Method and plant for producing methanol

Abstract

The invention relates to a method and a plant for producing methanol, comprising: carrying out (S10) a first reaction process at a first temperature (T1), wherein the first reaction process, using biomass and oxygen, produces a synthesis gas containing carbon dioxide (CO2); carrying out (S20) a second reaction process in the form of a reverse-water-gas-shift reaction at a second temperature (T2) using the produced synthesis gas, wherein the second reaction process increases a carbon monoxide component (CO) in the synthesis gas, wherein the second temperature (T2) is above 400°C; carrying out (S50) a methanol synthesis using the synthesis gas to produce methanol. The invention further relates to a plant configured to carry out the method.

Description

[0001] Description

[0002] Process and plant for producing methanol

[0003] Technical field of the invention

[0004] The present invention relates to a process for producing methanol and a plant for producing methanol.

[0005] Background of the invention

[0006] To produce fuels from renewable energies, it is known to first convert carbon dioxide or carbon monoxide with hydrogen to methanol in a methanol synthesis according to the following two reaction equations:

[0007] ( 1 ) CO2 + 3H2CH3OH + H20

[0008] ( 2 ) CO + 2H2CH3OH

[0009] The carbon dioxide or carbon monoxide required for methanol synthesis is provided, for example, in a synthesis gas that is produced by upstream combustion or gasification of biomass, which is also referred to as the combustion route or gasification route.

[0010] The combustion of biomass typically takes place under an excess of oxygen, so that the carbon contained in the biomass is mainly converted into carbon dioxide, as illustrated in the following reaction equation ( 3 ):

[0011] ( 3 ) Biomass + 02C02+ H20 (strongly exothermic)

[0012] The combustion exhaust gas therefore consists essentially of carbon dioxide and water. To provide a synthesis gas for methanol synthesis according to the reaction equation (1) above, hydrogen is finally added to the combustion exhaust gas.

[0013] Due to the high carbon dioxide content resulting from combustion – see reaction equation (3) – the water content produced in methanol synthesis according to the above reaction equation (1) must be significantly reduced in a downstream distillation stage in order to provide methanol with a certain degree of purity for the production of fuels. The provision and operation of the distillation stage is technically complex and cost-intensive.

[0014] As an alternative to the combustion route, the gasification route can be chosen. In this process, the methanol synthesis is preceded by the gasification of biomass under an oxygen deficiency or oxygen deficiency. The gasification produces a gasification exhaust gas or a synthesis gas consisting of carbon monoxide, carbon dioxide, and hydrogen according to the following reaction equation (4):

[0015] ( 4 ) Biomass + O2 + H20 CO + C02 + H2 (O2 partial reaction exothermic)

[0016] In methanol synthesis, carbon monoxide and carbon dioxide are converted into methanol or so-called crude methanol in the form of a mixture of methanol and water according to the ratios of the above reaction equations (1) and (2). Due to the carbon dioxide contained in the gasification exhaust gas or in the synthesis gas, the crude methanol contains a certain amount of water, which must be laboriously reduced by distillation.

[0017] The advantage of the gasification route is that, compared to the combustion route, less water is produced, which must be separated by distillation. On the other hand, combustion is a much more robust process than gasification. For example, biomass of low or heterogeneous quality can be easily converted by combustion, whereas the gasification route requires a biomass feedstock of comparatively high or constant quality.

[0018] In summary, it can be stated that it is established in the state of the art to either separate the carbon dioxide produced in the gasification route, so that the carbon yield of the biomass used decreases, or to convert it into methanol synthesis and according to the reaction equation

[0019] ( 1 ) the resulting water is to be separated by means of distillation.

[0020] Summary of the invention

[0021] Starting from the known prior art, it is an object of the present invention to provide an improved process for producing methanol, a corresponding plant for carrying out the process, and a plant for producing methanol.

[0022] The object is achieved by a process for producing methanol having the features of claim 1. Advantageous further developments emerge from the subclaims, the description, and the figures.

[0023] Accordingly, a process for producing methanol is proposed, comprising the following steps:

[0024] - carrying out a first reaction process at a first temperature, wherein the first reaction process produces a synthesis gas containing carbon dioxide using biomass and oxygen,

[0025] - carrying out a second reaction process in the form of a reverse water gas shift reaction at a second temperature using the produced synthesis gas, wherein the second reaction process increases a carbon monoxide content in the synthesis gas, wherein the second temperature is greater than 400 ° C, and - carrying out a methanol synthesis using the synthesis gas to produce methanol.

[0026] When the second reaction process is mentioned here, this refers to the "Reverse Water Gas Shift" reaction - abbreviated here to "RWGS" - or a corresponding RWGS reactor and vice versa.

[0027] Because the second temperature is higher than 400 ° C , the equilibrium of the known RWGS reaction equation

[0028] (5) CO2+H2<->CO + H20 can be designed particularly favorably to increase the carbon monoxide content in the synthesis gas and reduce the carbon dioxide content in the synthesis gas. The reaction equation (5) is sometimes abbreviated below as "RWGS reaction".

[0029] In the course of the present invention, it was discovered that, thanks to a significant reduction in the carbon dioxide content in the synthesis gas, which is used as a starting material in methanol synthesis, a distillation stage for separating water during methanol synthesis can be dispensed with. Eliminating the distillation stage saves more process engineering and equipment costs than would be incurred by providing an RWGS reactor or RWGS catalyst for carrying out the RWGS reaction.

[0030] Furthermore, it was recognized that, thanks to the RWGS reaction, there is no need to separate the unwanted carbon dioxide from the synthesis gas. Instead, thanks to the RWGS reaction, the carbon dioxide can be converted into the carbon monoxide required for methanol synthesis, thus increasing the carbon yield from the biomass used in the first reaction process. The invention is based, among other things, on the idea of ​​reducing proportions of unwanted components in the synthesis gas by means of an endothermic reaction and, at the same time, carrying out this endothermic reaction in a simple manner using process heat from neighboring reaction processes.

[0031] Because the second temperature, which is also referred to here as the RWGS temperature, only needs to be greater than 400 °C, process heat from the first reaction process or process heat from methanol synthesis can be easily used for the endothermic RWGS reaction. In this way, the advantages mentioned above can be achieved, for example increasing the carbon yield or saving the distillation step, while no significant additional energy expenditure is required to carry out the RWGS reaction. In other words, the effects of saving the distillation step or increasing the carbon yield clearly outweigh the effort required to carry out the RWGS reaction in the overall balance.

[0032] Furthermore, it was recognized in the course of the present invention that since there is less or no water in the methanol synthesis compared to the prior art, the distillation stage can be completely eliminated, particularly in the production of gasoline via the so-called "Methanol2Gasoline" route or kerosene via the so-called "Methanol2Kerosene" route, since a water content of up to 10% in the crude methanol is permissible in these two routes.

[0033] Furthermore, the aforementioned achievable reduction of carbon dioxide in the synthesis gas allows more heat to be generated in methanol synthesis, since the reaction enthalpy of the reaction equation (2) CO + 2H2CH3OH is higher than the reaction enthalpy of the reaction equation (1) CO2 + 3H2CH3OH + H2O. Thus, more process heat is available for further use without additional expenditure, which can further improve the overall balance.

[0034] Furthermore, it was recognized in the course of the present invention that the lifespan or service life of the methanol synthesis catalyst can be increased because there is less or no water in the methanol synthesis compared to the prior art.

[0035] According to one embodiment, the first reaction process can comprise gasification of the biomass with oxygen and steam, the synthesis gas produced containing carbon monoxide and hydrogen. In particular, the first reaction process can be gasification of the biomass. In other words, the first reaction process can be a thermo-chemical conversion of the biomass into the synthesis gas containing carbon dioxide. In particular, a gasification parameter known to those skilled in the art as the excess air number can be greater than zero and less than one. In other words, in this case the first reaction process takes place with an oxygen deficiency or oxygen shortage. According to this embodiment, the first reaction process is gasification without subsequent combustion.

[0036] Because the first reaction process can involve biomass gasification, the resulting synthesis gas can contain carbon monoxide and hydrogen in addition to carbon dioxide. In other words, the carbon dioxide content of the gasification route is lower than that of the combustion route. This means that less carbon dioxide needs to be converted in the second reaction process, and less hydrogen needs to be added.

[0037] According to a further embodiment, the first reaction process can comprise combustion of the biomass with oxygen, wherein the synthesis gas produced contains water. In particular, the first reaction process can be combustion of the biomass, i.e., so-called oxy-combustion or oxy-combustion of the biomass. In other words, the first reaction process can be the combustion process that results directly from the ignition of gases escaping from the biomass. In particular, the excess air number of the first reaction process, i.e., oxy-combustion, can be greater than one. In other words, the first reaction process takes place in an excess of oxygen. According to this embodiment, the first reaction process is combustion, which is naturally preceded by the outgassing of a flammable gas from the biomass.

[0038] Because the first reaction process can involve biomass combustion, a wide variety of different biomass reactants of varying quality or varying degrees of homogeneity can be converted into synthesis gas in the first reaction process. This allows for simple and robust process control of the first reaction process.

[0039] According to a further embodiment, the first reaction process can be carried out in the form of gasification in a gasification reactor and additionally in the form of combustion in a combustion reactor, wherein the synthesis gas produced in the gasification and the synthesis gas produced in the combustion are combined before the methanol synthesis is carried out. In other words, the gasification, the combustion and the methanol synthesis can take place in a Y-scheme. In particular, the second reaction process can be carried out after the aforementioned combining, i.e. after the node of the Y-scheme. In this way, the first reaction process can be operated simultaneously in two different variants, while only one RWGS reactor is required. Thus, a greater variety of biomass reactants can be processed while saving on an additional RWGS reactor.

[0040] According to a further development, the second temperature can be at most 300 Kelvin lower than the first temperature. For example, the first temperature in the form of a combustion temperature for burning the biomass can be 1000 °C, while the second temperature in the form of the RWGS temperature is at least 700 °C. Furthermore, for example, the first temperature in the form of a gasification temperature can be 500 °C, while the second temperature in the form of the RWGS temperature is kept at 400 °C. By limiting the temperature difference as mentioned above, process heat from the first reaction process, which is exothermic, can be used particularly effectively to carry out the RWGS reaction.

[0041] According to a further development, the first temperature can be between 700 and 1100 °C, and the second temperature between 380 and 1100 °C. Due to the comparatively high first temperature in the range of 700 and 1100 °C, a high quality of the synthesis gas to be produced can be achieved, i.e. a high proportion of the desired short-chain gaseous carbon compounds, in particular carbon dioxide in the case of combustion, or carbon monoxide and carbon dioxide in the case of gasification. Furthermore, the comparatively high first temperature of the exothermic first reaction provides a high potential for usable process heat.

[0042] In this case, it was recognized that a purification stage for cleaning the exhaust gas or synthesis gas generated by the first reaction process can be dispensed with if the gas is of high quality, i.e., the proportion of undesirable by-products, such as tars or wood condensate, is low. Thus, if the first reaction process is controlled in a way that results in high exhaust gas quality, the integration of an RWGS catalyst into an exhaust line of the first reaction process can be particularly simple.

[0043] Furthermore, as explained above, the RWGS reaction can be carried out over a comparatively broad temperature range, i.e., within a range of 720 Kelvin within the aforementioned range of 380-1100 °C. In this way, the RWGS reaction can be carried out, for example, at moderate temperatures around 450 °C, i.e., significantly lower than the first temperature, and thus be spatially decoupled from the first reaction. Due to the large temperature difference, the exothermic first reaction process can still provide process heat for the RWGS reaction despite spatial decoupling.

[0044] In the present context, temperatures below 350 ° C are referred to as low, temperatures above 750 ° C as high, and temperatures in between as medium.

[0045] In the course of the present invention, it was recognized that, thanks to a spatial decoupling of the RWGS reaction from the first reaction process, a synthesis gas purification process can be inserted between the first and second reaction processes. In this way, undesirable byproducts, such as tars or wood condensate, can be separated from the synthesis gas before the second reaction process, so that an RWGS catalyst used for the second reaction process is less likely to become contaminated, clogged, or worn away.

[0046] It was recognized that, in particular, catalysts designed for comparatively low RWGS temperatures, i.e., RWGS temperatures around 400-500 °C, should be protected from undesirable byproducts or residues in the synthesis gas. Thus, the proposed refinement enables the provision of a purification stage to achieve a long service life of the RWGS catalyst, while simultaneously supplying the RWGS reaction with process heat from the first reaction process.

[0047] According to a further development, the second temperature can be at least 80% of the first temperature. For example, the second temperature can be 80%, 90%, 110% or 120% of the first temperature or any value in between. In other words, the first and second temperatures can differ from each other by a maximum of 20%. If the second temperature is 80-100% of the first temperature, the RWGS reaction can be spatially coupled to the first reaction process in a simple manner, for example by integrating the RWGS catalyst into an exhaust gas line which is designed to discharge the synthesis gas produced from the first reaction process. In this way, the first and second reaction processes can be carried out equally at very high temperatures, for example around 1000 °C.In this way, a high-quality synthesis gas can be achieved, so that purification of the synthesis gas upstream of the RWGS catalyst may not be necessary. At the same time, due to the comparatively high RWGS temperature, the expert can use a particularly simple and robust RWGS catalyst designed for effective operation at high temperatures to configure the process.

[0048] According to a further embodiment, carrying out the first reaction process can comprise discharging the generated synthesis gas via an exhaust line, wherein carrying out the second reaction process is integrated into the discharging of the generated synthesis gas. In particular, an RWGS catalyst can be arranged in the exhaust line of the first reaction process. In this way, the temperature difference between the first and second reaction processes can be kept very small.

[0049] According to a further embodiment, the process can comprise the following step: supplying hydrogen, in particular in the form of an excess of hydrogen, on the reactant side of the second reaction process. In other words, additional hydrogen is provided as a reactant for the RWGS reaction, in particular more hydrogen than can typically be reacted with the synthesis gas produced in the RWGS reaction. In this way, the RWGS reaction equilibrium is influenced in favor of the desired products. In particular, the RWGS reaction can thus result in a very high or even complete conversion of carbon dioxide and hydrogen to carbon monoxide and water. For example, the residual carbon dioxide content in the synthesis gas can thus be reduced to below 1%.This makes it even more likely that the distillation step after methanol synthesis can be eliminated, since the maximum 1% carbon dioxide content results in a correspondingly low water content in the raw methanol. It has been recognized that with a water content of 1-10% in the raw methanol, the distillation step can be omitted if the raw methanol, with a corresponding methanol content of at least 90%, is used to produce certain so-called biofuels.

[0050] According to a further embodiment, the method may comprise the following steps:

[0051] - Passing the produced synthesis gas through a recuperator heat exchanger,

[0052] - Cooling the synthesis gas to a cleaning temperature,

[0053] - Cleaning the cooled synthesis gas,

[0054] - heating the purified synthesis gas to the second temperature by means of the recuperator heat exchanger, and

[0055] - Feeding the heated synthesis gas to the second reaction process.

[0056] Thanks to this use of the recuperator heat exchanger, the synthesis gas can be purified before it reaches the RWGS catalyst, while simultaneously using the process heat from the first reaction process to carry out the RWGS reaction. For example, the first reaction can take place at a high temperature of 800-1000 °C, and the purification can take place at a purification temperature in the range of 30-350 °C. Thanks to the high first temperature, the purified synthesis gas can be heated to an RWGS temperature of 400 °C, 600 °C, or 750 °C, for example, depending on the investment required for the design of the recuperator heat exchanger.

[0057] Additionally or alternatively, the procedure may include the following

[0058] Steps include: extracting process heat from the first reaction process and supplying the extracted process heat to the second reaction process. These steps enable the utilization of the process heat of the first reaction process when the RWGS reaction is carried out spatially decoupled from the first reaction process.

[0059] According to a further embodiment, the method may comprise the following steps:

[0060] - Cooling of the synthesis gas after the second reaction process,

[0061] - Compressing the cooled synthesis gas,

[0062] - optional: condensing water from the cooled synthesis gas and separating the condensed water from the cooled synthesis gas.

[0063] Methanol synthesis, for example, can be carried out using the well-known low-pressure process, i.e., at a pressure of 50 to 100 bar and a temperature of 200 to 300 °C. The first and second reaction processes can each take place at a comparatively low pressure of 1 to 15 bar. Cooling the synthesis gas to, for example, 40 °C allows the required compression of the cooled synthesis gas to be carried out economically, for example, to a synthesis pressure of 80 bar.

[0064] In the course of the present invention, it was recognized that during the cooling of the synthesis gas, any water present in the synthesis gas, particularly as a result of biomass combustion, can be condensed and separated particularly easily. By separating the water before compressing the synthesis gas, the volume flow of the gas to be compressed is significantly reduced. This reduces the energy required for compression and the equipment required to provide a compressor as needed.

[0065] Furthermore, the lifetime of a synthesis catalyst required for methanol synthesis is increased thanks to the reduction or absence of water in methanol synthesis. This is made possible by the aforementioned separation of water and the conversion of carbon dioxide to carbon monoxide thanks to the proposed RWGS reaction.

[0066] According to a further embodiment, carrying out the methanol synthesis can comprise a synthesis loop for producing crude methanol, wherein the crude methanol produced contains 90.0 to 99.5% methanol and a maximum of 10.0% water. In particular, carrying out the methanol synthesis can be carried out without methanol distillation for separating water from the crude methanol.

[0067] In this context, the synthesis loop refers to the process section or plant component of a methanol synthesis process or methanol synthesis plant in which the reactants hydrogen and carbon monoxide and / or carbon dioxide react to form methanol or crude methanol. Conventionally, the resulting water is separated from the crude methanol in a subsequent methanol distillation to obtain pure methanol.

[0068] The above-mentioned object is further achieved by a system having the features of claim 13. Advantageous developments of the method will become apparent from the present description and the figures. Accordingly, a system is proposed which is configured to carry out the method described above.

[0069] The technical effects and advantages explained above in relation to the proposed process apply equally to the proposed systems.

[0070] The above object is further achieved by a plant having the features of claim 14. Advantageous developments of the method emerge from the present description and the figures. Accordingly, a plant for producing methanol is proposed. The plant comprises a first reactor for producing a carbon dioxide-containing synthesis gas, set up for gasifying biomass and / or for burning biomass, the first reactor having an exhaust gas line for discharging the synthesis gas produced, and a second reactor in the form of a reverse water gas shift reactor, the second reactor, in particular a catalyst of the second reactor, being arranged within the exhaust gas line and adjacent to the first reactor.

[0071] Because the RWGS reactor, in particular the RWGS catalyst, is arranged within the exhaust line and adjacent to the first reactor, the temperature gradient between the gasification or combustion, i.e., the first and second reaction processes described above, and the RWGS reactor can be greatly reduced. Thus, the endothermic RWGS reaction can be carried out particularly easily using the process heat of the exothermic first reaction process.

[0072] The above-mentioned object is further achieved by a system having the features of claim 15. Advantageous developments of the method will become apparent from the present description and the figures.

[0073] Accordingly, a plant for producing methanol is proposed. The plant comprises a first reactor for generating a synthesis gas containing carbon dioxide, set up for gasifying biomass and / or for burning biomass, the first reactor having an exhaust gas line for discharging the carbon dioxide produced, a second reactor in the form of a reverse water gas shift reactor, a recuperator heat exchanger and a cleaning column. The cleaning column is arranged between the first and second reactors and is fluidically connected to them. The recuperator heat exchanger is set up to couple an outlet line of the first reactor to an inlet line of the second reactor in a heat-transfer manner.

[0074] Thanks to the purification column arranged between the first and second reactors, unwanted by-products, such as tars or wood condensate, can be separated from the synthesis gas produced in the first reactor, significantly increasing the service life of the second reactor, particularly its RWGS catalyst. Thanks to the proposed arrangement of the recuperator heat exchanger, the process heat from the exothermic first reaction process can be used to heat the purified synthesis gas, allowing the endothermic second reaction process to be carried out without additional energy expenditure, even if the first and second reactors are spatially decoupled due to the interposed purification column.

[0075] Description of the characters

[0076] Preferred further embodiments of the invention are explained in more detail in the following description of the figures. These schematically show:

[0077] Figure 1a is a flow diagram of a process for producing methanol according to a first embodiment,

[0078] Figure lb, cje an embodiment of a plant for carrying out the method,

[0079] Figure 2a is a flow diagram of a process for producing methanol according to a further embodiment,

[0080] Figure 2b shows an embodiment of a plant for producing methanol, Figure 3a shows a flow diagram of a process for producing methanol according to a further embodiment,

[0081] Figure 3b shows another embodiment of a plant for producing methanol, and

[0082] Figure 4 shows a further embodiment of a system for carrying out the method.

[0083] Detailed description of working examples

[0084] Preferred embodiments are described below with reference to the figures. Identical, similar, or equivalent elements in the various figures are provided with identical reference symbols, and a repeated description of these elements is partially omitted to avoid redundancies.

[0085] Figure 1a shows a schematic flow diagram of a process for producing methanol according to a first exemplary embodiment. Figures 1b and 1c show corresponding exemplary embodiments of a plant for carrying out the process. As can be seen in Fig. 1a, a first reaction process is first carried out S10 at a first temperature TI. The first reaction process uses biomass and oxygen to produce an exhaust gas containing carbon dioxide, which is also referred to herein as the produced synthesis gas. The first reaction process can, for example, be technical biomass gasification or biomass combustion in the form of so-called oxy-combustion. Alternatively, the first reaction process can be any other form of exothermic biomass utilization that produces a synthesis gas containing carbon dioxide.

[0086] Subsequently, a second reaction process S20 is carried out in the form of a reverse water gas shift reaction at a second temperature T2 using the generated synthesis gas. The person skilled in the art can select a suitable RWGS catalyst so that the RWGS reaction increases the carbon monoxide content in the synthesis gas according to the following reaction equation (5):

[0087] (5) C02+ H2CO + H20 (strongly endothermic)

[0088] Known RWGS catalysts achieve this starting at a second temperature T2, i.e. an RWGS temperature, of 400°C.

[0089] In step S21, an excess of hydrogen is fed to the RWGS reaction, whereby the amount of excess is determined by the carbon dioxide content of the synthesis gas produced in the first reaction, taking into account the above RWGS reaction equation.

[0090] After step S20, in step S30, the synthesis gas modified by the RWGS reaction, i.e. the synthesis gas with an increased carbon monoxide and reduced carbon dioxide content compared to the synthesis gas resulting directly from the first reaction process, is cooled.

[0091] The cooling step S30 involves a targeted condensation S32 of water, which is separated from the cooled synthesis gas in a further step S35. After cooling S30, the cooled synthesis gas is compressed S40, followed by performing a methanol synthesis S50 using the synthesis gas to produce methanol.

[0092] Steps S10, S20, and S30 can be carried out at a pressure between 1 and 15 bar, whereby the pressure can assume any value in between, regardless of the prevailing reaction temperature. Cooling S30 cools the synthesis gas to a temperature between 20°C and 100°C, for example, 30°C, 40°C, or 50°C.

[0093] In the present case, it was recognized that the pressure in the second reaction process can be variably adjusted, at least within the stated limits of 1-15 bar, without negatively affecting the second reaction process, i.e., without negatively affecting the desired reduction of the carbon dioxide content in the synthesis gas. Thus, the pressure in the second reaction process can be aligned with the pressure of the first reaction process, in particular, it can have essentially the same value. In this way, the integration of an RWGS catalyst into an exhaust line of the first reaction process can be carried out particularly easily.

[0094] By means of compression S40, the cooled synthesis gas is brought to the pressure required for methanol synthesis, for example a pressure between 50 and 100 bar for carrying out the known low-pressure process for methanol synthesis in step S50.

[0095] Fig. 1b shows a plant 1 configured to carry out the process according to the gasification route. Fig. 1c shows a corresponding plant 1 for the combustion route. As can be seen in Fig. 1b, the plant 1 comprises a first reactor 10 in the form of a gasification reactor 10 having an exhaust line 11 in which an RWGS catalyst 20 is arranged or integrated. The RWGS catalyst 20 integrated into the exhaust line thus assumes the function of the second reactor 20, i.e. the RWGS reactor 20.

[0096] A cooling stage 30 for cooling S30, a compressor 40 for compressing S40 and a synthesis loop 50 for carrying out S50 the methanol synthesis are connected successively downstream of the exhaust gas line 11.

[0097] The system 1 further comprises a supply line 21 for supplying S21 hydrogen, wherein the supply line 21 can be arranged upstream or downstream of the RWGS catalyst 20 in the flow direction according to the embodiment shown in Fig. 1b. The flow direction of the system 1 is oriented essentially from left to right in the present figures and is illustrated by the arrow directions of the synthesis gas, which is abbreviated to SynGas in the figures.

[0098] The plant 1 shown in Fig. 1c basically corresponds to the plant 1 shown in Fig. 1b with the difference that the first reactor 10 is in the form of a combustion reactor for carrying out S10 an oxy-combustion of biomass under an oxygen excess.

[0099] The synthesis gas generated by combustion is discharged from the first reactor 10 via the exhaust line 11, with the RWGS catalyst being arranged in the exhaust line 11. In this exemplary embodiment, hydrogen is supplied S21 upstream of the RWGS catalyst 20, i.e., between the first reactor 10 and the RWGS catalyst 20. Furthermore, a further supply S21 of hydrogen can be carried out downstream of the RWGS catalyst 20 (not shown in Fig. 1c).

[0100] Figure 2a schematically shows a flow diagram of a method for producing methanol according to a further exemplary embodiment, in which the synthesis gas generated by the first reaction process S10 and modified by the second reaction process S20 is purified before cooling S30. For this purpose, the synthesis gas, which in the second reaction process has a second temperature T2 greater than 400°C, for example around 700°C, is first cooled in a cooling step S13 to a purification temperature T3 in the range 250-350°C. The purification temperature T3 is selected such that a high proportion of the components to be separated in the purification step, such as tars or wood condensate, are separated or condensed out of the synthesis gas.

[0101] Subsequently, the synthesis gas, cooled to the purification temperature T3, is purified S14, for example by separating the separated or condensed components from the synthesis gas. This is followed by cooling S30, compression S40, and methanol synthesis S50, as described in the preceding embodiments.

[0102] Figure 2b schematically shows a plant 1 configured to carry out the process illustrated in Fig. 2a. The first reactor 10 can be a gasification reactor and / or a combustion reactor. If the first reactor 10 is a pure combustion reactor, hydrogen is fed into the exhaust gas line 11 via the feed line 21 upstream of the RWGS catalyst 20.

[0103] 1b, 1c and 2b, the RWGS catalyst 20 is each integrated into the exhaust gas line 11 of the first reactor 10. Thus, the pressure and temperature conditions in the RWGS catalyst 20 are similar to those in the first reactor 10. For example, the first reactor can be operated at any pressure between 1 and 15 bar and have a first temperature TI greater than 400 °C. In the example shown, the first temperature TI is greater than 750 °C. By arranging the RWGS catalyst 20 adjacent to the first reactor 10 within the exhaust gas line 11, it can be achieved that the second temperature T2 is only slightly lower than the first temperature TI, for example at most 50 Kelvin lower, as shown in Figs. 1b, 1c and 2b. In this way, no additional heat energy is required to carry out S20 the second reaction process.

[0104] In all embodiments, a particulate filter (not shown) can optionally be provided in the first reactor 10 and / or in the exhaust line 11 upstream of the second reactor 20 in order to reduce the particulate load for the RWGS catalyst 20 and to increase its service life.

[0105] Figure 3a shows a schematic flow diagram of a process for producing methanol according to a further exemplary embodiment. Figure 3b shows a schematic view of a plant 1 which is set up to carry out the process shown in Fig. 3a. As shown in Figs. 3a, 3b, the synthesis gas produced by means of the first reaction process in step S10 is first discharged from the first reactor 10 via the exhaust gas line 11, S11. The still hot synthesis gas is then passed through a recuperator heat exchanger 16, S12. The synthesis gas is then fed to a purification column 12, 13, where it is first cooled to a purification temperature T3, S13, and purified, S14. Undesired by-products, such as tars and wood condensate, are separated from the synthesis gas by means of the purification stage 14.

[0106] The purified synthesis gas is then fed via an inlet line 17 to the second reactor 20 for carrying out S20 the second reaction process, S17, wherein the inlet line 17 is guided through the recuperator heat exchanger 16, so that the recuperator heat exchanger 16 couples the outlet line 11 of the first reactor 10 to the inlet line 17 of the second reactor 20 in a heat-transfer manner. By means of this coupling of the recuperator heat exchanger 16, the purified synthesis gas is heated S16 from the low purification temperature T3 to the medium or high second temperature T2.

[0107] Furthermore, the method may additionally comprise the following steps: extracting S22 process heat from the first reaction process and supplying S24 the extracted process heat to the second reaction process. Accordingly, the system 1 may comprise a heat transfer device 22 configured to carry out steps S22 and S24.

[0108] The provision of the heat transfer device 22 makes it possible to dimension the recuperator heat exchanger 16 such that it is particularly cost-effective or can be operated at a high flow rate, so that the purified synthesis gas may not yet have reached the desired second temperature T2 when it is fed S 17 to the second reactor 20. In Fig. 3b, the temperatures of the synthesis gas are shown as examples and as follows: The gasification S 10 or combustion S 10 takes place, for example, at around 920 ° C. The synthesis gas produced thereby can therefore have a temperature of 900 ° C in step S 12, wherein it can cool down in the heat exchanger 16 by several fifty Kelvin, for example to 700 ° C, while giving off heat to the purified synthesis gas crossing in the heat exchanger 16.

[0109] In the subsequent step S 13, the synthesis gas is then cooled to a purification temperature T3 of, for example, 300 ° C. With the above-mentioned heat release, the purified synthesis gas can then be heated in the heat exchanger 16 by several fifty Kelvin, for example to 600 ° C. If an RWGS catalyst 20 is provided in the second reactor 20, in which the RWGS reaction takes place particularly favorably at high temperatures, for example above 700 ° C or above 750 ° C, the heat required for this can be provided simply by means of the heat transfer device 22 from the exothermic and sufficiently warm first reaction process.

[0110] By means of the embodiments shown in Fig. 3a, b, the synthesis gas can be purified thanks to the purification column 13+14 arranged upstream of the RWGS catalyst 20 in such a way that the service life of the RWGS catalyst 20 is further improved. At the same time, the heat loss required due to the purification can be compensated by the heat exchanger 16. In this way, the purification can take place without the need for additional external energy input to reheat the purified synthesis gas.

[0111] Figure 4 shows a schematic diagram of a further exemplary embodiment of a plant for carrying out the process, wherein the plant 1 comprises two first reactors 10, the synthesis gas streams produced from which are combined in a Y-scheme upstream of the methanol synthesis 50, in particular upstream of the cooling stage 30. In the example shown in Fig. 4, an RWGS catalyst is integrated into a respective exhaust gas line 11 of the two first reactors 10. In this way, the gasification reactor 10 and its associated RWGS catalyst 20 can be operated independently of the combustion reactor 10 and its associated RWGS catalyst 20 with regard to the reaction conditions of pressure and temperature. This allows a high degree of freedom in process control, while the downstream stages, i.e. the cleaning column 13 + 14 and the cooling stage 30, the compressor 40 and the synthesis loop 50 can be used jointly for the first two reactors 10.

[0112] Alternatively, when using two first reactors 10 in a Y-scheme, as basically shown in Fig. 4, a cleaning column 13 + 14 and a heat exchanger 16 can be arranged upstream of a single RWGS reactor 20, as basically shown in Fig. 3b. In this way, the advantages of the improved service life of the RWGS catalyst 20 can be combined with the advantages of the arrangement of two first reactors in the Y-scheme, namely that a greater variety of biomass reactants can be processed as needed by means of gasification or combustion, while saving on a second RWGS reactor.

[0113] Where applicable, all individual features illustrated in the embodiments can be combined and / or interchanged without departing from the scope of the invention. For example, the system illustrated in Figs. 1b, 1c can be operated at the temperatures mentioned in other embodiments, for example, according to Fig. 3b, and vice versa. Furthermore, the provision of the recuperator heat exchanger 16 can be provided in all embodiments, in particular if the RWGS catalyst 20 is not arranged adjacent to the first reactor 10.

Claims

Patent claims 1. A process for producing methanol comprising the following steps: - carrying out (S10) a first reaction process at a first temperature (TI), wherein the first reaction process produces a synthesis gas containing carbon dioxide (CO2) using biomass and oxygen (O2), - carrying out (S20) a second reaction process in the form of a reverse water gas shift reaction at a second temperature (T2) using the produced synthesis gas, wherein the second reaction process increases a carbon monoxide content in the synthesis gas, wherein the second temperature (T2) is greater than 400°C, and - performing (S50) a methanol synthesis using the synthesis gas to produce methanol.

2. The method according to claim 1, wherein the first reaction process comprises gasification of the biomass with oxygen (O2) and with water vapor (H 20) and wherein the synthesis gas produced comprises carbon monoxide (CO) and hydrogen (H 2 ) contains.

3. The method according to claim 1 or 2, wherein the first reaction process comprises combustion of the biomass with the oxygen (0 2 ) and wherein the synthesis gas produced comprises water (H 2 0) contains .

4. Method according to one of the preceding claims, wherein the second temperature (T2) is at most 300K lower than the first temperature (TI).

5. The method according to any one of the preceding claims, wherein the first temperature (T1) is between 700-1100°C and the second temperature (T2) is between 380-1100°C.

6. Method according to one of the preceding claims, wherein the second temperature (T2) is at least 80% of the first temperature (TI).

7. The method according to any one of the preceding claims, wherein carrying out (S10) the first reaction process comprises a sub-step of discharging (S11) the synthesis gas produced by means of an exhaust gas line (11), wherein carrying out (S20) the second reaction process is integrated into the discharging (S11) of the synthesis gas produced, in particular wherein a reverse water gas shift catalyst (20) is arranged in the exhaust gas line (11) of the first reaction process.

8. A method according to any one of the preceding claims, comprising: - Supply (S21) of hydrogen (H 2 ), especially in the form of an excess of hydrogen, on the reactant side of the second reaction process.

9. A method according to any one of the preceding claims, comprising: - passing (S12) the produced synthesis gas through a recuperator heat exchanger (16), - Cooling (S13) of the synthesis gas to a cleaning temperature (T3), - Cleaning (S14) of the cooled synthesis gas, - heating (S16) the purified synthesis gas to the second temperature (T2) by means of the recuperator heat exchanger (16), and - feeding (S17) the heated synthesis gas to the second reaction process.

10. A method according to any one of the preceding claims, comprising: - Extraction (S22) of process heat from the first reaction process, and - Supplying (S24) the extracted process heat to the second reaction process.

11. Method according to one of the preceding claims, comprising the following steps: - Cooling (S30) of the synthesis gas after the second reaction process, - Compressing (S40) the cooled synthesis gas, - optional: condensation (S32) of water (H 2 O) from the cooled synthesis gas and separating (S35) the condensed water from the cooled synthesis gas.

12. The method according to any one of the preceding claims, wherein carrying out (S50) the methanol synthesis comprises a synthesis loop for producing crude methanol, wherein the crude methanol produced contains 90.0 to 99.5% methanol and a maximum of 10.0% water, in particular wherein carrying out (S50) the methanol synthesis without a methanol distillation for separating water (H 2 O) from the crude methanol.

13. Installation (1) which is designed to carry out the method according to one of the preceding claims.

14. Plant (1) for producing methanol, comprising - a first reactor (10) for producing a carbon dioxide (CO 2 ) containing synthesis gas, arranged for gasifying biomass and / or for burning biomass, wherein the first reactor has an exhaust gas line (11) for discharging the synthesis gas produced, and - a second reactor (20) in the form of a reverse water gas shift reactor (20), wherein the second reactor (20), in particular a catalyst (20) of the second reactor, is arranged within the exhaust gas line (11) and adjacent to the first reactor (10).

15. Plant (1) for producing methanol, comprising - a first reactor (10) for producing a synthesis gas containing carbon dioxide (CO2), designed for gasifying biomass and / or for burning biomass, wherein the first reactor (10) has an exhaust gas line (11) for discharging the produced carbon dioxide (CO2), - a second reactor (20) in the form of a reverse water gas shift reactor (20), - a recuperator heat exchanger (16) and - a purification column (13, 14), wherein the purification column (13, 14) is arranged between the first and second reactors (10, 20) and is fluidly connected thereto, and - wherein the recuperator heat exchanger (16) is configured to heat-transfer an outlet line (11) of the first reactor to an inlet line (17) of the second reactor (20).

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