Method and system for efficiently producing methanol through eluent reinforced carbon dioxide hydrogenation

Abstract

The invention discloses a method and a system for synthesizing methanol through eluent reinforced carbon dioxide hydrogenation, which introduces eluent with selective solubility to water or methanol into a carbon dioxide hydrogenation reactor, thereby overcoming thermodynamic limitation and moving reaction equilibrium to a favorable direction. The system comprises a methanol synthesis unit, an eluent circulation unit and a product refining unit, the main body of the methanol synthesis unit is an eluent reinforced reactor which can be a one-section or multi-section reactor, and the eluent is introduced into the reactor or arranged among multiple sections of reaction units. According to the method, the high-heat-capacity eluent with the selective dissolving property on water or methanol is used for separating products in situ and removing reaction heat, so that the limitation of reaction balance is overcome, the conversion per pass of carbon dioxide is improved, the gas volume of a reaction outlet is reduced, the volume of a reactor is reduced, and heat management in the reactor is facilitated.

Description

Technical Field

[0001] The invention belongs to the technical field of direct production of methanol from carbon dioxide, and in particular relates to a method and system for direct production of methanol from carbon dioxide using an eluent-enhanced method. Background Art

[0002] Methanol, as a simple alcohol compound, has a wide range of applications, especially in the chemical industry and energy fields. Renewable methanol produced from biomass or from green hydrogen (hydrogen produced from renewable energy) and carbon dioxide can expand the use of methanol as a chemical raw material and help achieve carbon neutrality in industrial and transportation fuels, but the current production cost of renewable methanol is high and the output is relatively low. According to the Le-Chatelier principle, low temperature and high pressure are required to move the equilibrium of the reaction forward. At the same time, due to the high thermal stability of carbon dioxide molecules, its activation and subsequent formation of methanol require higher temperatures, and this high temperature is inconsistent with the thermodynamics of the reaction. Therefore, the conventional process system has a low carbon dioxide per-pass conversion rate, generally around 30-40%. On the other hand, the direct production of methanol from carbon dioxide is a highly exothermic process, and thermal management in the process is also an issue that needs to be addressed. Summary of the invention

[0003] In view of the problems existing in the traditional process of producing methanol by hydrogenation of carbon dioxide, the present invention proposes a method and system for producing methanol directly from carbon dioxide enhanced by an eluent. The reactor of the system is fed with an eluent that selectively dissolves water or methanol, and the eluent is dripped into the catalyst bed through a liquid distributor, and the water or methanol generated by the reaction is dissolved in the eluent, while the carbon dioxide, hydrogen and by-product carbon monoxide in the reaction system are difficult to dissolve in the eluent, so that the reaction equilibrium is moved toward the direction of methanol generation, thereby improving the carbon dioxide conversion rate.

[0004] The present invention first provides a method for efficiently producing methanol by hydrogenation of carbon dioxide intensified by an eluent, which comprises the following steps:

[0005] S1: Mix carbon dioxide and hydrogen as raw gas, pressurize the raw gas and preheat it to 200-280°C;

[0006] S2: The preheated raw gas is passed from bottom to top into the eluent-enhanced reactor, and is further heated by the heater in the reactor before entering the catalyst bed to react; the eluent is preheated to 140-200°C and then passed from top to bottom into the eluent-enhanced reactor, and drips into the catalyst bed after passing through the liquid distributor at the top of the reactor;

[0007] S3: The gas after the reaction is passed into a condenser, and the condensed gas phase is used as circulating gas, which is mixed with the raw gas after pressurization, and passed into the reactor after preheating, and the condensed liquid phase is passed into the methanol refining unit;

[0008] The eluent is drawn out from the bottom of the reactor and enters the flash tank. The liquid phase obtained by flash evaporation enters the eluent circulation unit, and the obtained gas phase is mixed with the reactor outlet gas and passed into the condenser.

[0009] As a preferred embodiment of the present invention, the preheating temperature in step S1 is preferably 220-260° C. The preheating temperature of the eluent in step S2 is preferably 160-180° C.

[0010] As a preferred embodiment of the present invention, the catalyst bed in the reactor can be arranged in sections, and a liquid distributor is arranged between the catalyst beds to ensure that the eluent is evenly distributed between the catalyst beds. A temperature sensor and a pressure sensor are arranged between the catalyst beds to monitor the temperature and pressure of each section of the catalyst bed in the reactor in real time, to ensure that the reaction conditions are in the best state, and to avoid the phenomenon of local overheating or uneven cooling of the catalyst bed.

[0011] As a preferred embodiment of the present invention, the methanol refining unit is used to separate water or methanol from the eluent, and the regenerated eluent is returned to the eluent circulation system and continuously used in the reaction process of hydrogenating carbon dioxide to methanol. This not only realizes the recycling of the eluent and reduces the consumption of the eluent, but also improves the economy and environmental friendliness of the system.

[0012] As a preferred embodiment of the present invention, the eluent has high solubility in water or methanol or both, and has low solubility in raw gas and by-product gas in the reaction system. Preferably, its solubility in methanol or water is S1, and its solubility in carbon dioxide, hydrogen and carbon monoxide is S2, satisfying S1 / S2≥50. Organic solvents or ionic liquids with extremely low saturated vapor pressure, high heat capacity and high selective solubility in water or methanol are preferably used to ensure that they can efficiently remove the reaction heat while efficiently dissolving the water or methanol generated by the reaction, while being insoluble or slightly soluble in carbon dioxide, hydrogen and carbon monoxide. The eluent used preferably includes, but is not limited to, tetraethylene glycol dimethyl ether, ethylene glycol oligomer (C 2n H 4n+2 O n+1 , n=3-6), 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]), 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]), 1-hexyl-3-methylimidazolium hexafluorophosphate ([HMIM][PF6]), 1-butyl-3-methylimidazolium nitrate ([BMIM][NO3]) and 1-ethyl-3-methylimidazolium acetate ([EMIM][OAc]).

[0013] The present invention also provides an eluent-enhanced system for efficiently producing methanol by hydrogenation of carbon dioxide, comprising:

[0014] A compressor, used to increase the pressure of the raw gas;

[0015] A raw material preheater, used to preheat the pressurized raw gas;

[0016] An eluent-enhanced reactor is used for reaction, the reactor has an eluent inlet and an inlet and a gas inlet and an inlet, and a liquid distributor and a catalyst bed are arranged inside the reactor;

[0017] The condensation tank is used to condense the gas after the reaction. The condensed gas is pressurized and mixed with the raw gas, and then preheated and passed into the reactor. The condensed liquid phase is passed into the methanol refining unit;

[0018] A flash tank receives the eluent from the eluent outlet of the reactor, flashes it, and the liquid phase obtained by flashing is sent to the eluent circulation unit, and the gas phase obtained is mixed with the gas from the gas outlet of the reactor and passed into the condenser;

[0019] The eluent circulation unit is used for circulating the eluent to the eluent inlet of the reactor.

[0020] As a preferred solution of the present invention, the liquid distributor adopts a porous plate structure to ensure that the eluent is evenly distributed on the catalyst bed, avoid local overheating or uneven cooling, and ensure the consistency and stability of the reaction conditions. The aperture of the porous plate is 1 to 5 mm, and the opening rate is 0.5 to 0.8, which ensures that the liquid flow rate of each hole is consistent and avoids the phenomenon of uneven liquid distribution; the liquid distributor adopts corrosion-resistant and high-temperature resistant materials, such as stainless steel or high-temperature resistant alloys, to ensure long-term stable operation under high temperature and high pressure environment; the liquid distributor is installed above each section of the catalyst bed to ensure that the eluent can evenly cover the entire bed; a certain distance is set between multiple distributors to prevent the liquid flow from being disturbed.

[0021] As a preferred embodiment of the present invention, the catalyst used in the catalyst bed is preferably a noble metal-supported catalyst, a copper-based catalyst, a cobalt-based catalyst, an iron-based catalyst, a molybdenum-based catalyst, a tungsten-based catalyst, a tin-based catalyst, etc.

[0022] In some optional embodiments, the catalyst bed is blended with a hydrophobic substance, which includes a hydrophobic polymer, such as polytetrafluoroethylene, polydivinylbenzene, or a hydrophobic metal compound, such as cobalt manganese carbide, a hydrophobic molecular sieve such as pure silica zeolite, and the like.

[0023] In some optional embodiments, the catalyst is hydrophobically modified so that the eluent does not wet the catalyst bed, such as by grafting the catalyst surface with organic silane.

[0024] More preferably, the present invention adjusts the microenvironment of the catalyst bed by blending hydrophobic substances and modifying the catalyst hydrophobically, so that the catalyst bed is not wetted by the eluent and the gas-solid reaction is better performed.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1) Improve the one-way conversion rate of carbon dioxide. The present invention introduces water or methanol produced by the eluent separation reaction to promote the chemical equilibrium to move toward the methanol generation direction, thereby greatly improving the one-way conversion rate of carbon dioxide.

[0027] 2) Enhance heat transfer effect. The eluent directly contacts the catalyst bed to effectively remove the reaction heat, maintain the appropriate temperature of the catalyst bed, and improve the reaction rate and efficiency. The combination of the multi-stage reaction system and the high-efficiency liquid distributor further optimizes the heat transfer effect and avoids local overheating or uneven cooling.

[0028] 3) Reduce equipment costs. The single-pass conversion rate of carbon dioxide is increased, the corresponding circulating gas volume is reduced, the required reactor size is reduced, and the amount of catalyst used is reduced, thereby reducing equipment costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The flowchart of the method for efficiently producing methanol by hydrogenation of carbon dioxide with enhanced eluent according to the present invention is as follows;

[0030] Figure 2 is a flow chart of the method and system of the present invention;

[0031] Figure 3 It is a schematic diagram of the reactor involved in the present invention.

[0032] In the figure, 1 is the first compressor; 2 is the first heat exchanger; 3 is the carbon dioxide hydrogenation reactor; 4 is the second heat exchanger; 5 is the gas-liquid separator; 6 is the condenser; 7 is the pump; 8 is the second compressor; 9 is the eluent storage tank; 10 is the flash tank; 11 is the pump; and 12 is the distillation tower.

[0033] In the figure, a, reaction gas outlet; b, eluent inlet; c, spray head; d, gas channel of liquid distribution plate; e, overflow port of liquid distribution plate; f, porcelain ball; g, catalyst; h, eluent outlet; i, reaction gas inlet. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0035] The embodiments of the present invention are further described in detail below with reference to the accompanying drawings.

[0036] like Figure 1 The figure shows the process flow of the method for efficiently producing methanol by hydrogenation of carbon dioxide enhanced by eluent of the present invention. The method of the present invention comprises the following steps:

[0037] S1: Mix carbon dioxide and hydrogen as raw gas, pressurize and preheat the raw gas to 220-260°C;

[0038] S2: The preheated raw gas is passed from bottom to top into the eluent-enhanced reactor, and is further heated by the heater in the reactor before entering the catalyst bed to react; the eluent is preheated to 160-180°C and passed from top to bottom into the eluent-enhanced reactor, and drips into the catalyst bed after passing through the liquid distributor at the top of the reactor;

[0039] S3: The gas after the reaction is passed into a condenser, and the condensed gas phase is used as circulating gas, which is mixed with the raw gas after pressurization, passed into the reactor after passing through a preheater, and the condensed liquid phase is passed into the methanol refining unit;

[0040] The eluent is drawn out from the bottom of the reactor and enters the flash tank. The liquid phase obtained by flash evaporation enters the eluent circulation unit, and the obtained gas phase is mixed with the reactor outlet gas and passed into the condenser.

[0041] In a specific embodiment of the present invention, using Figure 2 The system shown is used as an example of a specific method for synthesizing methanol, comprising the following steps:

[0042] 1. The raw carbon dioxide, hydrogen and the outlet of the gas-liquid separator 5 compressed by the first compressor 1 are mixed with the circulating gas from the second compressor 8, and then preheated (preheated to 220-260°C) by the first heat exchanger 2 and enter the reactor 3 for carbon dioxide hydrogenation reaction. The eluent enters the reactor through the pump 11, contacts the catalyst bed after passing through the liquid distribution plate, and is drawn out from the bottom of the reactor into the flash tank 10. During the reaction, water and methanol are generated in the catalyst bed. The eluent is soluble in water or methanol or both, and has a low solubility in the raw gas and by-product gas such as carbon dioxide, hydrogen and carbon monoxide in the reaction system. After passing through the liquid distribution plate, the eluent flows evenly through the catalyst bed to dissolve the product water or methanol. In this embodiment, the liquid distributor is provided with holes, and the eluent drips to the catalyst bed through the holes. The aperture of the opening is 1-5 mm, and the porosity is 0.5-0.8; the liquid distributor is provided with a gas channel, and the reaction gas passes through the liquid distribution plate through the gas channel. At the same time, the eluent washes the catalyst bed from top to bottom, and the reaction gas passes through the catalyst bed from bottom to top. The two are in countercurrent contact, and the eluent with a lower temperature passes through the catalyst bed and takes away the reaction heat by direct contact.

[0043] 2. The reaction gas is drawn out from the top of the reactor, containing unreacted carbon dioxide and hydrogen as well as a small amount of carbon monoxide byproduct. After passing through the first heat exchanger 2 and the second heat exchanger 4, the gas enters the gas-liquid separation tank 5 for gas-liquid separation. The gas phase separated from the gas-liquid separator 5 is used as the circulating gas, and the liquid phase enters the condensation tank 6 after decompression to further separate the unreacted carbon dioxide, hydrogen and carbon monoxide, wherein the purge gas can be used for pressure swing adsorption or flare.

[0044] 3. The eluent is drawn out from the bottom of the reactor and enters the flash tank 10. The gas phase is separated from the gas-liquid separation tank 5 and the liquid phase after decompression enters the condenser 6. The liquid phase of the condenser 6 is heat exchanged by the second heat exchanger 4, and then enters the distillation tower 12 through the pump 7. The light components at the top of the distillation tower are divided into product methanol.

[0045] In some implementation cases, multiple main equipment such as reactors or distillation towers are connected in series or in parallel.

[0046] In some implementation cases, in addition to the main material pipelines, there are additional start-up pipelines, etc.

[0047] In some specific embodiments, the reactor structure is arranged as follows Figure 3 As shown, it is a three-stage methanol reactor, and the relevant processes in the reactor are specifically described as follows:

[0048] After the eluent is preheated and controlled to a temperature of 160-180°C, it enters the reactor through the eluent inlet 2, drips onto the ceramic ball 5 through the overflow port of the liquid distribution plate, and the eluent is further evenly distributed on the ceramic ball and flows into the catalyst bed. The catalyst bed is filled with Cu / Zn / Al catalyst. After the feed gas is preheated and controlled to a temperature of 220-260°C, it enters the reactor from the bottom through the inlet 8, first contacts the catalyst bed to undergo a hydrogenation reaction, and the operating pressure is controlled at about 5MPa by a compressor and a regulating valve. The eluent flows from top to bottom through the catalyst bed, dissolving the product methanol or water, while directly exchanging heat with the catalyst bed, taking away the reaction heat, and finally leaves the reactor through the bottom eluent outlet 7.

[0049] In some implementation cases, the liquid distribution plate is in other forms or a showerhead.

[0050] In some embodiments, the reactor catalyst bed is divided into one or more stages.

[0051] In some embodiments, multiple reactors are connected in series or in parallel.

[0052] Tables 1 and 2 show the comparison of the relevant operating parameters of the methanol process without eluent enhancement in the prior art and the methanol process enhanced by the eluent of the present invention. Figure 3 The structure shown in the figure divides the catalyst bed into three sections, i.e., a three-section methanol process. The reactor of the methanol process without eluent enhancement adopts a one-section type. The total catalyst loading of the two reactors is the same, and the catalyst is Cu / Zn / Al catalyst. Except for not using eluent, the other process operating parameters (such as raw gas feed rate, reaction temperature, pressure, etc.) of the methanol process without eluent enhancement are the same as those of the methanol process with eluent enhancement of the present invention. The operating results of the two processes are as follows:

[0053] Table 1. Methanol process without eluent intensification

[0054]

[0055] Table 2. Three-stage methanol process with eluent enhancement

[0056]

[0057]

[0058] As can be seen from Table 1 and Table 2, the eluent-enhanced reaction of the present invention can significantly reduce boiler feed water and circulation ratio and improve the single-pass conversion rate. That is, the present invention promotes the chemical equilibrium to move toward the direction of methanol production by introducing the eluent, thereby improving the single-pass conversion rate of carbon dioxide. Accordingly, the circulating gas volume decreases, the required reactor size is reduced, and the equipment cost is reduced; the eluent at a lower temperature contacts the catalyst bed by direct contact, efficiently removing the reaction heat.

[0059] The above description is only a specific embodiment of the present application, which is intended to help those skilled in the art understand or implement the present application. It is obvious that those skilled in the art can make various modifications to these embodiments, and these general principles can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application should not be limited to the embodiments shown, but should be based on the maximum scope that conforms to the principles and novel features of the present application.

Claims

1. A method for efficiently producing methanol by hydrogenation of carbon dioxide enhanced by eluent, characterized in that: The following steps are involved: S1: Mix carbon dioxide and hydrogen as raw gas, pressurize the raw gas and preheat it to 200-280°C; S2: The preheated raw gas is passed from bottom to top into the eluent-enhanced reactor, and is further heated by the heater in the reactor before entering the catalyst bed to react; the eluent is preheated to 140-200°C and then passed from top to bottom into the eluent-enhanced reactor, and drips into the catalyst bed after passing through the liquid distributor at the top of the reactor; S3: The gas after the reaction is passed into a condenser, and the condensed gas phase is used as a circulating gas. After pressurization, it is mixed with the raw gas, and then passed into the reactor after preheating. The liquid phase obtained by condensation is passed into the methanol refining unit; the eluent is drawn out from the bottom of the reactor and enters the flash tank. The liquid phase obtained by flash evaporation enters the eluent circulation unit, and the obtained gas phase is mixed with the reactor outlet gas and passed into the condenser.

2. The method according to claim 1, characterized in that The eluent enters the catalyst bed through a liquid distributor; in the catalyst bed, the feed gas reacts with the catalyst layer to generate methanol and water, and the eluent selectively dissolves the methanol and / or water generated in the reactor.

3. The method according to claim 2, characterized in that The eluent passes through a liquid distributor, is evenly distributed and drips onto a catalyst bed, and flows through the catalyst bed from top to bottom; the catalyst bed is one-stage or multi-stage, and when the catalyst bed is multi-stage, a liquid distributor is provided between the beds for redistributing the eluent; the reaction gas passes through the catalyst bed from bottom to top, and contacts the eluent in countercurrent, and the eluent absorbs the reaction heat after contacting the catalyst bed.

4. The method according to claim 2, characterized in that: The eluent has high solubility in water or methanol or both, and low solubility in raw gas and by-product gas in the reaction system; its solubility in methanol or water is S1, and its solubility in carbon dioxide, hydrogen and carbon monoxide is S2, satisfying S1 / S2≥50.

5. The method according to any one of claims 1 to 4, characterized in that: The eluent is an organic solvent or an ionic liquid, wherein the organic solvent is tetraethylene glycol dimethyl ether or ethylene glycol oligomer; the ionic liquid is one or more of 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]), 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]), 1-hexyl-3-methylimidazolium hexafluorophosphate ([HMIM][PF6]), 1-butyl-3-methylimidazolium nitrate ([BMIM][NO3]) or 1-ethyl-3-methylimidazolium acetate ([EMIM][OAc]).

6. A system for implementing the method of claim 1, characterized in that: include: A compressor, used to increase the pressure of the raw gas; A raw material preheater, used to preheat the pressurized raw gas; An eluent-enhanced reactor is used for reaction, the reactor has an eluent inlet and an inlet and a gas inlet and an inlet, and a liquid distributor and a catalyst bed are arranged inside the reactor; The condensation tank is used to condense the gas after the reaction. The condensed gas is pressurized, mixed with the raw gas, and preheated before being introduced into the reactor. The condensed liquid phase is introduced into the methanol refining unit. A flash tank receives the eluent from the eluent outlet of the reactor, flashes it, and the liquid phase obtained by flashing is sent to the eluent circulation unit, and the gas phase obtained is mixed with the gas from the gas outlet of the reactor and passed into the condenser; The eluent circulation unit is used for circulating the eluent to the eluent inlet of the reactor.

7. The system according to claim 6, characterized in that: The liquid distributor is provided with holes, and the eluent drips onto the catalyst bed through the holes, the hole diameter is 1-5mm, and the porosity is 0.5-0.8; the liquid distributor is provided with a gas channel, and the reaction gas passes through the liquid distribution plate through the gas channel.

8. The system according to claim 6, characterized in that: The eluent circulation unit includes an eluent cooler and a pump; the eluent cooler is used to remove the heat generated by the reaction to keep the eluent within a suitable temperature range, and the pump transports the cooled eluent to the liquid distributor at the top of the reactor.

9. The system according to claim 6, characterized in that The catalyst bed is filled with a catalyst, which is a copper-based catalyst, a noble metal-supported catalyst, a cobalt-based catalyst, an iron-based catalyst, a molybdenum-based catalyst, a tungsten-based catalyst or a tin-based catalyst.

10. The system according to claim 9, characterized in that: The catalyst is hydrophobically modified or the catalyst bed is blended with a hydrophobic substance, and the hydrophobic substance is a hydrophobic polymer or a hydrophobic metal compound, so that the eluent does not wet the catalyst bed.

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