Process for the production of dimethyl ether

Abstract

A process for the production of dimethyl ether, comprising the following steps: - introducing a methanol-containing stream SFeed-RD into a reactive distillation unit RD, wherein - in at least one reaction zone RZ of the reactive distillation unit RD, methanol is reacted to form dimethyl ether and water in the presence of an acidic catalyst, and - a distillative separation is carried out into a fraction containing dimethyl ether, which exits the reactive distillation unit RD as the top stream SHead-RD, and a fraction containing water, which exits the reactive distillation unit RD as the bottom stream SSbottom-RD, - withdrawing a methanol-containing side stream SSide-RD from the reactive distillation unit RD, - introducing the methanol-containing side stream SSide-RD into a side reactor SR and reacting the methanol to form dimethyl ether and water in the presence of an acidic catalyst, obtaining a product stream SProduct-SR, which is dimethyl ether.It contains water and methanol and is drawn off from the side reactor SR.

Description

[0001] Dimethyl ether is an industrially important starting material for the production of dimethyl sulfate and is used as a propellant and refrigerant. Dimethyl ether is also of interest as a synthetic fuel, for example as a substitute for LPG and diesel fuel.

[0002] An overview of known methods for the production of dimethyl ether can be found in the following publications: Z. Azizi et al., “Dimethyl ether: A review of technologies and product challenges”, Chemical Engineering and Processing, 2014, 82, pp. 150-172; V. Dieterich et al., “Power-to-liquid via synthesis of methanol, DME or Fischer-Tropsch fuels: a review,” Energy Environ. Sci., 2020, 13, pp. 3207-3252; Th. Cholewa et al., “Process Intensification Strategies for Power-to-X Technologies,” ChemEngineering, 2022, 6(1), 13.

[0003] On an industrial scale, dimethyl ether (DME) can be produced in a reactor (e.g., a fixed-bed reactor) via the dehydration of methanol in the presence of an acidic catalyst. The dehydration reaction can be described by the following reaction equation: 2 CH3OH ⇌ CH3OCH3 + H2O

[0004] Typically, gaseous methanol is fed into the DME synthesis reactor and reacted to form dimethyl ether and water at a reaction temperature of approximately 220–400°C. The dehydration reaction taking place in the DME synthesis reactor is thermodynamically limited (equilibrium-limited reaction) and usually yields a conversion of no more than about 70–85%.

[0005] The DME synthesis reactor is typically followed by at least two distillation steps. In the first distillation step, dimethyl ether is separated from methanol and water, and in the second distillation step, methanol is separated from water. The distillation-separated methanol is recycled back into the DME synthesis reactor.

[0006] The methanol fed into the DME synthesis reactor can be produced from synthesis gas in a known manner. The methanol obtained directly in this synthesis is also referred to as crude methanol and typically contains significant amounts of water (e.g., 20–50 mol%), especially in sustainable methanol synthesis using synthesis gas rich in CO2 and containing renewable hydrogen. Therefore, a DME synthesis process in which the crude methanol can be used directly as the starting material (i.e., without further processing such as water removal) would be of interest.

[0007] If the DME synthesis reactor is supplied with hydrated crude methanol as the reactant stream, this has a detrimental effect on the conversion, as the equilibrium of the dehydration reaction shifts towards the reactant (methanol). Furthermore, the presence of significant amounts of water can impair the catalytic activity and stability of some acidic solid catalysts, such as γ-Al₂O₃. Therefore, it is common practice to supply the DME synthesis reactor with essentially anhydrous methanol as the reactant stream.

[0008] The conventional method for producing dimethyl ether is therefore disadvantageous both in terms of its energy balance and the equipment required, since - the water must be separated from the crude methanol to obtain essentially anhydrous methanol, which can then be fed into the DME synthesis reactor, - the methanol must be evaporated before being fed into the DME synthesis reactor and - the DME synthesis reactor is followed by at least two distillation stages in which dimethyl ether is first separated from water and methanol and then methanol is separated from water by distillation.

[0009] If the conversion of methanol to dimethyl ether and water occurs not in the gas phase but in the liquid phase, the DME synthesis reactor can, in principle, be operated isothermally, i.e., at a temperature optimized for catalytic activity. A fixed-bed reactor, for example, can be used for such isothermal operation. However, even with isothermal operation of the DME synthesis reactor, the hydration reaction of methanol to dimethyl ether and water is thermodynamically limited, so that a conversion of more than 85% is usually not achievable.

[0010] It is known that the equipment required for dimethyl ether synthesis can be reduced by using a reactive distillation unit. A reactive distillation unit (e.g., in the form of a reactive distillation column) contains one or more reaction zones in which reactants are reacted with each other, usually in the presence of a catalyst immobilized in the reaction zone, and one or more distillation separation zones in which reaction products and, if present, unreacted reactants are separated from each other.

[0011] US 2007 / 0066855 A1 describes a process for the production of dimethyl ether in which a methanol-containing stream is introduced into a reactive distillation column, methanol is converted to dimethyl ether and water in a reaction zone of the reactive distillation column in the presence of an acidic catalyst, and a distillative separation is carried out into an overhead stream consisting essentially of dimethyl ether and a bottom stream consisting essentially of water.

[0012] For a catalyst, there is usually an optimal reaction temperature for the reaction to be catalyzed; for example, high enough for sufficient catalytic activity, but not so high as to prevent thermal degradation of the catalyst material or to minimize undesirable side reactions. A chemical reactor can, in principle, be operated isothermally (i.e., at a temperature optimized for catalytic activity). However, when operating a reactive distillation unit, the temperature in the reaction zone typically decreases towards the column head. Therefore, the optimal reaction temperature can only be achieved in a portion of the reaction zone. Consequently, the reaction zone exhibits areas of decreasing catalytic activity.The average catalytic activity achievable in the reaction zone of a reactive distillation unit for a specific catalyst is more or less significantly below the maximum catalytic activity achievable with that catalyst.

[0013] To compensate for this, the volume of the reaction zone can be increased, for example. This requires the insertion of additional internals or packings with immobilized catalyst into the reaction zone, which is complex and expensive.

[0014] Z. Lei et al., “Synthesis of dimethyl ether (DME) by catalytic distillation”, Chemical Engineering Science, 2011, 66, pp. 3195-3203, describe, among other things, a process (referred to in the publication as “Process A”) in which (i) the methanol-containing stream is first introduced into a DME synthesis reactor to convert methanol to dimethyl ether and water in the presence of an acidic catalyst, and (ii) the product stream withdrawn from the DME synthesis reactor (containing dimethyl ether, water, and unreacted methanol) is immediately introduced into a reactive distillation unit to convert the remaining methanol to dimethyl ether and water and to perform a distillative separation into an overhead stream consisting essentially of dimethyl ether and a bottom stream consisting essentially of water.Since a DME synthesis reactor is connected upstream of the reactive distillation unit, and a large portion of the methanol has already been converted to dimethyl ether in this upstream DME synthesis reactor, the stream supplied to the reactive distillation unit contains the desired end product (dimethyl ether) in a relatively high concentration. Therefore, only the remaining methanol that is not converted in the DME synthesis reactor needs to be converted in the reactive distillation unit. The presence of the upstream DME synthesis reactor thus allows the reactive distillation unit to be smaller.

[0015] The “Process A” described in the publication by Z. Lei et al. (i.e., using an upstream DME synthesis reactor whose product stream is fed into a reactive distillation unit) is disadvantageous if crude methanol, i.e., methanol with a significant water content, is fed into the DME synthesis reactor. The presence of water in the reactant stream inhibits the conversion of the dehydration reaction of methanol to dimethyl ether and water in the DME synthesis reactor. To counteract this conversion loss, the reaction temperature in the DME synthesis reactor or the volume of the catalyst-containing reaction zone within the reactor could be increased. However, these measures increase the energy input of the process. Furthermore, increasing the reaction temperature requires that the acidic catalyst used for the methanol dehydration reaction has sufficiently high thermal stability.

[0016] One object of the present invention is the production of dimethyl ether via a process that is as efficient as possible (e.g., energy-efficient). In particular, the process should enable the efficient production of dimethyl ether even when crude methanol (i.e., methanol with a significant water content) is used as the starting material. As mentioned above, crude methanol with a high water content is produced, especially during sustainable methanol synthesis using a synthesis gas rich in CO2 and containing renewable hydrogen.

[0017] The problem is solved by a process for the production of dimethyl ether, which includes the following steps: - Introducing a methanol-containing stream S Feed-RD into a reactive distillation unit RD, wherein - in at least one reaction zone RZ of the reactive distillation unit RD, methanol is converted to dimethyl ether and water in the presence of an acidic catalyst and - a distillative separation into a fraction containing dimethyl ether and the reactive distillation unit RD as the overhead stream S Kopf-RD leaves, and a fraction containing water and the reactive distillation unit RD as bottom stream S Sumpf-RD leaves, occurs, - Withdrawal of a methanol-containing side stream S Seite-RD from the reactive distillation unit RD, - Introduction of the methanol-containing side stream S Seite-RD into a side reactor SR and conversion of the methanol in the presence of an acidic catalyst to dimethyl ether and water, obtaining a product stream S Produkt-SR , which contains dimethyl ether, water and methanol and is drawn off from the side reactor SR.

[0018] The process according to the invention is particularly suitable for the use of crude methanol (i.e., methanol with a significant water content) as the feed stream. During operation of the reactive distillation unit RD, which is fed with crude ethanol, the following occurs in the head stream S: Kopf-RD essentially the highly volatile dimethyl ether and in the bottom stream S Sumpf-RD Essentially, the high-boiling water is drawn off, while a side stream S forms at a suitable point or height of the reactive distillation unit RD. Seite-RD a side stream S, which has a significantly higher methanol concentration and a significantly lower water concentration compared to the crude methanol, is drawn off by the reactive distillation unit RD. Seite-RDDue to the reduced water concentration compared to crude methanol, a very efficient conversion of methanol to dimethyl ether is possible in the side reactor SR, which functions as a DME synthesis reactor. Thus, a product stream S can be generated in the side reactor SR. Produkt-SR with a high DME concentration, which, for example, after its return to the reactive distillation unit RD, also has a beneficial influence on the yield of dimethyl ether in the reactive distillation unit RD due to the high dimethyl ether concentration.

[0019] Within the scope of the present invention, the reactive distillation unit RD is thus used not only for the synthesis and distillative separation of the dimethyl ether, but also for providing a methanol source which has a lower water concentration compared to crude methanol and thus enables a higher DME yield (compared to crude methanol) in a DME synthesis reactor.

[0020] As mentioned above, in the process according to the invention a methanol-containing stream S Feed-RD introduced into a reactive distillation unit RD, whereby in at least one reaction zone RZ of the reactive distillation unit RD, methanol is converted to dimethyl ether and water in the presence of an acidic catalyst and a distillative separation into a fraction containing dimethyl ether and the reactive distillation unit RD as the overhead stream S Kopf-RD leaves, and a fraction containing water and the reactive distillation unit RD as bottom stream S Sumpf-RD leaves, happens.

[0021] The methanol-containing electricity S Feed-RD For example, it has a methanol concentration C1(MeOH) of at least 40 mol%, a water concentration C1(H2O) of at most 60 mol% and a total concentration of other components (i.e. components other than methanol and water), if present, of at most 5 mol%.

[0022] As mentioned above, the process according to the invention enables an efficient synthesis of dimethyl ether, even if the methanol-containing current used as starting material S Feed-RD contains a significant proportion of water. In a preferred embodiment, the methanol-containing stream S therefore contains Feed-RD a water concentration C1(H2O) of 15-60 mol%, preferably 25-50 mol%, and optionally contains components other than methanol and water in a total concentration of not more than 5 mol%.

[0023] For example, the methanol-containing electricity comes from S Feed-RD a methanol synthesis unit in which methanol was produced in a known manner (e.g. from synthesis gas, in particular CO2-rich synthesis gas).

[0024] Reactive distillation units suitable for the conversion of methanol to dimethyl ether and water and the distillative separation of the reaction products are known to those skilled in the art.

[0025] The reactive distillation unit RD (e.g., a reactive distillation column) has one or more reaction zones RZ and one or more distillation separation zones DT. The reaction zone RZ contains one or more acidic catalysts, in particular one or more acidic solid catalysts. Suitable acidic catalysts for the dehydration reaction of methanol to dimethyl ether and water are known to those skilled in the art. For example, the acidic catalyst is an ion exchange resin containing acidic groups, a zeolite, an aluminosilicate, an aluminum oxide, or an acidic ionic liquid (preferably immobilized on a support). In the distillation separation zone(s) DT, the distillative separation into the DME-containing fraction, which the reactive distillation unit RD discharges as the overhead stream S, takes place. Kopf-RD leaves, and the water-containing fraction, which the reactive distillation unit RD calls the bottom stream SSumpf- RD The distillative separation zones DT contain, for example, internals for distillative separation, in particular trays, packings, or structured packings, as are generally known to those skilled in the art. The immobilization of the catalyst in the reaction zone RZ of the reactive distillation unit RD can be carried out in a manner known to those skilled in the art, e.g., as a randomly packed packing; in the form of catalyst-filled wire mesh spheres; or as catalyst-shaped bodies mounted on a tray in the reaction zone RZ.

[0026] By using suitable internals or packings known to those skilled in the art, on which the acidic catalyst is located, the reaction zone RZ itself can already achieve sufficient distillative separation of the reaction products from one another. Preferably, however, the reactive distillation unit RD has at least one, and more preferably at least two, catalyst-free distillative separation zones DT. For example, in the reactive distillation column RD, a catalyst-free distillative separation zone DT can be located both above and below the reaction zone RZ.

[0027] The reactive distillation unit RD is operated, for example, in such a way that the reaction zone RZ has a temperature in the range of 100-180°C and / or a pressure in the range of 8-20 bar.

[0028] The methanol-containing current S is preferred Feed-RDin the reaction zone RZ of the reactive distillation unit RD. In principle, however, it is also possible to introduce the methanol-containing stream S Feed-RD to be introduced above or below the reaction zone RZ, for example in a catalyst-free distillative separation zone.

[0029] The highly volatile dimethyl ether leaves the reactive distillation unit RD as the overhead stream S. Kopf-RD , while water (i.e., the component with the highest boiling point) is used by the reactive distillation unit RD as the bottom stream S Sumpf-RD leaves.

[0030] The head current S Kopf-RD for example, has a dimethyl ether concentration of at least 50 mol%, preferably at least 95 mol%, and even more preferably at least 99 mol%.

[0031] The swamp stream, for example, has a water concentration of at least 50 mol%, preferably at least 90 mol%, and even more preferably at least 99 mol%.

[0032] In the process according to the invention, a methanol-containing side stream S Seite - RD The methanol is withdrawn from the reactive distillation unit RD (e.g., from the reaction zone RZ of the reactive distillation unit RD) and introduced into a side reactor SR. In the side reactor SR, the methanol is converted to dimethyl ether and water in the presence of an acidic catalyst, yielding a product stream S. Produkt-SR , which contains dimethyl ether, water and methanol and is drawn off from the side reactor SR.

[0033] In the reactive distillation unit (RD), dimethyl ether, due to its high volatility, accumulates in the column head, while water, as the component with the highest boiling point, accumulates in the column bottom. Fractions with a high methanol concentration can be drawn off as a side stream in the intermediate sections of the column. If the reactive distillation unit (RD) is fed with crude methanol, these side stream fractions can even have a higher methanol concentration (and thus a lower water concentration) than the crude methanol itself.

[0034] For example, the methanol-containing side stream S drawn from the reactive distillation unit RD exhibits Seite-RD A water concentration of C₂(H₂O) of at most 25 mol%, preferably at most 10 mol%, and even more preferably at most 5 mol%. Dimethyl ether and, if present, components other than methanol, water, and dimethyl ether are present in the methanol-containing side stream S.Seite- RD for example, in a total concentration of no more than 10 mol%.

[0035] A person skilled in the art can readily determine, based on their expertise, a suitable position or height in the reactive distillation unit RD at which a side stream with a high methanol concentration or a low water concentration can be discharged. For example, the methanol-containing side stream S Seite-RD at a position relatively high up in the reaction zone RZ, for example in the upper third or the upper quarter of the reaction zone RZ. Thus, if the reaction zone RZ has an upper end (i.e., facing the head of the reactive distillation unit RD) and a lower end (i.e., facing the bottom of the reactive distillation unit RD) and a length L (i.e., distance between the upper and lower ends of the reaction zone RZ), and the methanol-containing side stream S Seite-RD at a position P Swhen withdrawn from the reaction zone RZ, the position P can be determined. S for example, have a distance I from the upper end of the reaction zone RZ such that I / L ≤ 0.33, preferably I / L ≤ 0.25.

[0036] As mentioned above, the process according to the invention enables the highly efficient production of dimethyl ether even when a methanol with a high water content (crude ethanol) is used as the starting material. Within the scope of the present invention, the reactive distillation unit RD is used not only for the synthesis and distillative separation of the dimethyl ether, but also for providing a methanol source that has a lower water concentration than crude methanol and thus enables a higher DME yield (compared to crude methanol) in a downstream DME synthesis reactor.

[0037] According to an exemplary embodiment, the methanol-containing stream S introduced into the reactive distillation unit RD exhibits Feed-RD a water concentration C1(H2O) of 15-60 mol%, preferably 25-50 mol%, and the methanol-containing side stream S withdrawn from the reactive distillation unit RD Seite-RD has a water concentration C2(H2O) that satisfies the following condition: C2(H2O) ≤ 0.75 × C1(H2O).

[0038] The following condition is preferred: C2(H2O) ≤ 0.60 × C1(H2O).

[0039] For example, the methanol-containing stream S introduced into the reactive distillation unit RD exhibits Feed-RD a water concentration C1(H2O) of 15-60 mol%, preferably 25-50 mol%, and the side stream S withdrawn from the reactive distillation unit RD Seite-RD has a water concentration C2(H2O) of a maximum of 10 mol%.

[0040] As mentioned above, the methanol-containing stream S introduced into the reactive distillation unit RD contains Feed-RD Components other than methanol and water, preferably in a total concentration of not more than 5 mol%. As also mentioned above, the methanol-containing side stream S withdrawn from the reactive distillation unit RD contains Seite-RD Dimethyl ether and components other than methanol, water and dimethyl ether, in a total concentration of not more than 10 mol%.

[0041] The side reactor SR can be a reactor type commonly used for DME synthesis. For example, the side reactor SR is a fixed-bed reactor.

[0042] For the conversion of methanol to dimethyl ether and water, the side reactor SR contains one or more acidic catalysts, in particular one or more acidic solid catalysts. Suitable acidic catalysts for the dehydration reaction of methanol to dimethyl ether and water are known to those skilled in the art. For example, the acidic catalyst is an ion exchange resin containing acidic groups, a zeolite, an aluminosilicate, an aluminum oxide, or an acidic ionic liquid (preferably immobilized on a support).

[0043] To operate as energy-efficiently as possible, it can be advantageous if the side reactor SR is operated at a pressure and temperature at which the introduced methanol-containing side stream S Seite-RD and the received product stream S Produkt-SR at least partially in the liquid phase.

[0044] For example, the side reactor SR is operated at a temperature in the range of 130-200°C.

[0045] The side reactor SR is preferably operated isothermally. Isothermal operation is present when the temperature of the reactor in the region of the acidic catalyst fluctuates by a maximum of + / - 10°C, preferably + / - 5°C.

[0046] The SR side reactor, for example, is operated at a pressure of 20-150 bar.

[0047] The product flow S Produkt-SR The side reactor SR contains, for example, methanol at a concentration of no more than 50 mol%, preferably no more than 40 mol%. The molar ratio of dimethyl ether to water in the product stream S Produkt- SR The ratio is, for example, in the range of 4:6 to 6:4. If present, components other than dimethyl ether, water, and methanol are located in product stream S. Produkt-SR for example, in a total concentration of no more than 5 mol%.

[0048] In an exemplary embodiment, the product stream S, which is drawn from the side reactor SR and contains dimethyl ether, water and methanol, is Produkt-SR returned to the reactive distillation unit RD. For example, the product stream S Produkt-SR returned to the reaction zone RZ of the reactive distillation unit RD.

[0049] In another exemplary embodiment, the product stream S withdrawn from the side reactor SR is Produkt-SR The product stream is introduced into a gas-liquid separation unit SU. Within this gas-liquid separation unit SU, the product stream S is separated. Produkt-SR in a gaseous stream S G , containing dimethyl ether and methanol (e.g., in a total concentration of at least 80 mol%), and a liquid stream S L , which contains water and methanol (e.g., in a total concentration of at least 80 mol%). For separation, the product stream S Produkt-SRfor example, subjected to a pressure reduction. The gaseous flow S G and the liquid stream S L are returned separately to the reactive distillation unit RD, preferably to the reaction zone of the reactive distillation unit RD.

[0050] By separating the product stream S drawn from the side reactor SR Produkt-SR in a gaseous stream S G and a liquid stream S L and the separate return of these two currents S G and S L into the reactive distillation unit RD, compared to the direct return of the product stream S Produkt-SR A further improvement in the conversion of methanol to dimethyl ether will be achieved.

[0051] In the reactive distillation unit RD, the reaction zone RZ has a high water concentration and a low DME concentration in its lower region. Towards the top of the reactive distillation unit, the water concentration decreases, so that the upper region of the reaction zone has a very low water concentration. The product stream S drawn from the side reactor SR Produkt-SR It contains dimethyl ether and water (i.e., the reaction products of the hydration reaction of methanol taking place in side reaction SR) in relatively high concentrations. If the product stream S Produkt-SR For example, if the product stream S is returned directly to the upper (i.e., very low-water) region of the reaction zone RZ, this leads to an increase in the water concentration and thus inhibits the hydration reaction of the methanol in this region of the reaction zone RZ of the reactive distillation unit RD. Produkt-SRFor example, if the product stream S, drawn from the side reactor SR, is returned to a lower region of the reaction zone RZ (i.e., containing a lot of water but very little DME), the increased concentration of the low-boiling component (i.e., dimethyl ether) leads to a lower temperature and thus a lower conversion of the methanol hydration reaction in this region of the reaction zone RZ of the reactive distillation unit RD. This is achieved by separating the product stream S drawn from the side reactor SR. Produkt-SR in a gaseous stream S G , which contains predominantly DME and methanol, but little water, and a liquid stream S L , which contains predominantly water and methanol, but little DME, and the separate return of these two streams S G and S L into the reactive distillation unit RD at suitable positions, thus, in comparison to a direct return of the product stream S Produkt-SRA further improvement in the conversion of methanol to dimethyl ether will be achieved.

[0052] The gaseous stream S is preferred G at position P1 and the liquid stream S L The solution is introduced at position P2 into the reactive distillation unit RD (e.g., the reaction zone RZ) such that position P1 is located above position P2. "Above" means that position P1 is closer to the head of the distillation unit than position P2.

[0053] For example, position P1 is located in the upper third (preferably in the upper fifth) of the reaction zone RZ or in a catalyst-free distillative separation zone DT located above the reaction zone RZ, and position P2 is located in the lower half of the reaction zone RZ or in a catalyst-free distillative separation zone DT located below the reaction zone RZ.

[0054] A position P1 in the upper third of the reaction zone means the following: The reaction zone RZ has an upper end (i.e., facing the head of the reactive distillation unit RD) and a lower end (i.e., facing the bottom of the reactive distillation unit RD) and a length L (i.e., the distance between the upper and lower ends of the reaction zone RZ), and position P1 is at a distance I1 from the upper end of the reaction zone RZ such that I1 / L ≤ 0.33. For a position P1 in the upper fifth of the reaction zone RZ, the following applies: I1 / L ≤ 0.2.

[0055] A position P2 in the lower half of the reaction zone means the following: The reaction zone RZ has an upper end (i.e., facing the head of the reactive distillation unit RD) and a lower end (i.e., facing the bottom of the reactive distillation unit RD) and a length L (i.e., distance between the upper and lower ends of the reaction zone RZ), and position P2 has a distance I2 from the lower end of the reaction zone RZ such that I2 / L ≤ 0.5.

[0056] Suitable gas-liquid separation units for separating the product into a gas phase and a liquid phase are known to those skilled in the art. For example, the separation involves separating the product stream S Produkt-SRThe gas-liquid separation unit (SU) is subjected to pressure reduction in a container, causing the formation of a gaseous phase containing dimethyl ether and methanol, and a liquid phase containing water and methanol, from which the gaseous and liquid phases are separated. The SU gas-liquid separation unit, for example, is a pressure-reducing separator.

[0057] An exemplary embodiment of the present invention is described with reference to the Fig. 1. Described in more detail: A methanol-containing stream S is carried via line 1. Feed-RD The methanol-containing stream S is introduced into the reaction zone RZ of a reactive distillation column RD. Feed-RDFor example, this involves crude methanol, which, in addition to MeOH, also contains a significant proportion of H₂O (c₁(MeOH): methanol concentration; c₁(H₂O): water concentration). If the reaction zone RZ already exhibits sufficient distillative separation due to the internal components used, the presence of catalyst-free distillative separation zones can be omitted. In the Fig. In the illustrated embodiment 1, a catalyst-free distillative separation zone DT is located above and below the reaction zone RZ.

[0058] In the reactive distillation unit RD, methanol is reacted to dimethyl ether and water in the presence of an acidic catalyst, and a distillative separation takes place into a fraction containing dimethyl ether, which is carried out by the reactive distillation unit RD via a line as the headstream S Kopf-RDleaves, and a fraction containing water and the reactive distillation unit RD via line 3 as sump stream S Sumpf-RD leaves. The headstream S Kopf-RD The sump stream contains essentially dimethyl ether (e.g., in a concentration of at least 99 mol%) and the sump stream contains essentially water (e.g., in a concentration of at least 99 mol%).

[0059] A methanol-containing side stream S is carried via line 4. Seite-RD The product is drawn off from the reactive distillation unit RD and fed to a side reactor SR. The side stream S Seite-RD It contains predominantly methanol and small amounts of water and dimethyl ether (c2(MeOH): methanol concentration; c2(H2O): water concentration; c2(DME): dimethyl ether concentration). This withdrawn methanol-containing side stream S Seite-RD indicates, in relation to the current S introduced into the reactive distillation unit RD Feed-RDa higher methanol and lower water concentration (i.e., c2(MeOH) > c1(MeOH); c2(H2O) <c1(H2O)).

[0060] The side reactor SR is operated isothermally (e.g., at a temperature in the range of 130–200°C) and contains an acidic catalyst for the dehydration reaction of methanol to dimethyl ether and water. To operate as energy-efficiently as possible, the side reactor SR is operated such that the introduced methanol-containing side stream S Seite-RD and the received product stream S Produkt-SR In the side reactor SR, the gas is not completely in the gas phase, but at least partially in the liquid phase.

[0061] The product stream S containing dimethyl ether, water and methanol is carried via line 5. Produkt-SRThe product stream S is withdrawn from the side reactor SR (c3(DME): dimethyl ether concentration; c3(H2O): water concentration; c3(MeOH): methanol concentration) and returned to the reaction zone RZ of the reactive distillation unit RD. Since methanol is converted to dimethyl ether (and water) in the side reactor SR, the product stream S Produkt-SR opposite the side stream S Seite- RD a higher dimethyl ether and lower methanol concentration (c3(DME) > c2(DME); c3(MeOH) < c2(MeOH)).

[0062] The reactive distillation unit RD is used not only for the synthesis and distillative separation of the dimethyl ether, but also in the form of the methanol-containing side stream S withdrawn via line 4. Seite-RDfor the provision of a methanol source which has a lower water concentration than the crude methanol supplied to the reactive distillation unit RD via line 1 and thus a higher DME yield in the product stream S in the downstream side reactor (compared to crude methanol). Produkt-SR This enables the return of the DME-rich product stream S Produkt-SR The reactive distillation unit RD, in turn, has a beneficial influence on the yield of dimethyl ether in the reactive distillation unit RD.

[0063] A further exemplary embodiment of the method according to the invention is described using the Fig. 2 described in more detail. The in Fig. The process flow illustrated in point 2 differs from that in Fig. 1 illustrated the process flow as follows: The product stream S drawn off from side reactor SR via line 5 Produkt-SRThe product stream is introduced into a gas-liquid separation unit (SU). Within this gas-liquid separation unit (SU), the product stream S is separated. Produkt-SR in a gaseous stream S G , which contains predominantly dimethyl ether and methanol (e.g. in a total concentration of at least 80 mol%), and a liquid stream S L , which contains predominantly water and methanol (e.g., in a total concentration of at least 80 mol%). The gaseous stream S G is via line 6 and the liquid stream S L is returned to the reactive distillation unit RD via line 7.

[0064] As described above, the product stream S drawn from the side reactor SR can be separated. Produkt-SR in a gaseous stream S G and a liquid stream S L and the separate return of these two currents S G and S Linto the reactive distillation unit RD compared to a direct return of the product stream S Produkt-SR A further improvement in the conversion of methanol to dimethyl ether will be achieved.

[0065] Regarding all other characteristics of the in Fig. The exemplary embodiment illustrated in point 2 can be described in the above description. Fig. 1 will be referred. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] US 2007 / 0066855 A1

[0011] Cited non-patent literature

[0000] Z. Azizi et al., „Dimethyl ether: A review of technologies and product challenges“, Chemical Engineering and Processing, 2014, 82, S. 150-172

[0002] V. Dieterich et al., „Power-to-liquid via synthesis of methanol, DME or Fischer-Tropsch fuels: a review“, Energy Environ. Sci., 2020, 13, S. 3207-3252

[0002] Th. Cholewa et al., „Process Intensification Strategies for Power-to-X Technologies“, ChemEngineering, 2022, 6(1), 13

[0002] Z. Lei et al., „Synthesis of dimethyl ether (DME) by catalytic distillation“, Chemical Engineering Science, 2011, 66, S. 3195-3203

[0014]

Claims

[1] Process for the preparation of dimethyl ether comprising the following steps: - Introducing a methanol-containing stream S Feed-RD into a reactive distillation unit RD, wherein - in at least one reaction zone RZ of the reactive distillation unit RD, methanol is converted to dimethyl ether and water in the presence of an acidic catalyst and - a distillative separation into a fraction containing dimethyl ether and the reactive distillation unit RD as the overhead stream S Kopf-RD leaves, and a fraction containing water and the reactive distillation unit RD as bottom stream S Sumpf-RD leaves, occurs, - Withdrawal of a methanol-containing side stream S Seite-RD from the reactive distillation unit RD, - Introduction of the methanol-containing side stream S Seite-RDinto a side reactor SR and conversion of the methanol in the presence of an acidic catalyst to dimethyl ether and water, obtaining a product stream S Produkt-SR , which contains dimethyl ether, water and methanol and is drawn from the side reactor SR. [2] The method of claim 1, wherein the methanol-containing stream S introduced into the reactive distillation unit RD Feed-RD has a methanol concentration c1(MeOH) of at least 40 mol%, a water concentration C1(H2O) of at most 60 mol% and a total concentration of other components other than methanol and water of at most 5 mol%. [3] Method according to claim 1 or 2, wherein the methanol-containing stream S introduced into the reactive distillation unit RD Feed-RD a water concentration C1(H2O) of 15-60 mol%, preferably 25-50 mol%, and the methanol-containing side stream S withdrawn from the reactive distillation unit RD Seite-RDhas a water concentration c2(H2O) that satisfies the following condition: c2(H2O) ≤ 0.75 × c1(H2O). [4] A method according to any of the foregoing claims, further comprising the following step: - Return of the product stream S drawn from the side reactor SR Produkt-SR into the reactive distillation unit RD. [5] A method according to any one of claims 1 to 3, further comprising the following steps: - Introduction of the product stream S drawn from the side reactor SR Produkt-SR into a gas-liquid separation unit SU and separation of the product stream S Produkt-SR in a gaseous stream S G , which contains dimethyl ether and methanol, and a liquid stream S L , which contains water and methanol, - separate return of the gaseous flow S G and the liquid stream S L into the reactive distillation unit RD. [6] Method according to claim 5, wherein the gaseous stream S G at position P1 and the liquid stream S L at position P2 the product is introduced into the reactive distillation unit RD, and position P1 is located in the upper third of the reaction zone RZ or in a catalyst-free distillative separation zone DT above the reaction zone RZ, and position P2 is located in the lower half of the reaction zone RZ or in a catalyst-free distillative separation zone DT below the reaction zone RZ.

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