Prediction of biodiesel properties and its characterization using fatty acid profiles

Biodiesel, the mono-alkyl esters of vegetable oils or animal fats, is an eco-friendly alternative to petrodiesel. The molecular structures of biodiesels, fatty acid methyl esters were applied to predict the characteristics of biodiesel fuels. Based on the structural similarity of biodiesel and petroleum fractions, molecular weight of biodiesel was correlated with other characteristics including boiling point, viscosity and specific-gravity in the form of three equations. For 24 different kinds of biodiesel, the minimum average relative deviation (ARD) of these correlations was calculated to be 0.68%. Moreover, two correlations were developed to predict viscosity and flash point of biodiesel as a function of weighted-average number of carbon atoms (N _C ) and weighted-average number of double bonds (N _DB ) with ARD 3.72% and 4.24% respectively. Also, a high degree of correlation was shown by the logarithmic function with ARD 0.30% between specific gravity and viscosity of biodiesel. Proposed predictive models were verified by experimental data.     

Analysis of oxidized biodiesel by 1H‐NMR and effect of contact area with air

Biodiesel is continuously gaining attention and significance as an alternative diesel fuel. An important issue facing biodiesel is fuel stability upon exposure to air due to its content of unsaturated fatty acids. Numerous factors influence the oxidative stability of biodiesel, and several methods for its assessment have been developed. In the present work, a defined amount of biodiesel (methyl soyate) was heated in open beakers, with the only difference being the size of the beaker, i.e. the surface area of the biodiesel exposed to air. Biodiesel oxidized in this fashion was analyzed by ¹H‐NMR, kinematic viscosity and acid value. Acid values and kinematic viscosity increased with time and surface area. A previously developed ¹H‐NMR procedure was used to evaluate the unsaturation and “residual” fatty acid composition. The amounts of saturated fatty acids determined by this method increased, with monounsaturated and diunsaturated species increasing and then decreasing with time. After “flash” (3 h, 165 °C) oxidation, NMR shows the greatest effect on saturates and compounds with two double bonds, the former increasing and the latter decreasing. The double bond originally located at δ15 in 18:3 is largely retained, showing that other double bond positions in 18:3 are initially affected by oxidation. The methyl ester signal decreases, coinciding with the increase in acid value. An increasingly strong absorption was observed in the UV‐VIS spectra. Increasing surface area accelerated oxidation and affected fatty acid composition.     

Predicting cetane number,kinematic viscosity,density and higher heating value of biodiesel from its fatty acid methyl ester composition

Biodiesel is a renewable bio-fuel derived from natural fats or vegetable oils, and it is considered as a promising alternative to substitute diesel fuels. Cetane number, viscosity, density, and higher heating value are important properties to affect the utilization of biodiesel fuels, because they are involved in the definition of fuel quality and are required as input data for predictive engine combustion models. This work presents the characterization of two biodiesel samples made from beef tallow and soybean oil through their fatty acid methyl esters (FAMEs) profile. Empirical equations were developed to estimate four physical properties of methyl esters; and an average absolute deviation (AAD) of 5.95%, 2.57%, 0.11% and 0.21% for the cetane number, kinematic viscosity, density, and higher heating value were founded. Cetane number, viscosity, and higher heating value increases because of the increase of molecular weight and these physical properties decrease as the number of double bonds increases. Unlike that of above properties, density decreases as molecular weight increases and density increases as the degree of unsaturation increases. Two general mixing rules and five biodiesel samples were used to study the influence of FAMEs over the physical properties of biodiesel. The prediction of the cetane number, kinematic viscosity, density and higher heating value of biodiesel is very close to the experimental values.     

Effect of antioxidants on the oxidative stability of methyl soyate (biodiesel)

Biodiesel, an alternative diesel fuel derived from transesterification of vegetable oils or animal fats, is composed of saturated and unsaturated long-chain fatty acid alkyl esters. When exposed to air during storage, autoxidation of biodiesel can cause degradation of fuel quality by adversely affecting properties such as kinematic viscosity, acid value and peroxide value. One approach for increasing resistance of fatty derivatives against autoxidation is to treat them with oxidation inhibitors (antioxidants). This study examines the effectiveness of five such antioxidants, tert-butylhydroquinone (TBHQ), butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), propyl gallate (PrG) and α-Tocopherol in mixtures with soybean oil fatty acid methyl esters (SME). Antioxidant activity in terms of increasing oxidation onset temperature (OT) was determined by non-isothermal pressurized-differential scanning calorimetry (P-DSC). Analyses were conducted in static (zero gas flow) and dynamic (positive gas flow) mode under 2000 kPa (290 psig) pressure and 5 °C/min heating scan rate. Results showed that PrG, BHT and BHA were most effective and α-Tocopherol least effective in increasing OT. Increasing antioxidant loading (concentration) showed sharp increases in activity for loadings up to 1000 ppm followed by smaller increases in activity at higher loadings. Phase equilibrium studies were also conducted to test physical compatibility of antioxidants in SME-No. 2 diesel fuel (D2) blends. Overall, this study recommends BHA or TBHQ (loadings up to 3000 ppm) for safeguarding biodiesel from effects of autoxidation during storage. BHT is also suitable at relatively low loadings (210 ppm after blending). PrG showed some compatibility problems and may not be readily soluble in blends with larger SME ratios. Although α-Tocopherol showed very good compatibility in blends, it was significantly less effective than the synthetic antioxidants screened in this work.     

Biodiesel from activated sludge through in situ transesterification

BACKGROUND: The microbial biomass present in activated sludge contains lipidic compounds that can be used as biodiesel feedstock. In this study, the production of biodiesel from activated sludge from Tuscaloosa, AL was optimized based on the yield of fatty acid methyl esters (FAMEs). In situ transesterification was used with sulfuric acid as catalyst. A general factorial design of 4 × 6 × 5 for temperature, methanol to sludge ratio and catalyst concentration, respectively, was considered for optimization. RESULTS: Biodiesel yield can be adequately described by the quadratic response surface model with R² of 0.843 and statistically insignificant lack of fit (p = 0.152). Numerical optimization showed that an optimum biodiesel yield of 4.88% can be obtained at 55 °C, 25 methanol to sludge ratio and 4% volume sulfuric acid. The optimum experimental biodiesel yield was indeed obtained at that condition but with a value of 4.79 ± 0.02%. The highest error was 2.30% which indicates good agreement between the model and the experimental data. CONCLUSIONS: Acid‐catalyzed polymerization of unsaturated fatty acids or their esters at temperature above 60 °C significantly decreased biodiesel yield. The fatty acid profile of the biodiesel produced indicates that activated sludge may be used as biodiesel feedstock. Copyright © 2009 Society of Chemical Industry     

Oxidative stability and storage behavior of fatty acid methyl esters derived from used palm oil

Fatty acid alkyl esters, especially FAME, are the most commonly used liquid biofuel. Because biofuels are expected to be important alternative renewable energy sources in the near future, more studies on their stability against oxidation need to be addressed. Biofuel derived from vegetable oils is well researched, currently with more attention focused on the reuse of waste oil sources than on pure vegetable oil for such production. A method to convert used palm oil, i.e., used frying oil, and residual oil of spent bleaching earths (SPE) to their respective methyl esters has been established by the Malaysian Palm Oil Board. These methyl esters can be used as diesel substitute. However, the methyl esters obtained from used frying oil have a low induction period (3.42 h). In Europe, any methyl esters must have an induction period of at least 6 h in Rancimat stability to be usable as biodiesel, as required by European Biodiesel Standard (EN 14214). To meet this requirement, the used frying oil methyl esters (UFOME) obtained can be treated with different types of antioxidants, either synthetic or natural, at different treatment levels, such as vitamin E, 3-ert-butyl-4-hydroxyanisole (BHA), 2,6-di-tert-butyl-4-methyl-phenol (BHT), 2,5-di-tert-butyl hydroquinone (TBHQ), and n-propyl gallate (PG), to investigate their oxidative stability and storage behavior. The order of increasing antioxidant effectiveness with respect to the oxidative stability of UFOME is: vitamin E<BHT<TBHQ<BHA<PG. Because methyl esters derived from residual oil of SBE have an induction period of 14.6 h, their treatment with antioxidants is unnecessary.     

The Effect of Antioxidants on Corn and Sunflower Biodiesel Properties under Extreme Oxidation Conditions

Biodiesel is an alternative to mineral fuels, with advantages such as biodegradability. However, this makes biodiesel unstable to oxidation. In this way, the use of natural or synthetic antioxidants is necessary. Although many studies have paid attention to the effect of these antioxidants on oxidation stability, not much literature about their effect of them on other properties (before and during storage) was found. The aim of this research study was to characterize biodiesel from corn and sunflower by adding two antioxidants, butylated hydroxyanisole (BHA) and tert-butylhydroquinone (TBHQ), in order to improve its oxidation stability. Moreover, the effect of oxidation on the parameters of biodiesel was studied by using extreme oxidation conditions to accelerate the oxidation process. Both antioxidants improved the oxidation stability of biodiesel, whereas some parameters were altered (viscosity and acid number), which could make this biofuel, if high concentrations of antioxidants are used, unsuitable for commercialization according to standards.     

The Influence of Tocopherols on the Oxidation Stability of Methyl Esters

Tocopherols were found to be the principal natural antioxidants in biodiesel grade fatty acid methyl esters. The stabilising effect of α-, γ- and δ- tocopherols from 250 to 2,000 mg/kg was evaluated by thermal and accelerated storage induction times based on rapid viscosity increase, in sunflower (SME), recycled vegetable oil (RVOME), rapeseed (RME) and tallow (TME) methyl esters. Both induction times showed that stabilising effect is of the order of δ- > γ- > α-tocopherol, and that the stabilising effect increased with concentration. The correlation between the two induction times however was poor, which is probably due to the fact that the time they correspond to two different stages of oxidation. Tocopherols were found to stabilise methyl esters by reducing the rate of peroxide formation while present. The deactivation rates of tocopherols increased with unsaturation of the particular methyl ester and in the present work they were of the order of SME > RME > RVOME > TME. While α-tocopherol was found to be a relatively weak antioxidants, both γ- and δ- tocopherols increased induction times significantly and should be added to methyl esters without natural antioxidants.     

Winterization of biodiesel by micro process engineering

A new method for winterization of biodiesel based on waste cooking oil is demonstrated, using micro heat exchangers with channel diameters of 200 μm. Biodiesel is pumped from a vessel through a micro heat exchanger in such a way, that pure seed crystals of saturated fatty acid methyl esters are produced at the outlet of the micro channels and injected back into the biodiesel vessel. Thus micro process engineering allows the reduction of the sum of saturated fatty acid methyl esters within biodiesel based on waste cooking oil from 21.3% to 9.6%. This corresponds to a reduction in CFPP value of 11 K, which means that this biodiesel can be used at temperatures down to 264 K.     

Synergistic Effects of Antioxidants on the Oxidative Stability of Soybean Oil- and Poultry Fat-Based Biodiesel

Biodiesel is an alternative fuel composed of saturated and unsaturated methyl ester fatty acids that is very prone to oxidation attack. Exposure to air, heat, light, and metallic contaminants can lead to autoxidation, and the degradation of fuel properties such as kinematic viscosity and total acid number. This study examines the effectiveness of blends of primary antioxidants from combinations of butylated hydroxyanisole (BHA), propyl gallate (PG), pyrogallol (PY) and tert-butyl hydroquinone (TBHQ) to increase oxidative stability. Results indicate that binary antioxidant formulations: TBHQ:BHA, TBHQ:PG and TBHQ:PY were most effective at 2:1, 1:1, 2:1 weight ratio, respectively in both distilled soybean oil- (DSBO) and distilled poultry fat- (DPF) based biodiesel. Antioxidant activity increased as the loadings were increased. The synergisms of the antioxidant pairs were different with different biodiesel types, suggesting a dependence on the fatty acid methyl ester (FAME) composition. The best synergistic effect was observed with the TBHQ:BHA blends while the best stabilization factors (SF) were achieved by using the TBHQ:PY blends. Quantification of antioxidant content in stored biodiesel with TBHQ:PY blend demonstrates that the main factor of synergy is the regeneration of PY by TBHQ.     

Effect of oxidation under accelerated conditions on fuel properties of methyl soyate (biodiesel)

Biodiesel derived from transesterification of soybean oil and methanol is an attractive alternative fuel for combustion in direct-injection compression ignition (diesel) engines. During long-term storage, oxidation due to contact with air (autoxidation) presents a legitimate concern with respect to maintaining fuel quality of biodiesel. This work examines the effects of oxidation under controlled accelerated conditions on fuel properties of methyl soyate (SME). SME samples from four separate sources with varying storage histories were oxidized at elevated temperature under a 0.5 standard cm³/min air purge and with continuous stirring. Results showed that reaction time significantly affects kinematic viscosity (ν). With respect to increasing reaction temperature, ν, acid value (AV), PV, and specific gravity (SG) increased significantly, whereas cold flow properties were minimally affected for temperatures up to 150°C. Antioxidants TBHQ and α-tocopherol showed beneficial effects on retarding oxidative degradation of SME under conditions of this study. Results indicated that ν and AV have the best potential as parameters for timely and easy monitoring of biodiesel fuel quality during storage.     

Identification, FT-IR, NMR (H and C) and GC/MS studies of fatty acid methyl esters in biodiesel from rocket seed oil

Biodiesel was synthesized from rocket seed oil by base-catalyzed transesterification with methanol. The synthesis of biodiesel was confirmed by FT-IR and NMR (¹H and ¹³C) spectroscopy. Various fuel properties of the synthesized biodiesel were determined using ASTM methods and discussed accordingly. A total of eleven fatty acid methyl esters (FAMEs) were identified in rocket seed oil biodiesel (RSOB) by the retention time and the fragmentation pattern data of GC/MS analysis. The identified FAMEs were, methyl 9-hexadecenoate (C16:1), 14-methyl pentadecanoate (C16:0), methyl 9,12-octadecadienoate (C18:2), methyl 9-octadecenoate (C18:1), methyl octadecanoate (C18:0), methyl 11-eicosenoate (C20:1), methyl eicosanoate (C20:0), methyl 13-docosenoate (C22:1), methyl docosanoate (C22:0), methyl 15-tetracosenoate (24:1) and methyl tetracosanoate (C24:0). The percentage conversion of triglycerides to corresponding methyl esters determined by ¹H NMR was 88.49%.     

Attempts to reduce NOx exhaust emissions by using reformulated biodiesel

Biodiesel is a renewable, domestically produced fuel that has been shown to reduce particulate, hydrocarbon, and carbon monoxide emissions from diesel engines. Under some conditions, however, biodiesel produced from certain feedstocks has been shown to cause an increase in nitrogen oxides (NO_x). This is of special concern in urban areas that are subject to strict environmental regulations. Although soy-based biodiesel may increase the emission of nitrogen oxides, it is the most easily accessible in North America. We investigated two routes to reformulate soy-based biodiesel in an effort to reduce nitrogen oxide emissions. In one of these, soy-oil methyl esters were modified by conversion of a proportion of the cis bonds in the fatty acid chains of its methyl esters to their trans isomers. In the other approach, polyol derivatives of soybean oil were transesterified to form soy methyl polyol fatty acid esters. The NO_x emissions of these modified biodiesels were then examined, using a Yanmar L100 single cylinder, four stroke, naturally aspirated, air cooled, direct injection diesel engine. Using either isomerized methyl oleate or isomerized soy biodiesel, at 20% blend level in petroleum diesel (‘B20’), nitrogen oxide emissions were elevated by between 1.5 and 3 percentage points relative to the combustion of a B20 blend of commercial biodiesel. Nitrogen oxide emissions were reduced in proportion to blend level during the combustion of polyol biodiesel, with a 20% blend in petrodiesel resulting in a reduction of about 4.5 percentage points relative to the emissions of a comparable blend of commercial soy biodiesel.     

Crystallization Behavior of Fatty Acid Methyl Esters

Biodiesel from most agricultural feedstocks has flow properties that are prone to startup and operability problems during cold weather. Biodiesel from soybean oil is generally a mixture of long-chain fatty acid alkyl esters composed of 0.15–0.20 mass fraction saturated esters (melting point [MP] ≫ 0 °C) mixed with unsaturated esters (MP < 0 °C). This work investigates the crystallization properties of two saturated fatty acid methyl esters (FAME) commonly found in biodiesel from soybean oil. Differential scanning calorimetry (DSC) heating and cooling scans of methyl palmitate (MeC16), methyl stearate (MeC18) and methyl oleate (MeC18:1) in pure form were analyzed. Crystallization behavior in ternary FAME mixtures was inferred by the application of thermodynamic models based on ideal solution and freezing-point depression theories. Activity coefficients for MeC16 and MeC18 in MeC18:1 solvent were determined by analyzing DSC cooling curves for binary FAME mixtures. Eutectic points were predicted by both models. Crystallization onset temperatures inferred from freezing point depression theory were more accurate than those for ideal solutions with respect to a direct DSC cooling curve analysis of corresponding ternary mixtures. This work shows that the crystallization onset temperature (cloud point) of biodiesel may be predicted by freezing-point depression theory if the activity coefficients of the component FAME are known. The use of trade, firm, or corporation names in this publication is for the information and convenience of the reader. Such use does not constitute an official endorsement or approval by USDA or ARS of any product or service to the exclusion of others that may be suitable.     

Methyl Esters (Biodiesel) from and Fatty Acid Profile of Gliricidia sepium Seed Oil

Increasing the supply of biodiesel by defining and developing additional feedstocks is important to overcome the still limited amounts available of this alternative fuel. In this connection, the methyl esters of the seed oil of Gliricidia sepium were synthesized and the significant fuel‐related properties were determined. The fatty acid profile was also determined with saturated fatty acids comprising slightly more than 35 %, 16.5 % palmitic, 14.5 % stearic, as well as lesser amounts of even longer‐chain fatty acids. Linoleic acid is the most prominent acid at about 49 %. Corresponding to the high content of saturated fatty acid methyl esters, cold flow is the most problematic property as shown by a high cloud point of slightly >20 °C. Otherwise, the properties of G. sepium methyl esters are acceptable for biodiesel use when comparing them to specifications in biodiesel standards but the problematic cold flow properties would need to be observed. The ¹H‐ and ¹³C‐NMR spectra of G. sepium methyl esters are reported.     

Production of mixed methyl/ethyl esters from waste fish oil through transesterification with mixed methanol/ethanol system

Biodiesel (mixed fatty acid methyl/ethyl esters) was prepared from waste fish oil through base-catalyzed transesterification with mixed methanol/ethanol system. Effect of methanol/ethanol (% v/v), type and concentration of the catalyst, mixed alcohols to oil molar ratio, the reaction temperature, and the reaction time on the biodiesel yield was optimized. Maximum biodiesel yield (97.30?wt%) was produced by implementing 1:1 methanol/ethanol (v/v), 1.0?wt% KOH, 6:1 mixed alcohols to oil molar ratio, 40°C reaction temperature, and 30?min of reaction time. Conversion of the waste fish oil to mixed methyl/ethyl esters was confirmed by ¹H NMR spectroscopy. Fuel properties of the resulting biodiesel in addition to its blends with petrodiesel were in good agreement with specifications of ASTM D6751 and ASTM D7467, respectively. Therefore, it was concluded that using mixed alcohol system for biodiesel production could reduce the production cost through reducing conditions required for maximum conversion.     

Kinematic viscosity of biodiesel components (fatty acid alkyl esters) and related compounds at low temperatures

Biodiesel, defined as the mono-alkyl esters of vegetable oils and animal fats is, has undergone rapid development and acceptance as an alternative diesel fuel. Kinematic viscosity is one of the fuel properties specified in biodiesel standards, with 40 °C being the temperature at which this property is to be determined and ranges of acceptable kinematic viscosity given. While data on kinematic viscosity of biodiesel and related materials at higher temperatures are available in the literature, this work reports on the kinematic viscosity of biodiesel and a variety of fatty acid alkyl esters at temperatures from 40 °C down to −10 °C in increments of 5 °C using the appropriately modified standard reference method ASTM D445. Investigating the low-temperature properties of biodiesel, including viscosity, of biodiesel and its components is important because of the problems associated with the use of biodiesel under these conditions. Such data may aid in developing biodiesel fuels optimized for fatty ester composition. An index termed here the low-temperature viscosity ratio (LTVR) using data at 0 °C and 40 °C (divide viscosity value at 0 °C by viscosity value at 40 °C) was used to evaluate individual compounds but also mixtures by their low-temperature viscosity behavior. Compounds tested included a variety of saturated, monounsaturated, diunsaturated and triunsaturated fatty esters, methyl ricinoleate, in which the OH group leads to a significant increase in viscosity as well as triolein, as well as some fatty alcohols and alkanes. Esters of oleic acid have the highest viscosity of all biodiesel components that are liquids at low temperatures. The behavior of blends of biodiesel and some fatty esters with a low-sulfur diesel fuel was also investigated.     

Branched‐Chain Fatty Acid Methyl Esters as Cold Flow Improvers for Biodiesel

Biodiesel is an alternative diesel fuel derived mainly from the transesterification of plant oils with methanol or ethanol. This fuel is generally made from commodity oils such as canola, palm or soybean and has a number of properties that make it compatible in compression‐ignition engines. Despite its many advantages, biodiesel has poor cold flow properties that may impact its deployment during cooler months in moderate temperature climates. This work is a study on the use of skeletally branched‐chain‐fatty acid methyl esters (BC‐FAME) as additives and diluents to decrease the cloud point (CP) and pour point (PP) of biodiesel. Two BC‐FAME, methyl iso‐oleate and methyl iso‐stearate isomers (Me iso‐C_18:1 and Me iso‐C_18:0), were tested in mixtures with fatty acid methyl esters (FAME) of canola, palm and soybean oil (CaME, PME and SME). Results showed that mixing linear FAME with up to 2 mass% BC‐FAME did not greatly affect CP, PP or kinematic viscosity (ν) relative to the unmixed biodiesel fuels. In contrast, higher concentrations of BC‐FAME, namely between 17 and 39 mass%, significantly improved CP and PP without raising ν in excess of limits in the biodiesel fuel standard specification ASTM D 6751. Furthermore, it is shown that biodiesel/Me iso‐C_18:0 mixtures matched or exceeded the performance of biodiesel/Me iso‐C_18:1 mixtures in terms of decreasing CP and PP under certain conditions. This was taken as evidence that additives or diluents with chemical structures based on long‐chain saturated chains may be more effective at reducing the cold flow properties of mixtures with biodiesel than structures based on long‐chain unsaturated chains.     

Transesterification of heated rapeseed oil for extending diesel fuel

Fatty acid methyl esters are well established as an alternative fuel called “biodiesel.” For economic reasons, used frying oil is an interesting alternative feedstock for biodiesel production. The chemical changes that occur during heating of rapeseed oil, especially the formation of polymers, were investigated. Heated rapeseed oil samples were transesterified with methanol and analyzed by size-exclusion chromatography. During heating, the amount of polymers in the starting oil increased up to 15 wt%, but only up to 5 wt% in the transesterified samples. So during transesterification, dimeric and trimeric triglycerides in the starting oil were mainly converted into monomeric and dimeric fatty acid methyl esters. The amount of polymeric fatty acid methyl esters had a negative influence on fuel characteristics. After 6 h of heating, the amount of Conradson carbon residue and after 16 h the viscosity exceeded that of the existing specifications for biodiesel. Therefore, the amount of polymers in waste oil is a good indicator for the suitability for biodiesel production. Presented in part at the 89th Annual Meeting, American Oil Chemists’ Society, Chicago, IL, May 1998.     

Determining the blend level of mixtures of biodiesel with conventional diesel fuel by fiber-optic near-infrared spectroscopy and 1H nuclear magnetic resonance spectroscopy

Biodiesel, defined as the alkyl esters (usually methyl esters) of vegetable oils, is miscible with conventional diesel fuel at all blend levels. Until the present time, no rapid and reliable analytical method has existed for determining the blend level of biodiesel in conventional diesel fuel. In the present work, near-infrared (NIR) and nuclear magnetic resonance (NMR) spectroscopies were used to determine the blend level of biodiesel in conventional diesel fuel. Several regions in the NIR region (around 6005 cm⁻¹ and 4800–4600 cm⁻¹) are suitable for this purpose. The method is rapid and easy to use, and does not require any hardware changes when using the same instrument for monitoring the biodiesel-producing transesterification reaction and determining biodiesel fuel quality. In ¹H NMR spectroscopy, the integration values of the peaks of the methyl ester moiety and the aliphatic hydrocarbon protons in biodiesel and conventional diesel fuel were used for determining blend levels. The results of NIR and NMR blend level determinations are in good agreement.