共查询到20条相似文献，搜索用时 62 毫秒
1.
杨树 《昆明师范高等专科学校学报》2005,27(4):65-67
利用硫酸氢钠作为酯化反应催化剂合成了己酸乙酯，确定了其最佳反应条件——催化剂用量为每0．1mol己酸0．3克，醇酸物质的量比为2．5：1，以3A分子筛为脱水剂，回流反应时问为3．5h，己酸的酯化率可达98．69％．实验表明：该催化剂催化效果好，使用量少，酯化率高，环境污染小，廉价易得，用3A分子筛脱水，操作简便，较有工业应用价值． 相似文献
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《化学教学》1997年第5期刊载了谭和生老师的文章,阐述了实验室用一体积酒精与三体积硫酸混合加热制取乙烯的现象及解释,得出了“碳是制取乙烯的催化剂”的结论．笔者经反复实验及研究,认为碳在制取乙烯反应中的作用机理不应以“催化剂”一词来描述．众所周知,由乙醇制备乙烯,实质上是乙醇的脱水过程．接反应条件不同,可以发生分子内脱水而生成乙烯,也可发生分子间脱水而生成乙醚．乙醇的分子内脱水反应是消除反应．浓硫酸在此反应中起着催化剂和脱水剂的作用．乙醇在硫酸存在下,发生醇的碳氧键断裂,并在o碳原子上消除一个氢原子生… 相似文献
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以草酸为催化剂,对环己醇脱水制备环己烯的反应进行了研究。考察了催化剂用量、反应时间等因素对产率的影响,得出了最佳反应条件：环己醇用量为20g,催化剂用量为16g,反应时间为0．3h,环己烯收率为67．3％,纯度为96．7％。催化剂价廉易得,且不对环境造成污染。 相似文献
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研究了在微波辐射条件下，SnCl4 5H2O催化环己醇脱水制环己烯的反应。考察了催化剂用量、微波辐射时间和功率对反应的影响。结果表明：在催化剂用量为2g，环己醇用量为10mL，微波辐射功率为600W，辐射时间为10min时，环己烯收率达68．4％。 相似文献
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无水三氯化铝催化合成环己烯 总被引：1，自引：0，他引：1
以无水三氯化铝作催化剂,对环己醇脱水制备环己烯的反应进行研究.考察了催化剂用量、反应温度、反应时间等因素对脱水反应的影响,得出了其最佳的反应条件:催化剂用量为环己醇质量的13.3%,反应时间80 m in,油浴温度200~210℃.在此条件下,产品收率可达87.8%,纯度达98.4%. 相似文献
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高中化学教材中,乙醇脱水制乙烯的实验通常选择浓硫酸、酸性或两性氧化物作催化剂,本文在等温固定床反应装置中探索了氧化镁、氧化钙、氧化铁等常见碱性氧化物和氧化铝为催化剂时的乙醇脱水情况,通过气相色谱对反应产物进行了定性、定量在线检测,并通过氨气程序升温脱附考察了催化剂的表面酸性,结合文献初步解析了碱性氧化物不能高效催化乙醇脱水制乙烯的机理。 相似文献
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苄醇催化脱水制取苄醚的研究 总被引：2，自引：0，他引：2
以单质碘为催化剂直接由苄醇催化脱水生产苄醚．考察了影响收率的因素．其最佳条件为：苄醇：催化剂：带水剂=2mol：1．2g：40ml。反应在回流温度下进行(158～160℃)。反应时间4h。产率91．2％． 相似文献
8.
邢入德 《中学化学教学参考》2007,(4):41-41
根据个人学习经历,教材中实验室制乙烯的方法都是用浓硫酸作催化剂,加热到170℃,使乙醇发生脱水反应。2006年6月发行的苏教版新教材《有机化学基础》,把实验室制乙烯的方法改为用石棉绒作催化剂,加热,使乙醇发生脱水反应,这种方法的创新性激发了我,进而对该方法进行了验证性实验。苏教版新教材第69面蓝框内有如下一段叙述:下列活动能帮助我们认识乙醇的脱水反应。 相似文献
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固体催化剂SnCl4/C的制备及其催化酯化反应研究 总被引：1，自引：0，他引：1
制备了固体催化剂SnCl4／C，并通过乙酸苄酯的合成考察了该催化剂对酯化反应的催化情况，结果表明，固体催化剂SnCl4／C对酯化反应有很好的催化活性。适宜的反应条件为：当酸的用量为0．20mol，醇酸物质的量比为1．4，催化剂用量为1．0g，带水剂甲苯为15mL，反应时间为2．5h，反应温度为100～110℃时，酯化率达92％以上。 相似文献
11.
罗艳萍 《读与写:教育教学刊》2008,5(6)
The communication of people partially is the communication of cultures. Culture has a direct effect on international commercial activities in all aspects. Different conceptions about time, space, equality, law and the like, lead people to deal with things in different ways. So to know cultures of the counterpart is to facil-itate our enterprises so as to have a smooth and successful communication in commercial activity. 相似文献
12.
Richard Denner 《海外英语》2007,(4):14-15
Rosco and I wait for the fishermen to return.I sit at a wooden bench near the store at Mt.Baker Resort and watch the clouds change shape. Rosco has my belt around his neck and an eight foot tow chain hooked to a tree. Dogs must be on a leash. Ducks and rabbits are loose. 相似文献
13.
Given a graph G,a subgraph C is called a clique of G if C is a complete subgraph of G maximal under inclusion and |C|≥2. A clique-transversal set S of G is a set of vertices of G such that S meets all cliques of G. The clique-transversal number, denoted as TC (G), is the minimum cardinality of a clique-transversal set in G. The clique-graph of G, denoted as K (G), is the graph obtained by taking the cliques of G as vertices, and two vertices are adjacent if and only if the corresponding cliques in G have nonempty intersection. Let F be a class of graphs G such that F={G|K(G) is a tree}. In this paper the graphs in F having independent clique-transversal sets are shown and thus TC (G)/|G|≤1/2 for all G ∈ F. 相似文献
14.
邱崇丙 《唐山师范学院学报》2014,(1):21-23
汉字的六书,《说文》对“转注”一类,语焉不详。后世学者提及转注,也仅限于许慎所举出的例字。《汉字例说》一文,作者从转注的角度综合考虑,对部分现代常用字作了分析,跟传统的解释有所不同。希望能抛砖引玉,互相切磋,以推进学术研究。 相似文献
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陈美曦 《山东教育学院学报》2008,23(2):103-107
Different nations have different social cultures, and the social culture of every nation is developing with the development of the nation, language is greatly influenced by social culture, which enables language to possess national and historical characteristics. Word is the smallest, independent, meaningful linguistic unit of language. It can well reflect the national and historical characteristics. From synchronic aspect, the social and cultural influence on word meaning is mainly embodied in conceptual and associative meanings of word. The incorrespondence of word meaning is a phenomenon that exists in both conceptual and associative meanings of word among different languages. From diachronic aspect, the development of social culture causes some changes of word meaning to some extent. Therefore, social culture plays a key role in vocabulary learning and mastery of a language. 相似文献
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Rachel Zupek 《海外英语》2007,(11):40-41
我们绝大部分人都同意一件事情——我们喜欢金钱。但是你对金钱的喜欢之情足够到让你创立一份事业么?.财富通常被人忽视,主要在于人们不能真正了 相似文献
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《海外英语》2007,(4):36
There are numbers of crossroads on our long and unpredictable life journey where we totally have no idea about which direction to choose. No matter what our decision is, we should not turn back, but face the music and go ahead instead. I am this kind of girl who always does try without regretting, one example is how I dealt with my love. 相似文献
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YANGShiguo 《重庆大学学报(英文版)》2004,3(1):86-88
The problem on the geometrc inequalities involving an n-dimensional simplex and its inscribed simplex is studied. Aninequality is established, which reveals that the difference between the squared circumradius of the n-dimensional simplex andthe squared distance between its circumcenter and barycenter times the squared circumradius of its inscribed simplex is not lessthan the 2(n-1)th power of n times its squared inradius, and is equal to when the simplex is regular and its inscribed siplex is atangent point one. Deduction from this inequality reaches a generalization of n-dimensional Euler inequality indicating that thecircumradius of the simplex is not less than the n-fold inradius. Another inequality is derived to present the relationship betweenthe circumradius of the n-dimensional simplex and the circumradius and inradius of its pedal simplex. 相似文献