Organic compounds -- part of the class 532-570 series – Organic compounds – Nitriles
Reexamination Certificate
1999-06-14
2001-03-06
McKane, Joseph K. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Nitriles
Reexamination Certificate
active
06197992
ABSTRACT:
DESCRIPTION
The present invention relates to monoolefinic C
5
mononitriles in which the C═C bond and the C≡N bond are not conjugated, to a process for their preparation by catalytic hydrocyanation of a 1,3-butadiene-containing hydrocarbon mixture, and to their use as intermediates for further processing to adiponitrile.
The preparation of mixtures of monoolefinic C
5
mononitriles which contain, for example, 3-pentenenitrile and 2-methyl-3-butenenitrile from pure 1,3-butadiene is extremely uneconomical, since the latter has to be isolated from industrially obtainable hydrocarbon mixtures by complicated extractive distillation.
1,3-Butadiene-containing hydrocarbon mixtures are obtainable on a large industrial scale. For instance, the processing of petroleum by steam-cracking naphtha gives rise to a hydrocarbon mixture which is known as the C
4
cut and which has a high total olefin content, of which about 40% is accounted for by 1,3-butadiene and the remainder by monoolefins and polyunsaturated hydrocarbons and also alkanes. These streams always also contain small proportions of, generally, up to 5% in terms of alkynes, 1,2-dienes and vinylacetylene, which can only be removed by complicated and hence costly processing measures.
One way of removing acetylenes and allenes from diolefin-containing hydrocarbon mixtures consists in partly hydrogenating these mixtures in the presence of catalysts capable of differentiating between these classes of substances. For instance, U.S. Pat. No. 4,587,369 describes selective hydrogenation catalysts based on Pd on an alumina support.
U.S. Pat. No. 4,704,492 describes Cu/Pd catalysts useful as selective hydrogenation catalysts.
For certain uses of the hydrocarbon mixture, it is desirable to minimize the loss of diolefin, for example 1,3-butadiene, while at the same time maximizing the removal of the acetylenes. U.S. Pat. No. 4,493,906 describes a catalyst based on finely divided copper on a &ggr;-Al
2
O
3
support with which acetylene is removed virtually completely from a butadiene-containing mixture and the butadiene loss is in the region of not more than 1%.
1,3-Butadiene is for example an important starting material for the production of adiponitrile, from which, for example, &agr;, &ohgr;-alkylenediamines can be prepared, an important component for the large scale industrial production of polyamides (nylon). These diamines are generally prepared starting from corresponding dinitriles and subjecting these to a hydrogenation. For instance, all industrially utilized processes for producing 1,6-diaminohexane pass through the intermediate stage of adiponitrile, of which annually about 1.0 million metric tons are produced worldwide. K. Weissermel, H.-J. Arpe, Industrielle Organische Chemie, 4th Edition, VCH Weinheim, pages 266 et seq., describe four fundamentally different routes for the production of adiponitrile:
1. dehydrating amination of adipic acid with ammonia in the liquid or gas phase via the diamide intermediate;
2. indirect hydrocyanation of 1,3-butadiene via the intermediate stage of the 1,4-dichlorobutenes;
3. hydrodimerization of acrylonitrile in an electrochemical process; and
4. direct hydrocyanation of 1,3-butadiene with hydrogen cyanide.
The last process produces in a first stage, by monoaddition, a mixture of isomeric pentenenitriles and methylbutenenitriles, which, in a second stage, is isomerized to predominantly 3- and 4-pentenenitrile. Subsequently, in a third stage, the adiponitrile is formed by anti-Markovnikov hydrogen cyanide addition to 4-pentenenitrile. The reaction takes place in the liquid phase in a solvent, for example tetrahydrofuran, at a temperature within the range from 30 to 150° C. and at atmospheric pressure. Nickel complexes with phosphine or phosphite ligands and metal salt promoters are used as catalysts. The abovementioned review contains no mention of a possible utility of an industrial C
4
cut instead of pure 1,3-butadiene as reactant.
Applied Homogeneous Catalysis with Organometallic Compounds, Vol. 1, VCH Weinheim, pages 465 et seq., describes the heterogeneously and homogeneously catalyzed addition of hydrogen cyanide to olefins in general terms. Catalysts used are especially catalysts based on phosphine and phosphite complexes of nickel and palladium which permit a high product selectivity, improved conversions and shortened reaction times. Adiponitrile is prepared by hydrocyanation of butadiene using in the main nickel(0) phosphite catalysts, optionally in the presence of a Lewis acid as promoter. In general, the reaction can be divided into three steps: 1. synthesis of mononitriles by hydrocyanation of 1,3-butadiene; 2. isomerization; 3. synthesis of dinitriles. The monoaddition product is an isomeric mixture of 3-pentenenitrile and 2-methyl-3-butenenitrile, and the selectivity in respect of the linear 3-pentenenitrile is within the range from about 70 to 90%, depending on the catalyst used. If this first reaction step is carried out in the absence of Lewis acids, generally no second addition of hydrogen cyanide takes place and the resulting product mixture can be subjected to an isomerization using the same catalyst systems as in the first reaction step, this time in the presence of a Lewis acid, for example ZnCl
2
, as promoter. The 2-methyl-3-butenenitrile isomerizes to 3-pentenenitrile on the one hand, and 3-pentenenitrile isomerizes to the various n-cyanonitriles on the other. The cited publication mentions that the thermodynamically most stable isomer, 2-pentenenitrile, in which the C,N triple bond is conjugated with the C,C double bond, inhibits the reaction, since it acts as a catalyst poison. The desired isomerization to 4-pentenenitrile is only possible as a result of the fact that 3-pentenenitrile is isomerized significantly more rapidly to 4-pentenenitrile than to 2-pentenenitrile.
EP-A-0 274 401 describes a process for hydrocyanating pure butadiene using a nickel catalyst containing a mixture of phenyl and m,p-tolyl phosphite ligands.
EP-A-315 551 describes a process for hydrocyanating pure dienes, for example 1,3-butadiene, 1,3-hexadiene, etc., by catalysis with a nickel(0) catalyst which contains an acid as promoter.
U.S. Pat. No. 4,434,316 describes a process for removing the alkenes from a mixture of alkenes and alkanedienes by reacting the mixture with hydrogen cyanide in the presence of a nickel(0) complex as catalyst. The alkadienes react preferentially to form the corresponding nitriles and can be separated from the unconverted alkenes. Such an alkene-alkadiene separation is necessary for example in industrial processes for the production of dinitriles in order that the alkenes, which cannot form dinitriles, can be separated from the alkadienes. The process described is suitable for separating alkenes having 2 to 5 carbon atoms, for example ethylene, propylene, butenes and propenes from alkadienes having 3 to 8 carbon atoms, for example propadiene, butadiene, pentadiene, hexadiene and octadiene. The presence of acetylenically and ethylenically-acetylenically unsaturated hydrocarbons is not considered disadvantageous for the separation process described. The reference does not mention the possibility of hydrocyanating a 1,3-butadiene-containing hydrocarbon mixture and especially a C
4
cut from petroleum refineries to produce C
5
monoolefin mixtures having a nitrile function.
However, the prior art processes for hydrocyanating 1,3-butadiene-containing hydrocarbon mixtures have the disadvantage that conjugated butenenitriles and/or pentenenitriles are obtained as unwanted by-products. These conjugated butenenitriles and/or pentenenitriles are impossible to separate completely from the nonconjugated products of value, 3-pentenenitrile and 2-methyl-3-butenenitrile, are not further hydrocyanable to adiponitrile and are also pronounced catalyst poisons.
It is an object of the present invention to provide a process for preparing mixtures of monoolefinic C
5
mononitriles which is free from the above-described disadvantages and which enables the adiponitrile to be pr
Fischer Jakob
Meyer Gerald
Mundinger Klaus
Siegel Wolfgang
BASF - Aktiengesellschaft
Keil & Weinkauf
McKane Joseph K.
Murray Joseph
LandOfFree
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