Production of h2 from methanol for a solid oxide electrolysis cell

Abstract

The present invention relates to a method for operating a solid oxide electrolysis cell (SOEC) stack, the SOEC having a fuel (cathode) side and an oxy (anode) side. The SOEC stack is adapted for at least steam electrolysis to hydrogen. The invention further relates to a system and a plant suitable for carrying out the method. Specifically, the invention relates to using methanol as a reducing agent or using methanol for supplying a reducing agent in an SOEC.

Description

[0001] PRODUCTION OF H2 FROM METHANOL FOR A SOLID OXIDE ELECTROLYSIS CELL

[0002] TECHNICAL FIELD

[0003] The present invention relates to a method for operating a solid oxide electrolysis cell (SOEC) stack, the SOEC having a fuel (cathode) side and an oxy (anode) side. The SOEC stack is adapted for at least steam electrolysis to hydrogen. The invention further relates to a system and a plant suitable for carrying out the method.

[0004] BACKGROUND

[0005] Solid oxide electrolysis cells (SOECs) can be used to electrochemically reduce water (H2O) to hydrogen (H2), carbon dioxide (CO2) to carbon monoxide (CO), or a combination of H2O and CO2to syngas i.e. a gas mixture containing H2and CO. This conversion occurs on the fuel- (cathode) side of the solid oxide electrolysis cell, whereas on the oxy-(anode) side of the cell, oxygen is electrochemically generated. The fuel-side and the oxy-side are interposed by an electrolyte layer. SOEC cells, as is well-known in the art, are normally stacked to form a SOEC stack.

[0006] RU 2 497 748 describes operation of a system that produces hydrogen from water, in which methanol is recirculated in the system, being cracked and then re-synthesized from the components. No methanol in the feed and no methanol source is apparent from the disclosure of this reference. There seems to be a methanol loop. One goal of RU 2 497 748 seems to be expanding the feedstock for the electrolyzer by the presence of aqueous alcohol mixtures and a resulting reduction of the pumping costs.

[0007] One of the challenges reducing the efficiency and the lifetime of an SOEC is inactivation of the active material on the fuel-side. Said inactivation may be further accelerated by transient operation, such as by multiple switches from start-up operation to normal operation. Solid oxide electrolysis cells are advantageously driven on electricity generated from renewable sources such as wind and solar. Due to the inherent intermittent nature of these electricity / power sources, the SOEC stack is often subject to fluctuations in operation. Consequently, there is a need for a robust method for operating a solid oxide electrolysis cell stack. SUMMARY

[0008] It has been found by the present inventor(s) that inactivation of the active material on the fuel-side of the SOEC stack can be limited by using methanol as a reducing agent in the SOEC. Specifically, methanol enables that the active material on the fuel-side is kept reduced despite penetration of oxygen from the oxy-side of the SOEC stack. The inventors have further realised that methanol, being easy / relative safe to store and handle, may advantageously replace known reducing agents such as hydrogen.

[0009] So, in a first aspect the present invention relates to a method of operating a solid oxide electrolysis cell (SOEC) stack for producing hydrogen, said SOEC stack comprising at least one solid oxide electrolysis cell (SOEC), said at least one SOEC comprising an electrolyte layer interposed between a fuel-side and an oxy-side, the method comprising : providing a first feed gas comprising methanol and steam, supplying at least a portion of the first feed gas comprising methanol and steam to the fuel-side of the at least one SOEC, or, converting at least a portion of the first feed gas comprising methanol and steam to a first intermediate stream comprising hydrogen and supplying at least a portion of the first intermediate stream to the fuel-side of the at least one SOEC; withdrawing from said at least one SOEC, a first fuel-side exit gas.

[0010] In a second aspect, the present invention relates to a system for production of hydrogen, the system comprising : a first feed gas stream arranged to receive methanol from a methanol unit; optionally, comprising a guard bed reactor; a solid oxide electrolysis cell (SOEC) stack comprising at least one solid oxide electrolysis cell (SOEC); one or more fuel-side exit gas stream(s); wherein the SOEC stack is arranged to receive at least a portion of the first feed gas stream, optionally via a guard bed reactor and provide one or more fuel-side exit gas stream(s) or wherein a guard bed reactor is arranged to receive at least a portion of the feed gas stream and convert at least a portion of the methanol to hydrogen so as to provide an intermediate stream and the SOEC is arranged to receive at least a portion of the intermediate stream. In a third aspect, the present invention relates to a chemical plant for production of methanol, the plant comprising : the system for production of hydrogen as disclosed herein, methanol synthesis unit, wherein the methanol synthesis unit is arranged to receive at least a portion of the fuel-side exit gas from the SOEC as a syngas stream; wherein the methanol synthesis unit is arranged to convert the syngas stream to a product methanol stream.

[0011] LEGENDS TO THE FIGURE

[0012] Fig. 1 schematically shows a first method of operating a solid oxide electrolysis cell (SOEC) stack for producing hydrogen.

[0013] Fig. 2 schematically shows a second method of operating a solid oxide electrolysis cell (SOEC) stack for producing hydrogen.

[0014] Fig. 3 schematically shows a system and a method for production of hydrogen.

[0015] Fig. 4 schematically shows a chemical plant for production of methanol and a method for operating same.

[0016] Fig. 5 schematically shows a chemical plant for production of methanol and a method for operating same.

[0017] DETAILED DISCLOSURE

[0018] Definitions

[0019] The term "SOEC" or "SOECs" means solid oxide electrolysis cell(s) and may be used interchangeably with the term "SOE cell(s)". The term "SOEC stack" means a stack assembly of SOECs.

[0020] The terms "fuel-side" and "cathode-side" may be used interchangeably. It would also be understood that "cathode" means fuel electrode in electrolysis operation mode.

[0021] The terms "oxy-side" and "anode side" may be used interchangeably. It would be understood that "anode" means oxygen (oxy-) electrode in electrolysis operation mode. The term "operation mode" is used to refer to one or more specific type(s) of operation such to differentiate between conditions of operation. Examples of operation modes include "transient operation" and "normal operation".

[0022] The term "transient operation" means non-continuous operation of the SOEC stack, where the stack has not reached a steady state corresponding to normal operation, including the supply of a continuous current. Thus, during transient operation there is often no hydrogen product gas being generated.

[0023] The terms "normal operation" and "electrolysis operation" may be used interchangeably. Normal operation means continuously applying a current of typically 0.1 or higher A / cm2, such as 0.45 A / cm2 or higher, and at normal SOEC stack operation temperature of 600- 1000°C, suitably 650-900°C, such as 700-750°C or 700-800°C.

[0024] The term "operating the SOEC stack under open-circuit voltage (OCV)" means that there is no external source connected and there is no electrical current and thereby also no product gases, e.g. hydrogen, being generated. The electrical potential difference is only due to pO2differences at the two electrodes.

[0025] The term "enriched in X", for instance where X is steam, is understood as "the concentration of X in a stream is increased compared to the concentration of X in the corresponding feed gas".

[0026] The term "electrochemically generated" refers to a process where chemical species are formed via an electrochemical process, i.e. a chemical process involving electron transfer. Such processes include e.g. the oxygen evolution reaction (2O2-= O2+ 4e ) and the water reduction reaction (H2O + 2e_= H2+ O2).

[0027] The use of the article "a" or "an" means at least one. For instance, the term "a guard bed reactor" means "at least one guard bed reactor".

[0028] Other definitions are provided in connection with one or more of the embodiments disclosed herein.

[0029] Method of operating a solid oxide electrolysis cell (SOEC) stack for producing hydrogen

[0030] Provided is a method of operating a solid oxide electrolysis cell (SOEC) stack for producing hydrogen, said SOEC stack comprising at least one solid oxide electrolysis cell (SOEC), said at least one SOEC comprising an electrolyte layer interposed between a fuel-side and an oxyside, the method comprising : providing a first feed gas comprising methanol and steam, supplying at least a portion of the first feed gas comprising methanol and steam to the fuel-side of the at least one SOEC, or, converting at least a portion of the first feed gas comprising methanol and steam to a first intermediate stream comprising hydrogen and supplying at least a portion of the first intermediate stream to the fuel-side of the at least one SOEC; withdrawing from said at least one SOEC, a first fuel-side exit gas.

[0031] The provided method of operating a solid oxide electrolysis cell (SOEC) stack is suitable for producing hydrogen, however the method may be applied for transient operation (suitably not providing product) and for operating in normal operation (providing product such as hydrogen). During operation producing hydrogen, the solid oxide electrolysis cell (SOEC) is used to electrochemically reduce water (H2O) to hydrogen (H2), i.e. by the water reduction reaction: H2O + 2e_= H2+ O2-. In this way, hydrogen is formed via an electrochemical process involving electron transfer. On the oxy-side of the solid oxide electrolysis cells, oxygen is electrochemically generated e.g. by the oxygen evolution reaction: 2O2-= O2+ 4e_. In this way, oxygen is formed via an electrochemical process further providing electrons to be transferred. The oxy-side may be arranged to receive an air feed and provide an oxygen (O2) stream. Suitably, the SOEC stack is operated by supplying steam i.e. water (H2O) to the fuel-side of the solid oxide electrolysis cell. Hence, the first fuel-side exit gas may comprise hydrogen.

[0032] In one aspect, the provided method comprises supplying at least a portion of the first feed gas comprising methanol and steam to the fuel-side of the at least one SOEC. The first feed gas comprises methanol, which is particularly advantageous as the methanol may act as a reducing agent for the fuel-side of the SOEC. This is particularly important as active metals at the fuel-side of the SOEC such as nickel may undergo undesirable oxidation by oxygen migrating from the oxy-side through the electrolyte (Ni may oxidise to NiO). The presence of a reducing agent may minimize or eliminate such effects. The methanol may act as a reducing agent both during an operation mode, providing product (e.g. hydrogen) as well as during transient operation. In this way, provided is a method that increases the lifetime of the active material on the fuel-side as the active material is kept reduced and active over time even through various operation modes.

[0033] In another aspect, the provided method comprises converting at least a portion of the first feed gas comprising methanol and steam to a first intermediate stream comprising hydrogen and supplying at least a portion of the first intermediate stream to the fuel-side of the at least one SOEC. In this aspect, the hydrogen comprised in the first intermediate stream may act as a reducing agent for the fuel-side of the SOEC. In this way, methanol may be used for supplying at least one reducing agent to the fuel-side of the SOEC. The first intermediate stream may further comprise methanol. Converting at least a portion of the methanol to hydrogen to provide the intermediate stream, followed by supplying the intermediate stream to SOEC, provides a method which may omit any unnecessary storage of hydrogen such as storage of hydrogen bottles or cylinders on site. This is a significant advantage as strict measures for safe handling and storage of hydrogen needs to be in place.

[0034] In one aspect, the first intermediate stream further comprises steam. Suitably, the first intermediate stream is substantially free of methane. By "substantially free of methane" is meant that the methane content of this stream is less than 100 ppm.

[0035] Typically, the first intermediate stream comprises 4 vol% hydrogen or less. This level of hydrogen should be sufficient to maintain the catalyst in the SOEC in its active state.

[0036] Specifically, the method comprises the step of providing a first feed gas comprising methanol and steam. A first feed gas comprising steam is particularly advantageous during heating or during operation at higher temperatures e.g. above 400°C, because the presence of steam may limit carbon formation formed from methanol. Suitably, the first feed gas may comprise 0.1-10 vol% methanol and > 90 vol% steam. The first feed gas may comprise 0.1-5 vol% methanol, and at least 95 vol% steam. The first feed gas may comprise l-2vol% methanol, and at least 98 vol% steam. Advantageously, the first feed gas may be a first purified feed such as a feed comprising < 50 ppb of silicon. The term "purified" is to be understood as a stream / feed has been subjected to removal of impurities, such as to removal of silicon, sulphur or a combination thereof. In this way, the content of volatile silica species may advantageously be minimised in downstream streams.

[0037] The first feed gas may comprise steam withdrawn from a steam drum, hence a steam drum may be comprised in the system. Preferably, the steam withdrawn from such steam drum is pure steam such as comprising >99 % H2O, such as consisting of steam. The steam withdrawn from such steam drum may further be purified. Alternatively, and preferably, the first feed gas may be provided by dosing the methanol such as liquid methanol in the steam drum, said steam drum being arranged to receive a water stream and provide the first feed gas comprising methanol and steam. Due to the lower boiling point of methanol compared to water, the methanol added will immediately evaporate within the steam drum. Suitably, the steam drum is arranged to receive a pure water stream such as a stream comprising >99 % H2O such as consist of water and / or a purified water stream. The methanol for dosing may be supplied as a recycle stream and / or be supplied from a methanol storage unit.

[0038] The first feed gas may comprise methanol advantageously supplied as a recycle stream from a methanol synthesis unit i.e. comprising a methanol synthesis loop and a methanol purification section. This is particularly advantageous when the method of operating a solid oxide electrolysis cell (SOEC) stack for producing hydrogen is combined with a method for methanol production. Additionally, or alternatively, the first feed gas may comprise methanol supplied from a methanol storage unit. Supplying methanol from a methanol storage unit may further comprise storing liquid methanol in a storage unit, evaporating said liquid methanol to provide methanol gas (optionally in the steam drum) and provide said methanol gas as at least a portion of the first feed gas. Methanol such as liquid methanol can generally be handled and stored without strict measures compared to measures necessary for handling gases such as hydrogen. In this way, the fact that the methanol may be provided from a methanol storage unit is a significant advantage for handling.

[0039] Regardless of whether the first feed gas is arranged to receive methanol from a recycle stream or from a methanol storage unit, the methanol supplied is preferably a pure methanol stream. A pure methanol stream may be defined as a product stream which essential comprises product such as 60 vol% methanol, however preferably above 90 vol% methanol such as above 95 vol% methanol, more preferably above 98 vol% methanol most preferably 99 vol% methanol or above 99 vol% methanol. The pure methanol stream may be fuel grade methanol or AA grade methanol or equivalent standards. Consequently, the method may further comprise supplying at least a portion of the first feed gas comprising methanol as a recycle stream from a methanol synthesis unit, and / or supplying at least a portion of the first feed gas comprising methanol from a methanol storage unit, wherein said portion being suitably a pure methanol stream.

[0040] Suitably, the first feed gas is substantially free of methane. By "substantially free of methane" is meant that the methane content of this stream is less than 100 ppm.

[0041] In one aspect, the first feed gas has a proportion of methanol to steam of below 10vol% or less, preferably 2vol% or less methanol to steam. Maintaining the proportion of methanol to steam in this range reduces the flammability of the feed gas, making the method / system of the invention safer.

[0042] The first feed gas may be arranged to receive a first steam feed. Arranging the first feed gas to receive a first steam feed allows for a change in composition of the gas received by the SOEC. In this way, the first steam feed may be suitable for providing a first feed gas enriched in steam, such provide flexibility to the system. Any suitable steam feed provided, such as a first steam feed, is a pure steam feed, hence the first steam feed may comprise >99 % H2O, such as consisting of water. Additionally, the first steam feed may be a purified steam feed, hence the feed may have been subjected to removal of impurities, such as to removal of silicon, sulphur or a combination thereof. The first feed gas may comprise steam supplied / withdrawn form a steam drum; hence a steam drum may be comprised in the system. The first feed gas and / or the first steam feed may further comprise carbon dioxide.

[0043] The provided method may comprise converting at least a portion of the first feed gas comprising methanol and steam to a first intermediate stream comprising hydrogen and supplying at least a portion of the first intermediate stream to the fuel-side of the at least one SOEC, the method comprises a first intermediate stream. The first intermediate stream comprises hydrogen and may further comprise methanol. Suitably, the first intermediate stream may comprise 2-10 vol% hydrogen. The first intermediate stream further comprises steam, and optionally carbon dioxide. Advantageously, the first intermediate stream may be a purified stream such as a stream comprising < 50 ppb of silicon. Again, such low levels of silicon in the first intermediate stream may advantageously minimise the content of volatile silica species in downstream streams.

[0044] Guard bed reactor

[0045] Preferably, the method further comprises supplying at least a portion of said first feed gas to a guard bed reactor and withdrawing from said guard bed reactor i) a first purified feed gas comprising methanol or ii) the first intermediate stream comprising hydrogen, the first intermediate stream optionally as a first purified intermediate stream comprising hydrogen. The guard bed reactor may thus act to purify a feed, specifically the guard bed reactor may act to purify the first feed gas to provide the first purified feed, or the guard bed reactor may act to purify the first intermediate stream to provide a first purified intermediate stream.

[0046] The guard bed reactor comprises a guard bed, more specifically a 3-dimensional (3D) bed structure. Suitably, the method comprises that the guard bed reactor is arranged to receive at least a portion of the first feed gas, said first feed gas comprising methanol and steam. The method may further comprise that the guard bed reactor is arranged to receive a second steam feed. In this way, steam or additional steam may be added to first feed gas in the guard bed reactor as it may be suitable for various operation modes.

[0047] The guard bed reactor may comprise a catalyst active in conversion of methanol to hydrogen such as through reacting methanol and steam to carbon dioxide and hydrogen. In this way, the catalyst may be active in methanol steam reforming, where the main reaction can be represented by the equilibrium equation: CH3OH + H2O CO + 3H2. Consequently, the guard bed reactor may act to convert at least a portion of the first feed gas comprising methanol to a first intermediate stream comprising hydrogen. Preferably, the guard bed reactor may convert essentially all methanol comprised in the first feed gas to hydrogen. Suitably, the first intermediate stream comprising hydrogen comprises less than 5% methanol such as less than 1% methanol.

[0048] The method may further comprise a catalyst such as a catalyst active in the conversion of methanol to hydrogen, where said catalyst is any of a catalyst comprising nickel (Ni), a catalyst comprising iron (Fe), or a combination thereof. Specifically, the method may comprise that the guard bed reactor comprises a bed comprising said catalyst active in the conversion of methanol to hydrogen, in which said catalyst comprises nickel and an active metal (Me) oxide; wherein the active metal (Me) is selected from the group consisting of alkaline earth metals including Ca, Mg, Sr; transition metals including Zr; rare earth metals including La and Ce; or mixtures thereof.

[0049] The catalyst active in conversion of methanol to hydrogen may be a monometallic nickel catalyst, or a monometallic iron catalyst. The catalyst comprising nickel may comprise 20- 60wt% Ni, and 40-80 wt% of any oxides of Al, Ca, Mg or combinations thereof, optionally promoted with a lanthanide group metal oxide, such as La2O3. The term "lanthanide" refers to any of the fifteen elements from La to Lu in the periodic table of elements, hence Lanthanum (La) is also a lanthanide. Specifically, the catalyst may be a Fe-based catalyst in the form of a monometallic catalyst system having Fe as the metal. Specifically, the catalyst may be a Ni-based catalyst in the form of a monometallic catalyst system having Ni as the metal.

[0050] Alternatively, or additionally, the catalyst active in conversion of methanol to hydrogen may be a bimetallic catalyst or a metal alloy selected from any of: Fe, Co, Ru, Ni or combinations thereof, such as a Fe-Co based catalyst. The Fe-Co catalyst may be bimetallic or an alloy. Hence, the catalyst may be a Fe-Co-based catalyst in the form of a bimetallic catalyst system having Fe and Co as a metal alloy. Alternatively, the catalyst may be a Ni-Co based catalyst in the form of a bimetallic catalyst system having Ni and Co as a metal alloy.

[0051] Suitably, the catalyst active in conversion of methanol to hydrogen is promoted with any of K2O, CaO, SiO2, AI2O3. Specifically, the catalyst comprising Ni may be supported, such as nickel supported on alumina i.e. Ni / AI2O3. The catalyst comprising Ni may also comprise an active metal (Me) oxide, wherein the active metal (Me) oxide could act as a promoter for the conversion of methanol to hydrogen, but not be active in itself. Specifically, the catalyst comprising Fe may be supported such as Fe-Co / AI2O3. The Fe-based catalyst or Fe-Co-based catalyst may be preferred as it may be more active than a monometallic Ni catalyst, thus may enable operation at lower temperatures, thus be suitable for transient operation. However, the catalyst comprising Ni may additionally act as an impurity-binding material thus act to purify a feed / stream by removal of impurities. In this way, a single material may provide dual-function of being active in conversion of methanol to hydrogen and further and as an impurity-binding material.

[0052] The guard bed reactor, alternatively or additionally to comprising the catalyst active in conversion of methanol to hydrogen, may further comprise a separate and distinct purifying material, i.e. an impurity-binding material. The term "impurity" may be used to refer to at least one of Si (silicon), N (nitrogen), S (sulphur), P (phosphorus), As (arsenic), or compounds thereof. An impurity may be silica SiO2(s) or volatile silica species such as Si(OH)4(g). An impurity may be NOX(nitrogen oxides). An impurity may be H2S (hydrogen sulphide) or SO2(sulphur dioxide). An impurity may be a combination of silica SiO2(s), volatile silica species such as Si(OH)4(g), NOX(nitrogen oxides), H2S (hydrogen sulphide), SO2(sulphur dioxide). The term "binding" is to be understood as a general term that encompasses several types of interactions between molecules or particles, such comprising adsorption, absorption and reaction. While adsorption, absorption and reaction are distinct processes, they can all be considered types of binding interactions between molecules and / or particles.

[0053] Specifically, the method may further comprise that the guard bed reactor comprises an impurity-binding material, said impurity-binding material being any of at least a silicon- binding material, a sulphur-binding material, or a combination thereof; wherein the impuritybinding material comprises a metal (Me) oxide, in which the metal (Me) is selected from the group consisting of alkaline earth metals including Ca, Mg, Sr; transition metals including Zr; rare earth metals including La and Ce; or mixtures thereof.

[0054] The impurity-binding material may be a silicon-binding material, such suitable for removing silicon-derived species such as silica (SiO2) and / or volatile silica species such as Si(OH)4. Such impurities may pose an issue as especially volatile silica species may deposit and / or react with metal oxides of downstream units or equipment, including the SOEC stack. In this way, formation of amorphous silica species on surfaces such as within the fuel-side of SOEC as well as downstream the SOEC may be minimised. The guard bed reactor comprising the impurity-binding material may be particularly suitable for purifying feed / steams comprising steam, such as the second steam feed, as the silicon content is reduced to ppb level in the guard bed reactor,

[0055] The guard bed reactor may be arranged to both purify a feed such as a first feed gas comprising methanol and / or such as a second steam feed and further to convert at least a portion of the first feed gas comprising methanol and steam to a first intermediate stream comprising hydrogen. For example, the guard bed reactor may comprise a catalyst active in conversion of methanol to hydrogen said catalyst comprising Fe, such as an Fe-Co-based catalyst, hence comprise a catalyst that does not comprise Ni. The guard bed reactor may further comprise silicon-binding material and a sulphur-binding material. The silicon-binding material may be an active metal (Me) oxide, while the sulphur-binding material may be a Ni- based catalyst material.

[0056] The guard bed reactor may be arranged with one or more beds for purifying a feed and / or converting the first feed gas. The method may be specified such that said catalyst active in the conversion of methanol to hydrogen and the impurity-binding material, are provided as separate and distinct materials, wherein the guard bed reactor comprises:

[0057] - a bed comprising both: said catalyst active in the conversion of methanol to hydrogen, and said impurity-binding material, suitably as silicon-binding material; and / or

[0058] - a bed comprising said catalyst active in the conversion of methanol to hydrogen; and a separate bed comprising said impurity-binding material, suitably as a silicon-binding material.

[0059] For example, the guard bed reactor may comprise a bed i.e. a single bed, which comprises a mixture of: pellets, balls or monoliths, provided as the catalyst active in conversion of methanol to hydrogen and separately yet within the same bed, pellets, balls or monoliths, provided as impurity-binding material, suitably as silicon- binding material.

[0060] The guard bed reactor may comprise a plurality of such single beds.

[0061] For example, the guard bed reactor may comprise separate beds; a bed which comprises pellets, balls or monoliths, provided as the catalyst active in conversion of methanol to hydrogen; and a separate (another) bed which comprises pellets, balls and monoliths, provided as the impurity-binding material, suitably as silicon-binding material, hence this separate bed being a Si-guard bed.

[0062] Additionally, combinations of the above-mentioned guard beds are also envisaged.

[0063] For example, suitably in sequential order: a single bed comprising both said catalyst active in conversion of methanol to hydrogen; and said impurity-binding material, suitably a silicon-binding material a bed comprising said catalyst active in conversion of methanol to hydrogen; and a separate bed comprising said impurity-binding material, suitably a silicon-binding material. Suitably, the Si-guard bed is arranged directly upstream of the fuel-side inlet of the SOEC or SOEC stack. The term "directly" is used to refer to that there are no intermediate units of process steps between the Si-guard bed and the fuel-side inlet of the SOEC. More generally the term "directly" means that there is no intermediate unit or step changing the composition of a process stream.

[0064] Suitably, the Si-guard bed comprises less than 50000 ppb, such as less than 1000 ppb, less than 100 ppb, or less than 10 ppb of Si on a molar basis. Preferably, the Si-guard bed comprises less than 10 ppb of Si on a molar basis. Another undesired species in the Si-guard bed is potassium oxide. Preferably, the Si-guard bed comprises less than 5000, such as less than 2000 or 1000 ppm on a molar basis of potassium (K).

[0065] It has been found that the Si-guard bed should preferably not contain any significant amount of Si and that the components of the Si-guard bed reactor as such should preferably not contain any significant amount of Si. Any Si present in the Si guard bed would risk reacting with the steam in the first feed gas and / or steam in the second steam feed and thus have adverse effects down-stream of the Si-guard bed.

[0066] When the Si-guard bed becomes saturated with silica or becomes less efficient, it can be regenerated or replaced. The regeneration is conducted in high temperature / high pressure steam.

[0067] Another impurity is sulphur (S). Accordingly, the guard bed reactor may be provided with a sulphur-binding material i.e. hence this bed being a S-guard bed; for instance, in series as two separate beds in a single vessel or the guard bed may comprise a sulphur-binding material in addition to the silicon-binding material or the silicon-binding material may also bind sulphur.

[0068] For example, the guard bed may comprise Ni as sulphur-binding material, thus advantageously the catalyst active in conversion of methanol to hydrogen is a catalyst comprising Ni, such as said catalyst comprising nickel and an active metal (Me) oxide; wherein the active metal (Me) is selected from the group consisting of alkaline earth metals including Ca, Mg, Sr; transition metals including Zr; rare earth metals including La and Ce; or mixtures thereof. The bed comprising this catalyst as a single material thus enables conversion of methanol to hydrogen, while at the same time removing at least sulphur and silicon impurities. A S-guard bed works by reacting with sulphur-containing compounds, such as hydrogen sulphide and sulphur dioxide, and binding them to the guard bed surface. The material used in a S-guard bed can vary, but common materials include metal oxides, such as zinc oxide, nickel oxide, copper oxide, or activated carbon.

[0069] Operation modes - transient operation

[0070] The provided method may comprise a variety of operation modes. Specifically, the method may comprise transient operation, hence the method may comprise non-continuous operation of the SOEC stack, where the stack has not reached a steady state corresponding to normal operation, including the supply of a continuous current. Thus, during the transient operation there is often no hydrogen product gas being produced. Transient operations may comprise start-up operation, hot-idle operation and shut-down operation. Consequently, the method may comprise transient operation, and said transient operation may be selected from any of start-up operation, hot-idle operation and / or shut-down operation.

[0071] In start-up operation, the method comprises heating up a SOEC stack, for instance from room temperature, by feeding a start-up gas feed to the SOEC. Said start-up gas feed may be the first gas feed such as a purified gas feed or the start-up gas feed may be the intermediate gas stream such as a purified intermediate gas stream. Suitably, the start-up gas feed comprises at least one reducing agent such as methanol and / or hydrogen. Specifically, the start-up operation may be initiated by an initial start-up cycle, which may be followed by additional start-up cycles. Each cycle comprises feeding a portion of the start-up gas feed to the SOEC, the start-up gas feed having a specific temperature. Suitably, the method comprises increasing the temperature of the start-up gas feed for each cycle starting from the initial stat-up cycle, thus heating up of the SOEC stack. Specifically relevant for start-up operation, the method may further comprise heating said first feed gas comprising methanol to a temperature of 400-900°C, such as 450-850°C or 500-800°C, optionally at the inlet of the SOEC such as at the inlet of the SOEC stack or at the inlet of the guard bed reactor.

[0072] In hot-idle operation, the method comprises operating the SOEC stack under open-circuit voltage (OCV) at temperatures lower than normal SOEC stack operation temperature. More specifically, the temperature is kept at 10-200°C such as 50-200°C or such as 100-200°C, hence lower than normal SOEC stack operation temperature of typically around 600-1000°C, suitably 650-900°C, such as 700-750°C or 700-800°C. Operating the SOEC stack under open-circuit voltage (OCV) means that there is no external source connected and there is no electrical current. The current density is 0 A / cm2. The electrical potential difference over the SOEC is only a result of the pO2 differences at the two electrodes. Hence, the first fuel-side exit gas provided during hot-idle operation is not a suitable product gas i.e. no hydrogen product gas is being produced. The "hot-idle operation" may also be referred to as "hot-idle" or "hot-idle mode".

[0073] Also considered a transient operation is "shut-down operation" or simply "shut-down". Shutdown operation means operation of the SOEC stack away from normal operation by cooling down the SOEC stack, for instance to room temperature, and removing the current applied during normal operation.

[0074] Typically, not only hot-idle operation but also start-up operation and shut-down operation comprises operating the SOEC stack under open-circuit voltage. Consequently, where the method comprises transient operation, preferably, the transient operation further comprises operating the SOEC stack under open-circuit voltage (OCV). During OCV, hydrogen is not outputted from the system, and it can therefore be recycled.

[0075] Operation modes - normal operation

[0076] The provided method may comprise normal operation. In normal operation, the first fuel-side exit gas comprises hydrogen. Thus, during the normal operation hydrogen product gas is being produced. The method may further comprise continuously applying a load, thus an electricity current, to the SOEC stack. In this way, the method further comprises the supply of a continuous current suitable for operation in electrolysis mode such that the solid oxide electrolysis cell (SOEC) is used to electrochemically reduce water (H2O) to hydrogen (H2), and oxygen is formed via an electrochemical process further providing electrons to be transferred. Preferably, the method may comprise continuous operation of the SOEC stack such to provide a continuous first fuel-side exit gas comprising hydrogen. Consequently, the method may further comprise withdrawing a portion of said first fuel-side exit gas, suitably the entire portion thereof, as a separate hydrogen stream, suitably as a hydrogen product stream.

[0077] In normal operation, the first feed gas may be arranged to receive a first steam feed and / or second steam feed, and the first fuel-side exit gas comprises hydrogen. Arranging the first feed gas to receive the first steam feed and / or the second steam feed allows for a change in composition of the gas received by the SOEC. In this way, the first steam feed may be suitable for providing a first feed gas enriched in steam, such provide flexibility to the system.

[0078] In normal operation, the first feed gas, the first steam feed and / or the second steam feed may further comprise carbon dioxide and the first fuel-side exit gas may comprise syngas i.e. a gas mixture containing hydrogen and carbon monoxide. Consequently, where present the first intermediate stream may also comprise carbon dioxide. When carbon dioxide is present in the first feed gas, the first steam feed and / or the second steam feed, and where present the first intermediate stream, the solid oxide electrolysis cell may be used to electrochemically reduce carbon dioxide (CO2) to carbon monoxide (CO). In this way, a combination of H2O and CO2may be converted to syngas i.e. a gas mixture containing H2and CO. The SOEC stack may be operated by supplying additional carbon dioxide gas to the fuelside of the solid oxide electrolysis cell. The first feed gas, the first steam feed and / or the second steam feed may be arranged to receive a first carbon dioxide feed. Any carbon dioxide feed provided is suitably a purified carbon dioxide feed such as a feed comprising < 50 ppb of silicon. Hence, the carbon dioxide feed may have been subjected to removal of impurities, such as to removal of silicon, sulphur or a combination thereof, again to minimise the content of volatile silica species in downstream streams / units.

[0079] In normal operation, the method preferably comprises operating the system at a temperature of 650-900°C. Specifically, the method may further comprise continuously heating the first feed gas comprising methanol and suitably steam to a temperature of 650-900°C. In systems comprising a guard bed reactor, preferably the method comprises heating the first feed gas and / or the second steam stream at the inlet of the guard bed reactor.

[0080] Change from a first operation to a second operation

[0081] The provided method may be suitable for variety of operations such as transient operation or normal operation, and additionally a first operation may be replaced by a second operation such as dependent on availability of e.g. electricity generated from renewable sources. Preferably, normal operation may replace transient operation such as e.g. after start-up or after hot-idle operation. Consequently, the method may further comprise: replacing at least a portion of said first feed gas comprising methanol and steam such to provide a second feed gas enriched in steam, supplying at least a portion of the second feed gas to the fuel-side of the at least one SOEC or, supplying at least a portion of the second feed gas to a guard bed reactor and withdrawing from said guard bed reactor a second intermediate stream comprising steam, and further supplying at least a portion of said second intermediate stream to the fuel-side of the at least one SOEC; withdrawing from said at least one SOEC, a second fuel-side exit gas. Specifically, the method may further comprise withdrawing a portion of said second fuel-side exit gas, suitably the entire portion thereof, as a separate hydrogen stream, suitably as a hydrogen product stream. Preferably, the method further comprises continuously applying a load, thus an electricity current, to the SOEC stack. Suitably, the method may comprise withdrawing a portion of said second fuel-side exit gas as a separate hydrogen stream starting from when applying said load to the SOEC stack.

[0082] The step of replacing at least a portion of the first feed gas with the second feed gas may preferably comprise gradually replacing said first feed gas comprising methanol and steam by first combining a first steam feed and / or a second steam feed with the first feed gas, and later interrupting the flow of the first feed gas, such as by interrupting the supply of the methanol stream to provide a second feed gas enriched in steam. In this way, the second feed gas provided by first steam feed and / or second steam feed may replace all the first feed gas. The second feed gas is enriched in steam, specifically the second feed gas may comprise 50 vol% steam, or above 90 vol% steam such as >95 vol% steam such as >99 vol% steam such as 100 vol% steam. The second feed gas comprising steam may further comprise a reducing agent such as between 0.5-10 vol% reducing agent such as 0.5 vol%, such as 1 vol%, such as 5 vol % such as 10 vol% reducing agent. Specifically said second feed gas may comprise methanol and / or hydrogen. Hence, said second feed gas may comprise between 0.5-10 vol% methanol, between 0.5-10 vol% hydrogen or between 0.5-10 vol% methanol and hydrogen. The second feed gas may optionally further comprise carbon dioxide.

[0083] Alternatively, the step of replacing at least a portion of the first feed gas with the second feed gas may preferably comprise gradually replacing only a portion of said first feed gas comprising methanol and steam by combining a first steam feed and / or second steam feed with the first feed gas comprising methanol and steam. Said first steam feed and / or second steam feed may further comprise carbon dioxide.

[0084] Changes in operation such as from transient mode to normal mode often relates to a change in temperature of the system. Suitably, the method may comprise heating said first feed gas comprising methanol and steam to a temperature of 400-900°C, such as 450-850°C or 500- 800°C, and wherein at least a portion of the first feed gas is replaced by the first steam feed and / or second steam feed so as to provide the second feed gas upon approaching or reaching normal operation temperature of the SOEC stack, said normal operation temperature being 600-1000°C, suitably 650-900°C. The method may further comprise continuously heating said second feed gas to a temperature of 650-900°C. Similarly to the method providing the first fuel-side exit gas, the method providing the second fuel-side exit gas may comprise the step of supplying at least a portion of the second feed gas, to a guard bed reactor. Suitably, the method may further comprise continuously heating said second feed gas to a temperature of 650-900°C, preferably at the inlet of the guard bed reactor. A guard bed reactor suitable for providing the first fuel-side exit gas is suitable for providing the second fuel-side exit gas.

[0085] At least a portion of the energy needed for heating the SOEC stack e.g. energy for heating any of the feeds and / or streams arranged to be received by the SOEC stack may advantageously be provided by heat exchange within the system. Specifically, the method may further comprise the heating of any of said first feed gas comprising methanol and steam, said second feed gas, said first steam feed, said second steam feed, said first intermediate stream, said second intermediate stream, the air feed, or a combination thereof, such as said method comprises heat exchange with said first or second fuel-side exit gas. In this way, heat energy may be transferred from one or more the fuel-side exit gases to any feed / stream.

[0086] Additionally or alternatively, the method may further comprise the heating of any of said first feed gas comprising methanol and steam, said first steam feed, said second steam feed, said first intermediate stream, said second intermediate stream, the air feed, or a combination thereof, by heat exchange with an oxy-side exit gas such as an oxygen (O2) stream provided from the oxy-side of the SOEC. More specifically, heat energy available in the first fuel-side exit gas, the second fuel-side exit gas and / or the oxy-side exit gas may be transferred via heat exchange to any feed / stream received by the SOEC such to allow for an energy efficient method and system.

[0087] A system for production of hydrogen

[0088] A system for production of hydrogen, the system comprising a first feed gas stream arranged to receive methanol from a methanol unit; optionally, comprising a guard bed reactor; a solid oxide electrolysis cell (SOEC) stack comprising at least one solid oxide electrolysis cell (SOEC); one or more fuel-side exit gas stream(s); wherein the SOEC stack is arranged to receive at least a portion of the first feed gas stream, optionally via a guard bed reactor and provide one or more fuel-side exit gas stream(s); or wherein a guard bed reactor is arranged to receive at least a portion of the feed gas stream and convert at least a portion of the methanol to hydrogen so as to provide an intermediate stream and the SOEC is arranged to receive at least a portion of the intermediate stream.

[0089] Preferably, the SOEC stack comprises at least one solid oxide electrolysis cell (SOEC), where at least one SOEC comprises an electrolyte layer interposed between a fuel-side and an oxyside. The oxy-side is typically arranged to receive an air feed and provide an oxygen (O2) stream.

[0090] Specifically, the methanol unit may be a storage unit such as a storage tank for storing methanol. Consequently, the first feed gas stream arranged to receive methanol from a methanol unit comprises methanol. The first feed gas stream further comprises steam. Specifically, the system may further comprise that the first feed gas stream is arranged to receive a first steam feed stream. In this way, additional steam may be added to the first feed gas stream. The first feed gas stream may further comprise carbon dioxide. Hence, the system may further comprise that the first feed gas stream is arranged to receive a carbon dioxide stream. In this way carbon dioxide may be added to the first feed gas stream and / or to the first steam feed stream.

[0091] Specifically, the system may further comprise a steam drum. Said steam drum may be arranged to receive a methanol stream such as a liquid stream and further to receive a water stream and to provide at least a portion of the first feed gas. Said steam drum may be arranged for dosing the methanol such as liquid methanol in the steam drum to provide the first feed gas comprising methanol and steam. Hence, the steam drum may be arranged to receive methanol from the methanol unit.

[0092] The system may further comprise a guard bed reactor. Specifically, the system may comprise that the first feed gas stream is arranged to receive a first steam feed and / or a second steam feed, wherein the guard bed reactor is arranged to receive the second steam feed.

[0093] Specifically, the system may further comprise a guard bed reactor, wherein the guard bed reactor is arranged to receive the first feed gas stream, and optionally a second steam feed stream so as to provide a first purified feed gas or a first intermediate stream, the first intermediate stream optionally as a first purified intermediate stream. Including said guard bed reactor in said system may advantageously provide for the SOEC to be operated at a higher steam conversion, such as above 70 wt% conversion. The guard bed reactor arranged to provide the first purified feed or the first intermediate stream, such as the first purified intermediate stream may also be arranged to provide the second purified feed or the second intermediate stream, such as the second purified intermediate stream. In this way, the system may comprise a guard bed reactor such as one or more guard bed reactors.

[0094] The guard bed reactor may comprise a catalyst active in conversion of methanol to hydrogen such as through reacting methanol and steam to carbon dioxide and hydrogen. The catalyst active in the conversion of methanol to hydrogen may be any of a catalyst comprising nickel (Ni), a catalyst comprising iron (Fe), or a combination thereof. Specifically, the guard bed reactor may comprise a bed comprising said catalyst active in the conversion of methanol to hydrogen, in which said catalyst comprises nickel and an active metal (Me) oxide; wherein the active metal (Me) is selected from the group consisting of alkaline earth metals including Ca, Mg, Sr; transition metals including Zr; rare earth metals including La and Ce; or mixtures thereof. Wherein the guard bed reactor comprises such catalyst active in conversion of methanol to hydrogen, the guard bed reactor may be arranged to provide a first intermediate stream. In this way, the SOEC stack is arranged to receive at least a portion of the first feed gas stream via a guard bed reactor. The active metal oxide is - in one embodiment - a magnesium aluminium oxide.

[0095] In one aspect, the fuel side of said SOEC stack comprises a nickel catalyst active in the conversion of methanol to hydrogen. Suitably, the first feed gas or the hydrogen in the first intermediate stream keeps the nickel catalyst on the SOEC fuel side in a reduced state.

[0096] The guard bed reactor may comprise an impurity-binding material, said impurity-binding material being any of at least a silicon-binding material, a sulphur-binding material, or a combination thereof; wherein the impurity-binding material comprises a metal (Me) oxide, in which the metal (Me) is selected from the group consisting of alkaline earth metals including Ca, Mg, Sr; transition metals including Zr; rare earth metals including La and Ce; or mixtures thereof. Wherein the guard bed reactor comprises such an impurity-binding material, the guard bed reactor may be arranged to provide a first purified feed gas or provide an intermediate stream such as a first purified intermediate stream. In this way, the SOEC stack is arranged to receive at least a portion of the first feed gas stream via a guard bed reactor.

[0097] Specifically, the guard bed reactor may comprise:

[0098] - a bed comprising both: said catalyst active in the conversion of methanol to hydrogen, and said impurity-binding material, suitably as silicon-binding material; and / or

[0099] - a bed comprising said catalyst active in the conversion of methanol to hydrogen; and a separate bed comprising said impurity-binding material, suitably as a silicon-binding material. The catalyst active in the conversion of methanol to hydrogen and the impurity-binding material, may be provided as separate and distinct materials. Additionally, or alternatively a catalyst with a dual function active in both conversion of methanol to hydrogen and in the impurity-binding may be provided. Wherein the guard bed reactor comprises both said catalyst active in the conversion of methanol to hydrogen and an impurity-binding material, the guard bed reactor may be arranged to provide a first purified intermediate stream. In this way, the SOEC stack is arranged to receive at least a portion of the first feed gas stream via a guard bed reactor.

[0100] The system may further comprise that the first steam feed, the second steam feed or a combination thereof, is / are arranged to provide a second feed gas and the system may further comprise means for closing off or partially closing off the first feed gas stream. In this way, the system allows for the first feed gas to be partially replaced by the first steam feed and / or the second steam feed or alternatively be fully replaced by the first steam feed and / or the second steam feed such that the first steam feed and / or the second steam feed becomes the second feed gas. Suitably, the system may further comprise a steam drum, wherein said steam drum is arranged to provide the first and / or second steam feed such that the provided steam feed is a pure steam feed.

[0101] The system may further comprise one or more heat exchangers, wherein one or more heat exchangers are arranged such that one or more of the first feed gas comprising methanol and steam, said second feed gas, said first steam feed, said second steam feed, said first intermediate stream, said second intermediate stream, the air feed, or a combination thereof receive(s) heat energy from one or more fuel-side gas stream(s). The system may further comprise one or more heat exchangers, wherein one or more heat exchangers are arranged such that one or more of the first feed gas comprising methanol and steam, said second feed gas, said first steam feed, said second steam feed, said first intermediate stream, said second intermediate stream, the air feed, or a combination thereof receive(s) heat energy from an oxy-side exit gas such as an oxygen (O2) stream provided from the oxy-side of the SOEC.

[0102] A chemical plant for production of hydrogen

[0103] A chemical plant for production of methanol is provided, the plant comprising the system for production of hydrogen as disclosed herein, methanol synthesis unit, wherein the methanol synthesis unit is arranged to receive at least a portion of the fuel-side exit gas from the SOEC as a syngas stream; wherein the methanol synthesis unit is arranged to convert the syngas stream to a product methanol stream.

[0104] Specifically, the chemical plant may be arranged such that a portion of the product methanol stream is recycled to the elsewhere in the plant, suitably as a portion of the first feed gas.

[0105] The methanol synthesis unit may further be specified to comprise: a methanol synthesis loop; a methanol purification section; wherein the methanol synthesis loop is arranged to receive at least a portion of the syngas stream to provide a raw methanol stream; and wherein the methanol purification section is arranged to upgrade said raw methanol stream to a product methanol stream.

[0106] Specific embodiments

[0107] Figure 1 schematically shows a first method of operating a solid oxide electrolysis cell (SOEC) stack for producing hydrogen, said SOEC stack comprising at least one solid oxide electrolysis cell (SOEC) (20), said at least one SOEC comprising an electrolyte layer interposed between a fuel-side and an oxy-side (21), the method comprising : providing a first feed gas (1) comprising methanol and steam, supplying at least a portion of the first feed gas (1) comprising methanol and steam to the fuel-side of the at least one SOEC, withdrawing from said at least one SOEC (20), a first fuel-side exit gas (23).

[0108] The first feed gas (1) comprising methanol and steam may be a first purified feed gas comprising < 50 ppb of silicon. The method may further comprise that the first feed gas (1) is arranged to receive a first steam feed (3a). Hence, the first steam feed (3a) allows for additional steam to be added to the first feed (1) such that the feed is enriched in steam before being feed as a feed to the at least one SOEC (20). Suitably, the first fuel-side exit gas (23) may comprise hydrogen.

[0109] In addition to the first feed gas (1) comprising methanol and steam, the first feed gas may further comprise carbon dioxide. Additionally, or alternatively the first steam feed (3a) may comprise carbon dioxide. In this way, the first feed gas (1) arranged to be received by the SOEC may comprise steam and carbon dioxide. In this way, during normal operation the first fuel-side exit gas (23) comprises syngas i.e. a gas mixture containing H2and CO.

[0110] The method may further comprise that the oxy-side is arranged to receive an air feed (2) and provide an oxygen (O2) stream (22).

[0111] Figure 2 schematically shows a second method of operating a solid oxide electrolysis cell (SOEC) stack for producing hydrogen, said SOEC stack comprising at least one solid oxide electrolysis cell (SOEC) (20), said at least one SOEC comprising an electrolyte layer interposed between a fuel-side and an oxy-side (21), the method comprising: providing a first feed gas (1) comprising methanol and steam, supplying at least a portion of the first feed gas (1, 11a) comprising methanol and steam to the fuel-side of the at least one SOEC (20), or, converting at least a portion of the first feed gas (1) comprising methanol and steam to a first intermediate stream comprising hydrogen (11 b, 11c) and supplying at least a portion of the first intermediate stream to the fuel-side of the at least one SOEC (20); withdrawing from said at least one SOEC (20), a first fuel-side exit gas (23).

[0112] The step of supplying at least a portion of the first feed gas (1) comprising methanol and steam to the fuel-side of the at least one SOEC (20) may be achieved by feeding the first feed gas (1) comprising methanol and steam to a guard bed reactor (10) and providing from said guard bed reactor (10) a first purified feed (11a). The guard bed reactor (10) is arranged to provide a first purified feed (11a) when the guard bed reactor (10) comprises an impurity-binding material. The first purified feed (11a) may comprise < 50 ppb of silicon. In this way, supplying at least a portion of the first feed gas (1, 11a) comprising methanol and steam to the fuel-side of the at least one SOEC (20), may be via a guard bed reactor (10) supplying a first purified feed to the fuel-side of the at least one SOEC.

[0113] Alternatively the step of converting at least a portion of the first feed gas (1) comprising methanol and steam to a first intermediate stream comprising hydrogen (11 b, 11c) and supplying at least a portion of the first intermediate stream to the fuel-side of the at least one SOEC (20) may be achieved by feeding the first feed gas (1) comprising methanol and steam to a guard bed reactor (10) and providing from said guard bed reactor (10) a first intermediate stream comprising hydrogen (11 b, 11c). The guard bed reactor (10) is arranged to provide a first intermediate stream (11 b, 11c) when the guard bed reactor (10) comprises a catalyst active in the conversion of methanol to hydrogen. The first intermediate stream comprising hydrogen may comprise the same level of impurities as the first feed gas (1).

[0114] The first intermediate stream comprising hydrogen may be a first purified intermediate stream (11 c), wherein the first purified intermediate stream (11c) comprises a lower level of impurities compared to the first feed gas (1). The guard bed reactor (10) is arranged to provide a first purified intermediate stream when the guard bed reactor (10) comprises an impurity-binding material.

[0115] The method may further comprise that the first feed gas is arranged to receive a first steam feed (3a) and / or the guard bed reactor (10) is arranged to receive a second steam feed (3b). In this way, the method advantageously allows for steam to be added to the first feed such that the first purified feed (11a) or the first intermediate stream (lib, 11c) is enriched in steam before being feed as a feed to the at least one SOEC. In this way, the first steam feed (3a) and / or the second steam feed, preferably the second steam feed (3b) may be suitable for replacing at least a portion of said first feed gas comprising methanol such to provide a second feed gas enriched in steam.

[0116] Hence, the method may further comprise: replacing at least a portion of said first feed gas (1) comprising methanol and steam such to provide a second feed gas enriched in steam, supplying at least a portion of the second feed gas to the fuel-side of the at least one SOEC (20) or, supplying at least a portion of the second feed gas to a guard bed reactor (10) and withdrawing from said guard bed reactor (10) a second intermediate stream comprising steam, and further supplying at least a portion of said second intermediate stream to the fuel-side of the at least one SOEC (20); withdrawing from said at least one SOEC, a second fuel-side exit gas.

[0117] In addition to the first feed gas (1) comprising methanol and steam, the first feed gas (1) may further comprise carbon dioxide. Additionally, or alternatively the first steam feed (3a) and / or the second steam feed (3b) may comprise carbon dioxide. In this way, the first purified feed gas (11a) or the first intermediate stream (lib, 11c) arranged to be received by the SOEC may comprise steam and carbon dioxide such that the first fuel-side exit gas may comprises syngas i.e. a gas mixture containing H2and CO.

[0118] The method may further comprise that the oxy-side (21) is arranged to receive an air feed (2) and provide an oxygen (O2) stream (22). Figure 3 schematically shows a system (100) for production of hydrogen, the system comprising : a first feed gas stream (1) arranged to receive methanol from a methanol unit (5); optionally, comprising a guard bed reactor (10); a solid oxide electrolysis cell (SOEC) stack comprising at least one solid oxide electrolysis cell (SOEC) (20); one or more fuel-side exit gas stream(s) (23); wherein the SOEC stack is arranged to receive at least a portion of the first feed gas stream (1, 11a), optionally via a guard bed reactor (10) and provide one or more fuel-side exit gas stream(s) (23), or wherein a guard bed reactor (10) is arranged to receive at least a portion of the feed gas stream and convert at least a portion of the methanol to hydrogen so as to provide an intermediate stream (11 b, 11c) and the SOEC is arranged to receive at least a portion of the intermediate stream.

[0119] Figure 3 further schematically shows the method(s) of operating a solid oxide electrolysis cell (SOEC) stack for producing hydrogen (any of the methods as disclosed for Figure 1 or Figure 2), with the addition of the method further comprises supplying at least a portion of the methanol comprised in the first feed gas stream (1) from a methanol unit (5). Optionally, this may be achieved via a steam drum.

[0120] Specifically, the methanol unit (5) may be a methanol storage unit (not shown) such as a storage tank for storing methanol. Alternatively, the methanol unit may be a methanol synthesis unit (30) comprising e.g. a methanol synthesis loop (40) and a methanol purification section (50) - cf. Figures 4 and 5.

[0121] Figure 4 schematically shows a chemical plant (200) for production of methanol, the plant comprising the system (100) for production of hydrogen, a syngas stream (25), optionally arranged to receive one or more fuel-side exit gas stream(s) (23) from said system (100); a methanol synthesis unit (30), wherein the methanol synthesis unit (30) is arranged to receive the syngas stream (25) and provide a product methanol stream (32).

[0122] Figure 4 further shows that the first feed gas stream (1) arranged to receive methanol (la) from a methanol synthesis unit (30) may preferably be arranged to receive methanol from said chemical plant (200) such as from methanol synthesis unit (30), optionally via a steam drum. In this way, a portion (32) of the product methanol stream (32) is recycled to the elsewhere in the plant, suitably as a portion of the first feed gas.

[0123] Figure 4 further schematically shows a method of operating a chemical plant (200) for production of methanol, wherein the method comprises operating a solid oxide electrolysis cell (SOEC) stack for producing hydrogen such to provide at least one fuel-side exit gas (23) comprising hydrogen and providing at least a portion of said hydrogen to a syngas stream (25), feeding at least a portion of the syngas stream (25) to a methanol synthesis unit and providing from said methanol synthesis unit a product methanol stream.

[0124] Figure 5 schematically shows a chemical plant (200) with the further specification of the methanol synthesis unit (30) compared to Figure 4. The methanol synthesis unit (30) may comprise: a methanol synthesis loop (40); a methanol purification section (50); wherein the methanol synthesis loop is arranged to receive at least a portion of the syngas stream (25) to provide a raw methanol stream (41); and wherein the methanol purification section (50) is arranged to upgrade said raw methanol stream to a product methanol stream (32).

[0125] Further embodiments

[0126] In a specific aspect of the invention, a system (100) is provided for production of hydrogen, the system comprising : a first feed gas stream (1) arranged to receive methanol from a methanol unit (5); optionally, comprising a guard bed reactor (10); a solid oxide electrolysis cell (SOEC) stack comprising at least one solid oxide electrolysis cell (SOEC) (20); one or more fuel-side exit gas stream(s) (23); wherein the SOEC stack is arranged to receive at least a portion of the first feed gas stream (1, 11a), optionally via a guard bed reactor (10) and provide one or more fuel-side exit gas stream(s) or wherein a guard bed reactor (10) is arranged to receive at least a portion of the feed gas stream and convert at least a portion of the methanol to hydrogen so as to provide an intermediate stream (11 b, 11c) and the SOEC is arranged to receive at least a portion of the intermediate stream. In this system the methanol unit (5) may be a methanol storage unit, such as a storage tank for storing methanol.

[0127] Also, this system may further comprise that the first feed gas stream (1) is arranged to receive a first steam feed (3a) and / or a second steam feed (3b), wherein the guard bed reactor (10) is arranged to receive the second steam feed (3b).

[0128] Also, this system may further comprise a guard bed reactor (10), wherein the guard bed reactor (10) is arranged to receive the first feed gas stream (1), and optionally a second steam feed stream (3b) so as to provide a first purified feed gas (11a) or a first intermediate stream (lib), the first intermediate stream optionally as a first purified intermediate stream (He).

[0129] Also, this system may further comprise that the first steam feed (3a), the second steam feed (3b) or a combination thereof, is / are arranged to provide a second feed gas and the system further comprises means for closing off or partially closing off the first feed gas stream (1).

[0130] Also, this system may further comprise one or more heat exchangers, and wherein one or more heat exchangers are arranged such that one or more of the first feed gas (1, 11a) comprising methanol and steam, said second feed gas, said first steam feed (3a), said second steam feed (3b), said first intermediate stream (lib, 11c), said second intermediate stream, the air feed, or a combination thereof, receive(s) heat energy from one or more fuelside gas stream(s) (23).

[0131] In another specific aspect of the invention, a chemical plant (200) is provided for production of methanol, the plant comprising: the system (100) for production of hydrogen according to the above specific aspect of the invention, a methanol synthesis unit (30), wherein the methanol synthesis unit (30) is arranged to receive at least a portion of the fuel-side exit gas (23) from the SOEC (20) as a syngas stream (25); wherein the methanol synthesis unit (30) is arranged to convert the syngas stream (25) to a product methanol stream (32).

[0132] Also, this chemical plant may be arranged such that a portion of the product methanol stream is recycled to the elsewhere in the plant, suitably as a portion of the first feed gas.

[0133] Also, in this chemical plant the methanol synthesis unit (30) may comprise: a methanol synthesis loop (40); a methanol purification section (50); wherein the methanol synthesis loop (40) is arranged to receive at least a portion of the syngas stream (25) to provide a raw methanol stream (41); and wherein the methanol purification section (50) is arranged to upgrade said raw methanol stream (41) to a product methanol stream (32).

Claims

28CLAIMS1. Method of operating a solid oxide electrolysis cell (SOEC) stack for producing hydrogen, said SOEC stack comprising at least one solid oxide electrolysis cell (SOEC) (20), said at least one SOEC (20) comprising an electrolyte layer interposed between a fuel-side and an oxy-side (21), the method comprising : providing a first feed gas (1) comprising methanol and steam, supplying at least a portion of the first feed gas (1, 11a) comprising methanol and steam to the fuel-side of the at least one SOEC (20), or, converting at least a portion of the first feed gas (1) comprising methanol and steam to a first intermediate stream comprising hydrogen (lib, 11c), and supplying at least a portion of the first intermediate stream (lib, 11c) to the fuel-side of the at least one SOEC (20); withdrawing from said at least one SOEC (20), a first fuel-side exit gas (23).

2. The method according to claim 1, wherein the first feed gas (1) is provided by dosing the methanol such as liquid methanol in a steam drum, said steam drum being arranged to receive a water stream and provide the first feed gas (1) comprising methanol and steam.

3. The method according to any one of the preceding claims, wherein the first feed gas (1, 11a) is supplied as a recycle stream from a methanol synthesis unit (30), and / or supplied from a methanol storage unit (5a).

4. The method according to any one of the preceding claims, wherein the first feed gas (1) is arranged to receive a first steam feed (3a).

5. The method according to any one of the preceding claims, wherein the method further comprises supplying at least a portion of said first feed gas (1) to a guard bed reactor (10) and withdrawing from said guard bed reactor (10) i) a first purified feed gas (11a) comprising methanol or ii) the first intermediate stream comprising hydrogen (lib, 11c), the first intermediate stream optionally as a first purified intermediate stream comprising hydrogen (He).

6. The method according to claim 5, wherein the guard bed reactor (10) is arranged to receive a second steam feed (3b).

7. The method according to any one of claims 5-6, wherein the guard bed reactor (10) comprises a catalyst active in conversion of methanol to hydrogen; such as through reacting methanol and steam to carbon dioxide and hydrogen.

8. The method according to any one of claims 5-7, wherein the guard bed reactor (10) comprises a catalyst such as a catalyst active in the conversion of methanol to hydrogen, wherein said catalyst is a catalyst comprising nickel (Ni), a catalyst comprising iron (Fe), or a combination thereof.

9. The method according to any one of claims 5-8, wherein the guard bed reactor (10) comprises a bed comprising said catalyst active in the conversion of methanol to hydrogen, in which said catalyst comprises nickel and an active metal (Me) oxide; wherein the active metal (Me) is selected from the group consisting of alkaline earth metals including Ca, Mg, Sr; transition metals including Zr; rare earth metals including La and Ce; or mixtures thereof.

10. The method according to any one of claims 5-9, wherein the guard bed reactor (10) comprises an impurity-binding material, said impurity-binding material being any of at least a silicon-binding material, a sulphur-binding material, or a combination thereof; wherein the impurity-binding material comprises a metal (Me) oxide, in which the metal (Me) is selected from the group consisting of alkaline earth metals including Ca, Mg, Sr; transition metals including Zr; rare earth metals including La and Ce; or mixtures thereof.

11. The method according to any one of claims 5-10, in which said catalyst active in the conversion of methanol to hydrogen and the impurity-binding material, are provided as separate and distinct materials, wherein the guard bed reactor comprises:- a bed comprising both: said catalyst active in the conversion of methanol to hydrogen, and said impurity-binding material, suitably as silicon-binding material; and / or- a bed comprising said catalyst active in the conversion of methanol to hydrogen; and a separate bed comprising said impurity-binding material, suitably as a silicon-binding material.

12. The method according to any one of the preceding claims, wherein the method comprises transient operation, and said transient operation is selected from any of start-up operation, hot-idle operation and / or shut-down operation.

13. The method according to any one of the preceding claims, wherein the method comprises transient operation, and the transient operation further comprises operating the SOEC stack under open-circuit voltage (OCV).

14. The method according to any one of the preceding claims, wherein the method comprises heating said first feed gas comprising methanol to a temperature of 400-900°C, such as 450-850°C or 500-800°C, optionally at the inlet of the SOEC such as at the inlet of the SOEC stack or at the inlet of the guard bed reactor.

15. The method according to any one of claims 1-14, wherein the first fuel-side exit gas (23) comprises hydrogen.

16. The method according to claim 15, wherein the first feed gas (1), the first steam feed (3a) and / or the second steam feed (3b) further comprises carbon dioxide and the first fuelside exit gas (23) comprises syngas i.e. a gas mixture containing hydrogen and carbon monoxide.

17. The method according to any one of the preceding claims, wherein the method further comprises: replacing at least a portion of said first feed gas (1) comprising methanol and steam such to provide a second feed gas enriched in steam, supplying at least a portion of the second feed gas to the fuel-side of the at least one SOEC or, supplying at least a portion of the second feed gas to a guard bed reactor (10) and withdrawing from said guard bed reactor (10) a second intermediate stream comprising steam, and further supplying at least a portion of said second intermediate stream to the fuel-side of the at least one SOEC (20); withdrawing from said at least one SOEC, a second fuel-side exit gas.

18. The method according to claim 17, wherein the method further comprises withdrawing a portion of said second fuel-side exit gas, suitably the entire portion thereof, as a separate hydrogen stream, suitably as a hydrogen product stream.

19. The method according to any one of claims 15-18, wherein the method further comprises continuously applying a load, thus an electricity current, to the SOEC stack.

20. The method according to any one of claims 17-19, wherein the method further comprises gradually replacing said first feed gas (1) comprising methanol and steam by firstcombining a first steam feed (3a) and / or second steam feed (3b) with the first feed gas (1), and later interrupting the flow of the first feed gas, such as by interrupting the supply of a methanol recycle stream (31) to provide a second feed gas enriched in steam.

21. The method according to any one of claims 17-20, wherein the method comprises heating said first feed gas comprising methanol and steam to a temperature of 400-900°C, such as 450-850°C or 500-800°C, and wherein at least a portion of the first feed gas (1) is replaced by the first steam feed (3a) and / or second steam feed (3b) so as to provide the second feed gas upon approaching or reaching normal operation temperature of the SOEC stack, said normal operation temperature being 600-1000°C, suitably 650-900°C.

22. The method according to any one of claims 17-21, wherein the method further comprises continuously heating said second feed gas, to a temperature of 650-900°C, preferably at the inlet of the guard bed reactor (10).

23. The method according to any one of the preceding claims, wherein the method further comprises the heating of any of said first feed gas (1, 11a) comprising methanol and steam, said second feed gas, said first steam feed (3a), said second steam feed (3b), said first intermediate stream (lib, 11c), said second intermediate stream, the air feed, or a combination thereof, such as said method comprises heat exchange with said first or second fuel-side exit gas (23).

24. The method according to any one of claims 9-23, wherein the fuel side of said SOEC stack comprises a nickel catalyst active in the conversion of methanol to hydrogen.

25. The method according to claim 24, wherein the first feed gas or the hydrogen in the first intermediate stream keeps the nickel catalyst on the SOEC fuel side in a reduced state.

26. The method according to any one of the preceding claims, wherein the first intermediate stream further comprises steam.

27. The method according to any one of the preceding claims, wherein the first intermediate stream is substantially free of methane.

28. The method according to any one of the preceding claims, wherein the first feed gas is substantially free of methane.3229. The method according to any one of the preceding claims, wherein the first feed gas has a proportion of methanol to steam of below 10vol% or less, preferably 2vol% or less methanol to steam.

30. The method according to any one of the preceding claims, wherein the first intermediate stream comprises 4 vol% hydrogen or less.

31. A system (100) for production of hydrogen, the system comprising : a first feed gas stream (1) arranged to receive methanol from a methanol unit (5); optionally, comprising a guard bed reactor (10); a solid oxide electrolysis cell (SOEC) stack comprising at least one solid oxide electrolysis cell (SOEC) (20); one or more fuel-side exit gas stream(s) (23); wherein the SOEC stack is arranged to receive at least a portion of the first feed gas stream (1, 11a), optionally via a guard bed reactor (10) and provide one or more fuel-side exit gas stream(s) or wherein a guard bed reactor (10) is arranged to receive at least a portion of the feed gas stream and convert at least a portion of the methanol to hydrogen so as to provide an intermediate stream (11 b, 11c) and the SOEC is arranged to receive at least a portion of the intermediate stream.

Images