Three-product pressure swing adsorption system.

Abstract

A three-product PSA system is described that produces three product streams from a feed gas mixture containing a low boiling limit component, at least one high boiling limit component, and at least one intermediate boiling limit component. The three-product PSA system produces a high pressure product stream enriched in the low boiling limit component, a low pressure tail gas stream enriched in at least one high boiling limit component, and an intermediate pressure vent gas stream enriched in at least one intermediate boiling limit component.

Description

[Technical Field]

[0001] (Statement of priority) This application claims priority to U.S. Provisional Patent Application No. 63 / 167,334, filed March 29, 2021, which is incorporated herein by reference in its entirety. [Background technology]

[0002] Hydrogen is expected to have significant growth potential because it is a clean-burning fuel. However, hydrogen production has traditionally been a significant source of CO2 emissions, and government regulations and societal pressures are increasingly taxing or penalizing CO2 emissions. As a result, intense competition is expected to drive down the cost of hydrogen production while capturing the by-product CO2 for subsequent geological sequestration to capture the growing market. While CO2 can be separated as steam that is fed into common pipelines, certain regions of the world currently lack CO2 pipeline infrastructure, so it will likely need to be produced in a liquefied form for easy transportation by truck or ship.

[0003] In some applications, CO2 capture of more than 95% from steam reforming or autothermal reforming, or even more than 90% including CO2 contribution from utilities, may be desirable and immediately necessary. However, even lower CO2 capture percentages from hydrogen production plants, such as 50% to 60%, may be desirable from an economic standpoint, especially when a CO2 capture system is retrofitted to an existing steam reforming plant. In such cases, CO2 can be economically captured from the shifted syngas (pre-combustion capture). In addition to steam reforming hydrogen plants, syngas CO2 capture may also be desirable in other hydrocarbon or fossil fuel conversion processes, such as autothermal reforming (ATR), gasification, or partial oxidation (POX).

[0004] Most existing hydrogen production processes utilize pressure swing adsorption (PSA) to recover high-purity product hydrogen from the shifted syngas. The low-pressure tail gas stream from the PSA unit is typically combusted to generate heat or steam for the process. If the stream is not sent to a combustor, a purge is required to prevent the buildup of impurities in the process.

[0005] U.S. Patent No. 8,021,464 describes a process for the combined production of hydrogen and CO2 from a mixture of hydrocarbons converted to synthesis gas. The synthesis gas is separated into a hydrogen-rich stream and a PSA off-gas stream in a PSA unit. The PSA off-gas is compressed and dried, followed by several successive steps of condensing and separating a CO2-rich condensate, each step lowering the temperature, which ranges from ambient to -56°C. However, this process results in a purge stream containing a significant amount of CO2 that must be removed from the process. A permeation module can be used to improve separation, but at the cost of increased power requirements.

[0006] U.S. Patent No. 8,241,400 describes a process for recovering hydrogen and CO2 from a mixture of hydrocarbons using a system including a reformer unit, an optional water-gas shift reactor, a PSA unit, and a low-temperature purification unit or catalytic oxidizer. The PSA unit produces three streams: a high-pressure hydrogen stream, a low-pressure CO2 stream, and a CH4-rich stream that is withdrawn during a CO2 co-purge step. Purified CO2 from a CO2 purification unit in the process is used as a co-purge in the PSA unit. The adsorption step is carried out at a pressure of 250 psig to 700 psig. The pressure during the co-purge step ranges from 300 psig to 800 psig, and the CO2 co-purge stream is preferably introduced at a higher pressure than during the adsorption step.

[0007] The use of a second high-pressure feed stream (a CO2 co-purge stream) increases the cost and complexity of the process in U.S. Patent No. 8,241,400. The need to have a segmented adsorber (or two separate vessels) with isolation valves between the two and an intermediate side draw further increases the cost and complexity of the process.

[0008] Therefore, there is a need for an improved hydrogen separation process with improved and cost-effective CO2 capture. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram of one embodiment of a three-product PSA unit for use in the three-product PSA system of the present invention. [Figure 2] FIG. 1 is a diagram of one embodiment of a method for increasing CO2 capture and hydrogen production from an existing steam reforming hydrogen production process using a three-product PSA unit of the present invention. [Figure 3] FIG. 1 is a diagram of another embodiment of CO2 capture and hydrogen production using a three-product PSA unit of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] A three-product PSA system produces three product streams from a feed gas mixture containing a low boiling limit component, at least one high boiling limit component, and at least one intermediate boiling limit component. The three-product PSA system produces a high-pressure product stream enriched in lights, a low-pressure tail gas stream enriched in at least one high boiling limit component, and an intermediate-pressure vent gas stream enriched in at least one intermediate boiling limit component. The lights are the most weakly adsorbing species, the heavy fraction is the most strongly adsorbing species, and the intermediate fraction is between the light and heavy fractions. The light and heavy fractions do not necessarily correspond to molecular weight.

[0011] The three-product PSA unit comprises PSA adsorption vessels. Generally, there are at least six vessels, typically eight to fourteen vessels. The vessels comprise one or more adsorbent layers, generally one to five, typically two to three. The bed percentage of the adsorbent layer is typically between 10% and 100%. Different adsorbent layers have different selectivities for the components in the overhead stream, as known to those skilled in the art. For example, in a hydrogen production process and CO2 recovery, some layers contain adsorbents for the selective adsorption of CO2 relative to methane, carbon monoxide, nitrogen, argon, and hydrogen, including, but not limited to, activated alumina, silica gel, and sodium Y zeolite. Other layers contain adsorbents for the selective adsorption of CO2, methane, carbon monoxide, nitrogen, and argon relative to hydrogen, including, but not limited to, activated carbon, silica gel, and molecular sieve zeolites (e.g., 5A or sodium X zeolite). Those skilled in the art will understand that other zeolites can be used and will know how to select an appropriate adsorbent.

[0012] The vessel has a first opening at one end and a second opening at the opposite end. For convenience, these ends are referred to as the top and bottom of the vessel. The first opening at the bottom is selectively connected to a high-pressure feed gas inlet line and a low-pressure tail gas outlet line. The second opening at the top of the vessel is selectively connected to a high-pressure product outlet line, a medium-pressure vent gas outlet line, and a low-pressure purge gas inlet line.

[0013] Feed gas enters the vessel at high pressure through a first opening at the bottom, undergoes a high-pressure cocurrent adsorption and product removal step, and the product exits the vessel at high pressure through a second opening at the top of the vessel. There is at least one cocurrent depressurization step, followed by a medium-pressure cocurrent depressurization and vent gas removal step. Medium-boiling limit components are removed through the top opening at medium pressure. There are countercurrent blowdown and countercurrent purge steps. Purge gas enters the vessel at low pressure through the top opening. High-boiling limit components can be removed at low pressure through the bottom opening of the vessel during one or both of the countercurrent blowdown and countercurrent purge steps. The countercurrent purge and tail gas removal steps are followed by at least one countercurrent repressurization step.

[0014] The three-product PSA unit of the present invention offers several advantages. The intermediate boiling point components are not removed at high temperatures. Instead, they are removed at an intermediate pressure between the high pressure at which the low boiling point components are removed and the low pressure at which the high boiling point components are removed, but which is much closer to the low pressure than to the high pressure. The intermediate pressure is typically less than 450 kPa.

[0015] Additionally, no high-pressure co-purge stream is used. Furthermore, the vessel is not segmented. The intermediate-boiling components are withdrawn through an opening at the top of the vessel. Therefore, no isolation valves or side-draw outlets are required between the two adsorbent beds. These factors make the three-product PSA unit much simpler and less expensive to build and operate than the PSA and process of U.S. Pat. No. 8,241,400.

[0016] The source of the feed gas mixture can be any process stream containing a low boiling limit component, at least one high boiling limit component, and at least one intermediate boiling limit component. Suitable process streams include, but are not limited to, process streams from new and existing hydrogen production processes such as steam reforming, ATR, gasification, or partial oxidation (POX). Another suitable process stream can be a hydrogen-containing by-product stream from a petroleum refinery, such as fluid catalytic cracking (FCC) off-gas.

[0017] One aspect of the present invention is a method for separating a feed gas mixture comprising a low boiling point component, at least one high boiling point component, and at least one medium boiling point component. In one embodiment, the method includes: introducing the feed gas mixture into a three-product pressure swing adsorption (PSA) system having a PSA cycle, the three-product PSA system including a three-product PSA unit; removing a high-pressure product stream enriched in the low boiling point component, the high-pressure product stream being substantially free of at least one medium boiling point component and at least one high boiling point component; removing a medium-pressure vent gas stream enriched in the at least one medium boiling point component through an opening at the top of the PSA unit; and removing a low-pressure tail gas stream enriched in the at least one high boiling point component through an opening at the bottom of a vessel.

[0018] In some embodiments, removing the high-pressure product stream comprises removing a high-pressure product stream during a high-pressure cocurrent adsorption step in the PSA cycle, removing a medium-pressure vent gas stream during a medium-pressure cocurrent depressurization step in the PSA cycle, and removing a low-pressure tail gas stream during at least one of a countercurrent depressurization step and a countercurrent purge step in the PSA cycle.

[0019] In some embodiments, the PSA cycle comprises: a high pressure co-current adsorption and product removal step; at least one cocurrent depressurization step following the high pressure cocurrent adsorption step and the product removal step; at least one co-current depressurization step followed by a medium pressure co-current depressurization and vent gas removal step; a medium pressure cocurrent depressurization and vent gas removal step followed by a countercurrent blowdown step and tail gas removal step; a countercurrent blowdown step followed by a countercurrent purge and tail gas removal step; a countercurrent purge and tail gas removal step followed by at least one countercurrent repressurization step; Includes.

[0020] In some embodiments, the PSA cycle further comprises at least one countercurrent repressurization step followed by a cocurrent feed repressurization step or at least one countercurrent repressurization step followed by a countercurrent product repressurization step.

[0021] The high pressure product stream is typically removed at a high pressure in the range of 1,000 to 6,000 kPa, or 2,000 kPa to 5,000 kPa, or 2,500 kPa to 4,500 kPa.

[0022] The temperature of the incoming feed gas mixture is typically within the range of 20° C. to 60° C., or 30° C. to 50° C., or 40° C. (or any combination of temperature ranges).

[0023] The concentration of the lower boiling point component in a conventional two-product PSA feed gas is generally in the range of 60 mol% to 90+ mol%. For example, the hydrogen concentration in the feed stream to a hydrogen PSA unit is typically 70 mol% to 80 mol%. It is generally recognized that it is difficult to process a feed stream having a hydrogen concentration of less than 50 mol% in a PSA unit.

[0024] In contrast, the hydrogen concentration in the feed gas mixture to the three-product PSA unit of the present invention is generally in the range of 20 mol% to 60 mol%. For example, the hydrogen concentration in the CO2 distillation column overhead gas in a CO2 recovery system for steam reforming plant tail gas is 30 mol% to 50 mol%, while the hydrogen concentration in fluid catalytic cracking (FCC) off-gas is 20 mol% to 40 mol%.

[0025] 80% to 90% of the low boiling point components in the feed gas mixture are typically recovered in the high-pressure product stream, which is substantially free of high- and medium-boiling point components. It typically contains less than 1%, or less than 0.1%, or less than 0.01% of the high-boiling point components relative to the feed gas mixture. It typically contains less than 10%, or less than 5%, or less than 2%, or less than 1%, or less than 0.1% of the medium-boiling point components relative to the feed gas mixture.

[0026] The low pressure product stream is typically removed at a low pressure in the range of 50 kPa to 250 kPa, or 100 kPa to 200 kPa.

[0027] The low pressure product stream typically contains 95% to 100% of the high boiling limit components in the feed gas mixture. It typically contains 10% of the low boiling limit components (e.g., 5% to 15%) of the feed gas mixture and 40% of the medium boiling limit components (e.g., 20% to 60%) of the feed.

[0028] The medium pressure product stream is removed at a medium pressure between the high pressure and the low pressure. The medium pressure is much closer to the low pressure than the high pressure, typically within the low pressure range of 400 kPa, or 300 kPa, or 200 kPa. Typically, the medium pressure product stream is removed at a pressure in the range of 150 kPa to 450 kPa, or 250 kPa to 350 kPa. There is some overlap between the medium and low pressure ranges, but it is understood that in certain cases the low pressure will be lower than the medium pressure.

[0029] The medium pressure vent gas stream typically contains 40% to 80% of the intermediate boiling point components in the feed gas mixture, which typically contains 10% of the lower boiling point components (e.g., 5% to 25%) of the feed gas mixture, and less than 5%, or less than 1%, or less than 0.1% of the higher boiling point components of the feed.

[0030] In some embodiments, the lower boiling point component is hydrogen.

[0031] In some embodiments, the higher boiling limit component is at least one of carbon dioxide and ethylene.

[0032] In some embodiments, the mid-boiling limit component is at least one of methane, carbon monoxide, nitrogen, and argon.

[0033] In some embodiments, the low boiling limit component is hydrogen, the high boiling limit component is at least one of carbon dioxide and ethylene, and the intermediate boiling limit component is at least one of methane, carbon monoxide, nitrogen, and argon.

[0034] Another aspect of the invention is a method for separating a feed gas mixture comprising at least one of hydrogen, carbon dioxide, and ethylene, and at least one of methane, carbon monoxide, nitrogen, and argon, the method comprising: introducing the feed gas mixture into a three-product pressure swing adsorption (PSA) system having a PSA cycle, the three-product PSA system comprising a three-product PSA unit; removing a high-pressure product stream enriched in hydrogen, the high-pressure product stream being substantially free of at least one of carbon dioxide and ethylene, and at least one of methane, carbon monoxide, nitrogen, and argon; removing a medium-pressure vent gas stream enriched in at least one of carbon monoxide, methane, nitrogen, and argon through an opening at the top of the PSA unit; and removing a low-pressure tail gas stream enriched in at least one of carbon dioxide or ethylene.

[0035] In some embodiments, removing the high-pressure product stream comprises removing a high-pressure hydrogen stream during a high-pressure cocurrent adsorption step in the PSA cycle, removing the intermediate-pressure vent gas stream comprises removing a intermediate-pressure vent gas stream during an intermediate-pressure cocurrent depressurization step in the PSA cycle, and removing the low-pressure tail gas stream comprises removing a low-pressure tail gas stream during at least one of a countercurrent depressurization step and a countercurrent purge step in the PSA cycle.

[0036] In some embodiments, the PSA cycle comprises: a high pressure co-current adsorption and product removal step; at least one cocurrent depressurization step following the high pressure cocurrent adsorption step and the product removal step; at least one co-current depressurization step followed by a medium pressure co-current depressurization and vent gas removal step; a medium pressure cocurrent depressurization and vent gas removal step followed by a countercurrent blowdown step and tail gas removal step; a countercurrent blowdown step followed by a countercurrent purge and tail gas removal step; a countercurrent purge and tail gas removal step followed by at least one countercurrent repressurization step; Includes.

[0037] In some embodiments, the method further comprises at least one countercurrent repressurization step followed by a cocurrent feed repressurization step or at least one countercurrent repressurization step followed by a countercurrent product repressurization step.

[0038] In some embodiments, at least one of the high-pressure product stream is removed at a pressure in the range of 1,000 kPa to 6,000 kPa, the medium-pressure vent gas stream is removed at a pressure in the range of 150 kPa to 450 kPa, and the low-pressure tail gas stream is removed at a pressure in the range of 100 kPa to 250 kPa.

[0039] Another aspect of the invention is a three-product PSA unit. In one embodiment, the three-product PSA unit comprises a PSA adsorption vessel having a first end and a second end, the PSA adsorption vessel containing at least one adsorbent bed, the PSA adsorption vessel having a first opening at the first end and a second opening at the second end, the first opening selectively fluidly communicating with a high-pressure feed gas inlet line and a low-pressure high-boiling component outlet line, and the second opening selectively fluidly communicating with a high-pressure product outlet line, an intermediate-pressure vent gas outlet line, and a low-pressure purge gas inlet line.

[0040] In certain applications, a three-product PSA unit produces high-purity hydrogen in a high-pressure product stream, a low-pressure tail gas stream containing CO and some impurities, and a medium-pressure vent gas stream containing most of the impurities. The medium-pressure vent gas stream has a pressure between the other two streams. The CO-rich tail gas stream can be compressed and sent to a CO capture system, where a high-purity liquid CO stream is recovered. The impurity-rich medium-pressure vent gas stream can be combusted in a fired heater or waste heat boiler to generate heat and steam for upstream processes. A portion may be recycled upstream of the reformer or water-gas shift reactor(s) for further reaction of impurities and recovery of hydrogen.

[0041] When the feed gas mixture is a reaction mixture effluent stream from a hydrogen production process, the lower boiling limit component is hydrogen, the higher boiling limit component is carbon dioxide, and the intermediate boiling limit component is at least one of methane, carbon monoxide, nitrogen, and argon.

[0042] When the feed gas mixture is a fluid catalytic cracking (FCC) off-gas stream, the lower boiling limit component is hydrogen, the higher boiling limit component is ethylene, and the intermediate boiling limit component is at least one of methane and nitrogen.

[0043] Utilizing a three-product PSA system instead of a conventional two-product PSA unit avoids the buildup of impurities in the process and eliminates the need to take a physical bleed stream to purge impurities that could result in the loss of valuable hydrogen in the bleed stream.

[0044] In certain processes, the feed gas mixture may be the effluent from a hydrogen production process. The effluent includes hydrogen as the low-boiling component, CO as the high-boiling component, and at least one of carbon monoxide, methane, nitrogen, and argon as intermediate-boiling components. The effluent may be separated into a hydrogen stream and a tail gas stream in a conventional PSA unit. The tail gas stream may be compressed and separated in a distillation column of a CO recovery unit into a bottoms stream containing CO and an overhead stream containing hydrogen, CO, and at least one of carbon monoxide, methane, nitrogen, and argon. The overhead stream is sent to a three-product PSA unit, which produces high-pressure pure hydrogen, a low-pressure CO2-rich tail gas stream, and a medium-pressure vent gas stream containing carbon monoxide, methane, nitrogen, and argon, as well as unrecovered hydrogen (10% of the hydrogen in the incoming overhead stream).

[0045] Extracting pure hydrogen directly from the overhead stream using a three-product PSA system has the potential to offer economic advantages over systems using a recycle configuration. Additional hydrogen production substantially improves process economics. Using a three-product PSA unit on the distillation column overhead stream avoids non-permeate losses of CO2 that occur with the use of membrane separation processes. Utilizing a three-product PSA system offers innovation and flexibility, reduces downstream equipment size and utility costs, and increases captured CO2 (because the impurities-rich purge stream does not contain significant CO2).

[0046] 1 shows a PSA unit 5 comprising a PSA adsorption vessel 10. Vessel 10 contains three adsorption beds 15, 20, and 25. Vessel 10 includes a first opening 30 at a first end 35 and a second opening 40 at a second end 45. Opening 30 is in selective fluid communication with a high-pressure feed gas inlet line 50 via valve 55 and with a low-pressure tail gas outlet line 60 via valve 65. Second opening 40 is in selective fluid communication with a high-pressure product outlet line 70 via valve 75, with an intermediate-pressure vent gas outlet line 80 via valve 85, and with a low-pressure purge gas inlet line 90 via valve 95.

[0047] During the high pressure co-current adsorption and product removal steps of the PSA cycle, valves 55 and 75 are open and valves 65, 85, and 95 are closed, allowing high pressure feed gas to enter vessel 10 and high pressure product stream to exit.

[0048] During at least one co-current depressurization step, valves 55, 65, 75, 85, and 95 are closed.

[0049] During the medium pressure co-current depressurization and valving step, valve 85 is open and valves 55, 65, 75, and 95 are closed.

[0050] During the countercurrent blowdown and tail gas removal steps, valve 65 is open and valves 55, 75, 85, and 95 are closed. The bed is depressurized through valve 65 and a portion of the CO2 is desorbed.

[0051] During the countercurrent purge and tail gas removal step, valves 65 and 95 are open and valves 55, 75, and 85 are closed. Purge gas is introduced and CO2 is removed.

[0052] During at least one countercurrent repressurization step, valves 55, 65, 75, 85, and 95 are closed.

[0053] FIG. 2 illustrates one embodiment of a hydrogen production process 100 incorporating the three-product PSA unit of the present invention. Natural gas 105 and water 110 are sent to the reaction section 112 of an existing steam reforming process unit 120, and assist fuel gas 114 and air 115 are sent to a furnace within the steam reforming process unit 120. Instead of natural gas, other hydrocarbon feed streams, including but not limited to naphtha and liquefied petroleum gas (LPG), can be used. Because PSA tail gas or vent gas does not provide sufficient heat to drive the process, the assist fuel gas is an additional fuel source to provide stability and sufficient heat for the reforming reaction. Suitable assist fuel gases include, but are not limited to, natural gas and other primarily hydrocarbon-containing fuels, such as refinery fuel gas, petrochemical complex synfuel gas, vaporized naphtha or vaporized liquefied petroleum gas (LPG), or blends of hydrocarbon-containing fuels with hydrogen, including virgin or pure hydrogen.

[0054] The steam reforming and water gas shift reactions produce an effluent stream 125 comprising hydrogen, CO, water, and at least one of methane, carbon monoxide, and nitrogen. A flue gas stream 130 and a steam stream 135 also exit the steam reforming process unit 120.

[0055] The effluent stream 125 has a temperature of 30° C. to 50° C. (after heat recovery and cooling within the steam reforming process) and a pressure of 2,000 to 3,000 kPa. The effluent stream 125 is sent to a hydrogen PSA unit 140 where it is separated into a high purity hydrogen stream 145 enriched in hydrogen and a hydrogen-depleted tail gas stream 150 containing a portion of the hydrogen, CO, water, and at least one of methane, carbon monoxide, and nitrogen.

[0056] The tail gas stream 150 is sent to a compressor 155 where it is compressed from a pressure in the range of 110 kPa to 150 kPa to a pressure in the range of 3,000 kPa to 6,000 kPa.

[0057] The compressed tail gas stream 160 is sent to a CO2 recovery unit 165 where it is dried to remove water stream 167, cooled to a temperature of -20°C to -50°C, and separated into a bottom stream 170 and an overhead stream 175. The bottom stream 170, which comprises liquid CO2, is recovered.

[0058] The overhead stream 175 is sent to a three-product PSA system 180 comprising a three-product PSA unit 185 where it is separated into three streams. A high-pressure hydrogen stream 190 is recovered. A low-pressure CO stream 195 is recycled to the compressor 155. A medium-pressure vent gas stream 200 comprising at least one of methane, carbon monoxide, and nitrogen is sent to the steam reforming process unit 120 as fuel.

[0059] A bypass line 202 routes the tail gas stream 150 to the furnace 118 in the existing steam reforming process unit 120 for combustion, allowing the steam reforming process unit 120 to continue operating without CO2 capture in the event of a problem with the compressor 155, the CO2 capture unit 165, or the three-product PSA system 180.

[0060] 3 illustrates another embodiment of a hydrogen production process 300 incorporating a three-product PSA unit of the present invention. Natural gas 305, water 310, and oxygen 315 are sent to an ATR / GHR process 320. Steam reforming and partial oxidation reactions produce a syngas effluent stream 325 that is sent to a water-gas shift reaction unit 330. The effluent 335 from the water-gas shift reaction unit 330 comprises hydrogen, CO, water, and at least one of methane, carbon monoxide, nitrogen, and argon.

[0061] The effluent 335 is sent to a PSA unit 340 where it is separated into a high purity hydrogen stream 345 enriched in hydrogen and a hydrogen-depleted tail gas stream 350 containing a portion of the hydrogen, CO, water, and at least one of methane, carbon monoxide, nitrogen, and argon.

[0062] Tail gas stream 350 is sent to compressor 355. Compressed tail gas stream 360 is sent to CO2 capture unit 365 for drying to remove water stream 367, cooling, and separation into understream 370 and overhead stream 375. Understream 370, comprising liquid CO2, is recovered.

[0063] Overhead stream 375 is sent to three-product PSA system 380, which includes three-product PSA unit 385, where it is separated into three streams. High-pressure hydrogen stream 390 is recovered. Low-pressure CO stream 395 is recycled to compressor 355. Medium-pressure vent gas stream 400, which comprises at least one of methane, carbon monoxide, nitrogen, and argon, is sent to the furnace as fuel.

[0064] Example 1 - Three Product PSA System with Three Product PSA Unit Tables 1-5 provide the results for a three-product PSA system equipped with a three-product PSA unit.

[0065] Table 1 shows a 10-bed cycle with three equalization steps. Table 2 provides a detailed description of the 10-bed PSA cycle of Table 1.

[0066] These cycles were used in experimental pilot plant tests of a three-product PSA unit as shown in Tables 3-5.

[0067] [Table 1]

[0068] [Table 2] * x = subcycle time (range 30 to 120 seconds)

[0069] The feed gas composition is shown in Table 3, and the bed packing is shown in Table 4. As shown in Table 5, the high-pressure hydrogen stream contains 82.5% of the hydrogen in the incoming overhead stream and no CO, CO, CH, or nitrogen. The low-pressure CO stream contains all the CO, 8.8% of the hydrogen, 30.8% of the CO, 49.8% of the CH, and 11.4% of the nitrogen. The medium-pressure vent gas stream contains 8.7% of the hydrogen, 69.2% of the CO, 50.2% of the CH, 88.6% of the nitrogen, and no CO.

[0070] [Table 3]

[0071] [Table 4]

[0072] [Table 5]

[0073] As used herein, the term "stream" may include a variety of hydrocarbon molecules and other substances.

[0074] As used herein, the terms "stream," "feed," "product," "portion," or "fraction" can include various hydrocarbon molecules, such as straight- and branched-chain alkanes, naphthalenes, alkenes, alkadienes, and alkynes, and, optionally, other substances, such as gases, e.g., hydrogen, or impurities, e.g., heavy metals, and sulfur and nitrogen compounds. Each of the above can also include aromatic and non-aromatic hydrocarbons.

[0075] As used herein, the term "overhead stream" can mean a stream recovered at or near the top of a vessel such as a distillation column.

[0076] As used herein, the term "underflow" can mean a stream recovered at or near the bottom of a vessel such as a distillation column.

[0077] As used herein, the term "unit" can refer to an area that includes one or more pieces of equipment and / or one or more subzones. Equipment can include, but is not limited to, one or more reactors or reaction vessels, separation vessels, distillation columns, heaters, exchangers, pipes, pumps, compressors, and controllers. Additionally, equipment such as reactors, dryers, or vessels can further include one or more zones or subzones.

[0078] The term "column" refers to one or more distillation columns for separating one or more components of different volatility. Unless otherwise specified, each column includes a condenser at the top of the column for condensing and refluxing a portion of the overhead stream that returns to the top of the column, and a reboiler at the bottom of the column for vaporizing and returning a portion of the bottom stream to the bottom of the column. The feed to a column may be preheated or precooled. The overhead or overhead pressure is the pressure of the overhead vapor at the vapor outlet of the column. The bottom temperature is the liquid bottom outlet temperature. The net overhead line and net bottom line refer to the net line from the column downstream of any reflux or reboil to the column, unless otherwise specified. A stripping column may omit the reboiler at the bottom of the column and instead provide the heating requirements and stripping from a fluidizing inert medium such as steam.

[0079] As illustrated, the process flow lines in the diagrams may be referred to as, for example, lines, pipes, feeds, gases, products, emissions, parts, portions, or streams.

[0080] The term "passing" means that material passes from a conduit or vessel to an object.

[0081] Specific Embodiments While the following is described in conjunction with specific embodiments, it will be understood that this description is illustrative and not intended to limit the scope of the foregoing description and the appended claims.

[0082] A first embodiment of the present invention is a method for separating a feed gas mixture comprising a low boiling point component, at least one high boiling point component, and at least one medium boiling point component, the method comprising: introducing the feed gas mixture into a three-product pressure swing adsorption (PSA) system having a PSA cycle, the three-product PSA system comprising a three-product PSA unit; removing a high-pressure product stream enriched in the low boiling point component, the high-pressure product stream being substantially free of at least one medium boiling point component and at least one high boiling point component; removing a medium-pressure vent gas stream enriched in the at least one medium boiling point component; and removing a low-pressure tail gas stream enriched in the at least one high boiling point component. One embodiment of the present invention is one, any, or all of the preceding embodiments of this paragraph up to and including the first embodiment of this paragraph, wherein the three-product PSA system includes a three-product PSA unit, removing a high-pressure product stream during a high-pressure cocurrent adsorption step in the PSA cycle, removing a medium-pressure vent gas stream during a medium-pressure cocurrent depressurization step in the PSA cycle, and removing a low-pressure tail gas stream during at least one of a countercurrent depressurization step and a countercurrent purge step in the PSA cycle. An embodiment of the present invention is one, any, or all of the preceding embodiments of this paragraph up to and including the first embodiment of this paragraph, wherein the PSA cycle includes a high-pressure cocurrent adsorption and product removal step, at least one cocurrent depressurization step following the high-pressure cocurrent adsorption and product removal step, a medium-pressure cocurrent depressurization and vent gas removal step following the at least one cocurrent depressurization step, a countercurrent blowdown step and tail gas removal step following the medium-pressure cocurrent depressurization and vent gas removal step, a countercurrent purge and tail gas removal step following the countercurrent blowdown step, and at least one countercurrent repressurization step following the countercurrent purge and tail gas removal step. An embodiment of the present invention is one, any, or all of the preceding embodiments of this paragraph up to and including the first embodiment of this paragraph, further including a cocurrent feed repressurization step following the at least one countercurrent repressurization step or a countercurrent product repressurization step following the at least one countercurrent repressurization step.An embodiment of the present invention is one, any, or all of the preceding embodiments of this paragraph up to the first embodiment of this paragraph, wherein the high-pressure product stream is removed at a pressure ranging from 1,000 kPa to 6,000 kPa. An embodiment of the present invention is one, any, or all of the preceding embodiments of this paragraph up to the first embodiment of this paragraph, wherein the medium-pressure vent gas stream is removed at a pressure ranging from 150 kPa to 450 kPa. An embodiment of the present invention is one, any, or all of the preceding embodiments of this paragraph up to the first embodiment of this paragraph, wherein the low-pressure tail gas stream is removed at a pressure ranging from 100 kPa to 250 kPa. An embodiment of the present invention is one, any, or all of the preceding embodiments of this paragraph up to the first embodiment of this paragraph, wherein the lower boiling limit component is hydrogen. An embodiment of the present invention is one, any, or all of the preceding embodiments of this paragraph up to the first embodiment of this paragraph, wherein the at least one higher boiling limit component is at least one of carbon dioxide and ethylene. An embodiment of the present invention is one, any, or all of the preceding embodiments of this paragraph up to and including the first embodiment of this paragraph, wherein the at least one intermediate boiling limit component is at least one of methane, carbon monoxide, nitrogen, and argon.An embodiment of the present invention is one, any, or all of the preceding embodiments of this paragraph up to and including the first embodiment of this paragraph, wherein the low boiling limit component is hydrogen, the at least one high boiling limit component is at least one of carbon dioxide and ethylene, and the at least one intermediate boiling limit component is at least one of methane, carbon monoxide, nitrogen, and argon.

[0083] A second embodiment of the present invention is a method for separating a feed gas mixture comprising at least one of hydrogen, carbon dioxide, and ethylene, and at least one of methane, carbon monoxide, nitrogen, and argon, the method comprising: introducing the feed gas mixture into a three-product pressure swing adsorption (PSA) system having a PSA cycle, the three-product PSA system comprising a three-product PSA unit; removing a high-pressure product stream enriched in hydrogen, the high-pressure product stream being substantially free of at least one of carbon dioxide and ethylene, and at least one of methane, carbon monoxide, nitrogen, and argon; removing a medium-pressure vent gas stream enriched in at least one of carbon monoxide, methane, nitrogen, and argon through an outlet on the same side of the adsorption bed as the high-pressure product; and removing a low-pressure tail gas stream enriched in at least one of carbon dioxide and ethylene. An embodiment of the present invention is one, any, or all of the preceding embodiments of this paragraph up to and including the second embodiment of this paragraph, wherein removing the high-pressure product stream comprises removing the high-pressure product stream during a high-pressure cocurrent adsorption step in the PSA cycle; removing the intermediate-pressure vent gas stream comprises removing the intermediate-pressure vent gas stream during an intermediate-pressure cocurrent depressurization step in the PSA cycle; and removing the low-pressure tail gas stream comprises removing the low-pressure tail gas stream during at least one of a countercurrent depressurization step and a countercurrent purge step in the PSA cycle. An embodiment of the present invention is one, any, or all of the preceding embodiments of this paragraph up to the second embodiment of this paragraph, wherein the PSA cycle includes a high-pressure cocurrent adsorption and product removal step, at least one cocurrent depressurization step following the high-pressure cocurrent adsorption and product removal step, at least one cocurrent depressurization step following the cocurrent depressurization step, a medium-pressure cocurrent depressurization and vent gas removal step following the medium-pressure cocurrent depressurization and vent gas removal step, a countercurrent blowdown step and tail gas removal step following the countercurrent blowdown step, a countercurrent purge and tail gas removal step following the countercurrent purge and tail gas removal step, and at least one countercurrent repressurization step following the countercurrent purge and tail gas removal step.An embodiment of the present invention is one, any, or all of the preceding embodiments of this paragraph through the second embodiment of this paragraph, further comprising a cocurrent feed repressurization step following at least one countercurrent repressurization step or a countercurrent product repressurization step following at least one countercurrent repressurization step.An embodiment of the present invention is one, any, or all of the preceding embodiments of this paragraph through the second embodiment of this paragraph, wherein at least one of the high-pressure product stream is removed at a pressure in the range of 1,000 kPa to 6,000 kPa, the medium-pressure vent gas stream is removed at a pressure in the range of 150 kPa to 450 kPa, and the low-pressure tail gas stream is removed at a pressure in the range of 100 kPa to 250 kPa.

[0084] A third embodiment of the present invention is an apparatus comprising a PSA adsorption vessel having a first end and a second end, the PSA adsorption vessel containing at least one adsorbent bed, the PSA adsorption vessel having a first opening at the first end and a second opening at the second end, the first opening selectively fluidly communicating with a high-pressure feed gas inlet line and a low-pressure high-boiling component outlet line, and the second opening selectively fluidly communicating with a high-pressure product outlet line, an intermediate-pressure vent gas outlet line, and a low-pressure purge gas inlet line.

[0085] Without further elaboration, it is believed that one skilled in the art can, using the preceding description, readily ascertain the essential characteristics of the present invention and make various changes and modifications to the present invention to adapt it to various uses and conditions, all without departing from the spirit and scope of the present invention. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way, and are intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.

[0086] Above, all temperatures are set forth in degrees Celsius and all parts and percentages are by weight unless otherwise stated. <Additional Notes> [Form 1] 1. A method for separating a feed gas mixture comprising a low boiling limit component, at least one high boiling limit component, and at least one intermediate boiling limit component, comprising: introducing the feed gas mixture into a three-product pressure swing adsorption (PSA) system having a PSA cycle, the three-product PSA system comprising a three-product PSA unit 5; removing said low boiling point component-enriched high pressure product stream (70), wherein said high pressure product stream (70) is substantially free of said at least one intermediate boiling point component and said at least one high boiling point component; removing said at least one intermediate-boiling limit component enriched medium-pressure vent gas stream (80); removing a low pressure tail gas stream (60) enriched in said at least one higher boiling limit component; A method comprising: [Form 2] The three-product PSA system comprises: removing said high pressure product stream (70) during a high pressure co-current adsorption step in said PSA cycle; removing said medium-pressure vent gas stream (80) during a medium-pressure cocurrent depressurization step in said PSA cycle; removing the low-pressure tail gas stream (60) during at least one of a cocurrent depressurization step and a countercurrent purge step in the PSA cycle; 2. The method of claim 1, comprising a tri-product PSA unit (5). [Form 3] the three-product PSA cycle a high pressure co-current adsorption and product removal step; at least one co-current depressurization step following said high-pressure co-current adsorption and product removal step; a step of medium pressure co-current depressurization and vent gas removal following said at least one co-current depressurization step; the medium pressure cocurrent depressurization and vent gas removal step followed by a countercurrent blowdown step and a tail gas removal step; a countercurrent purge and tail gas removal step following the countercurrent blowdown step; at least one countercurrent repressurization step following said countercurrent purging and tail gas removal step; 3. The method of any one of aspects 1 to 2, comprising: [Form 4] a cocurrent feed repressurization step following said at least one countercurrent repressurization step, or a countercurrent product repressurization step following said at least one countercurrent repressurization step. 4. The method of claim 3, further comprising: [Form 5] the high pressure product stream (70) is removed at a pressure in the range of 1,000 kPa to 6,000 kPa; the medium pressure vent gas stream (80) is removed at a pressure in the range of 150 kPa to 450 kPa; the low-pressure tail gas stream (60) is removed at a pressure in the range of 100 kPa to 250 kPa; 3. The method of any one of aspects 1-2, wherein the method is at least one of the following: [Form 6] 3. The method according to any one of aspects 1 to 2, wherein the low boiling point component is hydrogen. [Form 7] 3. The method of any one of aspects 1 to 2, wherein the at least one higher boiling limit component is at least one of carbon dioxide and ethylene. [Form 8] 3. The method of any one of aspects 1-2, wherein the at least one middle boiling limit component is at least one of methane, carbon monoxide, nitrogen, and argon. [Form 9] 3. The method of any one of claims 1 to 2, wherein the low boiling limit component is hydrogen, the at least one high boiling limit component is at least one of carbon dioxide and ethylene, and the at least one intermediate boiling limit component is at least one of methane, carbon monoxide, nitrogen, and argon. [Form 10] A three-product PSA unit (5), 1. A three-product PSA unit (5) comprising: a PSA adsorption vessel (10) having a first end (35) and a second end (45), the PSA adsorption vessel containing at least one adsorbent layer (15, 20, 25); the PSA adsorption vessel having a first opening (30) at the first end (35) and a second opening (40) at the second end (45), the first opening (30) selectively fluidly communicating with a high-pressure feed gas inlet line (50) and a low-pressure high-boiling component outlet line (60); and the second opening (40) selectively fluidly communicating with a high-pressure product outlet line (70), an intermediate-pressure vent gas outlet line (80), and a low-pressure purge gas inlet line (90).

Claims

1. 1. A method for separating a feed gas mixture comprising a low boiling limit component, at least one high boiling limit component, and at least one intermediate boiling limit component, comprising: introducing the feed gas mixture into a three-product pressure swing adsorption (PSA) system having a PSA cycle, the three-product PSA system comprising a three-product PSA unit (5); removing the low boiling point enriched high pressure product stream (70) at a pressure in the range of 1,000 to 6,000 kPa, wherein the high pressure product stream (70) is free of the at least one intermediate boiling point component and the at least one high boiling point component; removing said medium pressure vent gas stream (80) enriched in said at least one intermediate boiling limit component at a pressure less than 450 kPa; removing said low pressure tail gas stream (60) enriched in said at least one higher boiling point component at a pressure in the range of 50 kPa to 250 kPa; A method comprising:

2. the three-product PSA system comprising: removing said high pressure product stream (70) during a high pressure co-current adsorption step in said PSA cycle; removing said medium-pressure vent gas stream (80) during a medium-pressure cocurrent depressurization step in said PSA cycle; removing said low-pressure tail gas stream (60) during at least one of a countercurrent depressurization step and a countercurrent purge step in said PSA cycle; 2. The process of claim 1, comprising a three-product PSA unit (5).

3. A three-product PSA unit (5), 1. A three-product PSA unit (5) comprising: a PSA adsorption vessel (10) having a first end (35) and a second end (45), the PSA adsorption vessel containing at least one adsorbent layer (15, 20, 25); the PSA adsorption vessel having a first opening (30) at the first end (35) and a second opening (40) at the second end (45), the first opening (30) selectively fluidly communicating with a high-pressure feed gas inlet line (50) and a low-pressure tail gas outlet line (60); and the second opening (40) selectively fluidly communicating with a high-pressure product outlet line (70), an intermediate-pressure vent gas outlet line (80), and a low-pressure purge gas inlet line (90).

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