WO2013002643A2

WO2013002643A2 - Reactor system for polyester pre-condensation

Info

Publication number: WO2013002643A2
Application number: PCT/NL2012/050464
Authority: WO
Inventors: Edoardo Facchi
Original assignee: Stamicarbon B.V. Acting Under The Name Of Mt Innovation Center
Priority date: 2011-06-30
Filing date: 2012-06-29
Publication date: 2013-01-03
Also published as: EP2726194A2; CN103702752A; WO2013002643A3

Abstract

Disclosed is a reactor system for the production of polyester pre-condensate. The system comprises at least two reaction zones, operating at substantially different pressure. Reactants fed into the first zone are allowed to initially react and are then allowed to enter a second zone by means of pressure flow. In the second zone, a system of concentric spacers is present so as to ensure a sufficient path length of the reaction mixture to form a pre-condensate, as well as in internal heat exchanger. The pre-condensate is allowed to flow to a next (polymerization) stage by means of gravity flow on account of a standpipe present in the second reaction zone. Said standpipe has an inlet above the internal heating system in the second reaction zone.

Description

Title: REACTOR SYSTEM FOR POLYESTER PRE-CONDENSATION

Field of the invention

The invention pertains to a reactor system for conducting a pre- condensation in the production of polyester. The invention also pertains to a method for producing a polyester pre-condensate.

Background of the invention

Polyesters, such as Polyethylene Terephthalate (PET) are produced in batch as well as continuous processes, starting from a glycol (e.g.: Ethylene Glycol) and a di-basic acid (e.g.: Terephthalic Acid) or the corresponding methyl ester (e.g.: Dimethyl Terephthalate).

Independently of the selected type of starting material (Acid or Dimethylester) and on the selected type of process (continuous or batch), in all cases a sequence of two different reactions is generally employed to produce polyester. The first reaction serves to transform the starting materials into a pre-condensate ("monomer") releasing water (direct esterification reaction from the acid) or methanol (ester interchange reaction from the dimethylester). The second reaction stage is a polycondensation under vacuum, where the pre- condensate is transformed into a polymer.

The above-mentioned first stage is normally conducted in two steps, and in at least two vessels, where the first step is under a pressure higher than the second. In some cases the two vessel are compacted in a single reactor multiple stage. The first step can be with or without mechanical agitation, the transfer to the second stage (vessel) can be with or without pump, and the second stage (vessel) can be with or without mechanical agitation. In all this cases one or more mechanical pumps, and/or mechanical stirrers are required to transfer the pre-condensate to the next stage. It is desired to reduce, and preferably avoid, the presence of such mechanical equipment. The need to install such equipment generally goes with higher investment and operational costs, as well as with problems in handling the reaction mixture which, ultimately, could adversely affect product properties. In view of the complexity of polyester production, which involves two stages, and wherein the first stage involves two steps, it is particularly challenging to find a way to produce a polyester pre-condensate in such a way that it can be transferred to the polycondensation stage without the need of mechanical equipment to bring about the transfer.

Summary of the invention

In order to better address one or more of the foregoing desires, the invention presents, in one aspect, a reactor system for the production of polyester pre-condensate, comprising at least two reaction zones, operating at substantially different pressure, wherein a first reaction zone comprises a first reactant feeding zone, a heat exchanger, preferably comprising a vapor condensing system and a jacket, and a first product discharge zone comprising a flow line to a second reaction zone; said second reaction zone comprises a second reactant feeding zone, a second product discharge zone and an internal heat exchanger, preferably a heating coil, wherein the second product discharge zone comprises an elevated inlet extending to above the lowest point of the second reaction zone, and a plurality of substantially concentric, preferably cylindrical, spacers surrounding the elevated inlet of the discharge zone, wherein the spacers are arranged so as to provide an increased path length between the reactant feeding zone and the product discharge zone, and wherein the elevated inlet of the product discharge zone is situated above the internal heat exchanger.

In another aspect, the invention pertains to a process for the production of a polyester pre-condensate, comprising the following steps: (a) feeding a dihydric alcohol and a dicarboxylic acid or ester into the first zone of a reactor system as defined above so as to provide a reaction mixture;

(b) subjecting the reaction mixture to heat and pressure in said first reaction zone, so as to form an initial esterification mixture;

(c) allowing the initial esterification mixture to be transferred to the second zone of a reactor system as described above under the influence of differential pressure;

(d) allowing the initial esterification mixture to travel a path provided by the spacers of the above-described reactor system, so as to form a low-mole-weight polyester pre-condensate;

(e) allowing the low-mole-weight polyester pre-condensate to flow through the elevated outlet of a reactor system as defined above by means of gravity flow, so as to further store or use the pre-condensate.

Brief description of the drawings

Figure 1 is a schematic drawing representing one embodiment (denoted "A") of a system according to the invention. Figures 2-6 similarly are schematic drawings representing, respectively, embodiments B-F of the invention.

Detailed description of the invention The invention presents a reactor set-up that serves to address a good conversion of the reaction mixture, as well as a good homogeneity to the outlet (pre-condensate), together with a reduction of energy requirements, and particularly allowing to use a minimum number of mechanical (rotating) devices. Further, the invention provides a compact design for a vertical reactor. Specifically the elimination of the agitator devices in the

esterification stage 2 in the corresponding vertical room requires the insertion of the following internals.

The first and second reaction zones are preferably placed in a vertical arrangement such that the first reaction zone comprises a separate lower vessel, and the second reaction zone comprises an upper vessel, i.e.

above the first reaction zone, and the pressure in the first reaction zone is higher than that in the second reaction zone. This way the transfer of an initial esterification mixture from the first to the second reaction zone is capable of proceeding without mechanical means such as pumps, since this transfer is simply driven by differential pressure.

The inlet of the second reaction zone is situated above the above- mentioned jacket. Typically the inlet is in the form of a dip pipe extending from near the top of the vessel to the bottom of the vessel. Preferably the outlet of the dip pipe is positioned just below the liquid level of the reaction mixture.

In the second reaction zone the initial esterification mixture is heated by means of an internal heat exchanger. In order to provide a sufficient reaction time, spacers are provided that force the reaction mixture to reside for a sufficiently long time in the second reaction zone, so as to complete the conversion of the initial esterification mixture into a proper low-mole-weight polyester pre-condensate (preferably having a degree of polymerization of 8- 10). The spacers are provided in a concentric arrangement, so as to not only account for the aforementioned residence time, but also for a sufficient (non- mechanical driven) agitation so as to provide homogeneity of the reaction mixture. Particularly, the spacers serve to create the conditions of a symmetric radial flow path for the reacting mixture, avoiding the formation of dead spots without the use of any mechanical agitation. The spacers serve to force the pre-condensate into a symmetric path directed to the center of the reactor.

By arranging the inlet of the product discharge zone in the second reaction zone above the internal heat exchanger, this inlet is placed in a subzone of lower pressure than the subzone where, under the influence of heat, the reaction proceeds. Thus, having reached the end of the path provided by the aforementioned concentric spacers, the reaction mixture will undergo a pressure-driven flow towards the inlet of the product discharge zone. This inlet preferably comprises a funnel. The funnel is preferably designed with jagged edges. The product discharge zone preferably comprises a standpipe, with the inlet of the standpipe arranged as defined above.

The concentric spacers preferably take the form of a weir (i.e. a barrier) that is designed so as to have an external weir designed with an opening cut located in the upper part opposite (i.e. at 180°) to the inlet of the discharge zone. The inner weir is preferably designed with an opening cut located in the bottom part, at 180° (opposite) to the external weir opening cut.

The internal heat exchanger in the second reaction zone can be provided in any form providing a heating surface, but preferably comprises one or more heating coils. Such coils are preferably metal coils heated by a liquid heat transfer medium, or are embodied in an external built-in boiler-jacket.

The design of both the top and bottom part of the reactor can vary as is well known by the person skilled in the art. In one embodiment both the top and bottom part of the reactor are of a simple cylindrical type with or without an integrated heat exchanger.

The reactant feeding zone is typically in the form of a dip pipe extending from the top or the side of the vessel down to below the liquid level.

In this way the reactant can be fed in such a way as to avoid contact with the reactor walls and homogeneity will be improved. The bottom of the dip pipe will be preferably positioned at least 5 cm, more preferably at least 10 cm, most preferably at least 20 cm below the liquid level of the reaction mixture in the in the reaction zone.

The reactor system preferably is provided with a heat exchanging system taking the heat transfer medium (preferentially a eutectic mixture of diphenyl and diphenyl oxide) in vapor phase and condensing it on its walls: the release of the condensate from the heating surface in contact with the process back to the jacket is by gravity.

The invention, in one aspect, pertains to a plant for the production of polyester, comprising a reactor system as described hereinbefore, wherein the product discharge zone comprises a fluid connection to a polycondensation reactor. The latter refers to any suitable reactor, as is generally known to the skilled person, wherein the actual polymerization takes place, wherein pre- condensate is reacted to as to remove excess glycol, and to increase molecular weight.

Further, the invention pertains to a process for the production of a polyester pre-condensate, comprising the following steps:

(a) feeding a dihydric alcohol and a dicarboxylic acid or methyl-ester compound into the first zone of a reactor system according to any one of the claims 1-4 so as to provide a reaction mixture;

(c) allowing the initial esterification mixture to be transferred to the second zone of a reactor system according to any one of the claims 1-4 under the influence of differential pressure;

(e) allowing the low-mole-weight polyester pre-condensate to flow through the standpipe of a reactor system according to any one of the claims 1- 4, by means of gravity flow, so as to further store or use the pre-condensate.

The further use of the pre-condensate is particularly in producing polyester. Accordingly, the invention also pertains to a process for the production of a polyester, comprising preparing a low-mole-weight polyester pre-condensate as described above, and subjecting the pre-condensate to polymerization. This process is preferably conducted in a plant as defined hereinabove.

In the processes for producing polyester pre-condensate, and polyester, the dihydric alcohol is preferably ethylene glycol, and the

dicarboxylic compound is preferably terephthalic acid.

In operating the reactor, the following preferred conditions of temperature and pressure apply. The pressure in the second reaction zone (e.g. a top part of an integrated reaction vessel) is preferably from 1.0 to 1.7 bar, preferably from 1.2 to 1.5 bar, more preferably from 1.3to 1.5 bar. The pressure in the first reaction zone (e.g. the bottom part of an integrated reaction vessel) is from 2.0 to 4.0 bar, preferably from 2.5 to 3.5 bar, more preferably from 2.9 to 3.1 bar. The temperature in the second reaction zone is from 260°C to 280 °C, preferably from 265°C to275 °C, more preferably from 268 °C to 272 °C. The temperature in the first reaction zone is from 250 °C to 270 °C, preferably from 255 °C to 265 °C, more preferably from 259 to 261 °C. The conversion of terephthalic acid (generally PTA, purified terephthalic acid) in the first reaction zone is generally from 88.0 to 92.0 %, preferably from 89.0 to 91.0 %, more preferably from 89.5 to 90.5 % . The conversion of PTA in the second reaction zone is from 96.0 to 99.0 %, preferably from 96.5 to 98.5%, more preferably from 97.0 to 98.0%

The invention will hereinafter be illustrated further with reference to the following Figure descriptions of example reactor systems of the invention.

Fig. l schematically depicts embodiment A: a two stage reactor, El and E2 are integrated into one reaction vessel. The drawing includes the following references:

1 = Esterification stage I room

2 = Esterification stage II room

3 = Built in boiler room

4 = Liquid HTM heating coils ( boiler ) 5 = Main preater Ester 1

6 = Liquid HTM heating coils ( Ester 2 )

7 = Reactants inlet

8 = Precondensate transfer line

9 = Ester.1 vapour outlet

10 = Ester.2 vapour outlet

11 = Precondensate outlet

In El, flows are affected by free convection. The reactors are of a simple jacketed type with a built-in boiler. Boiling medium is an eutectic mixture of Diphenyl and Diphenyl Oxide. E-II has a separated heat exchanger (coils) in the reactor, and here the heat exchange medium is liquid HTM (a liquid heat transfer medium, typically a mixture of heavy organic components such as hydrogenated terphenyls).

Fig.2 schematically depicts embodiment B. This is the same as above but In El flows are affected by forced convection with the addition of a circulation pump. The reference list for Fig. 2 is:

1 = Esterification stage I room

2 = Esterification stage II room

3 = Built in boiler room

4 = Liquid HTM heating coils ( boiler )

5 = Main preater Ester.1

6 = Precondensate pump

7 = Liquid HTM heating coils ( Ester 2 )

8 = Reactants inlet

9 = Precondensate transfer line

10 = Ester.1 vapour outlet

11 = Ester.2 vapour outlet

12 = Precondensate outlet

Fig.3 (Embodiment C): same as embodiment A but the heat exchanger in El reactor is free convection built-in type (calandria). References: 1 = Esterification stage I room

2 = Esterification stage II room

3 = Built in boiler room

4 = Liquid HTM heating coils ( boiler )

5 = Built in heater ( main )Ester.1

6 = Liquid HTM heating coils ( Ester 2 )

7 = Reactants inlet

8 = Precondensate transfer line

9 = Ester.1 vapour outlet

10 ^ = Ester.2 vapour outlet

11 = Precondensate outlet

Fig.4 (Embodiment D): same as embodiment B but the heat exchanger in E2 reactor is a surface directly connected with the built-in boiler/jacket. References:

1 = Esterification stage I room

2 = Esterification stage II room

3 = Built in boiler room

4 = Liquid HTM heating coils ( boiler )

5 = Main preater Ester.1

6 = Precondensate pump

7 = Inner heating coils ( Ester 2 )

8 = Reactants inlet

9 = Precondensate transfer line

10 = Ester.1 vapour outlet

11 = Ester.2 vapour outlet

12 = Precondensate outlet

Fig.5 (Embodiment E): same as embodiment A but the heat exchanger in E2 reactor is a surface directly connected with the built-in boiler/jacket. References:

1 = Esterification stage I room 2 = Esterification stage II room

3 = Built in boiler room

4 = Liquid HTM heating coils ( boiler )

5 = Main preater ( Ester.1 )

6 =Inner heating coils ( Ester.2 )

7 = Reactants inlet

8 = Precondensate transfer line

9 = Ester.1 vapour outlet

10 = Ester.2 vapour outlet

11 = Precondensate outlet

Fig. 6 (Embodiment F): same as embodiment C but there are two separate built-in boilers: the lower for the El stage, the upper for the E2 stage The heat exchanger in E2 reactor is a surface directly connected with the upper built-in boiler/jacket. This last is considered the preferred embodiment. References:

1 = Esterification stage I room

2 = Esterification stage II room

3 = Boiler built in ( Ester.1)

4 = Liquid HTM heating coils ( boiler Ester.1) )

5 = Main heater Ester.1( built in )

6 = Reactants inlet

7 = Liquid HTM heating coils ( Ester 2 )

8 = Boiler built in ( Ester.2 )

9 = Inner heating coils ( Ester.2)

10 = Precondensate transfer line

11 = Ester.1 vapour outlet

12 = Ester.2 vapour outlet

13 = Precondensate outlet In all embodiments and the liquid transfer is by differential pressure: the top and bottom part of the reactor are in fluid communication with each other via pipe, that can be external or internal.

Claims

1. A reactor system for the production of polyester pre-condensate, comprising at least two reaction zones, operating at substantially different pressure, wherein a first reaction zone comprises a first reactant feeding zone, a heat exchanger, preferably comprising a vapor condensing system and a jacket, and a first product discharge zone comprising a flow line to a second reaction zone; said second reaction zone comprises a second reactant feeding zone, a second product discharge zone and an internal heat exchanger, preferably a heating coil, wherein the second product discharge zone comprises an elevated inlet extending to above the lowest point of the second reaction zone, and a plurality of substantially concentric, preferably

cylindrical, spacers surrounding the elevated inlet of the discharge zone, wherein the spacers are arranged so as to provide an increased path length between the reactant feeding zone and the product discharge zone, and wherein the elevated inlet of the product discharge zone is situated above the internal heat exchanger.

2. A reactor system according to claim 1, wherein the product discharge zone comprises a standpipe arranged so as to have its inlet elevated as defined in claim 1.

3. A reactor system according to claim 1 or 2, wherein the reactor system comprises a heat exchanging system comprising a vapor condensing system and a jacket.

4. A reactor system according to any one of the preceding claims, wherein the internal heat exchanger in the second reaction zone comprises one or more heating coils.

5. A reactor system according to any one of the preceding claims, wherein the spacers are cylindrical.

6. A reactor system according to any one of the preceding claims, wherein the first product discharge zone comprises a dip pipe extending from 1/3 to 2/3 of the cylindrical height of the vessel to below the cylindrical height inside the zone limited by the inferior head of the vessel, .

7. A reactor system according to claim 6, wherein the outlet of the dip pipe is positioned at least 10 cm, most preferably at least 20 cm below the liquid level of the reaction mixture.

8. A plant for the production of polyester, comprising a reactor system according to any one of the preceding claims, wherein the product discharge zone comprises a fluid connection to a polycondensation reactor.

9. A process for the production of a polyester pre-condensate, comprising the following steps:

(a) feeding a dihydric alcohol and a dicarboxylic acid or ester into the first zone of a reactor system according to any one of the claims 1-4 so as to provide a reaction mixture;

(c) allowing the initial esterification mixture to be transferred to the second zone of a reactor system according to any one of the claims 1-4 by means of differential pressure;

(e) allowing the low-mole-weight polyester pre-condensate to flow through the standpipe of a reactor system according to any one of the claims 1-

4, by means of gravity flow, so as to further store or use the pre-condensate.

10. A process for the production of a polyester, comprising preparing a pre-condensate in accordance with claim 9, and subjecting the pre-condensate to polymerization.

11. A process according to claim 10, conducted in a plant according to claim 8.

12. A process according to any one of the claims 9-11, wherein the dihydric alcohol is glycol, and the dicarboxylic compound is selected from the group consisting of terephthalic acid and dimethyl terephthalate.