Method and system for the preparation of dimethyl ether

Abstract

The invention relates to a method for the synthesis of dimethyl ether: a feed gas mixture (E) comprising carbon dioxide and / or carbon monoxide and hydrogen is conducted through reaction tubes (1) of a cooled tube bundle reactor (10) loaded with a first catalyst and a second catalyst; the carbon dioxide contained in the feed gas mixture (E) and / or the carbon monoxide contained in the feed gas mixture react at least partially with the hydrogen contained in the feed gas mixture on the first catalyst to form methanol; in the same tube bundle reactor (10) the methanol reacts at least partially on the second catalyst to form dimethyl ether. The reaction tubes (1) are loaded with the first and second catalysts in the form of a structured packing, the structured packing having two to four zones (11, 12, 13) in which the first and second catalysts are provided in different physical mixtures, the zones (11, 12, 13) being arranged such that the concentration of the first catalyst increases in the flow direction through the reaction tubes (1). The invention also relates to a system (100) for carrying out such a method.

Description

[Technical Field]

[0001] The present invention relates to a process and a plant for preparing dimethyl ether from synthesis gas according to the preambles of the independent claims. [Background technology]

[0002] Dimethyl ether (DME) is the simplest ether structurally. It contains two methyl groups as the organic group, is polar, and is used industrially for a variety of purposes.

[0003] Dimethyl ether can be prepared by a two-stage synthesis from synthesis gas via the intermediate methanol, as described, for example, in Chapter 4 of the DME Handbook, Japan DME Forum, Tokyo 2007, ISBN 978-4-9903839-0-9. The "two-stage" synthesis is characterized in that methanol is first prepared from synthesis gas, the methanol is separated from the unconverted synthesis gas, and then the methanol is separately dehydrated to dimethyl ether and water in a further step.

[0004] In contrast, in the one-stage synthesis of dimethyl ether, all reactions take place in one and the same reactor and on one and the same catalyst bed. Hereinafter, the term "direct synthesis" will also be used for the one-stage synthesis of dimethyl ether. The reaction proceeds by reacting hydrogen with carbon monoxide and / or carbon dioxide to give methanol, which is then (further) reacted to give dimethyl ether and water. The one-stage synthesis of dimethyl ether is known, for example, from U.S. Pat. Nos. 4,536,485 A and 5,189,203 A. Hybrid catalysts are typically used. The reaction is exothermic and typically takes place at temperatures of 200-300°C and pressures of 20-100 bar.

[0005] In particular with regard to the terminology used below, but also for fundamental considerations regarding the synthesis of dimethyl ether from synthesis gas, reference is made to the article by I. Kiendl et al., Chem. Ing. Tech. 2020, 92, No. 6, 736-745, to which the terminology in this specification corresponds.

[0006] The synthesis gas required for the preparation of dimethyl ether can be provided from a number of starting materials by a number of suitable techniques, as described, for example, by Hilleret et al. in the article "Gas Production" in Ullmann's Encyclopedia of Industrial Chemistry, online edition, December 15, 2006, doi 10.1002 / 14356007.a12_169.pub2.

[0007] In the two-stage synthesis of dimethyl ether, copper catalysts (hereinafter also referred to as "methanol catalysts") can be used for the conversion to methanol, and acidic catalysts, such as zeolite catalysts, γ-dialuminum trioxide-based catalysts, and aluminosilicate catalysts (hereinafter also referred to as "dehydration catalysts"), can be used for the subsequent dehydration. It is noted that synthesis gas for methanol production has a stoichiometry (see Kiendl et al. for definition) somewhat greater than 2.

[0008] High-purity dimethyl ether can be obtained through two-stage dimethyl ether synthesis. Methanol from the first stage is liberated from higher alcohols and then highly selectively dehydrated. In a single-stage process, methanol synthesis and dimethyl ether synthesis proceed in parallel, and the resulting higher alcohols are converted to olefins, which, depending on the boiling conditions, are generated in the product, creating an additional issue of by-products.

[0009] The one-step synthesis of dimethyl ether has not yet been industrially achieved. This is particularly due to the difficulty of integrating two catalysts into one reactor. In an integrated reactor, the reactants and products have different temperature and partial pressure conditions than the individual reactors, making it significantly more difficult to control the reaction temperature. For example, this can result in increased by-product concentrations or partial pressures, which can accelerate catalyst aging. A method for temperature control in the direct synthesis of dimethyl ether is described in WO 2019 / 122078 A1.

[0010] Compared to conventional methanol synthesis, the copper catalyst is prone to sintering under these conditions due to the high temperature and hydrogen partial pressure. Furthermore, literature has attributed increased mobility to secondary phases in the copper catalyst due to the occurrence of hydroxylation reactions (A. Prasnikar et al., Ind. Eng. Chem. Res., 2019, 58, 13021). This may further increase the mobility of copper particles. Furthermore, this results in the coating of copper particles, which in turn reduces their active surface area. Therefore, controlling the temperature and concentration / partial pressure parameters is a key challenge in implementing direct dimethyl ether synthesis.

[0011] In dimethyl ether synthesis, hydrogen and carbon monoxide react according to the following reaction: 2H2+CO⇔MeOH 2MeOH⇔DME+H2O CO+H2O⇔CO2+H2

[0012] These are equilibrium reactions, resulting in different product compositions depending on pressure, temperature, and feed composition.

[0013] If the feed gas contains no carbon dioxide and the ratio of hydrogen to carbon monoxide is 1, the following net reaction is observed: 3H2+3CO→DME+CO2

[0014] When the stoichiometry is 2, the following net reaction dominates: 2H2+CO→DME+H2O

[0015] Chain extension by carbon monoxide insertion can produce higher alcohols. This reaction occurs over a copper catalyst (cat.). Insertion proceeds via hydrogenation of the adsorbed carbon monoxide or re-adsorption of methanol on the already formed methyl species and prior cleavage of the carbon-oxygen bond. Further hydrogenation of the adsorbed C2 species leads to the formation of acetaldehyde or, after rapid hydrogenation, to the formation of ethanol. 2CH3OH+cat-OH→CH3O-cat+H2O CH3O-cat+CO→CH3COO-cat CH3COO-cat+H2→C2H5OH

[0016] Higher alcohols can be dehydrated to the corresponding olefins, which can be hydrogenated to paraffins.

[0017] Other studies, using DFT calculations, support the formation of carbon-carbon bonds by carbon monoxide insertion into adsorbed methyl species, for example, formed by hydrogenation of adsorbed carbon monoxide. If methanol is adsorbed after the carbon-oxygen bond is broken, carbon monoxide insertion also produces ethanol. Therefore, increasing the partial pressure of methanol may also increase the formation of by-products (see, for example, Z.-J. Zuo et al., J. Phys. Chem. C 2014, 118, 12890). Further studies on modified copper catalysts have even demonstrated the coupling of two methanol molecules to produce ethanol (J.J. Spifey & A. Egbebi, Chem. Soc. Rev., 2007, 36, 1514).

[0018] A further side reaction occurring in the case of zeolites is the formation of olefins from methanol and / or dimethyl ether. This occurs already at temperatures well below 300°C and is driven not only by the temperature but also by the residence time and the catalyst used. This side reaction is followed by the methanol-to-olefin (MTO) and methanol-to-propylene (MTP) mechanisms known from the literature.

[0019] In the direct synthesis of dimethyl ether, the following problems must be solved in particular in the reactor: · Relatively short catalyst life due to high catalyst aging as a result of prevailing reaction conditions. · Parallel synthesis of methanol and dimethyl ether, thus a by-product in the dimethyl ether product due to the inability to purify the intermediates. · Relatively low productivity in the downstream bed as a result of kinetically controlled conditions and low temperatures. · Temperature control of the reaction for controlled aging. High costs as a result of catalyst replacement and / or reactor over-design.

[0020] One advantage of the direct synthesis of dimethyl ether results from a shift in the equilibrium. As a result of the separate methanol synthesis in the upstream part of the reactor according to WO 2019 / 122078 A1, this advantage is only utilized in the downstream part of the reactor. Therefore, in this case, a lower yield is expected. This corresponds to a decrease in productivity in the upstream part of the reactor. Summary of the Invention [Problem to be solved by the invention]

[0021] The object of the present invention is to overcome the drawbacks mentioned in known processes for the direct synthesis of dimethyl ether. [Means for solving the problem]

[0022] This object is achieved by a process and a plant for preparing dimethyl ether from synthesis gas according to the respective independent claims. Advantageous configurations and developments are the subject of the dependent claims and the following description.

[0023] The present invention proposes a process for the synthesis of dimethyl ether, comprising conducting a feed gas mixture containing carbon dioxide and / or carbon monoxide and hydrogen through reaction tubes of a cooled shell-and-tube reactor provided with a first catalyst and a second catalyst (in particular in the form of the aforementioned methanol catalyst and the similarly mentioned dehydration catalyst), at least partially reacting the carbon dioxide present in the feed gas mixture and / or the carbon monoxide present in the feed gas mixture with the hydrogen present in the feed gas mixture over the first catalyst to give methanol, and at least partially converting the methanol into dimethyl ether over the second catalyst in the same shell-and-tube reactor.

[0024] In connection with the present invention, shell-and-tube reactors of conventional design in the art can be used. For further details regarding corresponding reactors, reference is made to the relevant technical literature, for example the article "Fixed-Bed Reactors" by G. Eigenberger in Ullmann's Encyclopedia of Industrial Chemistry, Volume B4, 1992, pp. 199-238. The use of multiple cooling and reaction zones for temperature control in shell-and-tube reactors is also known per se, as described therein in connection with Figures 4.1D and 4.1E. The present invention proposes a particularly advantageous zoning, as explained below.

[0025] According to the present invention, it is envisioned that the reactor tube comprises a first catalyst and a second catalyst in the form of a structured bed having two to four regions (also interchangeably referred to herein as zones) in which the first catalyst and the second catalyst are provided in a physical mixture at different mixing ratios, the regions being arranged such that the concentration of the first catalyst (i.e., the methanol catalyst) increases in the flow direction through the reactor tube.

[0026] In the context of the present invention, the term "structured bed" is understood to mean, in particular, a series of catalyst regions or zones in a reactor, each containing different proportions or contents of the first and second catalysts (methanol catalyst and dehydration catalyst). Within a region or zone, these proportions are the same or differ from one another only due to production-related fluctuations. In the downstream direction, the proportion or content of the first catalyst (methanol catalyst) increases from region to region or zone to zone. Within the regions or zones of a structured bed, a physical mixture of the first and second catalysts (methanol catalyst and dehydration catalyst) is predominantly present. A special form is called a bifunctional catalyst. Here, the two catalysts are applied to a common support and are not physically mixed. The catalysts may also be applied in random packings such as pellets, rings, or irregular shapes.

[0027] The present invention differs in particular from the so-called pre-beds known from the prior art, in which the methanol catalyst is diluted with an inert material and is followed downstream by a mixed bed in the form of a physical mixture of the methanol catalyst and the dehydration catalyst. Unlike homogeneous or separate beds, i.e., a uniform physical mixture of the methanol catalyst and the dehydration catalyst throughout the reactor (or in the region downstream of the pre-bed, if a pre-bed is used), structured beds allow for reaction regimes with different ratios of the methanol catalyst and the dehydration catalyst.

[0028] The first catalyst may in particular be a copper-based catalyst of the type described at the outset in connection with the present invention, for which reference may be made to the cited technical literature. The second catalyst may likewise be of the type commonly used in the art, in particular acidic catalysts on zeolites, γ-dialuminum trioxide and aluminosilicates.

[0029] In the context of the present invention, the process is in particular carried out in a pressure range of 30 to 80 bar and / or in a temperature range of 200 to 290°C and / or for a period of 1500 to 4000 h -1 The method may include operating the reactor at a gas hourly space velocity (GHSV) of 0.1 to 1.005.degree.

[0030] In the first configuration of the present invention, the number of zones with beds may in particular be two (shown in column 2 of Tables 1 and 2 below), the first zone being an upstream zone between 0% and 30% of the length of the reaction tube (identified as MIX1 in Tables 1 and 2) and the second zone being a downstream zone between 25% and 100% of the length of the reaction tube (MIX2) (empty table cells correspond to zones without beds).

[0031] The percentages shown in the table herein correspond to the length range of the respective reaction tube. In other words, a section of reaction tube having a length of X cm, designated A-B%, extends from a starting position of A x X / 100 cm to an ending position of B x X / 100 cm. In other words again, the first and second values ​​of the following ranges are a first length position of the reaction tube expressed as a percentage and a second length position of the reaction tube expressed as a percentage. The numerical values ​​of the overlapping ranges should be understood so that the overlapping ranges can be formed by one or the other section.

[0032] In the first configuration of the present invention, in the first region, the proportion of the first catalyst may be 1 and the proportion of the second catalyst may be X, and in the second region, the proportion of the first catalyst may be 1.5 to 4 and the proportion of the second catalyst may be X.

[0033] In the second configuration of the present invention, the number of zones with beds may in particular be three (column 3 of the table), the first zone (MIX1) being an upstream zone between 0% and 30% of the length of the reaction tube, the second zone (MIX2) being a central zone between 20% and 70% of the length of the reaction tube, and the third zone (MIX3) being a downstream zone between 50% and 100% of the length of the reaction tube.

[0034] In the second aspect of the present invention, in the first region, the proportion of the first catalyst may be 1 and the proportion of the second catalyst may be X; in the second region, the proportion of the first catalyst may be 1.5 to 2 and the proportion of the second catalyst may be X; and in the third region, the proportion of the first catalyst may be 3 to 4 and the proportion of the second catalyst may be X.

[0035] In the third configuration of the present invention, the number of zones with beds may in particular be four (column 4 of the table), where the first zone (MIX1) is an upstream zone between 0% and 25% of the length of the reaction tube, the second zone (MIX2) is an upstream central zone between 20% and 50% of the length of the reaction tube, the third zone (MIX3) is a downstream central zone between 50% and 75% of the length of the reaction tube, and the fourth zone (MIX4) is a downstream zone between 75% and 100% of the length of the reaction tube.

[0036] In the third configuration of the present invention, in the first region, the proportion of the first catalyst may be 1 and the proportion of the second catalyst may be X; in the second region, the proportion of the first catalyst may be 1.5 to 2 and the proportion of the second catalyst may be X; in the third region, the proportion of the first catalyst may be 2.5 to 3 and the proportion of the second catalyst may be X; and in the fourth region, the proportion of the first catalyst may be 4 and the proportion of the second catalyst may be X.

[0037] In all configurations, X may be the same or may be between 0.3 and 1.

[0038] The above-identified configurations are again exemplified below with reference to the tables already mentioned.

[0039] [Table 1]

[0040] [Table 2]

[0041] One of the advantages of direct synthesis of dimethyl ether is due to the increased equilibrium conversion. According to the prior art, this advantage is only utilized in the downstream part of the reactor as a result of separate methanol synthesis in the upstream part of the reactor. This combination helps with temperature control.

[0042] Productivity is low in the upstream part of the reactor. It has now been discovered that the benefits of such temperature control can also be obtained by using an appropriate mixture of two different catalysts. In addition to the benefits of temperature control, this also has the additional effect of increasing the space-time yield. This is particularly illustrated by Examples 1 to 3 described below.

[0043] In the front or upstream portion, the proportion of the first catalyst in the mixture is low, resulting in a low amount of methanol produced, and therefore low exothermicity, allowing for temperature control. At the same time, the high content of the dehydration catalyst ensures that the reaction from methanol to dimethyl ether is promoted and prevents the buildup of high methanol partial pressure, which, especially in the upstream portion of the reactor, leads to the production of by-products along with high carbon monoxide partial pressure. Even if equilibrium in the methanol reaction is reached, the proportion of the first catalyst here is low compared to other embodiments, and therefore side reactions will develop to the same extent.

[0044] At least one and up to three additional downstream beds should each be run with a higher proportion of the first catalyst. This allows for a controlled reaction temperature window. Peak temperatures above 280°C can thus be avoided. Ideally, temperatures are maintained within the range of 200°C to 280°C, particularly 220°C to 270°C. This prevents premature aging, for example, due to sintering effects on the copper component of the first catalyst. Better control of temperature peaks also allows for the avoidance of olefin formation or further reactions catalyzed by the second catalyst as a side reaction. The higher the proportion of the first catalyst in the downstream portion of the reactor, the lower the partial pressure of carbon monoxide, which is less detrimental to the formation of by-products. This fact is particularly demonstrated in Example 4 described below.

[0045] The Direct Synthesis of dimethyl ether becomes increasingly kinetically controlled as the copper component of the first catalyst ages. The proportion of the first catalyst contributes to a significant degree to the overall conversion rate of the Direct Synthesis. Therefore, copper activity loss has the greatest impact on the efficiency of the Direct Synthesis. Therefore, a higher proportion of the first catalyst toward the end of the bed generally results in better reactor utilization toward the end of the tube and lower synthesis gas conversion, which is controlled by low temperature and the partial pressures of hydrogen and carbon monoxide. This is particularly illustrated by a comparison of Examples 2 and 3 described below.

[0046] It is not uncommon for the first catalysts used in connection with the present invention to lose 20% to 30% of their activity within a short period of time, resulting in only 25% to 40% of their initial activity during use. Therefore, the downstream bed advantageously comprises approximately 1.5 to 4 times the proportion of this first catalyst relative to the first bed. Despite aging, structured beds for industrial processes allow high conversion rates to be achieved over longer periods because the downstream bed compensates for or mitigates the conversion losses of the upstream bed. This allows for extended use of the bed.

[0047] The methanol reaction is favored toward the end of the reactor compared to the dimethyl ether reaction. High selectivity to methanol is not a problem in the solution of the present invention, since methanol is often recycled to the dimethyl ether synthesis process via the dimethyl ether equilibrium reaction. Therefore, a high dehydration catalyst content at the start of the bed constitutes an opportunity for conversion of recycled methanol, while at the same time preventing the recycled amount of methanol from competing with the methanol synthesis equilibrium reaction. This is particularly demonstrated in Example 5 described below.

[0048] Therefore, temperature control is possible by reducing the amount of methanol catalyst in the mixture, i.e., adjusting the mixture ratio, or by using a low activity dehydration catalyst with the same methanol content in the mixture.

[0049] To achieve particularly high methanol production rates or space-time yields, it is possible not only to increase the content of the first catalyst but also to use a second catalyst with particularly high activity to significantly minimize recycled methanol. In this case, further reaction of DME to obtain olefins should be avoided. By using a structured bed, such side reactions can be avoided by controlling the reaction temperature. Such increased by-product formation can lead to coking of the dehydration catalyst, rapidly reducing its activity, as is known, for example, from methanol-to-olefin processes.

[0050] The plant proposed according to the invention for the synthesis of dimethyl ether comprises a cooled shell-and-tube reactor having reaction tubes equipped with a first catalyst and a second catalyst, and is arranged to lead a feed gas mixture comprising carbon dioxide and / or carbon monoxide and hydrogen through the reaction tubes of the shell-and-tube reactor, to at least partially react the carbon dioxide present in the feed gas mixture and / or the carbon monoxide present in the feed gas mixture with the hydrogen present in the feed gas mixture over the first catalyst to give methanol, and to at least partially convert the methanol into dimethyl ether over the second catalyst in the same shell-and-tube reactor.

[0051] According to the invention, the reactor tube is provided with a first catalyst and a second catalyst in the form of a structured bed, the structured bed having two to four regions in which the first catalyst and the second catalyst are provided in different physical mixtures, the regions being arranged such that the concentration of the first catalyst increases in the flow direction through the reactor tube.

[0052] The plant of the invention for preparing dimethyl ether comprises means for charging the plant to carry out the process as described above. The plant of the invention or advantageous developments and configurations thereof accordingly benefit in an analogous manner from the advantages of the respective corresponding process and vice versa.

[0053] Further features and advantages of the invention will now be described in detail with reference to examples and with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0054] [Figure 1] A simplified schematic diagram of one configuration of the plant of the present invention is shown. [Figure 2] 1 shows hydrocarbon selectivity as a function of average reactor temperature in one example. DETAILED DESCRIPTION OF THE INVENTION

[0055] In the figures, identical or mutually functionally corresponding elements are referred to by the same reference numerals. Descriptions of process steps are also applicable to apparatus components and vice versa.

[0056] 1 shows a dimethyl ether plant in greatly simplified form, generally designated 100. The plant includes a shell-and-tube reactor 10 having a number of reaction tubes 1, cooled with a coolant C. The coolant C is conducted through the shell space of the shell-and-tube reactor 10 in countercurrent to a feed gas mixture E conducted through the reaction tubes 1, optionally also in the form of multiple coolant circuits. A product mixture P is withdrawn from the shell-and-tube reactor 10.

[0057] The reactor tube 1 is provided with a first catalyst and a second catalyst in the form of a structured bed, which in the example described herein has three regions 11, 12, 13 in which the first catalyst and the second catalyst are provided in different physical mixtures, and the regions 11, 12, 13 are arranged such that the concentration of the first catalyst increases in the flow direction through the reactor tube 1. [Example]

[0058] Examples 1 to 3 In connection with Examples 1-3, Direct Synthesis was carried out using a catalyst bed according to the prior art of WO 2019 / 122078 A1. For comparison, Direct Synthesis was carried out under similar conditions using a structured bed according to the present invention. The structured bed consisted of two distinct zones containing a mixture of the first catalyst and the second catalyst. The upstream zone ranged from 0% to 30% of the reactor tube length. The first 0-30% was always different from the remaining 25-100%. The parameters are summarized in Table 3. Column 2 of the table lists the total content of the first catalyst (wt%), column 3 the gas hourly space velocity (GHSV), column 5 the carbon monoxide conversion (%), column 6 the space-time yield (STY) of methanol and dimethyl ether as dimethyl ether equivalents in grams of dimethyl ether per kilogram of catalyst per hour, and column 7 the selectivity to hydrocarbons.

[0059] The dimethyl ether equivalent is used to determine the space-time yield, so that methanol is essentially considered dimethyl ether and is included in the yield. For this purpose, the following formula may be used:

number

[0060] [Table 3]

[0061] In Example 1, a diluted methanol pre-bed according to the prior art was used, followed by a mixed catalyst bed. Example 1 was run at a first catalyst ratio of 48 wt. %, a pressure of 65 bar (abs.), and 2000 h -1The catalyst was run at a GHSV of 1.0, a hydrogen to carbon monoxide ratio of 1.5, and a stoichiometry of 1.2. The carbon monoxide conversion was 77.1%, the selectivity to dimethyl ether was 62.3%, the selectivity to methanol was 6.8%, the selectivity to carbon dioxide was 29.2%, the selectivity to hydrocarbons was 2.4%, and the space-time yield of methanol and dimethyl ether as dimethyl ether equivalents in grams per kilogram of catalyst per hour was 320 g / (kg×h).

[0062] In Example 2, a structured bed consisting of two zones with increasing first catalyst content was used. Example 2 was run at a first catalyst ratio of 46 wt. %, a pressure of 65 bar (abs.), and 3000 h -1 The experiments were carried out at a GHSV of 1.0, a hydrogen to carbon monoxide ratio of 1.5, and a stoichiometry of 1.2. The carbon monoxide conversion was 77.1%, the selectivity to dimethyl ether was 62.2%, the selectivity to methanol was 6.6%, the selectivity to carbon dioxide was 29.3%, the selectivity to hydrocarbons was 0.7%, and the space-time yield of methanol and dimethyl ether, as defined above, was 480 g / (kg×h).

[0063] In Example 3, a structured bed consisting of two zones with an increased content of the first catalyst was used. Example 3 was run at a first catalyst content of 68 wt. %, a pressure of 55 bar (abs.), and a run time of 3000 h. -1 The experiments were carried out at a GHSV of 1.0, a hydrogen to carbon monoxide ratio of 1.5, and a stoichiometry of 1.2. The carbon monoxide conversion was 79.1%, the selectivity to dimethyl ether was 60.7%, the selectivity to methanol was 9.7%, the selectivity to carbon dioxide was 28.9%, the selectivity to hydrocarbons was 1.5%, and the space-time yield of methanol and dimethyl ether, as defined above, was 480 g / (kg×h).

[0064] A comparison of Examples 1 and 3 shows that the use of a structured bed significantly improves space-time yield, and a comparison of Examples 2 and 3 shows that the copper content is important to the efficiency of the system.

[0065] Table 3 shows the temperature profiles for Examples 1-3, demonstrating that the structured bed allows for temperature control and enhances space-time yield compared to the prior art. It also demonstrates the possibility of accommodating a third zone between 50% and 100% of the tube length after a temperature peak at approximately 40% of the tube.

[0066] [Table 4]

[0067] Example 4 Figure 2 shows the reaction conditions under various conditions, i.e., hydrogen to carbon monoxide ratio of 1.5 to 2, and reaction times of 2000 to 4000 h. -1 The graph shows hydrocarbon selectivity (%) on the vertical axis as a function of average reactor temperature (°C) on the horizontal axis for various bed structures and resulting first catalyst loadings under conditions of GHSV of 1000 kJ / s, stoichiometry of 1 to 3, and pressure of 50 to 65 bar (abs.). A comparison between two structured beds (triangles indicate high first catalyst loadings, squares indicate low loadings) is shown with a prior art bed consisting of a methanol pre-bed followed by a mixed catalyst bed (circles).

[0068] The bed was divided into two distinct catalytic zones. The upstream zone consisted of approximately 30% of the length of the active tube of the cooled tubular reactor used. In all beds, the selectivity to by-products was found to increase with increasing temperature. Furthermore, in the structured bed, the formation of by-products was found to increase with increasing content of the first catalyst.

[0069] Furthermore, it was found that the prior art configuration produced the highest by-products even though its first catalyst content was similar to that of the structured bed with the lowest first catalyst content, and its total copper content was relatively 30% lower than that of the structured bed with the highest first catalyst content.

[0070] This means that with proper structuring, a higher content of the first catalyst can be introduced into the bed in order to increase the yield without increasing the formation of by-products, or to suppress the formation of by-products at the same yield.

[0071] Example 5 Example 5 demonstrates the feasibility of adding methanol to the catalyst bed inlet without significantly impairing the bed's performance. The catalyst bed consisted of a 1:1 mixture of the first and second catalysts. The results are shown in Table 4, where x indicates the molar ratio of each.

[0072] Two reference experiments (columns 1 and 3 of the table, "Standard") were carried out under the same conditions at two different times (time on stream, TOS), namely, 193 and 599 hours. Between these reference experiments (269 hours), an experiment in which methanol was added to the feed gas ("Methanol Addition 1") was carried out. Comparing these experiments, it is shown that the carbon monoxide conversion is hardly affected. This means that the impact of methanol recycle is small when using the mixed catalyst system.

[0073] [Table 5]

Claims

1. 1. A method for synthesizing dimethyl ether, comprising: conducting a feed gas mixture (E) containing carbon dioxide and / or carbon monoxide and hydrogen through reaction tubes (1) of a cooled shell-and-tube reactor (10) comprising a first catalyst and a second catalyst; at least partially reacting the carbon dioxide and / or the carbon monoxide present in the feed gas mixture (E) with the hydrogen present in the feed gas mixture over the first catalyst to produce methanol; and at least partially converting the methanol to dimethyl ether over the second catalyst in the same shell-and-tube reactor (10), wherein the reaction tubes (1) comprise the first and second catalysts in the form of a structured bed, the structured bed having two to four zones (11, 12, 13) in which the first and second catalysts are provided in different physical mixtures, the zones (11, 12, 13) being arranged such that the concentration of the first catalyst increases in the flow direction through the reaction tubes (1).

2. 2. The method of claim 1, wherein the structured bed is in the form of a series of catalyst regions each having a different proportion of the first and second catalysts, the proportion of the first and second catalysts within each region being essentially the same.

3. 2. The process according to claim 1, wherein the first catalyst is a copper-based catalyst and / or the second catalyst is an acidic catalyst, in particular based on one or more zeolites, gamma-dialuminum trioxide, and / or aluminosilicates.

4. The reactor is in a pressure range of 30 to 80 bar and / or in a temperature range of 200 to 290°C and / or in a temperature range of 1500 to 4000 h －１ 10. The process of claim 1, wherein the process is operated at a gas hourly space velocity of

5. 2. The method according to claim 1, wherein the number of zones (11, 12, 13) having beds is two, a first zone (11, 12, 13) is an upstream zone of 0% to 30% of the length of the reaction tube (1), and a second zone (11, 12, 13) is a downstream zone of 25% to 100% of the length of the reaction tube (1).

6. 6. The method of claim 5, wherein in the first region (11, 12, 13), the proportion of the first catalyst is 1 and the proportion of the second catalyst is X, and in the second region (11, 12, 13), the proportion of the first catalyst is 1.5 to 4 and the proportion of the second catalyst is X.

7. 2. The method according to claim 1, wherein the number of regions (11, 12, 13) having beds is three, a first of the regions (11, 12, 13) is an upstream region of 0% to 30% of the length of the reaction tube (1), a second of the regions (11, 12, 13) is a central region of 20% to 70% of the length of the reaction tube (1), and a third of the regions (11, 12, 13) is a downstream region of 50% to 100% of the length of the reaction tube (1).

8. 8. The method of claim 7, wherein in the first region (11, 12, 13), the proportion of the first catalyst is 1 and the proportion of the second catalyst is X, in the second region (11, 12, 13), the proportion of the first catalyst is 1.5 to 2 and the proportion of the second catalyst is X, and in the third region (11, 12, 13), the proportion of the first catalyst is 3 to 4 and the proportion of the second catalyst is X.

9. 2. The method according to claim 1, wherein the number of regions (11, 12, 13) having beds is four, a first region (11, 12, 13) is an upstream region covering 0% to 25% of the length of the reaction tube (1), a second region (11, 12, 13) is an upstream central region covering 20% ​​to 50% of the length of the reaction tube (1), a third region (11, 12, 13) is a downstream central region covering 50% to 75% of the length of the reaction tube (1), and a fourth region (11, 12, 13) is a downstream region covering 75% to 100% of the length of the reaction tube (1).

10. 10. The method of claim 9, wherein in the first region (11, 12, 13), the proportion of the first catalyst is 1 and the proportion of the second catalyst is X; in the second region (11, 12, 13), the proportion of the first catalyst is 1.5 to 2 and the proportion of the second catalyst is X; in the third region (11, 12, 13), the proportion of the first catalyst is 2.5 to 3 and the proportion of the second catalyst is X; and in the region of region (11, 12, 13), the proportion of the first catalyst is 4 and the proportion of the second catalyst is X.

11. 7. The method of claim 6, wherein X is 0.3 to 1.

12. A plant (100) for the synthesis of dimethyl ether, comprising a cooled shell-and-tube reactor (10) having reaction tubes (1) equipped with a first catalyst and a second catalyst, and arranged to guide a feed gas mixture (E) comprising carbon dioxide and / or carbon monoxide and hydrogen through the reaction tubes (1) of the shell-and-tube reactor (10), and to convert the carbon dioxide and / or the carbon monoxide present in the feed gas mixture (E) into at least a portion of the hydrogen present in the feed gas mixture over the first catalyst. and converting the methanol at least partially to dimethyl ether over the second catalyst in the same shell-and-tube reactor (10), the reactor tube (1) comprising the first catalyst and the second catalyst in the form of a structured bed, the structured bed having two to four zones (11, 12, 14) in which the first catalyst and the second catalyst are provided in different physical mixtures, the zones (11, 12, 13) being arranged such that the concentration of the first catalyst increases in the flow direction through the reactor tube (1).

13. A plant (100) as described in claim 12, configured to carry out the method as described in claim 1.

Images