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.     

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.     

连续化条件下超临界甲醇法制备生物柴油

在连续操作的管式反应器中,以大豆油为原料在压力11～19MPa,温度240～400℃的超临界甲醇条件下进行连续化制备生物柴油的研究。考察了在连续反应条件下醇油摩尔比、压力、温度、停留时间及共溶剂对大豆油转化率的影响。实验结果表明:较高的醇油摩尔比有利于油脂转化率的提高,但当醇油摩尔比超过40:1后提高醇油摩尔比对提高油脂转化率的影响不大;在11～15MPa范围内,压力升高对油脂转化率影响很大,但高于15MPa后压力对转化率的影响减弱;反应温度对油脂转化率有着重要影响,在300℃以上随着温度的升高,油脂转化率有较大幅度的上升,但温度太高油脂会发生分解反应;醇油摩尔比40:1,温度350℃,压力15MPa,停留时间1000s是该实验获得的最佳反应条件,在该条件下油脂转化率可达89%。实验还研究了添加共溶剂四氢呋喃对油脂转化率的影响。     

A review of laboratory-scale research on lipid conversion to biodiesel with supercritical methanol (2001-2009)

Biodiesel production from lipids (vegetable oils and animal fats) with non-catalytic supercritical methanol (SCM) has several advantages over that of homogeneous catalytic process, including a high production efficiency, environmentally friendliness and a wide range of possible feedstocks. This article reviews the effect of the operating parameters on the lipid conversion to biodiesel with SCM, such as the temperature, pressure, methanol to oil molar ratio, and reaction time, for both batch and continuous systems, including the effect of the mixing intensity and dispersion in tubular reactors. The operating temperature is the key parameter to control either extent of reaction or other parameters. Studies on evaluating the chemical kinetics, phase behavior, binary vapor-liquid equilibrium (VLE) of lipid conversion in SCM are summarized. The pseudo-first order model is suitable to simplify the system at high methanol to oil molar ratios, but it is inadequate at a low methanol concentration which instead requires the second order model. Transition temperatures of reaction mixture depend on the critical point of reaction mixture which is assigned by methanol to oil molar ratio and amount of co-solvents in the system. For binary VLE studies, no single thermodynamic model for the overall process is available, probably because of the differences in the polarity between the initial and the final state of the reaction system. Since traditional operating parameters of the lipid conversion in SCM involve elevated temperatures and pressures, techniques for allowing milder operating conditions that employ the addition of co-solvents or catalysts are discussed. The ongoing and more extensive research on co-solvents, heterogeneous catalysts, phase behavior and multicomponent VLE of lipid conversion to biodiesel with SCM should provide a better understanding and achieve the goal of green biodiesel production technology in the near future.     

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

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

Kinetics of hydrolysis and methyl esterification for biodiesel production in two-step supercritical methanol process

For high-quality biodiesel fuel production from oils/fats, the catalyst-free two-step supercritical methanol process has been developed in a previous work, which consists of hydrolysis of triglycerides to fatty acids in subcritical water and subsequent methyl esterification of fatty acids to their methyl esters in supercritical methanol. In this paper, therefore, kinetics in hydrolysis and subsequent methyl esterification was studied to elucidate reaction mechanism. As a result, fatty acid was found to act as acid catalyst, and simple mathematical models were proposed in which regression curves can fit well with experimental results. Fatty acid was, thus, concluded to play an important role in the two-step supercritical methanol 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.     

Biodiesel production from soybean oil and methanol using hydrotalcites as catalyst

Esters of fatty acids, derived from vegetable oils or animal fats, and known as biodiesel, are a promising alternative diesel fuel regarding the limited resources of fossil fuels and the environmental concerns. In this work, methanolysis of soybean oil was investigated using Mg-Al hydrotalcites as heterogeneous catalyst, evaluating the effect of Mg/Al ratio on the basicity and catalytic activity for biodiesel production. The catalysts were prepared with Al/(Mg + Al) molar ratios of 0.20, 0.25 and 0.33, and characterized by X-ray diffraction (XRD), textural analysis (BET method) and temperature-programmed desorption of CO₂ (CO₂-TPD). When the reaction was carried out at 230 °C with a methanol:soybean oil molar ratio of 13:1, a reaction time of 1 h and a catalyst loading of 5 wt.%, the oil conversion was 90% for the sample with Al/(Mg + Al) ratio of 0.33. This sample was the only one to show basic sites of medium strength. We also investigated the reuse of this catalyst, the effect of calcination temperature and made a comparison between refined and acidic oil.     

Continuous production of biodiesel fuel from vegetable oil using supercritical methanol process

A system for continuous transesterification of vegetable oil using supercritical methanol was developed using a tube reactor. Increasing the proportion of methanol, reaction pressure and reaction temperature can enhance the production yield effectively. However, side reactions of unsaturated fatty acid methyl esters (FAME) occur when the reaction temperature is over 300 °C, which lead to much loss of material. There is also a critical value of residence time at high reaction temperature, and the production yield will decrease if the residence time surpasses this value. The optimal reaction condition under constant reaction temperature process is: 40:1 of the molar ratio of alcohol to oil, 25 min of residence time, 35 MPa and 310 °C. However, the maximum production yield can only be 77% in the optimal reaction condition of constant reaction temperature process because of the loss caused by the side reactions of unsaturated FAME at high reaction temperature. To solve this problem, we proposed a new technology: gradual heating that can effectively reduce the loss caused by the side reactions of unsaturated FAME at high reaction temperature. With the new reaction technology, the methyl esters yield can be more than 96%.     

Biodiesel production using supercritical alcohols with a non-edible vegetable oil in a batch reactor

In the present work, the transesterification of non-edible oil with methanol and ethanol is studied. The reactor phase transitions are directly observed in a double windowed cylindrical reactor and the conversion to fatty esters is measured. The optimization of the process conditions was carried out based on a statistical design of experiments where the key process variables were studied over different ranges to obtain a reliable model for the efficiency of the reaction as a function of reaction time, temperature, pressure and alcohol to oil molar ratio. From direct observations and the modeling of the phase behavior, a better understanding of the supercritical alcohol transesterification process is obtained as well as the confirmation of the phase equilibrium predictions based on the GCA-EOS model.     

Palm oil transesterification in sub- and supercritical methanol with heterogeneous base catalyst

An environmentally benign process for the production of methyl ester using γ-alumina supported heterogeneous base catalyst in sub- and supercritical methanol has been developed. The production of methyl ester in refluxed methanol conventionally utilized double promoted γ-alumina heterogeneous base catalyst (CaO/KI/γ-alumina); however, this process requires a large amount of catalyst and a long reaction time to produce a high yield of methyl ester. This study carries out methyl ester production in sub- and supercritical methanol with the introduction of an optimized catalyst used in the previous work for the purpose of improving the process and enhancing efficiency. CaO/KI/γ-Al₂O₃ catalyst was prepared by precipitation and impregnation methods. The effects of catalyst amount, reaction temperature, reaction time, and the ratio of oil to methanol on the yield of biodiesel ester were studied. The reaction was carried out in a batch reactor (8.8 ml capacity, stainless steel, AKICO, Japan). Results show that the use of CaO/KI/γ-Al₂O₃ catalyst effectively reduces both reaction time and required catalyst amount. The optimum process conditions were at a temperature of 290 °C, ratio of oil to methanol of 1:24, and a catalyst amount of 3% over 60 min of reaction time. The highest yield of biodiesel obtained under these optimum conditions was almost 95%.     

New process for catalyst-free biodiesel production using subcritical acetic acid and supercritical methanol

The production of glycerol as a by-product is unavoidable in the current conventional biodiesel manufacturing processes. Since biodiesel production is expected to increase in the near future, effective utilization of glycerol will become an issue of interest. In this study, therefore, a process consisting of subcritical acetic acid treatment to convert rapeseed oil to fatty acids and triacetin followed by conversion of the obtained fatty acids to their fatty acid methyl esters in supercritical methanol treatment was investigated. The obtained results clearly revealed that this two-step reaction could proceed effectively at a high reaction rate, and that fatty acid methyl esters and triacetin could be obtained under milder reaction condition than the one-step process utilizing supercritical methyl acetate and supercritical methanol.     

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.     

Biodiesel production from supercritical carbon dioxide extracted Jatropha oil using subcritical hydrolysis and supercritical methylation

This study investigates supercritical carbon dioxide (SC-CO₂) extraction of triglycerides from powdered Jatropha curcas kernels followed by subcritical hydrolysis and supercritical methylation of the extracted SC-CO₂ oil to obtain a 98.5% purity level of biodiesel. Effects of the reaction temperature, the reaction time and the solvent to feed ratio on free fatty acids in the hydrolyzed oil and fatty acid esters in the methylated oil via two experimental designs were also examined. Supercritical methylation of the hydrolyzed oil following subcritical hydrolysis of the SC-CO₂ extract yielded a methylation reaction conversion of 99%. The activation energy of hydrolysis and trans-esterified reactions were 68.5 and 45.2 kJ/mole, respectively. This study demonstrates that supercritical methylation preceded by subcritical hydrolysis of the SC-CO₂ oil is a feasible two-step process in producing biodiesel from powdered Jatropha kernels.     

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.     

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.     

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.     

Biodiesel production from waste cooking oil via alkali catalyst and its engine test

Waste cooking oils (WCO), which contain large amounts of free fatty acids produced in restaurants, are collected by the environmental protection agency in the main cities of China and should be disposed in a suitable way. Biodiesel production from WCO was studied in this paper through experimental investigation of reaction conditions such as methanol/oil molar ratio, alkaline catalyst amount, reaction time and reaction temperature which are deemed to have main impact on reaction conversion efficiency. Experiments have been performed to determine the optimum conditions for this transesterification process by orthogonal analysis of parameters in a four-factor and three-level test. The optimum experimental conditions, which were obtained from the orthogonal test, were methanol/oil molar ratio 9:1, with 1.0 wt.% sodium hydroxide, temperature of 50 °C and 90 min. Verified experiments showed methanol/oil molar ratio 6:1 was more suitable in the process, and under that condition WCO conversion efficiency led to 89.8% and the physical and chemical properties of biodiesel sample satisfied the requirement of relevant international standards. After the analysis main characteristics of biodiese sample, the impact of biodiesel/diesel blend fuels on an YC6M220G turbo-charge diesel engine exhaust emissions was evaluated compared with 0# diesel. The testing results show without any modification to diesel engine, under all conditions dynamical performance kept normal, and the B20, B50 blend fuels (include 20%, 50% crude biodiesel respectively) led to unsatisfactory emissions whilst the B′20 blend fuel (include 20% refined biodiesel) reduced significantly particles, HC and CO etc. emissions. For example CO, HC and particles were reduced by 18.6%, 26.7% and 20.58%, respectively.     

Continuous production of biodiesel with supercritical methanol: Optimization of a scale-up plug flow reactor by response surface methodology

A scale-up plug flow reactor was evaluated for the continuous production of biodiesel from refined palm kernel oil (PKO) with supercritical methanol and optimized by response surface methodology. The effects of the operating temperature (270–350 °C), pressure (15.0–20.0 MPa) and methanol:PKO molar ratio (20:1–42:1) were evaluated at a constant residence time of 20 ± 2 min by using a central composite design. Analysis of variance demonstrated that a modified quadratic regression model gave the best coefficient of determination (R² = 0.9615) and adjusted coefficient of determination (Adj. R² = 0.9273). The interaction terms in the regression model illustrated small synergistic effects of both temperature–pressure and temperature–methanol:PKO molar ratio. The optimal conditions were 325 ± 5 °C, 18.0 ± 0.5 MPa and a methanol:PKO molar ratio of 42 ± 2:1, attaining a maximum production rate of 18.0 ± 1.5 g biodiesel/min with a fatty acid methyl ester content of 93.7 ± 2.1%. The product obtained from the optimal conditions had high cetane number, and could be considered as a fuel additive for cetane number enhancement.