1604
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLE I11 Initial Decrease Ka,, Photo- Steady State in Viscosity, scission 0 2 AbsorpAmine (0.03 X ) CP. %/Hou; tion h None (blank) C n-Butylamine Dibutylamine Tributylamme tsrt-Butvlamine Tetraethylenepentamine 20 .... 0.1 Polyethylenimine 0.11 0 0 Tetramethyldiaminisoqropanol 10 0.18 0 15 Ethylphenylethanolamine 7 0.08 0.1 0 First order rate constant. b Oxygen absorption expressed in 10-2 moles O d b a s e mole GR-S/hour after first 15 hours. C Original viscosity, 51 cp.
oxidant which is not a photosensitizer should function as a light stabilizer. The cause of the failure of the antioxidants studied to function as light stabilizers of GR-S is shown t o be related to the occurrence of a very low rate of oxidation of the GR-S despite the presence of the antioxidant. The cause of the viscosity rise in GR-S solutions on autoxidation appears t o be the formation of an intermolecular peroxide bond which is subject to induced scission.
..
The second hypothesis ia subject to test, for if it were true the amines xould not function as antioxidants a t room temperature in the dark. The third hypothesis might be called paint-drier behavior for such is the probable mechanism of the action of oilsoluble copper, cobalt, and iron salts in promoting autoxidation of drying oils. It would have to be assumed in addition t h a t a t high temperatures either the induced decomposition proceeds less efficiently with respect to free radical generation or that the labile peroxide is not even transiently formed. CONC LUSIOK S
Vol. 43, No. 7
LITERATURE CITED
(1) Blake, 3. T., and Bruce, P. L., ISD.ENG.CHEM., 33,1198 (1941). (2) Buclungham, R., and Planer 0. V., T r a n s . Inst. Rubber Ind., 21, 175 (1945). (3) Harvey, M. T., and Caplan, S , U. S. Patent 2,247,495 (Julz 1, 1941). (4) Lacau, J., and Magat, hl., Dzscussions Faraday SOC.,1947, No 2, p. 388. (5) Matheson, L. h.,and Boyer, R. F., U. S. Patent 2,287,188 (July 23, 1942). (6) Modern Metalcraft, Midland, Mich. (7) Sozaki, K., and Bartlett, P. D., J . Am. Chem. SOC.,6 8 , 1686 (1946). (8) Pauling, L., Wood, R. E., and Sturdivant, J. H., Science, 103, 388 (1946); J . Am. C h e n . Soc., 68, 795 (1946). (9) Spolsky, R., and Williams, H L., IXD.ENG.CHEM.,42, 1847 (1950). (10) Stevens, H. P., J . Soc. Chem. I d . , 64, 312 (1945). (11) Whitby, G. S.,Wellman, N., Flouts, V. W., and Stephens, H. I)., ISD. ENG.CHEM.,42,445,452 (1950). RECEIVED September 5 , 1950.
Photoscission of GR-S in ethylbenzene solution has been shown t o require the interaction of oxygen. I n principle then an anti-
Presented before the Division of High Polymer Chemistry, 118th Meeting of the AMERICANCHEMICAL SOCIETY Chicago, Ill.
Gum Formation in Shale-Oil Naphtha G. U. DINNEEN AND JV. D. BICICEL' U . S. Bureau of Mines, Laramie, Wyo. Two distinguishing characteristics of untreated shaleoil distillates are their dark color and large gum content. The work reported in this paper was undertaken in an effort to establish the factors responsible for this apparent instability. It was found that the gums from shale-oil naphthas contain about 89'0 nitrogen. This is the principal difference in elemental composition between them and gums obtained from petroleum naphthas. The nitrogen appearing in the gum comes both from pyrrole and pyridine-type
compounds found in t-e naphtha. Oxidation is far more important than light or heat in the formation of gum i n shale-oil naphtha. The rate of gum formation is very rapid when the naphtha is first exposed to accelerated oxidizing conditions, but decreases sharply after about 1 hour. Information on the factors and compounds responsible for gum formation in shale-oil naphtha is necessary as a basis for the development of handling and refining methods for shale-oil products.
T
oxidation, probably peroxides (5, 7 , 10, 11, 15-15), catalyze the oxidation of normally less reactive hydrocarbons to increase greatly the rate of gum formation. Most of the oxidation products are soluble in the naphtha but decompose during evaporation to give gum composed largely of acidic material ( I S ) . Shale-oil naphthas contain larger quantities of nitrogen and sulfur compounds than most cracked petroleum naphthas. As certain types of these compounds are reactive, it appears probable that factors in addition t o those responsible for the gum in cracked petroleum distillates may be involved in the formation of gum in shale-oil naphtha. Mapstone (9) has shown t h a t addition of nonpurified tar bases to a refined naphtha increased the gu111 content. He attributed this increase to the presence of pyrroles in the tar bases. A brief investigation ( l a ) by this laboratory of gum formation in a thermally cracked shale-oil naphtha indicated
HE color of shale-oil naphtha when first distilled ranges from
very pale yellow to amber. However, if exposed to ordinarv room conditions, it will become dark purple and start to deposit gum on the sides of the container within a very short time. Large quantities of existent gum are produced after a fe\T days or even hours of such storage. Consequently, knowledge of the major factors involved in this gum formation is of primary importance in the development of handling and refining procedures. The formation of gum in cracked petroleum naphthas has been studied extensively and it seems to be generally agreed that oxidation of certain types of reactive, unsaturated hydrocarbons ( 6 , 6 , 8 ) is the primary cause with sulfur compounds possibly being a contributing factor in some instances. The products of the initial 1 Present address, American Smelting and Refining Co., Grand Junction, Cola.
INDUSTRIAL AND ENGINEERING CHEMISTRY
July 1951
1605
content of about 8% in the gums indicates that nitrogen compounds are also a n important factor. A.S.T.M. Distillation, F. a t 760 Mm., Yo Although the gum contents of the naphthas vary Specific Sample Descrip- Gravity. Gravity, Init. End ReResiover a wide range, there is relatively little variaNo. tion 60°/600 F . ’ A.P.I. b.p. 10 50 90 point covery due Loss 0.4 1.6 tion in the nitrogen and oxygen contents of the 43.7 152 286 333 372 415 98.0 419 Primary 0.8077 95 154 305 401 411 95.0 53.1 128 Cracked 0 . 7 6 6 4 1.3 3.7 gums. The sulfur values show greater variation 97.0 1.1 1.9 49.0 116 207 323 369 399 130 Cracked 0,7839 1.0 2.5 and are dependent on the sulfur content of the 50.7 1 3 0 . 193 313 367 396 96.5 131 Cracked 0 . 7 7 6 8 48.6 132 199 327 386 408 97.5 0.9 1.6 132 Cracked 0.7856 97.0 1.3 1.7 ‘naphtha rather than On the amount Of gum 148 305 352 402 455 0.8164 41.8 133 Primary formed. The accelerated oxidation procedure employs oxygen pressure and an elevated temperature. To determine separately the effects of these variables, two that the gum content increases with boiling range and that there series of runs were made. I n the first, the samples were is a correlation between gum content and total nitrogen content, treated in the same manner as for the accelerated oxidation, residual nitrogen content after removal of tar bases, and tar base except that nitrogen was used instead of oxygen. The results content of fractions from the naphtha. showed that heating alone had little effect on the gum content. GUM CONTENT OF SHALE-OIL NAPHTHAS For example, heating sample 419 for 60 minutes under nitrogen pressure increased the gum content by less than 200 Samples of both primary and thermally cracked shale-oil naphthas were used in this work. Inspection data on the naphmg. per 100 ml. of sample. In the second series of runs, thas are given in Table I. The term “primary naphtha” is used oxygen pressure a t room temperature was used. Approximately half as much gum was formed a t this temperature as a t to designate a naphtha obtained from crude shale oil by simple 212’ F. These data further demonstrate the ease with which distillation. However, as the shale oil was produced by a retortshale-oil naphthas are oxidized. ing process employing elevated temperatures, the compositions of the primary and cracked naphthas are similar as shown in Table EFFECT OF OXIDATION T I M E 11.
TESTSO N SHALE-OILNAPHTHAS TABLE I. INSPECTION O
OF SHALE-OIL NAPHTHAS TABLE 11. COMPOSITION
Adsorption Analysis of Neutral Oil, Vnl
Sample KO. 419 128 130 131 132 133
Tar Acids, Vol. % 2.5 1.5 1.6 1.8 1.6 2.9
Tar Bases, Vol. % 7.1 8.1 6.7 6.1 6.5 7.5
Paraffins and cycloparsffins 34 28 36 27 30 25
Olefins 46 56 49 59 55 52
4.
Aromatics plus sulfur and nitrogen compounds 20 16 15 14 15 23
-
Existent gum (a)was determined on each of the raw naphthas as taken from storage which was in sealed containers under refrigeration. Results are shown in Table 111. Gum content was also determined on the samples after accelerated oxidation for 60 minutes under an oxygen pressure of 100 pounds per square inch gage and a t a temperature of 211’ to 212’ F. The procedure was the same as in the A.S.T.M. method for oxidation stability of aviation gasoline (S), except that filtration of the oxidized sample was omitted and the sample was transferred as completely as possible to the. beaker used in the existent gum determination. The gums obtained from the oxidized naphtha were analyzed for nitrogen by a Kjeldahl method (unpublished), for oxygen by the Unterzaucher method ( I ) , and for sulfur by a combustion-tube method. ,
PRODUCED BY THERMAL TABLE 111. GUMSO N NAPHTHAS PROCESSES
. .
A . S. T M Gum after BO Elemental A.S.T.M. Min. G~~ OxidatLon, Elemental Analysis of Gum Analysis of Sample ~ ~ . / 1 0 M 0 ~ . / ~ O Ifrom J Oxidized Naphtha, % Naphtha, % No. MI. MI. Nitrogen Oxygen Sulfur Nitrogen Sulfur 1.21 1.09 5284 8.15 9.09 2.47 419 494 1.36 0.90 0.57 1.92 2 8.57 9.19 128 90 2.45 1.05 0.96 9.25 130 274 3356 8.95 1.04 3.28 0.99 131 162 3770 8.40 10.28 1.87 0.90 0.78 7.75 132 322 4032 10.46 5 . 1 4 1 . 1 5 1.26 7 . 1 2 464 5956 9 . 5 9 133
The striking increase in gum content between the oxidized and original samples shows the importance of oxidation reactions in gum formation in shale-oil naphthas. However, the nitrogen
The accelerated oxidation time (60 minutes) was a n arbitrarily selected period which did not indicate the relationship of quantity and composition of the gum formed to oxidation time. Samples of primary naphtha (No. 419) were oxidized for times ranging from 2 minutes to 8 hours. A plot of the quantity of existent gum ( 2 ) against time of oxidation is shown in Figure 1. The rate of gum formation is so rapid that, even thobgh a strict time schedule was observed, the precision of results is poor. However, it is felt that the general trend shown by the curve of a very rapid rate of gum formation during the first 60 minutes of oxidation followed by a rather constant but slower rate is significant. The very short induction time makes the curve appear to differ from those obtained on petroleum (14), where a plot of the logarithm of the gum formed against storage or oxidation time usually gives a straight line.
“
-I
C 100
200 300 400 OXIDATION TIME, MINUTES
500
Figure 1. Quantity of Gum Formed in Shale-Oil Naphtha by Various Oxidation Times
The gums obtained from the oxidized naphthas were analyzed for nitrogen, oxygen, and sulfur, with the results shown in Table IV. The nitrogen and oxygen contents of the gum obtained by 2 minutes of oxidation are substantially greater than those of the gum obtained on the sample as taken from storage. The oxygen content continues to increase during the rapid oxidation stage mentioned previously but remains essentially constant a t extended oxidation times. The precision of the oxygen results is such t h a t the variations shown on the gums from 40 to 480 minutes of oxidation are not considered significant. The nitrogen
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
1606 TABLE IV. Time of Oxidation, Min. 0 2 5 10 20 30 40 66 120
EFFECTO F . \ c c ~ r , e r t a ~ sOXIDATION u TIMEO N GUM CONTENT O F s € l A L E - o I L N A P H T H A
Elemental Analysis of Gum, % Gum M ~ . / I O O ' M I . Sitrogen Oxygen Sulfur 7.06 8 75 8.92 8.93 8.94 8.38 8.18 8.15 8.13 8.13 8.12 7.99 7.56
180
240 360 480
5.16 6.67 6.71 7.16 7 39 7:62' 9.00 9.09 8 68 9 35 8.73 9.43 9.03
3. IS 3.11 2.60 2.52 2.44 2.86 2.65 2.47 2.50 2.38 2.48 2.40 2.69
content, increases only slightly from 2 to 20 minutes of oxidation and then decreases with longer oxidation times. It appears, therefore, that the reactions involving nitrogen and oxygen may vary with oxidation time. The sulfur cont8entdecremes slight,ly up to an oxidation time of 20 minutes. However, all the sulfur values lie between 2.38 and 3.1870, which is a much smaller variation than is showi in Table 111 for the sulfur contents of gunis obtained from different shaleoil naphthas. Oxidation time appears to have less effect on the aulfur content of the gum than does the character of tmhenaphtha from which the gum was obt,ained. EFFECT OF STOH.l(:E (:ONL)IrIONS
Tile large quantities o f gun) obt,:rinable by short periods o f accelerated oxidation make this proc:txlwe very attractive from a research standpoint. However, it is useful primarily if the gums obtained are similar to those produced during actual storage. Samples of primary naphtha were storetl under three different .sets of conditions: a t room temperature, with access to air and light; at room temperatwe, with access to air but in the dark; .and at 38' F., under an atmosphere of nitrogen. The quantity and composition of the gum obtained by storage for various periods of timtt under the first set of conditions are shown iiL Table V. Qualitatively, the results show the same relationships RS were obtained by accelerated oxidation. Approxinvately the same amount of gum was obtained after 3 weeks' storage ae w a i obtained by 8 hours of accelerated oxidation. The nitrogen allti C J X ~ ~contents ~ I I of the gums were slightly lower than those in tht. gums from the accelerated oxidation tests. Storage under tho ntq;o1rd set of conditionH gave results vcvy similar to those show11
Vol. 43, No. 7
naphthas. There are thought to be primarily two types of nitrogen compounds present in shale-oil naphthas (Q)-basic nitrogen compounds which probably consist mostly of pyridine homologs, and nonbasic nitrogen compounds which are largely pyrrole homologs. Tar bases are defined as the material that may be extracted by dilute aqueous acid. Unfortunately, the extraction procedure does not make a clean separation betu-een the two typee of nitrogen compounds so their respective roles in gum formation must be determined indirectly. Mapstone (9) has shown that purified tar bases may be added to refined shale-oil naphtha without increasing the gum content. However, as mentioned previously, he found that nonpurified tar bases increased the gum content and attributed this to the presence of pyrroles. The results obtained in the present study show that basic nitrogen compounds also contribute to the gum obtained from raw shaleoil naphthas. The quantity of nitrogen obtained in the gun1 from oxidized naphthas is compared in Table VI with the residual nitrogen in the raffinate after extraction of tar bases from the naphtha and nith the nonbasic nitrogen in the naphtha. The nonbasic nitrogen was determined as the difference between total nitrogen and basic nitrogen as estimated by titration with perchloric acid in glacial acetic acid as solvent.
TABLE VI. QUANTITY O F NITROGEN OBTAINED I N THE COMPARED WITH QUANTITIESOF NITROGENPRESEST IN NAPHTHA IN VARIOUS FORMS
Sample NO. 419 128 130 131 132 133
A.S.T.M. Gum after 60 Min. Oxidation, Mg./100 XIl. 5284 1922 3356 3770 4032 5956
Kitrogen Content of Gum Mg./l06 Ml. of Saphtha 43 1 165 300 317 3 12 424
Nitrogen Content of Naphtha. Mg./100
M1.
972 687 818 766 703 933
GUM. THE
Residual Nonbasic Nitrogen Ntrogen, after Diff. beExtraction tween Total of Tar and Basic Bases, Nitrogen, hIg./100
M1. of Saphtha 234 105 194 149 173 248
Mg./100 hll. of
Naphtha 129 69 171 178 70 154
The results in Table VI show that the nonbasic nitrogen content of the naphtha, as measured either by extraction or by titration, is significantly less in every case than the amount of nitrogen found in the gum. Therefore, it is concluded that, although the presence of a small quantity of pyrroles or other active material may be essential to the gum-forming reaction, i t is possible to obtain a substantial quantity of the basic nitrogen in the gum from oxidized shale-oil naphthas. SUMMARY
2 7
14 '21
206b
4698 6676 7450
7 90
a :,o
7 40 7 00
2 i
.,a
7 6q 7 43
3 12 1 99 2 29
2 38
in Table V , indicating that light has little effect on the rate of gum formation in this particular shale-oil naphtha. Storage for several months under the third set of conditions gave no appreciable increase in the gum content. Consequently, it may be concluded that the accelerated oxidation procedure is useful for investigating gum formation in shale-oil naphthas, and that free awes8 to air is a major factor in gum formation during actual storage of such naphthas. SOURCE OF RITROGEN IN GUM
As sulfur and oxygen have both been found in gums obtained from petroleum naphthas (11, IS) it appears that the high nitrogen content is a distinguishing feature of the gums from shale-oil
Oxidation is a governing factor in the formation of gum in raw shale-oil naphthas. Storage of shale-oil naphtha with free accesa to air produces several thousand milligrams of existent gum within a few days. The gum formed from shale-oil naphtha differs from that obtained from petroleum naphtha, primarily in that it contains 7 to 9% nitrogen. Much of this nitrogen comecl from compounds originally present in the shale-oil naphtha a8 tar bases. ACKNOWLEDGMENT
This work was done under the Synthetic Liquid Fuels Program authorized by Public Law 290, 78th Congress, and under the general supervision of W. C. Schroeder, chief of the Office of Synthetic Liquid Fuels, and R. A. Cattell, chief of the Oil-Shale Research and Demonstration Plant Branch. The authors wish to acknowledge the general guidance of H. P. Rue, chief of the Fuels Technology Division, Region IV, and H. M. Thorne, chief, Oil-Shale Research and Development Branch, Region IV. J. S. Ball, refinery engineer, was in direct charge of the investigation.
July 1951
INDUSTRIAL AND ENGINEERING CHEMISTRY
This work was done under a cooperative agreement between the Bureau of Mines, United States Department of the Interior, and the University of Wyoming. The authors wish to thank J. C. Neel, I. W. Kinney, and’R. T. Moore who performed various analyses reported in this paper. LITERATURE CITED
(1) Aluise, V. A., Hall, R. T., Staats, F. C., and Becker, W. W., A n a l . Chem., 19, 347 (1947). ( 2 ) Am. SOC.Testing Materials, A.S.T.M. Designation D 381-49. (3) Ibid., D 873-49. (4) Ball, J. S.,Dinneen, G. U., Smith, J. R., Bailey, C. W., and Van Meter, R., IND.ENC.CHEM.,41, 581 (1949). (5) Brooks, B. T., Ibid., 18, 1198 (1926). (6) Caesar. H. A,. Ibid.. 23. 1132 (1931). (7) Dryer,’C. G.,’Lowry, C’. D., JG., Morrell, J. C., and Egloff, G., Ibid., 26, 885 (1934).
1607
(8) Flood, D. T., Hladky, J. W., and Edgar, G., I b d . , 25, 1234 (1933). (9) Mapstone, G. E., Petroleum Refiner, 28, 111 (October 1949). (10) Martin, S. M., Gruae, W. A., and L o w , A., IND.ENG.CHEM., 25, 381 (1933). (11) Moirell, J. C., Dryer, C. G., Lowry, C. D., Jr., and Egloff, G., Ibid., 26, 497 (1934); 28, 465 (1936). (12) Secretary of the Interior, U. S. Bur. Mines, Rept. Invest. 4457, 49-50 (1949). (13) Story, L. G., Provine, R. W., and Bennett, H. T., IND. ENG. CHEW,21, 1079 (1929). (14) Walters, E. L., Yabroff, D. L., and Miner, H. B., Ibid., 40, 423 (1948). (15) Yule, J. A. C., and Wilson, C. P., Jr., Ibid., 23, 1254 (1931). RECBIVEDJanuary 3, 1951. Presented before the Division of Petroleum Chemistry at the 118th Meeting of the AMERICAN CHEMICAL SOCIETr, Chicago, Ill.
Equilibrium Flash Vaporization o f Petroleum Crude Oils or Fractions Method and Apparatus f o r Determination DONALD F. OTHMER, E. H. TEN EYCKl, AND STATLEY TOLIN2 Polytechnic Institute of Brooklyn, Brooklyn, N . Y . T h e process engineer frequently requires vapor-liquid equilibrium data for the design of equipment to separate multicomponent hydrocarbon mixtures. Data for the more complex systems are usually expressed as a family of isobaric curves on a plot of per cent vaporized versus temperature. A new method and a new type of apparatus for the study of these vapor-liquid phase relations are presented bhich are believed to be superior to the regular equipment currently in use. This has been accomplished by the design and use of a modified recirculating equilibrium still of the type used by numerous investigators with binary and ternary systems. The unit has been thoroughly evaluated at atmospheric and subatmospheric pressures for equilibrium conditions, entrainment, and pressure drop. Tests on a variety of petroleum stocks have shown this unit to be highly satisfactory for the determination of equilibrium vaporization curves, throughout practically the entire range of ratios of per cent volatilized.
I
N DESIGN calculations for equipment for the separation of multicomponent hydrocarbon mixtures it is frequently necessary to predict vapor-liquid equilibrium relations for mixtures of various unknown compositions at different amounts vaporized. The most common method of expressing these equilibrium data is by means of a so-called L‘equilibriumflash vaporization curve.” For a given mixture and a t a fixed pressure, the temperatures of the vapor-liquid phases in equilibrium with each other are plotted against the volume per cent of the material vaporized. These 1 2
Present address, E. I. du Pont de Nemours & Co., Ino., Belle, W. Va. Present address, General Foods Corp., Hoboken, N. J.
data are then used in the design of such units as d%tilTation columns, vaporizers, and condensers. Phase equilibrium data of this type are difficult to determine by the regular methods; and the common practice is to predict equilibrium flash vaporization curves from the results of standard American Society for Testing Materials or true boiling point distillations by empirical methods. This paper presents a method and equipment which make the determination of equilibrium flash vaporization curves a simple direct’ procedure ueing bench apparatus. These equilibrium data are at present determined in continuous vaporizers (3, 4, 8, 9),which, essentially, consist of a reproduction on a small scale of a continuous distillation plant, and t h u s require a complete set of controls, sufficient feed stock, and time t o come t o steady operating conditions. There are a feed supply tank with suitable back-pressure t o cause flow through the apparatus, a heating coil to heat the fluid t o the desired temperature, a disengaging section where the vapor is separated from the liquid, and a device for measuring the quantity of the liquid and condensed vapor streams. In addition, means are supplied for measuring the temperature and pressure in the disengaging section. A unit of this type has several disadvantages. The original cost of the equipment and controls is high. It requires a large operating space. The unit is continuous in operation and requires a large tes% sample and carefully controlled feed and other operating conditions. The exact point of equilibrium is often in doubt, owing to t h e changing pressure along the transfer line between the heater an& separator. The unit requires considerable time of highly skilled technicians for satisfactory operation.
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