Refining power generator

Abstract

To provide a refining power generator capable of efficiently carrying out the refining of molten aluminum and power generation by a suitable allocation therebetween according to the situation.SOLUTION: The refining power generator according to the present invention comprises: a cell group comprising a plurality of cells (X) each having a crucible (6) storing molten aluminum, a container (9) storing a molten salt in a manner capable of liquidly communicating with the molten aluminum, an anode (11) in contact with the molten aluminum, a cathode (21) in contact with the molten salt, and an electric circuit (C) connected between the anode and the cathode; and adjustment means of adjusting the power generation rate obtained between the anode and the cathode and a refining rate of the molten aluminum, by changing the combination of cells selected from the cell group or changing the electric resistance of the cell. The refining rate is, for example, the removal rate of Mg. The molten aluminum is prepared from, for example, a feed stock including scraps.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an apparatus and the like that can perform refining and power generation in parallel by utilizing an electrochemical reaction. [Background technology]

[0002] With the rise of environmental awareness, attention is being paid to decarbonization and efficiency of energy, regeneration and circulation of resources, etc. From this perspective, the following patent documents have proposed groundbreaking power generation devices. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2022-73424 Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Document 1 proposes a power generation device that extracts chemical energy obtained by causing an anodic reaction and a cathodic reaction between a liquid junction of an aluminum-based molten metal and a molten salt as electrical energy.

[0005] Patent Document 1 describes in detail the principles of power generation and examples of actual applications, but does not describe how to control the power generation device.

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a refining and power generation apparatus and the like that can generate power in parallel with the refining of an aluminum-based molten metal. [Means for solving the problem]

[0007] As a result of extensive research, the inventors have succeeded in achieving efficient operation by adjusting the balance between the refining of the aluminum-based molten metal and the electric power obtained at the time by changing the combination of multiple cells, etc. By expanding on this result, the present invention, which will be described below, has been completed.

[0008] Smelter Generator (1) The present invention provides a refining and power generation device comprising: a crucible for containing an aluminum-based molten metal; a vessel for containing molten salt capable of forming a liquid junction with the aluminum-based molten metal; a cell group having a plurality of cells each having an anode in contact with the aluminum-based molten metal, a cathode in contact with the molten salt, and an electric circuit connected between the anode and the cathode; and an adjustment means for adjusting the rate of power generation obtained between the anode and the cathode and the rate of refining the aluminum-based molten metal by changing the combination of cells selected from the cell group or the electric circuit of the cells.

[0009] (2) According to the refining and power generation apparatus (also simply referred to as the "apparatus") of the present invention, the balance between refining of aluminum-based molten metal (referred to as "Al-based molten metal") and power generation can be adjusted depending on the operating conditions, environment, etc., so that refining and power generation can be carried out efficiently.

[0010] 《Refining power generation method / Refined product》 The present invention can be understood as a refining and power generation method using the above-mentioned apparatus, and also as a result obtained by carrying out the method, i.e., a refined (purified) Al substrate (molten metal, ingot, etc.).

[0011] "others" (1) Unless otherwise specified, concentrations and compositions in this specification are expressed as mass percentages (mass%) relative to the total mass of the object (molten metal, molten salt, etc.). The mass percentages are indicated as "%" as appropriate. "X-based" materials include X alloys and compounds containing X as the main component (more than 50% of the total), as well as X itself. Al-based molten metals usually contain 60% or more, or even 80% or more, of Al relative to the total mass of the molten metal.

[0012] (2) The mechanism by which electricity is generated between the liquid junction of the Al-based molten metal and the molten salt is described in detail in Patent Publication (JP 2022-73424 A), the entire text (entire content) of which is incorporated herein by reference. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram showing the basic structure (basic cell) of a refining power generation device. [Figure 2] This is a scatter plot showing the relationship between the power generation rate and the Mg removal rate by the device. [Figure 3A] FIG. 10 is a schematic diagram illustrating the relationship between external resistance and supplied power. [Figure 3B] FIG. 2 is a schematic diagram illustrating the relationship between current and supplied power. [Figure 4] FIG. 1 is a schematic diagram showing a refining power generation system including a cell group. [Figure 5] This is a scatter plot showing the relationship between the power generation rate and the Mg removal rate by the device. DETAILED DESCRIPTION OF THE INVENTION

[0014] The above-described components of the present invention may be supplemented with one or more components selected from the present specification. The contents described in the present specification may be method components or product components.

[0015] 《Al-based molten metal》 The specific composition of the Al-based molten metal and the type of raw material used to prepare the molten metal are not important. If scrap Al-based components are used as the raw material for the Al-based molten metal, they can be reused or recycled. The Al-based molten metal may be in a solid-liquid coexistence state (semi-molten state). This is also true for molten salts.

[0016] When an Al-based molten metal contains a metal element α (such as Mg, Na, Li, etc.) that is less noble than Al, it undergoes an oxidation (anodic) reaction (α → α 2+ +2e - , α → α + +e -The metal element (α) is ionized and moves to the molten salt, decreasing its concentration in the Al-based molten metal depending on the amount of current flowing.

[0017] Mg, a type of metallic element (α), is a typical alloying element of aluminum alloys (also called "Al alloys") and is contained in many Al alloys (5000 series, 6000 series, 7000 series, etc.). Na is contained in cryolite (Na3AlF6), which is used when smelting aluminum from alumina (Hall-Yale process). In this regard, "refining" as used in the present invention may also be "smelting."

[0018] In this specification, the "noble / base" nature of a metal element is determined based on the standard free energy of formation (also simply referred to as "free energy") in a molten salt that comes into contact with an Al-based melt. The more negative the standard free energy of formation, the more base the metal element. The standard free energy of formation can be determined by data collection or potential measurement. For example, Knacke O., Kubaschwski O., Hesselmann K., "Thermochemical Properties of Inorganic Substances" (1991), SPring-8-Verlag, can be used. There, the free energy at 660°C is shown, but the trend is at least the same at temperatures between 660°C and 800°C.

[0019] Molten Salt Molten salts function as electrolytes. There are no restrictions on the specific component composition of the molten salt or the types of raw materials used to prepare it. For example, halide salts, carbonate salts, etc. can be used as the molten salt. By using halides (especially chlorides and bromides), stable molten salts can be prepared inexpensively.

[0020] For example, halides of metal elements (one or more of Ca, Na, Li, Sr, K, Cs, Ba, etc.) whose standard free energy of formation is smaller than that of Mg halide can be used as a base material (raw material) for molten salts. In particular, halides of Na and / or K are inexpensive and stable, making them suitable as base materials for molten salts. The molten salt may be a single type of salt or multiple types of salts (mixed salts). By combining multiple halide salts, for example, the melting point of the molten salt can be lowered.

[0021] Metal elements (β) more noble than Al contained in the molten salt are reacted with the cathode (β 2+ +2e - →β, β + +e - The metal element (β) can be deposited on or near the cathode depending on the amount of current flow.

[0022] Examples of the metal element (β) include Cu, Sn, Fe, Zn, and Mn. The metal element (β) is supplied to the molten salt, for example, as a simple substance or a compound. Using a compound of the metal element (β) can reduce the raw material costs required for power generation. Compounds include oxides and halides (especially chlorides). Using an oxide rather than a halide usually results in lower raw material costs. Furthermore, using an oxide of the metal element (β) makes it easier to remove elements (such as Mg) contained in the Al-based molten metal as oxides (such as MgO).

[0023] The metal element (β) is preferably a specific metal element (M) that is one or more of Cu, Zn, and Mn (particularly Cu). The standard free energy of formation of an oxide of a specific metal element is greater than or approximately equal to the standard free energy of formation of its halide (particularly chloride). Therefore, oxides of the specific metal element (M) (CuO, ZnO, MnO, etc.) are easily decomposed in a molten salt made of a halide. As a result, for example, the specific metal element (M) precipitates on the cathode, and O is dissolved in ions (Mg 2+ The reaction can be removed as oxides, as shown in the following reaction formula 1: MO + MgX2 → MX2 + MgO (X: halogen element, especially Cl, Br).

[0024] MX2 in the molten salt reacts, for example, as in reaction formula 2: MX2 + Mg → M + MgX2, and can also become a magnesium remover. In either reaction formula, the reaction tends to proceed in a stable direction where the free energy difference is negative (ΔG<0), that is, from the left side to the right side. The amount of magnesium removed from the Al-based molten metal varies depending on the amount of oxide (MO) supplied (added) to the molten salt, but the amount of MgX2 in the molten salt (the amount of magnesium in the molten salt) 2+ concentration) becomes almost constant.

[0025] 《Electrodes / Anodes / Cathodes》 (1) A cathode (positive electrode / negative electrode) that comes into contact with the molten salt is provided for each vessel (i.e., for each cell). An anode (negative electrode / positive electrode) that comes into contact with the Al-based molten metal can be shared by two or more cells or even the entire cell group. However, like the cathode, providing an independent anode for each cell (i.e., one pair of cathode and anode for each cell) makes it easier to adjust (control) refining and power generation for each cell.

[0026] The electrodes are preferably made of a material that does not adversely affect the redox reaction, such as graphite electrodes (graphite rods, graphite plates, etc.), which are heat-resistant and corrosion-resistant and relatively inexpensive.

[0027] (2) If the refining power generation device is considered a type of galvanic cell, the electrodes are current collectors. The electrodes (current collectors) may be used as output terminals directly connected to an electrical circuit (external circuit), or output terminals may be provided separately from the electrodes. Providing separate terminals not only improves connectivity with the electrical circuit, but also makes it possible to replace only the worn electrodes during maintenance. Furthermore, a liquid-permeable enclosure or the like may be provided within the vessel around the cathode to concentrate the positive electrode active material around the cathode and improve power generation efficiency.

[0028] "condition" The vessel contains the molten salt in a state where it can be in liquid junction with the aluminum-based molten metal. The vessel may also serve as a separator that separates the molten salt from the aluminum-based molten metal while allowing ionic conduction. This allows for stable refining and power generation.

[0029] The container can be of any material or shape, but it is preferable that it be porous and heat-resistant and allow ions to pass through. Specifically, it can be a biscuit-fired porous crucible that allows ions (including molten salt) to pass through but not the molten metal. The top of the container should have an opening for supplying or replenishing the raw materials for the molten salt and the positive electrode active material.

[0030] Note that a refining power generation system can also be realized with a configuration in which molten salt is placed in the crucible and Al-based molten metal is placed in the vessel (inverted configuration).If it is not necessary to partition the Al-based molten metal, it is more efficient to arrange vessels containing molten salt separately inside a large crucible containing the Al-based molten metal to refine the Al-based molten metal.

[0031] 《Adjustment means》 The amount (speed) of electricity generated between the anode and cathode and the amount (speed) of aluminum-based molten metal refined are adjusted depending on the operating conditions (requests), environment, etc. In this specification, the "speed" refers to the amount of electricity (electricity, etc.) or amount of refinement (rate of removing impurities, etc.) per unit time.

[0032] Such adjustments can be made by combining cells selected from a cell group, changing the current generated in the electrical circuit of each cell, or the like. For example, if a cell group is composed of multiple cells with a fixed distribution of power generation rate and refining rate, desired (arbitrary) cells (two or more) selected from the cell group can be combined. Furthermore, if a cell group is composed of multiple cells with the same configuration whose current value can be freely changed, the current value of each of two or more cells selected from the cell group can be individually adjusted. Such adjustments can achieve the desired specifications (power generation rate and refining rate). The current value generated in the electrical circuit can be changed by, for example, changing the resistance (including impedance) of the electrical circuit between the anode and cathode (or between the Al-based molten metal and the molten salt), as well as the capacitance, inductance, frequency (or angular frequency), etc.

[0033] The cell combination and the current value generated in the electric circuit may be adjusted stepwise or continuously, and may be adjusted manually or automatically by a preset program.

[0034] Electrical Circuits The DC power generated by each cell is supplied to an electric circuit (external circuit) and consumed. The electric circuit may include a converter that converts DC power to AC power, an inverter that adjusts the frequency, a transformer or boost circuit that changes the voltage, etc. The generated power may be used to operate the refining power generation device itself (mainly for refining). [Example]

[0035] After explaining a single cell (basic cell), a refining and power generation system including a plurality of cells (cell group) and an example of its operation will be described. The present invention will be further described in detail with reference to these specific examples.

[0036] [Base Cell] An overview of the basic cell X is shown in Figure 1. The basic cell X includes an anode 11, an anode terminal 12, a cathode 21, a cathode terminal 22, a crucible 6, and a separator 9 (container). The basic cell X is connected to an external circuit C (electrical circuit). The crucible 6 is housed in a holding furnace (not shown) equipped with a heat insulating material, and is heated to and maintained at a desired temperature by an electric heater (not shown).

[0037] Both the anode 11 and the cathode 21 are made of graphite electrodes (current collectors). The anode terminal 12 attached to the upper end of the anode 11 and the cathode terminal 22 attached to the upper end of the cathode 21 are made of copper. In this example, the anode 11 and the cathode 21 were made of graphite round bars with an outer diameter of 10 mm.

[0038] A graphite crucible (manufactured by TYK Corporation) was used as the crucible 6 containing the Al-based molten metal m1 (simply referred to as "molten metal m1"). A cylindrical porous alumina crucible with a bottom (manufactured by Nikkato Corporation) was used as the separator 9 containing the molten salt m2.

[0039] As shown in FIG. 1, the separator 9 containing the molten salt m2 is immersed in the molten metal m1 contained in the crucible 6. The separator 9 is entirely made of porous ceramics (biscuit porcelain) and does not allow the molten metal m1 to pass through, but allows ions (e.g., Mg 2+ ) and ions of molten salt m2 are allowed to pass through.

[0040] The electrical resistor 31 for adjusting the circuit resistance of the external circuit C may be a fixed resistor or a variable resistor.

[0041] "experiment" Using the basic cell X, removal of Mg (specific element) contained in the molten metal m1 (refining of the Al-based molten metal) and power generation (supply of power to the external circuit C) were carried out. Specifically, the procedure is as follows.

[0042] 1. Raw materials (1) Al-based molten metal An Al-Mg molten metal (molten metal m1) was prepared using commercially available pure Al and pure Mg. The process envisaged the removal of Mg (an impurity) from the raw molten metal obtained by melting scrap to be recycled, resulting in an Al-based molten metal.

[0043] 1500 g of an initial molten metal was prepared, in which the initial concentration of Mg (negative electrode active material) relative to the total molten metal was 0.74%. Concentration (%) is a mass percentage unless otherwise specified.

[0044] (2) Molten salt Using commercially available chlorides (reagents), 250 g of molten salt m2, which was KCl-41% NaCl-6% MgCl2, was prepared.

[0045] (3) Mg remover (positive electrode active material) As a magnesium removal agent, 2 g of a commercially available reagent, CuO (copper (II) oxide, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), was used.

[0046] 2. Processing The molten metal m1 and the molten salt m2 were kept at 680 to 690°C, and the Mg-removing agent was added to the molten salt m2 from the upper opening of the separator 9.

[0047] The electrical resistance 31 was adjusted to set the external resistance R between the anode terminal 12 and the cathode terminal 22 to either 0.05 Ω (R1), 0.1 Ω (R2), or 0.5 Ω (R3).

[0048] 3. Measurement The external resistance R was set at each value and maintained for 10 minutes. The amount of power supplied to the external circuit C and the change in the Mg concentration in the molten metal m1 (amount of Mg removed) were determined.

[0049] The amount of electric power was measured using a watt-hour meter connected to the external circuit C. The amount of Mg removed (%) was calculated based on the amount of charge Q (time integral of the current in the external circuit C) that passed through the external circuit C, and converted into a concentration using the following formula: w=(Q×M) / (z×F) w: Mg removed mass (g) Q: Amount of charge (C) that has passed through the external circuit C M: Atomic weight of Mg = 24.3 (g / mol) z: Number of charges in the Mg removal reaction = 2 F: Faraday constant = 96485 (C / mol) Amount of magnesium removed (%) = 100 x w / initial amount of molten metal (1500g)

[0050] The amount of power generated and the amount of magnesium removed obtained over a 10-minute measurement were converted (averaged) into hourly values ​​to determine the power generation rate (Wh / hr) and magnesium removal rate (% / hr), respectively. The relationship between the power generation rate and magnesium removal rate obtained for each external resistance R is summarized in Figure 2.

[0051] "evaluation" As is clear from Figure 2, it was found that the power generation rate and the Mg removal rate (refining rate) can be adjusted by changing the external resistance R. The molten metal treatment shown in this example is not limited to Mg removal, and can be expanded to adjust the concentration of other elements, precipitate and recover other elements, etc.

[0052] 《Consideration》 Figures 3A and 3B (collectively referred to as "Figure 3") show that power generation (supplied power) and refining (removal of impurities) can be adjusted by the resistance value of the electrical circuit between the Al-based molten metal (anode) and the molten salt (cathode).

[0053] Let us consider an equivalent circuit of basic cell X. In other words, the internal resistance between the Al-based molten metal and the molten salt is r, the electromotive force between them is E, the direct current flowing between them is I, the terminal voltage between them is V, the resistance is R, and the supplied power is P. In this case, P=RI 2 , I=V / R, V=E·R / (R+r).

[0054] In this case, the relationship between resistance and supplied power is as shown in Figure 3A. As is clear from Figure 3A, it is possible to adjust the power supply by changing the resistance. Furthermore, the relationship between current and supplied power is as shown in Figure 3B. As is clear from Figure 3B, it is also possible to adjust the power supply by changing the current. This current indicates the rate of the oxidation-reduction reaction (refining rate, Mg removal rate, etc.) between the Al-based molten metal and the molten salt. Therefore, it is clear from Figure 3 that the power generation rate and refining rate can be adjusted (controlled) by changing the resistance value.

[0055] Multiple Cells (1) A cell group consisting of three basic cells X was arranged in one crucible 6. This state is shown in Figure 4. The electrical resistance value of each cell, the selection or combination of cells, etc. are determined by, for example, an adjustment unit (adjustment means) as shown in Figure 4.

[0056] The basic cell X with its electrical resistance 31 (R) set to 0.05 Ω, 0.1 Ω, or 0.5 Ω is called cell A, cell B, or cell C, respectively.

[0057] (2) The power generation rate and Mg removal rate were measured for two and three cell combinations, with overlapping of cells A, B, and C allowed. The relationship between these rates is shown in Figure 5.

[0058] (3) As is clear from Figure 5, the power generation rate or Mg removal rate increased as the number of cells combined increased. Furthermore, even if the number of cells is the same, it was found that the ratio between the power generation rate and the Mg removal rate can be adjusted by changing the combination of cells with different resistance values.

[0059] Thus, it was confirmed that the present invention allows power generation and refining of Al-based molten metal to be efficiently performed by allocating these functions according to the situation. [Explanation of symbols]

[0060] X base cell C. External circuit (electrical circuit) m1 Al-based molten metal m2 molten salt 11 Anode 12 cathode 6 Crucible 9 Separator (container)

Claims

1. a crucible containing an aluminum-based molten metal; a cell group including a plurality of cells, each cell including a vessel for accommodating molten salt so as to be liquid junctionable with the aluminum-based molten metal, an anode in contact with the aluminum-based molten metal, a cathode in contact with the molten salt, and an electric circuit connected between the anode and the cathode; an adjusting means for adjusting the rate of power generation obtained between the anode and the cathode and the rate of refining the aluminum-based molten metal by changing the combination of cells selected from the cell group or the electrical circuit of the cells; A refining and power generation device comprising:

2. The refining and power-generating apparatus according to claim 1 , wherein the anode is provided for each of the cells.

3. The refining and power-generating apparatus according to claim 1 , wherein the refining rate is a Mg removal rate.

4. The refining and power generation system according to any one of claims 1 to 3, wherein the aluminum-based molten metal is prepared from raw materials including scrap.

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