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Патент USA US3069344

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Dec. 18, 1962
Filed June 9, 1958
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Dec. 18, 1962
Filed June 9, 1958
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trialkyl is constantly added at the same rate that it is being
consumed, with the formation of lead tetra-alkyl at the
anode and aluminum at the cathode.
In the further development of the process it became
apparent that unless special precautionary measures were
taken, the aluminum deposited at the cathode would re
act with the lead tetraalkyl forming lead which contami
nated the rest of the aluminum. This effect increased pro
portionately with an increase in the current density used
Patented Dec. 18, 1962
Karl Ziegler and Herbert Lehmkuhl, Mulheim (Ruhr),
Germany; said Lehmkuhl assignor to said Karl Ziegler,
Mulheim (Ruhr), Germany
Filed June 9, 1958, Ser. No. 740,623
Claims priority, application Germany June 12, 1957
22 Claims. (Cl. 204-59)
10 for the electrolysis.
This invention relates to a process and a device for the
When using higher current densities
the aluminum is not deposited at the cathode in form of
production of tetraethyl lead.
In our co-pending patent application Serial No. 548,862,
a compact metal but as a porous powder which reacts
with the lead tetraalkyl much more rapidly. These higher
current densities are, however, desirable for economic
?led November 25, 1955, now Patent No. 2,985,568, a
process is described for the production of lead tetraalkyls.
This process allows an overall result characterized by the
reasons. The contaminated aluminum thus obtained is
not pure aluminum suitable for industrial purposes, and
reaction equation:
if used for the conversion to aluminum alkyl compounds
in the production of lead tetraalkyl, complicates the proc
In said application Serial No. 548,862 it was proposed
Since a direct reaction between metallic lead, hydrogen
and ole?ns is not possible, the above result is realized by
a combination of two process steps.
to separate the electrolytic cell by means of a diaphragm
into an anode and a cathode space, in order to prevent
Aluminum is re
the contamination of the catholyte with the lead tetraethyl
containing anolyte and thus to obtain a re?ned aluminum.
The separation of the anode from the cathode space has,
acted in the ?rst step with an ole?n and hydrogen to form
aluminum trialkyl. In the second step the aluminum tri
alkyl is made electrically conductive by the addition of a
suitable compound, such as an alkali metal halide, and
however, far reaching consequences for the electrolysis.
The chemical reactions occurring during the electrolysis
change the composition of the now separate catholyte
and anolyte. The diaphragm prevents a comingling of
subsequently electrolized between an anode containing
lead and a cathode of any suitable material. In this step,
aluminum is deposited at the cathode while lead tetra
alkyl is formed at the anode and is separated from the 30 these two liquids and thus an adjustment of the differences
in the composition of the electrolyte resulting during the
electrolyte. The aluminum deposited at the cathode may
afterwards be reacted again with an ole?n and hydrogen
to form aluminum alkyl which is recycled into the process.
The reaction of the aluminum with an ole?n and hydro
electrolysis. Consequently during the electrolysis alumi
num trialkyl free from complex bonding with alkali halide
is formed in the anode space. This free aluminum tri
alkyl is removed together with the lead tetraalkyl and
can be separated from it only with difficulty. In this
manner, a part of the aluminum is lost during the process
in the form of aluminum trialkyl which contaminates the
gen in the ?rst step may be effected pursuant to our co‘
pending applications Serial No. 484,576, ?led January 27,
1955, and Serial No. 573,470, ?led March 23, 1956, and
Patent No. 2,835,689, according to the following reaction
by adding a certain amount of sodium aluminum tetra
alkyl to the electrolyte at the beginning of the electrolysis.
It was found, however, that this modification of the
and may, if desired, be effected in the presence of a dialkyl
process was not su?‘icient to avoid with certainty the above
aluminum halide catalyst.
‘In order to make the aluminum alkyl compounds elec
tr1cally conductive the above mentioned applications sug
mentioned complications resulting from the separation of
the electrolysis device into anode and cathode space.
One object of this invention is to avoid all the above
mentioned di?’iculties and allow the deposition of alumi
gest the use of additives such as an alkali halide, especially
sodium ?uoride. According to application Serial No.
548,862 a particularly suitable electrolyte consists of the
liquid complex compound of the composition NaF.2AlR
which is described in application Serial No, 379,294, ?led
September 9, 1953, of the applicant, now Patent No.
The direct production of lead tetraalkyl as proposed in
application Serial No. 548,862 may be represented by
the following reaction equation:
lead tetraalkyl obtained.
The applicants have proposed overcoming this di?iculty
num at the cathode which is suitable to be used as re
?ned aluminum outside the process, and the production of
lead tetraethyl which does not contain any aluminum tri~
ethyl at the anode. This and still further objects will be
come apparent from the following description read in con
junction with the drawings in which:
FIG. 1 is a diagrammatic perspective view of an em
bodiment of an arrangement of electrolysis cells for ef
fecting the process in accordance with the invention;
FIG. 2 diagrammatically shows'an arrangement in the
During the electrolysis, aluminum trialkyl is thus con 60
stantly used to the same extent as the lead tetraalkyl and
metallic aluminum are formed. When NaEZAlRE is used
form of a ?ow sheet for effecting the process in accord
ance with the invention; and
FIG. 3 is a ?ow sheet showing a further embodiment
of the process in accordance with the invention. a
as the electrolyte, this has the effect of constantly impov~
The invention relates to an improvement in the above
erishing the electrolyte in aluminum so that the electrolyte
described process for the electrolytic production of tetra
composition ?nally reaches a ratio of NaF:AlR3, of about 65 ethyl lead by ‘passing an electrolysis current between a
1:1, with the formation of a de?nite complex compound
cathode and lead-containing anode through an aluminum
NaF.AlR3 (1:1 compound). This compound may have
triethyl-containing electrolyte. In accordance with the
a high melting point and a substantially lower conductivity
invention a diaphragm is maintained between the cathode
than the compound of the type NaF.2AlR3 (1:2 com
and anode to thereby form separate cathode and anode
pound) and is therefore less suited for the electrolysis, e.g.
spaces which are separated from free ?ow communication
for economic reasons. It is apparent that stationary con
of the electrolyte with each other by means of the dia
ditions can be maintained in the electrolyte if aluminum
phragm. At least initially in anolyte is maintained in“
The combination of the Equations 4 and 5 results in
the anode space which essentially consists of a mixture
the new reaction equation:
of NaAl(C2H5)4 and NaF.Al(C2H5)3. The diaphragm
which is maintained between the cathode and anode must
be of such construction as to prevent migration of the
electrolyte between the cathode and anode spaces With
out substantially interfering with the passage of the cur
(transferring to the cathode).
The NaAl(C2I-I5)4 compound, which in accordance
with the invention is additionally present, enters the re
The NaAl(CzH5)4 and the NaF.Al(C2H5)3 are prefer
ably ‘present in equivalent amounts and the anolyte pref
action in the following manner:
erably additionally contains NaF.2Al(C2H5)3, this latter 10
compound preferably being present in amount of 0.16-l.7
and most preferably 0.67-1.70 mols per mol of the
Of the three Al(C2H5)3 compounds formed according to
Equation 7 only two can react to a 1:2 compound
The electrolysis may be continued until one of the 15
NaAl(C2H5)4 and NaF.Al(C2H5)3 has disappeared
The advantages obtained by the process according to
so that one Al(C2H5)3 compound is left which could
contaminate the lead tetraethyl.
Further according to the invention, the anolyte con
chemical reactions in the anolyte during the electrolysis.
additional free 1:1 compound. This 1:1 compound
For the purpose of illustrating the process of the in 20 combines with the remaining aluminum triethyl under
vention it will be supposed that the complex compound
formation of a 1:2 compound so that the anolyte now
NaF.2Al(C2H5)3 is present in the anolyte mixture. As
is free of Al(C2H5)3. According to Equation 4, for each
will be seen later, this is not absolutely necessary. The
one fourth Pb(C2H5)4 one Al(C2H5)3 compound is lib
1:2 compound decomposes into positive sodium ions and
erated and one Al(C2H5)2F compound formed which re
the invention are apparent from a consideration of the
the negative complex-radical
These ions are discharges at the anode where, in the
presence of lead going into solution, the following reac
tion occurs
quires for its “neutralisation” exactly one NaAl(C2H5)4.
It is, therefore, suitable if the 1:1 compound and the
NaAl(C2l-I5)4 compound are added to the anolyte mix
ture in equivalent amounts, although this equivalence is
not critical.
The reaction results are not affected if there
is no such equivalence; only in that case the electrolysis
is suitably discontinued at the very point at which the
component of which there is a deficiency has just dis
appeared or preferably even a little earlier. It is preferred
In the brackets at the right side of the equation there 35 to keep the molar proportion of
appears thus at ?rst a double molecule
NaAl (C2H5)4:
A1 (C2H5 ) a-Al (C2115) 2F
in the range of 3:1 to 1:3 with the commercial optimum
This decomposes into its two components
of one mole NaAl(C2H,-,)4 to one mole 1:1 compound.
As is apparent from the above equations, the 1:2 com
The sodium ions which, so to speak, remain behind in
the anode space partly transfer to the cathode space and
partly ?nd their electrochemical equivalent in the ?uorine
ions transferring through the diaphragm into the anode
pound is formed during the electrolysis from the anolyte
components, the 1:1 compound and the NaAl(C-2H5)4
compound. As a result, an anolyte mixture is conceivable
which contains originally only NaF.Al(C2H5)3 (1:1) com
pound and NaAl(C2H5)4 compound and no additional
2:1 compound. In practice, however, an anolyte mix
For each ——C2H5 group bound to lead going into solu
tion there thus results one free Al(C2H5)3 compound.
ture of this type has certain disadvantages. The melting
point is high so that high reaction temperatures are re
This can only be combined as 1:1 compound to the ex
quired. The conductivity is low since the 1:1 compound
tent to which sodium ions did not move out of the anode 50 has a considerably lower conductivity, amounting to about
space and ?uorine ions did transfer into the anode space
only one ?ftieth of the conductivity of the 1:2 electrolyte.
from the cathode space.
In practice, a particularly suitable anolyte contains per
Moreover, the Al(C2H5)2F compound formed accord
mole NaAl(C2I-l5)4 one mole of the 1:1 compound and
ing to Equation 4 has the greater tendency towards form
0.16 to 1.70 moles and preferably 0.67 to 1.70 moles of
ing complexes than the Al(C2H5)3 compound. As a re 55 the 1:2 compound.
sult, a reaction with the excess electrolyte
If the electrolysis is continued until these electrolytes
in the anode space have exactly the composition
( C2H5 ) 3
according to
60 then they contain 10 to 20%, preferably 10 to 15% lead
tetraethyl partly in solution, partly separated in liquid
Per kg. electrolyte a current of 331/3 to 66%
ampere hr., preferably 331/3 to 50 ampere hr. is required.
With these electrolyte mixtures it is of course not ab
takes place.
For each —C2H5 group bound to the lead, a substan
tial amount of aluminum triethyl is thus liberated and
separated in admixture with the tetraethyl lead.
solutely essential that the amount of current is exactly
as indicated. The stated amounts represent the limit up
to which the formation of free aluminum triethyl is
avoided. If the electrolysis is further continued, lead‘v
tetraethyl continues to be formed; however, according
According to the process of the. invention the elec 70 to the above equations and in the absence of at least one
trolysis is started with an anolyte which contains one
of the electrolyte components used in accordance with
compound each of the formula NaAl(C2H5)4 and of the
formula NaF.Al(C2H5)3 (1:1 compound). The effect of
these additions is illustrated by the following reaction
the invention, free aluminum triethyl will be formed which
comingles with the lead tetraethyl.
Suitably, the composition of the anolyte and the amount
of the current to be applied will be so selected that upon
removal of the used anolyte the 1:1 compound has been
anolyte is freed of lead tetraethyl and subsequently intro
reacted as far ‘as possible. On the one hand an incom
duced into the emptied cathode space.
plete reaction prevents the substantially optimum utilisa
According to the invention the process may, however,
tion of the electrolyte for the production of lead tetra
also be carried out continuously by continuously with
ethyl which is desirable for economic reasons. On the U1. drawing a certain proportion of both liquids, freeing the
other hand, the 1:1 compound is more readily soluble
Withdrawn anolyte from the lead tetraethyl and adding
than the 2:1 compound in the subsequent extraction of
fresh aluminum trialkyl to the catholyte and subsequently
the electrolyte for the recovery of the lead tetraethyl,
returning both portions into the other electrolyte space.
thereby interfering with the recovery of the lead tetraethyl.
In place of the intermittent exchange of the electrolyte
It is best to remain a few percent below the amount of 10 liquid With each other it is thus possible by a proper
the required ampere/hours since this gives the guaran~
combination of the rate of electrolysis carried out under
tee that on the one hand the reaction has progressed as
use of 1:1 compound and NaAl(C2H5)4 in the anolyte
far as possible whereas on the other hand the critical limit
and the corresponding continuous replenishment of the
at which one component part of the electrolyte disappears
has not yet been exceeded.
Also for the development in the cathode space, the
separation of the electrolysis device by a diaphragm pre
venting the admixing of anolyte and catholyte has far
reaching consequences. As a result of the arrangement
of the device in accordance with the invention the com
position of the catholyte is thus without any importance
catholyte containing these compounds to ‘arrive at such
a point that the condition in the anode space required
in accordance with the invention, i.e. the presence of the
1:1 compound and sodium aluminum tetraethyl in the
anolyte will be invariably maintained during an electro
lytical process of any given length of time. In this
20 manner, the critical limit is never exceeded beyond which
free aluminum triethyl is formed in the anolyte.
for the formation of lead tetraethyl in the anode space.
In accordance with a preferred embodiment of the
process of the invention part of the catholyte is thus con
Thus, any cathode liquid may be used provided it ful
?lls the condition of not becoming admixed with the
tinuously withdrawn from the electrolysis device, mixed
anolyte through the interposed diaphragm and not sub
with aluminum triethyl in an amount approximately equiv
stantially interfering with the current transport. For an
economic operation of the process under regeneration of
the used up aluminum alkyl compound, it is however suit
alent to the amount of aluminum separated from the re
moved part of the catholyte and the combined liquid added
to the anode space from which a corresponding amount
able to use also in the cathode space an electrolyte which
contains an aluminum ethyl compound.
If the original catholyte contains the complex com
of anolyte is continuously withdrawn, freed of the lead
tetraethyl and subsequently introduced into the cathode
This removal can be carried out at any given electro
pound NaF.2Al(C2H5)3, then sodium is primarily sepa
rated during the electrolysis. This sodium reacts with
1/sAl(C2H5)3 to 1/3Al+NaC2H5 which upon addition to
lye composition during the electrolysis provided the
catholyte already contains the 1:1 compound and so<
dium aluminum tetraethyl. The higher the concentra
tion of 1:1 compound and sodium aluminum tetraethyl
the diaphragm into the anode space and vice versa so
in the catholyte is, the smaller may be the volumes to
dium ions from the anode space into the cathode space.
be removed. For economic reasons it is suitable to keep
In the course of the electrolysis, more and more
the Withdrawal rates of the liquids to be exchanged as
NaAl(C2H5)4 is formed at the cathode. At the same 40 low as possible. The separation of lead tetraethyl out
time the aluminum triethyl disappears and as a result
sidde the electrolysis device can thus, for example, be
the 1:1 compound is developed from the 2:1 compound.
effected more easily from smaller amounts of anolyte
Suitably the 1:2 compound is thus used at the be
than if the amounts of anolyte to be Worked up are large
ginning of the electrolysis as catholyte. As a result
and obtained at high removal rates. Moreover,_ if the
of the primary separation of sodium at the cathode, the 45 concentration of 1:1 compound and sodium aluminum
immediate reaction with 1/sAl(C2I-I5)3 to sodium ethyl
tetraethyl in the catholyte is high, a higher yield of lead
and 1/3A1 there disappears for each separated equivalent
tetraethyl per volume anolyte can be obtained than if
aluminum 1/aAl(C2H5)3. The simultaneously obtained
these compounds are present in smaller concentrations
sodium ethyl reacts with a further Al(C2H5)3 compound I in the catholyte part to be introduced into the anode
Al(C2H5)3 forms NaAl(C2H5)4 (sodium aluminum tetra
ethyl). At the same time, fluorine ions pass through
to NaAl(C2H5)4.
For each Na(C2H5)4 there thus disappear 4/>,Al(C2I-I5)3,
50 space.
in other words, 4/3 1:1 compound are being formed from
the originally present 1:2 compound. As was just point
In the case of a continuous exchange of the electro
lytes the electrolysis is thus suitably started with the same
electrolyte composition than when working intermit
ed out above, in the anode space on the other hand just
tently. The electrolysis is now continued until the so
one NaAl(C2H5)4 and one NaF.Al(C2I-I5)3 (1:1 com 55 dium ‘aluminum tetraethyl, preferably however the 1:1
pound) react to the 1:2 compound.
compound has approximately disappeared under forma
Upon suitable selection in the composition of the
tion of the 1:2 compound in the anolyte, without exceed
anode and cathode liquids at the beginning of the electroly
ing this limit. From this point on small proportions of
sis there thus exists according to the invention the possi
catholyte are continuously withdrawn from the cathode
bility to regenerate the used up catholyte by addition of 60 space, mixed with an amount of aluminum trialkyl ap
an amount of aluminum triethyl corresponding to approxi
proximately equivalent to the amount of aluminum sepa~
mately the amount of aluminum deposited at the cathode
‘rated from the thus removed liquid amount and passed
which catholyte is subsequently used as anolyte. Vice
into the anode space from which a corresponding amount
versa, there exists the possibility to free the used up lead
of anolyte is continuously withdrawn, freed of the lead
tetraethyl containing anolyte of this lead tetraethyl and 65 tetraethyl and subsequently introduced into the cathode
to subsequently use it as catholyte.
According to the invention, the mutual exchange. of the
anolyte and catholyte may be effected intermittently by
electrolysing one charge until anolyte and catholyte have
the optimum composition for the exchange. Now the 70
entire catholyte is removed, an amount of fresh aluminum
triethyl approximately equivalent to the amount of sepa
rated aluminum added and subsequently introduced as
one charge into the anode space from which the entire
anolyte has been previously removed as one charge. This
The continuous process, as compared with the
intermittent process is thus characterized by the fact
that while both processes start with the same compo
sition of catholyte and anolyte, a stationary state is ob
tained in the continuous process in which the electrolyte
composition in the cathode and anode space are approxi
mately the reverse of the composition at the beginning
of the electrolysis. Contrary thereto, no such stationary
composition of the electrolyte is obtained in an inter
mittent exchange process, where the composition of the
possesses a certain solubility for the formed lead tetra
electrolyte varies intermittently between the two limits
at the beginning and the end of one charge.
ethyl. This solubility is approximately as follows:
Already in the said prior application Serial No.
548,862, it was pointed out that the aluminum trialkyl
—l0° C ________________ __. 3 g. Pb(CZH5)4/l00 cm.3.
10° C _______ -‘. __________ _. 4.5 g. Pb(C2H5)4/l00 cm}.
used for the production of the electrolyte and also the
aluminum trialkyl which is constantly added must be
free from any hydride. This requirement applies also
‘60° C __________________ _. 10 g. Pb(C2H5)4/v100 cm.3.
80° C __________________ _. 12 g. Pb(C2l-l5)4/l00 cm.3.
When working with an electrolyte temperature of 70° C.
in the cell, the anolyte would for example only then sep
arate liquid lead tetraethyl as second phase, it the content
to the process of this invention. It for example even
a small ‘amount of A1R2H is contained in the electro
lyte, the latter becomes immediately dark in colour as 10 of the latter would be above 11%. As a result of the
a result of the reaction with the formed lead tetraalkyl
cyclically ?owing anolyte according to the invention it is
and the formation of lead. The removal of any hy
now easily possible to cool the anolyte outside the elec
dride present may be effected in the manner described
trolysis cell to temperatures wihch are su?iciently low so
in application Serial No. 548,862 by treating the alumi
as not to exceed a predetermined maximum lead tetra
num trialk-yl or the electrolyte with ole?ns at tempera
tures between 60° C and 70° C.
For reasons of economy it is desirable to carry out the
ethyl content in the anolyte liquid. The lower limit of
this low temperature is restricted by the solidi?cation
point of the anolyte which is higher at the beginning of
electrolysis at the highest possible temperatures since
the conductivity of the electrolyte baths used increases
greatly with increasing temperatures. On the other
hand, the upper range of the electrolysis temperatures to
.be used is limited by the ‘fact that in the case of ex
cessively high temperatures, in particular during a pro
longed electrolysis, the electrolyte will again become dark
colored. For the process of the invention, temperatures
between the solidi?cation point of the electrolyte mixture
(in most cases in the range of room temperature and
about 40° C.) and about 110° C. are suitable, tempera
tures between 60° C. and 80° C. are preferred. A tem
operation when there is still a great amount of 1:1 com
pound and NaAl (C2H5)4 present than towards the end
when the composition approaches the 1:2 compound.
On the other hand the solubility of the lead tetraethyl in
the electrolyte is somewhat smaller at the beginning than
at the end.
In case of an intermittent execution of the
process, it is of course equally possible to maintain the
temperature of the total supply of anolyte at about 70° C.
without any separation of lead tetraethyl during the entire
electrolysis. In this case the total lead tetraethyl formed
at the end of the process is still present in dissolved form.
It is then possible to cool the anolyte to such a degree, for
perature of the electrolyte of about 70° C. is particu 30 example —5° C. that the larger proportion of the formed
larly suitable. This temperature permits the safe work
lead tetraethyl is separated out at once. With an anolyte
ing for any length of time without the appearance of any
interfering side reactions in the electrolyte composition.
For short periods of time, somewhat higher temperatures
which contains at the end of the operation approximately
10% lead tetraethyl itis thus possible to separate about
may also be applied.
70—80% lead tetraethyl in pure form.
Subsequent to the separation of the main lead tetra
According to the invention, the liquids used in the
anode and cathode space are cooled during the electroly
ethyl content the electrolytically exhausted anolyte must
in any case be completely freed of any lead before it can
sis in order to obtain a temperature of about 70° C. This
be used as catholyte.
measure is necessary since the speci?c heat of the elec
According to the invention, a particularly suited proc
trolyte is relatively low so that the amount of energy 40 ess for this separation is the liquid-liquid counter cur
added during the electrolysis would excessively increase
rent extraction. The extraction may be carried out in
the electrolyte temperature within a short time. Accord
particular with hydrocarbons, if desired under pressure.
ing to the invention this cooling is effected with particu
An excellent extracting agent is for example isooctane.
lar advantage by working not with stationary but with
The distribution coet?cient, for instance, of lead tetraethyl
?owing electrolytes.
in isooctane and 1:2 compound amounts to 16:1. In an
Substantially larger volumes of anolyte and catholyte
liquids than are required to ?ll the electrode spaces may
extraction with three theoretical steps it is thus very easy
to arrive at a very small lead content of for example 1
mg./ 100 cm.3. The volume of isooctane required for
be separately cycled through these spaces and cooled
this extraction corresponds approximately to that of the
outside the electrolysis device. In this manner, it is pos
sible to regulate the exit temperature of the electrolyte 50 electrolyte, the isooctane dissolving some of the electro
lyte. Upon stripping off the isooctane, the residue sep
liquid by an appropriate selection of flow rate and en
arates, however, into two layers; one consisting of a small
tering temperature of the electrolyte into the electrolysis
amount of electrolyte which is returned to the extraction,
device. In accordance with the invention, the tempera
the other of lead tetraethyl. This type of extraction,
ture di?ference of the electrolyte at the entrance and exit
point amounts preferably to 5° C. in particular to 2-4° C. 55 however, presents the difficulty that as result of the lead
tetraethyl content the density of the extraction agent ap
When working in this manner, there are obtained a num
proximates the density of the electrolyte to such a degree,
ber of further advantages in addition to the easy and re
that during the extraction with the ?rst portion of ex
liable adjustment of the temperature of the electrolyte.
tracting agent the layers separate only slowly, whereas
cooling system in the electrolysis cell which permits the 60 this di?iculty is not encountered with the subsequent por
For example it is not necessary to provide a complicated
construction of the cell in a very compact and economi
cal form.
Furthermore there are obtained other considerable ad
tions used in the extraction.
Thus, according to the invention an extraction agent
is suitably added to the electrolyte in the beginning.
This indifferent agent may be present in amounts of from
vantages for the unimpeded execution of the process of
the invention. it has already been pointed out that as 65 3 to 10% vol. of the electrolyte, the electrolyte being
preferably saturated therewith. The electrolyte absorbs
a result of the higher current densities which are desir
for example 5 cm.3 isooctane per 100 cm.3 electrolyte. By
able for economic reasons, the aluminum is deposited at
a carefully measured addition of a minute amount of addi
the cathode as a loose ?nely divided crystalline powder.
tional extraction agent subsequent to the electrolysis and
According to the invention, this metal powder can easily 70 by cooling to, for example 0° C. it is possible to more
be scraped from the cathode and subsequently discharged
easily extract larger amounts of lead tetraethyl. imul
from the electrolysis device together with the flowing
taneously the volume of the lead tetraethyl to be sep
catholyte. The operation in the anode space is also
arated is thus increased. This constitutes an additional
considerably simpli?ed as a result of the cyclical anolyte
advantage of the process according to the invention since
?ow according to the invention. The 2:1 electrolyte 75 experience has shown that the extraction of a small
amount of a second layer from a large amount of a ?rst
layer presents certain difficulties. Since only negligible
amounts of extraction agents are used up during the ?rst
step of the improved extraction of lead tetraethyl from
the anolyte, it is thus possible to carry out a same number
of further extractions, for instance, ?ve with the same
total amount of extraction agent.
When proceeding in this manner, and using for exam
ple isooctane as extraction agent for the separation of lead
in accordance with the invention. With the help of at
least one additional diaphragm, a center space for the
reception of an electrolyte can be formed between the
anode and cathode spaces. An electrolyte, which pref
erably does not contain any lead, can be conducted
through the center space in a slow stream. It absorbs the
lead tetraethyl portions transferring over from the anode
space and carries them immediately out of the electrolysis
In this manner, the catholyte can also be reli~
tetraethyl, the ?nal concentration of lead tetraethyl in the 10 ably protected against the diffusion of any lead com~
electrolyte amounts to about only one-?fth of the amount
obtained if the extraction agent is not admixed with the
electrolyte in the beginning.
The remaining traces of lead in the anolyte can be re
moved by an after-treatment of the anolyte, for instance
with a small amount of ?nely divided aluminum, the ?nely
divided aluminum obtained from the process itself being
particularly suitable since it shows a high activity for this
As has already been pointed out, the carrying out of
the process according to the invention requires a reliable
separation of catholyte from anolyte without, however,
substantially interfering with the current transport. Ac
cording to the invention, this is accomplished by separat
ing the cathode from the anode space by the use of at
least one diaphragm. In principle any material may be
used for this purpose which under the operating condi
tions prevailing in the electrolysis device will preserve its
stability against the relatively corrosive electrolyte over
pounds. After leaving the electrolytic cell, the electrolyte
?owing through the center space may, if necessary, be
puri?ed from any lead by addition of traces of ?nely
divided aluminum, suitably from the process itself, and
subsequently recycled.
The operation of the anode space during the elec
trolysis is relatively simple. It is merely necessary to
replace the used up proportions of lead by fresh lead.
This may, for instance, be readily accomplished by feed
ing lead rods through an opening provided for this pur—
pose into the anode space in the same amount in which
they are being used up during the electrolysis.
At the cathode, aluminum is deposited during the
electrolysis. Without any special precautionary measures,
this aluminum would be deposited at the cathode in the
form of crystals and might conceivably thus increase the
volume of the cathode until it reaches the diaphragm
which it may even pierce. It is therefore necessary to
prevent this accumulation of large amounts of aluminum
a longer period of time and the selective effect of which 30 crystals at the cathode. Good results are obtained, for
su?ices to retain the larger ions and the aluminum and
lead ethyl compounds and complexes in their respective
electrode spaces without any substantial interference
with the current transport by the smaller sodium and
?uorine ions.
It has been surprisingly found that cellulosic products
are a suitable material for these diaphragms, and are re
sistant against the chemical effect of these electrolytes
even at temperatures of about 100° C.
example, by the provision of mechanical stripping means
such as rods, grids, frames, etc. with cathode and stripping
means are moved relatively to each other. Thus, it is
possible to maintain the cathode stationary and to move
the stripping means or to ?x the stripping means and to
move the cathode. However, it is equally possible to
effect the removal of the aluminum from the cathode by
means of hydraulically working stripping means. At the
All types of
higher current densities the aluminum is depos
porous cellulosic products with sufficiently small pores 40 required
cathode in~?nely divided form and by selecting
may thus be used. It is preferred to use ?lter paper as
flow rate of the catholyte, the ?nely divided
diaphragm material. Suitable are for example materials
of which a round ?lter with a cross section of 15 cm.
shows a ?lter rate for 100 cm.3 distilled water at 20° C.
and a height of the column of water of 6 cm. in the range
of 30 to 200 see. A particularly suitable material is ?lter 45
paper which has been compacted or chemically impreg
nated in order to reduce the size of the pores. In this
manner, it is possible to use diaphragms with a thickness
aluminum can be separated from the cathode and re
moved from the electrolysis device by the ?owing elec
This hydraulic effect may, if necessary, be
enhanced by adding mechanically acting stripping ele
ments, such as small balls of glass or metal to the elec
trolyte which are then carried along in the circulating
stream. During this circulation, these balls strike the
loose aluminum powder at the cathode and remove it.
of only a few tenths of a mm. In order to increase the
mechanical resistance, these diaphragms may be rein 50 These mechanically working stripping elements are sepa
rated from the aluminum particles contained in the elec
forced by a ?lter consisting of cloth or by inserting the
trolyte outside the electrolysis device.
diaphragm between a fabric such as cotton. Other suit
Occasional troubles connected with the removal of the
able diaphragm materials are for instance glass ?ber webs
aluminum from the cathode which might still occur, can
or fabrics.
be corrected by cleaning the cathode completely by means
Any slow transfer of the anolyte into the cathode
of a temporary reversal of the direction of the current
chamber through the diaphragm which may possibly still
and without necessitating any complicated mechanical
occur can easily be eliminated by maintaining a de?nite
such as the dismantling of the electrolysis
difference in the electrolyte levels. This difference in
level is adjusted in such a manner that during the entire
In order to facilitate the removal of the aluminum
process a slow ?ow from the cathode into the anode (if)
the cathode, the cathode is suitably so developed
space through the diaphragm is maintained or that this
that larger amounts of aluminum can only be deposited
difference in level prevents at least a transfer of the
at the cathode with difficulty. Thus, continuous metal
anolyte into the cathode space. The di?ference in level
plates are suitably not used as cathode, but the cathode
to be maintained depends upon the pore size of the dia
65 is preferably constructed in such a manner that it con~
phragm so that with a diaphragm with very ?ne pores
sists of individual metal segments inserted in a carrier
a lower difference in level can be chosen than in the
plate. According to the invention, the cathode may,
case of a diaphragm with coarse pores. Inasmuch as the
for example, consist of metal wires embedded in a frame
total electrical resistance of the cell on the other hand
plate, preferably in oblique direction. The use of these
is largely dependent upon the pore size of the diaphragm, 70 metal wires provides for a particularly high current
the best technical effect consists in a compromise between
density in the conductive parts of the cathode thereby
these opposing in?uences which can very easily be estab
increasing the deposition of aluminum in ?nely divided
lished by a few experiments.
form. Moreover, the aluminum can accumulate only at
Alternatively, the reliable separation of anode and
cathode space may be obtained bylan auxiliary measure
these metal wires. If, for instance, mechanical scrapers
are used, this ?nely divided aluminum, can be spread over
mechanical movement are suitably moved together for
example by a lever system.
An electrolysis device suitable for the technical execu
the whole carrier plate. But by appropriate choice of
the material of which the carrier plate consists the adher
ence between aluminum and carrier plate can be so
tion of the process is diagrammatically shown in FIG. 1.
This device has the anode 1 and cathode 2 in the form
minimized that the aluminum is easily removed therefrom.
Any materials may be used for the construction of
cathode plate and the electrolysis device as a whole,
which are not electrically conductive and which permit
the safe carrying out of the electrolysis with the highly
of frame shaped plates which are stacked in alignment
side-by-side, separated by the diaphragms 3 and 4. A
whole series of alternately positioned anode and cathode
plates 1 and 2, each separated by a diaphragm, such as
reactive and self-in?ammatory electrolytes without giving
any chemical change in the materials themselves or in 10 diaphragms 3 and 4, may thus be positioned together
allowing a combination of individual electrolysis cells.
the electrolytes. Particularly suitable materials for the
The plates may be pressed together in position in any de
electrolytic cells and the carrier plate of the cathode are
sired manner as, for example, in the manner of a ?lter
laminated press materials of synthetic resins, especially
press, and at each end there may be positioned an end
Bakelite (phenol formaldehyde) resins, which may be
strengthened with fabrics in order to increase their elas 15 plate such as the end plate 5 made of insulating material
as, for example, synthetic resin orthe like. The hollow
ticity. This material permits the easy construction of
spaces in the interior of the frames serve to hold the
the individual parts of the cells which have to be very
electrolyte liquid and suitable openings or conduits may
carefully executed. Another suitable material is for
be provided through the tops and bottoms of the frames
example wood impregnated with polyethylene or with
for the introduction and withdrawal of the electrolyte.
high melting para?ines. According to the invention,
The anode plate is, of course, a lead-containing plate, and
annealing lacquers of an epoxy resin have proven them
the cathode plate may be formed, for example, of an in
selves as particularly suitable protection for those metal
sulating material, such as synthetic resin, or the like having
parts not designed for current transfer to the electrolyte.
bodies such as wires, or the like, of the conducting metal
As has already been pointed out, the conductivity of
the electrolyte according to the invention increases with 25 of the cathode, such as iron, aluminum, copper, brass, or
the like, embedded therein. It is also possible to press
increasing temperatures. However, in the process of the
suitable gaskets or packings of electric insulating material
invention the conductivity of the electrolyte mixture is
between the individual frame plates, such gaskets serving
restricted by the mentioned limitation of the reaction tem
to prevent leakage of the electrolyte, and to insulate the
peratures to about 70° C. At the reaction temperatures
plates one from another.
to be used in accordance with the invention, the resistance
As has already been mentioned, the carrying out of the
of the electrolyte is still comparatively high. Inasmuch
process according to the invention is however not limited
as the voltage in the electrolysis cell should not exceed
to an electrolysis device of this type. Any device may
2-10 volts, and preferably not 5 volts for reasons of limit
be used which prevents the comingling of anolyte and
ing the consumption of electrical energy and furthermore
since for various reasons higher current densities of about
Inasmuch as the electrolyte used in accordance with
3—15 amperes/dmF, preferably 5-10 amperes/dm.2 are
the invention is extremely oxygen-sensitive and self-ignit
preferred (separation of aluminum in form of ?nely di
ing it is preferably to carry out all operations in an inert
vided powder, restriction of size of cells, etc.) it is clear
that one must Work with electrodes which are spaced rela
tively closely together. Otherwise, it is either necessary
The invention will be described in further detail in the
following examples which are given by way of illustration
to increase the voltage excessively or to reduce the current
density too much. According to the invention, a distance
between the electrodes of about 1 cm. is particularly suit
and not limitation. In these examples the following com
pounds are used for the electrolytes:
able. At the reaction temperatures to be used one can
then work with a voltage of about 5 volts and a current
(a) Sodium aluminum triethyl ?uoride (NaAl(C2H5)3F)
(b) Sodium ?uoride aluminum triethyl (1:2 compound)
density of about 5 amperes/dm.2. It is equally possible
to select smaller distances between the electrodes for
the electrolysis.
(0) Sodium aluminum tetraethyl (NaAl(C2H5)4)
These three compounds are self-igniting and must there
_ In the technical application of the process according
to the invention the combination of the largest possible 50 fore be handled in an inert atmosphere. The compounds
(at) and (b) are obtained by mixing sodium ?uoride and
number of individual electrolytic cells in such a manner
1 mole or 2 moles aluminum triethyl at 120° C. for one
that they can be simultaneously operated in a simple way
hour with stirring. Compound (0) is obtained by mixing
is recommended. Practically all devices which permit
aluminum triethyl at 125° C. with metallic sodium in a
the simultaneous operation of any desired number of
electrolysis cells are thus suitable. Preferably the cathode ' molar ratio of 4:3 with stirring followed by separation of
the deposited aluminum from the melt (cf. A. von Grosse
spaces are connected with each other and anode spaces
are connected with each other in such a manner, that
electrolyte liquid from all of the cathode spaces is passed
and J. M. Mavity, Journal of Organic Chemistry 5, 1940,
page 111).
The electrolysis device used in the examples con
to and recycled back from a common supply and in the
sists in the simplest case as shown in FIG. 2 merely of a
same manner electrolyte liquid from all of the anode 60 lead plate 5 as anode and an equally large plate 6 consist
spaces is passed to and recycled from a common supply.
ing of a different metal,~such as iron, aluminum, copper
The cooling and if necessary treatment of the electrolyte
or brass as cathode. Anode and cathode are disposed
can be effected at these common supplies. In a fully con
parallel to each other and spaced 1 to 2 cm. apart. The
tinuous process in which a certain proportion of anolyte
plates are surrounded by an electrically insulating mate
and catholyte is continuously withdrawn and passed after
appropriate preliminary treatment to the other electrode
space, the electrolyte proportions to be exchanged are
suitably each taken from a different one of the common
supplies, the anolyte freed of tetraethyl lead; the catholyte
mixed with the necessary amount of aluminum triethyl and
each, subsequently introduced into the other common
rial corresponding to the plates in shape and form forming
for example the container 8. In the middle between the
two plates and parallel to them there is a thin diaphragm
7, dividing the container into spaces 9 and M. It is suit
ably formed of ?lter paper which is protected on both
sides by a fabric consisting of cellulose or glass ?bers. In
the space M between diaphragm and cathode there is
arranged a frame 11 which is covered with electrically
In this combination of individual electrolysis cells into
insulating stripping wires 12, this frame being moved to
one large electrolysis device the parts which require 75 and fro when in operation. Anode and cathode spaces
have openings through which liquid electrolytes may be
free of any lead compound. The electrolyte now has
introduced from the top and discharged at the bottom.
the composition NaF.2Al(C2H5)3 and may be safely used
In the case of larger runs several individual cells are suit—
ably combined as shown in FIG. 1. In that case, anodes
and cathodes are utilized on both sides (apart from the
as catholyte for a new electrolysis.
The extract containing 1.8 kg. lead tetraethyl is com
bined with the lower phase obtained by the cooling of the
anolyte. Its content of organo~aluminum compounds is
?rst and the last element). The frames may be provided
with apertures at the top through which it is possible to
low and amounts to about 600 g. NaF.2Al(C2I-I5)3. The
isooctane used as extraction agent is distilled off in vacuo
move the stripping means in the cathode spaces and to
replace the lead plates in the anode spaces. It the lead
at a pressure of 70 mm. Hg at 50° C. and can be used
plates have a thickness of 0.5 to 1 mm. it is easily possible 10 for further extractions. The lead tetraethyl is subse
to replenish the lead continuously. It was found to be
quently distilled oil in vacuo at 45 ° C. and 0.5 mm. Hg;
suitable to use in place of cathodes consisting of massive
the distillation residue of about 600 g. NaF.2Al(C2H5)3
metal plates equally large cathodes consisting of electri
is recycled into the next extraction.
cally insulating material in which obliquely disposed metal
At the end of the electrolysis the catholyte has the
wires are embedded.
All runs described in Examples 1 to 4 are carried out
in an inert atmosphere of nitrogen or argon.
Example 1
The catholyte consists of the compound
NaF.2Al ( C2H5 ) 3
The anolyte is obtained by mixing
14.85 kg. NaAl(C2H5)4 (c)
13.87 kg. NaA1(C2H5)3F (a) and
40.78 kg. NaF.2Al(C2H5)3 (b)
Anolyte (69.5 kg.) and catholyte (64.8 kg.) are ?lled
following composition:
14.84 kg. NaAl(C2H5)4
18.50 kg. NaAl(C-2H5)3F
amounting to a total of 66.15 kg. This mixture is stirred
with 3.4 kg. aluminum triethyl; the thus obtained reac
tion product consists of
14.85 kg.NaAl(C2H5)4
into two storage chambers (13 and 14) above the con
(a total amount of 69.5 kg.) and can be used as anolyte
tainer 8 and heated to 70° C. The anode 5 has a free
for a new electrolysis.
surface of 25 dm.2. Anolyte and catholyte are allowed 30
The yield in lead tetraethyl amounts to 6.9 kg, i.e. 96%
to ?ow through the anode space and the cathode space
of the theoretical value at a used current quantity of
respectively of the electrolysis device. The ?ow rate
2400 amperes/ hr.
amounts to approximately 4 liters per minute. The
Example 2
aluminum formed at the cathode 6 is scraped by the 35
mechanically moved stripping means 11 and carried out
The process of Example 1 is repeated, the catholyte
‘of the device in the liquid stream. The electrolysis is
being again NaF.2Al(C2H5)3. The anolyte, however, has
the following composition:
carried out with an amperage of 200 amperes, or a cur
rent density of 8 amperes/dmF. The terminal voltage
amounts to 8 volts. The resulting heat due to the cur 40
rent causes an increase in temperature of 3 to 4° C. in
the electrolyte e?luent, as compared to the entering elec
trolyte. The anolyte ?owspthrough the line 15 into a
storage vessel 16 from .where it is pumped by the pump 17
through line 18 into the upper storage chamber 13. Upon
leaving the electrolysis device the catholyte is ?rst led
At a current passage of 100 amperes and a terminal volt
age of 6 volts the anolyte is exhausted after 48 hours.
The isolation of the lead tetraethyl is effected in the same
Way as in Example 1. The lead tetraethyl yield amounts
to 14.1 kg. or 98% of the amount calculated for 4800
ampere hr.
through line 19 into a cylindrical separating chamber or
settlingv tower 20‘ where the electrolytically separated
aluminum which is carried along in the ?owing catholyte
is separated. The catholyte freed of the aluminum ?ows
through line 21 into a storage chamber 22 from which
it is recycled through line 23 into the upper storage cham
Upon completion of the run any liquid electrolyte still
present in the separation vessel 20 is siphoned oif from
the deposited ?nely divided aluminum. The aluminum is
suspended in 13.5 kg. aluminum triethyl and transferred
ber 14 by means of pump 24. The heat loss in the entire
device is so considerable that a special cooling of the
electrolyte is in general not required. However, if neces
sary, it may be effected in the upper storage chambers
13 and 14.
At a current passage of 200 amperes, the anolyte is
29.7 kg. NaAl(C2H5)4
27.7 kg- NaA1(C2H5)sF
12.1 kg. NaF.2Al(C2H5)3
into a rotating autoclave with a capacity of 50 liters.
A pressure of about 250 atmospheres electrolytic hy
drogen is applied and the autoclave heated to 120° C.
and rotated. After about 2 to 3 hours the pressure has
decreased by 200 atmospheres and remains constant after
exhausted after 12 hours of electrolysis. The 72.0 kg.
that. The reaction is ?nished. After cooling, excess hy
anolyte are mixed with 10 liters dry isooctane and cooled 60 drogen is blown off. Subsequently a pressure of 20 to
30 atmospheres ethylene is applied and the autoclave
to 0° C. Hereby, the anolyte separates into two phases.
again heated with rotation to 60 to 65° C. The appli
The lower layer of 9.65 kg. consists of 5.1 kg. lead tetra
cation of ethylene pressure is repeated several times.
ethyl and 4.55 kg. isooctane. The upper layer is com
posed as follows:
After three hours the addition of ethylene is ?nished.
65 After blowing oil the excess ethylene a small sample of
64.8 kg. NaF.2Al(C2H5)3
aluminum triethyl is taken from the autoclave and mixed
1.8 kg. Pb(C:,_H5)4 and
with a few drops of lead tetraethyl. If this sample does
2.5 kg. isooctane
not become dark in color as a result of the precipitation
Upon addition of isooctane and cooling to 0° C. it is
of lead, then the aluminum triethyl obtained does not
thus possible to separate 75% of the formed lead tetra
ethyl from the anolyte. The electrolyte which still con 70 contain any diethyl aluminum hydride and can be used
for the regeneration of the electrolyte. If the sample still
tains lead is now extracted with 32.4 liters isooctane in
becomes dark colored the treatment with ethylene has to
a 3-step extraction centrifuge in a countercurrent. Upon
repeated. There are obtained 20.23 kg. aluminum
completion of the extraction, the electrolyte still contains
triethyl, i.e. 6.73 kg. or 100% of the theoretical value
about 3 g. Pb(C2H5)4/65 liters. it is thus practically 75 have been formed.
The 6.73 kg. aluminum triethyl are admixed to the
catholyte which has then the following composition:
5. Improvement according to claim 4 in which about
0.67—1.70 moles of NaF.2Al(C2I-I5)3 are present per
29.7 kg. NaAl(C2H5)4
mole of NaF.Al(C2H5)3 and in which the electrolysis is
effected with about 50 ampere-hours/kg. electrolyte.
6. Improvement according to claim 1 in which the
12.1 kg. NaF.2Al(C2I-I5)3
electrolysis is continued until one of said NaAl(C2H5)4
it is then ready to be used ‘as anolyte during the next
and NaF.Al(C2H5)3 has been substantially completely
Example 3
Example 1 is repeated using the arrangement shown
7. Improvement according to claim 1 which includes
substantially continuously removing anolyte from said
anode space and substantially continuously replacing the
removed anolyte with fresh anolyte.
in FIG. 3.
fter passage of 2400 ampere hr., i.e. of
200 amperes during an electrolysis of 12 hours a liquid
8. Improvement according to claim 1 which includes
stream is branched otf from the cathode cycle at 25 at a
maintaining as the electrolyte in said cathode space a cath
rate of 5.5 kg./ hr. To this a stream of aluminum triethyl 15 olyte comprising NaF.2Al(C2H5)3.
is admixed from container 26 at a rate of 284 g./hr.
9. Improvement according to claim 1 which includes
The mixture is allowed to ?ow through line 27 into the
at least initially maintaining as the electrolyte in said
upper storage tank 13. Simultaneously a liquid stream
cathode space a catholyte essentially consisting of a mix
of 6.0 kg./ hr. is removed from the anode cycle at 28 and
tlll'? 'O‘f
and NaF.Al(C2H5)3.
10. Improvement according to claim 1 in which an
cooled to 0° C. in cooler 29. The lower phase formed 20
aluminum triethyl containing electrolyte is maintained in
is separated and subjected to a continuous counter-cur
rent extraction in the extraction centrifuge St}. The
electrolyte now free of any lead is led through line 31 to
the upper storage chamber 14 for the catholyte. Under
these circumstances the electrolysis may be continued as
long as desired.
Example 4
If the electrolytically deposited aluminum is not to be
said cathode space as catholyte and which includes after
at least partial exhaustion thereof regenerating the cath
olyte by the addition of an amount of aluminum triethyl
substantially equivalent to the amount of aluminum de~
posited at the cathode.
11. Improvement according to claim 1 which includes
removing exhausted anolyte from said anode space, free
ing the same of tetraethyl lead and recycling the same
used for the production of aluminum triethyl but is to
to said cathode space .as catholyte.
‘be recovered as re?ned aluminum, the following modi 30
12. Improvement according to claim 1 which in
?cation of the process is possible:
cludes substantially continuously removing anolyte from
The process is carried out as described in Examples 1
said anode space passing the same to a body of excess
‘to 3. Upon extraction of the anolyte with isooctane the
anolyte and recycling anolyte from said body back to
electrolyte still contains about 40 mg. lead tetraethyl
staid anode space and which includes substantially con
per liter. If this electrolyte is now used as catholyte the
tinuously removing catholyte from said cathode space
separated aluminum will always contain traces of lead.
In order to free the electrolyte of the small amounts of
lead compound, the anolyte is intensely stirred about
half an hour at 70° C. after the extraction with about
80 g. of the electrolytic aluminum.
Subsequently the
aluminum is allowed to settle. The electrolyte is si
phoned off. No lead earl be found in the electrolyte by
chemical-analytical determination; this may then be used
in the subsequent electrolysis as catholyte. The alumi
num used for the precipitation of the last traces of lead
can be repeatedly used for the same process. This oper
ating step is suitable also if the aluminum is to be con
verted again to aluminum triethyl since an aluminum
completely free of any lead reacts more quickly with
passing the same to a body of excess catholyte and sub
stantially continuously recycling catholyte from said
body back to said cathode space.
13. Improvement according to claim 1 in which the
catholyte maintained in the cathode space is a sodium
aluminum tetraethyl-sodium ?uoride aluminum triethyl
containing catholyte and which includes substantially
continuously removing catholyte from the cathode space,
and mixing an amount of aluminum triethyl therewith
substantially equivalent to the amount of aluminum
separated therefrom during the electrolysis and there
after passing the removed catholyte with the added
aluminum triethyl to the anode space and which includes
substantially continuously removing a corresponding
aluminum triethyl and hydrogen.
50 amount of anolyte from said anode space freeing the
We claim:
same of tetraethyl lead and passing the same into the
1. In the process for the electrolytic production of
tetraethyl lead by passing an electrolysis current between
14. Improvement according to claim 1 which includes
a cathode and lead containing anode through an alumi—
num triethyl containing electrolyte, the improvement 55 removing formed tetraethyl lead from the anolyte by
coo‘ing to a temperature of at least about 0° C.
which comprises maintaining a diaphragm between the
15. Improvement according to claim 1 which includes
cathode and anode to thereby form separate cathode and
removing tetraethyl lead formed during the electrolysis
anode spaces and at least initially maintaining as the
electrolyte in said anode space an anolyte essentially
from the anolyte by cooling to a temperature of at least
0° C. followed by extraction with an extraction agent.
consisting of NaAl(C2H5)4 and NaF.Al(C2H5)3, said 60
16. Improvement according to claim 15 in which said
NaAl(C2H5)4 and NaF.1>il(C2H5)3 being present in sub
extraction agent is isooctane.
stantially equivalent amounts, said diaphragm substan
17. Improvement according to claim 16 which in
tially preventing migration of electrolyte between the cath
ode and anode spaces without substantially interfering
cludes maintaining an amount of isooctane up to the
with the passage of said current.
2. Improvement according to claim 1 in which said
saturation quantity thereof in the anolyte during said
18. Improvement according to claim 1 in which the
maintained in the cathode space is an alumi
3. Improvement according to claim 2 in which
num triethyl containing catholyte, and which includes
NaAl(C2H5)4 and NaF.Al(C2H5)3 are present in sub
stantially equivalent amounts and in which about 0.16 to 70 stripping deposited aluminum from the cathode and sub
stantially continuously removing catholyte from the
1.70 moles of NaF. 2Al(C2H5)3 are present per mole of
anolyte additionally contains NaF.2Al(C2H5)3.
cathode space carrying therewith entrained, the stripped
4. Improvement ‘according to claim 3 in which not
19. Improvement according to claim 1 in which said
more than about 331/3—662/s ampere-hours/kg. electrolyte
are used for the electrolysis.
75 electrolysis is effected under an inert gasatmosphere.
20. Improvement according to claim 1 in which said
electrolysis is effected with a current density of between
References Cited in the ?le of this patent
about 3 to 15 amp./dm.2.
21. Improvement according to claim 1 in which said
anode and cathode are frame-shaped plates positioned 5
side by side in alignment with said diaphragm sand—
Wiched therebetween_
22. Improvement according t0 claim 21, 111 which
said frame plates are at least partially formed of ?ber
reinforced synthetic resin.
Hgopes ____________ __ Apr’ 25,
Blcck ______________ __ N0“ 21,
Bodamm- ____‘________ __ Man 6,
Ziegler et al. ________ __ July 22,
Ziegler et aL ________ __ Aug. 26’
smith ______________ __ Dec. 9,
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