Process for producing synthesis gas using a methane-rich off-gas as a feedstock

Abstract

A method for producing synthesis gas (syngas) is provided. The method includes obtaining a methane-rich tail gas stream from a hydrocarbon cracker unit and utilizing the methane-rich tail gas stream as a feed stream for a steam methane reformer reactor to produce a syngas product. Either or both of the hydrocarbon cracker unit and the steam methane reformer reactor are heated by electrical power, which can be generated from a renewable resource. The methane-rich tail gas can be subjected to one or more treatment stages prior to utilizing the methane-rich tail gas as a feed stream for the steam methane reformer reactor.

Description

Technical Field

[0001] This invention relates to a method for producing syngas (syngas) using a steam methane reformer. Suitablely, the method utilizes an electrically heated reactor and apparatus, wherein the electrical energy is provided by a renewable energy source. Background Technology

[0002] To address the considerable challenge of decarbonizing the global economy in order to achieve net-zero targets by the end of the 21st century, there is a growing trend towards using more renewable resources in industrial processes. While improvements in energy efficiency and the selection of renewable electrified manufacturing assets can help reduce carbon footprints, certain petrochemical processes, such as steam crackers, continue to generate waste streams (such as steam cracker tail gas). Conventionally, this tail gas is burned as fuel and used to power other refineries or petrochemical processes. However, with the advancement of electrification, methane-rich tail gas will no longer be burned.

[0003] EP3075704 relates to a furnace for steam reforming a feed stream of hydrocarbons, preferably methane. In addition to at least one burner configured to heat multiple reactor tubes, at least one voltage source is connected to the multiple reactor tubes in a manner that generates current for heating.

[0004] EP4081337 describes an electrically heated reactor with an outer surface area, an inlet, and an outlet. The reactor is a tube surrounded at a certain distance by an electrically heated device; the electrically heated device includes radiant sheets placed coaxially with respect to the reactor tube. The reactor can be used in many industrial-scale high-temperature gas conversion and heating technologies.

[0005] WO2022 / 219053 describes a modular reactor configuration utilizing resistance heating elements that extend through the reaction zone of the reactor module. Resistance heating is used in the reaction zone to facilitate the conversion of reactants into products when reactants are present.

[0006] WO2022 / 038230 describes the use of a hydrocarbon feedstock for electro-steam methane reforming (e-SMR) to produce a syngas stream. An upgrading section receives the syngas stream and generates a first product stream and an exhaust stream from it. A generator receives at least a portion of the exhaust stream and / or a portion of the first product stream from the upgrading section and / or a portion of the first feedstock for combustion to generate electricity that can be used to power the e-SMR.

[0007] Therefore, it is desirable to identify alternative methods for recycling methane-rich exhaust gases and gases that do not require combustion. This could increase value and methodological efficiency considerably, and also contribute to the overall goal of reducing carbon dioxide emissions. These and other objectives of the present invention will become apparent to those skilled in the art, thus providing a solution to these previously unmet needs. Summary of the Invention

[0008] The present invention provides the use of methane-rich tail gas as feedstock for valuable synthesis processes, where such methane-rich tail gas has been regarded as waste and / or designated as fuel gas for combustion.

[0009] In a first aspect, the present invention provides a method for producing syngas, the method comprising: obtaining a methane-rich tail gas stream from a hydrocarbon cracking unit; and using the methane-rich tail gas stream as a feed stream for a steam methane reformer reactor to produce syngas products, wherein either or both of the hydrocarbon cracking unit and the steam methane reformer reactor are heated by electrical energy.

[0010] In one specific embodiment of the invention, both the hydrocarbon cracker unit and the steam methane reformer reactor are heated by electrical energy.

[0011] In another embodiment of the invention, the electrical energy supplied to either or both of the hydrocarbon cracker unit and the steam methane reformer reactor is generated from renewable resources.

[0012] In one embodiment of the invention, either or both of the hydrocarbon cracker unit and the steam methane reformer reactor are heated by resistance heating.

[0013] According to another embodiment, the method further includes: utilizing syngas in one or more synthesis methods selected from the group consisting of: ammonia production; methanol production; hydrogen (H2) production, such as via water-gas shift (WGS) reaction; Fischer-Tropsch synthesis; and utilizing syngas in carbon capture and storage (CCS) methods.

[0014] In one specific embodiment of the invention, the method further includes an intermediate step of pretreating the methane-rich tail gas stream before using it as the feed stream for a steam methane reformer reactor. Suitably, the pretreatment method includes a desulfurization step. Optionally, the desulfurization step includes one or more of the following: using a sulfur-protected bed; amine treatment; and / or the use of hydrodesulfurization methods.

[0015] In another embodiment, the pretreatment method includes removing nitrogen from the methane-rich tail gas stream. Suitably, nitrogen removal includes one or more of the following: cryogenic distillation; membrane separation; molecular gate systems; solvent absorption; nitrogen sponge; and / or pressure swing adsorption.

[0016] A second aspect of the present invention provides a system for producing synthesis gas (syngas), the system comprising:

[0017] Hydrocarbon cracker unit; and

[0018] Steam methane reformer reactor;

[0019] Both the hydrocarbon cracker unit and the steam methane reformer reactor are electrically heated, and the methane-rich tail gas from the hydrocarbon cracker unit is directed as a feed stream to the steam methane reformer reactor. In one embodiment, the hydrocarbon cracker unit and the steam methane reformer reactor are configured to be heated by resistance heating.

[0020] In one specific embodiment, the system includes one or more tail gas treatment units located between a hydrocarbon cracking unit and a steam methane reformer reactor. Suitably, the one or more tail gas treatment units include a desulfurization unit selected from one or more of the following: a sulfur guard bed; an amine treatment unit; or a hydrodesulfurization unit. Optionally or additionally, the one or more tail gas treatment units may include a nitrogen removal unit selected from one or more of the following: a cryogenic distillation unit; a membrane separator; a molecular gate system; a solvent absorption unit; a nitrogen sponge; or a pressure swing adsorption unit.

[0021] Within the scope of this application, the various aspects, embodiments, examples, and alternatives, and in particular their individual features, that are expressly intended to be set forth in the foregoing paragraphs, claims, and / or the following description and drawings, may be employed independently or in any combination. That is, all embodiments and / or features of any embodiment may be combined in any manner and / or combination unless such features are incompatible. Attached Figure Description

[0022] Figure 1 A schematic diagram of a method flow according to an embodiment of the present invention is shown.

[0023] Figure 2 A schematic diagram of a method flow according to another embodiment of the present invention is shown.

[0024] Figure 3 A schematic diagram of a method flow according to another embodiment of the present invention is shown. Detailed Implementation

[0025] All references cited herein are incorporated herein by reference in their entirety. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0026] Before describing the present invention, a number of definitions are provided to aid in understanding the invention.

[0027] As used herein, the term "comprising" means that any of the listed elements must be included, and other elements may optionally be included. "consistently of" means that any of the listed elements must be included, excluding elements that would substantially affect the fundamental and novel characteristics of the listed elements, and other elements may optionally be included. "consisting of" means excluding all elements other than those listed. Embodiments defined by each of these terms are within the scope of this invention.

[0028] As used in this article, the term "reactor"

[0029] This should be understood to include any industrial-scale reaction and process heating.

[0030] Industrial reactors, and,

[0031] Therefore, the term reactor tube should be understood as...

[0032] Including any container in the form of a tube, wherein

[0033] The substance is heated to a high temperature.

[0034] The terms “feed,” “raw material,” or “feed stream” should be considered synonymous. These terms refer to at least one input reagent that is introduced into the reactor and the starting material and is designated as at least one output effluent from the reactor through chemical conversion, which may be in the form of a reaction product that contributes to the yield or as a byproduct (such as a waste stream).

[0035] As used herein, the term "renewable energy" generally refers to energy derived from one or more technologies that utilize supplemental energy sources such as water, wind, solar, geothermal, and biomass sources (such as energy crops). Such renewable energy sources can include, but are not limited to, wind turbines, solar panels, solar panel arrays, solar panel strings, wind turbines, hydroelectric power plants utilizing hydropower and hydroelectricity, combined heat and power plants utilizing biomass materials, biofuels, biodiesel, geothermal energy, and combinations thereof. Therefore, renewable electronics (e...) - () is a component of electricity supply derived from renewable energy sources.

[0036] When applied to the feed or product of a reaction, the term "treatment" is used herein to refer to one or more steps applied to the feed or product to remove contaminants and / or condition the feed or product for subsequent process steps. Typically, one or more treatment steps may include concentration, purification, drying (e.g., dehydration), removal of one or more contaminants, temperature alteration (e.g., cooling or heating), heat recovery (such as through a heat exchanger), and / or mixing with other feed streams. Where treatment is applied prior to a specified process step, the term may be considered synonymous with "pretreatment."

[0037] The petrochemical industry relies on the use of olefins as one of the most common structural units in a wide range of petrochemical products, such as solvents, polymers, resins, coatings, and fibers. Traditionally, the most efficient way to produce olefins is via thermal cracking of hydrocarbon feedstocks (raw materials) derived from crude oil or natural gas. Steam cracking is one such method, and it is an advantageous route.

[0038] Steam crackers are generally considered the core of olefin process equipment, especially when used for ethylene production. Because the cracking reaction is highly endothermic, the cracker unit has very high energy consumption. By subjecting feedstock hydrocarbons, typically high in ethane, to high temperatures under low pressure, they undergo dehydrogenation to primarily form ethylene and hydrogen. Other products may include methane, acetylene, propylene, propane, and butadiene. This series of products is obtained through a complex combination of free radical mechanisms. As mentioned, the net effect of these reactions is endothermic; therefore, to increase ethylene yield, external energy must be supplied to maintain the reactor temperature. Traditionally, the need for external energy is met by burning methane tail gas / exhaust gas, which is produced as a byproduct of various petrochemical refinery processes, including the aforementioned cracking reactions. However, there is a growing trend to reduce the production of carbon dioxide from burning tail gas / exhaust gas. This is achieved by supplying heat to the cracker unit using resistance heating technologies that utilize an electronic supply from renewable resources, known as e-crackers. However, this trend has led to the accumulation of exhaust gases that are no longer needed for combustion, and it is necessary to find a use for these gases in the process flow of petrochemical refineries.

[0039] Syngas (an abbreviation for synthesis gas) is a mixture of gases primarily composed of carbon monoxide (CO) and hydrogen (H2). It is a versatile intermediate with wide applications in various industrial processes. Syngas can be produced through different methods, including steam methane reforming (SMR). Syngas can be used in a wide variety of synthesis methods, including but not limited to: ammonia production; methanol production; hydrogen (H2) production, such as via water-gas shift (WGS) reaction; Fischer-Tropsch synthesis; and its use in carbon capture and storage (CCS) processes. Therefore, the versatility of syngas makes it a valuable component in the production of various industrial chemicals.

[0040] According to one embodiment of the invention, the methane-rich tail gas originates from a hydrocarbon cracking reaction, typically an ethane cracker, more preferably an ethane e-cracker, and optionally an ethane e-cracker capable of operating on renewable electricity. The methane-rich tail gas is used as feedstock for a steam methane reforming reaction, more preferably an electro-steam methane reforming (eSMR) reaction, optionally also an eSMR reaction capable of operating on renewable electricity. The product of the eSMR is syngas, which can be used in various synthesis methods. In this way, the methane-rich tail gas is not diverted to combustion for the purpose of heating various reactors or as a flare. Attached Figure Description

[0041] Figure 1 A method flow according to a first embodiment of the invention is illustrated. A hydrocarbon feed (HC) is provided to a cracker unit. The HC feed may contain a range of hydrocarbons typically used for cracking, including light alkanes (such as ethane, propane, butane, and LPG) and heavier alkanes (such as naphtha or heavy hydrocarbon liquid feed). In one specific embodiment, the HC contains a substantial proportion of ethane used to form lower olefins (such as ethylene). The cracker typically includes a reactor defining a cracking zone. If the cracker unit includes a steam cracker, an additional feed may contain steam. The reactor is surrounded by an electric heating device, suitably in the form of a layer of radiant sheets. This heat source results in the cracker being designated as a type of e-cracker. The electric heater is typically powered by renewable resources (in... Figure 1 The label is marked as renewable e - The electricity generated is supplied by the power plant.

[0042] The reactor effluent from the cracker unit includes lower olefins (such as ethylene) as reaction products. Exhaust gas (such as methane-rich tail gas) is another effluent stream. According to the invention, the tail gas is included in the feed for a steam methane reformer (SMR).

[0043] Exhaust gas can be pretreated before being introduced into the SMR. Generally, pretreatment may involve removing other acidic gases from the exhaust gas through alkaline scrubbing. The exhaust gas can then be cooled using refrigerant in a series of heat exchangers to effectively separate any hydrogen from the remaining exhaust gas and enrich the methane content. The methane can then be further separated from any remaining heavier exhaust gases and directed to the SMR.

[0044] The exhaust gas from the cracker can include a range of polluting sulfur compounds, such as acidic gas components. Sulfur can be present in small amounts as hydrogen sulfide (H2S), thiols (e.g., methanethiol, 1-ethanethiol, 2-propanethiol, 2-butanethiol, 2-methyl-2-propanethiol, pentamethiol, hexamethiol, heptathiol, octanethiol, nonanethiol, and thiophene), and / or thiophenes (e.g., thiophene, 2-methylthiophene, 3-methylthiophene, 2-ethylthiophene, benzothiophene, and methylbenzothiophene). Even small amounts of sulfur-containing compounds are known to deactivate or “poison” catalysts that can be used in downstream processes, including SMR reactions and subsequent reactions. Therefore, the removal of sulfur compounds from the exhaust gas can be achieved through a number of suitable methods, including but not limited to the use of sulfur-protected beds (with catalysts having Cu, Cu / Zn, Ni, Pd, Mo, Co, Ni / Mo, Co / Mo, etc.), amine treatment, and / or hydrodesulfurization methods similar to hydrotreating technologies used in other refinery processes. Catalysts that can be used as hydrodesulfurization catalysts can include Group VIIIB metals (such as cobalt, nickel, palladium), alone or in combination with other transition metals (such as molybdenum or tungsten), on a suitable support, such as alumina, silica-alumina, or titanium dioxide-zirconia. Hydrodesulfurization catalysts can also contain components from Groups VB and VIB of the periodic table, or mixtures thereof. The catalyst can contain Group VIB metals (such as molybdenum) and Group VIIIB metals (such as cobalt or nickel). Catalysts suitable for hydrodesulfurization reactions include cobalt-molybdenum, nickel-molybdenum, and nickel-tungsten. The metals are typically present as oxides supported on a neutral matrix (such as alumina or silica-alumina). The sulfur removal step can be carried out in a discrete unit or facility configured for this purpose.

[0045] In some refinery and petrochemical processes, methane-rich tail gas can be combined with other methane-containing feed streams that may contain a certain amount of nitrogen, either as a carrier gas or as a diluent from natural gas extraction. Nitrogen can be present in amounts up to about 20% m, and while it can be considered a predominantly inert component, its presence can cause problems for further downstream processing. First, nitrogen acts as a diluent, reducing the effective concentration of methane in the SMR reaction feed stream and thus affecting the yield of the resulting products. Second, there is evidence that nitrogen can contribute to the formation of small amounts of ammonia in the presence of certain types of catalysts, such as under SMR reaction conditions. In fact, the inventors have found that with a 20% m nitrogen content in the tail gas stream used for SMR, the SMR effluent may contain up to 0.02% m ammonia. As a contaminant, the highly reactive ammonia present in the feed stream used for downstream reactions can poison the SMR and the catalysts used in those downstream processes. Clearly, the continued presence of nitrogen in the tail gas feed for SMR results in the production of a certain amount of ammonia, albeit a small amount, which is sufficient to deactivate the catalyst used in the process over time.

[0046] Nitrogen can be removed during pretreatment using a range of techniques and strategies. Nitrogen removal can be performed in discrete units or facilities configured for this purpose. One commonly used nitrogen removal process involves cryogenic distillation, in which a series of steps are performed on the nitrogen-containing tail gas, including compression, Joule-Thomson (JT) / expander cooling, cryogenic fractionation into component gases, and recompression of the methane-rich fraction of the tail gas. Alternatively, specialized proprietary membranes can be used to remove nitrogen from the tail gas stream and select methane for further processing in SMR to produce the desired product. Adsorbent / absorbent methods, such as those using molecular gate systems, solvent absorption, or nitrogen sponges, can also be employed. Pressure swing adsorption (PSA) methods can also be used to separate nitrogen from the tail gas under pressure based on the molecular properties of nitrogen and its attraction to the adsorbent material at near-ambient temperatures. Specialized adsorbent materials are used as molecular sieves to adsorb hydrocarbon components (e.g., methane) under high pressure. The method then switches to a low pressure to desorb the adsorbent material, thereby releasing a nitrogen-poor, methane-rich stream.

[0047] In SMR, methane reacts with vapor in the presence of a catalyst (usually nickel-based) to produce carbon monoxide and hydrogen via the following reaction:

[0048] CH4 + H2O → CO + 3H2

[0049] Similar to the furnace contained within an e-cracker unit, the SMR reactor is suitably surrounded by an electric heating device, typically in the form of a layer of radiant sheets. This heat source results in the cracker being designated as a type of e-SMR. The electric heater is typically powered by renewable resources (in... Figure 1 The electricity generated is marked as renewable (e-).

[0050] The reactor effluent from the e-SMR is in the form of syngas, which can be used for various further synthesis methods. Figure 2 It shows Figure 1 The methods shown and described above are integrated with a range of these further synthetic methods. Syngas can be used as a feed stream for methanol (MeOH) production; hydrogen (H2) production, such as via water-gas shift (WGS) reaction; Fischer-Tropsch (FT) synthesis; and in carbon capture and storage (CCS) methods. Figure 3 It shows Figure 2 The method further incorporates one or more exhaust gas treatment steps (as described herein) to remove contaminants and enrich the methane content of the exhaust gas prior to the introduction of e-SMR. The exhaust gas treatment steps can be carried out in a separate unit or facility configured for this purpose.

[0051] The invention will now be further illustrated with reference to the following non-limiting embodiments.

[0052] Example

[0053] The typical tail gas composition from the e-cracker is shown in Table 1 below. Table 1 provides a baseline reference composition in which nitrogen is absent. This baseline composition is compared to an exemplary composition containing 20 mg% nitrogen that may be found in typical refinery processes.

[0054] Table 1

[0055]

[0056] The output of a typical e-SMR is a model simulated using methods for SMR (e.g., Aspen Plus). ® The method uses a baseline scenario and a 20% nitrogen tail gas composition as the feed stream. The results are shown in Table 2 below.

[0057] Table 2

[0058]

[0059] The presence of ammonia (0.02 m%) in the 20 m% nitrogen feed stream indicates that at least complete or partial removal of nitrogen from the tail gas would be desirable prior to the e-SMR stage of this method.

[0060] Although specific embodiments of the invention have been disclosed in detail herein, this has been done by way of example and for illustrative purposes only. The foregoing embodiments are not intended to limit the scope of the appended claims. The inventors anticipate that various substitutions, alterations, and modifications can be made to the invention without departing from the spirit and scope of the invention as defined in the claims.

Claims

1. A method for producing syngas (syngas), the method comprising: Obtain a methane-rich tail gas stream from the hydrocarbon cracking unit; as well as The methane-rich tail gas stream is used as the feed stream for a steam methane reformer reactor to produce syngas products. Either or both of the hydrocarbon cracker unit and the steam methane reformer reactor are heated by electrical energy.

2. The method according to claim 1, wherein both the hydrocarbon cracker unit and the steam methane reformer reactor are heated by electrical energy.

3. The method of claim 1, wherein the electrical energy provided to either or both of the hydrocarbon cracker unit and the steam methane reformer reactor is generated from renewable resources.

4. The method according to claim 1, wherein either or both of the hydrocarbon cracker unit and the steam methane reformer reactor are heated by resistance heating.

5. The method of claim 1, wherein the method further comprises utilizing the syngas in one or more synthesis methods selected from the group consisting of: ammonia production; methanol production; hydrogen (H2) production, such as via a water-gas shift (WGS) reaction; Fischer-Tropsch synthesis; and utilizing the syngas in carbon capture and storage (CCS) methods.

6. The method of claim 1, wherein the method further comprises an intermediate step of pretreating the methane-rich tail gas stream before using the methane-rich tail gas stream as a feed stream for the steam methane reformer reactor.

7. The method according to claim 6, wherein the pretreatment method includes a desulfurization step.

8. The method of claim 7, wherein the desulfurization step comprises one or more of the following: using a sulfur-protected bed; amine treatment; and / or the use of a hydrodesulfurization method.

9. The method of claim 6, wherein the pretreatment method comprises removing nitrogen from the methane-rich tail gas stream.

10. The method according to claim 9, wherein the removal of nitrogen comprises one or more of the following: cryogenic distillation; membrane separation; molecular gate system; solvent absorption; nitrogen sponge; and / or pressure swing adsorption.

11. A system for producing syngas (syngas), the system comprising: Hydrocarbon cracker unit; and Steam methane reformer reactor; Both the hydrocarbon cracker unit and the steam methane reformer reactor are electrically heated, and the methane-rich tail gas from the hydrocarbon cracker unit is directed as a feed stream to the steam methane reformer reactor.

12. The system of claim 11, wherein the hydrocarbon cracker unit and the steam methane reformer reactor are configured to be heated by resistance heating.

13. The system of claim 11, wherein the system comprises one or more tail gas treatment units located between the hydrocarbon cracker unit and the steam methane reformer reactor.

14. The system of claim 13, wherein the one or more exhaust gas treatment units comprise a desulfurization unit selected from one or more of the following: a sulfur protection bed; an amine treatment unit; or a hydrodesulfurization unit.

15. The system of claim 13, wherein the one or more exhaust gas treatment units comprise a nitrogen removal unit selected from one or more of the following: a cryogenic distillation unit; a membrane separator; a molecular gate system; a solvent absorption unit; a nitrogen sponge; or a pressure swing adsorption unit.

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