Review Article Alternate Strategies for Conversion of...

Hindawi Publishing CorporationISRN Renewable EnergyVolume 2013 Article ID 902053 7 pageshttpdxdoiorg1011552013902053

Review ArticleAlternate Strategies for Conversion of Waste Plastic to Fuels

Neha Patni Pallav Shah Shruti Agarwal and Piyush Singhal

Department of Chemical Engineering Institute of Technology Nirma University S G Highway Ahmedabad Gujarat 382481 India

Correspondence should be addressed to Neha Patni nehapatninirmauniacin

Received 31 March 2013 Accepted 28 April 2013

Academic Editors R S Adhikari and V Makareviciene

Copyright copy 2013 Neha Patni et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

The present rate of economic growth is unsustainable without saving of fossil energy like crude oil natural gas or coal There aremany alternatives to fossil energy such as biomass hydropower and wind energy Also suitable waste management strategy isanother important aspect Development and modernization have brought about a huge increase in the production of all kinds ofcommodities which indirectly generate waste Plastics have been one of the materials because of their wide range of applicationsdue to versatility and relatively low cost The paper presents the current scenario of the plastic consumption The aim is to providethe reader with an in depth analysis regarding the recycling techniques of plastic solid waste (PSW) Recycling can be dividedinto four categories primary secondary tertiary and quaternary As calorific value of the plastics is comparable to that of fuel soproduction of fuel would be a better alternative So the methods of converting plastic into fuel specially pyrolysis and catalyticdegradation are discussed in detail and a brief idea about the gasification is also includedThus we attempt to address the problemof plastic waste disposal and shortage of conventional fuel and thereby help in promotion of sustainable environment

1 Introduction

The increase in use of plastic products caused by suddengrowth in living standards had a remarkable impact onthe environment Plastics have now become indispensablematerials and the demand is continually increasing due totheir diverse and attractive applications in household andindustries Mostly thermoplastics polymers make up a highproportion of waste and this amount is continuously increas-ing around the globe Hence waste plastics pose a very seri-ous environmental challenge because of their huge quantityand disposal problemas thermoplastics do not biodegrade fora very long time

The consumption of plastic materials is vast and has beengrowing steadily in view of the advantages derived from theirversatility relatively low cost and durability (due to theirhigh chemical stability and low degradability) Some of themost used plastics are polyolefins such as polyethylene andpolypropylene which have a massive production and con-sumption in many applications such as packaging buildingelectricity and electronics agriculture and health care [1]In turn the property of high durability makes the disposalof waste plastics a very serious environmental problem land

filling being the most used disposal route Plastic wastescan be classified as industrial and municipal plastic wastesaccording to their origins these groups have different quali-ties and properties and are subjected to differentmanagementstrategies [2 3]

Plastic materials production has reached global maxi-mum capacities leveling at 260 million tons in 2007 wherein 1990 the global production capacity was estimated at 80million tons [1] Plastic production is estimated to growworldwide at a rate of about 5 per year [4] Polymer wastecan be used as a potentially cheap source of chemicals andenergy Due to release of harmful gases like dioxins hydrogenchloride airborne particles and carbon dioxide incinerationof polymer possesses serious air pollution problems Due tohigh cost and poor biodegradability it is also undesirable todispose by landfill

Recycling is the best possible solution to the environ-mental challenges facing the plastic industry These are cat-egorized into primary secondary tertiary and quaternaryrecycling Chemical recycling that is conversion of wasteplastics into feedstock or fuel has been recognized as anideal approach and could significantly reduce the net cost ofdisposalThe production of liquid hydrocarbons from plastic

2 ISRN Renewable Energy

Table 1 Plastics consumption by major world areas in kg and GNI dollars per capita

Main world areas Plastics consumption 000s tons Population millions Kgcapita GNIcapitaEurope W C and E 40 000 450 90 18 000Eurasia Russia and others 4 000 285 14 1 600North America 45 000 310 145 32 000Latin America 11 000 500 22 3 500Middle East including TR 4 000 200 20 2 500Africa North and South 2 500 190 13 2 000Other Africa 500 610 lt1 300China 19 000 1285 14 800India 4 000 1025 4 450Japan 11 000 125 90 35 000Other Asia Pacific rest 13 000 1120 11 600Total world 154 000 6 100 25 5 200

degradation would be beneficial in that liquids are easilystored handled and transported However these aims arenot easy to achieve [4] An alternative strategy to chemicalrecycling which has attracted much interest recently withthe aim of convertingwaste plastics into basic petrochemicalsis to be used as hydrocarbon feedstock or fuel oil for avariety of downstream processes [3] There are differentmethods of obtaining fuel from waste plastic such as thermaldegradation catalytic cracking and gasification [3 5]

2 Current Scenario of Plastics

Over many years a drastic growth has been observed inplastic industry such as in the production of syntheticpolymers represented by polyethylene (PE) polypropylene(PP) polystyrene (PS) polyethylene terephthalate (PET)polyvinyl alcohol (PVA) and polyvinyl chloride (PVC) Ithas been estimated that almost 60 of plastic solid waste(PSW) is discarded in open space or land filled worldwideAccording to a nationwide survey conducted in the year2003 more than 10000MT of plastic waste is generated dailyin our country and only 40wt of the same is recycledbalance 60wt is not possible to dispose off [4] India hasbeen a favored dumping ground for plastic wastemostly fromindustrialized countries like Canada Denmark GermanyUK the Netherlands Japan France and the United Statesof America According to the government of India importdata of more than 59000 tons and 61000 tons of plastic wastehave found its way into India in the years 1999 and 2000respectively [3 6]

21 Present Scenario in India With the formal and informalsector failing to collect plastic waste the packaging andpolyvinyl chloride (PVC) pipe industry are growing at 16ndash18 per year The demand of plastic goods is increasingfrom household use to industrial applications It is growingat a rate of 22 annually The polymers production hasreached the 85 million tons in 2007 Table 1 provides thetotal plastics waste consumption in the world and Table 2provides the total plastic waste consumption in India duringthe last decade National plastic waste management task

Table 2 Plastics consumption in India

S no Year Consumption (tons)1 1996 610002 2000 3000003 2001 4000004 2007 8500000

force in 1997 projected the polymers demand in the countryTable 3 documents the demand of different polymers in Indiaduring years 1995-96 2001-02 and 2006-07 The comparisonof demand and consumption from Tables 2 and 3 indicatesthat projections are correct More than one fourth of theconsumption in India is that of PVC which is being phasedout in many countries Poly bags and other plastic itemsexcept PET in particular have been a focus because it hascontributed to host problems in India such as choked sewersanimal deaths and clogged soils

3 Different Recycling Categories [1]

31 Primary Recycling It is also known as mechanical repro-cessing During the process the plastic waste is fed into theoriginal production process of basic material So we canobtain the product with same specification as that of the orig-inal oneThis process is feasible only with semiclean scrap soit is an unpopular choice with the recyclers Degraded plasticwaste partly substitutes the virgin material So on increasingthe recycled plastic fraction in feedmixture the quality of theproduct decreases This type of recycling requires clean andnot contaminated waste which is of the same type as virginresin

For this reason steps in the primary recycling process are

(1) separate the waste by specific type of resin and bydifferent colors and then wash it

(2) the waste has better melting properties so it shouldbe reextruded into pellets which can be added to theoriginal resin

ISRN Renewable Energy 3

Table 3 Polymers demands in India (million tons)

S no Type of polymer 1995-96 2001-02 2006-071 Polyethylene 083 183 3272 Polypropylene 034 088 179

3 Polyvinylchloride 049 087 129

4 Polyethyleneterephthalate 003 014 029

Source National Plastic Waste Management Task Force Projection (1997)

Waste plasticsCatalyst

Plastics knapper

Pyrolysisreactor

Condenser

Fuel gas

Mixed oil Diesel oil

Gasoline

Gas

Frac

tiona

ting

tow

er

Figure 1 Pyrolysis Process of generating fuel oil from the waste plastics [12]

This type of recycling is very expensive compared to othertypes of recycling due to the requirements of plastic proper-ties mentioned above

If the waste can be easily sorted by resin but cannot bepelletized due to mixed coloring contamination then wastecan be fed intomoulding application and regarding reactantsproperties it is less demanding

32 Secondary Recycling Secondary recycling uses PSW inthe manufacturing of plastic products by mechanical meanswhich uses recyclates fillers andor virgin polymers Theobjective of the process is to retain some energy which is usedfor plastic production to attain financial advantages Unlikeprimary recycling the secondary recycling process can usecontaminated or less separatedwaste However this waste hasto be cleaned The recycling process involves different prod-ucts and is different compared to original production process

33 Tertiary Recycling This process is also known as crackingprocess The process includes breaking down the plastics athigh temperatures (thermal degradation) or at lower tem-peratures in the presence of catalyst (catalytic degradation)which contain smaller carbon chains For any chemical pro-duction this feedstock can be used as basic material of lowerquality (eg polymerization or fuel fabrication)The originalvalue of the rawmaterial is lostThe tertiary recycling processis more important due to high levels of waste contaminationWe are able to recover the monomers of condensation poly-mersMechanisms like hydrolysismethanolysis or glycolysiscan be used for example PET (polyethylene terephthalate)polyesters and polyamide while addition of polymers likepolyolefin polystyrene and PVC requires stronger thermaltreatment gasification or catalytic degradation to be cracked

34 Quaternary Recycling This process includes the recoveryof energy content only As most plastic waste has high heatcontent so it is incinerated Generation of the heat energy isthe only advantage of this process The residual of this incin-eration has 20wt respectively 10 vol of the original wasteand are placed in landfills Solid waste problem is not solvedby this process in fact it leads to the problem of air pollution

4 Methods of Converting Plastic to Fuel

41 PyrolysisThermal Degradation Pyrolysis is a process ofthermal degradation of a material in the absence of oxygenPlastic is fed into a cylindrical chamber The pyrolytic gasesare condensed in a specially designed condenser systemto yield a hydrocarbon distillate comprising straight andbranched chain aliphatic cyclic aliphatic and aromatichydrocarbons and liquid is separated using fractional dis-tillation to produce the liquid fuel products The plastic ispyrolysed at 370∘Cndash420∘C

The essential steps in the pyrolysis of plastics involve(Figure 1)

(1) evenly heating the plastic to a narrow temperaturerange without excessive temperature variations

(2) purging oxygen from pyrolysis chamber

(3) managing the carbonaceous char by-product before itacts as a thermal insulator and lowers the heat transferto the plastic

(4) careful condensation and fractionation of the pyrol-ysis vapors to produce distillate of good quality andconsistency


Table 4 Main operating parameters for pyrolysis process [7]

Parameters Conventional Fast FlashPyrolysis temprature (K) 550ndash900 850ndash1250 1050ndash1300Heating rate (Ks) 01ndash1 10ndash200 gt1000Particle size (mm) 5ndash50 lt1 lt02Solid residence (s) 300ndash3600 05ndash10 lt05

Advantages of pyrolysis process [5] are(a) volume of the waste is significantly reduced (lt50ndash

90)(b) solid liquid and gaseous fuel can be produced from

the waste(c) storabletransportable fuel or chemical feed stock is

obtained(d) environmental problem is reduced(e) desirable process as energy is obtained from renew-

able sources like municipal solid waste or sewagesludge

(f) the capital cost is lowThere are different types of pyrolysis process Conventionalpyrolysis (slow pyrolysis) proceeds under a low heatingrate with solid liquid and gaseous products in significantportions [5 13] It is an ancient process used mainly forcharcoal production Vapors can be continuously removedas they are formed [5 14] The fast pyrolysis is associatedwith tar at low temperature (850ndash1250K) andor gas at hightemperature (1050ndash1300K) At present the preferred technol-ogy is fast or flash pyrolysis at high temperatures with veryshort residence time [5 15] Fast pyrolysis (more accuratelydefined as thermolysis) is a process in which a material suchas biomass is rapidly heated to high temperatures in theabsence of oxygen [5 15] Table 4 [7] shows the range of themain operating parameters for pyrolysis processes

411 Mechanism ofThermal Degradation Cullis and Hirsch-ler had proposed detailed study on the mechanism ofthermal degradation of polymers [3 16] The four differentmechanisms proposed are (1) end-chain scission or unzip-ping (2) random-chain scissionfragmentation (3) chainstrippingelimination of side chain (4) cross-linking Thedecompositionmodemainly depends on the type of polymer(the molecular structure)

Mlowast119899

997888rarr Mlowast119899minus1

+M (1)

Mlowast119899minus1


+M (2)

M119899997888rarr M

119909+M119910

(3)

Equations (1) and (2) represent the thermal degradation and(3) represents the random degradation route of the polymerspyrolysisThe fourth type ofmechanism that is cross-linkingoften occurs in thermosetting plastics upon heating at hightemperature in which two adjacent ldquostrippedrdquo polymer chainscan form a bond resulting in a chain network (a higher MWspecies) An example is char formation

42 Catalytic Degradation In this method a suitable catalystis used to carry out the cracking reaction The presenceof catalyst lowers the reaction temperature and time Theprocess results in much narrower product distribution ofcarbon atom number and peak at lighter hydrocarbonswhich occurs at lower temperatures The cost should befurther reduced to make the process more attractive froman economic perspective Reuse of catalysts and the useof effective catalysts in lesser quantities can optimize thisoption This process can be developed into a cost-effectivecommercial polymer recycling process for solving the acuteenvironmental problem of disposal of plastic waste It alsooffers the higher cracking ability of plastics and the lowerconcentration of solid residue in the product [3]

421 Mechanism of Catalytic Degradation Singh et al [3 17]have investigated catalytic degradation of polyolefin usingTGA as a potential method for screening catalysts and havefound that the presence of catalyst led to the decrease inthe apparent activation energy Different mechanisms (ionicand free radical) for plastic pyrolysis proposed by differentscientists are as given below

There are different steps in carbonium ion reactionmechanism such as H-transfer chainbeta-scission isomeri-sation oligomerizationalkylation and aromatization whichis influenced by acid site strength density and distribution[3 18] Solid acid catalysts such as zeolites favor hydrogentransfer reactions due to the presence ofmany acid sites [3 5]Both Bronsted and Lewis acid sites characterize acid strengthof solid acids The presence of Bronsted acid sites supportsthe cracking of olefinic compounds [3 19]The majority ofthe acid sites in crystalline solid acids are located within thepores of the material such as with zeolites [3 20] Thusmain feature in assessing the level of polyolefin crackingover such catalysts is the microporosity of porous solidacidsThe carbonium ionmechanism of catalytic pyrolysis ofpolyethylene can be described as follows [3 21] (see Table 5)

(1) Initiation Initiation may occur on some defected sites ofthe polymer chains For instance an olefinic linkage couldbe converted into an on-chain carbonium ion by protonaddition

ndashCH2CH2CH = CHCH

2CH2

minus

+HX

997888rarr CH2CH2

+CHCH2ndashCH2CH2+ Xminus

(4)

The polymer chain may be broken up through 120573-emission

ndashCH2CH2

+CHCH2ndashCH2CH2

minus

997888rarr CH2CH2CH = CH

2++CH2CH2

+

(5)


Table 5 List of catalysts in use

Sr no Catalyst Pore size (nm) Commercial name References1 USY 074 H-Ultrastabilised Y-zeolite [8ndash10]2 ZSM-5 055 times 051 H-ZSM-5 zeolite [8ndash10]3 MOR 065 times 070 H-Mordenite [8 9]4 ASA 315 Synclyst 25 (silica-alumina) [8 9]5 MCM-41 42ndash52 mdash [8 9 11]6 SAHA 328 Amorphous silica-alumina [10]7 FCC-R1 mdash Equilibrium catalyst [10]8 Silicalite 055 times 051 Synthesized in house [10]

Initiation may also take place through random hydride-ionabstraction by low-molecular-weight carbonium ions (R+)

ndashCH2CH2CH2CH2CH2ndash + R+

997888rarr ndashCHCH2

+CHCH2CH2

minus

+ RH(6)

The newly formed on-chain carbonium ion then undergoes120573-scission

(2)DepropagationThemolecularweight of themain polymerchains may be reduced through successive attacks by acidicsites or other carbonium ions and chain cleavage yieldingingan oligomer fraction (approximately C

30ndashC80) Further

cleavage of the oligomer fraction probably by direct 120573-emission of chain-end carbonium ions leads to gas formationon one hand and a liquid fraction (approximately C

10ndashC25)

on the other

(3) Isomerization The carbonium ion intermediates canundergo rearrangement by hydrogen- or carbon-atom shiftsleading to a double-bond isomerization of an olefin

CH2= CHndashCH

2ndashCH2ndashCH3

H+997888rarr CH

3

+CHndashCH2ndashCH2ndashCH3

H+997888rarr CH

3ndashCH = CHndashCH

2ndashCH3

(7)

Other important isomerization reactions are methyl-groupshift and isomerization of saturated hydrocarbons

(4) Aromatization Some carbonium ion intermediates canundergo cyclization reactions An example is when hydrideion abstraction first takes place on an olefin at a positionseveral carbons removed from the double bond the resultbeing the formation of an olefinic carbonium ion

R+1

+ R2CH = CHndashCH

2CH2CH2CH2CH3

larrrarr R1H + R

2CH = CHndashCH

2CH2CH2

+CHCH3

(8)

The carbonium ion could undergo intramolecular attack onthe double bond

Panda et al [3] and Sekine and Fujimoto [22] have pro-posed a free radical mechanism for the catalytic degradation

of PP using Feactivated carbon catalystMethyl primary andsecondary alkyl radicals are formed during degradation andmethane olefins and monomers are produced by hydrogenabstractions and recombination of radical units [3 23]

The various steps in catalytic degradation are shownbelow [3]

(1) Initiation Random breakage of the CndashC bond of the mainchain occurs with heat to produce hydrocarbon radicals

R1ndashR2997888rarr R∙

1

+ R∙2

(9)

(2) Propagation The hydrocarbon radical decomposes toproduce lower hydrocarbons such as propylene followed by120573-scission and abstraction of H-radicals from other hydro-carbons to produce a new hydrocarbon radical

R∙1

997888rarr R∙3

+ C2or C3

(10)

R∙2

+ R4997888rarr R

2or R∙4

(11)

(3)Termination Disproportionation or recombination of tworadicals

R∙5

+ R∙6

997888rarr R5+ R∙6

(12)

R∙7

+ R∙8

997888rarr R7ndashR8

(13)

During catalytic degradation with Fe activated charcoal inH2

atmosphere hydrogenation of hydrocarbon radical (olefin)and the abstraction of the H-radical from hydrocarbon orhydrocarbon radical generate radicals and thus enhancingdegradation rate At reaction temperature lower than 400∘Cor a reaction time shorter than 10 h many macromolecularhydrocarbon radicals exist in the reactor and recombinationoccurs readily because these radicals cannot move fast How-ever with Fe activated carbon in a H

2atmosphere these rad-

icals are hydrogenated and therefore combination may besuppressed Consequently it seems as if the decomposition ofthe solid product is promoted including low polymers whosemolecular diameter is larger than the pore size of the catalysts

43 Gasification In this process partial combustion of bio-mass is carried out to produce gas and char at the first stage


and subsequent reduction of the product gases chiefly CO2

and H2O by the charcoal into CO and H

2 Depending on the

design and operating conditions of the reactor the processalso generates some methane and other higher hydrocarbons(HCs) [5 24] Broadly gasification can be defined as thethermochemical conversion of a solid or liquid carbon-basedmaterial (feedstock) into a combustible gaseous product(combustible gas) by the supply of a gasification agent(another gaseous compound) The gasification agent allowsthe feedstock to be quickly converted into gas by means ofdifferent heterogeneous reactions [5 25ndash27] If the processdoes not occur with help of an oxidising agent it is calledindirect gasification and needs an external energy sourcegasification agent because it is easily produced and increasesthe hydrogen content of the combustible gas [5 28]

A gasification system is made up of three fundamentalelements (1) the gasifier helpful in producing the com-bustible gas (2) the gas clean up system required to removeharmful compounds from the combustible gas (3) the energyrecovery system The system is completed with suitablesubsystems helpful to control environmental impacts (airpollution solid wastes production and wastewater)

Gasification process represents a future alternative to thewaste incinerator for the thermal treatment of homogeneouscarbon based waste and for pretreated heterogeneous waste

5 Summary

Plastics are ldquoone of the greatest innovations of the millen-niumrdquo and have certainly proved their reputation to be truePlastic is lightweight does not rust or rot is of low costreusable and conserves natural resources and for these rea-sons plastic has gained this much popularity The literaturereveals that research efforts on the pyrolysis of plastics indifferent conditions using different catalysts and the processhave been initiated However there are many subsequentproblems to be solved in the near future The present issuesare the necessary scale up minimization of waste handlingcosts and production cost and optimization of gasoline rangeproducts for a wide range of plastic mixtures or waste

Huge amount of plastic wastes produced may be treatedwith suitably designed method to produce fossil fuel substi-tutes The method is superior in all respects (ecological andeconomical) if proper infrastructure and financial support isprovided So a suitable process which can convert waste plas-tic to hydrocarbon fuel is designed and if implemented thenthat would be a cheaper partial substitute of the petroleumwithout emitting any pollutants It would also take care ofhazardous plastic waste and reduce the import of crude oil

Challenge is to develop the standards for process andproducts of postconsumer recycled plastics and to adoptthe more advanced pyrolysis technologies for waste plasticsreferring to the observations of research and developmentin this field The pyrolysis reactor must be designed tosuit the mixed waste plastics and small-scaled and middle-scaled production Also analysis would help reducing thecapital investment and also the operating cost and thus wouldenhance the economic viability of the process

References

[1] T S Kpere-Daibo Plastic catalytic degradation study of the roleof external catalytic surface catalytic reusability and temperatureeffects [Doctoral thesis] University of London Department ofChemical Engineering University College London WC1E 7JE

[2] A G Buekens and H Huang ldquoCatalytic plastics cracking forrecovery of gasoline-range hydrocarbons from municipal plas-tic wastesrdquo Resources Conservation and Recycling vol 23 no 3pp 163ndash181 1998

[3] A K Panda R K Singh and D K Mishra ldquoThermolysis ofwaste plastics to liquid fuel A suitable method for plastic wastemanagement and manufacture of value added productsmdashaworld prospectiverdquo Renewable and Sustainable Energy Reviewsvol 14 no 1 pp 233ndash248 2010

[4] S M Al-Salem P Lettieri and J Baeyens ldquoThe valorizationof plastic solid waste (PSW) by primary to quaternary routesfrom re-use to energy and chemicalsrdquo Progress in Energy andCombustion Science vol 36 no 1 pp 103ndash129 2010

[5] R P Singhad V V Tyagib T Allen et al ldquoAn overview forexploring the possibilities of energy generation frommunicipalsolid waste (MSW) in Indian scenariordquo Renewable and Sustain-able Energy Reviews vol 15 no 9 pp 4797ndash4808 2011

[6] J Scheirs and W Kaminsky Feedstock Recycling of WastePlastics John Wiley amp Sons 2006

[7] A Demirbas ldquoBiorefineries current activities and future devel-opmentsrdquo Energy Conversion ampManagement vol 50 pp 2782ndash2801 2009

[8] W-C HuangM-S Huang C-F Huang C-C Chen and K-LOu ldquoThermochemical conversion of polymer wastes into hyd-rocarbon fuels over various fluidizing cracking catalystsrdquo Fuelvol 89 no 9 pp 2305ndash2316 2010

[9] T-T Wei K-J Wu S-L Lee and Y-H Lin ldquoChemical recy-cling of post-consumer polymer waste over fluidizing crackingcatalysts for producing chemicals and hydrocarbon fuelsrdquoResources Conservation and Recycling vol 54 no 11 pp 952ndash961 2010

[10] H-T Lin M-S Huang J-W Luo L-H Lin C-M Lee andK-L Ou ldquoHydrocarbon fuels produced by catalytic pyrolysisof hospital plastic wastes in a fluidizing cracking processrdquo FuelProcessing Technology vol 91 no 11 pp 1355ndash1363 2010

[11] J Aguado D P Serrano and J M Escola ldquoFuels from wasteplastics by thermal and catalytic process a reviewrdquo Industrial ampEngineering Chemistry Research vol 47 no 21 pp 7982ndash79922008

[12] G H Zhang J F Zhu and A Okuwaki ldquoProspect and currentstatus of recycling waste plastics and technology for convertingthem into oil in Chinardquo Resources Conservation and Recyclingvol 50 no 3 pp 231ndash239 2007

[13] S Katyal ldquoEffect of carbonization temperature on combustionreactivity ofbagasse charrdquo Energy Sources A vol 29 no 16 pp1477ndash1485 2007

[14] D Mohan C U Pittman Jr and P H Steele ldquoPyrolysis ofwoodbiomass for bio-oil acritical reviewrdquoEnergy Fuels vol 20no 3 pp 848ndash889 2006

[15] A Demirbas ldquoProducing bio-oil from olive cake by fast pyrol-ysisrdquo Energy Sources A vol 30 pp 38ndash44 2008

[16] C F Cullis and M M Hirschler The Combustion of OrganicPolymers Oxford Clarendon Press 1981

[17] B Singh and N Sharma ldquoMechanistic implications of plasticdegradationrdquo Polymer Degradation and Stability vol 93 no 3pp 561ndash584 2008


[18] A Corma ldquoInorganic solid acids and their use in acid-catalyzedhydrocarbon reactionsrdquo Chemical Reviews vol 95 no 3 pp559ndash614 1995

[19] H Ohkita R Nishiyama Y Tochihara et al ldquoAcid properties ofsilica-alumina catalysts and catalytic degradation of polyethy-lenerdquo Industrial and Engineering Chemistry Research vol 32 no12 pp 3112ndash3116 1993

[20] P Venuto and P Landis ldquoZeolite catalysis in synthetic organicchemistryrdquo Advances in Catalysis vol 18 pp 259ndash267 1968


[22] Y Sekine and K Fujimoto ldquoCatalytic degradation of PP withan Feactivated carbon catalystrdquo Journal of Material Cycles andWaste Management vol 5 no 2 pp 107ndash112 2003

[23] R P Lattimer ldquoDirect analysis of polypropylene compounds bythermal desorption and pyrolysis-mass spectrometryrdquo Journalof Analytical andApplied Pyrolysis vol 26 no 2 pp 65ndash92 1993

[24] H R Appel Y C Fu S Friedman P M Yavorsky and IWender ldquoConverting organic wastes to oilrdquo US Burea ofMinesReport of Investigation 7560 1971

[25] C Di Blasi ldquoDynamic behaviour of stratified downdraft gasi-fierrdquoChemical Engineering Science vol 55 no 15 pp 2931ndash29442000

[26] G Barducci ldquoTheRDF gasifier of Florentine area (Greve in Chi-anti Italy)rdquo in Proceedings of the 1st Italian-Brazilian Symposiumon Sanitary and Environmental Engineering 1992

[27] S Z Baykara and E Bilgen ldquoA feasibility study on solar gasifi-cation of albertan coalrdquo in Alternative Energy Sources IV vol 6Ann Arbor Science New York NY USA 1981

[28] W B Hauserman N Giordano M Lagana and V RecuperoldquoBiomass gasifiers for fuelcells systemsrdquo La Chimica amp LrsquoIndus-tria vol 2 pp 199ndash206 1997

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Table 1 Plastics consumption by major world areas in kg and GNI dollars per capita

Main world areas Plastics consumption 000s tons Population millions Kgcapita GNIcapitaEurope W C and E 40 000 450 90 18 000Eurasia Russia and others 4 000 285 14 1 600North America 45 000 310 145 32 000Latin America 11 000 500 22 3 500Middle East including TR 4 000 200 20 2 500Africa North and South 2 500 190 13 2 000Other Africa 500 610 lt1 300China 19 000 1285 14 800India 4 000 1025 4 450Japan 11 000 125 90 35 000Other Asia Pacific rest 13 000 1120 11 600Total world 154 000 6 100 25 5 200

degradation would be beneficial in that liquids are easilystored handled and transported However these aims arenot easy to achieve [4] An alternative strategy to chemicalrecycling which has attracted much interest recently withthe aim of convertingwaste plastics into basic petrochemicalsis to be used as hydrocarbon feedstock or fuel oil for avariety of downstream processes [3] There are differentmethods of obtaining fuel from waste plastic such as thermaldegradation catalytic cracking and gasification [3 5]

2 Current Scenario of Plastics

Over many years a drastic growth has been observed inplastic industry such as in the production of syntheticpolymers represented by polyethylene (PE) polypropylene(PP) polystyrene (PS) polyethylene terephthalate (PET)polyvinyl alcohol (PVA) and polyvinyl chloride (PVC) Ithas been estimated that almost 60 of plastic solid waste(PSW) is discarded in open space or land filled worldwideAccording to a nationwide survey conducted in the year2003 more than 10000MT of plastic waste is generated dailyin our country and only 40wt of the same is recycledbalance 60wt is not possible to dispose off [4] India hasbeen a favored dumping ground for plastic wastemostly fromindustrialized countries like Canada Denmark GermanyUK the Netherlands Japan France and the United Statesof America According to the government of India importdata of more than 59000 tons and 61000 tons of plastic wastehave found its way into India in the years 1999 and 2000respectively [3 6]

21 Present Scenario in India With the formal and informalsector failing to collect plastic waste the packaging andpolyvinyl chloride (PVC) pipe industry are growing at 16ndash18 per year The demand of plastic goods is increasingfrom household use to industrial applications It is growingat a rate of 22 annually The polymers production hasreached the 85 million tons in 2007 Table 1 provides thetotal plastics waste consumption in the world and Table 2provides the total plastic waste consumption in India duringthe last decade National plastic waste management task

Table 2 Plastics consumption in India

S no Year Consumption (tons)1 1996 610002 2000 3000003 2001 4000004 2007 8500000

force in 1997 projected the polymers demand in the countryTable 3 documents the demand of different polymers in Indiaduring years 1995-96 2001-02 and 2006-07 The comparisonof demand and consumption from Tables 2 and 3 indicatesthat projections are correct More than one fourth of theconsumption in India is that of PVC which is being phasedout in many countries Poly bags and other plastic itemsexcept PET in particular have been a focus because it hascontributed to host problems in India such as choked sewersanimal deaths and clogged soils

3 Different Recycling Categories [1]

31 Primary Recycling It is also known as mechanical repro-cessing During the process the plastic waste is fed into theoriginal production process of basic material So we canobtain the product with same specification as that of the orig-inal oneThis process is feasible only with semiclean scrap soit is an unpopular choice with the recyclers Degraded plasticwaste partly substitutes the virgin material So on increasingthe recycled plastic fraction in feedmixture the quality of theproduct decreases This type of recycling requires clean andnot contaminated waste which is of the same type as virginresin

For this reason steps in the primary recycling process are

(1) separate the waste by specific type of resin and bydifferent colors and then wash it

(2) the waste has better melting properties so it shouldbe reextruded into pellets which can be added to theoriginal resin








Plastics knapper

Pyrolysisreactor

Condenser

Fuel gas


Gasoline

Gas

Frac

tiona

ting

tow

er
























Mlowast119899


+M (1)

Mlowast119899minus1


+M (2)

M119899997888rarr M

119909+M119910

(3)







2CH2

minus

+HX

997888rarr CH2CH2


(4)


ndashCH2CH2

+CHCH2ndashCH2CH2

minus


2++CH2CH2

+

(5)







+CHCH2CH2

minus

+ RH(6)



30ndashC80) Further


10ndashC25)

on the other


CH2= CHndashCH

2ndashCH2ndashCH3

H+997888rarr CH

3


H+997888rarr CH


2ndashCH3

(7)



R+1

+ R2CH = CHndashCH

2CH2CH2CH2CH3

larrrarr R1H + R

2CH = CHndashCH

2CH2CH2

+CHCH3

(8)







1

+ R∙2

(9)


R∙1

997888rarr R∙3

+ C2or C3

(10)

R∙2

+ R4997888rarr R

2or R∙4

(11)


R∙5

+ R∙6

997888rarr R5+ R∙6

(12)

R∙7

+ R∙8


(13)









2 Depending on the




5 Summary




References


































FuelsJournal of







Advances in



Journal of


Renewable Energy





RotatingMachinery


EnergyJournal of
























Plastics knapper

Pyrolysisreactor

Condenser

Fuel gas


Gasoline

Gas

Frac

tiona

ting

tow

er
























Mlowast119899


+M (1)

Mlowast119899minus1


+M (2)

M119899997888rarr M

119909+M119910

(3)







2CH2

minus

+HX

997888rarr CH2CH2


(4)


ndashCH2CH2

+CHCH2ndashCH2CH2

minus


2++CH2CH2

+

(5)







+CHCH2CH2

minus

+ RH(6)



30ndashC80) Further


10ndashC25)

on the other


CH2= CHndashCH

2ndashCH2ndashCH3

H+997888rarr CH

3


H+997888rarr CH


2ndashCH3

(7)



R+1

+ R2CH = CHndashCH

2CH2CH2CH2CH3

larrrarr R1H + R

2CH = CHndashCH

2CH2CH2

+CHCH3

(8)







1

+ R∙2

(9)


R∙1

997888rarr R∙3

+ C2or C3

(10)

R∙2

+ R4997888rarr R

2or R∙4

(11)


R∙5

+ R∙6

997888rarr R5+ R∙6

(12)

R∙7

+ R∙8


(13)









2 Depending on the




5 Summary




References


































FuelsJournal of







Advances in



Journal of


Renewable Energy





RotatingMachinery


EnergyJournal of



























Mlowast119899


+M (1)

Mlowast119899minus1


+M (2)

M119899997888rarr M

119909+M119910

(3)







2CH2

minus

+HX

997888rarr CH2CH2


(4)


ndashCH2CH2

+CHCH2ndashCH2CH2

minus


2++CH2CH2

+

(5)







+CHCH2CH2

minus

+ RH(6)



30ndashC80) Further


10ndashC25)

on the other


CH2= CHndashCH

2ndashCH2ndashCH3

H+997888rarr CH

3


H+997888rarr CH


2ndashCH3

(7)



R+1

+ R2CH = CHndashCH

2CH2CH2CH2CH3

larrrarr R1H + R

2CH = CHndashCH

2CH2CH2

+CHCH3

(8)







1

+ R∙2

(9)


R∙1

997888rarr R∙3

+ C2or C3

(10)

R∙2

+ R4997888rarr R

2or R∙4

(11)


R∙5

+ R∙6

997888rarr R5+ R∙6

(12)

R∙7

+ R∙8


(13)









2 Depending on the




5 Summary




References


































FuelsJournal of







Advances in



Journal of


Renewable Energy





RotatingMachinery


EnergyJournal of























+CHCH2CH2

minus

+ RH(6)



30ndashC80) Further


10ndashC25)

on the other


CH2= CHndashCH

2ndashCH2ndashCH3

H+997888rarr CH

3


H+997888rarr CH


2ndashCH3

(7)



R+1

+ R2CH = CHndashCH

2CH2CH2CH2CH3

larrrarr R1H + R

2CH = CHndashCH

2CH2CH2

+CHCH3

(8)







1

+ R∙2

(9)


R∙1

997888rarr R∙3

+ C2or C3

(10)

R∙2

+ R4997888rarr R

2or R∙4

(11)


R∙5

+ R∙6

997888rarr R5+ R∙6

(12)

R∙7

+ R∙8


(13)









2 Depending on the




5 Summary




References


































FuelsJournal of







Advances in



Journal of


Renewable Energy





RotatingMachinery


EnergyJournal of




















2 Depending on the




5 Summary




References


































FuelsJournal of







Advances in



Journal of


Renewable Energy





RotatingMachinery


EnergyJournal of

































FuelsJournal of







Advances in



Journal of


Renewable Energy





RotatingMachinery


EnergyJournal of

















Review Article Alternate Strategies for Conversion of...

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