Steam reforming

Abstract

A process for steam reforming of a hydrocarbon feedstock containing one or more nitrogen compounds is described, the process comprising: passing a mixture of the hydrocarbon feedstock and steam through a catalyst bed consisting of one or more nickel steam reforming catalysts placed in a plurality of externally heated tubes in a tubular steam reformer, wherein each tube has an inlet to feed the hydrocarbon and steam mixture and an outlet to recover a reformate gas containing hydrogen, carbon monoxide, carbon dioxide, steam, ammonia and methane, and wherein at least at the outlet of the tube, the steam reforming catalyst is a structured steam reforming catalyst comprising nickel dispersed on the surface of a porous metal oxide present as a coating on a non-porous metal or ceramic structure, wherein the nickel content in the metal oxide coating is in the range of 5 to 50 wt.-% and the thickness of the coating is in the range of 5 to 150 micrometers.

Description

[0001] The present invention relates to a method for hydrocarbon steam reforming to produce syngas and an apparatus for carrying out the method.

[0002] Syngas comprises hydrogen and carbon oxides (carbon monoxide and carbon dioxide), and may contain nitrogen and other gases, such as argon and low amounts of methane. Syngas can contain more or less hydrogen and carbon oxides to suit specific end uses, such as hydrogen production in refineries or fuel cells, ammonia synthesis, methanol synthesis, dimethyl ether synthesis, or the Fischer-Tropsch process for liquid hydrocarbon synthesis. Syngas is typically produced through steam reforming.

[0003] In conventional steam reforming processes, a mixture of hydrocarbon feedstock and steam, and in some cases carbon dioxide, is passed under high pressure through a tube containing particulate catalyst, which is externally heated by a suitable heating medium (usually a hot gas mixture). The particulate catalyst is typically in the form of shaped units, such as cylinders with multiple through-holes, and is usually formed from a refractory support material such as α-alumina, calcium aluminate, or magnesium aluminate, impregnated with a suitable catalytically active metal such as nickel.

[0004] Hydrocarbon feedstocks typically contain small amounts of nitrogen, which are converted into ammonia by a steam reforming catalyst. Ammonia is not required in the syngas, but it is soluble in the process condensate, which is ideally returned to the process. Furthermore, processes have been proposed to minimize ammonia formation.

[0005] US5498404 discloses a method for catalytic steam reforming of a nitrogen-containing carbonaceous feedstock with reduced ammonia formation, wherein the feedstock is contacted with a supported nickel catalyst, the supported nickel catalyst further comprising 0.01 wt% to 10 wt% copper based on the amount of nickel in the catalyst. Preferably, the copper-containing catalyst is used as a sublayer in a fixed bed of a conventional nickel steam reforming catalyst. Example 1 shows that the steam reforming activity of the catalyst decreases with increasing copper content.

[0006] WO2009 / 054830 discloses a method for reforming natural gas without producing excess ammonia by using a first-stage catalyst with about 10% to about 25% nickel, a second-stage catalyst with less than 10% nickel, and a final-stage catalyst with a low concentration of 2% or less rhodium. Ammonia formation is suppressed by reducing the nickel content in the catalyst and the surface area at the hottest part of the tube facing the outlet. However, the conversion rate becomes undesirably low due to the reduced nickel content in the second stage, thus requiring a rhodium catalyst to provide sufficient syngas products. Precious metal catalysts are too expensive for large-scale syngas production in steam reformers, and the use of mixed catalysts increases the cost and complexity of catalyst loading, operation, and emissions. Furthermore, mixed catalysts present greater challenges for reprocessing in terms of metal recovery.

[0007] It has been found that ammonia formation can be reduced by using a nickel steam reforming catalyst instead of a rhodium catalyst, where nickel exists in a thin layer on the catalyst surface.

[0008] Accordingly, the present invention provides a method for steam reforming a hydrocarbon feedstock containing one or more nitrogen compounds, comprising: passing a mixture of hydrocarbon feedstock and steam through a catalyst bed composed of one or more nickel steam reforming catalysts, the nickel steam reforming catalysts being placed in a plurality of externally heated tubes in a tubular steam reformer, wherein each tube has an inlet for feeding the hydrocarbon and steam mixture and an outlet for recovering reformed gas containing hydrogen, carbon monoxide, carbon dioxide, steam, ammonia and methane, and at least at the outlet of the tube, the steam reforming catalyst is a structured steam reforming catalyst containing nickel, wherein the nickel is dispersed on a porous metal oxide surface as a coating on a non-porous metal or ceramic structure, wherein the nickel content in the metal oxide coating is in the range of 5% by weight to 50% by weight, and the thickness of the coating is in the range of 5 micrometers to 150 micrometers.

[0009] The hydrocarbon feedstock fed in this method may include any gaseous or low-boiling-point hydrocarbon feedstock, such as natural gas, associated gas, LPG, petroleum fractions, diesel oil, naphtha, or mixtures thereof, or exhaust gases from chemical processes, such as refinery exhaust gases or pre-reformed gases. Preferably, the hydrocarbon feedstock includes methane and may be pre-reformed gas, associated gas, or natural gas. Natural gas is a particularly preferred feedstock. The feedstock can be compressed to a pressure in the range of 10 to 100 bar absolute pressure. The pressure of the hydrocarbon feedstock can effectively control the pressure throughout the process. Preferably, the operating pressure is in the range of 15 to 80 bar absolute pressure, more preferably in the range of 20 to 50 bar absolute pressure, as this enhances the performance of the process.

[0010] If the hydrocarbon feedstock contains sulfur compounds before or preferably after compression, it can be desulfurized. Desulfurization may include hydrodesulfurization using a CoMo or NiMo catalyst and hydrogen sulfide absorption using a suitable hydrogen sulfide adsorbent such as a zinc oxide adsorbent. Ultrapure adsorbents can be effectively used downstream of the hydrogen sulfide adsorbent to further protect the steam reforming catalyst. Suitable ultrapure adsorbents may include copper-zinc oxide / alumina materials and copper-nickel-zinc oxide / alumina materials. To facilitate hydrodesulfurization and / or reduce the risk of carbon deposition in the reforming process, hydrogen may be added to the compressed hydrocarbon feedstock. The amount of hydrogen in the resulting mixed gas stream may range from 1 vol% to 20 vol%, but preferably from 1 vol% to 10 vol%, more preferably from 1 vol% to 5 vol%.

[0011] If the hydrocarbon feedstock contains other contaminants, such as chlorides or heavy metals, these contaminants can be removed using conventional adsorbents, either upstream or downstream of any desulfurization process, prior to reforming. Adsorbents suitable for chloride removal are known and include alkalized alumina materials. Similarly, adsorbents for heavy metals such as mercury or arsenic are known and include copper sulfide materials.

[0012] In the case of a methane-containing pre-reformed gas feedstock, this can be achieved by subjecting the hydrocarbon / steam mixture to an adiabatic cryogenic steam reforming step. The hydrocarbons can be hydrocarbon-rich natural gas, naphtha, or other hydrocarbon feedstocks with a hydrocarbon content exceeding that of methane. Pre-reformation methods are known. In such methods, the hydrocarbon / steam mixture is heated, typically to a temperature in the range of 400°C to 650°C, and then adiabatically passed through a fixed bed of a suitable particulate steam reforming catalyst, typically a precipitated catalyst with a high nickel content (e.g., above 40% by weight, expressed as NiO). During this adiabatic cryogenic pre-reformation step, any hydrocarbons with a content exceeding that of methane react with the steam to obtain a pre-reformed gas containing a mixture of methane, carbon oxides, and hydrogen. Using this adiabatic reforming step, commonly referred to as pre-reformation, is intended to ensure that the feedstock entering the tubular steam reformer contains no more hydrocarbons than methane and also contains a significant amount of hydrogen. This is ideal for minimizing the risk of carbon formation on the catalyst in the downstream tubular steam reformer.

[0013] In this method, the hydrocarbon feedstock may contain 0.1 vol% to 25 vol% of one or more nitrogen compounds. The content of the one or more nitrogen compounds in the hydrocarbon feedstock may be 0.5 vol% to 25 vol%, 1 vol% to 10 vol%, or 1 vol% to 5 vol%. The one or more nitrogen compounds may include one or more amines, but generally include nitrogen (N2) or consist of nitrogen. Therefore, the nitrogen content of the hydrocarbon feedstock may be 0.1 vol% to 25 vol% or 0.5 vol% to 25 vol%, preferably in the range of 1 vol% to 10 vol%, and more preferably in the range of 1 vol% to 5 vol%.

[0014] The raw material can be preheated. It can be easily preheated using a suitable heat source such as a flame heater after compression and before desulfurization.

[0015] The hydrocarbon feedstock is mixed with steam to form a reforming feed gas. Steam introduction can be achieved by directly injecting steam and / or by saturating the feedstock by contacting it with a stream of heated water. In some embodiments, the hydrocarbon feedstock is saturated in a saturator fed with hot water to form a saturated gas mixture. If desired, the steam content of the saturated gas mixture can be increased by directly adding steam. Preferably, the water includes one or more of the condensate stream recovered from the reforming gas, water recovered from the bottom of the saturator, and other condensates generated in the process. Ideally, the amount of steam introduced is sufficient to ensure that the steam-to-carbon ratio in the feedstock is at least 1.8:1, i.e., at least 1.8 moles of steam per gram of hydrocarbon carbon atoms. Preferably, the steam-to-carbon ratio is in the range of 1.8:1 to 5:1, more preferably in the range of 2.5:1 to 3.5:1, and especially in the range of 2.8:1 to 3.2:1, as this achieves an optimal balance between hydrogen production and efficiency.

[0016] Depending on the content of steam and nitrogen compounds, the reforming feed gas, including hydrocarbon feedstock and steam, may contain 0.02 vol% to 14.0 vol%, optionally 0.1 vol% to 10.0 vol%, or optionally 0.2 vol% to 6.0 vol% of one or more nitrogen compounds.

[0017] Then, ideally, the reforming feed gas mixture is preheated before reforming. In a preferred embodiment, the hydrocarbon / vapor mixture is heated by passing it through a flame heater. Ideally, the mixture is heated to an inlet temperature in the range of 300°C to 650°C or 450°C to 650°C, preferably in the range of 450°C to 600°C, and more preferably in the range of 450°C to 550°C. An inlet temperature in the range of 300°C to 550°C is particularly suitable in the absence of a pre-reformer, and a higher inlet temperature in the range of 550°C to 650°C is particularly suitable in the presence of a pre-reformer.

[0018] In the reforming process, methane reacts with steam to produce hydrogen, carbon monoxide, and carbon dioxide. Any hydrocarbon containing two or more carbon atoms present is converted to methane, thus undergoing steam reforming. Additionally, a reversible water-gas conversion reaction occurs. In summary, this is an endothermic process requiring heating tubes and a catalyst to sustain the reaction and achieve the desired conversion rate. Typically, the heat input to the steam reformer ensures that the temperature of the gas stream products at the tube outlet is higher than the inlet temperature, usually by 100 to 350 or 400 degrees Celsius.

[0019] A tubular steam reformer comprises multiple tubes, typically arranged vertically, through which a gas mixture passes, and heat is transferred to the tubes by flowing hot gas around their outer surfaces. The hot gas may include combustion gas or synthesis gas. The tube inlets are typically located at the top, so that the feed gas mixture is generally fed to the top of the steam reformer and flows downwards through the tubes.

[0020] Therefore, a tubular steam reformer may have an inlet for reforming feed gas, an outlet for reforming gas mixture, and multiple vertical tubes connected to the inlet through which the gas mixture passes, and heat is transferred to the vertical tubes by allowing hot gas to flow around the tubes in a heat exchange zone, wherein each tube contains one or more steam reforming catalysts provided as an inner layer of the tube, wherein at least the steam reforming catalyst layer adjacent to the outlet is a structured nickel steam reforming catalyst.

[0021] In this method, the catalyst adjacent to the pipe outlet is a structured steam reforming catalyst. A "structured steam reforming catalyst" refers to a steam reforming catalyst coated on a non-porous structure (typically a metal or ceramic structure). In this structured catalyst, nickel is dispersed on the surface of a porous metal oxide, which serves as a surface coating supported on the non-porous structure.

[0022] The metallic or ceramic structure is essentially non-porous, and therefore has a relatively small surface area largely defined by its shape. To provide sufficient activity, nickel in the structured catalyst is dispersed on a porous metal oxide coated on a non-porous metallic or ceramic support. The thickness of the nickel-containing porous metal oxide coating on the non-porous structure is in the range of 5 micrometers to 150 micrometers, preferably in the range of 10 micrometers to 100 micrometers, more preferably in the range of 10 micrometers to 80 micrometers, and most preferably in the range of 10 micrometers to 50 micrometers. These preferred ranges result in catalysts exhibiting optimal activity, adhesion, and cohesion.

[0023] Nickel can be applied to a structure using known wash-coating processes, whereby a slurry of metal oxides (which may include nickel oxides as a component) is applied to a metal or ceramic structure by impregnation or spraying, followed by drying and heat treatment to bond the metal oxides to the carrier. Nickel can also be applied to a metal oxide-coated carrier using impregnation techniques with soluble nickel compounds, followed by drying and calcination to convert the nickel compound into nickel oxides. Combinations of these techniques can be used, including the combined application of nickel in solution with a metal oxide carrier slurry.

[0024] The structural steam reforming catalyst contains nickel. The nickel content of the metal oxide coating is from 5% to 50% by weight, preferably from 10% to 30% by weight, and more preferably from 10% to 20% by weight. Optionally, platinum group metals selected from platinum, rhodium, ruthenium, or palladium, or mixtures thereof, may be included in the coating. If included, platinum group metal promoters can be present in the coating in an amount ranging from 0.05% to 1% by weight. The coating can be 10 g / m³. 2 Up to 150g / m 2 Preferably 10g / m 2 Up to 80g / m 2 More preferably 30g / m 2 Up to 60g / m 2 The amount within the range is applied to the non-porous carrier structure.

[0025] Alkali metal oxides, such as potassium oxides, may also be present in the porous metal oxide coating on this structure, but are generally not required. If present, the amount of alkali metal oxides can range from 0.5% to 7.0% by weight.

[0026] The porous metal oxide on which nickel is dispersed can be any suitable refractory oxide, including alumina, titanium dioxide, zirconium oxide, zinc oxide, magnesium oxide, cerium dioxide, praseodymium oxide, yttrium oxide, and lanthanum oxide. Preferred porous metal oxides include alumina, zirconium oxide, cerium dioxide, lanthanum oxide, and mixtures of two or more of them.

[0027] In some embodiments, the metal or ceramic structure can be a solid body, such as a sphere or cylinder, which may have one or more through-holes. Such structured catalysts can be used in a manner comparable to conventional granular steam reforming catalysts.

[0028] In some embodiments, the structured catalyst may comprise a metallic or ceramic structure with multiple channels through which process fluids can pass in an ordered rather than random direction. Such structured catalysts are preferred when reduced pressure drop and improved heat transfer are required. Therefore, the structured catalyst may comprise cylindrical units with a diameter complementary to that of the tube, the cylindrical units being placed within the tube, the cylindrical units comprising multiple channels through which process fluids can pass in an ordered rather than random direction. The term "complementary" means that the diameter of the cylindrical unit may be 1 mm to 20 mm smaller than the inner diameter of the tube in which the unit is placed, thereby allowing it to be neatly arranged within the tube. The cylindrical unit may comprise perforations and / or internal structures that allow process fluids to flow axially and radially as they pass through the unit. Preferably, the cylindrical units may be stacked, allowing them to be easily loaded onto each other and forming self-support within the tube. The advantage of using cylindrical units with multiple channels through which process fluids can pass in an ordered rather than random direction, rather than coated particles, is that the amount of catalyst coating can be reduced. For example, for coated metal or ceramic granules, the coating can be applied at approximately 100 kg to 150 kg of Ni (calculated as NiO) per cubic meter of pipe. For coated cylindrical structures with multiple channels through which process fluids can pass in an ordered rather than random direction, the amount of coating can be approximately 4 kg to 7 kg of Ni (calculated as NiO) per cubic meter of pipe.

[0029] Preferably, a structured catalyst prepared using commercially available stainless steel foil is used.

[0030] Preferred structured catalysts are described in US2012 / 0195801A1. These structured catalysts include a fan-shaped device in the form of a corrugated metal disc arranged on a central rod. The fan-shaped device has a radial fluid conduit formed of folded metal foil, which guides fluid flow in radial contact with the inner wall of the tube; the fan-shaped device has an upper surface, a lower surface, and an outer diameter surface such that the radial fluid conduit terminates along the outer diameter surface of the fan-shaped device to form a fluid conduit opening facing the inner wall of the tube. The fan-shaped device also has a flat or corrugated metal gasket in contact with the upper or lower surface of the fan-shaped device, wherein the gasket may be annular with an inner diameter and an outer diameter, the gasket contacting the upper or lower surface of the fan-shaped device such that the outer diameter of the gasket extends radially outward from the outer diameter surface of the fan-shaped device. The gasket may also have a separating protrusion extending radially outward from the outer diameter of the gasket, the separating protrusion separating the gasket from the inner wall of the tube such that the gasket creates a gap between the outer diameter surface of the fan-shaped device and the reactor tube. Alternative steam reforming catalysts may be supported on the structured catalyst arrangements including those described in US2012 / 0294779, US2012 / 0288420, US8257658, US8235361, US7976783, US7566487, US7761994, US8178075 and US7871579.

[0031] Each tube may contain a single type of structured catalyst, in which case the catalyst bed in the tube consists only of structured catalyst. Alternatively, there may be two, three or more layers of steam reforming catalyst in the tube, wherein in each case, at least the layer adjacent to the tube outlet is structured catalyst.

[0032] Therefore, the tube may include an unstructured steam reforming catalyst upstream of the structured catalyst. The relative thickness of the steam reforming catalyst can vary to achieve the desired conversion. In some embodiments, an unstructured catalyst layer and a structured catalyst layer are included near the tube outlet, where the structured catalyst layer may occupy 95% to 5% of the bed volume, or 80% to 20% of the bed volume, or 75% to 25% of the bed volume. Other steam reforming catalyst layers in the catalyst bed in the remaining portion of the tube may be conventional granular catalysts, wherein nickel is distributed in the granules or eggshell-type nickel-based catalysts, wherein the nickel layer exists only on the surface of the refractory metal oxide particles. Suitable unstructured catalysts consist of granules of nickel and optionally potassium oxide, supported on a refractory oxide carrier comprising alumina or alkaline earth metal aluminates such as calcium aluminate and / or magnesium aluminate.

[0033] When the catalyst bed consists of two or three layers of nickel steam reforming catalyst, preferably, the catalyst layer at the tube inlet is an unstructured granular nickel steam reforming catalyst. When an unstructured granular catalyst is used upstream of a structured steam reforming catalyst, preferably, the nickel content (expressed as NiO) of the unstructured granular catalyst is in the range of 10% to 30% by weight. Therefore, in some embodiments, the catalyst tube may include or consist of two layers of nickel steam reforming catalyst, wherein the catalyst layer adjacent to the tube outlet is a structured nickel steam reforming catalyst, and the catalyst layer adjacent to the tube inlet is an unstructured granular nickel steam reforming catalyst containing 10% to 30% nickel (expressed as NiO).

[0034] Typically, the catalyst is provided in oxidized form into the tubes of a tubular steam reformer and activated by the reduction of nickel oxide to form elemental nickel in situ. For example, the catalyst in oxidized form can be placed in the tubes, and the nickel oxide is reduced with a reducing agent such as a hydrogen-containing gas. Known reduction techniques can be used to produce active catalysts for steam reforming.

[0035] Alternatively, the nickel oxide in the catalyst can be reduced ex-situ, and then air diluted with an oxygen-containing gas such as air or nitrogen can be used to coat the elemental metal with a thin oxide passivation layer. A mixture of oxygen and carbon dioxide (optionally, with nitrogen) can also be used. In this way, the reduced catalyst can be safely transported to the user, and the time required to generate an active catalyst and the amount of hydrogen used during subsequent activation are reduced.

[0036] Various tubular steam reformer arrangements can be used. The tubular steam reformer can be a conventional top-fired or side-fired steam reformer. In such reformers, hot gas is provided by burning fuel gas using multiple burners located at the top of the tube or along its length. Alternatively, the steam reformer can be a gas heated reformer (GHR), where the hot gas can be provided by flue gas from the combustion process, or by syngas produced through catalytic or non-catalytic partial oxidation of hydrocarbons or by autothermal reforming of a mixture of hydrocarbons and / or reformed gases. Furthermore, the hot gas can be mixed with reformed gas that has already passed through the aforementioned multiple tubes. These tubes can have a circular cross-section and a length of 5 m to 15 m, and preferably an inner diameter in the range of 5 cm to 30 cm or 10 cm to 15 cm. In use, the tube operates along its length with a temperature gradient, and the tube inlet end is cooled by an endothermic steam reforming reaction. The temperature of the reactant gas at the inlet and inlet of the tube can be between 300°C and 650°C, or 450°C and 650°C, preferably between 450°C and 600°C, and more preferably between 450°C and 550°C. At the outlet end of the tube, where the conversion to form the syngas is substantially complete, the temperature of the tube is higher. The temperature of the reactant gas at the tube and outlet can be between 600°C and 950°C. The temperature of the catalyst in the tube can be expressed as the bed temperature, which is the average temperature of the catalyst between the inlet and outlet of one or more catalyst beds in the tube. Ideally, the bed temperature can be between 625°C and 775°C, or 640°C and 760°C.

[0037] Reformed gas or crude syngas is recovered from the tubular reformer outlet. This reformed gas contains hydrogen, carbon monoxide, carbon dioxide, water vapor, ammonia, and methane. Due to an equilibrium defect in the method, the reformed gas contains some methane. The methane content from the tubular reformer, or "methane leakage," indicates the efficiency of the process. Furthermore, methane can accumulate in downstream processes using the reformed gas, which is undesirable. Accordingly, low methane leakage is more desirable. Using a structured steam reforming catalyst and the reaction conditions described above, this method can provide low methane leakage, for example, less than 15% by volume based on dry gas. Preferably, where the crude syngas is not subsequently subjected to secondary or autothermal reforming, methane leakage is less than 10% by volume based on dry gas, and especially less than 5% by volume based on dry gas. The term "based on dry gas" means regardless of the steam content of the reformed gas and is used to allow comparison with other reformed gases having different steam contents.

[0038] Furthermore, the ammonia content of the reformed gas is unexpectedly low. Unbound by theory, the applicant believes that the presence of nickel as only a thin layer on the surface of the structure implies that the side reaction leading to ammonia formation is suppressed. Therefore, in this method, the ammonia content of the reformed gas, based on dry gas, can be less than 200 ppmv. In some embodiments, the ammonia content of the reformed gas, based on dry gas, can be less than 100 ppmv, preferably less than 50 ppmv, and more preferably less than 10 ppmv.

[0039] Accordingly, the present invention further provides the use of a structured steam reforming catalyst as described herein, the catalyst comprising: nickel dispersed on the surface of a porous metal oxide, the porous metal oxide existing as a coating on a non-porous metal or ceramic structure, wherein the nickel content of the metal oxide coating is in the range of 5% to 50% by weight, and the thickness of the coating is in the range of 5 micrometers to 150 micrometers, to suppress the formation of ammonia during catalytic steam reforming of nitrogen-containing hydrocarbon feedstocks.

[0040] The method may further include: cooling the reformed gas below its dew point to condense the vapor, and then separating the condensate to form syngas from the reformed gas. The condensate captures most (but not all) of the ammonia formed during the steam reforming process. The ammonia content of the condensate may be less than 400 mg / L, preferably less than 200 mg / L, more preferably less than 100 mg / L, most preferably less than 50 mg / L, or even 20 mg / L. In a preferred embodiment, at least a portion of the condensate is recycled and used to generate steam for the steam reforming process.

[0041] The method described in this invention can be used as part of a method for producing hydrogen, methanol, dimethyl ether, olefins, ammonia, urea, or liquid hydrocarbons such as diesel fuel obtained through Fischer-Tropsch synthesis. Therefore, the reformed gas can be further processed, including one or more steps such as cooling it below its vapor dew point, condensate separation, hydrogen separation, carbon dioxide separation, methanol synthesis, dimethyl ether synthesis, olefin synthesis, ammonia synthesis, or liquid hydrocarbon synthesis. Known methods can be used to accomplish these steps.

[0042] Combine the following Figures 1 to 6 The embodiments shown further describe the present invention, wherein:

[0043] Figure 1 It is a graph depicting the conversion of ammonia produced per second relative to ethane per mol% in a test using a reformer feed containing 2% N2 by volume.

[0044] Figure 2 It is a graph depicting the conversion of ammonia produced per second relative to ethane per mol% in a test using a reformer feed containing 5% N2 by volume.

[0045] Figure 3 It is a graph depicting the conversion of ammonia produced per second relative to ethane per mol% in a test using a reformer feed containing 8% N2 by volume.

[0046] Figure 4 This describes the conversion of ethane per mol% of catalyst relative to the conversion of ethane per m³ of catalyst in a reformer feed containing 2 vol% N₂ during a test. 2 A graph showing the ammonia produced per second in Ni;

[0047] Figure 5 This describes the conversion of ethane per mol% of catalyst relative to the conversion of ethane per m³ of catalyst in a reformer feed containing 5 vol% N₂ during a test. 2 A graph showing the ammonia produced per second in Ni; and

[0048] Figure 6 This describes the conversion of ethane per mol% of catalyst relative to the conversion of ethane per m³ of catalyst in a reformer feed containing 8 vol% N₂ during a test. 2 A graph showing the ammonia produced per second in Ni.

[0049] Example 1

[0050] Tests were conducted on conventional cylindrical granular steam reforming catalysts containing 17.6 wt% nickel or 7.2 wt% nickel, while the structured catalyst comprised a catalyst coating containing 13 wt% nickel and 0.25 wt% rhodium on stabilized alumina oxide, applied as a support coating to stainless steel particles (3.3 mm × 3.3 mm cylinders). The catalyst coating loading was 23 mg / in. 2 The thickness of the catalyst coating is approximately 30 micrometers.

[0051]

[0052] The catalyst described above was tested in a laboratory steam reformer with a single electrically heated reformer tube having an inner diameter of approximately 25 mm and a length of approximately 2100 mm. The reactor operated on an upward flow basis. Water for steam generation was supplied to the unit via a variable stroke pump and fed to the bottom of the reactor, where it was vaporized. Natural gas was fed through a separate desulfurization vessel and then delivered to the reactor via a thermal mass flow controller. Nitrogen and hydrogen were also supplied to the reactor via separate mass flow controllers if needed. Water and gases all entered the reactor through the same inlet pipe. The gaseous product exited the reactor via a pipe outlet and was cooled to ambient temperature to condense the vapor, which was then collected in a gas trap. A small amount of dried exhaust gas was fed to a Varian CP490 four-channel micro gas chromatograph (GC) analyzer. This gas was then returned to the outlet flow meter to allow for the calculation of complete mass balance from the reformer.

[0053] For each catalyst, the particle size was measured to determine how many particles were needed to produce 21080 mm. 2 The geometrical surface area (GSA) was calculated. For the structured catalyst, 363 coated particles were loaded, while for the comparative catalyst, 389 particles were loaded. The amount of nickel loaded into the reaction tube was 0.07 g for the structured catalyst and 3.45 g for the comparative catalysts 1(a) and 1(b). The particles were diluted to 100 mL with alumina fragments ranging from 3.35 mm to 4.00 mm and a mixture loaded into the reformer tube near the outlet. The remaining portion of the reformer tube was loaded with alumina fragments ranging from 3.35 mm to 4.75 mm.

[0054] The catalyst was reduced in N2 at 600 °C for 2 hours using 50 vol% H2.

[0055] Reforming was then carried out at a pressure of 27 bar using bed inlet temperatures ranging from 510°C to 800°C, with a steam-to-carbon ratio of 3:1. Catalyst conditioning was first performed by operating the reformer at inlet temperatures of 610°C, 685°C, 735°C, 800°C, and 735°C, each for at least 8 hours. Catalyst conditioning of the structured catalyst was then performed by operating the reformer at inlet temperatures of 510°C, 580°C, 610°C, 685°C, 735°C, 800°C, 735°C, 685°C, 610°C, 580°C, and 510°C, each for at least 8 hours, followed by a further treatment with H2 at 800°C for 16.5 hours to ensure all nickel was in its active reduced form. This additional conditioning was to ensure complete catalyst reduction and not to affect ammonia formation in subsequent tests.

[0056] After adjustment, each catalyst was tested at inlet temperatures of 685°C, 735°C, and 800°C.

[0057] The nitrogen content of the feed is adjusted to provide N2 based on 2 vol%, 5 vol%, and 8 vol% of wet gas in the feed gas mixture at the catalyst inlet.

[0058] Reformed gas is collected from the reformer and cooled below the dew point to condense the vapor and form an ammonia-containing condensate. The ammonia content in the condensate is proportional to the ammonia formed by the catalyst in the steam reformer. At the end of the 8-hour test period, a condensate sample (250 ml) is collected within 5 minutes and its ammonia content is analyzed.

[0059] The ammonia concentration in the condensate recovered from reformed gas was measured using a calibrated ion-selective electrode (ISE). Standard solutions containing 0.1 ppm (w / v), 1 ppm (w / v), and 10 ppm (w / v) of ammonia were prepared. Sodium hydroxide buffer was added to the above samples to release the ammonia. Once the ISE voltage measurement was stable, a linear calibration curve was generated using the readings against log10 ammonia concentration. The ammonia concentration in the above condensate was determined by deriving the voltage readings measured using the ISE from the calibration curve, thus analyzing the ammonia concentration in the condensate in the same manner.

[0060] Each catalyst was repeatedly tested using feed gases containing different amounts of nitrogen. This was done by introducing nitrogen at various flow rates via a nitrogen supply line to provide the required level of nitrogen in the feed gas fed to the reformer tubes.

[0061] The table below lists the results of ammonia production in the condensate of different catalysts using feed gases with different nitrogen contents.

[0062] Comparison of catalyst 1(a) Bed inlet temperature ℃ <![CDATA[[N2],vol.%]]> <![CDATA[[NH3],mg / L]]> 685 2 0.102 685 5 0.226 685 8 0.451 735 2 0.209 735 5 0.515 735 8 0.901 800 2 0.501 800 5 1.100 800 8 1.800

[0063] Comparison of catalyst 1(b) Bed inlet temperature ℃ <![CDATA[[N2],vol.%]]> <![CDATA[[NH3],mg / L]]> 685 2 0.050 685 5 0.081 685 8 0.144 735 2 0.071 735 5 0.210 735 8 0.420 800 2 0.166 800 5 0.435 800 8 0.807

[0064] Structured catalyst 1(c) Bed inlet temperature ℃ <![CDATA[[N2],vol.%]]> <![CDATA[[NH3],mg / L]]> 685 2 0.015 685 5 0.018 685 8 0.019 735 2 0.014 735 5 0.020 735 8 0.026 800 2 0.031 800 5 0.060 800 8 0.081

[0065] Within the inlet temperature range, the structured catalyst produces a lower amount of ammonia compared to the comparative example. However, the catalysts contain varying amounts of nickel, have different nickel surface areas, and exhibit different activities. If a catalyst is more active, the amount of steam consumed will be greater than that consumed by a less active catalyst. The ammonia concentration is affected when this unreacted steam condenses. Therefore, the molar flow rate of water is calculated based on an oxygen balance derived from knowledge of the composition and rate of the feed gas and gas chromatographic data of the reformed gas obtained using a GC system coupled to a steam reformer. The difference in the amount of oxygen entering and leaving the system can be used to determine the amount of ammonia produced per second.

[0066] Furthermore, this structured catalyst is able to produce reformate with a high conversion rate of hydrocarbons in natural gas.

[0067] Gas chromatography was used to analyze the reformed gas after condensate removal to determine the conversion rates of hydrocarbons to hydrogen and carbon oxides. Compared to reversible methane conversion, the ethane conversion rate in natural gas is more helpful in measuring overall catalyst activity.

[0068] Plotting ammonia concentration per second against ethane conversion illustrates the catalyst's effectiveness in terms of activity and ammonia production. Figures 1 to 3 The percentage of ammonia produced per second relative to the ethane conversion is shown. The results are listed below:

[0069]

[0070]

[0071]

[0072] Compared to the comparative catalyst, the structured catalyst initially exhibited a lower ethane conversion at the test temperature. However, it was observed that at 800 °C, the structured catalyst provided a higher ethane conversion compared to comparative catalyst 1(b), albeit with a small amount of ammonia production, at feed gas N2 contents of 2 vol%, 5 vol%, and 8 vol%. Comparative catalyst 1(a) at 735 °C achieved a comparable ethane conversion to the structured catalyst at 800 °C, but the latter contained a small amount of nickel. Testing the structured catalyst at higher inlet temperatures could further improve ethane conversion while maintaining a lower ammonia concentration.

[0073] Although the activity of this structured catalyst is lower than that of the standard granular catalyst for a given inlet temperature, it is meaningful to take into account the ammonia produced when the catalyst is operated at the same hydrocarbon conversion rate, as this better reflects the expected operation in use. Furthermore, the nickel grains in this structured catalyst are an order of magnitude smaller than those in the granular catalyst, resulting in a different nickel surface area (compared to 0.5 μm for catalyst 1(a)). 2 / g, while the structured catalyst is 8m 2 / g). With this in mind, the performance differences between structured catalysts and granular catalysts are described more clearly. Figure 4 , Figure 5 and Figure 6The figures show the percentage of ammonia produced relative to ethane conversion based on the nickel surface area. These figures illustrate that the amount of ammonia produced using the structured catalyst is significantly lower than that produced using a conventional granular catalyst. Furthermore, comparable activity to that of granular catalysts can be achieved with significantly less nickel, while producing significantly less ammonia. This has been achieved by dispersing nickel in a thin coating on a non-porous support. These results demonstrate that by using a structured catalyst near the reformer outlet, ammonia formation can be reduced without compromising overall reforming performance.

Claims

1. Use of a nickel steam reforming catalyst for producing a reformed gas having a reduced ammonia content in a process for steam reforming of a hydrocarbon feedstock containing from 1 to 10 vol% of nitrogen (N2), said process comprising: passing a mixture of the hydrocarbon feedstock and steam through a catalyst bed consisting of one or more nickel steam reforming catalysts placed in a plurality of externally heated tubes in a tubular steam reformer, wherein each tube has an inlet to feed the mixture of the hydrocarbon feedstock and steam and an outlet to recover a reformate gas containing hydrogen, carbon monoxide, carbon dioxide, steam, ammonia and methane, and wherein at least at the outlet of the tubes the nickel steam reforming catalyst is a structured steam reforming catalyst comprising nickel dispersed on a porous metal oxide surface present as a coating on a non-porous metal or ceramic structure, wherein the nickel content in the metal oxide coating is in the range of 5 to 50 wt%, the thickness of the coating is in the range of 5 to 150 microns, and wherein the ammonia content of the reformate gas is below 200 ppmv on a dry gas basis.

2. Use according to claim 1, wherein the thickness of the porous metal oxide coating containing the nickel on a non-porous structure is in the range of 10 to 100 microns.

3. Use according to claim 1, wherein the nickel content of the metal oxide coating is in the range of 10 to 30 wt%.

4. Use according to claim 1, wherein a platinum group metal promoter selected from platinum, palladium, rhodium or ruthenium or mixtures thereof is contained in the coating.

5. Use according to claim 4, wherein the platinum group metal promoter is present in the coating in an amount in the range of 0.05 to 1 wt%.

6. Use according to claim 1, wherein the porous metal oxide on which the nickel is dispersed is a refractory oxide comprising alumina, titania, zirconia, zinc oxide, magnesium oxide, ceria, praseodymium oxide, yttrium oxide and lanthanum oxide.

7. The use according to claim 1, wherein the amount of coating on the non-porous structure is in the range of 10 g / m 2 to 150 g / m 2 .

8. Use according to claim 1, wherein the structured steam reforming catalyst comprises a metal or ceramic structure having a plurality of channels through which process fluid can pass in an ordered rather than random direction.

9. Use according to claim 8, wherein the structured steam reforming catalyst comprises cylindrical elements having a diameter complementary to the tubes in which they are placed, the cylindrical elements comprising a plurality of channels through which process fluid can pass in an ordered rather than random direction.

10. Use according to claim 1, wherein the hydrocarbon feedstock comprises methane, pre-reformed gas, associated gas or natural gas.

11. Use according to claim 1, wherein the feedstock is compressed to a pressure in the range of 10 to 100 bar absolute.

12. Use according to claim 1, wherein the nitrogen content of the hydrocarbon feedstock is in the range of 1 to 5 vol%.

13. Use according to claim 1, wherein the steam to carbon ratio of the mixture of the hydrocarbon feedstock and steam is in the range of 1.8:1 to 5:

1.

14. Use according to claim 1, wherein the mixture of the hydrocarbon feedstock and steam is fed to the inlet of the tubes at an inlet temperature in the range of 300 to 650°C.

15. The use of claim 1, wherein the tubular steam reformer comprises a plurality of tubes through which the mixture of hydrocarbon feedstock and steam is passed and heat is transferred to the tubes by flowing a hot gas comprising combustion gas or syngas around the tubes.

16. The use of claim 1, wherein the catalyst bed consists of one, two, three or more layers of steam reforming catalyst, wherein in each case the layer of steam reforming catalyst adjacent to the outlet of the tubes is the structured steam reforming catalyst.

17. The use of claim 16, wherein there are two or more layers of steam reforming catalyst within the tubes and the layer of structured steam reforming catalyst comprises from 95% to 5% of the bed volume.

18. The use of claim 1, wherein the methane content of the reformate gas is less than 15% by volume based on dry gas.

19. The use of claim 1, wherein the ammonia content of the reformate gas is less than 100 ppmv based on dry gas.

20. The use of claim 1, wherein the method further comprises: cooling the reformate gas below the dew point to condense steam, and separating the condensate to form syngas from the reformate gas.

21. The use of claim 20, wherein the ammonia content of the condensate is less than 400 mg / L.

22. The use of claim 20, wherein at least a portion of the condensate is recycled and used to generate steam for the steam reforming process.

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