I
H. N. DUNNING and J. W. MOORE Petroleum Experiment Station, Bureau of Mines,
U. S. Department of the Interior, Bartlesville, Okla.
Decomposition of Metal-Porphyrin Complexes Gamma Irradiation
by
The protective action of petroleum may be important in the development of nuclear engineering processes R E S I D U E S of chlorophyll and hemoglobin, known as the porphyrins, are of practical importance throughout the petroleum industry. Because of their nitrogenous content and formation of stable complexes with metals such as vanadium and nickel, the porphyrins are highly poisonous to several refining catalysts and corrosive in special petroleum fuels. Porphyrins and similar substances affect the wettability of petroleum-reservoir surfaces and influence the flow of fluids in petroleum reservoirs. Studies of porphyrins and the trace metals with which they are complexed have yielded information valuable in petroleum exploration and in determining the origin of petroleum ( 8 ) . During a systematic study of the properties of porphyrin compounds, several samples of porphyrins, metal-porphyrin complexes, and crude oils containing metal-porphyrin complexes were subjected to high dosages of gamma irradiation ( 6 ) . The effects of gamma irradiation on the bulk properties of an asphaltic crude oil and a mid-continent lubricating stock also were investigated.
level. The rate of irradiation dosage for these experiments ranged from about 2.5 to 3 megar per hour. Dosages are reported by the facility from calibrations made by the cericcerous method on a basis of unperturbed volume. Rice and Way (79) estimate that the accuracy of dosimetry is to about =k 10% and that the perturbation error caused by insertion of a stainless steel canister of I/s-inch wall thickness is about 20%. The dosages at the top and bottom of the container averaged about lOy0 less than that at midplane. Duplicate ampoules were arranged in the container to compensate in so far as possible for this deviation. Tests were made in which the total dosages were 50,70, 100, and 200 megar. Analyses. Concentrations of synthetic porphyrins and of synthetic and natural metal-porphyrin complexes were determined spectrophotometrically. The concentrations of metal-porphyrin complex solutions containing light-absorbing additives were determined by the spectrophotometric method of Beach and Shewmaker (7) in which the “back-
ground” absorbance is subtracted from the peak height. Porphyrin contents of crude oils arid asphalts were determined by the hydrogen bromide-glacial acetic acid digestion method of Groennings (72) with spectrophotometric measurements of concentration ( 9 ) . The spectrophotometric method has enough precision to make analytical errors negligible compared to the uncertainties of dosage. The digestion procedure for crude oils is less precise but gives values within 3 ~ 5 % (Table 111). Sample Preparation. Mesoporphyrin I X dimethyl ester was prepared from hemin by the method of Corwin and Erdman (5) and the vanadium complex of this porphyrin by the method of Erdman and others (77). The melting points and spectral properties of these substances were in good agreemmt with the literature values (5, 77). In the first two tests (dosages of 50 and 70 megar) all samples were sealed under an atmosphere of air in glass ampoules. The porphyrins were prepared in solutions of benzene (ACS, reagent grade;.
Experimental Procedures
Gamma
Irradiation.
Crude oil, crude oil extracts, and synthetic porphyrins were irradiated in the gammairradiation facilities of the Phillips Petroleum Co. at Arco, Idaho. I n this facility spent fuel elements .from the Materials Testing Reactor are arranged in a water-filled canal around a test rack which holds sample containers about 3 inches in diameter. The ambient temperature is about 24’ C. The samples were sealed in glass ampoules and packed into an aluminum container having a wall thickness of 0.5 cm., an outside diameter of 7 . 5 cm., and a length of 30 cm. Calculations based on the irradiation logs and the data of Moteff (76) indicate that the average energy was in the range from 0.35 to 1.35 m.e.v. About 50% of the gamma energy was a t the 1.65m.e.v. level and 25% was at the 0.35
Table 1.
Decomposition of Porphyrin Materials in Benzene Solutions Is Nearly Complete after Gamma Irradiation of 70 Megar Porphyrin
Concn., Micromolal Orig. Final
Decompn.,
%
50 megara
MesoetioMeso-IX dimethyl ester Copper complex (syn.) Nickel complex (nat.) Vanadium complex (nat.)
124.0 91.5 26.3
Vanadium complex (nat.) Nickel complex (syn.) Vanadium complex (syn.) Vanadium complex (syn.)b Vanadium complex (syn.)” Vanadium complex (syn.)cd Vanadium complex (nat.). Meso-IX dimethyl estep
16.3 29.8 39.5 39.5 14.5 24.1 124.0
-0 -0
17.3 27.0
3.1 3.9 6.2
-100 -100 88 77 77
99
70 megara
...
1.2 2.7
97 93 92 71 77 16
1.1
6.9 28.5
...
Sealed under atmosphere of air unless otherwise indicated. Ampoule sealed inside petroleum-containing ampoule. Dehydrated, deaerated, sealed under vacuum or atmosphere of nitrogen. Contained 5 % propane-deasphalted Oklahoma petroleum. Irradiated in solid form, sealed under nitrogen. a
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1.2 1.0
” 1.0 z LLI
c
a
,“ .e 0 v)
.6
.4
a
-
.2
-
.2 0
4 50
550
500
650
600
450
500
WAVE LENGTH, m p
Figure 1. Absorption spectra of synthetic vanadiurn-porphyrin complex show complete decomposition by 70 megar
For the third test ( 7 0 megar) benzene was freshly distilled under a nitrogen atmosphere and had been dried by azeotropic distillation. The porphyrin samples were prepared and sealed in glass ampoules under an ‘atmosphere of nitrogen or under vacuum. In the fourth test, 200-ml. samples of the Oklahoma petroleum and of a SAE 30 mid-continent lubricating stock were irradiated with 100 and 200 megar. The ampoules were filled almost completely and sealed under a nitrogen atmosphere.
Results a n d Discussion
Porphyrins. Results of decomposing the synthetic vanadium porphyrin complex by gamma irradiation (70 megar) are shown in Figure 1. Essentially complete destruction of the porphyrin complex by this dosage is indicated. The effect of 50 megar on a natural vanadium-porphyrin complex isolated from a mid-continent crude oil (70)is illustrated in Figure 2. At this dosage about 7 7 % of the complex was decomposed. The natural vanadiumporphyrin complex, subjected to 7 0
Table 11.
megar, was more than 77% decomposed. The results of the irradiation tests with synthetic and natural porphyrin materials are sr,mmarized in Table I. The total decomposition of the free porphyrins in solution was expected from the results of earlier ultraviolet and x-ray irradiation studies, which showed that free porphyrins were photosensitive. The greater stability of the free porphyrin in solid form probably indicates that the solvent molecules take part in the decomposition reaction. The vanadium- and nickel-porphyrin complexes are considerably more stable than the free porphyrins in solution. However, they were extensively decomposed by 50 megar and virtually completely destroyed by 70 megar. Synthetic and natural vanadium-porphyrin complexes when irradiated in solid form were more stable than in solution, but appeared to be no more stable than the free porphyrins in the solid form. No appreciable differences were observed among the stabilities of the synthetic vanadium- and nickel-porphyrin complexes and those actually isolated from petroleum. The atmosphere in which the samples
Petroleum, Okla. Petroleum, Calif. Asphalt, Okla., petroleum Asphalt, Calif., petroleum Petroleum, Petroleum, Petroleum, Petroleum,
Okla. Okla.D Okla.’ Kan.
Petroleum, Okla.
Concn , LMicromolal Orig. Final 50 megar 345 815 1430 1560 70 megar 345 430
175 280 200 megar 345
Enriched with synthetic vanadium-porphyrin complex. oil.
1 62
INDUSTRIAL AND ENGINEERING CHEMISTRY
’
600
650
Figure 2. Absorption spectra show 7770 decomposition of natural vanadium-porphyrin complex by 50 megar
Porphyrin Materials in Petroleums and Asphalts Are Resistant to Gamma Irradiation Decomposition Material
550 W A V E LENGTH, rnp
Decompn.,
%
330 790 1380 1490
4 3 3 4
305 360 120 200
12 16 31 28
2 50
28
Diluted with Pennsylvania crude
-
were sealed and the oxygen content of the solvent apparently were not significant factors. The samples prepared in carefully dehydrated and deaerated benzene and sealed under vacuum or an atmosphere of nitrogen suffered essentially the same degree of decomposition as the samples sealed under air (footnote c, Table I). This, of course, does not entirely preclude the possibility of more rapid decomposition of samples containing appreciable amounts of oxygen or simultaneously exposed to oxygen and irradiation. Samples of crude oils and their propane-precipitated asphalts were subjected to dosages of 50, 70, and 200 megar (Table 11). Two oils that had been studied extensively in this laboratory were chosen for the early tests. Porphyrins are present in the asphaltic Oklahoma (Tatums field) oil mainly as the vanadium-porphyrin complex (8,70) and in the heavy California (North Belridge field) oil as the nickel-porphyrin complex ( 8 , 9 ) . The propane-precipitated asphalt from the Oklahoma oil and the pentane-precipitated asphalt from another California crude oil (Wilmington field) also were irradiated. The durability of the porphyrin components of the crude oils and asphalts was unexpected in view of the destruction of the metal-porphyrin complexes in benzene solutions, It seemed unlikely that the stability of the porphyrin components in petroleum was caused by simple shielding effects. because of the energy range of gamma radiation from fission products. To test this conclusion, four identical samples of a synthetic vanadium-porphyrin complex (39.5 micromolal) were prepared in benzene solutions. Two of these were sealed in simple ampoules as in the previous test. The other two were sealed in ampoules and centered in large ampoules filled with the Oklahoma crude oil (footnote b, Table I). The small difference in decomposition as a result of this “shielding” indicates that simple shielding by the petroleum is an insignificant factor.
M E T A L - P O R P H Y R I N COMPLEXES Crude petroleum may afford some protection against radiation-incuded oxidation, a rather common cause of radiation damage ( 2 ) . However, the data (footnote c, Table I) indicate that the metal-porphyrin complexes are extensively decomposed even under anaerobic conditions. The metal-porphyrin complexes used in this study were isolated from the Oklahoma crude oil by mild, physical methods (70). However, the possibility remained that the porphyrin complexes in the petroleum were chemically different from those isolated. Therefore, the average porphyrin concentration in the Oklahoma petroleum was increased from 345 to 430 (micromolality) by adding synthetic vanadium-porphyrin complex to the petroleum. Only slightly larger percentages of the porphyrin contents of the enriched petroleum samples were decomposed than were those of the original petroleum samples. The data in Table I11 illustrate the general deviations to be expected with the digestion method (original values) and the larger deviations caused by the use of small samples, extensive handling, and inequalities of irradiation (final values). A preliminary study was made of protective effects against irradiation afforded porphyrin materials by petroleum. Samples of the synthetic vanadium-porphyrin complex were prepared in benzene solutions containing 570 of the propane-deasphalted raffinate (70) of the Oklahoma crude oil. These samples were exposed to 70 megar; the results are shown in Table I (foot-
Table 111. The Synthetic VanadiumPorphyrin Complex Is Also Resistant to Gamma Radiation in Presence of Petroleum Concn., DeMicromolal compn,, Orig. Final yG
Material
note d ) . The decomposition of the vanadium complex in these solutions averaged 71y0. This increased stability, compared to that of the vanadium complex in pure benzene, corroborates the protective action of petroleum components. These data are interpreted as indicating that crude petroleum acts as a “protective” solvent for the metalporphyrin complexes. Such action has been the subject of considerable research (20) but is only incompletely understood even for simple systems ( 3 ) . However, petroleum may be a natural protective agent against gamma irradiation by either of the commonly accepted mechanisms (74, 75) in which the petroleum scavenges free radicals or provides a n effective medium for internal energy transfer. An additional possibility indicated by the results with solid porphyrins is that crude petroleum acts as though it were not a solvent a t allthat is, it may not enter into the reaction with the porphyrins; hence the porphyrins in crude oil have a stability approaching that of their solid form. However different this concept may appear. the effect remains essentially a protective solvent action. I t is possible that some of the complex constituents of petroleum serve as freeradical scavengers. This would be a specific action and the effective compound or compounds may prove exceedingly difficult to isolate but very valuable in radiation protection studies if isolated. However, synergistic action of the complex petroleum system, in which dissipation of radiational energy without decomposition of the porphyrin material would be permitted, appears even more likely. .4ccording to the concepts of Pfeiffer (77), an asphaltic petroleum contains micelles which have nuclei of high-
Table IV.
Gamma Irradiation Has Relatively Small Effect on Several Properties 0 , Lubricating Stock and Petroleum Lube Stock SAE 30 __
First irradiation, 70 megar Petroleum, Okla.
Av. Petroleum, Okla.‘ Av.
0
349 349 336 33 1 351 341 343
311 291
301
2
427 402 414
390 339 364
2
Specific gravity 6Oo/6O0 F. Gravity, OAPI
442
0.880
363
Av. 440 350 20 a Enriched with synthetic vanadiumporphyrin complex.
Viscosity, ASTM D 445, cs. At 100‘ F. At 130’ F. At 210’ F.a Evap. loss, wt. %, 400’ F., 61/2 hr.
Petroleum. Okla.
Irradiation. Megar 100 200 0 0.882
0,882
200
0.900
0.905
29.3
28.9
28.9
25.7
24.9
0.0
0.0
0.0
4.0
8.0
108.0 50.1 11.7
121.1 54.9 12.7
140.7 62.5 14.2
47.8 27.1 9.0
56.5 30.6 9.8
17.7
17.1
18.7
54.7
50.1
Carbon residue, ASTM D 524 (Ramsbottom, wt. yG)
Second irradiation, 70 megar Petroleum, Okla.” 437 336
molecular weight, fused-ring compounds. From the nucleus to the aliphatic intermicellar fluid, there is a series of compounds of decreasing aromaticity and molecular weight. Although this concept has not been entirely proved, it can be correlated with a great many data. The colloidal theory of petroleum, expounded deductively by Pfeiffer, among others, found substantial corroboration in the recent work of Ray, Witherspoon. and Grim (78). T h e work of Manion and Burton ( 7 5 ) shows that even simple hydrocarbon mixtures react in unexpected ways to irradiation-for example, cyclohexene is a sacrificial protector for benzene and benzene is a sponge-type protector for cyclohexene. A petroleum structure of the type described above would appear optimum for the dissipation of energy, without extensive decomposition. If this is the case, petroleum probably would be a “natural” protective solvent for many substances other than the porphyrins, and would offer considerable promise in nuclear engineering applications. Whatever the protection mechanism may be, it is likely that it is due to the asphaltic portions of petroleum rather than the aliphatic hydrocarbons. This is at once an advantage and a disadvantage. The asphaltic materials may be fractionated by methods such as propane precipitation and formulated with various solvents to give a wide variety of compounds. O n the other hand. synthesis of the asphaltic system as yet is a ~ ~ r o c e of s s nature not capable of duplication in the laboratorv. The protective action of petroleum indicated that petroleum might prove resistant to irradiation damage. If so, petroleum, or partly refined petroleum products, would be of interest in nuclear engineering applications. A4ccordingly
Interfacial tension, dynes/cm., 77’ F. 27.9 27.3 29.2 25.1 25.0 Displacement energy (int. tens. X cosine, contact angle), dynes/cm. 77’ F. 26 +27 +31 -2Zb $25 Total acid No., ASTM D 664 0.00 0.02 0.03 0.00 0.10 Calculated, ASTM D 341. Negative value indicates oil wets glass preferentially t o water.
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FEBRUARY 1959
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t 6,
23
’O 7 50 I
201
[,I -
’*
parable to that of various mineral oils studied by other investigators. The extreme stability of vanadiumand nickel-porphyrin complexes in petroleum indicates that removal of these metals from petroleum by radiation refining methods will be difficult. However, the results with the porphyrin complexes in a hydrocarbon solvent show that such methods may be much more applicable to partly refined petroleum fractions such as gas oils and distillates. The protective action of petroleum observed in these studies may have considerable practical importance in the development of nuclear engineering processes.
-
10IO
, , , , ,
IO0
I20
1
Acknowledgment
, , , , , , , , , 180
I60
140
TEMPERATURE,
O
200
F.
Figure 3. Viscosity chart shows radiation resistance of petroleum and lubricating stock
the effects of gamma irradiation on some of the bulk properties of petroleum and a SAE 30 mid-continent lubricating stock were investigated (Table IV). These results show that both the petroleum and the lubricating stock are resistant to gamma irradiation to the 200-megar level, as observed by King and Rice (73) and Carroll and Calish (4). Only moderate increases in specific gravities, viscosities, and acid numbers were observed. However, a marked increase in the carbon residue of the crude oil resulted from irradiation. The surface properties as measured by interfacial tension (pendent-drop method) and displacement energy (interfacial-tension capillarimeter) of the lubricating stock were relatively unaffected. However, irradiation changed the petroleum from a form that would spontaneously displace water from glass to one that would be displaced by water from glass. These results are interpreted as indicating the destruction or conversion of complex minor constituents of petroleum that often cause it to adhere strongly to mineral surfaces (7). The effect of irradiation on the viscosities of the lubricating stock and petroleum are illustrated in Figure 3 (ASTM, D 341-39, Chart C). The viscosity of the lubricating stock at 100’ F. increased 12% a t a dosage of 100 megar and 30y0 at 200 megar. These figures are in agreement with earlier reports (4, 73) and indicate relatively high resistance of petroleum oils to irradiation, T h e viscosity of the crude oil a t 100’ F. was increased only 15% after a dosage of 200 megar. .This petroleum sample compares favorably with the best industrial oils tested by Carroll and Calish (4),on a basis of viscosity change. Very small increases in viscosity index (ASTM D 567) were
1 64
observed with the lubricating stock. The viscosity index of the crude oil decreased slightly, from an original value of about 150 to about 145 after a dosage of 200 megar. This behavior resembles but is less marked than that of viscosity index-improved oils ( 4 ) and probably indicates damage to the colloidal system of the crude oil. Conclusions
Vanadium- and other metal-porphyrin complexes were substantially decomposed by 50 megar of gamma irradiation and underwent nearly complete decomposition during exposure to 70 megar. The complexes are considerably more stable to irradiation than the free porphyrins in solution. No appreciable differences were observed among the stabilities of the synthetic vanadium- and nickel-porphyrin complexes and those actually isolated from petroleum. I n view of the sensibly complete destruction of the metalporphyrin complexes. the durability of the porphyrin components in the crude oils and asphalts was unexpected. Crude petroleum acts as a protective solvent for metal-porphyrin complexes. I t appears that petroleum may be a natural protective agent against gamma irradiation by either of the commonly accepted mechanisms in which petroleum scavenges free radicals or provides a n effective medium for internal energy transfer. Irradiation, a t the 200-megar level, resulted in small increases in the viscosities, acid numbers, and specific gravities of an Oklahoma petroleum and a mid-continent lubricating stock. T h e carbon residue of the crude petroleum was doubled by this treatment. The radiation resistance of these oils is com-
INDUSTRIAL AND ENGINEERING CHEMISTRY
The authors are indebted to R. T. Johansen of this station for measurements of interfacial tension and to D. L. Hunke, Phillips Petroleum Co., Idaho Falls, Idaho, who was responsible for the irradiation treatments. literature Cited (1) Beach, L. K., Shewmaker, J. E., IND. ENG.CHEM.49, 1157-64 (1957). (2) Bolt, R. O., Carroll, J. G., Ibid., 50, 221-8 (1958). (3) Burton, M., Lipsky, S., Magee, J. L., Division of Physical and Inorganic Chemistry, 131st Meeting, ACS, Miami, Fla., April 7, 1957; Chem. Eng. News, 35, NO. 15, 27-9 (1957). (4) Carroll, J. G., Calish, S. R., Lubrication Eng. 13, No. 7, 388-92 (1957). (5) Corwin, A. H., Erdman, J. G., J . Am. 68. 2473-8 (19461. Chem. SOC. ( 6 ) Dunning, H. N., Ibid., 79,’5320 (1957). (7) Dunning, H. N., Johansen, R. T., Hsiao, L., Petrol. Engr. 26, No. 1, B82-90 (1 954). \ - - ’ / .
(8) Dunning, H. N., Moore, J. W., Bull. Am. Assoc. Petrol. Geologists 41, 2403-12 (1957). (9) Dunning, H. N., Moore, J. W., Myers, A. T., IND.ENG. CHEM.46, 2000-7 (1954). (10) Dunnin , H. N., Rabon, N. A., Zbid., 48, 951-5 71956). (11) Erdman, J. G., Ramsey, V. G., Kalenda, N. W., Hanson, W. E., J . Am. Chem. SOC.78, 5844-7 (1956). (12) Groennings, S., Anal. Chem. 25,938-41 (1953). (13) King, J. A., Rice, W. L. R., Lubrication Eng. 13, No. 5, 279-83 (1957). (14) Magee, J. L., J . Phys. Chem. 56, 555-9 11952). l.___,.
(15) Manion, J. P., Burton, M., Zbid., 56, 560-9 (1952). (16) Moteff, J . Nucleonics 13, No. 5, 28-31 (1955). (17) Pfeiffer, J. P., “Properties of Asphaltic Bitumen,” Elsevier, New York, 1950. (18) Ray, B. R., Witherspoon, P. A., Grim, R. E., J.Phys. Chem. 61,1296-302 (1957). (19) Rice, W. L. R., Way, J. H., ASTIA Document Service Center, Dayton, Ohio, AD 130807, WADC Tech. Rept. 57266 (June 1957). (20) Tolbert, B. M., Lemmon, R. M., Radiation Research 3, 52-76 (1955).
RECEIVED for review April 10, 1958 ACCEPTED September 4, 1958 Division of Petroleum Chemistry, 133rd Meeting, ACS, San Francisco, Calif., .4pril 1958.
