Transesterification kinetics of palm olein oil using supercritical methanol

Continuous transesterification of palm olein oil using supercritical methanol was investigated in the absence of a catalyst. The variables studied were reaction temperature (270–350 °C), pressure (20–40 MPa), and residence time (5–25 min), with a methanol-to-oil molar ratio of 40. Preheating at 245 °C was used to form a homogeneous phase in the absence of thermal decomposition of palm olein oil. The activation energies and reaction activation volumes of the fatty acid methyl ester (FAME), and those of the individual components (C16:0, C18:0, C18:1, and C18:2 methyl esters), were calculated. The entropies of activation (ΔS^‡) of the transesterification reactions were also obtained. As the transesterification of vegetable oil in supercritical methanol included a strongly negative (−175 J/mol K) entropy of activation, transesterification required harsh conditions.     

Transesterification of the crude Jatropha curcas L. oil catalyzed by micro‐NaOH in supercritical and subcritical methanol

Transesterification of the crude Jatropha curcas L. oil catalyzed by micro‐NaOH in supercritical/subcritical methanol was studied. The effects of various reaction variables such as the catalyst content, reaction temperature, reaction pressure and the molar ratio of methanol to oil on the conversion of crude Jatropha curcas L. oil to biodiesel were investigated. The results showed that even micro‐NaOH could noticeably improve this reaction. When NaOH was added from 0.2 to 0.5 to 0.8 wt‐‰ of triacylglycerols, the transesterification rate increased sharply; when the catalyst content was further increased, the reaction rate was just poorly improved. It was observed that increasing the reaction temperature had a favorable influence on the methyl ester yield. For the molar ratio ranging from 18 to 36, the higher the molar ratio of methanol to oil was charged, the faster the transesterification rate seemed. At the fixed stirring rate of 400 rpm, when the catalyst content, reaction temperature, reaction pressure and the molar ratio of methanol to oil were developed at 0.8 wt‐‰ NaOH, 523 K, 7.0 MPa and 24 : 1, respectively, the methyl ester yield could reach 90.5% within 28 min. Further, the kinetics of this reaction was involved and the results showed that it was a pseudo‐first‐order reaction whose apparent activation energy was 84.1 kJ/mol, and the pre‐exponential factor was 2.21×10⁵.     

Biodiesel production from highly unsaturated feedstock via simultaneous transesterification and partial hydrogenation in supercritical methanol

In this study, a supercritical one-pot process combining transesterification and partial hydrogenation was proposed to test its technical feasibility. Simultaneous transesterification of soybean oil and partial hydrogenation of polyunsaturated compounds over Cu catalyst in supercritical methanol was performed at 320 °C and 20 MPa. Hydrogenation proceeded simultaneously during the transesterification of soybean oil in supercritical methanol, and hydrogenation occurred during the reaction despite the absence of hydrogen gas. The polyunsaturated methyl esters obtained in the biodiesel were mainly converted to monounsaturated methyl esters by partial hydrogenation. Key properties of the partially hydrogenated methyl esters were improved and complied with standard specifications for biodiesel.     

Transesterification of soybean oil with nano-MgO or not in supercritical and subcritical methanol

Nano-MgO can apparently improve the transesterification reaction of soybean oil with supercritical/subcritical methanol. The variables affecting the yield of methyl ester during the transesterification reaction, such as the catalyst content, reaction temperature and the molar ratio of methanol to soybean oil were investigated and compared with those of non-catalyst. When nano-MgO was added from 0.5 wt% to 3 wt%, the transesterification rate increased evidently, while the catalyst content was further enhanced to 5 wt%, little increased in yield. It was observed that increasing the reaction temperature had a favorable influence on methyl ester yield. In addition, for molar ratios of methanol to soybean oil ranging from 6 to 36, the higher molar ratios of methanol to oil was charged, the faster transesterification rate was obtained. When the temperature was increased to 533 K, the transesterification reaction was essentially completed within 10 min with 3 wt% nano-MgO and the methanol/oil molar rate 36:1. Such high reaction rate with nano-MgO was mainly owing to the lower activation energy (75.94 kJ/mol) and the higher stirring.     

Lewis acid-catalyzed transesterification and esterification of high free fatty acid oil in subcritical methanol

Lewis acid catalysts are active for both esterification and transesterification, but the reaction is very slow due to mass-transfer limitations between methanol and oil phase. Because oil, FFA and Lewis acid catalysts are all soluble in the subcritical methanol phase, the esterification and transesterification will be enhanced when they are carried out under subcritical conditions. In this work, the esterification and transesterification of high FFA oil to biodiesel via Lewis acid catalysts such as Pb(OOCCH₃)₂, Cd(OOCCH₃)₂ and Zn(OOCCH₃)₂ were carried out in the subcritical methanol phase (2 MPa, 180°C, reaction time 30 min). The results show that the esterification conversion reaches 79.8-96.4% with Palmitic acid as feedstock, and the transesterification conversion reaches 56.8-73.4% with soybean oil as feedstock. With the mixture of Soybean oil and Palmitic acid (FFA content of 20.3 wt%) as feedstock, the content of fatty acid methyl esters (FAME) in products reaches 67.3-83.4%.     

Biodiesel synthesis from waste vegetable oil via transesterification reaction in supercritical methanol

Response surface methodology (RSM) was applied to analyze the effect of four independent variables (molar ratio of methanol to oil, reaction temperature, pressure and time) on the yield of the biodiesel production via supercritical methanol (SCM) method. Waste vegetable oil (WVO) was used as raw material and transesterification reaction was performed in a supercritical batch reactor. The central composite rotatable design was used to maximize the yield of the biodiesel. The optimal values of variables were determined by RSM to be 33.8:1 (methanol/oil molar ratio) 271.1 °C, 23.1 MPa and 20.4 min reaction time for the maximum predicted yield of 95.27% (g/g). Moreover, an irreversible first order kinetic model was successfully correlated to the experimental transesterification data with 3.37 (s⁻¹) and 31.71 (kJ/mol) as the frequency factor and activation energy of the process.     

Synthesis of biodiesel from soybean oil using supercritical methanol in a one-step catalyst-free process in batch reactor

The transesterification of soybean oil with supercritical methanol in a batch reactor with no added catalyst was investigated, studying the evolution of intermediate products (monoglycerides and diglycerides) as well as the conversion of triglycerides and the yield of fatty acid methyl esters and glycerol. Experiments were carried out in a temperature range of 250–350 °C (12–43 MPa) at reaction times of between 15 and 90 min for a methanol-to-oil molar ratio of 43:1. The best reaction conditions in this one-step supercritical process (325 °C/35 MPa and 60 min), in which triglyceride conversion was practically total, led to a maximum yield of fatty acid methyl esters of 84%. In these conditions an 8.1 wt% of monoglycerides and diglycerides remained in the medium. Although the use of more severe reaction conditions (longer reaction times and higher temperatures) reduced the content of these glycerides, the yield of methyl esters decreased due to their thermal decomposition.     

Production of biodiesel fuel from tall oil fatty acids via high temperature methanol reaction

Tall oil fatty acids are a byproduct of the paper industry and consist predominantly of free-fatty acids (FFAs). Although this feedstock is ideal for biodiesel production, there has been relatively little study of its conversion to biodiesel. Thus, the purpose of this study was to investigate the high temperature reaction of methanol with tall oil at subcritical and supercritical pressures to produce fatty acid methyl esters. This study investigates the effects of mixing, pressure, temperature, and methanol to oil molecular ratio in order to determine the potential use of tall oil as a biodiesel feedstock. In this work, tall oil fatty acids were successfully reacted with supercritical and subcritical methanol in a continuous tubular reactor, resulting in a reaction that is primarily temperature dependent. Conversions at subcritical pressures of 4.2 MPa and 6.6 MPa were 81% and 75%, respectively. Pressure seemed to have little correlation to conversion in both regimes, and conversions were comparable between the two. Additionally, it was found that tall oil fatty acids react well with methanol to give comparable conversions at the relatively low molecular flow ratio of 5:1 methanol to tall oil. Both of these observations suggest that hydrolyzed triglycerides or free fatty acid feedstocks would make the primary high temperature biodiesel reaction and the subsequent separation and purification operations less expensive than was previously believed.     

Lipase-catalyzed glycerolysis of soybean oil in supercritical carbon dioxide

The transesterification of soybean oil with glycerol, 1,2-propanediol, and methanol by an immobilized lipase in flowing supercritical carbon dioxide for the synthesis of monoglycerides is described. A lipase from Candida antarctica was used to catalyze the reaction of soybean oil with glycerol, 1,2-propanediol, ethylene glycol, and methanol. Reactions were performed in supercritical carbon dioxide at a density of 0.72 g/L and at a flow rate of 6 μL/min (expanded gas). The substrates were added at flows ranging from 2.5 to 100 μL/min. Monoglycerides were obtained at up to 87 wt%, and fatty acid methyl esters at nearly 100 wt%. The reactivity of the alcohols paralleled the solubility of the substrate in liquid carbon dioxide. Glycerol has the slowest reaction rate, only 2% of that of methanol.     

Hydroxyl content and refractive index determinations on transesterified soybean oil

Biodiesel, a promising alternative diesel fuel, is produced by transesterification of vegetable oils or animal fats with methanol. One of the main problems in the industrial application of the transesterification process is how to determine the conversion of oils to methyl esters. In this work, a quick analytical method was developed for monitoring the transesterification reaction of soybean oil with methanol. The conversion of oils to methyl esters could be determined by applying a simple linear correlation with hydroxyl content of the transesterified mixture or refractive index of the product. The results were in agreement with the values measured by ¹H NMR spectroscopy. Compared with existing chromatographic and other methods, this method for monitoring the transesterification of vegetable oils with methanol is simple, rapid, and inexpensive and is especially suitable for process control purposes.     

Transesterification of the crude oil of rapeseed with NaOH in supercritical and subcritical methanol

Transesterification reaction of the crude oil of rapeseed with supercritical/subcritical methanol in the presence of a relatively low amount of NaOH was successfully carried out, where soap formation didn't occur. The main factors affecting the methyl ester yield during the transesterification reaction were the catalyst content, the reaction temperature, the molar ratio of alcohol to oil and the water content. High methyl ester yield and fast reaction rate could be obtained even if the reaction pressure was relatively low. In addition, kinetics of the transesterification reaction was also discussed.     

Biodiesel production by the transesterification of cottonseed oil by solid acid catalysts

Methyl esters (biodiesel) were produced by the transesterification of cottonseed oil with methanol in the presence of solid acids as heterogeneous catalysts. The solid acids were prepared by mounting H₂SO₄ on TiO₂ · nH₂O and Zr(OH)₄, respectively, followed by calcining at 823K. TiO₂-SO₄ ²⁻ and ZrO₂-SO₄ ²⁻ showed high activity for the transesterification. The yield of methyl esters was over 90% under the conditions of 230°C, methanol/oil mole ratio of 12:1, reaction time 8 h and catalyst amount (catalyst/oil) of 2% (w). The solid acid catalysts showed more better adaptability than solid base catalysts when the oil has high acidity. IR spectral analysis of absorbed pyridine on the samples showed that there were Lewis and Br?nsted acid sites on the catalysts. Translated from The Chinese Journal of Process Engineering, 2006, 6(4): 571–575 [译自: 过程工程学报]     

Synthesis of biodiesel from edible,non-edible and waste cooking oils via supercritical methyl acetate transesterification

The use of methyl acetate instead of methanol for supercritical synthesis of glycerol-free biodiesel from vegetable oils is a new process and its study is very limited in the literature. In this work, it has been tested for the first time on three edible and non-edible oils with different fatty acid composition. The process was also applied to waste oil with higher free fatty acid (FFA) content. The results demonstrate that the oil composition does not significantly influence the biodiesel yield.The influence of temperature, pressure and molar ratio of reactants was studied. All the oils achieved complete conversion after 50 min at 345 °C, 20 MPa with methyl acetate:oil molar ratio equal to 42:1. The obtained data also allowed calculating the apparent rate coefficients and activation energies.Eventually, some new information on the process was obtained. Thermal degradation of triacetin, which substitutes glycerol as the by-product of the transesterification reaction, was observed. Some indicative experiments were performed to understand the role of the acetic acid produced by FFA esterification.     

Supercritical transesterification: Impact of different types of alcohol on biodiesel yield and LCA results

A series of experiments with transesterification of rapeseed oil in supercritical methanol and supercritical ethanol was carried out in a batch reactor at various reaction temperatures (250–350 °C), working pressure (8–12 MPa), reaction time (7, 15 and 30 min), and at a constant 42:1 alcohol to oil molar ratio. The effect of alcohol, temperature, pressure and reaction time on biodiesel yield was investigated using linear multiple regression models. In the observed range, temperature has the highest impact on yields, followed by reaction time and pressure. The relative importance of time and pressure in explaining yields is higher in the case of transesterification in supercritical ethanol. The results of environmental life cycle assessment have revealed that contrary to general belief the usage of ethanol instead of methanol cannot improve the sustainability and renewability of the transesterification process significantly.     

超临界甲醇中制备生物柴油

研究了超临界甲醇法制备生物柴油中反应条件对甲酯生成率的影响。结果表明,醇油摩尔比越大,大豆油转化率越高;升温有助于提高反应速率,在临界温度239℃附近,温度的影响尤其明显;当压力高于13.5 MPa时,压力对反应的影响不明显;原料油中,不同脂肪酸酯甲酯化的速率不同,按亚油酸酯、油酸酯、棕榈酸酯、硬脂酸酯的顺序依次降低;大豆油中w(游离油酸)<50%时,不影响反应转化率;原料油中w(H2O)<20%时对反应影响不大。当醇油摩尔比为42∶1,反应温度280℃,反应1 h,油脂转化率可达78%。     

Ionic liquids in supercritical methanol greatly enhance transesterification reaction for high‐yield biodiesel production

Biodiesel production is one of the most promising future alternatives to replacing fossil fuels. This work studies the use of ionic liquids (ILs) as potential catalysts in supercritical methanol for biodiesel production from non‐edible oil. The transesterification reaction of karanja oil was investigated in supercritical methanol in the presence of two respective ILs, [BMIM⁺][ ] and [Chol⁺][H₂ ]. The reaction was performed in a one‐step batch process at several temperatures and percentages by weight of catalyst (w/w_oil). The results obtained show that the IL [Chol⁺][H₂ ] allows a high yield of fatty acid methyl esters to be achieved in a short reaction time (above 95% in 45 min). A catalytic mechanism is also proposed for the IL that offered significant catalytic activity. This work investigates the effects of the use of ionic liquids as potential catalysts in supercritical methanol for the transesterification reaction of non‐edible oil. The reported reaction times to obtain biodiesel yields above 90% through the transesterification reaction of karanja oil range between 90 min and 8 h. ILs as catalysts in supercritical methanol drastically reduce reaction time (45 min) to obtain high fatty acid methyl ester yield (95.6%). © 2016 American Institute of Chemical Engineers AIChE J, 62: 3842–3846, 2016     

Transesterification of rapeseed oil in subcritical methanol conditions

In this study, transesterification of rapeseed oil using subcritical methanol conditions was studied. The objective of the work was characterizing the methyl esters for its use as biodiesel in compression ignition motors. The variables affecting the methyl ester yield during the transesterification reaction, such as, the catalyst type and content, reaction temperature and pressure, the presence of hexane as co-solvent, the methanol oil molar ratio and the methanol hexane molar ratio were investigated to optimize the reaction conditions. The evolution of the process was followed by gas chromatography, determining the concentration of the methyl esters at different reaction times. The biodiesel was characterized by its density, viscosity, saponification value, iodine value, acidity index and water content, according to ISO norms. High methyl ester yield and fast reaction rate could be obtained even if the reaction pressure was relatively low, which is quite favorable to the production of biodiesel in industry.     

Extraction of Lipids from Municipal Wastewater Plant Microorganisms for Production of Biodiesel

Municipal wastewater treatment plants in the USA produce over 6.2 × 10⁶ t of dried sewage sludge every year. This microorganism-rich sludge is often landfilled or used as fertilizer. Recent restrictions on the use of sewage sludge, however, have resulted in increased disposal problems. Extraction of lipids from sludge yields an untapped source of cheap feedstock for biodiesel production. Solvents used for extraction in this study include n-hexane, methanol, acetone, and supercritical CO₂. The gravimetric yield of oil was low for nonpolar solvents, but use of polar solvents gave a considerably increased yield; however, the percentage of saponifiable material was less. Extraction of lipids with a mixture of n-hexane, methanol, and acetone gave the largest conversion to biodiesel compared with other solvent systems, 4.41% based on total dry weight of sludge. In situ transesterification of dried sludge resulted in a yield of 6.23%. If a 10% dry weight yield of fatty acid methyl esters is assumed, the amount of biodiesel available for production in the USA is 1.4 × 10⁶ m³/year. Outfitting 50% of municipal wastewater plants for lipid extraction and transesterification could result in enough biodiesel production to replace 0.5% of the national petroleum diesel demand (0.7 × 10⁶ m³).     

Transesterification of leather tanning waste to biodiesel at supercritical condition: Kinetics and thermodynamics studies

Catalyst-free transesterification of leather tanning waste with high free fatty acid (FFA) content at supercritical condition was reported in this work. The experiments were performed in batch system at various temperatures (250–325 °C) under constant pressure of 12 MPa and methanol/fatty oil molar ratio of 40:1 for reaction time of 2–10 min. Kinetic modeling of formation of fatty acid methyl esters (FAMEs) that incorporate reversible esterification and non-reversible transesterification simultaneously was verified. The proposed semi-empirical model was fitted against kinetic experimental data over temperature range studied. The kinetic parameters (i.e. k′_TE, k′_E, and k_E′) were determined by nonlinear regression fitting. Thermodynamic activation parameters of the reactions were evaluated based on activation complex theory (ACT) and the following results are obtained: ΔG³ > 0, ΔH³ > 0, and ΔS³ < 0. The activation energy (E_a) of transesterification, forward and reverse esterification reactions was 36.01 kJ/mol, 28.38 kJ/mol, and 5.66 kJ/mol, respectively.     

Biodiesel fuel from Jatropha oil via non-catalytic supercritical methanol transesterification

Transesterification of Jatropha oil using supercritical methanol and in absence of a catalyst has been studied under different conditions of temperature (from 512 to 613 K), pressure (from 5.7 to 8.6 MPa) and molar ratio of alcohol to oil (from 10 to 43 mol alcohol per mol oil). The reaction products were analyzed for their content of residual triglycerides, glycerol, monoglycerides, diglycerides, esters and free acids by high performance liquid chromatography (HPLC), thin layer chromatography (TLC) and titration against KOH.The results have revealed that 100% yield of esters can be obtained using super critical methanol within four min only, at a temperature of 593 K and under a pressure of 8.4 MPa pressure. The molar ratio of methanol to oil was 43:1.