Process for the production of ethylene

Abstract

The invention provides a process for producing ethylene, the process comprising at least the following steps: (a) providing a CO-containing stream (10); (b) converting the CO-containing stream (10) provided in step (a) in an electrolytic cell (2), thereby producing an ethylene-containing vapor stream (30) and an ethanol-containing liquid stream (40); (c) hydrating at least a portion of the ethylene-containing vapor stream (30) as obtained in step (b), thereby obtaining a first ethanol-rich stream (90); (d) separating the first ethanol-rich stream (90) as obtained in step (c), thereby obtaining a second ethanol-rich stream (110) and a water-rich stream (120); and (e) dehydrating the second ethanol-rich stream (110), thereby obtaining ethylene (140).

Description

[0001] The present invention relates to a method for producing ethylene, in particular a method for producing ethylene from a CO-containing stream obtained by capturing CO2 from the atmosphere, flue gas, etc.

[0002] Ethylene is an important raw material for a variety of end products such as ethylene oxide, ethylene glycol, polymers, rubbers, plastics, etc. Processes for producing ethylene are known in the art.

[0003] To date, ethylene has been produced primarily via steam cracking of crude oil-derived hydrocarbons or via the conversion of natural gas.

[0004] An example of the selective production of ethylene from methane has been disclosed in WO 2021 / 009627 A1.

[0005] However, the increasing availability of low-cost renewable electricity and the desire to reduce carbon emissions through CO2 capture provide opportunities to produce carbon-based feedstocks and fuels via electrochemical reduction of carbon dioxide (CO2) to chemical feedstocks. As a result, the number of studies to identify pathways for electrochemical CO2 reduction to ethylene continues to increase.

[0006] Just as an example, the article "Ethylene Electrosynthesis. A comparative techno-economic analysis of alkaline vs membrane electrode vs CO2-CO-C2H4 tandems" by J. Sisler et al. in ACS Energy Lett. 2021, 6, 997-1002 discloses the use of an electrolyzer to convert CO2 "single-step" or "directly" into C2H4 (ethylene).

[0007] The problem with the process described in this article is that it requires separation of CO, ethylene and H2. This separation step can be cumbersome or at least expensive since it generally requires cryogenic distillation.

[0008] It is an object of the present invention to solve, minimize or at least reduce one or more of the problems set out above.

[0009] Another object of the present invention is to provide an alternative process for producing ethylene, in particular a process for producing ethylene from a CO-containing stream which has been obtained from CO2 captured from the atmosphere, flue gases or the like.

[0010] According to the present invention, one or more of the above or other objects can be achieved by providing a method for producing ethylene, the method comprising at least the following steps:

[0011] (a) providing a CO-containing stream;

[0012] (b) converting the CO-containing stream provided in step (a) in an electrolyser to produce a vapor stream containing ethylene and a liquid stream containing ethanol;

[0013] (c) hydrating at least a portion of the ethylene-containing vapor stream obtained in step (b) to obtain a first ethanol-rich stream;

[0014] (d) separating the first ethanol-rich stream obtained in step (c) to obtain a second ethanol-rich stream and a water-rich stream; and

[0015] (e) dehydrating the second ethanol-rich stream to obtain ethylene.

[0016] According to the present invention it has surprisingly been found that by "indirect" conversion of carbon monoxide (CO) into ethylene (via intermediate conversion into ethanol), the separation of CO, ethylene and H2 (via cryogenic distillation) can be avoided.

[0017] Another advantage of the process according to the invention is that ethanol can be easily stored, for example in low-cost tanks. This may be important in the case where the electrolyser is driven by renewable energy sources, such as wind, solar and other forms of renewable energy with intermittency problems. By using low-cost storage devices for ethanol, the use of relatively expensive batteries to ensure (otherwise required) continuous operation of the electrolyser can be avoided; this is because in the event that the electrolyser is not operating due to intermittency problems, the stored ethanol can be used in downstream processes (which usually operate continuously).

[0018] In step (a), a gas stream containing CO is provided. The gas stream containing CO is not subject to any limitation (in terms of composition, temperature, pressure, etc.) as long as it contains CO. The gas stream containing CO may have various sources.

[0019] Preferably, the CO-containing stream has been obtained from a CO2-containing stream, preferably CO2 captured from the atmosphere. Merely by way of example, the CO-containing gas stream may be obtained by: a thermochemical or electrochemical CO2 conversion pathway, a dimethane conversion pathway; gasification of biomass or waste; etc.

[0020] Preferably, the CO-containing stream provided in step (a) comprises at least 25 mol % CO, preferably at least 50 mol % CO.

[0021] Some other compounds such as nitrogen (N2), methane (CH4), carbon dioxide (CO2), water (H2O) and hydrogen (H2) may be present in the CO-containing stream. For example, if present, H2 is present in the CO-containing stream in an amount of up to 75 mol %, preferably up to 50 mol %. Preferably, the CO-containing stream is free of oxygen (O2) and sulfur compounds such as H2S and SO x ).

[0022] Typically, the CO-containing stream provided in step (a) has a temperature in the range of 0° C. to 90° C., preferably 15° C. to 80° C., more preferably below 65° C. Furthermore, the CO-containing gas stream provided in step (a) typically has a pressure in the range of 0.5 bara to 30.0 bara, preferably below 10.0 bara and preferably about 1.0 bara. If appropriate, the CO-containing stream may have been pretreated to obtain the desired composition and conditions.

[0023] In step (b), the CO-containing stream provided in step (a) is converted in an electrolyser to produce a vapor stream comprising ethylene and a liquid stream comprising ethanol.

[0024] Since those skilled in the art are familiar with electrolyzers, they will not be discussed in full detail here. Generally speaking, an electrolyzer uses electricity to drive an otherwise non-spontaneous chemical reaction. An electrolyzer will typically include an anode and a cathode separated by a diaphragm, and an electrolyte.

[0025] For more information on electrolyzers, see B. Endrodi et al., Continuous-flow electroreduction of carbon dioxide, Progress in Energy and Combustion Science, vol. 62, September 2017, pp. 133-154.

[0026] According to a preferred embodiment of the invention, the electrolyser is driven by a renewable energy source. The renewable energy source may be intermittent or continuous.

[0027] Those skilled in the art will readily appreciate that the components of the electrolytic cell may be constructed from a wide range of materials.

[0028] There is no particular restriction on the cathode used in the electrolytic cell. Typically, the cathode of the electrolytic cell is selected from copper, silver, gold, platinum, tin, lead, palladium, aluminum, zinc, titanium dioxide, carbon black, carbon nanotubes, graphene (doped or undoped with nitrogen, sulfur, phosphorus) or a combination thereof. Preferably, the electrolytic cell in step (b) has a cathode comprising copper (Cu) or a copper-based alloy.

[0029] In addition, there is no particular limitation on the anode used in the electrolytic cell. Preferably, the electrolytic cell in step (b) has an anode comprising a metal selected from the group consisting of nickel (Ni), iron (Fe), iridium (Ir), cobalt (Co), manganese (Mn), ruthenium (Ru) or a combination thereof. The anode may comprise an oxide of the above metals.

[0030] There is no particular limitation on the electrolyte. Typically, the electrolyte is an aqueous electrolyte containing a + , K + , Rb + , Cs + NH4 + A compound of the group consisting of carbonates, bicarbonates, hydroxides, halides, and deionized water, preferably KOH.

[0031] Although the temperature at which the electrolytic cell is operated is not limited, preferably the electrolytic cell in step (b) is operated at a temperature of 20° C. to 100° C., preferably 40° C. to 90° C. In addition, the electrolytic cell is preferably operated at a pressure of 0.5 bara to 30 bara, preferably 1.0 bara to 10 bara.

[0032] As mentioned above, in step (b) a vapour stream comprising ethylene and a liquid stream comprising ethanol are produced.

[0033] Preferably, the ethylene-containing vapour stream obtained in step (b) comprises at least 0.5 mol % ethanol, preferably at least 1.0 mol % ethanol.Preferably, the ethylene-containing vapour stream obtained in step (b) comprises at least 20 mol % ethylene.

[0034] Furthermore, the ethanol-comprising liquid stream obtained in step (b) comprises at most 5.0 mol-% ethylene, preferably at most 1.0 mol-%.

[0035] The ethanol-containing liquid stream produced in step (b) comprises at least 0.2 mol% ethanol, preferably at least 1.0 mol% ethanol. Typically, the ethanol-containing liquid stream also contains some electrolyte, acetate and propanol.

[0036] According to a particularly preferred embodiment of the process of the invention, before the hydration in step (c), the ethylene-containing vapour stream produced in step (b) is separated to obtain an ethylene-rich gas stream and a third ethanol-rich stream, and wherein the ethylene-rich gas stream is subjected to the hydration in step (c). Typically, the third ethanol-rich stream is a liquid.

[0037] Although not limited thereto, the ethylene-containing vapor stream is typically separated in a vapor / liquid separation vessel after first being flashed.

[0038] The ethylene-rich gas stream typically comprises at least 20 mol% ethylene, preferably at least 30 mol%. The ethylene-rich gas stream typically also contains some CO and H2.

[0039] The third ethanol-rich liquid stream is typically an aqueous stream and typically comprises at least 10 mole % ethanol, preferably at least 20 mole %.

[0040] In step (c), at least a portion, and preferably all, of the ethylene-containing vapour stream obtained in step (b) is hydrated, thereby obtaining a first ethanol-rich stream.

[0041] Since those skilled in the art are familiar with hydration, it will not be discussed in detail here. In addition to the first ethanol-rich stream, a residual CO-containing stream is usually obtained. This residual CO-containing stream (usually also containing some H2) can be recycled.

[0042] The first ethanol enriched stream typically comprises at least 20 mol% ethanol, preferably at least 30 mol% ethanol.Preferably, the first ethanol enriched stream (and preferably the third ethanol enriched stream) is temporarily stored prior to separation in step (d).

[0043] Temporary storage may be performed, for example, in a storage tank (hereinafter referred to as a "first buffer tank"). An important advantage of using such a storage tank (which may have a low cost) is that, in the case where the electrolyser is driven by renewable energy (such as wind, solar and other forms of renewable energy), intermittent problems can be accommodated without the use of expensive batteries. This is because in the event that the electrolyser is not operating due to intermittent problems, the stored ethanol can be used in downstream processes (which are typically operated continuously). Another advantage of using a storage tank is that it can be easily scaled up.

[0044] According to a particularly preferred embodiment of the process of the invention, the third ethanol-rich stream is combined with the first ethanol-rich stream formed in step (c) to obtain a combined ethanol stream, and wherein the combined ethanol stream is used in the separation of step (d). Likewise, it is preferred that the combined ethanol stream is temporarily stored before the separation in step (d).

[0045] The combined ethanol stream typically comprises at least 20 mole % ethanol, preferably at least 30 mole %.

[0046] In step (d), the first ethanol-rich stream (or the combined ethanol streams) obtained in step (c) is separated to obtain a second ethanol-rich stream and a water-rich stream.

[0047] Although the separation in step (d) can be carried out in many ways, the separation is usually accomplished by distillation. As such distillation is well known to those skilled in the art, it will not be discussed in further detail here.

[0048] The second ethanol-rich stream, which may be a vapor or a liquid, typically comprises at least 85 mole %, preferably at least 90 mole % ethanol.The second ethanol-rich stream typically also contains some water.

[0049] The water-rich stream typically comprises at least 90 mole percent water, and may also contain some ethanol, acetate / acetic acid, and propanol.

[0050] In step (e), the second ethanol-rich stream is dehydrated to obtain ethylene. Since the skilled person is familiar with this dehydration step, it will not be discussed in further detail here. If necessary, the obtained ethylene can be further purified; generally, some of the water produced during the dehydration step will be removed.

[0051] According to a particularly preferred embodiment of the present invention, the ethanol-containing liquid stream obtained in step (b) is separated so as to obtain a fourth ethanol-rich stream and an oxygen-rich gas stream.

[0052] Although not limited thereto, the ethanol-containing liquid stream is typically separated in a gas / liquid separation vessel after first being flashed.

[0053] The fourth ethanol-rich stream is typically a liquid and typically comprises at least 0.2 mol% ethanol, preferably at least 2.0 mol%. The fourth ethanol-rich stream typically also contains some CO and H2.

[0054] The oxygen-rich gas stream generally comprises at least 90 mol %, preferably at least 95 mol % oxygen. The remainder is generally water, and some trace amounts of CO2, ethanol and propanol.

[0055] Preferably, the fourth ethanol-rich stream is separated to obtain a fifth ethanol-rich stream and a propanol-rich stream.

[0056] Typically, separation of the fourth ethanol-rich stream is performed via distillation in an alcohol separation unit.

[0057] The fifth ethanol-enriched stream typically comprises at least 70 mol%, preferably at least 80 mol% ethanol.The fifth ethanol-enriched stream typically also contains some water.

[0058] The propanol-rich stream typically comprises at least 0.1 mol %, preferably at least 0.2 mol % propanol.The propanol-rich stream will typically also acquire some electrolyte, acetate and water.

[0059] According to a particularly preferred embodiment of the present invention, the fourth ethanol enriched stream is temporarily stored before being separated (as discussed below) to obtain the fifth ethanol enriched stream.

[0060] Temporary storage may be performed, for example, in a storage tank (hereinafter referred to as a "second buffer tank"). As mentioned previously, an important advantage of using such a storage tank (which may have a low cost) is that, in the case where the electrolyser is driven by renewable energy (such as wind, solar and other forms of renewable energy), intermittency issues may be accommodated without the use of expensive batteries.

[0061] Furthermore, it is preferred that a fifth ethanol-enriched stream is combined with the combined ethanol stream.

[0062] According to a particularly preferred embodiment of the process according to the invention, the propanol-rich stream is separated to obtain a purified propanol stream and an electrolyte-rich stream; wherein at least a portion of the electrolyte-rich stream is separated into another electrolyte-rich stream and an acetic acid-rich stream; wherein the acetic acid-rich stream is hydrogenated to obtain another ethanol stream; and wherein the another ethanol stream is dehydrated in step (e).

[0063] In another aspect, the present invention provides an apparatus suitable for carrying out the process for producing ethylene according to the present invention, the apparatus comprising at least:

[0064] an electrolyser for converting a CO-containing stream to produce a vapor stream containing ethylene and a liquid stream containing ethanol;

[0065] a hydration unit for hydrating at least a portion of the ethylene-containing vapor stream to obtain a first ethanol-rich stream;

[0066] an alcohol separation unit for separating the first ethanol-rich stream to obtain a second ethanol-rich stream and a water-rich stream; and

[0067] a dehydration unit for dehydrating the second ethanol-rich stream to obtain ethylene.

[0068] The present invention will be further described below by means of the following non-limiting drawings, in which:

[0069] Figure 1 A flow chart of a process for producing ethylene according to the present invention is schematically shown.

[0070] For description purposes, the same reference numbers will be used to refer to the same or like parts.

[0071] Figure 1The flow chart (generally indicated by the reference numeral 1) shows an electrolyzer 2, a first g / L container 3, a hydration process unit 4, an ethanol separation (distillation) unit 5, a dehydration unit 6, a first liquid storage tank 7, a molecular sieve unit 8, a second g / L container 9, an alcohol separation (distillation) unit 11, a second liquid storage tank 12, a propanol separation (distillation) unit 13, an acetate / acetic acid separation unit 14 and a hydrogenation unit 15.

[0072] During use, a CO-containing stream 10 is provided. The CO-containing stream 10 has preferably been obtained from a CO2-containing stream that has been captured from the atmosphere. The CO-containing stream 10 is fed to the electrolyser 2 together with an electrolyte 20. In the electrolyser 2, the CO-containing stream 10 is converted to produce a vapor stream 30 containing ethylene and a liquid stream 40 containing ethanol.

[0073] The ethylene-containing vapor stream 30 is subsequently separated in the first g / L vessel 3 after flashing in a flash separator (not shown) to obtain an ethylene-rich gas stream 50 and a liquid third ethanol-rich stream 60 .

[0074] At least a portion, but typically all, of the ethylene-rich gas stream 50 is hydrated in a hydration process unit 4 (via a process water stream 70) to obtain a liquid first ethanol-rich stream 90 and a residual CO-containing stream 80. This residual CO-containing stream 80 (typically also containing some H2) can be recycled to, for example, the output of a CO production unit (not shown) or combined therewith to obtain a CO-containing stream 10.

[0075] The third ethanol-rich stream 60 and the first ethanol-rich stream 90 are combined to obtain a combined ethanol stream 100. Figure 1 In the embodiment of the present invention, the combination occurs in the first storage tank 7 for temporary storage of the combined stream, but this can also occur before entering the first storage tank 7. In the absence of a first storage tank 7, the combination can occur somewhere before or in the ethanol separation (distillation) unit 5.

[0076] In the ethanol separation (distillation) unit 5 , the combined ethanol stream 100 is separated to obtain a second ethanol-rich stream 110 and a water-rich stream 120 .

[0077] Subsequently, the second ethanol-rich stream 110 is dehydrated in a dehydration unit 6, typically in the presence of additional water, to obtain an ethylene stream 130 and another water-rich stream 135. Figure 1 As can be seen, the ethylene stream 130 can be further purified in, for example, a molecular sieve unit 8 to obtain a purified ethylene stream 140 and a water stream 150 .

[0078] like Figure 1 As shown in the embodiment and as is particularly preferred according to the present invention, after flashing in a flash separator (not shown), the ethanol-containing liquid stream 40 is separated in a second g / L container 9 to obtain a liquid fourth ethanol-rich stream 160 and an oxygen-rich gas stream 170. The fourth ethanol-rich stream 160 is temporarily stored in a second storage tank 12 and subsequently separated in an alcohol separation (distillation) unit 11 to obtain a fifth ethanol-rich stream 190 and a propanol-rich stream 180. The fifth ethanol-rich stream 190 is combined with the combined ethanol stream 100. In Figure 1 In the embodiment of the present invention, the combining occurs in the ethanol separation (distillation) unit 5, but this can also be done upstream of the ethanol separation (distillation) unit 5.

[0079] like Figure 1 As shown in the embodiment of the present invention, the propanol-rich stream 180 (which also contains electrolyte, acetic acid and acetate) is separated in the propanol separation (distillation) unit 13 to obtain a purified propanol stream 200 and an electrolyte-rich stream 210 (which can be recycled to the electrolysis cell 2 (not shown)).

[0080] Figure 1 Also shown is an optional acetate / acetic acid separation unit 14 for separating (at least a portion of) the electrolyte-rich stream 210 into another electrolyte-rich stream 220 (which can be recycled to the electrolyzer 2) and an acetic acid-rich stream 230. The acetic acid-rich stream 230 can be treated in the hydrogenation unit 15 to obtain another ethanol stream 240, which can be fed to the ethanol separation (distillation) unit 5. Example

[0081] Figure 1 The flow diagram of (without acetate / acetic acid separation unit 14 and hydrogenation unit 15) is used to illustrate, in a non-limiting manner, the production of ethylene from a CO-containing stream. The compositions and conditions of the fluid (i.e., gas and liquid) streams in the various flow lines are provided in Table 1 below (V represents vapor, and L represents liquid).

[0082] The values ​​in Table 1 were calculated using a model generated by the commercially available Aspen Plus software, using a standard thermodynamics package, which was set up to simulate, for example, CO2 conversion, alcohol distillation, gas / liquid separation, etc. For the electrolyzer group, the carbon monoxide gas diffusion electrolysis that produces concentrated C2 products with high single-pass conversion can be obtained from D.S. Ripatti et al., "Carbon Monoxide Gas Diffusion Electrolysis that Produces Concentrated C2 Products with High Single-Pass Conversion", Joule, Vol. 3, No. 1, pp. 240-256, 2019 (DOI: https: / / doi.org / 10.1016 / j.joule.2018.10.007 ) were used to supplement the Aspen model.

[0083] Aqueous (1.98 mol%) KOH solution was used as electrolyte.

[0084] Table 1

[0085]

[0086]

[0087] Table 1 (continued)

[0088]

[0089]

[0090] discuss

[0091] As can be seen in Table 1, the process according to the invention allows an efficient way of producing ethylene from a CO-containing stream.

[0092] An important advantage of the present invention is that by "indirectly" converting carbon monoxide (CO) to ethylene (via intermediate conversion to ethanol), the separation of CO, ethylene and H2 (via cryogenic distillation) can be avoided.

[0093] Another important advantage of the process according to the invention is that ethanol can be easily stored, for example in low-cost tanks. This may be important in cases where the electrolyser is driven by renewable energy sources such as wind, solar and other forms of renewable energy with intermittency problems.

[0094] Those skilled in the art will readily appreciate that many modifications may be made without departing from the scope of the invention. In addition, those skilled in the art will readily appreciate that although the present invention may have been illustrated with reference to a particular combination of features and measures in some cases, many of these features and measures are functionally independent of other features and measures given in the corresponding embodiments, so that they can be applied independently in the same or similar manner in other embodiments.

Claims

1. A method for producing ethylene, said method comprising at least the following steps: (a) providing a CO-containing stream (10); (b) converting the CO-containing stream (10) provided in step (a) in an electrolyzer (2) to produce a vapor stream (30) containing ethylene and a liquid stream (40) containing ethanol; (c) hydrating at least a portion of the ethylene-containing vapor stream (30) obtained in step (b) to obtain a first ethanol-rich stream (90); (d) separating the first ethanol-rich stream (90) obtained in step (c) to obtain a second ethanol-rich stream (110) and a water-rich stream (120); and (e) dehydrating the second ethanol-rich stream (110) to obtain ethylene (140).

2. The process according to claim 1, wherein the CO-containing stream (10) provided in step (a) has been obtained from a CO2-containing stream.

3. The process according to claim 1 or 2, wherein the CO-containing stream (10) provided in step (a) comprises at least 25 mol % CO, preferably at least 50 mol % CO.

4. The method according to any one of the preceding claims, wherein the electrolytic cell (2) in step (b) has a cathode comprising copper (Cu).

5. The method according to any one of the preceding claims, wherein the electrolytic cell (2) in step (b) has an anode comprising a metal selected from the group consisting of nickel (Ni), iron (Fe), iridium (Ir), cobalt (Co), manganese (Mn), ruthenium (Ru) or a combination thereof.

6. The method according to any one of the preceding claims, wherein the electrolysis cell (2) in step (b) is operated at a temperature of 20 to 100°C, preferably 40 to 90°C.

7. The process according to any one of the preceding claims, wherein the ethylene-containing vapour stream (30) obtained in step (b) comprises at least 0.5 mol % ethanol, preferably at least 1.0 mol % ethanol.

8. The process according to any one of the preceding claims, wherein the ethanol-containing liquid stream (40) obtained in step (b) comprises at most 5.0 mol-%, preferably at most 1.0 mol-% of ethylene.

9. A process according to any one of the preceding claims, wherein the ethylene-containing vapor stream (30) produced in step (b) is separated prior to the hydration in step (c) to obtain an ethylene-rich gas stream (50) and a third ethanol-rich stream (60), and wherein the ethylene-rich gas stream (50) is subjected to the hydration in step (c).

10. The method according to claim 9, wherein the third ethanol-rich feed stream (60) and the first ethanol-rich feed stream (90) formed in step (c) are combined to obtain a combined ethanol feed stream (100), and wherein the combined ethanol feed stream (100) is used in the separation of step (d).

11. The process according to any one of the preceding claims, wherein the first ethanol-rich stream (90) obtained in step (c) is temporarily stored before separation in step (d).

12. The process according to any one of the preceding claims, wherein the ethanol-containing liquid stream (40) obtained in step (b) is separated to obtain a fourth ethanol-rich stream (160) and an oxygen-rich gas stream (170).

13. The process of claim 12, wherein the fourth ethanol-rich stream (160) is separated to obtain a fifth ethanol-rich stream (190) and a propanol-rich stream (180).

14. The process of claim 13, wherein the fourth ethanol-enriched stream (160) is temporarily stored before being separated to obtain the fifth ethanol-enriched stream (190).

15. The process of claim 10 and 13 or 14, wherein the fifth ethanol-enriched stream (190) is combined with the combined ethanol stream (100).

16. The method according to any one of the preceding claims 13 to 15, wherein the propanol-rich stream (180) is separated to obtain a purified propanol stream (200) and an electrolyte-rich stream (210); wherein at least a portion of the electrolyte-rich stream (210) is separated into another electrolyte-rich stream (220) and an acetic acid-rich stream (230); wherein the acetic acid-rich stream (230) is hydrogenated to obtain another ethanol stream (240); and wherein the another ethanol stream (240) is dehydrated in step (e).

17. A device (1) suitable for carrying out the process for producing ethylene according to any one of the preceding claims 1 to 16, said device (1) comprising at least: an electrolyser (2) for converting a CO-containing stream (10) to produce an ethylene-containing vapour stream (30) and an ethanol-containing liquid stream (40); a hydration unit (4) for hydrating at least a portion of the ethylene-containing vapour stream (30) to obtain a first ethanol-rich stream (90); an alcohol separation unit (5) for separating the first ethanol-rich stream (90) to obtain a second ethanol-rich stream (110) and a water-rich stream (120); and a dehydration unit (6) for dehydrating the second ethanol-rich stream (110) to obtain ethylene (140).

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