Title of Invention

'PROCESS AND UNIT FOR PRODUCTION OF PET PELLTS'

Abstract This invention relates to a process and apparatus for producing especially PET granulates, wherein terephthalic acid and ethylene glycol are fed in the form of a precondensate into a drip tower having a distributing drip nozzle after esterification and pre-polycondensation with the purpose of effecting granulation. The precondensate exits the distributing drip nozzle by forming drop-shaped pellets that are blown by a hot countercurrent nitrogen stream reducing the velocity of fall and accelerating crystallization at an increasing degree of crystallization. Dried, semi-crystallized round pellets are thus produced that are then subjected to solid phase polycondensation resulting in pellets possessing high viscosity and quality for further processing.
Full Text Description
The present invention relates to a process for the production of granules from polyfunctional carboxylic acids and alcohols, in particular PET granules, wherein terephthalic acid and ethylene glycol after their esterificatien and a prepolycondensstion are filtered as a low viscosity precondensaten granulated and passed to a solid phase polyeondervsation and are then available as Highly viscous partially crystalline granules- As is known-i PET denotes poly,(ethylene terephthalate) -
Such a process for the production of PET granules is known-i in which the precondensate formed by the esterification and prepolycondensation of ethylene glycol (E6> and terephthalic acid (PTA) is passed to a reactor operating under reduced pressure in order on the one hand to increase the viscosity of the predominantly liquid and short-chain polymer n and on the other hand to recycle the released ethylene glycol to the esterification. After the reactor treatment the polycondensate that is formed is cooled with demineralised water and chopped into granules so as to form cylindrical pellets-i which on the one hand are predominantly amorphous and on the other hand have projections on their cut ends that tend to break off during transportation and intermediate storage-) thereby producing dust- Before these pellets are available for processing in for example extruders o> they have to be partially crystallised in a separate process stage-* following which they are subjected to a solid phase polycondensation under the addition of nitrogen- A further crystallisation and increase in viscosity is thereby achieved-! with the result that highly viscous pellets are finally available. This

known process is however disadvantageous for various reasons- In the first place it is a disadvantage that the pellets tare present in a predominantly amorphous state after their granulation and accordingly have to fee partially crystallised in a subsequent separate treatment stage- Xn addition the projections in the region of the cut ends of the amorphous pellets readily break off during their transportation and storage and consequently tend to produce dust- Furthermore the expenditure on apparatus at\fi energy is a disadvantage sinc"i special treatment stages SPQ necessary-, such as the reactor stage operating under reduced pressure and a partial crystallisation stage-Besides this there is a significant need for desiineralised water for the granulation of the precondensate-
The object of the present invention is to provide a process whereby granules formed from polyfunctional tarboxylic acids anti alcohols -" in particular PET granules*! can be produced economically and conveniently as roundi dust-free pellets of uniform size ant! satisfactory quality in a solidified and partially crystallised modification with reduced expenditure on apparatus and energy. A further object of the invention is to provide an apparatus for carrying out the aforementioned process that is characterised by a simple and function-oriented design and construction.
This object is achieved by the invention in a generic process^ characterised in that for the purposes of the granulation the molten precondensate is added to a trickling tower with a heated distribution trickling nozzle arranged at the head of the trickling tower-, that the precondensate leaves the distribution trickling nozzle with the formation of droplet-shaped pellets and the pellets arm blasted 1 after a predetermined free falling height-i by a hot stream of nitrogen in countercurrent with a reduction of the falling velocity and acceleration of a

-3-
crystallisation with increasing degree of crystallisation-, and that the pellets leaving at the floor of the trickling tower are passed as dried and partially crystallised pellets to the solid phase polycondensation. As a result of these features of the invention the precondensate is converted by means of the distribution trickling nozzle into droplet-shaped and consequently round pellets-t and more specifically over practically the whole cross-section of the tower- In fact^ the formation of filaments is prevented with the aid of the distribution trickling nozzle. An outer skin already forms during the free falling trajectory. A further consolidation of the pellets is achieved by means of the nitrogen countercurrent. This nitrogen countercurrent can readily be adjusted so that no interfering turbulences occur-, and instead simply the falling velocity of the pellets is reduced and as a result of the nitrogen blasting a partial crystallisation is simultaneously achieved- By means of the nitrogen countercurrent the residence time of the pellets in the trickling tower can be adjusted so that the pellets are at the same time sufficiently dried and are converted into uniform drops and consequently uniformly round pellets of satisfactory quality- Surprisinglyi such a consolidation of the pellets is achieved over the free falling height and due to the blasting with nitrogen in countercurrentt that the latter do not adhere to one another even if-" by means of the distribution trickling nozzlei droplet-shaped pellets are produced in an increasingly dense distribution over the cross-section of the trickling tower and fall down the tower. The round and substantially consolidated as well as partially crystallised pellets can be transported and stored without virtually any formation of dust and-, in particular having regard to their uniform size-i can also uniformly polycondense in the solid phase polycondensation. As a result high quality granules formed from polyfunctional carboxylic acids and alcohols-, in particular PET pellets-, can be produced conveniently and economically

by the process according to the invention. This is achieved without any treatment in a reactor operating under reduced pressure and without cooling with demineralised water and the adoption of granulation measures that lead to the formation of cylindrical pellets having a tendency to produce dusti and finally without any partial crystallisation in a separate process stage-, since according to the teaching of the invention partially crystallised pellets with a predetermined degree of crystallisation are produced to start withi instead of mainly largely amorphous pellets- As a result the expenditure on apparatus and energy for the production of the pellets according to the invention can also be significantly reduced-
Further essential features according to the invention are discussed hereinafter. For examplei the invention envisages that the pellets in the trickling tower are subjected in an upper stage and a lower stage to a nitrogen countercurrent in order to achieve a residence time as long as possible and consequently high partial crystallisation and/or consolidation of the round pellets without interfering turbulence. Insteadn the process is carried out with a stepwise reduction of the falling velocity and acceleration of the partial crystallisationi with a constant increase in the degree of crystallisation-Preferably the nitrogen is fed in through the floor region of the trickling tower and the two nitrogen countercurrent stages are generated by a stepwise extraction of nitrogen-In this way different blasting velocities in the upper and lower stages can be achieved- The pellets &re conveniently blasted in countercurrent in the upper stage at a velocity of 1 to 3 m/sec-i and in the lower stage at a velocity of 3 to ? m/sec- To this end dry nitrogen at a temperature of XfeO°C to 25Q°C is fed to the trickling tower- Both features lead to an increase not only of the partial crystallisation but also of the viscosity of the pellets and consequently

their solidification- The nitrogen extracted from the trickling tower can be passed to an ethylene glycol separator and a nitrogen drier in order to recycle the recovered ethylene glycol to the esterification stage-, and more specifically without using an otherwise extremely costly reactor and without having to carry out an uneconomic elimination of the ethylene glycol in the course of a catalytic combustion-
The subject of the invention is also an apparatus for carrying out the claimed process-! including at least one esterification staget a prepolycondensation stagei a filtration stagei a granulation device and a solid phase polycondensation stagei which apparatus has a particularly simple and function-oriented design and construction and is characterised in that the granulation device has a trickling tower-i that the trickling tower has in the head region a heated distribution trickling nozzle for the added precondensate-* that the trickling tower has* after a predetermined free falling height for the droplet-shaped pellets leaving the distribution trickling nozzle-* at least one nitrogen extraction point-, that the trickling tower has a nitrogen feed in the floor region-, and that the nitrogen fed in at the floor region blasts the downwardly falling pellets in countercurrent- In this connection the trickling tower may ha\fe an tipper nitrogen extraction point and-t at a predetermined vertical distancei a lower nitrogen extraction point- Further nitrogen extraction points are also conceivable within the scope of the invention. The distribution trickling nozzle is designed in accordance oo^t-h the invention as a nozzle-shaped disc with a plurality of individual nozzles and/or nozzle outlet openings ana heating channels arranged on the inside- In this way a particularly uniform distribution of the droplet-shaped pellets can be achieved over the cross-section of the trickling tower. The nitrogen extraction points are conveniently arranged in the tower wall-* and include for

-6-
example circulating sieve passages with suction channels covering the said sieve passages and suction pumps connected thereto- A common ethylene glycol separator and nitrogen drier is preferably associated with the suction pumps. The dried and heated nitrogen is recycled to the trickling tower in the floor region in order to generate the nitrogen countercurrenti while the recovered ethylene glycol is-i as already mentioned hereinbefore-> returned to the esterification stage- The ethylene glycol separator communicates with the esterification stage- The invention furthermore envisages that the trickling tower has a for example circulating sieve passage arranged in the floor region and a feed channel covering the said sieve passage for the supply of dry and hot nitrogen- Furthermore the trickling tower may contain a pellet outlet in the floor region-i a gas-tight belt conveyor for removing the pellets and that can be charged with dry and hot nitrogen being arranged underneath the pellet outlet-, so that in practice a dry product conveyor is realised- The free falling height of the pellets is preferably 5 to 10 m and the vertical distance between the nitrogen extraction points is 10 to 3Q m-
Instead of nitrogen other inert gases such as for example CO2 can also be used within the scope of the invention.
The invention will be described in more detail hereinafter with the aid of drawings illustrating merely one example of implementation! in which:
Fig- 1 shows the apparatus according to the invention in the form of a flow diagrann and
Fig- 2 is a schematic section of the subject according to Fig. 1 in the region of the trickling tower.

-7-
The figures^how an apparatus for producing granules from polyfunctional carboxylic acids and alcohols^ in particular PET granulesi having at least one esterification stage 1 for terephthalic acid and ethylene glycoli a connected prepolycondensation stage 5 operating under reduced pressurei a following filtration stage 3 with a pump-, a granulation device Mi and a solid phase polycondensation stage 5-* wherein a transporting device t for the granules is arranged between the granulation device M and the solid phase polycondensation stage S-
The granulation device M includes a trickling tower ?- The trickling tower 7 includes in the head region a heated distribution trickling nozzle & for the fed-, filtered and molten precondensate- The trickling tower 7 also includes-, after a predetermined free falling height H for the droplet-shaped pellets 1 leaving the distribution trickling nozzle 6-i a nitrogen extraction point IQa- The trickling tower 7 furthermore contains a nitrogen feed 11 in the floor region- The nitrogen fed in at the floor region blasts in countercurrent the downwardly falling pellets 1 in the trickling tower 7. According to the example of implementation-, the trickling tower 7 has an upper nitrogen extraction point 3.0a and a lower extraction point 10b arranged at a predetermined vertical distance below the upper extraction point- The distribution trickling nozzle A is designed as a nozzle-shaped disc with a plurality of individual nozzles and heating channels arranged on the inside (not shown) - The nitrogen extraction points 10a-. 10b have for example circulating sieve passages 13 or belts arranged in the tower wallt with suction channels 13 covering the said sieve passages 12 and suction pumps 1M connected to the channels- An ethylene glycol separator 15 and a nitrogen drier Ik are arranged after the suction pumps 1M- The ethylene glycol separator IS communicates with the esterification stage %-

-8-
The trickling tower 7 has a for example circulating sieve passage 1? arranged in the floor region and a feed channel 1A for the supply of dry and hot nitrogen-i covering the said sieve passage- The nitrogen is purified in a nitrogen circulation system 11- This nitrogen circulation system 11 communicates on the one hand with the nitrogen drier Ib-i and on the other hand with the solid phase polycondensation stage 5- The trickling tower 7 also contains in the floor region a pellet outlet 20- A gas-tight belt conveyor 21 for removing the pellets 1i which can be charged with dry and heated nitrogen and consequently forms a dry product conveyor for transporting the granules to the solid phase polycondensation stage 5-. is arranged underneath the pellet outlet ED- The further processing of the pellets T takes place for example in an extruder- The free falling height H of the pellets is 5 to ID nti and the vertical distance between the nitrogen extraction points is 10 to 30 m-

10 WE CLAIM
1. Process for the production of granules from poiyfunctional carboxylic acids
and alcohols, inparticular PET granules, wherein terephthalic acid and
ethylene glycoi after their estenficatson and a prepolycondensation are
filtered as a low viscosity precondensate, granulated and passed to a solid
phase poiycondensation and are then available as highly viscous partially
crystalline granules, characterized in that for the purpose of the
granulation the precondensate is fed to a trickling tower with a heated
distribution trickling nozzle arranged at he head of the trickling tower, that
the precondensate leaves the distribution trickling nozzle with the
formation of droplet-shaped pellets and the said pellets after a
predetermined free falling height are blasted by a hot nitrogen stream
in countercurrent with a reduction of the falling velocity and acceleraion of the crystallization with increasing degree of crystallization, and that the pellets leaving the floor of the trickling tower are fed as dried and partially crystallized pellets to the solid phase poiycondensation.
2. Process as claimed in claim I, wherein the pellets in the trickling tower are
blasted in an upper stage and a lower stage with a nitrogen
countercurrent,
3. Process as claimed in claim 1 or 2, wherein the nitrogen is fed into the
floor region of the trickling tower and the two nitrogen countercurrent
stages are produced by a stepwise removal of nitrogen.
4. Process as claimed in any one of the claims 1 to 3, wherein the pellets in
the upper stage are blasted in countercurrent at a velocity of I to 3
m/sec. and in the lower stage at a velocity of 3 to 7 m/sec.
5. Process as claimed in any one of the claims 1 to 4, wherein dry nitrogen
at a temperature of 160°C to 250°c is fed to the trickling tew§F.

11
6. Process as claimed in any one of the claims 1 to 5, wherein the nitrogen
extracted from the trickling tower is fed to an ethylene glycol separator
and a nitrogen drier, and the recovered ethylene glycoi is fed to the
esterification stage.
7. Apparatus for carrying out the process as claimed in claim one of claims 1
to 6 comprising at least one esterification stage, a prepolycondensation
stage, a filtration stage, a granulation device and a solid phase
polycondensation stage, characterized in that the granulation device (4)
comprising a trickling tower (?) in that the trickling tower (7) has a heated
distribution trickling nozzle (8) in the head region for the supplied
precondensate in that the trickling tower (7) after a predetermined free
falling height (H) for the droplet-shaped pellets (9) leaving the distribution
trickling nozzle (8) has at least one nitrogen extration point (10a), in that
the trickling tower (7) has in the floor region a nitrogen feed (II) and in
that the nitrogen fed in through the floor blasts in countercurrent the
downwardly falling pellets (9),
8. Apparatus as claimed in claim 7, wherein the trickling tower (7) has an
upper nitrogen extraction point (10a) and, at a predetermined vertical
distance, a lower nitrogen extraction point (10b).
9. Apparatus as claimed in claim 7 of 8, wherein the distribution trickling
nozzle (8) is formed as a nozzle-shaped disc with a plurality of individual
nozzles and heating channels arranged on the inside.
iO.Apparatus as claimed in one of claim 7 to 9, wherein the nitrogen extration points (10a, 10b) have for example circulating sieve passages (12) arranged in'the tower wall, with suction channels (13) covering the said sieve passage (12) and suction pumps (14) connected to the said channels.

12 11.Apparatus as claimed in claims 7 to 10, wherein an ethylene glycol
separator (15) and a nitrogen drier (16) are arranged after the suction
pumps (14). 12,Apparatus as claimed in claims 7 to 10, wherein the ethylene giycol
seperator (IS) communicates with the esterification stage (1). 13.Apparatus as claimed in claims 7 to 12, wherein the trickling tower (7) has
for example a circulating sieve passage (17) arranged in the floor region,
and a feed channel (18) for the supply of dry and hot nitrogen, covering
the said sieve passage (17). H.Apparatus as claimed in claims 7 to 13, wherein the trickling tower (7) has
a pellet outlet (20) in the floor region, and a gas-tight belt conveyor (21)
for removing the peltets (9), which can be charged with dry and hot
nitrogen, is arranged underneath the pellet outlet (20), IS.Apparatus as claimed in one of claim 7 to 14, wherein the free falling
height (H) of the pellets is 5 to lGm, and the vertical distance between
the nitrogen extraction points is 10 to 30m,
This invention relates to a process and apparatus for producing especially PET granulates, wherein terephthalic acid and ethylene glycol are fed in the form of a precondensate into a drip tower having a distributing drip nozzle after esterification and pre-polycondensation with the purpose of effecting granulation. The precondensate exits the distributing drip nozzle by forming drop-shaped pellets that are blown by a hot countercurrent nitrogen stream reducing the velocity of fall and accelerating crystallization at an increasing degree of crystallization. Dried, semi-crystallized round pellets are thus produced that are then subjected to solid phase polycondensation resulting in pellets possessing high viscosity and quality for further processing.

Documents:


Patent Number 206628
Indian Patent Application Number IN/PCT/2001/00459/KOL
PG Journal Number 18/2007
Publication Date 04-May-2007
Grant Date 03-May-2007
Date of Filing 24-Apr-2001
Name of Patentee UHDE GMBH
Applicant Address FRIEDRICH-UHDE-STRASSE 15, D-44141 DORTMUND,
Inventors:
# Inventor's Name Inventor's Address
1 GEIER RUDOLF ISABELLASTRASSE 4, D-45130 ESSEN,
2 JURGENS THEO BORGHAGENER STRASSE 173 A, D-44851 CASTROP-RAUXEL,
3 VEIT MARK PLATTENWEILER 5, D-45239 ESSEN
PCT International Classification Number C08J 3/12
PCT International Application Number PCT/EP97331
PCT International Filing date 1999-10-02
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 198 49 485.8 1998-10-27 Germany