Applied Energy 86 (2009) S189–S196

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Applied Energy

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Life cycle assessment of palm biodiesel: Revealing factsand benefits for sustainability

Kian Fei Yee, Kok Tat Tan, Ahmad Zuhairi Abdullah, Keat Teong Lee *

School of Chemical Engineering, Universiti Sains Malaysia, Engineering Campus, Seri Ampangan, 14300 Nibong Tebal, Pulau Pinang, Malaysia

a r t i c l e i n f o a b s t r a c t

Article history:Received 15 January 2009Received in revised form 19 April 2009Accepted 19 April 2009Available online 22 May 2009

This article is sponsored by the AsianDevelopment Bank as part of theSupplement ‘‘Biofuels in Asia’’.

Keywords:BiodieselTransesterificationLife cycle assessmentEnergy balanceGreen house gas

0306-2619/$ - see front matter � 2009 Elsevier Ltd. Adoi:10.1016/j.apenergy.2009.04.014

* Corresponding author. Tel.: +60 4 5996467; fax: +E-mail address: chktlee@eng.usm.my (K.T. Lee).

Similarity between the properties of biodiesel and petroleum-derived diesel has made the former one ofthe most promising alternatives to a renewable and sustainable fuel for the transportation sector. InMalaysia, palm oil can be a suitable feedstock for the production of biodiesel due to its abundant avail-ability and low production cost. However, not many assessments have been carried out regarding theimpacts of palm biodiesel on the environment. Hence, in this study, life cycle assessment (LCA) was con-ducted for palm biodiesel in order to investigate and validate the popular belief that palm biodiesel is agreen and sustainable fuel. The LCA study was divided into three main stages, namely agricultural activ-ities, oil milling and transesterification process for the production of biodiesel. For each stage, the energybalance and green house gas assessments were presented and discussed. These are important data for thetechno-economical and environmental feasibility evaluation of palm biodiesel. The results obtained forpalm biodiesel were then compared with rapeseed biodiesel. From this study, it was found that the uti-lization of palm biodiesel would generate an energy yield ratio of 3.53 (output energy/input energy), indi-cating a net positive energy generated and ensuring its sustainability. The energy ratio for palm biodieselwas found to be more than double that of rapeseed biodiesel which was estimated to be only 1.44,thereby indicating that palm oil would be a more sustainable feedstock for biodiesel production as com-pared to rapeseed oil. Moreover, combustion of palm biodiesel was found to be more environment-friendly than petroleum-derived-diesel as a significant 38% reduction of CO2 emission can be achievedper liter combusted.

� 2009 Elsevier Ltd. All rights reserved.

1. Introduction

The escalating prices of petroleum in the world market, coupledwith the diminishing supply of non-renewable fossil fuels, haveraised concerns for a need for renewable energy sources as substi-tutes for fossil fuels. Also, as already commonly know, the utiliza-tion of fossil fuels triggers a substantial amount of green house gas(GHG) emissions, which subsequently pollute the environment.Hence, the quest for a renewable and environment-friendly sourceof energy has become inevitable for a sustainable future.

One of the alternatives to renewable energy that has been get-ting a lot of attention lately is biodiesel, which exhibits similarproperties as petroleum-derived diesel. Currently, biodiesel is pro-duced from edible and non-edible oils such as palm, sunflower andjatropha. These are inexhaustible sources of triglycerides, whichare essential elements in the transesterification process for biodie-sel production. Comparatively, biodiesel has several advantagesthan conventional diesel in terms of GHG emission and availability.Biodiesel, if widely adopted, could significantly reduce emissions

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from the road transportation sector. An in-vehicle performance ofbiodiesel and their potential carbon savings has been comparedand evaluated with conventional fuels. It was reported that theusage of biodiesel can reduce carbon emissions and also help in-crease energy security [1,2]. Moreover, local biodiesel productioncan significantly reduce dependence on foreign imports of dieselfuel, and increase the utilization of renewable energy sources suchas palm oil. Malaysia, as one of the world’s largest producers andexporters of palm oil and its products, has a great potential ofbecoming a major producer of palm biodiesel [3].

Palm biodiesel can be produced from palm oil via transesterifi-cation process between crude palm oil and alcohol with the pres-ence of an acidic or alkaline catalyst. Palm oil has the potentialto fulfill the high demand for biodiesel in the world market dueto its superior annual yield per hectare as compared to other oil-seeds. For instance, as shown in Table 1, the average annual yieldof palm oil is 3.68 tons/ha, while for other major oil crops suchas soybean and rapeseed, the yields are significantly lower at0.36 and 0.59 tons/ha, respectively [4]. Hence, it is not surprisingto note that about one-third of the global oil production comesfrom palm oil, although areas allocated for palm plantation aresmall compared to the plantation areas of other oil crops (Table

Nomenclature

CO2 carbon dioxideCPO crude palm oilCRO crude rapeseed oilEFB empty fruit bunchesEIA environmental impact assessmentFFB fresh fruit bunches

GHGs green house gasesIPM integrated pest managementLCA life cycle assessmentO2 oxygenPOME palm oil mill effluent

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1). In addition, biodiesel produced from palm oil is more environ-ment-friendly compared to petroleum-derived diesel in terms ofcarbon emission, since the carbon released during combustion pro-cess were those absorbed from the atmosphere by the crops.

Given the advantages of palm biodiesel as compared to non-renewable sources, it has been hailed as the solution for an afford-able and renewable source of energy in the future. However, thereare some negative claims regarding the sustainability of palm oil asa source of biofuel. Generally, it was reported that such large-scaleutilization of palm oil as biofuel would cause deforestation, whichin turn would lead to possible loss of one of the world’s largest nat-ural carbon sink, subsequently smearing the image of palm oil asan ideal source of renewable energy [5]. Hence, a systematic ap-proach to investigate all upstream and downstream processes orcradle-to-grave analysis of palm biodiesel is important to validatethe benefits or ‘cleanliness’ of this so-called ‘green energy’. One ofthe methods that can be used to assess the environmental meritsand demerits of a product is the life cycle assessment (LCA), whichentails a complete evaluation and analysis of a product throughoutits lifespan [6–8]. For instance, GHG emission and net energyrequirement in palm biodiesel production will be systematicallyquantified and compiled for every stage involved from the oil palmplantation stage up to the combustion process of palm biodiesel toaddress the tenacious issues on sustainability, climate change andglobal biodiversity [9].

In this LCA study, the aim is to compile an inventory of energyinput and output involved in the production of biodiesel from palmoil. An assessment of the GHG emission is also carried out to eval-uate the potential and benefits of palm biodiesel as a green andrenewable source of energy. Hence, a comprehensive investigationon the effect of utilizing palm biodiesel on the environment can becarried out scientifically, which is crucial in validating the advanta-ges of palm biodiesel compared to petroleum-derived diesel. Apartfrom that, assessment of energy balance and GHG emissions for ra-peseed oil are carried out using a similar approach in order to makea valid comparison with palm oil.

2. Methodology

2.1. Goal and scope definition

In this study, the methodology developed is based on LCA pro-cedures. The main goal of this study is to assess the energy balance

Table 1Oil productivity of major oil crops [4].

Oil crop Oil production (million tons) Total production (%) Ave

Soybean 33.58 31.69 0.36Sunflower 9.66 9.12 0.42Rapeseed 16.21 15.30 0.59Palm oil 33.73 31.84 3.68Others 12.76 12.04 –

Total 105.94 100 –

and GHG emission associated with the production of biodieselfrom palm oil in Malaysia. The scope of the system used in thisstudy comprises from the oil palm (Elaeis guineensis) plantationstage until the combustion of biodiesel in diesel engines. The en-ergy consumption in each stage is studied along with the life cycleof biodiesel. Energy consumption is defined as the sum of energyconsumed for each ton of biodiesel produced in every stage ofthe production path. The study also conducted a GHG assessmentto calculate the annual carbon dioxide (CO2) assimilation or emis-sion for each ton of biodiesel produced. For comparison purposes,the energy balance assessment and GHG assessment for rapeseedoil were also undertaken using a similar approach. Throughoutthe study, the functional unit used for energy and GHG evaluationis in GigaJoule (GJ)/ton crude palm oil (tCPO)/year and ton CO2/tonbiodiesel/year, respectively. The calculations were done using en-ergy coefficients reported in the literature. Energy coefficientsbasically give the energy content in a compound or the quantityof energy required to produce per unit of energy.

2.2. System boundary

The life cycle of palm biodiesel production is divided into threestages. The first stage is the plantation (agricultural) stage, fol-lowed by the palm oil milling stage, and finally the transesterifica-tion process of palm biodiesel production. The system boundaryused in this study is shown in Fig. 1. In the agricultural (plantation)stage, several processes are involved in the production of fresh fruitbunches (FFB) [10]. The processes include planning, nursery estab-lishment, site preparation, field establishment, field maintenance,harvesting and collection and replanting.

In the planning phase, feasibility studies and Environment Im-pact Assessment (EIA) are required for the development of newplantations exceeding 500 ha on a primary/secondary forest orinvolving a change in the type of plantation. If the land is foundto be suitable and its use is approved by relevant agencies, thenursery phase can then be established. Good quality seeds aresown in small poly bags where the seedlings will be cultivated un-til they are 3–4 months old. After that, the seedlings are transferredto and cultivated in large poly bags until they are 12–13 monthsold, when they are considered ready to be shifted to the planta-tions [11].

Next step is the preparation of the plantation which includesactivities like land survey, clearing of existing vegetation, estab-lishment of road and field drainage systems, soil conservation

rage oil yield (tons/ha/year) Planted area (million ha) Total area (%)

92.10 42.2422.90 10.5027.30 12.52

9.17 4.2166.55 30.52

218.02 100

Palm Kernel

Reactants

Fresh Fruit Bunch (FFB)

Crude Palm Oil (CPO)

Palm Oil Seedlings

Fiber & ShellsEmpty Fruit Bunches (EFB)Palm Oil Mill Effluent (POME)

Agricultural

Milling

Fertilizers

TransesterificationEnergy

Glycerol

Energy

Energy

Traction

Traction

Biodiesel

Fig. 1. System boundaries for the production of biodiesel from palm oil.

Table 2Inputs and outputs of the various stages involved in palm biodiesel production.

Stage Input Output

Agricultural Palm oil seed Fresh fruit bunches (FFB)

Palm oil mill Fresh fruit bunches (FFB) Crude palm oil (CPO)Palm kernelFiber and shellsEmpty fruit bunches (EFB)Palm oil mill effluent (POME)

Transesterification Crude palm oil (CPO) BiodieselMethanol GlycerolSodium hydroxide

Table 3Malaysia’s oil palm industry annual production at the end of 2007.

Material Production (ton)

Fresh fruit bunches (FFB) [14] 81,793,366Crude palm oil (CPO) [14] 15,823,368CPO for biofuel production [15] 128,193

Table 4Energy coefficient for various compounds.

Energy coefficient Energy

Steam [18] 1360 MJ/ton biodieselElectricity (transesterification) 0.0029 MJ/MJ biodieselCrude palm oil 1.0065 MJ/MJ biodieselMethanol 0.0585 kg/MJ biodieselSodium hydroxide 0.00018 kg/MJ biodieselGlycerol 0.0028 kg/MJ biodiesel

Fertilizers [25]Nitrogen (N) 48.9 MJ/kgPhosphorus (P2O5) 17.43 MJ/kgPotassium (K2O) 10.38 MJ/kg

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measures such as terracing, conservation bunds and silt pits andsowing of leguminous cover crops [10]. Subsequently, field estab-lishment activities will be carried out such as lining, holing andplanting of poly bag seedlings at a density of 136–148 bags perhectare, depending on the soil type. In addition, leguminous covercrops such as Pueraria javanica and Calopogonium caeruleum areplanted to obtain full ground coverage to minimize soil lossthrough runoff and also to improve the soil properties throughnitrogen fixation.

Throughout the maturing period, the plantation area is main-tained by field maintenance operations such as the integrated pestmanagement (IPM). Under the IPM, instead of using chemical pes-ticides which is harmful to our environment, natural pest control isadopted to control pest population in oil palm plantation. Harvest-ing and collection of FFB are undertaken up until 24–30 years afterfield planting, depending on the soil type and the managementpractices employed. The average lifespan of oil palm trees is 26years, and throughout this period, the trees can continuously pro-duce FFB [11]. At the end of its lifespan, replanting process willcommence, whereby oil palm trunks are shredded and placed backin the field as mulch given that zero-burning practice has beenlegalized in Malaysia since 1989 [12]. However, in some situations,new seedlings are planted under the old palm trees which will bethinned out progressively to allow the development of the newstand [10].

FFB harvested from the oil palm tree will be processed immedi-ately to prevent a rapid rise in free fatty acids (FFA) which couldadversely affect the quality of crude palm oil (CPO) [10]. Generally,palm oil mills are located near the plantations to facilitate timelytransportation and effective processing of FFB. Processing in palmoil mill involves four major unit operations, namely: sterilization;threshing and stripping of fruits; digestion; and oil extraction [13].

Initially, FFB is sterilized by live steam under a pressure of 26.4–31.6 tons per square meter for 50–75 min to deactivate enzymeswhich are responsible for the breakdown of oil to FFA. The sterili-zation process also helps loosen the fruits from their bunches sothat the oil can be extracted easily. The sterilized fresh fruitbunches (FFB) are then fed continuously into a rotary drum ma-chine in order to strip and separate the fruits from the bunch.The fruits will pass along channel bars running longitudinallyalong the drum, while the empty bunches are eventually dis-charged at the end of the drum for incineration. After stripping,the fruits are fed continuously into a digester which converts the

fruits into a homogeneous oil mash suitable for pressing. Finally,during the oil extraction phase, the digested mashes are pressedunder pressure, either hydraulically or mechanically, to extractthe crude palm oil (CPO).

Subsequently, CPO, the major product from the palm oil mill, istransported to a biodiesel plant as feedstock for biodiesel produc-tion. Biodiesel is conventionally produced via transesterificationreaction with methanol in a batch type reactor in the presence ofalkaline sodium hydroxide, which acts as the homogeneous cata-lyst. After the transesterification process, the mixture is kept over-night and allowed to separate by gravity, whereby two layers areformed. Methyl esters, a light yellow liquid, forms at the top layerwhereas, glycerol, a dark brown liquid, forms at the bottom layer.Alternatively, if the mixture is not kept overnight, the methyl es-ters can be separated from the glycerol by washing the mixturewith water and acetic acid until the washing water becomes neu-tral. Palm biodiesel is the main product from this transesterifica-tion process, while glycerol is the by-product which can be usedto produce soap or other materials.

2.3. Life cycle inventory

This inventory consists of all recognized inputs and outputs toor from the system boundary. Table 2 shows the inputs and out-puts of the various stages involved in palm biodiesel production.Table 3 shows the annual production of products from the Malay-sia oil palm industry at the end of 2007 [14,15]. The agriculturalstage produces 19.0 tons of FFB for each hectare of plantation land

Table 5Calorific value of products and fuel used for this study.

Item Energy

Biodiesel [19] 39,600 MJ/tonSodium hydroxide [43] 26,230 MJ/tonGlycerol [19] 18,050 MJ/tonFibers and shell [20] 19.89 GJ/tonDiesel [21] 40.3 MJ/lSteam 2604 MJ/tonStraw (biomass) 13,500 MJ/tonSteam 1586 MJ/ton rapeseed fruitHexane 44.75 MJ/kgElectricity 419 MJ/ton rapeseed fruitMethanol [44] 13.23 MJ/l methanol

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utilized [16]. On the other hand, there are several products and co-products that are produced from the palm oil mill. The main prod-uct is CPO, estimated yield of which is 0.20 ton for each ton of FFBprocessed. The co-products are fibers and shells, empty fruitbunches (EFB), and palm oil mill effluent (POME) which yields190 kg, 230 kg and 600–700 kg/ton of FFB, respectively [17]. Forthe transesterification process, the conversion of CPO to biodieselis at 99% efficiency, thus the annual production of palm biodieselis calculated at 126,888 tons or 0.99 ton biodiesel for each ton ofCPO feedstock. The energy coefficient of fuel utilized [18] and thecalorific value of products [19–21] are shown in Tables 4 and 5respectively.

3. Results and discussion

3.1. Energy balance assessment

The energy produced (output/ton biodiesel) to the energy con-sumed (input/ton biodiesel) for each unit of product in the produc-tion of palm biodiesel can be used as an index of techno-economicand environmental feasibility analysis. The energy balance assess-ment begins from the early stages of oil palm plantation to thecombustion of palm biodiesel in diesel engines of vehicles. The en-ergy flows during the life cycle of palm biodiesel are of two types,i.e., direct and indirect energy. A direct energy flow is the energyconsumed in the form of fossil fuel, steam and electricity, whilean indirect energy flow is the energy involved in transportationpurposes.

In the agricultural stage, both traction and transportation of fer-tilizers and pesticides involve the utilization of fossil fuel. For sim-plification reason, all fossil fuels used in oil palm plantations areregarded as petroleum-derived diesel. The activities of transferringFFB from oil palm plantations to palm oil mills and subsequentlythe removal of EFB from the palm oil mills to oil palm plantationsare carried out by tractors, which are the main mode of transpor-tation. Currently, EFB is used mainly as mulch in oil palm planta-tion to control weeds, prevent erosion, and maintain soilmoisture [22]. In 2007, the total oil palm plantation area in Malay-sia reached 4,304,914 ha, and the energy consumed by tractionwas estimated at 2368 MJ per hectare [23]. Hence, the annual en-ergy consumed by traction is 644.24 MJ/ton CPO.

Oil palm trees require several types of nutrients in the form offertilizers to achieve significant growth rates [24]. Nutrients suchas nitrogen (N), phosphorus (P2O5) and potassium (K2O) are usu-ally added as fertilizers, and the average usage of these nutrientsare 76 kg N/ha, 86 kg P2O5/ha, and 119 kg K2O/ha, respectively[24]. In addition, the energy content for each of these nutrients[25] are shown in Table 4. The annual total energy utilized for fer-tilizers is approximately 1.76 GJ/ton CPO. However, due to lack ofdata on electricity usage in administration, research, laboratoryand nursery buildings related to oil palm cultivation, the utilization

of electricity in overhead agricultural stage is assumed to be 1 MJ/ton of FFB harvested. Hence, this translates to 22.8 million kWh ofelectricity annually or 5.17 MJ energy/ton CPO/year.

In the palm oil mill stage, significant amounts of steam andelectricity are needed for the processes to obtain the desiredCPO. Normally, biomass is used for heat and/or power productionthrough direct combustion [26]. Hence, fibers and shells obtainedas by-products are incinerated to generate steam and subsequentlyused as a source of electricity for palm oil mills. Hence, palm oilmills are self-sufficient in terms of electricity consumption [27].Assuming that 80% of the total fibers and shells (0.79 ton/tonCPO) are fed into boilers, a massive 15.7 GJ/ton CPO of energycan be generated from the biomass per year (3023 MJ/ton FFB).On the other hand, the excess fibers and shells (20%) can be soldas fuel, with total energy content of approximately 3.9 GJ/tonCPO annually.

From the amount of energy generated from the fibers and shell,about 55.0–76.6% is being utilized in the milling processes in theforms of heat (steam) and power (electricity). These values wereobtained based on the data reported by seven selected palm oilmills in Perak State [28]. In this study, using an average value of65.6% would generate an equivalent energy consumption by thepalm oil mill of 10.3 GJ/ton CPO. The other 34.4% of the total energygenerated from the biomass per year (5.4 GJ/ton CPO) is consideredas energy output which is not being utilized in the palm oil mill. Inorder to process 1 ton of FFB, 0.73 ton of steam is required [17].Based on the calorific value of steam shown in Table 5, about9.83 GJ/ton CPO of steam is required. The distribution of the totalheat and power production is assumed at 9.99 GJ of steam/tonCPO and 0.31 GJ of electricity/ton CPO, respectively. From the9.99 GJ/ton CPO of steam produced, only 9.83 GJ/ton CPO of steamis required in the processes, where about 1.6% of steam energy isassumed to be lost to the atmosphere.

The required electricity for processing 1 ton of FFB is 52.2 MJ[29]. Thus, annually 0.27 GJ/ton CPO electricity is being utilizedin the process of producing CPO. Since the electricity generated isestimated at 0.31 GJ/ton CPO, about 13% excess electricity is as-sumed to be used locally in administrative and residence buildingsfor the workers. Apart from that, the utilization of diesel fuel in thepalm oil mill cannot be neglected. As far as start-up of boilers isconcerned, about 0.37 l of diesel is utilized per ton of FFB [30]. Inaddition, from the average value reported by the six selected palmoil mills in Malaysia, vehicles consumed roughly 7.6 MJ/ton FFB.

For the transesterification process, both steam and electricityare the main sources of energy utilized in palm biodiesel produc-tion. It was reported that a total of 1360 MJ of steam is neededfor the production of 1 ton of palm biodiesel, while 0.0029 MJ elec-tricity is consumed for each MJ biodiesel produced [18]. Based onthe total amount of CPO produced in the year 2007, 0.81% was usedfor biofuel production which is approximately 128,169 tons of CPO[15]. Based on the literature, conversion of CPO to biodiesel is 99%,which is equivalent to 126,888 tons palm biodiesel. The electricityneeded for 1 ton of palm biodiesel produced is about 31.9 kWh.The energy coefficients of the reactants are listed in Table 4. Theannual energy content of reactants such as CPO, methanol, and so-dium hydroxide catalyst are 319.62 MJ/ton CPO, 18.58 MJ/ton CPO,and 1.50 MJ/ton CPO, respectively. Thus, total energy utilized in thetransesterification stage is 1.80 GJ/ton CPO on a yearly basis.

Apart from the three stages (agricultural, palm oil mill, transe-sterification) that contributed to the total amount of energy inputin biodiesel production, the primary energy which is required toproduce raw materials and subsequently utilized in the processcannot be neglected as well. Table 6 shows the primary energy re-quired to produce fertilizers, petroleum diesel, methanol and so-dium hydroxide. By considering the amount of these inputmaterials and the energy contents, the total energy required for

Table 6Primary energy required for the production of input materials.

Input material Primary energy

Petroleum diesel [45] 1.20 MJ/MJ petroleum dieselMethanol [46] 25.77 MJ/l methanolSodium hydroxide [47] 33.13 MJ/kg NaOH

Fertilizers [48]Nitrogen (N) 69.53 MJ/kg NPhosphorus (P2O5) 7.70 MJ/kg P2O5

Potassium (K2O) 6.40 MJ/kg K2O

Table 8Summary of energy content in palm biodiesel, glycerol and biomass.

Product Quantity (energy/ton CPO/year)

Biodiesel 39,204.00 MJGlycerol 1981.38 MJFibers and shells (heat generated) 19,534.74 MJTotal 60.72 GJ

Table 9Plantation area and annual production of rapeseed oil in European Union (EU).

Material Production

Rapeseed fruit [49] 4.11 ton/ha/yearStraw (biomass) [50] 2.93 ton/haRapeseed oil [4] 16,210,000 ton/yearCRO for biofuel production [51] 10,050,200 ton/yearBiodiesel production 9,949,698 ton/yearPlantation area [4] 27,300,000 ha

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the production of these input materials is 2.78 GJ/ton CPO on anannual basis. Table 7 summarizes the annual energy utilizationin the production of palm biodiesel from the agricultural stage un-til the transesterification process, with total energy utilized calcu-lated at about 17.19 GJ/ton CPO.

On the other hand, the energy released from the combustion ofpalm biodiesel is 39,600 MJ/ton. As mentioned previously,126,888 tons of palm biodiesel are produced, thus the total annualenergy released from the combustion of palm biodiesel is about39.2 GJ/ton CPO. In addition, glycerol, which is the by-product fromthe process, contains huge amount of energy at 1981.38 MJ/tonCPO/year. The sum of the annual energy generated from biomassis about 19.53 GJ/ton CPO. Hence, the total annual energy contentin the palm biodiesel, glycerol and biomass is about 60.72 GJ/tonCPO, as shown in Table 8.

For comparison purposes, the energy life cycle assessment forrapeseed oil was also investigated using a similar approach as palmoil. Rapeseed oil was selected for the comparative study as it is cur-rently the major oil feedstock for the production of biodiesel in theEuropean Union (EU) [31–33]. The plantation area and annual pro-duction of rapeseed oil in EU are shown in Table 9. The systemboundaries for the life cycle study for the production of biodiesel

Table 7Summary of annual energy utilization in the production of palm biodiesel.

Stage Energy Quantity (energy/ton CPO/year)

Agricultural FuelDiesel (traction) 644.24 MJFertilizers 1755.06 MJElectricityOverhead 5.17 MJTotal 2404.47 MJ

Palm oil mill SteamProcess 9826.00 MJElectricityProcess 269.83 MJOverhead 0.39 MJDieselVehicles 39.29 MJBoiler start-up 77.08 MJTotal 10212.59 MJ

Transesterification Electricity 113.69 MJSteam 1346.40 MJCrude palm oil 319.62 MJMethanol 18.58 MJSodium hydroxide 1.50 MJTotal 1799.79 MJ

Primary energy to produce FertilizersNitrogen 1437.64Phosphorus 180.16Potassium 207.20Petroleum Diesel 913.25 MJMethanol 36.19 MJSodium hydroxide 1.89 MJTotal 2776.34 MJ

Grand total 17.19 GJ

from rapeseed oil are similar to those of palm oil as shown inFig. 1. Tables 4 and 5 show the energy coefficients and calorific val-ues of materials required for rapeseed oil analysis. The total annualenergy utilization in the production of rapeseed biodiesel and thetotal annual energy content in the products (i.e., rapeseed biodie-sel, glycerol and biomass) are shown in Tables 10 and 11,respectively.

Based on the energy life cycle analysis, the ratio of output en-ergy to input energy for the production of 1 ton of palm biodieseland rapeseed biodiesel is 3.53 and 1.44, respectively. These resultsrepresent a net positive energy for the production of biodiesel for

Table 10Summary of annual energy utilization in the production of rapeseed biodiesel.

Stage Energy Quantity (energy/tonCRO/year)

Agricultural FuelDiesel (traction) 3988.06 MJFertilizers 14933.54 MJElectricityOverhead 6.92 MJTotal 18928.52 MJ

Rapeseed oil mill Hexane (as extractionsolvent) steam

53.17 MJ

Process 1586.00 MJElectricityProcess 419.00 MJOverhead 0.39 MJDieselVehicles 52.61 MJBoiler start-up 103.21 MJTotal 2214.38 MJ

Transesterification Electricity 113.69 MJSteam 1346.40 MJCrude rapeseed oil 24464.47 MJMethanol 1421.93 MJSodium hydroxide 114.76 MJTotal 27461.25 MJ

Primary energy toproduce

FertilizersNitrogen 16393.81Phosphorus 739.17Potassium 1067.07Petroleum diesel 4975.55 MJMethanol 2769.99 MJSodium hydroxide 144.96 MJTotal 26090.56 MJ

Grand total 74.69 GJ

Table 11Summary of energy content in rapeseed biodiesel, glycerol and biomass.

Product Quantity (energy/ton CRO/year)

Biodiesel 39,204.00 MJGlycerol 1981.37 MJStraw (heat generated) 66,616.38 MJ

Total 107.80 GJ

Table 13Emission of CO2 per unit item.

Item CO2 emission

Peat land 1.70 ton CO2/ton CPO produceLight oil for industrial boiler [39] 2830 kg CO2/m3 light oilDiesel [49] 73.10 kg CO2/GJBiodiesel combustion in vehicles [42] 1.641 ton CO2/ton biodieselFertilizers [52] 1.22 kg CO2/kg fertilizersMethanol [46] 1.33 kg CO2/l methanolSodium hydroxide [53] 0.79 kg CO2/kg NaOHCPO in transesterification [54] 1161.10 kg CO2/ha/yearCRO in transesterification [55] 527 kg CO2/ha/yearBiomass 1.19 kg CO2/kg biomass

Table 14Fossil fuel CO2 emission for unit electricity generation in Malaysia [37].

Fuels kg CO2 emissions per kWh

Coal 1.18Petroleum 0.85Natural Gas 0.53Hydro 0.00Other 0.00

Table 15Comparison of some physiological parameters of oil palm and tropical rainforest [40].

Parameter Oil palm (plantation) Rainforest

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both oil crops, although palm oil has the advantage of a higher netpositive energy ratio than rapeseed oil. This clearly reveals thebenefits of using palm biodiesel and confirms its sustainability ascompared with rapeseed biodiesel.

3.2. Greenhouse gas assessment

Global warming and climate change have been receivingincreasing attention lately, and this can be attributed to thelarge-scale use of fossil fuels. Biofuels are primarily intended to re-place the utilization of fossil fuels due to its unstable market priceand to reduce GHG emissions. It is well known that excessive emis-sion of carbon dioxide (CO2) is one of the main reasons for the deg-radation of the environment. However, for many biofuels, it isuncertain how much CO2 reduction can be achieved by its utiliza-tion, instead of fossil fuels. Hence, GHG assessment needs to becarried out to determine the effect of biodiesel utilization onGHG emission.

Throughout the whole life cycle, from oil palm plantation to thecombustion of palm biodiesel, CO2 assimilations and emissionstake place simultaneously. Through the process of photosynthesis,oil palm trees absorb CO2, water and sunlight energy to producecarbohydrates and oxygen. However, for the process of respiration,the oxygen produced from photosynthesis is used to create CO2. Itwas estimated that oil palm crop emits 8–10 times more oxygen(O2) and absorbs up to 10 times more CO2 per hectare per yearcompared to annual crops grown in temperate countries [34]. Plan-tation of oil palm on the drained peat land also contributes to theemissions of CO2, which leads to most peat carbon above drainagelimit to be released to the atmosphere.

Producing 1 ton of CPO on peat land generates 15–70 tons ofCO2 over 25 years as a result of forest conversion, peat decomposi-tion and emission from fires associated with land clearance[35,36]. Hence, the average value of 42.5 tons of CO2 emissionsper ton CPO is used in this study. Consequently, using annual emis-sion as basis, 1.7 tons of CO2 is released from peat land for every1 ton of CPO produced and therefore this translates to211996.97 kg CO2 release per ton biodiesel produced. Currently,about 10% of the total oil palm plantation is planted on peat landas shown in Table 12. Apart from that, the utilization of fertilizersand traction activities in the plantation sites also release CO2 to theatmosphere with values of 11630.88 kg CO2 and 5872.81 kg CO2/ton biodiesel produce, respectively. During the production of CPOin the milling stage, the incineration of fiber and shell for in site en-ergy generation also releases 117234.33 kg CO2/ton biodiesel tothe atmosphere. On the other hand, the amount of CO2 emissioncoming from the usage of input materials (reactants) and fuel isshown in Table 13. The utilization of light oil for industrial boiler

Table 12Percentage of oil palm plantation in soil land and peat land.

Oil palm land Plantation area (hectares) Share (%)

Soil land 3,884,914 90.24Peatland [34] 420,000 9.76

Total [14] 4,304,914 100

start-up and diesel used in the traction release 702.65 kg CO2

and 358.16 kg CO2/ton biodiesel, respectively.The production of palm biodiesel in the biodiesel plant also con-

tributes to the emission of CO2 to the atmosphere. At the transeste-rification stage, the major CO2 emission comes from the electricitygeneration of and emission from the steam boilers. Table 4 showsthe energy coefficient for the electricity utilization in the transeste-rification process, and Table 14 shows the fossil fuel CO2 emissionfor unit electricity generation in Malaysia [37]. In Malaysia, naturalgas is the major fossil fuel among oil, coal and hydro for electricitygeneration [38]. By considering the amount of CO2 emitted fromgenerating electricity from natural gas and the amount of electric-ity required in the transesterification process, the amount of CO2

emitted was calculated to be about 2087.26 kg CO2/ton biodiesel.On the other hand, steam is one of the important utility used in

the transesterification process to produce palm biodiesel. Nor-mally, steam is produce on site using steam boiler. Thus, CO2 emis-sion occurs in the process of steam generation due to the burningof light oil in the boiler. The emission factor for light oil used inindustrial boiler is 2830 kg CO2 per m3 light oil consumed [39].Therefore, the CO2 emitted from steam boiler is calculated as199.01 kg CO2/ton biodiesel, based on the efficiency of 50%. Besidesthat, the reactants used in the transesterification process also leadto the emission of CO2, as CO2 is emitted during the production ofthese reactants. For every 1 l of methanol and 1 kg of sodiumhydroxide produced, 1.33 kg CO2 and 0.79 kg CO2 will be releasedto the atmosphere, respectively. Thus, by knowing the totalamount of methanol and sodium hydroxide required in this stage,

Gross assimilation (t CO2/ha/year) 161.0 163.5Total respiration (t CO2/ha/year) 96.5 121.1Net assimilation (t CO2/ha/year) 64.5 42.4Leaf area index 5.6 7.3Photosynthetic efficiency (%) 3.18 1.73Radiation conversion efficiency (g/M) 1.68 0.86Standing increment/year (t) 100 431Biomass increment/year (t) 8.3 5.8Dry matter production/year (t) 36.5 25.7

Table 16Summary of the CO2 assessment for palm biodiesel.

Parameter CO2 (kg CO2/ton biodiesel)

From atmosphere To atmosphere

PlantationGross assimilation 5462257.45Total respiration 3273961.76Peatland 211996.97N–P–K fertilizers 11630.88Traction (diesel) 5872.81

Palm oil millCPO productionBiomass incineration 117234.33Diesel for boiler start up 702.65Diesel for vehicles 358.16

TransesterificationBiodiesel productionCPO 39392.72Methanol 232.95Sodium hydroxide 5.63Electricity 2087.26Boiler 199.01Biodiesel combustion 1614.00

Total 5462257.45 3665289.12

Table 18Fuel efficiency and emissions by fuel type [41].

Petrol Diesel LPG Palm biodiesel

Fuel consumption (l/100 km) 12.0 11.5 17.2 12.0CO2 emissions (g CO2/km) 271 309 263 (NA)CO2 emissions (kg CO2/l) 2.2583 (NA) (NA) 1.3950

K.F. Yee et al. / Applied Energy 86 (2009) S189–S196 S195

the quantity of CO2 emission was calculated as 232.95 kg CO2 and5.63 kg CO2/ton biodiesel, respectively.

Studies have shown that oil palm plantations are as effective asrainforests in acting as carbon sinks areas of dry matter that serveto absorb the harmful GHG from the atmosphere. Table 15 showsthe comparison of some physiological parameters of oil palm andtropical rainforest [40]. From the table, it was shown that the grossassimilation in oil palm plantation is 161,000 kg CO2 per hectareper year (5462257.45 kg CO2/ton biodiesel), whereas the amountof CO2 release from the respiration process is 96,500 kg CO2 perhectare per year (3273961.76 kg CO2/ton biodiesel). This resultshows that oil palm trees generate a net sequestration of CO2 asopposed to forests, which only generate a dynamic CO2 equilib-rium. As net sequesterer of CO2, oil palm trees absorb more CO2

from the atmosphere compared to the volume of CO2 they emitto the air. Table 16 shows the summary of the CO2 assessmentwhich includes plantation, production, and combustion of palm

Table 17Summary of the CO2 assessment for rapeseed biodiesel.

Parameter CO2 (kg CO2/ton biodiesel)

From atmosphere To atmosphere

PlantationGross assimilation 441752.10Total respiration 264776.88N–P–K fertilizers 990.84Traction (diesel) 474.95

Rapeseed oil millCRO productionStraw incineration 1240.75Electricity 223.96Boiler 378.10Diesel 18.56

TransesterificationBiodiesel productionCRO 1445.98Methanol 232.91Sodium hydroxide 5.63Electricity 60.71Boiler 199.01Biodiesel combustion 1614.00

Total 441752.10 271662.29

biodiesel. From the table, it was found that the amount of CO2 gen-erated and released to the atmosphere in the palm biodiesel pro-duction process (3665289.12 kg CO2/ton biodiesel) is less thanthe amount of CO2 used by the plants during assimilation (growth)process (5462257.45 kg CO2/ton biodiesel). This shows that theutilization of palm biodiesel can sequestrate CO2 and is indeedan environmentally friendly fuel.

The CO2 life cycle assessment was also studied for the produc-tion of rapeseed biodiesel using a similar approach described forpalm biodiesel. The gross assimilation and total respiration for ra-peseed plant are assumed to be the same as palm tree. Table 17summarizes the results revealing that the amount of CO2 generatedand released to the atmosphere in the rapeseed biodiesel produc-tion process (271662.29 kg CO2/ton biodiesel) is also less thanthe amount of CO2 used by the plants during assimilation (growth)process (441752.10 kg CO2/ton biodiesel). This shows that theusage of both palm biodiesel and rapeseed biodiesel can result ina net reduction in CO2 concentration in the atmosphere.

For the comparison of CO2 emission from palm biodiesel andpetrol, the data for petrol fuel consumption and CO2 emissionsfrom petrol combustion should be obtained [41]. As calculatedusing the data shown in Table 18, it was found that 2.258 kgof CO2 is emitted for each liter of petrol combusted. On the otherhand, the combustion of palm biodiesel in the combustion en-gine of a European car only generated a mere 1.641 tons ofCO2/ton of biodiesel or 1.395 kg CO2/l palm biodiesel [42]. Com-paratively, an enormous amount of CO2 reduction (0.8633 kgCO2/l of biodiesel or 38% lesser) can be achieved when palm bio-diesel is utilized instead of petrol. The data for CO2 emissionfrom the combustion of 1 l petrol and palm biodiesel is summa-rized in Table 18.

4. Conclusion

From this study, it was found that the utilization of palm bio-diesel would generate an energy yield ratio of 3.53 (output en-ergy/input energy), indicating a net positive energy. The energyratio for palm biodiesel was found to be more than double the ra-tio for rapeseed biodiesel, which was only at 1.44. This indicatesthat palm oil would be a more sustainable feedstock for biodieselproduction as compared to rapeseed oil. In terms of GHG assess-ment, it can be concluded that the production of palm and rape-seed biodiesel brings no negative impact to the environment asthe amount of CO2 emitted to the atmosphere is much lower thanthe CO2 absorbed from the atmosphere. Also, the emission of CO2

from the combustion of 1 l of biodiesel is 38% less than that ofpetrol. Contrary to some reports which challenge the sustainabil-ity of palm oil as an environment-friendly source of energy, theresults of this LCA study has shown that palm diesel has the po-tential to become the major renewable energy in the future, withhuge positive energy ratio and significant reduction in CO2

emission.

Acknowledgements

The authors acknowledge Ministry of Science, Technology andInnovation (Malaysia) (ScienceFund-Project No.: 03-01-05-SF0138) and Universiti Sains Malaysia (Research University Grant,

S196 K.F. Yee et al. / Applied Energy 86 (2009) S189–S196

Short Term Grant and USM Fellowship) for the financial supportgiven.

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