Disposal methods for discarded tires

Abstract

This invention provides a waste tire processing method that desulfurizes the sulfurous components of the rubber rubber that make up the waste tires without using heat, thereby enabling the reuse of the rubber components. [Solution] The waste tire processing method comprises a removal step of crushing the waste tire to remove metal components from the waste tire and obtain crushed material, a crushing step of crushing the crushed material to obtain pulverized material, and a desulfurization step of adding a desulfurizing agent to the pulverized material, crushing the pulverized material, desulfurizing agent and pulverized balls in a ball mill, and adsorbing the sulfur contained in the pulverized material onto the desulfurizing agent to obtain desulfurized rubber from the pulverized material.

Description

Technical Field

[0001] The present invention relates to a method for treating waste tires, and particularly to a treatment method for preparing rubber from which sulfur has been removed from waste tires and reusing the rubber.

Background Art

[0002] After removing the metal components, waste tires are either burned as fuel or used as raw materials such as activated carbon. Sulfur has been vulcanized in waste tires for rubber modification, and when reusing the rubber as a resin, the sulfur acts as a barrier. Therefore, current reuse is extremely difficult, and it is mostly burned as described above. Therefore, in terms of effectively utilizing resources such as carbon neutrality, the utilization of waste tires cannot be said to be sufficient.

[0003] When removing the sulfur that becomes a problem when reusing the rubber component of waste tires, a method of heating waste tires to remove the sulfur component (desulfurization) has been proposed (see Patent Document 1). The method of Patent Document 1 requires a reaction involving high temperature and high pressure. Therefore, even if waste tire treatment can be achieved, the energy cost required for treatment is high. Therefore, considering effective resource utilization and suppression of carbon dioxide emissions, the method of Patent Document 1 is still not sufficient.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] As a result of intensive studies on the removal of sulfur vulcanized in the rubber component constituting waste tires, the inventors have achieved desulfurization from the rubber component under conditions milder than those of conventional desulfurization treatments.

[0006] The present invention has been made in view of the above points, and provides a waste tire processing method that desulfurizes the sulfur content of the rubber components constituting the waste tire without heating, thereby enabling the reuse of the rubber components. [Means for solving the problem]

[0007] In other words, the waste tire processing method of the embodiment is characterized by comprising: a removal step of crushing the waste tire to remove metal components from the waste tire and obtain crushed material; a crushing step of crushing the crushed material to obtain pulverized material; and a desulfurization step of adding a desulfurizing agent to the pulverized material, crushing the pulverized material and the desulfurizing agent in a ball mill, and adsorbing the sulfur contained in the pulverized material onto the desulfurizing agent to obtain desulfurized rubber from the pulverized material.

[0008] Furthermore, in the desulfurization process of the waste tire processing method, crushed iron balls may be introduced into the ball mill.

[0009] Furthermore, in the waste tire disposal method, the desulfurizing agent may be iron powder.

[0010] Furthermore, the waste tire processing method may include a magnetic separation step after the desulfurization step, in which a magnet is used to adsorb the desulfurizing agent and separate it from the desulfurized rubber.

[0011] Furthermore, the waste tire processing method may include a specific gravity separation step after the desulfurization step, in which a mixture of crushed material and desulfurizing agent is immersed in an aqueous solution and separated by specific gravity.

[0012] Furthermore, in the waste tire disposal method, the desulfurizing agent may be an organic acid.

[0013] Furthermore, the waste tire processing method may include an organic acid separation step after the desulfurization step, in which the desulfurizing agent is separated from the desulfurized rubber by filtration or centrifugation. [Effects of the Invention]

[0014] The waste tire processing method of the present invention comprises a removal step of crushing the waste tire to remove metal components from the waste tire and obtain crushed material, a crushing step of crushing the crushed material to obtain pulverized material, and a desulfurization step of adding a desulfurizing agent to the pulverized material, crushing the pulverized material and the desulfurizing agent in a ball mill, and adsorbing the sulfur contained in the pulverized material onto the desulfurizing agent to obtain desulfurized rubber from the pulverized material. As a result, the sulfur content of the vulcanized rubber component constituting the waste tire can be desulfurized without heating, and the reuse of the rubber component can be realized. [Brief explanation of the drawing]

[0015] [Figure 1] This is a chart of the X-ray diffraction results from an experimental example. [Figure 2] This is a chromatogram of the organic solvent-soluble components of a rubber tire sample. [Figure 3] This is the differential molecular weight distribution curve of the organic solvent-soluble components of a rubber tire sample. [Modes for carrying out the invention]

[0016] Sulfur is generally added to rubber to modify its elasticity and other properties. However, burning sulfur-containing hydrocarbon compounds such as rubber directly produces a sulfurous odor and generates sulfur oxides, which cause pollution. Therefore, the processing and utilization of waste tires have been limited to fuel applications that can be incinerated at high temperatures, and also to raw materials for activated carbon. As a result, the rubber components in waste tires are effectively used only once as a resource, and their effective utilization has not been pursued.

[0017] The waste tire processing method of this embodiment is a method for reducing the sulfur content from sulfur-vulcanized rubber products such as tires, without relying on high-temperature processing that requires energy costs such as combustion, in light of the effective utilization of the rubber components of waste tires as a resource as described above.

[0018] The waste tire treatment method of the embodiment is roughly classified into two types by a desulfurizing agent that removes (reduces) sulfur contained in the rubber component. The first treatment method is composed of the steps of "removal step, pulverization step, desulfurization step, and magnetic separation step". The second treatment method is composed of the steps of "removal step, pulverization step, desulfurization step, and organic acid separation step". In both treatment methods, the "removal step" and the "pulverization step" are common.

[0019] In the removal step, the waste tire is pulverized and the metal component is removed from the waste tire. A primary pulverized product is obtained from this step. The tire contains metal wires for reinforcement. Therefore, the purpose of the removal step is to remove the metal wires that become impurities. The collected waste tire is sheared by a known cutter, crusher, etc. and crushed into a primary pulverized product with a size of about 10 to 30 mm. Through the crushing, the metal wires built into the tire are separated, and the rubber component of the tire and the metal wires are separated. The metal wires are recovered as scrap iron, etc. and reused.

[0020] In the pulverization step, the crushed material is pulverized to obtain a pulverized product. The crushed material obtained from the removal step is a lump of rubber, so to speak. Therefore, in the next step, to promote a smooth reaction, that is, to expand the surface area of the crushed material, the crushed material is pulverized into a pulverized product. The crushed material is pulverized to a particle size of about 100 to 150 μm or less by a known pulverization device such as a cutter mill, and a powdery pulverized product is prepared. In addition, in order to make the particle size of the pulverized product as constant as possible, sieving by a sieve may be combined.

[0021] In the desulfurization process, a desulfurizing agent is added to the pulverized material, and the pulverized material and the desulfurizing agent are pulverized in a ball mill. In the first treatment method, iron powder is used as the desulfurizing agent. The iron powder is a powder with a particle size of 50 to 60 μm. The pulverized material of vulcanized rubber derived from waste tires and the iron powder of the desulfurizing agent are put into the ball mill. In addition, as a member for assisting pulverization, iron pulverizing balls are put into the ball mill. In the examples described later, the pulverizing balls are iron balls with a diameter of about 5 mm. In addition to iron balls, alumina, zirconia, or stainless steel balls may be used as the pulverizing balls. The blending ratio of the pulverized material and the iron powder is, from the examples described later, when the pulverized material is 1 part by weight, the iron powder is blended at 1 / 3 to 1 part by weight, preferably 1 / 2 part by weight. In addition to the ball mill, a planetary mill may be used.

[0022] The rotational speed, rotation time, continuous or intermittent operation, etc. of the container of the ball mill are appropriately set according to the size of the container of the ball mill itself, the processing amount of the pulverized material, and the pulverizing balls. When the ball mill is in operation, inside the container of the ball mill, the pulverized material and the iron powder are compressed by the inner wall surface of the container of the ball mill and the pulverizing balls, creating a state where the pulverized material and the iron powder are strongly adhered. Then, the sulfur in the pulverized material of vulcanized rubber derived from waste tires is released from the pulverized material and adsorbed by the iron powder of the desulfurizing agent.

[0023] Therefore, desulfurized rubber is produced from the pulverized material of vulcanized rubber derived from waste tires. As described above, when the ball mill is in operation, no special heating is required, and only the power to rotate the pulverizing container of the ball mill is needed. When the ball mill is pulverizing (when the container is rotating), frictional heat is generated when the pulverized material and the iron powder are compressed by the inner wall surface of the container of the ball mill and the pulverizing balls. The frictional heat promotes the softening of the rubber component of the pulverized material, making it easier for the iron powder of the desulfurizing agent to be mixed with the pulverized material. Since iron easily binds with sulfur, sulfur moves to the iron powder side from the vulcanized rubber component of the pulverized material, and sulfur remains in a state of being combined with the iron powder as it is.

[0024] By completing the desulfurization process, the sulfur in the pulverized material of vulcanized rubber derived from waste tires is removed (reduced), and desulfurized rubber is produced. In this state, since it is a mixed state of both, separation by a magnet or specific gravity is added.

[0025] In the magnetic separation process, after the desulfurization process, the desulfurizing agent is adsorbed using a magnet, and the desulfurized rubber is separated. The iron powder in the desulfurizing agent retains its magnetism even after adsorbing sulfur. Therefore, the iron powder that has adsorbed sulfur is separated from the desulfurized rubber by a magnet, taking advantage of the magnetism of the iron powder.

[0026] In the specific gravity separation process, a mixture of pulverized material and desulfurizing agent is immersed in an aqueous solution and separated by specific gravity. An aqueous solution of calcium chloride or the like at a predetermined concentration is prepared, and a mixture of desulfurized rubber and iron powder (the desulfurizing agent) is immersed (dispersed) in this aqueous solution. Since the iron powder, which has adsorbed sulfur, has a higher specific gravity than the desulfurized rubber, it settles in the aqueous solution. Therefore, the separation of the floating desulfurized rubber from the settled iron powder becomes easy. The desulfurized rubber is then washed with water as appropriate.

[0027] In the second processing method, a desulfurizing agent is added to the pulverized material, and the pulverized material and desulfurizing agent are ground together in a ball mill. However, instead of the iron powder mentioned above, an organic acid is used as the desulfurizing agent. Organic acids include carboxylic acids such as ascorbic acid, citric acid, succinic acid, maleic acid, aspartic acid, tartaric acid, butyric acid, oxalic acid, formic acid, maleic acid, glycine, and imoniacetic acid.

[0028] In the second processing method, pulverized vulcanized rubber derived from waste tires and an organic acid used as a desulfurizing agent are fed into a ball mill. In addition, iron crushing balls are fed into the ball mill as auxiliary components for crushing. A planetary mill may also be used instead of a ball mill. The rotation speed, rotation time, and continuous / intermittent operation of the ball mill container are set appropriately according to the size of the ball mill container itself, the amount of pulverized material to be processed, and the crushing balls. When the ball mill is in operation, the pulverized material inside the ball mill container is compressed by the inner wall of the container and the crushing balls, creating a state in which the pulverized material and the organic acid are strongly adhered to each other. As a result, the sulfur in the pulverized vulcanized rubber derived from waste tires is released from the pulverized material and adsorbed onto the organic acid. The organic acid contains carboxyl groups, and it is thought that iron is captured by chelation.

[0029] In the second processing method as well, desulfurized rubber is produced from the pulverized vulcanized rubber derived from waste tires. As mentioned above, no special heating is required for the operation of the ball mill; only the power to rotate the ball mill's grinding container is needed. During grinding in the ball mill (when the container rotates), frictional heat is generated when the pulverized material is compressed between the inner wall of the ball mill container and the grinding balls. This frictional heat promotes the softening of the rubber components of the pulverized material, making it easier for the desulfurizing organic acid to mix with the pulverized material. Iron readily forms chelate bonds with organic acids, so sulfur moves from the vulcanized rubber components of the pulverized material to the organic acid side, and the sulfur remains trapped in the organic acid.

[0030] By completing the second processing method, the desulfurization step, the sulfur in the pulverized vulcanized rubber derived from waste tires is removed (reduced), resulting in desulfurized rubber. In this state, since both are mixed, the organic acid, which is the desulfurizing agent, is separated from the desulfurized rubber by filtration or centrifugation in the organic acid separation step.

[0031] In the filtration process for separating organic acids, known filter media, filters, sieves, etc., are used. In the case of centrifugal separation, separation is possible due to the difference in specific gravity between the desulfurized rubber and the organic acid. After the organic acid separation process, the desulfurized rubber is washed with water as appropriate.

[0032] The desulfurized rubber obtained by the first and second processing methods has a reduced sulfur content compared to the original waste tire's rubber components, resulting in properties similar to those of unvulcanized rubber. Therefore, its uses, such as being added back into tires or used in other rubber products, can be considered.

[0033] As is clear from the series of explanations, the waste tire processing method of the embodiment allows for desulfurization of the rubber components constituting waste tires using only the operating cost of the ball mill. Since the reaction proceeds due to the frictional heat generated within the ball mill, heating, combustion, or other heat sources and energy are not required for desulfurization. Furthermore, since the resulting desulfurized rubber can be easily separated from other components, the desulfurized rubber can be easily utilized by adding it to existing rubber raw materials. Thus, waste tires can be effectively utilized as a resource without incurring energy costs. [Examples]

[0034] [Example of experiment] After cutting up the discarded tires and removing the metal wires, the material was crushed using a cutter mill to obtain a powder with a particle size of 100 mesh (approximately 150 μm) or less. A high-speed ball mill with a container capacity of 100 mL (manufactured by Fritsch Japan Co., Ltd.) and 5 mm diameter iron balls were prepared as grinding balls for the ball mill. In addition, iron powder with a particle size of 50 μm was prepared as a desulfurizing agent.

[0035] 2g of pulverized material, 2g of iron powder, and 60g of pulverized balls were placed in a high-speed ball mill and ground at 700 rpm for 10 minutes, then allowed to stand for 10 minutes. This 10-minute grinding process was repeated six times. This was designated as "Sample 1". Furthermore, a mixture consisting of 2g of pulverized material, 1g of iron powder, and 60g of pulverized balls was prepared, reducing the amount of iron powder, and pulverized under the same pulverization conditions as described above. This was designated "Sample 2".

[0036] After grinding, visual inspection of Sample 1 and Sample 2 revealed that unreacted (silver-black) iron powder remained in Sample 1. In Sample 2, the iron powder was almost entirely black (iron sulfide). Therefore, it can be said that it is preferable for iron powder to account for half the weight of the ground material.

[0037] Next, to confirm that the iron powder adsorbed sulfur from the rubber components of the discarded tires, the properties of the iron powder were identified by X-ray diffraction (XRD). The results are shown in the X-ray diffraction chart in Figure 1. The upper part of Figure 1 shows the diffraction results of iron powder from sample 1, and the lower part of Figure 1 shows the diffraction results of iron powder from sample 2. Only the peak of metallic iron was observed in sample 1. In contrast, peaks of iron sulfide (FeS) and amorphous sulfur (S) were observed in sample 2. Therefore, it was found that sulfur from the rubber components of the discarded tires was adsorbed onto the iron powder through grinding by the ball mill, and that desulfurization from the vulcanized rubber components was possible.

[0038] In addition, the iron powder from sample 1 and sample 2 were analyzed by X-ray fluorescence elemental analysis (XRF). This elemental analysis also revealed that the iron powder from both samples contained sulfur.

[0039] Subsequently, by bringing a magnet close to sample 1 and sample 2, the iron powder was attracted to the magnet. Thus, the separation of desulfurized rubber and iron powder with adsorbed sulfur was confirmed.

[0040] [Consideration] This experiment demonstrated that desulfurization of rubber products such as tires containing sulfur can proceed even under mild conditions that do not require heat energy such as heating or firing, such as by crushing with a ball mill. As a result, the waste tire processing method of this embodiment can be used for the reuse of waste tires that were not easy to recycle, at a relatively low energy cost.

[0041] [Dissolution of tires in organic solvents] Furthermore, the molecular weight and molecular weight distribution of the soluble components in waste tires (rubber tires) dissolved in an organic solvent were confirmed using GPC (gel permeation chromatography). THF (tetrahydrofuran) was used as the organic solvent.

[0042] Samples of discarded tires (rubber tires) were prepared in a 20.0 g / L THF (tetrahydrofuran) solution and allowed to stand overnight. This solution was filtered through a 0.45 μm membrane filter and subjected to GPC (TOSOH HLC-8320GPC) measurement. Measurement conditions Column: TSKgel SuperHZM-H / HZ4000 / HZ3000 / HZ2000 Column size: 6.0 mm I.D. × 150 mm Eluent:THF Flow rate: 0.6mL / min Detector: RI Column temperature: 40℃ Injection volume: 20μL Molecular weight was calculated on a polystyrene (PS) basis.

[0043] Figure 2 is a chromatogram of the organic solvent-soluble components of the rubber tire sample, with the horizontal axis representing time (minutes) and the values ​​shown being 10,000, 15,000, and 20,000 (minutes). The vertical axis represents voltage (mV) and the values ​​shown are 0,000, 5,000, and 10,000 (mV). Figure 3 is a differential molecular weight distribution curve of the organic solvent-soluble components of the rubber tire sample, with the horizontal axis representing molecular weight (LogM) on a logarithmic scale and the values ​​shown being 2, 3, 4, and 5 (LogM). The vertical axis represents the differential distribution value and the values ​​shown are 0,000, 50,000, and 100,000.

[0044] The numerical results are shown in Table 1. Table 1 shows the number-average molecular weight and weight-average molecular weight of peaks 1 and 2 in Figures 2 and 3. From Table 1, we were able to confirm the extraction of organic solvents from waste tires (rubber tires). Therefore, it is expected that the action of organic solvents will improve the efficiency of grinding when pulverizing the vulcanized rubber pulverized material derived from waste tires in the desulfurization process.

[0045] [Table 1]

Claims

1. A removal process involves crushing the waste tire to remove metal components from the waste tire and obtaining crushed material. A grinding step to obtain pulverized material by grinding the aforementioned crushed material, The process includes adding a desulfurizing agent to the pulverized material, grinding the pulverized material and the desulfurizing agent together in a ball mill, and adsorbing the sulfur contained in the pulverized material onto the desulfurizing agent to obtain desulfurized rubber from the pulverized material. A method for disposing of waste tires, characterized by the features described herein.

2. The waste tire processing method according to claim 1, wherein, in the desulfurization step, crushed iron balls are fed into the ball mill.

3. The waste tire disposal method according to claim 1, wherein the desulfurizing agent is iron powder.

4. The waste tire processing method according to claim 3, further comprising a magnetic separation step in which, after the desulfurization step, the desulfurizing agent is adsorbed using a magnet and separated from the desulfurized rubber.

5. The waste tire processing method according to claim 3, further comprising a specific gravity separation step in which, after the desulfurization step, the mixture of the pulverized material and the desulfurizing agent is immersed in an aqueous solution and separated by specific gravity.

6. The waste tire treatment method according to claim 1, wherein the desulfurizing agent is an organic acid.

7. The waste tire processing method according to claim 5, further comprising an organic acid separation step of separating the desulfurizing agent from the desulfurized rubber by filtration or centrifugation after the desulfurization step.

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