Continuous production of soybean biodiesel with compressed ethanol in a microtube reactor using carbon dioxide as co-solvent

This work investigates the production of fatty acid ethyl esters (FAEE) from the transesterification of soybean oil in supercritical ethanol in a continuous catalyst-free process using carbon dioxide as co-solvent. The experiments were performed in a microtube reactor in the temperature range of 523 K to 598 K, from 10 MPa to 20 MPa, oil to ethanol molar ratio from 1:20 to 1:40, and co-solvent to substrates mass ratio from 0.05:1 to 0.2:1. Results showed that ethyl esters yield obtained increased with increasing addition of carbon dioxide to the system. Considerable reaction yields were achieved at 598 K, 20 MPa, oil to ethanol molar ratio of 1:20 and using a CO₂ to substrate mass ratio of 0.2:1.     

Continuous production of soybean biodiesel with compressed ethanol in a microtube reactor

This work investigates the production of fatty acid ethyl esters (FAEEs) from the transesterification of soybean oil in supercritical ethanol in a continuous catalyst-free process. Experiments were performed in a microtube reactor in the temperature range of 523 K to 598 K, from 10 MPa to 20 MPa, varying the oil to ethanol molar ratio from 1:10 to 1:40, and evaluating the effects of addition of carbon dioxide as co-solvent. Results showed that ethyl esters yield obtained in the microtube reactor (inner diameter 0.76 mm) were higher than those obtained in a tubular reactor (inner diameter 3.2 mm) possibly due to improved mass-transfer conditions attained inside the microtube reactor. Non-negligible reaction yields (70 wt.%) were achieved along with low total decomposition of fatty acids (< 5.0 wt.%). It is shown that the use of carbon dioxide as co-solvent in the proposed microtube reactor did not significantly affect the ethyl esters yield within the experimental variable ranges investigated.     

Continuous enzymatic production of biodiesel from virgin and waste sunflower oil in supercritical carbon dioxide

A continuous process for biodiesel production in supercritical carbon dioxide was implemented. In the transesterification of virgin sunflower oil with methanol, Lipozyme TL IM led to fatty acid methyl esters yields (FAME) that exceeded 98% at 20 MPa and 40 °C, for a residence time of 20 s and an oil to methanol molar ratio of 1:24. Even for moderate reaction conversions, a fractionation stage based on two separators afforded FAME with >96% purity. Lipozyme TL IM was less efficient with waste cooking sunflower oil. In this case, a combination of Lipozyme TL IM and Novozym 435 afforded FAME yields nearing 99%.     

Hydro-liquefaction of woody biomass in sub- and super-critical ethanol with iron-based catalysts

Hydro-liquefaction of a woody biomass (Jack pine powder) in sub-/super-critical solution of ethanol without and with iron-based catalysts (5 wt% FeS or FeSO₄) was investigated with a stainless steel micro-reactor (10 mL) at temperatures of 473-623 K and an initial pressure of hydrogen varying from 2.0 to 10.0 MPa. Without catalyst, the oil yields were in the range of 17% and 44%, depending on temperature, reaction time and initial pressure of hydrogen. With catalysts, the Oil yields significantly increased while the yields of solid residue and gases and water decreased. A high oil yield of 63% was obtained with FeSO₄ at 623 K and 5 MPa of H₂ for 40 min. The elemental analyses and GC/MS measurements for the Oils revealed that the liquid products have much higher heating values than the crude wood sample and phenolic compounds were dominant in the Oils, irrespective of whether or what catalyst was used.     

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.     

Macauba oil as an alternative feedstock for biodiesel: Characterization and ester conversion by the supercritical method

In this work different samples of Brazilian macauba oil obtained from mechanical pressing were characterized and production of esters of fatty acids using a catalyst-free continuous process under supercritical alcohols was assessed. Analysis of oil samples showed that the major fatty acid on pulp oil was oleic acid (mean value 62.8%), the amount of free fatty acid (FFA) was very high (37.4–65.4%), samples contained glycerides (7.4–16.5% TAG, 14.2–16.8% DAG and 1.0–3.4% MAG) and moisture was around 1.0%. Oil was processed in a continuous reactor using supercritical methanol or ethanol and the effects of temperature (573, 598, 623 and 648 K), pressure (10, 15 and 20 MPa), oil to alcohol molar ratio (1:20, 1:30 and 1:40), water concentration (0, 5 and 10 wt% added) and the flow rate of reaction mixture (1.0, 1.5, 2.0, 2.5 and 3.0 mL/min) on process efficiency were evaluated. The highest ester content achieved in reactions with supercritical methanol was 78.5% (648 K, 15 MPa, 1:30 oil:methanol molar ratio, 5 wt% water and 2.5 mL/min flow rate), while with supercritical ethanol was 69.6% (598 K, 15 MPa, 1:30 oil:ethanol molar ratio, 5 wt% water and 2.0 mL/min flow rate). The extent of the reaction was explored using a novel parameter, convertibility, which corresponds to the maximum ester content attainable from the feedstock. According to the convertibility of macauba pulp oil, the highest ester content corresponded to efficiencies of 98.0% and 86.9%, respectively. Results demonstrate that macauba oil might be a potential alternative for biodiesel production, though purification steps should be taken into account to achieve biodiesel specifications.     

Simultaneous Enzymatic Transesterification and Esterification of an Acid Oil Using Fermented Solid as Biocatalyst

This work studied the enzymatic synthesis of fatty acid ethyl esters (FAEE) for potential use as biodiesel via simultaneous esterification and transesterification of acid oil from macaúba in a solvent-free system. A fermented and dry babassu cake with lipase activity from Rhizomucor miehei was used as biocatalyst. FAEE content above 85% was achieved after 96 h of reaction with enzyme loading of 13 U per g of oil, 120 mmol of hydrous ethanol (95% ethanol and 5% water)/20 mmol of oil (molar ratio ethanol:oil of 6:1), at 40 °C. After two consecutive enzymatic reactions, 90.8 wt% FAEE content was obtained. These results demonstrate a promising transesterification/esterification method for FAEE production from an acid and low-cost oil and the process has potential to decrease the costs of enzymatic biodiesel production.     

Study on supercritical extraction of lipids and enrichment of DHA from oil-rich microalgae

The present study aims to isolate the lipids from microalgae by supercritical CO₂ (SC-CO₂) extraction followed by a further enrichment of crude lipids to produce high-purity docosahexenoic acid (DHA) by an urea complexation method. Our systematic approach indicates the optimum conditions of supercritical CO₂ extraction were obtained as follows: 35 MPa, 40 °C, ethanol (95%, v/v) as the co-solvent, and the mass ratio of material to co-solvent 1:1. Under these conditions, 33.9% of lipid yield and 27.5% of DHA content were achieved. Despite the relatively low lipid yield, supercritical CO₂ extraction has exhibited many advantages over the Soxhlet extraction for the DHA enrichment such as high DHA purity and superb product quality. Furthermore, urea complexation method on DHA enrichment considerably increased the DHA purity from 29.7% to 60.4% with an enrichment ratio of 60.6%, under the optimum complexation conditions of urea/fatty acid 2:1, complexation time 8 h, and the complexation temperature of −10 °C.     

Fatty acid ethyl esters production from distillers corn oil by enzymatic catalysis

Distillers corn oil (DCO), a by-product from the corn ethanol production, is an alternative source of glycerides to produce biodiesel. In the present work, this feedstock was enzymatically converted into fatty acid ethyl esters (FAEE). DCO presented relative density of 0.912 g/cm³, peroxide index of 3.05 ± 0.3 (meq/1000 g of sample) and acidity of 13.1 ± 1.96 (wt.%), with prevalence of the oleic (18:1) and linoleic (18:2) acids (sum equal to 76.9%). Three strategies were evaluated to improve the FAEE content: ethanol stepwise addition (ethanol:oil molar ratio of 4:1 (1/2 of ethanol at 0 and 1.5 h) and 3:1 (1/3 of ethanol at 0 h and 2/3 at 1.5 h or 1/3 of ethanol at 0, 1 and 2 h)); consecutive reactions (with Novozym 40086 [Rhizomucor miehei lipase] as biocatalyst); and mixture of enzymes (Novozym 40086 (6 wt.%) + Novozym 435 (Candida antarctica B lipase) (2 wt.%). The concept of combi-lipases was evaluated for the first time using this raw material, resulting in a high ester content (>96%). The higher ester yields attained with DCO, compared to refined corn oil (33%) can be related to the better solubilization of ethanol and/or glycerol by-product in the medium with DCO. The combi-lipase system kept high than 80% of this initial activity after three repeated batches of reaction. The use of DCO enables the integration of corn ethanol and biodiesel production within the same general facility, which has logistic, environmental and, economic relevance.     

Transesterification of castor oil assisted by microwave irradiation

Microwave assisted transesterification of castor bean oil was carried out in the presence of methanol or ethanol, using a molar ratio alcohol/castor bean oil of 6:1, and 10% w/w of acidic silica gel or basic alumina (in relation to the oil mass) as catalyst. Under acid catalysis, the reaction occurred with satisfactory yields using H₂SO₄ immobilized in SiO₂, methanol under conventional conditions (60 °C for 3 h) as well as using microwave irradiation for 30 min. The best results were obtained under basic conditions (Al₂O₃/50% KOH) using methanol and conventional (60 °C, stirring, 1 h) or microwave conditions (5 min). In comparison with conventional heating, the catalyzed alcoholysis assisted by microwaves is much faster and leads to higher yields of the desired fatty esters.     

Near-critical carbon dioxide extraction of khoa (Satureja boliviana Benth Briq) using ethanol as a co-solvent: Experiment and modeling

In this work the volatile oil from khoa was extracted using pressurized CO₂ with and without ethanol as co-solvent. Kinetic experiments were performed at pressures of 6.5 and 7 MPa and temperatures of 294.15 K. The composition of the volatile oil was determined using gas chromatography. The volatile oil was formed predominantly by cymene, 1-8 cineole, isomenthone, pulegone, thymol and caryophyllene. Consequently, we present a mathematical modeling study of the extraction of essential oil from khoa. The overall extraction curves (OECs) obtained for khoa oil were modeled considering the mass transfer based on local equilibrium between solvent and a solid. The influence of pressure and co-solvent on the extraction kinetics was evaluated using a mathematical modeling. The model was solved numerically and validated with experimental data. A novel method for calculating the initial mass fraction of khoa-extract is proposed; data of the proposed model are in excellent agreement with the experimental data. Furthermore, the influence of fluid flow rate and particle size has been studied on the extraction efficiency. Finally, a methodology has been established to estimate extraction yield curves in large scale using the data obtained in small-scale experiments.     

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.     

Base/acid-catalyzed FAEE production from hydroxylated vegetable oils

In this study was developed a new methodology to produce fatty acid ethyl esters from castor oil. The base-catalyzed transesterification step was followed by on pot addition of sulfuric acid. That addition implicated the successful separation of FAEEs/glycerin phases due to soap breaking. The study was carried out through an experimental design where the variables studied in the first step were the molar ratio alcohol:oil and the catalyst amount in the transesterification process. As expected, the on pot addition of concentrated sulfuric acid yields FFAs that increase the acid value in the FAEEs phase. A second step esterification of these free fatty acids from FAEE raw mixture was investigated. The esterification of FFA was carried out in 60:1 and 80:1 M ratios (alcohol:free fatty acids) and concentrated sulfuric acid 5% and 10% w/w (based on free fatty acids). Consequently, these two steps yielded more fatty ethyl esters and assure that the following important requirements in the FAEEs production process from castor oil are satisfied: complete reaction, best separation of FAEEs/glycerin phases, removal of catalyst, limpid glycerin, and absence of free fatty acids.     

Supercritical fluid extraction of flavonoids from Maydis stigma and its nitrite-scavenging ability

Supercritical fluid carbon dioxide (SF-CO₂) extraction (SFE) of flavonoids from Maydis stigma and its nitrite-scavenging ability were investigated. The effects of extraction time, particle size and co-solvent composition in terms of water content in ethanol were first optimized. Then, a Box-Behnken design combined with response surface methodology (RSM) was employed to study the effects of three independent variables (temperature, pressure and co-solvent amount) on the extraction yield of flavonoids. A maximal extraction yield of flavonoids of approximately 4.24 mg/g of M. stigma by SFE was obtained under optimal conditions (a temperature of 50.88 °C, a pressure of 41.80 MPa, a co-solvent amount of 2.488 mL/g and an extraction time of 120 min with 0.4-mm particle sizes and 20% aqueous ethanol as the co-solvent). Furthermore, the nitrite-scavenging ability of the flavonoid-enriched SFE extracts was assessed using the Griess reagent. The flavonoid-enriched SFE extracts exhibited the highest scavenging ability on nitrite (88.1 ± 3.04%) at the concentration of 500 μg/mL and at pH 3.0. The nitrite-scavenging ability of the extracts appeared to be concentration dependent but negatively correlated with the pH.     

Stability of ethyl esters from soybean oil exposed to high temperatures in supercritical ethanol

It is well known that during the supercritical alcoholysis of vegetable oils the main transesterification reaction occurs simultaneously to several decomposition phenomena, In order to separately study the effect of such phenomena, pure ethyl esters from soybean oil (SBOEE) were mixed with ethanol at a molar ratio 40:3 (ethanol:SBOEE) and exposed for different periods to supercritical conditions in a continuous system, at 20 MPa and different temperatures from 250 to 375 °C. It was experimentally observed that the ester content of the processed samples were lower than that corresponding to the original SBOEE, indicating the occurrence of decomposition processes, which were more important as the temperature increased and the flow rate diminished. The content of polyunsaturated esters of the treated SBOEE was lower than that of the starting mixture, showing that the decomposition rate was highly dependent on the nature and instauration degree of the alkyl chain.     

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.     

Application of response surface methodology for optimization of biodiesel production by transesterification of soybean oil with ethanol

In this paper, the transesterification of soybean oil with ethanol is studied. The transesterification process can be affected by differing parameters. The biodiesel production process was optimized by the application of factorial design 2⁴ and response surface methodology. The combined effects of temperature, catalyst concentration, reaction time and molar ratio of alcohol in relation to oil were investigated and optimized using response surface methodology. Optimum conditions for the production of ethyl esters were the following: mild temperature at 56.7 °C, reaction time in 80 min, molar ratio at 9:1 and catalyst concentration of 1.3 M.     

Interfacial tension of marine lipids in contact with high pressure carbon dioxide

Interfacial tension (IFT) of fish oil triglycerides (TG) and fatty acid ethyl esters (FAEE) in contact with carbon dioxide (CO₂) was measured according to the pendant drop method at 40, 55 and 70 °C and pressures up to 25 MPa. The IFT of both TG and FAEE decreased substantially with CO₂ pressure. The IFT of FAEE vanished at elevated pressures, whereas that of TG decreased to a fairly constant level of about 2 mN/m. The IFT was correlated using a model taking into account the density, pressure and temperature of CO₂, thereby facilitating the calculation of the ideal pendant drop volume as well as the surface excess concentration of CO₂. In the pressure range studied, the pendant drop volume for FAEE decreased with pressure, whereas for TG it increased at elevated presssures due to the predominant effect of buoyancy. Furthermore, the change in IFT over time was determined at 55 °C for TG in contact with CO₂ at pressures up to 11.4 MPa showing a decrease of IFT over time at low pressures, whereas at higher pressures it remained nearly constant. IFT influences drop formation as well as the disintegration of falling films thereby affecting the performance of separation processes.     

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.