A membrane reactor for the cracking of hydrocarbons

Abstract

A membrane reactor for the cracking of hydrocarbons is disclosed. The reactor comprises a hydrocarbon feed inlet (11), a reaction zone (12) wherein hydrocarbons are cracked into reaction products composed of smaller molecules, energy supply means (13) configured to supply energy to said reaction zone (12), a membrane (14) configured to be selectively permeated by a permeate composed of at least part of the reaction products moving from the reaction zone (12) to a permeation zone (15) and separating from a retentate composed of a remaining part of the reaction products and unreacted hydrocarbons that remain in the reaction zone (12), an outlet (16) of the permeation zone (15) and an outlet (17) of the reaction zone (12). The membrane reactor comprises vibration generating means (18), configured to vibrate the membrane (14), said vibration generating means (18) being configured to generate ultrasonic vibrations.

Description

A Membrane Reactor for the Cracking of Hydrocarbons DescriptionTECHNICAL FIELD

[0001] The present disclosure concerns a membrane reactor for the cracking of hydrocarbons. Embodiments disclosed herein specifically concern a membrane reactor with means for the reduction of membrane fouling, degradation and insufficient performance. Also disclosed herein are methods for efficiently cracking of hydrocarbons in a membrane reactor and separating the reaction products.BACKGROUND ART

[0002] Hydrogen is emerging as a new energy vector and a viable fuel route. This is not only because hydrogen is the least polluting fuel, but also because different energy sources can be used to produce hydrogen and also because hydrogen can meet many energy needs, including residential applications, hydrogen fuel cell automobiles, energy carriers, and integrated heating and power generation systems.

[0003] However, hydrogen production techniques present technological challenges, including feedstock type, conversion efficiency, and the need for the safe integration of H2 production systems with H2 purification and storage technologies.

[0004] Hydrogen production may be based on renewable energy; on coal gasification and natural gas, along with CCS hydrogen generating systems; and on conventional fossil fuels. The majority of hydrogen is currently produced via the CCL-intensive steam methane reforming process. Electrolysis is a typical method that uses an electrical current to split water into oxygen and hydrogen and creates green hydrogen without any direct emissions of carbon dioxide. Renewable energy sources may be used to produce the necessary electricity. The expense of producing hydrogen, particularly for green hydrogen, is a significant hurdle.

[0005] In order to improve the production of hydrogen, membrane reactors are emerging as a technology useful to increase the reaction conversion and selectivity, and at the same time reduce energy requirements and allowing for smaller reactors size.

[0006] It is known that membrane reactors are physical devices that combine a chemical conversion process with a membrane separation process to add reactants or remove products of the reaction. The principle of membrane reactors is that the membrane acts as a barrier between the reactants and products, allowing the selective removal of one or more products from the reaction mixture. As a result, membrane reactors allow for increased conversion, because by removing one or more products from the reaction mixture, the equilibrium of the reaction can be shifted towards the products, leading to increased conversion, which can at the same time reduce the overall energy requirements of the process. Additionally, membrane reactors are smaller than reactors used for the same reaction which do not include membranes. This makes membrane reactors a promising technology for improving the efficiency of chemical reactions.

[0007] However, membrane reactors also have some drawbacks, including fouling, degradation, insufficient performance. Membrane fouling is the most frequent problem and is due to the membrane becoming clogged with impurities, which can reduce the efficiency of the reactor. Therefore, there are still some challenges that need to be addressed before membrane reactors can be widely adopted.

[0008] Accordingly, an improved system and method for more efficient membrane reactors would be beneficial and would be welcomed in the technology, both with regard to the production of hydrogen as a result of pyrolysis reactions of natural gas, and more in general for the cracking of hydrocarbons.SUMMARY

[0009] In one aspect, the subject matter disclosed herein is directed to a reactor for hydrocarbon cracking, the reactor comprising a membrane configured to be selectively permeated by at least part of the reaction products (called a permeate), wherein vibration generating means are configured to vibrate the membrane, said vibration generating means (18) being configured to generate ultrasonic vibrations. Both the permeate and the part of the reaction products that does not permeate the membrane, including unreacted hydrocarbons and called retentate, can comprise molecules of only one chemical compound or molecules of two or more chemical compounds. In particular, the permeate can comprise or can be composed of H2.

[0010] In another aspect, the subject matter disclosed herein is directed to a method for cracking of hydrocarbons in a reactor comprising a reaction zone and a membrane configured to be selectively permeated by at least part of the reaction products and vibration generating means configured to vibrate the membrane, the method comprising the steps of: feeding hydrocarbons to the reaction zone; supplying energy to the reaction zone to cause cracking of said hydrocarbons into reaction products composed of smaller molecules, a permeate composed of at least part of the reaction products permeating the membrane and moving to a permeation zone and separating from a retentate composed of a remaining part of the reaction products and unreacted hydrocarbons that remain in the reaction zone;- withdrawing the permeate from the permeation zone and withdrawing the retentate from the reaction zone; and- vibrating the membrane through the vibration generating means.

[0011] In one aspect, the step of vibrating the membrane comprises applying high frequency vibrations on the membrane, in particular ultrasonic vibrations with a frequency comprised between 15 and 400 kHz, preferably between 15 and 200 kHz, more preferably between 20 and 100 kHz.BRIEF DESCRIPTION OF THE DRAWINGS

[0012] A more complete appreciation of the disclosed embodiments of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:- Fig.1 illustrates a reactor for hydrocarbon cracking, according to a first embodiment; and- Fig.2 illustrates a reactor for hydrocarbon cracking, according to a second embodiment.DETAILED DESCRIPTION OF EMBODIMENTS

[0013] According to one aspect, the present subject matter is directed to a membrane reactor for the cracking of hydrocarbons, with the aim of increasing the reaction conversion and selectivity and decreasing the number of process units and the total required reactor volume by avoiding clogging of the membrane.

[0014] According to another aspect, the present subj ect matter is directed to a reactor for hydrocarbon cracking, the reactor comprising a hydrocarbon feed inlet, a reaction zone wherein hydrocarbons are cracked into reaction products composed of smaller molecules, energy supply means configured to supply energy to said reaction zone, a membrane configured to be selectively permeated by a permeate composed of at least part of the reaction products moving from the reaction zone to a permeation zone, an outlet of the permeation zone and an outlet of the reaction zone, wherein the reactor also includes vibration generating means that are configured to vibrate the membrane. The vibration generating means allow for in situ cleaning of the membrane and for preventing clogging of the membrane due to pores blockage. In particular, the present subject matter is applicable to different shapes and / or configurations of the membrane module, such as for example, but not limited to a single hollow cylinder with diameter smaller than the reactor diameter or multiple hollow cylinder (multi -tubular) with smaller diameter hung inside the reactor, other possible shapes including tubular, deadend, or U-type.

[0015] According to other aspects, both the permeate and the retentate can include molecules of only one chemical compound or molecules of two or more chemical compounds. Preferably, the permeate includes or is composed of H2.

[0016] According to one aspect, the vibration generating means are configured to generate ultrasonic vibrations with a frequency comprised between 15 and 400 kHz, preferably between 15 and 200 kHz, more preferably between 20 and 100 kHz.

[0017] According to another aspect, the membrane is made alternatively of a porous material or a dense material. The membrane can be made of a catalytic material, such as for example, but not limited to a material based on transition metals and metal oxides, in case natural gas or methane is reacted, preferably Ru, Ni, Co or Fe and bimetallic, intermetallic or trimetallic compounds thereof or Pd in the case of hydrogen production. The membrane can be made of a high temperature resistant material, suchas for example, but not limited to a ceramic material, namely perovskite or cement, cement membranes being a combination of a ceramic material as a pure proton conductor and a metallic material as a highly electron conductor, which may provide the durability needed by the contact with catalyst particles in case the reactor is a fluidized catalytic reactor with a fluidized suspension. The membrane can also be made of a combination of a ceramic and a metallic material.

[0018] According to one aspect, the energy supply means can be a microwave device or heating means, such as but not limited to an electrical heater, a fired heater, a heat exchanger configured to exchange heat with a combustor outlet fluid, a plasma device, steam.

[0019] According to one aspect, the reaction zone comprises a catalytic bed. In particular, the reactor can be a fixed bed, packed bed or fluidized catalytic bed reactor.

[0020] According to one aspect, when the hydrocarbon reacted in the reaction zone is natural gas or methane, the catalyst can be based on: iron, cobalt, nickel and bimetallic formulations thereof, and can be deposited on alumina or carbon. Preferably, the catalyst is a carbon based material, namely carbon black.

[0021] According to another aspect, the present subj ect matter is directed to a method for cracking of hydrocarbons in a reactor comprising a hydrocarbons feed inlet, a reaction zone wherein hydrocarbons are cracked into reaction products, energy supply means configured to supply energy to the reaction zone, a membrane configured to be selectively permeated by a permeate composed of at least part of the reaction products, to allow the permeate to move from the reaction zone to a permeation zone and to separate from a retentate composed of a remaining part of the reaction products that remain on the side of the reaction zone, an outlet of the permeation zone, an outlet of the reaction zone and vibration generating means configured to vibrate the membrane, the method comprising the steps of: feeding the hydrocarbons to the reaction zone; supplying energy to the reaction zone to cause cracking of the hydrocarbons into reaction products composed of smaller molecules, a permeate composed of at least part of the reaction products permeating the membrane and movingto the permeation zone and separating from a retentate composed of a remaining part of the reaction products that remain in the reaction zone;- withdrawing the permeate from the permeation zone through the outlet of the permeation zone and withdrawing the retentate from the reaction zone through the outlet of the reaction zone; and vibrating the membrane.

[0022] According to one aspect, the step of vibrating the membrane comprises applying high frequency vibrations, in particular ultrasonic vibrations, on the membrane. More in particular, the step of vibrating the membrane comprises applying vibrations with a frequency comprised between 15 and 400 kHz, preferably between 15 and 200 kHz, more preferably between 20 and 100 kHz.

[0023] Reference now will be made in detail to embodiments of the disclosure, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the disclosure, not limitation of the disclosure. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the scope or spirit of the disclosure. Reference throughout the specification to “one embodiment” or “an embodiment” or “some embodiments” means that the particular feature, structure or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrase “in one embodiment” or “in an embodiment” or “in some embodiments” in various places throughout the specification is not necessarily referring to the same embodiment s). Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.

[0024] When introducing elements of various embodiments the articles “a”, “an”, “the”, and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including”, and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.

[0025] Referring now to the drawings, Fig.1 shows a schematic of an exemplary reactor 10 for hydrocarbon cracking, the reactor comprising a membrane 14 configured to separate the products of the reaction of hydrocarbon cracking, according to a firstembodiment. In particular, the reactor 10 comprises a hydrocarbon feed inlet 11 and a reaction zone 12 wherein the hydrocarbons are cracked into reaction products composed of smaller molecules. Energy needed to sustain the cracking reaction is supplied to the reaction zone 12 by energy supply means 13, which can exemplarily be a microwave device or heating means, such as an electrical heater, a fired heater, a heat exchanger configured to exchange heat with a heating fluid, which can be in particular the combustor outlet fluid of a gas turbine, a plasma device or steam. A membrane 14 is arranged inside the reactor 10 and separate the reaction zone 12 from a different zone, called permeation zone 15. The membrane 14 is used to separate the reaction products on the basis of their size and / or their affinity with the material of the membrane 14, the membrane 14 allowing the permeation, i.e. the passage, of selected components of the gas mixture composed of the reaction products on the reaction zone side of the membrane 14 to the other side of the membrane 14, i.e. to the permeation zone 15. The mixture of components permeating the membrane 14 is called permeate and is withdrawn from the permeation zone 15 through an outlet 16 of the permeation zone 15. The mixture of remaining components of the reaction products, not permeating the membrane, is called retentate and can be collected from an outlet 17 at the bottom of the reaction zone 12. The reactor 10 for hydrocarbon cracking is supplied with vibration generating means 18, configured to vibrate the membrane 14. By vibrating the membrane 14, the vibration generating means 18 allows for cleaning of the membrane 14 and / or for preventing fouling and carbon deposition on the surface of the membrane, including clogging of the pores. In Fig.l, the membrane 14 is configured as a hollow cylinder, arranged inside the reactor 10, the reactor also being cylindrical. In some embodiments, the membrane can be configured as multiple hollow cylinders (multi -tubular membrane) hung inside the reactor, or also can have a tubular, deadend, or U-type shape.

[0026] In some embodiments, the membrane 14 is made of a porous material. In different embodiments, the membrane 14 is made of a dense material. In particular, the membrane 14 can be made of high temperature resistant materials, in particular a ceramic material, more in particular perovskite or cement. In some embodiments, the membrane 14 can be made of a combination of a ceramic and a metallic material. In some embodiments, the membrane 14 is made of a material acting as a catalyst in the reaction of cracking of hydrocarbons and / or separation of the products of the crackingreaction. In particular, the membrane 14 can be made of based on transition metals and metal oxides, and bimetallic, intermetallic or bimetallic compounds thereof.

[0027] In some embodiments, the vibration generating means 18 are configured to generate high frequency vibrations, in particular ultrasonic vibrations, with a frequency comprised between 15 and 400 kHz, preferably between 15 and 200 kHz, more preferably between 20 and 100 kHz.

[0028] In some embodiments, the energy supply means 13 is a microwave device or heating means, including but not limited to electrical heaters, a fired heater, plasma devices, steam, heat exchangers configured to exchange heat with heating fluids, including but not limited to a combustor outlet fluid.

[0029] The reactor 10 operates as follows. A stream of hydrocarbons is directed to the reaction zone 12 of the reactor 10, wherein the hydrocarbons are cracked into smaller product compounds, which can include hydrogen molecules. Depending on the operating condition, different types of cracking reaction can occur, including but not limited to cracking reaction caused by high temperatures (typically in the range 500-1000°C), presence of a catalyst, use of steam or hydrogen as a co-reactant or combinations thereof. The reaction products are composed of smaller molecules, the membrane 14 being selectively permeated by a part of the reaction products, called permeate, to allow said permeate to move from the reaction zone 12 to the permeation zone 15, while a remaining part of the reaction products, called retentate, remains in the reaction zone 12. The membrane 14, acting as a barrier between the reactants and products, therefore allowing the selective removal of one or more products from the reaction zone 12, allows for increased conversion of the reaction. In fact, by removing one or more products from the reaction zone 12, the equilibrium of the reaction can be shifted towards the products, leading to increased conversion, which can at the same time reduce the overall energy requirements of the process. Additionally, the membrane 14 also separates different types of reaction products. According to an exemplary embodiment, the cracking reaction is used to produce hydrogen starting from natural gas, the membrane 14 allowing separation of hydrogen, permeating the membrane 14, from solid carbon that can be collected from the outlet 17, at the bottom of the reaction zone 12. During operation of the reactor 10, solid carbon or other impurities can deposit on the surface of the membrane 14, or in the pores of the membrane 14. Vibratingthe membrane 14, either periodically or continuously during operation of the reactor 10, avoids the deposition of such impurities on the membrane or to clean the membrane 14. By mitigating fouling and deposition of fine carbon particles in the pores of the membrane 14, vibrating the membrane 14 allows for increasing the reaction conversion and selectivity, and at the same time reducing energy requirements, allowing for smaller reactors size and prolonging the lifetime of the membrane and catalyst, in the case catalyst is presence in the membrane. In particular, when natural gas or methane is used as reactant, the membrane 14 allowing permeation by hydrogen molecules, vibrating the membrane 14 allows for increased H2 purification efficiency and for in situ purification of H2 without using external equipment for hydrogen purification, which increases H2 production yield.

[0030] In some embodiments, the cracking reaction is conducted at atmospheric pressure. Due to the pressure drop between the reaction zone 12 and the permeation zone 15, such a low pressure of the cracking reaction implies the need for the permeation zone 15 to be maintained under a certain degree of vacuum to force the separation.

[0031] In some embodiments, according to the porous or dense structure of the membrane, the membrane can be vibrated by high frequency vibrations, in particular ultrasonic vibrations, with a frequency comprised between 15 and 400 kHz, preferably between 15 and 200 kHz, more preferably between 20 and 100 kHz.

[0032] With continuing reference to Fig. l, Fig.2 illustrates an embodiment of the reactor wherein a catalyst is used to operate the hydrocarbons cracking reaction. The same reference numbers designate the same or corresponding parts, elements or components already illustrated in Fig.1 and described above, and which will not be described again. The reactor 20 according to this embodiment is configured as a fluidized bed reactor, the reacting compound being preferably but not necessarily natural gas, more preferably methane. In this embodiment, carbon granules are used to catalyze the pyrolysis reaction and serve as a substrate for carbon deposition. Thus, the reaction can be conducted under moderate operating conditions and there is no need to regenerate the spent carbon. Natural gas and carbon granules 19 enter the reaction zone 12 of the reactor 20 through an inlet 21, at the bottom of the reaction zone 12. The spentcarbon granules are collected at the top of the reaction zone 12, though an outlet 22, together with the retentate.

[0033] In this embodiment, solid carbon from methane cracking and attrition of carbon granules with the surface of the membrane 14 can generate carbon dust, which obstructs membrane pores and diminish its performance. As a consequence, vibrating the membrane is needed in order to prevent coke deposition, fouling and pore obstruction. This result can be obtained by keeping the membrane under continuous or pulsed high frequency vibrations.

[0034] While the invention has been described in terms of various specific embodi- ments, it will be apparent to those of ordinary skill in the art that many modifications, changes, and omissions are possible without departing form the spirt and scope of the claims. In addition, unless specified otherwise herein, the order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments.

Claims

A Membrane Reactor for the Cracking of HydrocarbonsCLAIMS1. A reactor (10) for hydrocarbon cracking, the reactor comprising ahy- drocarbon feed inlet (11), a reaction zone (12) wherein hydrocarbons are cracked into reaction products composed of smaller molecules, energy supply means (13) configured to supply energy to said reaction zone (12), a membrane (14) configured to be selectively permeated by a permeate composed of at least part of the reaction products moving from the reaction zone (12) to a permeation zone (15) and separating from a retentate composed of a remaining part of the reaction products and unreacted hydrocarbons that remain in the reaction zone (12), an outlet (16) of the permeation zone (15) and an outlet (17) of the reaction zone (12), wherein vibration generating means (18) are configured to vibrate the membrane (14), said vibration generating means (18) being configured to generate ultrasonic vibrations.

2. The reactor of claim 1, wherein the reactor (10) is configured for gaseous hydrocarbon cracking.

3. The reactor of claim 1 or 2, wherein the membrane (14) is configured to be selectively permeated by a permeate including molecules of only one chemical compound.

4. The reactor of claim 1 or 2, wherein the membrane (14) is configured to be selectively permeated by a permeate including molecules of two or more chemical compounds.

5. The reactor of claim 3 or 4, wherein the membrane (14) is configured to be selectively permeated by a permeate separating from a retentate including molecules of only one chemical compound.

6. The reactor of claim 3 or 4, wherein the membrane (14) is configured to be selectively permeated by a permeate separating from a retentate including molecules of two or more chemical compounds.

7. The reactor of one or more of the preceding claims, wherein the membrane (14) is configured to be selectively permeated by a permeate including H2.

8. The reactor of claim 7, wherein said vibration generating means (18) are configured to generate vibrations with a frequency comprised between 15 and 400 kHz, preferably between 15 and 200 kHz, more preferably between 20 and 100 kHz.

9. The reactor of one or more of claims 1-8, wherein said membrane (14) is made of a porous material.

10. The reactor of one or more of claims 1-8, wherein said membrane (14) is made of a nonporous material.

11. The reactor of one or more of the preceding claims, wherein said membrane (14) is made of a ceramic material.

12. The reactor of claims 11, wherein said ceramic material is perovskite.

13. The reactor of one or more of the preceding claims, wherein said membrane (14) is made of a combination of a ceramic and a metallic material.

14. The reactor of one or more of the preceding claims, wherein said membrane (14) is made of a catalyst in the reaction of cracking of hydrocarbons and / or separation of the products of the cracking reaction.

15. The reactor of claim 14, wherein said catalyst is based on transition metals, including Ru, Ni, Co or Fe and bimetallic, intermetallic or trimetallic compounds thereof in case of cracking of natural gas or methane and / or Pd in case of hydrogen production.

16. The reactor of one or more of the preceding claims 1-15, wherein said energy supply means (13) comprises heating means (13).

17. The reactor of claim 16, wherein said heating means (13) is an electrical heater or fired heater.

18. The reactor of claim 16, wherein said heating means (13) is a heatexchanger configured to exchange heat with a combustor outlet fluid.

19. The reactor of claim 16, wherein said heating means (13) is a plasma device.

20. The reactor of claim 16, wherein said heating means (13) is steam.

21. The reactor of one or more of the preceding claims 1-15, wherein said energy supply means (13) is a microwave device.

22. The reactor of one or more of the preceding claims, wherein said reaction zone (12) comprises a catalytic bed.

23. The reactor of claim 21, wherein the reactor is a fluidized catalytic bed reactor.

24. The reactor of one or more of the preceding claims 22-23, wherein the hydrocarbon reacted in the reaction zone (12) is natural gas or methane and the catalyst is based on: iron, cobalt, nickel and / or bimetallic or trimetallic formulations thereof.

25. The reactor of claim 24, wherein the catalyst is deposited on alumina or carbon.

26. The reactor of claim 23, wherein the reacting compound is natural gas or methane and the catalyst is a carbon-based material, preferably carbon black.

27. A method for cracking of hydrocarbons in a reactor comprising a hydrocarbons feed inlet (11), a reaction zone (12) wherein hydrocarbons are cracked into reaction products composed of smaller molecules, energy supply means (13) configured to supply energy to said reaction zone (12), a membrane (14) configured to be selectively permeated by a permeate composed of at least part of the reaction products, to allow said permeate to move from the reaction zone (12) to a permeation zone (15) and to separate from a retentate composed of a remaining part of the reaction products and unreacted hydrocarbons that remain on the side of the reaction zone (12), an outlet (16) of the permeation zone (15), an outlet (17) of the reaction zone (12) and vibrationgenerating means (18) configured to vibrate the membrane (14), the method comprising the steps of: feeding said hydrocarbons to said reaction zone (12); supplying energy to said reaction zone (12) to cause cracking of said hydrocarbons into reaction products composed of smaller molecules, a permeate composed of at least part of the reaction products permeating the membrane (14) and moving to the permeation zone (15) and separating from a retentate composed of a remaining part of the reaction products and unreacted hydrocarbons that remain in the reaction zone (12);- withdrawing the permeate from the permeation zone (15) through the outlet (16) of the permeation zone (15) and withdrawing the retentate from the reaction zone (12) through the outlet (17) of the reaction zone (12); and applying ultrasonic vibrations on the membrane (14) through said vibration generating means (18).

28. The method of claim 27, wherein said hydrocarbons are gaseous hydrocarbons.

29. The method of claim 27 or 28, wherein the step of vibrating the membrane (14) comprises applying high frequency vibrations on the membrane.

30. The method of one or more of claims 27-29, wherein the step of vibrating the membrane (14) comprises applying ultrasonic vibrations on the membrane.

31. The method of one or more of claims 27-30, wherein the step of vibrating the membrane (14) comprises applying vibrations with a frequency comprised between 15 and 400 kHz, preferably between 15 and 200 kHz, more preferably between 20 and 100 kHz.

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