US3704224A

US3704224A - Process for manufacture of improved needle coke from petroleum

Info

Publication number: US3704224A
Application number: US77735A
Authority: US
Inventors: Warner E Scovill; Donald R Day
Original assignee: Standard Oil Co
Current assignee: Standard Oil Co
Priority date: 1970-10-02
Filing date: 1970-10-02
Publication date: 1972-11-28
Anticipated expiration: 1989-11-28
Also published as: BE773354A; GB1316737A; DE2146274A1; IT951931B; CA962619A; LU63988A1; JPS5010602B1; NL7113526A; FR2109847A5

Abstract

AN IMPROVED COKE FOR THE PRODUCTION OF GRAPHITE ELECTRODES IS PRODUCED FROM A PETROLEUM COKING FEEDSTOCK CONTAINING 0.01% BY WEIGHT OR MORE OF SPENT CRACKING CATALYST BY REDUCING THE SPENT CRACKING CATALYST CONTENT OF THE PETROLEUM COKING FEEDSTOCK TO LESS THAN 0.005% BY WEIGHT PRIOR TO THE COKING OF SAID FEEDSTOCK. WHEN A SMALL AMOUNT OF COLLOIDAL GRAPHITE IS ADDED TO THE PETROLEUM COKING STOCK HAVING LESS THAN 0.005% BY WEIGHT OF SPENT CRACKING CATALYST JUST BEFORE IT IS COKED, AN ADDITIONAL IMPROVEMENT IN THE COKE IS OBTAINED.

Description

United States Patent 3,704,224 PROCESS FOR MANUFACTURE OF IMPROVED NEEDLE COKE FROM PETROLEUM Warner E. Scovill, Lakewood, and Donald R. Day, Garfield Heights, Ohio, assignors to The Standard Oil Company, Cleveland, Ohio No Drawing. Filed Oct. 2, 1970, Ser. No. 77,735

Int. Cl. Cg 9/14 US. Cl. 208-131 3 Claims ABSTRACT OF THE DISCLOSURE An improved coke for the production of graphite electrodes is produced from a petroleum coking feedstock containing 0.01% by Weight or more of spent cracking catalyst by reducing the spent cracking catalyst content of the petroleum coking feedstock to less than 0.005% by weight prior to the coking of said feedstock. When a small amount of colloidal graphite is added to the petroleum coking stock having less than 0.005% by weight of spent cracking catalyst just before it is coked, an additional improvement in the coke is obtained.

The present invention relates to a process for the manufacture of improved needle coke and more particularly pertains to a process for preparing a petroleum coking feedstock which produces a superior coke for the production of graphite electrodes and the like.

Coke is produced from petroleum by well known methods and certain of this coke has been referred to as needle coke (see US. Pat. No. 2,775,549, for instance). Needle coke is particularly suited for use in the manufacture of graphite electrodes. Needle coke is produced generally by a procedure known as delayed coking. The quality of needle coke for the manufacture of metallurgical electrodes is conventionally determined by measuring the properties of the finished graphite electrode. Properties such as flexural strength, coefficient of thermal expansion, and electrical resistivity are of importance, although the property most critical and usually measured to determine the quality of the needle coke is the coefficient of thermal expansion (CTE).

It is generally accepted by those skilled in the art that preferred feedstocks for the manufacture of needle coke are highly aromatic in character and include such stocks as slurry and decanted oils from catalytic cracking and tars from thermal cracking. The stocks derived from catalytic cracking inherently contain varying amounts of spent catalyst fines. The spent catalyst fines, while mainly inorganic, have an amorphous carbon surface. Thermal tars can also contain spent catalyst fines when such stocks as slurry and decanted oils are used as feed to the thermal cracker. We have discovered that the presence of fine particulate spent catalyst in coker feed exerts a deleterious effect on needle coke structure which is reflected in poor CTE in graphite electrodes produced therefrom.

It is an object of this invention to provide an improved quality coke from a coker feedstock from the catalytic cracking process by removing most of the fine spent catalyst particles suspended in the coker feedstock by suitable means such as centrifuging, filtering, and the like. It is another object of this invention to recycle the spent catalyst fines removed from the coker feedstock to the cracking catalyst regenerator and back into the cracking system. It is another object of this invention to further improve the quality of needle coke by seeding the coker feedstock, which is essentially free of fine particulate matter, with a material of proper structure such as finely divided colloidal graphite particles. It is believed that the inclusion of a large number of finely divided graphite particles (usually less than one micron in size) into the coker feedstock just prior to coking promotes the formation of needle coke having a more ordered structure which ultimately will produce a graphite electrode having improved CTE and other desirable properties.

A typical catalytic cracking process is more completely disclosed in US. Pat. No. 3,129,107 and in Petroleum Refiner, September 1966, page 187. The feedstock preferred for the production of needle coke and ultimately graphite electrodes is called clarified slurry in the Petroleum Refiner article referred to above, and this material is also known to those skilled in the art as decanted oil or clarified oil. Decanted oil is produced from the top of the slurry settler and in most instances contains in the range of 0.01 to 1% by weight of spent cracking catalysts (such as silica-alumina) fines (typical 2-50 micron size range) suspended therein. We have found that decanted oil containing spent catalyst fines in this range produces a coke and ultimately a graphite electrode which is inferior to the coke and graphite electrodes produced by a decanted oil containing less than 0.01% by weight of spent catalyst fines. In accordance with our process, we remove spent catalyst fines from such a decanted oil by centrifugation or filtration of the oil so as to reduce the spent catalyst fines level in the decanted oil to be used as coker feedstock to a level about 0.005 by weight. In accordance with our process, the coke and graphite electrodes produced therefrom are of superior quality.

Our process includes the delayed coking of the decanted oil containing less than 0.005 by weight of spent catalyst fines. Delayed coking is more fully describedd in Petroleum Refiner, September, 1966, page 191. In our process, the decanted oil containing less than 0.005 by weight of spent catalyst fines is heated and charged to the lower portion of a fractionator. Here the charge meets the hot vapors from the coking drum and light components are flashed off. The heavy residue passes from the bottom of the fractionator to a furnace Where it acquires the heat of cracking. Then the heated residue is introduced into an insulated drum Where the residence time is suflicient for coke to form and settle from the mixture. The vapors from the coking drum return to the fractionator. Here the gas, gasoline, and gas oil are separated and leave the unit. The heavier materials appear in the bottom of the fractionator and are recycled to the coking operation. When coke builds up to a predetermined level in one of the coking drums, fiow is diverted to another drum so that the furnace operation is continuous. Thus, drums are operated in pairs with one on-stream while the other is being decoked. A full coke drum is removed from the process flow, steamed to strip light hydrocarbons from the coke, and cooled by water injection. More recent designs use high pressure (over 1000 p.s.i.g.) water jets to cut the coke from the drum. When graphite seeding is used according to our invention, the fine colloidal graphite particles are added to the oil as it passes from the furnace to the coke drum in the delayed coking process. It is preferred to add from about 0.2 to 20.0 parts per million by weight of graphite to the oil at this stage. In accordance with our process, the needle coke from the delayed coking process is calcined at about 1300 C. using known procedures to devolatilize, dehydrogenate, and densify the coke. For more details concerning the calcination of petroleum coke, see Petroleum Products Handbook, Sec tion 14 on Petroleum Coke, by S. W. Martin, page 14-1.

The calcined needle coke produced by our process usually is used in the production of graphite electrodes by procedures well known to those skilled in the art. One description of such a process appears in Industrial and Engineering Chemistry, January, 1954, pages 2-11, and particularly page 9. In this process, calcined petroleum needle coke and coal tar pitch are mixed together and the mixture is extruded in the shape of the desired electrode. The extruded shape is baked in an oven (about 950 C.) and passed into a graphitizer, which is an electric furnace 'which operates at about 2800 C. Graphitizing is a treatment which converts the relatively hard coke into graphite. The electrodes are removed from the graphitizing furnace and are machined to their final dimensions.

The coefiicient of thermal expansion (CTE) for the finished graphite electrodes is determined by a procedure described in a publication of the US. Department of Commerce entitled Research and Development on Advanced Graphite Materials, volume XXXVI, August 1964, produced by the Air Force Materials Laboratory, Research and Technology Division, Air Force Systems Command, Wright-Patterson Air Force Base, Ohio, at page 20. The CT E is determined by measuring the linear expansion of the graphite electrode when the temperature is raised from 30 to 100 C. The measurement is made parallel to the direction of preferred orientation (with the grain of the extruded electrode) and parallel to the molding direction. The difference in expansion between the electrode and an Invar standard is measured by means of an optical lever. The CTE is expressed in inches per inch per degree centigrade X The lower values for CTE are most desirable and represent the best graphite electrodes. In high-temperature operations such as the electrothermic furnace, increases in temperature cause significant dimensional changes of structural shapes and create serious stresses. The stresses can be of such magnitude as to cause spalling or even gross failure of the structural shape. Thus, in hightemperature applications, a graphite electrode that exhibits little or no change in dimensions with temperature variations (low CTE) has greater durability. Typical CTE values for graphite produced from regular-grade coke are 12-20 inches/inch/ C. 10- (US. Pat. No. 3,451,921). Typical CTE values for graphite produced from conventional needle coke are 6.0 inches/inch/ C. 10-' (US. Pat. No. 3,451,921) and 0.51 inches/inch/ C. 10 (US. Pat. No. 2,922,755).

The spent catalyst content of a given decanted oil sample is determined by a gravimetric Millipore procedure in which a one-pint sample of the decanted oil is weighed, diluted with two volumes of toluene, and filtered through a 1.2 micron Millipore filter. The Millipore filter is weighed, the filter apparatus is set up, and the toluene solution is filtered. The filter is dried and weighed and this weight is noted as insoluble residue for the total sample. The filter is then placed in a crucible and is ashed with a flame and placed in an oven at 750 C. for an hour. The crucible is cooled and weighed. The insoluble residue and ash (spent catalyst content) for the total sample are reported.

The process of our invention will be now fully described in the following illustrative examples in which the amounts of ingredients are expressed as part by weight unless otherwise indicated.

EXAMPLE 1 (A) A conventional needle coke was prepared by a process which is outside the scope of the present invention but will serve as a control experiment to illustrate the prior art. A decanted oil from a catalytic cracking operation was used which contained 0.0l50% by Weight of spent cracking catalyst solids. This decanted oil sample was coked, the coke was calcined and converted to a graphite electrode, and the electrode was found to have a CTE of 3.1 inches/inch/ C. 10-

(B) The procedure of A was repeated except that before coking the decanted oil was centrifuged to remove the spent cracking catalyst solids, and the decanted oil after centrifugation was found to contain 0.0023% by weight of spent catalyst solids. The spent cracking catalyst solids were recycled to the regeneration zone of the catalytic cracker process to be regenerated and reused in the cracking process. This decanted oil was coked and the coke was calcined and converted to a graphite electrode which was found to have a CTE of 2.7 inches/inch" C. 10- an improvement of 13% over the conventional needle coke.

EXAMPLE 2 (A) The procedure of Example 1(A) was repeated with the exception that in the delayed coking process 2.0 parts per million of fine particulate colloidal graphite having an average particle size of less than one micron were added to the oil just before it entered the coking drum. The resulting coke was calcined and converted to graphite electrodes which were found to have a CTE of 3.4 inches/inch/ C. 10-

(B) The procedure of Example 1(B) was repeated except that the centrifuged decanted oil contained 0.0015% by weight of spent catalyst and in the delayed coking process 2.0 parts per million of fine particulate colloidal graphite were added to the oil just before it entered the coking drum. The resulting coke was calcined and converted to graphite electrodes which were found to have a CTE of 1.7 inches/inch/ C. 10- an im provement of 45% over the conventional needle coke.

(C) The procedure of Example 1(B) was repeated except that the centrifuged decanted oil contained 0.003% by weight of spent catalyst and in the delayed coking process 0.2 part per million of fine particulate colloidal graphite were added to the oil just before it entered the coking drum. The resulting coke was calcined and converted to graphite electrodes which were found to have a CTE of 2.7 inches/inch/ C. 10", an improvement of 13% over the conventional needle coke.

(D) The procedure of Example 1(B) was repeated except that the centrifuged decanted oil contained 0.0028% by weight of spent catalyst and in the delayed coking process 20.0 parts per million of fine particulate colloidal graphite were added to the oil just before it entered the coking drum. The resulting coke was calcined and converted to graphite electrodes which were found to have a CTE of 1.9 inches/inch/ C. 10-", an improvement of 39% over the conventional needle coke.

We claim:

1. A process for preparing a superior coke for graphite electrodes from a coker feedstock of a highly aromatic character being selected from the group consisting of slurry and decanted oils from catalytic cracking and tars from thermal cracking containing from 0.01 to 1% by weight of solid spent catalyst comprising removing by centrifugation or filtration of the feedstock enough of said solid spent catalyst to produce a coker feed product containing no more than 0.005% by weight of solid spent catalyst, seeding the coker feed product with from about 0.2 to 20.0 parts per million by weight of fine particulate graphite and then coking the coker feed product by delayed coking.

2. The process of claim 1 wherein the catalyst is a cracking catalyst.

3. A process for preparing a superior coke for the production of graphite electrodes comprising adding from about 0.2 to 20.0 parts per million by Weight of colloidal graphite to a coker feedstock of a highly aromatic character being selected from the group consisting of slurry and decanted oils from catalytic cracking and tars from thermal cracking containing less than 0.005% by Weight of suspended solid material just prior to the delayed coking operation.

References Cited UNITED STATES PATENTS 2,775,549 12/1956 Shea 20850 5 3,326,796 6/1967 Muller 208-46 3,379,638 4/1968 Bloomer 208-131 3,365,384 1/1968 Pasternack 208106 T OBIAS E. LEVOW, Primary Examiner 10 A. P. DEMERS, Assistant Examiner U.S. C1. X.R.