See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/6141443
Coffee Oil as a Potential Feedstock for Biodiesel Production ARTICLE in BIORESOURCE TECHNOLOGY · JUNE 2008 Impact Factor: 4.49 · DOI: 10.1016/j.biortech.2007.05.074 · Source: PubMed
CITATIONS
READS
76
239
4 AUTHORS, INCLUDING: Leandro Soares Oliveira
Adriana S Franca
Federal University of Minas Gerais
Federal University of Minas Gerais
115 PUBLICATIONS 1,249 CITATIONS
120 PUBLICATIONS 1,663 CITATIONS
SEE PROFILE
SEE PROFILE
Vany Ferraz Federal University of Minas Gerais 58 PUBLICATIONS 539 CITATIONS SEE PROFILE
All in-text references underlined in blue are linked to publications on ResearchGate, letting you access and read them immediately.
Available from: Leandro Soares Oliveira Retrieved on: 04 February 2016
Available online at www.sciencedirect.com
Bioresource Technology 99 (2008) 3244–3250
Coffee oil as a potential feedstock for biodiesel production Leandro S. Oliveira a
a,*
, Adriana S. Franca a, Rodrigo R.S. Camargos a, Vany P. Ferraz
b
Nu´cleo de Pesquisa e Desenvolvimento em Cafe´, DEQ/UFMG, R. Espı´rito Santo, 6o andar, 30160-030 Belo Horizonte, MG, Brazil b Departamento de Quı´mica/UFMG, Av. Antoˆnio Carlos, 6627, 31270-901 Belo Horizonte, MG, Brazil Received 15 May 2007; received in revised form 15 May 2007; accepted 15 May 2007 Available online 13 August 2007
Abstract A preliminary evaluation of the feasibility of producing biodiesel using oil extracted from defective coffee beans was conducted as an alternative means of utilizing these beans instead of roasting for consumption of beverage with depreciated quality. Direct transesterifications of triglycerides from refined soybean oil (reference) and from oils extracted from healthy and defective coffee beans were performed. Type of alcohol employed and time were the reaction parameters studied. Sodium methoxide was used as alkaline catalyst. There was optimal phase separation after reactions using both soybean and healthy coffee beans oils when methanol was used. This was not observed when using the oil from defective beans which required further processing to obtain purified alkyl esters. Nevertheless, coffee oil was demonstrated to be a potential feedstock for biodiesel production, both from healthy and defective beans, since the corresponding oils were successfully converted to fatty acid methyl and ethyl esters. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Biodiesel; Defective coffee beans
1. Introduction Brazil is the largest coffee producer in the world (MAPA, 2006). Approximately 20% of its production consists of defective beans, which upon roasting decrease beverage quality (Oliveira et al., 2006). Regardless of growth, harvest and processing conditions, some defects are intrinsic in nature and will always be present. The ones that affect beverage quality the most are black, brown and immature beans. These defective beans are physically separated from the non defective beans prior to commercialization in international markets. However, since to coffee producers they represent an investment in growing, harvesting, and handling, these defective beans are commercialized in the internal market in Brazil, where the roasting industry uses them in blends with non defective beans. Thus, the quality of the roasted coffee consumed in Brazil is depreciated since, after separation from the exportable portion, defective beans may be representing *
Corresponding author. Tel.: +55 31 32381777; fax: +55 31 32381789. E-mail address:
[email protected] (L.S. Oliveira).
0960-8524/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2007.05.074
more than 50% of the coffee consumed in Brazil (Oliveira et al., 2006). In view of this situation, several studies are currently under development in order to find an alternative use for defective coffee beans. One of the alternatives being considered is biodiesel production. Biodiesel is a name applied to fuels manufactured by the esterification of renewable oils, fats and fatty acids. Biodiesel can be employed as a fuel for unmodified diesel engines (Graboski and McCormick, 1998). This type of fuel has been commercially produced in Europe since the early 1990s (Barnwal and Sharma, 2005). Research studies indicate that, when used as a diesel fuel substitute, biodiesel can replace diesel fuel without causing harmful effects to an unmodified diesel engine, while simultaneously reducing harmful exhaust emissions. In addition, biodiesel is completely miscible with petroleum diesel fuel and can be employed as a blend. However, biodiesel is still not economically feasible in comparison to petroleum diesel. Grain (soybean, rapeseed, sunflower seed) production costs are responsible for approximately 70% of total fuel production costs (Lotero et al., 2005). Such drawbacks could be minimized by the use of a ‘‘less valuable’’ feedstock, such
L.S. Oliveira et al. / Bioresource Technology 99 (2008) 3244–3250
as the oil of rejected defective beans, with the advantage of allowing coffee producers to produce and use their own fuel. Therefore, the present study aimed at an evaluation of the potential of using oil of defective coffee beans as a feedstock for biodiesel production. 2. Methods 2.1. Materials The coffee beans used in the present work, both healthy and defective, were acquired from Santo Antonio Estate Coffee, an association of coffee producers in Minas Gerais State, Brazil. The reference refined soybean oil (Liza, Brazil) was acquired from a local market. The reagents employed (methanol, ethanol, sodium methoxide) were acquired from Synth (Sa˜o Paulo, Brazil). Sodium methoxide was purchased as a 30% solution in methanol. Methanol and ethanol presented 0.02% and 0.2% water contents, respectively. Standards of fatty acids were purchased from Sigma–Aldrich (Sa˜o Paulo, Brazil). 2.2. Oil extraction Coffee beans were ground in a Rotatec grinder (Belo Horizonte, Brazil) prior to oil extraction. The oils of the ground healthy and defective coffee beans were obtained by solvent (hexane) extraction in an industrial Soxhlet apparatus (Sociedade Fabbe Ltda, Sa˜o Paulo, Brazil), with an extraction capacity of 25 kg of beans per batch. The oils were extracted in batches for 16 h of duration. After extraction, the solvent was removed in a rotary evaporator (Fisatom, mod. 5502, Sa˜o Paulo, Brazil) at 70 °C, under moderate vacuum, until no traces of hexane were detected by gas chromatography. 2.3. Transesterification reactions The direct transesterification of vegetable oils triglycerides was performed with the aim of producing alkyl esters of long chain fatty acids. The reactions were carried out with refined soybean oil and coffee oils from defective and healthy beans. The transesterification reactions were performed in a 500 mL cylindrical three-necked reactor, mechanically stirred and heated by a hot water jacket. The temperature of the water in the jacket was controlled ´ tica, Sa˜o Paulo, Braby a thermostatic water bath (Nova E zil) and it was set to keep the reacting medium at the desired temperature (55 °C when using methanol and 60 °C for ethanol). Eighty grams of oil were used in the transesterification experiments. Sodium methoxide (final concentration of 1% w/w based on the mass of oil) was used as an alkaline catalyst for both the soybean and healthy beans coffee oil. For the defective coffee beans oil, the amount of catalyst used was calculated as the minimum necessary for the transesterification of the triglyceride fraction plus that for
3245
the neutralization of the titrated free fatty acids. Methanol and ethanol were employed in a 6:1 alcohol-to-oil molar ratio. The reactions were carried out at ambient temperature (25 °C) and at 55 °C and 60 °C for methanol and ethanol, respectively. Stirring was kept at 600 rpm (Vicente et al., 2005). After completion of reaction, the pour-off time was 24 h, a time long enough to allow for the complete separation of an upper ester layer and a lower glycerol layer. The upper layer was collected and submitted to a rotary evaporation at 70 °C, under moderate vacuum, for the removal of alcohol. After alcohol removal, the ester phase was analyzed by gas chromatography (Varian 3380 Gas Chromatograph, Middelburg, The Netherlands) to determine the yield of fatty acid alkyl esters. The parameters used in the transesterification tests are presented in Table 1. All transesterification tests were conducted in duplicates. 2.4. Analyses of oils and alkyl esters of fatty acids Oil acidity was determined by AOCS method Cd 3d-63 (AOCS, 1998). Moisture content determination was based on mass difference by oven drying at 105 °C for 2 h (Pregnolatto and Pregnolatto, 1985). The samples taken after transesterification of the oils were analyzed by gas chromatography. Twenty-five microliters of the samples were dried in a nitrogen stream for the removal of the excess solvent and subsequently weighed and diluted in 1 mL methanol. The fatty acid methyl and ethyl esters were injected in a Varian 3380 gas chromatograph, equipped with a flame ionization detector (Middelburg, The Netherlands). The analytic conditions employed were: initial temperature of 200 °C, followed by a temperature increase at a rate of 10 °C per min up to 240 °C. The duration of the analysis was 10 min. A Carbowax 20 M column (Supelco, Bellefonte, PA, USA) was employed. Peak identification was carried out by comparison of the retention times with those for the respective fatty acid methyl esters standards (FAMEs), which were prepared by esterification of fatty acids standards with BF3 in methanol solution according to AOAC method 996.06 (AOAC, 1995). The ester conversions were calculated from the contents of alkyl esters in the ester phase as analyzed by GC and the Table 1 Parameters employed in the transesterification reactions Oil
Temperature (°C)
Reaction time (h)
Soybean Soybean Soybean Soybean Coffee healthy Coffee healthy Coffee healthy Coffee healthy Coffee defective Coffee defective Coffee defective Coffee defective
25 25 55 55 25 25 55 55 25 25 55 55
1.0 2.0 0.5 1.0 1.0 2.0 0.5 1.0 1.0 2.0 0.5 1.0
3246
L.S. Oliveira et al. / Bioresource Technology 99 (2008) 3244–3250
material balance, as described by Alcantara et al. (2000). Viscosity determinations for fatty acid alkyl esters were based on ASTM method D445-06 (Knothe et al., 2005).
result in phase separation, although some degree of transesterification was achieved. Emulsion and gel formation were observed in this case.
2.5. Statistical analyses
3.2. Optimization of reaction conditions
All determinations were performed randomly in a total of two replicates. The obtained data were submitted to analysis of variance and the mean values were compared by the Duncan test at 5% probability.
Reaction time and temperature were the two parameters chosen for the optimization of the transesterification reactions conditions. Reaction time was varied from 0.5 to 2 h and the selected temperature values were 25 °C, for both methanol and ethanol as esterifying agents, and 55 °C for methanol and 60 °C for ethanol. In the case of refined soybean oil, all the reaction products presented optimal separation of phases after 1 h of pour-off time. After 24 h, the ester-rich phases of all samples were crystal clear. The ester-rich phase was collected and the excess solvent (alcohol) was removed in a rotary evaporator. After removal of solvent, the ester phase was kept at rest for another 24 h and a new separation of phases occurred. In the solvent removal procedure, it was observed that the ester phase contained smaller amounts of methanol (20–30%) than those products obtained with ethanol (40–50%). For recovery of alcohol, losses ranged from 1% to 8% and could be attributed to differences in the samples handling during reaction and separation, and in the solvent removal procedures. Average values of the ester yields for all reactions with soybean oil are presented in Table 2. Standard deviation values ranged from 0.5% to 1.3% points. It is clear that the ester conversion does not vary significantly with an increase in reaction time, for a constant temperature. Reactions carried out at room temperature (25 °C) presented ester yields approximately 15% points higher than those at 55 °C, irrespective of reaction time. There was a 3% point increase in ester conversion with an increase in reaction time for the transesterifications carried out with ethanol. An increase in reaction temperature from 25 to 60 °C did not cause a significant increase (approximately 1%) in ester conversion. The reactions with methanol presented higher ester yields at room temperature than any other conditions. However, when using ethanol at 60 °C, the ester yields were 2% and 5% points higher than those obtained with methanol at 55 °C for reaction times of 30 min and
3. Results and discussion The yield of coffee beans oil ranged from 10 to 12% on a dry weight basis. The titrated acidities of the reference refined soybean oil and of the oils of healthy and defective coffee beans were 0.36 ± 0.08, 2.62 ± 0.29 and 10.04 ± 0.03% (w/w), respectively. It should be noted that the contribution of the defective beans to the acidity of the oil is fairly high, since these beans are partially comprised of fermented beans (black and brown). The triglyceride composition of the coffee oils, from both healthy and defective beans, were determined by a thermogravimetric procedure adapted from that proposed by Goodrum and Geller (2002). Coffee oil from healthy beans was determined to be comprised of 81% (w/w) triglycerides and the oil from defective beans presented a 76% (w/w) triglyceride fraction, both values falling within the range previously published in the literature (Speer and Ko¨lling-Speer, 2001; Oliveira et al., 2006). The oils were subjected to transesterification reactions without any refinement, i.e., with a 19% and 24% fraction of unsaponifiable matter for the oils of healthy and defective beans, respectively. The moisture contents of the oils were determined as 0.28 and 0.11 kgwater/kgoil for the oils of healthy and defective beans, respectively. The refined soybean oil presented a negligible amount of water. The fatty acid compositions of the coffee oils were determined in a previous study (Oliveira et al., 2006) and the major constituents are linoleic and palmitic acids (44% and 34%, respectively), followed by oleic (9%) and stearic (7%) acids. 3.1. Transesterification of oils Preliminary tests were performed for the transesterification of the soybean and coffee oils, using either sodium methoxide or sulfuric acid, to determine the type of catalyst to be used in the experiments. Transesterification and separation of phases were successfully accomplished with both basic and acid catalysts for the soybean oil, and only with the basic catalyst for the coffee oil of healthy beans. The transesterification of coffee oils using sulfuric acid as a catalyst produced a black gelatinous product that occupied most of the reactor volume with a thin black liquid layer on top of it. Thus, sulfuric acid was not further used as a catalyst in this study. The reaction with the oil of defective coffee beans, using sodium methoxide as a catalyst, did not
Table 2 Ester yields for the reactions with refined soybean oil Reaction conditions
Ester yield (%)
MetOH 25 °C 1 h MetOH 25 °C 2 h MetOH 55 °C 0.5 h MetOH 55 °C 1 h EtOH 25 °C 1 h EtOH 25 °C 2 h EtOH 60 °C 0.5 h EtOH 60 °C 1 h
96.1 ± 1.2a 95.7 ± 1.0a 81.2 ± 0.8d 80.4 ± 1.3d 84.0 ± 0.5c 87.2 ± 0.7b 82.7 ± 0.5d 85.2 ± 0.7c
Average value ± Standard deviation; values followed by the same letter in the same column do not differ significantly by the Duncan test at 5% probability.
L.S. Oliveira et al. / Bioresource Technology 99 (2008) 3244–3250
1 h, respectively. Overall, the results indicated that reactions carried out at room temperature lead to higher ester conversions than at higher temperatures, regardless of reaction time and type of alcohol employed. Furthermore, separation of phases after completion of reactions was easier to accomplish with methanol rather than with ethanol, thus, corroborating information previously reported in the literature (Schuchardt et al., 1998; Lotero et al., 2005). Negligible amounts of emulsified and gelatinous matter were observed in the products of reactions carried out at higher temperatures. The characteristics observed for the transesterification reactions with oils from healthy coffee beans are summaTable 3 Characteristics observed for the transesterification reactions with oils from healthy coffee beans Reaction conditions
Aspects of phase separation
MetOH 25 °C 1h MetOH 25 °C 2h MetOH 55 °C 0.5 h MetOH 55 °C 1h EtOH 25 °C 1 h EtOH 25 °C 2 h
Well-defined phase separation with presence of small amounts of emulsified matter in the upper layer Well-defined phase separation with presence of small amounts of emulsified matter in the upper layer Well-defined phase separation with presence of small amounts of emulsified matter in the upper layer Well-defined phase separation with presence of small amounts of emulsified matter in the upper layer No phase separation with presence of emulsified matter Partial phase separation with presence of emulsified matter No phase separation with presence of emulsion and gelatinous matter No phase separation with presence of emulsion
EtOH 60 °C 0.5 h EtOH 60 °C 1 h
3247
rized in Table 3. The oil samples reacted with methanol yielded optimal separation of phases during pour-off time, with negligible amounts of emulsified and gelatinous matter being observed in the products. When using ethanol, a partial separation of phases was observed only for the reaction carried out at room temperature for 2 h. The other reaction conditions did not lead to separation of phases during pour-off time. All the samples reacted with ethanol presented significant amounts of gelatinous matter in the reaction products. In order to evaluate whether ester conversion occurred or not, the reactions products that did not separate into two phases were diluted in alcohol and submitted to an acid treatment for neutralization of unreacted catalyst and to facilitate separation of phases. The non-soluble gel was separated by centrifugation, and the upper layer was removed and resubmitted to an evaporation procedure for alcohol removal. After solvent removal, a new separation of phases occurred and formation of gel was not observed. The ester layers were analyzed by GC. The chromatogram for the products obtained in the reaction with ethanol at 55 °C, for 1 h, is presented in Fig. 1. Peaks related to both ethyl and methyl esters are clearly noticeable. The methyl esters peaks are due to the presence of methanol in the solution in which the catalyst is commercially available (30% CH3ONa in methanol). All the other chromatograms presented similar ester profiles. The average ester conversion results for the reactions with healthy coffee oil are presented in Table 4. Standard deviation values ranged from 0.4% to 1.7% points. The conversions obtained for the coffee oil were lower than those for the refined soybean oil. These lower conversions
Fig. 1. Chromatogram for biodiesel from coffee oil (healthy beans) after 1 h transesterification with ethanol at 55 °C.
3248
L.S. Oliveira et al. / Bioresource Technology 99 (2008) 3244–3250
Table 4 Ester yields for the reactions with oil from healthy coffee beans Reaction conditions
Ester yield (%)
MetOH 25 °C 1 h MetOH 25 °C 2 h MetOH 55 °C 0.5 h MetOH 55 °C 1 h EtOH 25 °C 1 h EtOH 25 °C 2 h EtOH 60 °C 0.5 h EtOH 60 °C 1 h
70.1 ± 0.5a 68.4 ± 1.7a 62.3 ± 1.2b 60.4 ± 1.5b 35.0 ± 0.7d 45.2 ± 1.0c 63.9 ± 0.7b 64.2 ± 0.5b
Average value ± Standard deviation; values followed by the same letter in the same column do not differ significantly by the Duncan test at 5% probability.
may be attributed to the fact that part of the catalyst was consumed for the production of soap, since there was no addition of catalyst to compensate for the higher free fatty acid content of the healthy coffee oil (2.6%). In addition, the presence of unsaponifiable matter (19%) may have hindered the interactions between the reactants (triglycerides and alcohol). Likewise, the presence of emulsion in the products (Table 3) increased the solubility of alkyl esters in the glycerol-rich phase (Vicente et al., 2004), which was separated by centrifugation prior to the collection of samples for the analysis, and part of the produced ester may have been removed in that phase. When methanol was employed, there were no significant differences in ester conversion with an increase in reaction time. The reactions with ethanol presented lower conversions than those with methanol. In addition, regarding the reactions with ethanol, an increase in reaction time promoted higher ester conversions when the reaction was carried out at room
temperature, and did not affect the conversion for the reaction at 60 °C. Although ethanol is expected to lead to higher conversions in shorter reaction times, due to its higher miscibility with the oil, it is also known to hinder phase separation (Table 3). Thus, it makes the determination of the true ester yields difficult, as the reaction products should undergo further processing (acid treatment or addition of glycerine) to allow for good separation of phases. The oil of defective coffee beans was subjected to transesterification reactions employing the same conditions as for the oil of healthy beans with the exception that the amount of catalyst was recalculated to account for its higher free fatty acid content (10%). Saponification of the free fatty acids was observed instantaneously as the mixture of alcohol and catalyst was added to the reactor, causing an increase in the viscosity of the reactants mixture. As the alkyl esters began to form, the viscosity of the reacting medium decreased again. After completion of the reaction, the product was set to rest, not separating into phases and acquiring a paste-like texture as it cooled down. After alcohol removal (evaporation), the mixture acquired a solidlike texture. It was subsequently submitted to an acidified alcohol treatment as suggested in the literature (Encinar et al., 2005) and centrifuged afterwards. Following centrifugation, optimal separation of phases was attained. The ester layer was sampled and analyzed by GC. The chromatogram for the reaction with methanol at room temperature is presented in Fig. 2. All the other chromatograms presented similar ester profiles. The average ester yields for all the reactions carried out with defective beans oil are presented in Table 5. Standard
Fig. 2. Chromatogram for biodiesel from coffee oil (defective beans) after 1 h transesterification with methanol at 25 °C.
L.S. Oliveira et al. / Bioresource Technology 99 (2008) 3244–3250 Table 5 Ester yields for the reactions with oil from defective coffee beans Reaction conditions
Ester yield (%)
MetOH 25 °C 1 h MetOH 25 °C 2 h MetOH 55 °C 0,5 h MetOH 55 °C 1 h EtOH 25 °C 1 h EtOH 25 °C 2 h EtOH 60 °C 0,5 h EtOH 60 °C 1 h
73.8 ± 1.8a 71.3 ± 1.6a 68.4 ± 1.8a 71.0 ± 1.5a 72.2 ± 1.2a 73.0 ± 0.5a 55.2 ± 1.2b 71.1 ± 1.3a
Average value ± Standard deviation; values followed by the same letter in the same column do not differ significantly by the Duncan test at 5% probability.
deviation values ranged from 0.5% to 1.8% points. The ester yields in this case were higher than those obtained for the oil of healthy coffee beans. This can be attributed to the fact that the amount of catalyst used for the oil of defective beans was increased to compensate for a higher amount of free fatty acids. A higher amount of catalyst will allow for reactions with free fatty acids to produce soap and assure that the remaining amount of catalyst is enough to promote transesterification of the entire triglyceride fraction. Again, when compared to the results for the refined soybean oil, the ester yields were lower. It should be noted that the oil of defective coffee beans presented a 24% fraction of unsaponifiable matter that may have hindered interactions between reactants, thus contributing to the lower yields. The unsaponifiable fraction is responsible for imparting a higher viscosity to the oil. In this study, the viscosity of coffee oils was determined to be about four times higher than the viscosity of the refined soybean oil (170 mPa s against 43 mPa s). An increase in reaction time did not significantly affect conversions to esters, except for the reactions with ethanol at 60 °C. A major difference in ester yields was observed for the reactions with ethanol at 60 °C, when an increase of 30 min in reaction time caused an increase of 16% points in ester yield. In the case of ethanol, it is known from literature (Lotero et al., 2005) that the transesterification reaction is kinetically controlled, since the reactants (ethanol and oil) are completely miscible (no mass transfer resis-
3249
tance) and, also, the reaction rates are more dependent on temperature than when using methanol. Thus, at higher temperatures (60 °C), this dependence on temperature is evidenced and it is further supported by the fact that an increase in time did not favor the ester yield at 25 °C. Physical properties for the biodiesel produced from coffee oils are presented in Table 6, together with European specifications for commercial biodiesel and Diesel No. 2. All the physical properties for the coffee oil biodiesel were within the limits specified by European standards. Concerning the amount of free glycerol in the ester-rich phase, after one acidic methanol washing step (Tomasevic and Siler-Marinkovic, 2003) and a few water washing steps, it was determined to be in the range of 123–141 mg/kg. The method employed for the free glycerol determination was that proposed by Bondioli and Bella (2005). 4. Conclusion Oils extracted from healthy and defective coffee beans were successfully converted to alkyl esters of fatty acids by transesterification with both methanol and ethanol in the presence of sodium methoxide as an alkaline catalyst. The yields for the reactions with the oil of healthy coffee beans were lower than those for the oil of defective beans, indicating the need for correction of the amount of catalyst to be used due to the content of free fatty acids of the oil. Further studies regarding the identification of the factors affecting conversion are needed in order to optimize the production of alkyl esters using the oil from defective coffee beans. Removal of unsaponifiable matter prior to transesterification is envisaged to be a suitable processing step for improving the ester yield and reducing viscosity of the alkyl esters produced. Regardless of the ester yields obtained, coffee oil demonstrated potential as a candidate for feedstock in biodiesel production. Acknowledgements The authors acknowledge financial support from the following Brazilian Government Agencies: CAPES, CNPq and FAPEMIG.
Table 6 European biodiesela and diesel No. 2b specifications Property
Unit
Lower limita
Upper limita
Tobacco seed oil biodiesel b
Coffee oil fatty acid methyl estersc Defective
Healthy
Density Viscosity HHVd
Kg/m3 mm2/s kJ/kg
860 3.5** 35000
900 5** –
886.8 3.5**; 6* 39811
894.1 4.9**; 8.9* 38414
892.5 3.1**; 3.4* 38498
* ** a b c
Value at 25 °C. Value at 40 °C. Knothe et al. (2005). Usta (2005). This study, reactions with methanol at 25 °C.
Soybean oil biodieselc
Diesel No. 2b
876.7 5.7* 39100
841.5 2.9** 44631
3250
L.S. Oliveira et al. / Bioresource Technology 99 (2008) 3244–3250
References Alcantara, R., Amores, J., Canoira, L., Fidalgo, E., Franco, M.J., Navarro, A., 2000. Catalytic production of biodiesel from soy-bean oil, used frying oil and tallow. Biomass Bioenerg. 18, 515–527. AOAC – Association of Official Analytical Chemists. 1995. Official Methods of Analysis of AOAC International, 16th ed. Gaithersburg, Maryland, USA, AOAC International. AOCS (American Oil Chemists Society). 1998. Official Methods and Recommended Practices of the AOCS, 5th ed. Champaign, IL, AOCS. Barnwal, B.K., Sharma, M.P., 2005. Prospects of biodiesel production from vegetable oils in India. Renew. Sustain. Energ. Rev. 9, 363–378. Bondioli, P., Bella, L.D., 2005. An alternative spectrophotometric method for the determination of free glycerol in biodiesel. Eur. J. Lipid Sci. Technol. 107, 153–157. Encinar, M., Gonza´lez, J.F., Rodriguez-Reinares, A., 2005. Biodiesel from used frying oil. Variables affecting the yields and characteristics of the biodiesel. Ind. Eng. Chem. Res. 44, 5491–5499. Graboski, M.S., McCormick, R.L., 1998. Combustion of fat and vegetable oil derived fuels in diesel engines. Prog. Energ. Combust. Sci. 24, 125–164. Goodrum, J.W., Geller, D.P., 2002. Rapid thermogravimetric measurements of boiling points and vapor pressure of saturated medium- and long-chain triglycerides. Bioresource Technol. 84, 75–80. Knothe, G., Van Gerpen, J., Krahl, J., 2005. The Biodiesel Handbook. AOCS Press, Champaign, IL.
Lotero, E., Liu, Y., Lopez, D.E., Suwannakarn, K., Bruce, D.A., Goodwin Jr., J.G., 2005. Synthesis of biodiesel via acid catalysis. Ind. Eng. Chem. Res. 44, 5353–5363. Oliveira, L.S., Franca, A.S., Mendonc¸a, J.C.F., Barros-Ju´nior, M.C., 2006. Proximate composition and fatty acids profile of green and roasted defective coffee beans. Lebensm. Wiss. Technol. 39, 235– 239. MAPA (Ministe´rio da Agricultura, Pecua´ria e Abastecimento) 2006. Coffee Statistics, Report 1727–2006, December 2006, Brazil (in Portuguese). Pregnolatto, W., Pregnolatto, N.P., 1985. Normas Analı´ticas do Instituto Adolfo Lutz, third ed. IAL, Sa˜o Paulo, Brazil (in Portuguese). Schuchardt, U., Sercheli, R., Vargas, R.M., 1998. Transesterification of vegetable oils: a review. J. Braz. Chem. Soc. 9, 199–210. Speer, K., Ko¨lling-Speer, I., 2001. Lipids. In: Clarke, R.J., Vitzthum, O.G. (Eds.), Coffee. Recent Developments. Blackwell Science Ltd., London, pp. 33–49. Tomasevic, A.V., Siler-Marinkovic, S.S., 2003. Methanolysis of used frying oil. Fuel Processing Technology 81, 1–6. Usta, N., 2005. Use of tobacco seed oil methyl ester in a turbocharged indirect injection diesel engine. Biomass Bioenerg. 28, 77–86. Vicente, G., Martı´nez, M., Aracil, J., 2004. Integrated biodiesel production: a comparison of different homogeneous catalysts systems. Bioresource Technol. 92, 297–305. Vicente, G., Martı´nez, M., Aracil, J., Esteban, A., 2005. Kinetics of sunflower oil methanolysis. Ind. Eng. Chem. Res. 44, 5447–5454.
