Green methanol process and plant

Abstract

A process for the synthesis of methanol (MeOH) comprising the following steps: (a) passing a water-containing stream (3) through an electrolysis unit (4) to produce a cathode-side stream (5) comprising hydrogen (H2) and an anode-side stream (6) comprising oxygen (O2); (b) heat-exchanging said cathode-side stream (5) and optionally said anode-side stream (6) in one or more indirect heat exchanger(s) (7, 8, 32, 33) to obtain a cathode-side heat-exchanged stream (9) and optionally an anode-side heat-exchanged stream (10); (c) condensing said cathode-side heat-exchanged stream (9) to separate a liquid condensate product (11) and a syngas (12); said cathode-side stream (5) and / or said syngas (12) comprise carbon dioxide and optional carbon monoxide added through a separate stream (2); (d) compressing said syngas (12) in a compressor (27, 28) and then feeding compressed syngas (13) to a MeOH synthesis loop (14) wherein catalytic conversion of said compressed syngas (13) into MeOH is carried out under methanol synthesis conditions, thus obtaining a crude methanol stream (15); (e) distilling said crude methanol stream (15) in one or more distillation column(s) (16, 17) to give a refined MeOH product (19, 22); (i) recycling as feed to the electrolysis unit (4) at least a portion of at least one of: (A) a portion (31) of said compressed syngas (13); and / or (B) a bottom water stream (20) of a distillation column (16, 17).

Description

[0001] Green methanol process and plant

[0002] DESCRIPTION

[0003] Field of application

[0004] The invention is in the field of methanol (MeOH) production. The invention particularly pertains to a process and a plant for the synthesis of methanol.

[0005] Prior art

[0006] At present, synthesis gas (syngas) required for methanol synthesis is produced by reformation of natural gas in approx. 65% of the existing plants, while the remaining part is based on coal gasification. One of the main drawbacks of the current plants is that the involved processes are highly carbon intensive, i.e. , they produce high emissions of carbon dioxide (CO2).

[0007] Growing concerns about global climate changes make it urgent to investigate alternative pathways to produce methanol.

[0008] Among others, the so-called “green methanol” synthesis pathway entails the use of renewable energy to produce hydrogen (H2) and of CO2 from sustainable process or recovery (e.g., from flue gases or Direct Air Capture).

[0009] Syngas obtained through existing electrolysis technologies - such as alkaline water electrolysis or proton exchange membrane electrolysis - has a composition that does not conform exactly to methanol synthesis due to high amounts of carbon dioxide and a substantial lack of carbon monoxide (CO). A high concentration of CO2 in the syngas results in corresponding high amounts of water produced due to the reaction stoichiometry, thus reducing the reaction yield to give methanol and reducing the expected lifetime of the synthesis catalyst.

[0010] EP 4 345 086 A1 , WO 2023 / 217704 A1 , and EP 0 127 092 B1 belong to the known art.

[0011] In view of these considerations, it is highly desirable to develop an energy- efficient, environmentally friendly, and economically viable process and plant for the synthesis of methanol on an industrial scale.

[0012] Summary of the invention

[0013] The aim of the present invention is to solve the drawbacks of the prior art.

[0014] The invention is based on the judicious insight that methanol synthesis produces one or more electrolysis effluent(s) whose calorific content can be exploited within the methanol synthesis process and plant, making said process more efficient.

[0015] More precisely, the effluents from the electrolysis unit (e.g. comprising SOECs), in view of their high temperature, contain a high amount of heat that can be reused in the methanol synthesis process and / or in the electrolysis itself.

[0016] Accordingly, one aspect of the present invention is a process, preferably a thermally integrated process, for the synthesis of methanol (MeOH) comprising the following steps:

[0017] (a) passing a water-containing stream through an electrolysis unit to produce a cathode-side stream comprising hydrogen (H2) and an anode-side stream comprising oxygen (O2);

[0018] (b) heat-exchanging said cathode-side stream and optionally said anodeside stream in one or more indirect heat exchanger(s) to obtain a cathode-side heat-exchanged stream and optionally an anode-side heat- exchanged stream;

[0019] (c) condensing said cathode-side heat-exchanged stream to separate a liquid condensate product and a syngas; said cathode-side stream (5) and / or said syngas (12) comprise carbon dioxide (CO2) and optional carbon monoxide (CO) added through a separate stream (2);

[0020] (d) compressing said syngas in a compressor and then feeding compressed syngas to a MeOH synthesis loop wherein catalytic conversion of said compressed syngas into MeOH is carried out under methanol synthesis conditions, thus obtaining a crude methanol stream;

[0021] (e) distilling said crude methanol stream in one or more distillation column(s) to give a refined MeOH product; said process further comprising:

[0022] (i) recycling at least a portion of at least one of:

[0023] (A) a portion of said compressed syngas; and / or

[0024] (B) a bottom water stream of a distillation column;

[0025] (C) optionally a steam-containing stream taken from the MeOH synthesis loop; and / or optionally a portion of said syngas; as feed to the electrolysis unit.

[0026] A further aspect of the present invention is a plant for the synthesis of methanol (MeOH) comprising:

[0027] - an electrolysis unit fed with a water-containing stream and arranged to produce a cathode-side stream comprising hydrogen (H2) and an anodeside stream comprising oxygen (O2);

[0028] - one or more indirect heat exchanger(s) in a heat-exchanging relationship with said cathode-side stream and optionally said anode-side stream to obtain a cathode-side heat-exchanged stream and optionally an anodeside heat-exchanged stream;

[0029] - a condenser of said cathode-side heat-exchanged stream to separate a liquid condensate product and a syngas;

[0030] - a line for adding carbon dioxide (CO2) and optional carbon monoxide (CO) to said cathode-side stream and / or said syngas through a separate stream (2);

[0031] - at least one compressor for compressing said syngas;

[0032] - at least a MeOH synthesis loop fed with compressed syngas and arranged for a catalytic conversion of said compressed syngas into MeOH under methanol synthesis conditions, thus obtaining a crude methanol stream;

[0033] - one or more distillation column(s) for distilling the crude methanol stream to give a refined MeOH product;

[0034] - one or more lines for recycling at least a portion of at least one of:

[0035] (A) a portion of said compressed syngas; and / or

[0036] (B) a bottom water stream of a distillation column;

[0037] (C) optionally a steam-containing stream taken from the MeOH synthesis loop; and / or optionally a portion of said syngas; as feed to the electrolysis unit.

[0038] Advantageous effects of the invention

[0039] Advantageously, methanol synthesis can be performed with a co-electrolysis of water and CO2, preferably using solid-oxide electrolysis cells (SOECs).

[0040] The expression “co-electrolysis” means that electrolysis of H2O and CO2 is performed in the same electrolysis unit (see, e.g., unit 4 in the figures) at the same time.

[0041] On one side, co-electrolysis provides stoichiometrically suitable amounts of carbon monoxide, carbon dioxide and hydrogen in the syngas for an improved MeOH synthesis.

[0042] According to another advantageous aspect, a H2O / CO2 co-electrolysis allows to feed water (steam) and carbon dioxide to the electrolysis unit thus producing - on a cathode side - a syngas comprising steam, CO, CO2 and H2, basically converting CO2 into CO while producing H2 and - on an anode side - a stream of oxygen (O2) by electrolysis in the same stack.

[0043] Advantageously, the process of the present invention provides a heat integration that can reduce the global energy consumption up to 30%.

[0044] Advantageously, the process of the present invention can be implemented in existing plants, replacing partially or totally the existing syngas generation section, without changing the methanol synthesis loop drastically.

[0045] Advantageously, since SOECs and distillation both involve energy demanding processes, heat integration achieved by the present process and plant is beneficial to at least in part satisfy energy requirements and lowering global energy consumption.

[0046] Advantageously, the products of electrolysis are produced at high temperatures, so that their residual heat can be partially recovered by the feed effluent(s) and / or can be partially used to produce steam under pressure. This recovered steam may be used within the SOECs, or exported to other units of the plant to further lower energy consumption, or can be exported from the plant, e.g. to a CO2 capture unit such as a stripper reboiler of a carbon dioxide recovery.

[0047] Advantageously, the process and plant of the present invention allow to achieve a reduction of the total number and / or size of installed equipment either inside battery limits (ISBL) or outside battery limits (OSBL).

[0048] Advantageously, methanol synthesis effluents - such as volatile compounds, and / or fusel oil, and / or flash gases - can be recycled to the SOECs as feed for recovering hydrogen.

[0049] Advantageously, the process and plant of the present invention allow to reduce CAPEX and OPEX due to the reduction of overall wastewater and related apparatuses. In fact, the heat recovered from SOECs can be used to generate additional steam through the addition of a saturator column section or a film saturator column, exploiting the wastewater from distillation as process water (feed).

[0050] A further advantage is that an efficient reuse of the aqueous streams produced in the plant can be achieved and no methanol purification treatment of said aqueous stream is required.

[0051] Still a further advantage is that water loss is minimized in the plant since all the water produced can be recycled in the process.

[0052] Still a further advantage is that if the CO2 source is biogenic, thus it contains methane, such component is converted into additional syngas, through a reforming reaction in the SOEC, instead of being fed as inert compound to the methanol synthesis loop.

[0053] Advantageously, the process and plant of the present invention enable an improvement or optimization of the composition of the produced syngas in terms of CO, CO2 and H2 ratio since it enables to set the stoichiometric number M in the here described range.

[0054] Description of the preferred embodiments

[0055] Preferably, said electrolysis unit 4 comprises solid-oxide electrolysis cells (SOECs).

[0056] According to different embodiments, said stream 2 may be a flue gas, an industrial waste gas, a stream of air-captured CO2, and / or a stream of biogenic CO2.

[0057] According to another embodiment, said steam-containing stream 29 taken from the MeOH synthesis loop is a process stream.

[0058] According to a preferred embodiment, said cathode-side stream 5 is obtained by passing said water-containing stream 3 and at least part of said stream 2 through said electrolysis unit 4. In this embodiment, said electrolysis unit 4 is a co- electrolysis unit of the water-containing stream 3 and of said part of said stream 2.

[0059] Preferably, any remaining part 43 of said stream 2 containing CO2 is arranged to by-pass said electrolysis unit 4 and to mix with said cathode-side stream 5 and / or said syngas 12 in order to obtain a desired molar ratio M, such molar ratio M being defined as:

[0060] M = (H2- CO2) / (CO+CO2).

[0061] Said desired molar ratio M is preferably comprised from 1.90 to 2.15, more preferably from 1.95 to 2.10.

[0062] According to a preferred embodiment, said one or more indirect heat exchanger(s) 7, 8, 32, 33 provide a heat input to said one or more distillation column(s) 16, 17, and / or to said MeOH synthesis loop 14, and / or to said electrolysis unit 4.

[0063] According to another embodiment, said heat input is a direct heat input.

[0064] Preferably, said cathode-side stream 5 and optionally said anode-side stream 6 exchange heat with a process fluid or process fluids of said one or more distillation column(s) 16, 17, and / or of said MeOH synthesis loop 14, and / or of said electrolysis unit 4 in said one or more indirect heat exchanger(s) 7, 8.

[0065] In the present description “direct” means that there is no (intermediate) heatexchanging medium / media that transfers heat from the cathode-side stream 5 and / or said anode-side stream 6 to said process fluid or process fluids.

[0066] According to another embodiment, said heat input is an indirect heat input.

[0067] Preferably, said cathode-side stream 5 and optionally said anode-side stream 6 exchange heat with one or more heat-exchanging medium / media (such as water or steam) in said one or more indirect heat exchanger(s) 7, 8. Said one or more heat-exchanging medium / media further exchange(s) heat with a process fluid or process fluids of said one or more distillation column(s) 16, 17, and / or of said MeOH synthesis loop 14, and / or of said electrolysis unit 4 in one or more further indirect heat exchanger(s).

[0068] Preferably, said one or more distillation column(s) 16, 17 is / are a topping column

[0069] 16 and / or a refining column 17.

[0070] According to still another embodiment, said one or more distillation column(s) 16,

[0071] 17 is at least a topping column 16 comprising at least a bottom boiler.

[0072] Preferably, said bottom boiler is said one or more indirect heat exchanger(s) 7, 8, or is in a heat-exchanging relationship with said one or more indirect heat exchanger(s) 7, 8, for providing said heat input to said topping column 16.

[0073] More preferably, said process comprises:

[0074] (f) feeding said crude methanol stream 15 to the topping column 16 to separate volatile compounds 18, such as H2, CO, CO2, and a bottom MeOH solution 19 as a refined MeOH product or topped MeOH product from said crude methanol stream 15.

[0075] According to a further embodiment, said one or more distillation column(s) 16, 17 is at least a refining column 17 comprising at least a bottom boiler. Preferably, said distillation columns 16, 17 may be more than two, e.g. from two to four refining columns 17.

[0076] Preferably, said bottom boiler is said one or more indirect heat exchanger(s) 7, 8, or is in a heat-exchanging relationship with said one or more indirect heat exchanger(s) 7, 8, for providing said heat input to said refining column 17.

[0077] Even more preferably, said process comprises a topping column 16 and a downstream refining column 17; and said process comprises:

[0078] (g) feeding said bottom MeOH solution 19 separated in the topping column 16 to the refining column 17; and

[0079] (h) distilling said bottom MeOH solution 19 to obtain a bottom water stream 20, a stream of fusel oil 21 , and a MeOH stream 22 as a refined MeOH product.

[0080] In the present description “fusel oil” means a mixture of heavier compounds comprising water, higher alcohols, methanol, and alkanes.

[0081] According to further embodiments, said one or more indirect heat exchanger(s) 7, 8 provide said heat input to a boiler feed water which is used as cooling medium in heat-exchange bodies 23, 24 of an isothermal catalytic converter of the MeOH synthesis loop 14 and / or of the electrolysis unit 4.

[0082] According to further embodiments, said one or more indirect heat exchanger(s)

[0083] 7, 8 provide said heat input to steam produced in heat-exchange bodies 23, 24 of an isothermal catalytic converter of the MeOH synthesis loop 14 and / or of the electrolysis unit 4.

[0084] According to another embodiment, at least one of said one or more indirect heat exchanger(s) 32, 33 is a feed-effluent heat exchanger of the electrolysis unit 4.

[0085] The MeOH synthesis loop preferably comprises a catalytic converter provided with a fixed bed that operates in the pressure range comprised from 50 bar to 120 bar and in a temperature range comprised from 200 °C to 300 °C.

[0086] Said electrolysis unit 4 or said SOECs is / are preferably powered by a renewable energy source 25.

[0087] Said electrolysis unit 4 (e.g. comprising SOECs) is more preferably operated in exothermic mode.

[0088] According to an embodiment of the plant, said one or more distillation column(s) 16, 17 is at least a topping column 16 and / or at least a refining column 17 comprising at least a bottom boiler.

[0089] Preferably, said bottom boiler is said one or more indirect heat exchanger(s) 7,

[0090] 8, or is in a heat-exchanging relationship with said one or more indirect heat exchanger(s) 7, 8, for providing said heat input to said at least one topping column 16 and / or at least one refining column 17.

[0091] According to another embodiment, said one or more indirect heat exchanger(s) 7, 8 provide said heat input to a circulating water stream in order to generate process steam in a saturator column or film saturator column fed with said stream 2 containing CO2 and optional CO and / or said portion of syngas 30 and with said bottom water stream 20 of the distillation column 16, 17 as a source of water.

[0092] The plant 1 preferably comprises at least one indirect heat exchanger 8 in a heatexchanging relationship with said cathode-side stream 5 and at least one indirect heat exchanger 7 in a heat-exchanging relationship with said anode-side stream 6.

[0093] According to an embodiment, said plant 1 comprises a line for passing at least part of said stream 2 through said electrolysis unit 4 to obtain said cathode-side stream 5, said electrolysis unit 4 being a co-electrolysis unit of the watercontaining stream 3 and of said stream 2.

[0094] According to another embodiment, said plant comprises a by-pass line of said electrolysis unit 4 arranged for mixing any remaining part 43 of said stream 2 containing CO2 with said cathode-side stream 5 and / or said syngas 12 in order to obtain a desired molar ratio M. In other words, said by-pass line connects a point upstream of said electrolysis unit 4 to a point downstream of said unit 4 so that said remaining part 43 is not subjected to electrolysis in the electrolysis unit 4. Said molar ratio M is defined as before.

[0095] The plant preferably comprises a renewable energy source 25 powering said electrolysis unit 4 or solid-oxide electrolysis cells (SOECs).

[0096] The renewable energy source 25 preferably comprises one or more photovoltaic panel(s) and / or wind turbine(s) and / or water turbine(s).

[0097] Description of the figures

[0098] Figures from 1.A to 5 show schematic process layouts of a methanol plant according to preferred embodiments of the present invention.

[0099] Detailed description of the preferred embodiments

[0100] Fig. 1 .A shows a plant 1 for the synthesis of methanol (MeOH) according to a first preferred embodiment of the present invention. Such plant 1 comprises an electrolysis unit 4, one or more indirect heat exchanger(s) 7, 8, 32, 34, a condenser 26, a compressor 27, a MeOH synthesis loop 14, and one or more distillation column(s) 16, 17.

[0101] A water-containing stream 3 is passed through a second heat exchanger 33 and then through a further second heat exchanger 35, and is then fed to the electrolysis unit 4.

[0102] The electrolysis unit 4 is powered by an electrical source (e.g., a renewable energy source 25) to produce - by electrolysis - a cathode-side stream 5 comprising hydrogen (H2) and optional steam, and an anode-side stream 6 comprising oxygen O2.

[0103] The anode-side stream 6 is heat exchanged in a first heat exchanger 32 and then in the indirect heat exchanger 7 so that an anode-side heat-exchanged stream 10 is obtained. This stream 10 can be exported from the plant.

[0104] The cathode-side stream 5 is cooled - by indirect heat exchange - in the second heat exchanger 33 with the water-containing stream 3, and then it goes through the indirect heat exchanger 8 so that a cathode-side heat-exchanged stream 9 is obtained.

[0105] The cathode-side heat-exchanged stream 9 is then fed to a condenser 26, wherein it is separated in a liquid condensate product 11 containing condensed steam and a syngas 12.

[0106] Carbon dioxide (CO2) and optional carbon monoxide (CO) is / are added to said cathode-side stream 5 and / or said syngas 12 through a separate stream 2.

[0107] A first portion 30 of said syngas 12 may be recycled as feed the co-electrolysis unit 4 after compression in a recycle compressor 36. A second portion 37 - having the same composition of said first portion 30 being split from the same stream of syngas 12 - is compressed in a compressor 27 to obtain a compressed syngas 13. Multistage compression in two or more compressors 27, 28 - see e.g. Fig. 2 - may be used to obtain said compressed syngas 13. A portion of said compressed syngas 13 may be used as feed for the electrolysis unit 4.

[0108] The compressed syngas 13 is then fed to the MeOH synthesis loop 14 wherein catalytic conversion of said compressed syngas 13 into MeOH is carried out under methanol synthesis conditions. A crude methanol stream 15 is thus obtained as an effluent of the MeOH synthesis loop 14. A steam-containing stream 29 may be taken from the MeOH synthesis loop 14 as feed for the electrolysis unit 4.

[0109] Said crude methanol stream 15 is distilled in one or more distillation column(s) 16, 17 to give a refined MeOH product 19, 22. Distillation in said one or more distillation column(s) 16, 17 may provide also a stream of volatile compounds 18, a stream of fusel oil 21 , and a bottom water stream 20. Said bottom water stream 20 may be used as feed for the electrolysis unit 4.

[0110] In this embodiment, said one or more indirect heat exchanger(s) 7, 8 provide a heat input to said one or more distillation column(s) 16, 17, either a direct or an indirect heat input.

[0111] More precisely, said one or more distillation column(s) 16, 17 may comprise at least a bottom boiler. Said bottom boiler may be embodied by said one or more indirect heat exchanger(s) 7, 8, or it may be in a heat-exchanging relationship with said one or more indirect heat exchanger(s) 7, 8, for providing said heat input to said distillation column(s) 16, 17. In particular, a bottom stream 38 is withdrawn from the distillation column(s) 16, 17 and sent to said one or more indirect heat exchanger(s) 7, 8 as one or more first stream(s) 39, 40 for exchanging heat with said cathode-side stream 5 and said anode-side stream 6. After heat exchange, one or more heat-exchanged first stream(s) 41 , 42 are returned to the distillation column(s) 16, 17. Fig. 1.B shows a plant 1 for the synthesis of methanol (MeOH) according to a second preferred embodiment of the present invention.

[0112] As a difference with respect to the embodiment of Fig. 1 .A, at least part of a stream 2 containing CO2 as main component is passed through a first heat exchanger 34 and is then fed to the electrolysis unit 4 together with the watercontaining stream 3.

[0113] In the electrolysis unit 4, said cathode-side stream 5 is produced by coelectrolysis of the water-containing stream 3 and of said separate stream 2. The cathode-side stream 5 thus comprises steam, CO2, CO, and H2.

[0114] Any remaining part 43 of said stream 2 is arranged to by-pass said electrolysis unit 4 and to mix with said cathode-side stream 5 and / or said syngas 12 in order to obtain a desired molar ratio M.

[0115] According to a preferred embodiment, said first heat exchanger 34 may be a feedeffluent heat exchanger, so that the heat exchangers numbered with 32 and 34 may be the same apparatus wherein said anode-side stream 6 and said CO2- containing stream 2 exchange heat by indirect heat exchange.

[0116] Fig. 2 shows a plant 1 for the synthesis of methanol (MeOH) according to a third preferred embodiment of the present invention. This plant differs from the plant of Fig. 1.B in that the distillation columns comprise at least a topping column 16 and at least a refining column 17.

[0117] The crude methanol stream 15 is fed to the topping column 16 to separate volatile compounds 18 and a bottom MeOH solution 19 from said crude methanol stream 15. The bottom MeOH solution 19 is fed to the refining column 17, wherein said bottom MeOH solution 19 is distilled to obtain a bottom water stream 20, a stream of fusel oil 21 , and a MeOH stream 22.

[0118] A bottom stream 38 is withdrawn from the topping column 16 and sent to said indirect heat exchangers 7, 8 as first streams 39, 40 for exchanging heat with said cathode-side stream 5 and said anode-side stream 6. After heat exchange, heat-exchanged first streams 41 , 42 are returned to the topping column 16.

[0119] Fig. 3 shows a plant 1 for the synthesis of methanol (MeOH) according to a fourth preferred embodiment of the present invention. This plant differs from the plant of Fig. 2 in that the bottom stream 38 is withdrawn from the at least one refining column 17 and sent to said indirect heat exchangers 7, 8 as first streams 39, 40 for exchanging heat with said cathode-side stream 5 and said anode-side stream 6. After heat exchange, heat-exchanged first streams 41 , 42 are returned to the refining column 17.

[0120] Fig. 4 shows a plant 1 for the synthesis of methanol (MeOH) according to a fifth preferred embodiment of the present invention. This plant differs from the plant of Fig. 1 .B in that said one or more indirect heat exchanger(s) 7, 8 provide a heat input to the MeOH synthesis loop 14 and, in particular, to a boiler feed water which is used as cooling medium in an isothermal catalytic converter of the MeOH synthesis loop and / or to superheat steam produced by an isothermal catalytic converter of the MeOH synthesis loop. More precisely, said one or more indirect heat exchanger(s) 7, 8 provide said heat input the boiler feed water which is used as cooling medium to one or more heat-exchange bodies 23 of the catalytic converter and / or to superheat the steam produced by the isothermal catalytic converter of the MeOH synthesis loop.

[0121] Fig. 5 shows a plant 1 for the synthesis of methanol (MeOH) according to a sixth preferred embodiment of the present invention. This plant differs from the plant of Fig. 1 .B and of Fig. 4 in that said one or more indirect heat exchanger(s) 7, 8 provide a heat input to the co-electrolysis unit 4 and, in particular, to one or more heat-exchange bodies 24 of the electrolysis unit 4. LIST OF THE REFERENCE SIGNS

[0122] 1 plant for the synthesis of methanol

[0123] 2 stream containing carbon dioxide and optional carbon monoxide

[0124] 3 water-containing stream, e.g. steam-containing stream

[0125] 4 electrolysis unit, preferably co-electrolysis unit

[0126] 5 cathode-side stream

[0127] 6 anode-side stream

[0128] 7 indirect heat exchanger

[0129] 8 indirect heat exchanger

[0130] 9 cathode-side heat-exchanged stream

[0131] 10 anode-side heat-exchanged stream

[0132] 11 liquid condensate product

[0133] 12 syngas

[0134] 13 compressed syngas

[0135] 14 MeOH synthesis loop

[0136] 15 crude methanol stream

[0137] 16 distillation column, in particular topping column

[0138] 17 distillation column, in particular refining column

[0139] 18 volatile compounds

[0140] 19 refined MeOH product, in particular bottom MeOH solution 20 bottom water stream

[0141] 21 stream of fusel oil

[0142] 22 refined MeOH product, in particular MeOH stream

[0143] 23 heat-exchange bodies of the catalytic converter

[0144] 24 heat-exchange bodies of the co-electrolysis unit

[0145] 25 renewable energy source

[0146] 26 condenser

[0147] 27 compressor, preferably main compressor of the MeOH synthesis loop

[0148] 28 compressor

[0149] 29 steam-containing stream

[0150] 30 portion of syngas

[0151] 31 portion of compressed syngas

[0152] 32 first heat exchanger, preferably first feed-effluent heat exchanger

[0153] 33 second heat exchanger, preferably second feed-effluent heat exchanger

[0154] 34 first heat exchanger

[0155] 35 second heat exchanger

[0156] 36 recycle compressor

[0157] 37 second portion of syngas

[0158] 38 bottom stream

[0159] 39 first stream first stream heat-exchanged first stream heat-exchanged first stream remaining part of stream 2

Claims

CLAIMS1 ) A process for the synthesis of methanol (MeOH) comprising the following steps:(a) passing a water-containing stream (3) through an electrolysis unit (4) to produce a cathode-side stream (5) comprising hydrogen (H2) and an anode-side stream (6) comprising oxygen (O2);(b) heat-exchanging said cathode-side stream (5) and optionally said anodeside stream (6) in one or more indirect heat exchanger(s) (7, 8, 32, 33) to obtain a cathode-side heat-exchanged stream (9) and optionally an anode-side heat-exchanged stream (10);(c) condensing said cathode-side heat-exchanged stream (9) to separate a liquid condensate product (11 ) and a syngas (12); said cathode-side stream (5) and / or said syngas (12) comprise carbon dioxide (CO2) and optional carbon monoxide (CO) added through a separate stream (2);(d) compressing said syngas (12) in a compressor (27, 28) and then feeding compressed syngas (13) to a MeOH synthesis loop (14) wherein catalytic conversion of said compressed syngas (13) into MeOH is carried out under methanol synthesis conditions, thus obtaining a crude methanol stream (15);(e) distilling said crude methanol stream (15) in one or more distillation column(s) (16, 17) to give a refined MeOH product (19, 22); said process further comprising:(i) recycling at least a portion of at least one of:(A) a portion (31 ) of said compressed syngas (13); and / or(B) a bottom water stream (20) of a distillation column (16, 17); and / or(C) optionally a steam-containing stream (29) taken from the MeOH synthesis loop (14); and / or optionally a portion (30) of said syngas (12); as feed to the electrolysis unit (4).2) The process according to claim 1 , wherein said cathode-side stream (5) is obtained by passing said water-containing stream (3) and at least part of said stream (2) through said electrolysis unit (4); said electrolysis unit (4) being a co-electrolysis unit of the water-containing stream (3) and of said part of said stream (2); preferably said electrolysis unit (4) comprising solid-oxide electrolysis cells (SOECs).3) The process according to claim 2, wherein any remaining part (43) of said stream (2) containing CO2 is arranged to by-pass said electrolysis unit (4) and to mix with said cathode-side stream (5) and / or said syngas (12) in order to obtain a desired molar ratio M, such molar ratio M being defined as:M = (H2- CO2) / (CO+CO2).4) The process according to claim 3, wherein said desired molar ratio M is comprised from 1 .90 to 2.15, preferably from 1 .95 to 2.10.5) The process according to any of the previous claims, wherein said one or more indirect heat exchanger(s) (7, 8, 32, 33) provide a heat input to said one or more distillation column(s) (16, 17), and / or to said MeOH synthesis loop (14), and / or to said electrolysis unit (4).6) The process according to claim 5, wherein said heat input is a direct heat input, said cathode-side stream (5) and optionally said anode-side stream (6) exchanging heat with a process fluid or process fluids of said one or more distillation column(s) (16, 17), and / or of said MeOH synthesis loop (14),and / or of said electrolysis unit (4) in said one or more indirect heat exchanger(s) (7, 8).7) The process according to claim 5, wherein said heat input is an indirect heat input, said cathode-side stream (5) and optionally said anode-side stream (6) exchanging heat with one or more heat-exchanging medium / media, such as water or steam, in said one or more indirect heat exchanger(s) (7, 8), and wherein said one or more heat-exchanging medium / media further exchange(s) heat with a process fluid or process fluids of said one or more distillation column(s) (16, 17), and / or of said MeOH synthesis loop (14), and / or of said electrolysis unit (4) in one or more further indirect heat exchanger(s).8) The process according to any of the previous claims, wherein said one or more distillation column(s) (16, 17) is a topping column (16) and / or a refining column (17).9) The process according to any of the previous claims, wherein said one or more indirect heat exchanger(s) (7, 8) provide said heat input to a boiler feed water which is used as cooling medium in heat-exchange bodies (23, 24) of an isothermal catalytic converter of the MeOH synthesis loop (14) and / or of the electrolysis unit (4).10) The process according to any of the previous claims, wherein said one or more indirect heat exchanger(s) (7, 8) provide said heat input to a circulating water stream in order to generate process steam in a saturator column or film saturator column fed with said stream (2) containing carbon dioxide (CO2) and optional carbon monoxide (CO) and / or said portion of syngas (30) and with said bottom water stream (20) of the distillation column (16, 17) as a source of water.11 ) The process according to any of the previous claims, wherein at least one of said one or more indirect heat exchanger(s) (32, 33) is a feed-effluent heat exchanger of the electrolysis unit (4).12) The process according to any of the previous claims, wherein said electrolysis unit (4) is powered by a renewable energy source (25) and is operated in exothermic mode.13) A plant (1 ) for the synthesis of methanol (MeOH) comprising:- an electrolysis unit (4) fed with a water-containing stream (3) and arranged to produce a cathode-side stream (5) comprising hydrogen (H2) and an anode-side stream (6) comprising oxygen (O2);- one or more indirect heat exchanger(s) (7, 8, 32, 33) in a heatexchanging relationship with said cathode-side stream (5) and optionally said anode-side stream (6) to obtain a cathode-side heat-exchanged (9) stream and optionally an anode-side heat-exchanged stream (10);- a condenser (26) of said cathode-side heat-exchanged stream (9) to separate a liquid condensate product (11 ) and a syngas (12);- a line for adding carbon dioxide (CO2) and optional carbon monoxide (CO) to said cathode-side stream (5) and / or said syngas (12) through a separate stream (2);- at least one compressor (27, 28) for compressing said syngas (12);- at least a MeOH synthesis loop (14) fed with compressed syngas (13) and arranged for a catalytic conversion of said compressed syngas (13) into MeOH under methanol synthesis conditions, thus obtaining a crude methanol stream (15);- one or more distillation column(s) (16, 17) for distilling the crude methanol stream (15) to give a refined MeOH product (19, 22);- one or more lines for recycling at least a portion of at least one of:(A) a portion (31 ) of said compressed syngas (13); and / or(B) a bottom water stream (20) of a distillation column (16, 17); and / or(C) optionally a steam-containing stream (29) taken from the MeOH synthesis loop (14); and / or optionally a portion (30) of said syngas (12); as feed to the electrolysis unit (4).14) The plant according to claim 13, comprising a line for passing at least part of said stream (2) through said electrolysis unit (4) to obtain said cathode-side stream (5); said electrolysis unit (4) being a co-electrolysis unit of the watercontaining stream (3) and of said part of said stream (2).15) The plant according to claim 14, comprising a by-pass line of said electrolysis unit (4) arranged for mixing any remaining part (43) of said stream (2) with said cathode-side stream (5) and / or said syngas (12) in order to obtain a desired molar ratio M, such molar ratio M being defined as:M = (H2- CO2) / (CO+CO2). preferably said desired molar ratio M being comprised from 1.90 to 2.15, more preferably from 1.95 to 2.10.16) The plant (1 ) according to any of claims 13-15, wherein said electrolysis unit (4) comprises solid-oxide electrolysis cells (SOECs); said plant preferably comprising a renewable energy source (25) powering said electrolysis unit (4).

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