Petroleum Derived Carbons - ACS Publications

7 Active Carbon Can So Be Made Out of Petroleum HENRY C. MESSMAN

Downloaded by UNIV LAVAL on July 11, 2016 | http://pubs.acs.org Publication Date: June 1, 1976 | doi: 10.1021/bk-1976-0021.ch007

Box 267, Mamaroneck, N.Y. 10543

In the e a r l y pages of the 1951 e d i t i o n of an a u t h o r i t a t i v e text ( 1 ) , there appears the clause, "----whereas coke, formed from hydrocarbons, r e s i s t s most known methods of a c t i v a t i o n . " This i s still gene r a l l y true, although on occasion it has been rather too broadly interpreted as meaning that a c t i v e carbon can not be derived from petroleum. Pyrolyses of heavy hydrocarbons, that have not first been mixed with or reacted with other materials, do indeed y i e l d coke residues that are quite r e f r a c t o r y with respect to the s e l e c t i v e oxidation that we call a c t i v a t i o n . For practical purposes, it is virtually impossible to make usefully active carbon out of delayed coker or fluid coker petroleum coke a f t e r it has been calcined to 1000° C. Much the same i s true of coal coke, i n c i d e n t a l l y . Terminology employed i n the activated carbon industry can be confusing and some clarification is in order: 'Active' and 'activated' are commonly used interchangeably to describe u s e f u l l y adsorptive carbon. The term, 'reactive', however, r e t a i n s its conventional chemical meaning? so that 'regeneration' i s employed to i n d i c a t e renovation of spent a c t i v e carbon. 'Char' s i g n i f i e s a carbonaceous residue from p y r o l y s i s of s o l i d organic matter, whereas 'coke' r e f e r s to a corresponding residue from p y r o l y s i s of f l u i d organic matter. I n c i d e n t a l l y , 'coke' made from coal i s consistent with t h i s usage, because coking coal passes through a p l a s t i c ( f l u i d ) temperature range before i t begins to carbonize. P y r o l y s i s of non-coking c o a l y i e l d s coal char. Ordinary wood charcoal e x h i b i t s appreciable adsorptive capacity, which was recognized during B i b l i c a l times. The f i r s t modern a c t i v e carbon was bone char, developed f o r sugar processing at Napoleon's behest. It s t i l l i s employed to some extent by the cane sugar 77

Deviney and O'Grady; Petroleum Derived Carbons ACS Symposium Series; American Chemical Society: Washington, DC, 1976.

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industry, even though i t t y p i c a l l y assays ±0% or less carbon and has a BET-nitrogen (2) pore surface area of only about 100 square meters per gram. For comparison, many commercial activated carbons on the market today have corresponding pore surface areas of 1000 or more s q meters/gram. The development of a c t i v e carbon was given great impetus by the Introduction of chemical warfare i n War I. E f f e c t i v e gas masks had to be provided f o r troops at the f r o n t , and adsorptlve carbons had to be developed f o r t h e i r cannlsters. With respect to the a r t of making and using a c t i v e carbon, the f i r s t r u l e i s that there are nearly always at l e a s t a few exceptions to every pertinent r u l e * For t h i s reason, most statements i n t h i s paper must be more or less q u a l i f i e d . One such r u l e i s that chars are more amenable to a c t i v a t i o n than cokes, Chars u s u a l l y are somewhat porous at the outset, because i n shrunken form they tend to r e t a i n the general s t r u c ture pattern of t h e i r parent raw material, whereas most cokes e x h i b i t r e l a t i v e l y few small pores. And chars are commonly more r e a c t i v e than cokes; so that they may be oxidized more r e a d i l y . In commercial production of a c t i v e carbon, no two manufacturers employ the same process or even the same raw material, with a few exceptions. And a l l manufacturers guard t h e i r process d e t a i l s as proprietary secrets. This accounts f o r the aura of mystery or b l a c k magic that characterizes a c t i v e carbon production technology, as well as f o r the dearth of useful process know-how to be found i n the literature. I f there i s such a thing as a conventional approach to making a new a c t i v e carbon, perhaps i t i s depicted by Don W. Green et a l i n t h e i r work (3) at the University of Kansas during 1970, These men experimentally attempted to make granular a c t i v e carbon out of green Mid-Continent delayed petroleum coke with various combinations of chemical treatment and steam a c t i v a t i o n at around 1550°F (843°C), At r e l a t i v e l y high burn-off rates they were able to approach commercial q u a l i t y . The p r i n c i p a l reason f o r c i t i n g t h i s reference, however, i s to i l l u s t r a t e the d i f f i c u l t y of acquiring background f o r R. & D, i n the a c t i v e carbon f i e l d . I t s authors were doubtless well-trained and conscientious; so we may assume that they started with a competent search of conventional l i t e r a t u r e . Yet many of t h e i r observations would be judged quite amateurish by t e c h n i c a l personnal experienced i n the p r a c t i c a l production and u t i l i z a t i o n


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of a c t i v e carbon. For one example, they state that, "Materials that contain mineral ingredients (e.g. bones) are i d e a l f o r making d e c o l o r i z i n g carbons." From t h i s , a reader may conclude that bone char i s a popular and e f f i c i e n t d e c o l o r i z i n g carbon, which i s not the case. The f a c t that some bone char continues to be employed by the cane sugar industry, i s not due to i t s d e c o l o r i z i n g capacity* Another example i s the statement that, "A q u a l i t y of the micropore structure (100 angstroms or l e s s ) i s shown by the iodine t e s t and the macropore structure of the carbon (iOO angstroms or larger) i s indicated from the molasses t e s t . " A c t u a l l y , substantial molasses color can be adsorbed In micropores between 28 A and 100 A. And with respect to d e f i n i t i o n , one reputable U.S. manuf a c t u r e r has published: "Micropores may be a r b i t r a r i l y defined as pores whose diameters ranee from 10 to 1000 (4) On the other hand, Dubinin (5) c l a s s i f i e s MICROPORES as those having e f f e c t i v e r a d i i l e s s than 18 - 20 A, TRANSITIONAL pores as larger up to about 500 - 1000 A and MACROPORES as having e f f e c t i v e r a d i i greater than about 500 - 1000 A In support of Don Green and h i s associates, however, o l d references often suggested 100 A as the e f f e c t i v e radius d i s t i n g u i s h i n g micro-» from macropores. This comment i s intended s o l e l y to i n d i c a t e d i f f i c u l t i e s inherent i n the f i e l d of research on which these authors reported and i t i s i n no way any r e f l e c t i o n on t h e i r a b i l i t y or i n t e g r i t y . Delayed coker coke i s u s u a l l y less r e a c t i v e than most char, while f l u i d coker coke tends to be even less r e a c t i v e than delayed coke. S t i l l , i t i s possible to make a c t i v e carbon out of green f l u i d coker coke. This was observed i n the course of developing a method f o r d e s u l f u r i z i n g coke (6) Impregnated with an a l k a l i metal compound, by steam f l u i d l z a t i o n at around 1400°F (760°C) The p o s s i b i l i t y was not pursued because i t appeared at the time that materials of construction were not a v a i l a b l e to withstand commercial process conditions. Cast alumina r e f r a c t o r i e s being offered today, however, may contain the reaction s a t i s f a c t o r i l y * Accordingly i t would appear that an on-40-mesh f r a c t i o n of high s u l f u r f l u i d coker coke might warrant a new look as a possible raw material f o r spheroidal granular a c t i v e carbon production. Perhaps t h i s i s not s u r p r i s i n g because, grossly i n i t s onion-layered spheroidal form, f l u i d coke tends to be more i s o t r o p i c than delayed coke. Figures 1, and 2 , are electron microphotographs ( r e p l i c a technique) of f l u i d coker coke p a r t i c l e s before and a f t e r such treatment. I f one assumes that inner layers of the coke i n F i g . 2 , are #

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etched i n much the same manner as i t s e x t e r i o r surface, the p o t e n t i a l f o r development of useful pore surface area i s apparent. I t i s a l s o noteworthy that a by-product of t h i s method showed promise as an a c t i v e carbon i n powder form: Following d e s u l f u r i z a t i o n , the a l k a l i z e d , steam treated coke was leached with water to remove a l k a l i metal compounds. When the (dark green a l k a l i - m e t a l organic) washings were evaporated to dryness and the s o l i d reldue was pyrolized to around 1600°F (87i°C), i t could be cooled and washed to y i e l d a remarkably a c t i v e carbon powder. Indeed i t was found that simple leaching of raw f l u i d coke with hot caustic soda (or potash) r e s u l t e d i n greater y i e l d of a s i m i l a r residue. As an example of current commercial production based on petroleum, one U.S. manufacturer (7) makes about 5,000,000 annual pounds (8) of durable, regenerable, spheroidal a c t i v e carbon out of ( s u l f u r i c ) a c i d sludge r e s u l t i n g from the r e f i n i n g of white mineral o i l . While i t s process i s proprietary, we may specul a t e that i t i s something about as follows: Acid sludge preheated to around 500°F (260°C) i s continuously mixed with hot, previously coked p a r t i c l e s . The hot coke p a r t i c l e s become coated with sludge, which i s simultaneously desulfurlzed. The coated p a r t i c l e s recycle to a coking zone operating a t some 1000°F(538°C), from whence the make i s continuously e l u t r i a t e d to subsequent conventional gas a c t i v a t i o n , which l i k e l y employs more or less steam a t a temperature on the order of 1500 F(8i6°C), depending on the type of carbon being produced. Another U.S. manufacturer (9) i s known to have employed a c i d sludge as one of i T s raw materials and probably makes a substantial p o r t i o n of i t s gas phase, granular carbon i n a somewhat s i m i l a r manner. Therefore, i n t h i s country we presently have commercial production of at l e a s t one, and probably of two, active carbons derived from petroleum. Perhaps i t i s s i g n i f icant that both are granular. As a r u l e , a c t i v e carbon powder i s easier to make than granular form. Accordingly, granular material t y p i c a l l y commands two or three times the unit-weight p r i c e of corresponding material i n powder form. The c o r o l l a r y question i s , why not mix powder with a c a r bonizable binder, compact the mix and p y r o l l z e the compacts to make granular a c t i v e carbon? Hundreds of attempts to implement t h i s l o g i c a l approach have been unsuccessful. The problem appears to be twofold: Binders tend to block the pores of f i l l e r carbons. And cokes r e s u l t i n g from p y r o l y s i s of binders are u s u a l l y o


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less reactive than f i l l e r carbons; so that subsequent a c t i v a t i o n ( s e l e c t i v e oxidation) of product granules tends to burn the f i l l e r carbon p r e f e r e n t i a l l y . At l e a s t one European manufacturer (10) has an exception (it) I t has developed a p r o c e s s T h a t employs hardwood t a r f o r binding p a r t i c u l a t e hardwood or charcoal powder to make granular a c t i v e carbon. Some of your colleagues i n the petroleum Industry appear to have made an important contribution by employing acid sludge as a binder. In t h e i r case, the sludge i s not a by-product* Rather, i t Is t a i l o r e d to i t s purpose by a c i d treatment of a selected r e f i n e r y stream. Coal char, wood charcoal, acid sludge coke or some s i m i l a r material, preferably sized to pass through 100 mesh or f i n e r , i s mixed with the sludge* Even powdered a c t i v e carbon may be the f i l l e r carbon* Some uncarbonized bituminous coals are also suitable* Proper formulation and mixing uniquely permit format i o n of rounded granules i n the mixer* The r e s u l t i n g grains are strong enough to withstand screening, handl i n g and p y r o l y s i s . Bonding of the sludge to the f i l l e r material survives carbonization, which converts the sludge to a hard, strong, porous carbon matrix that does not b l i n d pores of the f i l l e r carbon to any serious extent* F i n a l l y , the product Is gas-activated by conventional means to develop pore s i z e d i s t r i b u tions s u i t a b l e f o r gas phase or f o r l i q u i d phase a p p l i c a t i o n s , as desired* This process has been patented, p i l o t e d and made a v a i l a b l e f o r l i c e n s e (12) by a leading U.S. o i l company (13)* A Japanese process that has been under development f o r several years, i s c u r r e n t l y emerging (14)· It i s reported to make high q u a l i t y , a c t i v e , petroleum p i t c h carbon i n spherical grain form and may be b r i e f l y described about as follows: 1. Pitch i s melted and mixed with a 'modifier i n a heated mixer. 2. The molten mixture i s dispersed i n hot water, where i t forms i n t o discrete s p h e r i c a l grains under cont r o l l e d temperature and pressure (probably with some sort of mechanical a g i t a t i o n ) . 3. Water i s drained o f f and the grains are dried* 4* The thermoplastic grains are thermoset by oxidative heat treatment. 5. The thermoset grains are then carbonized, probably to about 900° C. 6. F i n a l l y , the carbonized grains are more or less conventionally gas-activated to develop required pore size d i s t r i b u t i o n . (Steps 5, and 6, probably can be combined i n one u n i t , perhaps a multiple 0


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hearth furnace.) We may speculate that the 'modifier i s a f i l l e r , possibly -100 mesh low-rank coal char or wood charcoal i n a weight proportion at least equal to the p i t c h . Or i t could be a cheap carbonizable material such as f i n e sawdust or pulverized coal that co-carbonizes with the p i t c h . And i t i s l i k e l y that high-sulfur p i t c h , not suitable f o r binder p i t c h or f o r electrode q u a l i t y coke production, may be employed because considerable d e s u l f u r i z a t i o n doubtless occurs during a c t i v a t i o n with steam; so that r e s i d u a l s u l f u r i n the a c t i v e carbon product i s t i g h t l y bound and t o l e r a b l e . Each of the many activated carbons on the market, has properties d i s t i n g u i s h i n g i t from others that are made from d i f f e r e n t raw materials and/or by d i f f e r e n t process patterns. Most such carbons r e a d i l y oxidize at moderately elevated temperature, e s p e c i a l l y i n the presence of i n c i d e n t a l c a t a l y s t s , lead compounds f o r example. One d i s t i n g u i s h i n g feature of a c t i v e carbons derived from petroleum, i s that they generally tend to be somewhat more temperature r e s i s t a n t with respect to oxidation, than corresponding carbons based on other raw materials. This can be an important advantage i n some applications* I f a c t i v e carbon technology i s a b i t confusing, researching I t s market i s scarcely less so. A h o r r i b l e example appeared nearly three years ago, when a feature a r t i c l e i n a reputable p u b l i c a t i o n (15) quoted a presumably competent authority as s t a t i n g : "Present consumption f o r a c t i v a t e d carbon made from petroleum coke i s approximately 250 tons/day. But there i s a great p o t e n t i a l f o r increase i n t h i s market by 1975,— ·" Considering v o l a t i l e loss and burn-off, t h i s implied a new and growing market f o r some 500 tons green coke per day. Worse s t i l l , some readers jumped to the conclusion that s u b s t a n t i a l l y a l l of the a c t i v e carbon produced i n the U.S. during 1971, must have been made out of petroleum coke, because 250 tons/day i s equivalent to about 180 m i l l i o n lbs*/yr* I f one assumes the common commercial d e f i n i t i o n of petroleum coke, which r e f e r s only to delayed coker and f l u i d coker coke, the quoted statement was completely f a l s e . More c h a r i t ably, i t s estimate was only some 900% high, i f a c i d sludge coke i s included. While not conducive to errors of such magnitude, there i s another p o t e n t i a l p i t f a l l f o r those who would estimate actual production from nominal plant capacity* P a r t i c u l a r i l y i n the case of manufacturers that have only one production l i n e , there i s a r e l a t i v e l y wide discrepancy between nameplate capacity and a c t u a l pro-


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auction, even when business i s good. For example, a f a i r l y recent p u b l i c a t i o n (8) l i s t e d one producer s capacity as 250% of i t s actual 1974 production and commented that i t was enjoying a good year. In conclusion, perhaps some (hopefully better) estimates are i n order: Discounting the p o s s i b i l i t y of a long business recession, my c a r b o n - f i l l e d c r y s t a l b a l l projects an average annual growth rate of about 11$ f o r a l l a c t i v e carbon production i n the U.S. over the coming ten years. This includes a growing proport i o n of cheap, recycleable, a c t i v e carbon powder to be made from waste f o r waste-water treatment (16), The same c r y s t a l b a l l shows a f i g u r e of 110,000 tons of actual 1974 U.S. production, including powder, g r a i n and bone char. During 1985, therefore, the United States may use over a h a l f b i l l i o n pounds of the black magic that has enjoyed your kind a t t e n t i o n today.


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Literature Cited 1) Hassler, John W. "ACTIVE CARBON" 12 Chemical Publishing Co., N.Y. 1951 2) Brunauer, Emmett & T e l l e r , J.ACS (1938) 60 309 3) Green, Hardy, Beri & Vickburg "Hydrocarbon Processing" (1971) 50 (1) 105-108 4) Pittsburgh Activated Carbon Co., "Basic Concepts of Adsorption on Activated Carbon" 3 5) Dubinin, M.M. "Uspekhi Khim" (1955) 24 3 6) Murphy, R.M. et a l "Process f o r D e s u l f u r i z i n g Carbonaceous M a t e r i a l s " U.S.Pat.3,387,941 (6-11-68) 7) Witco Chemical Co.,Inc., N.Y. 10017 8) "Activated Carbon Heads f o r Sell-Out Year" C&EN (1974) 52 (29) 7&8 9) Carbon Prod. Div., Union Carbide Corp., Chicago 10) Degussa, Frankfurt (Main), West Germany 11) Smisek & Cerny "ACTIVE CARBON" Chan.2 American E l s e v i e r Publishing Co.,Inc. (1970) 12) Kiikka, O l i v e r A. "Acid Sludge as Binder f o r the Production of Shaped Carbonaceous A r t i c l e s and A c t i v a t i o n Thereof" U.S.Pat.3,592,779 (7-13-71) 13) The Standard O i l Company(Ohio), Cleveland 44115 14) "New Process Uses Thermal Cracking of Residual O i l s " O i l & Gas Jour. (1975) 73 (21) 96-103 15) "Juggling Crude-Oil Bottoms" Chemical Engineering (1972) 79 (9) 29 16) Nickerson, R.D. et al "Making Active Carbon from Sewage Sludge" U.S.Pat.3,887,461 (6-3-75)


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