EA007455B1 - Integrated process for making acetic acid and methanol - Google Patents

Abstract

The present invention provides a plant and a process that produces both methanol and acetic acid under substantially stoichiometric conditions, wherein an unadjusted syngas having an R ratio less than 2.0 is provided (R = [(H- CO)/(CO + CO)]). All or part of the unadjusted syngas is supplied to a separator unit to recover CO, CO and hydrogen. At least a portion of any one or combination of the recovered CO, CO and hydrogen is added to any remaining syngas not so treated or alternatively combines in the absence of any remaining unadjusted syngas to yield an adjusted syngas with an R ratio of 2.0 to 2.9 which is used to produce methanol. Any recovered COnot used to adjust the R ratio of the unadjusted syngas can be supplied to the reformer to enhance CO production. At least a portion of the recovered CO is reacted in the acetic acid reactor with at least a portion of the produced methanol to produce acetic acid or an acetic acid precursor by a conventional process.

Description

The present invention relates generally to a method for producing acetic acid and methanol from synthesis gas.

Prior art

The production of acetic acid from carbon monoxide and methanol using a carbonylation catalyst is well known in the art. Typical examples disclosing this and similar processes include US Pat. Nos. 1961736, issued to Cag1sh e1 a1. (Tepekkee RgokiSk); 3769329, issued in the name of Raiyk e1 a1. (MoikaShaw); 5155261, issued in the name Magyop e1 a1. (Veshu 1iki81pek); 5672743, issued in the name of Cag1aik e1 a1. (VR Sketkak); 5728871, issued in the name of the company e1 a1. (Nakogok Torkoe); 5773642, issued in the name Eepk e1 a1. (Acelech Sysh1e); 5817869, issued in the name Ηίηepatkater e1 a1. (OnStock SNet1sa1 Sogrogayoi); 5877347 and 5877348 issued in the name of OTskhe1 e1 a1. (VR Sketkak); 5883289, issued in the name Eepk e1 a1. (Acelech Syt1e); and 5883295, issued in the name of 8ip1eu e1 a1. (VR Sketkak), which are all included in this description by reference.

The primary raw materials for the production of acetic acid are, of course, carbon monoxide and methanol. In a typical acetic acid plant, methanol is supplied externally, and carbon monoxide, due to the difficulties associated with its transportation and storage, is produced locally, usually by reforming natural gas or another hydrocarbon with steam and / or carbon dioxide. Therefore, attention has recently been focused on the construction of integrated plants producing both methanol and acetic acid. A significant part of the costs of constructing new acetic acid production facilities is accounted for by the capital costs of equipment needed to produce carbon monoxide. It would be highly desirable to substantially eliminate or reduce such capital expenditures.

Market conditions in different regions from time to time can lead to the formation of relatively low methanol prices (excess demand) and / or high prices for natural gas (deficit), which can make methanol production unprofitable. Owners of existing methanol production facilities may be faced with the need to decide whether to continue or terminate unprofitable methanol production in the hope of a gradual return of product prices to the previous level and / or reduction of raw material prices to a level that ensures production profitability. The present invention also relates to a method for modifying an existing unprofitable methanol plant to increase its profitability at a low level of methanol prices and / or a high level of gas prices.

The following references disclose synthesis gas production: Mau1aik (US Patent No. 2,622,089); Mine (US patent No. 3859230); 81bgd e1 a1. (US patent No. 5767165); Ragk e1 a1. (US patent No. 5855815); B, e1 a1. (US patent No. 5180570); Ms8kea, III, e1 a1. (US patent No. 4927857); and Wapdiu (US Pat. Nos. 4,888,130 and 4,999,133). It is believed to be reliably established that in large-scale production, pure autothermal reforming can be a more economical process for producing syngas, since large capital costs are saved due to the lack of the need to build large primary reforming plants. However, its disadvantage is the impossibility of full use of all carbon-containing molecules, leading to the emission of large quantities of CO ₂ that are undesirable. As far as the applicant knows, in the prior art there is no description of the regulation of the ratio B, where B = [(Н ₂ - СО ₂ ) / (СО + СО ₂ )], for the synthesis gas of an autothermal reforming (ATP) plant for methanol production, as well as supply of stoichiometric amounts of MeOH and CO for the production of acetic acid, for example, with flexible control of both methanol production and acetic acid production, especially in cases where coefficient B is less than 2.0.

SUMMARY OF THE INVENTION

The invention relates to adjusting the value of the coefficient B of the synthesis gas used to produce methanol by separating at least a portion of the syngas not adjusted in composition into streams with a significantly increased content of carbon monoxide, hydrogen and carbon dioxide, and then (1) adding, as necessary , carbon dioxide, carbon monoxide and / or hydrogen from these streams to the remaining unregulated syngas, or (2) combining such streams, in the absence of a syngas residue, to produce corrections compositionally syngas having a coefficient B [B = (Н2-СО2) / (СО + СО2)] from 2.0 to 2.9, and using compositionally adjusted syngas to produce methanol, some of which is then used to conduct the reaction with at least a portion of the carbon monoxide stream in an approximately stoichiometric ratio for direct or indirect production of acetic acid.

Embodiments of the present invention provide a method for the production of both methanol and acetic acid under essentially stoichiometric conditions in which the syngas not adjusted in composition has a coefficient B of less than 2.0. All of the syngas not corrected in composition or part of it is fed to the separator unit for the release of CO2, CO and hydrogen. At least a portion of any of the streams or a combination of the separated streams of CO ₂ , CO and hydrogen is added to the syngas residue not subjected to such treatment or, alternatively, in the absence of an unadjusted residue

- 1 007455 syngas according to the composition, they are combined to obtain a syngas corrected by composition, having a coefficient coefficient I from 2.0 to 2.9, which is used for the production of methanol. Preferably, the compositionally adjusted syngas has a coefficient I of 2.00 to 2.05. All of the CO ₂ emitted that is not used to control the coefficient I of the syngas not corrected for the composition can be fed to the reformer to increase the production of CO. At least a portion of the CO emitted is used to react in an acetic acid reactor with at least a portion of the methanol obtained to produce acetic acid or an acetic acid precursor in a conventional manner. As noted above, the separated hydrogen can be fed to the MeOH synthesis unit for methanol production. To the extent that the amount of hydrogen produced exceeds the methanol synthesis requirements of the present invention, it can also be used to produce ammonia or other products, burned as fuel, or supplied to external consumers. Any excess methanol exceeding the requirements for the production of acetic acid can be used, for example, as an intermediate material for other products, such as methylamines, or sold as a product.

Excess carbon dioxide can be fed to the reforming unit, which receives natural gas and steam (water) to obtain a syngas that is adjusted in composition. Syngas is formed in a reforming unit in which natural gas and carbon dioxide are reformed to form syngas having a higher carbon monoxide content compared to reforming without the addition of carbon dioxide.

The hydrogen evolved, to the extent that its production exceeds the requirements of methanol synthesis in this method, can also be used to carry out the reaction with nitrogen in the usual way for the production of ammonia. In addition, part of the acetic acid produced can be used to carry out the reaction in the usual way with oxygen and ethylene to form a vinyl acetate monomer. Oxygen can be fed to an autothermal reforming unit to produce syngas. Nitrogen for the production of ammonia and oxygen for the production of vinyl acetate monomer and / or an autothermal reforming unit can be obtained in a conventional air separation unit.

Generally speaking, the present invention provides, in one aspect, a method for controlling the value of the syngas coefficient I intended for use in the production of methanol, alone or in combination with the production of acetic acid. The method regulates the value of the coefficient I of the syngas not corrected by the composition by dividing at least part of the syngas not adjusted by the composition into streams with a high content of СО ₂ , СО and hydrogen, and then adding to the residue of the syngas not corrected by the syngas composition one or more of the flows of СО2, СО and hydrogen or, alternatively, in the absence of the remainder of the syngas not adjusted in composition, combining a sufficient amount of these flows to obtain a composition-corrected for syngas having a coefficient of I ranging from 2.0 to 2.9.

In another aspect, at least a portion of the CO stream is used to react with at least a portion of the methanol produced in a stoichiometric ratio to produce acetic acid or an acetic acid precursor in a conventional manner. The production volumes of each product can be controlled taking into account the relative economic indicators of the production of acetic acid and methanol. For example, all methanol can be used to produce acetic acid, or less acetic acid can be produced by using more of the extracted CO to produce methanol rather than acetic acid, as a result of which the production of methanol will exceed the requirements for the production of acetic acid. Alternatively, the isolated CO can be used to produce methanol or taken out of the system for use by nearby external consumers, whereby acetic acid will not be produced.

This invention can be implemented in large-capacity methanol plants in which synthesis gas is produced by autothermal catalytic reforming of natural gas with oxygen, and a sufficient volume of carbon monoxide is diverted to the production of acetic acid, and the remainder of the synthesis gas is mixed with recirculating gases and enters the circuit methanol synthesis in approximately stoichiometric ratio.

The proposed method eliminates the disadvantages indicated above in the description of the prior art by combining the installation of acetic acid with a large-capacity installation of methanol. Syngas is produced by an autothermal reforming unit after all raw materials are preheated, after which part of this syngas enters the separation unit, which consists of a CO2 removal unit and a cryogenic separation unit, to produce a carbon monoxide stream, which is used in the plant for producing acetic acid by carbonylation. All other flows from the separation unit are recycled with the rest of the syngas not corrected for the composition to obtain the adjusted syngas, which then enters the methanol synthesis circuit. A sufficient volume of carbon monoxide stream is taken from the syngas so that the syngas after correction has a composition close to the stoichiometric ratio required for production

- 2 007455 methanol. This method eliminates the capital costs associated with the construction of primary reforming plants, and another advantage is that the methanol plant, in itself, is environmentally friendly, since the emission of carbon compounds is reduced to almost zero.

The reaction step may include a direct catalytic reaction of methanol and carbon monoxide to form acetic acid, as, for example, in the Mopgap1o-BP process, or, alternatively, may include intermediate formation of methyl formate and isomerization of methyl formate to acetic acid, intermediate reaction of CO and two moles methyl alcohol to form methyl acetate and hydrolysis of methyl acetate to acetic acid and methanol, or carbonylation of methyl acetate to form acetic anhydride.

The method may further include the step of carrying out the reaction of hydrogen from the stream with a high content of hydrogen with nitrogen to produce ammonia. In a modernized embodiment, in which the initial methanol unit produces a stream with a high hydrogen content, including a purge stream from a methanol synthesis unit that is reacted with nitrogen to produce ammonia, the modernized unit may use any excess amount of a stream with a high hydrogen content from the separation unit as the primary source of hydrogen for ammonia production. In some cases, additional ammonia may be produced compared to the original installation.

The method may further include constructing a vinyl acetate monomer production unit for reacting a portion of acetic acid with ethylene and oxygen to produce a vinyl acetate monomer. An air separation unit for oxygen production can be built for the installation of vinyl acetate monomer, as well as for an autothermal reforming unit, if it is part of a new or upgraded unit, the amount of nitrogen produced in the unit for air separation preferably corresponds to the amount of nitrogen required for the production of ammonia .

The process preferably uses a molar ratio of carbon dioxide to hydrocarbon-containing natural gas in the feed stream at the reforming stage from about 0.1 to 0.5, and a steam to natural gas ratio from about 2 to 6. The process may further include the step of carrying out a hydrogen reaction from a stream with a high content of hydrogen with nitrogen in the ammonia synthesis reactor to produce ammonia. The process may also include the step of separating air into a nitrogen stream and an oxygen stream and supplying a nitrogen stream to an ammonia synthesis reactor. In cases where the product includes acetic acid or an acetic acid precursor that is converted to acetic acid, the process may further include the step of supplying an oxygen stream from the air separation unit to the vinyl acetate synthesis reactor together with a portion of the acetic acid from the carbon monoxide-ethanol reaction step and ethylene to obtain a stream of vinyl acetate monomer. In the presence of an autothermal reforming unit, the process may further include the step of supplying oxygen from the air separation unit to the autothermal reforming unit.

In yet another aspect, the present invention provides a method for producing hydrogen, a product selected from the group consisting of acetic acid, acetic anhydride, methyl formate, methyl acetate and combinations thereof, from a hydrocarbon through intermediate steps to produce methanol, carbon monoxide and carbon dioxide, and optionally additional methanol, excessive in comparison with the needs of the product. The process includes (1) reforming the hydrocarbon with steam to produce a syngas not adjusted in composition, containing hydrogen, carbon monoxide and carbon dioxide, and having a coefficient B value of less than 2.0, (2) heat recovery of an unregulated syngas with the formation of a cooled stream of unregulated composition syngas, (3) compressing at least part of the cooled stream of unregulated syngas to the separation pressure, (4) separating compressed syngas not adjusted by composition in the installation section flows to a high content of carbon monoxide, hydrogen and carbon dioxide, (5) supplying to the methanol synthesis unit any residue of an unregulated syngas, and a sufficient amount of one or more streams with a high content of carbon monoxide, hydrogen and carbon dioxide and, optionally, carbon dioxide from another source to form a syngas that is adjusted in composition so that the syngas are adjusted in composition (i.e. total feed stream) entering the methanol synthesis unit had a K coefficient in the range from 2.0 to 2.9, (6) operating a methanol synthesis unit to conduct a hydrogen reaction with carbon monoxide and carbon dioxide contained in a compositionally adjusted syngas, in a stoichiometric ratio, to produce a methanol stream, and (7) reacting at least a portion of the carbon monoxide-rich stream from the separation unit with at least a portion of the methanol stream from the methanol synthesis unit, blended in a substantially stoichiometric ratio to form a product selected from the group consisting of acetic acid, acetic anhydride, methyl formate, methyl acetate and combinations thereof.

In cases where the product comprises acetic acid, the reaction step preferably includes the reaction of methanol, methyl formate or a combination thereof in the presence of a reaction mixture containing carbon monoxide, water, a solvent and a catalyst system comprising at least

- 3 007455 at least one halogenated promoter and at least one compound of rhodium, iridium, or combinations thereof. The reaction mixture preferably has a water content of up to 20 wt.%. In those cases where the reaction step involves simple carbonylation, the water content in the reaction mixture is preferably from about 14 to about 15 wt.%. In those cases where the reaction step involves carbonylation at a low water content, the water content in the reaction mixture is preferably from about 2 to about 8 wt.%. In those cases where the reaction step involves isomerization of methyl formate or a combination of isomerization and carbonylation of methanol, the reaction mixture preferably contains a non-zero amount of water not exceeding 2 wt.%. The reaction step is preferably carried out continuously.

Another embodiment of the invention provides a process for pre-processing the feed stream to obtain a lower vapor / carbon ratio for use in an autothermal reforming unit with reduced soot formation, and associated processing equipment. In this method, a stream with a high hydrogen content is added to a feed gas stream containing higher hydrocarbons (2 or more carbon atoms), the resulting mixture is contacted with a hydrogenation catalyst at a hydrogenation temperature, and the hydrogenated mixture is fed to an autothermal reforming unit with steam and oxygen to receiving syngas. The hydrogen-rich stream is preferably a purge gas or a fraction thereof from a methanol synthesis loop into which syngas or a portion or fraction thereof is fed. Adding a stream with a high hydrogen content, preferably, is carried out in an amount providing at least a stoichiometric amount of hydrogen for hydrogenation of higher hydrocarbons to methane. The hydrogenation temperature may preferably be from 300 to 550 ° C. Technological equipment in this embodiment includes a source of feed gas containing higher hydrocarbons; a preliminary hydrogenation reactor including a hydrogenation catalyst for converting higher hydrocarbons to form a stream with a lower content of higher hydrocarbons (non-base metals such as platinum, palladium, cobalt, molybdenum, nickel or tungsten supported on an alumina or zeolite substrate are usually used as a catalyst ); an autothermal reformer for reacting a stream with a lower content of higher hydrocarbons with steam and oxygen to form a syngas stream; methanol synthesis loop for reacting hydrogen and carbon monoxide from a syngas stream to form methanol; a purge gas stream from a methanol synthesis loop; and a feed line for a portion of the purge gas stream to the preliminary hydrogenation reactor.

Since the reaction is exothermic, the hydrogenation process can be carried out in one or more reactors, using, if necessary, intermediate refrigerators. This hydrogenation step is particularly well adapted for use with autothermal reforming units having a low vapor / carbon ratio in the feed mixture.

Brief Description of the Drawings

FIG. 1 (prior art) is a general flowchart for a typical methanol / ammonia plant using hydrogen from a purge gas of a methanol synthesis loop for ammonia production, which can be upgraded to produce acetic acid.

FIG. 2 is a general flowchart for the installation of FIG. 1 after its modernization in accordance with the present invention to obtain acetic acid, a vinyl acetate monomer and an additional amount of ammonia.

FIG. 3 is a simplified flow diagram of a process for an integrated plant producing methanol and acetic acid in accordance with the present invention.

FIG. 4 is a simplified flowchart for the integrated installation of FIG. 3, comprising a preliminary hydrogenation reactor in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIG. 1, the initial unit includes a conventional steam reforming unit 10, a methanol synthesis unit (MeOH) 12 and, preferably, an ammonia synthesis unit 14, in which a purge stream 16 from the methanol synthesis loop is used as the hydrogen for the ammonia synthesis unit 14.

The reformer 10 is typically a combustible fuel furnace including parallel bundles of tubes filled with a conventional reforming catalyst, such as, for example, nickel oxide on an alumina support. The feedstock for the reformer (s) is any conventional feedstock for the reformer, such as a lower hydrocarbon, naphtha or natural gas are typical.

The reforming unit may be a one-way reforming unit or a two-stage reforming unit, or any other commercially available reforming unit,

- 4 007455 such as, for example, the KKE8 installation manufactured by Ke11odd, ΒΐΌ \ νπ & Κοοΐ, known to specialists in this field of technology. The effluent of the reforming unit of the initial methanol production unit can have any usual ratio of H ₂ : CO, but usually its value is close to 2.0 for plants producing only methanol, and significantly higher, for example, 3.0 and higher, for plants producing as a separate product, hydrogen or an intermediate hydrogen-containing stream, for example, for the synthesis of ammonia. Purge stream 16 from the loop of a methanol synthesis unit 12, which is necessary to prevent an increase in the content of hydrogen and inert materials in the synthesis gas recycled to the methanol synthesis unit 12, is usually used as a hydrogen-containing stream.

In accordance with the present invention, the initial installation of FIG. 1 is being modernized (or a new plant is being built) for the production of acetic acid (HAC) using a reforming unit 10 and a methanol synthesis unit 12, while maintaining the existing ammonia synthesis units 14, as shown in FIG. 2. The oxygen stream 66 from the new air separation unit 50 is supplied to the reforming unit 10, and in this embodiment, the reforming unit 10 may include an autothermal reforming unit (ATP) connected in parallel with the existing steam reforming unit, or the ATP is used instead of the steam reforming unit. A portion of the effluent 18 from the reformer 10 is discharged from the methanol synthesis unit 12 via line 20 to a new CO ₂ removal unit 22. The effluent 18 has a coefficient K. less than 2 in the case of using only ATP, and in the range from 2 to 3 for a combination of Asia-Pacific and the classic steam reforming plant. The CO ₂ 22 removal unit separates the stream coming in line 20 into a stream with a high content of CO ₂ and a stream with a low content of CO ₂ 26 using conventional equipment and a methodology for CO2 extraction, such as, for example, by absorption-stripping using a solvent such as water, methanol, usually aqueous alkanolamines, such as ethanolamine, diethanolamine, methyldiethanolamine and the like, aqueous alkali metal carbonates, such as sodium and potassium carbonates, and the like. Such CO ₂ absorption-stripping processes are commercially available under the trade names CbO1O1. 8ιι1Γίπο1. Kesyso1, Rshtso1, P1iot, VA8P (AMOEA), etc. A stream with a high content of CO ₂ may be supplied via line 24 to the feed stream of the reforming unit 10 and / or to the methanol synthesis loop 12 via line 60.

The CO2 stream extracted in the CO2 removal unit 22 or coming from another source can be supplied to the methanol synthesis loop 12 to control the coefficient K of the feed coming there.

The CO2 stream can also be fed to the reformer 10 in parallel or alternatively. An increase in the CO ₂ content in the feed stream of the reformer 10 increases the CO content in the effluent 18. Similar to steam reforming, when a hydrocarbon reacts with steam to produce synthesis gas, the reaction of a hydrocarbon with dioxide carbon is often called CO2 reforming. With an increase in the carbon dioxide content in the feed stream of the reforming unit, the relative fraction of carbon in the form of carbon monoxide in the synthesis gas product 18 supplied with carbon dioxide increases and its fraction supplied with hydrocarbon decreases. Thus, for a given CO performance, the need for hydrocarbon feed is reduced.

In the initial stages of reforming, heavy hydrocarbons are converted to methane:

HC + H ₂ O => cn ₄ + co ₂

The main reactions of steam and CO2 reforming is the conversion of methane to hydrogen and carbon monoxide:

CH ₄ + H ₂ O <=> zn ₂ + co

СН ₄ + СО ₂ <=> ЗН ₂ + 2СО

The conversion reaction converts carbon monoxide to carbon dioxide and additional hydrogen:

The conversion of heavy hydrocarbons proceeds to the complete consumption of raw materials. Steam reforming, CO2 reforming, and the conversion reaction are limited by equilibrium conditions. The overall reaction is highly endothermic.

The reforming unit 10, if necessary, can be modified to provide additional heat for additional CO ₂ reforming and utilization of additional heat.

As noted above, the effluent 18 from a modified or autothermal reforming unit 10 has a molar ratio (hydrogen minus CO2) to (CO plus CO2) (which is referred to in the description and claims as K = (H ₂ - CO ₂ ) / (CO + CO ₂ )) less than 2. As will be described later, the K coefficient can be adjusted and optimized for methanol synthesis, preferably in the range from 2.0 to 2.9, by adding CO ₂ along line 60, CO along

- 5 007455 of line 64 and / or hydrogen along line 62 to any residual syngas not adjusted in composition to obtain adjusted syngas 38 in composition with the required coefficient K.

The stream with a reduced CO ₂ 26 content contains predominantly CO and hydrogen and can be divided in a CO 28 separation unit into streams with a high CO 30 and 64 content and a stream with a high hydrogen content 32. The separation unit 28 may include any equipment and / or use any methods for separating a CO / hydrogen mixture into relatively pure CO and hydrogen flows, such as, for example, semipermeable membranes, cryogenic fractionation, and the like. Cryogenic fractional distillation is preferred and may include simple partial condensation without using any columns, partial condensation using columns, optionally with a pressure compensation unit (P8A) and a hydrogen recirculation compressor, or washing with methane. Typically, partial condensation using columns is sufficient to produce CO and hydrogen of sufficient purity to produce acetic acid and ammonia, respectively, which will minimize equipment and operating costs, although the P8A unit and hydrogen recirculation compressor can be installed additionally to increase the degree of purity hydrogen and CO performance. For the production of acetic acid, the CO stream 30 preferably contains less than 1000 ^-1 million (ppm) of hydrogen and less than 2 mol.% Nitrogen plus methane. For the production of ammonia, the hydrogen stream 32 entering the nitrogen flushing unit (not shown) preferably contains at least 80 mol.% Hydrogen, more preferably at least 95 mol.% Hydrogen.

Part of the hydrogen stream 32 enters the existing ammonia synthesis unit 14 instead of the purge stream of the methanol circuit 16. The amount of hydrogen produced in stream 32 is usually much higher than the amount previously received through line 16. This is largely due to the fact that the modernized plant produces less methanol, due to which for the synthesis of methanol uses less hydrogen. Additionally produced hydrogen can be used as fuel or as a source of raw hydrogen in another process, such as, for example, increasing the conversion of ammonia. Additional ammonia can be obtained by supplying part of the additional hydrogen to the existing ammonia synthesis reactor 14, in which the yield of the ammonia synthesis reaction can be increased, and / or by mounting an additional ammonia synthesis plant 33. Increased ammonia production capacities can be supplemented by the availability of existing means handling, storage and transportation of ammonia, which can be used to service additional ammonia production with negligible and with or without modifications.

The methanol synthesis unit 12 is a conventional methanol conversion unit, such as, for example, a 1C1 reactor. The methanol synthesis unit 12 of the upgraded unit shown in FIG. 2 is essentially the same as the initial setup before the upgrade, except that the amount of methanol produced is significantly less, preferably about half of the initial setup. Accordingly, a loop recirculation compressor (not shown) operates at a lower capacity and the purge stream 16 is much smaller. As indicated above, the purge stream 16 is no longer needed to supply hydrogen to the ammonia conversion device 14, since now, in the modernized plant, it comes from the hydrogen stream 32, taken directly from a part of the effluent 18 of the reforming unit 10, removed from the feed stream of the synthesis unit methanol 12 via line 20. If necessary, purge stream 16 can now be used as fuel and / or as a hydrogen source for hydrodesulfurization of the feed stream of reforming unit 10. Since olee there is no need to send the excess hydrogen through the methanol synthesis unit 12 for use in installing ammonia 14, the composition of the feed stream methanol synthesis unit 12, i.e. effluent 18 can be optimized to increase methanol conversion efficiency as described above. It may also be necessary to modify the methanol synthesis unit 12, if this is desirable during the upgrade to include any other modifications that are not present in the initial unit, which became common and were developed for the methanol synthesis loop after the initial unit was constructed, but were not previously implemented for her.

The amount of syngas in the effluent 18 of the reforming unit 10, which is diverted to separate CO ₂ / CO / H ₂ , is preferably controlled until a stoichiometric ratio of methanol and CO is achieved to produce acetic acid from them in an acetic acid synthesis unit 34. Preferably, the ratio of CO to line 30 and methanol in line 38 is approximately equal to or methanol is produced with a molar excess of 10-20%, for example, with a molar ratio of from 1.0 to about 1.2. To obtain such a ratio of methanol and CO, a relatively large amount (total, in kg / h) of the effluent 18 is diverted to line 20, and the remaining small portion is fed via line 38 to the methanol synthesis unit 12.

The installation of the synthesis of acetic acid 34 uses conventional equipment and a methodology for the production of acetic acid, well known and / or technically available to specialists in this field, for example, from one or more patents relating to the production of acetic acid mentioned above. For example, the normal BP / Mo8a1o1 process or refinement may be used.

- 6 007455 BP / Mop§ap1o process using BP-Sayua technology (iridium catalyst), CC1aps5c technology with low water content (lithium-rhodium acetate catalyst), M111 technology with low water content (catalyst based on rhodium phosphorus oxides) , Leslcx technology (rhodium-iridium catalyst) and / or a double methanol carbonylation process - isomerization of methyl formate. The reaction generally includes reacting methanol, methyl formate, or a combination thereof in the presence of a reaction mixture containing carbon monoxide, water, a solvent, and a catalyst system comprising at least one halogenated promoter and at least one rhodium, iridium compound, or a combination thereof. The reaction mixture preferably has a water content of up to 20 wt.%. In cases where the reaction involves simple carbonylation, the water content in the reaction mixture is preferably from about 14 to about 15 wt.%. In cases where the reaction involves low carbonation, the water content in the reaction mixture is preferably from about 2 to about 8 wt.%. In those cases where the reaction includes isomerization of methyl formate or a combination of isomerization and carbonylation of methanol, the reaction mixture preferably contains non-zero amount of water not exceeding 2 wt.%. The reaction is typically carried out continuously. The product of acetic acid is obtained through line 40.

If necessary, part of the acetic acid from line 40 can be fed to a conventional vinyl acetate monomer synthesis unit 42, where it is reacted with ethylene coming in line 44 and at least part of the oxygen coming in line 46 to form a monomer product stream 48. Oxygen in line 46 can be obtained, for example, using a conventional (preferably cryogenic) air separation unit 50, which also produces a nitrogen stream 52 corresponding to the amount of air in line 54 needed to obtain and 46, the amount of oxygen sufficient to supply the vinyl acetate monomer 42 synthesis unit and the reforming unit 10. The amount of air supplied to the separation can be brought into correspondence with the amount of nitrogen required for supply via line 52 to the additional ammonia production capacities added to installation of the synthesis of ammonia 33, as described above.

In FIG. 3 schematically shows a plant 100 in accordance with one embodiment of the integrated process for producing acetic acid and methanol of the present invention. Natural gas 102 and air 104 are supplied to the heat and electricity co-production unit 110 to produce electricity 108 and steam 106. The generated energy supplies one or two air separation units 112 that produce oxygen and nitrogen (not shown). If unit 100 does not include an ammonia plant, then only a small fraction of the nitrogen will be used in other plants (instrumentation and safety fluid).

The oxygen stream is combined with desulfurized natural gas and steam and preheated in a heater 114 to a sufficiently high temperature (400 to 750 ° C.) to initiate catalytic oxidation of the feed stream of the autothermal reforming unit 116. The autothermal reforming unit 116 operates at high pressure in the range from 2 to 8 MPa (20-80 bar), and at high temperature (from 800 to 1250 ° C).

The main advantages of this process are that: (1) a simpler syngas compressor (not shown) having only one or two stages is used to produce syngas 118 with high pressure; and (2) a high outlet temperature provides a very low content of unreacted methane (methane concentration in syngas). Unregulated syngas 118 will typically have a factor B value of less than 2.

High temperatures are utilized using heat exchangers (not shown) to heat the feed streams and / or to generate steam.

The cooled syngas portion 120 is sent to a CO ₂ 122 removal unit using ethanolamines to produce a stream with a high content of CO2 124 and a mixed stream of H ₂ / CO 126. Then, a separation unit 128 produces a stream with a high content of CO 130 and a stream with a high content H ₂ 132. The separation unit 128 may be, for example, a partial condensation refrigerator with two columns.

In this embodiment, streams 124 and 132 can be mixed with another syngas portion 134 to obtain a syngas-corrected composition 136 having a coefficient B ranging from 2.0 to 2.9, preferably about 2, before being fed to the methanol synthesis loop 138 A compositionally corrected syngas 136 having a B value of about 2 gives a purge stream of hydrogen 140 at a low flow rate. Preferably, the compositionally adjusted syngas coefficient B is in the range of 2.00 to 2.05.

The methanol synthesis loop 138 uses a low pressure synthesis reaction to produce a methanol stream 146, and to generate steam.

Depending on economic indicators, the purge stream 140 can be used to utilize its calorific value or divided into membranes or in a pressure fluctuation compensation unit (P8A) 142 to extract hydrogen 144 and recycle it into the main synthesis cycle 138.

Part 148 of the produced methanol is fed to the acetic acid unit 150 for carbonylation with a stream of CO 130 from the separation unit 128 to form an acetic acid stream 152.

- 7 007455

Another portion 154 of the methanol stream 146 is a methanol product.

Presented in FIG. 4, an embodiment of the process 200 is similar to that depicted in FIG. 3, but includes a pre-hydrogenation unit 202 and a purge gas recirculation line 204. The pre-hydrogenation unit 202 contains a hydrogenation catalyst, for example, nickel-cobalt-molybdenum catalyst, commonly used for steam reforming, and is operated at a suitable hydrogenation temperature, for example, 300-550 ° C.

The recycle purge gas feeds a high hydrogen stream to the pre-hydrogenation unit to convert any higher hydrocarbons in the feed gas stream to lower hydrocarbons, such as methane. Sufficient hydrogen must be supplied from the recycle stream for stoichiometric hydrogenation or cracking of higher hydrocarbons in the feed stream of natural gas to lower hydrocarbons, preferably methane.

The remainder of the purge gas may enter the ATR to recover all carbon-containing molecules. In this case, the accumulation of inert compounds, such as nitrogen or argon, in the methanol circuit is not allowed, since part of the syngas enters the CO separation unit, and such inert compounds usually accompany the CO stream.

The natural gas feed stream, preferably consisting primarily of methane, is desulfurized prior to the pre-hydrogenation unit and preferably has a low water vapor content. The pre-hydrogenation unit preferably works in general at a low water content, i.e. without supplying steam, which can be mixed with the effluent of the pre-hydrogenation unit for heating in the usual way, except that higher heating temperatures can be used due to the lower content of higher hydrocarbons. Many natural gas sources, such as associated gas, contain significant amounts of ethane, propane, butane and C5 + hydrocarbons, which can cause soot formation in the autothermal reforming unit 116, as described in US Pat. No. 6,375,916. The pre-hydrogenation unit converts higher hydrocarbons to lower hydrocarbons hydrocarbons i.e. methane, and allows you to operate the reformer at a lower steam / carbon ratio without the formation of soot. The use of a purge gas bypass stream may allow proportionally reducing the size or performance of the membrane separation unit / P8L and / or completely abandoning their use. Since recycled hydrogen is an internal cycle, the overall material balance of production capacity remains essentially unchanged.

Claims (13)

1. A method of producing syngas for the production of methanol or methanol derivatives, comprising the steps of combining a hydrogen-containing stream with a natural gas feed stream containing higher hydrocarbons to form a hydrogen-containing feed stream; contacting said feed stream with a hydrogenation catalyst at a hydrogenation temperature to obtain a heated stream with a reduced content of higher hydrocarbons; feeding said heated stream, steam, and oxygen into an autothermal reforming unit to produce a syngas not adjusted in composition, containing at least hydrogen, carbon monoxide, and optionally carbon dioxide. 2. The method according to claim 1, in which the unregulated syngas has a coefficient K (K = [(H ₂ -CO ₂ ) / (CO + CO ₂ )]) less than 2, the method further comprising isolating at least parts of the syngas not adjusted in composition to a stream with a high hydrogen content, a stream with a high content of carbon monoxide and a stream with a high content of carbon dioxide and the preparation of a composition-adjusted syngas having a coefficient K from 2.0 to 2.9 by combining at least parts of at least two streams, selected from the group consisting of any unregulated syngas residue, a stream with a high hydrogen content, a stream with a high content of carbon monoxide, a stream with a high content of carbon dioxide and an additional source of carbon dioxide; supply of a syngas adjusted in composition to the methanol synthesis loop for methanol production. 3. The method according to claim 1 or 2, further comprising obtaining a product selected from acetic acid and an acetic acid precursor by reacting at least a portion of the methanol produced with at least a portion of the stream with a high content of carbon monoxide in a stoichiometric ratio. 4. The method according to claim 3, in which the product includes a precursor of acetic acid; wherein the method further includes the step of converting the acetic acid precursor to acetic acid. - 8 007455 5. The method according to any one of claims 1 to 4, wherein said feed stream at said contacting step does not contain added steam to maintain low water content during hydrogenation. 6. The method according to claim 2, further comprising separating the purge gas stream from the methanol synthesis loop and recycling at least a portion of the purge gas stream to the contacting step as a hydrogen-containing stream. 7. The method according to claim 6, further comprising separating hydrogen gas from said purge stream containing hydrogen gas, and recirculating the hydrogen gas to a syngas not adjusted in composition. 8. The method according to claim 6, comprising recirculating said purge stream of hydrogen gas before the autothermal reforming unit. 9. The method according to any one of claims 2 to 8, further comprising carrying out the reaction of at least a portion of the stream with a high content of carbon monoxide from a separation unit with at least a portion of the methanol stream from the methanol synthesis unit, in substantially stoichiometric ratio to form the product selected from the group consisting of acetic acid, acetic anhydride, methyl formate, methyl acetate and combinations thereof. 10. The method according to claim 9, in which the product is selected from the group consisting of acetic acid, acetic anhydride, methyl formate, methyl acetate and combinations thereof. 11. The method according to any one of the preceding claims, in which the reforming unit is an autothermal reforming unit operating at a pressure in the range of 2-8 MPa (20-80 bar) and a temperature of from 800 to 1250 ° C. 12. The method according to any one of claims 2-11, wherein a portion of the stream with a high carbon dioxide content is fed to a reforming unit to increase carbon monoxide production. 13. The method according to any one of claims 2 to 12, in which the coefficient I of the syngas adjusted in composition has a value from 2.00 to 2.05.