Process for preparing methanol
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2026-02-04
- Publication Date
- 2026-08-13
Smart Images
Figure 00000019_0000
Abstract
Description
[0001] Process for the production of methanol
[0002] The invention relates to a process for the production of methanol, hydrogen and carbon dioxide.
[0003] Methanol is being discussed in the scientific community as a replacement for fossil fuels and as an alternative to pure hydrogen. The methanol is intended to be synthesized from renewable raw materials. The methanol produced in this way is also referred to as renewable methanol, regenerative methanol, or green methanol. In one possible synthesis process, hydrogen reacts with carbon dioxide to form methanol, whereby the carbon dioxide is extracted from the ambient air and hydrogen is obtained from water via electrolysis. However, the renewable methanol produced in this way is very expensive, as extracting the carbon dioxide from the ambient air is costly due to the very low carbon dioxide concentration in the air and the high energy requirements.
[0004] The invention is based on the objective of providing an alternative process for the production of renewable methanol.
[0005] The invention is solved by a method with the features of claim 1. Further advantageous embodiments of the invention are contained in dependent claims 2 to 12. The inventive method for producing renewable methanol comprises the process steps
[0006] a) Seawater is acidified and heated to a temperature of at least 45°C, and the gas mixture expelled from the seawater, consisting mainly of carbon dioxide, is collected.
[0007] b) Removal of oxygen and optionally other volatile components from the gas mixture obtained in step a) to obtain purified carbon dioxide,
[0008] c) Distillation of a portion of the low-carbon seawater remaining after extraction in step a) to obtain distilled water and an aqueous brine concentrated with NaCl,
[0009] d) Carrying out electrolysis with the distilled water from step c) to obtain hydrogen and oxygen,
[0010] e) Recovery of acid and an alkaline residue from the NaCl-enriched aqueous brine from step c)
[0011] f) Use of the acid obtained in step e) to acidify the seawater in step a).
[0012] g) Recovery of at least some of the waste heat generated in steps b) to e) and use of the waste heat to heat the seawater that has not yet been reduced in carbon dioxide in step a).
[0013] h) Synthesis of methanol from the hydrogen from step d) and the carbon dioxide from step b) and separation of the methanol from the
[0014] Product mixture. The oceans contain approximately 50 times more carbon than the atmosphere. The oceans act as large carbon dioxide sinks, absorbing about one-third of the carbon dioxide released by human activities. Cold water dissolves more carbon dioxide than warm water. Seawater contains carbon dioxide in dissolved form as well as in carbonic acid, in equilibrium with bicarbonates and carbonates. By acidifying the seawater according to the invention in step a), the equilibrium shifts towards carbon dioxide. By simultaneously heating the seawater to a temperature of at least 45 °C in step a), as provided for in the invention, the carbon dioxide is driven out of the seawater. Preferably, the heating is carried out to at least 50 °C, particularly to at least 60 °C, and most preferably to at least 70 °C. Advantageously, the heating does not exceed a temperature of 90 °C.The gas mixture obtained in this way contains predominantly carbon dioxide, but also oxygen and other volatile components. Since oxygen in particular significantly interferes with the reaction of carbon dioxide with hydrogen to form methanol, the gas mixture obtained in step a) is purified of the oxygen in step b), and pure carbon dioxide is obtained for use in methanol synthesis in step h).
[0015] A portion of the low-carbon seawater remaining after extraction in step a) is distilled in step c), yielding distilled water and an aqueous brine concentrated with NaCl. Distillation is preferably carried out by vacuum distillation. Advantageously, the distilled water is further subjected to membrane distillation to increase its purity. The highly pure water from step c) is then subjected to electrolysis in process step d), separating the water into pure hydrogen and oxygen. The oxygen obtained is advantageously used for energy production. The hydrogen obtained is used for the production of methanol.
[0016] In step e), acid is obtained from the NaCl-enriched aqueous brine from step c). Advantageously, the brine is subjected to an electrodialysis process. Alternatively, the acid can also be obtained from the brine by chlor-alkali electrolysis. In a preferred embodiment of the invention, hydrochloric acid is obtained in step e).
[0017] The acid from step e) is used in step f) to acidify the seawater in step a).
[0018] The hydrogen obtained in step d) and the purified carbon dioxide react in step h) to form methanol and water. The methanol is separated from this product mixture. The remaining water may still contain traces of carbon dioxide and methanol. In a preferred embodiment of the invention, the resulting reaction water is fed back into step a). Instead of discarding this reaction water, it is thus efficiently recycled back into step a) of the carbon dioxide release process. The contaminated water is not disposed of but reintegrated into the process, thereby reducing the overall fresh water requirement and preventing the seawater from being polluted by the discharge of contaminated water. The carbon dioxide traces dissolved in the water are separated again in step a), further increasing the efficiency of the process.
[0019] In a preferred embodiment of the invention, the seawater is acidified in step a) to a pH value below 6.5, advantageously to a pH value between 6.5 and 5.0, and particularly to a pH value between 6.5 and 5.5. The lower the pH value, the more carbon dioxide is driven off from the seawater due to the shift in equilibrium. However, lowering the pH value requires acid, which must first be produced using energy. Surprisingly, it has been found that lowering the pH value to a moderate value between 6.5 and 5.5 represents a good compromise between the amount of carbon dioxide driven off the seawater and the amount of energy expended for acid production.
[0020] In an advantageous embodiment of the invention, the thermal energy contained in the heated seawater after carbon dioxide extraction in step a) is at least partially recovered and used to heat the seawater in step a) before carbon dioxide reduction is removed. Particularly preferably, more than 90%, and especially more than 94%, of the energy required for heating the seawater is recovered from the heated seawater after carbon dioxide extraction. This significantly improves the energy balance for carbon dioxide production. According to the invention, this efficient use of heat recovery ensures that the heat generated and available in the process is used in a targeted manner without thermally impacting the surrounding seawater. Instead, solar energy, which would naturally heat the sea anyway, is preferably used to make the process efficient.The waste heat from the chemical processes is not wasted, but specifically used for heating and evaporation. This increases the overall energy efficiency of the process.
[0021] In a particularly preferred embodiment of the invention, the alkaline residue remaining after the production of the acid in step e) is used to neutralize the acidified seawater after the carbon dioxide extraction from step a). The seawater thus leaves the process with an almost identical pH value to that which it had before being introduced into the process.
[0022] The process is advantageously carried out, at least predominantly, on an offshore platform. This makes seawater immediately available in very large quantities, eliminating long transport routes.
[0023] In an advantageous embodiment of the invention, the energy required to carry out the process is obtained at least predominantly, and in particular entirely, from renewable energy sources, especially offshore. It is particularly preferred that the energy is obtained at least partially from solar energy via solar panels, and that the resulting waste heat is stored and used to heat the seawater in step a). This allows the solar energy to be used with a significantly higher efficiency. The energy required to carry out the process is, of course, understood to mean that energy which is not already provided by heat recovery in step g).
[0024] The combined use of electricity and heat in the process according to the invention demonstrates that, despite the significant stoichiometric differences between carbon dioxide and hydrogen production, highly energy-efficient methanol production is possible. The innovative integration of all energy sources and the efficient heat recovery make this process more sustainable and cost-effective than previous approaches to carbon dioxide capture and methanol production.
[0025] The following section explains key aspects of the energy balance of the process according to the invention. The figures presented refer to the production of 1 kg of methanol (CH3OH). This forms the basis for the subsequent consideration of the required material and energy flows as well as the technologies employed.
[0026] One kilogram of methanol contains 125 grams of hydrogen, 375 grams of carbon, and 500 grams of oxygen. One of the key challenges is the ratio of the required material flows. To produce one kilogram of methanol, approximately 1.125 kilograms of water are needed for electrolysis. The carbon for the carbon dioxide is obtained from the dissolved inorganic carbon (DIC) in seawater, which has a concentration of about 25 to 31 mg per liter. This means that roughly 12,000 to 15,000 liters of seawater must be processed to obtain the carbon. In comparison, the amount of water required for electrolysis is more than four orders of magnitude smaller. Despite these significant differences in the material flows, a surprising balance emerges in the energy budget: The waste heat generated during electrolysis and methanol synthesis is almost entirely sufficient to heat the seawater required for CO2 production.
[0027] Alkaline electrolysis, with an efficiency of about 70% and the production of enough hydrogen to produce 1 kg of methanol, has an electricity requirement of approximately 7.036 kWh, releasing about 2.111 kWh of waste heat.
[0028] The exothermic reaction of methanol synthesis releases an additional approximately 0.425 kWh per kg of methanol. This waste heat is lower than that generated by the currently used waste heat from the use of carbon monoxide and hydrogen.
[0029] The process according to the invention preferably includes electrodialysis, in which acid is produced that lowers the pH of the water, preferably to pH 6, and supports the release of carbon dioxide from dissolved inorganic carbon (DIC) in the water. For example, approximately 876 g of hydrochloric acid (HCl) are required to lower the pH of 12,000 liters of Mediterranean water to pH 6. The electricity required for this is approximately 3.83 kWh and results from the production of chlorine and hydrogen via electrolysis, which are subsequently converted to HCl. The production of 876 g of hydrochloric acid releases a total of approximately 1.96 kWh of waste heat. This is preferably used efficiently in the subsequent thermal process steps.
[0030] The combined electricity requirement of 11.3 kWh per kilogram of methanol is remarkably low, especially considering the complex stoichiometry associated with CO2 extraction from seawater. This low requirement is further reduced by the efficient utilization of waste heat from electrolysis and methanol synthesis employed in a preferred embodiment of the invention. In this preferred embodiment, the released waste heat contributes significantly to the system's energy efficiency, as it can be used almost entirely for heating the seawater and meeting other thermal requirements of the process. Furthermore, the heat recovery of more than 90%, and particularly more than 94%, provided for in an advantageous embodiment of the invention significantly reduces the effective external energy requirement for heating the seawater.This interplay between electricity demand and waste heat utilization enables extremely sustainable and economical methanol production.
[0031] It is advantageous to use seawater from a depth of at least 25 m in step a). For this purpose, the seawater is pumped directly from this depth via a pipeline and fed into step a). At this minimum depth, the seawater has a higher CC concentration compared to water just below the surface. Pumping deep water minimizes the impact on marine ecosystems, as surface water and its organisms are less affected.
[0032] Deep water contains fewer microorganisms and algae due to its cooler temperatures and lower biological activity. This leads to a reduction in biofouling on system components, which lowers maintenance costs and extends equipment lifespan. Since deep water contains fewer organic contaminants and suspended solids, it is often purer than surface water. This facilitates filtration processes and improves the efficiency of carbon dioxide capture, as fewer contaminants need to be removed. The more stable physical conditions at ocean depths greater than 25 m, such as constant temperatures and pressures, can contribute to more uniform and predictable chemical reactions for CO2 capture.
[0033] In an advantageous embodiment of the invention, the lye obtained in step e) is fed together with seawater or treated seawater in a step eo) to a solid precipitation reactor, wherein the lye serves as a precipitating agent and calcium carbonate and magnesium hydroxide precipitate as solids.
[0034] These solids are advantageously processed into pellets. The solid precipitation reactor is advantageously designed as a fluidized bed, fluidized bed, or stirred-bed reactor with a sedimentation zone. Particularly preferably, the seawater is first subjected to nanofiltration in step ao), and the resulting retentate is fed to the solid precipitation reactor as treated seawater. The permeate from step ao) is either fed to a neutralization and discharge module or further processed.
[0035] Advantageously, the seawater in step a), or alternatively or additionally, the permeate from step ao), is subjected to reverse osmosis before heating in step ai). This increases the concentration of dissolved, inorganic carbon in the form of carbonates and bicarbonates in the retentate. The retentate is then processed further in step a), either alone or together with more seawater. The reverse osmosis is preferably carried out before the seawater or the permeate from step ao) is acidified in step a).
[0036] An embodiment of the invention is explained below with reference to the diagram shown in Fig. 1. The features of the method described therein can also be the subject of the invention in other combinations.
[0037] Fig. 1 shows an embodiment of the method according to the invention.
[0038] Seawater is drawn from the sea at a sampling point 2 and fed to a pre-filter 6 via a seawater pump 4, where it is freed of at least some of the solids contained in the seawater. In process step a) 8, the purified seawater is acidified with acid 36 to a pH value of 5.5–6.5 and heated to a temperature of at least 45 °C. The gas mixture 10, consisting mainly of carbon dioxide, which is driven off from the seawater in this process, is collected and, in step b), subjected to a purification process 12 in which oxygen is removed from the gas mixture and purified carbon dioxide 13 is obtained.
[0039] A portion of the low-carbon seawater 11 remaining after extraction from step a) is distilled in step c) by vacuum distillation 14, yielding water vapor 16 and a NaCl-concentrated brine 18. The water vapor 16 is purified of any remaining carbon dioxide 20 and, as distilled condensate 22, is fed to a membrane distillation 24 for further purification of the distilled water.
[0040] The highly purified water 26 obtained in this process is subjected to electrolysis 28 in process step d) and thereby separated into hydrogen 30 and oxygen.
[0041] In step d), the brine 18 from distillation 14 is fed to an electrodialysis unit 34 via a brine pump 32. In this unit, acid 36, in particular hydrochloric acid, and an alkaline residue 38 are obtained from the brine 18. The acid 36 is used in step f) to acidify the seawater. The alkaline residue 38, in turn, is fed to a neutralization and discharge module 40 and mixed there with the acidified, low-carbon-dioxide seawater to neutralize this water. It is then discharged back into the sea at a feed point 42 located away from the intake point 2.
[0042] The hydrogen 30 obtained in step d) and the purified carbon dioxide 13 react in step h), shown in section 44, to form methanol 46 and water 48, which may still contain traces of carbon dioxide and methanol. The methanol is fed to a tank or pipeline 52 via a product pump 50. The resulting reaction water 48 is fed back to step a).
[0043] The waste heat generated in steps b) to e) is recovered and used in step g) to heat the seawater in step a) that has not yet been carbon dioxide reduced. Likewise, the thermal energy contained in the heated seawater after carbon dioxide extraction in step a) is at least partially recovered and used to heat the seawater in step a) that has not yet been carbon dioxide reduced.
[0044] The process according to Fig. 1 is carried out at least predominantly on an offshore platform 54. The energy required to carry out the process is obtained at least predominantly, and in particular entirely, from renewable energy sources, especially offshore. Reference numeral
[0045] 2 extraction points from the sea
[0046] 4 Seawater pump
[0047] 6 pre-filters
[0048] 8. Expulsion of carbon dioxide from acidified and heated seawater 10. Gas mixture
[0049] 12. Purification to remove oxygen
[0050] 13 purified carbon dioxide
[0051] 14 Vacuum distillation
[0052] 16 Water vapor
[0053] 18 NaCl concentrated brine
[0054] 20. Capture of remaining carbon dioxide
[0055] 22 distilled condensate
[0056] 24 Membrane distillation
[0057] 26 highly purified water
[0058] 28 Electrolysis
[0059] 30 Hydrogen
[0060] 32 brine pump
[0061] 34 Electrodialysis
[0062] 36 Acid
[0063] 38 alkaline residue
[0064] 40 Neutralization and exhaust module
[0065] 42 Discharge point into the sea Methanol synthesis from hydrogen and carbon dioxide Methanol
[0066] formed reaction water
[0067] Product pump
[0068] tank or pipeline
[0069] Offshore platform
Claims
Claims 1. Process for the production of methanol, comprising the process steps a) Seawater is acidified and heated to a temperature of at least 45°C and the gas mixture driven off from the seawater, consisting mainly of carbon dioxide, is collected, b) Removal of oxygen and optionally other volatile components from the gas mixture obtained in step a) to obtain purified carbon dioxide, c) Distillation of a portion of the low-carbon seawater remaining after extraction in step a) to obtain distilled water and an aqueous brine concentrated with NaCl, d) Carrying out electrolysis with the distilled water from step c) to obtain hydrogen and oxygen, e) Recovery of acid and an alkaline residue from the NaCl-enriched aqueous brine from step c) f) Use of the acid obtained in step e) to acidify the seawater in step a). g) Recovery of at least some of the waste heat generated in steps b) to e) and use of the waste heat to heat the seawater that has not yet been reduced in carbon dioxide in step a). h) Synthesis of methanol from the hydrogen from step d) and the carbon dioxide from step b) and separation of the methanol from the Product mixture.
2. Method according to claim 1, characterized in that the seawater is acidified in step a) to a pH value of less than 6.5, in particular to a pH value of 5.5 to 6.
5.
3. Method according to one of the preceding claims, characterized in that the heat energy contained in the heated seawater after the carbon dioxide extraction in step a) is at least partially recovered and used to heat the seawater that has not yet been carbon dioxide reduced in step a).
4. Method according to one of the preceding claims, characterized in that the distilled water is obtained in step c) by means of vacuum distillation.
5. Method according to one of the preceding claims, characterized in that the distilled water from step c) is further purified by membrane distillation.
6. Method according to one of the preceding claims, characterized in that the acid in step e) is obtained from the brine produced in step c) by means of chlor-alkali electrolysis.
7. A method according to any one of the preceding claims, characterized in that the acid in step e) is obtained from the brine produced in step c) by means of an electrodialysis process.
8. A method according to any one of the preceding claims, characterized in that the alkaline residue remaining during the production of the acid in step e) is used to neutralize the acidified seawater after the carbon dioxide extraction from step a).
9. Method according to one of the preceding claims, characterized in that the reaction water produced in step e) alongside methanol, which still contains traces of methanol and carbon dioxide even after the separation of methanol, is added to the seawater in step a).
10. Method according to one of the preceding claims, characterized in that the method is carried out at least predominantly on an offshore platform.
11. Method according to one of the preceding claims, characterized in that the energy required to carry out the method is obtained at least predominantly, in particular completely, from renewable energy sources, especially offshore.
12. Method according to claim 11, characterized in that the energy is obtained at least partially from solar energy via solar panels and the waste heat generated is stored and used to heat the seawater in step a).