Highly Aromatic Petroleum Solvent Naphthas W. J. SWEENEY AND E. H. MCARDLE Standard Oil Development Company, Elizabeth, N. J.
Highly aromatic naphthas of suitable quality can be produced from petroleum to augment present supplies from coal-tar light oils. In the higher boiling ranges where coal tar is deficient, petroleum sources can meet any present demands. Already aromatic naphtha No. 3 has become useful in the trend toward the higher baking temperatures demanded by automotive finishing schedules, and if still higher boiling aromatic naphthas are needed, they can be made available. Further, should occasion demand, the petroleum industry has the materials and proGesses for the separation and commercial production of a number of individual aromatics of any required degree of purity. ETROLEUM crudes are exceedingly complex mixtures, but much has been learned of their composition in recent years. Rosini and co-workers (6,10, 11, 18, $7, 88, 29), Fenske et al. (20, Zl), and others (3, 6) have separated and identified over seventy hydrocarbons in the gas and gasoline boiling ranges. These include all the normal paraffins, a good number of the possible isoparaffins, the simple naphthenes, cyclopentane and cyclohexane, and several alkylated cyclopentanes and cyclohexanes. Most of the Ci to Clo aromatics have also been separated and identified. From the fractions boiling above 200' C. not many pure hydrocarbons have yet been separated, although work is proceeding in this direction. Considerable information regarding the general types of these hydrocarbons, however, has already been obtained by comparing the physical properties of narrow petroleum cuts with those of pure high-boiling hydrocarbons obtained from other sources or by synthetic methods (4,7,i2,IS,14, $4, $6). The commercial availability of pure petroleum hydrocarbons and of concentrates of special types has increased rapidly during the past ten years. Propane, n- and isobutane, n- and isopentane, and mixed aromatics of various boiling ranges have been separated in quantities amounting to several hundred barrels daily. In addition, the industry has developed hydrocarbon conversion methods to make isooctane, mixed octanes, neohexane, mixed isomeric paraffins (the alkylates, Cr to (310and higher), and mixed aromatics in quantities up to several thousand barrels daily. Some idea of the potential capacity of the petroleum industry as a source of pure hydrocarbons or hydrocarbon concentrates can be gained from a comparison of the crude run to stills with the coal-tar distillate production (98)of the United States in 1937 (Table I).
P
Although wartime production of coke-oven products will exceed the 1937 rates, it may be expected that petroleum will keep apace. The 1937 production of coke-oven distillates amounted to approximately 0.3 per cent of the production of crude oil. Already the petroleum industry is producing pure hydrocarbons or hydrocarbon concentrates in excess of this figure. Some of them are being used as intermediate stocks within the oil industry itself for special products or for aviation fuel; others, such as narrow-cut aromatic solvent naphthas, are sold in that form. Aromatic hydrocarbons were produced during the first World War from Borneo and similar type crudes, but not until 1926 were aromatic petroleum solvent naphthas made commercially available to the protective coatings industry. The first series of three moderately aromatic naphthas was manufactured from selected California crudes. The first large-scale production of highly aromatic petroleum naphthas in the East was effected by high-pressure destructive hydrogenation of selected feed stocks (19). These naphthas were soon adopted by the protective coatings industry, particularly for automotive finishes. They ranged in solvency from half that of toluene in the case of hydrogenated naphtha 1, through two thirds the solvency of xylene for No. 2, to solvencies approaching those of heavy coal-tar naphthas in solvents 3 and 4.
787
TABLEI. BY-PRODUCTS FROM COKE-OVEN OPERATIONS IN UNITEDSTATES IN 193P Benzene crude and refined Motor bkeene Toluene, crude and refined Solvent naphtha Xylene. Other light oil product8 Tots1 Crude oil run t o stills Gasoline producsda 0
b 8
Gallons/Year 21 660 522 95'526'695 20:896:724 6,725,918 4,582,344 8,130,103
Barrelsb/Dsy 1,400 6,240 1,360 370 300 530
156,502,306 49,700,000,000 24,000,000,000
10,200 3,240,000 1,570,000
THI
Minerals Yearbook, p. 902 (1939). 42-gallon barrels. U.8. Bur. of Mines, Annual Petroleum Statement, 1937.
New Methods of Manufacture Owing to increased demand for aromatic thinners, as well as to the need for hydrogenating capacity for making other products, it soon became necessary to investigate additional sources of supply or methods of manufacture. It was shown (22) that virgin naphthas differ widely in composition, Some are predominantly paraffinic, others naphthenic. Aromatics may be present in both types, but contrary to popular belief, there is a tendency toward occurrence in relatively greater amounts in naphthas of the so-called para&& type. Aromatic content varies from as low as 2 or 3 per cent up to 25
INDUSTRIAL AND ENGINEERING CHEMISTRY
788
% Original gasoline0 Benzene Toluene Xylenes ethylbenzene Co aromatics Residue ~~
+
55
R s rni z
5
of Original Gasoline
17.0 0.7 3.1 5.1 4.9 3.4
-
Vol. 33, No. 6
yo of Total Aromatics 100 ~. . 4.1 18.0 29.7 28.4 19.8
-
17.2 100.0 Independent acid extraction of original gasoline.
FIQURE 1. ANALYSISOF A HIGHLY AROMATIC P. C. NAPHTHA
W
P c
I
2
Y
(I
z
2 0 m
VOLUME PERCENT OF CHARGE DISTILLED OVER
or 30 per cent, particularly in the boiling range from 100' to 200" C. The analysis of a typical highly aromatic virgin naphtha is shown in Figure 1. The distillation was carried out in a one-barrel-capacity 75-plate tower at the Petroleum Refining Laboratory of Pennsylvania State College at 40 to 1 reflux ratio; the analysis represents the combined efforts of that laboratory and the Esso Laboratories of the Standard Oil Development Company. From this naphtha, containing 0.7 per cent benzene, 3.1 toluene, 5.1 ethylbenzene and xylenes, 4.9 COaromatics, and 3.4 higher boiling aromatics (a total of 17.2 per cent), it is possible to manufacture a range of aromatic solvent naphthas which find application in the pairft, varnish, and resin trades and in the automotive industry. A series of commercial thinners with evaporation rates matching those of conventional coal-tar naphthas is a t present manufactured from a naphtha of this type. They are designated as P. C. Solves60s. (P. C . is the abbreviation of the refinery term "prime cut" which is applied to virgin naphthas as distinguished from cracked or catalytically converted stocks.) They will be referred to here as aromatic naphthas 1,2, and 3. Compositions of these products are shown by the analytical distillations shown in Figure 2, made in a &foot laboratory column equivalent to 18 plates, a t 20 to 1 reflux ratio. Added t o each charge of 400 ml. of thinner were 40 ml. of highly aromatic bottoms, having A. S. T. M. initial boiling points a t least 38" C. (68" F.) above the A. S. T. M. final boiling points of each thinner. For example, aromatic naphtha 3 (175-211" C. or 347-412" F.) was used as bottoms for the distillation of aromatic naphtha 1 (99-137" C. or 210279' F.). I n this way column holdup was partly compensated for, and it is believed that the distillation curve is cor-
rectly representative of the composition of 98 per cent of the thinner taken overhead. ARONATIC NAPHTHA1. From Figure 2 the toluene content of aromatic naphtha 1 is estimated to be about 65 per cent, after due weight is given to the boiling point and refractive index curves. The presence of benzene is indicated by the small peak of the refractive index curve a t 3 per cent distilled. It was estimated by redistilling the first 10 per cent and was found to be 0.8 per cent of the total thinner. Accurate determination of ethylbenzene is difficult in view of the presence of xylenes. An infrared spectrographic study of the 86-96 per cent fraction, however, indicated a content of 1.4 per cent based on the whole naphtha. The predominance of toluene in the thinner is illustrated in Figure 3, where infrared absorption spectra of these two materials are plotted
OF AROMATIC NAPHTHAS TABLE11. PROPERTIES
Solvesso 1
Solvesso 2
Solveaao 3
33.0 0.860 30 85
+
28.7 0.883 +25 128
270 279 280 294 325 33s 351 353
347 354 357 373 396 401 408 412
93.3 80.6 88.8 17.0
84.1 74.0 80.3 22.7
0.1 110 0.07
0.7 125 0.55
1,4914 1.4235, 1 4239 93 5 3.8 2 6
.. .. ..
.. ..
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
June, 1941
one above the other. Isomeric xylenes are estimated from Figure 2 to be present to the extent of about 6 per cent in aromatic naphtha 1. Thus the total aromaticity of approximately 72 to 73 per cent corresponds to the figure of 73 per cent obtained by proximate analysis (Table 11). AROMATIC NAPHTHA 2. The aromatic content is shown in Figure 2 to be divided about equally between xylenes and Cg aromatics. I n this respect aromatic naphtha 2 resembles coal-tar solvent naphtha of similar boiling range, although its aromaticity is 3 or 4 per cent lower (16) than highly refined coal-tar solvent naphtha. Aromatic naphtha 2, however, has a comparatively low content of pseudocumene. It does not possess the familiar pseudocumene odor characteristic of coal-tar solvent naphtha, and its distillation curve shows no decided plateau corresponding to pseudocumene. Table I11 reveals that pseudocumene is only a moderately good thinner for typical synthetic resins, a circumstance which in part may account for the unexpectedly high resin solvency of aromatic mphtha 2 in comparisonwith conventional coal-tar solvent naphtha (as regards aromaticity). AROMATIC NAPHTHA 3. In this boiling range (175-211' C.) there are a large number of isomeric CBand Cl0 mononuclear aromatics, together with some naphthalene and possibly hydronaphthalenes. The naphthalene content is small, however, as shown by the fact that the crystal point of aromatic naphtha 3, when seeded with naphthalene, is below -29' C.(-20" F.), Aromatic naphtha 3 is employed largely in conjunction with mineral spirits or with aromatic naphtha 2 to obtain better leveling of protective coatings and to prevent a loss of resin solvency as the film sets up and dries (8). This solvent is noteworthy as the first highly aromatic naphtha of satisfactory boiling range and purity to be made available to the protective coatings industry in the boiling range above coal-tar high-flash naphtha.
largely for automotive finishes, during the past four years. Solvency and performance comparisons in terms of empirical tests have been disseminated generally within the protective coatings industry, and some representative new data of this type are presented in Table 11. The following are significant : KAURI-BUTANOL VALUEis the number of milliliters of thinner required to produce a cloud when titrated with 20 grams of a filtered 20 per cent solution of natural kauri resin in n-butanol, Kauri-butanol solvent power (1, 2) relates i t to & value of 100 for pure benzene, 94 for toluene, 84 for xylene, and 25.4 for n-heptane. A more recent kauri-buta-
Control Tests for Solvency Several million gallons each of aromatic naphthas 1, 2, and 3 have been used as thinners,
FIGURE 2. ANALYTICAL DISTILLATIONS OF AROMATIC NAPHTHAS 1,2,AND 3 Boiling Major Aromatic Point, Components F. Aromatia Naohtha 1 Toluene 231 Eth lbenzene 276 Met%yloyolohexane 214 Dimethylcyolohexanes 247-265 Average paraffins 225 Aromatic Naphtha 2 o-Xylene 29 1 m-Xylene 279 p-Xylene 281 Pseudooumene 337 Mesitylene 328 Cumene 306 Methylethylbenzenes 322-328 Hemimellitene
349
Refractive Index,
n% 1.4969 1.4985 1.4240 1.427 1.40 1.5046 1.4973 1.4957 1.5045 1.4881 1.4912 1.4831.504 1,5139
Aromatio NaDhtha 3 Hemimellitene
I-Methyl-3-propylbenzene
Dimethylethylbenzenes Dimethyl ropylbenzenes
349 359 363-372 403-408
Methyletfylisopropylbenx.enes About 418 424 404
Naphthalene Tetralin
1.5139 1.4951 1.605 1.500 1.497 1 &3
789
PER
CENT DISTILLED
790
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 33, No. 6
the thinner to cont,ain less than 1 per cent of olefins and no corrosive sulfur compounds. Advantage of proximate analysis lies in the fact that once the composition of a thinner or pair of thinners is known, a substitution or modification can be made in the coating formula and the desired result obtained on the first trial. Volatilities Boiling ranges of aromatic naphthas 1 and 2 were chosen to conform to conventional evaporation rates, that of No. 3 to correspond to the evaporation rate of the upper boiling half of mineral spirits. Since all three are more highly aromatic than the hydrogenated naphthas which they have replaced, they have lower average boiling points while mainWAVE LENGTH IN MICdONS taining the same evaporation rates. (AroABSORPTIONSPECTRA (THICKNESS OF CELL,0.08 MM.) matic hydrocarbons have higher latent heats FIGURE 3. INFRARED of vaporization than correspondingly boiling naphthenes and paraffins.) Evaporation rates no1 solvency (16) relates it t o a value of 100 for toluene and of aromatic naphthas 1, 2, and 3 are plotted in Figure 4, to40 for a standard primary-reference mineral spirits. gether with those of common fractions derived from petroleum MIXED ANILINE POINT,which replaces straight aniline and coal tar. The volumetric evaporometer used in these point as a solvency test for highly aromatic naphthas betests was patterned after that of Wetlaufer and Gregor (26), cause of the comparatively high freezing point of aniline, rewith three significant changes: Six evaporation tubes, quires no temperature control and provides an excellent measure of aromaticity for naphthas of similar boiling ranges. As now widely accepted for specification control test work, mixed aniline point is the critical solution temperature of a mixture of 10 ml. of anhydrous aniline, 5 ml. of thinner B '' ti under test, and 5 ml. of any naphtha having a 3 ! straight aniline point of 60.0" C. 0 PROXIUTE COMPOSITION, as determined by the method of the Philadelphia Paint and Varnish Production Club (9, 16, 179, has been found well adapted to the analysis of petroleum and coal-tar 30 naphthas which have been sufficiently well refined f 2o to eliminate all but traces of olefins and sulfur compounds-i. e., naphthas which consist almost entirely of aromatic, naphthenic, and paraffinic hvdrocarbons. It thus covers most uresent-dav TIME IN MINUTES commercial aromatic thinners, since FIGURE 4. EVAPORATION RATESOB SOLVESSOS AND OTHER PETROLEUM performance in metal baking enamels requires AND COAL TARTHINNERS
2
5 ~
TABLB 111. SYNTHETIC RESIXDILUTIONRATIOS
placed in parallel, receive equal quantities of air through stainless steel needle valves; an appreciably lower air rate is + used in order to prevent rippling of the pool of liquid; and each tube ends in a cylindrical tip, of uniform bore and 2-ml. capacity, and is calibrated with xylene a t 25' C. to read directly in per cent evaporated, in 5 per cent intervals. Before %. series of runs the six valves are equalized by evaporab ing toluene in each tube and adjusting the air flow until the six evaporation curves coincide. VISCOSITIESOF 50 PERCENTCOLDCUTSBY The apparatus is operated in a constant-temperaTABLE IV. GARDNER-HOLDT WEIGHT O F SYNTHETIC RESINSAND A SYNTHETIC RESINVARNISH I N HraHLY ture room held a t 25" C, and 50 per cent relative AROMATIC NAPHTHAS humidity. 3 Vola. AroCoalToluene matic TarTechLiterature Cited Aromatic + 1 Vol. Naph- Solvent nioal
toluene 69.5 Aromatic naphtha 1 46.3 3 vol. toluene 1 vol. lacquer diluent 45.8 loo xylene 59.9 Aromatic naphtha 2 53.6 Coal-tar solvent naphtha 54.1 Technical pseudocumene 49.0 a Milliliters of mineral spirits of 60' C. aniline point tolerated by a coldcut solution of 10 grams of freshly powdered Amberol 801 in 40 grams of highly aromatic naphtha, titrated a t 25O C. 2 O
2"
Toluene
Naphtha Laoquer IO" 1 DiluentO Xylene
tha 2
Naph- Pseudothab cumene
Gly tal 2452, solid T T W Y B/C g/C C Beciasol 1, solid &F E/B I/J 25-gal. Bakelite BR254tungoilvarnish A1/A2 Al/A2 Al/A2 A1 A/A1 A/Al C a Lac uer diluent is a straight-run petroleum naphtha of 60' A. P.I. gravity, boiling from 200-275' b
F.
Contains 96% aromatic hydrocarbons; boils in the same range as aromatic naphtha 2.
(1) Baldeschwieler, Morgan, and Troeller, IND.ENG. CHEM.,Anal. Ed., 9, 540 (1937). (2) Baldeschwieler, Troeller, and Morgan, Ibid., 7, 374 (1935). (3) Bruun, Hicks-Bruun, and Faulconer, J.Am. Chsm. SOC.,59,2355 (1937). (4) Egloff, "Physical Constants of Hydrocarbons", A. C . S. Monoeraoh. 78. New York. Reinhold
Pub. Gorp., 1939.
June,
INDUSTRIAL AND ENGINEERING CHEMISTRY
1941
(5) Glasgow, J . Research Natl. Bur. Standards, 21,535 (1938). (6) Hicks-Bruun, Bruun, and Faulconer, J . A m . Chem. SOC.,61,3099 (1939). (7) Hufferd and Kranta, A. C. S,Meeting, Boston, 1939. (8) McArdle, E. H.,IND.ENQ.CHEM.,Anal. Ed., 11,450(1939). (9) McArdle, Moore, Terrell, Haines, and cooperators, Ibid., 11, 248 (1939). (10) Mair, Beveridpe, and Willingham, J. Research Natl. Bur. Standnrd* 21- , (iX.5 -. -_,-- - I1F)RR). - - - -, (11) Mair and Streiff, Ibid., 24,395 (1940). (12) Mikeska, IND.ENQ.CHEM.,28, 971 (1936). (13) Mikeska, Smith, and Lieber, J . Org. C h m . , 2,499 (1938). (14) Petrov, J . Gen. Chem. (U. 8.S . R.) 9,509(1939). (15) Philadelphia P a i n t and Varnish Production Club, Natl. Puint, Varnish Lacouer Assoc., Sci. sect., Circ. 546,273 (1937). (16) Ibid., 568 (1938). (17) Philadelphia P a i n t and Varnish Production Club, Oficial Digest Federation Paint & Varnish Production Clubs, 1939,115.
.
*
791
(18) Rossini, Proc. A m . Petroleum Inst., 111, 18,36-59 (1937). (19) Sweeney and Tilton, IND.ENQ.CREM.,26,693 (1934). (20) Tongberg, Fenske, and Nichols, Ibid., 29, 70 (1937). (21) Tongberg, Quiggle, and Fenske, Ibid., 28, 201 (1936). (22) Tongberg, Sweeney, and Fenske, Ibid., 30, 166 (1938). (23) U.8. Tariff Commission. Rept. 136,2nd series (1938). (24) Vluater, Waterman, and Van Western, J . Inst. Petroleum Tech., 21, 661 (1935). (25) Waterman. Ibid.. 25. 805 (1939). (26j Wetlaufer 'and Gregor, IND. ENG. CHEM., Anal. E d . , 7, 290 (1935). (27) White and Glasgow, J . Research Natl. Bur. Standards, 22, 137 (1939). (28) White and Rose, Ibid., 21, 151, 167 (1938). (29) White et al., Ibdd., 22,316 (1939). PRESENTBD before the Division of Petroleum Chemistry at the 100th Meeting of the American Chemical Society, Detroit, Mich.
Calculation of the Boiling Points of Aromatic Hydrocarbons CORLISS R. ICINNEY University of U t a h , Salt Lake City, Utah
T
HE method of calculating The boiling points of aromatic hydronucleus upon the boiling point boiling points from molecumay be by using the which has no precise counterpart in aliphatic structures. lar structure I'( has been boiling point equation and the boiling point applied to the aromatic hydroThe conjugation of double bonds characteristic Of the aromatic in open-chain derivatives raises carbons. The boiling point i s hydrocarbons. The method is useful in the boiling point; consequently, calculated from the boiling point number of the molecule (B. P. predicting the boiling points of new cornbenzene would be expected to pounds a s well a s checking the boiling have a higher boiling point also. N.) by means of the boiling point equation* The B**' N' is !he However, it is not possible to points of those appearing in the literature, summation of the boiling point estimate the amount. The certain Ones Of which are numbers (b. p. n.'s) of the variinB. P. N. adopted for benzene ous atomic and structural groupcorrect or have other structures. Also, of 20.0 allows only 0.8 for ings in the molecule. The boiling point numbers may be used with the aromaticity of the ring. limitations to determine the structure of This is much less than the value method, while empirical, approximates the complex forces of 2.4 found for the conjugated unknown hydrocarbons. which affect the boiling points triolefins. The b. p. n. of the of organic molecules and which phenyl group is obtained by cannot be evaluated quantitatively a t present. The relalowering the B. P. N. of 20.0 one unit for each hydrogen tive effects of varying structure upon the boiling point are atom displaced. brought out by this procedure, and consequently b. p. n.'s The following example demonstrates the method of calmay be used for structural studies in ways not possible culating the boiling point of a simple derivative of benzene. with other physical properties less sensitive to structural The boiling point may be calculated from the B. P. N. of the variations. molecule by means of the boiling point equation, Boiling Points of Alkyl Benzenes B. P. = 2 3 0 . 1 4 q B m - 543 The B. P. N. of a simple alkyl derivative of benzene is obor i t may be obtained from the previous calculations given in tained by summing up the b. P. n.'s for the particular strutTable I1 of the work on aliphatic hydrocarbons (2). The ture, using the b. P. a ' s &en in 'l'able 1- Emphasis muat be calculation of the boiling point of sec-butylbenzene is as follaid on the requirement that the b. p. n.'s of all alkyl radicals lows. attached to benzene be calculated by using the b. p. n.'s of Benzene less 1 hydrogen 19.0 0.8 and 1.0 for each carbon and hydrogen atom, respectively, 3 crtrbon's in the main chain 2.4 6 hydro ens in the main chain 6.0 in the longest continuous chain beginning a t the point of 1 m e t h a branched chain 3.05 attachment of the benzene ring. Any side chains not conCalculated B. P. N. 30.45 Calculated B. P . 176.7' C. tained in the longest chain of each radical are assigned the Observed B. P. 173.5' C. b. p. n.'s of the branched alkyl groups. The boiling point of Certain polysubstituted benzene derivatives require the the benzene nucleus cannot be calculated from aliphatic additional b. p. n.'s gven in Table I to obtain satisfactory b. p. n.'s alone because of the uncertainty of the effect of the 8
