Patent Application
20250206608
Systems and methods are provided for separating products generated by methane pyrolysis.
Methane pyrolysis (or more generally hydrocarbon pyrolysis) is a process that can convert natural gas to hydrogen and solid carbon products. One advantage of this method for hydrogen generation is that the carbon primarily forms a solid phase, and therefore the large majority of the carbon does not need to be separated from the product stream containing the hydrogen. The resulting hydrogen product stream is further purified to achieve a desired product purity, typically 95-99.9%.
Although the majority of the carbon is converted into solid carbon in methane pyrolysis, one of the current limitations for methane pyrolysis as a source of hydrogen generation is the ability to separate the hydrogen generated by the pyrolysis process into a high purity stream. This is due in part to the fact that typical natural gas streams (and/or other methane-containing hydrocarbon streams) typically also contain N2, O2, and/or oxygen-containing compounds such as water. Some removal of these nitrogen- and oxygen-containing substances can be performed prior to performing pyrolysis. But typical hydrocarbon streams used for a pyrolysis process still contain some nitrogen and oxygen (and/or oxygen-containing compounds). The oxygen and/or oxygen-containing compounds can result in the presence of water, CO, and CO2 in the hydrogen-containing product stream. Thus, to achieve target purities of higher than 95% for the hydrogen-containing product stream, additional separations need to be performed.
In addition to nitrogen and carbon oxides, the hydrogen-containing product stream typically also contains unreacted methane that needs to be recycled back to the pyrolysis reactor. In the recycle, contaminants that enter with the feed (and that are separated out from the hydrogen-containing product stream) can build up. A purge stream is typically incorporated to remove contaminants such as nitrogen and CO2.
Another challenge of using methane pyrolysis for hydrogen production is the relatively low pressure of the resulting hydrogen product stream. Compared to other hydrogen production processes such as steam methane reforming (SMR) and autothermal reforming (ATR), methane pyrolysis operates at low pressures, typically ranging from 1-10 bar. This low pressure limits the pressure ratio available for a conventional pressure swing adsorption (PSA) separation process. It would be desirable to have improved methods for using swing adsorption processes for producing high purity hydrogen product streams from methane pyrolysis effluents, while still incorporating a high percentage of the hydrogen from the methane pyrolysis effluent into the hydrogen product stream.
U.S. Patent 2010/0000408 describes a hydrogen gas separation method and a separation apparatus. The method includes exposing a gas for separation sequentially to activated carbon followed by a molecular sieve corresponding to Ca-A-type molecular sieve, Ca—Z-type molecular sieve, or Li—X-type molecular sieve.
U.S. Pat. No. 7,179,324 describes a continuous feed three-bed pressure swing adsorption system. The process cycle for the system includes purge steps.
U.S. Patent Application Publication 2018/0001301 describes examples of structured adsorbent beds.
U.S. Patent Application Publication 2021/0331918 describes performing methane pyrolysis using stacked fluidized beds.
In an aspect, a method for separating hydrogen from methane pyrolysis products using a plurality of adsorbent beds is provided. The method includes performing pyrolysis on a feed containing C1-C4 hydrocarbons to form a pyrolysis effluent. The pyrolysis effluent can contain, on a dry basis, 60 vol % or more of H2 and 1.0 vol % or more CH4. Additionally, the method includes separating at least a portion of the pyrolysis effluent to form a hydrogen-containing effluent, a recycle stream, and a purge stream. The hydrogen-containing stream can contain 98.0 vol % or more H2. Optionally, the hydrogen-containing stream can contain 70 vol % or more of the H2 contained in the feed and/or the recycle stream can contain 80 vol % or more of the CH4 contained in the feed.
Optionally, the feed can further include N2. In such an optional aspect, the pyrolysis effluent can contain 7.0 vol % or less of N2 and/or the hydrogen-containing stream can contain 1.0 vol % or more N2.
Optionally, the separating at least a portion of the pyrolysis effluent can correspond to using a separation process that comprises a pressure of 50 kPa-a or less to form the hydrogen-containing effluent, the recycle stream, and the purge stream.
Optionally, the separating at least a portion of the pyrolysis effluent can correspond to exposing the at least a portion of the pyrolysis effluent to a parallel channel contactor to form the hydrogen-containing effluent, the recycle stream, and the purge stream. An example of a parallel channel contactor can be a monolith. Optionally, the parallel channel contactor can have a void fraction of 36% or less.
In another aspect, a method for separating hydrogen from methane pyrolysis products using a plurality of adsorbent beds is provided. The method includes performing pyrolysis on a feed containing C1-C4 hydrocarbons to form a pyrolysis effluent containing, on a dry basis, 60 vol % or more of H2 and 1.0 vol % or more CH4. Additionally, the method includes separating at least a portion of the pyrolysis effluent using a separation process including exposing the at least a portion of the pyrolysis effluent to a structured adsorbent contactor to form a hydrogen-containing effluent, a recycle stream, and a purge stream, the hydrogen-containing stream containing 98.0 vol % or more H2. Optionally, the hydrogen-containing stream can contain 70 vol % or more of the H2 contained in the feed and/or the recycle stream can contain 80 vol % or more of the CH4 contained in the feed.
All numerical values within the detailed description and the claims herein are modified by “about” or “approximately” the indicated value, and take into account experimental error and variations that would be expected by a person having ordinary skill in the art.
In various aspects, systems and methods are provided for separation of a high purity hydrogen stream from methane pyrolysis effluents. The methods can allow for increased recovery of hydrogen from the methane pyrolysis effluent while maintaining a target purity for the hydrogen product stream of 98.0 vol % or more, or 99.0 vol % or more, such as up to being substantially composed only of hydrogen (99.9 vol % or more).
Conventionally, the requirements for forming a high purity hydrogen-containing product stream in combination with the low starting pressure of the pyrolysis effluent has resulted in separation processes that can achieve a target purity, but at the cost of limiting the amount of hydrogen that is recovered from the pyrolysis effluent. The hydrogen not recovered is lost as purge gas and/or recycled back to the process along with the methane, thus increasing required reactor volumes.
In some aspects, systems and methods are provided for improving recovery of hydrogen from a pyrolysis effluent while maintaining a target purity for the hydrogen-containing product (such as a product stream) by eliminating the need for using a portion of the hydrogen-containing product as a purge stream for the sorbent bed during the process. In such aspects, use of a purge stream can be avoided by using a vacuum pressure swing adsorption (VPSA) cycle with an appropriate selection of steps. For example, in some aspects, a cycle can be used where the sorbent is evacuated at a pressure of less than 90 kPa-a for a time period that is at least twice as long as the time the sorbent is exposed to a flow of pyrolysis effluent. An adsorbent can be used that improves or maximizes methane recovery while also increasing the portion of nitrogen that is removed with the hydrogen-containing product. The resulting hydrogen-containing product can be formed with an H2 content of 98.0 vol % or more, or 99.0 vol % or more, such as up to being substantially entirely composed of hydrogen (99.9 vol % or more).
Additionally or alternately, in some aspects, systems and methods are provided for improving productivity and recovery of hydrogen from a pyrolysis effluent while maintaining target purity for the hydrogen-containing stream by performing pressure swing adsorption using adsorption vessels that contain a structured adsorbent. By using a structured adsorbent with an appropriate sorbent material, contact between a pyrolysis effluent and the sorbent can be improved, resulting in improved recovery of hydrogen while maintaining high purity in the product stream. A structured adsorbent can also improve the productivity of the process. The structured adsorbent can correspond to substantially parallel channel monolith configuration, with sorbent material coated on interior surfaces of the parallel channels.
Further additionally or alternately, pressure swing adsorption (PSA) processes (performed without reducing the pressure below 90 kPa-a) are provided that use an improved separation cycle to increase hydrogen recovery while maintaining a target purity. Optionally, a structured adsorbent can be used to further improve recovery in such PSA processes. The resulting hydrogen-containing product can be formed with an H2 content of 80 vol % or more, or 90 vol % or more, or 95 vol % or more, or 98.0 vol % or more, or 99.0 vol % or more, such as up to being substantially entirely composed of hydrogen (99.9 vol % or more).
Additionally or alternately, the hydrogen-containing product can also contain an increased or maximized amount of the hydrogen that is present in the pyrolysis effluent prior to separation to form the hydrogen-containing product. In some aspects, the hydrogen-containing product (such as a product stream) can contain 70 vol % or more of the H2 contained in the pyrolysis effluent prior to separation, or 80 vol % or more, such as up to 98 vol % or possibly still more.
In some optional aspects, if the pyrolysis effluent contains N2, the resulting hydrogen-containing product can contain 0.5 vol % or more of N2, or 1.0 vol % or more, such as up to 2.5 vol % or possibly still more. Additionally or alternately, the N2 in the hydrogen-containing product can contain 5.0 vol % or more of the N2 contained in the pyrolysis effluent, or 10 vol % or more, or 15 vol % or more, such as up to 25 vol % or possibly still more.
The pyrolysis effluent can also typically contain unreacted methane. Separation of the pyrolysis effluent can also result in formation of a recycle stream that includes at least a portion of the unreacted methane. This can allow the unreacted methane to be returned to the pyrolysis process. In some aspects, a recycle stream can be formed that contains 70 vol % or more of the methane present in the pyrolysis effluent, or 80 vol % or more, or 85 vol % or more, or 90 vol % or more, such as up to 99 vol % or possibly still higher.
Typically, the pyrolysis effluent can also contain carbon oxides (CO or CO2). In some aspects, the pyrolysis effluent can contain 5.0 vol % or less of carbon oxides, or 3.0 vol % or less, such as down to 0.1 vol % or possibly still lower. In such aspects, the recycle stream can contain 90 vol % or less of the carbon oxides contained in the pyrolysis effluent, or 85 vol % or less, or 80 vol % or less, such as down to 65 vol % or possibly still lower. Such a recycle stream can also contain 90 vol % or less of the N2 contained in the pyrolysis effluent, or 85 vol % or less, or 80 vol % or less, or 75 vol % or less, such as down to 65 vol % or possibly still lower.
In some aspects, the sorbent materials used for the VPSA and/or PSA processes can correspond to conventional materials for separation of H2 from CO2 and CH4. Examples of such materials include zeotype materials (such as zeolitic materials) and activated carbon.
In some aspects, at least a first portion of a purge stream and/or an evacuation stream can be used for recycle to the pyrolysis process, while a second portion of the purge stream and/or evacuation stream can be purged from the separation system so as to avoid buildup of contaminants such as N2. Optionally, such a purged portion of the purge stream and/or evacuation stream can be used as a fuel for other processes.
In this discussion, a zeolite is defined to refer to a crystalline material having a porous framework structure built from tetrahedra atoms connected by bridging oxygen atoms. Examples of known zeolite frameworks are given in the “Atlas of Zeolite Frameworks” published on behalf of the Structure Commission of the International Zeolite Association”, 6th revised edition, Ch. Baerlocher, L. B. McCusker, D. H. Olson, eds., Elsevier, New York (2007) and the corresponding web site, http://www.iza-structure.org/databases/. Under this definition, a zeolite can refer to aluminosilicates (i.e., zeolites) having a zeolite framework structure as well as crystalline structures containing oxides of heteroatoms different from silicon and aluminum. Such heteroatoms can include any heteroatom generally known to be suitable for inclusion in a zeotype framework, such as gallium, boron, germanium, phosphorus, zinc, and/or other transition metals that can substitute for silicon and/or aluminum in a zeotype framework. It is noted that under this definition, a zeotype can include materials such as silicoaluminophosphate (SAPO) materials or aluminophosphate (AlPO) materials.
In this discussion, a siliceous zeolite is defined as a crystalline material including both silicon and aluminum as atoms in the framework structure, wherein the silicon to aluminum ratio for the framework structure is 70 or more, or optionally 100 or more, such as up to 600 or possibly still higher. More generally, a zeolite can have a silicon to aluminum ratio of 3 or more, or 10 or more, or 30 or more.
In various aspects, a vacuum pressure swing adsorption cycle can be used to provide improved recovery of hydrogen while maintaining a target purity of 98.0 vol % or more, or 99.0 vol % or more, such as up to 99.9 vol % or possibly still higher. Using simulations, it has been discovered that a purge step can be avoided by using a cycle that includes a sufficient length of bed evacuation at pressures below 90 kPa-a.
An example of a twelve step process cycle will be illustrated using a configuration involving twelve sorbent beds, with the sorbent beds being roughly comparable in size and the vessels containing the sorbent beds being roughly comparable in volume. However, it is understood that any convenient number of sorbent beds can be used that is consistent with performing the cycle. In the illustrative example, each step of the cycle is the same length, to allow for synchronization between beds at certain points in the cycle. It is understood that with a different number of sorbent beds, other process synchronization cycles could be developed.
The vacuum pressure swing adsorption cycle described herein can provide a variety of advantages, including increasing or maximizing hydrogen recovery in the hydrogen-containing product; increasing or maximizing methane recovery for recycle back to the pyrolysis process; and reducing or minimizing the moles of inert compounds (such as N2) that are recycled to the pyrolysis process.
In this example, both Step 1 and Step 2 correspond to adsorption steps, where the sorbent is exposed to a flow of the pyrolysis effluent. This produces a sorbent with an increased loading of methane and carbon oxides, and an adsorption effluent that has an H2 (hydrogen) content of 98.0 vol % or more, or 99.0 vol % or more. This step is performed at a pressure between 500 kPa-a and 2000 kPa-a. It is noted that a typical pressure for a pyrolysis effluent produced by a pyrolysis process is between roughly 100 kPa-a and 1000 kPa-a. In some aspects, no compression may be needed for the pyrolysis effluent. In other aspects, compression can be performed to increase the pressure of the pyrolysis effluent to a target pressure for the start of the separation process.
In the adsorption steps corresponding to Step 1 and Step 2, various temperatures can be used. Temperatures near room temperature can be convenient for processing, but lower temperatures can potentially provide a higher purity adsorption effluent. In some aspects, the temperature can be between −50° C. and 40° C. The velocity of gas in the sorption environment during the adsorption steps can vary depending on the configuration of the sorbent environment. In some aspects, the gas velocity during the sorption steps can be roughly between 0.01 m/s to 10 m/s, or 0.01 m/s to 5.0 m/s, or 0.01 m/s to 1.0 m/s. The resulting adsorption effluent having an H2 content of 98.0 vol % or more is produced at a pressure similar to the pressure during the adsorption step.
It is noted that the hydrogen-containing product formed during Step 1 and Step 2 can include a reduced or minimized amount of the methane present in the pyrolysis effluent. In various aspects, the hydrogen-containing product can contain 5.0 mol % or less of the methane that was contained in the pyrolysis effluent, or 4.0 mol % or less, such as down to 1.0 mol % or possibly still less. Additionally or alternately, the hydrogen-containing product can contain a reduced or minimized amount of carbon oxides (CO and CO2). In various aspects, the hydrogen-containing product can contain 0.2 mol % or less of the carbon oxides that were contained in the pyrolysis effluent, or 0.1 mol % or less, such as down to having substantially no carbon oxide content.
Step 3 corresponds to a first pressure equalization step, where the first bed is placed in fluid communication with a second bed that is at a different (lower pressure) step in the process cycle. The pressure from the first bed is allowed to equalize with the pressure in the second bed. In some aspects, this pressure equalization is performed by connecting only one end of the first bed with one end of the second bed. Pressurizing using a flow only from one end of the pressurized bed can assist with improving the purity of the H2 stream generated by the separation process. This is in contrast to a pressure equalization process where pressure equalization is performed using gas flows from both ends of the pressurized bed. At the start of the pressure equalization step, the first bed will be at a pressure between 500 kPa-a and 1500 kPa-a, while the second bed will be at a pressure between 180 kPa-a and 500 kPa-a. After equalization, the pressure in the both beds will roughly correspond to an average of the pressures prior to equalization. In some aspects, the pressure in the first bed and second bed after equalization can be 350 kPa-a to 1000 kPa-a. Additionally or alternately, in some aspects, the final pressure in both beds after equalization can correspond to a pressure that is 60% to 80% of the pressure in the first bed prior to the start of the equalization step. In other words, a ratio of the pressure in the first bed at the end of the first equalization step to a pressure in the first bed prior to the start of the first equalization step is between 0.60 and 0.80. Because this is a pressure equalization step, the output flow from the first bed serves as the input flow to the second bed.
Step 4 corresponds to a second pressure equalization step, where the first bed is placed in fluid communication with a third bed that is at a different (lower pressure) step in the process cycle than either the first bed or the second bed. The pressure from the first bed is allowed to equalize with the pressure in the third bed. In some aspects, at the start of the pressure equalization step, the first bed will be at a pressure between 350 kPa-a and 1000 kPa-a (based on the first equalization step). Additionally or alternately, in some aspects, the pressure in the first bed can be 60% to 80% of the pressure in the first bed during the first and second adsorption steps. In various aspects, prior to the second pressure equalization, the pressure in the second bed can be between 5.0 kPa-a and 60 kPa-a. After equalization, the pressure in both beds will roughly correspond to an average of the pressures prior to equalization. In some aspects, the pressure in the first bed and third bed after equalization can be 180 kPa-a to 500 kPa-a. In some aspects, the final pressure in both beds after equalization can correspond to a pressure that is 50% to 60% of the pressure in the first bed prior to the start of the second equalization step. In other words, a ratio of the pressure in the first bed at the end of the second equalization step to a pressure in the first bed prior to the start of the second equalization step is between 0.50 and 0.60. Because this is a pressure equalization step, the output flow from the first bed serves as the input flow to the third bed. It is noted that the pressure in the first bed at the end of the second pressure equalization step should be high enough so that desorption of methane and/or CO2 from the sorbent bed is reduced or minimized. This reduces, minimizes, and/or prevents transfer from the first bed, which is about to be regenerated, to another bed that is about to start an adsorption step for production of hydrogen-containing product.
Step 5 corresponds to a blowdown step, to reduce the pressure in the first bed to roughly ambient pressure (roughly 100 kPa-a). Because pressure is being released, no input flow is needed for the blowdown step. The blowdown step generates a blowdown exhaust. In some aspects, the blowdown exhaust can correspond to a counter-current flow, relative to the direction of flow in the first bed in Steps 1 to 4. Due to the reduction in pressure, the methane and carbon oxides adsorbed in the sorbent bed are at least partially desorbed during the blowdown. Thus, in addition to containing H2 the blowdown exhaust corresponds to a stream with an increased content of methane and CO2 relative to the composition of the pyrolysis effluent. In various aspects, blowdown exhaust can contain 20 vol % to 50 vol % of methane, relative to the volume of the blowdown exhaust. This blowdown exhaust can be compressed and recycled back to the pyrolysis process.
Steps 6 to 9 correspond to vacuum evacuation steps. During Step 6, Step 7, Step 8, and Step 9, the pressure in the first bed is reduced to 5.0 kPa-a to 60 kPa-a. In some aspects, the evacuation effluent corresponds to a counter-current flow, relative to the direction of flow in the first bed in Steps 1 to 4. The evacuation effluent generated during Steps 6 to 9 can also be compressed and recycled to the pyrolysis process. By recycling both the blowdown exhaust and the evacuation effluent, substantially all of the methane not included in the hydrogen-containing product is recycled back to the pyrolysis process for additional hydrogen production.
Step 10 corresponds to a third pressure equalization step. In Step 10, a fourth bed that is at a higher pressure is equalized with the first bed. At the start of the third pressure equalization step, the pressure in the first bed can be between 5.0 kPa-a to 60 kPa-a. The pressure in the fourth bed can be 350 kPa-a to 1000 kPa-a. After equalization, the pressure in both beds will roughly correspond to an average of the pressures prior to equalization. In some aspects, the pressure in the first bed and fourth bed after equalization can be 180 kPa-a to 500 kPa-a. In some aspects, the final pressure in both beds after equalization can correspond to a pressure that is 50% to 60% of the pressure in the fourth bed prior to the start of the third equalization step. In other words, a ratio of the pressure in the fourth bed at the end of the third equalization step to a pressure in the third bed prior to the start of the second equalization step is between 0.50 and 0.60. Because this is a pressure equalization step, the output flow from the fourth bed serves as the input flow to the first bed.
Step 11 corresponds to a fourth pressure equalization step. In Step 11, a fifth bed that is at a higher pressure is equalized with the first bed. At the start of the fourth pressure equalization step, the pressure in the first bed can be between 180 kPa-a to 500 kPa-a. The pressure in the fifth bed can be 500 kPa-a to 1500 kPa-a. After equalization, the pressure in the both beds will roughly correspond to an average of the pressures prior to equalization. In some aspects, the pressure in the first bed and fifth bed after equalization can be 350 kPa-a to 1000 kPa-a. Additionally or alternately, in some aspects, the final pressure in both beds after equalization can correspond to a pressure that is 60% to 80% of the pressure in the fifth bed prior to the start of the equalization step. In other words, a ratio of the pressure in the fifth bed at the end of the fourth equalization step to a pressure in the fifth bed prior to the start of the fourth equalization step is between 0.60 and 0.80. Because this is a pressure equalization step, the output flow from the fifth bed serves as the input flow to the first bed.
Finally, Step 12 corresponds to a re-pressurization step to prepare the first bed for the next cycle (i.e., the Step 1 adsorption step for making the hydrogen-containing product). In Step 12, a portion of the hydrogen-containing product (and/or a stream from another source that has a hydrogen content equal to or greater than the hydrogen-containing product) is used to re-pressurize the first bed to a pressure that is close to the pressure for performing the adsorption in Step 1 of the next cycle. In some aspects, all of the re-pressurization can be performed using the hydrogen-containing product. In other aspects, the hydrogen-containing product can be used to increase the pressure in the first bed to 85% or more of the target pressure for performing Step 1 of the process cycle, or 90% or more, or 95% or more, such as up to 100%. After reaching 85% or more of the target pressure (or 90% or more, or 95% or more), the pyrolysis effluent can then be used to increase the pressure in the first bed to the target pressure for performing Step 1 of a the next cycle.
Table 1 shows an example of a process cycle based on the above 12 steps. As an example of timing for the process cycle shown in Table 1, each step can last for roughly the same amount of time, such as 5 seconds. In some aspects, each step can last for 3 to 15 seconds.
In
As an example of process conditions that can be used for a sorbent bed such as the sorbent bed shown in
As an alternative to using vacuum pressure swing adsorption, a pressure swing adsorption cycle can be used to provide improved recovery of hydrogen while maintaining a target purity of 98.0 vol % or more, or 99.0 vol % or more, such as up to 99.9 vol % or possibly still higher. One of the advantages of pressure swing adsorption is that the additional cost and equipment for reducing sorbent environments to pressures below 90 kPa-a is avoided.
An example of a twelve step process cycle will be illustrated using a configuration involving ten sorbent beds, with the sorbent beds being roughly comparable in size and the vessels containing the sorbent beds being roughly comparable in volume. This process is further illustrated in
In this example, Step 1 corresponds to a co-current pressurization step. The gas flow in this step enters the bed from the same end of the bed as Step 2, where adsorption will occur for production of high purity hydrogen-containing gas. The pyrolysis effluent is used as the input flow for the co-current pressurization. This step increases the pressure in the sorbent environment to the target pressure for performing the adsorption step.
Step 2 corresponds to the adsorption step, where the sorbent is exposed to a flow of the pyrolysis effluent. This produces a sorbent with an increased loading of methane and carbon oxides, and an adsorption effluent that has an H2 (hydrogen) content of 98.0 vol % or more, or 99.0 vol % or more. This step is performed at a pressure between 500 kPa-a and 1500 kPa-a. It is noted that a typical pressure for a pyrolysis effluent produced by a pyrolysis process is between roughly 100 kPa-a and 1000 kPa-a. In some aspects, no compression may be needed for the pyrolysis effluent. In other aspects, compression can be performed to increase the pressure of the pyrolysis effluent to a target pressure for the start of the separation process.
In the adsorption step corresponding to Step 2, various temperatures can be used. Temperatures near room temperature can be convenient for processing, but lower temperatures can potentially provide a higher purity adsorption effluent. In some aspects, the temperature can be between −50° C. and 40° C. The velocity of gas in the sorption environment during the adsorption steps can vary depending on the configuration of the sorbent environment. In some aspects, the gas velocity during the sorption steps can be roughly between 0.01 m/s and 1.0 m/s. The resulting adsorption effluent having an H2 content of 98.0 vol % or more is produced at a pressure similar to the pressure during the adsorption step.
It is noted that the hydrogen-containing product formed during Step 2 can include a reduced or minimized amount of the methane present in the pyrolysis effluent. In various aspects, the hydrogen-containing product can contain 5.0 mol % or less of the methane that was contained in the pyrolysis effluent, or 4.0 mol % or less, such as down to 1.0 mol % or possibly still less. Additionally or alternately, the hydrogen-containing product can contain a reduced or minimized amount of carbon oxides (CO and CO2). In various aspects, the hydrogen-containing product can contain 0.2 mol % or less of the carbon oxides that were contained in the pyrolysis effluent, or 0.1 mol % or less, such as down to having substantially no carbon oxide content.
Steps 3, 4, and 5 correspond to pressure equalization steps for reducing the pressure in the first bed while increasing the pressure in other beds. In each of Step 3, Step 4, and Step 5, the first bed is placed in fluid communication with different beds that are at different (lower pressure) steps in the process cycle. In each of Step 3, Step 4, and Step 5, the pressure from the first bed is allowed to equalize with the pressure in another bed. In some aspects, this pressure equalization is performed by connecting only one end of the first bed with one end of the second bed. Pressurizing using a flow only from one end of the pressurized bed can assist with improving the purity of the H2 stream generated by the separation process. This is in contrast to a pressure equalization process where pressure equalization is performed using gas flows from both ends of the pressurized bed.
The pressure equalization steps allow the pressure in the first bed to be reduced while a) reducing or minimizing hydrogen included in purge gas and b) reducing or minimizing the amount of additional pressurization that will be needed in a co-current pressurization step to return the other beds to the target pressure for performing adsorption. After equalization, the pressure in the both beds involved in the equalization step will roughly correspond to an average of the pressures prior to equalization.
At the start of Step 3, the first bed will be at a pressure between 600 kPa-a and 1500 kPa-a, while the second bed will be at a pressure between 350 kPa-a and 800 kPa-a. In some aspects, the pressure in the first bed and second bed after equalization can be 500 kPa-a to 1100 kPa-a. Additionally or alternately, in some aspects, the final pressure in both beds after equalization can correspond to a pressure that is 60% to 80% of the pressure in the first bed prior to the start of the equalization step. In other words, a ratio of the pressure in the first bed at the end of the first equalization step to a pressure in the first bed prior to the start of the first equalization step is between 0.60 and 0.80. Because this is a pressure equalization step, the output flow from the first bed serves as the input flow to the second bed.
At the start of Step 4, the first bed will be at a pressure between 500 kPa-a and 1100 kPa-a, while the third bed will be at a pressure between 220 kPa-a and 500 kPa-a. In some aspects, the pressure in the first bed and third bed after equalization can be 350 kPa-a to 800 kPa-a. Additionally or alternately, in some aspects, the final pressure in both beds after equalization can correspond to a pressure that is 60% to 80% of the pressure in the first bed prior to the start of the equalization step. In other words, a ratio of the pressure in the first bed at the end of the first equalization step to a pressure in the first bed prior to the start of the first equalization step is between 0.60 and 0.80. Because this is a pressure equalization step, the output flow from the first bed serves as the input flow to the third bed.
At the start of Step 5, the first bed will be at a pressure between 350 kPa-a and 800 kPa-a, while the fourth bed will be at a pressure between 90 kPa-a and 120 kPa-a. In some aspects, the pressure in the first bed and fourth bed after equalization can be 220 kPa-a to 500 kPa-a. Additionally or alternately, in some aspects, the final pressure in both beds after equalization can correspond to a pressure that is 60% to 80% of the pressure in the first bed prior to the start of the equalization step. In other words, a ratio of the pressure in the first bed at the end of the first equalization step to a pressure in the first bed prior to the start of the first equalization step is between 0.60 and 0.80. Because this is a pressure equalization step, the output flow from the first bed serves as the input flow to the third bed.
Step 6 corresponds to a blowdown step, to reduce the pressure in the first bed to roughly ambient pressure (roughly 100 kPa-a). Because pressure is being released, no input flow is needed for the blowdown step. The blowdown step generates a blowdown exhaust. In some aspects, the blowdown exhaust can correspond to a counter-current flow, relative to the direction of flow in the first bed in Step 2. Due to the reduction in pressure, the methane and carbon oxides adsorbed in the sorbent bed are at least partially desorbed during the blowdown. Thus, in addition to containing H2 the blowdown exhaust corresponds to a stream with an increased content of methane and CO2 relative to the composition of the pyrolysis effluent. In various aspects, blowdown exhaust can contain 20 vol % to 50 vol % of methane, relative to the volume of the blowdown exhaust. This blowdown exhaust can be compressed and recycled back to the pyrolysis process.
Step 7 is a purge step. During Step 7, a portion of the hydrogen-containing product stream is used as a purge gas to remove an additional portion of the CO2 and CH4 that is adsorbed on the sorbent. After compression, the purge stream can be recycled to the methane pyrolysis reactor.
It is noted that in order to provide a synchronized process, the combined time for Step 6 and Step 7 can be the same as the combined time as Step 1 and Step 2. As an example, Step 1 and Step 6 can have the same length, while Step 2 and Step 7 have the same length. In some aspects, the adsorption in Step 2 and the blowdown in Step 7 can be longer than Step 1 and Step 6, such as Step 2 and Step 7 being twice as long as Step 1 and Step 6. More generally, the length of Step 2 and Step 7 can be between 1.5 to 3.0 times as long as the length of Step 1 and Step 6.
Steps 8 to 10 correspond to pressure equalization steps to re-pressurize bed 1. Steps 8 to 10 are mirror images of Steps 3 to 5, but with the first bed as the low pressure bed and the other beds as the higher pressure beds. For synchronization, Step 8 can have the same time length as Step 5, Step 9 can have the same time length as Step 4, and Step 10 can have the same time length as Step 3. Optionally, each of Step 3, Step 4, and Step 5 can be of substantially equal length. Optionally, Step 1 can be of substantially the same length as at least one of Step 3, Step 4, and Step 5.
Table 2 shows an example of a process cycle based on the above 10 steps. As an example of timing for the process cycle shown in Table 2, each step can last for roughly 10 seconds, with the exception of Step 2 and Step 7, which can last for 20 seconds. In some aspects, each step can last for roughly 5 to 20 seconds, with the exception of Step 2 and Step 7, which can last for 1.5 time to 3.0 times longer than the other steps.
In various aspects, a VPSA process or PSA process can be performed using a plurality of sorbent beds working in conjunction to provide a continuous process for separating hydrogen from a pyrolysis effluent. In some aspects, a packed bed of sorbent particles can be used. The particles can be composed entirely of a sorbent material, or the particles can correspond to a sorbent material supported on a support.
In other aspects, a structured adsorbent contactor can be used, such as a contactor with sorbent coated on interior walls of channels in the contactor. In such a structured adsorbent contactor, the channels can optionally be substantially parallel to one another. A monolith is an example of a structured adsorbent contactor that can have substantially parallel channels. An advantage of a structured adsorbent contactor is that the void volume for the sorbent can be reduced or minimized. In conventional packed beds, sufficient void volume needs to be present so that a gas (such as a pyrolysis effluent) can flow through the packed bed without having excessive pressure drop. Flowing the gas through the packed bed allows the gas to contact the sorbent material, resulting in selective sorption of one or more components from the gas flow. However, for regularly shaped particles such as spheres, there are limits on the potential packed density of the particles. This can alternatively be described as regularly shaped particles having a minimum void volume within the packed bed. Structured beds can reduce the void fraction for the adsorbent bed while still allowing good contact between sorbent and gas flow and reducing or minimizing pressure drop.
For a structured adsorbent, such as a monolith or other contactor having substantially parallel channels, the void fraction can be reduced relative to a conventional packed bed. The void fraction is defined as the percentage of the volume through which inlet or outlet let gas can flow. That is the volume of the adsorption bed less the volume of adsorbent particles, binding material particles and all possible support structures. This definition is applicable to both packed bed as well as structured adsorbent contactors. The micropore and possibly mesopore volume within the adsorbent particles themselves in which adsorption takes place is not considered part of the void volume. However, porosity within the adsorbent layer or a pellet is part of the void volume.
In some aspects, a monolith (or other contactor having substantially parallel channels) can have a void fraction of 70% or less, or 60% or less, or 50% or less, or 40% or less, or 36% or less, or 34% or less, or 32% or less, such as down to 25% or possibly still less.
Depending on the aspect, the porosity of the sorbent layer on interior channels of a monolith can be between 0.15 to 0.40, or 0.15 to 0.35, or 0.15 to 0.30, or 0.20 to 0.40, or 0.20 to 0.35, or 0.20 to 0.30.
The sorbent material for the sorbent bed can be either a kinetically selective adsorbent or an equilibrium selectivity adsorbent. Examples of kinetically selective adsorbents include, but are not limited to, titanoslicate ETS-4 or carbon molecular sieve (CMS) sorbents. Such sorbents have kinetic selectivity for adsorption of N2 relative to CH4. However, due to the low concentration of N2 in a typical pyrolysis effluent, such an approach would require significant amount of material due to limitations on adsorbent capacity for N2.
For adsorbents based on equilibrium selectivity, working capacity towards CH4 and CH4/N2 selectivity are typically the most important considerations. Examples of materials with suitable working capacity and selectivity can include, but are not limited to, activated carbons, silica gel, and siliceous zeolitic materials. For example, siliceous MFI (ZSM-5) zeolite exhibits reasonable selectivity between CH4 and N2 on the order of 3-4, and working capacity on the order of ˜0.3 mmol/g. Another example is FER zeolite that features comparable methane capacity and CH4/N2 selectivity.
In some aspects, a stacked bed of adsorbents can be used, such as an initial portion of activated carbon for sorption of CO2 and CH4, followed by a zeolitic adsorbent that has high selectivity for sorption of N2 and CO. Examples of zeolitic adsorbents for use in such a stacked bed arrangement can include, but are not limited to, zeolite 13X and MFI framework structure zeolites.
In various aspects, the separations described herein can be performed on a pyrolysis effluent generated from any convenient type of pyrolysis process that produces a pyrolysis effluent containing 60 vol % or more of hydrogen, or 70 vol % or more, or 75 vol % or more, or 80 vol % or more, or 85 vol % or more, such as up to 99 vol % or possibly still higher. Various types of pyrolysis reactors are available. Optionally, the pyrolysis effluent can also contain N2, such as 7.0 vol % or less of N2, or 5.0 vol %, or 3.0 vol %, such as down to 0.1 vol % or possibly still lower. A fluidized bed process is described herein as an example, but it is understood that other pyrolysis configurations can be used.
Fluidized bed pyrolysis of methane, natural gas, or another suitable hydrocarbon-containing feed can be performed at a temperature of 1000° C. to 1600° C., or possibly still higher temperatures. The temperature in the pyrolysis reactor can be between 100 kPa-a to 1000 kPa-a, or 200 kPa-a to 1000 kPa-a. The feed can be any convenient feed that includes 50% or more of C1-C4 alkanes, or 75 vol % or more, or 95 vol % or more, such as up to substantially all of the feed corresponding to C1-C4 hydrocarbons. Coke particles can be a convenient particle for forming the fluidized bed, but other particles such as sand could also be used. The residence for the hydrocarbon-containing feed in the fluidized bed can range from 0.1 seconds to 500 seconds, or 0.1 seconds to 100 seconds, or 1.0 seconds to 100 seconds. The flow rate for the hydrocarbon-containing feed can be sufficient to provide fluidization for the bed. Optionally, a plurality of fluidized beds can be used, such as the configuration shown in U.S. Patent Application Publication 20210331918.
In the example shown in
The optionally compressed pyrolysis effluent 785 is then passed into a separation stage 790 to separate a hydrogen-containing product stream 795 from the optionally compressed pyrolysis effluent 785. Separation stage 790 can correspond to a plurality of swing adsorption beds, such as one of the twelve bed configurations shown in
It is noted that tail gas 793 can correspond to a mixture of bed exhausts and/or purge streams that may be at different pressures, as the tail gas can be formed from several different steps in a process cycle. The different bed exhausts and/or purge streams can optionally be compressed so that all exhausts/streams are at roughly the same pressure prior to mixing, or the exhausts/streams can be mixed to form a mixture and then compressed. The compression of the tail gas 793 can be performed by recycle compressor 791, which forms a compressed recycle stream at roughly the pressure of the pyrolysis process 770. A purge stream 799 can also be formed from tail gas 793. Purge stream 799 allows compounds such as N2 that are not removed or consumed during the pyrolysis and separation processes to be purged from the system.
A process model was used to simulate the performance of various sorbent bed configurations for both VPSA and PSA processes. For the VPSA model calculations described below, the process cycle illustrated in
For the PSA model calculations described below, the process cycle illustrated in
For the PSA model calculations, packed bed size was chosen to have bed diameter of 3.5 m and bed length of 6 m. For the VPSA calculations where a monolith was used, a monolith providing roughly the same volume as the packed bed volume was used.
For all of the calculations, a model pyrolysis effluent stream was used. The pyrolysis effluent stream has a pressure of roughly 1,000 kPa-a (10 bar) and a temperature of 45° C. The composition of the stream (on a dry basis) is 90.9 mol % H2, 8.0 mol % CH4, 0.8 mol % N2, and 0.3 mol % CO2.
A vacuum pressure swing adsorption (VPSA) process was simulated using a twelve bed configuration similar to
Table 3 shows the compositions of the modeled gas flows labeled S1 to S5 in
Table 4 shows the ratio of moles of each type of gas in the hydrogen-containing product stream S2 versus the moles of each type of gas in the input stream S1.
As shown in Tables 3 and 4, in the example process that was modeled, the recycle molar flow rate to the pyrolysis reactor was 19% of the total number of moles of gas which was fed to the VPSA process through stream S1. The hydrogen recovery is 89%, meaning 89% of the moles of hydrogen sent to the VPSA process in stream S1 are passed into the hydrogen-containing product stream S2. This high level of recovery of the hydrogen in input flow S1 is achieved while also producing a hydrogen-containing product S2 that has an H2 content of 99 mol %. Similarly, the methane recovery is 92.6%, meaning 92.6% of the methane fed to the VPSA process in S1 is captured and recycled back to the pyrolysis reactor in S5.
Of the nitrogen (N2) fed to the VPSA in stream S1, 33% passes through the bed and exits with the hydrogen-containing product gas S2, while the remaining nitrogen is recycled back to the pyrolysis reactor. On the other hand, only 3.4% of CO2 in stream S1 exits with stream S2, with the remaining 96.6% being recycled back to the pyrolysis reactor.
The adsorption profiles within the adsorption step were also characterized, and are provided in
As shown in
At the end of the blowdown step, the adsorbed concentration profiles for both CO2 and CH4 are similar to the end of the adsorption step. This indicates that merely reducing the pressure from the adsorption pressure of 1000 kPa-a to the blowdown pressure of 100 kPa-a, in the absence of a purge gas, did not result in substantial release of either CO2 or CH4. However, substantially all of the H2 adsorbed by the bed is removed by the end of the blowdown process.
At the end of the evacuation steps, substantially all of the CO2 is desorbed. There is a baseline level of CH4 still adsorbed to the bed. However, this does not pose an issue, as this baseline level of CH4 will substantially remain adsorbed to the bed during the adsorption step in the next process cycle.
A series of different adsorbents, including combinations (stacked beds) of adsorbents, were used to model pressure swing adsorption (PSA) processes using the empirical modeling tool. The PSA processes were simulated using a twelve bed configuration similar to
Table 5 shows results from modeling of PSA processes using various adsorbents in the sorbent beds. In Table 5, the Cycle column indicates if any changes were made relative to the bed configuration and conditions shown in
In Table 5, two dispositions are shown for the purge output stream from the bed. The first disposition is to recycle the purge stream to the reactor. The second disposition is to use the purge stream as a fuel.
The results shown in Table 5 are discussed in connection with each case. Cases 1, 3, and 5 have similar configurations and are described first.
Case 1—PSA, Stacked bed of activated carbon and zeolite 13X. Blowdown and purge pressure are atmospheric. Activated carbon layer length is 0.5 m and the zeolite layer length is 5.5 m. Table 6 lists the calculated stream flowrates and compositions for Case 1. The column V/VFEED refers to the ratio of stream molar flow rate to that of feed stream.
The values obtained for Case 1 were: Hydrogen recovery: 77.8%. Hydrogen purity: 99%. For purge out stream used for fuel, N2 rejection 15.18% and CH4 recovery 85.7%. For purge out stream recycled back to reactor, N2 rejection 8.9% and CH4 recovery 91.2%. The productivity was 6.19 kmol/hr/m3 bed. Based on the configuration shown in
It is noted that CH4 recovery and N2 rejection in Cases 1, 3, and 5 varies based on whether the purge out stream is used for recycle or for fuel in another process. When the purge out stream is used for recycle, the CH4 recovery is defined the total moles of CH4 that are recycled (blowdown plus purge out) divided by the total moles of CH4 that enter the reactor (feed and the pressurization). When purge out is used for recycle, N2 rejection is total moles of N2 that exit via the hydrogen-containing product divided by total moles of N2 that enter the reactor (feed and the pressurization). By contrast, when the purge out stream is used for fuel, the CH4 recovery is defined the total moles of CH4 that are recycled (blowdown only) divided by the total moles of CH4 that enter the reactor (feed and the pressurization). When purge out is used for fuel, N2 rejection is total moles of N2 that exit via the hydrogen-containing product and via the purge divided by total moles of N2 that enter the reactor (feed and the pressurization).
Case 3—PSA, Activated carbon. Blowdown and purge pressure are atmospheric. Activated carbon layer length was 6.0 m. Table 7 lists the calculated stream flowrates and compositions for Case 3. The column V/VFEED refers to the ratio of stream molar flow rate to that of feed stream.
The values obtained for Case 3 were: Hydrogen recovery: 71.1%. Hydrogen purity: 99%. For purge out stream used for fuel, N2 rejection 18.7% and CH4 recovery 83.6%. For purge out stream recycle back to reactor, N2 rejection 11.7% and CH4 recovery 93.022%. The productivity was 4.34 kmol/hr/m3 bed. Based on the configuration shown in
Case 5—PSA, MFI zeolite. Blowdown and purge pressure are atmospheric. Activated carbon layer length was 6.0 m. Table 8 lists the calculated stream flowrates and compositions for case 5. The column V/VFEED refers to the ratio of stream molar flow rate to that of feed stream.
The values obtained for Case 5 were: Hydrogen recovery: 71.1%. Hydrogen purity: 99%. For purge out stream used for fuel, N2 rejection 16.8% and CH4 recovery 82.9%. For purge out stream recycle back to reactor, N2 rejection 9.5% and CH4 recovery 93.01%. The productivity was 4.6 kmol/hr/m3 bed. Based on the configuration shown in
Case 2—PSA with internal recycle, Stacked bed of activated carbon and zeolite 13X. Blowdown and purge pressure are atmospheric. Activated carbon layer length is 0.5 m and the zeolite layer length is 5.5 m. Table 9 lists the calculated stream flowrates and compositions for case 2. The column V/VFEED refers to the ratio of stream molar flow rate to that of feed stream. It is noted that in Case 2, instead of using feed to re-pressurize, a portion of the blowdown is compressed to 1000 kPa-a and used to re-pressurize. This increases hydrogen recovery.
The values obtained for Case 2 were: Hydrogen recovery: 87.8%. Hydrogen purity: 99%. For purge out stream used for fuel, N2 rejection 42.7% and CH4 recovery 60.4%. For purge out stream recycle back to reactor, N2 rejection 11.2% and CH4 recovery 91.6%. The productivity was 4.8 kmol/hr/m3 bed. Based on the configuration shown in
It is noted that CH4 recovery and N2 rejection in Case 2 varies based on whether the purge out stream is used for recycle or for fuel in another process. When the purge out stream is used for recycle, the CH4 recovery is defined the total moles of CH4 that are recycled (blowdown plus purge out) divided by the total moles of CH4 in the feed. When purge out is used for recycle, N2 rejection is total moles of N2 that exit via the hydrogen-containing product divided by total moles of N2 in the feed. By contrast, when the purge out stream is used for fuel, the CH4 recovery is defined the total moles of CH4 that are recycled (blowdown only) divided by the total moles of CH4 in the feed. When purge out is used for fuel, N2 rejection is total moles of N2 that exit via the hydrogen-containing product and via the purge divided by total moles of N2 in the feed.
Case 4—VPSA with internal recycle, Activated carbon. After blowdown to atmospheric pressure, bed is evacuated to further remove adsorbed components. In Case 4, an evacuation pressure of 20 kPa-a was used. Activated carbon layer length is 6.0 m. Table 10 lists the calculated stream flowrates and compositions for case 2. The column V/VFEED refers to the ratio of stream molar flow rate to that of feed stream. It is noted that in Case 2, instead of using feed to re-pressurize, a portion of the blowdown is compressed to 1000 kPa-a and used to re-pressurize. This increases hydrogen recovery.
The values obtained for Case 2 were: Hydrogen recovery: 73.3%. Hydrogen purity: 99%. For evacuation out stream used for fuel, N2 rejection 43.6% and CH4 recovery 56.9%. For evacuation out stream recycle back to reactor, N2 rejection 15.6% and CH4 recovery 93.2%. The productivity was 7.58 kmol/hr/m3 bed. Based on the configuration shown in
It is noted that CH4 recovery and N2 rejection in Case 5 varies based on whether the evacuation out stream is used for recycle or for fuel in another process. When the evacuation out stream is used for recycle, the CH4 recovery is defined the total moles of CH4 that are recycled (blowdown plus evac out) divided by the total moles of CH4 in the feed. When purge out is used for recycle, N2 rejection is total moles of N2 that exit via the hydrogen-containing product divided by total moles of N2 in the feed. By contrast, when the evacuation out stream is used for fuel, the CH4 recovery is defined the total moles of CH4 that are recycled (blowdown only) divided by the total moles of CH4 in the feed. When evacuation out is used for fuel, N2 rejection is total moles of N2 that exit via the hydrogen-containing product and during evacuation divided by total moles of N2 in the feed.
Table 11 compares the performance of PVSA and PSA cycles with the structured and packed beds. It is seen that with the packed bed configurations the H2 recovery is ˜73%, while for the structured bed the recovery increases to ˜89%. This is the result of a lower voidage in the monolithic adsorbent as opposed to the packed bed. Also the productivity of the structured adsorbent is higher due to higher flow rates.
Embodiment 1. A method for separating hydrogen from methane pyrolysis products using a plurality of adsorbent beds, comprising: performing pyrolysis on a feed comprising C1-C4 hydrocarbons to form a pyrolysis effluent comprising, on a dry basis, 60 vol % or more of H2 and 1.0 vol % or more CH4; separating at least a portion of the pyrolysis effluent to form a hydrogen-containing effluent, a recycle stream, and a purge stream, the hydrogen-containing stream comprising 85.0 vol % or more H2, wherein the hydrogen-containing stream contains 50 vol % or more of the H2 contained in the feed, and wherein the recycle stream contains 80 vol % or more of the CH4 contained in the feed.
Embodiment 2. A method for separating hydrogen from methane pyrolysis products using a plurality of adsorbent beds, comprising: performing pyrolysis on a feed comprising C1-C4 hydrocarbons to form a pyrolysis effluent comprising, on a dry basis, 60 vol % or more of H2 and 1.0 vol % or more CH4; separating at least a portion of the pyrolysis effluent using a separation process comprising exposing the at least a portion of the pyrolysis effluent to a structured adsorbent contactor to form a hydrogen-containing effluent, a recycle stream, and a purge stream, the hydrogen-containing stream comprising 85 vol % or more H2, wherein the hydrogen-containing stream contains 50 vol % or more of the H2 contained in the feed, and wherein the recycle stream contains 80 vol % or more of the CH4 contained in the feed.
Embodiment 3. The method of Embodiment 1 or 2, wherein the feed further comprises N2, wherein the pyrolysis effluent comprises 7.0 vol % or less of N2 (or 5.0 vol % or less, or 3.0 vol % or less), and wherein the hydrogen-containing stream comprises 1.0 vol % or more N2.
Embodiment 4. The method of Embodiment 3, a) wherein the hydrogen-containing stream comprises 10 vol % or more of the N2 contained in the feed, or b) wherein the recycle stream comprises less than 85 vol % of the N2 contained in the feed, or c) wherein the purge stream contains 6.0 vol % or more of the N2 contained in the feed, or d) a combination of two or more of a), b), and c).
Embodiment 5. The method of any of the above embodiments, wherein the feed further comprises 5.0 vol % or less of carbon oxides, and wherein the recycle stream contains less than 85 vol % of the carbon oxides contained in the feed.
Embodiment 6. The method of any of the above embodiments, wherein the pyrolysis effluent comprises 80 vol % or more of H2.
Embodiment 7. The method of any of the above embodiments, wherein the hydrogen-containing stream comprises 70 vol % or more (or 80 vol % or more) of the H2 contained in the pyrolysis effluent.
Embodiment 8. The method of any of the above embodiments, wherein the separating at least a portion of the pyrolysis effluent comprises using a separation process that comprises a pressure of 50 kPa-a or less to form the hydrogen-containing effluent, the recycle stream, and the purge stream.
Embodiment 9. The method of any of the above embodiments, wherein the sorbent comprises activated charcoal, a silica gel, a zeolite, or a combination thereof.
Embodiment 10. The method of any of the above embodiments, wherein the sorbent comprises a siliceous zeolite.
Embodiment 11. The method of Embodiment 10, wherein the sorbent comprises a siliceous zeolite having an MFI framework structure, an FER framework structure, or a combination thereof.
Embodiment 12. The method of any of Embodiments 2-11, wherein the structured adsorbent contactor comprises a parallel channel contactor, or wherein the structured adsorbent contactor comprises a monolith.
Embodiment 13. The method of any of Embodiments 2-12, wherein the structured adsorbent channel contactor comprises a void fraction of 36% or less.
Embodiment 14. The method of any of the above embodiments, wherein the separating comprises: passing at least a portion of the pyrolysis effluent into a first sorption environment containing a first sorbent bed comprising a sorbent with selectivity for sorption of N2 and CO2 relative to H2 at a first sorption pressure of 500 kPa-a to 1500 kPa-a to form a hydrogen-containing product effluent having an H2 content of 98.0 vol % or more and a loaded first sorbent comprising adsorbed CO2, the first sorption environment containing an additional volume of the hydrogen-containing product at the end of the passing; flowing a first portion of the additional volume of the hydrogen-containing product into a second sorption environment containing a second sorbent bed comprising the sorbent to reduce the pressure in the first sorption environment to a first reduced pressure and increase the pressure in the second sorption environment; flowing a second portion of the additional volume of the hydrogen-containing product into a third sorption environment containing a third sorbent bed comprising the sorbent to reduce the pressure in the first sorption environment to a second reduced pressure and increase the pressure in the third sorption environment; exhausting a blowdown portion of the additional volume of the hydrogen-containing product to reduce the pressure in the first sorption environment to 120 kPa-a or less; desorbing at least a portion of the adsorbed CO2 to form a CO2-containing stream, the feed comprising C1-C4 hydrocarbons further comprising a first portion of the CO2-containing stream; purging a second portion of the CO2-containing stream; passing a first pressurization stream comprising an H2 content of 98.0 vol % or more into the first sorption environment from a fourth sorption environment to increase the pressure in the first sorption environment to a pressure greater than 200 kPa-a; passing a second pressurization stream comprising an H2 content of 98.0 vol % or more into the first sorption environment from a fifth sorption environment to increase the pressure in the first sorption environment to a pressure between the first reduced pressure and the second reduced pressure; and passing a re-pressurization stream comprising 98 vol % or more H2 into the first sorption environment to increase the pressure in the first sorption environment to a second sorption pressure, a ratio of the second sorption pressure to the first sorption pressure being between 0.9 and 1.1.
Embodiment 15. The method of Embodiment 14, wherein the re-pressurization stream comprises a portion of the hydrogen-containing product effluent; or wherein the method further comprises compressing a recycle portion of the blowdown portion, the re-pressurization stream comprising the recycle portion of the blowdown portion; or a combination thereof.
Embodiment 16. The method of Embodiment 14 or 15, wherein desorbing at least a portion of the adsorbed CO2 comprises reducing the pressure in the first sorption environment to 50 kPa-a or less, the desorbing at least a portion of the adsorbed CO2 optionally comprising maintaining the pressure of the first sorption environment at a pressure of 50 kPa-a or less for an exhaust time that is greater than a time for performing the passing of the at least a portion of the pyrolysis effluent.
Embodiment 17. The method of any of Embodiments 14 to 16, wherein desorbing at least a portion of the adsorbed CO2 comprises purging the first sorption environment with a purge flow comprising a portion of the hydrogen-containing product stream, a portion of the blowdown portion of the additional volume of hydrogen-containing product, or a combination thereof.
Embodiment 18. The method of any of Embodiments 14 to 17, wherein a ratio of the first reduced pressure to the first sorption pressure is 0.60 to 0.80, or wherein a ratio of the second reduced pressure to the first reduced pressure is 0.50 to 0.80, or a combination thereof.
Embodiment 19. The method of any of the above embodiments, wherein the method further comprises compressing the pyrolysis effluent to a pressure between 600 kPa-a and 1500 kPa-a.
While the present invention has been described and illustrated by reference to particular embodiments, those of ordinary skill in the art will appreciate that the invention lends itself to variations not necessarily illustrated herein. For this reason, then, reference should be made solely to the appended claims for purposes of determining the true scope of the present invention.
This Non-Provisional Patent application claims priority to U.S. Provisional Patent Application No. 63/613,340, filed Dec. 21, 2023, and titled “Separations For Methane Pyrolysis”, the entire contents of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 63613340 | Dec 2023 | US |
