Method for production of methanol from co 2 and hydrogen with improved carbon efficiency

Abstract

The present invention provides a method for production of methanol from CO2 and hydrogen, preferably where biogenic CO2 and hydrogen (from electrolysis) are used directly to produce methanol.

Description

[0001] Method for Production of Methanol from CO2 and Hydrogen with Improved Carbon Efficiency

[0002] FIELD OF THE INVENTION

[0003] The present invention belongs to the field of methanol production. It relates to a method of producing methanol from CO2 and hydrogen obtained from electrolysis, incorporating a high temperature two-phase separator to improve the carbon efficiency of the methanol production process.

[0004] BACKGROUND OF THE INVENTION

[0005] Traditional methods for production of methanol often involve the use of fossil fuels, leading to substantial carbon emissions. Recent developments have focused on green methanol production, utilizing CO2 and hydrogen. However, these methods often suffer limited carbon availability. There is therefore a need for a method that improves carbon efficiency in the production of methanol from CO2 and hydrogen. The most common process for large-scale production of synthesis gas for methanol synthesis is combined reforming or autothermal reforming. These processes involve the use of oxygen-fueled reactors and catalysis at an elevated temperature. The characteristics of the synthesis gas and the process temperature have been found to give the subsequent methanol synthesis a tendency to catalyze wax as a by-product of methanol. This byproduct causes major production problems in, inter alia, the methanol condensation process as it settles in pipes, heat exchangers and other process equipment and reduces their capacity. The wax may also lead to operational problems further downstream in the process due to deposits and plugging of flow meters and instruments. The wax deposit will result in lost production in the form of noncondensed methanol, reduced production capacity and possible shutdown for removing wax from the heat exchangers and equipment. There are also instances of wax formation causing a breakdown of rotating equipment because liquid separators have malfunctioned due to wax deposit. Methanol synthesis is a continuous process and consequently the preprocessing of the crude methanol is preferably also a continuous process.

[0006] WO 07 / 040401 discloses a method for pre-processing a raw-methanol product gas containing methanol, water, waxes (paraffins) and rests of synthesis gas, the method comprising the steps of cooling the product gas, partly condensing the product gas to a temperature over the melting point of the waxes, separating the condensate from the gas phase to obtain a first, wax containing condensate stream, condensing the gas phase further by cooling to a temperature under the boiling point of methanol to obtain a second substantially wax-free condensate stream and optionally separating the wax from the first condensate stream and combining the two condensate streams for further work-up. This document provides a system and a process for the handling the wax issue from methanol synthesis such that plant shutdowns are avoided, preventing wax deposit and blockage of heat exchangers and similar equipment whilst obtaining a high-capacity utilization of the crude methanol. The invention is based on the fact that virtually all the wax can be condensed out in liquid form, together with methanol and water, ahead of the final cooler, at a temperature and using a cooling medium that do not cause wax deposit in the heat exchangers. The wax containing condensate, with dissolved gases, is separated from the product gas and passes to a separate process for wax separation before the methanol is passed back to the process.

[0007] US 11753359 discloses a system and method for processing crude methanol, wherein a crude methanol stream comprising methanol and paraffin wax is produced from syngas (CO, CO2 and H2). The crude methanol stream is cooled to form a partially condensed crude methanol stream, which is further separated in a vapor-liquid separator to form a liquid stream and a gas stream. The liquid stream is further cooled in a dewaxing unit to remove paraffin wax. The dewaxing unit includes two or more cooling units arranged in parallel such that when one of the cooling units is offline for cleaning, the methanol system does not need to be shut down.

[0008] The present invention, provides a process to separate the liquid fraction of a methanol containing effluent of the methanol reactor from a gas fraction, by cooling said effluent and, partly condensing it to a temperature below the condensation temperature of the methanol reactor(s) effluent, separating the condensate from the gas phase to obtain a first methanol containing condensate stream (3), condensing the gas phase further by cooling it again to a temperature below the condensation temperature of methanol reactor(s) effluent to obtain a second methanol containing condensate stream (4). The methanol containing effluent is a product gas from the methanol reactor, comprising methanol, water, byproducts and unconverted synthesis gas.

[0009] In the standard solution where the turndown of the methanol loop is typically not lower than 50-70% the gas velocity in the vertical pipe is sufficient to avoid phase separation. By separating methanol and water at lower temperature more CO2 is dissolved in the raw methanol. This CO2 will be lost in the downstream distillation step.

[0010] None of the cited prior art documents address the problem of how to, when producing methanol: handle phase separation by decreasing the CO2 amount dissolved in raw methanol while increasing it in the gas phase; and manage fluctuations associated to renewable sources of energy, in particular when producing green methanol obtained directly from CO2 (e.g. biogenic CO2) and hydrogen (e.g. hydrogen from water electrolysis).

[0011] For a green methanol loop operating with a feed gas comprising CO2 and hydrogen generated by electrolysis from renewable power the load of the methanol loop will follow the power availability. This induces an extended turndown requirement normally not seen in methanol plants and an associated challenge of handling two phase flow in cooling section downstream the methanol reactor.

[0012] This can be solved by introducing a two-phase separator downstream the F / E exchanger at low point. The gas part can then move in vertical direction for further cooling / condensation with downwards slope to the high-pressure separation step. By introducing a hot separation step (e.g. 120°C) to separate said first methanol containing condensed stream (3) from the gas phase taken further into a second separation step, it is observed that the carbon efficiency of the methanol loop increases due to lower solubility of CO2 in the condensed water / methanol mixture at higher temperature compared to the approx. 40°C in the high pressure separation step.

[0013] SUMMARY OF THE INVENTION

[0014] The present invention provides a method for production of methanol from CO2 and hydrogen, preferably where biogenic CO2 and hydrogen (from electrolysis) are used directly to produce methanol:

[0015] CO2+ 3H2^ CH3OH + H2O wherein a hot two-phase separator (A) is positioned downstream to a feed effluent exchanger or first cooling section.

[0016] In one embodiment, the feed effluent exchanger or cooling section operates at a temperature between 100 and 140 degrees Celsius, ideally at approximately 120 degrees Celsius. This operational temperature range will vary depending on the condensation temperature of the methanol reactor(s) effluent, which is affected by varying operation conditions such as e.g. pressure. The solubility of CO2 in water and methanol decreases with increasing temperature. Thus, a hot separation step will remove less CO2 from the methanol loop through the crude methanol. The hot separation step is introduced downstream the F / E exchanger or first cooling step at around 120°C. Since the gas is further cooled in downstream cooler(s) the separation step will not affect inlet temperature to the recycle compressor, which would otherwise result in increased power consumption. This layout therefore results in an improvement in carbon efficiency between approximately 0,20% and 0,30%, e.g. 0,25%. The improved carbon efficiency is due, at least in part, to the decreased solubility of CO2 in methanol / water mixtures at high temperatures, such as between 100 and 140 degrees Celsius. This makes CO2 more available for conversion, thus improving the overall efficiency of the process.

[0017] Introducing an additional hot separation step in the methanol production has several advantages especially in green methanol loop:

[0018] 1. It ensures that liquid is not accumulating at the low point downstream the F / E exchanger at low loads. Said liquid accumulation results in slug flow in the following vertical line before further cooling and condensation. Slug flow is known to cause pipe vibrations and damage to the equipment.

[0019] 2. In a green methanol loop with hydrogen being produced by electrolysis, e.g. from renewable sources of electricity, the rate of capacity change is also following the power availability. With a fast rate of change, sudden separation at low load creates pressure instability in the methanol loop. 3. Due to scarcity of biogenic carbon for green methanol plants high carbon efficiency is imperative, by introducing this hot separation step, carbon efficiency is increased by approximately 0.3%.

[0020] DETAILED DESCRIPTION OF THE INVENTION

[0021] Sources of CO2 in the present invention may be produced from biological sources (biogenic CO2) or e.g. obtained from industrial emissions, such as power generation from fossil fuels or cement production, which produce large amounts of CO2 as a byproduct. This CO2 can be captured and used as a feedstock for methanol production. CO2 may also be captured from biomass power plants, biofuel production facilities, direct (ambient) air capture (DAC) or other suitable source.

[0022] In the present invention, CO2 is preferably biogenic, i.e., naturally produced through biological processes, such as combustion of biomass, fermentation and waste treatment. Alternatively, it can also derive from respiration of living organisms or decomposition of organic matter.

[0023] Hydrogen is preferably obtained from electrolysis of water, electrolysis of CO2 and / or coelectrolysis, preferably using renewable sources of electricity. Another means to obtain hydrogen can be via biomass gasification where organic material is converted into hydrogen-rich syngas, which can then be used to produce hydrogen or e.g. via reforming of hydrocarbons such as natural gas.

[0024] Electrolysis is a process where water is split into hydrogen and oxygen using electricity. If the electricity comes from renewable sources, this can be a very environmentally friendly way of producing hydrogen. In the present invention all suitable forms of electrolysis are applicable.

[0025] Co-electrolysis is a process that simultaneously electrolyzes water (H2O) and carbon dioxide (CO2) to produce a syngas mixture (CO and H2). A solid oxide electrolysis cell (SOEC) can be used, being driven by electrical energy, most preferably from renewable sources.

[0026] Electrolysis of carbon dioxide (CO2) is a process that uses electrical energy to convert CO2 into different products. Depending on the specific conditions and catalysts used, CO2 can be reduced to various products such as CO, which can then be used to produce syngas or other fuels.

[0027] Carbon capture, or carbon capture and storage (CCS), is a process that involves trapping the carbon dioxide (CO2) at its emission source, preventing it from being released into the atmosphere, and then storing it in a way that it cannot escape. It is seen as a crucial strategy in efforts to combat global climate change.

[0028] Once captured, the CO2 is then transported and stored, usually underground in depleted oil and gas fields or deep saline aquifer formations. Carbon Capture and Utilization (CCU) involves capturing CO2 and then converting it into useful products, such as chemicals (e.g. methanol), fuels, or building materials. This can provide an economic incentive for carbon capture, although the amount of CO2 that can be utilized is generally much less than the amount that can be stored.

[0029] In a preferred embodiment gas feed stream (1) comprises biogenic CO2 and H2 obtained preferably from water electrolysis and said gas feed stream (1) is fed into one or more methanol reactor(s) to generate a methanol reactor effluent.

[0030] In another preferred embodiment gas feed stream (1) is a synthesis gas comprising CO, CO2 and H2 and can be produced by co-electrolysis of H2O and CO2. In another preferred embodiment, CO2 and hydrogen may be mixed and converted at least partially into a CO containing synthesis gas by electrified reforming. In another preferred embodiment, CO2 may be at least partially converted into CO by CO2 electrolysis. When the gas feed stream (1) is a synthesis gas stream, said syngas is fed into one or more methanol reactors to generate a methanol reactor effluent.

[0031] Regardless of the source for the methanol reactor effluent, said effluent is cooled in a first cooling section, before being partially condensed in a first hot separator (A) where a liquid fraction (3) is separated from a gas fraction, preferably at 10-50°C below the condensation temperature of the methanol reactor(s) effluent, said gas fraction being further cooled and condensed in a second separator (B) where a liquid fraction (4) is separated from a gas fraction comprising unreacted gases, which is recycled back into the one or more methanol reactor(s).

[0032] The cooling and condensation of the product stream from a methanol reactor typically involve the following steps: Cooling: The hot product stream exiting the reactor is first cooled down. This is usually done by passing the product stream through a heat exchanger, where it gives up its heat to another fluid (often water or another process stream). This cooling process not only helps to recover some of the heat energy for use elsewhere in the plant, but also begins the process of condensing the methanol out of the product stream.

[0033] Partial Condensation: After the initial cooling, the product stream enters a partial condenser. Here, further cooling causes some of the methanol and water vapor in the product stream to condense into a liquid phase, while the unreacted gases and inerts remain in a gas phase. Cooling and partial condensation can be carried out in same heat exchanger.

[0034] Phase Separation: The partially condensed product stream then enters a phase separator, typically a flash drum or knockout drum or other. Here, the liquid methanol and water are separated from the gas phase due to the difference in density. The liquid collects at the bottom of the separator, while the gases are removed from the top. Recycle of Unreacted Gases: The unreacted gases from the top of the phase separator are recycled back into the reactor, preferably after being mixed with fresh synthesis gas. This helps to improve the overall efficiency of the methanol production process.

[0035] Purification of Liquid Methanol: The liquid phase from the bottom of the phase separator, which contains methanol and water, is sent to a distillation step for further purification. Here, the methanol is separated from the water and any other impurities, resulting in a high-purity methanol product.

[0036] The methanol reactor(s) effluent comprises methanol, water, unreacted synthesis gas and optionally other byproducts, such as, dimethyl ether, ketones and higher alcohols.

[0037] The lighter components like dimethyl ether, ketones and any dissolved gas in the liquid phase from the bottom of the phase separator are typically removed in a light ends distillation column prior to the distillation step separating water and higher alcohols from the methanol product.

[0038] The condensation temperature of the methanol reactor effluent varies depending on the methanol loop pressure, i.e., the condensation temperature of a fluid (in this case, the methanol reactor effluent) is the temperature at which a phase change occurs under a given pressure. In other words, it's the temperature at which the fluid starts to condense from a gas to a liquid or boil from a liquid to a gas.

[0039] As the loop pressure increases, the condensation temperature also increases. Therefore, it requires a higher temperature to achieve this phase change. So, if the pressure in the methanol loop is increased, the condensation temperature of the reactor effluent will also increase. This means that the effluent will remain in a gaseous state at higher temperatures.

[0040] The additional benefit of having the hot separator is that it ensures condensate is separated from the stream at the low point in the methanol loop. This allows for operation at low load say down to e.g. 10% without flow instabilities from slug flow in a two phase vertical flow line from the F / E exchanger to the downstream cooler. This is particularly relevant for methanol production based on hydrogen generated from electrolysis powered by renewable electricity, where extended turndown to follow the hydrogen production profile is required. The low turndown results in low fluid velocity and the lines and therefore possibility of slug flow in vertical lines. This is normally not the case for conventional methanol production process, where load is substantial constant around its design capacity.

[0041] Preferred embodiments

[0042] The present invention is a method and system for production of methanol, where the use of CO2 is optimized when compared to the prior art, the method comprising the steps of: a) converting, in one or more methanol reactor(s), at least part of a gas feed stream (1,2) comprising CO2 and H2 into a methanol reactor(s) effluent comprising methanol, water, other byproducts and unreacted synthesis gas, b) cooling said methanol reactor(s) effluent to below its condensation temperature to partially condense the crude methanol and separating a liquid fraction (3) from a gas fraction, in a first hot separator (A), c) further cooling said gas fraction of the methanol reactor(s) effluent to further condense the crude methanol, separating a liquid fraction (4) from a gas fraction, in a second separator (B), and d) unreacted gases from the second separation step (B) being recycled back into the one or more methanol reactor(s), wherein the separated liquid fraction(s) contain a lower amount of CC hen when a single separation step (B) is performed.

[0043] In a preferred embodiment, said unreacted gases may be mixed with gas feed stream (1,2) before entering the one or more methanol reactor(s). The unreacted gases comprise CO2, H2 and also CO, this CO deriving from the RWGS taking place in the methanol loop, over the methanol shift catalysts.

[0044] 2. Method according to embodiment 1, wherein the hot separation step (A) takes place at 10-50°C below the condensation temperature of the methanol reactor(s) effluent.

[0045] 3. Method according to any one of embodiments 1 or 2, wherein methanol is green methanol, produced from biogenic CO2 and H2.

[0046] 4. Method according to the previous embodiment wherein hydrogen is obtained from electrolysis.

[0047] 5. Method according to any one of the previous embodiments wherein condensed crude methanol (3,4) is distilled, to produce pure or almost pure methanol.

[0048] 6. Method according to any one of the previous embodiments wherein the crude methanol (3) separated from the hot separator (A) and the crude methanol (4) separated from the second separator (B) can be added directly to one or more distillation column(s), at different feed locations.

[0049] 7. Method according to any one of the previous embodiments, wherein the crude methanol (3) separated from the hot separator (A) is cooled to substantially the same temperature as the crude methanol (4) separated from the second separator (B) and (3,4) are mixed and distilled together. 8. Method according to any one of embodiments 1 to 7 wherein the feed stream (1,2) comprises CO2, H2 and CO.

[0050] 9. Method according to any one of embodiments 1 to 8 wherein electrolysis of water (H2O) and carbon dioxide (CO2) produce a synthesis gas mixture comprising CO, CO2 and H2.

[0051] 10. Method according to any one of embodiments 1 to 9, wherein electrolysis of CO2 at least partly converts it to CO.

[0052] 11. Method according to any one of embodiments 1 to 10 wherein mixed CO2 and hydrogen are converted at least partially into CO containing synthesis gas (1) by electrified RWGS.

[0053] This optional embodiment takes place upstream to the main layout.

[0054] In addition, a RWGS reaction takes place over the methanol shift catalyst in the methanol loop, originating some CO in the unreacted gases recycled.

[0055] The reverse water gas shift (RWGS) reaction is exothermic, meaning it releases heat and combines carbon dioxide (CO2) and hydrogen (H2) to produce carbon monoxide (CO) and water (H2O):

[0056] CO2+ H2^ CO + H2O

[0057] 12. System for production of methanol comprising the following:

[0058] (a) CO2 sourcing section;

[0059] (b) hydrogen sourcing section;

[0060] (c) one or more methanol reactor(s);

[0061] (d) a first cooling section;

[0062] (e) a first hot separator (A);

[0063] (f) a second colling section;

[0064] (g) a second separator (B), wherein one or more methanol reactor(s) are fed with feed gas (1,2) and produce a methanol reactor(s) effluent which is then cooled below its condensation temperature in a first cooling section, to partially condense the crude methanol and separating a liquid fraction (3) from a gas fraction, in a first hot separator (A), further cooling said gas fraction of the methanol reactor(s) effluent to further condense the crude methanol, separating a liquid fraction (4) from a gas fraction, in a second separator (B), and unreacted gases from the second separator (B) being recycled back into the one or more methanol reactor(s), wherein the separated liquid fraction(s) contain a lower amount of CC then when there is a single separator (B).

[0065] 13. System according to embodiment 12 wherein the carbon dioxide sourcing section (a) comprises one or more carbon capture and / or storage units. 14. System according to any one of embodiments 12 or 13 wherein the hydrogen sourcing section comprises one or more electrolysers.

[0066] 15. System according to the previous embodiment wherein the electrolyser(s) is one or more solid- oxide electrolyser(s) or SOEC.

[0067] EXAMPLE

[0068] The present invention provides a novel method for production of green methanol with improved carbon efficiency.

[0069] This provides a valuable contribution to the field of sustainable methanol production, wherein there is an improvement in carbon efficiency of about 0.25% when compared to the standard system for production of methanol without the extra hot separator (A) downstream to the feed / effluent exchanger and upstream to the standard separator (B).

[0070] The improved carbon efficiency is due, at least in part, to the decreased solubility of CO2 in methanol / water mixtures at high temperatures, such as between 100 and 140 degrees Celsius, thus improving the overall efficiency of the process since less CO2 needs to be supplied to the process in stream 1.

Claims

Claims1. A method for production of methanol, the method comprising the steps of: a) converting, in one or more methanol reactor(s), at least part of a gas feed stream (1,2) comprising CO2 and H2 into a methanol reactor(s) effluent comprising methanol, water, other byproducts and unreacted synthesis gas, b) cooling said methanol reactor(s) effluent to below its condensation temperature to partially condense the crude methanol and separating a liquid fraction (3) from a gas fraction, in a first hot separator (A), c) further cooling said gas fraction of the methanol reactor(s) effluent to further condense the crude methanol, separating a liquid fraction (4) from a gas fraction, in a second separator (B), and d) unreacted gases from the second separation step (B) being recycled back into the one or more methanol reactor(s), wherein the separated liquid fraction(s) contain a lower amount of CC hen when a single separation step (B) is performed.

2. Method according to claim 1, wherein the hot separation step (A) takes place at 10-50°C below the condensation temperature of the methanol reactor(s) effluent.

3. Method according to any one of claims 1 or 2, wherein methanol is green methanol, produced from biogenic CO2 and H2.

4. Method according to the previous claim wherein hydrogen is obtained from electrolysis.

5. Method according to any one of the previous claims wherein condensed crude methanol (3,4) is distilled.

6. Method according to any one of the previous claims wherein the crude methanol (3) separated from the hot separator (A) and the crude methanol (4) separated from the second separator (B) are added directly to distillation column, at different feed locations.

7. Method according to any one of the previous claims wherein the crude methanol (3) separated from the hot separator (A) is cooled to substantially the same temperature as the crude methanol (4) separated from the second separator (B), and (3,4) are mixed and distilled together.

8. Method according to any one of claims 1 to 7 wherein the feed stream (1,2) comprises CO2, H2 and CO.

9. Method according to any one of claims 1 to 8 wherein electrolysis of water (H2O) and carbon dioxide (CO2) produce a synthesis gas mixture comprising CO, CO2 and H2.

10. Method according to any one of claims 1 to 9, wherein electrolysis of CO2 at least partly converts it to CO.

11. Method according to any one of claims 1 to 10 wherein mixed CO2 and hydrogen are converted at least partially into CO containing synthesis gas (1) by electrified RWGS.

12. System for production of methanol comprising the following:(a) CO2 sourcing section;(b) hydrogen sourcing section;(c) one or more methanol reactor(s);(d) a first cooling section;(e) a first hot separator (A);(f) a second colling section;(g) a second separator (B), wherein one or more methanol reactor(s) are fed with feed gas (1,2) and produce a methanol reactor(s) effluent which is then cooled below its condensation temperature in a first cooling section, to partially condense the crude methanol and separating a liquid fraction (3) from a gas fraction, in a first hot separator (A), further cooling said gas fraction of the methanol reactor(s) effluent to further condense the crude methanol, separating a liquid fraction (4) from a gas fraction, in a second separator (B), and unreacted gases from the second separator (B) being recycled back into the one or more methanol reactor(s), wherein the separated liquid fraction(s) contain a lower amount of CC hen when there is a single separator (B).

13. System according to claim 12 wherein the carbon dioxide (a) sourcing section comprises one or more carbon capture and / or storage units.

14. System according to any one of claims 12 or 13 wherein the hydrogen sourcing section comprises one or more electrolysers.

15. System according to the previous claim wherein the electrolyser(s) is one or more solid-oxide electrolyse r(s).

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