28

Converting Waste Plastics intoLiquid Fuel by Pyrolysis:Developments in ChinaYUAN XINGZHONGDepartment of Environmental Science and Engineering, Hunan University, Changsha,Hunan Province, 410082 P.R.China

1 PROGRESS IN CONVERTING WASTE PLASTICS INTO LIQUID FUELBY PYROLYSIS

Since the 1970s, shortage of energy and environmental pollution have become more andmore serious. As a way to ease this problem, the pyrolysis of waste plastics for recoveryof liquid fuel has been paid more and more attention, and various pyrolysis technologieshave been developed. The thermal cracking technology for waste plastics was investigatedin the early 1970s [1]. It was found that under high temperature, the carbon chains can bebroken up and various monomers, active molecular groups and some small molecules willbe formed. As a result, liquid products with relatively high H/C ratio can be obtained. Theprocess and mechanism of thermal cracking have been studied extensively [24], and aseries of thermal cracking processes such as the United Carbon process [5], the HamburgUniversity process [6] and the BP process [7] were developed and industrialized.

The thermal cracking process is characterized by low costs and simple operation, butthe high energy consumption and the low conversion efficiency and yield have seriouslyhampered its development. To improve the quality and yield of liquid fuel, great effortshave been made by many researchers and a large number of experimental studies havebeen carried out by introducing suitable catalysts [830], as listed in Table 28.1. Theuse of catalysts can not only lower the activation energy, reduce the energy consumptionand increase the treatment efficiency, but can also improve the selectivity and quality ofproducts significantly. Some plastic pyrolysis processes have been developed and commer-cialized, such as the Veba process [31], the USS process [32] and the Mazda process [33].The Veba process has been shut down recently. Further improvement of the quality and

F eeds tock R ecycling and P yrolys is of Was te P las tics: Converting Waste Plastics into Diesel and Other Fuels Edited byJ. Scheirs and W. Kaminsky 2006 John Wiley & Sons, Ltd ISBN: 0-470-02152-7

730 YUAN XINGZHONG

Table 28.1 Laboratory experiments on catalytic plastics cracking

Investigator Reactor Plastics species Catalysts

Uemichi et al. [811] Flow reactor PE, PP Silicaalumina, CaXzeolite, activated carbon,metal supported onsilicaalumina oractivated carbon

Ishihara et al. [1216] Batch flow reactor PE, PP, PS Active charcoal,silicaalumina, NaYzeolite

Mordi et al. [17, 18] Sealed reactor LDPE, PP HZSM-5, H-mordenite,H-theta-1 zeolite

Beltrame et al. [19, 20] Flow reactor PE, PS Silica gel, alumina,silicaalumina, rareearths, Y and H-Yzeolites

Vasile et al. [2123] Flow reactor LDPE, HDPE, PP Silicaalumina, ZSM-5zeolite, dealkylationcatalyst

Ueno et al. [24, 25] Flow reactor PE, PS Silicaalumina, HZSM-5zeolite, active carbon,metal oxides

Sakata et al. [2628] Flow reactor LDPE, HDPE, PP,PET, PVC

Silicaalumina

Gongzhao Liu et al. [29] Continuousagitator reactor

PE, PP, PS Silicaalumina, aluminate

Zhiyuan Yao et al. [30] Flow reactor PE, PP, PS, PVC,PET

Reformed ZSM-5 zeolite

yield of liquid fuel products can be achieved by crackingcatalytic reforming [3436],which is also called the two-step process. This kind of process has been widely appliedin industry with good results. Currently, processes using this technology include the Fujirecycling process [37, 38], the BASF process [39], the Likun process [40], the HunanUniversity process [41, 42] and so on.

2 THEORY OF PLASTICS PYROLYSIS

2.1 MASS BALANCE FOR THE PYROLYSIS PROCESS

Waste plastic may be converted into gasoline-range hydrocarbons by pyrolysis [43]. Thethermal cracking of waste plastics proceeds by typical random decomposition, with prod-ucts being mainly alkanes, alkenes as well as high-boiling-point hydrocarbon products(carbon number > 24). The products of catalytic cracking are, however, composed ofmore iso-alkanes and aromatics, which are highly desirable gasoline-range hydrocarbons.Reforming catalysts have the highest selectivity to aromatics, and the products after cat-alytic reforming are mainly aromatics.

All the plastics have their own activation energy when cracked. The correspondingreaction temperatures required are different. At appropriate temperature, pressure and with

DEVELOPMENTS IN CHINA 731

a suitable catalyst applied, high yield of high-commercial-value products such as gasolineand diesel can be achieved. PE and PP will be degraded under high temperature (>350C)and the yields of light fractions will keep growing with the increase of temperature: at lowtemperature, the products will be mainly composed of high-boiling-point hydrocarbon andpolymers; At moderate temperature (400500C), gas will account for 2040% of theproducts, liquid 3570% and residue 1030% [45]. At high temperature (800C), themain products will be ethylene, propylene and methane [46]. When LDPE is pyrolyzedfor 2 h at 420C, the products will be mainly composed of olefins (60%), terminal olefinicbond hydrocarbons (35%) and non-terminal olefinic bond hydrocarbons (5%). High yieldof oil products (94.5%), mainly C10 C30, hydrocarbons will be achieved by pyrolysis ofHDPE at 400450C, and the gas fraction, which is mainly hydrogen gas and hydrocarbon(C1 C5), will account for only 5.5% of the products. At 400C, a conversion rate of 95%is achieved. The oil products mainly consist of C9 hydrocarbons (mainly composed of2,4-dimethylheptene) and C6, C11 and C14 hydrocarbons. When PP is pyrolyzed in afluid-bed reactor at 450640C, a conversion rate of 5085% can be achieved. And ifcatalyst is introduced, oil products with a research octane number (RON) of 83 can easilybe obtained by hydrogenation of PP in a high-pressure reactor. The liquid fuel obtainedis absolutely qualified for gasoline use. If water is added, the RON can even reach ashigh as 86, and 40% of the oil products will be alkenes.

The components of products from thermal and catalytic cracking of HDPE, LDPE,LP, PP, PS were analyzed [48], and the results are shown in Table 28.2 and Table 28.3.The products from thermal cracking of HDPE, LDPE and LP (linear polyethylene) aremainly wax-like substances at normal temperature. The fraction under 200C recoveredfrom HDPE accounts for 16% of the total cracking products, while that from LP accountsfor 23%. Compared with the products of PE, PP produces less solid residue, but moreliquid components, and PS produces the highest proportion of liquid fraction, which is99.17% by thermal cracking and 99.56% by catalytic cracking.

In another experiment conducted by Sakata [49], the degradation of PE produced liquidproducts which consisted of C5 C25 hydrocarbons with a yield of 70 wt%. In con-trast, the degradation of PVC produced only 4.7 wt% liquid products which consistedof C5 C20 hydrocarbons while the degradation of PET surprisingly produced no liquidproducts. The addition of either PVC or PET to PE decreased the overall liquid productyield, however, it promoted the degradation of PE into low-molecular liquid hydrocarbonproducts.

Table 28.2 Mass balance on thermal cracking of polyolefins

Feedstock HDPE LDPE LP PP PS

Liquid yield (%) 91.30 91.71 93.80 91.05 99.02State of liquid Milk white Milk white Milk white Yellow Rufous

products atnormaltemperature

Wax Wax Wax Solid and liquidmixture

Liquid

Gas yield (wt%) 7.61 7.42 5.60 7.60Coke yield (%) 0.14 0.15 0.14 0.14 0.15Total (%) 99.05 99.28 99.54 98.79 99.17Rufous = reddish-brown

732 YUAN XINGZHONG

Table 28.3 Mass balance on catalytic cracking of polyolefins

Feedstock HDPE LDPE LP PP PS

Liquid yield (%) 76.81 77.40 85.20 87.20 86.20State of liquid Solid and Solid and Light yellow Light yellow Rufous

products at liquid mixture liquid mixture liquid liquid liquidnormaltemperature

Gas yield (wt%) 14.04 14.08 8.15 9.34 0.34Coke yield (%) 8.30 8.04 6.52 3.35 13.02Total (%) 99.15 99.79 99.87 99.89 99.56

2.2 ENERGY BALANCE FOR THE PYROLYSIS PROCESS

The temperature required in the process of catalytic cracking of waste plastics is muchlower than that of thermal cracking, and further heat supply is unnecessary when thecatalytic bed is preheated to some extent, because the energy carried by the gas productsfrom the reactor is enough to sustain the required reaction temperature. Therefore, onlythe energy balance on the thermal cracking part is discussed here for simplification. TakePE for example, after degradation and condensation, PE is converted into liquid fuel (amixture of gasoline and diesel oil) and gas fuel. To simplify the calculation, the averagemolecular weight of PE is taken as 8.75 104, and the average degree of polymerizationis considered to be 3125. The components of fuel gas, gasoline, diesel oil and residualoil are represented by C3H8, C8H18, C16H34, C30H62 respectively.

2.2.1 Energy Balance Calculation

The mass flow of thermal degradation of PE is shown in Figure 28.1. For the thermaldegradation of 1 kg PE feedstock, the overall energy needed [51] is calculated by:

Q =out

niHi

in

niHi (28.1)

where Q is the overall energy required in the thermal cracking process (kJ), ni is themolar number of component i (mol), Hi is the enthalpy of component i (kJ mol1).

1kg PE (solid)0.02kg petroleum gas(gas)0.46kg gasoline (gas)

0.34kg diesel oil (gas)0.18kg residual oil (liquid)

T1 (Temperature of feedstock) T2 (Temperature of pyrolysis production)

Pyrolysis Reactor

Figure 28.1 Mass Flow of PE pyrolysis

DEVELOPMENTS IN CHINA 733

According to Equations (28.228.4), the enthalpy of formation of C3H8, C8H18 andC16H34 (all gases) at temperature of T2 can be calculated respectively [52]:

Hf(C3H8, g, T2) = 59.94 kJ mol1,Hf(C8H18, g, T2) = 92.88 kJ mol1Hf(C16H34, g, T2) = 156.08 kJ mol1

CnH2n+2(g, T1)HCnH2n+2(g, T2) (2)

Hf(CnH2n+2, g, T2) = Hf(CnH2n+2, g, T1) + H (3)in which,

H = T2

T1

cp(CnH2n+2, g, T )dT (4)

According to Equations (28.528.8), the enthalpy of formation of C30H62 (liquid) atT2 is obtained: Hf(C30H62, l, T2) = 384.69 kJ mol1

C30H62(g, T1)H1C30H62(g, Tb)

HVC30H62(l, Tb)H2C30H62(l, T2) (5)

Hf(C30H62, g, T2) = Hf(C30H62, g, T1) + H1 HV + H2 (6)

H1 = Tb

T1

cp(g, T )dT (7)

H2 = T2

Tb

cp(l, T )dT (8)

in which Tb and Hv are the boiling point and the heat of evaporation under normalpressure.

Based on the amount of mass flow of products and the enthalpy of formation calculated,the overall output enthalpy is obtained, which is 808.6 kJ kg1. Under the conditions of101203 MPa, 200300C, the overall output enthalpy can be obtained as 2124.7 kJkg1 according to Equation (28.9):

n(CH2 = CH2)(g, T1, 0.1MPa) n(CH2 = CH2)(g, Tr, 0.1MPa) n(CH2 = CH2)(g, Tr, 150MPa) (-CH2 = CH2-)n(s, Tr, 150MPa) (9)(-CH2 = CH2-)n(s, T1, 0.1MPa) (-CH2 = CH2-)n(s, Tr, 0.1MPa)

in which Tr is the reaction temperature.According to Equation (28.1), the total energy needed for the thermal degradation of

PE can be obtained as 1316.1 kJ kg1.

2.2.2 Estimation of Energy Profit

Supposing PE is converted to gasoline, diesel oil, residual oil and fuel gas, the net energyprofit can be obtained by:

Qj =

wiQi Q (10)

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Table 28.4 The components and yield of thermal degradation products of PE

Gasoline Diesel oil Residual oil Petroleum gas

Percentage (%) 4349 3137 1719 13Yield/(mol kg1) 3.774.30 1.371.64 0.400.45 0.230.68

Table 28.5 The heat values and net energy profit of various products (104 kJ kg1)

Gasoline Diesel oil Residual oil Petroleum gas Net energy profit

Theoretical heat value 4.320 4.290 4.180 4.620 4.170Experimental heat value 4.462 5.263 6.571 4.900

in which wi and Qi are the weight percentage (shown in Table 28.4) and the heat value(kJ kg1) of component i, respectively.

The theoretical [53] and experimental heat values of various products and net energyprofit are shown in Table 28.5.

Taking the heat value of standard coal (29260 kJ kg1) as the basis, the theoretical andexperimental values of net energy profit for the thermal degradation of 1 kg PE will beapproximated to the calorific value of 1.43 and 1.67 kg standard coal, respectively.

2.3 MECHANISM OF PLASTICS PYROLYSIS

Thermal degradation of plastics can be classified as depolymerization, random decom-position and mid chain degradation [54, 55]. In the process of depolymerization, theconjunction bonds between monomers are broken up, which leads to the forming ofmonomers. Depolymerization type plastics mainly include -polymethyl styrene, poly-methyl methacrylate and polytetrachloroethylene. In the random decomposition process,scission of carbon chains occurs randomly, and low-molecular hydrocarbons are pro-duced. Random-decomposition-type plastics include PP, PVC and so on. In most cases,both decompositions take place. To be more specific, the degradation of polyolefins canbe classified as the following three types:(a) polymers are degraded to monomers;(b) the chains break up randomly and low-molecular polymers are generated (random

chain scission happens in the pyrolysis of most polyolefins);(c) the substituent groups or functional groups are removed and low molecular polymers

are produced, accompanied by the formation of unsaturated hydrocarbons and cross-linking, even coking.

A comprehensive treatment of the mechanism of plastics pyrolysis has been presentedby Cullis and Hirschler [56]. Four types of mechanisms of plastics pyrolysis have beenproposed:(a) End-chain scission or depolymerization: the polymer is broken up from the end

groups, successively yielding the corresponding monomers; this is also consideredthe main manner of polymer pyrolysis by Prakash et al. [57] and Songip et al. [58].

DEVELOPMENTS IN CHINA 735

(b) Random-chain scission: the polymer chain is broken up randomly into fragments ofuneven length.

(c) Chain-stripping: elimination of reactive substitutes or side groups on the polymerchain, leading to the evolution of a cracking product on one hand, and a charringpolymer chain on the other.

(d) Cross-linking: formation of a chain network, which often occurs for thermosettingpolymers when heated.

These different mechanisms and product distributions, to some extent, are related tothe bond dissociation energies, the chain defects of the polymers, and the degree ofaromaticity, as well as the presence of halogen and other heteroatoms in the polymerchains. Large amount of styrene monomers can be obtained by pyrolysis of PS, while awide range of hydrocarbons are produced by random degradation of PE and PP [3, 59,60].

Thermal degradations are carried out by a free radical mechanism, while catalyticdegradation are realized by carbonium ions, which consist of hydrocarbon ions carryinga single positive charge.

A mechanisms of catalytic pyrolysis of waste plastics was proposed by Buekens [61],using PE as an example, in which FCC catalyst is adopted and the main content include:

1. Initiation may occur on some defect sites of the polymer chains. For instance, anolefinic linkage could be converted into an on-chain carbonium ion by proton addition.Then the polymer chain may be broken up through -scission. Initiation may also takeplace through random hydride ion abstraction by low-molecular-weight carbonium ions(R+), The newly formed on-chain carbonium ion then undergoes -scission.

2. Depropagation: the molecular weight of the main polymer chains may be reducedthrough successive attacks by acidic sites or other carbonium ions and chain cleav-age, yielding an oligomer fraction (approximately C30 C80). Further cleavage of theoligomer fraction probably by direct -scission of chain-end carbonium ions leads togas formation on the one hand, and a liquid fraction (approximately C10 C25) on theother.

3. Isomerization: the carbonium ion intermediates can undergo rearrangement by hydro-gen or carbon atom shifts, leading to, e.g. a double-bond isomerization of an olefin.Other important isomerization reactions are methyl group shift and isomerization ofsaturated hydrocarbons.

4. Aromatization: some carbonium ion intermediates can undergo cyclization reactions.An example is when hydride ion abstraction first takes place on an olefin at a positionseveral carbons removed from the double bond, the result being the formation of anolefinic carbonium ion. This carbonium ion could undergo intramolecular attack onthe double bond, which provides a route to cyclization and formation of aromatics.

2.4 METHODS FOR PLASTICS PYROLYSIS

There are mainly three methods for pyrolysis of plastics, namely: thermal cracking, cat-alytic cracking, and crackingcatalytic reforming [62]. Each has its own suitable process,as shown in Figure 28.2. Other methods for plastics pyrolysis include hydrogenation

736 YUAN XINGZHONG

Pyrolysis ofwaste plastics

Fixed-bedthermal pyrolysis

Catalytic cracking

Cracking-Catalytic reforming

Flow-bedthermal pyrolysis

Thermal cracking Catalytic reforming

Thermal cracking

Catalytic cracking Catalytic reforming

Flow-bedthermal pyrolysis

Fixed-bedthermal pyrolysis

Mixing of catalystand waste plastics

Melted Waste Plastics Flowthrough catalyst layer

Normal fixed-bed

Melting fixed-bed

Sand fixed-bed

Figure 28.2 Main methods for waste plastics pyrolysis and their relative processes

[63, 64], gasification [65, 66], pyrolysis in supercritical water [67, 68], coliquefactionwith coal [6971], and so on.

2.4.1 Thermal Cracking

Thermal cracking is the simplest form of waste plastics pyrolysis. In the process of thermalcracking, plastics are degraded simply by heat, which overcomes the required activationenergy [72]. The process is simple, but quite rough at the same time, and hydrocarbonswith a wide range of boiling points are produced; furthermore, the yields of oil products(mainly gasoline and diesel oil) are low. The gasoline obtained contains large amounts ofolefins and has a very low RON value. The diesel oil produced is high in freezing pointand low in cetane value. Most products of PE by pyrolysis are straight-chain alkanes and-alkenes [48].

2.4.2 Catalytic Cracking

In the process of catalytic cracking, characteristic reactions such as chain scission, hydro-gen transfer and condensation take place under certain temperature and pressure conditionsand when an appropriate catalyst is utilized, products with certain range of molecularweights and structures are obtained. Catalysts with surface acid sites and with the abilityof hydrogen ion donation such as silicaalumina and molecular sieve catalyst have beenalready widely utilized. These catalysts can also enhance the isomerization of productsand increase the yield of isomeric hydrocarbons. However, large amounts of coke willdeposit on the surface of catalysts and consequently lead to their deactivation. Therefore,the recycling of catalysts is difficult to achieve.

DEVELOPMENTS IN CHINA 737

With thermal cracking and catalytic cracking taking place at the same time, the processcan achieve very high reaction rates. Large amounts of isomers and aromatics can beproduced in a short period of time. The catalyst is usually mixed, however, with sandcontained in the plastics and the coke produced, which will result in difficult recycling.To solve this problem, various processes have been developed such as precleaning thewaste plastics and making the melted plastics flow through a bed of catalyst [7375].

2.4.3 CrackingCatalytic Reforming

In crackingcatalytic reforming (also called the two-step process, as distinct from the one-step process described above), plastics are first cracked under high temperature and thenundergo catalytic reforming; oil products with relatively high quality are finally obtainedthe end. The liquid fuel products of thermal cracking consist mainly of hydrocarbons witha wide range of boiling points, among which the yields of light fraction such as gasolineand diesel oil are low, and the quality is poor. In order to improve the RON, the contentof isomers, cycloparaffins and aromatics must be improved, which can be achieved bycatalytic reforming. To further raise the reaction rate, catalysts can also be added duringthermal cracking. High yields of liquid fuel with good quality can be obtained by thecrackingcatalytic reforming process; moreover, the operation is flexible. This methodis also suitable for the treatment of mixed waste plastics, and most important of all, thecatalysts can be recycled. All these have greatly contributed to the fast development ofthis technology and made it the most widely applied process in industry.

2.4.4 Other Methods

Hydrogenation [63, 64] or hydrocracking involves the pyrolysis of plastics under a hydro-gen atmosphere at a pressure of approximately 10 MPa, in three steps: depolymerization;hydrogenation of the liquid phase; and hydrogenation of the products. Owing to the pres-ence of hydrogen, saturated hydrocarbons are produced in the reaction process. Moreover,plastics containing heteroatoms (e.g. Cl, N, O, S) can be easily treated by hydrogenation.

Gasification [65, 66] is the partial oxidation and pyrolysis of plastics under high tem-perature, with steam and oxygen as gasification agents. This process produces productswhich consist mainly of H2, CO, CO2 and CH4. No pretreatment is needed here, andmixtures of various plastics, even mixtures of plastics and municipal solid waste, can beeasily degraded. And most of all, this technology can effectively prevent coking.

Pyrolysis in supercritical water [67, 68]: owing to the many special characteristics ofsupercritical water, waste plastics can be degraded efficiently in supercritical water, whichhas recently received great attention has been studied comprehensively. This technologycan not only realize the recovery of valuable products from waste plastics, but also providea solution to the ever-growing energy crisis and environmental pollution. No catalysts orreaction agents are needed here, so the cost is very low.

Coliquefaction with coal [6971]: in the process of coal and waste plastics coliquefac-tion, the hydrogen atoms contained in plastics transfer from plastics to coal, leading topartial or even total liquefaction of coal. On the one hand, as hydrogen donors, plasticscan reduce the hydrogen consumption for coal coliquefaction dramatically. On the other

738 YUAN XINGZHONG

hand, the existence of coal as catalyst can also greatly promote the pyrolysis of plastics.This technology has not only provided a solution for the white pollution problem, butalso reduced the cost of coal coliquefaction.

3 PROCESS OF PLASTICS PYROLYSIS

A series of industry-scale processes for recovery of liquid fuel from waste plastics havebeen developed and applied in countries such as the United States, Japan, Germany andEngland. Some of the processes, such as the Veba process, the BP process, the Fuji processand the Hunan University process have been applied widely and successfully in industry.Some typical pyrolysis processes are listed in Table 28.6.

3.1 VEBA PROCESS

In the Veba process [31], a mixture of vacuum residue, lignite and waste plastics ispyrolyzed under conditions similar to the case of crude oil hydrogenation. The mainproducts include gaseous hydrocarbons, alkanes, cyclanes and aromatics.

The main difference between Veba process and other processes lies in that hydrogena-tion technology is used in this process, which improves the quality of products. At thesame time, waste plastics are stirred and fully mixed by hydrogen. This whole appara-tus is capable of disposing of 40 000 tons of waste plastics per year, but is relativelycomplicated and expensive.

3.2 BP PROCESS

The BP process [7] is based on a sand fluidized-bed pyrolysis reactor. The crackingtemperature is kept at 400600C. Low-molecular hydrocarbons can be obtained. Theprocess mainly involves converting waste plastics into normal linear hydrocarbons, theaverage molecular weight of which is 300500. Most plastics can be treated by thisprocess. Polyolefins are decomposed into small molecules with the same linear structure.PS is converted into styrene monomers and PET into mixture of hydrocarbons, carbonmonoxide and carbon dioxide. A maximum of 2% PVC is allowed in this process, and thecontent of chlorine in the products is lower than 5 ppm. The distribution of alkene productsin this process is like that in petroleum pyrolysis. The BP process was industrialized in1997.

The biggest difference between this process and the others lies in the reactor, whichwas originally a fixed-bed reactor. A sand fluidized-bed reactor has been adopted for theBP process, which can guarantee a uniform temperature in the reactor due to the uniformparticle size and fluidized nature of sand. In traditional processes, because of the poor heattransfer properties of plastics, a uniform temperature is difficult to achieve in the plasticsfeedstocks so a long reaction time was always required. On the other hand, after wasteplastics are heated and melted, they usually adhere to the surface of reactors owing totheir poor flow characteristics. The BP process has successfully solved all these problems,and a continuous production of liquid oil is achieved.

DEVELOPMENTS IN CHINA 739Tab

le28

.6Ty

pica

lpyr

olys

ispr

oces

so

fwas

tepl

astic

s

Dev

elop

erSc

ale

Feed

stock

Rea

ctor

Tem

pera

ture

( C)

Cata

lyst

Mai

npr

oduc

tsY

ield

of

prod

ucts

(%)

Uni

ted

Carb

onCo

mpa

ny35

70

kg/d

PE,P

P,PS

,PV

C,PA

,PE

TEx

trude

r42

060

0W

ax

Japa

nese

Carb

onCo

mpa

ny

PE,P

P,PS

Extru

der

500

600

Mon

omer

s

FujiR

ecyc

leCo

mpa

ny50

00t/a

PE,P

P,PS

(indu

strial

was

te)

Mel

ting

furn

ace

390

ZSM

-5G

asol

ine

80

90

FujiR

ecyc

leCo

mpa

ny40

00t/a

PE,P

P,PS

,PET

(PC