INDUSTRIAL AND ENGINEERING CHEMISTRY
April 1953
lecular weight due t o splitting of the less stable compounds. I n the light of the present data this mechanism appears more probable than one of thermal cracking of the benzene-insoluble materials followed by a saturation of the fragments.
TABLE 111. ULTIMATECOMPOSITION OF BENZENE-INSOLUBLES REMAINING Expt. No.
.
Initial Hydrogen Pressure, Reaction Lb./Sq. Time, Inch Gage Min. Hydrogen
1607 1630 1754
1000 1000 1000
30 60
1601 1633 1745
2000 2000 2000
1622 1664 1755
3000 3000 3000
0
5.4 5.20 5.32
30 60
0
5.3 5.85 5.76
0 30 60
5.73 5.79 5.60
Benzene-Insolubles Carbon Nitrogen Sulfur Catalyst, Tin 79.35 82.33 84.25
Oxygen
H/C Atom Ratio
1.9 2.07 2.14
0.85 0.98 1.44
12.5 9 42 6.84
0.817 0.758 0.758
79.9 81.80 84.91
1.90 1.94 2.03
0.95 1.30 2.77
11.95 9.12 4.51
0.796 0.858 0.814
81.83 82.50 79.80
1.97 1.87 2.02
0.82 2.14 3.90
9.60 7.65 8.66
0.840 0.842 0.842
Catalyst, Molybdenum 77.70 2.02 80.57 2.09
1976 1734
500 500
18 32
5.19 5.51
2.17 3.38
12,92 8.44
0.801 0.821
1982 1733
1000 1000
32
21
5.64 5.52
78.84 78.63
1.95 2.02
2.56 3.54
11.01 10.30
0.858 0.842
1970 1761
2000 2000
23 36
5.59 5.19
78.43 73.55
1.87 1.86
3.15 6.75
10.96 12.65
0.855 0.847
1969 1759
3000 3000
24 34
5.72 5.15
75.96 70.84
1.77 1.69
5.54 5.73
11.01 16.59
0.904 0.872
1977 1758
4000 4000
21 34
5.64 5.18
74.72 70.44
1,63 1,82
5.07 6.39
12.94 16.17
0.906 0.882
might be a direct addition of hydrogen to the benzene-insoluble fraction, with concomitant removal of carbon dioxide, water, and gaseous'hydrocarbons. This implies that the formation o f benxene-solubles probably proceeds by means of saturation of the benzene-insolubles, with a possible subsequent decrease of the mo-
(6) Weller, S., Pelipets, M. 42, 330-4 (1950).
809
LITERATURE CITED
(1) Falkum, Einar, and R. A., Fuel, 29, (1950). (2) Pelipets, M.,Kuhn, Friedman, S., and
Glenn, 178-84
E. M., Storch, H. H., IND.ENG.CHEM.,
40,1259-64 (1948). (3) Pelipetr, M. G., Weller, S., and Clark, E. L., Fuel, 29, 208-11 (1950). (4) Weller, S., and Pelipetz, M. G., IND.ENG.CHEM.,43, 1243-6 (1951). (5) Weller, S., Pelipetz, M. G., and Friedman, S., Ibid., 43, 1572-9 (1951). G., Friedman, S., and Storch, H. H., Ibid.,
RECEIVED for review May 15, 1952. ACCEPTED December 10, 1952. Presented before t h e Division of Gas and Fuel Chemistry, AMERICAN CHEMICAL SOCIETY, State College, Pa., May 5, 1952.
Action of Light on Tar Fractions U
C. R. KINNEY AND M. B. DELL The Pennsylvania State College, State College, Pa.
T
HE deposition of insoluble matter frequently observed when
..
I
3
.
solutions of various bituminous products, particularly coal tars, are allowed to stand is familiar to everyone who has worked with these materials, but the cause is obscure. Hubbard and Reeve, working with carbon disulfide solutions of tars, suspected that a reaction with the solvent occurred (IO), but later considered the possibility of oxidation (9). Weiss e(16, 1 7 ) compared aniline and toluene solutions and found that while the aniline solutions remained clear a precipitate appeared in the toluene solutions. He also found that the longer tars were allowed to stand in contact with solvents, such as benzene, toluene, carbon disulfide, and chloroform, partly in solution, the greater was the amount of insoluble matter obtained on filtration. Joestes and Siebert (11) observed that cresol-Tetralin extracts of a Hessian brown coal deposited a precipitate when exposed to sunlight. And in 1948, Green and Thakur (8) reported analyses of precipitates obtained from benzene solutions of tar on standing. The analyses suggested, although Green and Thakur did not so state, that oxidation was involved in the precipitation. These authors also investigated the effect of ultraviolet light on the deposition of free carbon and found a definite increase. Oxidation, accelerated b y the action of light, has been shown by Thurston and Knowles (16)to increase the rate of weathering of bituminous binders and coatings. I n view of these results, i t was of interest to determine whether precipitation from tar extracts was related to this weathering prop.erty of tars. For this investigation, pentane extracts of several
tars and bituminous materials containing the so-called tar oils were exposed to light under various conditions. SAMPLES USED
The properties of the four bituminous materials investigated in detail are given in Table I.
TABLE I. PROPERTIES OF TARS Property Sp gr. 2O0/2Oo ASTM' dist.. D 2030, O C.. wt. 70 RT-170 170-235 235-270 270-300 300-350 350-400 Pentane-soluble, wt. %
Coke Oven 1.18
Dehydrated Water Gas 1.16
Horizontal Retort 1.25
2.3 7.2 10.0 6.1
0.7 15.0 13.0 8.1
...
... ...
0.6 4.9 7.4 4.9 11.3
...
( uies to tungsten lamp fitted with various filters)
Filtei
Sone Cu804solutionb NaNOz solutionC S o . 338d KzCr207 solutione S o . 243d
Transmitted Wave Length, A.
Ppt.a Wt. %
3300-6700 -411 above 4200 All above 5000 .411 above 5700 All above 6500
0.14 0.12 0.15 0.03 0.04 0.00
Wt. Yo of tar oils. b 10 grams CuSO4.5HzO per SO grams Hz0. c 80 grams SaNOz per 100 grams Hz0. d Glass filters manufactured by Corning Glass Works, Corning, N. Y. e 7.6 grams KzCrnO7 per 100 grams Hz0. a
OF TEMPERATURE O N PHOTOLYSIS OF TABLE VI. EFFECT i.2% EXTRACT OF DEHYDRATED WATERGASTAR
(12-hour exposures t o tungsten lamps A and B) Temp. of photolysis a C. 21 2 21 Temp. before filtration, C. 25 25 0 Time at temp. before filtration hours 14 12 12 Ppt.. 4t. % of t a r Lamp A 0.11 0.15 0.15 Lamp B 0.06 0.08 0.09
The appearance of an adherent film of product on the cell wall nearest the light source suggested that a part of the precipitation might have been caused b y heat effects a t the glasspentane interface, although the cells were jacketed with cooling water a t 21" C. For this reason, photolyses using ice water as coolant were compared with the normal procedure (Table VI). The experiments were run in duplicate with a second (identical) microscope-lamp arrangement. It will be observed that cooling had an effect but that i t was in the direction of increasing rather than decreasing the yield. Cooling the solution after photolysis at 21 C. gave the same increased yield as cooling during photolysis. These results suggest that cooling simply decreased the solubility of the product. Thus, it appears that the reaction was essentially photolytic and not thermal in nature. This was further verified b y experiments in which infrared radiation was also found t o be ineffective. The differences in yields with the two lamps shown in Table VI are believed to be due to differences in light energy transmitted to the two cells. O
Vol. 45. No. 4
EFFECTOF OXYGEN. The reaction definitely involves sniall amounts of oxygen. Thus, in Figure 6 it will be seen that as the amount of flushing with oxygen-free nitrogen (passed through alkaline pyrogallol solution) was increased, the yield of precipitate from the horizontal retort tar with 3-hour exposure to the mercury lamp decreased until a minimum value, amounting to about one fifth of that in the presence of oxygen, was obtained. After the photolyzed oxygen-free solution had been filtered and saturated with air, a normal precipitate of 0.47% was obtained compared with the original value of 0.42%. However, when air or oxygen was bubbled through the solution during photolysis, the yield of precipitate was not increased. From this it is apparent, that, although oxygen is involved in the formation of a large part of the precipitate, the amount of light available is the controlling factor under normal conditions. All of the four tar extracts gave much smaller yields when flu'shed with nitrogen, as will be observed in Table 11. The residual yields may be due to traces of oxygen remaining in the solution, but i t seems more likely that the tar oils contain minor amounts of compounds that undergo polymerization on exposure to light. Oxygen was also removed directly from the pentane solution by alkaline pyrogallol and by Fieser's reagent. With the extract from the water gas tar, no visible precipitate appeared when either the tungsten or the mercury lamp was used. T h a t alkali was not responsible for the prevention of the precipitation vias shown by obtaining a normal yield after shaking the pentane solution with alkali prior to photolysis. However, alkaline treatment of extracts from the coke oven tar and the fluidizer tar gave decreases from 0.52 to 0.38% and from 1.14 to 0.74%, respectively. As these tar. contain more phenolic derivatives than water gas tar derived from petroleuni residues, i t is possible that these tars contained phenolic deriva t i v e s c a p a b l e of undergoing the photolytic reaction. Because the precipitation appeared to be essentially a photooxidation process, the effect of adding antioxidants was investigated. Hydraquinone was too insoluble in pentane to have much effect,b u t p - tert - butylcatechol, instead of decreasing the precipitation, ino0 01 0.2 0.3 0.4 0.5 creased it by about AMOUNT OF NITROGEN IGU F T 1 50%. Even the Figure 6. Effect of Kitrogen amount Of PreFlushing o n Yield of Precipitate cipitation occurring on standing in the dark was increased, The effect of nietallic sodium was similar to that of sodium hydroxide. Although elemental oxygen did not increase the amount of precipitate, the addition of benzoyl peroxide markedly increased it. In one experiment 10 ml. of a saturated solution of benzoyl peroxide in pentane (0.59%) was added to 67 ml. (41.6 grams) of a 4.2y0 pentane extract of the dehydrated water gas tar and then photolyzed 21 hours with the microscope lamp. The product amounted to 0.98% of the tar oils, compared with 0.18% with no added peroxide, When the peptane solution of benzoyl peroxide was exposed to light, no precipitation occurred. I n another series of experiments, a 3.44% extract of the samr tar
t-
April 1953
INDUSTRIAL AND ENGINEERING CHEMISTRY
was treated in the same way for six successive exposures, 10 mi. of benzoyl peroxide solution being added before each photolysis. The percentage of precipitate amounted to 1.38, 1.19, 0.84, 0.92, 0.93 and l.22y0, respectively. A part of the variation was due to the use of different microscope lamps, but as before there appeared t o be little tendency for the yield to decrease markedly. The successiveprecipitates became lighter in color and approached a light tan. EFFECT OF OTHER REAGENTS. On the assumption that bromine might react with the structures which are involved with the photo-oxidative process and thereby prevent the reaction, bromine in excess was added to a pentane extract of the water gas tar. After the excess bromine and hydrobromic acid had been neutralized with sodium bicarbonate and filtered, a yield of 0.8% of a black precipitate was obtained, compared with O.lyo of light brown precipitate from the unbrominated extract, on photolyzing for 21 hours with the microscope lamp. Concentrated sulfuric acid, on the other hand, completely removed the photosensitive material from the above pentane extract. At the same time it decreased the concentration of tar oils from 4.8y0to 2.5y0. Dilute sulfuric acid (25%) wasmuch less effective. With extracts from the coke oven and the fluidizer tars, the amount of precipitate on exposure to the mercury lamp for 3 hours was decreased from 0.5 to 0.3y0and from 1.1to 0.9%, respectively. Because certain aromatic hydrocarbons which undergo photooxidation also react with maleic anhydride (W), the latter reaction was applied to an extract of the dehydrated water gas tar. Two 4-gram samples from which the pentane had been removed were dissolved in 35 ml. of benzene and to one 6.3 grams of sublimed maleic anhydride were added. The two solutions were refluxed for 35 hours and allowed to stand in the dark for 1 week. Nothing separated from either solution. After the benzene had been removed the two residues were extracted with 120 grams of pentane, filtered, and photolyzed for 21 hours with the microscope lamps. From the solution which had not been treated with maleic anhydride the usual quantity of precipitate was obtained, but none from the other. This result seemed to confirm the hypothesis that the photosensitive structures also react with maleic anhydride, which suggests that they are aromatic in character or a t least contain the diene structure. On this basis the action of concentrated sulfuric acid may be readily explained. The photoreactive material was also adsorbed on activated carbon. Five times the weight of solute, using Nuchar, resulted in the complete removal of the photosensitive material. This treatment also eliminated the Tyndall effect. Smaller quantities of the absorbant did not completely remove the sensitive constituents. Norit, Celite No. 270, and activated alumina were less effective, in that order, than Nuchar. If the photosensitive compounds EFFECT OF FRACTIONATION. were largely aromatic hydrocarbons, i t should be possible to vacuum-distill them, unless their molecular weights were too high or they were thermally unstable. For the purpose of determining these factors, tar oils from the water gas tar were fractionated and then irradiated in the following manner. The tar oils were extracted from the undehydrated water gas tar emulsion by extracting with 4.2 times its weight (10 times the weight of dry t a r ) of pentane. After the pentane had been distilled off, the extract was fractionated at 12 mm. with microbubbles of oxygen-free nitrogen t o avoid bumping. The fractions, including the partially carbonized residue of 1.S%, were dissolved in or extracted with pentane to give approximately 4y0 solutions, filtered, and irradiated for 21 hours with the microscope lamp. Not all of the high-boiling fractions were soluble in pentane. This may be partly due t o thermal polymerization, but it may also be due in part to the separation of solubilizing Iowet boiling hydrocarbons present in the original extract.
Up to 180' C. (12 mm.) none of the fractions gave photolytic precipitates, but all above that temperature from 180 O to 260" C., including the residue, gave precipitates. The total yield was,
813
however, only 0.05% compared with yields of 0.10 to 0.16% obtained from the extracts of the thermally dehydrated tar under similar conditions. These results indicate that about half of the precipitate was formed from distillable substances. These extracts were even sensitive to the removal of pentane by distillation. For example, a 4.08y0 pentane extract of the coke oven tar was distilled until the concentration reached 15.070. On subsequent dilution with pentane to 4.16% and photolyzing for 5 hours in the mercury lamp apparatus, the precipitate amounted to 0.77%, compared with o.45y0 from the original extract under identical conditions. 1.0,
I
J
0.2 0.1
Figure 7.
Optical Densities of Precipitates
PROPERTIES OF PRECIPITATES. The photo-oxidation precipitates from pentane extracts were soluble in aromatic hydrocarbons, acetone, chloroform, carbon disulfide, and pyridine, but only partly soluble in alcohol and insoluble in pentane and "iso-octane." Microanalyses indicated an atomic carbon-hydrogen ratio of greater than 1 and the presence of over 7% oxygen (by difference), while the precipitate obtained with added benzoyl peroxide contained over Byo. The normal precipitates did not give the peroxide test, using the method of Nozaki (lQ),and on pyrolysis little free oxygen was obtained. For the latter purpose a micro gas-analysis apparatus was used similar to that described by Blacet and Leighton (a),with yellow phosphorus as the absorbant. From the decomposition of 24 mg. of precipitate from the water gas tar extract, a t 245" C., 0.12 ml. of gas was obtained and the contraction in contact with phosphorus was 1.4y0. This seems to show that the photolytic products from pentane extracts of tars, for the most part, were not transannular peroxides of aromatic compounds which yield oxygen on pyrolysis ( 4 ) : however, the small amount of oxygen released probably came from such structures. On the other hand, it seems that a considerable part of the precipitate was similar to the resinous precipitates observed in the irradiation of certain aromatic compounds (1, 6,1s). The optical densities of the photolytic products from the four tars and the steam-reduced petroleum asphalt are shown in Figure 7. The spectra were measured with a Beckman Model D U quartz spectrophotometer using 1.0-cm. cells and chloroform solutions of 10 mg. per liter concentration. The optical densities of the water gas, coke oven, and horizontal retort tar products were remarkably similar and suggest similar fundamental structures. The absorption of the fluidizer tar product was also similar, b u t the smaller absorption a t the shorter wave lengths suggested dilution of the characteristic structure with some other less absorbant material. The curve for the petroleum-asphalt product indicated still greater differences in structure, particularly structures responsible for the greater absorption in the longer wave lengths and less absorption in the shorter region. The absorptions of these photolytic precipitates are similar in shape to that obtained from neutral resins prepared from vertical retort tar by Green and Muckherji ( 7 ) . This similarity in absorption suggests that these various products may be related in struc-
814
INDUSTRIAL AND ENGINEERING CHEMISTRY
ture. Jones ( l a )found that only polyphenyl hydrocarbon derivatives have a single maximum in the region of maximum absorption of the tar photolytic products-i.e., 2440 to 2480 A. Gillam and Hey ( 6 ) report single maxima for the metapolyphenyls of 2500 to 2600 A. in chloroform solution and for parapolyphenyls, variable maxima between 2500 and 2900 A. These data suggest the possibility that the light-sensitive components of tars contain fundamental structures to which phenyl groups are attached. Several 9,lO-diphenylanthracene derivatives ( 1 , 6, I S ) have been found to undergo photo-oxidation. CONCLUSIONS
The precipitation of insoluble matter from pentane extracts of tars has been found to be a photo-oxidation process and, therefore, appears to be related to the weathering of bituminous materials when exposed to air and sunlight. The effective range of wave lengths lies in the region below 5000 8 . ,where complete absorption by the tar extracts occurs. I n contact with air, the amount of precipitation varied with the intensity of the incident light and the time of exposure. Under ordinary conditions sufficient dissolved oxygen was available for many hours of photolysis, but removal of oxygen from the solution effectively stopped the precipitation. An attempt to inhibit the reaction by the addition of an antioxidant was unsuccessful, but it is possible that other reagents would be more effective. The similarity of the absorption spectra of the photolysis products suggests that the
Vol. 45, No. 4
same types of structures in each of the tars are involved in the formation of the precipitates on irradiation and are aromatics of higher molecular weight. LITERATURE CITED
Allais, A., Compt. rend., 220, 202 (1945). Bergmann, W., and AIcLean, M . J., Chem. Reus., 28,367 (1941). Blacet, F. P., and Leighton, P.A., IND.EXG. CHmr., ANAL. ED.,3,266 (1931). Dufraisse, C., Bull. soc. chim., 53, 789 (1933). Dufraisse, C., hlellier, M. T., and Ragu, G., Compt. ?end., 218, 121 (1944). Gillam, A. E., and Hey, D. H., J . Chem. Soc., 1939, 1170. Green, S. J., and Muckherji, S. &I., J . Soc. Chem. I n d . , 67, 438 (1948). Green, S.J.,and Thakur, B., IEid., 67, 423 (1948). Hubbard P.. and Reeve. C. S..IND.EXG.CHEbr.. 5 . 15 11913). Hubbard, P.',and Reeve,' C. S.,'Proc. Anz. Soc. T e s ' t k i Materiais, 10,420 (1910). Joestes, F., and Siebert, K., Oel u. Kohle, 14,777 (1938). Jones, R. N., Chem. Reos., 32, 1 (1943). Mellier, M. T., Compt. rend., 219, 188 (1944). Nozaki, K., IND.EN^. CHEM.,ANAL.ED.,18, 583 (1936). Thurston, R. R., and Knowles, E. C., ISD. ENG.CHEV.,33, 320 (1941). Weiss, J. M.,Vol. 3, p. 527, "Colloid Chemistty" by J. 41exander, New York, Chemical Catalog Co., 1931. Weiss, J. R i . , J. IND.EXG.CHsnr., 6, 279 (1914). RECEIVED for review -4ugust 16, 1952. ACCEPTED December 2 2 , 1962. Presented before the Division of Gas and Fuel Chemistry, AXERICANCHEMICAL SOCIETY, State College, Pa., May 6 , 1952.
Volumetric and Phase Behavior of Mixtures of Nitric Oxide and Nitrogen Dioxide F. T. SELLECK, H. H. REAMER, ANI B. H. SAGE California Institute of Technology, Pasadena, Calif.
T
HE phase behavior of mixtures of nitric oxide and nitrogen dioxide has not been studied a t elevated pressures. Epstein and Cirkova (3)determined the two-phase pressures of mixtures of these oxides of nitrogen containing as much as 0.38 weight fractim of nitric oxide a t temperatures between 68" and 140" F. for pressures below 240 pounds per square inch. The compositions of the mixtures investigated were related to the earlier measurements of Baume and Robert ( I ) , who studied this binary system a t temperatures below 68" F. Wittorf (19) determined the limits of solubility of nitric oxide in nitrogen dioxide in the same range of temperature as was reported by Baume and Robert. Puree11 and Cheesman (9) measured the solubility of nitric oxide in nitrogen dioxide a t temperatures below 51 F. for pressures less than 68 pounds per square inch. Whittaker and coworkers (17') determined the two-phase pressure for six mixtures of nitric oxide and nitrogen dioxide for compositions containing up to 0.169 weight fraction of nitric oxide. The measurements were made at temperatures between -40' and 59' F. Their results are in reasonable agreement with those of Baume and Robert (1). The effect of pressure and temperature upon the specific volume of the components has been investigated in some detail. Briner and coworkers (E) established the volumetric behavior of nitric oxide at low temperatures and Johnston and Weimer (6) determined the second virial coefficient a t temperatures up to 70" F. for pressures below 1 atmosphere. Recently the volumetO
ric behavior of this compound was studied a t pressures up to 2500 pounds per square inch for temperatures between 40" and 220' F. ( 4 ) . Verhoek and Daniels ( 1 6 ) and Rlittasch and conorkers (8) dctermined the volumetric behavior of nitrogen dioxide in the gaseous region for temperatures below 113" F. Scheffer and Treub (12) measured the vapor pressure of this compound up to the critical temperature. Recently additional measurenients have extended the knowledge of the volumetric behavior of the liquid and gas phases of this compound to temperatures of 340" F. and pressures up to 7000 pounds per square inch (10, I S ) . Kobe and Pennington (7') recently revie13 ed the thermochemical characteristics of nitrogen and its oxides. The present measurements are concerned with the volumetric behavior of 15 mixtures of nitric oxide and nitrogen dioxide a t compositions containing as much as 0.2 weight fraction nitric oxide a t pressures up to 7000 pounds per square inch in the temperature interval between 40' and 340' F. Four of these mixtures were investigated in detail and the remainder mere studied throughout the indicated temperature interval a t nearly a single specific volume, The dew point and bubble point states for four mixtures were determined as a function of temperature. METHODS
The methods employed in this investigation were similar to those described earlier for the study of the volumetric behavior
