WO2015092006A2 - Two-layer catalyst bed - Google Patents

Two-layer catalyst bed Download PDF

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Publication number
WO2015092006A2
WO2015092006A2 PCT/EP2014/078843 EP2014078843W WO2015092006A2 WO 2015092006 A2 WO2015092006 A2 WO 2015092006A2 EP 2014078843 W EP2014078843 W EP 2014078843W WO 2015092006 A2 WO2015092006 A2 WO 2015092006A2
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Prior art keywords
catalyst
temperature
catalyst layer
gas
precursor
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PCT/EP2014/078843
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French (fr)
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WO2015092006A3 (en
Inventor
Andreas Haas
Andrian Milanov
Heiko Urtel
Peter Odermatt
Ekkehard Schwab
Marius HACKEL
Ute HERRLETT
Claudia KRIER
Nathalie Schmitt
Stefan Walter
Original Assignee
Basf Se
L'air Liquide, Societe Anonyme Pour I'etude Et I'exploitation Des Procedes Georges Claude
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Publication of WO2015092006A2 publication Critical patent/WO2015092006A2/en
Publication of WO2015092006A3 publication Critical patent/WO2015092006A3/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/005—Spinels
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
    • B01J23/74—Iron group metals
    • B01J23/755—Nickel
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
    • B01J23/76—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
    • B01J23/78—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36 with alkali- or alkaline earth metals
    • B01J35/19—
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/08—Heat treatment
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/16—Reducing
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C1/00—Preparation of hydrocarbons from one or more compounds, none of them being a hydrocarbon
    • C07C1/02—Preparation of hydrocarbons from one or more compounds, none of them being a hydrocarbon from oxides of a carbon
    • C07C1/04—Preparation of hydrocarbons from one or more compounds, none of them being a hydrocarbon from oxides of a carbon from carbon monoxide with hydrogen
    • C07C1/0425—Catalysts; their physical properties
    • C07C1/043—Catalysts; their physical properties characterised by the composition
    • C07C1/0435—Catalysts; their physical properties characterised by the composition containing a metal of group 8 or a compound thereof
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C1/00—Preparation of hydrocarbons from one or more compounds, none of them being a hydrocarbon
    • C07C1/02—Preparation of hydrocarbons from one or more compounds, none of them being a hydrocarbon from oxides of a carbon
    • C07C1/04—Preparation of hydrocarbons from one or more compounds, none of them being a hydrocarbon from oxides of a carbon from carbon monoxide with hydrogen
    • C07C1/0425—Catalysts; their physical properties
    • C07C1/0445—Preparation; Activation
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C1/00—Preparation of hydrocarbons from one or more compounds, none of them being a hydrocarbon
    • C07C1/02—Preparation of hydrocarbons from one or more compounds, none of them being a hydrocarbon from oxides of a carbon
    • C07C1/04—Preparation of hydrocarbons from one or more compounds, none of them being a hydrocarbon from oxides of a carbon from carbon monoxide with hydrogen
    • C07C1/0455—Reaction conditions
    • C07C1/047—Processes in which one or more parameters are changed during the process; Starting-up of the process
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C1/00—Preparation of hydrocarbons from one or more compounds, none of them being a hydrocarbon
    • C07C1/02—Preparation of hydrocarbons from one or more compounds, none of them being a hydrocarbon from oxides of a carbon
    • C07C1/04—Preparation of hydrocarbons from one or more compounds, none of them being a hydrocarbon from oxides of a carbon from carbon monoxide with hydrogen
    • C07C1/0485—Set-up of reactors or accessories; Multi-step processes

Definitions

  • the present invention relates to a catalyst bed comprising a first catalyst layer and a second catalyst layer.
  • the second catalyst layer comprises according to an embodiment of the invention a catalyst precursor which has high temperature stability but it can be converted into an active form only under relatively high temperature.
  • the present invention also provides processes for activating the second catalyst precursor in the catalyst bed, and further relates to activated catalyst beds obtainable in accordance with these processes.
  • the present invention features a reaction system comprising the above catalyst bed or activated catalyst bed, and processes for chemical synthesis using the reaction system.
  • catalyst beds for e.g. chemical reactions in the gas phase is well known in the art.
  • Such catalyst beds typically comprise solid catalyst in particulate form which for carrying out the chemical reaction is contacted with a stream of a reaction gas.
  • An example of a catalytic gas phase reaction carried out on an industrial scale is the reforming of hydrocarbons.
  • methanation used for the production of substitute natural gas as described e.g. in WO 201 1/004251 , EP 2 261 308 or EP 0 241 902. Methanation involves the conversion of synthesis gas comprising CO and hb into ChU and H2O in an exothermic reaction.
  • Various catalysts are known in the art for carrying out methanation. On an industrial scale, nickel- containing catalysts are typically used.
  • nickel-containing catalysts Suitable examples of such nickel-containing catalysts are described e.g. in DE 2 255 909. Solid catalysts based on e.g. Cu, Co or Ni require a metal in elemental form, i.e. in the oxidation state zero as the active phase. On the other hand, metals such as Cu, Co or Ni are not stable against oxidation in air. Therefore, catalysts based on these metals are typically provided in the form of oxidized, non-active catalyst precursors that need to be activated by reduction before being employed in a catalytic reaction. For example, nickel containing catalysts are typically provided as a catalysts precursor in Ni(ll) form and are activated, i.e. reduced to the catalytically active Ni(0) form before use.
  • Catalytic gas phase reactions in a given industrial plant can, once started, be carried out for very long durations, such as e.g. up to several years.
  • the maximum duration of such processes is inter alia limited by the lifetime of the used catalyst.
  • the temperature stability of the catalyst has to be taken into consideration. It has been observed that catalyst particles can degrade under elevated temperatures which ultimately can adversely affect their catalytic efficiency. Thus, it is desired to use catalysts of high temperature stability for avoiding these problems.
  • the temperature stability of a given catalyst can e.g. be classified based on its average lateral compression strength after treatment for a defined duration at elevated temperature, as further defined herein.
  • a further object of the present invention is the provision of a reaction system comprising a catalysts bed of long lifetime without requiring extra equipment for activation of catalyst precursors.
  • An additional object of the present invention is to provide methods for conveniently activating catalyst precursors of high temperature stability.
  • a further object is the provision of catalyst bed for gas phase reactions that can be carried out at higher temperatures and/or less dilution of the reaction gas.
  • the present invention employs a two-layer arrangement of catalyst layers in a catalyst bed.
  • the present invention is based on the finding that a catalyst precursor being activatable at only relatively high temperatures but having a high temperature stability can be activated using thermal energy and/or reaction gas obtained from a further catalyst layer upstream thereof.
  • convenient activation of a catalyst bed on the one hand and long life time as well as high temperature stability and the other hand can be achieved by employing two different catalyst layer, wherein the first catalyst layer provides for convenient activation of the second catalyst layer, and the second catalyst layer provides for long lifetime and/or high temperature stability.
  • the present invention relates to a catalyst bed comprising a first catalyst layer and a second catalyst layer, wherein
  • the first catalyst layer comprises a first catalyst or precursor thereof, wherein the first catalyst is catalytically active at a temperature below 340°C or the first catalyst precursor is activatable at a temperature below 340°C;
  • the second catalyst layer comprises a second catalyst precursor, wherein the second catalyst precursor comprises nickel in Ni(ll) form and is activatable to a second catalyst comprising nickel in Ni(0) form at a temperature above 360°C, wherein the second catalyst has an average lateral compression strength after 500 h at a temperature of 650°C of at least 30 N.
  • the average lateral compression strength is used in this context as a measure of the stability of catalyst particles under conditions of elevated temperatures for prolonged durations.
  • Degradation of catalyst particles occurring at higher temperatures can be characterized by determining the average lateral compression strength of the catalyst particles as defined in further detail below.
  • the degradation also leads to an increased pressure drop in the catalytic reactor.
  • the average lateral compression strength is used in the context of the present invention for characterizing the temperature stability of the catalyst.
  • the first catalyst employed in the catalyst bed according to the invention in the first catalyst layer is not specifically limited as long as it is active or activatable at moderate temperatures such as below 340°C.
  • the first catalyst comprises as the catalytically active metal a noble metal selected from Ru, Rh, Pd, Ag, Os, Ir, Pt, and Au.
  • noble metal catalysts are known in the art and comprise the catalytically active metal already in active form so that no activation is necessary.
  • a first catalyst precursor being activatable at temperatures below 340°C is employed in the first catalyst layer.
  • Catalyst precursors suitable for the first catalyst layer are known in the art. Illustrative examples thereof are described e.g. in DE 2 255 877.
  • the first catalyst precursor comprises nickel in Ni(ll) form.
  • the first catalyst precursor is obtainable by depositing nickel in Ni(ll) form onto a carrier, e.g. onto carrier materials as described in DE 2 255 877 cited above. It is believed that deposition onto the surface of a carrier material on the one hand is related to the ease of activation of such catalyst precursors.
  • the second catalyst precursor employed according to the invention in the second catalyst layer of the catalyst bed is not specifically limited as long as it has the required temperature stability.
  • the second catalyst precursor is based on a spinel type carrier having intercalated therein Ni(ll).
  • the second catalyst precursor is obtainable by a process comprising mixing a fusible Ni(ll) salt with a hydrotalcite-comprising material and thermally treating the mixture under conditions under which the fusible Ni(ll) salt is present in the form of a melt.
  • Illustrative catalyst precursors of this kind are e.g. described in US
  • a catalyst derived from the second catalyst precursor as defined above can be employed in the first catalyst layer after ex-situ reduction and passivation steps.
  • the catalyst can be reactivated with typical reaction gas such as synthesis gas at a temperature below 340°C.
  • the first catalyst layer is employed in connection with the activation of the second catalyst precursor in the second catalyst layer.
  • the major portion of the overall catalytic activity for the desired chemical conversion over the whole lifetime of the catalyst bed is on the other hand provided by the catalyst in the second catalyst layer.
  • only a small amount of first catalyst relative to the amount of second catalyst is needed.
  • the present invention provides in one embodiment a catalyst bed as defined above, wherein the ratio ST/FT of the thickness of the second catalyst layer (ST) to the thickness of the first catalyst layer (FT) is 10 to 50, preferably 1 1 to 40, more preferably 13 to 30.
  • the volume ratio SV/FV of the volume of the second catalyst layer (SV) to the volume of the first catalyst layer (FV) is 10 to 100, preferably 1 1 to 80, more preferably 13 to 70.
  • the weight ratio SW/FW of the weight of the catalyst employed in the second catalysts layer (SW) to the weight of the catalyst employed in the first catalyst layer (FW) is 10 to 65, preferably 1 1 to 50, more preferably 13 to 40.
  • the present invention also relates to processes for activating the second catalyst precursor in the catalyst bed as defined above.
  • the use of a separate gas such as hydrogen that can be diluted with an inert gas like nitrogen for activating the catalyst precursor can be avoided. Rather, the second catalyst precursor can be activated used the desired reaction gas.
  • the invention relates to a process for activating the second catalyst precursor in a catalyst bed as defined above, comprising the step of applying under adiabatic conditions a flow of synthesis gas to the first catalyst layer at a temperature of below 340°C but equal to or higher than the temperature at which the first catalyst is active or the first catalyst precursor is activated, and subsequently directing the resulting gas flow onto the second catalyst layer.
  • the above process does not comprise a step of applying a gas mixture comprising H2 in addition to the amount of H2 contained in the synthesis gas, and wherein the process preferably does not comprise a step of applying a gas mixture comprising more than 25 Vol%, more preferably more than 20 Vol% H2.
  • the catalyst bed according to the invention is not limited to the use in and activation by methanation reactions. Rather, any gas phase reaction suitable to be catalyzed with the catalysts employed can be carried out.
  • the catalyst bed can also be activated using the reverse reaction of methanation, i.e. reforming. This reverse reaction is endothermic as opposed to methanation. Therefore, thermal energy for activating the second catalyst precursor has to be provided separately. It is, however, also not necessary to use a separate gas mixture such as hydrogen for activation when the catalyst bed is employed for the reverse reaction. Rather, in this case, the second catalyst precursor is then activated using the gas mixture obtained in the first catalyst layer.
  • the present invention relates in a further embodiment to a process for activating the second catalyst in a catalyst bed as defined above, comprising the step of applying a flow of reaction gas comprising CH4 and H2O and optionally N2 to the first catalyst layer at a temperature of above 360°C sufficient for activating the second catalyst, and subsequently directing the resulting gas flow onto the second catalyst layer.
  • the above process does not comprise a step of applying a gas mixture comprising H2 in an amount more than 10 Vol%, preferably more than 5 Vol% H2.
  • the present application also is directed to an activated catalyst bed obtainable according to the processes outlined above.
  • the present invention further covers reaction systems comprising the catalyst bed or the activated catalyst bed defined above.
  • the catalyst bed is arranged in the reaction system in an adiabatic reaction zone. Upstream of the reaction zone a preheating zone is arranged to heat the gas stream to the required temperature. It is understood that according to the invention, the second catalyst layer is arranged downstream the first catalyst layer.
  • the present invention also provides to chemical processes carried out using the above reaction system.
  • the present invention relates to a process for providing CO and H2 comprising the steps of
  • the amount of ChU in the reaction gas in the above processes for activating the second catalyst precursor or for providing CO and hb is according to the invention preferably about 0.9 to about 1 .1 times the amount of H2O.
  • the present application relates to a process for providing ChU, comprising the steps of
  • the synthesis gas employed for the above processes for activating the second catalyst precursor or for providing ChU comprises H2 and CO and optionally N2.
  • the amount of H2 in said synthesis gas is about 2.8 to about 3.2 times the amount of CO. It is further preferred that the amount of N2 in said synthesis gas is 90 Vol% or lower, more preferably is 80 to 60 Vol%.
  • the catalyst bed is activated using and is employed for methanation, i.e. synthesis gas is used for activating the second catalyst precursor and the obtained activated catalyst bed is employed for providing ChU from synthesis gas.
  • the first catalyst precursor comprises according to this embodiment nickel deposited on a carrier and has an activation temperature of about 300°C.
  • the synthesis gas is heated before application to the first catalyst layer to a temperature of about 300°C to about 320°C.
  • the second catalyst precursor comprises nickel intercalated into a spinel type carrier, is activatable at a temperature of about 400°C and has an average lateral compression strength after 500 h at a temperature of 650°C of at least 60 N.
  • the term "average lateral compression strength" used herein is as defined in US 2005/0222436 and refers to the force required for achieving fracture of the catalyst bodies.
  • the catalyst bodies are placed in each case by onto the planar metal platform of a corresponding measuring device, in successive measurements.
  • the catalyst bodies have the shape of a cylinder, the rounded side face is placed on the metal platform so that the two plane-parallel end faces are in the vertical direction.
  • a planar metal die is then lowered onto the catalyst bodies at a rate of advance of 1.6 mm/min and the progress of the force acting on the catalyst bodies is recorded until fracture.
  • the lateral compression strength of each individual catalyst body corresponds to the maximum force.
  • the average lateral compression strength is determined by averaging the results of several individual measurements such as e.g. 30 measurements.
  • the average lateral compression strength is used in accordance with the invention to characterize the temperature stability of a given catalyst. Therefore, the average lateral compression strength is determined according to the invention after treating the catalyst particles for 500 h at a temperature of 650°C at reaction conditions, such as the presence of synthesis gas, in particular the presence of synthesis gas as defined below in connection with the term "activatable".
  • synthesis gas is employed according to the invention as known in the art and refers to a gas mixture consisting primarily of CO, hb and optionally N2, CO2, and/or steam.
  • adiabatic or “adiabatic conditions” is used herein as known in the art and refers to conditions where a process is carried out without transfer of heat between a system and its surroundings. In particular, in adiabatic processes no cooling or heating of the system such as a reaction zone is applied.
  • activatable refers to the reduction of a catalyst precursor present in oxidized form. In one embodiment, the temperature at which reduction, i.e.
  • the present invention provides a catalyst bed comprising a first catalyst layer and a second catalyst layer as defined above.
  • the catalyst bed of the invention can be employed in gas phase reactions.
  • it is possible to activate a second catalyst precursor of high temperature stability without applying separate equipment specifically used for activation of the second catalyst precursor. Rather, the reaction gas in a given gas phase reaction can be directly used for activating a second catalyst precursor even if this second catalyst precursor is only activatable at high temperature.
  • the first catalyst layer comprises a first catalyst or precursor thereof, wherein the first catalyst is catalytically active at a temperature below 340°C or the first catalyst precursor is activatable at a temperature below 340°C.
  • the first catalyst or precursor include a first catalyst comprising as the catalytically active metal a noble metal selected from Ru, Rh, Pd, Ag, Os, Ir, Pt, and Au; or a first catalyst precursor comprising nickel in Ni(l l) form, wherein preferably the first catalyst precursor is obtainable by depositing nickel in Ni(l l) form onto a carrier.
  • a first catalyst precursor obtainable by depositing nickel in Ni(ll) form onto a carrier is employed in the first catalyst layer.
  • a suitable example of a first catalyst precursor preferred according to the invention is manufactured by precipitating the compound Ni6Al2(OH)i6-C03-4 H2O from aqueous solution, drying it at a temperature of from 80 to 180°C, and calcining it at a temperature of from 300 to 550°C. Between the drying stage and the calcination stage the temperature is preferably raised at a rate in the range from
  • Suitable carriers include e.g. ceramic supports, such as aluminum oxide, hydrated alumina, such as bayerite, boehmite, hydrargillite or their mixtures, titanium dioxide, silica, zirconium dioxide, magnesium oxide and artificial and natural silicates, for example magnesium silicate or aluminosilicates, wherein hydrated aluminas are preferred.
  • the obtained catalyst precursors are typically activatable at temperatures below 340°C such as at about 300°C.
  • the average lateral compression strength of such catalysts after prolonged application of heat is typically relatively low, such as below 20 N after 500 h at 650°C.
  • such catalyst precursors may have an average lateral compression strength of such catalysts after prolonged application of heat.
  • the second catalyst layer comprises a second catalyst precursor, wherein the second catalyst precursor comprises nickel in Ni(l l) form and is activatable to a second catalyst comprising nickel in Ni(0) form at a temperature above 360°C, wherein the second catalyst has an average lateral compression strength after 500 h at a temperature of 650°C of at least 30 N.
  • the second catalyst precursor has an average lateral compression strength after 500 h treatment at 650°C under reaction conditions as defined above of at least 40 N, more preferably at least 60 N, such as at least 80 N.
  • a preferred example of second catalyst precursor comprises Ni(ll) intercalated into a spinel type carrier.
  • the second catalyst precursor is obtainable by mixing a fusible Ni(l l) salt with a hydrotalcite-comprising material and thermally treating the mixture under conditions under which the fusible Ni(ll) salt is present in the form of a melt.
  • the second catalyst precursor can be obtained by
  • catalyst precursors are described in US 2013/01 16351 , which is incorporated herein by reference.
  • the obtained catalysts are typically activatable at temperatures above 360°C such as at about 400°C.
  • the average lateral compression strength of such catalysts after prolonged application of heat is typically high, such as at least 30 N after 500 h at 650°C.
  • such catalyst precursor may have an average lateral compression strength after 500 h treatment at 650°C under reaction conditions as defined above of at least 40 N, more preferably at least 60 N, such as at least 80 N.
  • such catalyst precursors may have an average lateral compression strength of about 168 N after 500 h at 650°C, especially when having a shape of a cylinder of about 5 mm length and about 3 mm diameter.
  • the second catalyst precursor in a catalyst bed according to the invention is activated by applying under adiabatic conditions a flow of synthesis gas to the first catalyst layer at a temperature of below 340°C but equal to or higher than the temperature at which the first catalyst is active or the first catalyst precursor is activated (such as 300°C), and subsequently directing the resulting gas flow onto the second catalyst layer.
  • the activation process does not require a step of applying a gas mixture comprising hb in addition to the amount of hb contained in the synthesis gas.
  • the activation process preferably does not comprise a step of applying a gas mixture comprising more than 25 Vol%, more preferably more than 20 Vol% H 2 .
  • the catalyst bed according to the invention is arranged within a reaction system.
  • the reaction systems according to the invention are based on conventional reactions system known in the field and are characterized in that a catalyst bed of the invention is employed instead of conventional catalysts beds.
  • the reaction system according to the invention is further characterized in that the reaction zone including the catalyst bed of the invention is adiabatic.
  • reaction systems according to the invention may be characterized in that no separate means for activating catalyst precursors are present such as means for applying hydrogen.
  • the present invention provides a reaction system comprising the catalyst bed of the invention in an adiabatic reaction zone, and upstream thereof a preheating zone, wherein the second catalyst layer is downstream the first catalyst layer.
  • the reaction system of the invention comprises only one adiabatic vessel and only one preheater.
  • the preheater can be designed in view of the required temperature for the methanation reaction in the first catalyst layer. In preferred embodiments it is sufficient to heat the synthesis gas to a temperature of about 300°C.
  • preheater dimensions usually applied in the field in connection with high temperature catalysts are not necessary according to the invention. This allows operation of similar equipment and similar conditions like with conventional methanation catalysts but at the same time allowing the use of high temperature resistant catalysts.
  • the reaction system may further comprise pipes for conducting the reaction gas mixture in a recycle through the reaction zone, at least one circulation pump, a cooler downstream the reaction zone, a separator downstream the cooler for separating condensate, means for separating a gas mixture from the recycle, means for feeding gas to the recycle, and means for feeding vapor to the recycle.
  • a medium temperature methanation catalyst as described above is placed on top of a high temperature methanation catalyst.
  • the thin layer of the first catalyst is activated at the inlet of the catalyst bed using synthesis gas at about 300°C.
  • synthesis gas at about 300°C.
  • the above catalyst bed can be employed for processes carried out at higher temperatures as commonly used, less dilution of the synthesis gas is required and thus higher turnover can be achieved.
  • the resulting waste heat can be used to provide side products of high temperature, such as high temperature steam, that can advantageously be used for other processes in integrated production plants.
  • the present invention relates to a methanation process for the production of ChU, the process comprising the steps of
  • the synthesis gas used in the invention comprises hb and CO and optionally N2, wherein the amount of H2 is about 2.8 to about 3.2 times the amount of CO, and the amount of N2 is preferably 90 Vol% or lower, more preferably 80 to 60 Vol%.
  • the amount of H2 in the synthesis gas is preferably about 14 to about 17 Vol%.
  • the amount of CO in the synthesis gas is preferably about 4 to about 6 Vol%.
  • the amount of N2 in the synthesis gas is preferably about 75 to about 77 Vol%.
  • the synthesis gas may further contain CO2 in an amount of about 0 to about 1 Vol%. Methanation may be carried out as dry or wet methanation.
  • the synthesis gas comprises in preferred embodiments H2O in an amount of about 0 to about 3 Vol%.
  • the pressure for carrying out the methanation is not specifically limited. That is to say, methanation may be carried out at atmospheric pressure or at increased pressure. In one embodiment, methanation is carried out at a pressure of atmospheric pressure (about 101 .3 kPa) to about 10000 kPa, preferably atmospheric pressure to about 8000 kPa, more preferably at about 3000 to about 7000 kPa such as about 3000 kPa to about 5000 kPa..
  • the throughput of synthesis gas is preferably adjusted so as to reach a temperature in the reaction zone of about 600°C to about 700°C.
  • a first catalyst layer comprising a first catalyst precursor obtainable by precipitating the compound Ni6Al2(OH)i6-C03-4 H2O from aqueous solution, drying it at a temperature of from 80 to 180°C, and calcining it at a temperature of from 300 to 550°C, and
  • a second catalyst layer comprising a second catalyst precursor obtainable by contacting of a fusible nickel salt such as nickel nitrate and finely divided hydrotalcite-comprising starting material, intimate mixing of the fusible nickel salt and the hydrotalcite-comprising starting material, thermal treatment of the fusible nickel salt and hydrotalcite-comprising starting material and storage of the mixture under conditions under which the nickel salt is present in the form of a melt, preferably at a temperature in the range from 30 to 250°C, low-temperature calcination of the mixture at a temperature of below 500° C, preferably at a temperature in the range from 250 to 500°C, with the duration of the low-temperature calcination preferably being in the range from 0.1 to 24 hours, preferably less than 2 hours, in the case of a continuous process preferably 1 hour or less, molding or shaping, high-temperature calcination of the mixture obtained in the preceding steps at a temperature of at least 500°C, preferably at a temperature in
  • a Ni-containing catalyst precursor was used as the first catalyst precursor.
  • the preparation of the first catalyst precursor is generally described in DE 2 255 877.
  • the catalyst particles have a BET surface area of 192 m 2 /g and an elemental composition, based on oxides of 20.0 wt.-% Al, 0.01 wt.-% Na, 71 .0 wt.-% Ni, and 8.9 wt.-% Zr.
  • the average lateral compression strength of fresh catalyst is 132 N.
  • the average lateral compression strength of catalyst used for 500 h at a temperature of 650°C in the presence of the synthesis gas mixture defined below adjusted to a CO content of 6 Vol% using dilution with nitrogen
  • the catalyst precursor can be activated using synthesis gas at a temperature of about 300°C.
  • a Ni-containing catalyst precursor was used as the second catalyst precursor.
  • the preparation of the second catalyst precursor is generally described in US 2013/1 16351.
  • the catalyst particles have a BET surface area of 92 m 2 /g and an elemental composition, based on oxides of 23.9 wt.-% Al, 1 1 .8 wt.-% Mg, and 14.5 wt.-% Ni.
  • the average lateral compression strength of catalyst used for 500 h at a temperature of 650°C in the presence of the synthesis gas mixture defined below adjusted to a CO content of 6 Vol% using dilution with nitrogen has been found to be 168 N.
  • synthesis gas temperatures of more than 400°C such as 430°C are required.
  • the synthesis gas used in the example has a composition of 72 ⁇ 1 .0 Vol% hb, 20 ⁇ 0.5 Vol% CO, 3 ⁇ 0.3 Vol% CH4, and 1 ⁇ 0.3 Vol% N2.
  • the synthesis gas was further diluted with N2. Dilution with N2 is obtained by filling the reaction system with N2 and adding the synthesis gas in small portions.
  • the gas composition in the recycle is controlled to ensure that the CO content is not exceeding 6 Vol%.
  • CO is used up by the reaction
  • another portion of synthesis gas is added.
  • the reaction system flushed with nitrogen at a pressure of 300 kPa and heated up to a temperature of 300°C. Then steam was introduced into the system (15 mol% of the recycle).
  • Synthesis gas was added to the reaction system in small portions keeping the CO content at 6 Vol% or below. Subsequently, the pressure was increased to 4000 kPa. Beginning of methanation was observed by a drop in the CO concentration and a raise in temperature. A well reduced catalyst bed was obtained.

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Abstract

The present invention relates to a catalyst bed comprising a first catalyst layer and a second catalyst layer, wherein the first catalyst layer comprises a first catalyst or precursor thereof active or activatable at a temperature below 340°C; and the second catalyst layer comprises a second catalyst precursor, wherein the second catalyst precursor comprises nickel in Ni(ll) form and is activatable to a second catalyst comprising nickel in Ni(0) form at a temperature above 360°C, wherein the second catalyst has an average lateral compression strength after 500 h at a temperature of 650°C of at least 30 N.

Description

Two-Layer Catalyst Bed
The present invention relates to a catalyst bed comprising a first catalyst layer and a second catalyst layer. The second catalyst layer comprises according to an embodiment of the invention a catalyst precursor which has high temperature stability but it can be converted into an active form only under relatively high temperature. The present invention also provides processes for activating the second catalyst precursor in the catalyst bed, and further relates to activated catalyst beds obtainable in accordance with these processes. Furthermore, the present invention features a reaction system comprising the above catalyst bed or activated catalyst bed, and processes for chemical synthesis using the reaction system.
Background of the invention
The use of catalyst beds for e.g. chemical reactions in the gas phase is well known in the art. Such catalyst beds typically comprise solid catalyst in particulate form which for carrying out the chemical reaction is contacted with a stream of a reaction gas. An example of a catalytic gas phase reaction carried out on an industrial scale is the reforming of hydrocarbons. A further example is methanation used for the production of substitute natural gas as described e.g. in WO 201 1/004251 , EP 2 261 308 or EP 0 241 902. Methanation involves the conversion of synthesis gas comprising CO and hb into ChU and H2O in an exothermic reaction. Various catalysts are known in the art for carrying out methanation. On an industrial scale, nickel- containing catalysts are typically used. Suitable examples of such nickel-containing catalysts are described e.g. in DE 2 255 909. Solid catalysts based on e.g. Cu, Co or Ni require a metal in elemental form, i.e. in the oxidation state zero as the active phase. On the other hand, metals such as Cu, Co or Ni are not stable against oxidation in air. Therefore, catalysts based on these metals are typically provided in the form of oxidized, non-active catalyst precursors that need to be activated by reduction before being employed in a catalytic reaction. For example, nickel containing catalysts are typically provided as a catalysts precursor in Ni(ll) form and are activated, i.e. reduced to the catalytically active Ni(0) form before use. It is known in the art to activate such catalyst precursors by reducing with hydrogen-containing mixtures such as more than 20 Vol% H2 in nitrogen at a temperature of about 200-400°C before the desired chemical reaction is carried out. However, a separate activation step using hydrogen involves certain drawbacks. For example, it is necessary to provide hydrogen/nitrogen mixtures and extra equipment for handling these gases on the production plant. Thus, overall costs of the production process increase.
Catalytic gas phase reactions in a given industrial plant can, once started, be carried out for very long durations, such as e.g. up to several years. The maximum duration of such processes is inter alia limited by the lifetime of the used catalyst. If the process is carried out at elevated temperatures, such as in methanation or reforming of hydrocarbons, the temperature stability of the catalyst has to be taken into consideration. It has been observed that catalyst particles can degrade under elevated temperatures which ultimately can adversely affect their catalytic efficiency. Thus, it is desired to use catalysts of high temperature stability for avoiding these problems. The temperature stability of a given catalyst can e.g. be classified based on its average lateral compression strength after treatment for a defined duration at elevated temperature, as further defined herein.
In order to avoid degradation of catalyst particles due to prolonged heating, it is known in the art to carry out gas phase reactions at lower temperatures. In case of exothermic gas phase reactions, this can be achieved by diluting the reaction gas with an inert gas such as nitrogen. However, as a result, high dilution of the reaction gas with an inert gas decreases the overall turnover rates of the reaction system. Thus, there is a need in the art for catalytic systems for carrying out gas phase reactions at high temperature requiring less dilution with inert gas. The waste heat produced in such processes carried out at higher temperatures can advantageously be used in integrated production plants. As an alternative to the above-mentioned activation of catalyst precursors using hydrogen e.g. hydrogen in admixture with an inert gas such as nitrogen, it is in principle possible to activate the catalyst precursors using directly the respective reaction gas. For example, synthesis gas can in principle be used for activating Ni(ll)-containing catalyst precursors. However, higher activation temperatures are typically required according to this alternative. In this respect, it has been observed that catalysts of higher temperature stability may also require higher
temperatures for activation. Thus, higher costs for additional energy and more sophisticated heating equipment may be involved for activating catalysts of high temperature stability.
In view of the above, there is a need in the art for methods of activating catalyst precursors of high temperature stability at moderate temperatures avoiding the use of extra equipment.
Summary of the invention
It is an object of the present invention to provide a catalyst bed comprising a catalyst precursor of high temperature stability, wherein the catalyst bed can be activated at moderate
temperatures without using mixtures of hydrogen and an inert gas like nitrogen. A further object of the present invention is the provision of a reaction system comprising a catalysts bed of long lifetime without requiring extra equipment for activation of catalyst precursors. An additional object of the present invention is to provide methods for conveniently activating catalyst precursors of high temperature stability. A further object is the provision of catalyst bed for gas phase reactions that can be carried out at higher temperatures and/or less dilution of the reaction gas.
The present invention employs a two-layer arrangement of catalyst layers in a catalyst bed. The present invention is based on the finding that a catalyst precursor being activatable at only relatively high temperatures but having a high temperature stability can be activated using thermal energy and/or reaction gas obtained from a further catalyst layer upstream thereof. In other words, according to the present invention, convenient activation of a catalyst bed on the one hand and long life time as well as high temperature stability and the other hand can be achieved by employing two different catalyst layer, wherein the first catalyst layer provides for convenient activation of the second catalyst layer, and the second catalyst layer provides for long lifetime and/or high temperature stability.
Thus, the present invention relates to a catalyst bed comprising a first catalyst layer and a second catalyst layer, wherein
(i) the first catalyst layer comprises a first catalyst or precursor thereof, wherein the first catalyst is catalytically active at a temperature below 340°C or the first catalyst precursor is activatable at a temperature below 340°C; and
(ii) the second catalyst layer comprises a second catalyst precursor, wherein the second catalyst precursor comprises nickel in Ni(ll) form and is activatable to a second catalyst comprising nickel in Ni(0) form at a temperature above 360°C, wherein the second catalyst has an average lateral compression strength after 500 h at a temperature of 650°C of at least 30 N.
The average lateral compression strength is used in this context as a measure of the stability of catalyst particles under conditions of elevated temperatures for prolonged durations.
Degradation of catalyst particles occurring at higher temperatures can be characterized by determining the average lateral compression strength of the catalyst particles as defined in further detail below. The degradation also leads to an increased pressure drop in the catalytic reactor. Thus, the average lateral compression strength is used in the context of the present invention for characterizing the temperature stability of the catalyst.
The first catalyst employed in the catalyst bed according to the invention in the first catalyst layer is not specifically limited as long as it is active or activatable at moderate temperatures such as below 340°C. In one embodiment, the first catalyst comprises as the catalytically active metal a noble metal selected from Ru, Rh, Pd, Ag, Os, Ir, Pt, and Au. Such noble metal catalysts are known in the art and comprise the catalytically active metal already in active form so that no activation is necessary.
Alternatively, or from the viewpoint of costs preferably, a first catalyst precursor being activatable at temperatures below 340°C is employed in the first catalyst layer. Catalyst precursors suitable for the first catalyst layer are known in the art. Illustrative examples thereof are described e.g. in DE 2 255 877. In one embodiment, the first catalyst precursor comprises nickel in Ni(ll) form. In a preferred embodiment, the first catalyst precursor is obtainable by depositing nickel in Ni(ll) form onto a carrier, e.g. onto carrier materials as described in DE 2 255 877 cited above. It is believed that deposition onto the surface of a carrier material on the one hand is related to the ease of activation of such catalyst precursors. On the other hand, catalysts derived from such catalyst precursors typically may have insufficient temperature stability. Within the definition provided above, the second catalyst precursor employed according to the invention in the second catalyst layer of the catalyst bed is not specifically limited as long as it has the required temperature stability. In one embodiment, the second catalyst precursor is based on a spinel type carrier having intercalated therein Ni(ll). On the other hand, it is believed that conventional activation conditions may not be sufficient for activating intercalated catalyst precursor material. In a preferred embodiment, the second catalyst precursor is obtainable by a process comprising mixing a fusible Ni(ll) salt with a hydrotalcite-comprising material and thermally treating the mixture under conditions under which the fusible Ni(ll) salt is present in the form of a melt. Illustrative catalyst precursors of this kind are e.g. described in US
2013/01 16351 .
In an alternative embodiment, a catalyst derived from the second catalyst precursor as defined above can be employed in the first catalyst layer after ex-situ reduction and passivation steps. In this form the catalyst can be reactivated with typical reaction gas such as synthesis gas at a temperature below 340°C.
According to the present invention, the first catalyst layer is employed in connection with the activation of the second catalyst precursor in the second catalyst layer. The major portion of the overall catalytic activity for the desired chemical conversion over the whole lifetime of the catalyst bed is on the other hand provided by the catalyst in the second catalyst layer. Thus, only a small amount of first catalyst relative to the amount of second catalyst is needed.
Accordingly, the present invention provides in one embodiment a catalyst bed as defined above, wherein the ratio ST/FT of the thickness of the second catalyst layer (ST) to the thickness of the first catalyst layer (FT) is 10 to 50, preferably 1 1 to 40, more preferably 13 to 30. Alternatively or additionally, the volume ratio SV/FV of the volume of the second catalyst layer (SV) to the volume of the first catalyst layer (FV) is 10 to 100, preferably 1 1 to 80, more preferably 13 to 70. In a further alternative or additional embodiment, the weight ratio SW/FW of the weight of the catalyst employed in the second catalysts layer (SW) to the weight of the catalyst employed in the first catalyst layer (FW) is 10 to 65, preferably 1 1 to 50, more preferably 13 to 40.
The present invention also relates to processes for activating the second catalyst precursor in the catalyst bed as defined above. According to the present invention, the use of a separate gas such as hydrogen that can be diluted with an inert gas like nitrogen for activating the catalyst precursor can be avoided. Rather, the second catalyst precursor can be activated used the desired reaction gas. Thus, in one embodiment, the invention relates to a process for activating the second catalyst precursor in a catalyst bed as defined above, comprising the step of applying under adiabatic conditions a flow of synthesis gas to the first catalyst layer at a temperature of below 340°C but equal to or higher than the temperature at which the first catalyst is active or the first catalyst precursor is activated, and subsequently directing the resulting gas flow onto the second catalyst layer. In a further embodiment, the above process does not comprise a step of applying a gas mixture comprising H2 in addition to the amount of H2 contained in the synthesis gas, and wherein the process preferably does not comprise a step of applying a gas mixture comprising more than 25 Vol%, more preferably more than 20 Vol% H2.
The catalyst bed according to the invention is not limited to the use in and activation by methanation reactions. Rather, any gas phase reaction suitable to be catalyzed with the catalysts employed can be carried out. For example, the catalyst bed can also be activated using the reverse reaction of methanation, i.e. reforming. This reverse reaction is endothermic as opposed to methanation. Therefore, thermal energy for activating the second catalyst precursor has to be provided separately. It is, however, also not necessary to use a separate gas mixture such as hydrogen for activation when the catalyst bed is employed for the reverse reaction. Rather, in this case, the second catalyst precursor is then activated using the gas mixture obtained in the first catalyst layer. Accordingly, the present invention relates in a further embodiment to a process for activating the second catalyst in a catalyst bed as defined above, comprising the step of applying a flow of reaction gas comprising CH4 and H2O and optionally N2 to the first catalyst layer at a temperature of above 360°C sufficient for activating the second catalyst, and subsequently directing the resulting gas flow onto the second catalyst layer. In a further embodiment, the above process does not comprise a step of applying a gas mixture comprising H2 in an amount more than 10 Vol%, preferably more than 5 Vol% H2.
The present application also is directed to an activated catalyst bed obtainable according to the processes outlined above.
The present invention further covers reaction systems comprising the catalyst bed or the activated catalyst bed defined above. The catalyst bed is arranged in the reaction system in an adiabatic reaction zone. Upstream of the reaction zone a preheating zone is arranged to heat the gas stream to the required temperature. It is understood that according to the invention, the second catalyst layer is arranged downstream the first catalyst layer.
The present invention also provides to chemical processes carried out using the above reaction system. In one embodiment, the present invention relates to a process for providing CO and H2 comprising the steps of
(i) feeding a reaction gas comprising CH4 and H2O and optionally N2 to the preheating zone of the above reaction system,
(ii) heating the reaction gas to a temperature of above 360°C sufficient for activating the second catalyst, and directing the heated reaction gas onto the first catalyst layer, and subsequently
(iii) directing the resulting gas flow onto the second catalyst layer. The amount of ChU in the reaction gas in the above processes for activating the second catalyst precursor or for providing CO and hb is according to the invention preferably about 0.9 to about 1 .1 times the amount of H2O. In another embodiment, the present application relates to a process for providing ChU, comprising the steps of
(i) feeding synthesis gas to the preheating zone of the above reaction system,
(ii) heating the synthesis gas to a temperature of below 340°C but equal to or higher than the temperature at which the first catalyst is active or the first catalyst precursor is activated, and directing the heated synthesis gas onto the first catalyst layer, and subsequently
(iii) directing the resulting gas flow onto the second catalyst layer.
The synthesis gas employed for the above processes for activating the second catalyst precursor or for providing ChU comprises H2 and CO and optionally N2. In preferred
embodiments, the amount of H2 in said synthesis gas is about 2.8 to about 3.2 times the amount of CO. It is further preferred that the amount of N2 in said synthesis gas is 90 Vol% or lower, more preferably is 80 to 60 Vol%.
In a preferred embodiment, the catalyst bed is activated using and is employed for methanation, i.e. synthesis gas is used for activating the second catalyst precursor and the obtained activated catalyst bed is employed for providing ChU from synthesis gas. More preferably, the first catalyst precursor comprises according to this embodiment nickel deposited on a carrier and has an activation temperature of about 300°C. Thus, according to this preferred embodiment, the synthesis gas is heated before application to the first catalyst layer to a temperature of about 300°C to about 320°C. In addition, it is further preferred according to this preferred embodiment that the second catalyst precursor comprises nickel intercalated into a spinel type carrier, is activatable at a temperature of about 400°C and has an average lateral compression strength after 500 h at a temperature of 650°C of at least 60 N. Further embodiments of the present invention are apparent from the following detailed description and the appended claims.
Detailed Description of the Invention In the following, illustrative embodiments of the present invention are described in more detail.
The term "average lateral compression strength" used herein is as defined in US 2005/0222436 and refers to the force required for achieving fracture of the catalyst bodies. In order to determine the lateral compression strength, the catalyst bodies are placed in each case by onto the planar metal platform of a corresponding measuring device, in successive measurements. In case the catalyst bodies have the shape of a cylinder, the rounded side face is placed on the metal platform so that the two plane-parallel end faces are in the vertical direction. A planar metal die is then lowered onto the catalyst bodies at a rate of advance of 1.6 mm/min and the progress of the force acting on the catalyst bodies is recorded until fracture. The lateral compression strength of each individual catalyst body corresponds to the maximum force. The average lateral compression strength is determined by averaging the results of several individual measurements such as e.g. 30 measurements. The average lateral compression strength is used in accordance with the invention to characterize the temperature stability of a given catalyst. Therefore, the average lateral compression strength is determined according to the invention after treating the catalyst particles for 500 h at a temperature of 650°C at reaction conditions, such as the presence of synthesis gas, in particular the presence of synthesis gas as defined below in connection with the term "activatable".
The term "synthesis gas" is employed according to the invention as known in the art and refers to a gas mixture consisting primarily of CO, hb and optionally N2, CO2, and/or steam. The term "adiabatic" or "adiabatic conditions" is used herein as known in the art and refers to conditions where a process is carried out without transfer of heat between a system and its surroundings. In particular, in adiabatic processes no cooling or heating of the system such as a reaction zone is applied. The term "activatable" as used herein refers to the reduction of a catalyst precursor present in oxidized form. In one embodiment, the temperature at which reduction, i.e. activation, occurs is determined using synthesis gas, especially a gas mixture comprising 18 Vol% H2, 6 Vol% CO, 0.75 Vol% CH4, and 75.25 Vol% N2. The present invention provides a catalyst bed comprising a first catalyst layer and a second catalyst layer as defined above. The catalyst bed of the invention can be employed in gas phase reactions. In accordance with the present invention it is possible to activate a second catalyst precursor of high temperature stability without applying separate equipment specifically used for activation of the second catalyst precursor. Rather, the reaction gas in a given gas phase reaction can be directly used for activating a second catalyst precursor even if this second catalyst precursor is only activatable at high temperature. Although the present invention is not specifically limited with respect to special gas phase reactions, first or second catalysts, provided that the above definitions are met, the following detailed description is focused on illustrative embodiments predominantly based on methanation reactions using Ni- containing catalysts. A person skilled in the art will comprehend that catalysts different from those described below and/or other gas phase reactions such as the reverse reaction of methanation (reformation) while still achieving the benefits of the present invention.
The first catalyst layer comprises a first catalyst or precursor thereof, wherein the first catalyst is catalytically active at a temperature below 340°C or the first catalyst precursor is activatable at a temperature below 340°C. Examples of the first catalyst or precursor include a first catalyst comprising as the catalytically active metal a noble metal selected from Ru, Rh, Pd, Ag, Os, Ir, Pt, and Au; or a first catalyst precursor comprising nickel in Ni(l l) form, wherein preferably the first catalyst precursor is obtainable by depositing nickel in Ni(l l) form onto a carrier.
Thus, in a preferred embodiment, a first catalyst precursor obtainable by depositing nickel in Ni(ll) form onto a carrier is employed in the first catalyst layer. A suitable example of a first catalyst precursor preferred according to the invention is manufactured by precipitating the compound Ni6Al2(OH)i6-C03-4 H2O from aqueous solution, drying it at a temperature of from 80 to 180°C, and calcining it at a temperature of from 300 to 550°C. Between the drying stage and the calcination stage the temperature is preferably raised at a rate in the range from
1 .66°C/minute to 3.33°C/minute. Corresponding catalyst precursors are described in DE 2 255 877, which is incorporated herein by reference. Suitable carriers include e.g. ceramic supports, such as aluminum oxide, hydrated alumina, such as bayerite, boehmite, hydrargillite or their mixtures, titanium dioxide, silica, zirconium dioxide, magnesium oxide and artificial and natural silicates, for example magnesium silicate or aluminosilicates, wherein hydrated aluminas are preferred. The obtained catalyst precursors are typically activatable at temperatures below 340°C such as at about 300°C. However, the average lateral compression strength of such catalysts after prolonged application of heat is typically relatively low, such as below 20 N after 500 h at 650°C. For example, such catalyst precursors may have an average lateral
compression strength of about 10 N after 500 h at 650°C.
Furthermore, in a preferred embodiment of the present invention, the second catalyst layer comprises a second catalyst precursor, wherein the second catalyst precursor comprises nickel in Ni(l l) form and is activatable to a second catalyst comprising nickel in Ni(0) form at a temperature above 360°C, wherein the second catalyst has an average lateral compression strength after 500 h at a temperature of 650°C of at least 30 N. Preferably, the second catalyst precursor has an average lateral compression strength after 500 h treatment at 650°C under reaction conditions as defined above of at least 40 N, more preferably at least 60 N, such as at least 80 N. A preferred example of second catalyst precursor comprises Ni(ll) intercalated into a spinel type carrier. More preferably the second catalyst precursor is obtainable by mixing a fusible Ni(l l) salt with a hydrotalcite-comprising material and thermally treating the mixture under conditions under which the fusible Ni(ll) salt is present in the form of a melt.
In a preferred embodiment, the second catalyst precursor can be obtained by
(i) contacting of a fusible nickel salt such as nickel nitrate and finely divided hydrotalcite- comprising starting material,
(ii) intimate mixing of the fusible nickel salt and the hydrotalcite-comprising starting material,
(iii) thermal treatment of the fusible nickel salt and hydrotalcite-comprising starting material and storage of the mixture under conditions under which the nickel salt is present in the form of a melt, preferably at a temperature in the range from 30 to 250°C,
(iv) low-temperature calcination of the mixture at a temperature of below 500° C, preferably at a temperature in the range from 250 to 500°C, with the duration of the low-temperature calcination preferably being in the range from 0.1 to 24 hours, preferably less than 2 hours, in the case of a continuous process preferably 1 hour or less,
(v) molding or shaping,
(vi) high-temperature calcination of the mixture obtained in the preceding steps at a
temperature of at least 500°C, preferably at a temperature in the range from 500 to
1000°C, with the duration of the high-temperature calcination preferably being in the range from 0.1 to 24 hours, preferably less than 2 hours, in the case of a continuous process preferably 1 hour or less. Such catalyst precursors are described in US 2013/01 16351 , which is incorporated herein by reference. The obtained catalysts are typically activatable at temperatures above 360°C such as at about 400°C. Moreover, the average lateral compression strength of such catalysts after prolonged application of heat is typically high, such as at least 30 N after 500 h at 650°C.
Preferably, such catalyst precursor may have an average lateral compression strength after 500 h treatment at 650°C under reaction conditions as defined above of at least 40 N, more preferably at least 60 N, such as at least 80 N. For example, such catalyst precursors may have an average lateral compression strength of about 168 N after 500 h at 650°C, especially when having a shape of a cylinder of about 5 mm length and about 3 mm diameter. In a preferred embodiment, the second catalyst precursor in a catalyst bed according to the invention is activated by applying under adiabatic conditions a flow of synthesis gas to the first catalyst layer at a temperature of below 340°C but equal to or higher than the temperature at which the first catalyst is active or the first catalyst precursor is activated (such as 300°C), and subsequently directing the resulting gas flow onto the second catalyst layer. The activation process does not require a step of applying a gas mixture comprising hb in addition to the amount of hb contained in the synthesis gas. Thus, the activation process preferably does not comprise a step of applying a gas mixture comprising more than 25 Vol%, more preferably more than 20 Vol% H2. For carrying out gas phase reactions such as methanation the catalyst bed according to the invention is arranged within a reaction system. Principally, the reaction systems according to the invention are based on conventional reactions system known in the field and are characterized in that a catalyst bed of the invention is employed instead of conventional catalysts beds. The reaction system according to the invention is further characterized in that the reaction zone including the catalyst bed of the invention is adiabatic. Thus, according to the invention it is not necessary to protect the catalytically active material from degradation at high temperatures using e.g. high dilution of the reaction gas with an inert gas such as nitrogen, since a second catalyst of high temperature stability is employed as the main catalyst. Furthermore, the reaction systems according to the invention may be characterized in that no separate means for activating catalyst precursors are present such as means for applying hydrogen. In particular, the present invention provides a reaction system comprising the catalyst bed of the invention in an adiabatic reaction zone, and upstream thereof a preheating zone, wherein the second catalyst layer is downstream the first catalyst layer.
In a preferred embodiment, the reaction system of the invention comprises only one adiabatic vessel and only one preheater. The preheater can be designed in view of the required temperature for the methanation reaction in the first catalyst layer. In preferred embodiments it is sufficient to heat the synthesis gas to a temperature of about 300°C. Thus, preheater dimensions usually applied in the field in connection with high temperature catalysts are not necessary according to the invention. This allows operation of similar equipment and similar conditions like with conventional methanation catalysts but at the same time allowing the use of high temperature resistant catalysts.
In addition to a preheater in a preheating zone, a adiabatic reaction zone downstream the preheating zone comprising the catalysts bed of the invention, wherein the first catalysts layer is arranged upstream of the second catalyst layer, the reaction system may further comprise pipes for conducting the reaction gas mixture in a recycle through the reaction zone, at least one circulation pump, a cooler downstream the reaction zone, a separator downstream the cooler for separating condensate, means for separating a gas mixture from the recycle, means for feeding gas to the recycle, and means for feeding vapor to the recycle.
In accordance with this preferred embodiment, a medium temperature methanation catalyst as described above is placed on top of a high temperature methanation catalyst. The thin layer of the first catalyst is activated at the inlet of the catalyst bed using synthesis gas at about 300°C. When the first catalyst layer is partly reduced methanation will start directly and the catalyst bed is heated up by the exothermal effect of the reaction, so that the high temperature catalyst in the second catalyst layer is likewise activated.
Since the above catalyst bed can be employed for processes carried out at higher temperatures as commonly used, less dilution of the synthesis gas is required and thus higher turnover can be achieved. In addition, the resulting waste heat can be used to provide side products of high temperature, such as high temperature steam, that can advantageously be used for other processes in integrated production plants.
In a further preferred embodiment, the present invention relates to a methanation process for the production of ChU, the process comprising the steps of
(i) feeding synthesis gas to the preheating zone of the above reaction system,
(ii) heating the synthesis gas to a temperature of below 340°C but equal to or higher than the temperature at which the first catalyst is active or the first catalyst precursor is activated, and directing the heated synthesis gas onto the first catalyst layer, and subsequently (iii) directing the resulting gas flow onto the second catalyst layer. In preferred embodiments, the synthesis gas used in the invention comprises hb and CO and optionally N2, wherein the amount of H2 is about 2.8 to about 3.2 times the amount of CO, and the amount of N2 is preferably 90 Vol% or lower, more preferably 80 to 60 Vol%. The amount of H2 in the synthesis gas is preferably about 14 to about 17 Vol%. Furthermore, the amount of CO in the synthesis gas is preferably about 4 to about 6 Vol%. The amount of N2 in the synthesis gas is preferably about 75 to about 77 Vol%. The synthesis gas may further contain CO2 in an amount of about 0 to about 1 Vol%. Methanation may be carried out as dry or wet methanation. Thus, the synthesis gas comprises in preferred embodiments H2O in an amount of about 0 to about 3 Vol%.
The pressure for carrying out the methanation is not specifically limited. That is to say, methanation may be carried out at atmospheric pressure or at increased pressure. In one embodiment, methanation is carried out at a pressure of atmospheric pressure (about 101 .3 kPa) to about 10000 kPa, preferably atmospheric pressure to about 8000 kPa, more preferably at about 3000 to about 7000 kPa such as about 3000 kPa to about 5000 kPa..
The throughput of synthesis gas, more precisely the partial pressure of CO in the reaction system, is preferably adjusted so as to reach a temperature in the reaction zone of about 600°C to about 700°C.
The catalyst system according to the present invention can in alternative embodiments defined as comprising
(i) a first catalyst layer comprising a first catalyst precursor obtainable by precipitating the compound Ni6Al2(OH)i6-C03-4 H2O from aqueous solution, drying it at a temperature of from 80 to 180°C, and calcining it at a temperature of from 300 to 550°C, and
(ii) a second catalyst layer comprising a second catalyst precursor obtainable by contacting of a fusible nickel salt such as nickel nitrate and finely divided hydrotalcite-comprising starting material, intimate mixing of the fusible nickel salt and the hydrotalcite-comprising starting material, thermal treatment of the fusible nickel salt and hydrotalcite-comprising starting material and storage of the mixture under conditions under which the nickel salt is present in the form of a melt, preferably at a temperature in the range from 30 to 250°C, low-temperature calcination of the mixture at a temperature of below 500° C, preferably at a temperature in the range from 250 to 500°C, with the duration of the low-temperature calcination preferably being in the range from 0.1 to 24 hours, preferably less than 2 hours, in the case of a continuous process preferably 1 hour or less, molding or shaping, high-temperature calcination of the mixture obtained in the preceding steps at a temperature of at least 500°C, preferably at a temperature in the range from 500 to 1000°C, with the duration of the high-temperature calcination preferably being in the range from 0.1 to 24 hours, preferably less than 2 hours, in the case of a continuous process preferably 1 hour or less. Examples
The present invention will be further illustrated by means of a working example.
The experiment was performed in a pilot plant comprising a catalyst system according to the invention in an adiabatic reaction zone. The following catalyst precursors where used:
Table 1 : Details of catalyst precursors and catalyst bed
Figure imgf000013_0001
A Ni-containing catalyst precursor was used as the first catalyst precursor. The preparation of the first catalyst precursor is generally described in DE 2 255 877. The catalyst particles have a BET surface area of 192 m2/g and an elemental composition, based on oxides of 20.0 wt.-% Al, 0.01 wt.-% Na, 71 .0 wt.-% Ni, and 8.9 wt.-% Zr. The average lateral compression strength of fresh catalyst is 132 N. However, the average lateral compression strength of catalyst used for 500 h at a temperature of 650°C (in the presence of the synthesis gas mixture defined below adjusted to a CO content of 6 Vol% using dilution with nitrogen) has been found to be 10 N. Thus, this type of catalyst has a low temperature stability. The catalyst precursor can be activated using synthesis gas at a temperature of about 300°C.
A Ni-containing catalyst precursor was used as the second catalyst precursor. The preparation of the second catalyst precursor is generally described in US 2013/1 16351. The catalyst particles have a BET surface area of 92 m2/g and an elemental composition, based on oxides of 23.9 wt.-% Al, 1 1 .8 wt.-% Mg, and 14.5 wt.-% Ni. The average lateral compression strength of catalyst used for 500 h at a temperature of 650°C (in the presence of the synthesis gas mixture defined below adjusted to a CO content of 6 Vol% using dilution with nitrogen) has been found to be 168 N. For activation of this type of catalyst precursor with synthesis gas temperatures of more than 400°C such as 430°C are required. The synthesis gas used in the example has a composition of 72±1 .0 Vol% hb, 20±0.5 Vol% CO, 3±0.3 Vol% CH4, and 1 ±0.3 Vol% N2. To perform the reaction the synthesis gas was further diluted with N2. Dilution with N2 is obtained by filling the reaction system with N2 and adding the synthesis gas in small portions. The gas composition in the recycle is controlled to ensure that the CO content is not exceeding 6 Vol%. When CO is used up by the reaction, another portion of synthesis gas is added. The reaction system flushed with nitrogen at a pressure of 300 kPa and heated up to a temperature of 300°C. Then steam was introduced into the system (15 mol% of the recycle). Synthesis gas was added to the reaction system in small portions keeping the CO content at 6 Vol% or below. Subsequently, the pressure was increased to 4000 kPa. Beginning of methanation was observed by a drop in the CO concentration and a raise in temperature. A well reduced catalyst bed was obtained.

Claims

Claims
Catalyst bed comprising a first catalyst layer and a second catalyst layer, wherein
(i) the first catalyst layer comprises a first catalyst or precursor thereof, wherein the first catalyst is catalytically active at a temperature below 340°C or the first catalyst precursor is activatable at a temperature below 340°C; and
(ii) the second catalyst layer comprises a second catalyst precursor, wherein the
second catalyst precursor comprises nickel in Ni(ll) form and is activatable to a second catalyst comprising nickel in Ni(0) form at a temperature above 360°C, wherein the second catalyst has an average lateral compression strength after 500 h at a temperature of 650°C of at least 30 N.
Catalyst bed according to claim 1 , wherein
(i) the first catalyst comprises as the catalytically active metal a noble metal selected from Ru, Rh, Pd, Ag, Os, Ir, Pt, and Au; or the first catalyst precursor comprises nickel in Ni(ll) form, wherein preferably the first catalyst precursor is obtainable by depositing nickel in Ni(ll) form onto a carrier; and/or
(ii) the second catalyst precursor comprises Ni(ll) intercalated into a spinel type carrier, wherein preferably the second catalyst precursor is obtainable by mixing a fusible Ni(ll) salt with a hydrotalcite-comprising material and thermally treating the mixture under conditions under which the fusible Ni(ll) salt is present in the form of a melt.
Catalyst bed according to claim 1 or 2, wherein the ratio ST/FT of the thickness of the second catalyst layer (ST) to the thickness of the first catalyst layer (FT) is 10 to 50, preferably 1 1 to 40; and/or
wherein the volume ratio SV/FV of the volume of the second catalyst layer (SV) to the volume of the first catalyst layer (FV) is 10 to 100, preferably 1 1 to 80, more preferably 13 to 70, and/or
wherein the weight ratio SW/FW of the weight of the catalyst employed in the second catalysts layer (SW) to the weight of the catalyst employed in the first catalyst layer (FW) is 10 to 65, preferably 1 1 to 50, more preferably 13 to 40.
A process for activating the second catalyst precursor in a catalyst bed according to any one of claims 1 to 3, comprising the step of applying under adiabatic conditions a flow of synthesis gas to the first catalyst layer at a temperature of below 340°C but equal to or higher than the temperature at which the first catalyst is active or the first catalyst precursor is activated, and subsequently directing the resulting gas flow onto the second catalyst layer.
The process according to claim 4, wherein the process does not comprise a step of applying a gas mixture comprising hb in addition to the amount of hb contained in the synthesis gas, and wherein the process preferably does not comprise a step of applying a gas mixture comprising more than 25 Vol%, more preferably more than 20 Vol% hb.
A process for activating the second catalyst in a catalyst bed according to any one of claims 1 to 3, comprising the step of applying a flow of reaction gas comprising ChU and H2O and optionally N2 to the first catalyst layer at a temperature of above 360°C sufficient for activating the second catalyst, and subsequently directing the resulting gas flow onto the second catalyst layer.
The process according to claim 6, wherein the process does not comprise a step of applying a gas mixture comprising H2 in an amount more than 10 Vol%, preferably more than 5 Vol% H2.
8. Activated catalyst bed obtainable according to the process of any one of claims 4 to 7.
9. Reaction system comprising the catalyst bed according to any one of claims 1 to 3 or the activated catalyst bed according to claim 8 in an adiabatic reaction zone, and upstream thereof a preheating zone, wherein the second catalyst layer is downstream the first catalyst layer.
A process for providing CO and H2 comprising the steps of
(i) feeding a reaction gas comprising ChU and H2O and optionally N2 to the preheating zone of the reaction system according to claim 9,
(ii) heating the reaction gas to a temperature of above 360°C sufficient for activating the second catalyst, and directing the heated reaction gas onto the first catalyst layer, and subsequently
(iii) directing the resulting gas flow onto the second catalyst layer.
The process according to claim 6, 7, or 10, wherein the amount of ChU in the reaction gas is about 0.9 to about 1.1 times the amount of H2O.
A process for providing ChU, comprising the steps of
(i) feeding synthesis gas to the preheating zone of the reaction system according to claim 9,
(ii) heating the synthesis gas to a temperature of below 340°C but equal to or higher than the temperature at which the first catalyst is active or the first catalyst precursor is activated, and directing the heated synthesis gas onto the first catalyst layer, and subsequently
(iii) directing the resulting gas flow onto the second catalyst layer.
13. The process according to claim 4, 5, or 12, wherein the synthesis gas comprises H2 and CO and optionally N2, wherein the amount of H2 is about 2.8 to about 3.2 times the amount of CO, and the amount of N2 is preferably 90 Vol% or lower, more preferably is 80 to 60 Vol%.
14. The process according to any one of claims 4, 5, 12, or 13, wherein
(i) the first catalyst precursor comprises nickel deposited on a carrier and has an
activation temperature of about 300°C; and/or
(ii) the synthesis gas is heated before application to the first catalyst layer to a
temperature of about 300°C to about 320°C; and/or
(iii) the second catalyst precursor comprises nickel intercalated into a spinel type carrier, is activatable at a temperature of about 400°C and has an average lateral compression strength after 500 h at a temperature of 650°C of at least 60 N.
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