US 3856664 A
A suitable substrate modified by the presence therein of chemically bound sulfur provides a highly selective sorbent for removal of heavy metal contaminants from liquids containing the same.
Claims available in
Description (OCR text may contain errors)
United States Patent 1191 1111 3,856,664 Whitehurst Dec. 24, 1974 SORBENT FOR HEAVY METALS 2,392,846 l/l946 Friedman 208/25] R D 3,105,038 9/1963 Ayers 208/251 R  lnvemor- D l Duayne wh'iehurst 3,785,968 1/1974 Whitehurst at al. 208/251 R Tlwsvlllei 3,791,968 2/1974 Whitehurstet al. 208/251 R 3,793,185 2/1974 Whitehurst et al1 208/25] R  Asslgnee' 2? Corpmatmn New York 3,799,870 3 1974 l-leilweil 208/25] R 22 'l d: F 1974 1 F] 6 ch 21 Primary Examiner-Delbert E. Gantz 1 1 pp 444,610 Assistant ExaminerJuanita M. Nelson Related US Application Data Attorney, Agent, or Firm-Andrew L. Gaboriault;  Continuation of Ser. No. 319,098, Dec. 27, 1972, Mlchael abandoned, which is a continuation-in-part of Ser. No, 270,913, July 12, 1972, Pat. No. 3,785,968.
 ABSTRACT  U.S. Cl 208/253, 208/251 R, 208/252 i 511 Int. Cl ..C10g 17/00 A sultable Substrate modlfied by the Pressnce therein 5 Field of Search 20 R, 253 252 290 Of chemically bound sulfur provides a highly selective sorbent for removal of heavy metal contaminants from  References Cited liquids containing the same.
UNITED STATES PATENTS 9 Claims, 4 Drawing Figures 1,112,650 10/1914 Parsons 208/251 R Y 9O Absorbonce i A Trcmsmifionce 8 f 80 8 w 7 A 52 70 i $1 5 g 1 m 1- 6 O m 60 I! 0. 7: 5 25 0 z 50 o t s 4 m a 4O g a 3 3. 3o s I l l l l l l l l l IO 20 3O 4O 5O 6O 7O 8O 9 I00 "I, Pb REMOVAL SORBENT FOR HEAVY METALS CROSS-REFERENCE TO RELATED APPLICATIONS This disclosure is a continuation of U.S. application Ser. No. 319,098 filed Dec. 27, 1972 now abandoned which in turn is a continuation-in-part of U.S. Pat. application, Ser. No. 270,913 filed July 12, 1972 and which issued as U.S. Pat. No. 3,785,968 on Jan. 15, 1974.
BACKGROUND OF THE INVENTION In many instances, it is desirable to effect removal of heavy metal contaminants from liquids. Thus, the presence of metals, such as nickel, copper and iron, even in minute quantities, in hydrocarbon charge stocks conducted to catalytic cracking units are known to poison and shorten the life of the cracking catalyst with which such metal contaminated stocks come into contact.
It is also desirable to remove trace metals from lubricating oils or to recover soluble metal catalysts from reactor effluents. The removal of heavy metals such as mercury, silver, cadmium and the like from the water effluents of chemical or photographic plants is also highly desired from an ecological standpoint.
It is known that residues of alkyl lead from combustion of leaded gasoline tend to poison catalysts available for cleaning up automotive exhaust gas by oxidation of carbon monoxide and unburned hydrocarbons in the exhaust. Such poisoning severely shortens the useful life of exhaust combustion catalysts. It has heretofore been proposed that lead-free gasoline be supplied for use in automobiles equipped with emission control devices in the nature of combustion catalysts.
The normal network of petroleum product distribution involves railroad tank cars, pipelines, water bourne tankers, tank trucks and bulk storage tanks. For commercial operation these are presently set up to handle different products. For example, the same pipeline will be used to convey a shipment of regular grade gasoline, premium grade gasoline, distillate fuel and other light liquid products in succession.
When leaded gasoline containing tetraethyl lead, tetramethyl lead or a mixture or transalkylation product of the two is contacted with the metal surfaces of transportation and storage facilities a significant amount of lead is left deposited in scale and on the metallic surfaces. Upon using the same facilities for lead-free gasoline, the latter product becomes contaminated to the extent of 0.07 grams of lead per gallon or more. These amounts of lead are sufficient to impair the life of ex haust emission catalysts.
It is accordingly highly desirable to provide selective means for effecting removal of heavy metal contaminant from liquids containing the same without interfer ing with or otherwise impairing the intended effectiveness of such liquids.
DESCRIPTION OF THE PRIOR ART Techniques have heretofore been known for removal of dissolved or suspended heavy metal contaminants from liquid products.
In catalytic cracking operations, the use of guard chambers containing a variety of sorbents intended to remove heavy metal contaminant from the charge stock before contact is made with the cracking catalyst has been described.
Systems for removal of lead from gasoline have also been proposed. Presently known techniques require considerable time or are non-selective in effecting removal from the gasoline of those: additives which are desired to be retained, such as anti-oxidants, anti-icing additives, metal passivators and the like.
One previously proposed system for removing lead is described in U.S. Pat. No. 2,368,261. There, acid activated clay such as bentonite which has been treated with hydrochloric or sulfuric acid is used. Leaded gasoline is percolated through the clay to remove of the lead present. Acid activated clays will also remove the additives which are required for proper protection and functioning of automotive equipment.
Another approach is that described in U.S. Pat. No. 2,392,846. A five gallon lot of leaded gasoline is treated with 20 ml. of stannic chloride followed by addition of grams of activated carbon. This results in decomposition of the tetraalkyl lead and adsorption on the activated carbon thus drastically reducing the lead content. The gasoline is removed from the activated carbon by decantation. This is a very slow process which permits the processing of about 35 gallons of gasoline per hour. Here also the additives desired to be retained will be adsorbed by the activated carbon.
Both the processes described in the cited prior patents depend for effectiveness on a chemical conversion of the tetraalkyl lead. The lead compounds can be reacted with such materials as halogens, halogen acids, metal halides, metal salts, sulfur dioxide, carboxylic acids, metals in the presence of hydrogen etc. The resulting decomposition products are not readily soluble in hydrocarbons and hence are adsorbed on high surface adsorbents. This avoids the property of tetraalkyl leads which presents the greatest difficulty in this separation namely infinite solubility in hydrocarbons.
SUMMARY OF THE INVENTION According to the present invention, there is provided a selective sorbent for lead and other heavy metal contaminants consisting essentially of a suitable substrate modified by the presence therein of sulfur. Preparation of such compositions involves reaction of readily available cross-linked polystyrene resins with elemental sulfur at elevated temperature in the presence of a substantially inert solvent, such as a chlorinated hydrocarbon. The resultant porous solid contains a substantial quantity, generally between about 2 and about 30 weight percent, of chemically bound sulfur. Such compounds may also be prepared by incorporating the sulfur through other chemical reactions such as sulfonation reduction to produce phenyl thiols or chloromethylation "93 sulfide replacement to produce benzyl thiols. Alternately, sulfur may be incorporated into other porous substrates such as silica, alumina, or other inorganic oxides by linking a thiol-containing organosilane to the surface of these solids.
In one embodiment, lead free motor fuel may be handled through the normal distribution system of tankers, pipelines, bulk storage, etc., alternatively with leaded gasoline in a manner that suits the convenience of the operator in maximum utilization of capital facilities. Means are provided at the point of distribution, namely service station pumps, for selective removal of such amounts of tetraalkyl lead as may [have been picked up by the fuel in storage or transit by passage of the fuel through a zone occupied by the sulfur-modified, crosslinked polystyrene resin described above. Thus, a cartridge of such composition may be installed at any point in the system for local storage and dispensing of lead-free gasoline at the service station.
In a preferred embodiment the cartridge is placed in the discharge line from the service station pump. This permits utilization of presently installed equipment and avoids the changes in design which would be required if the treating agent were installed in the fill pipe to the local storage tank, in the tank itself, in the suction line to the pump or within the pump housing, all of which alternatives are contemplated within the scope of the invention. A further alternative is placement of the lead removal cartridge in the automotive fuel system between the fuel tank of the vehicle and the carburetor. Flow rates are very small compared to those in bulk and retail distribution equipment, permitting long residence times and small volume cartridges.
BRIEF DESCRIPTION OF THE DRAWING FIG. 1 of the drawings attached hereto represents a typical service station gasoline pump modified according to the present invention.
FIG. 2 is an enlarged view of the canister for containing the sulfur-modified, cross-linked polystyrene resin sorbent in the combination of FIG. 1.
FIG. 3 is a view in fragmentary section of a cartridge for containing the sulfur-modified, cross-linked polystyrene resin sorbent.
Figure 4 is a standard analytical curve for measuring lead removal.
DESCRIPTION OF PREFERRED EMBODIMENTS As shown in FIG. 1, a gasoline dispensing pump of conventional design includes a housing indicated generally at within which are contained a motor driven pump and a metering device, not shown. The metering device drives, through suitable gearing, indicators within a panel 11 to report gasoline dispensed and price for the amount so dispensed. The fuel after passing through the metering device, is conducted to the outside of the housing through a pipe connection 12 and into a discharge hose 13 equipped with a valve nozzle 14.
The modification to conventional dispensing pumps is a canister 15 connected to the fuel discharge 12 by a pipe 16 provided with a valve for which the operating handle is shown at 17. Fuel from the pipe 16 is conducted to the top of canister 15 from which it passes through a cartridge of the sulfur-modified, cross-linked polystyrene resin sorbent and is thence discharged to hose l3 and nozzle 14.
A typical cartridge is shown in FIG. 3 as constituted by a gauze container 18 within a wire mesh supporting cage 19. Disposed within the container gauze 18 is a mass of the cross-linked polystyrene resin modified by the presence therein of chemically bound sulfur which characterizes this invention.
For the usual service station, a cartridge having a diameter of twenty-four inches and a length of twelve inches will be adequate to reduce the lead content to acceptable levels over a period of about one month. When it is desired to change the cartridge, valve 17 is closed, the hose 13 is drained and the canister 15 is removed by unthreading from the top portion thereof. It
is thus a simple matter to replace the cartridge in a very short period of time and return the dispensing pump to duty.
The sulfur-modified, cross-linked polystyrene composition of this invention is suitably prepared by reacting a cross-linked polystyrene resin, preferably intrinsically porous with elemental sulfur at a temperature in the approximate range of to 300C. in the presence of a solvent inert with respect to sulfur, such as halogenated hydrocarbon solvents. The resultant solid, after removal of the solvent and extraction of any unreacted sulfur contains a substantial quantity, generally between about 2 and about 30 weight percent and preferably between about 5 and about 15 weight percent of chemically bound sulfur.
The polystyrene resin is preferably a solid, crosslinked, intrinsically porous material. It may be a copolymer of styrene with any of a number of comonomers, for example, vinyl pyridine, acrylic derivatives, or substituted sytrenes. The cross-linking agents may be any of those commonly used in commercial practices, for example, divinyl aromatics, acrylic esters, or other diolefins.
The reaction of the above' polymers with elemental sulfur may be carried out in the presence of a halogenated hydrocarbon solvent such as chlorinated aromatic or aliphatic compounds, for example, chlorobenzene, ortho, meta, or paradichlorobenzene, any trichlorobenzene isomer, a -chloronaphthalene, 2,2- dichlorobiphenyl, l,l,2,2-tetrachloroethane, hexachlorocyclohexane or pentachlorocyclopentane. Reaction takes place at an elevated temperature, generally the reflux temperature of the particular solvent employed. The desired extent of reaction is usually complete after 2 to 100 hours, preferably between about 5 and about 40 hours.
The weight proportion of polystyrene resin to sulfur is generally in the range of 10:1 to 1:10. The reaction may be conducted in air, but is suitably carried out in an inert atmosphere, such as helium, argon, nitrogen, carbon dioxide, hydrogen sulfide or carbon monoxide.
After the reaction is completed, the solvent is removed from the solid reaction product by any suitable means such as filtration, centrifuging, or other means of separation. Any unreacted sulfur may be extracted by washing with a suitable solvent such as carbon disulfide, sulfur dioxide, liquid ammonia, aromatic hydrocarbons, halogenated hydrocarbons, such as dichloromethane, freon, diiodomethane or chloronated aromatlCS.
The resulting sulfur-modified, cross-linked polystyrene resin may be employed for removing heavy metal contaminant as described above. Such heavy metal removed may comprise one or more of the following: cobalt, iron, nickel, rhodium, platinum, palladium, lead, manganese, copper, mercury, gold, silver, iridium, cadmium and thallium. In some instances and circumstances, it is contemplated that the above metals, particularly precious metals, may be economically recovered by burning off the resin sorbent.
It has further been found that the above-described sulfur-modified, cross-linked polystyrene resin in combination with a salt ofa metal such as mercury, tin, copper or silver and particularly these metals in their higher valence state such as the mecuric, stannic or cupric state, affords exhanced removal of lead from gasoline. The amount of metal salt employed for said purpose is generally between about 5 and about 50 weight EXAMPLE 1 The polymer used for this preparation was a standard macroreticular porous cross-linked polystyrene polymer manufactured by Rohm and Hass Company under the trade name Amberlite XAD-l.
The physical characteristics of this material, as received, are tabulated below:
Solids (Saturated with water) Porosity (ml. pore/ml. bead) Surface Area (mF/g. dry basis) Effective Size (mm.)
Harmonic Means Particle Size (mm.)
Average Pore Diameter (A) True Wet Density (g.ml.)
Skeletal Density (g./rnl.)
Bulk Density (lbs/ft) 4 One liter of the polymer as received was cleaned by chromatographically washing with 5 liters of distilled water, 4 liters methanol, and 4 liters benzene. The adsorbed solvents were then removed by evaporation in a rotary evaporator at 70C. in vacuo. The yield of dry material was 442 grams.
15.3 grams of this cleaned resin and 46 grams of sulfur were refluxed together in 300 ml. of 1,2,4- trichlorobenzene at a temperature of 220C. for 64 hours.
Evolved H 5 was trapped in a suitable adsorbent (Malcosorb and Aquasorb). The net gain in weight of the product so obtained was 4.2 grams. Elemental analysis of such product showed it to be composed, on a weight basis of the following:
Carbon 69.7% Hydrogen 3.6% Sulfur 21.2%
EXAMPLE 2 The cleaned resin described in Example 1, in the amount of 100 grams, and 100 grams of sulfur were stirred together in 860 ml. of orthodichlorobenzene at reflux temperature and in helium atmosphere for 16 hours.
The orthodichlorobenzene solvent was removed from the resulting reaction product mixture while hot by filtration.
This solid product remaining was refluxed in approximately 1,000 ml. of fresh orthodichlorobenzene for about one half hour.
The orthodichlorobenzene solvent was again removed from the solid remaining product, which was then rinsed with fresh orthodichlorobenzene.
The solid product was then soaked for 1 hour in approximately l,000 ml. of carbon disulfide. The carbon disulfide was removed from the solid by filtration and the solid product was rinsed with fresh carbon disulfide. Adhering carbon disulfide was then removed from the solid in a rotary evaporator at C. and in vacuum.
The finished resin product, in the amount of grams, analyzed, on a weight basis, as follows:
Carbon 89.74% Hydrogen 7.23% Sulfur 3.06%
EXAMPLE 3 The cleaned resin described in Example 1, in the amount of 300 grams, and 500 grams of sulfur were stirred together in 1,050 ml. of 1,2,4-trichlorobenzene and heated to reflux at 220C. for 24 hours in a helium atmosphere.
The effluent gas from such reaction was passed through a mixture containing 400 grams of zinc nitrate, 2,000 ml. of ammonium hydroxide and 2,000 ml. of distilled water at 23C.
Liquid in the resulting reaction product mixture was removed by filtration. The remaining solid product was washed with refluxing orthodichlorobenzene.
The latter was then removed by filtration and the remaining solid cooled to approximately 25C. and washed extensively with carbon disulfide.
The washed solid was then dried on a rotary evaporator yielding 343.7 grams of product which analyzed on a weight basis, as follows:
Carbon 84.39% Hydrogen 6.32 Sulfur 8.30%
EXAMPLE 4 The sulfur-containing resin product of Example 2 (approximately 0.5 gram) was contacted with approximately 3 ml. of a benzene solution containing about 10 milligrams of dicobalt octacarbonyl at room temperature.
Carbon monoxide evolution was noted and the solu tion became colorless. Infrared spectroscopy established that sorption of cobalt by the sulfur-containing resin had taken place.
EXAMPLE 5 Five grams of the sulfur-containing resin product of Example 1, ml. of orthodichlorobenzene and 0.9 gram of [tris-triphenylphosphine]rhodium chloride were refluxed together for five hours.
After cooling and filtering, the resin product was washed with approximately 500 ml. of carbon tetrachloride and dried overnight in a vacuum at 1 10C. The dry weight of the product obtained was 5.45 grams.
Establishment of attachment of rhodium to the sulfur-containing resin was confirmed by the catalytic use of this material as follows:
Into a 300 0.0. stirred autoclave were charged 3 grams of the above resin product and 100 ml. of lhexene, together with carbon monoxide and hydrogen as a 1:1 volume mixture.
Hexane l-Hexane 4 2 & 3-Hexane 5 n-Heplanal iso-Heptanals The above analyses indicates that the rhodium had been adsorbed and was catalytically active.
EXAMPLE 6 One (1) gram of the sulfur-containing resin product of Example 3, ml. of benzene and enough rhodium carbonyl chloride to give a 0.5% coating to one gram of the resin product were contacted overnight at room temperature.
Benzene was then removed and the remaining product was washed lightly with l-hexene.
Attachment of rhodium to the resin product was confirmed by catalytic use of this material in a manner similar to that described in Example 5.
Thus, into a 300 c.c. stirred autoclave were charged 1 gram of the above product and 100 ml. of l-hexene, together with carbon monoxide and hydrogen as a 1:1 volume mixture.
The autoclave contents were heated to reaction temperature and pressurized with the H /CO mixture. Pressures were maintained between 900 and 1,000 psig and the temperature was 200F. for 8 hours and then raised to 245F. for 27 hours.
Analysis of a sample after this time showed that 2 and 3 hexenes, nand iso-heptanal had been formed thus establishing that the rhodium had been adsorbed and was catalytically active.
Lead Removal Via Sulfur Modified Polystyrene EXAMPLE 7 The resin product of Example 1 was used for the removal of lead from commercial gasoline. A commercial regular grade gasoline containing 2.41 g./gal. lead as tetraethyl and tetramethyl lead was contacted at about 25C. with such resin product in a relative volume ratio of 10/1 respectively for a period of about 19 hours. Analysis of the gasoline at the end of this time showed that the lead level had been reduced to 0.9 g./gal. as a result of the described treatment.
EXAMPLE 8 The resin product of Example 3 was contacted with a benzene solution containing 23 g./l. of anhydrous stannic chloride and allowed to stand for about 2 hours. The solution was removed by filtration and the treated resin product washed with benzene. The resultant material was used to sorb lead from the same commercial gasoline as described in Example 7. At the end of the contact period (about 19 hours) the gasoline was found to have the lead content lowered to 0.38 g./gal.
EXAMPLE 9 The resin product described in Example 3 was used in conjunction with stannic chloride (about 30 wt. percent) on a separate support for effecting removal of lead from commercial gasoline similar to the one described in Example 7. The gasoline was treated at about 25C. for 10 minutes employing 10 volumes of gasoline and 1 volume of the supported stannic chloride and 1 volume of the resin product of Example 3.
Results obtained are summarized below:
Un- Supported and Sulfurtreated SnCl Modified Resin Lead in Gasoline g./gal. 2.53 1.45 0.50
EXAMPLES 10ll These tests consisted of contacting approximately three to six volumes of gasoline containing 2.5 g of lead/gal. of gasoline with one volume of sorbent under ambient conditions, followed by a lead analysis of the contacted gasoline.
Following the contacting of the 2.5 grams of lead/gal lone of gasoline fuel with the sorbent prepared as previously described, the lead content of the treated gaso' line was analyzed as follows:
A five part by volume sample of gasoline was treated with 1 part by volume of a saturated solution of silver nitrate (AgNO in absolute ethanol. After standing for 10 minutes, the content of reduced silver in the sample was determined by turbidometric technique. These measurements were done of 425 nm or 500 nm depending on the gasoline used. The measured transmission was compared with a standard analytical curve similar to the one illustrated by FIG. 4.
Carbon 69.7% Hydrogen 3.6% Sulfur 2 I .271
XAD-2 substrate may be defined as a crosslinked polystyrene.
EXAMPLE 12 A substrate was modified with a sulfur functional group having a weak Lewis base character.
To this functionalized substrate was added tin chloride (SnCl The tin distribution in the substrate matrix was determined by electron microprobe techniques; leaded gasoline was passed over a volume sample of the sorbent until it was no longer able to remove 50% of the initial lead concentration (0.4 gm/gal) at 11-13 LHSV according to the following flowing test procedure:
The general procedure involved passing a 0.5 gm Pb/gal. gasoline fuel through a 10 part by volume quantity of resin supported on a glass frit. The flow rates were controlled by varying the of stroke on a variable displacement pump while a 1 to 2 part by volume v gasoline hydraulic head was maintained above the resin by means of a fine adjustment stoplock.
Next, the lead distribution in the sorbent was determined by microprobe techniques. The tin efficiency, that is the of the original tin which operated to removed lead, was calculated for the sorbent.
TABLE 1 illustrates performance of the sorbent and its physical properties.
mMoles Sn/lO cc. sorbent .43. mMoles Pb removed at vol. 1/2.. .08. Percent Sn efficiency 19.
Volume of gasoline passed over volumes of sorbent while still maintaining at. least removal of the initial Pb (-.4 gmJgal.) at 11-13 LHSV. 1 dThe percent of the original Sn which operated efliciently in removing No'rE.-E GDM= Ethylene glycol dimethacrylate.
Examples 10-12 illustrate additional examples which more clearly define the sulfur compound, and are illustrative of substrate characteristics, which embody this invention. For purposes of this disclosure, the group designations referred to are as defined in Langes Handbook of Chemistry at 58-61 (10th ed. 1967).
What is claimed is:
l. A method for effecting removal of heavy metal contaminant from a substantially hydrocarbon solution containing the same which comprises contacting said solution with a sorbent comprising a porous solid selected from the group consisting of cross-linked polystyrene, and inorganic oxides. for said metal contaminant in a flowing system said sorbent comprising a substrate having a minimum surface area of about 10 m /g and pores with a minimum pore diameter of about 10A modified by sulfur having weak Lewis base character, the available electrons which produce the Lewis base character being available from the sulfur atom.
2. The method claimed in claim 1 wherein said sorbent is further modified by the addition of at least one metal halide, said metal halide having a Group 13, IIB, IIIA, IVA, VA, WA or VIII metal, having an atomic number greater than 12, said sulfur acting as a bridging member between said substrate and said metal halide.
3. The method claimed in claim 2 wherein said metal halide is tin chloride.
4. A process for distributing and dispensing motor fuel comprising transportation means and storage means used alternatively for leaded and unleaded fuels and at least one substantially lead-free fuel dispensing station comprising storage means, pumping means; conduit means connecting said storage means and said pump; and conduit discharge means from said pump; the improvement which comprises contacting said fuel in a flowing system with a sorbent comprising a porous solid selected from the group consisting of cross-linked polystyrene and inorganic oxides comprising a substrate having a minimum surface area of about 10m /g and pores with a minimum pore diameter of about 10A modified by sulfur having weak Lewis base character, the available electrons which produce the Lewis base character being available from the sulfur atom.
5. The process of claim 4 wherein said sorbent is further modified by the addition of at least one metal halide, said metal halide having a Group 18, I1B,IIIA, IVA, VA, VIA .or VIII metal, having an atomic number greater than 12 said sulfur acting as a bridging member between said substrate and said metal halide.
6. The process of claim 5 wherein said metal halide is tin chloride.
7. A method for distributing and dispensing substantially lead-free motor fuels through transport and storage facilities used alternatively for leaded and unleaded fuel which comprises contacting the fuel intended to be substantially lead free but which has acquired a minor amount of alkyl lead amt-knock compounds through contact with equipment also used for leaded fuels with a sorbent in a flowing system, said sorbent comprising a porous solid selected from the group consisting of cross-linked polystyrene and inorganic oxides compris' ing a substrate having a minimum surface area of about IOm /g and pores and a minimum pore diameter of about 10A modified by sulfur having weak Lewis base character, the available electrons which produce the Lewis base character being available from the sulfur, said contacting occurring at temperatures of about 50C. to C. and at space velocities of up to about 40 LHSV; and removing said substantially lead-free fuel.
8. The method claimed in claim 7 wherein said sorbent is further modified by the addition of at least one metal halide, said metal halide having a Group 18, IIB, IIA, IIIA, IVA, VA, VIA or VIII metal, having an atomic number greater than 12, said sulfur acting as a bridging member between said substrate and said metal halide.
9. The method claimed in claim 8 wherein said metal halide is tin chloride.
3,856,664 December 24, 1974 Patent No. Dated Dar'rell Duayne *Whitehurst Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
The term of this patent subsequent toFebTuaTy 12, 1991, has been disclaimed.
Signed. and Sealed this twe' t [SEAL] 1 f June 1976 A nest:
RUTH C. MASON Commissioner of Patents and Trademarks (233? STATES-PATENT OFFICE CERTIFICATE OF CORRECTION 5, P515563! Dated December 2 1-97 1 PAGE 2 Inventor) p rrell Duagme 'alnitenurst It is certified that error appears in the above-identified patent and that aid Letters Patent; are hereby con-acted as shown below:
cha=racter should. --charecter Column LO, line 3-3 (electron dc n0rj--,
Signed and sealed this 3rd day of June 1975.
C MARSHALL DANN RUTH C. MASON Commissioner of Patents and Trademarks Attesting Officer UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 3,856,664 December 24, 1974 Patent No. Dated It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
The term of this patent subsequent toFebruary 12, 1991, has been disclaimed.
Signed. and Scaled this I e' t I I [SEAL] w nymnth f June 1976 A nest:
:UTfl C. MA SON C. MARSHALL DANN ttestmg Officer Commissioner uflatems and Trademarks