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.     

The use of a modified TDSP for biodiesel production from soybean, linseed and waste cooking oil

In this study, the Transesterification Double Step Process (TDSP) for the production of biodiesel from vegetable oil was modified to yield a shorter reaction time and products with improved quality. TDSP consists in a two step transesterification procedure which starts with a basic catalysis, followed by an acidic catalysis. The process modifications included a reduction in the concentration of catalysts, a reduction in the reaction time of the first step and the direct mixing of methanol/acid solution, without cooling the system between the first and second step. A comparison between washed and unwashed biodiesel demonstrates that the final washing and drying procedure is necessary for satisfactory results. The products were analyzed by ¹H-NMR and nineteen different biodiesel analyses specific for international quality certification. The modified procedure resulted in a high conversion index (97% for waste cooking oil and soybean oil and 98% for linseed oil) and high yield (87 ± 5% for waste cooking oil, 92 ± 3% for soybean and 93 ± 3% for linseed oil). The biodiesel produced by the modified TDSP met ASTM, EN ISO and ABNT standards before the addition of stabilizer.     

Risk assessment for prion protein reduction under the conditions of the biodiesel production process

Due to the increased demand for biofuels, all different feedstocks from oils and fats have to be considered for biodiesel production. Animal fats have proved to be excellent sources for biodiesel due to their high cetane number and good stability. Large amounts of fat from so‐called high‐risk material, possibly contaminated with infectious prions, are available for biodiesel production. In this paper, the grade of destruction of prions during the biodiesel production process, including pre‐esterification with conc. sulfuric acid followed by KOH‐catalyzed transesterification, was studied. The starting material of the different production steps was spiked with purified and highly infectious prion rods, and the destruction of these prions was determined by gel electrophoresis (SDS‐PAGE) and Western blot. The pre‐esterification step led to a destruction factor of at least 100, the transesterification led to a factor of at least 250, and the distillation of the final biodiesel showed a destruction factor of at least 1000. During all experiments, no traces of prions could be detected after the different reaction steps. Based on these data, a complete and unequivocal risk assessment regarding the industrial process of biodiesel production was carried out, leading to a calculated overall risk of 5.8×10^?15 ID₅₀ units/person and year, which means that a hypothetical BSE contamination from biodiesel is more than 10⁹ times lower than the background risk.     

A Density Functional Theory Study on the Acid-Catalyzed Transesterification Mechanism for Biodiesel Production from Waste Cooking Oils

The acid-catalyzed transesterification reaction has been one of the most effective methods to produce biodiesel, especially from waste cooking oils (WCO) with high contents of water and free fatty acids (FFA). However, in the acid-catalyzed processes, the H⁺ action mechanism and the controlling step of the reaction rate have been ambiguous. To clearly understand the reaction process, the DMol3 module based on the density functional theory (DFT) was employed to investigate the acid (H⁺-)-catalyzed transesterification mechanism of methanol and oleic acid monoacylglycerol (OAM). The one step transesterification without a catalyst and the feasible paths of SN2 (substitution nucleophilic bimolecular) and SN1 (substitution nucleophilic unimolecular) reaction mechanisms with H⁺-based catalysts were built as Path 1, Path 2, and Path 3, respectively. The calculated structures, thermodynamic, and kinetic data revealed that the H⁺-based catalysts could effectively reduce the activation energy for the transesterification reaction, and the Path 2 based on the SN2 reaction mechanism was the optimal reaction path. A tetrahedral intermediate (IM2-2) could be generated with the highest active energy of 15.383 kcal mol⁻¹, implying that there was the most stable structure of IM2-2 as the key species in the transesterification process. Hence, the increasing decomposition rate of IM2-2 accelerated the forward reaction in H⁺-based biodiesel processes. The calculated active energy of 15.383 kcal mol⁻¹ was in good agreement with the kinetic data for the monoacylglycerol transesterification of 15.067 kcal mol⁻¹. Our calculations should provide basic and reliable theoretical data for further understanding the mechanism of transesterification of WCO to biodiesel products in the future work.     

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.     

In situ transesterification of coconut oil using mixtures of methanol and tetrahydrofuran

The conventional biodiesel production method requires oil extraction followed by transesterification with methanol. The solubility of vegetable oils in methanol is low which decreases the overall rate of reaction. To eliminate the oil extraction step and improve the overall reaction rate, simultaneous extraction, esterification and transesterification were conducted by directly mixing methanol and tetrahydrofuran (THF) co-solvent and sulfuric acid catalyst with ground, desiccated coconut meat (copra) in a batch process and continuing the reaction until the system reached steady state. After separation of the mixture, yield was obtained by measuring the content of triglycerides, diglycerides and monoglycerides in the biodiesel phase. The yield increases with THF:methanol ratio, methanol:oil molar ratio and temperature. Within the range of conditions tested, the highest yield achieved was 96.7% at 60 °C, THF:methanol volume ratio of 0.4 and methanol:oil molar ratio of 60:1. The methanol:oil molar ratio is necessarily high in order to completely wet the copra mass, but is still lower than in previous studies by other researchers on in situ transesterification. Product assays show that the resulting biodiesel product is similar to conventionally produced coconut biodiesel. The results indicate that the in situ transesterification of copra using methanol/THF mixtures merits further study.     

Transesterification of Camellia japonica and Vernicia fordii seed oils on alkali catalysts for biodiesel production

Camellia japonica and Vernicia fordii seed oils were employed as a feedstock for production of biodiesel by transesterification with methanol on alkali catalysts. The composition and physicochemical properties were investigated in the raw seed oils and the biodiesel products. The fatty acid methyl ester (FAME) contents in the biodiesel produced from the seed oils were above 96% on KOH catalyst in the reaction. It was acceptable for the limit of European biodiesel qualities for BD100. Other qualities such as cetane number, acid value, density, and kinematic viscosity, of the produced biodiesels also matched the biodiesel qualities.     

Biodiesel Production Using a Carbon Solid Acid Catalyst Derived from β‐Cyclodextrin

A novel carbon solid acid catalyst was prepared by incomplete hydrothermal carbonization of β‐cyclodextrin into small polycyclic aromatic carbon sheets, followed by the introduction of –SO₃H groups via sulfonation with sulfuric acid. The physical and chemical properties of the catalyst were characterized in detail. The catalyst simultaneously catalyzed esterification and transesterification reactions to produce biodiesel from high free fatty acid (FFA) containing oils (55.2 %). For the as‐prepared catalyst, 90.82 % of the oleic acid was esterified after 8 h, while the total transesterification yield of high FFA containing oils reached 79.98 % after 12 h. By contrast, the obtained catalyst showed comparable activity to biomass (such as sugar, starch, etc.)‐based carbon solid acid catalyst while Amberlyst‐15 resulted in significantly lower levels of conversion, demonstrating its relatively high catalytic activity for simultaneous esterification and transesterification. Moreover, as the catalyst can be regenerated, it has the potential for use in biodiesel production from oils with a high FFA content.     

Biodiesel production from high FFA rubber seed oil

Currently, most of the biodiesel is produced from the refined/edible type oils using methanol and an alkaline catalyst. However, large amount of non-edible type oils and fats are available. The difficulty with alkaline-esterification of these oils is that they often contain large amounts of free fatty acids (FFA). These free fatty acids quickly react with the alkaline catalyst to produce soaps that inhibit the separation of the ester and glycerin. A two-step transesterification process is developed to convert the high FFA oils to its mono-esters. The first step, acid catalyzed esterification reduces the FFA content of the oil to less than 2%. The second step, alkaline catalyzed transesterification process converts the products of the first step to its mono-esters and glycerol. The major factors affect the conversion efficiency of the process such as molar ratio, amount of catalyst, reaction temperature and reaction duration is analyzed. The two-step esterification procedure converts rubber seed oil to its methyl esters. The viscosity of biodiesel oil is nearer to that of diesel and the calorific value is about 14% less than that of diesel. The important properties of biodiesel such as specific gravity, flash point, cloud point and pour point are found out and compared with that of diesel. This study supports the production of biodiesel from unrefined rubber seed oil as a viable alternative to the diesel fuel.     

Use of dolomite catalyst in biodiesel production via transesterification of waste cooking oil in oscillatory baffled reactor

Biodiesel has recently gained popularity due to its environmental issues and the fact that it is generated from renewable resources. However, the cost of the synthesis of biodiesel is the major impediment to commercialization. The utilization of leftover cooking oils as raw material, the adaptation of a continuous transesterification process, and the use of cheap catalysts are the major possibilities for investigating the cost of biodiesel. In this work, a dolomite catalyst was prepared from natural dolomite rocks and used for the evaluation of continuous transesterification of biodiesel from oleic acid as a model compound of waste cooking oil (WCO). The dolomite catalyst was prepared by activation under vacuum at a surface area of 34.5 m²/g. The characterization tests showed good thermal stability of the catalyst and evolution of the CaO and MgO compounds at high concentrations. A kinetic study was conducted to obtain kinetic parameters of catalytic transesterification of the WCO. The kinetic experiments were carried out at 298–333 K, and residence time up to 80 min. The results presented that the catalytic transesterification is the first-order reaction, and the activation energy was 43 kJ/mol. The oscillatory baffled reactor (OBR) was used to evaluate the dolomite catalyst for the continuous production of biodiesel via transesterification. The evaluation study was conducted at a methanol: oil mole ratio of 6:1 and the effect of different operation variables on oleic acid conversion to biodiesel was studied. These variables were temperature (323, 333, and 343 K), residence times (5–40 min), the amplitude of oscillation (2–8 mm), and frequency of oscillation (1, 2, 3, 4, and 4.3 Hz). The results showed an outstanding performance and stable activity of the dolomite catalyst as a conversion of 96% was obtained at 333 K, 4.3 Hz, 8 mm amplitude, and 40 min residence time.     

Non-catalytic biodiesel process with adsorption-based refining

Different feedstocks of varying acidity ranks and water contents were subjected to a series of discontinuous steps that simulated a biodiesel production process. The three steps comprised: (i) the non-catalytic transesterification with supercritical methanol at 280 °C; (ii) the distillation of the unreacted methanol, water and volatile products; and (iii) the adsorption of the impurities with adequate adsorbents. Refined soy oil, chicken oil and waste cooking oil were subjected to the same simple procedure. The process produced biodiesel complying with the water, acid, glycerides and methyl esters content specifications of the EN 14214 standard.Biodiesel production by the reaction of oils in supercritical methanol at 280 °C and methanol-to-oil molar ratios of 15 and 20 produced amounts of glycerol as small as 0.02%. This simplified the subsequent refining of the biodiesel and is considered an advantage over the classic alkali-catalyzed process (that produces 10% of glycerol by-product) because washing steps can be spared.The contents of methyl esters, water and free fatty acids showed a volcano pattern when plotted as a function of the reaction time. In the case of the free fatty acids this was attributed to the initial reaction of water and triglycerides to form acids and glycerol that increased the acidity of the product mixture. At longer reaction times these acids were likely transformed into methyl esters or were decarboxylated to hydrocarbons and CO₂. Water formation was attributed to glycerol decomposition and esterification of free fatty acids.The design of a simple process for biodiesel production using a single reaction step with negligible glycerol production and an adsorption-based refining step was thus studied. A possible scheme integrating reaction, methanol recycling, biodiesel purification and heat recovery was discussed. Advantages and disadvantages of process units were analyzed on terms of operating cost and simplicity.     

Influence of impurities on biodiesel production from Jatropha curcas L. by supercritical methyl acetate process

Generally, water and free fatty acid (FFA) content in oils could cause a serious problem during conventional transesterification such as saponification. Thus, without any pre-treatment, vegetable oil, especially with high FFA content, will be affected. In this study, a non-catalytic supercritical methyl acetate (SCMA) process was utilized to produce biodiesel from Jatropha curcas L. oil. The effects of water and FFA content on the yield of biodiesel were investigated. The results obtained for the effects of water on the yield of biodiesel were compared with the supercritical methanol (SCM) process and conventional catalytic reaction. Results revealed that the catalytic reaction suffers from low yield with the presence of high water content in oil. Meanwhile, the yield of both the SCM and SCMA reactions were found to increase slightly with the increment of water content in the mixture. On the other hand, the results for the effect of FFA on the yield of biodiesel were compared with the SCM reaction. It was found that the presence of FFA has a negligible effect in both the SCMA and SCM reactions. These findings demonstrate that pre-treatment procedures are not necessary in the SCMA process for Jatropha oil which normally contains a high FFA content.     

Process optimization design for jatropha-based biodiesel production using response surface methodology

Biodiesel of non food vegetal oil origin is gaining attention as a replacement for current fossil fuels as its non-food chain interfering manufacturing processes shall prevent food source competition which is expected to happen with current biodiesel production processes. As a result, non edible Jatropha curcas plant oil is claimed to be a highly potential feedstock for non-food origin biodiesel. CaO–MgO mixed oxide catalyst was employed in transesterification of non-edible J. curcas plant oil in biodiesel production. Response surface methodology (RSM) in conjunction with the central composite design (CCD) was employed to statistically evaluate and optimize the biodiesel production process. It was found that the production of biodiesel achieved an optimum level of 93.55% biodiesel yield at the following reaction conditions: 1) Methanol/oil molar ratio: 38.67, 2) Reaction time: 3.44 h, 3) Catalyst amount: 3.70 wt.%, and 4) Reaction temperature: 115.87 °C. In economic point of view, transesterification of J. curcas plant oil using CaO–MgO mixed oxide catalyst requires less energy which contributed to high production cost in biodiesel production. The incredibly high biodiesel yield of 93.55% was proved to be the synergetic effect of basicity between the active components of CaO–MgO shown in the physicochemical analysis.     

Modeling Effects of Mass Transfer Rate and Catalyst Concentration on Biodiesel Production in Batch Reactors

This article presents a new approach to investigate the kinetics of sunflower and rapeseed oils methanolysis. Due to its heterogeneous nature, the methanolysis reaction is affected by different physical properties such as mass transfer coefficients and specific surface area of the dispersed phase. Considering these parameters, a model was developed, and was evaluated by comparing the results of the model with the experimental data found in the literature. The mean absolute deviation obtained for sunflower and rapeseed oils is 0.039 mol L^?1, which demonstrates the accuracy of the model. The results show that the mixing speed is more effective in the first few minutes of the process. Furthermore, at mixing speed above 700 rpm, the process is controlled only by the reactions. The rate of biodiesel production increases with increasing catalyst concentration; however, catalyst concentration above 1.5 wt% has little or no significant effect on the rate of biodiesel production. In addition, because of its higher activation energy the rapeseed oil transesterification is more temperature dependent than the sunflower transesterification.     

Production of biodiesel from wet activated sludge

BACKGROUND: The production of biodiesel from activated sludge obtained from Tuscaloosa, AL was optimized based on the yield of fatty acid methyl esters (FAMEs) using an in situ transesterification process. An orthogonal central composite response surface design was considered to investigate the main and interaction effects of temperature, methanol to sludge ratio, and catalyst concentration. RESULTS: The biodiesel yield can be satisfactorily described by the quadratic response surface model with R² of 0.836 and a statistically not significant lack of fit (p = 0.254). Coded regression coefficients, main effect plots and surface plots indicated that maximum biodiesel yield may be obtained at 75 °C, 30 mL g^?1 (methanol/sludge) and 10% volume (catalyst concentration). Numerical optimization showed that at this reaction condition, a biodiesel yield of 3.78% (weight) can be obtained. Experimental verification gave a biodiesel yield of 3.93 ± 0.15% (weight) giving a model error of 7.35%. This indicates high reliability of the model. CONCLUSIONS: The economic analysis showed that the in situ transesterification of wet activated sludge (84.5% weight moisture) is less economical than the in situ transesterification of dried sludge (5% weight moisture). However, sensitivity analysis indicated that the process can be made more economical by reduction of water to 50% (weight). At this level of moisture, a biodiesel break‐even price of around $7.00 per gallon is attainable, which is still more expensive than petroleum‐based diesel (～$2.95 per gallon). For the biodiesel from activated sludge to be economically competitive, a biodiesel yield of at least 10% (weight) is necessary. Copyright © 2010 Society of Chemical Industry     

Synthesis of economically viable biodiesel from waste frying oils (WFO)

In present communication, waste frying oil (WFO) has been used as a feedstock for biodiesel synthesis. WFO, procured from a local Indian restaurant possessed an acid value of 0.84 mg KOH/g, which is low enough for single step transesterification reaction. Biodiesel (fatty acid methyl esters) was washed after transesterification reaction and the yield got lowered substantially (from 96% to 86.36%) after water washing owing to loss of esters. 30:100 vol% (methanol to oil), 0.6 wt% NaOCH₃, 60°C temperature and 600 rpm agitation in 1 h reaction time was found to be optimum for transesterification reaction. ¹H NMR spectrum showed a high conversion (95.19%) of fatty acids in WFO to biodiesel in 2 h reaction time. Almost complete conversion (99.68%) was attained in 2 h reaction time. © 2011 Canadian Society for Chemical Engineering     

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.     

Intensification of biodiesel production from vegetable oils using ultrasonic-assisted process: Optimization and kinetic

Intensification of biodiesel production process using low frequency ultrasonic irradiation (20 kHz, 200 W) is elucidated in this study. Effects of five process variables in an ultrasonic-assisted reactor catalyzed by SrO through transesterification of vegetable oils are investigated. RSM was employed and the optimum conditions were at an ultrasonic pulse on of 9 s followed by 2 s of pulse off within a reaction time of 30.7 min. The optimum ultrasonic power was found to be 130 W using an oil amount of 52 g (R² = 0.97). The model was applicable to different types of oil with errors less than 10%. FFA content was responsible for the different yields obtained with different oils. Three steps of the transesterification process were measured to obtain the kinetic study. The results revealed that the reaction followed a second-order kinetic. The activation energies varied between 70.63 kJ/mol and 136.93 kJ/mol showing relatively high coefficient of determinations.     

Synthesis of Biodiesel through Catalytic Transesterification of Various Feedstocks using Fast Solvothermal Technology: A Critical Review

The fossil fuel reserves are depleting at a more rapid rate as a result of the population growth and the ensuing energy utilization. Biodiesel is a mixture of fatty acid methyl esters produced from the transesterification of plant oils or animal fats. Moreover, the source of raw materials and manufacturing costs have become the major hurdle in the commercialization of biodiesel; thus, alternative sources such as the use of waste oils and non-edible oils together with biodiesel production techniques have long been considered. Selecting an appropriate feedstock and increasing production yield are two important approaches to decrease the costs of biodiesel production. Typically, biodiesel, which operates with electrical or conventional heating to generate high efficiency of the product, consumes a huge amount of power in a long reaction time. In contrast, chemical reactions speed up by microwave irradiation which results in producing high yields of product in a shorter chemical reaction time. In this extensive article, an effort has been made to review the use of microwave technology including multi-feedstock and recent studies on microwave-assisted heterogeneously catalyzed processes for biodiesel production. The heterogeneous catalyst performance has also been covered, including the measurement of their pysico-chemical properties. The microwave irradiation used for the synthesis of biodiesel is also included. In addition, the reaction variables impacting the transesterification process, such as heating system, microwave power, type and amount of heterogeneous catalyst, oil/methanol molar ratio, reaction time, temperature and mixing intensity, are covered. The final part of this article will cover the details of previously performed work on heterogeneous catalysts. Finally, energy balances for the traditional and microwave-based processes, conclusions, and recommendation on the topic are presented. The aim this article is to focus on recent studies on microwave-assisted heterogeneously catalyzed processes.