US2891005A - Removal of metal contaminants from high boiling oils - Google Patents

Description

June 16, 1959 R. L. HEINRICH 2,891,005

REMOVAL OF METAL CONTAMINANTS FROM HIGH BOILING OILS Filed Dec. 27, 1955 REA c 70/? l8 HYDROGEN FEED 5 7 a a i i F 9 0 5 4 a f a P 2:: K 5:: H \1 m w 42 W .n T 0 A 2 P M 3 L4 5 0/ I j s m 9 n A 2 W m a 2 M m u 0 7 2 z m R 0 M m 3 m 5 L m s a m 0 E 2 H E H FUEL 0/1.

INVENTQR. Raymond L. HeI'nr/bl), BY

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ATTORNEY. I

United States Patent fifice 2,891,005 Patented June 16, 1959 REMOVAL OF METAL CONTAMINANTS FROM IHGH BOILING OILS Raymond L. Heinrich, Baytown, Tex., assignor, by mesne assignments, to Esso Research and Engineering Company, Elizabeth, N.J., a corporation of Delaware Application December 27, 1955, Serial No. 555,628

11 Claims. (Cl. 208--253) The present invention is directed to a method for removal of organic contaminants from high boiling oils containing same. More specifically, the invention is concerned with removal of metal contaminants and compounds which form stack solids and the like from high boiling residual oils and asphalts. In its more specific aspects, the invention is concerned with recovery from residual petroleum fractions of valuable oils and products which are substantially free of compounds forming stack solids and other contaminants.

The present invention may be briefly described as a method for removing deleterious organic compounds, such as metal contaminants and compounds, which form stack solids on burning the oils, from petroleum fractions the major portion of which boils above about 900 F. containing the metal contaminants and the stack solidforming compounds. In the present invention the petroleum fractions, as have been described before, are contacted at a temperature in the range from about 750 to about 825 F. with a sulfur-insensitive hydrogenation catalyst in the presence of hydrogen and at a sufficient pressure and space velocity to form coky particles separable from the contacted fraction and containing said metal contaminants and stack solid-forming compounds. The contacted fraction is removed from contact with the catalyst and the coky particles are then separated from the contacted fraction to allow recovery of the contacted fraction to obtain a fraction containing a substantially reduced amount of the metal contaminants and the stack solid-forming compounds. i

The temperatures at which the present invention may be conducted suitably range from about 750 to about 825 F. With a preferred temperature range from about 775 to about 825 F. It is preferred to operate with a temperature gradient in the range from 775 to 825 F.

The reaction involved in the present invention is an exothermic reaction wherein the outlet, temperature of the reaction zone is preferably about 50 F. greater than that of the inlet to the reaction zone. A temperature gradient in the reaction zone where the temperature increases by about 50 F. is particularly beneficial.

It is quite desirable and necessary to operate within the temperature range given. 750 F. there is loss of conversion and the deleterious compounds are not formed into a readily separable condition. Above about 825 F. coking and fouling of the catalyst bed occurs which may make the process completely inoperable. 1

that a temperature in the range from 775 to 825 be employed for domestic petroleum fractions treated in the practice of the present invention. Where heavy petroleum fractions, such as those originating in Venezuela boiling above about 900 F., are employed, a preferred temperature range is from 775 to 825 F. and a temperature gradient within that range.

Pressures employed in the practice of the present invention may range from about 400 to 3000 pounds per square inch gauge with a preferred range from 800 to 2000 pounds per square inch gauge. Quite satisfactory results are obtained in the range from about 800 to about 1600 pounds per square inch gauge.

The petroleum fraction contacts the catalyst at a space velocity in the range from about 0.25 to about 5 volumes of petroleum fraction per volume of catalyst per hour with a preferred space velocity in the range from about 0.5 to about 2 volumes of petroleum fraction per volume of catalyst per hour.

The feed stocks employed in the practice of the present invention are suitably petroleum fractions which are contaminated with metals, such as nickel, vanadium, iron which may comprise porphyrins and diflicultly soluble carbonaceous material. These contaminated materials are usually the fractions boiling above about 900 F. and may include gas oils, reduced crudes, vacuum flashed crude petroleum residua, extract and ratfinate fractions from solvent extraction, fractions of heavy crude petroleum, fractions obtained by deasphalting crude petroleum fractions and heavy crude petroleum obtained by other separatory processes; also, asphalt from Hawkins crude, such as found in Texas, crude petroleum residua from Venezuelan crude, such as Bachaquero, and other fractions which contain metal contaminants and/or compounds which tend to form stack solids on combustion of fuel oil.

Other heavy fractions may be employed in the practice of the present invention. For example, asphaltic fractions such as those obtained from Texas crude petroleums may be used. Suitably, the feed stock may contain some lighter fractions but usually will consist essentially of the heavier fractions of which about 50% to 100% by volume boil above about 900 F. For example, a suitable feed stock for the present invention is a mixture of West Texas and Coastal crude asphalts having following composition:

Table I Vol. percent IBP-430 F. 11.8 430-650 F. 6.3 650-950 F. 5.9 95010l5 F. 5.8 l015 F.+ 70.2

Otherwise, below about u It will be noted that this feed mixture contained 76% In practicing the present invention, it has been found by volume of fractions boiling about 950 F. Thus, it is contemplated that the major portion of the feed will boil above about 900 F.

The catalyst employed in the present invention is suitably a sulfur-resistant or insensitive hydrogenation catalyst and may be a supported sulfur-resistant or insensitive hydrogenation catalyst. As examples of the supported type catalyst may be mentioned cobalt or nickel molyb: date, molybdenum oxide, molybdenum sulfide, cobalt or nickel vanadate, vanadium sulfide, cobalt nickel, or tungsten sulfides or mixtures thereof, and the like, suitably supported on supports, such as alumina, magnesia, carbon, zirconia, diatomaceous earth, and the like. The catalytic material suitable for support on the catalyst'is in an 3 amount in the range from about 2% to about 25% by weight of the catalyst. The non-supported sulfur resistant hydrogenation catalyst may suitably include cobalt sulfide, nickel sulfide, tungsten sulfide,'molybdenum sulfide ormixtures thereof.

p The practice of the present invention involves the employment of hydrogen. A hydrogen-containing gas or a pure hydrogen may be employed. The amount of hydrogen used may suitably range from about 1500 to 6000 standard cubic feet per barrel of feed at 60 F. with a preferred amount of the hydrogen being in the range from 2000 to 4000 standard cubic feet per barrel of feed at '60 F.

Thepresent ihvention will be further illustrated by reference to the drawingin which the singlefigure is a flow diagram of a preferred inode.

Referring now t'o t'he drawing, numeral 11 designates a charge line by way of which a feed stock of the nature described supra is introduced into "the system from a source, not shown. The pump 12 in line 11 pumps the feed stock into a furnace 'or heater 13 providedwith a heating coil 14. Prior to introduction into coil 14, the feed stock has hydrogen admixed therewith introduced thereto by line 15. The mixture of hydrogen and feed stock is heated in heater 13 to a temperature in the range indicated with heat being supplied to the heater 13 by means of gas burners or other heating means 16.

The heated mixture of hydrogen and feed stock is Withdrawn from coil 14 by line 17 and is introduced thereby into areact'ion zone indicated by the numeral 18 which contains a bed "of catalyst 19, such 'as a cobalt molybda'te catalyst supported on alumina. After contact with the catalyst for 'the' specified time, the contacted petroleum fraction discharges from reaction zone '18 by line 20, passes through a heat exchanger or other temperature adjusting 'rneansfsuc'has 21, and then is introduced thereby'into a separator 22. In separator 22 fixed gases are separatedfr'om'the liquid material and the fixed gases are withdrawn 'by line 23 and preferably are recycled by line 15 to line 11. A portion of the fixed gases may be discharged by line2 3byopening valve 24. If desired,makeup hydrogen may be introduced into line 15 by way of line'25 controlled by valve 26. v

A particular feature'o'f the present invention is that the specified conditions res'ultin the metal contaminants 'present in'the 'feed and'other deleterious bodies being formed into what is termed microcoke. This microcoke -is readily, separable from the contacted fraction but does not, t'o-alarge extent, foul 'the'catalyst 'bed 10. In other words, the microcoke remains suspended 'in the"frac'tion as it passes through the reaction zone 18 and the separator 22 until a sufiicient residence time is provided for gravity settling or a separation treatment is practiced. This microcoke may have 'particle'diameters in the range from about 0.1 -to about 1000 microns, preferably 2 to 20 microns. Analysis of the coke showed particle diameters -of e -to microns.

Therefore, in accordance -with-the present invention, the

or which may be a plurality of fractional distillation towers, each equipped with suitable internal baffling equipment, such as bell cap trays and the like, wherein intimate contact between liquid and vapor is obtained. Also, fractional distillation zone 31 is understood to include suitable means for inducing reflux and means for cooling and/ or condensing the overhead fractions and other fractions separated therefrom.

Temperature and pressure conditions in zone 31 may suitably be adjusted by heating means generally indicated by steam coil 34 to obtain an overhead fraction by way of line 35 which may suitably be a gasoline fraction boiling in the range from 100 to 350 F. and intermediate higher boiling fractions which may be withdrawn by side streams or lines 36, 37 and 38. A fuel oil fraction may be discharged from distillation zone 31 by line 39 controlled by valve 40 for use in industrial and domestic fuels as may be desired. It may be desirable under some conditions, however, to recyclethe fraction withdrawn by line 39 to line 11 by way of branch line 41 containing a control valve 42 and pump 43. p

The 'fractions Withdrawn by lines 35, '36, 37 and 38 may suitably be used-as motor fuels, diesel oils, cracking stocksyand the'like. 'Particularlyt he'heavier fractions will "be suitable cracking stocks by virtue of their low contents of metals and by virtue also of their low level of contamination with other deleterious compounds.

It will be seen from the foregoing description taken M with the drawings that a new and "improved process has been provided byway of which metal contaminants and other deleterious organic compounds, which form stack solids on combustion, are removed frornliigh boiling petroleum'fr'actions. Further, it may be seen that a process has been provided for producing fractions having reduced metal and other contaminant content which are suitable as feed stocks for catalytic cracking operations.

While the present invention has been illustrated with a -fixed bed reactor,"it is to be clearly understood that the reaction zone 18 may be one of the fluidized powder type wherein the catalyst is suspended in the vaporized feedstock. Also, the catalyst may be suspended in'the liquid feed stock under high pressure conditions to form a slurry and treated thereby. Thus, with the fluidized bed or slurry type operationa great advantage may inure to' the practice'of the present invention in that the microcoke particles are'kept 'in motion and are easily carried out of the reactor in the liquid product.

- in order to illustrate the invention further, runs were conducted with an asphalt obtained from Texas crudes liquid fraction from separator 22 is discharged therefrom by line 27 into a separation zone indicated generally by the numeral 28. The separation zone may suitably comprise a tank,'a precoat filteroperated at a high temperature, acentrifuge-or -a centrifuge-filter or any other separating procedures for separating the microcoke from the contacted fraction. For purposes-of illustration only and not by way of limitation, separator 28 may beconsidered to bee centrifuge operated at a sufiicient speed to separatesubstantially-all the microcoke from the'contacted fraction. The separator 28-may operate-at atemperature in the range from to 600 F., preferably at a temperature in the range from 150 F. to 400 F. Microcoke is withdrawn from separator 28 by line 29 while the "liquid contacted fraction is discharged 'by line 30 into a fractionator zone indicated generally by numeral 31 which may be a single fractional distillation towcr which was heatedandthencon'ta'cted with a cobalt molybdate on alumina catalyst at apressure ofabout 400pounds per square inch gauge'and'under'conditionsina reaction zone whichencompassed a top temperature of 750 F., a center temperature of 784 'F., and 'a bottom 'outl'et temperature of 801 F. The feed rate of liquid to the reaction zone'containing theco'balt molybdate on alumina catalyst'was 0.47 'v./v.-/hr. with a hydrogen feed rate of 3280 standard-cubic feet per barrel of feed. 'Underthese conditions the metal contaminants in thefeed stock were formed and contained in microcoke *which visually settled on the bottom of the container into which -the product was fed. The total product from this operation had a sulfur content of 1.47 weight percent,*a' modified naphtha insolubles content of 13.2 weight percent and a gravity lyst under temperature conditions ranging ifrom 750 to 800 ='F. aslcompared with' temperatu'reconditions from 775 to 825 F. These operations were conducted at 800 pounds per square inch gauge. The results of these runs are presented in the following table which compares conversion conditions of non-microcoking as compared present invention, operations were conducted at varying pressures on an asphalt from a mixture of West Texas and Coastal crudes (Table I) at temperatures in the range from 750 to 800 F., employing a cobalt molybto microcoking: date on alumina catalyst as has been described supra. The

Table II Asphalt From a Mixture of West 1,100 F.+Residuun1 From Texas 1 and Coastal Orudes Bachaquero Crude Conversion Conditions Conversion Conditions Feed Feed Non-Micro- Micro- N on-Micro- Mierocoking coking coking coking Reactor Temperature, F.:

Inlet 750 775 750 775 Outlet 800 825 800 825 Prodtuct Yield, Wt. Percent of Total Prod- Liquid 97. 8 95. 2 98. 5 90. 2 Microcoke 2. 2 4. 8 1. 5 9. 8 Inspection:

Total Product Sulfur, Wt. Percent 2.80 0.48 0.70 3. 58 1.29 0.93 MNI, Wt. Percent 12.2 7. 2 9. 3 20. 9 13.0 8. 8 Liquid Product Sulfur, Wt. Percent 0. 48 0.69 1.19 0.83 MNI, Wt. Percent. 7. 5 7.1 13.1 7. 5 Nickel, p.p.n1. 33 12 108 72 27 Vanadium, p.p.m 44 23 15 772 374 125 M N I is modified naphtha insolubles in the oil. 1 The composition of this material is given in Table I.

It may be seen from the foregoing Table II that with the asphalt from the West Texas and Coastal crudes the inspections of the total and liquid products showed a substantial improvement for conversion conditions involving microcoking. It will be noted that under the nonmicrocoking conditions, the modified naphtha insolubles content in the liquid product is substantially the same as that in the total product, While under microcoking conditions the modified naphtha insolubles content in the liquid product is substantially less than that in the total product indicating the separation of the contaminating materials. Comparing the data from the Bachaquero Venezuelan crude under non-microcoking and microcoking conditions, it will be seen that the results are even more striking than for the West Texas and Coastal asphalt. Under non-microcoking conditions the modified naphtha insoluble content was substantially the same whereas under microcoking conditions the modified naphtha insoluble level in the total product was substantially reduced and the modified naphtha insoluble content in the liquid product was even less than that of the total product.

Other inspection characteristics were similarly improved. The lowered nickel and vanadium contents of the liquid products produced under microcoking conditions .are especially noteworthy. Nickel and vanadium are considered quite deleterious as contaminants in cracking stocks and in oils such as charged to fluid catalytic cracking operations. The presence of these metal contaminants results in the formation of gaseous and coky products with degradation of the desired products whereas the presence of these materials in fuel oils either for domestic or industrial purposes results in deleterious effects on burners and furnaces.

The data in the several examples are especially noteworthy as to the eiiect of pressure. It will be seen, considering the first operation at 400 pounds per square inch gauge, that it is possible to operate at a temperature between 750 and 825 F. but at 800 pounds per square inch gauge the preferred temperature range of 775 to 825 F. must be employed. Otherwise, the deleterious contaminants, such as metal and compounds which form stack solids, remain in suspension and solution and are not readily separable either hy gravity, filtering or centrifuging from the contacted product. i 12- p fi f 0 illus rate the effect of pressurein the results of these operations are presented in the following From these operations it was observed that at 400 pounds per square inch gauge pressure instead of 800 pounds per square inch pressure a significant increase in conversion to distillate was obtained but less desulfurization was obtained than at 800 pounds per square inch gauge pres sure. It is particularly significant that at pressures above 400 pounds per square gauge the modified naphtha insolubles content was no greater than that of the feed and microcoking was obtained such that the contaminating particles were easily separable.

At 200 and 300 p.s.i.g. the modified naphtha insolubles content was greatly increased over the feed modified naphtha insolubles content, desulfurization was much less than at 400 or 800 p.s.i.g. and there appeared in the product a finely divided carbonaceous material which partly settled out upon standing, This material was produced in such quantities as to impair operation of the unit through plugging of the catalyst retaining screen and the valves in the product drawoii line. The catalyst dis played a rapid loss in aci-vity during this microcoking at 200 and 300 p.s.i.g. whereas this catalyst deactivation was not detectable in operations at 400 and 800 p.s.i.g. The results indicate that pressures below 400 p.s.i.g. are not practical because of thevery frequent air regeneration of the catalyst which would be required. Pressures below 800 p.s.i.g. may be employed if desulfurization and modified naphtha insolubles reduction .are not primary considerations, that is if conversion to distillate material is the prime objective.

The modified naphtha insolubles referred to in the specification and in the several examples is a measure of the contaminating particles and may include besides asphaltenes, sulfur, both elemental and combined, metals such as iron, nickel and vanadium present in the feed stock,

The metals may be inthefor-m of organo metallic compounds. Actually it has been determined that the socalled .rnicrocoke contains .a substantial Part of the metals and other contaminating deleterious bodies. The modified naphtha-insolubles itselfmay be described as follows:

(1) 1.0:01 gram of the sample to be tested is weighed to the nearest milligram in a clean, dry, tared,

125 ml. glass stoppered Erlenmeyerflask.

(2) Exactly ml. of chemically pure carbon bisulfide is added to the flask. The flask is whirled a number of times to dissolve the sample as completely as possible.

(3) Exactly 100 ml. of 86 naphtha is added to the flask.

86 naphtha is defined as follows: It is cut from a parafiin lbase crude. It has a gravity in the range from 86 to 88 API. In an Engler distillation, not less than thereof distills over between 95 and 150 F. The aniline point of the naphtha is between 152 and 156 when calculated from the aniline point test on a blend of 35% naphtha and 60% normal heptane.

(4) The stopper is placed in the flask and the latter, with its contents, is shaken vigorously for one minute.

(5) The flask is placed in a water bath such that the 1 water level in the bath is above the liquid level in the flask. The flask remains in the bath for at least two hours at 100i1 F.

(6) The flask is removed from the water bath and the contents immediately filtered through a tared Gooch crucible. Suction is applied gently at first and is then increased to a pressure of 20 inches of mercury in the filtering flask. Care must be taken to prevent loss of sample during filtration.

(7) The [flask and stopper are Washed with two 50 ml. portions of 86 naphtha and the washings filtered through the tared crucible.

(8) The crucible, flask and stopper are dried for one hour in an air oven at 221 F., cooled in a desiccator, and weighed to the nearest milligram.

(9) The increase in weight of crucible, flask and stopper represents the total amount insoluble in the naphtha plus CS This is reported as percent of the original sample.

(10) It is preferred to make the test in duplicate, and use the resulting average value, provided the individual results do not differ from the mean by more than 5 percent of the mean. If the individual results do differ by more than 5% of themean, two additional tests should be made, the least concordant result discarded, and the remaining three averaged.

In order to illustrate the removal of deleterious compounds from feed fractions in accordance with the present invention, microcoke separated by centrifugation from the contacted product was analyzed. In the following table an analysis of a microcoke from an asphalt from West Texas and Coastal crudes is given:

Table IV Microcoke:

Sulfur, wt. percent 1.56 Modified naphtha insolubles, wt. percent 48.8 Nickel, pupim. 170 Vanadium, ppm. 160

Iron, pipim In another operation microcoke centrifuged from a contacted Bachaquero residuum was analyzed and found to comprise contaminating bodies as indicated in the following table:

-vention is conducted with conventional equipment, does not require major capital investment, and is economical to operate. Therefore, the present invention is of considerable utilityand advantage.

The nature and objects of the present invention having been completely described and illustratechwhat I wish to claim as new and useful and to secure by Letters Patent is:

1. A method for removing metallic contaminants from a residual asphaltic petroleum fraction the major portion of which boils above about 900 F. containing metallic contaminants which comprises contacting said petroleum fraction at a temperature gradient in the range between 750 and 825 F. with a sulfur-insensitive cobalt molybdate hydrogenation catalyst in the presence of hydrogen at a pressure in the range from 400 to 3000 pounds per square inch gauge and at a space velicity in the range between 0.25 and 5.0 v./v./hr. to form microcoke particles separable from the contacted fraction and containing said contaminants, removing said cont-acted fraction from contact with said catalyst, sepa-rating said microcoke particles from said contacted fraction, and recovering said contacted fraction containing a substantially reduced amount of metallic contaminants.

2. A method in accordance with claim 1 in which the microcoke particles are separated by centrifuging.

3. A method in accordance with claim 1 in which the microcoke particles are separated by filtering.

4. A method for removing organic metallic contaminants from a residual asphaltic petroleum fraction boiling above about 900 F. containing organic contaminants which comprises contacting said petroleum fraction at a temperature in the range between 750 and 825 F. with a sulfur-insensitive cobalt molybdate hydrogenation catalyst'in the presence of hydrogen at a pressure in the range from 400 to 3000 pounds per square inch gauge and at a space velocity in the range between 0.25 and 5.0 v./ v./ hr. to form microcoke particles separable from the contacted fraction and containing said organic contaminants, removing said contacted fraction from contact with said catalyst, separating said microcoke particles from said contacted fraction, and recovering said contacted fraction containing a substantially reduced amount of organic metallic contaminants.

5. A method in accordance with claim 4 in which the microcoke particles are separated by centrifuging.

6. A method in accordance with claim 4 in which the microcoke particles are separated by filtering.

7. A method for removing organic metal contaminants from 'a residual asphaltic Venezuelan petroleum fraction boiling above about 900 F. containing metal contaminants which comprises contacting said petroleum fraction at a temperature gradient in the range between 775 and 825 F. with a sulfur-insensitive cobalt molybdate hydrogenation catalyst in the presence of hydrogen at a sufficient pressure in the range from 400 to 3000 pounds per square inch gauge and at a space velocity in the range :between'0.25 and 5.0 v./ v./ hr. to form microcoke particle's separable from the contacted fraction and contalnmg said organic metal contaminants, removing sard contacted fraction :from contact with said catalyst, separating said microcoke particles from said contacted fraction, and recovering said contacted fraction containing a substantially reduced amount of organic metal contaminants.

8. A method for removing organic metallic contaminants from a residual asphaltic petroleum fraction boiling above about 900 F. containing metal contaminants which comprises contacting said petroleum fraction at a tempearture gradient in the range between 775 and 825 F. with a sulfur-insensitive cobalt molybdate hydrogenation catalyst in the presence of hydrogen at a sulficient pressure in the range from 400 to 3000 pounds per square inch gauge and at a space velocity in the range between 0.25 and 5.0 v./v./hr. to form microcoke particles separable from the contacted fraction and containing said organic metal contaminants, removing said contacted fraction from contact with said catalyst, separating said microcoke particles from said contacted fraction, and recovering said contacted fraction substantially free of organic metallic contaminants.

9. A method for removing metal contaminants from in the range from 400 to 3000 pounds per square inch gauge and at a space velocity in the range between 0.25 and 5.0 v./v./hr. to form microcoke particles separable from the contacted fraction and containing said metal contaminants, removing said contacted fraction from contact with said catalyst, separating said microcoke particles from said contacted fraction, and recovering said contacted fraction substantially free of metal contaminants.

10. A method in accordance with claim 1 in which the microcoke particles are separated by gravity settling. 11. A method in accordance with claim 4 in which the microcoke particles are separated by gravity settling.

References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. A METHOD FOR REMOVING METALLIC CONTAMINANTS FROM A RESIDUAL ASPHALTIC PETROLEUM FRACTION THE MAJOR PORTION OF WHICH BOILS ABOVE ABOUT 900* F. CONTAINING METALLIC CONTAMINANTS WHICH COMPRISES CONTACTING SAID PETROLEUM FRACTION AT A TEMPERATURE GRADIENT IN THE RANGE BETWEEN 750* AND 825* F. WITH A SULFUR-INSENSITIVE COBALT MOLYBDATE HYDROGENATION CATALYST IN THE PRESENCE OF HYDROGEN AT A PRESSURE IN THE RANGE FROM 400 TO 3000 POUNDS PER SQUARE INCH GUAGE AND AT A SPACE VELICITY IN THE RANGE BETWEEN 0.25 AND 5.0 V./V./HR. TO FORM MICOCOKE PARTICLES SEPARABLE FROM THE CONTACTED FRACTION AND CONTAINING SAID CONTAMINANTS, REMOVING SAID CONTACTED FRACTION FROM CONTACT WITH SAID CATALYST, SEPARATING SAID MICROCOKE PARTICLES FROM SAID CONTACTED FRACTION, AND RECOVERING SAID CONTACTED FRACTION CONTAINING A SUBSTANTIALLY REDUCED AMOUNT OF METALLIC CONTAMINANTS.

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