Removal of hydrogen impurities in the gas stream

Abstract

Trace hydrogen can be removed from dry gas by passing the dry gas through at least one layer of a first Hopcalite catalyst at a temperature of about 0 °C to about 60 °C to produce a product gas that is at least substantially hydrogen-free, wherein the first Hopcalite catalyst has a copper to manganese molar ratio greater than 0.55. Advantages over an equivalent process using a standard Hopcalite catalyst with a Cu / Mn molar ratio of 0.45 to 0.55 include increased hydrogen capacity, reduced feed and regeneration temperatures, and reduced sensitivity to carbon dioxide.

Description

BACKGROUND OF THE INVENTION

[0001] The present invention generally relates to the removal of hydrogen gas (H2) as an impurity from a gas stream, typically accompanied by the removal of carbon monoxide (CO) as another impurity in the gas stream. Specifically, the present invention relates to the removal of these impurities from a gas. A particular application of the present invention is the production of high purity (HP) and ultra-high purity (UHP) nitrogen gas (N2).

[0002] In many chemical processes, carbon monoxide and hydrogen gas are undesirable substances in nitrogen gas due to their chemical reactivity. For example, the electronics industry requires UHP nitrogen gas (typically, both CO and H2 are less than 10 parts per billion by volume (ppbv)) to provide an inert atmosphere for the production of semiconductor materials. The presence of impurities in nitrogen gas during the formation of silicon wafers greatly increases the chip failure rate.

[0003] When air is subjected to cryogenic separation to produce nitrogen gas, since carbon monoxide has a boiling point similar to that of nitrogen gas, the carbon monoxide present in the feed air will essentially end up in the product nitrogen gas. Hydrogen gas is enriched in the product nitrogen gas to approximately twice its concentration in the feed air. Therefore, the production of UHP nitrogen gas in the electronics industry, i.e., nitrogen gas that is at least substantially free of carbon monoxide and hydrogen gas, requires a process for removing hydrogen gas and / or carbon monoxide from an air or nitrogen gas stream.

[0004] In a conventional process for cryogenic separation of air to recover nitrogen gas and oxygen gas (O2), the feed air is compressed, cooled to a low temperature, and then introduced into a cryogenic distillation unit (or called an air separation unit or ASU) that typically includes one or two distillation columns. If not removed, the water and carbon dioxide present in the feed air will freeze and block the heat exchangers used to cool the gas before distillation. The separation unit used to remove water and carbon dioxide is usually called a front-end unit (FEU).

[0005] Before entering the FEU, the atmosphere is typically compressed to a high pressure of 50 to 150 psig (0.45 to 1.1 MPa), then water-cooled and the condensed water is removed. A cooling water tower and direct contact after cooling (DCAC) can be used to further cool the cold air (about 100°F (38°C) at that time) to 40°F (4.5°C). Most of the water present in the air is removed by condensation and phase separation. Subsequently, the gas is sent to the molecular sieve bed or alumina / molecular sieve mixed bed of the FEU, and the remaining water and carbon dioxide are removed by adsorption. This separation utilizes the fact that both water and carbon dioxide are more adsorbable by solid adsorbents than oxygen and nitrogen gases, so they are preferentially removed from the gas stream by the adsorbent. Subsequently, the gas stream that is at least substantially free of carbon dioxide and water leaving the bed is sent to the cryogenic distillation unit.

[0006] Eventually, the adsorbent's capacity to adsorb water and carbon dioxide is exhausted, and water and / or carbon dioxide will begin to "break through" the adsorption bed and exit the FEU. The exhausted bed is taken "offline," i.e., removed from the inlet gas stream, and regenerated to desorb some of the water and carbon dioxide and restore the adsorbent's adsorption capacity. To achieve a constant feed and product gas flow rate, at least two

[0007] Bed regeneration is carried out by heating the bed to a higher temperature (temperature swing adsorption, or TSA, see for example US4541851 and US5137548), or by reducing the gas pressure in the bed without heating (pressure swing adsorption, or PSA, see for example US5232474). The heating step in the TSA method can be carried out at the original feed pressure, or more commonly, at a lower pressure of 2 to 15 psig (0.1 to 0.2 MPa). In any case, a gas stream that is at least substantially free of carbon dioxide and water is used to purge the bed simultaneously. The present invention generally includes a thermal regeneration step, but cases where PSA regeneration can be applied are possible.

[0008] During thermal regeneration, a portion of the purified air from the feed bed, a portion of the UHP nitrogen product gas from the cryogenic distillation unit, or some of the waste gas stream from the cold box is heated to 200 to 250 °C. The hot gas passes through the adsorption bed being regenerated for a period of time equal to approximately half of the total regeneration time. After this step, subsequently, a flowing cooling regeneration gas (e.g., 5 to 30 °C) is passed for the remaining regeneration time to cool the bed to this temperature. Regeneration is typically carried out in the reverse direction relative to the adsorption step and is usually carried out at a lower pressure of 2 to 15 psig (0.1 to 0.2 MPa).

[0009] Conventional TSA FEUs are capable of removing carbon dioxide and water from air well. However, alumina or molecular sieve beds are not effective in removing carbon monoxide or hydrogen. The application of UHP nitrogen in the electronics field typically specifies the specifications for both hydrogen and carbon monoxide. Therefore, a process for the combined removal of carbon monoxide and hydrogen from air is needed.

[0010] A common method for producing UHP nitrogen is air pretreatment and includes the following steps: oxidizing carbon monoxide and hydrogen in the inlet gas, and then removing the carbon dioxide and water generated in the FEU. This method is attractive because the oxidation reaction in the gas stream is very thermodynamically favorable and the equilibrium conversion is essentially complete. Additionally, the by-products formed in this process are convenient for existing FEUs to handle.

[0011] In the absence of a catalyst and in the presence of oxygen, the oxidation of carbon monoxide to carbon dioxide and hydrogen to water occurs readily at high temperatures (e.g., above 500 °C). Oxidation at lower temperatures in air generally requires a catalyst. In this regard, Hopcalite is used to oxidize carbon monoxide, and noble metal catalysts are used to oxidize hydrogen.

[0012] Examples of using such catalysts to remove carbon monoxide and hydrogen from air in the FEU of a cryogenic ASU are provided in US6511640, which describes a TSA unit including an adsorption bed that includes a first layer for removing water, a second layer for oxidizing carbon monoxide, a third layer for removing carbon dioxide, a fourth layer for oxidizing hydrogen, and a final adsorption layer for removing water and carbon dioxide. The oxidation of carbon monoxide in the lower catalyst layer specifies a Hopcalite catalyst, and a noble metal (e.g., a noble metal) catalyst must be used to oxidize hydrogen in the upper catalyst layer to produce water. Hydrogen is removed by a chemisorption process rather than a typical reaction mechanism, as shown by the breakthrough curve. Carbon dioxide interferes with chemisorption and subsequent removal of hydrogen from the gas, so the noble metal catalyst is placed after water removal (aluminum oxide layer) and carbon dioxide removal (13X). The final 13X layer is placed above the noble metal catalyst to capture any water produced in the oxidation of hydrogen.

[0013] However, known processes for removing hydrogen or carbon monoxide and hydrogen using in-bed techniques such as those disclosed in US6511640 have some problems.

[0014] First, removing hydrogen requires the use of expensive supported metal catalysts, typically noble metal catalysts based on palladium, platinum, ruthenium, rhodium, etc. supported on alumina, zeolite, or silica. The demand for noble metals is usually high and is affected by market forces, so noble metals are very expensive per unit mass. The cost of support, catalyst manufacture, transportation, etc. are additional expenses for the final catalyst. In addition, catalysts using noble metals usually load the minimum amount of metal, and noble metals make the catalyst more prone to poisoning.

[0015] Second, the noble metal catalysts used in in-bed techniques are thermally regenerated in an oxygen-containing stream (usually the oxygen-rich exhaust gas from the ASU). It is well known that noble metals are resistant to oxidation, but over time, the noble metals will slowly oxidize and lose their catalytic activity under these conditions.

[0016] Third, bed technologies designed to remove both carbon monoxide and hydrogen typically have multiple catalyst layers, one for carbon monoxide oxidation and another for hydrogen oxidation. This arrangement is particularly suitable when there is a reason to perform carbon monoxide oxidation and hydrogen oxidation at different locations within the TSA unit. For example, carbon monoxide oxidation typically occurs after dehydration (since water deactivates the catalyst) and before carbon dioxide removal (so that the carbon dioxide formed by oxidation is also removed). Hydrogen oxidation typically occurs after water and carbon dioxide removal. Noble metal-based catalysts can be designated for the two separate catalyst layers. However, it is well known that Hopcalite is very effective in converting carbon monoxide to carbon dioxide. It is much cheaper than noble metal catalysts. This has led to a wide specification of Hopcalite for the carbon monoxide oxidation catalyst layer and noble metal-based catalysts for the hydrogen oxidation catalyst layer. Alternatively, it is known to use silver-exchanged zeolite to adsorb and remove carbon monoxide, followed by a metal-based catalyst for hydrogen reaction. Adding stratification in a packed bed leads to increased complexity in loading and replacing the bed and incurs additional costs associated with the screens used for layer separation. Some TSA vessel designs are not well-suited for multiple beds (such as radial flow designs), so too many layers may even make the process infeasible.

[0017] Finally, most TSA designs that include oxidation catalysts utilize a final layer of adsorbent to capture any water or carbon dioxide formed by the oxidation of hydrogen and carbon monoxide in the catalyst layer. The adsorbent layer increases the volume and thus the investment cost of the TSA vessel (in addition to the cost of the adsorbent), as well as the operating costs due to increased regeneration power and gas requirements due to the larger vessel and greater adsorbent usage. It also increases the void volume, thereby reducing the effective recovery rate of the purified gas from the TSA. Removing the deactivated catalyst becomes more difficult because the adsorbent layer must be removed first. Finally, the catalyst is not regenerated as effectively as at the product end of the bed. This is because the hot purge gas is transferred from the product end to the feed end of the bed, so the effect of heat loss (external loss of the environment and energy for desorption) becomes more significant when the catalyst layer is placed further away from the product end of the bed.

[0018] EP2662653A of Linde AG and EP2789376A of Air Products and Chemicals, Inc. teach the removal of hydrogen and carbon monoxide impurities from dry gas using only Hopcalite catalyst at low temperatures (0 °C to 60 °C).

[0019] The term "Hopcalite" is a general term for a series of catalysts, typically consisting mainly of a mixture of manganese oxide and copper oxide. Since at least 1920 (e.g., see US1345323), Hopcalite catalysts have been known and used to oxidize carbon monoxide to form carbon dioxide.

[0020] In EP2789376A, the inventors observed that hopcalite can simultaneously (i) oxidize carbon monoxide to carbon dioxide; (ii) chemisorb hydrogen; and (iii) oxidize hydrogen to form water, and in addition adsorb the resulting carbon dioxide and water. The mechanism of action of carbon monoxide is as follows:

[0021]

[0022] That is, CO in the gas adsorbed on the catalyst surface

[0023]

[0024] That is, the adsorbed CO reacts with oxygen on the catalyst surface to form CO2

[0025]

[0026] That is, CO2 is desorbed into the gas phase

[0027] A similar mechanism is also used to remove hydrogen (replacing "CO" with "H2" in these reaction mechanisms).

[0028] At the relevant time, although the oxidation of carbon monoxide was already known, it was not known at that time that hopcalite could simultaneously remove hydrogen. In fact, based on the then state of the art, it was completely unexpected that hydrogen would be removed by an adsorption mechanism. During the catalytic removal of hydrogen, the feed stream hydrogen is converted into water. Thus, in a pure catalytic process, the feed impurities are converted into another substance. However, the experimental results reported in EP2789376A clearly show that hydrogen is removed by adsorption. In this regard, hydrogen passes through the bed and continues to increase in concentration until the bed is saturated and approaches the feed inlet concentration. Although the formation of water was not observed, it is admitted that some hydrogen in the dry gas may also form water, but any product water must then be adsorbed by the catalyst. However, the inventors noted that restricting the hydrogen removal mechanism to adsorption determines the size of the adsorption bed.

[0029] Hopcalite is used as both a catalyst and an adsorbent. Prior to EP2789376A, the observation that hydrogen can be removed by adsorption had not been revealed because for hydrogen removal to occur, the hopcalite layer must meet certain criteria.

[0030] First, before the intake air enters the hopcalite, at least substantially all water and carbon dioxide must be removed from the intake air because they both compete with hydrogen for chemisorption sites in the catalyst. In this regard, the water and carbon dioxide contents are preferably reduced to no more than 10 parts per million by volume ("ppmv"), preferably no more than 1 ppmv. This means that the hopcalite layer must be placed downstream of the water and carbon dioxide removal layers in an adsorption unit such as a TSA unit. As described above, this is not the case for carbon monoxide oxidation using hopcalite in the relevant prior art TSA beds.

[0031] Second, it has been found from laboratory tests that a minimum residence time in the catalyst layer is necessary for effective removal of hydrogen by chemisorption. In the art, when using hopcalite for carbon monoxide oxidation after removing water and carbon dioxide, the residence time of the gas in the catalyst bed is less than 1.2 s. The inventors in EP2789376A found that significant hydrogen chemisorption on hopcalite requires a greater residence time of the gas in the catalyst layer, generally at least 1.5 s, more preferably more than 2 s.

[0032] Since hopcalite is a relatively inexpensive catalyst, this method enables the design and construction of a simpler and less costly layered TSA bed for the FEU. Another advantage of this method is that since it is a mixture of metal oxides, hopcalite does not suffer from excessive oxidation during the thermal regeneration of the oxygen-rich purge gas.

[0033] The copper to manganese molar ratio of a typical hopcalite catalyst for carbon monoxide oxidation is from 0.45 to 0.55, such as about 0.5, and its surface area (N2 BET at 77K) is greater than 250 m 2 / g, such as from 280 m 2 / g to 320 m 2 / g, and its total pore volume is from 0.4 to 0.5 cm 3 / g. Hereinafter, such a hopcalite catalyst is referred to as a "standard" hopcalite catalyst.

[0034] In this case, an example of the standard hopcalite catalyst is the one used in EP2662653 and EP2789376A 300 (Carus Corporation).

[0035] It has now been found that hydrogen impurities can be removed more effectively from dry gas (especially air) by means of a Hopcalite catalyst having a composition different from that of the standard Hopcalite catalyst used for removing carbon monoxide. Specifically, the inventors have found that the removal of trace hydrogen is improved by means of a Hopcalite catalyst having a greater copper to manganese (Cu / Mn) molar ratio than the standard Hopcalite catalyst.

[0036] According to a first aspect of the present invention, there is provided a process for removing hydrogen from dry gas comprising hydrogen as an impurity, the process comprising passing the dry gas through at least one layer of a first Hopcalite catalyst at a temperature of from about 0 °C to about 60 °C to produce a product gas substantially free of hydrogen, wherein the first Hopcalite catalyst has a copper to manganese molar ratio greater than 0.55.

[0037] It is known from the prior art that as the copper to manganese molar ratio increases, the carbon monoxide capacity of the Hopcalite catalyst tends to decrease. However, to the inventors' knowledge, the effect of the Cu / Mn molar ratio on the hydrogen capacity of the Hopcalite catalyst has not been revealed. In this regard, the inventors have observed that if the molar ratio of copper to manganese is higher than that of the standard Hopcalite catalyst, the hydrogen capacity (mmol / g) of the Hopcalite catalyst is greater. Therefore, there is an opportunity to improve the process disclosed in EP2789376A by carefully selecting the Hopcalite catalyst.

[0038] The inventors have observed that as the Cu / Mn molar ratio increases from about 0.5, the hydrogen capacity of the Hopcalite catalyst increases and reaches a peak when the Cu / Mn ratio reaches about 3. Accordingly, the molar ratio of copper to manganese in the first Hopcalite catalyst is generally at least 0.6 or at least 0.7 or at least 0.8 or at least 0.9 or at least 1 or at least 1.1 or at least 1.2 or at least 1.5.

[0039] Furthermore, the inventors have further observed that the hydrogen capacity of a Hopcalite catalyst having a Cu / Mn molar ratio greater than about 7 (such as about 10) is less than that of the standard Hopcalite catalyst. Therefore, there is generally an "optimum point" for the Cu / Mn molar ratio in terms of hydrogen capacity.

[0040] The molar ratio of copper to manganese in the first Hopcalite catalyst is generally not greater than 7, for example, not greater than 6 or not greater than 5. Preferably, the molar ratio of copper to manganese in the first Hopcalite catalyst is in the range of from about 0.6 to about 4, such as in the range of from about 0.6 to about 3 or from about 1 to about 4.

[0041] As mentioned above, it has been observed that the hydrogen capacity of the Hopcalite catalyst reaches a peak when the Cu / Mn molar ratio is about 3. Thus, in some embodiments, the molar ratio of copper to manganese in the first Hopcalite catalyst ranges from about 1 to about 5, such as from about 2 to about 4, for example from about 2.5 to about 3.5. The inventors expect such Hopcalite catalysts to be particularly suitable for catalyst layers where the emphasis is on removing trace hydrogen rather than trace carbon monoxide.

[0042] Also as mentioned above, the Hopcalite capacity for carbon monoxide tends to decrease as the Cu / Mn molar ratio increases beyond about 0.5. Thus, in other embodiments, the molar ratio of copper to manganese in the first Hopcalite catalyst ranges from about 0.6 to about 1.2, for example from about 0.8 to about 1.2, or from about 0.9 to about 1.2, or from about 1 to about 1.2. The inventors have observed that Hopcalite catalysts having a Cu / Mn molar ratio within these ranges, particularly Hopcalite catalysts having a Cu / Mn molar ratio of 1, tend to achieve an acceptable balance between an increase in hydrogen capacity and a loss in carbon monoxide capacity. The inventors expect such Hopcalite catalysts to be particularly suitable for catalyst layers where the emphasis is on removing both trace hydrogen and trace carbon dioxide.

[0043] The dry gas can pass through one or more layers of the first Hopcalite catalyst to remove both hydrogen and carbon monoxide impurities.

[0044] In some embodiments, trace hydrogen and trace carbon monoxide can be removed by passing the dry gas through a single layer of the first Hopcalite catalyst. In such embodiments, the Cu / Mn molar ratio in the first Hopcalite catalyst can range from about 0.6 to about 3, such as from about 0.6 to about 1.2, for example from about 0.8 to about 1.2, or from about 0.9 to about 1.2. Another suitable range for the Cu / Mn molar ratio can be from about 1 to about 3, such as from about 1 to about 1.2.

[0045] In other embodiments, trace hydrogen and trace carbon monoxide can be removed mainly in separate layers of the Hopcalite agent. For example, trace carbon monoxide can be removed by passing the dry gas through at least one layer of a standard Hopcalite catalyst or a high-Cu Hopcalite catalyst or a mixture thereof, and trace hydrogen can be removed by passing the dry gas through at least one layer of a high-Cu Hopcalite catalyst.

[0046] In such embodiments, the Cu / Mn molar ratio in the high-Cu Hopcalite catalyst for removing trace carbon monoxide can be in the range of about 0.6 to about 3, such as about 0.6 to about 1.2, for example about 0.8 to about 1.2, or about 0.9 to about 1.2, or in the range of about 1 to about 1.2. Additionally or alternatively, the Cu / Mn molar ratio of the high-Cu Hopcalite catalyst for removing trace hydrogen can be in the range of about 0.6 to about 4, such as about 2 to about 4, for example, in the range of about 2.5 to about 3.5.

[0047] In embodiments comprising at least two layers of Hopcalite catalyst, a carbon dioxide adsorption material layer can be provided between adjacent Hopcalite catalyst layers.

[0048] The inventors have observed that, compared to standard Hopcalite catalysts, high-Cu Hopcalite catalysts are less sensitive to the presence of carbon dioxide in dry gas. In this regard, EP2789376A discloses that the inlet gas entering the catalyst layer must contain no more than 10 ppmv of carbon dioxide to achieve the removal of hydrogen by adsorption through Hopcalite. However, the inventors have demonstrated that both hydrogen and carbon monoxide can still be effectively removed in the presence of 400 ppmv of carbon dioxide.

[0049] Without wishing to be bound by any particular theory, the inventors believe that high-Cu Hopcalite catalysts are less affected by carbon dioxide because the surface area of the catalyst is smaller than that of the standard Hopcalite catalyst. Thus, the first Hopcalite catalyst generally has a surface area of less than 280 m 2 / g, for example not greater than 250 m 2 / g, for example about 150 m 2 / g to about 250 m 2 / g, or such as not greater than 200 m 2 / g, for example about 100 m 2 / g to about 200 m 2 / g.

[0050] The total pore volume and / or the average pore diameter may also contribute to improving the performance of the high-Cu Hopcalite catalyst in the presence of carbon dioxide.

[0051] In this regard, the total pore volume of the first Hopcalite catalyst is generally less than 0.4 cm 3 / g. In a preferred embodiment, the total pore volume of the first Hopcalite catalyst is in the range of about 0.1 cm 3 / g to about 0.3 cm 3 / g.

[0052] Advantages of the preferred embodiment of the present invention are that, compared with the concentrations disclosed in EP2789376A, this process can accommodate higher concentrations of hydrogen and carbon monoxide impurities in dry gas. In this regard, the dry gas of this process usually contains up to about 40 ppmv of hydrogen, for example, from greater than 20 ppmv to about 40 ppmv. Additionally or alternatively, the dry gas may contain up to 50 ppmv of carbon monoxide.

[0053] As mentioned above, this process can accommodate a larger amount of carbon dioxide in dry gas. In this regard, the process can accommodate up to about 900 ppmv of carbon dioxide in dry gas, for example, up to 600 ppmv or up to 500 ppmv of carbon dioxide. The amount of carbon dioxide that the process will usually allow in dry gas is greater than 10 ppmv to about 600 ppmv, such as about 20 ppmv to about 600 ppmv, for example, about 50 ppmv to about 500 ppmv.

[0054] EP2789376A illustrates the regeneration of a standard Hopcalite catalyst layer at a temperature of 180°C. In contrast, the high-Cu Hopcalite catalyst used in the present invention can be regenerated at a temperature lower than 180°C (for example, not exceeding 150°C or not exceeding 100°C, for example, about 50°C to 100°C or about 70°C or about 60°C).

[0055] The lower regeneration temperature expands the scope of the air pre-purification cycle, in which both carbon monoxide and hydrogen can be removed using Hopcalite. In this regard, this process can be incorporated into a temperature swing adsorption (TSA) cycle, a thermal pressure swing adsorption (TPSA) cycle, or a thermally enhanced pressure swing adsorption (TEPSA) cycle, which have reduced regeneration temperature levels of about 200°C, about 180°C, and about 60°C, respectively. In TEPSA or PSA, the price of the high-Cu Hopcalite catalyst is significantly lower than that of noble metal catalysts.

[0056] Another advantage of the preferred embodiment of the present invention is that the preferred feed temperature can be lower. In this regard, the dry gas in EP2789376A is most preferably at a temperature of about 15°C to about 30°C. However, in the present invention, the temperature of the dry gas can be lower than 15°C to about 10°C.

[0057] The dry gas usually passes through the first Hopcalite catalyst layer within a pressure range of about 3 bar to about 45 bar (0.3 Mpa to 4.5 MPa) (usually within about 3 bar to about 30 bar (0.3 MPa to 3 MPa)).

[0058] The dry gas can pass through at least one layer of the second Hopcalite catalyst upstream of the first layer of the first Hopcalite catalyst layer, wherein the copper-to-manganese molar ratio of the second Hopcalite catalyst is not greater than 0.55. In these embodiments, the dry gas generally passes through a carbon dioxide adsorption material layer downstream of the second Hopcalite catalyst and upstream of the first Hopcalite catalyst.

[0059] Thus, in one embodiment of the first aspect, there is provided a process for removing hydrogen from dry air comprising hydrogen as an impurity, the process comprising passing the dry air through at least one layer of a first Hopcalite catalyst at a pressure of about 3 bar to about 30 bar (0.3 MPa to 3 MPa) and a temperature of about 0 °C to about 60 °C to produce dry air that is at least substantially free of hydrogen, wherein the copper-to-manganese molar ratio of the first Hopcalite catalyst is in the range of about 2 to about 4.

[0060] Additionally, in a second embodiment of the first aspect, there is provided a process for removing hydrogen and carbon monoxide from dry air comprising hydrogen and carbon monoxide as impurities, the process comprising passing the dry air through at least one layer of a first Hopcalite catalyst at a pressure of about 3 bar to about 30 bar (0.3 MPa to 3 MPa) and a temperature of about 0 °C to about 60 °C to produce dry air that is at least substantially free of hydrogen and carbon monoxide, wherein the copper-to-manganese molar ratio of the first Hopcalite catalyst is in the range of about 0.6 to about 1.2, for example, about 0.9 to about 1.2.

[0061] In a second aspect of the present invention, there is provided an adsorption unit for removing water, carbon dioxide, hydrogen, and carbon monoxide impurities from a gas comprising impurities, the unit comprising an adsorption bed having a feed end and a product end opposite the feed end, the adsorption bed consisting of:

[0062] A water adsorption material layer provided at the feed end of the bed for removing water from the gas to produce dry gas;

[0063] At least one layer of a first Hopcalite catalyst having a copper-to-manganese molar ratio greater than 0.55 for removing hydrogen impurities from the dry gas to produce a product gas substantially free of hydrogen; and

[0064] At least one layer of a carbon dioxide adsorption material for removing carbon dioxide from the dry gas; and

[0065] Optionally

[0066] At least one layer of a second Hopcalite catalyst located upstream of the first Hopcalite catalyst layer for removing carbon monoxide from the dry gas, wherein the copper-to-manganese molar ratio of the second Hopcalite catalyst is not greater than 0.55.

[0067] Various arrangements of the layers in the adsorption bed are possible. In this regard, the adsorption bed can consist of the following (in the "operating" sequence):

[0068] · A layer of water adsorption material, a single layer of the first Hopcalite catalyst, and a single layer of carbon dioxide adsorption material

[0069] · A layer of water adsorption material, a single layer of carbon dioxide adsorption material, and a single layer of the first Hopcalite catalyst, preferably when this unit is a TEPSA unit

[0070] · A layer of water adsorption material, a single layer of carbon dioxide adsorption material, a single layer of the first Hopcalite catalyst, and a single layer of carbon dioxide adsorption material

[0071] · A layer of water adsorption material, the first layer of the first Hopcalite catalyst, a single layer of carbon dioxide adsorption material, and the second layer of the first Hopcalite catalyst, preferably when this unit is a TSA unit, a TPSA unit, or a TEPSA unit

[0072] · A layer of water adsorption material, a single layer of standard Hopcalite catalyst, a single layer of carbon dioxide adsorption material, and a single layer of the first Hopcalite catalyst, preferably when this unit is a TSA unit, a TPSA unit, or a TEPSA unit

[0073] · A layer of water adsorption material, a single layer of standard Hopcalite catalyst, a single layer of the first Hopcalite catalyst, and a single layer of carbon dioxide adsorption material

[0074] · A layer of water adsorption material, a single layer of carbon dioxide adsorption material, a single layer of standard Hopcalite catalyst, and a single layer of the first Hopcalite catalyst

[0075] In each of the three arrangements described above as preferred, using a high-Cu Hopcalite catalyst results in a lower total amount of catalyst used than when only using a standard Hopcalite catalyst.

[0076] According to a third aspect of the present invention, a Hopcalite agent with a copper-to-manganese molar ratio greater than 0.55 is used to remove hydrogen as an impurity from dry gas containing impurities.

[0077] Hopcalite catalyst is generally the only catalyst currently used to remove hydrogen. Therefore, an advantage of a preferred embodiment of the present invention is to remove hydrogen impurities from dry gas without a noble metal catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0078] Figure 1 A flowchart depicting an embodiment of the present invention having three layers in each TSA unit.

[0079] Figure 2Flow chart depicting an embodiment of the present invention having four layers in each TSA unit.

[0080] Figure 3 Graph depicting the relationship between the hydrogen absorption capacity (mmol / g) and the Cu / Mn molar ratio in the synthetic Hopcalite agent (Example 1).

[0081] Figure 4 Graph depicting the relationship between the hydrogen absorption capacity and the carbon monoxide absorption capacity (mmol / g) and the Cu / Mn molar ratio in the commercially available Hopcalite agent (see Example 1).

[0082] Figure 5 Graph depicting the hydrogen breakthrough versus normalized time of the Hopcalite agent with a Cu / Mn molar ratio of 0.5 compared to the Hopcalite agent with a molar ratio of 1.0 at 14 °C, 25 °C, 40 °C and 130 psig (0.9 MPa) in air containing 2 ppmv hydrogen and 10 ppmv carbon monoxide (see Example 2).

[0083] Figure 6A Graph depicting the normalized breakthrough time of 10 ppb hydrogen versus the Cu / Mn molar ratio of the Hopcalite agent (see Example 2).

[0084] Figure 6B Graph depicting the normalized breakthrough time of 10 ppb hydrogen versus the surface area of the Hopcalite agent (see Example 2).

[0085] Figure 6C Graph depicting the normalized breakthrough time of 10 ppb hydrogen versus the pore volume of the Hopcalite agent (see Example 2).

[0086] Figure 7 Graph depicting the hydrogen breakthrough concentration versus time of the Hopcalite agent with a Cu / Mn molar ratio of 0.5 compared to the Hopcalite agent with a molar ratio of 1.0 at 25 °C and 130 psig (0.9 MPa) after a regeneration temperature of 70 °C in air containing 5 ppmv hydrogen and 10 ppmv carbon monoxide (see Example 2).

[0087] Figure 8 Graph depicting the water loading versus the regeneration temperature of the standard Hopcalite catalyst and the high Cu Hopcalite catalyst.

[0088] Figure 9 Depicting different stratification options in the adsorption bed of the adsorption unit according to the second aspect of the present invention.

[0089] Figure 10Graph depicting the normalized residence time required for 10 ppb hydrogen in the product case for standard Hopcalite catalyst and high-Cu Hopcalite catalyst at different feed temperatures under the feed conditions of Example 2C.

[0090] Figure 11 Schematic diagram of a layered adsorption bed containing a standard Hopcalite catalyst compared to a layered adsorption bed containing a high-Cu Hopcalite catalyst for achieving air-equivalent end purity. Detailed Description

[0091] A process for removing hydrogen from dry gas including hydrogen as an impurity, the process comprising passing the dry gas through at least one layer of a first Hopcalite catalyst at a temperature of about 0°C to about 60°C to produce a product gas that is at least substantially free of hydrogen, wherein the first Hopcalite catalyst has a copper to manganese molar ratio of at least 0.6.

[0092] In the absence of a noble metal catalyst, hydrogen impurities or trace hydrogen are typically removed from dry gas.

[0093] Hopcalite is typically the only catalyst currently used for removing trace hydrogen. The Hopcalite catalyst is either only a high-Cu Hopcalite catalyst or a combination of a high-Cu Hopcalite catalyst and a standard Hopcalite catalyst. In the case of using a combination of different Hopcalite agents, although there may be one or more layers of mixed Hopcalite agents, the different Hopcalite catalysts are preferably in different layers from each other.

[0094] In embodiments where the copper to manganese molar ratio is in the range of about 0.6 to about 10, the first Hopcalite catalyst typically comprises about 5 wt% to about 40 wt% manganese and about 25 wt% to about 70 wt% copper, and in embodiments where the copper to manganese molar ratio is in the range of about 0.6 to about 3, it comprises about 15 wt% to about 40 wt% manganese and about 25 wt% to about 60 wt% copper. In this regard, "wt%" is based on the total metal content of the catalyst measured by X-ray fluorescence or XRF.

[0095] The first Hopcalite catalyst may consist mainly of oxides of manganese and copper. However, in a preferred embodiment, the catalyst comprises at least one (and preferably each) additional metal substance selected from the group consisting of potassium, sodium, calcium, silicon, and aluminum. The additional metal substances are typically present in a total amount of about 2 wt% to about 10 wt%.

[0096] The first Hopcalite catalyst can have any suitable form, but is typically in the form of granules, such as extruded granules. The catalyst granules typically have an average diameter in the range of about 1 mm to about 6 mm (such as about 2.5 mm to 3.5 mm) and an average length in the range of about 1 mm to about 10 mm (such as about 3 mm to about 7 mm).

[0097] The residence time of the dry gas in the high-Cu Hopcalite layer is generally at least 0.1 s, such as at least 0.2 s, for example at least 0.3 s. The residence time of the dry gas in the high-Cu Hopcalite catalyst is preferably not greater than about 5 s, such as not greater than 4 s, for example not greater than 3 s or not greater than 2 s. The residence time can be from 0.1 s to 5 s, from 0.2 s to 4 s or from 0.3 s to 3 s. However, due to the greater reactivity of the catalyst towards hydrogen, the residence time is generally shorter than that required in EP2789376A.

[0098] In the context of the present invention, "residence time" is defined as the volume of the catalyst layer divided by the volumetric inlet gas flow rate evaluated at the temperature and pressure within the catalyst layer.

[0099] The hydrogen content of the dry gas is generally not greater than about 40 ppmv. The hydrogen content in the dry gas can be as low as about 0.1 ppmv, for example from about 0.1 ppmv to about 40 ppmv, for example from greater than 20 ppmv to about 40 ppmv.

[0100] The carbon monoxide content in the dry gas is generally not greater than about 50 ppmv, and is generally from about 0.5 ppmv to about 20 ppmv.

[0101] The water in the dry gas is generally not greater than about 10 ppmv, generally not greater than about 1 ppmv, and generally not greater than 0.5 ppmv.

[0102] Since the catalyst comprises a mixture of metal oxides, the catalyst itself can provide the oxygen required to oxidize carbon monoxide and / or hydrogen. In this regard, carbon monoxide is oxidized to carbon dioxide according to the following reaction mechanism:

[0103] CO + MnO2 → CO2 + MnO

[0104] On this basis, there is no need for oxygen (O2) to be present in the gas for oxidation. That is to say, oxygen may be present in the dry gas, and if present, it can act as the oxidant for the oxidation reaction. The amount of oxygen that may be present is from about 1 mol.% to about 99.9 mol.%. In some embodiments, the dry gas is oxygen containing, for example, at most 1 mol.% hydrogen as an impurity. In other embodiments, in addition to oxygen, the dry gas can include at least one other gas component such as nitrogen and / or one or more inert gases. In such embodiments, the amount of oxygen that may be present is from about 1 mol.% to about 50 mol.%. In a preferred embodiment, the dry gas is air.

[0105] The process can be carried out at any suitable pressure, for example, at atmospheric pressure or about 1 bar (0.1 MPa). The increase in gas pressure leads to an increase in the partial pressure of the impurities to be removed. Since the adsorption capacity increases with the increase in partial pressure, operating this process at a higher pressure can enhance the adsorption capacity of the bed, thereby reducing the size of the bed. Therefore, this process is preferably operated at a high pressure greater than 1 bar (0.1 MPa) and generally less than 50 bar (5 MPa), such as about 3 bar to about 25 bar (0.3 to 2.5 MPa). Throughout the document, the pressures given in metric units are calculated on an absolute basis.

[0106] The dry gas is usually at a temperature of about 0 °C to about 60 °C, such as about 5 °C to about 50 °C, such as about 15 °C to about 30 °C, i.e., about ambient temperature, or about 10 °C to about 15 °C.

[0107] The product gas usually contains no more than about 1 ppmv of carbon monoxide, such as no more than about 500 ppb, preferably no more than about 50 ppb, and more preferably no more than about 10 ppb.

[0108] The product gas usually contains no more than about 1 ppmv of hydrogen, such as no more than about 500 ppb, preferably no more than about 50 ppb, and more preferably no more than about 10 ppb.

[0109] The dry gas can be formed by passing the inlet gas through at least one adsorption layer to remove water and carbon dioxide. The adsorbent layer can include alumina alone or potassium carbonate-promoted alumina (to remove water and carbon dioxide), or a first layer of alumina or potassium carbonate-promoted alumina (to remove mainly water) together with a second layer of zeolite (such as 13X) to remove carbon dioxide.

[0110] There may be a layer of carbon dioxide adsorption material (e.g., 13X zeolite) after the catalyst layer to capture carbon dioxide in the product gas passing through the catalyst layer.

[0111] In a preferred embodiment, the catalyst layer is regenerated. In this regard, the catalyst must be thermally regenerated to restore the chemisorption capacity of the catalyst for hydrogen. The catalyst layer is preferably regenerated by passing a regeneration gas through the catalyst layer at a temperature in the range of about 60 °C to about 200 °C, or about 60 °C to less than 180 °C. The regeneration gas usually passes through the catalyst layer for no more than 6 h and generally no more than 4 h.

[0112] The catalyst layer is usually regenerated by passing a regeneration gas through the catalyst layer at a temperature of at least 60 °C for at least 25 min. More preferably, at a temperature of at least 150 °C, the regeneration gas passes through for at least 2 h.

[0113] Any suitable gas can be used as the regeneration gas. For example, the regeneration gas can include the waste gas from a cryogenic distillation process. In another example, the regeneration gas includes a portion of the product gas. In yet another example, the regeneration gas includes oxygen and its temperature is at least the same as the temperature of the product gas when used as the regeneration gas to supply oxygen to the catalyst surface.

[0114] The present invention will now be described with reference to Figure 1 and Figure 2 the flowcharts described in

[0115] According to Figure 1 , an air stream 10 is compressed to a high pressure of 3 bar to 25 bar (0.3 to 2.5 MPa) in a main air compressor 12. The compressed air stream is cooled in a cooler 14, a portion of the water in the air stream is condensed and separated from the gas, and discharged through a valve 16. The cooled and partially dried air stream 17 at a temperature of 5 to 60 °C then enters a container 24 through a valve 20. The containers 24 and 26 each contain the same adsorbent and catalyst layers.

[0116] Inside the container, the feed air enters the first layer (24a or 26a) of the water adsorbent that dries the feed air. Due to the co-adsorption of carbon dioxide and water, this layer can also remove a portion of the carbon dioxide in the inlet air. This layer typically consists of alumina, alkali-promoted alumina, or silica gel.

[0117] Subsequently, the dried feed air enters the second layer (24b or 26b), where the carbon dioxide is removed to a level of 10 ppmv or lower. This layer consists of a zeolite adsorbent, such as NaX, NaLSX, or CaX.

[0118] The dry, carbon dioxide-free air is then conveyed to a layer of high copper hopcalite (24c or 26c), where carbon monoxide is oxidized to carbon dioxide, hydrogen is chemisorbed, and may react to form water. The resulting trace amount of carbon dioxide and any water produced by these reactions are adsorbed onto the hopcalite.

[0119] The air stream continues to flow for a predetermined time, and the dimensions of each layer should be such that water, carbon dioxide, carbon monoxide, and hydrogen are retained in the bed and the purified air stream (containing no more than 0.5 ppmv of water, no more than 1 ppmv of carbon dioxide, no more than 500 ppb of carbon monoxide, and no more than 500 ppb of hydrogen) is discharged from the container 24. The purified air passes through a valve 36 and is introduced as an air stream 40 into a cryogenic distillation system (not shown), where UHP nitrogen is produced.

[0120] While container 24 processes the feed stream, container 26 undergoes a heat regeneration step. The regeneration desorbs water from layer 26a and carbon dioxide from layer 26b. Additionally, the heat regeneration of the hopcalite catalyst in layer 26c restores the material's hydrogen chemisorption capacity. The heat regeneration can be carried out at a temperature of at least 60 °C, more preferably at least 150 °C (e.g., about 180 °C) in order to drive the chemisorbed hydrogen / water from the catalyst.

[0121] The regeneration is carried out by heating a dry, carbon dioxide-free purge gas stream 47 via heater 52 to produce a hot purge gas stream 48, which is delivered to container 26 through manifold 42 and valve 46. The purge gas can be part of the product gas 40 or the waste gas from a cryogenic distillation unit. The hot purge gas passes through layers 26c, 26b, and 26a of container 26, thereby regenerating the catalyst and adsorbent. The gas discharged from bed 26 passes through valve 32 and manifold 28 and is then discharged from the process as gas stream 34. Once each layer is sufficiently heated and regenerated, the bed is cooled by closing or bypassing heater 52, and a cooling purge gas at a temperature of 10 to 60 °C is passed through the bed.

[0122] The feed and regeneration steps are carried out as described for a predetermined period of time, after which the functions of containers 24 and 26 are switched, with container 26 "online" and receiving the inlet gas, and container 24 "offline" and being regenerated. The containers alternate between feed and regeneration to maintain a continuous production of purified air.

[0123] Those skilled in the art will recognize that the regeneration step can be carried out in different ways to help improve the efficiency of the process. The regeneration bed can first be depressurized to near atmospheric pressure through valve 30 or 32 to the exhaust port 34, and the heating and cooling steps can be carried out at a lower pressure. A hot purge fluid can be fed into the container until the entire container reaches a higher regeneration temperature, and then the cooling gas flow is started. This is known in the art as a TSA cycle. However, in the preferred embodiment, only a portion of the hot purge gas required to heat the entire contents of the container is used before starting the cooling step. This creates a heat pulse that sequentially passes through all layers of the catalyst and adsorbent, and the energy capacity of the pulse decreases as it travels to the feed side of the container, which is known in the art as a TPSA or TEPSA cycle (due to heat losses and providing energy for the desorption of water and carbon dioxide).

[0124] Figure 1 A two-bed TSA process is shown, but the system can also use three or more containers.

[0125] A second embodiment of the present invention is in Figure 2is shown, where additional adsorbent layers 24d, 26d are added after the catalyst layers 24c, 26c. Although the carbon dioxide adsorption capacity of the Hopcalite catalyst is significant, the capacity is also limited. Therefore, breakthrough of the carbon dioxide formed by carbon monoxide oxidation in the catalyst may limit Figure 1 the time the system shown is on line. In such cases, longer on-line times can be achieved by adding short layers 24d, 26d of carbon dioxide adsorbent after the Hopcalite layer. This layer consists of a zeolite adsorbent such as 13X, CaX, or NaLSX.

[0126] Aspects and embodiments of the present invention include:

[0127] #1. A method for removing hydrogen from dry gas including hydrogen as an impurity, the method comprising passing the dry gas through at least one layer of a first Hopcalite catalyst at a temperature of about 0°C to about 60°C to produce a product gas that is at least substantially free of hydrogen, wherein the copper to manganese molar ratio of the first Hopcalite catalyst is greater than 0.55.

[0128] #2. The method according to #1, wherein the copper to manganese molar ratio in the first Hopcalite catalyst is less than 7.

[0129] #3. The method according to #1 or #2, wherein the copper to manganese molar ratio in the first Hopcalite catalyst is in the range of 0.6 to 4.

[0130] #4. The method according to any one of #1 to #3, wherein the copper to manganese molar ratio in the first Hopcalite catalyst is in the range of 2 to 4.

[0131] #5. The method according to #4, wherein the dry gas passes through a single layer of the first Hopcalite catalyst.

[0132] #6. The method according to #4, wherein the dry gas passes through two layers of the first Hopcalite catalyst.

[0133] #7. The method according to #6, wherein the dry gas passes through a carbon dioxide adsorption material layer between the two layers of the first Hopcalite catalyst.

[0134] #8. The method according to any one of #1 to #3, wherein the copper to manganese molar ratio in the first Hopcalite catalyst is in the range of 0.6 to 1.2, preferably in the range of about 0.9 to about 1.2.

[0135] #9. The method according to #8, wherein the dry gas passes through a single layer of the first Hopcalite catalyst.

[0136] #10. The method according to any one of #1 to #9, wherein the surface area of the first Hopcalite catalyst is less than 280 m 2 / g.

[0137] #11. The method according to any one of #1 to #10, wherein the surface area of the first Hopcalite catalyst is in the range of 100 m 2 / g to 200 m 2 / g.

[0138] #12. The method according to any one of #1 to #11, wherein the total pore volume of the first Hopcalite catalyst is less than 0.4 cm 3 / g.

[0139] #13. The method according to any one of #1 to #12, wherein the total pore volume of the first Hopcalite catalyst is in the range of 0.1 cm 3 / g to 0.3 cm 3 / g.

[0140] #14. The method according to any one of #1 to #13, wherein the hydrogen impurities are present in the dry gas in an amount of at most 40 ppmv.

[0141] #15. The method according to any one of #1 to #14, wherein the hydrogen impurities are present in the dry gas in an amount exceeding 20 ppmv.

[0142] #16. The method according to any one of #1 to #15, wherein the dry gas comprises carbon dioxide in an amount of at most 900 ppmv.

[0143] #17. The method according to #1, wherein the dry gas comprises carbon dioxide in an amount of at most 600 ppmv.

[0144] #18. The method according to any one of #1 to #16, wherein the dry gas comprises carbon dioxide in an amount exceeding 10 ppmv.

[0145] #19. The method according to any one of #1 to #18, wherein the first Hopcalite catalyst layer is regenerated at a temperature below 200 °C.

[0146] #20. The method according to any one of #1 to #19, wherein the first Hopcalite catalyst layer is regenerated at a temperature not exceeding 150 °C.

[0147] #21. The method according to any one of #1 to #20, wherein the first Hopcalite catalyst layer is regenerated at a temperature not exceeding 80 °C.

[0148] #22. The method according to any one of #1 to #21, wherein the temperature of the dry gas is in the range of 10°C to 15°C.

[0149] #23. The method according to any one of #1 to #22, wherein the dry gas passes through the first Hopcalite catalyst layer within a pressure range of 3 bar to 45 bar (0.3 Mpa to 4.5 Mpa).

[0150] #24. The method according to any one of #1 to #23, the method comprising passing the dry gas through at least one layer of a second Hopcalite catalyst located upstream of the first Hopcalite catalyst layer, wherein the copper to manganese molar ratio of the second Hopcalite catalyst does not exceed 0.55.

[0151] #25. The method according to #24, wherein the dry gas passes through a carbon dioxide adsorption material layer downstream of the second Hopcalite catalyst and upstream of the first Hopcalite catalyst.

[0152] #26. A method for removing hydrogen from dry air including hydrogen as an impurity, the method comprising passing the dry air through at least one layer of a first Hopcalite catalyst at a pressure of 3 bar to 45 bar (0.3 MPa to 4.5 MPa) and a temperature of about 0°C to 60°C to produce at least substantially hydrogen-free dry air, wherein the copper to manganese molar ratio of the first Hopcalite catalyst is in the range of 2 to 4.

[0153] #27. A method for removing hydrogen and carbon monoxide from dry air including hydrogen and carbon monoxide as impurities, the method comprising passing the dry air through at least one layer of a first Hopcalite catalyst at a pressure of 3 bar to 45 bar (0.3 MPa to 4.5 MPa) and a temperature of 0°C to 60°C to produce at least substantially hydrogen and carbon monoxide-free dry air, wherein the copper to manganese molar ratio of the first Hopcalite catalyst is in the range of 0.6 to 1.2, preferably in the range of about 0.9 to about 1.2.

[0154] #28. The method according to any one of #1 to #27, wherein the dry gas is oxygen.

[0155] #29. The method according to any one of #1 to #27, wherein the dry gas is air.

[0156] #30. An adsorption unit for removing water, carbon dioxide, hydrogen and carbon monoxide impurities from a gas including impurities, the unit comprising an adsorption bed having a feed end and a product end located downstream of the feed end, the adsorption bed consisting of:

[0157] A water adsorption material layer, disposed at the feed end of the bed for removing water from the gas to produce dry gas;

[0158] At least one layer of a first Hopcalite catalyst having a copper to manganese molar ratio greater than 0.55 for removing hydrogen impurities from the dry gas to produce a product gas substantially free of hydrogen; and

[0159] At least one layer of a carbon dioxide adsorption material for removing carbon dioxide from the dry gas; and

[0160] Optionally

[0161] At least one layer of a second Hopcalite catalyst, located upstream of the first Hopcalite catalyst layer, for removing carbon monoxide from the dry gas, wherein the copper to manganese molar ratio of the second Hopcalite catalyst is not greater than 0.55.

[0162] #31. The adsorption unit according to #30, wherein the adsorption bed consists of: the water adsorption material layer, a single layer of the first Hopcalite catalyst, and a single layer of the carbon dioxide adsorption material.

[0163] #32. The adsorption unit according to #30, wherein the adsorption bed consists of: the water adsorption material layer, a single layer of the carbon dioxide adsorption material, a single layer of the first Hopcalite catalyst, and optionally a single layer of the carbon dioxide adsorption material.

[0164] #33. The adsorption unit according to #32, wherein the unit is a TEPSA unit.

[0165] #34. The adsorption unit according to #30, wherein the adsorption bed consists of: the water adsorption material layer, a first layer of the first Hopcalite catalyst, a single layer of the carbon dioxide adsorption material, and a second layer of the first Hopcalite catalyst.

[0166] #35. The adsorption unit according to #30, wherein the adsorption bed consists of: the water adsorption material layer, a single layer of the second Hopcalite catalyst, a single layer of the carbon dioxide adsorption material, and a single layer of the first Hopcalite catalyst.

[0167] #36. The adsorption unit according to #35, wherein the unit is a TSA unit, a TPSA unit, or a TEPSA unit.

[0168] #37. The adsorption unit according to #35, wherein the single layer of the carbon dioxide adsorption material is located downstream of the single layer of the first Hopcalite catalyst.

[0169] #38. The adsorption unit according to #35, wherein the single layer of the carbon dioxide adsorption material is located upstream of the single layer of the second Hopcalite catalyst.

[0170] #39. Use Hopcalite with a copper to manganese molar ratio greater than 0.55 to remove hydrogen as an impurity from dry gas including impurities.

[0171] Examples

[0172] The present invention will now be described in the following examples. In all examples, the units of ppmv and ppb are based on moles.

[0173] Example 1 - Preparation of Hopcalite Catalysts with Different Cu / Mn Molar Ratios and Measurement of Hydrogen and Carbon Monoxide Absorption Capacities

[0174] Samples of Hopcalite catalysts with copper to manganese molar ratios of 0.3, 0.7, 1.0, 3.0, and 10.0 were prepared by a method comparable to that of Hutchings et al. (Applied Catalysis A: General 166 (1998) 143 - 152). Thus, a copper(II) nitrate solution was mixed with a manganese(II) nitrate solution at the target Cu / Mn ratio, deposition was carried out by adding an aqueous solution of sodium carbonate (Na2CO3), and it was rinsed with water to remove excess dissolved sodium. The solid was air-dried at 90 °C and then calcined at 400 °C to remove carbon dioxide. The surface area of the compositions prepared in this way was lower than that of commercially available Hopcalite, where the surface area was less than 100 m 2 / g. The particle sizes from the individual compositions were determined to be similar from the broadening of the powder X-ray diffraction lines of the diffraction peaks. Thus, the differences in hydrogen absorption are attributed to differences in the Cu / Mn ratio rather than changes in particle size or surface area.

[0175] The hydrogen (H2) absorption capacity of the synthesized Hopcalite catalysts was measured on a commercial gas isotherm measurement device (VTI Co HPA 300 adsorption unit). Two grams of each Hopcalite powder were used. The powder was vacuum-activated overnight at 200 °C and then maintained at 30 °C for the duration of the hydrogen absorption measurement. In the packed column breakthrough experiment, hydrogen was added at increasing partial pressures with an equilibration time of 5.5 seconds to simulate the contact time. After 5.5 seconds, the absorption capacity was recorded by the instrument, and the next hydrogen increment pressure was applied.

[0176] The comparative hydrogen absorption capacities at a partial pressure of 75 Torr (10 kPa) are as Figure 3 shown. In this regard, the hydrogen capacities of the Hopcalites with copper to manganese molar ratios of 1 and 3 increased significantly, but the hydrogen capacity of the Hopcalite with a copper to manganese molar ratio of 10 decreased.

[0177] Using a Micromeritics 3-Flex commercial gas isotherm measurement device, similar measurements to those above were made on the hydrogen and carbon monoxide (CO) absorption capacities of commercial Hopcalite catalysts. Commercially available standard and high-copper Hopcalite catalysts were selected, and their typical properties are shown in Table 1.

[0178]

[0179] *Based on a 240-min operating time, 130 psi (9 bar g), 25 °C inlet conditions, and the impurity concentrations in air given in the table. Normalized relative catalyst residence time to that of the standard Hopcalite agent in the case of only a 2-ppm H2 impurity challenge.

[0180] Table 1

[0181] Two grams of each Hopcalite catalyst were vacuum-activated overnight at 200 °C and then held at 25 °C for the duration of the hydrogen or carbon monoxide absorption measurement. Hydrogen or carbon monoxide was added at increasing partial pressures, with a 10-s equilibration time. After 10 s, the absorption capacity was recorded by the instrument, and the next incremental pressure was applied to the hydrogen or carbon monoxide.

[0182] Figure 4 The comparison results of the hydrogen and carbon monoxide absorption capacities at partial pressures of 5 Torr (0.7 kPa) and 10 Torr (1.4 kPa) are shown respectively. The commercial Hopcalite agent with a copper-to-manganese ratio of 0.5 has a higher carbon monoxide capacity than the commercial Hopcalite agent with a copper-to-manganese ratio of 0.9.

[0183] In the case of the lower carbon monoxide capacities of these Hopcalite agents, the increase in the hydrogen capacity of the Hopcalite agent with a higher Cu / Mn molar ratio was unexpected.

[0184] Example 2 - Through Experiment

[0185] The inlet gas passed through a reaction vessel filled with Hopcalite agent, and the gas effluent concentration was monitored to demonstrate the performance differences between the standard and high-Cu Hopcalite agents. Sampling ports were installed along the length of the reactor for the reaction vessel.

[0186] The same commercially available standard Hopcalite agent and high-Cu Hopcalite catalyst materials used in Example 1 were tested in Example 2. The typical material properties are shown in Table 1.

[0187] Before the feeding step, the catalyst was regenerated by heating to 200 °C (standard Hopcalite catalyst) or 70 °C (high-Cu Hopcalite catalyst) in a stream of air for at least 4 h and then cooled to room temperature.

[0188] Dry air is pre-treated (to remove carbon dioxide and trace amounts of hydrogen and carbon monoxide) and used as the feed gas, and a dilution mixture of carbon monoxide, hydrogen, and / or carbon dioxide in nitrogen (spike gas) is mixed with the feed air to obtain the desired feed gas composition. Different hydrogen, carbon monoxide, and carbon dioxide concentrations in the air are described in Examples 2A to 2F below. The column pressure is maintained at 130 psig (0.9 MPa), and the reactor temperature is controlled by an external coil that circulates water for cooling or heating to a temperature of 14 °C, 25 °C, or 40 °C. The feed gas flow rate is 3.5 scfm (1.7×10 -3 m 3 / s).

[0189] The feed step is initiated by starting the required air and peak gas flows into the column and sampling the gas at various sampling ports using a residual gas analyzer (Peak Performer 1 from Peak Laboratories) to detect hydrogen and carbon monoxide. The analyzer can also be used to measure the outlet carbon dioxide content (Teledyne GFC7000TU) and the dew point (Meeco Aquamatic+). Under some conditions, it was found that on the high-Cu hopcalite catalyst, carbon dioxide penetrated before hydrogen, but water was never observed in the effluent.

[0190] During operation, sampling at multiple sampling ports allows the evaluation of the breakthrough performance at different gas residence times, where the residence time is defined as the volume of the catalyst bed from the feed end to the selected sampling port divided by the volumetric feed gas flow rate evaluated at the reactor temperature and pressure.

[0191] Breakthrough curves are used to calculate the relative residence time requirements shown in Table 1 for different feed conditions in Examples 2A to 2E. The results of Example 2F are shown in Figure 7 . The results of Example 2C at different feed gas temperatures and extended to lower temperatures are shown in Figure 10 .

[0192] Example 2A 2 ppmv hydrogen

[0193] Example 2B 10 ppmv carbon monoxide

[0194] Example 2C 2 ppmv hydrogen and 10 ppmv carbon monoxide

[0195] Figure 5 The hydrogen breakthrough results for this feed gas composition and a residence time of 2.4 s in the catalyst bed are plotted.

[0196] At all test temperatures, the high-Cu hopcalite catalyst had a significantly longer hydrogen breakthrough time compared to the standard hopcalite catalyst.

[0197] During the entire experiment, carbon monoxide and water were not detected. Carbon dioxide (formed by the oxidation of carbon monoxide) was detected from the high-Cu Hopcalite catalyst rather than the standard Hopcalite catalyst.

[0198] As described in Example 2C and as Figure 6A (Cu / Mn molar ratio), Figure 6B (surface area), and Figure 6C (pore volume) were shown for different commercially available Hopcalite materials, and the optimal range of the change characteristics of the hydrogen capacity of the Hopcalite materials was determined by a breakthrough test. The surface area and pore volume were measured by N2 isotherms (Micrometrics 3Flex) at 77 K, and the Cu / Mn ratio was measured by an X-ray fluorescence spectrometer (Axios WDXRF spectrometer).

[0199] Example 2D 2 ppmv hydrogen and 400 ppmv carbon dioxide

[0200] Example 2E 2 ppmv hydrogen, 10 ppmv carbon monoxide, and a 10 ppmv hydrogen peak lasting 30 minutes

[0201] In this set of experiments, the hydrogen concentration increased from 2 ppmv to 10 ppmv approximately 210 minutes after the start of the feed step. The peak lasted for 30 minutes before the hydrogen concentration was restored to 2 ppmv.

[0202] Example 2F 2 ppmv hydrogen and 10 ppmv carbon monoxide at a regeneration temperature of 70 °C

[0203] After the feed step of the test described in Example 2C, further experiments were conducted on the standard Hopcalite agent and the high-Cu Hopcalite catalyst.

[0204] Before the feed step, the regeneration step was carried out only at 70 °C instead of 200 °C. Subsequently, the feed step was run under the same conditions as described in Example 2C, while measuring the hydrogen concentration leaving the gas bed at a residence time of 3.5 s.

[0205] Carbon monoxide was not detected in the product gas during the experiment.

[0206] Figure 4 and Figure 5 showed that the high-Cu Hopcalite catalyst had a significantly higher hydrogen capacity compared to the standard Hopcalite catalyst, enabling the high-Cu Hopcalite agent to be used for the removal of hydrogen and carbon monoxide in a gas purification cycle using low-temperature regeneration (as described in US5614000, which discloses TEPSA purification before low-temperature distillation, but not limited thereto).

[0207] Example 3 - Residual Water Loading of Standard Hopcalite and High Cu Hopcalite at Different Regeneration Temperatures

[0208] As described in Example 1 above, commercial standard hopcalite and high-Cu hopcalite were saturated with adsorbed water by sealing in a 100% RH humidified chamber overnight. Each sample was then sampled in 50 mg aliquots for residual water loading measurement in a thermogravimetric analyzer or TGA (TA Instruments Q5000IR). The TGA sample cell was purged with nitrogen, and the following heating method was used:

[0209] (i) heating at 10°C / min to the regeneration temperature;

[0210] (ii) 12 hours at the regeneration temperature;

[0211] (iii) heating to 400°C at a rate of 10°C / min; and

[0212] (iv) Dwell at 400°C for 30 min.

[0213] The regeneration temperature includes 60°C, 100°C, 150°C, 180°C, 200°C, 220°C and 250°C.

[0214] Calculate the residual water (wt%) using the following formula:

[0215] 100×(weight loss between regeneration temperature and 400°C)

[0216] (Sample weight after dwelling at 400°C)

[0217] like Figure 8 As shown, at any given regeneration temperature, the high-Cu hopcalite catalyst has less residual water than the standard hopcalite catalyst. It is known in the art that adsorbed water deactivates catalysts. Therefore, these results indicate that the high-Cu hopcalite catalyst can be regenerated at lower temperatures than the standard hopcalite catalyst.

[0218] Example 4 - Different layered arrangements of air pre-cleaning units

[0219] Air pre-purification adsorption units can be designed to remove water, carbon dioxide, hydrogen, and carbon monoxide using different adsorbents.

[0220] An air feed at a pressure of 130 psig and a temperature of 25°C may contain 1900 ppmv water, 400 ppmv carbon dioxide, 2 ppmv hydrogen, and 10 ppmv carbon monoxide. Figure 9 As shown, many possible layering configurations can achieve the removal of these impurities.

[0221] Compared to the corresponding arrangement according to the present invention, Figure 11 the arrangement exemplified in Figure 1 EP2789376A is shown (wherein a standard Hopcalite catalyst (Carulite 300) is used as a single layer at the product end of the bed to remove hydrogen and carbon monoxide). In this regard, by using a high-Cu Hopcalite catalyst, divided into two layers, less catalyst is required to reduce hydrogen and carbon monoxide impurities to below 0.1 ppmv respectively. Alumina and 13X can be used in any configuration to reduce water and carbon dioxide to below 1 ppmv in the product gas (i.e., purified air).

[0222] Such an adsorption unit can operate cyclically, where before cooling the adsorption bed and repressurizing the unit back to the feed conditions to start another operating cycle, the purge gas extracted from the downstream cryogenic distillation process can be used to regenerate the material in the adsorption unit at ambient pressure and a temperature of 200 °C.

[0223] The feed air can also be cooled by the device to a temperature in the range of 10 °C to 15 °C to achieve further advantages resulting from the use of the high-Cu Hopcalite catalyst. At a lower feed temperature, the overall size of the adsorption unit can be reduced because the colder air contains less water vapor and thus requires less alumina. In addition, the adsorption capacity of alumina and 13X for water and carbon dioxide will increase at lower temperatures. However, although the demand for the Hopcalite catalyst will increase at colder temperatures, the increase in demand for the high-Cu Hopcalite catalyst will be less than that for the standard Hopcalite catalyst, as Figure 11 shown.

[0224] Regarding the embodiment of the present invention according to Figure 11 the most practical arrangement is usually to have a layer of water-absorbing material (e.g., alumina) at the front end of the bed.

[0225] The next step can be to use a first layer of Hopcalite catalyst to remove trace carbon monoxide. This layer can be a standard Hopcalite catalyst or a high-Cu Hopcalite catalyst. If a high-Cu Hopcalite catalyst is used, a reasonable amount of residence time can also be used to remove at least substantially all of the trace hydrogen (see Table 1). The advantage of using a high-Cu Hopcalite catalyst at this position (immediately after the alumina layer) is that it is closer to the temperature increase caused by water adsorption on the alumina, where the higher the temperature, the greater the capacity of the catalyst layer ( Figure 5 ). Due to the sensitivity of Hopcalite to carbon dioxide, the standard Hopcalite cannot be placed immediately after the alumina layer (see EP2789376A).

[0226] Hopcalite catalysts with a lower surface area will have a lower carbon dioxide capacity. The lower surface area of the high-Cu Hopcalite catalyst requires the presence of a carbon monoxide oxidation layer upstream of the carbon dioxide removal layer. If carbon monoxide is still present in the inlet gas, the low-surface-area Hopcalite agent cannot be the last layer, otherwise the carbon dioxide produced by carbon monoxide oxidation will ultimately enter the product stream. Therefore, the next layer is typically a layer of carbon dioxide adsorbent material (e.g., 13X).

[0227] In embodiments where there is a relatively large amount of hydrogen, carbon monoxide, and / or carbon dioxide in the inlet gas, the second layer of high-Cu Hopcalite catalyst can be used as the final purification layer.

[0228] As taught in EP2789376A, a standard Hopcalite catalyst must be placed after a layer for removing water and a layer for removing carbon dioxide, because these impurities will poison the Hopcalite catalyst and significantly reduce its effectiveness for the oxidation of hydrogen and carbon dioxide.

[0229] Conversely, the high-Cu Hopcalite catalyst is less sensitive to carbon dioxide. Without wishing to be bound by any particular theory, the inventors attribute this insensitivity to (a) a higher Cu / Mn ratio resulting in higher hydrogen activity, and (b) a relatively low surface area and a higher CuO content reducing the material's affinity for water, which typically poisons the activity of the Hopcalite agent. Although the carbon monoxide removal efficiency is lower than that of the standard Hopcalite agent, compared to simply using the standard Hopcalite agent, those skilled in the art can design a front-end adsorption unit using less overall catalyst (see Table 1).

[0230] Table 1 provides details of the relative contact times required, showing how the high-Cu Hopcalite catalyst reduces the amount of residence time required compared to the standard Hopcalite agent for different impurities in the inlet gas.

[0231] Using a "high copper" or "high-Cu" Hopcalite catalyst to remove hydrogen impurities enables shortening the catalyst bed length, reducing the investment cost (less container steel), and reducing the operating cost (lower pressure drop / power and regeneration energy).

[0232] Additional advantages of using a high-Cu Hopcalite catalyst to remove trace hydrogen from dry gases such as dry air compared to the standard Hopcalite catalyst include:

[0233] · Increasing the hydrogen capacity (and thus increasing the operating time) at ambient temperature (see Figure 4 and Figure 5 ) and at temperatures below (e.g., at 14 °C) (see Figure 5 )

[0234] ·Reduced sensitivity to the presence of carbon dioxide (see Example 2D, Table 1), and reduced sensitivity to the peak hydrogen feed concentration (see Example 2E)

[0235] ·Easier to regenerate (Figure 6 and Figure 7 ), resulting in less energy required in the TSA system. TSA versions that use less regeneration heat, such as the temperature swing pressure swing adsorption (TPSA) cycle (see, for example, US5855650), may be more readily achievable

[0236] ·Due to the reduced regeneration temperature required, Hopcalite is used to remove trace hydrogen in a wider range of air pre-purification cycles, with the range extended to include the thermally enhanced pressure swing adsorption (TEPSA) cycle (e.g., see US5614000) or the pressure swing adsorption (PSA) cycle. In cases where noble metal catalysts are used in the prior art to remove trace hydrogen (e.g., see US5202096 or US5906675), in TEPSA or PSA, the high-Cu Hopcalite catalyst will be cheaper than the noble metal catalyst

[0237] These advantages enable a more flexible configuration of the air pre-purification system for high-purity nitrogen( Figure 9 ). Purifiers using high-copper Hopcalite catalysts require less catalyst, especially in cases where there are larger amounts of hydrogen impurities in the inlet gas. For example, this is useful when retrofitting existing plants that unexpectedly generate more hydrogen impurities in the feed from new industrial facilities during nearby operations

[0238] Although the present invention has been described with reference to the preferred embodiments depicted in the accompanying drawings, it should be understood that the present invention is not limited to the details described above with reference to the preferred embodiments, but many changes and variations can be made without departing from the spirit and scope of the present invention as defined in the following claims

[0239] In this specification, unless otherwise expressly stated, the word "or" is used to indicate an operator that returns a true value when either or both of the stated conditions are satisfied. In contrast, the operator "exclusive or" requires only one of the conditions to be satisfied. The word "comprising" is used to mean "including" rather than "consisting of"

[0240] All of the foregoing prior teachings are incorporated herein by reference. The acknowledgement of any prior published document herein should not be taken as an admission or indication that its teachings are common general knowledge in Australia or elsewhere where it was published

[0241] Non-limiting embodiments of the present disclosure include the following

[0242] Item 1. A method for removing hydrogen from dry gas including hydrogen as an impurity, the method comprising passing the dry gas through at least one layer of a first Hopcalite catalyst at a temperature of about 0 °C to about 60 °C to produce a product gas that is at least substantially free of hydrogen, wherein the copper to manganese molar ratio of the first Hopcalite catalyst is greater than 0.55.

[0243] Item 2. The method according to Item 1, wherein the copper to manganese molar ratio in the first Hopcalite catalyst is less than 7.

[0244] Item 3. The method according to Item 1, wherein the copper to manganese molar ratio in the first Hopcalite catalyst is in the range of about 0.6 to 4.

[0245] Item 4. The method according to Item 1, wherein the copper to manganese molar ratio in the first Hopcalite catalyst is in the range of about 2 to about 4.

[0246] Item 5. The method according to Item 1, wherein the copper to manganese molar ratio in the first Hopcalite catalyst is in the range of about 0.6 to about 1.2.

[0247] Item 6. The method according to Item 1, wherein the surface area of the first Hopcalite catalyst is less than 280 m 2 / g.

[0248] Item 7. The method according to Item 1, wherein the surface area of the first Hopcalite catalyst is in the range of about 100 m 2 / g to about 200 m 2 / g.

[0249] Item 8. The method according to Item 1, wherein the total pore volume of the first Hopcalite catalyst is less than 0.4 cm 3 / g.

[0250] Item 9. The method according to Item 1, wherein the total pore volume of the first Hopcalite catalyst is in the range of about 0.1 cm 3 / g to about 0.3 cm 3 / g.

[0251] Item 10. The method according to Item 1, wherein the hydrogen impurity is present in the dry gas in an amount of at most 40 ppmv.

[0252] Item 11. The method according to Item 1, wherein the hydrogen impurity is present in the dry gas in an amount exceeding 20 ppmv.

[0253] Item 12. The method according to Item 1, wherein the dry gas includes carbon dioxide in an amount of at most 900 ppmv.

[0254] Item 13. The method as described in Item 1, wherein the first Hopcalite catalyst layer is regenerated at a temperature below 200 °C.

[0255] Item 14. The method as described in Item 1, wherein the first Hopcalite catalyst layer is regenerated at a temperature not exceeding 150 °C.

[0256] Item 15. The method as described in Item 1, wherein the first Hopcalite catalyst layer is regenerated at a temperature not exceeding 80 °C.

[0257] Item 16. The method as described in Item 1, wherein the temperature of the dry gas ranges from about 10 °C to about 15 °C.

[0258] Item 17. The method as described in Item 1, wherein the dry gas passes through at least one layer of the first Hopcalite catalyst at a pressure ranging from about 3 bar to about 45 bar (0.3 Mpa to 4.5 Mpa).

[0259] Item 18. The method as described in Item 1, the method comprising passing the dry gas through at least one layer of a second Hopcalite catalyst upstream of the first Hopcalite catalyst layer, wherein the copper to manganese molar ratio of the second Hopcalite catalyst does not exceed 0.55.

[0260] Item 19. A method for removing hydrogen from dry gas comprising the hydrogen as an impurity, the method comprising passing the dry air through at least one layer of a first Hopcalite catalyst at a pressure of about 3 bar to about 45 bar (0.3 MPa to 4.5 MPa) and a temperature of about 0 °C to about 60 °C to produce dry air that is at least substantially free of hydrogen, wherein the copper to manganese molar ratio of the first Hopcalite catalyst ranges from about 2 to about 4.

[0261] Item 20. A method for removing the hydrogen and the carbon monoxide from dry air comprising hydrogen and carbon monoxide as impurities, the method comprising passing the dry air through at least one layer of a first Hopcalite catalyst at a pressure of about 3 bar to about 45 bar (0.3 MPa to 4.5 MPa) and a temperature of about 0 °C to about 60 °C to produce dry air that is at least substantially free of hydrogen and carbon monoxide, wherein the copper to manganese molar ratio of the first Hopcalite catalyst ranges from about 0.6 to about 1.2.

Claims

1. A method for removing hydrogen from dry gas including hydrogen as an impurity, the method comprising passing the dry gas through at least one layer of a first Hopcalite catalyst at a temperature of 0 °C to 60 °C to produce a product gas substantially free of hydrogen, wherein the copper to manganese molar ratio of the first Hopcalite catalyst is in the range of 0.8 - 7.

2. The method according to claim 1, wherein the copper to manganese molar ratio in the first Hopcalite catalyst is in the range of 0.8 - 4.

3. The method according to claim 1, wherein the copper to manganese molar ratio in the first Hopcalite catalyst is in the range of 2 to 4.

4. The method according to claim 1, wherein the copper to manganese molar ratio in the first Hopcalite catalyst is in the range of 0.8 to 1.

2.

5. The method according to claim 1, wherein the surface area of the first Hopcalite catalyst is less than 280 m 2 / g.

6. The method according to claim 1, wherein the surface area of the first Hopcalite catalyst is in the range of 100 m 2 / g to 200 m 2 / g.

7. The method according to claim 1, wherein the total void volume of the first Hopcalite catalyst is less than 0.4 cm 3 / g.

8. The method according to claim 1, wherein the total void volume of the first Hopcalite catalyst is in the range of 0.1 cm 3 / g to 0.3 cm 3 / g.

9. The method according to claim 1, wherein the hydrogen impurity is present in the dry gas in an amount of up to 40 ppmv.

10. The method according to claim 9, wherein the hydrogen impurity is present in the dry gas in an amount exceeding 20 ppmv.

11. The method according to claim 1, wherein the dry gas includes up to 900 ppmv of carbon dioxide.

12. The method according to claim 1, wherein the first Hopcalite catalyst layer is regenerated at a temperature below 200 °C.

13. The method according to claim 1, wherein the first Hopcalite catalyst layer is regenerated at a temperature not exceeding 150 °C.

14. The method according to claim 1, wherein the first Hopcalite catalyst layer is regenerated at a temperature not exceeding 80 °C.

15. The method according to claim 1, wherein the temperature of the dry gas is in the range of 10 °C to 15 °C.

16. The method according to claim 1, wherein the dry gas passes through the first Hopcalite catalyst layer at a pressure in the range of 3 bar to 45 bar.

17. The method according to claim 1, the method comprising passing the dry gas through at least one layer of a second Hopcalite catalyst upstream of the first Hopcalite catalyst layer, wherein the copper to manganese molar ratio of the second Hopcalite catalyst does not exceed 0.

55.

18. A method for removing hydrogen from dry air including hydrogen as an impurity, the method comprising passing the dry air through at least one layer of a first Hopcalite catalyst at a pressure of 3 bar to 45 bar and a temperature of 0 °C to 60 °C to produce dry air substantially free of hydrogen, wherein the copper to manganese molar ratio of the first Hopcalite catalyst is in the range of 2 to 4.

19. A method for removing the hydrogen and carbon monoxide from dry air including hydrogen and carbon monoxide as impurities, the method comprising passing the dry air through at least one layer of a first Hopcalite catalyst at a pressure of 3 bar to 45 bar and a temperature of 0 °C to 60 °C to produce dry air substantially free of hydrogen and carbon monoxide, wherein the copper to manganese molar ratio of the first Hopcalite catalyst is in the range of 0.8 to 1.2.

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