Hydrogen production from steam cracking tail gas using membrane reactors

Abstract

A method for producing hydrogen (H2) is provided. The method includes: steam cracking a feedstock to produce an olefin product and a tail gas containing methane; reforming the methane to form a syngas containing H2 and carbon monoxide (CO); providing the syngas to a region outside a tubular membrane within a reaction vessel; providing steam to the region within the reaction vessel; performing a water-gas shift reaction (WGS) on the syngas in the reaction vessel to form a product gas containing H2 and carbon dioxide (CO2); diffusing H2 in the product gas through a tubular H2 selective membrane and into its lumen; discharging the H2 from the lumen of the tubular H2 selective membrane; discharging the remainder of the product gas from the external region; and using the H2 as fuel to generate heat, wherein the heat is used for the steam cracking.

Description

Priority requirements

[0001] This application claims priority to U.S. Patent Application No. 18 / 410,288, filed January 11, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This disclosure relates to methods and systems for producing hydrogen (H2) from the tail gas of steam cracking using a membrane reactor. Background Technology

[0003] With increasing concern about climate change and greenhouse gas emissions, governments and businesses are seeking ways to reduce their energy intensity and carbon footprint. Renewable energy sources such as solar, wind, and geothermal energy are often part of a technology mix that addresses climate change and complements current methods of carbon dioxide (CO2) capture. Hydrogen (H2) is gaining increasing attention as a clean energy carrier because it can be produced, for example, through water electrolysis using renewable energy sources. H2 can also be produced from fossil fuels through processes such as coal gasification, biomass gasification, or reforming or partial oxidation of natural gas or other hydrocarbons. The produced H2 can be used as feedstock in chemical processes such as fuel cells, ammonia production, aromatization, hydrodesulfurization, and the hydrogenation or hydrocracking of hydrocarbons. Hydrogen can also be used as fuel for the decarbonization of industrial assets and for power generation via combustion in fuel cells or gas turbines or combustors. Summary of the Invention

[0004] This disclosure describes techniques related to methods and systems for producing hydrogen from steam cracking tail gas using a membrane reactor. Attached Figure Description

[0005] Figure 1 It is a block diagram showing the production of hydrogen (H2) from the tail gas of a steam cracker using a membrane reactor.

[0006] Figure 2 It is a block diagram showing the production of H2 from the tail gas of a steam cracker using a membrane reactor and a separate reforming unit.

[0007] Figure 3 It is a membrane reactor used for the production and separation of hydrogen (H2).

[0008] Figures 4A-4B This is a process flow diagram of the H2 production method.

[0009] Figure 5 This is a graph showing H2 flux and methane conversion.

[0010] Figure 6The graph shows the carbon monoxide (CO) conversion rate at 450°C with and without a membrane reactor.

[0011] Figure 7 The graph shows the carbon monoxide (CO) conversion rate at 500°C with and without a membrane reactor. Detailed Implementation

[0012] The embodiments described herein provide methods and systems for producing hydrogen (H2) from steam cracking tail gas. The petrochemical industry, which accounts for approximately 5% of global carbon dioxide (CO2) emissions within energy-intensive industrial sectors, relies heavily on steam cracking processes for the production of petrochemical products such as ethylene, propylene, butadiene, and aromatics. On average, a steam cracking unit generates approximately 0.9-1 tonnes of CO2 per tonne of high-value chemicals produced. The fuel gases in steam cracking units are typically combusted to provide the endothermic energy required for the cracking process, resulting in significant CO2 emissions.

[0013] Modern steam cracking units are highly optimized where fuel gases are generated by the process itself, contributing to overall energy efficiency. Further efforts to reduce CO2 emissions include replacing methane fuel with lower-carbon alternatives such as hydrogen (H2), capturing CO2 from flue gas, using renewable electricity to power furnace coils, and oxy-fuel combustion of methane with CO2 capture. In H2 production, a methane-rich stream (potentially supplemented with natural gas) undergoes impurity removal and reforming to produce syngas (H2 and CO). A water-gas shift (WGS) reactor then produces H2 and CO2, with the latter separated from H2 using pressure swing adsorption (PSA) or a solvent system. The resulting low-carbon hydrogen is used as fuel for the cracking unit, while CO2 is disposed of or used for value-added products.

[0014] The methods and systems for H2 production from steam cracking tail gas described in this disclosure utilize membrane reactor systems with hydrogen-selective membranes to improve process efficiency and reduce carbon footprint. Palladium or palladium alloy membranes can be used in the membrane reactors, and tail gas from the steam cracking unit can be reformed to produce H2 at pressures suitable for the requirements of the steam reforming unit's cracking furnace, while CO2 is captured and separated. The membrane reactors can be used to produce H2 via steam methane reforming (SMR). Furthermore, the membrane reactors can be combined with autothermal (ATR) processes to form syngas (H2 and CO) in a separate reforming unit, followed by a water-gas shift reaction (WGS) of the syngas in the membrane reactor.

[0015] Therefore, various implementations can reduce the overall carbon footprint of the steam cracking process by, for example, using the produced H2 to fuel the steam cracking unit, thereby achieving near 100% CO2 capture (e.g., over 95%), eliminating multiple process units such as CO2 capture amine systems and PSA systems, and lowering the SMR process temperature. Thus, the methods and systems described herein can reduce investment and operating costs while minimizing the economic and energy costs of olefin product manufacturing.

[0016] In the following text, refer to Figure 1 A method for producing H2 from steam cracking tail gas via SMR in a membrane reactor is described. Then refer to... Figure 2 A method is described involving an ATR followed by a WGS in a membrane reactor. (See reference...) Figure 3 The tubular design of the membrane reactor is described. Figures 4A-4B This is an exemplary process flow diagram of a method for producing H2 from steam cracking tail gas. Then refer to... Figure 5-7 The experimental results of the examples are described.

[0017] Steam methane reforming (SMR) via membrane reactor

[0018] Figure 1 This is a block diagram of hydrogen (H2) production 100. In various embodiments, H2 production is part of an oil and gas refining facility that converts crude oil feedstock into petrochemical products. Integrated processes for converting crude oil into petrochemical products (including olefins and aromatics, as well as fuel products) include mixed feedstock steam cracking and naphtha conversion into chemically rich reformate. Figure 1 In this process, feedstock 102 is delivered to steam cracking unit 104 to produce olefin product 106 and tail gas 108. In some embodiments, feedstock 102 may be naphtha or a specific type of hydrocarbon such as ethane. As used herein, the term "naphtha" refers to hydrocarbons that boil in the range of about 20-205, 20-193, 20-190, 20-180, 20-170, 32-205, 32-193, 32-190, 32-180, 32-170, 36-205, 36-193, 36-190, 36-180, or 36-170°C. Olefin product 106 may comprise ethylene, propylene, mixed C4 hydrocarbons, cracked gasoline, and pyrolysis oil, etc. Although in Figure 1 Not specifically shown, but the steam cracking unit 104 can be coupled (connected or coupled) to a unit for recycling some alkanes such as ethane and propane.

[0019] The tail gas 108 may contain H2 and methane (CH4), which can be recovered as fuel. Therefore, in some embodiments, the tail gas 108 may be treated first to separate the initial fuel gas containing H2 before it is fed to the membrane reactor 110. For example, the tail gas 108 after separating the initial fuel gas may contain about 90-93% CH4, and the remainder may be H2 and H2O. The tail gas 108 may also contain other trace components (e.g., less than 1% of the total), such as CO, C2H4, and C2H6.

[0020] Membrane reactor 110 can be used for steam methane reforming (SMR) to produce syngas (a mixture of H2 and CO). Reactions associated with SMR include:

[0021]

[0022] Reaction (2) is called a water-gas shift reaction (WGS) and can occur in a membrane reactor after reaction (1). Increasing the amount of water in membrane reactor 110 can shift reactions (1), (2), and (3) to the right toward the products, which can lead to increased H2 and CO2 production. In some embodiments, steam (water vapor) can be added to membrane reactor 110 as an additional feed 112 accordingly. In some embodiments, the additional feed 112 may also contain additional hydrocarbons, such as natural gas input, to enhance H2 production in membrane reactor 110.

[0023] Membrane reactor 110 may be packed with an SMR catalyst. The SMR catalyst may be a metal-based catalyst, such as a nickel catalyst. In some embodiments, a heat source provides heat to membrane reactor 110 to regulate the temperature within membrane reactor 110. For example, an electric heater, furnace, or heat loop provides heat to membrane reactor 110.

[0024] Membrane reactor 110 includes an H2-selective membrane, such as a palladium or palladium alloy membrane, in which H2 can selectively permeate and is recovered as permeate fuel gas 114. Retained gas 116 can be a CO2-rich tail gas, and CO2 can be captured instead of released into the atmosphere.

[0025] The H2 produced from the exhaust gas 108 can be used for power generation or as fuel for various facilities, such as boilers and steam cracking units. In some embodiments, the produced H2 is used to provide some or all of the heat required by the steam cracking unit 104 to continuously steam crack the feedstock. Therefore, the permeate fuel gas 114 can be fed to a heater 118 connected to the steam cracking unit 104. In some embodiments, the heater 118 is part of or includes a cracking furnace configured to generate heat by burning the H2 in the permeate fuel gas 114. The generated heat can be provided to the steam cracking unit 104.

[0026] Autothermal reforming (ATR), followed by water-gas shift (WGS) in a membrane reactor.

[0027] Figure 2 This is a block diagram showing the production of H2 from the tail gas of the steam cracking unit 108 (referred to as tail gas 108) using a membrane reactor 110 and a separate reforming unit 202. The same numbered items are as per [reference to...]. Figure 1 As described, and therefore will not be repeated in detail. Figure 2 As shown, H2 production 200 can utilize a separate reforming unit 202 positioned upstream of membrane reactor 110. Tail gas 108 can be fed to the separate reforming unit 202 to reform hydrocarbons (e.g., methane) in the tail gas. In some embodiments, the separate reforming unit 202 can be used for autothermal reforming (ATR) of methane to produce syngas 206. Reactions associated with ATR include:

[0028]

[0029] The ATR in the separate reforming unit 202 can be a non-catalytic process. To achieve reactions (4) and (5), in addition to tail gas 108, reforming feed 204 can be fed to the separate reforming unit 202. The reforming feed can contain oxygen (O2) and steam. In some embodiments, the reforming feed can also contain additional hydrocarbons (e.g., natural gas input) to enhance overall H2 production through the process.

[0030] Syngas 206 produced in a separate reforming unit 202 can be fed to membrane reactor 110 for further H2 production via water-gas shift reaction (WGS). In some embodiments, additional steam can be added to syngas 206 before it is fed to membrane reactor 110. The addition of steam can shift the WGS equilibrium towards producing more H2. In one or more embodiments, reforming unit feed 204 does not contain steam, and additional steam is added only after the separate reforming unit 202. Membrane reactor 110 can be packed with a WGS catalyst. The WGS catalyst can be a metal oxide catalyst, such as an iron oxide catalyst or a copper-based catalyst. The produced H2 can then be recovered as permeate fuel gas 114, while the retrieval gas 116 can be a CO2-rich tail gas, and the CO2 can be captured instead of released into the atmosphere.

[0031] As referenced above Figure 1 and 2 As described, membrane reactor 110 can be configured to perform SMR and WGS together. Figure 1 ), or perform WGS with a separate ATR ( Figure 2 In some implementations, the mode and configuration of the membrane reactor 110 can be selected taking into account the final H2 flow requirements for steam cracking. While not wishing to be bound by any theoretical limitations, the SMR-WGS mode offers greater process integration and lower H2 production costs compared to the ATR-WGS mode, which offers higher H2 production capacity, because it does not require a separate reforming unit. Therefore, the ATR-WGS mode can be chosen for processes with larger olefin production capacity, such as 1800 kT / year (KTA).

[0032] Membrane reactor design

[0033] Figure 3 This is an exemplary simplified diagram of a membrane reactor 110 for hydrogen (H2) production and separation. As described above, the membrane reactor 110 can be configured for SMR and WGS, or WGS only. (Refer to...) Figure 3 Two embodiments are described. The membrane reactor 110 includes a reaction vessel 302 and an H2-selective membrane 304 disposed within the reaction vessel 302. The reaction vessel 302 can be a cylindrical or tubular vessel. The reaction vessel 302 can have, for example... Figure 3 The H2 selective membrane 304 can be horizontally oriented, or vertically oriented, as shown. It may be tubular with a lumen (pore or channel) 305. In some embodiments, both the reaction vessel 302 and the H2 selective membrane 304 are tubular, and they are coaxially positioned. Figure 3In one embodiment, the H2 selective membrane 304 is shown as a single tube housed within a reaction vessel 302. In some embodiments, multiple tubes may be bundled together and housed within the reaction vessel 302, and each tube may include the H2 selective membrane 304.

[0034] like Figure 3 As shown, in operation, carbon feed 306 and steam 308 are fed into region 307 outside the H2 selective membrane 304 within the reaction vessel 302. For SMR-WGS mode, carbon feed 306 can be primarily hydrocarbons such as methane. For WGS mode, carbon feed 306 can be primarily syngas.

[0035] In the SMR-WGS mode, the carbon feed 306 undergoes steam methane reforming (SMR) in the reaction vessel 302 to produce H2 and CO. Water-gas shift reaction (WGS) can also occur, converting CO to CO2 and producing additional H2. These reactions take place in region 307 within the reaction vessel 302, outside the H2 selective membrane 304. This region 307 can be considered the reaction space and is the retentate side of the H2 selective membrane 304. In the WGS mode, since methane reforming has already been performed in a separate reforming unit, only WGS occurs in the reaction vessel 302.

[0036] Hydrogen molecules diffuse (permeate) through the wall of the H2 selective membrane 304 and enter its lumen 305. Lumen 305 is the internal space of the H2 selective membrane 304 and can be labeled as the lumen. Lumen 305 is the permeate side of the H2 selective membrane 304.

[0037] Permeate fuel gas 114 is rich in H2 and exits from the lumen 305 of the H2 selective membrane 304 and from the membrane reactor 110. Permeate fuel gas 114 can be, for example, at least 90 mol% H2. Retained gas 116 is rich in CO2 and exits from the membrane reactor 110 from the region 307 (reaction space) surrounding and outside the H2 selective membrane 304. Retained gas 116 may contain less than 10 mol% (total) H2 and CO combination on a dry basis. Retained gas 116 may contain unreacted vapors. Retained gas 116 can be at least 90 mol% CO2 (dry basis), thus allowing it to be used directly for further compression in certain situations for geological storage or enhanced oil recovery (EOR), or for further purification, and therefore the CO2 can be used as a feedstock for other processes. In some embodiments, retained gas 116 may be dewatered before compression or further purification. In various embodiments, the retentate gas 116 may be at approximately the operating pressure within the reaction vessel 302, for example, in the range of about 10 bar (1 MPa) to about 50 bar (5 MPa). Therefore, the retentate gas 116 can provide concentrated and pressurized CO2 suitable for subsequent containment.

[0038] In some embodiments, a purge gas (e.g., steam or nitrogen (N2)) is supplied to the lumen 305 of the H2 selective membrane 304 to flow through the lumen 305, thereby displacing H2 from the lumen 305 and the membrane reactor 110. This displacement of H2 can maintain or enhance the driving force for hydrogen to permeate from the region 307 (reaction space) outside the H2 selective membrane 304 through the membrane wall and into the lumen 305. In one or more embodiments, the purge gas can be provided, and this purge gas can flow in a countercurrent direction relative to the feed of the carbon-containing feed 306 and the steam 308. Therefore, in those embodiments, the permeate fuel gas 114 can be discharged from the end opposite to the end from which the retentate gas 116 is discharged from the membrane reactor 110.

[0039] Since the reforming process is typically endothermic, heat 310 can be provided to the membrane reactor 110 using a suitable heat source (e.g., a resistance heater). The heat source can be inside or outside the membrane reactor 110. In some embodiments, the reaction temperature in the membrane reactor 110 is below about 600°C, for example, from about 550°C to about 600°C. In one or more embodiments, the reaction temperature is below about 550°C. The use of the membrane reactor 110 allows operation in such a lower temperature range compared to non-membrane reactor systems of SMR (e.g., above about 850°C). 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).

[0040] In various embodiments, one or more catalysts for 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 a copper-based catalyst. The catalyst can be disposed on the inner surface 312 of the reaction vessel 302. Furthermore, in the SMR-WGS mode, the SMR catalyst can be disposed upstream of the reaction vessel 302, and the WGS catalyst can be disposed downstream of the reaction vessel 302. In some embodiments, the catalyst is not in contact with the H2 selective membrane 304.

[0041] The H2 selective membrane 304 can be characterized or labeled as a cylindrical membrane or a hollow membrane. 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 made of metal or metal oxide.

[0042] In some embodiments, due to incomplete conversion, some residual methane and CO remain in the retrieval gas 116, but their concentration in the retrieval gas 116 can approach zero if the residence time is long enough. Effective removal of H2 from region 307 outside the H2 selective membrane 304 can shift the equilibrium of reactions (1)-(3) to the right.

[0043] Compared to SMR or WGS systems using non-membrane systems, the use of membrane reactor 110 can be more efficient in terms of operating and investment costs. The highly selective palladium-based membrane, which serves as the tubular membrane in membrane reactor 110, can facilitate the production of high-purity H2 (e.g., about 90 mol% to about 99.9 mol% or higher), thereby reducing downstream processing of hydrogen before it can be used for pure hydrogen applications.

[0044] Furthermore, the membrane reactor 110 can also provide high-purity CO2 in the truncated gas 116. In some embodiments, the truncated gas 116 can undergo cryogenic CO2 separation, which can produce liquid CO2 containing high-purity CO2 droplets of micron size. Therefore, the H2 production method of this disclosure can facilitate the economical capture of CO2, for example, producing more than 90 mol% CO2 in H2 production, which can be higher than that of solvent-based processes, such as 65 mol% CO2. In some embodiments, the captured CO2 can be in a liquid state and can be further pressurized for transport by pumping at a relatively low energy cost without compression. The energy saved in compression can improve the overall system efficiency.

[0045] In various implementations, the hydrogen yield per mole of methane feed is increased compared to non-membrane processes because the thermodynamic conversion limitations are overcome by using a membrane reactor design. Furthermore, methane slippage can be reduced.

[0046] Therefore, by utilizing the methods and systems of this disclosure, higher energy efficiency and reduced CO2 emissions in steam cracking processes can be achieved by integrating the production of H2 from steam cracking tail gas and the use of the produced H2 as fuel for steam cracking. H2 can be obtained at pressures suitable for fuel use, and CO2 can be obtained as a concentrated stream at higher pressures, resulting in lower costs and energy consumption. Furthermore, the process flexibility of membrane reactors allows these methods to be applied to various olefin production facilities with different capacity requirements.

[0047] The integration of membrane reactor systems allows for process intensification by combining water-gas shift (WGS), CO2 capture, and H2 purification processes. As a result, various high-cost systems, such as solvent-based CO2 capture systems and pressure swing adsorption (PSA) systems used for H2 purification, can be eliminated.

[0048] Figures 4A-4B This is a process flow diagram of a method for producing hydrogen (H2) from steam cracking tail gas. Figure 4AIn one embodiment, a method 400 begins by steam cracking the feedstock 402 to produce olefin products and a tail gas containing methane, followed by reforming the methane 404 to form syngas containing hydrogen (H2) and carbon monoxide (CO). This reforming of methane at this stage can be carried out in a separate reforming unit for autothermal reforming (ATR) or in a membrane reactor configured to carry out subsequent reactions such as water-gas shift reaction (WGS). The syngas is then supplied 406 to a region outside a tubular membrane within the reaction vessel, wherein steam is supplied 408 to this region within the reaction vessel. Method 400 then continues with WGS 410 of the syngas in the reaction vessel to form a product gas containing H2 and carbon dioxide (CO2). The H2 in the product gas is then diffused 412 through the tubular membrane and into the lumen of the tubular membrane, which is hydrogen-selective. Next, H2 is discharged from the lumen of the tubular membrane 414, and the remainder of the product gas is discharged from the region outside the tubular membrane 416. H2 is then used as fuel to generate heat 418, which is used for steam cracking.

[0049] exist Figure 4B In another method 420 according to one embodiment, the feed is steam-cracked 402 to produce olefin products and a tail gas containing methane, followed by reforming the methane in a reforming unit 424 to form syngas containing hydrogen (H2) and carbon monoxide (CO). The syngas and steam are then supplied 426 to a region outside a tubular membrane within a reaction vessel. Method 420 then continues with WGS 410 of the syngas in the reaction vessel to form a product gas containing H2 and carbon dioxide (CO2). H2 in the product gas is then diffused 412 through the tubular membrane and into the lumen of the tubular membrane, which is hydrogen-selective. Next, H2 is discharged from the lumen of the tubular membrane 414, and the remainder of the product gas is discharged from the region outside the tubular membrane 416. H2 is then used as fuel to generate heat 418, which is used for steam cracking.

[0050] Example

[0051] To demonstrate the method for H2 production from steam cracking tail gas, laboratory and pilot-scale experiments were conducted in 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, with methane and steam as feedstock. 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 the membrane performance. Figure 5 This is a graph showing H2 flux and methane conversion. Maintaining a high conversion rate of over 70% for long-term operation exceeding 600 h, and with the H2 flux remaining almost constant after approximately 300 h, confirms the stability of the membrane reactor system under operating conditions and its ability to produce H2 from methane feed via SMR.

[0052] For the WGS mode, a membrane reactor system using a PdAu membrane was also investigated. A commercial Cu-based high-temperature WGS catalyst was used in the same membrane reactor as in previous experiments, with a 15 cm palladium-gold membrane and CO and steam as feed. The reaction was carried out at 450 °C to 500 °C and 10 bar (1 MPa) to 40 bar (4 MPa). Figure 6 and 7 CO conversion rates at 450 °C and 500 °C with and without membrane reactors are shown. At both temperatures, the membrane reactor consistently exhibits higher or similar CO conversion rates compared to the non-membrane reactor system, confirming the advantages of the membrane system. At 450 °C, the benefit of the membrane reactor system in terms of CO conversion rate is significant at higher pressures (e.g., 30 bar (3 MPa) or higher). On the other hand, at 500 °C, the membrane reactor system exhibits higher CO conversion rates at all pressures examined. At both temperatures, CO conversion rates are higher at higher pressures, and close to 100% (e.g., 90% or higher) conversion rates are achieved at 30 bar (3 MPa) or higher. Furthermore, despite the moderate exothermic nature of the WGS reaction, the high CO conversion rates at these temperatures improve the thermal integration of the SMR-WGS process and help minimize the number of unit operations and reactors.

[0053] Material and energy balances have been calculated for both SMR-WGS and ATR-WGS modes. (Using AspenPlus) ® The V12.1 software was used to model steam cracking units, ATR, membrane SMR reactors, and membrane WGS reactors, and these models were used for process calculations. Two different ethylene production scales were calculated: 1000 kT / year (KTA) and 1800 KTA. The SMR-WGS model was used for the 1000 KTA, and the ATR-WGS model was used for the 1800 KTA. For each model, the material and energy balances for naphtha feed and ethane feed were calculated.

[0054] Table 1 summarizes the feed and energy balance for a steam cracking (1000 KTA) of naphtha produced from H2 in steam cracking tail gas using a steam methane reforming (SMR)-water gas shift (WGS) mode. Steam cracking of naphtha at a rate of 422 t / h requires approximately 711 MW of energy input. It is assumed that methane and steam (plus H2O) from steam cracking are used as feed for the SMR-WGS in the membrane reactor. The initial H2 obtained from steam cracking is separated from the tail gas and is not included in the feed for the membrane reactor. With an energy input of approximately 305 MW, H2 production at the membrane reactor is 24.6 t / h, which can be used to provide heat for steam cracking. Assuming that CO2 (129.5 t / h) can be captured and not released into the atmosphere, the final CO2 emission from this process can be 38.4 t / h, which is significantly lower than the CO2 emission of a steam cracking process without H2 production (140.8 t / h).

[0055] Table 1: Material and energy balance for steam cracking (1000 KTA) of naphtha produced from H2 of steam cracking tail gas using steam methane reforming (SMR)-water gas shift (WGS) mode.

[0056]

[0057] Table 2 summarizes the feed and energy balance for a steam cracking (1000 KTA) process using a steam methane reforming (SMR)-water gas shift (WGS) model with ethane produced from H2 in the steam cracking tail gas. In this calculation, the feed for the SMR-WGS in the membrane reactor includes additional methane besides the methane from steam cracking and steam (additional H2O). Steam cracking of ethane at a rate of 157.8 t / h requires an energy input of approximately 392 MW. The initial H2 obtained from steam cracking is separated from the tail gas and is not included in the feed for the membrane reactor. With an energy input of approximately 153 MW, H2 production at the membrane reactor is 11.7 t / h. Assuming that CO2 (61.7 t / h) can be captured and not released into the atmosphere, the final CO2 emissions from this process can be zero. On the other hand, a steam cracking process without H2 production at the same ethylene production rate results in approximately 77.6 t / h of CO2 emissions.

[0058] Table 2: Material and energy balance for steam cracking (1000 KTA) of ethane produced from H2 in steam cracking tail gas using steam methane reforming (SMR)-water gas shift (WGS) mode.

[0059]

[0060] Table 3 summarizes the feed and energy balance for a steam cracking (1800 KTA) process using an autothermal reforming (ATR) followed by a water-gas shift reaction (WGS) to produce naphtha from H2 produced by steam cracking tail gas. Steam cracking of naphtha at a rate of 750 t / h requires approximately 1154 MW of energy input. It is assumed that methane, oxygen (O2), steam (additionally H2O), and additional methane from steam cracking are used as feed for the ATR. The initial H2 obtained from steam cracking is separated from the tail gas and is not included in the ATR feed. Syngas is generated by the ATR and fed to a membrane reactor for use in the WGS. The syngas may have the following composition: 9.7 mol% CO; 9.4 mol% CO2; 37.4 mol% H2; and 2.5 mol% CH4. H2 production at the membrane reactor is 34.6 t / h, which can be used to provide heat for steam cracking. Assuming that CO2 (285.9 t / h) can be captured and not released into the atmosphere, the final CO2 emissions from this process can be zero. On the other hand, a steam cracking process without H2 production results in approximately 228.6 t / h of CO2 emissions.

[0061] Table 3: Material and energy balance for steam cracking (1800 KTA) of naphtha produced from H2 of steam cracking tail gas using the water-gas shift (WGS) mode following autothermal reforming (ATR).

[0062]

[0063] Table 4 summarizes the feedstock and energy balance for a steam cracking (1800 KTA) of ethane produced from H2 in steam cracking tail gas using an autothermal reforming (ATR) followed by a water-gas shift reaction (WGS). Steam cracking of ethane at a rate of 300.1 t / h requires approximately 726 MW of energy input. It is assumed that methane, oxygen (O2), steam (additionally H2O), and additional methane from steam cracking are used as feedstock for the ATR. The initial H2 obtained from steam cracking is separated from the tail gas and is not included in the ATR feed. Syngas is generated by the ATR and fed to a membrane reactor for use in the WGS. The syngas may have the following composition: 9.1 mol% CO; 7.9 mol% CO2; 39.94 mol% H2; and 1.9 mol% CH4. H2 production at the membrane reactor is 21.8 t / h, which can be used to provide heat for steam cracking. Assuming that CO2 (158 t / h) can be captured and not released into the atmosphere, the final CO2 emissions from this process can be zero. On the other hand, a steam cracking process without H2 production results in approximately 143.8 t / h of CO2 emissions.

[0064] Table 4: Material and energy balance for steam cracking (1800 KTA) of ethane produced from H2 in steam cracking tail gas using autothermal reforming (ATR) followed by water-gas shift (WGS) mode.

[0065]

[0066] Implementation

[0067] One embodiment described herein provides a processing method comprising: steam cracking a feedstock to produce an olefin product and a tail gas containing methane; reforming the methane to form a syngas containing hydrogen (H2) and carbon monoxide (CO); supplying the syngas to a region outside a tubular membrane within a reaction vessel; supplying steam to the region within the reaction vessel; performing a water-gas shift reaction (WGS) on the syngas in the reaction vessel to form a product gas containing H2 and carbon dioxide (CO2); diffusing the H2 in the product gas through the tubular membrane and into a lumen (pore or bore) of the tubular membrane, wherein the tubular membrane is hydrogen selective; venting the H2 from the lumen of the tubular membrane; venting the remainder of the product gas from the region outside the tubular membrane; and using the H2 as fuel to generate heat, wherein the heat is used for the steam cracking.

[0068] In one aspect that can be combined with any other aspect, the reforming of the methane is carried out in the reaction vessel, and the method further includes providing the tail gas to the region within the reaction vessel; and performing steam methane reforming (SMR) on the tail gas in the reaction vessel to form the syngas.

[0069] In one aspect, the method further includes providing additional hydrocarbons to the region outside the tubular membrane within the reaction vessel.

[0070] In one aspect, the method further includes maintaining the reaction temperature in the reaction vessel at 550°C to 600°C during the SMR.

[0071] In one aspect that can be combined with any other aspect, the method includes separating the CO2 from the remainder of the product gas.

[0072] In one aspect that can be combined with any other aspect, the heat required for the steam cracking is entirely provided by the H2.

[0073] In one aspect that can be combined with any other aspect, the steam cracking forms a byproduct H2, and the method further includes separating the byproduct H2 before providing the tail gas to the region within the reaction vessel.

[0074] One embodiment described herein provides a processing method comprising: steam cracking a feedstock to produce an olefin product and a tail gas containing methane; reforming the methane in a reforming unit to form a syngas containing hydrogen (H2) and carbon monoxide (CO); providing the syngas and steam to a region outside a tubular membrane within a reaction vessel; performing a water-gas shift reaction (WGS) in the reaction vessel to form a product gas containing H2 and carbon dioxide (CO2); allowing the H2 in the product gas to diffuse through the tubular membrane and into a lumen of the tubular membrane, wherein the tubular membrane is hydrogen-selective; discharging the H2 from the lumen of the tubular membrane; discharging the remaining portion of the product gas from the region outside the tubular membrane; and using the H2 as fuel to generate heat, wherein the heat is used for the steam cracking.

[0075] In one aspect that can be combined with any other aspect, the reforming is autothermal reforming, and the method further includes providing oxygen (O2) to the reforming apparatus.

[0076] In one aspect that can be combined with any other aspect, the method includes supplying steam to the reforming unit.

[0077] In one aspect that can be combined with any other aspect, the method includes providing additional hydrocarbons to the reforming unit.

[0078] In one aspect that can be combined with any other aspect, the method includes maintaining the reaction temperature in the reaction vessel at 450°C to 500°C during the WGS.

[0079] In one aspect that can be combined with any other aspect, the method includes separating the CO2 from the remainder of the product gas.

[0080] In one aspect that can be combined with any other aspect, the heat required for the steam cracking is entirely provided by the H2.

[0081] In one aspect that can be combined with any other aspect, the steam cracking forms a byproduct H2, and the method further includes separating the byproduct H2 before providing the tail gas to the region within the reaction vessel.

[0082] One embodiment described herein provides a steam cracking system comprising: a steam cracking unit for generating olefin products and a tail gas containing methane from a feed; a membrane reactor coupled to the steam cracking unit, the membrane reactor comprising: a reaction vessel for generating a product gas containing hydrogen (H2) from the feed gas from the steam cracking unit; and a tubular H2 selective membrane in the reaction vessel for allowing H2 to diffuse through the tubular H2 selective membrane and into a lumen of the tubular H2 selective membrane; and a heater coupled to the steam cracking unit and the membrane reactor, the heater being configured to: receive H2 from the lumen, generate heat from the H2, and provide the heat to the steam cracking unit.

[0083] In one aspect that can be combined with any other aspect, the steam cracking system further includes a reforming unit disposed between the steam cracking unit and the membrane reactor, wherein the reforming unit is configured to reform the tail gas to form syngas, wherein the feed gas contains syngas.

[0084] In one aspect that can be combined with any other aspect, the reaction vessel is tubular, and the reaction vessel and the tubular H2 selective membrane are coaxially arranged.

[0085] In one aspect that can be combined with any other aspect, the reaction vessel includes an outlet for discharging the remainder of the product gas, and the lumen includes an outlet for discharging the H2.

[0086] In one aspect that can be combined with any other aspect, the reaction vessel includes a catalyst for producing the H2.

[0087] Although the invention has been described with reference to illustrative embodiments, this description is not intended to be limiting. Various modifications and combinations of the illustrative and other embodiments of the invention will be apparent to those skilled in the art upon reference to this description. Therefore, it is intended that the appended claims cover any such modifications and embodiments.

Claims

1. A processing method, the method comprising: The feed is steam-cracked to produce olefin products and tail gas containing methane; The methane is reformed to form syngas containing hydrogen (H2) and carbon monoxide (CO); The synthesis gas is supplied to the region outside the tubular membrane within the reaction vessel; Steam is supplied to the area within the reaction vessel; The syngas is subjected to a water-gas shift reaction (WGS) in the reaction vessel to form a product gas containing H2 and carbon dioxide (CO2); The H2 in the product gas diffuses through the tubular membrane and enters the lumen of the tubular membrane, wherein the tubular membrane is hydrogen-selective; The H2 is discharged from the lumen of the tubular membrane; The remaining portion of the product gas is discharged from the region outside the tubular membrane; and The H2 is used as fuel to generate heat, which is used for the steam cracking.

2. The method according to claim 1, wherein the reforming of the methane is carried out in the reaction vessel, the method further comprising: The exhaust gas is supplied to the area within the reaction vessel; and The tail gas is subjected to steam methane reforming (SMR) in the reaction vessel to form the syngas.

3. The method of claim 2, further comprising providing additional hydrocarbons to the region outside the tubular membrane within the reaction vessel.

4. The method of claim 2, further comprising maintaining the reaction temperature in the reaction vessel at 550°C to 600°C during the SMR.

5. The method of claim 1, further comprising separating the CO2 from the remaining portion of the product gas.

6. The method of claim 1, wherein the heat required for the steam cracking is entirely provided by the H2.

7. The method of claim 1, wherein the steam cracking forms byproduct H2, the method further comprising separating the byproduct H2 before supplying the tail gas to the region within the reaction vessel.

8. A method of processing, the method comprising: The feed is steam-cracked to produce olefin products and tail gas containing methane; The methane is reformed in a reforming unit to form syngas containing hydrogen (H2) and carbon monoxide (CO); The synthesis gas and steam are supplied to the region outside the tubular membrane within the reaction vessel; A water-gas shift reaction (WGS) is carried out in the reaction vessel to form a product gas containing H2 and carbon dioxide (CO2); The H2 in the product gas diffuses through the tubular membrane and enters the lumen of the tubular membrane, wherein the tubular membrane is hydrogen-selective; The H2 is discharged from the lumen of the tubular membrane; The remaining portion of the product gas is discharged from the region outside the tubular membrane; and The H2 is used as fuel to generate heat, which is used for the steam cracking.

9. The method of claim 8, wherein the reforming is autothermal reforming, and the method further comprises providing oxygen (O2) to the reforming apparatus.

10. The method of claim 8, further comprising providing steam to the reforming unit.

11. The method of claim 8, further comprising providing additional hydrocarbons to the reforming unit.

12. The method of claim 8, further comprising maintaining the reaction temperature in the reaction vessel at 450°C to 500°C during the WGS.

13. The method of claim 8, further comprising separating the CO2 from the remaining portion of the product gas.

14. The method of claim 8, wherein the heat required for the steam cracking is entirely provided by the H2.

15. The method of claim 8, wherein the steam cracking forms byproduct H2, the method further comprising separating the byproduct H2 before supplying the tail gas to the region within the reaction vessel.

16. A steam cracking system, the system comprising: A steam cracking unit for producing olefin products and tail gas containing methane from a feedstock; A membrane reactor coupled to the steam cracking unit, the membrane reactor comprising: A reaction vessel for generating a product gas containing hydrogen (H2) from feed gas from the steam cracking unit, and A tubular H2 selective membrane in the reaction vessel, the tubular H2 selective membrane being used to allow H2 to diffuse through the tubular H2 selective membrane and into the lumen of the tubular H2 selective membrane; as well as A heater coupled to the steam cracking unit and the membrane reactor is configured as follows: Receive the H2 from the lumen. Heat is generated by the H2, and The heat is supplied to the steam cracking unit.

17. The system of claim 16, further comprising a reforming unit disposed between the steam cracking unit and the membrane reactor, the reforming unit being configured to reform the tail gas to form syngas, wherein the feed gas contains the syngas.

18. The system of claim 16, wherein the reaction vessel is tubular, and wherein the reaction vessel and the tubular H2 selective membrane are coaxially arranged.

19. The system of claim 18, wherein the reaction vessel includes an outlet for discharging the remainder of the product gas, and wherein the lumen includes an outlet for discharging the H2.

20. The system of claim 16, wherein the reaction vessel includes a catalyst for producing the H2.

Images