Heat-integrated method for producing c2-c4 olefins

Abstract

The invention relates to a method for producing C2-C4 olefins from dimethyl ether and optionally methanol, having the steps of: A) providing a dimethyl ether-containing flow A; B) mixing at least one part of the flow A with at least one hydrocarbon return flow R, which contains C2-C6 hydrocarbons, and with a water vapor flow G2, a feed flow B being obtained; C) heating the feed flow B to a temperature ranging from 430 to 500 °C in one or more heat exchangers and feeding same to an olefin fixed-bed reactor, wherein the heating process can also be carried out before individual sub-flows are mixed in order to form the feed flow B in step B); D) catalytically converting the feed flow B at a temperature ranging from 430 to 520 °C in order to form a product gas flow D, which contains C2-C4 olefins, additional C2-C6 hydrocarbons, methanol, and water vapor; E) cooling the product gas flow D to a temperature ranging from 170 to 220 °C in one or more heat exchangers by exchanging heat with the feed gas flow B; F) further cooling the product gas flow D to a temperature ranging from 35 to 65 °C by bringing the product gas flow into contact with at least one water-containing quenching circuit flow K, wherein water and methanol are condensed out of the product gas flow, and a hydrocarbon product gas flow F which is depleted of water and methanol is obtained; G) separating at least one sub-flow G1 of the at least one water-containing quenching circuit flow K and heating and evaporating the sub-flow G1 in one or more heat exchangers by exchanging heat with medium-pressure water vapor or heating and evaporating the sub-flow G1 by means of an electric heating process, a water vapor flow G2 being obtained, and feeding the water vapor flow G2 to step B); and H) separating one or more C2-C4 olefin-containing product flows P and obtaining at least one hydrocarbon return flow R, which contains C2-C6 hydrocarbons, from the hydrocarbon product gas flow F and returning same to step B).

Description

[0001] Heat-integrated process for the production of C2-C4 olefins

[0002] Description

[0003] The invention relates to a heat-integrated process for the production of C2-C4 olefins from dimethyl ether and optionally methanol.

[0004] It is known to produce propylene by converting a methanol / dimethyl ether mixture in a fixed-bed reactor (methanol-to-propylene, MTP reactor). Conventional fixed-bed reactors operate with zeolite catalysts at temperatures of approximately 480°C. This requires heating the methanol / DME-containing feed gas stream to high temperatures before entering the reactor.

[0005] L. Jiang et al., Chinese Journal of Chemical Engineering 26 (2018), 2102–2111, describe a process for producing propylene from methanol, in which methanol is first converted to dimethyl ether (DME), and the product mixture is then converted to propylene and other products. Referring to Figure 8 of this publication, the process is described as follows: Methanol is preheated by heat exchange with the product gas from the DME reactor in a heat exchanger, vaporized, and further heated. The methanol vapor is fed into the DME reactor at a temperature of 270°C. A first partial stream of the product gas from the DME reactor is then cooled to a temperature of 150°C by heat exchange with a hydrocarbon recycle stream, cold methanol, and circulating cooling water, and the resulting gas / liquid mixture is separated in a phase separator.The gas phase is reheated while the liquid phase is further cooled, and the gas and liquid phases are fed into the individual trays of the propylene fixed-bed reactor (MTP reactor). Alternatively, only methanol can be fed into the individual trays of the MTP reactor. The second partial stream of product gas from the DME reactor is mixed with the hydrocarbon recycle stream and steam, heated to a temperature of approximately 460°C with a burner, and fed into the propylene reactor, where virtually all of the methanol and DME are converted to propylene and other hydrocarbons.

[0006] A disadvantage of the described process is that a large portion of the heat required to heat the reactant streams fed into the propylene reactor is provided by burning natural gas or other fossil hydrocarbons in a burner. This has a very negative impact on the CO2 balance of the overall process. However, against the backdrop of intensifying anthropogenic climate change, there is an increasing trend towards industrial production processes that emit little or, better yet, no net CO2 of fossil origin into the atmosphere. The object of the invention is to provide a heat-integrated process for the production of C2-C4 olefins starting from dimethyl ether, in which the provision of process heat by burning non-process fossil hydrocarbons during stationary operation can be dispensed with.

[0007] The problem is solved by a process for the production of C2-C4 olefins from dimethyl ether and optionally methanol with the following steps:

[0008] A) providing a stream A containing dimethyl ether;

[0009] B) mixing at least a portion of stream A with at least one hydrocarbon recycle stream R containing C2-C6 hydrocarbons and a steam stream G2, thereby obtaining a feed stream B;

[0010] C) heating the feed stream B in one or more heat exchangers to a temperature in the range from 430 to 500 °C and feeding it into an olefin fixed bed reactor, wherein the heating can also take place before the mixing of individual partial streams to form the feed stream B in step B);

[0011] D) catalytic conversion of the feed stream B at a temperature in the range of 430 to 520 °C to a product gas stream D containing C2-C4 olefins, further C2-C6 hydrocarbons, methanol and steam;

[0012] E) cooling the product gas stream D in one or more heat exchangers to a temperature in the range of 170 to 220 °C by heat exchange with the feed gas stream B;

[0013] F) further cooling the product gas stream D to a temperature in the range from 35 to 65 °C by bringing it into contact with at least one water-containing quench cycle stream K, whereby water and methanol are condensed out and a hydrocarbon product gas stream F depleted in water and methanol is obtained;

[0014] G) separating at least one partial stream G1 of the at least one water-containing quench cycle stream K and heating and evaporating the partial stream G1 in one or more heat exchangers by heat exchange with medium-pressure steam, or heating and evaporating the partial stream G1 by electrical heating, whereby a steam stream G2 is obtained, and feeding the steam stream G2 into step B);

[0015] H) Separation of one or more product streams P containing C2-C4 olefins and recovery of at least one hydrocarbon recycle stream R containing C2-Ce hydrocarbons from the hydrocarbon product gas stream F and recycling in step B).

[0016] In one embodiment of the process according to the invention, in step A), a stream A consisting essentially of DME (> 90 wt. % DME) is fed into the process and divided into two substreams. The first substream A-1 comprises a maximum of 80 wt. % of stream A and is used as described in step B). The second substream is mixed with a substream G3 of the water-containing quench recycle stream mentioned in step G) and fed as stream A-2 without further heating into one or more individual trays of the olefin fixed-bed reactor of step C). It is also possible to operate the olefin fixed-bed reactor isothermally. Isothermal operation can, for example, take place in the manner described in WO2017 / 102096 A1. For example, heat exchanger surfaces can be installed in the olefin fixed-bed reactor, which are operated, for example, with molten salt or high-pressure steam as the heat transfer medium.As the heat transfer medium flows through the heat transfer surfaces in the reactor, the resulting reaction heat is removed from the reactor, thus operating it isothermally.

[0017] In a preferred embodiment of the method according to the invention, the step

[0018] A) feeding a methanol-containing feed gas stream A1 into a dimethyl ether fixed-bed reactor and catalytically converting methanol to dimethyl ether, yielding a product gas stream comprising dimethyl ether, methanol, and steam. If stream A1 contains ethanol, product stream A will contain ethanol and ethylene in addition to dimethyl ether, methanol, and steam.

[0019] C2-C4 olefins are ethylene, propylene, 1-butene, 2-butenes, and isobutene. Ethylene and / or propylene are preferably produced using the process according to the invention.

[0020] In a preferred embodiment, the method according to the invention thus comprises the steps:

[0021] A) feeding a methanol-containing feed stream A1 into a dimethyl ether fixed bed reactor and catalytically converting methanol to dimethyl ether, whereby a product stream A containing dimethyl ether, methanol and steam is obtained;

[0022] B) mixing at least a portion of the product stream A with at least one hydrocarbon recycle stream R containing C2-C6 hydrocarbons and a steam stream G2, thereby obtaining a second feed stream B;

[0023] C) heating the second feed stream B in one or more heat exchangers to a temperature in the range from 430 to 500 °C and feeding it into an olefin fixed bed reactor, wherein the heating can also take place before the mixing of individual partial streams to form the feed stream B in step B);

[0024] D) catalytic conversion of the feed stream B at a temperature in the range of 430 to 520 °C to a product gas stream D containing ethylene, propylene, other C2-C6 hydrocarbons, methanol and water vapor;

[0025] E) cooling the product gas stream D in one or more heat exchangers to a temperature in the range of 170 to 220 °C by heat exchange with the feed stream B;

[0026] F) further cooling the product gas stream D to a temperature in the range from 35 to 65 °C by bringing it into contact with at least one water-containing quench cycle stream K, whereby water and methanol are condensed out and a hydrocarbon product gas stream F depleted in water and methanol is obtained;

[0027] G) separating at least one partial stream G1 of the at least one water-containing quench cycle stream K and heating and evaporating the partial stream G1 in one or more heat exchangers by heat exchange with medium-pressure steam, or heating and evaporating the partial stream G1 by electrical heating, whereby a steam stream G2 is obtained, and feeding the steam stream G2 into step B);

[0028] H) Separation of one or more product streams P containing ethylene and / or propylene and recovery of at least one hydrocarbon recycle stream R containing C2-Ce hydrocarbons from the hydrocarbon product gas stream F and recycling in step B).

[0029] In step A), a feed stream A1 containing methanol is preferably fed into a dimethyl ether fixed bed reactor and methanol is catalytically converted to dimethyl ether, whereby a product stream A containing dimethyl ether, methanol and steam is obtained.

[0030] A methanol-containing feed stream A1, which preferably originates from an upstream methanol synthesis plant, is evaporated and heated to a temperature of generally 250 to 300°C, for example 275°C, and fed into the dimethyl ether fixed-bed reactor. Gamma-alumina is generally used as the catalyst. The reaction temperature is generally 250 to 400°C, and the pressure is generally 1 to 25 bar, for example 4 bar. The first product gas stream leaving the dimethyl ether fixed-bed reactor has a temperature of generally 350 to 400°C, for example 370°C. The methanol conversion is generally 50 to 90%, preferably 65 to 85%, for example 75%. The product gas stream A is cooled by heat exchange with the methanol-containing feed stream A1. The first product gas stream after heat exchange generally has a temperature of 180 to 250 °C.

[0031] In a step B), at least a portion of this stream A is mixed with a hydrocarbon recycle stream comprising C2-C6 hydrocarbons and a steam stream G2, to obtain a feed gas stream B. This portion of stream A generally amounts to at least 50% by weight and preferably up to 80% by weight. A further portion A-2 of stream A, preferably at least 20% by weight, can be fed directly to one or more trays of the olefin fixed-bed reactor. If this portion of stream A originates from an upstream dimethyl ether reactor, it is generally cooled, preferably to a temperature in the range from 30 to 60°C, before being fed into the trays of the olefin fixed-bed reactor. This partial stream A-2 is preferably fed into the reactor in liquid form.

[0032] Cooling by substream A-2 can also be omitted if the olefin fixed-bed reactor is operated and cooled isothermally. Isothermal operation can be carried out, for example, in the manner described in WO2017 / 102096 A1. Heat exchanger surfaces can be installed in the olefin fixed-bed reactor, which are operated, for example, with molten salt or high-pressure steam as the heat transfer medium. As the heat transfer medium flows through the heat exchanger surfaces in the reactor, the resulting reaction heat is removed from the reactor, thus operating it isothermally. To adjust the desired product distribution in the product gas stream D, a substream A-2 can also be fed to an intermediate stage of the olefin fixed-bed reactor.

[0033] In a further embodiment, a methanol-containing stream is fed directly to one or more trays of the olefin fixed-bed reactor. Preferably, a portion of the methanol-containing first feed stream A1, which originates, for example, from an upstream methanol synthesis plant, is fed directly into the olefin fixed-bed reactor. This portion of the methanol-containing feed stream A1 can amount to up to 60 wt. % of the total feed stream A1.

[0034] The hydrocarbon recycle stream R, which originates from the separation of the C2-C4 olefins, generally contains C4-C6 hydrocarbons. Depending on whether ethylene, propylene, or butenes are obtained as the product of value in step H), the hydrocarbon recycle stream R can also contain ethylene, propylene, and / or butenes. If, for example, the amount of C2-C4 olefin obtained as product in step H) contains at least 85% by weight of propylene, stream R consists of at least 50% by weight of C4-C6 hydrocarbons. The hydrocarbon recycle stream R generally has a temperature in the range from 100 to 175°C, preferably in the range from 130 to 160°C, before mixing. The hydrocarbon recycle stream R is preferably heated by heat exchange with medium-pressure steam and has a temperature of generally 30 to 100 °C, preferably 50 to 80 °C, before heating.

[0035] Product stream A of the dimethyl ether fixed-bed reactor is further mixed with a steam stream G2. The steam stream G2 generally has a temperature in the range of 100 to 200 °C, preferably in the range of 100 to 150 °C. According to the invention, this steam stream is heated by heat exchange with medium-pressure steam.

[0036] The feed stream B thus obtained generally contains 15 to 50 wt.%, preferably 20 to 40 wt.%, of steam. It generally also contains 5 to 10 wt.% of methanol, 10 to 20 wt.% of dimethyl ether, and 25 to 50 wt.% of C2-C6 hydrocarbons.

[0037] In step C), feed stream B is heated in one or more heat exchangers to a temperature in the range of 430 to 500 °C and fed into an olefin fixed-bed reactor. Heating can also take place before the mixing of individual substreams in step B).

[0038] In general, the feed stream B, when fed into the olefin fixed-bed reactor, has a temperature in the range of 430 to 500°C, for example 470°C. The heating of the feed stream B to this temperature takes place by heat exchange with the (second) product gas stream D of the olefin fixed-bed reactor. By heating the steam stream G1 according to the invention by heat exchange with medium-pressure steam, a temperature of 430 to 500°C can be achieved in the feed stream B by heat exchange with the (second) product gas stream D, without the need for additional heating with a burner during steady-state operation. The small temperature differences between the two gas streams B and D increase the required heat transfer area. In plants with high production capacities, this can lead to disproportionately large heat exchangers.In such cases, the final part of the heating of feed stream B can also be carried out using an electric heat exchanger, which increases the temperature difference in the heat exchangers between streams B and D. This reduces the required heat transfer area to a feasible level. As long as the electricity is generated without burning fossil fuels, the heating of stream B continues to be CO2-free.

[0039] In one embodiment of the process according to the invention, the heating of the second feed gas stream B in step C) is carried out partly by means of an electric heat exchanger.

[0040] This is followed in step D) by catalytic conversion in the olefin fixed-bed reactor to form a product gas stream D comprising ethylene, propylene, further C2-C6 hydrocarbons, methanol, and steam. The conversion is generally carried out over a zeolite catalyst, preferably over a catalyst based on a ZSM-5 zeolite. The reaction temperature is generally 430 to 500°C, preferably 460 to 480°C. The pressure is generally 1.3 to 4 bar. The resulting second product gas stream D is preferably composed as follows: 1 to 15% by weight of ethylene, 1 to 15% by weight of propylene, 35 to 70% by weight of water, 20 to 65% by weight of C2-C6 hydrocarbons, and C6 + -hydrocarbons and 0.1 to 1.5 wt.% methanol and DME.

[0041] The olefin fixed-bed reactor is generally designed as a tray reactor. The number of trays is preferably 4 to 6. In one embodiment, a total of up to 50 wt. % of gas stream A is fed directly to one or more trays of the olefin fixed-bed reactor, preferably to all trays of the olefin fixed-bed reactor. In a further embodiment, a methanol-containing stream is fed directly to one or more trays of the olefin fixed-bed reactor, preferably to all trays of the olefin fixed-bed reactor.

[0042] The (second) product gas stream D has a temperature of generally 430 to 520°C, preferably 460 to 480°C, upon leaving the reactor.

[0043] In a step E), the product gas stream D is cooled in one or more heat exchangers to a temperature in the range of 160 to 220°C by heat exchange with the feed gas stream B. After this cooling step, the temperature of the (second) product gas stream D is generally 160 to 220°C, preferably 170 to 210°C, for example 190°C.

[0044] In a step F), the product gas stream D is further cooled to a temperature in the range of 35 to 60°C by contacting it with one or more water-containing quench cycle streams, whereby water and methanol are condensed out and a water- and methanol-depleted hydrocarbon product gas stream F is obtained. The hydrocarbon product gas stream F thus obtained essentially contains ethylene, propylene, and other C2-C6 hydrocarbons.

[0045] In a step G), a portion of the water from the at least one quench cycle stream K is separated, and this partial stream G1 is heated and evaporated according to the invention in one or more heat exchangers by heat exchange with medium-pressure steam, or this partial stream G1 is heated and evaporated by electrical heating, thereby obtaining a heated steam stream G2. This heated steam stream G2 is mixed in step B) with the first product stream A (or the feed stream A) originating from the dimethyl ether fixed-bed reactor.

[0046] In general, the water-containing quench cycle stream in step G) is heated to at least 50%, based on the amount of heat supplied, by heat exchange with medium-pressure steam or via electric heating. In addition, the substream G1 of the water-containing quench cycle stream in step G) can be further heated and vaporized by heat exchange with the product gas stream D.

[0047] Before heating, the separated substream G1 of the quench recycle stream K is liquid and generally has a temperature in the range of 70 to 100 °C. After heating and evaporation, the steam stream G1 has a temperature in the range of 100 to 150 °C, preferably 120 to 140 °C, and correspondingly a pressure of 1 to 6 bar, preferably 2 to 4 bar.

[0048] In a first embodiment, the water stream G1 withdrawn from the quench circuit is heated by heat exchange with medium-pressure steam. Medium-pressure steam within the meaning of the present invention is steam having a temperature of at least 150°C and a pressure of at least 5 bar, preferably a temperature in the range from 150 to 250°C, more preferably 150 to 200°C, and correspondingly a pressure in the range from 5 to 17 bar, preferably 5 to 11 bar.

[0049] All pressures indicated are absolute pressures.

[0050] The medium-pressure steam stream used in step G) preferably originates from a methanol synthesis upstream of step A) and / or from a synthesis gas production upstream of this methanol synthesis. The medium-pressure steam stream can originate from spatially adjacent, separate production plants.

[0051] In a second embodiment, the water stream G1 taken from the quench circuit is heated by electrical heating. The electrical heating can be provided, for example, in a boiler with built-in electrical heating elements. According to the invention, the electrical energy supplied to the electrical heating is generated predominantly from renewable sources, i.e., without the combustion of fossil fuels. The electrical energy supplied to the electrical heating is thus provided largely without climate-damaging CO2 emissions.

[0052] Medium-pressure steam can also be generated by electrical heating. This can be achieved, for example, in a boiler with built-in electric heating elements.

[0053] In a step H), one or more product streams P containing C2-C4 olefins are separated from the hydrocarbon product gas stream F, and at least one recycle stream R containing C2-C6 hydrocarbons is obtained. The total recycle stream R is generally composed of several individual recycle streams. In general, the total recycle stream R containing C2-C6 hydrocarbons essentially contains, i.e., >95 wt.%, C2-C6 hydrocarbons.

[0054] The hydrocarbon recycle stream R containing C2-C6 hydrocarbons can also be heated by heat exchange with medium-pressure steam.

[0055] The hydrocarbon recycle stream R containing C2-C6 hydrocarbons can be heated by heat exchange with the product gas stream D before mixing with stream A to form the feed stream B.

[0056] In general, step H) comprises steps H1) to H7):

[0057] H1) Compression of the hydrocarbon product gas stream F, wherein a propylene, C4, C5 and C6 + -a liquid hydrocarbon stream H11 containing hydrocarbons and a gaseous hydrocarbon stream H12 containing ethane, ethene and propylene are obtained;

[0058] H2) separating water from the liquid hydrocarbon stream H11 by phase separation, thereby obtaining a liquid hydrocarbon stream H21;

[0059] H3) Separation of a propylene-containing stream H31 from the liquid hydrocarbon stream H21, wherein a C4, C5 and C6 + -hydrocarbons-containing stream H32 is obtained; or separation of a stream H31 containing propylene and C4 hydrocarbons, wherein a C4, C5 and C6 + -hydrocarbon-containing stream H32 is obtained;

[0060] H4) Separation of a C6 + -hydrocarbon-containing stream H41 from the C4, C5 and C6 +-hydrocarbons-containing stream H32, whereby a stream H42 containing C4, C5 and Cß hydrocarbons is obtained; optionally the stream H41 contains aromatic Ce hydrocarbons and the stream H42 contains aliphatic Ce hydrocarbons; H5) separating a propylene-containing stream H51 from the gaseous hydrocarbon stream H12 containing ethane, ethene and propylene, whereby a stream H52 containing ethane and ethene is obtained;

[0061] H6) Separation of a butene-containing stream H61 from the C4-, C5- and Ce-hydrocarbon-containing stream H42, whereby a C5- and Ce-hydrocarbon-containing stream H62 is obtained; and / or separation of a propylene-containing stream H63 from the stream H31, whereby a butene-containing stream H64 is obtained;

[0062] H7) Obtaining at least one recycle stream R from one or more of the streams selected from the C4, C5 and C8 hydrocarbon-containing stream H42, the C5 and C12 hydrocarbon-containing stream H62, the propylene-containing stream H31, the propylene-containing stream H51, the propylene-containing stream H63, the butene-containing stream H61, the butene-containing stream H64 and the ethane- and ethene-containing stream H52.

[0063] Steps H3), H4), H5), and H6) are carried out in conventional distillation apparatus. Suitable distillation apparatuses are, in principle, those familiar to those skilled in the art for such separation tasks. In addition to the actual column body with internals, the distillation column also contains, as usual, a top condenser and a bottom evaporator. The column body can be equipped, for example, with packings, random packings, or trays. The distillation apparatuses can be designed and operated using the general knowledge of the skilled person.

[0064] Preferably, the process according to the invention for preparing C2-C4 olefins from dimethyl ether and optionally methanol follows a process for preparing methanol, the process for preparing methanol comprising the following steps:

[0065] (a) a synthesis gas (II) containing carbon monoxide, carbon dioxide and hydrogen is produced from a carbon-containing feedstock (I) in a synthesis gas production unit;

[0066] (b) the synthesis gas (II) from stage (a) is fed to a methanol synthesis unit and converted at a temperature of 150 to 300°C and a pressure of 5 to 10 MPa abs in the presence of a methanol synthesis catalyst to a reaction mixture comprising methanol, water, carbon monoxide, carbon dioxide, hydrogen, dimethyl ether and methane, from which a crude methanol stream (III) enriched with methanol and water is condensed, and the crude methanol stream (III) and a gaseous stream (IV) comprising carbon monoxide, carbon dioxide, hydrogen and methane are discharged from the methanol synthesis unit;

[0067] (c) the crude methanol stream (III) from stage (b) is expanded in a decompression unit to a pressure of 0.1 to 2 MPa abs, and a decompression gas (V) comprising carbon dioxide and methane and a degassed crude methanol stream (VI) enriched with methanol and water are obtained; (d) from the degassed crude methanol stream (VI) from stage (c), a low-boiling stream (VII) comprising carbon dioxide and dimethyl ether is separated by distillation in a distillation apparatus, and a bottom stream (VIII) enriched with methanol and water is obtained; and

[0068] (e) Optionally, a water-containing high-boiling stream (IX) is separated from the bottom stream (VIII) from step (d) in a further distillation apparatus, and methanol is obtained by distillation as stream (X). Step (e) can also be omitted, since anhydrous methanol is not required.

[0069] The bottom stream (VIII) enriched with methanol and water or, if appropriate, the methanol pure stream (X) can be used in the process according to the invention.

[0070] The medium-pressure steam stream used according to the invention in step G) of the propylene production preferably originates from the synthesis gas generation unit of step (a) of the methanol production and / or the methanol synthesis unit of step (b) of the methanol production.

[0071] Preferably, the process for producing methanol also comprises the following steps:

[0072] (f) the valuable components carbon monoxide, carbon dioxide, dimethyl ether and methane of the streams (IV) and of at least one of the two streams (V) and (VII) are fed to a combustion unit and burned therein with the addition of an oxygen-containing gas (XI) which has an oxygen content of 30 to 100% by volume, and carbon dioxide-containing flue gas (XII) is formed;

[0073] (g) a carbon dioxide-enriched stream (XIV) is separated from the carbon dioxide-containing flue gas (XII) from stage (f) in a carbon dioxide recovery unit to form a waste gas stream (XIII); and

[0074] (h) the stream (XIV) from stage (g) separated in the carbon dioxide recovery unit and enriched with carbon dioxide is recycled to the synthesis gas production unit of stage (a) and / or to the methanol synthesis unit of stage (b).

[0075] Such a process, comprising steps (f), (g) and (h), is described in WO 2020 / 048809 A1.

[0076] The medium-pressure steam stream used in step G) of the production of C2-C4 olefins preferably originates from the synthesis gas generation unit of step (a) of methanol production and / or the methanol synthesis unit of step (b) of methanol production. A wide variety of carbon-containing feedstocks can be used as synthesis gas-generating feedstocks in this process, regardless of whether they are solid, liquid, or gaseous, and regardless of their chemical nature. For example, both coal and hydrocarbons, as well as carbon- and hydrogen-containing compounds, can be used to generate synthesis gas.Preferred carbon-containing feedstocks include natural gas, biogas, coal, wood, plastics, crude oil, bionaphtha, or hydrocarbon-containing streams from crude oil or natural gas processing, from chemical production processes, from renewable raw materials, or from plastics recycling. In the case of coal or wood, synthesis gas is produced, for example, through a gasification process, also known as coal gasification or wood gasification. Suitable feedstocks from crude oil or natural gas processing include naphtha, LPG, gasoline, heavy fuel oil, or vacuum residue. Hydrocarbon-containing streams from chemical production processes include, for example, hydrocarbon-containing streams that arise as by-products and can be used as feedstocks for the production of synthesis gas instead of purely thermally.

[0077] The use of methane-containing streams is particularly preferred, and natural gas or biogas is even more preferred. It is possible and even advantageous to also feed the carbon dioxide present in natural gas and, especially, biogas into the synthesis gas production unit.

[0078] In the synthesis gas generation unit, a synthesis gas (II) containing carbon monoxide, carbon dioxide, and hydrogen is first produced from the carbon-containing feedstock (I). Natural gas typically contains 75 to 100% methane by volume. Besides methane, other constituents include the higher hydrocarbons ethane, propane, butane, and ethylene. Biogas typically contains 40 to 75% methane by volume and, as constituents, mainly carbon dioxide, water, nitrogen, and oxygen.

[0079] Typically, the synthesis gas (II) is produced by the production processes commonly used on an industrial scale, whereby the type of carbon-containing feedstock (I) also plays a role. For methane-containing feedstocks, such as natural gas or biogas, the synthesis gas (II) is preferably produced in step (a) by steam reforming, autothermal reforming, a combination of steam reforming and autothermal reforming, or partial oxidation.

[0080] A particular advantage of partial oxidation is that no separate fuel gas needs to be supplied to the synthesis gas generation unit, thus eliminating the need to produce carbon dioxide-containing flue gas. In partial oxidation, the energy required to generate synthesis gas is obtained directly from the methane-containing feedstock through partial oxidation, and the resulting combustion gases, carbon dioxide and carbon monoxide, are also used in methanol synthesis. Therefore, partial oxidation of methane-containing streams, such as natural gas or biogas, is preferred. The product stream from partial oxidation must be cooled. This is achieved via heat exchangers with water as the cooling medium. The water is evaporated and superheated, producing high-pressure steam (p = 100–130 bar, T = 300–450 °C).This high-pressure steam can be expanded to the required pressure and temperature level of medium-pressure steam in the range of 150 to 250 °C and 5 to 17 bar. Alternatively, heating steam is generated during heat removal from the methanol synthesis reactor at a pressure range of 5 to 17 bar.

[0081] The synthesis gas (II) produced contains carbon monoxide, carbon dioxide, and hydrogen, with their combined concentration typically being 50 to 100 vol.%, preferably > 80 vol.%, and particularly preferably > 90 vol.%. Possible accompanying substances include, in particular, unreacted components of the carbon-containing feedstock used and by-products from its conversion, such as nitrogen, argon, water, or methane. In addition to carbon monoxide, carbon dioxide, and hydrogen, the synthesis gas (II) typically also contains methane, nitrogen and argon, which may have been introduced, for example, through the use of air in the synthesis gas production process.

[0082] The conversion of the synthesis gas (II) takes place in a methanol synthesis unit at a temperature of 150 to 300°C and a pressure of 5 to 10 MPa abs in the presence of a methanol synthesis catalyst. For this purpose, the synthesis gas (II) is typically compressed to the desired pressure by a compressor and converted in a reactor under the conditions mentioned.

[0083] The reaction preferably takes place at a temperature of > 170°C and particularly preferably at > 190°C and preferably at < 280°C and particularly preferably at < 260°C. The reaction preferably takes place at > 6 MPa abs and preferably at > 9 MPa abs.

[0084] In principle, any reactor suitable for the exothermic conversion of synthesis gas to methanol under the specified process conditions can be used. Reactors for the synthesis of methanol from synthesis gas are generally known to those skilled in the art. Examples include the adiabatic and quasi-isothermal reactors, variable-bar reactors, and so-called double-walled superconverters mentioned in Ullmann's Encyclopedia of Industrial Chemistry, Chapter "Methanol," Section 5.2.1 "Reactor Design," 2012, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany.

[0085] Methanol synthesis catalysts are generally known to those skilled in the art. Examples include heterogeneous catalysts containing copper and zinc. These generally also contain other elements, such as aluminum, rare earths, or chromium.

[0086] During the conversion of the synthesis gas (II), which contains carbon monoxide, carbon dioxide, and hydrogen, methanol and water are formed. Dimethyl ether is formed as a typical by-product. Furthermore, the complete hydrogenation of carbon monoxide or carbon dioxide also produces methane as a further by-product. The reaction mixture produced in the reactor thus contains methanol, water, dimethyl ether, carbon monoxide, carbon dioxide, hydrogen, and methane. Furthermore, under the reaction conditions mentioned, other by-products are usually also formed, such as methyl formate, acetic acid, higher alcohols with carbon numbers > 2, esters and ethers with carbon numbers > 2, and paraffins.

[0087] To separate the complex reaction mixture, a crude methanol stream (III) enriched with methanol and water is first condensed. For this purpose, the reaction mixture produced in the reactor is typically fed to a condenser. Condensers that can be used are apparatuses known to those skilled in the art that are suitable for obtaining a condensate enriched in methanol and water by targeted cooling under the prevailing conditions. Generally, the reaction mixture is cooled to a temperature below the dew point of methanol. Depending on the solubilities and vapor pressures of the components present in the reaction mixture, the crude methanol stream (III) enriched with methanol and water still contains dissolved gases such as hydrogen, carbon monoxide, carbon dioxide, dimethyl ether, methane, and components boiling higher than methanol.The condensed crude methanol stream (III) is then discharged from the methanol synthesis unit for further processing and led to step (c).

[0088] The uncondensed gas stream contains, in particular, the unconverted feedstocks carbon monoxide, carbon dioxide, and hydrogen, as well as methane. In order to maintain a high partial pressure of the synthesis gas components hydrogen, carbon monoxide, and carbon dioxide, a portion of the uncondensed gas stream is typically discharged. If necessary, this discharged gas stream is fed to a hydrogen separation unit to increase the partial pressure of hydrogen in the reactor. A higher partial pressure of hydrogen in the reactor reduces the formation of byproducts and, in particular, suppresses the Fischer-Tropsch reaction. The majority of the uncondensed gas stream is returned to the methanol synthesis unit as recycle gas and passed over the methanol synthesis catalyst to achieve the best possible utilization of the synthesis gas and thus high methanol yields.

[0089] Accordingly, the methanol synthesis unit in stage (b) advantageously contains a compressor for compressing the synthesis gas (II), a reactor for converting the synthesis gas (II), a condenser for condensing the crude methanol stream (III) and a line for returning non-condensed gas to the reactor.

[0090] The uncondensed gas stream not recycled as synthesis cycle gas is discharged from the methanol synthesis unit as gaseous stream (IV) and optionally fed to stage (f). In stage (c) of the process, the crude methanol stream (III) condensed in stage (b) and discharged from the methanol synthesis unit is expanded in a decompression unit to a pressure of 0.1 to 2 MPa abs, yielding a decompression gas (V) comprising carbon dioxide and methane and a degassed crude methanol stream (VI) enriched with methanol and water. The decompression is typically carried out in an apparatus in which the gas phase and liquid phase can be readily separated from one another. This apparatus is typically a liquid separator. Suitable apparatus for this purpose are known to those skilled in the art.

[0091] The pressure is preferably reduced to a pressure of > 0.2 MPa abs and particularly preferably to > 0.4 MPa abs and preferably to < 1.5 MPa abs and particularly preferably to < 1 MPa abs. In general, the temperature of the reduced-pressure mixture is 0 to 150°C, preferably > 10°C and particularly preferably > 20°C and preferably < 120°C and particularly preferably < 60°C.

[0092] The degassed crude methanol stream (VI) is further enriched in methanol and water, but also contains other components depending on the solubilities and vapor pressures of the components contained in the crude methanol stream (III), such as gases dissolved therein such as hydrogen, carbon monoxide, carbon dioxide, dimethyl ether, methane or components boiling higher than methanol.

[0093] The expansion gas (V) containing carbon dioxide and methane is preferably fed to stage (f). Alternatively, the expansion gas (V) can also be discharged from the methanol synthesis plant and, for example, thermally recycled or disposed of in another way. However, its use within the methanol synthesis plant as a feed stream to the combustion unit of stage (f) is preferred.

[0094] In step (d) of the process, the degassed crude methanol stream (VI) obtained in step (c) is separated by distillation in a distillation apparatus into a low-boiling stream (VII) containing carbon dioxide and dimethyl ether and a bottoms stream (VIII) enriched with methanol and water.

[0095] The low-boiling components stream (VII) separated by distillation primarily contains carbon dioxide and dimethyl ether as separated low-boiling components and, based on the composition of the degassed crude methanol stream (VI), also other low-boiling components, such as methane, and, depending on the separation efficiency and operation of the distillation apparatus, also methanol or components boiling higher than methanol, such as water. The low-boiling components stream (VII) containing carbon dioxide and dimethyl ether is also preferably fed to stage (f). If the flash gas (V) is fed to the combustion unit of stage (f) and is thus already reused within the methanol synthesis plant, the low-boiling components stream (VII) can alternatively be discharged from the methanol synthesis plant and, for example, thermally utilized or otherwise disposed of. However, its use within the methanol synthesis plant as a feed stream to the combustion unit of stage (f) is preferred.The bottom stream (VIII) enriched with methanol and water also contains other components boiling higher than methanol, such as by-products from methanol synthesis boiling higher than methanol, such as acetic acid, higher alcohols, higher esters, higher ethers or paraffins.

[0096] To obtain the methanol, a water-containing high boiler stream (IX) is finally separated from the bottom stream (VIII) obtained in step (d) in a further distillation apparatus in step (e), and methanol is obtained by distillation as stream (X).

[0097] The high-boiling stream (IX) contains water as well as other components with higher boiling points than methanol, such as byproducts from methanol synthesis with higher boiling points than methanol, such as acetic acid, higher alcohols, higher esters, higher ethers, or paraffins. This stream can be fed, for example, to wastewater treatment.

[0098] Methanol can be obtained via stream (X) in a high purity of > 95 wt.%, preferably > 98 wt.%, and particularly preferably > 99 wt.%. Accompanying substances include residual amounts of low and high boilers not completely separated by distillation, particularly water, and very small amounts of ethanol, esters, and ethers.

[0099] During the stepwise processing of the reaction mixture to obtain methanol as stream (X), streams (IV), (V), and (VII) are separated. However, these still contain valuable components, such as carbon monoxide, carbon dioxide, methane, and dimethyl ether. The aim is to largely reuse the carbon from these valuable components for the further synthesis of methanol while simultaneously avoiding carbon dioxide emissions. The additional process steps (f), (g), and (h) make it possible to specifically reuse the carbon from the valuable components for the further synthesis of methanol, i.e., to produce further valuable product, while simultaneously avoiding carbon dioxide emissions from the methanol synthesis. Steps (f), (g), and (h) are described in detail in WO 2020 / 048809 A1.

[0100] The invention is explained in more detail with reference to Figures 1 to 10. They show:

[0101] Figure 1 shows a non-inventive operation using a burner 4 for heating the feed stream B, wherein a DME-containing partial stream A-2 is fed into individual trays of the reactor 2 after cooling in the heat exchanger HE8 for cooling the reactor 2.

[0102] Figure 2 shows a procedure according to the invention, wherein a partial stream A-2 containing DME is fed into individual trays of the reactor 2 after cooling in the heat exchanger HE8 for cooling the olefin fixed bed reactor 2.

[0103] Figure 3 shows a procedure according to the invention, wherein a DME-containing partial stream A-2 is

[0104] Cooling in heat exchanger HE8 is fed into individual trays of reactor 2 for cooling the olefin fixed-bed reactor 2. At the same time, electric heat exchanger EH1 is used to increase the temperature difference in apparatus HE4 and thus significantly reduce the heat transfer area.

[0105] Figure 4 shows a non-inventive procedure using a burner 4 for heating the feed stream B, wherein a DME-containing partial stream A-2 is fed into individual trays of the olefin fixed bed reactor 2 without cooling, and the reactor 2 is operated isothermally.

[0106] Figure 5 shows a procedure according to the invention, wherein a DME-containing partial stream A-2 is fed into individual trays of the olefin fixed bed reactor 2 without cooling, and the reactor 2 is operated isothermally.

[0107] Figure 6 shows a procedure according to the invention, wherein a DME-containing substream A-2 is fed into individual trays of the olefin fixed-bed reactor 2 without cooling, and the reactor 2 is operated isothermally. At the same time, electric heat exchanger EH1 is used to increase the temperature difference in the apparatus HE4 and thus significantly reduce the heat transfer area.

[0108] Figure 7 shows a non-inventive procedure using a burner 4 for heating the feed stream B, wherein a methanol partial stream A1-2 is fed into individual trays of the reactor 2 for cooling the olefin fixed bed reactor 2.

[0109] Figure 8 shows a procedure according to the invention, wherein a methanol partial stream A1-2 is fed into individual trays of the reactor 2 for cooling the olefin fixed bed reactor 2.

[0110] Figure 9 shows a procedure according to the invention, wherein a methanol substream A1-2 is fed into individual trays of reactor 2 for cooling the olefin fixed-bed reactor 2. At the same time, electric heat exchanger EH1 is used to increase the temperature difference in apparatus HE4 and thus significantly reduce the heat transfer area.

[0111] Figure 10 shows a non-inventive operation without a DME pre-reactor using a burner 4 for heating the feed stream B, wherein a DME partial stream A-2 is fed into individual trays of the reactor 2 for cooling the olefin fixed bed reactor 2.

[0112] Figure 11 shows a procedure according to the invention without a DME pre-reactor, wherein a DME partial stream A-2 is fed into individual trays of the reactor 2 for cooling the olefin fixed bed reactor 2.

[0113] Figure 12 shows a procedure according to the invention without a DME pre-reactor, wherein a DME substream A-2 is fed into individual trays of reactor 2 to cool the olefin fixed-bed reactor 2. At the same time, an electric heat exchanger EH1 is used to increase the temperature difference in apparatus HE4 and thus significantly reduce the heat transfer area. Figure 13 shows a procedure not according to the invention without a DME pre-reactor using a burner 4 to heat the feed stream B, wherein a DME substream A-2 is fed into individual trays of the olefin fixed-bed reactor 2 and reactor 2 is operated isothermally.

[0114] Figure 14 shows a procedure according to the invention without a DME pre-reactor, wherein a DME partial stream A-2 is fed into individual trays of the olefin fixed bed reactor 2 and the reactor 2 is operated isothermally.

[0115] Figure 15 shows an inventive procedure without a DME pre-reactor, wherein a DME substream A-2 is fed into individual trays of the olefin fixed-bed reactor 2 and the reactor 2 is operated isothermally. At the same time, an electric heat exchanger EH1 is used to increase the temperature difference in the apparatus HE4 and thus significantly reduce the heat transfer area.

[0116] List of reference symbols:

[0117] 1 DME pre-reactor

[0118] 2 olefin fixed bed reactor

[0119] 3 Product gas quench

[0120] 4 burners

[0121] 5 Product separation section

[0122] 6 Compressor

[0123] HE1 to HE9 heat exchangers

[0124] EH1 Electric Heat Exchanger

[0125] A1 stream containing methanol

[0126] A1-1 , A1-2 partial streams of A1

[0127] A DME-containing stream

[0128] A-1 , A-2 partial streams of A

[0129] B DME, recycled hydrocarbons and steam-containing feed stream to the olefin fixed bed reactor

[0130] D Product gas stream of the olefin fixed bed reactor F Product gas stream containing hydrocarbons G1, G2, G3 Water streams

[0131] H 1 Hydrocarbon recycle stream

[0132] K Quench water recycle stream

[0133] P Product hydrocarbons

[0134] W Wastewater stream

[0135] Q1 to Q12 heat flows

[0136] Examples

[0137] The heat flows Q1 to Q11 according to the operating modes shown in Figures 1 to 15 were calculated for a production of 60 t / h of propylene with minimal production of ethylene and butylene. The results are summarized in the table below.

Claims

Patent claims 1 . Process for the preparation of C2-C4 olefins from dimethyl ether and optionally methanol, comprising the steps: A) providing a stream A containing dimethyl ether; B) mixing at least a portion of stream A with at least one hydrocarbon recycle stream R containing C2-C6 hydrocarbons and a steam stream G2, thereby obtaining a feed stream B; C) heating the feed stream B in one or more heat exchangers to a temperature in the range from 430 to 500 °C and feeding it into an olefin fixed bed reactor, wherein the heating can also take place before the mixing of individual partial streams to form the feed stream B in step B); D) Catalytic conversion of the feed stream B at a temperature in the range of 430 to 520 °C to a product gas stream D containing C2-C4 olefins, further C2-C6 hydrocarbons, methanol and steam; E) cooling the product gas stream D in one or more heat exchangers to a temperature in the range of 170 to 220 °C by heat exchange with the feed gas stream B; F) further cooling the product gas stream D to a temperature in the range from 35 to 65 °C by bringing it into contact with at least one water-containing quench cycle stream K, whereby water and methanol are condensed out and a hydrocarbon product gas stream F depleted in water and methanol is obtained; G) separating at least one partial stream G1 of the at least one water-containing quench cycle stream K and heating and evaporating the partial stream G1 in one or more heat exchangers by heat exchange with medium-pressure steam, or heating and evaporating the partial stream G1 by electrical heating, whereby a steam stream G2 is obtained, and feeding the steam stream G2 into step B); H) Separation of one or more product streams P containing C2-C4 olefins and recovery of at least one hydrocarbon recycle stream R containing C2-Ce hydrocarbons from the hydrocarbon product gas stream F and recycling in step B).

2. Process according to claim 1, characterized in that no additional heat generated by combustion of fossil fuels is used to heat the second feed gas stream B in step C).

3. Process according to claim 2, characterized in that the heating of the second feed gas stream B in step C) is carried out partly by means of an electric heat exchanger.

4. Process according to one of claims 1 to 3, characterized in that the medium-pressure steam stream has a temperature in the range of 150 to 250 °C and a pressure in the range of 5 to 17 bar.

5. Process according to one of claims 1 to 4, characterized in that the medium-pressure steam stream is produced in a methanol synthesis upstream of step A) and / or in a synthesis gas production upstream of this methanol synthesis.

6. Process according to one of claims 1 to 5, characterized in that the partial stream G1 of the water-containing quench cycle stream in step G) is additionally heated and evaporated by heat exchange with the product gas stream D.

7. Process according to one of claims 1 to 6, characterized in that the partial stream G1 of the water-containing quench cycle stream in step G) is heated to at least 50%, based on the amount of heat supplied, by heat exchange with medium-pressure steam.

8. Process according to one of claims 1 to 7, characterized in that the hydrocarbon recycle stream H1 containing C2-C6 hydrocarbons is additionally heated by heat exchange with medium-pressure steam.

9. Method according to one of claims 1 to 8, characterized in that step H) comprises: H1) Compression of the hydrocarbon product gas stream F, wherein a propylene, C4, C5 and C6 + -a liquid hydrocarbon stream H11 containing hydrocarbons and a gaseous hydrocarbon stream H12 containing ethane, ethene and propylene are obtained; H2) separating water from the liquid hydrocarbon stream H11 by phase separation, thereby obtaining a liquid hydrocarbon stream H21; H3) Separation of a propylene-containing stream H31 from the liquid hydrocarbon stream H21, wherein a C4, C5 and C6 +-hydrocarbons-containing stream H32 is obtained; or separation of a stream H31 containing propylene and C4 hydrocarbons, wherein a C4, C5 and C6 + -hydrocarbon-containing stream H32 is obtained; H4) Separation of a C6 + -hydrocarbon-containing stream H41 from the C4, C5 and C6 + -hydrocarbons-containing stream H32, whereby a C4-, C5- and Ce-hydrocarbon-containing stream H42 is obtained; optionally the stream contains H41 aromatic Cß hydrocarbons and the stream H42 aliphatic Cß hydrocarbons; H5) separating a propylene-containing stream H51 from the ethane, ethene and propylene-containing gaseous hydrocarbon stream H12, whereby a stream H52 containing ethane and ethene is obtained; H6) Separating a butene-containing stream H61 from the C4, C5 and Ce hydrocarbon-containing stream H42, thereby obtaining a C5 and Ce hydrocarbon-containing stream H62; and / or separating a propylene-containing stream H63 from the stream H31, thereby obtaining a butene-containing stream H64; H7) Obtaining at least one recycle stream R from one or more of the streams selected from the C4, C5 and Ce hydrocarbon-containing stream H42, the C5 and Ce hydrocarbon-containing stream H62, the propylene-containing stream H31, the propylene-containing stream H51, the propylene-containing stream H63, the butene-containing stream H61, the butene-containing stream H64 and the ethane and ethene-containing stream H52.Process according to one of claims 1 to 9, characterized in that step A) comprises feeding a methanol-containing feed stream A1 into a dimethyl ether fixed-bed reactor and catalytically converting methanol to dimethyl ether, obtaining a product stream A comprising dimethyl ether, methanol, and steam. Process according to claim 10, characterized in that the methanol fed in step A) is produced in an upstream methanol production process comprising the steps of: (a) a synthesis gas (II) containing carbon monoxide, carbon dioxide and hydrogen is produced from a carbon-containing feedstock (I) in a synthesis gas production unit; (b) the synthesis gas (II) from stage (a) is fed to a methanol synthesis unit and converted at a temperature of 150 to 300°C and a pressure of 5 to 10 MPa abs in the presence of a methanol synthesis catalyst to a reaction mixture comprising methanol, water, carbon monoxide, carbon dioxide, hydrogen, dimethyl ether and methane, from which a crude methanol stream (III) enriched with methanol and water is condensed, and the crude methanol stream (III) and a gaseous stream (IV) comprising carbon monoxide, carbon dioxide, hydrogen and methane are discharged from the methanol synthesis unit; (c) the crude methanol stream (III) from stage (b) is expanded in a pressure expansion unit to a pressure of 0.1 to 2 MPa abs and a carbon dioxide and methane-containing expansion gas (V) and a degassed crude methanol stream (VI) enriched with methanol and water are obtained; (d) from the degassed crude methanol stream (VI) from stage (d) a low-boiling stream (VII) containing carbon dioxide and dimethyl ether is produced in a distillation apparatus separated by distillation and a bottom stream (VIII) enriched with methanol and water is obtained; and (e) optionally, a water-containing high-boiling stream (IX) is separated from the bottom stream (VIII) from stage (d) in a further distillation apparatus, and methanol is obtained by distillation as stream (X). The process according to claim 11, characterized in that the methanol preparation also comprises steps (f) to (h): (f) the valuable components carbon monoxide, carbon dioxide, dimethyl ether and methane of the streams (IV) and of at least one of the two streams (V) and (VII) are fed to a combustion unit and combusted therein with the addition of an oxygen-containing gas (XI) having an oxygen content of 30 to 100% by volume, and carbon dioxide-containing flue gas (XII) is formed; (g) a carbon dioxide-enriched stream (XIV) is separated from the carbon dioxide-containing flue gas (XII) from stage (f) in a carbon dioxide recovery unit to form a waste gas stream (XIII); and (h) the carbon dioxide-enriched stream (XIV) from stage (g) separated in the carbon dioxide recovery unit is recycled to the synthesis gas production unit of stage (a) and / or to the methanol synthesis unit of stage (b). The process according to claim 11 or 12, characterized in that the medium-pressure steam stream used in step G) of producing C2-C4 olefins originates from the synthesis gas production unit of step (a) of methanol production and / or the methanol synthesis unit of step (b) of methanol production.

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