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Purification of glycerol from transesterification using activated carbon prepared from Jatropha Shell for biodiesel production
Journal of Environmental Chemical Engineering 7 (2019) 103303
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Journal of Environmental Chemical Engineering journal homepage: www.elsevier.com/locate/jece
Purification of glycerol from transesterification using activated carbon prepared from Jatropha Shell for biodiesel production Hiroaki Habakia, Tomoki Hayashib, Patima Sinthupinyob, Ryuichi Egashiraa,
T
⁎
a
Department of Transdisciplinary Science and Engineering, School of Environment and Society, Tokyo Institute of Technology, Address: 12-1, O-okayama-2-chome, Meguro-ku, Tokyo 152-8550, Japan b Department of International Development Engineering, Graduate School of Science and Engineering, Tokyo Institute of Technology, Address: 12-1, O-okayama-2-chome, Meguro-ku, Tokyo 152-8550, Japan
A R T I C LE I N FO
A B S T R A C T
Keywords: Biodiesel fuel production Inedible plant oil Glycerol purification Activated carbon from waste
To improve biodiesel production from jatropha, its shell, a waste material, was thermally treated to produce activated carbon (AC) and the AC was applied to purification of glycerol from transesterification. The AC was prepared by chemical activation method using H3PO4 as the activation agent. The yield of the chemically activated carbon was better than the physically activated carbon in the higher range of thermal treatment temperature, and the prepared AC had a sufficient specific surface area. For purification of the glycerol obtained from transesterification to remove impurities such as methanol and monoolein, the AC was also used for measuring the adsorption equilibria with the model glycerol solutions containing impurities, and adsorption isotherms of these compounds were prepared. The AC could absorb and remove the impurities in the model glycerol phase. The adsorption of the impurities was enhanced by chemical activation because of a larger specific surface area, and the effects of surface modification by the activation were inefficient for the adsorption. A rough process assessment suggested that the amount of AC prepared from the shell was sufficient to purify glycerol.
1. Introduction Biodiesel is gaining popularity as a renewable energy source. Although biodiesel is generally produced from edible plant oils, the production has been of great concern because of the competition from production of food materials from such plants. As a result, utilization of these plant oils as fuels has become more expensive. Therefore, increasing attention has been focused on the production of fuel from inedible plant oils such as jatropha [1–4], castor [5,6], and pongamia oil [7,8]. They are generally cultivated in marginal places with low irrigation requirements and places not competing with the cultivation of general food plants. Jatropha is the most attractive plant among these [9], and considerable research has been conducted to develop an effective method for the production of oil from this plant [1–4,10–16]. On the other hand, these plants should be newly cultivated and it is necessary to exploit not only the effective production of biodiesel from these plants, but also the utilization of their residues. In the case of jatropha, residues such as the shell and hull were thermally treated to prepare activated carbon (AC) [17,18], which was further used for the separation of some organic and inorganic compounds from aqueous solutions via adsorption [19]. Utilization of the residues is one of the
⁎
methods to improve the entire process of biodiesel production. Another approach to enhance the process efficiency is the purification of crude glycerol obtained from transesterification [20–22]. Generally, the crude glycerol contains water, organic and inorganic salts, soap, alcohol, and unreacted glycerides. Although the separation and recovery of methanol as alcohol was commercially conducted by vacuum distillation, some concerns regarding trace amount of residual methanol and decomposition of glycerol were reported [22]. In this study, we aimed to purify glycerol from transesterification using AC prepared from the waste material, i.e., shell of jatropha. The jatropha shell was thermally treated to prepare the AC, and the removal of impurities from the crude glycerol obtained after transesterification was studied. The adsorption equilibria of methanol and monoolein impurities in the glycerol with the AC and purification of the glycerol were also studied. 2. Purification of crude glycerol using activated carbon from jatropha shell Fig. 1 shows the conceptual diagram of biodiesel production incorporating glycerol purification using the AC prepared from jatropha
Corresponding author. E-mail address: [email protected] (R. Egashira).
https://doi.org/10.1016/j.jece.2019.103303 Received 7 May 2019; Received in revised form 2 July 2019; Accepted 18 July 2019 Available online 12 August 2019 2213-3437/ © 2019 Elsevier Ltd. All rights reserved.
Journal of Environmental Chemical Engineering 7 (2019) 103303
H. Habaki, et al.
Nomenclature ABET Fj Ki qi q*i Tt xi xPG1,i YAC yAC YPG1,i
Subscript
BET surface area of AC [m2 (kg–AC)–1] mass of material i in experiment [kg], mass flow rate of material i in Figure 1 [kg hr−1] Langmuir parameter of componenti [–] adsorption amount of componenti per unit mass of AC [kg (kg–AC)–1] saturated adsorption amount of componenti per unit mass of AC [kg (kg–AC)–1] thermal treatment temperature [K] mass fraction of componenti in glycerol solution [–] mass fraction of componenti in FPG1 [–] yield of AC based on jatropha fruit [–], yield of AC based on jatropha shell [–] yield of componenti in FPG1 based on jatropha fruit [–]
AC BDF CG i j JF JO JS MeOH MO PO PG1 PG2
activated carbon from jatropha shell biodiesel fuel crude glycerol componenti materialj jatropha fruit crude jatropha oil jatropha shell methanol monoolein pretreated jatropha oil purified glycerol 1 purified glycerol 2
were of analytical grade and purchased from FUJIFILM Wako Chemical Corp. Table 2 shows the experimental conditions for chemical impregnation. The shell was crushed and sieved into the desired range of sizes, and the sieved particles of the shell were impregnated with H3PO4 for 24 h. Following this, they were dried at 333 K in the oven for another 24 h. The impregnated shell was kept in a desiccator for thermal treatment. Table 3 lists the principal conditions of thermal treatment, and Fig. 2 shows the schematic diagram of the thermal treatment reactor. The reactor consisted of a horizontal tubular reactor inserted into an electrically heated furnace (KTF-040 N from KOYO Thermo Systems Co., Ltd.) equipped with temperature control and thermocouple. An average of 0.020 kg sample was filled into the sample holder, which was placed at the center of the reactor. Nitrogen gas was purged into the reactor for 10 min before the heating began. In the case of steam thermal treatment, preheated deionized water was supplied using a micro-plunger pump (LC10-ADVP, Shimadzu Corp.). The gas flow from the reactor outlet was collected in a condenser, and the condensate drum was immersed into an isothermal bath at 273 K. After holding the system isothermally at the desired temperature for 30 min, the heater was turned off, and the reactor was cooled down. The masses of the residue left in the holder, AC, and condensate in the drum were measured. The AC was boiled for 2 h to remove the tar inside the particles. Following this, it was dried for 24 h and kept in a desiccator. The specific surface area, SAC, total pore volume, VAC, and micro pore volume of the obtained AC were analyzed using the nitrogen adsorption isotherm obtained from a surface area and pore volume analyzer (BELSORP-max: BEL JAPAN Co.). The trace amounts of methanol and monoolein remaining in glycerol after Catalyst Removal and Methanol Recovery were subsequently removed using AC as the adsorbent. The principal conditions of adsorption equilibrium measurements are listed in Table 4 . The batch adsorption studies with the model glycerol solutions and prepared ACs were carried out in a 100 × 10−6 m3 Erlenmeyer flask with a screw cap, in which a mixture of 1 × 10−3 kg AC and 100 × 10−6 m3 methanol or monoolein in glycerol were kept at 303 K. The mixture was continuously shaken at a constant temperature in a thermostated rotary shaker for 72 h, within which the equilibrium was reached. The commercial activated carbon, purchased from FUJIFILM Wako Chemical Corp. and abbreviated as CAC, was used as the reference activated
shell. The treatment of the crude glycerol obtained by transesterification was assessed using the simple mass balance relation and adsorption equilibrium. First, jatropha fruit, FJF, is processed to obtain crude jatropha oil (FJO) and shell (FJS) at Oil Extraction. Based on the work by Singh et al. [23], the mass ratios of FJO and FJS relative to feed FJF, i.e., FJO/FJF and FJS/FJF, were determined to be 0.318 and 0.682, respectively. FJO is sent to Oil Pretreatment, where impurities such as phospholipid, water, and free fatty acids (FFAs) are removed. While phospholipid and water are removed, FFA is esterified to fatty acid methyl ester. The detailed procedures and conditions are given in Appendix A and our previous study [4,13]. The pretreated oil is transesterified with methanol to obtain the fatty acid methyl ester and crude glycerol phases. Then, the crude glycerol is treated to remove the catalyst, methanol, and water to obtain purified glycerol1, FPG1. Table 1 shows the composition of FPG1. FPG1 contains trace amounts of methanol and monoolein impurities that can be treated with the AC prepared from jatropha shell. Based on the mass balances of AC from jatropha shell, impurities in FPG1, and adsorption of the impurities, the treatment of FPG1 by AC are discussed. 2.1. Experimental The jatropha shell, collected from a jatropha plantation in Suphanburi, Thailand, was used as the precursor of AC. It was washed with deionized water and dried at 333 K in an oven for 24 h. H3PO4 was used as the activating agent for chemical activation. Methanol and monoolein were used as model impurities in the pretreated glycerol obtained by transesterification. All the chemicals used in this study
Table 1 Composition of FPG1 (mass fraction).
Fig. 1. Conceptual diagram of biodiesel production incorporating glycerol purification. 2
Methanol
Monoolein
Glycerol
0.00102
0.0188
0.976
Journal of Environmental Chemical Engineering 7 (2019) 103303
H. Habaki, et al.
Table 2 Experimental conditions for chemical impregnation.
Table 4 Experimental conditions for adsorption equilibrium.
System
System
Feed biomass Chemical for impregnation Conditions Mass of feed Mass fraction of KOH or H3PO4 in aqueous solution Mass ratio of feed to solution Particle size Temperature Contact Time
jatropha shell H3PO4
Adsorbent
[kg]
0.03
[–] [–] [m] [K] [h]
0.1 1.0 1.7 × 10−3–0.425 303 24
Adsorbate Conditions Mass of adsorbent Volume of feed Mass fraction of adsorbate Contact time Temperature, Ta
activated carbon prepared from jatropha shell, commercial activated carbon (CAC) monoolein, methanol [kg] [m3] [–] [h] [K]
2.0 × 10−4 2.0 × 10−5 1.0 × 10−4–1.0 × 10−1 72 303
Table 3 Experimental conditions for thermal treatment. System Feed biomass Atmospheric gas Conditions Mass of feed Temperature, Tt Pressure [Pa] Time at specified Tt Gas flow rate
jatropha shell with/without impregnation nitrogen, steam [kg] [K] [h] [m3 h−1]
0.03 423–1073 1.01 × 105 0.5 2.0 × 10−3 (nitrogen), 3.0 × 10−3 (steam)
carbon, and the adsorption of methanol or monoolein was compared with that with the AC from the jatropha shell. Following this, the mixture was filtered, and the obtained solution was analyzed by gas chromatography to determine the mass fraction of methanol or monoolein remaining in the glycerol solution. The amount of methanol or monoolein adsorbed was calculated using a mass balance.
Fig. 3. Effects of impregnation and thermal treatment on the yield of activated carbon.
compound i, Langmuir constant of compound i, and mass fraction of compound i, respectively, in the glycerol phase. The effects of impregnation and thermal treatment on yAC are demonstrated in Fig. 3. For all the cases, yAC decreased continuously with increase in the thermal treatment temperature. yAC under steam atmosphere was similar to that under nitrogen atmosphere up to 773 K. At this temperature, char gasification under steam would become the dominant reaction, as evident from the sharper decrease in yAC beyond this temperature. Generally, hemicellulose and cellulose should be thermally decomposed in relatively low and higher temperature ranges, respectively. On the other hand, the decomposition of lignin should happen under wide temperature range from ambient to around 1100K [24]. During chemical activation around 800 K or above, H3PO4 promoted the cleavage of aliphatic and ether linkages between cyclic structural units, and the recombination reactions forming larger and more rigid crosslinked units. Moreover H3PO4 facilitated the bonding of volatile materials into the fixed carbon content [25]. The cross-linked complexes could retard the tar formation and char gasification, leading to an increment of yAC compared with that under steam activation. SAC, VAC, and micropore volume of the ACs are listed in Table 5. SAC and VAC were compared with those under thermal treatment at 923 and 1073 K. At 923 K, both these parameters were higher with steam as the
2.2. Results and discussion The yields of AC from FJF and FJS, denoted as yAC and YAC, respectively, are given by
yAC =
FAC FJS
(1)
YAC =
FAC , FJF
(2)
where FAC, FJS, and FJF represent the masses of AC, feed jatropha shell, and feed jatropha fruit, respectively. The yield of impurity component i in FPG1 relative to FJF is given by
YPG,i =
x i,PG FPG1 , FJF
(3)
where xi,PG represents the mass fraction of component i in FPG1. The Langmuir isotherm of component i can be expressed as
qi =
qi* Ki x i 1 + Ki x i
,
(4)
where q*i, Ki, and xi represent the saturated adsorbed amount of
Fig. 2. Apparatus for thermal treatment of jatropha shell. (1) Tubular reactor, (2) Feed/solid product (activated carbon), (3) Sample holder, (4) Electric tubular furnace, (5) Thermocouple, (6) Micro-plunger pump, (7) Valves, (8) Condensers, (9) Liquid product trap, (10) Iced bath. F.I.: Flow rate indicator, T.I: Temperature indicator.
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Journal of Environmental Chemical Engineering 7 (2019) 103303
H. Habaki, et al.
Table 5 List of BET surface area and pore volume of activated carbon. Conditions Condition No. Tt Atmospheric gas Impregnation Results BET surface area Pore volume Micropore volume
[K]
[m2 kg−1] [m2 kg−1] [m2 kg−1]
1 923 Steam no
2 1073 Steam no
3 923 N2 H3PO4
4 1073 N2 H3PO4
516 × 103 2.65 × 10−4 1.99 × 10−4
590 × 103 3.22 × 10−4 1.51 × 10−4
158 × 103 1.12 × 10−4 3.30 × 10−5
813 × 103 4 .34 × 10−4 1.97 × 10−4
Fig. 4. Adsorption isotherms of methanol (a) and monoolein (b) with the prepared and commercial activated carbons.
Fig. 5. Relationship between saturated adsorbed amounts of methanol or monoolein and specific surface area of the prepared activated and commercial carbons.
Table 6 List of saturated adsorbed amount, q*i, and Langmuir parameter, Ki. Condition No. Adsorption q*MeOH KMeOH Adsorption q*MO KMO
of MeOH [kg (kg-AC)−1] [–] of MO [kg (kg-AC) −1] [–]
CAC*
1
2
3
4
0.141 447
0.144 747
0.103 461
0.157 527
0.228 309
0.127 348
0.138 304
0.0842 206
0.165 215
0.233 304
* CMC: commercial activated carbon.
atmospheric gas, as compared with that under chemical activation. The activating agent should promote the incorporation of volatile compounds into the fix carbon but hinder the development of pore structure, resulting in higher yA and lower SAC and VAC. At 1073 K, these two parameters were higher under H3PO4 activation than under steam activation, and SAC was found to be 813 × 103 m2 kg−1. Although the steam activation could increase SAC and VAC with increasing activation temperature, the reaction between steam and shell at 1073 K was so fast
Fig. 6. Relationship between mass ratio of each impurity (methanol or monoolein) in FPG1 relative to FJF and adsorption capacity of each impurity relative to FJF.
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Journal of Environmental Chemical Engineering 7 (2019) 103303
H. Habaki, et al.
Then, it was found that the AC prepared from jatropha shell with larger SAC might be effective for the purification of glycerol produced as a byproduct of the transesterification reaction. The mass flow rates of methanol or monoolein that can be removed using the AC from jatropha shell per unit mass flow rate of the fruit jatropha, YACq*i, were plotted against the mass flow rate ratio of methanol or monoolein in FPG1 per unit mass flow rate of the fruit jatropha, YPG1,i= ((xPG1,iFPG1) / FJF) (Fig. 6). The crucial flow rates were decided based on the experimental results shown in this paper and those reported in our previous studies [13] (Table 7). In any case, YAC q*i was much higher than YPG1,i, and the treatment of glycerol with the AC suggested here might be one of the promising methods to purify glycerol. As mentioned above, although the adsorbability of the AC prepared in this study was lower than that of the CAC, we could prepare the AC whose adsorption performance and yield were sufficient to treat with the crude glycerol in the biodiesel production process. However thermal treatment of all the jatropha shells for the production of AC was found to be unnecessary and the necessary amount of jatropha shell required to treat FPG1 should be decided. It is important to study the effective utilization of the residual jatropha shell.
Table 7 Mass flow ratio around operations in biodiesel production. Oil Extraction FJS/FJF: 0.682 FJO/FJF: 0.318, Oil Pretreatment FPO/FJF: 0.316 Transesterification FBDF/FJF: 0.297, FCG/FJF: 0.166 Glycerol Treatment (Catalyst Removal and MeOH Recovery) FPG1/FJF: 0.0909
that the steam was unable to diffuse deeply into the shell particles and activate them homogenously [26]. It was perhaps due to this that the micropore volume was reduced at elevated temperatures. Although it was reported that dehydrogenation with H3PO4 activated the shell particles effectively in the temperature range around 773–973 K [24], the activation at 923 K might have been insufficient to develop the pore structure because of the short operation time, while SAC and VAC increased at higher temperature. The SAC of the commercial activated carbon was 1577 × 103 m2 kg−1, almost twice as large as that of AC prepared at 1073 K with chemical activation, and the activated carbon with higher performance was unable to prepare under the conditions in this study. Fig. 4 shows the adsorption isotherms of methanol and monoolein in glycerol solution, and the q*is and Kis of the respective compounds determined using Langmuir isotherm equation (Eq. (4)) are listed in Table 6. The AC prepared from jatropha shell could adsorb both methanol and monoolein from glycerol. Fig. 5 shows the relationship between q*i and SAC. The saturated adsorbed amount of methanol and monoolein, q*MeOH and q*MO, respectively increased with SAC. Then, q*i of the CAC was the largest, followed by the activated carbon with chemical activation at 1073 K. As shown in this figure, q*i increased linearly as SAC increased since the surface properties of the activated carbon were less effective to the adsorption of methanol or monoolein. Although some specific functional groups on the activated carbon surface should generally have been generated during the chemical activation to show the specific adsorption, these functional groups generated might have been ineffectual to the adsorption and the activation was effective to simply enhance the specific surface area in this study.
3. Conclusions To improve the biodiesel production from jatropha fruit, the shell was thermally treated to produce AC, which was used to purify glycerol. The AC from jatropha shell was chemically activated with H3PO4 as the activating agent. Although the prepared AC was effective in removing the impurities in pretreated glycerol obtained by transesterification, the chemical activation was less effective to modify the surface property of the AC for better adsorption. It was found that the amount of AC prepared from the shell was enough to purify the glycerol. A more detailed study of the purification of glycerol is necessary for further development of biodiesel production from the inedible plant, jatropha.
Acknowledgement This work was supported by JSPS KAKENHI Grant Number 15K00601.
Appendix A To determine the composition of FPG1 (Fig. 1) and the mass flow ratio (FPG1/FJF), the following operations were conducted. The crude jatropha feed oil was first pretreated in three steps, namely, dephosphorization, deacidification, and dehydration. The dephosphorization was carried out with aqueous H3PO4, to remove the phospholipids. The deacidification would convert the FFA in the feed oil to esters using methanol and sulfuric acid catalyst. The dehydration was carried out using magnesium sulfate crystals. The detailed procedure is reported in our previous work [4,13], and the conditions are listed in Table A1 . After the pretreatment, the obtained feed oil was transesterified with methanol and sodium hydroxide catalyst. The detailed procedure is given in the previous work, and the conditions are listed in Table A2. Then, methyl ester, biodiesel (FBDF), and crude glycerol Table A1 Experimental conditions for pretreatment of crude jatropha oil. Dephosphorization Mass fraction of H3PO4 in aqueous solution Mass ratio of H3PO4 solution to crude jatropha oil Reaction temperature Reaction time Deacidification (Esterification) Mass fraction of H2SO4 in aqueous solution Mass ratio of H2SO4 solution to feed oil Molar ratio of methanol to feed oil Reaction time Temperature
5
[–]
0.85
[–] [K] [h]
0.0001 343 0.25
[–]
0.98
[–] [–] [h] [K]
0.03 7.5 1.5 333
Journal of Environmental Chemical Engineering 7 (2019) 103303
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Table A2 Experimental conditions for transesterification. System Feed Alcohol Catalyst Conditions Molar ratio of methanol to feed oil Mass ratio of NaOH to feed oil Reaction time Temperature
pretreated jatropha oil methanol NaOH
[–] [–] [h] [K]
0.98 0.03 1 333
Table A3 Experimental conditions for catalyst removal. System Feed Acid Conditions Mass fraction of H3PO4 Volume ratio of feed to acid solution Reaction time Temperature
crude glycerol aqueous H3PO4 [–] [–] [h] [K]
0.85 26.7 0.5 333
(FCG) were obtained. FCG was treated in two steps to remove the catalyst and methanol at Catalyst Removal and Methanol Recovery (Fig. 1), respectively. At Catalyst Removal, H3PO4 was added to generate sodium phosphate to remove sodium salt; the conditions are listed in Table A3. For methanol recovery, the glycerol phase was heated at 378 K to vaporize and recover methanol. Then, the obtained FPG1 was analyzed by HPLC. The ratios of the respective mass flows and the compositions of the glycerol phases are listed in Table 1. In FPG1, methanol, monoolein, and glycerol were detected by HPLC. The biodiesel phase should mainly contain methyl esters and trace amounts of FFA, triglycerides, diglycerides, and monoglycerides. Among these, monoglycerides are the most hydrophilic. The other compounds with high hydrophobicity are difficult to dissolve in glycerol. The FFAs should be converted to the neutral form upon contact with H3PO4 at Catalyst Removal and be removed with the salt. The jatropha oil contained the glycerides of oleic acid most, and then only monoolein might have been detected.
461–466. [15] H. Habaki, T. Hayashi, R. Egashira, Transesterification rate of model vegetable oil in heterogeneous system with a stirred vessel, JECE 2 (2014) 1543–1550. [16] H. Habaki, T. Hayashi, R. Egashira, Deacidification process of crude inedible plant oil by esterification for biodiesel production, JECE 6 (2) (2018) 3054–3060. [17] V. Sricharoenchaikul, C. Pechyen, D. Ahtong, D. Atong, Preparation and characterization of activated carbon from the pyrolysis of physic nut (Jatropha curcas L.), Waste. Energ. Fuel 22 (2008) 31–37. [18] D. Xin-hui, C. Srinivasakannan, P. Jin-hui, Z. Li-bo, Comparison of activated carbon prepared from Jatropha hull by conventional heating and microwave heating, Biomass Bionerg. 35 (2011) 3920–3926. [19] C. Namasivayam, D. Sangeetha, R. Gunasekaran, Removal of Anions, Heavy Metals, Organics and Dyes from Water by Adsorption onto a New Activated Carbon from Jatropha Husk, an Agro-Industrial Solid Waste, Process Saf. Environ. 85 (B2) (2007) 181–184. [20] K.C. Yong, T.L. Ooi, K. Dzulkefly, Y.W.M.Z. Wan, A.H. Hazimah, Characterization of glycerol residue from Palm Kernel Oil Methyl Ester Plant, J. Oil Palm Res. 13 (2) (2001) 1–6. [21] T.L. Ooi, K.C. Yong, K. Dzulkefly, Y.W.M.Z. Wan, A.H. Hazimah, Crude glycerine recovery from glycerol residue waste from a Palm Kernel Oil Methyl Ester Plant, J. Oil Palm Res. 13 (2) (2001) 16–22. [22] Y. Xiao, G. Xiao, A. Varma, A universal procedure for crude glycerol purification from different feedstockes in biodiesel production: experimental and simulation study, Ind. Eng. Chem. Res. 52 (2013) 14291–14296. [23] R.N. Singh, D.K. Vyas, N.S.L. Srivastava, M. Narra, SPRERI experience on holistic approach to utilize all parts of Jatropha Curcas fruit for energy, Renew. Energy 33 (2008) 1868–1873. [24] H. Yang, R. Yan, H. Chen, D.H. Lee, C. Zheng, Characteristics of Hemicellulose, cellulose and lignin pyrolysis, Fuel 86 (2007) 1781–1788. [25] M. Jagtoyen, F. Derbyshire, Some Consideration of the Origins of Porosity in Carbons from Chemically Activated Wood, Carbon 31 (7) (1993) 1185–1192. [26] H. Kitagawa, Report of the National Research Institute for Pollution and Resources vol. 12, (1979).
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Purification of glycerol from transesterification using activated carbon prepared from Jatropha Shell for biodiesel production Hiroaki Habakia, Tomoki Hayashib, Patima Sinthupinyob, Ryuichi Egashiraa,
T
⁎
a
Department of Transdisciplinary Science and Engineering, School of Environment and Society, Tokyo Institute of Technology, Address: 12-1, O-okayama-2-chome, Meguro-ku, Tokyo 152-8550, Japan b Department of International Development Engineering, Graduate School of Science and Engineering, Tokyo Institute of Technology, Address: 12-1, O-okayama-2-chome, Meguro-ku, Tokyo 152-8550, Japan
A R T I C LE I N FO
A B S T R A C T
Keywords: Biodiesel fuel production Inedible plant oil Glycerol purification Activated carbon from waste
To improve biodiesel production from jatropha, its shell, a waste material, was thermally treated to produce activated carbon (AC) and the AC was applied to purification of glycerol from transesterification. The AC was prepared by chemical activation method using H3PO4 as the activation agent. The yield of the chemically activated carbon was better than the physically activated carbon in the higher range of thermal treatment temperature, and the prepared AC had a sufficient specific surface area. For purification of the glycerol obtained from transesterification to remove impurities such as methanol and monoolein, the AC was also used for measuring the adsorption equilibria with the model glycerol solutions containing impurities, and adsorption isotherms of these compounds were prepared. The AC could absorb and remove the impurities in the model glycerol phase. The adsorption of the impurities was enhanced by chemical activation because of a larger specific surface area, and the effects of surface modification by the activation were inefficient for the adsorption. A rough process assessment suggested that the amount of AC prepared from the shell was sufficient to purify glycerol.
1. Introduction Biodiesel is gaining popularity as a renewable energy source. Although biodiesel is generally produced from edible plant oils, the production has been of great concern because of the competition from production of food materials from such plants. As a result, utilization of these plant oils as fuels has become more expensive. Therefore, increasing attention has been focused on the production of fuel from inedible plant oils such as jatropha [1–4], castor [5,6], and pongamia oil [7,8]. They are generally cultivated in marginal places with low irrigation requirements and places not competing with the cultivation of general food plants. Jatropha is the most attractive plant among these [9], and considerable research has been conducted to develop an effective method for the production of oil from this plant [1–4,10–16]. On the other hand, these plants should be newly cultivated and it is necessary to exploit not only the effective production of biodiesel from these plants, but also the utilization of their residues. In the case of jatropha, residues such as the shell and hull were thermally treated to prepare activated carbon (AC) [17,18], which was further used for the separation of some organic and inorganic compounds from aqueous solutions via adsorption [19]. Utilization of the residues is one of the
⁎
methods to improve the entire process of biodiesel production. Another approach to enhance the process efficiency is the purification of crude glycerol obtained from transesterification [20–22]. Generally, the crude glycerol contains water, organic and inorganic salts, soap, alcohol, and unreacted glycerides. Although the separation and recovery of methanol as alcohol was commercially conducted by vacuum distillation, some concerns regarding trace amount of residual methanol and decomposition of glycerol were reported [22]. In this study, we aimed to purify glycerol from transesterification using AC prepared from the waste material, i.e., shell of jatropha. The jatropha shell was thermally treated to prepare the AC, and the removal of impurities from the crude glycerol obtained after transesterification was studied. The adsorption equilibria of methanol and monoolein impurities in the glycerol with the AC and purification of the glycerol were also studied. 2. Purification of crude glycerol using activated carbon from jatropha shell Fig. 1 shows the conceptual diagram of biodiesel production incorporating glycerol purification using the AC prepared from jatropha
Corresponding author. E-mail address: [email protected] (R. Egashira).
https://doi.org/10.1016/j.jece.2019.103303 Received 7 May 2019; Received in revised form 2 July 2019; Accepted 18 July 2019 Available online 12 August 2019 2213-3437/ © 2019 Elsevier Ltd. All rights reserved.
Journal of Environmental Chemical Engineering 7 (2019) 103303
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Nomenclature ABET Fj Ki qi q*i Tt xi xPG1,i YAC yAC YPG1,i
Subscript
BET surface area of AC [m2 (kg–AC)–1] mass of material i in experiment [kg], mass flow rate of material i in Figure 1 [kg hr−1] Langmuir parameter of componenti [–] adsorption amount of componenti per unit mass of AC [kg (kg–AC)–1] saturated adsorption amount of componenti per unit mass of AC [kg (kg–AC)–1] thermal treatment temperature [K] mass fraction of componenti in glycerol solution [–] mass fraction of componenti in FPG1 [–] yield of AC based on jatropha fruit [–], yield of AC based on jatropha shell [–] yield of componenti in FPG1 based on jatropha fruit [–]
AC BDF CG i j JF JO JS MeOH MO PO PG1 PG2
activated carbon from jatropha shell biodiesel fuel crude glycerol componenti materialj jatropha fruit crude jatropha oil jatropha shell methanol monoolein pretreated jatropha oil purified glycerol 1 purified glycerol 2
were of analytical grade and purchased from FUJIFILM Wako Chemical Corp. Table 2 shows the experimental conditions for chemical impregnation. The shell was crushed and sieved into the desired range of sizes, and the sieved particles of the shell were impregnated with H3PO4 for 24 h. Following this, they were dried at 333 K in the oven for another 24 h. The impregnated shell was kept in a desiccator for thermal treatment. Table 3 lists the principal conditions of thermal treatment, and Fig. 2 shows the schematic diagram of the thermal treatment reactor. The reactor consisted of a horizontal tubular reactor inserted into an electrically heated furnace (KTF-040 N from KOYO Thermo Systems Co., Ltd.) equipped with temperature control and thermocouple. An average of 0.020 kg sample was filled into the sample holder, which was placed at the center of the reactor. Nitrogen gas was purged into the reactor for 10 min before the heating began. In the case of steam thermal treatment, preheated deionized water was supplied using a micro-plunger pump (LC10-ADVP, Shimadzu Corp.). The gas flow from the reactor outlet was collected in a condenser, and the condensate drum was immersed into an isothermal bath at 273 K. After holding the system isothermally at the desired temperature for 30 min, the heater was turned off, and the reactor was cooled down. The masses of the residue left in the holder, AC, and condensate in the drum were measured. The AC was boiled for 2 h to remove the tar inside the particles. Following this, it was dried for 24 h and kept in a desiccator. The specific surface area, SAC, total pore volume, VAC, and micro pore volume of the obtained AC were analyzed using the nitrogen adsorption isotherm obtained from a surface area and pore volume analyzer (BELSORP-max: BEL JAPAN Co.). The trace amounts of methanol and monoolein remaining in glycerol after Catalyst Removal and Methanol Recovery were subsequently removed using AC as the adsorbent. The principal conditions of adsorption equilibrium measurements are listed in Table 4 . The batch adsorption studies with the model glycerol solutions and prepared ACs were carried out in a 100 × 10−6 m3 Erlenmeyer flask with a screw cap, in which a mixture of 1 × 10−3 kg AC and 100 × 10−6 m3 methanol or monoolein in glycerol were kept at 303 K. The mixture was continuously shaken at a constant temperature in a thermostated rotary shaker for 72 h, within which the equilibrium was reached. The commercial activated carbon, purchased from FUJIFILM Wako Chemical Corp. and abbreviated as CAC, was used as the reference activated
shell. The treatment of the crude glycerol obtained by transesterification was assessed using the simple mass balance relation and adsorption equilibrium. First, jatropha fruit, FJF, is processed to obtain crude jatropha oil (FJO) and shell (FJS) at Oil Extraction. Based on the work by Singh et al. [23], the mass ratios of FJO and FJS relative to feed FJF, i.e., FJO/FJF and FJS/FJF, were determined to be 0.318 and 0.682, respectively. FJO is sent to Oil Pretreatment, where impurities such as phospholipid, water, and free fatty acids (FFAs) are removed. While phospholipid and water are removed, FFA is esterified to fatty acid methyl ester. The detailed procedures and conditions are given in Appendix A and our previous study [4,13]. The pretreated oil is transesterified with methanol to obtain the fatty acid methyl ester and crude glycerol phases. Then, the crude glycerol is treated to remove the catalyst, methanol, and water to obtain purified glycerol1, FPG1. Table 1 shows the composition of FPG1. FPG1 contains trace amounts of methanol and monoolein impurities that can be treated with the AC prepared from jatropha shell. Based on the mass balances of AC from jatropha shell, impurities in FPG1, and adsorption of the impurities, the treatment of FPG1 by AC are discussed. 2.1. Experimental The jatropha shell, collected from a jatropha plantation in Suphanburi, Thailand, was used as the precursor of AC. It was washed with deionized water and dried at 333 K in an oven for 24 h. H3PO4 was used as the activating agent for chemical activation. Methanol and monoolein were used as model impurities in the pretreated glycerol obtained by transesterification. All the chemicals used in this study
Table 1 Composition of FPG1 (mass fraction).
Fig. 1. Conceptual diagram of biodiesel production incorporating glycerol purification. 2
Methanol
Monoolein
Glycerol
0.00102
0.0188
0.976
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Table 2 Experimental conditions for chemical impregnation.
Table 4 Experimental conditions for adsorption equilibrium.
System
System
Feed biomass Chemical for impregnation Conditions Mass of feed Mass fraction of KOH or H3PO4 in aqueous solution Mass ratio of feed to solution Particle size Temperature Contact Time
jatropha shell H3PO4
Adsorbent
[kg]
0.03
[–] [–] [m] [K] [h]
0.1 1.0 1.7 × 10−3–0.425 303 24
Adsorbate Conditions Mass of adsorbent Volume of feed Mass fraction of adsorbate Contact time Temperature, Ta
activated carbon prepared from jatropha shell, commercial activated carbon (CAC) monoolein, methanol [kg] [m3] [–] [h] [K]
2.0 × 10−4 2.0 × 10−5 1.0 × 10−4–1.0 × 10−1 72 303
Table 3 Experimental conditions for thermal treatment. System Feed biomass Atmospheric gas Conditions Mass of feed Temperature, Tt Pressure [Pa] Time at specified Tt Gas flow rate
jatropha shell with/without impregnation nitrogen, steam [kg] [K] [h] [m3 h−1]
0.03 423–1073 1.01 × 105 0.5 2.0 × 10−3 (nitrogen), 3.0 × 10−3 (steam)
carbon, and the adsorption of methanol or monoolein was compared with that with the AC from the jatropha shell. Following this, the mixture was filtered, and the obtained solution was analyzed by gas chromatography to determine the mass fraction of methanol or monoolein remaining in the glycerol solution. The amount of methanol or monoolein adsorbed was calculated using a mass balance.
Fig. 3. Effects of impregnation and thermal treatment on the yield of activated carbon.
compound i, Langmuir constant of compound i, and mass fraction of compound i, respectively, in the glycerol phase. The effects of impregnation and thermal treatment on yAC are demonstrated in Fig. 3. For all the cases, yAC decreased continuously with increase in the thermal treatment temperature. yAC under steam atmosphere was similar to that under nitrogen atmosphere up to 773 K. At this temperature, char gasification under steam would become the dominant reaction, as evident from the sharper decrease in yAC beyond this temperature. Generally, hemicellulose and cellulose should be thermally decomposed in relatively low and higher temperature ranges, respectively. On the other hand, the decomposition of lignin should happen under wide temperature range from ambient to around 1100K [24]. During chemical activation around 800 K or above, H3PO4 promoted the cleavage of aliphatic and ether linkages between cyclic structural units, and the recombination reactions forming larger and more rigid crosslinked units. Moreover H3PO4 facilitated the bonding of volatile materials into the fixed carbon content [25]. The cross-linked complexes could retard the tar formation and char gasification, leading to an increment of yAC compared with that under steam activation. SAC, VAC, and micropore volume of the ACs are listed in Table 5. SAC and VAC were compared with those under thermal treatment at 923 and 1073 K. At 923 K, both these parameters were higher with steam as the
2.2. Results and discussion The yields of AC from FJF and FJS, denoted as yAC and YAC, respectively, are given by
yAC =
FAC FJS
(1)
YAC =
FAC , FJF
(2)
where FAC, FJS, and FJF represent the masses of AC, feed jatropha shell, and feed jatropha fruit, respectively. The yield of impurity component i in FPG1 relative to FJF is given by
YPG,i =
x i,PG FPG1 , FJF
(3)
where xi,PG represents the mass fraction of component i in FPG1. The Langmuir isotherm of component i can be expressed as
qi =
qi* Ki x i 1 + Ki x i
,
(4)
where q*i, Ki, and xi represent the saturated adsorbed amount of
Fig. 2. Apparatus for thermal treatment of jatropha shell. (1) Tubular reactor, (2) Feed/solid product (activated carbon), (3) Sample holder, (4) Electric tubular furnace, (5) Thermocouple, (6) Micro-plunger pump, (7) Valves, (8) Condensers, (9) Liquid product trap, (10) Iced bath. F.I.: Flow rate indicator, T.I: Temperature indicator.
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Table 5 List of BET surface area and pore volume of activated carbon. Conditions Condition No. Tt Atmospheric gas Impregnation Results BET surface area Pore volume Micropore volume
[K]
[m2 kg−1] [m2 kg−1] [m2 kg−1]
1 923 Steam no
2 1073 Steam no
3 923 N2 H3PO4
4 1073 N2 H3PO4
516 × 103 2.65 × 10−4 1.99 × 10−4
590 × 103 3.22 × 10−4 1.51 × 10−4
158 × 103 1.12 × 10−4 3.30 × 10−5
813 × 103 4 .34 × 10−4 1.97 × 10−4
Fig. 4. Adsorption isotherms of methanol (a) and monoolein (b) with the prepared and commercial activated carbons.
Fig. 5. Relationship between saturated adsorbed amounts of methanol or monoolein and specific surface area of the prepared activated and commercial carbons.
Table 6 List of saturated adsorbed amount, q*i, and Langmuir parameter, Ki. Condition No. Adsorption q*MeOH KMeOH Adsorption q*MO KMO
of MeOH [kg (kg-AC)−1] [–] of MO [kg (kg-AC) −1] [–]
CAC*
1
2
3
4
0.141 447
0.144 747
0.103 461
0.157 527
0.228 309
0.127 348
0.138 304
0.0842 206
0.165 215
0.233 304
* CMC: commercial activated carbon.
atmospheric gas, as compared with that under chemical activation. The activating agent should promote the incorporation of volatile compounds into the fix carbon but hinder the development of pore structure, resulting in higher yA and lower SAC and VAC. At 1073 K, these two parameters were higher under H3PO4 activation than under steam activation, and SAC was found to be 813 × 103 m2 kg−1. Although the steam activation could increase SAC and VAC with increasing activation temperature, the reaction between steam and shell at 1073 K was so fast
Fig. 6. Relationship between mass ratio of each impurity (methanol or monoolein) in FPG1 relative to FJF and adsorption capacity of each impurity relative to FJF.
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Then, it was found that the AC prepared from jatropha shell with larger SAC might be effective for the purification of glycerol produced as a byproduct of the transesterification reaction. The mass flow rates of methanol or monoolein that can be removed using the AC from jatropha shell per unit mass flow rate of the fruit jatropha, YACq*i, were plotted against the mass flow rate ratio of methanol or monoolein in FPG1 per unit mass flow rate of the fruit jatropha, YPG1,i= ((xPG1,iFPG1) / FJF) (Fig. 6). The crucial flow rates were decided based on the experimental results shown in this paper and those reported in our previous studies [13] (Table 7). In any case, YAC q*i was much higher than YPG1,i, and the treatment of glycerol with the AC suggested here might be one of the promising methods to purify glycerol. As mentioned above, although the adsorbability of the AC prepared in this study was lower than that of the CAC, we could prepare the AC whose adsorption performance and yield were sufficient to treat with the crude glycerol in the biodiesel production process. However thermal treatment of all the jatropha shells for the production of AC was found to be unnecessary and the necessary amount of jatropha shell required to treat FPG1 should be decided. It is important to study the effective utilization of the residual jatropha shell.
Table 7 Mass flow ratio around operations in biodiesel production. Oil Extraction FJS/FJF: 0.682 FJO/FJF: 0.318, Oil Pretreatment FPO/FJF: 0.316 Transesterification FBDF/FJF: 0.297, FCG/FJF: 0.166 Glycerol Treatment (Catalyst Removal and MeOH Recovery) FPG1/FJF: 0.0909
that the steam was unable to diffuse deeply into the shell particles and activate them homogenously [26]. It was perhaps due to this that the micropore volume was reduced at elevated temperatures. Although it was reported that dehydrogenation with H3PO4 activated the shell particles effectively in the temperature range around 773–973 K [24], the activation at 923 K might have been insufficient to develop the pore structure because of the short operation time, while SAC and VAC increased at higher temperature. The SAC of the commercial activated carbon was 1577 × 103 m2 kg−1, almost twice as large as that of AC prepared at 1073 K with chemical activation, and the activated carbon with higher performance was unable to prepare under the conditions in this study. Fig. 4 shows the adsorption isotherms of methanol and monoolein in glycerol solution, and the q*is and Kis of the respective compounds determined using Langmuir isotherm equation (Eq. (4)) are listed in Table 6. The AC prepared from jatropha shell could adsorb both methanol and monoolein from glycerol. Fig. 5 shows the relationship between q*i and SAC. The saturated adsorbed amount of methanol and monoolein, q*MeOH and q*MO, respectively increased with SAC. Then, q*i of the CAC was the largest, followed by the activated carbon with chemical activation at 1073 K. As shown in this figure, q*i increased linearly as SAC increased since the surface properties of the activated carbon were less effective to the adsorption of methanol or monoolein. Although some specific functional groups on the activated carbon surface should generally have been generated during the chemical activation to show the specific adsorption, these functional groups generated might have been ineffectual to the adsorption and the activation was effective to simply enhance the specific surface area in this study.
3. Conclusions To improve the biodiesel production from jatropha fruit, the shell was thermally treated to produce AC, which was used to purify glycerol. The AC from jatropha shell was chemically activated with H3PO4 as the activating agent. Although the prepared AC was effective in removing the impurities in pretreated glycerol obtained by transesterification, the chemical activation was less effective to modify the surface property of the AC for better adsorption. It was found that the amount of AC prepared from the shell was enough to purify the glycerol. A more detailed study of the purification of glycerol is necessary for further development of biodiesel production from the inedible plant, jatropha.
Acknowledgement This work was supported by JSPS KAKENHI Grant Number 15K00601.
Appendix A To determine the composition of FPG1 (Fig. 1) and the mass flow ratio (FPG1/FJF), the following operations were conducted. The crude jatropha feed oil was first pretreated in three steps, namely, dephosphorization, deacidification, and dehydration. The dephosphorization was carried out with aqueous H3PO4, to remove the phospholipids. The deacidification would convert the FFA in the feed oil to esters using methanol and sulfuric acid catalyst. The dehydration was carried out using magnesium sulfate crystals. The detailed procedure is reported in our previous work [4,13], and the conditions are listed in Table A1 . After the pretreatment, the obtained feed oil was transesterified with methanol and sodium hydroxide catalyst. The detailed procedure is given in the previous work, and the conditions are listed in Table A2. Then, methyl ester, biodiesel (FBDF), and crude glycerol Table A1 Experimental conditions for pretreatment of crude jatropha oil. Dephosphorization Mass fraction of H3PO4 in aqueous solution Mass ratio of H3PO4 solution to crude jatropha oil Reaction temperature Reaction time Deacidification (Esterification) Mass fraction of H2SO4 in aqueous solution Mass ratio of H2SO4 solution to feed oil Molar ratio of methanol to feed oil Reaction time Temperature
5
[–]
0.85
[–] [K] [h]
0.0001 343 0.25
[–]
0.98
[–] [–] [h] [K]
0.03 7.5 1.5 333
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Table A2 Experimental conditions for transesterification. System Feed Alcohol Catalyst Conditions Molar ratio of methanol to feed oil Mass ratio of NaOH to feed oil Reaction time Temperature
pretreated jatropha oil methanol NaOH
[–] [–] [h] [K]
0.98 0.03 1 333
Table A3 Experimental conditions for catalyst removal. System Feed Acid Conditions Mass fraction of H3PO4 Volume ratio of feed to acid solution Reaction time Temperature
crude glycerol aqueous H3PO4 [–] [–] [h] [K]
0.85 26.7 0.5 333
(FCG) were obtained. FCG was treated in two steps to remove the catalyst and methanol at Catalyst Removal and Methanol Recovery (Fig. 1), respectively. At Catalyst Removal, H3PO4 was added to generate sodium phosphate to remove sodium salt; the conditions are listed in Table A3. For methanol recovery, the glycerol phase was heated at 378 K to vaporize and recover methanol. Then, the obtained FPG1 was analyzed by HPLC. The ratios of the respective mass flows and the compositions of the glycerol phases are listed in Table 1. In FPG1, methanol, monoolein, and glycerol were detected by HPLC. The biodiesel phase should mainly contain methyl esters and trace amounts of FFA, triglycerides, diglycerides, and monoglycerides. Among these, monoglycerides are the most hydrophilic. The other compounds with high hydrophobicity are difficult to dissolve in glycerol. The FFAs should be converted to the neutral form upon contact with H3PO4 at Catalyst Removal and be removed with the salt. The jatropha oil contained the glycerides of oleic acid most, and then only monoolein might have been detected.
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