DE1073368B - Process for the production of graphitized carbon electrodes - Google Patents

Description

Method of Making Graphitized Carbon Electrodes The Invention relates to an improved method of manufacturing for use in electrical Oven -suitable graphitized carbon electrodes made from petroleum coke, which have a relatively contain a large amount of sulfur.

Most technical petroleum cokes contain 19% or more sulfur as an impurity, in the form of complex compounds of carbon and sulfur is present. - These carbon-sulfur compounds are common during normal action of calcining and firing at temperatures of about 1000 to 1300 ° C Links. However, the molded body made of coal is subjected to further heating Subjected to temperatures of 500 ° C and higher, the carbon-sulfur complex compounds decompose with the release of the sulfur they contain. This decomposition of the carbon-sulfur complex compounds however, causes the structure of the molded body to burst or tear. Also can the evaporation of the sulfur contained under certain circumstances a 20 to 250 per cent Increase in volume, based on the original volume of the carbon-containing molded body, cause.

In order to remedy these difficulties, it has already been proposed that the carbon-containing molded body during firing salts or oxides sulfide-forming Metals, e.g. B. of iron, manganese, aluminum or calcium, .Add to the sulfur to bind and im the speed of the sulfur evolution from the existing coal Reduce the object at temperatures of around 1500 ° C and higher. Although this Additives in this regard have a certain effect and through them also that The extent of the volume expansion of the object made of coal is reduced, so their use creates certain further difficulties. One of the main ones Disadvantages of this known method is that after the coal existing object has been graphitized, usually at very high temperatures, such as is carried out above 2000 ° C, certain amounts of the metal remain in the graphitized carbon object and the later removal of the Metal can only be carried out by further heating to temperatures of 3000 ° C and higher which, however, requires high costs and is therefore economically inexpedient is.

If an iron salt or iron oxide is used as a sulfur binder, thus the burned coal article is contaminated with a residue of iron. This However, residue is disadvantageous if the coal object is later graphitized, because iron is a catalyst for the oxidation of graphite. It has now been found that .the above disadvantages eliminated and graphitized from high-sulfur petroleum coke Carbon electrodes can be made when used as sulfur binding and removing agents Salts of the alkali metals of Group I of the Periodic Table can be used, such as for example sodium carbonate or potassium carbonate, of which sodium carbonate is preferred will.

The new process for the production of graphitized carbon electrodes is that of a petroleum coke, which contains 1% or more sulfur as an impurity, and a carbonaceous binder, e.g. B. pitch, existing mixture formed an electrode, the hydrocarbon content of the binder is removed or decomposed by heating to 1000 to 1300 ° C, the then cooled electrode is impregnated with a sodium or potassium carbonate solution in an amount of about 2 parts by weight of carbonate per 100 parts by weight of electrode and the impregnated electrode is graphitized by heating to 2500 to 3000 ° C.

Although it is known that amorphous carbon is converted into the graphitic form can be when a mixture of petroleum coke and sodium carbonate to higher temperatures is heated (U.S. Patent 983,888). The sodium carbonate delivers when heated Sodium oxide, which is then replaced by carbon to form sodium and carbon monoxide reduced, the latter then further reduced and graphitic by the sodium vapors Carbon is deposited. However, it has not yet been recognized that, if the process is carried out according to the invention, the alkali metal salts mentioned also include the sulfur largely removed from preformed electrodes and the aforementioned known disadvantage "Inflation" of the electrodes and the reduction of the electrode density prevented can be.

The aforementioned alkali carbonate additives are made at this temperature easily volatilized and in this way from the object made of coal removed along with a substantial amount of the bound sulfur.

Sodium carbonate also has the advantage over the above-mentioned, previously used sulfur-removing agents that its evaporation temperature is higher in relation to these, which means that it remains associated with the high-sulfur coke for a sufficient time to perform its function as a sulfur-binding and -removing agent to meet. In this way, however, a larger amount of the sulfur contained in the shaped body is bound and the expansion of the shaped body is largely prevented. Furthermore, due to the particular preference of sodium carbonate for sulfur, the thermally unstable sulfur compounds formed above 1500 ° C are retained in the coal, which enables most of the sulfur contained to be removed with the evaporating sodium carbonate at around 1800 ° C. In this way, a graphite product of higher purity is obtained and the usual side effects such as puffing, excessive porosity and low real density are reduced.

In the table below, the advantageous results are given on the basis of an exemplary embodiment, which were obtained by the method improved according to the invention using sodium carbonate as the sulfur binder in a high-sulfur coke with an original sulfur content of 1.65% after heating to 2200 ° C: Volume Real Back Sulfur binder increase density of permanent per 100 g of coke sulfur ° / og / cms ° / o None ......... 20.5 1.83 0.28 2 g sodium carbonate ...... 4.1 2.13 0.27 In the absence of the sulfur binder when the coal was fired, a strongly expanded, fired shaped body was obtained, the increase in volume of which amounted to 20.5% of the original volume of the coal blank. However, if sodium carbonate was used as the sulfur binder, an electrode made of precisely regulated graphite mass of high purity was obtained. The use of the sulfur binders mentioned not only delays the rapid escape of sulfur, but also enables, due to its low evaporation temperature of about 18,000 ° C., that substantial amounts of the sulfur contained are removed together with the vapors. As a result of the action of sodium carbonate both as a sulfur binder and as an anti-swelling agent, electrodes are thus obtained whose volumetric expansion is 4.10 / 0, whose real density is 2.13 g / cms and whose remaining sulfur content is 0.27%, without that in order to: remove the sodium from the graphitized electrodes, expensive high temperature firing is required.

Claims (1)

PATENT CLAIM: Process for the production of graphite carbon electrodes by heating a shaped mixture of a carbonaceous material and an alkali carbonate at graphitization temperature, characterized in that from any petroleum coke containing 10% or more sulfur as an impurity, and a carbonaceous binder, e.g. B. bad luck, an existing mixture Eelectrode shaped, the hydrocarbon content of the binder by heating Removed or decomposed to 1000 to 1300 ° C, the then -cooled electrode with a sodium or potassium carbonate solution in an amount of about 2 parts by weight Carbonate per 100 parts by weight of the electrode impregnates the impregnated electrode is graphitized by heating to 2500 to 3000 ° C. Considered publications: German Patent No. 882 220; U.S. Patent No. 983,888; Q. Kausch, “The Graphit ”(1930), p. 95.