Biodiesel Production. A Brief Review

10TH INTERNATIONAL CONFERENCE ON SUSTAINABLE ENERGY AND ENVIRONMENTAL PROTECTION (JUNE 27TH – 30TH, 2017, BLED, SLOVENIA), BIOENERGY AND BIOFUELS J. Krope, A.Ghani Olabi, D. Goričanec & S. Božičnik

Biodiesel Production. A Brief Review EUGÊNIA LEANDRO ALMEIDA, CID MARCOS GONÇALVES ANDRADE & ONÉLIA APARECIDA ANDREO DOS SANTOS37 Abstract Diesel plays a significant role in the economy of a country, being used in industrial machines, electric generators, locomotives, trucks, buses, etc. Currently, there is a worldwide concern with the depletion of nonrenewable energy sources, also with the emission of gases from its burning, which contribute to the worsening of the greenhouse effect. Studies have been developed in search of alternatives for partial or total replacement of petroleum diesel. These alternatives must be technically feasible, economically competitive and do not harm the environment. Biodiesel is a possible substitute. Biodiesel is a renewable fuel, which can be obtained from different raw materials such as vegetable oil, animal fat and oil / waste fat. Biodiesel can be produced by various processes, including enzymatic catalysis, basic or acid catalysis. The objective of this work was to carry out a review of the different biodiesel production methods, regarding raw materials and chemical production routes. Keywords: • Biodiesel • Biofuel • Biodiesel production • Renewable energy • Catalysis •

CORRESPONDENCE ADDRESS: Eugenia Leandro Almeida, M.Sc, Universidade Estadual de Maringá, Chemical Engineering Department, Av. Colombo, 5790 – Vila Esperança, Maringá – Paraná, Brasil, email: [email protected] Cid Marcos Gonçalves Andrade, Ph.D, Universidade Estadual de Maringá, Chemical Engineering Department, Av. Colombo, 5790 - Vila Esperanca, Maringá - Paraná, Brasil,email: [email protected]. Onélia Aparecida Andreo dos Santos, Ph.D, Universidade Estadual de Maringá, Chemical Engineering Department, Av. Colombo, 5790 - Vila Esperanca, Maringá - Paraná, Brasil,email: [email protected]. https://doi.org/10.18690/978-961-286-048-6.33 © 2017 University of Maribor Press Available at: http://press.um.si.

ISBN 978-961-286-048-6

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10TH INTERNATIONAL CONFERENCE ON SUSTAINABLE ENERGY AND ENVIRONMENTAL PROTECTION (JUNE 27TH – 30TH, 2017, BLED, SLOVENIA), BIOENERGY AND BIOFUELS E.L. Almeida, C.M.G. Andrade & O.A.A. Santos: Biodiesel Production. A Brief Review

Introduction

Diesel consumption represents a significant part of a country's economy, since it is used in several economic sectors. One of the sectors with the highest demand for diesel, derived from petroleum, is the road sector [1]. In Brazil the road sector is the main transportation system in the country. According to the National Department of Land Transport, linked to the Ministry of Transportation, there are 119,936 kilometers of federal highways in the country. Studies show that the consumption of diesel oil in the Brazilian market tends to increase between 2014 and 2023 [2]. However, with the increase in the demand for fossil fuels, in the case in particular diesel, there is in parallel a concern regarding the amount of gases emitted from the burning of this fuel, being this concern not only national but also worldwide. These gases from the combustion process of diesel contribute directly to the worsening of the greenhouse effect [3]. In this context, studies have been carried out with the objective of developing sustainable and renewable alternatives for partial or total replacement of diesel obtained from petroleum fractionation [4] [5]. A possible successor to diesel is biodiesel. Biodiesel, as well as diesel, can be used in cycle engines, such as trucks, buses, etc. And in stationary motors, such as electric power generators [6]. One of the advantages of using biodiesel when compared to diesel, non-renewable fossil fuel is the fact that biodiesel is a renewable fuel [7] [8]. Biodiesel can be used pure or mixed with diesel. When mixed, it receives the designation B2, B5, or B20, etc., referring to the percentage of biodiesel present in diesel, respectively, 2%, 5% and 20%, etc. It can also be called B100, representing pure biodiesel. In Brazil the biodiesel blend in diesel started in 2004, through the National Program for the Production and Use of Biodiesel (PNPB), launched by the federal government. In 2004 the 2% blend was experimental only. Between 2005 and 2007 the mixture of 2% became optional. And in 2008 the 2% mix became mandatory throughout the national territory. This percentage gradually increased. Currently, in 2017 the percentage of biodiesel in diesel is 7% [9]. Due to the demand for biodiesel in the current scenario, studies have been carried out with the purpose of proposing biodiesel production routes that present higher conversions without causing damage to the environment and that are at the same time economically viable. In this way, the work aims to present a literature review highlighting the main methods of obtaining biodiesel and the main raw materials used. 2

Raw Material

Biodiesel is a fuel obtained from the chemical reaction of compounds present in vegetable oils, animal fats or waste oils and fats, reacting with alcohol, usually methanol or ethanol, in the presence of a catalyst [10]. Methanol when compared to ethanol has higher reactivity. It exhibits greater efficiency in both the speed and yield of the reaction. The use of methanol in the reaction to obtain biodiesel makes


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the separation of glycerine from biodiesel in the biodiesel purification process easier and more efficient. Low economic cost is one of the most relevant factors for your choice. However, the use of methanol has some drawbacks, such as its high toxicity. Methanol in Brazil is produced from natural gas. The fact of producing one of the reagents from a non-renewable source causes biodiesel to partially escape the concept of green fuel. There are methods where methanol can be produced from biomass. However, in Brazil it is still not economically feasible when compared to the low cost of the product obtained from natural gas [11]. Ethanol produced in Brazil is predominantly of vegetable origin. Unlike methanol, ethanol has no toxicity. However, the limited use of ethanol is due to a number of factors, including the fact that ethanol is less reactive than methanol. In this way, demanding greater product surplus, higher temperature and longer reaction time, consequently, causes a significant increase in the operational cost. Ethanol also favours the formation of an emulsion, making it difficult to separate the product, thus contributing to an increase in operating costs. Therefore, in the current context, it only economically compensates to produce biodiesel from the ethanol route when ethanol presents a significantly lower price than that of methanol [11]. Other reagents used in the biodiesel production process are vegetable oils and / or animal fats, formed basically by triglycerides and fatty acids. One of the main raw materials used in the production of biodiesel is vegetable oils. Brazil is a country mostly agricultural and has a wide array of fertile lands and a climate conducive to the cultivation of different oil crops. This makes biodiesel production from vegetable oil larger when compared to other raw materials. Among the oil seeds used in the biodiesel production process we can highlight soybean, palm, cottonseed, colza, babaçu, sunflower seed and castor bean. Soybean is currently the most used oilseed in the process of obtaining biodiesel in Brazil [12]. To obtain the vegetable oil the raw material undergoes an extraction process. Prior to the extraction process, regardless of the method or crop to be used as feedstock, the oilseed normally undergoes a preparation process, which basically includes cleaning, for removal of bark and impurities, crushing, rolling and baking . Vegetable oil can be extracted by two methods, mechanical pressing and mixed pressing, also called chemical extraction. In the mixed press, besides the use of the mechanical press, the use of an organic solvent, usually hexane, is attributed. In the mechanical pressing there is a loss of approximately 6% of oil in the remaining pie, already in the chemical extraction, this loss is reduced to 1% [13]. Other sources of raw materials that can be employed in the process of obtaining biodiesel are animal fats. Among them are bovine tallow, fish oils, pork fat, etc. Being the most used bovine tallow. Bovine tallow is a by-product from the meat market [3]. It consists basically of fatty acids of saturated chain, presenting a structure similar to the vegetable oil. The fact that it has a saturated chain causes the clogging to occur at higher temperatures, at approximately 19 °C, which is the maximum clogging temperature allowed by the National Agency for Petroleum, Natural Gas and Biofuels (Brazil). One way to decrease the clogging point is to mix the bovine tallow with vegetable oil with a decrease of approximately 10 °C. When comparing bovine

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tallow with soybean oil, we have the advantage of not competing with the food market, there is no risk of crop failure and it presents lower cost [14][15][16]. Finally, we have that the residual oils can also be used as raw material for biodiesel production. The residual oils are rich in triglycerides, however, they also present significant amount of fatty acids, which depending on the methodology applied for the biodiesel production process requires a pre-treatment of the raw material [17]. Residual oils can be collected in snack bars, industrial, commercial and domestic kitchens. The use of the residual oil promotes the correct disposal and less aggressive to the environment. 3

Biodiesel Production Processes

Biodiesel appears in the world context from the interest in replacing diesel of non-renewable fossil origin with a fuel that is sustainable and renewable. Therefore, several studies have been and are being developed with the objective of producing biodiesel from renewable sources or alternative sources that have high energy potential, as in the case of oils and residual fats. And, at the same time, develop routes that use reagents less aggressive to the environment and provide satisfactory yields. Finally, to enable large-scale production [18][19] [20]. Biodiesel can be obtained from the esterification or transesterification reaction. The esterification reaction is also known as Fischer's reaction (1895). The reaction is characterized by forming a specific ester, from the reaction of a carboxylic acid with an alcohol, usually methanol or ethanol. It is a slow reaction at room temperature (25 ° C). Thus, heating and / or use of catalyst is required [21]. The esterification reaction is usually used to treat the raw material for biodiesel production, in order to reduce the concentration of free fatty acids. In the transesterification reaction, the ester is always obtained from another ester. In the case of biodiesel the precursor ester is a triglyceride, receiving this connotation because it has three groups of esters [21]. In the production of biodiesel by transesterification reaction, the triglyceride reacts with alcohol, methanol or ethanol, in the presence of a catalyst, forming biodiesel and glycerin [22]. Biodiesel can be obtained from different routes: basic catalysis, acid or enzymatic. The catalysts are used in the production process with the aim of modifying the kinetics of the reaction, increasing the reaction rate and selectivity in relation to the desired product [23]. The following will be presenting the main methodologies used in its production. 3.1

Process of biodiesel production via alkaline catalysis

Among the biodiesel production methods we can highlight the transesterification via basic catalysis. This production route can be divided into two groups, basic homogeneous catalysis and basic heterogeneous catalysis. The most common homogeneous basic catalysts are sodium hydroxide (NaOH), potassium hydroxide (KOH), sodium methoxide (NaOCH3) and sodium ethoxide (NaOCH2CH3). According to the literature, the most heterogeneous basic catalysts used are calcium hydroxide (Ca (OH) 2) and oxides of magnesium (MgO), calcium (CaO), strontium (SrO), barium (BaO) and zinc ZnO) [24].


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Industrially, basic homogeneous catalysis is the most employed. The most homogeneous basic catalysts used in large scale production are sodium hydroxide (NaOH) and potassium hydroxide (KOH). This is due to the low economic cost of the catalysts and the fact that they have high conversion rates [25]. To obtain the maximum yield, anhydrous alcohol is used and preferably raw materials with low concentrations of free fatty acids. The high moisture content in the reaction medium causes the hydrolysis of triglycerides to occur, this hydrolysis favours the formation of fatty acids. High concentrations of fatty acids in contact with basic catalysts provide the production of soap. Soap formation, in turn, makes it difficult to purify biodiesel during the washing process [26]. The work developed by Lee et al. (2016) aimed to investigate the catalytic activity of mixed metal oxides in biodiesel production using as raw material jatropha oil via the methyl route. The catalysts used were: CaO-MgO, CaO-ZnO, CaO-: La2O3 and MgO-ZnO. The results show that the catalysts of mixed metal oxides presented higher catalytic activity than the pure metal oxides. According to the authors, the catalysts of mixed metal oxides present high density and strong basicity, being excellent properties for transesterification reaction. The mixed catalysts based on CaO showed higher catalytic activity, good reuse and low leaching. Among them, the CaO-ZnO catalyst was the one that favoured greater biodiesel conversion [27]. Veillette et al. (2016) proposed the production of biodiesel from oil extracted from Scenedesmus obliquus microalgae. The basic catalysts used were potassium hydroxide and strontium oxide. The experimental parameters used were: proportion of methanol with respect to lipid mass 31.4% and mass of catalyst with respect to oil mass 2.48%, reaction time and temperature of 22.2 min and 60 ° C. The results demonstrate that potassium hydroxide presented higher yield compared to strontium oxide. Although it presented a lower yield, the strontium oxide proved to be an effective catalyst, since it presented a yield of 76%. However, the authors caution that the use of alkaline earth metals, such as strontium oxide, should be avoided due to leaching of the catalyst in the reaction medium. They conclude that the leaching occurs due to the presence of free fatty acids and moisture. Thus, the use of basic heterogeneous catalysts requires that the raw material be free of free fatty acids and moisture [28]. 3.2

Process of biodiesel production via acid catalysis

One of the problems related to the use of conventional catalysis is the formation of soaps due to the reaction of the basic catalyst with the free fatty acids. In this way, studies have been developed with the objective of finding alternatives technically, environmentally and economically feasible. Acid catalysis has been studied as a possible partial or complete substitute biodiesel production route of the conventional route. Acid catalysis has the advantage of obtaining biodiesel both through the esterification reaction of fatty acids and transesterification of triglycerides. Thus, acid catalysis makes it possible to use raw materials with a significant content of fatty acids, which in turn is economically more viable. It also eliminates, even partially, the pre-treatment step of the raw material present in the traditional process. Vieira et al. (2013) evaluated the use of heterogeneous acid catalysts in biodiesel production. The catalysts used were: La2O3, SO42- / La2O3, HZSM-5 (zeolite) and SO42- / La2O3 /

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HZSM-5 (SOL / HZSM-5). The experimental parameters evaluated were: molar ratio of oleic oil per methyl alcohol, percentage of catalyst with respect to oleic oil mass and reaction temperature. According to the authors, temperature was the parameter that most influenced the catalytic process. The results show that the SOL / HZSM-5 catalyst showed the highest conversion. The best results were obtained at the temperature 100 ° C and molar ratio of 1: 5, with the exception of the HZSM-5 catalyst which was 1: 2. The authors conclude that the results presented a good performance by the catalysts and can be used in the biodiesel production process [29]. The work performed by Peres et al. (2016) had as objective to evaluate the performance of the metallic oxides catalysts spinel type in the biodiesel production. These catalysts are characterized by being bifunctional, presenting acidic and basic sites. It can act on esterification of fatty acids and transesterification of triglycerides. The catalysts used were zinc aluminate (ZnAl 2 O 4) and cobalt aluminate (CoAl 2 O 4). The parameters evaluated were: catalyst concentration, alcohol / oil molar ratio and temperature on yield. Using as raw material oils and residual fats. The results showed that at concentrations above 7% the ZnAl2O4 catalyst yields higher than 80% yield regardless of the temperature and alcohol / oil molar ratio. In the case of CoAl.sub.2 O.sub.4 to obtain yields of greater than 80% at 7% concentration it is necessary to work at a temperature of 140 °C and an alcohol / oil molar ratio of 1: 6 or 100 °C and alcohol / oil molar ratio of 1: 9. According to PERES et. Al (2016) the process of transesterification using the zinc and cobalt aluminate catalysts may be an alternative for the production of biodiesel from waste oils and fats [30]. 3.3

Process of biodiesel production via enzymatic catalysis

Another route of biodiesel production is enzymatic catalysis. Enzymes are organic polymers formed by amino acids. They have in their structure active sites that can act as biological catalysts with high specificity [31][32]. In the literature the enzyme lipase stands out in the biodiesel production process. The enzyme can be obtained from Aspergillus niger (lipase A), Mucor javanicus (lipase M), Burkholderia cepacia (lipase PS), Pseudomonas fluorescens (lipase AK), among other microorganisms [33]. The lipase enzyme is classified as hydrolase by acting on the ester bond of various compounds. The enzymes are generally immobilized in order to obtain biocatalysts with higher catalytic activity and also with higher thermal and chemical stability. One of the disadvantages of using lipase is due to its financial cost. The immobilization of the lipase allows to recover the biocatalyst and reuse again in the process, reducing the cost of production. The most frequent immobilization techniques are adsorption, ionic and covalent bonding [31]. Souza et al. (2016) studied the production of biodiesel using Jatropha (Jatropha curcas L.) oil as raw material via enzymatic ethyl ester transesterification. Commercial lipases immobilized by covalent attachment on epoxy-SiO2-PVA were used. The immobilized lipases of Pseudomonas fluorescens (lipase AK) and Burkholderia cepacia (lipase PS) showed better yield of ethyl ester, being 91.1 and 98.3% in 72 hours of reaction. The reactions that occurred under microwave irradiation presented higher yield and productivity when compared to the conventional heating method. According to the authors the biocatalysts have shown satisfactory results and that the


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same can be applied in the production of biodiesel. The authors emphasize that the use of biocatalysts requires a solvent-free medium [34]. The work developed by Nordblad et al. (2016) proposed a pre-treatment of rapeseed oil that will be used as raw material in the biodiesel production process, via basic catalysis. Pretreatment was performed through enzymatic catalysis using the enzyme lipase B (Novozym 435), focusing on the initial concentration of free fatty acids and methanol, in order to obtain the best experimental parameters. The authors found that using 5% of catalyst and 4% of methanol at 35 ° C, the concentration of 15% of fatty acids present in the raw material could be reduced to 0.5% in one hour of reaction. The authors conclude that the suggested pretreatment process is an efficient method to reduce the concentration of fatty acids. It can be used in raw materials with a concentration of up to 20% of fatty acids [35]. 4

Conclusion

Biodiesel has characteristics similar to diesel from petroleum, being a possible substitute. Studies show great interest in production in biodiesel production, since, compared to conventional diesel, biodiesel has the advantage of being renewable and less aggressive to the environment. Biodiesel can be produced from different raw materials. However, it is possible to conclude that the main raw material is vegetable oils, because it can produce biodiesel from various oilseeds. Several biodiesel production routes were presented. However, the production of biodiesel through the basic catalysis was to the route that showed the best results regarding conversion, reaction time and economic cost. Acid catalysis, in turn, has proved to be a possible route to be used as pre-treatment of raw materials with high levels of fatty acids. Finally, enzymatic catalysis despite having many advantages, such as its high specificity, is not yet economically feasible.

Acknowledgements The authors would like to thank Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) for the financial support. References [1] [2] [3] [4] [5] [6]

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10TH INTERNATIONAL CONFERENCE ON SUSTAINABLE ENERGY AND ENVIRONMENTAL PROTECTION (JUNE 27TH – 30TH, 2017, BLED, SLOVENIA), BIOENERGY AND BIOFUELS E.L. Almeida, C.M.G. Andrade & O.A.A. Santos: Biodiesel Production. A Brief Review [32] [34] [33] [34]

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