Ep 0526572 B1

Europaisches Patentamt European Patent Office © Publication number: 0 526 572 B1 Office europeen des brevets

@ Date of filing: 16.04.91

RECOVERY OF ETHYLENE GLYCOL AND DIMETHYL TEREPHTHALATE FROM POLYETHYLENE TEREPHTHALATE.

® Priority: 24.04.90 US 521070 © Proprietor: EASTMAN KODAK COMPANY (a New Jersey corporation) @ Date of publication of application: 343 State Street 10.02.93 Bulletin 93/06 Rochester, New York 14650 (US) © Publication of the grant of the patent: 05.07.95 Bulletin 95/27 @ Inventor: NAUJOKAS, Andrius, Algimantas 972 Garden Lane © Designated Contracting States: Webster, NY 14580 (US) AT BE CH DE DK ES FR GB GR IT LI LU NL SE Inventor: RYAN, Kevin, Michael 202 Darla Drive © References cited: Brockport, NY 14420 (US) DE-B- 1 247 291 US-A- 3 037 050 US-A- 3 321 510 US-A- 3 488 298 US-A- 3 776 945 US-A- 4 163 860 © Representative: von Hellfeld, Axel, Dr. US-A- 4 578 502 Dipl.-Phys. et al Wuesthoff & Wuesthoff Patent- und Rechtsanwalte Schweigerstrasse 2 00 D-81541 Munchen (DE) CM m CO CM m Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid (Art. 99(1) European patent convention). Rank Xerox (UK) Business Services (3. 10/3.09/3.3.3) 1 EP 0 526 572 B1 2

Description terephthalate by interchange in a substantially an- hydrous methanol medium in the presence of a This invention relates to the recovery of eth- magnesium methylate catalyst. ylene glycol and dimethylterephthalate from scrap U.S. Patent 3,701,741 relates to a method of polyethylene terephthalate polyesters. More par- 5 recovering substantially pure poly- ticularly, it relates to a simplified method of obtain- ethyleneterephthalate) from scrape poly- ing the constituent monomers of polyethylene ethyleneterephthalate) contaminated with impuri- terephthalate from scrap wherein the process is ties by dissolving the contaminated material at ele- practiced under atmospheric conditions without de- vated temperatures and super-atmospheric pres- terioration of the yields. io sure in a volatile solvent. This patent does not relate to the recovery of the monomeric ingredients Description of Related Art that comprise the polymer. U.S. Patent 3,488,298 relates to a process for Various methods have been disclosed here- recovering dimethylterephthalate and ethylene gly- tofore for the recovery of ethylene glycol and 75 col from poly(ethyleneterephthalate) scrap by for- terephthalic acid or derivatives thereof. ming a mixture comprising the poly- U.S. Patent 3,776,945 teaches a process of ethyleneterephthalate) scrape, catalyst and metha- depolymerizing polyethylene terephthalate waste to nol, heating the mixture to approach equilibrium, obtain dimethylterephthalate and ethylene glycol treating the partially hydrolyzed mixture with an by subdividing the waste into dimensions between 20 excess of phosphorus-containing compound, heat- 4 and 35 mesh and treating at a temperature of ing the treated mixture to fractionate the constitu- 100°C to 300 °C and a pressure from 1 to 150 ents and recovering methanol, ethylene glycol and atmospheres with methanol in a quantity that the dimethylterephthalate. proportion of methanol to waste is between 1:1 and It can be seen from the above-recited art that 10:1 by weight in the presence of acid catalysts. 25 many different techniques have been employed in U.S. Patent 3,321,510 relates to a process of the recovery of the monomeric constituents from decomposing polyethyleneterephthalate by first poly(ethyleneterephthalate) resins. treating with steam at a temperature of from about These resins have found wide spread use in 200 °C to 450 °C and then reducing the steam- many and varied applications. For example, poly- treated polyethyleneterephthalate in the form of a 30 (ethyleneterephthalate) polyester resins find appli- brittle solid product to a powder having a mean cations in the preparation of many types of films, particles size of from about 0.0005 to 0.002 mil- including photographic film base, in fibers and in limeters and subsequently atomizing the fine pow- the preparation of food containers such as bottles. der with a gaseous substance including inert gas Thus, there is a widespread need for a simple and and methanol vapor to form an aerosol which is 35 economical method of treating such polyesters to conducted through a reaction zone at a tempera- recover the initial ingredients utilized in the prep- ture of 250 ° C to 300 ° C in the presence of excess aration of the polyester polymers. methanol vapors. U.S. Patent 3,037,050 relates to the recovery of Summary of the Invention terephthalate acid dimethyl ester by treating 40 polyethyleneterephthalate in the form of bulky or The invention provides an improved method (in lumpy solid masses with super-heated methanol particular at atmospheric pressure) of recovering vapor in the presence of any suitable esterification ethylene glycol and dimethylterephthalate from catalyst substantially at atmospheric pressure. polyethyleneterephthalate scrap resins by dissolv- U.S. Patent 4,578,502 relates to a procedure 45 ing the scrap polyester resin in oligomers of the for recovering monomeric polycarboxylic acids and same monomers as present in the scrap, passing polyols from solid scrap polyesters by granulating super-heated methanol through the solution and the scrap resin, slurring the resin with sufficient recovering the ethylene glycol and dimethyltereph- solvents such as water or methanol, depolymeriz- thalate. In the process according to the invention ing the slurried resin by the application of heat and 50 the scrap is heated to a temperature of 20° to pressure for a time sufficient to convert substan- 270 °C during the contact with methanol. The pro- tially all of the resin into its monomeric compo- cess is also advantageous in that the recovered nents, crystallizing the monomeric polycarboxylic dimethylterephthalate add ethylene glycol is freed acid present by flash crystallization and recovering of impurities by this method. Thus, the make up of the polycarboxylic acid and then the polyol by 55 the scrap polyester from which the constituents are distillation. recovered need not be considered prior to the U.S. Patent 4,163,860 relates to a process for recovery procedure and the inventive method is converting a bis-(diol) terephthalate to dimethyl- very satisfactory. For example, the following scrap

2 3 EP 0 526 572 B1 4 sources are available even if they contain large control means may be employed, Fig. 1 depicts a amounts of impurities: container 25 having contents 27 which cane be (1) ground bottle scrap including all the compo- maintained at a suitable constant temperature by nents present, such as, bottle contents, bottle an external heating means (not shown). The con- caps, labels and polyethylene bottom cups; 5 tents 27 may be a salt bath for example. Container (2) subbed film scrap; 25 is provided with a means (not shown) for raising (3) photographic film; and lowering in order that reactor 1 1 can be posi- (4) washed film scrap; tioned relative with respect to the contents 27 of (5) still dregs from polyester recovery plant; and container 25. A reservoir 29 is connected by (6) scrap polyester containing polymers includ- io means of conduit 31 with sparging means 15. Con- ing acetate resins, polyvinyl chloride and the duit 31 has disposed therein pump 33 for de- like. By oligomers of the same monomers is livering the contents of reservoir 29 to sparging meant, that the monomers which form constitu- means 15 via conduit 31. Conduit 31 has asso- ent parts of the oligomer are the same as that of ciated therewith a heating means which in the case the polymer, i.e., ethylene glycol and tereph- is as shown is a length of conduit 31 doubled upon thalic acid or dimethylterephthalate. In accor- itself and disposed within heating medium 27 in dance with Grant and Hacks Chemical Dictio- container 25. Reactor 11 is further provided with nary, Fifth Edition, published by MaGraw-Hill outlet means 35 connected to first distillation de- Book Company, an oligomer is "a polymer vice 37 by conduit 39. Conduit 41 is provided to whose properties change with the addition or 20 return the overheads from distillation device 37 to removal of one or a few repeating units. The reservoir 29. Conduit 43 conveys the higher boilers properties of a true polymer do not change to second distillation device 45. markedly with such modification". In accordance In operation, oligomers of dimethylterephthalate with this invention an oligomer is any low molec- and ethylene glycol are introduced into reactor 11 ular weight polyester polymer of the same con- 25 to at least approximately 50% of the volume of the stituency as that of the scrap material being reactor 11 and agitator 13 and heating means de- employed as the starting component wherein picted as container 25 and contents thereof 27 the scrap polymer will dissolve in the low molec- actuated to bring the temperature of the oligomers ular weight oligomer. The constituent units of to from 220 °C to 270 °C. Scrap feeding means 17 the oligomer used in accordance with this inven- 30 loaded with polyethylene-terephthalate scrap resin tion will repeat "n" times wherein the "n" will is actuated to deliver scrap resin to the contents of vary between 2 and 100 and a molecular range reactor 11. Pump 33 is actuated to deliver metha- of between 384 and 19200. In this oligomer nol from reservoir 29 through conduit 31 wherein composition, many polymer units of varying the methanol is super-heated and delivered through chain links is present. Values of n as low as 2 to 35 sparging means 15 into the contents of reactor 11 5 or as hight as 50 to 100 are suitable in as a vapor which passes through the solution of the accordance with this invention. polyethyleneterephthalate and the oligomer thereof. The methanol is recovered by passing out through Brief Description of the Drawing outlet 35 through conduit 39 and distillation device 40 37 back through conduit 41 to the methanol reser- Figure 1 is a schematic flow diagram illustrat- voir 29. The recovered dimethylterephthalate and ing an apparatus suitable for use in practicing the ethylene glycol also exits via outlet 35 through process of this invention. conduit 39, are separated from the methanol in distilling device 37 and past via conduit 43 to Description of Preferred Embodiments 45 second distillation device 45 where the ethylene glycol is collected overhead while the dimethyl- Figure 1 illustrates in diagrammatic fashion a terephthalate is removed below. It may be desir- flow chart for practicing the process in accordance able for conduit 39 to be provided with a heating with this invention. Reactor 11 is equipped with an means in order to prevent the condensation of any agitator 13 driven by a motor (not shown), a tem- 50 of the three components exiting from reactor 1 1 . perature sensing means (now shown), a sparging It is, of course, to be understood while the means 15 for introducing a gas into the reactor 11 process described above is semi-continuous in na- and a scrap introduction means 17 made up of ture, that the method in accordance with this inven- hopper 19, barrel 21 and auger 23. The auger is tion may be carried out as a batch, a semi-continu- provided with a motor means (not shown) for rotat- 55 ous or continuous method. In the semi-continuous ing the auger 23 within barrel 21 . The reactor 1 1 is method depicted above, which involves the feeding provided with a means for controlling the tempera- of polyester scrap into the reactor at a rate sub- ture of the contents thereof. While any suitable stantially equivalent to product formation, impurities

3 5 EP 0 526 572 B1 6 will accumulate in reactor 11 necessitating periodic omers as that of the scrap, passing super- clean out. In a continuous mode of operating the heated methanol through the solution and re- process in accordance with this invention for exam- covering the ethylene glycol and dimethyl- ple, a small slip stream of the reactor contents terephthalate. would continuously be removed, the rate being 5 based on the rate of impurities being introduced 2. The method of claim 1 wherein the process is into the reactor. An advantage associated with all of conducted under atmospheric pressure. the three techniques, whether it be batch, semi- continuous or continuous, is that any catalyst em- 3. The process of claim 1 wherein the scrap is ployed in the preparation of the virgin poly- io heated to a temperature of from 20 ° to 270 ° C ethyleneterephthalate) resin will not enter the prod- during the contact with methanol. uct vapor stream but will be removed along with the impurities due to the low volatility of these 4. The method of claim 1 wherein an excess catalysts. quantity of methanol is passed through the The invention will be illustrated by the following is solution. examples in which parts are by weight unless oth- erwise specified: 5. The method of claim 1 wherein the ethylene glycol and dimethylterephthalate are recovered Example 1 by distillation. 20 A reactor 11 is charged with 2000 parts of Patentanspruche polyethylene terephthalate oligomers containing a mixture having between 10 and 20 repeating units 1. Verfahren zur Ruckgewinnung von Ethylengly- heated to 250 °C to render the mass molten. Clean kol und Dimethylterephthalat aus Polyethylen- polyethylene terephthalate powder is fed by means 25 terephthalatpolyestern, wobei Ab- 17 at the rate of 3.5 parts/minute and methanol is fall/AusschuB/Reste aus Polyester in oligome- feed at the rate of 20 part by volume and sparged ren der gleichen Monomeren wie denjenigen through the molten resin by means 15. The metha- des Abfalls/Ausschusses/der Reste aufgelost nol is returned to reservoir 29 via distillation col- werden, uberhitztes Methanol durch die L6- umn 37 and conduit 41 . The dimethyl terephthalate 30 sung geleitet wird und das Ethylenglykol und and ethylene glycol are recovered from distillation Dimethylterephthalat zuruckgewonnen werden. column 45. 2. Verfahren nach Anspruch 1 , wobei das Verfah- Example 2 ren unter atmospharischem Druck durchge- 35 fuhrt wird. A reactor similar to that of Example 1 is charged with about 630 parts of the oligomer mix- 3. Verfahren nach Anspruch 1, wobei der Ab- ture of Example 1 heated to 225 °C to render it fall/Ausschul3/die Reste auf eine Temperatur molten. Methanol is feed to the sparging means 15 von 20 bis 270 °C wahrend des Kontakts mit at a rate of 4 parts by volume/minute and ground 40 dem Methanol erwarmt wird. scrap polyethylene terephthalate bottles including polyolefin bottom cups, aluminum bottle caps, la- 4. Verfahren nach Anspruch 1, wobei eine Uber- bels and any adherents used for the labels and schuBmenge an Methanol durch die Losung bottom caps are fed to the reactor at a rate of 2.5 geleitet wird. parts/minute. As in Example 1 the methanol is 45 returned to reservoir 29 and the ethylene glycol 5. Verfahren nach Anspruch 1, wobei das Ethyl- and dimethyl terephthalate recovered from distilla- englykol und Dimethylterephthalat durch De- tion column 45. Crystalline dimethyl terephthalate stination zuruckgewonnen werden. with a light layer of polyolefins and aluminum col- lecting at the bottom of the melt are removed from 50 Revendicatlons the reactor. 1. Procede de recuperation de I'ethylene glycol Claims et du terephtalate de dimethyle a partir de polyesters du type polyterephtalate d'ethylene, 1. A method of recovering ethylene glycol and 55 ledit procede consistant a dissoudre des de- dimethylterephthalate from polyethylenetereph- chets de polyester dans des oligomeres des thalate polyesters which comprises dissolving memes monomeres que ceux constituant les scrap polyester in oligomers of the same mon- dechets, a faire passer du methanol surchauffe

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a travers la solution et a recuperer I'ethylene qlycol et le terephtalate de dimethyle.

2. Procede selon la revendication 1, dans lequel le procede est mis en oeuvre a la pression 5 atmospherique.

3. Procede selon la revendication 1, dans lequel les dechets sont chauffes a une temperature de 20 ° a 270 ° C pendant le temps de contact 10 avec le methanol.

4. Procede selon la revendication 1, dans lequel on fait passer un exces de methanol a travers la solution. is

5. Procede selon la revendication 1, dans lequel I'ethylene glycol et le terephtalate de dimethyle sont recuperes par distillation. 20

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