Method for producing dimethylether

Abstract

The invention relates to a method for producing dimethylether, having 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 in the presence of an acid catalyst in order to form dimethylether and water, and - the stream is separated by means of distillation into a fraction which contains dimethylether and which leaves the reactive distillation unit (RD) as a head flow (Shead RD) and a fraction which contains water and which leaves the reactive distillation unit (RD) as a sump stream (Ssump RD), - drawing 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 in the presence of an acid catalyst in order to form dimethylether and water, thereby obtaining a product stream (Sproduct SR) which contains dimethylether, water, and methanol and which is drawn from the side reactor (SR).

Description

[0001] Process for the preparation of dimethyl ether

[0002] 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 replacement for LPG and diesel fuel.

[0003] An overview of known processes for the production of dimethyl ether can be found in the following publications:

[0004] Z. Azizi et al., "Dimethyl ether: A review of technologies and product challenges", Chemical Engineering and Processing, 2014, 82, pp. 150-172;

[0005] 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;

[0006] Th. Cholewa et al., "Process Intensification Strategies for Power-to-X Technologies", ChemEngineering, 2022, 6(1), 13.

[0007] Dimethyl ether (DME) can be produced industrially in a reactor (e.g., a fixed-bed reactor) by dehydrating methanol in the presence of an acid catalyst. The dehydration reaction can be represented by the following reaction equation:

[0008] 2 CH3OH CH3OCH3 + H2O

[0009] Typically, gaseous methanol is fed into the DME synthesis reactor and converted to dimethyl ether and water at a reaction temperature of approximately 220-400°C. The dehydration reaction occurring in the DME synthesis reactor is thermodynamically limited (equilibrium-limited reaction) and typically yields a conversion of no more than approximately 70-85%.

[0010] 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 methanol separated by distillation is recycled to the DM E synthesis reactor.

[0011] The methanol fed to the DME synthesis reactor can be produced from synthesis gas in a conventional 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%), particularly in sustainable methanol synthesis using a CCh-rich synthesis gas containing regenerative hydrogen. Therefore, a DM E synthesis process in which the crude methanol can be used directly as a starting material (i.e., without further processing such as water separation) would be of interest.

[0012] Feeding water-containing crude methanol as a reactant stream to the DME synthesis reactor has a detrimental effect on conversion, as the equilibrium of the dehydration reaction is shifted toward the reactant (methanol). Furthermore, the catalytic activity and stability of some acidic solid catalysts, such as Y-Al2O3, can be impaired by the presence of significant amounts of water. Therefore, it is common practice to feed essentially anhydrous methanol as a reactant stream to the DME synthesis reactor.

[0013] The conventional process for producing dimethyl ether is therefore disadvantageous both in terms of its energy balance and the equipment required, since the water in the crude methanol must be separated in order to obtain a substantially anhydrous methanol, which can then be fed to 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.

[0014] If the conversion of methanol to dimethyl ether and water takes place in the liquid phase rather than in the gas 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 a conversion of more than 85% is usually not achievable.

[0015] 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 one another, usually in the presence of a catalyst immobilized in the reaction zone, and one or more distillative separation zones in which reaction products and, if present, unreacted reactants are separated from one another.

[0016] US 2007 / 0066855 A1 describes a process for preparing dimethyl ether, in which a methanol-containing stream is introduced into a reactive distillation column, methanol is converted into dimethyl ether and water in a reaction zone of the reactive distillation column in the presence of an acid catalyst, and a distillative separation into a top stream consisting essentially of dimethyl ether and a bottom stream consisting essentially of water takes place.

[0017] For a catalyst, there is usually an optimal reaction temperature with respect to the reaction to be catalyzed, e.g., high enough for sufficient catalytic activity, but not too high to avoid thermal degradation of the catalyst material or to minimize undesirable side reactions. A chemical reactor can, in principle, be operated isothermally (e.g., at a temperature optimized for catalytic activity). However, when operating a reactive distillation unit, the temperature in the reaction zone typically decreases toward the top of the column. Therefore, the optimal reaction temperature can only be achieved in part of the reaction zone. Thus, the reaction zone exhibits regions of decreasing catalytic activity.The average catalytic activity of a specific catalyst that can be achieved in the reaction zone of a reactive distillation unit is more or less significantly below the maximum catalytic activity that can be achieved with this catalyst.

[0018] 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, however, complex and costly.

[0019] 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 as “Process A” in the publication) in which (i) the methanol-containing stream is first introduced into a DM E synthesis reactor in order to convert methanol to dimethyl ether and water in the presence of an acidic catalyst, and (ii) the product stream withdrawn from the DM E synthesis reactor (containing dimethyl ether, water and unreacted methanol) is directly introduced into a reactive distillation unit in order to convert the remaining methanol to dimethyl ether and water and to carry out a distillative separation into an overhead stream consisting essentially of dimethyl ether and a bottom stream consisting essentially of water.Since a DM E synthesis reactor is installed upstream of the reactive distillation unit, and a large portion of the methanol has already been converted to dimethyl ether in this upstream DM E synthesis reactor, the stream fed to the reactive distillation unit contains the desired end product (dimethyl ether) in a relatively high concentration. Therefore, only the methanol unconverted in the DME synthesis reactor needs to be converted in the reactive distillation unit. The presence of the upstream DM E synthesis reactor allows the reactive distillation unit to be smaller.

[0020] However, "Process A" described in the publication by Z. Lei et al. (i.e., use of an upstream DME synthesis reactor whose product stream is introduced into a reactive distillation unit) is disadvantageous if crude methanol, i.e., methanol with a significant proportion of water, is fed to 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 DM E synthesis reactor. To counteract this loss of conversion, the reaction temperature in the DM E synthesis reactor or the volume of the catalyst-containing reaction zone present in the DME synthesis reactor could be increased. However, these measures increase the energy input of the process. Furthermore, an increase in the reaction temperature requires that the acidic catalyst used for the dehydration reaction of the methanol has sufficiently high thermal stability.

[0021] One object of the present invention is the production of dimethyl ether using a process that is as efficient (e.g., energy-efficient) as possible. In particular, the process should enable efficient production of dimethyl ether even when crude methanol (i.e., methanol with a significant water content) is used as the starting material. As already mentioned above, particularly in sustainable methanol synthesis using a CO2-rich synthesis gas containing regenerative hydrogen, crude methanol with a high water content is produced. This object is achieved by a process for the production of dimethyl ether, which comprises the following steps:

[0022] Introducing a methanol-containing stream Speed-RD into a reactive distillation unit RD, wherein in at least one reaction zone RZ of the reactive distillation unit RD methanol is converted in the presence of an acid catalyst to dimethyl ether and water and a distillative separation into a fraction which contains dimethyl ether and leaves the reactive distillation unit RD as the top stream SKOPPRD, and a fraction which contains water and leaves the reactive distillation unit RD as the bottom stream Ssum P f-RD leaves, occurs,

[0023] Withdrawing a methanol-containing side stream Sseite-RD from the reactive distillation unit RD,

[0024] Introducing the methanol-containing side stream Sside-RD into a side reactor SR and converting the methanol in the presence of an acid catalyst to dimethyl ether and water to obtain a product stream Sp rOduct-sR, which contains dimethyl ether, water and methanol and is withdrawn from the side reactor SR.

[0025] The process according to the invention is particularly suitable for the use of crude methanol (i.e. methanol having a significant water content) as the starting stream. During operation of the reactive distillation unit RD fed with crude methanol, essentially the highly volatile dimethyl ether is produced in the top stream SKOPT-RD and the bottom stream Ssum Pf-RD, essentially the high-boiling water is withdrawn, while at a suitable location or height of the reactive distillation unit RD, a side stream Sside-RD can be discharged, which has a significantly higher methanol concentration or a significantly lower water concentration than the crude methanol. This side stream Sside-RD withdrawn from the reactive distillation unit RD enables a very efficient conversion of the methanol to dimethyl ether in the side reactor SR, which functions as a DME synthesis reactor, due to the reduced water concentration compared to the crude methanol. Thus, a product stream Sp rOproduct-sR with a high DM E concentration can be produced, 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. Within the scope of the present invention, the reactive distillation unit RD is thus used not only for the synthesis and distillative separation of dimethyl ether, but also for the provision of 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 DM E synthesis reactor.

[0026] As mentioned above, in the process according to the invention, a methanol-containing stream Speed-RD is introduced into a reactive distillation unit RD, wherein in at least one reaction zone RZ of the reactive distillation unit RD, methanol is converted in the presence of an acid catalyst to dimethyl ether and water, and a distillative separation into a fraction which contains dimethyl ether and leaves the reactive distillation unit RD as the top stream SKOPT-RD, and a fraction which contains water and leaves the reactive distillation unit RD as the bottom stream Ssum P f-RD leaves.

[0027] For example, the methanol-containing stream Speed-RD has a methanol concentration Ci(MeOH) of at least 40 mol%, a water concentration CI(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%.

[0028] As already mentioned above, the process according to the invention enables an efficient synthesis of dimethyl ether, even if the methanol-containing stream used as starting material Sp ee d-RD contains a significant proportion of water. In a preferred embodiment, the methanol-containing stream Speed-RD therefore has a water concentration CI(H2O) of 15-60 mol%, more preferably 25-50 mol%, and optionally contains components other than methanol and water in a total concentration of at most 5 mol%.

[0029] For example, the methanol-containing stream Sp ee d-RD of a methanol synthesis unit in which methanol was produced in a known manner (e.g. from synthesis gas, in particular CO2-rich synthesis gas).

[0030] 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 the person skilled in the art.

[0031] The reactive distillation unit RD (e.g., a reactive distillation column) has one or more reaction zones RZ and one or more distillative 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 the person 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 distillative separation zone(s) DT, the distillative separation takes place into the DME-containing fraction, which leaves the reactive distillation unit RD as the overhead stream SKOPT-RD, and the water-containing fraction, which leaves the reactive distillation unit RD as the bottoms stream Ssumpf-RD.The distillation separation zones DT contain, for example, internals for the distillation separation, in particular trays, random packings, or structured packings, as are generally known to those skilled in the art. The catalyst can be immobilized in the reaction zone RZ of the reactive distillation unit RD in a manner known to those skilled in the art, e.g., as random packing; in the form of catalyst-filled wire mesh spheres; or as shaped catalyst bodies mounted on a tray in the reaction zone RZ.

[0032] By using suitable internals or packings known to those skilled in the art, on which the acidic catalyst is present, the reaction zone RZ itself can achieve sufficient distillative separation of the reaction products from one another. However, the reactive distillation unit RD preferably has at least one, 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 present above and below the reaction zone RZ.

[0033] The reactive distillation unit RD is operated, for example, in such a way that a temperature in the range of 100-180°C and / or a pressure in the range of 8-20 bar is present in the reaction zone RZ.

[0034] The methanol-containing stream Sp is preferred eed-RD is introduced into the reaction zone RZ of the reactive distillation unit RD. In principle, however, it is also possible to introduce the methanol-containing stream Speed-RD above or below the reaction zone RZ, for example, in a catalyst-free distillation separation zone.

[0035] The very volatile dimethyl ether leaves the reactive distillation unit RD as the top stream SKOPT-RD, while water (i.e. the component with the highest boiling point) leaves the reactive distillation unit RD as the bottom stream Ssum P f-RD. The overhead stream SKOPT-RD, for example, has a dimethyl ether concentration of at least 50 mol%, more preferably at least 95 mol%, even more preferably at least 99 mol%.

[0036] The bottom stream has, for example, a water concentration of at least 50 mol%, more preferably at least 90 mol%, even more preferably at least 99 mol%.

[0037] In the process according to the invention, a methanol-containing side stream Sside-RD 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 to obtain a product stream Sp. rO duct-sR, which contains dimethyl ether, water and methanol and is withdrawn from the side reactor SR.

[0038] In the reactive distillation unit (RD), dimethyl ether, due to its high volatility, accumulates in the column head, and water, as the component with the highest boiling point, accumulates in the column bottom. In the intermediate sections of the column, fractions with high methanol concentrations can be withdrawn as side streams. If the reactive distillation unit (RD) is fed with crude methanol, these fractions, which can be withdrawn as side streams, can even have a higher methanol concentration (and thus also a lower water concentration) than the crude methanol.

[0039] For example, the methanol-containing side stream Sside-RD withdrawn from the reactive distillation unit RD has a water concentration C2(H2O) of at most 25 mol%, more preferably at most 10 mol%, 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 Sside-RD, for example, in a total concentration of at most 10 mol%.

[0040] 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 can be readily determined by a person skilled in the art based on his or her specialist knowledge. For example, the methanol-containing side stream Sside-RD is withdrawn at a position relatively high up in the reaction zone RZ, for example in the upper third or upper quarter of the reaction zone RZ. Thus, if the reaction zone RZ has an upper end (i.e., facing the top 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 end of the reaction zone RZ) and the methanol-containing side stream Sside-RD is withdrawn from the reaction zone RZ at a position Ps, the position Ps can, for example, have a distance I from the upper end of the reaction zone RZ such that l / L < 0.33, more preferably l / L < 0.25.

[0041] As already mentioned above, the process according to the invention enables the very efficient production of dimethyl ether even when methanol with a high water content (crude methanol) 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 dimethyl ether, but also for the provision of 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 DM E synthesis reactor.

[0042] According to an exemplary embodiment, the methanol-containing stream Sp introduced into the reactive distillation unit RD ee d-RD has a water concentration CI(H2Ü) of 15-60 mol%, more preferably 25-50 mol%, and the methanol-containing side stream Sseite-RD withdrawn from the reactive distillation unit RD has a water concentration C2(H2Ü) that satisfies the following condition:

[0043] C2(H2O) < 0.75 x CI(H2O).

[0044] The following condition applies preferentially:

[0045] C2(H2O) < 0.60 x CI(H2O).

[0046] For example, the methanol-containing stream Speed-RD introduced into the reactive distillation unit RD has a water concentration CI(H2Ü) of 15-60 mol%, more preferably 25-50 mol%, and the side stream Sseite-RD withdrawn from the reactive distillation unit RD has a water concentration C2(H2Ü) of at most 10 mol%.

[0047] As already mentioned above, the methanol-containing stream Sp introduced into the reactive distillation unit RD contains ee d-RD contains components other than methanol and water, preferably in a total concentration of no more than 5 mol%. As already mentioned above, the methanol-containing side stream Sside-RD withdrawn from the reactive distillation unit RD contains dimethyl ether and components other than methanol, water, and dimethyl ether, in a total concentration of no more than 10 mol%. The side reactor SR can be a reactor type commonly used for DM E synthesis. For example, the side reactor SR is a fixed-bed reactor.

[0048] 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).

[0049] In order 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 Sside-RD and the resulting product stream Sp rO duct-sR is present at least partially as a liquid phase.

[0050] For example, the side reactor SR is operated at a temperature in the range of 130-200°C.

[0051] The side reactor SR is preferably operated isothermally. Isothermal operation occurs when the temperature of the reactor in the area of ​​the acid catalyst fluctuates by a maximum of + / - 10°C, preferably + / - 5°C.

[0052] The side reactor SR, for example, is operated at a pressure of 20-150 bar.

[0053] The product stream Sp rO For example, the product stream SR of the side reactor SR contains methanol in a concentration of not more than 50 mol%, more preferably not more than 40 mol%. The molar ratio of dimethyl ether to water in the product stream Sp rO For example, the product-SR ratio is in the range of 4:6 to 6:4. If present, components other than dimethyl ether, water, and methanol are present in the product stream Sproduct-SR, for example, in a total concentration of a maximum of 5 mol%.

[0054] The product stream Sp rO The methanol contained in the product stream sR can, for example, be at least partially recycled as a reactant to the reactive distillation unit RD. In an exemplary embodiment, at least 20 mol%, more preferably at least 50 mol% of the methanol contained in the product stream Sp rO The methanol contained in the product-sR is returned to the reactive distillation unit RD.

[0055] In an exemplary embodiment, the product stream Sproduct-sR withdrawn from the side reactor SR and containing dimethyl ether, water and methanol is recycled to the reactive distillation unit RD. For example, the product stream Sp rO duct-sR is returned to the reaction zone RZ of the reactive distillation unit RD.

[0056] For example, the product stream Sproduct-sR withdrawn from the side reactor SR is recycled directly to the reactive distillation unit RD. However, within the scope of the present invention, it is also possible for the product stream Sp withdrawn from the side reactor SR rO duct-sR is divided into at least two substreams, and at least one of these substreams is recycled to the reactive distillation unit RD. For example, all substreams can be recycled to the reactive distillation unit. Alternatively, it is also possible for at least one of the substreams not to be recycled, for example because it contains dimethyl ether (i.e., the desired product of the process) in high concentration or because it contains undesirable by-products that can be removed from the process in this way.

[0057] In an exemplary embodiment, the product stream Sp withdrawn from the side reactor SR rOproduct-sR is divided into three or more substreams, one of which has a dimethyl ether concentration of at least 98 mol% or even consists of dimethyl ether, and this dimethyl ether is not recycled to the reactor distillation unit RD (since it is the desired product of the process). The substream consisting essentially of dimethyl ether is separated, for example, via a distillative separation (e.g. from the product stream Sp rO product-sR). Alternatively, one of the substreams contains one or more undesirable by-products, and these by-products are not recycled to the reactive distillation unit but are removed from the process. Preferably, at least two of the substreams are recycled to the reactive distillation unit.

[0058] In a further exemplary embodiment, the product stream Sp withdrawn from the side reactor SR rOduct-sR is introduced into a gas-liquid separation unit SU. In this gas-liquid separation unit SU, the product stream Sp is separated rO product-sR into a gaseous stream SG containing dimethyl ether and methanol (e.g., in a total concentration of at least 80 mol%), and a liquid stream Si_ containing water and methanol (e.g., in a total concentration of at least 80 mol%). For the separation, the product stream Sp rO duct-sR, for example, is subjected to a pressure reduction. The gaseous stream SG and the liquid stream SL are recycled separately to the reactive distillation unit RD, preferably to the reaction zone of the reactive distillation unit RD.

[0059] By separating the product stream Sproduct-sR withdrawn from the side reactor SR into a gaseous stream SG and a liquid stream SL and the separate recirculation of these two streams SG and SL into the reactive distillation unit RD, compared to the direct recirculation of the product stream Sp rO dukt-sR a further improvement in the conversion of methanol to dimethyl ether can be realized.

[0060] In the reactive distillation unit RD, the reaction zone RZ has a high water concentration and a low DM E 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 Sp withdrawn from the side reactor SR rOduct-sR contains dimethyl ether and water (ie the reaction products of the hydration reaction of methanol taking place in the side reaction SR) in relatively high concentrations. If the product stream Sp rO If, for example, the product stream Sp is returned directly to the upper (i.e., very little water-containing) area of ​​the reaction zone RZ, this leads to an increase in the water concentration and thus inhibition of the hydration reaction of the methanol in this area of ​​the reaction zone RZ of the reactive distillation unit RD. Alternatively, if the product stream Sp rOFor example, if the product stream SR is returned to a lower area 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 area of ​​the reaction zone RZ of the reactive distillation unit RD. By separating the product stream Sp withdrawn from the side reactor SR rO product-sR into a gaseous stream SG, which contains predominantly DME and methanol, but little water, and a liquid stream SL, which contains predominantly water and methanol, but little DME, and the separate recirculation of these two streams SG and SL into the reactive distillation unit RD at suitable positions can thus be compared to a direct recirculation of the product stream Sp rOdukt-sR a further improvement in the conversion of methanol to dimethyl ether can be realized.

[0061] Preferably, the gaseous stream SG is introduced into the reactive distillation unit RD (e.g., the reaction zone RZ) at a position P1 and the liquid stream SL at a position P2, so that position P1 is located above position P2. "Above" means that position P1 is closer to the top of the distillation unit than position P2.

[0062] For example, position P1 is located in the upper third (more 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. 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 top 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 P1 is at a distance h from the upper end of the reaction zone RZ such that h / L < 0.33. For a position P1 in the upper fifth of the reaction zone RZ, the following applies: h / L < 0.2.

[0063] 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 top 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 position P2 has a distance l2 from the lower end of the reaction zone RZ such that h / L < 0.5.

[0064] 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 Sp rOThe product-sR is subjected to a pressure reduction in a vessel, so that a gaseous phase containing dimethyl ether and methanol and a liquid phase containing water and methanol form, and the gaseous and liquid phases are separated from each other. The gas-liquid separation unit SU, for example, is a flash separator.

[0065] An exemplary embodiment of the present invention is described in more detail with reference to Figure 1:

[0066] A methanol-containing stream Sp is fed via line 1 eed-RD is introduced into the reaction zone RZ of a reactive distillation column RD. The methanol-containing stream Speed-RD is, for example, crude methanol, which, in addition to MeOH, also contains a significant proportion of H2O (Ci(MeOH): methanol concentration; Ci(H2O): water concentration). If the reaction zone RZ already has a sufficient distillative separation effect due to the internals used, the presence of catalyst-free distillative separation zones can be dispensed with. In the embodiment illustrated in Figure 1, a catalyst-free distillative separation zone DT is present above and below the reaction zone RZ.

[0067] In the reactive distillation unit RD, methanol is converted into dimethyl ether and water in the presence of an acid catalyst and is separated by distillation into a fraction containing dimethyl ether, which leaves the reactive distillation unit RD via line as the top stream SKOPPRD, and a fraction containing water, which leaves the reactive distillation unit RD via line 3 as the bottom stream Ssum. P f-RD. The overhead stream SKOPT-RD essentially contains dimethyl ether (e.g., at a concentration of at least 99 mol%), and the bottoms stream essentially contains water (e.g., at a concentration of at least 99 mol%).

[0068] A methanol-containing side stream Sside-RD is withdrawn from the reactive distillation unit RD via line 4 and fed to a side reactor SR. The side stream Sside-RD 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 Sside-RD has a higher methanol and lower water concentration than the stream Speed-RD introduced into the reactive distillation unit RD (i.e., C2(MeOH) > Ci(MeOH); C2(H2O)). <CI(H2O)).

[0069] 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 methanol-containing side stream Sside-RD and the resulting product stream Sp rO duct-sR in the side reactor SR is not completely in the gas phase, but at least partially in the liquid phase.

[0070] The product stream Sp containing dimethyl ether, water and methanol is fed via line 5 rO product-sR 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 Sp rOduct-sR has a higher dimethyl ether and lower methanol concentration compared to the side stream Sside-RD (c3(DME) > C2(DME); c3(MeOH) < c2(MeOH)).

[0071] The reactive distillation unit RD is not only used for the synthesis and distillative separation of dimethyl ether, but also in the form of the methanol-containing side stream Sside-RD withdrawn via line 4 for the provision of a methanol source which has a lower water concentration than the crude methanol fed to the reactive distillation unit RD via line 1 and thus provides a higher DM E yield in the product stream Sp in the downstream side reactor (compared to the crude methanol). rO duct-sR. The recirculation of the DME-rich product stream Sp rO duct-sR to the reactive distillation unit RD in turn has a beneficial influence on the yield of dimethyl ether in the reactive distillation unit RD.

[0072] A further exemplary embodiment of the method according to the invention is described in more detail with reference to Figure 2. The process illustrated in Figure 2 differs from the process illustrated in Figure 1 as follows:

[0073] The product stream Sp withdrawn from the side reactor SR via line 5 rO duct-sR is introduced into a gas-liquid separation unit SU. In this gas-liquid separation unit SU, the product stream Sp is separated rO duct-sR into a gaseous stream SG, which predominantly contains dimethyl ether and methanol (e.g., in a total concentration of at least 80 mol%), and a liquid stream SL, which predominantly contains water and methanol (e.g., in a total concentration of at least 80 mol%). The gaseous stream SG is recycled to the reactive distillation unit RD via line 6, and the liquid stream SL is recycled via line 7.

[0074] As already described above, by separating the product stream Sp withdrawn from the side reactor SR rO product-sR into a gaseous stream SG and a liquid stream SL and the separate recirculation of these two streams SG and SL into the reactive distillation unit RD compared to a direct recirculation of the product stream Sp rO dukt-sR a further improvement in the conversion of methanol to dimethyl ether can be realized.

[0075] With regard to all further features of the exemplary embodiment illustrated in Figure 2, reference can be made to the above description of Figure 1.

Claims

Claims process for the production of dimethyl ether, comprising the following steps: Introducing a methanol-containing stream Sp ee d-RD into a reactive distillation unit RD, wherein in at least one reaction zone RZ of the In the reactive distillation unit RD, methanol is converted to dimethyl ether and water in the presence of an acidic catalyst, and a distillative separation is performed into a fraction containing dimethyl ether, which exits the reactive distillation unit RD as the overhead stream Sxopf-RD, and a fraction containing water, which exits the reactive distillation unit RD as the bottom stream Ssum. P f-RD leaves, occurs, Withdrawal of a methanol-containing side stream Sseite-RD from the reactive distillation unit RD, Introducing the methanol-containing side stream Sseite-RD into a side reactor SR and converting the methanol to dimethyl ether and water in the presence of an acidic catalyst to obtain a product stream SprO duct-sR, which contains dimethyl ether, water, and methanol and is withdrawn from the side reactor SR. A process according to claim 1, wherein the methanol-containing stream Speed-RD introduced into the reactive distillation unit RD has a methanol concentration Ci(MeOH) of at least 40 mol%, a water concentration Ci(H2O) of at most 60 mol%, and a total concentration of other components, other than methanol and water, of at most 5 mol%. A process according to claim 1 or 2, wherein the methanol-containing stream Sp introduced into the reactive distillation unit RD ee d-RD has a water concentration CI(H2O) of 15-60 mol%, preferably 25-50 mol%, and the methanol-containing side stream Sseite-RD withdrawn from the reactive distillation unit RD has a water concentration c2(H2O) that satisfies the following condition: C2(H2O) < 0.75 x CI(H2O). Method according to one of the preceding claims, wherein the Sp in the product stream rOThe methanol contained in the duct-sR is at least partially recycled to the reactive distillation unit RD. A process according to one of the preceding claims, wherein the product stream Sp withdrawn from the side reactor SR rO The duct-sR is recycled to the reactive distillation unit RD. A method according to any of the preceding claims, further comprising the following steps: Introducing the product stream Sproduct-sR, drawn from the side reactor SR, into a gas-liquid separation unit SU and separating the product stream Sp rOThe process according to claim 6, wherein the gaseous stream SG containing dimethyl ether and methanol is introduced into the reactive distillation unit RD at position P1 and the liquid stream SL at position P2, and position P1 is located in the upper third 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.

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