US 3865713 A
A carbonaceous reagent is provided for modifying a carbonaceous binder used in the manufacture of fired carbon articles and carbon-bonded refractories. The reagent serves to increase the carbonization yield of the binder. The reagent contains one or more functional groups each of which has one or more oxygen atom, has an atomic ratio of oxygen to carbon of from 0.05 to 0.30, and a carbonization yield per se of at least 50 percent.
Claims available in
Description (OCR text may contain errors)
United States Patent Kawai et al.
1 CARBONACEOUS REAGENT FOR CARBONACEOUS BINDER USED IN THE MANUFACTURE OF FIRED CARBON ARTICLES AND CARBON-BONDED REFRACTORIES Inventors: Yoshio Kawai; Kiro Asano; Kiyoshi Yamaki, all of Tokyo, Japan Assignee: Kureha Kagaku Kogyo Kabushiki Kaisha, Tokyo, Japan Filed: June 7, 1973 Appl. No.: 367,449
Foreign Application Priority Data  References Cited UNITED STATES PATENTS 3,238,116 3/1966 Hammer et al. 208/6 3,775,289 11/1973 Kishi et al 208/ Primary Examiner-Veronica OKeefe Attorney, Agent, or F irm-Flynn & Frishauf  ABSTRACT A carbonaceous reagent is provided for modifying a carbonaceous binder used in the manufacture of fired carbon articles and carbon-bonded refractories. The reagent serves to increase the carbonization yield of the binder. The reagent contains one or more functional groups each of which has one or more oxygen June 12, 1972 Japan 47-57655 atom, has an atomic ratio of oxygen to carbon of from U S Cl i I i I 208/6 208/44 0.05 to 0.30, and a carbonization. yield per se of at Int. Cl..::::: C10c 3/04 east 50 Percent- Field of Search 208/6, 44 11 Claims, 3 Drawing Figures CD CD MIXING RATlO OF REAGENT TO BINDER PlTCH (WT./o)
PATENTEDFEBI 5 1865.713
SHEET 1 OF 2 FIG. 1
CARBONIZATION YIELD OF BINDER PITCH (WT. 03
MIXING RATIO OF REAGENT TO BINDER PITCH (WP/o) G *5 Lu '-'-':1: 10.15: o 3 2t ZR 5;: 0Q E 010 E 99 9 2% 2 (IO 0 5005- 25 E4 E t a; 2& u-
HEAT TREATMENT TEMPERATURE FIG. 3
CARBONIZATION YIELD OF BINDER PITCH WT /o) ATOMIC RATIO O/C IN HEAT TREATED OXIDIZED PITCH ll AR o A EoUs REAGENT FOR CARBONACEOUS BINDER USED IN THE MANUFACTURE OF FinEn CARBON ARTICLES AND CAnBoN-BoNnEn REFRACTORIES This invention relates to carbonaceous reagents useful for modifying carbonaceous binders used in the manufacture of fired carbon articles and Carbonbonded refractories, and to a method for forming said reagents. The reagents are capable of increasing the carbonization yield of said binders when said articles or refractories are fired, thereby providing products of high density and great mechanical strength.
As used herein, the term carbonization yield of a binding material is defined to mean an amount in percent by weight of a residual mass derived from an original binding material when heated up to l,000C in increments of C per minute in an atmosphere of inert gas.
Shaped and fired carbon articles, for example, carbon electrodes are manufactured from coke, anthracite, graphite or carbon black finely divided for use as a filler by adding to the filler a proper amount of binding material such as tar, pitch, phenolic resin or furan resin, kneading the mixture, and molding the kneaded mass, followed by firing. In a special case, these binding materials themselves are fired for carbonization and may be made into carbon articles by the same process as described above with no use of fillers. In any case, the binding material, when fired, is generally carbon ized to an appreciably low degree and gives forth volatile matter possibly to make the resulting product undesirably porous, presenting difficulties in providing articles of high density and great mechanical strength. To compensate for such defects, it is customary practice to impregnate fired material with tar or pitch and again fire the impregnated mass so as to enable the final product to increase in density and mechanical strength and decrease in specific electric resistance.
To eliminate the above-mentioned troublesome procedure, it is considered advantageous to use a binder giving as high a carbonization yield as possible. Therefore, the world tends to accept the so-called heavy pitch, which provides a high carbonization yield. This heavy pitch has an aromatic structure and a large molecular weight, and in consequence indicates a high softening point and melt viscosity. However, these properties present great difficulties in kneading a mixture of heavy pitch and filler and molding or extruding the kneaded mass, imposing considerable limitation on application of the heavy pitch.
On the other hand, study is in progress to add a small amount of reagent to pitch used as a binder. Attempts have been made to use, for example, dinitronaphthalene or 2,3-naphthoquinone as a reagent. However, such a reagent itself is not only carbonized to a low extent and mostly volatilized when tired, but is also extremely expensive, failing to be put to industrial application in any way.
It is accordingly the object of this invention to provide an inexpensive reagent having a high carbonization yield per se and little soluble in a binding material preventing the softening point thereof from being raised.
To this end, the reagent of this invention is prepared by oxidizing tar, pitch or coal by an oxidation process to introduce therein functional groups containing oxygen atoms to such an extent that the atomic ratio of oxygen to carbon in said reagent falls within the range of from 0.05 to 0.30.
Other important objects and advantageous features of this invention will be apparent from the following description and accompanying drawings, wherein the specific embodiments of the invention are set forth in detail.
FIG. 1 is a curve diagram showing the relationship between the carbonization yield of a binder pitch and the mixing ratio of the reagent to the binder pitch used in Example 1;
FIG. 2 is a curve diagram showing the relationship between the atomic ratios of oxygen to carbon and hydrogen to carbon in a reagent and the temperature at which the reagent itself was heat-treated in Example 2; and
FIG. 3 is a curve diagram showing the relationship between the carbonization yield of a modified binder pitch and the atomic ratio of oxygen to carbon in the heattreated reagent of Example 2.
The reagent of this invention not only presents a high carbonization yield itself but also is little soluble in a binder, preventing the binder mixed with said reagent from being raised in the softening point. Further, the reagent acts as a sort of filler in the steps of kneading a mixture of raw carbonaceous material and binder and molding or extruding the kneaded mass.
From such features, the reagent itself may be deemed as a special raw carbonaceous material.
Moreover, with the reagent of this invention, functional groups introduced therein improve the wetting of the reagent to a binder, attaining an easy and homogeneous mixture thereof. When the kneaded mass is fired, the functional groups of the reagent react with the binder prominently to increase the carbonization yield of the binder. Therefore, application of the reagent does not exert any harmful effect on the molding or extrusion of the kneaded mass, but facilitates the manufacture of carbon articles of high density and mechanical strength and low specific electric resistance. The reagent of this invention can be applied in manufacturing for not only the tired carbon artciles but also refractories using a carbonaceous binder.
The raw material of the reagent of this invention may consist of ordinary tar or pitch, those obtained by polycondensation which is derived from heat-treatment and/or oxidation of petroleum. The reagent should preferably be formed of a raw material of highly aromatic structure so as to permit the easy introduction of functional groups in said raw material by oxidation and enable the resultant reagent to have a low solubility and meltability and to have a high carbonization yield itself.
The raw material of the reagent may consist of not only the above-mentioned types of tar and pitch but also finely ground coal. The preferred coals are anthracite and a bituminous type low in ash content, but any other kind of coal is acceptable.
Oxidation of the raw materials of the reagent is generally effected by various processes. Most convenient is the use of oxidizing gas, for example, oxygen, ozone, air, sulfur trioxide, or nitrogen dioxide. It is also possible to treat the raw materials of the reagent with an oxidizing aqueous solution of nitric acid, sulfuric acid, mixed acid thereof, hypochlorous acid or dichromic acid.
It does not matter whether the raw materials of the reagent are oxidized in the form of powders, fibers, molten mass or solution. While not subject to any particular limitation in temperature, the oxidation is generally carried out at to 400C so as to prevent undue oxidation. If the raw materials are again heattreated for aging at lower temperatures than about 500C in an atmosphere of inert gas after the abovementioned oxidation, then the raw materials will present a prominent effect.
The oxidation causes the hydrocarbon molecules constituting the raw materials of the reagent to contain functional groups having an oxygen atom in the form of a carboxyl-, carbonyl- (of quinone, ketone or aldehyde type), hydroxy- (of phenol or alcohol type), ether-, or peroxy group. Said oxidation also gives rise to polycondensation among te hydrocarbon molecules, and this causes the reagent prominently to decrease in solubility in binding materials and indicate a low meltability thereof. Depending on the kind of oxidizing agent used, some amount of, for example, nitro group, halogen group or sulfur group may sometimes be carried into the raw materials of the reagent, which, however, does not obstruct the function of the reagent.
The functional groups can be identified or their amounts can be quantitatively determined by the infrared spectrum analysis, elementary analysis or ordinary chemical analysis. The quantitative analysis of the individual functional groups is difficult to carry out and also unnecessary. It is sufficient to determine the atomic ratio of the total oxygen atoms to the carbon atoms contained in the reagent. The indispensable requisite for the reagent of this invention is that the atomic ratio of oxygen to carbon be defined within the range of 0.05 to 0.30 or preferably 010 to 0.25. It has been found that where the above-mentioned requisite is fully met, the atomic ratio of hydrogen to carbon falls within the range of about 0.2 to 0.8. If the atomic ratio of oxygen to carbon decreases from 0.05, then the reagent will not fully display its effect. Again where said ratio increases over 0.3, the reagent does not indicate any increased effect. Therefore, any process resulting in such excessively large atomic ratio of oxygen to carbon is not only useless but also undesirably reduces the carbonization yield of the reagent per se.
The oxidation in producing the reagent gives rise to cross linking among its molecules and minimizes the content of volatile matter, enabling the reagent to present a high carbonization yield. The reagent thus prepared has a carbonization yield of at least 50 percent, generally ranging from 60 percent to 92 percent.
As mentioned above, the reagent of this invention is substantially insoluble in the binding materials and contains functional groups having affinity with the binding materials, and can be uniformly dispersed therein due to good wettability. Further, the reagent undergoes little chemical reaction with the binding materials at kneading and molding temperature, preventing the softening point or viscosity of the mixed binding materials from being elevated and consequently causing the mixture of filler and binder to be little reduced in moldability.
High temperature firing after molding gives rise to a chemical reaction between the reagent and binder, leading to not only the binding of the molecules of both constituents but also a chain reaction therebetween, thereby promoting polycondensation among the binder molecules. Accordingly, mere addition of a small amount of reagent to the binder considerably improves its carbonization yield, providing fired articles of increased density, mechanical strength,,corrosion resistance and electric conductivity.
While varying with the particle size distribution of the filler, the mixing ratio of the filler to the binder and the kind of binder used, it may be generalized that the reagent should preferably be added at the ratio of l to 50 weight parts per weight parts of the binder. As previously described, it is possible to apply the reagent itself as a filler, using very little filler or with its use entirely omitted. In such case, 2.5 to 100 weight parts of the binder are mixed with 50 weight parts of the reagent. In a special case, carbon articles can be prepared from reagent and a binder (cf. Example 5).
The modifier of this invention has a variety of applications such as carbon electrodes, carbon blocks, carbon articles used with mechanical or electric machinery, amorphous carbon material to be stamped for use as lining, carbon paste for Soederberg electrodes and refractories.
The reagent of the present invention will be more fully understood by reference to the following examples.
EXAMPLE 1 Into the steam superheated to about 2,000C was introduced a vapour of petroleum naphtha preheated to 350C. The vapour was thermally cracked for 0.003 second at l,l00C, followed by quenching, obtaining residual tar with a yield of about 20 percent by weight in addition to ethylene, acetylene, benzene and naphthalene. The tar was later distilled up to 300C at vacuum of 5 mml-lg to remove light weight components, producing pitch in an amount about half the original weight of the tar.
The pitch indicated a hydrogen to carbon atomic ratio of 0.51 calculated from measure of contents of hydrogen and carbon using the elementary analysis. The carbonization yield of said pitch was 64 percent. One gram of the pitch was put in a cylinder 1 cm in cross sectional area which was provided at the lower end with a nozzle 1 mm in diameter used in a Flow Tester. When the pitch was increasingly heated in increments of 10C per minute at a pressure of 10 Kglcm the pitch indicated a softening point of 218C as measured from the temperature at which the pitch commenced to run out. The aforesaid hydrogen to carbon atomic ratio in the pitch suggested that it consisted of a large amount of polycondensed aromatic components. This assumption was also confirmed by the IR spectrum and the NMR spectrum using carbon disulfide as a solvent.
After being crushed, the pitch was heated for oxidation to 250C by raising the temperature in increments of lC per minute in air containing 3 percent by volume of nitrogen dioxide gas, obtaining a product having the properties given in Table 1 below.
Table 1 Properties of Oxidized Pitch Difficult to measure (above 400C) bg weight) Table l-Continued Properties of Oxidized Pitch Solubility in anthracene oil Carbonization yield of its own The instrumental analysis such as the IR spectrum method and ordinary chemical analysis qualitatively proved that the oxidized pitch obtained contained carboxy1-, carbonyl-, hydroxyland nitro groups, and oxygen of ether type.
The oxidized pitch, that is, a reagent of this invention was pulverized to such a particle size as passed the 100 Tyler mesh screen. The powders obtained were mixed in various proportions with coal tar binder pitch of which softening point and carbonization yield were 78C and 46 percent respectively. Every 5 grams of the mixed mass was placed in a porcelain crucible having a capacity of 30 c.c., and was heated to l,000C by raising temperature in increments of 5C per minute in an atmosphere of nitrogen. FIG. 1 presents the carbonization yields of the binder pitch at different mixing ratios of the reagent to the binder pitch. Said yield was calcu- EXAMPLE 2 The oxidized pitch obtained in Example 1 having the properties set forth in Table 1 was heat-treated in an atmosphere of nitrogen at temperatures of 300, 400 500, 600, 700 and 900C respectively. The elementary analysis was made of the each oxidized pitch thus heat-treated to determine the atomic ratio of oxygen to carbon and hydrogen to carbon in the pitch, the results being presented in FIG. 2.
20 parts by weight of each heat-treated oxidized pitch were mixed with eighty parts by weight of the same petroleum pitch as used in Example 1. The carbonization yield of the petroleum pitch mixed with the heat-treated oxidized pitch was determined in the same manner as in Example 1, the results being set forth in FIG. 3. As apparent from FIGS. 1, 2 and 3, the oxidized pitch heat-treated at temperatures of about 250 to about 500C prominently elevated the carbonization yield of a binder pitch. Where, however, said heattreatment was effected at higher temperatures than 500C, the oxidized pitch thus heat-treated indicated a sharp decline in the oxygen to carbon atomic ratio and in consequence a noticeable decrease in the ability to increase the carbonization yield of the binder.
EXAMPLE 3 An oxidized pitch was prepared in the following manner.
Five hundred grams of blown asphalt having a penetration index of 10 to 20, composed of 85.5 Weight percent carbon and 9.67 weight percent hydrogen, the hy drogen to carbon atomic ratio thereof being 1.36, were melted at 380C. Nitrogengas was made to bubble through the molten asphalt for 60 minutes at the rate of 2 l per minute for dry distillation, and further distilled 3 hours at 300C and vacuum of 10* mmHg, obtaining pitch having a softening point of about 180C with a yield of 29 percent by weight. The pitch was formed of 86.1 percent carbon and 7.62 percent hydrogen and indicated a hydrogen to carbon atomic ratio of 1.06.
Those pulverized portions of the above-mentioned pitch which passed through the 10 0 Tyler mesh screen were used. Saidpulverized portions were oxidized 3 hours at C in air containing 1.5 percent by volume of ozone. The oxidation was repeated in the same air by raising the temperature to 260C in increments of 1C per minute. Final heat treatment was carried out 30 minutes at 350C in an atmosphere of nitrogen. A reagent obtained consisted of 76.1 percent carbon, 3.63 percent hydrogen and 20.1 percent oxygen, and indicated an oxygen to carbon atomic ratio of 0.20, a hydrogen to carbon atomic ratio of 0.57, and a carbonization yield of 65 percent.
On the other hand, weight parts of calcined petrocoke having the particle size distribution shown in Table 2 below and 33 weight parts of an ordinary binder pitch were mixed to provide a control.
Table 2 Particle size distribution of calcined petrocoke by weight Particle sizes from 3 to 1.5 mm about 20 Particle sizes smaller than 1.5 mm and over 200 Tyler mesh about 30 Particle sizes under 200 Tyler mesh about 50 To the above-mentioned calcined petrocoke, the binder pitch and the reagent prepared from the aforesaid asphalt were mixed in the proportions given in Table 3 below. Every mixed mass was kneaded, extruded, baked and graphitized in succession. All the steps were carried out as follows. Initially, the mixed mass was kneaded 40 minutes at to C and extruded at a pressure of 50 Kg/cm into rods each 25.4 mm in diameter and 100 mm long. The rods were buried in coke breeze and heated to 700C in 50 hours and maintained 2 hours at said temperature. Later, the rods were heated to 2,600C in 3 hours and maintained 1 hour at said temperature to complete graphitization.
The kneading was carried out in a Z-type kneader having a capacity of l I. There was no difficulty in kneading and extruding the samples of the control. The graphitized samples indicated the properties given in Table 3 below as measured by the methods specified in the Japanese Industrial Standards (JIS) R 7201 to R 7202.
Table 3 Composition of raw materials and properties of graphit'wed samples The carbonization yield of the binder pitch shown in Table 3 was calculated by deducting the residual amount of the calcined petrocoke and the reagent when they were graphitized singly.
EXAMPLE 4 Coal tar pitch composed of 92.30 wt. percent carbon, 4.50 wt. percent hydrogen, 0.20 wt. percent sulfur, 1.12 wt. percent nitrogen and 1.88 wt. percent oxygen, in which the oxygen to carbon atomic ratio and the hydrogen to carbon atomic ratio were 0.01 and 0.59 respectively, was dry-distilled 1 hour at 380C while nitrogen gas was made to bubble through the pitch as in Example 3, and further distilled 1 hour at 270C at vacuum to obtain with a yield of 52 percent a pitch having a softening point of about 195C, containing 92.40 weight percent carbon and 3.67 weight percent hydrogen and indicating the hydrogen to carbon atomic ratio of 0.48.
Five hundred grams of those pulverized portions of the pitch which passed through the 100 Tyler mesh screen were placed in a l lflask. Air was made to pass through the flask at the rate of l l per minute while gently stirring the flask. The charged pitch was heated from room temperature to 150C in 10 minutes, further heated to 260C by raising temperature in increments of 1C per minute, and maintained 10 hours at that LII temperature for oxidation. The oxidized pitch (reagent) thus obtained was formed of 71.9 weight percent carbon, 2.81 weight percent hydrogen and 23.64 weight percent oxygen, and indicated the oxygen to carbon atomic ratio of 0.25 and the hydrogen to carbon atomic ratio of 0.47, and had its own carbonization yield of 62 percent.
A plurality of mixed samples were prepared by mixing a filler formed of pulverized pitch coke having a particle size distribution in which particle sizes ranging from 170 to 325 accounted for 25 percent by weight and those finer than 325 Tyler mesh occupied 75 percent by weight; a coal pitch binder having a softening point of 88C as measured by the ring and ball method; and the aforesaid oxidized pitch in the proportions shown in Table 4. Each mixture was kneaded 30 minutes at 150C, and the kneaded mass was charged in a metal mold 5 cm wide, 5 cm high and 20 cm long. The charge was molded at a pressure of 200 Kg/cm at l50C. The shaped samples were buried in coke breeze and heated to 700C in 50 hours. Later, the samples were transferred to a graphitizing furnace, heated to 2,700C in 4 hours and maintained 1 hour at that temperature to complete graphitization. Thus were obtained samples of graphite electrode used in NaCl electrolysis. The samples presented the properties given in Table 4.
Table 4 Composition of raw materials and properties of graphite samples by weight):
Table 4-Continued Composition of raw materials and properties of graphite samples Properties of graphite sample:
Bulk density 1.60 1.62 Bending strength (Kglcm 180 220 S ecific resistance 90 85 Weight loss by electrolytic oxidation (mg/amp. hour) 1.30 1.02
EXAMPLE Anthracite mined in North Vietnam was pulverized into fine particles passing through the 100 Tyler mesh screen. The pulverized mass was heated to 230C by raising temperature in increments of 1C per minute in air containing 1.5 percent by volume of nitrogen dioxide gas and maintained 30 minutes at that temperature for oxidation. The mass thus treated indicated, as measured by elementary analysis, the oxygen to carbon atomic ratio of 0. l 4 and the hydrogen to carbon atomic ratio of 0.34, and a carbonization yield of 85 percent. The oxidized anthracite was fully insoluble in various types of pitch, and chemically analyzed to contain 5 X mol/g of carbonyl group, 2 X 10' moi/g of carboxyl group and l X l0 moi/g of phenol type bydroxyl group.
The oxidized anthracite was used as both filler and reagent. Namely, 70 parts by weight of powders of the oxidized anthracite were mixed with 30 parts by weight of the pitch obtained by thermal decomposition of naphtha in Example 1. The mixed mass was kneaded at 250C and, after cooling, pulverized into fine particles passing through the 200 Tyler mesh screen. Water was added as a molding agent in the ratio of 5 parts by weight per 100 parts by weight of the powders. The mass was molded into a round column 30 mm in diameter and 30 mm long at room temperature and a pressure of 300 Kg/cm The molded sample was buried in coke breeze and heated to 1,000C by raising temperature in increments of 100C per hour for carbonization to obtain a homogeneous compact article having a volumetric contraction coefficient of 35 percent, porosity of 14 percent, compressive strength of 2,600 Kglcm Shore hardness of 110, bulk density of 1.39, and carbonization yield of about 90 percent.
EXAMPLE 6 The pitch obtained by thermal decomposition of naphtha in Example 1 was pulverized into fine particles passing through the 200 Tyler mesh screen. One hundred grams of the powders obtained were mixed with 1 [of 8 N water solution of nitric acid. Both materials were reacted 30 minutes at 40C. The reaction product was filtered and washed with water. The resultant cake was dried 3 hours with hot air at 120C. Thus obtained reagent indicated the oxygen to carbon atomic ratio of 0.069, the hydrogen to carbon atomic ratio of 0.42 and the carbonization yield of 75 percent.
A mixture of said reagent and coal tar was used as a binder, and there were prepared for trial samples of carbonaceous magnesia refractory, whose properties are presented in Table 5 below.
Table 5' Composition of raw materials and properties of refractory samples samples (Kg/cm) What we claim is:
1. A method for preparing a carbonaceous reagent for a carbonaceousbinder used in the manufacture of tired carbon articles and carbon-bonded refractories in order to increase the carbonization yield of said binder, which comprises oxidizing a carbonaceous raw material at a temperature of from 15C. to 400C. with an oxidizing agent to provide an atomic ratio of oxygen to carbon therein of from 0.05 to 0.3 0.
2. The method of claim 1, wherein an oxygen containing functional group is introduced into said raw material by said oxidation.
3. A method according to claim 1, wherein the carbonaceous raw material is one selected from the group consisting of a tar, a pitch and a coal.
4. A method according to claim 3, wherein the tar is coal tar or petroleum tar.
5. A method according to claim 3, wherein the pitch is coal pitch or petroleum pitch.
6. A method according to claim 3, wherein the coal is anthracite or bituminous coal.
7. A method according to claim 1, wherein the oxidizing agent is a gas selected from the group consisting of oxygen, ozone, air, sulfur trioxide and nitrogen dioxide.
8. A method according to claim 1, wherein the oxidizing agent is an aqueous solution of an acid selected from the group consisting of nitric acid, sulfuric acid, a mixed acid of nitric and sulfuric acids, hypochlorous acid and dichromic acid.
9. A method for preparing a carbonaceous reagent for a carbonaceous binder used in the manufacture of fired carbon articles and carbon-bonded refractories in and carbon-bonded refractories, said reagent increasing the carbonization yield of said binder, characterized in that said reagent contains a functional group having an oxygen atom, has an atomic ratio of oxygen to carbon of from 0.05 to 0.30, and a carbonization yield per se of at least 50 percent.
11. A carbonaceous reagent according to claim 10, wherein the functional group is selected from the group consisting of carboxyl-, carbonyl-, hydr0xy-, etherand peroxy groups.