Economic Evaluation of Biodiesel Production from ... - ScienceDirect

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ScienceDirect Energy Procedia 105 (2017) 237 – 243

The 8th International Conference on Applied Energy – ICAE2016

Economic evaluation of biodiesel production from palm fatty acid distillate using a reactive distillation Lida Simasatitkula*, Amornchai Arpornwichanopb a

Department of Industrial Chemistry, Faculty of Applied Science, King Mongkut's University of Technology North Bangkok, Bangkok 10800, Thailand b Computational Process Engineering Research Unit, Department of Chemical Engineering, Faculty of Engineering, Chulalongkorn University, Bangkok 10330, Thailand

Abstract Economic evaluation of a reactive distillation for biodiesel production is performed. Palm fatty acid distillate (PFAD) consisting of a mixtures of triglycerides, moisture and free fatty acids is considered a feedstock. A simulation model of the biodiesel production process based on a reactive distillation is developed using Aspen Plus. Effect of key operating parameters, such as the number of reactive stages and liquid holdup, is investigated. The economic analysis considers total investment costs, operating costs and economic indicators, such as return on investment (ROI) and net present value (NPV). Performance of the reactive distillation processes is compared with a conventional process using two continuous reactors. The simulation results show that a single step acid – catalyzed process can be carried out in a reactive distillation for higher biodiesel productivity and purity. Although the conventional process has lower total production cost, the reactive distillation process is more economical process providing a higher ROI and NPV. The biodiesel production using a reactive distillation without recycling upstream is the most preferred configuration. Furthermore, the reactive distillation process can save the energy requirement of 51.2% compared with the conventional process. © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license © 2016 The Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Selection and/or peer-review under responsibility of ICAE

Peer-review under responsibility of the scientific committee of the 8th International Conference on Applied Energy.

Keywords: Economic evaluation, Palm fatty acid distillation, Biodiesel production, reactive distillation

1. Introduction Biodiesel is an alternative fuel that can replace petroleum diesel. Traditionally, it is produced from transesterification between refined vegetable oils and methanol in the presence of basic catalysts. A large excess methanol is generally required due to the chemical equilibrium of the transesterification.

* Corresponding author. Tel.: +662-555-2000 E-mail address: [email protected]

1876-6102 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the scientific committee of the 8th International Conference on Applied Energy. doi:10.1016/j.egypro.2017.03.308

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Lida Simasatitkul and Amornchai Arpornwichanop / Energy Procedia 105 (2017) 237 – 243

Therefore, a number of unit operations is required for a purification process. A reactive distillation that is one of a process intensification can conquer the drawback of a conventional process. It can improve the productivity and purity of biodiesel [1]. Although a reactive distillation cannot completely separate glycerol that is a byproduct from the transesterification, it can separate water that is byproduct from esterification of oleic acid [2]. In previous studies, biodiesel production from pure vegetable oil and fatty acids was investigated. Furthermore, high free fatty acid contents and moisture in feedstock are not mentioned. Biodiesel production from palm fatty acid distillate (PFAD) using a reactive distillation is an interesting option although it is still not commercialized [3]. In general, the reactive distillation is run under high pressure and methanol is vaporized before it is fed into the reactive distillation, leading to a low liquid holdup within the trays. In the previous studies, the effect of key parameters on the reactive distillation performance was investigated in terms of conversion, yield and purity to determine its optimum conditions. However, an economic study is also great importance to evaluate the feasibility of biodiesel production. The feasibility study of the biodiesel production from cottonseed oil consisting of mixed triglyceride and oleic acid was evaluated in term of total annualized cost [4] and the results indicated the advantage of the reactive distillation process over a batch process. To date, there is no detail in the economic evaluation of reactive distillation for biodiesel production from PFAD. In this work, a single step biodiesel production process from PFAD using a reactive distillation is preliminary designed. Two configurations of the reactive distillations, i.e., the reactive distillation with and without upstream recirculation, is analyzed. Economic analysis based on total investment, total production cost and economic indicators of biodiesel production using a reactive distillation is performed and compared to a conventional biodiesel process using two – steps catalyzed process. 2. Methodology 2.1 Process Modelling Material and energy balances of a biodiesel production process is performed by Aspen Plus process simulator. In this work, triglyceride with three identical fatty acid chains is considered. Therefore, tripalmitin is assumed to be a triglyceride in PFAD. The composition of PFAD is identified according to [3]. Because tripalmitin and fatty acids are pseudocomponents in Aspen Plus, some binary interaction parameters for vapor – liquid equilibrium are not available in the database. Here, NRTL is used to predict thermodynamic properties and equilibrium calculation while UNIFAC – LL is used to predict two liquid phases. Fig. 1(a) shows that NTRL prediction is found to be a good agreement with experimental data [5]. Kinetic parameters for acid – catalyzed esterification of PFAD is verified with [6] in term of conversion. Fig. 1(b) shows liquid – liquid equilibrium between methanol, methyl linoleate and glycerol. 2.2 Process design Fig. 2 shows the flowsheet of a conventional biodiesel production process. PFAD (stream 1) is preheated through a heater (B5) and sent to an esterification reactor (B1) while methanol (stream 3) is mixed with H2SO4 (stream 11). The ratio of methanol to PFAD is three according to [6]. The products are send to distillation (B2) to remove excess methanol that is recycled back to the reactor. This column consists of five stages including a total condenser and a partial reboiler. The downstream of distillation is fed to a transesterification reactor (B6) with additional methanol. The distillation column (B4) is employed to remove excess methanol which is recycled back to the second reactor. Therefore, a decanter (B10) is required to separate glycerol. Other distillation columns (B13 and B14) involve a purification process


until the purity of biodiesel is 99.65%. Fig. 3 shows a flowsheet of the acid – catalyzed process using a reactive distillation. PFAD (stream 1) is preheated to the reaction temperature through heater (B5) and fed into reactive distillation (RD) at 2nd stage. Methanol (stream 3) and H2SO4 (stream 11) are mixed before they are fed into the reactive distillation at the 6th stage. The reactive distillation has 10 stages including a total condenser and a partial reboiler and is modelled by using a RadFrac module in Aspen Plus. The downstream of reactive distillation (stream 2) is cooled down before catalyst removal. Crude methyl esters is introduced to a vacuum distillation with partial condenser to purify methyl esters (99.65%). The number of stages of this column is 8 stages. All reactors and distillation columns are computed by sizing mode in Aspen Plus. In this process, there are two design options: RD with and without upstream recirculation. Reflux ratio, feed location and number of stages are considered key design parameters to achieve the desired conversion of free fatty acids (99.5%). (a)

(b)

Fig. 1. (a) Vapor – liquid equilibrium of methyl laurate and methyl myristate at 13.33 kPa and (b) LL equilibrium of methanol, methyl linoleate and glycerol

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Option 2 (upstream recirculation)

Fig. 2. A two – steps catalyzed biodiesel production process using two continuous reactors Option 2 (upstream recirculation)

Fig. 3. A single step of biodiesel production process using a reactive distillation

3. Results and Discussions 3.1 Effect of Parameters Fig. 4(a) shows effect of number of reactive stages on the conversion of fatty acids with reflux ratio of 0.01, distillate rate of 126 kmol/h and liquid holdup of 0.7 m3. Two configurations of RD is also compared. The molar ratio of methanol to PFAD is fixed at three. It can be seen that the conversion of free fatty acid is increased with an increase in the number of reactive stages. This is because increasing the reactive stages causes increased reactant content in the column. Furthermore, the rate of esterification is increased as a temperature profile is rising due to endothermic reaction. Methanol in vapor phase is also decreased. However, the upstream recirculation results in a decrease in liquid holdup due to the fact that water, a byproduct from esterification, is also recycled back within the column. Thus, accumulation of water within the column hinders a forward reaction. In addition, an amount of methanol is an insignificant factor on the reaction rates. The conversion of free fatty acid for RD without the recirculation and with the recirculation is 99.3% and 98%, respectively. When the optimum number of reactive stages is 9 stages. Another important factor is a liquid holdup because the reaction occurs in the liquid phase. According to Fig. 4 (b) when the number of reactive stages is fixed at five stages and reflux ratio is 0.01, large liquid holdup will improve reaction rate as well as retention time. Biodiesel production using RD without upstream recirculation gives high performance. The optimum liquid holdup that gives 99%

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(b)

100

90

80 RD without recirculation RD with recirculation 70 2

4

6

8

10

12

14

Number of reactive stages

100

Conversion (%)

Conversion (%)

(a)

80

60 RD without recirculation RD with recirculation 40 0.1

16

0.2

0.3

0.4

0.5

0.6

0.7

Liquid holdup (m3)

0.8

0.9

1

Fig. 4 Effect of (a) a number of reactive stages and (b) liquid holdup on conversion of fatty acids (a)

(b)

1

0.8

0.6

Methanol Methyl ester PFAD Water

0.4

0.6

Methanol Methyl ester PFAD Water

0.4 0.2

0.2 0 1

Mass fraction

Mass fraction

0.8

1

2

3

4

5

6

Stage

7

8

9

10

0 1

2

3

4

5

6

Stage

7

8

9

10

Fig. 5 Composition profiles: (a) reactive distillation without upstream recycle and (b) reactive distillation with upstream recycle

conversion is 0.7 m3. The composition profile along the column at optimum conditions is shown in Fig. 5 (a) and 5 (b). In the liquid phase, the concentrations of methanol and water are increased at the top of column. Free fatty acids concentration is maximum at the 2nd stage which is the feed stage location. It decreases along the column and is completely consumed at the bottom of column. This implies that the RD without upstream recirculation can remove water from methyl esters. 3.2 Economic evaluation Economic analysis is performed taking into account a total investment cost, total production cost and economic indicators. The price of chemicals is shown in Table 1. The project year is 20 years and interest rate is 20% per year. Fig. 6(a) shows that the total investment cost (TIC) of all processes depends on total bare module cost (BMC) with respect to equipment size. The TIC of Biodiesel production using RD is lower than the conventional process because of a high conversion of fatty acids in the RD process. This factor reduces a cost of reactors and distillation columns for water and glycerol separation whereas the conventional process requires additional reactor to improve the productivity. In addition, a diameter and number of stages of distillation for purification of biodiesel in the RD process is lower than those of the conventional process. For the RD process, cost of heat exchanger is reduced due to the fact that reboiler of RD is used to transfer heat for reaction and separation simultaneously. RD without upstream recirculation is preferred because it shows the lowest value of TIC (5.45 x 106 $). A distribution fraction

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of the manufacturing costs in all the processes is shown in Fig. 6(b). It is found that the manufacturing cost depends on raw material costs and utilities. Direct manufacturing cost depends on an amount of raw materials. From the simulation results, the PFAD cost of RD without upstream recycle is 0.75 of manufacturing cost that is the lowest value when comparing with other processes whereas the indirect cost depends on fixed capital cost. It shows that the cooling cost has less effect on the total production cost. Stream cost of RD without stream recycle is the lowest value due to the lowest energy requirement. On the other hands, biodiesel production process using the RD is an uneconomic process in term of manufacturing cost as a molar ratio of methanol to PFAD is fixed. Therefore, a fresh methanol feed in the biodiesel production using RD is more required. This implies that cost of raw materials is the most significant factor followed by utilities cost of steam. From economic indicators in Table 2 (ROI is the ratio of annual profit and TIC), the RD without upstream recycle provides the highest yield of methyl esters. This process offers the highest profit and the lowest TIC. Therefore, this process is the most economical process due to the highest ROI and NPV. Table 1. Price of chemicals Chemical

Price

Chemical

Price

Palm fatty acid distillate

0.579 $/kg

Glycerol

0.062 $/kg

Methanol

0.33 $/kg

H2SO4

0.22 $/kg

Biodiesel

0.813 $/L

NaOH

0.54 $/kg

(a)

(b) Process 1 Process 2.1 Process 2.2

total BMC Contingency cost Auxiliary cost Fixed capital cost Working capital cost TIC 0

5

10 ($)

15 6 x 10

Process 1 Process 2.1 Process 2.2

Indirect manufacturing cost Laboratory analysis Maintenance Cooling Steam Supervisory Operating labor Other raw materials PFAD 0

0.2

0.4

0.6

0.8

1

Fig. 6. (a) Total capital investment costs and (b) manufacturing costs. Process 1 is conventional process, Process 2.1 is biodiesel production using RD without recycling upstream, Process 2.2 RD with recycling upstream.

4. Conclusions In this study, a reactive distillation is applied to the biodiesel production from PFAD and can improve the performance of reaction and separation. The optimum reactive stages and liquid holdup is 9 stages and 0.7 m3, respectively. The simulation results show that a reactive distillation process can reduce production cost and total investment cost when comparing with a conventional process using two – steps catalysed process. In addition, a reactive distillation without upstream recirculation offers more benefits than a reactive distillation with upstream recirculation due to the lowest total investment cost and energy


requirement. Although the total production cost of biodiesel production using reactive distillation without recycling upstream is high, this process is an economical process in terms of the highest of ROI and NPV. 5. Acknowledgements Support from the Faculty of Applied Science (KMUTNB), the National Research University Project, Office of Higher Education Commission and Chulalongkorn Academic Advancement into its 2nd Century Project is gratefully acknowledged. References [1] Boon-anuwat N, Kiatkittipong W, Aiouache F, Assabumrungrat S. Process design of continuous biodiesel production by reactive distillation: Comparison between homogeneous and heterogeneous. Chem Eng Process 2015;92:33-44. [2] Banchero M, Kusumaningtyas RD, Gozzelino G. Reactive distillation in the intensification of oleic acid esterification with methanol – A simulation case-study. J Ind Eng Chem 2014;20:4242-9. [3] Cho HJ, Kim JK, Hong SW, Yeo YK. Techno-Economic Study of a Biodiesel Production from Palm Fatty Acid Distillate. Ind Eng Chem Res 2012;52:462-8. [4] Souza TPC, Stragevitch L, Knoechelmann A, Pacheco JGA, Silva JMF. Simulation and preliminary economic assessment of a biodiesel plant and comparison with reactive distillation. Fuel Process Technol 2014;123:75-81. [5] Corazza M, Fouad WA, Chapma WG. Application of molecular modeling to the vapor–liquid equilibrium of alkyl esters (biodiesel) and alcohols systems. Fuel 2015;161:34-42. [6] Aranda D, Santos R, Tapanes N, Ramos AD, Antunes O. Acid-Catalyzed Homogeneous Esterification Reaction for Biodiesel Production from Palm Fatty Acids. Catal Lett 2008;122:20–5.

Biography Dr. Lida Simasatitkul works as a lecturer at Department of Industrial Chemistry, Faculty of Applied Science, King Mongkut's University of Technology North Bangkok (KMUTNB), Thailand. Her research interests focus on process design and process simulation.

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