Purification of carbon monoxide by cryogenic distillation

Abstract

A method for separating a stream (1) containing at least 97 mol% carbon monoxide, the stream (1) containing at least one lighter compound and at least one heavier compound, wherein the stream is separated in columns (K1) and (K2), one of which is a denitrification column and the other is a column for purification in argon to form a carbon monoxide-rich stream (15).

Description

[Technical Field]

[0001] This invention relates to a method and apparatus for purifying carbon monoxide. In particular, the purified product must contain between 99 mol% and 99.999 mol%, and in fact even up to 99.9999 mol% of carbon monoxide. [Previous Technology]

[0002] WO18111719 describes the purification of carbon monoxide to produce pure carbon monoxide containing 0.1 ppm or less of carbon dioxide and hydrogen.

[0003] The electronics industry requires products containing between 99 mol% and 99.999 mol%, actually even up to 99.9999 mol% of carbon monoxide. This product must contain very little nitrogen (less than 2 ppm, actually even less than 0.5 ppm) and / or very little argon (less than 2 ppm, actually even less than 0.5 ppm).

[0004] Depending on the circumstances, the mixture to be purified contains less than 99% carbon monoxide or less than 99.999% carbon monoxide or less than 99.9999% carbon monoxide.

[0005] It may also contain at least one of the following elements: nitrogen, argon, hydrogen, methane or oxygen.

[0006] There are many patents on CO purification, but they are usually based on the separation of one of the following mixtures: CO / H2, CO / CH4 or CO / N2.

[0007] There has been no previous research on the continuous separation of nitrogen and argon, or the separation of CO / Ar. On the other hand, the literature describes:

[0008] - For Ar-CO equilibrium:

[0009] Duncan AG and Staveley LAK, 1966, Trans. Faraday Soc., 62, 3, pp. 548 - 552, Christiansen LJ and Fredenslund A., 1973, Cryogenics, p. 405

[0010] - For N2-CO equilibrium:

[0011] Sprow FB and Prausnitz JM, 1966, AICh.EJ, 12, 4, 780

[0012] Hirata M., Ohe S. and Nagahama K., 1975, Computer Aided Data Book of Vapor-Liquid Equilibrium, Tokyo, Kodanska Ltd., Elsevier [Summary of the Invention]

[0013] Like methane, argon has a higher liquefaction temperature than CO (because it is heavier), but CO / CH4 separation cannot effectively remove argon, which is lighter than methane.

[0014] The separation of CO / Ar binary mixtures is as complex as that of CO / N2 binary mixtures because they consist of molecules with very similar physical properties. In this specific case, the distances between CO and N2 are almost equal: • Boiling point of N2 at Patm = -195.8°C • Boiling point of CO at Patm = -191.5°C • Boiling point of Ar at Patm = -185.85°C

[0015] Therefore, only the "low-temperature distillation column" technology can achieve very low levels of nitrogen and argon impurities in CO at an acceptable cost. On the other hand, there is little information about CO / Ar and CO / N2 binary mixtures at these purity levels, which complicates the size design of such distillation columns.

[0016] One proposed solution is a double distillation column, which consists of: • a first distillation column that removes nitrogen and all other components lighter than CO (if present); • a second distillation column that removes argon and all other components heavier than CO (if present).

[0017] Alternatively, the heavier components can be removed first in the first column, followed by the removal of the lighter components.

[0018] In both cases, the two columns are preferably assembled one on top of the other and thermally connected by a heat exchanger. This exchanger serves as the reboiler for the upper column and the condenser for the lower column. The first column is also equipped with a reboiler (“main reboiler”) at the bottom, thereby generating a liquid / vapor reflux sufficient to distill impurities to the desired purity level. The second column is equipped with a top condenser located at its top to condense this reflux.

[0019] The column can be placed in any desired order without discrimination: purifying nitrogen, then purifying argon, and vice versa. In a conventional distillation column with a top evaporator, the light component (in this case, CO) can be separated from the heavy component (in this case, argon). Without a bottom reboiler, the feed stream entering the bottom contaminates the liquid removed from the bottom, contaminating it and reducing its purity. Therefore, it is not possible to successfully extract all CO from the feed stream into the top gas of the column. This phenomenon is exacerbated when the two components have similar thermodynamic properties, as is the case here.

[0020] When a certain amount of pure carbon monoxide needs to be produced, a large amount of vapor flow needs to be circulated in the tower, which will also cause a large amount of liquid to fall.

[0021] In order to obtain a large steam flow rate, a bottom reboiler is added at the bottom of the column to increase the steam flow rate without increasing the feed flow rate.

[0022] This increases the amount of vapor circulating in the column and allows for the recycling of most of the liquid in the column. The amount of liquid withdrawn from the bottom of the column can be very low.

[0023] The method is improved by adding a theoretical plate between the reboiler and the feed flow arrival point and by drawing liquid from the reboiler instead of from the bottom of the column.

[0024] Optional characteristics (some of which can be combined): • The developed solution has a production mole flow rate / boiling mole flow rate ratio between 8% and 25%. • The production mole flow rate is the flow rate of carbon monoxide purified in argon and nitrogen, and the boiling mole flow rate is the amount of gas produced by the bottom reboiler of the lowest column of the dual-column system. • The total height of the dual columns is less than 30 m. • The distillation columns operate at pressures below 5 bar, thus avoiding the use of compressors: the mixture at the equipment inlet is depressurized directly from the pressurized storage tank. • The fluid purified in the first column and fed into the second column is extracted in the gas phase. Extraction in the liquid phase may cause operational instability due to the small difference in operating pressure between the two columns. • The main reboiler is located outside the columns, thus limiting the total height of the dual distillation columns. • The main reboiler includes a heat exchanger (e.g., a submerged tube) to allow at least partial cooling and liquefaction of CO at the equipment inlet and to reduce the power of the main exchanger of the reboiler. • The main reboiler may include one or more electric heaters as a heat source. • The top condenser supplies liquid nitrogen. • There is one or more adsorbers in front of the twin towers to remove impurities such as CO2 or water.

[0025] For example, a distillation column can be developed to achieve such purity under the following conditions: • production flow rate to boiling flow rate ratio = 12.5% ​​• distillation column height 26 m • yield of 75% or higher

[0026] In one example: • Impurities such as hydrogen, oxygen, and methane can also be removed from CO. • It is decided to place the denitrification tower below the deargon removal tower. • The main reboiler is offset. • The main reboiler consists of an exchanger (immersion tube) to cool and liquefy the CO upstream of the denitrification tower and electric heater. • Liquid nitrogen is fed into the top condenser. • The top condenser and the inter-tower condenser are plate exchangers.

[0027] Advantages of the present invention: • The present invention achieves CO purity that cannot be achieved by simple denitrification and / or demethanization towers, which are two types of CO purification towers. • Using a double distillation tower, with the two sections stacked on top of each other, eliminates the need for machinery (pumps), thereby improving plant reliability. • The recommended flow ratio stems from the optimization of operating conditions. This is because the conventional equation of state for CO / N2 / Ar mixtures cannot yield accurate results for the desired purity level. Developing a specific equation of state for this mixture allows for precise determination of the distillation tower dimensions, thereby optimizing operating conditions: temperature, pressure, reflux flow rate, utility consumption, tower height, and distillation tower output. Reflux flow rate and utility consumption are directly related. By limiting the reflux to a strictly necessary flow rate, less liquid nitrogen and less electricity are consumed. • Furthermore, by limiting the height of the distillation tower (by reducing the theoretical or actual number of trays), the complexity of equipment transportation and mechanical manufacturing is simplified, thereby reducing equipment costs.

[0028] According to the present invention, a method is provided for purifying a first feed stream containing at least 97 mol% carbon monoxide, the first feed stream containing at least one lighter component and at least one heavier component, wherein: i) cooling the first feed stream to produce a cooled feed stream, feeding the cooled feed stream to a first column operating at less than 5 bar, wherein it is separated by distillation to form a top gas rich in the lighter component and a bottom liquid rich in the heavier component; ii) cooling according to step i) by heat exchange with the first feed stream and at least partially evaporating at least a portion of the bottom liquid by at least one electric heater, and feeding at least a portion of the at least partially evaporated liquid to the first column; iii) feeding a second feed stream from the first column to an intermediate level of a second column, the second feed stream consisting of: a) at least a portion of the evaporated bottom liquid, or b) at least a portion of the gas extracted at the top of the first column. iv) Separating the second feed stream in the second column to form a top gas and a bottom liquid of the second column, and a') if the second feed stream consists of at least a portion of the evaporated bottom liquid, extracting a liquid rich in heavier components at the bottom of the second column and extracting a gaseous product at the top of the second column, or b') if the second feed stream consists of at least a portion of the gas extracted at the top of the first column, extracting a gaseous product at the bottom of the second column and extracting a gaseous product rich in lighter components at the top of the second column, and v) compared to the first feed stream, the gaseous product contains at least 99 mol% carbon monoxide and less of lighter and heavier components, such as nitrogen and argon, and the ratio of the flow rate of the gaseous product to the flow rate of the evaporated bottom liquid in stage ii) is between 8 mol% and 25 mol%.

[0029] Other configurations may be selected as needed: • The main lighter component is nitrogen; • The main heavier component is argon; • The gaseous product of the second column contains at least 99.99 mol% or at least 99.999 mol%, actually even at least 99.9999 mol% carbon dioxide; • The first feed stream contains at least 99 mol% carbon dioxide; • The gaseous product contains less than 2 ppm, actually at least 0.5 ppm nitrogen; • The gaseous product contains less than 2 ppm, actually at least 0.5 ppm argon; • The first pressure is less than 5 bar absolute pressure; • The feed stream is depressurized upstream of the first column; • The feed stream is used to at least partially evaporate at least a portion of the bottom liquid; • The first feed stream is at least partially condensed by heat exchange with the bottom liquid; • At least one electric heater is used to provide at least 55%, actually even at least 65%, of the heat required to evaporate at least a portion of the bottom liquid. • At least one electric heater is used to provide at least 55% to 85%, practically even at least 65% to 72%, of the heat required to evaporate at least a portion of the bottom liquid. • The pressure difference between the first and second columns is less than 2 bar, practically even less than 1.8 bar. • The top condenser of the second column is cooled by a refrigerant from an external source, such as liquid nitrogen. • The feed stream also contains hydrogen and / or oxygen and / or methane. • The feed stream is purified in water and / or carbon dioxide upstream of the first column. • According to alternative form a) a'), liquid is not sent from the top of the first column to the top of the second column. • According to alternative form b) b'), the evaporated bottom liquid is not sent to the second column. • The bottom liquid is not sent from the first column to the second column in liquid form. • The bottom liquid is not sent from the first column to the second column. • The top liquid is not sent from the first column to the second column. • Liquid is not sent from the second column to the first column. • The bottom liquid stream is extracted from the columns and sent to a reboiler, where it is partially evaporated by the first feed stream and at least one electric heater. The twin towers are at least 20 m high, and the liquid stream is extracted from the reboiler, which preferably constitutes the final product or effluent.

[0030] According to another aspect of the present invention, an apparatus is provided for purifying a first feed stream containing at least 97 mol% carbon monoxide, the first feed stream containing at least one lighter component and at least one heavier component. The apparatus comprises a first column and a second column, a component for cooling the first feed stream to produce a cooled feed stream, an electric heater for heating at least a portion of the bottom liquid, a component for feeding the cooled feed stream to the first column for separation by distillation to form a top gas rich in the lighter component and a bottom liquid rich in the heavier component, a component for cooling the first feed stream to allow indirect heat exchange between the first feed stream and at least a portion of the bottom liquid that has been evaporated, a component for feeding at least a portion of the evaporated liquid to the first column, and a component for feeding a second feed stream from the first column to an intermediate level of the second column, the second feed stream consisting of: i) at least a portion of the evaporated bottom liquid, or ii) at least a portion of the gas extracted at the top of the first column. The second column is adapted to separate the second feed stream to form the top gas and the bottom fluid of the second column, and a') if the second feed stream consists of at least a portion of the evaporated bottom liquid, there are components for extracting the liquid rich in heavier components at the bottom of the second column and components for extracting the gaseous product at the top of the second column, or b') if the second feed stream consists of at least a portion of the gas extracted at the top of the first column, there are components for extracting the gaseous product at the bottom of the second column and components for extracting the gas rich in lighter components at the top of the second column, and the gaseous product contains at least 99 mol% carbon monoxide and less of the lighter and heavier components, such as nitrogen and argon, compared to the first feed stream.

[0031] Other configurations may be selected as needed: • The top of the first tower is thermally connected to the second tower; • A reboiler is connected to the bottom of the second tower to condense the top gas of the first tower; • The first and second towers constitute a twin-tower configuration, with the second tower above the first tower; • The total height of the combined first and second towers is less than 30 m; • The cooling assembly for the first feed stream is composed of a reboiler, preferably located outside either tower; • The reboiler includes a device for discharging the effluent liquid; • The device includes an assembly for cooling the top of the second tower by indirect heat exchange, preferably supplying refrigerant from an external source; • The device includes a reboiler located outside either tower, the tower containing an assembly for cooling the first stream and at least one electric heater and an assembly for delivering the bottom liquid to the reboiler; • The device includes an assembly for extracting the unevaporated bottom liquid from the reboiler.

Implementation Method

[0033] The apparatus of [Figure 1] includes a first distillation column K1 operating at a first pressure and a second column K2 operating at a second pressure lower than the first pressure. The first pressure is preferably less than 5 bar absolute pressure; for example, the first pressure may be 3.5 bar absolute pressure and the second pressure may be 1.8 bar absolute pressure. The temperature of the first column is between 92 K and 93 K, and the temperature of the second column is between 87 K and 88 K.

[0034] The first and second columns K1 and K2 contain structured encapsulation to facilitate mass and heat exchange within the columns, thereby enabling distillation.

[0035] The first tower K1 is used to remove nitrogen from the stream 1 containing at least 97 mol% carbon monoxide, and the second tower K2 is used to remove argon from the stream.

[0036] The second tower K2 includes a first reboiler C at the bottom, which is connected to condense the top gas of the first tower K1 and heat the bottom liquid of the second tower, and includes a condenser E2 at the top. The condenser E2 is cooled by a liquid nitrogen stream 11 originating from the storage tank S, which indirectly transfers heat at the top of the tower, thereby evaporating the liquid nitrogen.

[0037] The feed stream can be provided from a gas storage tank or a truck transporting gas cylinders containing relatively impure carbon monoxide. The gas is depressurized to a pressure of 7 bar absolute pressure and then sent as stream 1 to the heat exchanger E1 of the second reboiler R. The bottom reboiler R is used to feed vapor to the bottom of the first column K1 and to provide feed gas to the second column K2. It is located next to the vertical column K1 to reduce the overall height of the combination of columns K1 and K2, but can also be incorporated into column K1.

[0038] Gas 1 may contain at least 97% carbon monoxide (or at least 99% carbon monoxide) as well as argon and nitrogen. It may also contain oxygen and / or methane and / or hydrogen.

[0039] If it contains water and / or carbon dioxide, such impurities are removed upstream of the reboiler R by adsorption or deposition as described in WO18111719.

[0040] Gas 1 enters heat exchanger E1 at a temperature close to ambient temperature at a flow rate of approximately 50 Nm³ / h. It condenses in E1, is depressurized to 3.8 bar in valve 4, and is sent to the intermediate level of the first column in a two-phase form. It is separated by distillation, and a nitrogen-depleted bottom liquid is found at the bottom of the column, at least a portion of which is sent as stream 3 to reboiler R for evaporation. Since feed gas 1 is insufficient to evaporate stream 3, at least one electric heater 21 also provides heat. Generally, two-thirds of the heat of evaporation is provided in this manner.

[0041] The evaporated gas is divided into two parts. One part 5 is sent to the bottom of the first tower K1, and the other part 7 is sent to the middle level of the second tower K2 as the only feed stream.

[0042] A portion of the bottom liquid 2 can be drained.

[0043] Extract nitrogen-rich gas 13 at the top of the first tower K1.

[0044] Gas 9 is extracted at the top of the second tower K2, the gas containing at least 99.99 mol% or at least 99.999 mol%, actually even at least 99.9999 mol% of carbon monoxide, and an argon-rich fluid 15, which may be in gaseous or liquid state, is extracted at the bottom of the second tower K2.

[0045] Due to the high carbon monoxide content, streams 2, 13, and 15 are sent to a scrubbing tower or another conversion or passivation device.

[0046] If required by the customer, product 9 can be heated to a temperature higher than that of the second tower K2 by a heater.

[0047] The liquid will not be transferred from the top of the first tower K1 to the top of the second tower K2.

[0048] No part of the liquid from the bottom of the first tower K1 is sent to the second tower K2 in liquid form.

[0049] The ratio of production flow rate 9 to boiling flow rate 5 plus 7 is between 8% and 25%.

[0050] The production flow rate is the flow rate of carbon monoxide 9 purified in argon and nitrogen, and the boiling flow rate is the amount of gas 5 plus 7 produced by the bottom reboiler of the lowest column of the double column used.

[0051] [Figure 2] shows alternatives for removing argon in the first tower K1 and removing nitrogen in the second tower K2.

[0052] The apparatus of [Figure 2] includes a first distillation column K1 operating at a first pressure and a second column K2 operating at a second pressure lower than the first pressure. The first pressure is preferably less than 5 bar absolute pressure; for example, the first pressure may be 3.5 bar absolute pressure and the second pressure may be 1.8 bar absolute pressure. The temperature of the first column is between 92 K and 93 K, and the temperature of the second column is between 87 K and 88 K.

[0053] The first and second columns K1 and K2 contain structured encapsulation to facilitate mass and heat exchange within the columns, thereby enabling distillation.

[0054] The first tower K1 is used to remove argon, and the second tower is used to remove nitrogen.

[0055] The second column K2 includes a first reboiler C at the bottom, which is connected to condense the top gas of the first column K1 and feeds vapor to the bottom of the second column, and includes a condenser E2 at the top. The condenser E2 is cooled by a liquid nitrogen stream 11 originating from the storage tank S, which indirectly transfers heat at the top of the column, thereby causing the liquid nitrogen to evaporate to form gas 19.

[0056] The feed stream can be provided from a gas storage tank or a truck transporting gas cylinders containing relatively impure carbon monoxide. The gas is reduced to a pressure of 7 bar absolute by the Joule-Thomson vacuum method, and then sent as stream 1 to the heat exchanger E1 of the second reboiler R. The bottom reboiler R is used to feed vapor to the bottom of the first column K1. It can be located next to column K1 to reduce the overall height of the combination of columns K1 and K2, or it can be incorporated into column K1.

[0057] Gas 1 may contain at least 97% carbon monoxide (or at least 99% carbon monoxide) as well as argon and nitrogen. It may also contain oxygen and / or methane and / or hydrogen.

[0058] If it contains water and / or carbon dioxide, such impurities are removed upstream of the reboiler R by adsorption or deposition as described in WO18111719.

[0059] Gas 1 enters heat exchanger E1 at a temperature close to ambient temperature at a flow rate of approximately 50 Nm³ / h. It condenses in E1, is depressurized to 3.8 bar in valve 4, and is sent to the intermediate level of the first column in a two-phase form. It is separated by distillation, and an argon-rich bottom liquid is found at the bottom of column K1, at least a portion of which is sent as stream 3 to reboiler R for evaporation. Since feed gas 1 is insufficient to evaporate stream 3, at least one electric heater 21 also provides heat. Typically, two-thirds of the heat of evaporation is provided in this manner. For example, electric heater 21 can contribute at least 55% to 85%, practically even at least 65% to 72%, of the heat required to evaporate at least a portion of the bottom liquid.

[0060] The evaporated gas 5, rich in argon, is sent to the bottom of the first tower K1.

[0061] The liquid 2 extracted from the second reboiler R will be discharged.

[0062] Argon-depleted gas 13 is extracted at the top of the first tower K1, depressurized in a valve, and sent as the sole feed stream to the middle level of tower K2.

[0063] A nitrogen-rich gas 9 is extracted at the top of the second column K2, and a nitrogen-poor gaseous product 15 containing at least 99.99 mol% or at least 99.999 mol% carbon monoxide, and actually even at least 99.9999 mol% carbon monoxide, is extracted at the bottom of the second column K2. Liquid 14 may be discharged from the bottom of the second column K2 if necessary.

[0064] Due to the high carbon monoxide content, streams 2, 9, and 14 are sent to a scrubbing tower or a passivation tower.

[0065] If required by the customer, product 15 can be heated to a temperature higher than that of the second tower K2 by a heater.

[0066] No part of the argon-rich bottom liquid 3 is sent to the second tower K2.

[0067] The ratio of production flow rate to boiling flow rate is between 8% and 25%.

[0068] The production flow rate is the flow rate of carbon 15 purified in argon and nitrogen, and the boiling flow rate is the amount of gas 5 produced by the bottom reboiler of the lowest column of the double column used.

[0069] In the embodiments, the lighter component is nitrogen and the heavier component is argon, but other components are also possible. [Simplified Explanation of the Diagram]

[0032] The invention will be described in more detail with reference to the accompanying drawings, in which: [Figure 1] illustrates the method according to the invention. [Figure 2] illustrates the method according to the invention.

Claims

1. A method for purifying a first feed stream (1) containing at least 97 mol% carbon monoxide, the first feed stream (1) containing at least one lighter component and at least one heavier component, wherein: i) Cooling the first feed stream to produce a cooled feed stream, which is then fed to a first column (K1) operating at less than 5 bar, wherein it is separated by distillation to form a top gas (13) rich in lighter components and a bottom liquid (3) rich in heavier components; ii) Cooling the first feed stream according to stage i) by heat exchange with it and at least partially evaporating at least a portion of the bottom liquid by at least one electric heater (21), and feeding at least a portion (5) of the at least partially evaporated liquid to the first column; iii) Feeding a second feed stream (7, 13) from the first column to an intermediate level of a second column (K2), the second feed stream consisting of: a) at least a portion of the evaporated bottom liquid (7), or b) at least a portion of the gas (13) extracted at the top of the first column. iv) Separate the second feed stream in the second column to form the top gas (9) and the bottom fluid (15) of the second column, and a') if the second feed stream consists of the at least portion of the evaporated bottom liquid, the bottom fluid is a liquid rich in heavier components extracted at the bottom of the second column, and the top gas is a gaseous product extracted at the top of the second column, or b') if the second feed stream consists of the at least portion of the gas extracted at the top of the first column, the gas (15) is extracted at the bottom of the second column, and the top gas is a gaseous product rich in lighter components extracted at the top of the second column, and v) compared with the first feed stream, the gaseous product (9) contains at least 99 mol% carbon monoxide and less nitrogen and argon, and the flow rate of the gaseous product (9) is between 8 mol% and 25 mol% of the flow rate of the evaporated bottom liquid (5+7, 5) of stage ii).

2. The method of claim 1, wherein the gaseous product (9) of the second tower (K2) contains at least 99.99 mol% carbon dioxide.

3. The method of claim 2, wherein the gaseous product (9) of the second tower (K2) contains at least 99.999 mol% carbon dioxide.

4. The method of claim 3, wherein the gaseous product (9) of the second tower (K2) contains at least 99.9999 mol% carbon dioxide.

5. The method of claim 1 or 2, wherein the first feed stream (1) contains at least 99 mol% carbon dioxide.

6. The method of claim 1 or 2, wherein the gaseous product (9) contains less than 2 ppm of nitrogen.

7. The method of claim 6, wherein the gaseous product (9) contains less than 0.5 ppm of nitrogen.

8. The method of claim 1 or 2, wherein the gaseous product (9) contains less than 2 ppm of argon.

9. The method of claim 8, wherein the gaseous product (9) contains less than 0.5 ppm of argon.

10. The method of claim 1 or 2, wherein the bottom liquid (3) is extracted from the first column and fed to a reboiler (R), wherein it is partially evaporated by the first feed stream (1) and the at least one electric heater.

11. The method of claim 10, wherein the liquid stream (2) is extracted from the reboiler (R).

12. The method of request item 1 or 2, wherein the first feed stream (1) is depressurized upstream of the first tower.

13. The method of claim 1 or 2, wherein the first feed stream (1) is at least partially condensed by heat exchange with the bottom liquid (3) removed from the first column.

14. The method of claim 1 or 2, wherein the at least one electric heater is used to provide at least 55% of the heat required to evaporate at least a portion of the bottom liquid (3) removed from the first tower.

15. The method of claim 14, wherein the at least one electric heater is used to provide at least 65% of the heat required to evaporate at least a portion of the bottom liquid (3) removed from the first tower.

16. The method of request item 1 or 2, wherein the pressure difference between the first tower and the second tower (K1, K2) is less than 2 bar.

17. The method of claim 16, wherein the pressure difference between the first tower and the second tower (K1, K2) is less than 1.8 bar.

18. The method of claim 1 or 2, wherein the top condenser (E2) of the second tower (K2) is cooled by refrigerant (11) from an external source (S).

19. The method of claim 18, wherein the refrigerant (11) is selected from liquid nitrogen.

20. The method of claim 1 or 2, wherein the first feed stream (1) is purified in water and / or carbon dioxide upstream of the first tower (K1).

21. An apparatus for purifying a first feed stream (1) containing at least 97 mol% carbon monoxide, the first feed stream containing at least one lighter component and at least one heavier component, the apparatus comprising a first column (K1) and a second column (K2), an assembly (E1) for cooling the first feed stream to produce a cooled feed stream, an assembly for feeding the cooled feed stream to the first column for separation by distillation to form a top gas (13) rich in the lighter component and a bottom liquid (3) rich in the heavier component, an assembly for cooling the first feed stream to allow indirect heat exchange between the first feed stream and at least a portion of the bottom liquid that has been at least partially evaporated, at least one electric heater (21) for heating the at least portion of the bottom liquid, an assembly for feeding at least a portion (5) of the at least partially evaporated liquid to the first column, and an assembly for feeding a second feed stream (7, 13) from the first column to an intermediate level of the second column, the second feed stream comprising: i) at least a portion of the evaporated bottom liquid, or ii) at least a portion of the gas extracted at the top of the first column, the second column being adapted to separate the second feed stream to form the top gas (9) of the second column and the bottom fluid (15) of the second column, and a') if the second feed stream consists of the at least a portion of the evaporated bottom liquid, there is a component of extracting a liquid rich in heavier components at the bottom of the second column as the bottom fluid and extracting a gaseous product at the top of the second column as the top gas, or b') if the second feed stream consists of the at least a portion of the gas extracted at the top of the first column, there is a component of extracting a gas at the bottom of the second column as the bottom fluid and extracting a gaseous product rich in lighter components at the top of the second column as the top gas, and the gaseous product (9) contains at least 99 mol% carbon monoxide and fewer lighter and heavier components compared to the first feed stream.

22. The apparatus of claim 21, wherein the lighter component and the heavier component are selected from nitrogen and argon.

23. The apparatus of claim 21, comprising a reboiler (R) located outside any column, the column containing components (E1) for cooling the first feed stream (1) and the at least one electric heater (21) and components for feeding the bottom liquid (3) to the reboiler.

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