Biomass Petro Chem

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Resources, Conservation and Recycling 53 (2009) 513528

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Resources, Conservation and Recycling

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Basic petrochemicals from natural gas, coal and biomass: Energy use and CO 2emissions

Tao Ren , Martin K. PatelDepartment of Chemistry, Copernicus Institute for Sustainable Development and Innovation, Utrecht University, Heidelberglaan 2, 3584 CS Utrecht, The Netherlands

a r t i c l e i n f o

Article history:Received 22 October 2008Received in revised form 22 March 2009Accepted 1 April 2009Available online 9 May 2009

Keywords:CoalBiomassBasic petrochemicalsEnergy use and CO 2 emissions

a b s t r a c t

While high-value basic petrochemicals (HVCs) are mostly produced through conventional naphtha andethane-based process routes, it is also possible to produce them through coal and biomass-based routes.In this paper, we compared these routes in terms of energy use and CO 2 emissions per ton of HVCs.(The term ton and abbreviation t should be read in this paper as a metric ton or 1000kg.) Within thecradle-to-grave system boundary, we found the following:

The total energy use of the conventional routes is the lowest (about 60 GJ/t HVCs, of which 50 GJ is thecaloric value of HVCs) whereas that of the methane-based routes is 30% higher, and that of the coaland biomass-based routes is about 60150% higher.

The total CO 2 emissions of conventional and methane-based routes are about 45 tons CO 2 /t HVCswhereas those from the biomass-based routes range from 2 tons CO 2 /t HVCs (a maize-based ethanolrelated route) to 4 tons CO 2 avoided per ton HVCs (a lignocellulosic biomass-based FischerTropschroute). Avoided CO 2 emissions are due to electricity co-generation. The total CO 2 emissions of coal-based routesare by farthe highest (811 tons CO 2 /t HVCs). An exception is a coal-based route with CO 2capture and sequestration features, for which CO 2 emissions are similar to those of the conventionalroutes. It is technically possible to add CO 2 capture and sequestration features to any of the routesmentioned above.

Given the large differences shown above, more research into energy efciency improvement of coaland biomass-based routes is recommended. However, the total energy use of biomass and coal-basedroutes is unlikely to match that of the conventional state-of-the-art routes any time soon.

2009 Elsevier B.V. All rights reserved.

1. Introduction

Basic petrochemicals such as ethylene, propylene and aromaticsarethe building blocksof thechemistry industry. Currently,mostof them are produced via conventional process routes utilizing naph-tha (derived from crude oil) and ethane (derived from natural gas).In 2004,the production of basic petrochemicalsaccounted forabout3 EJ of primary energy use (due to the combustion of fossil fuels;the caloric value of basic petrochemicals excluded) and about 200million tons 1 of CO2 emissions 2 (due to the combustion of fossil

Corresponding author. Tel.: +31 30 253 7600; fax: +31 30 253 7601.E-mail address: [email protected] (T. Ren).

1 The term ton and abbreviation t should be read in this paper as a metric ton or1000kg.

2 3 EJ is about 20% of the total nal energy use (combusted fuels; caloric valueof chemicals excluded) in the global chemical industry while the 200 million ton of CO2 is about 18% of the total CO 2 emissions from the global chemical industry ( IEA,2007 ). Also,3 EJis less than 1%of theglobalprimary energyusewhile200 million is

fuels) ( IEA, 2007; Neelis et al., 2006 ). Recently, alternative processroutes utilizing methane, coal and biomass to produce basic petro-chemicals have attracted a great deal of attention. Studies into theenergy use and CO 2 emissions of these routes may be of interest.

With respect to biomass-based alternative routes that producepetrochemicals via ethanol and syngas (FischerTropsch synthe-sis), a number of recent studies indicate that the CO 2 emissions of these routes can be quite low ( Gielen and Yagita, 2002; Joosten,2001; Patel et al., 2005 ). With respect to making feedstocks suit-able for petrochemicals production, one study argued that not onlybiomass-based technologies but also coal-based technologies withCO2 captureand sequestration featurescan potentiallyachieve verylow CO 2 emissions( Williams,2005 ). Wecomparedmethane-basedroutes with state-of-the-art conventional routes utilizing naphtha

less than 1% of CO 2 emissions related to global energy use ( IEA, 2007 ). Data on CO 2emission factors for the production of one ton of basic petrochemicals can be foundin Neelis et al. (2005) .

0921-3449/$ see front matter 2009 Elsevier B.V. All rights reserved.

doi: 10.1016/j.resconrec.2009.04.005
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514 T. Ren, M.K. Patel / Resources, Conservation and Recycling 53 (2009) 513528

and ethane ( Ren et al., 2008 ). However, we did not nd any stud-ies that have compared all the routes mentioned above in terms of energy use and CO 2 emissions.

Given this knowledgegap, the researchquestion is: how do alter-native routes score in comparison with conventional routes in termsof energy use and CO 2 emissions ? The conventional routes here referto the most commonly used routes, which utilize the conventionalprimary energy sources (e.g. crude oil) that are currently dominantin the production of basic petrochemicals. For conventional routes,state-of-the-art technologies are assumed. The alternative routesrefer to those routes that utilize alternative primary energy sources(i.e. plastic waste, methane, coal, biomass),whichhavenot yet beenusedin the current production of basic petrochemicals on the com-mercial scaleand aretherefore alternativesto conventionalprimaryenergy sources.

The main research method used in this paper is the analysis of energyandCO 2 emissions, whichhas been describedin ( Blok,2006;Ren et al., 2008 ). When applying this method, we rst describe theprocess routes, then characterize them in terms of energy use andCO2 emissions, and nally discuss uncertainties. The main indica-tors are the total energy use and the total CO 2 emissions per ton of high-value basic petrochemicals, or HVCs.

The analysis in this paper is based on scientic and technical journals, books, conferences proceedings and technical papers. Forcomparison purposes, we chose technologies that have recentlybeen researched and that are relatively well understood (meaningthat sufcient data for analysis exist).

The state-of-the-art conventional steam-cracking routes utiliz-ingnaphtha derived from crude oiland ethanederived from naturalgas are being used as the benchmark for comparison ( Ren et al.,2006 ). As far as the alternative routes are concerned, this paper isa prospective study. We expect the alternative routes mentionedin this paper possibly to be applied in the long-term future (or20302050). While it is impossible to predict exactly when theseroutes will be used, it is nevertheless of interest to study theirenergy use and CO 2 emissions based on the current knowledge.The economics of these routes have been discussed in Ren (2009)

and will therefore not be included in this paper.The content of this paper is as follows. First, denitions and

methodologies used in this paper are explained in Section 2. Then,twenty-four routes basedon crudeoil, naturalgas,coal andbiomassas primary energy sources are briey described in Section 3. InSection 4, the alternative routes are compared against the conven-tional routes in terms of their energy use and CO 2 emissions. InSection 5, uncertainties are discussed. Finally, several conclusionsand recommendations are given in Section 6.

2. Denitions

2.1. Primary energy sources, feedstocks and petrochemicals

In this paper, the term primary energy sources refers to crudeoil, natural gas, coal, biomass 3 and plastic waste. Feedstocks refer

3 There are many purposes for biomass use, such as biomass-derived transporta-tion fuels, electricity and wood and bio-based chemicals apart from olens. Sincethere is an increasing demand for biomassfor these applications,biomass is becom-ing an i ncreasingly scarce resource. This raises the question which of the numerousoptions of biomass use is most attractive from an environmental point of view.In order to comprehensively answer this question, all options would need to beassessed simultaneously. This is far beyond the scope of this paper, which focuseson basic petrochemicals. However, scattered information is available which makesit possibleto providea rst replyto thequestion: Patel (2008) argued thatbiomass-based ethanol (even whenthe currenttechnologiesare used) canreduce morefossilenergy use (GJ saved per ton of ethanol) when used to substitute for petrochemical

ethanol in comparison to its use as a transportation fuel (i.e. as a replacement for

to intermediate products such as naphtha, 4 ethane, methanol andethanol. Their caloric values on a dry basis are shown in Table 1 ,expressed as lower heating values (LHVs). When mentioned in thispaper, coal refers to black coal (i.e.bituminous, sub-bituminousandanthracite). It should be noted that the black coal found at differentlocationscan havedifferent caloricvalues (see Table 1 ) andchemi-cal compositions (see Table3 ). HVCs aredened onthe basis of theireconomic values, meaning that light olens aregiven 100% weight-ing perunit mass, whereas non-olens aregiven50% weightingperunit mass ( Ren et al., 2008 ).5

2.2. Electricity

Excess electricity is treated with the credit approach, wherebyelectricity is assumed to come from a standalone natural gas-redpower plant at an energy efciency of 55% ( Ren et al., 2008 ). Sen-sitivity tests regarding other energy efciencies will be discussedin Section 5. Depending on whether electricity is imported or co-generated, energy use forelectricityproduction is eitheraddedtoorsubtracted from theactual input of fossilenergy.For some biomass-basedroutes, the input of fossil energy is less than the fossil energyuse avoided (fossil energy use is avoided because biomass energyis used to produce electricity that would otherwise have to be pro-duced using fossil fuels) and the total fossil energy use is thereforenegative (these cases are shown in Table 4 ). Oxygen, if used, isassumed to have been produced by the fractional distillation of airin a process that uses electricity.

2.3. Energy use and CO 2 emissions

The term cumulative process energy use refers to the sum of energy use in the two steps of a whole route. Each route consists of feedstock production and petrochemicals production.

Energy use is calculated by subtracting the caloric values of allproducts from the total energy input, which is the sum of the pro-cess energy (e.g. fuels) and the caloric values of the reactants (e.g.biomass); the amount of primary energy use needed to produceco-generated electricity is also deducted, wherever applicable. 6

The term cumulative process CO 2 emission refers to the sum of CO2 emissions from the same two steps. These terms have beenused in Ren et al. (2008) . In this paper, total energy use and total CO 2emissions are used as the main indicators. The term total energy useis the sum of cumulative process energy use and the caloric valueofHVCs. The caloricvalue ofHVCsis assumed tobe losthereas we

gasoline; Patel, 2008 ). This indicates that biomass use for the production of basicpetrochemicals is an attractive option even under the condition that biomass is ascarce resource.

4 In general, the renery processes produce two types of naphtha: light naphtha,heavy naphtha and full range naphtha. In the past, it was often said that heavynaphthawas suitablefor producing gasolinethrough catalyticreforming whilelight

naphthawas suitable for making petrochemicals throughsteam cracking.Full rangenaphtha is the most often used naphtha for petrochemicals production. In recentyears,it is becomingincreasingly common toconvertlightnaphthainto high-octanegasolinethrough isomerization. This type of process is now being used in hundredsof renerysites worldwide. Theenergyuse andrelatedCO 2 emissions of thisprocessare much lower than those of steam cracking (at around 8001000 C).

5 HVCs can also be dened on a mass basis. A sensitivity analysis was conductedto analyze the effect of different HVC denitions on the results of the energy andCO2 emissionsanalysis ( Ren etal.,2008 ). No signicant differences were found. Thisnding is also valid for all of the 24 routes discussed in this paper.

6 In case of an endothermic reaction, we do not include the theoretical energyrequirement (i.e. heat of reaction) in the energy use (following the denition of energy use in this paper). The reasoning behind this approach is that the energyinvested in an endothermic reaction is embedded in the end products and is there-forenotlost (from anenergybalance perspective) during theprocess.Steamcracking(heat of reaction at about 45 GJ/t HVCs) and the conversion of ethanol to ethylene(heat of reaction at about 1.6GJ/t ethylene) discussed in this paper areendothermic

reactions. See further explanations on endothermicity in Ren et al. (2006) .


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Fig. 1. Naphtha-related conventional and alternative routes to basic petrochemicals (solid lines refer to technologies that are already commercialized; dashed lines refer totechnologies that are not yet commercialized).

assume waste incineration of products derived from HVCs withoutenergy recovery. 7

For fossil energy-based routes, the total CO 2 emissions are thesum of cumulative process CO 2 emissions and from the combustionof end products derived from HVCs (i.e. assuming that the carboncontent of the HVCs is released into the atmosphere).

For biomass-based routes, the total CO 2 emissions are the emis-sions from fossil energy use only. The combustion of nal productsmade from biomass-based HVCs does not add CO 2 to the atmo-sphere. The carbon content of HVCs originates from CO 2 existingin the atmosphere and was captured by biomass during plantgrowth. When products derived from HVCs eventually becomewaste and if they are incinerated, the CO 2 emitted will cancel outthe CO 2 captured by biomass earlier. Therefore, the waste incin-eration of biomass-derived products does not lead to net CO 2emissionsunlike the waste incineration of products derived fromfossil energy.

During the production processes of crude oil, natural gas andcoal, a small amount of methane (a greenhouse gas or GHG) isleakedor ared dueto a varietyof factors ( Delucchi,2003 ). The indi-rect GHGemissions given in Delucchi (2003) are inCO 2 equivalentsnot signicant if compared to our results on CO 2 emissions. 8

The production and use of fertilizers required for biomass culti-vation leads to the release of GHG emissions, especially of CO 2 andN2 O. These indirect GHGemissions are also notsignicant andtheyhave a minor effect on the results of the CO 2 emissions analysis. 9

7 There are many methods for waste management, but each method would havenearly the same effect on all of the routes. Therefore, for the purpose of cross com-parison, it is sufcient here to assume a single waste management method.

8 These GHG emissions given in Delucchi (2003) a re less than 2% of the totalCO2 emissions (in terms of t/t HVCs) of crude oil, natural gas and coal-based routesdiscussed in this paper. See our results on CO 2 emissions in Section 4.2.

9 Based on Smeets (2008) and Hamelinck (2004) , we found that these indirectemissionsare not signicant (i.e. less than 0.1 tonCO 2 equivalent per ton HVCs) andthey do not affect the results of the CO 2 emissions analysis (no percentage is given

here because some routes have negative emissions). See the results in Section 4.2 .

3. Route description

Conventional routes and several methane-based routes havealready been discussed before ( Ren et al., 2006 , 2008), so they areonly briey described here. The main focus here is on alternativeroutes that utilize coal and biomass. The schemes of all routes areshown in Fig. 1 (mostly naphtha-related) and Fig. 2 (mostly relatedto methanol or ethanol).

In the following sections, each route will be described in twosteps: the rst step is feedstock production and the second stepis petrochemicals production . In the rst step ( feedstock produc-tion ), naphtha, methanol or ethanol is produced. In the secondstep ( petrochemicals production ), naphtha steam cracking, ethanoldehydration or a methanol-to-olens process is used to producepetrochemicals. Data for the rst steps are shown in Tables 24while data for the second step are shown in Tables 57 .

3.1. Conventional routes

The conventional routes are the basis for comparison with allother routes. Steam cracking of naphtha derived from crude oil asa feedstock is referred to as Oil Naphtha SC . Similarly, Ethane SC is steam cracking of ethane derived from natural gas and catalyticcracking is termed Oil ByproductCC . Details of these routes are givenin Ren et al. (2006) .

In the petrochemicals production step of Oil Byproduct CC, thecatalytic pyrolysis process (CPP) is used. This is currently onlyapplied at a few locations in the world. Oil Byproduct CC is con-sidered a conventional route in this paper because its feedstocks(heavy oils, etc.) are byproducts derived from crude oil, whichis a conventional primary energy source used for petrochemicalsproduction. Also, the design of Oil Byproduct CC is based on theuidized catalytic cracking process (FCC), which is a conventionaltechnology used to produce gasoline and propylene.

3.2. Alternative routes

In contrast to conventional routes, the feedstocks used in alter-

native routes are derived from alternative primary energy sources.


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Table 2Feedstock production in crude oil and natural gas-based routes (the 1st step of a route).

Primary energy source

Crude Oil details can be found in(Ren et al., 2006 )

Natural Gas details can be foundin ( Ren et al., 2008 )

Routes Oil Naphtha SC Waste Naphtha SC Oil Byproduct CC Ethane SC FT Naphtha SC Meth

Feedstock Naphtha Byproducts Ethane Naphtha Metha

Feedstock production Crude oil distillation Hydrogen pyrolysis Separation fromrenery/petrochemical

products

Separation from natural gas Syngas production andFischerTropsch process

Reaction Separation of parafnic

rich C 5 -C11Breaking up of polymers(C2 H4 )n or (C3 H6 )n

Separation of C 4 C9 orheavier than C 10

Separation of C 2 H6 fromothers

CH4 + O2 CO+2H2 O;CH4 + H2 O CO+3H2nCO+2nH2 Cn H2n +nH2 O

Yield of feedstock (wt.) 10% of renery products 45% (35% aromatics andconversion gases; 80%naphtha-value equivalent)

Up to 70% (depending on thechemical composition of thebyproducts)

115% (depending on thechemical composition of thenatural gas)

1530% (81% naphtha-valueequivalent)

Fossil energy use (GJ/tfeedstock); caloricvalue of feedstockexcluded; noelectricityco-generation

3 (Hydrocarbon Processing,2002; Neelis et al., 2006 )

8 (ECN, 2000 ) 3 (Xie and Wang, 2002 ) 2 (Hydrocarbon Processing,2002; Neelis et al., 2006 )

17 (energy use of currenttechnologies is 1020%higher than 17 ( Navqvi,2000 )


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Table 3Feedstock production in coal-based routes (the 1st step of a route).

Primary energy source Coal

Content (wt. excluding minerals/metals) C: 7585% in bituminous, 7080% in sub-bituminous and 6570% in lignite (lignite used for Coal DirectNaphtha SC only); H: 45% in bituminous, sub-bituminous and lignite; O: 510% in bituminous, 1020% insub-bituminous and 20% in lignite; N: 12% in bituminous, sub-bituminous and lignite; S: 110% inbituminous, sub-bituminous and lignite (C: 8090% H: 34% and O: 25% in anthracite; not suitable for CoalDirect Naphtha SC, but suitable for others)

Routes Coal MTO I Coal MTO II Coal MTO CCS Coal DirectNaphtha SC

Coal FTNaphtha SC I

Feedstock Methanol Naphtha

Feedstock production Methanol production(via syngas)

Directliquefaction(no syngasinvolved)

FischerTropsch (viasyngas)

Main reactions (CH 0.8 )O xS yN z isgasied and cleaned;12C6 H5 + 36O 2 72CO+30H 2 ;there are also CO 2 , SO x,NO x, and other lessvaluable byproducts;

CO+2H 2 CH3 OH

Cm Hn OoS pNq isconverted intoCn H2n andother C 4 C22liquids (alsoCO2 , SO x, NO x,

and other lessvaluablebyproducts)

(CH0.8 )O xS yN z isgasied and cleaned;12C6 H5 + 36O 2 72CO +there are also CO 2 , SOx ,NOx , and other lessvaluable byproducts;

CO+2H 2 CH3 OH

Yield of feedstock (wt.) 74% 30% 74% Naphtha 10%(the total yieldof naphtha-valueequivalentproducts is42%)

Naphtha 9%(the total yieldof naphtha-valueequivalentproducts is31%)

Energy use (GJ/t feedstock) beforededucting fossil energy use for electricityproduction (caloric value of feedstockexcluded); all fossil energy

17 70 18 38 30

Electricity co-generated (GJ e /t feedstock) 0 20 0 0 0

Energy use (GJ/t feedstock) after deductingfossil energy use for electricityproduction (caloric value of feedstockexcluded); all fossil energy

17 34 18 38 30

References Larson and Ren (2003) Williams andLarson (2003)

Bechtel (2003) andGray (2005)


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Table 4Feedstock production in biomass-based routes (the 1st step of a route).

Biomass

Routes Ligno FTNaphtha SC I

Ligno FTNaphtha SC II

Ligno MTO Ligno ETE I Ligno ETE II

Feedstocks FT naphtha(Hamelinck, 2004 )

Methanol(Hamelinck,2004 )

Ethanol ( Hamelinck, 2004;Patel et al., 2005; Spath andDayton, 2003 )

Feedstock production FischerTropsch (viasyngas)

Methanolproduction (viasyngas)

Ethanol (C 5 H10 O5 ) production throughhydrolysis and fermentation (nosyngas involved)

Main reactions Lignocelluloses C 6 H10 O5 are gasied; the

products are syngas (a mixture of CO and H 2 )and a small amount of CO 2 , CH4 , and H 2 O.

Lignocelluloses

(C6 H10 O5 )n +nH2 O

n(C6 H12 O6 );glucose/sugar C 6 H12 O6 2C2 H5 OHsugar/starch 3C 5 H10 O5 5C2 H5 OH

nCO+2nH2 Cn H2n +nH2 OCO+2H 2 CH3 OH

Yield of feedstock (wt.) Naphtha 3% (the total yield of naphtha-value equivalent products is1214%)

49% 31% 25%

Energy use GJ/t feedstock before deducting energy use for electricityproduction (caloric value of feedstock excluded)

17 (fossil) 13 (fossil) 6 (fossil) 9 (fossil) 8 (fossil) 8 (f100 (biomass-derived)

124 (biomass-derived)




Electricity co-generated (GJ e /t feedstock) 12 38 0 3 14 3

Energy use GJ/t feedstock after deducting energy use for electricityproduction (caloric value of feedstock excluded)

5 (fossil) 56 (fossil) 6 (fossil) 4 (fossil) 18 (fossil) 100 (biomass-derived)






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Table 5Petrochemicals production in crude oil and natural gas-based routes (the 2nd step of a route).

Primary energy sources

Crude oil, see details in Ren et al. (2006) Natural gas see details in Ren et al. (2008)

Routes Oil Naphtha SC Waste NaphthaSC

Oil ByproductCC

Ethane SC FT Naphtha SC Methane MTO Methane

Petrochemical production Steam cracking Catalyticcracking

Steam cracking Methanoldehydration

Reactions C 5 C11 crackedinto C 2 H4 ,C3 H6 , etc.

C4 C9catalyticallycracked intoC3 H6 , etc.

C2 H6 crackedinto C 2 H4

C5 -C11 crackedinto C 2 H4 ,C3 H6 , etc.

2CH3 OH H3 COCH3 + H2 OH3 COCH3 isdehydrated andthe main

products areC2 H4 and C 3 H6(no C 2 H4 isproducedin thecase of MTP)

Yield (wt.) of HVCs as % of feedstocks

70% 50% 84% 75% 43% 40%

Energy use (GJ/t HVCs); noelectricity co-generationexcept for Methane OCM Iand II; caloric value of HVCsexcluded

6 5 9 6 5 9


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T. Ren, M.K. Patel / Resources, Conservation and Recycling 53 (2009) 513528 521

Fig. 2. Ethane, methanol, and ethanol-related routes to basic petrochemicals (solid lines refer to technologies that are already commercialized; dashed lines refer totechnologies that are not yet commercialized).

Alternative routes can be categorized into naphtha , methanol andethanol -related routes and methane processing by oxidative coupling routes.

3.2.1. Naphtha routes: from methane, plastic waste, coal andbiomass

Allthe naphtha-relatedalternative routesare based on thesamefeedstock (naphtha) and the same petrochemicals production pro-cess (naphtha steam cracking) as the second step (see Fig. 1).However, the rst step in these routes, naphtha production, isbasedon differentprimaryenergy sources,namelymethane,plasticwaste, coal and biomass.

Methane (i.e. 80100% of natural gas found worldwide) can beconvertedinto so-calledFischerTropsch (FT)naphtha throughnat-ural gas-to-liquids (GTL) processes. The ethylene yield from steamcracking of FT naphtha is about 40%, nearly 10% higher than that of oil-derived naphtha ( Dancuar et al., 2003; Shell, 2002 ). However,dueto thelack of aromatics, thetotal yield of HVCs is only 5%higherthan that of OilNaphthaSC. We chose a natural gas-to-liquids(GTL)

process with maximum naphtha yield and high-energy efciencyas the design of the rst process step in the route. The route isreferred to hereinafter as Methane FT Naphtha SC . This route hasbeen applied by Shell in Malaysia and by Mossgas in South Africa.The most recent overviews are presented in Navqvi (2000) andSmith (2004) .

Plastic waste, especiallypolyolens(e.g. the polypropyleneusedin plastic bags), can be converted into naphtha through a seriesof liquefaction, pyrolysis and separation processes. The route ishereafter referred to as Waste Naphtha SC . The technology wasdevelopedby BASF to comply with regulations in Germany,but waslater abandoned ( ECN, 2000; Heyde and Kremer, 1999 ). Itis not yetbeing usedon thecommercial scale.Currently, thedominantmeth-ods for the disposal of plastic waste are landlls, incineration ormaking secondary plastics. The utilization of plastic waste for theproduction of naphtha and petrochemicals is a potential methodfor plastic waste disposal.

Coal can be converted into naphtha via either direct or indi-rect liquefaction ( Bechtel, 2003; Williams andLarson, 2003; Zhang,

Table 6Petrochemicals production in coal-based routes (the 2nd step of a route).

Primary energy sources: Coal

Routes Coal MTO I, Coal MTO II and Coal MTOCCS

Coal Direct Naphtha SC Coal FT Naphtha SC I, CoalFT Naphtha SC II andCoal-ligno FT Naphtha SC

Feedstock Methanol Naphtha FT naphthaPetrochemical production Methanol dehydration Steam cracking

Reactions 2CH 3 OH H3 COCH3 + H2 O; H3 COCH3is dehydrated and the main productsare C 2 H4 and C 3 H6

FischerTropsch liquids(C5 C11 ) are crackedinto C 2 H4 , C3 H6 , etc.

Yield (wt.) of HVCs as % of feedstock 43% ( Ren et al., 2008 ) 55% 75% (Ren et al., 2006 )

Energy use (GJ/t HVCs); no electricity co-generation;caloric value of HVCs excluded

5 (Ren et al., 2008 ) 8 (higher than the 6 in the column onthe right because heavy naphtha isused)

6 (Ren et al., 2006 ) (in thecase of Coal-ligno FTNaphtha SC, 3.6 comesfrom coal and 2.4 comesfrom biomass)


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Table 7Petrochemicals production in biomass-based routes (the 2nd step of a route and a summary of both steps).

Primary energy source: Biomass

Routes Ligno FT Naphtha SC I Ligno FTNaphtha SC II

Ligno MTO Ligno ETE I Ligno ETE II Lig

Feedstock FT naphtha Methanol

Petrochemical production Steam cracking Methanol dehydration Ethanol dehy

Reactions C 5 C11 is cracked intoC2 H4 , C3 H6 , etc.

2CH3 OH H3 COCH3 + H2 O;H3 COCH3 is dehydrated andthe main products are C 2 H4and C

3H

6

C2 H5 OH C2 H4 + H2 O

Yield of HVCs as % of feedstock (wt.) 75% ( Ren et al., 2006 ) 43% (Ren et al., 2008 ) 61% (Patel et al., 2005 )

Energy use in the 2nd step (GJ/t HVCs);electricity use negligible; caloricvalue of HVCs excluded

6 (biomass-derivedenergy) ( Ren etal., 2006 )

5 (fossil energy) ( Ren et al.,2008 )

2 (fossil energy) ( Patelet al., 2005 )

Total fossil energy use in the 1st and2nd steps (GJ/t HVCs); caloric valueof HVCs excluded

6 72 14 8 27 4

Total biomass-derived energy use inthe 1st and 2nd steps (GJ/t HVCs);caloric value of HVCs excluded

137 170 53 51 76 54


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2005 ). Several designs for direct coal liquefaction 10 have been stud-iedin recentdecades. In contrastto FT naphtha (with no aromatics),the naphtha produced by this route is rich in aromatics and there-foreleads to lower HVCsyields thanoil-derived naphtha (estimatedtobe 15%lower than that ofOil NaphthaSC). 11 Thisrouteishereafterreferred to as Coal Direct Naphtha SC and has not yet been appliedon the commercial scale.

Coal can also be converted into FT naphtha via FT processes, orso-called indirect liquefaction. Three designs, Coal FT Naphtha SCI, Coal FT Naphtha SC II and Coal-ligno FT Naphtha SC, have beenselected for the following reasons: in the case of Coal FT Naph-tha SC I, only FT liquids are produced and very little electricity isco-generated ( Gray, 2005 ). In the case of Coal FT Naphtha SC II, arelatively small outputof FT liquids is produced anda large amountof electricity is co-generated ( Bechtel, 2003 ). In the case of Coal-ligno FT Naphtha SC, coal and lignocellulosic biomass (e.g. woodand switchgrass) are used to produce FT liquids and a moderateamount of electricity is co-generated while nearly all the CO 2 iscaptured and used for the purpose of enhanced oil recovery (EOR)(Williams,2005; Williams et al., 2006 ). Coal-ligno FT Naphtha SC ischosen because it has the exibility to use both coal and biomass.None of the three coal-based routes (Coal FT Naphtha SC I, II andCoal-ligno FT Naphtha SC) has been used on the commercial scaleso far.

Similar to methane and coal, biomass can also be converted intoFT naphtha through FT processes. The most recent, comprehen-sive study found so far is Hamelinck (2004) . Among many designscovered in Hamelinck (2004) , one design has maximum output of FT liquids and minimum electricity co-generation and the otherhas maximum electricity co-generation and minimum output of FTliquids. In this paper, the two routes with these two designs arereferred to as Ligno FT Naphtha SC I and II, respectively. These tworoutes have not yet been used on the commercial scale.

3.2.2. Methanol routes: from methane, coal and biomassFive of the six methanol-related routes discussed in this paper

are based on the same petrochemicals production process, theMethanol-To-Olens (MTO) technology developed by UOP PLC(Ren etal., 2008 ). It hasbeen chosen because of itshigh-energyef-ciency and high light-olen yield. The natural gas-based methanolroute (i.e.methanolproduction frommethaneplus MTO) is referredto hereinafter as Methane MTO. Another route, based on Lurgismethanol-to-propylene (MTP), has been chosen for its high propy-lene yield. This is referred to hereinafter as Methane MTP. Sincemethanol production and methanol to HVCs were described indetails in Ren et al. (2008) , we will focus on the rst step of coaland biomass-based methanol routes only, i.e. methanol productionfrom coal and biomass.

Methanol canbe produced from coal viasyngas. Themost recentand the most comprehensive study found so far is Larson andRen (2003) . Among the six designs described in Larson and Ren

(2003) , we chose three designs for methanol production since theycover a wide range of technical specications, such as electricityco-generation, recycling and CO 2 capture. 12 These three routes arereferred to hereinafter as Coal MTO I (with recycling, without CO 2capture and with the smallest net electricity net co-generation),

10 There are two other major direct liquefaction processes. One is the SRC(SolventRened Coal) process, which was developed by Gulf Oil and implemented in pilotplants in the US in the 1960sand 1970s.The other is thelow temperaturecarboniza-tion (LTC) or Karrick process, which was developed in the 1920s. No recent data onthese processes were found.

11 This information was given by Mr. H. van Steen (ABB Lummus, The Hague)through personal communication in 2006.

12 They were chosen for illustration purposes. It is technically possible to add CO 2

capture features to any of the routes mentioned.

Coal MTO II (without recycling, without CO 2 capture and with themost electricity co-generation) and Coal MTO CCS (with recycling,with CO 2 capture and with the greatest net electricity import).These routes are new, but there are plans to use them on the com-mercial scale in China ( Zhang, 2005 ).

Biomass of all kinds can be converted into methanol viaprocesses that are similar to coal-based methanol production.Biomass-based methanol production has been described in detailin Hamelinck (2004) and Patel et al. (2005) . Among the designsdescribed in Hamelinck (2004) , we chose a design with the highestenergyefciency forthis analysis. In this paper, theroute is referredto as Ligno MTO and it has not yet been used on the commercialscale.

3.2.3. Ethanol routes: from biomassAll ethanol related routes use the same petrochemicals pro-

duction process as the second step, where ethanol is convertedinto ethylene through a rather well-known dehydration process(ethanol to ethylene or ETE) ( Patel et al., 2005 ). Their differenceslie in the rst step, feedstock production or ethanol production inthis case. There are three well-known methods to convert biomassinto ethanol:

Direct fermentation of sugar/starch rich biomass (sugar cane,sugar beet or maize starch) to ethanol ( Patel et al., 2005 ). Seereaction formulas in Table 4 .

Hydrolysis of lignocellulosic biomass (e.g. agricultural waste,wheat and wood), followed by fermentation to ethanol. See reac-tion formulas in Table 4 .

Gasication of lignocellulosic biomass, followed by either micro-bial conversion (fermentation) ( BRI, 2005; Coskata, 2008 ) orchemical conversion (with a proprietary catalyst) ( Rangefuels,2008; TSS, 2005 ). The yield of this process is similar to the twomethods mentioned above. Due to lack of data, this process willnot be discussed further in this paper.

Two improved ethanol process designs were chosen for the rstmethod mentioned above (their energy requirements are 56GJ/tethanol lower than the current technologies) ( Patel et al., 2005 ).One utilizes maize starch while another utilizes sugar cane. In thispaper, they arereferredto hereinafter as Maize Starch ETE and Sugar Cane ETE , respectively. Maize Starch ETE does not have electricityco-generation, but Sugar Cane ETE does. The ethanol productiontechnologies applied in these two routes are currently used inmany locations throughout the world. Today, there is no knownethylene production frombiomass-derived ethanol in commercial-scale operation, but this route is currently experiencing acomeback. 13

Three designs were chosen for the second method mentionedabove: one design has the least electricity co-generation, anotherone has the most electricity co-generation and the last one hasthe moderate electricity co-generation ( Hamelinck, 2004; Patel etal., 2005 ). They were chosen because they include the full rangeof technical options regarding electricity co-generation. The threeroutes are referred to hereinafter as Ligno ETE I (with the leastelectricity co-generation), Ligno ETE II (with the most electric-ity co-generation) and Ligno ETE III (with moderate electricityco-generation). The ethanol production technologies based on lig-nocellulosic biomass are still undergoing development and these

13 Sugar cane-based ethanol-to-ethylene plants in Brazil were in operation dur-ing the 1980s, but were shut down in the early 1990s when the oil prices fell. In2007, plans for the construction of three such plants in Brazil (to be in operation in20092011 witha total capacityof 600,000ton of ethylene) were announced( Schut,

2008; Sunopta, 2007 ).


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Fig. 3. Total energy use in various routes to high-value chemicals (HVCs) (both fossil and biomass-derived energy included; error bars representing the result of using aneconomic value-based allocation approach to allocate the total energy use to both electricity and HVCs).

technologies have not yet been used on the commercial scale toproduce ethylene. 14

3.2.4. Oxidative coupling routes: from methaneRatherthan being convertedintoHVCsvia naphtha ormethanol,

methane can also be converted to ethylene through the oxidativecoupling chemistrydescribed in Swanenberg (1998) . Two oxidativecoupling routes, DSM OCM I and II, were analyzed in detail in Renet al. (2008) and they will be compared with other routes in thispaper. They are referred to hereinafter as Methane OCM I and II.These routes have not yet been used on the commercial scale.

4. Energy use, CO 2 emission analysis and land use

Data used in the analysis of energy use and CO 2 emissions forvariousroutes areshown in Tables27 . L ower heating values (LHVs)and emission factors are shown in Table 1 . Data on feedstock pro-duction, or the rst step of each route, are shown in Table 2 (oil andnatural gas), Table 3 (coal) and Table 4 (biomass). Data on petro-chemicals production, or the second step of each route, are shownin Table 5 (oil and natural gas), Table 6 (coal) and Table 7 (biomass).

4.1. Results of energy analysis

The overall results of energy analysis for the routes discussed inthis paper areshown in Fig.3 . Whenthe total energy use (consistingof fossil and biomass-based energy) is compared, the conventionalroutes (basedon crudeoil andethane)are themostenergy efcient.Thetotal energyuseof theconventionalroutes isabout60 GJ/t HVCs(the cumulative process energy use of 10GJ/t HVCs plus the caloricvalue of HVCs about 50 GJ/t HVCs). The total energy use for WasteNaphtha SC is relatively high due to the use of hydrogen.

14 There arecurrentlyseveralpilot plantsin operation anda numberof plans fortheconstruction of commercial-scale lignocellulosic ethanol plants (above 10 million

gallons ethanol per year) have been announced ( Sunopta, 2007 ).

The total energy use of methane-based routes is about 80 GJ/tHVCs. This is about 30% more than those of conventional routes.This is in contrast to the case of the current electricity productionbased on various primary energy sources where power plants redby natural gas (mostly methane) are the most energy efcient.

Fig. 3 shows that the total energy use of coal and biomass-based routes is roughly 60150% higher than that of conventionalroutes. The totalenergyuse (consisting of fossil and biomass-basedenergy) of most of coal and biomass-based routes is in the range of

90130 GJ/t HVCs.The cumulative process energy use of most coal and biomass-

based routescan even be 48timesas much as that of conventionalroutes. In particular, the cumulative process energy use of thoseroutes with large amountof electricity co-generation (i.e. Coal MTOII, Coal FT Naphtha SC II, Ligno FT Naphtha SC I and II) is 913 timesas much as that of conventional routes. The routes with the highesttotal and cumulative process energy use are Ligno FT Naphtha SC IandII. Their totalenergy uses are high: about180and 150GJ/tHVCs,respectively. This is primarily due to the low yields of FT naphthaproduction in thesetwo routes (12 and14%, respectively), whicharemuch less than the yields of feedstock production in other routes.The yields of feedstock production in those routes are shown inTables 4 and 7 .

Fig. 3 shows that the CO 2 separation unit of Coal MTO CCS doesnot lead to substantially higher energy use than other two coal-based methanol routes. About 6% of the total coal input in primaryenergy terms is used in recycling and CO 2 capture (in the case of Coal MTO CCS) (Larson and Ren, 2003 ). The energy impact of CO 2separation is limited because the concentrationandpressureof CO 2are high after gasication. Electricity use for drying and compress-ing CO2 is about 0.4 GJ e /t CO2 . The total electricity consumptionin Coal MTO CCS is 3.2GJ e /t methanol (2.7 GJ e is co-generated and0.5GJe is imported).

4.2. Results of CO 2 emissions analysis

Fig. 4 shows the total CO 2 emissions (cradle-to-grave) of all

routes. For biomass-based routes, the carbon content of the HVCs


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Fig. 4. Total CO 2 emissions (cradle-to-grave) in various routes for production of high-value chemicals (HVCs) (including the CO 2 emissions from feedstock production andpetrochemicals production as well as the carbon content of HVCs; dotted barsrepresent the fossil carbon physically embodied in HVCs; the carbon content of HVCsproducedthrough biomass-based routes is zero since it originates from the atmosphere).

originates from the atmosphere (carbon captured by biomass fromthe air during plant growth) and is then sequestered in HVCs. If theproducts derived from HVCs (e.g. polyethylene plastic bags) areincinerated in the context of post-consumer waste management,the carbon content of the HVCs is released to the atmosphereand nally cancels out the carbon that was originally captured bybiomass.

Fig. 4 shows that CO 2 emissions from feedstock production due

to the combustion of fossil fuels in several biomass-based routesare negative. This is because the CO 2 emissions avoided by electric-ity co-generation are larger than the CO 2 emissions due to the useof fossil energy. As stated earlier, electricity is always assumed tohave been produced by a natural gas-red power plant and elec-tricity co-generation leads to CO 2 emissions being avoided. Notall biomass-based routes have electricity co-generation. The more

electricity a biomass-based route co-generates,the moreavoidanceof CO2 emissions it leads to. As Fig. 4 indicates, the biomass-basedroute with the most electricity co-generation, Ligno FT Naphtha SCII, avoids the most CO 2 emissions.

The totalCO 2 emissions of conventional routes are slightly morethan 4 tons CO 2 /t HVCs. The total CO 2 emissions of methane-basedroutes are about 10% more than those of conventional routes ( Renet al., 2008 ). CO2 emissions of the coal-based routes are the highest

(811 tons CO 2 /t HVCs) with an exception of Coal MTO CCS (withCO2 capture and sequestration features), for which total CO 2 emis-sion is nearly the same as that of the conventional routes. It is tech-nically possibleto equipanyroute mentionedin this paperwith CO 2capture/sequestration features to achieve very low CO 2 emissions.

Table 2 and Fig. 3 show that the energy use in feedstock (naph-tha) production of Methane FT Naphtha SC is 17 GJ/t naphtha,which

Fig. 5. Landuse for growingvarious typeof biomassfor biomass-basedroutesto high-value chemicals(HVCs)(the default is large round dots; the distance betweentwo largeround dots for each route represents a possible range of land use if the total energy use is allocated to HVCs only; the distance between the ends of the error bars represents

a possible range of land use if an economic value-based allocation approach is used to allocate the total energy use to both electricity and HVCs).


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is nearly 6 times that of Oil Naphtha SC (3 GJ/t naphtha). However,Fig. 4 shows that CO 2 emissions for naphtha production from theformer are only slightly higher than for the latter. In the case of naphtha production using Methane FT Naphtha SC, only 6 out of 17 GJ/t naphtha is supplied by the combustion of methane and therest (11 GJ/t naphtha) is supplied by partial oxidation of methane.Partial oxidation of methane leads to the formation of water andhydrocarbon liquids, but not CO 2 (see Table 2 f or reaction equa-tions). In the case of naphtha production by Oil Naphtha SC, 3 GJ/tnaphtha is supplied by the combustion of renery gas. Becausethe emission factor of methane is lower than that of renery gas,the CO 2 emissions from the naphtha production step in these tworoutes are similar.

4.3. Land use analysis

Basedon the yields of feedstock per ton of biomass (see Table 4 )and the yields of HVCs per ton of feedstocks (see Table 7 ), theyield of HVCs per ton of biomass can be calculated. The reasonableranges of biomassyieldin terms of tons/hectare/year in themediumterm (now2030) and the long term (20302050) are expected tobe 620 (lignocellulosic), 15 79 (maize) and 2027 (sugar cane)(Hamelinck, 2004; Hoogwijk, 2004; Smeets et al., 2007 ). Usingthese data, a gure can be calculated for the land use per ton of HVCs for each of the biomass-based routes (see large round dots inFig. 5). With the exception of Ligno FT Naphtha SC I/II andLigno ETEII, all other routes use less than one hectare to produce one ton of HVCs.

The values represented by large round dots in Fig. 5 are not fullycomparable. In Fig. 5, only the yield of HVCs per ton of biomasshas been considered (i.e. all biomass use is allocated to HVCs)while several routes (i.e. Ligno FT Naphtha SC I/II and Ligno ETEII) co-generate large amounts of electricity. This is the reason whythe land use for Ligno FT Naphtha SC I/II and Ligno ETE II can begreater than one hectare per ton of HVCs. It is possible to allocatebiomass use to both HVCs and electricity through the use of aneconomic value-based approach. The results will be discussed inSection 5.

5. Discussion

The data on individual routes can be affected by various uncer-tainties to a limited extent, as indicated in the sources cited for thisanalysis.However, whether alone or combined, these uncertaintiesdo notchange theoverallresults in Section 4 (e.g. Figs.3and4 showthe signicant differences between the feedstock production stepsof conventional and alternative routes). The only signicant uncer-tainty introduced by ourselves is the assumed energy efciency inelectricity co-generation, 55%. In this section, we will discuss analternative method for treating electricity in energy allocation.

The results presented in Section 4 were calculated by applyinga credit approach in those cases where electricity co-generation isinvolved. This poses two problems.

First, in the cases where the credit approach based on a physi-cal property (i.e. the primary energy use in electricity production)is used, we also used the allocation approach, which is based oneconomic values used for dening naphtha value-equivalent feed-stocks and olen value-equivalent HVCs. In fact, we have used acombined credit/allocation approach as the main approach in Sec-

15 The yield of lignocellulosic biomass has a wide range since it can be grown onpoorland andcan alsocome fromagricultural wastesor forests(forestland is gener-ally unt for agricultural purposes). A yield of 20 ton/ha/year is only possible underfavorable conditions regarding fertilization effects, technological improvement, cli-

mate and soil quality ( Hoogwijk, 2004 ; Smeets et al., 2007).

tion 4. The combination of one physical property-based approachand another economic value-based approach could therefore raisequestions about consistency and should be discussed further.

Secondly, while using the credit approach, we have assumed adefault energy efciency of 55% for the use of natural gas for elec-tricity production. However, as discussed in the last section, 55%is not valid as the energy efciency for electricity production fromcoal or biomass, which is generally known to be lower than thatof electricity production from natural gas. Tests using values of 40and 60% against the default energy efciency of 55% for those coaland biomass-based routes with electricity co-generation indicatedthat the total energy use in these routes is quite sensitive to theenergy efciency assumed for electricity co-generation. The testresults nevertheless do not change our earlier nding that coal andbiomass-basedroutesuse muchmore energythan the conventionalroutes.

One way to tackle the two problems described above is toapply only the economic value-based allocation approach for allroutes for allocating the total energy use to both the productionof HVCs and electricity generation (therefore not using the creditapproach at all). This requires the values of HVCs and electricity tobe expressed in common units. The unit cannot be $/ton (whichwould be meaningless for electricity), so $/GJ ($/GJ e for electricity)is a more suitable common unit for expressing the values.

The global market prices of HVCs in the past ten years wereroughly in the range of $500/t to $800/t (largely following crude oilprices) ( CMAI, 2006; EIA, 2008; Pettman,2002 ), whichare $10/GJto$16/GJ if expressedin terms of $ perGJ of caloric value.In thesameperiod, the wholesale prices of electricity in major industrial coun-tries were roughly in the range of $0.03/kWh to $0.05/kWh (largelydetermined by coal and gas prices) ( EIA, 2008; IEA, 2004b, 2005 ),which are $8/GJ e to $14/GJ e if expressed in $/GJ e . Based on thesehistorical data, HVCs and electricity can be considered to have thesame economic value in terms of $/GJ. As a thought experiment, wecan simply treat electricity in the same way as HVCs. We can there-fore conduct an allocation approach based on the caloric contentof HVCs and of the co-generated power.

The result of applying the economic value-based allocationapproach is represented by the error bars in Fig. 3. Applying theeconomic value-based allocation approach leads to a clear conver-gence of energy use among these routes. As the error bars in Fig. 3show,the totalenergyuse of methane-based routes is about 80GJ/tHVCs and that of most biomass and coal-based routes is now inthe range of 90130 GJ/t HVCs ( note : Ligno FT Naphth SC I is anexception).

The economic value-based allocation approach mentionedabove can also be used to correct the land use for those biomass-based routes that co-generate large amount of electricity (seeSection 4.3 and Fig. 5). When the economic value-based alloca-tion approach is used, co-generated electricity is converted to tonsof HVCs equivalent since their values in $/GJ are the same (as

explained above). The error bars in Fig. 5 represent the result of applying the economic value-based allocation approach. The rangeof land use has been narrowed to an extent that means almost allbiomass-routes (except for Ligno FT Naphtha SC I) use a similarrange of areas (less than one hectare) to produce one ton of HVCs.

The biomass input differs substantially across the biomass-based routes studied, with Ligno FT Naphtha II requiring mostbiomass (e.g. 5 times more than Ligno MTO). One can argue thata fair comparative analysis should assume identical biomass inputacross all biomass-based routes. Excess biomass i.e. the differencebetween thebiomass input of theroute using themost biomass (i.e.Ligno FT Naphtha II) and that of the route studied can be assumedto be co-combusted in a coal co-red power plant with an energyefciency of 40%. The electricity generated in the co-red power

plant can be assumed to replace electricity that would otherwise


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