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951.
Torben?H.?Roenne Xuebing?Xu Tianwei?TanEmail author 《Journal of the American Oil Chemists' Society》2005,82(12):881-885
Enzymatic synthesis of esters of lactic acid and straight-chain alcohols with different chain lengths (C6–C18) were investigated in batch reactions with hexadecanol (C16) as the model alcohol. Cyclohexane was the best solvent for higher ester yields, and the best biocatalyst was the immobilized Candida antarctica lipase B (Novozym 435) as well as the textile-immobilized Candida sp. lipase. A method was established to obtain ester yields in the range of 71 to 82% for the different alcohols, and the most favorable conditions for the esterification reaction using Novozym 435 were an equimolar ratio of lactic acid to alcohol, each at a concentration of 120 mM each; a 50°C reaction temperature; 190 rpm shaking speed; and the addition of 100 mg molecular sieves (4 Å) for drying. The ester yield increased with increasing lipase load, and a yield of 79.2% could be obtained after 24 h of reaction at 20 wt% of Novozym 435. The immobilized Candida sp. lipase prepared in the laboratory also could be used to produce esters of lactic acid and straight-chain alcohols, but it had a much lower activity than Novozym 435 with a temperature optimum of 40°C. 相似文献
952.
Daan Verkoeijen Gerard A. PouwGabriël M. H. Meesters Brian Scarlett 《Chemical engineering science》2002,57(12):2287-2303
Population balance models have been used in chemical engineering since the 1960s and have evolved to become the most important tools for design and control of particulate processes. In this paper we show that the intrinsic particle parameter that determines changes in the process and should thus be included in the population balance is the particle volume. The basic population that is modeled should be the mass distribution, or the volume distribution if the density is constant. The population balance thus describes the change of the volume distribution of volume with time. Furthermore, we suggest that the “birth” and “death” terms that are often used to describe discrete events in particulate processes can almost always be replaced by a rate of change term.To design and control existing and future processes, a multi-dimensional population balance model is required. We propose a volume-based model in which the particle properties that are modeled are the volumes of solid, liquid, and air, respectively. In the most general case the model will consist of a properties vector and a distribution tensor. Depending on the complexity of the process, one or more of the properties may be omitted from the model. This is shown in three examples of increasing complexity: comminution, sintering, and granulation. 相似文献
953.
Thiosulfate has been considered as one of the most promising of the non-toxic alternatives to cyanide for the leaching of gold and much work has been carried out with the aim of understanding and improving the ammoniacal thiosulfate leaching process. In particular the behaviour of gold in thiosulfate solutions containing copper in the absence of ammonia has received little attention. It has been shown in this study involving electrochemical and leaching tests that copper ions catalyze not only the oxidation of thiosulfate but also the dissolution of gold in alkaline thiosulfate solutions. Electrochemical studies have shown that copper has a positive effect on the anodic dissolution of gold with increasing concentrations of copper resulting in higher dissolution rates of gold at a potential of 0.3V. Studies on the dissolution of gold powder in alkaline oxygenated thiosulfate solutions containing low concentrations of copper have shown that the role of copper in enhancing the dissolution rate of gold is possibly associated with the formation of a copper–thiosulfate–oxygen intermediate which is more reactive in terms of cathodic reduction than dissolved oxygen. The electrochemical experiments have been complemented by a leaching study which has shown that milling of gold powder in the presence of copper (added as ions, metal, or oxide) assists with the dissolution of gold in thiosulfate solutions. 相似文献
954.
Tong?WangEmail author Yongzhi?Jiang Earl?G.?Hammond 《Journal of the American Oil Chemists' Society》2005,82(2):111-117
Randomized corn oil TAG oxidized much faster than natural oil, but after purification with alumina, they oxidized at the same
rate. We showed that this effect could not be attributed to a difference, in total tocopherols in the randomized and natural
oils. Polar material recovered from the alumina treatment was fractionated by TLC, and a pro-oxidant effect was found in the
fractions containing MAG and DAG. However, MAG and DAG, although mild pro-oxidant could not account for the pro-oxidant effect
generated by randomization. No other compounds could be detected in the MAG fraction by MS. The pro-oxidant effect of randomized
oil disappeared when EDTA or citric acid was added in sufficient amounts. The pro-oxidant effect of randomized corn oil was
increased by the incorporation of additional copper or iron at a concentration that did not catalyze oxidation of the purified
oil. Treatment of corn oil with ascorbic acid, ascorbyl-6-palmitate, ethyl acetoacetate, ethyl diacetoacetate, and acetylacetone
did not reproduce the effect of the unknown pro-oxidant. Although the identity of the pro-oxidant is still unknown, we have
confirmed that it is produced during randomization; it does not have pro-oxidant activity alone, but it facilitates the catalytic
activity of the transition metal ions. 相似文献
955.
Retardation of volatile aldehyde formation in the exhaust of frying oil by heating under low oxygen atmospheres 总被引:2,自引:0,他引:2
Mariko?Fujisaki Yasushi?Endo Kenshiro?FujimotoEmail author 《Journal of the American Oil Chemists' Society》2002,79(9):909-914
Volatile aldehydes were generated in the exhaust of high-oleic safflower oil during heating at 180°C by spraying water into
atmospheres with four levels of oxygen concentrations (2, 4, 10, and 20%). These aldehydes were quantitatively analyzed by
HPLC after the conversion to 2,4-dinitrophenyl hydrazones. Ten alkanals (C2 through C10), eight 2-alkenals (C3 through C10) and three 2,4-alkadienals (C7, C9, and C10) were found. These aldehyde levels were found to be positively correlated with both the heating time and the atmospheric
oxygen concentration. The total amounts of aldehydes were the lowest in the oil heated in an atmosphere with 2% O2, and corresponded to 1/10 of those in the atmosphere with 20% O2. Acrolein was not found in oils heated in the atmosphere with 2% oxygen. These results suggest that frying in atmospheres
with low oxygen levels can effectively decrease the generation of volatile aldehydes in the exhaust. 相似文献
956.
957.
Gerhard?KnotheEmail author Robert?O.?Dunn 《Journal of the American Oil Chemists' Society》2003,80(10):1021-1026
During storage and use, vegetable oil-derived industrial products such as biodiesel and biodegradable lubricants can be subjected
to conditions that promote oxidation of their unsaturated components. The materials arising during oxidation and subsequent
degradation can seriously impair the quality and performance of such products. Therefore, oxidative stability is a significant
issue facing these vegetable oil-derived products, and enhanced understanding of the influence of various components of vegetable
oils and storage parameters is necessary. In this work, the oil stability index (OSI) was used for assessing oxidation of
monoalkyl esters of FA by varying several parameters. Neat fatty compounds and prepared mixtures thereof were studied for
assessing the influence of compound structure and concentration. Small amounts of more highly unsaturated compounds had a
disproportionately strong effect on oxidative stability. The recently developed concept of bis-allylic equivalents correlated
more closely than the iodine value with the OSI times of mixtures of fatty esters. The OSI times of free acids were shorter
than those of the corresponding alkyl esters. The presence of copper, iron, and nickel also reduced oxidative stability, but
their effect was less than the presence of more highly unsaturated fatty compounds. Of these metals, copper had the strongest
catalytic effect on OSI time. OSI may be an alternative to long-term storage tests for determining the influence of extraneous
materials such as metals on oxidative stability. 相似文献
958.
Conium maculatum, a Eurasian weed naturalized in North America, contains high concentrations of piperidine alkaloids that act as chemical defenses against herbivores. C. maculatum was largely free from herbivory in the United States, until approximately 30 yr ago, when it was reassociated via accidental introduction with a monophagous European herbivore, the oecophorid caterpillar Agonopterix alstroemeriana. At present, A. alstroemeriana is found in a continuum of reassociation time and intensities with C. maculatum across the continent; in the Pacific Northwest, A. alstroemeriana can cause severe damage, resulting in some cases in complete defoliation. Studies in biological control and invasion biology have yet to determine whether plants reassociated with a significant herbivore from the area of indigeneity increase their chemical defense investment in areas of introduction. In this study, we compared three locations in the United States (New York, Washington, and Illinois) where C. maculatum experiences different levels of herbivory by A. alstroemeriana to determine the association between the intensity of the interaction, as measured by damage, and chemical defense production. Total alkaloid production in C. maculatum was positively correlated with A. alstroemeriana herbivory levels: plants from New York and Washington, with higher herbivory levels, invested two and four times more N to alkaloid synthesis than did plants from Illinois. Individual plants with lower concentrations of alkaloids from a single location in Illinois experienced more damage by A. alstroemeriana, indicative of a preference on the part of the insect for plants with less chemical defense. These results suggest that A. alstroemeriana may act either as a selective agent or inducing agent for C. maculatum and increase its toxicity in its introduced range. 相似文献
959.
Haiqing?Liu S.?Kay?ObendorfEmail author Michael?J.?Leonard Timothy?J.?Young Michael?J.?Incorvia 《Journal of surfactants and detergents》2005,8(4):311-317
The adsorption of aroma chemicals on cotton fabric was studied relative to the surfactant concentration, surfactant type,
water solubility, and fiber morphology. The adsorption increased with increasing surfactant concentration to a maximum near
the critical micelle concentration, then decreased with further increases in surfactant concentration. The adsorption also
was found to be highly dependent on the fiber surface area and pore structure; dramatic differences were observed between
untreated and mercerized cotton fabric and are believed to be due to morphological differences. Cationic and anionic surfactants
increased the aroma chemical adsorption, which varied with surfactant type, with cetyltrimethylammonium chloride (CTAC)>sodium
dodecyl sulfate (SDS)>H2O. Water solubility also influenced adsorption; in most cases, adsorption increased with water solubility. In addition, adsorption
was also influenced by chemical structure and hydrophobic interactions. The adsorption of aroma chemicals on cotton fabric
can be attributed to the aqueous solution being physically held in capillaries and pore structures within the fibular structure
of cotton fiber and also to molecular interactions among the aroma chemical molecules, surfactants, and cotton substrate. 相似文献
960.
Clinical trial results support a preference for using CLA preparations enriched with two isomers rather than four isomers in human studies 总被引:1,自引:0,他引:1
CLA mixtures are now commercially available. They differ from each other with respect to their content of CLA isomers and
their degree of purification. As a group of natural FA, CLA have been widely assumed to be safe. However, the suspected presence
of both impurities and particular isomers might induce undesirable side effects. Despite this potential health risk, only
a few CLA preparations have been tested under rigorous conditions for clinical efficacy and safety. Based on the limited results
available, it is possible to suggest that preparations enriched in c9,t11 and t10,c12 isomers are preferable for human consumption compared to preparations containing four isomers, in terms both of safety
and efficacy. 相似文献