酯化-酯交换两步法制备生物柴油的动力学

以潲水油（WCO）为原料,探讨了酯化-酯交换两步法制备生物柴油的反应动力学。以活性炭负载硫酸铁［Fe₂(SO₄)₃/AC］为负载型催化剂,通过测定不同反应温度、不同甲醇/脂肪酸（FFA）摩尔比条件下WCO中游离脂肪酸的转化率,以此确定酯化反应的动力学控制步骤及动力学方程中的待定参数,从而建立了在实验温度范围内酯化反应的动力学方程,并根据碱催化酯交换反应机理,在简化的动力学模型基础上,推导出了WCO中甘油三酯（TG）与甲醇发生酯交换反应的宏观动力学方程。结果表明,酯化反应和酯交换反应的动力学方程在实验条件范围内都能较好地描述各自的反应过程。     

An ideal feedstock, kusum (Schleichera triguga) for preparation of biodiesel: Optimization of parameters

Kusum (Schleichera triguga), a non-edible oil bearing plant has been used as an ideal feedstock for biodiesel development in the present study. Various physical and chemical parameters of the raw oil and the fatty acid methyl esters derived have been tested to confirm its suitability as a biodiesel fuel. The fatty acid component of the oil was tested by gas chromatography. The acid value of the oil was determined by titration and was found to 21.30 mg KOH/g which required two step transesterification. Acid value was brought down by esterification using sulfuric acid (H₂SO₄) as a catalyst. Thereafter, alkaline transesterification was carried out using potassium hydroxide (KOH) as catalyst for conversion of kusum oil to its methyl esters. Various parameters such as molar ratio, amount of catalyst and reaction time were optimized and a high yield (95%) of biodiesel was achieved. The high conversion of the feedstock into esters was confirmed by analysis of the product on gas chromatograph-mass spectrometer (GC-MS). Viscosity and acid value of the product biodiesel were determined and found to be within the limits of ASTM D 6751 specifications. Elemental analysis of biodiesel showed presence of carbon, hydrogen, oxygen and absence of nitrogen and sulfur after purification. Molar ratio of methanol to oil was optimized and found to be 10:1 for acid esterification, and 8:1 for alkaline transesterification. The amounts of H₂SO₄ and KOH, 1% (v/v) and 0.7% (w/w), respectively, were found to be optimum for the reactions. The time duration of 1 h for acid esterification followed by another 1 h for alkaline transesterification at 50 ± 0.5 °C was optimum for synthesis of biodiesel.     

Esterification of sludge palm oil using trifluoromethanesulfonic acid for preparation of biodiesel fuel

Trifluoromethanesulfonic acid (TFMSA) was used to reduce the high free fatty acids (FFA) content in sludge palm oil (SPO). The FFA content of SPO was converted to fatty acid methyl ester (FAME) via esterification reaction. The treated sludge palm oil was used as a raw material for biodiesel production by transesterification process. Several working parameters were optimized, such as dosage of catalyst, molar ratio, reaction temperature and time. Less than 2% of the FFA content was the targeted value. The results showed that the FFA content of SPO was reduced from 16% to less than 2% using the optimum conditions. The yield of the final product after the alkaline transesterification was 84% with 0.07% FFA and the ester content was 96.7%. All other properties met the international standard specifications for biodiesel quality such as EN 14214 and ASTM D6751.     

Reduction of high content of free fatty acid in sludge palm oil via acid catalyst for biodiesel production

In this study, sulphuric acid (H₂SO₄) was used in the pretreatment of sludge palm oil for biodiesel production by an esterification process, followed by the basic catalyzed transesterification process. The purpose of the pretreatment process was to reduce the free fatty acids (FFA) content from high content FFA (> 23%) of sludge palm oil (SPO) to a minimum level for biodiesel production (> 2%). An acid catalyzed esterification process was carried out to evaluate the low content of FFA in the treated SPO with the effects of other parameters such as molar ratio of methanol to SPO (6:1-14:1), temperature (40-80 °C), reaction time (30-120 min) and stirrer speed (200-800 rpm). The results showed that the FFA of SPO was reduced from 23.2% to less than 2% FFA using 0.75% wt/wt of sulphuric acid with the molar ratio of methanol to oil of 8:1 for 60 min reaction time at 60 °C. The results on the transesterification with esterified SPO showed that the yield (ester) of biodiesel was 83.72% with the process conditions of molar ratio of methanol to SPO 10:1, reaction temperature 60 °C, reaction time 60 min, stirrer speed 400 rpm and KOH 1% (wt/wt). The biodiesel produced from the SPO was favorable as compared to the EN 14214 and ASTM D 6751 standard.     

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.     

Kinetics of methyl ester production from mixed crude palm oil by using acid-alkali catalyst

The production of biodiesel from high free fatty acid mixed crude palm oil using a two-stage process was investigated. The kinetics of the reactions was determined in a batch reactor at various reaction temperatures. It was found that the optimum conditions for reducing high free fatty acid (FFA) in MCPO (8-12 wt.%/wt oil) using esterification was a 10:1 molar ratio of methanol to FFA and using 10 wt.%/wt of sulfuric acid (based on FFA) as catalyst. The subsequent transesterification reaction to convert triglycerides to the methyl ester was found to be optimal using 6:1 molar ratio of methanol to the triglyceride (TG) in MCPO and using 0.6 wt.%/vol_TG sodium hydroxide as catalyst. Both reactions were carried out in a stirred batch reactor over a period of 20 min at 55, 60 and 65 °C. The concentration of compounds in each sample was analyzed by Thin Layer Chromatography/Flame Ionization Detector (TLC/FID), Karl Fischer, and titration techniques. The results were used for calculating the rate coefficients by using the curve-fitting tool of MATLAB. Optimal reaction rate coefficients for the forward and reverse esterification reactions of FFA were 1.340 and 0.682 l mol⁻¹ min⁻¹, respectively. The corresponding optimal transesterification, rate coefficients for the forward reactions of TG, diglyceride (DG), and monoglyceride (MG) of transesterification were 2.600, 1.186, and 2.303 l mol⁻¹ min⁻¹, and for the reverse reactions were 0.248, 0.227, and 0.022 l mol⁻¹ min⁻¹, respectively.     

Microwave irradiation-assisted transesterification of soybean oil to biodiesel catalyzed by nanopowder calcium oxide

This study examined the effect of a heterogeneous base catalyst on the transesterification of soybean oil assisted by microwave irradiation. The results showed that nanopowder calcium oxide (nano CaO) was very efficient in converting soybean oil to biodiesel, and microwave irradiation is more efficient than the conventional bath for biodiesel production. However, the water content of methanol can not improve the conversion rate catalyzed by nano CaO.The suitable reaction conditions that can reach a 96.6% of conversion rate were methanol/oil molar ratio, 7:1; amount of catalyst used, 3.0 wt.%; reaction temperature, 338 K; and reaction time, 60 min. The biodiesel produced is within the limits prescribed by the standard of EN-14214.     

Conversion of waste cooking oil to biodiesel using ferric sulfate and supercritical methanol processes

In this comparative study, conversion of waste cooking oil to methyl esters was carried out using the ferric sulfate and the supercritical methanol processes. A two-step transesterification process was used to remove the high free fatty acid contents in the waste cooking oil (WCO). This process resulted in a feedstock to biodiesel conversion yield of about 85-96% using a ferric sulfate catalyst. In the supercritical methanol transesterification method, the yield of biodiesel was about 50-65% in only 15 min of reaction time. The test results revealed that supercritical process method is probably a promising alternative method to the traditional two-step transesterification process using a ferric sulfate catalyst for waste cooking oil conversion. The important variables affecting the methyl ester yield during the transesterification reaction are the molar ratio of alcohol to oil, the catalyst amount and the reaction temperature. The analysis of oil properties, fuel properties and process parameter optimization for the waste cooking oil conversion are also presented.     

Production of ethyl ester from crude palm oil by two-step reaction with a microwave system

The production of ethyl esters of fatty acids from a feed material of crude palm oil (CPO) with a high free fatty acid (FFA) content under microwave assistance has been investigated. Parametric studies have been carried out to investigate the optimum conditions for the esterification process (amount of ethanol, amount of catalyst, reaction time, and microwave power). As a result, a molar ratio of FFA to ethanol of 1:24 with 4% wt./wt. of H₂SO₄/FFA, a microwave power of 70 W, and a reaction time of 60 min have been identified as optimum reaction parameters for the esterification process aided by microwave heating. At the end of the esterification process, the amount of FFA had been reduced from 7.5 wt.% to less than 2 wt.%. Similar results were obtained following conventional heating at 70 °C, but only after a reaction time of 240 min. Transesterification of the esterified palm oil has been accomplished with a molar ratio of CPO to ethanol of 1:4, 1.5 wt.% KOH as a catalyst, a microwave power of 70 W, and a reaction time of 5 min. This two-step esterification and transesterification process provided a yield of 80 wt.% with an ester content of 97.4 wt.%. The final ethyl ester product met with the specifications stipulated by ASTM D6751-02.     

Optimization of process conditions using response surface methodology for the microwave-assisted transesterification of Jatropha oil with KOH impregnated CaO as catalyst

A transesterification reaction of Jatropha curcas oil with methanol in the presence of KOH impregnated CaO catalyst was performed in a simple continuous process. The process variables such as methanol/oil molar ratio (X₁), amount of catalyst (X₂) and total reaction time (X₃) were optimized through response surface methodology, using the Box–Behnken model. Within the range of the selected operating conditions, the optimal ratio of methanol to oil, amount of catalyst and total reaction time were found to be 8.42, 3.17% and 67.9 min, respectively. The results showed that the amount of catalyst and total reaction time have significant effects on the transesterification reaction. For the product to be accepted as a biodiesel fuel, its purity must be above 96.5% of alkyl esters. Based on the optimum condition, the predicted biodiesel conversion was 97.6% while the actual experimental value was 97.1%. The above mentioned results demonstrated that the response surface methodology (RSM) based on Box–Behnken model can well predict the optimum condition for the biodiesel production.     

Esterification of Free Fatty Acids in <Emphasis Type="Italic">Zanthoxylum bungeanum</Emphasis> Seed Oil for Biodiesel Production by Stannic Chloride

In this study, SnCl₄ was chosen as a solid catalyst for esterification of free fatty acids (FFA) in Zanthoxylum bungeanum seed oil (ZSO). A central composite rotatable design was used to investigate the effect of the methanol-to-oil molar ratio, catalyst amount and reaction time on the SnCl₄-catalyzed esterification of FFA. The methanol-to-oil molar ratio and reaction time clearly affected the conversion efficiency of FFA in the test ranges. Response surface methodology was used to optimize the conditions for SnCl₄-catalyzed esterification. A quadratic polynomial equation was obtained for conversion efficiency of FFA by multiple regression analysis and verification experiments confirmed the validity of the predicted model. Under the optimum conditions, the conversion efficiency of FFA in vegetable oil reached above 96 %. This study demonstrates the effectiveness of SnCl₄ as an acid catalyst for the reduction of high FFA content in vegetable oils to a low level by one-step esterification.     

Optimization of pretreatment reaction for methyl ester production from chicken fat

In biodiesel production, to use low cost feedstock such as rendered animal fats may reduce the biodiesel cost. One of the low cost animal fats is the chicken fat for biodiesel production. It is extracted from feather meal which is prepared from chicken wastes such as chicken feathers, blood, offal and trims after rendering process. However, chicken fats often contain significant amounts of FFA which cannot be converted to biodiesel using an alkaline catalyst due to the formation of soap. Therefore, the FFA level should be reduced to desired level (below 1%) by using acid catalyst before transesterification. For this aim, sulfuric, hydrochloric and sulfamic (amidosulfonic) acids were used for pretreatment reactions and the variables affecting the FFA level including alcohol molar ratio, acid catalyst amount and reaction time were investigated by using the chicken fat with 13.45% FFA. The optimum pretreatment condition was found to be 20% sulfuric acid and 40:1 methanol molar ratio based on the amount of FFA in the chicken fat for 80 min at 60 °C. After transesterification, the methyl ester yield was 87.4% and the measured fuel properties of the chicken fat methyl ester met EN 14214 and ASTM D6751 biodiesel specifications.     

A hybrid feedstock for a very efficient preparation of biodiesel

Biodiesel has been synthesized from karanja, mahua and hybrid {karanja and mahua (50:50 v/v)} feedstocks. A high yield in the range of 95-97% was obtained with all the three feedstocks. Conversion of vegetable oil to fatty acid methyl esters was found to be 98.6%, 95.71% and 94% for karanja, mahua and hybrid feedstocks respectively. The optimized reaction parameters were found to be 6:1 (methanol to oil) molar ratio, H₂SO₄ (1.5% v/v), at 55 ± 0.5 °C for 1 h during acid esterification for the three feedstocks. During alkaline transesterification, a molar ratio of 8:1 (methanol to oil), 0.8 wt.% KOH (wt/wt) at 55 ± 0.5 °C for 1 h was found to be optimum to achieve high yield for karanja oil. For mahua oil and the hybrid feedstock, 6:1 (methanol to oil) molar ratio, 0.75 (w/w) KOH at 55 ± 0.5 °C for 1 h was optimum for alkaline transesterification to obtain a high yield. High yield and conversion from hybrid feedstock during transesterification reaction was an indication that the reaction was not selective for any particular oil. ¹H NMR has been used for the determination of conversion of the feedstock to biodiesel.     

Biodiesel synthesis via homogeneous Lewis acid-catalyzed transesterification

Lewis acids (AlCl₃ or ZnCl₂) were used to catalyze the transesterification of canola oil with methanol in the presence of terahydrofuran (THF) as co-solvent. The conversion of canola oil into fatty acid methyl esters was monitored by ¹H NMR. NMR analysis demonstrated that AlCl₃ catalyzes both the esterification of long chain fatty acid and the transesterification of vegetable oil with methanol suggesting that the catalyst is suitable for the preparation of biodiesel from vegetable oil containing high amounts of free fatty acids. Optimization by statistical analysis showed that the conversion of triglycerides into fatty acid methyl esters using AlCl₃ as catalyst was affected by reaction time, methanol to oil molar ratio, temperature and the presence of THF as co-solvent. The optimum conditions with AlCl₃ that achieved 98% conversion were 24:1 molar ratio at 110 °C and 18 h reaction time with THF as co-solvent. The presence of THF minimized the mass transfer problem normally encountered in heterogeneous systems. ZnCl₂ was far less effective as a catalyst compared to AlCl₃, which was attributed to its lesser acidity. Nevertheless, statistical analysis showed that the conversion with the use of ZnCl₂ differs only with reaction time but not with molar ratio.     

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.     

Study on the glycerolysis reaction of high free fatty acid oils for use as biodiesel feedstock

Biodiesel is the main alternative to fossil diesel and it may be produced from different feedstocks such as semi-refined vegetable oils, waste frying oils or animal fats. However, these feedstocks usually contain significant amounts of free fatty acids (FFA) that make them inadequate for the direct base catalyzed transesterification reaction (where the FFA content should be lower than 4%). The present work describes a possible method for the pre-treatment of oils with a high content of FFA (20 to 50%) by esterification with glycerol. In order to reduce the FFA content, the reaction between these FFA and an esterification agent is carried out before the transesterification reaction. The reaction kinetics was studied in terms of its main factors such as temperature, % of glycerin excess, % of catalyst used, stirring velocity and type of catalyst used. The results showed that glycerolysis is a promising pre-treatment to acidic oils or fats (> 20%) as they led to the production of an intermediary material with a low content of FFA that can be used directly in the transesterification reaction for the production of biodiesel.     

Optimization of biodiesel production from crude palm oil using ultrasonic irradiation assistance and response surface methodology

BACKGROUND: Production of biodiesel from crude palm oil (CPO) with 6 wt% of free fatty acid (FFA) using a low‐frequency ultrasonic irradiation (40 kHz) technique was investigated in the present work. The objective of this study was to determine the relationship between various important parameters of the alkaline catalyzed transesterification process to obtain a high conversion to biodiesel. Response surface methodology (RSM) was used to statistically analyze and optimize the operating parameters of the process. A central composite design (CCD) was adopted to study the effects of the methanol to oil molar ratio, the catalyst concentration, reaction temperature, and irradiation time on conversion to biodiesel. RESULTS: The result from the RSM analysis indicated that the methanol to oil molar ratio, catalyst concentration and irradiation time have the most significant effects on the conversion to biodiesel. Moreover, a coefficient of determination (R²) value of 0.93 shows the fitness of a second‐order model for the present study. Based on this second‐order model, the optimum conditions for alkaline catalyzed transesterification of CPO were found to be a methanol to oil molar ratio of 6.44:1, catalyst concentration 1.25 wt%, reaction temperature 38.44 °C and irradiation time 25.96 min. At the calculated optimum condition, the conversion to biodiesel reached 97.85%. Under these same conditions, the experimental value was 98.02 ± 0.6%. CONCLUSIONS: The mathematical model developed has been proven to adequately describe the range of the experimental parameters studied and provide a statistically accurate prediction of the optimum conversion to biodiesel. Copyright © 2011 Society of Chemical Industry     

Application of full factorial design and Doehlert matrix for the optimisation of beef tallow methanolysis via homogeneous catalysis

The transesterification of triglycerides by means of alkaline catalysts is the most widely used route for biodiesel production and reaction optimisation by multivariate methods has been used for biodiesel production from different vegetable oils. However, the application of simultaneous optimisation for biodiesel production from beef tallow has received little attention. In an effort to optimize the beef tallow biodiesel production, a combination of the full factorial design and the Doehlert matrix was applied, and the effects of temperature, reaction time, catalyst concentration and alcohol:tallow molar ratio and their reciprocal interactions were assessed. The response variables under study were purity and yield of the final biodiesel product. In the selected condition [alcohol:tallow molar ratio (M) = 7.5:1, catalyst:tallow mass ratio (C) = 1.5%, reaction time (t) = 20 min and temperature = 50 °C], the conversion yield of tallow biodiesel was 88.4% and the purity was 99.4%. The final biodiesel obtained was analysed and showed to have good quality characteristics.     

Optimization of ultrasonic-assisted heterogeneous biodiesel production from palm oil: A response surface methodology approach

The use of ultrasonic processor in the heterogeneous transesterification of palm oil for biodiesel production has been investigated. Response surface methodology was employed to statistically evaluate and optimize the biodiesel production process catalyzed by two alkaline earth metal oxide catalysts i.e. BaO and SrO. SEM, surface analysis, AAS analysis and the Hammett indicator methods were used for characterization of the catalysts. Four different variables including reaction time (10-60 min), alcohol to oil molar ratio (3:1-15:1), catalyst loading (0.5-3.0 wt.%) and ultrasonic amplitude (25-100%) were optimized. Mathematical models were developed and used to predict the behavior of the process. The models were able to accurately predict the biodiesel yield with less than 5% error for both catalysts. The basic strength of the catalysts was the main reason of their high activities. This study confirmed that the ultrasonic significantly improved the process by reducing the reaction time to less than 50 min and the catalyst loading to 2.8 wt.% to achieve biodiesel yields of above 95%. The optimum alcohol to oil ratio was found to be at 9:1 while the best amplitudes were ∼ 70 and ∼ 80% for the BaO and SrO catalysts, respectively.     

Rape oil transesterification over heterogeneous catalysts

This work studies the application of KNO₃/CaO catalyst in the transesterification reaction of triglycerides with methanol. 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, amount of KNO₃ impregnated in CaO, the total catalyst content, reaction temperature, agitation rate, and the methanol/oil 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, cetane index, saponification value, iodine value, acidity index, CFPP (cold filter plugging point), flash point and combustion point, according to ISO norms. The results showed that calcium oxide, impregnated with KNO₃, have a strong basicity and high catalytic activity as a heterogeneous solid base catalyst.The biodiesel with the best properties was obtained using an amount of KNO₃ of 10% impregnated in CaO, a methanol/oil molar ratio of 6:1, a reaction temperature of 65 °C, a reaction time of 3.0 h, and a catalyst total content of 1.0%. In these conditions, the oil conversion was 98% and the final product obtained had very similar characteristics to a no. 2 diesel, and therefore, these methyl esters might be used as an alternative to fossil fuels.