Organic compounds -- part of the class 532-570 series – Organic compounds – Unsubstituted hydrocarbyl chain between the ring and the -c-...
Reexamination Certificate
1999-03-01
2002-03-05
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
06353100
ABSTRACT:
The invention relates to a process for the preparation of &egr;-caprolactam, in which, in a first step (a), a compound having the general formula:
O=CH—(CH
2
)
4
—C(O)—R (1)
wherein R represents —OH, —NH
2
or —OR′, and wherein R′ represents an organic group with from 1 to 10 carbon atoms, is brought into contact with ammonia and hydrogen in a suitable solvent at elevated pressure and in the presence of a hydrogenation catalyst, to form a mixture of primary amino compounds and &egr;-caprolactam. This is then followed by a separate second step (b) in which the primary amino compounds are reacted to form &egr;-caprolactam.
Such a process is described in U.S. Pat. No. 4,730,041. This patent describes a process in which methyl 5-formylvalerate is first reacted with excess ammonia and hydrogen in the pressence of methanol as solvent, and in the presence of a catalyst, such as Raney-nickel, in the liquid phase at 80° C. to yield a mixture of about 89% methyl 6-aminocaproate and about 3% &egr;-caprolactam. This mixture is subsequently heated to 225° C. to yield 78% &egr;-caprolactam. The total concentration of all of the reactants in the different process steps was about 10 wt %.
A disadvantage of the process described in this U.S. Pat. No. 4,730,041 is that relatively large-sized process equipment for the (step (b)) cyclization section is required. This is due to the low concentration of reactants in that step. According to the patent the cyclization is also performed at super atmospheric pressures, requiring special process equipment. From an economical/investment point of view, smaller-sized, less expensive, process equipment is generally desired. However, merely using smaller-sized process equipment (which might otherwise seem possible simply by increasing the reactant concentration in the cyclization step) is disadvantageous since a loss of yield is to be expected due to the increased formation of oligomers. See discussion in the article by Mares and Sheehan in Ind. Eng. Chem. Process Des. Dev., Vol. 17, No. 1, 1978, 9-16
The principal object of this invention is to provide a process which can be effectively operated in process equipment of a smaller volume for the cyclization section (step b) as compared to processes of the current state of the art.
This object is achieved by employing the combination of conditions wherein the solvent used in step (a) is an aqueous medium, including water, and the &egr;-caprolactam yield obtained in step (a) is brought to at least 10%, calculated on the initial molar amount of the compound according to formula (1), and that the &egr;-caprolactam is separated from the aqueous mixture obtained from step (a) by extraction using an organic extraction agent, and with the aqueous mixture resulting from the extraction step, containing the primary amino compound, is then used as the feed into step (b).
The above results in the following process according to the invention preparing for &egr;-caprolactam, wherein, in a first step (a), a compound having the general formula:
O=CH—(CH
2
)
4
—C(O)—R (1)
wherein R is —OH, —NH
2
or O—R′, and wherein R′ is an organic group with 1 to 10 carbon atoms, and in an aqueous medium as solvent,
is contacted at an elevated pressure with ammonia and hydrogen in the presence of a hydrogenation catalyst to form a mixture of &egr;-caprolactam and primary amino compounds,
and wherein the yield to &egr;-caprolactam in step (a) is carried to a level of at least 10 molar%, calculated on the initial molar amount of said compound,
and extracting &egr;-caprolactam from said aqueous mixture obtained from step (a) with an organic extraction agent
to form an organic extractant solution of &egr;-caprolactam and a separate residual aqueous mixture,
followed by a separate second step (b) wherein said primary amino compounds in said residual aqueous mixture are further reacted to form &egr;-caprolactam.
By using an aqueous medium (including water) as the solvent in step (a) and by increasing the &egr;-caprolactam yield in step (a), &egr;-caprolactam can be advantageously separated from the reaction mixture prior to step (b) by extraction. Then, as a result of the separation of the &egr;-caprolactam prior to step (b), a smaller-sized volume of process equipment can be effectively used in step (b) while avoiding the drawbacks of the present state of the art.
A further advantage of the present invention is that a substantial part of the &egr;-caprolactam can be prepared at the relatively low temperature used in the first step (a). By contrast, in the process of U.S. Pat. No. 4,730,041, almost all of the &egr;-caprolactam is prepared in the second step (b) at relatively high temperatures, for example 300° C. This is a significant temperature difference. By operating according to the present invention, the overall consumption of energy required to prepare one mol of &egr;-caprolactam of the process will be less than that of the present state of the art process.
Further, the fact that less &egr;-caprolactam is exposed to the higher temperature of the second step is also advantageous in that the level of impurities in the &egr;-caprolactam obtained is lowered. Moreover, at higher temperatures &egr;-caprolactam tends to react more readily to impurities than at lower temperature levels.
Another advantage of the present invention is that &egr;-caprolactam can be obtained in higher overall yields than was possible with the state of the art process as described in U.S. Pat. No. 4,730,041.
Examples of processes which yield more than 10% of &egr;-caprolactam in a process comparable to step (a) are generally not reported in the prior art, probably because at such higher yields &egr;-caprolactam oligomers can be formed. Oligomer formation is as a rule considered to be disadvantageous when the desired product is &egr;-caprolactam. However, we have now found that such oligomer formation in step (a) does not have to result in a reduction of the overall &egr;-caprolactam yield.
It has further been found that &egr;-caprolactam can be exclusively separated from an aqueous mixture containing 6-aminocaproic acid, 6-aminocaproamide and/or their respective oligomers. These primary amino compounds are the most important reaction products of step (a) and are the starting compounds for the further reaction to &egr;-caprolactam in step (b).
The extraction of &egr;-caprolactam from the aqueous mixture can be performed with any organic extraction solvent which is substantially immiscible with the aqueous mixture. By substantially immiscible is here meant that the mixture of organic extraction solvent and the aqueous mixture results in two segregated phases at the extraction temperature. Preferable the mutual solubility under the conditions of the extraction is not higher than 30 wt. % and more preferably less than 20 wt. %.
Examples of such solvents include ethers, for example methyl tert-butylether, aromatics, for example toluene, benzene and xylene and parafinic solvents, for example decaline. Preferably chlorinated hydrocarbons with 1 to 10 carbon atoms are used. Examples are dichloromethane, chloroform or 1,1,1-trichloroethane.
Examples of another class of extraction agents are phenol and alkyl phenols. A preferred class of alkyl phenols are those which have a boiling point higher than that of &egr;-caprolactam. Preferably, the alkyl phenol has a boiling point higher than the boiling point of &egr;-caprolactam, which is 270° C. at 0.1 MPa. Alkyl phenols have high boiling points at atmospheric pressure. Therefore, in this context, the boiling points are advantageously compared at reduced pressures of, for example, 1.3 kPa (10 mmHg). Caprolactam has a boiling point of 140° C. at 10 mmHg, while dodecyl phenol, for example, has a boiling point of 190° C. at that pressure. By preference, the boiling point of the alkyl phenol is at least about 5° C., and in particular, at least about 15° C. above the boiling point for caprolactam at 1.3 kPa (10 mmHg). The upper limit for the boiling point of the alkyl phenol
Buijs Wim
Guit Rudolf P. M.
DSM N.V.
Kifle Bruck
Pillsbury Madison & Sutro LLP
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