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

A NEW ROUTE TO RECOVER BISPHENOL A ANDDIMETHYL CARBONATE FROM WASTEÀPOLYCARBONATE IN IONIC LIQUIDS
Fusheng Liu*, Zhuo Li, ShitaoYu, Xiao Cui, Xiaoping Ge
College of Chemical Engineering, Qingdao University of Science and Technology,
Qingdao 266042, China.
E-mail: 636390@public.qd.sd.cn
Abstract: An new strategy for methanolysis of polycarbonate (PC) to recover bisphenol
A(BPA) and dimethyl carbonate(DMC) was studied in which PC could be methanolyzed inionic liquid 1-n-butyl-3-methylimidazolium chloride([Bmim][Cl]) without any acid or basecatalyst under moderate conditions. Under the conditions of m(PC):m([Bmim][Cl]):m(CH3OH)=1:1:1.5, reaction time 2.5h and temperature 105℃, themethanolysis conversion of PC was almost 100% and the yields of both BPA and DMC wereover 95%. After easily separated from the product, the ionic liquid could be reused 8 times
without obvious decrease in the conversion of PC and yields of BPA and DMC. The strategy
can overcome the disadvantages existed in traditional methods such as unfeasible reuse of
catalyst, tedious workup procedure and environmental problem.
1. Introduction
With the rapid increase of production and consumption of polycarbonate (PC), theproblem about the treatment of waste PC is now an important issue all over the world. For thepurpose of chemical recycling of waste PC, there have been reported a number ofmethods[1-5]. In order to recover pure monomer bisphenol A (BPA) and dimethyl carbonate(DMC), the most important chemical recycling methods reported are methanolysis catalyzed
by acids or bases in methanol media. However, due to the insolubility of PC in methanol, thereported methanolysis methods require high temperature and pressure and in presence of a lot
amount of concentrated acids or bases. The acid or base catalysts used in traditional methods
cannot be reused and result in other disadvantages such as equipment corrosion, tediousworkup procedure and environmental problem. Although supercritical method can overcome
some of above-mentioned shortcomings [4-8], it has its own disadvantages such as severe
conditions, so its application is limited. Therefore, it is necessary to explore a new approachfor methanolysis of PC.
The room temperature ionic liquid, a kind of environmentally friendly solvent andcatalyst, due to its adjustable physical and chemical properties, got broadly attention of- 266 -PARTⅤ SOLVOLYSIS
scholars from various fields such as synthesis, catalysis and separation [9-11]. But to the bestof our knowledge, no article about ionic liquid used in methanolysis of PC has been published.
In this paper, we prepared several ionic liquids (Fig. 1) and used them in methanolysis of PC.
To our surprise, [Bmim][Cl] was of excellent catalytic activity and reusability.
2. Experimental
2.1 Chemicals and Instruments
Pure PC pellets (3 mm length and 2.5 mm diameter with MW. about 20000) were used asmodel plastics. 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 of Ionic Liquids
2.2.1 General 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],[Amim][Cl], [Cemim][Cl] and [Epydin][Br] were prepared with a similar procedure.
[Bmim][BF4] and [Omim][PF6] were synthesized according to the references[12-14].
2.2.2 Metholysis of PC
Weighed amounts of PC(w1), methanol and ionic liquid were added in an autoclave witha stirrer and a thermometer. The mixture was heated up to the given temperature for certaintime. The reaction mixture was added an equal volume of ethyl acetate. The unreacted PC(w2)was removed by filtration. The obtained filtrate was separated into two phases. The upper
phase which is mainly composed of BPA, DMC, methanol and ethyl acetate was analyzed bya HP 5890 gas
N_+ N Cl+ N
N[Bmim][Cl]N+ N BF4+ N_N

N+ N ClCl

N_+ N Cl_[Omim][Cl]_Br[Emim][Br]_Cl

N[Bymim][Cl][Bmim][BF4]+ N_Cl+ N PF6_[Omim][PF6]
N+_Br

N

[Amim][Cl][CEmim][Cl][Epydin][Br]Fig. 1 Structures of ionic liquids prepared and used in this paper.
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The 5th ISFR (October 11-14, 2009, Chengdu, China)
chromatograph with DB-5 glass capillary column of 50m and calculated to obtained weightsof BPA(w3) and DMC(w4), the lower phase which is mainly ionic liquid was reused directly
as solvent and catalyst. Conversion of PC and yield of BPA and DMC were calculated byfollowing formula:Conversion of PC = [(w1–w2) / w1] x 100%; Yield of BPA = (w3/ w5 )x100%; Yield of DMC = (w4/ w6) x 100%; Where w5 and w6 are the weights of BPA and DMC
respectively that should obtained theoretically.
3. Results and Discussion
Methanolysis of PC in different ionic liquids was investigated (Tab. 1). Surprisingly,
ionic liquids have a significant influence on methanolysis results of PC. Especially,[Bmim][Cl] (entry 2) exhibited an outstanding performance for methanolysis of PC undermoderate conditions and without any acid or base catalyst, the conversion of PC was almost
100%. This may be due to a good dissolubility of PC in [Bmim][Cl] and the weak basicity of
the ionic liquid. Methanolysis of PC did not take place in absence of ionic liquid under thegiven conditions (entry 1). Moreover, we can see from Tab.1 that the cations and anions ofionic liquids have significant effect on methanolysis results of PC. When the anion is [Cl], theconversion is much better (entries 2, 5) than when the anion is [BF4]( entry 7) or [PF6] (entry8).When using [Emim][Br] as medium, the conversion is much better (entries 3) than using[Epydin][Br] ( entry 6).When using 1- R-3-methylimidazolium chloride as medium, the R
group is of significant influence on methanolysis results of PC(entries 2, 4, 5, 9 10).
The effect of reaction conditions on methanolysis results was showed in Tab. 2. As canbe seen from tab. 2, temperature is very important for the methanolysis of PC. Whentemperature is 85℃, the conversion of PC is only about 10% (entry 1) under given conditions.
However, when the temperature was increased to 105℃, the methanolysis of PC almost
finished (entry 3) under the same conditions. With decreasing of [Bmim][Cl] dosage from 2g
to 0.5g, the conversion of PC decreased from 100%(entry 3) to 96%(entry 6), and whenincreasing of methanol dosage from 2g to 4g, the conversion of PC decreased from 100%(entry 5) to 90.6%(entry 8). All the results mentioned above can be explained by thedifference in dissolubility of PC in the reaction mixture. The higher the temperature is, themore rapidly PC can dissolve in the reaction mixture. Moreover, both too less [Bmim][Cl]dosage and too much methanol dosage are unfavorable to improve the dissolubility of PC in
the reaction mixture. It is suggested that the dissolubility of PC in the reaction mixture is therate-determining step of the mathanolysis of PC.

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Tab. 1 Effects of different ionic liquids on methanolysis reaction. a)
Entry12345678910a)

Ionic liquids

Dosage(g)PC conversion(%)

b)

01.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.00100
64.7
38.1
2.10
4.6
000

[Bmim][Cl][Emim][Br][Amim][Cl][Omim][Cl][Epydin][Br][Bmim] [BF4][Omim][PF6][CEmim][Cl][Bymim][Cl]PC 2g, CH3OH 3g, t=2.5h, T= 105 oC; b) Using another 3g CH3OH instead of ionic liquid.

Tab. 2 Effects of reaction conditions on methanolysis results.c)
EntryTemp.(oC)

CH3OH
Dosage(g)[Bmim][Cl]Dosage(g)PCconversion(%)

123456788595105105105105105105

2.0
2.0
2.0
2.0
2.0
2.0
3.0
4.0

2.0
2.0
2.0
3.0
1.00.5
1.0
1.0

10.4
30.5
100
10010096.010090.6c)

PC 2g, t=2.5h

Tab. 3 Reusability results of [Bmim][Cl] d)d)Cycle

12345678

PC conversion
(%)

100

100

100

100

100

100

100100

Yield of BPA
(%)

95.6

95.8

94.5

96.0

95.4

95.7

95.4

94.7

Yield of DMC
(%)

96.5

96.8

96.4

96.3

95.9

94.7

95.6

95.3

PC 2g, CH3OH 3g, [Bmim][Cl] 2g, t=2.5h, T= 105 oC- 269 -The 5th ISFR (October 11-14, 2009, Chengdu, China)
Fig. 2 shows the effects of reaction time on PC conversion at different temperature. At105 C, the conversion of PC was almost 100% when methanolysis was carried out for about
2.5h. However, at 95 oC, the conversion of PC was still lower than 75% after 5.5h.
The reusability of ionic liquid [Bmim][Cl] for methanolysis of PC was examined and theresults were showed in tab. 3. It is showed that the ionic liquid can be reused for 8 times
without obvious decrease in the conversion of PC and yields of BPA and DMC under given
conditions. Therefore, the ionic liquid has excellent reusable performance in methanolysis ofPC. It is well known that the main factor which affects the reuse performance of ionic liquid
is its stability under the reaction temperature and reaction fluid surroundings. Because ionicliquid [Bmim][Cl] itself is of a good thermal stability, the reaction mixture is almost neutral
and the reaction temperature is only 105 oC, it is reasonable that it has good reusableperformance in the methanolysis of PC.
The obtained BPA was characterized by IR using a Nicolet 510P FT-IR spectrometer inthe range of 4000–400 cm-1, using KBr powder containing ca. 1 wt% of sample. The IRospectrum was showed in Fig. 3 and the spectra data were as follows: ν(cm-1)3362,2964,

12080

Transmittance/%

PC conversion(%)

10060
4090

60

2030001

2

3

45Reaction time(h)Fig. 2 Changes of PC conversion withreaction time at 105 oC(■) and 95 oC(●).

64000

3000

20001000

Wave numbers/cm-1Fig. 3 IR spectrum of obtained BPA product1612,1598,1510,1446,1362,1239,1221,1178,829,553. The IR spectrum and spectra data are
identical with those of standard BPA. It is demonstrated that PC is completely depolymerized
into BPA and DMC monomers and no intermediates of oligomers exist.
4. Conclusion
PC can be methanolysized to its starting monomer BPA and DMC in presence of ionicliquid [Bmim][Cl] without any acid or base catalyst under moderate conditions. Under theconditions of PC 2g, CH3OH 3g, [Bmim][Cl] 2g, reaction time 2.5h and temperature 105 oC,
the methanolysis conversion of PC was almost 100% and the yields of both BPA and DMC
were over 95%. The ionic liquid could be reused 8 times without obvious decrease in the- 270 -PARTⅤ SOLVOLYSIS
conversion of PC and yields of BPA and DMC. The strategy can overcome the disadvantages
existed in traditional methods such as unfeasible reuse of catalyst, tedious workup procedureand environmental problem.
Acknowledgements
This work was financially supported by the National Natural Science Foundation ofChina (No.20776072).
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