PETROLEUM-COMPOSITION fictional crude oil, but i t might have some value in predicting trends in refining or other usgs. ACKNOWLEDGMENT
The author is very grateful to C. M. McKinney, Ella Mae Shelton, and Tom Felton, who have contributed to this paper by making many of the calculations and correlations that were required, and also to many colleagues in the Bureau of Mines who, during the past decade or more, have been making Bureau of Mines routine crude-oil analyses upon which many of the data presented in this report are based. LITERATURE CITED
sot. Test. ~ ~ ~‘ ~ A~S ~Standards,” M ~ i ~part l5, D ~ ~ , nation D 875-46T, Philadelphia, Pa., 1949. (2) Ball, J. S., Rall, H. T., Waddington, G., andsmith, H. M., paper presented a t Symposium on Composition of Petroleum, Petroleum Division, 119th Meeting AM. CHEM.Soc., Cleveland, April 1961. ( 1 ) Am.
i
(3) Ball, J. S., Whisman, M. L., and Wenger, W. 23,1632-41 (November 1951).
J., Anal. Chem.,
(4) Gruse, W. A., and Stevens, D. R., “The Chemical Technology of Petroleum,” New York, McGraw-Hill Book Co., 1942. (5) Holliman, W. C., Smith, H. M., McKinney, C. M., and Sponsler, C. R.. U. S. Bur. Mines. Tech. Paver 722 11950). (6) Lipkin,’M. R., Martin, L. C., and-Kurtz, S. S.,’Jr., IND. ENG. CHEM.,ANAL.ED., 18, 376 (1946). (7) Mair, B. J., and Rossini, F. D., “Science of Petroleum,” Vol. V, p. 126, New York, Oxford University Press, 1950. (8) Sachanen, A. N., 1bid., p. 53. (9) Sachanen, A. N., “The Chemical Constituents of Petroleum,” New York, Reinhold Publishing Corp., 1945. (10) “Science of Petroleum,” Vol. 11, pp. 839-930, New York, Ox.ford University Press, 1938. (11) Silliman, B., Am. Chemist,2,18 (1871-2). (12) . . Smith. H. M.. “Science of Petroleum.” Vol. V, p. 1, New York, Oxford University Press, 1950. (13) Smith, H. M., U. S. Bur. Mines, Tech. Paper610 (1940). ~(14)~Stanfield, ~ - K. E. and Hubbard, R. L.,Ibid., 717 (1949). RECEIVED for review June 25, 1951. ACCEFTED August 11, 1952. Presented a8 part of the Symposium on Composition of Petroleum and Its Hydrooarbon Derivatives before the Division of Petroleum Chemistry a t the 119th Meeting of the AMERICAN CHEMICAL SOCIETY, Cleveland, Ohio, April 1951.
Metalliferous Substances Adsorbed at Crude Petroleum-Water Interfaces CHARLES C. DODD’ AND JOHN W. MOORE Petroleum Experiment Station, Bureau of Mines, U. S. Department of the Interior, Bartlesuille, Okla. MILTON 0. DENEKAS Department of Chemistry, University of Tulsa, Tulsa 4, Okla.
3
Film-forming and surface active constituents in crude petroleum affect the flow of fluids in petroleum reservoirs and the analysis of reservoir rock core samples. The discovery of metallic elements in these substances has stimulated a study of the nature of the interfacially active materials with respect to the role of the metals. Compounds of zinc, copper, nickel, titanium, calcium, and magnesium were found to be adsorbed selectively at petroleum-water interfaces; vanadium was adsorbed to a minor extent and iron to an intermediate degree. The results indicate that
all eight elements occur in petroleum in oil-soluble forms, possibly as porphyrin-metal chelate complexes or other complexes with nitrogen-containing compounds. Although inconclusive, the results support the assumption that film-forming and surface active constituents of petroleum result from biochemical diagenesis of organic matter in sediments. The films may consist of waxes and resins with stabilizing porphyrin-metal complexes. Free porphyrins, porphyrin ring oxidation products, and protein-metal salts or complexes also may be present.
T
presence is undesirable. Finally, i t was thought t h a t efforts aimed a t more complete knowledge of the occurrence of metals in petroleum might provide insight into the problem of the origin of petroleum. A previous publication (4) described early work on crude petroleum produced in the Oklahoma City field. The bulk of material isolated by adsorption a t a n extended crude oil-water interface was identified as a mixture of normal paraffins of unusually high molecular weight containing 50 t o 70 carbon atoms per molecule and melting at 95” to 108”C. In addition, minute amounts of other materials present were moderately surface active and burned t o a black ash insoluble in dilute hydrochloric acid. Subsequent studies of materials isolated from a Rio Bravo, Calif, oil b y adsorption a t oil-water interfaces have disclosed the presence of smaller amounts of giant normal paraffins and appre ciably greater quantities of film-forming and surface active mate-
HE isolation and identification of naturally occurring filmforming and surface active constituents in crude petroleum have been among objectives of this laboratory. Primary impetus for such a study resulted from considerations of the possible effect of these substances on the wetting of petroleum reservoir rock by oil and water. Of interest also in petroleum production-engineering work is the manner in which these constituents complicate the analysis of core samples in the laboratory and cause the formation of stock-tank emulsions in the field. Discovery of the metal content of these materials indicated t h a t their study would be of interest to those concerned with a current problem of the petroleum refining industry involving the analysis and control or removal of trace (or larger) quantities of metals in crude oils. Metals in petroleum poison cracking catalysts and are carried over into certain refined products where their 1 Present
address, Continental Oil Co., Ponca City, Okla.
November 1952
INDUSTRIAL AND ENGINEERING CHEMISTRY
2585
rials compared with the Oklahoma City oil. Particularly noteworthy was the discovery in extracts from the Rio Bravo oil, and later in those from the Oklahoma City crude, of appreciable quantities of transition elements belonging t o the first long period (the fourth period) of the periodic table. I n addition, the alkaline earths magnesium and calcium appeared to be present. The apparent solubility of the metal-containing extracts in oils and organic solvents and their insolubility in water suggested t h a t
Figure 1.
Extraction and Isolation Procedure Used with Rio Bravo Crude Oil R B crude oila (1 liter)
I
Extracted in water-spray column. Spray solution 0.001 M AICI8, p H = 4.3
Extractives (coalesced darkbrown "emulsion" in separatory funnel) Extracted crude oil (removed from Excess water separated, columns and benzene added, funnel stored) shaken, 2 phases separated
I
Benzene-insoluble portion (light-tan, flocculent material)
J.
Excess water removed by centrifugation and drying under vacuum a t not
over400C. R B I (black, tarry solid)
Approx. yield = 200 mg.
Water (to waste)
Benzene solution
1
Re-extracted in water-spray columns
Second extractive (light-tan, flocculent material)
!
Excess water removed by centrifugation and drying under vacuum a t not over 40" C.
RBS (black, tarry solid) Approx. yield = 80 mg. T h e R B crude oil generally was dilluted with about 30% benzene b y volume to lower its viscosity. a
the metals might occur in organic complexes. Sulfur and nitrogen were found in the extracts, and there was some evidence of a n atom ratio of nitrogen to metal of approximately 4 to 1, which would imply t h a t one type of compound in which the metals might occur is in coordination complexes with nitrogen. A crude oil from the Lagunillas, Venezuela, field was also investigated.
EXPERIMENTAL PROCEDURES Sources and Properties of Crude Petroleum Samples. The source of the Oklahoma City Wilcox crude oil (referred t o hereinafter as OCW) was described in a previous publication (4). Additional samples had essentially the same specific gravity and viscosity as that described previously. The Wilcox sand is of Ordovician age. Three samples of crude petroleum, referred t o as R B in this paper, were obtained from the Rio Bravo, Calif., field. All of the samples were obtained from the central gathering tank in section 28 of the Superior Oil Co. unitized, pressure-maintenance operation in the Rio Bravo field in Kern County, 15 miles northwest of Bakersfield, Calif. The oil had a specific gravity of 0.828, 60/60° F. (39.4' API) and a viscosity of 2.68 cp. (37.4 Saybolt seconds at 77" F.).
2586
Wells in the Rio Bravo field produce from the Rio Bravo zone of Lower Miocene age. They are dual completions in the upper "Rio Bravo sand" and the lower "Vedder sand." The reservoir is of the gas-expansion type. The oil is the same as that studied in considerable detail by Bartell and Kiederhauser ( d ) . A lesser amount of work was done on a sample of crude petroleum (designated herein as LV) from the Lagunillas field on the eastern shore of Lake Maracaibo in the State of Zulia, Venezuela. A sample of the oil was available a t this station, and its properties have been described by Blade, Garton, and McKinney (@. It was selected for the present study because it was known t o have a vanadium content of approximately 250 p,p.m Producing formations in the Lagunillas field are of Miocene and Pliocene age. Isolation of Surface-Active Extracts by Adsorption a t OilWater Interfaces. The extraction apparatus and procedure were similar to those described previously ( 4 ) . Additional filmforming and surface active extracts isolated from the OCW crude oil were obtained in the same manner as described in that paper. When water-spray extraction work was done on the R B crude, certain changes were made in the procedure as shown in Figure 1. All benzene used for dilution of the crude oils and treatment of the extracts was ACS reagent grade, thiophene-free material, random samples of which were selected for interfacial tension measurements against water to ensure the absence of surface active contaminants. When the R B I or RBS fractions were dried completely a t temperatures higher than 40" C., shiny black solids were obtained vihich dissolved with difficulty in benzene or chloroform and only partly in pyridine. If drying was stopped a t the tarry or semisolid stage, the extracts were soluble in all three solvents. Irreversible solubility properties of this sort indicated that the solutions probably were colloidal. The OCJV-F fraction was obtained in the same way as the RBS, but carbon tetrachloride was used, rather than benzene. to separate the insoluble portion. Samples of the LV crude oil were subjected to nater-spray extraction in a similar manner. This oil vias so viscous that i t was necessary to dilute it with 4 volumes of benzene before extraction. The resulting extractive was treated with benzene and the insoluble portion corresponding to the RBI was used in further studies. It will be designated in this paper as LVI. Solvent-Extraction Purification of Water-Spray Extracts. Purification of extracts from the water-spray columns by solvent extraction in a Soxhlet apparatus was attended with only moderate success. No appreciable concentrations of film-forming or surface active constituents were effected by repeated evtraction with 30" to 60" C. petroleum ether, ethyl ether, benzene, chloroform, and pyridine in that order. Chromatographic Fractionation of Water-Spray Extracts. The work of Bartell and Niederhauser ( 9 ) indicated that filmforming constituents of crude oils were adsorbed most tenaciously by polar solids. Initially this discouraged the use of chromatographic fractionation techniques as purification methods for t h e water-spray extracts because it seemed probable that suitable eluents would be unavailable. Nevertheless, a n exploratory chromatographic run on a n alumina column demonstrated that the benzene-soluble fraction of the OCW-F water-spray extract could be fractionated extensively and that more than 85% of the original material could be recovered from the column; but there did not appear t o be a significant concentration of the surface active or film-forming materials in any fraction. Subsequent chromatographic fractionations have been carried out using crushed and sized calcite crystals. Crystalline calcium carbonate is a less polar adsorbent than alumina or silica gel, and constituents of the extracts are desorbed more readily from its surface; also if elution is not complete, the column can be dissolved in acid. Selected calcite crystals containing no spectroscopically detectable traces of metals other than calcium, crushed and sized
I N D U S T R I A L A N D E N (3 I N E E R I N G C H E M I S T R Y
Vol. 44, No. 11
PETROLEUM-COMPOSITION Table I.
Distribution of Metals i n Original and Extracted Crudes and Extractsa
Oklahoma City Wilcox (OCW)
Element Vanadium Iron Zino
Crude Oil Before After exextractraction tion M. M M M n m
Extractives OCW-Eb 0 M
OCW-Fb
OCW-Gb
M M
0
7
..
..
Rio Bravo (RB) Crude Oil Before After exextraotracExtractives tion tion RBI RBS A M M M M
m
t
Lagunillas, Venezuela (LV) Crude Oil Before After exextractl action tion LVI
--
M
Magnesium rn rn 0 t M a Qualitative analyses were made by aro emission spectroscopy; approximate oonoentrationa are indioated as: M = major constituent, approximately 1% to 100%; m = minor oonstituent, approximatelyO.l% to 1 .o; t trace constituent, less thanapproximatelyO.l%; and 0 = none. b The OCW fractions E, F, and G were described in an ear%, pGer (4).
between 70- and 140-mesh screens, were used for all the subsequent chromatographic runs described in this paper. A series of chromatographic separations was made to determine if the surface active and film-forming substances resent in the R B I water-spray extract could be concentrated. &e of the more successful procedures involved putting a 15-mg. sample of RBI in chloroform solution on a 6 mm. X 10 cm. calcite column followed by washing with about 20 ml. each of additional chloroform and a series of selected eluents.' Finally the column was washed with water, which failed t o elute any adsorbed material. The column was then dissolved completely in reagentgrade hydrochloric acid because the crushed calcite had not returned t o its original white color. This liberated an insoluble tarry material which was combined with a cupferron precipitate from the acid solution for spectroscopic analysis. An abbreviated larger scale chromatographic procedure was also investigated. About 200 mg. of either the RBI or RBS extract were dissolved in 10 ml. of chloroform and adsorbed on a 1.2 X 52 om. calcite column. Additional chloroform and then pyridine (20 ml. each) were employed as developers. A dark band moved down the column with each eluent. Three fractions were collected with the eluents: a chloroform band, solution ahead of pyridine, and a pyridine band. I n addition, the column was dissolved in hydrochloric acid, an insoluble tarry material was removed by filtration, and the acid-soluble metals were precipitated with cupferron. Qualitative Determination of Metals by Arc Emission Spectroscopy. Samples available from chromatographic fractionations usually amounted t o only a few milligrams, and the metallic content of most of the samples was below 5%. For this reason wet methods of chemical analysis, either macro or micro, which require prior ashing of the sample were inapplicable. Furthermore, most spectrographic procedures require larger samples. For trace analysis such as this, the eye is more sensitive than photographic emulsions. Visual arc emission spectroscopic procedures were applied directly to samples as small as 1 mg. by noting the occurrence of flashes of characteristic spectra. Apparatus and procedures for spectroscopic analysis have been described by Peterson, Kauffman, and Jaffe ( 1 4 , Gabriel, Jaffe, and Peterson (6), and Jaffe (8). The apparatus used for this work was similar. Samples for analysis were ground in a micro mortar with spectroscopically pure graphite powder and pressed into compacted cylinders in a pelleting machine. Intensities of the various spectral lines of the elements vary greatly. Concentration of the respective elements can be ascertained only approximately by observation of line intensities. T o the observer, differences can be recorded as flashes, lines, and steady burning, strong lines. For purposes of quantitative estimation of the corresponding concentrations in Tables I, IV, and V, these observations are interpreted as trace constituent, minor constituent, and major constituent, respectively. The procedures of J&e and coworkers (6, 8) were modified for the detection of nickel and copper, especially in the presence of iron. To determine nickel, the spectrum was scanned for strong lines a t 5477, 5086, and 4715 A. which, however, are adjacent to iron lines. If these were found, the presence of nickel was confirmed by noting the presence of the weaker lines
November 1952
a t 5115 and 5035 A. which are not too close to interfering iron lines. The nickel lines a t 5115 and 5086 A. are not listed by Peterson, Kauffman, and Jaffe (14). The copper lines a t 5218, 5153, and 5105 A. recommended by Peterson, Kauffman, and Jaffe were difficult t o recognize in the presence of iron. Strong copper lines a t 5782 and 5700 A. were more useful in determining copper, especially the former which is not interfered with by iron lines. If the 5782 A. line was faint, it was necessary to use the group of 5218, 5153, and 5105 A. to confirm copper. Copper also was found t o be particularly volatile in the carbon arc in the samples studied during this work. To detect copper and nickel, i t was necessary to arc the sample a t not more than 3 to 4 amperes to avoid volatilization of these elements. Miscellaneous Analytical Procedures. Crude oils were converted to representative inorganic residues by wet oxidation of 50 grams of oil with 50 ml. of concentrated sulfuric acid in 250-ml. fused-silica beakers, followed by ignition t o 550" C. in an electric muffle furnace. Quantitative analyses for vanadium on residues from the LV crude oil were made by a standard macro volumetric procedure in which vanadic acid is titrated with standardized ferrous sulfate solution. Visible absorption spectra were determined with a Beckmann spectrophotometer. Microanalyses were performed by Clark Microanalytical Laboratory, Urbana, Ill. Measurements of Surface Activity and Film-Forming Tendency of Crude Oils and Water-Spray Extracts. Significant measurements of interfacial tensions a t oil-water interfaces are particularly difficult when crude oils, their solutions, or solutions of their extracts constitute the oil phase. The pendent-drop method ( 1 ) is most suitable for such systems because it permits observations of the rate of change with time of interfacial tension more satisfactorily than any other method. It is usable with highly viscous crude oils, does not depend on any contact angle, and has been found t o be suitable for use with solutions of surface active substances and film-forming materials such as proteins (7). The pendent-drop instrument used in the present work was similar to that of Mack, Davis, and Bartell (11)and Bartell and Niederhauser ( 2 )but employed a zirconium arc lamp as an optical point source together with an improved camera and optical system. Calculations of interfacial tension based on drop measurements were made with the aid of the new tables of Fordham (6) and Niederhauser and Bartell ( l a ) . Surface activities of the various crude oil solutions, water-spray extract solutions, and fractionated extract solutions were studied by determining interfacial-tension aging curves of the oil phases against distilled water saturated with the particular organic solvent used. Solutions of the extracts and extract fractions were made up in benzene or chloroform t o concentrations of about 0.1 mg. of solid extract per ml. of solvent. A drop of the solution waB held a t a glass tip in an external aqueous phase in the pendent-drop optical cell. The final lowering of the interfacial tension of the system a t the end of 2 hours compared with the interfacial tension of the
INDUSTRIAL AND ENGINEERING CHEMISTRY
2587
Table 11.
- Before Extraction
Crude Oil
Ash, p.g.iii.
Vanadium, p.p.m.
Lagunillas, Venezuela Rio Bravo
1330 93
305
...
After Extraction Ash, Vanadium, p.p.m. p.p.m.
720
65
260
...
pure solvent against water was taken as a measure of the surface activity of the solution. Film-forming strengths of the same solutions used to determine surface activity were measured by receding pendent drops that had been permitted to age in contact with water for about 5 minutes, The point of recession was noted a t which the receding drop just began t o ‘(neck down” and show evidence of a folded, transparent “skin” or ‘Yilm’’ around the drop. If the residual drop lengths were greater than 50% of the original length of the drop before recession, the film-forming tendency of the oil phase was rated strong. When residual drop lengths were less than 30% of the original length, the film-forming tendency was moderate, and when measurable but less than 30%, the rating was weak. This system is similar to that employed by Bartell and Niederhauser (3). RESULTS
Distribution of Metals in Original Crudes, Extracted Crudes, and Extracts. Qualitative analyses by visual micro emission spectroscopic methods indicated approximately the extent to which various metallic elements were extracted from crude petroleum by adsorption a t petroleum-water interfaces. The distribution of vanadium, iron, zinc, copper, nickel, titanium, calcium, and magnesium found is shown in Table I. Other elements besides the eight listed in Table I occurred in the oils and extracts. Probably minor concentrations of several elements were not detected spectroscopically. Sodii m was present in many samples but its occurrence was not studied during this work. Aluminuin was found in some extracts but not in the ash of any of the crude oils; thus any aluminum in the extracts must have come from the 0.001 M solution of aluminum chloride used for the extraction process (4). Quantitative sulfated ash analyses of the LV and R B crude oils and vanadium analyses of the ash obtained from the LV oil were made to determine the effectiveness of the water-sprag extraction process in removing inorganic constituents, particularly vanadium. The results are presented in Table 11. Surface Activities and Film-Forming Tendencies of Original Crude Oils and Water-Spray Extracts. Interfacial tension and film-forming studies made by the pendent-drop method confirmed the presence of surface-active and film-forming constituents in the original crude oil samples and the water-spray extracts. It was also found that the amounts of these constituents originally present in the crude oils were reduced by water-spray extraction. The results are presented in Table 111. Fractionation of Water-Spray Extracts by Chromatography. Results obtained by chromatographic purification of 15-mg. batches of the R B I water-spray extract are presented in Table IV. The bulk of the film-forming activity of the RBI was isolated in fractions 1 and 2, whereas essentially all the interfacial tension depressants, with the exception of those which could not be eluted from the calcite column, were concentrated in fractions 5 and 6. The LVI extract was chromatographed by a similar procedure and, although the original LV crude oil demonstrated only very weak interfacial activity and very little film-forming tendency, the chromatographic fractions that did possess some surface activity or film-forming tendency were eluted with the corresponding solvents used for the RBI run. Furthermore, corre-
2588
syonding fractions contained the Same metals. The titanium-bearing in the LVI extract was also adsorbed so tenaciously by the calcite column that Reduction, Yo Ash Vanadium it could not be desorbed bv eluents iust 46 15 as in the case of RBI. 30 .. Detailed results obtained with thc larger scale abbreviated chromatographic procedure are presented in Table V. This procedure proved t o be of particular interest because it was possible, after evaporat,ion of most of the pyridine from the third fraction, to remove a water-soluble substance that imparted a blue, blue-green, or green’color to a water solution. Blue-green prismatic needles of the material, sometimes as large as 5 mm. long and 0.5 mm. thick, could be crystallized from pyridine solutions. Poorly crystallized masses were obtained from water. The green crystalline material was hygroscopic and soluble in water but insoluble in ether, benzene, and chloroform. When a tiny crystal was held on a platinum inicrospatula near a microburner, decomposition occurred before melting. The electriral conductivity of the aqueous solution indicated appreciable ionization. Upon treatment with concentrated sulfuric acid, the material was decomposed, liberating an acid-forming gas and precipitating a colorless material. Treatment with 5 S acid under conditions of t,he test for carbonate ion did not liberate carbon dioxide. The Barger isothermic-distillation micro molecular weight procedure (IS)indicated a particle weight. of 300 or slightly less. The visible absorption spectrum of a pyridine solution of the crystals consist,ed of a sharp, high peak in the near ultraviolet at, 306 mp, a broad, lower peak a t about 730 to 755 mp in the visible range, and a broad minimum at about 565 to 575 mp.
Reduction in Total Sulfated Ash and Vanadium Content of Crude Oils by Water-Spray Extraction
Table 111. Surface Activity and Film-Forming Tendency of Crude Oils, Extracted Crudes, and Extracts Final Interfacial Tension a t Water Dynes/Cm’. Interfacea 16 16 to 18 20 25
FilmTendency6 Forming
S
S S
m
Extracted crude oils 19 to 22 €3 R B (1:l dilution) 24 S OCW (undiluted) 31 R‘ LV (1 :4 dilution) Extracts 20 S R B I (0.1 mg. per ml.) 22 S RBS (0.1 mg. per mi.) 25 S OCW-F (0.1 mg. per ml.) 30 m LVI (0.1 mg. per ml.) Control Pure benzene-water interface Sone (mutually saturated phases) 33 7 a Measurements were taken after “aging” a drop for about 2 hours. All dilutions are in benzene. Measurements were made at 25.0’ & 0.2’ C. b Semiquantitative estimates of film-forming tendency follow the scheme proposed by Bartell and Siederhauser (2). S means strong; m, moderate; a n d w, weak (see text).
Quantitative microanalyses for carbon and hydrogen (performed by other laboratories) were somewhat variable from batch to batch. Samples of green crystals from the RBI extract contained 40 t o 43% carbon and 4.0 to 4.3% hydrogen, resulting in hydrogen-carbon ratios of about 1 to 1. One quantitative analysis for nitrogen indicated 6.1%. A sample of crystals from the RBS extract contained 28.9% carbon and 3.8% hydrogen. Nitrogen was found in all samples of the crystals analyzed qualitatively while sulfur occurred in some and not in others. In addition, nitrogen and sulfur were found in chromatographic fractions 1 and 3 and in fraction 3 minus the green crystals. Comparison of Tables IT and indicates a difference in the film-
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 44, No. 11
PETROLEUM-COMPOSITION Tabte IV.
Chromatographic Fractionation of RBI Water-Spray Extract on Calcite Column Final Interfacial a t Water Interfaceb, Dynes/Cm. 24 25
FilmRelativeof Approximate Metal ContentR Amount Forming Chromatographic Fractions Original 1’ Tendencyb Cu Ti Ca Mg Fe Zn 1 (chloroform) Moderate t ‘ t O O O t t S 2 (chloroform and ethyl alcohol, 95:5) Large in m t O O m m S 3 (chloroform and ethyl alcohol, 1 : l ) Minor .. .. .. .. .. .. .. 4 (ethyl alcohol) Minor .. .. .. .. .. 5 (ethyl alcohol and pyridine, 1 : l ) Large 0 t M M O M M ii W 6 (pyridine) Large 0 t M M 0 M M 18 W 7 (water) Minor .. .. .. .. .. .. .. 8 (residue on column) Moderate t in 0’ 0 M .. m .. .. a Concentrations of metals are indicated in the same manner as in Table I ; nickel was not determined on these samples: fractions 3, 4 , and 7 were too small for analysis. b .Measurements of surface activity and film-forming tendency were similar to those in,Table 111. I
Table V.
.
Larger Scale Chromatographic Fractionation of the RBI Water-Spray Extract Approx. Per Cent of Ori inal
FilmForming Tendencyb
Approximate Metal ContentR Chromatographic Fractions R%I V Fe Zn Cu Ni Ti Ca Mg 1 (chloroform band) 2 (ahead of pyridine hand) 3 (pyridine band) Green crystals from 3 3 minus ereen crvstals O O t Cupferron precipitate of HCl solution O O O O O M . . O of calcite column .. m O O O M . . M HC1-insoluble material left on column .. t a Concentrations of metals are indicated in the same manner as in Table I. b Measurements of surface activity and film-forming tendency were similar to those in Table 111.
forming tendencies of chloroform-eluted fractions. The Season for this is not clear unless it is a function of the ratio of sample to column size. Microanalyses of Benzene-Soluble Soxhlet Fractions of the Water-Spray Extracts. In addition to oil solubility of the waterspray extracts, other evidence indicating the possible presence of metals in chelate-type compounds was obtained by microanalyses of benzene-soluble fractions resulting from solvent extraction of the water-spray extracts in a Soxhlet apparatus. Results of the microanalyses together with wax contents, densities, bromine values, and particle weights are presented in Table VI. The data shown in Table VI were used t o make approximate calculations of the nitrogen-metal gram atom ratio. On the basis of the assumption that a metal of atomic weight 50 constitutes ’/IO of the wax-free ash from the carbon-hydrogen microdeterminations, ratios of 5.0 and 3.5 were calculated for the RBI and OCW-F benzene-soluble fractions, respectively. I n view of the approximations made in the calculations and the probable experimental errors in the residue determinations caused by incomplete combustion and volatility, these results are close enough t o 4 (the theoretical value to be expected for metallic complexes of porphyrin rings) t o justify further study of this possibility. The RBI, RBS, and OCW-F benzene-soluble fractions were subjected t o qualitative analysis for functional groups that might be present; but only negative results were obtained except in the case of unsaturation tests. All of the samples absorbed bromine. The calculated bromine values are given in Table VI. The unsaturation that might be indicated by such a reaction could be either aromatic or olefinic or both. Infrared spectra of the samples did not yield much additional information. All of thesamples were amorphous to x-rays.
DISCUSSION A portion of the vanadium and iron present in the crude oil samples studied was removed by extraction in water-spray columns. The vanadium removed was found in traces in most of the chromatographic fractions but was concentrated only in the film-forming fraction from the RBI. Only a small percentage of November 1952
Final Interfarial Tension a t Water Interfaceb Dynes/Cm.’ 29 24 1Q 30 lQ
S
.. .. ..
..
..
the vanadium present in LV crude was concentrated a t interfaces. Iron was concentrated to a much greater extent in the interfacially active materials. Compounds of zinc, copper, and nickel were extracted more selectively by the water-spray process and were found in comparatively large amounts in the surface-active fractions as well as in the inactive portions of the extracts; however they were not found in materials adsorbed a t interfaces to the extent that titanium, magnesium, and iron were. Titanium was always associated with the most active fractions and was removed most consistently by the water-spray process. Whenever the water-spray extractives were chromatographed, it was impossible to elute the titanium-bearing material with any of the solvents used. Calcium and magnesium both were extrtbcted selectively by the water-spray process and were concentrated in the surface active fractions, but magnesium appeared to be present in a compound which was adsorbed more strongly a t interfaces, almost as strongly aa was titanium. All of these eight metals present in the water-spray extracts,
Table VI. Microanalyses of Benzene-Soluble Fractions from Soxhlet Extractions of Water-Spray Extracts %
Wax content b y vacuum distillation (1 mm.) to360’C. Microanalyses corrected for wax content Carbon Hydrogen Nitrogen Sulfur Residue from C H H:C ratio Density, gram per ml. Bromine value Approximate particle weight as indicated b y Rast camphor methodb
Dec. RBS,(little .%
OCW-F, %
32.8
distillate)
36.3
81.48 6.81 2.53 0.83 2.56 1.00 1.102 53.8
82.80 8.25 Presenta Present‘l 2.46 1.19
81.00 6.79 1.74 1.65 2.50 1.00 1.033 52.5
344
97.5 1000
286
Not determined quantitativelv. b Molecular weight determinations on mixtures such as these samples probably have limited significance. It was observed that “cracking” of the sample materials occurred during the determinations.
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with the exception of some iron oxide extracted from the OCW oil, occurred in compounds soluble in organic solvents. If the extracts were not dried completely, oil solubility was retained throughout the various separation and purification processes. If the metals were not present originally in the crude oils as oilsoluble, chelatetype metal complexes, they must have occurred as oil-soluble metallic salts or as solubilized colloidal substances. Reduction of the total sulfated ash of the LV crude oil by one pass through a water-spray extraction column was about three times as great as reduction of the vanadium content. Other elements, such as magnesium, titanium, nickel, and zinc, must have been removed from this oil in greater relative amounts than vanadium. These experiments indicate that a water-spray extraction process could not be used t o remove all undesirable metallic constituents of crude oils, They also suggest t h a t the various metals occur in petroleum in more than one kind of molecular form or a t least in a range of molecular sizes. Nevertheless, microanalyses of the benzene-soluble fractions obtained in a Soxhlet apparatus are surprisingly similar except for the slightly higher hydrogen and carbon content of the RBS fraction as shown in Table VI. The ash analyses of all three samples and the carbon and hydrogen contents and hydrogen-carbon ratio of the R B I and OCU7-F samples are almost identical; thus the water-spray extracts from the RB and OCW oils may contain similar substances. The calculated nitrogen-metal atom ratios might indicate the presence of nitrogen chelating molecules such as porphyrins in each oil. The water-soluble, metal-containing crystalline material separated by the large scale chromatographic procedure suggests the presence of proteins and their decomposition products. The green crystals contained large amounts of copper (probably around lo%), and the visible spectrum of pyridine solutions of the crystals was similar t o spectra of solutions of copper salts of fatty acids and to spectra of solutions of copper complexes of proteins such as bovine albumin (9).
TENTATIVE CONCLUSIONS Experimental results described above are inconclusive with respect to the chemical nature of film-forming and surface-active constituents in crude petroleum. A great deal of work remains t o be done, but the results obtained t o date permit development of several novel correlations. The evidence a t hand supports the proposals of investigators such as Treibs (16) and Skinner (16), who have postulated the occurrence of vanadium in petroleum as oil-soluble, chelate complexes of the porphyrins which are derived from plant and animal source material. The remaining seven elements studied in this work also may occur in such complexes, but other forms of occurrence must not be ruled out. It also appears that a given metal may occur in petroleum in more than one chemical form. Results of this work have led the writers to think t h a t some of the metalliferous substances extracted from petroleum by the water-spray process may be of biochemical origin. ZoBell ( 1 7 ) has studied the role of bacteria in the diagenesis of petroleum sediments and has considered t h a t proteins might be transformed into hydrocarbons by bacteria. H e has emphasized the role of bacterial enzymes in catalyzing chemical processes involved in the diagenesis of sediments. Enzymes and chromoproteins are made up of proteinaceous material together with attached prosthetic groups which frequently are hematins, that is, porphyrinmetal complexes. On the basis of these possibilities, it would not be surprising t o find metals occurring in petroleum both as porphyrin-metal complexes and as protein-metal complexes. The possible presence of enzyme systems consisting of proteins, together with porphyrin-metal complexes as prosthetic groups, might explain the reported occurrence of films apparently only after crude oils are exposed t o oxygen ( 2 ) . Many enzymes are capable of complex, but often reversible, oxidation-reduction reac-
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tions. For example, cytochrome C may be adsorbed on kaolin in the oxidized state and eluted follom.ingreduction (10). I n common with other protein-containing substances, enzymes are also sensitive t o changes in the hydrogen-ion concentration and other environmental variables. Bartell and Kiederhauser concluded that film-forming substances do not occur in petroleum reservoirs because reducing conditions prevail there (2). This conclusion should be re-examined when more information concerning the chemical nature of the films is available. The nature of the film-forming and interfacially active constituents of petroleum has not been determined by this investigation; however, the results described herein may be reconciled if it is assumed that films formed at interfaces between crude petroleum and water or rocks consist of mixtures of resins, waxes, porphyrin-metal complexes, free porphyrins, and possibly decomposition producta of proteins and their metal salts. The films probably are stabilized by the most interfacially active materials in the mixture, the porphyrins and their metal complexes. It is hoped that results of this work will stimulate further investigations of film-forming and surface active constituents of petroleum.
ACKNOWLEDGMENT The writers wish to thank W.L. Martin and H. N. Dunning for measuring film-forming tendencies and surface activities of the various crude oils and their extracts. J. M. Clingenpeel operated the water-spray columns and prepared the extracts. W.E. Hanson of the Mellon Institute and H. M. Smith of this station have contributed constructive criticisms and discussions of the work.
LITERATURE CITED Andreas, J. M., Hauser, E. A., and Tucker, W. B., J . Phys. Chem., 42, 1001 (1938).
Bartell, F. E., and Niederhauser, D. O., “Fundamental Research on Occurrence and Recovery of Petroleum 1946-47,” pp. 57-80, Kew York, American Petroleum Institute, 1949. Blade, 0. C., Garton, E. L., and McKinney, C. M., U. S. Bur. Mines, Regt. Invest. 4657 (1950). Denekas, M. O., Carlson, F. T., Moore, J. W., and Dodd, C. G., INDENG.CHEM.,4 3 , 1 1 6 5 (1951). Fordham, S., Proc. Roy. SOC.(London), 194A, 1 (1948). Gabriel, A,, Jaffe, H. W., and Peterson, M.J., Proc. A.S.T.M., 47,1111 (1947).
Hauser. E. A,. and Swearingen. L. E.. J . Phus. Chem., 45, 644 (i94i).
Jaffe, H. W., Am. Mineral., 3 4 , 6 6 7 (1949). Klotz, I. M., “Colloid Chemistry,” Vol. VII, p. 232, New York, Reinhold Publishing Corp., 1950. Lemberg, R., and Legge, J. W.,“Hematin Compounds and Bile Pigments,” p. 347, New Pork, Interscience Publishers, Inc., 1949. Mack, G. L., Davis, J. X., and Bartell, F. E., J . Phys. C h m . , 4 5 , 8 4 6 (1941).
Niederhauser, D. O., and Bartell, F. E., “Fundamental Research on Occurrence and Recovery of Petroleum 1948-49,” pp. 114-46, New York, American Petroleum Institute, 1950. Niederl, J. B., and Niederl, V., “Micromethods of Quantitative Organic Analysis,” pp. 230-8, New York, John Wiley & Sons, Inc., 1942. Peterson, M. J., Kauffman, A. J., Jr., and Jaffe, H. N’.,Am. Mineral., 3 2 , 3 2 2 (1947). Skinner, D. A,, IND.ENG.CHEM.,44, 1159 (1952). Treibs, A., Ann., 509, 103 (1934); 510, 42 (1934); 517, 172 (1935).
ZoBell, C. E., “Fundamental Research on Occurrence and Recovery of Petroleum 1946-47,” pp. 100-32, New York, American Petroleum Institute, 1949. RECEIVED for review September 12, 1952. ACCEPTEDSeptember 22, 1952. Presented as part of the Symposium on Nonhydrocarbon Constituents of Petroleum before the Division of Petroleum Chemistry a t the 121st Meeting SOCIETY, Milwaukee, Wis., March 31, 1952. of the AUERICANCHEMICAL Second paper in a series [started with reference (411 describing studies of film-forming and surface active constituents naturally present in crude petroleum.
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 44, No. 11
