IMPURITIES in BENZENE Nonbenzenoid Hydrocarbons and Toluene in Refined Coke-Oven Benzene JOHN H. ANDERSON AND CARL J. ENGELDEH Mellon Institute and University of Pittsburgh, Pittsburgh, Pa, LTHOUGH “nitration beweno” ( I ) , the most important
referred to as paraffins) in benzene (I). Results of these testa on nitration benzene indicate a correlation between “paraffin” content and freezing point, the latter being depressed about 0.67’ C. per volume % of “paraffins”. An examination of the saturatod nonbenzenoid hydrocarbon impurities in nitration benzene seemed to be important in connection with the purification of benzene for use as a secondary physicochemical standard, and in connection with the use of nitration benzene in synthetic, especially industrial, organic chemistry. The sample (I) employed met the specifications for nitration benzene ( I ) , and the boiling range and freezing point specifications recommended by the AMERICANCHEMICAL SOCIETY (3) for analytical reagent benzene. We believc sample I is a typical produrt; i t was prepared in a modern by-product coke plant in
commercial grade of benzene, and analytical reagent benzme (3)may be relatively impure, very little attention appears to have been paid to tho identification of any impurities except thiophene. Stinzendarfer (8) concludes that most of the hydrocarbon impurities in a European refined coke-plant benzene arc iiaphthenes, and that the main hydrocarbon impurity is methylcyclohexane. Practical purification methods such as those of Swietoslawski (6) throw additional light on the nature of the hytlrocarbon impurities, and certain hydrocarbons boiling near benr w c have been isolated from high-temperature coal tar ( 9 ) . IVhitmore (10) states that the only impurity in “nitration benzol” is a small amount of thiophene. Standard methods of test have k e n devised for nonsulfonlttnble hydrocarbons (conveniently
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Figure 1. Plot of Condensation Temperature and Refractive Index as a Function of Volume for Saturated Nonbenzenoid Hydrocarbons Plus Some n-Pentane
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which an efficient batch benzene column is utilized in conjunction with the sulfuric acid refining process. Figure 1 is a distillation curve, giving condensation temperatures of distillate a t 760 mm., of a sample of saturated nonbenzenoid hydrocarbons secured from sample I, plus some n-pentane. Figure 1 also presents the results of refractive index (n2:) determinations of fractions of the distillate, and the normal boiling points (solid circles) and refractive indices (open circles) of the
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INDUSTRIAL AND E N G I N E E R I N G CHEMISTRY
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umn was constructed from the design of Mair and Foraiati (4, and their technique (6)was used. The sample was followed by the addition of 2175 ml. of n-pentane (na21.3575; condensation range 0.2' C.), and then by the addition of 3790 ml. of methanol (tested for hydrocarbons by extraction, with negative resulb). The refractive indices of the fractions of filtrate withdrawn at the bottom of the column are plotted against the total volume of filtrate withdrawn (Figure 2). When methanol was added to the adsorption column, a red zone immediately developed a t the top of the adsorbent. This zone was displaced by the addition of more methanol and was completely removed in the last fractions of the aromatic portion. The first fifteen fractions (1168 ml.) from the separation by adsorption were combined and fractionated under high reflux in a still with a column (1000 mm. high and 26 mm. in internal diameter) made of Pyrex and packed to a height of 960 mm. with singleturn 4-mm. (approx.) Pyrex helices. The column was jacketed by two other Pyrex tubes concentric with it, and the inner jacket was electrically heated. After the bulk of the n-pentane had been dutilled, the distillation data in Figure 1 were obtained, A total of 527 ml. of the distillate indicated was distilled from the column, after which the remainder (74 ml.) was carefully distilled from a 200-ml. distilling flask. The condensation temperatures were corrected for pressure fluctuations using 0.045' C./mm. for dl/dp. Data for the pure hydrocarbons shown in Figure 1 were taken, with permission, from reports of the American Petroleum Institute Research Project 44 a t the National Bureau of Standards.
Figure 2. Results on Separation of Saturated Nonbenzenoid Hydrocarbonsfrom Benzene by Adsorption
paraffins, cyclopentanes, and cyclohexanes whose normal boiling points are within the condensation temperature range of the bulk of the sample (7). The saturated nonbenzenoid hydrocarbon impurities were secured from sample I by the combined process of fractional crystallization and fractional adsorption. The sample of impurities is composed almost entirely of compounds which have boiling points between 80' and 101' C.; the bulk of the sample is composed of compounds boiling above 90' C. The measurements of condensation temperature and refractive index indicate that it is a complex mixture which is preponderantly naphthenic. The presence of cyclohexane, methylcyclohexane, 3-methylhexane or 3ethylpentane (or both), n-heptane or 2,2,4-trimethylpentane (or both), 1,l-dimethylcyclopentane,and trans-l,2-dimethylcyclopentane or truns-l,3-dimethylcyclopentane(or both) is indicated by the condensation temperature and refractive index measurements; however, all the paraffins and cyclopentanes and cyclohexanes whose boiling points are within the condensation temperature range of the sample may be present. A small amount of toluene was also detected in nitration benzene, and evidence has been obtained which suggests that an appreciable amount of unsaturated impurities may be present. EXPERIMENTAL PROCEDURE
Sample A (28.5 liters), consisting of the mother liquor from the first commercial crystallization (2) of a large lot of sample I, was fractionally crystallized until 770 ml. of a highly contaminated product (B) was obtained. Intermediate fractions, which at the end of more than two hundred crystallizations became so small in volume as to be practically negligible, were added to the purified fraction (C). The solidifying temperatures ( 1 ) were as follows: I, 5-20' C.; A, 3.50'; B, approximately -50"; C, 4-68" C. The boiling range (I) of sample I was 0.8' C. and the acidwash color (I) O+. Total sulfur in sample I was 0.003470;in A, 0.015% (Harris lamp). Fraction B was filtered through 2825 grams of silica gel (Davison Chemical Corporation, specification 659528-2000) contained a in Pyrex column 250 cm. high and 5 om. in diameter; the col-
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Figure 3. A , Plot of Condensation Temperature as a Function of Volume for Aromatic Hydrocarbons Found in Fraction B (Plus Some n-Pentane and p-Cymene); B, Data Obtained between Benzene and p-Cymene Plateaus Plotted to a Wider Scale
The aromatic portion (indicated in Figure 2) was extracted with several portions of water, and then washed eight times with sulfuric acid (specific gravity 1.84) a t about 25' C., in amounts equal to 3% of the volume of the extracted product. During the water extraction a considerable sludge developed; this was removed before the extracted product was washed with sulfuric acid. The acid-wash color ( 1 ) of the acid layer was 7f throughout the first five treatments; then it gradually fell to If. The acid-washed product was neutralized with a 10% aqueous solution of sodium hydroxide, washed twice with water, and dried over anhydrous calcium sulfate. Twenty-five milliliters of p cymene (a middle fraction, condensation range 0.2" C., from Eastman White Label) was added, and the product was fractionated under high reflux in a still with a column (1150 mm. high and 11 mm. in internal diameter) made of Pyrex and packed to a height of 1000mm. with single-turn 4mm. (approximately) Pyrex
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INDUSTRIAL AND ENGINEERING CHEMISTRY
helices. The distillation data, after the bulk of the n-pentane had been removed, are shown in Figure 3A. That fraction of the distillate (13ml.) intermediate between the benzene and p-cymene plateaus, indicated in Figure 3B, was examined by ultraviolet spectrophotometry with the following results (in per cent) : benzene, 33.1; toluene, 32.8;p-cymene, 33.3; other material, 0.8, The following volumes of various products were found in fraction B: saturated nonbenzenoid hydrocarbons, 567 ml. (Figure 1); benzene, 84.3 ml. (Figure 3A); toluene, 4.3 ml. (spectrophotometric analysis); loss, 114.4ml. (by difference).
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ACKNOWLEDGMENT
We are pleased to acknowledge the kind cooperation of Wojciech Swietoslawski and William L. Glowacki, both of Mellon Institute. We are also grateful to B. E. Stewart and Frank C. Lauer of Jones and Laughlin Steel Corporation, for furnishing the samples, and to Alberta 5.Jones, who assisted with some of the crystallizations. The spectrophotometric analyses were kindly made by N. D. Coggeshall and M. Muskat, of Gulf Research & Development Company. LITERATURE CITED
DISCUSSION
Since the purpose of this work was to characterize only the saturated nonbeneenoid hydrocarbon impurities, fraction B was not analyzed for thiophene, bromine number, or acid-wash color. However, the behavior of that fraction in the adsorption column (unlike a blank run on the same lot of adsorbent), the large quantity of sludge and acid-wash color$ developed during treatment of the so-called aromatic portion, and the large amount of unrecovered material suggest the presence of unidentified impurities; some of these are believed to be unsaturated hydrocarbons. Fraction B was obtained from 28.5 liters of sample A by purification of the latter through a change of solidifying point equal to 1.18” C. I n the absence of a better method of calculation, this information and the volumes of products recovered from fraction B may be used to estimate the order of magnitude of the amounts of impurities in the original nitration benzene. Our estimate (in volume per cent) follows: saturated nonbeneenoid hydrocarbons, 0.6; toluene, 0.004;unidentified, 0.1,
(1) Altieri, V. J., “Gas Chemists’ Book of Standards for Light Oils and Light Oil Products”, New York, Am. Gas Assoc., 1943. (2) Campbell and Wagner, U.S.Patent 1,991,844(Feb. 19,1935). (3) Collins, W. D.,et al., IND. ENGI.CHEM.,ANAL. ED., 4, 347 (1932). (4) Mair and Forziati, J. Research Natl. Bur. Standards, 32, 151 (1944). (5) Ibid., 32, 165 (1944). (6) Morton, H. A., “Laboratory Technique in Organic Chemistry”, p. 61,New York, McGraw-Hill Book Co., 1938. (7) Rossini, Mair, Forziati, Glasgow, and Willingham, Oil Gas J., 41, 106 (1942); Petroleum Rejiner, 21,73 (1942). (8) Stinzendarfer, Oel u. Kohle, 38, 193 (1942). (9) U.S. Bur. Mines, B d l . 412 (1938). (10) Whitmore, F. C., “Organic Chemistry”, p. 698, New York, D.Van Nostrand Co., 1937. TAKBIN in part from a Ph.D. thesis submitted by J. R. Anderson to the University of Pittsburgh. Contribution 652 of the Department of Chemistry, University of Pittsburgh. J. R. Anderson holds an Industrial Fellowship of the Pittsburgh Steel Company a t Mellon Institute.
Reactions of Hydrocarbons in the Presence of Cracking Catalysts J
POLYMERIZATION OF GASEOUS OLEFINS’ CHARLES L. THOMAS Universal Oil Products Company, Riverside, 111.
T
HE synthetic cracking catalysts are capable of accelerating a variety of hydrocarbon reactions. The type of reaction depends on the hydrocarbon involved and the thermodynamic conditions applied to the system containing the hydrocarbon and the catalyst. It has already been shown that the synthetic cracking catalysts readily sever carbon-carbon bonds in olefins such t\9 octene and hexadecene at atmospheric pressure and 350500’ C. to produce olefins of lower molecular weight (9). I n one sense this cracking of olefins can be regarded as depolymerization. A classical catalyst-that is, a substance that hastens equilibrium-should be capable of accelerating the reverse reaction, polymerization, if the appropriate changes in thermodynamic conditions are made. I n the work reported here, several different synthetic catalysts which had been shown to be active wwking catalysts were studied. Gaseous olefins have already been polymerized by masses containing silica and alumina. The natural clay known 9a. floridin or Florida earth has been studied extensively. Apparently Gurvich (8) was the first to observe that it would polymerize gaseous olefins. This clay is a hydrosilicate of alumina containing 1
The four previous articles in thie seriea appeared in J . Am. Chem. Soc.,
61, 3671 (1939); 66, 1686, 1689, 1694 (1944).
both iron and magnesium compounds. This and numerous similar clays, either with or without acid treatment, have received considerable scientific (2, 16, 16, 21, 82, 84, 86) and technical (7,10,16,14, 19,10, 26) study as polymerization catalysts. I n general the polymers resulting were dimers, trimers, and tetramers, although small proportions of still higher polymers may have been formed. Isobutylene was especially easy to polymerize. Floridin is capable of polymerizing isobutylene at temperatures as low as -100’ C. (16,82). The molecular weight of the isobutylene polymers was found to increase as the temperature was lowered, The higher-molecular-wcight polymers were elastomers. Apparently Gayer (6) ww the first to report work on a synthetic silica-alumina catalyst for the polymerization of gaseous olefins, His catalyst was prepared by the hydrolytic adsorption of alumina on a silica xerogel. The resulting catalyst contained about 1% alumina. This catalyst produced mainly dimers and trimers under the conditions studied. The same type of catalyst was investigated in considerable detail by Hoog, Smittenberg, and Visser (9) and KazanskiY and Rosengart (19). Related synthetic silica-alumina catalysts have been described for olefin polymerization (1,4,6, ff,18).
