摘要
在对尿素与甲醇合成碳酸二甲酯(DMC)反应进行热力学分析的基础上较详细地研究了乙酸锌和二丁基氧化锡对该反应的催化作用。实验表明,以乙酸锌作催化剂时,DMC收率随尿素浓度增加而增加,但随催化剂用量的增加而下降,而且以尿素浓度的影响为更强;结合观察催化剂在反应前后的色泽、形态变化和XRD分析,证明存在着乙酸锌与甲醇作用生成氧化锌、乙酸甲酯和水的副反应。水分是抑制催化剂活性的主要因素。以正交实验评价了各因素对二丁基氧化锡催化作用的影响,得到以下较佳因素水平:甲醇/尿素摩尔比44,二丁基氧化锡/尿素摩尔比0.2,反应温度180℃,反应时间6h。由极差分析该4因素的重要性次序为:反应温度>反应时间>原料摩尔比>催化剂用量。最后,就乙酸锌、二丁基氧化锡、异丙醇铝和氯化锌均对尿素和甲醇合成DMC反应有催化活性,认为该反应为Lewis酸催化反应。提出了其反应机理为甲醇在催化剂表面上发生解离吸附,形成的甲氧基进攻氨基甲酸酯的羰基碳与氨基进行交换形成碳酸二甲酯。
<Abstrcat>The thermodynamic analysis for the reaction of urea and methanol to dimethyl carbonate (DMC) has been made, and then the catalytic properties of zinc acetate and dibuthyl tin oxide have been investigated more intensively. The experimental results showed that when zinc acetate is used as catalyst, (1) yield of DMC increases with the rising of urea concentration but decreases with the rising of amount of zinc acetate; (2) it has been confirmed from the observation of changes of zinc acetate' color and morphology before and after reaction, and from XRD analysis that there is a sidereaction in which zinc acetate reacts with methanol to zinc oxide, methyl acetate and water; (3) water is a main factor inhibiting the activity of zinc acetate. Effect of several factors on the catalytic properties of dibutyl tin oxide has been evaluated by orthogonal experiment, and the following more suitable reaction conditions have been obtained: molar ratio of methanol to urea 44, molar ratio of dibutyl tin oxide to urea 0.2, reaction temperature of 180℃, and reaction time of 6 h. Data analysis showed that the importance of the four factors is in following order: reaction temperature>reaction time> molar ratio of methanol to urea> molar ratio of dibutyl tin oxide to urea. DMC synthesis reaction is considered as being catalyzed by Lewisacid catalyst, for zinc acetate, dibutyl tin oxide, isopropxyl aluminum, and zinc chloride have catalytic activity for this reaction. The reaction mechanism was proposed including dissociative adsorption of methanol on the surface of Lewisacid catalyst. The formed methoxyl group attacking the carbonyl carbon in the molecule of methyl carbamate to exchange with the amino group to form DMC.
出处
《化学反应工程与工艺》
CAS
CSCD
北大核心
2002年第3期200-205,共6页
Chemical Reaction Engineering and Technology
基金
国家自然科学基金资助项目(20176008)
教育部科学技术研究重点项目(编号:01008)。
