Science & Technology


Biodiesel Synthesis via Esterification of Feedstock with High Content of Free Fatty Acids

The objective of this work was to study the synthesis of ethyl esters via esterification of soybean oil deodorizer distillate with ethanol, using solid acid catalysts and commercial immobilized lipases, in a solvent-free system. Three commercially
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  Biodiesel Synthesis via Esterification of Feedstock with High Content of Free Fatty Acids Marcella S. Souza  &  Erika C. G. Aguieiras  & Mônica A. P. da Silva  &  Marta A. P. Langone Received: 21 May 2008 /Accepted: 13 November 2008 / Published online: 9 December 2008 # Humana Press 2008 Abstract  The objective of this work was to study the synthesis of ethyl esters viaesterification of soybean oil deodorizer distillate with ethanol, using solid acid catalysts andcommercial immobilized lipases, in a solvent-free system. Three commercially immobilizedlipases were used, namely, Lipozyme RM-IM, Lipozyme TL-IM, and Novozym 435, allfrom Novozymes. We aimed for optimum reaction parameters: temperature, enzymeconcentration, initial amount of ethanol, and its feeding technique to the reactor (stepwiseethanolysis). Reaction was faster with Novozym 435. The highest conversion (83.5%) wasobtained after 90 min using 3 wt.% of Novozym 435 and two-stage stepwise addition of ethanol at 50°C. Four catalysts were also tested: zeolite CBV-780, SAPO-34, niobia, andniobic acid. The highest conversion (30%) was obtained at 100°C, with 3 wt.% of CBV-780after 2.5 h. The effects of zeolite CBV 780 concentration were studied, resulting in aconversion of 49% using 9 wt.% of catalyst. Keywords  Esterification .SODD.Biodiesel .Ethanol .Immobilizedlipase .Zeolite Appl Biochem Biotechnol (2009) 154:253  –  267DOI 10.1007/s12010-008-8444-4M. S. Souza :  M. A. P. da SilvaEscola de Química, Universidade Federal do Rio de Janeiro, Rio de Janeiro CEP 21949-900, BrazilM. A. P. da Silvae-mail: E. C. G. AguieirasInstituto de Biologia Roberto Alcântara Gomes, Universidade do Estado do Rio de Janeiro,Rio de Janeiro, BrazilM. A. P. Langone ( * )Instituto de Química, Universidade do Estado do Rio de Janeiro, Rua São Francisco Xavier, 524, PHLC,IQ, sl. 427, Rio de Janeiro CEP 20559-900, Brazile-mail:   Introduction The growing interest for renewable sources of energy is responsible for the worldwideefforts towards the development of biofuels. Biodiesel in particular is synthesized viatransesterification of triglycerides from vegetable oils with ethanol or methanol [1].Biodiesel is a mixture of mono-alkyl esters of higher fatty acids. The use of biodiesel as analternative fuel has a promising potential since it is based on renewable resources likevegetal oils and animal fats, does not present sulfur and aromatic chemicals in itscomposition, reduces the life cycle of carbon dioxide besides being biodegradable, and isnon-toxic [2].The industrial process of biodiesel production is usually carried out by heating anexcess of alcohol with vegetables oils, called transesterification or alcoholysis, in presence of an inorganic catalyst (NaOH, KOH). A disadvantage of alkali-catalyzed processes is that catalysts are lost to the glycerol layer and cannot be reused.Furthermore, neutralization to prevent toxic wastes is necessary and the purification of glycerol is more difficult when large amounts of catalyst are present. Besides, the useof more expensive refined oils is necessary so as to have low free fatty acids content (inferior to 1%).Thus, the current production costs of biodiesel are not competitive with diesel due to arelatively high cost of lipid feedstocks, usually edible-grade refined oils. An alternativeroute to biodiesel is based on esterification of free fatty acids present in high concentrationsin the by-product obtained from vegetable oil refining [3, 4]. Soybean oil deodorizer distillate (SODD) is an important by-product in the soybean oilrefining process. About 80 wt.% of SODD corresponds to free fatty acids plus triglycerides[3]. Biodiesel production via esterification of fatty acids present in SODD is undoubtedly a promising alternative, since the unit price of this material is significantly lower than that of refined oils [5].In conventional esterification processes for production of biodiesel, strong acids are usedas catalysts. The process is highly energy consuming and fluids are difficult to handle,causing problems of corrosion in equipment and producing waste acid, with seriousenvironmental impact. Also, synthesis schemes are such that poor reaction selectivity andundesirable side reactions often occur [3].The current demand for cleaner and more selective processes has motivated thedevelopment of solid catalysts for organic synthesis in general as well as for biodieselsynthesis. The possibility of catalyst reuse is also an important factor, considering thereduction in the operational costs.The use of heterogeneous catalysts, less polluting and more selective, has led to thedevelopment of enzyme supported catalysts in organic synthesis. Lipases are a class of enzymes known as triacylglycerol ester hydrolases. Most of these enzymes show highselectivity including stereo-selectivity, work on mild operation conditions, and give products of high purity. Esterification reactions between alcohols and free fatty acids canalso be catalyzed by lipases in non-aqueous or microaqueous media. The production of esters can be achieved either by synthesis with free fatty acids and alcohols or bytransesterification [6  –  9].Motivated by the fact that Brazil is the largest world producer of ethanol and the secondlargest producer of soybeans, the objective of this work was to study the synthesis of mono-alkyl esters (biodiesel) from esterification of SODD with ethanol, using solid acid catalystsand commercial immobilized lipases in a solvent-free medium. This work studied theeffects of ethanol concentration and its feeding technique to the reactor, temperature, 254 Appl Biochem Biotechnol (2009) 154:253  –  267  enzyme concentration, and type of immobilized lipase as well as to esterification reactionsusing solid acids catalysts (CBV-780, SAPO-34, niobia, and niobic acid). Experimental MaterialsSODD from soybean oil refining process was provided by Piraquê S. A. (Rio de Janeiro,Brazil). Commercial lipases used were: Lipozyme RM-IM (lipase from  Rhizomucor miehei ,immobilized on macroporous anion exchange resin), Lipozyme TL-IM (lipase from Termomyces lanuginosus ), Novozym 435 (lipase from  Candida antarctica , immobilized onacrylic macroporous resin), all kindly donated by Novozymes Latin America Ltda(Araucária, Brazil).Two commercial catalysts, CBV 780 (zeolite type SDUSY-ZEOLYST TM) andniobic acid (CBMM) and two synthesized catalysts, SAPO-34 (molecular sieve-typealumino-silicate-phosphate) and niobia, were tested. The choice of these catalysts isrelated to the fact that among various catalysts tested previously CBV 780 presentedthe highest activity in esterification of palmitic acid and ethanol [10]. Niobic acid(CBMM) is the commercial catalyst used in a biodiesel process by AGROPALMA/Braziland niobia is very similar. Regarding SAPO-34, it was used because of its high density of acid sites. SAPO-34 was obtained according to the procedure reported by Prakash andUnnikrishnan [11] and calcination of the solid was carried out by a procedure adaptedfrom Gomes et al. [12]. Niobia was synthesized according to a methodology adapted fromChuah et al. [13]. Synthesis of niobia consisted of addition of NH 4 OH to an aqueoussolution of ammonia complex of niobium (CBMM-AD 2698). The preparation wascarried out in a rotavapor during 96 h to 95°C. The pH was maintained at 9.0. Then thematerial was filtered and dry in oven at 100°C for 24 h. The calcination was performedunder flow of air at 500°C (1°C/min) for 12 h.Ethanol P. A., acetone P. A., and sodium hydroxide were supplied by Vetec QuímicaFina Ltda (Rio de Janeiro, Brazil).SODD CharacterizationAcidity and acid value of SODD were determined according to AOCS Te 1a-64 [14].Iodine index and humidity were determined according to AOCS Cd 1d-64 [14] and Ca 2e-84 [14], respectively.Fatty acids present in SODD were determined according to AOCS Ce 1f-96 [14], in aHP 6890N GC, equipped with flame ionization detector and capillary column SP 2340.Measurement of Lipase ActivityThe esterification activity of commercial lipases Lipozyme RM-IM, Lipozyme TL-IM,and Novozym 435 was measured by the consumption of oleic acid at 45°C in theesterification reaction with butanol (oleic acid/butanol molar ratio of 1) with the enzymeconcentration of 3 wt.%. One unit of enzymatic activity (U) in this process was defined as1  μ  mol of oleic acid consumed/min under the experimental conditions described herein.The option for butanol instead of ethanol is related to the fact that ethanol promotes aquick deactivation of the enzyme due to dehydration effects. Appl Biochem Biotechnol (2009) 154:253  –  267 255  The activity of commercial lipases Lipozyme RM-IM, Lipozyme TL-IM, and Novozym435 was 1,510, 454, and 2,960 ( μ  mol acid/min g), respectively.Solid Acid Catalyst CharacterizationThe chemical composition of catalysts was determined by X-ray fluorescence (XRF),using a spectrometer Rigaku, Rix 3100 model equipped with a rhodium X-raygenerator tube. X-ray diffraction (XRD) analyses were carried out in a RigakuMiniflex diffractometer using CuK  α   radiation ( α =1.5417 Å) operating at 30 kV and15 mA. Textural analyses were carried out according to the BET method in equipment Micromeritics ASAP model 2000, using N 2  at 196°C. The degree of hydration and thethermal stability of the catalysts were determined in a thermogravimetric balance(RIGAKU-TAS100) under flow of nitrogen from 25 to 600°C and heating rate of 10°C/min.Temperature-programmed desorption of ammonia (TPD) analyses were carried out ina multipurpose unity coupled with a Balzers QUADSTAR 422 QMS 200 massspectrometer. For the TPD analyses, NH 3  adsorption was carried out at 100°C, bysubmitting the samples to a 4% NH 3 /He mixture flow of 60 ml/min during 30 min;desorption was carried out by heating the samples from 100 to 550°C at 10°C/min, under He flow of 60 ml/min.Before each TPD analysis, CBV-780 and SAPO-34 were dried under He flow of 30 ml/minsimultaneously with heating from ambient temperature to 500°C at 10°C/min. Niobia andniobic acid were dried at 250°C using a similar procedure.Reaction SystemEsterification reactions took place in a closed 15-ml batch reactor magnetically stirred andcoupled to a condenser in order to avoid alcohol loss. Water circulating in the condenser was cooled by a thermostatic bath. Reacting medium temperature was kept constant bycirculating hot ethylene glycol through the reactor jacket. A thermostatic bath (HAAKED10) allowed a close control over the process temperature. The mass of SODD used was8 g in all experiments.Quantification of Free Fatty AcidsReaction progress was monitored by taking duplicate samples (100  μ  l) each 30 min until2.5 h of reaction. Free fatty acids present in reaction medium samples were analyzed bytitration with NaOH 0.02 M using a Mettler DL 25 autotitrator. Results and Discussion Characterization of SODDAcidity, acid value, iodine index, and humidity of SODD are shown in Table 1.The chemical composition of SODD regarding fatty acids is shown in Table 2.The concentration of linoleic and palmitic acids are atypical most probably due to partialhydrogenation of the srcinal soybean oil as well as blending with palm oil. 256 Appl Biochem Biotechnol (2009) 154:253  –  267  Esterification Reactions using Lipases  Effects of Ethanol Concentration A generic esterification process mediated by a biocatalyst is represented by the followingstoichiometry:  Lipase R 1 COOH + R 2 OH R 1 COOR 2  + H 2 O   fatty acid alcohol   ester water  Since the reaction is reversible, one reagent should be in excess so as to displace theequilibrium towards products. Thus, the effects of ethanol concentration on the fatty acidconversion were investigated. The amount of SODD was always 8 g while the ethanol massranged between 1 and 4 g. Based on the SODD composition shown in Table 2, we canadmit that the proportion 8 g of SODD:1 g of alcohol corresponds to a molar ratio 1:1 of fatty acids to ethanol. Figure 1 shows that an increase in ethanol concentration leads to adecrease in fatty acid conversion. The highest conversion observed was 59%, using 3 wt.%Lypozyme RM-IM and 1 g of ethanol at 50°C after 2.5 h. Notice that triglycerides present in SODD can react directly with ethanol-producing ethyl esters for immobilizedcommercial lipases such as Lipozyme RM-IM and Novozym 435, which also catalyzetransesterification reactions. However, in this work, only the consumption of free fatty acidswas measured. Acidity (%) 72.6Acid value (mg KOH/g) 144.4Iodine index 63.8Humidity (%) 0.173 Table 1  Physicochemical analy-sis of SODD.Fatty acid Number of carbon atomsInsaturationnumber Composition(%)Capric acid 10  –   0.1Lauric acid 12  –   0.1Myristic acid 14  –   0.7Palmitic acid 16  –   30.9Palmitoleic acid 16 1 0.2Stearic acid 18  –   23.7Oleic acid 18 1 23.8Linoleic acid 18 2 6.4Linolenic acid 18 3 0.3Arachidic acid 20  –   0.4Behenic acid 22  –   0.3Other fatty acid  – –   1.0Total trans isomer   – –   12.1 Table 2  Chemical compositionof SODD.Appl Biochem Biotechnol (2009) 154:253  –  267 257
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