Biochar as porous media for thermally-induced non-catalytic transesterification to synthesize fatty acid ethyl esters from coconut oil

Energy Conversion and Management 145 (2017) 308–313

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Biochar as porous media for thermally-induced non-catalytic transesterification to synthesize fatty acid ethyl esters from coconut oil Jong-Min Jung a,1, Jechan Lee a,1, Dongho Choi a, Jeong-Ik Oh b, Sang-Ryong Lee c, Jae-Kon Kim d, Eilhann E. Kwon a,⇑ a

Department of Environment and Energy, Sejong University, Seoul 05006, Republic of Korea Advanced Technology Department, Land & Housing Institute, Daejeon 34047, Republic of Korea Animal Environment Division, National Institute of Animal Science, Jeollabuk-do 55365, Republic of Korea d Research Institute of Petroleum Technology, Korea Petroleum Quality & Distribution Authority, Cheongju 28115, Republic of Korea b c

a r t i c l e

i n f o

Article history: Received 7 April 2017 Received in revised form 4 May 2017 Accepted 4 May 2017

Keywords: Biochar Fatty acid ethyl ester (FAEE) Transesterification Coconut oil Biodiesel

a b s t r a c t This study put great emphasis on evaluating biochar as porous media for the thermally-induced noncatalytic transesterification reaction to synthesize fatty acid ethyl esters (FAEE) from coconut oil. Thermogravimetric analysis (TGA) of coconut oil experimentally justified that the bond dissociation of fatty acid from the backbone of triglycerides (TGs) could be achieved, which finding could be applied to the non-catalytic transesterification reaction. To use biochar as porous medium, the surficial morphology of maize residue biochar (MRB) was characterized, revealing that biochar possessed the wider pore size distribution ranging from meso- to macro-pores than SiO2. The highest yield of FAEE from noncatalytic transesterification of coconut oil in the presence of MRB was 87% at 380 °C. To further enhance the FAEE yield, further studies associated with the production of FAEE with biochar made from different biomasses and various pyrolytic conditions should be performed. Ó 2017 Elsevier Ltd. All rights reserved.

1. Introduction To sustain our high social metabolisms for carbon in accordance with economic prosperities, actual global demand for carbon has been increasing since the industrial revolution. Exploiting carbon from fossil resources (i.e., coal, petroleum, and natural gas) for energies, chemicals, and commodities has broken the natural carbon balance, which has posed climate change [1,2]. Therefore, the comprehensive efforts covering social, scientific, and engineering aspects have been paid to alleviate climate change, which brought force two strategical guidelines (i.e., mitigation and adaptation) [3,4]. As part of these strategical guidelines, many researches for carbon capture and storage (CCS) and energy production from non-carbon resources (i.e., wind power, photovoltaic cell, geothermal energy, tidal energy, etc.) has been carried out [5]. Indeed, their practical implementations have been also established with strong public acceptance [6,7]. Moreover, the political enactment has been legislated to secure and expand renewable energies [8,9]. Nevertheless, our demand for carbon has not been diminished [10,11]. Therefore, this becomes a driving for developing ⇑ Corresponding author. 1

E-mail address: [email protected] (E.E. Kwon). These authors contributed equally to this work.

http://dx.doi.org/10.1016/j.enconman.2017.05.009 0196-8904/Ó 2017 Elsevier Ltd. All rights reserved.

the new concept of bio-refinery due to intrinsic carbon neutrality of biomass [12–14]. Biofuels such as bio-hydrogen, biogas, bioethanol, and biodiesel can be an initial step for bio-refinery [15–17]. Thus, particularly, biofuels from edible crop (i.e., first generation of bioethanol and biodiesel) have been implemented commercially [18,19]. Also, their practical uses (e.g., biodiesel and bioethanol) are relatively easy and reliable due to their high compatibilities with the current distribution networks for petroleum and with the modern IC engines [20,21]. Nevertheless, unlike petroleum, biodiesel and bioethanol generates the less amount of pollutants such as SOx, NOx, particulate matters, and unburned hydrocarbons [20,21]. Despite their merits, expansion of the first generation of biofuels has been limited due to ethical dilemma and price increase of crop [22,23]. To cope with these stated problems, the second (i.e., biofuels from inedible crops) and third (i.e., biofuels from aquatic biomass such as micro/micro-algae) generation of biofuels have been proposed and a great deal of researches has been conducted [22–24]. Unfortunately, to date, the technical maturity has not been fully established. Especially, a reliable/concrete technique for pretreatment, saccharification, and fermentation of lignocellulosic biomass has not been established [25,26]. However, the technical huddles for producing biodiesel are relatively lower since the conversion of

J.-M. Jung et al. / Energy Conversion and Management 145 (2017) 308–313

biodiesel is achieved via the well-established chemical process called transesterification. Fatty acid methyl esters (FAMEs) commonly refer biodiesel, produced via transesterification of triglycerides (TGs) and methanol. One of demerits of producing biodiesel is to use methanol since methanol is toxic and industrially produced from petroleum [27]. Also, there are a high explosion risk due to the low boiling point of methanol [28]. Thus, as an effort to reduce the use of the toxic petroleum-based chemical for biodiesel production, ethanol has been used as a non-toxic reactant for producing biodiesel [29,30]. Furthermore, ethanol can be produced from renewable resources such as biomass [31–33]. In these respects, employing ethanol in transesterification of TGs, producing fatty acid ethyl esters (FAEEs), would be a principle strategy to boost sustainability of biodiesel production process. Moreover, FAEE-biodiesel has a better lubricity [34] and a higher cetane number than FAMEbiodiesel [35]. Based on evaluating emissions of NOx, smoke, and CO2, FAEEs have a less negative effect on environment than FAMEs [36]. FAEEs also facilitate low-temperature engine operation [37]. Conventional catalytic transesterification reactions for producing biodiesel have disadvantages. For instance, during alkalicatalyzed transesterification, FFAs turns into soap by saponification reaction, decreasing the biodiesel yield and leads to a difficult condition for glycerol separation. Acid-catalyzed transesterification can be a feasible alternative, but the reaction rate of transesterification in acid catalyst is very slow [38]. To overcome these technical demerits of acid and/or base catalyzed reactions, a great deal of researches associated with non-catalytic transesterification at supercritical conditions (i.e., 250–450 °C and 250–450 bar) of alcohol has been performed [39,40]. Despite many technical advantages, biodiesel production at supercritical conditions needs high capital cost. Therefore, there is high demand for the technical advances enabling the production of biodiesel without using conventional catalytic sites and discharging any wastewaters during the process. Thus, the development of economically viable production of biodiesel is highly desirable. To this end, non-catalytic transesterification using porous materials was reported in our previous studies [41–44]. A porous material such as SiO2 was used to provide numerous pores where collision frequency for reactants were expedited. The transmethylation technique using a porous material exhibited an extraordinarily high tolerance against impurities such as FFAs, water, and hydrocarbons [45]. In these regards, finding a suitable porous material can be a key to improve the conversion of biodiesel. In other words, transforming lipid into biodiesel is highly contingent on the physical properties (i.e., porosity, pore size, pore distribution, etc.) of porous medium. However, SiO2 is an expensive and non-sustainable porous material; thus, it is essential to find a new class of porous materials for the noncatalytic transesterification. Biochar, a porous material made by pyrolysis of biomass, is being used for soil amendment, carbon sequestration medium to mitigate greenhouse gas reduction [46,47]. It can be a good candidate for porous material in non-catalytic transesterification since properties of biochar can be modified via controlling pyrolytic conditions. The functionalized structures of biochar varied with raw materials also provide a great venue for offering a viable option for selecting biomass [48]. This study placed great emphasis on the mechanistic understanding of non-catalytic transesterification using biochar as porous material. As a case study, biochar generated from maize residue were used as a porous material. Furthermore, ethanol was used as acyl acceptor to improve the physico-chemical properties of biodiesel (e.g., FAEEs) in this study. To experimentally evaluate the effectiveness of biochar in non-catalytic transesterification, we chose coconut oil as the initial feedstock.

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2. Materials and methods 2.1. Materials and chemicals A coconut oil (acid contents: 12.2%; water content: 0.2%) used in the study was purchased from a local market. Methanol (99.9%), anhydrous ethanol (99%), dichloromethane (99.9%), and SiO2 (particle size: 60–100 mesh) were purchased from Sigma-Aldrich (St. Louis, MO, USA). 2.2. Thermo-gravimetric analysis The thermal degradation of coconut oil in N2 was characterized with a Mettle Toledo TGA system (Switzerland). The TGA experimental work was done at a heating rate of 10 °C min 1 from 25 to 900 °C. The total flow rate of reactive and protective gas controlled by the embedded the MFCs in the TGA unit were 60 mL min 1 and 9.3 ± 0.05 mg of coconut oil was loaded for the TGA test. To ensure reproducibility, the TGA test was conducted three times. 2.3. Biochar production and characterization Maize residue was gathered from agricultural local field. To produce maize residue biochar (MRB), biomass was dried using a furnace at 80 °C for 24 h and uniformalized to 25 mesh sieve. Pyrolysis of maize residue was done at 450 °C (heating rate: 10 °C min 1) for 3 h in N2. Properties of MRB was measured by a Micromeritics ASAP 2010 and a Hitachi S-4300 field emissionscanning electron microscopy equipped with an energydispersive X-ray spectrometry. 2.4. Transesterification of coconut oil and analysis of FAMEs and FAEEs A bulkhead union (2 mL) (Swagelok, Solon, OH, USA) were used as a reactor for the reaction. The bulkhead was filled with SiO2 or MRB (200 mg). After that, 3.43 mmol of alcohol and 0.01 mL of the coconut oil were loaded in the bulkhead. The bulkhead was sealed with two plugs (Swagelok, Solon, OH, USA). It was heated by a furnace with a heating rate of 20 °C min 1 to a target temperature. After reaching the target temperature, it was held for 1 min. After a reaction finished, the reactor was quenched in a cold water bath. The produced FAMEs and FAEEs were diluted 15-fold in dichloromethane before injecting to a Varian GC-FID (Santa Clara, CA, USA). Calibration of FAMEs and FAEEs was conducted using 37 component FAME mixture and saturated and unsaturated FAEE standards purchased from Sigma-Aldrich (St. Louis, MO, USA). Detailed information about the GC analysis of FAMEs and FAEEs are given in supporting information (see Tables S1, S2, and S3). 3. Results and discussion 3.1. Thermal degradation of coconut oil To find the possible experimental temperature for initiating the non-catalytic transesterification reaction, the TGA test with coconut oil was done. The representative thermogram (i.e., the mass decay curve according to temperature) was shown in Fig. 1. The thermal degradation rate depicted as the differential thermogram (DTG) curve was also shown in Fig. 1 to effectively differentiate the thermal decomposition of coconut oil. Due to the negligible experimental deviations for each TGA run with coconut oil, error bar was not included in Fig. 1. As shown in Fig. 1, thermal deconstruction of coconut oil is initiated at 330 °C and completed at

310

J.-M. Jung et al. / Energy Conversion and Management 145 (2017) 308–313 Table 1 Characterization of SiO2 and MRB.

2

1

Surface area (m g ) Pore volume (cm3 g 1) Pore size (nm) Mobile matter (wt.%) Resident matter (wt.%) Moisture (wt.%) Ash (wt.%) Elemental analysis (wt.%)

Fig. 1. Representative the mass decay and DTG curves from the thermal decomposition of coconut oil.

450 °C. Moreover, Fig. 1 clarifies that the thermal degradation rate of coconut oil reaches the maximum at 410 °C. The mass decay initiating at 330 °C can be explained by the direct bond dissociation of fatty acids (FAs) from the backbone of TGs. For example, the boiling point (Tb) of TGs (i.e., lipid) cannot be measurable since the direct bond dissociation of FAs from the backbone of TGs rather than evaporation of TGs predominantly occurs. The observation in Fig. 1 regarding the direct bond dissociation of FAs is of importance for the non-catalytic transesterification reaction because the initial step for the transesterification reaction mechanistically occurs first by means of the bond dissociation of FAs from the backbone of TGs before proceeding the substitution of two reagents [49,50]. Thus, mass decay via the bond scission of FAs from the TG backbone signifies that the non-catalytic transesterification reaction can be achievable without using any catalysts via adding the thermal energy from the external heating source. Our previous studies experimentally justified the concept of non-catalytic transesterification reaction using porous materials such as SiO2 [49,50]. Considering the boiling point of MeOH (65 °C), the heterogeneous reaction (i.e., the gas phase of MeOH and the liquid phase of TGs) can be easily developed at temperatures higher than 65 °C. The development of heterogeneous reaction imparts the mobility differences to reactants inside numerous pores: the pores act as small reactors where the gas phase of MeOH and the liquid phase of TGs react with each other [49,50]. Thus, it is very similar with the catalytic mechanisms since catalytic phenomenon is generally achieved by chemical and/or physical bonding of one of chemical reagents. Therefore, we hypothesize that biochar can be a viable candidate for a porous material for the non-catalytic (pseudocatalytic) transesterification reaction. 3.2. Characterization of the surficial morphology of MRB To use biochar as porous medium for the non-catalytic transesterification reaction, the surficial properties of biochar including surface area, pore volume, and pore size can be a key factor. Thus, the surficial properties of MRB and SiO2 were measured, listed, and compared in Table 1. In our previous studies, SiO2 was used as porous medium for the non-catalytic transesterification reaction, thus,

C O Si K

SiO2

MRB

451.0 0.9 6.0 – – – –

5.5 0.01 17.3 12.7 43.7 4.4 39.2

– – – –

65.2 20.2 1.2 13.4

comparison of their surficial properties with MRB will be a key index for the mechanistic understanding of the non-catalytic transesterification reaction. As summarized in Table 1, surface area and pore volume measured from SiO2 is much larger than MRB. Surface area and pore volume of SiO2 are 80 and 60 times larger than those of MRB, respectively. However, average pore diameter of MRB is bigger than that of SiO2. Thus, Table 1 signifies that MRB possesses meso-/macro-pores rather than micro-pores. Pore size distribution of SiO2 and MRB is compared in Fig. S1. As shown in Fig. S1, SiO2 and MRB exhibit a different surficial morphology. Most pores range from 6 to 8 nm for SiO2 while those range from 18 to 36 nm for MRB. SiO2 has a narrow pore distribution than MRB. This suggests that SiO2 mostly has very uniformed meso-pores, but MRB has both meso- and macro-pores, which is accordance with the previous interpretation in Table 1. Thus, it is desirable to explore the influence of surficial morphology associated with pore size distribution for the non-catalytic transesterification reaction. 3.3. FAMEs and FAEEs conversion under the equimolar condition of MeOH and EtOH Prior to evaluating the effectiveness of biochar for the noncatalytic transesterification reaction, it is very desirable to evaluate any steric factors from the different molecular size of MeOH and EtOH for the non-catalytic transesterification reaction. In general, the conversion efficiency of FAEEs is inferior to that of FAME even under the longer reaction time [51]. However, it has not been fully studied for the non-catalytic transesterification reaction. For better understanding of this, the non-catalytic transesterification of coconut oil with an equimolar mixture of MeOH and EtOH with SiO2 and MRB at 380 °C was conducted. The representative chromatogram of the mixture of FAMEs and FAEEs were depicted in Fig. 2 and their compositions (weight basis) are listed and compared in Table 2. A difference in C18:0 FAMEs and FAEEs can be explained by a small amount of C18:0 fatty acid in coconut oil. As evidenced in Fig. 2 and Table 2, FAMEs were produced more than FAEEs. This indicates that the reaction rate to form FAMEs is indeed faster than FAEEs, but the reaction rate to form FAEE is not much different in the non-catalytic transesterification. In addition, all FAME and FAEE components are very much consistent with other literatures [19,52]. Therefore, this observation implies that the thermal degradation of FAMEs and FAEEs does not occur at 380 °C. However, it is necessary to investigate the steric factors from MeOH and EtOH for the non-catalytic transesterification reaction at the different experimental temperature. For the further investigation, the same experimental work was conducted at 365 °C and the experimental results were shown in Fig. 3. As evidenced in Fig. 3, the yield of biodiesel (i.e., mixture of FAMEs and FAEEs) is

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Fig. 2. Representative chromatogram for the mixture of FAMEs and FAEEs generated from the non-catalytic transesterification of coconut oil in the presence of SiO2 at 380 °C using the equimolar mixture of MeOH and EtOH.

Table 2 Quantification of FAMEs and FAEEs made from the non-catalytic transesterification of coconut oil with SiO2 and MRB at 380 °C using the equimolar mixture of MeOH and EtOH. C6:0

C8:0

C10:0

C12:0

C14:0

C16:0

C18:0

C18:1

SiO2

FAMEs (mg) FAEEs (mg)

40 30

480 320

320 220

2530 1770

870 680

330 230

110 50

200 198

MRB

FAMEs (mg) FAEEs (mg)

38 29

472 315

328 226

2496 1746

899 703

332 232

122 55

192 190

Fig. 3. FAME and FAEE yield from the non-catalytic transesterification reaction of coconut oil in the presence of SiO2 at 365 and 380 °C using the equimolar mixture of MeOH and EtOH.

proportional to the experimental temperature. For example, the yield of biodiesel at 365 and 380 °C is 71 and 87%, respectively. An interesting thing is that the ratio of FAMEs to FAEEs is nearly the same (58:42), which is consistent with the previous results in Table 2 and Fig. 2. Therefore, this elucidates that the steric factors from MeOH and EtOH for the non-catalytic transesterification reaction is not influenced by reaction temperature. 3.4. FAEE yield as a function of temperature In Fig. 3, the yield of biodiesel is proportional to the temperature. Thus, it is highly desirable to establish the FAEE yield with

Fig. 4. The yield of FAEE as a function of experimental temperature from the noncatalytic transesterification reaction of coconut oil using SiO2 and MRB.

temperature. As discussed in Section 3.2, wide pore distribution of MRB as compared to that of SiO2 provides a favorable condition for transforming coconut oil into biodiesel. To confirm this, the FAEE yields from the non-catalytic transesterification of coconut oil in the presence of SiO2 and MRB were compared. Fig. 4 shows that the overall FAEE yield is proportional to the experimental temperature. However, the FAEE yield from the non-catalytic transesterification of coconut oil using MRB at temperatures lower than 380 °C is higher than that using SiO2. This is consistent with the hypothesis in Section 3.2. However, despite no occurrence of thermal cracking, the further FAEE yield cannot

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be achieved at temperatures higher than 380 °C. This observation suggests that the total surface area is also another crucial factor for enhancing the non-catalytic transesterification. In these respects, it is highly recommended that finding new biochars suitable for the non-catalytic transesterification can be a key to enhance the FAEE yield. The surficial morphology of biochar is highly contingent on the source of biomass and pyrolytic conditions. Thus, the further study using biochars that is generated from various biomass resources and/or from various pyrolytic conditions should be followed to establish a reliable non-catalytic platform to produce biodiesel. 4. Conclusions This work studied a use of biochar as porous medium for the noncatalytic transesterification reaction to synthesis of FAEEs. The wide pore distribution in biochar provided a favorable condition for enhancing the yield of FAEEs, thereby resulting in 87% yield of FAEE at 380 °C. Thus, this study significantly suggests that biochar can be used as an effective porous material for the non-catalytic transesterification. However, to enhance the yield of biodiesel, the further study using biochar generated from various sources from biomass and various pyrolytic conditions should be followed. Acknowledgements This work was supported by the New & Renewable Energy Core Technology Program of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) granted financial resource from the Ministry of Trade, Industry & Energy, Republic of Korea (No. 20163010092290). Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.enconman.2017. 05.009. References [1] Capellán-Pérez I, Arto I, Polanco-Martínez JM, González-Eguino M, Neumann MB. Likelihood of climate change pathways under uncertainty on fossil fuel resource availability. Energy Environ Sci 2016;9:2482–96. [2] Gustavsson L, Haus S, Lundblad M, Lundström A, Ortiz CA, Sathre R, et al. Climate change effects of forestry and substitution of carbon-intensive materials and fossil fuels. Renew Sustain Energy Rev 2017;67:612–24. [3] Brown C, Alexander P, Holzhauer S, Rounsevell MDA. Behavioral models of climate change adaptation and mitigation in land-based sectors. Wiley Interdiscip Rev Clim Change 2017;8:e448. [4] Spencer B, Lawler J, Lowe C, Thompson L, Hinckley T, Kim SH, et al. Case studies in co-benefits approaches to climate change mitigation and adaptation. J Environ Plan Manage 2017;60:647–67. [5] Boyle G. Renewable energy: power for a sustainable future. 3rd ed. Oxford University Press; 2012. [6] Shin J, Hwang WS. Consumer preference and willingness to pay for a renewable fuel standard (RFS) policy: focusing on ex-ante market analysis and segmentation. Energy Policy 2017;106:32–40. [7] Correa DF, Beyer HL, Possingham HP, Thomas-Hall SR, Schenk PM. Biodiversity impacts of bioenergy production: microalgae vs. first generation biofuels. Renew Sustain Energy Rev 2017;74:1131–46. [8] Amini Z, Ong HC, Harrison MD, Kusumo F, Mazaheri H, Ilham Z. Biodiesel production by lipase-catalyzed transesterification of Ocimum basilicum L. (sweet basil) seed oil. Energy Convers Manage 2017;132:82–90. [9] Hill J, Tajibaeva L, Polasky S. Climate consequences of low-carbon fuels: the United States Renewable Fuel Standard. Energy Policy 2016;97:351–3. [10] Kwon EE, Cho SH, Kim S. Synergetic sustainability enhancement via utilization of carbon dioxide as carbon neutral chemical feedstock in the thermochemical processing of biomass. Environ Sci Technol 2015;49:5028–34. [11] Kwon EE, Jeon EC, Castaldi MJ, Jeon YJ. Effect of carbon dioxide on the thermal degradation of lignocellulosic biomass. Environ Sci Technol 2013;47:10541–7. [12] Ahlgren S, Björklund A, Ekman A, Karlsson H, Berlin J, Börjesson P, et al. Review of methodological choices in LCA of biorefinery systems - key issues and recommendations. Biofuels Bioprod Biorefin 2015;9:606–19.

[13] Kajaste R. Chemicals from biomass - managing greenhouse gas emissions in biorefinery production chains - a review. J Clean Prod 2014;75:1–10. [14] Venkata Mohan S, Nikhil GN, Chiranjeevi P, Nagendranatha Reddy C, Rohit MV, Kumar AN, et al. Waste biorefinery models towards sustainable circular bioeconomy: critical review and future perspectives. Bioresour Technol 2016;215:2–12. [15] Dessì P, Lakaniemi AM, Lens PNL. Biohydrogen production from xylose by fresh and digested activated sludge at 37, 55 and 70 °C. Water Res 2017;115:120–9. [16] Elreedy A, Ibrahim E, Hassan N, El-Dissouky A, Fujii M, Yoshimura C, et al. Nickel-graphene nanocomposite as a novel supplement for enhancement of biohydrogen production from industrial wastewater containing monoethylene glycol. Energy Convers Manage 2017;140:133–44. [17] Zhuang X, Wang W, Yu Q, Qi W, Wang Q, Tan X, et al. Liquid hot water pretreatment of lignocellulosic biomass for bioethanol production accompanying with high valuable products. Bioresour Technol 2016;199:68–75. [18] Jung JM, Lee J, Kim J, Kim KH, Kwon EE. Pyrogenic transformation of oil-bearing biomass into biodiesel without lipid extraction. Energy Convers Manage 2016;123:317–23. [19] Pimngern N, Punsuvon V. Optimization of esterification and transesterification reactions for biodiesel production from crude coconut oil using RSM techniques. Key Eng Mater 2017:610–5. [20] Aldhaidhawi M, Chiriac R, Badescu V. Ignition delay, combustion and emission characteristics of Diesel engine fueled with rapeseed biodiesel – a literature review. Renew Sustain Energy Rev 2017;73:178–86. [21] Can Ö, Öztürk E, Yücesu HS. Combustion and exhaust emissions of canola biodiesel blends in a single cylinder DI diesel engine. Renew Energy 2017;109:73–82. [22] Rozina, Asif S, Ahmad M, Zafar M, Ali N. Prospects and potential of fatty acid methyl esters of some non-edible seed oils for use as biodiesel in Pakistan. Renew Sustain Energy Rev 2017;74:687–702. [23] Zhang H, Li H, Pan H, Liu X, Yang K, Huang S, et al. Efficient production of biodiesel with promising fuel properties from Koelreuteria integrifoliola oil using a magnetically recyclable acidic ionic liquid. Energy Convers Manage 2017;138:45–53. [24] Gerardo ML, Van Den Hende S, Vervaeren H, Coward T, Skill SC. Harvesting of microalgae within a biorefinery approach: a review of the developments and case studies from pilot-plants. Algal Res 2015;11:248–62. [25] Pandey A, Tiwari S, Tiwari KL, Jadhav SK. Relation between sugar consumption and bioethanol production potential in lignocellulosic biomass. Res J Biotechnol 2016;11:52–7. [26] Stolarski MJ, Krzyzaniak M, Łuczyn´ski M, Załuski D, Szczukowski S, Tworkowski J, et al. Lignocellulosic biomass from short rotation woody crops as a feedstock for second-generation bioethanol production. Ind Crops Prod 2015;75:66–75. [27] Stamenkovic´ OS, Velicˇkovic´ AV, Veljkovic´ VB. The production of biodiesel from vegetable oils by ethanolysis: current state and perspectives. Fuel 2011;90:3141–55. [28] Leung DYC, Wu X, Leung MKH. A review on biodiesel production using catalyzed transesterification. Appl Energy 2010;87:1083–95. [29] Silva C, Weschenfelder TA, Rovani S, Corazza FC, Corazza ML, Dariva C, et al. Continuous production of fatty acid ethyl esters from soybean oil in compressed ethanol. Ind Eng Chem Res 2007;46:5304–9. [30] Allen CAW, Watts KC, Ackman RG, Pegg MJ. Predicting the viscosity of biodiesel fuels from their fatty acid ester composition. Fuel 1999;78:1319–26. [31] Sindhu R, Binod P, Pandey A. Biological pretreatment of lignocellulosic biomass – an overview. Bioresour Technol 2016;199:76–82. [32] Kim J, Lee J, Kim K-H, Ok YS, Jeon YJ, Kwon EE. Pyrolysis of wastes generated through saccharification of oak tree by using CO2 as reaction medium. Appl Therm Eng 2017;110:335–45. [33] Frankó B, Galbe M, Wallberg O. Bioethanol production from forestry residues: a comparative techno-economic analysis. Appl Energy 2016;184:727–36. [34] Knothe G. Dependence of biodiesel fuel properties on the structure of fatty acid alkyl esters. Fuel Process Technol 2005;86:1059–70. [35] Encinar JM, González JF, Rodríguez JJ, Tejedor A. Biodiesel fuels from vegetable oils: transesterification of Cynara cardunculus L. oils with ethanol. Energy Fuels 2002;16:443–50. [36] Yusoff MFM, Xu X, Guo Z. Comparison of fatty acid methyl and ethyl esters as biodiesel base stock: a review on processing and production requirements. J Am Oil Chem Soc 2014;91:525–31. [37] Joshi H, Moser BR, Toler J, Walker T. Preparation and fuel properties of mixtures of soybean oil methyl and ethyl esters. Biomass Bioenergy 2010;34:14–20. [38] Kwon EE, Kim S, Jeon YJ, Yi H. Biodiesel production from sewage sludge: new paradigm for mining energy from municipal hazardous material. Environ Sci Technol 2012;46:10222–8. [39] Schürer J, Bersch D, Schlicker S, Thiele R, Wiborg O, Ziogas A, et al. Operation of a small-scale demonstration plant for biodiesel synthesis under supercritical conditions. Chem Eng Technol 2016;39:2151–63. [40] Xu QQ, Li Q, Yin JZ, Guo D, Qiao BQ. Continuous production of biodiesel from soybean flakes by extraction coupling with transesterification under supercritical conditions. Fuel Process Technol 2016;144:37–41. [41] Lee J, Tsang YF, Jung J-M, Oh J-I, Kim H-W, Kwon EE. In-situ pyrogenic production of biodiesel from swine fat. Bioresour Technol 2016;220:442–7. [42] Jung J-M, Lee J, Oh J-I, Kim H-W, Kwon EE. Estimating total lipid content of Camelina sativa via pyrolysis assisted in-situ transesterification with dimethyl carbonate. Bioresour Technol 2017;225:121–6.

J.-M. Jung et al. / Energy Conversion and Management 145 (2017) 308–313 [43] Jung J-M, Lee J, Kim K-H, Jang IG, Song JG, Kang K, et al. The effect of lead exposure on fatty acid composition in mouse brain analyzed using pseudocatalytic derivatization. Environ Pollut 2017;222:182–90. [44] Lee J, Jung J-M, Oh J-I, Ok YS, Lee S-R, Kwon EE. Evaluating the effectiveness of various biochars as porous media for biodiesel synthesis via pseudo-catalytic transesterification. Bioresour Technol 2017;231:59–64. [45] Jung J-M, Cho J, Kim K-H, Kwon EE. Pseudo catalytic transformation of volatile fatty acids into fatty acid methyl esters. Bioresour Technol 2016;203: 26–31. [46] Igalavithana AD, Lee SE, Lee YH, Tsang DCW, Rinklebe J, Kwon EE, et al. Heavy metal immobilization and microbial community abundance by vegetable waste and pine cone biochar of agricultural soils. Chemosphere 2017;174:593–603. [47] Shaheen SM, Antoniadis V, Kwon EE, Biswas JK, Wang H, Ok YS, et al. Biosolids application affects the competitive sorption and lability of cadmium, copper, nickel, lead, and zinc in fluvial and calcareous soils. Environ Geochem Health 2017. http://dx.doi.org/10.1007/s10653-017-9927-4.

313

[48] González ME, Cea M, Reyes D, Romero-Hermoso L, Hidalgo P, Meier S, et al. Functionalization of biochar derived from lignocellulosic biomass using microwave technology for catalytic application in biodiesel production. Energy Convers Manage 2017;137:165–73. [49] Jung J-M, Lee J, Kim K-H, Lee SR, Song H, Kwon EE. Biodiesel conversion via thermal assisted in-situ transesterification of bovine fat using dimethyl carbonate as an acyl acceptor. ACS Sustain Chem Eng 2016;4:5600–5. [50] Kim J, Jung J-M, Lee J, Kim K-H, Choi TO, Kim J-K, et al. Pyrogenic transformation of Nannochloropsis oceanica into fatty acid methyl esters without oil extraction for estimating total lipid content. Bioresour Technol 2016;212:55–61. [51] Gómez-Coca RB, Fernandes GD, Pérez-Camino MDC, Moreda W. Fatty acid ethyl esters (FAEE) in extra virgin olive oil: a case study of a quality parameter. LWT Food Sci Technol 2016;66:378–83. [52] Samuel OD, Giwa SO, El-Suleiman A. Optimization of coconut oil ethyl esters reaction variables and prediction model of its blends with diesel fuel for density and kinematic viscosity. Biofuels 2016;7:723–33.