Process and installation for producing methanol

Abstract

The invention relates to a method (100, 200) for producing methanol, having the steps of purifying a raw carbon dioxide flow (103) in order to obtain a pure carbon dioxide flow (104), feeding the pure carbon dioxide flow (104) into a methanol synthesis circuit, and discharging a raw methanol flow (111) from the methanol synthesis circuit, the step of purifying the raw carbon dioxide flow (103) being carried out absorptively and using the raw methanol flow (111) or a portion (111a) thereof as an absorption liquid. The invention also relates to a corresponding installation.

Description

[0001] Description

[0002] Process and plant for the production of methanol

[0003] Area

[0004] The present disclosure relates to a process for the production of methanol and a corresponding plant.

[0005] background

[0006] To date, the production of methanol and derivatives such as dimethyl ether is mostly based on the reaction of synthesis gas, which contains carbon monoxide and hydrogen, in a so-called methanol synthesis cycle. The synthesis gas, a mixture of hydrogen and carbon oxides, is typically obtained in conventional processes from fossil carbon-containing raw materials such as natural gas or coal through steam reforming or partial oxidation, releasing carbon dioxide.

[0007] To limit the extent of global climate change caused by carbon dioxide emissions, the use of carbon dioxide as a carbon source for methanol production has been proposed. The carbon dioxide can be mixed with hydrogen, obtained, for example, through the electrolysis of water, to form synthesis gas.

[0008] Overview

[0009] Against this background, a process for the production of methanol and a corresponding plant with the features of the independent claims are proposed. Embodiments are the subject of the dependent claims and the following description.

[0010] The proposed process for the production of methanol comprises the purification of a crude carbon dioxide stream to obtain a pure carbon dioxide stream, the feeding of the pure carbon dioxide stream into a methanol synthesis cycle and the discharge of a crude methanol stream from the methanol synthesis cycle, wherein the purification of the crude carbon dioxide stream is carried out absorptively and using the crude methanol stream or a portion thereof as the absorption liquid.

[0011] In the proposed process, the raw carbon dioxide stream is purified, particularly with regard to certain components that are detrimental to methanol synthesis, using raw methanol, specifically in a scrubbing column. Compared to water, for example, raw methanol has a higher capacity to absorb such substances. The raw methanol, now loaded with the components separated from the raw carbon dioxide stream during scrubbing, is fed into a methanol processing unit. There, it enters a topping column to remove dissolved gases and low-boiling components, which are then extracted as so-called light ends or purge gas, for example, to be used as fuel gas. Further advantages are explained below in connection with specific embodiments.

[0012] In certain embodiments of the proposed process, the scrubbing column used to purify the raw carbon dioxide stream is operated at a pressure between 5 and 35 bar. However, it is also possible to carry out the purification at a higher pressure, for example between 50 and 100 bar, corresponding to the pressure at which the methanol synthesis cycle is operated. This variant has the advantage that the resulting pure carbon dioxide stream can be fed into the methanol synthesis cycle without further compression.

[0013] In certain embodiments of the proposed process, the crude methanol contains a portion composed of water and methanol, which in turn comprises 45 to 95 mol% methanol and the remainder water. The methanol and water content is determined by the composition of the feedstock, in particular by the ratio of carbon dioxide to carbon monoxide. It is understood that the crude methanol may also contain a portion not composed of water and methanol, comprising certain impurities. Such crude methanol exhibits a particularly good capacity for absorbing the components to be separated from the crude carbon dioxide stream.In certain embodiments of the proposed process, the portion of the crude methanol stream used for purifying the crude carbon dioxide stream is fed, together with the portion of crude methanol not used for purification, into a methanol purification process that is commonly used in the industry and known from the prior art for obtaining pure methanol. Here, the components absorbed from the crude carbon dioxide stream can be removed again without additional effort.

[0014] In certain embodiments of the proposed process, methanol purification is carried out using at least two purification columns, the first of which is used to remove lighter components, including those absorbed from the crude carbon dioxide. However, in principle, all known processes for purifying crude methanol to pure methanol can be used.

[0015] In certain embodiments of the proposed process, it is provided that a first portion of the crude methanol stream is used for purifying the crude carbon dioxide stream, and carbon dioxide is driven off from a second portion of the crude ethanol stream using hydrogen, with the driven-off carbon dioxide or a part thereof being returned to the methanol synthesis cycle.

[0016] In certain embodiments of the proposed process, the methanol synthesis cycle includes a methanol synthesis reactor from which a product stream containing methanol, water, and carbon dioxide is extracted. It is understood that the product stream also includes, for example, carbon monoxide and other components such as inert materials and byproducts of methanol synthesis. The product stream is subjected to partial condensation, yielding the crude methanol stream and a recycled stream.

[0017] The methanol synthesis cycle is operated at the aforementioned pressure level and can be constructed in a manner known per se.

[0018] In certain embodiments of the proposed process, the methanol synthesis reactor is designed as an isothermal reactor comprising a catalyst bed in which wound steam generation tubes are arranged. These steam generation tubes are supplied with boiler feedwater, and steam, particularly saturated steam, is generated by means of the steam generation tubes. The methanol synthesis reactor can, in particular, be designed as a so-called Linde isothermal reactor, as described in the literature.

[0019] As described, for example, in Lembeck, M., “Linde isothermal reactor for methanol synthesis”, Linde Reports from Technology and Science, Volume 58, pages 5 to 8, such a reactor has an arrangement with wound steam generation tubes housed in a fixed-bed catalyst. The feedwater passed through the interior of these tubes is converted to medium-pressure steam and thereby absorbs the heat of reaction released during the exothermic methanol synthesis, thus enabling an isothermal process.

[0020] In certain embodiments of the proposed process, the recycled stream, or a portion thereof, is combined with carbon dioxide from the pure carbon dioxide stream and hydrogen, compressed, heated, and fed back into the methanol synthesis reactor. This closes the synthesis cycle.

[0021] In certain embodiments of the proposed process, the methanol synthesis reactor is operated using a catalyst containing copper, zinc oxide, and aluminum oxide. Such catalysts particularly benefit from carbon dioxide purification.

[0022] In certain embodiments of the proposed process, the purification of the crude carbon dioxide stream is carried out in such a way that the content of at least one sulfur-containing compound and / or at least one nitrogen-containing compound and / or at least one halogen compound and / or hydrogen cyanide in the purified carbon dioxide stream is below a predetermined threshold. In particular, this may involve adjusting the proportion of the crude methanol stream used for purifying the crude carbon dioxide stream.

[0023] In certain embodiments of the proposed process, it is provided that oxygen-containing raw hydrogen is subjected to oxygen removal using a catalytic purification unit in order to obtain hydrogen for introduction into the methanol synthesis cycle.

[0024] The proposed plant for the production of methanol is designed to purify a raw carbon dioxide stream to obtain a pure carbon dioxide stream, to feed the pure carbon dioxide stream into a methanol synthesis cycle, and to discharge a raw methanol stream from the methanol synthesis cycle, wherein the purification of the raw carbon dioxide stream is carried out absorptively and using the raw methanol stream or a portion thereof as the absorption liquid.

[0025] For further features and advantages of a corresponding system and its embodiments, reference is expressly made to the above explanations concerning the method proposed according to the invention and its embodiments, since these apply in the same way.

[0026] The same applies to a system which, according to an embodiment of the invention, is equipped to carry out a process according to any embodiment of the present invention.

[0027] Drawings

[0028] Exemplary embodiments of the solutions proposed here are described below with reference to the attached drawing, wherein

[0029] Figure 1 illustrates a comparison procedure;

[0030] Figure 2 illustrates a method according to one embodiment; and

[0031] Figure 3 illustrates a method according to one embodiment.

[0032] Designs

[0033] The embodiments and configurations described below are provided solely to assist the reader in understanding the claimed and previously explained features. They represent only representative examples and are not intended to be considered exhaustive or limiting with regard to the features of the proposed methods and devices.

[0034] All percentages used here may refer to molar, quantity, or volume fractions. Unless otherwise stated, pressure values ​​in bar are to be understood as absolute pressures.

[0035] When referring to a "part" of a material stream, this can mean a fraction with the same composition that has simply been diverted from an original stream, but also a fraction with a different composition and possibly only a component of the original stream that is formed by a process such as condensation, evaporation, boiling, distillation, rectification, absorption, adsorption, flash filtration, membrane separation, deposition, or the like, or that remains as a residue after a corresponding step. A "part" can also exist after a combination of any of the aforementioned steps, for example, after separation processing of a diverted fraction.

[0036] There are essentially two main pathways for the production of methanol from carbon dioxide:

[0037] The first pathway can be described as the direct hydrogenation of carbon dioxide, whereby carbon dioxide is fed into the methanol synthesis cycle along with a hydrogen-containing co-injection. The overall reaction that takes place in such a cycle can be described by the reaction equation (1) given below.

[0038] CO2 + 3 H2CH3OH + H2O (1)

[0039] The second approach involves carbon dioxide electrolysis or co-electrolysis, by which at least some of the carbon dioxide input is converted to carbon monoxide, which is then fed into a cycle similar to the conventional methanol synthesis cycle. The overall reaction in the electrochemical conversion of carbon dioxide to carbon monoxide can be described by the reaction equation (2) given below.

[0040] CO + 2 H2CH3OH (2)

[0041] Regardless of whether the direct hydrogenation of carbon dioxide according to reaction equation (1) or a carbon monoxide-based process according to reaction equation (2) is used, the general design of a corresponding cycle can be described as follows, where the designs proposed here relate to the variant according to reaction equation (1).

[0042] The respective feed streams are combined and compressed to a pressure of typically 50–100 bar. Depending on the origin of the feed materials, the different feed streams can be compressed separately or after combination. A correspondingly formed combined feed stream is then blended with a recycled material stream, preheated, and reacted in one or more catalyst beds. The resulting product stream is cooled, the main reaction products are at least partially condensed and removed from the cycle, and the gaseous reactants are at least partially transferred to the aforementioned recycled material stream. The liquid reaction products are purified, typically in one or more distillation columns.

[0043] The carbon dioxide used in these processes can originate from various sources. For example, it can be separated from flue gases, synthesis gases, or gases of biogenic origin. The carbon dioxide can therefore contain a wide variety of impurities. As mentioned, the hydrogen can come from any source, but especially from water electrolysis of any type.

[0044] Hydrogen and carbon dioxide can therefore be mixed after suitable purification and fed as makeup gas into the methanol synthesis cycle upstream of a synthesis reactor equipped with a suitable catalyst. The catalyst can, in particular, contain the components copper, zinc oxide, and aluminum oxide (Cu-ZnO-AhOs). A portion of the components fed into the synthesis reactor reacts within the reactor to form methanol. By cooling a mixture of components at the reactor outlet, the condensable components can be separated as crude methanol. The liquid crude methanol consists primarily of methanol and water, as well as, in small concentrations, byproducts of methanol synthesis such as higher alcohols, dimethyl ether, methyl formates, and ketones, and in small amounts of dissolved gases, primarily carbon dioxide, carbon monoxide, and hydrogen.

[0045] Unreacted hydrogen and carbon dioxide, as well as any carbon monoxide formed, remain primarily in the gas phase. These are separated in a separator, mixed with makeup gas, and returned to the synthesis reactor. The crude methanol then undergoes purification to remove light and heavy components and water. This purification typically occurs through a single- or multi-stage distillation process.

[0046] The aforementioned catalysts, which may also contain other components, are characterized by the fact that a number of compounds can act as catalyst poisons when certain concentrations are exceeded. Catalyst poisons lead, in particular, to a more rapid deactivation of the catalyst. The permissible concentrations of such compounds differ between catalyst manufacturers and can be found in the respective specifications. A makeup gas, for example, can contain water, oxygen, hydrogen, carbon monoxide, ethylene, and unsaturated hydrocarbons, as well as sulfur compounds such as hydrogen sulfide, sulfur oxides and organic sulfur species, chlorine, halogens, halogenated compounds, hydrogen cyanide, nitrogen oxides, ammonia, amines, alkali metals, silicon species, and heavy metals, with at least some of these compounds potentially acting as catalyst poisons.

[0047] Among other things, sulfur-containing compounds adsorb onto the copper surface and block it. Therefore, these must be removed to very low concentrations (typically less than 0.1 ppmv, i.e., parts per million by volume). Nitrogen-containing compounds (ammonia, amines, nitrogen oxides) also act as catalyst poisons. Furthermore, the presence of these compounds on the catalyst leads to the formation of trimethamine, which negatively affects methanol quality due to its strong odor. Hydrogen cyanide is sometimes considered non-critical for synthesis catalysts, depending on the type of catalyst used. Nevertheless, some catalyst manufacturers classify hydrogen cyanide as a low-specification catalyst poison (free or less than 0.1 ppmv). The hydrogen used is usually very pure, with only oxygen (and possibly...) present.Potassium hydroxide (due to alkaline electrolysis) must be removed, which is done for oxygen in a purification step downstream of the electrolysis by catalytic conversion (so-called DeOxo reactor).

[0048] Depending on the source and separation process, the carbon dioxide used may contain one or a combination of the above-mentioned impurities, which necessitate a purification process.

[0049] Typical cleaning methods by which the above-mentioned components can be removed are given in Table 2 below, but are not intended to limit the present invention in any way:

[0050] Table 2 The proposed designs are based on the understanding that the purification of carbon dioxide, particularly with regard to sulfur components (sulfur oxides, hydrogen sulfide, organic sulfur such as mercaptans and thiophenes), ammonia, amines, nitrogen oxides, hydrogen cyanide, and higher hydrocarbons, can be achieved by using crude methanol downstream of a high-pressure separator in a carbon dioxide scrubbing column. Methanol has a higher absorption capacity for these substances compared to water scrubbing.

[0051] The crude methanol is then fed into the so-called topping column, as in the standard process, where dissolved gases and low-boiling components are removed and can be used as so-called light ends or purge gas, for example as fuel gas.

[0052] The carbon dioxide can be brought into contact with the crude methanol separator, particularly under elevated pressure (approximately 5 to 30 bar). This can be done in a washing column, which, depending on the required amount of detergent, is designed as a packed column or a tray column, sometimes requiring only a few theoretical separation stages (for example, 4 to 15).

[0053] A particular advantage is that the crude methanol exhibits increased solubility towards the target impurities, allowing for their removal more effectively than in a water wash. This solubility is increased, for example, by a factor of 10 for hydrogen sulfide and by a factor of 7 for sulfur oxides. Table 3 below provides an overview of the assumed concentrations and the corresponding increase in solubility, each at 298 K. The assumed concentrations and target values ​​represent only those in an exemplary feed stream or an assumed maximum concentration in a makeup gas within the methanol synthesis cycle. These values ​​do not limit the invention. The last column indicates the solubility in methanol relative to the assumed solubility in water (1) as a rounded factor. Table 3

[0054] Based on solubilities and simulations, sulfur oxides, organic sulfur, ammonia, amines, hydrogen cyanide, hydrogen chloride, and other hydrogen halides, as well as higher hydrocarbons, can be removed particularly well in the configurations proposed here. Hydrogen sulfide and carbonyl sulfide can be removed to a limited extent, especially when using an increased amount of crude methanol as a detergent. This may result in increased carbon dioxide losses. Nitrogen oxides and oxygen cannot be removed in the proposed configurations.

[0055] Another advantage is the stripping effect of carbon dioxide on the (small) amount of hydrogen dissolved in the crude methanol. This hydrogen can be desorbed and is then available again for methanol synthesis. In the crude methanol separator, the crude methanol is already saturated with carbon dioxide at elevated pressure (for example, 50 to 100 bar absolute pressure), so that, depending on the pressure, less or no further carbon dioxide dissolves in the crude methanol.

[0056] Both aspects are particularly evident from the following Tables 4a and 4b, which show carbon dioxide and methanol losses in an exemplary methanol process for pressures of 30 bar (Table 4a) and 10 bar (Table 4b) in the washing and / or

[0057] Washing column specifications. With Nm 3 / h refers to standard cubic meters per hour.

[0058] Table 4a

[0059] Table 4b

[0060] The washed carbon dioxide can be added to the hydrogen after the washing column and can be brought to synthesis pressure.

[0061] Figure 1 shows a comparison procedure, which is labelled as 90 overall.

[0062] A hydrogen stream 101, which may originate, for example, from an electrolysis process (not shown) and may contain residual amounts of oxygen, is supplied to the comparative process 90. A catalytic oxygen removal unit 1 may be provided to remove the oxygen, from which a correspondingly purified hydrogen stream 102 is extracted.

[0063] A raw carbon dioxide stream 103 is fed into the comparative process 90, which is compressed in a carbon dioxide compressor 2 and purified in a carbon dioxide purification unit 3. A purified carbon dioxide stream 104 is extracted from the carbon dioxide purification unit 3. The purified hydrogen stream 102 and the purified carbon dioxide stream 104 are combined to form a fresh feed stream 105, which is compressed in a fresh feed compressor 4 and can then be fed into the actual methanol synthesis cycle.

[0064] The methanol synthesis cycle comprises a recirculated stream 106, which, after joining with the feedstock stream 105, is compressed as a combined stream 106 in a recirculated compressor 5 and subsequently heated in a feed-effluent heat exchanger 6 before being fed into a methanol synthesis reactor 7. A steam generation unit 8 is associated with the methanol synthesis reactor 7, which is supplied with boiler feedwater 107 and from which saturated steam 108 is extracted. However, this is not essential for the subject matter of the present invention.

[0065] A product stream 109 is drawn from the methanol synthesis reactor 7 and cooled in the feed-effluent heat exchanger 6 and subsequently in a water cooler 9, where it partially condenses. Further cooling stages may also be interposed, such as heat integration to a reboiler of a distillation column, an air cooler, or other forms of heat extraction. A resulting two-phase stream 110 is fed to a separator 10, from the top of which the recirculated stream 106 is extracted in gaseous form, and from the bottom of which a crude methanol stream 111 is drawn off.

[0066] The further treatment of the crude methanol stream 111 is not illustrated separately here and can be carried out in any manner known and suitable from the prior art. A methanol processing unit is schematically represented by 11 as an example of different configurations. In particular, such a methanol processing unit 11 may include a so-called topping column and a so-called refining column. Various material streams 112 are withdrawn from the methanol processing unit 11, which may include, for example, a methanol product stream, a fusel oil stream, a water stream, and a stream containing lighter components.

[0067] Figure 2 illustrates a process according to an embodiment proposed here and is designated 100 in its entirety. The carbon dioxide purification, designated 2 in Figure 1, is carried out here using a crude methanol washing column 20, which is operated with a portion 111a of the crude methanol stream 111 as a washing agent. Further purification steps can be carried out additionally, for example, if the crude methanol washing is insufficient to achieve the required input quality. The washing agent loaded with absorbed components is combined with a portion 111b of the crude methanol stream 111 not used as a washing agent and fed as a combined stream 111c to the methanol processing unit 11.

[0068] Figure 3 illustrates a method according to a further embodiment proposed here and is labelled in its entirety as 200.

[0069] Method 200 is particularly suitable for cases in which only a portion of the crude methanol is required for the removal of catalyst poisons from the crude carbon dioxide stream 103. In this case, the remaining crude methanol can be fed to a hydrogen stripper 30, which can be operated with the hydrogen stream 102 as stripping gas. In this way, carbon dioxide contained in the crude methanol stream 111 or 111b can be at least partially transferred into a headstream 113, which can be recycled as illustrated.

Claims

Patent claims 1. Process (100, 200) for the production of methanol, comprising: Purification of a raw carbon dioxide stream (103) to obtain a pure carbon dioxide stream (104); Feeding the pure carbon dioxide stream (104) into a methanol synthesis cycle; and Extraction of a crude methanol stream (111) from the methanol synthesis cycle; wherein the purification of the crude carbon dioxide stream (103) is carried out absorptively and using the crude methanol stream (111) or a portion (111a) thereof as the absorption liquid.

2. Method (100, 200) according to claim 1, wherein the purification of the raw carbon dioxide stream (103) is carried out at a pressure in a pressure range of 5 to 100 bar.

3. Method (100, 200) according to claim 1 or 2, wherein the crude methanol has a proportion formed by methanol and water, comprising 45 to 95 mol% methanol and water in the remaining residue.

4. Method (100, 200) according to one of the preceding claims, wherein the crude methanol stream (111) or the portion (111a) of the crude methanol stream (111) used for purifying the crude carbon dioxide stream (103) is fed to a methanol processing unit (11) after its use for purifying the crude carbon dioxide stream (103).

5. Method (100, 200) according to one of the preceding claims, wherein the methanol purification is carried out using at least two purification columns.

6. Method (200) according to one of the preceding claims, wherein for purifying the crude carbon dioxide stream (103) a first fraction (111a) of the crude methanol stream (111) is used and carbon dioxide from a second fraction (111b) of the crude methanol stream (111) is extracted using hydrogen. is expelled, with the expelled carbon dioxide or a portion thereof being returned to the methanol synthesis cycle.

7. Method (100, 200) according to one of the preceding claims, wherein the methanol synthesis cycle comprises a methanol synthesis reactor (7) from which a product stream (109) containing methanol, water and carbon dioxide is taken, which is subjected to partial condensation to obtain the crude methanol stream (111) and a recycle stream (106).

8. Method (100, 200) according to claim 7, wherein the methanol synthesis reactor (7) is designed as an isothermal reactor having a catalyst bed in which wound steam generation tubes are arranged, wherein the steam generation tubes are supplied with boiler feedwater, and wherein steam is generated by means of the steam generation tubes.

9. Method (100, 200) according to claim 7 or 8, wherein the recirculated stream (106) or a part thereof is combined with carbon dioxide from the pure carbon dioxide stream (104) and hydrogen, compressed, heated and fed back into the methanol synthesis reactor (7).

10. Method (100, 200) according to claim 7 or 8, wherein the methanol synthesis reactor (7) is operated using a catalyst containing copper, zinc oxide and aluminium oxide.

11. Method (100, 200) according to one of the preceding claims, wherein the purification of the crude carbon dioxide stream (103) is carried out such that the content of the purified carbon dioxide stream (104) of at least one sulfur-containing compound and / or at least one nitrogen-containing compound and / or at least one halogen compound and / or hydrogen cyanide is below a predetermined threshold.

12. Method (100, 200) according to one of the preceding claims, wherein oxygen-containing raw hydrogen (101) is subjected to oxygen removal using a catalytic purification unit (1).

13. Plant for the production of methanol, which is set up to carry out the following steps: Purification of a crude carbon dioxide stream (103) to obtain a pure carbon dioxide stream (104); feeding the pure carbon dioxide stream (104) into a methanol synthesis cycle; and Extraction of a crude methanol stream (111) from the methanol synthesis cycle; wherein the purification of the crude carbon dioxide stream (103) is carried out absorptively and using the crude methanol stream (111) or a portion (111a) thereof as the absorption liquid.

14. System according to claim 13, which is set up to carry out a method according to any one of claims 1 to 12.

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