TECHNICAL FIELD

[0001] The present disclosure relates to methods of producing methanol; more specifically, the present disclosure relates to methods of producing methanol by a multi-stage process comprising two or more methanol synthesis reactors in series; still more specifically, the present disclosure relates to methods of producing methanol by a multi-stage process in which methanol is removed in each stage and only a hydrogen stream separated from a vapor product of the final stage is recycled back to the first stage.

BACKGROUND

[0002] Synthesis gas (syngas) is a mixture comprising carbon monoxide (CO) and hydrogen (H ₂ ), as well as small amounts of carbon dioxide (C0 ₂ ), water (H ₂ 0), and unreacted methane (CH ₄ ). Syngas is generally used as an intermediate in the production of methanol and ammonia, as well as an intermediate in creating synthetic petroleum to use as a lubricant or fuel.

[0003] Syngas is produced conventionally by steam reforming of natural gas (steam methane reforming or SMR), although other hydrocarbon sources can be used for syngas production, such as refinery off-gases, naphtha feedstocks, heavy hydrocarbons, coal, biomass, etc. SMR is an endothermic process and requires significant energy input to drive the reaction forward. Conventional endothermic technologies such as SMR produce syngas with a hydrogen content greater than that required for methanol synthesis. Generally, SMR produces syngas with an M ratio ranging from 2.6 to 2.98, wherein the M ratio is a molar ratio defined as (H ₂ -C0 ₂ )/(C0+C0 ₂ ).

[0004] In an autothermal reforming (ATR) process, a portion of the natural gas is burned as fuel to drive the conversion of natural gas to syngas resulting in relatively low hydrogen and high C0 ₂ concentrations. Conventional methanol production plants utilize a combined reforming (CR) technology that pairs SMR with autothermal reforming (ATR) to reduce the amount of hydrogen present in syngas. ATR produces a syngas with a hydrogen content lower than the required content for methanol synthesis. Generally, ATR produces syngas with an M ratio ranging from 1.7 to 1.84. In the CR technology, the natural gas feed volumetric flowrate to the SMR and the ATR can be adjusted to achieve an overall syngas M ratio of 2.0 to 2.06. Further, CR syngas has a hydrogen content greater than the required content for methanol synthesis. Furthermore, SMR is a highly endothermic process, and the endothermicity of the SMR technology requires burning fuel to drive the syngas synthesis. Consequently, the SMR technology reduces the energy efficiency of the methanol synthesis process.

[0005] Syngas can also be produced (non-commercially) by catalytic partial oxidation (CPO or CPOx) of natural gas. CPO processes employ partial oxidation of hydrocarbon feeds to syngas comprising CO and H ₂ . The CPO process is exothermic, thus eliminating the need for external heat supply. However, the composition of the produced syngas is not suitable for methanol synthesis, for example, owing to a reduced hydrogen content. Thus, there is an ongoing need for the development of systems and methods for methanol synthesis that utilize syngas production via CPO processes.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] For a detailed description of the preferred aspects of the disclosed methods, reference will now be made to the accompanying drawing in which:

[0007] Figure 1 is a schematic of a generic system I for a multi-stage methanol synthesis process, according to embodiments of this disclosure; and

[0008] Figure 2 is a schematic of a system II for an exemplary methanol synthesis process comprising four stages, according to embodiments of this disclosure.

DETAILED DESCRIPTION

[0009] The herein-disclosed multi-stage methanol synthesis system and method are designed to achieve higher per pass conversion and eliminate a conventional unreacted recycle stream, by utilizing, optionally, only a smaller volume recovered hydrogen recycle, as described hereinbelow. In this manner, the herein-disclosed multi-stage methanol synthesis system and method provide for a decrease in the size of equipment and a reduction of stream volumes in the methanol synthesis loop and a decrease in the concentration of inerts (e.g., methane, nitrogen and argon) within the loop. According to embodiments of this disclosure, a reactor feed comprising synthesis gas (e.g., a reformed gas) is compressed to a high pressure (e.g., 80 to 110 bar) and introduced to a methanol synthesis reactor (e.g., a water cooled reactor or an adiabatic reactor) of a first stage of the multi-stage process. The methanol synthesis reactor effluent is cooled (optionally with generation of steam), and sent to a flash drum or other gas-liquid separator to condense a methanol product comprising methanol and water in order to shift the equilibrium conversion toward favoring higher methanol conversion in the methanol synthesis reactor of the following stage. The crude liquid methanol product removed in each stage can be sent either directly to a crude methanol tank or to a gas-liquid separator (e.g., a flash drum) of the final stage in the methanol synthesis loop for maximum condensation of methanol product comprising methanol and water. The vapor from each stage except the final stage is heated and introduced to the methanol synthesis reactor of the following stage. In embodiments, the cooling and reheating of the gaseous streams can be heat integrated. In embodiments, the vapor effluent from the gas-liquid separator (e.g., flash drum) of the final stage is introduced into one or more hydrogen recovery units, and at least a portion of a recovered hydrogen stream is recycled back and combined with a synthesis gas feed to increase the M-value of the reactor feed to the methanol synthesis reactor of the first stage to enhance the per pass conversion of carbon monoxide and carbon dioxide. A purge gas rich in methane and hydrogen from the hydrogen recovery unit(s) is can be utilized as a fuel.

[0010] The procedure is repeated until a desired conversion, loop efficiency, and heat efficiency are achieved. As will be apparent to those of skill in the art upon reading this disclosure, for a given syngas quality, a certain number of methanol synthesis reactors and hydrogen recovery units can be utilized to achieve optimum methanol production and overall heat efficiency. In embodiments, each methanol synthesis reactor is cooled using water to generate medium pressure steam and to achieve an optimum temperature profile along the tubes thereof for maximized methanol formation per unit of size. In alternate embodiments, adiabatic reactors are utilized rather than or in conjunction with boiling water reactors. Because of a higher loop efficiency provided by the herein-disclosed multi stage methanol synthesis system and method, a greater amount of medium pressure steam may be generated relative to conventional methanol synthesis systems and methods which i) lack a step of separating each methanol reactor effluent stream into a crude methanol stream and a vapor stream, and/or (ii) lack a step of separating the vapor stream from the final stage in a hydrogen recovery unit into a hydrogen stream and a residual gas stream.

[0011] The herein-disclosed multi-stage processes for producing methanol comprise, for N stages x, where x is from 1 to N: (a) feeding a reactor feed RFx to a methanol reactor Rx of that stage; wherein the methanol reactor Rx is characterized by a reactor volume; wherein the methanol reactor Rx comprises a catalyst; wherein the methanol reactor Rx is characterized by a catalyst amount; wherein the reactor feed RFx comprises hydrogen (H ₂ ), carbon monoxide (CO), carbon dioxide (C0 ₂ ), and optionally water and/or hydrocarbons; wherein the reactor feed RF1 to the methanol synthesis reactor R1 of the first stage comprises synthesis gas 5 and a recycle hydrogen 40, and wherein the reactor feeds to any subsequent stage Rx, wherein x is from 2 to N, comprises at least a portion of a vapor stream Vx-1 from the prior stage, wherein at least a portion of the reactor feed RFx reacts, via a methanol synthesis reaction, in the methanol synthesis reactor Rx to produce a methanol reactor effluent REx; wherein the methanol reactor effluent REx comprises methanol, water, H ₂ , CO, C0 ₂ , and optionally hydrocarbons; (b) separating at least a portion of the methanol reactor effluent REx from each stage in a separator to provide a crude methanol product stream MPx and a vapor stream Vx; wherein the crude methanol product stream MPx comprises methanol and water; and wherein the vapor stream Vx comprises H ₂ , CO, C0 ₂ , and optionally hydrocarbons; (c) separating at least a portion of the vapor stream from the final or Nth stage V _N in a hydrogen recovery unit HR to provide a hydrogen stream 40 and a residual gas stream 35; wherein the hydrogen stream 40 comprises at least a portion of the hydrogen of the vapor stream V _N from the final stage; wherein the residual gas stream 35 comprises CO, C0 ₂ , and optionally hydrocarbons; and wherein at least a portion of the hydrogen stream 40 is fed to the first methanol reactor R1 in step (a). In embodiments, N is from 2 to about 10, from 2 to about 9, from 2 to about 8, from 2 to about 6, or from 2 to about 4. The herein-disclosed multi-stage process can further comprise: (d) separating at least a portion of the crude methanol product streams MPx from one or more stages into a methanol stream and a water stream. In embodiments, the catalyst of one or more stage x and the catalyst of one or more subsequent stage x ₊ are the same or different, and/or a catalyst amount of one or more methanol synthesis reactors R _x is greater than, less than, or equal to a catalyst amount of one or more subsequent methanol synthesis reactor R _x+ . In embodiments, for each stage x, where x is from 1 to N, the catalyst of stage x and the catalyst of stage x ₊₁ are the same or different, and/or a catalyst amount of methanol synthesis reactor R _x is greater than, less than, or equal to a catalyst amount of a subsequent methanol synthesis reactor R _x+i . In embodiments, as described further hereinbelow, the number N of stages x is selected to achieve a target CO conversion and/or a target C0 ₂ conversion for the overall multi-stage process.

[0012] Other than in the operating examples or where otherwise indicated, all numbers or expressions referring to quantities of ingredients, reaction conditions, and the like, used in the specification and claims are to be understood as modified in all instances by the term“about.” Various numerical ranges are disclosed herein. Because these ranges are continuous, they include every value between the minimum and maximum values. The endpoints of all ranges reciting the same characteristic or component are independently combinable and inclusive of the recited endpoint. Unless expressly indicated otherwise, the various numerical ranges specified in this application are approximations. The endpoints of all ranges directed to the same component or property are inclusive of the endpoint and independently combinable. The term“from more than 0 to an amount” means that the named component is present in some amount more than 0, and up to and including the higher named amount.

[0013] The terms“a,”“an,” and“the” do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. As used herein the singular forms“a,”“an,” and“the” include plural referents.

[0014] As used herein,“combinations thereof’ is inclusive of one or more of the recited elements, optionally together with a like element not recited, e.g., inclusive of a combination of one or more of the named components, optionally with one or more other components not specifically named that have essentially the same function. As used herein, the term“combination” is inclusive of blends, mixtures, alloys, reaction products, and the like.

[0015] Reference throughout the specification to“an embodiment,”“another embodiment,”“other embodiments,”“some embodiments,” and so forth, means that a particular element (e.g., feature, structure, property, and/or characteristic) described in connection with the embodiment is included in at least an embodiment described herein, and may or may not be present in other embodiments. In addition, it is to be understood that the described element(s) can be combined in any suitable manner in the various embodiments.

[0016] As used herein, the terms“inhibiting” or“reducing” or“preventing” or“avoiding” or any variation of these terms, include any measurable decrease or complete inhibition to achieve a desired result.

[0017] As used herein, the term“effective,” means adequate to accomplish a desired, expected, or intended result. [0018] As used herein, the terms“comprising” (and any form of comprising, such as“comprise” and“comprises”),“having” (and any form of having, such as“have” and“has”),“including” (and any form of including, such as“include” and“includes”) or“containing” (and any form of containing, such as“contain” and“contains”) are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

[0019] Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of skill in the art.

[0020] Compounds are described herein using standard nomenclature. For example, any position not substituted by any indicated group is understood to have its valency filled by a bond as indicated, or a hydrogen atom. A dash (“-”) that is not between two letters or symbols is used to indicate a point of attachment for a substituent. For example, -CFIO is attached through the carbon of the carbonyl group.

[0021] As used herein, the terms“C _x hydrocarbons” and“C _x s” are interchangeable and refer to any hydrocarbon having x number of carbon atoms (C). For example, the terms“C ₄ hydrocarbons” and “C ₄ s” both refer to any hydrocarbons having exactly 4 carbon atoms, such as n-butane, iso-butane, cyclobutane, 1 -butene, 2-butene, isobutylene, butadiene, and the like, or combinations thereof.

[0022] As used herein, the term“C _x+ hydrocarbons” refers to any hydrocarbon having equal to or greater than x carbon atoms (C). For example, the term“C ₂₊ hydrocarbons” refers to any hydrocarbons having 2 or more carbon atoms, such as ethane, ethylene, C s, C ₄ s, C ₅ s, etc.

[0023] As utilized herein, the‘methanol synthesis loop’ or‘methanol loop’ refers to the methanol synthesis section of a plant, comprising the multiple stages described hereinbelow. Even when a single pass is utilized, the series of methanol synthesis reactors is referred to herein as a‘loop’.

[0024] As utilized herein,“N” represents the total number of stages in a multi-stage process as described herein, and“x’ represents a series of successive integers from 1 to N, with each x representing a specific stage from the group comprising N total stages, including a first stage (x = 1) and a final, or Nth stage (x = N). For example, where N equals 2, x can equal 1 (i.e., a first stage), and 2 (i.e., a second, final, or N' ^h stage), where N equals 3, x can equal 1 (i.e, a first stage), 2 (i.e., a second stage), and 3 (i.e., a third, final, or N' ^h stage), and etc.. For equipment common to multiple stages, the subscript x denotes the stage. For example, the subscript“1” in reference to reactor feed RF,. reactor R ,. reactor effluent RF, . first heat exchanger H F I , . second heat exchanger HF.2,. and flash drum FD, indicates that the piece of equipment is in the first stage, i.e., x = 1.

[0025] Referring to Figure 1, a methanol production system I is disclosed. The methanol production system I generally comprises a synthesis gas feed line 5, one or more compressors 10; a plurality (equal to N) of methanol synthesis reactors Rx; a plurality (equal to N or (N-l)) of first heat exchangers FIE lx; a plurality (equal to N) of gas-liquid separators or flash drums FDx; a plurality (equal to (N-l)) of second heat exchangers FlE2x; a plurality (equal to N) of first steam lines S ix; a plurality (equal to N or (N- l)) of second steam lines S2x; a steam header 25; one or more (equal to M) hydrogen recovery units HRy; methanol product lines MP _X ; a purge gas line 35; and a hydrogen recycle stream 40.

[0026] As depicted in the embodiment of Figure 1, in embodiments a methanol synthesis system I of this disclosure comprises a multi-stage system comprising N stages (in series) including a plurality of (N- 1) of upstream stages X, and a final or N' ^h stage. Each upstream stage X includes a reactor feed line RFx, a methanol synthesis reactor R _x , a reactor effluent line REx, a first heat exchanger FIE lx, a gas- liquid separator or flash drum FDx, a second heat exchanger FlE2x, an outlet line RF _X+1 for a reactor feed to an immediately downstream methanol synthesis reactor R _x+1 , a first steam line S l _x , and a second steam line S2 _X , wherein x ranges from 1 to (N- l). The final or Nth stage comprises reactor RN and gas- liquid separator or flash drum FD _N , and can also comprise a first heat exchanger F1E1 _N , in embodiments. In embodiments, the multi-stage process has from 2 to about 10 stages (i.e., N is in a range of from 2 to about 10).

[0027] Accordingly, in embodiments, the methanol synthesis system I comprises a number N of methanol synthesis reactors including a final methanol synthesis reactor R _N and a number (N-l) of methanol synthesis reactors R _x upstream of final stage methanol synthesis reactor R _N , where N is in a range of from 2 to about 10, and where the number of upstream stages X ranges from 1 to (N-l). In embodiments, methanol synthesis system I comprises (N-l) first heat exchangers HE1 _X , where N is in a range of from 2 to about 10, and where x ranges of from 1 to (N- l). In alternative embodiments, a methanol synthesis system comprises a number N of first heat exchangers HE 1 , including (N-l) upstream stage heat exchangers HE1 _X and a final stage first heat exchanger HE1 _N (not shown in Figure 1) downstream of final methanol synthesis reactor R _N , where N is in a range of from 2 to 10, and where x ranges of from 1 to (N-l). In embodiments, methanol synthesis system I comprises a plurality of N gas-liquid separators or flash drums including a final flash drum FD _N and (N- l) gas- liquid separators or flash drums FD _X upstream of final flash drum FD _N , where N is in a range of from 2 to about 10, and where x ranges of from 1 to (N-l). In embodiments, a methanol synthesis system I comprises (N-l) second heat exchangers HE2 _X , where N is in a range of from 2 to about 10, and where x ranges of from 1 to (N-l). In embodiments, a methanol synthesis system I of this disclosure comprises a number M of hydrogen (H ₂ ) recovery units including a final (or sole) hydrogen recovery unit HR _M and a number y (which can be zero) of hydrogen recovery units HR _y upstream of final hydrogen recovery unit M _m , wherein M is in a range of from 1 to about 8, and where y ranges from 1 to (M-l). In embodiments, the methanol synthesis system I comprises a number N of first steam lines S I including a final first steam fine S 1 _N and a number (N-l) of first steam fines S l _x upstream of final first steam line S 1 _N , where N is in a range of from 2 to about 10, and where x ranges from 1 to (N-l). In embodiments, the methanol synthesis system I comprises a number (N-l) of second steam lines S2 including a final second steam fine S2 _N and (N-l) second stream fines S2 _X upstream of S2 _N , where N is in a range of from 2 to about 10, and where x ranges from 1 to (N- l). As will be appreciated by one of skill in the art, and with the help of this disclosure, methanol production system components shown in the Figures can be in fluid communication with each other (as represented by the connecting lines indicating a direction of fluid flow) through any suitable conduits (e.g., pipes, streams, etc.).

[0028] A methanol synthesis system of this disclosure can comprise from two to about ten, about nine, or about eight methanol synthesis reactors Rx (e.g., N = 2, 3, 4, 5, 6, 7, or 8). For example, in the embodiment of Figure 2, which is a schematic of a methanol synthesis system II, according to a specific embodiment of this disclosure, methanol synthesis system II comprises 4 methanol synthesis reactors Rl, R2, R3, and R4, including three upstream stage methanol synthesis reactors Rl, R2, and R3 and a final stage methanol synthesis reactor R4.

[0029] In embodiments, a process for producing methanol according to this disclosure comprises: (a) feeding a first reactant mixture or feed RF1 to a methanol reactor Rl of a first stage. The first reaction mixture RF1 comprises synthesis gas (or ‘syngas’), including hydrogen (H ₂ ), carbon monoxide (CO), carbon dioxide (C0 ₂ ), and optionally water and/or hydrocarbons. In embodiments, the first reactant mixture is characterized by a molar ratio of hydrogen to carbon monoxide (Fl ₂ /CO). In embodiments, the first reactant mixture is characterized by a molar ratio of hydrogen to carbon monoxide (Fl ₂ /CO) in a range of from about 2 to about 5, from about 2 to about 4.5, from about 2 to about 4, less than or equal to about 5, 4, or 3, and/or greater than or equal to about 1.8, 2, or 3. In embodiments, the first reaction mixture is characterized by an M ratio, wherein the M ratio is a molar ratio defined as (1¾-C0 ₂ )/(C0+C0 ₂ ). In embodiments, the first reaction mixture is characterized by an M ratio in a range of from about 1.6 to about 3.5, from about 1.6 to about 3.2, from about 1.7 to about 3.2, from about 1.7 to about 3.0, from about 1.8 to about 2.5, from about 1.8 to about 2.2, from about 1.8 to about 2.1, from about 1.8 to about 2.05, or less than or equal to about 3.5, 3.2, 3.0, 2.5, 2.2, 2.1, 2.05, 2.0, 1.9, 1.8, or 1.7, and/or greater than or equal to about 1.6, 1.7, 1.8, 1.9, 2.0, 2.05, 2.1, 2.2, 2.5, or 3.0.

[0030] At lower hydrogen to carbon oxides molar ratio, impurities start to form. In embodiments, the herein-disclosed methanol synthesis process and system solve this issue by recovering hydrogen through one or multiple hydrogen recovery units FIR in series, and recycling at least a portion of the recovered hydrogen to one or more stages (e.g., a first stage, a second stage, a third stage ... an N' ^h stage) via hydrogen recycle 40 to increase the hydrogen to carbon oxides ratios in the methanol synthesis loop, thereby increasing the conversion per pass.

[0031] Accordingly, in embodiments, first reactor feed RF1 is a hydrogen- enriched syngas formed by combining a synthesis gas in synthesis gas feed line 5 with a recycle hydrogen in recycle hydrogen line 40. Synthesis gas (syngas) is a mixture comprising carbon monoxide (CO) and hydrogen (H ₂ ), as well as small amounts of carbon dioxide (C0 ₂ ), water (H ₂ 0), and unreacted methane (CTf). In embodiments, the syngas in syngas feed line 5 is characterized by a molar ratio of hydrogen to carbon monoxide (H ₂ /CO). In embodiments, the syngas in syngas feed line 5 is characterized by a molar ratio of hydrogen to carbon monoxide (Ff/CO) that is less than the molar ratio (H ₂ /CO) of the first reactor feed RF1. In embodiments, the syngas in syngas feed line 5 is characterized by a molar ratio of hydrogen to carbon monoxide (H ₂ /CO) in a range of from about 2 to about 5, from about 2 to about 4.5, from about 2 to about 4, less than or equal to about 5, 4, or 3, and/or greater than or equal to about 1.8, 2, or 3. In embodiments, the syngas in syngas feed line 5 is characterized by an M ratio that is less than the M ratio of the first reaction mixture in first reactor feed RF 1. In embodiments, the syngas in syngas feed line 5 is characterized by an M ratio, wherein the M ratio is a molar ratio defined as (H ₂ -C0 ₂ )/(C0+C0 ₂ ). In embodiments, the syngas in syngas feed line 5 is characterized by an M ratio in a range of from about 1.6 to about 3.5, from about 1.6 to about 3.2, from about 1.7 to about 3.2, from about 1.7 to about 3.0, from about 1.8 to about 2.5, from about 1.8 to about 2.2, from about 1.8 to about 2.1, from about 1.8 to about 2.05, or less than or equal to about 3.5, 3.2, 3.0, 2.5, 2.2, 2.1, 2.05, 2.0, 1.9, 1.8, or 1.7, and/or greater than or equal to about 1.6, 1.7, 1.8, 1.9, 2.0, 2.05, 2.1, 2.2, 2.5, or 3.0.

[0032] In embodiments, the syngas stream in syngas feed line 5 and/or the first reactor feed RF1 comprises inert gases in an amount of less than or equal to about 15, 10, or 5 wt.%, based on the total weight of the first reactor feed RF 1 ; and/or the first reactor feed RF 1 comprises hydrocarbons in an amount of less than or equal to about 15, 10, or 5 wt.%, based on the total weight of the first reactor feed RF 1.

[0033] The synthesis gas in line 5 can be provided via any known methods. For example, the synthesis gas can be produced via partial oxidation (e.g., catalytic partial oxidation (CPO)), reforming, gasification, or the like, or combinations thereof. Reforming can comprise steam methane reforming (SMR), autothermal reforming (ATR), dry reforming, and the like. By way of example, the syngas in syngas feed line 5 can, without limitation, be formed via a combination of reforming and partial oxidation or SMR and ATR. A variety of feedstocks can be utilized to produce the synthesis gas in syngas feed line 5, including, without limitation, methane, natural gas, natural gas liquids, associated gas, well head gas, enriched gas, paraffins, shale gas, shale liquids, fluid catalytic cracking (FCC) off gas, refmei process gases, stack gases, LPG, naphtha, petcoke, coal, fuel gas from a fuel gas header, and the like, or combinations thereof.

[0034] In embodiments, the synthesis gas in syngas feed line 5 is a product of steam reforming of natural gas (steam methane reforming or SMR), although other hydrocarbon sources can be used for syngas production, such as refinery off-gases, naphtha feedstocks, heavy hydrocarbons, coal, biomass, etc. SMR is an endothermic process and requires significant energy input to drive the reaction forward. Conventional endothermic technologies such as SMR produce syngas with a hydrogen content greater than the required content for methanol synthesis. Generally, SMR produces syngas with an M ratio ranging from 2.6 to 2.98, wherein the M ratio is a molar ratio defined as (H ₂ -C0 ₂ )/(C0+C0 ₂ ).

[0035] In embodiments, the synthesis gas in syngas feed line 5 is a product of an autothermal reforming (ATR) process in which a portion of the natural gas is burned as fuel to drive the conversion of natural gas to syngas resulting in relatively low hydrogen and high C0 ₂ concentrations. In embodiments, the synthesis gas in syngas feed line 5 is a product of a combined reforming (CR) technology that pairs SMR with autothermal reforming (ATR) to reduce the amount of hydrogen present in syngas. ATR produces a syngas with a hydrogen content lower than the required content for methanol synthesis. Generally, ATR produces syngas with an M ratio ranging from 1.7 to 1.84. In the CR technology, the natural gas feed volumetric flowrate to the SMR and the ATR can be adjusted to achieve an overall syngas M ratio of 2.0 to 2.06. Further, CR syngas has a hydrogen content greater than the required content for methanol synthesis. Furthermore, SMR is a highly endothermic process, and the endothermicity of the SMR technology requires burning fuel to drive the syngas synthesis. Consequently, the SMR technology reduces the energy efficiency of the methanol synthesis process.

[0036] In embodiments, the synthesis gas in syngas feed line 5 is a product of catalytic partial oxidation (CPO or CPOx) of natural gas. CPO processes employ partial oxidation of hydrocarbon feeds to syngas comprising CO and H ₂ . The CPO process is exothermic, thus eliminating the need for external heat supply. However, the composition of the produced syngas is typically not directly suitable for methanol synthesis, for example, owing to a reduced hydrogen content.

[0037] One or more compressors 10 can be configured to increase the pressure of the first reactor feed RF 1 to a pressure for introduction into first methanol synthesis reactor Rl . For example, the one or more compressors 10 can increase the pressure of the first reactor feed RF 1 to a pressure in a range of from about 40 bar (4 MPa) to about 1 10 bar (1 1 MPa), from about 40 bar (4 MPa) to about 100 bar (10 MPa), from about 50 bar (5MPa) to about 1 10 bar (1 1 MPa), or less than or equal to about 1 10 bar (1 1 MPa), 100 bar (10 MPa), or 90 bar (9 MPa). One or more compressors 10 can, in embodiments, be steam driven compressors.

[0038] A first reactor feed heat exchanger 20 can be positioned between the one or more compressors 10 and first methanol synthesis reactor Rl . First reactor feed heat exchanger 20 is utilized to increase the temperature of the compressed first reaction mixture in first reaction mixture line RF1 downstream of the one or more compressors 10 for introduction into first methanol synthesis reactor Rl . For example, first reactor feed heat exchanger 20 can be operable to increase the temperature of the first reactor feed RF 1 to a temperature in a range of from about 150 °C to about 300 °C, from about 150 °C to about 250 °C, from about 160°C to about 300 °C, less than or equal to about 300 °C, 275 °C, or 250 °C, and/or greater than or equal to about 150 °C, 175 °C, or 200 °C.

[0039] Within the first methanol synthesis reactor Rl , at least a portion of the first reactor feed RF 1 reacts, via a methanol synthesis reaction, to produce a first methanol reactor effluent RE1. The first methanol reactor effluent RE1 comprises methanol, water, hydrogen (H ₂ ), carbon monoxide (CO), carbon dioxide (C0 ₂ ), and optionally hydrocarbons.

[0040] The methanol synthesis process can further comprise: (b) separating at least a portion of the first methanol reactor effluent RE1 in a first separator FD 1 into a first crude methanol product stream MP1 and a first vapor stream VI. The first crude methanol product stream MP1 comprises methanol and water, and the first vapor stream VI comprises FR, CO, C0 ₂ , and optionally hydrocarbons. The first methanol reactor effluent RE1 (as well as all reactor effluent streams REx) can be separated into the crude methanol stream MPx and the vapor stream Vx via any suitable gas- liquid separator FDx, such as, by way of nonlimiting example, a vapor-liquid separator, flash drum, knock-out drum, knock-out pot, compressor suction drum, etc.

[0041] Steam produced in first methanol synthesis reactor R1 can be removed from first methanol synthesis reactor R1 via first stage first steam line SR. The steam removed from first methanol synthesis reactor R1 can be introduced into steam header 25. Prior to (b) separating at least a portion of the first methanol reactor effluent stream REi in a first separator FDi into a first crude methanol product stream P, and a first vapor stream V,. the first reactor effluent RE, comprising methanol can be subjected to heat exchange in a first stage first heat exchanger TIER, to produce steam in first stage second steam line S2 _l ·

[0042] A methanol synthesis method of this disclosure can further comprise: (c) feeding a second reactor feed RF2 to a second methanol synthesis reactor R2. In embodiments, a temperature of the second reaction mixture RF2 is increased to a desired methanol synthesis feed temperature via passage through a first stage second heat exchanger Hf 2, prior to introduction into second methanol synthesis reactor R2. The second reactant mixture RF2 comprises at least a portion of the first vapor stream V 1 from the first stage. Within second methanol synthesis reactor R2, at least a portion of the second reactant mixture RF2 reacts, via a methanol synthesis reaction, to produce a second methanol reactor effluent RE2. The second methanol reactor effluent comprises methanol, water, FR, CO, C0 ₂ , and optionally hydrocarbons.

[0043] The methanol synthesis method of this disclosure can further comprise: (d) separating at least a portion of the second methanol reactor effluent stream RE2 in a second separator FD2 into a second crude methanol product stream MP2 and a second vapor stream V2. The second crude methanol stream MP2 comprises methanol and water, and the second vapor stream V2 comprises FR, CO, C0 ₂ , and optionally hydrocarbons. The vapor V2 can be heat exchanged in the second stage second heat exchanger HE2 ₂ , to provide a reactor feed RF3 for a third methanol synthesis reactor of a subsequent (i.e., third) stage.

[0044] As noted hereinabove and described with reference to the embodiment of Figure 1, a methanol synthesis system of this disclosure can comprise from 2 to about 10, 9, or 8 methanol synthesis reactors. Thus, second methanol synthesis reactor R2 can be the final methanol synthesis reactor when N = 2. In alternative embodiments, a multiple number N-l of upstream stages X are utilized upstream of a final or Nth stage, each upstream stage X comprising a methanol synthesis reactor Rx operable to produce methanol from a reactor feed Rx, a gas-liquid separator or flash drum FDx operable to separate the reactor effluent REx into a crude methanol product stream MPx comprising methanol and water, and a vapor stream Vx comprising H ₂ , CO, C0 ₂ , and optionally hydrocarbons. Each upstream stage X can further comprise a first heat exchanger HE lx upstream of gas-liquid separator or flash drum FDx and operable to reduce a temperature of the methanol synthesis reactor effluent REx to a desired temperature for separation in gas-liquid separator FDx and/or a second heat exchanger HE2x located downstream of gas-liquid separator or flash drum FDx and operable to increase a temperature of the vapor Vx to a desired temperature for introduction into a methanol synthesis reactor R _x+1 of the subsequent stage x+1. In such embodiments, a reactor feed RF _X is introduced into the x ^th reactor Rx to produce a methanol synthesis reactor effluent REx, the reactor effluent REx is subjected to heat exchange in xth first heat exchanger HE lx to produce steam in second steam line S2x, and the reduced temperature reactor effluent is introduced into gas-liquid separator or flash drum FDx. Within gas-liquid separator or flash drum FDx, liquid crude methanol product stream MPx is separated from vapor Vx comprising H ₂ , CO, C0 ₂ , and optionally hydrocarbons. At least a portion of the vapor Vx is introduced into a methanol synthesis reactor Rx+1 of the next or (x I I )' ^h stage, optionally via heating in the first heat exchanger HE2 of stage x, HE2x.

[0045] For example, with reference back to the specific embodiment of Figure 2 comprising three stages upstream of the final or fourth methanol synthesis reactor R4, within the third stage (x = 3), the third stage reactor feed RF3 is introduced into third methanol synthesis reactor R3 from which a third methanol synthesis reactor effluent RE3 is removed. The third methanol synthesis reactor effluent comprises methanol, water, H ₂ , CO, C0 ₂ , and optionally hydrocarbons. The third methanol synthesis reactor effluent RE3 is separated in gas- liquid separator or flash drum FD3 into a third crude methanol product stream MP3 and a third vapor V3. Prior to introduction into gas-liquid separator or flash drum FD3, the third methanol synthesis reactor effluent RE3 can be heat exchanged in the third stage first heat exchanger HE1 ₃ , to produce steam in third stage second steam line S2 ₃ . The third stage vapor V3 can be subjected to heat exchange in the third stage second heat exchanger HE2 ₃ , to increase the temperature and provide fourth (and final, N = 4) reaction mixture feed RF4 comprising at least a portion of the vapor V3.

[0046] After the penultimate methanol synthesis reactor (i.e., methanol synthesis reactor N-l, R _N _ , the reactor feed RF _X _, is introduced into the final or Nth methanol synthesis reactor R _N . The reactor effluent from the final or N' ^h methanol synthesis reactor R _N is introduced into a final gas-liquid separator or flash drum FD _N . As depicted in the Figures, the methanol product from each of the (N-l) upstream reactors can also be introduced into final gas-liquid separator or flash drum FD _N . For example, in the embodiment of Figure 2, the liquid crude methanol product streams MP1, MP2, and MP3 from the first, second and third stages are introduced into the final gas-liquid separator or flash drum FD _n . Final gas-liquid separator or flash drum FDN separates a crude methanol product MP _N from a vapor product which will be subjected to hydrogen recovery, as detailed further hereinbelow. [0047] In embodiments, a methanol synthesis method of this disclosure further comprises separating at least a portion of the crude methanol streams from one or more of the N stages (e.g., MPx, where x is from 1 to N) into a methanol stream and a water stream. In embodiments, a multi process for producing methanol as disclosed herein can thus comprise a step of separating at least a portion of one or more of the crude methanol streams MPx in a distillation unit to provide a methanol stream and a water stream, wherein the distillation unit comprises one or more distillation columns. The water stream comprises water and residual methanol. Generally, the one or more distillation columns can separate components of the one or more crude methanol streams MPx based on their boiling points. As will be appreciated by one of skill in the art, and with the help of this disclosure, the higher the water content of the one or more crude methanol streams MPx, the more distillation columns are necessary to purify the methanol.

[0048] According to this disclosure, hydrogen is recovered from the vapor V _N removed from the final gas-liquid separator or flash drum FD _N , and recycled to the first stage (e.g., to first methanol synthesis reactor Rl) and/or a subsequent stage via hydrogen recycle line 40.

[0049] The methanol synthesis method of this disclosure thus further comprises: (e) separating at least a portion of the final (e.g., the second, third, fourth, fifth, sixth, seventh, eighth, ninth, or tenth) vapor stream V _N in at least one hydrogen recovery HR unit to provide a hydrogen stream H and a residual gas stream 35; wherein the hydrogen stream comprises at least a portion of the hydrogen of the final vapor stream V _N ; wherein the residual gas stream comprises CO, C0 ₂ , and optionally hydrocarbons. The hydrogen recovery unit(s) HRy of each stage y of hydrogen recovery, where y is from 1 to about M, and where M is from 1 to about 8, can comprise a PSA unit, a membrane separation unit, a cryogenic separation unit, and the like, or combinations thereof.

[0050] As depicted in the embodiment of Figure 1, a number M stages of hydrogen recovery can include M-l stages of hydrogen recovery upstream of a final (or sole, when M- 1 ) stage M of hydrogen recovery. The total number of stages y of hydrogen recovery M is in the range of from 1 to about 10. Thus, in embodiments, the methanol synthesis system of this disclosure comprises from 1 to about 10 membrane separation units and/or pressure swing adsorption units. A number M-l of upstream stages of hydrogen recovery HRy, wherein y ranges from 0 to (M-l), can be upstream of final hydrogen recovery stage HR _M . In instances when M = 1, there are no hydrogen recovery stages upstream of the sole stage HR _M /HR ,. In alternative embodiments, when M is greater than 2, a number of M-l upstream hydrogen recovery stages Y separate hydrogen recovery stage feed HRFy, where y ranges from 1 to M-l, into a hydrogen stream recovered from that stage Hy and a residual gas stream which is introduced into a subsequent (y I I )' ^h hydrogen recovery stage as the hydrogen recovery feed for that stage HRF _y+1 . HRF1 comprises at least a portion of the final stage vapor stream V _N . At least a portion of the recovered hydrogen (e.g., H _y , where y ranges from 1 to M) can be combined as indicated in Figure 1, to provide recycle hydrogen 40. Hydrogen recycle 40 can be introduced into the first stage methanol synthesis reactor Rl, for example via combination with synthesis gas in synthesis gas feed line 5 upstream of the one or more compressors 10 and/or into a methanol synthesis reactor of one or more downstream stages via reactor feed RFx, where x is from 2 to N. In embodiments, at least a portion of the purge gas stream 35 can be purged. In embodiments, at least a portion of the purge gas stream 35 can be used as fuel, for example for pre-heating the first reactor feed RF 1.

[0051] In embodiments, at least a portion of the residual gas stream 35 from final or Mth hydrogen recovery stage HR _M is used as fuel in a syngas production process and/or for steam generation to power a steam-driven compressor, such as, for example, one or more of the one or more compressors 10.

[0052] According to this disclosure, a number N of stages (including N-l upstream stages and the final N' ^h stage) is selected as necessary to achieve a target CO conversion and/or a target C0 ₂ conversion for the overall multi-stage process. A conversion for the overall multi-stage process refers to the“per pass” conversion provided by a single passage through the N methanol synthesis reactors Rx of the N stages (i.e., the sum of the conversions from each of the methanol synthesis reactors Rx, wherein x is from 1 to N).

[0053] The methanol synthesis reactor Rx of each stage x, where x is from 1 to N, is configured to produce methanol via a methanol synthesis reaction in which at least a portion of a reactor feed RFx comprising H ₂ , CO, C0 ₂ , and optionally hydrocarbons reacts in the methanol synthesis reactor to produce a methanol reactor effluent REx, where x varies from 1 to N, comprising methanol, water, H ₂ , CO, C0 ₂ , and optionally hydrocarbons. In embodiments, at least a portion of recycle hydrogen stream 40 is combined with the syngas in syngas feed line 5 to yield a hydrogen enriched syngas for introduction into first stage methanol synthesis reactor Rl as first reactor feed RF1. As noted above, in embodiments, the syngas in syngas feed line 5 has an M ratio of equal to or greater than about 1.7, and/or a H ₂ /CO molar ratio of equal to or greater than about 1.8; the hydrogen enriched syngas in the first methanol synthesis reactor feed RF1 has an M ratio greater than the M ratio of the syngas in syngas feed line 5, and the hydrogen enriched syngas has a H ₂ /CO molar ratio greater than the H ₂ /CO molar ratio of the syngas in syngas feed line 5. The method can comprise compressing at least a portion of the hydrogen enriched syngas of RF1 in one or more compressors 10 (e.g., steam-driven compressors) to yield a compressed hydrogen enriched syngas; and feeding at least a portion of the compressed hydrogen enriched syngas to the first methanol reactor Rl as first stage reactor feed RF1. The reactant mixture or reactor feed RFx to each methanol synthesis reactor after the first methanol synthesis reactor RF1 (i.e., for methanol synthesis reactor Rx, where x varies from 2 to N) comprises at least a portion of an upstream vapor stream V _x-! from an upstream separator FDx_, .

[0054] The methanol synthesis reactors Rx, where x ranges from 1 to N, can comprise any reactor suitable for a methanol synthesis reaction from CO and H ₂ , such as for example a trickle bed reactor, a fluidized bed reactor, a sluny reactor, a loop reactor, a cooled multi tubular reactor, an adiabatic reactor, and the like, or combinations thereof.

[0055] Generally, CO and H ₂ can be converted into methanol (CH ₃ OH), for example as represented by Equation (1):

CO + H ₂ CH ₃ OH (1)

[0056] C0 ₂ and H ₂ can also be converted to methanol, for example as represented by Equation

(2):

C0 ₂ + 3H ₂ CH ₃ OH + H ₂ 0 (2)

[0057] Without wishing to be limited by theory, the lower the C0 ₂ content of the reactor feed RFx, the lower the amount of water produced in the methanol reactor Rx. As will be appreciated by one of skill in the art, and with the help of this disclosure, syngas produced by SMR has a fairly high content of hydrogen (as compared to the hydrogen content of syngas produced by CPO), and a syngas with an elevated hydrogen content can promote the C0 ₂ conversion to methanol, for example as represented by Equation (2), which in turn can lead to an increased water content in a crude methanol stream (e.g., crude methanol stream REx).

[0058] Methanol synthesis is an equilibrium limited chemical reaction. In conventional methanol synthesis loops, a recycle stream comprising 90-96% of the unreacted gases (carbon monoxide, carbon dioxide, hydrogen, methane, nitrogen, and impurities) is recycled, which leads to an increased concentration of inerts (methane, nitrogen, argon) in the loop. Buildup of inerts undesirably increases the compression cost and increases the size(s) of the methanol synthesis reactors. The herein- disclosed multi-stage methanol synthesis system and method eliminate this issue by employing a (e.g., single) train of multiple methanol synthesis reactors in series in order to increase the per pass conversion and eliminate the conventional recycle stream, which is replaced herein, in embodiments, with an optional small hydrogen recycle stream 40. Moreover, conversion per pass across the reactor/reactors system in the conventional process is about 80 to 92% for carbon monoxide and about 38 to 64% for carbon dioxide. In embodiments, the herein-disclosed multi-stage system and method enable increasing the conversion per pass to about 96 to 99% for carbon monoxide and about 89 to 96% for carbon dioxide. Increased conversion per pass is a result of the condensation of methanol product MPx after each methanol synthesis reactor Rx and removing the methanol product MPx from the methanol synthesis loop to shift the equilibrium conversion favoring formation of the methanol product (e.g., to the right in Equations 1 and 2).

[0059] In embodiments, each methanol synthesis reactor Rx, where x is from 1 to N, of the multi stage process can independently comprise an adiabatic reactor or a water-cooled reactor. The methanol synthesis reactors Rx can be tubular reactors, in embodiments. The water-cooled reactor generates steam, which can be removed from the methanol synthesis reactor of each stage x via first steam lines S ix, where x varies from 1 to N. The steam in first steam line Six can be combined in a steam header 25. In embodiments, at least a portion of the steam is used to power a steam-driven compressor, such as, for example, a compressor of the one or more compressors 10, a distillation reboiler, or a combination thereof.

[0060] In embodiments, the methanol reactor of each stage Rx, where x varies from 1 to N, is characterized by a reactor volume, and the volume of methanol synthesis reactor R _x+1 is greater than the volume of a downstream methanol reactor Rx. In embodiments, the herein-disclosed multi-stage process is characterized by a total reactor volume, wherein the total reactor volume is given by the sum of the volumes of each of the reactors of the N stages Rx, where x is from 1 to N, and the total reactor volume is decreased by greater than or equal to about 5, 10, or 15% when compared to the total reactor volume in an otherwise similar process that: (i) lacks a step of separating each methanol reactor effluent stream REx into a crude methanol product stream MPx and a vapor stream Vx, and/or (ii) lacks a step of separating hydrogen from the final vapor stream V _N from the final or Nth stage in one or more hydrogen recovery unit HRy, wherein y is from 1 to M, and M is from 1 to about 8, to provide a hydrogen stream 40 and a residual gas stream 35.

[0061] Methanol synthesis from CO, C0 ₂ and H ₂ is a catalytic process, and is most often conducted in the presence of copper based catalysts. The methanol reactors Rx can comprise a methanol production catalyst, such as any suitable commercial catalyst used for methanol synthesis. Nonlimiting examples of methanol production catalysts suitable for use in the methanol reactors Rx in the current disclosure include Cu, Cu/ZnO, Cu/Th0 ₂ , Cu/Zn/Al ₂ 0 ₃ , Cu/Zn0/Al ₂ 0 ₃ , Cu/Zr, and the like, or combinations thereof.

[0062] In embodiments, a methanol synthesis process of this disclosure utilizes different types of catalysts to increase reaction rates. For example, in embodiments, one or more first or upstream reactor(s) comprise catalysts that favor CO hydrogenation (e.g., as per Equation (1)) and one or more last or downstream methanol synthesis reactor(s) comprise catalysts that favor C0 ₂ hydrogenation (e.g., as per Equation (2)).

[0063] In embodiments, the methanol synthesis reaction comprises a reaction between H ₂ and CO to form methanol (e.g., as per Equation 1) and/or a reaction between H ₂ and C0 ₂ to form methanol (e.g., as per Equation 2); wherein a catalyst of one or more first methanol synthesis reactors of the N stages is different from a second catalyst of one or more second methanol synthesis reactors of one or more other of the N stages; wherein the one or more first methanol synthesis reactors are characterized by a first CO conversion and by a first C0 ₂ conversion, wherein the first CO conversion is greater than the first C0 ₂ conversion; wherein the one or more second methanol synthesis reactors are characterized by a second CO conversion and by a second C0 ₂ conversion, and wherein the second CO conversion is less than the second C0 ₂ conversion. In embodiments, one or more upstream methanol synthesis reactors comprises a first catalyst that favors the CO hydrogenation reaction of Equation 1 , and one or more downstream methanol synthesis reactors comprises a second catalyst that favors the C0 ₂ hydrogenation reaction of Equation 2. In embodiments, the one or more upstream methanol synthesis reactors that comprise the first catalyst that favors the CO hydrogenation reaction of Equation 1 are all upstream of the one or more downstream methanol synthesis reactors that comprise the second catalyst that favors the C0 ₂ hydrogenation reaction of Equation 2.

[0064] Each methanol synthesis reactor Rx comprises a catalyst. In embodiments, the catalyst of the N stages are the same or different. In embodiments, each methanol reactor Rx, where x varies from 1 to N, is characterized by a catalyst amount, and the catalyst amount of methanol synthesis reactor R _x _i is greater than an amount of catalyst in the downstream methanol reactor R _x .

[0065] In embodiments, each of the N stages of the multi-stage process can independently comprise heating the reactant mixture RFx, where x varies from 1 to N, prior to feeding to the associated methanol reactor Rx. For example, the first stage reactor feed RF1 to first methanol synthesis reactor R1 can be heated via first reactor feed heat exchanger 20, and the reactor feed RFx to each methanol synthesis reactor Rx subsequent to the first methanol synthesis reactor R1 (i.e., methanol synthesis reactors Rx, where x varies from 2 to N) can be heated via the second heat exchanger HE2 _x _i of the prior stage.

[0066] In embodiments, each of the N stages of the multi-stage process (or the N-l upstream stages) can independently comprise: (1) heating water while cooling the methanol reactor effluent stream REx by heat exchange in a first heat exchanger HE1 _X to yield steam in second steam line S2x and a cooled methanol reactor effluent stream that is introduced into gas-liquid separator FDx. In embodiments, each of the N stages comprises separating at least a portion of the cooled methanol reactor effluent stream or the methanol reactor effluent stream REx in the gas-liquid separator or flash drum FDx into a crude methanol product stream MPx and a vapor stream Vx. In embodiments, one or more steam-driven compressors are powered with at least a portion of the steam in second steam line(s) S2 _X .

[0067] As depicted in the embodiments of Figures 1 and 2, in embodiments, a methanol synthesis method of this disclosure further comprises introducing to the final gas-liquid separator or flash drum FD _N at least a portion of the first crude methanol stream and/or at least a portion of the crude methanol stream from each additional stage (e.g., from stage 2 to stage N-l).

[0068] At least a portion of the vapor streams Vx from each of the N-l upstream stages (i.e., Vx, where x ranges from 1 to N-l) can be heated via passage through second heat exchanger HE2x of that stage prior to introduction into the downstream methanol synthesis reactor R _x+1 .

[0069] The CO conversion for each methanol synthesis reactor Rx, where x is from 1 to N, is defined as [(CO ^m - C0 ^0ut )/( CO ^m )]* 100%, where CO ^m is the number of moles of CO that entered the methanol synthesis reactor R _x as part of the reactor feed RFx; and C0 ^0ut is the number of moles of CO that were recovered from the methanol synthesis reactor R _x as part of the reactor effluent RE _X . Fikewise, the C0 ₂ conversion for each methanol synthesis reactor Rx, where x is from 1 to N, is defmed as [(C0 ₂ ^m - C0 ₂ ^out )/( C0 ₂ ^m )]* 100%, where C0 ₂ ^m is the number of moles of C0 ₂ that entered the methanol synthesis reactor R _x as part of the reactor feed RFx; and C0 ₂ ^out is the number of moles of C0 ₂ that were recovered from the methanol synthesis reactor R _x as part of the reactor effluent RE _X .

[0070] In embodiments, the target CO conversion for the overall multi-stage process, which is defined as the sum of the CO conversions for each of the methanol synthesis reactors Rx, wherein x is from 1 to N, is greater than or equal to about 90%; and/or the target C0 ₂ conversion for the overall multi-stage process, which is defined as the sum of the C0 ₂ conversions from each of the methanol synthesis reactors Rx, where x is from 1 to N, is greater than or equal to about 80%.

[0071] In embodiments, the multi-stage process is characterized by a CO conversion and/or a C0 ₂ conversion for the overall multi-stage process that is increased by greater than or equal to about 5% and/or 10%, respectively, when compared to the CO conversion and/or the C0 ₂ conversion, respectively, in an otherwise similar process that (i) lacks a step of separating each methanol reactor effluent REx into a crude methanol stream MPx and a vapor stream Vx, and/or (ii) lacks a step of separating the final vapor stream from the final or Nth stage V _N in at least one hydrogen recovery unit HR to provide a hydrogen stream 40 and a residual gas stream 35.

[0072] Conventional methanol synthesis loops operate at high pressures ranging from 75 to 1 10 bar. In embodiments, the herein-disclosed methanol synthesis process and system allow operation of the methanol synthesis loop to provide the same (or better) conversion as the conventional processes at lower pressures, e.g., from 20 to 75 bar.

[0073] In embodiments, the multi-stage process is characterized by an operating pressure effective to achieve the target CO conversion and/or the target C0 ₂ conversion for the overall multi stage process that is decreased when compared to the operating pressure effective to achieve the same target CO conversion and/or the same target C0 ₂ conversion, respectively, in an otherwise similar process that: (i) lacks a step of separating each methanol reactor effluent R R into a crude methanol stream MP _X and a vapor stream Vx, and/or (ii) lacks a step of separating the vapor stream from the final or Nth stage V _N in at least one hydrogen recovery unit HR into a hydrogen stream 40 and a residual gas stream 35. In embodiments, the operating pressure of the multi-stage process is less than about 90, 85, 80 or 75 barg.

[0074] In some aspects, the methanol synthesis reactor Rx can be characterized by at least one operational parameter selected from the group consisting of a methanol synthesis reactor temperature (e.g., catalyst bed temperature); reactor feed RFx temperature; target reactor effluent REx temperature; a methanol synthesis reactor Rx pressure; a methanol synthesis reactor contact time; or a combination thereof. Methanol condensation conditions occur at a temperature below the critical temperature of methanol which is about 240 °C at 95 bar (9.5 MPa). The methanol synthesis reactors Rx can be characterized by a reactor feed RFx temperature of from about 150 °C to about 300 °C, alternatively from about 150 °C to bout 250 °C, or alternatively from about 160°C to about 300 °C. [0075] The methanol synthesis reactors Rx can be characterized by a methanol synthesis reactor effluent REx temperature of from about 200 °C to about 350 °C, alternatively from about 210 °C to about 400 °C, alternatively from about 220 °C to about 350 °C.

[0076] In an embodiment, the methanol synthesis reactors Rx can be characterized by any suitable reactor temperature and/or catalyst bed temperature. For example, the methanol synthesis reactors Rx can be characterized by a reactor temperature and/or catalyst bed temperature of greater than or equal to about 150 °C, alternatively greater than or equal to about 200 °C, alternatively greater than or equal to about 300 °C, alternatively less than or equal to about 350 °C, alternatively less than or equal to about 325 °C, alternatively less than or equal to about 300 °C, alternatively from about 150 °C to about 350 °C, alternatively from about 200 °C to about 350 °C, alternatively from about 150 °C to about 300 °C.

[0077] The methanol synthesis reactors Rx can be operated under adiabatic conditions, non- adiabatic conditions, isothermal conditions, near-isothermal conditions, etc. For purposes of the disclosure herein, the term“non-adiabatic conditions” refers to process conditions wherein a reactor is subjected to external heat exchange or transfer (e.g., the reactor is heated; or the reactor is cooled), which can be direct heat exchange and/or indirect heat exchange. As will be appreciated by one of skill in the art, and with the help of this disclosure, the terms“direct heat exchange” and“indirect heat exchange” are known to one of skill in the art. By contrast, the term“adiabatic conditions” refers to process conditions wherein a reactor is not subjected to external heat exchange (e.g., the reactor is not heated; or the reactor is not cooled). Generally, external heat exchange implies an external heat exchange system (e.g., a cooling system; a heating system) that requires energy input and/or output. External heat transfer can also result from heat loss from the catalyst bed (or reactor) due to radiation, conduction or convection. For example, this heat exchange from the catalyst bed can be to the external environment or to the reactor zones before and after the catalyst bed.

[0078] The methanol synthesis reactors Rx can be characterized by a pressure of equal to or greater than about 30 barg, alternatively greater than or equal to about 40 barg, alternatively greater than or equal to about 50 barg, alternatively greater than or equal to about 60 barg, alternatively greater than or equal to about 70 barg, alternatively greater than or equal to about 80 barg, alternatively greater than or equal to about 90 barg, alternatively greater than or equal to about 100 barg, alternatively less than about 120 barg, alternatively less than about 1 10 barg, alternatively less than about 100 barg, alternatively less than about 90 barg, alternatively from about 30 barg to about 120 barg, alternatively from about 30 barg to about 110 barg, alternatively from about 40 barg to about 120 barg.

[0079] In embodiments, a system and process for producing methanol as disclosed herein can advantageously display improvements in one or more process characteristics when compared to an otherwise similar system or process that: (i) lacks a step of separating each methanol reactor effluent stream REx into a crude methanol product stream MPx and a vapor stream Vx, and/or (ii) lacks a step of separating the final stage vapor stream V _N in at least one hydrogen recovei unit HR into a hydrogen stream 40 and a residual gas stream 35. For example, the herein-disclosed multi-stage methanol synthesis system and method can provide for better efficiency, lower energy consumption, reduced impurity formation, lower capital expenditures, or a combination thereof.

[0080] The multi-stage methanol synthesis process as disclosed herein can advantageously provide for an elimination of a conventional recycle stream comprising a substantial amount of inerts (e.g., methane, nitrogen, argon), thus allowing for a reduction of an amount of such inerts in the methanol synthesis reactors Rx and/or an increase in an amount of inerts (e.g., methane, nitrogen, argon) in a synthesis gas feed (e.g., in syngas feed line 5) utilized as a component of the reactor feed RF 1 to the first stage methanol synthesis reactor Rl . As the multi-stage system and method described herein allow for increased levels of inerts in the synthesis gas feed in syngas feed line 5, the syngas can itself, in embodiments, be produced from a feed (e.g., natural gas) comprising increased inerts (e.g., nitrogen). According to this disclosure, from one to about ten hydrogen recovery units or stages (e.g., membrane separation units or pressure swing adsorption units) can be utilized to recover hydrogen, at least a portion of which recovered hydrogen can be recycled to the first stage. Due to the reduction in inerts, equipment size and stream volumes within the methanol synthesis loop can be reduced according to this disclosure relative to conventional methanol synthesis loops.

[0081] The use of a gas-liquid separator FDx (e.g., a flash drum) and a first heat exchanger HElx in each stage after the methanol synthesis reactor Rx to cool and condense a methanol product MPx comprising methanol and water and any liquid products allows for a reduction in stream and reactor volumes within (and along) the methanol synthesis loop, in embodiments.

[0082] Utilizing a multi-stage methanol synthesis process as described herein, comprising a methanol synthesis reactor Rx in each of N stages x, where N is from 2 to about 10, enables the use of different catalyst types in reactors Rx of different stages of the methanol synthesis loop, in embodiments.

EXAMPTES

[0083] The embodiments having been generally described, the following examples are given as particular embodiments of the disclosure and to demonstrate the practice and advantages thereof. It is understood that the examples are given by way of illustration and are not intended to limit the specification or the claims in any manner.

Example 1: Utilizing a reformed gas having the composition provided in Table 1 as a feed to a methanol loop, the current state of the art technology has been determined to achieve the tabulated performance at a pressure of 91 bar. The herein-disclosed multi-stage methanol synthesis system and method can enable the same conversion at a pressure of less than 75 bar. Furthermore, the stream volumes within the methanol synthesis loop are reduced relative to those of the prior art by more than 30%. [0084]

[0085] While various embodiments have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit and teachings of the disclosure. The embodiments described herein are exemplai only, and are not intended to be limiting. Many variations and modifications of the subject matter disclosed herein are possible and are within the scope of the disclosure. Where numerical ranges or limitations are expressly stated, such express ranges or limitations should be understood to include iterative ranges or limitations of like magnitude falling within the expressly stated ranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4, etc.; greater than 0.10 includes 0.1 1, 0.12, 0.13, etc.). For example, whenever a numerical range with a lower limit, R _L and an upper limit, R, is disclosed, any number falling within the range is specifically disclosed. In particular, the following numbers within the range are specifically disclosed: R-R I k*(Ri -R ). wherein k is a variable ranging from 1 percent to 100 percent with a 1 percent increment, i.e., k is 1 percent, 2 percent, 3 percent, 4 percent, 5 percent, ... 50 percent, 51 percent, 52 percent, ... , 95 percent, 96 percent, 97 percent, 98 percent, 99 percent, or 100 percent. Moreover, any numerical range defined by two R numbers as defined in the above is also specifically disclosed. Use of the term "optionally" with respect to any element of a claim is intended to mean that the subject element is required, or alternatively, is not required. Both alternatives are intended to be within the scope of the claim. Use of broader terms such as comprises, includes, having, etc. should be understood to provide support for narrower terms such as consisting of, consisting essentially of, comprised substantially of, etc.

[0086] Accordingly, the scope of protection is not limited by the description set out above but is only limited by the claims which follow, that scope including all equivalents of the subject matter of the claims. Each and evei claim is incorporated into the specification as an embodiment of the present disclosure. Thus, the claims are a further description and are an addition to the embodiments of the present disclosure. The discussion of a reference is not an admission that it is prior art to the present disclosure, especially any reference that may have a publication date after the priority date of this application. The disclosures of all patents, patent applications, and publications cited herein are hereby incorporated by reference, to the extent that they provide exemplary, procedural, or other details supplementary to those set forth herein.

ADDITIONAL DESCRIPTION

[0087] The particular embodiments disclosed above are illustrative only, as the present disclosure may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the present disclosure. Alternative embodiments that result from combining, integrating, and/or omitting features of the embodiment(s) are also within the scope of the disclosure. While compositions and methods are described in broader terms of "having”,“comprising," "containing," or "including" various components or steps, the compositions and methods can also "consist essentially of’ or "consist of’ the various components and steps. Use of the term“optionally” with respect to any element of a claim means that the element is required, or alternatively, the element is not required, both alternatives being within the scope of the claim.

[0088] Numbers and ranges disclosed above may vary by some amount. Whenever a numerical range with a lower limit and an upper limit is disclosed, any number and any included range falling within the range are specifically disclosed. In particular, eveiy range of values (of the form, "from about a to about b," or, equivalently, "from approximately a to b," or, equivalently, "from approximately a-b") disclosed herein is to be understood to set forth every number and range encompassed within the broader range of values. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee. Moreover, the indefinite articles "a" or "an", as used in the claims, are defined herein to mean one or more than one of the element that it introduces. If there is any conflict in the usages of a word or term in this specification and one or more patent or other documents, the definitions that are consistent with this specification should be adopted.

[0089] Embodiments disclosed herein include:

[0090] A: A process for producing methanol comprising: (a) feeding a first reactant mixture to a first methanol reactor; wherein the first methanol reactor is characterized by a first reactor volume; wherein the first methanol reactor comprises a first catalyst; wherein the first methanol reactor is characterized by a first catalyst amount; wherein the first reactant mixture comprises syngas; wherein the syngas comprises hydrogen (H ₂ ), carbon monoxide (CO), carbon dioxide (C0 ₂ ), and optionally water and/or hydrocarbons; wherein the syngas is characterized by a hydrogen to carbon monoxide (H ₂ /CO) molar ratio of the syngas; wherein the syngas is characterized by an M ratio of the syngas, wherein the M ratio is a molar ratio defined as (H ₂ -C0 ₂ )/(C0+C0 ₂ ); wherein at least a portion of the first reactant mixture reacts, via a methanol synthesis reaction, in the first methanol reactor to produce a first methanol reactor effluent; and wherein the first methanol reactor effluent comprises methanol, water, H ₂ , CO, C0 ₂ , and optionally hydrocarbons; (b) separating at least a portion of the first methanol reactor effluent stream in a first separator into a first crude methanol stream and a first vapor stream; wherein the first crude methanol stream comprises methanol and water; and wherein the first vapor stream comprises H ₂ , CO, C0 ₂ , and optionally hydrocarbons; (c) feeding a second reactant mixture to a second methanol reactor; wherein the second methanol reactor is characterized by a second reactor volume, wherein the first reactor volume is greater than the second reactor volume; wherein the second methanol reactor comprises a second catalyst; wherein the first catalyst and the second catalyst are the same or different; wherein the second methanol reactor is characterized by a second catalyst amount, wherein the first catalyst amount is greater than, less than, or equal to the second catalyst amount; wherein the second reactant mixture comprises at least a portion of the first vapor stream; wherein at least a portion of the second reactant mixture reacts, via a methanol synthesis reaction, in the second methanol reactor to produce a second methanol reactor effluent; and wherein the second methanol reactor effluent comprises methanol, water, H ₂ , CO, C0 ₂ , and optionally hydrocarbons; (d) separating at least a portion of the second methanol reactor effluent stream in a second separator into a second crude methanol stream and a second vapor stream; wherein the second crude methanol stream comprises methanol and water; and wherein the second vapor stream comprises H ₂ , CO, C0 ₂ , and optionally hydrocarbons; (e) separating at least a portion of the second vapor stream in a hydrogen recovery unit into a hydrogen stream and a residual gas stream; wherein the hydrogen stream comprises at least a portion of the hydrogen of the second vapor stream; wherein the residual gas stream comprises CO, C0 ₂ , and optionally hydrocarbons; and wherein at least a portion of the hydrogen stream is fed to the first methanol reactor in step (a); and (f) separating at least a portion of the first crude methanol stream and/or the second crude methanol stream into a methanol stream and a water stream.

[0091] B: A multi-stage processes for producing methanol comprising: for each of N stages: (a) feeding a reactor feed comprising hydrogen (H ₂ ), carbon monoxide (CO), carbon dioxide (C0 ₂ ), and optionally water and/or hydrocarbons to a methanol synthesis reactor comprising a catalyst , wherein at least a portion of the reactor feed reacts via a methanol synthesis reaction to produce a methanol reactor effluent comprising methanol, water, H ₂ , CO, C0 ₂ , and optionally hydrocarbons; (b) separating at least a portion of the methanol reactor effluent in a separator to provide a crude methanol stream and a vapor stream, wherein the crude methanol stream comprises methanol and water, and wherein the vapor stream comprises H ₂ , CO, C0 ₂ , and optionally hydrocarbons; (c) separating at least a portion of the vapor stream from the final or N' ^h stage in a hydrogen recovery unit to provide a hydrogen stream and a residual gas stream, wherein the hydrogen stream comprises at least a portion of the hydrogen of the vapor stream from the final stage, wherein the residual gas stream comprises CO, C0 ₂ , and optionally hydrocarbons, wherein the methanol synthesis reactor feed to the methanol synthesis reactor of the first stage comprises a mixture of a synthesis gas stream and at least a portion of the hydrogen stream, and wherein the reactor feed to the methanol synthesis reactor of any subsequent stage, wherein x is from 2 to N, comprises at least a portion of the vapor stream from the prior stage.

[0092] C: A multi-stage system for producing methanol, the system comprising: N stages, each stage comprising (a) a methanol synthesis reactor comprising a catalyst and configured to convert at least a portion of a reactor feed comprising hydrogen (¾), carbon monoxide (CO), carbon dioxide (C0 ₂ ), and optionally water and/or hydrocarbons to a reactor effluent comprising methanol, water, H ₂ , CO, C0 ₂ , and optionally hydrocarbons; (b) a separator configured for separating at least a portion of the methanol reactor effluent into a crude methanol stream and a vapor stream, wherein the crude methanol stream comprises methanol and water, and wherein the vapor stream comprises H ₂ , CO, C0 ₂ , and optionally hydrocarbons, wherein each methanol synthesis reactor from stage 2 to stage N is fluidly connected with the separator of the prior stage whereby at least a portion of the vapor stream from the prior stage can be introduced as the reactor feed to the methanol synthesis reactor from stage 2 to stage N; (c) a hydrogen recovery unit configured for separating a hydrogen stream from the vapor stream from the final or N' ^h stage and provide a residual gas stream, wherein the hydrogen stream comprises at least a portion of the hydrogen of the vapor stream from the final stage, wherein the residual gas stream comprises CO, C0 ₂ , and optionally hydrocarbons, and (d) a recycle line fluidly connecting the hydrogen recovery unit with the first stage, whereby the at least a portion of the hydrogen stream can be combined with a synthesis gas stream to provide the reactor feed for the methanol synthesis reactor of the first stage.

[0093] Each of embodiments A, B, and C may have one or more of the following additional elements: Element 1 : wherein producing methanol is a multi-stage process, wherein a first stage comprises steps (a) and (b), wherein a second stage comprises steps (c) and (d), and wherein the multi stage process further comprises one or more additional stages downstream of the first stage and/or the second stage, as necessary to achieve a target CO conversion and/or a target C0 ₂ conversion for the overall multi-stage process. Element 2: wherein each additional stage comprises (i) feeding a reactant mixture to a methanol reactor; wherein the methanol reactor comprises a catalyst; wherein the reactant mixture comprises H ₂ , CO, C0 ₂ , and optionally hydrocarbons; wherein at least a portion of the reactant mixture reacts, via a methanol synthesis reaction, in the methanol reactor to produce a methanol reactor effluent; and wherein the methanol reactor effluent comprises methanol, water, H ₂ , CO, C0 ₂ , and optionally hydrocarbons; and (ii) separating at least a portion of the methanol reactor effluent stream in a separator into a crude methanol stream and a vapor stream; wherein the crude methanol stream comprises methanol and water; and wherein the vapor stream comprises H ₂ , CO, C0 ₂ , and optionally hydrocarbons. Element 3 : wherein the reactant mixture comprises at least a portion of an upstream vapor stream from an upstream separator. Element 4: wherein the methanol reactor is characterized by a reactor volume, wherein the reactor volume is less than the volume of an upstream methanol reactor; wherein the methanol reactor is characterized by a catalyst amount, and wherein the catalyst amount is less than the amount of catalyst in the upstream methanol reactor. Element 5: wherein the multi-stage process is characterized by a total reactor volume; wherein the total reactor volume is given by the sum of the first reactor volume, the second reactor volume, and each reactor volume from each additional stage; and wherein the total reactor volume is decreased by greater than or equal to about 15% when compared to the total reactor volume in an otherwise similar process that (i) lacks a step of separating each methanol reactor effluent stream into a crude methanol stream and a vapor stream, and/or (ii) lacks a step of separating the second vapor stream in a hydrogen recovery unit into a hydrogen stream and a residual gas stream. Element 6: wherein the multi-stage process is characterized by a CO conversion and/or a C0 ₂ conversion for the overall multi-stage process that is increased by greater than or equal to about 5% and/or 10%, respectively, when compared to the CO conversion and/or the C0 ₂ conversion, respectively, in an otherwise similar process that (i) lacks a step of separating each methanol reactor effluent stream into a crude methanol stream and a vapor stream, and/or (ii) lacks a step of separating the second vapor stream in a hydrogen recovery unit into a hydrogen stream and a residual gas stream. Element 7: wherein the multi-stage process is characterized by an operating pressure effective to achieve the target CO conversion and/or the target C0 ₂ conversion for the overall multi-stage process that is decreased when compared to the operating pressure effective to achieve the same target CO conversion and/or the same target C0 ₂ conversion, respectively, in an otherwise similar process that (i) lacks a step of separating each methanol reactor effluent stream into a crude methanol stream and a vapor stream, and/or (ii) lacks a step of separating the second vapor stream in a hydrogen recovery unit into a hydrogen stream and a residual gas stream. Element 8: wherein the operating pressure of the multi-stage process is less than about 80 barg. Element 9: wherein each stage of the multi-stage process can independently comprise heating the reactant mixture prior to feeding to the methanol reactor. Element 10: wherein each stage of the multi-stage process can independently comprise (1) heating water while cooling the methanol reactor effluent stream by heat exchange in a heat exchanger to yield steam and a cooled methanol reactor effluent stream; (2) separating at least a portion of the cooled methanol reactor effluent stream in a separator into a crude methanol stream and a vapor stream; and (3) optionally powering a steam-driven compressor with at least a portion of the steam. Element 1 1 : further comprising introducing to the second separator in step (d) at least a portion of the first crude methanol stream and/or at least a portion of the crude methanol stream from each additional stage. Element 12: wherein each methanol reactor of the multi-stage process can independently comprise an adiabatic reactor or a water-cooled reactor, wherein the water-cooled reactor generates steam, and wherein at least a portion of the steam is optionally used to power a steam-driven compressor. Element 13 : wherein the multi-stage process has from 2 to about 10 stages. Element 14: wherein the target CO conversion for the overall multi-stage process is greater than or equal to about 90%; and/or the target C0 ₂ conversion for the overall multi-stage process is greater than or equal to about 80%. Element 15: further comprising (1) combining at least a portion of the hydrogen stream with the syngas to yield a hydrogen enriched syngas; wherein the syngas has an M ratio of greater than or equal to about 1.7, and/or a l¾/CO molar ratio of greater than or equal to about 1.8; wherein the hydrogen enriched syngas has an M ratio greater than the M ratio of the syngas, and wherein the hydrogen enriched syngas has a H ₂ /CO molar ratio greater than the H ₂ /CO molar ratio of the syngas; (2) compressing at least a portion of the hydrogen enriched syngas in a steam-driven compressor to yield a compressed hydrogen enriched syngas; and (3) feeding at least a portion of the compressed hydrogen enriched syngas to the first methanol reactor in step (a). Element 16: wherein at least a portion of the residual gas stream is used as fuel in a syngas production process and/or for steam generation to power a steam-driven compressor. Element 17: wherein the first reactant mixture further comprises inert gases in an amount of less than or equal to about 15 wt.%, based on the total weight of the first reactant mixture; and/or wherein the first reactant mixture comprises hydrocarbons in an amount of less than or equal to about 15 wt.%, based on the total weight of the first reactant mixture. Element 18: wherein the methanol synthesis reaction comprises a reaction between H ₂ and CO to form methanol and/or a reaction between El ₂ and C0 ₂ to form methanol; wherein the first catalyst is different from the second catalyst; wherein the first reactor is characterized by a first CO conversion and by a first C0 ₂ conversion, wherein the first CO conversion is greater than the first C0 ₂ conversion; wherein the second reactor is characterized by a second CO conversion and by a second C0 ₂ conversion, and wherein the second CO conversion is less than the second C0 ₂ conversion. Element 19: wherein the hydrogen recovery unit comprises from 1 to about 10 membrane separation units and/or pressure swing adsorption units. Element 20: wherein N is from 2 to about 10. Element 21 : wherein a volume of the methanol synthesis reactor decreases from stage 1 to stage N.

[0094] While preferred embodiments of the invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the teachings of this disclosure. The embodiments described herein are exemplai only, and are not intended to be limiting. Many variations and modifications of the invention disclosed herein are possible and are within the scope of the invention.

[0095] Numerous other modifications, equivalents, and alternatives, will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to embrace all such modifications, equivalents, and alternatives where applicable. Accordingly, the scope of protection is not limited by the description set out above but is only limited by the claims which follow, that scope including all equivalents of the subject matter of the claims. Each and evei claim is incorporated into the specification as an embodiment of the present invention. Thus, the claims are a further description and are an addition to the detailed description of the present invention. The disclosures of all patents, patent applications, and publications cited herein are hereby incorporated by reference.