EA040722B1 - METHOD FOR PRODUCING METHANOL FROM GAS HYDROCARBONS - Google Patents

Description

The invention relates to a process for the production of methanol from gaseous hydrocarbons such as natural gas, associated petroleum gas, fuel gas produced in a refinery or certain chemical plants, or biogas.

The main purpose of the process to which this patent application relates is the production of methanol by reducing or eliminating CO2 emissions to the atmosphere, and converting the amount of CO2 present in the gaseous hydrocarbon feedstock into methanol. The process described and claimed is particularly well suited to industrial applications for the treatment of CO2 rich hydrocarbon gases where conventional CO2 separation and recovery is neither possible nor advantageous.

In this patent application, all operating conditions included in the text should be considered as preferred conditions, even if there is no unambiguous statement about it.

For the purposes of this specification, the terms comprise or include also include the terms consist of or essentially consist of.

For the purposes of this specification, range definitions will always include boundary elements unless otherwise indicated.

Methanol (CH3OH) is a colorless flammable liquid and, at ambient temperature and pressure, contains less oxygen and more hydrogen than any other liquid oxygenated fuel containing one carbon atom. It is the most widely produced and used commercial product of the chemical industry. Its consumption in 2017 was approximately 65 Mtpa (million tons per year), and the production capacity exceeds 70 Mtpa (HIS Chemical 2014, Methanol Report). Approximately 90% is used in the chemical industry and the remaining 10% is used in energy production.

Methanol can also be used as a fuel in internal combustion engines, mixed with other hydrocarbons, and this possibility, little used to date, shows great potential. The methanol synthesis reactions are highly exothermic and typically take place at temperatures in the range between 250°C and 350°C and pressures in the range between 50 atm. and 100 atm. Thermodynamic equilibrium imposes restrictions on the degree of conversion in one pass, and to increase it, enterprises include a recirculation loop. The main reactions occurring in reactors for the synthesis of methanol can be represented by equations [1-3].

CO ₂ + 3 H ₂ \u003d CH3OH + H ₂ O ΔΗ ° \u003d - 41 kJ / mol [ 1 ]

CO + 2 H ₂ \u003d CH3OH ΔΗ ° \u003d - 91 kJ / mol [2]

CO ₂ + H ₂ \u003d CO + H ₂ O ΔΗ ° \u003d 41 kJ / mol [3]

As can be seen, CO ₂ is a reagent in methanol synthesis processes, but in order to carry out the process at high yields, the synthesis gas composition must maintain the ratio M=(H ₂ CO ₂ )/(CO ₂ +CO) ([4]) by close to 2 (v/v) to avoid low conversions per pass and high purge gas volumes in the recycle loop. In addition to this, a high CO/CO ₂ ratio is also required to minimize the formation of by-products (eg CH4).

There are many flowsheets for methanol production that integrate sections for syngas production, water gas shift, methanol synthesis, Pressure Swing Adsorption (PSA), and separation and purification of products.

The thesis Methanol Production via Short Contact Time - Catalytic Partial Oxidation (Faculty of Civil and Industrial Engineering; Master's Degree Course in Chemical Engineering, Rome, Federica Scire; 1420915, A/A 2014/2015) describes the process flow shown in figure 4 and typically used for large scale plants using natural gas as hydrocarbon feedstock (5000 MTPG; CHEMSYSTEM PERP PROGRAM Methanol: 2012-5; 2013; A. Yang, Y.L. Song).

This method offers:

1) production of O ₂ (500) using an air separation unit (ASU);

2) desulfurization and removal of CO ₂ from natural gas (100, SEPDES);

3) condensation and stabilization of liquid hydrocarbons (300, STAB);

4) preheating the hydrocarbon feedstock to about 550-600° C. (SYNGEN);

5) pre-reforming process (SYNGEN);

6) production of synthesis gas using an autothermal reforming reactor (ATR,

SYNGEN) in accordance with the reactions [5-7]:

sn ₄ + 3/2 o ₂ \u003d co + 2 n ₂ o

CH ₄ + H ₂ O \u003d CO + 3 n ₂ co + n ₂ o \u003d co ₂ + n ₂

ΔΗ°= - 520 kJ/mol [5]

ΔΗ°= 206 kJ/mol [6]

ΔΗ°= - 41 kJ/mol [7]

It is also proposed to adjust the syngas composition to achieve an M value of approximately 2 (v/v) using a CO2 removal unit or a pressure swing adsorption (PSA) unit. This last unit separates a pure H2 stream (800) from an aliquot of recycle gas from the methanol synthesis loop, which is reintroduced into the synthesis gas, and a purge gas stream containing mainly CO and CO2 (900), which is combusted for power generation. . Synthesis gas having an M value of about 2 (v/v) is compressed from a pressure typically close to 30 atm to values in the range of 60 to 100 atm, which are suitable for methanol synthesis. The synthesis of methanol (MeOH) is carried out in accordance with the reactions [1-3]. The condensate is separated and the unreacted synthesis gas is recycled. The diagram in Fig. 4 includes a produced methanol purification unit (PUR) and a produced methanol storage unit (STOR).

This scheme ensures that there are three points at which CO2 is released:

(a) in a plant that removes CO2 from natural gas feedstocks or other hydrocarbon sources that may be used (for example, associated petroleum gas, fuel gas produced in refinery circuits or from other chemical plants, biogas);

(b) in ovens for preheating reactants fed into the synthesis gas section; and (c) in a section for adjusting the composition of the synthesis gas in order to achieve M = 2 (v/v) values in the methanol synthesis feedstock.

Thus, when considering the electricity consumption of an ASU oxygen plant, the calculation of the amount of CO2 emissions per unit of methanol produced must also take into account the emissions associated with the operation of this plant.

CO2 emissions are even more significant for plants that use steam reforming (SR) to produce synthesis gas, since in this case the emissions from the reformer required to supply heat for highly endothermic steam reforming reactions are even more significant, as is can be seen from the reactions [8-9].

CH ₄ + H ₂ O \u003d CO + 3 H ₂

ΔΗ°=

CH ₄ + CO ₂ \u003d CO + 2 H ₂

ΔΗ°=

CH ₄ + 1/2 O ₂ \u003d CO + H ₂

ΔΗ°=

206 kJ/mol [8]

247 kJ/mol [9]

-38 kJ/mol [10]

The thesis Methanol Production via Short Contact Time - Catalytic Partial Oxidation (Faculty of Civil and Industrial Engineering; Master's Degree Course in Chemical Engineering, Rome, Federica Scire; 1420915, A/A 2014/2015) also describes the process flow shown in FIG. 3.

This document also quantifies the emission reductions in SCT-CPO processes in the production of methanol and a natural gas feedstock containing 0.5 to 30.0% (v/v) CO ₂ .

For the case of combining the possibilities offered by SCT-CPO technology with the possibilities offered by water electrolysis systems, technological solutions are obtained that make it possible, above all, to avoid huge amounts of CO2 emissions, and which also consume a corresponding amount of them contained in natural gas or generally in any hydrocarbon gaseous feedstock containing CO2, such as biogas, associated petroleum gas, some gases from refineries and purge gases from some industrial processes.

Therefore, these solutions may replace or supplement the corresponding solutions currently used in high CO2 gas fields, such as amine scrubbing and re-injection in fields that are still able to accommodate it, or in fields where re-injection provides the opportunity carrying out operations within the framework of enhanced oil recovery (EOR) methods.

As it is important to note at this point, one point of CO2 emission in methanol synthesis processes can be avoided using the patented SCT-CPO technology, which does not require ovens to preheat the reactant feedstock, nor even a gaseous hydrocarbon feedstock pre-reformer. (Fig. 3). The chemical mechanism underlying the SCT-CPO methods has been described in numerous documents in the literature and essentially has two basic equations [10] and [7] at its core.

Patent applications WO 2016/016251, WO 2016/016253, WO 2016/016256 and WO 2016/016257 have described integrated processes using catalytic partial oxidation technology with short contact times.

In order to overcome the shortcomings and limitations known in the state of the art, the Applicant has discovered a process for the production of methanol from gaseous hydrocarbons such as natural gas, associated petroleum gas from oil fields, fuel gas produced in refineries and some chemical plants, and biogas. The process integrates syngas production, water electrolysis and methanol synthesis to avoid CO2 emissions and to

- 2 040722 consumption of CO2 present in gaseous hydrocarbons.

The purpose of this patent application is a process for the production of methanol from gaseous hydrocarbons, which includes the following steps:

a) treating said gaseous hydrocarbons in a desulfurization plant to produce a desulfurized gaseous hydrocarbon;

b) reacting said desulfurized gas with an oxidizing stream via a catalytic partial oxidation reaction with a short contact time to produce synthesis gas;

c) hydrogen production from water electrolysis;

d) mixing and compressing synthesis gas and hydrogen; And

e) sending said compressed mixture to a methanol synthesis plant to produce methanol.

Advantageously, using the described and claimed process, it is possible to integrate or completely replace the production of H2 obtained from a pressure swing adsorption (PSA) unit, which is typically included in methanol synthesis circuits known in the state of the art. The PSA unit has the function of separating the high pressure pure H2 stream from the CO2 and CO enriched purge stream, which is removed and typically combusted while hydrogen is re-injected into the methanol synthesis recycle.

H ₂ is mixed with synthesis gas to adjust the composition of the supplied feedstock in order to obtain a ratio of (H2 - CO ₂ )/(CO + CO2) close to 2 (vol./vol.).

Since the PSA process produces a high pressure H2 stream and a low pressure purge gas containing CO2 and CO, which is typically combusted, its partial or complete replacement by a water electrolysis system to produce H2 makes it possible to avoid associated CO2 emissions.

As a result of using Catalytic Incomplete Oxidation with Short Contact Time (SCT-CPO) technology, in particular the SCT-CPO technology owned by Eni S. p. A., it is possible to avoid the use of feed preheating ovens that would produce CO ₂ by using instead gas-to-gas heat exchangers using waste heat from the process described and claimed herein. An additional advantage is the possibility of sizing the water electrolysis plant in order to obtain access not only to the hydrogen, but also to the oxygen required for the synthesis gas production process, thus replacing both PSA and air separation units (ASUs). ).

If gaseous hydrocarbons contain significant amounts of CO2, for example, more than 5% (vol.), the described and claimed method allows the conversion of carbon dioxide to methanol, consuming it.

The electrical energy required for the electrolysis reaction can be obtained from various sources and in particular:

i) as a result of the expansion of vented process steam inside the steam turbine, ii) from renewable sources.

Therefore, the complete described and claimed method provides the possibility of eliminating or significantly reducing emissions of greenhouse gases (greenhouse gases or GHGs), and in particular carbon dioxide, which makes it environmentally friendly.

In addition, if gaseous hydrocarbons having a high level of CO2 content, such as biogas, are used in the described and claimed process, it is possible to produce methanol, which can be considered as an improved fuel for use in internal combustion engines.

The process described herein also allows a corresponding increase in methanol production with the same consumption of hydrocarbon feedstock and oxygen, almost doubling it when the CO ₂ content of gaseous hydrocarbons is 30% (vol./vol. ).

Therefore, the process described and claimed can process hydrocarbon streams, even those with high levels of CO ₂ , (turning it into methanol) by integrating already available technological solutions, such as reactors for the production of synthesis gas, reactors for water gas shift, installations for electrolysis, methanol synthesis reactors and separation and purification stages.

The method described and claimed is proposed as a process choice that consumes, reduces or eliminates CO2, as opposed to the solutions currently used where CO2 is removed and reinjected into acid gas fields, putting it back into circulation without ever eliminating it.

As has also been demonstrated, even if the hydrocarbon reactants used contain small volumes of CO2, the described and claimed process allows the production of methanol with much lower greenhouse gas emissions than prior art processes. This result is made possible by the use of short contact time catalytic partial oxidation (SCTCPO) technology and water electrolysis in flowsheets leading to methanol synthesis. The described and claimed method also allows the use of both sources of gaseous hydrocarbons of biological origin (for example, biogas) as a feedstock for the section for the production of synthesis gas, and renewable energy sources for generating electricity in order to supply it to the electrolysis process. , which improves the environmental safety of production methods leading to the production of methanol.

In conclusion, the method described and claimed allows some technological simplifications from an engineering point of view, since the introduction of an electrolysis plant allows the production of H ₂ and O ₂ within a single plant operation, and the PSA and ASU plants can be replaced.

In particular, as the applicants point out, the ASU process for air is an energy-intensive process that cannot always be optimally integrated into methanol synthesis. In fact, together with O2, the ASU process produces N2, Ar, He, and Ne streams that contribute to its feasibility. However, these gaseous products at the outlet of the process cannot always be improved in quality (particularly in the context of oil and gas production). The use of an electrolytic cell allows the production of both H2 and _O2 in very high purity and does not require steps to improve the quality of the other gases that are co-produced in the ASU process. The use of H2 produced from electrolysis reduces or completely eliminates the need for recirculating purge in the synthesis of methanol and significantly increases the yield of methanol based on the amount of hydrocarbon gas and oxygen consumed.

Additional objects and advantages of the present invention will become clearer by using the following description of the invention and the accompanying figures, presented solely as examples and not as limitations of the description of the method, instead of illustrating the preferred embodiments of the present invention.

In FIG. 1 illustrates one preferred embodiment according to the present invention in which (A) is a short contact time catalytic partial oxidation plant fed with already desulfurized gaseous hydrocarbon (1), preferably natural gas, a recycle stream from methanol synthesis (2 ), 99.9% high purity oxygen (3), superheated steam (4); (B) is a water gas shift unit, into which part of the produced synthesis gas (5) is fed, while the remainder (6) is mixed with a mixture of hydrogen and carbon dioxide (7) and sent to a two-phase separator (C ) in which water is condensed (10) while the separated top product is synthesis gas (8). Said synthesis gas (8) is mixed with hydrogen (19) obtained from the electrolysis of water (D). The resulting mixture is compressed in (C1) and mixed with recycle gas (13) before being fed to the methanol synthesis unit (E). The synthesis product (12) is separated (F and G) to obtain recycle gas (2), crude methanol (18) and by-products in aqueous solution and in the form of steam (17). A small amount of purge gas (15) is recovered from the recycle gas (14) and part (13) is compressed into (C2) to be sent back to the methanol synthesis unit, while the second minor part (2) is sent back to the reactor for production of synthesis gas.

In FIG. 2 illustrates one preferred embodiment of the present invention using the configuration of FIG. 1, but in addition there is a pressure swing adsorption or PSA (H) unit that separates hydrogen (20) producing waste gases in the presence of CO2 emissions (21). The PSA unit is fed a portion of the recycle stream generated from the methanol synthesis (22). This scheme can be used mainly in large-scale enterprises or when, for technical and/or economic reasons, an insufficient amount of electrical energy is available to supply energy to the electrolysis processes.

In FIG. 3 shows an integrated methanol synthesis process according to the state of the art. In FIG. 3 again shows the configuration of FIG. 1 and 2, where a pressure swing adsorption plant is used instead of a water electrolysis plant, generating waste gases (off-gases) in the presence of carbon dioxide emissions (21).

In FIG. 4 shows a general diagram of the process plants required for the production of methanol in accordance with the prior art, already previously described in the text. The method which is the subject of this patent application in relation to the production of methanol from gaseous hydrocarbons such as natural gas, associated petroleum gas, fuel gas produced in a refinery or specific chemical plants, or biogas, will now be described in detail, again under referring to FIG. 1 and FIG. 2.

- 4 040722

The gaseous hydrocarbons are fed to a desulfurization unit to reduce or eliminate the content of sulfur compounds and thus produce a desulfurized gaseous hydrocarbon. The desulphurized gas (1) is mixed with an oxidizing stream (3) selected from pure oxygen, air or oxygen-enriched air and sent to a catalytic partial oxidation plant, where a catalytic partial oxidation reaction is carried out with a short contact time (A) to produce synthesis gas (5). Superheated steam may be added to the desulfurized gas and oxidizing stream (4). The streams thus obtained can furthermore be preheated using steam obtained by cooling synthesis gas or process streams from other plants using gas-to-gas heat exchangers.

The synthesis gas produced can be partially processed in a water gas shifter (B) to which a steam stream (9) is fed, thus obtaining a mixture of hydrogen and carbon dioxide (7). The obtained synthesis gas (5) is cooled and sent to the separator (C) for water condensation (10).

The water electrolysis plant (D) produces hydrogen (19). The produced synthesis gas without condensed water is mixed with said hydrogen and compressed (C1).

The mixture of hydrogen and carbon dioxide produced by the water gas shift is also cooled and sent to a separator (C) to separate the condensation water (10). After that, this stream (8) can be mixed with hydrogen produced by electrolysis, and then compressed (C1). H2 produced by electrolysis is mixed with synthesis gas (8) to adjust the composition of the feedstock to the methanol synthesis unit to obtain a ratio of (H2 - CO ₂ )/(CO + CO2) equal to 2 (vol./vol.).

After compression, the gaseous mixture is fed to a methanol synthesis unit (E) to produce an effluent (12) which is subsequently separated (F and G) to obtain recycle gas (2), crude methanol (18) and impurities consisting of aqueous condensates and substances dissolved in them (17). The recycle gas can be partly (2) fed into the catalytic partial oxidation plant with a short contact time, in addition to the purge gas (15), and the remainder is compressed (14, C2) and recycled (13) to the methanol synthesis plant.

The SCT-CPO reactor produces synthesis gas at temperatures in the range of 650-1050°C, which is then cooled. Therefore, it is possible to use the heat contained in the synthesis gas to produce water vapor necessary for preheating the reactants by cooling the synthesis gas in heat exchangers. The synthesis gas can preferably be cooled to less than 350° C., producing the steam needed to preheat the reactants and feed into the SCT-CPO reactor.

In the process which is the object of this patent application, there may also be a pressure swing adsorption or PSA unit (FIG. 2, H) which separates hydrogen from the inlet gas at the pressure of the recycle loop in the methanol synthesis unit (20) with emission of CO2 at low pressure, usually atmospheric (21). The PSA unit is supplied with part of the recycle gas (22) obtained by separating the effluent from the methanol.

The operating conditions under which catalytic partial oxidation short contact time (SCT-CPO) technology and the methanol synthesis process are able to operate are given in the publication: Methanol Production via Short Contact Time - Catalytic Partial Oxidation; Thesis by F. Scire; Faculty of Civil and Industrial Engineering; Master of Science in Chemical Engineering (A/A 2014/2015).

The SCT-CPO reaction can proceed at ratios of O ₂ /C (moles of oxygen/moles of carbon present in the feedstock, excluding CO2) in the range between 0.15 and 0.70 (mol/mol), preferably between 0.45 and 0.65 (mol/mol), more preferably between 0.5 and 0.6 (mol/mol).

The SCT-CPO reaction can proceed at steam/C ratios (moles of water molecules/moles of carbon atoms, excluding CO ₂ present in the feedstock) in the range between 0.01 (mol/mol) and 3.5 (mol/mol/ mol), preferably between 0.5 and 2.4 (mol/mol).

In addition, the hydrocarbon feedstock may have CO2 volume levels ranging between 0 and 70%, preferably between 0.5 and 50%, and more preferably between 0.5 and 45%, (v/v).

The reactants can be fed into the SCT-CPO reactors at temperatures in the range between 50 and 400°C, preferably between 100 and 350°C. The reactants may be fed to the SCT-CPO reactors at pressures ranging between 0.0987 and 98.7 atm, preferably between 0.493 and 59.21 atm, more preferably between 9.87 and 39.6 atm.

The short contact time catalytic partial oxidation reaction may preferably take place in a reaction system which includes a short contact time catalytic partial oxidation reactor and a heat exchange system coupled to said reactor and located downstream of said reactor. The partial catalytic oxidation reactor may include a mixing zone into which reactants are fed, and a truncated catalytic zone with increasing cross section, in which reactions that consume the oxidant proceed and synthesis gas is produced, which is the off-product of the reaction.

The catalytic zone may preferably include a multi-layer catalyst bed, each layer of which contains a catalyst containing a carrier on which the active part of the catalyst is deposited. The catalytic zone may preferably be contained between two layers of material that function as heat shields located upstream and downstream of the catalyst bed. The total catalytic zone is preferably heated, by means of suitable devices for heating the mixture of incoming gases, and by means of the heat of reaction.

The catalyst present in each layer of the catalyst bed may include an active part containing a metal selected from the group of noble metals, Ni, Co and Fe, and a carrier selected from ceramic oxides, characterized by high thermomechanical strength and chemical stability under conditions of oxidation and reduction up to up to 1500°С.

The noble metals are selected from Rh, Ru, Pd, Pt, Ir, Au and mixtures thereof. Rh is the preferred noble metal.

Preferred carriers are selected from aluminas, including alpha, beta and delta phases; zirconium oxides, also stabilized with yttrium; cerium oxides; mixed oxides of magnesium and aluminum and/or mixed oxides of magnesium or manganese, more preferably selected from MgAl ₂ O ₄ and MgMn ₀ , ₂₅ Al ₁ , ₇₅ O ₄ , hexaaluminates, more preferably selected from LaAl11O ₁₉ and LaMnAl _n O ₁₉ , compounds with perovskite structure, more preferably selected from LaCrO ₃ or LaCoO ₃ , LaFeO ₃ , LaAlO ₃ , QaTiO ₃ , QaZrO ₃ . Alpha alumina is the preferred ceramic oxide.

The amount of noble metals present as an active ingredient varies within the range of 0.1-10% (wt.), preferably within the range of 0.2-5% (wt.).

The operating conditions that can be used to carry out the methanol synthesis are typically those used in the following methods from the companies: a) Haldor-Tops0e; b) Johnson Matthey Catalyst (JM) & Davy Process Technology (DPT); c) Lurgi; d) Toyo Engineering.

The gas fed to the methanol synthesis section must have a composition such that the modulus M = (H2 - CO ₂ )/(CO + CO2) is kept close to 2 (v/v).

In the method covered by this patent application, all water electrolysis methods can be used.

Preferably, the water electrolysis technology can be selected from 1) Alkaline, 2) PEM (Polymer Electrolyte Membrane), and 3) SOEC (Solid Oxide Electrolyzer Cell). Alkaline electrolysis is the most commonly known solution, even though it is still in the process of further development. PEM technology is newer and less widespread and has a high development potential. SOEC technology is not yet commercial. As exemplarily noted by Applicants, commercial alkaline electrolyzers are compact and use pressurized H2O where KOH is added to produce _H2 and _O2 with excellent energy efficiency, even under pressure (20-30 bar (ex.)). The heart of the process is a series of high performance bipolar electrolytic cells that produce H2 and O2. The splitting of water according to theory requires the use of approximately 3.55 kWh per Nm ³ H ₂ , and this requires a constant electric current. However, a proportion of the absorbed power is lost in the form of heat (energy efficiency claimed by manufacturers is in the range of 60-70%). The streams of H ₂ and O2 are filtered and separated from the moisture, which is sent for recycling in the cells. Excess heat is removed by using a water cooling system. In a tank having sufficient volume, demineralized water is placed to allow a reasonable operational autonomy, which is then transferred to the electrolytic system using a pump. Power from a three-phase grid power source is converted to DC using a transformer/inverter system, or power can be supplied as DC, such as from a photovoltaic (PV) or wind turbine. The system is included in a housing subdivided into two chambers separated by a double wall, one of which contains the process unit and the other a section for the power source. The resulting H2 stream is of very high purity (99.9995% (v/v)), and to achieve this, it is passed through filters that remove KOH, then to a catalytic reactor to remove O2, and then to two installations for water adsorption. Using solutions similar to those used for H2 purification, very high purity O2 can also be obtained.

Some examples of applications of the present invention will now be described, which are purely descriptive and non-limiting, and which are preferred embodiments of the present invention.

- 6 040722

Examples

Comparative example 1.

In the state of the art, methanol synthesis follows a scheme similar to that of FIG. 3. Desulphurized natural gas (1), part of the recycle gas from methanol synthesis (2), superheated steam (4) and a stream of high purity oxygen (99%) (3) at a pressure of 29.6 atm are preheated using steam produced by itself (not shown in FIG. 3) and mixed at the inlet to the catalytic partial oxidation reactor with a short contact time (A). The mixture thus formulated is converted into synthesis gas (5) by heating to approximately 850-1050°C. At the outlet of the reactor, the synthesis gas is cooled to less than 350° C. in a boiler to produce the steam flow needed to preheat the reactants and feed into the SCT-CPO reactor (not shown in FIG. 3).

The synthesis gas stream from the boiler does not have an optimal composition for feeding to the downstream section: in order to tune some of the performance relationships required for the technology currently used for methanol synthesis, some synthesis gas is sent to the reactor for water gas shift (B) together with steam flow (9), while the remainder is not fed into the water gas shift reactor (WGS). The effluent from the water gas shift reactor and the synthesis gas directly produced using the catalytic partial oxidation reactor (A) are mixed (7) and cooled in a heat exchanger to about 45°C, which allows more steam to be produced. The cooled synthesis gas at low temperature enters the two-phase separator (C), from the bottom of which condensed water is discharged to be poisoned for water treatment, while the anhydrous synthesis gas exits from the top, and it is sent to the methanol synthesis section ( 8).

However, stream (8) still has an M ratio less than the optimum value (2 (v/v)), and therefore an H ₂ stream (20) needs to be added to it. The required amount of H ₂ is separated using the PSA (H) plant, which also produces a waste gas stream (21), a CO ₂ emission point, while said PSA unit is supplied partly with synthesis gas coming from the separator, and partly with recycle gas from synthesis methanol (24): the more CO ₂ present in the natural gas feed to the process, the greater the amount of syngas that must be sent to the PSA process by producing methanol.

After the addition of hydrogen, the gas is compressed (C1) to about 79 atm (the pressure at which methanol synthesis proceeds) and mixed with some of the compressed recycle gas (C2) (13 and 14). After mixing, the resulting stream is fed into the methanol synthesis reactor (E); the product stream at the outlet of the reactor (12) is cooled to about 50°C, which allows the water and methanol present in it to condense. Finally, using a two-phase separator (F), the recycle gas is separated from the condensates (16), which are depressurized to 5 bar, and sent to the final separation stage (G), from which a gas stream (17) and crude methanol ( 18) (consisting of about 85% (w/w) methanol and 15% (w/w) water).

For the case of filing in the above method of natural gas flow, characterized by the composition shown in table. 1, get a material balance, the main elements of which are shown in table. 2.

Table 1

Natural gas % (about.) METHANE 82.15% ETHANE 9.59% PROPANE 2.85% ISOBUTANE 0.64% BUTANE 0.78% ISOPENTAN 0.26% PENTAN 0.22% HEXANE 0.92% H ₂ 0 1.01% CO ₂ 0.50% HYDROGEN 0.01% NITROGEN 1.06%

table 2

Synthesis of methanol as a result of the production of synthesis gas using SCT-CPO technology RAW INLET OUTPUT PRODUCT Natural gas [kg/h] 39948 - Oxygen [kg/h] 44395 - Water vapor [kg/h] 26779 - Waste gases [kg/h] - 15438 CO [kg/h] 440 7194 in waste gases and 19788 CO2 immediately after combustion of all waste gases Methanol [kg/h] - 63765

- 7 040722

In table. The output CO ₂ product is calculated in the form of two positions: the amount of emissions together with waste gases and the amount obtained from the combustion of all waste gases.

Some specific indicators related to natural gas and O ₂ consumption and CO ₂ emissions per tonne of methanol produced are presented in Table. 3. As it is considered, all compounds containing C and present in waste gases are oxidized to CO ₂ .

Table 3

SPECIFIC INDICATORS Hivf natural gas/tonnnameon 702.66 Nm ³ o2 / tonnameon 487.68 ton _B COG emissions/tonnameon 0.31 tonne of CO2 produced/tonneNameON 0.106

Comparative example 2.

In the method described in Comparative Example 1 and in FIG. 3 feeds a natural gas stream having a high CO2 content shown in Table 1. 4.

Table 4

Natural gas % (about.) METHANE 57.84% ETHANE 6.72% PROPANE 2.01% ISOBUTANE 0.55% BUTANE 0.45% ISOPENTAN 0.16% PENTAN 0.18% HEXANE 0.65% H ₂ O 0.71% CO ₂ thirty% HYDROGEN 0.73%

Get a material balance, the main elements of which are shown in table. 5, while in table. Figure 6 shows specific figures related to natural gas and O2 consumption and CO2 emissions per tonne of methanol produced. In table. 5 shows the amount of CO2 emissions together with waste gases and the amount of CO2 obtained from the combustion of all waste gases. As it is considered, all compounds containing carbon and present in waste gases are oxidized to CO ₂ .

Table 5

Synthesis of methanol as a result of the production of synthesis gas using SCT-CPO technology RAW INLET OUTPUT PRODUCT Natural gas [kg/h] 96750 - Oxygen [kg/h] 55751 - Water vapor [kg/h] 33629 - Waste gases [kg/h] - 70286 CO ₂ [kg/h] 47121.5 29338.5 in waste gases and 93862 immediately after combustion of all waste gases Methanol [kg/h] - 63840

Table 6

SPECIFIC INDICATORS Nm ³ _Natural gas/tONNameON 1253.07 Nm ³ o2 / tonnameon 611.71 ton _B COG emissions/tonnameon 1.47 ton of CO2 production/tonNaMeOH 0.279

Example 1.

With reference to FIG. 1 and comparative examples 1 and 2, the method includes two sections: the production of synthesis gas using the SCT-CPO method (A) and the synthesis of methanol (E).

The SCT-CPO reactor is fed with desulfurized natural gas (1), O ₂ (3), steam (4) and a recycle gas stream from methanol synthesis (2). After preheating and mixing (not shown in FIG. 1), the feed streams are fed into the reactor where they are converted to produce synthesis gas (5). Thereafter, it is cooled to approximately 350° C. in a boiler producing steam (not shown in FIG. 1).

In accordance with the above description of the invention, some synthesis gas is sent to the WGS reactor for water gas shift (B), while some of it bypasses this reactor through the bypass (6): in this way, the CO/CO2 characteristic ratio is adjusted for methanol synthesis. The two streams are combined and cooled to approximately 45° C. before being fed to a separator (C) to separate the condensation water (10). Synthesis gas (8) leaves the top of the separator and does not yet have an optimal M ratio for methanol synthesis. In this case, as in the previous case, it is again necessary to add the flow of H ₂ (19) to bring the value of M to 2 (v/v). In this case, H ₂ is no longer produced as a result of the separation of the latter from the synthesis gas and recycle gas using PSA, but is obtained from an alkaline cell (D) operating at a pressure in the range of 30-35 atm.

The synthesis gas thus adjusted is compressed to approximately 80 bar (C1), mixed with the compressed recycle gas (C2, 13) and then fed into the methanol synthesis reactor (E). The products leaving the reactor are separated and cooled (F, G) to separate the methanol stream (18) containing 85% (w/w) methanol and 15% (w/w) water from the recycle gas (2) . A small amount (1% (v/v)) of all recycle gas is removed (15) to limit the accumulation of inert compounds in the system.

By supplying a natural gas stream having the same composition as Comparative Example 2 (Table 4) with a high CO ₂ content to the process flow described above, a material balance is obtained, the main elements of which are shown in Table 1. 7, while the consumption of natural gas, O2 and CO2 per tonne of methanol produced is shown in Table. 8. In the table. 7 shows the amount of CO ₂ emissions together with waste gases and the amount of CO ₂ obtained from the combustion of all waste gases. It is believed that all compounds containing C and present in waste gases are oxidized to CO ₂ .

Table 7

Synthesis of methanol as a result of the production of synthesis gas using SCT-CPO technology RAW INLET OUTPUT PRODUCT Natural gas [kg/h] 96750 - Oxygen [kg/h] 58771 - Water vapor [kg/h] 35451 - Waste gases [kg/h] 8652 Natural gas [kg/h] - 7533 CO [kg/h] 47121.5 4175 in waste gases and production of 8686 as a result of combustion of all waste gases Methanol [kg/h] - 124944

Table 8

SPECIFIC INDICATORS Nm ³ _Natural gas/tONNameON 640.25 Nm ³ o2 / tonnameon 329.48 tonneCO2 emissions/tonnameon 0.07 tonne of CO2 consumption/tonneMeon 0.344 Nm ³ N2/tonneMeOH 769.89

Comparison of comparative example 2 and example 1 shows that the method corresponding to example 1 allows approximately twice the production of methanol at the same flow rate and composition of natural gas. As a matter of fact, in the first case, a significant part (approximately 50%) of the produced synthesis gas was sent to the PSA plant for the production of hydrogen required to correct the parameter M, while in the method corresponding to example 1, hydrogen was supplied using an external source (electrolyzer ), which makes it possible to use all the synthesis gas for methanol synthesis. By eliminating the need to install a PSA plant, waste gas production and, consequently, CO ₂ emissions are significantly reduced. In table. Table 9 describes the electricity consumption required for electrolysis processes at various methanol production capacities.

Table 9

Position Natural gas consumption _CO2 consumption _CO2 consumption _H2 consumption Nm ³ /hour Nm ³ /hour Nm ³ /day Nm ³ /hour A 640 175 4202 770 IN 6403 1751 42024 7699 WITH 9604 2626 63035 11548 D 19208 5253 126071 23097 E 40016 10944 262647 48118 F 80032 21887 525294 96236 G 133397 36482 875560 160406 H 152356 41667 1000000 183204 Position O2 consumption Required power methanol methanol Nm ³ /hour MW ton per hour ton per day A 329 3 1 24 IN 3295 33 10 240 WITH 4942 50 15 360 D 9885 100 thirty 720 E 20593 209 63 1500 F 41186 418 125 3000 G 68648 697 208 5000 H 78405 797 238 5711

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Claims (3)

It should be noted that up to positions C and D, the electrical power could be entirely produced from renewable sources, while for higher production capacities it would be necessary to connect the use of electricity produced from conventional and renewable sources. CLAIM 1. A method for the production of methanol from gaseous hydrocarbons, which includes the following steps: a) treating said gaseous hydrocarbons in a desulfurization plant producing a desulfurized gas containing hydrocarbons; b) reacting said desulphurized gas with an oxidizing stream via a catalytic partial oxidation reaction with a short contact time to produce synthesis gas; c) hydrogen production from water electrolysis; d) mixing and compressing synthesis gas and hydrogen; And e) sending said compressed mixture to a methanol synthesis plant to produce methanol. 2. The method of claim 1, wherein some of the produced synthesis gas is subjected to a water gas shift reaction to produce a stream containing carbon dioxide, carbon monoxide and hydrogen, and then said stream is mixed with hydrogen produced by electrolysis. 3. Process according to claim 1 or 2, wherein the desulfurized gas is mixed with superheated steam. 4. The method according to any one of claims 1 to 3, wherein the desulphurized gas is preheated using water vapor obtained by cooling the synthesis gas produced in the heat exchangers. 5. The method of claim 4, wherein the produced synthesis gas is cooled to less than 350° C. in a boiler producing steam. 6. A process according to any one of claims 1 to 5, further comprising a pressure swing adsorption unit that separates hydrogen from the gas entering the methanol synthesis unit at recycle pressure. 7. Process according to any one of claims 1 to 6, wherein the reactants are fed into the partial catalytic oxidation reactors with a short contact time at a temperature in the range of 50 to 400°C. 8. Process according to any one of claims 1 to 7, wherein the reactants are fed into the catalytic partial oxidation reactors with a short contact time at a pressure in the range of 0.0987 to 98.7 atm. 9. Process according to any one of claims 1 to 8, wherein the short contact time catalytic partial oxidation reaction proceeds at O ₂ /C ratios ranging from 0.15 to 0.7. 10. The process according to any one of claims 1 to 9, wherein the short contact time catalytic partial oxidation reaction proceeds at a steam/C ratio in the range between 0.01 and 3.5. 11. A process according to any one of claims 1 to 10, wherein the gaseous hydrocarbon feedstock has a CO2 volume content in the range of 0 to 70% by volume. 12. A process according to any one of claims 1 to 11, wherein the methanol synthesis reactors are operated at a temperature in the range of 250 to 350° C. and a pressure in the range of 50 to 100 atm. 13. The method according to any one of claims 1-12, in which water electrolysis is selected from technologies: 1) alkaline, 2) a polymer electrolyte membrane and 3) a cell of a solid oxide electrolyzer. -