Continuous transesterification of biodiesel in a helicoidal reactor using recycled oil

The main problem with biodiesel is the high cost of oils made from oleaginous crops. For this reason, various raw materials have been analysed with a view to reducing production costs and obtaining a product that can compete with the price of petrodiesel. Recycled oil is one of the most promising alternatives in the production of biodiesel because not only is the cheapest raw material but it also avoids the expense of treating the oil as a residue.Another way to reduce costs is to make the process more economical. Conventional technology uses sodium hydroxide as the basic catalyst and large-scale batch reactors, whose mechanical agitation requires high energy consumption due to residence times of at least 60 min and temperatures of 60 °C.In this paper we use a recycled pretreated oil to compare conventional transesterification with continuous transesterification in a tubular reactor. In this reactor the reactants (oil, methanol and sodium hydroxide) flow through a helicoidal tube submerged in a heating bath at 60 °C. The reactor has five outlets distributed non-uniformly to enable samples to be taken at different reaction times. This is to reduce the reaction time and avoid the need for mechanical agitation. With the aim of improving the quality of the biodiesel obtained, we varied the helicoidal system by incorporating a static micromixer and supplying energy in the form of ultrasound from the heating bath. This reactor produced biodiesel and glycerine at compositions roughly equal to those obtained in the batch process (89% FAME content at 75 min) but did so continuously (2.5 mL/min) and just 13 min after the reactants were integrated in a single line using a T device. Both the oil and the biodiesel were characterized and analysed in accordance with European standard UNE EN14214 for biodiesel.     

Biodiesel production using supercritical methanol/carbon dioxide mixtures in a continuous reactor

Fatty acid methyl esters (biodiesel) were produced by the transesterification of triglycerides with compressed methanol (critical point at 240 °C and 81 bar) in the presence of solid acids as heterogeneous catalyst (SAC-13). Addition of a co-solvent, supercritical carbon dioxide (critical point at 31 °C and 73 bar), increased the rate of the supercritical alcohols transesterification, making it possible to obtain high biodiesel yields at mild temperature conditions. Experiments were carried out in a fixed bed reactor, and reactions were studied at 150-205 °C, mass flow rate 6-24 ml/min at a pressure of 250 bar. The molar ratio of methanol to oil, and catalyst amount were kept constant (9 g). The reaction temperature and space time were investigated to determine the best way for producing biodiesel. The results obtained show that the observed reaction rate is 20 time faster than conventional biodiesel production processes. The temperature of 200 °C with a reaction time of 2 min were found to be optimal for the maximum (88%) conversion to methyl ester and the free glycerol content was found below the specification limits.     

Biodiesel production from vegetable oil using heterogenous acid and alkali catalyst

Zanthoxylum bungeanum seed oil (ZSO) with high free fatty acids (FFA) can be used for biodiesel production by ferric sulfate-catalyzed esterification followed by transesterification using calcium oxide (CaO) as an alkaline catalyst. Acid value of ZSO with high FFA can be reduced to less than 2 mg KOH/g by one-step esterification with methanol-to-FFA molar ratio 40.91:1, ferric sulfate 9.75% (based on the weight of FFA), reaction temperature 95 °C and reaction time 2 h, which satisfies transesterification using an alkaline catalyst. The response surface methodology (RSM) was used to optimize the conditions for ZSO biodiesel production using CaO as a catalyst. A quadratic polynomial equation was obtained for biodiesel conversion by multiple regression analysis and verification experiments confirmed the validity of the predicted model. The optimum combination for transesterification was methanol-to-oil molar ratio 11.69:1, catalyst amount 2.52%, and reaction time 2.45 h. At this optimum condition, the conversion to biodiesel reached above 96%. This study provided a practical method to biodiesel production from raw feedstocks with high FFA with high reaction rate, less corrosion, less toxicity, and less environmental problems.     

Analysis of parameters and interaction between parameters of the microwave-assisted continuous transesterification process of Jatropha oil using response surface methodology

A simple continuous process was designed for the transesterification of Jatropha curcas (J. curcas) oil to alkyl esters using microwave-assisted method. The product with purity above 96.5% of alkyl ester is called the biodiesel fuel. Using response surface methodology, a series of experiments with three reaction factors at three levels were carried out to investigate the transesterification reaction in a microwave and conversion of alkyl ester from J. curcas oil with NaOH as the catalyst. The results showed that the ratio of methanol to oil, amount of catalyst and flow rate have significant effects on the transesterification and conversion of alkyl ester. Based on the response surface methodology using the selected operating conditions, the optimal ratio of methanol to oil, amount of catalyst and flow rate of transesterification process were 10.74, 1.26 wt% and 1.62 mL/min, respectively. The largest predicted and experimental conversions of alkyl esters (biodiesel) under the optimal conditions are 99.63% and 99.36%, respectively. Our findings confirmed the successful development of a two-step process for the transesterification reaction of Jatropha oil by microwave-assisted heating, which is effective and time-saving for alkyl ester production.     

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.     

Production of biodiesel from palm oil using liquid core lipase encapsulated in κ-carrageenan

This work deals with the enzymatic transesterification of palm oil with methanol in a solvent-free system. Among the five lipases tested in the initial screening, lipase PS from Burkholderia cepacia resulted in the highest triglyceride conversion. Lipase PS was further investigated in a novel immobilized form by encapsulating within a biopolymer, κ-carrageenan. Using the immobilized lipase the production parameters of biodiesel from palm oil were optimized. The optimal conditions for processing 10 g of palm oil was: 30 °C, 1:7 oil/methanol molar ratio, 1 g water, 5.25 g immobilized lipase, 72 h reaction time and 23.7g relative centrifugal force. At the optimal conditions, triglyceride conversion of up to 100% could be obtained. The immobilized lipase was stable and retained 82% relative transesterification activity after five cycles. Liquid core lipase encapsulated in κ-carrageenan could be a potential immobilized catalyst for eco-friendly production of biodiesel.     

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.     

Variables affecting the in situ transesterification of microalgae lipids

This paper describes the effect of important reaction variables on the production of biodiesel from non-edible microalgae lipids, using the acid-catalysed in situ transesterification process. The specific gravity of the biodiesel product was used to monitor the conversion progress. The results indicate that increasing the reacting alcohol volume and the temperature lead to improved fatty acid methyl ester (FAME) conversions. With the exception of in situ transesterification carried out at room temperature (23 °C), the equilibrium FAME conversions appear to approach asymptotic limits for reaction times greater than 8 h for all temperatures investigated. Stirring the reaction vessel had a significant positive influence on the rate of biodiesel formation. Increasing the moisture content of the microalgae biomass had a strong negative influence on the equilibrium FAME yield, and in situ transesterification was inhibited when the biomass water content was greater than 115% w/w (based on oil weight).     

Producing biodiesel from high free fatty acids waste cooking oil assisted by radio frequency heating

Efficient biodiesel conversion from waste cooking oil with high free fatty acids (FFAs) was achieved via a two-stage procedure (an acid-catalyzed esterification followed by an alkali-catalyzed transesterification) assisted by radio frequency (RF) heating. In the first stage, with only 8-min RF heating the acid number of the waste cooking oil was reduced from 68.2 to 1.64 mg KOH/g by reacting with 3.0% H₂SO₄ (w/w, based on oil) and 0.8:1 methanol (weight ratio to waste oil). Then, in the second stage, the esterification product (primarily consisting of triglycerides and fatty acid methyl esters) reacted with 0.91% NaOH (w/w, based on triglycerides) and 14.2:1 methanol (molar ratio to triglycerides) under RF heating for 5 min, and an overall conversion rate of 98.8 ± 0.1% was achieved. Response surface methodology was employed to evaluate the effects of RF heating time, H₂SO₄ dose and methanol/oil weight ratio on the acid-catalyzed esterification. A significant positive interaction between RF heating time and H₂SO₄ concentration on the esterification was observed.     

Production of biodiesel through optimized alkaline-catalyzed transesterification of rapeseed oil

Present work reports an optimized protocol for the production of biodiesel through alkaline-catalyzed transesterification of rapeseed oil. The reaction variables used were methanol/oil molar ratio (3:1-21:1), catalyst concentration (0.25-1.50%), temperature (35-65 °C), mixing intensity (180-600 rpm) and catalyst type. The evaluation of the transesterification process was followed by gas chromatographic analysis of the rapeseed oil fatty acid methyl esters (biodiesel) at different reaction times. The biodiesel with best yield and quality was produced at methanol/oil molar ratio, 6:1; potassium hydroxide catalyst concentration, 1.0%; mixing intensity, 600 rpm and reaction temperature 65 °C. The yield of the biodiesel produced under optimal condition was 95-96%. It was noted that greater or lower the concentration of KOH or methanol than the optimal values, the reaction either did not fully occur or lead to soap formation.The quality of the biodiesel produced was evaluated by the determinations of important properties such as density, specific gravity, kinematic viscosity, higher heating value, acid value, flash point, pour point, cloud point, combustion point, cold filter plugging point, cetane index, ash content, sulphur content, water content, copper strip corrosion value, distillation temperature and fatty acid composition. The produced biodiesel was found to exhibit fuel properties within the limits prescribed by the latest American Standards for Testing Material (ASTM) and European EN standards.     

Intensification of biodiesel synthesis using metal foam reactors

This study presents a technology for continuous and high-efficiency alkali-catalyzed biodiesel synthesis using a metal foam reactor combined with a passive mixer. A metal foam reactor with higher pore density produces smaller droplets that result in higher efficiency of biodiesel synthesis. Compared with conventional stirred reactors, the time for high methyl ester conversion can be shortened remarkably by the use of metal foam reactors. Experimental results reveal that a metal foam reactor of 50 pores per inch exhibits an energy consumption per gram biodiesel of 1.01 J g⁻¹, merely 1.69% and 0.77% of energy consumption of the zigzag micro-channel and conventional stirred reactors, respectively. Moreover, biodiesel yield per reactor for the metal foam reactor is approximately 60 times that of the zigzag micro-channel reactor, thus overcoming the problem of numbering up an excessive number of reactors in the application. These results indicate the great potential of metal foam reactors in small-fuel biodiesel processing plants for distributive applications.     

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.     

Alkali catalyzed transesterification of safflower seed oil assisted by microwave irradiation

The safflower (Carthamus tinctorius L.) oil was extracted from the seeds of the safflower that grows in Diyarbakir, SE Anatolia of Turkey. Biodiesel has been prepared from safflower seed by transesterification of the crude oil under microwave irradiation, with methanol to oil molar ratio of 10:1, in the presence of 1.0% NaOH as catalyst. The conversion of C. tinctorius oil to methyl ester was over 98.4% at 6 min. The important fuel properties of safflower oil and its methyl ester (biodiesel) such as density, kinematic viscosity, flash point, iodine number, neutralization number, pour point, cloud point, cetane number are found out and compared to those of no. 2 petroleum diesel, ASTM and EN biodiesel standards. Compared with conventional heating methods, the process using microwaves irradiation proved to be a faster method for alcoholysis of triglycerides with methanol, leading to high yields of biodiesel.     

Biodiesel production from Croton megalocarpus oil and its process optimization

Production of biodiesel from non-edible feedstocks is attracting more attention than in the past, for the purpose of manufacturing alternative fuels without interfering with the food chain. Biodiesel was produced using Croton megalocarpus oil as a non-edible feedstock. C. megalocarpus oil was obtained from north Tanzania. This study aimed at optimizing the biodiesel production process parameters experimentally. The parameters involved in the optimization process were the amount of the catalyst, of alcohol, temperature, agitation speed and reaction time. The optimum biodiesel conversion efficiency obtained was 88% at the optimal conditions of 1.0 wt.% amount of potassium hydroxide catalyst, 30 wt.% amount of methanol, 60 °C reaction temperature, 400 rpm agitation rate and 60 min reaction time. The properties of croton biodiesel which were determined fell within the recommended biodiesel standards. Croton oil was found with a free fatty acid content of 1.68% which is below the 2% recommended for the application of the one step alkaline transesterification method. The most remarkable feature of croton biodiesel is its cold flow properties. This biodiesel yielded a cloud and pour point of −4 °C and −9 °C, respectively, while its kinematic viscosity lay within the recommended standard value. This points to the viability of using croton biodiesel in cold regions.     

麻疯树籽制备生物柴油的中试研究

以100 L反应釜进行了制备麻疯树生物柴油的中试实验,并研究了反应温度、醇油比、催化剂用量、搅拌速率对转化率的影响。实验结果表明,最佳反应条件为:反应温度60℃,醇油质量比为1∶4.5,催化剂KOH用量为油重1.2%,搅拌速率150 r/min,反应60 min时转化率达到最高值98.3%。所得产品基本达到GB/T20828—2007《柴油机燃料调合用生物柴油(BD100)》所规定的技术要求,净热值达到0#柴油的90.1%。     

Kalsilite based heterogeneous catalyst for biodiesel production

Kalsilite (KAlSiO₄) was used as a heterogeneous catalyst for transesterification of soybean oil with methanol to biodiesel. Kalsilite showed relatively low catalytic activity for transesterification reaction. The catalytic activity of this catalyst was significantly enhanced by introducing a small amount of lithium nitrate by the impregnation method. A biodiesel yield of 100% and a kinematic viscosity of 3.84 cSt were achieved at a mild temperature of only 120 °C over this lithium modified kalsilite catalyst (2.3 wt.% Li).     

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.     

A simple device to test biodiesel process intensification

In this paper, we have studied the KOH catalyzed transesterification reaction of vegetable oil with methanol in a tubular reactor filled with small spheres of stainless steel of different sizes. Three different packed bed configurations have been tested corresponding to different fluid dynamic situations. The first configuration corresponds to the tubular reactor filled with spheres of 2.5 mm of diameters; in the second configuration an opportune amount of spheres of 1 mm has been added to the mentioned spheres of 2.5 mm for filling the void volume of the octahedral cavities between the bigger spheres; in the third configuration an opportune amount of spheres of 0.39 mm has been added to spheres of 2.5 mm for filling the void volume of the tetrahedral cavities between the bigger spheres. The three mentioned configurations give place to the formation of micro-channels with an approximated size of respectively 1000 μm, 500 μm and 300 μm. These systems, subjected to fluid dynamic characterization, have shown a very high local turbulence (static mixer), in particular, when a packed bed reactor with dual size packing is used. Then, kinetic transesterification runs have been made by using the three mentioned packed bed reactors and a very high productivity has been obtained as a consequence of the induced local micro-mixing. A simplified kinetic model has been developed, which is able to describe many runs in batch conditions reported by the literature. This model resulted unsuitable to simulate the continuous runs performed in the described packed bed reactors. Our conclusion is that monophasic models, often proposed in the literature, are not able to describe the kinetic behavior of KOH catalysed transesterification in microchannels devices. At last, the described microchannels device represents, as it will be discussed, an ideal connection between a traditional tubular packed bed reactor and the recently appeared microreactors that are very efficient in mass and energy transfer operations for process intensification.     

Production of biodiesel through transesterification of Jatropha oil using KNO3/Al2O3 solid catalyst

The purpose of the work to study biodiesel production by transesterification of Jatropha oil with methanol in a heterogeneous system, using alumina loaded with potassium nitrate as a solid base catalyst. Followed by calcination, the dependence of the conversion of Jatropha oil on the reaction variables such as the catalyst loading, the molar ratio of methanol to oil, reaction temperature, agitation speed and the reaction time was studied. The conversion was over 84% under the conditions of 70 °C, methanol/oil mole ratio of 12:1, reaction time 6 h, agitation speed 600 rpm and catalyst amount (catalyst/oil) of 6% (w). Kinetic study of reaction was also done.