CONTINUOUS SOLID-STATE POLYMERIZATION PROCESS AND REACTOR COLUMN FOR USE THEREIN

Abstract

The invention relates to a continuous solid-state polymerization process for preparing a polyamide derived from diamine and dicarboxylic acid, wherein the salt is polymerized in a reactor column comprising successive multifunctional zones comprising heating sections and gas-outlet sections, wherein the heating sections comprise static heat exchangers. The invention also relates to the reactor column and use thereof in a continuous solid-state polymerization process.

Claims

1. A continuous solid-state polymerization process for preparing a polyamide derived from diamine and dicarboxylic acid, the process comprising steps of feeding solid diammoniumdicarboxylate salt into a reactor column comprising successive multifunctional zones comprising heating sections and gas-outlet sections; transporting the salt, or where applicable a polymerizing mixture or a polyamide resulting thereof, as a moving packed bed through the successive multifunctional zones, while heating the salt, respectively the polymerizing mixture and polyamide, in the heating sections, thereby polycondensing the salt to form a polymerizing mixture, respectively further polycondensing the polymerizing mixture to form a polyamide, and optionally further polycondensing the polyamide to form a polyamide with higher molecular weight, and producing water vapor, and removing the water vapor via gas-outlet sections; and discharging the resulting polyamide from the reactor column; wherein the salt, the polymerizing mixture and polyamide are kept in the solid-state and wherein the heating sections comprise static heat exchangers.

2. The process according to claim 1, wherein the solid diammoniumdicarboxylate salt is fed into the reactor column via a charging section and the resulting polyamide is discharged from the reactor column via a discharge section, and wherein a purge of inert gas is fed into the charging section, or into the discharge section, or into both.

3. The process according to claim 1, wherein the process is carried out at a gas pressure in the range of −0.1 to +0.5 BarG.

4. The process according to claim 1, wherein the static heat exchangers are heated to a temperature T.sub.HE being at least 15° C. below, below the lowest of the melting temperature of the salt (Tm-salt), the melting temperature of the reaction mixture (Tm-mixture), and the melting temperature of the polyamide (Tm-polyamide), wherein the melting temperature (Tm) is measured by the DSC method according to ISO-11357-3.2, 2009, in a nitrogen atmosphere with a heating rate of 20° C./min, in the first heating cycle.

5. The process according to claim 1, wherein the sections in the column are confined by wall sections of the column, and wherein wall sections of the heating sections are heated to a temperature TWS in the range from {T.sub.HE−10° C.} to and including {T.sub.HE+10° C.}, wherein T.sub.HE is the temperature of the static heat exchangers in the corresponding heating section.

6. The process according to claim 1, wherein the reactor column comprises at least 3 successive multifunctional zones comprising heating sections and gas-outlet sections, preferably at least 4 of these multifunctional zones.

7. The process according to claim 1, wherein the process comprises a cooling step, prior to the discharging step, comprising transporting the polyamide to and through a cooling section comprising static heat exchangers, while cooling the polyamide in the cooling section, and transporting the cooled polyamide to a discharge section.

8. The process according to claim 1, wherein the solid diammoniumdicarboxylate salt fed into a reactor column is a particulate material having a particle size distribution with a median particle size (d50) in the range of 0.05-5 mm, preferably 0.1-3 mm, more preferably 0.2-1 mm.

9. The process according to claim 1, wherein the solid diammoniumdicarboxylate salt comprises an aliphatic diamine and an aromatic dicarboxylic acid, and wherein the polyamide prepared by the process is a semi-crystalline semi-aromatic polyamide having a melting temperature, measured by the DSC method according to ISO-11357-3.2, 2009, in a nitrogen atmosphere with heating and cooling rate of 20° C./min, of at least 280° C.

10. Process according to claim 1, wherein the polyamide discharged from the reactor column has a viscosity number of at least 20 ml/g, preferably at least 50 ml/g, measured in 96% sulphuric acid (0.005 g/ml) at 25° C. by the method according to ISO 307, fourth edition; or wherein the polyamide has a conversion of carboxylic acid groups into amide groups of at least 90%, preferably at least 95%, more preferably at least 98%, relative to the carboxylic acid groups in the solid diammoniumdicarboxylate salt.

11. A reactor column for a continuous solid-state polycondensation process, the reactor column comprising at least three successive multifunctional zones, each of the multifunctional zones comprising a heating section comprising static heat exchangers and a gas-outlet section comprising gas-outlet devices.

12. The reactor column claim 11, wherein the static heat exchangers are selected from vertically or essentially vertically oriented tubular heat exchangers and vertically or essentially vertically oriented plate heat exchangers.

13. The reactor column according to claim 12, wherein the tubular heat exchangers have an inner diameter in the range of 0.5-5 cm and a core-to-core distance in the range of 1-8 cm.

14. The reactor column according to claim 12, wherein the plate heat exchangers have a thickness in the range of 0.25-3 cm, preferably 0.5-2 cm; and/or a core-to-core distance in the range of 1-12 cm, preferably 2-8 cm; and/or a plate-to-plate distance between the plates in the range of 0.5 mm-8 cm, preferably 1-6 cm, more preferably 2-5 cm.

15. The column according to claim 11, wherein the heating sections comprise one or more arrays of plate heat exchange elements regularly spaced from one another and distributed uniformly over a cross-section of the heating section.

16. The reactor column according to claim 11, wherein gas-outlet sections positioned between two heating sections comprise two arrays of gas-outlet devices substantially evenly spread over a cross-section of the gas-outlet section.

17. The reactor column according to claim 16, wherein the gas-outlet devices consist of elongated elements protruding essentially transversely with respect to the length-direction of the column into the gas-outlet sections, and wherein the elongated elements each comprise a gas-flow channel in length-direction of the elongated elements and a groove-opening or a slit-opening over the length of the elongated elements or a series of openings distributed over the length of the elongated elements.

18. The column according to claim 11, wherein circular wall sections confine the multifunctional zones, or wherein the multifunctional zones are confined by four wall sections comprising two essentially parallel opposite wall sections, preferably comprising two pairs of two essentially parallel opposite wall sections, more preferably confined by four wall sections constituting an essentially rectangular cross-section.

19. Process installation comprising a reactor column according to claim 11.

20. Use of the process installation according to claim 19, or the reactor column in a polycondensation process, more particular in a continuous solid-state polymerization process for preparing a polyamide derived from diamine and dicarboxylic acid.

Description

DESCRIPTION OF FIGURES

[0110] FIG. 1 is a schematic representation of an embodiment of a column according to the present invention. The figure shows a column (1) comprising a charging section (2), a discharging section (3), and 5 multifuntional zones (4). Each multifuntional zone (4) comprises a heating section (5) and a gas-outlet section (6). Each heating section (5) comprises heating elements (7). Each gas-outlet section (6) comprises an array of gas outlet devices (8) with a gas outlet (9).

[0111] FIG. 2 is a schematic representation of another embodiment of a column according to the present invention. The figure shows a column (1) comprising a charging section (2), a discharging section (3), and 5 multifuntional zones (4). Each multifuntional zone (4) comprises a heating section (5) and a gas-outlet section (6). Each heating section (5) comprises heating elements (7). Four of the five gas-outlet sections (6) comprises two arrays of gas outlet devices (8) with a gas outlet (9). The fifth gas-outlet section (6) comprises one array of gas outlet devices (8) with a gas outlet (9). (8a) constitutes a nearby array of gas outlet devices in respect of a heating section 7a positioned upstream in respect of heating section 7a. (8b) constitutes a nearby array of gas outlet devices in respect of a heating section 7a positioned downstream in respect of heating section 7a.

[0112] FIG. 3. Figure is a schematic representation of an array of gas-outlet devices (10) consisting of elongated elements (11) wherein the elongated elements each comprise a gas-flow channel (12) in length-direction of the elongated elements and a slit-opening (13) over the length of the elongated elements. The elongated elements can be positioned inside the reactor column such that the elongated elements are evenly spread over a cross section of the reactor column and protrude into the gas-outlet sections transversely, or essentially so, with respect to the length-direction of the column.

DESCRIPTION OF AN EXAMPLE OF A PROCESS ACCORDING TO THE INVENTION

[0113] A solid-state polymerization process according to the invention is carried out in a vertically positioned reactor column according to the invention. The reactor column used for the process comprised four multifunctional zones, each comprising a heating section followed by a gas-outlet section comprising two arrays of gas outlet devices, as well as a cooling and drying sections, with an additional gas inlet and additional gas outlet in the cooling and drying sections. The column further comprised a charging section with a nitrogen inlet to ensure that no air enters into the reactor column and a discharge section is fitted with a nitrogen inlet to ensure gases formed in the column do not leave with the product.

[0114] For the process, further a salt of a mixture of butane diamine and hexane diamine and terephthalic acid in the form of a solid granular material was used.

[0115] The solid granular material was inertized with nitrogen and fed to the top of the column, together with a small purge of nitrogen gas in the top of the column, after which the solid material passed through a first heat exchanger section wherein it was heated to a temperature just below reaction temperature. Moisture released from the solids was pushed downward by the pressure of the water vapor and the nitrogen purge in the top of the column. After the first heat exchanger, the solids passed a first gas-outlet section, where nitrogen and moisture leave the column via a first array of gas outlet devices. Passing further down, the solids passed another array of gas outlet devices in the same gas-outlet section, where moisture from below flows counter-currently to the solids flow into the gas outlet devices. Progressing further downward, the solids passed the second heat exchanger. On passing through the second heat exchanger, the solids heated up further and moisture was released by the endothermic condensation reaction. About halfway through the second heat exchanger, the direction of the gas flow changed from counter-current up-flow, to co-current down flow. After the second heat exchanger, the gasses collect in another gas-outlet section, from which it could escape via a first array of gas outlet devices, followed by a second array of gas outlet devices that collected gases coming from below. On progressing further, the solids passed two further multifunctional zones comprising a heat exchanger and a gas-outlet section wherein the solids were further heated, and water vapor produced upon polycondensation was removed via the gas-outlet sections. Progressing further down, the solids passed a first cooling and drying section wherein the solids were cooled to a temperature of around 180° C. Nitrogen gas was let in via a gas inlet and removed via two gas-outlet sections, one above and one below the gas inlet, to drive off residual moisture. The drying section was followed by a cooling section, wherein the solid product was further cooled to a temperature below 60° C. The solids were discharged via the discharge section, which is fitted with a nitrogen inlet to create a small counter-current upward flow of nitrogen, to ensure that gases formed in the column do not leave with the product. During the process the throughput was adjusted to ensure sufficient conversion of the salt. The product obtained by the process was a semi-crystalline semi-aromatic polyamide in the form of a solid granular material.