Soybean and Soybean/Beef-Tallow Biodiesel: A Comparative Study on Oxidative Degradation During Long-Term Storage

Vegetable oils are the primary raw materials used in biodiesel production; however, they usually present oxidative stabilities inferior to the EN 14214 specifications. An alternative to improve the oxidative quality of vegetable oil biodiesel is blending it with animal fat biodiesel. In this paper, we studied the oxidative degradation of soybean/beef-tallow biodiesel (SB) 70/30 and 50/50 (w/w) during long-term storage. Soybean biodiesel (SO) was used as a control sample. The biodiesel samples were stored for 350 days and analyzed periodically via oxidative stability, tocopherol content, peroxide value, polar compounds, and kinematic viscosity. The results showed that SB 70/30 and 50/50 biodiesel samples presented higher oxidative stabilities than SO biodiesel. Additionally, the blends met the limits proposed by EN 14214 for oxidative stability (8 h). During long-term storage, the SB biodiesel showed greater resistance to oxidative degradation, which was indicated by the lower formation of hydroperoxides and polar compounds. Similarly, the decline in the tocopherol content was slower in SB biodiesel. Blends of soybean and beef-tallow biodiesel at levels of 70/30 and 50/50 are, therefore, proper alternatives to improve the oxidative quality of this biofuel.     

The Effect of Natural and Synthetic Antioxidants on the Oxidative Stability of Biodiesel

A significant problem associated with the commercial acceptance of biodiesel is poor oxidative stability. This study investigates the effectiveness of various natural and synthetic antioxidants [α-tocopherol (α-T), butylated hydroxyanisole (BHA), butyl-4-methylphenol (BHT), tert-butylhydroquinone (TBHQ), 2, 5-di-tert-butyl-hydroquinone (DTBHQ), ionol BF200 (IB), propylgallate (PG), and pyrogallol (PY)] to improve the oxidative stability of soybean oil (SBO-), cottonseed oil (CSO-), poultry fat (PF-), and yellow grease (YG-) based biodiesel at the varying concentrations between 250 and 1,000 ppm. Results indicate that different types of biodiesel have different natural levels of oxidative stability, indicating that natural antioxidants play a significant role in determining oxidative stability. Moreover, PG, PY, TBHQ, BHA, BHT, DTBHQ, and IB can enhance the oxidative stability for these different types of biodiesel. Antioxidant activity increased with increasing concentration. The induction period of SBO-, CSO-, YG-, and distilled SBO-based biodiesel could be improved significantly with PY, PG and TBHQ, while PY, BHA, and BHT show the best results for PF-based biodiesel. This indicates that the effect of each antioxidant on biodiesel differs depending on different feedstock. Moreover, the effect of antioxidants on B20 and B100 was similar; suggesting that improving the oxidative stability of biodiesel can effectively increase that of biodiesel blends. The oxidative stability of untreated SBO-based biodiesel decreased with the increasing indoor and outdoor storage time, while the induction period values with adding TBHQ to SBO-based biodiesel remained constant for up to 9 months.     

Comparisons of Biodiesel Produced from Unrefined Oils of Different Peanut Cultivars

Biodiesels were prepared according to standard procedures from unrefined oils of eight commercially available peanut cultivars and compared for differences in physical properties important to fuel performance. Dynamic viscosity, kinematic viscosity and density were measured from 100 to 15 °C, and differences (p < 0.05) in these physical properties occurred more frequently at lower temperatures when comparing the different cultivars. Unlike data for the oil feedstocks, no meaningful correlations among biodiesel fatty acid profiles and either fuel viscosity or density were observed. Low temperature crystallization of the peanut biodiesels was measured via differential scanning calorimetry. Increased concentrations of long chain saturated fatty acid methyl esters (FAME) were associated with an increased propensity for low temperature crystallization, and the single FAME category most associated with low temperature crystallization was C:24. Tempering at 10 °C followed by analysis of the soluble fractions (winterization), improved crystallization properties and confirmed the importance that long chain saturated FAMEs play in the final functionality of peanut biodiesel. Peanut data is also compared to data for canola and soy biodiesels, as these feedstocks are more common worldwide for biodiesel production. Overall, this work suggests that minimizing the concentration of long chain saturated FAMEs within peanut biodiesel, either through processing and/or breeding efforts would improve the low temperature performance of peanut biodiesel.     

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.     

Behaviour of the antioxidant tert-butylhydroquinone on the storage stability and corrosive character of biodiesel

The behaviour of the antioxidant tert-butylhydroquinone (TBHQ) on the storage stability of biodiesel was investigated. Storage conditions were simulated through static immersion corrosion tests in biodiesel (with and without TBHQ) using copper coupons. Measurements of oxidation stability (Rancimat induction period) and metal release at different stages of corrosion were performed. After 24 h of the static immersion test, the neat and TBHQ-doped biodiesels presented induction times below the EN 14214 limit (6 h). Copper release was more intense in the neat biodiesel which evidenced that TBHQ retarded the corrosion process as a corrosion inhibitor. Ion trap–time-of-flight mass spectrometry (IT–TOF-MS) revealed the presence of considerable amounts of tert-butylquinone (TBQ) in the TBHQ-doped biodiesel exposed to the corrosion process. As TBHQ molecules adsorb at the copper surface to inhibit corrosion, these molecules are catalytically oxidised to TBQ. IT–TOF-MS also indicated the formation of new molecules of high molecular weight only presented in the TBHQ-doped biodiesel deteriorated by the corrosion process. MS² spectra gave clear evidence of the formation of new complexes between free radicals of long-chain molecules (fatty acid derivatives) and TBQ radicals during biodiesel deterioration.     

An Empirical Equation for Estimation of Kinematic Viscosity of Fatty Acid Methyl Esters and Biodiesel

Kinematic viscosity (µ) is an important physical property of fatty acid methyl esters (FAME) and biodiesel. In this work, the Martin's rule of free energy additivity is extended to cover the kinematic viscosity of saturated and unsaturated FAME commonly found in nature. The proposed model can also be extended to estimate kinematic viscosity of biodiesel. The kinematic viscosity of a FAME or a biodiesel can be easily estimated from its carbon number (z), number of double bonds (n_d) at different temperatures (T) without a prior knowledge of the viscosity of individual FAME. Both z_ave and n_d(ave) can be derived from its fatty acid composition. Thus, kinematic viscosity of biodiesel at temperatures between 20 and 100 °C and at atmospheric pressure can be estimated. The average absolute deviation (AAD) estimated at 20–100 °C for saturated, unsaturated FAME, biodiesels and biodiesel blends are 4.15, 3.25, 6.95 and 2.79 %, respectively. The biodiesels collected in this study (191 data points) have the z_ave and n_d(ave) between 14.10 and 17.96 and 0.21–1.54, respectively. The standard deviation was 0.249. The proposed model would be good for estimation of viscosity of biodiesel containing normal fatty acids, generally found in biodiesel feed stocks.     

The Effect of Monoglyceride Polymorphism on Cold-Flow Properties of Biodiesel Model Fuel

The cloud point (CP) of biodiesel refers to the temperature at which crystallization begins on cooling. However, solid precipitates are often formed at a temperature higher than the CP during storage. Such precipitates are known to consist largely of monoglycerides (MGs) as intermediate compounds. MGs have high melting points, which are detrimental to the cold‐flow properties of biodiesel. MGs have several polymorphic forms, including α, β′ and β, with different melting points (α < β′ < β), and this fact makes the behavior of biodiesel at low temperature complicated. In this study, the precipitation behavior of MGs in biodiesel is discussed focusing on polymorphism using 1‐monopalmitin and methyl oleate mixtures as a model biodiesel fuel. The CPs measured were close to the calculated solid‐liquid equilibrium curve for α‐type 1‐monopalmitin. However, precipitates formed at temperatures higher than the CP when the mixtures were held at temperatures lower than the equilibrium curve of the β′ form. This indicates that the β′ form causes a risk of precipitation at temperatures above the CP and that the CP is not a suitable indicator of the cold‐flow properties of biodiesel.     

Storage Stability of Carrot Chips

Water activity combined with the glass transition temperature can be used to predict the shelf life of foods. Water sorption isotherms and glass transition as a function of moisture content were determined for carrot chips after vacuum frying. The GAB model was fitted to the measured sorption data while the Gordon Taylor equation was used to model the water plasticization effect. The critical moisture content and the critical water activity at which the glass transition occurs were obtained at selected storage temperatures. The changes in moisture content, fat content, water activity, breaking force, β-carotene content, ascorbic acid, and acid value of vacuum-fried carrot chip at selected storage temperatures (0, 10, 25°C) during a 6-month storage period were investigated. The estimated shelf life of carrot chip, defined by the degradation time of the acid value at different storage conditions, was determined.     

Storage Stability of Carrot Chips

Water activity combined with the glass transition temperature can be used to predict the shelf life of foods. Water sorption isotherms and glass transition as a function of moisture content were determined for carrot chips after vacuum frying. The GAB model was fitted to the measured sorption data while the Gordon Taylor equation was used to model the water plasticization effect. The critical moisture content and the critical water activity at which the glass transition occurs were obtained at selected storage temperatures. The changes in moisture content, fat content, water activity, breaking force, β-carotene content, ascorbic acid, and acid value of vacuum-fried carrot chip at selected storage temperatures (0, 10, 25°C) during a 6-month storage period were investigated. The estimated shelf life of carrot chip, defined by the degradation time of the acid value at different storage conditions, was determined.     

以废食用油为原料的生物柴油研制

介绍了废食用油脂在KF/CaO催化剂作用下,与乙醇通过酯交换反应,生产生物柴油的研究。通过研究废食用油的预处理,反应时间,反应温度,原料与催化剂配比及催化剂用量等操作条件对反应的影响,摸索反应的最佳操作条件。实验结果表明,KF/CaO催化剂,在活性白土为载体,在KF与CaO质量比为1/3时,温度为800℃,烧制4 h时得到的催化剂活性最好。该反应得最适宜的操作条件是：醇油体积比为6∶1,催化剂量KF/CaO为原料油质量的2%,反应温度为70℃,反应时间为60min。     

Influence of Storage on Physicochemical and Volatile Features of Enriched and Aromatized Wax Organogels

In this study, virgin olive oil (VOO) organogels were produced with beeswax (BW) and sunflower wax (SW) and enriched with β‐carotene, vitamin D₃ and E as well as aromatized with strawberry, banana, and butter aromas. The physicochemical, thermal, structural, and sensorial properties of the fresh organogel samples were determined. The peroxide values, antioxidant activities, firmness, and volatile compositions of the fresh samples and those stored for 3 months were also determined. The organogels were not only stable, uniform, and homogenous during the storage period but also the added components did not affect the organogel properties. The panel defined three appearance, four texture, three mouthfeel, four aroma, and four flavor terms to describe the organogels sensorially. Moreover, the added aroma (banana, strawberry, and diacetyl‐butter) components of the fresh and stored organogels were quantified by GC/MS‐SPME. In conclusion, these results demonstrated that beeswax and sunflower wax are very suitable to preserve the aromatic characteristics of these types of spreadable products.     

Optimization of Cottonseed Oil Ethanolysis to Produce Biodiesel High in Gossypol Content

Transesterification of cottonseed oil was carried out using ethanol and potassium hydroxide (KOH). A central composite design with six center and six axial points was used to study the effect of catalyst concentration, molar ratio of ethanol to cottonseed oil and reaction temperature for percentage yield (% yield) and percentage initial absorbance (%A _385nm) of the biodiesel. Catalyst concentration and molar ratio of ethanol to cottonseed oil were the most significant variables affecting percentage conversion and %A _385nm. Maximum predicted % yield of 98% was obtained at a catalyst concentration of 1.07% (wt/wt) and ethanol to cottonseed oil molar ratio of 20:1 at reaction temperature of 25 °C. Maximum predicted %A _385nm of more than 80% was obtained at 0.5% (wt/wt) catalyst concentration and molar ratio of 3:1 at 25 °C. The response surfaces that described % yield and %A _385nm were inversely related. Gossypol concentration (% wt), oxidative stability and %A _385nm of biodiesel were found to be highly correlated with each other. Hence, color %A _385nm is a measure of the amount of pigments present in biodiesel fuels that have not yet been subjected to autoxidation. High gossypol concentration also corresponds to a fuel with high oxidative stability. The fatty acid ethyl esters (FAEE) produced from cottonseed oil had superior oxidative stability to fatty acid methyl esters (FAME) produced from cottonseed oil.     

Total Acid Number Determination of Biodiesel and Biodiesel Blends

The repeatability and accuracy of the total acid number (TAN) measurement for soy oil-based biodiesel–diesel blends using the ASTM D664 method was studied. ASTM D664 is the standard reference method for measuring the acid number of both biodiesel and petroleum-derived diesel, which specifies procedures for the determination of acidic components in biodiesel and diesel, and claims good repeatability and mediocre reproducibility during application, but cites no information on accuracy. However, the accuracy of this method is very important for setting the specifications for biodiesel blends, especially for B20 (a mixture composed of 20% biodiesel with 80% diesel) because of its wide commercial production. The accuracy of ASTM D664 was measured to be within 4.13% for B20 in the acid number range of 0.123–0.332 mg KOH/g. The maximum repeatability was approximately 5.21% at an acid number of 0.123 mg KOH/g. Within the ASTM D6751-07b specification for TAN (0.5 mg KOH/g), good accuracy and repeatability were also obtained. Accuracy specification and electrode operation suggestions for ASTM D664 are also given.     

脱硫胶粉改性沥青工艺及储存稳定性研究

在较高温度下高速剪切混合脱硫胶粉和沥青制备脱硫胶粉改性沥青,考察了温度、时间、脱硫胶粉粒径、脱硫胶粉加量及稳定剂加量对沥青性能、改性沥青粘度和储存稳定性的影响,以探究脱硫胶粉改性沥青的工艺条件及其对改性沥青性能、粘度和储存稳定性的影响.结果表明:改性温度的升高和时间的延长可以改善改性沥青性能,60目脱硫胶粉且加量为20%质量百分数时,改性沥青的性能最优,储存稳定性最高,稳定剂的加入显著地改善了脱硫胶粉-沥青体系的交联度,进一步改进了改性沥青的性能,增加了体系的稳定性;在脱硫胶粉/总量=0.2(质量比,60目)、温度200 ℃、时间60 min及稳定剂加量为0.4%(质量百分数)时,脱硫胶粉改性沥青的性能最佳、稳定性最高.     

Biodiesel influence on tribology characteristics of a diesel engine

This paper deals with the influence of biodiesel on some tribology characteristics of a bus diesel engine with a mechanically controlled fuel injection system. The tests have been performed on a fully equipped engine test bed, on a fuel injection test bed and on a discharge coefficient testing device. The tested fuel was neat biodiesel produced from rapeseed. Attention was focused on the biodiesel influence on the pump plunger surface roughness, on the carbon deposits in the combustion chamber, on the injector and in the injector nozzle hole. The pump plunger surface was analyzed by experimentally determined roughness parameters and by a microscope. The carbon deposits at fuel injector and in the combustion chamber were examined using endoscopic inspection. The deposits in the injector nozzle were investigated indirectly by measuring the nozzle discharge coefficient. Numerical simulation has been performed in order to estimate the influence of the discharge coefficient variation on the computed injection characteristics. The obtained results indicate that biodiesel usage may even improve the pump plunger lubrication conditions. Furthermore, the carbon deposits in the combustion chambers did not vary significantly in quantity but they were noticeably redistributed. Finally, it was found out that the variation of the nozzle discharge coefficient has to be taken into account only if high accuracy of numerical simulation is desired.     

丙烯酸（酯）副产物在储存期间粘度升高的原因及解决方法

对丙烯酸（酯）副产物储存期间出现的粘度升高现象进行了探索和研究,通过对影响因素的分析,找出了使丙烯酸（酯）副产物粘度升高的主要原因,并通过试验,选择了合适的溶剂,将该溶剂加入到丙烯酸（酯）副产物中后,使其长期储存时粘度能保持在稳定状态,解决了因粘度升高、生产无法稳定运行的问题。     

有机功能材料信息存储研究最新进展

信息技术的发展要求存储器件必须具备超高存储密度、超快的存取速率及长的存储寿命。目前,广泛应用的磁存储和光存储介质正在接近其物理极限。科学家们多年前就开始积极探索新的存储理论、技术和材料,以期突破数据存储的极限。简要地介绍了近来有机功能材料信息存储研究的进展。     

Flaxseed Cyclolinopeptides: Analysis and Storage Stability

Fourteen cyclolinopeptides (CLPs) from flaxseed oil and meal were separated, identified and quantified by HPLC coupled to an Orbitrap MS. The oxidative stability of the cyclolinopeptides was assessed during storage of flaxseed oil and meal. A significant decrease in the amounts of the methionine containing CLPs, namely CLP-B, CLP-J and CLP-M, and a concurrent increase in the amounts of methionine sulfoxide containing CLPs, such as CLP-C, CLP-E and CLP-G were observed. The cyclolinopeptides with two methionine units, CLP-L and CLP-M, exhibited the greatest decrease, followed by CLP-J, the major flaxseed oil bitter taste precursor, and CLP-B, a biologically active cyclolinopeptide. At the end of the storage period, the amount of the bitter CLP-E increased fourfold in the oil while the immunosuppressive cyclolinopeptides A remained unchanged. No significant changes in the amount of each of the CLPs were observed in the stored flaxseed meals. A fast and reliable procedure has been developed for quantitative analysis of cyclolinopeptides. Due to the high predisposition of methionine containing cyclolinopeptides to oxidation and the easiness of CLPs’ quantification with the proposed method, it is possible to reliably assess the extent of flaxseed meal and oil oxidation.     

改性凹凸棒土用于制备生物柴油

研究了凹凸棒土作为催化剂载体和吸附剂,用于制备及精制生物柴油的工艺。研究表明：以凹凸棒土作为固体酸催化剂载体,优选SO^2-4／ZrA为催化剂于100℃下预焙烧,1mol／L硫酸溶液浸泡,600℃下焙烧后催化反应,生物柴油产率达87．8％,可重复使用3次;产物分离后,经改性凹凸棒土吸附残留甘油,生物柴油纯度可达98．6％,产物久置无絮状物产生,大大缩短了后处理时间,提高了生物柴油品质。     

Biodiesel blend effects on common-rail diesel combustion and emissions

Biodiesel (fatty acid methylesters) blends with fossil diesel at a mixing ratio between 0.5 and 5 vol.% are widely offered as automotive fuels in Europe. The target for the future is to bring this ratio to at least 10%, in order to increase the share of renewable energy in transport. There is however limited evidence on the effects of such blends on the combustion and emissions of diesel engines not originally designed to operate on biodiesel blends. In this study, a number of experiments with 10 vol.% (B10) biodiesel fuel of palmoil origin were performed on a light-duty common-rail Euro 3 engine. The measurements included in-cylinder pressure, pollutants emissions, and fuel consumption. Combustion effects were limited but changes in the start of ignition and heat-release rate could be identified. Emission effects included both higher and lower smoke and NOx, depending on the operation point. The results on the engine bench were compared against a Euro 3 common-rail light-duty vehicle driven on the chassis dynamometer, in order to include the effects of emission control systems (EGR and oxidation catalyst). In addition to the palm biodiesel, an RME-diesel blend was also tested to examine the effects of a fuel with different characteristics. Both biodiesel blends reduced PM emissions and only marginal effects on NOx over the certification test could be identified. The results of this study show that up to 10% biodiesels could be used on current diesel vehicles, without significantly affecting vehicle emission performance.