Method for producing dimethyl ether (DME) from synthesis gas

Abstract

The invention relates to a method for producing dimethyl ether (DME). According to the invention, the first and the second reaction zone are arranged in a common synthesis reactor, in which the catalyst filling is arranged between two adjacent pillow plates and can be passed through by a respective input gas. A fluid cooling medium may pass through the pillow plate. The DME-containing product gas stream exiting the synthesis reactor is split into a DME end product stream, a gas by-product stream containing unconverted carbon oxides and hydrogen, a methanol by-product stream, and a wastewater stream. The gaseous by-product stream is sent at least partially back to the reactor influent to increase the overall achieved DME yield.

Description

Technical Field

[0001] The present invention relates to a method for producing dimethyl ether (DME) from synthesis gas containing hydrogen and carbon oxides. Background Art

[0002] The catalytic production of dimethyl ether (DME) from methanol by catalytic dehydration has been known for many years. US Pat. No. 2014408 describes a process for producing DME from methanol over catalysts such as aluminum oxide, titanium oxide and barium oxide, wherein temperatures of 350° C. to 400° C. are preferred.

[0003] Further information on the prior art and current practice in the production of dimethyl ether can be found in Ullmann's Encyclopedia of Industrial Chemistry, 6th edition, 1998 Electronic Release, keyword "Dimethyl Ether". Chapter 3 "Production" states, inter alia, that the catalytic reaction of pure gaseous methanol is carried out in a fixed bed reactor.

[0004] From the perspective of reaction engineering, the catalytic dehydration of methanol in the gas phase to provide DME preferably uses fixed bed reactors, because they are known for their simple design. Thus, German laid-open specification DE 3817816 describes a method, which is integrated in a methanol synthesis plant, for producing dimethyl ether by catalytic dehydration of methanol without prior separation of the synthesis gas that is not converted in the methanol reactor. The dehydration reactor used is a simple fixed bed reactor. If the reactor is configured without additional measures for temperature control but is only surrounded by external insulation to avoid heat losses, it is also called an adiabatic fixed bed reactor.

[0005] The dehydration of methanol to provide dimethyl ether is an exothermic equilibrium reaction according to the following reaction equation,

[0006] 2CH3OH=(CH3)2O+H2O

[0007] It follows that, from a thermodynamic point of view, high conversions are achieved at the lowest possible reaction temperature. In contrast, from a reaction kinetic point of view, a minimum reaction temperature is required to achieve a sufficient reaction rate and thus an acceptable methanol conversion. A disadvantage of the adiabatic fixed bed reactors used to date is that it is not possible to ensure optimal temperature management in order to ensure high conversions and to minimize the formation of by-products.

[0008] At higher temperatures, by-products such as carbon monoxide CO, carbon dioxide CO2, hydrogen H2 and methane CH4 are preferentially formed. The suspected possible reason for the formation of the first three by-products mentioned is that the steam formed as a by-product of the reaction causes the steam cracking of the methanol in the input stream or the previously formed DME. Methane may be formed, for example, by the subsequent reaction of the formed carbon oxides with hydrogen. The formation of these by-products is undesirable because they have an adverse effect on the purity of the reaction product and reduce the selectivity of the reaction to DME.

[0009] Theoretical study "Modeling and Optimization of MeOH to DME Isothermal Fixed-bed Reactor", Farsi et al., International Journal of Chemical Reactor Engineering, Vol. 8, 2010, Article A79 describes an optimal temperature profile for the catalytic dehydration of methanol to provide a reactor temperature of dimethyl ether in a quasi (or substantially) isothermal fixed-bed reactor in which a solid catalyst is arranged in tubes having partially evaporated water flowing around them on the shell side as a cooling medium. A genetic algorithm taking into account the thermodynamic and kinetic aspects of the dehydration reaction calculates as optimal a temperature profile that decreases exponentially from the reactor inlet to the reactor outlet, with a reactor inlet temperature of about 800 K and a reactor outlet temperature of about 560 K. Based on this axial temperature profile, a methanol conversion of about 86% is calculated for the optimized isothermal reactor, while only about 82% for the adiabatic reactor. However, the above-mentioned paper does not provide information on how to configure the design of an optimized fixed-bed reactor for the production of DME from methanol. In addition, only the methanol conversion, without the formation of any by-products, is used as an optimization criterion.

[0010] The shortcoming of the method for producing DME discussed above is that they need to produce methanol at first, and separate in an expensive and inconvenient manner. Then in the second step, carry out the conversion of methanol to the target product DME. The two-step method for DME synthesis has the shortcoming that in general: required synthesis unit comprises two different reactors, therefore needs a larger amount of equipment locations under considerable capital expenditure. The methanol produced in the first synthesis step further needs to be removed, purified and cooled.

[0011] So-called direct DME synthesis processes have therefore been discussed in the prior art, in which no intermediate product methanol occurs and / or is not separated, but the synthesis proceeds directly from the synthesis gas to the target product DME. For example, US patent specification US10501394 B2 discloses a process for producing DME from synthesis gas, in which at least one synthesis gas stream is subjected to at least one synthesis step and in which the components present in the input stream are at least partially converted into dimethyl ether (DME) to obtain at least one crude product stream containing at least DME and unconverted components of the input stream. The at least one synthesis step is therefore carried out under isothermal conditions.

[0012] However, such one-step synthesis or DME direct synthesis method has the following disadvantages:

[0013] - One-step synthesis produces many by-products, such as methanol, methane, carbon dioxide, small amounts of C2+ hydrocarbons and unconverted synthesis gas components.

[0014] - More unconverted compounds have to be recycled to the synthesis reactor to ensure a high DME yield.

[0015] The selectivity of the one-step synthesis of -DME is generally poor.

[0016] -The H2 / CO ratio of the synthesis gas has a great influence on the selectivity.

[0017] - The service life of the catalyst is often too short. Summary of the invention

[0018] It is therefore an object of the present invention to propose a process for producing DME which avoids the listed disadvantages of the one-step and two-step production processes known hitherto from the prior art. This object is achieved in a first aspect of the invention by a process having the features of claim 1. Further aspects of the invention are apparent from the dependent process claims.

[0019] Suitable methanol synthesis conditions for converting synthesis gas to methanol and suitable DME synthesis conditions for converting methanol to DME are known to those skilled in the art from the prior art, such as the disclosures discussed at the outset. These are the physicochemical conditions under which measurable, preferably industrially relevant, conversions of synthesis gas to methanol / methanol to DME are achieved. Those skilled in the art make the necessary adjustments to these conditions based on routine experimentation to suit the respective operating requirements. Any specific reaction conditions disclosed may be used as a guide but should not be considered as limiting the scope of the invention.

[0020] Unless otherwise stated, the solid, liquid and gas / vapor states of matter mentioned should always be considered relative to the local physical conditions existing in the respective process step or the respective plant component. In this patent application, the gas and vapor states of matter should be considered synonymous.

[0021] Thermal separation methods in the present invention include all separation methods based on the establishment of thermodynamic phase equilibrium. These preferably include distillation or rectification, in each case repeatedly adjusting the vapor-liquid equilibrium, or splitting gas-liquid mixtures or vapor-liquid mixtures in phase separation equipment under simple adjustment of the vapor-liquid equilibrium. However, in principle, other thermal separation methods can also be used, such as absorption, extraction or extractive distillation.

[0022] In the present invention, the division or splitting / separation of a material stream is understood to mean the generation of at least two substreams from an initial material stream, wherein the division / separation is associated with an intentional change in the material composition of the resulting substreams relative to the initial material stream, for example by applying a thermal separation method or at least a thermal separation step to the initial material stream. In contrast, the division of the initial material stream is generally not associated with a change in the material composition of the resulting substreams.

[0023] The pillow plate in the present invention is composed of two metal sheets (hot plates), which are welded together at the edges and have multiple welding spots distributed on their surfaces, which also join the two plates to each other. Such pillow plates can be produced by robots in an automated manner, so they are very cost-effective. After welding, the metal sheets are expanded by hydraulic forming, that is, usually injecting fluid under high pressure, thereby creating pillow-shaped channels between the metal sheets, which can be freely passed through by cooling or heating fluids. The pillow plates can be oriented parallel to each other on the horizontal axis in the synthesis reactor or perpendicular to the horizontal axis orientation. The space between the two pillow plates can be filled with a filler of a solid particulate catalyst. The appropriate arrangement of three or more pillow plates obtains a sandwich structure, which has a catalyst to inflow and outflow material streams, such as good accessibility of input gas and product gas and a very good heat transfer between the catalyst filler and the one cooling fluid or heating fluid.

[0024] The present invention provides a two-step DME synthesis in a shared synthesis reactor without separating the intermediate methanol, so as to ideally obtain the advantages of two synthesis routes while minimizing the disadvantages. To this end, a first reaction zone in which synthesis gas is converted into methanol is combined with a second reaction zone in which methanol is further reacted to provide DME. Both reaction zones are arranged in a shared pressure-bearing reactor shell (shell and tube), and no separation and purification of the intermediate produced methanol is performed.

[0025] Both reaction steps are carried out on a filling of solid particulate catalysts dedicated to the respective partial reactions. The present invention provides that the catalyst filling is arranged between two adjacent pillows in each case and can be passed through by the respective input gas. The pillow can be passed through by a fluid cooling medium. The sandwich-like arrangement of the catalyst layer and the cooling layer leads to very good thermal management in the catalyst bed, resulting in or at least approximately achieving isothermal conditions in a single catalyst bed. In particular, so-called hot spots, i.e. local high temperature areas, are avoided or reduced in the catalyst bed. Hot spots have an adverse effect on the possible service life of the catalyst and, in the case of an exothermic equilibrium reaction, reduce the conversion rate of the reactant components that can be achieved as a whole on the catalyst bed.

[0026] The DME-containing product gas stream leaving the synthesis reactor is fed to a separation device operated according to at least one thermal separation method; this can be, for example, a one-step or multi-step distillation. The separation device achieves the splitting of the DME-containing product gas stream into a DME final product stream, a gaseous by-product stream containing unconverted carbon oxides and hydrogen, a methanol by-product stream and a wastewater stream. The gaseous by-product stream is at least partially fed back to the reactor inflow to increase the overall achieved DME yield.

[0027] Since the control of reaction temperature and pressure is important for achieving maximum conversion, various embodiments of the present invention involve utilizing various material streams as coolants and conducting them through the synthesis reactor. The coolant used may include a special heat transfer fluid, but may also include reactant and / or product streams of the reaction zone.

[0028] The pressure in the synthesis reactor according to the invention is about 40 to 90 bar absolute, preferably 60 to 80 bar absolute. Preference is given to synthesis gases whose CO concentration is higher than their CO concentration, since this leads to reduced water formation and improved DME selectivity. However, other synthesis gases can also be used, for example mixtures comprising CO and hydrogen, with little or no CO admixed therein.

[0029] The temperature in the first reaction zone is preferably between 180°C and 350°C, most preferably between 200°C and 280°C.

[0030] Preferably, the temperature in the second reaction zone is between 220° C. and 350° C., more preferably between 240° C. and 320° C., and most preferably between 260° C. and 300° C. Studies have shown that high yields of DME and low yields of by-products are achieved within these temperature ranges.

[0031] The coolant used may include a special heat transfer fluid, but may also include reactants and / or product streams of the reaction zone. In a first example, water is used as the cooling medium, wherein for example fresh water or water produced in the reaction or a mixture of the two may be used. In a second example, cold synthesis gas is used as the cooling medium and is therefore itself preheated, thereby reducing the heating energy requirement of the method. In a third example, a methanol byproduct stream from a separation unit is used as the cooling medium. This reduces the energy requirement for the downstream production of pure methanol.

[0032] One advantage of the process according to the invention is its ability to start up quickly. For this purpose, the second reaction zone (DME synthesis) is first put into operation with methanol supplied from an external source and synthesis gas is passed through the second reaction zone as cooling medium to achieve the required temperature, and then the first reaction zone (methanol synthesis) is put into operation.

[0033] Advantageously, in the process according to the invention, the synthesis reactor enables minimization of by-products while achieving a conversion close to equilibrium (40% DME, 40% H2O, 20% unconverted methanol). The compounds obtained as intermediates (methanol) and end products (DME, CO, CO2, hydrogen and methane) are not catalyst poisons for the catalysts used, which are commercially available per se.

[0034] A maximum reaction temperature of 400°C should not be exceeded in the second reaction zone to minimize the extent of methanation.

[0035] Further aspects of the invention

[0036] The second aspect of the process according to the invention is characterized in that a first portion of the gaseous byproduct stream is recycled to the DME synthesis reactor and introduced into the DME synthesis reactor together with the first input gas stream. This increases the conversion rate of the reactant components and the DME yield.

[0037] A third aspect of the process according to the invention is characterized in that a second portion of the gaseous by-product stream is discharged from the process as a purge stream. This prevents the accumulation of any inert components in the two partial reactions, such as methane.

[0038] A fourth aspect of the process according to the invention is characterized in that at least a portion of the methanol byproduct stream is recycled to the DME synthesis reactor and introduced into the interstitial space and / or catalyst packing in the second reaction zone. This makes it possible to increase the yield in the second partial reaction (DME synthesis) in particular.

[0039] A fifth aspect of the process according to the invention is characterized in that a first cooling water stream is used as the first fluid cooling medium and a second cooling water stream is used as the second fluid cooling medium. This makes it easy to establish the optimum temperature in the first and second reaction zones.

[0040] A sixth aspect of the method according to the invention is characterized by using a common cooling water stream as the first fluid cooling medium and as the second fluid cooling medium. This aspect enables resource-efficient utilization of cooling water.

[0041] A seventh aspect of the process according to the invention is characterized in that the common cooling water stream is first passed through one reaction zone and then, after optional cooling, through another reaction zone. This aspect enables resource-efficient use of cooling water while providing more options for establishing an optimal temperature.

[0042] An eighth aspect of the process according to the invention is characterized in that the common cooling water stream is first passed through the second reaction zone and then, after optional cooling, through the first reaction zone. This aspect enables resource-efficient use of cooling water while providing more options for establishing an optimal temperature. The common cooling water stream then flows through the synthesis reactor in countercurrent to the reactants and product gases.

[0043] A ninth aspect of the process according to the invention is characterized in that the common cooling water stream is first passed through the first reaction zone and then, after optional cooling, through the second reaction zone. This aspect enables resource-efficient use of cooling water while providing more options for establishing an optimal temperature. The common cooling water stream then flows through the synthesis reactor in parallel with the reactants and product gases.

[0044] A tenth aspect of the process according to the invention is characterized in that the first cooling water stream and / or the second cooling water stream and / or the common cooling water stream flows through the first reaction zone and / or the second reaction zone in parallel with the gas flow through the first reaction zone and / or the second reaction zone. This aspect relates to the flow direction of the cooling medium in the reaction zone.

[0045] According to an eleventh aspect of the process of the invention, the first cooling water stream and / or the second cooling water stream and / or the common cooling water stream are passed through the first reaction zone and / or the second reaction zone in countercurrent with respect to the gas flow through the first reaction zone and / or the second reaction zone. This aspect relates to the flow direction of the cooling medium in the reaction zone.

[0046] A twelfth aspect of the process according to the invention is characterized in that after optional cooling, at least part of the wastewater stream is used as first cooling water stream and / or second cooling water stream and / or common cooling water stream. This aspect enables particularly resource-efficient utilization of cooling water.

[0047] A thirteenth aspect of the process according to the invention is characterized in that at least part of the first cooling water stream and / or the second cooling water stream and / or the common cooling water stream at least partially evaporates while passing through the first reaction zone and / or the second reaction zone and is discharged as a vapor or a vapor-liquid two-phase mixture. Due to the phase change and the associated particularly large enthalpy change, a particularly large cooling effect is achieved.

[0048] A fourteenth aspect of the process according to the invention is characterized in that before at least a portion of the first input gas stream and / or at least a portion of the gas by-product stream recycled to the DME synthesis reactor is introduced into the DME synthesis reactor, at least a portion of the first input gas stream and / or at least a portion of the gas by-product stream recycled to the DME synthesis reactor is used as a first fluid cooling medium and / or as a second fluid cooling medium. This saves cooling medium, such as cooling water or heat transfer oil, and preheats the corresponding gas stream.

[0049] The fifteenth aspect of the method according to the present invention is characterized in that at least a portion of the methanol by-product stream is introduced into the first reaction zone as the first fluid cooling medium, wherein the methanol by-product stream is heated and then introduced into the interstitial space and / or catalyst filling in the second reaction zone. This can especially increase the yield in the second partial reaction, i.e., DME synthesis. Simultaneously save cooling medium, such as cooling water or heat transfer oil, and preheat the methanol by-product stream.

[0050] A sixteenth aspect of the process according to the invention is characterized in that the second reaction zone (DME synthesis) is first put into operation with methanol supplied from an external source and synthesis gas is passed through the second reaction zone as cooling medium to achieve the desired temperature, and then the first reaction zone (methanol synthesis) is put into operation. This enables the process according to the invention to be put into operation particularly quickly.

[0051] A seventeenth aspect of the process according to the invention is characterized in that a maximum reaction temperature of 400° C. is not exceeded in the second reaction zone. This minimizes the extent of methanation.

[0052] The eighteenth aspect of the process according to the invention is characterized in that the temperature in the first reaction zone is between 180° C. and 350° C., most preferably between 200° C. and 280° C., and in that the temperature in the second reaction zone is between 220° C. and 350° C., more preferably between 240° C. and 320° C., most preferably between 260° C. and 300° C. Studies have shown that high yields of DME and low yields of by-products are obtained within these temperature ranges.

[0053] The nineteenth aspect of the process according to the invention is characterized in that the operating pressure of the DME synthesis reactor is not less than 90 bar absolute pressure, and the minimum operating temperature of the two reaction zones is not less than 250° C., preferably not less than 260° C. This enables the DME synthesis reactor to be operated without condensation inside the reactor, especially in the first and second reaction zones. DETAILED DESCRIPTION

[0054] Further features, advantages and possible applications of the invention are apparent from the following description of operating and numerical embodiments and from the accompanying drawings. All features described and / or depicted, alone or in any combination, constitute the subject matter of the invention, whether they are combined in the claims or they are dependent references. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] In the attached picture:

[0056] Figure 1 A schematic diagram showing the process according to the invention in an exemplary embodiment of a DME synthesis reactor,

[0057] Figure 2 A detailed view showing the first reaction zone of a DME synthesis reactor according to the invention,

[0058] Figure 3 Design details showing the bolster plate (schematic diagram).

[0059] "Not shown" hereinafter means that an element in the figure in question is not represented graphically, but is still present according to the description.

[0060] Figure 1 A schematic diagram of a method according to the invention in an exemplary embodiment of a DME synthesis reactor 1 is shown. In a common pressure-bearing shell tube 10 arranged vertically relative to its longitudinal axis, a first reaction zone 11 and a second reaction zone 12 are arranged one above the other. Synthesis gas is introduced as an input stream via a conduit 13 into the DME synthesis reactor 1 and flows through the reactor from top to bottom; this is indicated by dashed flow arrows. The input stream enters the first reaction zone 11 via a first inlet (not shown), the catalyst zone of which is filled with a commercially available particulate catalyst active for methanol synthesis.

[0061] In the first reaction zone 11, the input stream is at least partially converted into methanol under methanol synthesis conditions. The at least partially converted methanol-containing input stream is discharged from the first reaction zone 11 as a first methanol-containing product gas stream via a first outlet (not shown) and then introduced into the second reaction zone 12 via a second inlet (not shown) for the first product gas.

[0062] In the second reaction zone 12, the first methanol-containing product gas stream is at least partially converted to DME under DME synthesis conditions. This provides a second DME-containing product gas stream, which is discharged from the second reaction zone via a second outlet (not shown) and is discharged from the DME synthesis reactor 1 via a conduit 15 (product outlet) on the shell tube 10 and sent to a separation device (not shown) operated according to at least one thermal separation method.

[0063] The separation device realizes the splitting of the product gas stream containing DME into a DME final product stream, a gas byproduct stream containing unconverted carbon oxides and hydrogen, a methanol byproduct stream and a wastewater stream. In one example, the DME final product stream is supplied to a DME storage, a DME final purification and / or a DME further processing (all not shown). The gas byproduct stream is preferably at least partially recycled to the DME synthesis reactor 1 and introduced into the reactor via conduit 13. The methanol byproduct stream is preferably at least partially recycled to the DME synthesis reactor 1, introduced into the reactor via conduit 14 and directly sent to the second reaction zone. In one example, the wastewater stream is discharged from the method. In another example, the wastewater stream is recycled to the DME synthesis reactor 1 as a cooling medium after optional cooling.

[0064] The first fluid cooling medium is introduced into the first reaction zone 11 via conduit 16 and an inlet (not shown). The first fluid cooling medium absorbs at least a portion of the reaction heat of the exothermic methanol synthesis and is thus heated itself. The heated first fluid cooling medium is discharged from the first reaction zone 11 via an outlet (not shown) and conduit 17.

[0065] The second fluid cooling medium is introduced into the second reaction zone 12 via the conduit 18 and the inlet (not shown). The second fluid cooling medium absorbs at least a portion of the reaction heat of the exothermic synthesis of DME from methanol and is thus heated itself. The heated second fluid cooling medium is discharged from the second reaction zone 12 via the outlet (not shown) and the conduit 19.

[0066] In one example, the pressure in the synthesis reactor according to the invention is 40 to 90 bar absolute, preferably 60 to 80 bar absolute. In one example, it is preferred to introduce a synthesis gas whose CO concentration is higher than its CO2 concentration into the DME synthesis reactor 1, because this leads to reduced water formation and improved DME selectivity. However, other synthesis gases can also be used, for example a mixture comprising CO2 and hydrogen, with little or no CO admixed therein.

[0067] In one example, the temperature in the first reaction zone 11 is preferably between 180° C. and 350° C., most preferably between 200° C. and 280° C. In one example, the temperature in the second reaction zone 12 is between 220° C. and 350° C., more preferably between 240° C. and 320° C., and most preferably between 260° C. and 300° C. Studies have shown that high yields of DME and low yields of by-products are achieved within these temperature ranges.

[0068] The coolant used may include a special heat transfer fluid, but may also include reactants and / or product streams of the reaction zone. In one example, water is used as the cooling medium, wherein for example fresh water or water produced in the reaction or a mixture of the two may be used. In another example, cold synthesis gas is used as the cooling medium and is therefore itself preheated, thereby reducing the heating energy requirement of the method. In another example, a methanol byproduct stream from a separation device is used as the cooling medium. This reduces the energy requirement of the downstream production of pure methanol.

[0069] Figure 2 A detailed view of the first reaction zone 11 of a DME synthesis reactor 1 according to the invention is shown. The second reaction zone 12 has essentially the same construction, but the catalyst zone is filled with a catalyst active for the synthesis of DME from methanol.

[0070] The first reaction zone 11 preferably has pillow plates 30 arranged in parallel and at equal intervals. Figure 3 The detailed construction of the pillow plate 30 is explained. The arrangement of the pillow plates results in a gap space 20, which is filled with a filling of a solid particulate catalyst active for methanol synthesis. Both ends of the gap space are permeable to the gas stream. The lower end of the gap space, and preferably also the upper end of the gap space, contains a carrier / positioning device (not shown) for the catalyst filling, such as a sieve tray, a porous plate or a wire mesh. The positioning device, which is preferably attached to the inflow side of the gas flow entering the first reaction zone 11, can therefore advantageously also be used to homogenize and distribute the input gas stream on each catalyst bed.

[0071] The first fluid cooling medium is introduced into the pillow plate 30 in the first reaction zone 11 via the conduit 16 and the inlet (not shown). The first fluid cooling medium absorbs at least a portion of the reaction heat of the exothermic methanol synthesis and is thus heated itself. The heated first fluid cooling medium is discharged from the first reaction zone 11 via the outlet (not shown) and the conduit 17. The introduction / exit of the first fluid cooling medium into / from the pillow plate 30 is achieved via a distributor system (not shown). This is indicated by the conduits 16 and 17 as shown by the arrows.

[0072] Figure 3a shows an xy view of the pillow plate 30 on the area of ​​the sheet metal forming one side of the pillow plate 30. Points 311 to 319 represent so-called welding points, with which the sheet metal is joined to a sheet metal (not shown) on the opposite side by additional spot welding. Points 311 to 313, 313 to 316 and 316 to 319 are each arranged along a corresponding straight line, and the points of every other straight line are alternately arranged again along a straight line in the respective other dimension. The straight lines extend parallel to each other and have a spacing d5.

[0073] Since the pillow plate is not only welded at the edges of the two superposed metal sheets, but also has additional weld points 311 to 319 arranged thereon, an xz view through the pillow plate gives Figure 3 b is a cross-sectional view along the straight line AA′. Channels 321 and 322 are formed between the individual welds 311 to 319, which are usually produced by pressure forming, particularly preferably by hydroforming. The diameter d2 of such a channel 321 or 322 describes the distance between the two metal sheets 30a and 30b at the maximum channel range, while the diameter d4 describes the thickness of the welds 311 to 319. The distance between two welds 311 to 319 corresponds to d3, which also corresponds exactly to the distance between two welds 311 to 319 along a straight line. Preferably, d3>d2>d4.

[0074] Numerical Example

[0075] The following table summarizes exemplary operating conditions for a DME synthesis reactor according to the present invention, which allows the reactor to operate without falling below the dew point temperature and therefore without condensation in the reactor. This is important to ensure that the uptime and potential service life of the catalyst is not compromised.

[0076] Table: Exemplary operating conditions of DME synthesis reactor

[0077] Ratio / mol% p / bar Dew point / ℃ p / bar Dew point / ℃ Total pressure 90.0 60.0 DME 40.0 36.0 24.0 water 40.0 36.0 250 24.0 225 Methanol 20.0 18.0 12.0

[0078] It is therefore advantageous to select an operating pressure of the DME synthesis reactor according to the invention of not less than 90 bar absolute and a minimum operating temperature of the two reaction zones of not less than 250° C., preferably not less than 260° C.

[0079] List of Reference Symbols

[0080] 1 DME synthesis reactor

[0081] 10 Shell and tube

[0082] 11. First reaction zone

[0083] 12. Second reaction zone

[0084] 13. Conduit (input gas flow)

[0085] 14 Conduit (methanol side feed)

[0086] 15 Conduit (product gas stream)

[0087] 16 Conduit (first fluid cooling medium inlet)

[0088] 17 Conduit (first fluid cooling medium outlet)

[0089] 18. Conduit (second fluid cooling medium inlet)

[0090] 19 Conduit (second fluid cooling medium outlet)

[0091] 20 Catalyst filling in the gap space between the pillow plates (hatched lines)

[0092] 30 Pillow Plate

[0093] 31 Solder Points

[0094] 32 Vacant Interior

Claims

1. A process for producing dimethyl ether (DME) from synthesis gas containing carbon oxides and hydrogen, comprising the steps of: (a) providing a DME synthesis reactor, which comprises the following components: (a1) a first reaction zone having a first inlet for synthesis gas as a first input gas and a first outlet for a first methanol-containing product gas, wherein the first reaction zone comprises a plurality of pillows arranged as follows: - a filling of a solid particulate catalyst which is active for the synthesis of methanol from synthesis gas and which can be passed through by the synthesis gas is arranged in each case between two adjacent pillow plates, - the pillow plates include an inlet for the first fluid cooling medium and an outlet for the first fluid cooling medium, and their interiors can be penetrated by the first fluid cooling medium; (a2) a second reaction zone having a second inlet for the first product gas and a second outlet for the second DME-containing product gas, wherein the second reaction zone comprises a plurality of pillow plates arranged as follows: - a filling of a solid particulate catalyst which is active for the synthesis of DME from methanol and which can be passed through by the first product gas is arranged in each case between two adjacent pillow plates, - the pillow plates contain an inlet for the second fluid cooling medium and an outlet for the second fluid cooling medium, and their interiors can be penetrated by the second fluid cooling medium; (a3) an external pressure-bearing shell tube, inside which a first reaction zone and a second reaction zone separated from the first reaction zone by an interstitial space are arranged, wherein the shell tube comprises a reactant inlet for introducing synthesis gas as a first input gas at an end adjacent to the first reaction zone and a product outlet for discharging a second DME-containing product gas at an end adjacent to the second reaction zone; (b) introducing a synthesis gas stream as a first input gas stream into the DME synthesis reactor via a reactant inlet on a shell and tube and into a first reaction zone via a first inlet; (c) reacting a first input gas stream in a first reaction zone under methanol synthesis conditions; (d) withdrawing a first methanol-containing product gas stream from the first reaction zone; (e) introducing the first methanol-containing product gas stream into a second reaction zone; (f) reacting the first product gas stream in a second reaction zone under DME synthesis conditions; (g) discharging a second DME-containing product gas stream from the second reaction zone via a second outlet and from the DME synthesis reactor via a product outlet on the shell tube; (h) supplying the DME-containing product gas stream to a separation device operated according to at least one thermal separation method, in which the DME-containing product gas stream is split into a DME final product stream, a gas by-product stream containing unconverted carbon oxides and hydrogen, a methanol by-product stream and a wastewater stream.

2. The method according to claim 1, characterized in that A first portion of the gaseous by-product stream is recycled to the DME synthesis reactor and introduced into the DME synthesis reactor together with the first input gas stream.

3. The method according to claim 1 or 2, characterized in that A second portion of the gaseous byproduct stream is discharged from the process as a purge stream.

4. A method according to any one of the preceding claims, characterised in that At least a portion of the methanol by-product stream is recycled to the DME synthesis reactor and introduced into the interstitial space and / or catalyst packing in the second reaction zone.

5. A method according to any one of the preceding claims, characterised in that A first cooling water stream is used as the first fluid cooling medium and a second cooling water stream is used as the second fluid cooling medium.

6. A method according to any one of the preceding claims, characterised in that A common cooling water stream is used as the first fluid cooling medium and as the second fluid cooling medium.

7. The method according to claim 6, characterized in that The common cooling water stream is passed first through one reaction zone and then, after optional cooling, through the other reaction zone.

8. The method according to claim 7, characterized in that The common cooling water stream is first passed through the second reaction zone and then, after optional cooling, through the first reaction zone.

9. The method according to claim 7, characterized in that The common cooling water stream is first passed through the first reaction zone and then, after optional cooling, through the second reaction zone.

10. The method according to any one of claims 5 to 9, characterized in that The first cooling water stream and / or the second cooling water stream and / or the common cooling water stream passes through the first reaction zone and / or the second reaction zone in parallel with the gas flow passing through the first reaction zone and / or the second reaction zone.

11. The method according to any one of claims 5 to 9, characterized in that The first cooling water stream and / or the second cooling water stream and / or the common cooling water stream passes through the first reaction zone and / or the second reaction zone countercurrently with respect to the gas flow passing through the first reaction zone and / or the second reaction zone.

12. A method according to any one of the preceding claims, characterised in that After optional cooling, at least part of the wastewater stream is used as first cooling water stream and / or second cooling water stream and / or common cooling water stream.

13. A method according to any one of the preceding claims, characterised in that At least a portion of the first cooling water stream and / or the second cooling water stream and / or the common cooling water stream at least partially evaporates while passing through the first reaction zone and / or the second reaction zone and is discharged as vapor or a vapor-liquid two-phase mixture.

14. A method according to any one of the preceding claims, characterised in that Before at least a portion of the first input gas stream and / or at least a portion of the gas by-product stream recycled to the DME synthesis reactor are introduced into the DME synthesis reactor, at least a portion of the first input gas stream and / or at least a portion of the gas by-product stream recycled to the DME synthesis reactor is used as a first fluid cooling medium and / or as a second fluid cooling medium.

15. A method according to any one of the preceding claims, characterised in that At least a portion of the methanol by-product stream is introduced into the first reaction zone as a first fluid cooling medium, wherein the methanol by-product stream is heated and then introduced into the interstitial space and / or catalyst packing in the second reaction zone.

16. A method according to any one of the preceding claims, characterised in that The second reaction zone (DME synthesis) is initially put into operation with methanol supplied from an external source and synthesis gas is passed through the second reaction zone as cooling medium to achieve the desired temperature, and then the first reaction zone (methanol synthesis) is put into operation.

17. A method according to any one of the preceding claims, characterised in that A maximum reaction temperature of 400° C. was not exceeded in the second reaction zone.

18. A method according to any one of the preceding claims, characterised in that The temperature in the first reaction zone is between 180°C and 350°C, most preferably between 200°C and 280°C, and is characterized in that the temperature in the second reaction zone is between 220°C and 350°C, more preferably between 240°C and 320°C, most preferably between 260°C and 300°C.

19. A method according to any one of the preceding claims, characterised in that The operating pressure of the DME synthesis reactor is not less than 90 bar absolute pressure, and the minimum operating temperature of the two reaction zones is not less than 250°C, preferably not less than 260°C.

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