Title of Invention	"A METHOD FOR SEPARATION AND SIMULTANEOUS RECOVERY OF MONOMERS AND OLIGOMERS FROM NYLON-6 OLIGOMERIC WASTE"
Abstract	A method for separation and simultaneous recovery of monomers and oligomers, from nylon-6 oligomeric waste has been described. The invention discloses recovery of particularly cyclic and linear oligomers and of monomers, particularly caprolactam and aminocaproic acid monomers from the oligomeric waste. The process comprises heating the nylon-6 oligomeric waste preferably containing 10 to 20% of oligomers in presence of at least more than equal volume of water to a temperature of more than 60 C, then gradually cooling to a temperature between 25 & 40°C, separating the solid mass/ residue by centrifugation and recovering oligomers from the residue by washing the said residue and monomers by conventional methods of crystallization or fractional distillation.

Title of Invention

"A METHOD FOR SEPARATION AND SIMULTANEOUS RECOVERY OF MONOMERS AND OLIGOMERS FROM NYLON-6 OLIGOMERIC WASTE"

Abstract

A method for separation and simultaneous recovery of monomers and oligomers, from nylon-6 oligomeric waste has been described. The invention discloses recovery of particularly cyclic and linear oligomers and of monomers, particularly caprolactam and aminocaproic acid monomers from the oligomeric waste. The process comprises heating the nylon-6 oligomeric waste preferably containing 10 to 20% of oligomers in presence of at least more than equal volume of water to a temperature of more than 60 C, then gradually cooling to a temperature between 25 & 40°C, separating the solid mass/ residue by centrifugation and recovering oligomers from the residue by washing the said residue and monomers by conventional methods of crystallization or fractional distillation.

Full Text	Field of the Invention: The present invention relates to a method for separation and simultaneous recovery of monomers and from nylon-6 oligomeric waste. More particularly, it relates to the method of simultaneous recovery of cyclic and linear oligomers, and caprolactam and aminocaproic acid monomers from the nylon-6 oligomeric waster from caprolactam distillation still or from caprolactam recovery plant. Even more particularly, it relates to the method of simultaneous recovery of oligomers and monomers from the nylon-6 oligomeric waste, which at least comprises of 10 to 20% of oligomers or caprolactam. Background of the Invention: During purification of nylon-6 chips, a small amount of oligomers are also extracted along with un-reacted monomers particularly caprolactam. These oligomers along with others generated during the distillation process of crude monomers, particularly caprolactam are recovered as distilled residue from the caprolactam recovery plant. This residue is termed waste, particularly waste from caprolactam distillation still or from caprolactam recovery plant. According to the present state of the art, such waste is generated, when the polymer chips along with water are added to an extractor and the temperature is raised to about 100°C, which results in waste -water, containing lactam and oligomer to divide into two parts. A portion of the wash water is added to a depolymerisation chamber to condense the depolymerisation products, as a result, at the exit of the depolymerisation chamber, the concentration of the caprolactam in the feed increases to about 40 to 45%. This was added to the second portion of the initial wash water, which results in about 18 to 20% final concentration of the monomers, particularly caprolactam and of oligomers. Water from mixture of the monomers, particularly caprolactam and of oligomers is evaporated to result in a concentration of about 85% of the monomers and oligomers and fed to a distillation tank. Upon distillation of caprolactam from this mixture, the residue left, primarily contains cyclic and linear oligomers along with certain impurities, but when the distillation tower is shut down to remove the residue a small amount of caprolactam present in the form of vapors gets condensed and trapped in the oligomeric waste, which is the source of small percentage of caprolactam present in the waste and is referred herein as the waste, particularly a waste from caprolactam distillation still or from caprolactam recovery plant, The monomers, particularly caprolactam with small amount of aminocaproic acid, and oligomers are useful raw materials for further polymerization processes. Therefore, efforts had been on to separate and to recover monomers, particularly caprolactam with small amount of aminocaproic acid, and oligomers from such wastes. The presently known methods of the art relates to separation and recovery of monomers, particularly caprolactam with small amount of aminocaproic acid by way of depolymerisation. Such known methods result in conversion of oligomers in to monomers, particularly in to caprolactam monomers, which separate out being in higher percentage. The main drawback of such known methods is that, these methods result in conversion of oligomers in to monomers, particularly in to caprolactam monomers and therefore adds to additional steps during further polymerization of oligomers, which calls for first polymerization of caprolactam to oligomers and then further polymerization. Such methods find application where recovery of caprolactam is the only objective. However, such objective is met with certain limitation, such as recovered lactam is of comparatively poor quality and the low conversion rate, about 75% and hence making the process uneconomical. Another drawback of such known methods is that, these methods do not result in recovery of pure oligomers and hence do not result in separation and recovery of monomers, particularly caprolactam, and of oligomers from such wastes. Still another drawback of such known methods is that, the depolymerisation, as stated herein above, is required to be carried out at a higher temperature generally using HTHP steam followed by distillation, which is economically not viable. Still further drawback of such known methods is that, the cleaning frequency of the depolymerisation chamber is higher. Yet another drawback of such known methods is that, the choking frequency of the depolymerisation chamber is higher, which some times result in hazardous reaction, the probability of which is further increased due to property of oligomers to catch fire due to presence of oxidising reagents. Yet further drawback of such known methods is that, the consumption of KMn04, H3PO4 and NaOH is higher. The above drawbacks and limitations of such known methods compel the oligomeric waste to go unused resulting in their dumping in landfills impairing environment quality. Need of the Invention: Therefore, there is need to develop a process for separation and recovery of monomers, particularly caprolactam and of oligomers from oligomeric waste, as referred herein above, which can overcome some of the limitations and drawbacks of the presently known methods. Particularly, the requirement is of a method, which can first separate the monomers, particularly caprolactam and oligomers, and then result in their recovery from their respective waste or impurities to overcome the main drawback of hazardous reaction due to property of oligomers to catch fire due to presence of oxidising agents. Objects of the Invention: This is the main object of the present invention is to make a disclosure of a process for separation and recovery of monomers particularly caprolactam and of oligomers from oligomeric waste, as referred herein above, which can overcome some of the limitations and drawbacks of the presently known methods. The another object of this invention is to make a disclosure of a method, which can first separate the monomers, particularly caprolactam and oligomers, and then result in their recovery from their respective waste or impurities to overcome the main drawback of the presently known methods, that is of an hazardous reaction due to property of oligomers to catch fire due to presence of oxidising agents. This is yet another object of this invention to make a complete disclosure of a method for simultaneous recovery of oligomers and monomers from the oligomeric waste, particularly of a method of simultaneous recovery of cyclic and linear oligomers, and caprolactam and aminocaproic acid monomers from the nylon-6 oligomeric waste, more particularly of a method of simultaneous recovery of cyclic and linear oligomers, and caprolcatam and aminocaproic acid monomers from the nylon-6 oligomeric waste from caprolactam distillation still or from caprolactam recovery plant, even more particularly of a method of simultaneous recovery of oligomers and monomers from the nylon-6 oligomeric waste which at least comprises of 10 to 20% of oligomers or caprolactam. Yet another an object of the present invention is that the depolymerisation step is totally eliminated, hence the following drawbacks and limitations associated with the step of depolymerisation are totally eliminated, such as: - a) conversion of oligomers in to monomers, particularly in to caprolactam monomers, therefore reduces an additional step and associated cost during further polymerization of oligomers, b) poor quality of recovered caprolactam, c) need to carry out the reaction at higher temperature generally using HTHP steam followed by distillation, d) higher cleaning frequency of the depolymerisation chamber, e) higher choking frequency of the depolymerisation chamber, hence resulting in reduction of chances of occurrences of hazardous reaction, f) higher consumption of KMnCU, HsPCU and NaOH. Further objects and the preferred embodiments of the present invention will be more apparent from the following description. Brief description of the Invention: Accordingly, this invention provides a method for separation and simultaneous recovery of monomers and oligomers from nylon-6 oligomeric waste, which comprises heating the nylon-6 oligomeric waste in presence of at least more than equal volume of water to a temperature of more than 60 C, then gradually cooling to a temperature between 25 & 40°C, separating the solid mass/ residue by centrifugation, optionally concentrating the supernatant, and recovering oligomers from the residue by washing the said residue and monomers by conventional methods of crystallization or fractional distillation. The nylon-6 oligomeric waste, which is generally generated from caprolactam distillation still or from caprolactam recovery plant is used as a starting material. More particularly the nylon-6 oligomeric waste employed comprises at least of 10 to 20% of said oligomers or said monomers. The heating is carried out under stirring. In accordance to the preferred embodiments of the present invention the oligomers, particularly cyclic and linear oligomers are recovered from solid mass/residue and monomers, particularly caprolactam and aminocaproic acid are recovered from solution. According to the present invention the said solid mass/residue is given washing in a wash tank, preferably while stirring followed by centrifugation, for recovery of said oligomers with very small quantity of soluble impurities. Further, in accordance to the present invention the supernatant is concentrated in a concentrator by evaporating excess of water preferably under vacuum before recovery of monomers by crystallization. The resulted crystals are generally mixture of caprolactam and aminocaproic acid. In accordance to another preferred embodiment of the present invention, the solution is optionally treated with small quantity of alkali after concentration in the concentrator, to get a pH of about 7 to 8 before subjected to fractional distillation. In accordance to the preferred embodiment, the said oligomers as recovered from the said waste are about 50% and the said monomers as recovered from the said waste are about 30% of the total waste. Detail description of the Invention: Accordingly, this invention makes a complete disclosure of a method for separation and simultaneous recovery of oligomers, particularly cyclic and linear oligomers, and of monomers, particularly caprolactam and aminocaproic acid monomers from the oligomeric waste, particularly from nylon-6 oligomeric waste, which is generally generated from caprolactam distillation still or from caprolactam recovery plant, wherein the said waste is treated with water, preferably three to four times, in a reactor. The temperature of the reacting mass is increased to about 60 to 90°C preferably while stirring for a period of about 15 to 45 minutes. The reacted mass is then allowed to cool down to about 40°C preferably while stirring, then finally to about room temperature. In accordance to the present invention the cooled reacted mass is centrifuged in a centrifuger, which results in separation of oligomers, particularly cyclic and linear oligomers, and of monomers, particularly caprolactam and aminocaproic acid. In accordance to the preferred embodiments of the present invention the oligomers, particularly cyclic and linear oligomers are obtained as solid cake containing said oligomers along with oxidised cyclic and linear and other unknown structures of oligomers and small quantity of impurities, and monomers, particularly caprolactam and aminocaproic acid are obtained as solution containing said monomers along with some soluble impurities and small quantity of oligomers, which are simultaneously subjected to recovery of said oligomers and monomers. According to the present disclose method of separation and recovery of said oligomers and said monomers, the cake containing said oligomers is about 52% and the solution containing said monomers is about 48%. According to the present invention the said solid cake containing said oligomers along with oxidised cyclic and linear and other unknown structures of oligomers and small quantity of impurities is given washing in a wash tank, preferably while stirring followed by centrifugation, which results in recovery of said oligomers with very small quantity of soluble impurities. The oligomers, as obtained in accordance to the preferred embodiment of the present invention show about 50 meq/kg of NH2 end groups and intrinsic viscosity of about 0.12 dl/gm in m-cresol at about 25°C. Further, in accordance to the present invention the solution containing said monomers along with some soluble impurities and small quantity of oligomers is concentrated in a concentrator by evaporating excess of eater preferably under vacuum at a temperature of about 60 to 80°C to about one fifth of the original volume of the said solution. The concentration solution is then subjected to crystallization in a crystallizer, while cooling to about a temperature lower than room temperature. The resulted crystals are filtered, which are generally mixture of said monomers, particularly of caprolactam and aminocaproic acid, which have been verified by nuclear magnetic spectroscopic study. In accordance to another preferred embodiment of the present invention, the solution containing said monomers along with some soluble impurities and small quantity of oligomers is alternately treated with small quantity of alkali, preferably with NaOH after concentration in the concentrator, to optimise the pH of the said concentrated solution to about 7 to 8 pH. This concentrated solution having pH of about 7 to 8 is subjected to fractional distillation. In accordance to the preferred embodiment of the present invention the fractional distillation, which results in recovery and separation of pure caprolactam and pure aminocaproic acid, is carried out at a temperature of about 130 to 150°C, more preferably at about 138 to 143°C under pressure of about 10 mmHg, particularly of caprolactam. The separated and recovered caprolactam and aminocaproic acid have been identified by nuclear magnetic spectroscopic study and melting point. The recovered caprolactam shows melting point ofabout65°C. In accordance to the preferred embodiment, the said oligomers as recovered from the said waste are about 50%, which find their applications as fillers in polymer matrix and in further polymerization to form various polymers of polyamides class, as described in our co-pending patent application number 749/DEL/1999, and the said monomers as recovered from the said waste are about 30% of the total waste, which find their application to manufacturer pure nylon-6 etc. We Claim: 1. A method for separation and simultaneous recovery of monomers and oligomers from nylon-6 oligomeric waste, which comprises heating the nylon-6 oligomeric waste in presence of at least more than equal volume of water to a temperature of more than 60 C, then gradually cooling to a temperature between 25 & 40 C, separating the solid mass/ residue by centrifugation, optionally concentrating the supernatant, and recovering oligomers from the residue by washing the said residue and monomers by conventional methods of crystallization or fractional distillation. 2. A method as claimed in claim 1 wherein the waste used for separation and recovery contains 10 to 20 % of oligomers. 3. A method as claimed in claim 1, wherein said waste is heated with water three to four times of the waste. 4. A method in claims 1 & 2, wherein the heating is effected to a temperature in therangeof60°Cto90°C. 5. A method, as claimed in claims 1 to3, wherein the heating is carried out under stirring and for a period of about 15 to 45 minutes. 6. A method, as claimed in claim 1, wherein the cooling is conducted under stirring. 7. A method as claimed in claim 1 wherein the supernatant is concentrated at a temperature between 60°C to 80°C, preferably under vacuum, to about one fifth of the original volume, prior to subjecting to recover of monomers. 8. A method, as claimed in claims 1 wherein the crystallization is carried out while cooling to about a temperature lower than room temperature. 9. A method as claimed in claim 1 wherein pH of the said separated solution is adjusted to between 7 & 8 by adding alkali, preferably NaOH when the monomers are recovered by fractional distillation. 10. A method as claimed in claim 1 wherein the fractional distillation for recovery of the monomers is carried out at a temperature in the range of 130°C to 150°C, preferably at 138°C to 143°C and under pressure. 11. A method for separation and simultaneous recovery of monomers and oligomers from nylon-6 oligomeric waste substantially as herein described.

Full Text

Field of the Invention:
The present invention relates to a method for separation and simultaneous recovery of monomers and from nylon-6 oligomeric waste.
More particularly, it relates to the method of simultaneous recovery of cyclic and linear oligomers, and caprolactam and aminocaproic acid monomers from the nylon-6 oligomeric waster from caprolactam distillation still or from caprolactam recovery plant. Even more particularly, it relates to the method of simultaneous recovery of oligomers and monomers from the nylon-6 oligomeric waste, which at least comprises of 10 to 20% of oligomers or caprolactam.
Background of the Invention:
During purification of nylon-6 chips, a small amount of oligomers are also extracted along with un-reacted monomers particularly caprolactam. These oligomers along with others generated during the distillation process of crude monomers, particularly caprolactam are recovered as distilled residue from the caprolactam recovery plant. This residue is termed waste, particularly waste from caprolactam distillation still or from caprolactam recovery plant. According to the present state of the art, such waste is generated, when the polymer chips along with water are added to an extractor and the temperature is raised to about 100°C, which results in waste -water, containing lactam and oligomer to divide into two parts. A portion of the wash water is added to a depolymerisation chamber to condense the depolymerisation products, as a result, at the exit of the depolymerisation chamber, the concentration of

the caprolactam in the feed increases to about 40 to 45%. This was added to the second portion of the initial wash water, which results in about 18 to 20% final concentration of the monomers, particularly caprolactam and of oligomers. Water from mixture of the monomers, particularly caprolactam and of oligomers is evaporated to result in a concentration of about 85% of the monomers and oligomers and fed to a distillation tank. Upon distillation of caprolactam from this mixture, the residue left, primarily contains cyclic and linear oligomers along with certain impurities, but when the distillation tower is shut down to remove the residue a small amount of caprolactam present in the form of vapors gets condensed and trapped in the oligomeric waste, which is the source of small percentage of caprolactam present in the waste and is referred herein as the waste, particularly a waste from caprolactam distillation still or from caprolactam recovery plant,
The monomers, particularly caprolactam with small amount of aminocaproic acid, and oligomers are useful raw materials for further polymerization processes. Therefore, efforts had been on to separate and to recover monomers, particularly caprolactam with small amount of aminocaproic acid, and oligomers from such wastes.
The presently known methods of the art relates to separation and recovery of monomers, particularly caprolactam with small amount of aminocaproic acid by way of depolymerisation. Such known methods result in conversion of oligomers in to monomers, particularly in to caprolactam monomers, which separate out being in higher percentage.
The main drawback of such known methods is that, these methods result in conversion of oligomers in to monomers, particularly in to caprolactam monomers and therefore adds to additional steps during further polymerization of oligomers, which calls for first polymerization of caprolactam to oligomers and then further

polymerization. Such methods find application where recovery of caprolactam is the only objective. However, such objective is met with certain limitation, such as recovered lactam is of comparatively poor quality and the low conversion rate, about 75% and hence making the process uneconomical.
Another drawback of such known methods is that, these methods do not result in recovery of pure oligomers and hence do not result in separation and recovery of monomers, particularly caprolactam, and of oligomers from such wastes.
Still another drawback of such known methods is that, the depolymerisation, as stated herein above, is required to be carried out at a higher temperature generally using HTHP steam followed by distillation, which is economically not viable.
Still further drawback of such known methods is that, the cleaning frequency of the depolymerisation chamber is higher.
Yet another drawback of such known methods is that, the choking frequency of the depolymerisation chamber is higher, which some times result in hazardous reaction, the probability of which is further increased due to property of oligomers to catch fire due to presence of oxidising reagents.
Yet further drawback of such known methods is that, the consumption of KMn04, H3PO4 and NaOH is higher.
The above drawbacks and limitations of such known methods compel the oligomeric waste to go unused resulting in their dumping in landfills impairing environment quality.
Need of the Invention:

Therefore, there is need to develop a process for separation and recovery of monomers, particularly caprolactam and of oligomers from oligomeric waste, as referred herein above, which can overcome some of the limitations and drawbacks of the presently known methods. Particularly, the requirement is of a method, which can first separate the monomers, particularly caprolactam and oligomers, and then result in their recovery from their respective waste or impurities to overcome the main drawback of hazardous reaction due to property of oligomers to catch fire due to presence of oxidising agents.
Objects of the Invention:
This is the main object of the present invention is to make a disclosure of a process for separation and recovery of monomers particularly caprolactam and of oligomers from oligomeric waste, as referred herein above, which can overcome some of the limitations and drawbacks of the presently known methods.
The another object of this invention is to make a disclosure of a method, which can first separate the monomers, particularly caprolactam and oligomers, and then result in their recovery from their respective waste or impurities to overcome the main drawback of the presently known methods, that is of an hazardous reaction due to property of oligomers to catch fire due to presence of oxidising agents.
This is yet another object of this invention to make a complete disclosure of a method for simultaneous recovery of oligomers and monomers from the oligomeric waste, particularly of a method of simultaneous recovery of cyclic and linear oligomers, and caprolactam and aminocaproic acid monomers from the nylon-6 oligomeric waste, more particularly of a method of simultaneous recovery of cyclic and linear oligomers,

and caprolcatam and aminocaproic acid monomers from the nylon-6 oligomeric waste from caprolactam distillation still or from caprolactam recovery plant, even more particularly of a method of simultaneous recovery of oligomers and monomers from the nylon-6 oligomeric waste which at least comprises of 10 to 20% of oligomers or caprolactam.
Yet another an object of the present invention is that the depolymerisation step is totally eliminated, hence the following drawbacks and limitations associated with the step of depolymerisation are totally eliminated, such as: -
a) conversion of oligomers in to monomers, particularly in to caprolactam
monomers, therefore reduces an additional step and associated cost during
further polymerization of oligomers,
b) poor quality of recovered caprolactam,
c) need to carry out the reaction at higher temperature generally using HTHP
steam followed by distillation,
d) higher cleaning frequency of the depolymerisation chamber,
e) higher choking frequency of the depolymerisation chamber, hence resulting in
reduction of chances of occurrences of hazardous reaction,
f) higher consumption of KMnCU, HsPCU and NaOH.
Further objects and the preferred embodiments of the present invention will be more apparent from the following description.
Brief description of the Invention:

Accordingly, this invention provides a method for separation and simultaneous recovery of monomers and oligomers from nylon-6 oligomeric waste, which comprises heating the nylon-6 oligomeric waste in presence of at least more than equal volume of water to a temperature of more than 60 C, then gradually cooling to a temperature
between 25 & 40°C, separating the solid mass/ residue by centrifugation, optionally
concentrating the supernatant, and recovering oligomers from the residue by washing
the said residue and monomers by conventional methods of crystallization or fractional
distillation.
The nylon-6 oligomeric waste, which is generally generated from caprolactam
distillation still or from caprolactam recovery plant is used as a starting material.
More particularly the nylon-6 oligomeric waste employed comprises at least of 10 to
20% of said oligomers or said monomers.
The heating is carried out under stirring.
In accordance to the preferred embodiments of the present invention the oligomers, particularly cyclic and linear oligomers are recovered from solid mass/residue and monomers, particularly caprolactam and aminocaproic acid are recovered from solution.
According to the present invention the said solid mass/residue is given washing in a wash tank, preferably while stirring followed by centrifugation, for recovery of said oligomers with very small quantity of soluble impurities.
Further, in accordance to the present invention the supernatant is concentrated in a concentrator by evaporating excess of water preferably under vacuum before recovery

of monomers by crystallization. The resulted crystals are generally mixture of caprolactam and aminocaproic acid.
In accordance to another preferred embodiment of the present invention, the solution is optionally treated with small quantity of alkali after concentration in the concentrator, to get a pH of about 7 to 8 before subjected to fractional distillation.
In accordance to the preferred embodiment, the said oligomers as recovered from the said waste are about 50% and the said monomers as recovered from the said waste are about 30% of the total waste.
Detail description of the Invention:
Accordingly, this invention makes a complete disclosure of a method for separation and simultaneous recovery of oligomers, particularly cyclic and linear oligomers, and of monomers, particularly caprolactam and aminocaproic acid monomers from the oligomeric waste, particularly from nylon-6 oligomeric waste, which is generally generated from caprolactam distillation still or from caprolactam recovery plant, wherein the said waste is treated with water, preferably three to four times, in a reactor. The temperature of the reacting mass is increased to about 60 to 90°C preferably while stirring for a period of about 15 to 45 minutes. The reacted mass is then allowed to cool down to about 40°C preferably while stirring, then finally to about room temperature. In accordance to the present invention the cooled reacted mass is centrifuged in a centrifuger, which results in separation of oligomers, particularly cyclic and linear oligomers, and of monomers, particularly caprolactam and aminocaproic acid.

In accordance to the preferred embodiments of the present invention the oligomers, particularly cyclic and linear oligomers are obtained as solid cake containing said oligomers along with oxidised cyclic and linear and other unknown structures of oligomers and small quantity of impurities, and monomers, particularly caprolactam and aminocaproic acid are obtained as solution containing said monomers along with some soluble impurities and small quantity of oligomers, which are simultaneously subjected to recovery of said oligomers and monomers. According to the present disclose method of separation and recovery of said oligomers and said monomers, the cake containing said oligomers is about 52% and the solution containing said monomers is about 48%.
According to the present invention the said solid cake containing said oligomers along with oxidised cyclic and linear and other unknown structures of oligomers and small quantity of impurities is given washing in a wash tank, preferably while stirring followed by centrifugation, which results in recovery of said oligomers with very small quantity of soluble impurities. The oligomers, as obtained in accordance to the preferred embodiment of the present invention show about 50 meq/kg of NH2 end groups and intrinsic viscosity of about 0.12 dl/gm in m-cresol at about 25°C.
Further, in accordance to the present invention the solution containing said monomers along with some soluble impurities and small quantity of oligomers is concentrated in a concentrator by evaporating excess of eater preferably under vacuum at a temperature of about 60 to 80°C to about one fifth of the original volume of the said solution. The concentration solution is then subjected to crystallization in a crystallizer, while cooling to about a temperature lower than room temperature. The resulted crystals are filtered, which are generally mixture of said monomers,

particularly of caprolactam and aminocaproic acid, which have been verified by nuclear magnetic spectroscopic study.
In accordance to another preferred embodiment of the present invention, the solution containing said monomers along with some soluble impurities and small quantity of oligomers is alternately treated with small quantity of alkali, preferably with NaOH after concentration in the concentrator, to optimise the pH of the said concentrated solution to about 7 to 8 pH. This concentrated solution having pH of about 7 to 8 is subjected to fractional distillation. In accordance to the preferred embodiment of the present invention the fractional distillation, which results in recovery and separation of pure caprolactam and pure aminocaproic acid, is carried out at a temperature of about 130 to 150°C, more preferably at about 138 to 143°C under pressure of about 10 mmHg, particularly of caprolactam. The separated and recovered caprolactam and aminocaproic acid have been identified by nuclear magnetic spectroscopic study and melting point. The recovered caprolactam shows melting point ofabout65°C.
In accordance to the preferred embodiment, the said oligomers as recovered from the said waste are about 50%, which find their applications as fillers in polymer matrix and in further polymerization to form various polymers of polyamides class, as described in our co-pending patent application number 749/DEL/1999, and the said monomers as recovered from the said waste are about 30% of the total waste, which find their application to manufacturer pure nylon-6 etc.

We Claim:
1. A method for separation and simultaneous recovery of monomers and oligomers
from nylon-6 oligomeric waste, which comprises heating the nylon-6
oligomeric waste in presence of at least more than equal volume of water to a
temperature of more than 60 C, then gradually cooling to a temperature
between 25 & 40 C, separating the solid mass/ residue by centrifugation,
optionally concentrating the supernatant, and recovering oligomers from the residue by washing the said residue and monomers by conventional methods of crystallization or fractional distillation.
2. A method as claimed in claim 1 wherein the waste used for separation and
recovery contains 10 to 20 % of oligomers.
3. A method as claimed in claim 1, wherein said waste is heated with water three
to four times of the waste.
4. A method in claims 1 & 2, wherein the heating is effected to a temperature in
therangeof60°Cto90°C.
5. A method, as claimed in claims 1 to3, wherein the heating is carried out under
stirring and for a period of about 15 to 45 minutes.
6. A method, as claimed in claim 1, wherein the cooling is conducted under
stirring.
7. A method as claimed in claim 1 wherein the supernatant is concentrated at a
temperature between 60°C to 80°C, preferably under vacuum, to about one fifth
of the original volume, prior to subjecting to recover of monomers.

8. A method, as claimed in claims 1 wherein the crystallization is carried out while
cooling to about a temperature lower than room temperature.
9. A method as claimed in claim 1 wherein pH of the said separated solution is
adjusted to between 7 & 8 by adding alkali, preferably NaOH when the
monomers are recovered by fractional distillation.
10. A method as claimed in claim 1 wherein the fractional distillation for recovery
of the monomers is carried out at a temperature in the range of 130°C to 150°C,
preferably at 138°C to 143°C and under pressure.
11. A method for separation and simultaneous recovery of monomers and oligomers
from nylon-6 oligomeric waste substantially as herein described.

Documents:

742-del-1999-abstract.pdf

742-del-1999-claims.pdf

742-del-1999-correspondence-others.pdf

742-del-1999-correspondence-po.pdf

742-del-1999-description (complete).pdf

742-del-1999-form-1.pdf

742-del-1999-form-13.pdf

742-del-1999-form-19.pdf

742-del-1999-form-2.pdf

742-del-1999-form-62.pdf

742-del-1999-gpa.pdf

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Patent Number

215762

Indian Patent Application Number

742/DEL/1999

PG Journal Number

12/2008

Publication Date

21-Mar-2008

Grant Date

03-Mar-2008

Date of Filing

17-May-1999

Name of Patentee

DEAN, INDUSTRIAL RESEARCH AND DEVELOPMENT (IRD),INDIAN INSTITUTE OF TECHNOLOGY,DELHI (IITD)

Applicant Address

INDIAN INSTITUTE OF TECHNOLOGY, DELHI (IITD) HAUZ KHAS, NEW DELHI-110 016, INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	DEAN, INDUSTRIAL RESEARCH AND DEVELOPMENT (IRD)	INDIAN INSTITUTE OF TECHNOLOGY, DELHI (IITD) HAUZ KHAS, NEW DELHI-110 016, INDIA.
2	CHIEF EXECUTIVE, M/S MODIPON FIBRES COMPANY (A DIVISION OF MODIPON LIMITED)	MODINAGAR,-201204, U.P., INDIA.
3	ASHWINI KUMAR AGRAWAL	DEPARTMENT OF TEXTILE TECHNOLOGY, INDIA INSTITUTE OF TECHNOLOGY, HAUZ KHAS, NEW DELHI-110 016, INDIA.
4	PUSHPA BAJAJ	DEPARTMENT OF TEXTILE TECHNOLOGY, INDIA INSTITUTE OF TECHNOLOGY, HAUZ KHAS, NEW DELHI-110 016, INDIA.
5	SAMRAT MUKHOPADHYAY	DEPARTMENT OF TEXTILE TECHNOLOGY, INDIA INSTITUTE OF TECHNOLOGY, HAUZ KHAS, NEW DELHI-110 016, INDIA.
6	MS.PREETI LODHA	DEPARTMENT OF TEXTILE TECHNOLOGY, INDIA INSTITUTE OF TECHNOLOGY, HAUZ KHAS, NEW DELHI-110 016, INDIA.

PCT International Classification Number

C08

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA