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Rancic Et Al Kinetic Study of PET Glycolysis [4]

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1 13 th International Conference Research and Development in Mechanical Industry RaDMI 2013 12 - 15. September 2013, Kopaonik, Serbia THE KINETIC STUDY OF PET GLYCOLYSIS REACTION Milica Rančić 1 , Jelena D. Rusmirović 1 , Svetlana D. Pešić 1 , Dušan M. Janković 2 , Enis S. Džunuzović 3 , Pavle M. Spasojević 3 , Aleksanddar D. Marinković 3 1 Faculty of Forestry Science, University of Belgrade, Kneza Višeslava 1, 11030 Belgrade, SERBIA 2 Military Academy, Pavla Jurišić
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  1 13 th  International Conference Research and Development in Mechanical Industry   RaDMI 2013 12 - 15. September 2013, Kopaonik, Serbia   THE KINETIC STUDY OF PET GLYCOLYSIS REACTION Milica Rančić 1 , Jelena D. Rusmirovi ć 1 , Svetlana D. Pešić 1 ,   Dušan M. Janković 2 , Enis S. Džunuzović 3 , Pavle M. Spasojević 3 , Aleksand dar D. Marinković 3 1 Faculty of Forestry Science, University of Belgrade, Kneza Višeslava 1, 11030 Belgrade, SERBIA   2 Military Academy, Pavla Jurišića - Šturma 33, 11000, Belgrade , SERBIA  3 Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, 11120 Belgrade, SERBIA Summary:  Polyethylene terephthalate (poly(ethylene terephthalate), PET, is a thermoplastic polyester resin and is used in synthetic fibers. Due to the presence of the ester functional group, PET polymer can react with different reagents and in that process, macromolecular polymer chains split into shorter oligomer chains. Following reagents can be used: water (hydrolysis process), alcohols (alcoholysis), two hydroxyl alcohols (glycolysis) and different amines (aminolysis). Herein, we report the investigation of kinetics of the glycolysis reaction, i.e. chemical depolymerization of the PET polymer, the reaction that takes part in the PET recycling proccess. The glycolysis reaction was performed with different diols, such as DEG, DG, DPG, Gly, TMP, TEG in order to study the kinetics of the PET glycolysis reaction and the influence of the type of the glycol reagent and catalyst. Keywords:  poly(ethylene terephthalate) (PET), recycling of PET 1. INTRODUCTION Polyethylene terephthalate  (poly(ethylene terephthalate),  PET , is a thermoplastic polymer resin of the  polyester family and is used in synthetic fibers; beverage, food and other liquid containers; thermoforming applications; and engineering resins often in combination with glass fiber (CAS 25038-59-9). Structural  part of polyethylene terephthalate is presented in Fig.1. Figure 1.  Structural formula of polyethylene terephthalate Depending on its processing and thermal history, polyethylene terephthalate may exist both as an amorphous (transparent) and as a semi-crystalline polymer. The semicrystalline material might appear transparent (particle size < 500 nm) or opaque and white (particle size up to a few microns) depending on its crystal structure and particle size. Its monomer (bis-  β  -hydroxyterephthalate) can be synthesized by the esterification reaction between terephthalic acid and ethylene glycol with water as a byproduct, or by transesterification reaction between ethylene glycol and dimethyl terephthalate with methanol as a  byproduct. Polymerization is through a  polycondensation reaction of the monomers (done immediately after esterification/transesterification) with water as the byproduct [1].  2 The majority of the world's PET production is for synthetic fibers (in excess of 60%), with bottle  production accounting for around 30% of global demand. In the context of textile applications, PET is referred to by its common name, polyester, whereas the acronym PET is generally used in relation to  packaging. Polyester makes up about 18% of world polymer production and is the third-most-produced  polymer;  polyethylene (PE) and  polypropylene (PP) are first and second, respectively. PET consists of  polymerized units of the monomer ethylene terephthalate, with repeating C 10 H 8 O 4  units. PET is commonly recycled, and has the number 1 as its recycling symbol. Due to the presence of the ester functional group, PET polymer can react with different reagents and in that process, macromolecular polymer chains split into shorter oligomer chains. Following reagents can be used: water (hydrolysis process), alcohols (alcoholysis), two hydroxyl alcohols (glycolysis) and different amines (aminolysis) [2-7]. Herein, we report the investigation of kinetics of the glycolysis reaction. This paper presents the study of the kinetics of the PET glycolysis reaction with different glycols in order to study the influence of the catalyst and structure of the glycol reagent. 2. TECHNICAL REQUIREMENTS 2.1. Materials All chemicals were purchased from Fluka, Sigma-Aldrich and Zorka-pharma and used as received and Eurocat 9555 catalyst was purchased from Cores System d.o.o., Belgrade. 2.2. Instrumental analysis Gas chromatographic analysis was performed on Varian 3400 apparatus which is equipped with flame ionization detector and a coloumn filled with OV-101with lenght of 2 m and diameter of 0.3175 cm (1/8’’). Analysis conditions: -Injector temperature: 250  C; -Detector temperature: 270  C; -Coloumn temperature: 80 o C (1 min) → 10 o C/min → 200 o C (15 min) -Carrying gas: nititrogen (purity 99,99%) - flow 1 cm 3 /min. -Airflow: 250 cm 3 /min (purity 99,99%); -Hydrogen flow: 25 cm 3 /min (purity 99,99%). The UV absorption spectra were measured with a Shimadzu 1700 UV/Vis spectrophotometer. 2.3. Method of catalytic PET depolimerization The appropriate amounts of PET, glycol and catalyst (Eurocat 9555) were placed in a four-necked flask (250 ml or 500 ml) equiped with reflux condenzator, mechanical stirrer, termometer and system for N 2  introduction. The glycolysis reaction was performed during 5 h at 205-220 ºC. Different glycols were used: diethylene glycol (DEG), propylene glycol (PG), dipropylene glycol (DPG), triethylene glycol (TEG), trimethylolpropane (TMP) and glycerol (Gly), with different glycol/PET molar proportion. When reaction ended, the glycolysis product was poured out, cooled down and, successively, purificated by dissolving in appropriate amount of dichloromethane, washed out twice with destilled water and dried with anhydrous sodium sulphate. After vacuum filtration, dichloromethane was removed by destilation and product was additionally dried on vacuume to remove water completely, as well as residual ethylene glycol. 3. RESULTS AND DISCUSSION  3 3.1. PET glycolysis kinetics in the presense Eurocat 9555 catalyst The chemism of the PET depolimerisation reactions, which could cotribute the overall kinetics of the investigated system, is presented on Figure 2. As it can be seen from the reaction pattern presented on the Figure 2, reaction system is very complex, so some assumptions should be made [8-15]. T: Structural unit of terephtalic acid -O 2 CC 6 H 4 CO 2 - E: Structural unit of ethylene glycol -CH 2 CH 2 - D: Structural unit of glycolysis reagent Figure 2.  The PET glycolisys reaction Starting from the PET and glycolysis reagents, diols (HODOH), following changes can be expecting: 1.   Glycolysis of the PET chains gives two kinds of oligomers with hydroxyl groups at their terminals, one with DOH group and the other with EOH group (reaction 1; k  1 ). 2.   Futher glycolysis of the PET chains, by glycolysis reagents or oligomers with terminal hydroxyl groups, gives shorter chains. During the first reaction, HODOH is consumed and diol structural unit is embeded into chains. The extraction of EG occurs in reactions 6 (k  12 ) and 4 (k  7 ). 3.   The   formation   of    statistic   copolymer    structure   is   the   consequence   of    the   large   number    of    equilibrium reactions. At the beginning, the mixture consists of two phases: solid (PET) and liquid (HODOH). If the chemical structure (molar mass and composition) of the polyester is soluble, they transit to the solution what has two main consequences for the liquid phase:    Increasing of the UV absorbance because of the presence of the terephthalic acid structural units    Decreasing of the HODOH concentration as the consequence of the reaction with polyesters Therefore, important data can be obtained by analyzing of liquid phase:    The UV absorbance show the portion of dissolved polyesters    Free glycols, HODOH and MEG, can be determined by gas chromatography 3.2. The PET glycolysis with different glycols The PET glycolysis with DEG, DPG, Gly and PG was performed at 220 o C without catalyst and at 190 o C with Eurocat 9555 catalyst. Using of the large glycol amount is necessary for the adequate dissolution of the PET flakes. Molar ratio, glycol/PET=4/1. Samples were analyzed by gas chromatography to follow the  portion of free glycols formed. While EG is the reaction product, and its amount range from zero, characteristic marginal value determined by equilibrium, the change of the amount of glycolysis reagent (HODOH) is less pronounced. At the beginning of the reaction, PET is insoluble, so glycolysis reagent  presents 100%. Afterwards, its amount decreases to the marginal value, because of pseudo-dissolving of  polyesters in macroscopic homogenous solution and the incorporation of glycol structure units in polyestar chains by chemical reaction. Four typical glycolysis curves are presented on Figure 3.  4 Figure 3.  Typical curves of the decreasing of the glycol portion during the glycolysisreaction    Curve (a): Fast decreasing of glycol portion at the beginning corresponds to the complete dissolving of  polyester without chemical reaction, while futher slow decreasing corresponds to the chemical reaction. This corresponds to non-catalyzed glycolysis reaction with DPG.    Curve (b): Very small initial glycol portion decreasing corresponds to weak polyester dissolving. It can  be noticed that reactivity and solubility are very weak (e.g. Gly).    Curve (c): Fast decreasing of the glycol portion, where chemical reaction and polyester dissolving occur at the same time (e.g. DEG at 220 o C without catalyst).    Curve (d): Similar decreasing as for curve (b) (e.g. PG). 3.3. Non-catalyzed glycolysis at 220 o C It was derived that increasing the EG portion is much faster with DEG, considering that for the other glycols, it takes more than 5 hours until the stabilization of the reaction and more than 20 hours till the end of the reaction. Depending on the glycol used, there is also difference in the initial time of the reaction:    DEG - 15 min.    DPG - 4 h i 30 min.    Gly - 90 min.    PG - 90 min. This results imply that non-catalyzed PET glycolysis with DPG, Gly and PG is slow reaction because of weak DPG chemical reactivity, while in Gly and PG, PET has low solubility, as well as polyester oligomers. Order of reactivity in non-catalyzed glycolysis at 220 o C is: DEG >> PG >Gly>> DPG 3.4. Catalyzed glycolysis at 190 o C The EG formation is faster during glycolysis with DEG than with DPG (Figure 4). The portion of EG reaches equilibrium value after one hour during glycolysis with DEG, while the time required for achieving the EG eqiulibrium value during glycolysis with DPG is 2 h i 30 min. It can be also noticed, that initial reaction time with DPG is 15 min. For the reactions with Gly and PG, reaction times are much longer- for Gly 2 h and for PG 90 min. After that time, the EG portion continiously increases unless it reaches 5 % from marginal value 18 hours after the beginning of the reaction.

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Jul 26, 2017
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