INDUSTRIAL AND ENGINEERING CHEMISTRY
88
Recently Swanson (16) subjected the diastatic power of wheat and flour to an extended investigation by the new Blish method. No explanation is given for the great differences which existed between the activities of the ground wheats and the flours prepared therefrom, the former often being much more active. In the solution of such a problem the measurement of the liquefying and saccharifying powers of the ground wheat and flour may be of assistance. The development of resistance on the part of bread starch during staling is illustrated by data published by Whymper ’ (17) in 1930 showing again that the lightly cooked starch present in bread crumb develops marked resistance in the staling process. Here baked loaves were permitted to become stale and the susceptibility to attack of the starch by malt diastase was measured from day to day. Marked resistance to diastase attack developed. We still do not know to what extent the saccharogenic, liquefying, and saccharifying powers of malt and flour are due to one or several diastatic enzymes. This discussion has , been confined entirely to plant diastase, as illustrated by the amylases of flour and barley malt. It was impractical to include the extremely important amylases secreted by molds and by bacteria, and those of animal origin, because of the intricacy of the subject. Surely the factors inherent in the subject of starch resistance to diastase attack are worth studying, especially since
VOL. 28, NO. 1
the worker now has before him the possibility of linking his discoveries with the chemical and physical studies on starch now being so brilliantly conducted by others.
Literature Cited (1) Bailey, “Chemistry of Wheat Flour,” New York, Chemical Catalog Co., 1925. (2) Blish and Sandstedt, Cereal Chem., 10, 189 (1933). (3) Gore, J . Assoc. Oficial Agr. Chem.. 16,403 (1933). (4) Green, Reynolds, “Soluble Ferments and Fermentation,” Cambridge Univ. Press, 1901. (5) Hanes, Biochem. J . , 26, 1406 (1932). Johnston and Jozsa, J . Am. Chem. SOC.,57, 701 (1935). Jozsa and Gore, IND.ENG.CHISM., Anal. Ed., 2,26 (1930). Jozsa and.Johnston, Ibid., 7, 143 (1935). Xirchoff, Schweios J . , 14,389 (1815),from Green’s “Soluble Ferments and Fermentation.” Kjeldahl, series of papers from Carlsberg Lab., 1879; 2. ges. Brauw., 3,49,84,123,149,179,222 (1880). Landis, paper presented before meeting of Am. Assoc. of Cereal Chemists, Denver, Colo., June, 1935. Lintner, J. prakt. Chem.. [2]34,378 (1886); 36,481 (1888). Mangels, Cereal Chem., 3,316 (1926). Rumsey, Am. Inst. Baking, Bull. 8 (1922). Schultz and Landis, Cereal Chem., 9,305 (1932). Swanson, Ibid., 12,89 (1935). Whymper, Arlcady Rev., 7, 45 (1930). R ~ C E I V EJune D 16, 1935. Presented a6 part of the Symposium on Starch before the Division of Agricultural and Food Chemistry at the 89th Meeting of the American Chemical Society, New York, N. Y.,April 22 to 26.1935.
Oxygen Absorption Tests on ASPHALT CONSTITUENTS ROBERT R. THURSTON AND EDWIN C. KNOWLES T h e Texas Company, New York, N. Y. FIG. I . APPARATUS FOR OXYGEN
ABSORPTION MEASUREMENTS
@T
MANOMETE
HE process of oxidizing residua obtained from the distillation of petroleum oils with air a t elevated temperatures has been known for a long time and has been commercially practiced in the United States for nearly forty years (3). This process is relatively simple and consists in intimately contacting the residuum’with air in a suitable still a t a suitable temperature until a product of the desired consistency is obtained. The residuum so treated changes its physical characteristics and becomes harder, heavier in gravity, lower in ductility, and higher in softening point. The chemical reactions which cause these physical changes are rather complex, but it is known that the proportion of solid and liquid constituents in the asphalt as well as the nature of these constituents has a definite bearing on the characteristics of the products. The extent to which physical and chemical changes take place, and the relationship obtainable between hardness, ductility, and softening point, depend not only upon the source and characteristics of the original residuum but also upon the processing of that residuum previous to oxidation and upon the conditions of oxidation. From an economic standpoint this process is extremely important because useful asphalts can be made by it from petroleum residua not suitable for the manufacture of asphalts
JANUARY , 1936
INDUSTRIAL AND ENGINEERING CHEMISTRY
89
volume of asphalt. This product can be purified with fresh by the usual distillation processes. It is also possible to manufacture asphalts of high softening points which are naphtha which will remove 6 to 7 per cent of occluded resins from the asphaltenes. Pure asphaltenes will not melt but pliable, have excellent resistance to weathering, and are less will swell on heating and will decompose. Impure asphaltenes susceptible to temperature changes than other types of asphalts. fuse. The dried precipitated product is a brown-to-black, It is known that the oxidation of petroleum residua is an easily powdered material, with a specific gravity of 1.167. exothermic reaction (%'), and that water and carbon dioxide It is soluble in solvents such as benzene, carbon disulfide, carbon tetrachloride, and Dvridine. AsDhaltenes are the are eliminated. It is also known that oxygenated compounds essential constituent of as(12) of v a r i o u s types are phalt that distinguish it from eliminated, and that nitrogen Soft and air-blown Mexican asphalt, other petroleum products and and oxygen are present in the gilsonite, and other asphalts were examare responsible for its plastic products only in very small ined and groups of constituents sepaproperties (11). From the amounts ( 5 ) . analysis in Table I, there is rated-asphaltous acids, asphaltenes, peExact knowledge of the evidently 3 to 4 per cent of chemical composition of astroleum resins, asphaltic resins, and oils. oxygen present in these asphalts is negligible, but progThe original asphalts and the constituphaltenes. ress has been made in the ents of soft Mexican asphalt were subThe group of constituents recognition of distinct conjected to treatment with oxygen in a other than acids and asphaltstituent groups by Jacobsen enes are termed "petrolenes." closed system at 200' C. and under atmos(a), Marcusson (6),RichardThese were further separated son (10), N e l l e n s t e y n (7), pheric pressure. The volume of oxygen into three groups of materials Poell(8), and others (1,6,9). absorbed was measured and the distribuby treating with fuller's earth In dhe p r e s e n t w o r k t h e tion of it in the products of the reaction and subsequently extracting following constituents have determined. I t was found that the solid with various solvents. This been considered, and oxygen is carried out, after distilling constituents, the asphaltenes, oxidized absorption tests have been off the naphtha used to prerun on those constituents most readily and the oils were more cipitate the asphaltenes, by usually occurring in suffiresistant. The effect of oxygen on the absorption with about five ciently large proportions to be properties of the constituents is discussed. times their weight of fuller's of interest: asphaltous acid earth. Hot extraction with and anhydrides, asphaltenes, naphtha in a Soxhlet apparatus of the fuller's earth separates asphaltic resins, petroleum resins, petroleum oils, carbenes, the oils. Subsequent extraction with carbon disulfide separates carboids, and inorganic material. the so-called petroleum resins, and extraction with hot benzene Constituents of Asphalt separates some of the asphaltic resins. Some resins are retained by the earth, and prolonged contact with the earth Soft Mexican asphalt of 238 penetration at 77" F. (25" C.), reduces the yield of petroleum resins. The resins not reobtained by atmospheric steam reduction of heavy Mexican covered are shown in Table I as asphaltic resins. For many crude, was used as a source of material for most of this investipurposes petroleum and asphaltic resins are combined as total gation. This asphalt was separated into five constituents by resins. Both resins have moderate drying properties when the method of Marcusson (6); tests on these constituents exposed to the air in thin films. This is more pronounced are shown in Table I. in the asphaltic resins which are heavier and more viscous Asphaltous acids and acid anhydrides were separated by than the petroleum resins. dissolving the asphalt in benzene and refluxing with normal Table I shows the yield, specific gravity, iodine value, alcoholic potash. The aqueous alcoholic layer was then sulfur, carbon, hydrogen, and ash on these constituent groups, separated, acidified, extracted with ether, and evaporated to It is evident that no oxygen is present in any constituent dryness. Only 0.3 per cent of brownish, sticky acids were except the asphaltenes and probably the acids. The sulfur found in this asphalt, and, inasmuch as the acid content of is well distributed and is highest in the asphaltic resins, This most asphalts is very low, no extensive work was done on fact is probably due partially to the tendency of fuller's earth this constituent. When not separated by this method, the used in the separation of these constituents to absorb and acids are undoubtedly included in the asphaltenes (9). retain complex sulfur compounds. All constituents show Asphaltenes are the components which are insoluble in considerable iodine value, but the significance of this property low-boiling petroleum naphtha, and 88" BB. straight-run as an indication of unsaturation in these products is questionPennsylvania naphtha was used for most of this work. Forty able. The ratio of carbon to hydrogen is highest for the volumes of naphtha precipitate the asphaltenes from one asphaltenes, diminishing in the liauid constituents. The ash-is concentrated in the asphaltenes. As is usually the OF SOFTMEXICAN ASPHALT TABLE I. CONSTITUENTS case in p r o p e r l y refined asphalt, no Original Asphal- Asphaltic Petroleum Oile Asphalt Acide tenee Resins Resins carboids are present (indicated by the Yield 70 100 0.3 28.0 15.7 22.0 34.0 solubility of the original soft asphalt in Sp. ,&. at 77' F. ( 2 5 O C.) 1.024 .. ,. ,. 651.107 52 0.995 0.995 0.946 carbon disulfide), and no carbenes are Iodine value 51 55 42 Sulfur 97, 6.1 ., ,. ,. 79.61 8.09 8.55 5.60 4.04 present (indicated by the high solubility Carbon 85.05 82.19 82.70 85.39 Hydrogen 10.38 . , , 7.79 10.38 10.89 11.39 in carbon tetrachloride). Aah 0.27 . . . 0.59 Trace 0.0 0.0 A "
_ _ - - _ _
Total M P ball and ring O F (' C.) Pe'neiration at 770 b. (i50 c.) Flash Clevelandopencup, OF. (" C . ) Soly. in CSZ Soly. in CCla
101.73 101 (38.3) 238 460 (237.8) 99.7 99.7
96.08
.. .. .. .. .. .. .. .. .. .. .. .. .. .. .......
101.12
99.19
.....
....
.....
.... .... ....
..... ..... .....
....
100.82
Method of Determining Oxygen Absorption The apparatus used for determining the oxygen absorption of bituminous materials is shown in Figure l. This appara-
90
INDUSTRIAL AND ENGINEERING CHEMISTRY
tus enabled the oxygen absorbed to be measured in a closed system at atmospheric pressure without the disadvantages of the m e t h o d s i n w h i c h a l l of the reaction products remain in contact with the s a m p l e and inhibit further reaction : After testing the apparatus for leaks under 10 to 16 mm. of xylene pressure, samples weighing one gram a r e intimately mixed with 25 grams of standa r d A. s. T . M . sand and placed in the flask. Cock D is then closed t o the a t m o s p h e r e but OXYGEN ASSORPT/ON T/ME IN MINUTES open t o circulation, and cock E is oDen t o the atmosphere. The apparatus is sweptlfor several hours with oxygen; during the latter part of this period cocks F , B , and Care opened to insure that the entire apparatus is dry and completely filled with oxygen. Cock G is now closed, E is closed t o atmosphere, water and steam are turned on the jackets, and the reaction flask is packed with ice. When temperature equilibrium is established, the volume at atmospheric pressure is recorded as the initial reading. The ice bath is then replaced with an oil bath maintained at 200" C., and volume readings are taken until a maximum is reached after 8 to 10 minutes. This time is considered the start of the oxidation period. During oxidation, cocks C and G are closed, and A and B opened, thus permitting fresh oxygen from the buret to enter the reaction flask directly over the sample. Continuous circulation and removal from the reaction flask of oxidized volatile constituents is accomplished by means of the steam jacket, the trap, and the cold water jacket. Water is collected in the trap and in tube N continuously during the oxidation. The thermos bottle is kept a t 32" F. (0" C.) to prevent the zylene vapor used in the manometer from being carried over into the reaction flask. Additional oxygen is added to the system throu h cock C at intervals during the run. A volume reading is first faken, and cock A is closed during the addition of oxygen; then a new reading is taken and cock A is opened again. A constant pressure of 2 to 3 mm. of xylene is maintained on the system by means of the mercury bulb. Volume readings are taken at intervals during the oxidation which is normally carried on for 3 hours. The oil bath is then replaced by an ice bath, and a final volume reading is taken under the same conditions as at the start of the run. The absorption tubes are now opened to the system at cock D,and oxygen is slowly swept through with cocks F and G open. By weighing the tubes and reaction flask, the water and carbon dioxide evolved are determined, and the loss or gain in weight of the sample is found.
Tests on Constituents of Soft Mexican Asphalt The oxygen absorbed in cubic centimeters per gram in 3 hours at 200" C. by each constituent from soft Mexican asphalt is shown graphically in Figure 2. The oxygen absorbed by the soft Mexican asphalt, from which the constituents were separated, is also shown and the amount (95.1 cc.) checks the amount that should be absorbed by the total constituents calculated from the proportions present and their individual absorption data (96.3 cc.). Contrary to what might be expected, the solid constituents of asphaltnamely, the asphaltenes-oxidize more readily under the conditions of this test than any one of the other constituents
VOL. 28, NO. 1
or the original asphalt itself. The oils are the most resistant to oxidation. The oxygen used in per cent by weight of the sample, during 3 hours compared to the iodine value, sulfur, and carbonhydrogen ratio of both soft Mexican asphalt and its constituents is shown in Table 11. The oxygen used bears a general relationship to the iodine value and the sulfur cantent and quite a definite relationship to the ratio of carbon to hydrogen. The higher this ratio, the more oxygen is absorbed. It is also of interest to note that the asphaltene group is the only one to gain weight during oxidation, which shows that oxidized asphaltenes or carboids contain oxygen; 23.6 per cent of the oxygen used is accounted for in this manner. The resin and oil constituents lost weight by dehydrogenation and elimination of carbon dioxide and other volatile products of the reaction. As we go from the constituents of high molecular weight and high carbon-hydrogen ratio to the low, a greater proportion of the oxygen is used in the major reaction of dehydrogenation and a smaller proportion to the formation of carbon dioxide. The oxygen not accounted for is apparently used in the formation of oxygenated compounds ( I @ , such as alcohols, aldehydes, and ketones, which were not recovered in these tests. The presence of these oxidation products was always evidenced by a dark colored deposit in the part of the apparatus surrounded by the steam jacket, and except in the case of asphaltenes, by a brown deposit in the trap. TABLE11. OXIDATION OF CONSTITUENTS FROM SOFTMEXICAN ASPHALT AT 200" C. Original Asphal- Asphaltic PetroAsphalt tenes Resins leum Resins Oils 100 28.0 15.7 22.0 34 0
Content, % Tests:, Iodine value 51 6.1 Sulfur, Ratio. 8.2 Oxidation: Oxygen used 7 of sample 17.3 Change in deiggt,b % of sample -5.0 Oxygen Used: Absorbed by sample, % . .. Recovered a8 Hz0 67.9 Recovered a8 COz 14.2 Unaccounted for 17.9
zH Q
.
-
65 8.09 10.2
52 8.55 7.9
55 5.60 7.6
23 6
1.85
15.4
$2.7
-2.3
-3.137
23.6 59.6 12.9 3.9
. . ..
71.3 10.7 18.0
-
., , .
72.1 9.2 18.7
-
42 4.04 7.5 13 4
a .. .
-2
71.5 8 9 19.6
-
100.0 100.0 100.0 100.0 100.0 Total a Three hours at 200' C. plus oxygen absorbed during starting and stopping of runs. b Gain in weight, plus sign; loss in weight, minus sign.
These results indicate that the mechanism of oxidation of asphaltic materials takes place in the following three ways: 1. Addition of oxygen, which forms unstable compounds from which water is eliminated, leaving unsaturated compounds which polymerize. 2. Oxidation with the formation of carboxyl derivatives from which carbon dioxide is eliminated, followed b polymerization. 3. Elimination of volatile oxidation prodY,cts other than water and carbon dioxide from the above types of unstable oxygen compounds, followed by polymerization.
Tests on Asphaltenes from Other Sources Because of the fact that asphaltenes are the most easily oxidimble constituents in asphalts, further work was done in order to determine the susceptibility to oxidation of asphaltenes from various sources. Three-hour runs were made on those obtained from several asphalts with the results shown in Figure 3. It is easily seen that there is considerable variation in the readiness with which various asphaltenes will oxidize, depending upon their source. Asphaltenes obtained from soft unoxidized Mexican asphalt do not oxidize any more readily than those from highly
~
JANUARY, 1936
INDUSTRIAL AND ENGINEERING CHEMISTRY
oxidized Mexican asphalt. Those from gilsonite and selected domestic sources oxidize less readily than t h o s e f r o m Mexican asphalt. an asDhalt made bv Asphaltenes air-blowine from cracked
TABLE111.
91
ANALYSES OF ASPHALTENES FROM VARIOUS SOURCES Soft Vacuum Mexican Air-Blown Reduced Air-Blown Air-Blown Asphalt” Mexican Mexican Gulf Coast Cracked 238 Pen Asphaltb Asphalt 0 Asphaltd Gilsonite Asphaltd
-
Source of asphaltenes:
%Fgen
79.61 81.31 79.70 83.99 85.48 90.73 residuum oxidize less readily-than any 7.79 7.91 7.83 8.26 10.14 6.30 of those investigated. Ratio C:H 10.2 10.4 10.2 10.2 8.4 14.4 8.09 7.79 8.25 1.70 0.65 0.89 Analyses of these asphaltenes before 0.59 0.24 0.34 1.25 0.19 0.06 o x i d a t i o n are shown in Table 111. Oxygen by difference 3.92 2.75 3.88 4.80 3.63 2.02 They all contain from 2 to 5 per cent $$~$~+;~3&00 F. (104.40 c.) Melting point’ 200’ F. (93.3’ C.). of oxygen, as determined by difference; d Melting point: 201’ F.(93.9’’ C.). this figure is probably a little high because of a small amount of nitrogen a n d possibly traces of chlorine. Astion of oxygen went to dehydrogenation, but larger proporphaltenes obtained from air-blown asphalts do not show any tions of oxygen went to carbon dioxide and products unmore oxygen than those from asphalts which were never airaccounted for than the calculated. blown. This fact shows that oxidation does not take place in an It is also of interest that the sulfur content is largely deasphalt in the identical manner indicated from the oxidation pendent upon the original source of the material, but also of the separate constituents. Oxidation under the conditions to a slight extent upon the method of processing the asphalt of this test is considerably more severe than the usual oxidafrom which the asphaltenes were obtained. The ratio of tion of asphalt because the material is very thinly distributed carbon to hydrogen averages close to 10.3 for all ordinary over a large surface area which is exposed to pure oxygen, petroleum asphalts but is considerably lower than this (8.4) whereas, in ordinary air-blowing, the material is in a liquid in the case of asphaltenes obtained from gilsonite and higher state exposed to air bubbles. (14.4) in the case of the cracked asphalt. Typical analyses of asphaltenes obtained from a hard steam-reduced Mexican asphalt and carboids made from them Discussion of Results by oxidation are as follows: Oxidation of isolated asphaltenes produces carboids which Asphaltenee Carboids are insoluble in carbon disulfide and oxidation a t 200’ C. for Carbon 81.50 74.26 3 hours in this test results in a product which is 96 per cent Hydrogen 5.13 7.50 Sulfur insoluble. Only one-sixth as much oxygen is absorbed at 8.16 8.50 Chlorine Trace . ... 150’ C., and the product is 68 per cent insoluble. Oxidation Aah 0.51 0.50 Nitrogen 1 . 1 6 1.10 of the petroleum resins in this test a t 200” C. for 3 hours Oxygen 0.73 10.86 produced a product which is 31 per cent insoluble. Heating Total 100.00 100.00 asphaltenes for a comparable period at 150” C. in the absence Sol. in CSg, % 99.7 3.0 of oxygen results in a product which is only 7 per cent inC:H ratio 10.9 14.5 Saponification value 6.4 124 soluble; this shows that oxidation and not merely heat Aoid value 3.0 4.0 polymerization is the essential reaction. Ordinary asphalts made by air oxidation do not contain The presence of considerable oxygen in the carboids is carboids, judging from their high solubility in carbon diindicated from the above analysis by difference, and this sulfide. This is probably due not only to the fact that the finding is substantiated when we consider the relatively low conditions of oxidation are not nearly as severe as in this acid value of both the asphaltenes and carboids and the high test, but also to the fact that the asphaltenes are not isolated saponification value of the carboids, indicating the presence and e x p o s e d i n of oxygen in the form of esters. timately t o the The relation of sulfur to carbon in the asphaltenes and action of o x y g e n carboids appears almost constant, and therefore it is probable but are in a soluthat sulfur does not enter into the oxidatmionprocess but is t i o n of oils and present in very stable compounds. resins. If the d a t a i n Literature Cited the first column of (1) Abraham, H . , “Asphalts and Allied Substances,” 3rd ed., Table I1 on oxida1929. tion of the original (2) Brooks, B. T., “Non-Benzenoid Hydrocarbons,” Chap. 11 a s p h a l t is calcu(1922). lated from t h e (3) Byerly, F.X.,U. S. Patent 524,130 (AUK.7, 1894). (4) Jacobsen, Chem. Tech. Rept., 2, 107 (1869). data on oxidation (5) Kats, M., Can. J . Research, 10,435-51 (1934). of the constituents (6) Marcusson, J., “Die Naturliche und kunstlichen Asphalte,” obtained from this 1931. a s p h a l t i n their (7) Nellensteyn, F. J., J. I n s t . Petroleum Tech., 10, 31 (1924). proper propor(8) Poell, H., Er&Z u. Teer, 7, 350-2 (1931). (9) Purdue Univ., Bull. 43, 48 (1932). tions, it is found (IO) Richardson, C.,“Modern Asphalt Pavement,” 1908. that actual oxida(11) Saal, R. N . J., and Koens, G., J. Inst. Petroleum Tech., 19, tion of the original 176 (1933). asphalt caused a (12) Spielman, P.,“Bituminous Substances,” Chap. 11 (1925). (13) Strieter, 0.G.,Bur. Standards J . Research, 5, 247-53 (1930). g r e a t e r loss i n w e i g h t than the R~CEIVE June D 8, 1935. Presented before the Division of Petroleum Techcalculated. T h e nology rtt the 89th Meeting of the American Chemical Society, New York, calculated proporOXYOEN ABSORPT/ON TIM€ IN MlNME.5 N. Y., April 22 to 26, 1935.
zlhf‘‘ C
