US3515739A - Tetramethyllead recovery - Google Patents

Description

United States Patent 3,515,739 TETRAMETHYLLEAD RECOVERY Shirl E. Cook, Baton Rouge, La., and Thomas O. Sistrunk, Birmingham, Mich., assignors to Ethyl Corporation, New York, N.Y., a corporation of Virginia No Drawing. Continuation-impart of application Ser. No. 200,965, June 8, 1962, which is a continuation-in-part of applications Ser. No. 809,609, Apr. 29, 1959, Ser. No. 41,783, July 11, 1960, Ser. No. 91,598, Feb. 27, 1961, and Ser. No. 104,773, Apr. 24, 1961. This application Feb. 6, 1969, Ser. No. 797,260 The portion of the term of the patent subsequent to Aug. 14, 1979, has been dedicated to the Public Int. Cl. C07f 7/26 U.S. Cl. 260-437 3 Claims ABSTRACT OF THE DISCLOSURE Tetramethyllead is subjected to steam distillation while associated with a hydrocarbon such as toluene. This enables recovery of the tetramethyllead while protecting it against thermal decomposition.

This application is a continuation-in-part of our co pending application Ser. No. 200,965, filed June 8, 1962 which in turn is a continuation-in-part of our applications Ser. No. 809,609, filed Apr. 29, 1959, now U.S. 3,049,558; Ser. No. 41,783, filed July 11, 1960, now abandoned; Ser. No. 91,598, filed Feb. '27, 1961, now abandoned; and Ser. No. 104,773, filed Apr. 24, 1961, now abandoned.

This invention relates to tetramethyllead associated with a specific hydrocarbon complement which confers upon the resultant composition an unusually great re sistance against the adverse consequences of thermal decomposition such as might occur upon exposure to heat.

According to the present invention essentially pure i.e., highly concentrated-tetramethyllead is stabilized against thermal decomposition during its recovery from a reaction product mixture by associating with the tetramethyllead from about 20 to about 45 weight percent, based on the total weight of said composition, of a hydrocarbon having a boiling point at atmospheric pressure in the range of from about 90 to about 150 C., said hydrocarbon being selected from the group consisting of alkanes and mononuclear aromatics containing only aromatic unsaturation. In short, we provide in accordance with this invention a method of recovering tetramethyllead by steam distillation while associated with from about 20 to about 45 weight percent, based on the total weight of the composition, of a hydrocarbon of the type just described. This hydrocarbon can be a single material such as toluene, isooctane (i.e., 2,2,4-trimethylpentane) or other similar material. However, if desired, equally good results are obtainable by using mixtures of such hydrocarbons so long as they possess the physical and structural characteristics specified above. We especially prefer to use toluene or isooctane (i.e., 2,2,4-trimethylpentane), or a mixture of the two, since these particular materials are plentiful, inexpensive and very effective as thermal stabilizers. Moreover, both of these materials are of considerable value as blending stocks in the finished gasolines for which the tetramethyllead concentrates find their predominant usage.

Another preferred embodiment of this invention is to use hydrocarbons as above defined which are liquids at room temperature and at least a portion of which boils at or above 110 C. Very desirably only minor portions of such preferred hydrocarbons boil below 110 C.

Although it is most desirable to employ from about 20 to about 45 weight percent of the various hydrocarbons described above as thermal stabilizers for the tetramethyllead, it has been found that amounts as low as about 3,515,739 Patented June 2, 1970 ice percent give good results in many cases (e.g., when using toluene or isooctane). Accordingly, the invention is not intended to be limited to the precise concentration range specified above although it will be understood that marked departures from the foregoing range of the concentrations are undesirable from a number of standpoints including cost effectiveness, ease of processing, and the like. Thus, if the concentration is significantly less than about 15 percent on a weight basis inadequate thermal stability is very likely to be encountered. Conversely if the amount of hydrocarbon liquid is substantially in excess of about 45 percent on a weight basis not only is the cost excessively increased but the resultant concentrate becomes too dilute from a storage and shipment point of view. Therefore, in general, hydrocarbon concentrations ranging from about 20 up to about 45 weight percent are the most suitable for use in accordance with this invention.

The above tetramethyllead-hydrocarbon compositions are preferably prepared via the process described in our prior application Ser. No. 809,609, filed Apr. 29, 1959, now U.S. 3,049,558. Thus, in effecting this preferred mode of preparation reference should be had to the disclosure of that application for the operating details. A particular advantage of forming the compositions by conducting that process technique is that the tetramethyllead so-produced is intimately associated with the thermal stabilizer complement from the time that the tetramethyllead is formed. Accordingly, the tetramethyllead is continuously protected against the potential ravages of thermal decomposition not only during its formation but during all subsequent handling and storage operations involving the resultant compositions.

The above compositions may, however, be prepared by mixing the appropriate diluent with tetramethyllead formed by other procedures. In this embodiment it is desirable to admix the appropriate concentrations of the tetramethyllead and of the thermal stabilizers at an early stage in the processing operations so that the time during which the tetramethyllead is in its concentrated state is reduced to a minimum. In effecting this mixing operation use can be made of conventional tyms of reaction vessels, proportioning pumps, or the like.

Excellent results flow from the unification of the present ingredients in accordance with this invention. In the first place, the thermal stability of the tetramethyllead is markedly increased as compared with unstabilized, pure tetramethyllead itself. In fact, experiments have shown that the thermal stability of the tetramethyllead-hydrocarbon compositions is frequently 500 times as great as the stability of pure tetramethyllead. Furthermore, these compositions are improved in thermal stability characteristics in at least two respects. For one thing, their rate of decomposition is substantially reduced as compared with the rate of decomposition of unstabilized tetramethyllead. In ad- .dition to this, these compositions develop far less decomposition pressure than unstabilized tetramethyllead.

The present thermal stabilizersi.e., the alkanes and mononuclear aromatics containing only aromatic unsaturation as described aboveare substantially more effective for this purpose than naphthalene and styrene which were among the most effective thermal stabilizers heretofore known for alkyllead antiknock compounds (see U.S. Pats. 2,660,591 through 2,660,596, inclusive). This is a singularly unexpected result since by definition the present thermal stabilizersi.e., the alkanes and the mononuclear aromatics containing only aromatic unsaturation having boiling points at atmospheric pressure in the range of from about to about C.-are not fused ring aromatic hydrocarbons nor are they compounds characterized by possessing conventional olefinic unsaturation.

The presence of the inert hydrocarbon liquid provides a highly desirable component of an antiknOck liquid,

providing a component of high antiknock value in itself and also being itself particularly susceptible to antiknock or octane number improvement.

EXAMPLE I In the following operations an autoclave was employed which was fitted with an internal agitator and a jacket for circulating a heat transfer fluid. In addition, vapor and liquid return lines, to a condenser, provided for condensing and reflux of liquid as desired.

The autoclave was charged with monosodium lead alloy flakes in the proportion of approximately 22 pounds per cubic foot of reaction space. In addition, approxi mately percent by Weight, based upon the alloy, of graphite was introduced as a reaction lubricant, plus approximately 0.2 percent of aluminum, as trimethylaluminum. Toluene, in the proportion of percent of the alloy weight, was introduced. The reactor and contents were heated to approximately 80 C., and a feed of liquid methyl chloride was then started at a rate of about 10 parts per minute per 100 parts of alloy charge. Reaction occurred promptly, as shown by a further significant rise in operating temperature. The pressure was also allowed to rise to 180 p.s.i.g., and at this time reflux of vapor, principally methyl chloride, was initiated to maintain the pressure at this level. The temperature of the reaction mixture was thus controlled in the range of 95 to about 80 C. by variation of the degree of cooling for refluxing purposes. The methyl chloride feed was continued until a total of approximately 5 8 parts by Weight per 100 parts by weight of alloy charged had been introduced, this corresponding to approximately 160 percent excess of the theoretical requirement. The reaction conditions continued for several hours after termination of the feed, and then the temperature stopped rising and began to drop slightly. The excess pressure was vented shortly thereafter and the autoclave contents cooled to approximately ambient temperature. The charge was then discharged from the autoclave into ta pool of water in a steam distillation vessel, and the tetramethyllead and toluene were recovered in high yield.

EXAMPLE II In this operation, substantially the same procedure was employed as in Example I above, except that the sodium lead alloy was charged in the proportions of about 40 pounds per cubic foot of reaction volume. In addition, the reactor was charged with toluene in the proportions of about 10 parts per 100 parts of the alloy, and trimethylaluminum in proportions providing about 0.2 weight percent aluminum based on the sodium lead alloy. The autoclave and contents were heated to about 90 C., and then methyl chloride feed was initiated. Reaction started almost immediately and the pressure rose rapidly, condensation of vapor and reflux being started by condenser cooling at about 130 pounds per square inch pressure. The bulk of the reaction was conducted at a pressure of about 210 pounds per square inch gauge. The temperature during the feeding and in the reaction zone was readily controlled in this manner, rising in one short period to about 113 C., but the mean temperature was about 100 C. Upon termination of the reaction, the reacted mixture was discharged from the autoclave to a steam distillaiton operation, and a yield of approximately 70-75 percent of tetramethyllead was obtained, admixed with about weight percent toluene. The operation during the entire reaction period was smooth and readily controlled.

EXAMPLE III In this operation the alloy was charged to an autoclave in proportions of 57 pounds per cubic foot of reaction space. In addition, and at the start of the cycle, a mixture of toluene and methyl aluminum sesquichloride catalyst was charged to the reactor, in the proportions of 10 parts of toluene per 100 parts of alloy and methyl aluminum 4 sesquichloride in the proportions of about 0.8 part based on 100 parts of alloy. Further, methyl chloride liquid, in the proportions of 94 pounds per 100 parts of alloy was fed at the very start. This charge corresponded to proportions of about 4.3 times the stoichiometric requirements of the reaction.

The vessel was then heated by circulating hot water at C. through a jacket, while agitating the contents. The temperature was raised to about 70 C. and reaction started smoothly and continued without any difliculty of control, until the reaction was essentially complete. The temperature of the reaction mixture during this period rose from 70 to 100 C., the mean temperature being 85 C. The pressure of operating during the reaction period was maintained at about 205 pounds per square inch gauge.

At the termination of the reaction, the excess pressure was vented and the autoclave charge was cooled by circulating a cooling medium in the jacket. The contents were then discharged and subjected to a steam distillation, and a yield of about 70 percent tetramethyllead was obtained, accompanied by toluene in a concentration of about 35 percent.

EXAMPLE IV The same procedure as employed in Example III above was used in charging the autoclave, except that the meth-- refluxing of liquefied vapors, at about 170 p.s.i.g. Reac-.

tion occurred very smoothly and the temperature continued to rise at a reasonable rate up to as high as 118 C., the mean temperature being at or slightly above C. After several hours reaction with easy control, the autoclave and contents were cooled and excess pressure was vented. The reacted charge was discharged and steam distilled. A high yield, of the order of about 65 percent tetramethyllead, accompanied by about 35 weight percent of toluene was recovered.

EXAMPLE V When Examples I through III are repeated, except that the toluene is introduced in the proportionsof about 20 percent, based on the alloy, similar results are achieved,

except that the average temperature of operation is slightly higher.

When the conditions of operation of Example IV areused, the toluene or other inert hydrocarbon should not be used in proportions significantly above 11 or 12 weight percent of the alloy, in order to be below the preferred upper limit of 50 volume percent of the methyl chloride provided.

In addition to operation at higher concentrations of inert hydrocarbon, as exemplified above, perfectlysatisfactory results are achieved when the hydrocarbon is substantially reduced in concentration, as illustrated by the.

following example.

EXAMPLE VI Generally, the same procedure as described in Example I was followed, the loading of the reaction zone or autoclave being about 37 pounds of alloy per cubic foot. :Instead of providing toluene in the proportions of about 10 parts to parts of alloy, however, the concentration was lowered to about only 7 parts per 100 parts of alloy. The catalyst employed was in the proportions of .44 part of trirnethylaluminum per 100 parts of alloy. Upon raise ing the temperature by external heating, and feeding methyl chloride in the proportions of about 1.6 times theoretical requirements, very eflicient operation was obtained, the pressure being stabilized at 180 pounds per square inch gauge, and the temperature rising and being controlled at a maximum level of about 110 C., and a 6 ployed in limited quantity in the above process are highly effective in inhibiting the decomposition of tetramethyllead. The following data illustrate clearly the magnitude of this benefit. A series of operations were conducted in which specimens of pure tetramethyllead, or tetramethylminimum temperature of about 85-90 C. After reaction, lead with defined quantities of inert liquids were subjected the reacted m1xture was discharged and steam distilled to a procedure designed to cause decomposition, and anal a dhigh yield pg 130 t1percelnt tetramlethyillead was allow measurement of the rapidity and/or severity of the ac ieve accompanie y e to u'ene emp oye decomposition. This procedure involved inserting the If desired, the inert hydrocarbon concentration can be specimen in a closed steel vessel having a wire passing iiivi lfl ioli s iafififi iii? 521355 1523"? i i fi the ii h .i i -"1 erng qu e e wire was en ea e y passing e ectrrca current operable. However, the best results are usually provided therethrough. The temperature of the specimen was also when a concentration of at least 10 pounds per 100 pounds measured. Recording pressure devices, in some cases of of lead is used. the oscilloscope type, were employed to provide a clear EXAMPLE VII and accurate record of the time-pressure history. In a when Examples I through IV are repeated, except that, series of OPGIZIUOHS of th1s character, the following results instead of toluene, either 10 or percent of 2,2,4-triwere Obtame methylpentane (isooctane) is substituted for the toluene, 9 similar results are achieved, except that the temperature Initiation Maximum Maximum ggg gg; of operation at comparable pressures are slightly lower speclmen p pp s e t (see) than the case of the foregoing examples using toluene. Pure 105 265 1,030 About M In addrtron, when a low excess of methyl chloride is used, wt. percent 0 as in Example IV, the upper limit of the amount of iso- 25 fifi%%"}' j5; 'gfig 1 5 165 100 50 octane should be reduced, desrrably, to not over about /2 toluene 105 80 5 the liquid volume of the methyl chloride reactant.

Instead of pure hydrocarbon compositions, mixtures or foregQmg Shows effect of the Presence Of toluene blends can be employed, and in some cases are preferred, on improving the stability of tetramethyllead. It is seen as shown by the following example. that an increase 1n stability of from 175 to .500, at least,

PLE I in improvement is realized. Similar benefits were demon- EXAM VII strated when the decomposition of specimens was initiated The procedure of Examples I through IV is repeated in y lgllltlqll Famed y a thefmlte reaction In these p operations wherein, instead of toluene, an aromatic type 9 a slmllar p f Was used: except that the electllc solvent is employed having an initial boiling point of wire was used to initiate a thermite reaction. The thermite about 100 c. and a final boiling point of abouit 13(31 1?. e ga p u lp se p Similar yields and ease of operation are attaine an t e ure 0 Over S0 t 18 tec nlque provl es a very tetramethyllead is accompanied, during steam distillation drastic test. In these experiments the effectiveness of typirecovery, by a satisfactory concentration of the solvent cal thermal stabilizers of this invention was directly comcomponents. Similar results are achieved in the foregoing 4O pared with the effectiveness of styrene and of naphthalene, operations. It is also observed that a more uniform distritwo of the most effective alkyllead thermal stabilizers bution of inert liquid is observed, accompanyin the heretofore known. Thus, in Run A below the composition tetramethyllead product, during the steam distillation, than of this invention contained approximately 39 percent by is obtained when using a pure isooctane diluent material. weight of toluene and in Run B it contained approximately 26 percent by weight of isooctane. For comparative pur- EXAMPLE 1X 1 f 11 d poses the tetramethyllead used in Runs C and D contained The procedure followed in Examp e III is o owe approximately 31 percent by weight of styrene and apgenerally, except that an alloy containing 20 weight perproximately 26 percent by weight of naphthalene, respeccent sodium is used. The charge to the reactor consists of tively. The results of these operations were as follows:

Decom- Initiation Maximum Maximum position Run Specimen temp. temp. pressure time (sea) A 40 g. TML+30 ml. toluene 230 360 7. 5

B 40 g. TML+20 ml. isooctane 410 25 C 40 g. TML+20 ml. styrene. 105 335 1275 3 D 40 g. TML+25.9 wt. percent" 105 2, 000 0. 5

Parts From the above, it is seen that the presence of the hydro- Alloy 2 carbon solvents results in improvement in the stability of Methyl chlorlde g 0 from 70 to 250 times the stability of tetramethyllead Toluene alone. Moreover, the thermal stability of the compositions Trrmethylalummum 2 The quantity of methyl chloride used amounts to 1.4 theories, plus a slight excess to occupy the free space in the reaction system. After charging these reactants, the autoclave and contents are heated to suitable temperatures to begin reaction, and the bulk of the reaction is carried out at approximately 100 C. and a pressure of about pounds. After completion of the reaction, the reacted mixture is discharged and the tetramethyllead is steam distilled, a high yield being accompanied by about 25 percent toluene.

One of the particular beneficial efiects of the present invention is the fact that a highly stable system is achieved and maintained. It is found that the inert materials emof Runs A and B was to be over 200 percent as great as the thermal stability of a corresponding composition which contained styrene as the thermal stabilizer. Furthermore, the maximum pressure produced in Runs A and B were far less than that developed in Run C. By the same token the compositions of Runs A and B were vastly superior from the thermal stability standpoint as compared to the composition composed of tetramethyllead and naphthalene used in Run D. In fact the compositions of Runs A and B had decomposition times that were at least 15 times as long as the decomposition time of the naphthalene-containing composition. Moreover, the maximum pressure developed was far less with the compositions of Runs A and B than it was in the case of the naphthalene-containing composition.

Similar results are achieved when, instead of determining the rate of decomposition of a tetramethyllead product which has been separated from the other components of the reaction, a determination is made of the reacted mixture (reaction mass) prior to separation. Tests have shown that the rate of decomposition is reduced by a factor of at least about 4 and usually over 6. Hence, the tetramethyllead is stabilized during the reaction as well as during subsequent separation and after segregation of the tetramethyllead product.

The foregoing shows the great degree of improvement in stability even when the specimen is subject to the severe shock of a thermite type reaction. A highly significant benefit in the present operation is that it assures that the inert liquid is in the presence of the tetramethyllead from the moment it is synthesized and remains with, or accompanies the product, during recovery operations. The most effective recovery operations involve a partial pressure operation to isolate a tetramethyllead product fraction. Hence, it is of importance that the volatility of the inert liquid be in the neighborhood or approaching the volatility of tetramethyllead, at least with respect to some components thereof. Toluene, having a boiling point of 110.6" C. is ideal in this respect. However, commercial hydrocarbon streams, having a boiling range which overlaps the normal boiling point of tetramethyllead, are quite acceptable. These may be pairafiinic or aromatic in char-.

acter provided they possess the physical and chemical characteristics described above.

We claim:

1. In a method of recovering tetramethyllead, the improvement according to which the tetramethyllead is steam distilled While associated with a hydrocarbon have ing a boiling point at atmospheric pressure in the range 1 of from about to about 150 C. in amount sufiicie'nt to stabilize the tetramethyllead against thermal decomposition, said hydrocarbon being selected from the group consisting of alkanes and mononuclear aromatics containing only aromatic unsaturation.

2. The method of claim 1 wherein said hydrocarbon is an aromatic type solvent having an initial boiling pointof about C. and a final boiling point of about C.

3. The method of claim 1 wherein said hydrocarbon is:

TOBIAS E. LEVOW,

H. M. S. SNEED, Assistant Examiner Primary Examiner