Process and plant for the production of methanol from a carbon-containing feedstock

Abstract

The invention relates to a process for producing methanol from a carbon-containing feedstock. In a process where efficiency and energy use are optimized, at least the following steps are included: processing of at least one carbon-containing feedstock; gasification in a gasifier and / or pyrolysis in a pyrolysis furnace of the processed carbon-containing feedstock to obtain a crude synthesis gas; processing of the crude synthesis gas to obtain a synthesis gas; methanol synthesis to obtain crude methanol; distillation of the crude methanol to obtain methanol and at least one by-product; extraction of a partial stream from the methanol synthesis and feeding at least a part of the partial stream into the gasifier and / or pyrolysis furnace.

Description

[0001] The invention relates to a process for producing methanol from a carbon-containing feedstock.

[0002] In addition, the invention relates to a plant for the production of methanol from a carbon-containing feedstock.

[0003] Methanol is produced through an exothermic reaction that uses hydrogen and carbon oxides as reactants, which are fed as a gas stream into a suitable reactor for methanol synthesis. These substances can be obtained from various sources.

[0004] One approach involves subjecting a carbon-containing energy carrier stream to steam reforming or catalytic partial oxidation, resulting in a synthesis gas consisting primarily of hydrogen and carbon oxides. Depending on the type of energy carrier and the synthesis gas production method, different proportions of hydrogen and carbon oxides—and thus different stoichiometry—are achieved in the synthesis gas. The resulting stoichiometry can then be adjusted through various measures, such as a water-gas shift reaction. An advantage of this approach is that the energy carrier itself—e.g., natural gas—can typically be supplied at high pressure, meaning that only a relatively small pressure increase is required after synthesis gas production to reach the pressure necessary for methanol synthesis.

[0005] Another way to provide the reactants for methanol synthesis is to use a gas stream with a high carbon dioxide content and no hydrogen. Such a gas stream can be obtained, for example, from flue gas, i.e., exhaust gas from a combustion process. Similarly, such a gas stream could be obtained from a bioethanol production plant. Since such flue gas contains no hydrogen, the hydrogen in this variant must be supplied from another source, such as electrolysis. For methanol synthesis, the gas containing the reactants is typically circulated in a closed loop, as a single pass of this gas through the reactor usually does not result in sufficiently complete conversion to methanol.

[0006] The methanol consumed is regularly removed from the circulating gas by condensation. However, inert substances also accumulate during circulation, and these cannot be sufficiently removed by condensation. To remove these substances from the cycle, it is necessary to discharge a portion of the circulating gas as purge gas, which can then be, for example, combusted.

[0007] Future-oriented processes and plants utilize an organic substance, such as biomass, which is gasified to synthesize methanol. Various approaches exist for this. Compared to plants for synthesizing methanol from fossil fuels, these plants and processes require more complex pretreatments and gas purification.

[0008] In a typical methanol plant, gasification is carried out using steam and oxygen. The reason for using steam is that the biomass undergoes thermal decomposition, and the required steam reacts with the carbon from the organic matter to form hydrogen. Methanol synthesis takes place under high pressure, and if air is used for the synthesis, the nitrogen it contains increases the power required and also reduces the efficiency of the methanol synthesis. Therefore, the use of oxygen is preferred.

[0009] Conventional plants that have so far operated without biomass are only conditionally competitive in terms of cost as plant systems for the synthesis of methanol specifically from biomass.

[0010] The invention is therefore based on the objective of providing a process and a plant for the production of methanol from a carbon-containing feedstock, in particular biomass, in which efficiency and energy use are optimized.

[0011] This problem is initially solved in the present invention by the features of claim 1 in that the process comprises at least the following steps: processing of at least one carbon-containing feedstock; gasification in a gasifier and / or pyrolysis in a pyrolysis furnace of the processed carbon-containing feedstock to obtain a crude synthesis gas; processing of the crude synthesis gas to obtain a synthesis gas; methanol synthesis to obtain crude methanol; distillation of the crude methanol to obtain methanol and at least one by-product; extraction of a partial stream from the methanol synthesis and feeding at least a part of the partial stream into the gasifier and / or pyrolysis furnace.

[0012] A carbon-containing feedstock is understood to mean, in particular, carbon-containing solids and / or carbon-containing liquids. Preferably, the carbon-containing feedstock is biomass. Particularly preferably, the carbon-containing feedstock is waste, for example, household waste, plastics, etc.

[0013] Accordingly, the processing of the carbon-containing feedstock can be designed in various ways, and it is clear to those skilled in the art that the processing can and must differ for different feedstocks. The processing can include steps such as drying, torrefaction, carbonization, and / or comminution of the carbon-containing feedstock.

[0014] Depending on how the gasification and / or pyrolysis of the processed carbonaceous feedstock takes place, the processing must be adapted accordingly. With a fluidized bed gasifier, it is generally necessary to break down the structure of the carbonaceous material to achieve an acceptable result. With fixed-bed or fluidized bed gasifiers, the processing is usually less complex.

[0015] Methanol synthesis takes place in a suitable reactor system. Adiabatic and quasi-isothermal reactors are the most common. In adiabatic reactors with a single catalyst bed, the reaction is quenched at multiple points by the addition of cold gas. The temperature profile along the reactor axis is therefore sawtooth-shaped. In reactors where the synthesis gas flows through several axially arranged reactor layers, the heat of reaction is removed by intercoolers. In these reactors, the synthesis gas flows axially, radially, or axially / radially through the catalyst beds.

[0016] The standard quasi-isothermal reactor consists of a tubular reactor cooled by water. The catalyst is located in tubes surrounded by water at its boiling point to dissipate the heat of reaction. The temperature of the cooling medium is controlled by a preset pressure in the steam drum. The synthesis gas flows axially through the tubes.

[0017] The crude methanol leaving the reactor contains water and other impurities. The amount and composition of these impurities depend on the reaction conditions, the feed gas, and the type and lifetime of the catalyst. The crude methanol contains low-boiling and high-boiling components (light and heavy). The light components mainly include dissolved gases (e.g., CO₂), dimethyl ether, methyl formate, and acetone. The heavy components include higher alcohols, long-chain hydrocarbons, higher ketones, and esters of lower alcohols.

[0018] The impurities in crude methanol are generally separated in two stages. First, all components that boil at a lower temperature than methanol are removed in a low-boiling column. The pure methanol is then distilled overhead in one or more distillation columns. If the columns operate at different pressures, the heat of condensation from the vapors in the higher-pressure column can be used to heat the lower-pressure column.

[0019] Some components form azeotropic mixtures with methanol, e.g. acetone, ethyl formate, methyl acetate, ethyl acetate and methyl propionate.

[0020] This proposed configuration, with the extraction of a partial stream from the methanol synthesis and the feeding of at least a portion of this stream into the gasifier, also allows for a reduction or even elimination of CO2 separation in gasification technologies / processes where CO2 is used as the feed gas for the feedstock, since the unreacted gas from the methanol synthesis can be used as the feed gas. The reduced need for CO2 means that less solvent is required in the CO2 separation device, and consequently, less energy is needed for regeneration. Furthermore, compression of the CO2 gas stream to the gasifier's operating pressure is no longer necessary if the gasifier is operated at elevated pressure.

[0021] Further preferred embodiments of the invention result from the other features mentioned in the dependent claims.

[0022] In a first embodiment of the process according to the invention, at least a portion of the partial flow is introduced upstream of the methanol synthesis. This creates a recycling loop, whereby only a portion is returned to the reactor and, according to the invention, a portion is directed back to the gasifier and / or pyrolysis furnace. The recycled flow is not entirely fed to the methanol reactor, but partially to the biomass gasification process. During gasification, certain components, such as hydrocarbons, are partially converted to synthesis gas. This gas then enters the gas processing unit along with the synthesis gas produced from biomass or waste during gasification and is finally fed to the methanol synthesis process.

[0023] Depending on the conditions and specifications of the process, i.e., the procedure or the plant, the ratio between the portion of the partial stream that is fed into the methanol synthesis without further treatment or intermediate operations and the portion of the partial stream that is fed into the gasifier and / or pyrolysis furnace can be adjusted. Preferably, the quantitative ratio between the portion of the partial stream (low in methanol and hydrogen) that is fed into the gasifier and / or pyrolysis furnace and the portion of the partial stream that is fed into the methanol synthesis is less than 1, preferably less than 0.5, and particularly preferably less than 0.1.

[0024] In a further embodiment of the process according to the invention, the partial stream is directed into a methanol recovery unit before being fed into the gasifier and / or pyrolysis furnace, whereby a methanol-laden stream and a methanol-poor partial stream are produced in the methanol recovery unit. The methanol recovery unit is, in particular, a methanol scrubbing column.

[0025] Furthermore, in a further embodiment of the process according to the invention, it can be provided that the methanol-laden stream is directed to distillation. This advantageous configuration allows methanol to be separated from this methanol-containing stream as a valuable product.

[0026] In a further embodiment of the process according to the invention, the partial stream can be routed to a hydrogen recovery unit before being fed into the gasifier and / or pyrolysis furnace. The hydrogen recovery unit can be combined with the methanol recovery unit, with the hydrogen recovery unit being located upstream or downstream of the methanol recovery unit. The hydrogen recovery unit produces a hydrogen-rich stream and a hydrogen-poor partial stream, with the hydrogen-rich stream being fed to the methanol synthesis process. After the removal of crude methanol, the unreacted synthesis gas still contains methanol and a significant proportion of hydrogen. The methanol content can be significantly reduced by scrubbing. The hydrogen can be separated by hydrogen recovery and fed directly to the methanol reactor.The following two technologies are particularly suitable for hydrogen recovery: membrane processes and pressure swing adsorption (PSA).

[0027] In a further preferred embodiment of the process according to the invention, a hydrogen stream and an oxygen stream are generated by means of water electrolysis, and the hydrogen stream is introduced upstream of or into the methanol synthesis, while the oxygen stream, or a portion thereof, is introduced into the gasifier. To increase the carbon yield, it is advantageous to add external hydrogen, for example, from water electrolysis. In a plant configuration with water electrolysis, the oxygen produced during water splitting can be used in the gasification process. In this case, no additional oxygen source, for example, from an air separation unit (ASU), is necessary.

[0028] In a further advantageous embodiment of the method according to the invention, an oxygen stream is generated by means of air separation and introduced into the carburetor. Additional oxygen can be added by means of an air separation unit (ASU) without water electrolysis. This can be advantageous if no external hydrogen is required.

[0029] The aforementioned problem is further solved by a plant for the production of methanol from a carbon-containing feedstock, comprising at least the following components: a device for processing the carbon-containing feedstock; a gasifier for gasification and / or a pyrolysis furnace for the pyrolysis of the processed carbon-containing feedstock to obtain crude synthesis gas; a device for processing the crude synthesis gas to obtain synthesis gas; a device for methanol synthesis to obtain crude methanol; a distillation unit for distilling the crude methanol to obtain methanol and at least one by-product; and a recirculation system from the methanol synthesis device to the device for the gasifier and / or pyrolysis furnace. The plant for the production of methanol is configured and designed to carry out a process according to the invention.The preceding statements concerning the method according to the invention also apply accordingly to the plant according to the invention.

[0030] In a first embodiment of the plant according to the invention, a methanol recovery unit is provided in the return process, wherein a methanol-laden stream and a first methanol-poor partial stream are generated in the methanol recovery unit.

[0031] In a further embodiment of the plant according to the invention, a hydrogen recovery unit is provided, wherein the hydrogen recovery unit is fluidically connected to the methanol recovery unit and the device for methanol synthesis.

[0032] Unless otherwise stated in individual cases, the various embodiments of the invention mentioned in this application can be advantageously combined with one another.

[0033] The invention is explained below using exemplary embodiments with reference to the accompanying drawings. These show: Fig. 1 a schematic representation of an embodiment of a plant or process for the production of methanol from biomass, Fig. 2 a schematic representation of an exemplary embodiment of an optimized plant or process for the production of methanol from biomass, Fig. 3 a schematic representation of a further embodiment of an optimized plant or process for the production of methanol from biomass and Fig. 4 a schematic representation of a further embodiment of an optimized plant with methanol and hydrogen recovery.

[0034] Fig. Figure 1 schematically shows a process or plant 1 for the production of methanol from a carbon-containing feedstock. First, at least one carbon-containing feedstock, in this case biomass, biological material, or carbon-rich material, is prepared for further processing in a preparation unit 2. After preparation 2, the biomass is gasified in a gasifier 3 and / or pyrolyzed in a pyrolysis furnace (not shown), yielding crude synthesis gas. This crude synthesis gas is treated in a crude synthesis gas treatment unit 4 to obtain synthesis gas. Subsequently, the synthesis gas is converted to methanol or crude methanol in a methanol synthesis unit 5, which includes at least one reactor 6. Crude methanol leaving reactor 6 contains water and other impurities.Therefore, a distillation unit 7 is planned downstream of reactor 6 to obtain pure methanol. During distillation unit 7, byproducts, process water, and unreacted substances are thermally separated from the methanol.

[0035] In the present embodiment, a water electrolysis unit 8 is additionally provided, which supplies oxygen for the gasifier and hydrogen for methanol synthesis. N2 or CO2 is typically used as the carrier gas for the biomass. Some gasification technologies do not use a carrier gas.

[0036] Fig. Figure 2 shows an optimized process or plant 1 for the production of methanol from a carbon-containing feedstock. In this embodiment, an air separation unit (ASU) 9 is provided for the supply of oxygen to the carburetor 3.

[0037] Furthermore, a recirculation system 10 is provided through which a partial stream is extracted from the methanol synthesis unit 5. In the present embodiment, this partial stream is divided again, so that one part is returned directly to the methanol synthesis unit 5 without further processing, while another part is directed to the gasifier 3. The recirculation to the gasifier 3 allows the CO2 separation to be reduced or even eliminated, since the unreacted gas from the methanol synthesis can be used as a feed gas. CO2 as a carrier gas from the raw synthesis gas processing unit 4 is therefore no longer necessary and is shown only as a dashed line. The reduced need for CO2 means that less solvent is required in the CO2 separation unit, and consequently, less energy is needed for regeneration.Furthermore, compression of the CO2 gas flow to the operating pressure of the carburetor is also unnecessary if it is operated at increased pressure.

[0038] The cycle flow is not entirely fed to the methanol reactor, but partially to the biomass gasification unit. In gasifier 3, certain components, such as hydrocarbons, are partially converted to synthesis gas. This gas then enters the gas processing unit along with the synthesis gas produced from biomass or waste during gasification and is finally fed to the methanol synthesis unit. Depending on the conditions and specifications of the process, i.e., the procedure or the plant, the ratio between the portion of the cycle flow that is directed to the methanol synthesis unit 5 without further treatment or intermediate operations and the portion of the cycle flow that is directed to the gasifier can be adjusted.In the present embodiment, the quantitative ratio between the part of the partial flow that is directed into the carburetor 3 and the part of the partial flow that is directed into the methanol synthesis device 5 is less than 1.

[0039] Fig. Figure 3 shows a configuration that largely corresponds to the embodiment shown in the illustration. Fig. 2 agrees. However, instead of the air separation plant 9, a water electrolysis plant 8 is used, whereby the oxygen produced is at least partially directed into the gasifier 3, while the hydrogen produced is introduced into the process upstream of the methanol synthesis plant 5.

[0040] Fig. Figure 4 shows a configuration in which the portion of the partial stream that is returned to the gasifier 2 is first directed into a methanol recovery unit 11 in the form of a methanol scrubbing column. In the methanol recovery unit 11, a methanol-laden stream in the form of a water-methanol mixture and a methanol-poor partial stream are produced. Additionally, downstream of the methanol recovery unit 11, the methanol-poor partial stream is directed into a hydrogen recovery unit 12 before being fed into the gasifier. This results in a hydrogen-rich stream and a hydrogen- and methanol-poor partial stream. The hydrogen-rich stream is then fed to the methanol synthesis unit 5. After the removal of crude methanol, the unreacted synthesis gas still contains methanol and a significant proportion of hydrogen. The methanol content can be significantly reduced by scrubbing.The hydrogen can be separated using hydrogen recovery and fed directly into the methanol synthesis process. The following two technologies are particularly suitable for hydrogen recovery: membrane processes and pressure swing adsorption (PSA).

[0041] Furthermore, in Fig. As can be seen in Figure 4, the water-methanol mixture is directed to distillation unit 7. This results in a total of four possible recycling streams. An internal recycling stream, which is fed back into methanol synthesis unit 5 untreated. A recycling stream that directs the methanol-water mixture into distillation for methanol separation. A hydrogen-rich stream, which can be obtained by the hydrogen recovery unit 12 and fed back into methanol synthesis unit 5. And an external recycling stream, as part of the partial stream that is returned to the gasifier. This external stream is low in hydrogen and methanol. Reference symbol list 1 Annex 2. Processing of a carbon-containing feedstock 3 carburetors 4. Equipment for processing the raw synthesis gas 5. Methanol synthesis apparatus 6 Reactor 7 Distillation 8 Water electrolysis 9 Air separation plant (ASU) 10 Repatriation 11 Methanol recovery unit 12 hydrogen recovery units

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