Orthohydrogen and parahydrogen conversion catalyst and preparation method thereof

Abstract

The invention discloses a preparation method of an ortho-parahydrogen conversion catalyst. According to a method for loading active components through in-situ precipitation, a polymeric ferric hydroxide solution obtained through polycondensation and hydrolysis reaction of Fe < 3 + >, H2O and OH <-> in an alkaline solution is utilized, and in-situ precipitation loading is carried out after OH <-> is in contact with the interior and the surface of an activated carbon pore channel. Compared with a traditional catalyst preparation process, the method has the advantages that a heat dispersion step is omitted, so that the loading uniformity of the active component is higher, and more energy is saved.

Description

Technical Field

[0001] The invention belongs to the field of catalyst synthesis, and in particular relates to an activated carbon-based ortho-parahydrogen conversion catalyst and a preparation method thereof. Background Art

[0002] In recent years, with the introduction of national, provincial and municipal hydrogen energy development plans, the hydrogen energy industry chain has flourished, driving the research and development and breakthroughs of hydrogen energy related technologies. The storage and transportation process of hydrogen in the downstream of the industry chain is a high-energy consumption and high-risk process. The current mature hydrogen storage process is compressed gaseous hydrogen, but the energy density of gaseous hydrogen is much lower than that of liquid hydrogen. When the tank and pipeline materials meet the requirements of liquid hydrogen storage and transportation, liquid hydrogen is a more ideal hydrogen storage and transportation state. There are two hydrogen nuclei in the hydrogen molecule, orthohydrogen with the same spin direction and parahydrogen with opposite spin directions. At room temperature, hydrogen contains about 75% orthohydrogen and 25% parahydrogen. As the temperature decreases, orthohydrogen will spontaneously convert into parahydrogen. In the liquid hydrogen temperature range, the equilibrium concentration of parahydrogen is close to 100%. However, the reaction heat of orthohydrogen conversion is greater than the latent heat of vaporization of liquid hydrogen, resulting in continuous evaporation loss of liquid hydrogen during the spontaneous conversion process, and causing a sharp increase in the pressure of the storage tank, which brings safety risks. Orthohydrogen conversion catalysts are needed to complete the orthohydrogen conversion during the liquefaction process of hydrogen, obtain stable parahydrogen, and reduce vaporization losses at the same time.

[0003] Iron-based catalysts are the most common type of catalysts for the conversion of ortho-parahydrogen, and are mature in commercialization. They have significant advantages over other metal catalysts in terms of cost and stability. The active component of traditional iron-based catalysts is hydrous iron oxide. The preparation method usually uses a mixture of a trivalent iron salt solution and a strong base to obtain an iron hydroxide precipitate, which is then filtered, dried, activated, and mixed with a carrier and a binder to form a solid. However, in the traditional method, in order to remove salt anions and hydroxide ions as much as possible during the washing of the precipitated filter cake, the amount of water used for washing is generally several dozen times the volume of the filter cake, causing subsequent water treatment problems for the salt solution; at the same time, in the traditional method, the iron hydroxide is mixed with the carrier through a thermal dispersion process, which will lead to uneven dispersion or decomposition of the active component, because the decomposition temperature and activation temperature of the active component of iron hydroxide are relatively low, generally less than 150°C, but thermal dispersion usually needs to be carried out at above 300°C, and the two conflict with each other. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides a para-hydrogen conversion catalyst and a preparation method thereof. A novel in-situ precipitation and loading active component method is adopted, in which the precipitation and loading of iron hydroxide are carried out simultaneously, and the washing, drying and activation steps are completed in-situ in the reactor, which greatly reduces the treatment amount of salt-containing wastewater, reduces environmental pollution, and improves the dispersibility of the active component.

[0005] According to a first aspect of the present invention, the present invention provides a method for preparing a para-hydrogen conversion catalyst.

[0006] The preparation method of the ortho - para hydrogen conversion catalyst includes the following steps: (1) Provide a reactor: The reactor includes a shell, a heating facility provided at the bottom of the shell, and a condensed water interlayer provided at the top of the shell. The interior of the shell includes a liquid storage tank and a platform above the liquid storage tank; (2) Prepare an iron salt solution and a sodium hydroxide solution respectively. While stirring, drop the sodium hydroxide solution into the iron salt solution to obtain a nearly saturated dark brown polymeric iron hydroxide solution; (3) Take activated carbon raw powder, add it to the polymeric iron hydroxide solution obtained in step (2), stir and impregnate, then filter to obtain activated carbon raw powder with polymeric iron hydroxide loaded in the pores; (4) Spread the activated carbon raw powder obtained in step (3) on the platform of the reactor described in step (1), and inject ammonia water into the liquid storage tank; (5) Through the heating facility, heat up the materials in the reactor. After the ammonia water vapor penetrates the activated carbon raw powder above the platform, it is cooled by the condensed water interlayer at the top of the reactor, and the ammonia water droplets drip and pass through the activated carbon raw powder layer to achieve one - step in - situ precipitation loading and washing; Drain the ammonia water from the reactor, close the cooling water, and discharge the free ammonia water vapor from the reactor. The obtained in - situ loaded activated carbon is successively dried (preferably vacuum - dried) and activated; (6) Mold the in - situ loaded activated carbon obtained in step (5) to obtain an activated carbon - based ortho - para hydrogen conversion catalyst.

[0007] Further, the reactor is a cubic - shaped reactor, such as a horizontal tank structure, preferably a closed - cavity structure. One end of the reactor is open and provided with a flip - up door; the other closed end is provided with an exhaust port, and the exhaust port is connected to the absorption liquid in the tail gas absorption tank through a pipeline. The inner layer material of the reactor is stainless steel.

[0008] Further, the platform is placed on a slide rail and can slide outward or inward along the slide rail, which is convenient for replacing raw materials of different batches. The platform is of a drawer - type structure and is fixed in the reactor by support rods. A number of small holes are evenly distributed on the platform. A drain port is provided at the bottom of the liquid storage tank below the platform, which is convenient for discharging and replacing the liquid.

[0009] Further, the reactor is provided with pressure and temperature sensors.

[0010] Further, the iron salt in step (2) is generally one or more of ferric chloride, ferric sulfate, and ferric nitrate, preferably ferric chloride. The preparation concentrations of the iron salt solution and the sodium hydroxide solution are both 0.2 - 0.5 mol / L, preferably 0.3 - 0.5 mol / L. The final dropping amounts of the two solutions should make the Fe 3+ and OH- The molar ratio is between 1:2.8 and 3, and Fe is used 3+ under alkaline conditions reacts with H 2 O and OH - through the stepwise hydrolysis and polycondensation reactions to obtain a nearly saturated neutral iron hydroxide solution with a high degree of polymerization. Among them, the dropping and stirring mixing adopt conventional methods in the art, such as a stirrer can be selected to complete it.

[0011] Furthermore, in step (3), the activated carbon raw powder generally selects an activated carbon raw powder with a relatively high proportion of mesopores and macropores. Generally, the pore volume ratio of pores with a pore size range of more than 5 nm in the total pore volume is more than 50%, and the specific surface area is 300 - 600 m 2 / g, preferably 300 - 450 m 2 / g, and the particle size is generally 30 - 50 mesh. The addition amount of activated carbon is generally 4 - 5 times the mass of the iron salt added in the solution prepared in step (2). During the impregnation process, stirring is required to make the solution and the solid fully contact. The stirring rate is the same as that in step (2), the impregnation time is 10 - 30 min, preferably 20 - 30 min, and the temperature is room temperature.

[0012] Furthermore, in step (4), the platform surface is provided with small holes with uniform distribution and the same pore size. The mesh number of the small holes is generally 60 - 80 mesh, slightly larger than the particle size of the activated carbon raw powder. If the pore size is too large, the activated carbon particles will leak from the platform. If the pore size is too small, water cannot penetrate and flow down from the platform under the action of surface tension. The concentration of the ammonia water is generally 10 - 25 wt%, preferably 20 - 25 wt%. The addition amount of ammonia water is generally more than 5 times the volume of the activated carbon solid and can be recycled batch by batch.

[0013] Furthermore, a heat insulation layer is also provided around the reactor shell. Furthermore, in step (5), the in-situ precipitation loading, washing, drying, and activation processes are as follows: Open the heating jackets on the side and bottom and the condensed water on the top layer. The bottom heating jacket heats the ammonia water to boiling to make the internal temperature of the reactor around 100 °C, so that the reactor is filled with ammonia water vapor. The two side heat insulation jackets insulate the reactor to prevent the ammonia water vapor from condensing on the inner wall of the reactor. The activated carbon raw powder placed above the platform will absorb water in the high-concentration ammonia water vapor environment, making the inner pores of the activated carbon and the nearly saturated neutral iron hydroxide impregnated on the surface in a locally formed solution environment. The OH produced by the hydrolysis of ammonia molecules -This will cause the rapid precipitation of iron hydroxide in the solution, and in-situ precipitation loading is achieved on the surface and within the pores of the activated carbon. The cooling water sandwich at the top of the reactor will cause some ammonia water vapor to condense into droplets and drip onto the activated carbon platform. While further achieving in-situ precipitation loading, it will wash the anionic impurities in the activated carbon and penetrate and drip down through the holes of the platform back into the lower ammonia water tank, and continuously evaporate and condense to wash the activated carbon under heating conditions. Moreover, the anionic impurities obtained by washing in the solution will basically not evaporate with the solution during the circulation process, so the activated carbon will not be re-polluted. The in-situ precipitation washing process generally lasts for 20 - 40 minutes. Then, the cooling water at the top layer is turned off, and the top pressure relief valve is opened to discharge the free ammonia gas into the absorption tank. Thanks to the high solubility of ammonia gas, water can be used as the absorption liquid, and the ammonia water is discharged by opening the bottom drain port. After the pressure inside the reactor returns to atmospheric pressure, the top pressure relief valve and the bottom drain valve are closed, the top vacuum pump is opened, and in-situ heating is carried out. The temperature inside the reactor is monitored to be maintained at 80 - 100 °C for 3 - 4 hours for catalyst drying, and then the temperature is raised to 120 - 140 °C and maintained for 1 - 2 hours for catalyst activation.

[0014] Furthermore, the shaping described in step (6) can adopt conventional operations in the art. For example, the activated carbon loaded in step (5) can be added to a binder such as carboxymethyl cellulose and mixed evenly, and the evenly mixed material is poured into a hydraulic press mold and shaped for a certain time under certain temperature and pressure. The pressure for hydraulic shaping is generally 7 - 10 MPa, the shaping temperature is 120 - 140 °C, and it is maintained for 15 - 25 minutes.

[0015] According to the second aspect of the present invention, the present invention also provides an activated carbon-based ortho-para hydrogen conversion catalyst with in-situ loaded hydrated iron oxide, which is obtained by the preparation method described above.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The present invention innovatively introduces a method for in-situ precipitation loading of active components. By using the polycondensation and hydrolysis reactions of Fe in an alkaline solution with H₂O and OH⁻ to obtain a polymeric iron hydroxide solution, in-situ precipitation loading is carried out when contacting OH⁻ inside and on the surface of the activated carbon pores. Compared with the traditional catalyst preparation process, the step of thermal dispersion is omitted, making the loading uniformity of the active components higher and more energy-saving. 3+ in 2 with - and the in-situ precipitation loading is carried out after contacting OH⁻. Compared with the traditional catalyst preparation process, the step of thermal dispersion is omitted, making the loading uniformity of the active components higher and more energy-saving. -

[0017] 2. The present invention innovatively uses ammonia water to complete in one step the precipitation loading and anion washing. Compared with the traditional method, it greatly reduces the water consumption for filter cake washing and reduces the subsequent treatment volume of salty wastewater. At the same time, the ammonia water containing anions can be recycled batch by batch, maximizing the utilization of ammonia in the solution and not causing secondary pollution to the catalyst, being more energy-saving and environmentally friendly. ​

[0018] 3. By independently designing the reactor, the present invention innovatively completes the processes of precipitation loading, washing, drying, and activation in situ through multiple steps, significantly reducing the cumbersome nature of the catalyst preparation steps. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic structural diagram of the reactor used in the present invention.

[0020] In the figure, each numerical label corresponds to: 1 - safety valve group, 2 - pressure sensor, 3 - temperature sensor, 4 - tail gas absorption tank, 5 - water, 6 - catalyst drawer platform, 7 - cooling water sandwich, 8 - reactor opening, 9 - drawer slide rail, 10 - ammonia water tank, 11 - ammonia water, 12 - liquid discharge port, 13 - heating jacket, 14 - vacuum pump, 15 - heat preservation jacket. EMBODIMENTS

[0021] The technical content and effects of the present invention will be further described below in conjunction with the embodiments, but the present invention is not limited to the scope of the described embodiments.

[0022] Examples 1 - 6 Examples 1 - 6 respectively provide ferric chloride salts with different concentrations, activated carbon raw powders with different specific surface areas, different impregnation times, and different activation conditions, as shown in Table 1 below.

[0023] Table 1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Concentration of iron salt solution (mol / L) 0.2 0.4 0.4 0.4 0.4 0.4 <![CDATA[Specific surface area of raw powder (m 2 / g)]]> 400 400 600 400 400 400 Impregnation time (min) 30 10 30 30 30 30 Washing time (min) 30 30 30 30 30 30 Drying time (h) 3 3 3 3 3 3 Drying temperature (°C) 100 100 100 80 100 100 Activation time (h) 2 2 2 2 2 2 Activation temperature (°C) 140 140 140 140 120 140 The preparation methods of the catalysts in Examples 1 - 6 are as follows: Prepare the iron salt solution and sodium hydroxide solution with the corresponding concentrations in Table 1, and stir and drip the sodium hydroxide solution into the iron salt solution within 10 minutes. The final dripping amounts of the two solutions should make the molar ratio of Fe 3+ and OH - be 1:2.8. The stirring speed is generally 500 rpm to obtain a dark brown high - polymerization - degree neutral ferric hydroxide solution. Pour the activated carbon raw powder particles with a particle size of 50 mesh and a mass 5 times that of the iron salt and the corresponding specific surface area into the obtained solution, stir and impregnate for the corresponding time at a rotation speed of 500 rpm to finally obtain the impregnated activated carbon raw powder. Spread it flat on the surface of the reactor platform and add 25% mass - fraction concentrated ammonia water 10 times the volume of the activated carbon to the ammonia water tank below the platform.

[0024] After placing the materials, close the reactor door; turn on the reactor heater, heat until the ammonia water boils, and maintain the temperature in the reactor at about 100°C for 25 minutes. Turn off the top cooling water, open the top pressure relief valve to discharge the free ammonia gas into the absorption tank, and open the bottom drain port to discharge the ammonia water. After the pressure in the reactor returns to normal pressure, close the top pressure relief valve and the bottom drain valve, turn on the top vacuum pump, heat in situ, monitor the drying of the reactor under certain temperature and time conditions, and then heat to the corresponding activation temperature and maintain the corresponding time to activate the catalyst.

[0025] After heating is finished and the temperature has naturally cooled, take out the solids in the upper drawer and place them in a dry environment for later use.

[0026] Take 80 parts by weight of the activated carbon powder loaded with active components and 10 parts by weight of sodium carboxymethyl cellulose, mix them thoroughly, add 10 parts by weight of water to the evenly mixed powder, stir evenly, pour into a hydraulic press to form, and finally obtain a formed activated carbon catalyst.

[0027] Comparative Examples 1-3 The preparation of the catalyst is the same as that of Examples 1-6, except that different processing conditions are used in Comparative Examples 1-3.

[0028] Comparative Example 4 The catalyst was prepared by conventional methods. First, iron salt solutions and sodium hydroxide solutions of corresponding concentrations in Table 2 were prepared. The final dropwise addition amount of the two solutions was such that Fe 3+ and OH - The molar ratio of substances is 1:3.2. The sodium hydroxide solution is stirred and added dropwise to the iron salt solution within 10 minutes. The stirring speed is generally 500 rpm to obtain an iron hydroxide precipitate in a weakly alkaline environment. The precipitate is filtered and washed to neutrality, dried at 100°C for 4 hours, and activated at 140°C for 2 hours. The activated solid is crushed to a particle size of about 50 mesh, and activated carbon raw powder particles with a particle size of 50 mesh and 5 times the mass of the iron salt with the corresponding specific surface area are mixed with the activated solid powder, and thermally dispersed at 350°C for 3 hours to obtain activated carbon powder loaded with active substances. The molding method is the same as that of Examples 1-6.

[0029] The processing conditions of Comparative Examples 1-4 are listed in Table 2.

[0030] Table 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Concentration of salt solution (mol / L) 0.4 0.4 0.4 0.4 <![CDATA[Specific surface area of raw powder (m 2 / g)]]> 1500 400 400 400 Impregnation time (min) 30 30 30 30 Washing time (min) 30 30 0 30 Drying time (h) 3 3 3 3 Drying temperature (°C) 100 100 100 100 Activation temperature / °C 2 2 2 2 Activation time / h 140 140 100 140 Catalyst performance test: The evaluation method used for the catalysts prepared in Examples 1-6 and Comparative Examples 1-4 is the same. The catalytic performance of the conversion of parahydrogen was tested by a Langxi LX3370N parahydrogen concentration tester. The pretreatment conditions were degassing at 100°C for 6 hours, the catalyst loading was 4 mL, and then the catalyst was heated at a high-purity hydrogen space velocity of 100 h.-1 The following test uses a TCD detector to online monitor the concentration of para-hydrogen after hydrogen passes through the bed according to the difference in the thermal conductivity of ortho-hydrogen and para-hydrogen. The unit is %, the test temperature is the liquid nitrogen temperature, and the test results are listed in Table 3.

[0031] Table 3 Outlet para-hydrogen concentration of hydrogen in the liquid nitrogen temperature range Outlet concentration of para-hydrogen (%) Example 1 39.5 Example 2 39.8 Example 3 40.3 Example 4 41.4 Example 5 37.8 Example 6 42.2 Comparative Example 1 27.4 Comparative Example 2 27.9 Comparative Example 3 34.8 Comparative Example 4 26.2 It should be noted that at room temperature, the para-hydrogen concentration in hydrogen is about 25%, and the para-hydrogen equilibrium concentration, i.e., the limit concentration, at liquid nitrogen temperature is about 47%. As can be seen from Table 3, different iron salt solution concentrations, activated carbon specifications, and impregnation, drying, and activation conditions in Examples 1-6 all have a certain impact on the final performance of the catalyst. Among them, the conditions in Example 6 are relatively optimal treatment conditions, and the outlet para-hydrogen concentration has approached the para-hydrogen limit concentration at liquid nitrogen temperature; the decrease in the iron salt solution concentration will reduce the loading of the final iron oxyhydroxide (FeOOH), resulting in a decrease in the catalyst activity; at the same time, the increase in the specific surface area of the activated carbon raw powder means an increase in the proportion of micropores and a decrease in the proportion of macropores, while the grain size of iron hydroxide is generally in the order of dozens of nanometers, and the reduction of macropores is not conducive to its formation and loading in the pores, and it is easy to cause shedding during the washing process, so the catalytic performance is reduced; the reduction of the impregnation time is the same as the reduction of the iron salt solution concentration, both of which are not conducive to the full loading of the active components, resulting in a performance decline; finally, the lower drying temperature and the lower activation temperature are not conducive to the formation of the optimal crystalline form of iron oxyhydroxide, resulting in a decrease in catalytic activity.

[0032] As can be seen from Comparative Example 1, the activated carbon raw powder with an extremely high specific surface area has almost no macropores and cannot load the active components, resulting in poor final performance; as can be seen from Comparative Example 2, there is no polymerization and complexation reaction in the reaction of ferric sulfate and sodium hydroxide, and the loading amount of the directly formed iron hydroxide precipitate in the pores of the activated carbon is very low, and subsequent washing will cause only the shedding of the loaded components, resulting in poor final performance; as can be seen from Comparative Example 3, a large amount of residual chloride ions under the non-washing condition has a great impact on the performance; as can be seen from Comparative Example 4, too high a dispersion temperature in the thermal dispersion step of the conventional catalyst preparation method will cause the catalytically active iron oxyhydroxide to lose water excessively to form iron oxide, resulting in poor final performance.

Claims

1. A preparation method of a normal - para hydrogen conversion catalyst, characterized in that, it includes the following steps: (1) Provide a reactor: The reactor includes a shell, a heating facility arranged at the bottom of the shell, and a condensed water interlayer arranged at the top of the shell. The interior of the shell includes a liquid storage tank and a platform above the liquid storage tank; (2) Prepare an iron salt solution and a sodium hydroxide solution respectively. Drop the sodium hydroxide solution into the iron salt solution under stirring to obtain a nearly saturated dark brown polymeric iron hydroxide solution; (3) Take activated carbon raw powder, add it to the polymeric iron hydroxide solution obtained in step (2), stir and impregnate, then filter to obtain activated carbon raw powder with polymeric iron hydroxide loaded in the pores; (4) Spread the activated carbon raw powder obtained in step (3) on the platform of the reactor described in step (1), and inject ammonia water into the liquid storage tank; (5) Through the heating facility, heat up the materials in the reactor. After the ammonia water vapor penetrates the activated carbon raw powder above the platform, it is cooled by the condensed water interlayer at the top of the reactor, and the ammonia water droplets drip and pass through the activated carbon raw powder layer to achieve one - step in - situ precipitation loading and washing; Drain the ammonia water from the reactor, close the cooling water, and discharge the free ammonia water vapor from the reactor. The in - situ loaded activated carbon is successively dried and activated; (6) Mold the in - situ loaded activated carbon obtained in step (5) to obtain an activated carbon - based normal - para hydrogen conversion catalyst.

2. The preparation method according to claim 1, characterized in that, one end of the reactor is provided with a flip - up door at the opening; the other closed end is provided with an exhaust port, and the exhaust port is connected to the absorbent liquid in the tail gas absorption tank through a pipeline.

3. The preparation method according to claim 1, characterized in that, the platform is placed on a slide rail and can slide outward or inward along the slide rail to facilitate the replacement of raw materials in different batches; the platform is of a drawer - type structure and is fixed in the reactor by a support rod; a number of small holes are evenly distributed on the platform; a drain port is provided at the bottom of the liquid storage tank below the platform to facilitate the discharge of the replaced liquid.

4. The preparation method according to claim 1, characterized in that, the reactor is provided with pressure and temperature sensors.

5. The preparation method according to claim 1, characterized in that, the iron salt described in step (2) is one or more of ferric chloride, ferric sulfate, and ferric nitrate.

6. The preparation method according to claim 1, characterized in that, the concentrations of both the iron salt and the sodium hydroxide solution are 0.2 - 0.5 mol / L.

7. The preparation method according to claim 1, characterized in that, The final addition amounts of the two solutions should make the molar ratio of Fe 3+ and OH - between 1:2.8 and 3.

8. The preparation method according to claim 1, characterized in that, In step (3), the specific surface area of the raw activated carbon powder is 300 - 600 m 2 / g, and the particle size is 30 - 50 mesh.

9. The preparation method according to claim 1, characterized in that, the addition amount of activated carbon is 4 - 5 times the mass of the iron salt added in the solution prepared in step (2).

10. The preparation method according to claim 1, characterized in that, the surface of the platform described in step (4) is provided with small holes with the same aperture and evenly distributed, and the mesh number of the small holes is 60 - 80 mesh.

11. The preparation method according to claim 1, characterized in that, The concentration of the ammonia water is 10-25 wt%, and the addition amount of the ammonia water is more than 5 times the volume of the activated carbon solid.

12. According to the preparation method described in claim 1, it is characterized in that in step (5), the bottom heating jacket heats the ammonia water to boiling so that the internal temperature of the reactor is about 100 °C.

13. According to the preparation method described in claim 1, it is characterized in that in step (5), the in-situ precipitation washing process lasts for 20-40 min; the drying temperature of the catalyst is 80-100 °C, and the drying time is 3-4 h; the activation temperature of the catalyst is 120-140 °C, and the activation time is 1-2 hours.

14. According to the preparation method described in claim 1, it is characterized in that the forming process described in step (6) is as follows: adding the activated carbon loaded in step (5) to the binder and mixing evenly, pouring the evenly mixed material into the hydraulic press mold for forming; the pressure for hydraulic forming is 7-10 MPa, the forming temperature is 120-140 °C, and the forming time is 15-25 minutes.

15. An activated carbon-based ortho-para hydrogen conversion catalyst obtained by the preparation method according to any one of claims 1-14.

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