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, and a residence zone comprising at least one gas-inlet section, 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 diammonium dicarboxylate salt into a reactor column comprising successive multifunctional zones comprising heating sections and gas-outlet sections, and a residence zone comprising at least one gas-inlet section; 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 further transporting the polyamide as a moving packed bed through the residence zone, while introducing a gaseous diamine into the residence zone via a first gas-inlet section inside the residence zone; and optionally introducing an inert gas into the reactor via a second gas-inlet section below the first gas-inlet section; 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 diammonium dicarboxylate 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 reactor column comprises at least 3 successive multifunctional zones comprising heating sections and gas-outlet sections, preferably at least 4 of these multifunctional zones.

6. The process according to claim 1, wherein the solid diammonium dicarboxylate 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.

7. The process according to claim 1, wherein the solid diammonium dicarboxylate 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.

8. 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 diammonium dicarboxylate salt.

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

10. The reactor column according to claim 9, 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.

11. The column according to claim 9, 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.

12. The reactor column according to claim 9, 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.

13. Installation comprising a reactor column according to claim 9.

14. Use of the installation according to claim 13, 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

[0129] 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), 4 multifunctional zones (4) and a residence zone (10). Each multifunctional 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). The residence zone (10) comprises a first gas-inlet section (11) with a gas inlet (12) and an array of gas inlet devices (13) and a second gas-inlet section (14) with a gas inlet (15) and an array of gas inlet devices (16). According to the present invention the first gas-inlet section (11) is used for introducing a gaseous diamine into the residence zone. According to a preferred embodiment of the present invention the second gas-inlet section (14) is used for introducing an inert gas into the residence zone, more particular at a slight overpressure relative to the pressure of the gas in the diamine inlet section.

[0130] 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), 4 multifunctional zones (4) and a residence zone (10). Each multifunctional 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. The residence zone (10) comprises a gas-inlet section (11) with a gas inlet (12) and an array of gas inlet devices (13) and a section (17) comprising heat-exchange elements (18). According to the present invention the gas-inlet section (11) is used for introducing a gaseous diamine into the residence zone. According to a preferred embodiment of the present invention the heat-exchange elements (18) are used to further control or steer the temperature of the moving packed by in the residence zone by contact heating or cooling.

[0131] FIG. 3 is a schematic representation of an array of gas-outlet devices (19) consisting of elongated elements (20) wherein the elongated elements each comprise a gas-flow channel (21) in length-direction of the elongated elements and a slit-opening (22) 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 EXAMPLES OF THE PROCESS ACCORDING TO THE INVENTION

[0132] A continuous, solid-state polymerization process according to the invention was implemented in a vertically positioned reactor column according to the invention. The total equipment height is about 11 m (including transport, and charging sections), whereas the column used for the process has a height of about 7 m (including discharging section), and a virtually square cross-section of about 0.15 m.sup.2. The reactor column comprises three multifunctional zones, each comprising a heating section followed by a gas-outlet section comprising two arrays of gas outlet devices. Following the third multifunctional zone in the downward direction, there is an amine dosing section, comprising a heat exchanger, a residence section and an amine inlet device, which is followed by a residence zone, another heat exchange section, a drying section and a final cooling section.

[0133] The residence zone that is located below the amine dosing section has one gas inlet section positioned just above the heat exchange section. The function of the residence zone is to allow sufficient time to increase the molecular weight of the product on its way down the column, before reaching the next (cooling) heat exchanger, followed by the drying and final cooling sections. The latter sections are in the bottom of the column and have an additional gas inlet and an additional gas outlet to allow nitrogen to pass through the product and dry off residual water. Drying is enhanced by the relatively high temperature of around 170° C. of the product in this zone. The product temperature in the drying zone can be tuned with the heat exchanger located above the drying zone, so that drying is sufficient, and (water forming) reactions are stopped.

[0134] The column further comprises a charging section at the top of the column with a nitrogen inlet to ensure that no air enters into the reactor column and a discharge section at the bottom of the column fitted with a nitrogen inlet to ensure gases formed in the column do not leave with the product.

[0135] For the process, a salt made of a mixture of butane diamine (DAB), hexane diamine (HMDA) and terephthalic acid (TPA), in the form of a solid granular material was used. The salt granules had a particle size in the range of 0.1-0.5 mm. Before starting the polymerization, the column was filled with already reacted polymer granules, of the same particle size and shape as the salt particles, obtained previously by reacting the same salt granules in a batch reactor facility.

[0136] All viscosity numbers obtained in Examples 1-3 herein below were measured in 96% sulphuric acid (0.005 g/ml) at 25° C. by the method according to ISO 307(2019).

[0137] All levels of water content in Examples 1-3 given in ppm (or mg/kg) are on a mass basis, and were determined using Karl-Fischer coulometric titration, based on ISO 15512 (2019).

[0138] All end-group concentration values in Examples 1-3 (mEq/kg, or mmol_end_groups/kg) were determined by using .sup.1H NMR measurements in dry, deuterated sulphuric acid. .sup.1H NMR measurements were performed as described by C. D. Papaspyrides, A. D. Porfyris, R. Rulkens, E. Grolman, A. J. Kolkman in Journal of Polymer Science. Part A. Polymer Chemistry, vol. 54, issue 16, 2016, pages 2493-2506.

[0139] The melting temperature is measured by the DSC method according to ISO-11357-3.2 (2009), in a nitrogen atmosphere with heating rate of 20° C./min, in the first heating cycle.

Example 1

[0140] At first, the heat exchangers of the multifunctional zones were heated to their respective set points and after 2 hours the solids flow rate was slowly increased to 4 kg/h, which was maintained until the polymer granules inside and in-between the multifunctional zones were heated to a temperature that was about the temperature of the heat exchanger located at nearest location, as was detected by temperature sensors positioned below each multifunctional zone. Further, heating elements in the form of electrical tracing were switched on to heat the outside of the column, which together with suitable mineral-wool insulation prevented cooling from the outside. Polymer granules were added to the hopper at the top of the column in the same manner as described for the salt herein below.

[0141] The solid granular salt material was fed from 20 kg bags into a discharge cabinet at ground level, and transported with nitrogen gas from the bottom discharge point of the cabinet to a receiving vessel at the top of the column by pneumatic transport, using nitrogen as transport gas. From the receiving vessel, the salt intermittently flowed by gravity through a valve, into a feeding hopper that was connected to the top of the reactor column. Nitrogen purged into the charge hopper of the column ensured an inert atmosphere around the granular salt material before entrance to the reactor. The feed rate of the granular salt material was gradually increased from zero to 8 kg/h within one hour time, by gradually increasing the rotational speed of the previously calibrated transport screw at the bottom of the reactor.

[0142] After entering the reactor column, the solid material passed through the first multifunctional zone wherein it was heated by the first heat exchanger, which was set to a temperature of 228° C. After the first heat exchanger, the solids passed the first gas-outlet section, where nitrogen and water vapor left the column via the first array of gas outlet devices. Passing further down, the solids passed the next array of gas outlet devices in the same gas-outlet section of the first multifunctional zone. Here, water vapor from below could flow counter-currently to the solids and leave the reactor via this second array of gas outlet devices. Progressing further downward, the solids passed the second multifunctional zone, set to a temperature of 244° C. On passing through the second heat exchanger, the solids (part salt and part polymer at this stage) were heated further, and the endothermic condensation reaction proceeded, releasing water vapor from the condensation reaction into the granule bed, which then circulated to the gas-outlet sections by means of the slight overpressure in the (superheated) steam generated under said conditions of high temperature and close-to-atmospheric pressure. After the second heat exchanger, the material passed through the second gas-outlet section, through which gases coming from above and below left the reactor column. Then, the solids passed the third multifunctional zone, wherein the solid granular material was heated further by the third heat exchanger, set to a temperature of 259° C. and water vapor produced upon further polycondensation was again removed via the gas-outlet sections located above and below the third heat exchanger. For Example 1, the granules passed through the next heating and amine dosing sections essentially unaltered, i.e. without further reaction or significant changes in composition, because the polymer was already acid-end-group terminated at this stage (all amine end-groups were used up, as shown by end-group analysis of the product herein below).

[0143] Progressing further down, the solids passed via the cooling heat exchanger into the drying section at a temperature of about 170° C. Nitrogen gas was introduced via a gas inlet in the drying section and removed via two gas-outlet sections, one above and one below the gas inlet, to evaporate residual water. After passing the drying section, the solid granular material passed through the final cooling section, wherein the solids were further cooled to a temperature below 60° C. The solids were discharged via the discharge section, comprising a hopper and a discharge screw, while a nitrogen gas was fed to the nitrogen inlet just above the discharge screw to create a counter-current upward flow of nitrogen in the bottom part of the column. The amount of nitrogen at this point was tuned so as to maintain a slight overpressure relative to the column's vapor-outlet pressure at this position. The latter was to ensure that gases formed in the column did not evaporate from the product. It took around 3 days to completely fill the column with fresh material and another 2 days to reach a steady state. A dry polymer granulate material was obtained with a relative viscosity (VN) of 52 to 55 ml/g. The column was operated at essentially atmospheric pressure in all Examples 1-3.

[0144] Thus, the polycondensation reaction from salt to polymer was completed, ending in an acid-end-group terminated polymer and the water formed during reaction was effectively removed in the three multifunctional zones. The drying section further reduced the water level to between 1000 and 1500 ppm in the final product.

[0145] The fact that the product was a loose powdery material in Examples 1-3, and that the process could proceed for days, also shows that stickiness and lumping have been avoided by the measures taken, i.e. water vapor was released and removed in the multifunctional zones, while avoiding condensation of water onto colder surfaces and cold product. In the multifunctional zones where the main conversion took place, nitrogen was not applied. In these zones, water vapor escaped as superheated steam, and was collected in the exhaust gas collecting channels that were connected to the gas outlets of the column.

[0146] The relatively low molecular weight (VN) obtained in Example 1 was due to the loss of volatile diamines that evaporated from the product together with the water vapor, as described herein above. This was verified by determining the end-group concentration of the product, thereby obtaining a concentration of less than 40 mEq/kg of residual amine end-groups (below the detection limit of the NMR method used), compared to a concentration of 260 mEq/kg of acid end-groups. The acid-to-amine balance was further controlled by applying the process as described in Example 2 and Example 3 herein below.

Example 2

[0147] By applying the same conditions of temperature and flow rate as in Example 1, the amine dosing was switched on and a concentrated aqueous solution of HMDA and DAB was fed to an array of gas distributor devices via a heater-evaporator, adjusted to match the temperature of the polymer bed and the heat exchanger located just above it, thereby preheating and vaporizing the aqueous solution. The diamine containing vapor mixture was led into the amine dosing section of the reactor via the amine inlet device. The diamine-water-nitrogen vapor mixture was forced to flow upward, counter-current to the granular bed, by the nitrogen from the nitrogen inlet located below the amine feed point. Thus, the diamine was absorbed effectively by the polymer granulate in a counter-current contacting pattern. Any non-absorbed diamine, nitrogen and water vapor were led out of the column via the gas outlet section positioned above the amine dosing section. Progressing further down, the solids passed through the same drying and cooling sections as described in Example 1. The viscosity of the material obtained slightly varied over time, as the amine dosing rate was adjusted to the correct value, reaching a reasonably steady state around 30 hours after starting the amine dosing.

[0148] A loose and free-flowing polyamide polymer powder with a VN between 65 and 80 ml/g was obtained, with the concentration of amine end-groups between 90 and 110 mEq/kg and the concentration of acid end-groups between 110 and 130 mEq/kg. Water levels ranged from 1000 to 1500 ppm and the melting point (Tm) of the polymer was 346° C.

[0149] Example 2 shows that the current invention allows end group content and molecular weight to be controlled to reach a commercially relevant range useful for commercial applications as it is important to be able to steer the process to obtain products with different molecular weights to match the requirements set for different applications. Further, the process according to the present invention enables obtaining polymer specifications to be reached in a single-pass apparatus, thus saving on cost and energy, since alternative methods require re-heating, amine addition and cooling in an (costly) additional process step.

Example 3

[0150] For carrying out Example 3, the solids flow rate was increased further, from 8 kg/h to 14 kg/h in 3 hours. The amine dosing amounts were gradually increased to match, i.e. to maintain the same amine to solids ratio as described in Example 2. The temperatures of the heating sections were gradually increased to match the increased heat load required for pre-heating and reaction, i.e. zone one was increased to a final set point of 230° C., the second zone to 246° C. and the third zone to 265° C. The temperature sensors in each multifunctional zone were used to monitor the local granule temperatures and heater temperatures were adjusted to maintain reasonably stable granule temperatures. 24 hours after adjusting the solids flow rate, samples taken at 2 hour intervals showed a stable VN.

[0151] The product obtained by the process as described in Example 3 was a semi-crystalline semi-aromatic polyamide in the form of a free-flowing solid granular material. The shape of the particles in the solid granular material was the same to the shape of the salt material fed into the column. The polyamide product had a melting temperature (Tm) of 345° C., measured by DSC, a viscosity number (VN) of 70-72 ml/g, amine end-groups concentration between 93 and 97 mEq/kg and acid end-groups concentration between 118 and 222 mEq/kg, with water levels ranging from 1200 to 1800 ppm.

[0152] Example 3 shows that with stable operation, VN and the level of end-groups concentration can be kept stable within a narrow range, that a higher production rate can be reached by tuning the temperature of the heat exchangers in the multifunctional zones and that the end-groups concentration level and VN can be controlled by tuning the amount of amine dosing to match the flow rate of the salt.