceptor in the reaction zone and removed from the product and the reaction zone.
• the invention further provides a novel process and reactor schemes that employ single or multiple catalyst and/or hydrogen acceptor moving beds as well as a reactor that contains multiple fixed and moving beds of catalyst and hydrogen acceptor particles.
• the invention also provides several catalyst and/or hydrogen acceptor recycle and regeneration process schemes. According to these schemes, the catalyst and/or hydrogen acceptor particles are regenerated simultaneously or separately in single or in separate vessels and then returned back to the reactor for continuous (uninterrupted) production of aromatics and hydrogen.
• the aforementioned insitu hydrogen removal in the moving bed state allows for overcoming of 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 in the reaction zone.
• Figure 1 shows a schematic diagram of an embodiment of the invention
• aromatization reactor with a radial flow with catalyst and hydrogen acceptor particles intermixed in a single moving bed configuration.
• the catalyst and hydrogen acceptor particles are moving in a direction perpendicular to the gas feed flow.
• Figure 2 shows a schematic diagram of another embodiment of the invention: aromatization reactor with catalyst and hydrogen acceptor particles in separate stacked multiple moving beds configuration. The catalyst and hydrogen particles are moving in opposite direction to each other but both are perpendicular to the direction of the gas feed flow.
• Figure 3 shows a schematic diagram of yet another embodiment of the invention: aromatization reactor with multiple stacked beds of catalyst particles in fixed bed configuration and hydrogen acceptor particles in moving bed configuration. The hydrogen acceptor particles are moving in a direction perpendicular to the direction of the gas feed flow.
• Figure 4 shows a schematic diagram of an embodiment of the invention:
• FIG. 5 shows a schematic diagram of another embodiment of the invention:
• Figure 6 shows a schematic diagram of another embodiment of the invention:
• FIG. 7 shows a schematic diagram of another embodiment of the invention:
• 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 be 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.
• the conversion of a methane-containing gas stream is carried out at a gas hourly space velocity of from 100 to 60,000 h "1 , a pressure of from 0.5 to 10 bar and a temperature or from 500 to 900 °C. More preferably, the conversion is carried out at gas hourly space velocity of from 300 to 30,000 h "1 , a pressure of from 0.5 to 5 bar and a temperature of from 700 to 875 °C.
• the conversion is carried out at gas hourly space velocity of from 500 to 10,000 h "1 , a pressure of from 0.5 to 3 bar and a temperature of from 700 to 850 °C.
• Various co-feeds such as CO, C0 2 or hydrogen or mixtures thereof that react with coke precursors or prevent their formation during methane aromatization can be added at levels of ⁇ 10 % vol. to the methane-containing feed to improve the stability performance or regenerability of the catalyst.
• the methane aromatization is then carried out until conversion falls to values that are lower than those that are economically acceptable.
• the aromatization catalyst has to be regenerated to restore its aromatization activity to a level similar to its original activity. Following the regeneration, the catalyst is again contacted with a methane-containing gas stream in the reaction zone of the aromatization reactor for continuous production of aromatics.
• the catalyst typically comprises one or more active metals on an inorganic oxide support and optionally comprises promoters and other beneficial compounds.
• the active metal or metals, promoters, compounds and the inorganic support all contribute to the overall aromatization activity, mechanical strength and performance of the aromatization catalyst.
• the active metal component(s) of the catalyst may be any metal that exhibits catalytic activity when contacted with a methane-containing gas stream under methane 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.
• the promoter or promoters may be any element or elements that, when added in a certain preferred amount and by a certain preferred method during catalyst synthesis, improve the performance of the catalyst in the methane aromatization reaction.
• 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 a 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 preferably 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 Si0 2 /Al 2 0 3 ratio of 10 to 100.
• 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 Si0 2 /Al 2 0 3 ratio of 10 to 100.
• the zeolite is selected from the group consisting of ZSM-5, ZSM-22, ZSM-8, ZSM-11, ZSM- 12
• Si0 2 /Al 2 0 3 ratio of the zeolite is in the range of 20-50. Even more preferably the
• Si0 2 /Al 2 0 3 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. 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.
• the final shaped catalyst could be in the form of cylindrical pellets, rings or spheres.
• the preferred catalyst shape of this invention is spherical (for moving bed operation) or pellets (for fixed bed operation).
• the spherical or pelletized catalyst of this invention could be prepared by any method known to those skilled in the art.
• 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 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.
• the spherical catalyst of this invention has particle diameter in the range of 50-200 microns. More preferably, the spherical catalyst of this invention has particle diameter in the range of 50- 200 microns.
• the pelletized catalyst of this invention is prepared by extrusion of suitable extrusion mix containing appropriate concentration of zeolite powder and optionally binder.
• the hydrogen acceptor used in this reaction can be any metal-containing alloy or a compound that has the ability, when subjected to aromatization operating conditions, to selectively accept or react with hydrogen to form a sufficiently strong hydrogen-acceptor bond.
• the hydrogen acceptor preferably reversibly binds the hydrogen in such a way that during operation in the moving bed reactor the hydrogen is strongly bound to the acceptor under the methane containing gas aromatization conditions.
• the hydrogen acceptor is preferably able to release the hydrogen when transported to the regeneration section where it is subjected to regeneration conditions that favor release of the previously bound hydrogen and regeneration of the hydrogen acceptor.
• Suitable hydrogen acceptors include Ti, Zr, V, Nb, Hf, Co, Mg, La, Pd, Ni, Fe, Cu, Ag, Cr, Th as well as other transition metals, elements or compounds or mixtures thereof.
• the hydrogen acceptor may comprise metals that exhibit magnetic properties, for example Fe, Co or Ni or various ferro-, para- or dimagnetic alloys of these metals.
• One or more hydrogen acceptors that exhibit appropriate particle sizes and mass for moving bed operation may be used in the reaction zone to achieve the desired degree of hydrogen separation and removal.
• the aromatization reaction of this invention is carried out in a moving bed reactor.
• a moving bed reactor To enable this, suitably shaped and sufficiently robust catalyst and hydrogen acceptor particles that are able to sustain the rigors of high severity moving or moving and fixed bed operation are prepared and used for the reaction.
• the use of the catalyst and hydrogen acceptor in a moving bed reactor provides several advantages over prior art.
• the most significant advantage of the process of this invention is that it provides for insitu removal of hydrogen from the reaction zone and as a consequence, an 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 This is enabled by mixing and placing the catalyst and hydrogen acceptor particles in a moving-bed state in the reaction zone or the aromatization reactor (see Figures 1-3).
• the usage of hydrogen acceptor particles moving bed reactors 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.
• Figure 1 shows a reactor 10 with a single moving bed 12 that comprises a mixture of catalyst and hydrogen acceptor particles.
• the catalyst and hydrogen acceptor particles flow downward as shown by arrow 14, and the process gas flows upward through the center section and outward through the moving bed 12 as shown by arrows 16.
• Figure 2 shows a reactor 110 with multiple separate moving beds comprising catalyst or hydrogen acceptor particles.
• the reactor contains catalyst moving beds 120 and hydrogen acceptor moving beds 122. The catalyst and hydrogen acceptor particles move through each bed and the process gas flows upward as shown by arrow 116.
• Figure 3 shows a reactor 210 with multiple moving beds 222 comprising hydrogen acceptor particles and multiple fixed beds 220 comprising catalyst.
• the process gas flows upward as shown by arrow 216.
• Another advantage of the present invention is that it allows for volume expansion of the hydrogen acceptor particles during the process of binding of hydrogen to take place under moving bed operation conditions. Hydrogen acceptors undergo significant volume expansion in the process of binding hydrogen and at some point in the process the hydrogen acceptor will bind so much hydrogen that it reaches its maximum hydrogen binding capacity. If the acceptor were used in a fixed bed reactor configuration it would expand and agglomerate in the confined bed volume. This would cause agglomeration of the hydrogen acceptor particles, plugging and significant reactor pressure drop, and suppression of the aromatization reaction.
• Another advantage of the present invention is that, the particle shapes, sizes and mass of both hydrogen acceptor and catalyst particles can be designed and selected in such a way so that they can be combined together in the reactor to form the desired moving bed. Also, the invention provides for two or more different by chemical formula and/or physical properties hydrogen acceptors to be simultaneously used with the catalyst in the moving bed reactor to achieve the desired degree of hydrogen separation from the aromatization reaction zone.
• Another advantage of the process of this invention is that it provides for the catalyst and the hydrogen acceptor particles to be simultaneously and continuously withdrawn from the reaction zone, regenerated in a separate vessel or vessels according to one of the schemes illustrated in Figures 4-7 and then continuously returned back to the reactor for continuous aromatics and hydrogen production.
• the hydrogen acceptor and catalyst regeneration can be accomplished either simultaneously or stepwise in the same vessel as illustrated in Figure 4 or separately in separate vessels as illustrated in Figures 5-7. These later operation schemes provide for maximum flexibility to accomplish the hydrogen release or regeneration of the acceptor and catalyst under different and suitable for the purpose operating conditions.
• the regeneration of catalyst and hydrogen acceptor can be accomplished in fixed, moving or fhiidized bed reactor vessels schematically shown in Figures 4-7.
• the hydrogen acceptor particles can 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.
• the hydrogen acceptor of this invention can be selected from the group of materials exhibiting ferro-, para-or diamagnetic properties and comprising Fe, Co or Ni.
• the hydrogen acceptor particles are separated from the catalyst particles in the reactor or reactor zone and therefore do not need to be separated before entering their regeneration vessel.
• Figure 4 shows a regenerator vessel 300 that is used to regenerate the catalyst and regenerate the hydrogen acceptor.
• the catalyst and hydrogen acceptor particles are introduced via inlet 302 and are then removed via outlet 304.
• Hydrogen removed from the hydrogen acceptor and gases produced by catalyst regeneration are removed from the regenerator via one or more outlets (not shown).
• regenerator system 400 comprises a separation step 402 to separate the catalyst from the hydrogen acceptor that is fed from the reactor via line 404.
• the catalyst is fed to catalyst regeneration vessel 406, and the hydrogen acceptor is fed to hydrogen acceptor regeneration vessel 408.
• the catalyst and hydrogen acceptor are then mixed back together in mixing step 410 and then fed back to the reactor via line 412.
• FIG 6 shows a regeneration system 500 that comprises a regeneration vessel for the catalyst 502 and a regeneration vessel for the hydrogen acceptor 504. No separation step is required because this regeneration scheme is used for a reaction system like that shown in Figure 2 where the catalyst and hydrogen acceptor are kept separate.
• Figure 7 shows that the catalyst is regenerated insitu in the fixed catalyst beds 620 shown in Figure 3.
• the hydrogen acceptor is transported from the moving beds 622 to a regeneration vessel 630 for removing the hydrogen from the hydrogen acceptor.
• the methane aromatization catalyst forms coke during the reaction.
• the coked catalyst has to be removed at a certain carefully chosen frequency from the reaction zone of the aromatization reactor and regenerated in a regeneration vessel(s) as illustrated in Figures 4-6.
• a regeneration vessel(s) as illustrated in Figures 4-6.
• the coked catalyst is regenerated insitu in the reactor.
• the regeneration of the catalyst could be conducted by any of the methods known to those skilled in the art while the hydrogen acceptor particles are completely withdrawn or still moving through the reaction zone of the reactor.
• the regeneration of the catalyst can be carried out by any method known to those skilled in the art.
• two possible regeneration methods are hot hydrogen stripping and oxidative burn 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 hydrogen acceptor. Additionally, fresh hydrogen may be fed to the catalyst regeneration vessel as needed to properly supplement the hydrogen released from hydrogen acceptor and to complete the catalyst regeneration. If the regeneration is carried out in the same vessel (see Figure 4), then the hydrogen removed from the hydrogen acceptor insitu or exsitu can at least partially hydrogen strip and regenerate the catalyst.
• the operating conditions of each vessel can be selected and maintained to favor the regeneration of the catalyst or the hydrogen acceptor respectively.
• Hydrogen removed from the hydrogen acceptor can be used to at least partially hydrogen strip and regenerate the catalyst.
• Yet another advantage of the process of this invention is that it provides for the release of the hydrogen that is bound to the hydrogen acceptor when the saturated acceptor is subjected to the regeneration conditions in the regeneration vessel(s). Furthermore, the released hydrogen can be utilized to regenerate the catalyst or subjected to any other suitable chemical use or monetized to improve the overall aromatization process economics.
• Another advantage of the present invention is that, it allows for different regeneration conditions to be used in the different regeneration vessels to optimize and minimize the regeneration time required for the catalyst and hydrogen acceptor and to improve performance in the aromatization reaction.
• 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 moving 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

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