Leticia Ledo Marciniuk; Camila Martins Garcia; Ulf Friedrich Schuchardt. "USE OF IN TRANSESTERIFICATION", p.853-860. In Luis Augusto Barbosa Cortez (Coord.). Sugarcane bioethanol — R&D for Productivity and Sustainability, São Paulo: Editora Edgard Blücher, 2014. http://dx.doi.org/10.5151/BlucherOA-Sugarcane-SUGARCANEBIOETHANOL_71 24

USE OF ETHANOL IN TRANSESTERIFICATION

Leticia Ledo Marciniuk, Camila Martins Garcia and Ulf Friedrich Schuchardt

Due to the unrestrained energy consumption reduction of its availability over the years, as it is associated with growing environmental concern, presently happening in most developing countries research is being encouraged in many diverse (GARCIA, 2006). areas, to search for alternative resources, which As readily available sources, vegetable oils were neglected until recently, principally re- have been gaining in importance in current energy newable energy resources such as wind, tides programs. They provide a decentralized energy and biomass. generation, bringing benefits to more distant loca- Among these energy resources, biomass has tions and less affluent regions. Its production also received special attention because due to the large means supporting family farming and enhancing number of applications e.g. ethanol and biodie- regional development (RAMOS, 2003). sel, which are the object of great interest in the Several researchers propose the direct use of world economy. vegetable oils as alternative fuels for petroleum- They can be burned directly or used indirectly based such as diesel oil. However, despite being after chemical, biological or thermochemical trans- vegetable oils energetically favorable due to their formations. Among these are the transesterifica- high calorific value, their direct use may prejudice tion of vegetable oils, fatty esterification, operations and durability of diesel engines, increas- pyrolysis, gasification, extractions with super- ing their maintenance costs (MACEDO, 2004). critical fluid, anaerobic digestion and fermentation. This is due to the high viscosity of these oils, These processes can use various feedstocks such approximately 11 to 17 times greater than diesel as agricultural wastes, which otherwise would fuel, low volatility and high molecular weight be- cause serious environmental problems if left in cause of the large chain of triacylglycerides. These the fields as it is the case of sugarcane bagasse factors may prevent their complete combustion, (MARCINIUK, 2007). leading to the formation of carbon deposits inside In addition, the use of biomass reduces pol- the engine and obstruction of oil filters and injec- lution, because its main components are formed tion systems. Furthermore, the thermal decom- from carbon dioxide and water, using sunlight as a position of , present in vegetable oils, can source of energy. This gives biomass a strategic po- lead to the release of acrolein, a highly toxic and sition for the solution of problems related to global carcinogenic substance (TEIXEIRA, 2006). warming. If you consider that during combustion of Several processes have been studied which biomass, carbonic gas emitted to the atmosphere would allow to obtain renewable fuels with physi- is absorbed by photosynthesis during growth, the cochemical properties similar to diesel oil, with- mass balance for CO2 is more favorable than zero. out requiring engine modifications or additional However, for this becoming a reality, a sustain- technology investment. An example is the use of able consumption of biomass is needed, without , which can be obtained from vegetable 854 A New Model for Industrial Production and Final Uses of Ethanol oils or other sources of fatty materials, such as consumption of a plant that produces ethylic animal or waste oils, by transesterification biodiesel is higher when compared to methylic with short-chain . The fuel compatibility biodiesel. However, for Brazil, from the economic with conventional diesel has characterized it as the point of view, the use of ethanol is more advanta- most appropriate alternative which can be used in geous, since the country is considered to be the fleet of most diesel vehicles existing on the market second largest producer. (XIE et al., 2006). The transesterification of vegetable oils is a When compared to mineral diesel, biodiesel reversible reaction, whose kinetics is governed by has as major advantages such as the reduction of the principle of Le Chatelier. Thus, the conversion emissions, biodegradability, higher flash point and of the reaction depends on shifting the chemical increased lubrication. equilibrium towards the formation of products The term “transesterification” (or alcoholysis) through the optimization of the variables such as describes an important class of organic reactions in temperature, concentration of catalyst, its acidic which an is transformed into another through or basic strength and the amount of reagents. the exchange of their groups. In this reac- One of the most important variables that af- tion, the triacylglycerides present in vegetable oils, fect the conversion to is the react with an in the presence of a catalyst to alcohol molar ratio. Using an excess of alcohol, producing a mixture of monoalkyl esters of fatty the equilibrium is shifted towards the product, acids and glycerol, as shown in Figure 1. however, an excessive increase will also favor Various alcohols can be used in such reactions, the solubility of glycerol in biodiesel, making its however, only or ethanol will produce separation difficult (GARCIA, 2006). According biodiesel. Both can be obtained from renewable to the literature, vegetable oil to alcohol molar sources such as dry distillation of wood and fer- ratios are normally in the range of 1:6 to 1:30. In mentation of sugarcane, respectively. the case of ethanol, ratios of 1:6 and 1:12 show According to the technical aspects of trans- satisfactory results. esterification, the use of methanol (methanolysis) ENCINAR et al. (2002) have studied the is advantageous because it allows the spontaneous ethanolysis of Cynara oil by varying the oil to separation of glycerol and as a consequence the re- ethanol molar ratio from 1:3 to 1:15. The best duction of the number of process steps. Moreover, results were obtained for reactions carried out it gives a high conversions using homogeneous with the molar ratio between 1:9 and 1:12. The catalysts in basic or acidic conditions. On the other reactions employing molar ratios below 1:6 were hand, this alcohol has a high toxicity. incomplete and problems in the glycerol separa- The use of ethanol (ethanolysis), even an- tion step were found when using a molar ratio hydrous, creates problems in the separation of of 1:15. The temperature and reaction time also glycerin from the reaction mixture. The power influence these reactions. High temperatures al-

FIGURE 1 Transesterification of a triacylglycerides. Use of Ethanol in Transesterification 855 low higher conversions in shorter reaction times. reaction; after this period it is preferable that the However, it is necessary to evaluate whether the reaction is conducted under milder agitation. This energy expenses used for heating do not exceed procedure reduces the dispersion of glycerol drop- the economic gains. lets and thus shortens the glycerin coalescence at Methanol and ethanol are not miscible with the end of the reaction. vegetable oils at room temperature. To increase GARCIA (2006) found that the yield of esters the reagents’ miscibility, transesterification re- in transesterification reactions of soybean oil with actions are largely promoted at temperatures ethanol at 70 ºC in the presence of potassium hy- between 60 ºC and 70 ºC under vigorous stirring droxide was directly proportional to the amount in order to promote the phase transfer. These of catalyst used, however, the formation of a conditions usually cause the formation of an emul- transparent and thermodynamically stable micro- sion which, in the case of methanolysis, is rapidly emulsion was observed, which does not allow the broken with the interruption of agitation, leading coalescence of the glycerol, reducing the amount to the separation of glycerol. In ethanolysis, these of ethyl esters isolated and increasing the difficulty emulsions are much more stable and sometimes to purify the product. On the other hand, the alco- difficult to brake (MEHER et al., 2006). holysis at 25 ºC, catalyzed by The emulsions formed during transesterifica- or by sodium or potassium hydroxide, resulted in tion are partly due to the presence of diacilglyc- systems that allowed the complete separation of erides (DAG) and monoacilglycerides (MAG), glycerin which was observed immediately after intermediaries in the alcoholysis of triacylglyc- switching off the agitation. For all three reactions erides (TAG), which are good surfactants. In the total conversion was observed. alcoholysis process the catalyst is dissolved Since methanolic solutions of sodium or potas- in the alcohol and, after its complete dissolution, sium methoxide are now commercially available, is mixed with the triacylglyceride. The reaction the problems of the ethyl esters and glycerin is initially controlled by phase transfer, however, separation are reduced, so that the water con- in the course of the reaction the concentration of tent of ethanol is now a major variable causing intermediaries decreases, reaching a critical level problems in the separation of the products. This at which the formation of emulsions is favored. should not be higher than 0.2%. Although the use When the concentrations of MAG and DAG in the of these commercial catalysts has bypassed much reaction medium reach very low values, the emul- of the problem of the separation of glycerin, the sion is broken. However, the emulsion formed in time required for full separation is larger for the the course of ethanolysis provides a large contact production of biodiesel with ethanol compared to of glycerol with the ethyl esters, thus making the that with methanol. phase separation more difficult (GARCIA, 2006). LIMA et al. (2006) reported the production The presence of glycerol in the reaction medium of biodiesel from babassu (Orbingnya species) oil shifts the equilibrium of the reaction towards the with methanol or ethanol at room temperature for reactants. Consequently, the conversion is de- 30 min, using as catalyst. The creased and intermediate surfactants will remain yields were 71.8% and 62.2% (by mass) which in the system in concentrations that enable their was attributed to the formation of soap, since the performance as emulsion stabilizers. alcohols used were not anhydrous. FERRARI et al. Another important aspect for the reaction is (2005) used the ethylic route in the transesteri- the agitation speed. After homogenization of the fication of neutral soybean oil in the presence of system, vigorous agitation may cause glycerol sodium hydroxide to demonstrate the rapid con- droplets to disperse in the reaction medium, mak- version into ethyl esters after 5 min. at 45 ºC. This ing its separation longer. This variable is much reaction time is sufficient for the full conversion more important in ethanolysis, in which the agita- into esters, as verified by the sudden darkening of tion should be vigorous only in the first minutes of the mixture which then returned to the original 856 A New Model for Industrial Production and Final Uses of Ethanol color (confirmed by gas chromatography). After of sodium or potassium (SCHUCHARDT the reaction, 600 g of glycerin were added to the et al., 1998). system in order to accelerate the formation of the Heterogeneous , on the other hand, lower phase, facilitating the separation of biodiesel has several advantages over homogeneous cataly- and glycerol. sis, considering the ease of catalyst recovery and As can be seen, the appearance of the reaction reuse, as long as the catalyst does not leach to the mixture during the reaction is very relevant. The reaction medium. Furthermore, a purer fraction of beginning of the transesterification of vegetable glycerin and an easy recovery of alcohol are ob- oils is characterized by changes in the color of the tained. The catalysts allow a continuous process, reaction system. This change of color ceases in using a fixed bed reactor, and thus a decrease in methanolysis, regardless of the reaction tempera- production costs (MARCINIUK, 2007). Moreover, ture, and the reaction system becomes opalescent. the transformation of a homogeneous catalyst into In ethanolysis, carried out between 60 and 70 ºC, a heterogeneous catalyst and the development of the reaction mixture becomes clear and transpar- alternative solid catalysts are of great importance ent, as if a solution had been formed. In ethanolysis for organic synthesis, because the catalytic activity at room temperature, the end of color change is is closely related to the surface used in the absorp- followed by a loss of transparency of the reaction tion of the reagents (BAZI et al., 2006). mixture and coalescence of glycerol, which starts LÓPEZ et al. (2008) reported the synthesis of immediately after interruption of agitation (GAR- three modified zirconia: SZ, WZ and TiZ (sulfated CIA, 2006). zirconia, tungstated zirconia and titania zirconia, Most of the implications cited are conse- respectively), calcined at temperatures of 400 ºC quences of the use of homogeneous catalysts in to 900 ºC. The catalytic activity of the different the transesterification of vegetable oils, which zirconia was evaluated as a function of the calci- requires the steps of washing and purification of nation temperature in the reaction of tricaprylin the products. The attempt to recover the catalysts with ethanol at 75 ºC for 8 h. Although the sulfated that are dissolved in the reaction medium will lead zirconia SZ is the most active in this reaction, its to a series of environmental problems since large catalytic activity is not easily recovered, even when amounts of solvents and energy are used (DOSSIN recalcinated at 500 ºC. The TiZ was more active et al., 2006). Furthermore, the use of homoge- than the WZ, due to the presence of basic sites, neous basic catalysts can lead to the production according to the authors. The yields of ethyl cap- of soap by secondary reactions, such as the neu- rylates were, however, only in the order of 10%. tralization of free fatty acids and saponification of The WZ catalyst proved to be most active in the and/ or mono-esters formed. These esterification of oleic , giving a yield of 100% reactions are undesirable because they consume at 120 ºC after 8 h and of 80% at 75 ºC after 22 h part of the catalyst and make the separation of of reaction (LÓPEZ et al., 2008). glycerin more difficult. This means higher costs SHIBASAKI-KITAKAWA et al. (2007) used a of ester production and possible damage to the variety of ionic resins in the transesterification of environment (LIU et al., 2007). triolein with ethanol. The anionic resins showed However, the basic homogeneous catalysis greater activity than the cationic. The ethyl oleate still prevails as the common technology used by was obtained with a conversion of 98.8% using a industry, because it is a simple process and the triolin: ethanol molar ratio of 1:20, 4% (w/w) of catalysts are more easily manipulated and less catalyst at 50 ºC for 1 h of reaction. corrosive than acid catalysts for industrial plants MARCINIUK (2007) evaluated the catalytic (BUNYAKIAT et al., 2006). It provides very high activity of various phosphates of trivalent metals conversions to esters, even at room temperature, for the production of esters. The catalysts were and allows a faster reaction when compared to acid shown to be very efficient in the transesterification catalysis. The catalysts used are the hydroxides or of vegetable oils and in the esterification of free Use of Ethanol in Transesterification 857 fatty acids, giving more than 95% yield of methyl zirconia as well as the niobium catalyst converted and ethyl esters. The reactions conditions were 2 oleic acid into methyl oleate, however, the niobium h in methanolysis and 1.5 h in ethanolysis, 175 ºC, catalyst was not active in the transesterification of molar ratio of oil: methanol of 1:12 and oil: ethanol soybean oil (GARCIA et al., 2008). of 1:9 and 5% (w/w) catalyst. RATNASAMY et al. (2006) developed bime- It was found that these catalysts do not lose tallic cyanides (Fe-Zn) which were shown to be their catalytic activity in the presence of water, al- highly active in both transesterification of veg- lowing the use of hydrated ethanol in the reactions. etable oils and esterification of free fatty acids. This can be demonstrated by the yield of esters These catalysts have acid sites which are resistant of 90% and 97% for the reactions of soybean oil to the presence of water, probably due to the with ethyl alcohol containing 20% and 5% (w/w) hydrophobic characteristic of their surface, and water, respectively. In addition, the solids can be can be reused several times without significant recycled, however, a loss of their catalytic activities loss of their activity. Conversion of vegetable oils from the second re-use is observed, due to leaching increased with the amount of catalyst used, result- of phosphate groups (SCHUCHARDT et al., 2006). ing in yields of methyl esters of 99% at 170 ºC. As GARCIA (2006) synthesized the sulfated expected, an increase of conversion with increas- zirconia S-ZrO2, through an alternative route with- ing oil:ethanol molar ratio was observed, giving out solvents and precipitation, and SZ, through a 100% yield at a molar ratio of 1:15 (RATNASAMY different precipitation method. In addition, non- et al., 2006). sulfated zirconia (ZrO2) was used. The catalytic The largest biodiesel factory in Latin America, activity of zirconia was evaluated in the methano- Naturoil Combustíveis Renováveis S.A., is being lysis and ethanolysis of soybean oil at 120 ºC and constructed in Ourinhos (São Paulo) which will 1 h reaction time using 5% (w/w) of catalyst. The produce 227 million liters per year. French tech- results show that the non-sulfated zirconia (ZrO2) nology (Esterfip-H) will be employed, using zinc is not active in the methanolysis of soybean oil. aluminate (ZnAl2O4) as a catalyst for the trans- The sulfated zirconia (SZ) showed a low catalytic esterification of different vegetable oils and tallow. activity (8.5% conversion), compared to the very In addition to all the advantages of hetero- active S-ZrO2 (98.6% yield of methyl ester and 92% geneous catalysis, the great difference in using a yield of ethyl ester). heterogeneous acid catalyst for transesterification The performance of the sulfated zirconia (S- is the easy separation and recovery of the catalyst,

ZrO2) and a commercial niobium catalyst (niobic the elimination of washing steps and the possibility acid supported on graphite) was compared in of using vegetable oils with high levels of free fatty the esterification of oleic acid with methanol and acids which are typically found in the north and transesterification of soybean oil. The sulfated northeast of Brazil, in waste oils and animal fats.

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