In processes of preparing unsaturated dinitriles from olefins, unsaturated mononitriles, and a monoadduct reaction product of an olefin and an unsaturated mononitrile in which undesirable internally unsaturated monoadduct is formed, the improvement of inhibiting the formation of internally unsaturated monoadduct by decomposing at least a portion of the recycle stream of monoadduct to form olefin and unsaturated mononitrile, and passing the thus-formed olefin and unsaturated mononitrile to the reaction.

This invention relates to an improved process for the preparation of 
unsaturated dinitriles. In another aspect, this invention relates to an 
improved process for producing C.sub.10 dinitriles from acrylonitrile and 
isobutylene whereby the production and buildup of 5-methyl-4-hexenenitrile 
is minimized. In accordance with a further aspect, this invention relates 
to an improved process for producing unsaturated C.sub.10 dinitriles from 
acrylonitrile, isobutylene, and an unsaturated C.sub.7 nitrile 
(monoadduct) by subjecting at least a portion of the recycle stream of 
monoadduct to decomposition conditions which produces isobutylene and 
acrylonitrile, which materials are passed to the initial reaction for 
monoadduct formation. In still another aspect, this invention relates to a 
method for producing mixed isomeric C.sub.10 dinitriles useful for 
producing fiber grade polyamides. 
U.S. Pat. No. 3,840,583 discloses a process for the production of 
unsaturated dinitriles from the reaction of two moles of acrylonitrile 
with one mole of isobutylene. Said dinitriles are formed in a stepwise 
reaction in which an intermediate unsaturated mononitrile is first formed 
from one mole of acrylonitrile and one mole of isobutylene. For 
convenience in the discussion hereinafter, the unsaturated mononitrile 
will be referred to as monoadduct and the unsaturated dinitrile as 
diadduct. It is also known that the hydrogenation of said diadduct 
produces a saturated diamine mixture which is predominantly 
5-methyl-1,9-nonanediamine (MND) and which can be employed in the 
preparation of various condensation type polymers. In particular, it has 
been found that MND with terephthalic acid produces a polyamide which has 
a very desirable set of properties for use as a fiber, e.g., U.S. Pat. No. 
3,839,295. 
In the course of the development of fiber grade polyamides from the 
above-mentioned saturated diamines (MND) and dibasic acids, it was 
discovered that certain lots of diamine (MND) produced from the diadduct 
provided polymer properties having reduced values in tenacity and the 
like. It was discovered by careful analysis of the various lots of MND 
that certain highly branched isomeric diamines appeared to be responsible 
for the undesirable properties in the final polyamide polymer. In 
particular, the compound 4-isopropyl-1,7-heptanediamine was identified as 
one isomer which produced the undesirable polyamide properties. It was 
found that the occurrence of this isomer could be traced back to an 
isomerization reaction in the monoadduct. Specifically, the principal 
isomeric compound in the monoadduct is 5-methyl-5-hexenenitrile which can 
isomerize to 5-methyl-4-hexenenitrile. It is also possible that the latter 
compound may form directly from isobutylene and acrylonitrile in a small 
amount. Whether or not the compound is formed directly or by isomerization 
of the principal monoadduct product, it is known that the 
5-methyl-4-hexenenitrile on reaction with acrylonitrile produces 
4-isopropenylheptane-dinitrile which on hydrogenation gives rise to the 
undesirable isomer 4-isopropyl-1,7-heptanediamine. It is believed that 
for acceptable fiber properties in the polyamide produced from MND and 
terephthalic acid that the amount of said undesirable isomer should be 
less than about 0.5 weight percent of the diamine employed. 
The problem caused by the undesirable isomer precursor, 
5-methyl-4-hexenenitrile, is further magnified by the process employed to 
produce the diadduct. In said preferred process, the monoadduct serves as 
the reaction diluent, and in a single reaction zone acrylonitrile and 
isobutylene are introduced in the presence of preformed monoadduct to 
produce the diadduct with suitable adjustments of the molar ratios of 
acrylonitrile to isobutylene so that there is essentially no net gain nor 
loss of the monoadduct in the reaction mixture. The effluent from the 
above-described reaction zone is simply fractionated to provide monoadduct 
which is recycled to the reaction zone and diadduct which is then taken to 
the hydrogenation step for production of the diamine. It has been 
discovered that the undesirable isomer precursor, 
5-methyl-4-hexenenitrile, reacts with acrylonitrile three to four times as 
slow as the normal monoadduct 5-methyl-5-hexenenitrile and thus on 
continued recycle of the monoadduct to the reaction zone where diadduct is 
being formed will eventually provide for a buildup of a significant amount 
of the precursor of the undesired diamine isomer. This, of course, 
explains why the presence of the 4-isopropyl-1,7-heptanediamine was not 
observed until after the process had been operating for some time and the 
level of monoadduct precursor for this undesired isomer had built up to a 
substantial or significant degree. 
Since the undesirable isomer monoadduct precursor reacts significantly 
slower than the normal monoadduct isomer, one possible solution would be 
to simply draw off a portion of the monoadduct recycle stream and purify 
it by fractional distillation to effectively remove the 
5-methyl-4-hexenenitrile isomer. However, this has proved to be 
essentially impractical because of the very close boiling points of the 
two isomeric monoadducts. 
Another possible solution would be to simply withdraw a portion of the 
recycle monoadduct stream and discard the same. However, this would 
obviously be an expensive solution and would effectively consume valuable 
chemicals without producing the desired diadduct from the process. 
Furthermore, a suitable means of disposal would also be required that 
would satisfy environmental considerations in the method utilized for said 
disposal. This also could add to the economic penalty for this solution to 
the problem. 
Neither of the two possible solutions to the above-described problem appear 
to be desirable, and thus the instant invention is seen as a means of 
solving the above-described problem in a simple and yet economically 
valuable manner. 
Accordingly, an object of this invention is to minimize the formation of 
undesirable internally unsaturated monoadduct in processes of preparing 
unsaturated dinitriles. 
A further object of this invention is to provide a process for preparing 
isomeric C.sub.10 unsaturated dinitriles in which the formation of 
C.sub.10 unsaturated dinitriles unsuitable for the production of fiber 
grade polyamides is minimized. 
Other objects, aspects, and the several advantages of the invention will be 
apparent to those skilled in the art upon a study of this disclosure and 
the appended claims. 
According to the invention, an improved process is provided for the 
preparation of unsaturated dinitriles from an olefin, an unsaturated 
mononitrile, and a monoadduct reaction product of an olefin and an 
unsaturated mononitrile whereby the production of and buildup of 
undesirable internally unsaturated monoadduct is minimized by subjecting 
at least a portion of the recycle stream of monoadduct to conditions of 
temperature and for a period of time sufficient to decompose the 
monoadduct into olefin and unsaturated mononitrile which materials can be 
passed to the initial reaction. It has been found that the treatment of 
the recycle stream of monoadduct as set forth herein prevents the buildup 
of an undesirable slower reacting monoadduct isomer. 
According to a specific embodiment of the instant invention, the 
above-described problem of preventing a significant accumulation of 
5-methyl-4-hexenenitrile in the monoadduct which in turn gives rise to 
4-isopropenylheptanedinitrile and ultimately to 
4-isopropyl-1,7-heptanediamine is achieved by withdrawing a portion of the 
recycle monoadduct stream and thermally cracking or pyrolyzing said bleed 
stream to products comprising acrylonitrile and isobutylene. Since 
acrylonitrile and isobutylene are reactants in the process for making 
monoadduct and subsequently diadduct, they can be recycled to the reaction 
zone from the cracking zone after separation from other materials which 
may be present. It is readily apparent that this method of treating the 
bleed stream from the monoadduct recycle stream provides a very desirable 
solution to the problem in that acrylonitrile and isobutylene are 
regenerated and that 5-methyl-4-hexenenitrile can be maintained at an 
acceptably low level in the monoadduct stream. 
The amount of monoadduct recycle stream which is bled off to the cracking 
zone is broadly within the range of from about 5 to about 50 and 
preferably from 10 to 20 weight percent. The amount of undesired isomer 
formed in the reaction zone in a given time period will generally depend 
on the reaction conditions and thus the level of said undesired isomer in 
the monoadduct recycle stream will also generally depend on the reaction 
conditions. It is, of course, possible for analysis to be carried out from 
time to time on the monoadduct recycle stream in order to provide a check 
on the level of the undesired isomeric compound. Such analysis results 
then could be employed to change the amount of recycle stream which is 
bled off to the cracking zone. Generally speaking, the lower the amount of 
undesired monoadduct isomer required in the monoadduct stream, the larger 
the amount of recycle stream which may be taken off to the cracking zone. 
As indicated above, the portion of the recycle stream of monoadduct treated 
in accordance with the invention is subjected to conditions including an 
elevated temperature and a period of time and other process variables 
sufficient to cause decomposition of the monoadduct to form olefin and 
unsaturated mononitrile. The decomposition can be carried out under 
pyrolysis or cracking conditions which can vary appreciably, dependent 
upon the temperature employed and the length of time the monoadduct is 
subjected to the elevated temperature. 
In general, the monoadduct cracking zone is operated broadly within a 
temperature range of from about 480.degree. C. to about 650.degree. C. and 
preferably from 525.degree. C. to 575.degree. C. 
The residence time for the monoadduct bleed stream in the cracking zone can 
be broadly from 0.1 second up to 10 minutes, but preferably from 1 to 20 
seconds. Since the cracking step is predominantly the conversion of one 
molecule of diadduct to two molecules of product, it is expected that the 
reaction would be favored by the use of reduced pressure in the cracking 
zone. However, the cracking step can be carried out at a pressure of from 
about 0.14 to about 690 kPa and preferably from 34 to 205 kPa 
(kiloPascals). 
It is optional though presently preferred that the bleed stream from the 
monoadduct recycle stream be admixed with an essentially inert gaseous 
diluent before entering the cracking zone. Suitable diluents which can be 
employed in this embodiment include helium, argon, nitrogen, carbon 
dioxide, and steam. Broadly, the gaseous diluent can be utilized in a 
molar ratio of diluent/monoadduct of from 0.1/1 to 50/1. 
The cracking reaction under the conditions described above can be carried 
out in any convenient reactor configuration such as, for example, a heated 
pipe or a pipe filled with essentially inert material such as glass beads, 
carbon rings, stainless steel beads, and the like. 
As described above, the cracking of the bleed stream from the monoadduct 
recycle stream provides an effluent from the cracking zone which comprises 
acrylonitrile and isobutylene. The selectivity to acrylonitrile and 
isobutylene can be as high as 88 percent at a 90 percent conversion of 
monoadduct bleed stream. The effluent from the cracking zone may also 
contain unreacted monoadduct as well as smaller amounts of heavy material, 
usually 6 percent or less. The products from the cracking zone can be 
easily and conveniently separated by distillation and the acrylonitrile 
and isobutylene returned directly to the reaction zone for the preparation 
of monoadduct and diadduct. Unreacted monoadduct can, of course, be 
recycled to said same reaction zone or to the cracking zone. 
The reaction conditions, ratios of reactants, etc., for the preparation of 
unsaturated dinitriles from olefins, unsaturated mononitriles, and a 
monoadduct reaction product can vary appreciably and are generally set 
forth in U.S. Pat. No. 3,840,583, which is incorporated herein by 
reference. Any suitable reaction conditions for either a batch process or 
a continuous process can be employed. As seen in column 3, lines 49-50 of 
U.S. Pat. No. 3,840,583 the olefin hydrocarbon contains from 3 to 12 
carbon atoms with 1 to 2 ethylenically unsaturated, nonconjugated double 
bonds and as seen in column 3, lines 63 to 72 the mononitrile has from 3 
to 10 carbon atoms per molecule and is represented by the formula RCH = CR 
-- CN, wherein each R is independently selected from alkyl, cycloalkyl, 
and aryl hydrocarbyl radicals and combinations thereof and hydrogen.

EXAMPLES 
The monoadduct cracking runs were carried out according to the instant 
invention in the following manner: 
The feed is charged to a Fischer-Porter pressure tube and pressurized with 
nitrogen, from which it is passed through a Rotometer and into a tee, at 
which point nitrogen is admixed therewith also through a Rotometer. From 
the tee the feed/nitrogen mixture is passed to the cracking reactor. From 
the cracking reactor the effluent passes through a sample port from which 
samples are withdrawn for analysis and to a wet ice trap followed by a dry 
ice trap which recovers the condensible products from the cracking zone. 
In the runs of Example I, the cracking reactor itself was a heavy walled 
nickel tube of 19 millimeters in internal diameter by 660 millimeters in 
length. In the runs of Examples II and III, the reactor was a stainless 
steel tube of 19 millimeters internal diameter by 330 millimeters in 
length filled with 85 milliliters of glass beads of 4 millimeter diameter. 
EXAMPLE I 
In the apparatus described above, a series of runs were carried out in 
which a monoadduct stream of approximately 98 percent by weight of 
5-methyl-5-hexenenitrile and 2 percent by weight of 
5-methyl-4-hexenenitrile was thermally cracked to produce an effluent 
comprising isobutylene and acrylonitrile and unreacted monoadduct. Samples 
of the effluent for GLC analysis were taken downstream of the cracking 
zone and prior to the first ice trap. The results obtained in these runs, 
as well as the conditions employed, are shown below in Table I. 
TABLE I 
__________________________________________________________________________ 
Flow Rates.sup.(d) 
Residence 
GLC Area Percent.sup.(c) 
Run 
Temp., 
MA.sup.(a), 
N.sub.2, 
Time, Iso- 
No. 
.degree. C. 
cc/min 
cc/min 
Seconds 
butylene 
ACN.sup.(b) 
MA.sup.(a) 
__________________________________________________________________________ 
1 490 20 10 26.4 1.5 1.7 98 
2 550 60 21 9 18 40 25 
3 575 60 21 9 22 65 -- 
4 579 60 21 9 19 48 3.3 
__________________________________________________________________________ 
.sup.(a) MA = monoadduct. 
.sup.(b) ACN = acrylonitrile. 
.sup.(c) Other products in the GLC samples for Runs 2 - 4 were not 
identified. 
.sup.(d) Flow rates are for gaseous state. Molar ratios of N.sub.2 /MA ar 
approximately the same as the respective flow rate ratios. 
EXAMPLE II 
Other runs were carried out employing the same monoadduct composition as 
used in the runs of Example I in a different reactor which is described 
above. The results from these runs are presented in Table II below. 
TABLE II 
__________________________________________________________________________ 
Flow Rates.sup.(a) 
Residence 
GLC Area %.sup.(b) 
Run 
Temp., 
MA, N.sub.2, 
Time, Iso- 
No. 
.degree. C. 
cc/min 
cc/min 
Seconds 
butylene 
ACN MA 
__________________________________________________________________________ 
5 562 60 20 9 36 34 10 
6 558 60 60 6 35 38 11 
7 568 120 60 4.2 33 29 25 
__________________________________________________________________________ 
.sup.(a) See Footnote (d) of Table I. 
.sup.(b) Other products in the GLC samples were not identified. 
EXAMPLE III 
Other runs were carried out using the same reactor as employed in the runs 
of Example II, but in these runs the monoadduct feed to the cracking zone 
was composed of approximately equal parts by weight of 
5-methyl-5-hexenenitrile and 5-methyl-4-hexenenitrile. The results of 
these runs are shown below in Table III along with the reaction conditions 
employed. 
TABLE III 
__________________________________________________________________________ 
Flow Rates.sup.(a) 
Residence 
GLC Area %.sup.(b) 
Run 
Temp., 
MA, N.sub.2, 
Time, Iso- 
No. 
.degree. C. 
cc/min 
cc/min 
Seconds 
butylene 
ACN MA 
__________________________________________________________________________ 
8 640 48 26 10.2 46 12 -- 
9 615 32 26 13.2 46 13 4 
10 585 26 26 13.8 34 12 14 
11 560 26 26 13.8 35 12 21 
12 530 26 26 13.8 12 4 62 
__________________________________________________________________________ 
.sup.(a) See footnote (d) of Table I. 
.sup.(b) See footnote (b) of Table II. 
The results shown in Tables I, II, and III demonstrate that the monoadduct 
over a wide range of composition for the isomeric unsaturated mononitriles 
can be thermally cracked to produce reaction mixtures comprising 
isobutylene and acrylonitrile.