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Patented Nov. 19,’ 1946
2,411,346 ‘
John W. Teter and Walter J. Merwln, Chicago,Iil.,
assignors to Sinclair Re?ning Company, New "
York, N. Y., a corporation of Maine
No Drawing. Application October 6, 1943,
Serial No. 505,196‘ ,
3 Claims.
This invention ‘relates to the re?ning of
nitriles and relates more particularly to an im
proved method. of separating hydrocarbon im
purities from nitriles of three to four carbon
atoms per molecule, 1. e. propionitrile and butyro
These nitriles may with advantage be pre
pared by the amination of ole?nic hydrocarbon
(Cl. 202-42)
carbon impurity from the other nitriles noted '
may be readily effected by distillation.
Utilizing this peculiarity of acetonitrile and
the hydrocarbon contaminant to form a readily
separable azeotrope in the presence of propio
nitrile and butyronitriles', the processing of our_
presentinventlon comprises adding acetonitrlle
the nitrile-hydrocarbon mixture and, frac
at an elevated-temperature. The crude, stabi- ' to
tionally distilling the mixture to separate the
lized nitrile product of such amination isusually 10 acetonitrlle-hydrocarbon
azeotrope from ‘the
composed primarily of a mixture of propionitrile, ‘ other nitriles.
proportion of aceto
iso-butyronitrile, and normalibutyronitrile and
nitrlle to be added will depend primarily upon
frequently contains hydrocarbon impurities.
the proportion of the hydrocarbon contaminant
These nitriles may be isolated by close fractional
distillation of the crude product. However, the 15 Most of the hydrocarbon readily separates
thus isolated nitriles are frequently contaminated ,
by hydrocarbons which distill off within the same
temperature range as the nitrile and which pass
fromthe acetonitrlle constituent of the azeotrope '
fraction as an upper layer uponvcooling the frac
tion to room temperature and more may be re
over with the respective nitriles from the frac
moved by chilling. The lower acetoni'trile layer
tionating operation in varying amounts, as an 20 will
contain most, if not all, of any propionitrile
over with the azeotrope fraction and may
The complete separation of such hydrocarbon
be recycled with the decanted acetonitrlle to'the
impurities from these nitriles by direct fractional
nitrile puri?cation tower. The upper hydrocar
distillation has heretofore been extremely di?i- , bon layer will usually contain about 1.5% of dis
cult, if not impossible.
,- solved acetonitrlle, at room temperature. This
Our present invention provides a method
acetonitrlle may be recovered by water washing,
whereby substantial complete removal of these
hydrocarbon, impurities from these nitriles. may
be effected by direct fractional distillation.
dried and returned to the nitrile purification
The invention has also been found to be ap
We have discovered that the hydrocarbon con 30 plicable to the direct puri?cation of a stabilized
taminant of the nitrile fractions forms an azeo
mixed nitrile product resulting, for instance,
trope with acetonitrile in the presence of the
from the catalytic amination of propylene. This
otherrespective nitriles, which azeotrope'has a
product, as previously noted,_ usually contains
boiling point substantially below that of these
various nitriles along with hydrocarbon im
other nitriles and may be separated therefrom 35 purities and sometimes contains small amounts
by fractional distillation without substantial loss
of acetonitrile. In accordance with this aspect
of the other nitriles.
of my invention the hydrocarbon impurities may
The boiling point of pure propionitrile, for ex
be removed directly from the nitrile mixture
ample, is approximately 97° _C. and that of pure
prior to isolation of the respective nitriles. Usu- -
acetonitrile is 82° C. The azeotrope formed by 40 illy the amount of acetonitrile present, if any, is
, acetronitrile and the hydrocarbon contaminants
insu?‘icient to carry o?’ completely the hydrocar
has been found to boil slightly below 82° C.. at
atmospheric pressure.
bon impurities. Accordingly it is usually neces
sary to add to the mixture acetonitrlle from an
‘ Further, theacetontrile has been found not to
extraneous source. However, wev have found that
form binary azeotropes with anymaterial quan 45 the proportion of acetonitrile in the stabilized
product can be regulated somewhat by the choice
tity of either of the other nitriles previously noted
of the catalyst used and other operating condi
herein, or ternary azeotropes with these nitriles
tions of the amination process. By this applica
and the hydrocarbon impurities, to any substan¢
tion of my invention the hydrocarbon impurities
tial extent. A small amount of propionitrile may
be carried over with ‘the acetonitrlle “but this v50 are distilled from the mixture with the aceto
amount is so small as to have little aifect on the \ nitrile and thereafter propionitrile and the
e?iciency of the operationeven if not subse-, . butyronitriles substantially free from hydrocar
bon impurities may be directly obtained.
quently recovered. Thus substantially complete
Our present invention contemplates either'
removal of the added acetontrile and the hydro 65
batch or continuous operation. In either type of
an equal volume of acetonitrlle, no extraneous
' operation, the acetonitrlle layer of the azeotrope
' bottoms being added. The acetonitrlle-hydro
'carbon fraction came o? at a temperature of 4
fraction is with advantage recycled to the nitrile
puri?cation zone to carry off further hydrocar
bons. In this way the acetonitrlle requirement
80.5-81° C., the temperature remaining substan
tially constant until about 50% of the charge was
distilled off and then rapidly rising to 101° C.
and ?nally gradually rising to 102° C. There
'fractive index of‘ the acetonitrlle-hydrocarbon
is considerably reduced. Intermediate fractions
may [also be recycled for further puri?cation.
In small scale operation, particularly, we have
found it frequently desirable to add, in addition
fraction at 20° C. was 1.3462 but toward-the end
to the acetonitrlle, ‘a portion of astable higher
boiling liquid to constitute a residual liquid in 10 of the cut dropped to 1.3441, approximating that
of pure acetonitrile and indicating that the hy
' the still, which will not be decomposed or dis
drocarbon impurities of the mixture had become
tilled off at the distillation temperature of the
nitriles or of the azeotrope. and which will not _ exhausted and that - more than the required
amount of acetonitrlle had been added. The niinterfere with separation of the acetonitrile-hy- _
drocarbon azeotrope from the mixture. We have 15 trogen content of the iso-butyronitrile fraction
foundcapronitrile, for instance, to be satisfac
tory for this purpose. By-its use, danger of poly
merizing and coking of the nitrile being distilled
is substantially avoided and a more complete re
covery of the nitrile is made possible. However, 20
was-19.3% and its refractive index was 1.3731,
substantially that of pure iso-butyronitrile, indi-.
cating complete removalof the hydrocarbon im
purities therefrom. About 820 cc. of the pure iso
butyronitrile was thus obtained, Its speci?c
' gravity was found to be 0.7712.
it will be understood that the use of such ex
traneous bottoms material is not essential to our '
puri?cation process.
The invention will be illustrated by the follow
ing specific examples:
- Example IV
25. To 100 cc. of a’ crude stabilized mixed nitrile
product, resulted from the direct amination‘of
propylene there, there was added 50 cc. of aceto
nitrile, The ‘mixture was then subjected to frac
Example I
A synthetic mixture was prepared from 20 cc.
tional distillation in‘ a 9.5 millimeter Stedman
of pure propionitrile, having a refractive index
of 1.3662 at 20° C., and 2.8 cc. of hydrocarbons 30 column.
Approximately 44 volume percent of the mix-
separated from hydrocarbon-contaminated pro
pionitrile by chilling it. To this mixture there
ture distilled off at?a temperature below 82° 0.,
was added 50 cc. of acetonitrile and the entire
mixture was subjected to fractional‘distillation
in a 9.5 millimeter Stedman column. The aceto
nitrile-hydrocarbon‘ fraction distilled off-at a
substantially constant temperature beginning at
78° C. and ?nally rising to about 81°C., indicat
29 volume percent of the charge was distilled off,
the distillate separated into two layers upon cool
ing to room temperature. The refractive index
' of the upper layer at 20° C. rose ‘from 1.412 to
ing‘exhaustion of the hydrocarbon contaminant.
‘ 1.420.
including 7.5% of material distilling oif below _
75° C. Between the point where 7.5 to that where ‘
Thereafter the distillate no longer sepa
The propionitrile fraction distilled off at about 40 rated upon cooling to room temperature and the
refractive index of the distillate fraction dropped
96°v C. and was foundlto ‘be substantially free
sharply to ‘1.351 and ?nally to 1.3450 at a tem
from hydrocarbon impurities as indicated by a
perature of 82° C., indicating that the hydrocar
nitrogen content of 24.6% and a refractive index
bon impurities, originally present in, the mixture,
of 1.366‘ at 20° C., which is substantially that of
the propionitrile used in the preparation of the 4: had been substantially exhausted and relatively
pure acetonitrlle was being distilled off.
synthetic mixture.
After about 44 volume .per cent had been‘ dis
Example II ‘
tilled off the temperature rose sharply to 94° C.
and at 94 to 96° C. a fraction was obtained hav
4160 cc. of a normal butyronitrile'product, con-4
taminated with hydrocarbons and having a re 5'0 ing a refractive index‘ of .l.3655'and a, nitrogen
content of 24.1%, indicating that it was rela
fractive index at 20° C. of _ 1.3850 and a nitrogen
tively pure propionitrile. Finally at 116.5° C. a
content of 19.3%, was subjected to fractional dis
fraction was obtained having a refractive index
tillation in a two inch Stedman column with an
at 20° C. of 1.3840 and containing 19.4% nitro
equal volume of acetonitrile. In this distillation,
1930 cc. of capronitrile also was added toact as 5 gen, indicating that it was substantially pure
normal butyronitrile. Thus, ‘by our improved
an extraneous bottoms. The acetonitrlle-hy
process, the respective nitriles, uncontaminated
drocarbon fraction distilled off at a temperature
of 80 to 81° C.,‘ the temperature ?nally rising
by hydrocarbons may be obtained directly from
a crude mixture of the nitriles containing hydro
gradually to 82° C. for a brief period indicating
exhaustion of the hydrocarbon impurity. from the 60 carbons.
The hydrocarbon contaminant normally pres .
sharply to 114° C. and then gradually to 118° C.
' ent in these nitrile products has been found by
.1 mixture.
analysis to consist of about 12.6% paramns, 64%
40% of the charge, excluding the extraneous bot
ole?ns, 20.6 naphthenes, and " 2.8% aromatics. ~
toms, was obtained andv this fraction was found 65 The identity and composition of the hydrocarbon ‘
to contain approximately 20% nitrogen and to
contaminants may vary somewhat. However, we
have a refractive index of 20° C. of 113840, indi
have consistently found them to be substan
cating itjto be substantially pure normal butyr
tially completely removable from propionitrile or '
In this last mentioned temperature range over
‘Example III
1390 cc. of an iso-butyronitrileproduct, con
taminated with hydrocarbon and‘ having a re
. fractive index ‘at 20° C. of 1.3737 and containing I
19.9% nitrogen, was subjected to fractional dis
tillation in van one inch Stedman column with ‘
the butyronitriles or mixtures thereof by out im-" ’
70 proved distillation process. ‘
The invention is speci?cally illustrated in the - '
foregoing examples by ‘complete fractional dis
tillations of the mixture. It will be understood.
however, that the invention also contemplates
75 an operation wherein the distillation proceeds
only to the point where the acetonitrile-hydro
carbon fraction has been distilled oil’.
We claim:
1. In a process for removing from nitriles of
the class consisting ‘of propionitrile, normal
butyronitrile, and isosbutyronitrile, hydrocarbon
impurities having boiling points. such that in mix
tures with said nitriles they normally distil in
approximately the same temperature, range as said
said nitriles, the improvement which comprises
adding acetonitrile to the hydrocarbon-contam
inated nitrile and distilling oi‘! the hydrocarbon
contaminant and acetonitrile as an azeotrope.
3. In a process for removing from nitriles 0'!
the class consisting of propionitrile, normal
butyronitrile and iso-butyronitrile, hydrocarbon
impurities having boiling points such that in mix
tures withis'ai'd nitriles they normally distil in
nitriles, the improvement which comprises sub 10 approximately the same temperature range as
jecting the hydrocarbon-contaminated nitrile
said nitriles, the improvement which. comprises
product to fractional distillation in admixture
subjecting the hydrocarbon-contaminated nitrile
with acetonitrile and distilling oil! the hydrocar
product to fractional distillation in admixture‘
bon-contaminant and acetonitrile as an azeo
with acetonitrile, distilling oil a fraction compris—
trope. '
ing acetonitrile and the hydrocarbon-contami
2. In a process for removing from nitriles of
nant, cooling said traction; whereby the distillate
the class consisting of propionitrile, normal
is separated into an upper hydrocarbon layer and
butyronitrile and iso-butyronitrile, hydrocarbon
a lower acetonitrile layer and returning the lower
impurities having boiling points such that in
layer to the zone of fractional distillation.
mixtures with said nitriles they normally distil in '20
_ >
approximately the same temperature range as
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