Process for providing syngas and producing methanol

Abstract

The invention relates to a method for producing synthesis gas, in particular synthesis gas for methanol synthesis. The process comprises the steps of: providing a sulfur-containing hydrocarbon stream; providing an electrolytically produced hydrogen stream; supplying a portion of the electrolytically produced hydrogen stream to at least a portion of the sulfur-containing hydrocarbon stream to obtain a hydrogen-rich sulfur-containing hydrocarbon stream; subjecting the stream obtained according to step (c) to desulfurization in a hydrodesulfurization unit (HDS unit) (12) to obtain a sulfur-free hydrocarbon stream; supplying a portion of the hydrogen stream produced by electrolysis to at least a portion of the stream obtained according to step (d) to obtain a hydrogen-rich sulfur-free hydrocarbon stream; and converting at least a portion of the stream obtained according to step (e) into a syngas stream in the presence of oxygen as oxidant in a reforming step.

Description

Technical Field

[0001] The present invention relates to a method for producing synthesis gas. The present invention also relates to a method for producing methanol, which comprises the method for producing synthesis gas. Background Art

[0002] Large-scale industrial production of methanol is produced from synthesis gas. Synthesis gas is mainly a mixture of hydrogen (H2), carbon monoxide (CO) and carbon dioxide (CO2). The term "carbon oxides" is generally used to cover carbon monoxide and carbon dioxide. Among other things, the following two equilibrium reactions (1) and (2) occur simultaneously over a solid methanol synthesis catalyst.

[0003] (1)

[0004] (2)

[0005] The composition of the synthesis gas is characterized by the so-called stoichiometric number SN, defined as

[0006] Here n is in [mol].

[0007] The stoichiometrically balanced synthesis gas composition for methanol synthesis is characterized by a stoichiometric number SN of 2.0. Values ​​less than 2.0 indicate a hydrogen deficiency, while values ​​greater than 2.0 indicate an excess of hydrogen. Synthesis gas with a stoichiometric number less than 2.0 is also called substoichiometric synthesis gas.

[0008] Hydrogen-deficient synthesis gas is usually obtained in processes that include a partial oxidation step. These include partial oxidation (POX) itself and autothermal reforming (ATR).

[0009] The main elements of the ATR reactor are the burner, combustion chamber and catalyst bed in a refractory lined pressure jacket. In the ATR reactor, a hydrocarbonaceous input stream is partially oxidized by substoichiometric oxygen and then the partially oxidized hydrocarbonaceous input stream is steam reformed over a fixed bed of steam reforming catalyst.

[0010] For methane as hydrocarbon, partial oxidation is carried out in particular according to the following reaction equation (3).

[0011] (3)

[0012] Thus, the exothermic partial oxidation provides steam and the required heat energy for the endothermic steam reforming reaction, which proceeds according to reaction equation (4).

[0013] (4)

[0014] Due to the high temperatures, steam reforming (4) also occurs to a certain extent in the combustion chamber of the reactor without the presence of a catalyst.

[0015] According to reaction equation (5), the steam reforming reaction is accompanied by a water-gas shift reaction, which is also exothermic.

[0016] (5)

[0017] The gas at the outlet of the ATR reactor is usually at or close to thermodynamic equilibrium for the steam reforming and water gas shift reactions.

[0018] In the ATR, the hydrocarbons used are usually added with steam. The exact composition of the synthesis gas at the reactor outlet depends on the hydrocarbon to steam ratio of the input stream, the process temperature and the process pressure. The temperature of the gas mixture at the outlet of the ATR reactor is usually in the range of 950°C to 1050°C. The process pressure is usually 30 to 80 bar.

[0019] An alternative method for producing synthesis gas is partial oxidation itself, also known as POX. The main elements of a POX reactor are a burner and a combustion chamber, which are arranged in a refractory lined pressure vessel. A POX reactor partially oxidizes a hydrocarbon-containing input stream due to a substoichiometric amount of oxygen. Some (non-catalytic) steam reforming also occurs, and a water-gas shift reaction accompanies the partial oxidation. Therefore, the above reaction equations (3) to (5) also apply. The temperature of the gas mixture at the reactor outlet is typically in the range of 1250° C. to 1450° C. The process pressure is typically 30 to 100 bar.

[0020] As mentioned above, the above two processes usually provide a significantly substoichiometric synthesis gas, i.e. a synthesis gas with a stoichiometric number significantly below 2.0. Such a synthesis gas exhibits a hydrogen deficiency in methanol synthesis. If such a synthesis gas is used directly to produce methanol, the hydrogen is almost completely consumed, while most of the carbon oxides are not converted. This leads in particular to a higher than expected content of by-products (especially higher alcohols and ketones) and an unsatisfactory methanol yield.

[0021] Therefore, industrial processes usually supply a pure hydrogen stream to a substoichiometric synthesis gas stream to increase the stoichiometric number SN of the synthesis gas to at least 1.9, preferably 2.0 or higher.

[0022] To this end, conventional methods separate a portion of the reformed synthetic gas from the main stream and separate hydrogen from this substream, usually by pressure swing adsorption (PSA) or a membrane system. The tail gas produced by pressure swing adsorption contains hydrocarbons and / or carbon monoxide and can therefore be used as fuel gas for ATR or POX reactors.

[0023] If an electrolyser is used to provide hydrogen instead, part of the synthesis gas required for methanol synthesis can be saved, thus improving the plant's CO2 emissions.

[0024] Therefore, EP 3 658 494 B1 proposes mixing hydrogen from the electrolyser with a synthesis gas stream from a POX or ATR reactor. In addition, oxygen from an air separation plant is used as oxidant to operate the burner of the POX or ATR reactor.

[0025] The hydrogen provided by the electrolyzer usually contains up to 1% by volume or more of residual oxygen. This is related to the inevitable diffusion process between the anode space and the cathode space inside the electrolysis cell. In particular, a certain amount of oxygen produced at the anode always diffuses from the anode space to the cathode space through the membrane or diaphragm, thereby contaminating the hydrogen produced at the cathode.

[0026] Oxygen is a catalyst poison for methanol catalysts, so it is ideally necessary to quantitatively remove oxygen from the hydrogen stream produced at the cathode before it is mixed with the synthesis gas stream from the POX or ATR unit. This is carried out in a so-called deoxygenator (deoxygenator for short). This comprises a catalytic stage for quantitatively converting the contaminating oxygen in the hydrogen stream with the hydrogen into water. The water produced in this way catalytically can then be bound by adsorption (e.g. on molecular sieves). This provides an oxygen- and water-free hydrogen stream.

[0027] The most important hydrocarbon-containing input material for the production of synthesis gas is natural gas. Natural gas usually contains sulfur compounds, which need to be removed due to their activity as catalyst poisons in the ATR process or in the downstream methanol synthesis. Desulfurization is usually carried out in a so-called hydrodesulfurization unit (HDS unit). Sulfur compounds such as mercaptans, sulfides, disulfides and thiophenes are hydrogenated over a catalyst at a temperature of 300° C. to 500° C. by supplying hydrogen, thereby forming hydrogen sulfide, a sulfur-containing compound that is easy to remove. Hydrogen sulfide can subsequently be removed from the hydrocarbon mixture by, for example, amine washing methods. Usually before hydrogenation, the hydrogen content in the natural gas should be about 3%. Summary of the invention

[0028] The object of the present invention is to propose a method for improving the integration of the above-mentioned method, in order in particular to reduce the carbon dioxide emissions in the synthesis gas production and optionally the subsequent methanol synthesis.

[0029] Another object of the present invention is to reduce the consumption of natural gas or other hydrocarbon-containing input materials in the production of synthesis gas and optionally in the subsequent methanol synthesis.

[0030] The independent claims contribute to at least partially achieving at least one of the above-mentioned purposes. The dependent claims provide preferred embodiments that contribute to at least partially achieving at least one of the purposes. The preferred embodiments of the components of one category in the present invention are, where relevant, also preferably used for the same name or corresponding components of the corresponding other category in the present invention. The terms "having", "including" or "containing" etc. do not exclude the possible presence of other elements, components, etc. The indefinite article "a" does not exclude the possible presence of a plurality.

[0031] The above objects are at least partially achieved by a method for producing synthesis gas, in particular synthesis gas for methanol synthesis, comprising the following steps:

[0032] (a) providing a sulfur-containing hydrocarbon stream;

[0033] (b) providing a hydrogen gas stream generated by electrolysis;

[0034] (c) supplying a portion of the hydrogen gas stream produced by electrolysis to at least a portion of the sour hydrocarbon stream to obtain a sour hydrocarbon stream enriched in hydrogen;

[0035] (d) desulfurizing the stream obtained according to step (c) in a hydrodesulfurization unit (HDS unit) to obtain a sulfur-free hydrocarbon stream;

[0036] (e) supplying a portion of the hydrogen stream produced by electrolysis to at least a portion of the stream obtained according to step (d) to obtain a sulfur-free hydrocarbon stream enriched in hydrogen;

[0037] (f) converting at least part of the stream obtained according to step (e) into a synthesis gas stream in a reforming step in the presence of oxygen as oxidant.

[0038] According to the invention, the hydrogen produced by electrolysis can be used both for the desulfurization of the sour hydrocarbon stream and for enriching the produced synthesis gas with hydrogen. The latter is achieved, counter-intuitively, by supplying hydrogen to the desulfurized hydrocarbon stream before it is supplied to the reforming step of step (f), i.e. before synthesis gas production rather than after it.

[0039] The hydrogen stream produced by the electrolysis is utilized at least twice, i.e. for the desulfurization of the sulfur-containing hydrocarbon stream and for the enrichment of the synthesis gas with hydrogen. If a correspondingly configured electrolyzer is used, it is not necessary to separate a synthesis gas substream from the process in order to be used only for the production of hydrogen in order to subsequently feed this hydrogen into the main synthesis gas stream for the enrichment with hydrogen. This significantly reduces the proportion of hydrocarbon-containing process gas.

[0040] At least two utilizations of the hydrogen produced by electrolysis also allow for more flexible utilization of the required electrolyzer. If the hydrogen produced by electrolysis is less due to changes in the supply of renewable energy, then this less amount can be used, for example, entirely for desulfurization, and only partially for the enrichment of hydrogen in the synthesis gas. The amount of hydrogen lacking in the enrichment of hydrogen in the synthesis gas can be provided by, for example, a hydrogen recovery device, such as a PSA device (pressure swing adsorption device), which is typically a part of downstream methanol synthesis. There, a hydrogen recovery device (such as a PSA device or a membrane system) can be used to separate hydrogen from a purge stream.

[0041] Prior to converting the hydrocarbon stream into synthesis gas according to step (f), the hydrogen stream produced by electrolysis is counterintuitively supplied to the sulfur-free hydrocarbon stream according to step (e). The hydrogen stream produced by electrolysis is supplied to the sulfur-free hydrocarbon stream, in particular upstream of a corresponding reactor configured for the reforming step. The reactor is in particular a POX reactor or an ATR reactor. The resulting hydrogen-rich sulfur-free hydrocarbon stream is then converted into synthesis gas according to step (f) in the presence of oxygen as an oxidant.

[0042] Therefore, according to the invention, the conversion according to step (f) can be carried out using a hydrogen stream produced by oxygen-containing electrolysis. If, according to the prior art, the hydrogen stream produced by electrolysis is fed to the synthesis gas stream only after the conversion according to step (f), it is necessary to quantitatively remove oxygen from the hydrogen stream produced by electrolysis. As mentioned above, oxygen represents a catalyst poison for methanol synthesis catalysts and other types of catalysts.

[0043] Therefore, the reforming step according to step (f) is necessarily a reforming step in which oxygen is used in substoichiometric amounts relative to the hydrocarbon used. If this is not the case, it is not possible to produce a synthesis gas stream from a hydrogen-containing input gas stream. Therefore, the oxygen used is preferably completely consumed according to step (f), so that the synthesis gas stream produced contains no oxygen.

[0044] In one example, a portion of the hydrogen stream produced by electrolysis according to step (c) is provided to the complete sulfur-containing hydrocarbon stream.

[0045] In one example, a portion of the hydrogen stream produced by electrolysis according to step (e) is provided to the completely sulfur-free hydrocarbon stream produced according to step (d).

[0046] In another example, the hydrogen gas stream produced by electrolysis is divided into two sub-streams, which are used entirely in steps (c) and (e).

[0047] The sulfur-containing hydrocarbon stream is preferably a natural gas stream comprising methane as the main component. Methane preferably accounts for a proportion of at least 50% by volume, preferably at least 75% by volume, more preferably at least 90% by volume, more preferably at least 95% by volume, more preferably at least 99% by volume.

[0048] The stream obtained according to step (c) preferably has a hydrogen content ranging from 1% to 10% by volume, preferably from 1% to 5% by volume, more preferably from 2% to 4% by volume.

[0049] The hydrogen stream produced by electrolysis can be produced by any electrolysis process familiar to those skilled in the art. The electrolysis process is preferably water electrolysis. Examples include alkaline electrolysis, proton exchange membrane electrolysis (PEM electrolysis), anion exchange membrane electrolysis (AEM electrolysis), high temperature electrolysis (HTE), and electrolysis using a solid oxide electrolyzer cell (SOEC).

[0050] The synthesis gas stream comprises synthesis gas. Synthesis gas is a gas mixture comprising at least carbon oxides (carbon monoxide or carbon dioxide) and hydrogen. Synthesis gas preferably comprises carbon monoxide, carbon dioxide and hydrogen.

[0051] The reforming step is understood in principle to mean the chemical reaction of hydrocarbons with oxygen and / or steam to produce synthesis gas.

[0052] A preferred embodiment of the process according to the invention is characterized in that the hydrogen gas stream produced by electrolysis contains oxygen as a concomitant, wherein

[0053] - oxygen is not removed from the portion of the hydrogen stream produced by the electrolysis supplied to the sulfur-free hydrocarbon stream according to step (e), and

[0054] - removing oxygen from the portion of the hydrogen stream produced by the electrolysis of the sulphur-containing hydrocarbon stream supplied according to step (c).

[0055] As mentioned above, the hydrocarbon stream rich in electrolytic hydrogen for reforming with oxygen does not need to be oxygen-free. Therefore, a portion of the hydrogen stream produced by electrolysis can be supplied to the sulfur-free hydrocarbon stream as the raw hydrogen stream in step (e). It is also not necessary to remove water from this hydrogen substream, because, in particular in the ATR process according to the above reaction equation, steam is both formed and consumed.

[0056] A preferred embodiment of the process according to the invention is characterized in that the reforming step comprises autothermal reforming (ATR) or partial oxidation (POX) of the stream obtained according to step (e). It is preferred that the reforming step is autothermal reforming.

[0057] A preferred embodiment of the method according to the invention is characterized in that

[0058] - converting a portion of the stream obtained according to step (d) into a synthesis gas substream in an endothermic steam reforming step, and

[0059] - enriching according to step (e) a portion of the stream obtained according to step (d) with hydrogen to obtain a hydrogen-rich sulfur-free hydrocarbon substream, and

[0060] - According to step (f), the above substreams are combined and converted into a synthesis gas stream in a reforming step in the presence of oxygen as oxidant.

[0061] The endothermic steam reforming step is preferably a SMR (steam methane reforming) process. The reforming step in the presence of oxygen is preferably an ATR process.

[0062] In the above embodiment, a portion of the sulfur-free hydrocarbon stream is subjected to an endothermic steam reforming step without being enriched in hydrogen. The resulting synthesis gas is combined with the sulfur-free hydrocarbon stream enriched in hydrogen. The resulting mixed stream, which already contains synthesis gas from the endothermic steam reforming process, is subjected to a reforming step according to step (f) in the presence of oxygen as an oxidant.

[0063] In the present context, the reforming step is in particular an autothermal reforming step. The autothermal reforming step has an endothermic steam reforming step, in which a portion of the sulfur-free hydrocarbon stream is reformed with steam arranged upstream thereof. This procedure in principle provides a synthesis gas with a higher stoichiometric number than that obtained in a pure ATR process. Therefore, a smaller amount of hydrogen is required to adjust the stoichiometric number of the synthesis gas to a value suitable for methanol synthesis. Therefore, the electrolyzer can be made smaller.

[0064] Alternatively, excess electrolytically produced hydrogen can be used to underfire the endothermic steam reforming process.

[0065] A preferred embodiment of the process is therefore characterized in that part of the hydrogen gas stream produced by the electrolysis provided according to step (b) is used as fuel in the endothermic steam reforming step.

[0066] In this case, the electrolytically produced hydrogen stream preferably contains oxygen as a concomitant and oxygen is not removed from the portion of the electrolytically produced hydrogen stream used as fuel in the endothermic steam reforming step.

[0067] Since combustion requires a supply of combustion air or oxygen, it is not necessary to remove oxygen from the electrolytic hydrogen substream used for steam reformer underfiring.

[0068] In this case, a preferred embodiment of the method is characterized in that part of the hydrogen stream produced by electrolysis used as fuel is combined with part of the sulfur-containing hydrocarbon stream provided according to step (a) to obtain a mixed fuel stream containing hydrogen and hydrocarbons used as fuel in the endothermic steam reforming step. Alternatively, part of the desulfurized hydrocarbon stream can also be used for the mixed fuel stream. In this case, it is not necessary to desulfurize (remove sulfur oxides) the flue gases formed by the endothermic steam reforming process.

[0069] A preferred embodiment of the process according to the invention is characterized in that the amount of hydrogen produced by the electrolysis supplied to the sulfur-free hydrocarbon stream according to step (e) is adjusted so that the synthesis gas stream obtained according to step (f) has a stoichiometric number SN of 1.9 to 2.5, preferably 2.0 to 2.4, wherein

[0070] Here n is in [mol].

[0071] This ensures that a synthesis gas stream is obtained which can be used directly (i.e. immediately) for downstream methanol synthesis. The resulting synthesis gas stream can be used at least for downstream methanol synthesis without further supply of hydrogen to the synthesis gas stream. The resulting synthesis gas stream can also be used immediately or at least without further supply of hydrogen for other syntheses requiring a synthesis gas composition with a corresponding stoichiometric number.

[0072] A preferred embodiment of the process according to the invention is characterized in that the hydrogen gas stream produced by electrolysis contains up to 5% by volume of oxygen or 0.01% to 5% by volume of oxygen or 0.1% to 3% by volume of oxygen or 0.1% to 1% by volume of oxygen as a concomitant.

[0073] A preferred embodiment of the process according to the invention is characterized in that the process comprises providing an electrolytically produced oxygen stream, wherein the electrolytically produced oxygen stream is used as oxidant in step (f).

[0074] The reforming step according to step (f) is carried out in principle in the presence of oxygen as an oxidant. Air, oxygen-enriched air or pure oxygen can be used here. The oxidant is supplied in particular to the burner of a POX or ATR unit, where a hydrocarbon stream rich in hydrogen reacts with a substoichiometric amount of oxygen to provide synthesis gas.

[0075] Electrolysers usually produce oxygen as a "by-product", wherein this by-product is usually not utilized. Therefore, the use of electrolytically produced oxygen as oxidant for the reforming step according to step (f) represents an improvement in the process integration of the process of the present invention.

[0076] A further embodiment of the process according to the invention is characterized in that the process comprises providing an oxygen stream produced by air separation, wherein the oxygen stream produced by air separation is used as oxidant in step (f).

[0077] Alternatively or in addition to using electrolytic oxygen, the method may further comprise providing an oxygen stream produced by air separation, wherein the oxygen stream produced by air separation is used as the oxidant in step (f).

[0078] Alternatively or additionally, oxygen may also be supplied to the process via a pipeline.

[0079] A preferred embodiment of the process according to the invention is characterized in that according to step (f) at least part of the stream obtained according to step (e) is converted in a reforming step in the presence of oxygen as oxidant to provide a synthesis gas stream, this being carried out by additionally supplying steam.

[0080] A steam stream is optionally supplied to the sulphur-free hydrocarbon stream prior to conversion according to step (f), in particular when the reforming step comprises autothermal reforming (ATR).

[0081] When the reforming step comprises autothermal reforming, additional steam is preferably supplied. This advantageously prevents carbon deposition on the catalyst used for endothermic steam reforming in the ATR reactor. The term "additional steam" is to be understood as steam that is not produced inside the reaction by partial oxidation reaction or hydrogen generation water reaction. Depending on whether the supply of the steam stream is carried out before or after the hydrogen stream produced by electrolysis is supplied to the hydrocarbon-containing input gas stream, the addition of the steam stream accordingly produces a steam-containing and hydrogen-rich hydrocarbon stream.

[0082] A preferred embodiment of the process according to the invention is characterized in that part of the hydrogen stream produced by electrolysis is fed to the synthesis gas stream produced according to step (f).

[0083] When the synthesis gas stream thus produced is subjected to subsequent methanol synthesis, it is preferred to remove oxygen from this part of the hydrogen gas stream produced by electrolysis. It is particularly preferred to remove oxygen from the substream of the hydrogen gas stream produced by electrolysis, and subsequently divide the oxygen-free hydrogen substream into two other hydrogen substreams. The first of these substreams is supplied to at least a portion of the sulfur-containing hydrocarbon stream according to step (c). The second of these substreams is supplied to the synthesis gas stream produced according to step (f) according to the above-mentioned embodiment. Therefore, the synthesis gas stream rich in oxygen-free hydrogen is preferably subjected to subsequent synthesis, preferably methanol synthesis.

[0084] The above-mentioned purpose is also at least partially achieved by a method for producing methanol, which comprises a method for producing synthesis gas according to any of the above-mentioned embodiments, and also comprises a step of reacting the synthesis gas flow on a solid methanol synthesis catalyst to obtain crude methanol, wherein the crude methanol comprises at least methanol (CH3OH) and water.

[0085] The synthesis gas stream produced is preferably directly converted into crude methanol in the solid methanol synthesis reactor, in particular without further modification steps, in particular without further supply of a hydrogen stream. The synthesis gas of the synthesis gas stream for methanol synthesis preferably has a stoichiometric number SN of 1.9 to 2.5, preferably 2.0 to 2.4.

[0086] The synthesis gas of the synthesis gas stream used for methanol synthesis and produced according to the present invention may also be referred to as synthesis make-up gas. In most cases, the synthesis gas can be distinguished from the synthesis gas actually introduced into the corresponding methanol synthesis reactor in terms of its composition. As known to those skilled in the art, methanol synthesis is usually configured as a synthesis loop on a large industrial scale, that is, after separating the condensed crude methanol, the unreacted synthesis gas in the methanol synthesis reactor is recycled to the reactor inlet. The recycled synthesis gas, also referred to as recycle gas or recycle gas, is mixed with the synthesis make-up gas. The resulting mixed synthesis gas has the same composition as at the reactor inlet, and its stoichiometric number may deviate from the above-mentioned interval of the synthesis make-up gas.

[0087] A preferred embodiment of the process for producing methanol according to the invention is characterized in that crude methanol is separated into pure methanol and water in a thermal separation process, wherein the thermal separation process provides a carbon-containing tail gas stream, wherein the carbon-containing tail gas stream is used as fuel in a heating device for preheating the stream obtained according to step (e) before converting the stream into synthesis gas according to step (f).

[0088] The distillation of crude methanol to obtain pure methanol usually produces a low-boiling by-product stream - referred to herein as tail gas stream - which can be used as fuel in a heating device for preheating the stream obtained according to step (e). Preferably, the stream obtained according to step (e) is preheated, optionally with steam, before the actual reforming step according to step (f). The heating device is in particular a combustion heating device.

[0089] The above-mentioned utilization of the tail gas stream generated in the crude methanol distillation further improves the process integration.

[0090] A preferred embodiment of the process according to the invention for producing methanol is characterized in that the water separated off in the thermal separation process is used as starting material for the electrolytically produced hydrogen stream.

[0091] The water separated in the thermal separation process is preferably treated and subsequently used as starting material for the electrolytically produced hydrogen. The water separated in the thermal separation process usually contains sodium hydroxide (NaOH), which must be removed before the water can be used, for example, in PEM electrolysis. If the electrolytically produced hydrogen stream is produced by alkaline electrolysis, the removal of sodium hydroxide is not absolutely necessary, since alkaline electrolysis uses a highly concentrated aqueous potassium hydroxide solution (KOH). aq ) or sodium hydroxide solution (NaOH aq ) as the electrolytic medium.

[0092] Utilizing the water separated in the thermal separation process as starting material for hydrogen produced by electrolysis can improve process integration, since fewer resources are needed to provide water for the electrolysis.

[0093] A preferred embodiment of the method for producing methanol according to the present invention is characterized in that a synthesis gas stream is reacted over a solid methanol synthesis catalyst to obtain crude methanol, a residual gas stream containing synthesis gas that has not been converted into crude methanol is produced, wherein a portion of the residual gas stream is separated as a purge gas stream, and wherein the purge gas stream is supplied to a hydrogen recovery unit to produce a non-electrolytically produced hydrogen stream, and

[0094] - the non-electrolytically produced hydrogen stream is at least partially additionally supplied to the sour hydrocarbon stream to obtain a sour hydrocarbon stream enriched in hydrogen and / or

[0095] - A non-electrolytically produced hydrogen stream is at least partly additionally supplied to the stream obtained according to step (d) in order to obtain a hydrogen-rich, sulfur-free hydrocarbon stream.

[0096] As mentioned above, on an industrial scale, the synthesis of methanol is usually carried out in a so-called synthesis loop. Due to the establishment of thermodynamic equilibrium, the reaction of synthesis gas on the methanol synthesis catalyst is incomplete, and not only condensable crude methanol is obtained at the outlet of each reactor, but also a non-condensable residual gas stream containing unconverted synthesis gas is obtained. A part of this residual gas stream is circulated to the reactor inlet to carry out a new reaction to obtain crude methanol. This circulating stream is referred to as a circulating gas stream or a recirculating gas stream. A part is separated as a purge gas stream to avoid accumulating compounds that are inert under methanol synthesis conditions in the synthesis loop.

[0097] Advantageously, this purge gas stream containing hydrogen from the unconverted synthesis gas (residual gas stream) is fed to a hydrogen recovery unit, thereby producing a non-electrolytically produced hydrogen stream. The hydrogen recovery unit is preferably a pressure swing adsorption unit (PSA). Alternatively, it can also be a membrane unit.

[0098] The non-electrolytically produced hydrogen stream can be at least partially additionally fed to the sulfur-containing hydrocarbon stream to obtain a hydrogen-rich sulfur-containing hydrocarbon stream. Alternatively or additionally, the non-electrolytically produced hydrogen stream can be at least partially additionally fed to the stream obtained according to step (d) to obtain a hydrogen-rich sulfur-free hydrocarbon stream.

[0099] Thus, the non-electrolytically produced hydrogen stream can enhance the electrolytically produced hydrogen stream, both in the production of a hydrogen-rich sulfur-containing hydrocarbon stream and in the production of a hydrogen-rich sulfur-free hydrocarbon stream. In the latter case, sufficient non-electrolytically produced hydrogen is supplied together with the electrolytically produced hydrogen stream to ensure that step (f) in turn preferably provides a synthesis gas having a stoichiometric number SN of 1.9 to 2.5, preferably having a stoichiometric number SN of 2.0 to 2.4.

[0100] Alternatively or additionally, a non-electrolytically produced hydrogen stream can be supplied to the synthesis gas stream downstream of a corresponding reforming step with oxygen as oxidant (POX or ATR) and upstream of the methanol synthesis.

[0101] Since a methanol plant with a synthesis loop always produces a purge gas stream, it can be advantageously utilized within the process. This makes it possible in particular to compensate for variations in the hydrogen production of an electrolyser, for example when the electrolyser produces hydrogen based on renewable electricity, which is not constantly available over time.

[0102] Exemplary embodiments

[0103] The invention is explained in more detail below by means of exemplary embodiments and numerical examples, but the invention does not limit its subject matter in any way.In the figures, components with the same or at least similar functions and / or structures have the same reference numerals.

[0104] In the figure:

[0105] Figure 1 A flowchart of the method of the present invention according to a first example is shown,

[0106] Figure 2 A flow chart of the method of the present invention according to a second example is shown.

[0107] Figure 1 A simplified flow chart of a method 1 for synthesis gas production and subsequent methanol production according to a first example of the present invention is shown.

[0108] Starting from a natural gas source 10 containing mainly methane as hydrocarbon, a stream of sour hydrocarbons is first supplied to a compressor 11 via a pipeline 30 and then conveyed on in compressed form via a pipeline 31 .

[0109] Raw water from a water source 16 is supplied to a water treatment unit 17 via a pipe 33. In the water treatment unit 17, the raw water is treated to make it suitable for subsequent water electrolysis. The treatment includes, for example, filtration, removal of dissolved salts and degassing. The treated water is supplied to an electrolyzer 18 via a pipe 34, which may be, for example, a PEM electrolyzer. In this case, the electrolytic medium is the water treated by the water treatment unit 17.

[0110] The electrolyzer 18 produces a hydrogen stream and an oxygen stream. The hydrogen stream is taken out of the electrolyzer 18 via a conduit 35 and subsequently divided into two substreams. The first substream is further transported via a conduit 37 and supplied to the deoxygenation unit 14. In the deoxygenation unit 14, the hydrogen stream produced by electrolysis is deoxygenated. The oxygen-free hydrogen stream is transported via a conduit 32 and mixed with the sulfur-containing hydrocarbon stream in the conduit 31, thereby producing a hydrogen-rich hydrocarbon stream in the conduit 31. The hydrogen-rich hydrocarbon stream contains a hydrogen content of about 3% by volume. The hydrogen-rich sulfur-containing hydrocarbon stream is transported to a hydrodesulfurization unit 12 (HDS unit 12), wherein the hydrocarbon stream is desulfurized.

[0111] The hydrocarbon stream thus desulfurized is discharged from the HDS unit 12 via conduit 39 .

[0112] The second hydrogen substream produced in the electrolyzer 18 is conveyed through the pipeline 36 without further purification through the deoxygenation device. This hydrogen substream is supplied to the pipeline 39 through the pipeline 36 to obtain a hydrogen-rich sulfur-free hydrocarbon stream in the pipeline 39. The amount of hydrogen supplied is adjusted so that the subsequent reforming reaction produces a synthesis gas with a predetermined stoichiometric number SN.

[0113] The electrolyzer 18 also produces an oxygen stream, which is discharged from the electrolyzer 18 through a pipe 45. The oxygen stream is supplied to the ATR reactor 13 (i.e., the autothermal reformer 13). A hydrogen-rich, sulfur-free hydrocarbon stream from a pipe 39 is also supplied to the ATR reactor 13. The ATR reactor 13 reforms the above stream into a synthesis gas stream, which is discharged from the ATR reactor through a pipe 44. The synthesis gas stream produced in the ATR reactor 13 is cooled in a heat recovery unit 25. The heat recovery unit 25 simultaneously produces steam, which can optionally be used to reform a hydrogen-rich hydrocarbon stream (not shown) in the ATR reactor 13.

[0114] The cooled synthesis gas stream is discharged from the heat recovery unit 25 via a conduit 46. Subsequently, the gas stream is supplied to the methanol synthesis unit 19 via the same conduit 46, which unit comprises at least a reactor with a solid methanol synthesis catalyst, a condenser and a gas / liquid separator (not shown) for producing crude methanol. In the methanol synthesis unit 19, the unconverted synthesis gas is recycled to the reactor inlet as a recycle gas (not shown). A portion of the recycle gas stream is taken out as a purge gas stream to prevent the enrichment of inert components under the methanol synthesis conditions in the methanol synthesis unit 19. The purge gas stream is discharged from the methanol synthesis unit 19 via a conduit 47 and subsequently supplied to a hydrogen recovery unit, here a PSA unit 22. In the PSA unit 22, a hydrogen stream (not produced by electrolysis in this case) and a tail gas stream are produced by the purge gas stream. The hydrogen stream is discharged from the PSA unit via a conduit 48 and supplied to the cooled synthesis gas stream in the conduit 46. Therefore, the hydrogen stream produced by non-electrolysis is used to adjust the stoichiometric number required for methanol synthesis of the synthesis gas supplied to the methanol synthesis unit 19. The stoichiometric number required for methanol synthesis can also be adjusted simply by feeding the hydrogen stream produced by electrolysis from conduit 36 ​​to conduit 39. In this case, the hydrogen produced by the PSA unit can be used for other purposes.

[0115] The crude methanol produced in the methanol synthesis unit 19 mainly includes methanol, water and unwanted by-products. The crude methanol is supplied to the distillation unit 20 through the pipeline 49 to be thermally separated into the desired components. The distillation unit 20 may include one or more distillation columns. The distillation unit 20 produces at least pure methanol and water of a predetermined purity. The produced water can be supplied to the water treatment unit 17 to be used as a starting material in the electrolyzer 18. The distillation unit 20 also produces a carbon-containing tail gas stream of low-boiling substances. The tail gas stream is discharged from the distillation unit 20 through a pipeline 51 and supplied to the combustion heating device 15. The combustion heating device 15 is used to preheat the sulfur-free hydrocarbon stream rich in hydrogen before supplying it to the ATR reactor 13. To this end, the combustion heating device 15 generates a heat flux 60 shown by the dotted arrow. The combustion heating device 15 also supplies a portion of the hydrocarbon stream from the natural gas source 10. In order to reduce the carbon dioxide emissions of the combustion heating device 15, hydrogen that is not required in the process from the electrolyzer 18 or the PSA unit 22 can be supplied as fuel.

[0116] The pure methanol produced in the distillation unit 20 is taken out of the distillation unit 20 via a pipeline 50 and further used as a methanol product 21 .

[0117] Figure 2 A simplified flow chart of a method 2 for synthesis gas production and subsequent methanol production according to a second example of the present invention is shown. The differences between method 2 and method 1 are mainly discussed below.

[0118] according to Figure 2 In method 2, a sulfur-free hydrocarbon stream is withdrawn from the HDS unit 12 via conduit 42. A substream of the desulfurized hydrocarbon stream is withdrawn from this conduit 42 via conduit 41. The remaining hydrocarbon substream is supplied to the SMR unit 23 via conduit 42 and subjected to endothermic steam reforming therein.

[0119] As according to Figure 1 As in the example of , the electrolyzer 18 produces a hydrogen stream which is divided into two sub-streams in conduit 37 and conduit 38. A portion of the sulfur-free hydrocarbon stream is taken out from conduit 42 and conveyed onwards via conduit 41. The hydrogen sub-stream in conduit 38 is supplied to the hydrocarbon sub-stream in conduit 41 to obtain a sulfur-free hydrocarbon sub-stream enriched in hydrogen. The sulfur-free hydrocarbon sub-stream is conveyed onwards via conduit 40 and is combined in conduit 43 with a synthesis gas sub-stream discharged from the SMR unit 23 as an endothermic steam reforming product. This results in the production of a mixture of synthesis gas and hydrogen-rich hydrocarbons in conduit 43. The mixture undergoes a further reforming step in the ATR reactor 13, in this case in the presence of oxygen. Similar to Figure 1 In the example of FIG. 4 , the oxygen used for reforming in the ATR reactor 13 is provided by the oxygen flow provided by the electrolyzer and is supplied to the ATR reactor through a pipeline 45 .

[0120] The endothermic nature of the steam reforming reaction means that the SMR unit 23 requires an SMR combustion device 24, which is typically composed of two or more rows of burners arranged in rows for firing catalyst-filled reforming tubes in a reforming furnace known to those skilled in the art. The oxygen required for the burners is transferred from line 45 and supplied to the SMR combustion device 24 via line 54. Thus, the required fuel is simultaneously taken from the natural gas source 10 and supplied to the SMR combustion device via line 53. The thermal energy provided by the SMR combustion device is shown in the form of a dashed arrow as heat flux 61 to the SMR unit.

[0121] The reforming of the synthesis gas substream provided by the SMR unit 23 and the sulfur-free hydrocarbon stream rich in hydrogen in the ATR reactor 13 provides a synthesis gas stream having a composition of Figure 1 The synthesis gas stream obtained by the method in the above method has a greater stoichiometric number. Therefore, the synthesis gas stream needs to be supplied with less hydrogen from the PSA unit 22 through the pipeline 48, and / or from the beginning, the hydrocarbon stream in the pipeline 41 needs to be supplied with less hydrogen through the pipeline 38.

[0122] The following numerical examples are based on simulation data and are used to further illustrate the present invention.

[0123] The following table shows simulation data for two comparative examples 1 and 2 and one embodiment of the present invention.

[0124]

[0125]

[0126] Each example produces in principle 3000 tons of methanol per day, wherein an autothermal reformer (ATR) is used to produce the synthesis gas.

[0127] In Comparative Example 1, a portion of the reformed gas (syngas) is used to obtain hydrogen in the PSA unit, thereby obtaining hydrogen for adjusting the stoichiometric number of the produced synthesis gas and for the HDS unit. Therefore, this hydrogen is only produced by PSA, which can also obtain purge gas from methanol synthesis as starting material. Therefore, Comparative Example 1 does not produce hydrogen by electrolysis.

[0128] According to Comparative Example 2, the majority of the required hydrogen is further produced by a PSA unit supplied with reformed gas (syngas). This is used to adjust the stoichiometric amount of the produced synthesis gas for methanol synthesis. The hydrogen required for the HDS unit is provided by an electrolyser.

[0129] In an embodiment of the present invention, most of the required hydrogen is provided by the electrolyzer. The PSA unit produces hydrogen only from the purge gas of methanol synthesis. No reforming gas (synthesis gas) is supplied to it. Therefore, most of the hydrogen required to adjust the stoichiometric number of the synthesis gas and the HDS unit is provided by the electrolyzer. Compared with the second comparative example, the procedure achieves a corresponding natural gas saving of more than 5%, and compared with the first comparative example, a corresponding natural gas saving of more than 6%. Surprisingly, it also shows advantages in terms of carbon dioxide emissions from the combustion heating device adopted. Therefore, compared with Comparative Example 2, the additional carbon dioxide emissions of the steam generator in the embodiment of the present invention are obviously overcompensated.

[0130] List of reference numbers of the accompanying drawings

[0131] 1.2 Methods

[0132] 10 Natural Gas Source

[0133] 11. Compressor

[0134] 12 HDS units

[0135] 13 ATR Reactor

[0136] 14 Deoxygenation Unit

[0137] 15 Combustion Heating Device

[0138] 16 Water

[0139] 17 Water treatment unit

[0140] 18 Electrolyzer

[0141] 19 Methanol Synthesis Unit

[0142] 20 distillation units

[0143] 21 Methanol Products

[0144] 22 PSA units

[0145] 23 SMR units

[0146] 24 SMR Combustion

[0147] 25 Heat recovery unit

[0148] 30 to 54 pipes

[0149] 60, 61 Heat flux

Claims

1. A method for producing synthesis gas, in particular synthesis gas for methanol synthesis (1, 2), comprising the following steps: (a) providing a sulfur-containing hydrocarbon stream; (b) providing a hydrogen gas stream generated by electrolysis; (c) supplying a portion of the hydrogen gas stream produced by electrolysis to at least a portion of the sour hydrocarbon stream to obtain a sour hydrocarbon stream enriched in hydrogen; (d) desulfurizing the stream obtained according to step (c) in a hydrodesulfurization unit (HDS unit) (12) to obtain a sulfur-free hydrocarbon stream; (e) supplying a portion of the hydrogen stream produced by electrolysis to at least a portion of the stream obtained according to step (d) to obtain a sulfur-free hydrocarbon stream enriched in hydrogen; (f) converting at least part of the stream obtained according to step (e) into a synthesis gas stream in a reforming step in the presence of oxygen as oxidant.

2. The method according to claim 1, characterized in that The hydrogen gas produced by electrolysis contains oxygen as a byproduct. - oxygen is not removed from the portion of the hydrogen stream produced by the electrolysis of the sulphur-free hydrocarbon stream supplied to step (e), and - removing oxygen from the portion of the hydrogen stream produced by the electrolysis of the sulphur-containing hydrocarbon stream supplied according to step (c).

3. The method according to claim 1 or 2, characterized in that: The reforming step comprises autothermal reforming (ATR) or partial oxidation (POX) of the stream obtained according to step (e).

4. A method according to any one of the preceding claims, characterised in that - converting a portion of the stream obtained according to step (d) into a synthesis gas substream in an endothermic steam reforming step, and - subjecting a portion of the stream obtained according to step (d) to hydrogen enrichment treatment with hydrogen according to step (e) to obtain a hydrogen-enriched sulfur-free hydrocarbon substream, and - According to step (f), the above substreams are combined and converted into a synthesis gas stream in a reforming step in the presence of oxygen as oxidant.

5. The method according to claim 4, characterized in that A portion of the electrolysis-produced hydrogen stream provided according to step (b) is used as fuel in the endothermic steam reforming step.

6. The method according to claim 5, characterized in that The electrolytically produced hydrogen stream contains oxygen as a concomitant, and oxygen is not removed from the portion of the electrolytically produced hydrogen stream that is used as fuel in the endothermic steam reforming step.

7. The method according to claim 5 or 6, characterized in that: The portion of the electrolytically produced hydrogen stream used as fuel is combined with a portion of the sulfur-containing hydrocarbon stream provided according to step (a) to obtain a mixed fuel stream containing hydrogen and hydrocarbons, which is used as fuel in the endothermic steam reforming step.

8. The method according to any one of the preceding claims, characterized in that The amount of hydrogen produced by the electrolysis supplied to the sulfur-free hydrocarbon stream according to step (e) is adjusted so that the synthesis gas stream obtained according to step (f) has a stoichiometric number SN of 1.9 to 2.5, preferably 2.0 to 2.4, wherein Here n is in [mol].

9. The method according to any one of the preceding claims, characterized in that The hydrogen gas stream produced by electrolysis contains up to 5% by volume of oxygen or 0.01% by volume to 5% by volume of oxygen or 0.1% by volume to 3% by volume of oxygen or 0.1% by volume to 1% by volume of oxygen as a concomitant.

10. The method according to any one of the preceding claims, characterized in that The method comprises providing an electrolytically produced oxygen stream, wherein the electrolytically produced oxygen stream is used as an oxidant in step (f).

11. The method according to any one of the preceding claims, characterized in that The process comprises providing an oxygen stream produced by air separation, wherein the oxygen stream produced by air separation is used as an oxidant in step (f).

12. The method according to any one of the preceding claims, characterized in that The conversion according to step (f) of at least a portion of the stream obtained according to step (e) into a synthesis gas stream in a reforming step in the presence of oxygen as oxidant is carried out with an additional supply of steam.

13. The method according to any one of the preceding claims, characterized in that The hydrogen stream produced by electrolysis is partly supplied to the synthesis gas stream produced according to step (f).

14. A method for producing methanol, comprising the method for producing synthesis gas according to any one of the preceding claims, further comprising the step of reacting the synthesis gas stream over a solid methanol synthesis catalyst to obtain crude methanol, wherein the crude methanol comprises at least methanol (CH3OH) and water.

15. The method according to claim 14, characterized in that The crude methanol is separated into pure methanol and water in a thermal separation process, wherein the thermal separation process obtains a carbon-containing tail gas stream, which is used as fuel in a heating device for preheating the stream obtained according to step (e) before converting the stream into synthesis gas according to step (f).

16. The method according to claim 14 or 15, characterized in that The water separated in the thermal separation process serves as starting material for the hydrogen stream produced by electrolysis.

17. The method according to any one of claims 14 to 16, characterized in that reacting a synthesis gas stream over a solid methanol synthesis catalyst to obtain crude methanol to produce a residual gas stream containing synthesis gas that has not been converted into crude methanol, wherein a portion of the residual gas stream is separated as a purge gas stream, and wherein the purge gas stream is supplied to a hydrogen recovery unit to produce a non-electrolytically produced hydrogen stream, and - additionally feeding the non-electrolytically produced hydrogen stream at least partly to the sour hydrocarbon stream to obtain a sour hydrocarbon stream enriched in hydrogen, and / or - additionally supplying a non-electrolytically produced hydrogen stream at least partly to the stream obtained according to step (d) in order to obtain a hydrogen-rich, sulfur-free hydrocarbon stream.

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