Oxidative Stability of Conventional and High-Oleic Vegetable Oils with Added Antioxidants

The oxidative stability of conventional and high-oleic varieties of commercial vegetable oils, with and without added antioxidants, was evaluated using the oil stability index (OSI). Oil varieties studied were soybean (SOY), partially-hydrogenated soybean (PHSOY), corn (CORN), sunflower (SUN), canola (CAN), high-oleic canola (HOCAN), very high-oleic canola (VHOCAN), oleic safflower (SAF) and high-oleic sunflower (HOSUN). One or more commercial antioxidants were added to the four most stable oils at supplier-recommended levels: rosemary extract (RM; 1,000 ppm), ascorbyl palmitate (AP; 1,000 ppm), tert-butylhydroquinone (TBHQ; 200 ppm), and mixed tocopherols (TOC; 200 ppm). OSI in hours (h) at 110 °C of the conventional oils were 5.2, 7.6, 8.4, 9.8, 10.9 and 14.3 h for SUN, SOY, CAN, CORN, PHSOY and SAF, respectively. OSI of high-oleic variants were 12.9, 16.5 and 18.5 h for HOCAN, HOSUN and VHOCAN, respectively. Maximum OSI values for the four most stable oils when treated with antioxidants, were 40.9, 48.5, 48.8 and 55.7 h for HOCAN, VHOCAN, SAF and HOSUN, respectively. Addition of TBHQ, alone and in combination with other antioxidants, resulted in the greatest increase in oxidative stability of SAF and other high-oleic oils evaluated. AP had a positive synergistic effect when used with TBHQ, while RM decreased TBHQ effectiveness.     

生物柴油稳定性及稳定剂研究进展

综述了国内外生物柴油稳定性和生物柴油稳定剂的研究发展状况,内容涉及生物柴油的化学组成与基本特征、生物柴油的稳定性及其影响因素、生物柴油的稳定性检测及评价方法、生物柴油稳定剂的种类及性能等,认为添加稳定剂是提高生物柴油稳定性的主要手段。     

Investigation on Decomposition Kinetic and Thermal Stability of Metallocene Catalysts

Data on thermal stability of metallocene catalysts such as bis(n-butyl cyclopentadienyl) zirconium dichloride and bis(t-butyl cyclopentadienyl) zirconium dichloride is required because of their application in high temperature polymerization process. In the present study, the thermal stability of the bis(n-butyl cyclopentadienyl) zirconium dichloride and bis(t-butyl cyclopentadienyl) zirconium dichloride was determined by differential scanning calorimetry (DSC) and simultaneous thermogravimetry-differential thermal analysis (TG-DTA) techniques. The results of TG analysis revealed that the main thermal degradation for the bis(n-butyl cyclopentadienyl) zirconium dichloride and bis(t-butyl cyclopentadienyl) zirconium dichloride occurs in the temperature ranges of 194–360 °C and 195–350 °C, respectively. On the other hand, TG-DTA analysis indicated that bis(n-butyl cyclopentadienyl) zirconium dichloride melts (about 98.7 °C) before it decomposes. However, the thermal decomposition of the bis(t-butyl cyclopentadienyl) zirconium dichloride was started simultaneously with its melting. Also, the kinetic parameters such as activation energy and frequency factor for both compounds were obtained from the DSC data by non-isothermal methods proposed by Kissinger and Ozawa. Based on the values of activation energy obtained by Kissinger and Ozawa methods, the following order for the thermal stability was noticed: bis(t-butyl cyclopentadienyl) zirconium dichloride >bis(n-butyl cyclopentadienyl) zirconium dichloride. Finally, the values of ΔS^#, ΔH^# and ΔG^# of their decomposition reaction were calculated.     

Effects of Antioxidants on the Oxidative Stability of Oils Containing Arachidonic,Docosapentaenoic and Docosahexaenoic Acids

The effects of ascorbyl palmitate at 0, 300, 600, 900, or 1,200 ppm, tocopherol at 0, 200, 400, 600, or 800 ppm, and β-carotene at 0, 3, 6, 9, or 12 ppm on the oxidative stabilities of Oil 1, Oil 2, and Oil 3 containing 0, 0.55, and 0.67% of combined arachidonic acid (AA), docosapentaenoic acid (DPA), and docosahexaenoic acid (DHA), respectively, were studied by a central composite experimental design. The oxidative stability of oil was evaluated by determining the induction time using the Oxidative Stability Index. Ascorbyl palmitate and tocopherol had a significant effect on the stability of all three oils at α = 0.05. β-Carotene did not have any effect on the stability of oils at α = 0.05. The interaction effect of ascorbyl palmitate and tocopherol was significant for the three oils at α = 0.05. The induction time of oils decreased as the total amounts of AA, DPA and DHA increased from 0 to 0.55% or 0.55 to 0.67%. The addition of 1,200 ppm ascorbyl palmitate, 800 ppm tocopherol and 12 ppm β-carotene to Oils 1, 2, and 3 increased the induction time from 13.5 to 29.9 h, from 11.8 to 27.0 h, and from 10.5 to 20.0 h, respectively. The coefficient of determination (r ²) for the linear regression between the experimentally determined and statistically predicted induction time of the three oils was greater than 0.95. The use of an optimum combination of ascorbyl palmitate and tocopherols from the response surface analysis could improve the oxidative stabilities of oils containing AA, DPA and DHA.     

Content of Antioxidants,Antioxidant Capacity and Oxidative Stability of Grape Seed Oil Obtained by Ultra Sound Assisted Extraction

The goal of this work was to investigate the relationship between antioxidants’ content and the oxidative stabilities of grape seed oils obtained from the Cabernet Sauvignon variety. The samples of grape seed oils were obtained by ultrasound assisted extraction. The time of extraction was varied, while the other relevant parameters: extraction temperature, solvent to solid ratio and sonication power were kept constant. For the sake of comparison, the extraction was also done using the conventional Soxhlet method. For all the oil samples obtained, the contents of total phenolic compounds (TPC), α-tocopherol and fatty acids were determined using relevant analytic methods. Importantly, in the present study, the modern analytical techniques for estimation of antioxidant capacity (measuring the chemiluminescence intensity of a luminol-hemin solution) and oxidative stability [differential scanning calorimetry (DSC), coupled with thermogravimetry (TG)] were proposed. The obtained results prove that ultrasonic irradiation enables effective extraction of grape seed oil. It was shown that the extractive yields and the amounts of total phenolic compounds and α-tocopherol increase with time of extraction; the optimum time was determined. Results obtained in this work show that, for both oxidative stability and antioxidant capacity, TPC have a more important role then α-tocopherol.     

Impacts of Refining and Antioxidants on the Physico-Chemical Characteristics and Oxidative Stability of Watermelon Seed Oil

Compositional analyses of seeds from two cultivars (Mateera and Sugar baby) was performed to evaluate their suitability as oilseeds. Watermelon seeds and kernels contained 21.9–25.5 % and 38.9–46.9 % oil of exceptionally high quality. The crude oil was expelled with a screw press and then refined to obtain a odor free and colorless oil. The moisture content, unsaponifiable matter content, refractive index, and specific gravity were within the narrow ranges. Refining influenced the color, acid value, saponification value, peroxide value, and free fatty acid contents. Linoleic acid (C18:2) was the principal fatty acid constituting 64.5–67.2 % of the total fatty acids. Oxidative stability increased with the addition of tocopherols, butylated hydroxyl anisole (BHA), and tert-butyl hydroxyl quinine (TBHQ). The high amount of polyunsaturated fatty acids (PUFA) along with physicochemical properties were similar to soybeans, sunflower and other common vegetable oils, suggesting the suitabilty of watermelon seed oil for industrial production.     

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.     

Enhancing the Thermal Stability of Polypropylene by Blending with Low Amounts of Natural Antioxidants

Natural antioxidants are added in very low amounts to protect a polypropylene (PP) matrix against thermo‐oxidative degradation during processing. Thus, PP is melt‐blended with caffeic, chlorogenic, trans‐ferrulic, and p‐coumaric acids, and also with flavone and 3‐hydroxyflavone at 0.1 wt% with respect to the PP matrix. Neat PP and PP blended with three traditional antioxidants are prepared for comparison. A complete structural, thermal, and mechanical characterization is conducted. Ferrulic acid and particularly caffeic acid increases the thermal stability, showing also the highest activation energy. The structural changes of PP‐based films due to the polymer thermal degradation at high temperature (i.e., 400 °C) followed by FTIR reveal that antioxidants effectively delay the thermal degradation process. The wettability and the mechanical performance are also studied to get information regarding the industrial application of such films. While caffeic acid provides a more flexible material, ferrulic acid provides higher water resistance. Finally, AFM‐QNM shows that PP with caffeic acid has the highest miscibility.     

Experimental Design Applied for Cost and Efficiency of Antioxidants in Biodiesel

Oxidation stability is a parameter of great importance for biodiesel quality control to both producers and subsequent consumers. To maintain the quality of biodiesel, currently the most effective and economical method is the addition of antioxidants that prevent or retard the biofuel oxidation reaction. In this study, efficiency and cost of synthetic antioxidants added to B100 biodiesel from soybean oil and pork fat were evaluated, using butylhydroxyanisole (BHA), butylhydroxytoluene (BHT) and tert-butylhydroquinone (TBHQ), in pure form or in mixtures, according to a simplex-centroid mixture experimental design. Results demonstrate an increased induction period (IP) in all trials when compared to the control sample, and TBHQ was the only antioxidant alone that met all the specification standards, while BHT and BHA alone met only the American standard specifications. The antioxidant mixture that presented the highest synergistic effect was that of TBHQ and BHA. Multi-response optimization indicated an optimum formulation containing 75 % TBHQ and 25 % BHA with an IP of 7.27 h at 110 °C and the antioxidant mixture cost of 31.31 USD, to be added for a ton of biodiesel. This simplex-centroid mixture experimental design shows an ability to be applied in the biodiesel, oils and fats industry to evaluate the oxidation stability and the occurrence of synergism between different mixtures of synthetic or natural antioxidants and their costs.     

Enhancement of Antioxidants in Olive Oil by Foliar Fertilization of Olive Trees

Oxidative stability (OS) of virgin olive oil is affected by different antioxidants whose levels may be influenced by nutrients availability. Changes in OS of virgin olive oil and antioxidants levels were evaluated according to foliar application of six nutrient-based treatments: T1 (rich in nitrogen), T2 (rich in boron, magnesium, sulfur and manganese), T3 (rich in phosphorus and potassium), T4 (rich in phosphorus and calcium), T5 (application of T1 and T2) and T6 (application of T1, T2, T3 and T4). The foliar applications were carried out during two successive growing seasons and oils were extracted and analyzed at the end of the experiment (after 2 years). T3 and T6 treatments improved oil stability by increasing the content of antioxidants, while T2 and T4 affected negatively the antioxidant profile of oils. Measured correlations between OS and compositional variables showed that total phenols had the highest value (R = 0.937, p < 0.001), followed by α-tocopherol (R = 0.775, p < 0.001) and oleic/linoleic ratio (R = 0.625, p < 0.05). These findings suggest that the changing levels of antioxidant compounds, due to fertilization, may be used to obtain oils with the highest quality.     

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.     

添加剂对橡胶籽油生物柴油氧化稳定性的改进

测定了橡胶籽油的物化性能及组成. 加入6种抗氧化剂,采用Rancimat法研究了其添加量及复配、温度、0#柴油添加量、金属铜、铁等对橡胶籽油生物柴油氧化稳定性能的影响. 结果表明,橡胶籽油所制生物柴油不饱和脂肪酸含量达82.1%,诱导期为0.81 h,达不到国家标准(6 h). 6种抗氧化剂在添加量为4000′10-6(w)时对橡胶籽油生物柴油的氧化稳定性能均有提升,其中TBHQ效果最好,使其氧化稳定性诱导期达13.09 h,6种抗氧化剂的抗氧化效果为TBHQ>BHT>D-TBHQ>OG>PG>BHA. PG与其他抗氧化剂复配后效果较好,而TBHQ与其他抗氧化剂复配后效果降低. 温度和0#轻柴油添加量对橡胶籽油生物柴油的氧化稳定性能影响很大,随温度升高,诱导期明显缩短,而随0#柴油添加量增大,诱导期增加,添加量较大时诱导期增幅很大. 铁、铜对其氧化稳定性能也有一定影响.     

Improvement of the Flavor and Oxidative Stability of Walnut Oil by Microwave Pretreatment

Walnut oil is in great demand due to its high nutritional value. However, it is easily oxidized and often loses its typical flavor. This study focused on the role of microwave pretreatment in improving the flavor and oxidative stability of walnut oil, and also investigated the effects of microwave pretreatment on unsaturated fatty acids (oleic, palmitoleic, linoleic, and linolenic acids) and antioxidant components (tocopherols and phytosterols). The results indicate that microwave pretreatment is effective in generating pyrazine compounds. The typical ‘roasted’ flavor was present when pretreatment for 2 min or more was applied. Meanwhile, compared with the control sample, only the highly treated sample (microwave‐pretreated for 4 min) showed higher oxidative stability. Only small changes were found in the composition of the unsaturated fatty acids, while the levels of tocopherols and phytosterols significantly decreased with increasing duration of microwave treatment (P < 0.05). The results suggest that the Maillard reaction caused the improvement of oxidative stability, since this reaction can also generate antioxidant products (melanoidins) in addition to pyrazines. Moreover, microwave pretreatment was found to be effective for enhancing the oil yield during pressing. Therefore, despite its adverse effects on tocopherols and phytosterols, microwave pretreatment could be used to improve the flavor and oxidative stability of walnut oil.     

Kinetics Analysis on Mixing Calcination Process of Fly Ash and Ammonium Sulfate

abstract The further development of the extraction of alumina that is produced in the calcination process of ammonium sulfate mixed with fly ash was limited because of the lack of systematic theoretica...     

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.     

Characterization and Oxidative Stability of Structured Lipids: Infant Milk Fat Analog

Structured lipids (SLs) for infant milk formulation were produced by enzymatic interesterification of tripalmitin with vegetable oil blends and fish oil. The SLs were characterized by fatty acid content and structure, melting profiles, oxidative stability index, free fatty acid (FFA) concentration, and tocopherol content. Oxidative stability was studied using accelerated methods by quantifying FFA, peroxides (peroxide value) and aldehydes (p-anisidine value) production. Total oxidation (TOTOX value) was calculated as 2 × (peroxide value) + (p-anisidine value). The structured lipids after purification by distillation and addition of antioxidants had melting profiles, oxidative stability index, and initial FFA concentration that were similar to that of the starting oil blends, while the fatty acid composition and structure of the SLs were similar to that of human milk fat. Oxidative stability of the SLs was improved with tocopherol addition as antioxidants and was comparable to that of the vegetable oils and oil blends.     

Polythiophene oxidation: Rate coefficients, activation energy and conformational energies

Polythiophene films reduced by prepolarization at different cathodic potentials were used as the initial states for their potentiostatic oxidation. At the chronoamperometric maxima the oxidation occurs under chemical kinetic control. The oxidation kinetic characteristics: rate coefficient (k), activation energy (E_a) and the reaction order of the oxidation reaction, change as a function of the cathodic potential of prepolarization. That means that k and E_a for the oxidation are functions of the oxidation overpotential, as for any oxidation kinetics, and of the cathodic potential of prepolarization. Rising cathodic potentials of prepolarization promote decreasing rate coefficients, k, and increasing E_a. Those variations are described by the electrochemical relaxation model. The activation energy includes two components: the constant activation energy of the electrochemical reaction and the conformational activation energy of the initial packed conformations that increases as the prepolarization potential rises.     

提高焦炭热强度稳定率的方法

结合韶关钢铁集团有限公司的生产实际情况,分析了影响焦炭热强度稳定率的主要因素,介绍了提高焦炭热强度稳定率的主要方法。热强度σn-1系数与焦炭热强度稳定率呈负相关,σn-1系数降低,则焦炭热强度稳定率提高。实践结果表明,在配煤炼焦过程中,通过完善配煤管理制度、稳定精煤质量、降低环境影响和规范配煤操作等措施,使σn-1系数从2011年的3.26降至2012年的2.27。     

Diaminofuroxan: Synthetic Approaches and Computer‐Aided Study of Thermodynamic Stability

Different approaches to synthesize diaminofuroxan are presented herein. Mathematical and quantum chemical methods were used to study the possible reasons for failures in the syntheses of diaminofuroxan. Additionally, structural isomers of this compound were generated. With the help of the results of quantum chemical calculations at levels of DFT B3LYP 6‐31G(d) and MP2 6‐31G(d), screening of the most stable isomeric forms in the gaseous phase and in water was performed. It was shown that diaminofuroxan is not the thermodynamically most stable isomer among its structural analogues.     

Poly(ethylene naphthalate) formation 1. transesterification of dimethylnaphthalate with ethylene glycol

The transesterification of dimethyl naphthalate (DMN) with ethylene glycol (EG) was kinetically investigated in the presence of various catalysts at 185 °C. The transesterification was assumed to obey first-order kinetics with respect to DMN and EG, and a rate equation was derived. The rate constant of transesterification which calculated from the quantity of methanol distilled from the reaction vessel was used to evaluate each metal compound in its activity. The first-order dependence on the catalyst concentration is valid below a critical concentration which was found to be dependent on the catalyst type. The order of decreasing catalytic activity of various metal ions was found to be: Pb Zn > Co > Mg > Ni Sb. But in the case of highly basic metal salts, the rate constants were found to be extremely large at the initial stage of the reaction, and then rapidly decreased with the progress of the reaction. Effects of reaction temperature were also discussed. The activation energies for zinc acetate and lead acetate were 97.84 and 97.2 KJ/mol, respectively, which were calculated from Arrhenius equation.