Life Cycle Assessment of Biodiesel Production from Microalgae Oil: Simulation Approach

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1 9 Life Cycle Assessment of Biodiesel Production from Microalgae Oil: Simulation Approach Netipon Sakulcha 1 and Thongchai Srinophakun 2 1 Department of Chemical Engineering, Faculty of Engineering, Kasetsart University, Bangkok, 10900, Thailand 2 Center for Petroleum, Petrochemicals, and Advanced Materials, Kasetsart University, Bangkok, 10900, Thailand Abstract Biodiesel production from microalgae is studied in this work by using Aspen Plus as a simulator of biodiesel production. In addition, the environmental impact assessment is evaluated in this work by using life cycle assessment method. The results show that human toxicity is the highest contribution during biodiesel production. Heat and methanol production are the major cause of human toxicity with 89% and 4.46% of heat and methanol, respectively. In addition, agricultural land occupation and fossil depletion are considerable impacts of biodiesel production. Keywords biodiesel production, microalgae, simulation, life cycle assessment, aspen plus 1. Introduction Presently, fossil fuel is the main fuel driving industrial activities, transportation, and household consumption. The shortage of fossil fuel is a significant issue in the world, stimulating the discovery of alternative fuels. There are several alternative fuels being developed, such as bioethanol, biohydrogen, biogas, and biodiesel. Biodiesel has been explored as an alternative energy source which plays an important role in addressing these issues. Biodiesel can be produced from vegetable oil (soybean, palm, jatropha, and waste cooking oil) and animal fat, as is widely known. In addition, microalgae oil can be the raw material to produce biodiesel since microalgae has a higher oil yield per crop area compared to other feedstocks [1]. Biodiesel is biodegradable and non-toxic. In terms of combustion, it has lower emissions of carbon monoxide, sulfur oxide, and other pollutants compared to petroleum-based diesel [2]. The higher flash point (150 ๐ C) of biodiesel means that it is safer than petroleum diesel for storage, transportation, and handling [3]. In addition, biodiesel can be mixed with petroleum diesel ฉบ บท 84 ป ท 26 เมษายน - ม ถ นายน 2556

2 10 ว ศวกรรมสาร มก. in different ratios in order to be utilized in diesel engines and to reduce petroleum diesel consumption. These benefits of biodiesel make it to be a suitable alternative fuel. The general method to produce biodiesel is by transesterification reaction, which has vegetable oil and methanol as reactants and which uses a catalyst. Glycerol and fatty acid alkyl ester (biodiesel) are the by-product and the main product of the reaction, respectively. The environmental impact of biodiesel production has been studied by several researchers. Life cycle assessment of biodiesel production was studied by Varanda et al. [4]. The study focused on four simulated processes of biodiesel production from virgin oils and two simulated processes of biodiesel production from waste cooking oils. In what concerns life cycle assessment, processes using waste cooking oils have lower overall environmental impacts than the processes using virgin oils. Life cycle of algae production was studied by Clarens et al. [5] focusing on environmental impacts by comparing with switchgrass, canola, and corn farming. The environmental impacts of these crops have lower impacts than algae in energy use, greenhouse gas emissions, and water. Algae can convert to biofuelsbiogas, biodiesel, bioethanol, biohydrogen, and microalgae gasification-studied by Singh and Olsen [6]. Comprehensive life cycle assessment of algal biofuels illustrating environmental benefits and impacts can be a tool for guiding technology development as well as for policy decisions. Algae-based biodiesel production was studied by Lardon et al. [7], considering the environmental impacts. The outcome confirms the potential of microalgae as an energy source but highlights the imperative necessity of decreasing energy and fertilizer consumption. Hou et al. [8] have reviewed several feedstocks-based biodiesel productionssoybean, jatropha, and microalgae-in China, including the environmental assessment. All of the preceding studies have emphasized that microalgae gives lower environmental impacts than other biodiesel feedstock options. Biodiesel is an efficient energy source that can be used instead of diesel and mixed with diesel for combustion. It is important to study the environmental assessment of biodiesel production since a biodiesel plant utilizes heat, electricity, and materials during production. Certainly, the environmental impacts of biodiesel production from microalgae must be analyzed as regards the value of environmental potential in many impact categories. Therefore, the environmental impact of biodiesel production is assessed in this work by using Life Cycle Assessment (LCA) as a tool for environmental impact assessment. Aspen Plus is software to simulate the production process using microalgae as feed. 2. Methods Process simulation of biodiesel production from microalgae is simulated by using Aspen Plus in order to obtain a life cycle inventory-mass and energy inputs and outputs. Life cycle inventory consists of mandatory data in the life cycle assessment. Methods consist of two main topics, which are process overview and life cycle assessment, as shown in the following subtopics. 2.1 Process overview Microalgae are the feedstock of biodiesel production in this work. After the completion of

3 Life Cycle Assessment of Biodiesel Production from Microalgae Oil: Simulation Approach 11 microalgae cultivation, harvesting, and extraction to obtain microalgae oil, the oil is transesterified by using methanol as a raw material, with sodium hydroxide as catalyst, in a reactor to produce free fatty acid methyl ester (FAME) as biodiesel and glycerol as by product. In addition, methanol, unconverted oil, and catalyst are utilized incompletely in the transesterification reaction. After completing the reaction, methanol is recovered in a methanol recovery column in order to send it back as raw material. Biodiesel and glycerol are separated. In addition, biodiesel is washed by warm water. Two streams are separated: the stream of biodiesel purification and that of the glycerol purification. Besides, catalyst removal appears in this work. Process simulation is an alternative tool to simulate biodiesel production. In addition, process simulation is selected to obtain the mass and energy data for the application of the environmental assessment. Aspen Plus simulator is the program utilized in this work. The simulation is used to propose a conceptual design of biodiesel production. However, most of the key components involved in the process are not defined in the standard Aspen Plus property databases, making it is necessary to estimate Methanol & Sodium Hydroxide Microalgae oil Trans esterification Methanol Methanol recovery Water and simulate these components in the Aspen Plus simulator. The process design is divided into six sections: transesterification reaction, methanol recovery, separation of biodiesel and glycerol, biodiesel washing and purification, alkali removal, and glycerol purification. 2.2 Life cycle assessment (LCA) LCA is a tool to evaluate the environmental impacts of the product over the whole process [9]. The environmental impacts of life cycle consist of seven categories-climate change, ozone depletion, human toxicity, terrestrial acidification, water depletion, and fossil depletion. LCA methodology in this study was based on the ISO framework [10] Goal and scope definition The goal of this work is to assess the environmental impacts of biodiesel production from microalgae. The scope of work is gate to gate excluding microalgae cultivation, harvesting, and extraction. The functional unit of this work is 1,000 kg of biodiesel production. ReCiPe is used in this work as a life cycle inventory assessment method of calculation. The system boundary is shown in Figure 1. Biodiesel & Glycerol separation Biodiesel Purification Methanol & Water Biodiesel Catalyst removal Glycerol Purification Glycerol H 2 SO 4 Na 2 SO 4 Figure 1 System boundary of biodiesel production from microalgae Methanol & Water ฉบ บท 84 ป ท 26 เมษายน - ม ถ นายน 2556

4 12 ว ศวกรรมสาร มก Life cycle inventory analysis Life cycle inventory analysis involves the material and energy inputs and outputs over the life cycle of 1,000 kg biodiesel production from microalgae. Data sources of biodiesel production (mass and energy) are obtained from the simulation by Aspen Plus. Heat source used during biodiesel production is heat coming from combustion of biomass. It is included in SimaPro program. Transportation in this work is used in order to carry chemicals to biodiesel plant. Lorry (diesel engine), ton, is selected for chemicals transportation with 10 km/l of fuel capacity Life cycle impact assessment From the inventory data from biodiesel production, the environmental impacts are evaluated. This is the midpoint impact assessment method covering human toxicity, climate change, ozone depletion, acidification, agricultural land occupation, water depletion, and fossil depletion. 3. Results and Discussion 3.1 Process simulation and design This section addresses the process design for biodiesel production from microalgae. Microalgae oil in this study consists of four main fatty acids as shown in Table 1 [11]. These fatty acids appear in the process flow diagram as the OIL stream: see Figure 3. The chemical structures were created by Aspen Plus, since there are no fatty acids in the database of the simulator. Table 1 The percentage of microalgae oil fatty acid Fatty acid of microalgae oil % wt. of fatty acid Palmitic acid Oleic acid 8.22 Linoleic acid Linolenic acid MEOH+H20 P8 19 V6 H4 MEOHRECO FLASH MEOH NAOH M1 OIL P2 GLYCEROL 1 P1 4 2 H H2 REACTOR H2O+MEOH P3 V1 D1 P4 WATER 11 H5 H2SO4 12 FAME EXTRACT D3 16 D2 15 FILTER 14 REACTOR2 13 UNCON SOLIDS Figure 2 Process flow diagram of biodiesel production from microalgae oil

5 13 The physical properties were estimated by Aspen Plus since they are necessary for computation. The WILSON property method is used in this simulation. The biodiesel production process consists of six sections-transesterification, methanol recovery, biodiesel and glycerol separation, biodiesel purification, catalyst removal, and glycerol purification-as shown in Figure 2. The process starts with mixing 200 kg/h of methanol and 10 kg/h of sodium hydroxide at the mixer (M1) before pumping the mixture to the heat exchanger (H1) to the temperature to 60 ๐ C. At the same time, 1,000 kg/h of microalgae oil is pumped to another the heat exchanger (H2) to heat it up to 60 ๐ C. Both the mixture of methanol and sodium hydroxide as well as microalgae oil are sent to the reactor (REACTOR) to react by transesterification at 60 ๐ C and atmospheric pressure. The products consist of a main product (biodiesel), byproduct (glycerol), and methanol, catalyst, and unconverted oil appearing in stream 6. These products are pumped into the distillation column (D1) in order to recover the methanol back to the mixer (M1). An extraction column (EXTRACT) is utilized for washing biodiesel by using water and for separating biodiesel and glycerol at the same time. FLASH is used to purify biodiesel for obtaining the 99.7% of biodiesel appeared in the FAME stream. Glycerol, sodium hydroxide, some water, and some methanol are separated in an extraction column. The function of the second reactor (REACTOR2) is to neutralize or change sodium hydroxide into sodium sulfate by using 13 kg/h of sulfuric acid: in other words, two moles of sodium hydroxide will be reacted with one mole of sulfuric acid to be sodium sulfate as solid. The filter (FILTER) is operated for the separation of these solids. The distillation columns (D2 and D3) are utilized to purify 107 kg/h of glycerol as USP grade (more than 93% concentration). 3.2 Life cycle assessment Result of inventory analysis Inventory analysis involves data collection and calculation procedures to quantify the relevant inputs and outputs of a production system. These inputs and outputs may include the use of resources and releases to air, water, and land associated with the system. Due to heat used in this process coming from biomass, pollutants releasing from biomass combustion are mainly CH 4 and N 2 O with kg/mj and kg/mj, respectively [12]. Table 2 shows the overall inventory analysis of this study obtained from the simulation Allocation method The allocation of environmental impacts to materials and products is a complex process. The appropriate method also depends on the perspective of the observer. Economic allocation is one of common attribution allocation. Glycerol and sodium sulfate (Na 2 SO 4 ) are generated as co-products during biodiesel production. Quantity and price of co-product including allocation factor from biodiesel production are shown in Table 3. ฉบ บท 84 ป ท 26 เมษายน - ม ถ นายน 2556

6 14 ว ศวกรรมสาร มก. Table 2 Inventory data of biodiesel production from microalgae Biodiesel Production Quantity Inputs Microalgae oil (kg) 1,000 NaOH (kg) 10 Methanol (kg) 200 Water (L) 50 Sulfuric acid (kg) 13 Electricity (kwh) 150 Heat (MJ) 2,482 Outputs Biodiesel (kg) 1,000 Glycerol (kg) Na 2 SO 4 (kg) Methanol (kg) 50 Emission to water Waste water (L) 67.5 Emission to air CH 4 (kg) N 2 O (Kg) Table 3 Quantity and price of co-product form biodiesel production from microalgae Main product and co-product Quantity Price Gross price (Baht/unit) (Baht) Allocation Biodiesel (kg) 1, , * Glycerol (kg) , Sodium sulfate, Na 2 SO 4 (kg) Summary 50, Remark: * is allocation factor, 1 USD = 32 Baht (2012) Results of impact assessment In this study, biodiesel production takes as its basis on 1,000 kg of biodiesel itself. The results show that biodiesel production makes the highest contribution on human toxicity impact as shown in Figure 3. Fossil depletion and climate change are the second and the third greatest contribution. Human toxicity at 0.52 Pt comes from nitrogen monoxide (NO), nitrogen dioxide (NO 2 ), methane (CH 4 ), nitrous

7 15 Pt Climate change Ozone depletion Human toxicity Water depletion Terrestrial acidification Fossil depletion Wastewater Heat Electricity Sulphuric acid Transport Sodium hydroxide Methanol Tap water Microalgae-based biodiesel Figure 3 The environmental impacts of biodiesel production oxide (N 2 O), and sulfur dioxide (SO 2 ), which are generated during heat production in biodiesel production. Heat production is a main cause of the environmental impact. It is generated for producing heat to supply heat exchangers as well as distillation columns. Fossil depletion at 0.15 Pt occurs by using fuel oil for methanol production to supply the biodiesel production and diesel fuel is used for chemicals transportation. Methanol is the greatest impact of biodiesel production since it can be investigated as regards its impacts of acidification and fossil depletion: analysis shows 35% and 93%, respectively. Refrigerant and heat pump for producing heat are causes of ozone depletion at 0.02 Pt. As mentioned, these effects come from methanol and heat production. This work consistent with a work of Hou et al. [8] for reducing the environmental impacts (human toxicity, ozone depletion, climate change, acidification, and fossil depletion) of biodiesel production from microalgae. 4. Conclusion This work has studied biodiesel production from microalgae. The purpose of this study is to investigate the life cycle of 1,000 kg of produced biodiesel. The results show that human toxicity is the highest impact during biodiesel production from microalgae. Heat and methanol production are the main causes of human toxicity impact, with 89% and 4.46% of the effect on human toxicity coming from heat and methanol, respectively. In addition, methanol makes the highest impact on fossil depletion at 93%. 5. Acknowledgements This research was supported by the followings: Center for Petroleum, Petrochemicals and Advanced Materials, Center for Advanced Studies in Industrial Technology; Department of Chemical Engineering, Faculty of Engineering, Kasetsart University and the Graduate School, Kasetsart University, Thailand. ฉบ บท 84 ป ท 26 เมษายน - ม ถ นายน 2556

8 16 ว ศวกรรมสาร มก. 6. References [1] Chisti Y., (2007), Biodiesel from microalgae. Biol Adv. Vol. 25. pp [2] Agarwal A.K., and Das L.M., (2001), Biodiesel development and characterization for use as a fuel in compression ignition engines. J.Eng.Gas Turbines Power. Vol pp [3] Krawczyk T., (1996), Biodiesel. INFORM7, Vol. 8. pp [4] Varanda M.G., Pinto G., and Martins F., (2011), Life cycle analysis of biodiesel production. Fuel Processing Technology. Vol. 92. pp [5] Clarens A.F., Resurreccion E.P., White M.A., and Colosi L.M., (2010), Environmental life cycle comparison of algae to other bioenergy feedstock. Environ. Sci. Technol. Vol. 44. pp [6] Singh A., and Olsen S.I., (2011), A critical review of biodiesel conversion, sustainability and life cycle assessment of algal biofuels. Applied energy. [7] Lardon L., Helias A., Sialve B., Steyer J.P., and Bernard O., (2009), Life-cycle assessment of biodiesel production from microalgae. Environmental science & technology. Vol. 43. pp [8] Hou J., Zhang P., Yuan X., and Zheng Y., (2011), Life cycle assessment of biodiesel from soybean, jatropha, and microalgae in China conditions. Renewable and sustainable energy reviews. Vol. 15. pp [9] Kiwjaroun C., Tubtimdee C., and Piumsomboon P., (2009), LCA studies comparing biodiesel synthesized by conventional and supercritical methanol methods. Journal of Cleaner Production. Vol. 17. pp [10] Lee K, and Inaba A., (2004), Life cycle assessment best practices of ISO series. Singapore: Asia-Pacific Economic Cooperation. [11] Caye M.D., Nghiem P.N., and Terry H.W., (2008), Biofuels Engineeing Process Technology. The McGraw-Hill Co., Inc., New York. [12] Tarnawski W., (2004), Emission Factors for Combustion of Biomass Fuels in the Pulp and Paper Mills. FIBRES & TEXTILES in Eastern Europe. Vol. 12. No. 3. pp 91-95