WO2017167605A1

WO2017167605A1 - Device and method for producing a product gas, in particular a synthesis gas

Info

Publication number: WO2017167605A1
Application number: PCT/EP2017/056671
Authority: WO
Inventors: Manfred Baldauf; Marc Hanebuth; Katharina Stark
Original assignee: Siemens Aktiengesellschaft
Priority date: 2016-03-31
Filing date: 2017-03-21
Publication date: 2017-10-05

Abstract

The invention relates to a device and a method for producing a product gas, in particular a synthesis gas, wherein the following are provided: a supply line (2a, 2b) for supplying a reagent gas into an electrochemical cell (10) of an electrolyser (1), wherein an addition of the reagent gas into a first electrode chamber (12) that is spatially separated from a second electrode chamber (14) by a membrane (13) can be carried out; a first discharge line (21a, 21b) for discharging the product gas from the first electrode chamber (12); a second discharge line (20) for discharging an additional product gas from the second electrode chamber (14); and a return line (30), leading out of the first discharge line (21a, 21b), for feeding back a portion of the product gas into the supply line (2a, 2b).

Description

description

Apparatus and method for producing a product gas, in particular synthesis gas

The importance of so-called renewable energy is becoming increasingly important, especially in Germany. Accordingly ^¬ speaking is currently being sought increasingly looking for ways to use temporarily existing income stream to produce Wertpro--products electrochemically. An approach for this is, for example, with the help of a dynamically operable

Electrolysers convert carbon dioxide CO ₂ into carbon monoxide CO and oxygen O ₂ . Electrolyzers, in particular CO 2 ^_ electrolysers, have so far only been the subject of basic research in the field of the materials used in each case. According to an internal prior art of the Applicant, a first Labormus ^¬ ter is set up currently, during its operation, first excess is worked with high CO2 and obtained the product gas with CO2 ver ^¬ thinned. This gas would have to be treated before further use by means of gas purification process to remove interfering CO2. Concepts for the targeted production ei ^¬ nes defined synthesis gas with a low C02 content by a suitable operating concept of an electrolysis stack are not known.

One design is a so-called low-temperature

Electrolyzer with aqueous electrolyte, in which the educt gas (CO2) is added by means of a gas diffusion electrode (GDE).

In a conventional electrolyzer, the reactant gas (CO2) flows through the electrolyzer only once, so that, depending on the CO 2 excess, a fixed CO: H 2: CO 2 ratio results, but in a large number of cases too much CO 2 and too little H 2 for contains use in downstream syntheses. Conventionally, mixtures of, for example CO: H-2 '· CC> 2 ~ 1, 5: 3: 0, 5 current knowledge, not him ^¬ reichbar. When using a conventional CO2

Electrolysers are variable parameters that primarily determine the product gas composition, the current density or voltage that corresponds to the applied load, and the CO2

Excess. Other variable conditions include the choice of egg ^¬ umpumprate the electrolyte, and pressure and temperature.

Conventionally, only a synthesis gas is formed, which contains too much CO2 and too little H2.

It is an object of the invention by means of electrolysis, insbesonde ^¬ re C02 electrolysis, a product gas, in particular, produce synthesis gas which is to be directly used in particular for downstream chemical syntheses, without numerous testing precleaning. It is a high proportion of unconverted feed gas, in particular a C02 ^~ content, be avoided in the product gas. Likewise, a proportion of a second electrolysis gas arising as a function of the electrolyte used should also be selectively adjustable in the product gas. It searches for the operation of an electrolyzer with a ratio in the product gas from a value of product gas for the second electrolysis gas for unconverted feed gas ge ^¬ aims is adjustable for conditions required a concept. In particular, a CO 2 electrolyzer is sought, with which the CO 2 content of the synthesis gas is kept low and a CO: H ² ratio can be set to a required value.

Feedstock gas is in particular supplied gas.

Product gas is especially gas discharged.

Product product gas is in particular a desired product gas for a preferred further use.

The object is achieved by a device according to the main claim and a method according to the independent claim.

According to a first aspect is an apparatus for the manufacture ^¬ development of a product gas, particularly a synthesis gas proposed, comprising a supply line for supplying a reactant gas in an electrochemical cell of an electrolyzer, wherein a

Metering of the reactant gas in a first by means of a membrane spatially separated from a second electrode space first

Electrode space is executable;

a first discharge line for removing the product gas from the first electrode space;

a second discharge line for removing an additional ^{product ¬} gases from the second electrode space;

a recirculation line led out of the first discharge line for returning a portion of the product gas into the supply line.

According to a second aspect, a method for producing a product gas, in particular a synthesis gas, is proposed with the following steps:

executed by means of a feed line supplying a feed gas in an electrochemical cell of an electrolyzer ^¬ Seurs, wherein a metered addition of the reactant gas can be performed in a spatially separated by a membrane from a second electrode space first electrode chamber;

removing the product gas from the first electrode space by means of a first discharge line;

discharging an additional product gas from the second electrode space by means of a second discharge line;

recycling a portion of the product gas into the feed line by means of a return line led out of the first discharge line.

According to the invention, it is proposed to recycle a significant part of the product gas into the feed stream for the educt gas of the electrolyzer and to introduce a gas cycle loop in this way. The recirculated gas is expediently metered in via a gas diffusion electrode (GDE).

Further advantageous embodiments are claimed with the subclaims. According to an advantageous embodiment, the electrolyzer can be a low-temperature electrolyzer, which is to be understood here as an electrolyzer operated at less than 100 ° C., the first electrode space being a cathode space, the second electrode space being an anode space, the membrane being ion space. be conductive, in particular cation-conducting, and a plurality of electrochemical cells may be fluidly connected in parallel to each other, wherein the cells are electrically connected in series with each other.

According to a further advantageous embodiment, the electrolyzer may be an aqueous electrolyte using CO ₂ - electrolyzer for converting carbon dioxide CO ₂ as educt gas in carbon monoxide CO as desired product gas and Sau ^¬ oxygen O ₂ as an additional product gas, the product gas in particular in addition to the carbon monoxide CO as value ^¬ product gas, hydrogen H ₂ as the second electrolysis gas and unconverted educt gas carbon dioxide CO ₂ may have.

According to a further advantageous embodiment, the electrolyzer may have a regulating device for adjusting the recirculated volume flow and thus a recycling rate, wherein the regulating device comprises a flow device arranged in the return line, in particular blower and / or a valve and / or a throttle flap, and / or a static or dynamic flow divider controls.

According to a further advantageous embodiment, the electrolyzer may have the regulating device for setting an electrical current density, wherein the regulating device regulates the current.

According to a further advantageous embodiment of the electrolyzer, the control device for adjusting the Have metered addition of Edukgases per period of time, the control device controls the Zudosierrate.

According to a further advantageous embodiment, the control device can regulate such that in the product gas a ratio of desired product gas to second electrolysis gas to unconverted feed gas, in particular of CO to H ₂ to CO ₂ , is selectively adjustable in the first discharge line after the branching of the return line ,

According to a further advantageous embodiment, ratios of CO: H2: CO2 ~ 1, 5: 3: 0, 5 and in particular CO: H2 ~

Ratios of 1: 1.5 to 1: 3 be adjustable.

According to a further advantageous embodiment, ratios of CO: CO ₂ greater than 1/5 with simultaneous H ₂ : CO

Be adjustable ratios of greater than 2.

The invention will be described in more detail by means of exemplary embodiments in conjunction with the figures. Show it:

Figure 1 is a representation of the prior art;

Figure 2 shows an embodiment of an inventive

Contraption;

Figure 3 shows an embodiment of an inventive

Procedure.

FIG. 1 shows a representation of the prior art. At the

Operation of a low-temperature electrolyzer with aqueous electrolyte, in which the educt gas (CO2) is metered by means of a gas diffusion electrode ^¬ (GDE), the CO2 is supplied to the electrochemical cell and carbon monoxide

CO reduced. If a current flow to the respective driven stöchiomet corresponding amount of CO2 available (λ = 1), it depends on ^¬ due to diffusion limitations at the cathode in addition to the formation of CO to the development of hydrogen H2. outward background is that the water of the electrolyte can also be electrolyzed. The result is gas, which can be referred to here as second electrolysis gas, here hydrogen. Conventionally, at λ = 1, a so-called Faraday efficiency is about 50% for CO and 50% for ^ formation. In

Consequence will be implemented only 50% of the CO2 offered electrochemical ^¬ mixed, so that a product gas with a combination ^¬ reduction of CO: H2: C02 = l: 1: 1 arises, all angege ^¬ surrounded ratios are based on quantities here.

If more CO2 than stoichiometrically necessary is offered, the diffusion limitation of the CO2 transport goes to the active ones

Centers of the electrode surface back and thus less H2 is formed. The so-called Faraday efficiency FE of CO formation increases. There are up to 90% with respect to CO FE mög ^¬ Lich, that is to say the products are then in a ratio of CO: H2 = 90: 10 is formed. However, the CO / H2 mixture is diluted by the excess CO2, so that typically

Product mixtures with compositions in the range

CO: H2: CO2 = 9: 1: 15 to 20 arise. The desired synthesis gas thus arises with too high a CO 2 content. If, on the other hand, ^less CO2 is offered as stoichiometrically necessary, the Faraday efficiency FE for CO decreases in favor of the ^ formation and, for example, synthesis gases are formed at λ = 0.5

CO: H2 = 20: 80, which are in turn diluted with CO2 because we ^¬ gen diffusion limitation unreacted CO2 is the Pro ^¬ duktgas. That is, the gas composition at λ = 0.5 is approximately CO: H ₂ : C0 ₂ = 1: 4: 1, 2 (20:80:25). The illustration according to FIG. 1 shows Faraday efficiencies FE relative to the products hydrogen and carbon monoxide and the achievable degrees of conversion of carbon dioxide as a function of the excess of carbon dioxide offered. When λ = 1 ent ^¬ the molar flow rate of CO2 OFFERED speaks exactly to the electrolysis current. For larger values there is an excess of CO2 · Figure 2 shows an embodiment of an inventive

Contraption. FIG. 2 shows an arrangement according to the invention of a CO 2 electrolyzer. By way of example, only one electrochemical cell is shown, wherein in reality a plurality of cells are arranged in the form of a cell stack. Not shown are the anode and the aqueous electrolyte ^¬ lyt with the corresponding circuits or

Gas / liquid separators. Reference numeral 1 denotes the inventive arrangement of a C02 ^_ electrolyzer for the production of a synthesis ^¬ gas. 2a and 2b indicate a reactant feed, wherein 2a represents the access of CO2 and 2b additionally recycled

Product contains. Reference numeral 10 denotes an electrochemical cell of the C02 ^_ electrolyzer, which is exemplified for ei ^¬ NEN entire cell stack. Reference numeral 11 denotes a gas diffusion electrode (GDE). Reference numeral 12 denotes a cathode compartment. Reference numeral 13 denotes a membrane which may be provided, for example, cation-conductive to separate gas spaces. Bezugszei ^¬ chen 14 represents an anode chamber, wherein in Figure 2, the anode is not shown. Reference numeral 20 denotes the anode gas produced, which is oxygen here. ^Reference symbols 21a and 21b denote the produced cathode gas as a product of value. It contains in addition to CO and H2 as partly unreacted CO2 · reference numeral 30 denotes a ^¬ he invention proper recirculation, in an inventive Ge ^¬ blower is arranged 31st It can also be inventively a re ^¬ gelbares valve and / or a throttle and / or a static or dynamic flow divider can be installed as control devices in the return line.

A control device 40 regulates such that in the product gas, a ratio of desired product gas to second electrolysis gas to unconverted educt gas, in particular of CO to H ₂ to CO ₂ , 30 is selectively adjustable in the first discharge line 21b after the diversion of the return line. According to the invention, the synthesis gas is partially ^recirculated , so that a further portion of the ^CO.sub.2 still present in the synthesis gas is present in the second and optionally further

Runs is converted to CO and so the CO: CO 2 ratio is increased. Since, however, with constant electric current density for the electrolysis operation, the CO2

Excess in the cathode compartment of the electrolyzer goes back, the Faraday efficiency is also shifted in favor of ^ formation and thus normalized to the newly formed CO amount produces a higher H2 ~ amount. This also shifts the CO: ^ ratio in the product gas to higher ^ contents.

On the other hand, the syngas must not be excessively recycled in the electrolysis system either. First, the H2 content would steadily increase because of the continuous depletion of CO2. Too high H2 ~ contents are just as meaningless, since chemical syntheses mean a CO: ^ ratio of 1: 1.5 to 1: 3 need. Second, the amount of gas in the system increases as a result of ^ production, which would lead to an increase in pressure.

The aim of the proposed concept is to remove just enough product gas and introduce the right amount of additional CO2 so that a desired ratio of CO: H2: CO2 is achieved in the product gas by having exactly the composition required for the use of the synthesis gas ,

Both the injection of CO2 and the discharge of product gas can take place continuously or batchwise. Likewise, a dynamic operation is executable.

According to the invention has the following advantageous Ausgestal ^¬ obligations:

1. An aqueous electrolyte C02 electrolyzer is operated to produce a mixture of H2 and CO. The produced gas should have the lowest possible amount of CO2 and a certain ratio of H2: CO, for example, at least 1.5: 1, more preferably more than 2: 1, but not more than 3: 1. 2. To achieve a desired product composition, a recycle through which a significant portion of the product gas is directed into the reactant gas is provided. The return contains a controllable blower and / or a valve or a throttle valve and / or a static or dynamic flow divider, with which the volume flow of this return or the recycling rate can be varied.

3. In addition to the recycling rate, there are the control parameters

Current density, voltage and C02 ^_ dosing.

With these three control parameters in addition to a desired product gas composition, a dynamic operation of the electrolyzer can be realized.

According to the invention a new operating and Steuerungskon ^¬ concept for a C02 ^_ electrolyzer is proposed, in which a required synthesis gas ^¬ composition can be adjusted by means of gas return, by the fraction of the discharged product gas and the amount of the newly supplied CO2 depending on the use of the synthesis gas.

According to the inventive concept are compared to

The prior art has provided additional control parameters that can be used to set variable product gas compositions that are conventionally unachievable and that are distinguished by meeting the specification for a synthesis gas for delivery to chemical syntheses. These are in particular CO: CO 2 ^_ ratios above 1.5 with simultaneous H2: CO ratio of 2 or more.

According to the invention, a control concept is proposed in which by means of selection of the control parameters mass or volume menfluss in the recycle stream, recycle rate as a proportion of the out ^¬ infiltrated fraction, and mass or volumetric flow of the re-dosed CO2 as a function of the current density which corresponds to the electrical ^¬ rule load product concentration on, a defined CO: H2: C02 Ratio can be adjusted. Thus it can be dispensed with aufwän ^¬ digestion treatment of the gas stream after the C02-electrolysis with the aid of the proposed concept, since the product gas can be used directly in a nachfol ^¬ constricting synthesis.

Fig. 3 shows an embodiment of a method according to the invention. The method is used for producing a Pro ^¬ duktgases, particularly a synthesis gas, comprising the following steps. (S1) supplying a starting gas into an electrochemical cell (10) of an electrolyzer (1) by means of a supply line (2), wherein a metered addition of the educt gas into a spatially separated from a second electrode space (14) by means of a membrane (13) first electrode space (12) is executable. (S2) removing the product gas from the first electrode space (12) by means of a first discharge line (21); (S2) removing a supplementary product gas from the second electrode space (14) by means of a second discharge line (20);

(S3) recycling a portion of the product gas into the supply line (2) by means of a return line (30) made from the first discharge line (21).

Claims

claims

1. Apparatus for producing a product gas, in particular a synthesis gas, comprising

a supply line (2) for supplying a reactant gas into an electrochemical cell (10) of an electrolyzer (1), where ^¬ at a metered addition of the educt gas into a by means of a membrane (13) from a second electrode space (14) spatially separated first electrode space (12 ) is executable;

a first discharge line (21) for removing the product gas from the first electrode space (12);

a second discharge line (20) for discharging an additional product gas from the second electrode space (14);

a recirculation line (30) led out of the first discharge line (21) for returning a portion of the product gas into the supply line (2).

2. Device according to claim 1,

characterized in that

the metered addition can be carried out through a gas diffusion ^electrode arranged in the cell (10).

3. Apparatus according to claim 1 or 2,

characterized in that

the electrolyser (1) is a low-temperature electrolyzer, the first electrode space (12) is a cathode space, the second electrode space (14) is an anode space, the membrane (13) is ion-conducting, in particular cation-conducting, and a plurality of electrochemical cells (10) fluidically connected in parallel to each other.

4. Apparatus according to claim 1, 2 or 3,

characterized in that

the electrolyser (1) is a C0 ₂ electrolyzer using an aqueous electrolyte for converting carbon dioxide CO ₂ as educt gas into carbon monoxide CO as desired product gas and oxygen O ₂ as additional product gas, the product gas in particular in addition to the carbon monoxide CO being used as value product gas, hydrogen H ₂ as a second electrolysis gas and unconverted educt gas carbon dioxide CO ₂ having.

5. Apparatus according to claim 1, 2, 3 or 4,

characterized in that

the electrolyser (1) comprises a control device (40) for adjusting the recirculated gas flow and therefore a recycling rate, wherein the control means into the return line (30) tung arranged Strömungseinrich-, in particular blower (31) and / or a valve for STEU ^¬ augmentation the ratio of the mass flows in the return line (30) and the product ^discharge line (21b).

6. Apparatus according to claim 5,

characterized in that

the electrolyzer (1) has the regulating device (40) for setting an electrical current density, wherein the regulating device controls the current density.

7. Device according to claim 5 or 6,

characterized in that

the electrolyzer (1) has the regulating device (40) for adjusting the metered addition of the educt gas per period of time, wherein the regulating device controls the metering rate.

8. Device according to one of the preceding claims 5, 6 or 7,

characterized in that

, the control means (40) controls such that in the product ^¬ gas has a ratio of a value product gas to second electrolysis ^¬ gas to unconverted feed gas, in particular of CO to H ₂ to CO _2, in the first discharge line (21b) after the Ab ^¬ branching Return line (30) is specifically adjustable.

9. Device according to claim 8, characterized in that

In the product gas ratios of CO: H2: C02 ~ l, 5: 3: 0, 5 and ^{¬ in} particular CO: ^ ratios of 1: 1.5 to 1: 3 are adjustable.

10. Device according to claim 8,

characterized in that

in the product gas ratios of CO: C02 1.5 greater at the same time ^¬ H2: CO ratios can be set greater. 2

11. A method for producing a product gas, insbesonde re ^¬ a synthesis gas, comprising the steps of:

(51) supplying a educt gas by means of a feed line (2) into an electrochemical cell (10) of an electrolyzer (1), wherein a metered addition of the educt gas into a spatially separated from a second electrode space (14) by means of a membrane (13) first electrode space (12) is executable;

(52) removing the product gas from the first electrode space (12) by means of a first discharge line (21);

(52) by means of a second discharge conduit executed (20) discharging an additional product gas from the second Elect ^¬ clear space (14);

(53) recycling a portion of the product gas into the supply line (2) by means of a return line (30) made from the first discharge line (21).

12. The method according to claim 11,

characterized in that

the metered addition is carried out by a gas diffusion ^electrode arranged in the cell (10).

13. The method according to claim 11 or 12,

characterized in that

the electrolyser (1) is a low-temperature electrolyzer, the first electrode space (12) is a cathode space, the second electrode space (14) is an anode space, the membrane (13) is ion-conducting, in particular cation-conducting, and a plurality of electrochemical cells (10) are fluidly connected in parallel to each other.

14. The method according to claim 11, 12 or 13,

characterized in that

the electrolyzer (1) is an aqueous electrolyte using C0 ₂ electrolyser for the conversion of carbon dioxide CO ₂ as educt gas in carbon monoxide CO as desired product gas and oxygen O ₂ as an additional product gas, the product gas in particular in addition to the carbon monoxide CO as value ^¬ product gas, hydrogen H ₂ as the second electrolysis gas and unconverted educt gas carbon dioxide CO ₂ has.

15. The method according to claim 11, 12, 13 or 14,

characterized in that

the electrolyser (1) has a regulating device (40) for setting the recirculated volume flow and thus a recycling rate, wherein the regulating device comprises a flow device arranged in the recirculation line (30), in particular a fan (31) and / or a valve and / or a throttle flap and / or a static or dynamic flow divider for controlling the ratio of the mass flows in the recirculation line (30) and the product discharge line (21b).

16. The method according to claim 15,

characterized in that

17. The method according to claim 15 or 16,

characterized in that

has for the input position, the metered addition of the reactant gas per time duration of the electrolyzer (1) the control means (40), wherein the control means the Zudosierrate re ^¬ gel.

18. The method according to any one of the preceding claims 15, 16 or 17,

characterized in that

, the control means (40) controls such that the in the product gas, a ratio of a value product gas to second electrolysis ^¬ gas to unconverted feed gas, in particular of CO to H ₂ to CO _2, in the first discharge line (21b) after the Ab ^¬ branching Return line (30) is specifically adjustable.

19. The method according to claim 18,

characterized in that

Ratios of CO: H2: C02 ~ l, 5: 3: 0, 5 and in particular CO: H2 ^~ ratios of 1: 1.5 to 1: 3 are adjustable.

20. The method according to claim 18 or 19,

characterized in that

Ratios of CO: C02 greater than 1.5 with simultaneous H ₂ : CO ratios of greater than 2 are adjustable.