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Process for purification of caprolactam obtained from depolymerization of polyamide-containning carpet
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A technology of caprolactam and crude caprolactam, which is applied in the directions of separation/purification of lactam, preparation of lactam, chemical instruments and methods, etc., can solve problems such as unacceptable results and achieve the effect of reducing investment
Inactive Publication Date: 2003-12-10
肖工业集团公司
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As reported in Comparative Example 2 below, the results were also unacceptable
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example 1
[0055] Crude caprolactam 1 (120 g) was distilled at 400 Pa (3 Torr or mmHg) and 120°C in a laboratory setup set up for simple distillation. 95 g of distillate are obtained. The content of the distillation flask was decanted from the flask at 120°C. The distillate was crystallized and washed according to the procedure of Example 1 above. The crystals were analyzed for water content. A second crystallization and wash was performed as described above. The crystal has a permanganate value of 2 and a color of 2.
[0056] Preparation of Crude Caprolactam 2
[0057] The procedure for the preparation of crude caprolactam 1 was repeated 3 times, except that the water-caprolactam vapor from the reactor was sent to the condenser, and the coolant was adjusted to a level that could condense the caprolactam aqueous solution. Most of the steam composed of water vapor is condensed by the second condenser. The carpet contains 46% nylon 6. The aqueous caprolactam condensates were combine...
example 2
[0061] Crude caprolactam 2 (635 g) was distilled at 533 Pa (4 Torr). 508 g of distillate were obtained, which analysis showed 98.7% caprolactam. The temperature in the kettle is 132-134°C. Analysis of the 127 g of material in the kettle indicated that it contained 94% caprolactam. The contents of the kettle flowed easily at 120°C. The mass balance for caprolactam showed that of the 622 g started, 621 g (99.8%) found their way through (501 g in the distillate and 119 g in the kettle).
example 3
[0063] Crude caprolactam 2 (635 g) was distilled at 933 Pa (7 Torr). 501 g of distillate was obtained, which analysis showed 98.6% caprolactam. The temperature in the kettle is 137-140°C. Analysis of the 134 g of material in the kettle showed it to contain 88.8% caprolactam. The contents of the kettle flowed easily at 120°C. The mass balance for caprolactam showed that of the 622 g started, 613 g (98.5%) found their way through (494 g in the distillate and 119 g in the kettle).
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Abstract
The present invention provides a process for the preparation of purified caprolactam comprising the steps of: (a) depolymerizing polyamide-containing carpet in the presence of steam to obtain crude caprolactam and steam; (b) removing substantially all of said water from said crude caprolactam and steam; (c) distilling the resulting concentrated crude caprolactam at a pressure of less than about 8 mmHg and a temperature from about 110 DEG C to about 145 DEG C so as to form overheads and bottoms of the caprolactam; and (d) crystallizing the caprolactam overheads to obtain caprolactam crystals and mother liquor. The resulting purified caprolactam may then be used to make polycaprolactam which may then be used in engineered materials or spun into fiber.
Description
[0001] The present invention relates to a process for the purification of caprolactam obtained by depolymerizing polyamide-containing carpets. Background of the invention [0002] A method for preparing caprolactam, according to Kirk-Othmer Encyclopedia of Chemical Technology (Encyclopedia of Chemical Technology), 4,830-832 (1992), involves liquid-phase catalytic hydrogenation of phenol to generate cyclohexanone, and the generated cyclohexanone reacts with hydroxylamine sulfate to generate Cyclohexanone oxime, and the generated cyclohexanone oxime undergoes Beckmann rearrangement with oleum to generate crude caprolactam. Typical impurities in this crude caprolactam are benzene, cyclohexanone oxime, aniline, swazine, acetic acid, phenol, adipimide, ammonium benzenesulfonate, ammonium 3-cyclohexanonesulfonate and ammonium 2-hydroxycyclohexanone sulfate. Purification methods for such crude caprolactam include oxidation, as disclosed in U.S. Patents 4,148,792, 4,178,287, 4,248,78...
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