Influence of feedstock source on the biocatalyst stability and reactor performance in continuous biodiesel production

Journal of Industrial and Engineering Chemistry 20 (2014) 881–886

Contents lists available at SciVerse ScienceDirect

Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec

Influence of feedstock source on the biocatalyst stability and reactor performance in continuous biodiesel production William Costa e Silva a, Larissa F. Teixeira a, Ana K.F. Carvalho a, Adriano A. Mendes b, Heizir F. de Castro a,* a b

Engineering School of Lorena, University of Sa˜o Paulo, P.O. Box 116, 12602-810 Lorena, SP, Brazil Laboratory of Biocatalysis, Federal University of Sa˜o Joa˜o del-Rei, 35701-970 Sete Lagoas, MG, Brazil

A R T I C L E I N F O

Article history: Received 10 March 2013 Accepted 9 June 2013 Available online 19 June 2013 Keywords: Biodiesel Packed bed reactor Lipase Babassu oil Macaw palm oil

A B S T R A C T

A biodiesel process in a packed bed reactor was used as a model system to show the strong dependence of the reactor behavior on the developing of chemical environment within the reactor. Ethanolysis runs of babassu and macaw palm oils were carried out in a solvent-free system using Burkholderia cepacia lipase immobilized on silica–PVA matrix. The best performance was found for the reactor running on macaw palm oil, which resulted in a stable operating system and an average yield of 87.6  2.5%. This strategy also gave high biocatalyst operational stability, revealing a half-life of 478 h. ß 2013 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.

1. Introduction Industrial production of biodiesel from vegetable oil and fat is performed by chemical alkaline or acidic processes. However, these methods require complex downstream processes, including the recovery of salt-containing glycerol (byproduct), and the treatment of wastewater. Thus, an enzymatic transesterification process using lipase can overcome the drawbacks of the chemical process, as it allows easy recovery of biodiesel and glycerol [1–3]. The main disadvantage of the enzyme-catalyzed process, however, is the high cost of the lipases and therefore the key step in this process lies in the successful immobilization of the enzyme, which allows for its easy recovery and reuse [4]. High operational stability of the immobilized enzyme was reported in several studies [5–7], making it possible in a continuous system, which reduces the influence of catalyst cost. The development of operational system employing immobilized enzyme involves a large number of decisions and parameter adjustments such as suitable choice of support to enzyme immobilization, most appropriate reactor set-up and its running method. In addition, understanding the reaction kinetics is necessary to establish a stable operational system to produce a large amount of product at

* Corresponding author. Tel.: +55 12 3159 5063. E-mail address: [email protected] (H.F. de Castro).

the lowest cost, possible maintaining steady productivity through time [8]. After successful enzyme immobilization, the development of the appropriate reactor is one of the critical points in enzymatic biodiesel production at industrial scale. The enzymatic transesterification of vegetable oils can be carried out substantially faster and more economically feasible in continuous reactors. Packed bed reactor (PBR) has been extensively investigated and is one of the most commonly employed reactor for solid–fluid contacting in heterogeneous catalysis (i) because it allows reuse of the enzyme without the need prior separation (ii) it permits the handling low substrates solubility by using large volumes containing low concentrations of substrate, (iii) it is suitable for long-term and industrial scale production, different from a stirred-tank reactor where enzymes granules would be susceptible to break because of the mechanical shear stress, (iv) it is more cost effective than the batch operation and (v) the ratio between substrate and enzyme is much lower in a PBR than in conventional batch reactors and it results in higher reaction performance [9,10]. Usually, this type of reactor provides greater surface area for reaction per unit volume of membrane reactor for which its kinetic is favorable than continuous reactors with stirring and there is no drawbacks about higher shear stress in mechanical stirring [11–13]. Previously studies carried out in our lab [14] demonstrated that is possible to run continuously a packed bed reactor to obtain biodiesel from ethanolysis of babassu oil (Orbignya sp.) in solventfree system. However, a rigorous temperature control was required

1226-086X/$ – see front matter ß 2013 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jiec.2013.06.018

882

W.C. Silva et al. / Journal of Industrial and Engineering Chemistry 20 (2014) 881–886

to avoid substrate solidification due to the high-saturated fatty acid composition (83%) present in this feedstock. Therefore, alternative feedstock to biodiesel synthesis is a great opportunity to carry out feasible continuous PBR, without additional energetic cost. Among the variety of feedstock to biodiesel production with high commercial exploitation, macaw palm oil can be considered an attractive feedstock due to its lower saturated fatty acids (less than 70%). Such differences on the oil composition may help to overcome the mentioned operational problems. Moreover, macaw palm is the second oleaginous plant most productive (1500– 5000 kg oil/ha), inferior only to palm oil (Elaeis guineensis), being considered a promising feedstock for biodiesel synthesis [15]. To our knowledge, this is the first report dealing with the use of macaw palm oil as feedstock to produce biodiesel under continuous run. The aim of this study was to determine the reactor performance running on two vegetable oils (babassu and macaw palm) in a solvent-free system using lipase from Burkholderia cepacia immobilized on silica-polyvinyl alcohol composite as catalyst and ethanol as acyl acceptor. Comparison was based on the fatty acid ethyl esters (FAEE) yield (wt.%) and productivity for reactor running under the same operational conditions. 2. Experimental 2.1. Materials All experiments were carried out with commercial lipase preparation from B. cepacia manufactured by Amano Enzyme Inc. (Nagoya, Japan) and purchased from Sigma–Aldrich Chemical Co. (Milwaulkee, WI, USA). Tetraethoxysilane (TEOS) and epichlorohydrin (99%) were acquired from Aldrich Chemical Co. (Milwaukee, WI, USA). Polyvinyl alcohol (MW 88,000, 88%) was from Acros Organic. Hydrochloric acid (minimum 36%), anhydrous ethanol (minimum 99.8%), tert-butanol and hexane were supplied by Reagen (RJ, Brazil). Babassu oil was kindly supplied by Pulcra Chemicals (Jacarei, SP, Brazil), macaw palm oil was acquired from Association of Small Farmers D’Antas (Montes Claros, MG, Brazil) and commercial olive oil (Carbonell) was bought at local market. Polyethylene glycol (MW 1500) and powder gum Arabic were supplied by Synth (SP, Brazil). The other reagents were of analytical grade.

the detector and injector were set at 280 8C and 250 8C, respectively. The column temperature was kept at 100 8C for 5 min, heated to 215 8C at 5 8C/min and kept constant for 34 min. The volume injected was 1.0 mL. 2.3. Support synthesis and lipase immobilization A polysiloxane–polyvinyl alcohol composite (SiO2–PVA) was prepared activated with epichlorohydrin and used to immobilize the lipase according to the methodology reported by Da Ro´s et al. [18]. The properties of the support were as follows: diameter (0.175 mm), average pore diameter (22.91 A˚); surface area (461 m2/g) and porous volume (0.275 cm3/g). To perform this work, four batches of immobilized derivatives were prepared and average measured hydrolytic activity was 2445  97 IU/g biocatalyst. One international unit (IU) of enzyme activity was defined as the amount of enzyme that liberates 1 mmol of free fatty acid per min under the assay conditions (37 8C, pH 7.0, 150 rpm). The biochemical, kinetic properties, thermal stability and operational stability of this immobilized lipase preparation are described elsewhere [18,19]. 2.4. Continuous runs Ethanolysis of babassu and macaw palm oils was carried out in a PBR jacketed glass column (internal diameter – 16 mm; height – 55 mm and total volume – 11 mL) with a water jacket connected to a circulating water bath to maintain the temperature at 50 8C. A schematic diagram of the PBR is shown in Fig. 1. The continuous run was started by loading the reactor with the biocatalyst and substrate was continuously pumped (peristaltic pump Perista Pump SJ-1211, Atto Bioscience & Biotechnology, Tokyo, Japan) from a reservoir, through marprene tubing (Watson Marlow 913.AJ05.016), to the bottom end of the bioreactor at constant flow rate of 0.78 mL/h. Reflux condenser system was connected to the feeding vessel to avoid ethanol losses. Heating tapes containing a thermostated electrical resistance (25 W) were used to avoid heat loss in the inlet and outlet tubing. For each run, an amount of 7.8 g biocatalyst was used which corresponds to a bulk volume of 4.2 cm3. Immobilized derivative density was determined as 1.865 g/mL. The substrate was prepared at molar ratio oil to

2.2. Feedstock properties The physical–chemical properties (acid number, peroxide value, iodine value, saponification value and viscosity) of triglyceride feedstocks were evaluated following methods described by the American Oil Chemists’ Society [16] and results summarized in Table 1 were within required limits to be used as feedstock in enzymatic transesterification reactions [17]. Fatty acid composition was determined by a capillary gas chromatograph – CGC Agilent 6850 Series GC System, capillary column: DB23 Agilent (50% cyanopropyl) – methylpolysiloxane, size 60 m, Ø int 0.25 mm, 0.25 mM film. Helium was used as carrier gas at rate of 1.00 mL/min and linear speed of 24 cm/seg. The temperatures of

Table 1 Physical–chemical properties of the tested feedstocks. Property

Babassu oil

Macaw palm oil

Acid number (mg KOH/g) Peroxide value (mEq/Kg) Viscosity (mm2/s) Iodine value (g I2/100 g) Saponification value (mg KOH/g)

0.6 1.8 29.5 25 238

10.1 5.7 29.8 28 223

Fig. 1. Schematic diagram of the experimental apparatus: (1) thermostatic bath; (2) magnetic stirrer; (3) substrate reservoir; (4) reflux condenser; (5) peristaltic pump; (6) PBR-packed bed reactor; (7) product outlet.

W.C. Silva et al. / Journal of Industrial and Engineering Chemistry 20 (2014) 881–886

ethanol of 1:7 following conditions previous established [14,20]. Samples were collected each 24 h during the operation of the PBR and stored at 2 8C for further analyses. The space time was calculated according to Levenspiel [21] as described in Eq. (1):

t¼

V

(1)

v0

where t is the space time (h), V is the useful volume of reactor (mL) and n0 is the flow rate (mL/h). 2.5. Operational stability of the immobilized derivative

t 1=2 ¼

ln 2 kd

(2)

(3)

where A0 is the initial activity of the immobilized lipase, and At is the final activity after each run. 2.6. Properties of packed-bed reactor: flow characterization To characterize the pipe flow through the enzyme particles in the column, Reynolds number was calculated according to Eq. (4) as proposed by Lide [23]: Re ¼

dp  y  r

m

2.8. Purification of biodiesel The volume of sample collected from the bioreactor was transferred into decanting funnel in which the same quantity of distilled water was added. Then, vigorous agitation was carried out and the mixture was allowed to stand for 6 h, for phase separation. This procedure was performed three times, in sequence. The superior phase, consisting of FAEE (biodiesel) was evaporated by rotatory-evaporator. Then, the solution was dried sodium sulfate and the lower phase, consisting of glycerol and wastewater, was disposed of. 2.9. Viscosity and density of biodiesel

The biocatalyst stability was assessed by measuring the hydrolytic activity of the immobilized derivatives at the end of each continuous run taking the original activity as 100%. The recovered immobilized lipase was then washed with tert-butanol in order to remove any substrate or product eventually retained in the matrix. Hydrolytic activity was determined by the olive oil emulsion method according to the modification proposed by Soares et al. [22]. Inactivation constant (kd) and half-life (t1/2) for the immobilized lipase were calculated according to the Eqs. (2) and (3), as follows: ln At ¼ ln A0  kd  t

883

(4)

where dp is the enzyme particle diameter (0.3025 mm), y is the fluid velocity calculated as flow/cross area of column, and, r is the fluid specific mass (850 kg/m3), m is the fluid viscosity (8.64  103 kg/m s) of the reactant mixture measured as 1 atm at 40 8C with Brookfield Viscometer  LVDVII (Brookfield Viscometers, England). The flow was hereafter characterized as turbulent if Re  4000 or laminar if Re  2000 [23]. 2.7. Monitoring ethyl esters The ethyl esters formed in the transesterification reaction were analyzed in a FID gas chromatography (Varian CG 3800, Inc., Corporate Headquarters, Palo Alto, CA, USA) using a 5% DEGS CHRWHP 80/100 mesh 6 ft 2.0 mm ID and 1/800 OD column (Restek Frankel Commerce of Analytic Instruments Ltd., SP, Brazil) following previous established conditions [24]. Nitrogen was used as the carrier gas with a flow rate of 25 mL/min. The detector and injector temperatures were 190 8C. The column temperature was first set to 90 8C for 3 min and then programmed at 25 8C/min to 120 8C for 10 min and 170 8C for 15 min. Data was collected using Galaxie Chromatography Data System software version 1.9. Theoretical ester concentrations were calculated by taking into account the fatty acid composition and its initial weight mass in the reaction medium and the transesterification yield (%) was defined as the ratio between the produced and theoretical esters concentrations [24].

The absolute viscosity of purified biodiesel was determined by Brookfield Viscometers model LVDVII (Brookfield Viscometers Ltd., England) using the cone CP 42. All assays were carried out at 40 8C using a 0.5 mL aliquot of the sample. The biodiesel density was determined by digital densimeter model DMA 35 N EX (Anton Paar). In this test, all assays were performed at 20 8C using 2.0 mL aliquot of each sample. 3. Results and discussion 3.1. Properties of the vegetable oils The choice of feedstock is a key factor in the transesterification reaction, since the molecular structure of the alkyl ester obtained and their physical and chemical properties depend on the length of the carbon chain, and the amount of unsaturated bond present in the triglyceride [25]. Moreover, the transesterification yield for the reactions catalyzed by lipases is influenced by the chemical composition of triglycerides due to their specificity toward different fatty acids [26,27]. The fatty acid profile of the vegetable oils used in this work is summarized in Table 2. There are three main types of fatty acids that can be present in a triglyceride: saturated (Cn:0), monounsaturated (Cn:1) and polyunsaturated with two or three double bonds (Cn:2,3). According to the composition, two parameters based on the type of fatty acids were defined: degree of unsaturation (DU) and long chain saturated factor (LCSF). Both parameters are also shown in Table 2. By the fatty acid profile it can be verified that both babassu and macaw palm oils have high lauric acid content (35–45 wt.%), Table 2 Fatty acid compositions (wt.%), degree of unsaturation (DU) and long-chain saturated factor (LCSF) of the tested vegetable oils. Fatty acid

Babassu oil

Macaw palm oil

3.5 4.5 44.7 17.5 9.7 3.1 15.2 1.8

5.4 3.9 36.1 10.2 8.7 3.6 27.7 3.4

Saturated Monounsaturated

83.0 15.2

68.0 27.7

Polyunsaturated (2,3) Degree of unsaturation (DU) Long-chain saturated factor

1.8 17.6 2.5

3.4 34.0 2.7

C8:0 C10:0 C12:0 C14:0 C16:0 C18:0 C18:1 C18:2

Caprylic Capric Lauric Myristic Palmitic Stearic Oleic Linoleic

Degree of unsaturation (DU) and long chain saturated factor (LCSF) were determined according to the fatty acid composition taking into account, respectively, the amount of monounsaturated and polyunsaturated fatty acids (wt.%) present in the oil and the composition of saturated fatty acids and lending more weight to the composition of fatty acids with a long chain [23].

W.C. Silva et al. / Journal of Industrial and Engineering Chemistry 20 (2014) 881–886

3.2. Synthesis of biodiesel in continuous PBR system Microbial lipase from B. cepacia immobilized on hybrid matrix SiO2–PVA showed high activity in the transesterification of lauric oils (babassu and macaw palm) with ethanol, attaining high yields in batch runs [17]. This study focused on the continuous enzymatic production of biodiesel from these vegetal oils in a solvent free system. For such, a packed bed reactor (PBR) configuration was selected based on its suitability to perform typical lipase-catalyzed reactions [19,29]. Fig. 2a and b shows the ethyl esters content during the continuous runs using immobilized B. cepacia lipase in the ethanolysis of babassu and macaw palm oils at molar ratio 1:7 oil to ethanol in a solvent-free system [14,20]. For babassu oil, the bioreactor was packed with 7.8 g (dry weight) of the immobilized derivative corresponding to a catalytic loading of 17,316 IU (Fig. 2a). The reactor ran for over 15 days with oscillations caused by operating problems such as clogging and an air bubble in the bioreactor column and solidification of babassu oil in the connections. It was also observed that reactants within the bed form a two-phase liquid system, despite stirring the substrate in the reservoir. To overcome this limitation, it was necessary to install a hot air mini-heater recirculation next to the reaction. The steady state was reached at 72 h and average ethyl esters content was 60.6  4.2 wt.% which corresponded to transesterification yield of 78.0  5.4%. A different profile was verified when the reactor ran on macaw palm oil under the same operating conditions. In this case, the steady state in the ethanolysis of macaw palm oil (Fig. 2b) was achieved at 24 h (4 space times) so that PBR ran for 15 days without interruptions and no operational problems. The ethyl ester content varied between 51.1 and 67.5 wt.%, corresponding to transesterification yields and productivities from 65.7 to 86.9% and 72.9 to 96.4 mg/g h, respectively. The higher ethyl ester formation can be credited to the lower lauric acid content which enhances the oilethyl alcohol miscibility and helps to overcome the mass transfer restraints as well. This enables a stable reactor operation in relation to the ester concentration under steady state conditions for up to 15 days, as well as minimizes the inhibition effect on the biocatalyst. These results are in accordance with previous study reported by Chang et al. [30] in the isopropanolysis of soybean oil catalyzed by immobilized C. antarctica lipase (Novozym 435) in a continuous

80

Ethyl ester concentration (wt%)

followed by myristic (10.2–17.5 wt.%) and oleic (15.2–27.7 wt.%.) acids, respectively. The highest percentage of oleic acid (27.7%) present in macaw palm oil gives the required fluidity at room temperature and makes its to run through the packed bed reactor easier. Woodcock et al. [28] studied the continuous production of alkyl esters by direct esterification of carboxylic acids (hexanoic, octanoic and lauric acids) and short-chain alcohols (methanol, ethanol and butanol) in a miniaturized PBR catalyzed by immobilized Candida antarctica B lipase onto macroporous acrylic resin (Novozym 435). The authors reported that the production of alkyl esters at room temperature was performed in hexane medium to avoid the solidification of lauric acid in the flow system (solid at room temperature). However, the use of vegetable oils having high concentration of unsaturated fatty acids in their composition, e.g. palm oil, reduces possible operational problems during the production of ethyl esters in a continuous process due to its high fluidity [28]. It is important to mention that the high free fatty acid content (FFA) present in macaw palm oil, around 17-fold higher than babassu oil (see Table 1), is not expected to cause negative impact on the production of alkyl esters, since lipase can catalyze both esterification and transesterification reactions [1–3,27].

Babassu oil-(a) 75 70 65 60 55 50 45 40 2

4

6

8

10

12

14

16

Time (days) 80

Macaw palm oil -(b)

75

Ethyl ester concentration (wt%)

884

70 65 60 55 50 45 40 2

4

6

8

10

12

14

16

Time (days) Fig. 2. Ethyl ester formation in the ethanolysis of babassu oil (a) and macaw palm oil (b) in PBR operating at 50 8C, molar ratio oil to ethanol 1:7, space time 7 h using immobilized B. cepacia lipase on silica–PVA as biocatalyst.

packed-bed reactor. Under optimized conditions (flow rate 0.10 mL/min, 51.5 8C, with a 1:4.14 molar ratio oil:isopropanol), maximum molar conversion was 76.62  1.52%. In another study, Pseudomonas cepacia lipase immobilized onto magnetic Fe3O4 nanoparticles was used to catalyze a continuous methanolysis of soybean oil in a single packed bed reactor [13]. The authors also reported that maximum conversion was 75% at 12 h of reaction, followed by a stationary phase up to 132 h. However, the conversion rate dropped to 45% after 240 h reaction. Enzymatic synthesis of ethyl esters (biodiesel) from residual palm oil was performed in a packed bed reactor using combined immobilized lipases from Candida rugosa (Lipase AY) and Pseudomonas fluorescens (Lipase AK) on microporous polypropylene powder (Accurel EP-100) and maximum biodiesel production was found to be 67% [31]. Further information on the reactor behavior was given in terms of the biocatalyst half-life by measuring the enzymatic activity at the beginning and end of each run. This is a parameter of fundamental importance when working with processes that involve immobilized enzymes. This stability depends on a series of factors, such as: linkage of the enzyme with the support, obstruction of the pores by both sludge and by-products (glycerol), support loss by friction and obstruction of the fixed-bed, causing bypass [19,27]. High lipase stability would turn continuous reaction more attractive to industrial plants, mainly due to the high cost of the lipase [27].

W.C. Silva et al. / Journal of Industrial and Engineering Chemistry 20 (2014) 881–886 Table 3 Comparative performance of ethanolysis of vegetable oils (babassu and macaw palm) in a PBR using lipase B. cepacia immobilized on silica–PVA. Parameter

Babassu oil

Macaw palm oil

Biocatalyst (initial activity, IU/g) Biocatalyst (residual activity, IU/g) Total operating time (days) Deactivation coefficient (kd, h1)  103 Biocatalyst half-life (h) Ethyl ester concentration (wt.%) Productivity (mgester/gsubstrate h) Transesterification yield (%) Kinematic viscosity (mm2/s)

2220  84 1280  70 15 1.53 453 60.6  4.2 81.9  6.0 78.0  5.4 9.7  1.4

2670  110 1580  107 15 1.45 478 65.0  5.0 93.4  6.9 85.8  6.6 6.8  0.9

At the end of ethanolysis runs, the biocatalysts were recovered from the reactor and treated with tert-butanol to remove substrate and product eventually retained in the matrix particles. For the reactor running on babassu oil, the residual hydrolytic activity of immobilized derivative was 1280  70 IU/g which corresponded to a loss of activity around 43% compared with its initial activity. The deactivation coefficient (kd) and half-life (t½) were evaluated applying Eqs. (2) and (3) and the following results were obtained 1.53  103 h1 and 453 h, respectively. In relation to the macaw palm oil, the residual hydrolytic activity of immobilized derivative was 1580  107 IU/g which corresponded to an approximate 41% loss of activity when compared to their initial activity. The deactivation coefficient (kd) and half-life (t½) were 1.45  103 h1 and 478 h, respectively. The reduction of catalytic activity of the biocatalyst may be attributed to distortion of the three-dimensional structure of enzyme molecules by influence of the temperature reaction [32] or possible adsorption of glycerol on the microenvironment of the support [27,33]. However, such results were favorable comparable with those reported in the literature using packed bed reactors running on different feedstocks in the presence of solvents such as tert-butanol [7,28,30,13]. A comparative bioreactor performance running on different vegetable oils is displayed in Table 3. According to these results, the different performance for each bioreactor is due to saturated fatty acid composition in the vegetable oils tested, since babassu oil presents 83% content of saturated fatty acids, higher than that macaw palm oil. This parameter leads a rigorous temperature control in all parts of the process, including substrate reservoir and connections, thus facilitating the reactor operation. 3.3. Evaluation of the packed-bed reactor The characterization of pipe flow through the enzyme particle in the column was evaluated by calculating the Reynolds number (Eq. (4)). The value obtained was 3.21  105 indicating a laminar flow behavior (Re  2000). Hence, the flow seems to be dominated by viscous force with, in theory, uniform nonturbulent flow in parallel layers with little mixing between layers [23]. Xu et al. [34] also observed laminar flow at different tested flow velocities for the biodiesel production by transesterification reaction of rapessed oil and ethanol catalyzed by lipase from Thermomyces lanuginosus immobilized on a hydrophobic polymeric resin (NS 88001) in a packed-bed reactor. Based on these results, an ethanolysis process in a continuous packed-bed reactor configuration is feasible in terms of biodiesel synthesis from vegetable oil with predominance of lauric composition, employing immobilized B. cepacia on silica– PVA as biocatalyst in a solvent-free system. Although, the mentioned parameters should be improved to maximize alkyl esters yields.

885

4. Conclusions Increasing biodiesel consumption requires optimized production processes that are compatible with high production capacities and that feature simplified operations, high yields, and the absence of special chemical requirements and waste streams. The high quality of the glycerol by-product obtained is also a very important economic parameter. A heterogeneous catalysis continuous process allows all these objectives to be attained. All results obtained showed that the ethanolysis of macaw palm oil in a solvent-free system achieved higher content of ethyl ester, high productivity and most favorable condition to carry out a continuous packed bed reactor system than that of babassu oil, under the same conditions. Nevertheless, some parameters of PBR system must be improved to achieve higher FAEE yields. In addition, the results indicate that FAEE (biodiesel) formed in a single continuous PBR run in an enzymatic transesterification is suitable for vegetable oil with lower contents of saturated fatty acid in their composition. Hence, macaw palm oil is promising alternative feedstock in the enzymatic ethanolysis of biodiesel in a continuous system. Acknowledgments The authors gratefully acknowledge the financial support of CNPq (Conselho Nacional de Desenvolvimento Cientı´fico e Tecnolo´gico) and CAPES (Coordenac¸a˜o de Aperfeic¸oamento de Pessoal de Nı´vel Superior). References [1] I.M. Atadashi, M.K. Aroua, A.R. Abdul Aziz, N.M.N. Sulaiman, J. Ind. Eng. Chem. 19 (2013) 14. [2] H.F. Castro, A.A. Mendes, L. Freitas, J.C. Santos, in: A.J. Marsaioli, A.L.M. Porto (Eds.), Modificac¸a˜o enzima´tica de o´leos e gorduras para a obtenc¸a˜o de biocombustı´veis e produtos de interesse do setor alimentı´cio, Schoba, Salto, Brazil, 2010, p. 275. [3] T. Tan, J. Lu, K. Nie, L. Deng, F. Wang, Biotechnol. Adv. 28 (2010) 628. [4] M.K. Modi, J.R.C. Reddy, B.V.S.K. Roa, R.B.N. Prasad, Bioresour. Technol. 98 (2007) 1260. [5] L. Li, W. Du, D. Liu, L. Wang, Z. Li, J. Mol. Catal. B: Enzym. 43 (2006) 58. [6] K. Nie, F. Xie, F. Wang, T. Tan, J. Mol. Catal. B: Enzym. 43 (2006) 142. [7] D. Royon, M. Daz, G. Ellenrieder, S. Locatelli, Bioresour. Technol. 98 (2007) 648. [8] A. Gog, M. Roman, M. Tosa, C. Paizs, F.D. Irimie, Renew. Energy 39 (2012) 10. [9] C.G. Laudani, M. Habulin, Z. Knez, C.D. Porta, E. Reverchon, J. Supercrit. Fluids 41 (2007) 74. [10] S.W. Chang, J.F. Shaw, C.K. Yang, C.J. Shieh, Process Biochem. 42 (2007) 1362. [11] J.P. Chen, G.H. Lin, Appl. Biochem. Biotechnol. 161 (2010) 181. [12] S.F.A. Halim, A.H. Kamaruddin, W.J.N. Fernando, Bioresour. Technol. 100 (2009) 710. [13] X. Wang, X. Liu, C. Zhao, Y. Ding, P. Xu, Bioresour. Technol. 102 (2011) 6352. [14] A.S. Simo˜es, Sı´ntese enzima´tica de biodiesel a partir de babac¸u pela rota etı´lica em reator de leito fixo: estabelecimento das condic¸o˜es operacionais em meio isento de solvent, Engineering School of Lorena – University of Sa˜o Paulo, Lorena, Brazil, 2011 (MSc Dissertation). [15] E.F. Moura, M.C. Ventrella, S.Y. Motoike, Sci. Agric. 67 (2010) 399. [16] Official Methods and Recommended Practices of American Oil Chemists’ Society, 5th ed., American Oil Chemists’ Society Press, Champaign, 2004. [17] A.K.F. Carvalho, Sı´ntese de biodiesel por transesterificac¸a˜o pela rota etı´lica: comparac¸a˜o do desempenho de catalisadores heterogeˆneos, Engineering School of Lorena – University of Sa˜o Paulo, Lorena, Brazil, 2011 (MSc Dissertation). [18] P.C.M. Da Ro´s, G.A.M. Silva, A.A. Mendes, J.C. Santos, H.F. de Castro, Bioresour. Technol. 101 (2010) 5508. [19] L. Freitas, J.C. Santos, G.M. Zanin, H.F. de Castro, Appl. Biochem. Biotechnol. 161 (2010) 372. [20] L. Freitas, P.C.M. Da Ro´s, J.C. Santos, H.F. de Castro, Process Biochem. 44 (2009) 1068. [21] O. Levenspiel, Chemical Reaction Engineering, 2nd ed., John Wiley, New York, 1972. [22] C.M.F. Soares, H.F. de Castro, F.F. Moraes, G.M. Zanin, Appl. Biochem. Biotechnol. 77/79 (1999) 745. [23] D.R. Lide, CRC Handbook of Chemistry and Physics, 87th ed., CRC Press, Boca Raton, 2006–2007. [24] D. Urioste, M.B.A. Castro, F.C. Biaggio, H.F. de Castro, Quim. Nova 31 (2008) 407. [25] M.J. Ramos, C.M. Ferna´ndez, A. Casas, L. Rodrı´guez, A. Pe´rez, Bioresour. Technol. 100 (2009) 261. [26] A. Salis, M. Pinna, M. Monduzzi, V. Solinas, J. Mol. Catal. B: Enzym. 54 (2008) 19. [27] A.E. Ghaly, D. Dave, M.S. Brooks, S. Budge, Am. J. Biochem. Biotechnol. 6 (2010) 54.

886

W.C. Silva et al. / Journal of Industrial and Engineering Chemistry 20 (2014) 881–886

[28] L.L. Woodcock, C. Wiles, G.M. Greenway, P. Watts, A. Wells, S. Eyley, Biocatal. Biotransform. 26 (2008) 501. [29] G. Dors, L. Freitas, A.A. Mendes, A. Furigo Jr., H.F. de Castro, Energy Fuels 26 (2012) 5977. [30] C. Chang, J.H. Chen, C.M.J. Chang, T.T. Wu, C.J. Shieh, New Biotechnol. 26 (2009) 187.

[31] K. Tongboriboon, B. Cheirsilp, A. H-Kittikun, J. Mol. Catal. B: Enzym. 67 (2010) 52. [32] G.K. Khor, J.H. Sim, A.H. Kamaruddin, M.H. Uzir, Bioresour. Technol. 101 (2010) 6558. [33] E. Se´verac, O. Galy, F. Turon, C.A. Pantel, J.S. Condoret, P. Monsan, A. Marty, Enzyme Microb. Technol. 48 (2011) 61. [34] Y. Xu, M. Nordblad, J.M. Woodley, J. Biotechnol. 162 (2012) 407.