Removal of hydrogen impurity from gas streams

Abstract

A process for removing hydrogen from a dry gas comprising hydrogen as an impurity using at least one layer comprising, e.g., consisting of, hopcalite is improved where the hopcalite has a zero-point-of-charge (ZPC) in a range from about 6.9 to about 7.7 and / or an ionic conductivity as a 10 wt % slurry in deionized water of no more than about 500 µS / cm.

Description

REMOVAL OF HYDROGEN IMPURITY FROM GAS STREAMSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from U.S. Non-Provisional Application No. 63 / 593083 filed on 25 October 2023.BACKGROUND OF THE INVENTION

[0002] The present invention relates generally to the removal of hydrogen (H2) as an impurity from gas streams, typically together with the removal of carbon monoxide (CO) as a further impurity in the gas streams. In particular, the invention relates to the removal of these impurities from air. The invention has particular application in the production of high purity (HP) and ultra-high purity (UHP) nitrogen (N2) gas.

[0003] The invention involves the use of a hopcalite material. The term "hopcalite" is a generic term for a range of materials or catalysts, typically comprising primarily a mixture of copper oxide and manganese oxide. Hopcalite catalysts have been known and used since at least 1920 (see, for example, US1345323) to oxidize carbon monoxide to form carbon dioxide.

[0004] Typical hopcalites used for oxidation of carbon monoxide have a molar ratio of copper to manganese of 0.45 to 0.55, e.g., about 0.5, with a surface area (N2BET at 77K) of more than 250 m2 / g, e.g., from 280 m2 / g to 320 m2 / g, and a total pore volume from 0.4 to 0.5 cm3 / g. Such hopcalite catalysts may be referred to as "standard" hopcalite catalysts and, by way of example, include Carulite® 300 (Carus Corporation).

[0005] More recently, hopcalites having various copper / manganese (Cu / Mn) ratios has been used in air pre-purifiers to remove trace hydrogen and carbon monoxide from air to make UHP nitrogen gas in cryogenic air separation plants.

[0006] By way of example, in EP2789376A, a standard hopcalite catalyst is used to simultaneously (i) oxidize carbon monoxide to carbon dioxide; (ii) chemisorb hydrogen; and (iii) oxidize hydrogen to form water, in addition to adsorbing the resultant carbon dioxide and water so produced. At the relevant time, while it was already known for carbon monoxide oxidation, hopcalite was not known for the simultaneous removal of hydrogen. Indeed, based on the state of the art then, it was entirely unexpected that hydrogen would be removed by an adsorption mechanism because, as determined by the Inventors in that case, the effect is masked by carbon dioxide in the feed gas. Indeed, the Inventors identified that, for hydrogenadsorption to be observed, the dry gas feed must be substantially free of carbon dioxide and that there must be sufficient residence time in the catalyst layer.

[0007] In addition, EP3991826A and US11173451 B disclose that the hydrogen capacity of a hopcalite catalyst increases as the Cu / Mn molar ratio increases from about 0.5 and peaks as the Cu / Mn ratio reaches about 3. In contrast, the capacity of hopcalite for carbon monoxide tends to reduce as the Cu / Mn molar ratio increases beyond about 0.5. On this basis, it was determined that hopcalite catalysts having a molar ratio in a range from about 0.6 to about 4 may be used in applications where the focus is for removing trace hydrogen rather than trace carbon monoxide, whereas hopcalite catalysts having a molar ratio in a range from about 0.6 to 1.2 tend to strike an acceptable balance between gain in hydrogen capacity and loss of carbon monoxide capacity and, on this basis, such catalysts would be expected to be particularly suitable for use in catalyst layers where the focus is on removing both trace hydrogen and trace carbon monoxide.

[0008] The Inventors in EP3991826A and LIS11173451 B noted that the high Cu hopcalite catalysts are less sensitive to the presence of carbon dioxide in the dry gas than standard hopcalite catalysts. Thus, the feed gas to a high Cu hopcalite catalyst layer may contain significantly more carbon dioxide than the 10 ppmv maximum threshold disclosed in EP2789376A.

[0009] As disclosed in FR1329522A, hopcalite catalysts may be prepared by combining soluble precursors, such as copper nitrate, manganese nitrate, and sodium carbonate, to form an insoluble precipitate which is then washed thoroughly prior to any calcination and forming steps to remove any unreacted soluble components, such as sodium carbonate.

[0010] Previous work has shown variation in the carbon monoxide oxidation activity of hopcalite depending on the surface content of residual sodium cations (see Mirzaei et al., Catalysis Comm., 4, pp 17-20, 2003). In this regard, lower levels of sodium cations on the surface increases this activity until the level was less than 0.1 Na / Mn ratio where the activity leveled off. In contrast, Guo et al. (RSC Adv., 6, pp 7181-7188, 2016) discloses that adding potassium hydroxide (KOH), which increases the surface zero-point-of-charge (ZPC), improves carbon monoxide oxidation activity in the presence of 1 mol. % carbon dioxide.

[0011] As far as the Inventors are aware, no work has been carried out to date to investigate the influence of residual trace soluble components, such as carbonates, on the hydrogen capacity and hydrogen oxidation activity of hopcalites which is understood to not necessarily be correlated with carbon monoxide oxidation.

[0012] The Inventors note that trace soluble acid components may also be present on hopcalites, for example from incomplete neutralization of soluble metal precursors during precipitation of a hopcalite precursor which is subsequently calcined to prepare the hopcalite or could be added in trace levels during a forming step (see, for example, US3393156 or Jiang et al, Fuel, 301 , pp 121049, 2021). The impact of these trace acid impurities on hydrogen uptake performance is also not disclosed in the art.

[0013] There is a need for new hopcalites having improved reliability and performance, in particular having improved hydrogen adsorption capacities and / or improved activities for hydrogen oxidation, and for new processes for removing trace hydrogen from gas streams, particularly air.SUMMARY OF THE INVENTION

[0014] The Inventors have determined that the presence of residual soluble precursors / components, such as sodium carbonate, on hopcalites decreases the hydrogen oxidation performance of the hopcalites, and that removal of these precursors / components improves performance. Specifically, the Inventors have determined that hopcalites having a zero-point-of-charge (ZPC) and / or ionic conductivity within particular defined ranges have improved reliability and activity for hydrogen oxidation and removal.

[0015] Thus, according to a first aspect of the present invention, there is provided a process for removing hydrogen from a dry gas comprising hydrogen as an impurity, said process comprising passing said dry gas though at least one layer comprising, e.g., consisting of, a hopcalite to produce product gas that is at least substantially free of hydrogen, wherein said hopcalite has a ZPC in a range from about 6.9 to about 7.7 and / or an ionic conductivity as a 10 wt % slurry in deionized water of no more than about 500 micro-Siemens per centimeter (pS / cm).

[0016] The Inventors note that, during the initial precipitation of hydrous copper oxide and manganese oxide mixtures following neutralization of soluble copper and manganese precursors, soluble ionic byproducts are generated or are present in excess and must be washed away. These can include excess bicarbonate or carbonate as well as soluble conjugate base salts coming from the copper and manganese precursors. Depending on the final pH during neutralization or forming, traces of acidic Cu(ll) or Mn(ll) or basic Cu(OH)3‘ could remain or be formed as water soluble ionic impurities. The Pourbaix diagrams for copper and manganese depicted in FIG. 2 show the potential for residual Cu2+and Mn2+to be formed even at near neutral pH values.

[0017] According to a second aspect of the present invention, there is provided a hopcalite comprising a mixture of copper oxide and manganese oxide and having a ZPC in a range from about 6.9 to about 7.7, e.g., in a range from about 7 to about 7.4, and / or an ionic conductivity as a 10 wt % slurry in deionized water of no more than about 500 pS / cm, e.g., no more than about 450 pS / cm or no more than about 410 pS / cm.

[0018] According to a third aspect of the present invention, there is provided an adsorption unit for purifying a gas comprising at least hydrogen as an impurity, the unit comprising an adsorbent bed having a feed end with a gas inlet and a product end opposite the feed end with a gas outlet, the adsorbent bed comprising at least one layer comprising, e.g., consisting of, a hopcalite according to the second aspect.

[0019] According to a fourth aspect of the present invention, there is provided a process for increasing hydrogen adsorption capacity of a hopcalite after calcination, said process comprising washing said hopcalite with deionized water, for example until the hopcalite has a ZPC in a range from about 6.9 to about 7.7, e.g., in a range from about 7 to about 7.4, and / or an ionic conductivity as a 10 wt % slurry in deionized water of no more than about 500 pS / cm, e.g., no more than about 450 pS / cm or no more than about 410 pS / cm.

[0020] According to a fifth aspect of the present invention, there is provided use of a hopcalite according to the second aspect to remove hydrogen as an impurity from a dry gas comprising the impurity.BRIEF DESCRIPTION OF DRAWINGS

[0021] FIG. 1 is a simplified flowsheet for an embodiment of the first aspect of the present invention involving a TSA unit for air purification in which the adsorbent bed has three layers including one layer of a hopcalite catalyst according to the second aspect.

[0022] FIG. 2 depicts Pourbaix diagrams for copper and manganese in water.

[0023] FIG. 3 is a graph that plots the hydrogen uptake (mmol / g) against ZPC for the hopcalite samples exemplified herein.

[0024] FIG. 4 is a graph that plots the hydrogen uptake (mmol / g) against conductivity (pS / cm) for the hopcalite samples exemplified herein.DETAILED DESCRIPTION OF THE INVENTION

[0025] The invention will now be described with reference to the specific non-limiting embodiments depicted in the figures and exemplified below.

[0026] The term "zero-point-of charge" (or ZPC) refers to a point on a surface where the net charge of variable charge components is zero due to the total charge of any residual cations adsorbed on the surface being cancelled out by the total charge of any residual anions adsorbed on the surface. The ZPC value is dimensionless and is used to define the surface pH of a material.

[0027] The term "hydrogen adsorption capacity" refers to the capacity of a material (in this case, hopcalite) to adsorb not only hydrogen but also any water that is generated by oxidation of the adsorbed hydrogen.

[0028] The term "ppmv" refers to parts per million volume. The term "ppbv" refers to parts per billion volume. Both ppmv and ppbv are calculated on a molar basis unless otherwise stated.

[0029] As indicated above, in the first aspect invention concerns a process for removing hydrogen gas (H2) from a dry gas comprising hydrogen gas as an impurity. The process comprising passing the dry gas though at least one layer comprising, e.g., consisting of, a hopcalite to produce product gas that is at least substantially free of hydrogen.

[0030] The Inventors have discovered that hydrogen uptake is improved when the hopcalite has a ZPC in a range from about 6.9 to about 7.7, and preferably in a range about 7 to about 7.4.

[0031] The Inventors have also demonstrated that hydrogen uptake is improved when the ionic conductivity of the hopcalite in the form of a 10 wt % slurry in deionized water is no more than about 500 pS / cm, e.g., no more about 450 pS / cm or no more than 410 pS / cm. The hopcalite in this form may have an ionic conductivity approaching 0 pS / cm, e.g., 0.1 pS / cm or 1 pS / cm. However, in most embodiments, the hopcalite may have a practical lower limit of ionic conductivity of no less than 100 pS / cm, or no less than about 50 pS / cm. A suitable hopcalite may have an ionic conductivity in the form of a 10 wt % slurry in deionized water in a range from about 50 pS / cm to about 500 pS / cm.

[0032] Deionized (or DI) water used to form the 10 wt % aqueous slurry may be Type III Purified Water (which has an ionic conductivity from 1 to 50 pS / cm) but is preferably deionized water having an ionic conductivity of less than 1 pS / cm. Typically, the deionized water is eitherType II Pure Water (which has an ionic conductivity of 1.0 to 0.1 pS / cm) or Type I Ultra-Pure Water (which has an ionic conductivity of 0.01 to 0.0555 pS / cm).

[0033] Typically, the hopcalite comprises less than 0.5 wt %, preferably less than 0.4 wt %, e.g., less than 0.25 wt % or less than 0.1 wt %, residual soluble components including, e.g., sodium carbonate.

[0034] The hopcalite may be a "standard" hopcalite catalyst as described above. Thus, the hopcalite may have a Cu / Mn molar ratio in a range from about 0.45 to about 0.55, e.g., about 0.5, with a surface area (N2BET at 77K) of more than 250 m2 / g, e.g., from 280 m2 / g to 320 m2 / g, and a total pore volume from 0.4 to 0.5 cm3 / g. An example of such a catalyst is Carulite® 300 (Carus Corporation).

[0035] In preferred embodiments, however, the hopcalite is a "high copper" or "high Cu" hopcalite, i.e., has a higher Cu / Mn molar ratio than standard hopcalites. In this regard, the hopcalite may have a molar ratio of copper to manganese of more than about 0.55, e.g., 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. In these embodiments, the molar Cu / Mn ratio is typically no more than 7, e.g., no more than 6 or no more than 5. Preferably, the molar ratio of copper to manganese in the hopcalite is in a range from about 0.6 to about 4, e.g., from about 0.6 to about 3 or from about 1 to about 4.

[0036] In some embodiments, the molar ratio of copper to manganese in the hopcalite is in a range from about 1 to about 5, such as from about 2 to about 4, e.g., from about 2.5 to about 3.5. The Inventors expect that such hopcalite would be particularly suitable for removing trace hydrogen rather than trace carbon monoxide.

[0037] In other embodiments, the molar ratio of copper to manganese in the hopcalite is in a range from about 0.6 to about 1.2, e.g., 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 expect that such hopcalite would be particularly suitable for removing both trace hydrogen and trace carbon dioxide.

[0038] The dry gas may be passed through one or more layers of the hopcalite to remove both hydrogen and carbon monoxide impurities.

[0039] In some embodiments, trace hydrogen and trace carbon monoxide may be removed by passing the dry gas across a single layer of the hopcalite according to this invention. In such embodiments, the Cu / Mn molar ratio of the hopcalite may be in the range from about 0.6 to about 3, such as from about 0.6 to about 1 .2, e.g., from about 0.8 to about 1.2 or from about0.9 to about 1.2 or from about 0.9 to about 1. Another suitable range for the Cu / Mn molar ratio may be from about 1 to about 3, such as from about 1 to about 1.2.

[0040] In other embodiments, trace hydrogen and trace carbon monoxide may be removed in primarily in separate layers of hopcalite. For example, trace carbon monoxide may be removed by passing the dry gas across at least one layer of either a standard hopcalite or a high Cu hopcalite or a mixture thereof, and trace hydrogen may be removed by passing the dry gas across at least one layer of a hopcalite, e.g., a high Cu hopcalite.

[0041] In such embodiments, the Cu / Mn molar ratio of the high Cu hopcalite used to remove trace carbon monoxide may be in the range from about 0.6 to about 3, such as from about 0.6 to about 1.2, e.g., 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. Additionally or alternatively, the Cu / Mn molar ratio of the high Cu hopcalite used to remove trace hydrogen may be in the range from about 0.6 to about 4, such as from about 2 to about 4, e.g., from about 2.5 to about 3.5.

[0042] In embodiments involving at least two layers of hopcalite, a layer of carbon dioxide adsorbent material may be provided between adjacent layers comprising, e.g., consisting of, the hopcalite(s).

[0043] Without wishing to be bound by any particular theory, the Inventors believe that a high Cu hopcalite is less affected by carbon dioxide because the surface area of the catalyst is less than the surface area of a standard hopcalite. Thus, the high Cu hopcalite preferably has a surface area of less than 280 m2 / g, such as no more than 250 m2 / g, e.g., in a range from about 100 m2 / g to about 250 cm2 / g or in a range from about 150 m2 / g to about 250 m2 / g, or no more than 200 m2 / g, e.g., in a range from about 100 m2 / g to about 200 m2 / g, or about 150 m2 / g.

[0044] Preferred high Cu hopcalites typically have a total pore volume of less than 0.4 cm3 / g. In preferred embodiments, the hopcalite catalyst has a total pore volume in a range from about 0.1 cm3 / g to about 0.3 cm3 / g, e.g., in a range from about 0.2 cm3 / g to about 0.3 cm3 / g.

[0045] The bulk density of suitable high Cu hopcalites may be at least about 0.7 g / cm3, e.g. in a range from about 0.8 g / cm3to about 1 g / cm3.

[0046] The layer(s) of hopcalite may be regenerated at a temperature of about 180°C or higher. However, in embodiments using high Cu hopcalites, the hopcalite may be regenerated at a temperature of no more than about 150°C or no more than 100°C, e.g., from about 50°C to about 100°C.

[0047] The dry gas is typically at a temperature in a range from about 0°C to about 60°C, e.g., in a range from about 10°C to about 40°C, or in a range from about 15°C to about 30°C.

[0048] The dry gas is typically passed through the layer(s) of the hopcalite at a pressure in a range from about 3 bar to about 45 bar (0.3 MPa to 4.5 MPa), e.g., in a range from about 3 bar to about 30 bar (0.3 MPa to 3.0 MPa).

[0049] The hydrogen impurity is typically present in the dry gas in an amount of up to about 80 ppmv, e.g., in a range from about 20 ppmv to about 40 ppmv.

[0050] The dry gas typically comprises carbon dioxide in an amount of up to about 900 ppmv, e.g., in a range from about 10 ppmv to 600 ppmv.

[0051] The dry gas typically comprises no more than 10 ppmv, preferably no more than 1 ppmv, water. This means that a hopcalite layer in an adsorption unit such as a TSA unit is typically be placed downstream of water and carbon dioxide removal layer(s).

[0052] The residence time of the dry gas in the layer(s) of hopcalite according to the present invention is typically more than 1.2 seconds (or "s"), e.g., at least 1.5 s or at least 2 s.

[0053] The dry gas is typically air although the invention may be applied to the removal of hydrogen impurity from other dry gases such as nitrogen.

[0054] The product gas may comprise no more than 1 ppmv hydrogen, e.g., no more than 50 ppbv hydrogen or no more than 10 ppbv hydrogen. A practical minimum limit for the amount of hydrogen in the product gas may be 1 ppbv.

[0055] In its broadest sense, the process for increasing hydrogen adsorption capacity of a hopcalite after calcination comprises washing the hopcalite with deionized water. The hopcalite may be washed in any suitable way. However, in preferred embodiments, the washing involves the steps of (a) soaking the hopcalite in deionized water; (b) after soaking, removing the hopcalite from the deionized water; and (c) drying the hopcalite. Typically, at least steps (a) and (b), e.g., steps (a) to (c), are repeated at least once, e.g., two, or three or more times.

[0056] The deionized water preferably has a conductivity of less than 1 pS / cm and may be either Type II Pure Water or Type I Ultra-Pure Water discussed above. Additionally or alternatively, the deionized water is at a temperature in a range from about 20°C to about 80°C, e.g., at about room temperature or about 20°C to about 25°C.

[0057] The hopcalite is typically soaked for at least 10 mins, e.g., about 30 mins, after optional agitation, e.g., by stirring. Agitation may take place more than once, e.g., every 10 min.

[0058] The hopcalite may be removed from the deionized water by suitable means although filtration is preferred. Any form of filtration may be used but vacuum filtration is preferred.

[0059] The hopcalite may be dried between washings in an oven, for example at a temperature in a range from about 90°C to about 110°C for perhaps at least 6 h, e.g., from 6 h to 12 h or overnight.

[0060] After washing, a final calcination step to no more than 325°C is typically performed to fully remove water and activate the sample. This step is usually done after a final forming step.

[0061] According to FIG. 1 , a stream 10 of air is compressed to an elevated pressure from 3 bar to 25 bar (0.3 to 2.5 MPa) in a main air compressor 12. The compressed stream is cooled in cooler 14 and a portion of the water in the air stream is condensed and separated from the gas and discharged through valve 16. A stream 17 of cooled, partially dried air at a temperature of 5 to 60°C is then passed to vessel 24 via valve 20. Vessels 24 and 26 are each packed with identical layers of adsorbent and catalyst.

[0062] Within the vessels, the feed air passes to a first layer (24a or 26a) of water adsorbent which dries the feed air. This layer can also remove a portion of the carbon dioxide in the feed gas due to co-adsorption of carbon dioxide with water. This layer typically consists of alumina, base-promoted alumina, or silica gel.

[0063] The dried feed air then passes to a second layer (24b or 26b) where carbon dioxide is removed to a level of 10 ppmv or less. This layer consists of a zeolitic adsorbent such as NaX, NaMSX, NaLSX or CaX.

[0064] The dried, carbon dioxide-free air is then passed to a layer (24c or 26c) of high Cu hopcalite where not only is carbon monoxide oxidized to carbon dioxide but also hydrogen is chemisorbed and reacted to form water. The resultant trace level of carbon dioxide and any water produced from these reactions are adsorbed onto the hopcalite.

[0065] Air flow continues for a predetermined period of time, and the various layers are sized so that water, carbon dioxide, carbon monoxide, and hydrogen are retained in the bed and a stream of purified air (containing no more than 0.5 ppmv water, no more than 1 ppmv carbon dioxide, no more than 500 ppbv carbon monoxide, and no more than 500 ppbv hydrogen)exits the vessel 24. This purified air passes through valve 36 and is directed as stream 40 to a cryogenic distillation system (not shown) where UHP nitrogen is produced.

[0066] Vessel 26 is subjected to thermal regeneration steps while vessel 24 is processing the feed stream. Regeneration desorbs water from layer 26a and carbon dioxide from layer 26b. In addition, thermal regeneration of the hopcalite catalyst in layer 26c restores the hydrogen chemisorption capacity of the material. Thermal regeneration may be conducted at a temperature of at least 60 °C, more preferably at least 150°C, for example at about 180°C, in order to drive chemisorbed hydrogen / water from the catalyst.

[0067] Regeneration is conducted by heating a stream 47 of dry, carbon dioxide-free purge gas through heater 52 to produce a stream 48 of warm purge gas which is fed to vessel 26 via manifold 42 and valve 46. The purge gas can be taken as a portion of the product gas 40 or from waste gas from the cryogenic distillation unit. The warm purge gas passes through layers 26c, 26b, and 26a of vessel 26, thereby regenerating the catalyst and adsorbent. The effluent gas from bed 26 passes through valve 32 and manifold 28 before being vented from the process as stream 34. Once the layers have been sufficiently warmed and regenerated, the bed is cooled by turning off or by-passing heater 52 so that cool purge gas at a temperature from 10 to 60°C flows through the bed.

[0068] The feed and regeneration steps are conducted as described for a predetermined period of time, after which the functions of vessels 24 and 26 are switched so vessel 26 comes "on-line" and accepts feed gas, and vessel 24 goes "off-line" and is regenerated. The vessels alternate between feed and regeneration to maintain constant production of purified air.

[0069] Those familiar with the art will realize that the regeneration step can be conducted in different ways to help improve the efficiency of the process. The bed undergoing regeneration can first be depressurized to essentially atmospheric pressure via valves 30 or 32 and vent 34, and the heating and cooling step can be conducted at the lower pressure. The warm purge fluid can be fed to the vessel until the entire vessel reaches the higher regeneration temperature, and then the cooling gas flow can be started. This is known in the art as a TSA cycle. However, in preferred embodiments, only a portion of the warm purge gas needed to heat the entire contents of the vessel is used before starting the cooling step. This generates a heat pulse that sequentially passes through all the layers of catalyst and adsorbent, and the energy content of the pulse decreases as it passes to the feed side of the vessel, known in the art as TPSA or TEPSA cycles (due to heat loss and providing energy for water and carbon dioxide desorption).

[0070] FIG. 1 illustrates a two-bed TSA process, but systems utilizing three or more vessels are also possible.

[0071] In other embodiments, there may be an additional adsorbent layer (not shown) is added after the catalyst layer 24c, 26c. Although the hopcalite has a significant capacity for carbon dioxide adsorption, the capacity is finite. It is therefore possible that breakthrough of carbon dioxide formed from carbon monoxide oxidation in the catalyst would limit the time during which the system illustrated in Fig. 1 is on-line. In that case, a longer on-line time can be achieved by adding a short layer of carbon dioxide adsorbent after the hopcalite layer. This layer may consist of a zeolitic adsorbent such as 13X, CaX, or NaLSX.

[0072] Different arrangements of adsorbents / layers within the adsorbent bed are possible such as those arrangements disclosed in FIG. 9 of EP3991826A or LIS11173451 B in which the layer(s) of high Cu hopcalite are hopcalites according to the second aspect of the present invention. The teaching of both EP3991826A and LIS11173451 B is incorporated herein by reference.

[0073] The present invention will now be exemplified in the following examples.

[0074] EXAMPLES

[0075] Samples of three different commercial hopcalite catalysts, known to have different hydrogen removal performance, were tested. All three samples are in the form of 3 mm diameter extrudates having a Cu / Mn ratio in a range from 0.9 to 1 ; a bulk density in a range from 0.8 to 1 g / cm3; a surface area of about 150 m2 / kg; and a total pore volume in a range from 0.2 to 0.3 cm3 / g. Of the three, the best and worst performing samples were thoroughly washed with deionized water and retested after activation by heating to about 200°C under vacuum.

[0076] Hopcalite washing was performed via a serial washing method. First, the hopcalite samples were submerged in a 2: 1 w / w (water to hopcalite) bath of deionized water. Deionized water conductivity was taken prior to use in washings, and values were ensured to be less than 1 pS / cm. The hopcalite samples were allowed to soak in the deionized water for 30 min after minor agitation via stirring. Once 30 min had elapsed, samples were vacuum filtered and the hopcalite was allowed to dry in air until it was not visibly wet. This procedure was repeated two additional times, for a total of three washings to remove any impurities. After the final air dry, samples were placed in an oven at a temperature in a range from 90°C to 110°C oven to fully dry overnight before further analysis.

[0077] T otal soluble ionic impurities of various hopcalite samples were identified by measuring the conductivities of 1 :10 weight ratios of each sample in deionized water (Type II) after 4 h equilibration. Impact of these soluble impurities on surface pH was determined by measuring the ZPC of 2 g hopcalite samples suspended in 10 g deionized water.

[0078] The methods described herein in the following examples were characterized by the following techniques using the instrumentation described.

[0079] Hydrogen single point uptake vs time measurements on hopcalite samples were collected on a Micromeritics 3-Flex or ASAP 2020 Isotherm measuring device using the following procedure. Samples were activated under dynamic vacuum of about 1 x 10'4torr (1.3 x 10'2Pa) and heated to 200°C, for at least 8 h. 0.25 to 0.3 g of each activated sample was loaded into a 3-Flex or ASAP 2020 cell, and hydrogen dosed from a starting pressure of at least 900 torr (120 kPa) and set to target a 760 torr (101 kPa) equilibration point with a 90% tolerance. This procedure allowed hydrogen uptake vs. time to be recorded at a 0.5 s / point frequency for at least 20 min. A helium free space was used to subtract void volume from the hydrogen uptake experiment.

[0080] ZPC measurements were carried out used a Fisherbrand XL150 pH meter on 2 g of the samples of hopcalite, which had been shaken in 10 mL water and then allowed to settle for 30 min.

[0081] Conductivity measurements were taken using a Fisherbrand Traceable Expanded Range Conductivity meter using an epoxy K=1.0 probe. Hopcalite samples were prepared for conductivity measurements in the following manner. One weight equivalent of each hopcalite sample was added to 10 weight equivalents of deionized water. The deionized water used had a conductivity of less than 1 pS / cm. The slurry sample was vigorously agitated for 15 s and then allowed to settle for 30 min and agitated again at 120 and 240 minutes to aid the dissolution of soluble impurities. The conductivity was then measured by placing the conductivity probe in the slurry and taking the reading after the conductivity stabilizes (usually after 1 min).

[0082] Pourbaix diagrams shown in FIG. 2 were calculated using the Eh - pH function of the HSC Chemistry 7.1 Software.

[0083] Performance of the three "as-received" hopcalite samples (Samples A to C) and two washed samples (Samples A-washed & C-washed) was analyzed based on hydrogen uptake capacity of small samples over a period of 28 min. This measure was observed to correlate well with large scale hydrogen breakthrough capacities. As shown in Table 1 and in FIG. 3and FIG. 4, certain samples were found to have significantly reduced performance compared to others and the performance of these samples was strongly correlated with the ZPC of the hopcalite sample as well as the conductivity of the 10 wt % slurries of those samples in deionized water.TABLE 1

[0084] Sample A had the highest ZPC (nearly 8) and highest conductivity (more than 1000 pS / cm). However, the hydrogen capacity of this sample was only 15% of the best performing sample (Sample C). Thorough washing of Sample A reduced the ZPC value to about 7.6 and the conductivity value to about 490 pS / cm.

[0085] Double filtration of the washing solutions to remove any suspended particles and subsequent drying determined that the amount of soluble impurities was equal to 2.04 wt% of the initial hopcalite mass. The hydrogen uptake performance of the washed sample (Sample A-washed) is over three times higher than that for the unwashed sample (Sample A). The over 50% decrease in conductivity of this sample after washing suggests it originally contained significant levels of soluble ionic impurities.

[0086] The drop in ZPC further implies these impurities were mildly basic. Hopcalite compositions with minimal levels of soluble weakly basic impurities are clearly desirable, and the removal of said impurities greatly improves performance.

[0087] There is a correlation between total dissolved solids and ionic conductivity (IOP Conf. Series: Earth and Environmental Science 118 (2018) 012019.) In general, the ratio of dissolved solids and ionic conductivity is between 0.55 and 0.75 mg / L per 1 pS / cm. Based on this correlation, a target of less than 500 pS / cm for ionic conductivity corresponds to between 260 to 375 mg / L dissolved solids. Because the ionic conductivities of the hopcalites in the context of this invention are for 10 wt% slurries of the hopcalites in deionized water, 500 pS / cm would correspond to ~ 0.3 to 0.4 wt% dissolvable solids in dry hopcalites. From this correlation, the total soluble ionic impurities in the hopcalite should be less than about 0.4 wt% and preferably less than about 0.25 wt%.

[0088] Conductivity and ZPC of the best performing "as received" hopcalite sample (Sample C) were also measured. As shown in FIG. 3 and FIG. 4, the hydrogen uptake capacity of this sample is two times higher than Sample A-washed described above, while the conductivity of this sample (242 pS / cm) is half that of Sample A-washed. The ZPC value (7.1) of Sample C is also significantly lower than that of Sample A-washed. Remarkably, when this already high- performing Sample was washed with deionized water, its hydrogen uptake capacity improved by an additional 17%. Conductivity of this sample post-washing (133 pS / cm) decreased by 45% over the "as-received" sample prior to washing, indicating the unwashed sample still contained some level of soluble ionic impurities.

[0089] Surprisingly, the ZPC of Sample C-washed (7.2) increased compared with the original unwashed Sample C (7.1) which suggests that the removal of trace levels of soluble, weakly acidic, ionic impurities from the hopcalite is also beneficial. While the specific impurity or impurities are unknown, their acidity is consistent with traces of Cu2+salts either remaining in the as precipitated hopcalite or being generated in the forming process.

[0090] The ZPC results (see FIG. 3) demonstrate that the hopcalite samples with the best hydrogen uptake have a ZPC value in a range from about 6.9 to about 7.7, e.g., from about 7 to about 7.6, for 2 g of sample dissolved in 10 g of deionized water. Lower and higher pH values are associated with a significant reduction in hydrogen removal performance.

[0091] The conductivity results (see FIG. 4) show a clear performance increase as the quantity of soluble ionic impurities in the hopcalite sample is decreased.

[0092] To further validate the impact of soluble impurities, 0.5, 1.0, and 2.0 wt% sodium carbonate (Na2COs) was impregnated into fresh Sample C, the best performing sample without rinsing. Surprisingly, as little as 0.5 wt% sodium carbonate significantly reduced performance by 10%, with 2 wt% sodium carbonate reducing hydrogen uptake by 22% (see Table 2). This result suggests that the amount of soluble impurities in the sample should be less than about 0.5 wt%.TABLE 2

[0093] The Inventors have determined that desired hopcalites may form a 10% slurry in type II deionized water with an ionic conductivity preferably less than about 403 pS / cm. This figure was determined by taking the change in Sample A conductivity (1131 pS / cm to 488 pS / cm, which is 643 pS / cm) and assuming that 643 pS / cm equates to 2 wt% sodium carbonate. 0.5 wt% sodium carbonate (160.75 pS / cm) was then added to the base number for Sample C (242 pS / cm + 160.75 pS / cm = 402.5 pS / cm).

[0094] Based on these results, the Inventors are able to define a subgroup of hopcalite catalysts with given Cu / Mn ratios, surface areas and total pore volumes having reduced residues of soluble ionic impurities and with ZPC values between 6.9 and 7.7, preferably in the range from about 7.0 to about 7.4. Specifically, the ionic conductivities of 10 wt% slurries in deionized water of the hopcalite according to this invention are no more than 500 pS / cm, preferably no more than about 450 pS / cm, e.g., no more than about 410 pS / cm.

[0095] While the invention has been described with reference to the preferred embodiments depicted in the figures, it will be appreciated that various modifications are possible within the spirit or scope of the invention as defined in the following claims.

[0096] In this specification, unless expressly otherwise indicated, the word "or" is used in the sense of an operator that returns a true value when either or both of the stated conditions are met, as opposed to the operator "exclusive or" which requires only that one of the conditions is met. The word "comprising" is used in the sense of "including" and incorporates "consisting of" rather than meaning "consisting of' exclusively.

[0097] All prior teachings above are hereby incorporated herein by reference. No acknowledgement of any prior published document herein should be taken to be an admission or representation that the teaching thereof was common general knowledge in Australia or elsewhere at the date thereof.

Claims

CLAIMS1. A process for removing hydrogen from a dry gas comprising hydrogen as an impurity, said process comprising passing said dry gas though at least one layer comprising a hopcalite to produce product gas that is at least substantially free of hydrogen, wherein said hopcalite has a zero-point-of-charge (ZPC) in a range from about 6.9 to about 7.7 and / or an ionic conductivity as a 10 wt % slurry in deionized water of no more than about 500 pS / cm.

2. A process as claimed in Claim 1 , wherein the ZPC of said hopcalite is in a range from about 7 to about 7.4.

3. A process as claimed in Claim 1 or Claim 2, wherein the ionic conductivity of said hopcalite is no more than about 410 pS / cm.

4. A process as claimed in any of the preceding claims, wherein said hopcalite comprises less than 0.5 wt % residual soluble impurities.

5. A process as claimed in any of the preceding claims, wherein said hopcalite has a molar ratio of copper to manganese of more than 0.55, e.g., in a range from about 0.6 to about 4.

6. A process as claimed in any of the preceding claims, wherein said hopcalite has a surface area in a range from about 100 m2 / g to about 250 m2 / g, e.g., in a range from about 100 m2 / g to about 200 m2 / g.

7. A process as claimed in any of the preceding claims, wherein said hopcalite has a total pore volume of less than 0.4 cm3 / g, e.g., in a range from about 0.1 cm3 / g to about 0.3 cm3 / g.

8. A process as claimed in any of the preceding claims, wherein said layer(s) of said hopcalite is / are regenerated at a temperature of no more than about 150°C.

9. A process as claimed in any of the preceding claims, wherein the dry gas is at a temperature in a range from about 0°C to about 60°C, e.g., in a range from about 10°C to about 40°C.

10. A process as claimed in any of the preceding claims, wherein the dry gas is passed through said layer(s) comprising said hopcalite at a pressure in a range from about 3 bar to about 45 bar (0.3 MPa to 4.5 MPa), e.g., in a range from about 3 bar to about 30 bar (0.3 MPa to 3.0 MPa).

11. A process as claimed in any of the preceding claims, wherein said hydrogen impurity is present in said dry gas in an amount of up to about 40 ppmv, e.g., in a range from about 20 ppmv to about 40 ppmv.

12. A process as claimed in any of the preceding claims, wherein said dry gas comprises carbon dioxide in an amount of up to about 900 ppmv, e.g., in a range from about 10 ppmv to 600 ppmv.

13. A process as claimed in any of the preceding claims, wherein the product gas comprises no more than 1 ppmv hydrogen, e.g., no more than 50 ppbv hydrogen.

14. A process as claimed in any of the preceding claims, wherein said dry gas is air.

15. A hopcalite comprising a mixture of copper oxide and manganese oxide and having a ZPC in a range from about 6.9 to about 7.7 and / or an ionic conductivity as a 10 wt % slurry in deionized water of no more than about 500 pS / cm.

16. An adsorption unit for purifying a gas comprising at least hydrogen as an impurity, the unit comprising an adsorbent bed having a feed end with a gas inlet and a product end opposite the feed end with a gas outlet, the adsorbent bed comprising at least one layer comprising a hopcalite, said hopcalite comprising a mixture of copper oxide and manganese oxide and having a ZPC in a range from about 6.9 to about 7.7 and / or an ionic conductivity as a 10 wt % slurry in deionized water of no more than about 500 pS / cm.

17. A process for increasing hydrogen adsorption capacity of a hopcalite after calcination, said process comprising washing said hopcalite with deionized water.

18. A process as claimed in Claim 17, wherein said washing of said hopcalite involves the steps of:(a) soaking said hopcalite in deionized water;(b) after soaking, removing said hopcalite from said deionized water;(c) drying said hopcalite; and optionally(d) repeating at least steps (a) and (b) at least once, e.g., twice.

19. A process as claimed in Claim 17 or Claim 18, wherein the deionized water has a conductivity of less than 1 pS / cm.

20. A process as claimed in any of Claims 17 to 19, wherein the deionized water is at a temperature in a range from about 20°C to about 80°C.

21. A process as claimed in any of Claims 17 to 20, wherein said hopcalite is soaked for at least 10 mins, e.g., about 30 mins, after optional agitation, e.g., by stirring.

22. A process as claimed in any of Claims 17 to 21, wherein said hopcalite is removed from said deionized water by filtration, e.g., vacuum filtration.

23. A process as claimed in any of Claims 17 to 22, wherein said hopcalite is subsequently dried and activated.

24. Use of a hopcalite having a zero-point-of-charge (ZPC) in a range from about 6.9 to about 7.7, e.g., in a range from about 7 to about 7.4, and / or an ionic conductivity as a 10 wt % slurry in deionized water of no more than about 500 pS / cm, e.g., no more than 410 pS / cm, to remove hydrogen as an impurity from a dry gas comprising the impurity.

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