Process for production of 2-methyleneglutaronitrile

From an acrylonitrile-dimerization liquid product prepared by contacting acrylonitrile with a specific catalyst composed of a metal halide and a trialkylamine, 2-methyleneglutaronitrile is efficiently recovered by a process which comprises contacting the reaction liquid product under stirring with benzene, toluene or xylene as well as with water in specific ratios, and then separating the resulting aromatic hydrocarbon layer from the mixture to recover 2-methyleneglutaronitrile.

BACKGROUND OF THE INVENTION 
This invention relates to a process for producing 2-methyleneglutaronitrile 
(hereinafter sometimes referred to as MGN) by liquid phase-dimerization of 
acrylonitrile (hereinafter sometimes referred to as AN). More 
particularly, this invention relates to a process for recovering MGN 
efficiently from the liquid dimerization product. 
Hitherto, a process for preparation of MGN comprising contacting AN in 
liquid phase with a catalyst composed of a metal halide and a 
trialkylamine has been known. According to this process, an MGN solution 
is obtained, but the MGN cannot always be recovered readily from the 
resulting liquid reaction product. 
Distillation methods may be used to recover MGN from the liquid reaction 
product. However, MGN itself is a readily polymerizable compound, and, 
moreover, the polymerization of MGN readily occurs when it is heated in 
the presence of a catalyst for the synthesis of MGN. Thus, the recovery of 
MGN by distillation is very low, and, moreover, formation of MGN polymers 
causes trouble in the operation of apparatus. Therefore, such a 
distillation method is not practical on a commercial scale. 
It may be readily anticipated that the problems of the marked 
polymerization in the case of recovering MGN by distillation from the 
reaction liquid product can be solved to some extent by deactivating or 
removing the remaining catalyst. Accordingly, a method has been proposed 
which comprises deactivating the remaining catalyst by treating the 
reaction product with an aqueous acid solution or an aqueous alkali 
solution, transferring it to the aqueous layer, and then separating the 
aqueous layer by stationary separation. According to this method, however, 
separation of the aqueous layer from the oily layer is very difficult 
because an emulsion forms, and, moreover, the separation operation is very 
complicated because lumps of polymer form. In addition, the treatment of 
the drainage water containing a metal halide and a halogen is also 
required. Thus this method is very troublesome as a commercial process. 
SUMMARY OF THE INVENTION 
An object of the present invention is to solve the above described 
problems. This object has been achieved in this invention by treating MGN 
with a specific extraction solvent and a small quantity of water, which 
are used in combination. 
In accordance with the present invention, there is provided, in the 
preparation of 2-methyleneglutaronitrile which comprises dimerization of 
acrylonitrile by contacting acrylonitrile in a liquid phase with a 
catalyst composed of a trialkylamine and a metal halide represented by the 
general formula MeX.sub.n wherein: Me stands for aluminum, titanium, 
vanadium, iron, cobalt or zinc; X stands for a halogen; and n is an 
integer equal to the valence of the metal Me, a process characterized by 
the steps of contacting the resulting reaction liquid product under 
agitation with an aromatic hydrocarbon selected from benzene, toluene and 
xylene as well as water, and then separating the resulting aromatic 
hydrocarbon layer from the mixture to obtain 2-methyleneglutaronitrile, 
the quantities of the aromatic hydrocarbon and water being, respectively, 
1 to 50 fold by weight and 1 to 10 percent by weight relative to that of 
the reaction liquid product. 
When the AN-dimerization liquid product is subjected to extraction with an 
extraction solvent selected from aromatic hydrocarbons such as benzene, 
MGN moves to the upper extraction solvent layer, and polymeric materials 
and catalyst component descend to the lower layer. Thus the extraction 
solvent layer is separated, and MGN can be readily recovered therefrom. It 
may be said that this selective extractability possessed by the specific 
aromatic hydrocarbon was totally unexpected. 
The most unique and unexpected effect in the present invention is the 
dissolution of the precipitates in the lower layer by the water used 
together with the aromatic hydrocarbon. More specifically, we have had a 
knowledge that the polymeric material and catalyst component which 
precipitate in the lower layer when the AN-dimerization liquid product is 
extracted with the specific aromatic hydrocarbon are then solidified into 
rigid resinous materials and deposited on the bottom of a stationary 
separation vessel. It is difficult to draw out the deposited material, 
which is not readily dispersed even by agitation. We have further found 
that the solidification of the polymeric material and the like can be 
prevented by the presence of a small quantity of water in the course of 
the extraction treatment. Such behavior by water was totally unexpected. 
In this connection, because the amount of water used in this case is 
small, the above-mentioned problem accompanying the treatment of drainage 
water is substantially reduced.

DETAILED DESCRIPTION OF THE INVENTION 
1. Catalytic Dimerization of AN 
A process for preparation of MGN which comprises contacting acrylonitrile 
with a catalyst composed of a metal halide and a trialkylamine in a liquid 
phase to dimerize acrylonitrile has been known (e.g., as disclosed in 
Japanese Patent Publication No. 6892/71, No. 15492/71 and No. 8287/72). 
The metal halide, constituting one component of the catalyst, is 
represented by the general formula MeX.sub.n, wherein Me stands for 
aluminum, titanium, vanadium, iron, cobalt or zinc, X stands for a 
halogen, and n represents the valence of the metal Me. Examples of such 
metal halides are aluminum trichloride, aluminum triiodide, titanium 
trichloride, titanium tetrachloride, titanium tetrabromide, vanadium 
tribromide, titanium tetraiodide, ferrous chloride, ferrous bromide, 
ferrous iodide, cobalt chloride, cobalt bromide, cobalt iodide, zinc 
chloride, zinc bromide, and zinc iodide. Of these halides, the chlorides 
and especially zinc chloride are preferred. These halides can be used in 
combination with each other. 
The other component of the catalyst is a trialkylamine. The alkyl groups 
can be the same or different from each other. Each of the alkyl groups 
preferably does not have more than 8 carbon atoms. Examples of such 
trialkylamines are trimethylamine, triethylamine, tripropylamines, 
tri-n-butylamine, triisobutylamine trihexylamines, and trioctylamines. 
Among these, lower trialkylamines and especially triethylamine are 
preferred. These trialkylamines can be used in combination. 
The above described two components are used generally in an amine/metal 
halide molar ratio of 0.1 to 20, preferably in the molar ratio of 0.5 to 
10, and most preferably in the molar ratio of 1 to 5. When the molar ratio 
is over 20, the yield of MGN to the resulting catalyst is lowered. On the 
other hand, when the molar ratio is less than 0.1, the reaction velocity 
substantially decreases. Thus the above-mentioned ranges are defined. The 
catalyst is used in a quantity such that the metal halide is not less than 
0.5% by weight of the AN, preferably in the range of 2 to 10% by weight of 
the AN. 
The dimerization of AN in the liquid phase can be carried out in any manner 
that ensures the contact between the catalyst system composed of the 
above-mentioned two components and the AN. A reaction solvent is not 
especially required unless it is used for a special purpose. The 
above-mentioned catalyst components can be added to the AN, separately or 
as a mixture. The reaction temperature and pressure can be in optional 
ranges that maintain the AN in liquid phase but it is generally preferred 
that the temperature be in the range of 0.degree. to 70.degree. C. and the 
pressure be atmospheric pressure. 
2. Extraction of MGN 
(1) Material subjected to extraction 
The reaction liquid product obtained from the above-described reaction is 
subjected to an extraction treatment. When no reaction solvent is used, 
the MGN concentration in the resulting reaction liquid product is in a 
range of the order of 45 to 76% by weight. 
In a preferred embodiment of the present invention, the reaction liquid is 
pretreated and then subjected to the extraction. In the pretreatment, 
low-boiling materials such as unreacted AN and the trialkylamine used as a 
catalyst component and a solvent used optionally (having a lower boiling 
point than MGN) are distilled off preferably under a reduced pressure. If 
such unreacted AN and the like is not removed prior to the extraction, a 
larger quantity of the extraction solvent is required. 
(2) Extraction solvent and extraction 
The extraction solvent to be used in the present invention is benzene, 
toluene or xylenes (hereinafter sometimes referred to as BTX), of which 
toluene is especially preferred. 
When BTX is added to the liquid product of the AN dimerization (preferably 
the liquid from which AN and the trialkylamine have been removed), MGN 
moves to the BTX layer, and polymeric materials and the catalyst 
components descend to the lower layer. The BTX layer is separated and MGN 
is recovered therefrom. 
The quantity of the BTX to be used is 1 to 50-fold by weight and preferably 
2 to 5-fold by weight that of the reaction liquid product (when unreacted 
AN and the trialkylamine have been distilled off, the amount of reaction 
liquid product before the distillation step). When the BTX is used in a 
quantity less than 1-fold by weight that of the liquid product, sufficient 
extraction cannot be achieved. Even if the quantity of the BTX is over 
50-fold by weight, the resulting extraction efficiency cannot be further 
enhanced, and the recovery of MGN from the extract is disadvantageous. 
The extraction is normally carried out by contacting the reaction liquid 
product with the extraction solvent under a suitable agitation conditions 
at 20.degree. to 70.degree. C., preferably at 30.degree. to 50.degree. C. 
In general, the quantity of the BTX used becomes less at a higher 
temperature. 
The dimerization of AN may be carried out in the presence of a reaction 
solvent. A BTX can be used as the reaction solvent (c.f. the above-cited 
Japanese Patent Publication No. 6892/71). In this case, therefore, the 
extraction with BTX of the dimerization liquid product can be said to have 
also been accomplished in the course of the reaction. The present 
invention is intended to also include such an embodiment thereof. 
(3) Treatment with water 
In the present invention, the above described extraction with BTX is 
carried out in the presence of water. Water is added at the same time as 
the addition of BTX (not before the addition of BTX) or after the addition 
of BTX with agitation to maintain a solidifiable polymer in a liquid 
state. 
The quantity of water to be used should be 1 to 10% by weight, preferably 2 
to 6% by weight, of the reaction liquid product (when unreacted AN and the 
trialkylamine have been distilled off, the quantity of the reaction liquid 
product before the distillation step). When the quantity of water is less, 
polymers form red-brown lumps which are difficult to take out. If the 
amount of water is greater, yellow viscous materials will be formed which 
will cause clogging in standing vessels and draw-off pipes. 
(4) Separation of BTX layer and recovery of MGN 
Separation of the MGN-containing BTX layer obtained as an upper layer after 
the extraction with BTX and recovery of MGN from the BTX layer can be 
conducted, for example, by separation thereof by decantation of a formed 
upper layer and distillation under a reduced pressure, or by other 
appropriate procedures. 
We have found that the MGN in which the above mentioned catalyst remains 
unseparated and from which unreacted AN and the like have been removed 
undergoes marked polymerization upon heating, whereas the MGN treated 
according to the present invention is caused to have a markedly smaller 
thermal polymerization liability. However, since MGN is a compound having 
an ethylenically unsaturated bond, polymerization and solidification of 
the MGN obtained by this invention upon heating still cannot be avoided. 
Accordingly, upon obtaining MGN by distillation of the MGN from the BTX 
extract, it is desirable to prevent polymerization of the MGN by some 
measure. 
A suitable polymerization inhibitor has been generally added to a 
polymerizable compound when it is subjected to distillation. However, a 
polymerization inhibitor which is fully effective for the distillation of 
crude MGN to be treated in the present invention has not yet been found. 
When such polymerizable materials are subjected to distillation, not only 
is a large amount of the material lost because of polymerization thereof, 
but the resulting distillation still residue fails to maintain its 
fluidity because of the increase in viscosity due to polymerization, which 
results in failure of the distillation operation. To prevent 
high-viscosity due to polymerization of the still residue, it may be 
possible to leave unrecovered a portion of the product monomer, which is a 
good solvent for the polymerized product, to maintain the fluidity of the 
still residue, but the loss of the product is not negligible. On the other 
hand, distillation of such heat-polymerizable materials should be 
conducted at a low temperature under reduced pressure, but it is necessary 
to fully investigate the polymerization properties of the material for 
setting a suitable temperature range for the distillation. 
We have found that formation of the polymer is substantially negligible in 
the case where the crude MGN which has been obtained by treatment 
according to the present invention and then by removal of the BTX used is 
distilled under the temperature-time conditions given in the region 
indicated by the shaded portion of FIG. 1, for example, under the 
conditions of 10 hours or less at 150.degree. C. or lower, 2 hours or less 
at 170.degree. C. or lower, 30 minutes or less at 185.degree. C. or lower 
or 10 minutes or less at 200.degree. C. or lower. In other words, the 
distillation of the crude MGN to obtain MGN should be carried out in a 
distiller having a residence time of .tau. (minutes) at a temperature of T 
(.degree.C.) satisfying the following requirement: 
EQU T.ltoreq.227-28 log.sub.10 .tau. 
It is preferable that the following requirement is satisfied: 
EQU 70.ltoreq.T.ltoreq.200-28 log.sub.10 .tau. 
When the distiller has a temperature range, the above requirement should 
preferably be satisfied at each temperature and also with respect to the 
integration of the residence time at respective temperatures. It is to be 
noted that the above temperature-residence time relationship indicates 
only the conditions of heating the liquid to be distilled, and does not 
necessarily restrict the boiling point in the distilling operation. 
FIG. 2 shows the vapor pressure curve of MGN. 
One of the preferred modes of practice to realize such temperature-time 
relations is to employ the liquid film evaporation method those of the 
falling film type and the centrifugal type in the distillation of the 
crude MGN to purify MGN. For example, in the falling film evaporation 
method, the crude MGN is caused to fall down, after or while being heated, 
in a thin film state in a distiller, during which MGN is evaporated off to 
leave heavy end. By this method, it is possible to hold the liquid-heating 
time to a few seconds to a few minutes. The liquid film evaporation 
methods can also be used effectively for distilling off the unreacted AN 
and amine from the dimerization reaction liquid product. Moreover, the 
evaporation methods can also be applied to distilling off the BTX from the 
BTX extract. 
(5) Flow sheet 
FIG. 3 is a flow sheet showing essential apparatus for one example of 
preferred mode of practice of the present invention. 
In FIG. 3, the starting material AN is supplied via a line 1, dehydrated 
sufficiently through a molecular sieve-packed dehydration tower 2, and 
then introduced into a dimerization reaction vessel 3. If desired, the AN 
is cooled prior to reaction to a specific temperature by a cooling 
apparatus 4. Then a specific quantity of an anhydrous metal halide is 
supplied via a line 5. A trialkylamine is supplied via a line 6, 
dehydrated sufficiently through a molecular sieve-packed dehydration tower 
7, and then is added dropwise via a line 8 to the AN in the reaction 
vessel 3 under stirring. The reaction temperature is preferably in the 
range of 0.degree. to 70.degree. C. For controlling the reaction 
temperature to a specific temperature, the rate of addition of the 
trialkylamine is regulated and the reaction liquid is cooled by the 
cooling apparatus 4. 
After the reaction has been carried out for a specific period of time, 
unreacted AN and the trialkylamine are recovered at a distillation 
apparatus 10 via a line 9. The recovered unreacted AN-containing 
trialkylamine can be reused as a reaction material via a line 11. The 
AN-amine mixture can be stored, depending on the necessity, in a reservoir 
12 and used as a starting material when necessary. Because the mixture 
shows white turbidity when stored as it is, a small quantity (for example, 
about 0.3 to 0.5% by weight) of water is added to the mixture. The 
resulting aqueous mixture can be stored for a long period at a temperature 
of 30.degree. C. or lower and reused. The AN-amine mixture can be stored 
more safely by adding thereto both water and 10 to 100 ppm of a 
polymerization inhibitor such as hydroquinone monomethyl ether, but the 
addition of only a polymerization inhibitor without water is not 
desirable. 
The bottom liquid supplied from the distillation apparatus 10 is introduced 
via a line 13 to an extraction vessel 14, and then a specific quantity of 
BTX such as toluene is added thereto via a line 16 (and a line 17). After 
agitation, a specific quantity of water is added thereto via a line 18, 
and the mixture is allowed to stand. In this case, it is preferable to add 
the water in a dispersed or, more preferably, sprayed state before 
precipitates in the toluene solution descend. 
The high-density product in the lower layer is taken out through a line 19, 
and the upper toluene solution layer is sent via a line 20 to a 
distillation apparatus 21 to recover the toluene. The recovered toluene is 
reusable via a line 17. The MGN from which toluene has been recovered is 
sent via a line 22 to a distillation apparatus 23, and is purified and 
obtained via a line 24. High-boiling impurities are discharged via a line 
25. 
In case the whole system is operated batchwise, it is possible to use a 
single distillation apparatus for all the operations carried out in the 
apparatus 10, 21 and 23 according to the above explanation. 
3. Examples of Experiments 
In order to indicate more fully the nature and utility of the present 
invention, the following specific examples of practice are set forth, it 
being understood that these examples are presented as illustrative only 
and are not intended to limit the scope of the invention. 
EXAMPLE 1 
(Synthesis) 
A 3-liter glass lined autoclave was charged with 1,260 g of AN and 60 g of 
anhydrous zinc chloride. This step was followed by the addition thereto of 
240 g of triethylamine. The mixture was subjected to reaction at 
25.degree. to 30.degree. C. for 25 hours. By gas-chromatographic analysis 
of the resulting reaction liquid, it was found that the content of MGN was 
64% and that the balance consisted essentially of triethylamine and the 
trimer or higher polymers of AN. 
EXAMPLE 2 
(Removal of unreacted AN, etc.) 
Unreacted AN and triethylamine were distilled off under a reduced pressure 
of 105 Torr in a thin-film type distiller from the reaction liquid 
produced in Example 1, to obtain crude catalyst-containing MGN. By 
gas-chromatographic analysis, polymerization loss of MGN was found to be 
1%. 
EXAMPLE 3 
(Extraction) 
Four hundred (400) g of the crude catalyst-containing MGN obtained in 
Example 2 and 400 g of toluene were mixed, and then 20 g of water was 
added. The mixture was stirred at 50.degree. C. for 30 minutes and then 
subjected to stationary separation. Thus 760 g of an oily phase consisting 
essentially of MGN and toluene in the upper layer and 60 g of high-density 
liquid consisting essentially of polymers, the metal salt and water in the 
lower layer were obtained. The lower layer was in a liquid state and 
readily separated from the oily phase. 
EXAMPLE 4 
(Reference) 
Crude MGN produced by recovering toluene from the toluene phase obtained in 
Example 3 was heated to 185.degree. C., whereupon polymerization of 5% 
occurred in 30 minutes, and 18% of a polymer was formed in 60 minutes. 
When the crude MGN was heated to 170.degree. C., a polymer was produced in 
a quantity of 2% in 30 minutes and 15% in 100 minutes. When it was heated 
to 150.degree. C., no formation of a polymer was observed in 60 minutes. 
EXAMPLE 5 
(Reference) 
The crude MGN produced by recovering toluene from the oily phase obtained 
in Example 3 was distilled under a reduced pressure of 1.4 Torr in a 
thin-film distiller. MGN having a purity of 99.4% was recovered in a yield 
of 99%. The viscosity of the distillation residue was 50 cp at 
98.9.degree. C. In the distillation operation, the heating temperature was 
147.degree. C., and the average residence time of the liquid was 6 
minutes. 
EXAMPLE 6 
(Comparative) 
The crude catalyst-containing MGN obtained in Example 2 was heated to 
150.degree. C., and a polymer was produced in a quantity of about 50% in 
60 minutes.