Vegetal oil, also known as triglycerides, is a mixture of fatty acid triesters of glycerol. In the triglycerides alkyl chains of Jatropha curcas oil, predominate the palmitic, oleic and linoleic fatty acids. The process usually used to convert these triglycerides to biodiesel is called transesterification. The overall process is a sequence of three equivalent, consecutive and reversible reactions, in which di- and monoglycerides are formed as intermediates. Semi-empirical AM1 molecular orbital calculations were used to investigate the reaction pathways of base-catalyzed transesterification of glycerides of palmitic, oleic and linoleic acid. The most probable pathway and the rate determining-step of the reactions were estimated from the molecular orbital calculations. Our results suggest the formation of only one tetrahedral intermediate, which in a subsequent step rearranges to form the products. The rate determining-step is the break of this tetrahedral intermediate. 相似文献
The aim of this paper is to analyze the influence of the nature of the orthodontic archwires on the friction coefficient and wear rate against materials used commonly as brackets (Ti–6Al–4V and 316L Stainless Steel). The materials selected as orthodontic archwires were ASI304 stainless steel, NiTi, Ti, TiMo and NiTiCu. The array archwire’s materials selected presented very similar roughness but different hardness. Materials were chosen from lower and higher hardness degrees than that of the brackets. Wear tests were carried out at in artificial saliva at 37 °C. Results show a linear relationship between the hardness of the materials and the friction coefficients. The material that showed lower wear rate was the ASI304 stainless steel. To prevent wear, the wire and the brackets have high hardness values and in the same order of magnitude. 相似文献
Chymotrypsin was purified from jumbo squid hepatopancreas (HP) with 2.4-fold and yield 1.9%, and characterized with a molecular weight of 31 kDa, as estimated by sodium dodecyl sulfatepolyacrylamide gel electrophoresis (SDS-PAGE). Chymotrypsin effect over collagen extracted from the mantle, fins and arms of the jumbo squid was evaluated. The enzyme exhibited the maximum activity at pH 7 and 65°C using Suc-Ala-Ala-Pro-Phe-p-nitroanilide (SAAPNA) as a substrate and it was identified using the specific inhibitors N-tosyl-L-phenylalaninechloromethyl ketone (TPCK) and phenyl methyl sulfonyl fluoride (PMSF), showing residual activities of 6% and 0%, respectively. Furthermore, high activity was observed in the pH range of 4.0 to 8.0. Purified enzyme showed a moderate in vitro activity using muscle collagen as a substrate. Although further research is needed, the results suggest that the enzyme has a potential application where acidic or slightly alkaline conditions are needed. 相似文献
The friction of a copper surface, which is exposed to diethyl disulfide (DEDS), dimethyl disulfide (DMDS) or dimethyl trisulfide (DMTS) while rubbing by a tungsten carbide pin, are explored in an ultrahigh vacuum tribometer to investigate the effect of the sulfur-to-carbon stoichiometry on gas-phase lubrication. Surface analyses by Auger spectroscopy of the wear scars after rubbing reveal that the amount of sulfur increases with sulfur content of the gas-phase lubricant, as anticipated. It is found that the friction reduction depends on the normal load, where the friction coefficient tends to decrease more at lower loads, and that the load at which the most friction-reducing tribofilm is formed depends on the stoichiometry of the gas-phase lubricant. DEDS (with a sulfur to carbon ratio of 0.5) only reduces the friction coefficient to a minimum value of ~0.28 at a normal load of 0.25 N, for DMDS (S/C = 1.0) friction is reduced to ~0.28 for loads below ~0.7 N, and DMTS (S/C = 1.5) reduces friction to this value for all loads tested. 相似文献
Abstract Optimal conditions for lubricated transport of very heavy crude oils in a horizontal pipeline are established. A central core annular flow is obtained using water as the lubricating fluid and heavy oil as the core of the flow. The pressure drop along the pipe using lubricated transport is 50 times less than the pressure drop required to transport the heavy oil without lubrication. When the conditions of temperature, viscosity, and pressure at the injection nozzle are maintained within a certain range, the lubricated transport, with 70% heavy oil in the center and 30% water in the outer annulus, remains stable regardless of the pipe wall temperature. 相似文献
The objective of the present work is to characterize the influence of cold work on the thermoelastic martensitic transformation and on the apparent elastic modulus of the Ni-free Ti-21.6Hf-23.7Nb-1Zr alloy in order to determine the key factor that promotes the desired shape memory properties and/or low apparent elastic modulus. A vacuum arc melted button of each alloy was heat treated at 1100 °C during 1.5 h and quenched with a mixture of ethanol/water at 0 °C. Samples of the alloy were cold rolled from 5% up to 95% and, finally, microstructurally and mechanically characterized. The apparent elastic modulus for each condition as well as the reversibility percentages were evaluated by instrumented nanoindentation using a Berkovich tip and a spherical tip, respectively. A higher proportion of martensite was found in the low cold work percentages compared to the untreated material as it was observed by optical and TEM microscopy. A decrease in the apparent elastic modulus was observed when increasing the cold work percentage. The lowest value was found in the 99% cold work condition with 44 GPa, value closer to that of cortical bone. Cyclic nanoindentation tests show an increase in the reversibility percentages in the cold worked condition compared to the untreated material. 相似文献
The synthesis and characterization of an inexpensive porous MoxCy/SiO2 material is presented, which was obtained by mixing ammonium hexamolybdate, sucrose, and a mesoporous silica (SBA-15), with a subsequent heat treatment under inert atmosphere. This porous material presented a specific surface area of 170 m2/g. The catalytic behavior in CO2 hydrogenation was compared with that of Mo2C and α-MoC1?x obtained from ammonium hexamolybdate and sucrose, using different Mo/C ratios. CO2 hydrogenation tests were performed at moderate (100 kPa) and high pressures (2.0 MPa), and it was found that only CO, H2O and CH4 are formed at moderate pressures by the three materials, while at higher pressures, methanol and hydrocarbons (C2H6, C3H8) are also obtained. Differences in selectivity were observed at the high pressure tests. Mo2C presented higher selectivity to CO and methanol compared with MoC1?x, which showed preferential selectivity to hydrocarbons (CH4, C2H6). The porous MoxCy/SiO2 material showed the highest CO2 hydrogenation activity at high temperatures (270 and 300 °C), being a promising material for the conversion of CO2 to CO and CH4.