Magnesium@high-sulfur coke hydrogen storage material and preparation method thereof

Abstract

The present invention disclosures a magnesium@high-sulfur coke hydrogen storage material and a preparation method thereof. The method comprises: ball milling magnesium powder with high-sulfur coke in an inert atmosphere to obtain a mixture; subjecting the mixture to pressing to form a pressed tablet, followed by melt infiltration in an inert atmosphere to obtain an infiltrated product and a magnesium vapor; and subjecting the infiltrated product to adsorption and condensation of the magnesium vapor to obtain the magnesium@high-sulfur coke hydrogen storage material. The prepared magnesium@high-sulfur coke has low plateau temperature, high hydrogen storage capacity, fast hydrogen absorption/desorption rate, and other advantages.

Claims

1. A method comprising: ball milling magnesium powder with coke in a first inert atmosphere to obtain a mixture; forming a pressed tablet by pressing the mixture, followed by melt infiltration in a second inert atmosphere to obtain an infiltrated product; and subjecting the infiltrated product to adsorption and condensation of magnesium vapor; wherein the method further comprises preparing the coke by: mixing petroleum coke with an alkali, followed by calcination activation and carbonization in a third inert atmosphere, neutralization with an acid, and washing with water and drying; wherein the mass ratio of the magnesium powder to the coke is in a range of 9:1 to 20:1; wherein the pressing comprises placing the mixture in a pressing mold and pressing the mixture at 20-40 MPa for 0.5-1.5 h; wherein the alkali is KOH or NaOH; wherein the mass ratio of the petroleum coke to the alkali is in a range of 1:2 to 1:5; wherein the calcination activation and carbonization in the third inert atmosphere is conducted at 900-1000 C. for 0.5-1.5 h; wherein the heating rate during the activation and carbonization is 3-8 C./min; wherein the adsorption and condensation are conducted in an adsorption condensation bed by fixing the pressed tablet at a sand core of the adsorption condensation bed, followed by introducing the magnesium vapor; and wherein circulating cooling water is introduced to an outer layer of the adsorption condensation bed during the adsorption and condensation.

2. The method according to claim 1, wherein the acid is hydrochloric acid, sulfuric acid, phosphoric acid or nitric acid.

3. The method according to claim 1, wherein the ball milling is conducted at the ball-to-powder ratio in a range of 40:1 to 50:1 for 5-7 h.

4. The method according to claim 1, wherein the pressing is conducted at 30 MPa for 1 h.

5. The method according to claim 1, wherein the melt infiltration comprises heating the pressed tablet to 656-711 C. for 7-85 min.

6. The method according to claim 5, wherein the melt infiltration further comprises, after heating, cooling the pressed tablet in the second inert atmosphere at a cooling rate of 3-10 C./min, and replacing the second inert atmosphere with a hydrogen atmosphere when the pressed tablet reaches 300-400 C.

7. The method according to claim 6, wherein the melt infiltration further comprises, when the pressed tablet reaches 200 C., further cooling the pressed tablet at a rate of 5-10 C./min, and replacing the hydrogen atmosphere with the second inert atmosphere when the pressed tablet reaches 70-90 C.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) The accompanying drawings constituting a part of the present invention are provided for further understanding for the present invention. Exemplary embodiments of the present invention and descriptions thereof are used for explaining the present invention and do not constitute an improper limitation on the present invention.

(2) FIG. 1 is a schematic diagram illustrating principles of magnesium@high-sulfur coke hydrogen storage material of the present invention.

(3) FIG. 2 is a flow chart showing preparation process of magnesium@high-sulfur coke hydrogen storage material of the present invention.

(4) FIG. 3 shows magnesium loading rate data of magnesium@high-sulfur coke hydrogen storage material in Example 2 of the present invention.

(5) FIG. 4 is a schematic diagram of temperature-pressure controlled adsorption condensation bed in Example 3 of the present invention.

(6) FIG. 5 shows comparison of magnesium@high-sulfur coke hydrogen storage materials prepared in Example 1 and Example 3 of the present invention.

(7) In the figure, 1gas inlet; 2abrasive plug; 3water outlet; 4sand core; 5water inlet; 6gas outlet.

DETAILED DESCRIPTION

(8) It should be noted that the following detailed descriptions are all exemplary and are intended to provide a further description of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as commonly understood by a person of ordinary skill in the art to which the present invention belongs.

(9) The present invention will be further described below in conjunction with the examples.

(10) The materials used in the examples and comparative examples are all commercially available unless otherwise specified.

EXAMPLE 1

(11) A method for preparing magnesium@high-sulfur coke hydrogen storage material, as shown in the flowchart of FIG. 2, including:

(12) Step 1: Preparation of High-Sulfur Coke

(13) 11) High-sulfur petroleum coke was mixed with KOH at a mass ratio of 1:5, and subjected to chemical activation and high-temperature carbonization in a high-purity argon atmosphere in a tubular furnace. The temperature was increased to 1000 C. at a rate of 5 C./min, held at this temperature for 1 hour, and then cooled to room temperature for later use.

(14) 12) The prepared high-sulfur coke was neutralized and adjusted to pH=7 with a 1 mol/L HCl solution.

(15) 13) Finally, the high-sulfur coke was subjected to repeated suction filtration and water washing, followed by drying to obtain the final sample.

(16) Step 2: Mixing and Ball Milling of Magnesium with High-Sulfur Coke

(17) 21) 0.56 g of magnesium powder and 0.06 g of high-sulfur coke powder (used as a milling aid) were placed in a ball mill and ball-milled under an argon atmosphere. The ball-to-powder ratio was controlled at 40:1.

(18) 22) The total ball milling time was 6 h, including 30 min of forward rotation, 30 min of reverse rotation, and a 10-minute interval, a rotation speed was 400 rpm, and finally, a mixed sample was removed after milling.

(19) Step 3: Pressing

(20) 31) 0.1 g of the high-sulfur coke and 0.3 g of the mixed sample after ball milling were placed in a pressing mold, and pressed at 30 MPa for 1 h.

(21) 32) A pressed tablet of the mixture of the nano-metal magnesium and the high-sulfur coke was prepared to increase the contact area between magnesium and the high-sulfur coke, thereby effectively reducing the diffusion path and resistance of the magnesium melt. A cylindrical pressed tablet was then removed.

(22) Step 4: Melt Infiltration

(23) 41) The pressed tablet prepared in step 3 was placed in a tubular furnace and subjected to high-temperature sintering in an argon atmosphere, with a heating rate was 5 C./min.

(24) 42) The temperature was raised from 20 C. to 666 C., and maintained for 22 min.

(25) 43) After that, the temperature was decreased, with a cooling rate of 5 C./min, and when the temperature dropped to around 360 C., the argon atmosphere was replaced by a hydrogen flow.

(26) 44) When the temperature dropped to 200 C., programmed cooling was performed, and the hydrogen flow was switched back to the argon atmosphere when the temperature dropped to around 80 C., the remaining hydrogen in the tubular furnace was discharged, and finally the sample was removed.

(27) By carbonization and activation with KOH, a super high-sulfur petroleum coke (HSPC) with a specific surface area of 856.3 m.sup.2/g, pore volume of 0.7 cm.sup.3/g, an average pore size of 3.3 nm, and micropores of <6 nm accounting for about 50% was prepared. Using this material, a magnesium-based hydrogen storage material with a hydrogen storage rate of 0.6 wt. % and capable of reversible hydrogen absorption and desorption at 100 C. was successfully obtained.

(28) The composite hydrogen storage material prepared in the above example was characterized. Analysis data of the specific surface area, pore volume, and others of the material were obtained by BET analysis. The magnesium loading rate was calculated using the following formula based on the changes in mass and pore volume before and after melt infiltration, as well as the density of magnesium: n=(M.sub.1V.sub.1-M.sub.2V.sub.2)P.sub.Mg/[(M.sub.1V.sub.1-M.sub.2V.sub.2)P.sub.Mg+M.sub.c]; where: M.sub.1 and M.sub.2 represent the mass before and after melt infiltration, respectively, in grams (g); V.sub.1 and V.sub.2 are the pore volumes before and after melt infiltration, respectively, in cm.sup.3/g; P.sub.Mg is the density of magnesium, which is 1.74 g/cm.sup.3; and M.sub.c is the mass of the high-sulfur petroleum coke activated carbon, in grams (g).

(29) The magnesium loading rate of the prepared hydrogen storage material was calculated to be 36%. The reason is that the evaporation temperature of the nano-magnesium clusters in pores of <6 nm is much lower than the phase transition temperature of 94010 K, at which the magnesium particles of about 70 nm held in the gaps are melted to enter the capillary-to micro-channels, resulting in simultaneous evaporation and escape of magnesium in theses pores. The scale effect of the 20-40 nm magnesium particles in the remaining gaps and the nano-magnesium in the pores of about 10 nm is weakened.

EXAMPLE 2

(30) The preparation method of the composite hydrogen storage material in this example is the same as that of Example 1, except that Step 1 and Step 4 are excluded, and the conditions and Steps 2-3 remain unchanged.

(31) Step 1:

(32) 11) High-sulfur petroleum coke was mixed with KOH at a mass ratio of 1:5, soaked in 90% anhydrous ethanol and 10% deionized water, ultrasonicated for 2 h, and then removed and dried at 120 C. for later use.

(33) 12) High-sulfur petroleum coke was subjected to chemical activation and high-temperature carbonization in a high-purity argon atmosphere in a tubular furnace, by heating up to 1000 C. or 900 C. at a heating rate of 5 C./min, holding at this temperature for 1 h, and then cooling to room temperature for later use.

(34) 13) The prepared high-sulfur coke was neutralized and adjusted to pH=7 with a 1 mol/L HCl solution.

(35) 14) Finally, the high-sulfur coke was subjected to repeated suction filtration and water washing, followed by drying to obtain the final sample.

(36) Step 4: Melt Infiltration

(37) 41) The pressed tablet prepared in step 3 was placed in a tubular furnace and subjected to high-temperature sintering in an argon atmosphere, with a heating rate was 5 C./min.

(38) 42) The temperature was raised from 20 C. to 636 C., 651 C., 666 C., 681 C., 696 C., and 711 C. respectively, and maintained for 22 min.

(39) 43) After that, the temperature was decreased, with a cooling rate of 5 C./min, and when the temperature dropped to around 360 C., the argon atmosphere was replaced by a hydrogen flow.

(40) 44) When the temperature dropped to 200 C., programmed cooling was performed, the hydrogen flow was switched to the argon atmosphere when the temperature dropped to around 80 C., the remaining hydrogen in the tubular furnace was discharged, and finally the sample was removed.

(41) As shown in FIG. 3, the Mg@high-sulfur coke with the high-sulfur coke (C (1000)) prepared at 1000 C. as the matrix exhibits the highest magnesium loading rate, reaching up to 38%; and the composite hydrogen storage material prepared by melt infiltration into the high-sulfur coke soaked in an alkaline solution (C(1000 alkaline solution)) has the lowest Mg loading rate, at only 29%.

(42) Therefore, on the basis of Example 1, the influence of the melt infiltration temperature on the loading rate of Mg was investigated. From FIG. 3, it can be seen that as the melt infiltration temperature increases, the magnesium loading rate first increases and then decreases, with the highest loading rate occurring at 666 C.

EXAMPLE 3

(43) In this example, the composite hydrogen storage material is prepared with the addition of Step 5, while the conditions and Steps 1-4 remain the same as those in Example 1, as follows:

(44) Step 5:

(45) 51) Based on step 4, where the magnesium vapor was evaporated, the prepared infiltrated sample in step 4 was placed at of a sand core in an adsorption condensation bed with controlled temperature and pressure in an argon atmosphere, as shown in FIG. 4. The magnesium vapor evaporated in step 4, along with the argon atmosphere, was introduced into the adsorption condensation bed, with an argon flow rate of 150 ml/min. An outer layer of the adsorption condensation bed was cooled by circulating water, flowing in from the bottom and out from the top at a temperature of 20 C. and a flow rate of 500 ml/min. The adsorption and condensation were completed again, and finally the sample was removed.

(46) The magnesium loading rate of the prepared hydrogen storage material was 65%.

(47) As shown in FIG. 5, when the melt infiltration temperature increased from 636 C. (Infiltration method 1) to 666 C. (Infiltration method 2), the capillary filling effect of magnesium droplets in the pores became significant, and the pore volume per unit mass decreased sharply, where the volume of pores of <2 nm and 4-8 nm decreased at a larger rate. When the temperature was raised to 711 C., the pore volume of the system did not decrease, but increased instead, which was due to the evaporation and escape of almost all of the small-scale nano-magnesium during the confined synthesis. However, after the magnesium@high-sulfur coke hydrogen storage material was prepared by using the three-stage confined loading method, significant changes were achieved compared to the initial result.

(48) In summary, nano-metal magnesium was successfully loaded on high-sulfur coke in the present invention. For solid-phase magnesium, the particle size was controlled to improve the ratio of surface atom. Under the conditions that magnesium equally at the nanoscale was obtained by ball milling, an appropriate proportion of high-sulfur coke was added and used as a millig aid during the ball milling to produce nano-magnesium, to prevent the aggregation and growth of magnesium during the ball milling and greatly improve the ball milling efficiency. Moreover, the lubricating effect of the high-sulfur coke was conducive to the formation of small-sized magnesium particles, whereby magnesium was well ball milled to obtain the nano-magnesium. Through capillary force, van der Waals force and other effects, the molten liquid-phase magnesium constantly and spontaneously entered from high-concentration mesopores and meso-macro pores into a large amount of low-concentration micropores connected thereto. The nano magnesium in the pores was not prone to agglomeration and growth, and was firmly confined within the pores of the high-sulfur petroleum coke activated carbon, thus effectively overcoming the instability of the nano-magnesium. The partial pressure and relative concentration of the magnesium vapor were adjusted, and the pressure inside the adsorption condensation bed, the bed temperature, and the temperature gradient were changed, such that the magnesium vapor was controlled to fully condensed and nucleated during the adsorption, collision, and penetration through the bed layer, to form nano magnesium fine crystals of small grains. The thermodynamic properties of the prepared magnesium@high-sulfur coke hydrogen storage material were significantly improved.

(49) The above-described examples are only preferred examples of the present invention and are not intended to limit the invention. For those skilled in the art, the present invention can be modified in various ways. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention, should be included within the scope of the invention's protection.