Process mode for preparing methanol through direct conversion

Abstract

The invention relates to the technical field of preparation of methanol from natural gas, and discloses a process for preparing methanol by direct conversion, which comprises six core units, namely raw material pretreatment, vaporization and steam addition, natural gas conversion, methanol synthesis, methanol rectification and carbon capture and recovery. The method comprises the following steps: pretreating raw materials to remove impurities, mixing the raw materials with recovered steam to adjust the water-carbon ratio, directly converting to generate synthesis gas, circulating the synthesis gas to synthesize crude methanol, rectifying and purifying the crude methanol to obtain refined methanol, and capturing CO2 in flue gas to supplement a raw material unit system. Raw material pretreatment adopts nickel-molybdenum hydrogenation catalyst desulfurization and series-parallel desulfurization reactor design, a vaporization link maintains a water-carbon ratio of 2.5: 1 through double-path steam supply, natural gas conversion is combined with a pre-conversion and one-stage conversion process, methanol synthesis adopts a double-reactor parallel circulation system, rectification adopts a three-tower mode, and process water is recycled. The process has the advantages of high methane conversion rate, low energy consumption, high carbon utilization rate, low investment cost and the like.

Description

Technical Field

[0001] This application relates to the field of natural gas to methanol technology, specifically a direct conversion process for methanol production. Background Technology

[0002] Methanol is an important chemical raw material and clean fuel, widely used in chemical synthesis, energy, and other fields. With the global energy transition and the advancement of "dual carbon" goals, the demand for methanol continues to grow, making the exploration of efficient and low-energy-consumption production processes crucial for the industry.

[0003] Current mainstream methanol production processes mostly employ conversion routes of "coal gasification → syngas → methanol" or "natural gas → syngas → methanol," which generally suffer from drawbacks such as lengthy processes, high energy consumption, and high carbon emission intensity. These processes require complex steps including feedstock gasification, deep purification of syngas, and compression, relying on large-scale equipment such as steam reformers, gasifiers, and synthesis towers, resulting in extremely high initial equipment investment costs. Especially in the coal-based syngas preparation stage, pure oxygen is usually required to ensure reaction efficiency, which directly increases the construction cost of the supporting air separation unit, further exacerbating the overall investment and long-term operational economic burden of the project.

[0004] Even with natural gas as feedstock, traditional processes face similar bottlenecks. This technology employs a combined "pre-conversion + primary conversion" process route, first cracking heavy hydrocarbon components into lighter, smaller molecules before feeding them into the converter for reaction. This breaks through the limitations of traditional processes from a thermodynamic perspective, significantly improving the single-pass methane conversion rate, far exceeding the 80% upper limit of traditional primary conversion processes. This greatly reduces energy consumption and equipment load pressure caused by unreacted methane recycling. Through a dual-steam supply process design, 90% of process water can be recovered to generate saturated steam, and all excess water generated by the distillation system is recycled back to the saturation tower. The synthesis system does not require additional purchased hydrogen, and the purge gas can be recovered to the converter as fuel. This alone can recover approximately 27MW of calorific value, reducing overall energy consumption by more than 15% compared to traditional processes. The methanol feedstock gas consumption can be controlled at a highly efficient level of ≤330Nm³ / t. In addition, this technology is equipped with a carbon capture system, which can recover carbon from the converter flue gas. It is then returned to the raw material system, compared to approximately 3.5-4 tons for traditional coal-to-methanol production. This process improves carbon utilization by over 20% per ton of methanol, resulting in significant carbon reduction. The entire process requires no pure oxygen, completely avoiding the high power consumption of air separation units, and generates no phenol or cyanide-containing wastewater, significantly reducing environmental treatment costs. Furthermore, this technology eliminates complex intermediate steps such as syngas preparation and deep purification, and does not require auxiliary facilities like air separation units, resulting in a significantly lower overall equipment investment compared to traditional coal gasification routes. The reactor adopts a "series-parallel skid-mounted" design, supporting online catalyst replacement. The parallel layout of two reactors allows for flexible load balancing, significantly reducing operation and maintenance costs. This technology is compatible with various methane-containing feedstocks such as natural gas, coke oven gas, and refinery tail gas, and is suitable for methanol production units of different scales, possessing strong applicability and promotional value. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this application provides a direct conversion process for methanol production, which improves the single-pass conversion rate of methane, overcomes the thermodynamic limitations of traditional processes, reduces the amount of synthesis recycle gas, lowers compressor load and energy consumption, and comprehensively recovers and utilizes process water and flue gas. This will enable low-carbon production, reduce investment in auxiliary facilities, and lower equipment costs and operating energy consumption.

[0006] To achieve the above objectives, this application provides the following technical solution: a direct conversion process for methanol production, comprising the following steps: raw material pretreatment, vaporization and steam addition, natural gas conversion, methanol synthesis, methanol distillation, and carbon capture and recovery—six core units; the process route is as follows: after pretreatment to remove impurities, the raw material is mixed with recovered steam to adjust the water-to-carbon ratio, and then directly converted to generate syngas. The syngas is recycled to synthesize crude methanol, which is then purified by distillation to obtain refined methanol, while simultaneously capturing carbon from the flue gas. Replenishment of raw material unit system.

[0007] This application utilizes a combined pre-conversion and primary-stage conversion process, where heavy hydrocarbons are first decomposed into lighter components before entering the conversion furnace for reaction. This overcomes the thermodynamic limitations of traditional processes, achieving a high single-pass methane conversion rate, far exceeding the 80% upper limit of traditional primary-stage conversion processes. This reduces energy consumption and equipment load caused by unreacted methane recycling. The dual-steam supply design recovers 90% of the process water to generate saturated steam, and excess water from distillation is recycled back to the saturation tower. The synthesis system does not require additional circulating hydrogen. Purge gas is recovered and supplied to the conversion furnace for combustion, recovering approximately 27MW of calorific value. The overall energy consumption is reduced by more than 15% compared to traditional processes, with methanol feedstock gas consumption ≤830 kW. Add a carbon capture system to recover carbon from the converter flue gas. Replenishment of raw material unit system, traditional coal-to-methanol The process generates approximately 3.5-4 tons of methanol per ton of methanol. Carbon utilization is increased by over 20%, significantly reducing carbon emissions. It eliminates pure oxygen consumption, avoiding the high power consumption of air separation units, and produces no wastewater containing phenols or cyanides, resulting in a substantial reduction in environmental treatment costs. This application eliminates complex intermediate steps such as syngas preparation and purification, reducing investment in auxiliary facilities like air separation units, and lowering overall equipment investment compared to traditional coal gasification routes. The series-parallel desulfurization reactor design allows for online catalyst replacement, and the parallel dual-reactor system facilitates balanced operating loads, significantly reducing maintenance costs. This application can process various methane-containing gas feedstocks such as natural gas, coke oven gas, and refinery tail gas, and is suitable for methanol production units of different scales, with a wide range of applications. Detailed Implementation

[0008] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application are described clearly and completely. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0009] The main equipment specifications involved in this process are shown in the following examples:

[0010] Saturation tower: Specifications ф4200*145000mm, used to recover process water to generate saturated steam;

[0011] Pre-conversion reactor: φ3400 / 45000mm, for heavy hydrocarbon decomposition;

[0012] Conversion furnace: catalyst loading 8400kg, conversion furnace tubes 560, radiant heat load 448MW;

[0013] Synthesis reactor (2 units in parallel): φ5000*10000mm, equipped with copper / zinc catalyst;

[0014] Distillation column: 3 units in series to achieve crude methanol purification and process water circulation.

[0015] Example 1

[0016] This embodiment uses high-methane-content natural gas as raw material to implement the direct conversion to methanol process.

[0017] Raw material pretreatment: Natural gas (feed rate 128t / h, temperature 20℃, methane content 96.6%, containing trace amounts of sulfur and chlorine impurities) is divided into two equal parts and passes through a buffer tank to remove heavy components. After being mixed with hydrogen-rich gas from the methanol synthesis loop, organic sulfur is converted into hydrogen sulfide under the action of nickel-molybdenum hydrogenation catalyst. Then, it is further desulfurized by a series-parallel desulfurization reactor to ensure that the sulfur and chlorine content is reduced to below the catalyst tolerance threshold.

[0018] Vaporization and Steam Addition: A dual-supply design is adopted. One supply line directly contacts the circulating water through a saturation tower (feed temperature 200℃, feed rate 65t / h), recovering process water to generate 112.24t / h of saturated steam (tower top temperature 192℃, pressure 2.88MPa(A), steam temperature 380℃); the other supply line directly adds process steam, maintaining a water-to-carbon ratio of 2.5:1 through a water-to-carbon ratio controller. A fixed steam flow branch is set downstream of the pre-conversion reactor for purging protection in case of reactor failure.

[0019] Natural gas conversion: The mixed gas is preheated to 450-500℃ (500℃ in this embodiment) by a heater, and then enters a pre-conversion reactor (feed rate 243.55t / h, pressure 2.7MPa), where heavy hydrocarbons are decomposed into lighter components, with an outlet temperature of 430℃. The material then enters a conversion furnace (feed temperature 625℃, feed rate 257t / h), where it is directly converted into syngas at a reaction temperature of 850-880℃ (850℃ in this embodiment). In this embodiment, the pre-conversion reactor is filled with... Composite catalyst; the first-stage conversion furnace is sequentially filled in sections along the flow direction of the reactants. Modified Catalyst layer and Solid solution co-catalyst layer.

[0020] Methanol synthesis: Syngas enters a dual-parallel reactor at a pressure of 7.5-8.0 MPa (7.5 MPa in this example) and a feed temperature of 225°C. The reaction proceeds under the action of a copper / zinc catalyst. The exothermic reaction is used to generate medium-pressure steam. The outlet temperature is 250°C. The mixed gas exiting the synthesis reactor is cooled and then enters a separator. The crude methanol product is discharged to the distillation unit via the bottom of the separator. Most of the unreacted gas carrying inert gases is pressurized by a circulating compressor and returned to the reactor. A small amount of dry gas is discharged as fuel for the reformer. The entire system requires no additional circulating hydrogen.

[0021] Methanol distillation: Crude methanol is purified by distillation using a three-tower system. Flash vapor is sent to the converter for combustion to recover heat, and excess water produced by distillation is recycled to the saturation tower. Alcohols dissolved in the water re-participate in the conversion reaction along with the water circulation.

[0022] Carbon capture and recovery: Chemical absorption is used to capture carbon in the flue gas exiting the converter. , will be recycled It is added to the raw material pretreatment system. In addition, chemical absorption, physical adsorption, membrane separation, or cryogenic separation methods can be used to capture the flue gas exiting the converter. This application does not impose specific limitations on this.

[0023] Product results: 215.5 t / h of refined methanol was obtained with a purity of ≥99.9%, methane conversion rate of 88%, carbon utilization rate improved by 22% compared with traditional process, and overall energy consumption was reduced by 18%.

[0024] Example 2

[0025] This embodiment uses hydrogen-rich oil refining tail gas as raw material to demonstrate the process's feedstock adaptability.

[0026] Raw material pretreatment: The raw gas (feed rate 180t / h, temperature 30℃, methane content 25%, hydrogen content 55%, other hydrocarbon content 20%) is divided into two equal parts and passed through a buffer tank to remove heavy components. After being mixed with hydrogen-rich gas from the methanol synthesis loop, organic sulfur is converted into hydrogen sulfide under the action of nickel-molybdenum hydrogenation catalyst. Then, it is further desulfurized by a series-parallel desulfurization reactor to ensure that the sulfur and chlorine content is reduced to below the catalyst tolerance threshold.

[0027] Vaporization and steam addition, natural gas conversion, methanol distillation and carbon capture and recovery: the steps and conditions are the same as in Example 1. The natural gas conversion step also utilizes the aforementioned gradient catalytic system.

[0028] Methanol Synthesis: Synthesis gas enters a dual-parallel reactor at a pressure of 8.0 MPa and a feed temperature of 230°C for the synthesis reaction. In this embodiment, a ceramic-polymer composite membrane separator is installed between the parallel outlet of the dual reactors and the circulating compressor. The composite membrane separator... The rejection rate is ≥98%, and the permeability coefficient for inert gases is 18 times. The hydrogen-rich gas separated by the membrane separator is returned to the inlet of the circulating compressor, and the inert gas on the permeate side is discharged from the system; the separated crude methanol liquid is directly sent to the distillation unit.

[0029] Product results: 195 t / h of refined methanol was obtained with a purity of ≥99.9% and a methane conversion rate of 87%. There was no pure oxygen consumption. The investment cost was reduced by 35% and the operating energy consumption was reduced by 16% compared with the traditional process.

[0030] Example 3

[0031] This embodiment uses coke oven gas with a complex composition as raw material and adopts a full-process optimization scheme.

[0032] Raw material pretreatment: The raw gas (feed rate 1208t / h, temperature 35℃, methane content 40%, olefin content 15%, other carbon compounds content 45%) is divided into two equal parts and the heavy components are removed in a buffer tank. After being mixed with the hydrogen-rich gas in the methanol synthesis loop, the organic sulfur is converted into hydrogen sulfide under the action of nickel-molybdenum hydrogenation catalyst. Then, it is further desulfurized by a series-parallel desulfurization reactor to reduce the sulfur and chlorine content to below the catalyst tolerance threshold.

[0033] Vaporization and steam addition, methanol distillation and carbon capture and recovery: the steps and conditions are the same as in Example 1.

[0034] Natural gas conversion: The steps and conditions are the same as in Example 1, and the gradient catalytic system described above is used.

[0035] Methanol synthesis: The steps and conditions are the same as in Example 2, and the ceramic-polymer composite membrane separator described above is used for gas separation.

[0036] Product results: 180 t / h of refined methanol was obtained with a purity of ≥99.9%, methane conversion rate of 86%, and carbon utilization rate increased by 20%.

[0037] Example 4

[0038] This embodiment, based on Embodiment 1, integrates a gradient catalysis system and membrane separation technology to demonstrate the optimization effect of the entire process.

[0039] Raw material pretreatment: Natural gas (feed rate 128 t / h, temperature 20℃, methane content 96.6%, containing trace amounts of sulfur and chlorine impurities) is divided into two equal parts and passed through a buffer tank to remove heavy components. After being mixed with hydrogen-rich gas from the methanol synthesis loop, organic sulfur is converted into hydrogen sulfide under the action of a nickel-molybdenum hydrogenation catalyst. Then, it undergoes deep desulfurization in a series-parallel arrangement of desulfurization reactors to ensure that the sulfur and chlorine content is reduced to below the catalyst tolerance threshold.

[0040] Vaporization and steam addition: The steps and conditions are the same as in Example 1;

[0041] Natural gas conversion: The steps and conditions are the same as in Example 1, and the gradient catalytic system described above is used.

[0042] Methanol Synthesis: Synthesis gas enters a dual-parallel reactor at a pressure of 7.80 MPa and a feed temperature of 225°C for the synthesis reaction. In this embodiment, a ceramic-polymer composite membrane separator is installed between the parallel outlet of the dual reactors and the circulating compressor. The composite membrane separator... The rejection rate is ≥98%, and the permeability coefficient for inert gases is 16 times. The hydrogen-rich gas separated by the membrane separator is returned to the inlet of the circulating compressor, and the inert gas on the permeate side is discharged from the system; the separated crude methanol liquid is directly sent to the distillation unit.

[0043] Methanol distillation: The steps and conditions are the same as in Example 1.

[0044] Carbon capture and recovery: The steps and conditions are the same as in Example 1.

[0045] Product results: 199 t / h of refined methanol was obtained, with a purity of ≥99.9%, methane conversion rate of 85%, and carbon utilization rate increased by 17%.

[0046] Regarding the gradient catalytic system, it should be noted that the gradient catalytic system used in the natural gas conversion step is filled with [material missing] in the pre-conversion reactor. The composite catalyst can directionally decompose heavy hydrocarbons at 450-500℃ and 0.8-1.2MPa, with a decomposition rate ≥99%. It is loaded in stages along the reaction stream direction within the primary converter. modified Catalyst and The solid solution co-catalyst layer works synergistically, with the front-end catalyst mainly undergoing methane steam reforming, while the back-end co-catalyst layer can remove 5%-8% of the methane from the feedstock. In-situ conversion to CO, thereby reducing the CO / The ratio remains stable at 2.8-3.2:1, eliminating the need for additional independent [equipment / facilities]. Conversion reactor.

[0047] For example, the Composite catalysts can be prepared by the sol-gel method, wherein... The doping amount is 15%-20% of the Ni mass fraction, and this structure can effectively suppress the sintering of Ni particles; modified In catalyst With a loading of 3%-5%, it can improve methane conversion activity and anti-carbon deposition performance; In the solid solution co-catalyst layer, the molar ratio of Ce to Zr is 1:1, which enhances the catalyst through its oxygen vacancy effect. Adsorption and activation.

[0048] Regarding the membrane separation coupling, it should be noted that the methanol synthesis and distillation units are coupled via a ceramic-polymer composite membrane separator. This membrane separator has a H2 rejection rate of ≥98% and a permeability coefficient for inert gases (such as H2 and CH4) that is 15-20 times that of H2. After separation, the inert gas content in the circulating gas can be controlled at 3%-5% of the total, and the hydrogen-rich gas is directly returned to the reactor inlet, thus eliminating the need for a traditional dry gas exhaust branch. The separated crude methanol also does not need to pass through a cooling separation tank and can be directly sent to the pre-distillation column of the three-tower distillation system. The ceramic-polymer composite membrane can use Al2O3 ceramic as the support layer and polyimide as the separation layer, with a membrane pore size of 50-80 nm, an operating temperature of 80-100℃, and a pressure of 6.5-7.0 MPa.

[0049] A preferred thermal integration solution involves exchanging heat between the overhead vapor phase of the pressurized distillation column and the shell side of the composite membrane separator. This utilizes the residual heat from distillation to provide the necessary heat for membrane separation, reducing the overall system energy consumption by 12%-15% compared to traditional processes. Furthermore, before being returned to the saturated column, the alcohol-containing process water produced during distillation can be pre-treated with a molecular sieve adsorption column to remove residual alcohols, reducing the alcohol content to below 50 ppm to avoid potential poisoning risks to downstream catalysts.

[0050] In summary, the raw materials may also include other methane-containing gases besides natural gas, coke oven gas, and oil refinery tail gas. The production capacity can be adjusted according to project needs and is suitable for methanol production units with a scale of 1,000 to 25,000 t / d.

[0051] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0052] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

[0053] Those skilled in the art should understand that the above descriptions are merely several specific embodiments of this application, and not all embodiments.

Claims

1. A direct conversion process for methanol production, characterized in that, Includes the following steps: The system comprises six core units: raw material pretreatment, vaporization and steam addition, natural gas conversion, methanol synthesis, methanol distillation, and carbon capture and recovery. The process route is as follows: after pretreatment to remove impurities, the raw material is mixed with recovered steam to adjust the water-to-carbon ratio, and then directly converted into syngas. The syngas is recycled to synthesize crude methanol, which is then purified by distillation to obtain refined methanol. Simultaneously, carbon capture and recovery are performed on the flue gas. Replenishment of raw material unit system.

2. The direct conversion to methanol process according to claim 1, characterized in that, The raw material pretreatment step includes: the raw material is divided into two equal parts and the heavy components are removed by a buffer tank. The raw material is divided first and then enters the tank. After being mixed with the hydrogen-rich gas in the methanol synthesis loop, the organic sulfur is converted into hydrogen sulfide by a nickel-molybdenum hydrogenation catalyst. Then, it is deeply desulfurized by a desulfurization reactor arranged in series and parallel to ensure that the sulfur and chlorine content is reduced to below the catalyst tolerance threshold.

3. The direct conversion to methanol process according to claim 1, characterized in that, The vaporization and steam addition steps adopt a dual-steam supply design: one path directly contacts the circulating water through a saturation tower to recover 90% of the process water and generate saturated steam; the other path directly adds process steam, and the water-to-carbon ratio is maintained at 2.5:1 by a water-to-carbon ratio controller. A fixed steam flow branch is set downstream of the pre-conversion reactor for purging protection in case of reactor failure.

4. The direct conversion to methanol process according to claim 1, characterized in that, The natural gas conversion steps include pre-conversion and primary conversion: after the mixed gas is preheated at 450-500℃, the heavy hydrocarbons are decomposed into light components in the pre-conversion reactor and then enter the conversion furnace. The reaction temperature is maintained at 850-880℃ using the residual heat of the flue gas in the radiant section, and the gas is directly converted into syngas under the action of a catalyst.

5. The direct conversion to methanol process according to claim 1, characterized in that, The methanol synthesis adopts a dual-reactor parallel circulation system: the synthesis gas reacts under a copper / zinc catalyst and a pressure of 7.5-8.0 MPa, and the exothermic reaction is used to generate medium-pressure steam; the mixed gas from the synthesis reactor is cooled and then enters a separation tank. The crude methanol product is discharged to the distillation unit through the bottom of the separation tank. Most of the unreacted gas carrying inert gases is pressurized by the circulating compressor and returned to the reactor. After being discharged, it is used as fuel for the reformer. The entire system does not require additional circulating hydrogen.

6. The direct conversion to methanol process according to claim 1, characterized in that, The methanol distillation adopts a three-tower mode. The flash vapor is sent to the conversion furnace for combustion to recover heat, and the excess water produced by distillation is sent back to the saturation tower for recycling. The alcohols dissolved in the water participate in the conversion reaction again with the water circulation.

7. The direct conversion to methanol process according to claim 1, characterized in that, The added carbon capture system employs chemical absorption, physical adsorption, membrane separation, or cryogenic separation to capture carbon in the flue gas exiting the converter. , will be recycled It is added to the raw material unit system to improve carbon utilization and increase methanol production.

8. The direct conversion to methanol process according to claim 1, characterized in that, The raw materials include methane-containing gases such as natural gas, coke oven gas, and oil refinery tail gas. The production capacity can be adjusted according to project needs and is suitable for methanol production units with a scale of 1,000 to 25,000 t / d.

9. The direct conversion to methanol process according to claim 4, characterized in that, The preconversion reactor is filled with The composite catalyst operates at a temperature of 450-500℃ and a pressure of 0.8-1.2MPa. The conversion furnace is sequentially filled in sections along the flow direction of the reactants. Modified Catalyst layer and Solid solution co-catalyst layer.

10. The direct conversion to methanol process according to claim 5, characterized in that, A ceramic-polymer composite membrane separator is installed between the parallel outlet of the dual reactors and the circulating compressor; The composite membrane separator has a H2 rejection rate of ≥98% and a permeability coefficient for inert gases that is 15-20 times that of H2. The hydrogen-rich gas separated by the membrane separator is returned to the inlet of the circulating compressor, and the inert gas on the permeate side is discharged from the system; the separated crude methanol liquid is directly sent to the distillation unit.