US2500209A - Production of shaped carbon articles - Google Patents

Description

Patented Mar. 14, 1950 PRODUCTION OF SHAPED CARBON ARTICLES Frederick L. Shea, Jr., Chicago, and Leslie H. J uel, Morton Grove, 111., assignors to Great Lakes Carbon Corporation, Morton Grove, 111., a our:

notation of Delaware No Drawing. Application July 11, 1946, SerialNo. 682,924

1 Claims. (01. 1854.7)

Our invention relates to certain improvements n th r du t on o c rbon, e trodes or o her ca on. tic e w ich re. hap d y extr i n molding.

More particularly it. relates to improvements in extruded carbon articles attained by employing a potentially reactive polar lubricant in the carbonaceousmixture which is to be extruded into variously shaped articles.

It i s the generalpracticeto add to extrudable carbonaceous mixtures composed of divided carbonaceous solids such as coke and the likeand hydrocarbonaceous binder material such as pitch and the like, a quantity of oil. lubricant known as black oil or summer oil shortly" before the mixing is completed. The purpose of the oil is to facilitate shaping in an extrusion operation primarily by lubricating the metal Walls of the extrusion apparatus and the die in contact with the carbonaceous mixture. lubricant used generally amounts to, by weight, about 2-3 parts per 100 parts of carbonaceous solids in the solids-binder mixture. The conditions under which the oil lubricant is applied to. the mixture are such as to form a superficial film, more or less, upon the surfaces of granules or balls of the aggregated solids and binder which are formed during the preceding-period of mixing.

'In the usual mixing operations, the divided carbonaceous solids and binder are mixed to gether until a condition of granular aggregates is obtaine'd, requiring from about 20 minutes to about-50 minutesrnixing time to secure the optimum granular consistency at temperatures of aboutllO-IGO" C. The timeof mixing at a given temperature is generally dependent uponthe viscosity of the binder and upon the particle size distribution ofcarbonaceous solids in the mix, for example, with a given binder, the greater the proportion of pulverized particles the longer the time of mixing. After such mixing, the oil lubricant is addedand coated over the granular aggregated particle's'during an additional mixing time of from about 2 minutes to about minutes afterwhich the batch is discharged for extrusion.

Aside from the desirable lubricating characteristics of the usual oil lubricant, certain disadvantagesdo arise from its use which are detrimental to the quality of finished carbon articles. For instance, extruded pieces are sometimes found which show concentriclaminations or coring. These laminations. constitute planes of weakness which frequently cause early failure of electrodes to occur in use. The coring effect is partly due tothe iactthat the,usualoillubricant,

The quantity of oil besides having practically no binding power for carbonaceous solids, is not compatible or appreciably miscible with binders, such aspitch, and therefor prevents the proper coalescence or fusion of aggregated carbon-binder granules which are separated by a film of the oil. Again, the usual oil lubricant is not reactive with the binder and is substantially volatilized out of the green carbon articles when baked tocarbonize the binder. This behavior of the oil lubricant tends to increase the porosity-of the baked carbon article since the oil contributes little or no carbon residue to the baked carbon article. Other properties of baked or graphitized electrodes and other carbon articles are also adversely affected, for instance, the electrical resistivity thereof is in-v creased by the interference of, the usual. oillubricant with the proper bonding of .the divided carbonaceous solids with such as a pitch binder.

It is among the objects of the present invention to overcome the foregoing. disadvantages, to provide adequate lubrication for extrusion and to generally improve the properties of carbon electrodes and other carbon articles. These objects are accomplished by employing a potentially re,- active polar compound as the lubricant, hereinafter referred to as reactive lubricant, and which is compatible to a high degree with the usual binders, such aspitch, or any other hydrocarbonaceous binder which may be employed.

As reactive lubricant we, preferably employ nitro-aromatic compounds, although as a nonfully equivalent alternative. we may employ chloro-aromatic compounds either, alone or in admixture with nitro-aromatic compounds. The nitro-aromatic compounds are, however, preferred by reason of their greater reactivity.

These compounds may also contain other activeor functional substituent groups,.such as, chloro, hydroxy, methoxy, amino. These reactive lubri-; cants should melt below about 6., preferably below about 80 C. and boil above about 200 0., preferably above 225 C. These reactive lubricants should remain potentially reactiveduring their mixing period, that is they should not. react with the hydrocarbonaceous binder below about 200 C., and preferably should remain unreactive below about, C. However, abovethese temperatures and during theusual baking operations, our lubricants react with the binders.- and actually contribute to the carbon content of the articles, such as. electrodes, to. provide products of enhanced density, conductivity, etc. The compounds employed by us need not be in pure state and the; comn'iercial crude; forms have. been.

3 found satisfactory for our purposes. Examples of the foregoing compounds which we may employ for the reactive lubricant, although not restricted to the particular compounds named, are as follows:

(a) Nitro-aromatic compounds:

Nitrobenzene m-Dinitrobenzene o-Nitrophenol o-Nitroanisole o-Nitroaniline o-Nitrochlorobenzene m-Nitrochlorobenzene 2,4,dinitrochlorobenzene o-Nitrotoluene Monoand dinitroxylenes o-Nitrodiphenyl a-Nitronaphthalene (b) Chloro-aromatic compounds:

p-Chlorophenol Mono-chloroanilines Monoand poly-chlorodiphenyls a-Chloronaphthalene It is also among the objects of the present invention to utilize the foregoing compounds under conditions which bring into play their lubricating qualities for extrusion of carbon articles in the green state, and which thereafter become reactive with the binder during baking of the green carbon article.

Thus, the temperatures at which the reactive lubricant is combined with the carbonaceous solids-binder mixture should not exceed about 200 C., and preferably should be below about 175 C. in order to avoid premature reaction which may impair the working and lubricating properties thereof in the formation and extrusion of the green carbon bodies.

Since our reactive lubricant is compatible or miscible to a high degree with hydrocarbonaceous binders, the disadvantage of weak bonding between the aggregated carbon-binder granules resulting from the use of the usual oil lubricant is overcome when we employ our reactive lubricant instead of the hitherto conventional oil. The polar nature of our reactive lubricant is of importance for maintaining a high strength lubricating film upon the metal surfaces of the extruder when under extreme pressure.

The conditions under which the reactive lubricant is added to the granular carbon-binder mixture, that is during the brief period described before completion of the mix in any suitable mixing apparatus, prevents it from being materially taken into the binder although miscible therewith and thus there is a sufficiently high proportion of the reactive lubricant in the film upon the granules to provide excellent lubrication during extrusion.

The proportions of reactive lubricant which we employ may be considerably higher than for the usual oil lubricants because it is reactive with the binder during baking to increase the coke residue from the binder. Thus we may add to a carbonaceous extrusion mixture as much as about 10 parts by weight of reactive lubricant per 100 parts by weight of carbonaceous solids therein. The least proportions necessary for good lubrication will be from about 2 parts to about 5 parts by weight of the reactive lubricant. Proportions above 5 parts reactive lubricant are in some cases desirable to improve the baked carbon article as well as to serve for lubricating the extrusion molding of green carbon article.

The example which follows illustrates more clearly the practice of the present invention without intended limitationthereof.

A granular aggregated mix of coke'and hard pitch binder was prepared by mixing 100 parts by weight of pulverized calcined petroleum coke and. 38 parts by weight of the binder at 150 C. in a dough-type mixer for 45 minutes, after which 2 parts by weight of a reactive lubricant, ortho-nitrodiphenyl, was added and the mixing was continued for 10 minutes more to coat the granules of the mix with a lubricating film.

After cooling the completed mixture somewhat, it was easily extruded at C. under a pressure of 2250 pounds per square inch to form cylindrical green carbon rods. These were baked to a temperature of 1000 C. to form amorphous carbon electrodes having an apparent density of 1.54, an electrical resistivity of 0.0018 ohm per cubic inch, a crushing strength of approximately 6,000 pounds per square inch or better, and in which the carbonized residue amounted to 60.3% of the binder plus the reactive lubricant. Moreover, no pieces were found which showed a cor-.

ing or lamination therein. Baked carbon electrodes prepared under the same conditions from a similar carbonaceous mixture employing the usual black oil lubricant contained appreciably less carbon binder-residue, a lower apparent density, a higher resistivity, and many pieces had an inferior strength due to coring or laminations found therein in consequence of which such pieces are usually rejected.

We claim as our invention:

1. A process of forming shaped carbon articles.

which comprises mixing particles of coke with a hydrocarbonaceous binder, adding to the resultant mixture, as a lubricant, a polar aromatic compound potentially reactive with said binder at a temperature above C. to deposit carbon in the article, and miscible in said binder below 175 C., the proportion of said compound being at least 2 parts by weight per 100 parts of coke, mixing the resultant composition at a temperature below 175 C. for a period of time sufiicient to deposit a film of said lubricant on said particles without substantial absorption of said lubricant by the binder, forming the resulting mixture under pressure into a shaped article at a temperature below 175 C. and then heating said article at a temperature above 1'7 5 C.

2. The process of claim 1 wherein the lubricant is a nitroaromatic compound melting below about 100 C. and boiling above about 200 C.

3. The process of claim 1 wherein the lubricant is a chloroaromatic compound melting below about 100 C. and boiling above about 200 C.

4. The process of claim 1 wherein the lubricant is added in proportions of between about 2 and about 10 parts by weight per 100 parts by weight of coke.

5. The process of claim 1 wherein the lubri cant is o-nitrodiphenyl.

6. The process of claim 1 wherein the lubricant is o-nitrotoluene.

7. The process of claim 1 wherein the lubricant is l-chloronaphthalene.

FREDERICK L. SHEA, JR. LESLIE H. JUEL.

(References on following page) REFERENCES CITED Number The folluwing references are of record in the 1,861,415 file of this patent: 2,088,422 UNITED STATES PATENTS 5 17 2,365,055 Number Name Date 1,028,926 Aylesworth June 11, 1912 Name Date Hunter May 31, 1932 Kemmer July 27, 1937 Thrune Jan. 13, 1942 Cole Dec. 12, 1944

Claims (1)

1. A PROCESS OF FORMING SHAPED CARBON ARTICLES WHICH COMPRISES MIXING PARTICLES OF COKE WITH A HYDROCARBONACEIOUS BINDER, ADDING TO THE RESULTANT MIXTURE, AS A LUBRICANT, A POLAR AROMATIC COMPOUND POTENTIALLY REACTIVE WITH SAID BINDER AT A TEMPERATURE ABOVE 175*C. TO DEPOSIT CARBON IN THE ARTICLE, AND MISCIBLE IN SAID BINDER BELOW 175*C., THE PROPORTION OF SAID COMPOUND BEING AT LEAST 2 PARTS BY WEIGHT PER 100 PARTS OF COKE, MIXING THE RESULTANT COMPOSITION AT A TEMPERATURE BELOW 175*C. FOR A PERIOD OF TIME SUFFICIENT TO DEPOSIT A FILM OF SAID LUBRICANT ON SAID PARTICLES WITHOUT SUBSTANTIAL ABSORPTION OF SAID LUBRICANT BY THE BINDER, FORMING THE RESULTING MIXTURE UNDER PRESSUR INTO A SHAPED ARTICLE AT A TEMPERATURE BELOW 175*C. AND THEN HEATING SAID ARTICLE AT A TEMPERATURE ABOVE 175*C.