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11.
Azeotropic liquid mixture cannot be separated by conventional distillation. But extractive distillation or combination of the two can be valid for them. An experiment to separate benzene and cyclohexane by batch extractive distillation was carried out with N,N-dimethylformide (DMF), dimethyl sulfoxide (DMSO) and their mixture as extractive solvent. The effect of the operation parameters such as solvent flow rate and reflux ratio on the separation was studied under the same operating conditions. The results show that the separation effect was improved with the increase of solvent flow rate and the reflux ratio; all the three extractive solvents can separate benzene and cyclohexane, with DMF being the most efficient one, the mixture the second, and DMSO the least. In the experiment the best operation conditions are with DMF as extractive solvent, the solvent flow rate being 12.33 mL/min, and the reflux ratio being 6. As a result, we can get cyclohexane from the top of tower with the average product content being 86.98%, and its recovering ratio being 83.10%. 相似文献
12.
In order to clarify the equilibrium components in the hydrolysis solution of boron trifluoride(BF_3-H_2O),the BF_3-H_2O was prepared by mixing BF_3-CH_3OH with large amount of water,in which the stoichiometric concentration of BF_3 is less than 0.1 mol/L.Two ionic equilibrium models were proposed to simulate the hydrolysis equilibrium of BF_3 and tested by special acid-base titration technique.The most accurate ion equilibrium constants were determined.The model,which was assumed to have no HF,was proved to be more representative for the real system and used to simulate the hydrolysis equilibrium of BF_3.The simulation suggested that H~+,BF_4~-,BF_3OH~- and H_3BO_3 were the main species in the dilute hydrolysis solution,while BF_2(OH)_2~- and F~- were insignificant species whose concentrations were both in the order of 10~(-4) mol/L magnitude,and BF(OH)_3~- could be omitted because its concentration almost equaled zero.Meanwhile,the equilibrium constant of the overall ionic reaction at 25℃ was obtained as 161.6. 相似文献
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从优选论来看．儿童语言习得过程是一个随着所感知到的同一语素的不同表层形式在数量上的不断增加而不断地调整、补充、制约条件层级体系和不断地重新构建词项底层表达的动态过程。本文简要从儿童语言习得的重要阶段,语音、词汇、语法、词语的意义,以及隐喻的习得等方面。阐述在优选论下的儿童语言习得过程。 相似文献
15.
Synthesis of Enriched 10B Boric Acid of Nuclear Grade 总被引：2，自引：2，他引：0
An economic and effective method of preparing enriched 10 B boric acid was established by chemical reaction of enriched 10BF3 and CaCO3. A process of boron trifluoride reacting with water was investigated under certain conditions. Calcium carbonate was selected to counteract hydrofluoric acid followed on. Some key operation factors were investigated, such as temperature, reaction time and the ratio of CaCO3 to 10BF3. The results showed that the yield of enriched 10 B boric acid could reach 97. 2% and the purity was up to 94. 1% under the following conditions: the temperature was 50—60,℃, the reaction time was 28 h and the ratio of CaCO3 to 10BF3 was 4. In addition, after recrystallization and titration analysis, the purity of the product could reach over 99. 2% from 94.1%. 相似文献
16.
In this study, methanethiol(MT)-degradation bacteria were cultivated by using MT, methanol and trimethylamine as carbon sources under anaerobic conditions. It was found that the batch bacteria used MT and methanol as carbon sources grew faster than those used trimethylamine. The enriched bacteria used MT and methanol as the carbon sources were respectively inoculated in different biotrickling filters. The biological conversion performance of MT under anaerobic conditions was investigated in biotrickling filters. The results showed that the performance of the biotrickling filter inoculated with the bacteria enriched using MT was better than that inoculated with the bacteria enriched using methanol. When the inlet concentration of MT was 0.005vol%(50,ppm), the empty bed residence time was 50 s, p H value was 8.0, and the flow rate of the nutrient solution was 10 L/h, the removal efficiency of MT reached 95.3%. Adding methanol stimulated the growth of the biomass and the degradation of MT, but caused that some bacteria only degrading methanol outcompeted the bacteria only degrading MT. The concentration of sodium bicarbonate in the nutrient solution needed to be controlled lower than 30 g/L, otherwise, it would be harmful to the degradation of MT. 相似文献
17.
核心素养导向下的单元教学评价是小学艺术课程实施的重要议题,它在科学评价学生美术核心素养发展和学科学业质量高低,以及促进教学评一致性的教学转型等方面有着重要的价值与意义。教师要把握住素养导向下美术主题单元教学评价的整体性与系统性、情境性与表现性、阶段性与进阶性等特点之间的关系,并从单元教学评价的各个要素中形成实施的策略,进而实现学科育人的目标。 相似文献
18.
徐姣 《小溪流(作文画刊)》2004,(3)
我的爸爸相貌平平,但是只要一笑,两颗小虎牙便调皮地钻了出来。有那两颗牙齿的点缀,爸爸显得更加滑稽了。你可别小看这两个“小丑”,它们的用途可大了,在吃东西的时候,可就派上了大用场,爸爸也因此变成了无人不知、没人不晓的“明星”。 相似文献
19.
随着信息技术时代的发展,“教育云”时代的来临,小学美术课堂进入一个新的环境中,这种先进技术的引入,使美术课堂发生了一个质的转变。它颠覆了以往传统课堂教学模式,把从教师为中心的讲解传授过程转变为以生探索发展,自主学习为主的过程。更是让孩子在新环境的美术课堂中感受到了无与伦比的快乐,使生的学习效率更快,兴趣更浓,积极性更高,学习自主性更强,正真做到学有所得,学有所乐! 相似文献
20.
A method was proposed to determine boron trifluoride in boron trifluoride complex using fluoride ion selective electrode(ISE). Hydroxide was chosen to mask aluminum for the determination of 0.01—0.1 mol/L of fluoride. The simulation indicated that the permissible aluminum masked at a certain p H value was limited and hardly related to F-concentration and boric acid. It is better to control p H value below 11.5 and the aluminum concentration within 0.025 mol/L to minimize the interference of hydroxide to the fluoride ISE. The decomposition conditions of boron trifluoride by aluminum chloride were investigated. It is found that the F-detection ratio will approach 1.0 if the Al/F molar ratio is 0.3—0.7 and aluminum concentration is no more than 0.02 mol/L when heated at 80 ℃ for 10 min. In one word, hydroxide is quite fit to mask aluminum for samples which contain high content of fluoride and aluminum and the BF3 content can be successfully determined by this method. 相似文献