WO2023126620A1

WO2023126620A1 - Method of producing methanol

Info

Publication number: WO2023126620A1
Application number: PCT/GB2022/053183
Authority: WO
Inventors: Kar Chi YIU; Guangyong Xiong; Lijun Zhang; Liangping HU; Erqiang SU; Zhenpeng YU; Peng Zhang; Ling Zhong
Original assignee: Johnson Matthey Davy Technologies Limited; Johnson Matthey (Shanghai) Catalyst Co., Ltd; Johnson Matthey Clean Energy Technologies (Beijing) Co., Ltd
Priority date: 2021-12-30
Filing date: 2022-12-13
Publication date: 2023-07-06
Also published as: CN116375560A

Abstract

A method of producing methanol, the method comprising: providing a syngas comprising carbon dioxide, carbon monoxide, hydrogen and sulphur-containing gas; forming a sulphur-depleted syngas by removing at least some of the sulphur-containing gas from the syngas without removing more than 50 vol. % of the carbon dioxide from the syngas, the 50 vol. % based on the total volume of carbon dioxide in the syngas; converting at least a portion of the sulphur-depleted syngas to methanol; and recovering the methanol.

Description

METHOD OF PRODUCING METHANOL

FIELD OF THE INVENTION

The invention relates to a method of producing methanol.

BACKGROUND OF THE INVENTION

Methanol can be produced from syngas, a fuel gas mixture containing, inter alia, carbon monoxide and hydrogen. Carbon monoxide and hydrogen in the syngas react over a catalyst to produce methanol. Today, the most widely used catalyst is a mixture of copper and zinc oxides, supported on alumina, as first used by ICI in 1966. At 5-10 MPa (50- 100 atm) and 250 °C (482 °F), the reaction is characterized by high selectivity (>99.8%):

CO + 2H₂ CH₃OH

Typical syngas contains carbon dioxide in addition to carbon monoxide and hydrogen. Reaction of carbon dioxide with hydrogen also produces methanol according to the following reaction:

CO₂ + 3H₂ CH3OH + H₂O where the H₂O by-product is recycled via the water-gas shift reaction: co + H₂O co₂ + H₂

A conventional industrial methanol production technique involves the following steps. First, a carbonaceous material, such as coal, is gasified to form a syngas containing carbon dioxide, carbon monoxide, hydrogen and water. The ratio of hydrogen to carbon monoxide in the syngas is typically about 0.8, and therefore below the desirable stoichiometric ratio for methanol production, which is 2. To increase the ratio of hydrogen to carbon monoxide, a water-gas shift reaction is typically carried out to convert come of the carbon monoxide to carbon dioxide and provide additional hydrogen. Prior to conversion to methanol, the syngas then undergoes an acid gas removal step to remove, inter alia, sulphur- containing gases that may poison the methanol conversion catalyst and carbon dioxide, which is considered excess carbon. It is then compressed and passed over a catalyst at elevated temperature to form methanol, which is then typically recovered via distillation. The acid gas removal step is typically carried out using a methanol-based solvent such as Rectisol®. In a typical coal-based methanol plant, Rectisol® is used to remove sulphur down to 0.1 ppmw. However, acid gas removal units also typically remove around 85% to 95% of the carbon dioxide in the syngas. Carbon dioxide may be recovered from the acid gas removal unit, but only at low pressures, typically atmospheric pressure. Such recovered carbon dioxide is either released to the atmosphere, which is bad for the environment, or compressed for storage or re-use. While it is possible to purify and re-pressurise the carbon dioxide and introduce it back into the syngas, this is highly inefficient.

CN209854029U describes a method of producing methanol in which the water-gas shift stage is omitted and “green hydrogen” (hydrogen produced by splitting of water using renewable energy) is added into the syngas to convert the un-shifted carbon monoxide to methanol. Such a method has the desired effect of maintaining the carbon in the syngas stream but is limited by the gasified coal gas CCkCCh ratio and still removes carbon dioxide from the process. For the removed carbon dioxide to be used in the process it must be repressurised before being re-introduced into the syngas. Accordingly, while the method of CN209854029U enables more methanol to be produced per unit of fossil fuel, this can only be achieved by the use of an energy-intensive carbon dioxide re-pressurisation step.

The inventors have therefore investigated a process where the acid gas removal step is omitted or adjusted to reduce the CO2 removal from the process and thereby provide additional carbon to form methanol.

The present invention seeks to tackle at least some of the problems associated with the prior art or at least to provide a commercially acceptable alternative solution thereto.

SUMMARY OF THE INVENTION

One aspect of the present disclosure is directed to a method of producing methanol, the method comprising: providing a syngas comprising carbon dioxide, carbon monoxide, hydrogen and sulphur-containing gas; forming a sulphur-depleted syngas by removing at least some of the sulphur- containing gas from the syngas without removing more than 50 vol. % of the carbon dioxide from the syngas, the 50 vol. % based on the total volume of carbon dioxide in the syngas; converting at least a portion of the sulphur-depleted syngas to methanol; and recovering the methanol, wherein providing a syngas comprising carbon dioxide, carbon monoxide, hydrogen and sulphur-containing gas comprises gasification of coal.

Another aspect of the present disclosure is directed to a method of producing methanol, the method comprising: providing a syngas comprising carbon dioxide, carbon monoxide, hydrogen and sulphur-containing gas; forming a sulphur-depleted syngas by contacting the syngas with a solvent at a pressure of at least 2 MPa to dissolve at least some of the sulphur-containing gas; converting at least a portion of the sulphur-depleted syngas to methanol; and recovering the methanol.

Another aspect of the present disclosure is directed to a method of producing methanol, the method comprising: providing a syngas comprising carbon dioxide, carbon monoxide, hydrogen and sulphur-containing gas; forming a sulphur-depleted syngas by contacting the syngas with a solvent having carbon dioxide dissolved therein, preferably at a concentration of at least 70 vol.% of the saturated carbon dioxide content, more preferably at about 100 vol.% of the saturated carbon dioxide content; converting at least a portion of the sulphur-depleted syngas to methanol; and recovering the methanol.

Another aspect of the present disclosure is directed to a method of producing methanol, the method comprising: providing a syngas comprising carbon dioxide, carbon monoxide, hydrogen and sulphur-containing gas; forming a sulphur-depleted syngas by contacting the syngas with a solvent to dissolve sulphur-containing gases therein; converting at least a portion of the sulphur-depleted syngas to methanol; and recovering the methanol, wherein carbon dioxide is dissolved from the syngas into the solvent, and the method further comprises: stripping dissolved carbon dioxide from the solvent using a hydrogen gas at an absolute pressure of 3 to 9 MPa to form a carbon dioxide-containing hydrogen gas, and introducing the carbon dioxide-containing hydrogen gas into the sulphur-depleted syngas prior to the step of converting at least a portion of the sulphur-depleted syngas to methanol.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a flow diagram of a method of producing methanol according to the present invention.

Figure 2 shows a flow diagram of a plant suitable for carrying out the method of producing methanol according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In a first aspect, the present disclosure is directed to a method of producing methanol, the method comprising: providing a syngas comprising carbon dioxide, carbon monoxide, hydrogen and sulphur-containing gas; forming a sulphur-depleted syngas by removing at least some of the sulphur- containing gas from the syngas without removing more than 50 vol. % of the carbon dioxide from the syngas, the 50 vol. % based on the total volume of carbon dioxide in the syngas; converting at least a portion of the sulphur-depleted syngas to methanol; and recovering the methanol. Each aspect or embodiment as defined herein may be combined with any other aspect(s) or embodiment(s) unless clearly indicated to the contrary. In particular, any features indicated as being preferred or advantageous may be combined with any other feature indicated as being preferred or advantageous.

Surprisingly, the method may enable a large amount of the carbon dioxide in the syngas to be converted to methanol without the need to carry out a carbon dioxide re-pressurisation step. As a result, in comparison to conventional methanol production methods, the method of the present invention requires less energy and is therefore lower cost and/or more environmentally friendly. Advantageously, this may be achieved while avoiding significant poisoning of a methanol conversion catalyst.

The term “syngas” or “synthesis gas” as used herein may encompass a fuel gas mixture. In the method of the present invention, the syngas comprises carbon dioxide (i.e. CO2), carbon monoxide (i.e. CO), hydrogen (i.e. molecular hydrogen H2) and sulphur-containing gas, e.g. hydrogen sulphide (i.e. H2S). The syngas may comprise other gases such as, for example, water and methane, as well as solid species such as, for example, dust and coke. Syngas is typically produced from the gasification of a carbonaceous material such as a fossil fuel, typically coal. The components of the syngas will vary depending on its method of manufacture and the starting materials used.

The method involves forming a sulphur-depleted syngas by removing at least some of the sulphur-containing gas from the syngas without removing more than 50 vol. % of the carbon dioxide from the syngas, the 50 vol. % based on the total volume of carbon dioxide in the syngas. By retaining at least 50 vol.% of carbon dioxide in the syngas, it is possible to convert a large portion of the carbon dioxide from the original syngas to methanol using additional hydrogen, such as so-called green hydrogen generated by the electrolysis of water, or so-called blue hydrogen generated in processes that capture co-produced carbon dioxide. As a result, in comparison to conventional methanol production processes, the amount of methanol produced per unit of fossil fuel increases. This reduces the environmental impact and increases the efficiency of the method. Furthermore, this can be achieved without the need for an energy intensive carbon dioxide re-pressurisation step. Forming the sulphur- depleted syngas is preferably carried out without removing more than 30 vol.% of the carbon dioxide from the syngas, more preferably without removing more than 20 vol.% of the carbon dioxide from the syngas, even more preferably without removing more than 10 vol.% of the carbon dioxide from the syngas, still even more preferably without removing more than 5 vol.% of the carbon dioxide from the syngas, still even more preferably without removing substantially any carbon dioxide from the syngas.

The syngas contains, inter alia, sulphur-containing gas. Syngases produced from the gasification of carbonaceous materials, such as coal, typically contain sulphur-containing gases. The term “sulphur-containing gas” as used herein may encompass a gas of molecules having at least one sulphur atom. An example of a typical sulphur-containing gas present in the syngas is hydrogen sulphide. Sulphur-containing gases are removed from the syngas to avoid poisoning of downstream catalysts used in the methanol conversion. The sulphur- depleted syngas preferably comprises less than 0.5 ppmw (parts per million volume) sulphur- containing gas, more preferably less than 0.3 ppmw sulphur-containing gas, even more preferably less than 0.1 ppmw sulphur-containing gas. In other words, removing at least some of the sulphur-containing gas from the syngas preferably comprises removing at least 50 vol.% of the sulphur-containing gas from the syngas based on the total volume of sulphur-containing gas in the syngas, more preferably removing at least 70 vol.% of the sulphur-containing gas from the syngas, even more preferably removing at least 90 vol.% of the sulphur-containing gas from the syngas, still even more preferably removing at least 95 vol.% of the sulphur- containing gas from the syngas, still even more preferably removing substantially all of the sulphur-containing gas from the syngas. Lower levels of sulphur-containing gas results in reduced poisoning of the methanol conversion catalysts. This may increase the yield and/or efficiency of the process and will reduce the need to replace the catalyst, which may be time consuming and expensive.

Removing at least some of the sulphur-containing gas from the syngas preferably comprises a wet desulphurisation technique and/or a dry desulphurisation technique. Such techniques are suitable to be used in an industrial methanol production plant.

Removing at least some of the sulphur-containing gas from the syngas preferably comprises a wet desulphurisation technique. Wet desulphurisation techniques are capable of reducing high levels of sulphur-containing gas from syngas, and are suitable to be employed in conventional methanol production plants. In contrast to dry desulphurisation techniques, wet desulphurisation techniques tend to be lower cost and have a reduced environmental impact.

The wet desulphurisation technique preferably comprises contacting the syngas with a solvent at a pressure of at least 2 MPa to dissolve at least some of the sulphur-containing gas. Such a technique may be particularly suitable for removing sulphur-containing gases from syngas. Contacting the syngas with a solvent may be performed either at a pressure based on gasifier outlet pressure or at methanol synthesis pressure if the gasifier outlet pressure is higher than methanol synthesis pressure. Contacting the syngas with a solvent is preferably carried out at a pressure of from 2.5 to 9 MPa, for example from 2.76 to 6.89 MPa. In a preferred embodiment, the contacting the syngas with a solvent is preferably carried out at a pressure of from 5 to 9 MPa. Higher pressures increase the amount of sulphur-containing gas that is dissolved in the solvent. Therefore, in some arrangements it may be advantageous to operate the removal of sulphur compounds downstream of syngas compression to the methanol synthesis pressure. Preferably, contacting the syngas with a solvent is carried out at a similar pressure to that employed during a subsequent methanol conversion step, for example from 5 to 9 MPa.

The solvent preferably comprises a physical solvent selected from one or more of dimethyl ethers of polyethylene glycol, methanol, N-methyl-2-pyrrolidone and propylene carbonate. Alternatively, the solvent may be a reactive solvent such as an aqueous solution of an amine or potassium carbonate. Suitable amines include monoethanolamine (MEA), diethanolamine (DEA), methyl-diethanolamine (MDEA) and diglycolamine (DGA). Such solvents are particularly suitable for dissolving sulphur-containing gases from syngas.

The solvent more preferably comprises dimethyl ethers of polyethylene glycol. Advantageously, the use of such a solvent may result in high levels of dissolution of sulphur- containing gas with low levels of dissolution of carbon dioxide. As a result, it may be possible to retain over 70% or even over 80% of the carbon dioxide in the syngas while removing substantially all of the sulphur. A commercial example of a particularly effective solvent comprising dimethyl ethers of polyethylene glycol is Selexol®. The solvent with which the syngas is contacted preferably has carbon dioxide dissolved therein, more preferably at a concentration of at least 70 vol.% of the saturated carbon dioxide content, even more preferably at about 100 vol.% of the saturated carbon dioxide content. The saturated carbon dioxide content of the solvent refers to the saturated carbon dioxide content at the temperature and pressure at which the solvent is contacted with the syngas. By having carbon dioxide already dissolved therein, the solvent has less capacity to dissolve carbon dioxide from the syngas. In this regard, the solvent preferably comprises methanol.

In a preferred embodiment, carbon dioxide is dissolved from the syngas into the solvent, and the method further comprises: stripping dissolved carbon dioxide from the solvent using a hydrogen gas at an absolute pressure of 3 to 9 MPa to form a carbon dioxide-containing hydrogen gas, and introducing the carbon dioxide-containing hydrogen gas into the sulphur-depleted syngas prior to the step of converting at least a portion of the sulphur-depleted syngas to methanol.

The stripping may be carried out, for example, in a stripping column or stripping tower. Suitable stripping techniques and apparatus are known in the art. Advantageously, carrying out the stripping using hydrogen gas means that the “stripped” gas, i.e. the carbon dioxide-containing hydrogen gas, has a composition suitable for it to be introduced back into the sulphur-depleted syngas without the need to carry out a purification step, or with only a minor purification step. The stripping is particularly effective when the hydrogen gas is employed at an absolute pressure of from 3 to 9 MPa. When an absolute pressure of from 5 to 9 MPa is employed, then the stripped gas can be re-introduced back into the syngas without the need for an energy-costly re-pressurisation step. When an absolute pressure of from 3 to less than 5 MPa is employed, then a re-pressurisation step may be required. However, such a re-pressurisation step is less energy intensive in comparison to a repressurisation step from atmospheric pressure. To avoid the need for an energy-costly repressurisation step, the stripping is preferably carried out at the same pressure, or substantially the same pressure, used in the downstream methanol conversion step. In this preferred embodiment, the solvent preferably comprises methanol. The carbon dioxide-containing hydrogen gas is preferably pressurised to an absolute pressure of from 5 to 9 MPa prior to introducing the carbon dioxide-containing hydrogen gas into the sulphur-depleted syngas. This may ensure that the sulphur-depleted syngas is kept at a pressure particularly suitable for methanol conversion.

Removing at least some of the sulphur-containing gas from the syngas preferably comprises a dry desulphurisation technique.

The dry desulphurisation technique preferably comprises contacting the syngas with an absorbent and/or a molecular sieve, more preferably an absorbent. Advantageously, the use of an absorbent and/or molecular sieve may result in significantly all of the carbon dioxide being retained in the synthesis gas. As a result, in comparison with conventional methanol production methods, the amount of methanol produced per unit of fossil fuel is increased. In comparison to a wet desulphurisation technique, the amount of carbon dioxide retained in the syngas using a dry desulphurisation technique may be higher.

The adsorbent preferably comprises one or more of activated carbon, zinc oxide, iron oxide and manganese oxide. Such absorbents are low cost and widely available and are particularly effective at removing sulphur-containing gases from syngas without removing significant levels of carbon dioxide.

Removing at least some of the sulphur-containing gas from the syngas preferably comprises a wet desulphurisation technique and a dry desulphurisation technique. The combination of both a wet desulphurisation technique and a dry desulphurisation technique may provide a favourable combination of high sulphur removal, high carbon dioxide retention and low environmental impact. Preferably, the wet desulphurisation technique is carried out before the dry desulphurisation technique. In this case, advantageously, the majority of the sulphur can be removed using the wet desulphurisation technique, which has a lower environmental impact, and then the substantial remainder of the sulphur can be removed using the subsequent dry desulphurisation technique.

Providing a syngas comprising carbon dioxide, carbon monoxide, hydrogen and sulphur-containing gas preferably comprises gasification of coal. Coal is low cost and widely available, and syngas produced from coal may be particularly suitable for the production of methanol. Gasification is a technique known in the art. During gasification, the coal is blown through with oxygen and steam (water vapour) while also being heated (and in some cases pressurized). It is essential that the oxidizer supplied is insufficient for complete oxidation (combustion) of the fuel. During the reactions mentioned, oxygen and water molecules oxidize the coal and produce a gaseous mixture of carbon dioxide, carbon monoxide, water vapour, and molecular hydrogen. Advantageously, heat may be recovered from the gasification for use in other steps of the method.

The syngas fed to the methanol synthesis step preferably has a stoichiometry number, R, based on the molar concentrations of hydrogen and the carbon oxides in the syngas, defined as R = ([H2]-[CO2])/([CO2]+[CO]) of about 2. Because CO2 is being utilised for methanol synthesis, in order to achieve this stoichiometry number, the method further comprises introducing hydrogen into the syngas, especially wherein at least a portion the hydrogen that is introduced into the syngas is produced by splitting water with electricity (e.g. via electrolysis). The electricity may be generated by a steam turbine using steam produced using heat energy recovered from the process, or is desirably provided by renewable energy. As discussed above, increasing the hydrogen to carbon oxides ratio has conventionally been carried out by performing a water-gas shift reaction to convert at least some of the carbon monoxide in the syngas with steam to form hydrogen and carbon dioxide. The introduction of hydrogen to increase the hydrogen to carbon oxides ratio means that there is no need to carry out a water-gas shift reaction. As a result, there is less carbon dioxide that needs to be retained in the syngas during the desulphurisation step. Furthermore, substantially the entire carbon content of the syngas can be converted to methanol, meaning that the amount of methanol produced per unit of fossil fuel increases. Producing hydrogen by splitting water using renewable energy (e.g. wind, solar, tidal, geothermal, hydro etc.) renders the method more environmentally friendly. Furthermore, oxygen produced during the splitting of water can be passed to a gasification furnace for generation of the syngas. Heat recovered from the gasification may be used to generate the energy, e.g. by the production of steam.

The method preferably further comprises removing dust and/or coke from the syngas prior to removing at least some of the sulphur-containing gas from the syngas. The presence of dust and/or coke in the syngas during the desulphurisation step contaminates the downstream process and may degrade solvents used in a wet desulphurisation technique and/or contaminate absorbents and molecular sieves used in a dry desulphurisation technique.

Converting at least a portion of the sulphur-depleted syngas to methanol preferably comprises contacting the sulphur-depleted syngas with a catalyst, more preferably wherein the contacting occurs at a temperature of from 200 to 300 °C (preferably from 225 to 275 °C) and/or at a pressure of from 5 to 12 MPa (preferably from 5 to 9 MPa), and/or wherein the catalyst comprises alumina-supported copper oxides and alumina- supported zinc oxides.

The use of such a catalyst, in particular under such conditions, may be particularly suitable for producing methanol.

Recovering the methanol preferably comprises distillation. Distillation is a particularly suitable technique for recovering methanol.

In a further aspect, the present invention provides a method of producing methanol, the method comprising: providing a syngas comprising carbon dioxide, carbon monoxide, hydrogen and sulphur-containing gas; forming a sulphur-depleted syngas by contacting the syngas with a solvent at a pressure of at least 2 MPa to dissolve at least some of the sulphur-containing gas; converting at least a portion of the sulphur-depleted syngas to methanol; and recovering the methanol.

The advantages and preferably features of the first aspect of the invention apply also to this aspect of the invention. Use of the solvent may remove at least some of the sulphur- containing gas from the syngas without removing more than 50 vol. % of the carbon dioxide from the syngas, the 50 vol. % based on the total volume of carbon dioxide in the syngas.

The solvent preferably comprises dimethyl ethers of polyethylene glycol. Use of a solvent comprising dimethyl ethers of polyethylene glycol may be particularly effective to remove at least some of the sulphur-containing gas from the syngas without removing more than 50 vol. % of the carbon dioxide from the syngas, the 50 vol. % based on the total volume of carbon dioxide in the syngas.

In a further aspect, the present invention provides a method of producing methanol, the method comprising: providing a syngas comprising carbon dioxide, carbon monoxide, hydrogen and sulphur-containing gas; forming a sulphur-depleted syngas by contacting the syngas with a solvent having carbon dioxide dissolved therein, preferably at a concentration of at least 70 vol.% of the saturated carbon dioxide content, more preferably at about 100 vol.% of the saturated carbon dioxide content; converting at least a portion of the sulphur-depleted syngas to methanol; and recovering the methanol.

The advantages and preferably features of the first aspect of the invention apply also to this aspect of the invention. The saturated carbon dioxide content of the solvent refers to the saturated carbon dioxide content at the temperature and pressure at which the solvent is contacted with the syngas. By having carbon dioxide already dissolved therein, the solvent has less capacity to dissolve carbon dioxide from the syngas. Suitable solvents having carbon dioxide dissolved therein include, for example, a physical solvent selected from one or more of dimethyl ethers of polyethylene glycol, methanol, N-methyl-2-pyrrolidone and propylene carbonate. Alternatively, the solvent may be a reactive solvent such as an aqueous solution of an amine or potassium carbonate. Suitable amines include monoethanolamine (MEA), diethanolamine (DEA), methyl-diethanolamine (MDEA) and diglycolamine (DGA).

In a further aspect, the present invention provides a method of producing methanol, the method comprising: providing a syngas comprising carbon dioxide, carbon monoxide, hydrogen and sulphur-containing gas; forming a sulphur-depleted syngas by contacting the syngas with a solvent to dissolve sulphur-containing gases therein; converting at least a portion of the sulphur-depleted syngas to methanol; and recovering the methanol, wherein carbon dioxide is dissolved from the syngas into the solvent, and the method further comprises: stripping dissolved carbon dioxide from the solvent using a hydrogen gas at an absolute pressure of 3 to 9 MPa to form a carbon dioxide-containing hydrogen gas, and introducing the carbon dioxide-containing hydrogen gas into the sulphur-depleted syngas prior to the step of converting at least a portion of the sulphur-depleted syngas to methanol.

The advantages and preferably features of the first aspect of the invention apply also to this aspect of the invention. Advantageously, carrying out the stripping using hydrogen gas means that the “stripped” gas, i.e. the carbon dioxide-containing hydrogen gas, has a composition suitable for it to be introduced back into the sulphur-depleted syngas without the need to carry out a purification step, or with only a minor purification step. The stripping is particularly effective when the hydrogen gas is employed at an absolute pressure of from 3 to 9 MPa. When an absolute pressure of from 5 to 9 MPa is employed, then the stripped gas can be re-introduced back into the syngas without the need for an energy-costly re-pressurisation step. When an absolute pressure of from 3 to less than 5 MPa is employed, then a repressurisation step may be required. However, such a re-pressurisation step is less energy intensive in comparison to a re-pressurisation step from atmospheric pressure. Suitable solvents for stripping dissolved carbon dioxide from the solvent include, for example, physical solvents such as, methanol, glycol ethers such as dimethyl ethers of polyethylene glycol, N-methyel-2-pyrrolidine and propylene carbonate, in which the carbon dioxide is physisorbed. If necessary, a step of compression of the carbon dioxide-containing hydrogen gas may be performed prior to introducing the carbon dioxide-containing hydrogen gas into the sulphur-depleted syngas.

The invention will now be described in relation to the following non-limiting examples. EXAMPLES

Figure 1 shows a flow diagram of a method of producing methanol according to the present invention (generally at 1), the method comprising: 2 providing a syngas comprising carbon dioxide, carbon monoxide, hydrogen and sulphur-containing gas; 3 forming a sulphur-depleted syngas by removing at least some of the sulphur-containing gas from the syngas without removing more than 50 vol. % of the carbon dioxide from the syngas, the 50 vol. % based on the total volume of carbon dioxide in the syngas; 4 converting at least a portion of the sulphur-depleted syngas to methanol; and 5 recovering the methanol.

Figure 2 shows a flow diagram of a plant suitable for carrying out the method of producing methanol according to the present invention. At gasification unit A, a syngas is produced from coal a, water b, and oxygen c. The generated syngas is then passed to heat recovery unit B to generate steam from the syngas. The steam is used to generate power in the power generation unit C (such as a steam turbine) that provides electrical energy for the electrolysis of water in the electrolysis unit D, which also utilises renewable energy d (e.g. from solar, wind, water and/or hydro-electric). The syngas is passed from the heat recovery unit B to the dust removal and decoking unit E to remove solid species such as dust and coke from the syngas. The syngas is then passed to the syngas desulphurisation unit F to remove sulphur-containing gases from the syngas. In the desulphurisation unit F, substantially all of the carbon dioxide is retained and/or re-incorporated back into the syngas. The syngas is then converted to methanol in the methanol synthesis unit G, where it is recovered using, for example, distillation. Oxygen c generated at D is passed to the gasification unit A. Hydrogen e generated in the electrolysis unit D is passed to the methanol synthesis unit G and is incorporated into the syngas to provide a desirable hydrogen to carbon monoxide ratio prior to methanol conversion.

Three different arrangements have been modelled to illustrate the invention.

Case 1 is a comparative example based on a conventional process comprising a gasifier feeding crude syngas to a water-gas shift unit that provides a shifted syngas mixture to an acid gas removal unit that provides a CO2 stream and a CCh-depleted syngas to a methanol synthesis unit. Case 2 is a comparative example according to CN209854029U that omits the water- gas shift unit and includes additional green hydrogen to produce additional methanol.

Case 3 is according to the present invention wherein the acid gas removal unit is adjusted to remove sulphur compounds and only 10% of the CO2 from the syngas from the gasifier. In this case, the water-gas shift unit is also omitted, but it could be included upstream of the desulphurisation unit.

The R ratio, which reflects the syngas stoichiometry, may be calculated from R = (H2-CO2) / (CO + CO2).

The foregoing detailed description has been provided by way of explanation and illustration, and is not intended to limit the scope of the appended claims. Many variations in the presently preferred embodiments illustrated herein will be apparent to one of ordinary skill in the art and remain within the scope of the appended claims and their equivalents.

Claims

1. A method of producing methanol, the method comprising: providing a syngas comprising carbon dioxide, carbon monoxide, hydrogen and sulphur-containing gas; forming a sulphur-depleted syngas by removing at least some of the sulphur- containing gas from the syngas without removing more than 50 vol. % of the carbon dioxide from the syngas, the 50 vol. % based on the total volume of carbon dioxide in the syngas; converting at least a portion of the sulphur-depleted syngas to methanol; and recovering the methanol, wherein providing a syngas comprising carbon dioxide, carbon monoxide, hydrogen and sulphur-containing gas comprises gasification of coal.

2. The method of claim 1 , wherein forming the sulphur-depleted syngas is carried out without removing more than 30 vol.% of the carbon dioxide from the syngas, preferably without removing more than 20 vol.% of the carbon dioxide from the syngas.

3. The method of claim 1 or claim 2, wherein the sulphur-depleted syngas comprises less than 0.5 ppmw sulphur-containing gas, preferably less than 0.3 ppmw sulphur-containing gas, more preferably less than 0.1 ppmw sulphur-containing gas.

4. The method of any preceding claim, wherein removing at least some of the sulphur- containing gas from the syngas comprises a wet desulphurisation technique.

5. The method of claim 4, wherein the wet desulphurisation technique comprises contacting the syngas with a solvent at a pressure of at least 2 MPa to dissolve at least some of the sulphur-containing gas.

6. The method of any of claims 5, wherein the solvent comprises one of more of a physical solvent selected from one or more of dimethyl ethers of polyethylene glycol, methanol, N-methyl-2-pyrrolidone and propylene carbonate, or a reactive solvent selected from an aqueous solution of an amine or potassium carbonate.

7. The method of any of claims 5 or claim 6, wherein the solvent comprises dimethyl ethers of polyethylene glycol.

8. The method of any of claims 5 to 7, wherein the solvent with which the syngas is contacted has carbon dioxide dissolved therein, preferably at a concentration of at least 70 vol.% of the saturated carbon dioxide content, more preferably at about 100 vol.% of the saturated carbon dioxide content.

9. The method of any of claims 5 to 7, wherein carbon dioxide is dissolved from the syngas into the solvent, and the method further comprises: stripping dissolved carbon dioxide from the solvent using a hydrogen gas at an absolute pressure of 3 to 9 MPa to form a carbon dioxide-containing hydrogen gas, and introducing the carbon dioxide-containing hydrogen gas into the sulphur-depleted syngas prior to the step of converting at least a portion of the sulphur-depleted syngas to methanol.

10. The method of claim 9, wherein the carbon dioxide-containing hydrogen gas is pressurised to an absolute pressure of from 5 to 9 MPa prior to introducing the carbon dioxide-containing hydrogen gas into the sulphur-depleted syngas.

11. The method of any of claims 8 to 10, wherein the solvent comprises methanol.

12. The method of any preceding claim, wherein removing at least some of the sulphur- containing gas from the syngas comprises a dry desulphurisation technique.

13. The method of claim 12, wherein the dry desulphurisation technique comprises contacting the syngas with an absorbent and/or a molecular sieve.

14. The method of claim 13, wherein the adsorbent comprises one or more of activated carbon, zinc oxide, iron oxide and manganese oxide.

15. The method of any of claims 5 to 14, wherein removing at least some of the sulphur- containing gas from the syngas comprises a wet desulphurisation technique and a dry desulphurisation technique.

16. The method of any preceding claim, wherein the syngas fed to the methanol synthesis step has a stoichiometry number, R, based on the molar concentrations of hydrogen and the carbon oxides in the syngas, defined as R = ([H2]-[CO2])/([CO2]+[CO]) of about 2, and the method further comprises introducing hydrogen into the syngas.

17. The method according to claim 16, wherein at least a portion the hydrogen that is introduced into the syngas is produced by splitting water with electricity.

18. The method of any preceding claim, further comprising removing dust and/or coke from the syngas prior to removing at least some of the sulphur-containing gas from the syngas.

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19. The method of any preceding claim, wherein converting at least a portion of the sulphur-depleted syngas to methanol comprises contacting the sulphur-depleted syngas with a catalyst, preferably wherein the contacting occurs at a temperature of from 200 to 300 °C and/or at a pressure of from 5 to 12 MPa, and/or wherein the catalyst comprises copper, zinc oxide and alumina.

20. The method of any preceding claim, wherein recovering the methanol comprises distillation.

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