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981.
982.
983.
984.
Hydrolysis of olive oil, soybean oil, mink fat, lard, palm oil, coconut oil, and a hydrogenated, hardened oil with lipase
from anAspergillus sp. has been studied. The lipase had high specific activity (60,000 U/g) and did not show any positional specificity. The
lipase proved to be a more effective catalyst than Lipolase fromA. oryzae, with an optimal activity at 37°C and pH 6.5–7.0. It was activated by Ca2+ but inactivated by organic solvents such as isopropanol and propanone. All substrates examined could be hydrolyzed to corresponding
fatty acids with this enzyme at concentrations of 5–30 U/meq with yields of 90–99% in 2–24 h. The degree of hydrolysis was
almost logarithmically linear with reaction time and occurred in two stages. The lipase was stable and could be repeatedly
recycled for hydrolysis. 相似文献
985.
本文用沉积-沉淀法制备了新型纳米载体低碳醇合成催化剂,并与共沉淀法所制备的催化剂进行了对比,结果表明,纳米载体催化剂活性高、耐热性能好、醇收率高纳米载体对纳米载体催化剂活性大小的影响顺序为:纳米Al2O3>纳米ZnO-ZnAl2O4>纳米MgAl2O4>纳米MgO.工艺参数对反应性能的影响结果表明,反应温度低,甲醇选择性高;但温度太高(>320℃)CO2。选择性升高,且整个反应为动力学控制;压力升高可提高活性和C1-C2OH选择性,但C4OH选择性下降;结合空速对产物分布的影响,反应可能按Smith和Anderson的缩聚机理进行. 相似文献
986.
987.
Shape‐memory polyurethane/multiwalled carbon nanotube (SMP–MWNT) composites with various multiwalled carbon nanotube (MWNT) contents were synthesized, and the corresponding SMP–MWNT fibers were prepared by melt spinning. The influence of the MWNT content on the spinnability, fracture morphology, thermal and mechanical properties, and shape‐memory behavior of the shape‐memory polymer was studied. The spinning ability of SMP–MWNTs decreased significantly with increasing MWNT content. When the MWNT content reached 8.0 wt %, the fibers could not be produced because of the poor rheological properties of the composites. The melt‐blending, extrusion, and melt‐spinning processes for the shape‐memory fiber (SMF), particularly at low MWNT contents, caused the nanotubes to distribute homogeneously and preferentially align along the drawing direction of the SMF. The crystallization in the SMF was promoted at low MWNT contents because it acted as a nucleation agent. At high MWNT contents, however, the crystallization was hindered because the movement of the polyurethane chains was restricted. The homogeneously distributed and aligned MWNTs preserved the SMF with high tenacity and initial modulus. The recovery ratio and recovery force were also improved because the MWNTs helped to store the internal elastic energy during stretching and fixing. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 相似文献
988.
Large amounts of amorphous carbon nanotubes (ACNTs) were prepared with Co-Ni alloy powders as catalyst in hydrogen gas atmosphere by a modified arc discharging furnace which can control temperature during the electric arcing process. The experimental results indicate that the cooperative function of temperature and catalyst plays an important role in the soot production rate and the relative ACNT purity. When temperature increases from 25 °C to 700 °C, the soot production rate increases from around 1 g/h to 8 g/h, the best relative ACNT purity at 600 °C can reach up to 99% compared to the room temperature sample. Without catalyst, only plate graphite is formed at 25 °C and very few carbon nanotubes are found when temperature increases to 600 °C. TEM, SEM, HRTEM and XRD analysis showed that the as-prepared carbon nanotubes are almost amorphous. The soot production rate is 8 g/h and diameter range of amorphous carbon nanotubes is about 7-20 nm, respectively. 相似文献
989.
990.
信息可以改变竞争环境的本质与结构,作为现代信息媒介的网站则可作为一种战略工具。会计准则制定者与监管者鼓励企业在其治理机制中植入以互联网为基础的信息披露政策,但关于站点信息披露的战略控制知识还不完善。描述了IT治理因素及其与网站信息披露相关的战略控制机制,并评估这些因素与机制之间的内在关系,给出了一个基于IT治理、战略管理与基于网站的公司报告文化的概念框架。 相似文献