Chemical Catalysed Recycling of Waste Polymers Catalytic

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Chemical catalysed recycling of waste polymers: Catalyticconversion of polypropylene into fuels and chemicals over

spent FCC catalyst in a fluidised-bed reactor

Y.-H. Lin*, M.-H. Yang

Department of Biochemical Engineering & Graduate Institute of Environmental Polymer Materials, Kao Yuan University, 821 Kaohsiung, Taiwan, ROC

Received 27 October 2006; received in revised form 26 January 2007; accepted 31 January 2007

Available online 11 February 2007

Abstract

Polypropylene (PP) was pyrolysed over spent FCC commercial catalyst (FCC-s1) using a laboratory fluidised-bed reactor operating isother-

mally at ambient pressure. The influence of reaction conditions including catalyst, temperature, and ratio of polymer to catalyst feed and flow

rates of fluidising gas was examined. The yield of gaseous and liquid hydrocarbon products at 390 C for spent FCC commercial catalyst

(87.8 wt%) gave much higher yield than silicate (only 17.1 wt%). Greater product selectivity was observed with FCC-s1 as a post-use catalyst

with about 61 wt% olefins products in the C3eC7range. The selectivity could be further influenced by changes in reaction conditions. Valuable

hydrocarbons of olefins andiso-olefins were produced by low temperatures and short contact times used in this study. It is also demonstrated that

a post-use catalyst system under appropriate conditions the resource potential of polymer waste can be economically recovered and also can

address the recycling desire to see an alternative to solve a major environment problem.

2007 Elsevier Ltd. All rights reserved.

Keywords: Polymer; Fluidised-bed reactor; Pyrolysis; Catalyst; Selectivity

1. Introduction

Polymer waste can be regarded as a potential source of

chemicals and energy. Methods for recycling polymer waste

have been developed and new recycling approaches are being

investigated[1]. Chemical recycling, i.e., thermal and/or cata-

lytic conversion of waste polymers into fuels or chemicals, has

been recognised as an ideal approach and could significantlyreduce the net cost of disposal[2]. The most widely used con-

ventional chemical methods for waste polymer treatment are

pyrolysis and catalytic reforming. Since thermal degradation

demands relatively high temperatures and its products require

further processing for their quality to be upgraded, catalytic

degradation of polymer waste offers considerable advantages.

Suitable catalysts have the ability to control both the product

yield and product distribution from polymer degradation as

well as to reduce significantly the reaction temperature, poten-

tially leading to a cheaper process with more valuable products

[3e5].

Studies of the effects of catalysts on the catalytic degrada-

tion of polymer have been performed by (i) contacting melted

polymer with catalyst in fixed bed reactors[6e

8], (ii) heatingmixtures of polymer and catalyst powders in reaction vessels

[9e11] and (iii) passing the products of polymer pyrolysis

through fixed bed reactors containing cracking catalysts

[12e14]. However, the configuration of the pyrolysis-reform-

ing reactors poses serious engineering and economics con-

straints. For the study of these pyrolysis-reforming reactions,

it is difficult to measure the exact mass-flow rate of the

reactant from the pyrolysis to catalytic zones, and conse-

quently it is virtually impossible to identify and quantify the

reactant and to control its quality. In addition, the use of fixed* Corresponding author. Tel.: 886 7 6077777; fax: 886 7 6077788.

E-mail address: [email protected](Y.-H. Lin).

0141-3910/$ - see front matter 2007 Elsevier Ltd. All rights reserved.

doi:10.1016/j.polymdegradstab.2007.01.028

Polymer Degradation and Stability 92 (2007) 813e821www.elsevier.com/locate/polydegstab
mailto:[email protected]://www.elsevier.com/locate/polydegstabhttp://www.elsevier.com/locate/polydegstabmailto:[email protected]


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beds or adiabatic batch where polymer and catalyst are con-

tacted directly leads to problems of blockage and difficulty

in obtaining intimate contact over the whole reactor. Without

good contact the formation of large amounts of residue are

likely, and scale-up to industrial scale is not feasible. In order

to compare the polymer cracking properties of different cata-

lysts, it is preferable to examine the effects of catalysts withoutextensive complications due to reactions of primary cracking

products, e.g. olefins, with unconverted polymer by using tech-

niques that minimise such interactions. For this purpose, a lab-

oratory fluidized-bed reactor has been used to study catalytic

cracking of polymers by limiting the contact between primary

volatile products and the catalyst/polymer mixture[15e18].

The catalyst increases significantly the commercial potential of

a recyclingprocess based oncatalyticdegradation, as cracking cat-

alysts could cope with the conversion of plastic waste co-fed into

a refinery FCC unit. It is certainly possible to develop commercial

processes based on these approaches. Therefore, a more interest-

ingapproachis thatof addingpolymer waste into theFCC process,

under suitable process conditions with the use of zero value ofspent FCC catalysts, a large number of waste plastics can be eco-

nomically converted into valuable hydrocarbons. However, much

less is known about performance of fluid catalytic cracking (FCC)

commercial catalysts on the degradation of polymer waste. Al-

though spent FCC catalysts have been investigated in some trials,

the results for those studies are sketchy and were carried out by the

use of batch or fixed bed reactors[19,20]. Potential concepts has

been investigated (Part I) using thermalanalysis to estimate the ki-

netic behaviours andas a potential method to evaluate the effect of

spent FCC catalysts on the catalytic degradation of polypropylene

(PP). It is the objective of this work to investigate the product slate

of the FCC process made by PP recycled into the usual chemicalsandfuels, by means of its conversion over post-use FCC commer-

cial catalysts in a catalytic fluidised-bed reaction system, and spe-

cifically for identification of suitable reaction conditions for

enhancing the potential benefits of catalytic polymer recycling.

2. Experimental

2.1. Materials and experimental procedures

The catalysts employed are described inTable 1. All the cat-

alysts were pelleted, crushed and sieved to give particle sizes

ranging from 75 to 180 mm. The catalyst was then dried by

heating in flowing nitrogen (50 ml min1) to 120 C at

60 C h1. After 2 h the temperature was increased to 520 C

at a rate of 120 C h1 to active the catalyst for 5 h. In contrast

with the micrometer size of the crystals in conventional zeolites

[21], ZSM-5 and HUSY used in this work synthesised with

smaller crystallite sizes[22,23]present a high proportion of ex-ternal surface, which accounts for approximately 20e30% of

the total zeolite surface area. The polymer used in this study

was pure polypropylene (PP; isotactic, r 853.6 kg m3,MWz 332,000, Aldrich). High purity nitrogen was used as

the fluidising gas and the flow was controlled by a needle valve

and pre-heated in the bottom section of the reactor tube. Flow-

meters were used to measure the full range of gas velocities

from the incipient to fast fluidisation. Before catalytic pyrolysis

experiments were started, several fluidisation runs were per-

formed at ambient temperature and pressure to select (i) suit-

able particle sizes (both catalyst and polymer waste) and (ii)

optimise the fluidising gas flow rates to be used in the reaction.

The particle size of both catalyst (75e180mm) and polymer(75e250mm) were chosen to be large enough to avoid entrain-

ment but not too large as to be inadequately fluidised. High

flow rates of fluidising stream improve catalystepolymer

mixing and external heat transfer between the hot bed and the

cold catalyst. On the other hand, an excessive flow rate could

cause imperfect fluidisation and considerable entrainment of

fines.

2.2. Experimental procedures and product analysis

A process flow diagram of the experimental system is given

elsewhere [15] and shown schematically in Fig. 1. A three-zone heating furnace with digital controllers was used and

the temperatures of the furnace in its upper, middle and bottom

zones were measured using three thermocouples. By these

means the temperature of the pre-heated nitrogen below the

distributor and catalyst particles in the reaction volume could

be effectively controlled to within 1 C. The polymer feedsystem was designed to avoid plugging the inlet tube with

melted polymer and to eliminate air in the feeder. The feed

system was connected to a nitrogen supply to evacuate poly-

mer into the fluidised catalyst bed. Thus, commingled polymer

particles were purged under nitrogen into the top of the reactor

Table 1

Catalysts used in the catalytic degradation of polypropylene

Catalyst Si/Al Surface area (cm2/g) Pore size (nm) Commercial Name

BETa Micropore External

FCC-s1 2.1 147 103 44 eb Equilibrium catalystsc

ZSM-5 17.5 426 263 128 0.55 0.51 ZSM-5 zeolited

HUSY 13.6 547 429 118 0.74 Ultrastabilised Y zeolitec

HAHA 3.6 268 21 247 3.28e Amorphous silica aluminac

Silicalite >1000 362 297 65 0.55 0.51 Synthesized in-house

a Total surface area (BET).b The catalyst was a mixture of zeolite, a silicaealumina matrix and binder, not determined.c Chinese Petroleum Corp., CPC, Taiwan, ROC.d BP Chemicals, Sunbury-on-Thames, UK.

e Single-point BET determined.

814 Y.-H. Lin, M.-H. Yang / Polymer Degradation and Stability 92 (2007) 813e821


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and allowed to drop freely into the fluidised-bed at t 0 min.At sufficiently low polymer/catalyst ratios (as used in this

study) the outside of the catalyst particles are not wet with

polymer, so the catalyst particles move freely.

Volatile products leaving the reactor were passed through

a glass-fibre filter to capture catalyst fines, followed by an ice-acetone condenser to collect any condensable liquid product.

A three-way valve was used after the condenser to route product

either into a sample gas bag or to an automated sample valve

system with 16 loops. The Tedlar bags, 15 L capacity, were

used to collect time-averaged gaseous samples. The bags were

replaced at intervals of 10 min throughout the course of reac-

tion. The multiport sampling valve allowed frequent, rapid sam-

pling of the product stream when required. Spot samples were

collected and analysed at various reaction times (t 1, 2, 3, 5,8, 12, 15, and 20 min). The rate (Rgp, wt% min

1) of hydrocar-

bon production of gaseous products collected by automated

sample system in each run was defined by the relationship:

Gaseous hydrocarbon products were analysed using a gas

chromatograph equipped with (i) a thermal conductivity detec-

tor (TCD) fitted with a 1.5 m 0.2 mm i.d. molecular sieve13X packed column and (ii) a flame ionisation detector

(FID) fitted with a 50 m 0.32 mm i.d. PLOT Al2O3/KCl cap-illary column. A calibration cylinder containing 1% C1eC5hydrocarbons was used to help identify and quantify the gas-

eous products. The remaining solid deposited on the catalyst

after the polymer degradation was deemed residues and

contained involatile products and coke. The amount and nature

of the residues were determined by thermogravimetric analysis

(TGA).

3. Results and discussion

The reactor and various units of the collection system were

weighted before and after the runs to determine the mass bal-

ance. Catalytic pyrolysis products (P) are grouped together as

hydrocarbon gaseous (


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3.1. Degradation of PP over silicalite and spent FCC

commercial catalyst

Product distributions for PP degradation over silicalite (Si/

Al > 1000) in the 330e450C range are summarised in Table2. At temperatures below 390 C, a large amount of solid res-

idue, presumably unconverted commingled polymer and highmolecular weight degradation products, remained on the sili-

calite catalyst. The yield of gaseous and liquid hydrocarbon

products at 390 C was only 17.1 wt% (Table 2) compared

with 87.8 wt% (Table 3) when spent FCC commercial equilib-

rium catalyst (FCC-s1) was used. Typically thermal degrada-

tion productions were observed with silicalite showing

primary cracking products and an even spread of carbon num-

bers consisting of C3eC6 olefins products with some isomer-

isation of BTX. At higher temperatures, product streams

containing C1eC9 hydrocarbons were produced with gaseous

yield 21.2 wt% and liquid range yield 18.7 wt% of polymer

converted at 450 C.

Some similar trends in product yields were observed withspent FCC catalyst (FCC-s1) as the reaction temperature was

increased. Gaseous and coke yields increased and involatile

residues (unreacted or partially reacted PP) and liquids de-

creased. Product distributions with FCC-s1 catalyst contained

more olefinic materials in the range of C3eC7 (about 61 wt%

at 390 C) with minor products, methane and ethane, only

detectable at the higher reaction temperatures. The rate of hy-

drocarbon production as a function of time for PP degradation

over FCC-s1 catalyst at different reaction temperatures is com-

pared inFig. 2and, as expected, faster rates were observed at

higher temperatures. At 450 C, the maximum rate of hydro-

carbon production was 36 wt% min1 after only 2 min with

all the polymer degraded after approximately 11 min. As the

temperature of reaction was decreased, the initial rate of

hydrocarbon production dropped and the time for PP to be de-

graded lengthened. At 330 C the rate of hydrocarbon produc-

tion was significantly lower with the polymer being degraded

more slowly over 20 min.

3.2. Effect of reaction conditions on PP degradation

over spent FCC catalyst

The effect of reaction conditions including flow rates of flu-

idising gas (270e900 ml min1), ratios of polymer to catalyst

feed (1:1e1:6) and catalyst type (FCC-s1) has been investi-

gated. The results shown in Fig. 3illustrate that for efficient

PP degradation good mixing is required, with a dramatic

drop-off in the rate of degradation observed only at the lowest

Table 2

Summary of products of PP degradation over silicalite catalyst

Degradation results Temperature (C)

330 360 390 420 450

Yield (wt% feed)

Gaseous(P

C1eC4) 3.5 7.1 10.2 15.9 21.2

Liquid 2.5 4.3 6.9 13.0 18.7

Gasoline (P

C5eC9) 1.7 2.8 5.1 8.9 13.4

Condensate liquida 0.7 1.4 1.6 2.1 2.8

BTXb 0.1 0.1 0.2 0.2 0.4

Residuec 94.0 88.6 82.9 72.9 60.1

Distribution of C1eC9 hydrocarbon products (wt% feed)

C1 n.d n.d n.d ed 0.1

C2 n.d n.d n.d 0.1 0.1

C2] n.d 0.2 0.2 0.3 0.5

C3 n.d 0.1 0.3 0.8 0.9

C3] 1.8 2.8 4.2 5.6 6.8

C4 n.d 0.4 0.6 0.9 1.3

C4]

1.6 3.6 4.9 8.2 11.5C5 n.d n.d n.d 0.3 0.5

C5] 0.9 1.8 3.1 3.8 5.2

C6 n.d ed

ed 0.1 0.2

C6] 0.5 0.7 1.4 2.6 4.1

C7 n.d n.d 0.2 0.3 0.5

C7] 0.1 0.3 0.3 1.4 1.8

C8 n.d n.d n.d ed 0.2

C8]

ed

ed 0.1 0.3 0.6P

C9 n.d n.d ed 0.1 0.3

Fluidising N2 rate 600 ml min1, catalyst particle size 75e180mm, poly-

mer to catalyst ratio 30 wt% and total time of collection 60 min.a Condensate liquid: condensate in condenser and captured in filter.b BTX: benzene, toluene and xylene.c Residue: coke and involatile products.

d e: less than 0.01 (wt%); n.d: not detectable.

Table 3

Summary of products of PP degradation over FCC-s1 catalyst (fluidising N2rate 600 ml min1, catalyst particle size 75e180mm, polymer to catalystratio 30 wt%, and total time of collection 30 min)

Degradation results Temperature (C)

330 360 390 420 450

Yield (wt% feed)Gaseous (P

C1eC4) 20.8 22.3 26.9 31.2 34.2

Liquid 64.4 64.5 60.9 58.2 56.7

Gasoline (P

C5eC9) 57.4 56.9 54.3 52.7 50.9


BTXb 0.4 0.7 1.2 2.0 2.5

Residuec 14.8 13.2 12.2 10.2 9.1

Involatile residue 13.2 11.3 9.9 7.6 6.0

Coke 1.6 1.9 2.3 2.6 3.1

Mass balance (%) 88.2 89.3 91.8 92.7 93.2

Distribution of C1eC9 hydrocarbon products (wt% feed)

C1 n.d n.d ed

ed

ed

C2 n.d n.d ed

ed 0.2

C2]

ed 0.1 0.1 0.3 0.4

C3 1.1 1.5 1.7 2.3 2.7

C3]

5.6 6.6 8.8 10.3 11.2C4 1.9 1.6 2.2 2.9 3.2

C4] 12.2 12.6 14.1 15.4 16.5

C5 1.8 2.4 2.7 3.3 3.4

C5] 19.8 18.9 16.5 16.2 13.7

C6 3.4 3.5 3.5 3.2 4.6

C6] 17.5 16.2 14.2 11.9 10.3

C7 3.7 4.6 4.5 3.8 3.3

C7] 6.6 6.2 7.4 8.0 8.7

C8 1.2 1.2 1.5 1.8 2.1

C8] 2.8 3.1 2.8 2.8 3.2P

C9 0.6 0.8 1.2 1.7 1.6

a Condensate liquid: condensate in condenser and captured in filter.b BTX: benzene, toluene and xylene.c Residue: coke and involatile products.d e: less than 0.01 (wt%); n.d: not detectable.



5/9

fluidising flow used (300 ml min1). Furthermore, changing

the fluidising flow rate influences the product distribution. At

low flow rates (high contact times for primary products), sec-

ondary products are observed with increased amounts of coke

precursors (BTX) although the overall degradation rate is

slower as shown by increasing amounts of partially depoly-

merised products (Table 4).

The amount of FCC-s1 used in the degradation of PP poly-

mer remained constant and, therefore, as more waste polymers

were added to the reactor then fewer catalytic sites per unit

weight of catalyst were available for cracking. The overall ef-fect of increasing the polymer to catalyst ratio from 0.1:1 to

0.6:1 on the rate of hydrocarbon generation was small but pre-

dictable (Fig. 4). As the polymer to catalyst ratio increases, the

possibility of PP polymer adhesion to the reactor wall

increases as the amount of unreacted polymer waste in the re-

actor rises. The total product yield after 20 min showed only

a slight downward trend even after a 6-fold increase in added

polymer waste. This can be attributed to the sufficient cracking

ability of FCC-s1 and excellent contact between PP polymer

and catalyst particles. As more PP was added, lower C5eC9gasoline yields but higher liquid yields and involatile products

were observed (Table 5). More BTX (coke precursor) was pro-

duced but increasing the polymer to catalyst ratio had only vir-

tually no effect on C1eC4 hydrocarbon gases production.

Both the carbon number distribution of the products of PP

polymer cracking at 390

C over FCC-s1 catalyst, zeolitic cat-alysts (ZSM-5 and HUSY) and non-zeolitic amorphous silica

alumina (SAHA) used in this study and the nature of the prod-

uct distribution were found to vary with the catalyst used. As

shown in Table 6, the yield of volatile hydrocarbons for

0

5

10

15

20

25

30

35

40

0 2 4 6 8 10 12 14 16 18 20

Time (min)

Rgp(wt%/min)

330C

360C

390C

420C

450C

Fig. 2. Comparison of hydrocarbon yields as a function of time at different

reaction temperatures for the catalytic degradation of PP over spent FCC

commercial catalyst (FCC-s1) (rate of fluidisation gas 600 ml min1,catalyst particle size 75e180mm, polymer to catalyst ratio 30 wt%).

0

5

10

15

20

25

30

35

0 2 4 6 8 10 12 14 16 18 20

Time (min)

Rgp(wt%

/min)

900 ml/min

750 ml/min

600 ml/min

450 ml/min

300 ml/min


fluidisation gas for the degradation of PP over FCC-s1 catalyst (reaction

temperature 390C, catalyst particle size 75e180mm, polymer to catalyst

ratio 30 wt%).

Table 4

Product distributions shown from FCC-s1 catalysed degradation of PP at dif-

ferent fluidising N2 rates

Degradation results fluidising N2 rates (mL/min)

900 750 600 450 300

Yield (wt% feed)

Gaseous (P

C1e

C4) 29.6 28.8 26.9 26.3 26.1Liquid 60.5 60.4 60.9 60.7 60.1

Gasoline (P

C5eC9) 55.1 54.7 54.3 54.6 53.7


BTXb 0.5 0.8 1.2 1.6 2.1

Residuec 9.9 10.8 12.2 13.0 13.8


Coke 2.2 2.3 2.3 2.5 2.6

Mass balance (%) 89.2 89.6 91.8 90.3 94.1

Reaction temperature 390C, catalyst particle size 75e180mm, polymerto catalyst ratio 30 wt%, and total time of collection 30 min.a Condensate liquid: condensate in condenser and captured in filter.b BTX: benzene, toluene and xylene.c Residue: coke and involatile products.

0

5

10

15

20

25

30

35

0 2 4 6 8 10 12 14 16 18 20

Time (min)

Rgp(wt%/min)

10% wt/wt

20% wt/wt

30% wt/wt

40% wt/wt

60% wt/wt


ratios of polymer to catalyst for the degradation of PP over FCC-s1 catalyst

(reaction temperature 390C, catalyst particle size 75e180mm, rate of

fluidisation gas 600 ml min

1).

817Y.-H. Lin, M.-H. Yang / Polymer Degradation and Stability 92 (2007) 813e821


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zeolitic catalysts (ZSM-5zHUSY) gave higher yield than

spent FCC commercial catalyst (FCC-s1) and non-zeolitic cat-

alysts (FCC-s1z SAHA) and the highest was obtained for

ZSM-5 (nearly 90 wt%). Overall, the bulk of the products ob-

served with these acidic cracking catalysts (FCC-s1, ZSM-5,

HUSY and SAHA) were in the gaseous and liquid phase

with less than 13 wt% solid residues of involatile residue

and coke collected. The differences in the product distribu-

tions between those catalysts can be seen with ZSM-5 produc-

ing a much more C1eC4 hydrocarbon gases (56 wt%) than

FCC-s1, HUSY and SAHA catalysts. Some similarities

were observed between FCC-s1 and SAHA with C1eC4 and

C5eC9 yields, which were approximately 27e30 wt%

and 53e54 wt%, respectively. The highest level of uncon-

verted polymer was observed with silicalite, while the highest

coke yields were observed with HUSY. The rate of gaseous

hydrocarbon evolution further highlights the slower rate of

degradation over silicalite catalyst as shown in Fig. 5 when

comparing all catalysts under identical conditions. The results

of the products of PP degradation reflect the differing cracking

effect of FCC-s1 catalyst compared with the zeolite and non-

zeolitic materials. The maximum rate of generation was ob-

served after 2 min with the zeolite catalysts whereas the max-

imum was observed after 3 min with FCC-s1 and SAHA.

3.3. Variation of product stream with catalytic selectivity

and catalyst deactivation

Equilibrium ratios ofi-butene/P

butenes (i-C4]/P

C4]) and

i-butane/n-butane (i-C4/n-C4) were predicted using Gibbs free

energy minimisation on the PRO/II package for the tempera-tures used experimentally and are presented alongside the cor-

responding experimental results in Table 6. The i-butene/Pbutenes ratio is very close to the predicted equilibrium

values and thus the reactions involved in the production and

interconversion of butenes are very fast over FCC-s1, and their

ratio is primarily equilibrium controlled. The i-butane/n-bu-

tane ratio reflects the involvement of tertiary C4 carbenium

ions in bimolecular hydrogen transfer reactions and since ter-

tiary carbenium ions are more stable than primary ions,

a higher yield of iso-butane would be expected. As can be

seen in Table 7, the observed i-butane/n-butane ratios at

390 C are well above calculated equilibrium values consistent

with the cracking of long chain hydrocarbon molecules to

yieldiso-butylcarbenium ions which provide a source for i-bu-

tane, via hydrogen transfer, or i-butene. The selectivity could

be varied by changes in different operating conditions used

in this study. Further evidence of the increase in secondary re-

actions, for example, bimolecular hydrogen transfer, was seen

in the lowering of theP

olefin/P

paraffin (o/p 4.52 at330 C versus o/p 2.86 at 450 C) and i-butane/n-butane(i-C4/n-C4 3.23 at 330

C versus i-C4/n-C4 1.83 at450 C) ratios as temperature increases, in the experimental

range. At fast flow rates, primary cracking products are fav-

oured as evidenced by the increasing ratios of i-butene/P

butenes (i-C4]

/P

C4]

2.12 in 300 ml min

1 N2 fluidising

Table 5

Product distributions shown from FCC-s1 catalysed degradation of PP at dif-

ferent ratios of polymer to catalyst (reaction temperature 390C, catalystparticle size 75e180mm, fluidising N2 rate 600 ml min

1, and total time

of collection 30 min)

Degradation results Ratio of polymer to catalyst (% wt)

10 20 30 40 60

Yield (wt% feed)

Gaseous(P

C1eC4) 26.7 27.8 26.9 27.6 28.2

Liquid 63.2 61.7 60.9 60.3 59.2

Gasoline (P

C5eC9) 57.4 55.4 54.3 52.9 51.4


BTXb 0.9 1.0 1.2 1.6 1.8

Residuec 10.1 10.5 12.2 12.1 12.6


Coke 2.5 2.2 2.3 1.7 1.9

Mass balance (%) 89.5 90.6 91.8 92.5 90.4

a Condensate liquid: condensate in condenser and captured in filter.b BTX: benzene, toluene and xylene.c Residue: coke and involatile products.

Table 6

Summary of products of PP degradation over various commercial catalysts

Degradation results Catalyst type

FCC-s1 ZSM-5 HUSY SAHA Silicalite

Yield (wt% feed)

Gaseous(P

C1eC4) 26.9 56.2 33.5 30.2 10.2

Liquid 60.9 38.8 58.7 56.9 6.9

Gasoline (P

C5eC9) 54.3 33.5 54.8 52.9 5.1


BTXb 1.2 1.8 0.5 0.3 0.2

Residuec 12.2 5.0 7.8 12.9 82.9


Coke 2.3 1.9 4.9 2.4 2.6

Mass balance (%) 91.8 94.5 92.4 90.5 94.1

Reaction temperature 390C, fluidising N2rate 600 ml min1, polymer to

catalyst ratio 30 wt%, and total time of collection 30 min.a Condensate liquid: condensate in condenser and captured in filter.b BTX: benzene, toluene and xylene.

c Residue: coke and involatile products.

0

5

10

15

20

25

30

35

0 2 4 6 8 10 12 14 16 18 20

Time (min)

Rgp(wt

%/min)

FCC-s1

HUSY

ZSM-5

SAHA

Silicalite

Fig. 5. Comparison of hydrocarbon yields as a function of time for the cata-

lytic degradation of PP at 390C over different catalysts (waste polymer to

catalyst ratio 30 wt%, rate of fluidisation gas 600 ml min1).



7/9

rate versus i-C4]/P

C4] 3.53 in 900 ml min1 N2 fluidising

rate) andP

olefin/P

paraffin (o/p 3.65 in 300 ml min1 N2fluidising rate versus o/p 4.28 in 900 ml min1 N2fluidising

rate).

The relation in catalytic activity to catalyst deactivation

was examined by the transient change in the amount of gas-

eous compounds produced. Rapid variation in the product

stream of FCC-s1 and HUSY catalysts was observed (Fig. 6)

Table 7

Influence of reaction conditions on product selectivity for the catalysed degradation of PP over FCC-s1 catalyst: experimental and predicted equilibrium results

Ratio Reaction conditiona

Temperatureb (C) P/C ratioc (wt%) N2 rated (mlmin1)

330 390 450 10 30 60 300 600 900

i-Butene/P

butenes 0.55 0.49 0.43 0.57 0.52 0.54 0.46 0.51 0.59

i-Butene/P

butenese 0.54 0.50 0.45i-Butane/n-butane 3.23 2.47 1.83 3.46 2.47 2.29 2.12 2.47 3.53

i-Butane/n-butanee 1.04 0.89 0.77

SOlefins/P

paraffinsf 4.52 3.91 2.86 3.61 3.91 3.43 3.65 3.91 4.28

a Represents a series of runs with different reaction temperature, polymer to catalyst ratio and N2 fluidising rate.b Polymer to catalyst ratio 30 wt% and 600 ml min1 N2 fluidising rate.c Reaction temperature 390C and fluidising N2 600 ml min

1.d Polymer to catalyst ratio 30 wt% and reaction temperature 390C.e Predicted equilibrium data.f Denotes the ratio of the sum all olefinic to paraffinic products.

FCC-s1

0

10

20

30

Wt%

i-C4 tot C4= tot C5=

HUSY

0

10

20

30

Wt%

ZSM-5

0

10

20

30

Wt%

SAHA

0

10

20

30

0 1 2 3 4 5 6

0 1 2 3 4 5 6

0 1 2 3 4 5 6

0 1 2 3 4 5 6

Time (min)

Wt%

Fig. 6. Some of hydrocarbon products of isobutene (i-C4),P

butanes (tot C4]) andP

pentanes (tot C5]) as a function of time for PP degradation over different

catalysts.



8/9

when the spot samples, taken during the course of the reaction,

were analysed. The deactivation is reflected in the decrease of

the amount ofiso-butane (i-C4) produced (product of bimolec-

ular reaction) and the relative increase in olefins (product of

monomolecular reaction), exemplified by, C4] and C5

]. The

spent FCC-s1 catalyst with bimodal pore structures, which is

composed of both the micropore of zeolite and the mesoporeof silicaealumina, may allow bulky reactions to occur, ulti-

mately leading to the generation of coke and subsequently de-

activation of the catalyst. The deactivation was more

exaggerated in the case of HUSY with its large pore openings

and internal supercages. In contrast, ZSM-5 is resistant to cok-

ing when coke builds up on outer surface and the product

stream remains essentially unchanged, whereas the weakness

and lower density of the acid sites in SAHA along with the in-

creased tolerance to coke in the amorphous structure is most

likely the reason for the lack of variation in the product stream

over this catalyst.

4. Conclusions

A laboratory catalytic fluidised-bed reactor has been used to

obtain a range of volatile hydrocarbons by catalytic degradation

of polypropylene in the temperature range of 330e450 C. The

catalytic degradation of PP over spent FCC catalyst performed

in fluidised-bed reactor was shown to be a useful method for the

production of potentially valuable hydrocarbons. In the pres-

ence of the spent FCC commercial catalyst at 390 C used in

this work, conversion of PP polymer to volatile hydrocarbons

in the catalytic fluidised-bed reactor was more than 87 wt% of

feed in 20 min, while silicalite yielded less than 18 wt% offeed after 60 min. The use of fluidised-bed reaction system

coped with a spent FCC equilibrium catalyst can be a better

option from economical point of view since it can gives

a good conversion with comparable short reaction time, and

even its activity is lower than that of the zeolites (ZSM-5 and

HUSY) and silicaealuminas (SAHA), this can be compensated

by increasing the catalyst to PP ratio.

Product distributions with FCC-s1 catalyst contained more

olefinic materials in the range of C3eC7 (about 56 wt% at

390 C). Experiments carried out with FCC-s1 catalyst gave

good yields of volatile hydrocarbons with differing selectivity

in the final products dependent on reaction conditions. How-

ever, silicalite give very low conversions of polymer waste

to volatile hydrocarbons compared with spent FCC catalyst

(FCC-s1) under the same reaction conditions. The selectivity

could be further influenced by changes in operating condi-

tions; in particular, olefins and iso-olefins were produced by

low temperatures and short contact times. From a practical

point of view, the use spent equilibrium catalyst from FCC

units can be the most adequate solution. It is concluded that

the use of spent FCC commercial catalyst and under appropri-

ate reaction conditions can have the ability to control both the

product yield and product distribution from polymer degrada-

tion, potentially leading to a cheaper process with more valu-

able products.

Acknowledgements

The authors would like to thank the National Science Coun-

cil (NSC) of the Republic of China (ROC) for financial sup-

port (NSC 95-2211-E-244-013). Thanks also are due to

Professor M.D. Ger and Dr. C.-M. Chiu for samples of

ASA, spent FCC commercial catalyst and surface area/poresize measurements.

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Chemical Catalysed Recycling of Waste Polymers Catalytic