Improved water-gas shift catalyst

Abstract

The present invention relates to an improved water-gas shift catalyst, in particular an improved high-temperature shift catalyst and a method of using the same. The water-gas shift catalyst comprises Zn, Al, optionally Cu, and an alkali metal or an alkali metal compound, wherein the alkali metal (preferably K) content is in the range of 1-6 wt%, such as 1-5 wt% or 2.5-5 wt%, based on the weight of the oxidized catalyst, and wherein the water-gas shift catalyst has a pore volume of 240 ml / kg or more, such as 250 ml / kg or more, as determined by mercury intrusion porosimetry. The present invention also relates to a method for enriching synthesis gas with hydrogen by contacting the synthesis gas with the water-gas shift catalyst in a water-gas shift reactor.

Description

Technical Field

[0001] The present invention relates to an improved water-gas shift catalyst and a method of using the same. Background Art

[0002] The water-gas shift (WGS) is a well-known method for increasing the hydrogen content of synthesis gas (syngas), a gas produced, for example, by steam reforming of a hydrocarbon feedstock and containing hydrogen and carbon monoxide. The WGS increases hydrogen production and reduces the carbon monoxide content of the syngas, based on the equilibrium reaction: CO + H₂O = CO₂ + H₂.

[0003] Typically, hydrogen production is optimized by carrying out the exothermic water-gas shift reaction in separate reactors, such as separate adiabatic reactors with interstage cooling. Typically, the first reactor is a high temperature shift (HTS) reactor having an HTS catalyst disposed therein, and the second reactor is a low temperature shift (LTS) reactor having an LTS catalyst disposed therein. A medium temperature shift (MTS) reactor may also be included, or it may be used alone or in combination with an HTS reactor or with an LTS reactor. Typically, the HTS reactor operates in the range of 300-550°C, while the LTS operates in the range of 180-240°C. The MTS reactor typically operates in the temperature range of 210-330°C.

[0004] In industrial practice, high-temperature shift (HTS) reactors are typically started up with a superheated steam flow, which heats the reactor and the HTS catalyst inside, which is typically an iron-chromium-based catalyst. When the reactor temperature falls below the dew point of water, condensation can occur inside the reactor. The use of steam to heat HTS reactors is particularly common in older ammonia plant designs. Because of this, HTS catalysts, which typically contain water-soluble compounds, are not used in these plants due to concerns about leaching of these compounds and subsequent loss of catalytic activity.

[0005] Therefore, in ammonia plants and hydrogen plants, in order to avoid leaching, it is known that the HTS reactor is heated from ambient temperature to the process (operating or reaction) temperature without significant condensation by heating with a gas with a limited steam content (such as dry nitrogen), which is provided by a dedicated independent nitrogen circuit. Nitrogen is inert to the HTS catalyst. However, during startup operation, for example due to the design of the plant, it is desirable to avoid the use of such a dedicated independent nitrogen circuit and instead to be able to heat the cold reactor and the catalyst bed arranged therein to the process temperature, i.e., the operating temperature of the HTS reactor, by applying steam (e.g., superheated steam). Since water is a reactant in the water-gas shift reaction, steam is always available in such plants.

[0006] There are two main types of high temperature shift catalysts. The established type that dominates the market is based on iron / chromium (Fe / Cr) and contains small amounts of other components, usually copper. Another type of high temperature shift catalyst is based on a zinc oxide / zinc aluminum spinel structure promoted with one or more basic elements such as potassium. This type of HTS catalyst usually also contains copper as another promoter. This type of HTS catalyst is described in, for example, the applicant's patents US 7998897 B2, US 8404156 B2 and US8119099 B2. The basic promoter can be present in the form of a water-soluble compound such as a salt or hydroxide (for example, K2CO3, KHCO3 or KOH) over the entire temperature range required for HTS startup and normal operation (i.e., -100°C to 600°C).

[0007] Therefore, it is generally believed that when starting an HTS reactor using steam, the catalyst is an Fe / Cr-based catalyst or a similar catalyst that does not contain substances capable of forming water-soluble compounds (such as alkali metals or alkali metal compounds). Until now, it was believed that only Fe / Cr-based catalysts could withstand the conditions of condensing steam. Similarly, there is concern that the alkali metals or alkali metal compounds used as promoters in Zn / Al-based catalysts will leach from the catalyst, thereby losing most of its activity for the HTS reaction.

[0008] In fact, there is also a consensus in the industry that starting a shift catalyst with water-soluble compounds under condensing conditions, in particular in low temperature shift (LTS) reactors and HTS reactors, will lead to the leaching of these compounds and therefore to a deterioration of the catalytic activity. Thus, for example, EP 3368470 addresses the problem of soluble substances being washed out or redistributed in the catalyst bed under unstable conditions which lead to condensation in the LTS reactor. Furthermore, this document does not encourage the redeposition of soluble components in the copper-containing catalyst used. Therefore, during normal operation, in order to mitigate the effects of poisoning caused by halogen species present in the feed gas entering the LTS reactor (e.g. the first shifted synthesis gas from the upstream HTS reactor), it is known to provide a dedicated and insoluble protective or adsorbent material upstream of the first water-gas shift reactor (in particular the HTS reactor) or between the HTS reactor and the subsequent LTS reactor in order to capture halogen species, such as chloride species.

[0009] Furthermore, during normal operation of the LTS reactor, the use of alkali metals or alkali metal compounds in the LTS catalyst is desirable because they reduce the undesirable formation of methanol by-product due to the presence of copper in the catalyst and the relatively low operating temperatures of the LTS reactor.

[0010] US Pat. No. 6,455,464 discloses a non-chromium Cu-Al-O catalyst for the hydrogenolysis of carbonyl groups in organic compounds, wherein less than 60 wt. % of the catalyst has a copper aluminate (CuAl2O4) spinel structure and copper is a leachable compound. Upon activation of the catalyst by a reducing gas, the CuAl2O4 is converted to metallic copper (Cu) and aluminum oxide (Al2O3), so that the spinel structure is not present in the active form.

[0011] The applicant's WO 2017148929 A1 discloses an improved method for increasing the front-end capacity of a plant comprising a reforming section and a water-gas shift section. In the water-gas shift section, a high-temperature shift is performed to exchange the original iron-based catalyst with a non-iron-based catalyst. The non-iron-based catalyst is a commercial catalyst SK-501Flex. TM The catalyst comprises a Zn / Al molar ratio in the range of 0.5 to 1.0, an alkali metal content in the range of 0.4 wt% to 8.0 wt%, and a copper content in the range of 0-10%, based on the weight of the oxidized catalyst. The catalyst has a pore volume of about 230 ml / kg.

[0012] US 2011101277 A1 of the applicant discloses a chromium-free water gas shift catalyst (C8, Example 1) comprising zinc-aluminum spinel and ZnO, 1.73 wt% K and 1.83 wt% Cu, and a Zn / Al molar ratio of 0.57. The density of the pelletized cylindrical tablets is 1.80 g / cm 3 . Summary of the Invention

[0013] Therefore, the object of the present invention is to provide a novel water-gas shift catalyst containing an alkali metal or an alkali metal compound, which catalyst can be industrially started up under steam condensation conditions.

[0014] Another object of the present invention is to provide a novel water-gas shift catalyst which is resistant to poisoning by halogen species present in the feed gas supplied to a water-gas shift reactor in which the catalyst is disposed.

[0015] Another object of the present invention is to provide a novel water-gas shift catalyst that avoids the use of dedicated protection or adsorption materials to remove halogen species from the feed gas.

[0016] A further object of the present invention is to provide a novel water-gas shift catalyst which is able to maintain a high mechanical strength and which, at the same time, can be used for a higher number of starts without a significant loss of catalytic activity compared to known water-gas shift catalysts.

[0017] Another object of the present invention is to provide a simple water gas shift process for removing halogen species present in feed gas.

[0018] Another object of the present invention is to provide an advantageous water-gas shift process, in particular an HTS process.

[0019] The present invention addresses these and other objects.

[0020] Thus, in a first aspect, the present invention is a water-gas shift catalyst comprising Zn, Al, optionally Cu and an alkali metal or an alkali metal compound, wherein the water-gas shift catalyst is a Zn / Al-based catalyst, in particular an HTS catalyst, the active form of which comprises a mixture of zinc-aluminium spinel and optionally zinc oxide in combination with an alkali metal selected from K, Rb, Cs, Na, Li and mixtures thereof, wherein the Zn / Al molar ratio is in the range of 0.3-1.5 and the content of alkali metal (preferably K) is in the range of 1-6 wt%, for example 1-5 wt% or 2.5-5 wt%, based on the weight of the oxidized catalyst, and wherein the water-gas shift catalyst has a pore volume of 240 ml / kg or more, for example 250 ml / kg or more, as determined by mercury porosimetry.

[0021] This enables the provision of surprisingly robust water gas shift catalysts, suitably HTS catalysts, which have significant mechanical strength and no significant, if any, loss of catalytic activity.

[0022] It should be understood that the general embodiment described above includes Zn and Al; or may include Cu and other elements in addition to Zn and Al. In both cases, the remaining limitations of the embodiment are included, such as having an alkali metal or alkali metal compound, etc.

[0023] In one embodiment, the water gas shift catalyst has a pore volume in the range of 240-380 ml / kg or 250-380 ml / kg or 300-600 ml / kg or 300-500 ml / kg, for example 250, 300, 350, 400, 450 or 500 ml / kg, or in the range of 320-430 ml / kg, as determined by mercury porosimetry.

[0024] Mercury intrusion porosimetry was performed according to ASTM D4284.

[0025] By using a water-gas shift catalyst having the above-described pore volume, the amount of condensed water used to heat the catalyst to the dew point, or the amount of any liquid water formed during normal operation, will be less than the total pore volume of the catalyst. The condensed water, which may contain dissolved alkali or alkali metal compounds, will therefore be retained within the catalyst pores. When the temperature after continued heating rises above the dew point, the water contained in the catalyst pores will evaporate, leaving the alkali metal compounds on the catalyst surface. As a result, the majority of the catalyst will not lose any significant degree of activity, for example, because the alkali metal or alkali metal compound is no longer present and therefore cannot act as a promoter, or because the alkali metal and alkali metal compound are no longer present and therefore can no longer reduce any poisoning caused by the presence of halogens, or because the alkali metal or alkali metal compound is no longer present and therefore cannot reduce the formation of methanol by-products in, for example, the low-temperature shift reactor.

[0026] By providing a density of, for example, 1.4 or 1.5 or 1.6 or 1.7 g / cm 3 The pore volume, in particular the higher pore volume, can be achieved with water-gas shift catalyst particles of a preferred embodiment. The lower the particle density, the higher the pore volume. The term "particle" refers to a pellet, extrudate or tablet, e.g. which has been compacted into such a tablet by granulation or tabletting from a starting catalyst material (e.g. from a powder). Thus, in one embodiment according to the first aspect of the invention, the catalyst is in the form of a pellet, extrudate or tablet and has a density of 1.25-1.75 g / cm 3 , or 1.55-1.85g / cm 3 , for example 1.3-1.8 g / cm 3 , or for example 1.4 g / cm 3 , 1.5g / cm 3 , 1.6g / cm 3 , 1.7g / cm 3 Density is measured by simply dividing the weight of, for example, a tablet by its geometric volume.

[0027] Typically, the density of catalyst particles, such as that of HTS catalysts, is close to 2 g / cm2, as in US Pat. No. 7,998,897 or US Pat. No. 8,404,156 of the applicant. 3 , for example up to 2.5 g / cm 3 or about 1.8g / cm 3 or 1.9 g / cm 3 These relatively high densities contribute significantly to the mechanical strength of the granules (e.g. tablets), enabling them to withstand the impact of, for example, loading an HTS reactor from a relatively high height (e.g. 5 m). Therefore, it is often desirable to have a high granule density, e.g. 1.8 g / cm 3or higher. Through the present invention, it has also been found that by compacting (e.g. tableting) into a less dense shape, the pore volume of the particles is increased, thereby solving the leaching problem sought to be solved above, while at the same time the particles maintain sufficient mechanical strength to withstand shocks during loading or normal operation, and avoid an increase in the pressure drop across the reactor due to crushing of the particles during normal (continuous) operation.

[0028] In a particular embodiment, the present invention is a water-gas shift catalyst comprising, i.e., consisting of, only:

[0029] Zn, Al, optionally Cu, and an alkali metal or an alkali metal compound, wherein the water-gas shift catalyst is a Zn / Al-based catalyst, in particular an HTS catalyst, the active form of which comprises a mixture of zinc-aluminum spinel and optionally zinc oxide in combination with an alkali metal selected from K, Rb, Cs, Na, Li and mixtures thereof, wherein the Zn / Al molar ratio is in the range of 0.3-1.5 and the content of alkali metal (preferably K) is in the range of 1-6 wt%, for example 1-5 wt% or 2.5-5 wt%, based on the weight of the oxidized catalyst, and wherein the water-gas shift catalyst has a pore volume of 240 ml / kg or more, for example 250 ml / kg or more, as determined by mercury porosimetry.

[0030] Thus, it is understood that this particular embodiment includes Zn and Al; or that this particular embodiment includes Cu in addition to Zn and Al. In both cases, the remaining limitations of the embodiment are included, such as having an alkali metal or alkali metal compound, etc.

[0031] In one embodiment according to the first aspect of the present invention, the Zn / Al molar ratio is in the range of 0.5-1.0, such as 0.6 or 0.7.

[0032] According to the present invention, the content of alkali metal (preferably K) is in the range of 1-6 wt%, for example 1-5 wt% or 2.5-5 wt%. It has been found that within this specific range, the catalytic activity is quite constant, regardless of the amount of alkali metal compound present. By applying this specific range, the catalyst acts like a "base buffer", so that if a slight loss of alkali metal promoter occurs in one part of the reactor, the catalytic activity is not significantly impaired, thereby further increasing the number of start-ups without the catalyst losing activity. In addition, by operating with a catalyst having an upper limit of alkali metal content (for example 6 wt% K), the leaching of K will actually lead to a higher level of activity, as will also be seen from Example 3 below and the corresponding Figure 4This alkali buffering effect, or simply the buffering effect, becomes apparent in the literature. This occurs because, for example, during the startup of an HTS reactor, a 10% (relative) leaching of potassium will reduce the K content from, for example, 4 wt% K to 3.6 wt% K, which will not reduce catalyst activity. In fact, if the initial K content is, for example, 6 wt% K or lower, suitably 5 wt% K, then at 10% (relative) leaching, activity will increase, since a catalyst with 4.5 wt% K will be more active than one with 5 wt% K. The buffering effect is particularly advantageous near the reactor walls, for example, where more steam is required for heating due to their high heat capacity, and thus presents a higher risk of alkali leaching. However, any alkali leaching after multiple startups will still not significantly impair catalytic activity, or may even increase it.

[0033] Furthermore, if leaching of the base occurs during normal operation of the reactor (continuous operation), the buffering effect will result in the catalytic activity not being impaired.

[0034] Although events leading to alkali leaching throughout the catalyst bed may be rare, the buffering effect provides additional safety for good operation of the catalyst bed and therefore of the water-gas shift process, in particular the HTS process.

[0035] In one embodiment according to the first aspect of the present invention, Cu is in the range of 0.1-10 wt%, such as 1-5 wt%, based on the weight of the oxidized catalyst.Cu acts as an optional promoter and can be incorporated into the catalyst by conventional impregnation or coprecipitation methods.

[0036] According to the present invention, the alkali metal or alkali metal compound is leachable. In other words, the alkali metal or alkali metal compound is a substance that is able to form water-soluble compounds during operation of the catalyst, such as during normal operation or during transient operation, such as during start-up using steam.

[0037] In one embodiment according to the first aspect of the present invention, the water-gas shift catalyst is free of chromium (Cr). In another embodiment, the water-gas shift catalyst is free of iron (Fe). Thus, in one embodiment, the water-gas shift catalyst is free of chromium (Cr) and iron (Fe). This provides a more sustainable and environmentally friendly catalyst because it is free of Cr. Furthermore, the absence of Fe significantly reduces or even eliminates the formation of undesirable hydrocarbons such as methane.

[0038] As used herein, the term "chromium (Cr)-free and iron (Fe)-free" means that the Fe content is less than 0.05 wt% or the Cr content is less than 0.02 wt%. For example, the Fe and Cr contents are undetectable.

[0039] It has been found that under normal operation where it is necessary to operate a water gas shift reactor (e.g. an LTS reactor), under conditions close to the dew point, or even under transient conditions, such as unstable conditions or start-up conditions, and which may result in condensation, the washout (leaching) of alkali metal or alkali metal compounds is significantly reduced.

[0040] The startup of a water-gas shift reactor can be a method comprising the following steps: providing a water-gas shift catalyst comprising an alkali metal or an alkali metal compound; heating the water-gas shift catalyst to a reaction temperature of the water-gas shift reaction under steam condensation conditions by applying steam as a heat transfer medium for the water-gas shift catalyst, and wherein the water-gas shift catalyst has a pore volume measured by mercury intrusion porosimetry that is greater than the volume of liquid water formed during heating.

[0041] The term "reaction temperature" for the water-gas shift reaction is used interchangeably with the terms "operating temperature" and "process temperature." For example, for a high-temperature shift, the reaction temperature is in the range of 300-550°C.

[0042] The term "under steam condensing conditions" refers to heating at a temperature at which liquid water is formed, i.e., heating to the dew point of water; for example, about 12 atm (absolute) dew point (T sat ) is about 190° C. The term “under steam condensing conditions” can also be understood as cooling a steam-containing gas to a temperature below its dew point at a given steam pressure.

[0043] As long as the amount of liquid water (i.e. condensed water) formed during heating is lower than the pore volume of the catalyst, no transport of alkali metal or alkali metal compound between catalyst particles (e.g. catalyst pellets or catalyst tablets) will occur. The porosity of the particle (pore volume / total particle volume) determines how much water can be accommodated in the particle without external transport of water-soluble compounds. Even in cases where the amount of water exceeds the pore volume, the loss of alkali metal or alkali metal compound from the catalyst particle is controlled by diffusion inside the particle and by the difference in the concentration of the solution inside the particle and the concentration outside the particle. Diffusion in solution is a rather slow process (diffusion coefficient of about 10 -6 cm 2 / s), even if excess liquid water is formed in some parts of the reactor, the catalyst can be kept durable over many startups. Alkali metal or alkali metal compound content above the minimum required for optimal activity also increases the commercial life of the catalyst, as described in the above specific embodiments and as shown in Example 3 and the corresponding Figure 4 shown.

[0044] In one embodiment, the catalyst is in the form of pellets, extrudates or tablets and has a mechanical strength of ACS of 30-750 kp / cm 2 , for example 130-700kp / cm 2 or 30-350kp / cm 2 ACS is the abbreviation for axial compressive strength. Alternatively, the mechanical strength measured as SCS is in the range of 4-100, for example 20-90 kp / cm or up to 40 kp / cm. SCS is the abbreviation for lateral compressive strength, also known as radial compressive strength. For a given tablet density, the mechanical strength can vary significantly, depending on the machine used to compact the catalyst powder. Lower ranges of mechanical strength (ACS or SCS), for example up to ACS of 300 or 350 kp / cm 2 Or up to an SCS of 40 kp / cm corresponds to those obtained with small (about 100 g / h) hand-fed tablet presses, so-called Manesty machines. The upper limit of mechanical strength, for example up to an ACS of 750 kp / cm 2 Or up to an SCS of 90 kp / cm corresponds to those obtained using an automatic full-scale device (100 kg / h) (e.g., a Kilian RX machine with a rotary press). It is therefore understood that tablets obtainable using the Manesty machine have lower mechanical strength than tablets obtainable using the Kilian RX machine with a rotary press. ACS and SCS are measured in the oxidized form of the catalyst. Furthermore, mechanical strength is measured according to, i.e., in compliance with, ASTM D4179-11.

[0045] The resulting water gas shift catalyst also outperforms prior art catalysts, such as the applicant's US 7998897, as evidenced, for example, by the number of start-up runs that can be performed without the catalyst losing catalytic activity. While the HTS catalyst according to US 7998897 can provide 50 start-ups using steam without significant leaching, the catalyst of the present invention is capable of providing over 100 start-ups without significant loss of catalytic activity due to leaching.

[0046] It will be appreciated that the number of startups required for, for example, an HTS reactor in a year may be substantial, e.g., five startups per year. Thus, there is no longer a need for a dedicated nitrogen loop, typically installed to provide a gas with a limited steam content (e.g., dry nitrogen) for startup. Similarly, the present invention enables the use of steam, such as superheated steam, which is readily available and can be integrated into plants, such as hydrogen or ammonia production plants, thereby further simplifying plant operation and reducing plant capital expenditures. The catalyst of the present invention significantly increases the number of startups that can be performed before catalyst replacement is necessary.

[0047] In one embodiment according to the first aspect of the present invention, the alkali metal compound is selected from K, Rb, Cs, Na, Li and mixtures thereof. Preferably, the alkali metal compound is K. Potassium (K) suppresses the formation of undesirable methanol as a potential by-product in the LTS reactor due to the use of catalytically active elements (such as copper) in the water gas shift catalyst, and copper is known to catalyze methanol production at the low operating temperatures of the low temperature shift reactor, such low operating temperatures are typically in the range of 180-240°C. Potassium can also enhance (promote) the activity of Zn / Al type catalysts used in high temperature shift reactors, which are typically operated in the temperature range of, for example, 300-550°C.

[0048] In addition, the alkali metal or alkali metal compound is used to improve the resistance of the catalyst to halogen poisoning during normal operation, such as poisoning by chlorides present in the feed gas (e.g., in the synthesis gas or the first shifted synthesis gas from the HTS reactor), which is then shifted in the MTS or LTS reactor. In addition, when operating, for example, with an HTS reactor and a subsequent LTS reactor, the alkali metal or alkali metal compound in the HTS catalyst reacts or absorbs halogens, such as chlorides, thereby protecting the subsequent LTS catalyst.

[0049] As used herein, the term "alkali metal or alkali metal compound" refers to a base such as K in its elemental form (i.e., metallic form), or a compound thereof such as K2CO3, KHCO3, KOH, KCH3CO2, or KNO3, respectively. It should be understood that a water-gas shift catalyst in an oxidized state will not contain an alkali metal in its metallic form. Thus, terms such as "catalyst promoted by an alkali metal" or "base-promoted catalyst" or similar terms refer to a catalyst promoted with an alkali metal compound, which encompasses all possible compounds of the alkali metal that may serve as a co-catalyst.

[0050] Furthermore, for the purposes of this application, when the term "base" is used, it refers to an alkali metal or an alkali metal compound.

[0051] In one embodiment of the first aspect of the present invention, heating up to the reaction temperature is carried out at a temperature in the range of -100° C. to 600° C., for example in the range of 0-500° C. The initial (cold) temperature is, for example, 0° C., 2° C. or 50° C. It is also suitable to heat the water-gas shift catalyst up to the reaction temperature of the water-gas shift reaction solely by means of steam.

[0052] Advantages of the present invention include:

[0053] - providing a superior water-gas shift catalyst, in particular an HTS catalyst, and thereby a superior water-gas shift process, wherein the catalyst particularly exhibits an alkali buffering effect such that even if some alkali is leached or lost during water-gas shift operation, i.e. during startup or normal operation, the catalytic activity is maintained or even improved.

[0054] - The present invention teaches how to heat an alkali-containing water-gas shift catalyst, such as an alkali-promoted Zn / Al type HTS catalyst, in condensing steam at startup, having a sufficient pore volume and a sufficient content of alkali metal or alkali metal compound, the leaching of which is so small that it is insignificant for the expected industrial life of the catalyst.

[0055] In other words, the present invention allows heating to operating temperature (reaction temperature) under condensing conditions even when using base-containing catalysts without significant loss of catalytic activity due to leaching or loss of resistance to halogen poisoning.

[0056] - More specifically, for HTS reactors, when comparing two types of HTS catalysts, namely the older Fe / Cr-based catalysts and the newer alkali-containing Zn / Al-based catalysts, the latter type has several advantages. Importantly, it does not contain chromium, which is harmful to the environment and to health. Therefore, a more sustainable process is provided here. In addition, the selectivity of the alkali-containing Zn / Al-based catalysts is much higher because their tendency to form hydrocarbons (such as methane) from synthesis gas is much less pronounced than in the case of Fe / Cr-based catalysts. This difference is most evident when the HTS reactor is operated with a low steam / carbon molar ratio in the feed gas (such as the synthesis gas entering the reactor). The low steam / carbon molar ratio conveys the benefit of using less steam in the process / plant (such as a plant for producing, for example, hydrogen or ammonia), thereby significantly reducing the equipment size in the plant and with the accompanying energy savings in the form of reduced carbon dioxide emissions.

[0057] It is well known that iron-containing catalysts require operation above a certain steam-to-carbon molar ratio or above a certain oxygen-to-carbon molar ratio in the syngas entering the HTS reactor to prevent the formation of iron carbide and / or elemental iron, which can lead to a significant loss of mechanical strength and a corresponding increase in the pressure drop across the reactor. Alkali-containing Zn / Al-based catalysts are insensitive to the steam-to-carbon molar ratio and, during normal operation, do not lose mechanical strength due to low steam content in the feed gas (syngas) to the HTS reactor.

[0058] - The number of possible start-ups is significantly increased while still maintaining sufficient mechanical strength in the particles, thus avoiding losses due to increased pressure drop in the water-gas shift reactor.

[0059] - The ability of the copper-containing LTS catalyst to resist poisoning by halogen species, such as chloride species, eg, hydrogen chloride, is improved by being able to retain the alkali metal or alkali metal compound in the catalyst.

[0060] A second aspect of the invention comprises a method of enriching synthesis gas with hydrogen by contacting the synthesis gas with a water-gas shift catalyst according to any one of the above embodiments of the first aspect of the invention in a water-gas shift reactor.

[0061] As described in conjunction with the first aspect of the present invention, the benefits associated with the water gas shift catalyst also enable a superior water gas shift process.

[0062] In one embodiment according to the second aspect of the invention, the water-gas shift reactor is a low-temperature shift (LTS) reactor, a medium-temperature shift (MTS) reactor, or a high-temperature shift (HTS) reactor. In a particular embodiment, the method comprises combining an HTS reactor with an LTS reactor, wherein the first shifted gas formed in the HTS reactor is subsequently passed to the LTS reactor.

[0063] The water-gas shift reactor can also be used as a reverse water-gas shift reactor, wherein a feed gas rich in hydrogen and carbon dioxide is converted into carbon monoxide and water according to the reverse water-gas shift reaction: CO2+H2=CO+H2O.

[0064] In one embodiment according to the second aspect of the present invention, the water-gas shift reactor is a HTS reactor operated at a temperature in the range of 300-550°C and optionally also at a pressure in the range of 2.0-6.5 MPa.

[0065] In one embodiment according to the second aspect of the present invention, the water-gas shift reactor is a LTS reactor operated at a temperature in the range of 180-240°C and optionally also at a pressure in the range of 2.0-6.5 MPa.

[0066] In one embodiment according to the second aspect of the present invention, the water-gas shift reactor is an MTS reactor operated at a temperature in the range of 210-330°C and optionally also at a pressure in the range of 2.0-6.5 MPa.

[0067] In a third aspect, the present invention comprises a water-gas shift catalyst comprising, optionally consisting of, Cu, Zn, Al and an alkali metal or alkali metal compound, wherein the pore volume of the water-gas shift catalyst as determined by mercury porosimetry is 240 ml / kg or more, for example 250 ml / kg or more as determined by mercury porosimetry, and wherein the water-gas shift catalyst is a low temperature shift (LTS) catalyst, wherein the alkali metal is selected from K, Rb, Cs, Na, Li and mixtures thereof. In a particular embodiment, Cu, Zn and Al are present in oxide form, i.e. in the form of, for example, CuO, ZnO and Al2O3, respectively, or in the form of mixed oxides such as, for example, ZnAl2O4. This applies to oxidized ("supported") catalysts. The active form of the catalyst contains copper in reduced form, preferably in the form of elemental Cu.

[0068] Any of the embodiments of the first aspect of the invention and the associated benefits may be used with any of the embodiments of the second and third aspects, and vice versa.

[0069] BRIEF DESCRIPTION OF THE DRAWINGS

[0070] Figure 1 Shown is the temperature increase and thus the catalytic activity increase as a function of the reactor length when feeding a gas mixture after multiple starts in an HTS reactor according to Example 1.

[0071] Figure 2 The pore volume (PV) and mechanical strength (ACS, SCS) of the catalyst according to Example 2 are shown.

[0072] Figure 3 The carbon monoxide conversion with the HTS catalyst according to the invention relative to different alkali metals (promoters) is shown according to Example 3. For comparison, an unpromoted catalyst containing essentially no alkali metal compounds is included.

[0073] Figure 4 The carbon monoxide conversion using the HTS catalyst according to the invention according to Example 3 is shown relative to the weight of potassium as alkali metal (promoter) in the catalyst. Specific implementation plan

[0074] Example 1:

[0075] The HTS reactor was started under condensing steam at 11.85 atm (absolute) (i.e., about 12 atm (absolute)) with a dew point of T sat=188°C (i.e. about 190°C), which represents an industrial case. The amount of condensate depends on the quality of the steel (i.e. the reactor vessel), the quality of the catalyst contained in the reactor and on the initial temperature, which is typically between 0°C and 50°C. Table 1 shows typical volumes of liquid (water) that would form in an industrial HTS unit having an internal diameter of a small size (i.e. about 1 m) and an internal diameter of a large size (i.e. about 5 m). It is clear that the pore volume of the water-gas shift catalyst (which by the present invention is, for example, in the range of 240-380 ml / kg, 250-800 ml / kg) is sufficient to accommodate the total volume of liquid condensed during the heating process.

[0076] Table 1

[0077]

[0078] *Calculated as (1.52+3.27) / (67.9)×1000

[0079] Catalyst pellets or tablets placed immediately adjacent to the reactor wall are exposed to water condensing to heat the reactor vessel and catalyst charge. This means there is a region of the catalyst bed, confined to the reactor's periphery, where the entire pore volume is used to accommodate liquid condensing at the reactor wall. The width of this region depends on the pore volume of the catalyst, and it has been found that the larger pore volume near the reactor wall is able to absorb the additional water condensing at the wall.

[0080] Catalyst A:

[0081] The potassium-promoted Zn / Al type HTS catalyst is a catalyst according to Example 1 of the applicant's patent US 7998897 or US 8404156, and wherein the powders of ZnAl2O4 (spinel) and ZnO include Cu by co-precipitation with a copper salt. The pore volume as determined by mercury intrusion porosimetry, the tablet density (as measured by simply dividing the tablet weight by its geometric volume), the potassium content as measured by the ICP method, and the copper content are as follows: pore volume 229 ml / kg, tablet density 1.8 g / cm 3 , K content: 1.97 wt %, Cu content: 2.71 wt %, based on the weight of the oxidized catalyst.

[0082] A series of startups under condensing steam were carried out in the pilot plant. At the beginning of the test and after each startup, the catalyst was exposed to HTS conditions, where the gas mixture contained 35 vol% H2O, 16 vol.% CO, 4 vol.% CO2, and the balance H2. The reactor was operated in (pseudo)adiabatic mode. The temperature increase along the length of the reactor, corresponding to the fraction of the catalyst bed expressed in % in the figure, is a direct indicator of catalytic activity. Figure 1It showed that after the first start-up under condensing steam, there was only a slight loss of activity, and in subsequent tests, the activity was not affected.

[0083] The pilot study also showed that the start-up procedure in condensing steam provided approximately 50 starts without significant loss of activity under conditions identical to industrial condensing start-up conditions.

[0084] Example 2:

[0085] Catalyst B, C:

[0086] An improved HTS catalyst according to the invention, also of the potassium-promoted Zn / Al type, was also tested. Thus, two catalysts were prepared according to Example 1 of the applicant's patent US 7998897 or US 8404156, wherein the powders of ZnAl2O4 (spinel) and ZnO included Cu incorporated by coprecipitation of a copper salt. Furthermore, according to the invention, the pore volume of the particles was adjusted to 240 ml / kg, 250 ml / kg or higher, for example in the range of 240-380 ml / kg, by compacting (e.g., granulating) the particles (e.g., tablets) of the powdered starting catalyst material, e.g., after calcining the catalyst, impregnating them with a solution containing an alkali compound, e.g., a solution of K2CO3, and finally mixing them with a lubricant, e.g., graphite (as disclosed in Example 1 of the aforementioned US 7998897 or the aforementioned US 8404156, but before granulation). Therefore, instead of compacting the powder to a density of 1.8 or 2.1 g / cm2 as in Example 1 of US 7998897 or US 8404156, the powder was compacted to a density of 1.8 or 2.1 g / cm2, respectively. 3 The catalyst of the present invention is compacted intentionally and surprisingly to form a tablet with a lower density. The pore volume as determined by mercury intrusion porosimetry, the tablet density as measured by simply dividing the tablet weight by its geometric volume, the potassium content as measured by the ICP method, and the copper content are as follows:

[0087] Catalyst B: pore volume 451 ml / kg, tablet density 1.4 g / cm 3 , K content: 1.66 wt %, Cu content: 3.81 wt %, based on the weight of the oxidized catalyst.

[0088] Catalyst C: pore volume 320 ml / kg, tablet density 1.7 g / cm 3 , K content: 3.80 wt %, Cu content: 3.56 wt %, based on the weight of the oxidized catalyst.

[0089] Although Catalysts B and C were prepared with lower densities than Catalyst A, the mechanical strength of the former catalyst was maintained without compromising catalyst performance. Catalysts B and C demonstrated a start-up procedure in condensing steam identical to industrial condensing start-up conditions, with results for these catalysts demonstrating no significant leaching and consequently no significant activity loss over over 100 start-ups.

[0090] The additional samples DI in Table 2 below were prepared by compacting a single batch of powder having a Zn / Al molar ratio of 0.6 prepared according to Example 1 of the applicant's US 7,998,897 in a small hand-fed tablet press (a so-called Manesty tablet press). Higher mechanical strengths can be achieved at the same density by using an automatic full-scale device (such as a Kilian RX machine with a rotary press) for tableting. For 1.45-1.75 g / cm 3 We achieved tablet densities in the range of 50-100 kp / cm3 for SCS and 300-750 kp / cm3 for NPs using this device. 2 The ACS and PV values ​​for the catalysts are in the range of 450-300 ml / kg, thus similar to the results obtained for samples with similar tablet densities prepared on a Manesty machine. ACS and SCS are measured in the oxidized form of the catalyst. Furthermore, the mechanical strength values ​​mentioned above were measured according to ASTM D4179-11.

[0091] Table 2

[0092]

[0093] Figure 2 The data of Table 2 show the pore volume (upper curve) and mechanical strength (ACS kp / cm 2 or SCS kp / cm). Figure 2 It is clearly shown that the pore volume (PV) can be increased by reducing the tablet density, but even for low densities the mechanical strength (both ACS and SCS) can still be kept sufficiently high. For example, even at 1.25 g / cm 3 At lower densities, SCS is also 5 kp / cm, or alternatively ACS is 39 kp / cm 2 , which is sufficient mechanical strength for operation with high temperature catalysts.

[0094] Example 3:

[0095] The potassium-promoted Zn / Al type HTS catalyst is a copper-free catalyst according to, for example, Example 1 of the applicant's patent US Pat. No. 7,998,897. Figure 3The effect of alkali metals on catalytic activity at 380°C, in terms of CO conversion, is shown, particularly the high promoting effect of K, Rb, and Cs. Conversion was measured on aged catalysts. Aging was performed by exposing the catalysts to elevated temperatures from 330°C to 480°C over a 36-hour period. For example, K exhibited an approximately 4.5-fold increase in activity relative to the unpromoted catalyst, while Rb and Cs resulted in approximately 4-fold higher catalytic activity relative to the unpromoted catalyst.

[0096] Figure 4 The CO conversion of potassium as an alkali metal is shown, which surprisingly shows a high promoting effect, especially in the range of 1-6 wt% or 1-5 wt%. By operating with a catalyst with more potassium (e.g. about 6 wt%), any leaching of K actually leads to an increase in catalytic activity. If the potassium content is, for example, 2.5-5 wt%, any leaching of K will still maintain or increase the catalytic activity. The catalyst acts as a "base buffer" so that the catalytic activity is not significantly impaired. For example, a leaching of potassium of, for example, 10% (relative) will reduce the K content from, for example, 4 wt% K to 3.6 wt% K, which will not reduce the catalyst activity. In fact, if the initial K content is 5 wt% K, then at 10% (relative) leaching, the activity will increase because the catalyst with 4.5 wt% K has a higher activity than the catalyst with 5 wt% K. This feature, combined with the higher pore volume provided by the present invention, produces a surprisingly robust water-gas shift catalyst with significant mechanical strength and no significant (if any) loss of catalytic activity.

Claims

1. A water-gas shift catalyst comprising Zn, Al, optionally Cu, and an alkali metal or an alkali metal compound, wherein the water-gas shift catalyst is a Zn / Al-based catalyst comprising, in active form, a mixture of zinc-aluminum spinel and optionally zinc oxide and an alkali metal compound selected from the group consisting of K, Rb, Cs, Na, Li, and mixtures thereof, wherein the Zn / Al molar ratio is in the range of 0.5-1.0 and the alkali metal content is in the range of 2.5-6 wt% based on the weight of the oxidized catalyst, wherein the water-gas shift catalyst is free of chromium (Cr) and iron (Fe), and wherein the water-gas shift catalyst has a pore volume of 240 ml / kg or more as determined by mercury intrusion porosimetry. 2 . The water-gas shift catalyst according to claim 1 , wherein the alkali metal is K.

3. The water-gas shift catalyst according to claim 2, wherein the content of K is 4-4.5 wt% based on the weight of the oxidized catalyst.

4. The water-gas shift catalyst according to claim 2, wherein the content of K is 4-5 wt% based on the weight of the oxidized catalyst. 5 . The water-gas shift catalyst according to claim 1 , wherein the water-gas shift catalyst has a pore volume of 250 ml / kg or more as measured by mercury intrusion porosimetry. 6 . The water-gas shift catalyst according to claim 1 , wherein the water-gas shift catalyst has a pore volume of 240-380 ml / kg as measured by mercury intrusion porosimetry. 7 . The water-gas shift catalyst according to claim 1 , wherein the water-gas shift catalyst has a pore volume of 250-380 ml / kg as measured by mercury intrusion porosimetry.

8. The water-gas shift catalyst according to claim 1, wherein the water-gas shift catalyst has a pore volume of 300-600 ml / kg as measured by mercury intrusion porosimetry.

9. The water-gas shift catalyst according to claim 1, wherein the water-gas shift catalyst has a pore volume of 300-500 ml / kg as measured by mercury intrusion porosimetry.

10. The water-gas shift catalyst according to claim 1, wherein the water-gas shift catalyst has a pore volume of 320-430 ml / kg as measured by mercury intrusion porosimetry.

11. The water-gas shift catalyst according to claim 1, wherein the water-gas shift catalyst has a pore volume of 350-500 ml / kg as measured by mercury intrusion porosimetry.

12. The water-gas shift catalyst according to claim 1, wherein the water-gas shift catalyst has a pore volume of 400-450 ml / kg as measured by mercury intrusion porosimetry.

13. The water-gas shift catalyst according to any one of claims 1 to 12, comprising only Zn, Al, optionally Cu, and an alkali metal or an alkali metal compound.

14. The water-gas shift catalyst according to any one of claims 1 to 12, wherein the content of Cu is in the range of 0.1 to 10 wt% based on the weight of the oxidized catalyst.

15. The water-gas shift catalyst according to claim 14, wherein the content of Cu is 1-5 wt% based on the weight of the oxidized catalyst.

16. The water-gas shift catalyst according to any one of claims 1 to 12, wherein the catalyst is in the form of pellets, extrudates or tablets, and wherein the density of the catalyst is 1.2 to 1.9 g / cm 3 , measured by dividing the weight of the catalyst by its geometric volume.

17. The water-gas shift catalyst according to claim 16, wherein the density of the catalyst is 1.35-1.75 g / cm 3 .

18. The water-gas shift catalyst according to claim 16, wherein the density of the catalyst is 1.55-1.85 g / cm 3 .

19. The water-gas shift catalyst according to any one of claims 1 to 12, wherein the catalyst is in the form of pellets, extrudates or tablets, and wherein the mechanical strength is in the range of ACS 30-750 kp / cm 2 or SCS of 4-100 kp / cm, wherein ACS and SCS are measured in the oxidized form of the catalyst in accordance with ASTM D4179-11.

20. The water-gas shift catalyst according to claim 19, wherein the mechanical strength of the catalyst is in the following range: ACS is 130-700 kp / cm 2 ; or SCS is 20-90kp / cm.

21. The water-gas shift catalyst according to claim 19, wherein the mechanical strength of the catalyst is in the following range: ACS is 30-350 kp / cm 2 ; or SCS is 4-40kp / cm.

22. A method of enriching synthesis gas with hydrogen by contacting the synthesis gas with a water-gas shift catalyst according to any one of claims 1 to 21 in a water-gas shift reactor.

23. The process of claim 22, wherein the water-gas shift reactor is a high temperature shift (HTS) reactor.

24. The process according to claim 22 or 23, wherein the water-gas shift reactor is a HTS reactor operated at a temperature in the range of 300-550°C and optionally also at a pressure in the range of 2.0-6.5 MPa.

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