Biodiesel from soybean oil,castor oil and their blends

Even not being described in the EN 14112 standard, PDSC has been used for the determination of the biodiesel oxidative stability, by OIT and OT measurements. In this study, biodiesel blends were obtained by mixing soybean (BES) and castor (BEM) ethyl esters and its induction periods were measured by Rancimat and PDSC. The blends (BSM _X ) showed intermediate values of OSI, OT, and OIT, compared with BES and BEM. Although, the molar fraction of the components varied linearly in BSM _X , OSI, OT, and OIT values increased exponentially in relation to the castor biodiesel amount in the blends. Introduction of castor oil biodiesel increased the blend stability, so the BSM₃₀ blend reached the OSI limit of 6 h. OSI, OIT, and OT showed a high-linear correlation, pointing out that PDSC can be used in the analysis of this kind of biodiesel, with a smaller sample and analysis time, as compared to Rancimat. The use of biodiesel blends was a good alternative in the correction of the oxidative stability of the final product without the need of antioxidant addition.     

Thermal characterization of the poultry fat biodiesel

Chemical composition of oils and fats used in the biodiesel synthesis can influence in processing and storage conditions, due to the presence of unsaturated fatty acids. An important point is the study of the biodiesel thermal stability to evaluate its quality using thermal analysis methods. In this study the thermal stabilities of the poultry fat and of their ethyl (BEF) and methyl (BMF) biodiesels were determined with the use of thermogravimetry (TG/DTG), differential thermal analysis (DTA) and differential scanning calorimetry (DSC), in different atmospheres. The TG/DTG curves of the poultry fat in synthetic air presented three decomposition steps while only one step was observed in nitrogen (N₂) atmosphere. The DSC results indicated four exothermic enthalpic transitions in synthetic air and an endothermic transitions in N₂ atmosphere attributed to the combustion process and to the volatilization and/or decomposition of the fatty acids, respectively. For both biodiesels the TG/DTG curves in air indicated two mass loss steps. In the DSC curves four exothermic transitions were observed in synthetic air besides an endothermic one in N₂ atmosphere.     

Comparative study of biodiesel oxidation stability using Rancimat,PetroOXY, and low P-DSC

Oxidation stability of biodiesel is one of the most important factors used to evaluate its quality, allowing its commercialization and ensuring its shelf life. In this context, several accelerated methods have been used to measure oxidative stability to predict the maximum storage time at which biodiesel can be submitted without compromising its quality. In the present study, the oxidation stability of two commercial biodiesel and of their blends with two antioxidants was evaluated using the standard methods described in the EN 14214 norm (Rancimat Method) and in ASTM D7545 (PetroOXY method), as well as by low pressurized differential scanning calorimetry (low P-DSC). Both biodiesel were obtained from soybean oil, produced by methylic and ethylic route. The antioxidants, which were used in different concentrations, have the following active components: bisphenol and phenol. The three assessed methodologies can be used to determine the effect of the commercial antioxidants on the oxidative stability of the studied biodiesel. As each method is based on the measurement of different parameters to obtain the respective oxidation induction time, their results cannot be compared directly. But when the results are expressed in terms of the percentage change of the respective oxidation induction times, there is a higher correlation between those obtained by Rancimat and PetroOXY methods than when compared with the results obtained by low P-DSC. Because of their characteristics, the bisphenolic antioxidant is more effective than the phenolic one and, at a same antioxidant concentration, the oxidation stability of the ethylic biodiesel is higher than that of the methylic one. Considering analysis time and sensitivity, the low P-DSC method is the one that better attends both parameters among the applied methods.     

Determination of the oxidative stability of hazelnut oils by PDSC and Rancimat methods

The present study was conducted to determine the oxidative stability of hazelnut oil and compare it with more common and previously tested olive oil and rapeseed oil. The oxidative stability was determined by means of two independent methods, pressure differential scanning calorimetry (PDSC), and oxidative stability index (OSI) using TA Instruments DSC and Metrohm Rancimat equipment, respectively. Both the PDSC and Rancimat devices were set at five different isothermal temperatures in the range of 100–140 °C. The times to reach peak maximum (τ _max) obtained from PDSC exotherms were statistically related with the Rancimat induction times (τ _on) to obtain correlation coefficient >0.99 within linear relation. Based on the Arrhenius equation and activated complex theory, activation energies (E _a), pre-exponential factors (Z), and specific rate constants (k) for studied oils oxidations were calculated. To the best of our knowledge, this is the first study dealing with oxidative stability of hazelnut oil using PDSC technique. According to the results obtained, PDSC seems to be useful and quick method for kinetic analysis of lipid oxidation in hazelnut oil.     

Influence of the storage on the thermo-oxidative stability of methyl and ethyl esters by PDSC

Biodiesel oxidation is a complex process widely influenced by the chemical composition of the biofuel and storage conditions. Several oxidation products can be formed from these processes, depending on type and amount of the unsaturated fatty acid esters. In this work, fatty acid methyl and ethyl esters were obtained by base-catalyzed transesterification of soybean oil and physicochemically characterized according to standards from ASTM, EN, and ABNT. The thermal and oxidative stabilities of biodiesel samples were investigated during the storage process by pressure differential scanning calorimetry (PDSC) and by viscosity measurements. Absolute viscosities of biodiesels after accelerated aging were also determined. The viscosity increased as the aging temperature and time were raised. The results showed that oxidation induction can occur during storage, decreasing the biodiesel stability. PDSC analysis showed that during storage under climate simulation the values of high-pressure oxidative induction times (HPOIT) were reduced for both FAEE and FAME.     

An alternative method by pressurized DSC to evaluate biodiesel antioxidants efficiency

The purpose of this article is to present an alternative method developed using pressurized differential scanning calorimetry (P-DSC) to evaluate the oxidative behavior of biodiesel obtained from soybean oil, produced by ethylic route (BSET), with and without the addition of synthetic antioxidants, as well as to compare the results with those obtained by Rancimat Method, which were carried out according to the European Official Standard Method EN 14112. BSET samples were analyzed using four different types of synthetic antioxidants at concentrations varying between 250, 500, and 1000 mg kg⁻¹. The measurements done by P-DSC were performed using static air at 80 psi and isothermal conditions at 110 °C, the same operating temperature than the Rancimat method. The experimental results of the oxidative stability measured from both methods have shown good correlations, which depend on the antioxidant, showing a gradual improvement in the oxidative stability of BSET with increasing added concentration of antioxidants. Opposite result behavior occurred for the measurements done in the presence of one of the antioxidants, which was composed by a significant content of components volatile below 110 °C, which accelerate the induction of the biodiesel oxidation in P-DSC method, but apparently do not interfere in the electrical conductivity measurement method (Rancimat). The advantages of the developed method using P-DSC technique with respect to Rancimat method is that it allows one to use a smaller sample, increases sensitivity to antioxidant action, reduces the analysis time for the evaluation of the antioxidant efficiency and detects any occurring oxidative process, independently of the volatility of the formed products, which may form oxidated products that remain in the liquid phase and that are non detectable by Rancimat method.     

Evaluating antioxidants efficiency during storage of ethylic and methylic biodiesel by low pressurized DSC and Rancimat methods

Efficiencies of four commercial antioxidants used during the storage of two biodiesel, BS-ethyl and BS-methyl, respectively obtained from soybean oil by ethylic and methylic routes, were evaluated by measuring their oxidative stability using a low pressurized DSC (low P-DSC) method developed by the authors and by Rancimat method, which is specified by the American ASTM D6751 and European EN 14214 standard methods. The operating temperature of the low P-DSC method was the same as that used in the Rancimat procedure (110 °C). The antioxidants, used in 500 mg kg^?1 content, have the following active components: phenol, biphenol, phenol + amine mixture, and a hydroquinone + organic acid mixture. Samples of each biodiesel–antioxidant mixture were evaluated simultaneously by the two methods, right after their preparation and 30, 60, 90, and 120 days of storage at 23 ± 1 °C. A non-dimensional oxidative induction time parameter, defined as the ratio between the oxidation induction time (OIT) or induction time (IT) values at a storage time t and at t = 0, was used to evaluate the antioxidant activity. For the same mixture, changes of this non-dimensional parameter calculated from OIT or IT show a similar trend with storage time, indicating that it can be determined either from low P-DSC or Rancimat method data. As the efficiency of the studied antioxidants depends on their composition, their interaction with each biodiesel, and on the storage time, this parameter can be used to indicate the best storage time for each antioxidant–biodiesel mixture.     

Analysis of thermal and oxidative stability of biodiesel from Jatropha curcas L. and beef tallow

The oxidation of oils and biodiesels occurs due to several factors: the quantity of double bonds and the presence of allylic and bis-allylic hydrogens. Esters (biodiesel) that have large amounts of unsaturated fatty acids are more susceptible to oxidation than saturated. The aim of this work was to analyze the thermal and oxidative stability of ethyl biodiesel from Jatropha curcas L. and beef tallow by thermogravimetric, pressure differential scanning calorimetry, and PetroOxy methods. The samples of biodiesel from beef tallow present higher oxidation stability compared to biodiesel from J. curcas. In relation to calorimetric curves of biodiesel from J. curcas and beef tallow stored by 60 days without and with antioxidant, there was verified displacement of peak temperature of the transition to higher temperatures, respectively. Just a sample of biodiesel from beef tallow stored for 60 days with 3,000 ppm of antioxidant t-butyl-hydroxyquinone was within the standard established by Brazilian National Agency of Petroleum, Natural Gas, and Biofuels (ANP). The biodiesel from beef tallow was more stable in terms of thermal and oxidative stability than biodiesel from J. curcas. The thermal and oxidative stability of biodiesel depends on its chemical structure; this corroborates the fact that the oils with a predominance of saturated fatty acids are more stable than the unsaturated.     

Sunflower biodiesel

The higher is the degree of unsaturation in ester chain of a biodiesel, the smaller is its oxidation stability. Sunflower biodiesel obtained by the ethyl route possesses a high amount of unsaturated fatty acids, mainly oleic acid (C18:1) and linoleic acid (C18:2), thus being more prone to the oxidation process. In Brazil, with the purpose of meeting the specifications of the Brazilian National Agency of Petroleum, Natural Gas and Biofuels (ANP), antioxidant additives, from synthetic and natural origins, have been added to the biofuel. Antioxidants are an alternative to prevent the oxidative deterioration of the fatty acid derivatives, as they are substances able to reduce the oxidation rate. In this study, the oxidative stability of sunflower biodiesel, obtained by the ethyl route and additivated with different concentrations of the antioxidants butylated hydroxytoluene (BHT) and t-butylhydroquinone (TBHQ), was evaluated by means of Pressure differential scanning calorimetry (P-DSC) and the Accelerated oxidative stability test (Rancimat, Method EN 14112). The results obtained by the two techniques showed the same oxidation tendency. Thus, P-DSC can be used as an alternative to determine the oxidative stability of biodiesel. The antioxidant TBHQ, added to biodiesel at the concentrations of 2000 and 2500 mg kg⁻¹, raised the oxidation induction time to a value higher than 6 h, the limit established by the Resolution ANP number 7/2008, thus being the best alternative among the studied antioxidants.     

Determination of the oxidation stability of biodiesel and oils by spectrofluorimetry and multivariate calibration

Oxidation stability is an important quality parameter for biodiesel. In general, the methods used to evaluate the oxidation stability of oils and biodiesels are time-consuming. This work reports the use of spectrofluorimetry, a fast analytical technique, associated with multivariate data analysis as a powerful analytical tool to prediction of the oxidation stability. The prediction of the oxidation stability showed a good agreement with the results obtained by the EN14112 reference method Rancimat. The models presented high correlation (0.99276 and 0.97951) between real and predicted values. The R² values of 0.98557 and 0.95943 indicated the accuracy of the models to predict the oxidation stability of soy oil and soy biodiesel, respectively. The residual distribution does not follow a trend with respect to the predicted variables indicating the good quality of the fits.     

Non-conventional oils for biodiesel production: a study of thermal and oxidative stability

Vegetable oils with variable proportions of oleic, linoleic, and linolenic acids are more susceptible to oxidative processes. In this subject, this study evaluates the physical chemical properties and oxidative stability of non-conventional oils such as andiroba, babassu, sesame, oiticica, jatropha, and grape through accelerated oxidation techniques (pressurized differential scanning calorimetry, Rancimat and PetroOxy). It was verified that babassu and andiroba oil do not showed detectable induction period presenting high oxidative stability; moreover, it was observed that the enthalpic events occurred in 1.19, >10, 0.53, 0.49, 0.49, and 0.60 h for the andiroba oil, babassu oil, sesame seeds, jatropha, oiticica oils, and grapes, respectively, stimulating the conclusion of greater stability for the babassu oil.     

不同酯基结构的棕榈油生物柴油的性能研究

以棕榈油为研究对象,分别与甲醇、乙醇、异丙醇和异丁醇进行酯交换反应制备了不同酯基结构的生物柴油。利用差示扫描量热仪和应力控制流变仪分析了不同酯基结构棕榈油生物柴油的结晶行为和低温流变性能,同时分析了酯基结构对生物柴油的氧化稳定性,40℃时的动力黏度、20℃时的密度等重要性质的影响。结果表明,随着醇的碳链长度的增加,棕榈油生物柴油的析蜡点和胶凝点均降低,特别是棕榈油异丁酯的析蜡点和胶凝点分别降低到了-2.57和-8.09℃,低温流动性得到了明显改善,且氧化诱导期略有延长,氧化稳定性有所改善。生物柴油的密度和黏度随着酯基结构的不同而有所变化,但其数值都符合中国生物柴油标准。     

Evaluation of the oxidative induction time of the ethilic castor biodiesel

Oxidative stability is very important in the quality control of oils and biodiesel. Chemical characteristics, as acid, iodine and peroxide values, show the differences among samples and can be used by industries to evaluate the oxidation degree. In relation to advanced techniques, the use of PDSC to measure the oxidative induction time is very important. These measurements were used to evaluate the properties of castor oil after refining process and consequently the biodiesel characteristics. Oxidative induction time indicated that biodiesel samples were more stable than the refined oils. The biodiesel obtained from neutralized oil had a higher stability being probably related to the acid value.     

Influence of the purification process on the stability of <Emphasis Type="Italic">Jatropha curcas</Emphasis> biodiesel

The aim of this work was to evaluate the influence of the purification process on the stability of Jatropha curcas biodiesel. The biodiesel was obtained using a variety of purification processes: three wet methods with different drying processes (vacuum oven, conventional oven and anhydrous sodium sulfate) and one dry method (purification with adsorbent magnesium silicate). Biodiesel was characterized through the analysis of carbon residue, acidity index, infrared and gas chromatography. The composition J. curcas oil indicated 56.3 % of unsaturated fatty acids and 43.7 % of saturated fatty acids. Jatropha oil presented high quantity of saturated acids, which are less susceptible at oxidation. The biodiesel sample that was chemically purified (PUsq) presented better purity, indicating be the process more efficient in remove the residues of synthesis. Thermogravimetric curves of purified biodiesel by wet method, PUsq, with chemical drying using anhydrous sodium sulfate, and PUsv, with vacuum drying, showed the highest initial decomposition temperatures, indicating higher thermal stability. The carbon residue and infrared analyses suggested that contamination by catalyst residue is a determining factor in reduction of the oxidative stability of biodiesel. The oxidative stability was evaluated using Rancimat and pressure differential scanning calorimetry. Biodiesel samples showing better oxidative stability were purified using PUsq and PUsv, which obtained stability of 6 h using the Rancimat technique, the minimum limit set by Brazilian legislation, without the addition of antioxidant, suggesting that these methods least influenced the stability of biodiesel.     

By-products from fruit processing

The oxidative stability of soybean oil added of extracts from by-products generated in the pulp processing of mango (CM), Barbados cherry (CB) and guava (CG), as well as the combination of these extracts with the antioxidants butylated hydroxytoluene (BHT) and tertiary butylhydroquinone (TBHQ), were evaluated by pressurized differential scanning calorimetry (P-DSC) and Rancimat methods. Among the extracts, that obtained from CB showed the highest content of total extractible phenolic. Soybean oil added of CM extract showed greater (p < 0.05) oxidative stability in Rancimat analysis, while by P-DSC method CB was the extract more effective (p < 0.05) to protect soybean oil. Soybean oil added of CB extract showed higher (p < 0.05) OIT values compared to those added of CM, CG and synthetic antioxidants BHT and TBHQ. The combination of CB, CM and CG extracts with TBHQ showed synergistic effects, while CM and CB combined with BHT showed antagonistic effect on oxidative stability in soybean oil. The OIT results obtained from analysis by P-DSC and the OSI results obtained by Rancimat showed Pearson moderate correlation (r = 0.42). These results suggest the CB, CM and CG extracts as good source of antioxidant compounds with potential for combined application with synthetic antioxidants to prevent oxidation in soybean oil.     

Evaluation of antioxidants on the thermo-oxidative stability of soybean biodiesel

This work shows the evaluation of three antioxidants (2,6-di-t-butyl-4-methylphenol (BHT)—synthetic antioxidant, hydrogenated cardanol (HC), and alkyl hydrogenated cardanol (AHC)—both derived from cashew nut shell liquid) on the thermo-oxidative stability of the soybean biodiesel. The antioxidants were added at concentrations of 200, 300, and 400 ppm, and the oxidative stability of the biofuel with and without antioxidants were investigated by thermogravimetric analysis (TG-DTG and IPDT) and Metrohm 743 Rancimat per the EN 14112 method. The results showed that all antioxidants contributed for the thermo-oxidative stability of the soybean biodiesel as follows: soybean biodiesel < soybean biodiesel + BHT < soybean biodiesel + HC < soybean biodiesel + AHC. In the Rancimat method, the results showed that the antioxidants influenced the biodiesel stability with an increase of at least 71 %.     

Thermal behaviors of soy biodiesel

Biodiesel is a prospective and promising fuel for diesel engines. However, some aspects need improvement, to develop into an ideal fuel, such as flow properties at low temperatures and storage stability at high temperatures with exposure to the air. Thermal analysis is an efficient tool for measuring properties, such as crystallization temperature, and thermal and oxidative stabilities. In this study, the thermal behaviors of biodiesel at low and high temperatures were investigated by using thermogravimetric analyzer, differential scanning calorimetry, pressurized differential scanning calorimetry (PDSC), and sorption analyzer (SA). The soy biodiesel was obtained through a transesterification reaction with a homogeneous catalyst. The constituents of the soy biodiesel as determined by gas chromatography show that methyl esters content was 99?% and of these 84?% were unsaturated fatty acids. TG results illustrate that the total weight loss of the biodiesel was 99?% below 300?°C under nitrogen flow, indicating a high purity biodiesel. The onset decomposition temperature and the peak temperatrue of the soy biodiesel were 193 and 225?°C, respectively, implying the biodiesel has good thermal stability. PDSC results show that the oxidation onset temperature of the soy biodiesel was 152?°C, and the oxidative induction time was 24?min. DSC results demonstrate that the onset crystallization temperature of the soy biodiesel was 1.0?°C. The SA results point out that with increasing temperature and humidity, the soy biodiesel absorbed more water, and in which humidity was the dominant factor. The water absorption and desorption of the soy biodiesel is a non-reversible process. The preferable storage conditions for soy biodiesel occur when humidity is less than 30?% and the temperature is less than 30?°C. In summary, thermal analysis is a faster alternative for thermal behavior studies as compared with conventional standard methods.     

Thermal stability evaluation of methylic biodiesel obtained for different oilseeds

Biodiesel is defined as a mixture of mono- or di-alquil esters of vegetable oil or animal fats. During long-term storage, oxidation caused by contact with air (autoxidation) presents a legitimate concern in relation to monitoring and maintaining fuel quality. Extensive oxidative degradation may compromise the quality by adversely affecting kinematic viscosity, acid value, or peroxide value. The oxidation susceptibility of biodiesel, due to the presence of triacilglycerides of poly-unsaturated fatty acids, was evaluated in this study. Samples of sunflower, castor, and soybean biodiesels were obtained through the transesterification reaction, with the intention of achieving the thermal stability study through thermogravimetrical analyses and differential scanning calorimetry high pressure. It was furthermore observed through thermogravimetry and pressure differential scanning calorimetry curves that castor biodiesel exhibited the highest thermal and oxidative stability.     

Oxidative stabilities of enzymatically interesterified goose fat and rapeseed oil blend by rancimat and PDSC

Goose fat (GF) and rapeseed oil (RSO) 2:3 m m^?1 blend was enzymatically interesterified at 60 °C with and without microwaves assistance. As the catalyst, a commercial preparation of the immobilized lipase from Rhizomucor miehei (Lipozyme RM IM) containing 2 % of water was used, and the catalyst load was 8 % in each case. The starting mixture and the interesterified products were separated by column chromatography into pure triacylglycerols fraction (TAG) and a non-triacylglycerol fraction, which contained free fatty acids (FFA), mono- and diacylglycerols (MAG and DAG). The oxidative stabilities of fats studied and TAG derived from them were assessed by Rancimat at 100 °C and by pressure differential scanning calorimetry (PDSC) under oxygen at 110–140 °C. Interesterification reduced the oxidative stability of GF and RSO blend. The main factors influenced on the oxidative stabilities of fats studied were concentrations of tocopherols and the presence of FFA, MAG and DAG. The structures of TAGs were of minor importance. From the resulting PDSC exotherms, their times to reach the onset (τ _on) and peak maximum (τ _max) were measured and used for calculations of parameters of the Arrhenius type kinetics for thermaloxidative decomposition of fats studied.     

Antioxidative properties of hydrogenated cardanol for cotton biodiesel by PDSC and UV/VIS

Biodiesel is a non-toxic biodegradable fuel that consists of alkyl esters produced from renewable sources, vegetal oils and animal fats, and low molecular mass alcohols, and it is a potential substitute for petroleum-derived diesel. Depending on the raw materials used, the amount of unsaturated fatty acids can vary in the biodiesel composition. Those substances are widely susceptible to oxidation processes, yielding polymeric compounds, which are harmful to the engines. Based on such difficulty, this work aims to evaluate the antioxidant activity of cashew nut shell liquid (cardanol), as additive for cotton biodiesel. The oxidative stability was investigated by the pressure differential scanning calorimetry (PDSC) and UV/Vis spectrophotometer techniques. The evaluated samples were: as-synthesized biodiesel — Bio T₀, additivated and heated biodiesel — Bio A (800 ppm L⁻¹ of hydrogenated cardanol, 150°C for 1 h), and a heated biodiesel — Bio B (150°C, 1 h). The oxidative induction time (OIT) analyses were carried out employing the constant volume operation mode (203 psi oxygen) at isothermal temperatures of 80, 85, 90, 100°C. The high pressure OIT (HPOIT) were: 7.6, 15.7, 22.7, 64.6, 124.0 min for Bio T₀; 41.5, 77.0, 98.6, 106.6, 171.9 min for Bio A and 1.7, 8.2, 14.8, 28.3, 56.3 min for Bio B. The activation energy (E) values for oxidative processes were 150.0±1.6 (Bio T₀), 583.8±1.5 (Bio A) and 140.6±0.1 kJ mol⁻¹(Bio B). For all samples, the intensities of the band around 230 nm were proportional to the inverse of E, indicating small formation of hyper conjugated compounds. As observed, cardanol has improved approximately four times the cotton biodiesel oxidative stability, even after the heating process.