Process for manufacturing polyamides
The invention relates to a continuous process for manufacturing polyamides. The polyamides are of the type obtained from diacids and diamines. The process comprises an operation of continuous mixing of a compound which is rich in amine end groups and a compound which is rich in acid end groups and a polycondensation operation using the mixture. The invention relates to the starting phase of such a process, during which an aqueous solution comprising a mixture of monomers in substantially stoichiometric proportions is used.
1. A process for the continuous manufacture of polyamide, starting with dicarboxylic acids and diamines, comprising, in a permanent regime, the following steps:
(1) a starting phase,
(2) continuous mixing of two flows of polyamide precursors, one flow rich in acid end groups, and one flow rich in amine end groups,
(3) condensation of the mixture of the two flows, the mixing and condensation being carried out in the same plant or in different plants,
(4) recovery of a flow of product obtained from the condensation operation, at least one flow rate of the flows of precursor being coupled to the result of an analysis of the contents of acid and amine end groups in the mixture, the condensation medium, or the recovered flow, so as to keep these contents and/or their ratio between two nominal values,
wherein said starting phase comprises the following steps:
feeding to the condensation plant an aqueous solution comprising dicarboxylate ions and diammonium ions, in proportions such that their molar ratio is between 0.99 and 1.01,
establishing an operating regime in the condensation plant under temperature and pressure conditions such that there is condensation starting with the dicarboxylate ions and the diammoniun ions initially included in the aqueous solution,
recovery of a flow of the condensation product, and
supplying a flow of said precursors and activating the analysis and coupling of the flows.
2. Process according to claim 1 , wherein the flow of recovered product is fed into flashing and/or finishing plants so as to obtain a polyamide with a desired degree of polymerization.
3. Process according to claim 1 , wherein the condensation using the aqueous solution is performed at a temperature above 180° C., at a pressure above 5 bar, the product recovered having a degree of polycondensation of greater than 10, and in that the temperature and pressure are identical to the temperature and pressure in the permanent regime.
4. Process according to claim 1 , wherein the analysis is performed by Near InfraRed spectrometry.
5. Process according to claim 4 , wherein at least some of the flow of the condensation product from the solution is recovered and used to calibrate the Near InfraRed spectrometer in the desired range of contents of end groups and/or ratios of contents, the feeding with two flows, the analysis and the coupling being activated after this operation.
6. Process according to claim 4 , wherein the calibration is carried out by the method of dosed additions into the part of the flow recovered for this purpose.
7. Process according to claim 1 , wherein the diacid monomers are selected from the group consisting of adipic acid, glutaric acid, suberic acid, sebacic acid, dodecanedioic acid, isophthalic acid, terephthalic acid, azelaic acid and pimelic acid.
8. Process according to claim 1 , wherein the diamine monomers are selected from the group consisting of hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylenediamine, 5-methylpentamethylenediamine, undecamethylenediamine, dodecamethylenediamine and xylylenediamine.
9. Process according to claim 1 , wherein the diacid monomer comprises at least 80 mol % of adipic acid.
10. Process according to claim 1 , wherein the diamine monomer comprises at least 80 mol % of hexamethylenediamine.
11. Process according to claim 1 , wherein:
the flow which is rich in acid end groups is a mixture M 2 of diacid and of diamine with a diacid/diamine molar ratio of between 1.005 and 1.2
the flow which is rich in amine end groups is a mixture M 3 of diacid and of diamine with a diacid/diamine molar ratio of between 0.8 and 0.995
the two flows are fed in melt form into a stirred polymerization reactor in which the condensation is carried out
the condensation product is a prepolymer fed into flashing and/or finishing steps to obtain the desired degree of polymerization.
12. Process according to claim 11 , wherein the two flows are mixed together before feeding into the condensation plant.
13. Process according to claim 11 , wherein the polymerization reactor operates under an autogenous pressure or an adjusted pressure.
14. Process according to claim 11 , wherein the precursors M 2 and M 3 are obtained, in a permanent regime, by mixing a solution of diamine monomer with a mixture M 1 which is rich in diacid monomer.
15. Process according to claim 14 , wherein at least one of the flow rates of the flows for introducing diamine monomer solution and mixture M 1 which is rich in diacid monomer is coupled to the result of the continuous analysis of the acid and amine functions in the precursors M 2 and M 3 .
16. Process according to claim 11 , wherein the precursors are prepared in a permanent regime by mixing a flow of hexamethylenediamine with an adipic acid/hexamethylenediamine eutectic mixture.
17. Process according to claim 15 , wherein the precursors are prepared by a process comprising the following steps:
feeding each of the precursor preparation plants with an aqueous solution comprising dicarboxylate ions and diammonium ions in proportions such that their molar ratio is between 0.99 and 1.01
establishing the operating regime in the precursor preparation plants under the temperature and pressure conditions of the permanent regime
in each of the precursor preparation plants, feeding a flow of mixture M 1 which is rich in diacid monomer, a flow of hexamethylenediamine, activation of the coupling of at least one of the flows, feeding the product obtained into the mixing or condensation plant.
18. Process according to claim 15 , wherein the eutectic mixture M 1 is prepared by mixing a flow of adipic acid melt or solid, and a flow of hexamethylenediamine in pure form or in the form of a concentrated aqueous solution, with coupling of at least one of the flows to the result of the analysis of the content of acid and amine groups in the mixture M 1 , the process comprising the following steps:
feeding the plant for preparing the eutectic mixture with an aqueous solution comprising dicarboxylate ions and diammonium ions, in proportions such that their molar ratio is between 0.99 and 1.01
establishing the operating regime under the temperature and pressure conditions of the permanent regime
feeding a flow of adipic acid, a flow of hexamethylenediamine, activation of the coupling of at least one of the flows, feeding the product obtained into the precursor preparation plants.
19. Process according to claim 1 , wherein:
the flow which is rich in acid end groups is a dicarboxylic acid in melt form,
the flow which is rich in amine end groups is a diamine in pure form or in the form of a concentrated aqueous solution.
20. Process according to claim 18 , wherein the diacid is adipic acid and the diamine is hexamethylenediamine.