Process for preparing a polyamide, a nylon salt to be used therein and a process for making the salt
Processes for preparing a polyamide, a polyamide material obtained by such processes, a nylon salt to be used therein, and processes for making the nylon salt are disclosed. The processes for preparing the polyamide include a direct solid state polymerization process. The salt used herein is a granulate material, prepared by a process, comprising spraying an aqueous solution comprising a diamine and a dicarboxylic acid dissolved in an aqueous medium, or an aqueous slurry comprising a diammonium dicarboxylate salt dispersed in an aqueous medium directly obtained from such an aqueous solution, onto or in a fluidized bed of diammonium dicarboxylate salt particles, while evaporating the aqueous medium, thereby forming a granulate salt material.
1. A granulate salt material comprising a diammonium dicarboxylate salt which is a fluidized bed spray granulation product of an aqueous solution or an aqueous slurry comprising a diammonium dicarboxylate salt dissolved or dispersed in an aqueous medium, wherein the salt has the following physical properties:
(a) a particle size distribution with a median particle size (d50) in the range of 200-1000 μm, measured by laser granulometry with the method according to ISO 13320-1 at 20° C., and
(b) a tapped bulk density in the range of 350-750 kg/m3, measured by the method according to ASTM D6393.
2. The granulate salt material according to claim 1 , wherein the salt is obtained by a process comprising the steps of:
(i) spraying of the aqueous solution comprised of a diamine, or a mixture of diamines, and a dicarboxylic acid, or a mixture of dicarboxylic acids dissolved in an aqueous medium, or
(ii) spraying the aqueous slurry comprised of a diammonium dicarboxylate salt dispersed in an aqueous medium directly obtained from an aqueous solution comprising a diamine and a dicarboxylic acid dissolved in an aqueous medium, wherein
the aqueous solution or aqueous slurry is sprayed onto or in a fluidized bed of diammonium dicarboxylate salt particles, and wherein a preheated gaseous medium is led through the fluidized bed while evaporating the aqueous medium thereby forming the granulate salt material.
3. The granulate salt material according to claim 1 , wherein the aqueous medium comprises water and an alcohol, or consists of water.
4. The granulate salt material according to claim 1 , wherein the aqueous solution or aqueous slurry has a salt concentration of at least 5 wt. %, relative to the total weight of the solution or slurry.
5. The granulate salt material according to claim 2 , wherein the aqueous solution or aqueous slurry has a temperature of at least 35° C., the gaseous medium led through the fluidized bed has a temperature of at least 50° C., and the fluidized bed has a temperature of at least 35° C.
6. The granulate salt material according to claim 2 , wherein the process comprises preparing a fluidized bed of precursor particles, wherein the precursor particles are salt particles obtained by spray drying or fine particles obtained by separation in a classification step subsequent to a fluidized bed spray granulation step.
7. The granulate salt material according to claim 2 , wherein off-gas resulting from the gaseous medium led through the fluidized bed is exhausted or recycled and wherein the off-gas is passed through a filter or through a scrubber, or is dried, or any combination thereof, before being exhausted or recycled.
8. The granulate salt material according to claim 1 , wherein the granulate salt material has a particle size distribution with a median particle size (d50) in the range of 200-1000 μm, wherein the particle size distribution is measured with laser granulometry by the method according to ISO 13320-1 at 20° C.
9. The granulate salt material according to claim 1 , wherein the granulate salt material has a residual moisture content of at most 7.5 wt. %, relative to the total weight of the granulate salt material.
10. The granulate salt material according to claim 2 , wherein the diamine comprises an aromatic diamine and/or an aliphatic C2-C10 diamine and the dicarboxylic acid comprises a C4-C10 aliphatic dicarboxylic acid and/or an aromatic dicarboxylic acid.
11. The granulate salt material according to claim 10 , wherein the dicarboxylic acid consists for at least 75 mole % of terephthalic acid, wherein the mole % is relative to the total molar amount of the dicarboxylic acid and/or the diamine consists for at least 75 mole % of 1,6-hexamethylediamine (HMDA) or 1,4-diaminobutane (DAB), or a combination thereof, wherein the mole % is relative to the total molar amount of the diamine.
12. The granulate salt material according to claim 10 , wherein the dicarboxylic acid and the diamine are present in a molar ratio in the range of 0.95:1-1.05:1.