Organic compounds -- part of the class 532-570 series – Organic compounds – Unsubstituted hydrocarbyl chain between the ring and the -c-...
Reexamination Certificate
1999-10-25
2001-04-24
Kifle, Bruck (Department: 1611)
Organic compounds -- part of the class 532-570 series
Organic compounds
Unsubstituted hydrocarbyl chain between the ring and the -c-...
Reexamination Certificate
active
06222033
ABSTRACT:
DESCRIPTION
The present invention relates to a process for preparing cyclic lactams by converting an &ohgr;-aminocarbonitrile in the presence of at least one catalyst.
Cyclic lactams are widely used as starting materials for producing polyamides (nylons) by ring-opening addition polymerization. The most important lactam is &egr;-caprolactam, the cyclic amide of &egr;-aminocaproic acid, which is mainly used for producing nylon 6 (Perlon®). The most important way to produce &egr;-caprolactam is the cyclohexanone oxime route, whereby cyclohexanone is reacted with hydroxylamine to form the oxime which is then subjected to a Beckmann rearrangement to form &egr;-caprolactam. This classic production route is in need of improvement, since it requires more than one step and inevitably by-produces sulfates or other by-products.
More recent processes for preparing cyclic lactams therefore utilize &ohgr;-aminocarbonitriles as starting materials. 6-Aminocapronitrile, for example, is prepared by selective hydrogenation of one of the two nitrile groups of adiponitrile.
U.S. Pat. No. 4,628,085 describes the reaction of 6-aminocapronitrile with water in the gas phase over a specific acidic silica gel at 300° C. By diluting the substrate with water, ammonia and hydrogen
itrogen, it is possible to obtain caprolactam with quantitative conversion and a selectivity above 95%, but over just 150 h the silica gel deactivates with a marked reduction in conversion and selectivity.
A similar gas-phase process is described in U.S. Pat. No. 4,625,023. Here a very dilute gas stream of 6-aminocapronitrile, adiponitrile, ammonia, water and carrier gas is passed over a silica gel and a copper/chromium/barium titanium oxide catalyst bed. The caprolactam selectivity is 91% from a conversion of 85%. Here too the catalyst is found to deactivate rapidly.
U.S. Pat. No. 2,245,129 describes the preparation of linear polyamides in a two-step process. The first step comprises heating a 50% strength aqueous solution of 6-aminocapronitrile at 220° C. for 20 h to obtain a low molecular weight intermediate, which is further polymerized in the second step after ammonia and excess water have been removed.
U.S. Pat. No. 2,301,964 describes the uncatalyzed conversion of aminocapronitrile in the form of an aqueous solution into caprolactam at 285° C. The yield is distinctly below 80% and in addition an unspecified residue is obtained.
FR-A-2 029 540 describes a process for cyclizing 6-aminocapronitrile to caprolactam using catalysts selected from metallic Zn or Cu powder or oxides, hydroxides, halides, or cyanides of rubidium, of lead, of mercury or of elements having an atomic number within the range from 21 to 30 or 39 to 48. The catalysts described are used as suspension catalysts in stirred batch autoclaves. Caprolactam is obtained in yields of up to 83%. However, complete removal of the catalysts from the desired caprolactam presents problems, since caprolactam is capable of forming compounds with the soluble constituents of the metals used, or very fine particles can be formed by mechanical stirring.
U.S. Pat. No. 3,485,821 describes the cyclization to caprolactam of 6-aminocaproic acid in aqueous solution at 150-350° C.
DE-A-952 442 discloses a process wherein 5-formylvaleric esters are reductively aminated in two steps to obtain caprolactam as well as aminocaproic esters.
U.S. Pat. No. 3,988,319 describes a process for cyclizing 6-aminocaproic acid in methanol or ethanol as solvent. However, to avoid secondary reactions of the 6-aminocaproic acid, the amino acid has to be dissolved so slowly that it is not present as a solid. This requires temperatures of about 170° C. Furthermore, the water content of the solution must not exceed 40%, since open-chain polymers are otherwise formed. The water of reaction has to be removed if the alcohol is to be re-used.
Ind. Eng. Chem. Process Des. Dev., 17 (1978) 9-16 states that the cyclization of 6-aminocaproic acid in water to caprolactam leads to significant oligomer quantities unless concentrations below 13% and temperatures of around 300° C. are used.
A. Blade-Font, Tetrahedron Lett., 21 (1980) 2443-2446, describes the cyclization of 6-aminocaproic acid as a suspension in toluene in the presence of aluminum oxide or silica gel by removal of the water of reaction. For full desorption of the caprolactam, the catalyst has to be washed with methylene chloride/methanol and the polymer has to be precipitated with diethyl ether. The caprolactam yield after 20 h is 82% over aluminum oxide and 75% over silica gel.
EP-A-271 815 describes the cyclization of 6-aminocaproic esters to caprolactam by dissolving the ester in an aromatic hydrocarbon, cyclizing at 100 to 320° C. and at the same time removing the eliminated alcohol.
EP-A-376,122 describes the cyclization of 6-aminocaproic esters to caprolactam by dissolving the ester in an aromatic hydrocarbon and cyclizing at 230 to 350° C. in the additional presence of water.
It is known to crack nylon 6 back to caprolactam. Under the action of acidic or basic catalysts at elevated temperature, the cracking frequently takes place under the action of water vapor, ie. in the low pressure range.
Chem. Ing. Techn. 45 (1973) 1510 describes the industrial implementation of a cracking process for nylon 6 waste using superheated steam and concentrating a caprolactam/water solution to recover the caprolactam.
In EP-A-209021, the cracking is carried out in a fluidized aluminum oxide bed.
In EP-A 529 470, potassium carbonate is used as nylon 6 cracking catalyst and the reaction is carried out at 250 to 320° C. with simultaneous distillative removal of the caprolactam under reduced pressure.
All these processes for cracking nylon 6 to obtain caprolactam are disadvantageous because of the need to remove large amounts of water, which is very energy-intensive, and catalysts such as phosphoric acids and the salts thereof, potassium carbonate or alkali metal oxides. In the case of the gas-phase reactions, the polymer is heated to temperatures which are generally within the range from 270 to 400° C. and cracked together with water in a fluidized bed reactor. By-product formation and deactivation due to adhesive clumping of the catalyst bed are the consequence.
U.S. Pat. No. 4,568,736 describes a process for preparing polyamides by reacting &ohgr;-aminonitriles with water in the presence of a phosphorus-containing catalyst, for example phosphoric acid, phosphorous acid, hypophosphorous acid, etc. The reaction is carried out in a two stage process wherein the first stage comprises maintaining the process at a temperature between 200 and 300° C. and an elevated pressure between about 14 and 56 bar to form a low molecular weight polyamide intermediate and the second stage comprises reducing the pressure to less than or equal to atmospheric pressure and at the same time raising the temperature to polymerize the low molecular weight polyamide intermediate further to form high molecular weight polyamides. In general, this second step is carried out under inert gas. The products thus obtained are generally still phosphorus-comprising. Their quality does not equal that of products prepared by polymerization of cyclic lactams.
WO 95/14665 describes a process for preparing cyclic lactams by reacting aminocarbonitriles with water in the liquid phase in a fixed-bed reactor in the presence of heterogeneous catalysts having no soluble constituents under the reaction conditions. The reaction takes place in water or in aqueous solvent mixtures. The reaction temperature is generally within the range from about 140 to 320° C. at elevated pressures within the range of up to 250 bar. The disadvantage of this process is the formation of undesirable by-products, such as oligomers which are uncrackable under the reaction conditions and 6-aminocaproamide. Furthermore, when alcoholic solvent mixtures are used, unwanted esters will form, for example ethyl 6-aminocaproate.
DE-A-44 43 125 describes a process for preparing caprolactam by heating 6-aminocapronitrile in the presence of heterog
Fischer Rolf
Fuchs Eberhard
BASF - Aktiengesellschaft
Keil & Weinkauf
Kifle Bruck
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