INDUSTRIAL AND ENGINEERING CHEMISTRY
June, 1945
LITERATURE CITED
and neohexane (2,24methylbutane) were substantially absent,
aa was cyclopentane.
5s1
Bates, Kurtz, Rose, and Mills, IND.ENO.CHE~M., 34, 147 (1942). Houdry, Burt, Pew, and Peters, Oil ffcrs J., 37,40 (1938); Peterkin, Bates, and Broom, Refiner, 18, 504 (1939). (3) Thomas, Div. of Petroleum Chem., A.C.S., April, 1944; Block and Thomas, Zbiol.; Thomas, Hoekstra, and Pinkstone, Ibid. (4) Ward and Kurtz, IND.ENG.CHEM.,ANAL.ED., 10, 559 (1935).
(1) (2) ACKNOWLEDGMENT
The authors acknowledge the assistance of John Snyder, who performed the special fractionation work, and the research staff of the Houdry Laboratories, Catalytic Development Corporation, where all work in this investigation was performed.
P E ~ S ~ NaaTpart ~ D of the Symposium on Catalysis in the Petroleum Industry before the Division of Petroleum Chemistry at the 108th Meeting of t h e A M ~ E I C ACH~MICAL N SOCIETY in New York, N. Y.
PETROLEUM COKE Production of Compact Nonporous Coke A. G. V. BERRY AND Re EDGEWORTH-JOHNSTONE Trinidad Leaseholds Ltd., Pointe-a-Pierre, Trinidad, B. W. I . Experiments are described in which mixtures of pulverized petroleum coke and residuum or cracked asphalt were subjected to secondary coking. For the production of strong nonporous coke under conditions of rapid heating, two requirements were found necessary: (1) The volatile content of the primary coke should exceed 7%. (2) The calculated volatile content of the mixture of coke and binder should not exceed 22%. These findings are interpreted in the light of ideas in a previous paper ( I ) .
Twenty-five experiments were made with cracked asphalt as binder, and twelve experiments with residuum. The secondary cokes produced were examined for strength and compactness. The results are shown in Tables I1 and 111, Friability number was determined by a test described in the previous paper (I). Results are comparative only, a higher number denoting greater friability. SUMMARY OF RESULTS
1. Secondary cokes made from a primary coke of 7% volatile
A
PREVIOUS paper (1) reported a study bf the formation of
coke from asphaltic petroleum residues. It was found that the material always passes through an in tumescent stage. This confers a more or less cellular structure on the resulting coke. When intumescence takes place under pressure, the cells are reduced in size, but they cannot be entirely eliminated. For this reason i t is not ordinarily possible to produce nonporous coke from asphaltic residues in a single operation. The usual procedure is to take a suitable petroleum coke, pulverize it, blend with 10-20oJo of asphalt or pitch, and recoke the mixture. This is the method by which smokeless briquets, electrodes, etc., are made. The mixture of coke and binder is pressed and molded before the second coking or “baking” process. Such products may be generally referred to as secondary coke, to distinguish them from the primary coke obtained by the direct carbonization of asphaltic residues. The present paper describes laboratory experiments on the production of secondary cokes from mixtures of pulverized primary coke with residuum and cracked asphalt. These mixtures were not compressed before coking and were heated at a comparatively rapid rate. Any tendency towards intumescence and porosity could thus produce its maximum effect. PRODUCTION OF SECONDARY COKES
Samples of petroleum coke of known volatile content were pulverized to pass 40-mesh screen and mixed with various proportions of binder. Two different binders were used-a residuum from the cracking of topped crude and a cracked asphalt. The properties of these materials are given in Table I. For each experiment 300 grams of the mixture of pulverized coke and binder were coked in the 3-inch cylindrical pot still described in the previous paper (1). I n all cmes the coke temperature was finally raised to 800’ C. and maintained there for 2 hours.
content were weak and friable when rapidly heated, and tended to be porous when heated more slowly. 2. Secondary cokes made from primary coke having a volatile content of 11% or more tended to be compact and nonporous provided the total calculated volatile content of the mixture oi coke and binder did not exceed about 22%. 3. Secondary cokes made from mixtures of primary coke and binder in which the calculated volatile content exceeded about 22% tended to be strong but porous. The calculated volatile content of a mixture is taken as:
(
% volatiles in binder X O/n binder in blend
in coke X 5% coke in blend ) 4- ( % volatiles
100 These results may be interpreted in the light of ideas put forward in the previous paper (I). It was there suggested that the coking of asphaltic residues is represented by the series: Asphalt
- - - pitch
semipitch asphaltic coke
carboid coke
Semipitch has a volatile content of approximately 2 2 3 0 % and intumesces when heated. Asphaltic coke has a volatile content of 7-22y0, and carboid coke, of less than about 7%. Both the latter substances on heating lose volatile matter without intumescence. At precarbonization temperatures asphalt, pitch, semipitch, and asphaltic coke are more or less mutually soluble,
TABLE I. PROPERTIES OF BINDERS Reeiduum Nil 70.3 29.6 0.I
1:i%o 620 ...
Cracked Asphalt Trace 46.0
64.8
0.2
1.8 ... ... 126
INDUSTRIAL A N D ENGINEERING CHEMISTRY
552
Vol. 37, No. 6
TABLE 11. SECONDARY COKINQ OF MIXTURES OF PULVERIZED COKEAND CRACKED ASPHALT Expt. No. I I1 111 IV V VI VI1 VI11
Volatile Calcd. Rate of Content of Compn* Of bfixt., Volatile Heating, Yields, % Primary % Content of ' C..per Coke', % Coke Asphalt MixtSa, % Min. Distillate Coke 7 7 7 7 7 7 7 7
95 90
Volatile contenta, %
Properties of Secondary Coke Friability Bulk No. density General Veryfriable Same Same Same Very friable and weak in structure
...
5 10 16 20 26 22.6 22.6 30
8.9 10.8 12.7 14.6 16.5 16.6 16.6 18.4
3.8 4.7 6.1 5.0b 5.0) 6.2 2.7 2.7
6.3 6.7 7.4 10.0 11.0 12.3 9.0 9.0
90.7 87.0 86.0 82.3 81.7 81.3 78.0 80.3
1.6 2.1 1.9 2.5 2.4 1.8 2.2 2.1
70 77.K 72.6 76 70 76 80
80
22.6 27.5 26 30 25 20
18.4 18.7 20 3 19 6 24.0 22.5 21.0
1.6 1.5 1.5 1.5 1.5 1.5 1.5
6.7 7.5 10.3 10.7 12.0 11.0 10.7
80.0 81.0 80.0 80.7 81.7 76.0 79.0
1.8 0.9 1.1 1.0 1.4 1.5 1.7
14.6 9.2 3.5 4.6 3.6 3.0 10.6
0.667 0.533 0.667 0.673 0.728 0.732 0.574
21.7 21.7
1.6 3.0
11.0 10.0
76.7 76.0
1.7 1.8
2.8 4.6
0.715 0.537
86 80 75 77.6 77.6 70
19.4 60.1 41.5 18.5
IX X XI XI1 XI11 XIV
xv
7 11 11 11 16 15 15
X VI XVII
15 15
77.6 77.6
22.6 22.6
XVIII
15
77.5
22.5
21.7
6.6)
12.3
76.3
1.7
6.6
0.637
XIX
xx
15 17.6
77.5 86
22.6 14
21.7 21.4
0.5 1.S
4.3 9.3
79.7 81.0
1.4 1.3
6.0 4.2
0 590 0.668
XXI XXII
17.6 17.5
80 90
20 10
23 20.36
1.6 1.5
9.3 6.7
76 3 79.7
0 62 0.83
6.1 6.5
0.670 0.581
10 5
22.6 21.2
1.5 1.6
7.7 8.3
82.6 81.0
1.6 1.3
1.6 2.5
0.675 0.683
XXIII 20 90 XXIV 20 95 a. Organic volatile content, b Approximate.
Larne No. of fine uorea: verv difficult to fracture Less porous than VI11 and slightly stronger
.........,...,..
Less porous and more friable than XIV Less porous and more friable rhan XIV Compact and granular Compact and ranular. stronger than XI11 Less porous $an X I + but not quite so strong Very hard and strong in bulk Compact structure but numerous cracks d u e t o uneven contraction on cooling More porous than XVII; also more cracks and more friable Porous but fairly strong Colppact, very hard and strong; practically no pores Porous and very friable Compact and fairly strong, b u t not so strong as X X Poroua and weak in bulk Very hard, compact, and strong
TABLE 111. SECONDARY COKING OF MIXTURES OF PULVERIZED COKEAND RESIDUUM (Rate of heating was 1.5' C. per minute until 800' C. was reached; the temperature was maintained a t 800° C. for 2 hours) Volatile Compn. of Calpd. Content of Mixt.9 % Volatile Yields, % Primary Resid- Content of Coke', % Coke uum Mixt.0, % Distillate Coke 15 88 12 21.6 10.3 77.3
Properties of Secondary Coke
%
Friability No.
15 15 15
83 80 78
17 20 22
24.4 26.1 27.2
14.3 16.6 17.3
75.0 72.3 70.3
1.4 0.7 2.6 1.3
23 17 3.3 8.4
0.551 0.590 0.694 0.657
XXIX
16
78
22
27.2
17.3
69.7
1.9
4.8
0.661
xxx
15
74
26
29.4
19.0
68.7
1.0
2.7
0.689
XXXI
16
70
30
31.6
20.6
66.4
0.7
2.6
0.719
XXXII
15
67
33
33.4
23.1
64.9
0.9
3.6
0.715
XXXIII
20
92
8
24.0
10.3
76.0
0.3
4.8
0.632
Expt. No.
xxv
XXVI XXVII XXVIII
Volatile contenta,
Bulk density
XXXIV
20
90
10
26.0
11.0
75.7
0.4
4.3
0.631
xxxv
20
88
12
26.0
10.3
74.3
0.9
2.8
0.662
14
27.0
12.0
73.7
0.6
6.6
0.667
XXXVI 20 86 0 Organio volatile content.
owing to their content of asphaltic matter. When a mixture of any two of them is heated, the mutually soluble constituents appear to diffuse into one another before coking begins. The mixture, therefore, carbonizes like a homogeneous material with intermediate properties. For example, a mixture of asphaltic coke and pitch or asphalt in which the calculated volatile content lies between 22 and 30% will intumesce on heating like a semipitch of similar volatile content. If, on the other hand, the calculated volatile content is below about 22%, the mixture behaves on heating like an asphaltic coke; Le., it loses volatile matter without intumescence. Interdiffusion of asphaltic constituents between coke and binder creates a firm bond between them when the mixture is carbonized, and the baked product tends to be strong, compact, and nonporous. Coke with a volatile content below about 7% is classified as carboid coke and is almost completely insoluble in organic solvents. When it is heated with pitch or aaphalt, there is little or no interdiffusion and, hence, no firm bond between the primary coke and the binder. Unless the rate of heating is excessively
General Very powdery and weak Same Porous but fairly hard and strong Residuum added to pulverieed coke but not mixed: aecondsry coke varied considerably in quality; bottom portion fairly strong but porous Residuum and pulverized coke thoroughly mixed before heating; secondary coke better than X X V I I I ; strong, hard, and porous Best coke obtained with primary coke of 15% volatile content; cornpact, strong and hard; see X X X I I I More orous than X X X . no cooling cracks, but weater than X X X although quite strong Cracks due t o uneven contraction during cooling; weaker than XXXI b u t faii,ly strong Best coke obtained from rimary coke of 20% volatile content and simigr to X X X ; compact. hard, and strong Coke fairly porous in center, aides compact; hard and strong Fewer but larger pores than XXXIV; hard and strong Full of fine pores but fairly strong
slow, the binder itself intumesces and produces a secondary coke which is weak and friable. Porosity results when volatile matter is evolved a t such a rate that it cannot all be eliminated by diffusion through the maas of charge to the exposed surface. The excess volatile matter forms bubbles and may create fissures communicating with the surface of the mms. I n mixtures which comply with condition 2 above, the volatile products are soluble in the asphaltic primary coke. Hence the whole mass of charge can take part in the elimination of volatile matter by diffusion, and this permits a rapid rate of heating without the formation of bubbles. In mixtures conforming to condition 1, the volatile products are insoluble in the primary coke, and diffusion can take place only through the residual binder which fills the interstices between the primary coke particles. The total diffusion path is greatly restricted m compared with condition 2, and an excessively low rate of heating is necessary to avoid porosity (lower than the slowest rate employed in the foregoing experiments).
lune, 1945
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
Condition 1 corresponds to the procedure commercially e m ployed in the manufacture of electrodes, as described by Boex (9) and Mantell (3). According to Mantell, the heating of a batch of electrodes occupies a period of 12-20 days. Condition 3 again requires very slow heating to avoid porosity owing to the high percentage of volatile matter given off and to the fact that, even after an appreciable quantity has been evolved, the residual mass is still plastic. The conditions of composition for obtaining a compact, nonporous secondary coke in the shortest possible baking time appear to be as follows: (1) The primary coke should be asphaltic coke with a volatile content well above 7y0. (2) The calculated volatile content of the mixture of primary coke and binder should remain within the asphaltic coke range-i.e., below about 22%. A few preliminary experiments have been made with laboratory samples molded under pressure before baking. The results
853
tend to confirm the above interpretation. This investigation is at present suspended owing to pressure of more urgent work. The above results, and our conclusions regarding them, are published in the hope that they may be of interest to those engaged in the production of electrodes and other forms of commercial carbon. ACKNOWLEDGMENT
The authors' thanks are due to the Chairman and Board of Trinidad Leaseholds Ltd. for permission to publish this paper. LITERATURE CITED
(1) Berry, A. G. V.,and EdgeworthJohnstone, R., IND. ENQ.CHBM., 36, 1140 (1944). (2) Boex, U., Proc. Zwt. Msoh. Eng. (London), 125, 13 (1933). (3) Mantell, c. L.,Chem. & Met. Eng., 27, 109 st seq. (1922).
Treatment of Spent Pickling Liquors with Limestone and Lime RICHARD D. HOAK, C. J. LEWIS, AND W. W. HODGEI Mellon Institute, Pittsburgh, Pa. Where pickle liquor has been treated with lime and the sludge is oxidized, the stoichiometric quantity of lime is required; but where the sludge is discharged to a settling basin with a minimum of oxidation, approximately 95% of the theoretical amount of lime will afford complete treatment. Limestones vary widely in their rate of reaction with pickle liquor, and the rate depends upon particle size, chemical analysis, and a specific reactivity peculiar to a particular limestone. There is a critical partiole size, falling between 200 and 325 mesh, and differing for different limestones, for optimum reaction between this material and pickle liquor. Where magnesium carbonate is present in limestone in excess of about 2%, the rate of reaction
with pickle liquor is roughly inversely proportional to the percentage of this constituent. Dolomitic limestones are practically useless for pickle liquor treatment. The specific reactivity of limestonee is an important factor which cannot be correlated and is determinable only by trial. The rate a t which limestone removes iron from pickle liquor is a function of the rate at which ferrous iron oxidizes, Substantial economy i4 pickle liquor treatment can be realized by using pulverized high-calcium limestone, to neutralize free acid and precipitate part of the iron, and lime to oomplete the treatment. The commercial operation of a limestone-lime split treatment is described.
T
liquor contributes to the most efficient operation of the process under a particular set of conditions. Although a number of acids other than sulfuric (hydrochloric, nitric, hydrofluoric, phosphoric) are used in pickling steel, the quantities are small in comparison with sulfuric acid. Part of the experimental work reported in this paper was conducted with a straight sulfuric acid liquor, and part with a liquor containing small amounts of nitric and hydrofluoric acids in addition to the sulfuric acid which comprised the bulk of the pickling agent. The results of this investigation should be applicable to any of the wsste liquors commonly resulting from pickling. The authors (4) presented a scheme whereby determination of the basicity factor of an alkaline agent and the acid value of a waste liquor provides a rapid method for calculating the proportions of the two materials which should be combined to effect a desired result. This procedure has the advantage of quickly measuring the available basicity of an alkaline agent under the conditions of the treatment and eliminates speculation concern-
HE removal of the oxide film from steel, preparatory to further processing, is usually accomplished by pickling the metal in a sulfuric acid bath. This treatment resulta in a waste liquor which is substantially an aqueous solution of ferrous sulfate and sulfuric acid. Many steel companies can dispose of this liquor only after treating i t with lime to neutralize the free acid and precipitate the iron. Lime treatment of waste pickle liquor is expensive; occasionally the cost of disposing of the spent liquor is as great as the cost of pickling. Colton (8) patented a process, described by Rentschler (6),for manufacturing a building material from the sludge produced in lime treatment. I n many instances, however, no useful by-products can be recovered economically. Under these circumstances it is essential that the treating agent be utilized as effectively as possible. An appreciation of the importance of the several factors involved in the treatment of waste pickle 1 W.W. Hodge ia an Adviaory Fellow at Mellon Institute. His addrau is Weat Virginia University, Morgantown, W.Va.
