The 5th ISFR (October 11-14, 2009, Chengdu, China)

STUDY ON METHANOLYSIS OF WASTE POLY(ETHYLENE
TEREPHTHALATE) IN IONIC LIQUID
Fusheng Liu*, Xiao Cui, ShitaoYu, Zhuo Li, Xiaoping Ge
College of Chemical Engineering, Qingdao University of Science and Technology,
Qingdao 266042, China.
E-mail: 636390@public.qd.sd.cn
Abstract: The methanolysis of poly(ethylene terephthalate) (PET) was studied using ionicliquid 1- n-butyl-3-methylimidazolium chloride as solvent and zinc acetate as catalyst. The
effects of reaction temperature, time, dosages of solvent and catalyst on methanolysis results
were examined. The obtained optimum reaction conditions were reaction temperature 160℃,reaction time 3h, m(solvent):m(PET)=2:1, m(zinc acetate):m(reaction mixture)=1:20. Under
above conditions, the conversion of PET could reach 100%. After easily separated from theproduct, the system of solvent and catalyst could be reused 8 times without obvious decreasein conversion of PET. Therefore, an environmental friendly approach for methanolysis ofwaste PET was developed.
1. Introduction
Over the last decades, polyester (PET) consumption has tremendously increased due toits ever-increasing use in fiber manufacturing and packaging. With the rapid increase ofproduction and consumption of PET, the problem about the treatment of waste PET is now animportant issue in the world [1-2]. For the purpose of chemical recycling of waste PET, there
have been reported a number of degradation methods [3-6], among which methanolysis of
PET is an important one. However, due to the insolubility of PET in methanol, themethanolysis of PET require severe conditions such higher temperature and pressure [7-8] oreven under supercritical conditions[9-10]. Therefore, its application is limited. it is necessary
to explore a new approach for methanolysis of PET.
The room temperature ionic liquid, a kind of environmental friendly solvent and catalyst,
due to its adjustable physical and chemical properties, got broadly attention of scholars fromvarious fields such as synthesis, catalysis and separation [11-13]. But to the best of ourknowledge, no article about ionic liquid used in hydrolysis of PET has been published. In thispaper, we prepared several ionic liquids (Fig. 1) and used them in methanolysis of PET. The
results showed that 1-butyl-3- methylimidazolium chloride was a good solvent formethanolysis of PET.

- 272 -

PARTⅤ SOLVOLYSIS
2. Experimental
2.1 Chemicals and instruments
PET powder of 0.1-0.3mm was prepared from commercial PET pellets (Ø2.5x3mm,Mw=30000). n-Methylimidazole (MIM, 99%), n-butylchloride and other chemicals (AR)were commercially available and used without further purification. The IR spectra wererecorded by a Nicolete 510P FT-IR spectrometer in the range of 4500-400cm-1.
2.2 Synthesis Procedure for Synthesis of [Bmim][Cl]A mixture of 1-methylimidazole and n-butylchloride in a 1:1.2 molar ratio was reactedwith stirring at 70℃ for 72 h. The mixture was washed by ethyl acetate for three time toremove the unreacted starting materials and then distilled at 70℃ under reduced pressure (10mmHg) over 2 h to obtain [Bmim][Cl](yield 95%). [Bymim][Cl], [Omim][Cl], [Emim][Br]and [Epydin][Br] were prepared with a similar procedure. [Bmim][BF4] and [Omim][PF6]were synthesized according to the references[14-16].
2.3 Metholysis of PET
Weighed amounts of PET (w1), methanol and ionic liquids were added in an autoclavewith a stirrer and a thermometer. The mixture was heated up to the given temperature forcertain time. The reaction mixture was filtered to remove the unreacted PET (w2). The
obtained filtrate was diluted with an equal volume of water and a precipitate was obtained andfiltered. The obtained filtrate was distilled under vacuum to remove water and ethanediol, theresidue which is mainly composed of ionic liquid and catalyst was reused directly as solventand catalyst. The filter cake which is mainly composed of dimethyl terephthalate(DMT) wasdried to obtain DMT product (w3). Conversion of PET and yield of DMT were calculated byfollowing formula: Conversion of PET = [(w1–w2) / w1] x 100%. Yield of DMT = (w3 / w) x100%, where w is the weight of DMT that should obtained theoretically.
FN_+ N Cl[Bmim][Cl]N__+ NCl+ NN+N F B F_Br

[Bymim][Cl][Emim][Br]_+ NNF[Bmim][BF4]
F+ NN

ClN_F P FF

N+_Br

[Omim][Cl][Omim][PF6][Epydin][Br]Fig. 1 Structures of ionic liquids prepared and used in this paper
3. Results and Discussion
3.1 Effect of ionic liquid solvent on metholysis results of PET- 273 -The 5th ISFR (October 11-14, 2009, Chengdu, China)
Tab. 1 Effects of different ionic liquids on methanolysis reaction. a)

a)

Entry

Ionic liquids

Dosage(g)PETconversion(%)

12345678-b)[Bmim][Cl][Bmim] [BF4][Bymim][Cl][Omim][Cl][Omim][PF6][Emim][Br][Epydin][Br]

0
6.0
6.0
6.0
6.0
6.0
6.0
6.0

30.1
100
59.3
58.3
91.8
36.5
94.1
37.7

DMTYield(%)
20.2
88.7
51.4
49.9
83.4
28.8
88.6
30.1

PET 3g, CH3OH 12g, Zn(Ac)2 1g, t=3h, T= 160 oC; b) Using another 6g CH3OH instead of ionic liquid.

Tab.1 shows the effect of ionic liquid solvent on methanolysis results of PET. According
to Tab.1, using ionic liquids [Bmim][Cl], [Emim][Br] or [Omim][Cl] as reaction medium( entries 2, 5 and 7), the conversions of PET were much higher than that of without ionicliquid as solvent (Tab.1 entry 1). Especially, [Bmim][Cl] exhibited an outstanding
performance for methanolysis of PET. This is because the ionic liquids can improve thedissolubility of PET in the reaction system. It is difficult for PET to dissolve in methanol, sothe reaction result was poor when no ionic liquid solvent was used. Moreover, we can seefrom Tab.1 that the cations and anions of ionic liquids have significant effect on hydrolysis
results of PET.
3.2 Effect of PET particle size on hydrolysis results
Tab. 2 Effect of PET particle size on methanolysis resultsa
Particle size of PET
Ø2.5x3mm
0.40 mm0.15 mma)

PET Conversion (%)
77.7
89.8
100.0

DMT Yield (%)
69.3
80.1
88.7

PET 3g, CH3OH 12g, Zn(Ac)2 1g, t=3h, T= 160 oC

Tab. 2 shows the effect of PET particle size on methanolysis results. According to Tab.2,
the size of PET particle was of a significant influence on methanolysis results. Withdecreasing of the particle size, both the PET conversion and DMT yield increased greatly.
Under the given conditions, when the particle size was Ø2.5x3mm, PET conversion only
77.7%. However, when the particle size became 0.15mm, the methanolysis of PET almost
finished and DMT yield reached to 88.7%. This is because PET is a macromolecule and the- 274 -PARTⅤ SOLVOLYSIS
dissolving of PET in reaction mixture was very slowly. That is to say, the solubility of PET isthe methanolysis reaction rate determining step. Therefore, the smaller the particle size ofPET is, the more quickly the dissolving and methanolysis of PET are. On the other hand, PETwith decreased particle size has increased surface area available for the reaction. Thus, thereaction rate is increased and greater PET conversion and DMT yield can be obtained.
3.3 Effect of temperature and solvent dosage on methanolysis results of PET
100100PET conversion/%

PET conversion/%

9095

90

85

80

70

60
80

50
140

150

75

160

170

0 .5

180

1 .0

1 .5

2 .0

2 .5m(solvent):m(PET)

Temperature/℃Fig. 1 Effect of reaction temperature on PET
methanolysis results

Fig. 2 Effect of solvent dosage on PET
methanolysis results

The influences of reaction temperatures and solvent dosage on methanolysis results wereexamined and shown in Fig.1 and Fig.2. A great increase in PET conversion with increasing
reaction temperature was observed (Fig.1). When temperature is 140℃, the PET conversion isonly 87.5% after 3h. However, under the given conditions, when the temperature wasincreased to 160℃, the methanolysis of PET almost finished. It can be seen that with theincreasing of [Bmim][Cl] dosage, PET conversion was gradually increased. Under the givenconditions, when m([Bmim][Cl]):m(PET) =2:1, the methanolysis of PET almost finished.
3.4 Reusability results of system of solvent and catalyst
Tab. 3 Reusability results of system of solvent and catalyst a)
Cycle

12345678

PETconversion (%)
Yieldof DMT(%)

100

100

100

100

100

100

100

100

88.9

88.0

88.8

87.9

88.7

88.7

88.1

88.6a)PET 3g, CH3OH 12g, Zn(Ac)2 1g, t=3h, T= 160 oC

The system of solvent and catalyst was easily separated from the reaction mixture andreused directly as solvent and catalyst. The reusability of the system of solvent and catalyst- 275 -The 5th ISFR (October 11-14, 2009, Chengdu, China)
for the methanolysis of PET was examined and the results were showed in Tab.3. The results
showed that the system was reused for 8 times without obvious decrease in PET conversion
and DMT yield. Therefore, the system of solvent and catalyst has excellent reusable
performance in the methanolysis of PET.
4. Conclusion
The kind of ionic liquids used as solvent was of a significant influence on methanolysis
results of PET. Among the ionic liquids examined, [Bmim][Cl] is an excellent reaction
medium. A great increase in PET conversion was observed with increasing of [Bmim][Cl]dosage and reaction temperature. Under the optimum conditions of reaction temperature
160℃, reaction time 3h, m(solvent):m(PET)=2:1, m(zinc acetate):m(reaction mixture)=1:20,
the conversion of PET and the yield of DMT were almost 100% and ≥88% respectively. Aftereasily separated from the product, the system of solvent and catalyst could be reused 8 times
without obvious decrease in the conversion of PET and yield of DMT.
Acknowledgements
This work was financially supported by the National Natural Science Foundation ofChina (No.20776072).
References[1] L. Cesare, M. Piero, B. Corrado, B. Giancarlo, J Polym Environ., 2006, 14, 89.
[2] G. P. Karayannidis, D. S. Achilias, Macromol Mater Eng., 2007, 292, 128.
[3] R. Shukla, A. M. Harad, J Appl Polym Sci., 2005, 97, 515.
[4] R. D. Castro, G. J. Vidotti, A. F. Rubira, J Appl Polym Sci., 2006, 101, 2009.
[5] D. E. Nikles, M. S. Farahad, Macromol Mater Eng., 2005, 290, 13-30.
[6] F. G.Gallagher, US5710315 [P],1998.
[7] A. A. Naujokas,W. J. Gamble,N. Y. Webster, US5654470[P], 1997.
[8] T. Sako, I. Okajima, T. Sugeta, K. Otake, S. Yoda, Y. Takebayashi, C. Kamizawa,Polymer 2000, 32, 178-181.
[9] G. Motonbu, K. Hiroshi, K. Akio,A IChE Journal,2002, 48 (1), 136 - 143.
[10] A. C. Cole, J. L. Jensen, I. Ntai, K. L. T. Tran, K.J. Weaver, D. C. Forbes, J.H. Davis,J. Am. Chem. Soc. 2002, 124, 5962.
[11] Y. Q. Cai, Y. Q. Peng, G.. H. Song, Cata. Lett. 2006, 109, 61.
[12] H. B. Xing, T. Wang, Z. H. Zhou, Y. Y. Dai, Ind. Eng. Chem. Res. 2005, 44, 4147.
[13] G. H. Jonathan, E. V. Ann, M. W. Reichert, H. D. Willauer, G. A. Broker, R. D. Rogers,Green. Chem. 2001, 3, 156.
[14] P. Bonhote, A. P. Dias, N. Papageorgiou, Inorg. Chem. 1996, 5, 1168.
[15] P. A. Z. Suarez, J. E. L. Dullius, S. Einloft, Polyhedron 1996, 7, 1217.

- 276 -