Cracking Tars and Distillates from Coal G. B. ZIMMERMAN, W. E. LEMEN GUSTAV EGLOFF, JACQUE C. MORRELL Universal Oil Products Company, Chicago, Ill. greater corrosion is encountered and lower plant capacities are obtained. Somewhat greater gasoline and gas yields are obtained than would be expected, based on the specific gravity of the cracking stocks. The finished gasoline has a greater heating value per unit volume and is satisfactory in other respects, with particularly good antiknock quality. The gas is lower in molecular weight and heating value than that from petroleum cracking, but by fractionation useful concentrations of higher olefins may be produced for chemical derivative use or for the production of polymer gasoline.
Coal tars and distillates from them may be cracked by the modern process under proper conditions to produce gasoline, gas, and coke or fuel oil residues. Low-boiling phenols may be simultaneously produced from higher boiling tar acids. Commercial products include finished gasoline, cresylic acid, fuel oil, domestic coke, electrode carbon, and polymer gasoline. The quant i t y of tar acids produced from any coal tar fraction may be varied within limits by changing the boiling range of the whole distillate from the cracking unit. In comparison with petroleum cracking,
I
N R E C E S T years n a t i o n a l self-sufficiency h a s i n creased the importance of m e t h o d s of p r o ducing motor fuel from native materials. Because of its low cost, tremendous quantity, and wide distribution, coal has been a raw m a t e r i a l for s e v e r a l processes in the production of motor fuel. I n addition to the m o t o r b e n z e n e obtained from the light oil fraction in coal carbonization, either by high- or low-temperature operation, production of motor fuel as a m a j o r p r o d u c t on a commercial scale has been obtained by two methods. T h e s e a r e d i r e c t hydrogenation of coal (3) and the catalytic conversion of water gas obtained f r o m coal t o h y d r o carbons by the method of Fischer and Tropsch (8)*
As a source of light motor fuel the hydroc a r b o n s in t h e t a r s
THERMAL CRACKING UNIT WITH
A CAPACITY OF 2500 BARRELS OF CHARGING STOCKA DAY
39
r e s u l t i n g f r o m coal carbonization have received relatively little attention, although they represent 4 to 5 per cent of the coal charged to high-temperature retorts or about twice this proportion in the low-temperature processes (9, 13). Since most hydrocarbons may, under proper conditions, be decomposed to yield l i g h t e r hydrocarbons by thermal treatment, light motor fuels may be produced from coal tars and allied material by a cracking process similar to that used commercially to crack petroleum. To evaluate this type of material as a cracking stock, a number of tests were made charging coal tars, creosote oils, lignite tar fractions, and distillates from the low-temperature carbonization of c o al-o i 1 mixtures. These tests were carried out in a pilot cracking plant with a combined
INDUSTRIAL AND ENGINEERING CHEMISTRY
40
VOL. 32, NO. 1 I
I FRACTIONATING
TOWER
COOLINr.
E
CHAMBER
COIL ROL
RESIDUUM
COKING
GAS
CHAMBER
VALVES
ECEIVER A N D 1ABI.IZER GAS
I ISTILLATE
CONDENSER
~ S T ~ L L A TREE C E I V E R
I
ARGING L L A T E TO
PUMP
STORAGE
I COOLING
0 L
PUMP
ARGING
PLMP
I I
CRACKISG PILOT PLASTFOR RESIDUUM O R COKISG OPERATIOYS FIGTJRE 1 SIYGLE-COIL feed capacity of 5 to 7 gallons per hour. Both single-coil and two-coil operations were used, as illustrated in Figures 1 and 2. I n each test the desired boiling range of the distillate produced and the quality of the liquid residue were established by the temperature conditions under operating pressure in the fractionating column and flash chamber, respectively. In producing coke, the liquid residue was withdrawn to the chamber and reduced to coke; the distillate was returned to the system for further cracking. The conditions of pressure and temperature in the heating coil and reaction chamber were adjusted to give maximum distillate yield. The original tars and distillates were inspected to determine the A. P.I. gravity, sulfur content, viscosity, Engler distillation, and other characteristics which are customarily determined on petroleum cracking stocks. All cracked distillates produced were inspected for A. P. I. gravity, distillation, and antiknock quality (as octane number), in addition t o other tests of general interest. Liquid residues were tested for A. P. I. gravity, viscosity, and sediment, and proximate analyses mere made on coke residues. A. S. T. Ril. methods ( I ) mere employed in these tests. Specific gravities were ohtained by conversion from A. P. I. gravities when not directly determined. Engler viscosities were converted from determinations in the Universal or Furol instruments. Gas analyses were made by absorption and low-temperature fractionation methods (11). Tar acids and bases were determined by the reduction in volume of the oil layers on agitation with a 23.5 per cent solution of sodium hydroxide and 10 per cent sulfuric acid, respectively (11). Vertical-Retort T a r Tar recovered as a by-product in gas manufacture by carbonization of coal was obtained from Chile. The pioperties of this tar are shown in column 1, Table I : it is representatiye of those produced in vertical-retort carbonization processes. The acids and bases in this tar were necessarily determined on an 80 per cent overhead distillate. It is estimated that the tar acid content of the whole tar is of the order of 30 per cent. Acids in the original tar falling within the boiling range of phenol and cresylic acid represent approximately 3 per cent by volume of the tar. During preliminary tests, indications were obtained that in cracking this tar the quantity of tar acids in the lower boiling range increased, probably through partial decomposition of the higher boiling phenolic compounds. Cracking
tests, summarized in the first column of Table 11,were therefore conducted to produce a maximum yield of the valuable tar acids in the cresylic acid boiling range, together with gasoline, coke, and gas. The fractionating column was controlled to produce a distillate of approximately 430" F. (220" C.) end point in order to include fractions in the gasoline and cresylic acid boiling range. The operating conditions of 250 pounds per square inch with temperatures of 889" F. (476" C.) a t the furnace transfer and 835" F. (446' C.) in the reaction chamber are illustrative of the temperatures and pressures used in cracking coal t'ars. The 164 pounds of coke produced per barrel of tar from this operation may be considered as a finished product (solid domestic fuel) after screening to size. The low ash content makes this material suitable for reduction to electrode carbon by further processing. The gas is a high B. t. u. value fuel, useful for enriching lean gases or the heavier components of the gas; for example, the pentanes, may he recovered as gasoline whereas t'he higher olefins (e. g., propene and butenes) may be concentrated for further processing to polymer gasoline or chemical derivatives. C r e o s o t e Oils I n addition to the tar produced in coal carbonization, liquid hydrocarbons are recovered in the creosote oil distillates. Columns 2 and 3, Table I, show the properties of two creosote oils produced by high-temperature carbonization of English coal. These two creosote oils were separately cracked in singlecoil operation to produce gasoline and heavy liquid residue suitable for use as a road oil. In this operation t'he fractionating column was cont,rolled t'o produce a distillate of 385395" F. (196-202" C.) end point. I n this manner raw gasoline having the desired boiling range was obtained, and naphthalene, which might crystallize and plug the condenser, mas retained in the system for further cracking. I n addition, the tar acids which usually occur in high concentrations in the distillate boiling from 390-430" F. (199-221' C.) were also eliminated from the raw gasoline. Detailed results of these tests are shown in Table 11. A substantial yield of raw gasoline is obtained from either stock, and the volume of tar acids in the gasoline is much less than that in the original creosote oil. I n the absence of appreciable amounts of water in the products, this apparent loss of phenols may be largely accounted
JANUARY, 1940
INDUSTRIAL AND ENGINEERING CHEMISTRY
for by polymerization to higher boiling material appearing in the residuum. The residua, while considerably heavier than the original creosote oils, are only slightly more viscous. I n addition to use as road oils, these residua are suitable medium-viscosity fuel oils. For this purpose the low sediment (bottoms, settlings, and water) content and low cold test are particularly advantageous. Low-Temperature Tar Low-temperature coal Carbonization, while less extensively used than high-temperature carbonization, possesses a decided advantage in the yield of liquid hydrocarbons. The production of tar in the low-temperature process is roughly double that obtained in high-temperature operations. I n this study of coal tar cracking, low-temperature tar was represented by a product from Moundsville, W. Va. Because of the poor cracking characteristics of the whole tar as indicated by analysis, it was distilled to remove 54.2 per cent by volume as distillate cracking stock, and a briquetting pitch residue was left. The results of laboratory inspection of both the original tar as well as the distillate cracking stock are shown in Table I. The distillate from the low-temperature tar was cracked in single-coil operation to produce 410' F. (210' C.) end point raw gasoline with a fuel oil residue. In a second operation 395' F. (202' C.) end point raw gasoline with a coke residue was produced. Columns 4 and 5, Table 11,present the results of these tests. Yields in the residuum operation were 38.1 per cent raw gasoline with 50.0 per cent fuel oil residue. In the coking operation the gasoline yield was 51.6 per cent with 139 pounds of coke per barrel of charge. Based on the original low-temperature tar, the gasoline yield in the residuum operation was 20.6 per cent and in the coking run, 27.9 per cent. The high octane ratings shown for the gasolines were calculated from tests on a blend of the coal tar cracked gasoline and a reference fuel of 41 octane number. The residue has the requisite properties of a medium-viscosity fuel oil. The coke is high in volatile content as a result of moderate temperatures in the coke chamber.
Lignite Tar and Its Components I n Europe, particularly in Germany, lignite coal is extensively used through low-temperature carbonization. The
FRACTIONATING
COKE
DISTILLATE
TOWER
41
relatively large tar yield in this operation lends particular interest to further processing of this product. The properties of two raw lignite tars produced in Germany by low-temperature carboniaation of brown coal are shown in columns 6 and 7, Table I. Each of the lignite tars was cracked in a singlecoil operation to produce 39NOO' F. (199-204' C.) end point gasoline and heavy liquid residues. A detailed summary of the results obtained is given in Table 11. The yield of gasoline produced in cracking the 17.5' A. P. I. gravity tar was equivalent to 42.6 per cent by volume of the charge; a 51.4 per cent yield was obtained from the lighter, 19.0' A. P. I. gravity tar. The properties of the gasolines are comparable. However, the liquid residue was considerably heavier in the latter case, which would account for a part of the yield increase, the remainder being attributed to the lighter gravity of the charging stock. As in the case when other coal tar fractions were processed, a portion of original tar acids present in the raw lignite tar are converted to lower boiling tar acids which can be recovered from the gasoline. I n order to investigate further the cracking of German Lignite tar, the 19.0' A. P. I. gravity tar was separated into its tar acid and neutral oil components by extraction with an excess of 25 per cent sodium hydroxide solution, followed by treatment with 10 per cent sulfuric acid. I n carrying out this treatment, agitation with the reagents was a t 150-160" F. (66-71' C.), and a settling time of 8 hours was allowed before withdrawal of the extract. Each treatment was followed by a water wash. The tar acids were recovered from the sodium phenolate solution by neutralization with dilute sulfuric acid and settling. The neutral tar and the tar acids mere separately cracked to produce 390400' F. (199-204' C.) end point gasoline and heavy liquid residuum. Properties of the neutral tar and tar acids are shown in Table I following the properties of the original 19' A. P. I. gravity tar. Representative yields and analyses of the products are reported in Table 11. From examination of the boiling range of the tar acids removed from the 19.0' A. P. I. gravity raw lignite tar, it is evident that the original tar contained less than 1 per cent of tar acids boiling below 400' F. (204" C,). By cracking the whole tar, a 51.4 per cent yield of gasoline distillate was obtained which contained 11.9 per cent tar acids. Thus the yield of tar acids boiling below 400" F. (204' C.) was increased to 6.1 per cent
'
COKE- CHAMBER G A S
RECEIVER
.RECEIVER
AND
STABILIZER REACTION
COOLING
CHAMB
DISTILLATE
GAS COIL
R E C E I \I E R
I COOLING
OIL
PUMP CHARGING
PUMP
FIGURE 2. TWO-COIL SELECTIVE CRACKING PILOT PLANTFOR RESIDUUM OR COKING OPERATIONS
INDUSTRIAL AND ENGINEERING CHEMISTRY
42
VOL. 32, NO. 1
of the original raw lignite tar, and the yield of tar-acid-free gasoline amounted to 45.3 per cent. The neutral oil is similar in properties to a highly aromatic or naphthenic petroleum stock, and the 52.5 per cent yield of gasoline is approximately the yield that would be expected in cracking a petroleum stock of the same gravity and characterization factor. In cracking the tar acid fraction, a 44.8 per cent yield of distillate containing 21.0 per cent tar acids was obtained. Although the tar acids contained 1.8 per cent water as they entered the cracking plant, water amounting to 5.7 per cent of the charging stock was recovered with the distillate. This particular test indicates that the higher boiling phenolic molecules, of which the tar acid charging stock is chiefly composed, are cracked or partially decomposed to produce hydrocarbons in the gasoline boiling range, together with the production of a considerable amount of lower boiling tar acids and water. The yield of tar acids boiling below 400" F. (204' C.) is equivalent to only 2.1 per cent by volume of the original lignite tar as compared to the 6.1 per cent yield from cracking the whole tar. The combined yield of tar-acid-free gasoline produced in cracking the neutral oil and the tar acid fraction amounts to 46.6 per cent by volume of the original lignite tar as compared to the 45.3 per cent obtained in cracking the whole tar. The bottoms, settlings, and water precipitate by the regular A. S. T. M. test on the liquid residues was not the same type of material that is precipitated on residues from petroleum stocks, but rather represents a resinouslike component which is insoluble in benzene.
d
u
e
Lignite Tar Fractions The 19" A. P. I. gravity lignite tar described in the previous tests was fractionated at atmospheric pressure by steam distillation to remove 90.0 per cent by volume as overhead distillate; a heavy 6.3" A. P. I. (1.027 specific gravity) bottoms was left which is suitable for use as a briquetting pitch. A portion of the acid overhead was neutralized by successive treatment with 25 per cent sodium hydroxide solution and 10 per cent sulfuric acid to remove tar acids and bases, and a neutral oil was left. Properties of the acid overhead and neutral overhead are shown in Table I. The acid overhead distillate and the neutral distillate from the lignite tar were separately cracked in a single-coil operation to produce a high yield of highantiknock gasoline and liquid residue. Table I1 presents the results of the cracking tests. When the acid overhead is
JANUARY, 1940
INDUSTRIAL AND ENGINEERING CHEMISTRY
cracked, an appreciable yield of lower boiling tar acids is produced along with the gasoline. A number of advantages are evident when cracking the neutral overhead in comparison with the distillate containing tar acids. In addition to the reduction in corrosion, a gasoline is obtained which contains less sulfur and requires less treatment, a fuel oil of lower cold test and lower bottoms, settlings, and water content is produced, and greater capacity is obtained when products of similar quality are made. However, the yield of gasoline based on the whole tar is reduced and a negligible yield of tar acid is obtained.
Coal-Oil Distillates
43
granular sediment such as often occurs with petroleum, but rather a resinous material insoluble in benzene. In order to obtain data on the operation of coal in oil coking processes in connection with cracking where the cracked residue is returned to the retort as a coal suspending medium, the following test was made: Equal parts of pulverized coal and residuum from cracking the heavy coal-creosote oil distillate in the foregoing test were mixed and charged to a small aluminum retort. On heating to 950' F. (510' C.) until no further distillate came over, a yield of distillate amounting to 49.2 per cent by weight of charge was obtained having properties similar to the original heavy coal-oil distillate before cracking. The 47.8 per cent residue was a hard porous coke.
I n addition to the well known high- and low-temperature coal carbonization processes, a number of modifications have Recovery of Tar Acids and Bases been proposed and used in commercial-scale operation. Among these are processes for the treatment and conversion Although the presence of tar acids in the cracked gasolines of a suspension of pulverized coal in oil. Column 12, Table in concentrations of 1 per cent and more results in a higher I, presents the properties of a distillate produced from a coaloctane product, these acids must be removed during the petroleum oil blend treated in a special retorting process (2). treating process to obtain a finished gasoline. By chemical A portion of this distillate was agitated with sodium hydroxtreatment these low-boiling tar acids may be recovered as ide and separated from the alkali by a centrifuge to produce by-products of considerably higher value than the gasoline a dephenolated oil. The properties of this oil are shown in itself. Table I. Since the raw gasoline produced in cracking the verticalThe original and the dephenolated coal-oil distillates were retort tar contained 30 per cent tar acids, the following proseparately cracked in two-coil operation to produce raw gasocedure was followed in recovering these fractions: The line of 410' F. (210' C.) end point and heavy residuum whole cracked distillate was treated in the laboratory to resuitable for mixing with pulverized coal to be charged to move the tar acids by successive washes with sodium hycarbonization retorts. Typical results are shown in Table 11. droxide. The resulting sludge was separated and neutralized Comparison of the results on these two oils shows that the with sulfuric acid to liberate the tar acids which were then dephenolated oil produced practically the same yield of raw water-washed. The tar-acid-free distillate was subsequently gasoline as the original oil. However, the quantity of tar washed with sulfuric acid and the sludge neutralized with acids present in the raw gasoline is much lower when processsodium hydroxide to recover tar bases. ing the dephenolated stock, and hence the yield of finished Table I11 presents the yields and properties of the tar acids gasoline will be considerably higher. The presence of large and bases thus recovered. The specific gravity of the gasoline quantities of tar acids in the raw gasoline accounts for the fraction is high and indicates a highly aromatic composition. high octane rating. The boiling range of the tar acid fraction is largely above 360 'F. A considerably heavier distillate produced by coking coal (182" C.), as would be expected from the known boiling points in creosote oil rather than petroleum oil was also cracked. of individual phenols. The tar acids recovered were subseThe properties of such a coal-oil distillate are given in the quently distilled to remove a light fraction; a heavier residue last column of Table I. The cracking tests were similar to remained which had a specific gravity and boiling range correthose discussed in sponding to a comconnection with mercial cresylic acid processing the light used in the flotation coal oil d i s t i l l a t e . refining of copper Its high specific ores. This fraction gravity made derepresents 12.9 per phenolation difficent of the verticalcult, and tests were retort tar, an inconfined to cracking crease of approxithe original oil only. mately 10 per cent in As would be excresylic acid yield by pected f r o m i t s c r a c k i n g a s exg r e a t e r specific pressed on the basis gravity, a smaller of the original tar. raw gasoline yield Detailed yields and (39.2 per cent) was properties of the tar obtained. The acid fractions are gasoline contains also shown in the 27.8 per cent tar second section of acids, equivalent to TableIII. Approxi10.9 per cent of the mately 70 per cent of charge. Detailed the crude cresylic results are shown in a c i d f r a c t i o n is Table 11. The high within the boiling percentage bottoms, range, 374-403" F. settlings, and water (190-206" C . ) , shown in the residCRACKING UNITWITH CAPACITY OF 500 BARRELS A DAY; EQUIFLUX-TYPE which uum is not water or FURXACE TO THE RIGHT to the cresols.
44
INDUSTRIAL AND ENGINEERING CHEMISTRY
VOL. 32, NO. 1
By similar treatment the tar acid fractions may be recovered from the gasolines produced in cracking the various tars and distillates from coal.
Additional Treatment of Cracked Gasolines After removal of the tar acids and bases, additional treatment of the distillates is required in order to produce a marketable gasoline. An outline of the method used in treating the gasoline produced by cracking the vertical-retort tar follows: After removal of the tar acids and bases, the cracked gasoline was agitated with 93 per cent sulfuric acid in the proportion of 5 pounds of acid per barrel of gasoline while the temperature was maintained a t 30" to 40'F. (-1.l'to 1-4.4"C.). The gasoline was then separated from the acid sludge, neutralized with sodium hydroxide, rerun using a fire and steam distillation, and sweetened with sodium plumbite solution. An inspection of the gasoline free from tar acids and bases and of the acid-treated product are reported in columns 1 and 2 of Table IV. In order to investigate the blending characteristics the treated gasoline was blended with a commercial regular-grade gasoline, the blend containing 8 per cent by volume of the coal tar product. Inspections of the commercial gasoline and the blend shown in Table I V indicate that the copper-dish gums, sulfur content, and specific gravity of the commercial gasoline were increased while the storage stability as indicated by the induction period was improved by the addition of the cracked coal tar gasoline. The treated gasoline was also blended with an 82octane-number commercial polymer gasoline; the proportions were used which would be produced in cracking the vertical-retort tar, and the gases were polymerized by the catalytic process. The blend consisting of 97 per cent cracked coal tar gasoline and 3 per cent, poly-
,u.
INDUSTRIAL AND ENGINEERING CHEMISTRY
JANUARY, 1940
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TABLE111. RECOVERY OF TARACIDSAND BASES Yield, vol. yo of cracked dist. Gasoline T a r acids T a r bases Total Yield, vol. % of coal tar Gasoline T a r acids T a r bases Total Pro erties of gasoline free of tar acids and bases GPravity, 0 A. P. I. Specific gravity. 60' F. (15.6" C.) Sulfur % by weight Octanh No., A. S. T. M: motor y e t h o d 100-Cc: A. S. T. M. dlstil~atioa, F. ( " C.) Initial b. p. 10% over 50
67.3 30.0 2.7 100.0 35.7 15.9 1.5 53.1 36.5 0.8473 0.50 69 139 ( 59) 254 (123) 370 (188)
-
.. .. .. .. ....
.. .. .. ..
45
412 (211) 90 440 (227) E n d point 98.0 % over 1.0 yo bottoms 1.0 % loss Acids Bases Properties of tar acids and bases 9.0 24.2 Gravity O A: P. I. 1.0071 0.9088 Specifia'gravity, 60' F. (15.6' C.) Preparation of Cresylic Acid Fraction Yield, vol. 70of tar acids 157 Light tar acids 81.3 Cresylic acid fraction 3.0 Water 100.0 Total Yield, vol. % of coal tar 2.5 Light tar acids 12.9 Cresylic acid fraction 0.5 Water 15.9 Total Light t a r Cresyli? acid Properties of t a r acid fractions acids fraction 23.4 6.5 Gravity, a A: P. I. Specific gravity, 60" F. (15.6' C.) 0.9135 1.0253 100-cc. distillation, F. (" C.) Initial b. p. .... 372 189) 5Y0 over .... 382 1194) .... 384 196) 10 30 ., 390 (199) .... 395 (202) 50
. .
70 90 E n d point b y weight
.... Below 374'('190)
.... ....
403 (206) 416 213) 437 $225) 99.0 1.0
mer had an octane rating one point higher than the straightcracked coal tar gasoline. During the acid treatment a t reduced temperatures, naphthalene crystallized out on the sides of the treating vessel. I n rerunning the acid-treated gasoline, it was necessary to operate with a warm condenser toward the end of the distillation in order t o prevent solidification of the naphthalene. I n anticipation of difficulties from this source in the commercial production of a high end point gasoline from cracking coal tars, the untreated distillate free from tar acids and bases was rerun to yield 75 per cent by volume of 410" F. (210' C.) end point gasoline; it was thus separated from the material in the naphthalene boiling range. The 25 per cent bottoms from rerunning the cracked distillate were composed of approximately 33 per cent of crude naphthalene; the remainder was a dark reddish liquid a t room temperature, which became solid a t reduced temperatures. Similar treatment of the gasolines produced in cracking the creosote oils with larger proportions of sulfuric acid resulted in finished products of better than water-white (22+ O Saybolt) color, which contained only 0.21 per cent sulfur and had a low gum content with satisfactory storage stability. The high motor-method octane rating of the treated gasoline from creosote oil 2 makes this fuel particularly valuable as a blending agent with lower octane gasolines. Complete treating results are shown in Table IV. The properties of the acid-treated cracked gasoline prcduced from the low-temperature tar show excellent antiknock value, good color, and fair gum, and the sulfur content is
INDUSTRIAL AND ENGINEERING CHEMISTRY
46
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VOL. 32, NO. 1
considerably above that usually accepted. I t appears that the sulfur compounds present in this gasoline are particularly resistant to removal by sulfuric acid. In view of the high antiknock value of the final gasoline, it could be most advantageously used as a blending agent with a gasoline of lower sulfur content and antiknock rating. After removal of the tar acids and bases, the cracked gasoline produced from the 17.5" A. P. I. gravity raw lignite tar was treated by two methods: (a) by agitation with 6 pounds of 93 per cent sulfuric acid per barrel of gasoline and (b) treatment in the vapor phase with brass turnings in the presence of hydrochloric acid. The latter method is known as the U. 0. P. treating process. The acid-treated gasolines in each case were rerun in a fire and steam distillation t o remove polymers and were sweetened with sodium plumbite solution. Results are shown in Table IV. The treated gasolines are better than 22" Saybolt color and have reasonable sulfur content and good octane rating. The addition of a small quantity of inhibitor ensures good stability. Table IV also gives the results of additional treatment on the gasolines free from tar acids and bases, from each of the various lignite tar cracking stocks; 93 per cent sulfuric acid was used in the proportions indicated. Treating tests were conducted on the gasolines produced in cracking both the 14.4" A. P. I. gravity untreated and the dephenolated coal-oil distillate. The properties of the cracked gasolines after removal of tar acids and bases, together with the properties of the treated products, are reported in the last four columns of Table IV. The treating results show final yields of acid-treated gasoline from the original and dephenolated oils of 36.1 and 43.2 per cent, respectively, with octane ratings of 72 and 73. In spite of the large differences in density and other properties between the raw gasolines from the two types of charge, the final treated gasolines have similar characteristics. They are satisfactory motor fuels, although the sulfur content is greater than is permitted by some specifications. To demonstrate the value of the acid-treated gasoline from coal-oil distillate in a blend with one of inferior octane number, a 43-octane-number mid-continent straight-run gasoline was blended with each of the cracked gasolinesin the proportion of four parts of straight-run gasoline to one part of cracked gasoline. T h e o c t a n e n u m b e r of t h e resulting blend
JANUARY, 1940
INDUSTRIAL AND ENGINEERING CHEMISTRY
mas 53 in each case, and the calculated blending octane value of the cracked gasolines in these blends was 93 octane number. Since the straight-run gasoline contained only 0.04 per cent sulfur, the sulfur content of the blends was as low as 0.11 per cent and the gums were only 4 mg.
Corrosion It was anticipated and confirmed by experience during the foregoing tests that corrosion would be a problem in cracking ‘
coal tars and distillates containing tar acids and bases. Following preliminary trials, to minimize corrosion, all equipment in which cracking temperatures were maintained was made of 18-8 stainless steel, including tubes and headers of the cracking furnace and the entire reaction chamber. Some tests were conducted using tubes of 4-6 per cent chromium with 0.5 per cent molybdenum. Because of intermittent operation and relatively short test periods (20-30 hours), interspersed with operation on petroleum oils, no definite conclusions may be drawn from the service record of this equipment. Excessive corrosion of the alloy parts was not experienced, however. TABLEV. CORROSION BY COAL TARSAND DISTILLATES Raw HighNeutral Temp. Lignite Ligmte Tar Tar Coal Tar Trace 22.5 28+
Tar acid content, vol. yo Sulfur, wt. % 0.47 0.49 0.54 Reaction chamber conditions Temp., ’F. 850 850 835 Temp., ’C. 454 454 446 200 200 Pressure, lb./sq. in. Pressure, atm. 13.6 13.6 Test metal penetration rate, inch/month Mild steel 0.02684 0 . 0 2 9 5 0.0127
lie?
18-8 (18% Cr, 8% Ni, 0.2% C ) No. 2825 (28% Cr, 0.25y0 C) Cyclops 17 B (7.25% Cr, 19.3% Ni, 0.15% C) No. 1809 (17.23% Cr.0.09% C) Excelloy (12% Cr) 24-11 (24% Cr, 11 , Ni) Cyclops 17A ( 7 . 2 5 z C r , 19.3% Ni, 0.41% C )
0 . 0 0 8 1 4 0.00882 0.00125 0.00476 0 . 0 0 0 7 5 0.00659 0.00173 0.00343 0.00595
0.01249 0.00789 0.0051 0.00224
0.00419
0.01003
Dephenolated Coal Oil Dist. Below 1 0.93
885 474
:?I 0.009
To obtain information on the relative corrosion rates of various coal tars and distillates, the corrosion test procedure proposed by Calcott (4) was applied. Weighed test strips of mild steel and various alloys were suspended in the reaction chamber during a test run. After the run, the surfaces of the test strips were ground to the level of the deepest pit and the strips reweighed. From the duration of cracking temperatures during the test and the area and loss in weight of the test strip, corrosion was calculated to inches penetration per month. Results of a number of tests on various alloys with several of the coal tars are shown in Table V. Because of differences between pilot-plant and commercial operation with respect to temperature and duration of runs, these results must be considered as relative only. Although the highchromium steels appear to best advantage, their hardness makes fabrication difficult. The availability and workability of 18-8 stainless steel and its excellent physical properties when properly stabilized tend to favor this alloy for service in equipment for cracking coal tars.
Behavior of Tar Acids in Cracking The wide utility and high market value of the lower boiling phenols make the behavior of these materials in cracking of particular interest. The lower boiling phenols, in order of their boiling points, are as follows: Phenol +Cresol m-Cresol p-Cresol
O F .
“C.
360 376 397 397
182 191 203 203
O
Guaiacol Ethylphenols Xylenola
Cresol
F.
40 1 406-426 414437 432
O
e.
205 208-219 212-225 222
47
These compounds find many uses; among them are solvent refining of lubricating oils and inhibiting cracked gasolines (Y),production of synthetic resins (5, IO),as an absorbent in benzene recovery (6), as a disinfectant, and in the production of synthetic tannins (IO),and for the manufacture of synthetic dyes, perfumes, and explosives (11). Reviewing the results of cracking the various coal tars and distillates, the following will be noted: The concentration of tar acids in the distillate varies with the proportion of distillate in the boiling range of about 390-430’ F. (199-221 c.), or the range of most of the lower boiling phenols. The concentration of these compounds may be increased to exceed that in the charging stock, which indicates that the higher boiling phenols are decomposed to lower boiling phenols, as well as hydrocarbon fractions in the gasoline boiling range.
Comparison of Coal Tar and Petroleum Cracking Direct comparison of cracking coal tars and distillates with petroleum fractions is not practicable because of the wide variation in results between individual samples of either type. For petroleum cracking, gasoline, residue, and gas yields may be roughly related to density of the charge for normal stocks in any particular type of operation. Extrapolating a mean plot of such a relationship to the range of density of coal tars and distillates indicates that finished gasoline yields and gas production from the coal tars are somewhat greater than would be anticipated from the plot. Plant capacity is from one half to one tenth that obtained with petroleum stocks, and operating conditions, limited by coke deposition, are milder. The raw cracked gasolines are of high specific gravity and high octane number. On treatment the specific gravity decreases and the octane number falls to a varying degree. The final gasoline from coal tars in comparison with a petroleum cracked gasoline, is higher in density, and usually higher in antiknock quality, and has a very high oxygen bomb stability, apparently because of naturally occurring inhibitors. Sulfur reduction in treatment is difficult with these gasolines, and gum reduction requires attention. The gas, although somewhat greater than in petroleum cracking, is lower in density and heating value; it lies intermediate between dry natural gas and normal cracking plant gas. This difference is mainly due to a larger proportion of hydrogen and methane. By fractionation, useful concentrations of the higher olefin and paraffin constituents may be obtained for further processing to motor fuel by catalytic polymerization. Literature Cited (1) Am. SOC.Testing Materials, Standards on Petroleum Products and Lubricants, 1937. (2) Anonymous, I n d . Chemist, 12, 227-34, 283-91 (1936). (3) Berthelot, Chimie & industrie, 35, 768 (1936). Eso. CHEM.,15, 677-9 (1923). (4) Calcott, IND. (5) Ellis, “Chemistry of Synthetic Resins”, New York, Reinhold Pub. Corp., 1935. (6) Jacobson, Gluud’s International Handbook of the By-product Coke Industry, Am. Ed., New York, Chemical Catalog Co., 1932. (7) Kalichevsky and Stagner, “Chemical Refining of Petroleum”, A. C. S. Monograph 63, New York, Chemical Catalog Co., 1933. (8) Naphth$, Refiner Natural Gasoline M ~ T17, . , 47-51 (1938). (9) Porter, Coal Carbonization”, A. C. S. Monograph, New York, Chemical Catalog Co., 1924. (10) Schotz, “Synthetic Organic Compounds”, New I’ork, D. Van Nostrand Co., 1925. (11) Spielmann, “Constituents of Coal Tar”, London, Longmans, Green & Co., 1924. (12) Universal Oil Products Co., Laboratory ‘Pest Methods for Petroleum and its Products, Chicago, 1937. (13) Wigginton, “Coal Carbonization”, London, Baillibre, Tindall and Cox, 1929. PREBENTED before the Division of Gas and Fuel Chemistry at the 96th Meeting of the American Chemical Society. M;lwaukee. Wis.
