Patent Application
20250230043
This disclosure relates to methods and systems of hydrogen (H2) production from steam cracking tail gas using membrane reactor.
With the rising concerns of climate change and greenhouse gas emissions, governments and companies are looking for ways to reduce their energy intensity and carbon footprint. Renewable energy such as solar, wind and geothermal is often part of the technology portfolio addressing climate change and complementing current approaches using carbon dioxide (CO2) capture. Hydrogen (H2) is gaining traction as a clean energy carrier as it can be produced by, for example, water electrolysis using renewable power. H2 may also be produced from fossil fuels by, for example, coal gasification, biomass gasification, or the reforming or partial oxidation of natural gas or other hydrocarbons. The produced H2 can be a feedstock to chemical processes, such as fuel cells, ammonia production, aromatization, hydrodesulphurization, and the hydrogenation or hydrocracking of hydrocarbons. The hydrogen can also be used as a fuel for decarbonization of industrial assets, for power generation through fuel cell or through combustion in a gas turbine or combustor.
This disclosure describes technologies relating to methods and systems of hydrogen production from steam cracking tail gas using membrane reactor.
Implementations described herein provide methods and systems of hydrogen (H2) production from a steam cracking tail gas. The petrochemical industry, constituting approximately 5% of global carbon dioxide (CO2) emissions within energy-intensive industrial sectors, primarily relies on the steam cracking process for the production of petrochemicals such as ethylene, propylene, butadiene, and aromatics. The average steam cracker generates about a total of 0.9-1 ton of CO2 per ton of high-value chemicals produced. Steam cracker fuel gases can generally be combusted to provide required endothermic energy for cracking processes, resulting in significant CO2 emissions.
Modern steam crackers are highly optimized, with fuel gas generated from the process itself, contributing to overall energy efficiency. Efforts to further reduce CO2 emissions include replacing methane fuel with lower-carbon alternatives such as hydrogen (H2), capturing CO2 from flue gas, electrifying furnace coils using renewable electricity, and oxy-fuel combustion of methane with CO2 capture. In an H2-production approach, a methane-rich stream, potentially supplemented with natural gas, undergoes impurity removal and reforming to produce synthesis gas (H2 and CO). Water-gas shift (WGS) reactors then generate H2 and CO2, with the latter being separated from H2 using pressure swing adsorption (PSA) or solvent systems. The produced low carbon hydrogen serves as cracker fuel, while the CO2 is either disposed of or utilized for value-added products.
The methods and systems of H2 production form steam cracking tail gas described in this disclosure uses a membrane reactor system with a hydrogen selective membrane to improve the process efficiency and reduce carbon footprint. A palladium or palladium-alloy membrane can be used for the membrane reactor and the tail gas from a steam cracker can be reformed to produce H2 at a pressure suitable for steam reformer cracker furnace requirements while CO2 is captured and separated. The membrane reactor may be used to produce H2 via steam methane reforming (SMR). Further, the membrane reactor can be combined with autothermal (ATR) process to form a syngas (H2 and CO) in a separate reformer, followed by water-gas shift reaction (WGS) of the syngas in the membrane reactor.
Accordingly, various implementations can reduce the overall carbon footprint of the steam cracking process by, for example, fueling the steam cracker with the produced H2, achieving a nearly 100% CO2 capture rate, e.g., 95% or greater, eliminating multiple process units such as CO2 capture amine system and PSA system, and lowering a SMR process temperature. Therefore, the methods and systems herein can reduce capital and operational costs, while minimizing economic and energy penalties to olefin product manufacturing.
In the following, the method of H2 production form steam cracking tail gas via SMR in the membrane reactor is described referring to
The tail gas 108 can contain H2 and methane (CH4), which can be recovered as fuel. Accordingly, in some implementations, the tail gas 108 can be first treated for separation of an initial fuel gas containing H2 before sending the tail gas 108 to a membrane reactor 110. For example, the tail gas 108 after separating the initial fuel gas can contain about 90-93% CH4 and the remainder can be H2 and H2O. The tail gas 108 can also contain other minor components, e.g., below 1% combined, such as CO, C2H4, and C2H6.
The membrane reactor 110 can be used to carry out steam methane reforming (SMR) to generate a syngas (a mixture of H2 and CO). The reactions associated with the SMR include:
CH4+H2O↔3H2+CO (R1)
CO+H2O↔3H2+CO2 (R2)
CH4+2H2O↔4H2+CO2 (R3)
Reaction (2) is also known as the water-shift reaction (WGS) and can take place in the membrane reactor following Reaction (1). Increasing the amount of water in the membrane reactor 110 can shift both Reactions (1), (2), and (3) to the right toward the products, which can result in increased H2 and CO2 production. In some implementations, accordingly, a steam can be added as an additional feed 112 to the membrane reactor 110. In some implementations, the additional feed 112 can further include an additional hydrocarbon, e.g., a natural gas import, to enhance the H2 production in the membrane reactor 110.
The membrane reactor 110 can be charged with a SMR catalyst. The SMR catalyst can be a metal-based catalyst such as a nickel catalyst. In some implementations, a heat source provides heat to the membrane reactor 110 to regulate the temperature within the membrane reactor 110. For example, an electric heater, a furnace, or a heat loop provides heat to the membrane reactor 110.
The membrane reactor 110 includes a H2 selective membrane such as palladium or palladium-alloy membranes, in which H2 can selectively permeate and be recovered as a permeate fuel gas 114. A retentate gas 116 can be a CO2-rich tail gas and CO2 can be captured instead of releasing into the atmosphere.
The produced H2 from the tail gas 108 can be used for power generation or as fuel for various facilities such as boilers and steam crackers. In some implementations, the produced H2 is used to provide a part or all of the heat necessary for the steam cracker 104 to continuously perform the steam cracking of the feed. Accordingly, the permeate fuel gas 114 can be sent to a heater 118 that is connected to the steam cracker 104. In some implementations, the heater 118 is a part of or including a cracker furnace configured to generate heat by combusting H2 in the permeate fuel gas 114. The generated heat can be provided to the steam cracker 104.
2CH4+O2+CO2→3H2+3CO+H2O (R4)
4CH4+O2+2H2O→10H2+4CO (R5)
The ATR in the separate reformer 202 can be a non-catalytic process. To enable Reactions (4) and (5), in addition to the tail gas 108, a reformer feed 204 can be sent to the separate reformer 202. The reformer feed can include oxygen (O2) and a steam. In some implementations, the reformer feed can further include an additional hydrocarbon, e.g., a natural gas import, to enhance the overall H2 production by the process.
The syngas 206 produced in the separate reformer 202 can be sent to the membrane reactor 110 for additional H2 production via the water-shift reaction (WGS). In some implementations, an additional steam may be added to the syngas 206 before sending it to the membrane reactor 110. The addition of steam can shift the equilibrium of the WGS to producing more H2. In one or more implementations, the reformer feed 204 does not contain a steam and the additional steam is only added after the separate reformer 202. The membrane reactor 110 can be charged with a WGS catalyst. The WGS catalyst can be a metal-oxide catalyst such as an iron oxide catalyst or copper-based catalyst. The produced H2 can then be recovered as a permeate fuel gas 114, while a retentate gas 116 can be a CO2-rich tail gas and CO2 can be captured instead of releasing into the atmosphere.
As described above referring to
As illustrated in
For the SMR-WGS mode, the carbon-containing feed 306 is subjected to steam methane reforming (SMR) in the reaction vessel 302 to generate H2 and CO. The water gas-shift reaction (WGS) can also occur converting CO into CO2 and generate additional H2. The reactions occur in the region 307 in the reaction vessel 302 external to the H2-selective membrane 304. This region 307 can be seen as a reaction space and is the retentate side of the H2-selective membrane 304. For the WGS mode, since the methane reforming has been performed in a separate reformer, only the WGS takes place in the reaction vessel 302.
The hydrogen molecules diffuse (permeate) through the wall of the H2-selective membrane 304 wall into its bore 305. The bore 305 is the interior space of the H2-selective membrane 304 and may be labeled as a lumen. The bore 305 is the permeate side of the H2-selective membrane 304.
A permeate fuel gas 114 is rich in H2 and discharges from the bore 305 of the H2-selective membrane 304 and from the membrane reactor 110. The permeate fuel gas 114 can be, for example, at least 90 mole percent (mol %) H2. A retentate gas 116 is rich in CO2 and it discharges from the membrane reactor 110 from the region 307 (reaction space) around and external to the H2-selective membrane 304. The retentate gas 116 on a dry basis can contain less than 10 mol % of the combination of H2 and CO. The retentate gas 116 can contain unreacted steam. The retentate gas 116 can be at least 90 mol % CO2 (dry basis) making the retentate gas 116 available in certain instances directly for further compression for geological sequestration or enhanced oil recovery (EOR), or for further purification so the CO2 can be used as a feedstock for another process. In some implementations, the retentate gas 116 can be subjected to water removal before compression or further purification. In various implementations, the retentate gas 116 can be at about the operating pressure in the reaction vessel 302, for example, in the range of about 10 bar (1 MPa) to about 50 bar (5 MPa). Accordingly, the retentate gas 116 can provide a concentrated and pressurized CO2 that is suitable for subsequent sequestration.
In some implementations, a sweep gas, e.g., steam or nitrogen (N2), is provided to the bore 305 of the H2-selective membrane 304. to flow through the bore 305 to displace H2 from the bore 305 and the membrane reactor 110. This displacement of H2 may maintain or increase driving force for hydrogen permeation through the membrane wall from the region 307 (reaction space) external to the H2-selective membrane 304 into the bore 305. In one or more implementations, the sweep gas can be provided and flow in a countercurrent direction with respect to the feed of carbon-containing feed 306 and the steam 308. Thus, in those implementations, the permeate fuel gas 114 can discharge from the end opposite to the end that the retentate gas 116 discharges from the membrane reactor 110.
Since the process of reforming is generally endothermic, heat 310 may be provided to the membrane reactor 110 by using an appropriate heat source, e.g., electrical resistive heaters. The heat source can be internal or external to the membrane reactor 110. In some implementations, the reaction temperature in the membrane reactor 110 is less than about 600° C., for example, between about 550° C. and about 600° C. In one or more implementations, the reaction temperature is about 550° C. or less. The use of the membrane reactor 110 can enable the operation at this temperature range lower than a non-membrane reactor system for the SMR, e.g., about 850° C. or greater. The operating pressure in the reaction vessel 302 can be, for example, in the range of about 10 bar (1 MPa) to about 50 bar (5 MPa) or in the range of about 30 bar (3 MPa) to about 40 bar (4 MPa), or at least about 15 bar (1.5 MPa) or at least about 25 bar (2.5 MPa).
In various implementations, one or more catalysts for the SMR, WGS, or both can be used in the reaction vessel 302. For example, the SMR catalyst can be a metal-based catalyst such as a nickel catalyst, and the WGS catalyst can be a metal-oxide catalyst such as an iron oxide catalyst or copper-based catalyst. The catalyst can be disposed on an internal surface 312 of the reaction vessel 302. Further, in case of the SMR-WGS mode, the SMR catalyst can be disposed in an upstream of the reaction vessel 302 and the WGS catalyst can be disposed in a downstream of the reaction vessel 302. In some implementations, the catalyst is not in contact with the H2-selective membrane 304.
The H2-selective membrane 304 can be characterized or labeled as cylindrical membranes or hollow membranes. The material of the H2-selective membrane 304 can be, for example, a palladium alloy. The membrane can be a thin film of palladium alloy supported on a tubular porous substrate composed of a metal or metal oxide.
In some implementations, there are some residual methane and CO in the retentate gas 116 due to incomplete conversion, but if the residence time is long enough, their concentrations in the retentate gas 116 can approach zero. The efficient removal of H2 from the region 307 external to the H2-selective membrane 304 can shift the equilibrium of Reactions (1)-(3) to the right.
The use of the membrane reactor 110 can be more efficient with respect to operational and capital costs compared to SMR or WGS using a non-membrane system. A highly selective palladium-based membrane as the tubular membrane in the membrane reactor 110 can facilitate production of high-purity H2, e.g., about 90 mol % to about 99.9 mol % or greater, reducing downstream processing prior to utilization of the hydrogen in pure-hydrogen applications.
Further, the membrane reactor 110 can also provide a high-purity CO2 in the retentate gas 116. In some implementations, the retentate gas 116 can be subjected to low-temperature CO2 separation that can generate liquid CO2 including micron-sized, high-purity CO2 droplets. Accordingly, the method of H2 production in this disclosure can facilitate economic capture of CO2, e.g., 90 mol % or greater of the CO2 generated in the H2 production, which can be higher than solvent-based processes, e.g., 65 mol % of CO2. In some implementations, the captured CO2 can be at liquid state and further pressurized for transport by pumping at relatively lower energy cost without compression. The saved compression energy can increase the overall system efficiency.
In various implementations, hydrogen yield per mole of methane feed is improved in comparison to non-membrane processes as the thermodynamic conversion limitations are overcome through the membrane reactor concept. Further, slippage of methane can be reduced.
Accordingly, using the methods and systems in this disclosure, higher energy efficiency and CO2 emission reduction in the steam cracking process can be achieved by integrating H2 production from the steam cracking tail gas and using the produced H2 as fuel for the steam cracking. H2 can be obtained at a pressure useful as fuel and CO2 can be obtained as a concentrated stream and higher pressures, resulting in lower cost and energy penalty. Further, process flexibility with membrane reactor enables the adoption of the methods to diverse olefin production facilities with different capacity requirements.
The integration using the membrane reactor system allows to provide process intensification by combining water gas shift (WGS), CO2 capture and H2 purification process. As a result, various costly systems such as solvent based CO2 captures system and pressure swing adsorption (PSA) system for H2 purification system can be eliminated.
In
To demonstrate the methods of H2 production from the steam cracking tail gas, lab and pilot testing were carried out on the steam methane reforming (SMR) and membrane water-gas shift (WGS) reactors. For the SMR-WGS experiments, a commercial Ni-based SMR catalyst was used in a 15 cm palladium-gold (PdAu) membrane reactor, and methane and steam were used as a feed. The reaction was carried out at 550° C. and 30 bar (3 MPa), and the H2 flux was measured at 3 bar (0.3 MPa) to examine the stability of membrane performance.
The membrane reactor system using the PdAu membrane was also examined for the WGS mode. A commercial Cu-based high temperature WGS catalyst was used in the same membrane reactor as the previous experiments, and 15 cm palladium-gold membrane and CO and steam were used as a feed. The reaction was carried out at between 450° C. and 500° C. and between 10 bar (1 MPa) and 40 bar (4 MPa).
Material and energy balances have been calculated for both the SMR-WGS mode and the ATR-WGS mode. Aspen Plus® V12.1 software was used to model a steam cracker, an ATR, a membrane SMR reactor, and a membrane WGS reactor model, and the models were used to perform the process calculation. The two different ethylene production scales, 1000 Kilo Tons per Annum (KTA) and 1800 KTA, were calculated. The SMR-WGS mode was used for 1000 KTA and the ATR-WGS was used for 1800 KTA. For each mode, material and energy balances were calculated for a naphtha feed and an ethane feed.
Table 1 summarizes the material and energy balances for the steam cracking (1000 KTA) of naphtha with H2 production from the steam cracking tail gas with steam methane reforming (SMR)-water-gas shift (WGS) mode. The steam cracking of naphtha at the rate of 422 t/h requires an energy input of about 711 MW. The methane from the steam cracking and a steam (additional H2O) were assumed as a feed for the SMR-WGS in the membrane reactor. The initial H2 obtained from the steam cracking is separated from the tail gas and not included in the feed for the membrane reactor. With the energy input of about 305 MW, the H2 production at the membrane reactor is 24.6 t/h, which can be used to provide the heat for the steam cracking. Assuming the CO2 (129.5 t/h) can be captured and not released into the atmosphere, the final CO2 emission from the process can be 38.4 t/h, which is substantially reduced from the CO2 emission from the steam cracker process without H2 production (140.8 t/h).
Table 2 summarizes the material and energy balances for the steam cracking (1000 KTA) of ethane with H2 production from the steam cracking tail gas with steam methane reforming (SMR)-water-gas shift (WGS) mode. In this calculation, in addition to the methane from the steam cracking and a steam (additional H2O), an additional methane was included in the feed for the SMR-WGS in the membrane reactor. The steam cracking of ethane at the rate of 157.8 t/h requires an energy input of about 392 MW. The initial H2 obtained from the steam cracking is separated from the tail gas and not included in the feed for the membrane reactor. With the energy input of about 153 MW, the H2 production at the membrane reactor is 11.7 t/h. Assuming the CO2 (61.7 t/h) can be captured and not released into the atmosphere, the final CO2 emission from the process can be zero. On the other hand, the steam cracker process without H2 production at the same ethylene production rate results in the CO2 emission of about 77.6 t/h.
Table 3 summarizes the material and energy balances for the steam cracking (1800 KTA) of naphtha with H2 production from the steam cracking tail gas with autothermal reforming (ATR) followed by water-gas shift reaction (WGS). The steam cracking of naphtha at the rate of 750 t/h requires an energy input of about 1154 MW. The methane from the steam cracking, oxygen (O2), a steam (additional H2O), and an additional methane were assumed as a feed for the ATR. The initial H2 obtained from the steam cracking is separated from the tail gas and not included in the feed for the ATR. The syngas is generated by the ATR and sent to the membrane reactor for the WGS. The syngas can have a composition as follows: 9.7 mol % CO; 9.4 mol % CO2; 37.4 mol % H2; and 2.5 mol % CH4. The H2 production at the membrane reactor is 34.6 t/h, which can be used to provide the heat for the steam cracking. Assuming the CO2 (285.9 t/h) can be captured and not released into the atmosphere, the final CO2 emission from the process can be zero. On the other hand, the steam cracker process without H2 production results in the CO2 emission of about 228.6 t/h.
Table 4 summarizes the material and energy balances for the steam cracking (1800 KTA) of ethane with H2 production from the steam cracking tail gas with autothermal reforming (ATR) followed by water-gas shift reaction (WGS). The steam cracking of ethane at the rate of 300.1 t/h requires an energy input of about 726 MW. The methane from the steam cracking, oxygen (O2), a steam (additional H2O), and an additional methane were assumed as a feed for the ATR. The initial H2 obtained from the steam cracking is separated from the tail gas and not included in the feed for the ATR. The syngas is generated by the ATR and sent to the membrane reactor for the WGS. The syngas can have a composition as follows: 9.1 mol % CO; 7.9 mol % CO2; 39.94 mol % H2; and 1.9 mol % CH4. The H2 production at the membrane reactor is 21.8 t/h, which can be used to provide the heat for the steam cracking. Assuming the CO2 (158 t/h) can be captured and not released into the atmosphere, the final CO2 emission from the process can be zero. On the other hand, the steam cracker process without H2 production results in the CO2 emission of about 143.8 t/h.
An implementation described herein provides a method of processing, where the method includes: performing steam cracking of a feed to generate an olefin product and a tail gas including methane; reforming the methane to form a syngas including hydrogen (H2) and carbon monoxide (CO); providing the syngas into a reaction vessel to a region external to a tubular membrane in the reaction vessel; providing a steam into the reaction vessel to the region; performing water-gas shift reaction (WGS) of the syngas in the reaction vessel to form a product gas including the H2 and carbon dioxide (CO2); diffusing the H2 in the product gas through the tubular membrane into a bore of the tubular membrane, where the tubular membrane is hydrogen selective; discharging the H2 from the bore of the tubular membrane; discharging a remainder of the product gas from the region external to the tubular membrane; and generating heat using the H2 as fuel, where the heat is used for the steam cracking.
In an aspect, combinable with any other aspect, the reforming of the methane is performed in the reaction vessel, and the method further includes: providing the tail gas into the reaction vessel to the region; and performing steam methane reforming (SMR) of the tail gas in the reaction vessel to form the syngas.
In an aspect, the method further includes providing an additional hydrocarbon into the reaction vessel to the region external to the tubular membrane.
In an aspect, the method further includes maintaining a reaction temperature in the reaction vessel during the SMR between 550° C. and 600° C.
In an aspect, combinable with any other aspect, the method includes separating the CO2 from the remainder of the product gas.
In an aspect, combinable with any other aspect, a heat required for the steam cracking is provided entirely from the H2.
In an aspect, combinable with any other aspect, the steam cracking forms by-product H2, and the method further includes separating the by-product H2 prior to providing the tail gas into the reaction vessel to the region.
An implementation described herein provides a method of processing, where the method includes: performing a steam cracking of a feed to generate an olefin product and a tail gas including methane; reforming the methane in a reformer to form a syngas including hydrogen (H2) and carbon monoxide (CO); providing the syngas and a steam into a reaction vessel to a region external to a tubular membrane in the reaction vessel; performing a water-gas shift reaction (WGS) in the reaction vessel to form a product gas including the H2 and carbon dioxide (CO2); diffusing the H2 in the product gas through the tubular membrane into a bore of the tubular membrane, where the tubular membrane is hydrogen selective; discharging the H2 from the bore of the tubular membrane; discharging a remainder of the product gas from the region external to the tubular membrane; and generating heat using the H2 as fuel, where the heat is used for the steam cracking.
In an aspect, combinable with any other aspect, the reforming is autothermal reforming, the method further including providing oxygen (O2) into the reformer.
In an aspect, combinable with any other aspect, the method includes providing a steam into the reformer.
In an aspect, combinable with any other aspect, the method includes providing an additional hydrocarbon into the reformer.
In an aspect, combinable with any other aspect, the method includes maintaining a reaction temperature in the reaction vessel during the WGS between 450° C. and 500° C.
In an aspect, combinable with any other aspect, the method includes separating the CO2 from the remainder of the product gas.
In an aspect, combinable with any other aspect, a heat required for the steam cracking is provided entirely from the H2.
In an aspect, combinable with any other aspect, the steam cracking forms by-product H2, and the method further includes separating the by-product H2 prior to providing the tail gas into the reaction vessel to the region.
An implementation described herein provides a system of steam cracking including: a steam cracker to generate an olefin product and a tail gas including methane from a feed; a membrane reactor coupled to the steam cracker, the membrane reactor including, a reaction vessel to produce a product gas including hydrogen (H2) from a feed gas from the steam cracker, and a tubular H2-selective membrane in the reaction vessel to diffuse the H2 through the tubular H2-selective membrane into a bore of the tubular H2-selective membrane; and a heater coupled to the steam cracker and the membrane reactor, the heater configured to, receive the H2 from the bore, generate heat from the H2, and provide the heat to the steam cracker.
In an aspect, combinable with any other aspect, the system of steam cracking further includes a reformer disposed between the steam cracker and the membrane reactor, where the reformer is configured to reform the tail gas to form a syngas, where the feed gas includes the syngas.
In an aspect, combinable with any other aspect, the reaction vessel is tubular, and the reaction vessel and the tubular H2-selective membrane are positioned concentrically.
In an aspect, combinable with any other aspect, the reaction vessel includes an outlet to discharge a remainder of the product gas, and where the bore includes an outlet to discharge the H2.
In an aspect, combinable with any other aspect, the reaction vessel includes a catalyst for producing the H2.
While this invention has been described with reference to illustrative implementations, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative implementations, as well as other implementations of the invention, will be apparent to persons skilled in the art upon reference to the description. It is therefore intended that the appended claims encompass any such modifications or implementations.
