WO2021250002A2

WO2021250002A2 - Thermal oxidative coupling of methane process using renewable energy with possible co-production of hydrogen

Info

Publication number: WO2021250002A2
Application number: PCT/EP2021/065293
Authority: WO
Inventors: Romuald COUPAN; Christophe Thille
Original assignee: Total Se
Priority date: 2020-06-10
Filing date: 2021-06-08
Publication date: 2021-12-16
Also published as: WO2021250002A3

Abstract

The disclosure relates in its first aspect to a process for converting methane into chemicals. The process comprises the steps of (a) providing a first stream (1; 7) comprising methane; (b) providing a second stream (13) which is an oxygen-rich stream; (c) contacting said first stream (1; 7) with said second stream (13) under oxidation reaction conditions to obtain a third stream (15) comprising chemicals and water; (d) performing at least one separation step on said third stream (15) to recover a water stream (21) and a fourth stream (39) comprising chemicals; (e) subjecting said water stream (21) to an oxidation reaction under first reaction conditions to produce at least an oxygen stream (29), wherein the oxygen stream (29) is recycled into the second stream (13). In its second aspect, the disclosure relates to an installation for working the process of the first aspect.

Description

THERMAL OXIDATIVE COUPLING OF METHANE PROCESS USING RENEWABLE ENERGY WITH POSSIBLE CO-PRODUCTION OF HYDROGEN

Field of the disclosure

The present disclosure relates to the production of chemicals from methane.

Technical background

Natural gas is an available fossil resource mainly composed of light alkanes. The valorisation of natural gas as feedstock for the petrochemical industry is of interest as natural gas is cheap at source. Accordingly, the conversion of light alkanes into products like syngas, methanol, olefins or aromatics is highly valuable.

Oxygen-based processes are the current practices for natural gas conversion. However, processes involving the presence of oxygen leads unavoidably to the formation of carbon dioxide and water in the final product streams. The carbon efficiency of any processes contacting alkanes and oxygen does not exceed 75%.

In recent times, the Oxidative Coupling of Methane (OCM) was commercialized. It consists of a direct catalytic oxygen-based process to convert methane into ethylene as shown in the following chemical equation:

2 CH₄ + 0₂ ®· C2H4 + 2 H2O

All oxidative conversion processes imply the formation of carbon dioxide and water in the final product streams.

CH4 + 2 0₂ ®· C0₂ + 2 H2O

Further to ethylene (C2H₄), carbon dioxide (CO2) and water (H2O) other products generated during an oxidative conversion process of methane (CH₄) are ethane (C2H6), propane (C3H8), propylene (C3H6), C4+ hydrocarbons, and carbon monoxide (CO).

Another drawback for such oxidative coupling of methane is the high exothermicity (DH298_K— 281 kJ/mol).

Overall, with all the side products and under non-catalytic conditions, the selectivity in C2+ hydrocarbons, and in particular into ethylene, is relatively low (about 50%). This requires implementing considerable effort into the separation of those interesting products.

The documents WO2016/160563 and WO 2017/065947 disclose a process in which methane is contacted with oxygen in an oxidative coupling reactor to produce among other ethylene. The carbon dioxide that is formed can be, along with the unreacted methane, redirected in a methanation unit to regenerate methane in the process. Although such configuration reuses a part of the side products (i.e., the carbon dioxide) of the oxidative coupling reaction of methane, other side products such as water are not recycled.

Also, the issue with the formation of carbon oxide and water is then their further transformation into valuable chemicals, such as the conversion of water into hydrogen and the reaction of the hydrogen with the carbon dioxide to form various useful chemicals is highly demanding in energy.

There is, therefore, a need for gas to chemicals processes that are not hampered by the production of carbon oxides and water.

Summary of the disclosure

According to a first aspect, the disclosure provides a process for converting a stream comprising methane into chemicals, said process being remarkable in that it comprises the following steps: a) providing a first stream comprising methane (ChU); b) providing a second stream which is an oxygen-rich (0₂-rich) stream; c) contacting said first stream with the second stream under oxidation reaction conditions to obtain a third stream comprising C2+ hydrocarbons and water, wherein the third stream further comprises one or more carbon oxides selected from carbon dioxide and carbon monoxide; d) performing at least one separation step on the third stream to recover a water stream and a fourth stream comprising C2+ hydrocarbons, and at least one additional separation step to recover a carbon oxides stream; e) subjecting at least a part of the water stream recovered from step (d) to an oxidation reaction under first reaction conditions to produce at least an oxygen stream, wherein the oxygen stream is recycled into the second stream; f) optionally, recovering an ethylene stream from the fourth stream; wherein step (e) is a step of electrochemical carbon oxides conversion with water and step (e) comprises the following sub-steps of providing a carbon oxides stream, putting said carbon oxides stream into contact with at least a part of the water stream; reacting said water stream with said carbon oxides stream under said first reactions conditions to produce said oxygen stream.

The disclosure provides a process wherein the water and the carbon oxides formed during the oxidative coupling of natural gas, in particular methane, are recovered and further transformed into oxygen, which is one of the main reactants of the process. With such a process, both of the main side-products (/.e. water and the carbon oxides) of the oxidative coupling of methane are used efficiently, by recycling them into the oxygen stream that is required to perform the oxidative coupling of methane itself, rendering the whole process cost-effective, since it can increase the carbon efficiency and/or the energy efficiency of the process; while at the same time enhancing the ethylene production.

For example, the oxidation reaction is an anodic oxidation reaction performed under an electrical energy input.

For example, the first reaction conditions comprise an electrical energy input.

With preference, step (e) is a step of electrochemical carbon oxides conversion with water, said electrical energy input has a voltage of at least 0.7 V; preferably, at least 0.9 V, more preferably at least 1.1 V, even more preferably at least 1.3 V, most preferably at least 1.5 V.

With preference, step (e) is a step of electrochemical carbon oxides conversion with water, said electrical energy input has a current density of at least 0.2 A/cm²; preferably, at least 0.4 A/cm²; more preferably, at least 0.6 A/cm²; even more preferably, at least 0.8 A/cm²; most preferably, at least 1.0 A/cm².

With preference, step (e) is a step of electrochemical carbon oxides conversion with water, said electrical energy input has an electrical consumption ranging between 4 and 7 kWh/ton of carbon dioxide consumed, preferably between 4.2 and 6.8 kWh/ton, more preferably between 4.4 and 6.6 kWh/ton.

For example, when step (e) is a step of electrochemical carbon oxides conversion with water, said electrical energy input corresponds to an energy input of at least 700 kJ/mol of carbon dioxide consumed, preferably of at least 750 kJ/mol, more preferably of at least 800 kJ/mol, even more preferably of at least 900 kJ/mol, most preferably of at least 950 kJ/mol, even most preferably of at least 1000 kJ/mol or at least 1100 kJ/mol.

For example, when step (e) is a step of electrochemical carbon oxides conversion with water, said electrical energy input corresponds to an electrical energy input of at least 0.20 kWh/mol of carbon dioxide consumed, preferably of at least 0.22 kWh/mol, more preferably of at least 0.25 kWh/mol, even more preferably of at least 0.26 kWh/mol, most preferably of at least 0.28 kWh/mol . For example, step (a) of providing a first stream comprising methane comprises providing a natural gas comprising methane at a content of at least 75 mol.% based on the total molar content of said natural gas, preferably at least 80 mol.%, more preferably at least 90 mol.%, and even more preferably of at least 95 mol.% of methane based on the total molar content of said natural gas. For example, the first stream is a methane stream.

For example, step (a) of providing a first stream comprising methane comprises a sub-step of purifying the natural gas to remove sulphur and/or nitrogen. Optionally, step (a) of providing a first stream comprising methane comprises a sub-step of purifying the natural gas to remove oxygen, carbon dioxide and/or carbon monoxide. The removal of oxygen, carbon dioxide and/or carbon monoxide is performed when the content of these components is or become too high, for example, due to the presence of a recycling loop.

Advantageously, step (b) of providing a second stream which is an oxygen-rich stream is performed at the start of the process to initiate the conversion of methane into chemicals and is stopped as soon as step (e) recycles at least 50 vol.% of the oxygen-rich stream, preferably at least 70 vol.%, more preferably at least 80 vol.%, even more preferably at least 90 vol.%, most preferably at least 95 vol.%. Even most preferably, step (b) of providing a second stream which is an oxygen-rich stream is performed at the start of the process to initiate the conversion of methane into chemicals and is stopped as soon as step (e) recycles the whole of the oxygen-rich stream.

Even most preferably, a step (g) of subjecting a water stream to an electrolysis step to produce an oxygen-rich (0₂-rich) stream and a hydrogen (H2) stream is performed at the start of the process to initiate the conversion of methane into methanol. With preference, step (g) is performed under the same conditions as the ones described for the electrolysis of step (e).

With preference, step (c) is carried out in the absence of a catalyst. The fact that no catalyst is needed for the oxidation of methane into chemicals in the presence of an oxygen-rich stream allows having a cost-effective and simple process. Besides, there is no need for maintenance of the catalyst, such as activation steps and/or replacement of the catalyst in the reactors due to deactivation. This also suppresses the need for recycling the catalyst.

One or more of the following features can advantageously further define the step (c) of the present process which is carried out in the absence of a catalyst:

- The oxidation reaction conditions of step (c) comprise a temperature ranging between 600°C and 1200°C, preferably between 650°C and 1150°C, more preferably between 600°C and 1100°C, even more preferably between 700°C and 1050°C, most preferably between 750°C and 1000°C.

- The oxidation reaction conditions of step (c) comprise a pressure ranging from 0.1 MPa to 1.0 MPa, preferably between 0.2 MPa and 0.9 MPa, more preferably between 0.3 MPa and 0.8 MPa.

- The oxidation reaction conditions of step (c) comprise an oxygen to methane ratio ranging between 0.02:1 and 0.20:1, preferably between 0.020:1 and 0.15:1; more preferably between 0.025:1 and 0.10:1, and even more preferably between 0.03:1 and 0.06:1.

In this configuration, a carbon oxides stream that is external to the installation must be provided to render possible the transformation of the recovered water into oxygen. It is, however, advantageous that the carbon oxides stream comes from the side product generated in the methane oxidation reactor itself.

With preference, said first reaction conditions comprise one or more of the following:

- a temperature ranging between 180°C and 400°C, preferably between 180°C and 350°C, preferably between 180°C and 300°C, preferably between 180°C and 270°C, preferably between 190°C and 260°C, preferably between 200°C and 250°C, preferably between 210°C and 240°C, more preferably between 220°C and 230°C; and/or

- a pressure ranging between 1.0 MPa and 8.0 MPa, preferably between 1.5 MPa and 7.5 MPa, more preferably between 2.0 MPa and 7.0 MPa.

For example, the sub-step of contacting said water stream with said carbon oxides stream further produces a fifth stream comprising water and C2+ hydrocarbons. Wth preference, the fifth stream is recycled with the third stream.

For example, the C2+ hydrocarbons of the third stream comprising C2+ hydrocarbon and water, and/or of the fourth stream comprising C2+ hydrocarbon, further comprises acetylene and the step (d) of the process further comprises a step of contacting said acetylene with a hydrogen stream to convert acetylene into ethylene and/or ethane.

For example, the third stream further comprises one or more carbon oxides selected from carbon dioxide and carbon monoxide, and the step (d) further comprises at least one additional separation step to recover a carbon oxides stream, said at least one additional separation step comprising a first separation step subjected on the third stream to recover carbon dioxide and a remaining stream comprising C2+ hydrocarbons. Wth preference, the third stream further comprises carbon monoxide, unreacted methane and/or hydrogen, and the process further comprises the following additional separation steps: a) a first separation step conducted on the fourth stream or on the remaining stream when present, to recover a C2+ stream comprising C2+ hydrocarbons and a remaining gaseous stream comprising unreacted methane, carbon monoxide, hydrogen and/or carbon dioxide, and b) a second separation step conducted on the remaining gaseous stream to recover a sixth stream comprising carbon monoxide, carbon dioxide and hydrogen and a seventh stream comprising unreacted methane.

Optionally, the sixth stream is combined with the carbon oxides stream.

Optionally yet, a step of recycling the seventh stream into the first stream is conducted.

For example, the third stream comprising C2+ hydrocarbons and water and/or the fourth stream comprising C2+ hydrocarbons further comprises C3+ hydrocarbons, and step (d) of the process further comprises performing a separation of C3+ hydrocarbons from the third stream and/or the fourth stream, to recover a C3+ hydrocarbons stream.

According to a second aspect, the disclosure provides an installation for carrying out the process for converting a stream comprising methane into chemicals according to the first aspect, said installation is remarkable in that it comprises

- a methane conversion unit;

- a product separation unit;

- an oxygen-production unit; wherein the methane conversion unit, the product separation unit and the oxygen-production unit are fluidically connected in series; the product separation unit being downstream of said methane conversion unit and upstream of said oxygen-production unit; wherein said oxygen-production unit is supplied with an energy input; wherein said installation further comprises at least one line to conduct the oxygen stream exiting said oxygen-production unit to said methane conversion unit; and wherein said oxygen-production unit is a carbon oxides valorisation unit.

With preference, said carbon oxides valorisation unit comprising an electrochemical cell.

Description of the figures

Figure 1 illustrates an installation wherein the oxygen-production unit is a water electrolysis unit. Figure 2 illustrates the installation of the present disclosure, wherein the oxygen- production unit is an electrochemical cell.

Figure 3 illustrates a proton-exchange membrane reactor as an electrochemical cell that can be present in the carbon oxides valorisation unit of the present disclosure.

Detailed description

For the disclosure, the following definitions are given:

The feed stream of the process, i.e. the first stream comprising methane, is a gaseous stream, preferably natural gas and/or other rich-methane hydrocarbon sources. The first stream can be treated in an outside battery limit (OSBL) plant where the majority of one or more selected from sulphur-containing compounds and/or nitrogen are removed. The efficiency of the conversion of the feed stream can further be enhanced by removing oxygen, carbon dioxide and/or carbon monoxide.

Zeolite codes (e.g., MFL.) are defined according to the “Atlas of Zeolite Framework Types", 6^th revised edition, 2007, Elsevier, to which the present application also refers.

The Si/AI atomic ratio corresponds to the content of S1O₂ divided by the content of AI₂O₃ taking into account the fact there are two atoms of aluminium for one atom of silicon. The silicon to aluminium molar ratio (also stated as SAR) corresponds to the molar content of S1O₂ divided by the molar content of AI₂O₃ notwithstanding the proportion of the Si atoms over the Al atoms in the chemical formula of the zeolite. Therefore, the value of the SAR or Si/AI molar ratio always corresponds to twice the value of the Si/AI atomic ratio.

As used herein, the term “C# hydrocarbons”, wherein “#” is a positive integer, is meant to describe all hydrocarbons having # carbon atoms. C# hydrocarbons are sometimes indicated as just C#. Moreover, the term “C#+ hydrocarbons” is meant to describe all hydrocarbon molecules having # or more carbon atoms. Accordingly, the expression “C2+ hydrocarbons” is meant to describe a mixture of hydrocarbons having 2 or more carbon atoms.

The terms "comprising", "comprises" and "comprised of" as used herein are synonymous with "including", "includes" or "containing", "contains", and are inclusive or open-ended and do not exclude additional, non-recited members, elements or method steps. The terms "comprising", "comprises" and "comprised of" also include the term “consisting of”.

The recitation of numerical ranges by endpoints includes all integer numbers and, where appropriate, fractions subsumed within that range (e.g. 1 to 5 can include 1 , 2, 3, 4, 5 when referring to, for example, a number of elements, and can also include 1.5, 2, 2.75 and 3.80, when referring to, for example, measurements). The recitation of endpoints also includes the recited endpoint values themselves (e.g. from 1.0 to 5.0 includes both 1.0 and 5.0). Any numerical range recited herein is intended to include all sub-ranges subsumed therein.

The particular features, structures, characteristics or embodiments may be combined in any suitable manner, as would be apparent to a person skilled in the art from this disclosure, in one or more embodiments.

The process and the installation for carrying out the process will be jointly described by reference to figures 1 and 2.

The disclosure provides a process and an installation for the conversion of natural gas into chemicals, in particular ethylene, and optionally into a mixture of a refinery grade propylene product, namely a mixture of propylene and propane.

The process of the present disclosure is a process for converting a stream comprising methane into chemicals, said process being remarkable in that it comprises the following steps: a) providing a first stream (1; 7) comprising methane; b) providing a second stream 13 which is an oxygen-rich stream; c) contacting said first stream (1 ; 7) with the second stream (13) under oxidation reaction conditions to obtain a third stream (15) comprising C2+ hydrocarbons and water, wherein the third stream (15) further comprises one or more carbon oxides selected from carbon dioxide and carbon monoxide; d) performing at least one separation step on the third stream (15) to recover a water stream (21) and a fourth stream (39) comprising C2+ hydrocarbons, and at least one additional separation step to recover a carbon oxides stream (67); e) subjecting at least a part of the water stream (21) recovered from step (d) to an oxidation reaction under first reaction conditions to produce at least an oxygen stream (29; 113), wherein the oxygen stream (29; 113) is recycled into the second stream (13); f) optionally, recovering an ethylene stream (93) from the fourth stream (39); wherein step (e) is a step of electrochemical carbon oxides conversion with water and step (e) comprises the following sub-steps of providing a carbon oxides stream (67), putting said carbon oxides stream (67) into contact said water stream (21); reacting said water stream (21) with said carbon oxides stream under said first reactions conditions to produce said oxygen stream (113).

For example, the oxidation reaction is an anodic oxidation. The feed stream of the process

The first stream (1, 7) is the feed stream of the process. According to the disclosure, the first stream (1 , 7) is or comprises natural gas. For example, the first stream (1 , 7) is a natural gas comprising methane. For example, the first stream (1, 7) is a natural gas comprising methane at a content of at least 75 mol.% of the total molar content of said natural gas; preferably at least 85 mol.%, more preferably at least 90 mol.%, and even more preferably of at least 95 mol.% of methane.

The first stream (1 , 7) can also comprise C2+ hydrocarbons. The C2+ hydrocarbons present in the first stream (1 , 7) may include, for example, C2-C5 alkanes. As used herein, the term “C2-C5 alkanes” refers to ethane, propane, butane, pentane, or mixtures thereof.

To start the process, the first stream 1 is advantageously injected into a pre-treatment unit 95 of natural gas. The pre-treatment unit 95 can comprise a purification sub-unit 3. In this case, the first stream 1 comprising methane can be subjected to an optional preliminary step of purification to remove one or more selected from sulphur and/or nitrogen. Additionally or alternatively to said optional preliminary step of purification is carried out, it is also preferred, to enhance the conversion of methane, to remove also one or more selected from carbon dioxide, carbon monoxide and/or water. The pre-treatment unit 95 of natural gas may also comprise one or more heat exchangers 9. The purified first stream 7 exiting from the purification sub-unit 3, or the first stream 1 comprising methane, can be conveyed into said one or more heat exchangers 9, to provide a first stream having its temperature adapted to the operating conditions of the methane conversion unit 97 which comprises at least one methane oxidation reactor 11.

It is also advantageous that the first stream 1 comprising methane can be purged within the purification sub-unit 3, to recover a fuel gas stream 5.

Advantageously, the first stream 1 and/or the purified first stream 7 is directed to a heat exchanger 9, for example, arranged within the pre-treatment unit 95 as shown in figures 1 and 2, so that the first stream (1, 7) comprising methane reaches the required temperature for conversion before entering into the methane conversion unit 97. For example, the temperature of the first stream (1, 7) comprising methane is ranging between 600°C and 1200°C, preferably between 650°C and 1150°C, more preferably between 700°C and 1100°C, even more preferably between 750°C and 1000°C.

Conversion of the methane in the methane conversion unit 97 Within the methane conversion unit 85, the first stream (1 , 7) comprising methane enters into the methane oxidation reactor 11 , where the first stream (1, 7) comprising methane is put into contact with a second stream 13 which is an oxygen-rich stream. For example, the second stream 13 comprises at least 75 mol.% of oxygen based on the total molar content of the second stream 13, preferably at least 85 mol.%, more preferably at least 95 mol.%, even more preferably at least 99 mol.%. Most preferably, the second stream 13 comprises only oxygen.

For example, the operating conditions of the methane oxidation reactor 11 comprise a temperature ranging between 600°C and 1200°C, preferably between 650°C and 1150°C, more preferably between 700°C and 1100°C, even more preferably between 750°C and 1000°C, and/or a pressure ranging between 0.1 MPa and 1.0 MPa, preferably between 0.2 MPa and 0.9 MPa, more preferably between 0.3 MPa and 0.8 MPa, even more preferably between 0.4 MPa and 0.7 MPa.

The oxidation of methane into chemicals in the methane oxidation reactor 11 is preferably performed in the absence of a catalyst.

Advantageously, the oxidation of methane into the methane oxidation reactor 11 is performed with oxygen to methane ratio ranging between 0.02:1 and 0.20:1, preferably between 0.020:1 and 0.15:1 ; more preferably between 0.025:1 and 0.10:1, and even more preferably between 0.025:1 and 0.10:1 , more preferably between 0.03:1 and 0.06:1.

The conversion of methane into chemicals provides a third stream 15, comprising C2+ hydrocarbons and water. For example, the third stream 15 can comprise ethylene, ethane, acetylene, propylene, propane, carbon dioxide, carbon monoxide, water, hydrogen and unreacted methane. The conversion of methane is limited to about 10%-15% to ensure a selectivity to C2+ hydrocarbons of at least 50%. As the conversion of methane into chemicals is a thermodynamic based reaction, to increase the selectivity to C2+ hydrocarbons, one way could be to increase the temperature.

The third stream 15 is then conveyed into the product separation unit 99 where it can be processed to recover among other an ethylene stream 93.

Advantageously, step (b) of providing a second stream 13 which is an oxygen-rich stream is performed at the start of the process to initiate the conversion of methane into chemicals and is stopped as soon as step (e) recycles at least 50 vol.% of the oxygen-rich stream. The second stream 13 is a start-up feed of oxygen. More preferably, step (b) of providing a second stream which is an oxygen-rich stream is performed at the start of the process to initiate the conversion of methane into chemicals and is stopped as soon as step (e) recycles the whole of the oxygen-rich stream.

For example, a step (g) of subjecting a water stream to an electrolysis step to produce an oxygen-rich (0₂-rich) stream and a hydrogen (H2) stream is performed at the start of the process to initiate the conversion of methane into methanol. With preference, step (g) is performed under the same conditions as the ones described for the electrolysis of step (e).

Separation of water

The product separation unit 99 can comprise one or more distillation columns, such as a water separator 19 arranged at the inlet of the product separation unit 99. For example, the water separator 19 comprises two or three in-series water separation stages.

The third stream 15 comprising C2+ hydrocarbons and water can be advantageously directed into one or more heat exchangers 17 before entering the product separation unit 99, so that one or more temperature adjusting steps can be performed onto the third stream 15 before it enters the product separation unit 99. The third stream 15 is thus directed into the water separator 19 working at a temperature below 80°C, to recover a fourth stream 39 comprising C2+ hydrocarbons and a water stream 21. The fourth stream 39 comprising C2+ hydrocarbons may also comprise one or more selected from carbon dioxide, carbon monoxide, hydrogen and unreacted methane. The fourth stream 39 comprising C2+ hydrocarbons is a gaseous stream.

Separation of ethylene and optionally of C3+ hydrocarbons

For example, the fourth stream 39 is treated in a CC>2-separator 43 to remove carbon dioxide before performing the one or more further separation steps, and preferably before performing a separation step conducted on the fourth stream 39 through a demethanizer 51 to recover a liquid stream 53 comprising C2+ hydrocarbons and a gaseous stream 55 comprising at least unreacted methane.

The fourth stream 39 can be advantageously directed into one or more heat exchangers 41 before entering the CC separator 43, so that one or more temperature adjusting steps can be performed onto the fourth stream 39 before it enters the CC>2-separator 43

For example, the CC>2-separator 43 can comprise a CC>2-amine absorber that works at a temperature ranging between 30°C and 50°C, preferably between 35°C and 45°C and/or at a pressure ranging between 0.5 MPa and 20.0 MPa, preferably between 1.0 MPa and 10.0 MPa. The amine absorber of the CC>2-separator 43 can optionally be regenerated through an amine regenerator that advantageously works at a temperature comprised between 110°C and 130°C, preferably between 115°C and 125°C and/or at a pressure ranging between 0.10 MPa and 0.20 MPa, preferably between 0.12 MPa and 0.18 MPa. Upon its passage through the CC>2-separator 43, the fourth stream 39 can be isolated from a CC>2-containing stream 45 which can thus be recovered. The remaining stream 47 exiting the CC>2-separator 43 comprises preferably less than 3.0 mol.% of carbon dioxide based on the total molar content of said remaining stream 47, preferably less than 2.0 mol.%, more preferably less than 1.0 mol.%, even more preferably less than 0.1 mol%, most preferably devoid of carbon dioxide.

For example, the demethanizer 51 is a cryogenic distillation column. For example, the operating conditions of the demethanizer 51 comprise a temperature ranging between-120°C and -80°C, preferably between -110°C and -90°C, and/ora pressure ranging between 2.5 MPa and 3.5 MPa.

Optionally, one or more heat exchangers 49 are arranged between the C0₂-separator 43 and the demethanizer 51 , so that one or more temperature adjusting steps can be performed onto the remaining stream 47 before it reaches the demethanizer 51.

The gaseous stream 55 comprising at least unreacted methane further comprises one or more selected from carbon dioxide, carbon monoxide and hydrogen. A further step of recycling the unreacted methane into the first stream (1 , 7) can be then carried out and comprises a sub step of separating unreacted methane from the one or more selected from carbon dioxide, carbon monoxide and hydrogen to provide an unreacted methane stream 61 and a stream 63 comprising carbon monoxide and/or hydrogen. The process may comprise a step of recycling the unreacted methane stream 61 into the first stream (1, 7). This sub-step is performed within a CFU-separator 59. Optionally, the gaseous stream 55 can be directed into one or more heat exchangers 57 before entering the CFU-separator 59, so that one or more temperature adjusting steps can be performed onto the gaseous stream 55 before it enters the CFU- separator 59.

The C0₂-containing stream 45 and/or the stream 63 comprising carbon monoxide and/or hydrogen can exit the product separation unit 99 and be conveyed into a carbon oxides valorisation unit (103; 105) (see details about the carbon oxides valorisation unit (103; 105) in the below sections about respectively the first and second configurations).

The liquid stream 53 comprising C2+ hydrocarbons can be further separated, for example by one or more separation steps that can be carried out by distillation. Thus, it is advantageous that a de-ethanizer 75 is arranged downstream of the demethanizer 51. For example, the de- ethanizer 75 can be a cryogenic distillation column. With preference, the de-ethanizer 75 works under a temperature ranging between -15°C and 10°C, more preferably between -10°C and 5°C, and/or under a pressure ranging between 1.5 MPa and 2.5 MPa. Upon passage of the liquid stream 53 into the de-ethanizer 75, a C3+ hydrocarbons stream 77 is generated and can be optionally recovered. Said C3+ hydrocarbons stream 77 comprises notably refinery grade propylene product, namely a mixture of propylene and propane.

A C2 stream 79 is also recovered. The C2 stream 79 advantageously comprises less than 3 mol.% of C3+ hydrocarbons based on the total molar content of said C2 stream 79, preferably less than 1 mol.%, more preferably less than 0.5 mol.%, even more preferably less than 0.1 mol.%. In an embodiment, the C2 stream is devoid of C3+ hydrocarbons. The C2 stream 79 can, however, comprises acetylene. For example, the C2 stream 79 can comprise at most 15 mol.% of acetylene based on the total molar content of the C2 stream 79, preferably at most 10 mol.%.

An acetylene conversion reactor 83 can be therefore advantageously placed downstream the demethanizer 75. The C2 stream 79 can be optionally directed into one or more heat exchangers 81 before entering the acetylene conversion reactor 89. The acetylene conversion reactor 83 is fed with a hydrogen stream. For example, within the acetylene conversion reactor 83, the acetylene is converted into ethylene and/or ethane at a temperature which is preferably comprised between 30°C and 70°C, more preferably between 35°C and 65°C, even more preferably between 40°C and 60°C, and/or at a pressure which is preferably comprised between 1.0 MPa and 3.0 MPa, more preferably between 1.5 MPa and 2.5 MPa. The conversion of acetylene is total.

A stream 85 comprising ethylene and/or ethane, preferably comprising ethylene and ethane in a molar ratio ranging between 90:10 and 60:40, can thus be obtained and is then conveyed to at least one C2 splitter 89. Optionally, the stream 85 can be directed into one or more heat exchangers 87 before entering the C2 splitter 89, so that one or more temperature adjusting steps can be performed onto stream 85 before it enters the C2 splitter 89. For example, one or more C2 splitters are one or more cryogenic distillation columns. For example, the one or more C2 splitters work under a temperature ranging between -40°C and -20°C, more preferably between -35°C and -25°C, and/or under a pressure ranging between 1.5 MPa and 2.5 MPa, preferably between 1.7 MPa and 2.3 MPa. This allows the removal of the ethane from the C2 hydrocarbons stream 85 to recover an ethylene stream 93 and optionally an ethane stream 91.

Configuration wherein the oxygen-production unit is a water electrolysis unit_(figure 1) At least a part of said water stream 21 recovered from the water separator 19 can be conveyed into an oxygen-production unit 101 which is in this first configuration a water electrolysis unit and which comprises, for example, an electrolysis cell 25. For example, electrolysis cell 25 can be any state-of-the-art water electrolyser, such as an alkaline electrolysis cell, a proton- exchange membrane electrolysis cell ora solid oxide electrolysis cell. In there, the electrolysis reaction of water can be carried out under pressure conditions ranging from 0.1 MPa to 20.0 MPa, preferably from 1.0 MPa to 15.0 MPa, more preferably from 5.0 MPa to 10.0 MPa, and under temperature conditions ranging from 50°C and 1000°C, preferably from 100°C to 800°C, more preferably from 200°C to 600°C. Thus, thanks to an energy input 27, consisting preferentially of non-fossil renewable energy (i.e. green electricity coming from solar energy and/or wind energy), water is split into an oxygen stream 29 and a hydrogen stream (31; 35; 37).

For example, a voltage is applied in the range of 0.7 and 2.4 V, preferably between 0.9 V and 2.2 V, more preferably between 1.0 V and 2.0 V, and/or a current density ranging between 0.2 and 2.0 A/cm², preferably between 0.3 and 1.9 A/cm² is applied, and/or an electrical consumption ranging between 3 and 6 kWh/m³ of hydrogen produced, preferably between 3.1 and 5.9 kWh/m³ is required.

Thus, in this configuration, the oxidation reaction of water is performed at the anode of the electrolysis cell 25 and generates an oxygen stream 29. The oxygen stream 29 is recycled in the second stream 13 and therefore directed to the methane conversion unit 97. Before being recycled in the second stream 13, the oxygen stream 29 can be optionally dried into a drier system (not shown). This recycling loop increases the efficiency of the process and limits the costs since the oxygen needed to perform the oxidation reaction of methane is generated from one of the by-products (namely water) generated in the methane oxidation reactor 11.

Before being conveyed into the electrolysis cell 25, the water stream 21 can be directed to one or more heat exchangers 23 to be subjected to one or more temperature adjusting steps to reach the required level of temperature for the electrolysis reaction.

The hydrogen stream 31 can be optionally dried in a dryer system 33 to produce a dried hydrogen stream (35; 37). For example, dryer system 33 is a desiccant. For example, the desiccant can be one or more molecular sieves, such as one or more zeolites from the LTA family. Among the LTA family, zeolites from LTA-3A, LTA-4A and/or LTA-5A can be selected. At least a part of the hydrogen stream (31; 37) can be conveyed into the acetylene conversion reactor 83 so that there is no need for an external contribution of hydrogen to the installation of this configuration.

Concerning the carbon oxides valorisation unit 103 of said configuration, the CC>2-containing stream 45 and/or the stream 63 comprising carbon monoxide and/or hydrogen are advantageously combined into a compressor 65 to form a carbon oxides stream 67. The compressor 65 allows to pressurize the CC>2-containing stream 45 and/or the stream 63 comprising carbon monoxide and/or hydrogen at a pressure ranging between 6.0 MPa and 8.0 MPa, preferably between 6.5 MPa and 7.5 MPa. Therefore, the carbon oxides stream 67 exiting the compressor 65 can be preferably pressurized.

The carbon oxides stream 67, comprising carbon dioxide, carbon monoxide and/or hydrogen, can be then directed into a syngas-to-chemicals reactor 71 within the carbon oxides valorisation unit 103. Optionally, the carbon oxides stream 67 can be conveyed into one or more heat exchangers 69, so that one or more temperature adjusting steps can be carried out for the carbon oxides stream 67 to adjust its temperature before it reaches the syngas-to- chemicals reactor 71.

The syngas-to-chemicals reactor 71 is advantageously provided with two catalytic beds arranged in series.

The syngas-to-chemicals reactor 71 is provided with at least one catalyst selected from the list comprising Cu-ZnO/AhCh, ln203/ZrC>2, Fe203/KC>2, ZnO-ZrC>2, ZnGa2C>4, ZnAIO_x, Fe-Zn- Zr ; and with at least one catalyst selected from the list comprising SAPO-34, ZrS/SAPO-34, H-ZSM-5, Zn-ZSM-5, HY, mordenite. With preference, the syngas-to-chemicals reactor 71 is provided with Cu-ZnO/AhCh and SAPO-34. When the syngas-to-chemicals reactor 71 is advantageously provided with two catalytic beds arranged in series, the first catalytic bed is loaded with at least one catalyst selected from the list comprising Cu-ZnO/AhOs, In₂0₃/Zr0₂, Fe₂0₃/K0₂, ZnO-Zr0₂, ZnGa₂0₄, ZnAIO_x, Fe-Zn-Zr; preferably the first catalytic bed is loaded with Cu-ZnO/AhOs; and the second catalytic bed, which is downstream of said first catalytic bed, can be loaded with at least one catalyst selected from the list comprising SAPO-34, ZrS/SAPO-34, H-ZSM-5, Zn-ZSM-5, HY, mordenite; preferably the second catalytic bed is loaded with SAPO-34.

The syngas-to-chemicals reactor 71 is fed by a hydrogen stream, preferably by at least a part of the hydrogen stream (31, 35) exiting the oxygen-production unit 101. The hydrogen stream, external to the installation or coming from the syngas-to-chemicals reactor 71 can be a complementary source of hydrogen in the case of the carbon oxides stream 63 already comprises hydrogen. The molar ratio H2/(CO+CC>2) in the syngas-to-chemicals reactor 71 is thus ranging between 3 and 15, preferably between 5 and 13, more preferably between 7 and 11.

The reaction conditions implemented within the syngas-to-chemicals reactor 71 can advantageously comprise a molar ratio CO/CO2 ranging between 0:1 (absence of carbon monoxide) and 4:1 , preferably between 0.5:1 and 3.5:1; a temperature comprised between 200°C and 400°C, preferably between 210°C and 390°C; more preferably between 250°C and 350°C, and/or a pressure ranging between 0.1 MPa and 0.8 MPa, preferably between 0.2 MPa and 0.7 MPa.

The fifth stream 73 exiting the syngas-to-chemicals reactor 71 comprises therefore at least C2+ hydrocarbons and water, and can also comprise unreacted carbon dioxide, unreacted carbon monoxide and/or unreacted hydrogen. To increase the efficiency of the overall process, the fifth stream 73 can be directed into the product separation unit 99, in particular into the water separator 19, or as shown in figure 1 , be mixed with the third stream 15 exiting from the methane oxidation reactor 11. With this configuration, the carbon oxides, namely carbon dioxide and carbon monoxide, formed in the methane conversion unit 97 in the absence of a catalyst, have not been wasted because they have been further converted into C2+ hydrocarbons thanks to the use of one or more catalysts. Furthermore, the water exiting the methane oxidation reactor 11 has also been recovered and split into hydrogen within the water electrolysis unit which also acts as the oxygen-production unit 101 of the installation.

A configuration wherein the oxygen-production unit is or comprises an electrochemical cell (figure 2)

At least a part of the water stream 21 can be then conveyed into an oxygen-production unit 105 which is also, in this configuration a carbon oxides valorisation unit and which comprises, for example, an electrochemical cell 109. Although the electrochemical cell 109 can work in the absence of catalyst, it is advantageous to have one or more catalysts, such as copper- based catalysts, at the cathode side to orientate the reduction of carbon oxides to methane and C2 hydrocarbons. For example, the cathode of the electrochemical cell 109 can be in copper and acts therefore as a catalyst. Another example of copper-based catalysts can be Cu/ZnO/ZrC>2, preferably with a molar ratio of 0.5/0.2/0.3 respectively. Said electrochemical cell 109 can be preferably a proton-exchange membrane reactor, as represented in figure 3. Before entering into the electrochemical cell 109, the water can pass through one or more heat exchangers 107 so that one or more temperature adjusting steps can be performed. For example, the electrochemical cell 109 can comprise a cathode side and an anode side, the cathode side is separated from the anode side by a proton-conducting membrane such as a proton-conducting membrane made in ceramic materials. A perovskite-type material is an example of ceramic material that can be used as a membrane.

The CC>2-containing stream 45 and/or the stream 63 comprising carbon monoxide and/or hydrogen which have been recovered from the fourth stream 39 (see above section about the separation of ethylene) are advantageously combined into a compressor 65 to form a carbon oxides stream 67. The compressor 65 allows to pressurize the CC containing stream 45 and/or the stream 63 comprising carbon monoxide and/or hydrogen at a pressure ranging between 6.0 MPa and 8.0 MPa, preferably between 6.5 MPa and 7.5 MPa. Therefore, the carbon oxides stream 67 exiting the compressor 65 can be preferably pressurized.

The carbon oxides stream 67, comprising carbon dioxide, carbon monoxide and/or hydrogen, can be then directed into the electrochemical cell 109 of the carbon oxides valorisation unit 105. Optionally, the carbon oxides stream 67 can be conveyed into one or more heat exchangers 69, so that one or more temperature adjusting steps can be carried out in a way that the carbon oxides stream 67 adjusts its temperature before it reaches the electrochemical cell 109.

Upon an energy input 111 , the water from the water stream 21 , is subjected to anodic oxidation to produce an oxygen stream 113, which is recycled into the second stream 13. Before being recycled into the second stream 13, said oxygen stream 113 can be optionally dried in a drier system (not shown). Upon the same energy input 111 , the carbon oxides stream 67 is reduced at the cathode of the electrochemical cell into a fifth stream 73 comprising at least C2+ hydrocarbons and water.

For example, a voltage of at least 0.7 V is applied, preferably at least 0.8 V; and/or a current density of at least 0.2 A/cm², preferably at least 0.3 A/cm², is applied; and/or an electrical consumption ranging between 4 and 7 kWh/ton of carbon dioxide consumed, preferably between 4.1 and 6.9 kWh/ton is required. Said electrical energy input advantageously corresponds to an energy input of at least 700 kJ/mol of carbon dioxide consumed, preferably of at least 750 kJ/mol, more preferably of at least 1000 kJ/mol, even more preferably of at least 1100 kJ/mol.

The fifth stream 73 can also comprise unreacted carbon dioxide, unreacted carbon monoxide and/or unreacted hydrogen. To increase the efficiency of the overall process, the fifth stream 73 can be directed into the product separation unit 99, in particular into the water separator 19, or as shown in figure 2, be mixed with the third stream 15 exiting from the methane oxidation reactor 11. With this configuration, the carbon oxides, namely carbon dioxide and carbon monoxide, formed in the methane conversion unit 97 in the absence of a catalyst, have not been wasted because they have been further converted into C2+ hydrocarbons thanks to carbon oxides valorisation unit 105. Furthermore, the water exiting the methane oxidation reactor 11 has also been recovered since it has served as a reducing agent with regard to the carbon oxides formed in the methane conversion unit 97.

For example, the carbon oxides have been reduced to water and C2+ hydrocarbons within the carbon oxide valorisation unit/oxygen-production unit 105 at a temperature comprised between 180°C and 270°C, preferably 200°C and 250°C, more preferably at a temperature comprised between 210°C and 240°C and/or at a pressure comprised between 1.0 MPa and 8.0 MPa, preferably between 2.0 MPa and 7.0 MPa, more preferably between 3.0 MPa and 5.0 MPa.

Test and determination methods The energy efficiency (EE) is defined as the ratio between the heat value of the products related to the sum of the heat value of the reactants and the net energy consumed in the process.

The carbon efficiency (CE) is defined as the molar ratio between the amount of carbon products related to the carbon reactant consumed. If all the valorizable products that can be generated from the process of the present disclosure are considered, EE and CE are written as equations (I) and (II), where HHV is the higher heating value, F is the molar flow rate, and w_c is the carbon molar fraction.

Example

The advantages of the present disclosure are illustrated by the following examples. However, it is understood that the disclosure is by no means limited to the specific examples. T able 1 shows the results in term of molar flow rate obtained via a simulation thanks to ASPEN PLUS V9 software between installation devoid of any valorisation unit, an installation comprising only a carbon oxide valorisation unit and, an installation comprising an oxygen- production unit which is a water electrolysis unit (not shown). Table 1: Molar flow rate (t/h) of three different installations for carrying out a process for converting a stream comprising methane into chemicals

* A start-up feed of oxygen is provided, corresponding to a molar flow rate of 228 t/h, to launch the process. This start-up feed of oxygen is provided as the second stream 13 of the process of the disclosure. From the results indicated in table 1 , it is clear that the addition of an oxygen production unit which is a water electrolysis unit increases the energy efficiency of the process devoid of such components. The energy efficiency indeed increases from 47% to 66%. The addition of the water electrolysis unit allows the increase of the energy efficiency by producing hydrogen. Indeed, hydrogen haves a heating value of 142 MJ/kg, which is three times higher than the one of the methane feedstock, namely 56 MJ/kg.

Table 2 is also a simulation thanks to ASPEN PLUS V9 software and demonstrates a comparison between an installation comprising a water electrolysis unit and a carbon oxides valorisation unit 103 as shown in figure 1 and an installation comprising a carbon oxides valorisation unit as an oxygen-production unit 105 as shown on figure 2 and thus providing for the electro-conversion of carbon oxides. Table 2: Molar flow rate (t/h) of two different installations for carrying out a process for converting a stream comprising methane into chemicals

* A start-up feed of oxygen is provided, corresponding to a molar flow rate of 228 t/h, to launch the process. This start-up feed of oxygen is provided as the second stream 13 of the process of the disclosure.

The incorporation of carbon oxides valorisation unit 103 to an oxygen-production unit 101 being a water electrolysis unit (as shown in figure 1) further allows increasing the carbon efficiency, as is demonstrated in table 2. Thus, the carbon efficiency increases up to 90% and the energy efficiency up to 78%. The carbons are not lost since carbon dioxide and carbon monoxide are recovered under the form of C2+ hydrocarbons, mainly ethylene.

However, if the carbon oxides valorisation unit can provide for the electro-conversion of carbon oxides, via an electrochemical cell 109 as shown in figure 2, it is, therefore, possible to obtain a maximum carbon efficiency (92%) while having an energy efficiency (54%) which is still better than the energy efficiency that could be obtained from an installation devoid of valorisation unit (47%) (see table 1) or having simply a carbon oxides valorisation unit which does not produce oxygen (52%) (see table 1). Also, the production of ethylene is improved.

Claims

1. A process for converting a stream comprising methane into chemicals, said process being characterized in that it comprises the following steps: a) providing a first stream (1; 7) comprising methane; b) providing a second stream (13) which is an oxygen-rich stream; c) contacting said first stream (1; 7) with the second stream (13) under oxidation reaction conditions to obtain a third stream (15) comprising C2+ hydrocarbons and water, wherein the third stream (15) further comprises one or more carbon oxides selected from carbon dioxide and carbon monoxide; d) performing at least one separation step on the third stream (15) to recover a water stream (21) and a fourth stream (39) comprising C2+ hydrocarbons, and at least one additional separation step to recover a carbon oxides stream (67); e) subjecting at least a part of the water stream (21) recovered from step (d) to an oxidation reaction under first reaction conditions to produce at least an oxygen stream (29; 113), wherein the oxygen stream (29; 113) is recycled into the second stream (13); f) optionally, recovering an ethylene stream (93) from the fourth stream (39); wherein step (e) is a step of electrochemical carbon oxides conversion with water and step (e) comprises the following sub-steps of providing a carbon oxides stream (67), putting said carbon oxides stream (67) into contact at least a part of the water stream (21); reacting said water stream (21) with said carbon oxides stream under said first reactions conditions to produce said oxygen stream (113).

2. The process according to claim 1, characterized in that the oxidation reaction is an anodic oxidation reaction performed under an electrical energy input (27; 111).

3. The process according to claim 1 or 2, characterized in that the sub-step of contacting said water stream (21) with said carbon oxides stream further produces a fifth stream (73) comprising water and C2+ hydrocarbons.

4. The process according to claim 3, characterized in that the fifth stream (73) is recycled with said third stream (15).

5. The process according to any one of claims 1 to 4, characterized in that said first reaction conditions comprise a temperature ranging between 180°C and 400°C.

6. The process according to any one of claims 1 to 5, characterized in that said first reaction conditions comprise a pressure ranging between 1.0 MPa and 8.0 MPa.

7. The process according to any one of claims 1 to 6, characterized in that the C2+ hydrocarbons of the third stream (15) comprising C2+ hydrocarbon and water, and/or of the fourth stream (39) comprising C2+ hydrocarbons, further comprises acetylene and the step (d) of the process further comprises a step of contacting said acetylene with a hydrogen stream (38) to convert acetylene into ethylene and/or ethane.

8. The process according to any one of claims 1 to 7, characterized in that the third stream (15) further comprises one or more carbon oxides selected from carbon dioxide and carbon monoxide, and in that step (d) further comprises at least one additional separation step to recover a carbon oxides stream (67), said at least one additional separation step comprising a first separation step subjected on said third stream (15) to recover carbon dioxide and a remaining stream (47) comprising C2+ hydrocarbons.

9. The process according to claim 8 characterized in that the third stream (15) further comprises carbon monoxide, unreacted methane and/or hydrogen, and the process further comprises the following additional separation steps: a) a first separation step conducted on the fourth stream (39) or on the remaining stream (47) when present, to recover a C2+ stream (53) comprising C2+ hydrocarbons and a remaining gaseous stream (55) comprising unreacted methane, carbon monoxide, hydrogen and/or carbon dioxide, and b) a second separation step conducted on the remaining gaseous stream (55) to recover a sixth stream (63) comprising carbon monoxide, carbon dioxide and hydrogen and a seventh stream (61) comprising unreacted methane.

10. The process according to claim 9, characterized in that said sixth stream (63) is combined with the carbon oxides stream (67).

11. The process according to claim 9 or 10, characterized in that a step of recycling said seventh stream (61) into the first stream (1; 7) is conducted.

12. The process according to any one of claims 1 to 11 , characterized in that the third stream (15) comprising C2+ hydrocarbons and water, and/or the fourth stream (39) comprising C2+ hydrocarbons, further comprises C3+ hydrocarbons, and in that the step (d) of the process further comprises performing a separation of C3+ hydrocarbons from the third stream (15) and/or the fourth stream (39), to recover a C3+ hydrocarbons stream (77).

13. The process according to any one of claims 1 to 12, characterized in that step (c) is carried out in the absence of a catalyst.

14. The process according to claim 13, characterized in that, the oxidation reaction conditions of step (c) comprise a temperature ranging between 600°C and 1200°C, preferably between 750°C and 1000°C.

15. The process according to claim 13 or 14, characterized in that the oxidation reaction conditions of step (c) comprise a pressure ranging from 0.1 MPa to 1.0 MPa.

16. The process according to any one of claims 13 to 15, characterized in that the oxidation reaction conditions of step (c) comprise an oxygen to methane ratio ranging between 0.02:1 and 0.20:1 , preferably between 0.03:1 and 0.06:1.

17. The process according to any one of claims 1 to 16, characterized in that step (a) of providing a first stream comprising methane comprises providing a natural gas comprising methane at a content of at least 75 mol.% of the total molar content of said natural gas.

18. The process according to any one of claims 1 to 17, characterized in that step (a) of providing a first stream comprising methane comprises a sub-step of purifying the natural gas to remove sulphur.

19. The process according to any one of claims 1 to 18, characterized in that step (a) of providing a first stream comprising methane comprises a sub-step of purifying the natural gas to remove nitrogen.

20. Installation for carrying out the process for converting a stream comprising methane into chemicals according to any one of claims 1 to 19, said installation being characterized in that it comprises - a methane conversion unit (97);

- a product separation unit (99);

- an oxygen-production unit (101; 105); wherein the methane conversion unit (97), the product separation unit (99) and the oxygen-production unit (101; 105) are fluidically connected in series; the product separation unit (99) being downstream of said methane conversion unit (97) and upstream of said oxygen-production unit (101; 105); wherein said oxygen-production unit (101; 105) is supplied with an energy input (27; 111); wherein said installation further comprises at least one line to conduct the oxygen stream (29; 113) exiting said oxygen-production unit (101; 105) to said methane conversion unit (97); and wherein said oxygen-production unit (105) is a carbon oxides valorisation unit.

21. Installation according to claim 20, characterized in that said carbon oxides valorisation unit comprising an electrochemical cell (109).