Low-carbon-emission method for producing hydrogen from methanol

Abstract

The present invention relates to a low-carbon-emission method for producing hydrogen from methanol, comprising: decomposing methanol to obtain a mixed gas containing mixed hydrocarbons; cooling, water-washing, and drying the mixed gas to obtain purified mixed hydrocarbons; feeding the mixed hydrocarbons into a reactor for a catalytic decomposition reaction to generate hydrogen gas and a solid nanoscale carbon product; and separating tail gas produced in the previous reaction to obtain hydrogen gas. In the present invention, methanol is first decomposed into a gas containing mixed hydrocarbons, and then hydrogen elements in the mixed hydrocarbons are converted into hydrogen gas, while carbon elements in the mixed hydrocarbons are fixed by conversion into a solid nano-carbon material. The product has a higher added value and better economic benefits. While hydrogen production is achieved, massive CO2 emissions are avoided, thereby greatly improving the economic efficiency of the process of hydrogen production from methanol. The total amount of carbon monoxide and carbon dioxide generated per mole of hydrogen gas produced does not exceed 0.15 mol.

Description

A low-carbon emission method for methanol-to-hydrogen production Technical Field

[0001] This invention belongs to the field of methanol-to-hydrogen technology, specifically relating to a low-carbon emission method for methanol-to-hydrogen production. Background Technology

[0002] Methanol stream reforming is an important traditional hydrogen production technology. Existing methanol stream reforming for hydrogen production involves pressurizing a mixture of methanol and steam, and then, under catalytic conditions at a reaction temperature of 170-350°C, cracking the methanol to produce carbon monoxide and hydrogen. The carbon monoxide then reacts with water to produce carbon dioxide and hydrogen. These reactions are endothermic, thus requiring high-temperature and high-pressure conditions, with a reaction pressure of 0.8-2.7 MPa. The main components of the hydrogen produced in methanol stream reforming are H2 and CO2, in a ratio of approximately 3:1, meaning the maximum H2 content is about 75%, with a small amount of CO also present. Under ideal conditions, approximately 3.5 m³ / kg of methanol can produce hydrogen. 3 Hydrogen gas is produced along with a large amount of carbon dioxide. Theoretically, for every 1 mol of hydrogen produced, 1 / 3 mol of CO2 is generated.

[0003] Currently, there are no good ways to utilize CO2; it can only be purified and released into the atmosphere or stored deep in geological formations. In short, this will impose a significant carbon emission load on the environment, which is detrimental to environmental protection. On the other hand, the conversion of carbon in methanol into CO2, which is ultimately released into the environment, results in an environmental burden and a waste of carbon resources.

[0004] If the steam reforming unit is abandoned and methanol is directly cracked, it can theoretically be used to produce hydrogen, avoiding CO2 emissions. However, this would generate a large amount of CO. CO is highly toxic and is a poisonous gas that cannot be directly released into the atmosphere. According to material balance, direct methanol cracking to produce hydrogen theoretically generates 0.5 mol of CO for every 1 mol of hydrogen produced, causing serious health problems, environmental pollution, and a waste of carbon resources.

[0005] Methanol can also be partially oxidized to produce hydrogen, with the reaction equation: 2CH3OH + O2 = 4H2 + 2CO2. Theoretically, for every 1 mol of hydrogen produced, 0.5 mol of CO2 is emitted. Methanol can also be autothermally reformed to produce hydrogen, with the equation: 3CH3OH + H2O + O2 = 7H2 + 3CO2. Theoretically, for every 1 mol of hydrogen produced, 3 / 7 mol of CO2 is emitted. Summary of the Invention

[0006] To address the above problems, this invention provides a low-carbon emission method for methanol-to-hydrogen production, comprising the following steps:

[0007] S1: Methanol decomposes to produce a mixed gas containing mixed hydrocarbons;

[0008] S2: Cool the mixed gas, wash it with water, and dry it to obtain a purified mixed hydrocarbon;

[0009] S3: The mixed hydrocarbons are fed into the reactor to react and catalytically decompose to produce hydrogen and solid nanoscale carbon products. Most of the carbon elements in methanol are converted into solid nanoscale carbon products after the reaction.

[0010] S4: Separate the tail gas produced in step S3 to obtain hydrogen gas.

[0011] This invention completely abandons the traditional methanol-to-hydrogen approach. It first decomposes methanol into an intermediate product—a mixed gas containing mixed hydrocarbons and impurities. After purification, the hydrogen elements in the mixed hydrocarbons are converted into hydrogen gas, and the carbon elements are converted into solid nano-carbon materials and fixed. This process avoids large-scale CO2 emissions while producing hydrogen. The mixed gas contains a small amount of CO2, which is removed through purification, with only trace amounts being emitted. Compared to traditional methanol steam reforming for hydrogen production, this invention emits significantly less CO2 and, by transferring the carbon elements from methanol to solid nano-carbon products for fixation, the product has higher added value and greater economic benefits, greatly improving the economics of the methanol-to-hydrogen process.

[0012] The methanol-to-hydrogen method produces 1 mol of hydrogen, and the total amount of carbon monoxide and carbon dioxide generated does not exceed 0.15 mol.

[0013] Optionally, in step S1, methanol is fed into the first reactor and directly decomposed to obtain a mixed gas containing mixed hydrocarbons. The temperature of the methanol decomposition reaction is 350-550℃, and the catalyst used is selected from one of the molecular sieve catalysts SAPO-34 and ZSM-5.

[0014] In step S1, as the methanol decomposition reaction proceeds, carbon deposits will form on the catalyst, necessitating regeneration. Regeneration involves burning off the carbon deposits on the catalyst surface and within the pores with air to restore the catalyst's activity. When the catalyst is ZSM-5, it has a longer service life, reducing carbon deposits and the regeneration process, thus decreasing CO2 emissions.

[0015] Further optional, step S1 specifically includes:

[0016] (1) Activating the catalyst: The temperature of the first reactor is controlled at 400-600℃, and inert gas is introduced for about 1 hour to activate the catalyst;

[0017] (2) Gasification of methanol feedstock: A preheater is provided on the upstream side of the first reactor. Methanol feedstock is fed into the preheater for preheating and gasification.

[0018] (3) Methanol decomposition: Stop the inert gas flow and introduce methanol gas to carry out the catalytic decomposition reaction.

[0019] Optionally, in step (2), the methanol feedstock is a methanol-water solution with a methanol concentration of 75-92 wt%, and the methanol feedstock is added to the preheater at a rate of 10-20 kg / h; the methanol gas temperature at the preheater outlet is 300-320℃. The inert gas is selected from nitrogen, argon, or helium.

[0020] Optionally, the first reactor is a fluidized bed reactor, and in step (3), the WHSV of methanol gas in the first reactor is 2-5 h⁻¹. -1 The reaction temperature is 500-550℃.

[0021] Optionally, in step S1, methanol is first vaporized, and the methanol vapor is fed into the second reactor. Under the action of a catalyst, a dehydration reaction is carried out to generate dimethyl ether. Then, the dimethyl ether is separated from the unreacted methanol and fed into the first reactor for decomposition reaction to obtain a mixed gas containing mixed hydrocarbons.

[0022] Optionally, the dehydration reaction is carried out at a temperature of 230-400℃ and a pressure of 0.5-1.8 MPa, and the catalyst used in this step is ZSM molecular sieve, aluminum phosphate, or activated alumina. Dimethyl ether dehydration can be performed using conventional gas-phase or liquid-phase methods.

[0023] Alternatively, the reaction temperature of dimethyl ether in the first reactor is 450-500°C, and the catalyst used is a microsphere catalyst with dual active components of SAPO-18 and SAPO-34.

[0024] Optionally, in step S2, the mixed gas includes mixed hydrocarbons and impurities, including water, oxygen-containing organic matter and CO2; the molar percentage of water in the purified mixed hydrocarbons is not greater than 2.0%, so as to avoid affecting the catalyst in the high-temperature catalytic cracking reactor in step S3.

[0025] Further optionally, in step S2, the mixed gas is passed sequentially through a cooling tower, a water washing tower, and a drying tower; cooling water is sprayed into the cooling tower to cool the mixed gas; an alkaline solution (concentration of 1-10%) is sprayed into the water washing tower to neutralize CO2 and oxygen-containing organic matter in the mixed gas; and a 3A molecular sieve is installed in the drying tower to adsorb and dry the mixed gas.

[0026] The above treatment removes most of the impurities such as water, carbon dioxide, methanol, dimethyl ether, and oxygen-containing organic matter from the mixed gas, yielding a purified mixed hydrocarbon. The mixed hydrocarbon consists of C1-C6 hydrocarbons, with ethylene and propylene as the main components.

[0027] Optionally, in step S3, the high-temperature catalytic cracking reactor is first purged with nitrogen to fully replace the air and moisture inside the reactor; then, the mixed hydrocarbons are fed into the high-temperature catalytic cracking reactor to react with a catalyst containing transition metals, catalytically decomposing to generate hydrogen and solid nanoscale carbon products. The reaction tail gas contains hydrogen and unreacted mixed hydrocarbons. The high-temperature catalytic cracking reactor is selected from one of fluidized bed, fixed bed, moving bed, stirred bed, or rotary kiln.

[0028] Further optionally, the solid nanoscale carbon product is one of carbon nanotubes or nanoscale carbon fibers; the catalyst used in step S3 is a supported catalyst, supported with one of iron, cobalt, and nickel elements;

[0029] When generating nanoscale carbon fibers, the supported catalyst can also support copper; when generating carbon nanotubes, the supported catalyst cannot support copper.

[0030] When generating nanoscale carbon fibers, supported catalysts typically have a high loading of transition metals and can also be loaded with copper; when generating carbon nanotubes, supported catalysts typically have a low loading of transition metals compared to transition metal catalysts.

[0031] Alternatively, the reaction temperature in step S3 is 500-1200℃, and the pressure is atmospheric pressure.

[0032] Optionally, in step S4, the tail gas produced by the high-temperature catalytic cracking reactor includes hydrogen and unreacted mixed hydrocarbon gas; after cooling, dust removal, and drying, the tail gas is then fed into a gas separation device; the gas separation device is selected from either a pressure swing adsorption device or a membrane separation device.

[0033] Optionally, in the exhaust gas produced by the reaction in step S3, the hydrogen content is not less than 80% by molar percentage, and the total amount of carbon monoxide and carbon dioxide does not exceed 1%.

[0034] In the traditional methanol steam reforming process for hydrogen production, the hydrogen content in the generated decomposition gas can be as high as 75 vol%. Therefore, the hydrogen content of the methanol decomposition gas produced in this invention is even higher.

[0035] The separated mixed hydrocarbons can be sold commercially or fed back into a high-temperature catalytic cracking reactor for further reaction. When the separated mixed hydrocarbons are fed back into the high-temperature catalytic cracking reactor, in the methanol-to-hydrogen method, for every 1 mol of hydrogen produced, the total amount of carbon monoxide and carbon dioxide generated by the entire method does not exceed 0.08 mol.

[0036] Alternatively, the exhaust gas can be pressurized by a compressor to a pressure of 0.5-60 kg before being fed into a pressure swing adsorption unit; or the exhaust gas can be pressurized by a compressor to a pressure of 1-150 kg before being fed into a membrane separation unit.

[0037] More preferably, the exhaust gas is pressurized by a compressor to a pressure of 0.5-6 kg before being fed into the pressure swing adsorption device; or, the exhaust gas is pressurized by a compressor to a pressure of 1-6.5 kg before being fed into the membrane separation device.

[0038] Alternatively, when the gas separation device is a pressure swing adsorption device, that is, the existing VPSA adsorption process is adopted, and different processes (adsorption, desorption, pressure equalization rise, pressure equalization drop, reverse release, vacuuming, etc.) are carried out in several adsorption towers, and there is always one adsorption tower in the feeding adsorption process.

[0039] Alternatively, when the gas separation device is a membrane separation device, that is, a membrane separation process for hydrogen recovery is used.

[0040] When the dried exhaust gas passes through the separation membrane, due to the differences in solubility and diffusion coefficient of different gases in the membrane material, the relative permeability of different gases in the membrane material varies. Under the pressure difference on both sides of the separation membrane, hydrogen, which has a relatively fast permeation rate, permeates through the separation membrane and is enriched on the permeate side, while gases with relatively slow permeation rates (such as methane, nitrogen, carbon monoxide, argon, etc.) are enriched on the stagnation side of the separation membrane, thereby separating the exhaust gas.

[0041] At the inlet of the membrane separation device, the gas temperature is 35-40℃, the gas flow rate is 300-350mol / h, the separation membrane is a polyimide hollow fiber membrane, the gas flow rate on the permeate side of the membrane is 230-250mol / h, and the gas flow rate on the retentate side of the membrane is 70-100mol / h. Attached Figure Description

[0042] Figure 1 is a schematic diagram of the methanol-to-hydrogen equipment in Example 1;

[0043] Figure 2 is a transmission electron microscope image of the carbon nanotubes prepared in Example 1;

[0044] Figure 3 is a schematic diagram of the material balance in membrane separation in Example 2.

[0045] In the attached diagram, 1-first reactor, 2-preheater, 3-feed pump, 4-air inlet pipe, 5-exhaust port, 6-catalyst outlet, 7-catalyst inlet, 8-catalyst regenerator, 9-cooling tower, 10-water washing tower, 11-drying tower, 12-high temperature catalytic cracking reactor, 13-gas separation device. Detailed Implementation

[0046] Example 1

[0047] This embodiment provides a low-carbon emission method for producing hydrogen from methanol, including the following steps:

[0048] S1: Methanol decomposes to produce a mixed gas containing mixed hydrocarbons;

[0049] S2: Cool the mixed gas, wash it with water, and dry it to obtain a purified mixed hydrocarbon;

[0050] S3: Input the mixed hydrocarbons into the reactor to react and catalytically decompose them into hydrogen and solid nanoscale carbon products;

[0051] S4: Separate the tail gas produced in step S3 to obtain hydrogen gas.

[0052] As shown in Figure 1, step S1 is as follows:

[0053] (1) Activating the catalyst: The temperature of the first reactor 1 is controlled at 550℃, and helium gas is introduced for about 1 hour to activate the catalyst.

[0054] (2) Gasification of methanol feedstock: A preheater 2 is provided on the upstream side of the first reactor 1. The feed pump 3 is started to feed an 80wt% methanol aqueous solution into the preheater 2 at a rate of 15.37kg / h for preheating and gasification. The temperature of the methanol gas at the outlet of the preheater 2 is 300℃.

[0055] (3) Methanol decomposition: Stop the helium gas supply, control the temperature of the first reactor 1 at 500℃, and introduce methanol gas to carry out the catalytic decomposition reaction. The WHSV of methanol gas in the first reactor is 2-3 h⁻¹. -1 ;

[0056] The first reactor contains 6000g of SAPO-34 microsphere molecular sieve catalyst. The first reactor is a fluidized bed configuration, employing two fluidized bed reactors, one in operation and one on standby. An inlet pipe 4 is located at the bottom of the fluidized bed reactor for introducing methanol gas. A gas distribution plate is located at the bottom of the fluidized bed reactor to evenly distribute the methanol gas. An exhaust port 5 is located at the top of the fluidized bed reactor for discharging the generated mixed gas. A heating furnace and temperature control device are located outside the fluidized bed reactor to control the internal temperature. A catalyst outlet 6 is located at the bottom of the fluidized bed reactor, and a catalyst inlet 7 is located at the top. The catalyst outlet is connected to a catalyst regenerator 8 via a pipe, where the deactivated catalyst from the fluidized bed reactor is fed for combustion regeneration at 600℃ using air combustion. The outlet of the catalyst regenerator is connected to the catalyst inlet 7 via a pipe, returning the regenerated catalyst to the fluidized bed reactor.

[0057] In step S2, the mixed gas includes mixed hydrocarbons and impurities, including water, oxygen-containing organic matter, and CO2. The mixed gas is analyzed, and the approximate content of each component is as follows:

[0058] H2 content 1.56 g / h, CO content 30.12 g / h, CO2 content 60.12 g / h, H2O content 9691.20 g / h, CH4 content 98.28 g / h, C2H4 content 2427.60 g / h, C2H6 content 67.62 g / h, C3H6 content 1734.60 g / h, C3H8 content 131.28 g / h, CH3OH content 82.80 g / h, CH3OCH3 content 19.50 g / h, C4 content 539.4 g / h, C5 content 209.28 g / h, C6 content 52.92 g / h, carbon deposition 123.12 g / h.

[0059] In step S2, specifically: the mixed gas sequentially passes through cooling tower 9, water washing tower 10, and drying tower 11; cooling water is sprayed into the cooling tower to rapidly cool the mixed gas; an alkaline solution (concentration of 5 wt%) is sprayed into the water washing tower to neutralize CO2 and oxygen-containing organic matter in the mixed gas; the drying tower is equipped with 3A molecular sieves to adsorb and dry the mixed gas. After the above treatment, most of the water, carbon dioxide, methanol, dimethyl ether, oxygen-containing organic matter, and other impurities in the mixed gas can be removed, resulting in a purified mixed hydrocarbon. The mixed hydrocarbon is C1-C6 hydrocarbon, mainly composed of ethylene and propylene, with a water content of 217 ppm (molar percentage of water less than 2.0%).

[0060] In step S3, the high-temperature catalytic cracking reactor 12 adopts a fluidized bed configuration with an outer diameter of 325 mm and a wall thickness of 8 mm. The high-temperature catalytic cracking reactor is first purged with nitrogen for 30 minutes to fully replace the air and moisture in the reactor.

[0061] The reaction temperature of the high-temperature catalytic cracking reactor was set at 660℃, the catalyst was Fe-Ni-Co-Mo catalyst supported on Al2O3-MgO, and the catalyst addition amount was 69.43g.

[0062] Mixed hydrocarbons were fed into a high-temperature catalytic cracking reactor and reacted with a catalyst containing transition metals. After 60 minutes of chemical vapor deposition, the hydrocarbons were catalytically decomposed to produce hydrogen and carbon nanotubes. After deducting the weight of the catalyst, 3124.35 g of carbon nanotubes were obtained, representing a catalyst-to-carbon nanotube production ratio of 45 times. The diameters of the obtained carbon nanotubes ranged from 5 to 35 nm, with an average diameter of 15 nm and a specific surface area (BET) of 203 μm. 2 / g, the transmission electron microscope of the obtained carbon nanotubes is shown in Figure 2.

[0063] The tail gas from the high-temperature catalytic cracking reactor contains hydrogen and unreacted mixed hydrocarbons. In step S4, the tail gas is sequentially cooled by a tube heat exchanger, dusted by a bag filter, and dried by a 3A molecular sieve drying tower before being fed into the gas separation device 13. Before being fed into the gas separation device, the approximate contents of its components are as follows: H2 277.458 mol / h, CO2 0.537 mol / h, CH4 1.843 mol / h, C2H4 25.954 mol / h, C2H6 0.674 mol / h, C3H6 12.366 mol / h, C3H8 0.893 mol / h, C4 2.784 mol / h, C5 0.846 mol / h, and C6 0.184 mol / h. After purification, the H2 content is approximately 85.757% (molar percentage), the CO2 content is very low, approximately 0.166%, and there is no CO.

[0064] The purified exhaust gas has a high hydrogen concentration. The exhaust gas is then compressed to a pressure of 6 kg and fed into a pressure swing adsorption (PSA) unit for separation.

[0065] The pressure swing adsorption unit adopts a 6-1-3 VPSA process flow, that is, it uses 6 adsorption towers, of which 1 adsorption tower is always in the state of feed adsorption, and different processes are carried out in the 6 adsorption towers. The adsorption and regeneration process of the adsorption tower consists of adsorption, three consecutive pressure equalization and depressurization steps, reverse release, vacuum, three consecutive pressure equalization and pressurization steps, and product gas pressurization steps.

[0066] The adsorption tower measures DN100X1000. The device includes 36 stainless steel DN20-PN20 programmable valves, a Siemens SR-60 PLC controller, and a computer to achieve fully automated operation.

[0067] After processing by the pressure swing adsorption unit, the resulting product gas is 99.99% hydrogen (and also contains 0.01% CH4).

[0068] After processing by a pressure swing adsorption (PSA) device, the desorbed gas is a mixture of hydrogen and mixed hydrocarbons, with the following composition: 47.49% H2, 0.61% CO2, 2.06% CH4, 29.61% C2H4, 0.76% C2H6, 14.11% C3H6, 1.02% C3H8, 3.16% C4, 0.97% C5, and 0.2% C6.

[0069] Table 1 Gas composition before and after separation by the pressure swing adsorption unit

[0070] In the production process of this embodiment, the CO and CO2 generated in the methanol decomposition step S1 are at their peak values. The CO content in the mixed gas is 30.12 g / h, the CO2 content is 60.12 g / h, and the carbon deposition is 123.12 g / h. The carbon deposits adhere to the catalyst, and the catalyst needs to be oxidized and regenerated to restore its activity. The carbon deposits will be converted into CO2 in equal molar amounts. Therefore, the total emission of CO and CO2 per hour in step S1 is 12.692 mol.

[0071] The minimum hydrogen concentration produced in steps S3 and S4 is 5.283 Nm. 3 / h, which is 235.848 mol per hour, means that for every 1 mol of H2 produced in this embodiment, the total amount of CO and CO2 produced is 0.0538 mol.

[0072] If the desorbed gas is fed into the high-temperature catalytic cracking reactor for another reaction, more hydrogen can be produced, further reducing the total amount of CO and CO2 generated for every 1 mol of H2 produced in this embodiment.

[0073] The desorbed gas can also be further separated into individual components using a separation device, and then sold externally.

[0074] Compared to the industrially mature methanol-to-hydrogen technology, which produces 0.333-0.5 mol of CO and CO2 for every 1 mol of H2 produced, the CO2 and CO emissions in this embodiment are significantly reduced, representing a major transformation.

[0075] Example 2

[0076] This embodiment provides a low-carbon emission methanol-to-hydrogen method, which is the same as in Embodiment 1, except that the purified tail gas is separated using a membrane separation device, specifically:

[0077] The purified exhaust gas (component contents are shown in Table 1) is pressurized to 6.5 kg by a compressor and then fed into a membrane separator for separation. The gas temperature at the inlet of the membrane separator is 35°C to ensure optimal operating conditions. Two 2-inch polyimide hollow fiber membrane modules are used, one for standby.

[0078] The gas flow rate is 300-350 mol / h, the separation membrane is a polyimide hollow fiber membrane, the gas flow rate on the permeate side of the membrane is 230-250 mol / h, and the gas flow rate on the retentate side of the membrane is 70-100 mol / h.

[0079] During separation, a single-stage membrane separation process is used, with the permeate gas being hydrogen product gas and a hydrogen volume content of not less than 99.5%. The non-permeable gas pressure of the single-stage membrane is not less than 5.5 kg / min, which can be sold as commercial gas or fed back into the high-temperature catalytic cracking reactor for further reaction.

[0080] As shown in Figure 3, the hydrogen product gas has a total flow rate of 247.5 mol / h and a pressure of 1.2 kg. The composition of each component is as follows: H2 accounts for 99.51%, CH4 accounts for 0.02%, CO2 accounts for 0.13%, and C2+ accounts for 0.34%.

[0081] Non-permeable gas: The total flow rate of the separated gas enriched from unreacted and completely mixed hydrocarbons is 76.1 mol / h, the pressure is 5.5 kg, and the composition of each component is: H2 accounts for 41.04%, CH4 accounts for 2.38%, CO2 accounts for 0.29%, and C2+ accounts for 56.31%.

[0082] The CO2 content of the separated product gas and non-permeable gas is very low, indicating that the entire methanol-to-hydrogen process produces high levels of hydrogen, and the CO2 emissions are much lower than those of traditional methanol steam reforming for hydrogen production.

[0083] In the production process of this embodiment, the total CO and CO2 emissions per hour in step S1 are still 12.692 mol.

[0084] The final total flow rate of hydrogen product gas is 247.5 mol / h, and the hydrogen content is 99.51%. Therefore, in this embodiment, for every 1 mol of H2 produced, 0.0513 mol of CO and CO2 are generated.

[0085] If the non-permeable gas continues to be fed into the high-temperature catalytic cracking reactor for another reaction, more hydrogen can be produced, further reducing the total amount of CO and CO2 generated for every 1 mol of H2 produced in this embodiment.

[0086] Example 3

[0087] This embodiment provides a low-carbon emission methanol-to-hydrogen method, similar to Embodiment 1, except that the methanol concentration in step S1 is increased from 80% to 92%, and a 92wt% methanol-water solution is introduced into the first reactor at a rate of 13.365 kg / h. Furthermore, the catalyst loading in the first reactor in step S1 is 2900 g, and the WHSV is 4.24 h⁻¹. -1The space velocity of the methanol decomposition reaction can be adjusted by changing the amount of catalyst. Increasing the space velocity increases the amount of methanol processed per unit time per unit catalyst, thus increasing the amount of carbon deposits generated per unit time, shortening catalyst lifetime, and requiring more frequent carbon burning regeneration, leading to increased carbon dioxide emissions. Similarly, reducing the water content in the methanol feed also reduces catalyst lifetime, leading to more carbon deposits and requiring more frequent carbon burning regeneration, also resulting in increased carbon dioxide emissions.

[0088] In step S1, the catalyst carbon deposition rate is 327.52 g / h, equivalent to 27.268 mol. The carbon deposits adhere to the catalyst and, through oxidation and regeneration, are molarly converted into 27.268 mol of CO2. The total CO and CO2 produced in the methanol decomposition process of step S1 is 2.526 mol. Therefore, the total hourly CO and CO2 emissions from step S1 are 29.794 mol.

[0089] The minimum amount of hydrogen produced in step S4 is 5.017 Nm. 3 / h, which is 223.973mol per hour, means that for every 1mol of H2 produced in this embodiment, the total amount of CO and CO2 produced is 0.133mol.

[0090] Compared to the industrially mature methanol-to-hydrogen technology, which produces 0.333-0.5 mol of CO and CO2 for every 1 mol of H2 produced, the CO2 and CO emissions in this embodiment are significantly reduced, representing a major transformation.

[0091] Comparative Example 1

[0092] The methanol-to-hydrogen method in this comparative example is the same as that in Example 1, except that methanol is directly introduced into step S3 without going through steps S1 and S2. That is, methanol (purity ≥99.8%, water content ≤0.1%) is directly fed into the preheater at a flow rate of 12.296 kg / h. After being heated and vaporized, the methanol is introduced into the high-temperature catalytic cracking reactor in a gaseous state. The reaction is carried out at 660°C. After 1 hour, after deducting the catalyst, the carbon nanotube product obtained is only 85.92 g, and the catalyst ratio is 1.23 times.

[0093] It is evident that directly using the same catalyst as in Example 1, the activity of direct high-temperature catalytic cracking of methanol is poor, the catalyst efficiency is low, and most of the methanol is not catalytically cracked. Therefore, this comparative example lacks economic and engineering feasibility.

[0094] Example 4

[0095] This embodiment provides a low-carbon emission methanol-to-hydrogen method, which is the same as that in Embodiment 1. The difference is that in step S2, the molar percentage of water in the purified mixed hydrocarbon is 3%, and in step S3, the catalyst produces carbon nanotubes at a rate of 27 times. It can be seen that excessive water in the mixed hydrocarbon has an adverse effect on the catalyst.

[0096] Catalysts are expensive materials in the production process. A significant decrease in the catalyst ratio will lead to a significant increase in catalyst consumption, which will reduce the economics of the production process, greatly increase the cost of hydrogen production, and affect economic and engineering feasibility.

Claims

1. A low-carbon emission method for methanol-to-hydrogen production, characterized in that, Includes the following steps: S1: Methanol decomposes to produce a mixed gas containing mixed hydrocarbons; S2: Cool the mixed gas, wash it with water, and dry it to obtain a purified mixed hydrocarbon; S3: Input the mixed hydrocarbons into the reactor to react and catalytically decompose them into hydrogen and solid nanoscale carbon products; S4: Separate the tail gas produced in step S3 to obtain hydrogen gas.

2. The low carbon emission methanol-to-hydrogen process of claim 1, wherein, The methanol-to-hydrogen method produces 1 mol of hydrogen, and the total amount of carbon monoxide and carbon dioxide generated does not exceed 0.15 mol.

3. The low-carbon emission methanol-to-hydrogen method according to claim 1, characterized in that, In step S1, methanol is fed into the first reactor and directly decomposed to obtain a mixed gas containing mixed hydrocarbons. The temperature of the methanol decomposition reaction is 350-550℃, and the catalyst used is selected from one of the molecular sieve catalysts SAPO-34 and ZSM-5.

4. The low-carbon emission methanol-to-hydrogen method according to claim 2, characterized in that, Step S1 is as follows: (1) Activating the catalyst: The temperature of the first reactor is controlled at 400-600℃, and an inert gas is introduced to activate the catalyst; (2) Gasification of methanol feedstock: A preheater is provided on the upstream side of the first reactor. Methanol feedstock is fed into the preheater for preheating and gasification. (3) Methanol decomposition: Stop the inert gas flow and introduce methanol gas to carry out the catalytic decomposition reaction.

5. The low-carbon emission methanol-to-hydrogen method according to claim 1, characterized in that, In step S1, methanol is first vaporized, and the methanol vapor is fed into the second reactor. Under the action of a catalyst, a dehydration reaction is carried out to generate dimethyl ether. Then, the dimethyl ether is separated from the unreacted methanol and fed into the first reactor for decomposition reaction to obtain a mixed gas containing mixed hydrocarbons.

6. The low-carbon emission methanol-to-hydrogen method according to claim 1, characterized in that, In step S2, the mixed gas includes mixed hydrocarbons and impurities, including water, oxygen-containing organic matter and CO2; the molar percentage of water in the purified mixed hydrocarbons is no more than 2.0% to avoid affecting the catalyst in the high-temperature catalytic cracking reactor in step S3.

7. The low-carbon emission methanol-to-hydrogen method according to claim 1, characterized in that, The reactor in step S3 is a high-temperature catalytic cracking reactor, selected from one of fluidized bed, fixed bed, moving bed, stirred bed, and rotary kiln; the solid nanoscale carbon product is one of carbon nanotubes or nanoscale carbon fibers. The catalyst is a supported catalyst, supported on one of the elements iron, cobalt, and nickel; The reaction temperature in step S3 is 500-1200℃, and the pressure is atmospheric pressure. In the tail gas produced by the reaction in step S3, the hydrogen content is not less than 80% by molar percentage, and the total amount of carbon monoxide and carbon dioxide does not exceed 1%.

8. The low-carbon emission methanol-to-hydrogen method according to claim 1, characterized in that, In step S4, the tail gas produced by the high-temperature catalytic cracking reactor includes hydrogen and unreacted mixed hydrocarbon gas; after cooling, dust removal and drying, the tail gas is then fed into the gas separation device. The gas separation device is selected from either a pressure swing adsorption device or a membrane separation device.

9. The low-carbon emission methanol-to-hydrogen method according to claim 8, characterized in that, The exhaust gas is pressurized by a compressor to a pressure of 0.5-60 kg before being fed into a pressure swing adsorption (PSA) device.

10. The low-carbon emission methanol-to-hydrogen method according to claim 8, characterized in that, The exhaust gas is pressurized by a compressor to a pressure of 1-150 kg before being fed into a membrane separation device.

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