Determination of oxidation stability of soybean oil with the oxidative stability instrument: Operation parameter effects

Operation parameters of the oil stability index instrument were evaluated to determine their effect on the oxidative stability of commercial soybean oil. A factorial design was developed to evaluate the following three parameters, each at two levels, sample weight (2.5 or 5.0 g), conductivity tube temperature (20 or 30°C), and air flow rate (12 or 20 L/h), for a total of eight observations. Significance testing indicated that sample size and air flow rate affected oil oxidative stability independently (P<0.001), but not in combination. The conductivity tube temperature did not affect the oxidation stability index. Presented at the 1993 American Oil Chemists’ Society Meeting in Anaheim, California.     

Impact of antioxidant additives on the oxidation stability of biodiesel produced from Croton Megalocarpus oil

The increase in crude petroleum prices, limited resources of fossil fuels and environmental concerns have led to the search of alternative fuels, which promise a harmonious correlation with sustainable development, energy conservation, efficiency and environmental preservation. Biodiesel is well positioned to replace petroleum-based diesel. Biodiesel is a non-toxic, biodegradable and renewable biofuel. But the outstanding technical problem with biodiesel is that, it is more susceptible to oxidation owing to its exposure to oxygen present in the air and high temperature. This happens mainly due to the presence of varying numbers of double bonds in the free fatty acid molecules. This study evaluates oxidation stability of biodiesel produced from Croton megalocarpus oil. Thermal and Oxidation stability of Croton Oil Methyl Ester (COME) were determined by Rancimat and Thermogravimetry Analysis methods respectively. It was found that oxidation stability of COME did not meet the specifications of EN 14214 (6 h). This study also investigated the effectiveness of three antioxidants: 1,2,3 tri-hydroxy benzene (Pyrogallol, PY), 3,4,5-tri hydroxy benzoic acid (Propyl Gallate, PG) and 2-tert butyl-4-methoxy phenol (Butylated Hydroxyanisole, BHA) on oxidation stability of COME. The result showed that the effectiveness of these antioxidants was in the order of PY > PG > BHA.     

A rapid method for evaluation of the oxidation stability of castor oil FAME: influence of antioxidant type and concentration

The oxidation stability of castor oil fatty methyl ester (FAME), doped with four different phenolic antioxidants, was evaluated using a rapid method of thermal and air-contact degradation. The methodology is based on the induction times observed when the samples are contacted with pure oxygen at elevated pressures and temperatures. The results indicate different performances of the antioxidants as well as synergisms between antioxidants and biodiesel. In general, the addition of antioxidants increased from 6-15 times the stability of castor oil FAME., with BHA (butylated hydroxyanisol) showing the best results for improving antioxidation in castor oil biodiesel.     

Experimental and kinetic modeling study of ethyl butanoate oxidation in a laminar tubular plug flow reactor

This investigation examines the experimental and the kinetic modeling of the oxidation of ethyl butanoate (EB) selected as model molecule for fatty acid ethyl esters (FAEE). New experimental information of EB oxidation was generated from a laminar tubular plug flow reactor (PFR) operating at atmospheric pressure, under dilute conditions, over the temperature range 500–1200 K, with various equivalence ratios ranging from 0.5 to 1.6, and at residence times varying between 0.65 and 1.40 s under STP conditions. Concentration profiles of the reactants, stable intermediates, and final products, identified by GC/MS, were measured by infrared ray absorption and GC/TCD–FID analyses. Experiments of EB oxidation carried out in the tubular PFR were simulated using a detailed chemical kinetic oxidation mechanism (117 species and 1035 reactions) proposed in a previous work [Hakka et al. Int J Chem Kin 2010;42:226] and automatically generated from an improved version of EXGAS software. Globally, good agreement was observed between experimental and simulated results, confirming the validity of the proposed model for EB oxidation. Reaction flux and sensitivity analyses allowed to determine the main reaction pathways involved in the investigated conditions of EB oxidation.     

精对苯二甲酸装置氧化反应器操作新模式探讨

介绍了国内某PTA装置的氧化反应器操作情况,重点介绍了氧化反应器的原理、影响氧化反应的工艺因素,依据化学工程理论和专利商提供的数据以及生产实践积累的数据,寻找降低酸耗和提高装置负荷的方法,并在实践中得到验证,即氧化反应器采用低压、低溶剂比、高催化剂浓度的操作模式,可以在不增加装置投资的情况下,使操作负荷增加25%,酸耗降低10%。     

Experimental and modeling study of the kinetics of oxidation of ethanol-n-heptane mixtures in a jet-stirred reactor

The kinetics of oxidation of ethanol-n-heptane mixtures (20-80 and 50-50 mol.%) was studied experimentally using a fused-silica jet-stirred reactor. The experiments were performed in the temperature range 530-1070 K, at 10 atm, at two equivalence ratios (0.5 and 1), and with an initial fuel concentration of 750 ppm. A kinetic modeling was performed using schemes resulting from the merging of validated kinetic schemes for the oxidation of the components of the present mixtures (n-heptane and ethanol). Good agreement between the experimental results and the computations was observed under the present conditions when using detailed chemistry whereas the used of semi-detailed chemistry yielded acceptable but less accurate prediction of the fuel oxidation kinetics.     

Air oxidation of aqueous cyanides in a countercurrent fixed bed reactor

This study was conducted to discuss the removal of cyanides from water by air oxidation. Experiments were carried out in a countercurrent fixed bed reactor for three different values of temperature, concentration, gas and liquid flow rates. It was operated at pH 12 by using delrin (formaldehyde polymer) as packing material. Effects of some operating parameters on the conversion were studied, and it was observed that the conversion percent increased by increasing temperature and decreasing gas and liquid flow rates. Effect of concentration was not steady. A conversion of 89% was achieved under optimum conditions while it ranges from 44 to 79% at room temperature.     

Storage stability of FCC light cycle oil

This work deals with an evaluating of the storage stability of light cycle oil (LCO) which is produced by a fluid catalytic cracking technology. The LCO was aged according to two methods ASTM D2274 and ASTM D4625. The first test simulates an intensive oxidation stress and the second method is suitable for a long-time storage stability testing. The acid number, the iodine number, the carbon residue and the insolubles amount were chosen as parameters for the evaluation of the stability in both tests. Only the insolubles amount and the carbon residue varied (increased) during both tests. Four types of antioxidants were used as the oxidation inhibitors but no distinct effect on the oxidation stability of the LCO was observed.     

Axial gas phase dispersion in a molten salt oxidation reactor

Gas phase axial dispersion characteristics were determined in a molten salt oxidation reactor (air-molten sodium carbonate salt two phase system). The effects of the gas velocity (0.05–0.22 m/s) and molten salt bed temperature (870–970 °C) on the gas phase axial dispersion coefficient were studied. The amount of axial gas-phase dispersion was experimentally evaluated by means of residence time distribution (RTD) experiments using an inert gas tracer (CO). The experimentally determined RTD curves were interpreted by using the axial dispersions model, which proved to be a suitable means of describing the axial mixing in the gas phase. The results indicated that the axial dispersion coefficients exhibited an asymptotic value with increasing gas velocity due to the plug-flow like behavior in the higher gas velocity. Temperature had positive effects on the gas phase dispersion. The effect of the temperature on the dispersion intensity was interpreted in terms of the liquid circulation velocity using the drift-flux model.     

Modeling of photocatalytic oxidation of VOCs in a packed bed reactor under continuous and discontinuous illuminations

In this paper, a mathematical model is presented to describe the photocatalytic degradation of VOCs in a packed bed reactor. Here, the adsorption of VOCs on the wall of the reactor is taken into account and the diffusion of VOCs in the axial direction is neglected. First-order kinetics is used to describe the photocatalytic oxidation of VOCs. The analytical solution of the present model is obtained by traveling wave method. The solution shows that the reactor performance is totally dependent on the inlet concentration of VOCs when the time is large enough. The present model is validated through the experimental result of the photocatalytic oxidation of trichloroethylene in a packed bed and the predicted results accord well with the experimental data. The influence of flow rate and inlet concentration on the performance of the reactor is discussed in detail. High flow rate offers high reaction rate and low conversion efficiency. The different inlet conditions and different reaction patterns are also investigated. The model would be useful to estimate the rate constant and help to the design of the reactor.     

Oxidative stability of sunflower oil bodies

This study investigates the oxidative stability of sunflower oil body suspensions (10 wt‐% lipid). Two washed suspensions of oil bodies were evaluated over 8 days at three temperatures (5, 25 and 45 °C) against three comparable sunflower oil emulsions stabilized with dodecyltrimethylammonium bromide (DTAB), polyoxyethylene‐sorbitan monolaurate (Tween 20) and sodium dodecyl sulfate (SDS) (17 mM). The development of oxidation was monitored by measuring the presence of lipid hydroperoxides and the formation of hexanal. Lipid hydroperoxide concentrations in the DTAB, SDS and Tween 20 emulsions were consistently higher than in the oil body suspensions; furthermore, hexanal formation was not detected in the oil body emulsions, whereas hexanal was present in the headspace of the formulated emulsions. The reasons for the extended resistance to oxidation of the oil body suspensions are hypothesized to be due to the presence of residual seed proteins in the continuous phase and the presence of a strongly stabilized lipid‐water interface.     

Hydrotreated-LCO oxidation in a transported slurry reactor-hydrocyclon system reactor for a low emission fuel oil production: I Kinetic of reactions

Tetralin, indane, and fluorene molecules in a hydrogenated diesel were selectively oxidized with air to determine their kinetic behavior during the reaction. The oxidation of model molecules was performed in a continuous stirred tank reactor to obtain data to simulate diesel oxidation in a slurry (three-phase) reactor. The products of reactions were analyzed by elution in a silica column followed by GC-MS analysis of the fractions to determine the amount of product converted. The analytical procedure was calibrated using the model molecules. A lump model of 11 main reactions is considered here to evaluate the conversion of tetralin, indane, and fluorene into oxygenated compounds. The kinetic study was performed at different temperatures, space velocities, and reactant concentrations. A program using a genetic algorithm optimization tool was developed to calculate the values of the kinetics rate constants. The results indicated that the reaction can be modeled by a simple apparent first order of reaction with respect to hydrocarbon and around 0.3 orders of reaction respects to oxygen. The reactivity followed the order tetralin, indane, and then fluorene. The heterogeneous kinetic rate expressions of one active site represent the experimental results in the range of operating conditions studied. Under the experimental conditions, the ketones and ketols formed are strongly adsorbed in the active sites. Production of alcohols generates some poly-oxygenated compounds that reduce the storage stability of the fuel.     

Questions begging for answers (Part IV): Oil stability

The stability of edible oils is an important quality aspect. It has been studied extensively, but perhaps these studies have started from the wrong premise: it is not that oils are unstable; they are far more stable than would follow from their molecular structure. So research into their instability should be reoriented towards research into their remarkable stability. This research can use some observations and some specific questions as starting points and combine this with some novel analytical techniques to arrive at a novel approach that looks promising and justifiable. However, it is doubtful if anybody will pursue this research opportunity.     

Collaborative study of the oil stability index analysis

The Oil Stability Index Analysis method was subjected to a fifteen-laboratory collaborative study in which the participants used currently available commercial and home-built instruments to provide data to support the approval process as an Official Method of the American Oil Chemists’ Society. The overall average coefficient of variation was 11.3% for samples from 7 to 80 h of stability testing at 110°C.     

Thermochemistry of biodiesel oxidation reactions: A DFT study

Density functional theory (DFT) quantum chemical calculations have been used to evaluate the gas phase electronic and thermochemical properties of fatty acid esters. The calculated low relative energies of the corresponding radicals can explain the large variety of oxidation products observed in experiments. The first oxidation reaction step was determined to be non-spontaneous for all fatty acid esters studied. Ethyl and methyl esters showed similar susceptibilities to oxidation in the gas phase. All subsequent reaction steps leading to the secondary products of oxidation were observed to be spontaneous. The thermochemical stability order of one double bond oxidation in the gas phase was determined to be linoleate < γ-linolenate < α-linolenate < oleate < ricinoleate. Therefore, biodiesel produced from castor oil could be used as an additive to biodiesel produced from other vegetable oil sources in order to improve the oxidation stability properties of the final fuel blend.     

Effectiveness of antioxidants on lipid oxidation and lipid hydrolysis of cod liver oil

The capacity of the natural antioxidant from barley husks to retard oxidation of PUFA in cod liver oil (Gadus morhua) was investigated and compared to synthetic antioxidants. The results confirm the efficacy of a natural antioxidant derived from barley husks to slow down the progress of lipid hydrolysis and increase oxidative stability in cod liver oil. The rates of lipid hydrolysis and lipid oxidation were slowed down with increasing concentration of natural antioxidant used. Using 100 mg of the natural antioxidant was more effective than some synthetic antioxidants (BHA 200 mg and BHT 200 mg) against primary and secondary oxidation. The use of propyl gallate (PG) as an antioxidant (200 mg/kg in cod liver oil) was the most effective antioxidant employed in reducing the production of primary and delaying secondary oxidation products. The formation of free fatty acids (FFA) was significantly lower in samples with natural antioxidant (BE200 and BE100) than in the control samples. BHA and BHT were the most effective antioxidants employed to delay the lipid hydrolysis. Practical applications: The use of barley husks, which are residues of the brewing process, was optimized to obtain a crude antioxidant extract. Natural extracts of phenolic compounds with high antioxidant activity were obtained after prehydrolysis and delignification of barley husks. The raw extracts show more than two‐fold antioxidant capacity compared to BHT in terms of EC50. The results demonstrate the efficacy of a natural antioxidant derived from barley husks. The extract could be used in fatty foods (such as butter, oil, etc.) to prevent rancidity.     

Evaluation of the oxidation stability of diesel/biodiesel blends

Biodiesel is an alternative fuel derived from vegetable oils, animal fats and used frying oils. Due to its chemical structure, it is more susceptible to oxidation or autoxidation during long-term storage compared to petroleum diesel fuel. One of the major technical issues regarding the biodiesel blends with diesel fuel is the oxidation stability of the final blend, which is, nowadays, of particularly high concern due to the introduction of ultra low sulphur diesel, in most parts of the EU. This study examined the factors influencing the stability of several biodiesel blends with low and ultra low sulphur automotive diesel fuels. The aim of this paper was to evaluate the impact of biodiesel source material and biodiesel concentration in diesel fuel, on the stability of the final blend. Moreover, the effects of certain characteristics of the base diesels, such as sulphur content and the presence of cracked stocks, on the oxidation stability are discussed.     

一种CO优先氧化装置的实验研究

质子交换膜燃料电池需要CO含量低于10μL/L的富氢合成气作为燃料。CO优先氧化是一种深度脱除CO的有效方法。设计了一种CO优先氧化反应器,考察了催化剂装填方式、CO空速和氧碳比对反应器性能的影响。结果表明:对于所测试的操作条件,催化剂稀释之后分三段装填有利于反应器床层温度的均匀分布和出口CO浓度的降低;氧碳比越高出口CO浓度越低,当氧碳比为2.8时出口CO浓度为7μL/L。连续20 h的测试表明,反应器床层温度分布均匀,出口CO浓度保持在10μL/L以下。     

Comparison of a contactor catalytic membrane reactor with a conventional reactor: example of wet air oxidation

A wet air oxidation reaction was carried out in a gas/liquid catalytic membrane reactor of the contactor type. The oxidation of formic acid was used as a model reaction. The mesoporous top-layer of a ceramic tubular membrane was used as catalyst (Pt) support, and was placed at the interface of the gas (air) and liquid (HCOOH solution) phases.

A similar reaction was carried out in a conventional batch reactor, using a steering rate high enough to avoid gas-diffusion limitations, and exactly identical conditions than for the CMR (amount of catalyst, pressure, etc.). At room temperature, the CMR showed an initial activity three to six times higher than the conventional reactor. This activity increase was attributed to an easier oxygen access to the catalytic sites. Nevertheless, the catalytic membrane gradually deactivated after a few hours of operation. Different deactivation mechanisms are presented.     

Improvement of the oxidation stability of biodiesel as prepared by supercritical methanol method with lignin

An antioxidation effect of lignin‐derived products in biodiesel prepared using supercritical methanol (300°C/20 MPa) with molar ratio between rapeseed oil and methanol of 1:42 was studied. It was found that lignin could be decomposed to low molecular compounds that have a free radical‐trapping effect after supercritical methanol treatment. However, longer treatment time decreased the antioxidation effect of the lignin‐derived compounds. Rapeseed biodiesel prepared by supercritical methanol method at 300°C/20 MPa for 20 min with a small amount of added lignin showed an induction period longer than 6 h at 110°C in a Rancimat test. In addition, it was found that lignin had a catalytic effect in biodiesel production using the supercritical methanol method without significantly affecting other fuel properties of the prepared biodiesel. Thus, the study proved that lignin addition provides an inexpensive and technically acceptable way to improve the oxidation stability of biodiesel prepared by the supercritical methanol method with satisfactory fuel properties.