Organic compounds -- part of the class 532-570 series – Organic compounds – Unsubstituted hydrocarbyl chain between the ring and the -c-...
Reexamination Certificate
2001-08-10
2002-05-21
Kifle, Bruck (Department: 1624)
Organic compounds -- part of the class 532-570 series
Organic compounds
Unsubstituted hydrocarbyl chain between the ring and the -c-...
Reexamination Certificate
active
06392037
ABSTRACT:
The invention relates to a process for the preparation of &egr;-caprolactam comprising treating 6-aminocaproic acid, 6-aminocaproate ester, 6-amino-caproamide, oligomers or polymers of these compounds or mixtures comprising at least two of these compounds in a cyclisation reactor in the presence of superheated steam in which a gaseous product stream comprising &egr;-caprolactam, steam, lights and heavies is obtained.
Compounds having a higher boiling point than &egr;-caprolactam are designated as heavies in this specification. Examples are 6-aminocaproic acid, 6-aminocaproamide, oligomers of these compounds, &egr;-caprolactam cyclic oligomers N-substituted or C-substituted lactams and/or amides. Compounds having a lower boiling point than &egr;-caprolactam are designated as lights in this specification. Examples are N-methyl-&egr;-caprolactam, hexanoic acid, 5-hexenoic acid, valeric acid and valeramide.
Such a process is described in WO-A-9837063. This patent publication describes a process to prepare &egr;-caprolactam by treating 6-aminocaproic acid, 6-aminocaproate ester and/or 6-aminocaproamide with superheated steam at a temperature of between 250-400° C. and a pressure of between 0.5 and 2 MPa. The crude &egr;-caprolactam obtained still contains impurities and requires further purification. The crude &egr;-caprolactam product stream obtained in the cyclisation process as described in WO-A-9837063 also contains lights and heavies. The majority of these lights and heavies need first to be removed in order to make efficient purification of &egr;-caprolactam possible in the subsequent purification steps. Lights and heavies are usually separated from the &egr;-caprolactam product stream with distillation. A disadvantage of the separation of the heavies from the &egr;-caprolactam product stream is that it is almost impossible or very difficult to quantitatively separate &egr;-caprolactam from the heavies without degradation of &egr;-caprolactam and/or fouling of the separation equipment. Another disadvantage is that the valuable &egr;-caprolactam precursors are not recovered. For a commercially interesting process it is advantageous to recover the greatest part of &egr;-caprolactam and &egr;-caprolactam precursors from the heavies before the heavies are disposed off.
An object of the invention is to provide a simplified process for the preparation of &egr;-caprolactam. Still another object is to get a high yield of &egr;-caprolactam.
These objects are achieved in that the product stream, after condensation and at least partial removal of water and lights is split into a &egr;-caprolactam stream and a heavies stream containing heavies and &egr;-caprolactam and the heavies stream is recycled to a cyclisation reactor.
It has been found that with the process according to the invention high yields to &egr;-caprolactam can be achieved. Another advantage is that the separation of &egr;-caprolactam from the heavies does not need to be quantitatively. In the process according to the invention the distillative separation of &egr;-caprolactam and heavies can be performed at a less reduced pressure and/or temperature compared to a process in which there is no recycle of the heavies stream for obtaining comparable yields of &egr;-caprolactam.
Preferably the heavies stream is recycled to the cyclisation reactor from which the product stream is derived. This is advantageous from an economical/investment point of view because no additional cyclisation reactor is needed.
Before recycling the heavies stream to the cyclisation reactor, the heavies stream is optionally first fed to another separation unit in which the heavies stream is further split into a &egr;-caprolactam stream and a second heavies stream. This second heavies stream is subsequently recycled to the cyclisation reaction. Examples of possible separation units are extractors and stripper columns. A preferred separation unit is a stripper column. More preferably a gaseous stream containing steam is fed to the stripper column to strip &egr;-caprolactam from the heavies stream resulting in a gaseous -caprolactam containing top stream. The gaseous &egr;-caprolactam containing top stream can easily be integrated in the purification section (described below) of the product stream from the cyclisation reactor.
With a cyclisation reactor is meant a reactor in which an open-chain compound is converted into a compound that contains a ring, a process called cyclisation. In the process according to the invention 6-aminocaproic acid, 6-aminocaproate ester and/or 6-aminocaproamide is cyclised into &egr;-caprolactam.
The process according to the invention can be performed in a reactor which is provided with an inlet for the starting compound(s), an outlet for the steam/&egr;-caprolactam product and means for supplying steam such that the steam is contacted with the starting material. The reactor is optionally equiped with a heating device and optionally with a mixing device. To this reactor the starting compound and the steam can be continuously fed. A possible reactor is a fluidized bed reactor containing inert particles in which the bed is kept fluidized by the steam. Another example of a reactor is a horizontal tube reactor having a rotating axis on which axis means for mixing and/or transport are present. Also means are possible present which prevent fouling of the interior vessel wall and which promote an optimal steam/substrate contact area for mass-transfer.
Examples of suitable cyclisation reactors are a packed tower-type reactor, one or multiple staged bubble columns or a multi-tube reactor. In case the cyclisation reactor consists of two or more reactor vessels in series, the heavies stream or bottom stream from the stripper is preferably fed to the last reactor vessel.
A possible process according to the invention is schematically represented in FIG.
1
.
In the cyclisation reactor (
1
) the gaseous stream (
1
a
) comprising &egr;-caprolactam, steam, lights and heavies is obtained.
The starting mixtures comprising 6-aminocaproic acid, 6-aminocaproate ester, 6-aminocaproamide, oligomers of these compounds and/or polymers of these compounds can be obtained by various processes. For example in U.S. Pat. No. 4730040 a process is described in which an aqueous mixture is obtained containing 6-aminocaproic acid and some &egr;-caprolactam starting from 5-formylvalerate ester. Further in EP-A-729943 a process is described in which an aqueous mixture is obtained containing 6-aminocaproic acid, 6-aminocaproamide and &egr;-caprolactam also starting from a U.S. Pat. No. 5-formylvalerate ester. US-A-5068398 describes a process in which an aqueous mixture is obtained containing 6-aminocaproate ester and some &egr;-caprolactam starting from a 5-formylvalerate ester.
Other examples of starting mixtures which can be used in the process according to the invention are polycaprolactam processing waste, polycaprolactam carpet waste and/or polycaprolactam extraction wash water.
The starting compound or mixture of starting compounds which are obtainable by the above described processes, are preferably contacted with the superheated steam as a liquid, for example as a melt.
Polycaprolactam waste is preferably fed to the reactor as a melt. This feeding may be achieved by using an extruder, gear pump, or other means known in the art.
Starting mixtures can also be obtained starting from 6-aminocapronitrile as for example described in WO-A-9837063.
The cyclisation is preferably performed as described in WO-A-9837063.
The condensation and at least partial removal of water, lights and heavies from the product stream can be conducted in the following steps:
a) the product stream is fed to a partial condensation unit (
2
), and split in a top stream comprising steam (
2
t
) and a liquid bottom stream
(
2
b
) comprising &egr;-caprolactam, water, lights and heavies;
b) the bottom stream (
2
b
) is fed to a distillation column (
3
) of which the top stream (
3
t
) is mainly water and the bottom stream (
3
b
) comprises &egr;-caprolactam, lights and heavies;
c) the botto
Agterberg Frank P. W.
Guit Rudolf P. M.
Haasen Nicolaas F.
DSM N.V.
Kifle Bruck
Pillsbury & Winthrop LLP
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