JP2025529410A - Heat-integrated process for producing C2-C4 olefins - Google Patents

Abstract

The present invention relates to a process for producing _C2 - _C4 olefins from dimethyl ether and optionally methanol, comprising the steps of: A) providing a dimethyl ether-containing stream A; B) mixing at least a portion of stream A with at least one hydrocarbon return stream R containing _C2 - _C6 hydrocarbons and a steam stream G2 to obtain a feed stream B; C) heating feed stream B to a temperature in the range of 430-500°C in one or more heat exchangers and feeding it to an olefin fixed bed reactor, wherein the heating process can also be carried out before mixing the individual sub-streams to form feed stream B of step B); D) converting feed stream B into _C2 - _C4 olefins, further _C2 -C6 ... catalytically converting at a temperature in the range of 430-520°C to form a product gas stream D containing ₆ hydrocarbons, methanol and water vapor; E) cooling the product gas stream D to a temperature in the range of 170-220°C by exchanging heat with a feed gas stream B in one or more heat exchangers; F) further cooling the product gas stream D to a temperature in the range of 35-65°C by contacting the product gas stream with at least one water-containing quench circuit stream K to condense water and methanol from the product gas stream and obtain a water- and methanol-depleted hydrocarbon product gas stream F; G) separating at least one side stream G1 of the at least one water-containing quench circuit stream K, heating and vaporizing the side stream G1 in one or more heat exchangers by exchanging heat with medium pressure steam or by an electrical heating process to obtain a water vapor stream G2, which is fed to step B); H) separating at least one side stream G1 of the at least one water-containing quench circuit stream K from at least one of the water- and methanol-depleted hydrocarbon product gas streams _C2 -C3 and separating the _olefin -containing product stream P from the hydrocarbon product gas stream F to obtain at least one hydrocarbon return stream R containing C ₂ -C ₆ hydrocarbons, which is returned to step B.

Description

The present invention relates to a heat-integrated process for the preparation of _C2 to _C4 olefins from dimethyl ether with or without methanol.

It is known that propylene can be produced by converting a methanol/dimethyl ether mixture in a fixed-bed reactor (methanol to propylene, MTP reactor). Known fixed-bed reactors are operated with a zeolite catalyst at a temperature of about 480 °C. For this purpose, the methanol/DME-containing reaction gas stream must be heated to a high temperature before entering the reactor.

L. Jiang et al., Chinese Journal of Chemical Engineering 26 (2018), 2102–2111, describes a process for preparing propylene from methanol, in which methanol is first converted to dimethyl ether (DME), and then the product mixture is converted to propylene and additional products. Referring to Figure 8 of this publication, the process is described as follows: Methanol is preheated, vaporized, and further heated in a heat exchanger by heat exchange with the product gas from the DME reactor. The methanol vapor is fed to the DME reactor at a temperature of 270°C. A first substream 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. While the gas phase is reheated, the liquid phase is further cooled, and the gas and liquid phases are fed to individual trays of a propylene fixed-bed reactor (MTP reactor). Alternatively, only methanol can be fed to an individual tray of the MTP reactor. A second substream of product gas from the DME reactor is mixed with a hydrocarbon recycle stream and steam, heated to a temperature of about 460°C using a burner, and fed to the propylene reactor, where substantially all of the methanol and DME are converted to propylene and additional hydrocarbons.

A drawback of the described process is that the majority of the heat required to heat the reactant streams fed to the propylene reactor is provided by the combustion of natural gas or other fossil hydrocarbons in the burner. This has a significant negative impact on the _CO₂ balance of the entire process. However, against the backdrop of increasingly severe anthropogenic climate change, there is a growing desire to implement industrial manufacturing processes that emit only small amounts of fossil-derived _CO₂ into the atmosphere, or even better, none at all.

L. Jiang et al., Chinese Journal of Chemical Engineering 26 (2018), 2102-2111

The object of the present invention is to provide a heat-integrated process for preparing _C2 - _C4 olefins from dimethyl ether, which, in steady-state operation, makes it possible to dispense with the need for process heat provided by the combustion of external fossil hydrocarbons.

The object is a process for the preparation of _C2 - _C4 olefins from dimethyl ether with or without methanol, comprising:
A) providing a stream A comprising dimethyl ether;
B) mixing at least a portion of stream A with at least one hydrocarbon recycle stream R comprising C ₂ -C ₆ hydrocarbons and with a steam stream G2 to obtain a feed stream B;
C) heating feed stream B to a temperature in the range of 430-500°C in one or more heat exchangers and feeding it to an olefin fixed bed reactor, wherein heating may also precede the mixing of the individual sub-streams to provide feed stream B of step B);
D) catalytically converting feed stream B at a temperature in the range of 430-520°C to a product gas stream D comprising _C2 - _C4 olefins, additional _C2 - _C6 hydrocarbons, methanol and water vapor; and E) cooling product gas stream D to a temperature in the range of 170-220°C by heat exchange with feed gas stream B in one or more heat exchangers.
F) further cooling product gas stream D to a temperature in the range of 35-65°C by contacting it with at least one water-containing quench recycle stream K to condense water and methanol to obtain a water- and methanol-depleted hydrocarbon product gas stream F;
G) separating at least one sub-stream G1 of the at least one water-containing quench circulating stream K, heating and evaporating the sub-stream G1 in one or more heat exchangers by heat exchange with medium-pressure steam or by electrical heating to obtain a vapor stream G2, which is fed to step B);
H) separating one or more product streams P comprising _C2 - _C4 olefins from the hydrocarbon product gas stream F to obtain at least one hydrocarbon recycle stream R comprising _C2 - _C6 hydrocarbons, which is recycled to step B).

In one embodiment of the process of the present invention, in step A), a stream A consisting essentially of DME (greater than 90 wt. % DME) is fed to the process and split into two substreams. The first substream A-1 contains 80 wt. % or less of stream A and is used as described in step B). The second substream is mixed with the water-containing quench recycle substream G3 mentioned in step G) and fed, without further heating, as stream A-2 to one or more individual trays of the olefin fixed-bed reactor in step C). It is also possible to operate the olefin fixed-bed reactor isothermally. Isothermal operation can be achieved, for example, by the method described in WO 2017/102096. For example, a heat transfer surface installed in the olefin fixed-bed reactor can be present, operating using liquid salt or high-pressure steam as the heat transfer medium. The flow of the heat transfer medium through the heat transfer surface within the reactor removes the generated reaction heat from the reactor, which is therefore operated isothermally.

In a preferred embodiment of the process of the present invention, step A) comprises feeding a methanol-containing feed gas stream A1 to a dimethyl ether fixed-bed reactor for catalytic conversion of the methanol to dimethyl ether to obtain a product gas stream comprising dimethyl ether, methanol, and water vapor. When stream A1 comprises ethanol, product stream A comprises not only dimethyl ether, methanol, and water vapor, but also ethanol and ethylene.

_C2 to _C4 olefins are ethylene, propylene, 1-butene, 2-butene and isobutene. It is preferred to prepare ethylene and/or propylene by the process of the present invention.

Thus, in a preferred embodiment, the process of the present invention comprises:
A) feeding a feed stream A1 comprising methanol to a dimethyl ether fixed bed reactor to catalytically convert the methanol to dimethyl ether to obtain a product stream A comprising dimethyl ether, methanol, and water vapor;
B) mixing at least a portion of product stream A with at least one hydrocarbon recycle stream R comprising _C2 - _C6 hydrocarbons and with a steam stream G2 to obtain a second feed stream B;
C) heating the second feed stream B to a temperature in the range of 430-500°C in one or more heat exchangers and feeding it to an olefin fixed bed reactor, wherein heating may also precede the mixing of the individual sub-streams to provide the feed stream B of step B);
D) catalytically converting feed stream B to a product gas stream D comprising ethylene, propylene, additional _C2 - _C6 hydrocarbons, methanol and water vapor at a temperature in the range of 430-520°C;
E) cooling product gas stream D to a temperature in the range of 170-220°C by heat exchange with feed stream B in one or more heat exchangers;
F) further cooling product gas stream D to a temperature in the range of 35-65°C by contacting it with at least one water-containing quench recycle stream K to condense water and methanol to obtain a water- and methanol-depleted hydrocarbon product gas stream F;
G) separating at least one sub-stream G1 of the at least one water-containing quench circulating stream K, heating and evaporating the sub-stream G1 in one or more heat exchangers by heat exchange with medium-pressure steam or by electrical heating to obtain a vapor stream G2, which is fed to step B);
H) separating one or more product streams P comprising ethylene and/or propylene from the hydrocarbon product gas stream F to obtain at least one hydrocarbon recycle stream R comprising _C2 to _C6 hydrocarbons for recycling to step B).

In step A), preferably, a methanol-containing feed stream A1 is fed to a dimethyl ether fixed-bed reactor, where the methanol is catalytically converted to dimethyl ether to obtain a product stream A comprising dimethyl ether, methanol, and water vapor.

Methanol-containing feed stream A1, preferably originating from an upstream methanol synthesis plant, is vaporized and heated to a temperature typically between 250 and 300°C, e.g., 275°C, and fed to a dimethyl ether fixed-bed reactor. The catalyst used is typically gamma-alumina. The conversion temperature is typically between 250 and 400°C, and the pressure is typically between 1 and 25 bar, e.g., 4 bar. The first product gas stream leaving the dimethyl ether fixed-bed reactor is typically at a temperature between 350 and 400°C, e.g., 370°C. The methanol conversion is typically between 50% and 90%, preferably between 65% and 85%, e.g., 75%. Product gas stream A is cooled by heat exchange with methanol-containing feed stream A1. After heat exchange, the first product gas stream is typically at a temperature between 180 and 250°C.

In step B), at least a portion of this stream A is mixed with a hydrocarbon recycle stream comprising _C2 - _C6 hydrocarbons and a vapor stream G2 to obtain a feed gas stream B. Typically, this portion of stream A is at least 50% by weight, preferably at most 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 of 30 to 60°C, before being fed to the trays of the olefin fixed-bed reactor. This side stream A-2 is preferably fed to the reactor in liquid form.

If the olefin fixed-bed reactor is operated and cooled isothermally, cooling via side stream A-2 can be omitted. Isothermal operation can be achieved, for example, by the method described in WO 2017/102096. For example, a heat transfer surface may be installed in the olefin fixed-bed reactor, which is operated using liquid salt or high-pressure steam as the heat transfer medium. The flow of the heat transfer medium through the heat transfer surface within the reactor removes the generated reaction heat from the reactor, which is therefore operated isothermally. In this case, side stream A-2 can also be fed to an intermediate stage of the olefin fixed-bed reactor to establish the desired product distribution in product gas stream D.

In a further embodiment, the methanol-containing stream is fed directly to one or more trays of the olefin fixed-bed reactor. For example, it is preferred to feed a portion of the first methanol-containing feed stream A1, originating from an upstream methanol synthesis plant, directly to the olefin fixed-bed reactor. This portion of the methanol-containing feed stream A1 can be up to 60 wt. % of the total feed stream A1.

The hydrocarbon recycle stream R resulting from the removal of _C2 - _C4 olefins generally comprises _C4 - _C6 hydrocarbons. Depending on whether ethylene, propylene or butenes are obtained as valuable products in step H), the hydrocarbon recycle stream R may also comprise ethylene, propylene and/or butenes. If the amount of C2-C4 olefins obtained as product in step H) comprises propylene to an extent of at least 85% by weight, for example, stream R consists of _C4 - _C6 hydrocarbons to an extent of at least 50% by weight. The hydrocarbon recycle stream R before mixing is generally at a temperature in the range of 100-175°C, preferably in the range of 130-160°C. The hydrocarbon recycle stream R is preferably heated by heat exchange with medium-pressure steam and is generally at a preheating temperature of 30-100°C, preferably 50-80°C.

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

The feed stream B thus obtained generally contains 15% to 50% by weight, preferably 20% to 40% by weight, of steam. It generally further contains 5% to 10% by weight of methanol, 10% to 20% by weight of dimethyl ether and 25% to 50% by weight of _C2 to _C6 hydrocarbons.

In step C), feed stream B is heated in one or more heat exchangers to a temperature in the range of 430-500°C and fed to an olefin fixed-bed reactor. Heating may also precede the mixing of the individual substreams in step B).

Typically, feed stream B, when fed to the olefin fixed-bed reactor, has a temperature in the range of 430-500°C, e.g., 470°C. Feed stream B is heated to this temperature by heat exchange with the (second) product gas stream D from the olefin fixed-bed reactor. The inventive heating of steam stream G1 by heat exchange with medium-pressure steam makes it possible to achieve a temperature of 430-500°C in feed stream B by heat exchange with the (second) product gas stream D in steady-state operation without the need for additional heating by a burner. The small temperature difference between the two gas streams B and D increases the required heat transfer area. In plants with high production capacities, this can result in disproportionately large heat exchangers. In such cases, the final heating of feed stream B can also be performed using an electrical heat exchanger, thereby increasing the heat exchanger temperature difference between streams B and D. This reduces the required heat transfer area to a practical extent. As long as electricity is generated without the combustion of fossil energy carriers, stream B can still be heated without _CO2 emissions.

In one embodiment of the process of the present invention, the second feed gas stream B is heated in step C) in part by an electrical heat exchanger.

This is followed in step D) by catalytic conversion in an olefin fixed-bed reactor to 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 a catalyst based on ZSM-5 zeolite. The reaction temperature is generally between 430 and 500°C, preferably between 460 and 480°C. The pressure is generally between 1.3 and 4 bar. The resulting second product gas stream D preferably has the following composition: 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 also _C6 ⁺ hydrocarbons and 0.1% to 1.5% by weight of methanol and DME.

The olefin fixed-bed reactor generally takes the form of 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 of the trays of the olefin fixed-bed reactor. In a further embodiment, the methanol-containing stream is fed directly to one or more trays of the olefin fixed-bed reactor, preferably to all of the trays of the olefin fixed-bed reactor.

The (second) product gas stream D typically has a temperature of 430-520°C, preferably 460-480°C, upon exiting the reactor.

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

In step F), product gas stream D is further cooled to a temperature in the range of 35-60°C by contacting it with one or more water-containing quench recycle streams to condense the water and methanol, resulting in a water- and methanol-depleted hydrocarbon product gas stream F. The hydrocarbon product gas stream F thus obtained essentially comprises ethylene, propylene and additional _C2 - _C6 hydrocarbons.

In step G), a portion of the water in at least one quench recycle stream K is separated, and this substream G1 is heated and evaporated in accordance with the present invention by heat exchange with medium-pressure steam in one or more heat exchangers, or this substream G1 is heated and evaporated by electrical heating to obtain heated vapor stream G2. This heated vapor stream G2 is mixed in step B) with the first product stream A (or feed stream A) coming from the dimethyl ether fixed-bed reactor.

Typically, the water-containing quench recycle stream is heated in step G) by heat exchange with medium-pressure steam or via electrical heating to an extent of at least 50% based on the amount of heat supplied. Additionally, a substream G1 of the water-containing quench recycle stream can be further heated and evaporated in step G) by heat exchange with product gas stream D.

Before being heated, the side stream G1 separated off from the quench recycle stream K is in liquid form and generally has a temperature in the range of 70 to 100°C. After being heated and evaporated, the vapor stream G1 has a temperature in the range of 100 to 150°C, preferably 120 to 140°C, and a corresponding pressure of 1 to 6 bar, preferably 2 to 4 bar.

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 in the context of the present invention is steam at a temperature of at least 150°C and a pressure of at least 5 bar, preferably at a temperature in the range from 150 to 250°C, preferably from 150 to 200°C, and correspondingly at a pressure in the range from 5 to 17 bar, preferably from 5 to 11 bar.

All pressures stated are absolute pressures.

The medium-pressure vapor stream used in step G) preferably originates from methanol synthesis upstream of step A) and/or synthesis gas preparation upstream of said methanol synthesis. The medium-pressure vapor stream may also originate from a separate, spatially adjacent production plant.

In a second embodiment, the water flow G1 drawn from the quenching circuit is heated by electrical heating. This can be done, for example, in a tank in which an electrical heating element is installed.

According to the invention, the electrical energy supplied for the heating is generated primarily in a renewable manner, i.e. without the combustion of fossil energy carriers. The electrical energy supplied for the heating is therefore supplied largely without climatically harmful _CO2 emissions.

Medium-pressure steam can also be generated by electrical heating, for example, in a tank equipped with an electric heating element.

In step H), one or more product streams P comprising _C2 - _C4 olefins are separated from the hydrocarbon product gas stream F to obtain at least one recycle stream R comprising _C2 - _C6 hydrocarbons. The overall recycle stream R is typically made up of multiple individual recycle streams. Typically, the overall recycle stream R comprising _C2 - _C6 hydrocarbons comprises essentially, i.e., to an extent of greater than 95% by weight, _C2 - _C6 hydrocarbons.

The hydrocarbon recycle stream R, which comprises _C2 to _C6 hydrocarbons, may also be heated by heat exchange with medium pressure steam.

Hydrocarbon recycle stream R, comprising C ₂ -C ₆ hydrocarbons, may be heated by heat exchange with product gas stream D before being mixed with stream A to obtain feed stream B.

Generally, step H) comprises steps H1) to H7):
H1) compressing the hydrocarbon product gas stream F to obtain a liquid hydrocarbon stream H11 comprising propylene and _C4 , _C5 and _C6 ⁺ hydrocarbons, and an ethane, ethene and propylene containing gaseous hydrocarbon stream H12;
H2) Separating water from the liquid hydrocarbon stream H11 by phase separation to obtain a liquid hydrocarbon stream H21;
H3) Separating a propylene-containing stream H31 from the liquid hydrocarbon stream H21 to obtain a stream H32 containing C ₄ , C ₅ and C ₆ ⁺ hydrocarbons; or separating a stream H31 containing propylene and C ₄ hydrocarbons to obtain a stream H32 containing C ₄ , C ₅ and C ₆ ⁺ hydrocarbons;
H4) separating a stream H41 containing C6 ⁺ hydrocarbons from a stream H32 containing _{C4 , C5} and _C6 ⁺ hydrocarbons to obtain a stream H42 containing _C4 , _C5 and _C6 hydrocarbons, wherein stream H41 optionally contains aromatic _C6 hydrocarbons and stream H42 contains aliphatic _C6 hydrocarbons; H5) separating a propylene-containing stream H51 from an ethane-, ethene- and propylene-containing gaseous hydrocarbon stream H12 to obtain an ethane- and ethene-containing stream H52;
H6) separating a butene-containing stream H61 from a stream H42 containing C ₄ , C ₅ and C ₆ hydrocarbons to obtain a stream H62 containing C ₅ and C ₆ hydrocarbons; and/or separating a propylene-containing stream H63 from stream H31 to obtain a butene-containing stream H64;
H7) obtaining at least one recycle stream R from _one or more of the streams selected from stream H42 comprising C4, _C5 and _C6 hydrocarbons, stream H62 comprising _C5 and _C6 hydrocarbons, propylene-containing stream H31, propylene-containing stream H51, propylene-containing stream H63, butene-containing stream H61, butene-containing stream H64, and ethane- and ethene-containing stream H52.

Steps H3), H4), H5), and H6) are carried out in standard distillation equipment. Useful distillation equipment includes, in principle, equipment known to those skilled in the art for such separation operations. As well as the actual column body with its internals, the distillation column also typically comprises an overhead condenser and a reboiler. The column body may, for example, be equipped with structured packing, random packing, or trays. The distillation equipment can be designed and operated according to the common knowledge of those skilled in the art.

The process of the present invention for preparing _C2 - _C4 olefins from dimethyl ether with or without methanol is preferably a process for preparing methanol, comprising the following steps:
(a) producing a synthesis gas (II) comprising carbon monoxide, carbon dioxide and hydrogen from a hydrocarbonaceous feedstock (I) in a synthesis gas production unit;
(b) feeding the synthesis gas (II) from step (a) to a methanol synthesis unit and converting it into a reaction mixture containing methanol, water, carbon monoxide, carbon dioxide, hydrogen, dimethyl ether and methane in the presence of a methanol synthesis catalyst at a temperature of 150-300°C and a pressure of 5-10 MPa abs, condensing a crude methanol stream (III) enriched in methanol and water from the reaction mixture, and leading the crude methanol stream (III) and a gas stream (IV) containing carbon monoxide, carbon dioxide, hydrogen and methane from the methanol synthesis unit;
(c) expanding the crude methanol stream (III) from step (b) in an expansion unit to a pressure of 0.1-2 MPa abs to obtain an expanded gas (V) comprising carbon dioxide and methane and a degassed crude methanol stream (VI) enriched in methanol and water;
(d) separating the carbon dioxide and dimethyl ether-containing low boiler stream (VII) by distillation from the degassed crude methanol stream (VI) from step (c) in a distillation apparatus to obtain a methanol and water-enriched bottoms stream (VIII);
(e) optionally separating the water-containing high boiler stream (IX) from the bottoms stream (VIII) from step (d) in a further distillation apparatus and obtaining methanol by distillation as stream (X). Since anhydrous methanol is not required, step (e) can also be omitted.

The methanol and water-enriched bottoms stream (VIII), or in some cases the pure methanol stream (X), can be used in the process of the present invention.

The medium-pressure vapor stream used according to the present invention in step G) of the propylene preparation preferably originates from a synthesis gas production unit in step (a) of the methanol preparation and/or from a methanol synthesis unit in step (b) of the methanol preparation.

The process for preparing methanol preferably comprises the following steps:
(f) feeding the valuable carbon monoxide, carbon dioxide, dimethyl ether and methane components in stream (IV) and at least one of the two streams (V) and (VII) to a combustion unit in which they are combusted with a supply of oxygen gas (XI) having an oxygen content of between 30% and 100% by volume to form a carbon dioxide-containing flue gas (XII);
(g) separating the carbon dioxide enriched stream (XIV) from the carbon dioxide containing flue gas (XII) from step (f) in a carbon dioxide recovery unit to form an off-gas stream (XIII);
(h) recycling the carbon dioxide enriched stream (XIV) separated in the carbon dioxide recovery unit of step (g) to the synthesis gas production unit of step (a) and/or the methanol synthesis unit of step (b).

Such a process, including steps (f), (g) and (h), is described in WO 2020/048809.

The medium pressure vapor stream used in step G) of the preparation of C ₂ -C ₄ olefins preferably originates from a synthesis gas production unit in step (a) of the methanol preparation and/or from a methanol synthesis unit in step (b) of the methanol preparation.

The synthesis gas-producing feedstocks that can be used in this process are a wide variety of different carbonaceous feedstocks, regardless of their chemical nature, whether they are in solid, liquid, or gaseous form. For example, synthesis gas can be produced using coal or hydrocarbons and compounds containing carbon and hydrogen. Preferred carbonaceous feedstocks include natural gas, biogas, coal, wood, plastics, mineral oil, bionaphtha, or carbonaceous streams from mineral oil or natural gas processing, chemical production processes, renewable raw materials, or plastic recycling. In the case of coal or wood, synthesis gas is produced, for example, by a gasification process, also known as coal gasification or wood gasification. Suitable feedstocks from mineral oil or natural gas processing are, for example, naphtha, LPG, gasoline, heavy oil, or vacuum residue. Carbonaceous streams from chemical production processes, for example, carbonaceous streams obtained as by-products and not intended for purely thermal use, can also be used as feedstocks for synthesis gas production.

The use of a methane-containing stream is particularly preferred, and the use of natural gas or biogas is very particularly preferred. As with a synthesis gas production unit, it is possible and even advantageous here to supply carbon dioxide present in natural gas, in particular biogas.

In the synthesis gas production unit, synthesis gas (II) containing carbon monoxide, carbon dioxide, and hydrogen is first produced from the hydrocarbon feedstock (I). Natural gas typically contains 75% to 100% by volume of methane. Substances associated with methane include the higher hydrocarbons ethane, propane, and butane, among others, but also ethene. Biogas typically contains 40% to 75% by volume of methane, and accompanying substances essentially carbon dioxide, water, nitrogen, and oxygen.

Typically, synthesis gas (II) is produced by production methods customarily used on an industrial scale, although the nature of the carbonaceous feedstock (I) also plays a role here. In the case of methane-containing feedstocks, such as natural gas or biogas, 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.

A particular advantage of partial oxidation is that no separate fuel gas supply is required to the synthesis gas production unit, and therefore no carbon dioxide-containing flue gas is formed. In partial oxidation, the energy required to produce synthesis gas is obtained directly by partial oxidation from a methane-containing feedstock, 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 the partial oxidation must be cooled. This is accomplished by a heat exchanger using water as the cooling medium. This evaporates and superheats the water, forming high-pressure steam (p = 100-130 bar, T = 300-450°C). This high-pressure steam can be expanded to the required pressure and temperature levels of medium-pressure steam, ranging from 150-250°C and 5-17 bar. Alternatively, heat removal from the methanol synthesis reactor produces superheated steam in the pressure range of 5-17 bar.

The synthesis gas (II) produced contains carbon monoxide, carbon dioxide, and hydrogen, the total concentration of which is typically 50% to 100% by volume, preferably 80% by volume or more, and more preferably 90% by volume or more. Possible accompanying substances include, in particular, unconverted components of the carbonaceous feedstock used and by-products from its conversion, such as nitrogen, argon, water, or methane. Typically, synthesis gas (II) contains, in addition to carbon monoxide, carbon dioxide, and hydrogen, methane as a result of its preparation, as well as nitrogen and argon introduced, for example, by the use of air in synthesis gas production.

The conversion of synthesis gas (II) is carried out in a methanol synthesis unit in the presence of a methanol synthesis catalyst at temperatures of 150-300°C and pressures of 5-10 MPa abs. For this purpose, synthesis gas (II) is typically compressed to the desired pressure by a compressor and converted in a reactor under specified conditions.

The conversion is preferably carried out at a temperature of 170°C or higher, more preferably 190°C or higher, and preferably 280°C or lower, more preferably 260°C or lower. The conversion is preferably carried out at a pressure of 6 MPa abs or higher, preferably 9 MPa abs or higher.

The reactor used can, in principle, be any reactor suitable for the exothermic conversion of synthesis gas to methanol under the specified process conditions. Reactors for synthesizing methanol from synthesis gas are common knowledge to those skilled in the art. Examples include adiabatic and quasi-isothermal reactors, variobar reactors, and so-called double-walled superconverters, as 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.

Methanol synthesis catalysts are common knowledge to those skilled in the art. Examples include heterogeneous catalysts containing copper and zinc. Typically, these also contain additional elements, such as aluminum, rare earths, or chromium.

Conversion of synthesis gas (II), which contains carbon monoxide, carbon dioxide, and hydrogen, forms methanol and water.

A typical by-product formed is dimethyl ether. Furthermore, complete hydrogenation of carbon monoxide or carbon dioxide also produces methane as a further by-product. The reaction mixture produced in the reactor therefore contains methanol, water, dimethyl ether, carbon monoxide, carbon dioxide, hydrogen, and methane. However, under the reaction conditions mentioned, further by-products are typically also formed, such as methyl formate, acetic acid, higher alcohols with more than two carbon atoms, esters and ethers with more than two carbon atoms, and paraffins.

To separate the complex reaction mixture, the methanol- and water-enriched crude methanol stream (III) is first condensed. For this purpose, the reaction mixture produced in the reactor is typically fed to a condenser. The condenser used can be any device known to those skilled in the art that is suitable for obtaining a methanol- and water-enriched condensate by controlled cooling under these 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 methanol- and water-enriched crude methanol stream (III) still contains dissolved gases, such as hydrogen, carbon monoxide, carbon dioxide, dimethyl ether, methane, and components with higher boiling points than methanol. The condensed crude methanol stream (III) is then discharged from the methanol synthesis unit and directed to step (c) for further workup.

The uncondensed gas stream contains, among other things, unconverted carbon monoxide, carbon dioxide, and hydrogen feedstock, as well as methane. To achieve high partial pressures of the synthesis gas components, a portion of the hydrogen, carbon monoxide, and carbon dioxide uncondensed gas stream is typically vented. If necessary, this vented gas stream is sent to a hydrogen removal facility to increase the hydrogen partial pressure in the reactor. High hydrogen partial pressure in the reactor reduces the formation of secondary components and, in particular, inhibits the Fischer-Tropsch reaction. The majority of the uncondensed gas stream is recycled to the methanol synthesis unit as cycle gas and directed over a methanol synthesis catalyst to maximize utilization of the synthesis gas and, therefore, achieve a high methanol yield.

The methanol synthesis unit of step (b) therefore advantageously comprises 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 conduit for recycling the uncondensed gas to the reactor.

The uncondensed gas stream not recycled as synthesis cycle gas is discharged from the methanol synthesis unit as gas stream (IV) and optionally conducted to step (f).

In step (c) of the process, the crude methanol stream (III) condensed in step (b) and discharged from the methanol synthesis unit is expanded in an expansion unit to a pressure of 0.1 to 2 MPa abs to obtain an expanded gas (V) containing carbon dioxide and methane and a degassed crude methanol stream (VI) enriched in methanol and water. The expansion is typically carried out in a device capable of efficiently separating the gas and liquid phases from each other. Typically, this device is a liquid separator. Devices suitable for this purpose are known to those skilled in the art.

Expansion is preferably carried out to a pressure of at least 0.2 MPa abs, more preferably at least 0.4 MPa abs, and preferably at most 1.5 MPa abs, more preferably at most 1 MPa abs. Generally, the temperature of the expanded mixture is 0 to 150°C, preferably at least 10°C, more preferably at least 20°C, and preferably at most 120°C, more preferably at most 60°C.

The degassed crude methanol stream (VI) is further enriched in methanol and water, but also contains further components depending on the solubility and vapor pressure of the components present in the crude methanol stream (III), such as gases dissolved therein, such as hydrogen, carbon monoxide, carbon dioxide, dimethyl ether, methane, or components with a higher boiling point than methanol.

The expansion gas (V), which comprises carbon dioxide and methane, is preferably conducted to step (f). However, alternatively, the expansion gas (V) may also be discharged from the methanol synthesis plant and, for example, utilized thermally or disposed of in some other way. However, its utilization within the methanol synthesis plant as a feed stream to the combustion unit in step (f) is preferred.

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 boiler stream (VII) containing carbon dioxide and dimethyl ether and a bottoms stream (VIII) concentrated in methanol and water.

The distillation-separated low-boiler stream (VII) mainly contains carbon dioxide and dimethyl ether as the separated low-boiler streams, and, depending on the composition of the degassed crude methanol stream (VI), further low-boiler streams, such as methane, and, depending on the separation performance and operating mode of the distillation apparatus, methanol or components with higher boiling points than methanol, such as water. The low-boiler stream (VII) containing carbon dioxide and dimethyl ether is also preferably conducted to step (f). If the expanded gas (V) is conducted to the combustion unit of step (f) and thus directly reused in the methanol synthesis plant, the low-boiler stream (VII) may instead be discharged from the methanol synthesis plant and, for example, utilized thermally or disposed of in some other way. However, its use in the methanol synthesis plant as a feed stream to the combustion unit in step (f) is preferred.

The methanol and water-enriched bottoms stream (VIII) also contains further components with a boiling point higher than methanol, such as by-products from the methanol synthesis with a boiling point higher than methanol, such as acetic acid, higher alcohols, higher esters, higher ethers or paraffins.

Finally, in step (e), the water-containing high boiler stream (IX) is separated from the bottoms stream (VIII) obtained in step (d) in a further distillation apparatus to obtain methanol, which is obtained by distillation as stream (X).

The high boiler stream (IX) contains water and also further components with a boiling point higher than methanol, such as by-products from methanol synthesis with a boiling point higher than methanol, such as acetic acid, higher alcohols, higher esters, higher ethers or paraffins. This stream can be sent, for example, to wastewater treatment.

Via stream (X), methanol can be obtained with a high purity of at least 95% by weight, preferably at least 98% by weight, more preferably at least 99% by weight. Concomitant substances include residual amounts of low- and high-boiler matter that have not been completely removed by distillation, especially water, as well as very small amounts of ethanol, esters, and ethers.

In the stepwise workup 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 primarily to physically recycle the carbon in these valuable components for the further synthesis of methanol, while simultaneously avoiding carbon dioxide emissions. Additional process steps (f), (g), and (h) make it possible to recycle the carbon in the valuable components, particularly for the further synthesis of methanol, i.e., to produce further valuable products while simultaneously avoiding carbon dioxide emissions from the methanol synthesis. Steps (f), (g), and (h) are described in detail in WO 2020/048809.

The present invention is explained in more detail with reference to Figures 1 to 10.

FIG. 1 shows a non-inventive procedure in which burner 4 is used to heat feed stream B and DME-containing side stream A-2 is fed to individual trays of reactor 2 after cooling in heat exchanger HE8 to cool reactor 2. FIG. 1 shows a procedure of the invention in which the DME-containing side stream A-2 is fed to the individual trays of the olefin fixed-bed reactor 2 after being cooled in the heat exchanger HE8 to cool the reactor 2. 1 shows a procedure according to the invention in which the DME-containing side stream A-2 is fed to the individual trays of the olefin fixed-bed reactor 2 after being cooled in the heat exchanger HE8 in order to cool the reactor 2. At the same time, the electrical heat exchanger EH1 is used to increase the temperature difference within the device HE4 and thus significantly reduce the heat transfer area. FIG. 1 shows a non-inventive procedure in which burner 4 is used to heat feed stream B, and DME-containing side stream A-2 is fed to individual trays of olefin fixed-bed reactor 2 without cooling, operating reactor 2 isothermally. FIG. 1 illustrates a procedure of the present invention in which the DME-containing side stream A-2 is fed without cooling to the individual trays of the olefin fixed-bed reactor 2, which is operated isothermally. 1 shows a diagram of the inventive procedure in which the DME-containing side stream A-2 is fed without cooling to the individual trays of the olefin fixed-bed reactor 2, operating the reactor 2 isothermally. At the same time, the electrical heat exchanger EH1 is used to increase the temperature difference within the device HE4 and thus significantly reduce the heat transfer surface area. FIG. 1 shows a non-inventive procedure in which burner 4 is used to heat feed stream B and methanol side stream A1-2 is fed to individual trays of olefin fixed bed reactor 2 to cool reactor 2. FIG. 1 illustrates a procedure of the present invention in which a methanol side stream A1-2 is fed to individual trays of an olefin fixed bed reactor 2 to cool the reactor 2. 1 shows a diagram of the inventive procedure in which a methanol side stream A1-2 is fed to the individual trays of the olefin fixed-bed reactor 2 in order to cool the reactor 2. At the same time, an electrical heat exchanger EH1 is used to increase the temperature difference within the device HE4 and thus significantly reduce the heat transfer surface area. FIG. 1 shows a non-inventive procedure in which a DME pre-reactor is not used, burner 4 is used to heat feed stream B, and DME side stream A-2 is fed to individual trays of olefin fixed bed reactor 2 to cool reactor 2. FIG. 1 shows a procedure of the present invention in which a DME pre-reactor is not used and DME side stream A-2 is fed to individual trays of olefin fixed bed reactor 2 to cool reactor 2. 1 shows a diagram of the inventive procedure without a DME pre-reactor, in which DME side stream A-2 is fed to the individual trays of olefin fixed-bed reactor 2 to cool reactor 2. At the same time, an electrical heat exchanger EH1 is used to increase the temperature difference within unit HE4 and thus significantly reduce the heat transfer surface area. FIG. 1 shows a non-inventive procedure in which no DME pre-reactor is used, burner 4 is used to heat feed stream B, DME side stream A-2 is fed to individual trays of olefin fixed bed reactor 2, and reactor 2 isothermally operated. FIG. 1 shows a procedure of the present invention in which a DME pre-reactor is not used, DME side stream A-2 is fed to individual trays of olefin fixed bed reactor 2, and reactor 2 is operated isothermally. 1 shows a diagram of the inventive procedure without a DME pre-reactor, in which DME side stream A-2 is fed to the individual trays of olefin fixed-bed reactor 2, operating reactor 2 isothermally. At the same time, electrical heat exchanger EH1 is used to increase the temperature difference within unit HE4 and thus significantly reduce the heat transfer surface area.

EXAMPLES As an example, the heat flows Q1 to Q11 were calculated according to the procedures of Figures 1 to 15 to produce 60 t/h of propylene while minimizing the production of ethylene and butylene.

The results are summarized in the table below.

1 DME pre-reactor
2. Olefin fixed bed reactor
3. Rapid cooling of produced gas
4 Burner
5 Product separation section
6. Compressor
HE1~HE9 Heat exchanger
EH1 Electric Heat Exchanger
A1 methanol-containing stream
A1-1, A1-2 A1 sidestream
A DME-containing stream
A-1, A-2 A sidestream
B. Feed stream to olefin fixed bed reactor containing DME, recycled hydrocarbons and steam
D Product gas stream from olefin fixed bed reactor
F hydrocarbon-containing product gas stream
G1, G2, G3 water flow
H1 Hydrocarbon recycle stream
K quenching water circulation flow
P Product hydrocarbons
W wastewater stream
Q1～Q12 Heat flow

Claims (13)

A process for preparing _C2 - _C4 olefins from dimethyl ether with or without methanol, comprising:
A) providing a stream A comprising dimethyl ether;
B) mixing at least a portion of stream A with at least one hydrocarbon recycle stream R comprising C ₂ -C ₆ hydrocarbons and with a steam stream G2 to obtain a feed stream B;
C) heating feed stream B in one or more heat exchangers to a temperature in the range of 430-500°C and feeding it to an olefin fixed bed reactor, said heating may also precede said mixing of the individual sub-streams to give feed stream B of step B);
D) catalytically converting feed stream B to a product gas stream D comprising _C2 - _C4 olefins, additional _C2 - _C6 hydrocarbons, methanol and water vapor at a temperature in the range of 430-520°C;
E) cooling product gas stream D to a temperature in the range of 170-220°C by heat exchange with feed gas stream B in one or more heat exchangers; F) further cooling product gas stream D to a temperature in the range of 35-65°C by contacting it with at least one water-containing quench recycle stream K to condense water and methanol to obtain a water- and methanol-depleted hydrocarbon product gas stream F;
G) separating at least one sub-stream G1 of said at least one water-containing quench recycle stream K, heating and evaporating said sub-stream G1 in one or more heat exchangers by heat exchange with medium pressure steam or by electrical heating to obtain a vapor stream G2, which is fed to step B);
H) separating one or more product streams P comprising _C2 - _C4 olefins from the hydrocarbon product gas stream F to obtain at least one hydrocarbon recycle stream R comprising _C2 - _C6 hydrocarbons, which is recycled to step B). The process of claim 1, wherein the second feed gas stream B is heated in step C) without using additional heat generated by combustion of a fossil energy carrier. The process of claim 2, wherein the second feed gas stream B is heated in step C) in part by an electric heat exchanger. The process described in any one of claims 1 to 3, wherein 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. The process of any one of claims 1 to 4, wherein the medium-pressure vapor stream is generated in methanol synthesis upstream of step A) and/or synthesis gas preparation upstream of the methanol synthesis. The process of any one of claims 1 to 5, wherein the water-containing quench recycle substream G1 is further heated and evaporated in step G) by heat exchange with product gas stream D. The process of any one of claims 1 to 6, wherein the water-containing quench recycle substream G1 is heated in step G) by heat exchange with medium-pressure steam to an extent of at least 50%, based on the amount of heat supplied. 8. The process of any one of claims 1 to 7, wherein the hydrocarbon recycle stream H1 comprising _C2 to _C6 hydrocarbons is further heated by heat exchange with medium pressure steam. Step H)
H1) compressing the hydrocarbon product gas stream F to obtain a liquid hydrocarbon stream H11 comprising propylene and _C4 , _C5 and _C6 ⁺ hydrocarbons, and an ethane, ethene and propylene containing gaseous hydrocarbon stream H12;
H2) separating water from said liquid hydrocarbon stream H11 by phase separation to obtain a liquid hydrocarbon stream H21;
H3) separating a propylene-containing stream H31 from said liquid hydrocarbon stream H21 to obtain a stream H32 containing _C4 , _C5 and _C6 ⁺ hydrocarbons; or separating a stream H31 containing propylene and _C4 hydrocarbons to obtain a stream H32 containing _C4 , _C5 and _C6 ⁺ hydrocarbons; H4) separating a stream H41 containing _C6 ^{+ hydrocarbons from said stream H32 containing C4, C5 and C6+} _{hydrocarbons to obtain} ^a stream H42 containing _C4 , _C5 and _C6 hydrocarbons, wherein stream H41 optionally contains aromatic _C6 hydrocarbons and stream H42 contains aliphatic _C6 hydrocarbons;
H5) separating a propylene-containing stream H51 from said ethane-, ethene- and propylene-containing gaseous hydrocarbon stream H12 to obtain an ethane- and ethene-containing stream H52;
H6) separating a butene-containing stream H61 from the _C4 , _C5 and _C6 hydrocarbon-containing stream H42 to obtain a _C5 and _C6 hydrocarbon-containing stream H62; and/or separating a propylene-containing stream H63 from the stream H31 to obtain a butene-containing stream H64;
H7) obtaining at least one recycle stream R from _one or more of the streams selected from stream H42 comprising C4, _C5 and _C6 hydrocarbons, stream H62 comprising _C5 and _C6 hydrocarbons, said propylene-containing stream H31, said propylene-containing stream H51, said propylene-containing stream H63, stream H61 comprising butenes, stream H64 comprising butenes, and said ethane- and ethene-containing stream H52. The process of any one of claims 1 to 9, wherein step A) comprises feeding a methanol-containing feed stream A1 to a dimethyl ether fixed-bed reactor for catalytic conversion of the methanol to dimethyl ether to obtain a product stream A comprising dimethyl ether, methanol, and water vapor. The methanol provided in step A)
(a) producing a synthesis gas (II) comprising carbon monoxide, carbon dioxide and hydrogen from a hydrocarbonaceous feedstock (I) in a synthesis gas production unit;
(b) feeding the synthesis gas (II) from step (a) to a methanol synthesis unit and converting it into a reaction mixture containing methanol, water, carbon monoxide, carbon dioxide, hydrogen, dimethyl ether and methane in the presence of a methanol synthesis catalyst at a temperature of 150-300°C and a pressure of 5-10 MPa abs, condensing a crude methanol stream (III) enriched in methanol and water from the reaction mixture, and leading the crude methanol stream (III) and a gas stream (IV) containing carbon monoxide, carbon dioxide, hydrogen and methane from the methanol synthesis unit;
(c) expanding the crude methanol stream (III) from step (b) in an expansion unit to a pressure of 0.1-2 MPa abs to obtain an expanded gas (V) comprising carbon dioxide and methane and a degassed crude methanol stream (VI) enriched in methanol and water;
(d) separating a carbon dioxide and dimethyl ether-containing low boiler stream (VII) by distillation from said degassed crude methanol stream (VI) from step (d) in a distillation apparatus to obtain a methanol and water-enriched bottoms stream (VIII);
and (e) optionally separating, in a further distillation apparatus, a water-containing high boiler stream (IX) from the bottoms stream (VIII) from step (d) and obtaining methanol by distillation as stream (X). The methanol preparation comprises steps (f) to (h):
(f) feeding stream (IV) and the valuable carbon monoxide, carbon dioxide, dimethyl ether and methane components in at least one of said two streams (V) and (VII) to a combustion unit in which they are combusted with a supply of oxygen gas (XI) having an oxygen content of between 30% and 100% by volume to form a carbon dioxide-containing flue gas (XII);
(g) separating a carbon dioxide enriched stream (XIV) from said carbon dioxide containing flue gas (XII) from step (f) in a carbon dioxide recovery unit to form an off-gas stream (XIII);
12. The process of claim 11, further comprising the step of: (h) recycling the carbon dioxide enriched stream (XIV) separated in the carbon dioxide recovery unit of step (g) to the synthesis gas production unit of step (a) and/or the methanol synthesis unit of step (b). 13. The process according to claim ₁₁ or 12, wherein the medium-pressure vapor stream used in step G) of the preparation of C2 to _C4 olefins originates from the synthesis gas production unit of step (a) of the methanol preparation and/or from the methanol synthesis unit of step (b) of the methanol preparation.