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Method for purifying lactams
| Details |
Inventors: Gayet, Hubert; Leconte, Philippe; Perrona, Philippe;
Assignee: Rhodia Fiber and Resin Intermediates (Courbevoie Cedex, FR)
Primary Examiner: Dentz; Bernard
Assistant Examiner:
Attorney, Agent or Firm: Burns, Doane, Swecker & Mathis, L.L.P.
A method for purifying lactams by liquid-liquid extraction and/or processing with an ion exchange resin is disclosed. The method is useful for purifying lactams produced by the cyclising vapour-phase hydrolysis of an aliphatic aminonitrile, and comprises removing the major part of the ammonia before subjecting the lactam to liquid-liquid extraction by means of a solvent including an acidic solvent and/or contacting said lactam with a cation exchange resin. In most applications of the lactam, it is preferable to carry out a hydrogenation step on the compounds of the lactam solution comprising unsaturations, prior to or in addition to the liquid-liquid extraction step and/or the acidic resin contact step. The purification method may also include an oxidation step in addition to or instead of the hydrogenation step. Said method is preferably combined with a distillation step in the presence of a base. |
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DETAILED DESCRIPTION What is claimed is: 1.
Process for purifying a lactam obtained from the cyclizing vapour-phase hydrolysis of an aliphatic aminonitrile, without prior distillation of the lactam and after most of the ammonia contained therein has been removed, said process comprising subjecting lactam to a liquid/liquid extraction using a solvent comprising a solvent of acidic nature and/or placing said lactam in contact with a cation-exchange resin, wherein the lactam used comprises those lactams obtained by cyclizing vapour-phase hydrolysis of an aliphatic aminonitrile of formula (I): N.
tbd.
C--R--NH.
sub.
2 (I) wherein R represents an alkylene radical containing from 3 to 12 carbon atoms.
2.
Process according to claim 1, wherein the lactan used comprises those lactams obtained by cyclizing vapour-phase hydrolysis of an aliphatic aminonitrile of formula (I): N.
tbd.
C--R--NH.
sub.
2 (I) wherein R represents a linear alkylene radical containing 3, 4, 5 or 9 carbon atoms.
3.
Process according to claim 1 wherein the lactam used is caprolactam, prepared from 6-aminocapronitrile.
4.
Process according to claim 1 wherein the lactam to be purified is in the form of an aqueous solution whose lactam concentration is from 20% to 80% on a weight for weight basis.
5.
Process according to claim 1, wherein the aminonitrile represents up to 15 % of the weight of the lactam.
6.
Process according to claim 1, wherein the solvent of acidic nature used in the liquid/liquid extraction is an alkyl hydrogen phosphate.
7.
Process according to claim 1, wherein the solvent of acidic nature used in the liquid/liquid extraction is a dialkyl hydrogen phosphate in the formula of which the linear or branched alkyl groups contain from 1 to 12 carbon atoms.
8.
Process according to claim 1, wherein the solvent of acidic nature used in the liquid/liquid extraction is bis(2-ethylhexyl) hydrogen phosphate.
9.
Process according to claim 1, wherein the solvent of acidic nature is used as a mixture with another organic liquid diluent, the solubility of the lactam in the diluent being less than or equal to 200 grams per litre at 25
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