US2148138A - Process of making metal alkyls - Google Patents

Description

Feb. 21, 1939: F. w, SULLIVAN. JR 2,148,138

PROCESS OF MAKING METAL ALKYLS Filed Aug. 31, 1936 #eacf/bn 66477756!" 6 INVENTOR Freder/ck NSu/hvaqdr ATTORNEY Patented Feb. 1939' PATENT OFFICE 2,148,138 mocnss OF MAKING METAL ALKYLS' Frederick W. Sullivan, Jr., Flossmoor, Ill, assignor to Standard Oil Company, Chicago, Ill., a corporation of Indiana Application August 31, 1936, Serial No. 98,711

14 Claims.

This invention relates to processes of preparing organic compounds of lead and it comprises processes wherein a hydrocarbon such as methane, ethane, propane, butane, pentane, hexane, and

hydrocarbons occurring in gasoline, are dissociated by-the action of highly heated lead vapors and/or atomic hydrogen to form free alkyl radicals from such hydrocarbons, the resulting reactionmixture containing free alkyl radicals quick- 1y cooled and reacted with lead to form hydrocarbon compounds of lead.

In my United States Patent 'No. 2,087,660, issued July 20, 1937, of which the present application is a continuation-in-part, I have disclosed methods of making hydrocarbon compounds of lead wherein metallic lead, in solid form, is caused to react with a hydrocarbon gas contaning free alkyl radicals. As described in that application the reaction products can be condensed, or they can be absorbed in an absorbent oil to recover the lead hydrocarbon compounds as such. Or, as described in that application, I can leadize gasoline, by subjecting the gasoline to pyrolytic condit ons which result in the formation of some free alkyl radicals therein, react thes radicals with metallic lead, and condense a final product containing a small amount of lead-hydrocarbon compounds dissolved in a large volume of gasoline.

I have now discovered that the broad processes of said application can be improved as regards economy of operation, conservation of energy for dissociating the hydrocarbon material, and impound. I have now discovered that I can use the heat inherent in vaporized lead to pyrolytically dissociate the hydrocarbon starting material. I

have discovered that this method of initially forming quantit es of free alkyl radicals gives me higher yields of final products. Thus, for example, in broad aspects, I first vaporize lead at very low absolute pressures, generally about to 4 mm. of mercury, and rarely exceeding 30 to 50 45 mm. of mercury. Although lead boils at atmospheric pressure at a temperature of about 27'70 F., at a pressure of from to 4 mm. the boiling point is reduced markedly. Generally the boiling point under my conditions of low pressure varies from about 1800 to 2000 F.

Lead vapor at ths temperature and a e low pressure stated is then contacted with hydrocar bon vapor and the resulting mixture of reaction products is immediately and quickly cooled to 55 temperatures below the decomposition-tempera- -will react with lead to form lead alkyls.

provement in yield of lead hydrocarbon comture of lead hydrocarbon compounds. This temperature does not generally exceed about 150 C. The reaction products are then condensed and, if desired, hydrocarbon compounds of lead recovered therefrom. 5

There are many advantages in this procedure. Other things being equal, the yield of lead alkyls, such as tetraethyl lead, is dependent upon the quantity and physical form of lead associated with the free alkyls at the time of cooling. When 10 free alkyls, such as methyl or ethyl, are formed in the presence of lead, the alkyls can react in two different ways. They can either react with themselves or with the lead. But to secure high yields of lead compounds, the lead should be present in 15 intimate association with the gaseous mixture which contains the alkyls. Then, as this mixture is quickly cooled down to a temperature at which lead alkyls are stable, the lead is immediately available for reaction with the free alkyls. 20

The alkyl-yielding hydrocarbons can also be dissociated by means of atomic hydrogen to give gaseous mixtures containing free alkyls which This method of forming free alkyls is particularly ad- 25 vantageous and can be employed alone or in combination with the lead vapor thermal method of free radical formation. 1

On the attached sheet of drawngs I have indicated in flow-sheet form, apparatus arrange- 30 ments which can be used to practice the processes of the present invention. In the drawing I have shown suitable apparatus for dissociating hydrocarbons by means of lead vapors and to react the free alkyls with lead and. recover the reaction 35 products.

Referring to the drawing the numeral I indicates an electric arc furnace having an inlet 2 for charging the furnace with lead. Current leads are shown at 3 and 4 and the electrodes at 5. The body of molten lead isindicated at 6.

Lead vapors resulting from the heat developed by the electrodes leave the furnace through outlet I which conducts them to the reaction chamber I. This reaction chamber is composed of three zones 9, l0 and I I. Zone 9 is provided with a baflie l2 and hydrocarbon inlet l3 through which vaporized or normally gaseous hydrocar bons enter the system. Zone I0 is a cooling zone containing a cooling coil l4 supplied with a suitable refrigerant such as brine, liquefied gases and the like. Zone II is also kept cool by a water H jacket 5.

Cooling coils H are constructed of a suitable metal and zone 9 has heat insulating material It to reduce condensation of vaporized lead therein and if desired, it may be externally heated to prevent condensation. Any lead which does condense on the walls of zone 9 can be returned to the furnace through pipe I1.

Reaction products leave the zone II through outlet I8 leading to a condenser or cooler I9 which discharges through pipe 20 into a receptacle for lead alkyls 2I. Any uncondensed vapor passes through 22 to a pump 23 where it is pumped back to inlet I3 through line 24 assisted by a suitable pump 32 if desired. Some of this vapor can be led into the furnace I through line 25 to aid in the vaporization of the lead. If desired, it may be bubbled beneath the surface of the lead, and the bath may be heated by an electric induction furnace.

The uncondensed vapor can alternatively be passed through absorber 26 by vacuum pump 21 and line 28, where it may be drawn off overhead through line 30. Absorber 26 is supplied with a high-boiling hydrocarbon liquid such as absorber oil. Vacuum pump 21 maintains the necessary low pressure on the system and circulating pump 23 provides for recycling uncondensed gas. Alternatively, the uncondensed vapor may be passed through valved line 3| and recycled through line 24 if desired.

In the operation of the arrangement shown in the drawing the furnace is charged with lead, current applied and vacuum pump 2! is started to maintain the system under a pressure of about to 4 mm. of mercury absolute pressure. Care should be taken that all joints are airtight so that no air can enter the system. When lead vapors begin to distill from retort I and pass into zone 9 of reactor 8 hydrocarbon vapors are allowed to flow into zone 9 through inlet I3. As pointed out above, these hydrocarbon vapors are generally aliphatic hydrocarbons, although aromatic hydrocarbons can be used, provided they are heated sufliciently to be dissociated to yield free radicals which are capable of combining with lead. For most practical purposes I find that an ordinary gasoline fraction is advantageously used. I can, however, use propane, butane, or other low boiling hydrocarbons.

To prevent excessive condensation of metallic lead on the surfaces of zone 9 it is desirable that this zone be well insulated against loss of heat or auxiliary heating provided, and this is why I provide heat insulating covering I6. Likewise, it is preferred to preheat the hydrocarbon vapors admitted at I3 to a temperature of 750 to 1100 F. by any suitable means such as a heating coil not shown. The average temperature of zone 9 is in the neighborhood of 2000 F. This is high enough to insure that the introduced hydrocarbons decompose or dissociate instantly to give commercially useful quantities of free alkyl radicals. The velocity of the gases passing through reaction chamber 8 is exceedingly rapid due to the action of pumps 23 and 21 and condensation and cooling of vapors in condenser I9. It is essential that the hot gases composed of lead vapors and free alkyl radicals together with undecomposed hydrocarbons are passed quickly into contact with cooling coils I4. The cooling coils are operated at temperatures of about minus C. to plus 100 0., depending upon the refrigerant therein'and also upon the specific lead alkyl compounds produced. It is desirable to keep the cooling coil temperature above the boiling temperature of the lead alkyl product at the pressure employed. Thus, for lead tetraethyl film on cooling coils I4.

and a pressure of 3 mm. of mercury, the cooling coil temperature should be above 30? F. Consequently, the gases from zone 9 are quickly cooled down to temperatures below the decomposition temperature of the lead-hydrocarbon compounds. In zone II] the lead vapor almost instantaneously condenses either as a fog or mist of solid or liquid lead particles or as a thin Concurrently the free alkyl radicals react with the lead to form leadhydrocarbon compounds. The mixture flowing from zone In into zone I I now contains hydrocarbon compounds of lead and unreacted hydrocarbon. Advantageously zone II is provided with cooling jacket I5 to keep the mixture therein Well below the decomposition temperature of lead alkyls. The temperature of the vapors leaving zone II is generally about 100 to 140 C. The mixture then flows to condenser I9 where hydrocarbon vapors and hydrocarbon compounds of lead are condensed and collected in receiver 2|.

The life of the free alkyl radicals formed in zone 9 is limited. Ordinarily these free radicals exist for less than about one tenth of a second. and consequently it is necessary that they be reacted with lead almost instantly after their formation. This is facilitated by the low pressures at which I operate. Considerable quantities of uncondensed gas will leave the cooler. I9 through line 22. Methane is one of the more common constituents of such gas and this hydrocarbon is decomposed by lead vapors with somewhat more difiiculty than hydrocarbons of higher molecular weight. Because of this fact I find it advantageous to recycle a portion of the uncondensed vapors back into the retort I where the uncondensed gas is introduced through pipe 25. This gas helps to vaporize the lead and conduct heat to pyrolysis zone 9.

Should there be an excessive accumulation of lead on the cooling elements in zone I0, I can remove it by momentarily interrupting the flow of cooling liquid therethrough.

Product obtained in 2I generally consists of a hydrocarbon solution containing upwards of 0.5 to 2 percent of lead-hydrocarbon compounds. When gasoline is used as the source of hydrocarbon introduced through inlet I3 the final product flowing from receiver 2| is an anti-knock blending fuel containing lead-hydrocarbon compounds asthe anti-knock constituent. When I wish to prepare pure lead-hydrocarbon compounds it is better to use hydrocarbons which are normally gaseous, or which have relatively low boiling points, somewhat lower than tetramethyl lead. When this is done condenser I9 can be so regulated that mainly the lead-hydrocarbon compounds collect in receiver 2I and effiuent unreacted hydrocarbon gases are recycled back to inlet I3.

Absorber 26 is advantageously used to recover any traces of uncondensed lead alkyls and also any uncondensed hydrocarbons such as butane or pentane. The absorption liquid, such as gas oil, flows out of the absorber through line 26a and in through line 29. The liquid can be ,distilled for the recovery of the dissolved constituents.

specifically recited in the foregoing description but it is understood that these are susceptible to modifications depending upon the kind of hydrocarbon starting material. I find it best to work under low pressures, of the order of to 4 mm. of mercury and rarely exceeding about Operating conditions and pressures have been 50 mm. Gas flow through the reaction vessel must be rapid so that the free alkyls formed are cooled and contacted with lead almost instantaneously. The circulating pumps in the apparatus maintain the high velocity required.

1. In the process of preparing hydrocarbon compounds of lead by reacting lead with free alkyl radicals at a low subatmospheric pressure the steps which comprise pyrolytically dissociating a free alkyl-yielding hydrocarbon by the action of highly heated vaporized lead and then quickly cooling the mixture of lead vapor and free alkyls to a temperature below the decomposition temperature of the lead-hydrocarbon compounds.

2. In the process of preparing hydrocarbon compounds of lead by reacting lead with free alkyl radicals the steps which comprise. pyrolytically dissociating a free alkyl-yielding hydrocarbon by the action of highly heated vaporized lead at a pressure of about to 50 mm. ofmercury absolute and then quickly cooling the mixture of lead vapor and free alkyls at said pressure to a temperature below the decomposition temperature of thelead-hydrocarbon compounds.

3. The process as in claim 2 wherein the pressure is about 2 to 4 mm. of mercury absolute.

4. The process of preparing lead-hydrocarbon compounds which comprises vaporizing metallic lead-hydrocarbon compounds.

5. The process as in claim 4 wherein the pressure is about to 4 mm. of mercury absolute.

6. The process of preparing lead-hydrocarbon compounds which comprises vaporizing metallic lead'at a low subatmospheric pressure, conducting the lead vapor to a pyrolysis zone, introducing hydrocarbons-into said zone, said hydrocar-- bons being capable of yielding free alkyl radicals on pyrolysis, whereby free alkyl radicals are formed, rapidly passing the mixture of lead va-' par and free alkyl radicals into a cooling zone maintained at a temperature below the decomposition temperature of the lead-hydrocarbon compounds, and condensing reaction products.

7. The process as in claim 6 wherein the pressure is about 2 to 4 mm. of mercury absolute.

8. The process as in claim 1 wherein the hydrocarbon is gasoline.

9. The process as in claim 2 wherein the hydrocarbon is gasoline.

10. The process as in claim 4 wherein the hydrocarbon is gasoline.

11. The process as in claim 6 wherein the hydrocarbon is gasoline.

12. The process as in claim 2 wherein the hydrocarbon is gasoline. and the pressure is about /2 to 4 mm. of mercury absolute.

13. The process as in claim 4 wherein the hy-' drocarbon is gasoline and the pressure is about /2 to 4 mm. of mercury absolute.

14. The process as in claim 6 wherein the hydrocarbon is gasoline and the pressure is about /2 to 4 mm. of mercury absolute.

FREDERICK W. SULLIVAN, JR.

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