Ind. Eng. Chem. Prod.
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Hysol OS 1500; anhydride-cured aromatic epoxy, e.g., Emerson and Cumming's Stycast 1269 A and B; styrenated polyester, e.g., Crystal Cast; diallyl phthalate (DAP)/lauryl methacrylate (LMA), 80/20 (Usmani and Salyer, 1981); and DAP/epoxy interpenetrating polymer networks (IPN) (Usmani, 1981). The adhesion of the potting resin to the cap material and the retention of this adhesion after 1000 h under 85 "C/85% relative humidity are important. An Instron adhesion test using an improvised jig was developed and used. The bottom of the potted 5-cm3cups were removed by machining. Machined cups were inverted and placed on a die and pushed from the bottom by the Instron cross-head via a plunger. The plunger must precisely match the small diameter of the potted material. From the surface area and the force required to push out the potting resin, the adhesion expressed in psi was determined. Summarized results are given in Table IV. The 85 "(2185% relative humidity test for 1000 h had little effect on the polypropylene and TPX test cups. There was no visible effect on the cup and no discoloration was noted. Poor adhesion rules out the utility of polypropylene and TPX as cap materials, however. The polycarbonate test pieces were not discolored, but a whitening of the interface between the polycarbonate test cup and the epoxy potting resin was noted, indicating attack of the epoxy by moisture along the cup/potting resin interface. Nylon and Arylon T cups were found to discolor by the test conditions. To be useful, the cap material and the potting resin must be combined to make a functional assembly. Factors such as compatibility of cap material with potting resin, freedom from cracks, and separation between cap structure and the potting resin must be considered. The plastic-resin interface separation in combined assembly was determined before and after thermal shock. For quick temperature adaptability the combined assemblies were thermocycled ten times (5 min at 100 "C and then quickly quenched to 0 "C and held at 0 "C for 5 min is one cycle). The tested assemblies were inspected visually and under a microscope. They were then dye-stained and examined for separation with a microscope. The consolidated results expressed as reactions of potting resins with various cap materials are summarized in Table IV.
69 1
Compatible systems are those in which there is little or only slight attack of the potting resin on the cap during curing. This promotes adhesion of the potting resin to the cap. If the solvent attack is too great, it will cause deformation of the cap. Conclusions
For cycloaliphatic and aromatic epoxies as well as DAP/LMA potting resins Nylon 612 (Zytel 151 and 158), rubber-modified nylon, e.g., ST-801, and Arylon T, are better cap materials than polycarbonate. Their superiority stems from their good adhesion to epoxy potting resins and their ability to retain adhesion after 1000 h in an 85 "C/85% relative humidity environment. The effect of internal (attack of potting resins on cap materials) and external (heat, ultraviolet, moisture) hostile environments on plastic housings for small electronic devices must be considered in order to arrive at suitable materials. Acknowledgment
The author thanks Dr. A. G. Maadhah for many useful suggestions. Special thanks are given to Nihal Ahmad and K. N. Kishore for their help in preparing this paper. Registry No. Hysol OS 1500, 87335-94-2; Stycast 1269A, 87335-95-3; Crystal Cast, 87335-93-1; TPX-RT 20, 61328-36-7; RO-15, 25068-26-2; Zytel151L, 24936-74-1; Zytel801,80210-14-6; Vydyne 21X, 32131-17-2; Vydyne R220,61419-65-6;Vydyne 602 M, 78615-85-7; Arylon T, 78615-51-7; Tenite 650, 24968-12-5; XP-5272,59859-44-8;Stycast 1269B, 87335-96-4;DAP,131-17-9; LMA, 142-90-5;EVA, 24937-78-8; polyethylene, 9002-88-4;polypropylene, 9003-07-0; (adipic acid).(1,12-dodecanediamine) (copolymer), 36786-01-3. L i t e r a t u r e Cited Grzgorczyk, D.; Fineman, G. "Handbook of Plastics in Electronics"; PrenticeHall: Engelwood Cliffs, NJ, 1974. Usmani, A. M.; Salyer, I. 0. J. Mater. Sci. 1981, 16, 915. Usmani, A. M. J. Elastomers Plast. 1981, 13, 170. Usmani, A. M. Org. Coat. Appl. Polym. Sci. Proc. 1982, 4 7 , 282. Usmani, A. M.; Salyer, I. 0. J. Mater. Sci. lg83, 18, 348.
Received for review February 22, 1983 Revised manuscript received May 31, 1983 Accepted July 7, 1983 Presented at the 184th National Meeting of the American Chemical Society, Kansas City, MO, Sept 12-17, 1982, in the Division of Organic Coatings and Plastics Chemistry.
Trace Metals in Crude Oils from Saudi Arabia Mohammad F. All,* Ahmed Bukharl, and Mohammad Saleem Department of Chemistry, University of Petroleum and Minerals, Dhahran, Saudi Arabia
Samples of crude petroleum from nine different producing fields of Saudi Arabia are analyzed for 17 trace metals. The analytical data are examined for V/Ni ratios in Arab crude oils. The V/Ni ratio in these crude oils seems to be restricted to a small range of values. I n contrast, V/Fe, V/Mg, V/Cu, V/Cr, and V/Zn have a wide range of values. For the Cretacious crude oils, the V/Ni index is between the limits 2.78 and 3.10. For the upper Jurrasic oils, the V/Ni index ratio range from 3.76 to 4.35, indicating that the index increases with the age of oil. The correlations between sulfur and trace metals and between carbon residue and trace metals are discussed. The analyses of trace metals in the four marketable quality Arab crude oils are reported for the benefit of potential users. Introduction
Trace elements in petroleum have received increased attention in recent years because of their importance both 0196-4321/83/1222-0691$01.50/0
in genesis of petroleum and its refining. The nature of these metals and their abundance in crude oils can give information on the origin, migration, and maturation of 0 1983 American Chemical Society
692
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Table I. General Characteristicsof Crude Oils from Saudi Arabia
field
Fadhili Abqaiq
Ghawar Abu-Safah Khursani yah Zuluf
Safaniyah Marjan Well Marjan Lower Bahrain Arabian Berri
Arabian Light Arabian Medium Arabian Heavy
producing horizon
U. Jurassic U. Jurassic U. Jurassic U. Jurassic U. Jurassic
cretacious cretacious cretacious cretacious cretacious
ARAMCO export ARAMCO export ARAMCO export ARAMCO export
ASTM
viscosity at 100 "F (SUS), ASTM
content, ppm, ASTM
D 129
D 445
D 482
0.95 1.40 1.97 2.53 2.90 2.61 3.06 3.41 4.80 2.10 1.10 1.81 2.59 2.79
42.5 45.3 47.5 59.9 65.3 54.1 115 156 349 51.7 41 49 71 118
10 39 31 42 37 70 82 85 130 34 12 34 55 96
gravity, "API, ASTM
C residue, wt%,
S,wt%,
D 1298
D 189
37.7 35.3 34.0 30.0 28.4 31.3 28.0 24.8 20.0 31.3 38.5 33.7 30.4 28.03
1.78 2.59 3.94 4.58 4.22 2.46 4.99 6.14 5.97 3.82 2.0 3.58 5.87 6.75
petroleum. Also, the nature of metals in crude and residual oils is of interest to the refiner as they are the source of environmental pollutants and the cause of corrosion of equipment and poisoning of process catalysts. Vanadium and nickle have been studied more thoroughly than any other metallic element found in petroleum. One of the reasons is that these elements occur in part as nitrogen complexes (porphyrins) closely related to chlorophyll and hemoglobin, thus suggesting a biogenic origin for petroleum. Many correlations based on vanadium and nickel content have been made in attempts to obtain information on the geological origin of petroleum. Hodgson (1954) in a study of the oils of Western Canada measured V, Ni, and Fe and concluded that the V/Ni ratio decreased with increasing maturation. Hyden (1961) and Ball et al. (1960), however, presented data to show that V/Ni ratio increased with the age of the host rock. Similar conclusions were used by Al-Shahristani and Al-Atyia (1972) to suggest that a V/Ni ratio of less than 1 indicates that oil is of a younger age, e.g. tertiary, while, a ratio of more than 1 indicates that oil is of an older age, e.g., cretaceous. More recently, Abu-Elgheit et al. (1979) studied the total vanadium and nickel contents of petroleum residues from different oil fields in Egypt and concluded that the V/Ni index decreases with the age of oil. A V/Ni index of 1-1.44 was reported for the lower cretaceous oils and an index of 3.25-3.53 for the Micocene oils. Other authors (Demekova et al., 1958; Gilmanshin et al., 1971) have concluded that the V/Ni ratio does not correlate with age. This paper reports 17 trace metals in samples of crude oils obtained from nine producing fields of Saudi Arabia and one from Bahrain. The majority of these fields produce from upper Jurrasic Arab zone reservoirs, generally oolitic and dolomitic limestone. The Safaniyah field, the world's largest offshore oil field, produces principally from cretaceous reservoirs. The results of trace metal analysis on the four Arabian crude oil (ARAMCO export quality) are also included for the benefit of potential users. Experimental Section Oil Samples. Samples of crude petroleum from Safaniya, Zuluf, Marjan, Abqaiq, Abu-Safah, Fadhili, Ghawar, and Khursaniyah oil fields were provided by ARAMCO and used as received. Samples of Arab Berri, Arab Light, Arab Medium, and Arab Heavy were collected from the crude oil booster pumphouse, Ras Tanura (ARAMCO). Arabian Berri is a high API gravity, low sulfur, medium paraffinic crude oil. It is obtained from Berri fields which
ASTM
ash
extend under both land and water. Arabian Light is a moderately high API gravity, medium paraffinic crude oil. It is a blend of such fields as Abqaiq, Ain Dar, Shedgum, Uthmaniyah, Fadhili, Abu Hadriya, Haradh, Hawiyah, and Qatif. These fields are located in the northeast of Saudi Arabia. Arabian Medium is a medium gravity paraffinic waxcontaining crude oil. It is produced as multi-stage separated oil from a blend of Abu Safah, Khursaniyah, and Qatif fields. Arabian Heavy is a medium gravity paraffinic crude oil. It is from an offshore field, Safaniya,which is located about 125 miles northwest of the exporting terminal Ras Tanura. Safaniya is the world's largest offshore field. Before performing trace metals analysis on the crude oil samples, tests for API gravity, total sulfur, viscosity, ash content, and carbon residue were performed to make certain that these samples are representative of the current production. The properties are reported in Table I. Sulfur content and the API gravity are two properties which have the greatest influence on the value of the crude oil. Crude oils with higher sulfur content generally require more expensive processing than those with lower sulfur content. Viscosity plays a very important role in a variety of interesting engineering problems involving fluid flow and momentum transfer. Ash contents of the crude oils are roughly proportional to the total metal contents. Carbon residue is related to the asphalt content of crude oil and to the quantity of lubricating oil fraction that can be recovered. American Society for Testing and Materials (ASTM) methods of analysis were used for all measurements. The precision of these methods is very well established (Annual ASTM Standards, 1982). Chemicals. All the chemicals used for this analysis conformed to the specifications established by Committee on Analytical Reagents of the American Chemical Society. Oil Standards. Multielement oil standards (JarrellAsh) with concentration ranging from 0 to 50 ppm were used for instrument calibration. Apparatus. A Fisher/ Jarrell-Ash Model 850 Atomic Absorption Spectrometer was used for trace element determination. Sample Preparation. All glassware was washed with Alconox, rinsed with tap water and distilled water, and then soaked overnight in chromic acid cleaning solution. They were then thoroughly rinsed in distilled water and deionized-distilled water and dried by inverting on clean paper. The beakers were dried at 105-110 O C in an oven
Ind. Eng. Chem. Prod. Res. Dev., Vol. 22, No. 4, 1983 693
and were placed in desiccators to cool. The samples were prepared for analysis by the UOP wet ashing procedure (UOP Method 391-64, 1973; Sandell, 1959; ASTM Method D 1548,1982; Wright and Mellon, 1937). One hundred fifty grams of the crude oil sample was weighed into a 600-mL Pyrex beaker. The sample was wet-ashed with fuming sulfuric acid (10 mL) and the coke was burned off in a muffle furnace at 550 OC. The ash in the beaker was covered with a fine stream of water; 25 drops of concentrated sulfuric acid and 2 drops of concentrated nitric acid were added and the beaker was heated on a hot plate until the sulfuric acid fumes were seen. The beaker was allowed to cool and the contents were rinsed into a 25-mL volumetric flask and diluted to the mark with deionized-distilled water. A reagent blank was prepared by using 10 mL of fuming sulfuric acid in a clean beaker and the entire sequence of steps was followed as described for the crude oil sample preparation. The samples and the reagent blank thus prepared were aspirated directly into an atomic absorption spectrophotometer at the instrument and gas-flow setting recommended by the manufacturer. The reagent blank contained negligible amount (mostly below the detection limits of the instrument) of the elements. Each crude oil sample was analysed in duplicate and the analytical precision was determined from the variation in duplicate results. Duplicate results did not differ more than the following amounts. range, P P ~
0 to 2 >2
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The instrument was calibrated with aqueous metal solutions in the 0 to 50 ppm range prepared from multielement oil standards in a manner analogous to the treatment of the crude oil samples and reagent blank.
Results and Discussion Trace element analysis for the 17 metals in crude oils from 10 producing fields are given in Table 11. For each of the ten crude oils investigated, the most abundant trace metals observed were vanadium and nickel. Vanadium and nickle concentration ranged from 2 to 60 ppm and 0.5 to 17 ppm, respectively. Other metals, Le., Al, Ca, Cd, Cr, Fe, Mg, Pb, and Zn were observed at the 0.5-7 ppm level. Silver, copper, manganese and tin are present in very low level (0-0.5 ppm). The relatively high sodium, 34.8 ppm in Marjan lower, 21 ppm in Zuluf, and 13 ppm in Abqaiq field crude oil is noteworthy. This could be incidental due to the contact of crude oil with salt water. Among the trace-metal indices, the V/Ni index is the most widely applied parameter in the studies of petroleum trace metals. The V/Ni indices from different Arab crude oils studied are reported in Table 111. For the cretacious crude oils, the V/Ni index is between the limits 2.78 and 3.10. For the upper Jurrasic oils, the V/Ni index ratio range from 3.76 to 4.35, indicating that the index increases with the age of oil. Our findings are therefore in agreement with the results of Hyden (1961), Ball (1960), and AlShahristani and Al-Atiya (1972), but in conflict with the finding of Hodgson (1954) and Abu-Elgheit (1979). The fact that V and Ni may occur in two forms, porphyrin and nonporphyrin, may be responsible for the conflicting data on the relation of V/Ni concentration ratios with the age of crude oils (Valkovic, 1978). As a part of our continuing interest in this subject we have undertaken a study of the distribution of porphyrin and nonporphyrin Ni and V in the asphaltic components
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Ind. Eng. Chem. Prod. Res. Dav.. VoI. 22,No. 4, 1983
Table 111. Trace Metal Indices of Crude Oils from Saudi Arabia crude field V/Ni V/Fe V/Mg Fadhili 4.05 1.51 6.76 Absaiq
Ghawar Abu-Safah
Khursaniyah ZUlUf
Safaniya Marjan Well Marjan Lower Bahrain
3.90 4.36 3.84 3.90 2.84 3.07 3.11 2.98 2.78
1.83 71.54 33.53 8.46 18.43 75.08 1.75 8.22 5.36
2.58 114.47 76.83 203.00 73.75 69.71 350 44.03
v/cu
V/Cr
V/Zn
10.62 7.14 143.08 59.48
3.79 6.98 35.04 23.64
25.65 232.38 437 176.13 573
25.60 41.36 525 92.54 33.71
4.37 5.61 74.65 33.53 145.00 20.11 26.81 228.26 21.41 156.27
(V/S)x 10.' 2.35 4.49 8.72 7.29 7.00 6.78 15.95 15.40 11.38 8.19
Correlations between sulfur and trace metal (V,Ni) contents and carbon residue and trace metal (V,Ni) contents are shown respectively in Figures 1 and 2. These show an increase in metal content with an increase in sulfur content and carbon residue (wt %), confirming trends observed by other investigators (Volkovic, 1978). Corrosion of processing units and poisoning of catalysts during upgrading petroleum residues are serious industrial problems posed by the presence of sulfur and vanadium. The V/Ni ratios in Arabian oils seem to be restricted to a small range of values. V/Fe, V/Mg, V/Cu, V/Cr, and V/Zn all have the wide range of values and therefore are not discussed in detail. Trace metal analyses for the four export quality Saudi Arabian crude oils are also reported in Table 11. The amount of V and Ni ranged from 2.2 to 57.9 ppm and 0.55 to 16.7 ppm, respectively. The sulfur contents of these crude oils varied from 1.1 to 2.8 w t %.
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Acknowledgment The authors are grateful to the Ministry of Petroleum and Minerals of the Kingdom of Saudi Arabia for kind provision of crude oil samples. Financial support provided by Saudi Arabian National Center for Science and Technology (SANCST) for this work is gratefully acknowledged. Registry No. V, 7440-62-2;Ni, 7440-02-0;Fe, 7439-89-6;Mg, 7439-95-4;Cu,7440-50-8;Cr, 7440-47-3;Zn. 7440-66-6.
Literature Cited A b f i W . M.: Khaili. S. 0.:Barkat. A. 0.Rep.. Mv. Pel. Chem. Am. Chem. Soc. 1979. 24(3). 793. ALShahristani. H.: ALAtiya. M. J. gochm. cosmor".Acta 1972. 36. 979
Annual ASTM Standare. "Pebdemt Roducts and LuMeantS (1)''. Part 23. American Society lor TesUng and MBt&lo: F?l!adelphia. 1982. ASTM Method 0 1548. Annual ASTM Standsrds. Part 23. 1982. Ball. J. S.: Weng~r.W. J.: Hyhn. H. J.: Hwr. C. A,: Meyen. A. T. J . Chem. Eng. Dalil 1960. 5 . 553. DBmeukova. P. Y.: Znkharenkwa. L. N.: KutalS Kaya. A. P. Tr. Vses. Nelt. Nauk. IssM. Gwl. Inrl. 19511. 123. 59. GHmanrhl. A. F.: Gazinw. M. G.; BaMna. E. N. Tr. Taler. Nee. Nall 1s.W Inst. 1971. I S . 113. bigson. G. W. Bull. A m . A s w . Pel. W .(954. 38. 2537. Hyden. H. J. U . S . M .S m y EM. 1961. 1100-8. Sandell. E. B. "Colwimehic Detaminatbn of Traces of Metals". 3rd ed.: Interscbnce: New Y M . 1959 pp 665-673. LOP M e w 391-64. "Trace Metals in PebDCIum end organic R d u c t by Wet-Ashing: Flame RDlometric and S p e c b w h o t m b i c M e w : UnWersa Oil Roducts Ca.. Des P!Anes, IL. 1973. Vamovic. V. "Trace Elements In Petrob"'. Part 2. The Pebdeum PlblisMng Co.: Tulsa. OK, 1978; pp 62-83. Wright, E. R.: Mellon. M. G. I n d . Eng. U a m . Anal. Ed. 1937. 9 . 251.
(heavy ends) of the Arabian crude oils. The results, which will be published elsewhere, are expected to provide g e e
chemical information, not currently available, on Middle Eastern crude oils.
Received for review January 14, 1983 Reuised manuscript receiued May 11, 1983 Accepted June 6,1983
