Polyamide manufacturing process
A method for making polyamide is described. More particularly, a method for making a polyamide from at least one diacid and one diamine, that includes a step of concentrating an aqueous solution of diacid and diamine salt up to a salt weight concentration higher than 85%, and a polymerization step up to a desired polymerization degree is described.
1. A method for manufacturing a polyamide from at least one diacid and from at least one diamine, comprising the following steps:
a) concentrating by evaporating water from an aqueous solution of diacid and diamine salt obtained by mixing at least one diacid and at least one diamine in stoichiometric quantities, until a homogeneous aqueous solution is obtained, of which the weight concentration in water of the dissolved species is greater than 85%, wherein the pressure during step a) is less than 0.3 MPa; and
b) polymerizing with removal of water up to a desired degree of polymerization, comprising at least one step b1) of polymerizing under pressure.
2. The method according to claim 1 , wherein the temperature θ, during step a), is, at any moment, greater than or equal to θ c +3° C., wherein θ c is the crystallization temperature of the solution.
3. The method according to claim 1 , wherein the weight concentration of salt of the aqueous solution of diacid and diamine salt, before step a), is between 50% and 70%.
4. The method according to claim 1 , wherein the mixture obtained at the end of step a) is transferred into at least one polymerization reactor.
5. The method according to claim 1 , wherein the method further comprises at least one of the following steps:
a step b2) of expanding the polymerization medium in order to remove residual water via evaporation;
a step b3) of maintaining the temperature of the polymer, under atmospheric pressure or reduced pressure; and
a step b4) of forming the polyimide obtained.
6. The method according to claim 1 , wherein the process is a batch process.
7. The method according to claim 1 , wherein the diacid monomers are selected from the group consisting of adipic, glutaric, suberic, sebacic, dodecanedioic, isophthalic, terephthalic, azelaic, pimelic, naphthalenedicarboxylic and 5-sulphoisophthalic acids.
8. The method according to claim 1 , wherein the diamine monomers are selected from the group consisting of hexamethylenediamine, heptamethylenediamine, tetramethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylenediamine, 2-methylpentamethylenediamine, undecamethylenediamine, dodecamethylene-diamine, xylylenediamine and isophoronediamine.
9. The method according to claim 1 , wherein the diacid monomer comprises at least 80 mol % of adipic acid.
10. The method according to claim 1 , wherein the diamine monomer comprises at least 80 mol % of hexamethylenediamine.
11. The method according to claim 1 , wherein the weight concentration in water of the dissolved species is greater than or equal to 86%.
12. The method according to claim 1 , wherein the weight concentration in water is greater than or equal to 87%.
13. The method according to claim 1 , wherein the weight concentration in water of the dissolved species is greater than or equal to 88%.
14. The method according to claim 5 , wherein if the method further comprises step b4), then step b4) comprises forming the polyamide in the form of granules.