PARTⅠ PYROLYSISEFFECTS OF ZEOLITE ON THE CATALYTIC
DEGRADATION OF POLYPROPYLENE
Shwu-Jer Chiu
Department of Chemical Engineering, MingChi University of Technology,Taishan, Taipei, Taiwan
Abstract: Effects of zeolite on the catalytic degradation of polypropylene (PP) at atmosphericpressure were studied by a batch operation. The degradation of PP was carried out between
temperature 325 oC and 500 oC. HY, silica-alumina, and H-ZSM5 were shown degradation
activity. The percentage of PP degradation with active catalysts was more than 97% incomparison with that of 6.96% for thermal degradation at 400 oC. The product proportion
included liquid, gaseous, and solid residue for thermal and catalytic degradation weredifferent. The percentage degradation of PP was almost independent of the kinds of PP inthermal degradation. In catalytic degradation, the powder and film of PP samples with HY
had higher percentage degradation than pellet PP when the temperature was lower than 375oC. HY had shown the most active between temperatures 325 oC and 375 oC. Pyrolyzer

GC/MS was used to analyze the gaseous product distribution and showed not only the numberof gaseous product was reduced but also the products shifted to lower carbon number when
PP was degraded over HY and the results were different from the thermal and catalytic
degradation of PP with silica-alumina and H-ZSM5.
Keywords: polypropylene; degradation; catalyst; zeolite; plastic recycling

1. Introduction
Polypropylene is a very useful industrial plastic raw material to manufacture many kindsof useful products such as containers, fibers, battery cases, car bumpers, dashboards, film andsheet, and so on. According to the report [1], in the year of 2009, the global PP consumption
will reach 51.3 million m.t. and the global demand of PP will grow by 6.96% a year until
2010. Over the past five years from 2007, PP production has risen by 34% and PP
consumption by 35%, the production capacities will grow at an average of 5.9%. Such a large
amount of PP was used to manufacture variety of daily necessities and the PP wastes become
one of the main components in the solid waste stream. The recycling of post-consumer PPproducts, just like the other plastics products, become more and more important because ofboth environmental protection and economic benefits.

- 105 -The 5th ISFR (October 11-14, 2009, Chengdu, China)
Degradation (or pyrolysis) is a chemical method for recycling plastic wastes in theabsence of oxygen [2]. Degradation of plastics over an active catalyst has many advantages
and it is a resourceful treatment route [3]. The effects of catalyst on the PP degradation havebeen studied by many authors. Zeolite was the most frequently utilized as a catalyst in such aprocess. The zeolites had been tested as catalyst in PP degradation including ZSM-5 [4-9],silica-alumina [9-11], Y, L and mordenite [5], as well as silica gel and mesoporous silica [8,11]. The effects of each kind of catalyst on the PP degradation were different due to theirframe structures, properties, and reaction conditions.
In this work, thermal and catalytic degradation of PP with zeolite catalysts have beenstudied. Product proportions, effect of kinds of PP, reaction temperature, and time in catalytic
process were compared with those of thermal degradation. The effect of active catalysts on
the gaseous product distributions was also investigated by pyrolysis GC/MS analyses.
2. Experimental
PP pellet (BOPP grade, 3.0 mm in size and sphere in shape) was obtained from Formosa
Plastics Co., Taiwan. PP powder (0.5 ~ 1.0 mm in size) was prepared by grinding PP pellet
and PP film (3 x 3 mm in size and square in shape) was cut from a sheet of shrink film which
was made from PP pellet. The zeolite catalysts include HY, silica-alumina, hydrogen form ofZSM5, hydrogen form of mordenite, sodium form of mordenite, 13X, and 4A.
The apparatus and degradation procedures of PP were described in detail in previous
reports [12]. The product proportion was calculated as the ratio of the product weight to theinitial PP weight and multiplied by 100%. The percentage degradation of PP (α) is calculatedby the percentage of PP weight loss over the initial weight of PP. The analysis of gaseous
product distribution was performed using a pyrolyzer GC/MS with a HP-5MS capillarycolumn (f 0.25 mm x 30m).
3. Results and discussion
3.1 Effect of zeolite
Tab. 1 shows the effect of zeolites on the percentage of PP degradation (α). In thermaldegradation, α value of the pellet PP was only 6.96% at 400 oC. Values of α were very
different from PP catalytic degradation. HY, silica-alumina, and H-ZSM5 were found themost active in PP degradation. The pellet PP almost decomposed completely at 400 oC withthese active catalysts. The activity of H-mordenite on PP degradation was moderate, however,Na-mordenite was almost none. Zeolite with stronger acidity enhanced the degradation abilityof plastics as described by Sakata et al. [9]. The proportion of liquid, gaseous product andsolid residue of pellet PP thermal and catalytic degradations are listed in Tab. 2. In thermaldegradation, the proportion of liquid and gaseous product was minor and the solid residue wasmajor. The proportion of solid residues was 90.7%. The solid residue became minor when PP- 106 -PARTⅠ PYROLYSIS
was degraded with active catalysts, especially with HY (reduced from 90.7% to 0.41%). The
majority was gaseous product for PP catalytic degradation over active catalysts and theproportion could reach as high as 99.45% for HY and the lowest for silica-alumina (65.0%).
The proportion of liquid product, on the contrary, was the highest for silica-alumina (32.6%)
and the lowest for HY (0.14%).
Tab. 1 Effect of zeolite on pellet PP thermal and catalytic degradation a)α (%)

ZeoliteZeolitePP + Zeolite-－

6.96 b)Si-Al
HY
H-ZSM5H-mordenite
Na-mordenite
13X
4A

14.9
15.4
5.4
9.2
10.0
13.1
13.7

97.5
99.6
97.8
59.8
6.5
8.1
6.9a)reaction temperature: 400 oC, reaction time: 1 h, nitrogen flow rate:100 mL/min,weight ratio of PP/catalyst = 10/1

Tab. 2 Product proportions for pellet PP thermal and catalytic degradation a)
Weight (%)
thermalHY
H-ZSM5Si-Ala)

Gas

LiquidResidue

6.1
99.45
82.4
65.0

0.9
0.14
15.4
32.6

93.0
0.41
2.2
2.4

reaction temperature: 400 oC, reaction time: 1 h, nitrogen flow rate:100 mL/min

3.2 Effect of temperature
The dependence of α value for thermal and catalytic degradation of PP with HY on thedegradation temperature is shown in Tab. 3. The percentage of PP degradation was increased
dramatically from about 7% to 90% in the temperature range of 400 oC and 450 oC. When thetemperature was raised to 500 oC, PP samples could be decomposed nearly 100%. In thecatalytic degradation, the α value of PP with HY is much higher than that of in thermaldegradation. There are two different phenomena to be noticed between thermal and catalytic
process. First, the degradation onset temperature in catalytic process is much lower than inthermal process, especially for PP powder and film (much lower than pellet). Second, thepowder and film PP has better degradation ability than pellet PP when temperatures are lower
than 375 oC in catalytic degradation. When temperature was increased to 400 oC, all kinds of- 107 -The 5th ISFR (October 11-14, 2009, Chengdu, China)
PP samples with HY could be completely decomposed. The results suggested the degradation
ability of PP depends on the uniformity and extent of contact between PP and catalyst if
temperature is not high enough. The mixing is more uniform and/or the contact surface ismore sufficient resulted in higher percentage degradation of plastics. Fig. 1 illustrated theeffect of temperature on the percentage degradation of pellet PP with and without HY,H-ZSM5, and silica-alumina. The figure showed the degradation of PP was higher in catalytic
process than in thermal process when the temperature was higher than 325 oC. It also
demonstrated the degradation temperature could be lowered down about 75 oC to obtain thesame percentage degradation when active catalysts were added to the PP samples. In case ofpellet PP catalytic degradation over active catalysts, the α values of PP approximately kept
constant when degradation temperatures were lower than 325 oC or higher than 375 oC.
Nevertheless, PP with HY exhibited better degradation activity than H-ZSM5 andsilica-alumina between these two temperatures.
Tab. 3 Effect of temperature on pellet PP thermal and catalytic degradation with HY catalyst
α (%)

Temp (oC)PelletPowder

Film

0.02
6.96
91.8
99.4

1.17
7.01
94.1
99.2

0.20
7.13
89.4
99.1

5.3
22.2
58.6
99.6

30.0
46.4
76.1
99.331.846.2
75.599.7thermala)
350
400
450500PP+HYb)325
350375400a) time: 1 h, nitrogen flow rate:100 mL/min;b) time: 1 h, nitrogen flow rate:100 mL/min, weight ratio of HY/PP = 10/1

Percentage degradation (%)

10090
80
7060
50
40:thermal:Si-Al:HZSM5
:HY

30
20
100300

350

400

450

500

550

Temperature(oC)

Fig. 1 Effect of temperature on pellet PP degradation for 1 h- 108 -PARTⅠ PYROLYSIS
3.3 Effect of degradation time
Fig. 2 shows the percentage of pellet PP degradation in thermal and catalytic degradation
at 400 oC as a function of degradation time. A similar trend was found for the catalytic
degradation of pellet PP with HY, H-ZSM5, and silica-alumina. The degradation of PP
increased as the time increased and completely decomposed at time of 60 min. With HY, notonly the percentage of PP degradation was higher than with the other two zeolites but also
took a shorter time to reach the maximum decomposition. The percentage of PP degradationin thermal degradation was extremely small in comparison with the catalytic degradation.
110

Percentage degradation (%)

100908070605040:HY:Si-Al:HZSM5:thermal

30201000102030405060

70time(min)Fig. 2 Effect of time on PP degradation at 400 oC
3.4 Analysis of gaseous products
The gaseous product distributions were analyzed by pyrolyzer GC/MS at 445 oC for 6
seconds and the results were demonstrated in Fig. 3. In thermal degradation, the products
were in a broad distribution between 3 and 24 carbons. The main products were ranging fromC9 to C16 and the most abundant one was C14 with 16 wt%. In the catalytic degradation, theproduct distribution of PP with H-ZSM5 and with silica-alumina catalysts was also distributed
in a wide carbon number range and both were similar with the results of thermal degradation.
The main products for these two catalytic reactions were ranging from C14 to C16 and bothwere centered at C14 with the highest percentage (24% and 28%), respectively. In the case ofPP with HY, the result was very different from with thermal degradation and PP with theother two zeolites. The gaseous products obviously not only shifted to the compounds withlower carbon numbers but also narrowed down to the range of C4 to C12 and the main
products were between with 6 carbons and 10 carbons. The most abundant product was C8compounds and with the amount of 26 wt%. HY clearly has the ability to change the gaseous
product distribution and produces the hydrocarbon products with a lighter fraction. The
catalytic effect of zeolite HY on the degradation of PP was different from with the other two
kinds of zeolites.
- 109 -

Weight (%)

The 5th ISFR (October 11-14, 2009, Chengdu, China)
322824201612840(A)02468101214161820222426

Weight (%)

Carbon number
3228
24201612840(B)02468101214161820222426

Weight (%)

Carbon number
32
28
242016
12840(C)02468101214161820222426

Weight (%)

Carbon number
32
28
2420
1612840(D)0246810121416

1820

222426

Carbon number

Fig. 3 Carbon number distribution of pyrolyzed gaseous products of pellet PP at 445oC for
6 sec; (A) thermal, (B) PP+HY, (C) PP+Si-Al, (D) PP+H-ZSM
4. Conclusions
HY, H-ZSM5, and silica-alumina are effective zeolites in the catalytic degradation of PP.
It can substantially enhance the degradation ability of PP and change the product proportion.
HY is the most active catalyst. Degradation temperature is the most important factor on thedegradation of PP. In catalytic degradation, type of zeolite and contact between PP and zeolite
are the other important factors. HY is the zeolite not only could significantly change thegaseous product distributions but also shift the produced hydrocarbons to a lighter fraction.
References[1] http://mcgroup.co.uk/researches/P/18/Polypropylene[2] M. Blazso, J. Anal. Appl. Pyrolysis , 1997, 39, 1.
[3] S. R. Ivanova, E. F. Cumerova, K. S. Minsker, G. E. Zaikov, A. A. Berlin, Prog. Polym.
Sci. 1990, 15, 193.
- 110 -PARTⅠ PYROLYSIS[4] R. C. Mordi, J. Dwyer, R. Fields, Polym. Degrad. Stab. 1994, 46, 57[5] W. Zhao, S. Hasegawa, J. Fujita, F. Yoshii, T. Sasaki, K. Makuuchi, J. Sun, S. Nishimoto,Polym. Degrad. Stab. 1996, 53, 129..
[6] C. Vasile, P. Onu, V. Barboiu, M. Sabliovschi, G. Moroi, D. Ganju, M. Florea, Acta
Polymerica 1998, 39, 306.
[7] M. Uddin, Y. Sakata, A. Muto, Y. Shiraga, K. Koizumi, Y. Kanada, K. Murata,
Microporous and Mesoporous Materials 1998, 21, 557.
[8] P. Onu, C. Vasile, S. Ciocilteu, E. Iojoiu, H. Darie, J. Anal. Appl. Pyrolysis 1999, 49, 145.
[9] Y. Sakata, M. Uddin, A. Muto, J. Anal. Appl. Pyrolysis 1999, 51, 135.
[10] C. Vasile, P. Onu, V. Barboiu, M. Sabliovschi, G. Moroi, Acta Polymerica 1985, 36, 543.
[11] Y. Sakata, Macromol. Symp. 1998, 135, 7.
[12] S. J. Chiu and W. H. Cheng, Polym. Degrad. Stab. 1999,63 407.

- 111 -