Life cycle assessment of palm biodiesel: Revealing facts and benefits for sustainability

Life cycle assessment of palm biodiesel: Revealing facts and benefits for sustainability

Applied Energy 86 (2009) S189–S196 Contents lists available at ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy Life...

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Applied Energy 86 (2009) S189–S196

Contents lists available at ScienceDirect

Applied Energy journal homepage: www.elsevier.com/locate/apenergy

Life cycle assessment of palm biodiesel: Revealing facts and 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

Article history: Received 15 January 2009 Received in revised form 19 April 2009 Accepted 19 April 2009 Available online 22 May 2009 This article is sponsored by the Asian Development Bank as part of the Supplement ‘‘Biofuels in Asia’’. Keywords: Biodiesel Transesterification Life cycle assessment Energy balance Green house gas

a b s t r a c t Similarity between the properties of biodiesel and petroleum-derived diesel has made the former one of the most promising alternatives to a renewable and sustainable fuel for the transportation sector. In Malaysia, palm oil can be a suitable feedstock for the production of biodiesel due to its abundant availability and low production cost. However, not many assessments have been carried out regarding the impacts of palm biodiesel on the environment. Hence, in this study, life cycle assessment (LCA) was conducted for palm biodiesel in order to investigate and validate the popular belief that palm biodiesel is a green and sustainable fuel. The LCA study was divided into three main stages, namely agricultural activities, oil milling and transesterification process for the production of biodiesel. For each stage, the energy balance and green house gas assessments were presented and discussed. These are important data for the techno-economical and environmental feasibility evaluation of palm biodiesel. The results obtained for palm biodiesel were then compared with rapeseed biodiesel. From this study, it was found that the utilization of palm biodiesel would generate an energy yield ratio of 3.53 (output energy/input energy), indicating a net positive energy generated and ensuring its sustainability. The energy ratio for palm biodiesel was 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 compared to rapeseed oil. Moreover, combustion of palm biodiesel was found to be more environmentfriendly than petroleum-derived-diesel as a significant 38% reduction of CO2 emission can be achieved per liter combusted. Ó 2009 Elsevier Ltd. All rights reserved.

1. Introduction The escalating prices of petroleum in the world market, coupled with the diminishing supply of non-renewable fossil fuels, have raised concerns for a need for renewable energy sources as substitutes for fossil fuels. Also, as already commonly know, the utilization 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 source of energy has become inevitable for a sustainable future. One of the alternatives to renewable energy that has been getting a lot of attention lately is biodiesel, which exhibits similar properties as petroleum-derived diesel. Currently, biodiesel is produced from edible and non-edible oils such as palm, sunflower and jatropha. These are inexhaustible sources of triglycerides, which are essential elements in the transesterification process for biodiesel production. Comparatively, biodiesel has several advantages than conventional diesel in terms of GHG emission and availability. Biodiesel, if widely adopted, could significantly reduce emissions * Corresponding author. Tel.: +60 4 5996467; fax: +60 4 5941013. E-mail address: [email protected] (K.T. Lee). 0306-2619/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.apenergy.2009.04.014

from the road transportation sector. An in-vehicle performance of biodiesel and their potential carbon savings has been compared and evaluated with conventional fuels. It was reported that the usage of biodiesel can reduce carbon emissions and also help increase energy security [1,2]. Moreover, local biodiesel production can significantly reduce dependence on foreign imports of diesel fuel, and increase the utilization of renewable energy sources such as palm oil. Malaysia, as one of the world’s largest producers and exporters of palm oil and its products, has a great potential of becoming a major producer of palm biodiesel [3]. Palm biodiesel can be produced from palm oil via transesterification process between crude palm oil and alcohol with the presence of an acidic or alkaline catalyst. Palm oil has the potential to fulfill the high demand for biodiesel in the world market due to its superior annual yield per hectare as compared to other oilseeds. For instance, as shown in Table 1, the average annual yield of palm oil is 3.68 tons/ha, while for other major oil crops such as soybean and rapeseed, the yields are significantly lower at 0.36 and 0.59 tons/ha, respectively [4]. Hence, it is not surprising to note that about one-third of the global oil production comes from palm oil, although areas allocated for palm plantation are small compared to the plantation areas of other oil crops (Table

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Nomenclature CO2 CPO CRO EFB EIA FFB

carbon dioxide crude palm oil crude rapeseed oil empty fruit bunches environmental impact assessment fresh fruit bunches

GHGs IPM LCA O2 POME

1). In addition, biodiesel produced from palm oil is more environment-friendly compared to petroleum-derived diesel in terms of carbon emission, since the carbon released during combustion process were those absorbed from the atmosphere by the crops. Given the advantages of palm biodiesel as compared to nonrenewable sources, it has been hailed as the solution for an affordable and renewable source of energy in the future. However, there are some negative claims regarding the sustainability of palm oil as a source of biofuel. Generally, it was reported that such large-scale utilization of palm oil as biofuel would cause deforestation, which in turn would lead to possible loss of one of the world’s largest natural carbon sink, subsequently smearing the image of palm oil as an ideal source of renewable energy [5]. Hence, a systematic approach to investigate all upstream and downstream processes or cradle-to-grave analysis of palm biodiesel is important to validate the benefits or ‘cleanliness’ of this so-called ‘green energy’. One of the methods that can be used to assess the environmental merits and demerits of a product is the life cycle assessment (LCA), which entails a complete evaluation and analysis of a product throughout its lifespan [6–8]. For instance, GHG emission and net energy requirement in palm biodiesel production will be systematically quantified and compiled for every stage involved from the oil palm plantation stage up to the combustion process of palm biodiesel to address the tenacious issues on sustainability, climate change and global biodiversity [9]. In this LCA study, the aim is to compile an inventory of energy input and output involved in the production of biodiesel from palm oil. An assessment of the GHG emission is also carried out to evaluate the potential and benefits of palm biodiesel as a green and renewable source of energy. Hence, a comprehensive investigation on the effect of utilizing palm biodiesel on the environment can be carried out scientifically, which is crucial in validating the advantages of palm biodiesel compared to petroleum-derived diesel. Apart from that, assessment of energy balance and GHG emissions for rapeseed oil are carried out using a similar approach in order to make a valid comparison with palm oil.

green house gases integrated pest management life cycle assessment oxygen palm oil mill effluent

and GHG emission associated with the production of biodiesel from palm oil in Malaysia. The scope of the system used in this study comprises from the oil palm (Elaeis guineensis) plantation stage until the combustion of biodiesel in diesel engines. The energy consumption in each stage is studied along with the life cycle of biodiesel. Energy consumption is defined as the sum of energy consumed for each ton of biodiesel produced in every stage of the production path. The study also conducted a GHG assessment to calculate the annual carbon dioxide (CO2) assimilation or emission for each ton of biodiesel produced. For comparison purposes, the energy balance assessment and GHG assessment for rapeseed oil were also undertaken using a similar approach. Throughout the study, the functional unit used for energy and GHG evaluation is in GigaJoule (GJ)/ton crude palm oil (tCPO)/year and ton CO2/ton biodiesel/year, respectively. The calculations were done using energy coefficients reported in the literature. Energy coefficients basically give the energy content in a compound or the quantity of energy required to produce per unit of energy. 2.2. System boundary The life cycle of palm biodiesel production is divided into three stages. The first stage is the plantation (agricultural) stage, followed by the palm oil milling stage, and finally the transesterification process of palm biodiesel production. The system boundary used in this study is shown in Fig. 1. In the agricultural (plantation) stage, several processes are involved in the production of fresh fruit bunches (FFB) [10]. The processes include planning, nursery establishment, site preparation, field establishment, field maintenance, harvesting and collection and replanting. In the planning phase, feasibility studies and Environment Impact Assessment (EIA) are required for the development of new plantations exceeding 500 ha on a primary/secondary forest or involving a change in the type of plantation. If the land is found to be suitable and its use is approved by relevant agencies, the nursery phase can then be established. Good quality seeds are sown in small poly bags where the seedlings will be cultivated until they are 3–4 months old. After that, the seedlings are transferred to and cultivated in large poly bags until they are 12–13 months old, when they are considered ready to be shifted to the plantations [11]. Next step is the preparation of the plantation which includes activities like land survey, clearing of existing vegetation, establishment of road and field drainage systems, soil conservation

2. Methodology 2.1. Goal and scope definition In this study, the methodology developed is based on LCA procedures. The main goal of this study is to assess the energy balance

Table 1 Oil productivity of major oil crops [4]. Oil crop Soybean Sunflower Rapeseed Palm oil Others Total

Oil production (million tons) 33.58 9.66 16.21 33.73 12.76 105.94

Total production (%)

Average oil yield (tons/ha/year)

31.69 9.12 15.30 31.84 12.04

0.36 0.42 0.59 3.68 –

100



Planted area (million ha) 92.10 22.90 27.30 9.17 66.55 218.02

Total area (%) 42.24 10.50 12.52 4.21 30.52 100

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Palm Oil Seedlings Fertilizers Energy Traction

Agricultural

Fresh Fruit Bunch (FFB) Energy

Milling

Traction

Palm Kernel Fiber & Shells Empty Fruit Bunches (EFB) Palm Oil Mill Effluent (POME)

Crude Palm Oil (CPO) Reactants Energy

Transesterification

Glycerol

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

measures such as terracing, conservation bunds and silt pits and sowing of leguminous cover crops [10]. Subsequently, field establishment activities will be carried out such as lining, holing and planting of poly bag seedlings at a density of 136–148 bags per hectare, depending on the soil type. In addition, leguminous cover crops such as Pueraria javanica and Calopogonium caeruleum are planted to obtain full ground coverage to minimize soil loss through runoff and also to improve the soil properties through nitrogen fixation. Throughout the maturing period, the plantation area is maintained by field maintenance operations such as the integrated pest management (IPM). Under the IPM, instead of using chemical pesticides which is harmful to our environment, natural pest control is adopted to control pest population in oil palm plantation. Harvesting and collection of FFB are undertaken up until 24–30 years after field planting, depending on the soil type and the management practices employed. The average lifespan of oil palm trees is 26 years, and throughout this period, the trees can continuously produce FFB [11]. At the end of its lifespan, replanting process will commence, whereby oil palm trunks are shredded and placed back in the field as mulch given that zero-burning practice has been legalized in Malaysia since 1989 [12]. However, in some situations, new seedlings are planted under the old palm trees which will be thinned out progressively to allow the development of the new stand [10]. FFB harvested from the oil palm tree will be processed immediately to prevent a rapid rise in free fatty acids (FFA) which could adversely affect the quality of crude palm oil (CPO) [10]. Generally, palm oil mills are located near the plantations to facilitate timely transportation and effective processing of FFB. Processing in palm oil 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 enzymes which are responsible for the breakdown of oil to FFA. The sterilization process also helps loosen the fruits from their bunches so that the oil can be extracted easily. The sterilized fresh fruit bunches (FFB) are then fed continuously into a rotary drum machine in order to strip and separate the fruits from the bunch. The fruits will pass along channel bars running longitudinally along the drum, while the empty bunches are eventually discharged 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 pressed under pressure, either hydraulically or mechanically, to extract the crude palm oil (CPO). Subsequently, CPO, the major product from the palm oil mill, is transported to a biodiesel plant as feedstock for biodiesel production. Biodiesel is conventionally produced via transesterification reaction with methanol in a batch type reactor in the presence of alkaline sodium hydroxide, which acts as the homogeneous catalyst. After the transesterification process, the mixture is kept overnight and allowed to separate by gravity, whereby two layers are formed. Methyl esters, a light yellow liquid, forms at the top layer whereas, glycerol, a dark brown liquid, forms at the bottom layer. Alternatively, if the mixture is not kept overnight, the methyl esters can be separated from the glycerol by washing the mixture with water and acetic acid until the washing water becomes neutral. Palm biodiesel is the main product from this transesterification process, while glycerol is the by-product which can be used to produce soap or other materials. 2.3. Life cycle inventory This inventory consists of all recognized inputs and outputs to or from the system boundary. Table 2 shows the inputs and outputs of the various stages involved in palm biodiesel production. Table 3 shows the annual production of products from the Malaysia oil palm industry at the end of 2007 [14,15]. The agricultural stage produces 19.0 tons of FFB for each hectare of plantation land

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

Input

Agricultural

Palm oil seed

Output Fresh fruit bunches (FFB)

Palm oil mill

Fresh fruit bunches (FFB)

Crude palm oil (CPO) Palm kernel Fiber and shells Empty fruit bunches (EFB) Palm oil mill effluent (POME)

Transesterification

Crude palm oil (CPO) Methanol Sodium hydroxide

Biodiesel Glycerol

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

Production (ton)

Fresh fruit bunches (FFB) [14] Crude palm oil (CPO) [14] CPO for biofuel production [15]

81,793,366 15,823,368 128,193

Table 4 Energy coefficient for various compounds. Energy coefficient

Energy

Steam [18] Electricity (transesterification) Crude palm oil Methanol Sodium hydroxide Glycerol

1360 MJ/ton biodiesel 0.0029 MJ/MJ biodiesel 1.0065 MJ/MJ biodiesel 0.0585 kg/MJ biodiesel 0.00018 kg/MJ biodiesel 0.0028 kg/MJ biodiesel

Fertilizers [25] Nitrogen (N) Phosphorus (P2O5) Potassium (K2O)

48.9 MJ/kg 17.43 MJ/kg 10.38 MJ/kg

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

Energy

Biodiesel [19] Sodium hydroxide [43] Glycerol [19] Fibers and shell [20] Diesel [21] Steam Straw (biomass) Steam Hexane Electricity Methanol [44]

39,600 MJ/ton 26,230 MJ/ton 18,050 MJ/ton 19.89 GJ/ton 40.3 MJ/l 2604 MJ/ton 13,500 MJ/ton 1586 MJ/ton rapeseed fruit 44.75 MJ/kg 419 MJ/ton rapeseed fruit 13.23 MJ/l methanol

utilized [16]. On the other hand, there are several products and coproducts that are produced from the palm oil mill. The main product is CPO, estimated yield of which is 0.20 ton for each ton of FFB processed. The co-products are fibers and shells, empty fruit bunches (EFB), and palm oil mill effluent (POME) which yields 190 kg, 230 kg and 600–700 kg/ton of FFB, respectively [17]. For the transesterification process, the conversion of CPO to biodiesel is at 99% efficiency, thus the annual production of palm biodiesel is calculated at 126,888 tons or 0.99 ton biodiesel for each ton of CPO feedstock. The energy coefficient of fuel utilized [18] and the calorific value of products [19–21] are shown in Tables 4 and 5 respectively. 3. Results and discussion 3.1. Energy balance assessment The energy produced (output/ton biodiesel) to the energy consumed (input/ton biodiesel) for each unit of product in the production of palm biodiesel can be used as an index of techno-economic and environmental feasibility analysis. The energy balance assessment begins from the early stages of oil palm plantation to the combustion of palm biodiesel in diesel engines of vehicles. The energy flows during the life cycle of palm biodiesel are of two types, i.e., direct and indirect energy. A direct energy flow is the energy consumed in the form of fossil fuel, steam and electricity, while an indirect energy flow is the energy involved in transportation purposes. In the agricultural stage, both traction and transportation of fertilizers and pesticides involve the utilization of fossil fuel. For simplification reason, all fossil fuels used in oil palm plantations are regarded as petroleum-derived diesel. The activities of transferring FFB from oil palm plantations to palm oil mills and subsequently the removal of EFB from the palm oil mills to oil palm plantations are carried out by tractors, which are the main mode of transportation. Currently, EFB is used mainly as mulch in oil palm plantation to control weeds, prevent erosion, and maintain soil moisture [22]. In 2007, the total oil palm plantation area in Malaysia reached 4,304,914 ha, and the energy consumed by traction was estimated at 2368 MJ per hectare [23]. Hence, the annual energy consumed by traction is 644.24 MJ/ton CPO. Oil palm trees require several types of nutrients in the form of fertilizers to achieve significant growth rates [24]. Nutrients such as nitrogen (N), phosphorus (P2O5) and potassium (K2O) are usually added as fertilizers, and the average usage of these nutrients are 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 fertilizers is approximately 1.76 GJ/ton CPO. However, due to lack of data on electricity usage in administration, research, laboratory and 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 of electricity annually or 5.17 MJ energy/ton CPO/year. In the palm oil mill stage, significant amounts of steam and electricity are needed for the processes to obtain the desired CPO. Normally, biomass is used for heat and/or power production through direct combustion [26]. Hence, fibers and shells obtained as by-products are incinerated to generate steam and subsequently used as a source of electricity for palm oil mills. Hence, palm oil mills are self-sufficient in terms of electricity consumption [27]. Assuming that 80% of the total fibers and shells (0.79 ton/ton CPO) are fed into boilers, a massive 15.7 GJ/ton CPO of energy can be generated from the biomass per year (3023 MJ/ton FFB). On the other hand, the excess fibers and shells (20%) can be sold as fuel, with total energy content of approximately 3.9 GJ/ton CPO 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 the forms of heat (steam) and power (electricity). These values were obtained based on the data reported by seven selected palm oil mills in Perak State [28]. In this study, using an average value of 65.6% would generate an equivalent energy consumption by the palm oil mill of 10.3 GJ/ton CPO. The other 34.4% of the total energy generated from the biomass per year (5.4 GJ/ton CPO) is considered as energy output which is not being utilized in the palm oil mill. In order 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, about 9.83 GJ/ton CPO of steam is required. The distribution of the total heat and power production is assumed at 9.99 GJ of steam/ton CPO and 0.31 GJ of electricity/ton CPO, respectively. From the 9.99 GJ/ton CPO of steam produced, only 9.83 GJ/ton CPO of steam is required in the processes, where about 1.6% of steam energy is assumed 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 utilized in the process of producing CPO. Since the electricity generated is estimated at 0.31 GJ/ton CPO, about 13% excess electricity is assumed to be used locally in administrative and residence buildings for the workers. Apart from that, the utilization of diesel fuel in the palm oil mill cannot be neglected. As far as start-up of boilers is concerned, about 0.37 l of diesel is utilized per ton of FFB [30]. In addition, from the average value reported by the six selected palm oil mills in Malaysia, vehicles consumed roughly 7.6 MJ/ton FFB. For the transesterification process, both steam and electricity are the main sources of energy utilized in palm biodiesel production. It was reported that a total of 1360 MJ of steam is needed for the production of 1 ton of palm biodiesel, while 0.0029 MJ electricity is consumed for each MJ biodiesel produced [18]. Based on the total amount of CPO produced in the year 2007, 0.81% was used for 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 electricity needed for 1 ton of palm biodiesel produced is about 31.9 kWh. The energy coefficients of the reactants are listed in Table 4. The annual energy content of reactants such as CPO, methanol, and sodium 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 the transesterification stage is 1.80 GJ/ton CPO on a yearly basis. Apart from the three stages (agricultural, palm oil mill, transesterification) that contributed to the total amount of energy input in biodiesel production, the primary energy which is required to produce raw materials and subsequently utilized in the process cannot be neglected as well. Table 6 shows the primary energy required to produce fertilizers, petroleum diesel, methanol and sodium hydroxide. By considering the amount of these input materials and the energy contents, the total energy required for

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K.F. Yee et al. / Applied Energy 86 (2009) S189–S196 Table 6 Primary energy required for the production of input materials.

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

Input material

Primary energy

Product

Quantity (energy/ton CPO/year)

Petroleum diesel [45] Methanol [46] Sodium hydroxide [47]

1.20 MJ/MJ petroleum diesel 25.77 MJ/l methanol 33.13 MJ/kg NaOH

Fertilizers [48] Nitrogen (N) Phosphorus (P2O5) Potassium (K2O)

Biodiesel Glycerol Fibers and shells (heat generated) Total

39,204.00 MJ 1981.38 MJ 19,534.74 MJ 60.72 GJ

69.53 MJ/kg N 7.70 MJ/kg P2O5 6.40 MJ/kg K2O Table 9 Plantation area and annual production of rapeseed oil in European Union (EU).

the production of these input materials is 2.78 GJ/ton CPO on an annual basis. Table 7 summarizes the annual energy utilization in the production of palm biodiesel from the agricultural stage until the transesterification process, with total energy utilized calculated at about 17.19 GJ/ton CPO. On the other hand, the energy released from the combustion of palm biodiesel is 39,600 MJ/ton. As mentioned previously, 126,888 tons of palm biodiesel are produced, thus the total annual energy released from the combustion of palm biodiesel is about 39.2 GJ/ton CPO. In addition, glycerol, which is the by-product from the process, contains huge amount of energy at 1981.38 MJ/ton CPO/year. The sum of the annual energy generated from biomass is about 19.53 GJ/ton CPO. Hence, the total annual energy content in the palm biodiesel, glycerol and biomass is about 60.72 GJ/ton CPO, as shown in Table 8. For comparison purposes, the energy life cycle assessment for rapeseed oil was also investigated using a similar approach as palm oil. Rapeseed oil was selected for the comparative study as it is currently the major oil feedstock for the production of biodiesel in the European Union (EU) [31–33]. The plantation area and annual production of rapeseed oil in EU are shown in Table 9. The system boundaries for the life cycle study for the production of biodiesel

Material

Production

Rapeseed fruit [49] Straw (biomass) [50] Rapeseed oil [4] CRO for biofuel production [51] Biodiesel production Plantation area [4]

4.11 ton/ha/year 2.93 ton/ha 16,210,000 ton/year 10,050,200 ton/year 9,949,698 ton/year 27,300,000 ha

from rapeseed oil are similar to those of palm oil as shown in Fig. 1. Tables 4 and 5 show the energy coefficients and calorific values of materials required for rapeseed oil analysis. The total annual energy utilization in the production of rapeseed biodiesel and the total annual energy content in the products (i.e., rapeseed biodiesel, glycerol and biomass) are shown in Tables 10 and 11, respectively. Based on the energy life cycle analysis, the ratio of output energy to input energy for the production of 1 ton of palm biodiesel and rapeseed biodiesel is 3.53 and 1.44, respectively. These results represent a net positive energy for the production of biodiesel for

Table 10 Summary of annual energy utilization in the production of rapeseed biodiesel. Table 7 Summary of annual energy utilization in the production of palm biodiesel. Stage

Energy

Agricultural

Fuel Diesel (traction) Fertilizers Electricity Overhead Total

Palm oil mill

Quantity (energy/ton CPO/year)

Stage

Energy

Agricultural

Fuel Diesel (traction) Fertilizers Electricity Overhead Total

644.24 MJ 1755.06 MJ 5.17 MJ 2404.47 MJ

Steam Process Electricity Process Overhead Diesel Vehicles Boiler start-up Total

39.29 MJ 77.08 MJ 10212.59 MJ

Transesterification

Electricity Steam Crude palm oil Methanol Sodium hydroxide Total

113.69 MJ 1346.40 MJ 319.62 MJ 18.58 MJ 1.50 MJ 1799.79 MJ

Primary energy to produce

Fertilizers Nitrogen Phosphorus Potassium Petroleum Diesel Methanol Sodium hydroxide Total

1437.64 180.16 207.20 913.25 MJ 36.19 MJ 1.89 MJ 2776.34 MJ

Grand total

17.19 GJ

Rapeseed oil mill

Quantity (energy/ton CRO/year) 3988.06 MJ 14933.54 MJ 6.92 MJ 18928.52 MJ

Hexane (as extraction solvent) steam Process Electricity Process Overhead Diesel Vehicles Boiler start-up Total

53.17 MJ

Transesterification

Electricity Steam Crude rapeseed oil Methanol Sodium hydroxide Total

113.69 MJ 1346.40 MJ 24464.47 MJ 1421.93 MJ 114.76 MJ 27461.25 MJ

Primary energy to produce

Fertilizers Nitrogen Phosphorus Potassium Petroleum diesel Methanol Sodium hydroxide Total

16393.81 739.17 1067.07 4975.55 MJ 2769.99 MJ 144.96 MJ 26090.56 MJ

Grand total

74.69 GJ

9826.00 MJ 269.83 MJ 0.39 MJ

1586.00 MJ 419.00 MJ 0.39 MJ 52.61 MJ 103.21 MJ 2214.38 MJ

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

Table 13 Emission of CO2 per unit item.

Product

Quantity (energy/ton CRO/year)

Item

CO2 emission

Biodiesel Glycerol Straw (heat generated)

39,204.00 MJ 1981.37 MJ 66,616.38 MJ

Total

107.80 GJ

Peat land Light oil for industrial boiler [39] Diesel [49] Biodiesel combustion in vehicles [42] Fertilizers [52] Methanol [46] Sodium hydroxide [53] CPO in transesterification [54] CRO in transesterification [55] Biomass

1.70 ton CO2/ton CPO produce 2830 kg CO2/m3 light oil 73.10 kg CO2/GJ 1.641 ton CO2/ton biodiesel 1.22 kg CO2/kg fertilizers 1.33 kg CO2/l methanol 0.79 kg CO2/kg NaOH 1161.10 kg CO2/ha/year 527 kg CO2/ha/year 1.19 kg CO2/kg biomass

both oil crops, although palm oil has the advantage of a higher net positive energy ratio than rapeseed oil. This clearly reveals the benefits of using palm biodiesel and confirms its sustainability as compared with rapeseed biodiesel. 3.2. Greenhouse gas assessment Global warming and climate change have been receiving increasing attention lately, and this can be attributed to the large-scale use of fossil fuels. Biofuels are primarily intended to replace the utilization of fossil fuels due to its unstable market price and to reduce GHG emissions. It is well known that excessive emission of carbon dioxide (CO2) is one of the main reasons for the degradation of the environment. However, for many biofuels, it is uncertain how much CO2 reduction can be achieved by its utilization, instead of fossil fuels. Hence, GHG assessment needs to be carried out to determine the effect of biodiesel utilization on GHG emission. Throughout the whole life cycle, from oil palm plantation to the combustion of palm biodiesel, CO2 assimilations and emissions take place simultaneously. Through the process of photosynthesis, oil palm trees absorb CO2, water and sunlight energy to produce carbohydrates and oxygen. However, for the process of respiration, the oxygen produced from photosynthesis is used to create CO2. It was estimated that oil palm crop emits 8–10 times more oxygen (O2) and absorbs up to 10 times more CO2 per hectare per year compared to annual crops grown in temperate countries [34]. Plantation of oil palm on the drained peat land also contributes to the emissions of CO2, which leads to most peat carbon above drainage limit to be released to the atmosphere. Producing 1 ton of CPO on peat land generates 15–70 tons of CO2 over 25 years as a result of forest conversion, peat decomposition and emission from fires associated with land clearance [35,36]. Hence, the average value of 42.5 tons of CO2 emissions per ton CPO is used in this study. Consequently, using annual emission as basis, 1.7 tons of CO2 is released from peat land for every 1 ton of CPO produced and therefore this translates to 211996.97 kg CO2 release per ton biodiesel produced. Currently, about 10% of the total oil palm plantation is planted on peat land as shown in Table 12. Apart from that, the utilization of fertilizers and traction activities in the plantation sites also release CO2 to the atmosphere with values of 11630.88 kg CO2 and 5872.81 kg CO2/ ton biodiesel produce, respectively. During the production of CPO in the milling stage, the incineration of fiber and shell for in site energy generation also releases 117234.33 kg CO2/ton biodiesel to the atmosphere. On the other hand, the amount of CO2 emission coming from the usage of input materials (reactants) and fuel is shown in Table 13. The utilization of light oil for industrial boiler

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

Plantation area (hectares)

Share (%)

Soil land Peatland [34]

3,884,914 420,000

90.24 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 contributes to the emission of CO2 to the atmosphere. At the transesterification stage, the major CO2 emission comes from the electricity generation of and emission from the steam boilers. Table 4 shows the energy coefficient for the electricity utilization in the transesterification process, and Table 14 shows the fossil fuel CO2 emission for unit electricity generation in Malaysia [37]. In Malaysia, natural gas is the major fossil fuel among oil, coal and hydro for electricity generation [38]. By considering the amount of CO2 emitted from generating electricity from natural gas and the amount of electricity 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. Normally, steam is produce on site using steam boiler. Thus, CO2 emission occurs in the process of steam generation due to the burning of light oil in the boiler. The emission factor for light oil used in industrial boiler is 2830 kg CO2 per m3 light oil consumed [39]. Therefore, the CO2 emitted from steam boiler is calculated as 199.01 kg CO2/ton biodiesel, based on the efficiency of 50%. Besides that, the reactants used in the transesterification process also lead to the emission of CO2, as CO2 is emitted during the production of these reactants. For every 1 l of methanol and 1 kg of sodium hydroxide produced, 1.33 kg CO2 and 0.79 kg CO2 will be released to the atmosphere, respectively. Thus, by knowing the total amount of methanol and sodium hydroxide required in this stage,

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

kg CO2 emissions per kWh

Coal Petroleum Natural Gas Hydro Other

1.18 0.85 0.53 0.00 0.00

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

Oil palm (plantation)

Rainforest

Gross assimilation (t CO2/ha/year) Total respiration (t CO2/ha/year) Net assimilation (t CO2/ha/year) Leaf area index Photosynthetic efficiency (%) Radiation conversion efficiency (g/M) Standing increment/year (t) Biomass increment/year (t) Dry matter production/year (t)

161.0 96.5 64.5 5.6 3.18 1.68 100 8.3 36.5

163.5 121.1 42.4 7.3 1.73 0.86 431 5.8 25.7

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K.F. Yee et al. / Applied Energy 86 (2009) S189–S196 Table 16 Summary of the CO2 assessment for palm biodiesel. Parameter

CO2 (kg CO2/ton biodiesel) From atmosphere

Plantation Gross assimilation Total respiration Peatland N–P–K fertilizers Traction (diesel)

To atmosphere

5462257.45 3273961.76 211996.97 11630.88 5872.81

Palm oil mill CPO production Biomass incineration Diesel for boiler start up Diesel for vehicles

117234.33 702.65 358.16

Transesterification Biodiesel production CPO Methanol Sodium hydroxide Electricity Boiler Biodiesel combustion Total

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

39392.72 232.95 5.63 2087.26 199.01 1614.00 5462257.45

3665289.12

the quantity of CO2 emission was calculated as 232.95 kg CO2 and 5.63 kg CO2/ton biodiesel, respectively. Studies have shown that oil palm plantations are as effective as rainforests in acting as carbon sinks areas of dry matter that serve to absorb the harmful GHG from the atmosphere. Table 15 shows the comparison of some physiological parameters of oil palm and tropical rainforest [40]. From the table, it was shown that the gross assimilation in oil palm plantation is 161,000 kg CO2 per hectare per year (5462257.45 kg CO2/ton biodiesel), whereas the amount of CO2 release from the respiration process is 96,500 kg CO2 per hectare per year (3273961.76 kg CO2/ton biodiesel). This result shows that oil palm trees generate a net sequestration of CO2 as opposed to forests, which only generate a dynamic CO2 equilibrium. As net sequesterer of CO2, oil palm trees absorb more CO2 from the atmosphere compared to the volume of CO2 they emit to the air. Table 16 shows the summary of the CO2 assessment which includes plantation, production, and combustion of palm

Table 17 Summary of the CO2 assessment for rapeseed biodiesel. Parameter

CO2 (kg CO2/ton biodiesel) From atmosphere

Plantation Gross assimilation Total respiration N–P–K fertilizers Traction (diesel)

To atmosphere

441752.10 264776.88 990.84 474.95

Rapeseed oil mill CRO production Straw incineration Electricity Boiler Diesel

1240.75 223.96 378.10 18.56

Transesterification Biodiesel production CRO Methanol Sodium hydroxide Electricity Boiler Biodiesel combustion

1445.98 232.91 5.63 60.71 199.01 1614.00

Total

441752.10

271662.29

Fuel consumption (l/100 km) CO2 emissions (g CO2/km) CO2 emissions (kg CO2/l)

Petrol

Diesel

LPG

Palm biodiesel

12.0 271 2.2583

11.5 309 (NA)

17.2 263 (NA)

12.0 (NA) 1.3950

biodiesel. From the table, it was found that the amount of CO2 generated and released to the atmosphere in the palm biodiesel production process (3665289.12 kg CO2/ton biodiesel) is less than the amount of CO2 used by the plants during assimilation (growth) process (5462257.45 kg CO2/ton biodiesel). This shows that the utilization of palm biodiesel can sequestrate CO2 and is indeed an environmentally friendly fuel. The CO2 life cycle assessment was also studied for the production of rapeseed biodiesel using a similar approach described for palm biodiesel. The gross assimilation and total respiration for rapeseed plant are assumed to be the same as palm tree. Table 17 summarizes the results revealing that the amount of CO2 generated and released to the atmosphere in the rapeseed biodiesel production process (271662.29 kg CO2/ton biodiesel) is also less than the amount of CO2 used by the plants during assimilation (growth) process (441752.10 kg CO2/ton biodiesel). This shows that the usage of both palm biodiesel and rapeseed biodiesel can result in a net reduction in CO2 concentration in the atmosphere. For the comparison of CO2 emission from palm biodiesel and petrol, the data for petrol fuel consumption and CO2 emissions from petrol combustion should be obtained [41]. As calculated using the data shown in Table 18, it was found that 2.258 kg of CO2 is emitted for each liter of petrol combusted. On the other hand, the combustion of palm biodiesel in the combustion engine of a European car only generated a mere 1.641 tons of CO2/ton of biodiesel or 1.395 kg CO2/l palm biodiesel [42]. Comparatively, an enormous amount of CO2 reduction (0.8633 kg CO2/l of biodiesel or 38% lesser) can be achieved when palm biodiesel is utilized instead of petrol. The data for CO2 emission from the combustion of 1 l petrol and palm biodiesel is summarized in Table 18. 4. Conclusion From this study, it was found that the utilization of palm biodiesel would generate an energy yield ratio of 3.53 (output energy/input energy), indicating a net positive energy. The energy ratio for palm biodiesel was found to be more than double the ratio for rapeseed biodiesel, which was only at 1.44. This indicates that palm oil would be a more sustainable feedstock for biodiesel production as compared to rapeseed oil. In terms of GHG assessment, it can be concluded that the production of palm and rapeseed biodiesel brings no negative impact to the environment as the amount of CO2 emitted to the atmosphere is much lower than the CO2 absorbed from the atmosphere. Also, the emission of CO2 from the combustion of 1 l of biodiesel is 38% less than that of petrol. Contrary to some reports which challenge the sustainability of palm oil as an environment-friendly source of energy, the results of this LCA study has shown that palm diesel has the potential to become the major renewable energy in the future, with huge positive energy ratio and significant reduction in CO2 emission. Acknowledgements The authors acknowledge Ministry of Science, Technology and Innovation (Malaysia) (ScienceFund-Project No.: 03-01-05SF0138) and Universiti Sains Malaysia (Research University Grant,

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