The production of biodiesel from vegetable oils by ethanolysis: Current state and perspectives

At present, the homogeneous base-catalyzed methanolysis reaction of vegetable oils is a most often used process for the industrial biodiesel production. The toxicity of methanol, the risk of the methanol vapor explosion and the possibility of the ethanol production from biorenewable resources have contributed to the development of a vegetable oil ethanolysis process for the biodiesel production. In the reaction of vegetable oils and ethanol in the presence of a catalyst, completely agricultural fuels consisted of fatty acid ethyl esters (FAEE) are obtained having physico-chemical properties similar to those of the appropriate methyl esters and diesel fuel. The ethanolysis reaction of various oily feedstocks has been widely studied to optimize the reaction conditions and to develop new catalytic systems and processes based on chemical and biological catalysts, as well as the development of non-catalytic processes. Most researches investigate the application of homogeneous base catalysts. This paper studies the review of vegetable oil ethanolysis investigations for the biodiesel production done so far. The goals of the paper are to present the development of FAEE synthesis by catalytic and non-catalytic processes, their advantages and disadvantages, the influence of some operating and reaction conditions on the process rate and ethyl esters yield, the kinetics models describing the ethanolysis process rate, the process optimization and the possibilities for improving the FAEE synthesis process.     

Transesterification double step process modification for ethyl ester biodiesel production from vegetable and waste oils

In this study, the transesterification double step process (TDSP) was modified to enable the usage of ethanol as a transesterification agent in the production of biodiesel from vegetable and waste oils. The TDSP comprises a two-step transesterification procedure, which is initiated by a homogeneous basic catalysis step and followed by an acidic catalysis step. To optimize the transesterification parameters, different reaction mixtures and conditions were tested. Compared with methanol transesterification, larger ethanol and catalyst amounts as well as higher reaction times and temperatures were required. However, the results were consistent with those usually reported for ethanol transesterification. The obtained biodiesels (i.e., fatty acid ethyl esters (FAEEs)) were analyzed by standard physico-chemical techniques in addition to ¹H NMR, ¹³C NMR and FTIR spectroscopies, indicating high quality and purity biodiesel products. The obtained conversions were evaluated by ¹H NMR spectroscopy. For the optimized process, the triglyceride conversion to biodiesel was ?97% for all oils used. The overall process yields are considerably high when compared to the single basic catalysis yields.     

Transesterification of vegetable oil to biodiesel fuel using alkaline catalyst

Biodiesel is gaining more and more importance as an attractive fuel due to the depleting fossil fuel resources. Chemically biodiesel is monoalkyl esters of long chain fatty acids derived from renewable feed stock like vegetable oils and animal fats. It is produced by transesterification in which, oil or fat is reacted with a monohydric alcohol in presence of a catalyst to give the corresponding monoalkyl esters. This article reports experimental data on the production of fatty acid methyl esters from vegetable oils, soybean and cottonseed oils using sodium hydroxide as alkaline catalyst. The variables affecting the yield and characteristics of the biodiesel produced from these vegetable oils were studied. The variables investigated were reaction time (1-3 h), catalyst concentration (0.5-1.5 w/wt%), and oil-to-methanol molar ratio (1:3-1:9). From the obtained results, the best yield percentage was obtained using a methanol/oil molar ratio of 6:1, sodium hydroxide as catalyst (1%) and 60 ± 1 °C temperature for 1 h. The yield of the fatty acid methyl ester (FAME) was determined according to HPLC. The composition of the FAME was determined according to gas chromatography. The biodiesel samples were physicochemically characterized. From the results it was clear that the produced biodiesel fuel was within the recommended standards of biodiesel fuel.     

Advances on the development of novel heterogeneous catalysts for transesterification of triglycerides in biodiesel

This paper describes experimental work done towards the search for more profitable and sustainable alternatives regarding biodiesel production, using heterogeneous catalysts instead of the conventional homogenous alkaline catalysts, such as NaOH, KOH or sodium methoxide, for the methanolysis reaction. This experimental work is a first stage on the development and optimization of new solid catalysts, able to produce biodiesel from vegetable oils. The heterogeneous catalytic process has many differences from the currently used in industry homogeneous process. The main advantage is that, it requires lower investment costs, since no need for separation steps of methanol/catalyst, biodiesel/catalyst and glycerine/catalyst. This work resulted in the selection of CaO and CaO modified with Li catalysts, which showed very good catalytic performances with high activity and stability. In fact FAME yields higher than 92% were observed in two consecutive reaction batches without expensive intermediate reactivation procedures. Therefore, those catalysts appear to be suitable for biodiesel production.     

Techno-economic analysis of a biodiesel production process from vegetable oils

Biodiesel, which is defined as the monoalkyl esters of long chain fatty acids derived from a renewable lipid feedstock, has received considerable attention worldwide as a medium-term alternative to diesel fuel obtained from petroleum. Biodiesel can be produced by the transesterification of vegetable oils or animal fats using short-chain alcohols in the presence of a suitable catalyst and glycerol is the only byproduct obtained in significant quantities. In this work a techno-economic analysis of a process that produces biodiesel from vegetable oils is presented with the aim to investigate the dependence of the critical profitability indicators on the production capacity.     

Heterogeneously Catalyzed Esterification of FFAs in Vegetable Oils

The production of methyl esters (biodiesel) from free fatty acids (FFAs) contained in vegetable oils was studied using a heterogeneous acid catalyst. The feedstock was a by‐product of a vegetable oil refinery. The experiments were performed in a batch reactor, in a temperature range of 363.15–393.15 K, with an initial molar ratio of methanol to FFAs of 6.6/1, while the catalyst mass was fixed at 2 wt % of the total vegetable oil mass. A technical kinetic model has been developed which accounts for the reversible esterification reaction. Kinetic parameters were determined by fitting experimental data to the model.     

The Optimization of the Production of Methyl Esters from Corn Oil Using Barium Hydroxide as a Heterogeneous Catalyst

In recent years, vegetable oils, as renewable raw materials, became a promising feedstock for chemicals and biodiesel production. The main products derived from oils are esters of fatty acids, especially methyl esters, obtained by their transesterification with methanol, in presence of acid or alkaline catalysts. The use of such catalysts implies the need for washing operations, which leads to environmental pollution. In the present paper, the response surface methodology based on a central composite design, has been developed to optimize the process of transesterification of corn oil. Ba(OH)₂ in presence of diethyl ether was used as catalyst. A quadratic polynomial equation was obtained. It correlates the reaction parameters [methanol/oil molar ratio (x _r), reaction time (x _t) and catalyst concentration (x _c)] with methyl esters yield. Analysis of variance analysis showed that only methanol/oil molar ratio and catalyst concentration have had the most significant influences on the conversion. The maximum methyl esters yield was obtained using the following optimum parameters: methanol/corn oil ratio of 11.32, reaction time of 118 min and catalyst concentration of 3.6 wt%.     

Optimization of biodiesel production from edible and non-edible vegetable oils

The non-edible vegetable oils such as Jatropha curcas and Pongamia glabra (karanja) and edible oils such as corn and canola were found to be good viable sources for producing biodiesel. Biodiesel production from different edible and non-edible vegetable oils was compared in order to optimize the biodiesel production process. The analysis of different oil properties, fuel properties and process parameter optimization of non-edible and edible vegetable oils were investigated in detail. A two-step and single-step transesterification process was used to produce biodiesel from high free fatty acid (FFA) non-edible oils and edible vegetable oils, respectively. This process gives yields of about 90-95% for J. curcas, 80-85% for P. glabra, 80-95% for canola, and 85-96% for corn using potassium hydroxide (KOH) as a catalyst. The fuel properties of biodiesel produced were compared with ASTM standards for biodiesel.     

Biodiesel production from waste frying oil in sub- and supercritical methanol on a zeolite Y solid acid catalyst

Waste frying oil (WFO) is a very important feedstock for obtaining biodiesel at low cost and using WFO in transesterification reactions to produce biodiesel helps eliminate local environmental problems. In this study biodiesel was produced from WFO in sub- and super-critical methanol on a zeolite Y solid acid catalyst. The procedure was optimized using a design of experiments by varying the methanol to WFO molar ratio, the reaction temperature, and the amount of catalyst. Typical biodiesel yields varied from 83 to nearly 100% with methyl esters content ranging from 1.41–1.66 mol·L^-1 and typical dynamic viscosities of 22.1-8.2 cP. Gas chromatography was used to determine the molecular composition of the biodiesel. The reaction products contained over 82 wt-% methyl esters, 4.2 wt-% free acids, 13.5 wt-% monoglycerides, and 0.3 wt-% diglycerides. The transesterification of WFO with methanol around its critical temperature combined with a zeolite Y as an acid catalyst is an efficient approach for the production of biodiesel with acceptable yields.     

The heterogeneous catalyst system for the continuous conversion of free fatty acids in used vegetable oils for the production of biodiesel

Biodiesel produced by the transesterification of vegetable oils (VOs) has recently become more attractive on account of its environmental and economical benefits. In this work, a heterogeneous catalyst system was developed for the production of biodiesel from used VOs using a continuous process. The free fatty acids (FFA) contained in the used VOs, which cause several severe problems in transesterification catalysis, were converted to fatty acid methyl esters (FAME) before the main biodiesel production process. The activities of several heterogeneous catalysts on the conversion of FFA were tested, with a WO₃/ZrO₂ catalyst finally being selected. A method for preparing pellet-type catalysts was also developed. The pellet-type WO₃/ZrO₂ catalyst showed highly active and durable catalytic activities in the continuous flow process. The steady state conversion of ca. 70% was obtained in a 140 h durability test. The acidic property and catalytic activity of WO₃/ZrO₂ were attributed to the oxidation state of tungsten.     

Ethanolysis of used frying oil. Biodiesel preparation and characterization

The transesterification reaction of used frying oil by means of ethanol, using sodium hydroxide, potassium hydroxide, sodium methoxide, and potassium methoxide as catalysts, was studied. The objective of the work was to characterize the ethyl esters for its use as biodiesels in compression ignition motors. The operation variables used were ethanol/oil molar ratio (6:1–12:1), catalyst concentration (0.1–1.5 wt.%), temperature (35–78 °C), and catalyst type. The evolution of the process was followed by gas chromatography, determining the concentration of the ethyl esters at different reaction times. The biodiesel was characterized by its density, viscosity, flash point, combustion point, cold filter plugging point, cloud and pour points, Conradson carbon residue, characteristics of distillation, cetane index and high heating value according to ISO norms. The biodiesel with the best properties was obtained using an ethanol/oil molar ratio of 12:1, potassium hydroxide as catalyst (1%), and 78 °C temperature. The density, viscosity, cetane index, Conradson carbon residue and calorific power of the biodiesel obtained had values close to those of a no. 2 diesel. On the contrary, the cold filter plugging point, and cloud and pour points are higher than the conventional diesel fuel. Although higher, flash and combustion points fulfil the norms for ethyl esters derived from vegetable oils. In consequence, the final product obtained had very similar characteristics to a no. 2 diesel oil, and therefore, these ethyl esters might be used as an alternative to fossil fuels. The two-stage transesterification was better than the one-stage process, and the yields of ethyl esters were improved 30% in relation with the one-stage transesterification.     

Production of mixed methyl/ethyl esters from waste fish oil through transesterification with mixed methanol/ethanol system

Biodiesel (mixed fatty acid methyl/ethyl esters) was prepared from waste fish oil through base-catalyzed transesterification with mixed methanol/ethanol system. Effect of methanol/ethanol (% v/v), type and concentration of the catalyst, mixed alcohols to oil molar ratio, the reaction temperature, and the reaction time on the biodiesel yield was optimized. Maximum biodiesel yield (97.30?wt%) was produced by implementing 1:1 methanol/ethanol (v/v), 1.0?wt% KOH, 6:1 mixed alcohols to oil molar ratio, 40°C reaction temperature, and 30?min of reaction time. Conversion of the waste fish oil to mixed methyl/ethyl esters was confirmed by ¹H NMR spectroscopy. Fuel properties of the resulting biodiesel in addition to its blends with petrodiesel were in good agreement with specifications of ASTM D6751 and ASTM D7467, respectively. Therefore, it was concluded that using mixed alcohol system for biodiesel production could reduce the production cost through reducing conditions required for maximum conversion.     

Feasibility of Palm Oil as the Feedstock for Biodiesel Production via Heterogeneous Transesterification

The production of biodiesel has become popular recently as a result of increasing demand for a clean, safe and renewable energy. Biodiesel is made from natural renewable sources such as vegetable oils and animal fats. The conventional method of producing biodiesel is by reacting vegetable oil with alcohol in the presence of a homogenous catalyst (NaOH). However, this conventional method has some limitations such as the formation of soap, usage of significant quantities of wash water and complicated separation processes. Heterogeneous processes using solid catalysts have significant advantages over homogenous methods. Currently, more than 90 % of world biodiesel is produced using rapeseed oil. The production of biodiesel from rapeseed oil is considered uneconomical, considering the fact that palm oil is currently the world's cheapest vegetable oil. Therefore, the focus of this study is to show the feasibility of producing biodiesel from palm oil using montmorillonite KSF as a heterogeneous catalyst. The heterogeneous transesterification process was studied using design of experiment (DOE), specifically response surface methodology (RSM) based on a four‐variable central composite design (CCD) with α = 2. The transesterification process variables were reaction temperature, x₁ (50–190 °C), reaction period, x₂ (60–300 min), methanol/oil ratio, x₃ (4–12 mol mol^–1) and the amount of catalyst, x₄ (1–5 wt %). It was found that the conversion of palm oil to biodiesel can reach up to 78.7 % using the following reaction conditions: reaction temperature of 155 °C, reaction period of 120 min, ratio of methanol/oil at 10:1 mol mol^–1 and amount of catalyst at 4 wt %. From this study, it was shown that montmorillonite KSF catalyst can be used as a solid catalyst for biodiesel production from palm oil.     

Preparation of biodiesel from soybean oil using supercritical methanol and co-solvent

Transesterification of soybean oil in supercritical methanol has been carried out in the absence of catalyst. A co-solvent was added to the reaction mixture in order to decrease the operating temperature, pressure and molar ratio of alcohol to vegetable oil. With propane as co-solvent in the reaction system, there was a significant decrease in the severity of the conditions required for supercritical reaction, which makes the production of biodiesel using supercritical methanol viable as an industrial process. A high yield of methyl esters (biodiesel) was observed and the production process is environmentally friendly. Furthermore the co-solvent can be reused after suitable pretreatment.     

Biodiesel production using tetramethyl- and benzyltrimethyl ammonium hydroxides as strong base catalysts

In recent years, the acceptance of fatty acid methyl esters (biodiesel) as an alternative fuel has rapidly grown in EU. The most common method for biodiesel production is based on triglyceride transesterification to methyl esters with dissolved sodium hydroxide in methanol as catalyst. In this study, cottonseed oil and used frying oil were subjected to the transesterification reaction with tetramethyl ammonium hydroxide and benzyltrimethyl ammonium hydroxide as strong base catalysts. This work investigates the optimum conditions for biodiesel production using amine-based liquid catalysts. Biodiesel ester content was strongly related with the type of feedstock and the reaction variables, such as those of the catalyst concentration, methanol to oil molar ratio, and reaction time. The overall results suggested that the transesterification of cottonseed oil achieved high conversion rates with both catalysts, while the use of waste oil resulted in lower yields of methyl esters due to the possible formation of amides.     

A review of conventional and renewable biodiesel production

The need for sustainable fuels has resulted in the production of renewables from a wide range of sources, in particular organic fats and oils. The use of biofuel is becoming more widespread as a result of environmental and economic considerations. Several efforts have been made to substitute fossil fuels with green fuels. Ester molecules extracted from processed animal fats and organic plant materials are considered alternatives for the use in modern engine technologies. Two different methods have been adopted for converting esters in vegetable oils/animal fats into compounds consistent with petroleum products, namely the transesterification and the hydro-processing of ester bonds for the production of biodiesel. This review paper primarily focuses on conventional and renewable biodiesel feedstocks, the catalyst used and reaction kinetics of the production process.     

Tetramethylguanidine catalyzed transesterification of fats and oils: A new method for rapid determination of their composition

A new method for the rapid preparation of methyl esters from vegetable oils and fats, using tetramethylguanidine as catalyst, has been developed. This method is compared with the traditional method (Ce 2–66, using 20% BF₃ in methanol) and that proposed by Hartman and Lago (using NH₄Cl/H₂SO₄ in methanol). It is shown that the new method produces the methyl esters in quantitative yields and has certain advantages, as it is simpler, cheaper and does not result in isomerization of the fatty acids.     

疏水改性氧化钙催化制备生物柴油的研究

以溴化苄作为改性剂,采用化学键合方法对市售氧化钙进行表面改性,考察改性氧化钙固体碱催化菜籽油-甲醇酯交换反应制备生物柴油的性能,并在此基础上对该催化体系的耐水性进行考察。通过对反应体系中醇/油摩尔比、催化剂用量和反应时间进行优化,最终得出在醇/油摩尔比为15∶1,催化剂用量为5%以及表面改性剂溴化苄用量为0.2%时,表面改性氧化钙上生物柴油产率在反应3h即可达到99.8%,而未改性氧化钙为催化剂时在相同反应条件下生物柴油产率仅为35.3%。     

Soybean oil transesterification over zinc oxide modified with alkali earth metals

Fatty acid methyl esters, derived from vegetable oils or animal fats and better known as biodiesel, have received considerable attention because of their environmental benefits and the limited resources of fossil fuels. Most biodiesel is usually produced by the transesterification of vegetable oils with methanol in the presence of a catalyst. This study reports on the preliminary results of using alkaline earth metal-doped zinc oxide as a heterogeneous catalyst for transesterification of soybean oil. The highest catalytic activity was obtained with ZnO loaded with 2.5 mmol Sr(NO₃)₂/g, followed by calcination at 873 K for 5 h. When the transesterification reaction was carried out at reflux of methanol (338 K), with a 12:1 molar ratio of methanol to soybean oil and a catalyst amount of 5 wt.%, the conversion of soybean oil was 94.7%. Besides, tetrahydrofuran (THF), when used as a co-solvent, could increase the conversion up to 96.8%. However, the recovered catalyst exhibited the lower catalytic activity with a conversion of soybean oil of 15.4%. Furthermore, DTA-TG, IR and the Hammett indicator method were employed for the catalyst characterizations.