Characteristics of Petroleum Cokes Suitable for Manufacturing of

4 Characteristics of Petroleum Cokes Suitable for Manufacturing of Carbon Black WILLIAM W. GOTSHALL

Downloaded by GEORGETOWN UNIV on August 23, 2015 | http://pubs.acs.org Publication Date: June 1, 1976 | doi: 10.1021/bk-1976-0021.ch004

Carbon Development Corp., 2891 Haggerty Rd., Walled Lake, Mich. 48088

In 1964, Marathon O i l Company embarked on a research program to increase the markets f o r , and value of, petroleum coke. At that time, Marathon O i l Company had two cokers operating in their domestic refineries. One was a delayed coker operating with a relatively low sulfur feedstock at their Robinson, I l l i n o i s refinery, and a f l u i d coker operating on a high sulfur Wyoming residuum at their Detroit, Michigan refinery. Marketability of the Robinson coke has always been quite strong because of its quality and also i t s low sulfur content. On the other hand, those from the f l u i d coker i n Detroit suffered because of low prices and limited markets because ofitsanalysis: Figure I Typical Analysis - Detroit Fluid Coke Fixed Carbon 87.30% Sulfur 5.64 % v o l a t i l e matter 7.00 Ash 0.06 100.00%

Analysis of volatiles Oxygen 4.00% Hydrogen 1 . 5 0 % Methane 1.50% 7.00% Fluid coke has several characteristics which make it quite undesirable for most petroleum coke markets. These characterist i c s are; sulfur content, low v o l a t i l i t y , poor crystalline structure, and low grindability index. The sulfur content of most f l u i d cokes w i l l vary anywhere from five to eight percent, which obviously makes it rather undesirable for fuel uses and also for metallurgical use. Most f l u i d cokers were installed i n refineries operating on high sulfur feedstocks because of the lower capital investment required for the same throughput with a f l u i d coker versus delayed coker and the fact that it i s a continuous process rather than batch. Because of the savings i n capital and lower operating costs, and

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1155 16th St. N. W. Washington, D.InC.Petroleum 20036Derived Carbons; Deviney, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1976.


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also because the cokes would normally be quite undesirable due to sulfur content, many refiners chose f l u i d coking. The v o l a t i l e content of f l u i d coke i s extremely low because the material has been p a r t i a l l y calcined i n the burner portion of the process where temperatures usually vary between 1125° and 1175° F. Because of t h i s , the v o l a t i l e combustible matter i s only about 3%. I f f l u i d coke i s used as a f u e l , a minimum of 10% of other fuels must be used to sustain combustion since the v o l a t i l e content i s so low combustion cannot be maintained by burning f l u i d coke alone. The crystalline structure of f l u i d coke i s considerably d i f ferent than that of delayed coke because of the nature of the coke formation i n the process. Delayed coke formed i n the coke drum has time for the coke crystals to orient themselves upon one another so that a much more uniform c r y s t a l l i n i t y can be obtained which improves i t s characteristics for most electrode uses. Fluid coke i s formed by spraying residuum on a hot particle of coke. The residuum i s formed almost immediately into coke with complete d i s orientation with the c r y s t a l l i t e s i n the hot coke p a r t i c l e . Be cause of this disorientation of the crystalline structure, grain density maximums for f l u i d petroleum coke upon calcining are i n the range of 1.9 to 2.0 grams per cc, whereas delayed cokes can be calcined to reach grain densities as high as 2.1 grams per cc. Be cause of this crystalline disorientation, the e l e c t r i c a l conduc t i v i t y of f l u i d coke i s considerably less than that of delayed coke. Another problem which limits the marketability of f l u i d coke i s i t s extreme hardness and low grindability index. A soft, f r i able bituminous coal has a grindability index of 100 and Pennsyl vania anthracites w i l l vary from 30 to ho on the Hardgrove scale. Delayed petroleum coke w i l l also have a grindability index approx imating 100, whereas f l u i d petroleum coke normally i s i n the range of 20 to 30. Because of this extremely low grindability index, i t cannot be co-ground with most coals because of separation problems i n the pulverizer, and because other fuels are required to sustain combustion. One of the areas of research to upgrade f l u i d petroleum coke was i t β use to manufacture a rubber f i l l e r . I t was f e l t that i t was desirable for this non-fuel use because of i t s high fixed car bon content, low ash content, and the fact that the sulfur was t i e d up i n carbon-to-sulfur-to-carbon bonds which would render the sulfur inactive i n rubber compounding. The carbon black mar ket was also attractive because of i t s size. Carbon black i s the seventh largest dollar volume chemical sold i n the United States. The world-wide market approaches 7 b i l l i o n pounds per year, which could very easily use the l80 tons per day of f l u i d coke manufac tured i n Marathon's Detroit refinery. It was I n i t i a l l y f e l t that particle size was the principal c r i t e r i a . Methods of pulverizing were investigated, resulting i n the selection of a Majac Fluid Energy M i l l . I n i t i a l samples, how ever, showed an anomaly i n that the finer particles did not im-

In Petroleum Derived Carbons; Deviney, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1976.


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prove the reinforcing qualities of the f i l l e r and i n some cases actually decreased i t . These samples were produced using a i r as the pulverizing f l u i d . It vas suggested that i n pulverizing, carbon crystals vere being broken, exposing free radicals which reacted immediately v i t h oxygen i n the a i r , eliminating the surface a c t i v i t y essential for rubber reinforcement. It was decided to pulverize the material i n steam, [a non-oxidizing f l u i d at the temperature used], and subsequently protecting the surfaces exposed u n t i l the ground carbon could be compounded into rubber. The coating which we used was an o i l having a high solvency i n rubber so that the active surfaces were exposed after mixing with the rubber to allow the chemical a c t i v i t y on the surface to perform similarly to the reinforcing properties o f carbon black. The ground carbons produced exhibited properties which were not easily categorized with existing blacks, which i s not surprising, being made from an entirely different approach and also containing a spectrum of particle sizes rather than the narrow particle size range of most carbon blacks, however, the product produced from raw f l u i d coke shows that i t i s s l i g h t l y more reinforcing than thermal black and less reinforcing than semi-reinforcing furnace black as the following test i n Styrene-Butadlene Rubber indicates: Figure II Test Formulation SBR 1502 100.00 Zinc oxide 5.00 Stearic acid 2.00 Sulfur 1.75 Santocure 1.30 Ground carbon S 65 parts* m ê 75 parts» 307° F cure 300% TenTear Hard-creep sile Elong Set Mod 2Ϊ5Γ 720 650 53-U2 58~ 15' 150 I8l0 UU0 62-59 1U90 GC 30» 9 138 I85O 330 50· 66-63 k nko 288 51-UU k2 320 950 1390 15 165 61-59 8 Uoo 1000 1U90 30 12U 61-58 10 U50 I67O 1110 50· * Equal volume loading - compounded stock SpGr = 1.150 for GC vs. 1.230 for MT. Therefore, equivalent volumes equal 152 for GC vs. lU8 f o r MT f

MT

f

Subsequent work covered other sources of carbonaceous mate r i a l such as coal, both anthracite and bituminous, coke made from coal, coal char, and char from carbonization o f rubber products. Among the technology are several patents covering alteration of the surface chemistry of the ground particles which allow a f l e x i b i l i t y to manufacture several grades of reinforcing f i l l e r s



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using the same basic rav materials. Some of this work w i l l be shown so that this control of the surface chemistry w i l l become apparent. There are two methods of achieving this control. One i s by changing the crystalline structure of the carbon before pulverization, the other i s the alteration of the surface after grinding. Carbon has three basic structures, amorphous, graphite and diamond. The amorphous carbon can be converted to synthetic graphite by a time-temperature relationship. This allows the growth of c r y s t a l l i t e s on each plane, an ordering of these c r y s t a l l i t e s , and a reduction of the inter-planar spacing. Raw petroleum coke can have a specific gravity as low as l.U and can be calcined to a specific gravity of 2.1. Ground carbons made from primarily amorphous carbons have much lower reinforcing a b i l i t i e s i n rubber than the same carbon after calcining. An example of the differences achieved by this pretreatment of the carbon follows: Figure III Test Formula Natural rubber 100.00 Stearic acid 3.00 Zinc oxide 3.00 Benzothiazyl sulphide 0.60 Sulfur 2.50 Black as noted 300* Mod Tensile Elong Set SpGr Raw f l u i d coke 65 phr 30 cure 1330 I85O 390 l6 l.ll6 Calcined f l u i d coke 80 phr 30 cure 1950 2100 330 12 1.216 [It should be noted that the specific gravity of raw f l u i d coke i s 1.5 while calcined i s 1.9 which explains the weight difference i n loading. The two compounds y i e l d the same volume based upon compounded stock specific gravity.] These two blacks were made with the same basic raw material, except that the second was calcined at 2300° F for 1/2 hour, while the f i r s t had reached a maximum temperature of 1150° F i n the coking process. Alteration of the surfaces of the ground carbons after grinding can be obtained by oxidizing the surfaces of the carbon which reduces reinforcement and lengthens vulcanization time. To reduce and stabilize vulcanization time, the addition of small amounts of methanol to the surface and the subsequent evaporation of the methanol results i n constant cure times. Because of the abundance of active sites on the surface of the ground carbons, i t i s amenable to various other surface treatments. Marathon O i l Company shut down their f l u i d coker i n 1970, and f

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f e l t that this technology was too far a f i e l d from their a c t i v i t i e s to continue t h e i r development. Carbon Development Corporation was formed i n 1971 and licensed the world-wide rights to this technology. In summation, the following characteristics of the carbonaceous raw materials required for manufacture of carbon black substitutes from our technology are as follows: 1. Ash content - Obviously the higher the ash content, the lower fixed carbon content which w i l l be available on the surfaces of the finished product, resulting i n less reinforcement. 2. CrvBtalllnlty - The more crystalline the carbon feedstock, the higher i t s reinforcing characteristics. This c r y s t a l l i n i t y can be increased by high temperature treatment such as calcining. 3. Volatile combustible matter - The higher the v o l a t i l e combustible matter i n the raw material the more staining the resultant carbon black i s . One of the features of carbon blacks made from f l u i d petroleum coke, calcined petroleum coke, or metallurgical coke breeze i s the extreme non-staining characteristic of the resulting carbon black. This test i s made by extracting the o i l s from the surface of carbon black with either benzene or toluene and measuring the percent of discoloration of the solvent. This i s important for uses i n t i r e products, especially white wall t i r e s . k. Price and a v a i l a b i l i t y - Although yields from the raw material used i n these processes approximate 100% price of the raw material i s important. Therefore, relatively undesirable materials, such as f l u i d petroleum coke are particularly advantageous, not because of their characteristics, but s t r i c t l y because of price and a v a i l a b i l i t y . f


Characteristics of Petroleum Cokes Suitable for Manufacturing of

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