Petroleum-based soft pitch mixture and closing material for molten metal tapping hole

Abstract

Provided is a petroleum-based soft pitch mixture having a low polycyclic aromatic hydrocarbon concentration, wherein the viscosity of the petroleum-based soft pitch mixture is easily adjusted according to the use. Further provided is a closing material for a molten metal tapping hole, with which the discharge amount of polycyclic aromatic hydrocarbons can be made small during use.　This petroleum-based soft pitch mixture is obtained by mixing a petroleum-based soft pitch having a softening point of 40°C or higher and lower than 150°C and a distillate oil having a boiling point ranging between 230°C and 280°C, wherein the content of the distillate oil is 10%-45% by mass, and the remainder is the petroleum-based soft pitch and inevitable impurities. This closing material for a molten metal tapping hole is obtained by mixing the petroleum-based soft pitch mixture as a binder into a refractory raw material. The contents of benzo[a]pyrene and naphthalene as the polycyclic aromatic hydrocarbons are controlled.

Description

Petroleum-based soft pitch mixture and plugging material for molten metal tap holes

[0001] The present invention relates to a petroleum-based soft pitch mixture and a plugging material for a molten metal tap hole using the same as a binder.

[0002] Conventionally, anhydrous tar obtained by dehydrating coal tar has been used as a binder for molten metal tap port plugging materials (hereinafter also referred to as "mud materials"), such as blast furnace tap port plugging materials and electric furnace tap port plugging materials, and as a binder for paints. Among these, with regard to mud materials, Patent Document 1 discloses the use of anhydrous tar with a high fixed carbon content as a binder for refractory raw materials such as roseki, chamotte, and alumina, and refractory materials such as carbonaceous materials, silicon carbide, silicon nitride, and clay. Furthermore, Patent Document 2 discloses the use of a tar-based soft pitch obtained by tar distillation as a binder for mud materials.

[0003] JP 2003-286513 A JP 2006-028423 A

[0004] The anhydrous tar described in Patent Document 1 provides an excellent mud material, but since this anhydrous tar is produced from coal-based coal tar raw materials, it contains a large amount of polycyclic aromatic hydrocarbons, such as benzo[a]pyrene and naphthalene. Therefore, there is a problem that it volatilizes in high-temperature environments and has a negative impact on the environment. Furthermore, although it is preferable for this anhydrous tar to have a viscosity suitable for various applications, adjusting the viscosity is not easy.

[0005] Furthermore, the binder described in Patent Document 2 has a higher carbonization yield, which leads to a higher density of the molded product, and thus makes it possible to improve the strength. However, there is a problem in that the coal tar-based raw material may emit the above-mentioned polycyclic aromatic hydrocarbons, which may have a negative impact on the environment.

[0006] The present invention aims to provide a petroleum-based soft pitch mixture that has low concentrations of benzo[a]pyrene and naphthalene, which are typical polycyclic aromatic hydrocarbons, and whose viscosity can be easily adjusted, and further to provide a plugging material for a molten metal tap port that emits a small amount of polycyclic aromatic hydrocarbons during use.

[0007] The present inventors have conducted extensive research to achieve the above object, and as a result have found that a mixture of petroleum-based soft pitch, which has a low softening point, and distilled oil, which is a distillation fraction having a specific boiling point range, has a low content of polycyclic aromatic hydrocarbons and does not adversely affect the environment.

[0008] The present invention was completed based on these findings and through further investigation, and the gist of the present invention is as follows: [1] A petroleum-based soft pitch mixture comprising a petroleum-based soft pitch having a softening point of 40°C or higher and lower than 150°C and a distilled oil having a boiling point range of 230°C to 280°C, wherein the content of the distilled oil is 10% to 45% by mass, and the remainder is the petroleum-based soft pitch and unavoidable impurities. [2] The petroleum-based soft pitch mixture of [1] above, characterized in that it has a benzo[a]pyrene content of less than 500 ppm by mass and a naphthalene content of less than 1.00% by mass. [3] The petroleum-based soft pitch mixture of [1] or [2] above, characterized in that it has a viscosity at 60°C of 100 mPa·s to 2400 mPa·s. [4] A plugging material for a molten metal tap port, characterized in that it comprises the petroleum-based soft pitch mixture of any one of [1] to [3] above and a refractory raw material. [5] In the above [4], the mixing ratio of the petroleum-based soft pitch mixture to a total amount of 100 parts by mass of the refractory raw materials is 10 parts by mass to 25 parts by mass. A blocking material for a molten metal tapping port.

[0009] According to the present invention, it is possible to obtain a petroleum-based soft pitch mixture that can keep the concentrations of benzo[a]pyrene and naphthalene, which are representative polycyclic aromatic hydrocarbons, low and that can easily adjust the viscosity depending on the application. Furthermore, a plugging material for a molten metal tap port that uses this petroleum-based soft pitch mixture as a binder can reduce the amount of polycyclic aromatic hydrocarbons released.

[0010] The present invention will now be described in further detail.

[0011] [Petroleum-Based Soft Pitch Mixture] The petroleum-based soft pitch mixture of the present invention is a mixture of a specific petroleum-based soft pitch obtained by distilling and heat-treating petroleum-based heavy oil, and a distillation fraction (hereinafter also referred to as "distilled oil") having a specific boiling point range obtained by distilling petroleum itself or coal-based or petroleum-based tar.

[0012] [Petroleum-Based Soft Pitch] The petroleum-based soft pitch of the present invention is produced by a distillation process followed by a thermal reforming process using petroleum heavy oil having a carbon-to-hydrogen atomic ratio (C / H) of 0.70 or more as a raw material. More specifically, the process is as follows: Petroleum heavy oil is distilled by atmospheric distillation (for example, petroleum heavy oil is distilled in a distillation column at about 320°C for 1.0 hour), and the fraction below 280°C is distilled off. The distilled residue is then heat-treated at 300°C to 380°C for about 6.0 hours to obtain a petroleum-based soft pitch. The obtained petroleum-based soft pitch is hot-filtered to remove solids. The softening point of the resulting petroleum-based soft pitch is 40°C or higher and lower than 150°C. This is because a softening point below 40°C results in a low fixed carbon content, while a softening point above 150°C results in a high viscosity and low fluidity. The softening point is preferably 40° C. to 140° C., more preferably 40° C. to 110° C., even more preferably 40° C. to 70° C., and most preferably 40° C. to 57° C. The softening point can be adjusted by the heat treatment temperature and treatment time, and may also be adjusted, in some cases, by remixing the light fraction distilled off by distillation or heat treatment.

[0013] The resulting petroleum-based soft pitch has a boiling point of approximately 100°C or higher and is composed of many complex components. These components include, for example, pentadecane (C 15 H 32 ), and its compounds, and phenanthrene (C 14 H 10 ) and their compounds.

[0014] Petroleum-based heavy oil refers to heavy crude oil classified as having a specific gravity of 0.903 or more at 15 / 4°C, based on the physical properties of crude petroleum.

[0015] As for the properties of the petroleum heavy oil, the fixed carbon content is preferably 1.0 mass % to 40.0 mass %, more preferably 5 mass % to 30 mass %.

[0016] The carbon / hydrogen atom ratio (C / H) is preferably in the range of 0.70 to 1.30, and more preferably in the range of 0.75 to 1.25.

[0017] [Distilled Oil] As described above, distilled oil refers to a specific distillation fraction obtained by distillation of petroleum itself or distillation of coal- or petroleum-based tar, and the distilled oil of the present invention is a fraction having a boiling point range of 230° C. to 280° C. This is because if the boiling point is below 230° C., the fixed carbon content will be low, and if it exceeds 280° C., the viscosity will be high.

[0018] The material to be distilled may be petroleum itself or coal- or petroleum-based tar, but petroleum itself or petroleum-based tar is preferred from the viewpoint of low content of polycyclic aromatic hydrocarbons such as benzo[a]pyrene and naphthalene.

[0019] By mixing the distillate oil having the above boiling point range with the above-mentioned petroleum-based soft pitch, a petroleum-based soft pitch mixture containing almost no polycyclic aromatic hydrocarbons can be obtained. That is, the benzo[a]pyrene content described below can be reduced to less than 500 ppm by mass, and the naphthalene content can be reduced to less than 1.00% by mass.

[0020] [Polycyclic aromatic hydrocarbons] Polycyclic aromatic hydrocarbons are hydrocarbons consisting of condensed aromatic rings, without any heteroatoms or substituents such as nitrogen, oxygen, or sulfur. There are many such compounds. For example, the simplest example is naphthalene, which has two six-membered rings (benzene rings), anthracene and phenanthrene, which have three, pyrene and chrysene, which have four, and benzopyrene, which have five. There are also many compounds with six or more rings. Furthermore, many of these compounds, such as benzo[a]pyrene, are toxic and volatile, including carcinogenic.

[0021] [Benzo[a]pyrene, naphthalene] The present inventors focused on benzo[a]pyrene and naphthalene among the polycyclic aromatic hydrocarbons contained in petroleum-based soft pitch mixtures. These hydrocarbons are representative of polycyclic aromatic hydrocarbons and are substances that have adverse environmental effects, such as being carcinogenic. Therefore, it is important to limit the content of these substances.

[0022] First, benzo[a]pyrene is a polycyclic aromatic hydrocarbon with five benzene rings bonded together, and its chemical formula is C 20 H 12 It is a volatile substance with a boiling point of 310°C to 312°C, and is known to be carcinogenic to humans. Its isomer is benzo[e]pyrene, which has a different arrangement of benzene rings.

[0023] The benzo[a]pyrene content in the petroleum-based soft pitch mixture of the present invention is preferably less than 500 ppm by mass. This is because if it is 500 ppm by mass or more, the amount of carcinogenic substances increases. It is more preferably less than 200 ppm by mass, and most preferably less than 160 ppm by mass.

[0024] Next, naphthalene is the simplest polycyclic aromatic hydrocarbon with two benzene rings bonded together, and its chemical formula is C 10 It is designated H8. It has a boiling point of 218°C, is highly volatile, flammable, a sensitizer, and is also a carcinogen.

[0025] The naphthalene content in the petroleum-based soft pitch mixture of the present invention is preferably less than 1.00% by mass. If it is 1.00% by mass or more, it becomes a specified chemical substance. It is more preferably less than 0.80% by mass, even more preferably 0.70% by mass or less, and most preferably 0.55% by mass or less.

[0026] However, coal-derived pitch contains a large amount of polycyclic aromatic hydrocarbons, resulting in benzo[a]pyrene at approximately 500 mass ppm or more and naphthalene at 3 mass% or more. Therefore, the petroleum-based soft pitch mixture of the present invention has low contents of benzo[a]pyrene and naphthalene, demonstrating that it is an environmentally friendly material.

[0027] The content of polycyclic aromatic hydrocarbons such as benzo[a]pyrene and naphthalene can be measured by gas chromatography mass spectrometry.

[0028] [Viscosity Adjustment and Mixing Ratio] When a petroleum-based soft pitch mixture is mixed with a refractory raw material as a binder to produce a mud material, the viscosity of the binder has a significant effect on the hardness (durability) required for the refractory material (mud material). Therefore, it is necessary to adjust the viscosity of the binder. Here, the hardness required for the mud material can be measured using a needle penetration hardness tester, and the preferred hardness is 7000 N to 4000 N.

[0029] In the petroleum-based soft pitch mixture of the present invention, a petroleum-based soft pitch mixture with any viscosity can be obtained by changing the mixing ratio of the petroleum-based soft pitch and distillate oil. For mud material applications, the preferred range of viscosity of the petroleum-based soft pitch mixture at 60°C is 100 mPa·s to 2400 mPa·s. If the viscosity at 60°C is less than 100 mPa·s, the adhesion as a binder will be insufficient and the fixed carbon will decrease, which may result in inconveniences such as reduced durability. On the other hand, if the viscosity at 60°C exceeds 2400 mPa·s, the amount of petroleum-based soft pitch mixture required to achieve the required filling properties will increase, which may result in inconveniences such as increased porosity and reduced durability. A more preferred range is 400 mPa·s to 1200 mPa·s.

[0030] The fixed carbon content of the petroleum-based soft pitch mixture is preferably 20.0% by mass to 45.0% by mass, and the carbon / hydrogen atom ratio (C / H) is preferably 0.80 to 1.30. Within these ranges, the rate of hardness increase is small.

[0031] The above-described viscosity adjustment can be achieved by incorporating the petroleum-based soft pitch (A) and the distillate oil (B) in a mass ratio (%) of A:B = 55-90:45-10. That is, the petroleum-based soft pitch mixture of the present invention is a mixture of a petroleum-based soft pitch (A) having a softening point of 40°C or higher but less than 150°C and a distillate oil (B) having a boiling point range of 230°C to 280°C. The content of the distillate oil (B) is 10% by mass to 45% by mass, with the remainder being the petroleum-based soft pitch (A) and unavoidable impurities. Furthermore, a preferred mixing ratio is A:B = 71-90:29-10, and the most preferred mixing ratio is A:B = 76-86:24-14.

[0032] The method for mixing the petroleum soft pitch (A) and the distillate oil (B) is not particularly limited, and they may be mixed using a conventional mixer according to the mixing ratio of each.

[0033] [Inevitable impurities in the mixture] When the petroleum soft pitch and tar or petroleum distillate oil are mixed, impurities such as tar slag may be mixed in. The content of these impurities is acceptable if it is 0.1% by mass or less.

[0034] [Molten Metal Tap Gate Plugging Material (Mud Material)] Conventional mud materials using tar-based soft pitch (anhydrous tar) as a binder can lose their softness and become difficult to use when exposed to high ambient temperatures, particularly in ironworks and steelworks, due to the evaporation of volatile components such as naphthalene. In contrast, the mud material of the present invention is characterized by its excellent storage stability. That is, even when stored for a long period of time, the mud material's properties, such as its softness (hardness), do not change, and the low content of volatile components such as naphthalene does not adversely affect the working environment.

[0035] The petroleum-based soft pitch mixture of the present invention is useful for a wide range of applications, such as mud material, impregnation material for refractories and carbon materials, binder for carbon materials, paint binder, etc. Hereinafter, the use of the mixture in mud material will be described as an example.

[0036] The mud material of the present invention contains a petroleum-based soft pitch mixture and a refractory raw material. The refractory raw material may be any conventionally known refractory raw material for mud materials. Examples include rosestone, chamotte (a firebrick aggregate), alumina (bauxite), carbonaceous materials (graphite, coke, etc.), silicon carbide, silicon nitride, and clay (kaolin clay).

[0037] [Mixing ratio of mud material] The plugging material for a molten metal tap port (mud material) of the present invention is obtained by mixing the above-mentioned petroleum-based soft pitch mixture of the present invention in a ratio of 10 to 25 parts by mass with 100 parts by mass of the total amount of the above-mentioned refractory raw materials. If the mixing ratio of this petroleum-based soft pitch mixture is less than 10 parts by mass, the lubricity will decrease, which may result in inconveniences such as not being able to fill the required amount. On the other hand, if it is more than 25 parts by mass, the porosity will increase, durability will decrease, and inconveniences such as gas blowing in the opening due to not drying may occur. Therefore, the mixing ratio of the petroleum-based soft pitch mixture is preferably 10 to 25 parts by mass. More preferably, it is 15 to 20 parts by mass.

[0038] The mud material is produced by mixing an appropriate amount of petroleum-based soft pitch mixture with the above-mentioned refractory raw material, and the method is not particularly limited, and mixing can be carried out using a normal mixing device according to the respective mixing ratios.

[0039] The mud material of the present invention as described above exhibits little change in its softness (hardness). The hardness increase rate in the heat retention test described below is 30% or less, which is far superior to conventional mud materials.

[0040] The present invention will be described in more detail below with reference to examples. However, the following examples are merely provided to illustrate and explain the present invention in more detail, and are not intended to limit the scope of the present invention. In addition, "parts," "%," and "ppm" described below are based on mass unless otherwise specified.

[0041] Example 1 100 parts of petroleum heavy oil having a carbon concentration of 91.1% and a hydrogen concentration of 7.8%, i.e., a carbon-to-hydrogen atomic ratio C / H of 0.97, was distilled in a distillation column at approximately 320°C for 1.0 hour to remove fractions with a boiling point of less than 280°C, and then subjected to a heat treatment step at 360°C for 6.0 hours to obtain petroleum soft pitch A. Furthermore, the heat treatment step was carried out at 380°C for 6.0 hours to obtain petroleum soft pitch B. The obtained petroleum soft pitches A and B were hot filtered to remove solids. As a result, no solids such as petroleum soft pitch tar dregs were contained.

[0042] During the distillation of the petroleum heavy oil, the fraction at 230° C. to 280° C. was collected as distilled oil. This distilled oil did not contain any solid content.

[0043] The properties of the petroleum heavy oil used as the raw material, the distillate oil obtained, and the petroleum soft pitches A and B were measured by the following methods. The results are shown in Table 1.

[0044] (Viscosity Measurement Conditions) Viscosity was measured using a Brookfield B-type rotational viscometer in accordance with JIS Z 8803 (1991) "Viscosity of liquids - Measurement method."

[0045] (Conditions for measuring softening point) Measurement was carried out in accordance with "6. Method for measuring softening point of tar pitch (ring and ball method)" of JIS K 2425 (1983).

[0046] (Measurement conditions for fixed carbon) Measurement was carried out using an electric furnace in accordance with "9. Fixed carbon content determination method" of JIS K 2425 (1983).

[0047] (Conditions for measuring moisture content) Measurement was carried out by volumetric titration using the Karl Fischer method in accordance with JIS K 0068 (2001).

[0048] (Conditions for measuring the content of benzo[a]pyrene and naphthalene) Measurement was carried out using a gas chromatograph mass spectrometer, and quantitative analysis was carried out by the internal standard method.

[0049]

[0050] Petroleum-based soft pitch mixtures (Invention Examples 1 to 5 and Comparative Example 1) were obtained by mixing the petroleum-based soft pitch A or B obtained in Table 1 above with distilled oil in the ratios shown in Table 2 below. Their properties are shown in Table 2. In addition, 20 g of the obtained petroleum-based soft pitch mixture was placed in a beaker and left in an atmosphere at 35°C for one week, and the naphthalene content was measured. The results are shown in Table 2.

[0051] In Comparative Example 2, coal tar was heated to 235°C in a heating kettle over 24 hours and dehydrated to produce anhydrous tar. The viscosity of this anhydrous tar at 60°C was 280 mPa s, the fixed carbon content was 32 mass%, the moisture content was 0.1 mass%, the benzo[a]pyrene content was 500 mass ppm or more, and the naphthalene content was 10.90 mass%. Furthermore, 20 g of the obtained anhydrous tar was placed in a beaker and left to stand in an atmosphere at 35°C for 1 week, and the naphthalene content was measured, which was 8.90 mass%.

[0052]

[0053] Example 2 The following materials were prepared as refractory raw materials: burnt bauxite: 42%, silicon carbide: 20%, coke: 7%, silicon nitride iron: 17%, graphite: 4%, kaolin clay: 5%, pyrophyllite powder: 4%, and metallic silicon: 1%, total amount of which was 100% (% is by mass).

[0054] To 100 parts by mass of this refractory raw material, 18 parts by mass of the petroleum-based soft pitch mixture of Inventive Example 1 in Table 2 of Example 1 was added and mixed to prepare mud material 1.

[0055] The hardness of the samples of this mud material 1 before and after being kept at 70°C for 5 hours was measured using a needle penetration type hardness tester (crust hardness tester manufactured by Daiki Rika Kogyo Co., Ltd.), and the hardness increase rate was calculated using the formula {(hardness after keeping warm) - (hardness before keeping warm) / (hardness before keeping warm)} x 100.

[0056] Similarly, mud materials 2 and 3 were prepared using the petroleum-based soft pitch mixtures of Inventive Examples 2 and 3 in Table 2 of Example 1, and the hardness increase rate was determined in the same manner as for mud material 1.

[0057] In addition, 20 parts by mass of the petroleum-based soft pitch mixtures of Inventive Examples 4 and 5 in Table 2 of Example 1 were added to 100 parts by mass of the above-mentioned refractory raw material and mixed to prepare mud materials 4 and 5, and the hardness increase rate was determined in the same manner as for mud material 1.

[0058] In addition, using the petroleum-based soft pitch mixture of Example 1 of the present invention in Table 2 of Example 1, 25 parts by mass was added to 100 parts by mass of the above-mentioned refractory raw material and mixed to prepare Mud Material 6, and the hardness increase rate was determined in the same manner as for Mud Material 1.

[0059] In addition, the petroleum-based soft pitch mixture of Comparative Example 1 in Table 2 of Example 1 was used, and 18 parts by mass was added to 100 parts by mass of the above-mentioned refractory raw material and mixed to prepare Mud Material 7, and the hardness increase rate was determined in the same manner as for Mud Material 1.

[0060] Furthermore, 18 parts by mass of anhydrous tar from Comparative Example 2 in Table 2 of Example 1 was added to 100 parts by mass of the above refractory raw material and mixed to prepare a conventional mud material, and the hardness increase rate was determined in the same manner as for Mud Material 1. The above results are summarized in Table 3.

[0061]

[0062] As is clear from the results shown in Tables 1, 2, and 3, the petroleum-based soft pitch mixtures of Inventive Examples 1 to 5 contained small amounts of volatile components such as benzo[a]pyrene and naphthalene, and were easy to adjust to an appropriate viscosity. Furthermore, mud materials 1 to 5, which were made by mixing the petroleum-based soft pitch mixtures of Inventive Examples 1 to 5 with a refractory raw material in an appropriate ratio, were able to provide mud materials with a small rate of hardness increase.

Claims

1. A petroleum-based soft pitch mixture obtained by mixing a petroleum-based soft pitch having a softening point of 40°C or higher and less than 150°C with a distilled oil having a boiling point range of 230°C to 280°C, wherein the content of the distilled oil is 10% by mass to 45% by mass, and the remainder is the petroleum-based soft pitch and unavoidable impurities.

2. The petroleum-based soft pitch mixture according to claim 1, characterized in that the benzo[a]pyrene content is less than 500 ppm by mass and the naphthalene content is less than 1.00% by mass.

3. The petroleum-based soft pitch mixture according to claim 1, characterized in that it has a viscosity at 60°C of 100 mPa·s to 2,400 mPa·s.

4. A plug for a molten metal tap hole, comprising the petroleum-based soft pitch mixture according to any one of claims 1 to 3 and a refractory raw material.

5. A blocking material for a molten metal outlet port as described in claim 4, characterized in that the mixing ratio of the petroleum-based soft pitch mixture to a total amount of 100 parts by mass of the refractory raw materials is 10 parts by mass to 25 parts by mass.

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