US2597754A - Manufacture of tetraethyllead - Google Patents

Description

Patented May 20, 1952 2,597,754 MANUFACTURE; or TETRAETHYLLEAD Hymiu S a ir D o M h. ass s: o hy Corporation, New York, N. Y., a corporation of Delaware No; Drawing. Application August 16', 1950', Serial; No. 179,893

2 Claims.

This; invention-relates to an improved, method of; making tetraethyllead.

Tetraethyllea-d is an important commercial pmductsbecauseof itsex-tensive useasan antilsnock. agent. They present commercial, process for; itsmanufacturecomprises first forming coarse solidparticles of a sodium-lead alloy, and reacting these particlesrwith ethylchloride in a batch operation) at temperatures above 70 C., accordingi'to the following equation The sodium-lead alloy is made by first melting a, mixture containing the proper proportions of sodium. andlead, solidifying the melt and then breaking and grinding the solid alloy into. particles suitable for use in the reaction with ethyl chloride. The rate of reaction between alloy thus formed and ethyl chloride is not as high as desirable; particularly in a continuous process where reaction rate is of prime importance.

In a continuous or semi-continuous process for the-manufacture of tetraethyllead it is necessary to introduce the solid alloyto the reactor across a pressure differential. Suchan operationisdin ficu-lt; andthe state of subdivision of the alloy is important. It-is preferred that this operation be conducted with a fine particle size alloy to gain the-advantage of slurry introduction.

It'is, therefore, an object of my invention to prepare sodium-lead alloy in an unusual form which is particularly adapted to react with ethyl chloride.

The process of my invention is achieved by the submergedliquid comminution of a solid sodiumlead alloy.

A fast-reaction rateisimportant to the tetraethyllead process in that higher capacities are obtained, thereby substantially reducing equipment, costs. This: isparticularlytrue in a continuous; processwhere reaction rate is frequently the difierence between a profitable operation and an unproflt'able one. Furthermore, while the u1 ti-m'ate. percentage yield in a batch operation is v not substantially afiected by the reaction rate, the practical ultimate yield in a continuous operation is affected thereby. Thus myinvention is particularly' adapted for use in a continuous or a semir continuous process; However, a faster rate is also "advantageousin a batch operation because of the reduced cycle time obtained.

In one broad embodiment, the operation of my invention is conducted as follows: sodium and j lead in the proper proportions, preferably that corresponding to N'aPb, although alloys of other 2. proportionswill exhibit the; same; effect, such a NazPb andNa9Pb4, are; heated to a temperature sufficient to melt the mixture, which temperature is about 375 C. forNaPb. The cooled, solid alloy is their ground by suitable comminuting devices while submerged in a liquid, inert at the ternperature of grinding. Typical examples of such comminuting devices includehammer-mill, ballmill,burr-mi1l, colloidrmill, and roller-mill grinders. In addition to the above conventional methods for grinding, I can subdivide the solid alloy of my invention bypassing the alloy and a liquid. through pumping devices, wherein the subdivision occurs. Such pumping devices include centrifugal, impeller, and gear pumps. Other means for subdividing thealloy while it is submerged in a liquid can be employed and are within the spirit and scope of my invention.

Ethyl chloride is preferably used as th liquid medium for thegrinding operation, since-a slurry is formed which will'react .to produce tetraethyllead, when it is heated. to reaction temperature, which in the case of NaPb is between 40 and 100 C. When ethyl chloride is so used its temperature during the grinding operation must be kept below -.l0. C: in order to avoid reaction in this stage of my process.

In order to achieve a. rapid reaction rate between a solid. and a liquid iti-s known in general that introducing the solid in the form of finely commin-uted particles will achieve this result. However, in themanufacture of tetraethyllead I have found that this simple expedient will not achieve the desired result, and in many cases the rate of reaction is actually retarded by further reduction in the alloy particle size.

In order to illustrate the unexpected advantage obtained by employing my process for wet grinding alloy, a reaction time of 5minutes is selected, for-itisin-this period that theadvantage achieved by a continuous operation is most pronounced over a bath operation for the manufacture of tetraethyllead. For example, if an alloy in the particle size range of 8-20 mesh is prepared by dry grinding in the presence of, a highly purified nitrogen atmosphere, and is then reacted with ethyl chloride, the yield of tetraethyllead atthe end otfive minutes is 1A5 per cent based onthe lead" present in. the alloy. The alloy used in the present commercial: process consists of much larger particles than. the above example and gives a substantially lower yield. When dry ground alloy of l50-e200 mesh was employed, the yield of tetraethyllead in five minutes was notimproved overthat. for the 8-20 mesh alloy mentioned above, in spite of the increased surface available for reaction. Upon reducing the alloy particle size to minus 200 mesh its activity was actually reduced so that the yield of tetraethyllead, based on the lead in the alloy, was only 11.2 per cent. In each of the above examples extreme caution was employed to insure that the atmosphere in contact with the alloy contained only nitrogen, and was free of oxygen and moisture.

In contrast to the above examples I have obtained a yield of tetraethyllead of 20 per cent in five minutes with an alloy which was smaller than 150 mesh, prepared by grinding sodium-lead alloy while it was submerged under ethyl chloride at a temperature of C. Thus not only was the reactivity of the alloy substantially enhanced over an alloy of comparable size prepared by dry grinding, but also a significant improvement was obtained over the present used commercial alloy. Furthermore I obtained the unexpected result that this highly reactive alloy could be prepared under ethyl chloride without reaction occurring during the grinding operation.

Therefore by the process of my invention a reactive alloy of extremely small size can be obtained, in the very alkylating agent with which it is subsequently to be reacted. This alloy can be successfully introduced as a slurry by pumping or other means to a reactor for the continuous manufacture of tetraethyllead.

In a continuous process for the manufacture of tetraethyllead, utilizing the wet grinding process, it is preferred, as noted above, that the alloy be introduced to the reactor in an ethyl chloride suspension, since by this means the recovery of the resulting tetraethyllead is simplified and the number of steps required between the preparation of the alloy and the introduction of the slurry to the reactor is minimized. However, when this consideration is not controlling, other liquids,

inert at all ordinary temperatures to the sodiumlead alloy, can be employed as a wet grinding medium. The resulting slurry is introduced to the reactor concurrently with a stream of ethyl chloride. Examples of inert liquids which can be employed herein include hydrocarbons, such as kerosene and other petroleum fractions, amines, such as triethylamine, and the like. In general, any liquid can be employed which it is desired to add to the reaction mixture. For example, by this means I have provided a convenient method of introducing a catalyst or stabilizer to the reactor zone.

After the reaction between the alloy and the ethyl chloride is complete or substantially so, the reaction products are separated in the usual manner. The ethyl chloride used is preferably in excess of the amount required in the equation given above, the weight ratio of ethyl chloride to lead being between about 0.5 to 1 and 6.25 to 1. The pressure used should be suiiicient to maintain the ethyl chloride in the liquid phase at the reaction temperature employed. The preferable reactor temperature is between 40 C. and 100 C. The residence time is not critical, but for practical purposes should be between 3 minutes and 30 minutes.

The particle size of my wet ground alloy, while not critical, is important and for best results should be smaller than 4 mesh, preferably between 100 mesh and 300 mesh.

My invention can be further understood by referring to the following working examples and examples of prior art methods for comparison in which the parts are by weight and the yields and percentages are by weight and are based on the amount of lead charged. The particle size of the ground-alloy, as described in the following examples, was determined on U. S. Standard sieves. Examples I, II, and III illustrate the reaction rate of dry-ground alloy prepared by different methods.

Example I To a ball-mill was charged 100 parts of 8-20 mesh sodium-lead alloy and the ball-mill was sealed after introducing a purified nitrogen atmosphere. The ball-mill was rotated at 60 R. P. M. for a period of 24 hours. At the end of this period the particle size of the alloy was such that substantially all of the alloy passed through a 150-mesh screen. This alloy was added as a slurry with 112 parts of ethyl chloride and 0.2 parts of acetone to a reaction vessel equipped with an agitator, a, jacket for circulation of heating and cooling liquids, a reflux condenser and a discharging port through which the reaction products could be rapidly discharged. This reaction vessel contained 84 parts of ethyl chloride at a temperature of C. prior to the addition of the alloy. The reaction temperature was maintained at 80 C. for 5 minutes with the agitator in motion, at the end of which period the reaction mass was rapidly discharged into a vessel containing benzene at a temperature of 25 C. while venting ethyl chloride to the atmosphere. The resultant benzene suspension was filtered and the tetraethyllead remaining was further extracted with an additional quantity of benzene. The tetraethyllead recovered from the combined benzene extracts contained 21.3 parts or a yield of 15.2 per cent based on the lead in the sodiumlead alloy.

Example II Sodium-lead alloy of 8-20 mesh was passed through a burr-mill operated at 1750 R. P. M. in an atmosphere of nitrogen. The pulverized alloy was classified and parts of that material which passed through a 200 mesh screen was added to a reaction vessel as described in Example I above, and the further operations of heating, discharging and recovery were conducted also as above. From a series of six operations conducted in this manner we obtained an average of 19.4 parts of product, or a yield of 13.8 per cent of tetraethyllead based on the lead in the sodium-lead alloy.

Example III Sodium-lead alloy in the particle size range of 8-20 mesh was pulverized in a hammer-mill operating in a nitrogen atmosphere at 10,000 R. P. M. The alloy obtained from this Operation contained 32 per cent which was retained on a 200-mesh screen and 68 per cent which passed through a 200-mesh screen. This alloy in the amount of 100 parts was treated in a series of 12 operations as in Example I to produce an average yield of 22.7 parts of product, or a yield of 16.2 per cent based on the lead present in the sodium-lead alloy.

In the above examples the comminution was conducted in the absence of a liquid. To show the improvement in reaction rate obtained by the process of my invention the following examples are given:

Example IV To a steel ball-mill containing 1 inch steel balls and equipped with a jacket for circulating a coolingmedium was charged 100 parts of 8-20 mesh sodium-lead alloy, 112 partsv of ethyl chloride and 0.2 parts of acetone. The ball-mill was rotated at 15 R. P. M. for a period of 4 hours while maintaining a temperature of C. in the cooling jacket. The resultant slurry contained sodium-lead alloy of which 64 per cent was finer than 150 mesh. This slurry was treated with an additional 84 parts of ethyl chloride for a period of 5 minutes as described in Example I. The yield of product from this operation was 28.5 parts or a yield of 20.3 per cent based on the lead in the sodium-lead alloy.

Yields of tetraethyllead comparable to that obtained in Example IV above are obtained by employing alloy ground as in the proces of Examples II and 111 above but in the presence of ethyl chloride.

To illustrate another method of subdividing the alloy for the process of my invention, sodiumlead alloy was treated under iso-octane with a scraper type agitator revolving at 900 R. P. M. The alloy employed contained particles between inch and /3 inch. At the end of minutes the particle size was 434. of an inch and finer. In a similar operation in which an agitator was employed as a grinding medium the alloy after agitating for one hour consisted of 65.8 per cent larger than 50-mesh, 3.3 per cent between 50 and 100 mesh, 12.2 per cent between 100 and 200 mesh and 18.7 per cent finer than 200-mesh.

Still another method for making an alloy by my invention is accomplished by passing sodiumlead alloy of 8-20 mesh through a centrifugal pump in the presence of a heavy lubricating oil with the pump operating at 6000 R. P. M., 50 per cent of the material passing through the pump was finer than 100-mesh.

The alloys made by the above two examples when substituted for the alloy used in Example IV also give a yield in five minutes of about per cent.

Thus the above examples show that the reaction rate between alloy and ethyl chloride for my process is more than 133 per cent of that obtained in processes making and using dry ground alloy in the conventional way. Such an increase is significant and exceedingly important commercially.

The above examples are illustrative of my invention and it is to be understood that they may be varied widely without departing from the scope hereof.

I claim:

1. The process of making tetraethyllead which comprises comminuting a sodium-lead alloy to a particle size in the range of about to 300- mesh while it is submerged in an excess of ethyl chloride maintained at a temperature below that at which it reacts with said alloy, and then raising the temperature of the resulting slurry to between 40 C. and 100 C. for a residence time between 3 and 30 minutes while maintaining an excess of ethyl chloride in the ratio of ethyl chloride to lead between about 0.5 to 1 and 6.25 to 1.

2. The process of making tetraethyllead comprising first forming NaPb alloy particles in the size range of 4 to 300 mesh by wet grinding and then reacting said particles with an excess of ethyl chloride in the ratio of ethyl chloride to lead between about 0.5 to 1 and 6.25 to 1, for a residence time between 3 and 30 minutes, and at a temperature between about 40 C. and 100 C.

HYMIN SHAPIRO.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,697,245 Kraus et al Jan. 1, 1929 2,310,806 Nourse Feb. 9, 1943 FOREIGN PATENTS Number Country Date 453,271 Great Britain Sept. 1, 1936

Claims (1)

1. THE PROCESS OF MAKING TETRAETHYLLEAD WHICH COMPRISES COMMINUTING A SODIUM-LEAD ALLOY TO A PARTICLE SIZE IN THE RANGE OF ABOUT 100- TO 300MESH WHILE IT IS SUBMERGED IN AN EXCESS OF ETHYL CHLORIDE MAINTAINED AT A TEMPERATURE BELOW THAT AT WHICH IT REACTS WITH SAID ALLOY, AND THEN RAISING THE TEMPERATURE OF THE RESULTING SLURRY TO BETWEEN 40*C. AND 100*C. FOR A RESIDENCE TIME BETWEEN 3 AND 30 MINUTES WHILE MAINTAINING AN EXCESS OF ETHYL CHLORIDE IN THE RATIO OF ETHYL CHLORIDE TO LEAD BETWEEN ABOUT 0.5 TO 1 AND 6.25 TO 1