US3452069A - Process for manufacture of tetraalkyllead and reclamation of by-product lead - Google Patents

Description

3,452,069 PROCESS FOR MANUFACTURE OF TETRAALKYL- igil) AND RECLAMATION F BY-PRODUCT D Lawrence G. Cliver, Baton Rouge, La., assignor to Ethyl Corporation, New York, N.Y., a corporation of Virginia No Drawing. Filed July 29, 1966, Ser. No. 568,752 Int. Cl. C07f 7/26; C22b 13/02 US. Cl. 260-437 11 Claims ABSTRACT OF THE DISCLOSURE Process for the production of tetraalkyllead by the reaction of an alkyl chloride and a monosodium lead alloy and the reclamation of by-product lead by admixing an amorphous carbon such as petroleum coke or calcined coke with the reactants, recovering the tetraalkyllead from the sludge, passing the sludge into a smelting furnace, and recovering molten lead from the resulting smelted sludge.

This invention relates to a process for the production of tetraalkyllead compounds by the reaction of an alkyl chloride and a monosodium lead alloy and the reclamation of by-product lead by smelting sludge produced during the reaction. More specifically, the present invention concerns the use of amorphous carbon to lubricate the reaction and to aid in the smelting operation.

Tetraethyllead has been produced for a number of years by reacting an excess of ethyl chloride with a monosodium lead alloy. More recently, the production of tetramethyllead has begun in the same manner with the use of methyl chloride instead of ethyl chloride. The reaction conditions of methyl chloride with the monosodium lead alloy of course differ somewhat from those of the reaction of ethyl chloride with this alloy; however, both reactions are similar in that typically each utilizes graphite as a lubricant in order to reduce the load on agitators used during the reactions. In these reactions, the sodium of the alloy is to the greatest part converted into sodium chloride; part of lead from the alloy is converted into tetraalkyllead; and the greatest part of the remaining lead of the alloy is converted into metallic lead in a finely divided form.

After completion of the reaction, the excess of alkyl chloride is extracted by distillation (i.e. methyl chloride or ethyl chloride); the distillation residue, or sludge, includes lead particles, which constitutes an important byproduct. The usual process for the recovery of lead from the sludge containing lead as a by-product consists of drying the wet sludge in a continuously operating dryer in order to reduce the water content and subsequently smelting lead from the dried sludge in a reverberatory furnace.

The recovery of lead from the dried sludge in a single operation and by a practical process permitting a slag residue with a sufiiciently low lead content so that it may be discarded without subjecting the slag to a new recovery operation is an old problem. The difiiculties are due to the low melting rate of lead in the finely divided slurry, to the solubility of impurities in lead at the furnace temperatures required to melt the lead by-product, and to the fact that metallic lead does not separate sharply from impurities. The use of such additives as petroleum coke or calcined coke has thus been found to be of great benefit in recovering lead in the smelting furnaces inasmuch as the coke promotes the reduction of combined lead.

It is an object of the present invention to overcome the above noted disadvantages of the prior art. It is a further object of the present invention to overcome the above noted disadvantages of the prior art through an eflicient States Patent 0 and economical combination process. It is a further object of this invention to increase the production of lead from smelting furnaces and reduce the slag rate while permitting efficient operation of the tetraalkyllead reaction agitators. Other advantages and objects of the present invention will become apparent in the following descrip tion.

The present invention relates to a process for the production of tetraalkyllead by the reaction of an alkyl chloride and a monosodium lead alloy and the reclamation of by-product lead by smelting sludge produced by the reaction. This reaction comprises providing an alkyl chloride and a monosodium lead alloy and admixing therewith an amorphous carbon material as a lubricant. The reaction takes place in the presence of the amorphous carbon to produce a tetraalkyllead and a sludge containing amorphous carbon, unreacted lead and other compounds formed during the reaction. Subsequent to the reaction, the tetraalkyllead is recovered from the sludge and the remaining sludge is then passed into a smelting furnace. In the furnace the sludge is smelted to recover molten lead with the amorphous carbon in the sludge then serving as a smelting aid and additional amorphous carbon or other smelting aids may be added if desired. The amorphous carbon in the reactants comprises from about 0.5 percent to about 1.2 percent of the weight of the monosodium lead alloy. The reaction process is conducted at temperatures within the range of from about 122 F. to about 266 F. and the smelting process is conducted at a temperature within the range of from about 1000 F. to about 2500* F.

The amorphous carbon of the present invention is of such consistency that it is substantially volatile free within the temperature range of the reaction and substantially completely oxidized Within the temperature range of the smelting. Amorphous carbons are commonly made by heating organic matter to a moderately high temperature, either in the absence of air or in the presence of a limited amount of air, until the organic matter is converted to carbon, and then heating with air, steam, carbon dioxide and the like. The term amorphous carbon is used herein to mean carbons so made, including those made directly from animal or vegetable materials, such as Wood, nut shells and bones while retaining their original structures, as well as those made from unorganized organic substances, such as sugar and extracted lignin. Two amorphous carbons preferred in the practice of the present invention are petroleum coke and calcined coke.

The amorphous carbons of the present invention may be of any size and shape since agitation of the reactants during the reaction process serves to grind the carbon to the proper size and shape. However, it is generally preferred that the carbon be particulate. And, it is most preferred that the individual carbon particles average about A inch in diameter.

The substitution of amorphous carbon for graphite has several advantages including, first, amorphous carbon provides good lubrication in the reaction apparatus and is reactive in the lead recovery furnaces to promote the reduction of combined lead; in contrast, graphite is inactive, tends to interfere with efficient furnace operation and increases the amount of slag produced during operation of the furnaces; second, amorphous carbon is one of the additives in the recovery furnace and introduction of amorphous carbon through lead sludge allows better mixing of the sludge and the carbon and a reduction in the carbon required for efficient furnace operation. An added benefit is that amorphous carbon is much less expensive than graphite.

Having thus briefly set forth the invention, the following is a more detailed description thereof.

Tetraethyllead is manufactured by the present invention through reacting an excess of ethyl chloride with lead monosodium alloy. Tetramethyllead is similarly mannfactured employing methyl chloride in place of ethyl chloride. Both these manufacturing processes are well known and may be noted in numerous publications. For example, the commercial manufacture of tetramethyllead may be found in US. Patent 3,049,558.

In the tetramethyllead reaction a lubricant is highly desirable and it has been common prior to this invention to utilize graphite for that purpose. On the other hand, in the tetraethyllead reaction lubrication is not nearly so necessary. Therefore, little if any lubricant is used. Hence, while the present invention is applicable to both the manufacture of tetraethyllead and tetramethyllead, it is more preferably used in the manufacture of tetramethyllead. The following description is drawn therefore more specifically to operations involved with tetramethyllead.

The present invention utilizes amorphous carbon bot-h as a lubricant during the lead alkyl forming reaction and as a smelting aid during the subsequent smelting operation. The amorphous carbon must be of such a quality that it gives off substantially no volatile materials at the temperature of the lead alkyl forming reaction which is conducted at a temperature of from about 122 F. to about 266 F. Also, the amorphous carbon must burn at a temperature no greater than the temperature of the smelting operation which ranges from about 1000 F. to about 2500 F.

In the present invention an autoclave is charged with monosodium lead alloy, preferably as flakes, in the proportion of approximately 50 pounds per cubic foot of reaction space. In addition, from about 0.5 percent to about 1.2 percent by weight, based upon the amount of the alloy, of amorphous carbon is introduced as a reaction lubricant. This amorphous carbon later serves as a smelting aid. Additionally approximately 0.2 percent of aluminum, as methyl aluminum sesquichloride, may be introduced. Toluene, in proportions of about percent of the alloy weight may be further introduced. The reactor and contents are heated to approximately 176 F., and a feed of liquid methyl chloride is then started at a rate of about 10 parts per minute per 100 parts of alloy charge. The reaction occurs promptly and is shown by a significant rise in operating temperature. The pressure is allowed to rise to approximately 180 p.s.i.g. and at this time refiux of vapor, principally methyl chloride, is initiated to maintain the pressure at this level. Temperature of the reacting mixture is controlled in the range of about 176 F. to about 203 F. by variation of the degree of cooling for refluxing purposes. The methyl ohloride feed is continued until a total of approximately 35 pounds by weight per 100 pounds by Weight of alloy charge has been introduced, this corresponding to approximately 160 percent excess of the theoretical requirement. The reaction conditions are continued for several hours after termination of feed, and then the temperature stops rising and begins to drop slightly. The excess pressure is vented shortly thereafter and the auoclave contents cooled to approximately ambient temperatures. The charge is then discharged from the autoclave into a pool of water in a steam distillation vessel, and the tetramethyllead and toluene are recovered in high yield. The remaining reaction mass, which is referrcd to as wet sludge, is Water sluiced to a water filled pit. This reaction mass contains the amorphous carbon which will subsequently serve as a smelting aid during the smelting operation.

The wet sludge is removed from the water filled pit by a crane and placed in a hopper from which it is fed by a screw feeder to a continuously operating dryer. It is then processed in the dryer to reduce the Water content to a value of 6 percent or less. From the dryer, substantially dried sludge fiows by gravity to a dry hopper and is then screw fed into a furnace for smelting.

The furnace employed for the smelting process is a 4 reverberatory furnace, and the heat required for the smelting operation is preferably supplied by forced air natural gas burners. The heat supplied by the burners maintains the furnace temperature at from about 1600" F. to about 2500 As the sludge is melted, the level of lead increases and during smelting additional smelting aids such as coke and soda ash or others may be added if desired. When the maximum lead level is obtained, molten lead is removed from the furnace by means of gravity flow through lead run lines. Typically, this operation is repeated approximately every hour. Molten lead from the furnace flows into a heated vessel for weighing and purification. Slag, which results from the smelting operation is removed (from the furnace on the average of about every 8 hours. During the smelting operation the amorphous carbon is burned off having served its function as a smelting aid.

To further illustrate the operation of the present invention, the following examples illustrative typical results.

EXAMPLE L-EFFEGT OF COKE AND SODA ASH ON LEAD RECOVERY FROM TML SLUDGE CONTAINING GRAPHITE Lead Slag rate Graphite rod. (lbjcwt. Coke Soda ash Feed Source (lb. day) Pb) (lb/day) (lb./day) charge) TML l Sludge M 8. 2 367 860 20 Do M 7. 4 0 0 20 EXAMPLE IL-EFFECT OF SUBSTITUTION OF COKE FOR GRAPHITE ON LEAD RECOVERY FROM TML SLUDGE 1 Tetrametliyllead.

It is clear from the above examples that graphite introduced during the reaction as a lubricant is inactive, tends to interfere with efiicient furnace operation and increases the amount of slag produced during the operation of the furnaces Whereas the use of amorphous carbon as a substitute for graphite not only promotes lubrication of the reaction but aids in recovery of lead during the smelting operation.

It will be understood that while there have been given herein certain specific examples of the practice of this invention, it is not intended thereby to have this invention limited to or circumscribed by the specific details of materials, proportions, or conditions herein specified, other than where explicitly stated, in view of the fact that this invention may be modified according to individual perferences or conditions without necessarily departing from the spirit of the disclosure and the scope of the appended claims.

1 claim:

1. A process for the production of tetramethyllead by the reaction of methyl chloride and a monosodium lead alloy and the reclamation of by-product lead by smelt ing sludge produced by said reaction, comprising in combination,

(A) providing reactants comprising methyl chloride and a monosodium lead alloy;

(B) admixing an amorphous carbon selected from the group consisting of petroleum coke and calcined coke with said reactants,

(C) reacting said reactants in the presence of said amorphous carbon admixed therewith at a temperature of from about 122 F. to about 266 F. to produce tetraalkyllead and sludge containing said amorphous carbon,

(D) recovering said tetramethyllead from said sludge,

( E) passing said sludge to a smelting furnace,

(F) smelting said sludge containing said amorphous carbon at a temperature of from about 1000 F. to about 2500 F.,

(G) recovering molten lead from the resulting smelted sludge.

2. The process of claim 1 further characterized by the addition of aluminum to said reactants.

3. The process of claim 2 further characterized by the aluminum being added as methylaluminum sesquichloride.

4. The process of claim 1 further characterized by the addition of toluene, in proportions of about percent of the alloy Weight, to said reactants.

5. The process of claim 1 further characterized by said amorphous carbon being admixed in an amount comprising from about 0.5 percent to about 1.2 percent of the weight of said monosodium lead alloy.

6. The process of claim 1 further characterized by said amorphous carbon being substantially volatile free within the temperature range of said reaction and substantially completely oxidized within the temperature range of said smelting.

7. The process of claim 6 further characterized by said amorphous carbon being praticulate.

8. The process of claim 7 further characterized by the particulate amorphous carbon comprising particles being about inch in diameter.

9. The process of claim 6 further characterized by the further addition of smelting the sludge.

aids just prior to smelting 10. The process of claim 9 further characterized by the smelting aid being soda ash.

11. The process of claim 9 further characterized by the smelting aid being amorphous carbon.

References Cited UNITED STATES PATENTS 1,975,171 10/ 1934 Parmelee 260437 2,004,160 6/ 1935 Downing et a1. 260 -437 2,407,551 9/1946 Heron 260437 2,407,262 9/ 1946 lLlIlCh 260437 2,661,361 12/1953 Grandjean 2 437 2,763,673 9/1956 Gittins et al. 260-437 2,765,328 10/1956 Padgitt 260-437 2,853,378 9/1958 Mattison 260-437 XR 2,971,967 2/1961 Anderson 260437 3,049,558 8/1962 Cook et a1 260-437 1,827,820 10/1931 Kirsebom 78 XR 1,950,387 3/19-34 Betterton et a1. 7578 2,007,545 7/1935 Monson 7578 2,692,197 10/ 1954 Denison 7578 2,823,113 2/1958 Porro et a1. 7577 XR 2,834,669 5/ 1958 Pendar 7577 3,052,535 9/ 1962 Peters 7577 3,188,199 6/1965 Mattison 757'8 XR TOBIAS E. LEVOW, Primary Examiner. H. M. S. SNEED, Assistant Examiner.

U .8. Cl. X.R. 7577